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.