Process of imprinting catalytically active particles on membrane

A membrane and electrode structure is formed by surface hydrolyzing an ion exchange membrane and then applying electrode ink of catalytically active particles on the surface of the membrane. The membrane and electrode structure of the present invention is particularly useful in fuel cells and batteries. The inventive process prevents the membrane from swelling or distorting following application of the electrode ink and also improves adhesion between the electrode ink layer and the surface of the membrane.

FIELD OF THE INVENTION 
This invention relates to a method for making a membrane and electrode 
structure composed of an ion exchange membrane having a plurality of 
electrically conductive, catalytically active particles present on one, or 
both, surfaces of an ion exchange membrane. The electrically conductive, 
catalytically active particles serve as a particulate electrode when the 
membrane and electrode structure is used in an electrochemical cell. The 
membrane and electrode structures are particularly useful in fuel cells 
and batteries. 
BACKGROUND OF THE INVENTION 
So-called "M & E cells" are electrochemical cells employing a membrane and 
electrode structure. Such cells can be operated as an electrolytic cell 
for the production of electrochemical products, or they may be operated as 
fuel cells or batteries for the production of electrical energy, gas 
generating devices and processes, chemical synthesis devices, chemical 
treatment and processing devices and methods, gas dosimeters and sensing 
devices and the like. Electrolytic cells may, for example, be used for the 
electrolysis of an alkali metal halide such as sodium chloride or for the 
electrolysis of water. M & E cells are well known in the art. 
The contact of the gas-liquid permeable porous electrode with the ion 
exchange membrane is an important factor for the efficiency of the M & E 
cell. When the thickness of an electrode is nonuniform or the contact 
between the electrode with the ion exchange membrane is not satisfactory, 
a part of the electrode is easily peeled off adversely effecting the 
electrical properties of the cell. The advantages of the M & E structure 
are then decreased or lost. 
Membrane and electrode structures are currently manufactured by several 
techniques. U.S. Pat. No. 3,297,484 illustrates materials for electrode 
structures including exemplary catalyst materials for electrodes, ion 
exchange resins for membrane and electrode structures and current 
collecting terminals. Catalytically active electrodes are typically 
prepared from finely-divided metal powders, customarily mixed with a 
binder such as polytetrafluoroethylene resin. The electrode is formed from 
a mixture of resin and metal bonded upon one or both of the surfaces of a 
solid polymer matrix, sheet or membrane. 
In U.S. Pat. No. 3,297,484, the mixture of resin and catalytically active 
particles is formed into an electrode structure by forming a film from an 
emulsion of the material, or alternatively, the mixture of resin binder 
and catalytically active particles is mixed dry and shaped, pressed and 
sintered into a sheet which can be shaped or cut to be used as the 
electrode. The mixture of resin and catalytically active particles may 
also be calendered, pressed, cast or otherwise formed into a sheet, or 
fibrous cloth or mat may be impregnated and surface coated with the 
mixture. In U.S. Pat. No. 3,297,484, the described electrodes are used in 
fuel cells. In U.S. Pat. No. 4,039,409, the bonded electrode structure 
made from a blend of catalyst and binder is used as the electrode in a gas 
generation apparatus and process. 
U.S. Pat. No. 3,134,697 describes many ways for incorporating catalytically 
active electrodes onto the surfaces of an ion exchange membrane. In one 
embodiment, the electrode material made of catalytically active particles 
and a resin binder may be spread on the surface of an ion exchange 
membrane or on the press platens used to press the electrode material into 
the surface of the ion exchange membrane. The assembly of the ion exchange 
membrane and the electrode or electrode materials is then placed between 
the platens and subjected to sufficient pressure, preferably at an 
elevated temperature, sufficient to cause the resin in either the membrane 
or in admixture with the electrode material either to complete the 
polymerization if the resin is only partially polymerized, or to flow if 
the resin contains a thermoplastic binder. 
It is known to add binders, such as fluorocarbon polymers including 
polytetratluoroethylene and polyhexylfluoroethylene, to the electrode ink. 
It is also known to add viscosity regulating agents such as soluble 
viscous materials to the electrode ink. 
In certain embodiments, the electrode ink comprises: 
a. catalytically active particles (supported or unsupported), preferably 
5-40% by weight; 
b. a suspension medium which is preferably nonsolid at processing 
temperatures; and 
c. binders such as perfluorinated sulfonyl fluoride polymer, preferably 
0-25% by weight, such polymer preferably being NAFION.RTM. perfluorinated 
sulfonyl fluoride polymer (commercially available from E. I. du Pont de 
Nemours and Company), preferably in a solution of Fluorocarbon solvent, or 
perfluorinated sulfonic acid polymer, preferably 0-25% by weight, such 
polymer preferably being NAFION.RTM. perfluorinated sulfonic acid 
(commercially available from E. I. du Pont de Nemours and Company), 
preferably in a solution of isopropyl alcohol and water. 
A method to construct membrane and electrode structures is also described 
in "Methods to Advance Technology of Proton Exchange Membrane Fuel Cells;" 
E. A. Ticianelli, C. Derouin, A. Redondo and S. Srinivasan presented at 
Second Symposium "Electrode Materials and Processes for Energy Conversion 
and Storage," 171st Electrochemical Society Meeting, May, 1987. In this 
approach, a dispersion of a flocculent precipitate of 20% platinum on a 
catalyst and TEFLON.RTM. (commercially available from E. I. du Pont de 
Nemours and Company) is prepared. The flocced mixture is cast onto paper 
and then pressed onto a carbon paper substrate. The electrodes may then be 
sintered at elevated temperature, approximately 185.degree. C., for 30 
minutes. The electrode is next brushed with a solution of chloroplatinic 
acid and subsequently reduced with an aqueous mixture of sodium 
borohydride. The electrode is then washed and NAFION.RTM. (commercially 
available from E. I. du Pont de Nemours and Company) solution brushed on 
the surface of the electrode. 
Using transfer catalyzation wherein an electrode ink comprising a platinum 
catalyst on a carbon supporting material is printed on a suitable 
substrate, such as TEFLON.RTM. or paper, it has been possible to form 
electrodes containing as little as 0.2 mgm/cm.sup.2 of precious metal. In 
particular, these electrodes, which are essentially decals formed from a 
supported platinum catalyst electrode ink, are painted or sprayed on the 
substrate and then dried and hot pressed onto ion exchange membranes. 
In all of the foregoing techniques, it has been necessary to utilize 
liquid-based emulsion and several processing steps to form a film of the 
electrode material and thereafter bind or press the sheet of electrode 
material upon the ion exchange membrane, or it has been necessary to use 
binders and substantial quantities of expensive catalyst materials to 
prepare membrane and electrode structures. It has also been necessary to 
utilize large loadings of catalyst to make acceptable electrodes in these 
prior art methods. The process for preparing the electrodes is 
inefficient, the reproducibility is poor, and the electrode layer is prone 
to delamination or peeling, which adversely effects the electrical 
properties of the membrane and electrode structure. 
U.S. Pat. No. 4,272,353 tries to solve some of these problems by abrading 
or physically roughening the surface of the membrane to provide a support 
for locking, uniting or fixing the finely-divided catalyst particles to 
the surface of the membrane. Particularly, before the catalyst is 
deposited upon the surface of the membrane, the surface is subjected to a 
suitable abrading or roughening means. However, the abrasion process can 
result in deleterious effects to the strength, dimensional stability and 
electrical properties of the membrane. Moreover, abrading the membrane 
requires an additional process step. 
Moreover, directly applying the electrode ink to a membrane which is in the 
proton form has been largely unsuccessful. When the membrane is in the 
proton form, the composition of the electrode ink disadvantageously causes 
swelling and distortion, often uncontrollable swelling and distortion, of 
the membrane onto which it is applied. 
Directly applying such electrode ink to membranes, when the ink and the 
membrane are in the halogen form, particularly a fluorinated membrane 
having pendant sulfonyl group which are in the sulfonyl fluoride form, 
results in improved compatibility and adhesion between the electrode ink 
and the membrane. However, dissolution of the electrode may be difficult 
and it is typically necessary to use an expensive solvent to dissolve the 
electrode ink. If the electrode ink is in the proton form, it is generally 
incompatible with the membrane in the sulfonyl fluoride form, resulting in 
poor adhesion between the membrane and the electrode structure. 
Therefore, a method of making a membrane and electrode structure is needed 
in which the electrode may be efficiently, inexpensively, and reproducibly 
applied to an ion exchange membrane, so as to form a uniform electrode 
structure which preferably uses a relatively small loading s of catalyst, 
does not delaminate, peel, crack or deform during operation, does not 
adversely decrease ionic conductivity of the structure, while retaining 
the advantages of prior art methods. 
SUMMARY OF THE INVENTION 
The present invention is a method of making membrane and electrode 
structure having excellent characteristics which is formed by bonding the 
electrode to the membrane by a process wherein only the surface of the ion 
exchange membrane is hydrolyzed. The surface of the membrane is in the 
ionic form and the remainder of the membrane is in the non-ionic form. As 
such, the electrode ink, which is preferably in the ionic is form, is 
compatible with and readily adheres to the hydrolyzed surface of the 
membrane. The majority of the membrane does not, however, swell or expand 
when the electrode ink is applied. 
In particular, the process of the present invention comprises the following 
steps: 
a. Surface hydrolysis of a polymeric ion exchange membrane so as to place 
the surface of the membrane in the ionic form, while the remainder of the 
membrane is substantially in a non-ionic form; 
b. Application of electrode ink to the hydrolyzed surface or surfaces of 
the membrane. The electrode ink comprises a catalytically active material 
and a polymeric binder. 
The electrode ink is printed, coated or bonded onto the surface of the 
membrane. The electrode ink may optionally be pressed onto the surface of 
the membrane at elevated pressure and temperature. In an alternate 
embodiment the electrode ink is printed, painted or sprayed on a suitable 
substrate to form a so-called "decal." The decal is then hot pressed onto 
the surface of the ion exchange membrane. Advantageously, the majority of 
the surface hydrolyzed membrane does not swell or distort when the ink is 
applied. The ink readily adheres to the membrane thereby reducing the 
likelihood of delamination, peeling or cracking of the electrode 
structure, uniform application of the electrode layer, reduction in the 
formation of gas bubbles at the membrane/electrode interface and without 
adversely effecting the strength, dimensional stability or electrical 
properties of the membrane. 
The surface of the membrane may be hydrolyzed by methods known in the art. 
Prior to operation, the entire membrane and electrode structure should be 
hydrolyzed by methods known in the art. 
In the case of fluorinated ion exchange membranes derived from a 
fluorinated precursor polymer which contains pendant side chains in 
sulfonyl fluoride form, the sulfonyl fluoride functional groups may be 
converted to ionic form in various ways, for example, to sulfonate salts 
by hydrolysis with an alkaline material, to the sulfonic acid by 
acidification of the salts, and to the sulfonamide by treatment with 
ammonia. Examples of such teachings in the art can be found in U.S. Pat. 
Nos. 3,282,875; 3,784,399; and 3,849,243. 
The inventive membrane and electrode structure made by the inventive 
process is particularly useful in fuel cells and batteries.

DETAILED DESCRIPTION OF THE INVENTION 
The process of the present invention comprises the following steps: 
a. Surface hydrolysis of a polymeric ion exchange membrane so as to place 
the surface of the membrane in the ionic form, while the remainder of the 
membrane is substantially in a non-ionic form; 
b. Application of electrode ink to the hydrolyzed surface or surfaces of 
the membrane. 
Electrode Ink Composition 
The composition of the electrode ink is not limited and is well known in 
the art. The electrode ink typically comprises: 
a. catalytically active particles (supported or unsupported), preferably 
5-40% by weight; 
b. a suspension medium which is preferably nonsolid at processing 
temperatures; 
c. binders such as perfluorinated sulfonyl fluoride polymer, preferably 
0-25% by weight, such polymer preferably being NAFION.RTM. perfluorinated 
sulfonyl fluoride polymer (commercially available from E. I. du Pont de 
Nemours and Company), preferably in a solution of hydrocarbon solvent, or 
perfluorinated sulfonic acid polymer, preferably 0-25% by weight, such 
polymer preferably being NAFION.RTM. perfluorinated sulfonic acid 
(commercially available from E. I. du Pont de Nemours and Company), 
preferably in a solution of isopropyl alcohol and water. 
The electrode layer can be made from well-known catalytically active 
particles or materials. The anode is preferably formed by one or more 
platinum group metal such as platinum, ruthenium, rhodium, and iridium and 
electroconductive oxides thereof, and electroconductive reduced oxides 
thereof. The cathode is preferably formed by one or more of iron, nickel, 
stainless steel, a thermally decomposed product of a fatty acid nickel 
salt, Raney nickel, stabilized Raney nickel, carbonyl nickel and carbon 
powder supporting a platinum group metal. The catalyst may be supported or 
unsupported. The preferred catalyst is a platinum catalyst (manufactured 
by Precious Metals Corp.), particularly 20% platinum on a carbon support 
known as VULCAN.RTM. (manufactured by Cabot Corp.). 
The catalytically active material is conventionally incorporated in the ink 
in a form of a powder having a particle diameter of 100 Angstroms to 1000 
Angstroms, especially 120 Angstroms to 500 Angstroms. 
The hydrolyzed or unhydrolyzed sulfonyl fluoride polymer, preferably a 
polymer solution, is incorporated in the ink. Preferably, such polymer is 
in the hydrolyzed form, which promotes compatibility with and adhesion to 
the hydrolyzed surface of the membrane. The polymer is typically used as a 
binder for the electrode and the ion exchange membrane. The polymer 
facilitates the bond between the electrode ink and the surface of the 
membrane and provides the ionic conductivity of the electrode structure. 
The sulfonyl polymers (and the corresponding perfluorinated sulfonic acid 
polymers) with which the present invention is concerned are fluorinated 
polymers with side chains containing the group --CF.sub.2 CFR.sub.f 
SO.sub.2 X, wherein R.sub.f is F, Cl, CF.sub.2 Cl or a C.sub.1 to C.sub.10 
perfluoroalkyl radical, and X is F or Cl, preferably F. Ordinarily, the 
side chains will contain --OCF.sub.2 CF.sub.2 CF.sub.2 SO.sub.2 X or 
--OCF.sub.2 CF.sub.2 SO.sub.2 F groups, preferably the latter. Polymers 
containing the side chain --O(CF.sub.2 CH{CF.sub.3 }O).sub.k 
--(CF.sub.2).sub.j --SO.sub.2 F, where k is 0 or 1 and j is 2, 3, 4, or 5, 
may be used. Polymers may contain the side chain --CF.sub.2 CF.sub.2 
SO.sub.2 X where X is F or CI, preferably F. 
Preferred polymers contain the side chain --(OCF.sub.2 CFY).sub.r 
--OCF.sub.2 CFR.sub.f SO.sub.2 X, where R.sub.f, Y and X are defined above 
and r is 1, 2, or 3. Especially preferred are copolymers containing the 
side chain --OCF.sub.2 CF{CF.sub.3 }OCF.sub.2 CF.sub.2 SO.sub.2 F. Other 
suitable binders include fluorocarbon polymers such as 
polytetrafluoroethylene and polyhexylfluoroethylene. In order to improve 
the dispersibility, it is possible to incorporate a long chain hydrocarbon 
type surfactant or a fluorinated hydrocarbon type surfactant at a desired 
ratio. 
The suspension medium is not limited, but may for example be a hydrocarbon 
having an ether, epoxy or ketone linkage and an alcohol group, which is 
nonsolid at processing temperatures. A preferred suspension medium is 
1-methoxy 2-propanol. 
The suspension media act as a solvent, carrier or suspension agent for the 
catalytically active particles and the perfluorosulfonic acid polymer (or 
the perfluorinated sulfonyl fluoride polymer). Moreover, the suspension 
media do not significantly interact with the functional groups of the 
membrane or the binder, such as a perfluorosulfonic acid polymer (or the 
perfluorinated sulfonyl fluoride polymer), which could impair or reduce 
the ionic conductivity of the membrane and electrode structure during 
operation. In addition, the suspension media act as a viscosity regulating 
which facilitates the printing or coating of the electrode ink on the 
surface of the membrane, without interacting with the ion exchange 
polymers contained in the membrane. 
The preferred contents of the catalytically active particles and the ion 
exchange polymer in the ink are dependant upon characteristics of the 
electrode. In the case of fuel cell electrodes, the preferred ratio of ion 
exchange polymer to carbon support weight of the catalyst is in the ratio 
of about 1:3. 
The viscosity of the ink comprising the electrode powder is preferably 
controlled in a range of 1 to 10.sup.2 poises especially about 10.sup.2 
poises before printing. The viscosity can be controlled by (i) selecting 
particle sizes, (ii) composition of the catalytically active particles and 
binder, (iii) a content of water as the medium or (iv) preferably by 
incorporating a viscosity regulating agent. 
Suitable viscosity regulating agents include cellulose type materials such 
as carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and 
cellulose and polyethyleneglycol, polyvinyl alcohol, polyvinyl 
pyrrolidone, sodium polyacrylate and polymethyl vinyl ether. 
The amount of catalyst material which is deposited upon the surface of the 
membrane in accordance with the process of the present invention is not 
critical. In a publication entitled "Pseudohomogeneous Catalyst Layer 
Model for Polymer Electrolyte Fuel Cell," T. Springer and S. Gottesfeld, 
Los Alamos National Laboratory, Modeling of Batteries and Fuel Cells, 
Electrochemical Society, PV91-10, 1991, it was shown that fuel cell 
electrode thickness should be constructed to be about 5 microns thick. It 
has been found in accordance with the present invention that the ink of 
the present invention permits the deposition of surprisingly small 
quantities of catalyst material upon the surface of the membrane. This 
value includes the weight of the precious metal catalyst and excludes the 
support. In accordance with the present invention, catalyst particles may 
be deposited upon the surface of a membrane in a range from about 0.2 mg. 
catalyst/cm.sup.2 (supported) up to about 20 mg/cm.sup.2 (unsupported) and 
higher. However, at higher loadings, that is loadings of catalyst over 
about 2.0 mg/cm.sup.2, it may be more important to add a binder to cause 
better adhesion or fixing of the catalyst material upon the surface. 
However, binders are optional and are not required for structural 
integrity at loadings of catalyst of about 2.0 mg/cm.sup.2 or less. 
Catalyst is added to the surface of the membrane in an ink or ink form. The 
area of the membrane, which may be the entire area or only a select 
portion of the surface of the membrane, is covered with the catalytic 
material. The exact amount of catalyst may be placed upon the surface of 
the membrane, that is, the desired loading. If necessary, appropriate 
steps may be taken to remove the excess catalyst material, such as by 
vibration, electrostatics, shaking, pouring, brushing, vacuum, and the 
like. The catalyst ink may be deposited upon the surface of the membrane 
by spreading it with a knife or blade, brushing, pouring, dusting, 
electrostatics, vibrating and the like. Areas upon the surface of the 
membrane which require no catalyst material, can be masked, or other means 
can be taken to prevent the deposition of the catalyst material upon such 
areas. The desired loading of catalyst upon the membrane can be 
predetermined, and the specific amount of catalyst material can be 
deposited upon the surface of the membrane so that no excess catalyst is 
required. For example, if 0.25 mg/cm.sup.2 catalyst is desired upon the 
surface of the membrane, that specific amount of catalyst material can be 
deposited upon the surface and fixed thereon. In this manner, any waste of 
relatively expensive catalyst materials can be avoided. 
Method for Applying Ink to the Membrane 
There are a number of suitable ways for depositing the particles onto the 
membrane. For example, one can form a slurry of the catalytically active 
particles and paint or spray the slurry onto the membrane. Spraying the 
solution/dispersion onto the flat electrically conductive screen is used 
to advantage for covering large or irregular shapes. Pouring the 
solution/dispersion onto the membrane is sometimes used. Painting the 
solution/dispersion with brush or roller has been successfully employed. 
In addition, coatings may be easily applied with metering bars, knives, or 
rods. Usually, the coatings or films are built up to the thickness desired 
by repetitive application. 
A particular advantageous method of applying the catalytic particles to the 
membrane is to blend the ink which is to be imprinted on the surface of 
the membrane. The ink is printed on and bonded to the surface of the ion 
exchange membrane by the screen printing process. The conventional screen 
printing process can be employed. It is preferable to use a screen having 
mesh number of 10 to 2400 especially mesh number of 50 to 1000 and a 
thickness of 1 mil to 100 mils, especially 5 mils to 15 mils. When the 
mesh number is too large, the clogging of the screen results in nonuniform 
printing. When the mesh number is too small, excess of the ink is printed. 
When the thickness is too thick, too heavy a coating is caused. When the 
thickness is too thin, a printing for a desired amount of the ink is not 
attained. A screen mask is used for forming an electrode layer having a 
desired size and configuration on the surface of the ion exchange 
membrane. The configuration is preferably a printed pattern eliminating 
the configuration of the electrode. The thickness of screen mask is 
preferably in a range of 1 to 500 mu. The substances for the screen and 
the screen mask can be any materials having satisfactory strength such as 
stainless steel, polyethyleneterephthalate and nylon for the screen and 
epoxy resins for the screen mask. 
A screen and the screen mask are placed on the ion exchange membrane for 
the printing of the electrode layer. The ink is fed on the screen and is 
printed under a desired pressure by squeegee whereby the electrode layer 
having the configuration beside the screen mask, is formed on the surface 
of the membrane. The thickness of the electrode layer on the membrane 
depends on the thickness of the screen, the viscosity of the ink and the 
mesh number of the screen. It is preferable to control the thickness of 
the screen, the viscosity of the ink and the mesh of the screen so as to 
give the thickness of the electrode ranging from 1 micron to 50 microns, 
especially 5 microns to 15 microns. 
The gap between the screen and the membrane, the material of the squeegee 
and the pressure applied to mesh by the squeegee in the screen printing 
process, highly relate to the physical properties, thickness and 
uniformity of the electrode layer to be formed on the surface of the 
membrane. In order to give desired printing, the gap between the screen 
and the membrane is set depending upon the kind and viscosity of the ink 
preferably ranging from 0.5 mm to 5 cm. The hardness of the squeegee is 
selected according to the viscosity of the ink, preferably ranging from 50 
to 100 shore hardness. Preferably, uniform pressure of the squeegee is 
applied to the mesh. Thus, the electrode layer having uniform thickness is 
formed on one or both of the surfaces of the membrane in a high bonding 
strength. Thereafter, it is preferable to warm the electrode layer to 
about 50.degree. C. to 140.degree. C., preferably about 75.degree. C. The 
electrode layer may be warmed by a lamp, usually about one foot away from 
the membrane or by other conventional means. This screen printing process 
may be repeated until the desired loading of ink is achieved. Two to four 
passes, usually three passes, produce the optimum performance. 
Thereafter, it may be desirable to fix the ink on the surface of the 
membrane. The ink may be fixed upon the surface of the membrane by any one 
or a combination of pressure, heat, adhesive, binder, solvent, 
electrostatic, and the like. The preferred embodiment for fixing the ink 
upon the surface of the membrane are by pressure, by heat or by a 
combination of pressure and heat. Pressure and heat may be adjusted by one 
skilled in the art. It is preferable to press the electrode layer on the 
surface of the membrane at 100.degree. C. to 300.degree. C., preferably 
150.degree. C. to 280.degree. C., most preferably 130.degree. C. under a 
pressure of 510 to 51,000 kPa (5 to 500 atm) preferably 1015 to 101,500 
kPa (10 to 100 atm), most preferably 2030 kPa (20 atm) whereby a strongly 
bonded structure of the electrode layer and the ion exchange membrane can 
be obtained. 
The electrode layer formed on the membrane should preferably be a gas 
permeable porous layer. The average pore diameter is in a range of 0.01 to 
50 .mu.m, preferably 0.1 to 30 .mu.m. The porosity is generally in a range 
of 10 to 99%, preferably 10 to 60%. 
When heat is used to fix the ink upon the surface of the membrane, 
temperatures of about 80.degree. C. up to less than the decomposition 
temperature of the membrane are preferred. Pressure may be carried out by 
manual presses, flat plate presses, a roller or rollers pressing against a 
flat plate backup member or a roller or rollers pressing against a backup 
roller or rollers or by any suitable means of applying pressure, manually 
or automatically. Elevated temperatures suitable for fixing the particles 
upon the surface may be achieved by heating the membrane having catalyst 
ink upon the surface in an oven or other suitable heating device, by 
heating a pressure plate or plates, by heating a pressure roll or rollers, 
by external heat lamps, or by any other suitable heating devices or 
combination of the foregoing. When pressure and heat are applied 
simultaneously, the heating device may be incorporated in the pressure 
device such as the pressure plate or the pressure roller or rollers, or 
there may be any suitable combination of external sources of heat used in 
conjunction with pressure devices. 
Generally, the length of time for the application of heat is not critical 
and is dependent upon the temperature and/or pressure being applied to the 
surface of the membrane having catalyst particles or powder deposited 
thereon. Typically, heat is applied from less than about 1 minute to about 
2 hours, and when a pressure of about 2030 kPa (20 atm) is used with a 
temperature of about 130.degree. C., heat is applied for less than about 1 
minute to about 15 minutes, preferably about two minutes. 
In preferred embodiments, any pressure plate or roller surfaces used to fix 
the particles of catalyst materials upon the surfaces of the membrane may 
have a release surface, such as a coating of TEFLON.RTM., fluorocarbon or 
other suitable release material thereon. 
The electrode structure may also be applied to the surface of the membrane 
by the so-called decal process. In particular, an alternative to printing 
the catalyst layer directly onto the membrane electrolyte is to coat, 
paint, spray or screen print the catalyst onto a piece of substrate or 
paper and subsequently transfer the catalyst from the paper to the 
membrane. A version of this process is well known in fuel cell art. In 
this process the ink formulation is prepared and preferably mixed with 
water and an amount of TEFLON.RTM., preferably TEFLON.RTM. 30B 
(commercially available from E. I. du Pont de Nemours and Company) is 
added. TEFLON.RTM. should constitute 10% to 70%, preferably 30% to 50% of 
the catalyst layer dry weight. The mixture is flocced using heat or by 
acidification. The mixture is cast onto a piece of paper by a vacuum 
filtration. The water is withdrawn through the paper leaving the solid, 
flocced filtrate in a uniform layer on the paper. This paper is then 
placed, catalyst side down, on a piece of teflonated or wetproofed carbon 
paper. The carbon paper, catalyst layer and catalyst-layer paper backing 
are sandwiched between sheets of filter paper and the excess water is 
pressed out. The assembly is removed from the press and the filter paper 
is discarded. The paper is now sprayed lightly with water causing the 
paper fibers to swell. The paper can now be removed and what remains is a 
TEFLON.RTM.-bonded, diffusion-type fuel cell electrode. The electrodes are 
generally dried and sintered at about 332.degree. C. for about 15 to 30 
minutes. 
It is also possible to print the electrode onto a paper backing as 
described in the prior art. After the ink is dried, two such printed 
papers are placed on either side of a fluorinated ion exchange membrane 
which is preferably in the unhydrolyzed form, typically the sulfonyl 
fluoride form. The papers are placed so that the printed areas are placed 
facing the membrane. The membrane usually being transparent and the paper 
being somewhat translucent, permits easy registry of the two printed 
catalyst layers. The sandwich so formed is placed between the heated 
platens of a press. The press is closed and raised to a pressure of about 
1380 kPa (200 psi) at the surface of the membrane and to a temperature of 
about 127.degree. C. This condition is maintained for about 2 minutes 
after which the membrane and electrode structure package is withdrawn. To 
remove the paper from the membrane and electrode structure, water may be 
sprayed on the paper which causes the fibers to swell. The paper can now 
be peeled from the catalyst layer which is now firmly bonded to the 
membrane. 
The advantage of the decal approach is that it permits the removal of most 
ink solvents prior to pressing. These processes have also yielded layers 
which are less subject to mudcracking. The approach simplifies fixturing 
the membrane for printing. It also permits printing and storage of large 
quantities of catalyst layer, which also facilitates the production of 
customized membrane and electrode structures. 
Ion Exchange Membrane 
The term "membrane" refers to non-porous structures or barriers for 
separating compartments of an electrochemical cell, such as an 
electrolysis cell, a fuel cell or a battery, and which may have layers of 
different materials, formed, for example, by surface modification of films 
or by lamination, and to structures having as one layer a support, such as 
a fabric imbedded therein. 
The membrane on which the electrode layer is formed is not limiting. It can 
be made of a polymer having ion exchange groups such as carboxylic acid 
groups, sulfonic acid groups, phosphoric acid groups and phenolic hydroxy 
groups. Suitable polymers include copolymers of a vinyl monomer such as 
tetrafluoroethylene and chlorotrifluoroethylene and a perfluorovinyl 
monomer having an ion-exchange group such as sulfonic acid group, 
carboxylic acid group and phosphoric acid group or a reactive group which 
can be converted into the ion-exchange group. It is also possible to use a 
membrane of a polymer of trifluoroethylene in which ion-exchange groups 
such as sulfonic acid group are introduced or a polymer of styrene-divinyl 
benzene in which sulfonic acid groups are introduced. 
The ion exchange membrane is preferably made of a fluorinated polymer. The 
term "fluorinated polymer" generally means a polymer in which, after loss 
of any R group by hydrolysis to ion exchange form, the number off atoms is 
at least 90% of the total number of F, H and Cl atoms in the polymer. For 
chloralkali cells, perfluorinated polymers are preferred, through the R in 
any --COOR group need not be fluorinated because it is lost during 
hydrolysis. The fluorinated polymers are preferably so-called carboxyl 
polymers or so-called sulfonyl polymers. 
The carboxyl polymers have a fluorocarbon backbone chain to which are 
attached the functional groups or pendant side chains which in turn carry 
the functional groups. When the polymer is in melt-fabricable form, the 
pendant side chains can contain, for example --[--CFZ--].sub.t --W groups 
wherein Z is F or CF.sub.3, t is 1 to 12, and W is --COOR or --CN, wherein 
R is lower alkyl. Preferably, the functional group in the side chains of 
the polymer will be present in terminal O--[--CFZ--]--.sub.t --W groups 
wherein t is 1 to 3. 
Polymers containing --(OCF.sub.2 CF{CF.sub.3 })mOCF.sub.2 CF{CF.sub.3 }CN 
side chains, in which m is 0, 1, 2, 3, or 4, are disclosed in U.S. Pat. 
No. 3,852,326. Polymers may contain --(CF.sub.2 CFZ).sub.m OCF.sub.2 COOR 
side chains, where Z and R have the meaning defined above and m is 0, 1, 
or 2 (preferably 1). 
Polymers containing terminal --O(CF.sub.2).sub.v W groups, where W is 
defined as --COOR or --CN and v is from 2 to 12 are preferred. These 
groups may be part of --(OCF.sub.2 CFY).sub.m --O--(CF.sub.2).sub.v --W 
side chains, where Y=F, CF.sub.3 or CF2Cl. Especially preferred are 
polymers containing such side chains where v is 2, and where v is 3. Among 
these polymers, those with m=1 and Y=CF.sub.3 are most preferred. The 
above references also describe how to make these fluorinated ion exchange 
polymers. 
The fluorinated polymer may also be so-called sulfonyl polymers. The 
sulfonyl polymers with which the present invention is concerned are 
fluorinated polymers with side chains containing the group --CF.sub.2 
CFR.sub.f SO.sub.2 X, wherein R.sub.f is F, Cl, CF.sub.2 Cl or a C.sub.1 
to C.sub.10 perfluoroalkyl radical, and X is F or Cl, preferably F. 
Ordinarily, the side chains will contain --OCF.sub.2 CF.sub.2 CF.sub.2 
SO.sub.2 X or --OCF.sub.2 CF.sub.2 SO.sub.2 F groups, preferably the 
latter. For use in chloralkali membranes, perfluorinated polymers are 
preferred. Polymers containing the side chain --O(CF.sub.2 CF{CF.sub.3 
}O).sub.k --(CF.sub.2).sub.j --SO.sub.2 F, where k is 0 or 1 and j is 3,4, 
or 5, may be used. Polymers may contain the side chain --CF.sub.2 CF.sub.2 
SO.sub.2 X where X is F or Cl, preferably F. The above references also 
describe how to make these fluorinated ion exchange polymers. 
Preferred polymers contain the side chain --(OCF.sub.2 CFY).sub.r 
--OCF.sub.2 CFR.sub.f SO.sub.2 X, where R.sub.f, Y and X are defined above 
and r is 1, 2, or 3. Especially preferred are copolymers containing the 
side chain --OCF.sub.2 CF{CF.sub.3 }OCF.sub.2 CF.sub.2 SO.sub.2 F. 
Polymerization can be carried out by the methods known in the art. 
Especially useful is solution polymerization using ClF.sub.2 CFCl.sub.2 
solvent and (CF.sub.3 CF.sub.2 COO).sub.2 initiator. Polymerization can 
also be carried out by aqueous granular polymerization, or aqueous 
dispersion polymerization followed by coagulation. 
The perfluoro ion exchange polymer is typically a copolymer of 
tetrafluoroethylene with one of the functional comohomers disclosed 
herein. The ratio of tetrafluoroethylene to functional comonomers on a 
mole basis is 1.5 to 5.6:1. For each comonomer, the most preferred ratio 
of tetrafluoroethylene to functional comonomers is determined by 
experiment. Copolymers with high ratios of tetrafluoroethylene to 
comonomers are less soluble than those with low ratios. It is desirable to 
have a liquid composition with most micelies of less than 100 Angstroms, 
but an alternative is to remove the larger micelies by filtration or 
centrifugation. 
The polymer of the ion exchange membrane may also be formed from copolymers 
of monomer I with monomer II (as defined below). Optionally, a third type 
of monomer may be copolymerized with I and II. 
The first type of monomer is represented by the general formula: 
EQU CF.sub.2 =CZZ' (I) 
where: 
Z and Z' are independently selected from the group --H, --Cl, --F, or 
--CF.sub.3. 
The second type of monomer consists of one or more monomers selected from 
compounds represented by the general formula: 
EQU Y--(CF.sub.2).sub.a --(CFR.sub.f).sub.b --(CFR.sub.f).sub.c 
--O--[CF(CF.sub.2 X)--CF.sub.2 --O].sub.n --CF.dbd.CF.sub.2(II) 
where 
Y is selected from the group --SO.sub.2 Z, --CN, --COZ, and C(R.sup.3 
f)(R.sup.4 f)OH; 
Z is --I, --Br, --Cl, --F, --OR, or --NR.sub.1 R.sub.2 ; 
R is a branched or linear alkyl radical having from 1 to about 10 carbon 
atoms or an aryl; 
R.sup.3 f and R.sup.4 f are independently selected from the group 
consisting of perfluoroalkyl radicals having from 1 to about 10 carbon 
atoms; 
R.sub.1 and R.sub.2 are independently selected from the group consisting of 
--H, a branched or linear alkyl radical having from 1 to about 10 carbon 
atoms or an aryl radical; 
a is 0-6; 
b is 0-6 
c is 0 or 1; 
provided a+b+c is not equal to 0; 
X is --Cl, Br, --F, or mixtures thereof when n&gt;1; 
n is 0 to 6; and 
R.sub.f and R.sub.f are independently selected from the group --F, --Cl, 
perfluoroalkyl radicals having from 1 to about 10 carbon atoms and 
fluorochloroalkyl radicals having from 1 to about 10 carbon atoms. 
Particularly preferred is when Y is --SO.sub.2 F or --COOCH.sub.3; n is 0 
or 1; R.sub.f and R.sub.f are --F; X is --Cl or --F; and a+b+c is 2 or 3. 
The third, and optional, monomer suitable is one or more monomers selected 
from the compounds represented by the general formula: 
EQU Y'--(CF.sub.2).sub.a' --(CFR.sub.f).sub.b' --(CFR.sub.f).sub.c' 
--O--[CF(CF.sub.2 X')--CF.sub.2 --O].sub.n' --CF.dbd.CF.sub.2(III) 
where: 
Y' is --F, --Cl or --Br; 
a' and b' are independently 0-3; 
c is 0 or 1; 
provided a'+b'+c' is not equal to 0; 
n' is 0-6; 
R.sub.f and R.sub.f are independently selected from the group --Br, --Cl, 
--F, perfluoroalkyl radicals having from about 1 to about 10 carbon atoms, 
and chloroperfluoroalkyl radicals having from 1 to about 10 carbon atoms; 
and 
X' is --F, --Cl, --Br, or mixtures thereof when n'&gt;1. 
The copolymerization of the fluorinated olefin monomer and a monomer having 
sulfonic acid group or a functional group which is convertible into 
sulfonic acid group, if necessary, the other monomer can be carried out by 
methods known in the art. The polymerization can be carried out, if 
necessary, using a solvent such as halohydrocarbons by a catalytic 
polymerization, a thermal polymerization or a radiation-induced 
polymerization. A fabrication of the ion exchange membrane from the 
resulting copolymer is not critical, for example it can be known methods 
such as a press-molding method, a roll-molding method, an 
extrusion-molding method, a solution spreading method, a 
dispersion-molding method and a powder-molding method. 
The thickness of the membrane is typically 25 to 175 microns, especially 25 
to 125 microns. 
A preferred example of a commercial sulfonated perfluorocarbon membrane is 
sold by E. I. du Pont de Nemours and Company under the trade designation 
NAFION.RTM.. The sulfonic groups are chemically bound to the 
perfluorocarbon backbone, and prior to operation the membrane is typically 
hydrated to yield a membrane having at least about 25% water based upon 
dry weight of membrane. 
In the case of anion exchange resins the ionic group is basic in nature and 
may comprise amine groups, quaternary ammonium hydroxides, the guanidine 
group, and other nitrogen-containing basic groups. In both cases, that is, 
in those where the ionic groups are acidic groups or in those cases where 
the ionic groups are basic, the ionizable group is attached to a polymeric 
compound, typical examples of which are a phenolformaldehyde resin, a 
polystyrene-divinyl-benzene copolymer, a urea-formaldehyde resin, a 
melamine-formaldehyde resin, and the like. 
The membrane can be reinforced by supporting said copolymer on a fabric 
such as a woven fabric or a net, a nonwoven fabric or a porous film made 
of said polymer or wires, a net or a perforated plate made of a metal. 
Alternately, the ion exchange polymer may be impregnated on a substrate or 
fabric. 
The membrane and electrode structure may be stored in any convenient 
manner. Preferably, the membrane and electrode is pressed between a sheet 
of paper such as filter paper and stored in an airtight plastic bag. 
Surface Hydrolysis of the Membrane 
Hydrolysis of the functional groups of the ion exchange membrane may be 
carried out by any number of methods known in the art. Hydrolysis refers 
to the conversion of the pendant groups to the ionic form. Surface 
hydrolysis of the membrane must occur before applying the ink to the 
surface of the membrane. Surface hydrolysis is preferably performed by 
immersing the membrane in a solution of 5-15% NaOH or KOH at 
40.degree.-90.degree. C. for 5 to 30 minutes. 
In the case of a polymeric ion exchange membrane having pendant sulfonic 
groups, any sulfonyl halide groups that have been hydrolyzed will be in 
the form of sulfonic acid groups, or an alkali or alkaline earth metal 
salt thereof. In both cases, the form will depend on the nature of the 
last medium with which the polymer was treated, and will ordinarily be the 
salt of the strongest base in the medium (or the last medium) to which it 
is (or was) exposed. Interconversion between acid and salt forms can be 
accomplished by treatment with solutions of acids or bases, as desired. 
Treatment times must, of course, be increased as the thickness of the 
layer to be treated is increased. The treatment time should be limited to 
ensure that the majority of the membrane remains unhydrolyzed. 
The surface of the membrane may be hydrolyzed (i.e., converted to its ionic 
form) by reacting it with, in the case of --SO.sub.2 F pendant groups, 10 
wt. % NaOH under the following conditions: (1) immerse the film in about 
10 wt. % sodium hydroxide for about 0.1 hours at a temperature of about 
70.degree. C.; and (2) rinse the film twice in deionized water heated to 
about 90.degree. C., using about 30 to about 60 minutes per rinse. 
Industrial Utility 
The membrane and electrode structure is particularly useful in a fuel cell 
or a battery. As it is well known, fuel cells are devices capable of 
generating electricity by electrochemically combining an oxidizable 
reactant, termed a fuel, and a reducible reactant, termed an oxidant. The 
reactants are fluids, either liquids or gases, often hydrogen and oxygen, 
and usually fed continuously to the cell from separate external sources. 
The fuel cell is divided into compartments by the membrane and electrode 
structure. 
Each electrode is electronically conductive, adsorbs the fuel or oxidant 
employed, presents an active material for the electrode reaction, and does 
not oxidize unduly under the operating conditions of the cell. When fuel 
and oxidant are concurrently and separately supplied to the different 
electrodes of the fuel cell, an electrical potential will develop across 
the electrodes. When an electrical load is provided across the electrodes, 
an electrical current flows therebetween, the electrical energy thus 
represented being generated by the electrocatalytic oxidation of fuel at 
one electrode and the simultaneous electrocatalytic reduction of oxidant 
at the other. 
The membrane and electrode structure is also useful in electrolytic cells. 
In the operation of an electrolytic cell for the preparation of an alkali 
metal hydroxide by the electrolysis of an aqueous solution of an alkali 
metal chloride in the electrolytic cell, an aqueous solution of an alkali 
metal chloride is fed into the anode compartment partitioned by the cation 
exchange membrane and water is fed into the cathode compartment. Sodium 
chloride is usually used as the alkali metal chloride. It is also possible 
to use the other alkali metal chloride such as potassium chloride and 
lithium chloride. The corresponding alkali metal hydroxide can be produced 
from the aqueous solution in high efficiency and a stable condition for a 
long time. The electrolytic cell using the ion exchange membrane having 
the electrode layers can be a unipolar or bipolar type electrolytic cell.