U.S. patent application number 11/970049 was filed with the patent office on 2008-05-01 for hydrogen generator.
This patent application is currently assigned to The Gillette Company, a Delaware corporation. Invention is credited to In Tae Bae, Javit A. Drake, Andrew G. Gilicinski, Matthew R. Stone, Joseph E. Sunstrom.
Application Number | 20080102024 11/970049 |
Document ID | / |
Family ID | 34136116 |
Filed Date | 2008-05-01 |
United States Patent
Application |
20080102024 |
Kind Code |
A1 |
Bae; In Tae ; et
al. |
May 1, 2008 |
Hydrogen Generator
Abstract
A hydrogen generator includes a solid hydrogen source.
Inventors: |
Bae; In Tae; (Wrentham,
MA) ; Drake; Javit A.; (Waltham, MA) ;
Gilicinski; Andrew G.; (Westborough, MA) ; Stone;
Matthew R.; (Hudson, MA) ; Sunstrom; Joseph E.;
(Merrimack, NH) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
The Gillette Company, a Delaware
corporation
|
Family ID: |
34136116 |
Appl. No.: |
11/970049 |
Filed: |
January 7, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10640567 |
Aug 14, 2003 |
7344571 |
|
|
11970049 |
Jan 7, 2008 |
|
|
|
Current U.S.
Class: |
423/648.1 |
Current CPC
Class: |
Y02E 60/32 20130101;
C01B 3/065 20130101; F17C 11/005 20130101; Y02E 60/321 20130101;
B01J 7/02 20130101; B01J 8/009 20130101; Y02E 60/36 20130101; Y02E
60/362 20130101 |
Class at
Publication: |
423/648.1 |
International
Class: |
C01B 3/02 20060101
C01B003/02 |
Claims
1. A method of generating hydrogen comprising contacting a fluid
including a proton source and a dissolved transition metal salt
with a solid hydrogen source disposed within a housing having an
outlet configured to deliver the hydrogen to a hydrogen fuel
cell.
2. The method of claim 1, wherein contacting the fluid and the
solid hydrogen source includes introducing the fluid into a
hydrogen generator, the hydrogen generator comprising: the housing;
the solid hydrogen source; and an inlet configured to guide the
fluid to contact the solid hydrogen source.
3. The method of claim 2, wherein the solid hydrogen source
includes a solid hydride.
4. The method of claim 3, wherein the solid hydride is a pellet,
tablet, cylinder, layer, or tube.
5. The method of claim 3, wherein the solid hydride is sodium
borohydride.
6. The method of claim 1, wherein the solid hydrogen source
includes a solid hydride combined with a wicking material.
7. The method of claim 6, wherein the wicking material includes a
hydrophilic material.
8. The method of claim 2, further comprising passing the fluid
through the inlet to a hydrophilic material.
9. The method of claim 1, further comprising controlling the amount
of fluid reaching the solid hydrogen source.
10. The method of claim 9, wherein controlling the amount of fluid
reaching the solid hydrogen source includes determining an amount
of hydrogen exiting generator.
11. The method of claim 9, wherein the fluid includes water.
12. The method of claim 11, wherein controlling the amount of fluid
reaching the solid hydrogen source includes delivering water vapor
to the solid hydrogen source.
13. The method of claim 1, wherein the transition metal salt
includes a ruthenium salt.
14. The method of claim 1, wherein the transition metal salt
includes a cobalt salt.
15. The method of claim 1, wherein the transition metal salt
includes an iron salt.
16. The method of claim 1, wherein the transition metal salt
includes a transition metal chloride.
17. The method of claim 1, wherein the transition metal salt
dissolves in the fluid as the fluid contacts or passes into the
solid hydrogen source.
18. The method of claim 17, wherein the solid hydrogen source
includes a wicking material.
19. The method of claim 18, wherein the transition metal salt is
distributed on, dissolved in, or coated on the wicking
material.
20. The method of claim 1, wherein the fluid comprises the
dissolved transition metal salt before the fluid contacts the solid
hydrogen source.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of and claims
priority to U.S. Ser. No. 10/640,567, filed on Aug. 14, 2003, which
is hereby incorporated by reference.
TECHNICAL FIELD
[0002] This invention relates to a hydrogen generator.
BACKGROUND
[0003] An electrochemical cell is a device capable of providing
electrical energy from an electrochemical reaction, typically
between two or more reactants. Generally, an electrochemical cell
includes two electrodes, called an anode and a cathode, and an
electrolyte disposed between the electrodes. In order to prevent
direct reaction of the active material of the anode and the active
material of the cathode, the electrodes are electrically isolated
from each other by a separator.
[0004] In one type of electrochemical cell, sometimes called a
hydrogen fuel cell, the anode reactant is hydrogen gas, and the
cathode reactant is oxygen (e.g., from air). At the anode,
oxidation of hydrogen produces protons and electrons. The protons
flow from the anode, through the electrolyte, and to the cathode.
The electrons flow from the anode to the cathode through an
external electrical conductor, which can provide electricity to
drive a load. At the cathode, the protons and the electrons react
with oxygen to form water. The hydrogen can be generated from a
hydrogen storage alloy, by ignition of a hydride, or by hydrolysis
of a liquid solution or slurry of a hydride.
SUMMARY
[0005] In one aspect, a hydrogen generator includes a housing, a
solid hydrogen source disposed within the housing, and an inlet
configured to guide a fluid to contact the solid hydrogen source.
The inlet can contact a wicking region. The wicking region can
include a wicking material that has an affinity for the fluid. The
wicking material can include a hydrophilic material. The housing
can include a hydrogen gas outlet. The hydrogen generator can
include an end cap at one end of the housing including the inlet
and the hydrogen gas outlet. The hydrogen gas outlet can include a
gas permeable membrane. The inlet can be fluidly connected to a
fluid control system configured to control fluid flow rate to the
solid hydrogen source. The generator can be portable.
[0006] In another aspect, a method of generating hydrogen includes
contacting a fluid including a proton source and a solid hydrogen
source disposed within a housing having an outlet configured to
deliver the hydrogen to a hydrogen fuel cell. The fluid and the
solid hydrogen source can be contacted by introducing the fluid
into a hydrogen generator. The hydrogen generator can include the
housing. The solid hydrogen source and an inlet can be configured
to guide the fluid to contact the solid hydrogen source. The method
can include dissolving a catalyst in the fluid. In certain
circumstances, the method can include passing the fluid through the
inlet to a wicking material. The method can also include
controlling the amount of fluid reaching the solid hydrogen source,
for example, by determining an amount of hydrogen exiting
generator. The fluid can include water or another proton source,
which can be delivered as water vapor to the solid hydrogen
source.
[0007] In another aspect, a method of manufacturing a hydrogen
generator includes placing a solid hydrogen source in a housing,
the housing including an inlet configured to guide a fluid to
contact the solid hydrogen source. The method can include forming a
housing insert from the solid hydride, for example, by combining
the solid hydride with a wicking material. The solid hydride can be
combined with the wicking material by constructing a wicking region
from the wicking material and a region of the solid hydride. The
wicking region can be constructed by forming a channel of the
wicking material through the region of the solid hydride or by
forming a layer adjacent to the region of the solid hydride, for
example, by rolling the layer adjacent to the region of the solid
hydride to form a layered roll. The channel can extend along a long
axis of the housing, along a radial axis of the housing, or
combinations thereof. In certain circumstances, the wicking
material can be combined with a catalyst. The method can also
include placing an end cap in contact with the solid hydrogen
source, the end cap including the inlet and a hydrogen gas outlet.
The inlet can be fluidly connected to a fluid control system
configured to control fluid flow rate to the solid hydrogen
source.
[0008] The solid hydrogen source can include a wicking region, for
example, of a wicking material such as a hydrophilic material, and
a region of a solid hydride. The wicking region can form a layer
adjacent to the region of the solid hydride. For example, the
wicking region and the region of the solid hydride form a layered
roll. The wicking region can be a channel through the region of the
solid hydride, which can extend along a long axis of the housing,
along a radial axis of the housing, or along both dimensions of the
housing. For example, the housing can be cylindrical and the
channel can extend along the length of the cylinder.
[0009] The solid hydrogen source can include a solid hydride, such
as a hydride salt, including an alkali or alkaline earth hydride,
an aluminum hydride, or a borohydride. The borohydride can be
lithium borohydride, sodium borohydride, potassium borohydride, or
mixtures thereof. The solid hydride can be a pellet, tablet,
cylinder, layer, or tube. The solid hydride can be combined with a
wicking material. For example, the solid hydrogen source can be a
blend of the wicking material with the solid hydride. The wicking
material can include a catalyst. The fluid can include a proton
source capable of reacting within the solid hydrogen source to form
hydrogen gas. For example, the proton source can include water.
[0010] Embodiments of a hydrogen generator can include one or more
of the following advantages. The hydrogen generator can have
competitive volumetric and gravimetric capacities relative to other
hydrogen sources. For example, a solid hydrogen source increases
the volumetric energy density of the generator in comparison to
devices based on slurries or solutions of similar materials. The
design of wicking regions in the solid hydrogen source can lead to
more complete conversion of the materials contained within the
generator to hydrogen gas. The hydrogen generator can provide fuel
to a fuel cell safely and reliably, and in a controllable manner.
The addition of a catalyst throughout the solid hydrogen can
control or modulate hydrogen generation throughout the generator,
which can decrease the overall running temperature of the
generator, and improve safety factors. The components of the
hydrogen generator can be relatively inexpensive, compared to the
components of other hydrogen sources. The hydrogen generator can be
an economical, compact, portable, and/or disposable source of
hydrogen gas. The hydrogen generator based on a solid hydride can
be of a low weight relative to hydrogen sources employing
reversible metal hydride alloys.
[0011] Electrochemical cell performance can be improved as well. In
particular, solid sodium borohydride to which twice the
stoichiometric amount of water was added, has been calculated to
yield over a 50% improvement in runtime when compared to lithium
ion rechargeable batteries for powering portable consumer
electronic devices, using practical numbers for fuel cell system
components for such applications. In addition, the optimal solid
hydride utilization can be balanced with minimal volume allotted
for water infusion and hydrogen recovery, which can be adjusted or
modified by the placement of various hydrophobic and wicking
materials throughout a solid hydride matrix. This can allow
improved utilization of reactants and improved control of hydrogen
generation rate.
[0012] The details of one or more embodiments are set forth in the
accompanying drawings and the description below. Other features and
advantages will be apparent from the description and drawings, and
from the claims.
DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a schematic representation of an electrochemical
cell.
[0014] FIG. 2A is a perspective view of solid hydrogen source.
[0015] FIG. 2B is a top view of a solid hydrogen source.
[0016] FIGS. 3A and 3C are perspective views of various solid
hydrogen sources.
[0017] FIGS. 3B and 3D-F are top views of various solid hydrogen
sources.
[0018] FIG. 4A is a perspective view of solid hydrogen source.
[0019] FIG. 4B is a side view of a solid hydrogen source in a
housing.
[0020] FIG. 5 is a top view of a layered solid hydrogen source.
[0021] FIG. 6A is a side view of an end cap.
[0022] FIG. 6B is a top view of an end cap.
[0023] FIG. 6C is an end view of an end cap and solid hydrogen
source.
[0024] FIGS. 7A-C are schematic representations of fluid control
systems.
[0025] FIGS. 8A-C are schematic representations of fluid control
systems.
DETAILED DESCRIPTION
[0026] Referring to FIG. 1, an electrochemical system 10 includes a
hydrogen generator 12 includes a housing 14 defining an internal
volume 16. Disposed within the internal volume of the hydrogen
generator is a solid hydrogen source 18. An inlet 20 is configured
to guide a fluid, which is in fluid container 22, to contact the
solid hydrogen source 18. The inlet 20 can contact a wicking region
24, for example, of a hydrophilic material, that can be included in
the solid hydrogen source 18. The housing 12 can include a hydrogen
gas outlet 26, which can be configured to deliver the hydrogen to a
hydrogen fuel cell.
[0027] Hydrogen gas outlet 26 of housing 14 can include a gas
permeable membrane. The membrane can contain any liquid component
that could potentially exit through the outlet, thereby helping to
limit or prevent fluid leakage from the housing. The gas permeable
membrane allows gas, particularly hydrogen gas, to exit the housing
unimpeded while preventing solid particles from exiting the
hydrogen generation housing by filtration. The gas permeable
membrane can include a polymer, such as a poly(alkane),
poly(styrene), poly(methacrylate), poly(nitrile), poly(vinyl),
fluoropolymer, poly(diene), poly(xylylene), poly(oxide),
poly(ester), poly(carbonate), poly(siloxane), poly(imide),
poly(amide), poly(urethane), poly(sulfone), poly(aryl ether ether
ketone), or cellulose, or a porous materials, such as a fiber or
mineral sufficiently hydrophobic and microporous to restrict
liquid, yet permit hydrogen permeation, or combinations thereof.
Combinations suitable to form a gas permeable membrane include
co-polymers, polymer blends, and composites including
inorganic-organic composites. Although housing 14 in FIG. 1 has
only one hydrogen gas outlet, in some cases the housing has more
than one hydrogen gas outlet yet allow unimpeded exit of desired
hydrogen gas. To obtain adequate permeation rates, high surface
area configurations of the gas permeable membrane, for example,
parallel micro-tubes, channels or layers, can be used. The gas
permeable membrane(s) can be placed at the outlet 26 of the
generator or integrated within the generator.
[0028] The hydrogen generator 12 can include an end cap 30 at one
end of the housing. End cap 30 includes the inlet 20. In certain
embodiments, the end cap 30 includes the hydrogen gas outlet (not
shown in FIG. 1). The hydrogen gas outlet can include a gas
permeable membrane. Gas permeable hydrophobic material can also be
used as a pathway for moist gaseous hydrogen out of the cell.
[0029] Housing 14 can be a cylindrical housing. The housing can be
made of a metal such as nickel or nickel plated steel, stainless
steel, or aluminum-clad stainless steel, or a plastic such as
polycarbonate, polyvinyl chloride, polypropylene, a polysulfone,
ABS or a polyamide. The housing can have a length of between 1 cm
and 30 cm, and a width or diameter of between 1 cm and 20 cm. The
housing can have a volume of between 1 cm.sup.3 and 9,400
cm.sup.3.
[0030] The solid hydrogen source can include a solid hydride, such
as an alkali or alkaline earth hydride, an aluminum hydride, or a
borohydride. The borohydride can be lithium borohydride, sodium
borohydride, potassium borohydride, or mixtures thereof. The solid
hydride can be a pellet, tablet, cylinder, layer, or tube. In some
cases, the solid hydrogen source can include an oxidizable
material, such as a metal (e.g., zinc, aluminum, titanium,
zirconium, or tin).
[0031] The fluid that is guided by the inlet can include a proton
source capable of reacting within the solid hydrogen source to
generate hydrogen gas. For example, the proton source can include
water and the solid hydrogen source can include a solid hydride. A
catalyst can be included in the fluid, or added to the fluid as it
reacts within the solid hydrogen source to facilitate generation of
hydrogen gas. In general, hydrogen is generated by contacting the
fluid and the solid hydrogen source. The fluid and the solid
hydrogen source can be contacted by introducing the fluid into a
hydrogen generator. The amount of fluid reaching the solid hydrogen
source can be controlled, for example, by determining an amount of
hydrogen exiting generator.
[0032] The solid hydrogen source can include a binder. Examples of
binders include a polyethylene powder, a polypropylene, a
polybutylene, a nylon, a polyacrylamide, a polyacrylate, a
polyvinyl chloride, a polystyrene, a polymethylpentene, a Portland
cement, or a fluorocarbon resin, such as polyvinylidene fluoride or
polytetrafluoroethylene. In certain embodiments, the binder can be
a hydrophilic material, such as a fibrous polymer fabric (e.g.,
polyvinyl alcohol fibers). The solid hydrogen source can include
between 0.01% and 10% binder by weight.
[0033] The solid hydrogen source can include a wicking material,
which can form a portion of the region 24. The wicking material can
be a fibrous polymer. The wicking material can include a
hydrophilic material. Examples of a hydrophilic material include a
nylon, a polyacrylamide, a polyacrylate, a polyvinyl chloride, a
substituted polystyrene, or a polyvinyl alcohol. For example, the
wicking material can include polyvinyl alcohol fibers. The wicking
material can include other additives. For example, the wicking
material can include a surfactant (e.g., Triton X-100, available
from Sigma-Aldrich). The surfactant can help to wet the wicking
material, which can modify the rate of movement of the fluid
through the wicking material.
[0034] The catalyst can be a component of the fluid or the catalyst
can be distributed on, dissolved in, or coated on the wicking
material, in which case the catalyst can dissolve in the fluid as
the fluid contacts or passes into the solid hydrogen source. The
catalyst loading of the wicking material can be between 0.01% by
weight and 5% by weight. The catalyst can include a transition
metal salt, for example, a ruthenium or cobalt salt, or mixtures
thereof. The catalyst can be a water soluble transition metal salt
that activates the reaction of water with sodium borohydride, such
as cobalt(II) chloride and iron(II) chloride. The catalyst can
either be stored in dry form within the solid hydrogen source
matrix, as a dry metal or metal salt on an inert support (silica,
alumina, zeolite, etc.) dispersed within the solid hydrogen source
matrix, distributed within the solid hydrogen source configuration
separate from the solid hydrogen source matrix, or introduced as an
aqueous solution. Soluble metal salts have high activity due to the
high surface area of the catalytic native metal particles produced
upon reduction by sodium borohydride. Alternatively, the catalyst
surface can be a metal foil which can be co-laminated to the tape
to be rolled within the wound cell configuration.
[0035] The combination of wicking material and solid hydride in the
solid hydrogen source can form a wicking region of the wicking
material and a region of a solid hydride. The wicking material can
guide or wick the fluid to the solid hydride, which can improve the
overall yield of hydrogen gas by more completely consuming the
solid hydride in the generator. This can be accomplished by more
completely distributing the fluid throughout the volume of the
solid hydrogen source.
[0036] In one example, the wicking region can be incorporated into
a channel through the region of the solid hydride, which can extend
along a long axis of the housing, along a radial axis of the
housing, or along both dimensions of the housing. Referring to FIG.
2A, a channel 70 (or plurality of channels which can be evenly
distributed, as shown) can extend along the length of a cylindrical
pellet 72 of a solid hydride or a blend of a solid hydride with a
binder or additive. Referring to FIG. 2B, a channel 74 can be a
groove extending radially through a cylindrical pellet 76, which
can also extend along the length of the pellet. Referring to FIGS.
3A-F, tablets 80 can be stacked to form a structure such as a
cylinder that is configured to fit within the housing. Referring to
FIGS. 3A and 3C, layers 82 of wicking material can be interposed
between tablets 80 so that the wicking region extends radially with
respect to the long axis of the structure. The tablets or pellets
can be prepared by pressing a powder including the solid hydride.
Referring to FIGS. 3A and 3B, a single channel 84 of wicking
material extends along the length of the structure. The channels
can be prepared by drilling or otherwise forming lengthwise holes
in the pellet. Referring to FIGS. 3C-3E, multiple channels 86, for
example, 2 to 8 channels, can be distributed around a tablets 80.
Referring to FIG. 3F, a channel layer 88 of wicking material can
surround the periphery of tablets 80. Referring to FIGS. 3E and 3F,
a design in which the wicking material (channels 86 or channel
layer 88) can allow void volume 90 to be incorporated into the
generator design between housing 14 and tablets 80. The void volume
90 can be selected to accommodate the volume expansion that occurs
to the pellet as hydrogen is generated.
[0037] By forming cylindrical pellets of solid hydride, it is
possible to maximize utilization of can volume to produce hydrogen.
For example, solid hydride powder can be pressed into a pellet that
has an actual density that is nearly theoretical density for the
material (>98% of the theoretical density of 1.074 g/cc for
sodium borohydride. However, diffusion of water into and hydrogen
out of a large dense pellet of material can be inefficient due to
passivation of the hydride, bubbles captured in the pellet and
pockets of water blocking hydrogen flow. This can be overcome by
forming regions of hydrophilic and hydrophobic materials within or
between the solid pellets. Wicking material can be used as a
support for the catalyst. Fluid can then be wicked through the
catalyst to dissolve it and initiate reaction with the chemical
hydride. The relative dimensions of the regions can be selected
such that the diffusion length of fluid into the solid hydride can
be minimized as well as the volume that the wicking material
displaces. Certain structures can allow lateral diffusion and axial
diffusion of fluid simultaneously.
[0038] In another example, the region of the hydrophilic material
can form a layer adjacent to the region of the solid hydride.
Referring to FIG. 4A, cylindrical pellets 90 of a solid hydrogen
source can be formed by pressing a powdered material, such as a
solid hydride. Referring to FIG. 4B, cylindrical pellets 90 can be
stacked within a housing 14, and a hydrophilic material (not shown)
can be introduced into the within or around the stack of cylinders.
Referring to FIG. 5, the wicking region and the region of the solid
hydride can form wicking layer 100 and hydride layer 102, which can
be rolled to form a layered roll 104. For example, a layer of
sodium borohydride can be dispersed as a powder rolled between
hydrophilic/hydrophobic inert separators that would be used to
direct water to the reactant to enable hydrogen generation. A
single layer fuel tape can include sodium borohydride blended with
a hydrophilic binder and an array of hydrophilic fibers. A tape
made from this material can be made by a process akin to
paper-making. The fuel tape (paper) can be rolled with a
hydrophobic membrane to separate layers and allow for hydrogen to
diffuse out. In such a system, catalyst can be dissolved in water,
which could then be wicked into the roll from one end, or the
catalyst can be incorporated into the tape or the separator
layer.
[0039] More particularly, a tape consisting of the fuel/catalyst
system can be fabricated by making a mixture of powdered solid
hydride, which can have a uniform mesh size, and a hydrophilic
binder in a suitable solvent. Both the binder and solvent have to
be unreactive toward the solid hydride. Examples of an binder
include coathylene or isobutylene. Possible solvents include heavy
hydrocarbons such as Isopar G. The binder should be less than 10%
w/w of the solid hydride. The solid hydride/binder/solvent mixture
can be blended and rolled into flat sheets using a roll coater such
as a Rondo coater to form a sheet of fuel tape. A separate sheet of
hydrophilic cloth or wicking material can be impregnated with a
cobalt chloride solution and allowed to dry to form a catalyst
sheet which can be calendared together with the fuel tape to make
the structure. By rolling under tension, this can make more active
material available per unit volume. When the roll is placed in a
cylindrical housing and water can contact the wicking material
which in turn dissolves the catalyst and initiates reaction with
the fuel tape. Hydrogen diffuses through the holes covered with
hydrophobic material in end caps positioned at the ends of the
roll. The number of hydrogen outlets and choice of membrane (based
on hydrophobicity and gas permeability) can be selected to maximize
hydrogen generation rate. Hydrogen yields of up 85% or more can be
achieved. By distributing the fluid, the heat generated by the
solid hydrogen source can be controlled and maintained at or near
ambient temperature.
[0040] When the fluid includes water, it can be delivered to the
solid hydrogen source in a liquid phase or a gas phase. When
delivered in a gas phase, this approach can permit water to be
delivered more efficiently to the solid hydrogen source predictably
and reliably independent of geometric orientation of the device.
For example, a small resistive heater can be included in generator
that vaporizes liquid water in a reservoir prior to or while the
water passes through the inlet. In another example, a membrane
system can be utilized to enable controlled conversion of liquid
water to vapor-phase water that is then directed into the solid
hydrogen source. After the hydrogen generation begins, the heat
generated from the hydrogen generation can be utilized to provide
heat to vaporize liquid water, allowing resistive heating to be
needed at the beginning of use.
[0041] End cap 30 can be designed to control the safety of the
system and maximize utilization of the solid hydrogen source by
distributing the fluid throughout the solid hydrogen source. In
particular, end cap 30 can be designed to have a large contact area
between the fluid and the solid hydrogen source, which can minimize
the diffusion length of the fluid into the solid hydrogen source,
improving overall hydrogen yield from the device. Referring to
FIGS. 6A and 6B, end cap 30 includes the inlet 20 and hydrogen
outlets 110. Hydrogen outlets 110 can be distributed over the area
of the cap to maximize surface contact with the solid hydrogen
source, which can facilitate collection of generated gas. As
discussed previously, a gas permeable membrane, such as a
hydrophobic membrane, can cover the hydrogen outlets to contain
solids and liquids within the generator. Referring to FIG. 6C, end
cap 30 can be positioned over an end of solid hydrogen source 18,
depicted here as a layered roll. Hydrogen outlets 110 are
positioned over the end of solid hydrogen source 18 to facilitate
collection of generated hydrogen. Inlet 20 contact wicks 112, which
can be grooves or conduits of wicking material on the contact side
of cap 30. Wicks 112 can be patterned on the cap to distribute
water in a geometrical pattern that evenly distributes the fluid as
it is delivered to the solid hydrogen source. The wick can be
patterned to minimize the radial arc lengths of fuel tape between
the wicks.
[0042] Referring to FIG. 1, an electrochemical system 10 the
hydrogen gas outlet 26 of hydrogen generator 12 is connected to a
hydrogen fuel cell 50. The fuel cell 50 has a housing 52 defining
an internal volume 54. Within the internal volume are an anode 56
and a cathode 58, separated by an electrolyte 60. The housing also
has an oxygen or air inlet 62, an air and water outlet 64 through
which oxygen-depleted air can also escape, and a hydrogen inlet 66.
The hydrogen inlet 66 can be releasably connected to the hydrogen
gas outlet 26 of the hydrogen generator 12. The connection between
the hydrogen generator and the hydrogen fuel cell can provide a
conduit for hydrogen gas. Thus, hydrogen gas produced by the
hydrogen generator can travel to the fuel cell, where it can be
consumed by fuel cell anode 56. The connection between the hydrogen
generator and the fuel cell can be closed or opened as needed,
using a valve or other means of regulating hydrogen flow to the
fuel cell. A conductor 68 can connect anode 56 and cathode 58 to
drive a load when current is produced.
[0043] In fuel cell 50, anode 56 oxidizes hydrogen gas to produce
protons and electrons. The protons move through electrolyte 60 to
cathode 58, where the protons combine with oxygen, provided through
oxygen or air inlet 62, and electrons traveling through conductor
68 to produce water. The water can exit the fuel cell through air
and water outlet 64. A feedback collection conduit (not shown) can
collect water from the fuel cell cathode and feed the hydrogen
generator. The anode 56 of the fuel cell can be formed of a
material capable of interacting with hydrogen gas to form protons
and electrons. The material can be any material capable of
catalyzing the dissociation and oxidation of hydrogen gas. Examples
of such materials include, for example, platinum or noble metals,
platinum or noble metal alloys, such as platinum-ruthenium, and
platinum dispersed on carbon black. Cathode 58 can be formed of a
material capable of catalyzing the reaction between oxygen,
electrons, and protons to form water. Examples of such materials
include, for example, platinum, platinum alloys, transition metals,
transition metal oxides, and noble metals dispersed on carbon
black. Electrolyte 60 is capable of allowing ions to flow through
it while also providing a substantial resistance to the flow of
electrons. In some embodiments, electrolyte 60 is a solid polymer
(e.g., a solid polymer ion exchange membrane). Electrolyte 60 can
be a solid polymer proton exchange membrane (PEM). An example of a
solid polymer proton exchange membrane is a solid polymer
containing sulfonic acid groups. Such membranes are commercially
available from E.I. DuPont de Nemours Company (Wilmington, Del.)
under the trademark NAFION. Alternatively, electrolyte 60 can also
be prepared from the commercial product GORE-SELECT, available from
W.L. Gore & Associates (Elkton, Md.). In some cases,
electrolyte 60 can be a polyphosphazine membrane, or a membrane
including an inorganic filler. In some embodiments, electrolyte 60
can be an ionically conducting liquid electrolyte (e.g., aqueous
potassium hydroxide solution, aqueous sodium hydroxide solution,
aqueous sulfuric acid solution, or aqueous phosphoric acid
solution). The liquid electrolyte can be a free liquid or it can be
immobilized by the addition of a gelling agent, such as a polymer
(e.g., polyacrylic acid or polymethacrylic acid), or an absorbing
agent (e.g., silica gel, fumed silica, or clay).
[0044] Fuel cell housing 52 can be any conventional housing
commonly used in fuel cells. For example, housing 52 can be a
plastic, carbon, or metal container such as steel, stainless steel,
graphite, nylon, polyvinyl chloride, poly-tetrafluoroethylene,
polyvinylidene fluoride, perfluoro-alkoxy resin, or a combination
of metals, carbons, and plastics. Plastics may be filled, e.g.,
with mineral fillers. Alternatively, plastics may be unfilled. In
some embodiments, the anode can include a pressure control valve
that can regulate the hydrogen pressure in the cell.
[0045] The generation of hydrogen from the generator is controlled
by controlling delivery of the fluid (such as water or water
including dissolved catalyst) to the solid hydrogen source. More
specifically, the inlet can be fluidly connected to a fluid control
system configured to control fluid flow rate to the solid hydrogen
source. The fluid can be mechanically fed into the solid hydrogen
source. Referring to FIG. 7A, generator 12 can include fluid
control system 200, in which fluid container 22 contains fluid
chamber 202 and pressure chamber 204. Pressure chamber 204 is
pre-pressurized with a gas, for example, an inert gas such as
nitrogen, to a pressure P.sub.N2. The pressure P.sub.N2 in pressure
chamber 204 is sufficient to transmit all of the fluid in fluid
chamber 202 to the solid hydrogen source 18 through inlet 20 at a
pressure (P.sub.H2O) higher than the internal pressure of the
housing 12 (P.sub.H2.sub.--.sub.IN). A piston or diaphragm 206
moves in response to the pressure differential. A pressure actuated
valve (P), which can be a component of inlet 20, serves to
self-regulate the internal hydrogen pressure
(P.sub.H2.sub.--.sub.IN). A conformal buffer tank (BT) can
accommodate expansion of the solid hydrogen source and sudden load
changes, which lead to faster hydrogen consumption from the
generator. Hydrogen delivery pressure to the fuel cell
(P.sub.H2.sub.--.sub.OUT) is regulated to proper levels by a
forward pressure regulator 210.
[0046] Referring to FIG. 7B, generator 12 can include fluid control
system 200, in which fluid container 22 includes a piston or
diaphragm 206 that is actuated by spring 208 to transfer the fluid
to the solid hydrogen source 18. Spring 208 can be a compact
belleville-washer stack with a non-linear force-displacement curve,
which can deliver a relatively consistent force over the
displacement range of the piston. A pressure actuated valve (P),
which can be a component of inlet 20, serves to self-regulate the
internal hydrogen pressure (P.sub.H2.sub.--.sub.IN). A conformal
buffer tank (BT) can accommodate expansion of the solid hydrogen
source and sudden load changes, which lead to faster hydrogen
consumption from the generator. The void space around the spring
can be used as BT volume, decreasing wasted space. Hydrogen
delivery pressure to the fuel cell (P.sub.H2.sub.--.sub.OUT) is
regulated to proper levels by a forward pressure regulator 210.
[0047] Referring to FIG. 7C, a gas-permeable membrane 32 at outlet
34 of the solid hydrogen source 18 can contain materials within
container 36. Material in solid hydrogen source 18 expands as
hydrogen is produced and exits outlet 34. The expansion of the
material can actuate piston or diaphragm 206 toward fluid container
22, driving delivery of the fluid into the solid hydrogen source. A
pressure actuated valve (P), which can be a component of inlet 20,
serves to self-regulate the internal hydrogen pressure
(P.sub.H2.sub.--.sub.IN). A conformal buffer tank (BT) can
accommodate expansion of the solid hydrogen source and sudden load
changes, which lead to faster hydrogen consumption from the
generator. Hydrogen delivery pressure to the fuel cell
(P.sub.H2.sub.--.sub.OUT) is regulated to proper levels by a
forward pressure regulator 210. A check valve 209 can be included
adjacent to P to prevent back flow. This approach can be more
compact than systems that include mechanical moving parts.
[0048] In general, the hydrogen generator can be self-regulating,
switching on and off in response to power demands. To accomplish
self regulation, valve P can be configured as shown in FIGS. 8A and
8B. Referring to FIG. 8A, as hydrogen is consumed, the hydrogen
pressure in the generator (P.sub.H2.sub.--.sub.IN) decreases and
the valve 300 opens as piston 302 is actuated by spring 304 to
initiate further hydrogen production by fluidly connecting the
fluid container 22 and solid hydrogen source 18. Referring to FIG.
8B, an elastomeric diaphragm 306 can respond to the hydrogen
pressure in the generator to open and close the fluid connection
between fluid container 22 and solid hydrogen source 18. Referring
to FIG. 8C, pressure actuated valve P can be combined with outlet
pressure regulator 210 in an outlet pressure regulator/water
control valve 310. Valve 310 can regulate the hydrogen generator
pressure (P.sub.H2.sub.--.sub.IN) down to a lower, steady value
feeding into the fuel cell (P.sub.H2.sub.--.sub.OUT). Valve 310 is
normally open and thus as hydrogen flows, pressure builds up
downstream of the valve. As outlet pressure
(P.sub.H2.sub.--.sub.OUT) increases, it is transferred to the valve
through sensing orifice 312, which causes spring 314 to be
compressed, eventually sealing at seat 319. As hydrogen is consumed
and outlet pressure drops, the force on the spring is reduced and
the valve opens to let more hydrogen through. As hydrogen in the
generator is depleted, P.sub.H2.sub.--.sub.IN falls and the valve
must open further to maintain P.sub.H2.sub.--.sub.OUT at the
desired level. When the valve opens almost completely,
P.sub.H2.sub.--.sub.IN is slightly greater that
P.sub.H2.sub.--.sub.OUT, the inlet 20 is opened, allowing fluid to
move from fluid container 22 into solid hydrogen source 18 to
generate more hydrogen. The output pressure can be set using knob
318. Because the forward pressure regulator is a normally open
valve, a separate on/off valve can be used just before the fuel
cell to seal off hydrogen pressure and flow during periods of
non-use. However, the pressure regulator will maintain the working
pressure in the lines upstream of the on/off valve, which is useful
for fast fuel cell start-up.
[0049] In an alternative approach, the solid hydride, preferably in
a cylindrical tablet form to minimize the void volume, can be
dropped into the water containing a catalyst to promote gas
generation and the reaction efficiency. In this case, a runaway
situation more easily avoided since the maximum achievable hydrogen
pressure is determined by the tablet size. A stack of solid tablets
can be stored in a spring-loaded compartment which can be actuated
by a lowered hydrogen pressure to increase output.
[0050] Other embodiments are within the scope of the following
claims.
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