Role of g-C₃N₄ in Fabrication of BiVO₄/WO₃ Z-scheme Heterojunction for high Photoelectrochemical Performances with Enhanced Light Harvesting

Green technology such as harvesting solar light is a promising source for future energy supplies without generating any harmful environmental pollutions. We report a straightforward approach for improving the light harvesting properties of BiVO₄ photoanodes in order to enhance their photoelectrochemical performance. A facile sol–gel spin coating method was used to prepare the samples. The g-C₃N₄ powder was incorporated into the BiVO₄ precursor solution before being spin-coated onto fluorine-doped tin oxide glass. After annealing, a thin film of g-C₃N₄ modified BiVO₄ (CN-BiVO₄) was formed. A WO₃ film was coated onto CN-BiVO₄ (CN-BiVO₄/WO₃) to form a Z-scheme heterojunction and enhance the photoelectrochemical performance. The CN-BiVO₄ and CN-BiVO₄/WO₃ photoanodes outperformed unmodified photoanodes in terms of light harvesting and photoelectrochemical performance. The CN-BiVO₄/WO₃ had the highest light absorbance and photocurrent density (538 µA·cm^{− 2} at 1.23 V_RHE) and significantly enhanced resilience and stability (with a 35% decay for 1600 s) compared with unmodified electrodes. At 390 nm, the incident photon-to-current conversion efficiency was 14.8%, and the applied bias photon-to-current conversion efficiency was approximately 0.12% at 0.88 V_RHE. These findings reveal that the non-crystalline phases of CN-BiVO₄ grains help absorb and trap a broader range of wavelengths, thus improving photoelectrochemical performance.