CARBON PARTICLE HAVING DEPOSITED FINE PARTICLES, PROCESS FOR PRODUCING THE SAME, AND ELECTRODE FOR FUEL CELL
Carbon particles having fine particles deposited thereon which can be used as a substitute for the carbon particles having platinum deposited thereon and metallic platinum particles which are presently in general use as, e.g., a catalyst for electrodes in fuel cells. Compared to the conventional carbon particles having platinum deposited thereon, etc., the carbon particles are effective in greatly reducing the amount of platinum to be used. The carbon particles are characterized by comprising carbon particles and, deposited on the surface of the carbon particles, fine particles of a perovskite type composite metal oxide in each of which fine noble-metal particles are present throughout the whole particle. Also provided is a process for producing the carbon particles. The carbon particles having deposited fine particles have a constitution in which fine particles of a perovskite type composite metal oxide each having fine noble-metal particles present throughout the whole perovskite type oxide particle and having a crystallite size of 1-20 nm are deposited on carbon particles. The process for producing such carbon particles having fine particles deposited thereon comprises preparing a solution containing fine perovskite type composite oxide particles and complex ions of a metal for constituting fine noble-metal particles, subsequently repeating the step of impregnating the solution into carbon particles and dried the particles to thereby adsorb complex ions of the metal onto the carbon particles, and then subjecting the resultant particles to heat treatment.
1 . Fine particle-supporting carbon particles comprising carbon particles supporting fine perovskite type composite metal oxide particles and fine noble metal particles wherein the weight of the supported fine noble metal particles is from 1 to 20% based on that of the fine perovskite type composite metal oxide particles, said fine perovskite type composite metal oxide particles having a crystallite size of 1 to 20 nm, and fine noble metal particles smaller in particle diameter than said perovskite type oxide particles existing throughout the bodies of said perovskite type oxide particles.
2 . Fine particle-supporting carbon particles as claimed in claim 1 wherein said fine perovskite type composite metal oxide particles are represented by the general formula ABO 3 wherein A denotes one or more elements selected from the group consisting of lanthanum, strontium, cerium, calcium, yttrium, erbium, praseodymium, neodymium, samarium, europium, magnesium, and barium, and B denotes one or more transition metal elements selected from the group consisting of iron, cobalt, manganese, copper, titanium, chrome, nickel, niobium, lead, bismuth, antimony, and molybdenum.
3 . Fine particle-supporting carbon particles as claimed in claim 2 wherein said fine noble metal particles comprise one or more noble metal elements selected from the group consisting of platinum, ruthenium, palladium, and gold, or an alloy of said one or more noble metal elements and one or more transition metal elements selected from the group consisting of iron, cobalt, manganese, copper, titanium, chrome, nickel, niobium, lead, bismuth, antimony, and molybdenum.
4 . Fine particle-supporting carbon particles as claimed in any of claims 1 to 3 wherein the ratio by weight of said supported fine perovskite type composite metal oxide particles and fine noble metal particles ([weight of fine perovskite type composite metal oxide particles and fine noble metal particles]/[total weight of the fine particle-supporting carbon particles]) is in the range of 5 to 50 wt %.
5 . Fine particle-supporting carbon particles as claimed in any of claims 1 to 3 wherein the average particle diameter of said carbon particles that support fine perovskite type composite metal oxide particles and fine noble metal particles is in the range of 20 to 70 nm.
6 . Fine particle-supporting carbon particles as claimed in any of claims 1 to 3 wherein they have an average particle diameter of from 20 to 90 nm.
7 . A process for producing fine particle-supporting carbon particles as claimed in claim 1 comprising the following steps: first, preparing a solution containing complex ions of metals and noble metals that are to constitute said fine perovskite type composite metal oxide particles and noble metal particles, then repeating the operation of impregnating carbon particles with the resulting solution and drying them to achieve adsorption of said complex ions on said carbon particles, and heat-treating them.
8 . A process for producing fine particle-supporting carbon particles as claimed in claim 1 comprising the following steps: first, preparing a solution containing complex ions of metals and noble metals that are to constitute said fine perovskite type composite metal oxide particles and noble metal particles, then repeating the operation of impregnating carbon particles with the resulting solution and drying them to achieve adsorption of said complex ions on said carbon particles, drying them in a low humidity atmosphere, and heat-treating them in an inert gas so that said fine perovskite type composite metal oxide particles are deposited and supported on the surface of said carbon particles.
9 . An electrode for fuel cells comprising fine particle-supporting carbon particles as claimed in claim 1 .