FUEL CELL CATALYSTS.

A mathematical analysis of mass transport to the catalyst pore walls was performed indicating wide and short pores being the desirable geometric configuration. The optimum numerical values of length and radius are dependent on the diffusivity and the reaction rate constant. A series of low porosity carbon carriers and fine grid boron carbide samples were investigated for the support of platinum and platinum-ruthenium alloys. Owing to a defect surface structure boron carbide provides a better dispersion of platinum than obtainable with carbon. The crystallite size of platinum-ruthenium alloys on the other hand appears to be primarily dependent on the ruthenium content and less affected by the supporting surface. The performance of catalysts for the oxidation of methanol and propane does not necessarily correlate with the degree of metal dispersion indicated by the crystallite size. The ultimate performance of the catalyst is significantly affected by the porosity of the carrier and the shape and size of the catalyst particles. Performance declines considerably with increasing porosity of the carrier, particularly with propane. Carriers of very small particle size are undesirable as they adversely affect the porosity of the catalyst layer on the electrode. Author