Plasma‐Activated Solutions Regulate Surface‐Terminating Groups Enhancing Pseudocapacitive Ti3C2Tx Electrode Performance

2D transition metal carbides and nitrides (MXenes) are actively pursued as pseudocapacitive materials for supercapacitors owing to their advantages in electronic conductivity and surface reactivity. Increasing the fraction of ─O terminal groups in Ti₃C₂T_x is a promising approach to improve the pseudocapacitive charge storage in H₂SO₄ electrolytes, but it suffers from a lack of effective functionalization methods and stability of the groups in practical operation. Here a low-temperature and environment-friendly approach via the interaction of nonequilibrium plasmas with Ti₃C₂T_x dispersion is demonstrated to generate abundant and stable surface-terminating O groups. The impact of the discharge environment (Ar, O₂, and H₂) on the structural characteristics and electrochemical performance of Ti₃C₂T_x nanosheets is studied. The Ti₃C₂T_x modified in Ar and H₂ maintains their original morphology but a significantly lower F content. Consequently, an extraordinarily high content (78.5%) of surface-terminating O groups is revealed by the high-resolution X-ray photoelectron spectroscopy spectra for the Ti₃C₂T_x samples modified in H₂ plasma-treated solutions. Additionally, the Ti₃C₂T_x treated using H₂ plasmas exhibits the best capacitive performance of 418.3 F g^-1 at 2 mV s^-1, which can maintain 95.88% capacity after 10 000 cycles. These results contribute to the development of advanced nanostructured pseudocapacitive electrode materials for renewable energy storage applications.