Co-doped MnS/NiS/Ni3S2 grown in situ on hydrophilic nickel foam for energy-efficient urea-assisted alkaline hydrogen production

Abstract

The electrochemical oxidation of urea provides a promising pathway for hydrogen production with a theoretically reduced energy consumption of 93% lower than water electrolysis. Therefore, designing efficient bifunctional non-noble metal-based electrocatalysts capable of catalyzing both urea oxidation reaction and hydrogen evolution reaction are important. Herein, a Co-doped MnS/NiS/Ni₃S₂ catalyst with a complex structure of nanoparticles and nanosheets simultaneously grown on a 3D hydrophilic nickel foam (HNF) was prepared via electrodeposition and a two-step hydrothermal method. The resulting catalyst (Co-MnS/NiS/Ni₃S₂/HNF) exhibited a remarkable performance as a self-supported bifunctional electrode for UOR and HER, requiring overpotentials of only 1.313 V at 50 mA cm⁻² and 34 mV at 10 mA cm⁻², respectively. At a high current density of 100 mA cm⁻², an overpotential of only 1.343 V was required for UOR, which is about 202 mV lower than OER carried in 1 M KOH to achieve the same current density. Further, the performance of the electrocatalyst showed no apparent deterioration in the 96 h stability test for HER and UOR. Furthermore, we designed an alkaline electrolytic cell with the bifunctional Co-MnS/NiS/Ni₃S₂/HNF catalyst, which compared to the traditional electrolytic cell for water splitting (OER‖HER) showed a reduction in voltage by 300 mV, driving a current density of 100 mA cm⁻² at only 1.75 V in 1 M KOH + 0.33 M urea. The faradaic efficiency of hydrogen production was calculated to be about 100%. Overall, this work provides a new paradigm in the design of efficient bifunctional non-noble metal-based electrocatalysts for HER and UOR in alkaline media.