Fiber-based multifunctional nickel phosphide electrodes for flexible energy conversion and storage

Abstract

A fiber-based multifunctional nickel phosphide (NiP_x) electrode has been successfully prepared by facile electrodeposition of nickel nanoparticle arrays on a commercial carbon fiber (CF) followed by low-temperature phosphidation. As a result of the synergistic effect from the 3D porous structure, enhanced conductivity, and the two active components Ni²⁺ and P^δ− with rich valences, the resulting vertically aligned NiP_x nanoflakes grown on the CF (CF@NiP_x) electrode exhibit superior bifunctional electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in an alkaline electrolyte as well as an ultrahigh specific volumetric capacitance of 817 F cm⁻³ at a current density of 2 mA cm⁻². For practical applications, an efficient CF@NiP_x-based alkaline water electrolyzer, with strong durability, can achieve 10 mA cm⁻² water-splitting current at a cell voltage of only 1.61 V (iR uncorrected). Besides, a fiber-based flexible solid-state asymmetric supercapacitor device with CF@NiP_x as the cathode and reduced graphene oxide attached on CF@Ni (CF@Ni@RGO) as the anode was observed to achieve a remarkable volumetric energy density of 8.97 mW h cm⁻³, excellent flexibility and superior long term cycling stability. All these results render our fiber-based CF@NiP_x electrodes as an ideal platform for electrocatalysis and flexible electrochemical energy storage applications.