Exploring the electrochemical behavior of Mo1.33CTz MXene in aqueous sulfates electrolytes: Effect of intercalating cations on the stored charge

MXenes have been introduced as a high energy and power density electrochemical supercapacitor material owing to their high specific capacitance and electrochemical stability. The operating potential window and, in turn, energy density of MXene based symmetric and asymmetric supercapacitors can be effectively enhanced by the proper choice of aqueous electrolyte. Herein, we investigate the electrochemical behavior of vacancy-containing 𝑖-MXene (Mo1.33CTz) in sulfate based aqueous electrolytes with univalent (Li+, Na+, or K+) or divalent (Mg2+, Mn2+, or Zn2+) cations. The results show that the Mo1.33CTz MXene electrodes can be operated in a potential window higher than 1 V without degradation in these sulfate electrolytes. The Mo1.33CTz MXene electrodes deliver a high volumetric capacitance up to ~677 F cm-3 as measured in 1.0 M MnSO4 solution. Furthermore, symmetric (Mo1.33CTz//Mo1.33CTz) and asymmetric (Mo1.33CTz//nitrogen-doped activated carbon (NAC)) devices in 0.5 M K2SO4 solution can be operated with a cell voltage of about 1.1 V and 1.8 V, respectively. The asymmetric devices retain about 97% of their initial capacitance after 5000 charge/discharge cycles. Overall, the results reveal that the choice of the intercalating cations is a viable route to boost the performance of Mo1.33CTz MXene and to construct energy storage devices.