Self-growth Ni2P nanosheet arrays with cationic vacancy defects as a highly efficient bifunctional electrocatalyst for overall water splitting.

HYPOTHESIS: The transition metal phosphide is one of the promising bifunctional electrocatalysts for overall water splitting. Moreover, the activity of phosphide catalysts can be further enhanced by the cationic vacancy engineering. EXPERIMENTS: The self-growth Ni2P nanosheet arrays with abundant cationic vacancy defects (V-Ni2P/NF) has been synthesized via a facile multi-step reaction process involving hydrothermal, phosphorization and acid-etching of Mn which was doped in Ni2P nanosheets as a sacrificial dopant. Furthermore, the experimental studies and density functional theory (DFT) calculations were carried out to evaluate its electrochemical performance. FINDINGS: The chemical and electrocatalytic property of Ni2P were successfully optimized by cationic vacancy engineering and the obtained V-Ni2P/NF catalyst exhibited superior bifunctional catalytic performance for both hydrogen evolution (HER) and oxygen evolution reaction (OER) compared to pristine Ni2P and Mn-doped Ni2P in alkaline electrolyte. The V-Ni2P/NF can afford the current density of 10 mA cm-2 at a small overpotential of 55 mV for HER and 250 mV for OER. Additionally, the water electrolysis device assembled by the V-Ni2P/NF electrode as both the anode and cathode just requires a small voltage of 1.59 V to achieve 10 mA cm-2 and shows no obvious attenuation for 50 h.