Structurally stable Fe–Ni–Co phosphide/graphene and nitrogen-doped carbon/graphene constructed by atomic layer deposition for high-performance hybrid supercapacitor

Constructing high-volume hybrid supercapacitors (HSCs) based on transition metal phosphides (TMPs) cathode and porous carbon anode is an effective way to promote energy density of supercapacitors (SCs). Herein, FeNiCoP nanoneedles are uniformly and stably coated on reduced graphene oxide (FeNiCoP/rGO) by atomic layer deposition technology. The synergistic effect between the large surface area of rGO and high specific capacity of TMP improves electrode reaction kinetics by fully exposing the active sites of FeNiCoP/rGO and shortening the ion/electron transport path. Therefore, FeNiCoP/rGO reveals a high specific capacitance (184.8 mAh/g at 1 A/g), favorable rate performance (151.1 mAh/g at 10 A/g) and excellent structural stability. To better exploit the advantages of the performance of the FeNiCoP/rGO, an anode of porous nitrogen-doped carbon/rGO (N–C/rGO) was prepared. Benefitting from the rich void structure and the nitrogen doping, N–C/rGO delivers a specific capacitance of 240 F/g at 1 A/g. The HSC device assembled by them exhibits the maximum energy and power densities of 52.9 Wh/kg and 8579.5 W/kg. Moreover, the device maintains 82.8% specific capacity after 5000 cycles.