Intrinsic defects of nonprecious metal electrocatalysts for energy conversion: Synthesis, advanced characterization, and fundamentals

With the depletion of fossil fuels and environmental pollution, energy storage and conversion have become the focus of current research. Water splitting and fuel cell technologies have made outstanding contributions to energy conversion. However, the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) have slow kinetics, which limit the capacity of fuel cells. It is of great significance to develop catalysts for the OER and ORR and continuously improve their catalytic performance. Many studies have shown that intrinsic defects, especially vacancies (anion and cation vacancies), can effectively improve the efficiency of electrochemical energy storage and conversion. The introduction of intrinsic defects can generally expose more active sites, enhance conductivity, adjust the electronic state, and promote ion diffusion, thereby enhancing the catalytic performance. This review comprehensively summarizes the latest developments regarding the effects of intrinsic defects on the performance of non-noble metal electrocatalysts. According to the type of intrinsic defect, this article reviews in detail the regulation mechanism, preparation methods and advanced characterization techniques of intrinsic defects in different materials (oxides, non-oxides, etc.). Then, the current difficulties and future development of intrinsic defect regulation are analyzed and discussed thoroughly. Finally, the prospect of intrinsic defects in the field of electrochemical energy storage is further explored.