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

Abstract

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.