Anion exchange and successive ionic layer adsorption and reaction-assisted coating of BiVO4 with Bi2S3 to produce nanostructured photoanode for enhanced photoelectrochemical water splitting

Photoelectrochemical water splitting is an environmentally benign way to store solar energy. Properties such as fast charge recombination and poor charge transport rate severely restrict the use of BiVO4 as a photoanode for photoelectrochemical water splitting and many attempts were made to improve the current performance limit of the photoanode. To address these disadvantages, a highly efficient BiVO4/Bi2S3 heterojunction was fabricated applying facial anion-exchange (AE) and successive ionic layer adsorption and reaction (SILAR). The deposition of Bi2S3 on BiVO4 nanoworms by both AE and SILAR was confirmed through morphological, structural, and optical analyses. The morphological analysis indicated that Bi2S3 grown through SILAR has relatively more crystalline-amorphous phase boundaries than Bi2S3 generated using the anion-exchange method. The highest photocurrent density was observed for the SILAR-coated Bi2S3 on BiVO4, which is three times the value of the pristine BiVO4 measured under 1 sun illumination (100 mW cm−2 with Air mass (AM) 1.5 filter) in a 0.5 M Na2SO4 electrolyte at 1.6 V vs. RHE. In addition, the deposition of Bi2S3 through AE results in a twofold higher photocurrent density compared to uncoated BiVO4. The comparison of the two cost-effective AE and SILAR methods to deposit Bi2S3 on BiVO4 showed a negative shift in the flat band Mott-Schottky values, which coincides with the drifted onset potential values of the current density-voltage (J–V) curve. Furthermore, photoelectrochemical impedance spectroscopy (PEIS) analyses and band alignment studies revealed that SILAR-grown Bi2S3 creates an effective heterojunction with BiVO4, which leads to an efficient charge transfer.