Nickel-cobalt phosphide interfacial heterostructures as supercapacitor electrode material for electrochemical energy storage application

Transition metal phosphides have become one of the excellent electrode material choices for improving the electrochemical performance of supercapacitors due to their high theoretical capacity and good redox ability. The introduction of secondary metals in single metal phosphides can enhance the properties and chemical stability of their redox sites. Combining multiple types of transition metal phosphides can comprehensively utilize the properties of each component and improve the charge efficiency at the interface, thus exhibiting good electrochemical performance. Therefore, in this work, nickel–cobalt phosphide heterojunction Co2P/NiCoP/Ni2P was prepared. At the current density of 1 A/g, the specific capacitance of the Co2P/NiCoP/Ni2P electrode material is 174.2 mAh/g. And its specific capacitance is higher than each of its components at any current density. An asymmetric supercapacitor was assembled with Co2P/NiCoP/Ni2P as the positive electrode and activated carbon as the negative electrode. When the power density is 800 W kg−1, the device can exhibit an energy density of 42.29 W h kg−1, which shows a high energy density while maintaining the power density. At the current density of 2 A/g, the assembled supercapacitor could still maintain 90% of the initial specific capacitance after 10,000 cycles, showing high cycle stability. This provides ideas for future research on this type of energy storage materials.