No abstract

WO 3 mesoporous films were prepared using a sol-gel method to serve as the photoanode for water cleavage in a 1 M HClO 4 solution with Pt as the counter electrode. Post-treatment of the as-synthesized WO 3 film with methanol and ethanol vapors, especially with methanol, improves the photocurrent during photoelectrolysis of water. Water and hexane vapors have a deleterious influence on the WO 3 film. Scanning electron microscopy and X-ray diffraction analyses showed that treatment with methanol vapors did not alter the configuration of the nanocrystalline framework or the WO 3 mesoscopic structure. Optical absorption and W L 3 -edge X-ray absorption near-edge structural analyses also revealed that the W-ion electronic and oxidation states remained unchanged after methanol treatment. However, extended X-ray absorption fine structure analysis of the W L 3 -edge showed that the coordination number of W 6+ sites in the WO 3 film significantly increased with the methanol treatment, indicating a corresponding decrease in the defect-state density of the film. The observed increase in the coordination number resulted in a 25% increase in the electron transit rate of the WO 3 film and enhanced solar energy conversion by 32% for the photoelectrolysis of water. We conclude that post-treatment with methanol vapor remedies the defect region in nanocrystalline WO 3 films, and improves the film's electron transport performance in a photoelectrochemical cell.Scheme 1 Processes of charge transport, back transfer, and chemical interaction in a photoelectrochemical cell for water cleavage. The n-type semiconducting photoanode is positively biased for generation of O 2 gas, with corresponding H 2 gas generation on the counter electrode. V CB , V VB , V FB , and E F represent the conduction-band, valence-band, flatband, and Fermi-energy levels of the electrodes.

We demonstrate a high-performance photoanode composed of a nanoporous TiO2 film co-sensitized with CuInS2 quantum dots (QDs) and CdS polycrystalline layers, exhibiting the excellent performance in both photosynthetic and photovoltaic applications. The CuInS2 QDs are synthesized via a solvothermal route and the average particle size is 3.5 nm, attached on TiO2 surface by assistance of bifunctional linker. The subsequent CdS layers are coated using successive ionic layer adsorption and reaction. The back reaction of interfacial charge recombination can be prohibited by the CdS coating. Besides, the CdS shell coating results in remission of the quantum confinement of the QDs, leading to a widening of optical absorption spectra. In a photosynthetic photoelectrochemical cell, this heterostructural electrode exhibits a saturated photocurrent of 16 mA cm-2 under illumination of AM 1.5G at full sun intensity. On the other hand, this high-performance photoanode exhibits a power conversion efficiency of 4.08% in a sandwich-type quantum dot sensitized solar cells (QDSSCs) using CuS as counter electrode. The superior performance is mainly ascribed to the extension of the absorption spectra and significant enhancement of charge separation via CdS coating.