TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred components: The core particle has an average diameter no smaller than 0.8 nm and no larger than 5 (preferably no smaller than 0.8 nm and no larger than 3.5 nm). The shell layer has a thickness no smaller than 0.2 nm and no larger than 10 (preferably no smaller than 0.2 nm and no larger than 1 nm). The first material is any metal and/or alloy, which is nickel, copper, palladium, silver, gold, iridium, titanium, iron, cobalt, ruthenium (preferred), osmium, chromium, molybdenum, or tungsten. The second material is any metal is platinum (preferred), nickel, copper, palladium, silver, or gold. EXAMPLE - Ruthenium (III) chloride hydrate was dissolved in ethylene glycol to give a solution containing ruthenium (III) ions (0.1 mol/l). The solution was given an aqueous solution (10 ml) containing sodium hydroxide (0.5 mol/l). The resulting mixed solution was heated to 170 degrees C in 1 minute, and then it was kept at 170 degrees C for 1 hour so that the ruthenium (III) ions were reduced by ethylene glycol to obtain a dark brown fluid dispersion of ruthenium nanoparticles. Carbon black (2.88 g) was added to the fluid dispersion of ruthenium nanoparticles. The resulting fluid dispersion was given a solution containing sulfuric acid (0.5 mol/l). The resulting fluid dispersion was centrifuged to separate a mixture of ruthenium nanoparticles and carbon black. After removal of the supernatant liquid, there were obtained ruthenium nanoparticles supported on carbon black (50 ml), which were dispersed into deionized water (50 ml) with thorough stirring. They were settled by centrifugation and the supernatant liquid was removed. The precipitates were washed five times for purification and finally dried with nitrogen streams. The obtained ruthenium nanoparticles were found to have an average particle diameter of 1.4 nm. The ruthenium nanoparticles supported on carbon black were dispersed into deionized water (200 ml). An aqueous solution sodium tetrahydroborate (6.6 mol/l) and chloroplatinic acid hexahydrate (0.97 mol/l) was added drop wise to the resulting fluid dispersion. The platinum (IV) ions were reduced to form a platinum layer on the surface of the ruthenium nanoparticles. The solutions were added dropwise in such an amount that the resulting fine particles of core-shell structure contain platinum and ruthenium in a molar ratio of 3:2.