Abstract
This study employs aerosol-assisted chemical vapor deposition (AACVD) to fabricate WO(3)/BiVO(4) heterojunction photoanodes with an inverted architecture (WO(3) atop BiVO(4)). The unique permeable nanofiber morphology of WO(3) provides a solution to enhance water oxidation performance. By correlating precursor volume (10-40 mL) and spatial position within the deposition chamber (inlet/mid/outlet) with film properties, we demonstrate that a midreactor position yields "grass-like" WO(3) nanofibers (diameter: 100-230 nm, length: 3.5-3.98 μm), enabling dual functionality: (i) > 50% light transmittance to the underlying BiVO(4) absorber, and (ii) electrolyte penetration into the heterointerface between WO(3) and BiVO(4). In contrast, rod-like WO(3) produced near the inlet causes severe light scattering, reducing the incident photon-to-current efficiency (IPCE) by six times above wavelengths of 350 nm. Optimized samples, produced with a deposition volume of 30 mL to deposit WO(3) atop of BiVO(4) positioned in the middle of the deposition chamber (i.e., WO(3)-30/BiVO(4)-mid), achieve a photocurrent density of 0.82 mA·cm(-2) at 1.23 V(RHE) under 1 sun irradiance, which is 121% higher than single-layer BiVO(4) (0.37 mA·cm(-2)) and exceeds some conventional WO(3)-under/BiVO(4) heterojunctions in which WO(3) is underneath BiVO(4). Transient absorption spectroscopy confirms prolonged carrier lifetimes in our unique heterostructure through improved charge-carrier separation. This work challenges current traditional heterojunction design rules for the WO(3)/BiVO(4) system by showcasing how permeable WO(3) nanostructures atop BiVO(4) photoanodes can improve light harvesting and facilitate charge-carrier separation to significantly improve activity.