Highly efficient and durable core-shell catalyst with dual functions: Tungsten nitride quantum dots encapsulated in ultra-thin graphene

Abstract

An efficient and robust bifunctional catalyst that is comprised of tungsten nitride quantum dots encapsulated in ultrathin graphene (WN@C) is synthesized by in situ nitridation reduced pyrolysis method. The photocatalytic and co-catalytic effects of core-shell WN@C are systematically studied. After combining with typical semiconductor ZnIn2S4, the hydrogen evolution activity of the optimal WN@C/ZnIn2S4 composite exhibits 61 times larger than that of ZnIn2S4 and 12 times than that of WN-QDs@C under the visible light illumination (λ ≥ 400 nm). It can continuously produce hydrogen for 99 h without apparent reduction. The analysis and calculations suggest that the enhanced activity can be attributed to the synergistic effect of the lower overpotential of hydrogen evolution reaction (HER), the reduced apparent activation energy (Ea), the decreased Gibbs free energy of H adsorption (∆G*H) and the inhibited recombination of photocharges. This work opens an avenue of the synthesis on quantum dots core-shell structure with dual functions.