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

Ti 3 C 2 T x (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 Ti 3 C 2 T x 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-MnO 2 . 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 Ti 3 C 2 T x and δ-MnO 2 electrodes in 1 M H 2 SO 4, NaHSO 4, KOH, Na 2 SO 4, LiCl, and MgCl 2 electrolytes to check their performance. We found that highly acidic electrolytes, such as H 2 SO 4 and NaHSO 4, are unsuitable for δ-MnO 2 electrodes as a result of the dissolution of δ-MnO 2 in these electrolytes. On the other hand, a 1 M KOH electrolyte (highly alkaline) is not suitable for Ti 3 C 2 T x as a result of instability, while neutral aqueous electrolytes show promising results with both electrodes. With a 1 M aqueous Na 2 SO 4 electrolyte, the Ti 3 C 2 T x –δ-MnO 2 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 Ti 3 C 2 T x and δ-MnO 2 electrodes.