U.S. patent application number 11/818762 was filed with the patent office on 2007-10-18 for method and apparatus for facilitating a chemical reaction.
Invention is credited to Qin Liu, L. Chris Mann, Joesph W. Tsang.
Application Number | 20070243432 11/818762 |
Document ID | / |
Family ID | 32593317 |
Filed Date | 2007-10-18 |
United States Patent
Application |
20070243432 |
Kind Code |
A1 |
Liu; Qin ; et al. |
October 18, 2007 |
Method and apparatus for facilitating a chemical reaction
Abstract
A method of facilitating a chemical reaction includes raising a
temperature of a protective layer covering a catalyst in the
presence of a chemical solution.
Inventors: |
Liu; Qin; (Corvallis,
OR) ; Tsang; Joesph W.; (Corvallis, OR) ;
Mann; L. Chris; (Corvallis, OR) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
32593317 |
Appl. No.: |
11/818762 |
Filed: |
June 15, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10323948 |
Dec 18, 2002 |
7241527 |
|
|
11818762 |
Jun 15, 2007 |
|
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|
Current U.S.
Class: |
429/421 ;
429/416; 429/434; 429/513; 429/515; 44/532 |
Current CPC
Class: |
H01M 8/065 20130101;
Y02E 60/36 20130101; C01B 2203/066 20130101; H01M 8/04216 20130101;
Y10T 428/2938 20150115; C01B 3/065 20130101; Y02E 60/50 20130101;
Y10T 428/2991 20150115 |
Class at
Publication: |
429/019 ;
429/012; 044/532 |
International
Class: |
H01M 8/06 20060101
H01M008/06; C10L 11/00 20060101 C10L011/00 |
Claims
1-23. (canceled)
24. A fuel pellet comprising: a chemical solution; a heating
element; and a chemical catalyst covered by a protective layer
isolating said chemical catalyst from said chemical solution at
ambient temperatures.
25. The pellet of claim 24, further comprising a plurality of
compartmentalized fuel pellets, wherein each of said plurality of
compartmentalized fuel pellets comprises a separate chemical
solution, heating element, and chemical catalyst covered by a
protective layer.
26. The pellet of claim 25, wherein each fuel pellet is
independently operable by selectively activating said heating
elements.
27. The pellet of claim 25, wherein said heating elements further
comprise resistive heating elements.
28. The pellet of claim 25, wherein said chemical solution
comprises a metal borohydride.
29. The pellet of claim 28, wherein said metal borohydride is a
sodium borohydride solution.
30. The pellet of claim 25, wherein said protective coating
comprises a heat-removable layer.
31. The pellet of claim 30, wherein said heat-removable layer
comprises wax, polymers, or copolymers of olefins.
32-34. (canceled)
35. A fuel cell cartridge comprising: a hydrogen fuel source in the
presence of a catalyst; wherein said catalyst is insulated from
said hydrogen fuel source by a heat-sensitive protective coating;
and a heating element for removing said heat-sensitive protective
coating on demand.
36. The cartridge of claim 35, wherein said heating element is a
resistive heating element.
37. The cartridge of claim 35, wherein said hydrogen fuel source is
separated into a plurality of individual cells, each of said
plurality of individual cells comprising a catalyst insulated from
said hydrogen fuel source by a protective coating, and each of said
plurality of individual cells comprising a heating element.
38. The cartridge of claim 37, wherein each of said plurality of
individual cells comprises a cover layer with an initiator, said
initiator predisposed to open at above-ambient temperatures or
pressures to release hydrogen gas produced in said individual
cells.
39. The cartridge of claim 35, wherein said hydrogen fuel source is
an aqueous sodium borohydride solution.
40. The cartridge of claim 35, wherein said catalyst and said
heat-sensitive protective coating are generally planar or
spherical.
41. A fuel cell apparatus comprising: an anode; a cathode; an
electrolyte disposed between said anode and said cathode; a
hydrogen fuel source in the presence of a catalyst, said catalyst
insulated from said hydrogen fuel source by a heat-sensitive
protective coating; and a heating element for removing said
heat-sensitive protective coating on demand.
42. The apparatus of claim 41, wherein said heating element
comprises a resistive heating element.
43. The apparatus of claim 41, wherein said hydrogen fuel source is
divided into cells, and wherein each cell includes one or more of
said heating element and said catalyst insulated by said protective
coating.
44. An electronic device comprising: a fuel cell; a hydrogen
generating system; and an electrical load; wherein said hydrogen
generating system comprises a hydrogen-bearing chemical solution in
the presence of a catalyst, said catalyst being insulated from said
hydrogen-bearing chemical solution by a protective coating at
ambient temperatures, and a heating element for removing said
protective coating insulating said catalyst from said chemical
solution.
45. The device of claim 44, wherein said hydrogen generating system
further comprises a cover with an initiator predisposed to open at
elevated temperatures or pressures to release hydrogen gas when
said protective layer is removed from said catalyst.
46. The device of claim 44, further comprising a plurality of cells
containing said chemical solution, wherein each of said plurality
of cells includes one or more of said catalyst insulated by said
protective coating and one or more of said heating element.
47. The device of claim 46, wherein each heating element of said
plurality of cells is separately controllable.
48. A hydrogen generating apparatus comprising: means for
compartmentalizing a hydrogen-bearing fuel source; means for
catalyzing said hydrogen-bearing fuel source; means for insulating
said means for catalyzing from said hydrogen-bearing fuel source at
ambient temperatures; and means for removing said means for
insulating.
49. The apparatus of claim 48, further comprising means for
providing hydrogen produced from said hydrogen-bearing fuel source
to a fuel cell.
50. The apparatus of claim 49, wherein said means for providing
comprise a cover layer with an initiator, said initiator
predisposed to open at above-ambient temperatures or pressures to
release hydrogen gas produced in said means for
compartmentalizing.
51. The apparatus of claim 48, wherein said means for removing
comprises one or more thin film heating elements.
52-72. (canceled)
Description
BACKGROUND
[0001] During the past several years, the popularity and viability
of fuel cells for producing large and small amounts of electricity
has increased significantly. Fuel cells conduct an electrochemical
reaction with chemicals such as hydrogen and oxygen to produce
electricity and heat. Fuel cells are similar to batteries, but they
can be "recharged" while providing power, and are much cooler and
cleaner than devices that combust hydrocarbons.
[0002] Fuel cells provide a DC (direct current) voltage that may be
used to power motors, lights, computers, or any number of
electrical appliances. There are several different types of fuel
cells, each using a different chemistry. Fuel cells are usually
classified by the type of electrolyte used. The fuel cell types are
generally categorized into one of five groups: proton exchange
membrane (PEM) fuel cells, alkaline fuel cells (AFC),
phosphoric-acid fuel cells (PAFC), solid oxide fuel cells (SOFC),
and molten carbonate fuel cells (MCFC).
[0003] Each of the fuel cells mentioned above uses oxygen and
hydrogen to produce electricity. The oxygen for a fuel cell is
usually supplied by the ambient air. In fact, for the PEM fuel
cell, ordinary air may be pumped into the cathode. However,
hydrogen is not as readily available as oxygen. Hydrogen is
difficult to generate, store and distribute.
[0004] One common method for producing hydrogen for fuel cells is
the use of a reformer. A reformer produces hydrogen from
hydrocarbons or alcohol fuels. The hydrogen can then be fed to the
fuel cell. However, if the hydrocarbon fuel is gasoline or some of
the other common hydrocarbons, undesirable byproducts are produced,
such as SO.sub.x, NO.sub.x and others. These byproducts are not
only pollutants, but can damage the reformer. Sulfur, in
particular, must be removed from the reformer or may damage the
electrode catalyst. Additionally, reformers usually operate at high
temperatures and consume significant energy.
[0005] Alternatively hydrogen can be generated from a precursor at
ambient temperature using a catalyst. However, such chemical
reactions for producing hydrogen may require a pump to move the
precursor, a hydrogen-bearing chemical mixture, into a reaction
chamber filled with a catalytic agent. As soon as the chemical
mixture is exposed to a catalyst, the reaction rate is accelerated.
Thus, the chemical mixture and catalyst must be separated until
hydrogen production is to start. Consequently, a pump is needed to
selectively move the chemical mixture from storage to the reaction
chamber.
[0006] Further, for -portable fuel cell applications, it is
difficult to miniaturize the fuel cell and hydrogen-producing
system, and still produce hydrogen on demand. Once a chemical
reaction in the presence of a catalyst has begun, the reaction is
difficult to stop and/or restart. The electrical demands of
portable electronics may vary widely, therefore a fuel cell
providing power to portable electronics must be equipped to
efficiently provide varying amounts of hydrogen on-demand to
produce the electricity needed.
[0007] One solution to produce hydrogen on-demand is to use
micro-pumps to deliver a certain amount sodium borohydride
(hydrogen-bearing solution) to a catalyst bed. However, a
by-product of the sodium borohydride, sodium metaborate, tends to
absorb water and gel when allowed to cool. This hinders access to
the catalyst and renders the water needed for the reaction
unavailable.
[0008] Another solution is to heat the sodium borohydride, which
increases the rate of hydrogen production. However, using heat to
increase hydrogen production on-demand results in higher parasitic
losses.
SUMMARY
[0009] In one of many possible embodiments, a method of
facilitating a chemical reaction includes raising a temperature of
a protective layer covering a catalyst in the presence of a
chemical solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a diagrammatical illustration of a chemical
reaction system according to one embodiment of the present
invention.
[0011] FIG. 2 is a diagrammatical illustration of a chemical
reaction system according to another embodiment of the present
invention.
[0012] FIG. 3 is a diagrammatical illustration of a chemical
reaction system according to another embodiment of the present
invention.
[0013] FIG. 4 is a diagrammatical illustration of a chemical
reaction system according to another embodiment of the present
invention.
[0014] FIG. 5 is a flowchart illustrating a method of making a
chemical reactor according to another embodiment of the present
invention.
[0015] FIG. 6 is a flowchart illustrating a method of making a
chemical reactor according to another embodiment of the present
invention.
[0016] FIG. 7 is a disassembled view of a PEM fuel cell that may be
used with the chemical reactions systems according to another
embodiment of the present invention.
[0017] FIG. 8 is a block diagram of an electronic device with a
fuel cell and a chemical reaction system according to another
embodiment of the present invention.
[0018] In the drawings, identical reference numbers indicate
similar, but not necessarily identical, elements.
DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS
[0019] The principles, devices and methods described herein can be
implemented in a wide variety of chemical reactions including those
for producing hydrogen for fuel cells. The kinds of fuel cell
applications compatible with the disclosed principles include, but
are not limited to, PEM fuel cells, AFCs, PAFCs, SOFCs, and
MCFCs.
[0020] Turning now to the figures, and in particular to FIG. 1, a
chemical reaction system or cartridge, for example a hydrogen
generating system (40), is shown. According to the embodiment of
FIG. 1, the hydrogen generating system (40) may include one or more
chemical mixtures arranged in chambers, for example chemical
mixture cells (42). The chemical mixture cells (42) are preferably
supported on a common base (44) as shown in FIG. 1, but this is not
necessarily so. Each chemical mixture cell (42) may be completely
independent. Further, the number of chemical mixture cells (42) is
not limited to the two-cell configuration shown. There may be one
or more chemical mixture cells (42). The two-cell configuration is
merely an example for purposes of illustration. These cells (42)
may be arranged side-by-side, as in FIG. 1, or stacked.
[0021] The base (44) supports a plurality of walls (46) that divide
and define the cells (42) for holding the chemical mixture. Both
the base (44) and the walls (46) may be made of any material
compatible with the chemical mixture being contained. For example
the base (44) and walls (46) may include plastics, ceramics,
metals, composites, or other materials.
[0022] According to the present embodiment of the hydrogen
generating system (40), the chemical mixture may be a
hydrogen-bearing solution that releases hydrogen gas--especially at
elevated temperatures and/or in the presence of catalysts. For
example an aqueous sodium borohydride releases hydrogen gas at
elevated temperatures and in the presence of a catalyst. Other
hydrogen bearing solutions may also be used to generate hydrogen,
including, but not limited to: amino boranes and other metal
borohydrides.
[0023] Each of the chemical mixture cells (42) may include a
heating element (48), for example, a thin film heating element such
as those used in a thermal inkjet (TIJ) printhead. Electrical
current selectively supplied to the heating element (48) causes the
element (48) to produce heat and warm the chemical mixture in the
corresponding cell (42). The heating elements (48) may
advantageously be used in a selectively controlled manner such that
each of the heating elements (48) is activated independently of the
others. Alternatively, two or more of the heating elements (48) may
be activated at once by a single circuit. Further, the heating
element is not limited to the heating element shown. Any other
heating elements may also be used, including, but not limited to: a
simple resistor.
[0024] Each of the chemical mixture cells (42) may also include a
catalyst for facilitating the production of hydrogen gas from the
hydrogen-bearing chemical solution. The catalyst may include, but
is not limited to: ruthenium and platinum. According to the
embodiment of FIG.1, the catalyst is a layered or planar catalyst
(50) disposed on the heating element (48). However, the catalyst
(50) is not limited to the location shown adjacent to the heating
element (48). The catalyst (50) may be located in any position
within the chemical mixture cells (42).
[0025] Further, the layered catalyst (50) arranged in each cell
(42) is coated with a protective layer (52). The protective layer
(52) insulates the catalyst (50) from contact with the chemical
mixture contained in each cell (42) at ambient conditions.
Therefore, the catalyst (50) may advantageously be placed in the
presence of the chemical mixture without immediately increasing a
rate of chemical reaction. The protective layer or coating (52) and
the compartmentalized cells (42) facilitate the production of
hydrogen (or other products in other chemical reactions) on-demand.
By inserting a supply of chemical solution into the plurality of
cells (42) shown, the chemical solution is compartmentalized for
use on an as-needed basis.
[0026] The protective layer (52) is removed by elevating the
temperature of the cells (42) and/or the protective layer (52)
above ambient conditions. Materials that may adequately provide the
heat-removable protective layer (52) include, but are not limited
to: waxes, polymers or copolymers of olefins, fluorinated olefins,
or fluorinated ethers with appropriate molecular weights. These
materials readily melt at elevated temperatures (e.g. approximately
50 to 95.degree. C.), allowing the catalyst (50) to be selectively
exposed to the chemical mixture contained in the individual cells
(42). As the catalyst (50) is directly exposed to the chemical
mixture such as sodium borohydride, the rate of hydrogen production
also increases. Depending on the amount of hydrogen needed by a
fuel cell to power an electrical load, any number of the cells can
be activated by elevating the temperature in the individual cells
and thereby melting or removing the protective coating (52) from
the catalyst (50).
[0027] In order to raise the temperature of the protective coating
(52) and remove it from the catalyst (50), the heating elements
(48) are selectively activated. It will be understood by those of
skill in the art with the benefit of this disclosure that a control
circuit extending to each of the heating elements (48) may be
routinely designed to allow selective activation of individual
elements (48).
[0028] According to the embodiment of FIG. 1, the close proximity
of the protective coating (52) to the heating element (48) (with
only the layered catalyst (50) between the protective coating (52)
and the heating element (48)) advantageously facilitates low power
consumption to heat and therefore remove the protective coating
(52). Therefore, parasitic losses of a fuel cell--to which the
hydrogen generating system (40) may be providing hydrogen as a
fuel--are minimized.
[0029] In addition, as shown in FIG. 1, each of the cells (42) may
include a cover layer (54) to enclose the cells (42) and facilitate
operation of the cells (42) in any orientation. Portable
electronics are often manipulated in many different orientations.
Therefore, the hydrogen generating system (40) may need to operate
in any orientation in order to provide hydrogen to a fuel cell that
may be powering the portable electronics. Accordingly, the cover
layer (54) may include plastic, composite, metal, ceramic, or other
materials, and it may also include at least one initiator (56).
[0030] An initiator (56) is a feature designed for a first or
controlled failure. The initiator (56) may be a crimp, a weak spot,
a gap, or any other initiation mechanism at which the cover layer
(54) is designed to open based on predetermined conditions. As
hydrogen gas is generated, pressure increases within the cells
(42). When the pressure reaches a predetermined level, for example,
about 80% above ambient for shipping and other use considerations,
the initiator will cause a breach in the cover layer (54) at the
initiator (56) location. Accordingly, the produced hydrogen will
have a path to exit the cell (42), where it can be introduced to a
fuel cell anode (discussed further below) for electricity
production. In some embodiments, the initiator may be a hyrdophopic
membrane, such as gortex.
[0031] The protective layer (52) covering the catalyst (50) at
ambient conditions allows the hydrogen-bearing fuel to be stored in
the presence of the catalyst (50) in a stable condition until
hydrogen is needed. When hydrogen is needed, the temperature of the
protective layer (52) is raised by the heating element (48),
melting and removing the protective layer (52). Further, the
hydrogen-bearing fuel can be compartmentalized into a plurality of
cells (42) as shown, with each cell (42) having its own covered
catalyst (50) and separately controlled heating element (48). The
compartmentalizing of the hydrogen-bearing solution provides for
hydrogen production according to the demands of the fuel cell
and/or an electronic device powered by the fuel cell.
[0032] Referring next to FIG. 2, another embodiment of a hydrogen
generating system (140) is shown. Similar to the embodiment of FIG.
1, the hydrogen generating system (140) includes one or more
chemical mixtures arranged in one or more cells (142). The cells
(142) are preferably supported on a common base (144), as shown in
FIG. 2, but this is not necessarily so. Each chemical mixture cell
(142) may be completely independent. Further, the number of
chemical mixture cells (142) is not limited to the two-cell
configuration shown. There may be an number of cells. The two-cell
configuration is merely an example.
[0033] The base (144) preferably supports a plurality of walls
(146) that define the cells (142). The base (144) and walls (146)
may be similar or identical to the cells (42) and walls (44) of
FIG. 1. Therefore, the base (144) and walls (146) can be made of
any material compatible with the chemical mixture being
contained.
[0034] According to the present embodiment of the hydrogen
generating system (140), the chemical mixture may be a hydrogen
bearing solution which may contain one or more of these components:
alkali metal borohydrides such as lithium borohydride, sodium
borohydride, and potassium borohydride; alkali and alkaline metal
hydroxides that include but are not limited to: lithium hydroxide,
sodium hydroxide, potassium hydroxide, magnesium hydroxide, and
calcium hydroxide; a polymer as a viscosity modifier; and water. In
addition to the present embodiment, this or a similar chemical
mixture may be used with any embodiment of the present invention,
including all those illustrated and described herein.
[0035] As with the embodiment of FIG. 1, each of the cells (142)
includes a heating element (148), for example, a thin film heating
element such as those used in a thermal inkjet (TIJ) printhead. The
heating elements (148) may be used advantageously in a selectively
controlled manner, such that each of the heating elements (148) is
activated independently, or in combination, with the others.
[0036] Each of the chemical mixture cells (142) may also include a
catalyst (150) for facilitating the production of hydrogen gas from
the hydrogen-bearing chemical solution. The catalyst may include,
but is not limited to: ruthenium and platinum. According to the
embodiment of FIG. 2, however, the catalyst is formed into one or
more beads or spheres (150) that are placed in the cells (142). As
the cells (142) are filled with the hydrogen-bearing chemical
solution, the catalyst beads (150) tend to be distributed amongst
the solution. The number of catalyst beads (150) is adjustable
within any range to facilitate the reaction of the hydrogen-bearing
solution to generate hydrogen gas.
[0037] The catalyst beads (150) in each cell (142) are coated with
a protective layer (152). Similar to the embodiment of FIG. 1, the
protective layer (152) insulates the catalyst beads (150) from the
chemical mixture contained in each cell (142) at ambient
conditions. Therefore, the catalyst beads (150) may advantageously
be placed in the presence of a chemical mixture without immediately
increasing a rate of chemical reaction The protective layer or
coating (152) and the compartmentalized cells (142) facilitate the
production of hydrogen (or other products in other chemical
reactions) on-demand. The protective layer (152) of the present
embodiment is heat-removable and made of the same or similar
materials as described above with reference to the planar
protective layer (52, FIG. 1). Therefore, depending on the amount
of hydrogen needed by a fuel cell to power an electrical load, any
number of the cells (142) can be activated by elevating the
temperature in the individual cells (142) and removing the
protective coating (152) from the catalyst beads (150). As with the
embodiment of FIG. 1, heat may be supplied by the heating elements
(148) to remove the protective coating (152).
[0038] In addition, each of the cells (142) may include a cover
layer (154) and initiator (156) similar or identical to the cover
layer (52, FIG. 1) and initiator (56, FIG. 1) described above. The
cover layer (152) is provided to enclose the cells (142) and
facilitate operation of the cells (142) in any orientation. Due to
the initiator (156), the produced hydrogen will have a path to exit
the cell (142) and eventually be introduced to a fuel cell
anode.
[0039] The protective layer (152) covering the catalyst beads (150)
at ambient conditions allows the hydrogen-bearing fuel to be stored
in the presence of the catalyst (150) in a stable condition until
hydrogen gas is needed. When hydrogen gas is needed, the
temperature of the protective layer (152) is raised by the heating
element (148) (or any other heating element), which raises the
temperature of the hydrogen-bearing solution and removes (melts)
the protective layer (152). When the protective layer (152) is
removed from the catalyst beads (148), the chemical solution is
directly exposed to the catalyst beads (148) and the chemical
reaction rate for generating hydrogen is increased.
[0040] As mentioned above, the embodiments of FIGS. 1 and 2 include
cover layers (54 and 154, respectively) to facilitate operation of
the hydrogen generating systems (40 and 140) in any orientation.
However, other embodiments may also be operable in multiple
orientations without the need of the cover layers (54 and 154).
Referring next to FIGS. 3-4, alternative embodiments of a hydrogen
generating system (240/340) are shown.
[0041] As with the embodiments of FIGS. 1-2, the hydrogen
generating systems (240/340) of FIGS. 3-4 include one or more
chemical mixtures arranged in one or more cells (242/342). The
chemical mixtures, however, are gels (260/360) capable of holding
their shape. Therefore, it is not necessary to include a cover
layer (42, FIG. 1). A gel, as used herein, includes colloids in a
semisolid configuration.
[0042] According to the embodiments of FIGS. 3 and 4, the gels
(260/360) are hydrogen-bearing gels such as sodium borohydride
gels. The gels (260/360) are made by the addition of polymers or
oligomers of various compounds, such as poly(ethylene oxide),
polyethers, poly(ethyleneimine) or other amino polymers,
polyacrylates, in the proper concentration to the hydrogen
containing compounds.
[0043] Each of the gels (260/360) is part of a fuel pellet that
includes a chemical solution (in the present embodiment the sodium
borohydride gel), a heating element (248/348), and a catalyst
(250/350) covered by a protective layer (252/352). The heating
element (248/348) may be a TIJ heating element. The fuel pellets
may be compartmentalized as shown in FIGS. 3-4 into the one or more
cells (242/342). The catalyst of the fuel pellets may be arranged
in planar layers (250) as shown in FIG. 3, or the catalyst may
include one or more spheres or beads (350) as shown in FIG. 4.
Whether the catalyst is planar (250, FIG. 3) or beaded (350, FIG.
4), the catalyst includes a protective layer (252 in FIG. 3, 352 in
FIG. 4) insulating the catalyst (250/350) from the gel (260/360) at
ambient conditions.
[0044] As a fuel gas such as hydrogen is needed, the heating
elements (248/348) may be separately or collectively activated to
raise the temperature of the protective coatings (252/352) and thus
remove those coatings from covering the catalyst (250/350). The
number of cells (242/342) or fuel pellets activated will depend on
the demand for hydrogen or other fuel gas. As with the embodiments
of FIGS. 1-2, the protective coatings (252/352) of FIGS. 3-4 may
include waxes, polyolefins, and/or other non-reactive coatings that
are easily melted and removed at temperatures above ambient. When
the protective coatings (252/352) are removed, the catalyst
(250/350) is directly exposed to the gels (260/360), which
increases the rate of hydrogen production. The hydrogen gas may
then be supplied, for example, to a fuel cell.
[0045] Therefore, the embodiments described provide a heat-assisted
method and apparatus for producing hydrogen gas. The heat provided
by the heaters (48, etc.) is minimal as compared to hydrogen
generating systems that use heat as the primary mode of catalysis.
Further, these embodiments eliminate the need for micro-pumps and
their associated controls and electronics often used, to move
various amounts of hydrogen-bearing solution into the presence of a
catalyst.
[0046] A chemical reactor such as the hydrogen generating systems
(40, etc., FIG. 1) described above may be made by a number of
methods. For example, with reference to FIG. 5, a suitable
substrate can be presented with an array of addressable heating
elements (48, etc., FIG. 1), such as resistors. The resistors can
be incorporated by various methods ranging from simply placing
resistors on the substrate, to screen printing resistor elements,
to deposition and patterning the resistor elements with methods
commonly used in the electronics industry. These deposition and
patterning methods may include, but are not limited to: sputtering,
plating, CVD, PECVD, and photomask/etch and laser ablation. The
array of heating elements can be addressed by direct drive or with
logic depending on the final application. Methods commonly used in
the electronics industry are readily applicable to prepare these
control circuits with the benefit of this disclosure.
[0047] Depending on the application, which may range from an
on-board power supply for electronic devices, to sensors, to
automotive applications, various methods can be used to construct
the cell frames. Patterning photosensitive materials or screen
printing can be used for cells with small dimensions (micrometers
to millimeters). Injection molding of thermal plastics or molding
of polymers or composites may be used for larger dimensions. The
cell frames may be built right on top of the substrate, bonded to
the substrate (if they are prefabricated), or the cell frame and
the substrate may be integrated and made by injection molding a
single part.
[0048] The cover layer for the cells in the case of liquid
solutions may be bonded to the cell frame prior to or after the
introduction of the liquids. In the former case, another layer or
"plug" may be used to form a seal. Alternatively the cover layer
may be built as an integral part of the frame and the entire part
may be bonded to the substrate. Further, each of the one or more
individual cells (42, FIG. 1) may be filled with a hydrogen-bearing
chemical solution. However, in some embodiments, especially those
depicted in FIGS. 3-4, there is no cover enclosing each of the
cells (260).
[0049] According to some methods, a beaded catalyst covered with a
protective layer (as described above) may be added to the cells
and/or the hydrogen-bearing chemical solution. According to other
embodiments, the substrate is coated with a catalyst and then
insulated by a removable protective coating. It will be
appreciated, however, that the order of the method steps may be
altered and is not limited to the sequence discussed above or
presented in FIG. 5.
[0050] Yet another method of making the cells (42, FIG. 1) may
include embedding heating elements (48, etc., FIG. 1) in films,
which may then be constructed into bags or cells to hold solutions
and contain a catalyst covered with a protective layer. This method
may result in one or more cells, such as cells (42, FIG. 1) shown
above. However, the cells (42, FIG. 1) constructed of films may be
flexible and conform to any shape. Further, in some embodiments,
the films that define the cells (42, FIG. 1) may be coated with
catalyst and a removable protective layer to insulate the catalyst
from the solutions that may be contained by the cell (42, FIG. 1)
at ambient conditions. Again different patterning techniques may be
used to modulate the amount of heating elements or catalyst in the
films. The catalyst may also be added separately and/or with a
supply of hydrogen-bearing chemical solution as a beaded catalyst
coated by a removable protective layer. Some of the steps of the
method described above are illustrated by flowchart in FIG. 6. It
will be appreciated, however, that the order of the method steps
may be altered and is not limited to the sequence discussed above
or presented in FIG. 6.
[0051] The hydrogen generating systems described above may provide
hydrogen to any fuel cell type, including the ones mentioned in the
background of this disclosure. The hydrogen systems may operate as
cartridges connected or otherwise in fluid communication with a
fuel cell. The hydrogen generating systems of FIGS. 1-4 may,
however, be particularly useful for PEM fuel cells such as the one
shown in FIG. 7. FIG. 7 illustrates a PEM fuel cell (400), which
includes four basic elements: an anode (420), a cathode (422), an
electrolyte (PEM) (424), and a catalyst (426) arranged on each side
of the electolyte (424).
[0052] The anode (420) is the negative post of the fuel cell and
conducts electrons that are freed from hydrogen molecules such that
the electrons can be used in an external circuit (421). The anode
(420) may include channels (428) etched therein to disperse the
hydrogen gas as evenly as possible over the surface of the catalyst
(426).
[0053] The cathode (422) is the positive post of the fuel cell, and
has channels (430) etched therein to evenly distribute oxygen
(usually air) to the surface of the catalyst (426). The cathode
(422) also conducts the electrons back from the external circuit
(421) to the catalyst (426), where they can recombine with the
hydrogen ions and oxygen to form water. Theoretically, water is the
only by-product of the PEM fuel cell (400).
[0054] The electrolyte is the proton exchange membrane (PEM) (424).
The PEM (424) is a specially treated material that conducts
positively charged ions and prevents the passage of electrons.
[0055] The catalyst layer (426) is typically a platinum powder
thinly coated onto carbon paper or cloth. The catalyst layer (426)
is usually rough and porous so as to maximize the surface area that
can be exposed to the hydrogen or oxygen. The catalyst (426)
facilitates the electrochemical reaction of hydrogen and
oxygen.
[0056] In a working fuel cell, the PEM (424) is sandwiched between
the anode (420) and the cathode (422). The operation of the fuel
cell can be described generally as follows. Hydrogen gas (H.sub.2)
from one of the hydrogen generating systems described above enters
the fuel cell at the anode (420). When an H.sub.2 molecule comes
into contact with the platinum on the catalyst (426), it splits
into two H.sup.+ ions and two electrons (e.sup.-). The electrons
are conducted through the anode (420), where they make their way
through the external circuit (421) that may be providing power to
do useful work (such as turning a motor or lighting a bulb (423))
and return to the cathode side of the fuel cell (400).
[0057] Meanwhile, at the cathode (422), oxygen gas (O.sub.2) is
provided to the catalyst (426). In some PEM fuel cell systems, the
O.sub.2 source may be air. Oxygen reacts with H.sup.+ ions
transported through the PEM (424) and electrons from the external
circuit in the presence of the catalyst (426) to form water.
[0058] The PEM fuel cell reaction just described produces less than
1 volt under load. In order to raise the voltage and provide enough
power for practical applications, separate fuel cells are often
combined to form a fuel cell stack.
[0059] PEM fuel cells typically operate at fairly low temperatures
(about 80.degree. C./176.degree. F.), which allows them to warm up
quickly and to be housed in inexpensive containment structures
because they do not need any special materials capable of
withstanding the high temperatures normally associated with
electricity production.
[0060] Turning next to FIG. 8., an electronic device (500) is
shown. FIG. 8 represents in schematic format an overview of the
electronic device (500) using hydrogen generating systems and fuel
cells such as those described above. Other fuel cells different
from the embodiments shown may also be used.
[0061] According to the embodiment of FIG. 8, a fuel cell stack
(501) is in fluid communication with the hydrogen generating system
(40). The fuel cell stack (501) includes a plurality of the fuel
cells. And while FIG. 8 refers to the hydrogen generating system
(40) of FIG. 1, any of the other embodiments of the hydrogen
generating system (140/240/340) may also be used.
[0062] The hydrogen generating system (40) provides a supply of
fuel along a path represented by an arrow (502). A supply of oxygen
(that may be provided by ambient air) is also in fluid
communication with the fuel cell stack (501) as represented by
another arrow (504). As shown in FIG. 8, water (H.sub.2O) may be
produced as a byproduct of the operation of the fuel cell stack
(501).
[0063] The fuel cell stack (501) may provide power via an external
circuit (506) to an electrical load (508). The electrical load
(508) may include any electrically operated device including, but
not limited to: an automobile motor (and other automotive
electronics), a light, a camera, a home auxiliary power unit, a
computer, or other devices consuming electricity. The external
circuit (506) may also be connected to an optional electrical
capacitor or battery (510), which is shown in electrical parallel
with the fuel cell stack (501). The electrical capacitor or battery
(510) may provide auxiliary power to the electrical load (508).
[0064] As the electrical load (508) increases, individual cells
(42, FIG. 1) of the hydrogen generating system (40) may be
activated to provide a sufficient supply of hydrogen to the fuel
cell stack (501). The hydrogen-bearing solution contained by the
cells (42, FIG. 1) of the hydrogen generating system (40) is
conveniently stored in the presence of, but insulated from, the
catalyst (50, FIG. 1) until hydrogen is needed.
[0065] The preceding description has been presented only to
illustrate and describe various embodiments of the invention. It is
not intended to be exhaustive or to limit the invention to any
precise form disclosed. Many modifications and variations are
possible in light of the above teaching. It is intended that the
scope of the invention be defined by the following claims.
* * * * *