Boosting Hydrogen Production by Electrooxidation of Urea over 3D Hierarchical Ni4N/Cu3N Nanotube Arrays

Electrochemical splitting of water to produce hydrogen remains a great challenge owing to the sluggish reaction dynamics of the anodic oxygen evolution reaction (OER). Replacing the OER with the thermodynamically more favorable urea oxidation reaction (UOR) offers the prospect of energy-saving H-2 production together with urea-rich wastewater purification. In this study, 3D hierarchical Ni4N/Cu3N nanotube arrays are successfully fabricated, which exhibit excellent performance both in the hydrogen evolution reaction (HER, -0.098 V to achieve 10 mA cm(-2)) and in the UOR (1.34 V to achieve 10 mA cm(-2)). The excellent performance is benefited from the highly electrochemical active metal nitrides and unique hierarchically nanoarray structure. Remarkably, the symmetrical electrolyzer by using Ni4N/Cu3N/copper foam (CF) as both the cathode and the anode exhibits a low cell voltage of 1.48 V to reach the current of 10 mA cm(-2). It also possesses remarkable long-term stability (10 h at 100 mA cm(-2)) and near 100% Faradaic efficiency for hydrogen evolution.