Electric double layer engineering via salt additives for enhanced OER under weakly acidic conditions

The oxygen evolution reaction (OER) is the kinetic bottleneck in water electrolysis, particularly in acidic electrolytes. High-performance electrolyzers rely on strongly acidic conditions, which severely corrode cell components and increase system costs. To mitigate this issue, attempts have been made to operate water electrolyzers under weakly acidic conditions; however, OER performance remains limited under these conditions. This study systematically investigates how the effects of NaNO 3 addition on the electric double layer (EDL) and OER performance depend on electrolyte pH and salt concentration. Electrolytes with pH values of 1–6 and NaNO 3 concentrations of 0–0.1 M were examined using exchange current density, Tafel slope, effective double-layer capacitance, and charge-transfer resistance based on cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy measurements. The results show that NaNO 3 addition improves OER performance at pH 2–6, with 0.01 M NaNO 3 exhibiting the best kinetics among the tested salt concentrations. This behavior is interpreted as a pH-dependent balance between beneficial EDL compression and a detrimental contribution possibly associated with anion accumulation and reduced active-site accessibility. These findings demonstrate that electrolyte engineering via salt additives can effectively enhance OER performance in weakly acidic environments, offering insights into the design of cost-effective electrolytes in water electrolysis.