Synergy Between a Lewis Acid and a Brønsted Acid in Promoting Oxygen Reduction Reaction Catalyzed by Co‐Salophen Complexes

ABSTRACT The selective reduction of oxygen to water demands investigating interactions that govern both the rate and selectivity of the reaction. In this study, we examined the role of exogenous Lewis acid in the electrochemical oxygen reduction reaction (ORR) using Co‐Salophen and its derivatives as electrocatalysts. Acetic acid, (AA) served as an external Brønsted acid proton source, while calcium triflate, Ca(OTf) 2 , functioned as the Lewis acid. Cyclic voltammetry (CV) and RRDE measurements revealed a positive shift in the onset potential and an increase in water selectivity upon addition of Ca(OTf) 2 . This behavior could not be attributed to the electrostatic interactions between Ca 2+ and the catalyst solely, and the hydrolysis of Ca(OTf) 2 to triflic acid. The observed increase in selectivity toward water and the earlier onset potential instead arises from enhanced acidity of AA in the presence of Ca(OTf) 2 , supported by 1 H‐NMR and a positive OCP shift from ‐0.95 to ‐0.82 V versus Fc +/0 . This increase in Brønsted acidity stems from a synergistic interaction between AA and a Lewis acid, resulting in better H 2 O selectivity during ORR with Co‐Salophen catalysts.