Loading of Se/Ru/C electrocatalyst on a rotating ring-disk electrode and the loading impact on a H2O2 release during oxygen reduction reaction

The impact of the Se/Ru/C catalyst loading on the oxygen reduction reaction (ORR) was studied using the rotating disk (RDE) and rotating ring-disk electrode (RRDE) techniques. The catalyst was deposited on a glassy carbon tip and the catalyst loading varied from 5 to 200 μg cm−2. Two catalysts with a different metal to carbon support ratios were studied. When the amount of the catalyst deposited on the electrode was decreased, a dramatic decrease in the ORR activity was found. Lowering the catalyst loading led, simultaneously, to a larger fraction of H2O2 released into the electrolyte. These observations suggest that the oxygen reduction to H2O on the Se/Ru/C electrocatalyst occurs through a H2O2 intermediate. When the amount of the catalyst on the disk increases, H2O2 is efficiently reduced to H2O before it can escape from the catalyst layer into the solution, or towards a membrane in a fuel cell.