NOVELTY - A catalyst comprises platinum and chromium (not greater than 30 atomic%), and copper and/or nickel (at least 35 atomic%).    USE - For supported electrocatalyst powder used in electrochemical reactor devices, fuel cell electrode, fuel cell, fuel cell electrolyte membrane, and electrochemical conversion of hydrogen-containing fuel and oxygen to reaction products and electricity in fuel cell by oxidation or reduction reactions (all claimed).    ADVANTAGE - The catalyst increases the electrocatalytic cathodic activity during reduction of oxygen and electrocatalytic anodic activity during oxidation of hydrogen. The catalyst has excellent activity, corrosion resistance, and poison tolerance. The catalyst exhibits favorable electrocatalytic activity while having reduced amount of platinum. The catalyst is used in a powder form to increase the surface area, which in turn increases the number of reactive sites, and thus leads to improved efficiency of fuel cells in which the catalyst is being used.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) supported electrocatalyst powder comprising the catalyst and electrically conductive support particles on which the catalyst is dispersed;    (2) fuel cell electrode comprising electrocatalyst particles and an electrode substrate on which the electrocatalyst particles are deposited. The electrocatalyst particles comprise the catalyst;    (3) fuel cell (20) comprising an anode (22), a cathode (23), a proton exchange membrane (21) provided between the anode and cathode, and the catalyst for catalytic oxidation of hydrogen-containing fuel (F) or catalytic reduction of oxygen (O);    (4) electrochemical conversion of hydrogen-containing fuel and oxygen to reaction products and electricity in a fuel cell comprising an electrically conductive external circuit connecting the anode and cathode, which involves contacting the fuel or oxygen and the catalyst to catalytically oxidize the fuel or catalytically reduce oxygen; and    (5) fuel cell electrolyte membrane having an unsupported catalyst layer comprising the catalyst, provided on a surface.    DESCRIPTION OF DRAWING(S) - The figure shows an exploded, schematic structural view of the components of a fuel cell.    Fuel cell (20)    Proton exchange membrane (21)    Anode (22)    Cathode (23)    Hydrogen-containing fuel (F)    Oxygen (O)