Scaling up BiVO4 Photoanodes on Porous Ti Transport Layers for Solar Hydrogen Production

Commercialization of photoelectrochemical (PEC) water-splitting devices requires the development of large-area, low-cost photoanodes with high efficiency and photostability. Herein, we address these challenges by using scalable fabrication techniques and porous transport layer (PTLs) electrode supports. We demonstrate the deposition of W-doped BiVO4 on Ti PTLs using successive-ionic-layer-adsorption-and-reaction methods followed by boron treatment and chemical bath deposition of NiFeOOH co-catalyst. The use of PTLs that facilitate efficient mass and charge transfer allowed the scaling of the photoanodes (100 cm2 ) while maintaining ~90 % of the performance obtained with 1 cm2 photoanodes for oxygen evolution reaction, that is, 2.10 mA cm-2 at 1.23 V vs. RHE. This is the highest reported performance to date. Integration with a polycrystalline Si PV cell leads to bias-free water splitting with a stable photocurrent of 208 mA for 6 h and 2.2 % solar-to-hydrogen efficiency. Our findings highlight the importance of photoelectrode design towards scalable PEC device development.

Enhanced Photoredox Activity of BiVO4/Prussian Blue Nanocomposites for Efficient Pollutant Removal from Aqueous Media under Low-Cost LEDs Illumination

Bismuth vanadate (BiVO4, BV) is a widely explored photocatalyst for photo(electro)chemical applications, but its full photocatalytic potential is hindered by the fast recombination and low mobility of photogenerated charge carriers. Herein, we propose the photodeposition of different amounts of Prussian blue (PB) cocatalysts on the surface of monoclinic BV to obtain BV-PB composite photocatalysts with increased photoactivity. The as-prepared BV and BV-PB composites were characterized by an array of analytic techniques such scanning eletron microscopy (SEM), transmission eletron microscopy (TEM), X-day diffraction (XRD), and spectroscopic techniques including Fourier-transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS), photoluminescence (PL), and Raman spectroscopy. The addition of PB not only increases the absorption of visible light, as indicated by DRS, but also improves the charge carriers’ transfer across the photocatalysts/solution interface and hence reduces electron-hole (e−-h+) recombination, as confirmed by EIS and PL measurements. Resultantly, the BV-PB composite photocatalysts with optimum PB loading exhibited enhanced Cr(VI) photoreduction efficiency as compared to pristine BV under visible light illumination from low-power blue light-emitting diodes (LEDs), thanks to the cocatalyst role of PB which mediates the transfer of photoexcited conduction band (CB) electrons from BV to Cr(VI) species in solution. Moreover, as compared to pristine BV and BV + H2O2, a drastic increase in the methylene blue (MB) photo-oxidation efficiency was observed for BV-PB in the presence of a minute quantity of H2O2 due to a synergic effect between the photocatalytic and Fenton-like processes. While pure BV photodegraded around 70% of MB dye within 120 min, the BV-PB/H2O2 and BV/H2O2 system could degrade almost 100% of the dye within 20 min (kobs. = 0.375 min−1) and 40 min (kobs. = 0.055 min−1), respectively. The practical approach employed in this work may pioneer new prospects for synthesizing new BV-based photocatalytic systems with low production costs and high photoredox efficiencies.

The role of crystal facets and disorder on photo-electrosynthesis

Photoelectrochemistry has the potential to play a crucial role in the storage of solar energy and the realisation of a circular economy. From a chemical viewpoint, achieving high conversion efficiencies requires subtle control of the catalyst surface and its interaction with the electrolyte. Traditionally, such control has been hard to achieve in the complex multinary oxides used in PEC devices and consequently the mechanisms by which surface exposed facets influence light-driven catalysts are poorly understood. Yet, this understanding is critical to further improve conversion yields and fine-tune reaction selectivities. Here, we review the impact that crystal facets and disorder have on photoelectrochemical reactivity. In particular, we discuss how the crystal orientation influences the energetics of the surface, the existence of defects and the transport of reactive charges, ultimately dictating the PEC activity. Moreover, we evaluate how facet stability dictates the tendency of the solid to undergo reconstructions during catalytic processes and highlight the experimental and computational challenges that must be overcome to characterise the role of the exposed facets and disorder in catalytic performance.

Development and Functionalization of Visible-Light-Driven Water-Splitting Photocatalysts

With global warming and the depletion of fossil resources, our fossil fuel-dependent society is expected to shift to one that instead uses hydrogen (H₂) as a clean and renewable energy. To realize this, the photocatalytic water-splitting reaction, which produces H₂ from water and solar energy through photocatalysis, has attracted much attention. However, for practical use, the functionality of water-splitting photocatalysts must be further improved to efficiently absorb visible (Vis) light, which accounts for the majority of sunlight. Considering the mechanism of water-splitting photocatalysis, researchers in the various fields must be employed in this type of study to achieve this. However, for researchers in fields other than catalytic chemistry, ceramic (semiconductor) materials chemistry, and electrochemistry to participate in this field, new reviews that summarize previous reports on water-splitting photocatalysis seem to be needed. Therefore, in this review, we summarize recent studies on the development and functionalization of Vis-light-driven water-splitting photocatalysts. Through this summary, we aim to share current technology and future challenges with readers in the various fields and help expedite the practical application of Vis-light-driven water-splitting photocatalysts.