Regulating MXene Functionalization and Oxidation for High‐Rate, High Mass‐Loading Supercapacitors

ABSTRACT

Unlocking the commercial potential of MXene electrodes in high‐energy supercapacitors requires overcoming a fundamental limitation: severe performance decay at increased electrode thickness and mass loading. This work resolves the intrinsic trade‐off between surface functionalization and oxidation in MXene chemistry regulation by constructing a controlled redox environment. A urea‐assisted hydrothermal process effectively removes inert –F terminations while inducing the formation of a 3D MXene hydrogel enriched with –N active sites. Concurrently, L‐ascorbic acid is introduced as an antioxidant to suppress structural oxidation and enhance stability. As a result, the optimized MXene exhibits superior rate capability and long‐term cycling stability under high mass loadings. Specifically, at 10.97 mg cm ⁻² , a high specific capacitance of 597 F g ⁻¹ is achieved at 1 A g ⁻¹ , with 69.66% retention at 50 A g ⁻¹ , significantly outperforming that of pristine MXene (23.44%) and N‐doped MXene (59.03%). Even at an ultrahigh loading of 108.64 mg cm ⁻² , 44.50% of the capacitance is retained (from 564 F g ⁻¹ to 251 F g ⁻¹ ) over the current density range of 1 to 20 A g ⁻¹ . This work establishes an effective strategy for designing high‐performance MXene‐based electrodes via reaction pathway regulation, enabling practical operation at commercially relevant mass loadings.