Vertical Growth of Two-Dimensional TiO2 Nanosheets Array Films and Enhanced Photoelectrochemical Properties Sensitized by CdS Quantum Dots

A Simple Fabrication of Sb2S3/TiO2 Photo-Anode with Long Wavelength Visible Light Absorption for Efficient Photoelectrochemical Water Oxidation

An Sb₂S₃-sensitized TiO₂ (Sb₂S₃/TiO₂) photo-anode (PA) exhibiting a high photo-electrochemical (PEC) performance in water oxidation has been successfully prepared by a simple chemical bath deposition (CBD) technique. Herein, the Raman spectra and XPS spectrum of Sb₂S₃/TiO₂ confirmed the formation of Sb₂S₃ on the TiO₂ coatings. The Sb₂S₃/TiO₂ photo-anode significantly shifted the absorption edge from 395 nm (3.10 eV) to 650 nm (1.90 eV). Furthermore, the Sb₂S₃/TiO₂ photo-anode generated a photo-anodic current under visible light irradiation below 650 nm due to the photo-electrochemical action compared with the TiO₂ photo-anode at 390 nm. The incident photon-to-current conversion efficiency (IPCE = 7.7%) at 400 nm and -0.3 V vs. Ag/AgCl was 37 times higher than that (0.21%) of the TiO₂ photo-anodes due to the low recombination rate and acceleration of the carriers of Sb₂S₃/TiO₂. Moreover, the photo-anodic current and photostability of the Sb₂S₃/TiO₂ photo-anodes improved via adding the Co²⁺ ions to the electrolyte solution during photo-electrocatalysis.

Crystal Facet Engineering of Photoelectrodes for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising approach for solar-driven hydrogen production with zero emissions, and it has been intensively studied over the past decades. However, the solar-to-hydrogen (STH) efficiencies of the current PEC systems are still far from the 10% target needed for practical application. The development of efficient photoelectrodes in PEC systems holds the key to achieving high STH efficiencies. In recent years, crystal facet engineering has emerged as an important strategy in designing efficient photoelectrodes for PEC water splitting, which has yet to be comprehensively reviewed and is the main focus of this article. After the Introduction, the second section of this review concisely introduces the mechanisms of crystal facet engineering. The subsequent section provides a snapshot of the unique facet-dependent properties of some semiconductor crystals including surface electronic structures, redox reaction sites, surface built-in electric fields, molecular adsorption, photoreaction activity, photocorrosion resistance, and electrical conductivity. Then, the methods for fabricating photoelectrodes with faceted semiconductor crystals are reviewed, with a focus on the preparation processes. In addition, the notable advantages of the crystal facet engineering of photoelectrodes in terms of light harvesting, charge separation and transfer, and surface reactions are critically discussed. This is followed by a systematic overview of the modification strategies of faceted photoelectrodes to further enhance the PEC performance. The last section summarizes the major challenges and some invigorating perspectives for future research on crystal facet engineered photoelectrodes, which are believed to play a vital role in promoting the development of this important research field.

Enhanced photoelectrochemical properties of nanocrystalline TiO2 electrode by surface sensitization with CuxO quantum dots

Nanoporous anatase TiO2 films were fabricated by a screen-printing method, and CuxO quantum dots (QDs) were deposited on the TiO2 films through successive ionic layer adsorption and reaction (SILAR). The amount of CuxO QDs on the TiO2 films are controlled by changing the number of SILAR cycles. The morphology, microstructure, optical, and photoelectrochemical properties of different CuxO sensitized TiO2 films (CuxO/TiO2) were investigated in detail. The nanoporous TiO2 film offers a large surface area for anchoring QDs. QD deposited samples exhibited a significant improvement in photoelectrochemical performance than the bare of TiO2. CuxO/TiO2, prepared with 7 SILAR cycles, showed the best photoelectrochemical properties, where the photocurrent density was enhanced to 500.01 μA/cm2 compared with 168.88 μA/cm2 of bare TiO2 under visible light. These results indicate that the designed CuxO/TiO2 structure possesses superior charge separation efficiency and photoelectrochemical properties.