Surface reconstruction and charge distribution enabling Ni/W5N4 Mott-Schottky heterojunction bifunctional electrocatalyst for efficient urea-assisted water electrolysis at a large current density

Urea-assisted water electrolysis is regarded as an energy-efficient strategy for hydrogen production, but its po-tential use is still limited by sluggish kinetics in both anodic urea oxidation reaction (UOR) and cathodic hydrogen evolution reaction (HER). Herein, we report the facile synthesis of nickel foam (NF) supported Ni/ W5N4 Mott-Schottky heterojunction nano-microspheres as a highly active catalyst for both UOR and HER using a hydrothermal method followed by nitridation treatment. The as-prepared Ni/W5N4/NF catalyst with high electrochemically active surface area would reconstruct under oxidizing condition to form nickel tungsten oxyhydroxides to efficiently drive UOR, with a potential of only 1.34 V (versus reversible hydrogen electrode) at 10 mA cm-2. Impressively, thus-prepared catalyst benefited from charge redistribution only required an over -potential of 25 mV at 10 mA cm -2 for HER. In particular, the Ni/W5N4/NF catalyst couple used for urea-assisted water electrolysis just needed a cell voltage of 1.77 V at 1000 mA cm-2.

Automated summary

In this study, nickel foam-supported Ni/W5N4 Mott-Schottky heterojunction nano-microspheres were synthesized as a highly active catalyst for urea-assisted water electrolysis. The catalyst exhibited excellent activity for both anodic urea oxidation reaction and cathodic hydrogen evolution reaction, with a high electrochemically active surface area. The catalyst had a low over-potential and could efficiently drive urea oxidation reaction and facilitate charge redistribution for hydrogen evolution reaction.