Interface Electron Transfer Direction‐Tuned Urea Electrooxidation Over Multi‐Interface Nickel Sulfide Heterojunctions

Hydrogen can be produced by electrolyzing urea aqueous solution under smaller overpotentials, owing to the lower thermodynamic potential of urea oxidation reaction (UOR) at anode than oxygen evolution reaction (OER). The efficient and selective electrocatalysts for UOR are crucial to achieve this. Herein, two NiS-based NiS/Ni₃S₂ and NiS/NiS₂ heterojunctions with Ni cores embedding in nitrogen-doped carbon nanotubes (NiS/Ni₃S₂- and NiS/NiS₂-Ni@NCNT) are demonstrated as efficient UOR electrocatalysts. The electrocatalytic UOR performance over heterojunctions is efficiently tuned by altering the electron transfer direction on their interfaces. NiS/Ni₃S₂-Ni@NCNT with interface electrons transferring from Ni₃S₂ to NiS, delivers a 10 mA cm^-2 UOR current density in 1.0 m KOH with 0.5 m urea at 1.37 V, superior to NiS/NiS₂-Ni@NCNT with the electron transfer direction from NiS to NiS₂. Experimental and theoretical calculation results reveal that NiS/Ni₃S₂ Mott-Schottky heterojunctions facilitate the rapid in situ formation of NiOOH active species by removing electrons of Ni₃S₂, and also accelerate the adsorption and conversion of urea molecules and key intermediates of ^*CON₂ at its interfaces. This work demonstrates an interface electron transfer direction tuning strategy on heterojunctions for harvesting high-performance UOR electrocatalysts.