Interfacial Engineering in MXene-Based Supercapacitors

Abstract

MXene supercapacitors have been identified as the most promising advanced-generation electrochemical energy storage devices due to their unique features, including metallic nature, tunable surface chemistry, hydrophilicity, layered structure, and superb pseudocapacitance. However, pristine MXenes suffer from inherent drawbacks, including severe re-stacking of nanosheets, slow ionic kinetics at high current densities, oxidative instability, inadequate exploitation of electrochemically active sites, and interfacial charge-transfer resistance. Recently, interfacial engineering approaches have been successfully developed as a powerful solution to such issues by controlling surface/interlayer chemistry, nano-channel formation, hetero-interface coupling effects, electrolyte interactions, and charge-transfer pathways. Herein, this work systematically reviews the recent developments in interfacial engineering techniques for MXene supercapacitors based on the aspects of surface/interlayer engineering, intrinsic defects regulation, electrolyte-interface manipulation, and heterostructures design. Great attention is paid to proton desolvation, surface terminations, conductive nanobridges, electric fields, ion-selective nanochannels, and hierarchical structures responsible for controlling ion diffusion, electron transfer, electric double layer formation, and pseudocapacitive reactions. As opposed to existing literature, which usually emphasizes either synthesis methods or electrochemical properties of materials, the presented study presents an integrated interface-oriented approach providing a link between the structure of interfaces and their electrochemistry. Also, modern interfaces comprising MXenes with MOFs, COFs, LDHs, transition-metal compounds (oxides, sulfides, nitrides, phosphides), ionic liquids, water-in-salt electrolytes, and multipurpose gel electrolytes are comprehensively compared in relation to conductivity tuning, charge reorganization at interfaces, ion access, and cycling stability.