Double-Shell\nCo<sub>3</sub>O<sub>4</sub> with Rich\nSurface Octahedron Oxygen Vacancies for High-Selectivity Electrocatalytic\nChlorine Evolution

The\ndevelopment of non-noble-metal-based chlorine evolution reaction\n(CER) catalysts with excellent activity, kinetics, and selectivity\nis urgently needed but still remains a major challenge. In this study,\na morphology self-evolving and surface octahedron oxygen-vacancy-generating\nstrategy is applied at double-shell nanospheres to obtain the target\nhierarchical double-shell Co<sub>3</sub>O<sub>4</sub> nanospheres\nwith abundant surface oxygen vacancies (DS-Co<sub>3</sub>O<sub>4</sub>-OVs). The DS-Co<sub>3</sub>O<sub>4</sub>-OVs display an overpotential\nof only 52 mV to reach a current density of 10 mA cm<sup>–2</sup> in which an excellent chlorine selectivity of 98.9–99.9%\nis attained, which is better than that of the commercial RuO<sub>2</sub>/IrO<sub>2</sub>. Furthermore, density functional theory calculations\ndemonstrate that the involved oxygen vacancies can not only limit\nthe lattice oxygen mechanism of the oxygen evolution reaction process\nbut also significantly improve the kinetics of the Volmer step to\nenhance the CER performance. Meanwhile, the unique hierarchical double-shell\nnanospheres can enhance the mass feeding and promote the rate-determining\nstep of the Krishtalik step chlorine gas desorption reaction for enhanced\nkinetics. The self-evolution of non-noble catalysts with surface octahedron\nvacancies and the related exploration of the CER mechanism may provide\na novel design idea for CER catalysts.