Plasma-Activated Solutions Regulate Surface-Terminating Groups Enhancing Pseudocapacitive Ti 3 C 2 T x 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 Ti 3 C 2 T x is a promising approach to improve the pseudocapacitive charge storage in H 2 SO 4 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 Ti 3 C 2 T x dispersion is demonstrated to generate abundant and stable surface-terminating O groups. The impact of the discharge environment (Ar, O 2 , and H 2 ) on the structural characteristics and electrochemical performance of Ti 3 C 2 T x nanosheets is studied. The Ti 3 C 2 T x modified in Ar and H 2 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 Ti 3 C 2 T x samples modified in H 2 plasma-treated solutions. Additionally, the Ti 3 C 2 T x treated using H 2 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.