Core@shell structured NiCo@NiCoP nanorods vertically aligned on Ni foam as an efficient bifunctional electrocatalyst for overall water electrolysis

The development of efficient noble metal-free electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for practical applications in electrochemical water splitting. In this study, core@shell structured nickel cobalt alloy-nickel cobalt phosphide (NiCo@NiCoP) nanorods directly grown on nickel foam (NF) are successfully synthesized throughout hydrothermal, thermal reduction, anodic oxidation, and phosphidation process. The NiCoP shell contributes to excellent redox performance in the electrochemical reaction, while the NiCo alloy core functions as an electron highway, enhancing the electrical conductivity and charge transfer efficiency. The synthesized NiCo@NiCoP/NF exhibits outstanding HER activity with a low overpotentials of 130 mV at a current density of − 100 mA cm⁻² and a small Tafel slope of 36 mV dec⁻¹. Additionally, the overpotential required to acquire a current density of 100 mA cm⁻² and the Tafel slope is found to be 340 mV and 79 mV dec⁻¹, respectively, for OER. Furthermore, a symmetric water electrolyzer using NiCo@NiCoP/NF as a bifunctional electrocatalyst requires a cell voltage of only 1.55 V to deliver a current density of 10 mA cm⁻² and displays remarkable electrochemical durability of over 100 h. The facile synthetic procedure and excellent bifunctional electrocatalytic performance for both HER and OER would provide the great potential for practical application of water electrolysis and future energy conversion and storage technologies.