Highly Enhanced Pseudocapacitive Performance of Vanadium‐Doped MXenes in Neutral Electrolytes

Abstract

Abstract 2D titanium carbide (Ti 3 C 2 T x MXene) is recognized as a promising material for pseudocapacitor electrodes in acidic solutions, while the current studies in neutral electrolytes show much poorer performances. By a simple hydrothermal method, vanadium‐doped Ti 3 C 2 T x 2D nanosheets are prepared to tune the interaction between MXene and alkali metal adsorbates (Li + , Na + , and K + ) in the neutral electrolyte. Maintaining the 2D morphology of MXene, the coexisting V 3+ and V 4+ are confirmed to form surface V–C and V–O species. At a medium doping level of V:Ti = 0.17:1, the V‐doped MXene exhibits the highest capacitance of 365.9 F g −1 in 2 m KCl (10 mV s −1 ) and excellent stability (5% loss after 5000 cycles), compared to only 115.7 F g −1 of pristine MXene. Density functional theory calculations reveal the stronger alkali metal ion–O interaction on V‐doped MXene surface than unmodified MXene and a further capacitance boost to 404.9 F g −1 using Li + ‐containing neutral electrolyte is reported, which is comparable to the performance under acidic conditions.