Charge storage of Mo/Ti based MXenes for electrochemical capacitor application

This study provides insight into the preparation and energy storage response of double-transition metal carbides. Controlling etching parameters allows us to prepare Mo/Ti-based carbides with different energy storage performance. Effective strategies were employed to design MXene cells with more optimized and practical electrochemical performance. High-mass loading electrodes were integrated into symmetric and asymmetric systems using aqueous electrolytes with a wide pH range. Various alternatives, including asymmetric cell assembly, redox-active electrolytes, and replacing (+) MXene electrode by carbon electrode, were tested to improve the charge storage of the positive electrode, thereby improving the full cell response. In acidic media, an asymmetric cell based on (-) MXene and (+) BP2000 carbon black showed a high cell voltage (1.3 V) and a long cyclability (8000 cycles at 1 A g⁻¹) compared to the symmetric cell (0.8 V). We further showed that the cell capacitance in 1 M NaI can be significantly enhanced once (+) MXene is replaced by carbon black or activated carbon.