Directional electron transfer from CoS2 to Mo2C for weakening Mo–H bonds toward boosting photocatalytic H2 production

Abstract

Molybdenum carbide (Mo₂C) has been regarded as a potential cocatalyst for boosting the photocatalytic hydrogen-generation performance of photocatalysts owing to its unique Pt-mimetic electronic structure, which arises from the hybridization between Mo-4d and C-s/p orbitals. However, the overpowered Mo–H bonding promotes favorable H⁺ adsorption while hindering hydrogen desorption, thereby restricting its practical application in hydrogen evolution reactions (HERs). In this paper, the strategy of constructing a CoS₂–Mo₂C heterojunction leverages directional electron transfer from CoS₂ to Mo₂C to enhance the occupancy of antibonding orbitals at Mo sites for weakening Mo–H_ads bonds and significantly improving hydrogen-evolution activity. Herein, the CoS₂–Mo₂C heterojunction was successfully fabricated via a two-step calcination method, and then integrated with TiO₂ through ultrasonic assistance to prepare the CoS₂–Mo₂C/TiO₂ photocatalyst. The optimized CoS₂–Mo₂C/TiO₂ photocatalyst exhibited outstanding photocatalytic activity with a hydrogen-generation rate of 1964.53 μmol h⁻¹ g⁻¹, which is ca. 15.1 and 2.6-fold higher than that of pristine TiO₂ and Mo₂C/TiO₂, respectively. Experimental characterization and DFT calculations revealed that the antibonding orbital occupancy of Mo sites increased by the electron transfer from CoS₂ to Mo₂C in the CoS₂–Mo₂C heterojunction, leading to the weakened Mo–H_ads bond from 2.025 Å in Mo₂C to 1.976 Å in CoS₂–Mo₂C. This study proposes crucial design principles for Mo₂C-based heterojunction cocatalysts, fostering the advancement of sustainable hydrogen-production technologies.