Modulation of dual centers on cobalt-molybdenum oxides featuring synergistic effect of intermediate activation and radical mediator for electrocatalytic urea splitting

Abstract

Construction of dual sites to break adsorption-energy scaling limitations offers an effective means of facilitating urea electrolysis for H 2 production, but a fundamental understanding of their synergistic mechanisms remains incomplete. Herein, we report a facile H 2 vapor-assisted strategy for the controllable fabrication of the bimetallic active Co 2 Mo 3 O 8 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–N amine CO–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 CO 2 desorption to an exoergic reaction. In an alkaline H 2 evolution, Co atoms are the reaction sites for O–H bond cleavage of H 2 O, while Mo sites are considered to be the H 2 -evolving centers. Determination of the individual functionality of synergistic dual centers represents a critical step towards the rational design of highly-efficient electrocatalysts. • We report a facile H 2 vapor-assisted strategy for the fabrication of the Co 2 Mo 3 O 8 catalyst for the alkaline urea splitting. • In situ reconstructed Co 3 O 4 and high-valence Mo (VI) species on the surface are responsible for increased urea oxidation. • The short H-bonding and Co-C-N-Mo configuration are the key features determining a high reactivity for urea oxidation. • In an alkaline HER, Co atom accounts for cleavage of H-OH bond, while Mo site is identified as the H 2 -evolving center.