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.