U.S. patent application number 15/340485 was filed with the patent office on 2017-03-02 for fuel cell electrodes with conduction networks.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Steven J. Hamrock, Andrew T. Haug, Gregory M. Haugen, Mark A. Schonewill.
Application Number | 20170062835 15/340485 |
Document ID | / |
Family ID | 44653525 |
Filed Date | 2017-03-02 |
United States Patent
Application |
20170062835 |
Kind Code |
A1 |
Haug; Andrew T. ; et
al. |
March 2, 2017 |
FUEL CELL ELECTRODES WITH CONDUCTION NETWORKS
Abstract
A fuel cell electrode layer may include a catalyst, an
electronic conductor, and an ionic conductor. Within the electrode
layer are a plurality of electronic conductor rich networks and a
plurality of ionic conductor rich networks that are interspersed
with the electronic conductor rich networks. A volume ratio of the
ionic conductor to the electronic conductor is greater in the ionic
conductor rich networks than in the electronic conductor rich
networks. During operation of a fuel cell that includes the
electrode layer, conduction of electrons occurs predominantly
within the electronic conductor rich networks and conduction of
ions occurs predominantly within the ionic conductor rich
networks.
Inventors: |
Haug; Andrew T.; (Woodbury,
MN) ; Hamrock; Steven J.; (Stillwater, MN) ;
Haugen; Gregory M.; (Edina, MN) ; Schonewill; Mark
A.; (Bloomington, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
44653525 |
Appl. No.: |
15/340485 |
Filed: |
November 1, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14294936 |
Jun 3, 2014 |
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15340485 |
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12834531 |
Jul 12, 2010 |
8765327 |
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14294936 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/8828 20130101;
H01M 4/9075 20130101; H01M 8/1067 20130101; H01M 2300/0091
20130101; H01M 2008/1095 20130101; H01M 4/8673 20130101; H01M
4/8652 20130101; H01M 4/8668 20130101; H01M 8/1004 20130101; H01M
4/886 20130101; H01M 2300/0082 20130101; H01M 8/1044 20130101; Y02E
60/50 20130101 |
International
Class: |
H01M 4/86 20060101
H01M004/86; H01M 4/88 20060101 H01M004/88; H01M 4/90 20060101
H01M004/90 |
Goverment Interests
[0002] This invention was made with Government support under
Cooperative Agreement DE-FG36-07G017006 awarded by DOE. The
Government has certain rights in this invention.
Claims
1. A fuel cell subassembly, comprising: an electrode layer,
comprising: particles consisting of a first ionic conductor,
wherein a majority of the particles consisting of the first ionic
conductor being spheroid particles having a diameter greater than
50 nm: a second ionic conductor; a catalyst; and particles
comprising an electronic conductor; wherein a plurality of the
particles consisting of the first ionic conductor form an ionic
conductor rich network, and wherein at least a portion of particles
comprising the second ionic conductor and the catalyst are
intermixed and coat the particles comprising an electronic
conductor, and wherein the coated particles comprising second ionic
conductor form an electronic conductor rich network
2. The fuel cell subassembly of claim 1, wherein a majority of the
particles of the first ionic conductor have a substantially smooth
outer surface.
3. (canceled)
4. The fuel cell subassembly of claim 1, wherein a majority of the
particles consisting of the first ionic conductor have diameters in
a range of about 1 micrometer to about 15 micrometers.
5. The fuel cell subassembly of claim 1, wherein the first and
second ionic conductors have the same chemical structure.
6. The fuel cell subassembly of claim 1, wherein a majority of the
particles consisting of the first ionic conductor are spray dried
powdered ion conducting polymer particles.
7. The fuel cell subassembly of claim 1, wherein the particles
consisting of the first ionic conductor are non-uniformly
distributed in the electrode layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. patent
application Ser. No. 14/294936, (now allowed), filed Jun. 3, 2014,
which is a continuation application of U.S. Application Ser. No.
12/834531, filed Jul. 12, 2010, (granted U.S. Pat. No. 8,765,327),
the disclosures of which are incorporated by reference herein in
their entireties.
FIELD OF THE INVENTION
[0003] The present disclosure relates generally to fuel cells
and/or fuel cell subassemblies and methods for fabrication of fuel
cells and/or fuel cell subassemblies.
BACKGROUND
[0004] A fuel cell is an electrochemical device that combines
hydrogen fuel and oxygen from the air to produce electricity, heat,
and water. Fuel cells do not utilize combustion, and produce little
if any hazardous effluents. Fuel cells convert fuel gases directly
into electricity, and can be operated at much higher efficiencies
than many other types of electric generators.
[0005] A typical polymer electrolyte membrane (PEM) fuel cell
includes a membrane electrode assembly (MEA) comprising an ion
conducting membrane (the PEM) with an anode electrode disposed on
one side of the ion conducting membrane and a cathode electrode
disposed on the other side of the ion conducting membrane. Hydrogen
is reduced into hydrogen ions and electrons at the anode electrode.
The electrons provide an electrical current to drive an external
load and the hydrogen ions pass through the membrane. At the
cathode electrode, oxygen combines with the hydrogen ions to form
water as a byproduct. Fuel cell operation depends in part on the
degree of transportation of gases, liquids, electrons, and ions
through the materials that form the layers of the MEA.
SUMMARY
[0006] Embodiments described in the disclosure involve a fuel cell
electrode layer that includes a catalyst, an electronic conductor,
and an ionic conductor. Within the electrode layer are a plurality
of electronic conductor rich networks and a plurality of ionic
conductor rich networks that are interspersed with the electronic
conductor rich networks. A volume ratio of the ionic conductor to
the electronic conductor is greater in the ionic conductor rich
networks than in the electronic conductor rich networks. During
operation of a fuel cell that includes the electrode layer,
conduction of electrons occurs predominantly within the electronic
conductor rich networks and conduction of ions occurs predominantly
within the ionic conductor rich networks.
[0007] In some implementations, the ionic conductor may include
spray dried particles of an ion conducting polymer. The ionic
conducting polymer may comprise perfluorinated sulfonic acid
(PFSA), and/or perfluorinated imide acid (PFIA), and/or a
hydrocarbon, for example. Many particles, and in some embodiments a
majority of the particles, may be hollow spheroids which have outer
surfaces that are substantially smooth. A majority of the particles
may have diameters greater than 50 nm or diameters in a range of
about 1 .mu.m to about 15 .mu.m, for example.
[0008] In some implementations, the electronic conductor can be
catalyst coated electronic conductor particles, e.g., platinum
coated on carbon. Alternatively, the catalyst may be disposed on
support elements other than the electronic conductor, such as
nanostructured support elements. The electronic conductor may
include one or more of carbon, tin oxide, and titanium oxide. The
catalyst may be one or more of platinum, palladium, bimetals,
metallic alloys, and carbon nanotubes. The solvent may comprise
water, alcohol, and/or other hydrocarbons, for example.
[0009] The ionic conductor may comprise particles of a first ion
conducting polymer and the electrode layer may further include
particles of a second ion conducting polymer. According to some
aspects, the first ion conducting polymer has a first equivalent
weight and the second ion conducting polymer has a second
equivalent weight. A majority of the particles of the second ion
conducting polymer may have diameters less than about 50 nm and a
majority of the particles of the first ion conducting polymer may
have diameters greater than about 50 nm or greater than about 1
.mu.m or have an average diameter of about 3.5 .mu.m. In some
implementations, the particles of the second ion conducting polymer
form a film on the electronic conductor and the particles of the
first ion conducting polymer comprise a majority of the volume of
the ionic conductor. The particles of the first ion conducting
polymer having diameters greater than about 1 .mu.m may
substantially form the ion conducting networks.
[0010] The electrode layer may be disposed on a fuel cell
electrolyte membrane or on a gas diffusion layer. The electrode
layer can be disposed between a first surface of a fuel cell
electrolyte membrane and a first gas diffusion layer that are
components of a membrane electrode assembly (MEA). The MEA also
includes a second electrode layer disposed between a second surface
of the electrolyte membrane and a second gas diffusion layer. The
second electrode layer may or may not include ionic and electronic
networks. The fuel cell subassembly may further include first and
second flow field plates positioned, respectively, proximate the
first and second gas diffusion layers. Multiple MEAs may be
arranged to form a fuel cell stack.
[0011] A method of making a fuel cell electrode layer includes
combining an ionic conductor, an electronic conductor, a catalyst,
and a solvent to form an electrode ink. The ionic conductor
comprises smooth, spheroid particles, a majority of the particles
having diameters greater than about 50 nm or greater than 1 .mu.m,
or in a range between about 50 nm to about 15 .mu.m, for example.
The ionic conductor, the electronic conductor, the catalyst, and
the solvent of the electrode ink are mixed for a period of time.
The electrode ink is coated on a substrate and dries to form the
fuel cell electrode layer.
[0012] In some electrode inks, the electronic conductor is coated
with the catalyst. Some electrode inks include catalyst which is
disposed on support structures other than the electronic conductor.
The support structures can be nanostructured supports, for
example.
[0013] A fuel cell catalyst coated membrane (CCM) may be formed by
coating the electrode ink on a fuel cell electrolyte membrane. The
electrode ink may alternatively or additionally be coated on a fuel
cell gas diffusion layer.
[0014] In some implementations, the particles of the ionic
conductor comprise spray dried ionomer particles that can be
hollow, substantially spherical (spheroid), and/or can have
substantially smooth outer surfaces.
[0015] The method may involve substantially contemporaneously
combining the ionic conductor, the electronic conductor, and the
solvent prior to the mixing.
[0016] The method may involve forming a pre-mixture that includes
the electronic conductor and the solvent and mixing the pre-mixture
for a period of time. After mixing the pre-mixture, the ionic
conductor is added to the pre-mixture and the ionic conductor and
pre-mixture are mixed for a period of time.
[0017] The method may involve adding a second type or second form
of ionic conductor before and/or after mixing the ionic conductor,
the electronic conductor, the catalyst, and the solvent.
[0018] In several variations, the electrode ink may include
multiple types or forms of ionic conductors, including a first type
of ion conducting polymer and a second type of ion conducting
polymer. The electrode ink may include a first form and a second
form of the same ionic conductor. The electrode ink may include a
first ionic conductor having a first equivalent weight and a second
ionic conductor having a second equivalent weight.
[0019] The ionic conductor can comprise particles of a first ion
conducting polymer, a majority of the particles of the first ion
conducting polymer having diameters greater than about 1 .mu.m. A
majority of the particles of the second ion conducting polymer have
diameters less than about 50 nm.
[0020] In some implementations, a volume of the first ion
conducting polymer is greater that a volume of the second ion
conducting polymer.
[0021] During formation of the electrode layer, the particles of
the second ion conducting polymer may coat particles of the
electronic conductor.
[0022] The method further includes forming the ionic conductor by
spray drying an ion conducting polymer. An additive such as cerium
and/or manganese compounds may be added during the formation of the
spray dried ionic conductor and/or at other times during the
formation of the electrode ink.
[0023] Combining the components of the electrode layer may be
accomplished by one or more of ball mixing, stirring, and
sonication.
[0024] Some embodiments involve a fuel cell subassembly that
includes an electrode layer, comprising a catalyst, an electronic
conductor, and an ionic conductor intermixed with the electronic
conductor and the catalyst. The ionic conductor includes particles,
and a majority of the particles are spheroids having diameters
greater than about 50 nm.
[0025] In some implementations, a majority of the particles of the
ionic conductor have a substantially smooth outer surface and/or
are hollow and/or have diameters in a range of about 1 .mu.m to
about 15 .mu.m.
[0026] The electronic conductor may be a catalyst coated electronic
conductor and/or the catalyst may be coated on supports other than
the electronic conductor. The ionic conductor may be one or more of
perfluorinated sulfonic acid and perfluorinated imide acid.
[0027] The fuel cell subassembly may further include a second ionic
conductor of a form or type that is different from the ionic
conductor. For example, the first ionic conductor may have a first
equivalent weight and the second ionic conductor may have a second
equivalent weight. As another example, the second ionic conductor
may comprise particles, and a majority of the particles of the
second ionic conductor may have diameters less than about 50
nm.
[0028] The particles of the ionic conductor may be distributed
non-uniformly within the electrode layer and the particle of the
second ionic conductor may coat the electronic conductor.
[0029] The electrode layer can be disposed on a fuel cell
electrolyte membrane and/or on a fuel cell gas diffusion layer. The
electrode layer may be incorporated into a fuel cell membrane
electrode assembly and/or into a fuel cell stack.
[0030] A fuel cell subassembly includes an electrode layer that
includes a catalyst, an electronic conductor, a first ionic
conductor and a second ionic conductor that is different from the
first ionic conductor. The first ionic conductor and the second
ionic conductor are intermixed with each other, the electronic
conductor, and the catalyst within the electrode layer.
[0031] The first and second ionic conductors may be different types
of ionic conductor or may be different forms of the same type of
ionomer. Particles of the first ionic conductor may be larger than
particles of the second ionic conductor. Particles of the smaller
particled ionic conductor may form a film on the electronic
conductor. For example, a majority of particles of the second ionic
conductor may have diameters less than about 50 nm. Particles of
the first ionic conductor may be powdered spray dried particles or
powdered cryoground particles. Particles of at least one of the
ionic conductors, e.g., particles of the first ionic conductor, may
be non-uniformly distributed within the electrode layer.
[0032] The above summary is not intended to describe each
embodiment or every implementation. A more complete understanding
of various embodiments will become apparent and appreciated by
referring to the following detailed description and claims taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 depicts a typical fuel cell and the fuel cell's basic
operation;
[0034] FIG. 2A is a cross section diagram of a fuel cell electrode
in which the ionic conductor material and the electronic conductor
material is distributed substantially uniformly;
[0035] FIG. 2B is a close up representation of a region of the fuel
cell electrode of FIG. 2A;
[0036] FIG. 2C is a depiction of an ionic/electronic conductor
structure having an electronic conductor which is surrounded by
numerous small particles of the ionic conductor;
[0037] FIG. 2D illustrates a cross section of an ionic/electronic
conductor structure, in which the ionic conductor forms a film
surrounding a catalyst coated electronic conductor;
[0038] FIG. 2E is a cross section diagram of a fuel cell electrode
that comprises two ionic conductors;
[0039] FIG. 2F is a close up representation of a region of the fuel
cell electrode of FIG. 2E;
[0040] FIG. 2G illustrates a cross section of electrode layer that
includes micron sized powdered ionic conductor particles;
[0041] FIG. 2H is a close up representation of a region of the fuel
cell electrode of FIG. 2G;
[0042] FIG. 2I illustrates a cross section of electrode layer that
includes multiple powdered ionic conductors;
[0043] FIG. 2J is a close up representation of a region of the fuel
cell electrode of FIG. 2I;
[0044] FIG. 3A is a cross section diagram of a fuel cell electrode
that includes ionic and electronic conductor rich networks;
[0045] FIG. 3B is a close up representation of a region of the fuel
cell electrode of FIG. 3A;
[0046] FIG. 3C is a cross section diagram of a fuel cell electrode
that includes two ionic conductors, at least one of the ionic
conductors forming ionic conductor rich networks;
[0047] FIG. 3D is a close up representation of a region of the fuel
cell electrode of FIG. 2C;
[0048] FIG. 4A is a flow diagram of a fuel cell electrode
fabrication process that includes combining and mixing an ionic
conductor and electronic conductor;
[0049] FIG. 4B is a flow diagram of a fuel cell electrode
fabrication process that includes pre-mixing the electronic
conductor with a solvent prior to combining the pre-mixture with an
ionic conductor;
[0050] FIG. 5A is an optical image of a fuel cell electrode
fabricated using a solution-based ionomer as the ionic
conductor;
[0051] FIG. 5B is an optical image of a fuel cell electrode
fabricated using a powder-based ionomer as the ionic conductor;
[0052] FIG. 6 is a scanning electron microscope (SEMS) image of an
ionomer powder formed by spray drying;
[0053] FIGS. 7A and 7B are scanning electron microscope (SEMS)
images of an ionomer powder formed by cryogrinding;
[0054] FIG. 8 shows comparative polarization performance results
for MEAs with solution-based ionomer electrodes and powder-based
ionomer electrodes;
[0055] FIG. 9 compares MEA performance of solution-based ionomer
electrodes and powder-based ionomer electrodes at current densities
of 1.2 A/cm.sup.2 and 1.5 A/cm.sup.2;
[0056] FIG. 10 provides a comparison of the electrochemical surface
area of solution-based ionomer electrodes and powder-based ionomer
electrodes;
[0057] FIG. 11 provides a comparison of the catalytic activity of
electrodes formed using solution-based ionomer, cryoground powdered
ionomer, spray dried powdered ionomer, and spray dried powdered
ionomer with a premixture of electronic conductor and solvent;
[0058] FIG. 12 shows comparative polarization curves for electrodes
formed using solution-based ionomer, cryoground powdered ionomer,
spray dried powdered ionomer, and spray dried powdered ionomer with
a premixture of electronic conductor and solvent; and
[0059] FIG. 13 shows MEA performance at a current density of 1.2
A/cm.sup.2 for electrodes formed using solution-based ionomer,
cryoground powdered ionomer, spray dried powdered ionomer, and
spray dried powdered ionomer with a premixture of electronic
conductor and solvent.
[0060] Embodiments of the invention are amenable to various
modifications and alternative forms and are shown and described by
way of example in the drawings and the specification. It is to be
understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the scope of the invention as defined
by the appended claims.
DESCRIPTION OF VARIOUS EMBODIMENTS
[0061] Some of the basic components of a polymer electrolyte
membrane (PEM) fuel cell 110 (without subgaskets, gaskets, or
seals) are depicted in FIG. 1. In operation, hydrogen fuel,
H.sub.2, is introduced into the anode side of the fuel cell 110,
passing over the first flow field plate 112 and through the gas
diffusion layer (GDL) 114. Oxygen, O.sub.2, from the air flows
through the second flow field plate 119 and through the second GDL
118 at the cathode side of the fuel cell 110. The GDLs 114, 118
promote air and hydrogen diffusion to the anode and cathode
electrodes 115, 113, and aid in drawing end product water vapor and
liquid away from the electrodes 115, 113. A microporous layer (not
shown) may be disposed between the GDLs 114, 118 and the electrodes
115, 113. The flow field plates 112, 119 typically include a
pattern of flow channels designed to distribute reactant gases
across the active area of the fuel cell.
[0062] At the anode electrode layer 115, the hydrogen fuel is
separated into hydrogen ions (H.sup.+) and electrons (e.sup.-). The
electrolyte membrane 116 permits the hydrogen ions or protons and
water to pass through the electrolyte membrane 116 to the cathode
electrode layer 113 of the fuel cell 110. The electrons flow
through an external electrical circuit 117 in the form of electric
current. At the cathode electrode layer 113, oxygen, hydrogen ions,
and electrons combine to produce water (H.sub.2O) and heat. The
electrical current produced by the fuel cell 110 can power an
electric load 117, such as an electric motor, and/or can be
directed to an energy storage device, such as a rechargeable
battery. Five layers of the fuel cell, the membrane 116, electrodes
113, 115, and GDLs 114, 118, are often referred to as a membrane
electrode assembly (MEA).
[0063] Individual fuel cells, such as the fuel cell 110 shown in
FIG. 1, can be combined with a number of other fuel cells to form a
fuel cell stack. The number of fuel cells within the stack
determines the total voltage of the stack, and the surface area of
each of the cells determines the total current. The total
electrical power generated by a given fuel cell stack can be
determined by multiplying the total stack voltage by total
current.
[0064] The term "electrode" is used herein to refer to the layers
within the fuel cell MEA containing catalyst. The basic components
that make the fuel cell electrodes include a catalyst, an
electronic conductor, which may also support the catalyst, and an
ionic conductor. In some implementations, the electronic conductor
comprises carbon which may or may not be coated with a catalyst
such as platinum, platinum alloy, or another material. The ionic
conductor may comprise an ion conducting polymer. The ionic
conductor facilitates conduction of ions through the electrode
layer. The electronic conductor facilitates conduction of electrons
through the electrode layer. Electrodes generally contain a certain
amount of void space (pores) for gas and/or liquid diffusion into
and out of the electrode layer.
[0065] Some embodiments described herein involve fuel cell
electrodes that include multiple ionic conductors, wherein the
ionic conductors have different characteristics. For example, each
of the ionic conductors may comprise an ionomer and at least one of
the ionomers used in the electrode layer may have one or more
characteristics that differ from the characteristics of other
ionomers in the electrode layer. As a further example, the
electrode layer may include two or more ionomers differing in type
and/or equivalent weights (EWs) and/or form. As used herein, "type"
refers to characteristics of chemical structure and "form" refers
to characteristics of physical shape and size, e.g., different
particle sizes or shapes.
[0066] The electrode layer has two major surfaces, a width, length,
and thickness. In some implementations, the two or more ionomers in
the electrode layer may be distributed substantially uniformly
between the two major surfaces throughout the thickness and/or
length and/or width of the electrode layer. In some
implementations, the first ionomer may have a first distribution
with in the electrode layer and the second ionomer may have a
second distribution within the electrode layer. For example, one of
the ionomers may be substantially uniformly distributed through the
electrode layer and another of the ionomers may be non-uniformly
distributed through the electrode layer.
[0067] In some embodiments, only one or at least one ionic
conductor is used in the electrode layer, and the distribution of
the ionic conductor is non-uniform within the electrode layer. The
non-uniform distribution of the ionic conductor may provide
networks rich in the ionic conductor within the electrode layer
that enhance ionic conduction through the ionic conductor rich
networks. Complementary networks that are relatively poor in the
ionic conductor are also present in the electrode layer and these
complementary networks may be rich in the electronic conductor of
the electrode layer. Thus, both ionic conductor rich networks that
enhance conduction of ions and electronic conductor rich networks
that enhance conduction of electrons may simultaneously exist when
at least one ionic conductor is non-uniformly distributed in the
electrode layer.
[0068] Embodiments described herein involve methods for the
formation of fuel cell electrodes which include networks that
enhance ionic conduction and/or electronic conduction through the
electrode layer. The ionic and/or electronic conduction networks
may traverse or partially traverse the thickness of the electrode
layer. Fuel cell electrodes having ionic and electronic conduction
networks may been formed in a fabrication process that uses an
ionomer powder having particles with certain morphological
characteristics.
[0069] Fuel cell electrodes may be made from an "ink" formed by
mixing catalyst, electronic conductor, and an ionic conductor in
solvent. According to some implementations, the ionic conductor
used includes small particles of an ion conducting polymer (denoted
ionomer) suspended and/or dissolved in solution, e.g., ionomer
particles less than about 50 nm in diameter. An ionic conductor
with particles less than about 50 nm which are suspended and/or
dissolved in solution is referred to herein as "solution-based"
ionic conductor. Ionomer particles in this size range may be formed
by heating a solution of ionomer and water (or other solvent) in a
sealed enclosure to achieve high pressure at which point the
ionomer dissolves into particles having diameters under about 50
nm. These small particles of ionomer may be mixed with a solvent, a
catalyst, and an electronic conductor to form the electrode ink.
The electrode ink is applied to a substrate and dried to form an
electrode layer as illustrated in FIG. 2A.
[0070] FIG. 2A is a diagram of a cross section of a typical
electrode layer 200 that is formed using a solution-based ionomer
according to the process outlined in the preceding paragraph. The
electrode layer 200 is thin, having a thickness 291 which is small
compared to the width 292 of the electrode layer 200. FIG. 2B is a
close up representation of a region 210 (e.g., approximately a 2
micron.times.2 micron sized region) of the electrode layer 200. The
electrode structure illustrated in the close up representation of
the electrode layer region 210 results from mixing an ionic
conductor having small (<50 nm) particles in a solvent with a
catalyst and an electronic conductor. The particles of the
electronic conductor 220 (or catalyst coated electronic conductor)
may have diameters of about 100 nm, for example. The catalyst may
be coated on the electronic conductor 220 or may otherwise be
distributed within the electrode layer, e.g., coated on catalyst
support structures. FIG. 2B illustrates a cross section of the
electronic conductor particles 220 surrounded by the ionic
conductor particles 230 forming ionic/electronic conductor
structures 250. In this embodiment, the particles of the ionic
conductor 230 and electronic conductor 220 are distributed
substantially uniformly within the electrode layer 200.
[0071] Structure 250 in FIG. 2B may exist (as shown in FIG. 2C) as
a small particles 230 dispersed on the surface of the electronic
conductor (220) or as a coating (as shown in FIG. 2D) of ionomer
230 on the surface of electronic conductor 220. In all cases, the
electronic conductor 220 may or may not contain catalyst particles
dispersed over its surface. FIGS. 2B, 2C and 2D may be created
using solution-based ionomer.
[0072] FIG. 2C is a depiction of an ionic/electronic conductor
structure 250 having an electronic conductor 220 which is
substantially surrounded by numerous small particles of the ionic
conductor 230. In some embodiments, the electronic conductor 220
may be coated with a catalyst.
[0073] FIG. 2D illustrates a cross section of an ionic/electronic
conductor structure 250, in which the ionic conductor particles 230
are so small in comparison to the electronic conductor 220 that the
ionic conductor particles form a film surrounding the electronic
conductor 220. In this example, the electronic conductor 220 is
coated with the catalyst 293. In some embodiments, the catalyst 293
may be disposed on support structures rather than the electronic
conductor 220 and the catalyst coated support structures may be
dispersed within the electrode layer 200.
[0074] An electrode ink comprising an electronic conductor and a
solution-based ionic conductor forms electrode layers having
substantially uniform distribution of ionic and electronic
conductor materials through the electrode layer as illustrated in
FIG. 2B. Electrodes exhibiting substantially uniform distribution
of ionic and electronic conductor materials may not perform
optimally during fuel cell operation due to the incompatibility of
various competing transport and conduction functions of the fuel
cell electrode.
[0075] Some embodiments involve fuel cell electrodes that include
non-uniform distribution of only one or at least one ionic
conductor and/or include multiple ionic conductors which are
uniformly or non-uniformly distributed. In the embodiments using
multiple ionic conductors, each ionic conductor is different in
some characteristic from other ionic conductors in the electrode.
These non-uniform and/or multiple ionic conductor implementations
can provide enhanced durability and/or performance when compared
fuel cell electrodes having a single, uniformly distributed
solution based ionic conductor. In implementations that use
multiple ionic conductors, the multiple ionic conductors may
comprise different types of ionomers or may comprise the same type
of ionomer having different forms. The fuel cell electrodes may
also include multiple electronic conductors and/or multiple
catalysts, where each electronic conductor or catalyst is different
in some characteristic than the other electronic conductors or
catalysts, such as, e.g., equivalent weight.
[0076] FIGS. 2E and 2F provide an example of a multiple ionic
conductor embodiment. FIG. 2E illustrates a cross section of a fuel
cell electrode layer 201 having a first major surface 214 and a
second major surface 215. The electrode layer 201 includes two
ionic conductors 231, 241, e.g., two ionomers. In this example, a
majority of the particles of the first ionomer 241 have diameters
greater than about 1 .mu.m. Ionic conductors that include
particles, a majority of which have diameters greater than solution
based particles (e.g. greater than 50 nm or greater than about 1
.mu.m) are referred to herein as powdered ionic conductors. The
second ionomer 231 is a solution based ionomer, wherein a majority
of the particles of the second ionomer 231 have diameters less than
about 50 nm. In this embodiment, particles of the second ionomer
231 and the first ionomer 241 are intermixed with each other and
with the electronic conductor 221 throughout the electrode layer
201 between the first major surface 214 and the second major
surface 215.
[0077] FIG. 2F provides a close up representation of a region 211
of the electrode layer (e.g., approximately a 2 micron.times.2
micron sized region) that depicts each of the first and second
ionomers 241, 231, along with the electronic conductor 221. In this
implementation, particles of the second ionic conductor 231 coat
the electronic conductor 221, as shown in cross section in FIG. 2F.
Note that the electrode layer 201 also includes a catalyst (not
shown) which may be coated on the electronic conductor 221 and/or
otherwise distributed throughout the electrode layer 201, e.g., on
catalyst support structures.
[0078] The larger diameter particles of the first ionomer 241 may
be formed, for example, by cryogrinding, spray drying or other
techniques. Although the ionic and/or electronic conductor
particles 221, 231, 241 are represented by spheres having smooth
outer surfaces, the particles 221, 231, 241 may have morphologies
other than spheroid. For example, ionomer particles formed by
cryogrinding are not necessarily spheroid and may have rough
surfaces (see, e.g., FIGS. 7A and 7B). Ionomer particles formed by
spray drying are spheroid with substantially smooth outer surfaces
(see, e.g., FIG. 6). For example, substantially spherical
(spheroid) particles with substantially smooth outer surfaces may
have variations in diameter less than about 10% and surface
roughness less than about 5% of the diameter.
[0079] The use of two or more different ionomers may be beneficial
to meet the conflicting requirements of a fuel cell electrode. For
example, the second ionomer may provide superior catalyst support
corrosion resistance and/or catalyst dissolution resistance
characteristics to the electrode layer when compared to the first
ionomer, but provide reduced performance when compared to the first
ionomer. The use of these two types of ionomer mixed uniformly or
non-uniformly within the electrode layer may enhance both
durability and performance. For example, the first ionomer may have
a lower EW than the second ionomer. The first ionomer (lower EW
ionomer) provides superior performance when the fuel cell is
operating under hot/dry conditions. The second (higher EW ionomer)
provides superior performance when the fuel cell is operating under
cold/wet conditions. The small particles of the second ionomer may
coat the electronic conductor to provide corrosion resistance and
enhanced durability.
[0080] In some configurations, the ionomer particles may form
agglomerations of ionomer particles which are distributed
throughout the electrode layer. Without wishing to be bound by any
particular theory, the affinity of the ionomer particles to form
agglomerations may be related to the morphology of the ionomer
particles. For example, it is believed that the approximately
micron sized, substantially smooth, hollow, spheroid powdered
ionomer particles formed by spray drying are more likely to
associate in agglomerations.
[0081] FIG. 2G illustrates a cross section of electrode layer 202
that includes micron sized powdered ionomer particles and does not
include the smaller (<50 nm) solution-based ionomer particles.
FIG. 2H provides a close up representation of a region 212 of the
electrode layer 202 (e.g., approximately a 2 micron.times.2 micron
sized region) that depicts micron sized powdered ionomer particles
242. Catalyst may be coated on the electronic conductor particles
222 or may be otherwise distributed within the electrode layer
202.
[0082] In some embodiments, the electrode layer comprises multiple
types or forms of powdered ionic conductor particles and each type
or form of the ionic conductor particles can be uniformly or
non-uniformly distributed within the electrode layer. FIG. 21
illustrates a cross section of electrode layer 203 having a first
major surface 214 and a second major surface 215. The electrode
layer 203 includes particles of multiple powdered ionic conductors
233, 243. In this embodiment, particles of the first ionic
conductor 233 and particles of the second ionic conductor 243 are
intermixed with each other and with the electronic conductor 223
throughout the electrode layer 203 between the first major surface
214 and the second major surface 215. The electrode layer 203 may
or may not include the smaller (<about 50 nm) solution-based
ionomer particles.
[0083] FIG. 2J provides a close up representation of a region 213
of the electrode layer 203 (e.g., approximately a 2 micron.times.2
micron sized region) that includes first powdered ionomer particles
233 and second powdered ionomer particles 243. For example, the
multiple powdered ionic conductors 233, 243 may comprise different
types of powdered ionomers. As another example, the multiple
powdered ionic conductors may comprise the same type of powdered
ionomer, but may be different forms of the same type of powdered
ionomer, e.g., one form could be spray dried ionomer and the other
form could be cryoground ionomer. Catalyst may be coated on the
electronic conductor particles 223 and/or may be otherwise
distributed within the electrode layer 203.
[0084] Some embodiments involve fuel cell electrodes that include
regional ionic and/or electronic conductor-rich networks that at
least partially traverse the thickness of the electrode layer. The
ionic conductor and electronic conductor materials in these
electrodes are non-uniformly distributed so that regions within the
electrode layer have relatively more ionic conductor material,
e.g., as measured by weight or volume, than electronic conductor
material and/or regions within the electrode layer have relatively
more electronic conductor material, e.g., as measured by weight or
volume, than ionic conductor material. FIG. 3A is a diagram of a
cross section of an electrode layer 300 comprising powdered ionic
conductor particles that form ionic conductor rich networks. The
electrode layer 300 has a thickness 291 which is small compared to
the width 292 of the electrode layer. FIG. 3B provides a close up
representation of a region 310 of the electrode layer 300 (e.g.,
approximately a 2 micron.times.2 micron sized region). The
electrode structure illustrated in FIGS. 3A and 3B can be formed
from an electrode ink which is a mixture of a powdered ionic
conductor with powder particles greater than about 1 .mu.m, a
catalyst, an electronic conductor, and a solvent.
[0085] FIG. 3B illustrates the ionic conductor material 330 and the
electronic conductor material 320 distributed in a plurality of
ionic conductor rich networks 340 and a plurality of electronic
conductor rich networks 350. The ionic conductor rich networks 340
(also referred to herein as "ionic conductor networks") have a
volume ratio of ionic conductor to electronic conductor that is
greater than the volume ratio of ionic conductor to electronic
conductor within the electronic conductor rich networks 350 (also
referred to herein as "electronic conductor networks." The
electronic conductor networks 350 have a volume ratio of electronic
conductor to ionic conductor that is greater than the volume ratio
of electronic conductor to ionic conductor within the ionic
conductor networks 340. The electronic conductor networks 350 are
substantially discrete and separate from the ionic conductor
networks 340. The affinity for some types of ionomer particles
(micron sized particles that are smooth, spheroid and/or hollow) to
form particle agglomerations may contribute to the formation of the
ionic conductor networks 340 and/or the electronic conductor
networks 350. The ionic conductor networks 340 provide lower
resistance paths 341 for ion conduction when compared with the
electronic conductor networks 350. The electronic conductor
networks 350 provide lower resistance paths 351 for electron
conduction when compared with the ionic conductor networks 340.
When ionic conduction and electronic conduction networks are
present in the electrode layer, conduction of electrons can occur
predominantly within the electronic conductor rich networks and
conduction of ions can occur predominantly within the ionic
conductor rich networks when the fuel cell is in operation.
[0086] Fuel cell electrodes with ionic and electronic conductor
networks, as shown in FIGS. 3A and 3B, may exhibit superior
performance when compared to the electrode layers which have ionic
and/or electronic conductor materials that are substantially
uniformly distributed through the electrode layer. For example, the
superior performance characteristics of the networked electrodes
may include superior material transport and/or superior electrical
conduction properties. The electrodes having ionic and/or
electronic conductor networks may also exhibit superior durability
properties when subjected to the ranges of temperature, electrical
potential, and relative humidity encountered during fuel cell
operation.
[0087] Without wishing to be bound by any particular theory, the
formation of the substantially discrete ionic and/or electronic
conductor networks could be related to the phase of the ionic
conductor material when it is mixed with the electronic conductor
material during fabrication of the electrode layer. For example,
mixing the ionic conductor which comprises small size particles
(<about 50 nm particles suspended or dissolved solution) with
the electronic conductor appears to create an electrode layer that
exhibits a more uniform distribution of the ionic and electronic
conductors as in the electrode layer illustrated in FIGS. 2A and
2B. In contrast, mixing certain types or forms of ionic conductor
with the electronic conductor material produces an electrode layer
exhibiting ionic and electronic conductor networks as illustrated
in FIGS. 3A and 3B. Again, without wishing to be bound by any
particular theory, ionomer particles that are micron sized
spheroid, relatively smooth, and/or hollow appear to more readily
form the networks that provide enhanced ionic and electronic
conduction pathways.
[0088] In some implementations, multiple types of ionomer may be
used to form the electrode layer, with at least a first type of
ionomer contributing to ionic conductor networks in the electrode
layer. The second ionomer may or may not contribute to the ionic
conductor networks. The second ionomer may be distributed
substantially uniformly or non-uniformly in the electrode
layer.
[0089] FIG. 3C is a cross section illustrating an electrode layer
301 comprising an electronic conductor 380, e.g., catalyst coated
carbon, and first and second ionomers 375, 370. The electrode layer
301 includes a first major surface 312 and a second major surface
313. FIG. 3D provides a close up representation of a portion 311 of
the electrode layer 301 (e.g., approximately a 2 micron.times.2
micron sized region). The electrode structure illustrated in FIG.
3D can be formed from an electrode ink which is a mixture of a
first ionic conductor 375 comprising powdered particles greater
than about 1 .mu.m, a second ionic conductor 370 comprising
particles less than about 50 nm, a catalyst, an electronic
conductor 380, and a solvent. In this embodiment, particles of the
first ionic conductor 375 and particles of the second ionic
conductor 370 are intermixed with each other and with the
electronic conductor 380 throughout the electrode layer 301 between
the first major surface 312 and the second major surface 313. In
some implementations, the amount of the first ionic conductor 375
in the electrode layer is greater than the amount of the second ion
conductor 370 by volume. For example, the first ionic conductor 375
may comprise a spray dried and/or cryoground powdered ionomer and
the second ionic conductor 370 may comprise the solution based
ionomer as previously discussed.
[0090] The close up representation 311 illustrates the first ionic
conductor material 375 and the electronic conductor material 380
distributed in a plurality of ionic conductor rich networks 340 and
a plurality of electronic conductor rich networks 350. The second
ionic conductor material 370 may surround and/or coat the
electronic conductor particles 380 as depicted in FIG. 3D and/or
may be distributed relatively uniformly through the electrode
layer. The first ionic conductor 375 may comprise larger particles
than the second ionic conductor, and may form ionic conductor
networks 340 which facilitate transport of ions and water through
the electrode layer 301. Formation of the ionic conductor networks
340 may be promoted because the powdered ionomer 375 has an
affinity for agglomeration when the electrode layer is being
formed, and these agglomerations form at least portions of the
ionic conductor networks 340.
[0091] The ionic conductor networks 340 have a volume ratio of
ionic conductor to electronic conductor that is greater than the
volume ratio of ionic conductor to electronic conductor within the
electronic conductor rich networks 350. The electronic conductor
networks 350 have a volume ratio of electronic conductor to ionic
conductor that is greater than the volume ratio of electronic
conductor to ionic conductor within the ionic conductor networks
340. The ionic conductor networks 340 provide lower resistance
paths 341 for ion conduction when compared with the electronic
conductor networks 350. The electronic conductor networks 350
provide lower resistance paths 351 for electron conduction when
compared with the ionic conductor networks 340.
[0092] The electrode layer structure illustrated in FIG. 3D may
provide enhanced durability and/or performance. For example, the
second ionomer 370 may provide superior catalyst support corrosion
resistance and/or catalyst dissolution resistance characteristics
to the electrode layer 301 when compared to the first ionomer 375,
and the first ionomer 375 may provide enhanced performance
characteristics to the electrode layer 301 when compared to the
second ionomer 370. In some implementations, the second ionomer 370
may have a higher EW than the first ionomer. The second ionomer
(higher EW ionomer) may provide superior characteristics than the
first ionomer 375 when the fuel cell is operating under hot/dry
conditions. The first ionomer 375 (lower EW ionomer) may provide
superior characteristics than the second ionomer 370 when the fuel
cell is operating under cold/wet conditions.
[0093] Processes for forming electrode layers involve forming an
ink comprising a catalyst, an electronic conductor, an ionic
conductor, and a solvent. More than one type and/or form of
catalyst, electronic conductor, ionic conductor, and/or solvent may
be used. For example, the ionic conductor may comprise
perfluorinated sulfonic acid (PFSA), and/or perfluorinated imide
acid (PFIA), and/or a hydrocarbon. PFIA is described in commonly
owned U.S. Patent Application No. 61/325,062, filed Apr. 16, 2010,
Hamrock et al. which is incorporated herein by reference. The
solvent may comprise water, an alcohol, and/or a hydrocarbon, for
example. The catalyst may comprise platinum, palladium, bimetals,
metallic alloys, and/or carbon nanotubes. The catalyst may be
coated on the electronic conductor, e.g., the electronic conductor
and catalyst may comprise platinum coated carbon. In some
embodiments, the catalyst may be coated on support elements other
than the electronic conductor, such as the nanostructured supports
described in U.S. Pat. No. 5,879,827. The electronic conductor may
have particles with diameters of about 100 nm, for example, and may
comprise carbon, tin oxide, and/or titanium oxide, and/or other
suitable materials.
[0094] Specific amounts of each component of the electrode ink may
be varied to achieve a desired viscosity, e.g., about 1000
centipoise, and solids content, e.g., about 2% to about 40% solids
by weight. The electrode ink may be prepared by adding the ink
components and then mixing the ink components for a period of time.
In some implementations, the mixing may include adding media, such
as 6 mm diameter ceramic beads and then rolling or ball milling for
at least about 5 minutes. The prepared ink is then applied to a
substrate, such as a major surface of a fuel cell electrolyte
membrane, a GDL, or a liner, and dried. The dried ink layer forms
the fuel cell electrode.
[0095] FIGS. 4A and 4B illustrate exemplary processes for forming a
fuel cell electrode. As depicted in the flow diagram of FIG. 4A, an
electrode ink may be formed by combining 410 the electronic
conductor, catalyst, ionic conductor, and solvent and mixing 420
these ingredients for a period of time. For example, the electronic
conductor, catalyst, ionic conductor, and solvent may be combined,
e.g., combined substantially contemporaneously, and then mixed.
After mixing, the ink is coated 430 on a substrate and allowed to
dry 440 to form the fuel cell electrode layer. The ionic conductor
of the electrode ink may comprise only one type of ionic conductor,
e.g., an ionomer in the form of particles, a majority of which have
diameters greater than about 50 nm or greater than about 1 .mu.m.
These ionomer particles may have substantially smooth, spheroid,
and/or hollow morphology which can be produced by a spray drying
process. As previously discussed, ionomer particles of this size
and morphology may more readily form electrode layer structures
that include ionic conductor networks.
[0096] Multiple types of ionomer and/or multiple forms of the same
ionomer may be included in the ionic conductor forming the
electrode ink. When multiple forms of the same ionomer are used,
the multiple forms may be multiple different particle sizes and/or
the multiple types may be multiple different EWs of what is
otherwise the same type of ionomer. For example, a first ionomer of
the multiple ionomers may be powdered, with a majority of particles
having diameters greater than about 1 .mu.m, for example. A second
ionomer of the multiple ionomers may be solution based, with a
majority of particle diameters less than about 50 nm. The first and
second ionomers may be the same type of ionomer or may be different
types of ionomers.
[0097] FIG. 4B illustrates another exemplary process for forming a
fuel cell electrode. According to this process, an electrode ink
pre-mixture is formed 450 by combining the catalyst, electronic
conductor and solvent. The pre-mixture ingredients are mixed 452,
e.g., by ball milling, for a period of time, such as about 24
hours. After mixing the pre-mixture ingredients, a first ionic
conductor, e.g., powdered ionomer particles comprising
substantially smooth surfaced, hollow, spherical particles, a
majority of which have diameters greater than 50 nm or greater than
about 1 .mu.m are added 454 to the pre-mixture. A second ionomer,
e.g., having a majority of particles with diameters less than about
50 nm, may be used to form the pre-mixture, and/or may be added
along with the first ionomer and/or may be added later in the
process. After the first ionomer is added 454, the ink is mixed 456
for an additional time, e.g., about 30 minutes. Additional powdered
or solution based ionic conductors maybe added to the pre mixture
and/or at a later stage in the process. The electrode ink is coated
458 on a substrate and dried 460. In some implementations, forming
the ink may involve adding a first portion of an ionic conductor
along with the catalyst, electronic conductor, and solvent, mixing,
and then adding a second portion of the ionic conductor and mixing.
Mixing can be accomplished by a variety of processes, including
ball milling, stirring, shearing, sonication, etc.
[0098] The electrode structure resulting from the processes
described in connection with FIGS. 4A or 4B may be used to form
electrode layers having multiple ionomers and/or may be used to
form electrode layers having discrete networks rich in an ionic
conductor which are substantially separate and discrete from
networks rich in an electronic conductor material. FIG. 5A is an
optical image of the surface of a fuel cell electrode formed using
a solution based ionic conductor comprising small particles, a
majority of which have diameters less than about 50 nm. FIG. 5B is
an optical image of the surface of a fuel cell electrode layer
formed using a powdered ionomer which comprises larger particles, a
majority of which have diameters greater than about 1 .mu.m, and
having substantially smooth, spheroid, hollow morphology. The
optical image of FIG. 5B shows the larger ionomer particles which
may form ionomer rich zones 510.
[0099] As previously discussed, when multiple ionomers are used,
several different types of ionomers, or the same type of ionomer in
several different forms may be used. At least one of the ionomers
differs from the other ionomers in at least one characteristic. For
example, using different types or forms of the ionomer may involve
using different EW of what is otherwise the same type of ionomer
and/or using the same ionomer having different particles sizes
and/or different size ranges and/or different particle
morphologies. For example, using multiple different types of
ionomer may involve using PFIA as one of the multiple types of
ionomer and using PF SA as another of the multiple types of
ionomer. If different types of ionomer are used, each of the
ionomers may have the same form, or each ionomer may a different
form (e.g., one ionomer having small particles and the other
ionomer having larger particles), and/or the multiple ionomers may
comprise different EW materials. The same amount, measured for
example, by volume or weight, of each ionomer or a different amount
of each ionomer may be used in the electrode ink.
[0100] When forming the electrode, the different types or forms of
ionomer may be added simultaneously or sequentially to the mixture.
For example, sequentially adding the ionomers may involve forming
an electrode ink using a first ionomer (e.g., according to the
process described in connection with FIG. 4), grinding the
electrode ink, and then mixing the ground electrode ink with a
solvent and a second ionomer.
[0101] Spray drying is a useful method for forming a powdered
ionomer that can be used to make fuel cell electrodes that include
ionic conductor networks that are substantially discrete and
separate from electronic conductor networks as depicted, for
example, in FIG. 3B. As discussed in more detail in the examples
below, powdered ionomer formed by spray drying has been shown to
produce superior fuel cell electrodes when compared to powdered
ionomer that is produced by other methods. More specifically, fuel
cell electrodes fabricated using ionomer powder produced by spray
drying have shown superior performance with compared to fuel cell
electrodes fabricated using ionomer powder produced by
cryogrinding, for example. The difference in performance between
the electrodes formed using the spray dried ionomer powder and
electrodes formed using other types of ionomer powder may be
related to the morphology of the powder particles.
[0102] As illustrated in the scanning electron microscope (SEMS)
image of FIG. 6, spray drying ionomer can produce powder particles
that are spheroids, having outer surfaces that are substantially
smooth and which are hollow. The term spheroid is used to describe
a particle having a diameter that does not vary more than about
10%. The term "substantially smooth" is used to describe particles
having surface roughness less that about 5% of the diameter of the
particle.
[0103] The powdered ionomer particles produced by spray drying, for
example, may range in size from about 50 nm to about 30 .mu.m or
may range from 50 nm to about 15 .mu.m, or may range from about 1
.mu.m to about 15 .mu.m. The average diameter of the particles may
be about 3.5 .mu.m. The average size of the spray dried particles
can be controlled within a range of less than 1 micron to greater
than a 1 millimeter by changing the variables of the spray drying
process, including spray velocity, solution concentration, and
chamber temperature, for example. The diameter range can also be
controlled by varying these processing parameters. A majority of
the spray dried ionomer spheroids may be hollow. In some
implementations, an additive, such as cerium and/or manganese
compounds, may be used during the spray drying process and/or at
other stages during formation of the electrode ink.
[0104] For example, spray drying to achieve ionomer particles
having the characteristics described above may involve taking a
dispersion of fluorinated polymer and water, atomizing the
dispersion into small droplets of dispersion, then releasing the
dispersion droplets into a heated gas (air) which dries the
dispersion to produce flowable particles of polymer. These
particles have a dry exterior surface but an internal residual
moisture level of about 2% to 10%. The process variables for spray
drying include: 1) % solids of the input dispersion, 2) atomization
pressure of the feed, 3) feed rate, 4) inlet temperature of the
heated gas (e.g., air), and 5) outlet temperature of the cooled
gas. These variables affect the residual moisture level and/or the
distribution of the measured particle size of the polymer powder.
Exemplary ranges for the spray drying process variables that can
produce ionomer particles as described herein include: 1) percent
solids of dispersion in a range of about 9% to about 22%, or a
range of about 18% to about 20%, 2) atomization pressure in a range
from about 30 psi to about 60 psi, or a range of about 35 psi to
about 40 psi, 3) feed rate (as measured by pump speed) in a range
of about 50 rpm to about 140 rpm and adjusted based on % solids and
outlet temperature, 4) inlet temperature in a range of about
160.degree. C. to about 250.degree. C., or about 185 to about
200.degree. C., 5) outlet temperature in a range of about
65.degree. C. to about 95.degree. C., or about 85.degree. C. to
about 90.degree. C.
[0105] Cryogrinding is another process that produces a powdered
ionomer. However, in contrast to the smooth, hollow, spheroid
ionomer particles shown in the SEMS image of FIG. 6, cryogrinding
produces irregular particles with jagged surfaces, as illustrated
in SEMS images FIGS. 7A and 7B. The size of the cryoground
particles varies from very small dust-like particles of less than 1
micron to particles that exceed 20 microns.
[0106] The differences in the ionomer particle morphology, e.g.,
such as between particles formed by spray drying and particles
formed by cryogrinding, may influence ink rheology and/or fuel cell
electrode pore structure, and/or fuel cell electrode performance.
The spheroid, substantially smooth, and hollow ionomer particles
formed by spray drying appear to facilitate the formation of the
discrete ionic conductor rich and electronic conductor rich
networks within the fuel cell electrode.
[0107] Fuel cell electrodes must be capable of performing multiple
functions over a wide range of operating conditions. The functions
performed by the fuel cell electrodes include gas diffusion of fuel
or oxidant, transport of liquid water, and electronic and ionic
conduction through the electrode layer. Fuel cell electrodes need
to perform these functions over a wide range of conditions from
about -40 C to greater than about 100 C, with reactant gas humidity
ranging from 0 to 100%.
[0108] The fuel cell electrode is required to efficiently and
simultaneously perform multiple material transport and electrical
conduction functions when the fuel cell is operating. These
material transport and electrical conduction functions include
diffusion of fuel gases or oxidant gases, transport of liquid
water, and conduction of protons and electrons within the electrode
layer. All of these functions may not be simultaneously and
optimally accommodated in some fuel cell electrodes that have a
substantially uniform distribution of a single type of ionic
conductor. The ability with which the electrode layer can transport
liquid water is of particular interest with respect to the cathode
electrode where water is formed. Within the porous layers of a fuel
cell electrode, for example, enough pores must be sufficiently
hydrophobic to prevent liquid water from filling too much of the
layer. Overfilling of the layers or regions within the layer with
liquid water is typically known as "flooding". The flooding of
pores prevents reactant gases from penetrating the electrode and
reaching catalyst sites, resulting in performance loss.
[0109] An overly hydrophobic layer is also not ideal for fuel cell
operation. At cool temperatures, water must migrate from the
electrodes to the flow field as a liquid. If the layer through
which the water migrates is too hydrophobic, there are no liquid
connections through which water can readily move. The water must
percolate from pore to pore, a process which requires significant
build up of liquid pressure. This high liquid pressure results in
flooding of pores, reduction of gas transport and loss of fuel cell
performance. Appropriate engineering of hydrophilic and hydrophobic
pores can provide both liquid water and gas transport
simultaneously.
[0110] Substantially uniform distribution of small diameter ionic
conductor particles within a fuel cell electrode may produce small
pore sizes within the electrode layer, resulting in compromised
liquid transport and/or gas diffusion. Poor ionic and/or electronic
conduction may occur due to narrow pathways through the well mixed,
small particle size ionomer, electronic conductor, and catalyst.
Substantially uniform distribution of the ionomer may result in
reduced pathways for liquid transport due to the slightly
hydrophilic properties of the ionomer. Water transport may be poor
due to limitations on the maximum amount of ionomer allowed in an
electrode before flooding. Electron conduction may be reduced due
to poor carbon-carbon contact.
[0111] For optimal performance, the fuel cell electrodes need to
provide a porous layer that readily conducts gases to reaction
sites within the electrodes and also transports liquid water away
from the reaction sites. The electrode layer should have sufficient
hydrophilicity to allow easy liquid water transport yet sufficient
hydrophobicity to prevent flooding of the pores by the liquid
water. Regions of excessive hydrophobicity may create a "wall" with
the electrode that requires high liquid pressure for the liquid
water to break through the wall. A buildup of liquid pressure
behind the wall may create flooding of other regions, which
prevents fuel gases from reaching the reaction sites. If the fuel
cell electrode includes hydrophilic regions of sufficient number
and size, flooding can be prevented.
[0112] Fuel cell electrodes must include a sufficient amount of
ionic conductor to allow rapid ion conduction to the reaction sites
(in the cathode electrode) and to allow rapid ion conduction away
from the reaction sites (in the anode electrode). However the fuel
cell electrode must also include a sufficient amount of electronic
conductor to allow rapid electron conduction to the reaction sites
(in the cathode electrode) and rapid electron conduction away from
the reaction sites (in the anode electrode).
[0113] Fuel cell electrodes having discrete ionic and/or electronic
conductor networks can provide superior liquid and gas transport,
hydrophobicity, hydrophilicity, and electron an ion conduction when
compared with fuel cell electrodes having substantially uniformly
distributed ionic and electronic conductor materials.
[0114] The use of ionomer particles that are generally greater than
about 1 .mu.m in diameter in the fuel cell ink appears to
facilitate the formation of ionic and electronic conductor
networks. Furthermore, the morphology of particles used in the fuel
cell ink may also be a factor, with the substantially smooth and
hollow spheroid particles produced by the spray drying process
providing superior characteristics when compared to the jagged,
irregular particles produced by cryogrinding. The narrower size
range of the spray dried powder particles (in contrast with the
wider size range of the cyroground powder particles) may also
contribute to enhanced electrode performance.
[0115] The smooth, hollow spheroids produced by spray drying appear
to promote agglomerations of the ionomer powder particles and
creation of ionic conductor rich networks (which are relatively
electronic conductor poor). For example, when catalyst coated
carbon is used as the catalyst and electronic conductor, the
electronic conductor rich regions contain non-oxidized carbon
(natural C) which is hydrophobic. The carbon rich regions that
ideally substantially traverse the electrode layer provide pathways
that facilitate electronic conduction and also provide networks of
low liquid water content, thus allowing fast gas transport. The
ionic conductor rich regions are moderately hydrophilic. Uniform
distribution of the ionic conductor is subject to the formation of
pockets of flooding. However ionic conductor rich networks that
substantially traverse across the electrode layer provide pathways
for rapid proton and water conduction.
[0116] As previously discussed, the ionic conductor networks and
electronic conductor networks can provide complementary functions
with the fuel cell electrode. When these complementary networks are
present in the electrode layer, the conflicting performance
constraints of optimal electrode design (fuel and oxidant gas
transport, liquid water transport, and electron and proton
conduction) can be better accommodated. The presence of the
electronic and ionic conductor networks serve to maintain fuel cell
performance by facilitating transport of gases to and from the
reaction sites and conduction of ions and electrons to and from the
reaction sites of the electrode layer. The ionic conductor and
electronic conductor networks can provide an extended operating
range for the fuel cell. For example, because liquid water
transport is improved along the ionic conductor networks, a lower
EW ionomer may be used as the ionic conductor. The lower EW
material achieves better performance in hotter, drier conditions,
while preventing flooding at colder, wetter conditions.
Alternatively, the addition of a higher EW ionomer may be used to
increase the durability of the electrode layer.
[0117] Objects and advantages of this disclosure are further
illustrated by the following examples, but the particular materials
and amounts thereof recited in these examples, as well as other
conditions and details, should not be construed to unduly limit
this disclosure.
EXAMPLES
[0118] MEAs having four different types of fuel cell cathode
electrodes were constructed and tested. The MEAs were produced by
the same process, using identical materials, except for the cathode
electrode. The different cathode electrode types were formed from
1) electrodes formed using a solution-based ionomer (SOLN, SOLN 2)
having relatively small size particles (e.g., diameters less than
50 nm) in solution, 2) electrodes formed using a spray dried
ionomer powder (PDR, PDR 2), (see FIG. 6 and associated
discussion), 3) electrodes formed by pre-mixing the
catalyst/electronic conductor prior to combining the spray dried
ionomer powder (PDR postBM), and 4) electrodes formed using a
cryoground powder (cryoPDR) (see FIGS. 7A and 7B and associated
discussion). The fabrication parameters of the test MEAs are
provided in Table 1. The SOLN electrodes formed using the solution
based ionomer were fabricated by the process outlined in the
flowchart of FIG. 4A. The PDR electrodes formed using the spray
dried ionomer powder were fabricated by the process outlined in
FIG. 4A. The PDR post BM electrode was fabricated by process
outlined in FIG. 4B. The electrode formed using the cryo ground
ionomer powder was fabricated by process outlined in FIG. 4A.
TABLE-US-00001 TABLE 1 MEA with MEA with MEA with spray MEA with
cryoground spray dried dried powdered solution-based powdered
powdered ionomer ionomer ionomer ionomer electrode post electrode
electrode electrode ball milled (PDR (SOLN) (cryoPDR) (PDR) post
BM) Cathode design variables Ionomer/Catalyst 0.8 0.8 0.8 0.8
weight ratio Ionomer 3M800EW 3M800EW 3M800EW 3M800EW (available
from 3M Company, St. Paul, MN, USA) Form of ionomer Aqueous
Cryoground Spray dried Spray dried used for solution powder powder
powder electrode Catalyst TKK 10V30E TKK 10V30E TKK 10V30E TKK
10V30E (available from Tanaka Kikinzoku Kogyo (TKK), Tokyo, Japan)
Ink mixing Ball milling Ball milling Ball milling 2 step ball
technique after combining after after milling process all
components combining all combining all ionomer added components
components after ball milling catalyst and solvent Solvent Aqueous
Aqueous Aqueous Aqueous Ink solids 20% 20% 20% 20% content Catalyst
loading 0.3 0.3 0.3 0.3 (mg Pt/cm2) Electrode Hand painting Hand
painting Hand painting Hand painting coating method Annealing 150
C., 30 min. 150 C., 30 min. 150 C., 30 min. 150 C., 30 min. Anode
design variables Ionomer/Catalyst 0.8 0.8 0.8 0.8 ratio Ionomer
3M1000EW 3M1000EW 3M1000EW 3M1000EW (available from 3M Company, St.
Paul, MN, USA) Form of ionomer Aqueous Aqueous Aqueous Aqueous used
for solution-based solution-based solution-based solution-based
electrode ionomer ionomer ionomer ionomer Catalyst TKK 10V30E TKK
10V30E TKK 10V30E TKK 10V30E Ink mixing Ball milling Ball milling
Ball milling Ball milling technique Solvent Aqueous Aqueous Aqueous
Aqueous Ink solids 20% 20% 20% 20% content Catalyst loading 0.1 0.1
0.1 0.1 (mg Pt/cm2) Electrode Hand painting Hand painting Hand
painting Hand painting coating method Annealing 150 C., 30 min. 150
C., 30 min. 150 C., 30 min. 150 C., 30 min. Anode Design Variables
GDL type Hydrophobized Hydrophobized Hydrophobized Hydrophobized
carbon paper carbon paper carbon paper carbon paper with with with
with microporous microporous microporous microporous layer layer
layer layer Membrane Design Variables Membrane 3M800EW 3M800EW
3M800EW 3M800EW material Thickness 0.8 mil 0.8 mil 0.8 mil 0.8
mil
[0119] In one analysis, the MEAs with the spray dried powdered
ionomer electrodes (denoted PDR) were compared to the MEAs having
solution based ionomer electrodes (denoted SOLN). Three MEAs were
made using the spray dried powdered ionomer and three MEAs were
constructed using the solution based ionomer for each trial. Two
trials of each of the three MEAs constructed were completed for
each group. The results of the first trial of the spray dried
powdered ionomer electrode group are denoted PDR; the results of
the second trial of the spray dried powdered ionomer electrode
group are denoted PDR 2; the results of the first trial of the
solution based ionomer electrode group are denoted SOLN; the
results of the second trial of the solution based ionomer electrode
group are denoted SOLN 2.
[0120] Catalytic activity: Catalyst activity was measured and is
shown for MEAs with the spray dried powder ionomer electrodes and
the solution based ionomer electrodes in Table 2. The catalyst
activity of the powder based electrodes shows improvement when
compared with the catalyst activity of the solution based
electrodes. These activity gains may be explained by better three
phase interface (catalyst, ionomer, and reactant gas) created by
the powder based ionomer electrodes.
TABLE-US-00002 TABLE 2 Catalyst Loading SEF Activity Fuel cell Type
mg/cm2 (cm2/cm2) (m2/g) 1 solution 0.283 129 45.58 2 solution 0.315
139 44.12 3 solution 0.298 126 42.28 4 spray dried 0.294 156 53.06
powder 5 spray dried 0.291 153 52.58 powder 6 spray dried 0.295 154
52.20 powder
[0121] Galvano-dynamic polarization scanning (GDS) analysis: FIG. 8
shows the GDS polarization performance results for two trials of
the MEAs with solution-based ionomer electrodes (SOLN. SOLN 2) and
the powder-based ionomer electrodes (PDR, PDR 2). The test
conditions were as follows: cell temperature=70 C, anode and
cathode inlet humidification=100%, ambient operating pressure, fuel
(H2) stoichiometric ratio=1.4, oxidant (air) stoichiometric
ratio=2.5. For a given current density, the powder-based ionomer
electrodes show higher voltages than the solution-based ionomer
electrodes. This benefit is more significant at high current
densities.
[0122] FIG. 9 compares the MEA performance of the SOLN and PDR
electrodes at a current density of 1.2 A/cm2 and 1.5 A/cm2. The
data illustrated in FIG. 9 indicates that higher cell voltages are
achieved by the spray dried powdered ionomer electrodes (PDR, PDR
2) than the solution-based electrodes (SOLN, SOLN 2) at higher
current densities. Note that data at 1.5 A/cm2 was only recorded
for the second trial of electrodes (SOLN 2, PDR 2).
[0123] A follow up analysis was performed to compare various
properties of spray dried powdered ionomer electrodes formed by
adding ink components together and mixing (denoted PDR), spray
dried powdered ionomer electrodes formed by pre-mixing Pt coated
carbon and solvent (water) prior to adding the spray dried powdered
ionomer (denoted PDR post BM), cryoground powdered ionomer
electrodes (denoted cryoPDR), and solution based ionomer electrodes
(denoted SOLN).
[0124] Electrochemical Surface Area: The electrochemical surface
area (ECSA) of the catalyst was analyzed for each of the electrode
types PDR, PDR post BM, cryoPDR, SOLN listed in the preceding
paragraph. The ECSA analysis provides the catalyst surface that is
available to contribute to the fuel cell reaction. A larger ECSA is
associated with better fuel cell performance. The ECSA was
performed for electrodes under the following test conditions: 40 C
cell temperature, 70 C dew point (anode and cathode); H2/N2
(anode/cathode), flow rate 800/500 SCCM anode/cathode. The ECSA
readings were taken at 50 mV/s scan rate from 0.05 to 0.80 V. The
graph of FIG. 10 provides a comparison of the electrochemical
surface area of the electrode types listed above. As can be
appreciated from FIG. 10, the cryoground powdered ionomer (cryoPDR)
electrodes show the highest ECSA at 70 m2/g Pt. Both the PDR
electrodes and the PDR post BM electrodes also show ECSA
improvements over the solution based (SOLN) ionomer electrodes.
[0125] Catalytic Activity: The catalytic activity at 0.9 V was
measured for each MEA under the following conditions: T=80C, 100%
RH, H2/O2 (anode/cathode), 7.5/7.5 psig pressure (anode cathode).
The catalytic activity measurements for the MEAs are provided in
FIG. 11. The cryo ground powdered ionomer electrode performed
better than the solution based ionomer electrode in this test. The
spray dried powdered ionomer electrodes (PDR and PDR post BM)
exhibited more catalytic activity on average per unit mass than the
cryo ground powdered ionomer electrodes and the solution based
ionomer electrodes.
[0126] Follow-up galvano-dynamic polarization scanning (GDS):
Galvano-dynamic polarization scanning was performed for MEAs having
SOLN, PDR, cryoPDR and PDR post BM electrodes. The test conditions
were as follows: cell temperature=70 C, anode and cathode inlet
humidification =100%, ambient operating pressure, fuel (H2)
stoichiometric ratio=1.7, oxidant (air) stoichiometric ratio=2.5.
FIG. 12 shows the GDS polarization curve for the SOLN, PDR, cryoPDR
and PDR post BM MEAs. FIG. 13 provides the MEA performance at a
current density of 1.2 A/cm2 for each type of electrode. In this
analysis, all of the powder based electrodes outperformed the
solution based electrodes. The PDR and PDR post BM show the
greatest improvement over the solution based electrodes and were
exhibited improved high current density over that of the cryoPDR
electrodes.
[0127] Objects and advantages of this disclosure are further
illustrated by the following listing of representative embodiments,
but the particular materials, amounts, conditions and details,
recited in these embodiments should not be construed to unduly
limit this disclosure.
Embodiments
[0128] Embodiment 1 is a fuel cell subassembly, comprising:
[0129] an electrode layer, comprising: [0130] a catalyst; [0131] an
electronic conductor; [0132] an ionic conductor; [0133] a plurality
of electronic conductor rich networks within the electrode layer;
and [0134] a plurality of ionic conductor rich networks within the
electrode layer and interspersed with the electronic conductor rich
networks, wherein a volume ratio of the ionic conductor to the
electronic conductor is greater in the ionic conductor rich
networks than in the electronic conductor rich networks. [0135]
Embodiment 2 is the fuel cell subassembly of embodiment 1, wherein,
during operation of a fuel cell that includes the fuel cell
subassembly, conduction of electrons occurs predominantly within
the electronic conductor rich networks and conduction of ions
occurs predominantly within the ionic conductor rich networks.
[0136] Embodiment 3 is the fuel cell subassembly of embodiment 1,
wherein the ionic conductor comprises particles of a spray dried
ion conducting polymer. [0137] Embodiment 4 is the fuel cell
subassembly of embodiment 1, wherein the ionic conductor comprises
particles and a majority of the particles have an outer surface
that is substantially smooth. [0138] Embodiment 5 is the fuel cell
subassembly of embodiment 1, wherein the ionic conductor comprises
particles and a majority of the particles are spheroids having a
variation in diameter of less than about 10%. [0139] Embodiment 6
the fuel cell subassembly of embodiment 1, wherein the ionic
conductor comprises particles and a majority of the particles are
hollow. [0140] Embodiment 7 is the fuel cell subassembly of
embodiment 1, wherein the ionic conductor comprises particles and a
majority of the particles have diameters in a range of about 1
.mu.m to about 15 .mu.m. [0141] Embodiment 8 is the fuel cell
subassembly of embodiment 1, wherein the electronic conductor
comprises electronic conductor particles and the catalyst is
disposed on the electronic conductor particles. [0142] Embodiment 9
is the fuel cell subassembly of embodiment 1, wherein the catalyst
is disposed on nanostructured supports. [0143] Embodiment 10 is the
fuel cell subassembly of embodiment 1, wherein the electronic
conductor comprises one or more of carbon, tin oxide, and titanium
oxide. [0144] Embodiment 11 is the fuel cell subassembly of
embodiment 1, wherein the catalyst comprises one or more of
platinum, palladium, bimetals, metallic alloys, and carbon
nanotubes. [0145] Embodiment 12 is the fuel cell subassembly of
embodiment 1, wherein the ionic conductor comprises a first ion
conducting polymer and the electrode layer further comprises a
second ionic conductor comprising a second ion conducting polymer.
[0146] Embodiment 13 is the fuel cell subassembly of embodiment 12,
wherein the first ion conducting polymer has a first equivalent
weight and the second ion conducting polymer has a second
equivalent weight. [0147] Embodiment 14 is the fuel cell
subassembly of embodiment 12, wherein: [0148] the first ion
conducting polymer comprises particles, and a majority of the
particles of the first ion conducting polymer have diameters
greater than about 1 .mu.m; and [0149] the second ion conducting
polymer comprises particles, and a majority of the particles of the
second ion conducting polymer have diameters less than about 50 nm.
[0150] Embodiment 15 is the fuel cell subassembly of embodiment 14,
wherein the particles of the second ion conducting polymer form a
film on the electronic conductor and the particles of the first ion
conducting polymer comprise a majority of the volume of the ionic
conductor. [0151] Embodiment 16 is the fuel cell subassembly of
embodiment 14, wherein the first ion conducting polymer
substantially forms the ion conducting networks. [0152] Embodiment
17 is the fuel cell subassembly of embodiment 1, wherein the
electrode layer is disposed on an electrolyte membrane. [0153]
Embodiment 18 is the fuel cell subassembly of embodiment 1, wherein
the electrode layer is disposed on a gas diffusion layer. [0154]
Embodiment 19 is the fuel cell subassembly of embodiment 1, wherein
the electrode layer is disposed between a first surface of an
electrolyte membrane and a first gas diffusion layer, the fuel cell
subassembly further comprising additional components of a membrane
electrode assembly (MEA) including a second electrode layer
disposed between a second surface of the electrolyte membrane and a
second gas diffusion layer. [0155] Embodiment 20 is the fuel cell
subassembly of embodiment 19, further comprising:
[0156] a first flow field plate disposed proximate the first gas
diffusion layer; and
[0157] a second flow field plate disposed proximate the second gas
diffusion layer. [0158] Embodiment 21 is the fuel cell subassembly
of embodiment 19, further comprising multiple MEAs arranged to form
a fuel cell stack. [0159] Embodiment 22 is a method of making a
fuel cell electrode layer, comprising:
[0160] combining an ionic conductor, an electronic conductor, a
catalyst, and a solvent, the ionic conductor comprising spheroid
particles, a majority of the particles having diameters greater
than about 50 nm;
[0161] mixing the ionic conductor, the electronic conductor, the
catalyst and the solvent for a period of time to form an electrode
ink; and
[0162] coating the electrode ink on a substrate to form the fuel
cell electrode layer. [0163] Embodiment 23 is the method of
embodiment 22, wherein a majority of the particles have a diameter
greater than about 1 .mu.m. [0164] Embodiment 24 is the method of
embodiment 22, wherein the particles have a diameter range between
about 50 nm to about 15 .mu.m. [0165] Embodiment 25 is the method
of embodiment 22, wherein the electronic conductor is coated with
the catalyst. [0166] Embodiment 26 is the method of embodiment 22,
wherein the catalyst disposed on support structures. [0167]
Embodiment 27 is the method of embodiment 22, wherein the catalyst
is disposed on nanostructured supports. [0168] Embodiment 28 is the
method of embodiment 22, wherein the substrate comprises an
electrolyte membrane. [0169] Embodiment 29 is the method of
embodiment 22, wherein the substrate comprises a gas diffusion
layer. [0170] Embodiment 30 is the method of embodiment 22, wherein
the particles comprise spray dried ionomer particles. [0171]
Embodiment 31 is the method of embodiment 22, wherein a majority of
the particles are spheroids. [0172] Embodiment 32 is the method of
embodiment 22, wherein a majority of the particles have a
substantially smooth surface. [0173] Embodiment 33 is the method of
embodiment 22, wherein a majority of the particles are hollow.
[0174] Embodiment 34 is the method of embodiment 22, wherein
combining the ionic conductor, the electronic conductor, the
catalyst and the solvent comprises substantially contemporaneously
combining the ionic conductor, the electronic conductor, and the
solvent prior to the mixing. [0175] Embodiment 35 is the method of
embodiment 22, wherein combining the ionic conductor, the
electronic conductor, the catalyst and the solvent comprises:
[0176] forming a pre-mixture that includes the electronic conductor
and the solvent;
[0177] mixing the pre-mixture for a period of time;
[0178] after mixing the pre-mixture, adding the ionic conductor to
the pre-mixture; and
[0179] mixing the ionic conductor and the pre-mixture for a period
of time. [0180] Embodiment 36 is the method of embodiment 22,
further comprising after mixing the ionic conductor, the electronic
conductor, and the solvent, adding a second type of ionic conductor
with the mixture of the ionic conductor, the electronic conductor,
and the solvent. [0181] Embodiment 37 is the method of embodiment
22, wherein the ionic conductor comprises a first type of ion
conducting polymer and a second type of ion conducting polymer.
[0182] Embodiment 38 is the method of embodiment 22, wherein the
ionic conductor comprises a first form of an ion conducting polymer
and a second form of the ion conducting polymer. [0183] Embodiment
39 is the method of embodiment 22, wherein the ionic conductor
comprises a first equivalent weight ionic conductor and a second
equivalent weight ionic conductor. [0184] Embodiment 40 is the
method of embodiment 22, wherein the ionic conductor comprises:
[0185] particles of a first ion conducting polymer, a majority of
the particles of the first ion conducting polymer having diameters
greater than about 1 .mu.m; and
[0186] particles of a second ion conducting polymer, a majority of
the particles of the second ion conducting polymer having diameters
less than about 50 nm. [0187] Embodiment 41 is the method of
embodiment 40, wherein a volume of the first ion conducting polymer
is greater that a volume of the second ion conducting polymer.
[0188] Embodiment 42 is the method of embodiment 41, wherein the
particles of the second ion conducting polymer coat the electronic
conductor. [0189] Embodiment 43 is the method of embodiment 22,
further comprising forming the ionic conductor by spray drying an
ion conducting polymer. [0190] Embodiment 44 is the method of
embodiment 43, wherein forming the ionic conductor by spray drying
the ion conducting polymer comprises adding an additive to the ion
conducting polymer prior to or during the spray drying. [0191]
Embodiment 45 is the method of embodiment 44, wherein the additive
comprises one or more of cerium and manganese compounds. [0192]
Embodiment 46 is the method of embodiment 22, wherein combining
comprises one or more of ball mixing, stirring, and sonication.
[0193] Embodiment 47 is the method of embodiment 22, wherein the
solvent comprises one or more of a hydrocarbon and water. [0194]
Embodiment 48 is a fuel cell subassembly, comprising:
[0195] an electrode layer, comprising: [0196] a catalyst; [0197] an
electronic conductor; [0198] an ionic conductor intermixed with the
electronic conductor and the catalyst and comprising particles, a
majority of the particles being spheroid particles having diameters
greater than about 50 nm. [0199] Embodiment 49 is the fuel cell
subassembly of embodiment 48, wherein a majority of the particles
of the ionic conductor have a substantially smooth outer surface.
[0200] Embodiment 50 is the fuel cell subassembly of embodiment 48,
wherein a majority of the particles are hollow. [0201] Embodiment
51 is the fuel cell subassembly of embodiment 48, wherein a
majority of the particles have diameters in a range of about 1
.mu.m to about 15 .mu.m. [0202] Embodiment 52 is the fuel cell
subassembly of embodiment 48, wherein the catalyst is disposed on
the electronic conductor. [0203] Embodiment 53 is the fuel cell
subassembly of embodiment 48, wherein the catalyst is disposed on
nanostructured supports. [0204] Embodiment 55 is the fuel cell
subassembly of embodiment 48, wherein the ionic conductor comprises
one or more of perfluorinated sulfonic acid and perfluorinated
imide acid. [0205] Embodiment 56 is the fuel cell subassembly of
embodiment 48, further comprising a second ionic conductor. [0206]
Embodiment 57 is the fuel cell subassembly of embodiment 56,
wherein the ionic conductor has a first equivalent weight and the
second ionic conductor has a second equivalent weight. [0207]
Embodiment 58 is the fuel cell subassembly of embodiment 56,
wherein the second ionic conductor comprises particles, and a
majority of the particles of the second ionic conductor have
diameters less than about 50 nm. [0208] Embodiment 59 is the fuel
cell subassembly of embodiment 48, wherein a majority of the
particles of the ionic conductor are non-uniformly distributed
within the electrode layer. [0209] Embodiment 60 is the fuel cell
subassembly of embodiment 48, wherein the electrode layer is
disposed on an electrolyte membrane. [0210] Embodiment 61 is the
fuel cell subassembly of embodiment 48, wherein the electrode layer
is disposed on a gas diffusion layer. [0211] Embodiment 62 is the
fuel cell subassembly of embodiment 48, wherein the electrode layer
is disposed between a first surface of an electrolyte membrane and
a first gas diffusion layer, the fuel cell subassembly further
comprising additional components of a membrane electrode assembly
(MEA) including a second electrode layer disposed between a second
surface of the electrolyte membrane and a second gas diffusion
layer. [0212] Embodiment 63 is the fuel cell subassembly of
embodiment 62, further comprising:
[0213] a first flow field plate disposed proximate the first gas
diffusion layer; and
[0214] a second flow field plate disposed proximate the second gas
diffusion layer. [0215] Embodiment 64 is the fuel cell subassembly
of embodiment 62, further comprising multiple MEAs arranged to form
a fuel cell stack. [0216] Embodiment 65 is a fuel cell electrode
layer, comprising:
[0217] a catalyst;
[0218] an electronic conductor; and
[0219] a first ionic conductor; and
[0220] a second ionic conductor, wherein the first ionic conductor
is different from the second ionic conductor and the first ionic
conductor and the second ionic conductor are interspersed with each
other, the electronic conductor, and the catalyst within the
electrode layer. [0221] Embodiment 66 is the electrode layer of
embodiment 65, wherein the first ionic conductor and the second
ionic conductor are different types of ionic conductor. [0222]
Embodiment 67 is the electrode layer of embodiment 65, wherein the
first ionic conductor and the second ionic conductor are different
forms of the same type of ionic conductor. [0223] Embodiment 68 is
the electrode layer of embodiment 65, wherein the first ionic
conductor has a first equivalent weight and the second ionic
conductor has a second equivalent weight. [0224] Embodiment 69 is
the electrode layer of embodiment 65, wherein particles of the
second ionic conductor coat the electronic conductor. [0225]
Embodiment 70 is the electrode layer of embodiment 65, wherein
particles of the second ionic conductor are substantially smaller
than particles of the first ionic conductor. [0226] Embodiment 71
is the electrode layer of embodiment 65, wherein a majority of
particles of the second ionic conductor have diameters less than
about 50 nm and particles of the first ionic conductor are powdered
spray dried particles or powdered cryoground particles. [0227]
Embodiment 72 is the electrode layer of embodiment 65, wherein
particles of one or both of the first ionic conductor and the
second ionic conductor are non-uniformly distributed in the
electrode layer. [0228] Embodiment 73 is the fuel cell subassembly
of embodiment 1, wherein the ionic conductor comprises particles
and a majority of the particles have diameters in a range of 1
.mu.m to 15 .mu.m. [0229] Embodiment 74 is the fuel cell
subassembly of embodiment 1, wherein the ionic conductor comprises
particles and a majority of the particles have diameters in a range
of 1.5 .mu.m to 14 .mu.m. [0230] Embodiment 75 is the fuel cell
subassembly of embodiment 1, wherein the ionic conductor comprises
particles and a majority of the particles have diameters in a range
of 2 .mu.m to 12 .mu.m. [0231] Embodiment 76 is the fuel cell
subassembly of embodiment 12, wherein: [0232] the first ion
conducting polymer comprises particles, and a majority of the
particles of the first ion conducting polymer have diameters
greater than 1 .mu.m; and [0233] the second ion conducting polymer
comprises particles, and a majority of the particles of the second
ion conducting polymer have diameters less than 50 nm. [0234]
Embodiment 77 is the fuel cell subassembly of embodiment 12,
wherein: [0235] the first ion conducting polymer comprises
particles, and a majority of the particles of the first ion
conducting polymer have diameters greater than 1.5 .mu.m; and
[0236] the second ion conducting polymer comprises particles, and a
majority of the particles of the second ion conducting polymer have
diameters less than 50 nm. [0237] Embodiment 78 is the fuel cell
subassembly of embodiment 12, wherein: [0238] the first ion
conducting polymer comprises particles, and a majority of the
particles of the first ion conducting polymer have diameters
greater than 1 .mu.m; and [0239] the second ion conducting polymer
comprises particles, and a majority of the particles of the second
ion conducting polymer have diameters less than 40 nm. [0240]
Embodiment 79 is the fuel cell subassembly of embodiment 12,
wherein: [0241] the first ion conducting polymer comprises
particles, and a majority of the particles of the first ion
conducting polymer have diameters greater than 1.5 .mu.m; and
[0242] the second ion conducting polymer comprises particles, and a
majority of the particles of the second ion conducting polymer have
diameters less than 40 nm. [0243] Embodiment 80 is the method of
embodiment 22, wherein a majority of the particles have a diameter
greater than 50 nm. [0244] Embodiment 81 is the method of
embodiment 22, wherein a majority of the particles have a diameter
greater than 75 nm. [0245] Embodiment 82 is the method of
embodiment 22, wherein a majority of the particles have a diameter
greater than 1 .mu.m. [0246] Embodiment 83 is the method of
embodiment 22, wherein a majority of the particles have a diameter
greater than 1.5 .mu.m. [0247] Embodiment 84 is the method of
embodiment 22, wherein the particles have a diameter range between
50 nm to 15 .mu.m. [0248] Embodiment 85 is the method of embodiment
22, wherein the particles have a diameter range between 50 nm to 12
.mu.m. [0249] Embodiment 86 is the method of embodiment 22, wherein
the particles have a diameter range between 75 nm to 12 .mu.m.
[0250] Embodiment 87 is the method of embodiment 22, wherein the
particles have a diameter range between 1 .mu.m to 12 .mu.m. [0251]
Embodiment 88 is the method of embodiment 22, wherein the particles
have a diameter range between 1.5 .mu.m to 12 .mu.m. [0252]
Embodiment 89 is the method of embodiment 22, wherein the ionic
conductor comprises:
[0253] particles of a first ion conducting polymer, a majority of
the particles of the first ion conducting polymer having diameters
greater than 1 .mu.m; and
[0254] particles of a second ion conducting polymer, a majority of
the particles of the second ion conducting polymer having diameters
less than 50 nm. [0255] Embodiment 90 is the method of embodiment
22, wherein the ionic conductor comprises:
[0256] particles of a first ion conducting polymer, a majority of
the particles of the first ion conducting polymer having diameters
greater than 1.5 .mu.m; and
[0257] particles of a second ion conducting polymer, a majority of
the particles of the second ion conducting polymer having diameters
less than 50 nm. [0258] Embodiment 91 is the method of embodiment
22, wherein the ionic conductor comprises:
[0259] particles of a first ion conducting polymer, a majority of
the particles of the first ion conducting polymer having diameters
greater than 1 .mu.m; and
[0260] particles of a second ion conducting polymer, a majority of
the particles of the second ion conducting polymer having diameters
less than 40 nm. [0261] Embodiment 92 is the method of embodiment
22, wherein the ionic conductor comprises:
[0262] particles of a first ion conducting polymer, a majority of
the particles of the first ion conducting polymer having diameters
greater than 1.5 .mu.m; and
[0263] particles of a second ion conducting polymer, a majority of
the particles of the second ion conducting polymer having diameters
less than 40 nm. [0264] Embodiment 93 is the fuel cell subassembly
of embodiment 48, wherein a majority of the particles have
diameters in a range of 1 .mu.m to 15 .mu.m. [0265] Embodiment 94
is the fuel cell subassembly of embodiment 48, wherein a majority
of the particles have diameters in a range of 1.5 .mu.m to 15
.mu.m. [0266] Embodiment 95 is the fuel cell subassembly of
embodiment 48, wherein a majority of the particles have diameters
in a range of 1 .mu.m to 12 .mu.m. [0267] Embodiment 96 is the fuel
cell subassembly of embodiment 48, wherein a majority of the
particles have diameters in a range of 1.5 .mu.m to 12 .mu.m.
[0268] Embodiment 97 is the fuel cell subassembly of embodiment 56,
wherein the second ionic conductor comprises particles, and a
majority of the particles of the second ionic conductor have
diameters less than 50 nm. [0269] Embodiment 98 is the fuel cell
subassembly of embodiment 56, wherein the second ionic conductor
comprises particles, and a majority of the particles of the second
ionic conductor have diameters less than 40 nm. [0270] Embodiment
99 is the fuel cell subassembly of embodiment 56, wherein a
majority of the particles have diameters in a range of 1 .mu.m to
15 .mu.m, wherein the second ionic conductor comprises particles,
and wherein a majority of the particles of the second ionic
conductor have diameters less than 50 nm. [0271] Embodiment 100 is
the fuel cell subassembly of embodiment 56, wherein a majority of
the particles have diameters in a range of 1 .mu.m to 15 .mu.m,
wherein the second ionic conductor comprises particles, and wherein
a majority of the particles of the second ionic conductor have
diameters less than 40 nm. [0272] Embodiment 101 is the method of
embodiment 22, wherein at least 10% of the particles are hollow.
[0273] Embodiment 102 is the method of embodiment 22, wherein at
least 20% of the particles are hollow. [0274] Embodiment 103 is the
method of embodiment 22, wherein at least 30% of the particles are
hollow. [0275] Embodiment 104 is the method of embodiment 22,
wherein at least 40% of the particles are hollow.
[0276] The foregoing description of the various examples and
embodiments has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise forms disclosed. Many modifications and
variations are possible in light of the above teaching. It is
intended that the scope be limited not by this detailed
description, but rather by the claims appended hereto.
* * * * *