Tunable NiSe-Ni₃Se₂ Heterojunction for Energy-Efficient Hydrogen Production by Coupling Urea Degradation

Urea-assisted water splitting is a promising energy-saving hydrogen (H₂) 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 Ni₃Se₂, along with a conductive graphene-coated nickel foam skeleton (NiSe-Ni₃Se₂/GNF) is reported. The heterostructured NiSe-Ni₃Se₂ originates from the in situ selenization of graphene-coated nickel foam, allowing for careful regulation of the NiSe to Ni₃Se₂ ratio by simply adjusting the calcination temperature. Theoretical calculations of the charge transfer between NiSe and Ni₃Se₂ 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-Ni₃Se₂/GNF-based UOR-HER electrolyzer requires only 1.54 V to achieve a current density of 50 mA cm^-2, which is lower than many recent reports and much lower than 1.83 V of NiSe-Ni₃Se₂/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 H₂ production.