Engineering surface functional groups of MXenes for advanced catalysis and energy technology

MXenes, as an emerging class of two-dimensional transition metal carbides, nitrides, and carbonitrides, have attracted extensive attention in catalysis and energy technology owing to their unique properties, including metallic conductivity, hydrophilic surfaces, and structural diversity. A key distinguishing feature of MXenes lies in the richness and tunability of their surface functional groups (T_x, e.g., -O, -OH, -F), which serve as a powerful lever for precisely engineering the material's structural, electronic, mechanical, and chemical characteristics. The deliberate modulation of T_x, achieved through T_x engineering, including in situ synthesis control or post-synthetic treatments, directly governs critical properties such as work function, electrical conductivity, hydrophilicity, and oxidation stability. These tailored properties, in turn, drive performance enhancements in surface-sensitive applications: in electrocatalysis, T_x engineering optimizes intermediate adsorption and charge transfer for reactions like hydrogen evolution and CO₂ reduction; in energy storage devices such as batteries and supercapacitors, it enhances ion accessibility, redox activity, and cycling stability. This review systematically summarizes recent advances in surface T_x engineering of MXenes, elucidating the fundamental mechanisms linking T_x customization to property evolution and application-specific performance. By discussing T_x engineering strategies, structure-property-performance relationships, and mechanistic roles of distinct T_x, we aim to provide a deep understanding of how T_x tunability makes MXenes particularly suited for catalysis and energy technologies, while also outlining future directions for rational surface design in this rapidly evolving field.