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Abstract:
Urea-assisted electrolysis boosts hydrogen production by substituting the sluggish oxygen evolution reaction (OER) with the energetically favorable urea oxidation reaction (UOR), thereby lowering energy consumption. Rational heterojunction engineering modulates charge distribution and generates abundant active sites, facilitating urea adsorption and C─N bond cleavage. Herein, we report a facile electrodeposition strategy to construct g-C3N4/CoMoS2 hybrid electrocatalysts. The built-in electric field at the heterojunction creates electrophilic regions on g-C3N4 and nucleophilic regions on CoMoS2, selectively activating urea and promoting rapid bond cleavage. Anchoring g-C3N4 onto CoMoS2 enables remarkable bifunctional activity toward both UOR and HER, achieving potentials of 1.27 V vs. RHE in 1 m KOH + 0.33 m urea and -80 mV vs. RHE in 1 m KOH at 10 mA cm−2, respectively. Density functional theory (DFT) calculations reveal that interfacial electron transfer enriches CoMoS2 with electrons and depletes g-C3N4, enhancing charge transfer, optimizing urea adsorption, and lowering reaction energy barriers. Notably, the g-C3N4/CoMoS2//g-C3N4/CoMoS2 cell delivers 10 mA cm−2 at 1.34 V with excellent stability, demonstrating superior efficiency. This work provides a rational framework for designing efficient, energy-saving urea-assisted hydrogen production systems and reveals how intrinsic electric fields can precisely control charge distribution during catalysis.

Keywords:
built-in electric field, heterojunction, hydrogen production, urea oxidation