Porous NiO Nanosheet Bifunctional Electrodes Modified with Ultrafine Ni₃S₂ Quantum Dots for Green Hydrogen Production via Urea Electrolysis

Abstract

Electrolysis of urea can simultaneously produce molecular hydrogen and alleviate the environmental problems caused by urea-rich wastewater effluents. Therefore, it is of great significance to develop low-cost, highly active, and resistant electrodes and electrocatalysts to achieve high-efficiency urea electrolysis processes. In this study, porous NiO nanosheets (NiO/Ni3S2/NF) decorated with Ni3S2 quantum dots were prepared on the surface of nickel foam (NF) via the Kirkendall effect by the gas-phase vulcanization reaction. The obtained NiO/Ni3S2/NF exhibits good electrocatalytic activity and stability toward the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). An electrolyzer containing NiO/Ni3S2/NF||NiO/Ni3S2/NF on both the anode and cathode, immersed in an alkaline aqueous solution containing urea, is assembled, and only a cell voltage of 1.408 V is required to reach a current density of 10 mA cm–2, a value which is much lower than that for an electrolyzer made of RuO2/NF||Pt/C/NF (1.490 V). It is found that the superior catalytic performance of NiO/Ni3S2/NF is mainly attributed to the uniform pore structure on NiO nanosheets and the synergistic effect between Ni3S2 quantum dots and NiO nanosheets. This study provides a method to simultaneously construct the porous structure and heterostructure through gas-phase reactions.