Anodic nanoporous WO₃ modified with Bi₂S₃ quantum dots as a photoanode for photoelectrochemical water splitting

Although anodic nanoporous (ANP) WO₃ has gained a lot of attention for photoelectrochemical water splitting (PEC-WS), there is still a lack of efficient WO₃-based photoanodes with sufficient light absorption and good e^-/h⁺ separation and transfer. The decoration of ANP WO₃ with narrow bandgap semiconductor quantum dots (QDs) can enhance charge carrier transfer while reducing their recombination, resulting in a high PEC efficiency. In this study, ANP WO₃ was synthesized via an anodic oxidation process and then modified with Bi₂S₃ QDs via successive ionic layer adsorption and reaction (SILAR) process and examined as a photoanode for PEC-WS under ultraviolet-visible illumination. The ANP WO₃ photoanode modified with ten cycles of Bi₂S₃ QDs demonstrated the highest current density of 16.28 mA cm^-2 at 0.95 V vs RHE, which is approximately 19 times that of pure ANP WO₃ (0.85 mA cm^-2). Furthermore, ANP WO₃/Bi₂S₃ QDs (10) photoanode demonstrated the highest photoconversion efficiency of 4.1 % at 0.66 V vs RHE, whereas pure ANP WO₃ demonstrated 0.3 % at 0.85 V vs RHE. This can be attributed to the proper number of Bi₂S₃ QDs significantly enhancing the visible light absorption, construction of type-II band alignment with WO_3, and improved charge separation and migration. The modification of ANP WO₃ with nontoxic Bi₂S₃ QDs as a prospective metal chalcogenide for enhancing visible light absorption and PEC-WS performance has not yet been investigated. Consequently, this study paves the path for a facile technique of designing effective photoelectrodes for PEC-WS.