High-Index Faceted Porous Co₃O₄ Nanosheets with Oxygen Vacancies for Highly Efficient Water Oxidation

Because of sluggish kinetics of the oxygen evolution reaction (OER), designing low-cost, highly active, and stable electrocatalysts for OER is important for the development of sustainable electrochemical water splitting. Here, {112} high-index facet exposed porous Co₃O₄ nanosheets with oxygen vacancies on the surface have been successfully synthesized via a simple hydrothermal method followed by NaBH₄ reduction. As compared with the pristine and other faceted porous Co₃O₄ nanosheets (e.g., {110} and {111}), the as-prepared {112} faceted porous nanosheets exhibit a much lower overpotential of 318 mV at a current density of 10 mA cm^-2. Importantly, these nanosheets also give excellent electrochemical stability, displaying an insignificant change in the required overpotential at a current density of 10 mA cm^-2 even after a 14 h long-term chronoamperometric test. All these superior OER activity and stability could be attributed to their unique hierarchical structures assembled by ultrathin porous nanosheets, {112} high-index exposed facets with higher ratio of Co²⁺/Co³⁺ and oxygen vacancies on the surface, which can substantially enhance the charge transfer rate and increase the number of active sites. All these findings not only demonstrate the potency of our Co₃O₄ nanosheets for efficient water oxidation but also provide further insights into developing cost-effective and high-performance catalysts for electrochemical applications.