Metal oxides for the electrocatalytic reduction of carbon dioxide: Mechanism of active sites, composites, interface and defect engineering strategies

•CO2 reduction reaction (CO2RR) into fine-chemicals is the most instant approach for balancing the atmospheric CO2 level.•Herein, the recent advances in the product efficiency of CO2RR for metal oxide electrocatalysts are summarized.•The interface and vacancy defect engineering strategies, used to improve CO2RR performance are overviewed.•Overlooking the metal sites of metal oxide-based catalysts, M−O (metal–oxygen bond) active sites are discussed.