TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The platinum-family metal other than platinum is iridium (Ir), and the composition ratio of platinum to iridium to carbon is 1:(0.08 to 1.5):(0.46 to 2.2) wt. ratio. The platinum surface has a lattice constant of 3.875 to 3.916 Angstrom as calculated from X ray diffraction results. The platinum-family metal other than platinum is rhodium (Rh) and the composition ratio of platinum to rhodium to carbon is 1:(0.03 to 1.5):(0.46 to 2.2) (wt. ratio). The platinum-family metal other than platinum is gold (Au) and the composition ratio of platinum to gold to carbon is 1:(0.03 to 1.5):(0.46 to 2.2) (wt. ratio). The alloy consisting of platinum and platinum-family metal other than platinum have an average particle size of 3-20 nm. EXAMPLE - Commercially available carbon powder (4.95 g) of large specific surface area was added to and dispersed in pure water (0.5 l). A hexahydroxoplatinum nitrate solution containing platinum (4.05 g) and iridium nitrate solution containing iridium (1 g) were dropped into the fluid dispersion. The fluid dispersion was blended with the carbon. 0.1N Ammonia (100 ml) was added to the fluid dispersion and the fluid dispersion was adjusted to pH of 10. Corresponding hydroxides were formed on the carbon. The fluid dispersion was filtered and a powder obtained was dried in vacuum at 100degreesC for 10 hours. The powder was held in hydrogen gas atmosphere at 400degreesC for 2 hours so as to be reduced. The powder was then held in the presence of nitrogen gas at 600degreesC for 2 hours so as to be alloyed. The metal carrying densities of the platinum alloy carrying carbon powder catalyst (test) obtained were such that the catalyst contained platinum (40.51 wt.%) and iridium (9.98 wt.%). The weight ratio of the powder components i.e. the weight ratio of Pt to Ir to carbon was 1:0.25:1.2. The X-ray diffraction measurement showed only platinum peak and a shift of the peak of the platinum surface near 39degrees to a larger angle indicated the solid solution of iridium. The platinum had lattice constant of 3.91 Angstrom and a particle size of 4.2 nm as calculated from half-value width. A control catalyst having feed amounts of carbon, platinum and iridium of 2.92 g, 2.39 g and 4.70 g was prepared in a same manner as the test catalyst. The product ratio of platinum to iridium to carbon was 1:2:1.2 wt. ratio. The control catalyst had particle size of 4.2 nm and lattice constant of 3.870 Angstrom . The test/control catalyst was evaluated for initial cell voltage at 0.1A/cm2, cell voltage after endurance at 0.1 A/cm2 and cross leak amount. The results for test/control catalysts were: initial cell voltage at 0.1A/cm2 = 0.786/0.745 V, cell voltage after endurance at 0.1 A/cm2 = 0.745/0.660 V and cross leak amount = 0.0003/0.006 MPa respectively. The results showed that alloying platinum and iridium improved the initial performance and when the ratio of Pt to Ir was 1:0.08 to 1.5, the Pt/Ir catalyst exhibited high initial performance and low endurance voltage drop rate as compared to the control.