Electrochemical performance of molybdenum carbide MXene-few-layer graphene hybrid electrodes for aqueous supercapacitors

This work investigates the influence of ionic radius on the charge storage behavior of molybdenum carbide MXene electrodes (Mo2CCl2) produced through the molten salt etching method for application in aqueous-based supercapacitors (SCs). Various electrolytes, i.e., 3 M H2SO4, 1 M Li2SO4, 1 M Na2SO4, and 0.6 M K2SO4, were investigated, revealing that the small cation (H+) enhances the SCs capacitance through fast redox kinetics and high ionic mobility. To elucidate the role of anions, neutral electrolytes (8 m NaNO3, 2 M NaCl, and 1 M Na2SO4) were also explored, enabling a wide voltage window and stable operation of SCs. An asymmetric supercapacitor was assembled using Mo2CCl2/FLG (few-layer graphene) as the pseudocapacitive electrode and FLG/CG/(curved graphene) as the EDLC counterpart. In this configuration, FLG prevents MXene restacking while CG provides abundant electroactive sites, resulting in enhanced energy density and cycling durability. These results highlight the combined effect of electrolyte ion selection and hybrid electrode engineering toward high-performance, durable aqueous energy-storage devices.