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The oxygen reduction reaction (ORR) mechanism for electrochemical production of hydrogen peroxide is investigated for an Au-Pd catalyst with 25 at% palladium. The sample was prepared by chemical reduction of a precursor solution on a carbon-based substrate. Rotating ring-disk electrode (RRDE) measurements were performed for electrochemical characterization exhibiting H2O2 current efficiencies of about 75-78% at low disk potentials. The focus of this article is on the mathematical evaluation of the experimental data using the analytical method from Damjanovic et al. [J. Chem. Phys. 45, 4057 (1966)] and a powerful numerical data fitting technique based on RRDE simulations in MATLAB, which is capable of investigating reaction mechanisms with different structures. The latter method is presented in detail and the electro-kinetic parameters of the ORR mechanism at the considered catalyst resulting from both methods are compared quantitatively. It is found that the oxygen reductions via the 2-electron and the 4-electron pathways occur in parallel, whereas the hydrogen peroxide reduction pathway is found apparently inactive. [ABSTRACT FROM AUTHOR]

PdRh/C is a highly active electrocatalyst for methanol oxidation reaction in alkaline media. In this study, the methanol oxidation at PdRh/C was investigated electrochemically in half-cell experiments for various temperatures and various methanol concentrations in the electrolyte. The results obtained by these measurements were compared to the ones of Pd/C. Thus, new insights on how Rh influences the electrocatalytic activity of Pd were found. The apparent activation energies calculated from potentiostatic and potentiodynamic measurements show that the apparent activation energy of the methanol oxidation reaction on Rh-modified electrocatalysts is significantly lower than for Pd/C, which is attributed to the enhancement of CO ads oxidation on PdRh/C due to the oxophilic character of Rh. By determining the apparent reaction orders at different oxidation potentials (0.5–0.8 V) it was shown that for both catalysts the CO ads oxidation is the rate determining step at potentials < 0.8 V, but for PdRh/C the contribution of methanol adsorption to the apparent reaction order is higher than for Pd/C, which is also attributed to the enhanced CO ads oxidation on PdRh/C. [ABSTRACT FROM AUTHOR]