Electronic modulation and surface reconstruction on heterostructured CoP-Ni2P nanosheets with phosphate-rich surface for synergistically triggering oxygen evolution reaction

Abstract

Bimetallic phosphides have attracted research interest for their synergism and superior electrocatalytic activities for anodic oxygen evolution reaction (OER). The maximizing the synergism in bimetallic phosphides and identifying the accurate active sites might be of significance for developing OER electrocatalysts. Herein, the heterostructured CoP-Ni2P nanosheets on nickel foam (CoP-Ni2P/NF) with three-dimension (3D) architecture, clear heterointerface and phosphate-rich surface are rationally designed by hydrothermal and phosphorization process, and the optimal CoP-Ni2P/NF delivers excellent OER activity with low overpotential of 255 mV to achieve current density of 20 mA cm−2, low Tafel slope of 65.1 mV dec-1 and robust stability in alkaline electrolyte. The experimental characterizations and theoretical density functional theory (DFT) calculations unravel that the heterointerfacial charge transfer from Ni2P to CoP can increase the density of state at the Femi level, and further modulate the electronic structure of CoP-Ni2P. Moreover, the facilitating surface reconstruction on CoP-Ni2P/NF unveiled by in-situ UV–vis spectroscopy to generate CoOOH/NiOOH as active species enables the high intrinsic OER activity. Beyond, the phosphate-rich surface of CoP-Ni2P as a proton transport mediator can accelerate the deprotonation of OHads during OER process. Moreover, the double-electrode cell build on CoP-Ni2P/NF||Pt/C/NF couples only requires 1.63 V to drive the current density of 100 mA cm−2 with superior stability for overall alkaline water splitting.