Phosphorization Engineering of CoP/NiCoP Nanoneedle Arrays for Energy Storage

Abstract

It is undeniable that developing a simple fabrication procedure for transition-metal phosphides can significantly enhance their potential for commercial use in energy storage and conversion applications. This work focuses on the fabrication of cobalt–nickel phosphide nanoneedle arrays as supercapacitors using nickel foam (NF) as a substrate and a source of Ni ions. By controlling the phosphating process of the Co precursor/NF, it was strikingly found that different surface morphologies emerged in phosphorized NiCo-based electrodes. Taking advantage of nanoneedle/nanorod-type structures and transition phosphides, the CP2 electrode exhibits an exceptional specific capacitance of 2444 F/g (1222 C/g) at 1 A/g. It demonstrates an outstanding rate performance with a retention rate of 43.17% even at 25 A/g. The electrochemistry that occurs during storage at the positive poles was further investigated based on reaction kinetics, revealing intriguing electrochemical storage behaviors. Coupled with a power density of 872.08 W/kg, the CP2//PC supercapacitor demonstrates a significant energy density of 32.53 Wh/kg and displays favorable capacitance retention rate characteristics (58.7% for the initial 5000 cycles and 50.8% for the subsequent 5000 cycles). The enduring cycling performance of the CP2 electrode featuring a superior nanoneedle/nanorod array structure may be attributed to the inherent self-supporting design and enhanced phosphorization process. The design of high-performance supercapacitors is realized by reducing the dead volume and improving conductivity.