Selectivity of Ti/IrO₂ and Ti/RuO₂ electrodes for the competing oxygen evolution reaction and chlorine evolution reaction in neutral and alkaline seawater splitting

As the oxygen evolution reaction (OER) competes with the chlorine evolution reaction (CER) in electrocatalytic seawater splitting, it is desirable for the anodes to exhibit an overwhelmingly higher selectivity for OER than CER. This work focuses on the selectivity of the Ti/IrO₂ and Ti/RuO₂ electrodes for the OER and CER in neutral and alkaline seawater splitting. The CER during seawater splitting has been monitored by using a convenient UV–vis spectroscopic method, which has been shown to be reliable in both simulated and real seawater. A three-dimensional (3D) diagram is presented to comprehensively show the dependence of the concentration of CER product (ClO^-) on pH and potential. The Faradaic efficiency of CER and OER at pH 7 and pH 14 was determined simultaneously during seawater splitting. The contribution of CER to the anodic current is negligible compared to that of OER in alkaline seawater spitting. However, in neutral seawater splitting, CER dominates the anodic process with a reaction rate of approx. 6 and 4 times faster than that of OER on Ti/IrO₂ and Ti/RuO₂ electrodes, respectively. This work underscores the importance of pH in dictating the selectivity of electrocatalysts and highlights the need for catalysts that can suppress CER in neutral seawater electrolysis.