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/NiS and NiS/NiS heterojunctions with Ni cores embedding in nitrogen-doped carbon nanotubes (NiS/NiS- and NiS/NiS-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/NiS-Ni@NCNT with interface electrons transferring from NiS to NiS, delivers a 10 mA cm UOR current density in 1.0 m KOH with 0.5 m urea at 1.37 V, superior to NiS/NiS-Ni@NCNT with the electron transfer direction from NiS to NiS. Experimental and theoretical calculation results reveal that NiS/NiS Mott-Schottky heterojunctions facilitate the rapid in situ formation of NiOOH active species by removing electrons of NiS, and also accelerate the adsorption and conversion of urea molecules and key intermediates of CON at its interfaces. This work demonstrates an interface electron transfer direction tuning strategy on heterojunctions for harvesting high-performance UOR electrocatalysts.