Double-Shell Co₃O₄ with Rich Surface Octahedron Oxygen Vacancies for High-Selectivity Electrocatalytic Chlorine Evolution

The development of non-noble-metal-based chlorine evolution reaction (CER) catalysts with excellent activity, kinetics, and selectivity is urgently needed but still remains a major challenge. In this study, a morphology self-evolving and surface octahedron oxygen-vacancy-generating strategy is applied at double-shell nanospheres to obtain the target hierarchical double-shell Co₃O₄ nanospheres with abundant surface oxygen vacancies (DS-Co₃O₄-OVs). The DS-Co₃O₄-OVs display an overpotential of only 52 mV to reach a current density of 10 mA cm^-2 in which an excellent chlorine selectivity of 98.9-99.9% is attained, which is better than that of the commercial RuO₂/IrO₂. Furthermore, density functional theory calculations demonstrate that the involved oxygen vacancies can not only limit the lattice oxygen mechanism of the oxygen evolution reaction process but also significantly improve the kinetics of the Volmer step to enhance the CER performance. Meanwhile, the unique hierarchical double-shell nanospheres can enhance the mass feeding and promote the rate-determining step of the Krishtalik step chlorine gas desorption reaction for enhanced kinetics. The self-evolution of non-noble catalysts with surface octahedron vacancies and the related exploration of the CER mechanism may provide a novel design idea for CER catalysts.