Note: Descriptions are shown in the official language in which they were submitted.
W O 95121465 ~ ~ ~ PCT/US94101275
CONTAINING A CARBON FIBER PAPER COATEn
' WITH CATALYTIIC METAL PARTICLE
BACKGROUND OF THE INVENTm~N
. 1. Field of the Invention
This invention relates to electrodes for electrochemical cells
such as electrolytic and galvanic cells.
2. f?iscription of the Prior Art
Fuel cells are devices for directly converting the chemical energy of a
to fuel into electrical power. Generally, a fuel cell comprises two gas
diffusion
electrodes (an anode and a cathode) and an electrolyte impregnated matrix
between the two electrodes. A catalyst layer is present on the electrolyte
facing surface of each electrode. In operation, a typical fuel cell is fed
with a
hydrogen containing gas at the anode and an oxygen-containing gas is fed to
is the cathode. The gas is diffused through the electrodes to react at
catalyst
sites to yield water, heat and electrical energy. On the anode side of the
fuel
cell, hydrogen is electrochemically oxidized to give electrons. The electrical
current so generated is conducted from the anode through an external circuit
to the cathode. On the cathode side of the cell, the electrons are
2o electrochemically combined with oxygen. A flow of ions through the
electrolyte completes the circuit.
There is a constant search for ways in which to improve fuel cell
performance. Even slight increases in performance can make the difference
between a fuel cell which fills specific requirements in comparison with one
25 which does not. In addition, there is a constant search for ways in which
the
' cost of producing the elements of a duel cell can be reduced. Specifically,
the
i
CA 02181560 2004-O1-30
64693-5158
methods of fabricating fuel cell electrodes have involved
various procedures which generally are not suitable to
automated production.
SUMMARY OF THE INVENTION
A novel process is disclosed for the preparation
of a novel electrode for an electrochemical cell. The
method is particularly applicable to the preparation of
electrodes utilizing automated mass production techniques in
that the layer of catalytic metal particles/binder can be
applied in single or successive layers, on a continuous
basis, to a web of carbon fiber paper. Subsequently, the
carbon fiber paper coated with a catalytic layer is bonded
to an ion exchange membrane utilizing heat and/or pressure.
The novel electrode is particularly adapted for
use in fuel cells and in the preparation of solid polymer
electrodes. For use in electrolytic cells, the binder
selected for binding the metal catalyst particles to the
carbon fiber paper is a hydrophilic binder or a hydrophobic
binder such as a fluorinated hydrocarbon resin. For use in
galvanic electrochemical cells, the binder is selected from
hydrophobic resins.
Also disclosed is a novel electrochemical cell, a
novel membrane and electrode assembly, and a novel method of
generating an electric current in a fuel cell.
According to one aspect of the present invention,
there is provided a process for producing an electrode
characterized by: (A) preparing a uniformly coated carbon
fiber paper by applying an uncoagulated aqueous mixture
consisting essentially of catalytic metal particles and a
hydrophobic or hydrophilic resin binder to one side of a wet
2
CA 02181560 2004-O1-30
64693-5158
proofed carbon fiber paper, wherein said carbon fiber paper
is wet proofed by coating or impregnation with a hydrophobic
polymer and said catalytic metal particles are present on
said coated or impregnated carbon fiber paper in the amount
of 2 to 25 parts by weight of said metal particles per part
of said resin and (B) heating said coated carbon fiber paper
to a temperature of 275° - 350°C to sinter the binder.
According to another aspect of the present
invention, there is provided the process described herein,
wherein said aqueous mixture of said catalytic metal
particles and said hydrophilic or hydrophobic resin binder
is coated on said wet proofed carbon fiber paper from an
aqueous dispersion utilizing spray, metering bar, knife, or
metering rod application means.
DETAILED DESCRIPTION OF THE INVENTION
This invention is based upon the discovery of a
novel catalytic carbon fiber paper electrode assembly,
useful in the preparation of electrodes and membrane
assemblies for electrochemical cells, preferably, fuel
cells, most preferably, fuel cells having means for
supplying a stream of oxidant gas to one electrode element
and a stream of a fuel gas to the other of said electrode
elements. The electrode can be prepared on a continuous
basis
2a
WO 95/21465 PCTlU594/01275
utilizing automated, mass production coating methods. An improved
electrode exhibiting superior, reproducible voltage characteristics is
obtained.
' By the method of the invention, a carbon fiber paper, which serves as a
current collector, can be coated frorn an aqueous dispersion of catalytic
metal
s particles and binder so as to generally, provide as low as 0.5 mg,
preferably, .75 mg to 6.0 mg, and most preferably, 1.0 mg to 4.0 mg per
square centimeter of catalyst on the carbon fiber paper. In addition, by
coating in slurry form an aqueous mixture of metal catalyst particles and
binder, utilizing such coating means as a metering bar, a metering knife or
to rod, or spray application, an extremely uniform coating can be obtainied.
This
coating method which is suitable for automation provides a coating which is
uniform across the surface of the substrate, thus allowing the production of
reproducibly uniform performance .characteristics in the completed fuel cell
electrode.
15 In one embodiment of the electrode of the invention, the
proportion, by weight, of catalyst particles to binder generally is in the
ratio of
96% catalyst/4% binder to 85% catalyst/15% binder preferably, 96% to 88%
catalyst to 4% to 12% of hydrophobic binder resin. Usually the coatings of
catalyst and binder are buiR up upon one side of the carbon fiber paper
2o substrate by application of the metal catalyst particle/binder aqueous
mixture
in the form of a slurry. Subsequent to the application and drying of the
aqueous mixture of metal catalyst particles and binder, the assembly on
carbon fiber paper is heated at a temperature above the melting temperature
of the binder but below the decomposition temperature thereof and,
zs thereafter, the completed electrode can be assembled to form a membrane
' and electrode assembly by bonding the coated side of the carbon fiber paper
3
WO 95/21465 ~ ~ ~ ~ ~ ~~- PCT/US94l01275
to an ion exchange membrane utilizing elevated temperature and/or
pressure.
While the electrodes of the invention are particularly suitable for
use in fuel cells, the electrodes are also useful in electrolytic cells, such
as,
for the production of chlorine and caustic and in the generation of hydrogen
and oxygen in water electrolysis cells. A hydrophilic binder can be utilized
in
the metal particle/binder coating in the preparation of the electrode for use
in
certain electrolytic cells.
Although a number of different types of electrode structures in the
to prior art are suitable for use in fuel cells, each electrode, for optimum
performance in the cell, should be one which is electronically conductive, is
capable of gas diffusion, i.e., will adsorb the fuel or oxidant employed,
contains a catalyst for the electrode reaction, and will not itself oxidize
severely under the operating conditions of the cell.
is Suitable gas adsorbing metals generally include at least one of the
metals of Group VIII series of metals of the Periodic Table Of The Elements,
preferably, the noble metals, for instance, rhodium, ruthenium, palladium,
osmium, iridium, and platinum (platinum black). Other less suitable metals for
forming electrodes include the other metals of Group VIII, e.g., nickel, iron,
2o and cobalt, as well as other metals known to catalytically adsorb gases,
e.g.,
silver, copper and metals of the transition series, e.g., manganese, vanadium,
rhenium, etc.
In addition to electrodes formed of these metals, supported
electrodes are generally formed of platinum or palladium black which has
2s been deposited on a base metal support such as stainless steel, iron,
nickel
and the like. In addition, suitable electrodes, generally, are formed on metal
4
W095I21465 PCT/US9.t/OI275
oxides and on carbon, each of which have been activated by the addition of
platinum or palladium, or on carbon which has been activated with at least
' one of the oxides of iron, magnesium, cobalt, copper, etc.
Since the adsorption of Bases on solids is a surface phenomena, it
s is desirable that the electrodes be of the maximum practicable surface area
and that the surface of the metal particles preferably be in fts most active
state for the adsorption of gases. For maximum cell efficiency, the maximum
permissible area of one side of each electrode should be in complete contact
with the aqueous electrolyte and iihe maximum permissible surface of the
to other side of each electrode should be in contact with the fuel or oxidant
gas.
Foe these reasons, finely divided metal catalyst powders are preferred which
have highly developed surface areas, for example, at least 10 square meters
per gram, and generally up to 100 square meters per gram. Mixtures of two
or more metal catalysts may also be used. For maximum cell performance,
is preferably, the electrodes are made using the very active noble metals of
the
Group VIII metals, for example, platinum black, palladium black, Raney
nickel, etc. Use of the noble metals of the Group VIII series of metals have
the further advantage in that electrode corrosion is avoided when the
electrolyte is an acid. Acid electrolytes cause corrosion conditions at both
the
zo anode and cathode which shorten the life of the celis having electrodes
incorporating metals such as nickel, iron, copper, etc. The corrosive effect
is
not as pronounced in fuel cells using bases as the electrolyte. Long fuel cell
life may be obtained by using any metals which are resistant to bases, for
example, the Group VIII metals, including nickel, cobalt, etc., as well as
other
25 known gas adsorbing metals, e.g., rhenium, in cells having an aqueous base
' electrolyte. The choice between these materials is affected by design
s
W095I21465 _ PCTlUS9d101275
considerations, intended use, desired lifetime, gases used for fuel and
oxidant, etc.
1:
In the preparation of one embodiment of the electrode of the
invention, a subassembly consisting of a coating of catalytic metal particles
and a binder on a carbon fiber paper is first prepared. In the preparation of
an electrode for an electrolytic cell, an aqueous emulsion of a hydrophobic
resin, such as, a fluorinated hydrocarbon resin, such as,
polytetrafluoroethylene is mixed with sufficient metal particles so that the
layer prepared from this mixture is electronically conductive, for example,
l0 2-25 grams of finely divided platinum black per gram of
polytetrafluoroethylene solids in dispersion form is used.
In contrast to prior art methods of forming catalytic layers on
electrodes, it has been found most desirable to utilize the mixture of the
catalytic metal particles and binder in slurry form rather than in coagulated
is form. The advantage of the use of the slurry in forming the catalytic layer
of
the electrode is that this procedure allows the use of coating methods which
can be automated for mass production of the electrode. In addition, such
coating methods provide uniform coating addition, such coating methods
provide uniform coating layers which provide reproducible results in the
2o electrodes produced by the process of the invention. The slurry coating is
dried so as to remove water and the catalytic coating on the carbon fiber
paper is heated so as to sinter the binder, preferably at a temperature of
275°
to 350°C for 2 to 10 minutes. Thereafter, a membrane and electrode
assembly is formed by bonding an ion exchange membrane to the coated
2s side of the carbon fiber paper. Bonding can take place at a temperature,
generally, of 175°C and 500 pounds per square inch pressure,
preferably, '
6
W O 95/21465
PCT/U594/OI275
150 to 180 degrees centigrade and 300 to 800 psi. Thereafter, the
membrane and electrode assembly is cut to the desired shape.
The current collecting grid of the electrodes of the invention is
formed of a carbon fiber paper. Carbon fiber papers suitable for use as the
s coating substrate in the present invention can be purchased or prepared.
Suitable carbon papers are available from a number of commercial sources,
for example, Union Carbide Corporation, Stackpole Carbon Company and
Kureha Corporation. Carbon fiber paper substrates can be prepared from
resin bonded carbon fibers by knovm paper making techniques, as disclosed
to in U.S. 3,972,735. Such carbon papers are generally, wet proofed by
impregnation with a solution or dispersion of a hydrophobic polymer prior to
coating with a catalyst-binder aqueous mixture. The wet proofing treatment
allows gas flow through tile carbon fiber paper substrate in the presence an
aqueous liquid.
is A preferred method for preparing carbon paper substrates is the
process taught in U.S. 4,426,340. Briefly, the process of the '340 patent for
formation of the carbon fiber paper comprises selecting a dry mixture of
carbon fibers and thermosetting resin, depositing tha mixture in a mold, and
then heating and compacting the mixture to bond the fibers. The article so
2o formed is then carbonized in an inert atmosphere by increasing the
temperature at a rate of 40°C per hour to 950°C and holding at
950°C for
one hour. The substrate can be graphitized by heating at 2800°C.
The process of the invention for the production of an electrode
provides considerable latitude in the design of electrode substrates and
2s allows selection of porosity and pore sizes that are adapted to specific
applications. In general, it is desirable to maximize the porosity of the
7
WO 95/21465 ~ ~ ~ ~ ~ ~~ PCTIUS94101275
substrate while preserving the physical strength of the substrate. Carbon
fiber paper substrates having a porosity of between 65% and 80% are
preferred with a porosity between 70% and 80% being most preferred for the '
practice of the present invention. The selection 'of a particular pore size
s distribution depends upon the design of the particular cell and may be
determined by conventional fuel cell design techniques. A mean pore size,
generally, of 10 microns to 90 microns is suitable. A mean pore size of 20
microns to 70 microns is preferred forthe practice of the present invention.
The catalytically active metal particles, whether used in the
to preparation of anode or cathode electrodes are, generally finely divided
and
have a high surface area. For example, in the case of an oxygen or
hydrogen electrode fuel cell, platinum black (surface area greater than 25 sq.
meters per gram) or high surface area (800 to 1800 sq. meter per gram)
platinum on activated carbon powder (average particle size 10 to 30 microns)
is are suitable for use in the preparation of an electrode which is to serve
as the
anode or the cathode. In the case of a chlorine cell, an electrode can be
prepared in which ruthenium dioxide particles are prepared by thermal
decomposition of ruthenium nitrate for 2 hours at 450°C. The resulting
oxide
can then be ground to a fine particle size using a mortar and pestle and the
2o portion of the ground material which passes through a 325 mesh sieve (less
than 44 microns) can be used to prepare an electrode of the invention.
The hydrophobic polymer for use as a binder for the catalytic metal
particles which are coated on the carbon fiber paper substrate generally, can
be any hydrophobic polymer compatible with the electrolyte to be used in the ,
25 fuel cell or other electrochemical cell. Compatible flourinated hydrocarbon
polymers such as polytetrafluoroethylene and flourinated ethylene propylene,
s
WO95121465 PCT/US94/D1275
having molecular weights of 1 X 10f~ or greater are preferred.
Polytetraflourethylene is most preferred and is most widely used as a binder
in this technology. Particularly preferred for use in preparing the electrodes
of
the invention is the aqueous dispersion of polytetrafluoroethylene sold under
the trade designation T-30 by DuPont having a particle size of 0.2 microns.
The solid polymer electrolyte matrices, ion exchange membranes
or sheets which make up the base member of the membrane and electrode
assemblies of the present invention, are weal known in the art. The solid
polymer electrolyte membranes or sheets are composed of resins which
to include in their polymeric structure ionizable radicals, one ionic
component of
which is fixed or retained by the polymeric matrix with at least one ion
conponent being a mobile replaceable ion electrostatically associated with the
fixed component. The ability of the mobile ion to be transported andlor
replaced under appropriate conditians with other ions imparts ion exchange
is characteristics to these materials. The ion exchange resin membranes can
be prepared by polymerizing a mixture of polymerizable ingredients, one of
which contains a precursor of an ionic constituent.
Two broad classes of ration exchange resins are the so-called
sulfonic acid ration exchange resins and carboxylic acid ration exchange
2o resins. In the sulfonic acid membranes, the ration ion exchange groups are
hydrated sulfonic acid radicals which are attached to the polymer backbone
by sulfonation. In the carboxylic acid resins, the ion exchanging group is -
COO-. The ion exchange resins may also be in various salt forms such as
the sodium salt and the potassium salt.
25 In the anion exchange resin membranes, the ionic group is basic in
nature and may comprise amine groups, quarternary ammonium hydroxides,
9
WO 95/21x65 ~ ~ PCT/U59.J101275
the guanidine group, and other nitrogen-containing basic groups. In both the
cation and anion exchange resin membranes, that is, where the ionic groups
are acidic groups (cationic membranes} or where the ionic groups are basic
(anionic membranes} the ionizable group is attached to a polymeric
compound, typical examples of which are a phenol-formaldehyde resin, a
polystyrene-divinyl-benzene copolymer, a urea-forrrialdehyde resin, a
melamine-formaldehyde resin, and the like. The formation of these ion
exchange resins into membranes or sheets is also well known in the art. In
general, they are of two types, (1) the heterogeneous type, in which granules
to of ion exchange resin are incorporated into a sheet-like matrix of suitable
binder, for example, a binder of polyethylene, polytetrafluoroethylene, or
polyvinyl chloride, and (2) the continuous or homogeneous ion exchange
resin membrane in which the entire membrane structure has ion exchange
characteristics. These membranes are commercially available. A typical
is example of a commercially available cationic, sulfonated perfluorocarbon
membrane is the membrane sold by E. I. DuPont de Nemours & Co. under
the trade designation NAFION~. This commercial membrane is more
particularly described as one in which the polymer is a hydrated copolymer of
polytetrafluoroethylene (PTFE) and polysulfonyl flouride vinyl ether
containing
zo pendant sulfonic acid groups. The sulfonic groups are chemically bound to
the perfluorocarbon backbone through a long side chain and the membrane
is hydrated before use in the cell by soaking it in water, preferably at the
boil
for 10-60 minutes. A membrane having 30% to 35% water of hydration,
based upon the dry weight of membrane, is obtained.
25 A preferred class of ion exchange membranes are those having
sulfonic acid functional groups. These materials, on an equivalent weight
to
W095I21465 ~ PCT/US9-t/01275
basis, generally hydrate less, when immersed in water at the boil, in
accordance with prior art hydration procedures, than the sulfonated
' perfluorocarbon membranes sold winder the trade designation NAFION.
The general structure of the NAFION permselective membranes is
s characterized as having the functional sulfonic acid groups at the end of
long
pendant chains attached to the polymer backbone. In contrast, those
materials of the latter referenced patents have shorter chain pendant groups
for attachment of the sulfonic acid functional groups. It is believed that
this
structural difference accounts for the absorption of less water of hydration
in
io these ion exchange membranes when the same concentration of functional
groups is present, as indicated by equal equivalent weight, in the polymer, as
compared with the NAFION ion exchange membranes. As indicated above,
concentration of the functional groups in the ion exchange polymer
membrane is measured in the prioir art by equivalent weight. This is defined
is by standard acid-base titration as tine formula weight of the polymer
having a
functional group in the acid form required to neutralize one equivalent of
base.
Generally the ion exchange membrane is hydrated prior to use in
the electrolytic cell and subsequent to bonding to the electrodes of the
2o invention.A typical procedure for hydrationof an ion exchange
the
membrane or solid polymer electrodeassemblyis as follows.
The
membrane, prior to use, is first from salt form to the
converted the proton
form. The salt form (usually the sadium or potassium salt} is thus converted
by placing it in a strong acid solution, such as sulfuric acid. The membrane
is
zs subsequently washed and boiled. 'Water of hydration is incorporated into
the
membrane by boiling the membrane.
a
WO 95/21465 ~ ~ ~ ~ J ~ ~ - PCTIU59410b375
A method of generating an electric current is also contemplated
comprising feeding streams of a fuel gas and an oxidant gas to a fuel cell,
said fuel cell having at least two electrodes and an electrolyte-containing '
matrix between said electrodes, each electrode having a catalytic metal layer
.
s comprising a catalytic metal particle binder coatingv on one surface of a
.' .
carbon fiber paper and bonded to said matrix on the opposite surface of said
carbon fiber paper, wherein said catalytic metal particle layer comprises a
hydrophobic binder resin and wherein said catalytic metal particles are
present in the amount of 2 to 25 catalytic metal particles per part of binder.
to The improvement in such method comprises oxidizing a fuel at the catalyst
layer of one electrode to generate a stream of electrons, conducting the
electrons to a second electrode, combining the electrons with said oxidant at
the catalyst layer of the second electrode, and transferring ionic species
through the electrolyte to complete the circuit. In such method, the
electrodes
is exhibit superior voltage characteristics as the result of preparing said
catalytic
layer by coating an aqueous dispersion of said hydrophobic binder resin and
said catalytic metal particles utilizing spray application, a metering bar,
metering knife, or metering rod and thereafter heating said carbon fiber paper
and said catalytic metal layer to a temperature at or above the melting
2o temperature of said hydrophobic polymer but below the decomposition
temperature thereof.
The following examples illustrate the various aspects of the
invention but are not intended to limit its scope. When not otherwise
specified throughout this specification and claims, temperatures are given in
2s degrees centigrade and parts, percentages, and proportions are by weight.
12
64693-5158
CA 02181560 2004-O1-30
F_XAM_PLE 1
One embodiment of the electrode of the invention is prepared by
depositing onto one side of a carbon paper fiber substrate an efectrocatalytic
catalyst and, thereafter, bonding to the same side of said substrate an ion
s exchange membrane.
Prior to coating with a catalyst layer, a carbon fiber paper 10-20
mils in thickness, sold under the trade name PC-206 by the Stackpole Fibers
Company; is wet ~ proofed utilizing an aqueous . dispersion of
polytetrafluoroethylerie, sold under the tradename Teflon T-30: The carbon
TM
1o fiber paper can be coated or impregnated with the Teflon T-30 dispersion.
The coated or impregnated paper is dried under a heat lamp utilizing mild
heat and, thereafter, dried in an oven at a temperature of 110°C for 30
TM
minutes. The Teflon T-30 coated paper is, thereafter, sintered in an oven
held at a temperature of 325°C utilizing a heating period of 30
minutes.
~s After cooling the paper; the catalyst layer is applied using an
TM
uncoagulated mixture of Teflon T-30 and platinum black having an
TM
approximate composition of 0.176 grams of Teflon T-30 dispersion per grain
of platinum black. The coating is applied utilizing a number 40 Mayer coating
rod to spread the mixture utilizing 4 passes of the rod over the paper. The
2o coated electrode layer is dried under a heat lamp utilizing a mild heat
and,
thereafter, the electrode coated paper is heated in an oven held at a
temperature of 100°C while purging the oven -atmosphere with an inert
gas
(nitrogen). After 10 minutes of heating at 100°C, the oven is raised to
a
temperature of 325°C and the catalyst layer is heated at this
temperature for
2s a period of 5 to 10 minutes.
13
64693-5158
CA 02181560 2004-O1-30
After cooling, a membrane and electrode assembly is prepared in which the
electrode is bonded to an ion exchange membrane of 800 equivalent weight
and 0.004 inch thickness in accordance with the following procedure. The ion
exchange membrane is sandwiched between the coated sides of two layers
s of the catalytic layer coated carbon fiber paper prepared above. External to
this sandwich there are placed additional sandwich layers of a release paper
impregnated with polytetrafluoroethylene. Overlaying each of these layers
are respectively a first layer of a sheet of a silicon rubber of low
Durometer,
typically 50 -Durometer, and a rigid metal sheet having a thickness of 1!4
io inch. The assembly is, thereafter, placed in a flat platen press at ambient
temperature and the pressure is increased to 500 pounds per square inch
and the temperature is increased to 175°C. At these conditions, the
sandwich is maintained for a period of 5 minutes and then the assembly is
cooled under pressure and removed when the assembly has reached a
is temperature of 50°C. The final membrane and electrode assembly is,
thereafter, placed in a sealed container which contains a small amount of
deionized water.
E)CAMPLE 2 (Control-forming no part of this invention)
An electrode is prepared essentially in accordance with the
20 process described in Technigues of Electrochemistryr, volume 3, edited E:
Yeager and A. J. Salkind, pages 274-275 (1978).
TM
Utilizing a similar concentration of Teflon '~-30 and platinum black,
as in Example 1, a coagulum is prepared by continued stirring of the slurry or
heating, or the addition of a few drops of isopropyl alcohol. The coagulum is
2s placed upon a metal foil substrate (niobium or aluminum) and rolled out to
the
proper dimensions. After the coagulum has been spread onto the surface of
14
WO 95!21465 PCT/CJS94I01275
the substrate, the electrode layer so formed is sintered in a nitrogen
atmosphere in an oven held at a temperature of 325°C. After 10 minutes
of
heating, the catalyst layer is removed from the metal foil and, thereafter,
bonded to an ion exchange membrane and carbon fiber paper, in
accordance with the procedure described in Example 2. Alternatively, the
coagulum can be coated onto a piece of wet proofed carbon fiber paper, as
was used in Example 1. The metal foil or wet proofed carbon fiber paper can
be coated with the coagulum to the desired thickness and uniformity utilizing
a glass rod. A typical coating thickness is approximately 1-3 mils. This
to procedure is a minor modification of the process described on pages 274 and
275 of the Yager et al. (editor) reference cited above in that in the
procedure
of this example, the catalyst (platinum black) is not utilized in conjunction
with
a supporting material such as active carbon.
The electrodes of ExamKrles 1 and 2 were evaluated in a fuel cell '
I5 constructed generally in accordance with that described in Aircraft
Equipment
Division Report LANL-29, entitled J,~ rie m Rerzort. New h~embrane Cats~J,~rst
for
Solid Polymer Electrode Systernc, P.O. No 9-X53-D6272-1, by R.J.
Lawrence of the General Electric Company. A comparison of the electrodes
was made under polarization conditions as follows: The electrode of
2o Example 1 provided an open circuit potential of 1.06 volts, 0.927 volts at
100
amps per square foot, and .851 volts at 500 amps per square foot. The
electrode of Example 2 when tested similarly, provided an open circuit
voltage of 1.00 volts, 0.884 volts at 't00 amps per square foot, and 0.75
volts
at 500 amps per square foot. The electrodes were tested at 85°C
utilizing 40
,,
2s pounds per square inch guage of hydrogen and 60 pounds per square inch
gauge of oxygen pressure. The ion exchange membrane utilized to bond to
is
W095/21465 '~ ~ $ ~ ~~~ PCTIUS94101275
the coated side of the carbon fiber paper catalytic layer coating was
characterized as an 800 equivalent weight icn exchange membrane having a
thickness of 0.004 inch.
16
