Electrocatalytic reduction of oxygen on modified oxide surfaces

A first step which frequently occurs in the reduction of dioxygen, e.g., at the cathode of the alkaline fuel cell, is the two-electron reduction to the peroxyl ion, HO bar 2. For the efficiency of the fuel cell, this ion must be further reduced, or decomposed, to OH(-). Rate constants for HO bar 2 decomposition have been determined in 31 percent KOH at 25 C for the following catalysts in the form of suspended powders and Teflon-bonded electrodes: Pt, Au, cobalt tetrametoxyl phenyl porphyrin (CoTMPP), and La sub 0.5Pb sub 0.5MnO3. Rates were normalized to unit surface area measured by several methods as suitable. Where possible, four methods were used to measure rate constants: gasometric, oxygen probe, rotating disk electrode, and open-circuit potential decay. Steady-state polarization was also tried but was not as satisfactory. Comparisons are given for the methods in regard to reliability, applicability to the material, and convenience.