Ni–Mo–O@Ni–P nanowires as binder-free electrodes for aqueous asymmetric supercapacitors with high specific capacity and excellent stability

Introducing transition metal phosphides with high conductivity into binary metal oxides is considered as an effective strategy to solve the problems of poor conductivity, cyclic performance and low capacity of binary transition metal oxides. Herein, we designed a simple two-step method for the growth of Ni–Mo–O@Ni–P nanowires (NMP) on Ni foams by introducing Ni–P metal phosphides into Ni–Mo oxides (NMO), which shows a high specific capacity of 1864 C g^–1 at 2 Ag^–1 and 1104 C g⁻¹ at 20 Ag⁻¹ in a three-electrode system, which outperform that of NMO electrode. Importantly, the NMP//AC aqueous asymmetric supercapacitor configured with the NMP as the positive electrode and YP50F commercial activated carbon (AC) as the negative electrode shows a high energy density of 30.2 Wh kg^–1 at a power density of 507.6 W kg⁻¹ and superior rate capability of 80.4% initial specific capacity retention from 0.5 to 2 A g^–1. In addition, the specific capacity of the NMP//AC device has no decay after 20,000 cycles at 2 A g⁻¹, showing excellent cyclic stability. These results indicate the introduction of Ni–P transition metal phosphides is an effective method to improve the electrochemical performance of Ni–Mo oxides-based supercapacitors. This work provides a reference for the research on improving the electrochemical performance of other transition metal compounds.