Tunable NiSe-NiSe Heterojunction for Energy-Efficient Hydrogen Production by Coupling Urea Degradation.

Urea-assisted water splitting is a promising energy-saving hydrogen (H) production technology. However, its practical application is hindered by the lack of high-performance bifunctional catalysts for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). Herein, a heterostructured catalyst comprising highly active NiSe and NiSe, along with a conductive graphene-coated nickel foam skeleton (NiSe-NiSe/GNF) is reported. The heterostructured NiSe-NiSe originates from the in situ selenization of graphene-coated nickel foam, allowing for careful regulation of the NiSe to NiSe ratio by simply adjusting the calcination temperature. Theoretical calculations of the charge transfer between NiSe and NiSe components can optimize the reaction pathways and reduce the corresponding energy barriers. Accordingly, the designed catalyst exhibits excellent UOR and HER activity and stability. Furthermore, the NiSe-NiSe/GNF-based UOR-HER electrolyzer requires only 1.54 V to achieve a current density of 50 mA cm, which is lower than many recent reports and much lower than 1.83 V of NiSe-NiSe/GNF-based OER-HER electrolyzers. Moreover, the UOR-HER electrolyzer exhibited negligible cell voltage variation during a 28-h stability test, indicating satisfactory stability, which provides a new viable paradigm for energy-saving H production.