Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1997-04-17
1999-05-25
Bell, Bruce F.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204252, 204254, 204282, 204284, 429 30, 429 33, 429 40, 429 41, 429 46, C25B 1300
Patent
active
059067160
DESCRIPTION:
BRIEF SUMMARY
Proton-exchange membranes having a thin metal coating on the surface can be used in fuel cells. Here, the metal, e.g. platinum, serves as catalyst for the reactions proceeding in the fuel cell (Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol. A 12, p. 79). Proton-exchange membranes having a thin metal coating on the surface can also be used in electrolysis cells, e.g. for the electrolysis of water. Apart from pure metals, mixtures or alloys of metals and composites of catalytically active metals with carbon or other electrically conductive materials are also used.
GB 1 137 127 discloses a process for producing electrodes for fuel cells, in which a nonmetallic substrate having through pores, for example of plastic, is loaded with a reducing agent and subsequently treated with a solution of a readily reducible metal, for example palladium chloride, gold cyanide or chloroplatinic acid, so as to metallize the surface of the substrate. The metal layer produced is subsequently electrically strengthened. However, the porous substrates mentioned can only be used in fuel cells together with a liquid electrolyte. Use in solid electrolyte fuel cells is not possible.
The Japanese published specification 58-176 222 discloses a process for metallizing a cation-exchange membrane, in which a film of a perfluorinated, aliphatic polymer containing sulfonic acid groups is impregnated with a reducing agent, for example sodium borohydride, and is then treated with the solution of a metal salt which forms negative metal complex ions, e.g. H.sub.2 PtCl.sub.6. The metal salt is here reduced to the metal and the membrane surface is metallized. Possible applications of the membranes are given as electrolysis processes, e.g. chloralkali electrolysis.
As the Applicant has found, reducing agent always diffusing from the membrane into the solution of the metal salt to be reduced during the reduction process cannot be avoided in the above method. Even in the solution, metal is then formed which, however, does not deposit on the membrane. This metal loss decreases the economic viability of the process.
In other processes, a reducing agent diffuses from a first chamber through an ion-exchange film whose other side is in contact with a solution of hexachloroplatinic acid in a second chamber, so that platinum deposits on the surface (R. Liu, W. H. Her, P. S. Fedkiw, J. Electrochem Soc. 139, 15-23 (1992)). Apart from the great complication of this process, a further disadvantage is that, as a result of the action of the reducing agent diffusing through the membrane, the metal which is actually only required in the vicinity of the membrane surface also forms in deeper-lying layers of the membrane. This part of the metal produced by reduction does not come into contact with the fuel gases in a fuel cell and can therefore not show any catalytic activity. Thus, this process too does not make the catalyst available only where it has a favorable influence on the function of a fuel cell. The importance of localizing the platinum on the membrane surface has already been shown by E. A. Ticianelli, C. R. Derouin and S. Srinivasan (J. Electroanal. Chem. 251, 275-295 (1988)).
In the abovementioned publications, the material of the cation-exchange membranes comprises polymers having perfluorinated carbon main chains which are linked laterally to ionic groups, usually sulfonic acid groups. The stability of these polymers (e.g. to chlorine and alkali's) is high, but not completely necessary for use in fuel cells. Disadvantages are also their high price and the difficulty of processing the commercially available membranes.
EP-A 0 574 791 discloses a process in which the solution of a sulfonated polyether ketone is processed in dimethylformamide to give a film and platinum particles are pressed into the surface of the film. The cell potential of the metallized membrane obtained in a hydrogen/oxygen fuel cell was 700 mV and the current density was 175 mA/cm.sup.2.
DE-A 4 241 150 discloses an electrode/membrane composite in which a soluble cation-
REFERENCES:
patent: 4328086 (1982-05-01), Takenaka et al.
patent: 5164060 (1992-11-01), Eisman et al.
patent: 5271813 (1993-12-01), Linkous
patent: 5480518 (1996-01-01), Shane et al.
patent: 5525436 (1996-06-01), Savinell et al.
patent: 5599632 (1997-02-01), Samsone et al.
R. Holze et al., Jour. of Membrane Science, vol. 73, No. 1, 1992, p. 87 ff, no month available.
P. Fedkiw et al., Jour. of the Electrochem. Soc., vol. 136, No. 3, 1989, no month available, p. 899 ff.
Abstract of JP-A-57/054288, no month/year available.
Mertesdorf Petra
Schneller Arnold
Wagener Reinhard
Witteler Helmut
Bell Bruce F.
Hoechst Aktiengesellschaft
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