Unraveling the Charge Storage Mechanism of Ti₃C₂T_x MXene Electrode in Acidic Electrolyte

Two-dimensional Ti₃C₂T_x MXenes have been extensively studied as pseudocapacitive electrode materials. This Letter aims at providing further insights into the charge storage mechanism of the Ti₃C₂T_x MXene electrode in the acidic electrolyte by combining experimental and simulation approaches. Our results show that the presence of H₂O molecules between the MXene layers plays a critical role in the pseudocapacitive behavior, providing a pathway for proton transport to activate the redox reaction of the Ti atoms. Also, thermal annealing of the samples at different temperatures suggests that the presence of the confined H₂O molecules is mainly controlled by the surface termination groups. These findings pave the way for alternative strategies to enhance the high-rate performance of MXenes electrodes by optimizing their surface termination groups.