Doped Non-Ti MXenes for Supercapacitor Applications

The rapid development of high-performing energy storage technologies has increased the search for 2D electrode materials with tunable electronic structures, abundant electroactive sites, and rapid ion transportation. Although Ti-based MXenes have been extensively investigated, non-Ti MXenes offer a broader compositional space and distinctive physicochemical properties, yet their supercapacitor applications remain comparatively underexplored. In this review, we critically examine the emerging field of doped non-Ti MXenes for advanced supercapacitor applications, including Mo-, V-, Nb-, Cr-, W-, Zr-, Hf-, Ta-, Sc-, and Y-based systems. In this review, we establish the structural, chemical, and electrochemical characteristics of non-Ti MXenes and subsequently discuss M-, X-, and T-site doping, substitution, and multielement engineering strategies. We have discussed how heteroatom doping regulates electronic structure, charge distribution, defect chemistry, interlayer spacing, surface chemistry, and ion–accessible active sites. These modifications are correlated with their influence on electrochemical kinetics, capacitance, rate capability, and cyclic stability. Finally, computational and data-driven approaches, critical benchmarking, and critical challenges are integrated to establish structure–doping–mechanism–performance relationships and design principles for next-generation doped non-Ti MXene electrodes for supercapacitors.