U.S. patent application number 12/203435 was filed with the patent office on 2009-01-22 for liquid materials for use in electrochemical cells.
This patent application is currently assigned to The University of North Carolina at Chapel Hill. Invention is credited to Ginger M. Denison, Joseph M. DeSimone, Raymond Dominey, Jennifer Y. Kelly, Jason P. Rolland, Zhilian Zhou.
Application Number | 20090023038 12/203435 |
Document ID | / |
Family ID | 34976057 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090023038 |
Kind Code |
A1 |
DeSimone; Joseph M. ; et
al. |
January 22, 2009 |
LIQUID MATERIALS FOR USE IN ELECTROCHEMICAL CELLS
Abstract
Disclosed is the use of liquid precursor materials to prepare a
processible polymeric electrolyte, which can be used to form a
proton exchange membrane for use in an electrochemical cell. Also
disclosed is the use of liquid precursor materials to prepare a
processible catalyst ink composition, which can be conformally
applied to a proton exchange membrane and a electrode material for
use in an electrochemical cell. Also disclosed is the use of a
photocurable perfluoropolyether (PFPE) material to form a
microfluidic electrochemical cell.
Inventors: |
DeSimone; Joseph M.;
(Durham, NC) ; Kelly; Jennifer Y.; (Chapel Hill,
NC) ; Rolland; Jason P.; (Durham, NC) ; Zhou;
Zhilian; (Chapel Hill, NC) ; Denison; Ginger M.;
(Durham, NC) ; Dominey; Raymond; (Chapel Hill,
NC) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA, 101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
The University of North Carolina at
Chapel Hill
Chapel Hill
NC
|
Family ID: |
34976057 |
Appl. No.: |
12/203435 |
Filed: |
September 3, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11040317 |
Jan 21, 2005 |
7435495 |
|
|
12203435 |
|
|
|
|
60538706 |
Jan 23, 2004 |
|
|
|
60538878 |
Jan 23, 2004 |
|
|
|
Current U.S.
Class: |
429/410 |
Current CPC
Class: |
H01M 4/8828 20130101;
H01M 2300/0082 20130101; H01M 8/1072 20130101; Y02P 70/50 20151101;
H01M 8/1039 20130101; H01M 8/1025 20130101; C08J 5/2262 20130101;
C08J 2367/00 20130101; H01M 8/1032 20130101; H01M 8/1027 20130101;
H01M 8/1004 20130101; C08J 5/2256 20130101; H01M 8/0221 20130101;
H01M 8/0234 20130101; H01M 8/0258 20130101; Y02E 60/50 20130101;
H01M 8/103 20130101 |
Class at
Publication: |
429/33 |
International
Class: |
H01M 8/10 20060101
H01M008/10 |
Goverment Interests
GOVERNMENT INTEREST
[0002] This invention was made with U.S. Government support from
the Office of Naval Research Grant No. N00014210185 and the Science
and Technology Center program of the National Science Foundation
under Agreement No. CHE-9876674. The U.S. Government has certain
rights in the invention.
Claims
1. A polymeric electrolyte membrane, comprising: a polymerized 100%
solids liquid precursor material, wherein prior to polymerization
the 100% solids liquid precursor material is a liquid at about 40
degrees Celsius.
2. The polymeric electrolyte membrane of claim 1, wherein the
polymeric electrolyte membrane has an equivalent weight, and
wherein the equivalent weight is selected from the group consisting
of an equivalent weight less than about 1500 and greater than about
1000, an equivalent weight less than about 1000 and greater than
about 800, an equivalent weight less than about 800 and greater
than about 500, and an equivalent weight less than about 500.
3. The polymeric electrolyte membrane of claim 1, wherein the 100%
solids liquid precursor material comprises a material selected from
the group consisting of a proton conductive material, a precursor
to a proton conductive material, and combinations thereof.
4. The polymeric electrolyte membrane of claim 1, wherein the 100%
solids liquid precursor material comprises a material selected from
the group consisting of a monomer, an oligomer, a macromonomer, an
ionomer, and combinations thereof.
5. The polymeric electrolyte membrane of claim 4, wherein at least
one of the monomer, the oligomer, the macromonomer, and the ionomer
comprises a functionalized perfluoropolyether (PFPE) material.
6. The polymeric electrolyte membrane of claim 5, wherein the
functionalized perfluoropolyether (PFPE) material comprises a
backbone structure selected from the group consisting of:
##STR00026## wherein X comprises an endcapping group, and n is an
integer from 1 to 100.
7. The polymeric electrolyte membrane of claim 5, wherein the
functionalized PFPE material is selected from the group consisting
of: ##STR00027## wherein R is selected from the group consisting of
alkyl, substituted alkyl, aryl, and substituted aryl, and wherein m
and n are each independently integers from 1 to 100.
8. The polymeric electrolyte membrane of claim 4, wherein the
ionomer is selected from the group consisting of a sulfonic acid
material, a derivative of a sulfonic acid material, and a
phosphoric acid material.
9. The polymeric electrolyte membrane of claim 8, wherein the
derivative of a sulfonic acid material comprises a material
selected from the group consisting of: ##STR00028## wherein: Y is
selected from the group consisting of --SO.sub.2F and --SO.sub.3H;
R.sub.1 is selected from the group consisting of alkyl, substituted
alkyl, hydroxyl, alkoxyl; fluoroalkenyl, cyano, and nitro; X.sub.1
is selected from the group consisting of a bond, O, S, SO,
SO.sub.2, CO, NR.sub.2, and R.sub.3; X.sub.2 is selected from the
group consisting of O, S, and NR.sub.2, X comprises an endcapping
group; and wherein: R.sub.2 is selected from the group consisting
of hydrogen, alkyl, substituted alkyl, aryl, and substituted aryl;
and R.sub.3 is selected from the group consisting of alkylene,
substituted alkylene, aryl, and unsubstituted aryl; Ar is selected
from the group consisting of aryl and substituted aryl; B is
1,2-perfluorocyclobutylene; t is an integer from 1 to 3; m is an
integer from 0 to 1000; p is an integer from 1 to 1000; and q is an
integer from 1 to 5.
10. The polymeric electrolyte membrane of claim 1, wherein the 100%
solids liquid precursor material comprises a crosslinkable
material.
11. A polymeric electrolyte membrane, comprising a fluoropolymer
membrane having an equivalent weight of less than 850.
12. The polymeric electrolyte membrane of claim 11, wherein the
membrane has a conductivity of between about 0.085 S/cm and about
0.14 S/cm over a temperature range of between about 25 degrees
Celsius and about 80 degrees Celsius in hydrated form.
13. The polymeric electrolyte membrane of claim 11, wherein the
equivalent weight is less than 800.
14. The polymeric electrolyte membrane of claim 11, wherein the
equivalent weight is less than 660.
15. The polymeric electrolyte membrane of claim 14, wherein the
membrane has a conductivity of between about 0.13 S/cm and about
0.26 S/cm over a temperature range of between about 20 degrees
Celsius and about 80 degrees Celsius when fully hydrated.
16. The polymeric electrolyte membrane of claim 11, wherein the
equivalent weight is less than 550.
17. The polymeric electrolyte membrane of claim 16, wherein the
membrane has a conductivity of between about 0.25 S/cm and about
0.45 S/cm over a temperature range of between about 20 degrees
Celsius and about 80 degrees Celsius when fully hydrated.
18. The polymeric electrolyte membrane of claim 11, wherein the
fluorinated membrane comprises a crosslinkable material.
19. A membrane, comprising: a polymerized 100% solids liquid
precursor material comprising greater than about 50% by weight of a
sulfonic acid precursor and less than about 50% by weight of a
fluoropolymer, wherein the membrane has a conductivity of greater
than about 0.14 S/cm when fully hydrated.
20. The membrane of claim 19, wherein the membrane comprises a
crosslinkable material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/040,317, filed Jan. 21, 2005, which is based on and
claims the benefit of U.S. Provisional Patent Application Ser. No.
60/538,706, filed Jan. 23, 2004, and U.S. Provisional Patent
Application Ser. No. 60/538,878, filed Jan. 23, 2004, the contents
of all of which are incorporated herein by reference in their
entirety.
TECHNICAL FIELD
[0003] The presently disclosed subject matter relates to liquid
materials for use in electrochemical cells.
ABBREVIATIONS
[0004] AC=alternating current [0005] Ar=Argon [0006] .degree.
C.=degrees Celsius [0007] cm=centimeter [0008] CSM=cure site
monomer [0009] g=grams [0010] h=hours [0011]
HMDS=hexamethyldisilazane [0012] IL=imprint lithography [0013]
MCP=microcontact printing [0014] Me=methyl [0015] MEA=membrane
electrode assembly [0016] MEMS=micro-electro-mechanical system
[0017] MeOH=methanol [0018] MIMIC=micro-molding in capillaries
[0019] mL=milliliters [0020] mm=millimeters [0021] mmol=millimoles
[0022] M.sub.n=number-average molar mass [0023] m.p.=melting point
[0024] mW=milliwatts [0025] NCM=nano-contact molding [0026]
NIL=nanoimprint lithography [0027] nm=nanometers [0028]
Pd=palladium [0029] PDMS=polydimethylsiloxane [0030] PEM=proton
exchange membrane [0031] PFPE=perfluoropolyether [0032]
PSEPVE=perfluoro-2-(2-fluorosulfonylethoxy)propyl vinyl ether
[0033] PTFE=polytetrafluoroethylene [0034] SAMIM=solvent-assisted
micro-molding [0035] SEM=scanning electron microscopy [0036]
Si=silicon [0037] TFE=tetrafluoroethylene [0038] .mu.m=micrometers
[0039] UV=ultraviolet [0040] W=watts [0041]
ZDOL=poly(tetrafluoroethylene oxide-co-difluoromethylene
oxide).alpha.,.omega. diol
BACKGROUND
[0042] Fuel cells are a safe, environmentally friendly source of
electric energy for portable devices, vehicles (including hybrid
vehicles), generators, and aerospace and military applications. The
current technology of fuel cells, however, has not made a
significant impact on the mainstream market due to cost, size, and
the lack of an immediate need to replace current power sources,
such as batteries and gasoline- or diesel-powered internal
combustion engines. The long-term need to find alternative power
sources has become increasingly evident, however. For example, the
byproducts of gasoline- and diesel-powered internal combustion
engines are environmentally harmful. In contrast, the byproducts of
fuel cells are clean, and in some cases, comprise only water.
[0043] Further, with portable electronic devices, such as cell
phones, laptops, and handheld personal organizers becoming smaller,
the need for smaller power sources, such as micro fuel cells,
becomes evident. Present fuel cell technology, however, typically
requires large fuel cell stacks comprising high-cost flat proton
exchange membranes (PEMs).
[0044] Additionally, consumer products require power sources that
operate for an extended period of time without the need for
recharging. Micro fuel cells typically provide a longer lasting
energy output with one cartridge of fuel. For example, the chemical
fuels used in micro fuel cells promise to power devices up to ten
times as long as batteries on a single charge. Further, once the
energy source becomes low, the energy level can be restored by
merely replacing the fuel cartridge.
[0045] Most fuel cells employ a copolymer of tetrafluoroethylene
(TFE) and a perfluorinated monomer comprising sulfonic acid groups,
such as perfluorosulfonyl fluoride ethoxy propyl vinyl ether
(PSEPVE). One such copolymer is available as NAFION.RTM. (E. I.
duPont de Nemours and Co., Wilmington, Del., United States of
America), or a similar commercially available material. These
materials often are provided as a membrane in final form, e.g., a
non-thermoplastic form having a flat rectangular or square
geometry, for subsequent use. If the membrane is flat and smooth,
i.e., non-patterned, the catalyst layer also must be flat. Further,
such membranes typically must be of at least a certain minimum
thickness to be handleable. Additionally, the power density or
conductivity is usually directly proportional to the membrane
thickness; that is, the thicker the membrane, the lower the power
density.
[0046] Additionally, Lu et al., Electrochimica Acta, 49, 821-828
(2003) have described silicon-based materials for use in a micro
direct methanol fuel cell. Silicon-based micro direct fuel cells
are rigid, brittle devices that typically are expensive and time
consuming to manufacture. Also, incorporating actuating valves in
silicon-based materials is difficult or impossible due to the rigid
nature of the material. Further, the silicon-based micro direct
methanol fuel cell described by Lu et al. has a ratio of active
area versus macroscopic area equal to about one.
[0047] Also, in currently available fuel cell technologies it is
imperative to have good contact between the electrode, proton
exchange membrane (PEM), and catalyst. High power densities rely on
conformal contact between the electrode, the catalyst, and the PEM.
Much research has been invested in developing new PEMs and new
catalysts, but little has been investigated in terms of a new
catalyst ink composition. Conventional catalyst inks or tie layers
typically consist of a catalyst such as platinum, an electrode
material such as carbon black, and a dispersion of NAFION.RTM.,
water, and alcohol.
[0048] Further, PEMs currently available in the art consist of one
equivalent weight (EW), which gives rise to a trade-off between
power density and methanol permeability.
[0049] Thus, there is a need in the art for an improved
electrochemical cell, in particular a micro fuel cell that is
capable of providing power to small, portable electronic devices,
as well as a need for improved electrochemical cell components.
SUMMARY
[0050] The presently disclosed subject matter describes liquid
materials for use in an electrochemical cell, such a fuel cell, a
chlor-alkali cell, a battery, and the like. Accordingly, in some
embodiments, the presently disclosed subject matter provides a
composition for a polymeric electrolyte and a method for preparing
a polymeric electrolyte. In some embodiments, the method comprises:
(a) providing a 100% solids liquid precursor material, wherein the
100% solids liquid precursor material comprises from about 70% by
weight to about 100% by weight of polymerizable materials and (b)
treating the liquid precursor material to form a polymeric
electrolyte.
[0051] In some embodiments, the 100% solids liquid precursor
material comprises a material selected from the group consisting of
a proton conductive material, a precursor to a proton conductive
material, and combinations thereof. In some embodiments, the 100%
solids liquid precursor material comprises a material selected from
the group consisting of a monomer, an oligomer, a macromonomer, an
ionomer, and combinations thereof. In some embodiments, at least
one of the monomer, the oligomer, the macromonomer, and the ionomer
comprises a functionalized perfluoropolyether (PFPE) material.
[0052] In some embodiments, the functionalized perfluoropolyether
(PFPE) material comprises a backbone structure selected from the
group consisting of:
##STR00001##
wherein X is present or absent, and when present comprises an
endcapping group, and n is an integer from 1 to 100. Thus, in some
embodiments, the functionalized PFPE material is selected from the
group consisting of:
##STR00002##
wherein R is selected from the group consisting of alkyl,
substituted alkyl, aryl, and substituted aryl; and wherein m and n
are each independently integers from 1 to 100.
[0053] In some embodiments, the ionomer is selected from the group
consisting of a sulfonic acid material and a phosphoric acid
material. In some embodiments, the sulfonic acid material comprises
a derivative of a sulfonic acid material. In some embodiments, the
derivative of a sulfonic acid material comprises a material
comprising a perfluoro-2-(2-fluorosulfonylethoxy)propyl vinyl ether
(PSEPVE) of the following formula:
##STR00003##
wherein q is an integer from 1 to 5.
[0054] In some embodiments, the derivative of a sulfonic acid
material comprises a material selected from the group consisting
of:
##STR00004##
wherein:
[0055] Y is selected from the group consisting of --SO.sub.2F and
--SO.sub.3H;
[0056] R.sub.1 is selected from the group consisting of alkyl,
substituted alkyl, hydroxyl, alkoxyl; fluoroalkenyl, cyano, and
nitro;
[0057] X.sub.1 is selected from the group consisting of a bond, O,
S, SO, SO.sub.2, CO, NR.sub.2, and R.sub.3;
[0058] X.sub.2 is selected from the group consisting of O, S, and
NR.sub.2,
[0059] wherein: [0060] R.sub.2 is selected from the group
consisting of hydrogen, alkyl, substituted alkyl, aryl, and
substituted aryl; and [0061] R.sub.3 is selected from the group
consisting of alkylene, substituted alkylene, aryl, and
unsubstituted aryl;
[0062] Ar is selected from the group consisting of aryl and
substituted aryl;
[0063] B is 1,2-perfluorocyclobutylene;
[0064] t is an integer from 1 to 3;
[0065] m is an integer from 0 to 1000;
[0066] p is an integer from 1 to 1000; and
[0067] q is an integer from 1 to 5.
[0068] Thus, in some embodiments, the presently disclosed subject
matter provides a polymeric electrolyte comprising a 100% solids
liquid precursor material, wherein the 100% solids liquid precursor
material comprises from about 70% by weight to about 100% by weight
polymerizable materials.
[0069] In some embodiments, the presently disclosed subject matter
provides a method for preparing a patterned polymeric electrolyte,
the method comprising: [0070] (a) contacting a liquid precursor
material with a patterned substrate, wherein the patterned
substrate comprises a predetermined geometry and a macroscopic
surface area; and [0071] (b) treating the liquid precursor material
to form a patterned polymeric electrolyte.
[0072] In some embodiments, the liquid precursor material comprises
a material selected from the group consisting of a proton
conducting material, a precursor to a proton conducting material,
and combinations thereof. In some embodiments, the patterned
polymeric electrolyte has a surface area greater than the
macroscopic surface area of the patterned substrate.
[0073] In some embodiments, the presently disclosed subject matter
provides a method for preparing a polymeric electrolyte comprising
a plurality of equivalent weights, the method comprising: [0074]
(a) applying a first liquid precursor material having a first
equivalent weight to a substrate; [0075] (b) treating the first
liquid precursor material to form a first layer of treated liquid
precursor material on the substrate; [0076] (c) applying a second
liquid precursor material having a second equivalent weight to the
first layer of treated liquid precursor material on the substrate;
and [0077] (d) treating the second liquid precursor material to
form to form a polymeric electrolyte comprising a plurality of
equivalent weights.
[0078] In some embodiments, the method comprises repeating steps
(c) through (d) with a predetermined plurality of liquid precursor
materials comprising a plurality of equivalent weights to form a
polymeric electrolyte comprising a plurality of equivalent
weights.
[0079] In some embodiments, the first liquid precursor material,
the second liquid precursor material, and the plurality of liquid
precursor materials are selected from the group consisting of a
proton conducting material, a precursor to a proton conducting
material, and combinations thereof. In some embodiments, the first
equivalent weight is greater than the second equivalent weight. In
some embodiments, the second equivalent weight is greater than the
plurality of equivalents weights. Thus, a gradient of equivalent
weights is provided along the cross section of the polymeric
electrolyte.
[0080] The presently disclosed subject matter also provides a
method for forming a membrane electrode assembly (MEA). In some
embodiments, the method for forming a membrane electrode assembly
(MEA) comprises: [0081] (a) providing a patterned proton exchange
membrane; [0082] (b) providing a first catalyst material and a
second catalyst material; [0083] (c) providing a first electrode
material and a second electrode material; and [0084] (d)
operationally positioning the proton exchange membrane, the first
and the second catalyst material, and the first and the second
electrode material in conductive communication to form a membrane
electrode assembly.
[0085] In some embodiments, at least one of the first catalyst
material and the second catalyst material comprises a processible
catalyst ink composition. In some embodiments, the processible
catalyst ink composition comprises a liquid precursor material. In
some embodiments, the processible catalyst ink composition is
conformally applied to either or both of a proton exchange membrane
and an electrode material.
[0086] In some embodiments, the presently disclosed method for
forming a membrane electrode assembly comprises: [0087] (a)
providing a first electrode material; [0088] (b) providing a second
electrode material; [0089] (c) positioning the first electrode
material and the second electrode material in a spatial arrangement
such that a gap is formed between the first electrode material and
the second electrode material; [0090] (d) deposing a liquid
precursor material in the gap between the first electrode material
and the second electrode material; and [0091] (e) treating the
liquid precursor material to form a membrane electrode
assembly.
[0092] In some embodiments, the liquid precursor material is
selected from the group consisting of a proton conducting material,
a precursor to a proton conducting material, and combinations
thereof.
[0093] The presently disclosed subject matter also provides a
method for forming an electrochemical cell. In some embodiments,
the method comprises: [0094] (a) providing at least one layer of a
perfluoropolyether (PFPE) material comprising at least one
microfluidic channel; [0095] (b) providing a first electrode
material and a second electrode material, [0096] (c) providing a
first catalyst material and a second catalyst material; [0097] (d)
providing a proton exchange membrane; and [0098] (e) operationally
positioning the at least one layer of a PFPE material, the first
electrode material, the second electrode material, the first
catalyst material, the second catalyst material, and the proton
exchange membrane to form the electrochemical cell.
[0099] Further, in some embodiments, the presently disclosed
subject matter provides a method for operating an electrochemical
cell. Accordingly, the presently disclosed electrochemical cells
can be used to operate portable electronic devices, such as but not
limited to a portable electrical generator, a portable appliance, a
power tool, an electronic device, such as a consumer electronic
device and a military electronic device, a roadway or traffic sign,
a backup power supply, and a personal vehicle, such as an
automobile.
[0100] Accordingly, it is an object of the presently disclosed
subject matter to provide a novel liquid material for use in
electrochemical cells. This and other objects are achieved in whole
or in part by the presently disclosed subject matter.
[0101] An object of the presently disclosed subject matter having
been stated hereinabove, other aspects and objects will become
evident as the description proceeds when taken in connection with
the accompanying Drawings and Examples as best described herein
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0102] FIGS. 1A and 1B provide a schematic representation of an
embodiment of the presently disclosed method for preparing a proton
exchange membrane.
[0103] FIG. 1A is a schematic diagram of a peg mold that can be
interdigitated and can be used as a mold, e.g., a patterned
substrate, for forming a patterned proton exchange membrane of the
presently disclosed subject matter.
[0104] FIG. 1B is a schematic representation of a proton exchange
membrane prepared from the interdigitated peg mold provided in FIG.
1A.
[0105] FIGS. 2A and 2B are scanning electron micrographs of a
proton exchange membrane (PEM) comprising a shark-skin pattern
prepared by the presently disclosed method.
[0106] FIG. 2A is a scanning electron micrograph of the presently
disclosed PEM comprising a shark-skin pattern before
hydrolysis.
[0107] FIG. 2B is a scanning electron micrograph of the presently
disclosed PEM comprising a shark-skin pattern after hydrolysis.
[0108] FIGS. 3A and 3B are schematic diagrams of embodiments of the
presently disclosed method for using a patterned electrode pair as
a mold for forming a proton exchange membrane of the presently
disclosed subject matter.
[0109] FIG. 4 is a plot showing the conductivity of an embodiment
of a presently disclosed proton exchange membrane with an
equivalent weight of 1900 under fully hydrated conditions.
[0110] FIG. 5 is a plot showing the conductivity of an embodiment
of a presently disclosed proton exchange membrane with an
equivalent weight of 1250 under fully hydrated conditions.
[0111] FIG. 6 is a plot showing the conductivity of an embodiment
of a presently disclosed proton exchange membrane with an
equivalent weight of 850 under fully hydrated conditions.
[0112] FIG. 7 is a plot showing the conductivity of an embodiment
of a presently disclosed proton exchange membrane with an
equivalent weight of 660 under fully hydrated conditions.
[0113] FIG. 8 is a plot showing the conductivity of an embodiment
of a presently disclosed proton exchange membrane with an
equivalent weight of 550 under fully hydrated conditions.
[0114] FIGS. 9A and 9B are schematic diagrams of an embodiment of a
presently disclosed proton exchange membrane (PEM) comprising
liquid materials of varying equivalent weights, which provide a
gradient of equivalent weights along the cross section of the
PEM.
[0115] FIGS. 10A and 10B are schematic representations of an
embodiment of the presently disclosed method for forming a catalyst
ink tie layer.
[0116] FIG. 10A is a schematic representation of an embodiment of
the presently disclosed method for forming a catalyst ink tie layer
on a planar electrode material.
[0117] FIG. 10B is a schematic representation of an embodiment of
the presently disclosed method for forming a catalyst ink tie layer
on a patterned proton exchange membrane.
[0118] FIGS. 11A-11C are schematic representations of embodiments
of the presently disclosed method for coating a patterned proton
exchange membrane with a processible catalyst ink composition and
an electrode material.
[0119] FIG. 11A is a schematic representation of an embodiment of
the presently disclosed method for conformally coating a patterned
PEM with a processible catalyst ink composition followed by coating
with an electrode material to form a planarized surface of
electrode material.
[0120] FIG. 11B is a schematic representation of an embodiment of
the presently disclosed method for conformally coating a patterned
PEM with a processible catalyst ink composition followed by
conformally coating with an electrode material to form a conformal
surface of electrode material.
[0121] FIG. 11C is a schematic representation of an embodiment of
the presently disclosed method for conformally coating a patterned
PEM with a processible catalyst ink composition to form a
planarized surface of the processible catalyst ink composition
followed by conformally coating with an electrode material to form
a planarized surface of electrode material.
[0122] FIGS. 12A and 12B are scanning electron micrographs of
embodiments of the presently disclosed patterned PEMs conformally
coated with a catalyst by using an electrospray method.
[0123] FIG. 13 is a scanning electron micrograph of an embodiment
of a presently disclosed patterned PEM conformally coated with a
catalyst by using a vapor-deposition method.
[0124] FIGS. 14A and 14B are schematic representations of
embodiments of the presently disclosed membrane electrode
assemblies.
[0125] FIG. 14A is a schematic representation of an embodiment of a
presently disclosed three dimensional membrane electrode assembly
(MEA) with conformal catalyst loading prepared from a three
dimensional proton exchange membrane (PEM).
[0126] FIG. 14B is a schematic representation of an embodiment of a
presently disclosed two dimensional electrode with non-conformal
catalyst loading.
[0127] FIG. 15 is a schematic representation of an embodiment of a
presently disclosed three dimensional membrane electrode assembly
(MEA) prepared from a three dimensional proton exchange membrane
(PEM) and a three dimensional electrode with conformal catalyst
loadings.
[0128] FIG. 16 depicts a lithography method used to pattern an
electrode material, such as carbon black.
[0129] FIGS. 17A and 17B are schematic representations of an
embodiment of a presently disclosed microfluidic fuel cell.
[0130] FIG. 17A is a cross-sectional view of an embodiment of the
presently disclosed fuel cell.
[0131] FIG. 17B is a plan view of an embodiment of the presently
disclosed fuel cell.
[0132] FIGS. 18A-18C are a series of schematic end views depicting
the formation of a patterned layer of perfluoropolyether (PFPE)
material comprising microfluidic channels in accordance with the
presently disclosed subject matter.
DETAILED DESCRIPTION
[0133] The presently disclosed subject matter describes the use of
liquid materials in electrochemical cells, such as fuel cells,
chlor-alkali cells, and batteries. Accordingly, the presently
disclosed subject matter describes liquid materials for preparing a
polymeric electrolyte, such as a proton exchange membrane, for use
in an electrochemical cell, including proton exchange membranes
comprising a gradient of equivalent weights. The presently
disclosed subject matter also describes improved electrochemical
cell technologies incorporating patterned membranes and electrodes.
Further, the presently disclosed subject matter describes liquid
materials for preparing a membrane electrode assembly in which an
enhanced conformal contact between the electrochemical cell
components is demonstrated. Thus, the presently disclosed subject
matter also describes liquid materials for preparing processible
liquid catalyst ink compositions for use in electrochemical cells.
Additionally, the presently disclosed subject matter describes a
photocurable perfluoropolyether for fabricating a microfluidic
device for use in electrochemical cells, such as micro direct
methanol and hydrogen fuel cells. The presently disclosed subject
matter also describes a method for operating an electrochemical
cell.
[0134] The presently disclosed subject matter will now be described
more fully hereinafter with reference to the accompanying Examples
and Drawings, in which representative embodiments are shown. The
presently disclosed subject matter can, however, be embodied in
different forms and should not be construed as limited to the
embodiments set forth herein. Rather, these embodiments are
provided so that this disclosure will be thorough and complete, and
will fully convey the scope of the embodiments to those skilled in
the art.
[0135] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this presently described subject
matter belongs. All publications, patent applications, patents, and
other references mentioned herein are incorporated by reference in
their entirety.
[0136] Throughout the specification and claims, a given chemical
formula or name shall encompass all optical and stereoisomers, as
well as racemic mixtures where such isomers and mixtures exist.
I. Liquid Precursor Materials
[0137] The presently disclosed subject matter describes liquid,
pourable precursor materials that are processible, i.e., can be
formed into different shapes or can conform to different shapes,
and can be used to prepare a high surface area PEM. In some
embodiments, as provided in more detail herein below, the liquid
precursor materials can be patterned by a patterned substrate,
e.g., a mold, and treated (such as but not limited to cured into
solids) to form a patterned PEM.
[0138] As used herein, the term "100% solids liquid precursor
material" refers to a liquid polymeric precursor material in which
essentially all of the components are polymerized when treated,
e.g., cured. Thus, in some embodiments, a "100% solids liquid
precursor material" is essentially free of non-polymerizable
materials. This property of a "100% solids liquid precursor
material" distinguishes this material from a solution or dispersion
of a liquid precursor material known in the art, in which the
liquid material can comprise between about 80% by weight to about
98% by weight of solvent or other non-polymerizable material. For
example, one perfluorinated liquid composition commonly used in the
art to prepare ion exchange membranes comprises from about 2% by
weight to about 18% by weight of the polymeric material and about
82% by weight to about 98% by weight of solvent, which is
non-polymerizable. See U.S. Pat. No. 4,433,082 to Grot, which is
incorporated herein by reference in its entirety.
[0139] Accordingly, in some embodiments, the 100% solids liquid
material comprises from about 70% by weight to about 75% by weight
of polymerizable material. In some embodiments, the 100% solids
liquid material comprises from about 75% by weight to about 80% by
weight of polymerizable material. In some embodiments, the 100%
solids liquid material comprises from about 80% by weight to about
85% by weight of polymerizable material. In some embodiments, the
100% solids liquid material comprises from about 85% by weight to
about 90% by weight of polymerizable material. In some embodiments,
the 100% solids liquid material comprises from about 90% by weight
to about 95% by weight of polymerizable material. In some
embodiments, the 100% solids liquid material comprises from about
95% by weight to about 98% by weight of polymerizable material. In
some embodiments, the 100% solids liquid material comprises from
about 98% by weight to about 100% by weight of polymerizable
material. Thus, in some embodiments, the 100% solids liquid
material comprises from about 70% by weight to about 100% by weight
of polymerizable material.
[0140] Further, in some embodiments, the liquid precursor material
comprises a fluorinated system. In some embodiments, the
fluorinated system comprises a perfluoropolyether (PFPE) material.
In some embodiments, the PFPE material comprises a
vinyl-functionalized material, including, but not limited to, a
vinyl methacrylate.
[0141] In some embodiments, the liquid precursor material comprises
species, including vinyl acids, such as
perfluoro-2-(2-fluorosulfonylethoxy)propyl vinyl ether (PSEPVE),
that enhance proton conductivity. As used herein, the term "proton
conductive material" refers to a material within which a proton can
be transported. For example, in some embodiments, a proton is
transported from an anode through a proton conductive material to a
cathode. Proton conductivity can be measured, for example, by
alternating current (AC) impedance methods known in the art, and is
typically reported in units of Siemens/cm (S/cm). Such proton
conductive materials typically have a proton conductivity of
greater than about 0.01 S/cm.
[0142] In some embodiments, the liquid precursor material comprises
other species that regulate the physical properties of the
material, including modulus, permeability of methanol and other
liquids, wetting, tensile strength, toughness, flexibility, and
thermal properties, among others. For exemplary synthesis methods
for preparing the liquid precursor materials disclosed herein see
Examples 1-6.
[0143] Thus, in some embodiments, the method for preparing a
polymeric electrolyte comprises: [0144] (a) providing a 100% solids
liquid precursor material, wherein the 100% solids liquid precursor
comprises from about 70% by weight to about 100% by weight
polymerizable materials; and [0145] (b) treating the 100% solids
liquid precursor material to form a polymeric electrolyte.
[0146] In some embodiments, the 100% solids liquid precursor
material comprises a material selected from the group consisting of
a proton conductive material, a precursor to a proton conductive
material, and combinations thereof.
[0147] In some embodiments, the 100% solids liquid precursor
material comprises a material selected from the group consisting of
a monomer, an oligomer, a macromonomer, an ionomer, and
combinations thereof.
[0148] As used herein, the term "monomer" refers to a molecule that
can undergo polymerization, thereby contributing constitutional
units, i.e., an atom, a group of atoms, and/or groups of atoms, to
the essential structure of a macromolecule or polymer. The term
"oligomer" refers to a molecule of intermediate relative molecular
mass, the structure of which comprises a small plurality of
constitutional units derived from molecules of lower relative
molecular mass. The term "macromonomer" refers to a macromolecule
or polymer that comprises a reactive end group which enables the
macromonomer to act as a monomer and contribute a monomeric unit to
a chain of the final macromolecule or polymer. The term "ionomer"
refers to a macromolecule in which a plurality of the
constitutional units comprise ionizable groups, ionic groups, and
combinations thereof.
[0149] In some embodiments, at least one of the monomer, the
oligomer, the macromonomer, and the ionomer comprises a
functionalized perfluoropolyether (PFPE) material. In some
embodiments, the functionalized perfluoropolyether (PFPE) material
comprises a backbone structure selected from the group consisting
of:
##STR00005##
wherein X is present or absent, and when present comprises an
endcapping group, and n is an integer from 1 to 100.
[0150] In some embodiments, the functionalized PFPE material is
selected from the group consisting of:
##STR00006##
wherein R is selected from the group consisting of alkyl,
substituted alkyl, aryl, and substituted aryl; and wherein m and n
are each independently integers from 1 to 100.
[0151] In some embodiments, the functionalized PFPE material has
the following structure:
##STR00007##
[0152] In some embodiments, the ionomer is selected from the group
consisting of a sulfonic acid material and a phosphoric acid
material. In some embodiments, the ionomer comprises sulfonic acid
groups, derivatives of sulfonic acid groups, carboxylic acid
groups, derivatives of carboxylic acid groups, phosphonic acid
groups, derivatives of phosphonic acid groups, phosphoric acid
groups, derivatives of phosphoric acid groups, and/or combinations
thereof.
[0153] In some embodiments, the sulfonic acid material comprises a
derivative of a sulfonic acid material. In some embodiments, the
sulfonic acid material comprises a material comprising a
perfluoro-2-(2-fluorosulfonylethoxy)propyl vinyl ether (PSEPVE) of
the following formula:
##STR00008##
wherein q is an integer from 1 to 5.
[0154] In some embodiments, the derivative of a sulfonic acid
material comprises a material selected from the group consisting
of:
##STR00009##
wherein:
[0155] Y is selected from the group consisting of --SO.sub.2F and
--SO.sub.3H;
[0156] R.sub.1 is selected from the group consisting of alkyl,
substituted alkyl, hydroxyl, alkoxyl; fluoroalkenyl, cyano, and
nitro;
[0157] X.sub.1 is selected from the group consisting of a bond, O,
S, SO, SO.sub.2, CO, NR.sub.2, and R.sub.3;
[0158] X.sub.2 is selected from the group consisting of O, S, and
NR.sub.2,
[0159] wherein: [0160] R.sub.2 is selected from the group
consisting of hydrogen, alkyl, substituted alkyl, aryl, and
substituted aryl; and [0161] R.sub.3 is selected from the group
consisting of alkylene, substituted alkylene, aryl, and
unsubstituted aryl;
[0162] Ar is selected from the group consisting of aryl and
substituted aryl;
[0163] B is 1,2-perfluorocyclobutylene;
[0164] t is an integer from 1 to 3;
[0165] m is an integer from 0 to 1000;
[0166] p is an integer from 1 to 1000; and
[0167] q is an integer from 1 to 5.
[0168] In some embodiments, Y is --SO.sub.2F. In some embodiments,
Y is --SO.sub.3H.
[0169] Accordingly, in some embodiments, the ionomer can comprise a
commercially available acidic material, such as NAFION.RTM. (E. I.
duPont de Nemours and Co., Wilmington, Del., United States of
America) or a similar material, including, but not limited to
XUS.RTM. (Dow Chemical Company, Midland, Mich., United States of
America), ACIPLEX.RTM. (Asahi Chemical Industry Co., Tokyo, Japan),
BAM3G.RTM. (Ballard Advanced Materials, Burnaby, British Columbia,
Canada), or acid functionalized perfluorocyclobutane polymers as
described in U.S. Pat. No. 6,559,237 to Mao et al. and acid
functionalized fluoropolymers as described in U.S. Pat. No.
6,833,412 to Hamrock et al., each of which is incorporated herein
by reference in its entirety.
[0170] As used herein the term "alkyl" refers to C.sub.1-20
inclusive, linear (i.e., "straight-chain"), branched, or cyclic,
saturated or at least partially and in some cases fully unsaturated
(i.e., alkenyl and alkynyl)hydrocarbon chains, including for
example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl,
tert-butyl, pentyl, hexyl, octyl, ethenyl, propenyl, butenyl,
pentenyl, hexenyl, octenyl, butadienyl, propynyl, butynyl,
pentynyl, hexynyl, heptynyl, and allenyl groups. "Branched" refers
to an alkyl group in which a lower alkyl group, such as methyl,
ethyl or propyl, is attached to a linear alkyl chain. "Lower alkyl"
refers to an alkyl group having 1 to about 8 carbon atoms (i.e., a
C.sub.1-8 alkyl), e.g., 1, 2, 3, 4, 5, 6, 7, or 8 carbon atoms.
"Higher alkyl" refers to an alkyl group having about 10 to about 20
carbon atoms, e.g., 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or
carbon atoms. In certain embodiments, "alkyl" refers, in
particular, to C.sub.1-8 straight-chain alkyls. In other
embodiments, "alkyl" refers, in particular, to C.sub.1-8
branched-chain alkyls.
[0171] Alkyl groups can optionally be substituted with one or more
alkyl group substituents, which can be the same or different. The
term "alkyl group substituent" includes but is not limited to
alkyl, halo, arylamino, acyl, hydroxyl, aryloxyl, alkoxyl,
alkylthio, arylthio, aralkyloxyl, aralkylthio, carboxyl,
alkoxycarbonyl, oxo, and cycloalkyl. There can be optionally
inserted along the alkyl chain one or more oxygen, sulfur or
substituted or unsubstituted nitrogen atoms, wherein the nitrogen
substituent is hydrogen, lower alkyl (also referred to herein as
"alkylaminoalkyl"), or aryl.
[0172] "Cyclic" and "cycloalkyl" refer to a non-aromatic mono- or
multicyclic ring system of about 3 to about 10 carbon atoms, e.g.,
3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms. The cycloalkyl group can
be optionally partially unsaturated. The cycloalkyl group can be
also optionally substituted with an alkyl group substituent as
defined herein, oxo, and/or alkylene. There can be optionally
inserted along the cyclic alkyl chain one or more oxygen, sulfur or
substituted or unsubstituted nitrogen atoms, wherein the nitrogen
substituent is hydrogen, lower alkyl, or aryl, thus providing a
heterocyclic group. Representative monocyclic cycloalkyl rings
include cyclopentyl, cyclohexyl, and cycloheptyl. Multicyclic
cycloalkyl rings include adamantyl, octahydronaphthyl, decalin,
camphor, camphane, and noradamantyl.
[0173] "Alkylene" refers to a straight or branched bivalent
aliphatic hydrocarbon group having from 1 to about 20 carbon atoms,
e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,
18, 19, or 20 carbon atoms. The alkylene group can be straight,
branched or cyclic. The alkylene group can be also optionally
unsaturated and/or substituted with one or more "alkyl group
substituents." There can be optionally inserted along the alkylene
group one or more oxygen, sulfur or substituted or unsubstituted
nitrogen atoms (also referred to herein as "alkylaminoalkyl"),
wherein the nitrogen substituent is alkyl as previously described.
Exemplary alkylene groups include methylene (--CH.sub.2--);
ethylene (--CH.sub.2--CH.sub.2--); propylene
(--(CH.sub.2).sub.3--); cyclohexylene (--C.sub.6H.sub.10--);
--CH.dbd.CH--CH.dbd.CH--; --CH.dbd.CH--CH.sub.2--;
--(CH.sub.2).sub.q--N(R)--(CH.sub.2).sub.r--, wherein each of q and
r is independently an integer from 0 to about 20, e.g., 0, 1, 2, 3,
4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20,
and R is hydrogen or lower alkyl; methylenedioxyl
(--O--CH.sub.2--O--); and ethylenedioxyl
(--O--(CH.sub.2).sub.2--O--). An alkylene group can have about 2 to
about 3 carbon atoms and can further have 6-20 carbons.
[0174] The term "aryl" is used herein to refer to an aromatic
substituent that can be a single aromatic ring, or multiple
aromatic rings that are fused together, linked covalently, or
linked to a common group such as a methylene or ethylene moiety.
The common linking group also can be a carbonyl as in benzophenone
or oxygen as in diphenylether or nitrogen as in diphenylamine. The
term "aryl" specifically encompasses heterocyclic aromatic
compounds. The aromatic ring(s) can comprise phenyl, naphthyl,
biphenyl, diphenylether, diphenylamine and benzophenone, among
others. In particular embodiments, the term "aryl" means a cyclic
aromatic comprising about 5 to about 10 carbon atoms, e.g., 5, 6,
7, 8, 9, or 10 carbon atoms, and including 5- and 6-membered
hydrocarbon and heterocyclic aromatic rings.
[0175] The aryl group can be optionally substituted with one or
more aryl group substituents which can be the same or different,
where "aryl group substituent" includes alkyl, aryl, aralkyl,
hydroxyl, alkoxyl, aryloxyl, aralkyloxyl, carboxyl, acyl, halo,
nitro, alkoxycarbonyl, aryloxycarbonyl, aralkoxycarbonyl, acyloxyl,
acylamino, aroylamino, carbamoyl, alkylcarbamoyl, dialkylcarbamoyl,
arylthio, alkylthio, alkylene, and --NR'R'', where R' and R'' can
be each independently hydrogen, alkyl, aryl, and aralkyl.
[0176] Specific examples of aryl groups include but are not limited
to cyclopentadienyl, phenyl, furan, thiophene, pyrrole, pyran,
pyridine, imidazole, benzimidazole, isothiazole, isoxazole,
pyrazole, pyrazine, triazine, pyrimidine, quinoline, isoquinoline,
indole, carbazole, and the like.
[0177] The term "arylene" refers to a bivalent group derived from a
monocyclic aromatic hydrocarbon or a polycyclic aromatic
hydrocarbon by removal of a hydrogen atom from two carbon atoms on
the aromatic ring(s). Examples of an "arylene" group include, but
are not limited to, 1,2-phenylene, 1,3-phenylene, and
1,4-phenylene.
[0178] As used herein, the terms "substituted alkyl," "substituted
cycloalkyl," "substituted alkylene," "substituted aryl," and
"substituted arylene" include alkyl, alkylene, and aryl groups, as
defined herein, in which one or more atoms or functional groups of
the alkyl, alkylene, aryl or arylene group are replaced with
another atom or functional group, including for example, halogen,
aryl, alkyl, alkoxyl, hydroxyl, nitro, amino, alkylamino,
dialkylamino, sulfate, and mercapto.
[0179] "Alkoxyl" or "alkoxyalkyl" refer to an alkyl-O-- group
wherein alkyl is as previously described. The term "alkoxyl" as
used herein can refer to C.sub.1-20 inclusive, linear, branched, or
cyclic, saturated or unsaturated oxo-hydrocarbon chains, including,
for example, methoxyl, ethoxyl, propoxyl, isopropoxyl, butoxyl,
t-butoxyl, and pentoxyl.
[0180] The terms "halo", "halide", or "halogen" as used herein
refer to fluoro, chloro, bromo, and iodo groups.
[0181] The term "hydroxyl" refers to the --OH group.
[0182] The term "hydroxyalkyl" refers to an alkyl group substituted
with an --OH group.
[0183] The term "nitro" refers to the --NO.sub.2 group.
[0184] In some embodiments, the treating of the precursor material
comprises a process selected from the group consisting of: (a) a
curing process; (b) a chemical modification process; (c) a network
forming process; and (d) combinations thereof. In some embodiments,
the curing process comprises a process selected from the group
consisting of a thermal process, a photochemical process, and an
irradiation process. In some embodiments, the irradiation process
comprises irradiating the liquid precursor material with radiation,
wherein the radiation is selected from the group consisting of
gamma rays and an electron beam. In some embodiments, the chemical
modification process comprises a crosslinking process. Methods for
the radiolysis of fluoropolymers, including perfluoropolyether
materials, are provided in J. S. Forsythe, et al., Prog. Polym.
Sci., 25, 101-136 (2000), which is incorporated herein by reference
in its entirety.
[0185] Further, Published PCT International Application WO 99/61141
to Mao et al. describes a method of making crosslinked polymers
suitable for use in ion conductive membranes, such as a proton
exchange membrane, by (a) crosslinking a polymer having pendant
acid halide groups with a crosslinker which bonds to two or more
acid halide groups, or (b) crosslinking a polymer having pendant
amide groups with a crosslinker which bonds to two or more amide
groups. Also, Buchi et al., J. Electrochem. Soc., 142 (9), 3004
(1995), discloses proton exchange membranes made by sulfonating a
crosslinked polyolefin-polystyrene copolymer, which is crosslinked
during polymerization by addition of divinyl benzene. U.S. Pat. No.
5,438,082 to Helmer-Metzmann et al. discloses a method of
crosslinking a sulfonated aromatic polyether ketone with a
crosslinker comprising an amine functional group. Further, U.S.
Pat. No. 5,468,574 to Ehrenberg et al. and Published PCT
International Patent Application No. WO 97/19,480 to Graham et al.
disclose that certain sulfonated polymers will form direct bonds
between sulfonate groups upon heating; however, this method appears
to sacrifice sulfonic acid groups thereby resulting in the loss of
acidity in the membrane. The above-mentioned patents, publications,
and published patent applications are incorporated herein by
reference in their entirety.
[0186] Thus, in some embodiments, the presently disclosed subject
matter provides a polymeric electrolyte comprising a 100% solids
liquid precursor material as defined hereinabove, wherein the 100%
solids liquid precursor material comprises from about 70% by weight
to about 100% by weight polymerizable materials.
[0187] In some embodiments, the presently disclosed polymeric
electrolyte has an equivalent weight, wherein the equivalent weight
is selected from the group consisting of an equivalent weight less
than about 1500 and greater than about 1000, an equivalent weight
less than about 1000 and greater than about 800, an equivalent
weight less than about 800 and greater than about 500, and an
equivalent weight below about 500.
[0188] Further, in some embodiments, the presently disclosed
subject matter provides an electrochemical cell comprising the
polymeric electrolyte prepared from a 100% solids liquid precursor.
In some embodiments, the electrochemical cell is selected from the
group consisting of a fuel cell, a chlor-alkali cell, and a
battery.
[0189] Further, NAFION.RTM. and other PEM materials perform best
when relative humidity values are high, for example above about
90%. Incorporation of an alcohol into a NAFION.RTM.-like material
makes the material more hydrophilic, which can result in good
conductivity at lower relative humidities and/or reduced water loss
at higher temperatures. An example is provided in Scheme 11, which
provides a method for polymerizing components of a NAFION.RTM.-like
material with vinyl acetate. Simple hydrolysis reactions convert
the acetate to the alcohol while obtaining a sulfonic acid group on
the proton-conducting compound. Post fluorination on the material
can provide chemical and thermal stability of a perfluorinated
material.
[0190] Another limitation of NAFION.RTM. is its low acid content.
The acid content of NAFION.RTM. can not be much higher than is
currently available in commercial grades since increasing the acid
content (lowering the equivalent weight) by increasing the fraction
of PSEPVE incorporated into the TFE/PSEPVE copolymer leads to
molecular weight reduction because of the propensity of fluorinated
vinyl ethers to undergo .beta.-scission reactions during
polymerization. See Romack, T. J. and DeSimone, J. M.,
Macromolecules, 28, 8429-8431 (1995), which is incorporated by
reference in its entirety. Thus, as the acid content of NAFION.RTM.
is increased, the molecular weight of the polymer decreases and the
mechanical properties are compromised. Such a linear, low molecular
weight, high acid-containing NAFION.RTM.-like material has poor
film forming qualities and becomes water soluble, an unacceptable
property. This limitation in the reaction chemistry used to make
NAFION.RTM. limits commercial suppliers to selling grades of
NAFION.RTM. that do not contain a high enough acid content
necessary for very high proton conductivity. Indeed, the most
widely studied commercial grade of NAFION.RTM. has an equivalent
weight of 1100 with a proton conductivity of only 0.083 S/cm at
room temperature under fully hydrated conditions. See Mauritz, K.
A. and Moore, R. B., Chem. Rev., 104, 4535-4585 (2004), which is
incorporated herein by reference in its entirety. The presently
disclosed materials address these deficiencies and generate new
PEMs that have much higher conductivities, are more thermally
stable, more selective, more mechanically robust, and incorporate a
modular design that will allow for independent control of membrane
properties.
[0191] Without being bound to any one particular theory, it is
believed that the high conductivity in the presently disclosed
materials is due to a fundamentally different proton conduction
mechanism than is operative in NAFION.RTM.. According to most
reports, see, e.g., Mauritz, K. A. and Moore, R. B., Chem. Rev.,
104, 4535-4585 (2004), the morphology of NAFION.RTM. can be
considered as isolated clusters of acid groups embedded in a
Teflon-like matrix. Protons can hop from acid group to acid group
within the clusters, but in order for a proton to macroscopically
transport across the PEM, it must migrate in the form of a
hydronium ion through hydrophilic channels from one acid cluster to
the next. That is, in order for NAFION.RTM. to be highly proton
conductive, the presence of a threshold amount of water is a
requirement. This requirement for NAFION.RTM. to be hydrated in
order for it to be highly proton conductive, see Mauritz, K. A. and
Moore, R. B., Chem. Rev., 104, 4535-4585 (2004), presents a real
implementation barrier for the use of NAFION.RTM.-based fuel cells
at temperatures above the boiling point of water. Again, without
being bound to any one particular theory, it is believed that the
very high acid contents achievable in the presently disclosed
liquid precursors to cross-linked PEMs results in a continuum of
acid groups that are within proton hopping distances of each other.
As such, protons can macroscopically transport through the film
without the required water content associated with commercial
grades of NAFION.RTM. or any other emerging PEM material that has
equivalent weights >550.
[0192] In sum, the presently disclosed materials can be used in
traditional electrochemical cell applications, such as automotive
applications, as well as portable power, for example, for
electronic devices. In some embodiments, the presently disclosed
materials exhibit an improved mechanical stability at elevated
temperatures. In some embodiments, the presently disclosed
materials exhibit a decreased permeability for alkyl alcohols, such
as methanol. In some embodiments, the presently disclosed materials
provide an increased electrochemical cell performance at lower
relative humidity and an increase in the hydrophilicity of the
proton exchange membrane.
II. Method for Preparing a Patterned Proton Exchange Membrane
[0193] In some embodiments, the presently disclosed subject matter
provides a method for preparing a patterned proton exchange
membrane. One such embodiment is provided in FIGS. 1A-1B.
[0194] Referring now to FIG. 1A, a patterned substrate, e.g., mold
100, is provided. Mold 100 can comprise a material selected from
the group consisting of an inorganic material, an organic material,
and combinations thereof. In some embodiments, mold 100 has a
predetermined geometry 102, wherein predetermined geometry 102 has
a macroscopic area 104. For example, as depicted in FIG. 1A,
predetermined geometry 102 comprises a rectangular substrate 106
with a first planar surface 108, wherein first planar surface 108
further comprises a plurality of structural features 110, which are
depicted in FIG. 1A as a plurality of pegs extending from first
planar surface 108.
[0195] Further, as would be appreciated by one of ordinary skill in
the art upon a review of the present disclosure, the plurality of
structural features 110 can take any form, including but not
limited to a peg, a fluted peg, a roll-up cylinder, a pattern, a
wall, and an interdigitated surface (not shown). Accordingly, the
proton exchange membranes made by the presently disclosed method
can be made in various geometries, can have numerous pathways,
and/or can comprise a controlled or a variable surface area.
[0196] In some embodiments, the proton exchange membranes prepared
by the presently disclosed method have a greater "active surface"
area compared to "macroscopic surface" area. Thus, in some
embodiments, predetermined geometry 102 comprises a plurality of
structures 110 having a surface area 112, which is greater than the
macroscopic area 104 of mold 100. In some embodiments, the
plurality of structures 110 has a surface area 112 ranging from at
least about two times to about 100 times the macroscopic surface
area 104 of mold 100. In some embodiments, predetermined geometry
102 comprises a plurality of structures 110 having a surface area
112 at least two times greater than the macroscopic surface 104
area of mold 100. In some embodiments, predetermined geometry 102
comprises a plurality of structures 110 having a surface area 112
at least five times greater than the macroscopic surface area 104
of mold 100. In some embodiments, predetermined geometry 102
comprises a plurality of structures 110 having a surface area 112
at least twenty times greater than the macroscopic surface area 104
of mold 100. In some embodiments, predetermined geometry 102
comprises a plurality of structures 110 having a surface area 112
at least eighty times greater than the macroscopic surface area 104
of mold 100.
[0197] Referring now to FIGS. 1A and 1B, a liquid precursor
material 114 is contacted with mold 100. Liquid precursor material
114 can comprise any of the liquid precursor materials disclosed
hereinabove, that is liquid precursor material can comprise a
proton conducting material, a precursor to a proton conducting
material, and combinations thereof. Liquid precursor material 114
is treated by a treating process T.sub.r to form a treated liquid
precursor material 116 as depicted in FIG. 1B.
[0198] In some embodiments, treating process T.sub.r comprises a
process selected from the group consisting of a curing process, a
chemical modification process, a network forming process, a solvent
evaporation process, and combinations thereof. In some embodiments,
the curing process comprises a process selected from the group
consisting of a thermal process, a photochemical process, and an
irradiation process. Further, in some embodiments, the irradiation
process comprises irradiating the liquid material with radiation,
wherein the radiation is selected from the group selected from
gamma rays and an electron beam. In some embodiments, the chemical
modification process comprises a crosslinking process.
[0199] Referring now to FIG. 1B, treated liquid precursor material
116 is removed from mold 100 to provide a freestanding proton
exchange membrane 118 comprising a plurality of structural features
120, which correspond to the plurality of structural features 110
of mold 100. In some embodiments, the plurality of structures 110
and 120 have a dimension 122 of less than 10 mm. In some
embodiments, the plurality of structures 110 and 120 have a
dimension 122 of less than 1 mm. In some embodiments, the plurality
of structures 110 and 120 have a dimension 122 of less than 100
.mu.m. In some embodiments, the plurality of structures 110 and 120
have a dimension 122 of less than 10 .mu.m. In some embodiments,
the plurality of structures 110 and 120 have a dimension 122 of
less than 1 .mu.m. Said another way, in some embodiments, the
individual structures comprising the plurality of structures 110
and 120 can have a height having a dimension ranging from less than
about 10 mm to less than about 1 .mu.m and/or a width having a
dimension ranging from less than about 10 mm to less than about 1
.mu.m.
[0200] Thus, in some embodiments, the presently disclosed subject
matter provides a method for preparing a patterned polymeric
electrolyte, the method comprising: [0201] (a) contacting a liquid
precursor material with a patterned substrate, wherein the
patterned substrate comprises a predetermined geometry and a
macroscopic surface area; and [0202] (b) treating the liquid
precursor material to form a patterned polymeric electrolyte.
[0203] In some embodiments, the liquid precursor material comprises
a material selected from the group consisting of a proton
conducting material, a precursor to a proton conducting material,
and combinations thereof.
[0204] In some embodiments, the patterned substrate comprises a
material selected from the group consisting of an inorganic
material, an organic material, and combinations thereof.
[0205] In some embodiments, the predetermined geometry comprises a
non-planar geometry. In some embodiments, the non-planar geometry
comprises features having a predetermined dimension selected from
the group consisting of a dimension less than about 10 mm and
greater than about 1 mm, a dimension less than about 1 mm and
greater than about 100 .mu.m, a dimension less than about 100 .mu.m
and greater than 10 .mu.m, a dimension less than about 10 .mu.m and
greater than about 1 .mu.m, and a dimension less than about 1
.mu.m.
[0206] In some embodiments, the predetermined geometry is defined
by one of a catalyst layer and an electrode material comprising a
membrane electrode assembly. In some embodiments, the predetermined
geometry is defined by a membrane electrode assembly. In some
embodiments, the predetermined geometry comprises a structure
selected from the group consisting of a pattern, a peg, a wall, an
interdigitated surface, and a roll-up cylinder.
[0207] In some embodiments, the predetermined geometry comprises a
structure having a surface area greater than the macroscopic
surface area of the patterned substrate. In some embodiments, the
structure has a surface area ranging from at least about two times
to about 100 times the macroscopic surface area of the patterned
substrate.
[0208] In some embodiments, the treating of the liquid precursor
material comprises a process selected from the group consisting of:
(a) a curing process; (b) a chemical modification process; (c) a
network forming process; (d) a solvent evaporation process; and (e)
combinations thereof.
[0209] Thus, in some embodiments, the presently disclosed subject
matter provides a patterned proton exchange membrane prepared by
the presently disclosed method. In some embodiments, the patterned
proton exchange membrane comprises a material having an equivalent
weight, wherein the equivalent weight is selected from the group
consisting of an equivalent weight less than about 1500 and greater
than about 1000, an equivalent weight less than about 1000 and
greater than about 800, an equivalent weight less than about 800
and greater than about 500, and an equivalent weight below about
500.
[0210] In some embodiments, the presently disclosed subject matter
provides an electrochemical cell comprising the presently disclosed
patterned proton exchange membrane. In some embodiments, the
electrochemical cell is selected from the group consisting of a
fuel cell, a chlor-alkali cell, and a battery.
[0211] An example of a proton exchange membrane prepared by the
presently disclosed method is provided in FIGS. 2A and 2B, which
show a scanning electron micrograph of a PEM with a shark-skin
pattern before hydrolysis and a scanning electron micrograph of a
PEM with a shark-skin pattern after hydrolysis, respectively. The
shark-skin pattern was prepared as described in Example 7. The
feature size of the shark-skin pattern, i.e., a structure as
described immediately hereinabove, in this particular example is
about 2 .mu.m in width and about 8 .mu.m in height. By employing
the shark-skin patterns, the surface area of the patterned PEM is
about five times greater than the surface area of a flat,
unpatterned PEM of the same macroscopic dimensions. As indicated by
the scanning electron micrograph provided in FIG. 2A, high fidelity
structural features are obtained by the presently disclosed method.
Further, as shown by the scanning electron micrograph provided in
FIG. 2B, the patterns swell after the PEM undergoes hydrolysis, but
the structural features are still evident.
[0212] In some embodiments, the predetermined geometry of mold 100,
e.g., element 102 of FIG. 1A, and thus the geometry of the PEM
formed therein, is defined by a catalyst tie layer, as provided in
FIG. 10 herein below, and/or an electrode material of a membrane
electrode assembly. Further, because the presently disclosed liquid
precursor material, e.g., liquid precursor material 114 of FIG. 1A,
is a liquid, it is pourable. Thus, liquid precursor material 114
can be poured into existing structures, such as a structure defined
by electrode materials.
[0213] For example, referring now to FIGS. 3A and 3B, a first
electrode material 300 and a second electrode material 302 are
operationally positioned in a spatial arrangement such that a gap
304 is created therein between. A liquid precursor material 306 is
poured into gap 304. Liquid precursor material 306 can comprise any
of the liquid precursor materials disclosed hereinabove. Liquid
precursor material 306 is then treated by a treating process
T.sub.r to form a proton exchange membrane 308, which, in some
embodiments, remains in a functional position between first
electrode material 300 and second electrode material 302. Thus, in
some embodiments, the liquid precursor material, e.g., 306, is
infused directly into the preconfigured cavity, e.g., gap 304
formed between first electrode material 300 and second electrode
material 302, followed by treating process T.sub.r.
[0214] Referring once again to FIGS. 3A and 3B, in some
embodiments, the first electrode material 300 is coated with a
first catalyst material 310 and second electrode material 302 is
coated with a second catalyst material 312 before liquid precursor
material 306 is poured into gap 304.
[0215] In some embodiments, proton exchange membrane 308 comprises
a material having an equivalent weight, wherein the equivalent
weight is selected from the group consisting of an equivalent
weight less than about 1500 and greater than about 1000, an
equivalent weight less than about 1000 and greater than about 800,
an equivalent weight less than about 800 and greater than about
500, and an equivalent weight below about 500. The conductivities
of representative PEMs prepared from the presently disclosed liquid
materials having different equivalent weights at fully hydrated
conditions are provided in FIGS. 4 through 8.
III. Method for Preparing a Polymeric Electrolyte Comprising a
Gradient of Equivalent Weights
[0216] Further, the synthetic methods of the liquid precursor
materials disclosed herein can be varied to produce a gradient of
compositions to tailor the properties and to improve the
performance of the presently disclosed PEMs. Current PEMs typically
comprise materials having one equivalent weight (EW), a property
that results in a trade-off between power density and methanol
permeability. For example, NAFION.RTM.-based high equivalent weight
PEMs are less permeable to methanol. Such materials, however,
exhibit a relatively low conductivity. Low EW PEMs give higher
conductivity values relative to those with higher EW materials of
comparable components, but allow for high methanol permeability,
which results in a drastic decrease in power density.
[0217] The presently disclosed subject matter provides a PEM having
a gradient of equivalent weights. With a gradient of EWs as
disclosed herein, optimum performance in both areas (methanol
permeability and conductivity) can be achieved. For example, the
use of a material with a higher EW at the anode provides a PEM with
a low methanol permeability, whereas inclusion of materials having
a lower EW throughout the cross section of the PEM provides for a
higher power density.
[0218] Referring now to FIG. 9A, the preparation of a proton
exchange membrane 900 with a plurality of liquid materials 902 is
disclosed. In this embodiment plurality of liquid materials 902
comprise a plurality of liquid materials 902a through 902f. In some
embodiments, liquid materials 902a through 902f comprise a high
glass transition temperature (T.sub.g) NAFION.RTM.-like material.
Liquid materials 902a through 902f are not restricted to a high
T.sub.g material, however, and in some embodiments liquid materials
902a through 902f comprise a fluorinated or perfluorinated
elastomer-based material, or any material disclosed herein.
[0219] In some embodiments, each liquid material, e.g., 902a, 902b,
902c, 902d, 902e, and 902f, has a different equivalent weight
(e.g., EW.sub.a, EW.sub.b, EW.sub.c, EW.sub.d, EW.sub.e, and
EW.sub.f, respectively (not shown)). As used herein the term
"equivalent weight" refers to the mass of an acidic material that
contains one equivalent of acid functional groups. Thus, the
equivalent weight of a polymeric electrolyte as disclosed herein is
the number of acidic group equivalents in the polymeric electrolyte
divided by the weight of the polymeric electrolyte. Further, as
used herein, the term "different equivalent weight" refers to an
equivalent weight, e.g., EW.sub.a that varies about 50 g/mol from
another equivalent weight, e.g., EW.sub.b. For example, an
equivalent weight of about 800 would be considered to be different
from an equivalent weight of about 750.
[0220] Referring again to FIG. 9A, the liquid material closest in
proximity to the anode 904, i.e., layer 902a, has a higher EW as
compared to liquid materials 902b through 902f. In some
embodiments, the equivalent weights of liquid materials 902a
through 902f follow the trend of:
EW.sub.a>EW.sub.b>EW.sub.c>EW.sub.d>EW.sub.e>EW.sub.f,
with liquid material 902f, which is closest in proximity to cathode
906, having the lowest equivalent weight.
[0221] In some embodiments, at least one of liquid materials 902a,
902b, 902c, 902d, 902e, and 902f has an equivalent weight below
1500. In some embodiments, at least one of liquid materials 902a,
902b, 902c, 902d, 902e, and 902f has an equivalent weight below
1000. In some embodiments, at least one of liquid materials 902a,
902b, 902c, 902d, 902e, and 902f has an equivalent weight below
800. In some embodiments, at least one of liquid materials 902a,
902b, 902c, 902d, 902e, and 902f has an equivalent weight below
500. The conductivities of representative PEMs prepared from the
presently disclosed liquid materials having different equivalent
weights at fully hydrated conditions are provided in FIGS. 4
through 8.
[0222] Referring now to FIG. 9B, in some embodiments, to decrease
the methanol permeability of PEM 900 at anode 904, a high EW liquid
material, e.g., 902a having an equivalent weight EW.sub.a, is
disposed, e.g., applied or spin coated, onto a substrate, e.g.,
anode 904, to form a layer of liquid material 902a on anode 904,
followed by treating with treating process T.sub.r to form treated
liquid material 908a. Treated liquid material 908a is coated with a
lower EW liquid material, e.g., 902b, with an equivalent weight
EW.sub.b, which is then treated to form treated liquid material
908b (not shown). This procedure is repeated as often as desired to
form PEM 900 comprising a gradient of equivalent weights, e.g.,
EW.sub.a through EW.sub.f. Thus, in some embodiments, the treated
liquid material, e.g., 908f (not shown), closest in proximity with
cathode 906 has the lowest EW, e.g., EW.sub.f. Accordingly, the
presently disclosed method can provide for a decrease in methanol
permeability at anode 904 and can promote increasingly facile
proton transport through the cross section of PEM 900.
[0223] Thus, in some embodiments, PEM 900 comprises a plurality of
layers of a polymeric electrolyte, wherein the plurality of layers
of a polymeric electrolyte comprises at least a first layer of a
first polymeric electrolyte comprising a material having a first
equivalent weight and at least a second layer of a second polymeric
electrolyte comprising a material having a second equivalent
weight. In some embodiments, the plurality of layers of a polymeric
electrolyte comprises a gradient of equivalent weights.
[0224] Thus, in some embodiments, the presently disclosed subject
matter provides method for preparing a polymeric electrolyte
comprising a plurality of equivalent weights, the method
comprising: [0225] (a) applying a first liquid precursor material
having a first equivalent weight to a substrate; [0226] (b)
treating the first liquid precursor material to form a first layer
of treated liquid precursor material on the substrate; [0227] (c)
applying a second liquid precursor material having a second
equivalent weight to the first layer of treated liquid precursor
material on the substrate; and [0228] (d) treating the second
liquid precursor material to form a polymeric electrolyte
comprising a plurality of equivalent weights.
[0229] In some embodiments, the first liquid precursor material and
the second liquid precursor material are selected from the group
consisting of a proton conducting material, a precursor to a proton
conducting material, and combinations thereof. In some embodiments,
the first equivalent weight is greater than the second equivalent
weight.
[0230] In some embodiments, the substrate is selected from the
group consisting of an anode and a cathode. In some embodiments,
the treating of the first liquid precursor material, the second
liquid precursor material, and the plurality of liquid precursor
materials is selected from the group consisting of a curing
process, a chemical modification process, a network forming
process, a solvent evaporation process, and combinations
thereof.
[0231] In some embodiments, the method comprises repeating steps
(c) through (d) with a predetermined plurality of liquid precursor
materials comprising a plurality of equivalent weights to form a
polymeric electrolyte comprising a plurality of equivalent weights,
wherein the plurality of liquid precursor materials are selected
from the group consisting of a proton conducting material, a
precursor to a proton conducting material, and combinations
thereof. In some embodiments, the second equivalent weight is
greater than the plurality of equivalents weights.
[0232] Thus, in some embodiments, the presently disclosed subject
matter provides a polymeric electrolyte comprising a plurality of
equivalent weights prepared by the presently disclosed method. In
some embodiments, the presently disclosed subject matter provides
an electrochemical cell comprising the presently disclosed
polymeric electrolyte comprising a gradient of equivalent weights.
In some embodiments, the electrochemical cell is selected from the
group consisting of a fuel cell, a chlor-alkali cell, and a
battery.
[0233] The performance of the presently disclosed proton exchange
membranes can be evaluated by measuring the conductivity, power
density, durability, and longevity, among others.
IV. Method for Preparing a Membrane Electrode Assembly (MEA)
[0234] The presently disclosed subject matter also provides a
method for preparing a membrane electrode assembly (MEA). In some
embodiments, the method for preparing a membrane electrode assembly
comprises preparing a processible catalyst ink composition using
the presently described liquid precursor materials. Further, in
some embodiments, the method for preparing a membrane electrode
assembly comprises providing a proton exchange membrane prepared by
the presently disclosed methods, coating the proton exchange
membrane with a processible catalyst ink composition to form a
coated proton exchange membrane, and in some embodiments, applying
an electrode material to the coated proton exchange membrane.
IV.A. Method for Preparing a Processible Catalyst Ink
Composition
[0235] In some embodiments, the presently disclosed subject matter
describes a method for preparing a processible catalyst ink
composition, the method comprising: [0236] (a) providing a liquid
precursor material; and [0237] (b) mixing the liquid precursor
material with a catalyst to form a processible catalyst ink
composition.
[0238] In some embodiments, the liquid precursor material comprises
a liquid perfluoropolyether material. In some embodiments, the
liquid perfluoropolyether material comprises end groups, wherein
the end groups are chemically stable after curing. In some
embodiments, the chemically stable end groups are selected from one
of aryl end groups and fluorinated vinyl ether end groups. In some
embodiments, the aryl end groups comprise styrenyl end groups.
[0239] In some embodiments, the method further comprises mixing the
liquid precursor material with a monomer, such as a vinyl monomer,
and a crosslinking agent. In some embodiments, the vinyl monomer
comprises a proton conducting species. In some embodiments, the
proton conducting species is selected from one of an acidic
material and a precursor to an acidic material.
[0240] In some embodiments, the processible catalyst ink
composition comprises a catalyst. In some embodiments, the catalyst
comprises a metal selected from the group consisting of platinum,
ruthenium, molybdenum, chromium, and combinations thereof. In some
embodiments, the catalyst is selected from one of a platinum
catalyst and a platinum alloy catalyst. In some embodiments, the
processible catalyst ink composition comprises an electrode
material. In some embodiments, the electrode material comprises
carbon black.
[0241] In some embodiments, the method comprises treating the
processible catalyst ink composition. In some embodiments, the
treating of the processible catalyst ink composition comprises a
treating process selected from the group consisting of a curing
process, a chemical modification process, a network forming
process, a solvent evaporation process, and combinations
thereof.
[0242] Thus, in some embodiments, the presently disclosed subject
matter provides a processible catalyst ink composition prepared by
the method described herein.
IV.B. Method for Applying a Processible Catalyst Ink Composition to
a Substrate
[0243] In some embodiments, the presently disclosed subject matter
provides a method for applying a processible catalyst ink
composition to a substrate. In some embodiments, the substrate
comprises an electrode material. In some embodiments, the substrate
comprises a proton exchange membrane.
[0244] Referring now to FIG. 10A, in some embodiments, a
processible catalyst ink composition 1000, as described immediately
above, is applied to an electrode material 1002. In some
embodiments, electrode material 1002 comprises carbon cloth. In
some embodiments, electrode material 1002 comprises carbon paper.
Processible catalyst ink composition 1000 is subsequently treated
by a treating process T.sub.r to form a catalyst tie layer (not
shown), which provides for good contact with electrode material
1002.
[0245] Referring now to FIG. 10B, in some embodiments, processible
catalyst ink composition 1000 is applied to a patterned proton
exchange membrane 1004. Processible catalyst ink composition 1000
is subsequently treated by a treating process T.sub.r to form a
catalyst tie layer (not shown), which provides for good contact
with proton exchange membrane 1004.
[0246] The method used to coat one of or both of electrode 1002 and
proton exchange membrane 1004 can be selected from the group
including but not limited to chemical vapor deposition (CVD),
electrospray, electric field desorption, rf-plasma enhanced CVD,
flame spray deposition, ink jet printing, or pulse laser
desorption. In some embodiments, the method comprises treating the
processible catalyst ink composition. In some embodiments, the
treating of the processible catalyst ink composition comprises a
treating process selected from the group consisting of a curing
process, a chemical modification process, a network forming
process, solvent evaporation process, and combinations thereof.
[0247] The presently described methods can be performed
independently for use in different membrane electrode assemblies.
That is, in one membrane electrode assembly, the presently
disclosed method can be used to coat an electrode material, whereas
in another membrane electrode assembly, the presently disclosed
method can be used to coat a proton exchange membrane. Further,
both of these methods, e.g., the methods described in FIG. 10A and
FIG. 10B respectively, can be used to prepare the same membrane
electrode assembly.
IV.C. Method for Conformally Coating a Proton Exchange Membrane
[0248] In some embodiments, the presently disclosed subject matter
provides a method for conformally coating a proton exchange
membrane with at least one of a processible catalyst ink
composition and an electrode material. By "conformally coating" it
is meant that the coating of, for example, the processible catalyst
ink composition and/or the electrode material, is in conductive
contact with the features comprising, for example, the proton
exchange membrane, and thereby conforms to the geometry of the
features thereof.
[0249] Referring now to FIG. 11A, in some embodiments, a patterned
PEM 1100 is coated conformally with a processible catalyst ink
composition 1102 followed by coating with an electrode material
1104, such as carbon black, to form a planarized surface 1106 of
electrode material 1104. In some embodiments, processible catalyst
ink composition 1102 is then treated by a treating process T.sub.r.
When operationally positioned in a membrane electrode assembly (not
shown), the planarized coating of the electrode material allows the
membrane electrode assembly to have a flat surface on at least one
side.
[0250] Referring now to FIG. 11B, in some embodiments, patterned
PEM 1100 is coated conformally with processible catalyst ink
composition 1102, followed by coating with electrode material 1104
to form a conformal surface 1108 of electrode material 1104. In
some embodiments, processible catalyst ink composition 1102 is then
treated by a treating process T.sub.r.
[0251] Referring now to FIG. 11C, in some embodiments, patterned
PEM 1100 is coated conformally with processible catalyst ink
composition 1102 to form a planarized surface 1110 of processible
catalyst ink composition 1102. This step is followed by coating
with electrode material 1104 to form a planarized surface 1106 of
electrode material 1104. In some embodiments, processible catalyst
ink composition 1102 is then treated by a treating process T.sub.r.
When operationally positioned in a membrane electrode assembly (not
shown), the planarized coating of the electrode material allows the
membrane electrode assembly to have a flat surface on at least one
side.
[0252] Accordingly, in some embodiments, the method comprises
conformally applying the processible catalyst ink composition to at
least one of the proton exchange membrane and the electrode
material.
[0253] By way of example, scanning electron micrographs of a
patterned PEM conformally coated with a catalyst by using an
electrospray deposition technique are shown in FIGS. 12A and 12B.
Further, a scanning electron micrograph of a patterned PEM
conformally coated with a catalyst by using a vapor-deposition
technique is shown in FIG. 13. The preparation of each of these
PEMs is described in Example 8.
IV.D. Method for Preparing a Membrane Electrode Assembly (MEA)
[0254] The presently disclosed subject matter provides a method for
preparing a membrane electrode assembly. In some embodiments, the
method for preparing a membrane electrode assembly comprises at
least one of the presently disclosed methods for preparing a proton
exchange membrane, preparing a processible catalyst ink
composition, applying a processible catalyst ink composition to a
substrate, and conformally coating a proton exchange membrane.
[0255] Thus, in some embodiments, the method for forming a membrane
electrode assembly comprises: [0256] (a) providing a proton
exchange membrane, wherein the proton exchange membrane is prepared
from a liquid precursor material as described herein; [0257] (b)
providing a first catalyst material and a second catalyst material;
[0258] (c) providing a first electrode material and a second
electrode material; and [0259] (d) operationally positioning the
proton exchange membrane, the first and the second catalyst
material, and the first and the second electrode material in
conductive communication to form a membrane electrode assembly.
[0260] Referring now to FIG. 14A, an embodiment of the presently
disclosed method for forming a membrane electrode assembly is
provided. Continuing with FIG. 14A, a proton exchange membrane 1400
is provided. In some embodiments, proton exchange membrane 1400
comprises a three-dimensional geometry as depicted in FIG. 14A. In
some embodiments, a first catalyst material 1402 and a second
catalyst material 1404 are conformally contacted with proton
exchange membrane 1400. A first electrode material 1406 is
conformally contacted with first catalyst material 1402. A second
electrode material 1408 is contacted with second catalyst material
1404. In some embodiments, first electrode material 1406 and second
electrode material 1408 comprise a planar geometry. In some
embodiments, the components of the membrane electrode assembly can
be treated by a treating process T.sub.r to provide good contact
between the components and mechanical stability.
[0261] Thus, the presently disclosed subject matter provides a
membrane electrode assembly comprising a three-dimensional proton
exchange membrane and a two-dimensional electrode with conformal
catalyst loading. By three-dimensional it is meant that, for
example, the proton exchange membrane comprises features that
extend from a planar surface (see, for example, the plurality of
structural features 120 of FIG. 1B). By two-dimensional it is meant
that, for example, the electrode material comprises a planar
surface which is in conductive communication with the proton
exchange membrane (see, for example, first electrode material 1406
and second electrode material 1408 of FIG. 14A).
[0262] Referring now to FIG. 14B, a proton exchange membrane 1400
is provided. In some embodiments, proton exchange membrane 1400
comprises a three-dimensional geometry as depicted in FIG. 14B,
wherein the three-dimensional geometry comprises a plurality of
recesses 1410. In some embodiments, a first catalyst material 1412
and a second catalyst material 1414 are operationally disposed
within recesses 1410. A first electrode material 1406 is
conformally contacted with first catalyst material 1412. A second
electrode material 1408 is contacted with second catalyst material
1414. In some embodiments, first electrode material 1406 and second
electrode material 1408 comprise a planar, two dimensional
geometry. In some embodiments, the components of the membrane
electrode assembly can be treated by a treating process T.sub.r to
provide good contact between the components and mechanical
stability. Thus, the presently disclosed subject matter provides a
membrane electrode assembly comprising a three-dimensional proton
exchange membrane and a two-dimensional electrode with
non-conformal catalyst loading.
[0263] Referring now to FIG. 15, a proton exchange membrane 1500 is
provided. In some embodiments, proton exchange membrane 1500
comprises a three-dimensional geometry comprising a plurality of
recesses 1502. In some embodiments, a first catalyst material 1504
and a second catalyst material 1506 are conformally contacted with
proton exchange membrane 1500. In some embodiments, a first
electrode material 1508 is disposed in recesses 1502 and is
operationally contacted with first catalyst material 1504. In some
embodiments, a second electrode material 1510 is disposed in
recesses 1502 and is operationally contacted with catalyst material
1506. In some embodiments, the components of the membrane electrode
assembly can be treated by a treating process T.sub.r to provide
good contact between the components and mechanical stability. Thus,
the presently disclosed subject matter provides a three-dimensional
membrane electrode assembly comprising a three-dimensional proton
exchange membrane and three-dimensional electrode materials with a
conformal catalyst loading.
[0264] In some embodiments, the proton exchange membrane, e.g.,
1400 of FIGS. 14A and 14B and 1500 of FIG. 15, is preformed by a
method described herein. In some embodiments, the proton exchange
membrane is formed by operationally disposing a liquid precursor
material between two electrode materials, e.g., first electrode
material 1508 and second electrode material 1510 of FIG. 15, and
then treating the liquid precursor material.
[0265] Thus, in some embodiments, the presently disclosed subject
matter provides a method for preparing a membrane electrode
assembly, the method comprising [0266] (a) providing a first
electrode material; [0267] (b) providing a second electrode
material; [0268] (c) positioning the first electrode material and
the second electrode material in a spatial arrangement such that a
gap is formed between the first electrode material and the second
electrode material; [0269] (d) deposing a liquid precursor material
in the gap between the first electrode material and the second
electrode material; and [0270] (e) treating the liquid precursor
material to form a membrane electrode assembly.
[0271] In some embodiments, the liquid precursor material is
selected from the group consisting of a proton conducting material,
a precursor to a proton conducting material, and combinations
thereof.
[0272] In some embodiments, the method comprises: [0273] (a)
contacting the first electrode material with a first catalyst
material; [0274] (b) contacting the second electrode material with
a second catalyst material; and [0275] (c) positioning the first
electrode material and the second electrode material in a spatial
arrangement such that the first catalyst material and the second
catalyst material face each other and a gap is formed between the
first catalyst material and the second catalyst material.
[0276] Further, in some embodiments, at least one of the first
catalyst material and the second catalyst material comprises a
processible catalyst ink composition. In some embodiments, the
method further comprises applying the processible catalyst ink
composition to the proton exchange membrane. In some embodiments,
the method comprises applying the processible catalyst ink
composition to at least one of the first and the second electrode
material. In some embodiments, the method comprises applying the
processible catalyst ink composition to the proton exchange
membrane and at least one of the first electrode material and the
second electrode material.
[0277] In some embodiments, the processible catalyst ink
composition is applied by a process selected from the group
including, but not limited to, a chemical vapor deposition (CVD)
process; an electrospray process; an electric field desorption
process; a rf-plasma enhanced CVD process; a flame spray deposition
process; an ink jet printing process; and a pulse laser desorption
process.
[0278] In some embodiments, the electrode material is selected from
the group consisting of carbon cloth, carbon paper, and carbon
black. In some embodiments, the electrode material comprises a
patterned electrode material.
[0279] Thus, in some embodiments, the presently disclosed subject
matter provides a membrane electrode assembly (MEA) prepared by the
methods described herein.
[0280] In some embodiments, the electrode material, e.g., carbon
cloth, carbon paper, and/or carbon black, is treated to increase
its surface area to increase the power density of the
electrochemical cell within which the electrode material is
operationally disposed. Referring now to FIG. 16, an electrode
material 1600 is provided. Electrode material 1600 can be patterned
to form a patterned electrode material 1602 using traditional
lithography technologies (not shown) or patterned directly using an
electron beam, e.g., the etching agent EA of FIG. 16. In some
embodiments, electrode material 1600 can further comprise a
photoresist 1604, for example, for use in electron beam
lithography. In some embodiments, a mask 1606 can be provided, for
example for use in plasma etching, such as oxygen reactive ion
etching.
[0281] Thus, in some embodiments, the electrode material is
patterned by a process selected from the group including but not
limited to: [0282] (a) a lithography process; [0283] (b) a direct
electron beam process; [0284] (c) an electron beam lithography
process using a photoresist; and [0285] (d) a plasma etching
process using a mask.
[0286] In some embodiments, the plasma etching process comprises an
oxygen reactive ion etching process.
V. Method for Forming an Electrochemical Cell
[0287] In some embodiments, the presently disclosed subject matter
provides a method for forming an electrochemical cell, such as a
fuel cell. Referring now to FIG. 17A, a proton exchange membrane
1700 is provided. Proton exchange membrane 1700 can be prepared
from the presently disclosed liquid precursor materials by the
methods described herein. Proton exchange membrane 1700 is
operationally positioned between and contacted with a first
catalyst material 1702 and a second catalyst material 1704. In some
embodiments, first catalyst material 1702 and second catalyst
material 1704 each independently comprise a metal selected from the
group consisting of platinum, ruthenium, molybdenum, chromium, and
combinations thereof.
[0288] Continuing with FIG. 17A, first catalyst material 1702 is
operationally contacted with a first electrode material 1706. In
some embodiments, first electrode material 1706 comprises a first
surface 1706a and a second surface 1706b. Thus, in some
embodiments, at least one of first surface 1706a and second surface
1706b is operationally contacted with first catalyst material 1702.
In some embodiments, at least one of first surface 1706a and second
surface 1706b are coated with first catalyst material 1702. In some
embodiments, at least one of first surface 1706a and second surface
1706b is impregnated with first catalyst material 1702.
[0289] Continuing with FIG. 17A, second catalyst material 1704 is
operationally contacted with second electrode material 1708. In
some embodiments, second electrode material 1708 comprises a first
surface 1708a and a second surface 1708b. Thus, in some
embodiments, at least one of first surface 1708a and second surface
1708b is operationally contacted with second catalyst material
1704. In some embodiments, at least one of first surface 1708a and
second surface 1708b are coated with second catalyst material 1704.
In some embodiments, at least one of first surface 1708a and second
surface 1708b is impregnated with second catalyst material
1704.
[0290] Continuing with FIG. 17A, membrane electrode assembly 1710
is thus formed by operationally positioning proton exchange
membrane 1700, first catalyst layer 1702, first electrode material
1706, second catalyst layer 1704, and second electrode material
1708. Membrane electrode assembly 1710 can be operationally
positioned in an electrochemical cell, such as a fuel cell.
[0291] Continuing on with FIG. 17A, a first outer layer 1712 and a
second outer layer 1714 are provided. In some embodiments, first
outer layer 1712 and second outer layer 1714 are comprised of a
perfluoropolyether (PFPE) material as described herein. First outer
layer 1712 can further comprise a plurality of microfluidic
channels 1716 through which fuel F.sub.1 can be introduced and
second outer layer 1714 can further comprise a plurality of
microfluidic channels 1718 through which fuel F.sub.2 can be
introduced.
[0292] In some embodiments, first electrode material 1706 comprises
an anode and is in fluid communication with fuel F.sub.1, which, in
some embodiments, comprises an anodic fuel. In some embodiments,
the anodic fuel, e.g., fuel F.sub.1, is selected from the group
consisting of H.sub.2, an alkane, an alkyl alcohol, a dialkyl
ether, and a glycol. In some embodiments, the alkane is selected
from the group consisting of methane, ethane, propane, and butane.
In some embodiments, the alkyl alcohol is selected from the group
consisting of methanol, ethanol, propanol, butanol, pentanol, and
hexanol. In some embodiments, the alkyl alcohol comprises methanol.
In some embodiments, the dialkyl ether comprises dimethyl ether. In
some embodiments, the glycol comprises ethylene glycol.
[0293] In some embodiments, second electrode material 1708
comprises a cathode and is in fluid communication with fuel
F.sub.2, which, in some embodiments, comprises a cathodic fuel. In
some embodiments, the cathodic fuel, e.g., fuel F.sub.2, comprises
an oxygen (O.sub.2) containing gas, such as air. In some
embodiments, the cathodic fuel comprises an air/water mixture.
[0294] In some embodiments, the electrochemical cell comprises at
least one electrical output connection E.sub.o.
[0295] Referring now to FIG. 17B, in some embodiments, the
plurality of microfluidic channels 1716 comprises at least one
inlet aperture 1720. In some embodiments, inlet aperture 1720 is in
fluid communication with a fuel source 1722. In some embodiments,
fuel source 1722 comprises fuel F.sub.1. In some embodiments, fuel
F.sub.2 is selected from the group consisting of an anodic fuel and
a cathodic fuel.
[0296] Continuing with FIG. 17B, in some embodiments, the plurality
of microfluidic channels 1718 comprises at least one inlet aperture
1724. In some embodiments, inlet aperture 1724 is in fluid
communication with a fuel source 1726. In some embodiments, fuel
source 1726 comprises fuel F.sub.2. In some embodiments, fuel
F.sub.2 is selected from the group consisting of an anodic fuel and
a cathodic fuel.
[0297] In some embodiments, the plurality of microfluidic channels
1716 comprises an outlet aperture 1728. In some embodiments, outlet
aperture 1728 is in fluid communication with a fuel recirculation
channel 1730. In some embodiments, the outlet aperture is in fluid
communication with a waste exhaust port 1732.
[0298] In some embodiments, the plurality of microfluidic channels
1718 comprises an outlet aperture 1734. In some embodiments, outlet
aperture 1734 is in fluid communication with a fuel recirculation
channel 1736. In some embodiments, the outlet aperture is in fluid
communication with a waste exhaust port 1738.
[0299] In some embodiments, the plurality of microfluidic channels
1716 comprises a plurality of valves, e.g., 1740a, 1740b, and
1740c. In some embodiments, plurality of valves 1740a, 1740b, and
1740c comprise a pressure actuated valve (not shown). In some
embodiments, the plurality of microfluidic channels 1718 comprises
a plurality of valves, e.g., 1742a, 1742b, and 1742c. In some
embodiments, plurality of valves 1740a, 1740b, and 1740c comprise a
pressure actuated valve (not shown).
[0300] In some embodiments, the plurality of microfluidic channels
1716 and the plurality of microfluidic channels 1718 each comprise
a network of microfluidic channels (not shown).
[0301] In some embodiments, the microfluidic device is produced by
a soft lithography process. As used herein, the term "soft
lithography" refers to a process by which micrometer and
sub-micrometer features are transferred to a substrate through the
use of elastomeric stamps. Soft lithography has emerged as an
alternative to traditional photolithography processes for producing
feature sizes smaller than about 100 nm. As used herein, the term
"soft lithography" encompasses several processes including, but not
limited to, imprint lithography (IL), replica molding, microcontact
printing (MCP), micromolding in capillaries (MIMIC), and
solvent-assisted micromolding (SAMIM).
[0302] Referring now to FIGS. 18A-18C, a schematic representation
of an embodiment of the presently disclosed method for forming a
layer of perfluoropolyether (PFPE) material comprising a plurality
of microfluidic channels is shown. A substrate 1800 having a
patterned surface 1802 comprising a raised protrusion 1804 is
depicted. Accordingly, the patterned surface 1802 of the substrate
1800 comprises at least one raised protrusion 1804 which forms the
shape of a pattern. In some embodiments, the patterned surface 1802
of the substrate 1800 comprises a plurality of raised protrusions
1804 which form a complex pattern.
[0303] As best seen in FIG. 18B, a polymeric precursor 1806 is
disposed on patterned surface 1802 of substrate 1800. Polymeric
precursor 1806 can comprise a perfluoropolyether. As shown in FIG.
18B, polymeric precursor 1806 is treated by a treating process
T.sub.r, for example, irradiation with ultraviolet light, to form a
patterned layer 1808 of a photocured perfluoropolyether as shown in
FIG. 18C.
[0304] As shown in FIG. 18C, the patterned layer 1808 of the
photocured perfluoropolyether comprises a recess 1810 that is
formed in the bottom surface of the patterned layer 1808. The
dimensions of recess 1810 correspond to the dimensions of the
raised protrusion 1804 of patterned surface 1802 of substrate 1800.
In some embodiments, recess 1810 comprises at least one channel
1812, which in some embodiments of the presently disclosed subject
matter comprises a microscale channel. Patterned layer 1808 is
removed from patterned surface 1802 of substrate 1800 to yield
microfluidic device 1814. Thus, in some embodiments, the soft
lithography process comprises contacting a liquid precursor
material with a patterned substrate, e.g., a silicon wafer. In some
embodiments, the process further comprises treating the liquid
precursor material to form a crosslinked polymer. In some
embodiments, the treating process is selected from the group
consisting of a curing process, a chemical modification process, a
network forming process, and combinations thereof.
[0305] In some embodiments, the process further comprises of
removing the crosslinked polymer from the substrate, thereby
creating a "stamp" of the desired pattern.
[0306] A poly(dimethyl siloxane) (PDMS) elastomeric material
typically is used in such microfluidic devices. The swelling of the
PDMS material, however, limits its use in direct methanol fuel
cells and fuel cells comprising other organic liquids due to the
disruption of the micrometer-sized features. Further, PDMS
materials typically also are unstable to acids and bases.
[0307] The presently disclosed subject matter addresses the
above-mentioned problems with PDMS elastomers in whole or in part
by using a photocurable PFPE material. In some embodiments, the
PFFE material comprises a fluorinated, functionalized PFPE
material, which, in some embodiments, has liquid-like viscosities
and can be cured into durable elastomers that exhibit the chemical
resistance of typical fluoropolymers.
[0308] Thus, in some embodiments, the presently disclosed subject
matter comprises cured PFPE-based materials. In some embodiments,
the curing method comprises a free-radical cured method. In some
embodiments, the free-radical cured method further comprises adding
other monomers and macromonomers to the PFPE resin. The addition of
other monomers and macromonomers to the PFPE resin allows the
physical properties, including, but not limited to, modulus,
flexural strength, wetting characteristics, permeability, adhesion,
and reactivity, to be regulated.
VI. Method for Operating an Electrochemical Cell
[0309] The presently disclosed subject matter also provides a
method for operating an electrochemical cell, such as a fuel cell.
In some embodiments, the method comprises: [0310] (a) providing an
electrochemical cell comprising at least one layer of a
perfluoropolyether (PFPE) material comprising at least one
microfluidic channel; [0311] (b) dispensing a first electrode
reactant and a second electrode reactant into the electrochemical
cell; and [0312] (c) generating an electrical output from the
electrochemical cell.
[0313] In some embodiments, the proton exchange membrane of the
electrochemical cell comprises a polymeric electrolyte prepared
from a liquid precursor material as described herein.
[0314] In some embodiments, the first electrode reactant is
selected from the group consisting of H.sub.2, an alkane, an alkyl
alcohol, a dialkyl ether and a glycol. In some embodiments, the
alkane is selected from the group consisting of methane, ethane,
propane, and butane. In some embodiments, the alkyl alcohol is
selected from the group consisting of methanol, ethanol, propanol,
butanol, pentanol, and hexanol. In some embodiments, the alkyl
alcohol comprises methanol. In some embodiments, the dialkyl ether
comprises dimethyl ether. In some embodiments, the glycol comprises
ethylene glycol. In some embodiments, the second electrode reactant
comprises an oxygen (O.sub.2) containing gas, such as an air, and,
in some embodiments, an air/water mixture.
[0315] In some embodiments, the method comprises extracting the
electrical output generated by the electrochemical cell. In some
embodiments, the electrical output ranges from about 100 milliwatts
to about 20 watts.
[0316] In some embodiments, the method for operating an
electrochemical cell further comprises supplying electrical power
to a device. In some embodiments, the device comprises a stationary
device. In some embodiments, the stationary device comprises an
electrical generator. In some embodiments, the device comprises a
portable device. In some embodiments, the portable device is
selected from the group consisting of a portable electrical
generator, a portable appliance, a power tool, an electronic
device, a roadway or traffic sign, a backup power supply, and a
personal vehicle. In some embodiments, the electronic device is
selected from one of a consumer electronic device and a military
electronic device. In some embodiments, the device comprises an
automotive device.
EXAMPLES
[0317] The following Examples have been included to provide
guidance to one of ordinary skill in the art for practicing
representative embodiments of the presently disclosed subject
matter. In light of the present disclosure and the general level of
skill in the art, those of skill can appreciate that the following
Examples are intended to be exemplary only and that numerous
changes, modifications, and alterations can be employed without
departing from the scope of the presently disclosed subject
matter.
Example 1
Synthesis of Crosslinkable PFPE Liquid Precursors
Example 1.1 Synthesis of a Crosslinkable PFPE Liquid Precursor with
a Styrene Linkage
[0318] Styrene linkages are added to both chain ends of
poly(tetrafluoroethylene-co-difluoroethylene oxide) .alpha.,.omega.
diol (ZDOL) (PFPE, Average Mn ca. 3800 g/mol) by an interfacial
reaction. In a typical synthesis, PFPE (20 g, 5.26 mmol), solcane
(10 mL), and tetrabutylammonium hydrogen sulfate (1.0 g, 2.95 mmol)
are added into a round bottom flask. KOH (10 g, 0.18 mol) is
dissolved in deionized water (20 mL) and the aqueous KOH solution
is then added to the round bottom flask. After addition of
4-vinylbenzyl chloride (2 mL, 12.8 mmol), the reaction mixture is
allowed to stir vigorously at 45.degree. C. for 48 h. The product
is passed through a 0.22-.mu.m filter to remove the resulting brown
solid. The solution is then extracted by deionized water three
times and stirred with carbon black for 1 h to remove any
impurities. The mixture is passed through a 0.22-.mu.m filter to
remove the carbon black and vacuum dried at room temperature to
remove the solvent. The resulting product (S-PFPE) is a clear
viscous liquid.
Example 1.2 Synthesis and Photocuring of Functional PFPE
[0319] A representative scheme for the synthesis and photocuring of
functional PFPEs is provided in Scheme 1.
##STR00010##
Example 1.3
Representative Perfluoropolyethers
[0320] Perfluoropolyether materials of the presently disclosed
subject matter include, but are not limited to, perfluoropolyether
materials comprising a backbone structure as follows:
##STR00011##
Example 2
Synthesis of Crosslink Systems
Example 2.1
General Considerations
[0321] A strong acid and a multifunctional monomer are crosslinked
free radically or via a different chemical mechanism. The
multifunctional monomer can be a strong acid and can have a
functionality of at least two. An example of a strong acid that can
be used in these crosslink systems for electrochemical cell
applications is perfluoro-2-(2-fluorosulfonylethoxy)propyl vinyl
ether (PSEPVE). Other superacids that can function either as the
strong acid or as a multifunctional monomer are sulfonimide-based
compounds.
[0322] The strong acid and multifunctional monomer are mixed in a
round bottom flask under argon with fluorinated or perfluorinated
solvent as needed. The ratios of the two components are varied for
desired crosslink density and equivalent weight. Reaction
conditions, such as temperature and reaction time, can vary
depending on the particular components and ease of mixing.
[0323] A liquid precursor comprising the reaction mixture is poured
onto a glass slide or a patterned substrate, such as a mold. A
standard steel spacer is used to control the membrane thickness.
The liquid precursor is chemically crosslinked by irradiation with
UV light or thermally under nitrogen purge. The mechanism of
chemically crosslinking depends on the initiator used. Once
crosslinked networks are prepared, hydrolysis using base and acid
converts any remaining conducting site into the acid for increased
proton conduction.
Example 2.2
Multifunctional Monomer as a Fluorinated Divinylether
[0324] Nonconducting, difunctional monomers when reacted with
strong acid result in a mechanically stable proton conducting
network. Commercially available compounds with a functionality of
two or more, such as 4,4'-bis(4-trifluorovinyloxy)biphenyl
(Compound 1) are reacted with a strong acid, such as PSEPVE. In a
liquid precursor state, the reaction mixture takes on the shape of
the surface/mold and crosslinks free radically upon addition of
initiator, thermally or photochemically, in an inert
atmosphere.
##STR00012##
Example 2.3
Multifunctional Monomer as a Tris(Trifluorovinyl)Benzene
[0325] Liquid precursors lend themselves to be patternable if a
crosslinking mechanism is viable. Free radical curing with
trifunctional monomers provide a chemically crosslinked network
available for proton conduction when cured with a strong acid. An
example of a trifunctional monomer is
tris(.alpha.,.beta.,.beta.-trifluorovinyl)benzene (Compound 2) that
is prepared using 1,3,5-tribromobenzene (see Scheme 2). The
starting material in Scheme 2 can also represent a trifunctional
monomer for subsequent crosslinking with a strong acid. An example
of a strong acid is PSEPVE. The reaction mixture in a liquid
precursor state can be crosslinked as described in Example 2.2.
##STR00013##
Example 2.4
Multifunctional Monomer as a Fluorinated Divinylether
Sulfonimide
[0326] A difunctional macromonomer, which also is a superacid,
reacts with another strong acid, such as PSEPVE, to achieve a
highly conducting, mechanically stable network. In a liquid
precursor form this reaction takes on the shape of any mold prior
to crosslinking. Subsequent crosslinking results in high surface
area, highly conductive membranes. An example of a superacid used
as a difunctional macromonomer is a bis(PSEPVE-based) sulfonimide
(Compound 3), which is prepared via sulfonimide chemistry (see
Schemes 3 and 4). The reaction mixture can be cured under the
conditions described in Example 2.2.
##STR00014##
Example 2.5
Multifunctional Monomer as a Fluorinated Bisvinylether
Disulfonimide
[0327] Using a strong acid such as PSEPVE and a disulfonyl
fluoride, a bisvinylether disulfonimide is prepared using
sulfonimide chemistry to obtain this crosslinkable superacid
monomer (Compound 4, Scheme 6). The disulfonyl fluoride can be
prepared using a diiodoalkane, such as
.alpha.,.omega.-diiodoperfluoroalkane (Scheme 5). The bisvinylether
disulfonimide is reacted with another strong acid such as PSEPVE to
form a highly conducting membrane. The reactants can be cured under
the conditions described in Example 2.2.
##STR00015##
##STR00016##
##STR00017##
##STR00018##
##STR00019##
##STR00020##
Example 3
Synthesis of Crosslinkable Terpolymer
Example 3.1
General Considerations
[0328] A terpolymer comprising a fluoroolefin, and strong acid, and
a cure site monomer (CSM) of low molecular weight, is polymerized.
An example of a fluoroolefin is tetrafluoroethylene (TFE) and for a
strong acid, perfluoro-2-(2-fluorosulfonylethoxy) propyl vinyl
ether (PSEPVE) is chosen. A typical polymerization can be loaded
with 40% solids. The solvent chosen for TFE-based polymerizations
is optionally carbon dioxide (CO.sub.2). The initiator
concentration tunes the desired molecular weight. Higher initiator
concentration will lead to lower relative molecular weight, whereas
a lower initiator concentration would result in higher relative
molecular weight. The polymerization is conducted free radically
with a thermal initiator. Reaction times are varied upon desired
conversion. The polymerizations are preferably performed using cure
site monomers that are commonly used in fluoroelastomer and
perfluoroelastomer technologies. For example, the cure site
monomers can include cyanovinyl ethers, bromine containing
monomers, bromine containing olefins, bromine containing vinyl
ethers, iodine containing monomers, iodine containing olefins,
iodine containing vinyl ethers, fluorine containing olefins having
a nitrile group, fluorine containing vinyl ethers having a nitrile
group, 1,1,3,3,3-pentafluoropropene,
perfluoro(2-phenoxypropyl)vinyl ether, and non-conjugated
dienes.
[0329] Terpolymers formed by the polymerization of a fluoroolefin,
a strong acid, and a cure site monomer (CSM) can be crosslinked
after polymerization, prior to hydrolysis of the terpolymers. The
polymerization product comprises a gum or liquid with Mooney
viscosities of 160 and lower. The terpolymers are poured onto a
mold of a desired pattern or onto a glass slide in an inert
atmosphere. A standard steel spacer is used to control the membrane
thickness between glass slides. The terpolymer takes on the shape
of the patterned mold. Curing chemistry is optionally conducted as
in fluoroelastomer and perfluoroelastomer technologies. The liquid
precursor is chemically crosslinked by various cure systems
including thermal or gamma radiation. Depending on the CSM,
peroxide-based or bisphenolic cure systems also can be implemented.
A chemically crosslinked membrane is created with higher active
surface area than the geometric surface area occupied by the mold.
Subsequent hydrolysis, with base and acid, results in a patterned,
proton conducting membrane with high mechanical integrity.
Example 3.2
Terpolymer with Bromine-Containing Cure Site Monomer
[0330] A cure site monomer containing a bromine is selected for the
polymerization of a terpolymer comprising a fluoroolefin, and
strong acid and a cure site monomer. Bromine-containing compounds
used as cure site monomers can include vinyl bromide,
1-bromo-2,2-difluoroethylene, perfluoroallyl bromide,
4-bromo-1,1,2-trifluorobutene, 4-bromoperfluoro-1-butene,
4-bromo-3,3,4,4-tetrafluoro-1-butene, bromotrifluoroethylene, and
perfluorobromo-vinyl ether.
Example 3.3
Terpolymer with Cyanovinyl Ether-Containing Cure Site Monomer
[0331] A cure site monomer containing a cyanovinyl ether is
selected for the polymerization of a terpolymer comprising a
fluoroolefin, and strong acid and a cure site monomer. Cyanovinyl
ether-containing compounds used as cure site monomers can include
perfluoro(8-cyano-5-methyl-3,6-dioca-1-octene) and
perfluoro(9-cyano-5-methyl-3,6-dioxa-1-octene).
Example 4
Preparation of Other Liquid Materials
Example 4.1
Synthesis of NAFION.RTM. in CO.sub.2
##STR00021##
[0332] Example 4.2
Synthesis of Poly(TFE-Nb-PSEPVE)
##STR00022##
[0333] Example 4.3
Synthesis of Poly(TFE-PDD-PSEPVE)
##STR00023##
[0334] Example 4.4
Synthesis of a Norbornene Derivative
##STR00024##
[0335] Example 4.5
Vinyl Alcohol Containing PEM
##STR00025##
[0336] Example 5
Synthesis of Precursor to Proton Conductive Materials
Example 5.1
Synthesis of Styrene Sulfonate Ester
[0337] To a round bottom flask, 4-vinyl benzenesulfonyl chloride
(37.5 mmol), 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol
(37.5 mmol), triethylamine (10 mL), and pyridine (20 mL) are added
under Ar flow. The resulting slurry is stirred at room temperature
for 20 hours (h). The reaction mixture is then poured into excess
hydrochloric acid-ice bath to quench triethylamine. The aqueous
solution is extracted with diethyl ether three times, and the
combined ether layer is washed with water, 10% NaOH solution, and
10% NaCl solution sequentially. The ether solution is then dried
over MgSO.sub.4 for 1 h. MgSO.sub.4 is then filtered out and
diethyl ether is removed by vacuum evaporation. The resulting
styrene sulfonate ester is a yellow solid with a melting
temperature around 40.degree. C.
Example 5.2
Synthesis of Styrene Sulfonate Ester
[0338] To a round bottom flask, 4-vinyl benzenesulfonyl chloride
(37.5 mmol), 2,2,3,3,4,4,5,5,6,6,7,7,7-tridecafluoro-1-heptanol
(37.5 mmol), triethylamine (10 mL), and pyridine (20 mL) are added
under Ar flow. The resulting slurry is stirred at room temperature
for 20 h. The reaction mixture is then poured into excess
hydrochloric acid-ice bath to quench triethylamine. The aqueous
solution is extracted with diethyl ether three times, and the
combined ether layer is washed with water, 10% NaOH solution, and
10% NaCl solution sequentially. The ether solution is then dried
over MgSO.sub.4 for 1 h. MgSO.sub.4 is then filtered out and
diethyl ether is removed by vacuum evaporation.
Example 6
Preparation of Proton Exchange Membranes
Example 6.1
Preparation of EW1900 Proton Exchange Membranes
[0339] 70 wt % S-PFPE and 30 wt % styrene sulfonate ester are mixed
at room temperature. The mixture is heated above 40.degree. C. and
becomes a homogeneous yellow liquid. The liquid precursor is poured
onto a preheated glass slide. A standard steel spacer is used to
control the membrane thickness. The liquid precursor is chemically
crosslinked by irradiation with UV light (.lamda.=365 nm) for 10
min under nitrogen purge. The resulting membrane is in the ester
form, transparent and slightly yellow.
[0340] To convert the sulfonate ester group into sulfonic acid, the
membrane is immersed in a mixture of 30% NaOH aqueous solution and
methanol (5:6 by volume) overnight and then refluxed for 10 h. The
membrane is then rinsed with water and stirred with fresh 20 wt %
HCl solution four times over 24 h. The resulting membrane is in the
acid form. Residual HCl is removed by washing with water. The
produced PEM has an equivalent of 1900 g/mol. The conductivity of
the PEM at fully hydrated conditions is measured by AC impedance
and the results are shown in FIG. 4.
Example 6.2
Preparation of EW1250 Proton Exchange Membranes
[0341] 60 wt % S-PFPE and 40 wt % styrene sulfonate ester are mixed
at room temperature. The mixture is heated above 40.degree. C. and
became a homogeneous yellow liquid. The liquid precursor is poured
onto a preheated glass slide. A standard steel spacer is used to
control the membrane thickness. The liquid precursor is chemically
crosslinked by irradiation with UV light (.lamda.=365 nm) for 10
min under nitrogen purge. The resulting membrane is in the ester
form, transparent and slightly yellow.
[0342] To convert the sulfonate ester group into sulfonic acid, the
membrane is immersed in a mixture of 30% NaOH aqueous solution and
methanol (5:6 by volume) overnight and then refluxed for 10 h. The
membrane is then rinsed with water and stirred with fresh 20 wt %
HCl solution four times over 24 h. The resulting membrane is in the
acid form. Residual HCl is removed by washing with water. The
produced PEM has an equivalent of 1250 g/mol. The conductivity of
the PEM at fully hydrated conditions is measured by AC impedance
and the results are shown in FIG. 5.
Example 6.3
Preparation of EW850 Proton Exchange Membranes
[0343] 50 wt % S-PFPE and 50 wt % styrene sulfonate ester are mixed
at room temperature. The mixture is heated above 40.degree. C. and
becomes a homogeneous yellow liquid. The liquid precursor is poured
onto a preheated glass slide. A standard steel spacer is used to
control the membrane thickness. The liquid precursor is chemically
crosslinked by irradiation with UV light (.lamda.=365 nm) for 10
min under nitrogen purge. The resulting membrane is in the ester
form, transparent and slightly yellow.
[0344] To convert the sulfonate ester group into sulfonic acid, the
membrane is immersed in a mixture of 30% NaOH aqueous solution and
methanol (5:6 by volume) overnight and then refluxed for 10 h. The
membrane is then rinsed with water and stirred with fresh 20 wt %
HCl solution four times over 24 h. The resulting membrane is in the
acid form. Residual HCl is removed by washing with water. The
produced PEM has an equivalent of 850 g/mol. The conductivity of
the PEM at fully hydrated conditions is measured by AC impedance
and the results are shown in FIG. 6.
Example 6.4
Preparation of EW660 Proton Exchange Membranes
[0345] 40 wt % S-PFPE and 60 wt % styrene sulfonate ester are mixed
at room temperature. The mixture is heated above 40.degree. C. and
becomes a homogeneous yellow liquid. The liquid precursor is poured
onto a preheated glass slide. A standard steel spacer is used to
control the membrane thickness. The liquid precursor is chemically
crosslinked by irradiation with UV light (.lamda.=365 nm) for 10
min under nitrogen purge. The resulting membrane is in the ester
form, transparent and slightly yellow.
[0346] To convert the sulfonate ester group into sulfonic acid, the
membrane is immersed in a mixture of 30% NaOH aqueous solution and
methanol (5:6 by volume) overnight and then refluxed for 10 h. The
membrane is then rinsed with water and stirred with fresh 20 wt %
HCl solution four times over 24 h. The resulting membrane is in the
acid form. Residual HCl is removed by washing with water. The
produced PEM has an equivalent of 660 g/mol. The conductivity of
the PEM at fully hydrated conditions is measured by AC impedance
and the results are shown in FIG. 7.
Example 6.5
Preparation of EW550 Proton Exchange Membranes
[0347] 30 wt % S-PFPE and 70 wt % styrene sulfonate ester are mixed
at room temperature. The mixture is heated above 40.degree. C. and
became a homogeneous yellow liquid. The liquid precursor is poured
onto a preheated glass slide. A standard steel spacer is used to
control the membrane thickness. The liquid precursor is chemically
crosslinked by irradiation with UV light (.lamda.=365 nm) for 10
min under nitrogen purge. The resulting membrane is in the ester
form, transparent and slightly yellow.
[0348] To convert the sulfonate ester group into sulfonic acid, the
membrane is immersed in a mixture of 30% NaOH aqueous solution and
methanol (5:6 by volume) overnight and then refluxed for 10 h. The
membrane is then rinsed with water and stirred with fresh 20 wt %
HCl solution four times over 24 h. The resulting membrane is in the
acid form. Residual HCl is removed by washing with water. The
produced PEM has an equivalent of 550 g/mol. The conductivity of
the PEM at fully hydrated conditions is measured by AC impedance
and the results are shown in FIG. 8.
Example 7
Fabrication of High Surface Area PEMs by Soft-Lithography
Technique
[0349] Fabrication of PEMs with Shark-Skin Patterns
[0350] S-PFPE and styrene sulfonate ester are mixed in desired
ratios. The mixture is heated above 40.degree. C. and became a
homogeneous yellow liquid. The liquid precursor is poured onto a
preheated silicon wafer with shark-skin patterns. A standard steel
spacer is used to control the membrane thickness. The liquid
precursor is chemically crosslinked by irradiation with UV light
(.lamda.=365 nm) for 10 min under nitrogen purge. The patterned
membrane is released from the silicon wafer after curing. The
resulting membrane is in the ester form, transparent and slightly
yellow.
[0351] To convert the sulfonate ester group into sulfonic acid, the
membrane is immersed in a mixture of 30% NaOH aqueous solution and
methanol (5:6 by volume) overnight and then refluxed for 10 h. The
membrane is then rinsed with water and stirred with fresh 20 wt %
HCl solution four times over 24 h. The resulting membrane is in the
acid form. Residual HCl is removed by washing with water.
[0352] Scanning electron micrographs of the PEMs with shark-skin
pattern before and after hydrolysis are shown in FIGS. 2A and 2B.
The feature size of the shark-skin pattern is 2 .mu.m in width and
8 .mu.m in height. By employing the shark-skin patterns, the
surface area of the patterned PEMs is about five times bigger than
corresponding flat PEMs. As indicated by the figure, high fidelity
patterns are easily obtained by soft litho approach. After
hydrolysis, the patterns are swelled due to sorption of water, but
the features are maintained.
Example 8
Conformal Application of Catalyst onto the PEM
Example 8.1
Deposition of Catalyst onto PEM by Electro-Spray Technique
[0353] A catalyst including platinum or platinum dispersed on
carbon is deposited onto a three-dimensional PEM with shark-skin
patterns by electro-spray technique. FIGS. 12A and 12B show
scanning electron micrographs of the PEMs with a deposited
catalyst.
Example 8.2
Deposition of Catalyst onto PEM by Vapor Deposition
[0354] Platinum catalyst is deposited onto a three-dimensional PEM
with shark-skin patterns by vapor deposition. FIG. 13 shows a
scanning electron micrograph of the PEMs with a deposited
catalyst.
Example 9
Fabrication of Three-Dimensional MEAs
Example 9.1
[0355] The liquid precursor approach also provides a
three-dimensional membrane electrode assembly (MEA) and fuel cell
stacks. FIGS. 14A and 14B display a schematic representation of a
MEA structure based a three-dimensional membrane and
two-dimensional electrodes with conformal or non-conformal catalyst
loading.
Example 9.2
[0356] The liquid precursor approach also provides a
three-dimensional (3-D) membrane electrode assembly (MEA) and fuel
cell stacks. FIG. 15 displays a schematic representation of a MEA
structure based a three-dimensional membrane and three-dimensional
electrodes with conformal catalyst loading.
[0357] It will be understood that various details of the presently
disclosed subject matter can be changed without departing from the
scope of the presently disclosed subject matter. Furthermore, the
foregoing description is for the purpose of illustration only, and
not for the purpose of limitation.
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