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

摘要

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 (Ni_xCo_yP, x = 1,1.5, 2; y = 1, 1.5, 2) through hydrothermal reaction and in situ phosphory-lation. The NiCo_(1.5) 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 Ni_2CoP 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, Ni_2CoP also shows long-term durability lasting 80,000 s, and on this basis, there is no distinct deactivation. This work emphasizes that Ni_2P 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.