Rotating Ring-Disk Electrode Voltammetry for Determining the COR–OER Selectivity in Seawater Electrolysis under Neutral to Alkaline Conditions

Abstract

Hydrogen production through the direct electrolysis of seawater is gaining attention as a method for achieving carbon neutrality. The Cl⁻ anion oxidation reaction (COR) in seawater, which occurs at the counter electrode (anode) of hydrogen production and generates active chlorine species with a corrosive nature, should be suppressed as much as possible for hydrogen production and replaced with the oxidation of water, i.e., oxygen evolution reaction (OER). The COR and OER proceed competitively at the anode; however, no studies have separately investigated their behavior in a pH region close to that of seawater. This study uses a simple electrochemical method with a rotating ring-disk electrode (RRDE) to determine the independent behavior of COR and OER with respect to potential and pH in an aqueous NaCl solution, where IrO2 (COR dominant) and MnO2 (OER dominant) are used as catalysts. The results obtained based on the RRDE voltammetry in aqueous NaCl solutions at various pH values were consistent with the COR selectivity determined from product analysis. Thus, the described method will be a valid electrochemical protocol.