In situ transformation of sea urchin-like NixCoyP@NF as an efficient bifunctional electrocatalyst for overall water splitting

Transition metal phosphides (TMPs) are a hopeful noble-metal-free catalysts for water splitting. In this study, we used a three-dimensional nanostructure on nickel substrate to easily synthesize a nickel–cobalt phosphide electrocatalyst (NixCoyP, x = 1, 1.5, 2; y = 1, 1.5, 2) through hydrothermal reaction and in situ phosphorylation. The NiCo1.5 P exhibited relatively excellent oxygen evolution activity performance, and it only needed the overpotentials of 123 mV for HER in 1 M KOH to perform the current densities of 10 mA cm−2. It is worth mentioning that the Ni2CoP exhibited better bifunctional electrocatalyst characteristics. As to water splitting, the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) require 197 and 253 mV overpotentials separately to provide a current density of 10 mA cm−2. Its relatively excellent electrochemical performance can be ascribed to the high-density sea urchin-like three-dimensional structure, which provides greater specific surface area and more active site. Besides, Ni2CoP also shows long-term durability lasting 80,000 s, and on this basis, there is no distinct deactivation. This work emphasizes that Ni2P and CoP play a vital role relative to the good activity of HER. Moreover, the unique morphology with self-supported structure provides a larger specific surface area, making it possible the exposure of higher amount of active sites for HER. These self-supported electrocatalysts that do not require a binder could also make the electrode more active and stable. This work, therefore, presents a strategy that is controllable and feasible strategy for the synthesis of bimetallic phosphides with unique morphology and high HER and OER activity.