Key Takeaways & Executive Findings
- •• First demonstration of a gradient distributed oxygen vacancies (GOV) strategy to promote hole transport within FeOOH. • Clearly monitoring and verifying the progressive upward shift of the valence band within the shallow surface of FeOOH-GOV for enhancing holes transport capability. • Setting new photoelectrochemical activity and stability benchmarks of FeOOH based-BiVO4 photoanodes. • Achieving a photocurrent density of 5.37 mA cm−2 and operational stability up to 160 h at 1.23 VRHE.
Abstract
Highly active and stable FeOOH cocatalysts are essential for achieving optimal performance of BiVO4 (BVO) photoanodes. Despite offering remarkable structural stability, widely used thick FeOOH cocatalysts often suffer from insufficient hole transport capability, which hinders the overall activity. The present study demonstrates that a simple photoetching strategy is able to introduce gradient distributed oxygen vacancies (GOV) in the thick FeOOH layer and significantly enhances the photogenerated holes transport dynamics. The incorporation of GOV within FeOOH not only realizes the “relay transport” of photogenerated hole through the progressive upward shift of the valence band in the spatial distribution, but also provides abundant oxidation active sites by efficient hole trapping. These improvements effectively improve the oxygen evolution reaction (OER) activities and mitigate photocorrosion by the instantaneous hole extraction. Consequently, the FeOOH-GOV layer enables the BVO/FeOOH-GOV photoanode to achieve an impressive photocurrent density of 5.37 mA cm−2 and a robust operational stability up to 160 h at 1.23 VRHE, setting new benchmarks for current density and stability in FeOOH-based BVO photoanodes. This work provides an effective avenue to optimize OER cocatalysts for constructing highly efficient and stable photoelectrochemical water splitting devices.
1. Introduction
H2 production via photoelectrochemical (PEC) water splitting has been regarded as a promising approach for converting solar energy into sustainable clean fuel [1, 2]. The design of the suitable semiconductor photoanodes with efficient charge carrier transport and high surface oxidation reactivity is essential for practical PEC device [3, 4]. The bismuth vanadate (BiVO4, BVO) is notable among photoanode materials due to its narrow band gap (2.4 eV), suitable band edge positions, and high chemical stability. However, its solar energy conversion potential remains limited by severe carrier recombination, sluggish water oxidation kinetics, and susceptibility to photocorrosion [3, 5, 6]. Therefore, various modification strategies have been explored to overcome these challenges, including hetero-construction [7–10], nanostructuring [11], nanocrystal embedding [12], and defects engineering [13–16]. However, these methods have not yet fully resolved the sluggish water oxidation kinetics on the BVO surface, which is critical for achieving high solar conversion efficiency.
Coupling BVO with ultrathin iron oxyhydroxide (FeOOH) is a widely adopted strategy to enhance the PEC activity of BVO photoanodes [17–20]. As an oxygen evolution catalyst (OEC), FeOOH effectively extracts the photogenerated holes from the BVO surface, accelerating water oxidation with a reduced overpotential [18–21]. With the intensive efforts devoted to engineer FeOOH OEC in BVO photoanodes, such as crystalline phase control [19, 20], defects modulating [19, 22, 23], and heterogeneous atom doping [24, 25], the photocurrent density has reached a notable benchmark value as high as 5.2 mA cm−2 at 1.23 VRHE [19], while this high PEC activity of BVO photoanodes coupled with ultrathin FeOOH is unfortunately obtained at the expense of stability. This limited stability is primarily attributed to the generally employed ultrathin FeOOH layer that is intrinsically favors for holes transport but with the awkward feature of structural instability at high anodic potential (Fig. S1A). Therefore, creating efficient and stable BVO photoanodes requires precise control over the coupled OEC thickness for a better balance of the oxygen evolution reaction (OER) activity and durability [26, 27]. A recent study revealed that increasing OEC layer thickness to over 10 nm result
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Shiyuan Wang, Mengjia Jiao, Qian Ye, Jie Jian, Fan Li, Guirong Su, Lu Zhang, Ziying Zhang, Zelin Ma, Jiulong Wang, Yazhou Shuang, Fang Wang, Yalong Song, Lichao Jia, Hongqiang Wang (2026). FeOOH Cocatalysts with Gradient Oxygen Vacancy Distribution Enabling Efficient and Stable BiVO4 Photoanodes. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01987-8
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Frequently Asked Questions
What is the main innovation of this study?
The study introduces a gradient distributed oxygen vacancies (GOV) strategy in thick FeOOH cocatalysts via a simple photoetching method, which significantly enhances hole transport and stability of BiVO4 photoanodes.
How does the gradient oxygen vacancy distribution improve performance?
The GOV creates a progressive upward shift of the valence band, enabling 'relay transport' of photogenerated holes and providing abundant oxidation active sites, thus improving OER activity and mitigating photocorrosion.
What are the key performance benchmarks achieved?
The BVO/FeOOH-GOV photoanode achieves a photocurrent density of 5.37 mA cm−2 and operational stability up to 160 hours at 1.23 VRHE, setting new records for FeOOH-based BiVO4 photoanodes.
Why is the stability of FeOOH cocatalysts important?
Stability is crucial for practical PEC water splitting. Thick FeOOH layers offer structural stability but suffer from poor hole transport; the GOV strategy balances both, enabling long-term operation without significant performance loss.
What is the significance of this work for solar fuel production?
This work provides an effective avenue to optimize OER cocatalysts, which is essential for constructing highly efficient and stable photoelectrochemical water splitting devices, advancing solar-to-hydrogen conversion.
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