Probing the Effects of Acid Electrolyte Anions on Electrocatalyst Activity and Selectivity for the Oxygen Reduction Reaction

Abstract The local microenvironment at the electrode‐electrolyte interface plays an important role in electrocatalytic performance. Herein, we investigate the effect of acid electrolyte anion identity on the oxygen reduction reaction (ORR) activity and selectivity of smooth Ag and Pd catalyst thin films. Cyclic voltammetry in perchloric, nitric, sulfuric, phosphoric, hydrochloric, and hydrobromic acid, at pH 1, reveals that Ag ORR activity trends as follows: HClO 4 >HNO 3 >H 2 SO 4 >H 3 PO 4 >HCl≫HBr, while Pd ORR activity trends as: HClO 4 >H 2 SO 4 >HNO 3 >H 3 PO 4 >HCl≫HBr. Moreover, rotating‐ring‐disk‐electrode selectivity measurements demonstrate enhanced 4 e − selectivity on both Ag and Pd, by up to 35 %H 2 O 2 and 10 %H 2 O 2 respectively, in HNO 3 compared to in HClO 4 . Relating physics‐based modeling and experimental results, we postulate that ORR performance depends greatly on anion‐related phenomena in the double layer, for instance competitive adsorption and non‐covalent interactions.