Promoting the activation of H2O via vacancy defects over metal-organic framework-derived cobalt oxide for enhanced oxygen evolution

Abstract

Engineering the electronic structures of transition metal oxides via vacancy defects is an efficient approach to enhance their catalytic performances, while facilely creating vacancy defects and deeply exploring the effects still remain challenging. Herein, a facile reduction method was applied to introduce oxygen vacancy defects into metal-organic frameworks (MOFs)-derived cobalt oxide (Co3O4) polyhedron. Using zeolitic imidazolate framework-67 (ZIF-67) as Co source and self-sacrificial template, Co3O4 with polyhedron morphology and porous structure was synthesized, and then oxygen vacancy defects were introduced into the as-prepared Co3O4 through one-step NaBH4 reduction treatment. Strikingly, the obtained electrocatalyst (denoted as Co3O4-x) exhibited a larger current density (112.9 mA cm−2 vs. 1.75 V), a lower overpotential (335 mV at 10 mA cm−2) and a smaller Tafel slope (83 mV dec−1) than the Co3O4, which is even superior to the state-of-the-art IrO2 catalyst. Moreover, experiment results combined with density-functional theory (DFT) calculations revealed that the existence of oxygen vacancies could improve the conductivity, promote the activation of H2O and reduce the potential of potential-limited step (PLS), thus greatly boosting electrocatalytic oxygen evolution reaction (OER) performances. This work reported a strategy for preparing defect-rich OER electrocatalysts, and also provided a deep understanding of the defect effects on catalytic performances.