Design of 2D/2D heterostructure by coupling cobalt hydroxides with Mxene on nickel foam for high energy density supercapacitors

Two-dimensional (2D) layered transition metal compounds are promising pseudocapacitive materials for high-performance supercapacitors. Herein, the cobalt hydroxide coupled Ti₃C₂T_x MXene layers on nickel foam (Co(OH)₂-Ti₃C₂T_x@NF) is prepared by the facile hydrothermal method. The 2D/2D heterostructures by coupling layered double hydroxide (LDH) with MXene can expose the more specific surface area and boost the redox-active sites. Co(OH)₂-Ti₃C₂T_x@NF exhibits a higher specific capacitance (1400 F g⁻¹) than Co(OH)₂@NF (1106 F g⁻¹) and Ti₃C₂T_x@NF (844 F g⁻¹), and the capacitance retention is 98.2 % after 10,000 cycles implying outstanding cyclic stability. Excellent pseudocapacitive behavior is assigned to the redox reaction by the interaction of MXene with alkali metal ions and the valence variations of Co³⁺/Co²⁺. Furthermore, the assembled asymmetric Co(OH)₂-Ti₃C₂T_x@NF//AC supercapacitor shows an energy density of 13.7 μWh cm⁻² at 1.4 mW cm⁻². These results imply that the LDH/MXene hybrid with 2D/2D heterostructures can be considered promising pseudocapacitive electrode materials for high-energy supercapacitors.