Vacancy and strain engineering of CoO for efficient water oxidation.

CoO has been widely explored in electrocatalysis but seriously limited by its poor intrinsic ability. Defect engineering is an effective method to improve the electrocatalytic ability of catalysts by regulating electronic structure and optimizing the binding energy with surface adsorbates. Herein, in this work we have successfully integrated metal vacancies and tensile strain into CoO. With the formation of metal vacancies, the electronic structure of CoO has been regulated. Moreover, the d-band center of CoO has been modulated with the presence of tensile strain. The electrochemical oxygen evolution reaction (OER) ability of the obtained electrocatalyst was improved dramatically. The overpotential to reach 10 mA cm was only 327 mV. Reaction kinetics was rapidly facilitated as indicated by smaller Tafel slope and charge transfer resistance. Density Functional Theory (DFT) calculations revealed that the relocated atoms induced the formation of tensile strain and made d-band center of electrocatalyst near to Fermi level leading to enhanced the adsorption to reaction intermediates. What's more, the free energy barrier of rate-determining step (RDS) has been decreased with the integration of metal vacancies and tensile strain. This work provides an efficient strategy to develop defective and effective electrocatalysts.