CA1097307A

CA1097307A - Electrocatalysts and a method for the preparation thereof

Info

Publication number: CA1097307A
Application number: CA293,905A
Authority: CA
Inventors: Lawrence B. Welsh; Richard W. Leyerle
Original assignee: UOP LLC
Current assignee: Honeywell UOP LLC
Priority date: 1976-12-28
Filing date: 1977-12-23
Publication date: 1981-03-10
Also published as: AU515250B2; ZA777661B; BE862578A; US4090978A; GB1594034A; JPS5388685A; AU3206877A; FR2375905A1; IT1090370B; FR2375905B1; ES465969A1; JPS6338209B2; NL7714492A

Abstract

ABSTRACT OF THE DISCLOSURE
Electrocatalysts which may be used in the preparation of elec-trodes for electrochemical cells such as fuel cells comprise a carbonace-ous pyropolymer having the surface thereof impregnated with at least one catalytically active metal. The electrocatalysts may be prepared by treat-ing a refractory inorganic oxide with a pyrolyzable organic compound at pyrolysis conditions to form a carbonaceous pyropolymer on the surface of said refractory inorganic oxide. Thereafter the composite may be im-pregnated with a soluble salt of at least one catalytically active metal and thereafter the composite may be leached to remove the refactory inor-ganic oxide. Alternatively, the composite may be leached to remove the refractory inorganic oxide prior to impregnation with the catalytically active metal.

Description

~097~07 ELECTROCATALYSTS AND A METHOD
FOR THE PREPARATION THEREOF

SPECIFICATION

This invention relates to electrocatalysts and to a method for the preparation thereof, said electrocatalysts bein~ utilized -in the formation of electrodes which Form an element in an electrochemical cell.
Electrochemical cells are basically made up of an anode and a cathode which are positioned in an electrolyte and connected in an external circuit, one particular type of electrochemical cell being a fue'l ce'll. The e'lectrodescomprising the anode and cathode which make up one part of said electro chemical cells will contain, as one component thereof, an electrocatalyst.
The electrocatalyst which is utilized in the electrode will, oF necessity~
possess certain desirable characteristics such as stability as well as the ability to improve the perFormance of the electrochemical cell.

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lV~73~7 It is therefore an object of this invention to provide an elec-- trocatalyst which will possess the desired properties and which may be used in the formation of electrodes in an electrochemical cell, the electro-catalyst being one element which will- function in an efficient manner for a relatively long period of time in a stable manner.
[n one aspect an embodiment of this invention resides in a cata-lytic composition of matter comprising a high surface area carbonaceous pyropolymer impregnated with at least one catalytically active metal.
Another embod;ment of this invention is found in ~he method for the preparation of a catalytic composition of matter which comprises treating a refractory inorganic oxide with a pyrolyzable organic compound at pyrolysis conditions to form a carbonaceous pyropolymer on the surface .
of said refractory inorganic oxide, impregnating the resulting compound with a soluble salt of at least one catalytically ac~ive metal, leaching ~ the resulting composite with an acid or base to remove said re-fractory inorganic oxide, and recovering th2 resultant catalytic composition of matter.
Yet another embodiment of this invention resides in a method for the preparation of a catalytic compQsitiQn of matter which comprises treating a refractory ;norganic oxide with a pyrolyzable organic compound at pyrolysis conditions to form a carbonaceous pyropolymer on the surface o~ said refractory inorganic oxide, leaching the composite with an acid or base to remove said refractory inorganic oxide9 thereafter impregnating the remaining carbonaceous pyropolymer with a soluble salt of at least ~ 25 one catalyiically active metal, and recovering the resultant catalytic ; composition of ratten.

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, 9~7;~07 A specific embodiment of this invention is found in a catalytic composition of matter ~hich comprises a high surFace area carbonaceous pyropolymer impregnated with platinum, said platinum being present in a range of from about 5% to about 50% by weight of the carbonaceous pyro-polymer.
Another specific embodiment is found in a method for -~he prepara-tion of a catalytic composition of matter ~Ihich comprises treating alumina with a pyrolyzable organic compound at pyrolysis condi~ions to form a car-bonaceous pyropolymer on the surface of said alumina~ impregnating the resultant compound with a soluble salt of platinum~ leaching the resultant composite with phosphoric acid at a temperature in the range of f~om about ambient to about 250 C to remove said aluminaj and recovering the re-sultant catalytic composition of matter.
Other objects and embodiments wiil be found in ~he following further detailed description of the present invention.
As hereinbefore set Forth the present invention is concerned with a method for the preparation of electrocatalys~s which may be used in electrodes. Electrocatalysts which are used in acid or alkaline elec-trolyte fuel cell applications must meet certain requiremen~sJ said require-ments including electrical conductivlty, surface area, wettability of th2catalyst by the fuel cell electrolyte, electrochemical stability of the catalyst and the abilîty of the pyropolymer to resis~ the s;ntering or agglomeration of the catalytic metal particles. In this respect the performance of the fuel cell electrocatalysts will be substantially im- -proved when both the particle size of the catalyst particulate and the crystallite size of the catalytic metal or combination of metals are aE a minimum value, that is, the smallest grouping of metal atoms which will :~ i ' ~73C~7 maintain the metallic properties o~ larger crystals. The electrocatalyst of the present invention comprises a high surface area carbonaceous pyro-polymer having at least one catalytically active metal impregnated thereon.
This electrocatalyst will possess a conductivity at room temperature of from about 10 8 to about 10 inverse ohm-centimeters and ~ill form one element of an electro~e for electrochemical cells such as phosphoric acid electroly-te fuel cells, said compositions of matter being used in place of the noble metal impregnated carbon el-ectrocatalysts which have been used in the prior art.
The electrocatalyst of the present in~ention may be prepared by treating a refractory inorganic oxide of the type hereinbefore set forth~
that is, a refractory inorganic oxide possessing a surface area oF from 1 to about 500 square meters per gram, with a pyrolyzable organic compound at temperature conditions which are sufficient to pyrolyze the organic compound to form a carbonaceous pyropolymer containing carbon and hydrogen atoms in recurring units. Examples of refractory inorganic oxides which may be treated with the p~rolyzable organic compound will include aluminas such as gamma-alumina, eta-alumina, theta-alumina, sillca, alumina-silica, etc. In one method of prepar;ng the composite, the refractory inorganic ~ ox~de is heated to a temperature of from a~out 400 to about 1200C. ln a reducing atmosphere containing an organic pyrolyzable compound. The organic pyropolymer precursors most commonly and preferably used for the purposes of this invention are members of the group consis~ing of allphatic hydrocarbons, aliphatic halogen derivatives, aliphatic oxygen derivatives, aliphat;c sulfur derlvat~ves, aliphat;c n;trogen derivatives, organometal-lic compounds, alicyclic compounds, aromatic compounds, and heterocyclic compounds. Of the al;phatic hydrocarbons, the more common classes which ~, : :

~097~0~

may be utilized to perform this invention are alkanes~ alkenes, alkynes, and alkadienes. Ethane, propane, butane and pentane are among the alkanes which may be successfully used in the performance of this invention.
Similarly, alkenes which suffice include ethene, propene, l-butene, 2-butene, and l-pentene. Alkynes which may be successfully usecl include ethyne, propyne, l-butyne, 2-butyne, l-pentyne, and l-hexyne. l,3-Buta diene and isoprene are included among the alkadienes which may be utilized Among the aliphatic halo~en derivatives which suffice for the purposes of this invention are monohaloalkanes, polyhaloalkanes9 and unsaturated halo compounds. In the monohaloalkane subgroup~ chloromethane, bromo ethane, l-iodopropane, and l-chlorobutane m~y be used. Polyhaloalkanes such as carbon tetrachloride~ chloroform, 1,2-dichloroethane~ and 1,2~
dichlorobutane may also be utilized. One unsaturated halo compound which may be utilized is chloroprene.
The aliphatic oxygen derivatives appropriate for use in this invention include the classes of alcohols, ethers, halohydrides and alkene .
oxides, saturated aldehydes and ketones, unsaturated aldehydes and ketones, ketenes, acids, esters, salts and carbohydrates. Various alcohols which may be utilized include ethanol, 2-butanol, l-propanol, glycol, (e.~.
1,3-propanediol), and glycerol. Ethers utilized include ethyl ether and isopropyl ether. Appropri~ate halohydrins and alkene oxides include ethylene chlorohydrin, propylene chlorohydrin, ethylene oxideg and propylene oxide. Suitable saturated aldehydes and ketones include ~^ormaldehyde, .
acetaldehyde, acetone, and ethyl methyl ketones Unsaturated aldehydes 2~ and ketones which may be used include propenol, trans-2-butenal, and butenone. Ketene has also been successfully used as an organic pyrolyzable ~ ~ s~ubstance. Likewise, formic acid, acetic acid, oxalic acid, acrylic acid, :~ ' ' , ~0~73~7 chloroethanoic acid, formic anhydride and formyl chloride may also be utilized. Esters such as methyl formate, ethyl formate, and ethyl ace-tate may also be used. Salts such as sodium formate, potassium acetate, and calcium propionate may be utilized as may a variety of carbohydrates.
The broad classification of aliphatic sulfur derivatives may be broken down into the subclasses of alkanethiols, alkylthioalkanes, sulfonic acids, and alkyl sulfates and alkyl metallic sulfates. Suitable among the alkanethiols are ethyl mercaptan and n-propyl mercaptan. Among the alkylthioalkanes usable are the thioethers, alkyl sulfides, methyl sulfide, ethy1 sulfide, and methyl propyl sulFide. Ethyl sulFonic acid and n-propyl sulfonic ac,d are sulfonic acids which may also be successfully used.
~thyl sulfate and sodium laurel sulfate are also appropriate for use.
The broad class of aliphatic nitrogen derivatives may be broken down into the subclasses of nitroalkanes, amides, aminesa nitriles, and carbylamines. Nitroethane and l-nitropropane are exemplary of suitable nitroatkanes while acetamide and propionamide are among the appropriate am;des. Amines such as dimethylamine and ethylmethylamine, nitriles such as acetonitrile and propionitrile, and carbylamines such as ethyl isocyanid may also bé used for the organic pyrolyzable substance o~ this inven~ion.
Organometallic compounds such as tetraisopropyl titanate, tetrabutyl - titanate, and 2-ethylhexyl titanate may also be used.
Particularly appropriate and preferred for use as the organo pyrolyzable ~ubstance of this invention are the alicycl;c compounds.
Foremost among these are cyclohexane and cyclohexene. Aroma~ic compounds - ~25 inc1ude the subclasses of hydrocarbons, halogen compounds, oxygen deriva-; ~ tives, ethers, aldehydes~ ketones, quinones, aromatic acids, aromaticsulfur derivatives, and aromatic nitrogen compounds may also be utilized.

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73~7 Among the many suitable hydrocarbons, benzene, naphthalene, anthracene, and toluene were successfully utilized. Benzyl chloride and benzal chloride are appropriate halogen compounds ~hile phenol, o-cresol, benzyl alcohol and hydroquinone are amony the suitable derivatives. Ethers such as anisole and phenetole and aldehydes, ketones, and quinones, such as benzaldehyde, acetophenone, benzophenone, benzoquinone, and anthraquinone may also be used. Aromatic acids such as benzoic acid, phenylacetic acid, and hydrocinnamic acid may be utilized while the aromatic sulfur deriva~
tive of benzenesulfonic ac;d wiil also serve successfully. The aromatic nitrogen compounds of nitrobenzene~ l-nitronaphthalene, aminobenzene and 2-amine toluene may also be successfully used as the organic pyrolyzable substance of th;s invent;on. Among the heterocyclic compounds, five member ring compounds such as furan, proline7 coumarone, thionaphthene~
indole, indigo, and carbazole may be successfully utilized. Six member lS ring compounds such as pyran~ coumarin and acrid;ne may also be utilize~.As can be seen, an extremely wide latitude can be exerc;sed in the selection of the organic pyrolyzable substance, since virtually any organlc material that can be vaporlzed, decomposed and polymerized on the refractory oxide by heating will suffice.
In another embodiment the composite may be prepared by impreg-nating the refractory inorganic oxide with a solution of a carbohydrate material such as dextrose, sucrose, fructose~ starch, etc., and there-after drying the impregnated support. After drying~ the impregnated support is then subjected to pyrolysis ~emperatures in the range herein-`~ 25 before set forth whereby a carbonaceous pyropolymer similar in nature to those hereinbefore described is formed in at least a monolayer on the surface of the refractory inorganic oxide support.
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163~73~7 It has been found that the specific carbon concentration cor-responding to a particular conductivity is a Function of the pyrolyzable substance used to build the carbonaceous pyropolymer. For example, a carbon concentration of 31.7% in the pyropolymer produced from cyclohexane results in a conductivity of about 4 x 10 3 inverse ohm-centimeters, while a carbon concentration of 21.1% in the pyropolymer produced from benzene results in a conduc~ivity of about 4 x lo-2 inverse ohm-centimeters - This indicates a difference in the pyropolymer structure as between the pyropolymers produced -from different pyrolyzable substances. This dif-ference is due to organic residues not inc1uded in the extended, conjugateddouble-bond structure. Such a difference indicates that extraneous carbon structures may be eliminated from the pyropolymer by a proper choice of starting mater;als. One particularly advantageous choice is a mixture oP benzene and o-xylene. Demethylation of the xylene to produce the benzyl radical or diradical promotes the format;on of large aromatic polynuclear networks without extraneous, non-conjugated network elements by providing - a large concentration of nucleation radlcals. This results in an organic semiconducting material having a high coDductivi~y with a relatively low carbon concentration. Similar results can be achieved using mixtures of o-xylene and naphthalene, o-xylene and anthracene, and halogenated or dihalogenated benzene and benzene, naphthalene or anthracene. It h~s - -also been found that the greater the temperature of pyrolysis which is emp10yed, the greater will be the conductivity oP the resulting product.
In one e~bodiment the refractory inorganic oxide support may be ground to the desired size prior to treatment with the organic pyrolyzable ~ compound or, if so desired, the semiconducting material comprising the ; refractory inorganic oxide containing at least a monolayer of a carbonaceous , . ' ~73~

pyropolymer which consists of recurring carbon and hydrogen atoms on the surface thereof, may be ground to the desired size upon completion of the pyrolysis step of the process. In the preferred embodiment of the invention the particle sizes which are utilized for treatment with the S catalytically active metal will range from about 0.1 to about 5 microns in diameter, the preferred size for use in the preparation of an elec-trode for fuel cells being about l micron or less.
~ In one method of practicing the process of the present invention the novel catalytic composition of matter is prepared by impreynating the pyropolymer composite with a sclution of at least one catalytically active metal. The impregnation is effected by treating the composite with an aqueous or organic solution of the desired metal or combination of metals in an amount sufficient to deposit at least one catalytically active metal on the surface of the carbonaceous pyropolymer in an amount ranging frorn about 0.5 to about 20% by weight. Examples of catalytically ac~îve metals and mixture of metals will include platinum, platinum and rhenium9 platinum and ruthenium, platinum and tun~sten, platinum and nickel~ platinum and rhodium, platinum and lead, platinum and germanium, palladium9 palladium and rhenium, palladium and rhodium~ palladium and tungsten~ palladium ~nd nickel, palladium and ruthenium, palladium and lead, palladium and germanium, etc-. It is to be understood that the aforementioned list of catalytically active metals are only representative of the type of metals which may be impregnated on the surface of the carbonaceous pyropolymer and that the present lnvention is not necessarily l;mited thereto.
As hereinbefore set forth the solution which is util;zed to im-pregnate the carbonaceous pyropolymer-inorganic oxide support may be a4ueous ; in nature, specific examp1es of these being aqueous solutions of chloroplat;nic ~73C~7 acid, chloroplatinous acid, bromoplatinic acid, sodium platina~e, potassi~.
platinate, lithium platinatP, platlnous chloride, platinic chloride, as well as corresponding solutions of palladium and mixtures of platinum and rhenium, platinum and rhodium, platinum and germanium, platinum and ~in, palladium and rhodium, palladium and rhenium, palladium and tin~ etc.
AFter impregnation of the composite, the solvent is removed by heating ~o a temperature in the range uf from about 100 to about 40G C.~ the tempera-ture being that which is sufficient to evaporate said solvent and leave the metal or mixture of metals impregnated on the surface of the carbonaceous pyropolymer. Thereafter the composite may tnen be dried at elevated tem-peratures ranging from about 100~ ~o about 200~ C. for a periucl o~ time ranging from about 2 to about 6 hours or more. The final step in ~he prep~
aration of the electrocatalyst of the present invention is effected by subjecting the metal impregnated carbonaceous pyropolymer-inorganic refrac-15 tory oxide composite to a reducing step in the presence of a reducingatmosphere or medium such as hydrogen at elevated temperatures of from about 200 to about 600 C. for a period oF time ranging frorn about 0.5 to 4 hours or more whereby the metallic compound is reduced to the metal in the form of particles. The resulting catalytically active metal impreg-20 nated carbonaceous pyropolymer-inorganic refractory oxide composite will contain the catalytic metal or mixture of metals with metal loadings in a range of from about 0.5 to about 20% by weight, the mean particle si~e of the metal being in a range of from about 10 to allout 25 Angs~roms or more.
~ - Following the hereinbefore recited steps the base material is 25 then chemically leached from the catalytic composition of matter. The leaching is effected by treating said composite with either an acid or a base thereby forming a high surface area carbonaceous pyropolymer which is impregnate~ with a catalytically active metal. The leaching of the base ' - 11 -73~

material of the type herelnbefore set forth may be effected over a ~ide range of temperatures, said range being from about ambient (20-25 C.) to about 250 C. or mcre for a period of time which may range from about 2 to about 72 hours or more. It is to be understood that the operating parameters of the leaching step will vary over a wide range and will be dependent upon a combination of time, temperature, strength of the leaching solution, etc. Examples of acids or bases which may be utilized to leach out the base material, that is, the refrac~ory ;norganic oxide~ will include inorganic acids such as phosphoric acid, sulfuric acidl nitric acid, hydro-chlor;c acid, etc., organic acids such as methylsulfonic acid~ ethylsul-fonic acid, propylsulfonic acid, toluenesulfonic acid, etc.; strong bases such as sodium hydroxide, potassium hydroxide, lithium hydroxide~ rubidium hydroxide, cesium hydroxide, etc. It ;s to be understood that the afore-mentioned leaching materials are only representative oF the class of com-lS pollnds which may be used and that any chemical which will be capable of remo~ing the refractory inorganic oxide while (l) retaining the high surfacear~aof the carbonaceous pyropolymer and (2) retaining the small particle size of the catalyticaliy active metal which~may be used.
In another embodiment of the invention the novel catalytically active compositlon Of matter may be prepared by forming a carbonaceous pyropolymer on the surface of a refractory inorganic oxide in a manner similar to that hereinbefore set forth. Thereafter this earbonaceous ,, pyropolymer-refractory inorganic oxide composite may then be leached by :
~ - treatment with either an acid or a base at a temperature in the rang ~ ~ -hereinbefore set forth to form a high surface area carbonaceous pyropolymer.
Thereafter the carbonaceous pyropolymer may then be impregnated with a ~ . ~
~ ~ solution of at least one catalytlcally active metal in a manner similar to , ~ ~

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, that hereinbefore set forth to form the desired catalytically acii~Je com-position o~ matter.
It is also contemplated within the scope of this invention that an alternati~e method of -forming the desired catalytically active compo-sition of matter may be effected by producing a carbonaceous pyropolymeron a refractory inorganic oxide, thereafcer impregnating the resulting carbor,aceous pyropolymer-inorganic reFractory oxide composite with at least one catalytically active metal in the manner hereinbefore taught followed by drying and reduc;ng. ThereaFter the composite may then be formed into a porous gas-diffusion ~ype electrochemical cell electrode fal-lowed by removai of the ,e~ractory inorganic oxide by leaching with an acidor a base. The removal of che inorganic refractory oxide base will result in the formation of an electrocatalyst which possesses increased porosity and available surface area of the catalyst.
The electrocatalyst of thè present invention may then be uti-lized as a component o~ an electrode for an electrochemical cell such as a fuel cell byadmixing the eleccrocatalyst with a support. The electrode may be prepared by any manner known in the art~ For example, the electro-catalyst of the present invention which has been prepared ;n a manner hereinbefore set forth may be blended wi~h a powder of polytetra~luoro-ethylene and the resultin~ mixture m~y be suspended in a suitable so~vent such-as water or an alcohol to form a co-suspension which is then deposited in any manner so desired on a substrate. The substrate may comprise any - desired-compound such as a tantalum screen or a porous graphite, the depo-sition being accomplished or achieved by screen printing, spraying, filter transfer process, etc. The composite cons~isting of the substrate with the co-suspension deposited thereon may then be heated atan elevated ~7~

temperature ranging from about 300 to about 400 C. for a period of tirne sufficient to sinter the polytetrafluoroethylene which will cause the polytetrafluoroethylene to diffuse and allow the electrocatalyst to adhere to the carrier or substrate. While this is one example of how an electrode for a fuel cell may be prepared, it is contemplated that any other method known in the art may also be employed to prepare the desired composite.
The electrodes thus prepared may be utillzed in either alkaline or acid fuel cells. For example, the electrode may be used in an alkaline fuel cell comprising a housing -rormed of a suitable insulating material such as plexiglas provided with openings for the insertion of conducting wire leads. The housing is provided with a central hollow portion which forms a containment well for the electrolyte material such as sodium hydroxid~, armonium chloride, etc. A zinc anode may be cemented to one interior wall ~f the containment well. In addition9 an air well which possesses a communicating air inlet formed on the ~op portion of the housing and a communicating air vent formed on the lower portion of the housing is formed within said housing A cathode comprising an electrode of the type of the present invention may be pressed between the electro-lyte well and the air well. Another type of fuel cell which may be em-ployed comprises the acid type fuel cel1 in which the electrode of thetype herein described is affixed to a tantalum~screen or a porous graphite current collector which is then placed on each slde of a composite matrix.
.
In addition~ platcs configured for the passage of~air, oxygen and hydrogen and containing leads are pressed to the current collector to form the desired fuel cell. Air or oxyyen may be passed through the plates to the e1ectrodes which act as cathodes while hydrogen is passed through the plates to the electrodes which are utilized as fuel cell anodes.
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As will hereinafter be sho~Jn in grea~er detail in the eY~amples, which are appended to the specification, the catalytic compositions of matter may be utilized as electrocatalysts in electro~es in fuel cells.
- These examples are given merely for purposes of illustrating the novel catalytic compositions of matter and the method of preparation thereof and are not intended to limit the generally broad scope o~ the present invention in strict accordance therewith.
EXAMPLE I
A gamma-alumina with a particle size possessing a mean diameter of about 0.5 microns was calcined at a temperature of about 550 C. for a period of about 3 hours. Following this~ the alumina powder was placed in a rotary reactor and treated with benzene at a temperature of 800 C.
for a period of 0.75 hours.
The material prepared in the abo~e paragraph was then treated with a chloroplatinic acid solution in an amount sufficient to i~pregnate the material at a platinum level of 10% by weight. Thereafter the mixture was stirred in an evaporating dish for Q.5 hours at ambient temperature and dried in an oven at 100 C. for a period of 4 hours. After drying, the material was reduced by treatment with hydrogen at a temperature of 260 C. for a period of 2 hours in a vertical reactor. The catalytic composition of matter was then utilized to~prepare an electrode for use in fuel cells. The catalytic compos;tion of matter ~.~/as wet blended ~ith a polytetrafluoroethylene powder in an organic medium and after filtrat,on the catalyst layer was formed by a calendering operation. The electrode contained about 20% by weight of polytetrafluoroethylene ~Teflon) as a bonding and wet-proofing agent and about 5 mg/cm2 of the electrocatalyst material. The electrode after formation was cut into ~wo square inch * Trademark ' .

73~117 pieces and submerged in 100 cc of a 96% phosphoric acid solution which was mainta;ned at a temperature of 140 C. for a per;od of 24 hours. The effect of this leaching treatment was to leach the alumina from the elec-trode structure, the re~aining electrocatalyst in the electrode contained 34% by weight of platinum. After recovery of the leached electrode, it was washed ;n boiling deionized water for a period of ~ hours and used in a phosphoric electrolyte fuel cell.
The electrode evaluation was accomplished by forming a fuel cell in which the cell plates comprised a composite material molded from graphite and an acid resistant resin. The cell matrix consisted of a composite structure of Kynol fibers and a phenolic binder, the cell matrix-being ---- filled with phosphoric acid wh;ch had been pretreated with hydrogen per- -oxide. The electrodes were placed on each side of the cell matrix and - tested as fuel cell cathodes operating on air or oxygen and as fuel cell anodes operating on pure hydrogen. ThP electrodes which, after treatment, contain 46 wt. % of Te~lon and had a platinum loading of 0.54-mg/cm2 . .
showed the following results when operating the ~uel cell at a temperature of 160 C. w;th a current density of 100 ma/cm2.

TABLE I
.. . ... . .
2 Cathode H2 Anode Air Cathode Voltage Voltage ~ Gain Internal Resistance Terminal Corrected Term. IRC Term. IRC
-607 643 700 7~1 ~3 6~3 668 When the cel1 performance and reliab;lity of the electrodes were tested at 180 C., the following results were obtained:

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1~3~73~

TABLE II
2 Cathode H2 Anode Air Cathode Vo_t_~ Voltage 0 Gain Voltage Internal 5Resistance Terminal Corrected Term. IRC Term. IRC

, EXA~PLE II
In a manner similar to that set forth i~ Example I above, a semi-conducting carbonaceous pyropolymeric inorganic refractory oxide ma~erial was prepared by treating a gamma-alumina base similar in nature to that used in Example I with a benzene pyropolymer precursor in a rotary reac-tor . at 800 C. After stabilization of the material9 25 grams of said material ~ was admixed with 1.5 1iters of a 96% phosphoric acid solu~ion and-heated .: :
:~ 15 at a temperature of 180 C. for a period of 24 hours. After leaching of .. - the alumin~.-base from the material, the carbonaceous pyropolymer was -. filtered from the liquid, washed with deionized water and dried at a tem-~ perature.of 100 C. for.a period of 16 hours. Thereafter the carbonaceous l~ pyropolymeric material was commingled with a-28% chloroplatinic acid solu-~: 20 tion -and mixed with 50 grams of deionized water The mixture was stirred . in.an evaporating.dish:for 0.5~hours.at ambien~ temperature and thereafter . ~ . . .
~ was-evaporated from the material. After evaporation, ~he impregnated car-.
. ~ ~ bonaceous pyropolymeric material was dried in an oven a~ 100 C. and reduced . ~
~: by treatment with flowing hydrogen at a temperature of 2fiO C. for a period 25 of 2 hours. The platinum concentratlon of the finished electrocatalyst was ~ ~ 13 percent by weight. X-ray analysis of the finished electrocatalyst showed ::~ ~ 'chat 35% of -the platinum particles had mean diameters over 15 to 20 A (termed . ~ ; O
agglomerated) and the mean diameter of ~hose particles was 21 A. The surface : area of the platinum in the electrocatalyst was abo~e 140 m2/g.
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, ~33~307 The catalytic composition of matter which was prepared in the above paragraph may then be fabricated in~o a fuel cell elec~rode in a manner similar to that set forth in Example I above and may be tested as an air and oxygen cathode as well as a hydrogen anode ;n a phosphoric acid fuel cell.
EXAMPLE III
-A catalytic composition of matter was prepared by forming a semiconducting carbonaceous pyropolymeric inorganic refractory oxide material, impregnating this material with platinum and thereafter leaching the catalytic composition of mztter to remove the alumina base therefrom at a temperature of 180 C. with phosphoric acid for a period ranging up to 340 hours. In addition, a second catalytic composition of matter was prepared by impregnating carbon black with platinum and subjecting this composition of matter to a leaching procedure similar to that hereinbefore described. The sintering effect on the platinum which was present in both catalysts was studied by X-ray analysis with the following results:
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r ~ El ,_ O cr:
~D O CO ~ ~ O ~ C~J O ~
CU ~ C~t ~ ~
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~-~ E
v~ ~a~
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= _ = = o-= _ = = m u~
:~ ~ 3 c~l ~ ~ o LLI ~ O`- ' 'a~
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a) 3 I E
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o O d~ O O O ~ d- O O
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` a~ ~c '~ c o a~ > c ~I
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;36)7 It is noted ~rom -t~le above table ~hat the ca~alyst o~ t'ne ~resent invention showed a relatively small loss ~f surface area ~Il-th a rela-tively small gain of agglomeration of the platinum particles. In contradistinction to this, the catalyst ~lhich used carbon black as the base rather than the carbonaceous pyropolymer of the presen~ invention sho~ed a relatiYely sharp decrease in the surface area of the catalyst as well as a relatively large increas~ in the percent of a~Jglom2ra~ion of the platinu~ particles.
EXAMPLE I~
In a manner similar to that set forth in the above examples, an alumina which has a particle size possessing a mean o~ about 0.5 microns may be ealcined at a temperature af about 500 C. for a perioa o~
about 3 hours. Thereafter the alumina may be placed in a rotary reactsr and treated with benzene at a temperature of about 800 CD After recovery of the resulting semicondwcting carbonaceous pyropolymeric inorganic re-fractory oxide material7 the material is then treated with a solublechloropalladic acid in an amount sufficient to impregnate the carbonaceous-pyropolymer at a palladium level of about 10% by weight. Af~er drying the material at a temperature of about 100 C.~ it may then be reduced ; ~by treatment with hydro~en at an elevated temperature of about 250~ C>
2Q Thereafter the ma~erial may be leached by treatmen~ with sul~uric acid ata temperature of about 100~ C. for a period Gf about Z0 hours. The solid ma~erial ls recovered by filtr~tion and treated with deionized water at a temperature above 100 C. for a period o~ abou~ 4 ~iours. Thereaf~er ~he catalyt~c composition of ma~ter may then be ~ormed into an elec~rode for -~: 25 use in fuel cells~
~ ~In a manner ~imilar to that set fort~ in the above examples, :
~novel catalytic compositions of matter of the present invention may be : ~ :
. - ~0 -73~7 prepared by treating the carbonaceous pyropolymeric inorganic refractory oxide material resulting from the treatment of gamma-alumina or silica ~lit'n a pyropolymer precursor such as cyclohexane, benzene, n-hexane, etc., at pyrolysis conditions and treating the resultant carbonaceous pyropolymeric inorganic refractory oxide material with soluble solutions of platinum and rhenium, platinum and rhodium, palladium and ruthenium, etc., follow2d by leaching of the impregnated material with phosphoric acid at a temperature of about l80 C. to remove the refractory inorganic oxide such as alumina .
or silica. Thereafter the catalytic composition of matter comprising the ln carbonaceaus pyropolymer which is impregnated with the catalytically active metals may then be utili~ed in the formation af electrades for fuel cells.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electrocatalyst which may be used in preparation of an electrode for an electrochemical cell prepared by the steps which comprise:
(a) treating a refractory inorganic oxide with an organic pyrolyzable compound to form a carbonaceous pyropolymer having a conductivity at room temperature of from 10-8 to l0+2 inverse ohm-centimeters on the surface of said refractory inorganic oxide;
(b) leaching said carbonaceous pyropolymer deposited refractory inorganic oxide with an acid or base to remove said refractory inorganic oxide, said leaching being performed either prior or subsequent to impregnating the carbonaceous pyropolymer with a soluble salt of at least one catalytically active metal; and (c) recovering said catalyst.

2. The electrocatalyst of claim 1 in which said carbon-aceous pyropolymer deposited refractory inorganic oxide is leached prior to impregnating the carbonaceous pyropolymer.

3. The electrocatalyst of claim 1 in which said carbon-aceous pyropolymer deposited refractory inorganic oxide is leached subsequent to impregnating the carbonaceous pyropolymer.

4. The electrocatalyst of claim 1 in which said catalytically active metal is present in said composite in a range of from about 5% to about 50% by weight of the carbonaceous pyropolymer.

5. The electrocatalyst of claim 1 in which said catalytically active metal is platinum.

6. The electrocatalyst of claim 1 in which said catalytically active metal is palladium.

7. The electrocatalyst of claim 1 in which said catalytically active metals are platinum and rhenium.

8. The electrocatalyst of claim 1 in which said catalytically active metals are platinum and rhodium.

9. The electrocatalyst of claim 1 in which said catalytically active metals are palladium and ruthenium.

10. A method for the preparation of an electrocatalyst which may be used in the preparation of an electrode for an electro chemical cell which comprises treating a refractory inorganic oxide with a pyrolyzable organic compound at pyrolysis conditions to form a carbonaceous pyropolymer on the surface of said refractory inorganic oxide, leaching the resulting pyropolymer deposited refractory inorganic oxide with an acid or base to remove said refractory inorganic oxide, said leaching being per-formed either prior or subsequent to impregnating the carbonaceous pyropolymer with a soluble salt of at least one catalytically active metal, and recovering the resultant catalytic composition of matter.

11. The method of claim 10 in which said pyropolymer deposited refractory inorganic oxide is leached prior to impregnating the carbonaceous pyropolymer.

12. The method of claim 10 in which said pyropolymer deposited refractory inorganic oxide is leached subsequent to impregnating the carbonaceous pyropolymer.

13. The method of claim 10 in which said refractory inorganic oxide is alumina.

14. The method of claim 10 in which said refractory inorganic oxide is silica.

15. The method of claim 10 in which said catalytically active metal is platinum.

16. The method of claim 10 in which said catalytically active metal is palladium.

17. The method of claim 10 in which said catalytically active metals are platinum and rhenium.

18. The method of claim 10 in which said catalytically active metals are platinum and rhodium.

19. The method of claim 10 in which said catalytically active metals are palladium and ruthenium.

20. The method of claim 10 in which said leaching is effected at a temperature in the range of from about ambient to about 250°C.

21. The method of claim 10 in which said composite is leached by treatment with phosphoric acid.

22. The method of claim 10 in which said composite is leached by treatment with sulfuric acid.