NOVELTY - Cathode electrocatalyst comprising a ruthenium alloy, is new.    USE - The electrocatalyst is useful: for hydrogen peroxide cathode of fuel cells; in an ink for manufacture of fuel cells; for manufacturing a cathode of bipolar electrode and a membrane electrode assembly, which are useful in a fuel cell or semi-fuel cell; and in electroplating process (all claimed).    ADVANTAGE - The hydrogen peroxide cathodes are more efficient, less expensive to manufacture and durable and can deliver higher current densities with lower polarizations and can be operated in concentrated solutions of hydrogen peroxide.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) the preparation of the electrocatalyst;    (2) a supported electrocatalyst;    (3) a process for manufacture of a cathode, and a bipolar electrode comprising depositing the electrocatalyst on a substrate by electroplating, or electroless plating of the electrocatalyst on a substrate;    (4) a process for electroplating of the electrocatalyst layer for hydrogen peroxide cathodes, comprising (a) providing an electroplating bath for ruthenium alloys, which comprises (aa) a ruthenium electroplating bath obtainable from a solution of a ruthenium salt and sulfamic acid by heating, and (bb) 0.1-50 mol.%, based on the total content of metals of the platinum group in the electroplating bath for ruthenium alloys, of at least one electroplating bath for metals of the platinum group that is obtainable from sulfamic acid, a solution or suspension of a metal compound comprising palladium compounds, iridium compounds, osmium compounds, platinum compounds, and rhodium compounds by heating, (b) immersing a substrate in the electroplating bath, and (c) applying an electrical current to deposit a ruthenium alloy deposit on the substrate;    (5) an electroplating bath for plating of ruthenium alloys as electrocatalysts, comprising the ruthenium electroplating bath and electroplating bath for metals of the platinum group; and    (6) a method of using the electrocatalyst comprising operating a fuel cell or semi-fuel cell that comprises at least one electrocatalyst layer comprising ruthenium using a catholyte comprising hydrogen peroxide at a concentration of above 0.5 mol/l.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of a fuel cell.    Hydrogen peroxide cathode (500)    Anode (502)    Polymer electrolyte membrane (504)    Pipes (506, 508)    Tubes. (510)