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 WO3, 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.