Pseudocapacitance of Vanadium Carbide MXenes in Basic and Acidic Aqueous Electrolytes

Pseudocapacitive charge storage with Ti3C2Tx in protic electrolytes has received significant attention. However, other MXene compositions have received less attention so far. Additionally, pseudocapacitance of MXenes has only been reported in acidic electrolytes. Herein, we report on the pseudocapacitance of two vanadium carbide MXenes (V2CTx and V4C3Tx) in various basic electrolytes and sulfuric acid, showing distinct redox couples in their cyclic voltammograms. Freestanding V2CTx film electrodes could deliver gravimetric capacitances above 250 F g–1 in different basic electrolytes with the highest capacitance of 386 F g–1 in 1 M LiOH at 2 mV s–1. Moreover, the cycle life performance showed an increasing capacitance over thousands of cycles (121% of initial capacitance after 60,000 cycles at 10 A g–1 in 6 M KOH). Both materials also exhibit higher capacitances than Ti3C2Tx in 3 M sulfuric acid, with 475 and 284 F g–1 for V2CTx and V4C3Tx, respectively.