Comparing factors that affect kinetics of oxygen electroreduction on platinum- and palladium-containing catalysts

Abstract

The effect of blocking species, namely, oxygen-containing species adsorbed from water and blank electrolyte anions, on the kinetics of oxygen electroreduction on 40% Pt ETEK (denoted as 40Pt/C) and 20% Pd ETEK (20Pd/C) commercial catalysts, as well as on 20% Pd ETEK 6% Co (denoted as 20Pd6Co/C) and 20% Pd ETEK 5% Pt 2.9% Co (20Pd5Pt2.9Co/C) catalysts synthesized at the laboratory, is studied in sulfuric and perchloric acid solutions. It is shown that on a monopalladium catalyst, the first inhibiting factor prevails, whereas, on a monoplatinum catalyst, a substantial role in decelerating the reaction is played by the adsorption of HS anions. In the case of a trimetal catalyst, the adsorption curve of oxygen-containing species is noticeably shifted toward the curve typical of platinum. When perchloric acid is replaced with sulfuric acid, the potential of the kink point of the Tafel dependence of the oxygen electroreduction (on going from the low to high polarization) is shifted toward the less positive potentials. This shift of the kink potential is most clearly pronounced in the case of a monoplatinum catalyst.