Electronic modulation of CoP nanoarrays by Cr-doping for efficient overall water splitting

Herein, we constructed 3D self-supported Cr-doped CoP nanoarrays (Cr-CoP/CP) to promote water electrolysis. Due to the electronic modulation effect, Cr-CoP/CP exhibits preeminent activity toward pH-universal hydrogen evolution reaction (HER), with low overpotentials of 47, 131 and 67 mV at 10 mA·cm−2 in acidic, neutral, and alkaline medium, respectively. Cr-CoP/CP also shows outstanding performance for oxygen evolution reaction (OER) with an overpotential of 251 mV at 10 mA·cm−2 in alkaline electrolyte. And the voltages of 1.59 and 1.73 V are required to achieve 10 and 100 mA·cm−2 for the Cr-CoP/CP(+,-) cell. Importantly, the X-ray photoelectron spectroscopy and theoretical calculations confirmed the activation process of active sites for transition metal phosphides. In the early stage of electrocatalysis, M−P bonds of transition metal phosphides undergo the transformation from covalent to ionic bonds, and finally form metal cations as active sites. This work is of great significance for understanding the process of electrochemical water splitting catalyzed by transition metal phosphides.