Recent Progress on Defect-rich Transition Metal Oxides and Their Energy-Related Applications

The applications of many energy-related electrochemical energy conversion and storage devices are changing with each passing day. Oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) are the key steps in the commercial application of these energy conversion/storage equipment. Defect-rich transition metal oxides (TMOs), such as Co, Mn, Fe, Ni, etc., have always been one of the most promising electrocatalysts, which are cheap, easy to obtain, high in catalytic activity and stable during electrocatalysis. In this review, we first introduce the definition, classification, characteristics, and construction of defects. Then, the latest developments of defect-rich TMO electrocatalysts in electrocatalysis and energy conversion storage device is summarized. Furthermore, the relationship between defects and activity and the potential mechanism are also discussed. The defects in defect-rich TMOs can adjust the surface/interface electronic structure of the electrocatalyst, change the adsorption energy of the intermediate product, or increase the intrinsic catalytic activity of active sites, which are beneficial for enhanced catalytic performance. Finally, the current challenges and prospects of defect-rich TMO electrocatalysts are proposed. Therefore, the introduction of defects in TMO will be a potential strategy for the rational design of high-performance electrocatalysts in the future.