Effect of Aqueous Electrolytes on the Performance of a Ti3C2Tx (MXene)−δ-MnO2 Asymmetric Supercapacitor

Ti3C2Tx (MXene) has emerged as pseudocapacitive electrode material for supercapacitor applications as a result of its high conductivity, surface functional groups, and surface redox reactions. A symmetric Ti3C2Tx supercapacitor delivers very less energy density as a result of a low operational voltage window (0.6 V). The operational voltage window can be enhanced by making an asymmetric device with δ-MnO2. Prior to the asymmetric supercapacitor fabrication, proper selection of the electrolyte, which works with both negative and positive electrodes for enhancing the energy density, is very important. We address this issue by electrochemically characterizing Ti3C2Tx and δ-MnO2 electrodes in 1 M H2SO4, NaHSO4, KOH, Na2SO4, LiCl, and MgCl2 electrolytes to check their performance. We found that highly acidic electrolytes, such as H2SO4 and NaHSO4, are unsuitable for δ-MnO2 electrodes as a result of the dissolution of δ-MnO2 in these electrolytes. On the other hand, a 1 M KOH electrolyte (highly alkaline) is not suitable for Ti3C2Tx as a result of instability, while neutral aqueous electrolytes show promising results with both electrodes. With a 1 M aqueous Na2SO4 electrolyte, the Ti3C2Tx–δ-MnO2 asymmetric device delivered an energy density of 8.2 Wh kg–1 and a power density of 400 W kg–1. The voltage window of this device is 1.6 V, which is higher than the voltage window of the symmetrical supercapacitor made of Ti3C2Tx and δ-MnO2 electrodes.