TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The platinum dioxide is obtained by conversion of dihydrogen hexahydroxyplatinate precursor pre-adsorbed on the carbon support. The chemical reduction is carried out with a reducing agent. For (C1), the chemical reduction is also carried out in an aqueous solution. The conversion of the precursor is obtained by variation of pH and/or temperature. The variation of pH is obtained by the addition of caustic soda or ammonia. The addition of alkali or ammonia is effected up to a pH of 2 - 5. The variation of temperature consists of bringing the aqueous solution from room temperature to a final temperature of 30 - 100degreesC. The carbon black is slurried in a strong acid prior to the adsorption of the precursor. (P1) Additionally involves thermal treatment in a controlled (preferably reducing or an inert) atmosphere of 120 - 500degreesC. Preferred Components: The carbon support is a carbon black having an active area not less than 50 m2/g. The weight ratio of platinum to carbon support is 5 - 60. The reducing agent is selected from hydrogen gas, sodium borohydride and hypophosphite. The strong acid is selected from nitric acid, perchloric acid, hydrochloric acid and hydrobromic acid).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The platinum dioxide is obtained by conversion of dihydrogen hexahydroxyplatinate precursor pre-adsorbed on the carbon support. The chemical reduction is carried out with a reducing agent. For (C1), the chemical reduction is also carried out in an aqueous solution. The conversion of the precursor is obtained by variation of pH and/or temperature. The variation of pH is obtained by the addition of caustic soda or ammonia. The addition of alkali or ammonia is effected up to a pH of 2 - 5. The variation of temperature consists of bringing the aqueous solution from room temperature to a final temperature of 30 - 100degreesC. The carbon black is slurried in a strong acid prior to the adsorption of the precursor. (P1) Additionally involves thermal treatment in a controlled (preferably reducing or an inert) atmosphere of 120 - 500degreesC. Preferred Components: The carbon support is a carbon black having an active area not less than 50 m2/g. The weight ratio of platinum to carbon support is 5 - 60. The reducing agent is selected from hydrogen gas, sodium borohydride and hypophosphite. The strong acid is selected from nitric acid, perchloric acid, hydrochloric acid and hydrobromic acid).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The reducing agent is selected from formaldehyde, formic acid and oxalic acid. The strong acid is selected from trifluoroacetic acid, toluenesulfonic acid and trifluoromethanesulfonic acid. EXAMPLE - Dihydrogen hexahydrate platinate (468.75 g) was dissolved in a dilute nitric acid solution prepared by mixing deionized water (3 l) with 69% nitric acid (1.93 liters). Deionized water (25.07 liters) was added to the resultant solution over one hour under stirring. The mixture was stirred at room temperature for 30 minutes, then heated up to 70degreesC over two hours and maintained at 70degreesC over two and one hour. An orange-colored suspension was obtained, which was then neutralized with concentrated ammonia (about 2.4 liters of 30% NH3) until reaching a pH of approximately 5. Formic acid (300 ml) was then added to the suspension over one hour to reduce the platinum compound. The color of the suspension changed from orange to black, and the suspension was settled easily. After the supernatant liquid was decanted, the precipitate was filtered and washed with deionized water divided into six aliquots. The catalyst cake was then dried at 120degreesC, and the material obtained, was ball-milled to form platinum black catalyst having crystalline size of 5.3 nm. A rotating disk electrode (RDE) was evaluated for the catalytic activity of the catalyst to oxygen reduction. The electrode was placed in 0.5M sulfuric acid solution saturated with oxygen at 60degreesC by continuous bubbling. A platinum counter electrode and Hg-Hg2SO4 reference electrode were connected to a Gamry PC4/750 mA Potentiostat/Galvanostat along with the RDE. A potential scan was applied under 3600 RPM rotation and the relevant current-potential curve was recorded. The potential at one half of the plateau height (RDE half-wave potential, E1/2) was used as the analytical indicator for the oxygen reduction reaction on the catalyst. The platinum black catalyst showed that RDE half-wave potential (E1/2) of 174 mV.