PbS Quantum Dots-Decorated BiVO₄ Photoanodes for Highly Efficient Photoelectrochemical Hydrogen Production

While metal oxides such as TiO₂, Fe₂O₃, WO₃, and BiVO₄ have been previously studied for their potential as photoanodes in photoelectrochemical (PEC) hydrogen production, their relatively wide band-gap limits their photocurrent, making them unsuitable for the efficient utilization of incident visible light. To overcome this limitation, we propose a new approach for highly efficient PEC hydrogen production based on a novel photoanode composed of BiVO₄/PbS quantum dots (QDs). Crystallized monoclinic BiVO₄ films were prepared via a typical electrodeposition process, followed by the deposition of PbS QDs using a successive ionic layer adsorption and reaction (SILAR) method to form a p-n heterojunction. This is the first time that narrow band-gap QDs were applied to sensitize a BiVO₄ photoelectrode. The PbS QDs were uniformly coated on the surface of nanoporous BiVO₄, and their optical band-gap was reduced by increasing the number of SILAR cycles. However, this did not affect the crystal structure and optical properties of the BiVO₄. By decorating the surface of BiVO₄ with PbS QDs, the photocurrent was increased from 2.92 to 4.88 mA/cm² (at 1.23 V_RHE) for PEC hydrogen production, resulting from the enhanced light-harvesting capability arising from the narrow band-gap of the PbS QDs. Moreover, the introduction of a ZnS overlayer on the BiVO₄/PbS QDs further improved the photocurrent to 5.19 mA/cm², attributed to the reduction in interfacial charge recombination.