ABSTRACT Due to their versatile and tunable surface and bulk chemistry, MXenes have great potential as electrocatalysts for batteries and supercapacitors. When compared with other electrocatalytic processes, in electrocatalytic reactions, MXenes could improve ion diffusion and charge transfer by either providing functional groups binding to the surface metals to block the diffusion path or offering additional adsorption sites for metal cations or intermediate products on the material surface, so the electrocatalytic activity of MXenes should be sensitive to the surface configuration. Very recently, researchers revealed that introducing defects and strictly tuning the electronic property of the MXene surface could greatly improve its electrocatalytic efficiency; however, the exact mechanism by which defects could improve the electrocatalytic properties of MXenes was still unclear. In this study, authors classify surface defects in MXene, discuss the formation mechanism of each kind of defect, and demonstrate the application of atomic‐level characterization tools to track the evolution of defects. Furthermore, based on the defect mechanics principles, we propose a rational design approach for MXene surface structures. Additionally, this paper discusses the development and application of defect structures in electrocatalytic efficiency improvement. Based on the analysis of the challenges existing in the MXene electrocatalysis, a future research direction is proposed. In this review, we establish a conceptual framework for MXene applications in electrocatalysis. This study advances the development of MXene materials in energy systems, provides the defect design strategies for researchers in further investigation on MXenes, and offers the emerging trends in this field.
Wang et al. (Thu,) studied this question.