CA1104998A

CA1104998A - Platinum catalyst and method for making

Info

Publication number: CA1104998A
Application number: CA313,590A
Authority: CA
Inventors: Calvin L. Bushnell; Vinod M. Jalan
Original assignee: United Technologies Corp
Current assignee: RTX Corp
Priority date: 1977-11-23
Filing date: 1978-10-17
Publication date: 1981-07-14
Also published as: US4137373A

Abstract

ABSTRACT OF THE DISCLOSURE
The invention relates to a fuel cell including an improved catalyst comprising small platinum crystallites sup-ported on carbon particles. The crystallites have porous carbon deposited on and around them, the catalyst with the porous carbon deposits having been heated in an inert atmosphere or vacuum to within the temperature range of 1500°F to 2250°F, the temperature having been held within the above range for one-half to six hours. The invention also relates to a method for improving a catalyst of platinum crystallites which includes the steps of heating the catalyst in an inert atmosphere or vacuum to within the temperature range of 1500°F to 2250°F, and holding the temperature within the range for one-half to six hours.

Description

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BACKGROUND OF THE INVENTION
Field of the_In~ention - This in~ention relates to a platinum catalys~ and more particularly to a pla~inum catalyst supported on carbon particles.
Description of the Prior Art - Plat:inum ;s a well-known catalyst used in electrochemical cells. Electrode perEormance in a cell is directly related to the amou~t of surface arQa of platinum which can be reached by the various reacting species within the cell. This fact~ couplecl with the high cost of platinum, has resulted in co~siderable eor~ ~o get platinum into a usable form which has maximum surace area per unit weigh~ of platinumO The basic approach has been, and still is, to put the platinum on ~he surface of suitable particles called suppor~s~ -Carbon particles and graphite particles are COmmQn platinum suppor~s~n the fuel cell art. Several known techni~ues exist ~or depositing small platlnum particles o~ such supports. For e~ample; the support can be df.spersed in an aqueous solution o~ chloroplatitlic acld, dried, and exposed ~o hydroge~ Some other ~echnlques are descrlbed in U~S. Patents 3,857~737 to Kemp et al, 3~40J107 to Barber, 3,470,019 to Steele, and 3,532~556 to Steele. :
By these techniques platinum crys~als may be dis- -;
persed on the sur~aces of ~he support par~ieles so as to provide a high surface area of platinum.

, When carbon supported platinum is used a~ temperatures of greater than 100C in the presence oiE a liquid (or at higher temperatures in the presence of a gas) it has been found to lose sur-Eace area. This 105s of surface area is particularly pronounced in an acid fuel cell envir~nment, such as in fuel cells using phosphor~c acid as the electrolyte, which operate at temperatures anywhere from 120C and higher. The loss in sur~ace area is dramatic during the first few hours o cell operatio~, but it cvntinues at a slow but steady rate for a considerable period thereafter. A loss i~ cell per~ormance is directly attributable to this loss in platinum sur-Eace area.
O~e method ~or reducing this loss of surface area is described iu commonly owned U.S. Patent 4~028,274 to Harold R. Kunz. In that invention the sur~aces of graphitized carbon support particles were oxIdized in the presence of a metal oxidizing catalyst to ~orm pits in the surfaces of ~he partlcles. The me~al oxidizing catalyst was then removed and the platinum was deposited on the oxidized particlesO Based on the theory ~ha~
during use o~ ~he catalyst the pla~inum crystallites migrate over the surface of the carbon and combine with other platinum crystall~tes (i.e~, recrystallizin$) ~hereby losing surace area, it was felt that the pits in the surface of the Fupport material would hold the pla~inum crystaLlites more securely in place thereby red-lclng .
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migration and loss of surface area. While this method was an improvement over the prior art, it was not totally satis-factory and continued effort~ have resulted in the improved method of the present invention.

SU~RY OF TE:E INVE~TION
Accordingly, it is an object oi the present invention to make an improved platinum supported on carbon catalyst, and more particularly to make an improved fuel cell electrode using this catalyst.
Another object o the present invention is to reduce recrystallization of platinum supported on carbon by reducing the migration of the platinum over the surface of the carbon support particles during subsequent use of the cata].yst, such as in a fuel cell.
According to the present inventian a method for improving a catalyst of platinum crystallites supported on carbon comprises the steps of depositing carbon on and around the platinum crystallites and then heating the catalyst in an inert atmosphere or vacuum to a high temperature.
It is a still further object of the invention to provide an improved catalyst for a fuel cell electrode.
It is a still further object af the invention to provide a fuel cell electrode including the improved catalyst.
In accordance with the invention, a method for improving a catalyst of platinum crystallites supported on carbon comprises the steps of: depositing carbon on and around the supported platinum crystallites and then heating the catalyst in an inert atmosphere or vacu~un to within the temperature range of 1500F to 2250~ and holding the te~per-ature within said range for one-half to six hours~
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In accordance with an embodiment, a catalyst com-prisin~ small platinum crystallites supported on carbon includes porous carbon deposited on and around said crystal-lites, said catalyst having been subjected to heating in an inert atmosphere or vacuum within the temperature range of 1500F to 2250F, the temperature being held within said range ~or one-half to six hours.
In accordance with a further embodiment, a fuel cell electrode includes an improved catalyst comprising small platinum crystallites supported on carbon particles, said crystallites having porous carbon deposited thereon and there- .
around, said catalyst with said porous carbon deposits having been heated in an inert atmosphere or vacuum within the temperature ran~e of 1500F to 2250F, the temperature having been held within said range for one-half to six hours.
It has been found that a catalyst made by the methods described herein and used as an electrode catalyst in a phosphoric acid fuel cell has improved recrystalliza-- tion proper-ties in that the rate of loss of catalyst specific

2~ surface area during fuel cell operation is significantly reduced; additionally the catalyst has an initially higher - 4a N

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activity as compared to prior art platinum catalysts, the activity remaining higher than the prior art catalysts during use.
Commonly owned Canadian patent application having Serial No. 313,592, by V. Jalan and C~ Bushnell, filed on October 17, 1978 describes methods for deposit-ing carbon on and around carbon support~d platinum crystallites. As explained in this application, it is b~lieved that the porous carbon deposited on and around the platinum crystallites tends to more securely "set"
the platinum crystallites in position on the carbon support particle thereby significantly reducing the crystallites ability to migrate over the surface of the carbon support particle during use in a fuel cell. By reducing the rate of migration the rate and extent to which recrystallization occurs i~ significantly reduced.
We have found, quite unexpectedly, that if the catalysts made according to the foregoing application are further heat treated in an inert atmosphere or vacuum to within the temperature range of 1500F to 2250F and if the temperature is held within that range for one-halE to six hours the resulting catalyst recrystallizes to an even lesser extent. Additionally, and even more surprising, is that the activity of the platinum itself is increased by this high temperature heat treatment. This inarease in . . . . . ..

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platinum activity appears to be unrelated to the ~act that platinum recrystallization in the fuel cell is also reduced~
The me~hod for depositing ~he porous carbon on and around the platinum crystallites prior to the high tempera-ture heat treatment does not appear to be critical to the present invention; however, a preferred method is to heat a supported platinum catalyst in the presence of carbon monoxide gas su~h that the carbon monoxide decomposes in the vicinity o the platinum crystallites (which act as 1~ decomposltion catalys~) to deposit carbon thereon and therearound. Other methods for depositing porows carbon are hereina~ter disclosed; but the carbon monoxide method is preferred because of its simpllcity and low cost.
Basically~ all o the methods described her~in or depositing the porous carbon l~volve heating the catalys~
in the presence o~ a carbonaceous compound to decompose the compound ~hereby forming porous carbon deposits on and around the platinum crystallites. This does not mean~
howeverg tha~ other techniques for depositing carbon would not work, The foregoing and other objectsj features, and advan tages of the present invention will become more apparent in the light of ~he following detailed description of preferred embodiments thereof as illustrated in the accom-panying drawing.
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~6-' BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a graph showi.ng the improved fuel cell performance attained by subjecting a platinum sup-ported on carbon catalyst to a carhon monoxide heat treatment but not the high temperature heat treatment step of the present invention.
Fig. 2 is a graph illustrating that a catalyst made in accordance with the present invention loses surface area at a reduced rate when subjected to fuel cell condi- :
tions.
Fig~ 3 is a graph illustrating the improved catalytic activity of a catalyst made in accordance with the present invention.
DESCRIPTION OF THE PREFERREr) EMBODIME~TS
Methods for De,oosltincl Porous Carbon On and Around the Platinum Crvstallites of a Supported Platinu atalyst The following methods for depositing porous carbon on and around the platinum crystallites o platinum supported on carbon catalyst are the same methods as des-cribecl in the above mentioned Canadian patent application Serial No. 313,592~ The test data presented in Tables I, II, and III below are the same test data as is presented in those applications. The data presented in those tables does not reflect the advantages obtained by the present invention since the electrodes tested were not subjected to the high temperature 7 ~
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heat trea~ment of the present in~ention after ~he carbon was deposited. It i5 believed, however, that the optimum manner of applying the carbon deposits 9 as described ; herein and in the aforementioned copending patent applica-tions will also produce the best results with regard to the present invention~
A preferred method for depositing porous carbon on and around the platinum crystallites of carbon supporte~
platinum catalyst is to heat the cataLyst to within the ~emperature range of 500F to 1200F in a caxbon monoxide atmosphere. The platinum cr~stallites act as a catalyst to the decomposition of the carbon monoxide as represented by the ~ollowing formula:
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2co ~ heat ~ C ~ CO2 (1~
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Since without the presence of platinum the carbon monoxlde wlll not decompose within this temperature range, the carbon is only depositecl on and around the pla~inum crystallites. The heat treatment ~emperature range is coordinated with the time that the catalyst is held within that temperature range. The critical considerations are to make sure that the carbon deposits are sufficlently heavy to significantly reduce platinum migratLon, while at ~he same time they are not so dense and ~hick such that during use o~ the catalyst the reactant gas aod/or l~uid cannot easily reach the platinum crystallLtles.

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In other words the carbon deposits must be porous such that the performance of the catalyst does not suffer to such an extent that the benefits of the present i~ention are nullified.
Since it was not possible to calculate the optimum thick~ess or porosity of the carbon being deposited5 a number of catalyst samples were made using various ~e~-p~ratures and times. Electrodes were made with these samples using standard techniques. Table I below present~
a sampling of ~he data obtained. The electrode performance data are ~rom subscale cell tests using two ~nch ~y two inch cathodes with a ca~alyst loading of 0.25-0.50 mg/cm2 of electrode surface. A conventional anode was used.
The catalyst support material was a high surface area carbon black. The electrolyte in these tests was j phosphoric acid and the reactants air and hydrogen.

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From these tests and other information relating to heat treatment of supported platinum catalyst~ it is estimated that benefits will be observeld if the heat treating temperature is within the rang~e of 500F to 1200Fg and i the temperature is held~within this range for from one to sixty minutes. Obviously, the higher the - ~eat treating temperature, the shorter the ti~e the temperature should be maintained, a~d vice versa. From past experience it is known that temperatures i~ excess of about 1200F result in excessive thermal sin~ering o~
the platinum during the heat treating. In othex words, the high temperatuxe in and o itself would cause signiEi-cant migration of the platinum crystallites during the carbon monoxide ~reatment, resulting in an increase in platinum crys~aLlite size which may eliminate any b~nefits which might otherwise have been obtained~ A preferred heat treating temperature range is estimated to be 50~F
to 800F, the temperature belng held within the range for five to thirty minutes~ Best results were obtained by heatlng to a maximum temperature of about 700F and holdlng at that temperature for about 10 minutes.
Figo 1 shows a graph wherein time in a fuel cell is plotted on the horiæontsl sxis and fuel cell performance in ~erms of cell voltage is p~otted on the vertical axis.
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from Table I. The curves B and C are from cells using catalyst which had been carbon monoxide treated at 700F
for 10 minutes. Note that although dif~erences in initial performance were not meaningful, the treated catalysts were clearly superior over the long term as a xesult of smaller platinum surface area losses with time, Carbonaceous gases or vapors other than carbon monoxide may also be used in practicing the present invention, For example, a hydrocarbon gas such as methane, acetylene or ethylene may be used as well as benzene, he~ane, or heptane which should be used in the ~or~ o~ a vapor. The ~ollowing formulas represent the reactions which occur ~or two o~
these materials:

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methane - CH~ + heat Pt~ C + 2H2 ~2) benzene - C~H6 + heat ~ 6C -~ 3H2 (3 As with carbon monoxide~ tests would have to be run or each gas to develop optimum heat treatment tempera~ure ranges and the length of time that the temperature would have to be held within those ranges. A limited number of samples were made under a variety of conditions. Examples o~ some eleetrode test data using these samples i9 prese~ted in Table II below, Electrode size, catalys~ loadlng and other aspects of the fuel cell tests were the same as descri~ed a~ove ~i h regaxd to Table I.
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While these tests prove that the carbon may be deposi~ed using a variety of gases and vapors, not enough testing was done to develop preferred and optimum heat treatme~t conditions for these materials.
In yet another method for depositing porous carbon, a carbon supported platinum catalyst was soaked for ~ 15-30 minutes in an aqu~ous solution of about 10 weight - percent CllH22Oll commonly known as sucrose. The catalyst was then dried at a low temperature to remove the water, 10 leaving a coating of sucrose over the entire catalyst:
partLcle. The coated catalyst wa~ then heated in an inert atmosphere (a vacuum could have been used) to decom-pose the sucrose according to the following formula:

CllH22011 ~ heat ~ 3llc ~ llH20 (4) :

This leaves porous carbon deposits over all areas of the ; catalys~ including on and around the platinum crystallites as well as simply on the carbon suppoxt mater-lal. As Ln the other embodiments, the carbon which is deposited on or around ~he platinum ~rystallites serves the purpose o~
reducing migration o the platinum crystallites i~ accordance wi~h the teachings o the present invention. Carbon which is deposited elsewhere on the support does no harm since the catal~st support material is already carbon~` ~able III
displays ~est data for electrodes comprising catalyst made using the sucrose decomposition method. Electrode size, catalyst loading and other aspects of the fuel cell tests were the same as described above with regard to Table I.

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For benefits to be observed L~ is stimated the sucrose decomposition heat treatment temperature should be between 800F and 1200F and that the temperature should be held within this range for from one~half to ~ix hours. In ge~eral, the temperature need only be m~intained until all of the sucrose ls converted to carbon~ As the carbo~
is being deposited, if the temperature exceeds 1200F
excessive thermal sintering of the platinum during the sucrose decomposition step may occur and defeat the purpose o:~ the present invention, which is to maintain small platinum crystallite slzes. Te~lperatures less than 800F wlll not completely carbonize the sucrose~ It is believed that any soluble organic material which will decompose to carbon upon hea~ing may be used for the purpose of practicing the present lnvention~ Sucrose is one such soluble organic ~.
material. Examples o~ others are phenolic res~ns~ cellulose~
and polyvinyl alcohol~ Once the carbon has been deposite~
by any o the Eorego~ng methods, the further high tempera-ture heat t-reatme~t step (hereina~ter descri~ed~ of t-he present in~ention may be accomplished without fear of excessive ~hermal ~intering~

~_ Having deposited the porous carbon on the platinum : crystallites such as by one of the fore$oing methods or any other suitable method, the catalyst is then subjected to a high temperature he~t treatment in an ~ert atmosphere or vacuum. Tests wera conduc~ed ~o determine the op~imum heat treatment conditions. Some of the test data is pre-sented below in Table IV. Electrode sizeg catalyst loading and other aspects of the fuel cell test~ were the same as descxibed above with regard to Table I.
Catalyst #19 was the control catalyst and did not receive any treatment. Carbon was ~ot deposited prior to the high temperature heat treatment in the case of catalysts numbered 20 and 22; this, too, was for the purpose of judging the effectiveness of the present invention. All of the remaining cataly~ts were subjected to a 700F carbon mono~ide treatment for ten minutes prior to heat treati~g in an inert atmosphere or vacuum to the lndicate~ temperature.
In all of these tests the heat treatment in an ine~
atmosphere or vacuum was carried out by heatîng the catalyst sample from room temperature to the maximum heat treatment temperature at the rate indicated in the second column of the table. Tha time indicated in column 4 of the table is counted ~rom the momen~ the ~emperature reaches 1650F~ For example~ at 370F per hour catalyst ~21 would be heated from 1650F ~o 2150F in one hour and 20 minu~P~ e remaini~g time of ~he two and one-hal total time would be a~ 2150F.
Catalyst samples 27 and 29 were simply heated ~G ~650F at the rate indicated and held at 1650F for one hour. Catalyst ~24 was hea~ed up to 1650F at a rate of 200F/hr and then to 1900F at a rate of 400-F/hr.

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Although we started counting time at 1650F, it is believed that bene~its probably start to accrue at about 1500F. Temperatures in excess of abou-t 2250F may produce a degree of thermal sinterlng that virtually nullifies any beneEits produced by the heat treatment. With this in rnind, and based upon our test results and other experience~ it is estimated that a heat treatment within the temperature range o~ 1500F to 2250~F for from one-hal~ hour to six hours will ~e beneficial. Of course, lower maximum t:empera-tures and slower heating rat~s wlll require longer heat t~eat.ment times than higher ma~imum temperatures and faster heating rates. Raising the temperature too quickly can cause oxidation of the ~arbon support due to volatiliza-tion of irnpurities before they have had a chance to eseape from the carbon particles. For this reason it is recommended that the rate o~ heating should not exceed abo~t 600F per hour~ Our data indicates that a preferred heat treatment should be within the temperature range o 1650F to abou~ 1760F for ~rorn three~quarters ~o one and ~0 one-half hours~
Based on our e~perimental testing it was found that the high temperature heat treatment step improves the -~ catalyst in two major respects. First, recrystallization of the platLnum during use of the electrode in a fuel cell is reduced even beyond Lbat which is obtained by simply ~ :

~, 19 - ' depositing the porous carbon on the platinum crystallites without afterward subj ecting the catalyst to a high temperature heat treatment. Second, the initial activity of the platinum catalyst (i.e., before it is used in the fuel cell) is increased. The benefit of that initial increase is retained throughout use of the catalyst.
Initially it was attempted to ob~ain reduced platinum recrystallization using a high temperature heat treatment but without first depositing carbon on th~ platinum cxystallLtes. These tests were not particularly successfuL
due to excessive thermal sint~rlng (i.e., increasing of the platinum particle size) caused by the high heat treat-ment temperatures. With regard to the present invention it is theorized ~hat ~he porous carbon deposits significantly slow down the migration rate of the platinum crystall-Ltes during the high temperature heat treatment; and as the platlnum crystallites slowly move over the sur~ace of the carbon they are able to find suitable natural deects Ln ~he surace of the carbon support material which hold ~he platinum particles and further reduce migra~ion and recrystal~
lization upon use of the catalyst in ~he fuel cell~
Table V presents some catalyst surface area data for catalysts 19, 20, and 21 which were treated as indicated in Ta~le IV~ From the data presented in Tables IV and V we can make several observatlonsO Firstg it is clearly seen that C0 ~reatment (or other treatment for depositing porous ': :

carbon on ~he platinum crys~allites) prior ~o the high temperature heat treatment step is critical to the present invention. Second, despite the great improvement in initiaL
cathode potential as between catalyst 2~ and catalyst 21, catalyst 21 still has a lower initial cathode potential than the untreated catalyst 19; yet J after only 100 hours of operation in a fuel cell, the surface areas of catalysts 19 and 21 are almost the same. Given additional time in the fuel cell, the catalyst 21 will most likely exceed the lQ performance and surface area of the untreated catalyst 19 Thus, in the long run benefits will be obser~ed as a resul~
of the speci~ic treatment received by the catalys~ 21.
Third~ the treatment of catalyst 25 illustrates that even though ~he heat treatment temperature is not particularly high, excessive time a~ that temperature rP.sults in a signi~icant initial per~ormance penalty. Finally, it can ; generally be concluded that better results are obtained using lower temperatures and less heat treatment t~me~
such as the preferred temperature range of 1650F~to 1760'F for from threL-quarte~ s to one and one~balf hours .

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~ ~8 TABLE; V `
EFFECT OF CO TREAl~IENT PRIOR TO HEAT TREATMENT
ON PLATI~UM SURFACE AREA

Surface Area Catalyst # m2~gm Initial 100 hours dl9 140 45 d20 40 34 d21 60 43 10d see Table IV for treatment details~

The graph o~ F~g. 2 illustrates that the present invention provides a significant improvement over catalysts ,~ .
which ha~e had carbon deposited on the platinum crystallites but which were not thereafter heat treated accord;ng to the -~-present i~vention. In Fig. ~ time spent at uel cell condi- -tions is plotted on the horizontal axis and average platinum surace area is plotted on the vertical axis. The curveQ
are based on actual data. The cur~e labeled D ls untreated platinum supported on car~on catalyst. The curve labeled E
20 ~ ~iB a catalyst w~ich was~the same as the catalyst represented ;~
by the curve D except that porous carbon has been deposi~ed on and around the platinum crystallites in accordance with the carbon monoxide~ method hereinabove described. Cata}yst E was not, however, Qubjected to a~high temperature heat ~22-'',~:

treatment in an inert atmosphere. The curve labeled F is a catalyst which has been C0 treated and then subjected to the high temperature heat treatment according to the method of the present invention. That is, it is for a catalyst identical to the catalyst represented by the curve E but which was also subjected to a high temperature heat treatment in an inert atmosphere.
It can be seen that catalysts D and E start out with approximately the same platinum surface area~ which is greater than the platinum surface area o~ catalyst F.
In all cases platinum sur~ace area decreases during uel cell operation; however~ the surface area of catalyst decreases at a slower rate than either of~the other catalysts. After about 200 hours o~ ~uel cell operatlon the platinum surface area of catalyst F ex~eeds ~he surace area of catalyst D. A~ter about 2000 hours o fuel cell opera~ion the platinum surface area o~ catalyst F also exceeds the platinum sur~ace area of ca~alys~ E. ~liS
partially explains the improved per~ormance Q~ the ~uel cel~ using ~he catalyst o the present in~en~ion.
The graph of Fig. 3 is also based on experimen~al data and demonstrates that aside from the reduced recrystal-lization rate of the platinumg at least initially the platinum is in and o itself more active as a result of ~he present invention. In this graph time in the ~uel cell is again plo~ted on the horizontal axis and cataLyst acti~ity in .
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terms of fuel cell performance at 200 amps/ft~ is plotted on the vertical axisO It is immediately noted that the activity of the catalyst made according to the present invention ~curve G~ is inl.tially and always higher than the activity of the untreated catalyst (curve H) despite the fa~t that it initially has a smaller platinum surface area -: (see Fig. 2~. It is believed that even if after a long period of use the catalysts of curves G and H end up having ~ :
the same area (which is not the case) the activity of the catalyst represented by curve G will 5ti.11 be higher than that o~ the untreated catalyst~
Although the invention has been shown and described with respect to preerred embodiments thereof, it should be understood b~ those skilled in the ar~ tha~ other various changes and omissions in the form and detail thereof may be made therein without departing rom the spirit and the scope of tha invention.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for improving a catalyst of platinum crystallites supported on carbon comprising the steps of depositing carbon on and around the supported platinum crystallites and then heating the catalyst in an inert atmosphere or vacuum to within the temperature range of 1500°F to 2250°F and holding the temperature within said range for one-half to six hours.

2. The method according to claim l wherein said temperature range is from 1650°F to 1760°F and the temperature is held within said range for three-quarters to one and one-half hours.

3. The method according to claim 1 wherein said step of depositing carbon comprises the step of heating the catalyst in the presence of carbon monoxide gas to decompose said carbon monoxide and deposit porous carbon on and around said supported platinum crystallites.

4. The method according to claim 3 wherein the step of heating the catalyst in the presence of carbon monoxide gas includes heating to within the temperature range of 500°F to 1200°F and holding the temperature within that range for from one to sixty minutes.

5. The method according to claim 3 wherein the step of heating the catalyst in the presence of carbon monoxide gas includes heating to within the range of 500°F to 800°F
and holding the temperature within that range for from five to thirty minutes.

6. A catalyst comprising small platinum crystallites supported on carbon, and including porous carbon deposited on and around said crystallites, said catalyst having been subjected to heating in an inert atmosphere or vacuum within the temperature range of 1500°F to 2250°F, the temperature being held within said range for one-half to six hours,

7. The catalyst according to claim 6 wherein said porous carbon deposits have been applied by the step of heating the catalyst without said deposits in the presence of a carbonaceous component which decomposes to form said porous carbon deposits on and around said platinum crystallites.

8. The catalyst according to claim 6 wherein said temperature range was 1650°F to 1760°F, the temperature having been held within said range for three-quarters to one and one-half hours.

9. The catalyst according to claim 7 wherein said carbonaceous component was carbon monoxide and the step of heating in the presence of said carbonaceous component included heating to within the temperature range of 500°F
to 1200°F and holding the temperature within the range for from one to sixty minutes.

10. A fuel cell electrode including an improved catalyst comprising small platinum crystallites supported on carbon particles, said crystallites having porous carbon deposited thereon and therearound, said catalyst with said porous carbon deposits having been heated in an inert atmosphere or vacuum within the temperature range of 1500°F
to 2250°F, the temperature having been held within said range for one-half to six hours.

11. The fuel cell electrode according to claim 10 wherein said temperature range was 1650°F to 1760°F, the temperature having been held within said range for three-quarters to one and one-half hours.

12. The fuel cell electrode according to claim 10, said porous carbon having been deposited by heating the platinum supported on carbon catalyst without said carbon deposits in the presence of carbon monoxide gas to decom-pose said carbon monoxide and deposit porous carbon on and around said supported platinum crystallites.

13. The fuel cell electrodes according to claim 12 wherein heating in the presence of carbon monoxide gas included heating to within the temperature range of 500°F
to 1200°F and holding the temperature within that range for from one to sixty minutes.

14. The fuel cell electrodes according to claim 12 wherein heating in the presence of carbon monoxide gas included heating to within the temperature range of 500°F to 800°F and holding the temperature within that range for from five to thirty minutes.

15. The fuel cell electrode according to claim 10 wherein said porous carbon deposits have been applied by the step of heating the catalyst without said deposits in the presence of a carbonaceous compound which decomposes to form said porous carbon deposits on and around said platinum crystallites.