Ru-Doped CoO Nanoparticles as Efficient and Stable Electrocatalysts for the Chlorine Evolution Reaction.

The electrochemical chlorine evolution reaction (CER) is one of the most important electrochemical reactions. Typically, iridium (Ir)- or ruthenium (Ru)-based mixed metal oxides have been used as electrocatalysts for the CER due to their high activities and durabilities. However, the scarcity of Ir and Ru has indicated the need to develop alternative earth-abundant transition-metal-based CER catalysts. In this study, we report a CoO nanoparticle (NP) catalyst synthesized by a hydrothermal method. Furthermore, Ru was successfully incorporated into the CoO NPs (RuCoO NPs) for further improvement of catalytic performance in chlorine generation. Electrokinetic analyses combined with in situ X-ray absorption near-edge structure (XANES) results suggested an identical CER mechanism for the CoO NPs and RuCoO NPs. Various characterization techniques demonstrated that the homogeneous substitution of Ru ions into the Co octahedral sites enhanced the structural disorder and changed the electronic state of CoO, resulting in additional exposed active sites. Remarkably, the RuCoO NP electrode exhibited outstanding stability for more than 150 h even at a high current density of 500 mA/cm, which shows its commercial viability for active chlorine generation.