Engineering advanced BiVO 4 photoanodes for efficient photoelectrochemical water and ethylene glycol oxidation Htoo Thiri Htet 1,2,3 , Vishal Kakkarakunnel Jose* 1,2,3 , Bart Vermang 1,2,3 1 Hasselt University, Imo-imomec, Martelarenlaan 42, 3500 Hasselt, Belgium, 2 Imec, Imo-imomec, Thor Park 8320, 3600 Genk, Belgium, 3 EnergyVille, Imo-imomec, Thor Park 8320, 3600 Genk, Belgium Bismuth vanadate (BiVO 4 ) is a leading photoanode material for solar-driven water splitting due to its visible-light absorption and stability in alkaline media, though its performance is limited by poor charge transport and slow oxygen evolution kinetics. In this study, we developed advanced BiVO 4 photoanodes by integrating a NiO hole transport layer and a FeOOH co-catalyst to enhance charge separation and catalytic efficiency. BiVO 4 thin films were synthesized via spin-coating with optimized parameters for nanoporous morphology, high crystallinity, and strong light absorption. NiO layer was deposited by reactive sputtering to improve interfacial charge extraction and provide a stable scaffold for FeOOH, which was electrodeposited to accelerate oxygen evolution. We fabricated four configurations: pristine BiVO 4 (BVO), NiO/BVO, FeOOH/BVO, and FeOOH/NiO/BVO and evaluated them by XRD, FESEM, and photoelectrochemical testing under AM 1.5G illumination (100 mW cm -2 ). PEC measurements were conducted in 1 M KBi buffer for water oxidation and in a mixed electrolyte with 10 vol% ethylene glycols (EG) for organic oxidation. FeOOH/BVO and FeOOH/NiO/BVO achieved photocurrent densities of ~2.3 and ~1.8 mA cm -2 at 1.23 V RHE for water oxidation, around eightfold and sixfold higher than pristine BVO, confirming improved interfacial charge transport and catalytic performance. For EG oxidation, pristine BVO yielded the highest photocurrent (~3.5 mA cm -2 ), suggesting possible competing catalytically active sites on unmodified sample. All photoanodes exhibited higher photocurrents for EG oxidation than for water, highlighting the kinetic favorability of organic oxidation. These results emphasize the importance of interfacial engineering and requirement of further detailed surface analysis to attain optimized PEC performance. Building on this platform, the high-performing BVO photoanode was be integrated with a halide perovskite photovoltaic absorber to construct an artificial leaf device for unassisted solar fuel production. This monolithic tandem system is also designed to couple solar energy harvesting with selective oxidation reactions, aiming for high solar-to-fuel conversion efficiency. References 1. Chu, S. et al. Advanced Energy Materials vol. 12 (2022). 2. Huang, Z. F., et al. A review on recent progress. Nanoscale vol. 6 14044 (2014).
3. Shim, S. G. et al. Chemical Engineering Journal 430, (2022). 4. Chen, D., et al. Energy and Fuels vol. 36 9932–9949 (2022).
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