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

Abstract

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 proposes an electric double layer (EDL) modulation strategy using salt additives (NaNO3) in weakly acidic electrolytes to enhance OER performance. The effects of salt addition (0–0.1 M) across pH values of 1–6 were systematically evaluated in terms of 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 NaNO3 addition improves OER performance at pH 2–6, with optimal kinetics achieved at a salt concentration of 0.01 M. This behavior is attributed to a pH-dependent competition between beneficial EDL compression and detrimental adsorption-induced active-site blocking, which together govern the overall OER activity. These findings demonstrate that EDL 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.