Synergy of NiO quantum dots and temperature on enhanced photocatalytic and thermophoto hydrogen evolution

Abstract Solar-to-hydrogen holds a great sustainable energy solution, in which photocatalysis plays an important role. In this study, a composite photocatalyst with NiO quantum dots (NiO QDs) in graphitic carbon nitride (g-CN) was synthesized and evaluated in photocatalytic (PC) and thermophotocatalytic hydrogen evolution reaction (HER) under visible light. A sample of 9 wt% NiO QDs-g-CN achieved the highest PC-HER rate of 130 μmol·g−1·h−1 at ambient condition, 11 times higher than pristine g-CN. Meanwhile the thermophotocatalytic HER rate reached 260.2 μmol·g−1·h−1 at 55 °C. Photo-illumination led to the formation of C O bond between g-CN and NiO QDs to bridge photoelectron transport for low HER overpotential barriers and enhanced electrical conductivity. The higher thermophoto-induced HER can be ascribed to the increased electrical conductivity of NiO QDs-g-CN. This work underlines the importance of chemical binding in hetero-structures and quantum confinement effects in QDs-based composites, and it also demonstrates the thermal sensitivity effect in thermophotocatalytic HER process.