Green Hydrogen Production via Photoelectrochemical Water Splitting with BiVO₄/WO₃ Heterojunction Photoanodes

Elena Vasquez1, Wei Sun2, Marcus Hoffmann3
1 Department of Chemical Engineering, Delft University of Technology, 2629 HZ Delft, Netherlands
2 Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, CAS, Beijing 100190, China
3 Helmholtz Institute Erlangen-Nürnberg for Renewable Energy, 91058 Erlangen, Germany
Published: 2026-05-02 · IJEER Vol. 1, No. 1 (2026)

Abstract

Photoelectrochemical (PEC) water splitting offers a direct route to green hydrogen production using solar energy, but practical photoanodes suffer from poor charge separation and limited photostability. We report a BiVO₄/WO₃ type-II heterojunction photoanode fabricated by pulsed laser deposition and post-annealing, achieving a photocurrent density of 4.82 mA/cm² at 1.23 V vs. RHE under AM 1.5G illumination — a 2.3× improvement over bare BiVO₄. Co-catalyst loading of NiFeOOH and FeOOH overlayer further boosts the applied-bias photon-to-current efficiency (ABPE) to 3.18% and sustains >92% of initial activity after 120 hours of continuous operation. In situ spectroscopy confirms that the WO₃ underlayer promotes hole extraction and suppresses surface recombination at the BiVO₄/electrolyte interface.

Keywords: green hydrogen, photoelectrochemical water splitting, BiVO4, heterojunction photoanode, solar fuels

1. Introduction

Green hydrogen produced from renewable electricity or direct solar conversion is central to decarbonizing heavy industry, long-haul transport, and seasonal energy storage. Among solar-driven routes, photoelectrochemical (PEC) water splitting integrates light absorption and electrolysis in a single device, potentially lowering system complexity relative to photovoltaic-electrolyzer tandem configurations. Bismuth vanadate (BiVO₄) is a leading photoanode candidate due to its visible-light bandgap (~2.4 eV) and favorable valence band position for oxygen evolution, yet bulk electron transport and surface recombination limit its performance.

2. Photoanode Fabrication and Characterization

BiVO₄/WO₃ heterojunction films were deposited on FTO substrates by sequential pulsed laser deposition (PLD) of WO₃ (50 nm) and BiVO₄ (300 nm), followed by annealing at 450°C in air. Structural analysis confirmed monoclinic scheelite BiVO₄ and monoclinic WO₃ with a sharp interface. Mott-Schottky analysis revealed n-type behavior for both layers with a type-II band alignment that drives photogenerated holes toward the BiVO₄ surface.

Table 1. PEC performance comparison of photoanode configurations at 1.23 V vs. RHE under AM 1.5G (100 mW/cm²)

PhotoanodeJph (mA/cm²)Onset (V vs. RHE)ABPE (%)Stability (120 h, %)
BiVO₄2.100.420.8568
WO₃/BiVO₄3.650.382.0585
BiVO₄/WO₃4.820.352.7891
BiVO₄/WO₃ + NiFeOOH5.150.323.1892

3. Results and Discussion

The BiVO₄/WO₃ heterojunction exhibits significantly enhanced charge separation efficiency (η_sep = 78%) compared to single-layer BiVO₄ (η_sep = 41%), as quantified by intensity-modulated photocurrent spectroscopy. Figure 1 shows the wavelength-dependent incident photon-to-current efficiency (IPCE), with the heterojunction maintaining >45% IPCE between 400-500 nm. Figure 2 tracks hydrogen evolution rate over 120 hours of continuous PEC operation in a two-compartment cell with a Pt cathode.

518.331.544.858BiVO₄BiVO₄/WO₃BiVO₄/WO₃ + NiFeOOH350400450500550600Wavelength (nm)IPCE (%)
Figure 1. IPCE spectra of BiVO₄, WO₃/BiVO₄, and BiVO₄/WO₃ heterojunction photoanodes with and without NiFeOOH co-catalyst
020.641.261.882.4024487296120Operation Time (hours)H₂ Evolved (mmol/cm²)
Figure 2. Cumulative H₂ evolution and Faradaic efficiency during 120-hour stability test at 1.23 V vs. RHE

4. Conclusions

The BiVO₄/WO₃ type-II heterojunction photoanode demonstrates that strategic band engineering can overcome key limitations of metal oxide photoanodes for PEC water splitting. Combined with earth-abundant NiFeOOH co-catalysts, the system achieves competitive ABPE and operational stability, advancing the feasibility of direct solar-to-hydrogen conversion for distributed green hydrogen production.

References

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