U.S. patent application number 14/052695 was filed with the patent office on 2014-02-06 for method and apparatus for electro-chemical reaction.
This patent application is currently assigned to Encite, LLC. The applicant listed for this patent is Encite, LLC. Invention is credited to Stephen A. Marsh.
Application Number | 20140038074 14/052695 |
Document ID | / |
Family ID | 38619830 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140038074 |
Kind Code |
A1 |
Marsh; Stephen A. |
February 6, 2014 |
METHOD AND APPARATUS FOR ELECTRO-CHEMICAL REACTION
Abstract
A method and an apparatus of reacting reaction components. The
method comprises electro-chemically reacting reaction components on
opposite sides of at least one membrane with at least one catalyst
encompassing a respective volume. In another embodiment, the method
includes conducting electrolysis, such as electrolysis of water.
The apparatus includes at least one membrane with first and second
sides encompassing a respective volume. The apparatus further
includes at least one catalyst coupled to the first and second
sides to electro-chemically react reaction components on the first
and second sides in gaseous communication with the at least one
catalyst, and a cover coupled to the at least one membrane to
separate flow paths on the first and second sides.
Inventors: |
Marsh; Stephen A.;
(Carlisle, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Encite, LLC |
Burlington |
MA |
US |
|
|
Assignee: |
Encite, LLC
Burlington
MA
|
Family ID: |
38619830 |
Appl. No.: |
14/052695 |
Filed: |
October 11, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11713458 |
Mar 2, 2007 |
|
|
|
14052695 |
|
|
|
|
11521593 |
Sep 14, 2006 |
|
|
|
11713458 |
|
|
|
|
11322760 |
Dec 29, 2005 |
|
|
|
11521593 |
|
|
|
|
10953038 |
Sep 29, 2004 |
6991866 |
|
|
11322760 |
|
|
|
|
10985736 |
Nov 9, 2004 |
7029779 |
|
|
10953038 |
|
|
|
|
09949301 |
Sep 7, 2001 |
6815110 |
|
|
10985736 |
|
|
|
|
09449377 |
Nov 24, 1999 |
6312846 |
|
|
09949301 |
|
|
|
|
60778584 |
Mar 2, 2006 |
|
|
|
60778563 |
Mar 2, 2006 |
|
|
|
Current U.S.
Class: |
429/442 ;
204/228.1; 204/228.4; 204/228.6; 204/229.2; 204/230.2; 204/257;
204/263; 429/428; 429/482 |
Current CPC
Class: |
C25B 1/04 20130101; H01M
8/0289 20130101; C25B 9/10 20130101; H01M 2008/1095 20130101; C25B
15/02 20130101; H01M 8/1004 20130101; Y02E 60/36 20130101; H01M
8/1097 20130101; H01M 8/2415 20130101; Y02E 60/50 20130101; H01M
8/04 20130101 |
Class at
Publication: |
429/442 ;
204/263; 429/482; 429/428; 204/230.2; 204/228.1; 204/229.2;
204/228.6; 204/228.4; 204/257 |
International
Class: |
H01M 8/10 20060101
H01M008/10; H01M 8/04 20060101 H01M008/04; C25B 15/02 20060101
C25B015/02; C25B 9/10 20060101 C25B009/10 |
Claims
1. An apparatus for reacting reaction components, comprising: at
least one ion exchange membrane with first and second sides
encompassing a respective volume; at least one catalyst coupled to
the first and second sides to electro-chemically react reaction
components on the first and second sides in gaseous communication
with the at least one catalyst; and a cover coupled to the at least
one membrane to separate flow paths on the first and second
sides.
2. The apparatus of claim 1, wherein the at least one membrane is
at least one ion exchange membrane.
3. The apparatus of claim 1, wherein the at least one membrane with
the at least one catalyst is configured to electro-chemically react
reaction components through electrolysis.
4. The apparatus of claim 3, wherein the at least one membrane with
the at least one catalyst is configured to conduct electrolysis of
water.
5. The apparatus of claim 3, wherein the at least one membrane with
the at least one catalyst is configured to conduct electrolysis for
electrometallurgy or anodization.
6. The apparatus of claim 5, wherein the at least one membrane with
the at least one catalyst is configured to conduct electrolysis to
manufacture elements.
7. The apparatus of claim 6, wherein the at least one membrane with
the at least one catalyst is configured to produce hydrogen,
sodium, lithium, aluminum, or potassium.
8. The apparatus according to claim 1, further including a
controller to cause multiple membranes with catalysts to generate a
potential difference on opposite sides of the at least one
membrane.
9. The apparatus according to claim 8, wherein the controller
further is configured to cause the membranes with catalysts to
change the potential difference over time.
10. The apparatus according to claim 9, wherein the controller is
configured to cause the membranes with catalysts to increase the
potential difference to accelerate the reaction.
11. The apparatus according to claim 9, wherein the controller is
configured to cause the membranes with catalysts to decrease the
potential difference to decelerate the reaction.
12. The apparatus according to claim 8 wherein the controller is
configured to cause the membranes with catalysts to cycle the
potential difference.
13. The apparatus according to claim 8, wherein the controller is
configured to cause the membranes with catalysts to generate a
potential difference to cause heating at the at least one
membrane.
14. The apparatus according to claim 1, wherein the at least one
membrane is an array of membranes with catalysts and further
including a controller configured to operate a subset of the array
as fuel cells in a manner generating heat.
15. The apparatus according to claim 14, wherein the controller is
further configured to cause a set of membranes with at least one
catalyst to apply a potential difference to opposite sides of
membranes in a subset of the array in thermal proximity to the
subset generating heat.
16. The apparatus according to claim 1, further including a flow
path introducing at least one other reaction component to react
with the reaction components.
17. The apparatus according to claim 1, further including an outlet
configured to output a product produced by reacting the reaction
components.
18. The apparatus according to claim 17, wherein the output is
further configured to output the product in a manner selected from
a group consisting of: extracting, expelling, draining, releasing,
or venting.
19. The apparatus according to claim 17, wherein the product is at
least one of the components in a different state from the state
prior to the electro-chemical reacting.
20. The apparatus according to claim 17, wherein the at least one
membrane with at least one catalyst is in a proximity to
participate with at least one other reaction and wherein the output
is configured to present the product to the least one other
reaction.
21. The apparatus according to claim 20, wherein the output is
further configured to output a byproduct of the electro-chemical
reaction to the at least one other reaction.
22. The apparatus according to claim 1, wherein the reaction
components are selected from a group consisting of: solids,
pseudo-solids, liquids, pseudo-liquids, gases, or combinations
thereof.
23. The apparatus according to claim 1, further including a
controller configured to cause membranes with catalysts to apply a
potential difference across the at least one membrane selected from
a group consisting of: DC, AC, fixed frequency, arbitrary waveform,
or combinations thereof.
24. The apparatus according to claim 23, wherein the controller is
configured to cause a change in profile of a potential difference
during different stages of a reaction over a single stage of a
reaction.
25. The apparatus according to claim 1, further including a monitor
to monitor the electro-chemical reaction.
26. The apparatus according to claim 25, wherein the monitor
includes: a feedback output to feedback at least one metric
associated with the electro-chemical reaction measured; and wherein
the controller is configured to regulate or control the
electro-chemical reaction as a function of the at least one
metric.
27. The apparatus according to claim 26, wherein the at least one
metric includes at least one of the following: temperature,
pressure, humidity, time, or concentration of at least one of the
reaction components.
28. The apparatus according to claim 26, wherein the controller is
configured to cause the membranes with substrate to apply a
potential difference across the at least one membrane; and further
including a feedback unit to feed back at least one metric
associated with the electro-chemical reaction; and wherein the
controller is configured to adjust the potential differences a
function of the metric measured to control or regulate
electro-chemically reacting reaction components.
29. The apparatus according to claim 1, wherein the at least one
membrane is an array of membranes with catalysts configured to
electro-chemically react the different reaction components in
different reactions across the array of membranes.
30. The apparatus according to claim 1, wherein the volume is less
than one cubic millimeter.
Description
RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. application Ser.
No. 11/713,458 filed Mar. 2, 2007, which is a Continuation-in-part
of U.S. application Ser. No. 11/521,593 filed Sep. 14, 2006, which
is a Continuation of U.S. application Ser. No. 11/322,760, filed
Dec. 29, 2005, now abandoned, which claims priority to and is a
continuation application of U.S. application Ser. No. 10/953,038
filed on Sep. 29, 2004, now U.S. Pat. No. 6,991,866, and of U.S.
application Ser. No. 10/985,736 filed on Nov. 9, 2004, now U.S.
Pat. No. 7,029,779, which are a divisional application and a
continuation application, respectively, of U.S. application Ser.
No. 09/949,301 filed Sep. 7, 2001, now U.S. Pat. No. 6,815,110,
which is a continuation of U.S. application Ser. No. 09/449,377,
filed Nov. 24, 1999, now U.S. Pat. No. 6,312,846. Parent
application Ser. No. 11/713,458 also claims priority to U.S.
Application No. 60/778,584, filed Mar. 2, 2006, now expired, and
U.S. Application No. 60/778,563, filed Mar. 2, 2006, now expired.
The entire teachings of the above applications and patents are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Electro-chemical fuel cells are not new. Invented in 1839 by
Alexander Grove, electro-chemical fuel cells have recently been the
subject of extensive development. As environmental concerns mount
and energy legislation toughens, development of "green" energy
sources becomes more justified as a course of action, if not
required.
[0003] Within the last decade, development has addressed various
types of fuel cells designed to address various applications and
corresponding power levels, ranging from large stationary power
plants (kilowatts to megawatts), to transportation (bus,
automobile, scooter), and to smaller electronic devices (laptops,
cell phones, PDAs).
[0004] In U.S. Pat. Nos. 6,312,846 and 6,815,110, Marsh describes
an approach to Proton Exchange Membrane (PEM) fuel cells fabricated
on a semiconductor substrate. Using conventional semiconductor
fabrication methods, such fuel cells can be made extremely small,
in very great quantity, and at very low cost on a single
substrate.
SUMMARY OF THE INVENTION
[0005] In accordance with an example embodiment of the present
invention, a method and apparatus is provided which uses a
combination of self-assembled monolayers (SAMs), micro electrical
mechanical systems (MEMS), "chemistry-on-a-chip" and semiconductor
fabrication techniques to create a scalable array of fuel cells
directly on a substrate, preferably a semiconductor wafer. These
wafers may be "stacked" (i.e., electrically connected in series or
parallel, as well as individually programmed to achieve various
power (V*I) characteristics and application driven
configurations.
[0006] One embodiment of the present invention is a method of
reacting reaction components, comprising electro-chemically
reacting reaction components on opposite sides of at least one
membrane with at least one catalyst encompassing a respective
volume. In another embodiment, the method includes conducting
electrolysis, such as electrolysis of water. In yet another
embodiment, electro-chemically reacting reaction components
includes applying a potential difference on the opposite sites of
the at least one membrane.
[0007] One embodiment of the present invention is an apparatus for
reacting reaction components. The apparatus includes at least one
membrane with first and second sides encompassing a respective
volume. The apparatus further includes at least one catalyst
coupled to the first and second sides to electro-chemically react
reaction components on the first and second sides in gaseous
communication with the at least one catalyst, and a cover coupled
to the at least one membrane to separate flow paths on the first
and second sides.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of example embodiments of the invention, as illustrated
in the accompanying drawings in which like reference characters
refer to the same parts throughout the different views. The
drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0009] FIG. 1 is a schematic plan view of a semiconductor fuel cell
array in accordance with the invention.
[0010] FIG. 2 is a simplified schematic cross-sectional view taken
along the lines II-II of a fuel cell 12 of the invention.
[0011] FIGS. 3(a)-(h) is a schematic sectional process view of the
major steps in fabricating a PEM barrier structure 30 of the
invention.
[0012] FIG. 4 is a cross-sectional schematic view illustrating an
alternate cast PEM barrier invention.
[0013] FIG. 5 is a sectional view of a PEM structure
embodiment.
[0014] FIG. 6 is a sectional view of an alternate of the PEM
structure.
[0015] FIG. 7 is a sectional view of another alternate PEM
structure.
[0016] FIG. 8 is a block diagram of circuitry which may be
integrated onto a fuel cell chip.
[0017] FIG. 9 is a schematic of the wiring for an integrated
control system for the operation of individual cells or groups of
cells.
[0018] FIG. 10 is a schematic side view of a manifold system for a
fuel cell.
[0019] FIG. 11 is a schematic plan view of a plurality of cells
arranged side-by-side on a wafer to form a power chip and stocked
on top of each other to form a power disc.
[0020] FIG. 12 is a fragmented side-view of FIG. 11.
[0021] FIG. 13 is a schematic plan view of a semiconductor fuel
cell array in accordance with an embodiment of the present
invention.
[0022] FIG. 14 is a schematic view of a fuel cell in accordance
with the present invention.
[0023] FIG. 15 is a simplified schematic cross-sectional view of
the fuel cell of FIG. 14 of the present invention.
[0024] FIGS. 16A-16D are schematic cross-sectional views of the
fuel cell in accordance with embodiments of the present
invention.
[0025] FIG. 17 is a schematic plan view of a PEM surface with
"fins" to increase the active areas in accordance with an
embodiment of the present invention.
[0026] FIGS. 18A-18C are illustrations of comparing footprint areas
between a typical two-dimensional fuel cell and fuel cell designs
in accordance with embodiments of the present invention.
[0027] FIGS. 19A and 19B are schematic plan views of the cover
configuration of the fuel cell in accordance with an embodiment of
the present invention.
[0028] FIGS. 20A and 20B are schematic plan view of a power stack
in accordance with an embodiment of the present invention, and a
cross-sectional schematic view illustrating the hierarchical
construction of an exemplary power stack formed of multiple power
disks, each of which containing many power chips.
[0029] FIG. 21 is an illustration of incremental volumatic increase
in power density by stacking the fuel cells in accordance with an
embodiment of the present invention.
[0030] FIG. 22 is an illustration of incremental gravimetric
increase in power density by stacking the fuel cells in accordance
with an embodiment of the present invention.
[0031] FIG. 23 is a circuit diagram illustrating prior art with
respect to generation of regulated power from a battery, fuel cell,
or other such device.
[0032] FIG. 24 is a plot illustrating a typical voltage-current
(V-I) curve for a micro fuel cell, as well as variation with
ambient conditions.
[0033] FIG. 25 is an example showing inter-connection topology of a
series-parallel, switched arrangement of fuel cells.
[0034] FIG. 26 is a plot showing variation of voltage with output
current and with the number of columns switched into the circuit as
a load impedance is decreased.
[0035] FIG. 27 is an example switching topology for a series column
of a variable number of fuel cells.
[0036] FIG. 28 is a plot illustrating a transient response typical
of a fuel cell after it is switched into an operational set on
state.
[0037] FIG. 29 is a schematic diagram illustrating a typical
transfer function of a fuel cell.
[0038] FIG. 30 is a block diagram of an example closed loop control
system used to accomplish voltage regulation and optimal fuel usage
for an array of fuel or power cells.
[0039] FIG. 31 is a flow chart of an example control process
incorporated into a control system used to operate power cells,
such as fuel cells.
[0040] FIG. 32 is a flow chart for the control process of FIG. 9,
incorporating adaptation for temperature, humidity, pressure, and
device failure.
[0041] FIG. 33 is a plot that indicates how the V-I curve of an
aggregate array of fuel cells varies with the number of
series-connected fuel cell devices in a column.
[0042] FIG. 34 is a plot that indicates how the V-I curve of an
aggregate array of fuel cells varies with the number of
parallel-connected fuel cell devices in a row.
[0043] FIGS. 35A and 35B are plots that indicate total power
generated, internal power dissipation, power delivered to the load,
and power efficiency for a typical V-I curve.
[0044] FIGS. 36A and 36B are a circuit schematic diagram and
corresponding functional plot of current, respectively that
illustrate energy lost through repeated on-off switching of a power
cell to maintain an intermediate average value.
[0045] FIG. 37 is a switching topology of a fuel cell array
configured to supply multiple, independently regulated
voltages.
[0046] FIG. 38 is a block diagram of an array of power cells used
to generate power in a power amplifier configuration.
[0047] FIG. 39 is a block diagram illustrating an output waveform
generated by an array of power cells controlled to adjust an output
power to compensate for effects of a load.
[0048] FIG. 40 is a block diagram of an example array of power
cells having zones sequentially or otherwise selected to deliver
power to a load.
[0049] FIG. 41 is a block diagram of an array of power cells
operated in a manner to warm up the power cells during an example
start-up sequence.
[0050] FIG. 42 is a functional diagram of a controller having
kernel (basic) functions and higher functions configured to employ
the kernel functions.
[0051] FIG. 43 is a schematic diagram of a power cell being
connected to other power cells that generate a pulse or other
waveform to clean contaminants from the cell receiving the pulse or
other waveform.
[0052] FIG. 44 is a schematic plan view of a power cell for
conducting electro-chemical reaction.
DETAILED DESCRIPTION OF THE INVENTION
[0053] A description of example embodiments of the invention
follows.
[0054] Referring now to FIG. 1, there is shown in plan view a
conventional semiconductor wafer 10 upon which a plurality of
semiconductor fuel cells 12 have been fabricated. A plurality of
cells may be electrically interconnected on a wafer and provided
with gases to form a power chip 15. For simplicity, fuel cells 12
and chips 15 are not shown to scale in as much as it is
contemplated that at least 80 million cells may be formed on a 4''
wafer. One such cell is shown in fragmented cross-section in FIG.
2. In its simplest form, each cell 12 consists of a substrate 14,
contacts 16A and B, and a conductive polymer base 18 formed on both
sides of a first layer 20(a) of non-conductive layered polymer
support structure 20 and in intimate contact with the metal
electrical contacts.
[0055] A conductive polymer 22 with embedded catalyst particles 28
on both sides of the central structure 20 forms a PEM barrier
separating the hydrogen gas on the left side from the oxygen gas on
the right side. Etched channels 50B and 50A respectively for
admittance of the O.sub.2 and H.sub.2 gas and a heatsink lid 40
over the cell 12 is also shown in FIG. 2.
[0056] FIGS. 3a-3h are a series of schematic sectional views
showing the relevant fabrication details of the PEM barrier 30 in
several steps. FIG. 3a shows the bottom of a fuel cell channel
which has been etched into the semiconductor substrate 14. It also
shows the metal contacts 16 which are responsible for conveying the
electrons out of the fuel cell 12 to the rest of the circuitry.
These metal contacts are deposited by well-known photolithographic
processes in the metalization phase of the semiconductor
fabrication process.
[0057] FIG. 3b shows the conductive polymer base 18 as it has been
applied to the structure. Base 18 is in physical/electrical contact
with the metal contacts 16 and has been adapted to attract the
conductive polymer 22 of the step shown in FIG. 3a-3h.
[0058] FIG. 3c shows the nonconductive polymer base 20(a) as it has
been applied to the structure. It is positioned between the two
conductive polymer base sites 18 and is adapted to attract the
nonconductive polymer 20.
[0059] FIG. 3d shows a polymer resist 21 as applied to the
structure. Resist 21 is responsible for repelling the polymers and
preventing their growth in unwanted areas.
[0060] FIG. 3e shows the first layer 20B of nonconductive polymer
as it has been grown on its base 20A. This is the center material
of the PEM barrier. It helps support the thinner outer sides 22
when they are constructed.
[0061] FIG. 3f shows the subsequent layers of nonconductive polymer
20 which are laid down, in a layer by layer fashion to form a
vertical barrier. This vertical orientation allows for area
amplification.
[0062] FIG. 3g shows the first layer 22a of conductive polymer
grown on its base 18. This is the outside wall material with
catalyst of the PEM barrier.
[0063] FIG. 3h shows the subsequent layers of conductive polymer 22
laid down, in a layer by layer fashion on to the structure. FIG. 2
shows the completed structure after removal of the polymer resist
layer 21 and the addition of lid 40 and the pre-existing sidewalls
52 left out of FIG. 3a-3h for simplicity. This resist removal may
not be necessary if layer 21 was originally the passivation layer
of the final step in the semiconductor fabrication process.
[0064] Referring now to FIG. 2 again further details of the
elements forming the fuel cell 12 will be explained. The protein
exchange membrane is shown generally at 30 forms a barrier between
the fuel H.sub.2 and the oxidant O.sub.2.
[0065] The PEM barrier 30 is made up of three parts of two
materials. There is the first outside wall 22B, then the center 20,
and finally the second outside wall 22C. It is constructed with a
center piece 20 of the first material in contact with the two
outside walls which are both made of the second material.
[0066] The material 20 forming the center piece is preferably an
ionic polymer capable of passing the hydrogen ions (protons)
through from the hydrogen side to the oxygen side. It is
electrically nonconductive so that it does not, effectively, short
out the power cell across the two contacts 16A and 16B. It may be
made of Nafion.RTM. or of a material of similar characteristics. An
external load 5 as shown in dotted lines may be coupled across the
contacts to extract power.
[0067] The second material 22, forming the two outside walls, is
also a similar ionic polymer capable of passing the hydrogen ions.
In addition, it is doped with nano catalyst particles 28 (shown by
the dots), such as, platinum/alloy catalyst and is also
electrically conductive.
[0068] By embedding the catalyst particles 28 into the polymer 22,
maximum intimate contact is achieved with the PEM 30. This intimate
contact provides a readily available path which allows the ions to
migrate freely towards the cathode electrode 16B. Catalysis is a
surface effect. By suspending the catalytic particles 28 in the
polymer 22, effective use of the entire surface area is obtained.
This will dramatically increase the system efficiency.
[0069] By making the second material 22 electrically conductive, an
electrode is produced. The proximity of the electrode to the
catalytic reaction affects how well it collects electrons. This
method allows the catalytic reaction to occur effectively within
the electrode itself. This intimate contact provides a readily
available path which allows the electrons to migrate freely towards
the anode 16A. This will allow for the successful collection of
most of the free electrons. Again, this will dramatically increase
the system efficiency.
[0070] In addition to the electrical and chemical/functional
characteristics of the PEM 30 described above, there are some
important physical ones that are described below:
[0071] This self assembly process allows for the construction of a
more optimum PEM barrier. By design it will be more efficient.
[0072] First, there is the matter of forming the separate hydrogen
and oxygen path ways. This requires that the PEM structure to be
grown/formed so that it dissects the etched channel 50 fully into
two separate channels 50A, 50B. This means that it may be patterned
to grow in the center of the channel and firmly up against the
walls of the ends of the power cell. It may also be grown to the
height of the channel to allow it to come into contact with an
adhesive 42 on the bottom of lid 40.
[0073] Second, there is the matter of forming a gas tight seal.
This requires that the PEM structure 30 be bonded thoroughly to the
base structures 18 and 20A, the substrate 14 and the end walls (not
shown) of the power cell and to an adhesive 42 which coats the lid
40. By proper choice of the polymers, a chemical bond is formed
between the materials they contact in the channel. In addition to
this chemical bond, there is the physical sealing effect by
applying the lid 40 down on top of the PEM barrier. If the height
of the PEM 30 is controlled correctly, the pressure of the applied
lid forms a mechanical "O ring" type of self seal. Growing the PEM
30 on the substrate 14 eliminates any fine registration issues when
combining it with the lid 40. There are no fine details on the lid
that require targeting.
[0074] Turning now to FIG. 4, there is shown in simplified
perspective an alternate embodiment of a PEM barrier involving a
casting/injecting process and structure.
[0075] Using MEMS machining methods three channels 60A, 60B and 60C
are etched into a semiconductor substrate 140. The outside two
channels 60A and 60C are separated from the middle channel 60B by
thin walls 70A, 70B. These walls have a plurality of thin slits
S.sub.1 - - - S.sub.n etched into them. The resultant tines T.sub.1
- - - T.sub.n+1 have a catalyst 280 deposited on them in the area
of the slits. At the bottom of these thin walls, 70A, 70B, on the
side which makes up a wall of an outside channel 60A, 60C, a metal
electrode 160A, 160B is deposited. A catalyst 280 is deposited on
the tines after the electrodes 160 are in place. This allows the
catalyst to be deposited so as to come into electrical contact and
to cover to some degree, the respective electrodes 160 at their
base. In addition, metal conductors 90 are deposited to connect to
each electrode 160, which then run up and out of the outside
channels.
[0076] A lid 400 is provided with an adhesive layer 420 which is
used to bond the lid to the substrate 140. In this way, three
separate channels are formed in the substrate; a hydrogen channel
60A, a reaction channel 60B, and an oxygen channel 60C. In
addition, the lid 400 has various strategically placed electrolyte
injection ports or holes 500. These holes 500 provide feed pathways
that lead to an electrolyte membrane of polymer material (not
shown) in the reaction channel 60B only.
[0077] The structure of FIG. 4 is assembled as follows:
[0078] First, the semiconductor fabrication process is formed
including substrate machining and deposition of all electrical
circuits.
[0079] Next, the lid 400 is machined and prepared with adhesive
420. The lid 400 is bonded to the substrate 140. Then, the
electrolyte (not shown) is injected into the structure.
[0080] The thin walls 70A, 70B of the reaction channel 60B serve to
retain the electrolyte during its casting. The slits S.sub.1 - - -
S.sub.N allow the hydrogen and oxygen in the respective channels
60A, 60B access to the catalyst 280 and PEM 300. Coating the tines
T.sub.1 - - - T.sub.1+n with a catalyst 280 in the area of the
slits provides a point of reaction when the H.sub.2 gas enters the
slits. When the electrolyte is poured/injected into the reaction
channel 60B, it fills it up completely. The surface tension of the
liquid electrolyte keeps it from pushing through the slits and into
the gas channels, which would otherwise fill up as well. Because
there is some amount of pressure behind the application of the
electrolyte, there will be a ballooning effect of the electrolyte's
surface as the pressure pushes it into the slits. This will cause
the electrolyte to be in contact with the catalyst 280 which coats
the sides of the slits S.sub.1 - - - S.sub.N. Once this contact is
formed and the membrane (electrolyte) is hydrated, it will expand
even further, ensuring good contact with the catalyst. The
H.sub.2/O.sub.2 gases are capable of diffusing into the (very thin,
i.e. 5 microns) membrane, in the area of the catalyst. Because it
can be so thin it will produce a more efficient i.e. less
resistance (1.sup.2R) losses are low. This then puts the three
components of the reaction in contact with each other. The
electrodes 160A and 160B in electrical contact with the catalyst
280 is the fourth component and provides a path for the free
electrons [through an external load (not shown)] while the hydrogen
ions pass through the electrolyte membrane to complete the reaction
on the other side.
[0081] Referring now to the cross-sectional views of FIGS. 5-7,
various alternate configurations of the PEM structure 30 of the
invention will be described in detail. In FIG. 5, the central PEM
structure 20 is formed as a continuous nonconductive vertical
element, and the electrode/catalyst 16/28 is a non-continuous
element to which lead wires 90 are attached. FIG. 6 is a view of an
alternate PEM structure in which the catalyst 28 is embedded in the
non-conductive core 20 and the electrodes 16 are formed laterally
adjacent the catalyst. Lastly, in FIG. 7, the PEM structure is
similar to FIG. 5 but the center core 20.sup.1 is
discontinuous.
[0082] FIG. 8 is a schematic block diagram showing some of the
possible circuits that may be integrated along with a
microcontroller onto the semiconductor wafer 10 to monitor and
control multiple cells performance. Several sensor circuits 80, 82,
84 and 86 are provided to perform certain functions.
[0083] Temperature circuit 80 provides the input to allow the micro
processor 88 to define a thermal profile of the fuel cell 12.
Voltage circuit 82 monitors the voltage at various levels of the
configuration hierarchy or group of cells. This provides
information regarding changes in the load. With this information,
the processor 88 can adjust the system configuration to
achieve/maintain the required performance. Current circuit 84
performs a function similar to the voltage monitoring circuit 82
noted above.
[0084] Pressure circuit 86 monitors the pressure in the internal
gas passages 50A, 50B. Since the system's performance is affected
by this pressure, the microprocessor 88 can make adjustments to
keep the system running at optimum performance based on these
reading. An undefined circuit 81 is made available to provide a few
spare inputs for the micro 88 in anticipation of future
functions.
[0085] In addition, configuration circuit 94 can be used to control
at least the V*I switches to be described in connection with FIG.
9. The output voltage and current capability is defined by the
configuration of these switches. Local circuitry 92 is provided as
necessary to be dynamically programmed, such as the parameters of
the monitoring circuits. These outputs can be used to effect that
change. Local subsystems 94 are used by the micro 98 to control gas
flow rate, defect isolation and product removal. A local power
circuit 96 is used to tap off some part of the electricity
generated by the fuel cell 12 to power the onboard electronics.
This power supply circuit 96 will have its own regulation and
conditioning circuits. A two-wire communications I/F device 98 may
be integrated onto the chip to provide the electrical interface
between communicating devices and a power bus (not shown) that
connects them.
[0086] The microcontroller 8 is the heart of the integrated
electronics subsystem. It is responsible for monitoring and
controlling all designated system functions. In addition, it
handles the communications protocol of any external communications.
It is capable of "in circuit programming" so that its executive
control program can be updated as required. It is capable of data
storage and processing and is also capable of self/system
diagnostics and security features.
[0087] Referring now to FIG. 9, further details of the invention
are shown. In this embodiment, the individual power cells 12.sub.1,
12.sub.2 - - - 12.sub.4 are formed on a wafer and wired in parallel
across power buses 99A and 99B using transistor switches 97 which
can be controlled from the microprocessor 88 of FIG. 8. Switches
97B and 97A are negative and positive bus switches respectively,
whereas switch 97C is a series switch and switches 97D and 97E are
respective positive and negative parallel switches
respectively.
[0088] This allows the individual cells or groups of cells (power
chip 15) to be wired in various configurations, i.e., parallel or
series. Various voltages are created by wiring the cells in series.
The current capacity can also be increased by wiring the cells in
parallel. In general, the power profile of the power chip can be
dynamically controlled to achieve or maintain a "programmed"
specification. Conversely, the chip can be configured at the time
of fabrication to some static profile and thus, eliminate the need
for the power switches. By turning the switches on and off and by
changing the polarity of wiring one can produce both AC and DC
power output.
[0089] To implement a power management subsystem, feedback from the
power generation process is required. Circuitry can be formed
directly on the chip to constantly measure the efficiencies of the
processes. This feedback can be used to modify the control of the
system in a closed loop fashion. This permits a maximum level of
system efficiency to be dynamically maintained. Some of these
circuits are discussed next.
[0090] The quality of the power generation process will vary as the
demands on the system change over time. A knowledge of the realtime
status of several operational parameters can help make decisions
which will enable the system to self-adjust, in order to sustain
optimum performance. The boundaries of these parameters are defined
by the program.
[0091] For example, it is possible to measure both the voltage and
the current of an individual power cell or group of power cells.
The power output can be monitored and if a cell or group is not
performing, it can be removed if necessary. This can be
accomplished by the power switches 97 previously described.
[0092] An average power level can also be maintained while moving
the active "loaded" area around on the chip. This should give a
better overall performance level due to no one area being on 100%
of the time. This duty cycle approach is especially applicable to
surge demands. The concept here is to split the power into pieces
for better cell utilization characteristics.
[0093] It is expected that the thermal characteristics of the power
chip will vary due to electrical loading and that this heat might
have an adverse effect on power generation at the power cell level.
Adequate temperature sensing and an appropriate response to power
cell utilization will minimize the damaging effects of a thermal
build up.
[0094] The lid 40 is the second piece of a two-piece "power chip"
assembly. It is preferably made of metal to provide a mechanically
rigid backing for the fragile semiconductor substrate 14. This
allows for easy handling and provides a stable foundation upon
which to build "power stacks", i.e., a plurality of power chips 15
that are literally stacked on top of each other. The purpose is to
build a physical unit with more power.
[0095] FIG. 10 illustrates how the fuel 50A and oxidant/product
channels 50A (and 50B not shown) may be etched into the surface of
the substrate 14. These troughs are three sided and may be closed
and sealed on the top side. The lid 40 and adhesive 42 provides
this function of forming a hermetic seal when bonded to the
substrate 14 and completes the channels. A matrix of fuel supply
and oxidant and product water removal channels is thereby formed at
the surface of the substrate.
[0096] The lid 40 provides a mechanically stable interface on which
the input/output ports can be made. These are the gas supply and
water removal ports. The design may encompass the size transition
from the large outside world to the micrometer sized features on
the substrate. This is accomplished by running the micrometer sized
channels to a relatively much larger hole H. This larger hold will
allow for less registration requirements between the lid and
substrate. The large holes in the lid line up with the large holes
in the substrate which have micrometer sized channels also machined
into the substrate leading from the large hole to the power
cells.
[0097] Each wafer may have its own manifolds. This would require
external connections for the fuel supply, oxidant and product
removal. The external plumbing may require an automated docking
system.
[0098] FIGS. 11 and 12 illustrates one of many ways in which
several cells 12 (in this example three cells side-by-side can be
formed on a wafer 14 to form a power chip 15. Power disks can be
stacked vertically upon each other to form a vertical column with
inlet ports, 50HI, 50OI respectfully coupled to sources of hydrogen
and oxygen respectively. The vertical column of wafers with power
chips formed therein comprises a power stack (93).
[0099] FIG. 12 illustrates how stacking of a number of power discs
15 maybe used to form power stacks (93) with appreciable power. The
use of the word "stacking" is reasonable for it suggests the close
proximity of the wafers, allowing for short electrical
interconnects and minimal plumbing. In reality, the stacking
actually refers to combining the electrical power of the wafers to
form a more powerful unit. They need only to be electrically
stacked to effect his combination. However, it is desirable to
produce the most amount of power in the smallest space and with the
highest efficiencies. When considering the shortest electrical
interconnect (power bussing) alternatives, one should also consider
the possibility of using two of the main manifolds as electrical
power busses. This can be done by electrically isolating these
manifold/electrical power buss segments and using them to convey
the power from each wafer to the next. This reduces the big power
wiring requirements and permits this function to be done in an
automated fashion with the concomitant increased accuracy and
reliability.
[0100] A desirable manifold design would allow for power disc
stacking. In this design the actual manifold 95 would be
constructed in segments, each segment being an integral part of the
lid 40. As the discs are stacked a manifold (tube) is formed. This
type of design would greatly reduce the external plumbing
requirements. Special end caps would complete the manifold at the
ends of the power stack.
[0101] In summary of the disclosed embodiment thus far, one of the
primary objects of this invention is to be able to mass produce a
power chip 15 comprised of a wafer 10 containing multiple power
cells 12 on each chip 15 utilizing quasi standard semiconductor
processing methods. This process inherently supports very small
features. These features (power cells), in turn, are expected to
create very small amounts of power per cell. Each cell will be
designed to have the maximum power the material can support. To
achieve any real substantially power, many millions will be
fabricated on a single power chip 15 and many power chips
fabricated on a "power disc" (semiconductor wafer 10). This is why
reasonable power output can be obtained from a single wafer. A 10
uM.times.10 uM power cell would enable one million power cells per
square centimeter. The final power cell topology will be determined
by the physical properties of the constituent materials and their
characteristics.
[0102] The basic electro-chemical reaction of the solid polymer
hydrogen fuel cell is most efficient at an operating temperature
somewhere between 80 to 100 C. This is within the operating range
of a common semiconductor substrate like silicon. However, if the
wafers are stacked additional heatsinking may be required. Since a
cover is needed anyway, making the lid 40 into a heatsink for added
margin makes sense.
[0103] The fuel and oxidant/product channels are etched into the
surface of the semiconductor substrate. These troughs are
three-sided and may be closed and sealed on the top side. The lid
40 provides this function. It is coated with an adhesive to form a
hermetic seal when bonded to the semiconductor substrate and
completes the channels. This forms a matrix of fuel supply and
oxidant and product water removal channels at the surface of the
semiconductor substrate. The power cells two primary channels are
themselves separated by the PEM which is bonded to this same
adhesive. Thus, removing any fine grain is helpful in achieving
alignment requirements.
Power Cell and Power Chip Architecture
[0104] It should be understood that the power cells described above
may include a membrane having a three-dimensional geometric
structure that encompasses a volume and a cover coupled to the
membrane to separate a first flow path from a second flow path at
the membrane. Herein, "a power cell" and "fuel cell" are synonymous
and used interchangeably. The power cell may also include an anode
catalyst layer, a cathode catalyst layer on the cover. Optionally,
the power cell may include a substrate having holes for flow of
fuel or oxidant to the catalyst. Another embodiment of the present
invention is a power chip. The power fuel comprises an array of the
power cells of the first embodiment with a manifold in gaseous
communication with the first flow paths or at least one of the
second flow paths to distribute the fuel or oxidant. The power chip
also includes terminals electrically coupled to the first and
second catalyst to provide an interface to energy generated by the
power cells. The electrical interconnect may extend between the
power cells and switches, fuses, or metal links for the purpose of
configuring the array or a subset of the array and interfacing with
an external load. The configuration of the power chip may be
programmable and may include control electronics elements, such as
switches. The power chip may further include bond pads and package
supporting stacks of the power chips.
[0105] Another embodiment of the present invention is a power disk
that comprises an array of the fuel cells described in the first
embodiment with the substrate electrically interconnecting
electrodes with catalyst and optionally to an external load. The
electrical interconnect may extend between the fuel cells and
switches, fuses, or metal links in a configurable manner. The
configuration of the power chip may be programmable. The power disk
may further include bond pads and package supporting stacks of the
power chips.
[0106] Yet in another embodiment of the present invention is the
power stack. The power stack comprises an array of the power disks
with a plurality of the power disks, packaging including an
electrical interconnection, packaging including a parallel gas flow
interconnect, and a system of manifold(s) enclosing the array of
fuel cells to distribute the fuel or oxidant.
[0107] Other embodiments may include combinations of the following
which shall be described in further details: a fuel cell with
selected plan view geometric shape(s) (e.g., circle, square,
serpentine), a castellation of wall, a corrugation (fins on wall),
a catalyst on cover, a cover structure "low power" and "high power,
a bidirectional operation means (electrolyzer and fuel cell), and a
generalized micro-scale chemical reactor on a chip.
[0108] FIG. 13 shows a plan view of a conventional semiconductor
wafer 1305 upon which a plurality of semiconductor fuel cells have
been fabricated. Upon this wafer 1305 are constructed a plurality
of power chips 1310 using, with a few exceptions described below,
standard and well-established semiconductor and micro-electrical
mechanical systems fabrication methods. For simplicity, the power
chips 1310 are not shown to scale.
[0109] After manufacture and wafer-level testing, the power chips
may be separated and packaged as individual power-generation
devices, each containing one copy of the integrated circuit that is
being produced. Each one of these devices is called a "die". The
dimensions of each individual die may be 1 cm.sup.2 or smaller or
larger as dictated according to the needs of the application of the
power chip.
[0110] It should be understood that the substrate 1305 may be other
forms of substrate, such as metal, glass, silicon carbine and so
forth.
[0111] FIG. 14 describes the elements of a power chip 1410. Each
power chip includes several subcomponents. Each power chip can be
constructed on a substrate 1405, such as a standard silicon wafer,
upon which are constructed a large plurality of fuel cells 1412 by
means of various MEMS fabrication steps. Metal layers 1416, 1415a,
and 1415b are applied to the silicon and etched to form a suitable
electrical interconnection network among the power cells 1412.
Suitable insulation layers 1420, following conventional
semiconductor practices, interleave the metal layers to provide
electrical insulation and chemical, mechanical and environmental
protection.
[0112] Bond pads 1425 are constructed at the edges of the power
chip 1410, again following conventional practices, and provide a
means of electrical connection between the power chip 1410 to
external circuits (not shown). Bond leads (not shown) may connect
to a circuit board using customary chip-on-board methods, or to
contacts (not shown) at the edge of a molded package which
facilitates stacking of multiple power chips as described
below.
[0113] In addition, the silicon area underneath and between the
power cell structures 1412 of the power chip 1410 may contain
control electronics circuit elements 1430. These circuit elements
1430 include, but are not limited to, embedded control circuits,
RAM or FLASH or ROM memory, logic in, for example, digital
Application Specific Integrated Circuit (ASIC) form, A/D, sense and
switching devices, which, taken together, may supervise, control,
optimize and report to external devices and/or other fuel cells
upon the operation of the power chip 1410.
[0114] FIG. 15 shows a perspective view of a vertical cross section
of an embodiment of an individual fuel cell 1500. In accordance
with one embodiment of a fuel cell of the present invention, a
Proton Exchange Membrane (PEM) wall 1505 is configured to form a
three-dimensional geometric structure, defining a volume 1507 of a
first flow path 1510. That is, in the example of FIG. 15, the PEM
wall 1505 encompasses a volume 1507 in shape of, for example,
cylindrical shape and defines a portion of the first flow path. A
cover 1520 is coupled to the top of the three dimensional
geometrical structure formed by the PEM wall 1505 structure
creating a closed chamber and separating the first flow path 1510
from a second flow path 1515 at the PEM wall 1505. While coupling
the cover 1520 to the PEM wall 1505 seals one end of the volume
1507, the opposite end of the volume 1507 closer to the entrance of
the first flow path 1510 is open, thereby, accessible to a flow of
oxidant or fuel.
[0115] The cover 1520 may made of a gas impermeable material to
prevent shorting out between oxidant and fuel and can be made from
a different material or the same material from that of the PEM wall
1505. The PEM wall 1505 is preferably an ionic polymer capable of
passing the hydrogen ions (protons) through from the hydrogen side
to the oxygen side. The PEM wall 1505 is electrically nonconductive
so that it does not, effectively, electrically short out the fuel
cell 1500 across an anode 1530 and cathode 1535 on opposite sides
of the PEM wall 1505. The PEM wall 1505 may be made of Nafion.RTM.
or of a material of similar characteristics. A load (not shown) may
be coupled across contacts (e.g. metal wires 1545a, 1545b)
electrically connected to the anode 1530 and cathode 1535 to
extract power during operation of the fuel cell 1500. Additionally,
the PEM wall 1505 can be doped with catalyst particles, such as
platinum/alloy catalyst that are electrically conductive.
[0116] In one embodiment, the power cell includes a substrate 1540,
which can support the fuel cell 1500, as described above. However,
the substrate 1540 is an optional feature for the fuel cell 1500.
In other words, because the PEM wall 1505 is a three-dimensional
structure, the PEM wall 1505 can be an autonomous structure that
can stand upright by itself; therefore, the substrate 1540 is not a
necessary component for the fuel cell 1500 of the present
invention. When the substrate 1540 is employed, the PEM wall 1505
can be coupled to the substrate at a location through which the
fuel or oxidant can flow into the volume 1507. Further separating
the first flow path 1510 and the second flow path 1515, the cover
1520 is now coupled to PEM wall 1505 by a method commonly known by
one skilled in the art.
[0117] In one embodiment, the cover 1520 can be attached using an
appropriate combination of heat, solvent, adhesive, and sonic
welding and/or downward pressure. For example, it can be patterned
and etched. All these methods that are familiar in semiconductor
manufacturing practices can be applied. For example, PEM wall 1505
is bonded thoroughly to the substrate 1540 to form a gas tight seal
by an adhesive. Alternatively, the cover 1520 and PEM wall 1505 can
be attached by forming a chemical bond between the materials, for
example, using a polymer. In addition to this chemical bond, there
is the physical sealing effect by applying the cover 1520 down on
the top 1509 of the PEM wall 1505. If the height of the PEM wall
1505 is controlled correctly, the pressure of the applied cover can
form a mechanical "O-ring" type of self seal. Growing the PEM wall
1505 on the substrate 1540 can eliminate any fine registration
issues when combining it with the cover.
[0118] In some embodiments, the cover 1520 being in contact with
the top of the three-dimensional structure can be made "active"
(i.e., having electrodes covered with respective catalyst on each
side in similar configuration as the cylinder walls), thereby
increasing active surface area for production of electricity.
Furthermore, it should be understood that a third material (not
shown), non-gas permeable, can be constructed to the top of the PEM
wall 1505, and the cover 1520 can be affixed to the PEM wall 1505
via the third material. For example, a spacer (not shown) can be
placed on top 1509 of the PEM wall 1505 so that the cover 1520 is
not in physical contact with any part of the PEM wall 1505 while
maintaining gaseous communication with the first flow path 1510 for
production of electricity.
[0119] In another embodiment, depending upon the specific sequence
of process steps employed in fabrication, the catalyst coating may
extend to one or both sides of the cover as well, further
increasing the reactive surface area of the device. Alternatively,
the first layer of the cover can be provided with an adhesive layer
which is used to bond the cover to the top of the three-dimensional
structure shown in FIG. 15.
[0120] Continuing to refer to the fuel cell 1500 shown in FIG. 15,
the metal 1545a and metal 1545b are two separate metal layers
separated by insulation layers 1506. Metal 1545a is connected to
the fuel cell cathode 1535, and metal 1545b is connected to the
fuel cell anode 1530. The anode 1530 and the cathode 1535 are
separated by a layer of the PEM wall 1505.
[0121] In one embodiment, the catalyst 1530 and 1535 are embedded
on the sides of the PEM wall 1505. By embedding the catalyst,
maximum intimate contact is achieved with the PEM wall 1505.
Catalysis is a surface effect. This intimate contact provides a
readily available path which allows the ions to migrate freely
towards the cathode 1535. By suspending the catalysis in the PEM
wall 1505, effective use of the entire surface area is obtained.
This can dramatically increase the system efficiency.
[0122] Gaseous fuel (e.g. hydrogen) 1585 (i) can be introduced into
the volume 1507 through hole(s) 1512 in the substrate 1540
facilitating the first flow path 1510 at the fuel cell 1500 and
(ii) is reduced by contact with the anode catalyst 1530. Electrons
resulting from this reaction travel through the conductive
catalytic layer to the metal 1545b and, in turn, to the load (not
shown). Protons resulting from the reaction travel through the PEM
wall 1505 to the cathode 1535. Oxidant 1550 (e.g. oxygen) available
via the second flow path 1515 at the cathode 1535 at the fuel cell
1500 from ambient air 1555 combines with the protons flowing
through the PEM wall 1505 and electrons arriving from the load via
metal 1545a to produce water vapor.
[0123] Alternatively, the anode 1530 and cathode 1535 can be
assembled in the opposite configuration, where the anode 1530 is
connected to one metal 1545a, and the cathode 1535 is connected to
the other metal 1545b. In such a configuration, gaseous fuel is
introduced via the second flow path 1515, and the oxidant is
introduced via the first flow path 1510.
[0124] The PEM material can be initially deposited on the substrate
or the wafer by means of spin coating, spraying, dipping, or other
methods conventionally used in semiconductor manufacturing. The PEM
material can then be photolithographically patterned and etched to
form the wall contours shown as the PEM wall 1505 in FIG. 15. The
catalyst layers 1530 and 1535 may be applied to the PEM as a
coating, again using conventional semiconductor fabrication methods
with an appropriate combination of sputtering, evaporating,
spraying, transfer printing, and immersion. The resulting catalyst
layer may have a plurality of sub layers, constructed specifically
to support the conflicting requirements of large surface area to
contact the ambient gas and to maintain (i) ionic conductivity to
support proton transfer to the PEM and (ii) electrical conductivity
to support electron transfer to the metal layers on the substrate.
Due to the multiple layers of the catalyst, effective use of the
entire surface is obtained.
[0125] Although FIG. 15 shows a fuel cell of cylindrical form,
other shapes are possible, depending on performance characteristics
desired for a particular application. For example, the shapes shown
in plain view in FIGS. 16A-16D, or combinations or extension of
them, may be employed.
[0126] FIG. 16A shows a similar cylindrical structure 1600 as that
of shown in FIG. 15 in a simplified schematic cross-sectional plan
view of the power chip without a cover. The cylindrical structure
1600 with a circular cross-section area includes of a substrate
1610, a PEM wall 1605, which is positioned between catalyst layers
1615, 1620 serving as a cathode and anode, respectively, in one
embodiment. Formed in the center of the cylindrical structure 1600
is a flow path 1625 for flowing fuel or oxidant.
[0127] FIG. 16B shows the same components as that of FIG. 16A but
in a non-circular cross-sectional plan view of a structure 1650,
which permits more reactive surface area (i.e. wall length
multiplied by height) per unit of footprint area than does the
cylindrical structure with a circular cross-sectional area similar
to the one shown in FIG. 16A. However, the non-cylindrical shape
may be at the expense of less volume available for flow of fuel or
oxidant around the cathode if a high density array of
non-cylindrical fuel cells is constructed.
[0128] FIG. 16C is an example of a curvilinear construction 1660
including the same components as that of the cylindrical and
rectangular counterparts. The curvilinear construction 1660 offers
an even higher ratio of reactive surface area per unit footprint
area than the rectangular and cylindrical constructions.
Furthermore, the curvilinear construction 1660 can have one or more
flow paths 1665 facilitating flow of fuel or oxidant as shown in
FIG. 16C.
[0129] FIG. 16D is an example of fuel cell construction 1670 having
a serpentine shape in plan view.
[0130] FIG. 17 is another cross-sectional diagram that indicates a
further extension which is possible by etching fins 1710 onto the
castellated surface. This embodiment shows a section of a PEM wall
1705 from above, which could be applied to any part of any of the
general shapes shown in FIGS. 16A-16D. The fins 1710 can achieve a
dramatic further increase in surface area. If the aspect ratio of
the fins is too high, however, the fins may be less effective
because of the increasing effective resistance of the proton
conduction path. Furthermore, there may be a limit on the gains
achievable from this method depending on the characteristics of the
etching process employed. Note that the hydrogen may be either
dead-ended or flowing; oxygen flows in as well as out for water
removal via, for example, a manifold that is connected to a fuel
cell having the PEM 1710 with the fins 1705.
[0131] FIGS. 18A through 18C are plan view diagrams showing how the
reactive surface area of the device, which is used in achieving
high power density, is further increased. The reactive surface area
is increased using the constructions described above and can be
further increased, as described immediately below. FIG. 18A shows a
standard planar PEM 1805 typical of prior art planar fuel cells,
which, for example, might have dimensions of 40 um by 400 um, with
16,000 .mu.m.sup.2 foot-print and reactive surface area of 8000
.mu.m.sup.2. In FIG. 18B, creating a rectangular, three-dimensional
PEM 1810 structure in accordance with an embodiment of the present
invention on this same footprint yields 76,000 um.sup.2, or more
than 4 times that of the planar PEM of the FIG. 18A. FIG. 18C shows
how a castellation of the PEM wall 1815 can again double the
surface area, producing 8 times the surface area of a planar design
because the reactive surface area increases to 144,000 um.sup.2.
Since the cost of a semiconductor device tends to increase in
proportion to the silicon "footprint" area employed, this high
multiple results in correspondingly higher effective power density
and lower cost per watt generated.
[0132] FIGS. 19A and 19B are diagrams that show a useful variation
of the fuel cell design. As described above in reference to FIG. 1,
an embodiment of the present invention is an array of fuel cells
electrically interconnected and provided with gases and oxidants to
separate flow paths to form a power chip. The fuel cells
interconnected to form the power chip can include an array of any
embodiment of fuel cells disclosed herein. The power chip may
further include at least one plenum in gaseous communication with
flow paths for distributing fuel or oxidant and one pair of
terminals electrically coupled to the anode catalyst of at least a
subset of the array of power cells.
[0133] FIG. 19A is a diagram that depicts a power chip 1900a
including an array of fuel cells 1905a with a plurality of
membranes 1922 encompassing to three-dimensional geometric volumes
(i.e., cylindrical), in the interior of the fuel cells 1905a. Each
PEM wall 1922 is coupled to a cover 1910a, sealing the PEM wall
1922 and rendering each fuel cell 1905 dead-ended. Fuel is then
flown into the three-dimensional geometric volumes of PEM wall 1922
to be in gaseous communication with anode catalyst 1915a. Because
cathode catalyst 1925a is exposed to open air 1920, the cathode
catalyst 1925a effectively has access to oxidant (e.g., oxygen) in
the open air 1920 for reacting the fuel and oxidant at the power
chip 1900a to generate energy. The fuel cells of the power chip
1900a can be divided into subsets, each subset controlled by
enabling and disabling electron flow to or from the subset.
[0134] FIG. 19B is a diagram of power chip 1900b that illustrates
an alternative cover configuration to the cover configuration in
FIG. 19A. Here, the cover 1910b is the "negative" of the cover
1910a in FIG. 19A. Instead of having a plurality of covers as shown
in FIG. 19a, the power chip 1900b may use one contiguous cover to
be coupled to the membranes of the fuels cells. In such
configuration, a flow path through the interior of the cylinders
1905b is not dead-ended so that the power cell 1905b can more
effectively remove reaction by-products. In this embodiment, the
cathode 1925b and anode 1915b may be interchanged so that water or
other byproduct formed at the cathode may be removed more
readily.
[0135] A variation of the aforementioned designs may be useful in
high-power systems. In contrast to the configuration of FIG. 13,
the substrate or wafer (also referred to herein as a power disk) is
not designed to be divided and packaged in small units. In one
embodiment, the power disk can include (1) an array of any
embodiment of fuel cells disclosed herein, (2) at least one plenum
in gaseous communication with flow paths of the fuel cells to
distribute the fuel and oxidant, (3) at least one pair of terminals
electrically coupled to the anode and cathode catalyst of at least
a subset of the power cells to provide an interface to energy
generated by the power cells, and (4) at least one bus power
electrically coupled to the terminals. The metal layer
interconnections and control electronics (not shown) may be
configured to connect to individual fuel cells or substrate-wide.
In one embodiment, the power disk can further include switches to
interconnect the power chips in an electrically selective manner.
In a preferred embodiment, the power disk can also include
electronics to control the switches. It should be noted that when
the array of power cells is coupled to a substrate, the plenum is
configured to distribute the fuel or oxidant with substantially
uniform pressure. The plenum may be provided with at least one
outlet so that, for example, a byproduct of the reaction between
the fuel, oxidant and the power cells can be removed. A plurality
of these power disks may then be stacked in an electrically
parallel connection, forming a power stack.
[0136] In one embodiment of the power chip, instead of electrical
interconnect by wires or circuitry, the fuel cells are electrically
connected by a coat or film of metal on both sides of the
membranes. The coat of metal is in electrical communication with a
terminal at one edge of the power chip, where the terminal is
connected to an external load.
[0137] In another embodiment of a power stack, the power stack can
include a substrate on which at least one power chip is coupled.
The power chip can be any embodiment of power chip disclosed
herein. Yet another embodiment of a power chip can include a
substrate, an array of any embodiment of power cells disclosed
herein, a pair of electrodes coupled to respective cathode and
anode catalyst, and a pair of power disk buses electrically coupled
to the respective first electrode and the respective second
electrode.
[0138] In one embodiment of a power stack, the power stack can
include a power stack a structure, a plurality of power disks
connected to the structure, and power stack terminals associated
with the power stack structure and configured to be electrically
coupled to the disk terminals.
[0139] In one embodiment of the power stack, individual power disks
2005a, 2005b may be stacked such a way that the flows of oxidant
and fuel facilitated by separate manifold as shown in FIG. 20A. For
example, power disks 2005a, 2005b are fitted into a power stack
structure 2045 provided with a system of manifolds to provide paths
for distributing fuel and oxidant to reach power disks. Power disks
2005a, 2005b are positioned between upper plenums 2010a, 2010b and
lower plenums 2015a, 2015b. FIG. 20A shows that each power disk
2005a, 2005b includes one single individual power cell 2029a, 2029b
for illustrative purposes. Therefore, it should be understood that
while not shown in FIG. 20A, each power disk 2005a, 2005b can
include an array of power cells with other components for making a
functional power disk.
[0140] Continuing to refer to FIG. 20A, the power stack is provided
with a first input chase 2025 for an entry point for fuel or
oxidant. The first input chase 2025 has openings 2027a, 2027b so
that the fuel or oxidant can flow into upper plenums 2010a, 2010b.
For example, once the flow of oxidant reaches the upper plenums
2010a, 2010b, the oxidant is in contact with the cathode catalyst
2031a, 2031b of the power cells 2029a,2029b, which is coupled to
substrates 2041a, 2041b. Concurrently, a flow of fuel is entered
via a second input chase 2030, which is opened to the lower plenums
2015a, 2015b. Here, the fuel makes contact with an anode catalyst
2033a, 2033b, triggering a reaction between the fuel, oxidant and
catalyst for generating electrons. Each power disk 2005a, 2005b can
include electrodes electrically coupled to the catalyst for
electron transfer. Alternatively, the anode and cathode catalyst
can be assembled in the opposite configuration where the components
2031a, 2031b are the anode catalyst, and the components 2033a,
2033b are the cathode catalyst. In such a configuration, fuel is
introduced via the first input chase 2025, and oxidant is
introduced via the second input chase 2030.
[0141] Furthermore, the flow path starting at the first input chase
2025 disclosed in FIG. 20A is provided with an exit path. For
example, once the spent fuel or oxidant passes through a flow path
2047a, 2047b after reacting with respective catalyst, the fuel or
oxidant flows to an exit plenum 2043a, 2043b. Passing through the
exit plenums 2043a, 2043b, the spent fuel or oxidant reaches an
output chase 2040, which is provided with an exit 2045. In one
embodiment, this exit passage via the exit plenums 2043a, 2043b and
via the output chase 2040 provides an outlet for removing byproduct
that is produced by the reaction between the fuel, oxidant and the
fuel cells.
[0142] Continuing to refer to FIG. 20A, the fuel or oxidant flow
can be substantially parallel to each power disk, and relatively
little pressure drop may be encountered. Because the individual
reaction sites are extremely small, the stochiometric amounts of
reactant required at each site are very small. Dead-ended,
diffusion-based flow can be used very satisfactorily in many
situations.
[0143] In FIG. 20B is a diagram of another embodiment of a power
stack. A plurality of power disks 2055 are coupled to a power stack
structure 1560, which, in this embodiment, is formed of two or more
hollow paths. The power stack structure 2060, which may include
stiffener (not shown) connected to both hollow posts of the example
structure, is configured to provide a fuel (e.g. hydrogen) flow
path(s) 2070 (shown as dashed lines). The flow path(s) 2070 are in
gaseous communication with a power disk entrance 2051 through which
the fuel can flow into each power disks 2055 via at least one disk
manifold 2065. Because the power disks 2055 are exposed to ambient
air, the power disks 2055 have access to oxidant (i.e. oxygen) in
the air. As such, without a deliberate supply of oxidant through an
oxidant flow in the power stack structure 2060 and manifold in the
power disks 2055, the power stack can sufficiently generate
energy.
[0144] Power disks which are assembled according to such an
arrangement can generate substantial power. FIGS. 21 and 22
illustrate examples.
[0145] FIG. 21 includes a sequence of fuel cell structures and
associated dimensions that show how 10 KW per liter of volume can
be obtained based on a small amount of power density per reactive
surface area.
[0146] FIG. 22 includes other diagrams with dimensions and weight
that show a similar calculation for watts/kg.
Controlling an Array of Power Generators
[0147] Power cells, such as fuel cells, generally possess a source
impedance, and, hence, the voltage the devices can deliver is a
function of current being supplied. As a result, as a load demands
more current, the load tends to decrease the supply voltage that
can be created by placing a number of fuel cell devices in series.
For example, with fuel cells having an open circuit potential of
0.9 volts and a maximum current output capability of 1 milliampere
(mA) at 0.4 volts, a series connection of 12 such devices provides
4.8 volts at a maximum power output of 4.8 mW, and a series
connection of 6 such devices supplies 5.4 volts at zero mW output.
A power supply capacity of 1 ampere can be created by connecting
1,000 series-connected columns of such 1 mA devices together in
parallel, assuming no internal losses.
[0148] Most electronic components require voltage regulation to
within some tolerance, e.g., 5 volts.+-.10%. In some prior art
systems, voltage regulation is accomplished by external voltage
regulators or other similar power conditioning circuits.
[0149] In some embodiments, an arrangement of power cells
automatically switches the number of series devices, obviating need
for external power regulators and, thereby, increasing energy
efficiency, reducing generated heat, reducing circuit board space
requirements, and reducing total cost of a system.
[0150] It is characteristic of fuel cells and many other power
generators that their power conversion efficiency is higher at low
power levels because there is less power dissipation inside the
device. Depending on a shape of a voltage-current (V-I) curve
describing a power cell or equivalent characteristic, there may be
a power level offering optimum efficiency. Typically for fuel
cells, the optimum efficiency is as little voltage drop as
possible, hence minimum current. In this case, a trade-off exists
between fuel efficiency and the number of power devices, hence,
system cost and size.
[0151] Thus, an example optimal control technique for fuel cells
according to some embodiments of the present invention may include
a coarse control loop, which causes the number of series devices in
each column to be adjusted so that the voltage is within tolerance
for the actual load, and a fine control loop, which adds or
subtracts the number of columns of such devices that are connected
in parallel to adjust the voltage further by moving the system up
or down the V-I curve to supply the desired current.
[0152] Further, in embodiments employing a feedback control system,
a control technique may take into account individual, arrays, or
banks of cells, which, when switched into or out of the power
generating circuit, possess a transient response over time. Thus, a
filter or other control law may be used in feedback loop(s) to
ensure stable operation of the feedback control system in the
presence of load transients.
[0153] Further, the characteristics of the fuel cell devices, and,
consequently, coefficients within a feedback filter or other
control law, may depend upon the state of the fuel cell devices at
preceding times or, ambient conditions of temperature, humidity,
and pressure.
[0154] Example methods disclosed herein can be extended (i) to
control current (i.e., constant current source rather than constant
voltage source) delivery of multiple voltages or currents to
support loads, such as cellular telephones, PDAs, and laptop
computers, which typically require multiple voltages, and (ii) to
track a time-varying set-point voltage rather than a constant
set-point voltage. The tracking feature can be used, for example,
to produce a 60 Hz sinusoidal power output directly and efficiently
or used as an audio amplifier to drive a speaker in a cellular
telephone directly and efficiently.
[0155] In some applications, it is useful to allocate power
generated among available fuel cell devices in a manner making
efficient use of fuel while simultaneously delivering a required
power profile to the load. In portable power applications, such as
laptop computers, PDAs, and cellular telephones, power requirements
involve multiple voltages, each corresponding current varying with
time, and often involving significant transients in power
requirement and a very large peak/average ratio. A similar
requirement characterizes larger applications, such as power
sources for automobiles and buses.
[0156] Commercial success of fuel cell power systems is expected to
be determined by energy storage density (watt-hours/kilogram and
watt-hours per liter), peak and average power density (watts/liter
and watts/kilogram), and cost ($/watt, $/watt-hour). These metrics
may be applied to the complete system, including fuel storage, fuel
delivery, and the fuel cells themselves.
[0157] Accordingly, an embodiment of the present invention includes
a method or corresponding apparatus to control operation of an
assembly of many small fuel cells, each generating a small fraction
of total power generated by the entire assembly, in such a manner
that fuel consumption over time is minimized, power output to a
load is maintained with required regulation of voltage and/or
current at one or multiple voltages, and load transients are
supported within required tolerance. In some embodiments, a control
system employing the method or corresponding apparatus takes into
account variation of fuel cell performance with temperature,
humidity, and available gas pressures of both fuel and oxidant
(e.g., due to variation with altitude), and adjusts control
strategies, accordingly.
[0158] Another embodiment provides a method or corresponding
apparatus to control, such as optimally control, aggregate
operation of an assembly of many small power generators, where
those generators may be fuel cells, micro-batteries,
photo-electric, piezo-electric, other ambient vibration-driven
devices, or any other source of power whose efficiency depends upon
a level of operation according to some characteristic that is
generally analogous to a battery discharge curve or a fuel cell V-I
curve. The control of the aggregate operation may be performed by
optimal control principles or other form of control principles.
[0159] Again, although the specifics of the following disclosure
refer to fuel cells, the concepts, apparatus, or methods described
should be interpreted as applying to any such small or relatively
small power generating device.
[0160] FIG. 23 shows a conventional, prior-art power supply circuit
2300 using a fuel cell stack or battery as a prime power source
2301. A regulator 2302 is employed to maintain a target voltage
2303 at a load 2304, where the target voltage is a voltage level
within a range required for proper operation of the load 2304, such
as 5 Vdc.+-.0.5 v. The regulator(s) are employed because typically
the voltage of the prime power source 2301 varies with load in such
a way that the target voltage cannot otherwise be maintained. The
regulator may be a three-terminal linear regulator, or any of
several topologies of switching regulator (boost, buck, buck-boost)
as commonly known in the art. A filter capacitor 2305 is typically
employed to buffer transients caused by the load 2304 and absorb
power supply noise generated by the transients.
[0161] FIG. 24 is an illustration of a voltage-current (V-I) curve
2400 typical of a micro-fuel cell. The curve 2400 expresses a
variation of output voltage with current, or, implicitly, variation
of output voltage with load impedance, in accordance with Ohm's
Law. As is well known in the art, a fuel cell typically has three
regions of operation: activation energy dominated 2406, internal
resistance dominated 2407, and mass transport dominated 2408. The
entire curve 2400 tends to shift with temperature, as indicated by
a dashed line curve 2409 and with gas pressure and humidity. The
voltage value at I=0 current is referred to as an Open Circuit
Potential 2410.
[0162] Parallel Switching
[0163] With the V-I curve characteristics in mind, consider a
circuit topology 2500 shown in FIG. 25 which includes an array 2505
of fuel cells 2512, each having operational characteristics with a
curve similar to the curve 2400 illustrated in FIG. 24.
[0164] Referring to FIG. 25, the array 2505 contains a number of
series-connected columns 2511a, 2511b, . . . , 2511x of fuel cells
2512. Each column 2511a-x has a respective switch (2513a, 2513b, .
. . 2513x) between the fuel cells 2512 and a power bus 2515, such
that when the switches 2513a-x are closed, the corresponding series
columns 2511a-x are connected in parallel with each other and a
load 2514.
[0165] Consider first a situation where the leftmost switch 2513a
for the leftmost column 2511a is closed and the others 2513 b-x are
open. If the impedance of the load 2514 is very high, then a
voltage V.sub.1 across a load is close to the sum of the open
circuit potentials of the individual cells comprising the series
array. If the impedance of the load 2514 is lower, the current
output by the fuel cells 2512 in the leftmost column 2511a in this
example, which substantially is equivalent to a load current,
I.sub.1, increases, and the voltage generated by the column 2511a
of fuel cells 2512 decreases in accordance with the sum of the
individual device V-I curves. Next, consider a situation where a
second series column 2511b is connected by closure of its
corresponding switch 2513b. In this situation, the current flowing
through each column 2511a, 2511b is reduced by roughly half, and
the voltage of each column 2511a, 2511b increases, correspondingly.
Accordingly, an output voltage can be maintained within a
pre-established tolerance by connecting and disconnecting columns
2511a-x of cells 2512, which leads to a steady-state variation of
voltage as a function of load impedance, as shown in FIG. 26.
[0166] FIG. 26 is a plot illustrating a situation in which a load
impedance 2614 is reduced and a load current 2615 correspondingly
increases. As an increasing number of columns 2616 are switched
into the circuit (e.g., array 2505 of FIG. 25), the circuit
produces a saw-tooth variation in voltage 2617 as a function of
current 2615.
[0167] Series Switching
[0168] In many circumstances, a useful operating range of devices
is much greater than the voltage tolerance. In this case, it may be
useful to switch the number of devices in each series column as
well as the number of columns.
[0169] FIG. 27 is a circuit topology 2700 that includes switches
2720 in a column topology 2718 that provides for selecting a
varying number of series components 2719. This column topology may
be repeated multiple times in a parallel column topology to drive a
load 2714 with finely selectable levels of current.
[0170] Transient Response
[0171] Another consideration in the design of a control process is
transient response of the individual devices. When initially
switched into a load circuit, a device typically does not turn on
fully instantly, but experiences a transient response over
time.
[0172] FIG. 28 is a plot illustrating a step function of an
individual power generating device, such as a fuel cell. Connection
of the power generating device to the load circuit at time T1
results in a rise in current flow that is exponential over time,
illustrated by a solid line curve 2821, with a time constant that
is a function of the device. There may be an initial transport lag
2822 as well, depending on the state of the device, and, in the
case of a fuel cell, distribution of ions in a Proton Exchange
Membrane (PEM). The initial transport lag may also be a function of
temperature and inactivity (i.e., how long ago the device was
previously active). A typical variation with these latter
parameters is shown as dashed curves 2823.
[0173] Transient responses for a fuel cell are influenced by an
ability of the fuel cell to reach equilibrium. Areas in which
equilibrium is established include: i) hydration of a membrane
(e.g., Nafion) in a reaction layer, ii) water balance in the
reaction layer (e.g., is there residual liquid water in the pore
space preventing gas from reaching catalyst?), iii) oxidant/fuel
supply (e.g., is there enough reactant gasses to support the
desired load?), where areas ii and iii can be related. Optimizing
the operating conditions and architecture of the Proton Exchange
Membrane (PEM) is a factor in minimizing the transient response of
a fuel cell.
[0174] The transient response may be either positive or negative.
If the membrane is conditioned correctly and the cell has been
inactive for a period of time, so that water in the pore space of
the reaction layer has been removed and the reacting gasses have
had time to diffuse throughout the reaction layer and occupy all
possible active catalyst sites that otherwise would be isolated by
trapped liquid water, the transient response shows a peak power
decrease with time. The decrease in power may be due to a build-up
of liquid water in the pore space of the reaction layer that
isolates active catalyst. Steady state power results when the
accumulation of liquid water does not exceed its removal rate, but
some level of water has accumulated in regions where it is not
easily removed. If the system has been dehydrated or there is
disruption in a reactant gas supply, then the transient shows a
less than peak power and increases until steady state is reached.
Once the system is at "steady state," power fluctuates depending on
operating conditions and nature of construction. Thus, an ability
to manage water formation and its effect on reactant gas
distribution throughout the reaction layer is useful for
successfully operating fuel cells.
[0175] Consequently, it is useful that a control process take
account of these effects and incorporate control filtering or a
control law that does not result in instability.
[0176] FIG. 29 is an electrical model of a fuel cell illustrated as
an equivalent circuit 2900 in a general form. In addition to a
transport lag 2924, there is typically an ohmic source resistance
2925, a second resistance 2927 associated with activation losses,
and a capacitance 2926 resulting from the charge double layer at
the electrodes.
[0177] Voltage Servo-Loop Structure
[0178] In some embodiments, a feedback filter or control law in the
form of circuit elements or software, for example, may be used to
compensate measured current by an inverse of a transfer function of
the fuel cell or aggregate transfer function of multiple series or
parallel fuel cells in order to optimize or otherwise operate a
control loop. Characteristics of the fuel cell or other power cell
device may be established through characterization of the device
across temperature, humidity, pressure, and load, and incorporated
into Digital Signal Processing using established methods of control
theory and digital signal processing (DSP). Non-DSP devices and
techniques may also be employed. Sensors may be employed in the
system to provide measures of, for example, temperature and
humidity values, and these values may be used to index arrays of
coefficients for the DSP filter or other control law. The
coefficients may be tuned adaptively, such as by means of a neural
network, in which improved operation of the fuel cell under each
set of ambient conditions alters linkage of neural network nodes
(i.e., series-column and multiple parallel columns of fuel
cells).
[0179] FIG. 30 is a block diagram of an example control structure
to control an array of fuel cells 3038 or other forms of power
cells. There may be a set-point voltage 3029 which the array 3038
delivers to a load 3030 of time-varying impedance. The voltage
delivered to the load by the array 3038 may be sensed 3031 and fed
back to switching logic 3032 through an appropriate filter 3033 or
state space equations. This filter may operate with an input state
vector 3033, including voltages sensed at various points 3037 in
the array of fuel cells 3038. The input state vector 3020 may
include states in the form of analog or digital representations
from temperature sensor(s) 3015 and relative humidity sensors
3016a, 3016b. The DSP filter block 3033 may operate on the state
vector 3020 by applying a matrix operation following customary
practice, where a matrix (not shown) applied to the state vector
3020 during the matrix operation may represent an appropriately
modified inverse of a discrete transfer function, H(z), describing
the fuel cell array 3038 and, in some embodiments, may also account
for a model of the load 3030, as understood in feedback control
systems arts.
[0180] A resulting filtered output ("command") voltage 3035 from
the DSP filter block 3033 and the set point voltage 3029 are
together presented to the switching control block 3032, which may
be conveniently implemented as a memory array in which addresses
may be a function of the filtered output and set-point voltages,
and data 3026 in the memory 3025 may be binary words used to
control which switches 3036 in the array 3038 are on (i.e., closed)
and which are off (i.e., open). In one embodiment, for example,
each combination of command and set-point voltage values 3035, 3029
is mapped to exactly one location in the memory 3025, and that
location contains a bit pattern (not shown) of which switches 3036
are on and which are off. The contents of the memory array may be
refreshed or modified under control of a supervisory processor 3027
running a supervisory control process that controls temperature,
output humidity, and other factors as noted below. The contents of
the memory array may also be received from an external system (not
shown).
[0181] The comparator switch control block 3032 may execute a
switching process using a specific sequence of instructions
executed in a computer, combinatorial logic, parallel
implementation of combinatorial logic implemented in logic gates,
and so forth, which may be implemented in the form of both a coarse
loop, which switches the number of series components as a function
of both load voltage 3031 and load current 3034, and a fine loop,
which switches the number of parallel columns 3005a, 3005b active
in the array 3038. The fine loop may add columns 3005a, 3005b when
the filtered load voltage 3035 drops below a threshold and may
remove columns 3005a, 3005b when the filtered load voltage 3035
rises above a threshold. If the system departs by more than some
tolerance from an optimal or other point on the V-I curve from an
energy-efficiency point of view, for example, or if it approaches a
state where most of the parallel columns 3005a, 3005b are in use,
then an additional row of series elements 3007 can be switched into
the circuit in accordance with the coarse loop. Similarly, if the
system is too lightly loaded, then a row can be removed by the
coarse or fine loops.
[0182] Route Around Failed Cells
[0183] Occasionally, an individual fuel cell degrades or fails. In
a series-connected column 3005a, 3005b, the total column voltage is
the sum of the individual voltages of the cells at whatever current
is passing through them. Since the current is the same in each, it
is the current corresponding to the lowest-performing cell in the
column. This situation can be detected by means of small,
current-sensing resistors 3010a, 3010b in each column 3005a, 3005b
of FIG. 30 to produce respective voltages 3032', or, alternatively,
by sensing voltage 3037 at multiple points in the columns 3005a,
3005b and checking for uniformity. If significant non-uniformity is
detected, then it is likely that one or more cells 3007 are
dissipating excess energy, and the switch control block 3032 can
remove them from use by "delisting" an entire row from its memory
3025, for example, as long as other columns available can meet the
electrical current demand. Other techniques, such as requiring use
of fewer series-column cells but using more columns, if available,
may also be possible, depending on which cell in the series column
is faulty.
[0184] Many applications of interest may include a battery or a
capacitor to handle peak loads that exceed the capacity of the fuel
cell array which must meet average load, or to meet transient
requirements that exceed the response time of the cells. If the
peak/average ratio of the load profile is small, then a capacitor
3038 can support transients, as shown in FIG. 26. If the
peak/average ratio is high (as for example with a hard disk, or a
sensor which communicates by radio every so often), then a
rechargeable battery can support the peak periods in which the
active surface area of the array is not sufficient to provide the
peak current load. In this case, care may be taken to manage the
charge/discharge cycle or the battery properly. Most battery types
can support a limited number of charge/discharge cycles. The
battery may thus discharge through a number of cycles before being
recharged. In order to maximize battery life, this number should be
as large as possible, given the excess fuel cell capacity available
to recharge (i.e., peak energy and peak frequency vs. fuel cell
capacity excess over non-peak load). The control process may
monitor battery voltage and determine the recharge point based upon
either predetermined parameters or recent historical behavior of
the load.
[0185] FIG. 31 is a flow chart showing features of an example
control process using example coarse and fine control loops. After
a timer interrupt of a "fast" timer, which causes repeating the
control process 3100 at a relatively fast rate, the process 3100
starts (3105). It should be understood that other forms of
interrupts, such as on-demand and/or an event driven interrupt, may
also cause the process 3100 to start. In a coarse portion 3101 of
the process 3100, determinations are made with regard to large
changes in current (or voltage) with which to drive a load. This
entails removing rows from an array (3115) or adding rows to the
array (3125) based on whether the load voltage is sensed as
exceeding a high limit (3110) or being less than a low limit
(3120). In a fine portion (3102) of the process 3100,
determinations (3130, 3140) are made as to whether to remove (3135)
or add (3145) parallel columns from or to the array, respectively,
to remove or add current by fine amounts. The process 3100 ends
(3150) thereafter.
[0186] Temperature/Humidity Servo-Loop Structure
[0187] Further servo-loop considerations arise from a variation of
the V-I curve with temperature, pressure, and humidity. For
example, in many applications, it is preferable that air output
from a Hydrogen-air fuel cell be at a humidity and temperature that
does not result in condensation of vapor into water. Accordingly, a
control process may first check output humidity, and, if it is too
high, raise the operating temperature set-point which, for the same
water output, lowers Relative Humidity (RH). Lowering the relative
humidity can be accomplished by generating the same power from
fewer fuel cells, which can be effectuated, for example, by
altering the data 3026 in a look-up table (not shown) in the memory
3025 of the control block 3032 of FIG. 30. A separate loop may then
compare the operating temperature to its set-point and make
adjustments to the table, accordingly. However, fuel efficiency may
best be served by keeping the operating temperature as low as
possible by minimizing internal resistive losses. The temperature
set-point is thus driven by the control process to be as low as
possible unless this creates a humidity problem.
[0188] With some fuel cell structures, there may be an optimum
concentration of power (i.e., quantity of active cells), driven by
increased dissipation with increasing power versus less dissipation
with higher temperature.
[0189] Basing a control loop on concentration of power can be used
both to increase temperature during start-up and to maintain
optimal temperature during operation. If the system is operating
below its current sourcing capacity, then the control system
optionally cycles through the various available columns, so the
columns remain at a reasonable, uniform, average temperature.
[0190] FIG. 32 is a flow diagram of an example process to change
operating parameters of an array of fuel cells based on temperature
or considerations presented immediately above. FIG. 32 is a flow
diagram of a process 3200 that occurs at a slower rate that the
process 3100 of FIG. 31. Referring to FIG. 32, a timer interrupt
(slow) or other form of interrupt (3205) starts the process 3200. A
determination is made as to whether an output humidity is greater
than a high limit (3210). If the output humidity is less than the
high limit (3210), the process 3200 compares the output humidity to
a low limit (3215). If the output humidity is greater than the high
limit (3210), the process 3200 increases a set point temperature
(3220) to reduce the output humidity. If the output humidity is
less than the low limit (3215), the process 3200 attempts to
decrease the set point temperature (3225).
[0191] The process 3200 may also be configured to monitor the
temperature at a set point plus, optionally, hysteresis of a
temperature (3230). If the temperature is less than the set point
(plus hysteresis), the process 3200 determines whether the
temperature is less than the set point (minus hysteresis) 3235. If
the temperature is greater than the set point (plus hysteresis)
(3230), a new switching table to cool the power cells may be loaded
(3240). If the temperature is less than the set point (minus
hysteresis) (3235), the process 3200 may load a new switching table
to cause the power cells to warm (3245) by driving the load. As
previously described (i.e., less or more catalyst surface area), to
warm or cool the power cells typically means that fewer or more
power cells are used to drive a load.
[0192] The process 3200 may also include rotating banks of power
cells or columns of power cells to drive a load. A determination of
whether to cycle to different units in the array may be made (3250)
through use of an internal clock or counter (not shown). If it is
time (3250), the process 3200 may load (3255) a new switching table
in a processor or storage area that is accessed to determine which
power cells to use for driving the load. If it is not time to cycle
to a different unit in the array (3250), the process 3200
increments a cycle counter (3260). Thereafter, the process 3200
tests or reads a voltage, V.sub.sense for failed power cells. If
the power cells are determined to be functioning properly such as
by monitoring an output current or voltage (3265), the process 3200
exits (3275). If the power cells are determined to be faulty
(3265), the process 3200 calculates a new switching table and loads
it (3270). The process 3200 exits (3275) after that.
[0193] It should be understood that the flow diagrams of FIGS. 31
and 32 are merely examples. The number of decisions, order, flow,
or other aspects of the flow diagrams may be modified, changed, or
otherwise set forth without departing from the scope of the example
embodiments of FIGS. 31 and 32. Moreover, it should be understood
that the flow diagrams may be implemented in hardware, firmware, or
software. If implemented in software, the software may be written
in any form of software and executed by any processor suitable to
work in the context of the power generation as disclosed herein. It
should also be understood that the software can be implemented in
the form of instructions stored on any form of computer readable
medium, such as RAM, ROM, magnetic or optical medium, and so forth
loaded by a processor, and executed to cause the processor to
perform the processes 3100, 3200 or variations thereof as
understood in the art.
[0194] Rotation of Cells to Improve Life
[0195] A further set of decisions to consider in operating an array
of fuel cells or other power generating cells may be made based on
a time or time-integral of power (energy) basis to rotate active
cells among a larger quantity available in an array of fuel or
power cells. Rotation of active cells logic is typically executed
at a less frequent rate than the voltage control loop of FIG.
31.
[0196] Power Optimization
[0197] As described in reference to FIGS. 30 and 31, a coarse
voltage control loop, which changes the number of cells or banks of
cells in series, can be operated in combination with a fine voltage
control loop which changes the number of columns of cells or banks
of cells in parallel, to control aggregate output power by an array
of power cells. A reason for this choice of control of the array
may be the following. A typical voltage range per device may be
from 0.9 volts open circuit potential to about 0.4 volts at maximum
output, and typical current may be 1 milliamp or less, depending on
Reactive Surface Area (RSA) in the case of fuel cells. In this
situation, series switching of power cells in a column may be best
used as a coarse adjustment, and parallel switching of columns may
be best used as a fine adjustment. Implementation of coarse and
fine control loops is described immediately below in reference to
FIGS. 33 and 34.
[0198] FIG. 33 is a plot of multiple V-I curves that vary with the
number of fuel cells in series combination (i.e., a column).
Current through each cell in the series is the same, and the
voltage adds. The V-I curve may thus be translated upward, and its
slope increases because of additional source impedance introduced
by each series element. Curves 3339, 3340, and 3341, in that order,
represent an increase in a number of series cells. A line 3342
represents load voltage versus current according to Ohm's law,
V=IR.sub.L, for a particular value of load resistance R.sub.L. The
intersections of this line 3342 with the V-I curves are the
respective operating points for that load resistance. So, addition
of fuel cell(s) in series, while the load remains constant, changes
the voltage and current from, for example, the intersection of load
line 3342 with V-I curve 3339 to the intersection of the load line
3342 with curve 3340.
[0199] FIG. 34 illustrates an effect of stacking the cells in
parallel. Curves 3442, 3443, and 3444 represent increasing a number
of cells in parallel. In this case, the load voltage 3442 is the
same, and the current increases through the reduced source
impedance.
[0200] Since the number of series devices is typically small (e.g.,
four to six for a 3.3 volt supply), whereas the quantity in
parallel is large (e.g., 1000 for a 1 ampere supply), the change in
voltage resulting from adding a column is typically far less than
the change in voltage from adding a row, allowing tighter
regulation.
[0201] Beyond simple voltage regulation, the system may make
optimal use of energy stored in the fuel by operating the system
efficiently.
[0202] FIGS. 35A and 35B are plots that illustrate an example
relationship between operating point, delivered power, and
dissipated power. FIG. 35A is essentially a repeat of the V-I curve
shown in FIG. 24. FIG. 35 B shows total power 3545 generated from
fuel oxidation, total power exclusive of activation losses 3545',
power delivered to the load 3546, and power dissipated in the
device 3547. The activation energy is assumed to be constant with
current I; hence, the dissipated and delivered power are governed
by V.sub.INT 3548, the point at which an extension of the
approximately linear, resistive region of the V-I curve intercepts
the V-axis.
[0203] Total power 3545 to a first approximation,
P.sub.TOT=V.sub.INTI+P.sub.ACT
[0204] Excluding activation losses P.sub.ACT, which are small and
roughly constant with current I, P.sub.TOT is a linear function of
I with a slope of 1, as shown in the FIGS. 35A and 35B.
[0205] Power delivered to the load is
P.sub.del=V(I)I
P.sub.del=(V.sub.INT-R.sub.SI)I=IV.sub.INT-I.sup.2R.sub.S
where R.sub.S=the source resistance of the device.
[0206] Power dissipated in the device is:
P.sub.diss=P.sub.TOT-P.sub.del=V.sub.INTI-(IV.sub.INT-I.sup.2R.sub.S)
P.sub.dissI.sup.2R.sub.S
[0207] For devices having a V-I curve as shown in FIG. 35A, the
delivered power is quadratic in current and downward-concave,
producing a maximum delivered power at a point 3549, where
P.sub.del=P.sub.diss.
[0208] Optimum Power: Minimize Current Per Cell
[0209] Dissipated power is quadratic in current and upward-concave,
indicating that the lower the current, the less dissipation that
occurs. But, lower current means proportionally more devices are
required. Optimum efficiency is the ratio of delivered power to
total power. Efficiency thus decreases monotonically with
current.
[0210] As a practical matter, operating stability and other design
factors may result in choice of a slightly higher current operating
point, depending on the detailed characteristics of a particular
device, which are not part of the simple model above. In a
practical system, optimum efficiency may also be limited because
the less current per device, the more devices and, therefore, the
more cost associated with the system.
[0211] Optimum Power Switch Smallest Possible Increments
[0212] FIGS. 36A and 36B are a circuit diagram 3648 and current
waveform 3649, respectively, that illustrate another lesson that
may be drawn from the quadratic nature of the dissipated and
delivered power. In a situation where a device is switched on and
off at a 50% duty cycle to deliver average power VI by alternating
between zero current and 2I current for equal time intervals, the
power dissipated during the on times is four times as much for half
the time, or twice as much on average. First, consider a constant
current output 3650, which delivers power I.sup.2R.sub.L, and
dissipates power I.sup.2R.sub.s. Now, consider curve 3652, in which
the source current to a filter capacitor is switched between 0 and
21 with a fifty percent duty cycle. The average current delivered
to the load 3651 is still I, and varies only slightly at the filter
capacitor output 3653. However the dissipated power is:
[0213] P.sub.dis=(2I).sup.2R.sub.s/2=2I.sup.2R.sub.s, which is
twice as much as the constant current output (3650).
[0214] In other words, in order to minimize power consumption, the
control process switches as few devices as possible to maintain the
set-point voltage. The example control process disclosed above does
that.
[0215] Further, it follows that the smaller the individual devices,
or the groups of devices which are independently switched, the more
efficient the system is in its conversion of energy.
[0216] Multiple Voltage Outputs
[0217] FIG. 37 is a topology of a multi-voltage supply 3700 formed
from a power (e.g., fuel) cell array 3705 configured as multiple
subarrays or banks 3710a, 3710b, 3710n. The multi-voltage supply
3700 is an extension of the disclosed structure, which useful in
electronic devices which require multiple voltages. A modern cell
phone or laptop computer, for example, contains multiple voltage
regulators to provide different voltages to the display, logic hard
disk, RF devices, etc. An array of micro fuel cells or other power
generating cells can easily be configured to deliver such multiple
voltages without incurring the power dissipation, heat generation,
board cost and separate component cost associated with a
conventional power conditioning system in a phone or laptop. It
should be understood that the fuel cell array 3705 may be
configured with extra banks (e.g., 3710n-2, 3710n-1, and 3710n) to
provide redundancy, where the extra banks may be configurable to
provide any of the voltages provided by primary banks Moreover, all
of the banks 3710a-n may be configurable to supply any voltages to
allow for rotation of the banks for longevity purposes.
[0218] Current Source, AC Power Source, Audio Power Amplifier
[0219] Several further extensions of the basic structure are also
possible: the system may be configured to maintain constant current
with varying voltage (i.e., a current source instead of a voltage
source, which is useful for powering certain types of sensors, for
example); the system may track not a constant voltage or current
but instead track a time varying set-point, thus providing an AC
power source, for example, at 60 Hz for back-up power to a
household; or, the system may track an audio frequency signal to
form a very efficient power amplifier, for example, to drive a
speaker in a cellular phone. This arrangement may be the same as
the arrangement in FIG. 30 except that the constant set-point
voltage 3029 is replaced with a time-varying input.
[0220] Fabrication in the Power Chip
[0221] Using the MEMs structures and fabrication methods on a
silicon substrate which are described in prior Marsh patents (U.S.
Pat. Nos. 6,312,846 and 6,815,110), it may be cost effective to
incorporate the control system described above on the same silicon
substrate as the fuel cells, with minimal increase in silicon
surface area. First, a series of layers may be deposited,
patterned, and etched upon the substrate, following established
conventional semiconductor fabrication practice, which may produce
transistor switches for the power array, voltage and current
sensors, and an array of gates implementing the control process.
Alternatively, a structure comprising an FPGA or embedded processor
Central Processing Unit (CPU) plus memory may be employed. A Field
Programmable Gate Array (FPGA) configuration or program memory may
be Read Only Memory (ROM), One time Programmable (OTP) memory, or
FLASH memory, as desired, depending upon the need to customize the
device for different applications after manufacture. Using current
CMOS fabrication methods, any of these approaches may use a silicon
area, which is small compared to a 1 cm.sup.2 fuel cell array, and
can easily be built on the same silicon area under the MEMs fuel
cell structures.
[0222] Hierarchical Control of Power Disks, Power Stacks
[0223] For larger power sources, Marsh (U.S. Pat. Nos. 6,312,846
and 6,815,110) notes that a plurality of power cells may be
assembled on a power disk, and a plurality of power disks may be
assembled into a power stack. In this situation, a hierarchical
control system may be implemented, in which each power chip is
controlled in accordance with an example embodiment of the
invention, but with set-points determined by a similar control
system that operate at the power disk level upon the individual
power chips. Similarly, a plurality of power disks may be
controlled to optimize their aggregate power output when they are
assembled into a power stack.
[0224] Power Amplifier
[0225] FIG. 38 is a block diagram of a system 3800 using power
generators to perform a function of an amplifier that would
normally use voltage rails. In this example, an external device
3805 produces a low level voltage signal 3835 received by the
amplifier 3810. The amplifier 3810 includes a high impedance input
stage 3815, power generation cells controller 3820, electronics
power cells 3825, and signal generation power cells 3830. The
modules 3815, 3820, 3825, 3830 are interconnected in any typical
manner understood in the art such as through integration on a
single silicon wafer and interconnected as previously described
above. The high impedance input stage 3815 and power generation
cells controller 3820 are powered by the electronics power cells
3825 which provides sufficient power to operate the electronics in
the amplifier 3810. The high impedance input stage 3815 provides a
representation 3817 of the input waveform 3835 to the power
generation cells controller 3820, which, in turn, controls the
signal generation power cells 3830 in a manner to produce a voltage
or current waveform 3840 as an amplified form of the input waveform
3835. The output waveform 3830 may be used to drive a load 3845,
which may be a headset speaker in a cell phone, for example, or
other form of load having electrical characteristics suitable to be
driven by the example amplifier 3810.
[0226] FIG. 39 is a diagram of a pair of waveforms 3900 that
illustrate an example use of the power generation cells that are
controlled to produce a waveform. The pair of waveforms 3900
includes a sinusoidal power waveform 3905 and an adjusted power
waveform 3910. The adjusted power waveform 3910 is produced in a
shape that compensates for effects of a load 3915 waveform 3905. It
should be understood that the adjusted waveform 3910 is merely an
arbitrary example of an adjusted waveform that is not necessarily
to scale or expected to be implemented in practice. It is should
also be understood that the adjusted waveform 3910 may be used for
purposes of improving a power factor or power quality as understood
in the power delivery arts.
[0227] FIG. 40 is a block diagram of an array 4000 of power cells
(not shown) having A-I columns of power cells 4010a, 4010b, 4010c,
. . . 4010i. The array 4000 also includes a controller 4005 either
on a substrate integrated with the power cells or separate from the
substrate with the power cells. In either case, the controller may
be used to control which column(s) 4010a-i are used to deliver
power 4020 via a bus 4015 to a load 4025. In other words, the
controller 4005 may sequence through the columns 4010a-i or
otherwise select columns of power cells to generate power 4020 to
deliver to the load 4025. In the example embodiment, the controller
4005 sequentially steps from columns A-I to generate power and
accordingly, the power 4020 is delivered in a corresponding order
(i.e., column A 4010a has power P.sub.a delivered first, column B
4010b next delivers power P.sub.b, . . . , and finally column I
4010i delivers power P.sub.I).
[0228] FIG. 41 is a block diagram that illustrates a case in which
a power generation system 4110 includes a controller 4105
associated with an array of power cells 4107, 4110a-e. In this
example, starter cells 4107 are caused first to generate power Pout
4120 via a bus 4115 to an external load 4125 to cause the starter
cells 4107 to generate heat so as to warm surrounding, and
outwardly extending, power cells 4110a. Alternatively, the starter
cells 4107 may be caused to deliver power Pwarm 4122 to an optional
internal load 4140 on the same substrate 4102 as the array of power
cells. This allows the starter cells 4107 to warm up without having
to be connected to an external load 4125. It should be understood
that the location of the starter cells 4107 may be set in other
locations among power cells in the array 4110 a-e, such as more
centric to warm power cells in any of four directions.
[0229] In operation, the controller 4105 may receive temperature
feedback 4135 from the starter cells. As the temperature increases,
as determined by the controller 4105 as a function of the
temperature feedback 4135, the controller 4105 may engage power
generation cells 4110a surrounding the starter cells 4107. Then, as
the surrounding cells 4110a warm, the controller 4105 may engage a
next set of power cells 4110b surrounding the starter cells 4110a
to engage and produce power 4120 to deliver to the external load
4125 via the bus 4115. This process may continue until all of the
power generation cells 4110a-e are activated to generate power 4120
to deliver to the external load 4125.
[0230] It should be understood that the progression, as represented
by an arrow 4130, may not be diagonal as illustrated but, instead,
each of the zones 4107 and 4110a-e may be vertical sectors of power
cells as illustrated in FIG. 40 or FIG. 30. In whichever embodiment
is selected, it should be understood that the starter cells 4107
may be driven with a low efficiency to generate heat efficiently to
have a rapid warm up time, and each of the subsequent subsets of
power cells that are activated may also be driven with a given
efficiency to have a rapid or normal rate of warming to match a
given profile for starting the power cells for use in a given
environment.
[0231] FIG. 42 is a block diagram of a controller 4200 with two
levels of functions, kernel functions 4205 and "higher" functions
4210. The kernel functions 4205 may be basic power management and
control functions that are used, for example, to map voltage levels
to corresponding switch closures and also convert power requests
into a number of rows in column(s) and/or parallel columns to
produce the power by selecting which switches to close to configure
series and parallel combinations of power cells. Other basic
functions may also be employed within the kernel functions
4205.
[0232] The higher functions 4210 may include functions that provide
intelligent control of the power cells. Examples of higher
functions include cold start, sinewave control, arbitrary waveform
control, voltage regulation, current regulation, rotation of power
cells, adjustment, and decontamination. Vibration, as discussed
below in reference to FIG. 43 may also be an example of a higher
function as assist with accelerating correction of a "flooding"
event.
[0233] In one example embodiment, the controller 4200 has the
higher functions 4210 provide requests 4225 to the kernel functions
4205 to perform one of the aforementioned functions or other high
level functions. In turn, the kernel functions 4205 present control
signals 4215 to switches or other control elements, such as fuel or
oxidant flow control elements (e.g. MEMs switches), to execute the
requests 4225. Feedback 4220 may be returned to the kernel
functions 4205, which, in turn, present the feedback 4230 in a form
suitable for reading by the higher functions 4210. Alternatively,
the feedback 4220 may be presented directly to the higher functions
4210.
[0234] It should be understood that the controller 4200 may be
segmented in other ways and include other functions suitable for
use with a single power cell or array of power cells.
[0235] The controller 4200 may also include inter-controller or
intra- or inter-power disk/chip communication module(s) 4212 to
allow multiple controllers to act in a unified or distributed
manner. Inter-disk/chip communications may also provide support for
redundancy or vast arrays of virtually unlimited numbers of power
cells.
[0236] FIG. 43 is a schematic diagram of a system 4300 that
includes a power cell 4305, electrically coupled to a pulse
generator 4310, formed with power cells or, optionally, an
electronic pulse generator, through a pair of switches 4315a,
4315b. The switches 4315a, 4315b are utilized in this embodiment to
switch the power cell 4305 from delivering power to a load 4312 to
receiving a pulse 4325a or pulses 4325a, 4325b from the pulse
generator 4310. It should be understood that the pulse generator
4310 may be any form of signal generator to produce a typical or
atypical waveform, such as a sinewave, chirp, or other
waveform.
[0237] The purpose of the pulse 4325a is to apply a voltage or
current to catalyst on the sides of the walls. By driving the
catalyst with the pulses 4325a, 4325b, contaminant that may have
settled on the catalyst may be ejected, as represented by multiple
arrows 4330 projecting outward from the power cell. It should be
understood that a similar set of a multiple arrows 4330 may also be
occurring inside the volume encompassed by the power cell 4305, but
not shown for ease of understanding how the decontamination process
works. Further, it should be understood that either pulse 4325a,
4325b may also be a reference level, such as a ground potential, to
decontaminate one catalyst side more than the other.
[0238] Additionally, a 1 volt or other low voltage waveform may be
used to cause a catalyst coated membrane, which may be a very thin
film, used to form the power cell 4305 to vibrate. Vibration may be
used to accelerate a removal of a flood condition that can impair
power generation by the power cell 4305. To that end, the power
cell 4305 may be specially designed in thickness, height, diameter,
catalyst thickness, segmented, or other physical parameter, to
increase its ability to vibrate. Moreover, vibration (or heat) may
be used to increase energy for use in causing, accelerating or
otherwise affecting a reaction taking place in at the power cell
4305, and the power cell 4305 may be driven at amplitude(s) or
offsets at single- or multi-frequencies to improve energy delivery
or reduction for a particular reaction or step in a reaction.
[0239] In terms of testing, the power cell 4305 has an electrical
impedance, similar to a capacitor, since it has two "plates"
(outside and inside walls of the membrane) in the form of
electrically conductive catalyst. The impedance can be used for
automated testing, where a controller can be employed to switch
electrical paths from the power cell 4305 to pins at an edge of a
power chip or disk connected to a capacitance meter. In this way, a
vast array of power cells can be quickly tested or diagnosed.
[0240] Further, a control program implemented in a custom gate
array or ASIC hierarchical structure in which a plurality of power
cells are controlled as in an array of microprocessor generators
described above and assembled to create a power disk, where similar
processes control allocation of power generation to power cells on
the disk. In some embodiments, the hierarchical structure in which
a plurality of power disks are controlled and assembled to create a
power stack, where similar processes control the allocation of
power generation to power disks in the stack.
[0241] It should be understood that any of the aforementioned
control filters, control laws, or alternative control laws, such as
optimal control, fuzzy logic, neural networks, H-infinity control,
and so forth, can be executed in the form of software in a
processor to control the operation of power generation. Hardware or
firmware implementations may also be employed. The control program
may, in addition to the control described above, optionally be
adaptive to power cell characteristics over time as individual or
banks of devices age over time. The control program may also be
modified or upgraded after field installation or manufacturing to
give previously identical devices different operating
characteristics intended for different applications.
[0242] In one embodiment, the array of micro-power generators may
be configured as a hybrid system including a rechargeable battery,
capacitor, photovoltaic, vibration-harvesting generator, etc. The
battery charging cycle may be configured to enhance long battery
life.
Electro-Chemical Application of Power Cells
[0243] One embodiment of another aspect of the invention is a
method of reacting reaction components. One example method includes
electro-chemically reacting reaction components on opposite sides
of at least one membrane encompassing a respective volume in a
presence of at least one catalyst. The method referred to here can
be facilitated any embodiment of power cells, power chip, power
disk or power stack disclosed herein.
[0244] FIG. 44 illustrates an example of this embodiment of the
method in the invention. A power cell 4400 includes the same or
similar components as the ones described above in reference to
other power cells, including anode catalyst 4405, cathode catalyst
4410, and a membrane 4415 (e.g., an ion or proton exchange
membrane). The power cell 4400 can be coupled to a substrate 4420,
through which a reaction component can flow as indicated by an
arrow 4440. The membrane 4415 referred herein can be laminate of a
non-woven fabric and a membrane, such as an ion exchange membrane
or an proton exchange membrane. Similar to the power cells
configured to form a three-dimensional geometric structure, the
membrane encompasses a volume 4425. In micro-power cell
applications, the volume 4425 may be less than one cubic
millimeter. In other applications, the volume 4425 may be less than
one cubic centimeter, one cubic meter, or even less than one cubic
micrometer. An electrical circuit that includes a switch 4455 and a
load 4457 may be connected to the cathode 4410 and anode 4405. In
conjunction with another reaction component 4445 in or on the
opposite side of the separator 4415, the power cell 4400 can induce
an electrochemical reaction. For example, the power cell 4400 can
be used for performing use of electrolysis of water to produce a
hydrogen:
2H.sub.2O.sub.(l).fwdarw.2H.sub.2(g)+O.sub.2(g)
[0245] Electrolysis of water can be conducted by passing current
generated by the power cell 4400 through drop(s) of water 4440 (in
practice a saltwater solution increases the reaction intensity
making it easier to observe). Hydrogen gas is seen at the cathode
4410 using platinum electrodes, and oxygen bubbles at the anode
4405, also using platinum electrodes. If other metals are used as
the anode, there is a chance that the oxygen will react with the
anode instead of being released as a gas. For example using iron
electrodes in a sodium chloride solution electrolyte, iron oxide is
produced at the anode, which reacts to form iron hydroxide. Other
industrial uses include electrometallurgy, the process of reduction
of metals from metallic compounds to obtain the pure form of metal
using electrolysis. For example, sodium hydroxide in its metallic
form is separated by electrolysis into sodium and hydrogen, both of
which have important chemical uses. Also this example method can be
applied to manufacture aluminium, lithium, sodium, potassium, or
aspirin. Another practical use of electrolysis by a power cell is
anodization. It makes the surface of metals resistant to corrosion.
For example, ships in water are saved from being corroded by oxygen
in water by this process, which is done with the help of
electrolysis. This process is also used to make surfaces more
decorative.
[0246] Furthermore, the hydrogen gas that is generated by the
electrolysis of water can be used to fuel other additional
reaction. For example, the hydrogen gas 4460 can be flown through
an exit 4470 and collected as a fuel.
[0247] While the use of electrolysis described above is provided in
a context of a power cell, such method can also be applied to an
array of power cells, a power disk, or power disk, or power
stack.
[0248] Another embodiment of the method further includes applying a
potential difference for conducting an electro-chemical reaction.
Continuing to refer to FIG. 44, by turning on a switch 4480, the
power cell 4400 can be electrically connected to a battery 4482.
However, the battery 4480 is for illustrative purposes. Therefore,
other form of power can be applied to the power cell 4400 such as
DC, AC, fixed frequency, arbitrary waveform or any combination
thereof.
[0249] Applying a potential difference to an anode and a cathode
can induce a electro-chemical reaction. For example, a power cell
that includes a membrane made of material such as Nafion.RTM., can
vibrate when a current, such as a sinusoidal, pulse, chirp, or
other waveform, is applied therethrough. As such, applying a
potential difference through the power cell 4400 can induce or
enhance an electro-chemical reaction such as for generating heat
(i.e., at the membrane 4415), and converting a physical state
(i.e., liquid, pseudo-solid, gas, pseudo-liquid, or solid) to
anther physical state, and changing a profile of the potential
difference during difference stages of a reaction or within a
single stage of a reaction. When the potential difference is
applied to an array of power cells, it is also possible to apply
the potential difference to a subset of the array in thermal
proximity to the subject that is generating heat. It is also
possible to employ a sensor to monitor the electro-chemical
reaction.
[0250] For example, the system 4401 can include a sensor 4406 for
measuring the level of hydrogen gas inside of a housing 4403 during
the electrolysis of water. In turn, the system can be equipped with
a feed back system by monitoring feedback of a metric associated
with the reaction (e.g., concentration or temperature) or power
cells (e.g., temperature or pressure) to a typical reaction.
Monitoring of the electro-chemical reaction using the feedback
system can be useful to adjust, regulate and/or control an
electro-chemical reaction as a function at least one metric.
Metrics can include temperature, pressure, humidity, time,
concentration of at least one of the reaction components, for
example. Further, one can regulate when and how to apply the
potential difference. For example, an electro-chemical reaction can
decelerate or accelerate by decreasing or increasing the potential
difference, respectively, in typical reaction.
[0251] Furthermore, a product of an electro-chemical reaction can
be outputted using such manner as extracting, expelling, draining,
releasing or venting another electro-chemical reaction can follow
during or after the first electro-chemical reaction.
[0252] Introducing at least one other reaction component during or
after the first electro-chemical reaction can trigger a new
electro-chemical reaction or be used in a next stage of the ongoing
electro-chemical reaction. And the product of the new
electro-chemical reaction can be also outputted in a similar manner
as the earlier electro-chemical reaction.
[0253] A 1st specific embodiment is a method of reacting reaction
components comprising: electro-chemically reacting reaction
components on opposite sides of at least one exchange membrane with
at least one catalyst encompassing a respective volume.
[0254] A 2nd specific embodiment is a method according to the 1st
specific embodiment, wherein the at least one membrane is at least
one ion exchange membrane and wherein reacting reaction components
includes reacting reaction components on opposite sides of the at
least one ion exchange membrane.
[0255] A 3rd specific embodiment is a method according to the 1st
specific embodiment, wherein electro-chemically reacting reaction
components includes conducting electrolysis.
[0256] A 4th specific embodiment is a method according to the 3rd
specific embodiment, where electro-chemical reacting reaction
components includes conducting electrolysis of water.
[0257] A 5th specific embodiment is a method according to the 3rd
specific embodiment, wherein electro-chemical reacting reaction
components includes conducting electrolysis for electrometallurgy
or anodization.
[0258] A 6th specific embodiment is a method according to the 5th
specific embodiment, wherein electro-chemical reacting reaction
components includes conducting electrolysis to manufacture
elements.
[0259] A 7th specific embodiment is a method according to the 6th
specific embodiment, wherein conducting electrolysis includes
producing hydrogen, sodium, lithium, aluminum, sodium, or
potassium.
[0260] An 8th specific embodiment is a method according to the 1st
specific embodiment, wherein electro-chemically reacting reaction
components includes applying a potential difference on the opposite
sides of the at least one membrane.
[0261] A 9th specific embodiment is a method according to the 8th
specific embodiment, wherein applying the potential difference
includes changing the potential difference over time.
[0262] A 10th specific embodiment is a method according to the 9th
specific embodiment, wherein applying the potential difference
includes increasing the potential difference to accelerate the
reaction.
[0263] An 11th specific embodiment is a method according to the 9th
specific embodiment, wherein applying the potential difference
includes decreasing the potential difference to decelerate the
reaction.
[0264] A 12th specific embodiment is a method according to the 8th
specific embodiment, wherein applying the potential difference
includes cycling the potential difference.
[0265] A 13th specific embodiment is a method according to the 8th
specific embodiment, wherein applying the potential difference
includes generating a potential difference to cause heating at the
at least one membrane.
[0266] A 14th specific embodiment is a method according to the 1st
specific embodiment, wherein the at least membrane is an array of
membranes with catalyst and further including operating a subset of
the array as fuel cells in a manner generating heat.
[0267] A 15th specific embodiment is a method according to the 14th
specific embodiment, further including applying a potential
difference on opposite sides of membranes in a subset of the array
in thermal proximity to the subset generating heat.
[0268] A 16th specific embodiment is a method according to the 1st
specific embodiment, further including introducing at least one
other reaction component and further electro-chemically reacting
the reaction components.
[0269] A 17th specific embodiment is a method according to the 1st
specific embodiment, further including outputting a product
produced by electro-chemically reacting the reaction
components.
[0270] An 18th specific embodiment is a method according to the
17th specific embodiment, wherein outputting the product includes
outputting the product in a manner selected from a group consisting
of: extracting, expelling, draining, releasing, or venting.
[0271] A 19th specific embodiment is a method according to the 17th
specific embodiment, wherein the product is at least one of the
components in a different state from the state prior to the
electro-chemical reacting.
[0272] A 20th specific embodiment is a method according to the 19th
specific embodiment, wherein the different state is a different
thermal state or physical state.
[0273] A 20th specific embodiment is a method according to the 17th
specific embodiment, further including participating with at least
one other reaction and wherein outputting the product includes
presenting the product to the at least one other reaction.
[0274] A 22nd specific embodiment is a method according to the 21st
specific embodiment, further including outputting a byproduct of
the electro-chemical reaction to the at least one other
reaction.
[0275] A 23rd specific embodiment is a method according to the 1st
specific embodiment, wherein the reaction components are selected
from a group consisting of: solids, pseudo-solids, liquids,
pseudo-liquids, gases, or combinations thereof.
[0276] A 24th specific embodiment is a method according to the 1st
specific embodiment, further including applying a potential
difference across the at least one ionic exchange membrane selected
from a group consisting of: DC, AC, fixed frequency, arbitrary
waveform, or combinations thereof.
[0277] A 25th specific embodiment is a method according to the 24th
specific embodiment, further including changing a profile of the
potential difference during different stages of a reaction or
within a single stage of a reaction.
[0278] A 26th specific embodiment is a method according to the 1st
specific embodiment, further including monitoring the
electro-chemical reaction.
[0279] A 27th specific embodiment is a method according to the 26th
specific embodiment, wherein monitoring the electrochemical
reaction includes: feeding back at least one metric associated with
the electro-chemical reaction measured by the monitoring; and
regulating or controlling the electro-chemical reaction as a
function of the at least one metric.
[0280] A 28th specific embodiment is a method according to the 27th
specific embodiment, wherein the at least one metric includes at
least one of the following: temperature, pressure, humidity, time,
or concentration of at least one of the reaction components.
[0281] A 29th specific embodiment is a method according to the 27th
specific embodiment, further including: applying a potential
difference across the at least one ionic exchange membrane; and
feeding back at least one metric associated with the
electrochemical reaction measured by the monitoring; and adjusting
the potential difference as a function of the parameter measured to
control or regulate electro-chemically reacting the reaction
components.
[0282] A 30th specific embodiment is a method according to the 1st
specific embodiment, wherein the at least one ionic exchange
membrane is an array of membranes and further including
electro-chemically reacting the different reaction components in
different reactions across the array of membranes.
[0283] A 31st specific embodiment is a method according to the 1st
specific embodiment, wherein the volume is less than one cubic
millimeter.
[0284] A 32.sup.nd specific embodiment is an apparatus for reacting
reaction components, comprising: at least one ion exchange membrane
with first and second sides encompassing a respective volume; at
least one catalyst coupled to the first and second sides to
electro-chemically react reaction components on the first and
second sides in gaseous communication with the at least one
catalyst; and a cover coupled to the at least one membrane to
separate flow paths on the first and second sides; further
including an outlet configured to output a product produced by
reacting the reaction components, wherein the product is at least
one of the components in a different state from the state prior to
the electro-chemical reacting, and wherein the different state is a
different thermal state or physical state.
[0285] While this invention has been particularly shown and
described with references to example embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *