Electrochemical Activation of 2D MXene‐Based Hybrid for High Volumetric Mg‐Ion Storage Capacitance

Abstract Electrochemical capacitors are considered as a strong candidate of energy storage device due to their high power density and long cycle lifetime. However, commercial carbon‐based electrochemical capacitors provide only about 60 F cm −3 of volumetric capacitance due to low packing density and intrinsic areal capacitance. Two‐dimensional (2D) transition metal carbides/nitrides, known as MXenes, have received attention due to their high electronic conductivity, surface modification, and abilities to achieve superior ion intercalation and packing density. Here, we report the improved volumetric Mg‐ion storage capacitance of 2D MXene/reduced graphene oxide (rGO) hybrid through electrochemical activation. Along with high volumetric capacitance of 439 F cm −3 at 2 mV s −1 , MXene/rGO hybrid electrode exhibits superior capacitive retention of 87 % after 10,000 cycles in aqueous Mg‐ion system. Thus, our hybrid electrode and electrochemical activation approach opens new avenues to store Mg and other multivalent ions for high volumetric capacitance of electrochemical capacitors.