NiCoP/MXene nanocomposites via electrostatic self-assembly for high-performance supercapacitor electrodes

Bimetallic phosphides have attracted a significant amount of attention in the field of energy storage due to their high specific capacity. However, the cycle stability of supercapacitors has been hampered by the volume expansion and sluggish reaction kinetics of phosphides during charge and discharge. Herein, NiCoP/MXene was successfully prepared by the solvothermal method and subsequent phosphidization. The impacts of the amount of MXene nanosheets on the electrochemical properties of the NiCoP/MXene composite were investigated. The optimized electrode (NCP/MX-20/CC) exhibited a high specific capacity of 848.83 C g^-1 at 1 A g^-1 and outstanding cyclic stability (86.57% retention after 5000 cycles). The enhanced charge storage performance observed after forming composites with MXene originates from the larger specific surface area, accelerated diffusion process, and enhanced conductivity. These factors lead to an increased number of electrochemically accessible sites and more facile redox kinetics. The NCP/MX-20/CC exhibits battery-type behavior, and surface-controlled processes provide primary support for the charge storage mechanism. The as-assembled asymmetric supercapacitor (NCP/MX-20//activated carbon ASC) delivers an energy density of 49.7 W h kg^-1 at 800.1 W kg^-1, and it is durable towards repetitive charge-discharge cycles. This work demonstrates that NiCoP/MXene composite materials are potential candidates for use as supercapacitor electrodes.