An aqueous 2.1 V pseudocapacitor with MXene and V-MnO₂ electrodes

MXenes have shown record-breaking redox capacitance in aqueous electrolytes, but in a limited voltage window due to oxidation under anodic potential and hydrogen evolution under high cathodic potential. Coupling Ti₃C₂T_x MXene negative electrode with RuO₂ or carbon-based positive electrodes expanded the voltage window in sulfuric acid electrolyte to about 1.5 V. Here, we present an asymmetric pseudocapacitor using abundant and eco-friendly vanadium doped MnO₂ as the positive and Ti₃C₂T_x MXene as the negative electrode in a neutral 1 M Li₂SO₄ electrolyte. This all-pseudocapacitive asymmetric device not only uses a safer electrolyte and is a much less expensive counter-electrode than RuO₂, but also can operate within a 2.1 V voltage window, leading to a maximum energy density of 46 Wh/kg. This study also demonstrates the possibility of using MXene electrodes to expand the working voltage window of traditional redox-capable materials.