Effective silicon nanowire arrays/WO3 core/shell photoelectrode for neutral pH water splitting

Recent Advances in Self-Supported Semiconductor Heterojunction Nanoarrays as Efficient Photoanodes for Photoelectrochemical Water Splitting

Growth of semiconductor heterojunction nanoarrays directly on conductive substrates represents a promising strategy toward high-performance photoelectrodes for photoelectrochemical (PEC) water splitting. By controlling the growth conditions, heterojunction nanoarrays with different morphologies and semiconductor components can be fabricated, resulting in greatly enhanced light-absorption properties, stabilities, and PEC activities. Herein, recent progress in the development of self-supported heterostructured semiconductor nanoarrays as efficient photoanode catalysts for water oxidation is reviewed. Synthetic methods for the fabrication of heterojunction nanoarrays with specific compositions and structures are first discussed, including templating methods, wet chemical syntheses, electrochemical approaches and chemical vapor deposition (CVD) methods. Then, various heterojunction nanoarrays that have been reported in recent years based on particular core semiconductor scaffolds (e.g., TiO₂ , ZnO, WO₃ , Fe₂ O₃ , etc.) are summarized, placing strong emphasis on the synergies generated at the interface between the semiconductor components that can favorably boost PEC water oxidation. Whilst strong progress has been made in recent years to enhance the visible-light responsiveness, photon-to-O₂ conversion efficiency and stability of photoanodes based on heterojunction nanoarrays, further advancements in all these areas are needed for PEC water splitting to gain any traction alongside photovoltaic-electrochemical (PV-EC) systems as a viable and cost-effective route toward the hydrogen economy.

Fabrication of spherical porous pAg2O-nWO3/Ag/GNS heterostructure with enhanced photocatalytic activity through plasmonic S-scheme mechanism and its complementing biological interest

The synthesis and characterization of Ag₂OWO₃/Ag/GNS heterostructure with desired modifications has been elucidated in the contemporary study. The fabrication involves a simple hydrothermal method for the configuration of fascinating heterostructures intended to photo-catalytically degrade Eosin Yellow (EY) dye. The toxic dye molecules were converted into non-toxic molecular intermediates, also the elimination of heavy metals from industrial wastewater, being trapped in the pores of heterostructure. The pn junction photocatalyst with plasmonic resonance of Ag for abolition of electron and hole coupling, enhances the photo-response where the catalyst abides S-Scheme mechanism. The work functions of active photocatalysts as calculated for Ag₂O is 6.61eV and WO₃ is 6.04eV. Furthermore, the Ag₂OWO₃/Ag/GNS photocatalysts recovery and reuse in several trials without any noticeable loss of photocatalytic activity, complimented the recyclability of the heterostructure. To ensure the safety of the environment on heterostructure being released, toxicity analysis were carried out. These Ag₂OWO₃/Ag/GNS heterostructures had optimistic result on cytotoxicity assay, and on Musmusculus skin melanoma cells (B16-F10), with anti-microbial/fungal properties. Thereby, the contemporary experiment upholds efficient photocatalysis and ropes multiple errands on biological applications.

Enhanced photoelectrochemical performance of NaNbO3 nanofiber photoanodes coupled with visible light active g-C3N4 nanosheets for water splitting

Sodium niobate nanofibers (NaNbO₃-NF) have been synthesized using a hydrothermal technique and further coupled with visible light responsive graphitic carbon nitride (g-C₃N₄) nanosheets in different concentration ratios of 2:1 (2-CN), 4:1 (4-CN) and 8:1 (8-CN). A significant improvement in the photoelectrochemical (PEC) performance of the g-C₃N₄/NaNbO₃-NF (4-CN) nanostructured photoanode compared to the bare NaNbO₃ photoanode is observed. A current density of 12.55 mA cm^-2 at 1 V with respect to the Ag/AgCl reference electrode is achieved for the g-C₃N₄/NaNbO₃-NF (4-CN) photoanode, which is ∼3 times higher than the NaNbO₃-NF photoanode. Also, compared to NaNbO₃-NF, the g-C₃N₄/NaNbO₃-NF (4-CN) nanocomposite photoanode showed ∼3 times improvement in the incident photon-to-current conversion efficiency. The improvement in the PEC performance of visible light active g-C₃N₄/NaNbO₃-NF (4-CN) nanocomposite is attributed to the improved photoresponse of NaNbO₃-NF due to the coupling of g-C₃N₄ and the formation of a type-II heterojunction between them leading to the enhanced separation of the photogenerated charge carriers. A possible reaction mechanism for the improved PEC water splitting performance has been proposed for the g-C₃N₄/NaNbO₃-NF (4-CN) photoanode.

Tungsten oxide nanostructures and nanocomposites for photoelectrochemical water splitting

Hydrogen production from photoelectrochemical (PEC) water splitting using semiconductor photocatalysts has attracted great attention to realize clean and renewable energy from solar energy. The visible light response of WO3 with a long hole diffusion length (∼150 nm) and good electron mobility (∼12 cm2 V-1 s-1) makes it suitable as the photoanode. However, WO3 suffers from issues including rapid recombination of photoexcited electron-hole pairs, photo-corrosion during the photocatalytic process due to the formation of peroxo-species, sluggish kinetics of photogenerated holes, and slow charge transfer at the semiconductor/electrolyte interface. This work highlights the approaches to overcome these drawbacks of WO3 photoanodes, including: (i) the manipulation of nanostructured WO3 photoanodes to decrease the nanoparticle size to promote hole migration to the WO3/electrolyte interface which benefits the charge separation; (ii) doping or introducing oxygen vacancies to improve electrical conductivity; exposing high energy crystal surfaces to promote the consumption of photogenerated holes on the high-active crystal face, thereby suppressing the recombination of photogenerated electrons and holes; (iii) decorating with co-catalysts to reduce the overpotential which inhibits the formation of peroxo-species; (iv) other methods such as coupling with narrow band semiconductors to accelerate the charge separation and controlling the crystal phase via annealing to reduce defects. These approaches are reviewed with detailed examples.