Oxygen reduction at carbon supported ruthenium–selenium catalysts: Selenium as promoter and stabilizer of catalytic activity

Carbon supported ruthenium-based catalysts (Ru/C) for the oxygen reduction in acid electrolytes were investigated. A treatment of Ru/C catalysts with selenious acid had a beneficial effect on catalytic activity but no influence on intrinsic kinetic properties, like Tafel slope and hydrogen peroxide generation. Reasons for the increased activity of RuSe _x/C catalysts are discussed. Potential step measurements suggest that at potentials around 0.8 V (NHE) a selenium or selenium-oxygen species protects the catalyst from formation of inactive RuO ₂-films. This protective effect leads to an enhanced activity of RuSe _x/C compared to Ru/C. No evidence was found for a catalytically active stoichiometric selenium compound. The active phase may be described as a ruthenium suboxide RuO _x ( x < 2) layer integrated in a RuSe _y phase or RuSe _yO _v ( y < 2, v < 2) layer at the particle surface.