Abstract: Photoelectrochemical gas-phase solar water splitting represents a promising avenue for sustainable hydrogen production, fulfilling the energy demands of the future. In this work, we present the fabrication and optimization of the functional performance of visible-light active BiVO4/WO3 photoanodes with a tailored multi-layered structure. The photoanodes are manufactured in a reproducible way by an automated spray pyrolysis technique, including BiVO4 (top layer) and WO3 (bottom layer) in a multi-layered structure with different ratios (80:20; 50:50; 20:80). The photoactive surfaces are fully characterized and then evaluated in a divided filterpress reactor operated in continuous mode under visible light irradiation (100 mW cm? 2 ), where a platinized titanium plate is used as dark cathode. The results demonstrate the pivotal role of mass ratio in optimizing charge transfer kinetics and recombination rates in the photoanode. We demonstrate the synergistic effects between BiVO4 and WO3, elucidating their contributions to enhance light absorption, and reduce electron-hole recombination, determining an optimal ratio of 80:20 for both hydrogen production (155.7 ?mol m? 2 s ? 1 ) and on-off current density gap (0.66 mA cm? 2 ). The developed multi-layered BiVO4/WO3 surfaces thus offer a compelling pathway for advancing gas-phase photoelectrochemical water splitting technology, underscoring the significance of electrode design and paving the way for sustainable solar hydrogen production.

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