U.S. patent application number 10/391547 was filed with the patent office on 2004-05-06 for fuel cells.
Invention is credited to Buenviaje, Cynthia, Fleckner, Karen, Fuji, H. Sho, Hergesheimer, Jeremy, Huang, Yao, Lim, David, Pedersen, Jeff, Treiber, Michael, Zheng, Feng.
Application Number | 20040086768 10/391547 |
Document ID | / |
Family ID | 26874365 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040086768 |
Kind Code |
A1 |
Fleckner, Karen ; et
al. |
May 6, 2004 |
Fuel cells
Abstract
A novel design and process for: (a) a membrane electrode
assembly (MEA) with aligned carbon nanotubes as a nano-scale gas
distrubutor which yield better gas conversion efficiencies in PEM
fuel cells, and (b) doped silicon flow field plates (FFP) which
increase electrode conductivity of the membrane-catalyst-gas
diffusion layer (GDL)-FFP interfaces of the proton exchange
membrane fuel cell (PEMFC). Also, part of the invention are a
stacking configuration and a gas distribution design that also
enhance conductivity of carbon/metal catalyst/electrode, GDL, and
FFP interface surfaces without crushing the FFPs. Aligned carbon
nanoscale gas distributors are employed at the interfaces, thereby
increasing the overall performance of th PEMFC. The FFPs are easy
to manufacture and mass-producible, yet mechanically sturdy and
significantly lighter in weight than their conventional
counterparts. Another novel feature of the invention is an
integrated monitoring and communication/Internet system located
directly or connected to the FFP.
Inventors: |
Fleckner, Karen; (Tacoma,
WA) ; Zheng, Feng; (Seattle, WA) ; Buenviaje,
Cynthia; (Seattle, WA) ; Huang, Yao;
(Vancouver, WA) ; Pedersen, Jeff; (Tacoma, WA)
; Lim, David; (Seattle, WA) ; Fuji, H. Sho;
(Seattle, WA) ; Hergesheimer, Jeremy; (Seattle,
WA) ; Treiber, Michael; (Seattle, WA) |
Correspondence
Address: |
Steven H. Arterberry, Esq.
DORSEY & WHITNEY LLP
Suite 3400
1420 Fifth Avenue
Seattle
WA
98101
US
|
Family ID: |
26874365 |
Appl. No.: |
10/391547 |
Filed: |
March 17, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10391547 |
Mar 17, 2003 |
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09642198 |
Aug 18, 2000 |
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6589682 |
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60178494 |
Jan 27, 2000 |
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Current U.S.
Class: |
429/457 ;
427/115; 429/458; 429/483; 429/514; 429/535; 502/101 |
Current CPC
Class: |
H01M 8/0234 20130101;
Y02P 70/50 20151101; H01M 8/04388 20130101; H01M 8/04992 20130101;
H01M 8/1004 20130101; H01M 8/0432 20130101; H01M 8/0491 20130101;
H01M 8/04559 20130101; Y02E 60/50 20130101; H01M 8/04952 20160201;
H01M 8/04649 20130101; H01M 8/04761 20130101; H01M 8/04395
20130101; B82Y 30/00 20130101; H01M 8/04589 20130101; H01M 8/04753
20130101; H01M 8/04701 20130101; H01M 8/0488 20130101; Y10S 977/948
20130101 |
Class at
Publication: |
429/038 ;
429/030; 429/044; 429/032; 429/022; 429/025; 429/033; 502/101;
427/115 |
International
Class: |
H01M 008/02; H01M
008/24; H01M 008/10; H01M 004/96; H01M 004/92; H01M 008/04; H01M
004/88; B05D 005/12 |
Claims
What is claimed is:
1. A fuel cell which comprises: first and second flow field plates;
an electrolyte between the flow field plates; catalytic electrodes
on first and second, opposite faces of the electrolyte for
promoting the dissociation of a fuel at the first face of said
electrolyte and the formation of water at the second face of the
electrolyte, and a system for delivering a gaseous fuel through the
first flow field plate to the first face of the electrolyte, said
system comprising an array of nanotubes oriented to discharge said
fuel into contact with the catalyst on the first face of the
electrolyte.
2. A fuel cell as defined in claim 1 in which the nanotubes are
carbon fullerenes.
3. A fuel cell as defined in claim 1 in which the nanotubes are
impregnated in said first flow field plate.
4. A fuel cell as defined in claim 1 in which said nanotubes are
attached to a surface of said first flow field plate.
5. A fuel cell as defined in claim 4 in which said nanotubes are
attached to the flow field plate by sputtering.
6. A fuel cell as defined in claim 4 in which the nanotubes are
attached to the flow field plate by chemical vapor deposition.
7. A fuel cell as defined in claim 4 in which the flow field plates
are attached to the flow field plate by physical vapor
deposition.
8. A fuel cell as defined in claim 1 in which the nanotubes are
placed only on selected areas of the FFP.
9. A fuel cell as defined in claim 1 in which the gaseous fuel
delivery system: comprises gas inlet channels in the flow field
plate to which the fuel can be transferred from an external source;
said nanotubes being in fluid communication with said gas inlet
channels.
10. A fuel cell as defined in claim 1 which has a system comprising
an array of aligned nanotubes for delivering a gaseous oxidizer
into contact with the catalyst on the second face of the
electrolyte.
11. A fuel cell as defined in claim 1 in which the electrolyte is a
proton exchange membrane.
12. A fuel cell as defined in claim 1 which includes circuitry
comprising said nanotubes for conducting electrons liberated at the
first face of the electrolyte to an external load.
13. A fuel cell as defined in claim 1 in which said nanotubes are
impregnated in a carrier and said carrier is placed on said the
face of the electrolyte.
14. An electrical power generation device comprises a stacked array
of fuel cells as defined in claim 1.
15. A fuel cell which comprises: first and second flow field
plates; an electrolyte between the flow field plates; and catalytic
electrodes on first and second, opposite faces of the electrolyte
for promoting the dissociation of a fuel at the first face of the
electrolyte and the formation of water at the second face of the
membrane; said electrodes both comprising a catalyst which is
platinum or a platinum alloy embedded in an active carbon
carrier.
16. A fuel cell as defined in claim 15 in which the catalyst is the
dried residue of an ink comprising platinum or a platinum alloy,
active carbon, and a solution of the same polymer from which the
electrolyte is fabricated.
17. A fuel cell as defined in claim 16 in which the ink also
comprises a constituent for promoting the spreading of the ink over
the face of the electrolyte to which the ink is applied.
18. A fuel cell as defined in claim 16 in which the ink also
contains a setting agent for the polymer.
19. A fuel cell as defined in claim 15 in which the polymer is a
perfluorinated ionomer.
20. A fuel cell which comprises: first and second flow field
plates; an electrolyte between the flow field plates; and a system
for hydrating said membrane; at least one of said first and second
flow field plates having a gas distribution channel therein; and
the system for hydrating said membrane comprising a component for
introducing atomized water into said channel.
21. A fuel cell as defined in claim 20 in which the system for
hydrating the membrane comprises a flow component for atomizing the
water introduced into said gas distribution channel.
22. A fuel cell which comprises: first and second flow field
plates; and an electrolyte between said flow field plates; said
flow field plates being fabricated from silicon doped with an
impurity capable of significantly reducing the resistance of
silicon to the flow of an electrical current.
23. A fuel cell as defined in claim 22 in which the flow field
plates are doped with boron, arsenic, or phosphorous.
24. A fuel cell as defined in claim 22 in which only selected areas
of said flow field plates are doped, so as to reduce dissipative
electron flow loss.
25. The combination of a fuel cell and a system for delivering a
gaseous fuel to said cell: said fuel cell comprising: first and
second flow field plates; an electrolyte between the flow field
plates; and a sealing arrangement for confining fuel delivered to
said cell to a cavity defined by the first flow field plate and the
electrolyte.
26. A multistage fuel cell stack: said stack comprising an array of
juxtaposed, serially connected fuel cells; and each of said fuel
cells comprising: first and second flow field plates; an
electrolyte between the flow field plates; catalytic electrodes on
first and second, opposite faces of the electrolyte for promoting
the dissociation of a fuel at the first face of the electrolyte and
for promoting the formation of water at the second face of the
electrolyte; and a system for delivering fuel to the first face of
the electrolyte via the first flow field plate and an oxidizer to
the second face of the electrolyte via the second flow field
plate.
27. A fuel cell stack as defined in claim 26 which comprises: a
dual function plate configured to distribute fuel to the first flow
field plate of one fuel cell in said stack and to distribute
oxidizer to the second field flow plate of a second, adjacent fuel
cell in said stack; there being first and second flow channels in
said one flow field plate for: (a) delivering a fuel to the first
face of the membrane of said one fuel cell; and, (b) delivering an
oxidizer to the second face of the adjacent fuel cell in said
stack.
28. A fuel cell stack as designed in claim 26 which has a first
manifold at one end of the fuel cell array and a second manifold at
a second end of the array for delivering a fuel, an oxidizer, and
hydrating water to said array and for removing excess water,
oxidizer, and/or fuel from the fuel cell stack.
29. A fuel cell stack as defined in claim 26 which has a system
comprising arrays of fuel cell nanotubes for conducting electrons
liberated at the anodes of the fuel cells in said stack to an
external load.
30. A fuel cell stack as defined in claim 26 which comprises a
monitoring system for providing information relating to at least
one attribute of the stack, said system comprising a sensor mounted
to a component of said stack.
31. A fuel cell stack as defined in claim 26 which comprises an
arrangement using electrical power generated in said stack to power
the monitoring system.
32. A fuel cell stack as defined in claim 26 in which the system
for delivering fuel to the first face of the electrolyte comprises
channels in said first flow field plate.
33. A fuel cell stack as defined in claim 32 in which the system
for delivering fuel to the first face of the electrolyte comprises
an array of aligned nanotubes providing fluid communication between
the channels in the first flow field plate and said first face of
the electrolyte.
34. A fuel cell stack as defined in claim 32 which comprises a
system for delivering a gas state oxidizer to the second face of
the electrolyte, said system comprising channels in the second flow
field plate.
35. A fuel cell stack as defined in claim 34 herein the system for
delivering the oxidizer to the second face of the electrolyte
comprises an array of aligned nanotubes providing fluid
communication between the channels in the second flow plate and
said second face of the electrolyte.
36. A fuel cell stack as defined in claim 26 which comprises: a
casing surrounding the array of fuel cells making up said stack;
and seals for isolating the interior of said casing from the
ambient surroundings.
37. A fuel cell stack as defined in claim 26 which comprises first
and second current collectors at opposite ends of the array of fuel
cells making up the stack for electrically connecting the cells to
an external load or grid.
38. The combination of a fuel cell and a system for monitoring and
controlling the operation of said fuel cell: said fuel cell
comprising a sensor for measuring an operating parameter of the
fuel cell; and said monitoring system comprising a microcontroller
having an input for data received from said sensor.
39. A combination as defined in claim 38 wherein: said fuel cell
comprises a silicon-based component; and said microcontroller is
embedded in said component.
40. A combination as defined in claim 38 in which Java is the
native language which the microcontroller runs.
41. A combination as defined in claim 38 which comprises flow
components for controlling the flow of a fuel and an oxidizer to
the fuel cell; and wherein the microcontroller has the capability
of outputting control data for said flow components.
42. A combination as defined in claim 38 in which said sensor has
the capability of monitoring one of the following: fuel pressure
fuel flow rate oxidizer pressure oxidizer flow rate fuel cell
temperature fuel cell internal resistance fuel cell output voltage
fuel cell external current level.
43. A combination as defined in claim 40 wherein said
monitoring/control system has an arrangement for making information
generated by the microcontroller available at a location removed
from the fuel cell.
44. A combination as defined in claim 43 wherein said arrangement
comprises the Internet.
45. A combination as defined in claim 43 wherein said arrangement
comprises a local area network.
46. A combination as defined in claim 43 in which said arrangement
comprises a unit with video capabilities and user-actuatable
components for generating microprocessor input commands.
47. The combination of a fuel cell and a system for handling d.c.
electrical energy generated by said fuel cell. said system
comprising: a unit for storing the electrical energy generated by
the fuel cell; an inverter for converting the d.c. electrical
energy to a.c.; and a switch for connecting said inverter to an
electrical grid or an electricity consumer.
48. A method for making a membrane/electrolyte assembly from a
proton exchange membrane fuel cell, said method comprising the
steps of: sizing a membrane of a perfluorosulfonate monomer; so
treating said membrane as to effect a positive ion exchange;
applying a layer of a catalyst-containing ink to first and second,
opposite faces of the membrane; drying said ink to form catalytic
electrodes on said faces of the membrane; hot processing the
assemblage of membrane and ink coatings to facilitate bonding of
the catalytic electrodes with the membrane surface; and treating
the hot pressed assemblage of membrane and ink coatings with a
sulfuric acid solution at an elevated temperature to convert the
perfluorosulfonate polymer to an acid in, H.sup.+ form.
49. A method as defined in claim 48 in which the assemblage is
stored in an aqueous medium to prevent dehydration of the
membrane.
50. A method as defined in claim 48 in which the perfluorosulfonate
ionomer has the general chemical structure 2where x* is a sulfonic
functional group and M.sup.+ is a metal cation in the neutralized
form of the ionomer and H.sup.+ in the acid form of the
ionomer.
51. A method as defined in claim 48 wherein the ion exchange is
effected by boiling the membrane in a 0.1 to 10 mol solution of
sodium hydroxide for a period of 10 to 60 minutes.
52. A method as defined in claim 48 in which the ink is applied to
the faces of the membrane by one of the following techniques: spray
coating screen printing physical vapor deposition chemical vapor
deposition dip coating blade or knife coating precipitation
followed by in situ reaction solution chemical reaction
53. A method as defined in claim 48 in which said ink comprises
platinum or a platinum alloy supported on active carbon.
54. A method as defined in claim 53 which is an alloy and has one
of the following formulations: 3 to 17 wt percent Pt, balance Ru 3
to 17 wt percent Pt, balance M, where M is a metal or combination
of metals selected from the transition elements and/or from the
metals in Groups IIIA and IVA of the Periodic Table.
55. A method as defined in claim 48 wherein the ink further
comprises a 3 to 5 wt percent solution of the same ionomer from
which the membrane is formed, the catalyst and ionomer being
present in the following proportions based on the total weight of
the ink; Catalyst: 5 to 20 percent Ionomer: 3 to 5 percent.
56. A method as defined in claim 55 in which the ink contains a
curing agent in an amount effective to thermally set said ion
owner.
57. A method as defined in claim 55 in which the ink contains an
effective amount of a chemical constituent capable of promoting the
spreading of the ink over the membrane face to which the ink is
applied.
58. A method as defined in claim 48 in which the perfluorosulfonate
in the assemblage of membrane and catalytic electrodes is converted
to the acidic form by boiling the assemblage in a 0.1 to 10 mol
solution of sulfinic acid.
59. A method of fabricating a membrane electrode assembly as
defined in claim 48 in which the assembly of membrane and catalytic
electrodes is treated at an elevated temperature, under a pressure,
and for a time effective to the material constituting the
electrodes in the membrane.
60. A method as defined in claim 59 in which the assembly is
subjected to temperatures of80.degree. to 300.degree. C. and
pressures of 90-900 Mpa.
61. A method of manufacturing a flow field plate assemblage for a
proton exchange membrane fuel cell, said method comprising the
steps of: providing a substrate; forming a flow channel in and
opening onto a first face of the substrate; porting the flow
channel with a passage extending from said channel through the
substrate to a second, opposite face of the substrate; and sealing
said port with a static face seal which surrounds said passage and
is located on said second side of the substrate.
62. A method of manufacturing a fuel cell stack comprising a fuel
cell array: each said fuel cell in the array comprising a
membrane-type electrolyte between first and second flow field
plates; and said fuel cell stack further comprising at least one
dual function flow field plate which has one ported channel for
delivering fuel to the membrane of a fuel cell located adjacent to
said dual function flow field plate and a second ported channel for
delivering an oxidizer to the second face of an adjacent fluid flow
plate.
63. A method of manufacturing a proton exchange membrane fuel cell,
said method comprising the steps of: providing a proton exchange
membrane with first and second catalytic electrodes on first and
second opposite faces thereof; so assembling as to provide an
assemblage of fuel cell components; a first flow field plate
adjacent to the first face of the proton exchange membrane; a first
gas distribution device for conveying a fuel from the first flow
field plate to the first catalytic electrode; the proton exchange
membrane; a second gas distribution device for conveying an
oxidizer from a second flow field plate to the second catalytic
electrode; and the second flow field plate; said method further
comprising the step of so applying a uniform force to the
assemblage as to increase electrical conductivity across the
interfaces between: (a) the first and second catalytic electrodes
and the first and second gas distribution devices, and (b) said gas
distribution devices and the first and second flow field
plates.
64. A method as defined in claim 63 in which said forces is applied
by: confining the aforesaid components between first and second
casing components; installing fasteners through said casing
components; and torquing said fasteners to draw the casing
components together.
65. A method as defined in claim 63 in which said pressure is
applied to the assemblage of fuel cell components by: disposing the
assemblages in a cavity defined by complementary casing components
and so drawing said casing components together as to exert said
pressure.
66. A method as defined in claim 63 wherein it is a stacked array
of fuel cell assemblages as aforesaid that is disposed in the
cavity defined by the complementary casing components.
67. A method as defined in claim 63 which includes the step of
locating between each two adjacent fuel cells in said array a dual
function flow component with features for delivering a fuel to one
of said adjacent fuel cells and features for delivering an oxidizer
to the other of said adjacent fuel cells.
68. A method as defined in claim 65 which includes the steps of:
locating a fuel supply manifold in said cavity of one end of said
array of fuel cells; and locating an oxidizer supply manifold in
said cavity of the second end of said array.
69. A method as defined in claim 63 in which said manifolds, said
dual function flow components, and the flow field plates are so
configured and related that: (a) fuel is delivered from the fuel
supply manifold to all of the fuel cells in said array, and (b)
oxidizer is delivered from the oxidizer supply manifold to all of
the fuel cells in the array.
70. A method as defined in claim 69: in which the fuel and oxidizer
supply manifolds, the dual function flow component(s), and the fuel
cell flow field plates have communicating flow passage segments;
and wherein static face seals are employed to prevent the escape of
gases through the joints between said passage segments.
Description
RELATION TO ANOTHER APPLICATION
[0001] The present application is related to provisional
application No. 60/178,494 filed 27 Jan. 2000. The benefit of the
filing date of the provisional application is claimed.
TECHNICAL FIELD OF THE INVENTION
[0002] In one aspect, the present invention relates to novel,
improved proton exchange membrane ("PEM") fuel cells.
[0003] In a second aspect, the present invention relates to novel,
improved components for PEM fuel cells and fuel cell stacks and to
processes for manufacturing and assembling those components.
[0004] In still other aspects, the present invention relates to
novel stacking configurations, humidification features, and gas
distribution designs for PEMs.
DEFINITIONS
[0005] In the interest of clarity and brevity, abbreviations will
be employed extensively in this specification. These abbreviations
are listed below:
1 Term Abbreviation Proton Exchange Membrane PEM Membrane Electrode
Assembly MEA Solid Polymer Electrolyte SPE Gas Diffusion Layer GDL
Flow Field Plate FFP Nanoscale Gas Distribution System NGDS Single
Walled Nanotube SWNT Chemical Vapor Deposition CVD Physical Vapor
Deposition PVD Single Walled Carbon Nanotubes SWNT Programmable
Logic Device PLD
BACKGROUND OF THE INVENTION
[0006] Sir William Grove in 1839 showed that he could create
electrical energy from chemical energy, the reverse of electrolysis
of water, by using platinum electrodes. More recently, major
efforts have been directed to the development of PEM fuel cells.
PEM fuel cells have been used in NASA's Space Programs for over 20
years, and are currently of greater interest as a means of
addressing the growing concerns of pollution related to the use of
internal combustion engines in our society.
[0007] The basic components of a fuel cell include: an anode, a
cathode, an electrolyte, and delivery systems for fuel and oxygen.
When the cell is in operation, the electrodes are connected to an
external load by conducting wires. In a PEM fuel cell, the
electrolyte is comprised of a thin membrane made of a polymer
similar to polytetrafluoroethylene (commonly known under the trade
name TEFLON), but incorporating sulfonic acid groups within the
polymer's molecular structure. NAFION.RTM. 117, NAFION.RTM. 112,
and NAFION.RTM. 115 are typical. These are solid polymer
electrolytes ("SPE") available from E.I. DuPont de Nemours &
Co. The sulfonic acid groups are acid ions and constitute the
active electrolyte. The membrane functions to conduct hydrogen
nuclei (H.sup.+ ions or protons) from one face through the membrane
to the opposite face while effectively blocking the flow of
diatomic hydrogen molecules through the membrane. The electrodes,
catalyst, and membrane electrolyte together form the MEA.
[0008] Hydrogen is oxidized at the anode as it comes into contact
with a catalyst (typically platinum), and is disassociated into
protons and electrons. The protons are solvated by water in the
membrane, and travel through the membrane by passing from one
sulfonic acid group to the next. As the protons migrate across the
SPE the electrons travel through the external load to the cathode.
Reduction occurs at the cathode where oxygen reacts with the
protons and electrons to form water and heat, the sole byproducts.
In the PEM fuel cell, the two reactions are:
2H.sub.2.fwdarw.4H.sup.++4e.sup.- at the anode side of the cell,
and
O.sub.2+4H.sup.++4e.sup.-.fwdarw.2H.sub.2O at the cathode side of
the cell.
[0009] Since the maximum electrochemical potential for the reaction
of water is 1.23 volts with an electrical efficiency of about
0.5-0.8 for a single cell at room temperature, a stacking
arrangement of single cells in series is needed to deliver currents
at various desired voltages for most practical applications.
[0010] Typical problems which inhibit the efficiency of heretofore
proposed PEM fuel cells are gas distribution, current collection,
and membrane hydration, which affects hydrogen/oxygen conversions
and internal resistances. Other problems associated with the
currently existing PEM fuel cells focus on economic issues such as
the ability to mass produce the fuel cells, and how to monitor and
maintain them once they have been delivered to the consumer.
[0011] One of the more significant problems posed by currently
existing PEM fuel cells is the reactant gas efficiency. The
efficiency of converting the reactant gases to the product is
related, in large part, to the hydrogen/oxygen gas distribution
within the cell at the anode and cathode respectively. Because not
all reactant gas introduced to the fuel cell is converted from
chemical to electrical energy, a greater supply of fuel is needed
to produce a desired output than is suggested by the foregoing
equations, thereby lessening the otherwise beneficial attributes of
the system.
[0012] The poor reactant gas efficiency is primarily due to the
crossover of unreacted gases through the SPE. In traditional PEM
fuel cells, the electrodes are comprised of a
carbon/platinum/polymer-based slurry that is deposited onto the
SPE. When a fuel gas (i.e. hydrogen) locates the catalyst, it must
bind to the catalyst site, yield an electron, and be immediately
solvated into the electrolyte. A problem arises because the
reactant gases do not always find a catalyst reaction site covered
or enveloped by the electrolyte with which to bind and react. The
lack of transport control of reactant gases to the catalyst
reaction sites therefore limits the kinetics of the reaction and
produces an inefficient result.
[0013] One solution to this problem is to provide a higher
concentration of catalyst in the electrode slurry. This, however,
has disadvantages because the catalyst is often a precious metal,
the increased use of which significantly adds to the overall cost
of the fuel cell.
[0014] An additional problem with currently existing PEM fuel cells
is the low conductivity of the traditional carbon/metal-catalyst
electrode's gas diffusion layer (GDL) and flow field plate (FFP)
interface surfaces. In order to direct the electrical energy
produced by the fuel cell to the external load, a means must be
provided to: (a) collect the electron flow over the entire area of
the membrane; and (b) ensure an uninterrupted electrically
conductive flow path from the catalyzed surfaces (electrodes) of
the membrane to these current-collector devices. Conductivity of
these layers is usually limited to the conductivity or resistivity
of the collection plate material (e.g., graphite has a resistivity
of 1100 .mu..OMEGA..multidot.cm). Some collector plates and/or GDLs
are made of metals such as corrosion resistant stainless steel.
Although use of this material will increase conductivity of the
collector plate, such use will also undesirably increase the weight
of the fuel cell, particularly when it is incorporated into a
stacked configuration to produce the desired output. Other
materials, incorporating metals in varying concentrations, are
available to increase the conductivity of the collector plate, but
their use is not cost-effective for the mass production of PEM fuel
cells. Moreover, the manufacture of traditional carbon graphite
FFPs is costly and also results in a heavy collection plate (carbon
graphite has a bulk density of 1.77 g/cm.sup.3), making the
stacking needed for a desired voltage range less effective in terms
of power-to-weight ratio.
[0015] A third efficiency problem associated with currently
existing PEM fuel cells relates to the issue of hydration. Because
the SPE membrane's conductivity is coupled to the amount of water
present, particularly in relation to the anode, a means of keeping
the membrane moist to a controlled degree is necessary.
SUMMARY OF THE INVENTION
[0016] There have now been invented and disclosed herein certain
new and novel PEM fuel cells incorporating stacking configurations
which provide for the delivery of current at voltages consistent
with the practical application of the fuel cells, which is not true
of the prior art PEM fuel cells. Confining the reactant gases to
the desired areas of flow in a membrane-minimizing configuration is
optimized for PEM fuel cells in accord with the principles of the
present invention by effecting the uniform distribution of a force
on the fuel cell components that increases the conductivity of the
carbon/metal-catalyst electrode, GDL, FFP interface surfaces,
thereby increasing fuel cell performance with higher current
densities. It is an important and novel feature of the present
invention that this force can be applied without crushing the
FFPs.
[0017] The present invention further provides both a new and novel
MEA for fuel cells and processes of manufacturing the same in a
more cost effective manner with more efficient current collection
devices and gas diffusion features than the prior art MEAs. These
new MEAs incorporate nanoscale tubes using fullerene products to
provide gas distribution directly to the reaction sites at the
doped silicon electrode interfaces. This nanoscale gas delivery
system improves gas efficiencies by delivering the reactant gases
directly to the immediate vicinity of the reaction sites, thus
limiting the amount of catalyst necessary for efficient operation
by concentrating the catalyst at the interface with the SPE where
the proton nuclei can be most effectively solvated and passed
through the SPE membrane to the cathode.
[0018] The present invention also comprises new and novel doped
silicon FFPs with humidification features and a
monitoring/communication interface. This interface produces higher
membrane conductivity and a more efficient collection of electrical
current with a reduced weight and a greater cost efficiency in
comparison to the prior art PEM fuel cells. Doping the silicon with
an electrically active impurity reduces the resistivity of the
silicon by several orders of magnitude, which results in a more
efficient electrical collection device with a lower weight than
currently existing carbon graphite devices. Silicon offers high
mechanical strength, and can be readily patterned and etched using
both dry (plasma) and wet chemical procedures to produce customized
gas channel configurations in the substrate. In addition, since the
silicon is a planar substrate, the option of using `Soft
Lithographic` techniques to pattern and etch the surface are also
available. Soft lithography represents a patterning scheme that is
based on self-assembly and replica molding of microstructures and
nanostructures. This technique offers a low-cost and effective
methodology for the formation and manufacture of the features
needed for fabrication of the PEM fuel cells of the present
invention.
[0019] The objects, features, and advantages of the present
invention will be apparent to the reader from the foregoing and the
appended claims and as the ensuing detailed description and
discussion proceeds in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] In the drawings, like reference numerals refer to like parts
throughout the various views unless otherwise indicated.
[0021] FIG. 1 is a block diagram of an electrical power generating
system which employs a fuel cell stack embodying the principles of
the present invention;
[0022] FIG. 2 is perspective view generally illustrating an
assembled single stage fuel cell of the present invention; the
respective layers of the fuel cell are not drawn to scale;
[0023] FIG. 2A is an exploded view of the FIG. 2 fuel cell;
[0024] FIG. 3 is a view like FIG. 2 illustrating the internal
architecture of the FFP design, and the gas delivery channels of a
multi-stage fuel cell;
[0025] FIG. 4 is an exploded view of the multi-stage fuel cell
illustrated in FIG. 3;
[0026] FIG. 5 is an exploded cross-sectional view of a multistage
fuel cell stack embodying the principles of the present
invention;
[0027] FIG. 6 is an enlarged partial view of a GDL illustrated in
FIG. 4, illustrating an array of aligned nanotubes;
[0028] FIG. 7 is a view like FIG. 6 wherein the aligned nanotubes
are embedded in and extend through the GDL;
[0029] FIG. 8 is an enlarged, partial cross-sectional view of an
assembled fuel cell as shown in FIG. 5, illustrating the relative
position of the aligned nanotubes in conjunction with other
elements of the fuel cell;
[0030] FIG. 9 is a block diagram illustrating the communication and
control interfaces with which a fuel cell of the present invention
is designed to function;
[0031] FIG. 10 is a flow diagram illustrating the fuel cell
monitoring and communication features of the present invention, and
interactions between the controller and the fuel cell system;
[0032] FIG. 11 illustrates the relationship of the hardware
components of a system for controlling the fuel cell system of the
present invention; and
[0033] FIG. 12 is a schematic diagram of a heating/cooling system
employed in accordance with the principles of the present invention
to promote efficient operation by keeping constant the operating
temperature of an associated fuel cell or fuel stack also embodying
the principles of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0034] Referring now to the drawings, FIG. 1 is a block diagram of
an electrical power generating system shown generally at 10 wherein
a fuel cell stack 12 uses reactant gases from oxygen supply 14 and
hydrogen supply 16 to generate an electrical current at a specified
voltage (the number of fuel cells stacked in series determines the
voltage output of the system). The direct current produced by the
cell may be converted to alternating current by power inverter 18
and transmitted to an external load or power grid. An SPE membrane
incorporated within the fuel cell in accordance with the present
invention and described below is moistened by use of the membrane
hydration feature 20 to promote efficient conductivity of the
membrane for proton nuclei produced by the oxidation reactions at
the anodes of the individual fuel cells incorporated within fuel
cell stack 12.
[0035] Monitoring instrumentation 22 mounted in accordance with the
present invention on the individual fuel cells or elsewhere in fuel
cell stack 12 provides information to monitoring system 24
regarding particular attributes of the fuel cells including but not
limited to the functional status, output, and/or fuel levels. This
information is routed via communication system 26 to an Internet
site or other specific destination. The communication system 26 may
be comprised of any number of analog or digital devices such as a
personal computer, a local area network, or a relay station for
wireless communication. The fuel cell's own electrical output may
be used to power such a system from a remote location,
circumventing the need for an additional power supply to maintain
the transmission of information on the status of the fuel cell
power generation system 10.
[0036] Having observed the general interaction of the fuel cell
with a monitoring and communication system of the present
invention, attention may now be directed to the particular
characteristics of the fuel cells of the present invention.
[0037] Plates or casing components 36, 38 are fastened together by
a series of bolts 40 and 41 positioned around the periphery of the
fuel cell to isolate the interior of the cell from environmental
contaminants and exert pressure on the components housed in the
cavities of plates 36 and 38 by making the conducting of
electricity across the interfaces more efficient. This force or
pressure improves element-to-element surface contact and thereby
improves fuel cell performance. The wanted, efficiency improving
force on the fuel cell components can be obtained by torquing bolt
40 to a selected level.
[0038] References characters 41-46 in FIG. 2 identify conduit/port
arrangements which have the following functions:
2 Reference Character Function of Identified Component 41 Fuel
(H.sub.2) In 42 Excess Fuel Out 43 Oxidizer (O.sub.2) In 44
Oxidizer (O.sub.2) Out 45 Coolant In 46 Coolant Out
[0039] Components 45 and 46 are elements of a coolant
heating/cooling system described hereinafter. As will there be
discussed in more detail, the coolant is circulated through the
fuel cell to keep the fuel cell operating temperature constant.
[0040] The two outermost layers 50, 52 are the cell's FFPs which
deliver the reactant gases, provide an avenue of exhaust for
unreacted gas and water generated at the fuel cell cathode, collect
the electrical energy produced by the cell, and provide a means of
hydrating the cell's membrane to facilitate more efficient
conversion of the reactant gases to water and electrical energy.
The next two fuel cell elements 54, 56 are the cell's GDLs, which
provide a conductive, gas distribution system between FFPs 50, 52
and the thin catalytic electrodes 58, 60 applied to the two sides
of PEM 62.
[0041] The electrical energy collected by cathode FFP is
transmitted to the exterior of the fuel cell by current collector
64 for transmission to an external load or power grid as previously
described in reference to FIG. 1. The electrical circuit is
completed from the load (or a power grid) to the cathode FFP of the
fuel cell by internal conductor 65.
[0042] FIG. 3 illustrates a single fuel cell unit 73 with gas flow
passages 66 and FFPs 74, 80 (see FIG. 4) along with dual function
flow components 68 and 70. The fuel cell 73 and flow field
components are designed to be incorporated into a fuel cell stack
in order to achieve acceptable current densities at the higher
voltages required for many practical applications.
[0043] Turning now to FIG. 4 which is an exploded view of the
single, multistage design fuel cell of FIG. 3, dual function flow
components 68, 70 form a non-conductive barrier between individual
fuel cells of a stacked configuration and provide a means of
facilitating gas flow from one cell to the next via gas flow
communication flow passage segments of passages 66. These segments
are machined into the plates.
[0044] Elastomeric face seals 72 seal the gas flow passages and
passage segments within the individual fuel cell. The hydrogen FFP
74 has a circular groove 76 machined into the inner surface thereof
for receiving elastomeric static face seal 78. Face seal 78 seals
the PEM fuel cell cavity in which the chemical reactions liberate
protons and electrons. The oxygen FFP 80 is identical in all
respects to the hydrogen FFP except that its surface is flat and
contains no groove, instead having a surface against which
elastomeric static face seal 78 can be sealed.
[0045] Each FFP may be manufactured from boron, arsenic, or
phosphorous-doped silicon using standard silicon industry practices
as described in, for example, VSLI Technology, S. M. Sze, Chapter
6, pp. 219-264 and Solid State Technology, 1976, Monokowski, J. and
Stach, J., "System Characterization of Planar Source Diffusion."
The doped FFP is machined to form the interdigitalized channels 82
which provide a means of gas delivery to the GDLs 84, 86 located at
the interior surface of each FFP in the assembled fuel cell. The
channels can also, and may preferably be, formed by sequential
masking and etching steps, see VSLI Technology, supra, Chapter 7,
pp. 267-300.
[0046] Although the resistivity of silicon is greater than the more
traditionally used carbon graphite, this can be an advantage when
the silicon is doped, causing its resistivity to become negligible.
Selective areas only of the FFP may in this way be made highly
conductive while the rest of the FFP remains resistive, allowing
for effective electron conduction to an external load or power grid
without excessive dissipative voltage loss. Another advantage of
doped silicon FFPs is ease of mass-producibility.
[0047] As suggested above, aligned arrays of fullerenes can be
adhered to the surfaces of the FFPs to form the GDL's of the fuel
cells disclosed herein. U.S. Pat. Nos. 5,879,827; 4,328,080; and
5,795,672 disclose vapor deposition processes which can be used in
accord with the principles of the present invention to achieve this
objective.
[0048] One above-discussed advantage of using fullerenes to deliver
fuel and oxidizer to the catalytic electrodes of the novel fuel
cells disclosed herein is that of greater structural rigidity. This
rigidity is due to the presence of the nanoscale carbon structures,
whether associated with an FFP or a conventional GDL material.
[0049] As just discussed, the fullerene gas distributors can be
affixed to the FFPs of the fuel cell to form the requisite GDL.
Alternatively, the GDLs can be fabricated by affixing the nanotubes
to a conventional, porous GDL material such as one fabricated from
a conventional GDL material such as Teflon-impregnated carbon
paper, an aerogel, or a carbon fibermat. In these GDLs, the
nanotubes significantly increase resistance to crushing, a problem
which conventional GDLs have.
[0050] The nanotubes 94 (illustrated in FIGS. 6-8) in this subject
embodiment of the invention provide a gas conduit from the flow
field interfaces to catalyst sites located on the PEM 92. FIG. 6 is
a partial, enlarged view of GDL 85 (see FIG. 4) illustrating a
particular embodiment of this aspect of the present invention
wherein the aligned nanotubes 94 are fixed to a layer of GDL
material 86 and conduct gas from the interdigitalized FFP channels
82 (see FIG. 4) directly to the catalytic cathode on PEM 62. This
not only enhances gas delivery, but also enhances current
collection and facilitates the transmission of electrons from the
reaction sites and conductive GDL to the FFP 74 (see FIG. 4) and an
external load or grid. The aligned nanotubes 94 also act as
conductors to transmit electrons from the fuel cell cathode to the
FFP at that electrode.
[0051] The placement of the nanotubes 94 may be effected by various
methods such as those described in the above-described patents. The
nanotubes may also be impregnated within the FFP and/or extended
through the GDL to most efficiently deliver the reactant gases to
the catalyst sites on the PEM 92. FIG. 7 illustrates the nanotubes
94 passing directly through or embedded in the GDL.
[0052] FIG. 8 is a cross-sectional view of an assembled fuel cell
such as that in FIG. 5 where the nanotubes 94 have been impregnated
into the FFPs 96, 98 and pass directly through GDL layers 100, 102
to catalytic electrodes 104 and 105 on opposite sites of PEM 92.
The interdigitalized channels 106 of FFPs 96, 98 supply gas to the
ends of the aligned nanotubes for distribution over the catalyst
sites on PEM 92.
[0053] Referring now primarily to FIG. 5, we illustrate an exploded
cross-sectional view of a stacking configuration for multistage (or
stacked) fuel cells of the present invention. Non-conductive casing
components 108, 110 enclose the assembled, functional components of
the PEM fuel cell stack 111. Each casing component has gas flow
passages (or channels) 112 to deliver gas to a fuel cell in the
stack. Elastomeric face seals 114 seal the gas flow passages within
the stack and between each successive layer or individual fuel cell
unit or component.
[0054] A single sided manifold plate 116 is incorporated into the
stack at each end of the stack to direct the flow of reactant gases
into and out of the stacked fuel cells. Fuel and oxygen FFPs 120,
122 surround the other, casing-housed functional components of the
individual fuel cell as described previously in relation to FIG. 4.
Conductive, gas distributing GDLs 124, 126 are located between FFPs
120, 122 and the proton exchange membrane 128, which has a
catalytic electrode layer (not shown) on each side thereof.
Although FIG. 5 depicts a stack of only three individual fuel
cells, the stacking configuration is suited for stacks
incorporating a larger number of fuel cells shown in that
figure.
[0055] A double sided, stackable manifold 1 18 separates each
individual fuel cell in stack 111 from the adjacent fuel cell and
provides a means of conducting the reactant gases from one fuel
cell to the next. This double sided manifold plate provides gas
flow passages for FFPs located on either side thereof, and
incorporates all necessary gas seal grooves for seating the
requisite static face seals in the gas flow passages. An
elastomeric static face seal 130 seals the interior of each
individual fuel cell unit.
[0056] Electrically, the fuel cells in stack 111 are connected in
series by conductors 131a-d. Conductors 131a and 131d are in turn
connected to collectors 64 and 65, the latter in turn being
connected to external load or grid circuitry.
[0057] The electrodes (FFPs), GDLs, catalyst, and membrane
electrolyte (PEM) together form the membrane electrode assembly
("MEA"), and constitute the functional components making up the
individual fuel cell units.
[0058] A number of materials and fabrication techniques may be
employed to produce a MEA. An improved method of manufacturing a
high quality MEA capable of achieving high fuel cell power
densities is set forth in Example I below:
EXAMPLE I
[0059] A commercially available Nafion.RTM. membrane is the
preferred choice for the PEM fuel cell electrolyte. Nafion is a
perfluorosulfonate ionomer; it is described at Internet web site
http://www.psrc.usm.edu/mau- ritz/nafion.htm.
[0060] The general chemical structure of Nafion is: 1
[0061] where X is a sulfonic functional group and M.sup.+ is: (a) a
metal cation in the neutralized form of the isonomer and H.sup.+ in
the acid form of the ionomer.
[0062] Nano-scale platinum and platinum alloy powders embedded in
active carbon particles may be used for the electrode material (Pt
is known to catalyze the electro-chemical reaction at the normal
operating temperatures of the PEM fuel cell).
[0063] The fabrication of the membrane/catalyst layers is as
follows:
[0064] 1. Cut Nafion.RTM. membrane into desired size;
[0065] 2. Clean membrane by boiling in hydrogen peroxide for 1
hr.;
[0066] 3. Boil membrane in a sodium hydroxide solution for 1 hr. to
convert the Nafion from the acidic (H.sup.+) to a neutral
(Na.sup.+) form. This increases the stability of the Nafion's
sulfonic groups and water uptake and facilitates the steps which
follow;
[0067] 4. Rinse the membrane in deionized water;
[0068] 6. Frame and dry membrane;
[0069] 7. Prepare a Pt/C ink by mixing Pt, 20 wt % on VULCAN.TM.
XC-72R carbon w/Nafion.RTM. solution, isopropyl alcohol, a glycerol
spreading promoter, and t-butyl ammonium hydroxide (curing agent).
The ratio of catalyst to Nafion.RTM. is preferably within the range
of 5:2 to 3:1 based on the weight of the solids in the
solution.
[0070] 8. Apply Pt/C ink to each side of the membrane;
[0071] 9. Dry the ink (120 min. @135.degree. C. in a vacuum
oven);
[0072] 10. Hot-press the MEA @150.degree.-180.degree. C. for 60-100
sec. @77 atm.;
[0073] 11. Rinse MEA in deionized water;
[0074] 12. Boil the MEA in 0.5M H.sub.2SO.sub.4 solution for 1 hr.
to convert the Nafion back to its acidic form. This is done so that
the electrolyte will be capable of conducting protons (H.sup.+
ions) from the anode to the cathode of the fuel cell;
[0075] 13. Rinse and store MEA in deionized water to prevent
dehydration Application of the Pt/C ink solution to the membrane
may be accomplished by air brushing, spin coating, dip coating,
screen printing, sputtering, physical vapor deposition,
precipitation reaction, or by implementation of a sol-gel process.
Application of the catalyst material by air brushing is a common
technique, but other techniques may produce more uniform
distribution of catalyst and greater control over the thickness of
the catalyst layer. The thickness may range from 1 to 2,000
angstroms.
[0076] The catalyst layer is preferably prepared from the Pt/C ink
described above, but the catalyst component of the ink in general
be a mixture of: platinum and: (a) ruthenicum., or (b) one or more
transition metal elements or a metal selected from Groups IIIA or
IVA of the periodic table of elements. Suitable Pt alloys are:
[0077] 3 to 17 wt. percent Pt, balance Ru
[0078] 3 to 17 wt percent Pt, balance M, where M is an element as
just described.
[0079] The heat treatment or hot press of the MEA set forth in
Example I above may be accomplished by any combination of pressure,
temperature, and time sufficient to partially embed the electrolyte
materials in the membrane. The precise conditions used depend in
part on the nature of the alloy or metal employed as the catalyst.
Typical temperatures range between 80.degree. and 300.degree. C.,
most preferably between 100.degree. and 150.degree. C. Typical
ranges for pressure are between 90 and 900 MPa, most preferably
between 180 and 270 MPa.
[0080] Hydration of the MEA (required for it to operate
effectively) may be achieved with an acid boil, a water boil, a
cold-water soak, or any combination thereof.
[0081] The application of nanotubes or other fullerenes to the FFPs
or to a conventional GDL material support may be accomplished by a
variety of methods including the vapor deposition techniques
described in those patents cited above. There are several routes to
synthesize "single-walled" carbon nanotubes in situ, one preferred
technique for providing aligned nanotube arrays in accord with the
principles of the present invention. One in situ technique which
can advantageously be used is chemical vapor deposition ("CVD") of
various hydrocarbon compounds such as methane at controlled
locations on a substrate using patterned catalytic islands. This
combined synthesis and microfabrication technique allows a large
number of ohmically contacted nanotube devices of controllable
length to be placed on a single substrate.
[0082] The synthesis of bulk amounts of high quality single-walled
carbon nanotubes ("SWNTS") can be accomplished by optimizing the
chemical compositions and textural properties of the catalyst
material used in the CVD of methane. A series of catalysts have
been derived by systematically varying the catalytic metal
compounds and support materials. The optimized catalysts are Fe/Mo
bimetallic species supported on a multicompound silica-alumina
multicomponent material. The high SWNT yielding catalyst exhibits
high surface area and large mesopore volume at elevated
temperatures. The nanotube material consists of individual and
bundled SWNTs that are free of defects and amorphous carbon
coating.
[0083] Another method for fabricating large arrays of parallel
carbon nanotubes is by pyrolysis of acetylene on cobalt within a
hexagonal, close-packed, nano-channel alumina template. This
method, which is based on template growth, has an advantage over
other methods in that it is nonlithographic and does not require a
clean room. The arrays of carbon nanotubes produced by this method
have an unprecedented level of periodicity and uniformity.
[0084] The preparation of the FFPs, aside from the incorporation of
aligned nanotubes, may be accomplished using standard silicon wafer
doping and etching techniques such as those identified above
wherein a layer of the silicon is doped with a semi-conducting
element, and then etched into a desired pattern. This is followed
by application of ohmic contacts to serve as interfaces for
external electrical connections. The FFPs are also designed to
accommodate a novel integrated silicon nozzle for hydrating the
fuel cell membrane. The nozzle (shown at 200 in FIG. 2A) produces a
fine colloidal mist of water vapor which is entrained in the
reactant gas. The gas is delivered to the reaction sites on the
surface of the membrane.
[0085] The FFPs of the present invention are further constructed to
accommodate an electrical connection for receipt and transmission
of communications and monitoring information regarding several
aspects of the fuel cell.
[0086] Referring now to FIGS. 9-11, FIG. 9 illustrates the
interrelationship of a fuel cell monitoring and communication
system with various electronic devices ("monitoring" will also
typically include "control" capabilities and functions). This novel
communication and interface system can be employed in fuel cells
designed to be incorporated into homes (smart homes), offices, and
elsewhere. The fuel cell monitoring/communication system is
connected to the fuel cell at the FFP and can have Ethernet,
Internet, and burst packet communications capabilities as well as
other analog and digital communications capabilities.
[0087] The electronic circuitry which provides the communication
and monitoring capabilities of the fuel cells, including
microprocessor 140, can be embedded in the FFP with the circuitry
being isolated by undoped silicon. The communication and monitoring
electronics are thereby insulated from the power generation
component of the FFP. Alternatively, the circuitry and FFP can be
fabricated separately and connected to the FFP by various methods
such as welding, fusing, and gluing; or the circuit components may
be mechanically attached using a holder, horseshoe clip, tongue and
groove system, or any other means of attachment. This integrated
monitoring system allows for direct monitoring of single and
aggregate fuel cell stacks. The fuel cell itself can be the power
source for the monitoring/communication system, which may include a
wireless LAN acting as a relay station for wireless (digital)
devices, i.e., computers, laptops, personal communication systems,
retinal eye scanning devices, etc.
[0088] Currently, no developed systems exist which implement a
remote monitoring application for fuel cells. By creating such a
system which permits remote power application of fuel cells to
residential and commercial sites, an individual user can be freed
from an expensive utility grid, or have an alternative source of
electricity during peak hours or in the event of some disruption in
service from the utility provider.
[0089] In order to ensure that the fuel cell system is functioning
correctly, it must be under constant monitoring and control and, as
such, an embedded control system that can perform such a task
without constant human intervention and supervision is
required.
[0090] Referring now primarily to FIGS. 10 and 11, an embedded
microcontroller/microprocessor 140 controls the flow of information
between the fuel cell(s) and a remote site from which one may
execute a variety of commands to control or monitor the status of
the fuel cell's operation or fuel levels, etc. Parameters which may
be monitored and/or controlled include, but are not limited to:
[0091] fuel pressure
[0092] fuel flow rate
[0093] oxidizer pressure
[0094] oxidizer flow rate
[0095] fuel cell temperature
[0096] fuel cell internal resistance
[0097] fuel cell output voltage
[0098] fuel cell external current level
[0099] One or more sensors typically but not necessarily associated
with a fuel cell FFP are provided to measure the parameter. The
sensor may be incorporated in the FFP as shown at 120 in FIG. 4 or
may be fabricated separately and attached to the FFP by any
appropriate technique (not part of the present invention).
[0100] A microprocessor 140 with RAM/ROM 141 executes the commands
received by the system to direct the fuel cell's function and the
switching of the electrical supply from a power grid to the fuel
cell, or to another power grid, home, or business, etc.
[0101] A digital-to-analog converter 142 converts the signals from
the microprocessor to analog form and conveys the signals to a data
demultiplexer 144 provided so that the respective signals can then
be directed over control lines 146 to specific elements of the fuel
cell or power management system.
[0102] Hydrogen and oxygen mass flow controls 148, 150 control the
flow of reactant gases from hydrogen and oxygen storage tanks 149,
151 into the fuel cell stack 152 based on the user's electrical
output requirements. Monitoring lines 154 ultimately enable the
user to view the status of the individual fuel cell units in the
stack in terms of voltage and/or current production, as well as
internal resistance and membrane status for evaluating water
management issues.
[0103] A direct current ("DC") output signal 156 output from the
fuel cell stack may also be communicated to the user for evaluating
whether changes need to be implemented in the operation of the fuel
cell aggregate.
[0104] The fuel cell electrical output is stored in a battery 158
which will provide power when called upon to do so. The DC current
160 coming from the battery is measured to provide user feedback,
and is transmitted to an inverter 162 for conversion to alternating
current ("AC") 164 capable of being used in a typical home or
office or elsewhere in the same way that electrical power from a
utility provider is used.
[0105] The ultimate arbiter directing the flow of electrical energy
is a switch 166, controlled by the user, system operator, etc.
which allows electrical energy to be sent to, or received from, a
variety of sources such as a power grid 168; a transformer 170; a
home or business 172, etc.
[0106] Measurement information from the power generation and
management system is received by a data multiplexer 174. The
multiplexer brings about the serial transmission of the several
input signals to analog-to-digital converter 176. The digital
signal is then transmitted to the embedded
microcontroller/microprocessor 140 from which it may be directed
over a data bus 178 to a network or local area network chip 180
where the status and control information can ultimately be
communicated over LAN 181 and/or the Internet 182 to the
user/controller.
[0107] As a further example, and as is shown in FIG. 11, data can
be transmitted to, and control signals received from, a PDA or
other modem-connected or wireless device. The typical device 190
shown in FIG. 11 includes a video chip 192, video RAM 194, a video
display 196, and a touchpad 198 by which commands can be input to
microprocessor 140.
[0108] Having the ability to interact with the power generation and
management system of the present invention provides the user or
power system controller with the ability to remotely activate the
power generating system in the event of a brownout, or during peak
electrical demands when the cost of electrical power may be
excessive. Such access also provides an emergency source of
electrical power in the event of a blackout or other disruption in
the supply of power from the local utility company.
[0109] Data may be acquired so that the user can evaluate the
pressure and flow rates of the reactant gases, the temperature of
the heating and/or cooling features of the cells, the voltage and
current for each individual fuel cell, fuel cell stack, or
aggregate of fuel cell stacks, as well as internal resistance and
membrane status for water management as discussed above. This
information allows one to monitor the fuel cell's status, and to
change system parameters from a remote location to meet the user's
present demands. The interface also permits one to switch
connections to and from different utilities or locations depending
on users' needs and the availability and costs associated with
electrical power from other sources.
[0110] A preferred implementation of this subject
monitoring/control uses a PSC1000 microprocessor, available from
Patriot Scientific Corp., a TCP/UDP/IP through Java communications
protocol, and an Ethernet chip for the hardware communication. The
PSC1000's native Java performance will enable any device to easily
connect to the Internet for communication of information and data
to and from the user.
[0111] It was pointed out above that installations embodying the
principles of the present invention preferably have a
heating/cooling system for promoting efficient fuel cell operation
by keeping the operating temperature of the fuel cell or fuel cell
stack constant (typically at a temperature in the range of
6.degree.-90.degree. C.). A representative system 2.sub.--s shown
in FIG. 12. That system includeds a reservoir 206 for the coolant
(typically water), a pump 208 for effecting the flow of the coolant
from reservoir 206 to fuel cell or fuel cell stack 210, a heater or
charger 212 for adjusting the temperature of the coolant, and
plumbing identified collectively by reference character 214 for
connecting the foregoing components in series with each other and
fuel cell unit inlet and outlet ports 45 and 46. A controller 220
with feedback from fuel cell unit thermocouple 222 controls the
operation of heat exchanger 212 and pump 214, adjusting the
temperature and/or flow rate of the coolant as needed to keep the
fuel cell component operating temperature constant. Typically, this
will involve the cooling of the coolant. However, there are
circumstances--such as start-up--when heating the coolant may be
advantageous.
[0112] As will be apparent to the reader, the present invention may
be embodied in many forms without departing from the spirit or
essential characteristics of the invention. The present embodiments
are therefore to be considered in all respects as illustrative and
not restrictive. The scope of the invention is indicated by the
appended claims rather than by the foregoing description and the
drawings; and all changes which come within the meaning and range
of equivalency of the claims are intended to be embraced
therein.
* * * * *
References