Electrosprayed heterojunction WO₃/BiVO₄ films with nanotextured pillar structure for enhanced photoelectrochemical water splitting

We demonstrate that the addition of a tungsten oxide (WO₃) layer beneath a bismuth vanadate (BiVO₄) photocatalyst layer with a nanotextured pillar morphology significantly increases the photocurrent density in photoelectrochemical water splitting. The WO₃-BiVO₄ bilayer films produced a photocurrent of up to 3.3 mA/cm² under illumination at 100 mW/cm² (AM1.5 spectrum). The bilayer film was characterized by scanning electron microscopy, X-ray diffraction, and photoelectrochemical methods, which confirmed the superiority of the bilayer film in terms of its morphology and charge separation and transport ability. Both WO₃ and BiVO₄ were deposited by electrostatic spraying under open-air conditions, which resulted in nanotextured pillars of BiVO₄ atop a smooth WO₃ film. The optimal coating conditions are also reported.