LAUSR

Abstract Construction of dual sites to break adsorption-energy scaling limitations offers an effective means of facilitating urea electrolysis for H2 production, but a fundamental understanding of their synergistic mechanisms remains incomplete. Herein, we report a facile H2 vapor-assisted strategy for the controllable fabrication of the bimetallic active Co2Mo3O8 electrocatalyst for alkaline urea splitting, with an applied voltage of only 1.50 V required to deliver 50 mA cm−2. Direct spectroscopic evidence and theoretical investigation demonstrate that the Co sites are responsible for the activation of intermediates, whereas the assisting Mo centers are identified as the OH or H radical mediators. Specifically, the synergistic effect of the Co–Mo dual sites was conclusively verified by the in-situ Raman and X­ray photoelectron spectroscopy. Theoretical calculations reveal that the short H-bonding (Mo-HO∙∙∙H–NamineCO–Co) and Co–C–N–Mo configuration formed at the Co–Mo bridge are the key features determining a high reactivity for urea oxidation. The accelerated reaction rate is attributable to the conversion of the endoergic CO2 desorption to an exoergic reaction. In an alkaline H2 evolution, Co atoms are the reaction sites for O–H bond cleavage of H2O, while Mo sites are considered to be the H2-evolving centers. Determination of the individual functionality of synergistic dual centers represents a critical step towards the rational design of highly-efficient electrocatalysts.