Interface engineering of ZIF-67 decorated GdxBi1-xVO4/ByC3-yN4 dual S-scheme heterojunction for solar driven hydrogen production

Abstract

The deliberately modified BiVO₄/g-C₃N₄ heterojunction was prepared with B³⁺ and Gd³⁺ ions incorporated in g-C₃N₄ and BiVO₄ lattices, respectively. The Gd_xBi_1-xVO₄ nanoparticles were nucleated over the surface of B_yC_3-yN₄ sheets. The functionalized decoration of ZIF-67 over the surface led to augmented visible light absorption and facilitated adsorption of water molecules on the catalytic active sites. The configuration of band edge positions of individual catalysts prompted the formation of dual S-scheme heterojunction which promotes unidirectional flow of electrons. The formation of a dual S-scheme heterojunction enabled the composite to encompass wide range of redox potentials and retain stronger charge carriers at the band edges. The heterojunction presented a threefold enhanced photocurrent density when compared to raw samples. Scanning Kelvin probe measurements were done to understand the band bending and junction kinetics. It provided direct evidence for heterojunction formation and electron accumulation at the catalyst surface. Under direct sunlight, a maximum hydrogen production rate of 1993 µmol/h/g was obtained with an apparent quantum yield (AQE) of 2.25 %. Density functional theory calculations were employed to understand the distribution of energy states in individual catalyst material and their corresponding Fermi level positions were computed.