Gas diffusion electrode

A gas diffusion electrode is now prepared which offers extended, efficient operation. For this, the electrode matrix may include a hydrophobic layer containing hydrophobic polymer. The electrode has hydrophilic ingredient of particulate carbon bound by hydrophilic, halogenated polymer binder. The particulate carbon used is a catalyzed carbon. The resulting efficient electrode is capable of extended operation. Moreover, on the one hand carbon catalysis can now be done in economical, straightforward manner, while on the other hand the electrode can have a surface overlay of a dimensionally stable, thin non-cellulosic paper. Such paper may be pressed against the underlying component material by a foraminous overlay, e.g., a metal mesh.

BACKGROUND OF THE INVENTION 
Porous electrodes containing catalytic particulates have been developed to 
enhance the commercialization of electrolytic devices such as fuel cells 
and metal-air batteries. The electrodes can be useful as oxygen cathodes 
in such batteries and fuel cells. To enhance their commercial potential, 
efforts have been extended to augment the electrode capability to operate 
at high current densities coupled with acceptable durability. 
Attention has also been paid to the development of efficient and economical 
electrodes capable of performing in the harsh chemical environments 
created by acid or alkaline electrolytes. It has been necessary to attempt 
to maintain a balance for the permeability of the liquid electrolyte and 
for the gaseous reactant. Progress in electrode development has led to, 
for example, electrodes capable of sustained performance at current 
densities substantially above about 400 milliamps per square centimeter, 
while exhibiting acceptable resistance to electrolyte. However, long 
operating life with sustained, desirable performance including resistance 
to electrode flooding while retarding undesirable depletion of catalytic 
activity is still needed. 
SUMMARY OF THE INVENTION 
An electrode has now been Prepared which, especially as a gas diffusion 
electrode, offers efficient operation coupled with prolonged electrode 
life. Moreover, efficient electrode start up can now be achieved together 
with highly desirable electrode working potentials at high current 
density. It is further contemplated in such application, e.g., as an 
electrode for a metal-air battery, that the usual electrode backing layer 
may be dispensed with. Additionally, in such application, it is 
contemplated to prepare an electrode having a backing layer, but where the 
active layer is free from gas supplying material. 
Furthermore there is now provided rapid, economical blending of macrocyclic 
compound catalyst with particulate catalyst carrier, e.g., particulate 
carbon to be used in the electrode. Such mixing is achieved without 
inefficient solvent processing. Moreover, gas diffusion electrodes have 
now been prepared which have enhanced dimensional stability and resistance 
to elevated gas pressure An electrode of multi-layer construction is 
fabricated that not only has such stability but also ease and economy of 
manufacture. It is also contemplated that the developed technology can be 
further useful for enhanced catalyst utilization such as in solid polymer 
electrolyte application. 
In a broad aspect, the invention pertains to an electrode of extended 
performance at high current density, the electrode comprising a gas 
supplying, gas porous layer containing hydrophobic polymer, and an 
electrolyte porous active layer comprising catalyst containing carbon 
particles intimately blended with, and uniformly distributed throughout, 
hydrophilic, halogenated polymer binder for said catalyzed carbon 
particles. 
In another aspect, the invention is directed to the above-described 
electrolyte Porous active layer as such electrode without a gas supplying 
layer. Moreover, where such gas supplying layer is present, the invention 
is further directed to an active layer which is free from gas supplying 
material. 
In further aspects, the invention is directed to a blended particulate 
mixture for preparing such electrodes, as well as to methods for preparing 
both such a mixture or the electrode itself. In another aspect the 
invention is directed to a gas diffusion electrode of enhanced stability 
having non-cellulosic paper in pressed engagement with the electrolyte 
face of the electrode. In yet a still further aspect the invention 
pertains to the straightforward preparation of catalytically active carbon 
for use in the electrode. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The terms "gas diffusion electrode" or "sheet electrode" as they are used 
herein relate to not only the air or oxygen cathodes as find application 
in metal-air batteries, such as aluminum air batteries, but also relates 
to such electrodes as may find use in applications such as for solid 
polymer electrolyte application and related fuel cell applications. It is 
therefore meant to be understood that the electrode of the present 
invention need not be limited to use as an air cathode, i.e., limited to 
use for oxygen reduction, but can be employed in a variety of reactions 
including hydrogen oxidation, sulphur dioxide oxidation and organic fuel 
oxidation. 
Moreover, a variety of electrolytes may come into contact with the gas 
diffusion electrode of the present invention, as represented by acid 
electrolytes, alkaline electrolytes and saline electrolytes. The 
electrolytes may be non-aqueous systems, and therefore the electrode may 
find use in applications such as organic electrolyte batteries. Where the 
electrode of the present invention may be made up from two layers, there 
will be used terms herein to describe the one, or hydrophobic layer, such 
as the "wetproof layer" or "backing layer" or "gas supplying layer." This 
layer can be made of "hydrophobic ingredient" or "gas supplying material". 
Then the other, or hydrophilic layer, may often be referred to herein as 
the "active layer" and the material used in preparing it as the "active 
material" or "hydrophilic ingredient". Such active material can consist of 
a mixture of finely-divided catalyzed carbon plus hydrophilic binder, 
e.g., hydrophilic polymer. 
A "dual phase active layer" will contain both active material plus gas 
supplying material. The gas supplying material for this use, as well as 
for the gas supplying layer itself, can be composed of uncatalyzed 
particulate substance, e.g., carbon, plus hydrophobic binder such as 
hydrophobic polymer. 
More specifically in the active layer composition there will be present a 
catalyzed carbon. The suitable carbons for the catalyzed carbon can 
include amorphous as well as crystalline carbons. Representative carbon 
blacks that may be employed as the particulate carbon are the furnace 
blacks and acetylene blacks. It is contemplated that where active carbons 
are present, they may be activated in any manner known for preparing such 
particulate carbon. As used herein, the term "particulate carbon" is meant 
to include both carbon black as well as activated carbon. In use in 
preparing the electrode, the particulate carbon will most typically be 
very finely divided. Suitable materials will usually have particle size on 
the order of from 5 to 300 nanometers, e.g., activated carbons having size 
within the range of from about 5 to about 150 nanometers, but with 
agglomeration, agglomerated particles may reach sizes of 1000 to 10,000 
nanometers. A preferred particulate carbon for the active layer is steam 
activated acetylene black. 
In the processing for preparing the active layer, the particulate carbon is 
combined with catalyst, thereby forming catalyzed carbon. Representative 
catalysts can include catalysts such as for methanol oxidation as well as 
electrochemically active substances. The electrochemically active 
substances may be platinum group metals or platinum group metal oxides, as 
well as other metal oxides. Where the electrode will be used in solid 
polymer electrolyte application, the utilization of a platinum group metal 
catalyst as metal or oxide or both can be especially serviceable. Suitable 
catalyst can also be prepared during heating of macrocyclic compound 
substances. The term "macrocyclic compound" catalyst is used herein for 
convenience, although it will be understood that it is the residue 
remaining upon heating such compound, e.g., at an elevated temperature of 
at least about 400.degree. C., that provides the catalytic activity. For 
the platinum group metal catalysts, one or more of ruthenium, palladium, 
rhodium, platinum, and iridium may be employed. For the platinum group 
metal oxides there can be used any of those known for their 
electrochemical activity. For the other metal oxide catalysts, such can 
include magnetites, ferrites, spinels, e.g., cobalt spinel, perovskites 
and the like. Mixed metal oxide coatings such as a solid solution of a 
film-forming metal oxide and a platinum group metal oxide may also be 
serviceable. For the macrocyclic compound group, these can include 
tetramethoxyphenyl porphyrin complexes, e.g., the cobalt complex (CoTMPP), 
cobalt and iron phthalocyanine, tetracarboxylated iron phthalocyanine 
complex, tetra-aza annulene complexes and tetraphenylporphyrin complexes, 
such as of cobalt and iron. 
Preferably, for most efficient operation, the catalyzed carbon for a gas 
diffusion electrode used in a metal-air battery application contains 
CoTMPP residue as catalyst. That is, the CoTMPP compound is blended with 
the carbon and by heating to leave a residue, the catalyzed carbon is 
prepared. Usually the heating will be at an elevated temperature within 
the range from about 500.degree. C. to about 900.degree. C. Such heating 
will be in an inert atmosphere, e.g., argon or nitrogen, and for a time 
few hours, with about two hours being sufficient. Although the cobalt 
complex is preferred, it is to be understood that other metals may be 
employed, including iron, nickel, copper, vanadium, chromium, ruthenium, 
rhodium, palladium and silver, as well as combinations thereof. 
Although conventional solvent methods may be employed for combining 
macrocyclic compound catalyst with the particulate carbon, it is a 
particular feature of the present invention that such combination be 
provided by direct mixing or wet milling procedure. For direct dry 
blending, such may be initiated by any blending operation useful for 
combining Particulate, free-flowing solids. Suitable equipment for such 
blending can include cone blenders, V-blenders, ribbon blenders and the 
like. It is advantageous for a most intimate blending of catalyst and 
carbon that after an initial moderate blending operation, such blend be 
then subjected to a vigorous milling operation or the like, e.g., 
ultrasonic agitation. There usually results from such operation a mixed, 
dry particulate having particles more finely-divided then about 20 
microns. Serviceable milling apparatus for this more vigorous blending 
include hammer mills and ball mills. 
As an alternative to direct dry blending, the macrocyclic compound may also 
be wet blended with the Particulate carbon. As in the above described dry 
blending operation, this wet method is similarly free from dissolution of 
the macrocyclic compound in blending medium. For this operation, 
crystalline macrocyclic compound can be dispersed in suitable wet milling 
liquid medium, usually an organic liquid medium such as isopropyl alcohol, 
with the milling generally proceeding at a low temperature, e.g., a 
temperature of about room temperature or above, but not exceeding the 
boiling point of liquid medium. The particulate carbon can be added while 
the dispersion is agitated. As an alternative, the blended solids may be 
sprayed with organic liquid during blending to provide the wet milling 
mixing operation For use in the wet milling operation, suitable equipment 
includes ball mills and colloid mills. The resulting mixture from the wet 
milling will then be typically filtered and dried and any remaining liquid 
medium can be volatilized from the resulting filter cake during the 
subsequent heating step for preparing the catalyst from the macrocyclic 
compound. 
In the continuation of the preparation of the active material, the 
catalyzed carbon is blended with hydrophilic halogenated polymer. In the 
blend, the particulate, catalyzed carbon will usually provide from about 
35 to about 90 weight percent of the blend. Less than about 35 weight 
percent may provide insufficient reaction sites in the active layer as 
finally prepared. On the other hand, greater than about 90 weight percent 
of particulate carbon may lead to insufficient Presence of polymer binder 
and thus deleterious tensile strength of the resulting active layer. 
Usually, the particulate, catalyzed carbon will be present in the blend in 
an amount sufficient to provide the active material with such catalyzed 
carbon in an amount from about 60 to about 80 weight percent 
As mentioned hereinabove, the blend for preparing the active material 
contains catalyzed carbon present with hydrophilic halogenated polymer. 
Generally, all of the polymer for the active material will be hydrophilic 
halogenated polymer, although it is contemplated that such polymer other 
than halogenated polymer can be included. For the halogenated polymer, 
chlorinated and fluorinated polymer, or those which are both may be used. 
Advantageously for efficiency, the polymer will be a halogenated 
fluorinated polymer. In selecting polymer to be used, it is preferred if 
it can be solubilized, as will be more particularly discussed hereinbelow. 
Also, the polymer selected should be stable in the environment in which 
the electrode is used, for example in an aluminum-air battery the polymer 
should be stable in strongly alkaline solutions at temperatures well above 
ambient, e.g., up to 80.degree. C. or more. 
Typically, there will be present in the active material layer from about 10 
weight percent up to about 65 weight percent of the hydrophilic polymer, 
basis weight of polymer plus particulate catalyzed carbon. Use of less 
than about 10 weight percent of the polymer will not provide sufficient 
tensile strength for the electrode in use. On the other hand, greater than 
about 65 weight Percent of the polymer can deleteriously affect the 
activity of the electrode. Usually there will be present from about 10 to 
about 40 weight percent of the polymer, basis total particulate catalyzed 
carbon and polymer weight 
As mentioned hereinbefore, preferred hydrophilic polymers are those which 
can be solubilized, in whole, or in part, for best blending with the 
catalyzed carbon, although it is contemplated that serviceable polymers 
may essentially be only well dispersed in liquid medium The resulting 
solution, or in some instances a mixture more nearly approximating a 
dispersion, can then be mixed with the catalyzed carbon. Whether the 
polymer is totally or partly solvated, or present as essentially a 
dispersion, for convenience herein such may be referred to as a "solution" 
of the polymer, or reference may merely be made to the polymer having been 
"established" or "prepared" or the like in a solvent medium for same. 
Preferred fluorinated polymers as the hydrophilic polymers have functional 
groups on the fluorocarbon chain which are pendant to the main polymer 
backbone. These polymers may be prepared from at least two monomers that 
include fluorine substituents. One of the monomers can be represented by 
tetrafluoroethylene and the other by substances such as fluorocarbon vinyl 
ethers having an acid or acid precursor group. The polymers may have 
functional groups including pendant sulfonyl, carboxyl or, in some cases, 
phosphonic acid groups. Additionally, esters, amides or salts based upon 
the functional groups, may be useful, e.g., the lithium salt form of the 
sulfonyl group. Where the blend of catalyzed carbon plus polymer may be 
used in a solid polymer electrolyte application, it will be useful to 
employ the polymer as the ionizable hydrogen form. Representative 
hydrophilic fluorocarbon polymers which may be termed herein "fluorinated 
ionomers", can be represented by those containing sulfonate groups, and 
these can be referred to for convenience herein as perfluorosulfonate 
ionomers (PFSI's). 
Although hydrophilic fluorinated polymers are preferred, solutions which 
are especially preferred for economy have at least a major amount of PFSI. 
Typically those solutions consisting solely of PFSI have on the order of 5 
to 10 weight percent of such polymer. In general, the polymer solutions 
may be prepared in a solvent of polar organic compounds or low boiling 
alcohols. A composition of especial interest for economy, is the lithium 
salt form of PFSI solubilized in sulfolane. In solution, the hydrophilic 
polymer can be mixed with the catalyzed carbon by any suitable means for 
combining a particulate solid with a solution, e.g., merely adding the 
catalyzed carbon to the polymer solution accompanied by vigorous 
agitation. Following the blending, the resulting dispersion can be dried 
to a damp material, usually having a consistency initially of a mud, and 
then finally to a more form stable, dry product, usually all at a moderate 
temperature and pressure, if pressure above normal pressure is employed. 
It will then most always be desirable to communicate the resulting dry 
product A coarse grinding or chopping action is serviceable for at first 
preparing coarse particulates. These coarse particulates may then be 
processed by any method for preparing a very finely divided product, e.g., 
vigorous milling. The milling should proceed for a time sufficient to 
provide a product having a particle size finer than about 40 microns 
Usually, such particles will not be more finely divided than about one 
micron, with all particles typically being within the size range of from 
about one micron to about 25 microns. Individual particles can be expected 
to have catalyzed carbon particles bound with the hydrophilic polymer. 
Where the sheet electrode will serve as a gas diffusion electrode, another 
component that may be present in the active layer is the hydrophobic 
ingredient. This ingredient can be in particulate form and processed right 
along with the active material. In this processing, there can be mixed 
together particles of active material along with particulate hydrophobic 
ingredient. When the active layer comprises active material plus 
hydrophobic ingredient, it will be possible to prepare a serviceable gas 
diffusion electrode without a backing layer. Also, where a backing layer 
is used, the active layer may or may not contain hydrophobic ingredient. 
This hydrophobic ingredient whether Present as a separate backing layer or 
as an active layer component with the active material, usually comprises a 
mixture of particulate substance, e.g., particulate carbon such as 
uncatalyzed carbon, with hydrophobic polymer. It will sometimes however be 
suitable to employ just the hydrophobic polymer, e.g., when added to the 
active material for preparing the active layer, or when Preparing the 
backing layer itself. The particulate carbons which may be employed where 
the polymer plus particulate carbon are used, are most always those which 
are typically poorly catalytic and usually more crystalline. Graphite may 
also serve as a suitable particulate carbon in the hydrophobic ingredient. 
When particulate, uncatalyzed carbon is used with hydrophobic polymer, it 
will usually be very finely divided, having all particles finer than about 
0.3 micron with the useful carbons usually having particles sized within 
the range from about 5 to about 200 nanometers. In use, the particulate 
carbon can be expected to contain agglomerates composed of these most 
finely-divided particles. Advantageously, for economy, the suitable 
particulate carbons will include acetylene black and similar low surface 
carbon blacks having an average Particle size of on the order of about 50 
nanometers. 
For the hydrophobic polymer, contributing to this polymer there can be one 
or more of polymers such as various vinyl resins, as well as polyethylene 
and polypropylene type hydrocarbon polymers of molecular weight 
approaching 1,000,000 or even more. Most always the useful polymer will be 
a halocarbon polymer including the fluoropolymers. Particularly useful 
fluoropolymers are polytetrafluoroethylene (PTFE), 
polychlorofluoroethylene and ethylene-propylene copolymer (FEP). Mixtures 
of these resins are also serviceable. 
Typically, the particulate, uncatalyzed carbon or the like will be blended 
with finely-divided dry hydrophobic polymer or with a liquid dispersion of 
the polymer. If a dispersion is used, subsequent heating is employed to 
prepare a dry blend, as well as remove wetting agents that can be 
incorporated in the dispersion. Most always for such blend the polymer 
will contribute from about 20 to about 60 weight percent of the blend, 
basis polymer plus particulate. Less than about 20 weight percent can 
provide insufficient polymer for desirably binding all particles, e.g., 
uncatalyzed carbon particles, while greater than about 60 weight percent 
of polymer can lead to low gas porosity for a material such as a backing 
layer made from the blend. 
After mixing, the blend can then be heat treated to bind the carbon and/or 
similar particulates of the blend with the polymer. Usually, sufficient 
heat is applied to melt and diffuse the polymer. For example, with a blend 
of PTFE and FEP heating at a temperature of about 250.degree.-350.degree. 
C. and for a time of approximately 1 to 4 hours will usually be 
sufficient. Upon cooling, the resulting heat treated blend can be 
comminuted, such as by milling, to form finely-divided particles of the 
particulate substance bound with hydrophobic polymer, with all such 
finely-divided particles usually being within the size range of from about 
one micron to about 50 microns. 
Where a gas supplying layer will be prepared from this resulting 
particulate blend, or will be prepared from particles of hydrophobic 
polymer itself, or be prepared from a mixture of these materials, the 
blend or the polymer itself or the mixture may first be dispersed in a 
liquid medium. Such a medium will usually be a low boiling organic liquid 
medium, as from an alcohol such as isopropanol or from a blend of 
alcohols. The particles can be vigorously mixed into the medium by any 
suitable means for blending a solid particulate into a liquid to form a 
uniform dispersion. Where such dispersion technique is employed for 
forming the gas supplying layer, the dispersion medium can then be 
filtered onto a separable substrate, e.g., an asbestos paper or similar 
filter paper. After formation of a freshly deposited damp layer on the 
separable filter substrate, the damp layer will generally be dried as by a 
heat treatment to volatilize dispersion liquid medium by heating at a 
moderate temperature of about the boiling point, or above, for the liquid 
medium, e.g., on the order of 100.degree. C., while under moderate 
pressure, such as 100-500 psi. Continuing drying, but at elevated 
pressure, is usually sufficient for providing the gas supplying layer. 
For preparing an active layer, such as from active material but more 
usually from a blend of active material plus gas supplying material, the 
layer formation can be initiated in similar manner. That is, particulate 
ingredients may be uniformly dispersed in liquid medium, e.g., an alcohol 
medium. Where both active material and gas supplying material are present, 
this blending will combine at least from about 1.5 weight parts of the 
active material with about one weight part of the gas supplying material. 
Less than about 1.5 weight parts can be insufficient for desirable 
catalysis at efficient reaction rates. Since the gas supplying material 
can be diminished to the point of elimination in the active material, all 
proportions greater than 1.5 to 1 are contemplated. The uniform dispersion 
of particulates in liquid medium can then be filtered to provide the 
initial, wet active layer. Where the above-described gas supplying layer 
will be used in sheet electrode preparation, such layer may serve as the 
"filter paper". By this means, the dispersion medium of active ingredient 
then is passed through the gas supplying layer leaving the active layer in 
intimate deposition thereon. As in the formation of the gas supplying 
layer, the damp, freshly deposited active layer can then be dried, e.g., 
at a moderate temperature usually at, or slightly above the boiling point 
of the dispersion liquid medium, while under a moderate, mechanical 
pressure, such as approximately 100-500 psi, although a very elevated 
Pressure, e.g., on the order of 2000-3000 psi or so may be employed. The 
resulting dried layer will then be sintered, under pressure. Typically, 
again only a moderate pressure, of on the order of approximately 100 to 
500 psi will be employed, although a more elevated pressure of 1000 psi or 
a very elevated pressure of usually not in excess of 3000 psi can be used. 
This sintering is conducted at a temperature sufficiently low enough so as 
not to endanger any deleterious polymer decomposition. Generally sintering 
temperatures will not exceed above about 350.degree. C. Where sulfonic 
acid groups are present in the hydrophilic fluorinated polymer and these 
groups are to be preserved during heating, the heating will not exceed 
about 280.degree. C. Heating times of on the order of about a few minutes, 
e.g., 5 to 10 minutes, to not more than about one-half hour are 
sufficient, although a duration of heating of 1 to 2 hours or more may be 
used. 
For preparing a more rugged, self-sustaining electrode, there may be used 
on broad planar faces of the sheet electrode a foraminous overlay, e.g., a 
mesh structure. Such can be a screen of woven wire cloth or expanded metal 
or fiber metal having an extensive open area, although materials other 
than metal meshes may be used. The extensive open area permits ready 
access through the foraminous overlay of air or electrolyte to the 
underlying sheet electrode. Regardless of specific construction, the 
preferred structure will usually be referred to herein as simply the 
"mesh." The material of the mesh may be electrically conductive and, 
particularly when in contact with electrolyte, is most always corrosion 
resistant, i.e., resistant to corrosion by the electrolyte, including 
caustic battery electrolyte. By being electrically conductive, a grid on 
the face of the hydrophilic layer face of a gas diffusion electrode can 
serve as a cathode current collector. 
Where metal meshes are used, the metal of the mesh may typically be nickel, 
lead, tantalum, gold, silver, or silver plated nickel, or silver plated 
copper, possibly with a strike such as a nickel strike. Other materials 
that may be used for the mesh include corrosion resistant plastics if 
electrical conductivity is not needed, as well as valve metals for acid 
electrolytes. Differing meshes can be used on each side of an electrode, 
e.g., on both the gas face as well as the electrolyte face of a gas 
diffusion electrode. For example, an expanded nickel mesh can be used on 
the electrolyte face and a nickel woven metal cloth grid can be used on 
the gas face. For the woven wire meshes, these will typically be comprised 
of wires that are from about 0.1 to about 0.2 millimeter in diameter 
These meshes are pressed into the face of the electrode. The meshes can be 
pressed into dried electrode material, which may then be sintered. More 
usually, the meshes are pressed into damp, freshly deposited electrode 
material before such material is heat treated. The pressure employed can 
range from a moderate pressure of on the order of about 500 psi, which 
will be sufficient for desirably pressing the overlayed mesh into the 
underlying sheet electrode face, up to elevated pressures of 1000 psi or 
so, or ranging up to a very elevated pressure of about 3000-4000 psi or 
more. 
It is of particular interest in the present invention, that the electrolyte 
face of a gas diffusion electrode be provided with an overlay of a 
wettable, liquid-permeable and dimensionally-stable sheet of 
non-cellulosic paper. This paper can serve as a gas barrier when wetted, 
thereby resisting gas blow-through from the pressurized gas side of the 
electrode. Such paper, together with the mesh, thereby assists in 
providing a most durable form-stable electrode. Suitable papers include 
asbestos paper and other electrolyte absorbent mineral fiber papers as 
well as glass paper and ceramic papers. For use with the electrode, such 
papers should have thickness on the order of less than about 20 mils for 
best liquid permeability. By being dimensionally stable it is meant that 
the paper will be resistant to deleterious swelling or other change, e.g., 
substantial separation from the underlying electrode, while in contact 
with the electrolyte medium. Such medium, for example caustic battery 
electrolyte, can wet and swell cellulosic paper and will also be 
corrosive. Hence suitable paper needs to be corrosion resistant. 
These papers can be "staked" to the electrode face by a foraminous overlay, 
e.g., metal mesh, during a pressing operation. Thus the Paper may be used 
without employing adhesives or other similar fastening means, there being 
needed only the mechanical pressure of the overlay compressed to the 
electrode. Where such papers may be temperature sensitive, e.g., subject 
to some degradation at temperatures approaching 250.degree.-350.degree. 
C., it is advantageous to stake the papers to the sheet electrode after 
the sintering operation. During the "staking" operation of the paper to 
the electrode substrate with the foraminous overlay, the paper may be 
stretched as well as staked thereby providing a most desirable close 
contact between paper and underlying electrode component.

The following examples show ways in which the invention has been practiced 
but should not be construed as limiting the invention. 
EXAMPLE 1 
Preparation of catalyzed carbon by direct combination 
The conventional method of application of cobalt tetramethoxyphenyl 
porphyrin (CoTMPP) to carbon is from a solvent. But it has been found that 
an at least equally active catalyst can be prepared by intimately mixing 
carbon and CoTMPP by a milling operation, followed by heat treatment. For 
this, a 50 gram (gm.) sample of steam activated acetylene black 
(Shawinigan.TM. Black) was blended with 5.55 gms. of crystalline CoTMPP in 
a V blender (Patterson Kelly) for 15 minutes. The mixture was then 
comminuted by passing through a hammer mill. Subsequently the 
carbon-catalyst mixture was transferred to a silica tray and placed in a 
controlled atmosphere furnace. Nitrogen was allowed to flow through the 
furnace for 60.degree. C. in minutes and then the furnace was set to reach 
800.degree. C. 120-150 minutes, held at 800.degree. C. for two (2) hours, 
and then cooled to room temperature with nitrogen flowing continuously. 
Scanning Electron Microscopy studies show that CoTMPP is uniformly 
distributed on the carbon during heat treatment by this direct combination 
method. 
EXAMPLE 2 
Catalyzed carbon treated with hydrophilic polymer binder 
An 87 gm. sample of hydrophilic fluorinated polymer, more particularly a 
perfluorosulfonate ionomer produced by E. I. du Pont de Nemours under the 
trademark of NAFION and having an equivalent weight of 1100, was soaked in 
an aqueous solution of 10 weight percent HCl at room temperature for three 
(3) hours. This soaking was repeated and then the polymer was rinsed in 
deionized water. The rinsed polymer was soaked for 17 hours in 150 gms. 
per liter of LiOH, washed and dried. A 40 gm. sample of the polymer was 
cut into small pieces, placed into a reactor with 360 gms. of sulfolane 
and stirred at 250.degree. C. for 90 minutes in nitrogen atmosphere. This 
resulted in an apparent solution of the polymer sample. 
A 10 gm. portion of the catalyzed carbon, plus 8.4 milliliters (mls.) of 
the above-prepared 10 percent polymer solution together with 100 mls. of 
acetone were then dispersed for 30 minutes in an ultrasonic bath, and 
dried to the consistency of a mud at room temperature. Finally, sulfolane 
was removed at 200.degree. C. in a vacuum oven, during an 18-hour period. 
The product was then finely chopped in a coffee grinder and hammermilled 
to a fine powder having a particle size of less than about 5 microns. 
EXAMPLE 3 
A 24.7 mls. sample of hydrophilic fluorinated polymer solution (duPont 
NAFION 1100EW polymer having SO.sub.3 H functionality, as a 5 weight 
percent solution in lower aliphatic alcohols and water) together with 150 
mls. of isopropanol, and 10 gms. of catalyzed carbon were stirred for 30 
minutes in an ultrasonic cleaning bath. The mixture was then dried with 
constant stirring to minimize film formation as it dried. The product was 
chopped and pulverized as in Example 2 to prepare an active material 
having a particle size of less than about 5 microns. 
A gas supplying material was prepared by dispersing 70 weight parts of 
carbon black (Shawinigan Black) in water. To this there were added 
dispersions of particulate polytetrafluoroethylene (PTFE) (TEFLON.TM. 30 
dispersion from duPont) and of particulate ethylene-propylene copolymer 
(FEP)(FEP-120 dispersion from duPont) sufficient to provide 10 weight 
parts of PTFE and 20 weight parts of FEP. The resulting dispersion was 
dried and heat treated at 300.degree. C. for 20 hours to destroy the 
wetting agents which were originally in the fluoropolymer dispersions 
used. The product was then hammermilled to a fine powdered gas supplying 
material having a particle size of less than about 50 microns. 
The two materials, the active material and the gas supplying material, can 
then be combined to form the active layer of a gas diffusion electrode. 
EXAMPLE 4 
A gas supplying layer was prepared by filtration from isopropanol on a 
separable filter paper. For this layer, the material used was an alcohol 
dispersion of the carbon black/PTFE/FEP fine powder described in Example 
3. Sufficient dispersion was deposited on the filter paper to deposit 10 
milligrams (mg.) (dry basis) of material solids per sq. cm. (cm.sup.2) of 
filter substrate. A silvered nickel 50.times.25 mesh current collector was 
cold pressed in the resulting damp layer of solids, which freshly 
deposited layer was then dried at about 100.degree. C. while compressed at 
about 500 psi. The mesh current collector was silver plated, nickel coated 
copper wire of about 0.12 mm. diameter with 25 individual wires per inch 
in one direction and 50 wires per inch in the other direction, the mesh 
weighing 35 milligrans/cm.sup.2 (mg/cm.sup.2). The filter paper was 
removed and the dried layer was then pressed flat at 1,000 psi while at a 
temperature of 110.degree. C., thereby forming an air cathode backing 
layer. 
A mixture of the finely powdered active material prepared as the product in 
Example 2, together with the gas supplying material of Example 3 was 
blended in isopropanol. The mixture was filtered on the above-prepared 
backing layer which provided a freshly deposited active layer containing 
14 mg/cm.sup.2 of active material and 9 mg/cm.sup.2 of gas supplying 
material, both dry basis, in the active layer. 
An open expanded nickel mesh was pressed into the face of this active layer 
of the electrode. The mesh is designated as 5Ni7-1/0 by the fabricator of 
the expanded mesh, i.e., the mesh has 5 mils thick, 7 mils wide strands 
and a 1/0 pattern providing 65 openings/in.sup.2 of mesh. 
The resulting dual phase electrode was dried and pressed at 2000 psi, 
vacuumed to remove isopropanol absorbates and finally sintered at 
300.degree. C. under a moderate pressure of 200 psi, completing the 
preparation of the electrode. 
EXAMPLE 5 
One square inch of an electrode prepared as indicated in Example 4, was 
life tested as an air cathode in a cell having a chemically inert nickel 
counter-electrode, a heater, stirrer, a thermostat and a D.C. power 
source. The nickel anode evolved oxygen at the same rate at which the air 
cathode consumed oxygen from a circulating air supply. The air supplied 
was scrubbed substantially free of CO.sub.2, and flowed at four times the 
theoretical requirement. The cell electrolyte was a mixture of 4N KOH and 
lN KAlO.sub.2, and was maintained at 80.degree. C. 
An hour after wet-down, current was applied and reached 450 milliamps (ma) 
per cm.sup.2, in steps, 4 hours after starting at 50 ma/cm.sup.2. At 450 
ma/cm.sup.2, the cathode voltage was initially 0.53 volt, measured against 
the reversible hydrogen electrode, and improved to 0.77 volt within 3 
hours. Current was then maintained at 450 ma/cm.sup.2 for the duration of 
the test. Voltage slowly declined to 0.54 volt over the next 134 days, at 
which point the test was discontinued. 
In addition to attaining a lifetime not previously achieved, a notable 
feature of the start-up was the speed with which the electrode reached a 
satisfactory working voltage at the high current density tested. 
EXAMPLE 6 
Another electrode was prepared identically to the electrode of Example 5 
with the exceptions that the hydrophilic fluorinated polymer used in the 
active material binder was in the hydrogen form rather than the lithium 
salt form, and was used at a higher level, i.e., 30 percent, as opposed to 
the 10 percent, as shown in Example 2. When the electrode was tested as an 
air cathode in a similar manner as in Example 5, a two-month life was 
achieved. 
Still another electrode, prepared as above-described and using 30 percent 
of the hydrogen form of the hydrophilic fluorinated polymer binder was 
tested. The electrode operated for 115 days at 450 ma/cm.sup.2 as an air 
cathode before electrode failure. 
Samples of electrode active layers made similarly to those above described 
were then subjected to tensile strength testing. This test was conducted 
by preparing a sintered dual phase active layer, without metal mesh or 
expanded metal, in the shape of a test specimen and pull testing it in the 
plane of the layer. For this test, the electrodes used were each of 1/2 
mm. thickness. As shown in the table below, samples for each composition 
were tested after sintering at different temperatures, while under 200 psi 
compression. 
For each test sample, the active layer constituted 60 weight percent active 
material and 40 weight percent gas supplying material. Results are 
reported in the table below. 
TABLE 
______________________________________ 
Tensile Strength, psi At 
Indicated Sinter 
Weight Percent NAFION 1100EW 
Temperatures 
In Layer Active Material 
250-265.degree. C. 
285-300.degree. C. 
______________________________________ 
10% 0 0 
30% 31 43 
40% 45 53 
______________________________________ 
Additionally, the gas supplying material, only, was made in to a layer of 
about 2/3 mm. thickness and sintered at the two temperatures indicated. 
The tensile strength for the material was 34 and 36 psi, respectively, at 
the lower and higher sintering temperatures, indicating that the strength 
of the layer was controlled by the weaker component of the two. 
EXAMPLE 7 
For protecting an electrode with a gas barrier paper, an electrode of 
bilayer construction was selected. The paper was 5 mil thick Ce Quin 
binder-containing ceramic paper, manufactured by Quin T Corporation. The 
paper layer was juxtaposed to the face of the active layer of the 
electrode before adding the face mesh. The mesh used was the 5Ni7-1/0, 
mesh described in Example 4, which was then flattened and placed atop the 
ceramic paper and pressed at a very elevated pressure of 3,000 psi to 
embed the mesh and paper in the electrode face. After pressing, it could 
be determined by visual inspection that this procedure not only staked the 
paper to the electrode at the line of contact, but also stretched it as 
well, bringing it to close proximity to the underlying electrode.