In situ transmission electron microscopy characterization of MXene interfaces: a review

As an emerging class of two-dimensional layered transition metal carbides, nitrides and carbonitrides, MXenes show enormous application potential in energy storage and conversion, catalysis, sensing, and electromagnetic shielding, owing to their excellent electrical conductivity, tunable surface chemistry, unique interlayer structure, and good mechanical performance. The intrinsic interfaces (such as surface functional groups, defects, and interlayers) and heterojunction interfaces formed by compounding with polymers, metals, semiconductors, etc., are central to regulating their macroscopic properties. The microstructure of these interfaces (atomic arrangement, chemical bonding, element distribution, dynamic evolution) directly determines MXenes' electron/ion transport efficiency, catalytic activity, structural stability, and functional synergy in practical applications. Transmission electron microscopy (TEM) has become an indispensable tool for studying MXene interfaces, featuring atomic-level spatial resolution, excellent elemental and chemical state analysis, and reliable in situ dynamic characterization capabilities that can simulate actual working environments such as high temperature and electrochemical reaction conditions. Specifically, HRTEM and C_s-corrected STEM (especially HAADF-STEM) visualize atomic structures, surface terminations, and defects at the atomic scale with high clarity; EELS and EDS allow accurate qualitative-quantitative analysis of interfacial elements and valence states to clarify chemical composition differences; in situ TEM captures real-time dynamic interfacial evolution under multi-physical fields like heating and electrochemical cycling. Previous reviews mainly treat TEM as a tool for specific applications or performance studies, while this work centers on TEM as the main theme to elucidate the atomic-scale interfacial science, including both intrinsic and heterojunction interfaces. This paper systematically reviews TEM techniques' application in MXene interface research, highlights in situ TEM in revealing reaction mechanisms, analyzes current characterization challenges such as sample damage during observation, and prospects future directions, providing solid theoretical and technical support for MXene interfacial engineering, performance optimization, and new application exploration.