Fabrication Of BiVO₄ And TiO₂ For Photoelectrochemical Application

With the rapid development of social economy, the non-renewable energy such as coal, oil,natural gas has been consuming, energy shortage has become a global problem. Many countries are looking for new energy to protect environment and promote development. Among the various approaches pursued by the scientific community, photoelectrochemical water splitting has been considered to be one of the most promising methods for producing H2 fuel from solar energy and water since the pioneering work by Fujishima and Honda using TiO₂ as a photocatalyst. It is very important that prepared photocatalyst materials with high chemical propertie.BiVO₄ and TiO₂ which has attracted more and more attention as semiconductor catalyst because of their low cost and high photoelectrochemical performance.In the second part of this paper, the monoclinic BiVO₄ film was prepared in an aqueous medium with the assistance of a BiVO₄ seed layer. In order to improve the photochemical properties of monoclinic bismuth vanadate films in the process of oxygen evolution, we had taken these measuers（a） electrochemical reduction at a bias of-1.0 V vs. SCE（b） joined NaBH4 and electrochemical reduction at a bias of-1.0 V vs. SCE. The samples were characterized by means of SEM, XRD, UV-vis, XPS, EIS and so on. The photocurrent response of the BiVO₄ film under visible light illumination was tested to evaluate photochemical performance.A photocurrent as high as 2.3 mA cm-2at a bias of 1.0 V vs. SCE can be achieved under visible light illumination（λ > 420 nm）. The bismuth vanadate films we treated by electrochemical reduction and NaBH4 reduction.To the best of our knowledge,the value is the largest photocurrent of monoclinic BiVO₄ under visible light illumination.The increased photoelectrochemical performance for the reduced Bi VO₄ is found to be a result of the increased carrier concentration via self-doping of V4+, which promotes the separation of photo-generated electron–hole pairs.In the third part of this paper, a facile hydrothermal method using Ti（OC4H9）4 as raw material was developed for growing highly oriented, crystalline anatase TiO₂ nanorods on transparent conducting substrates. The phase and morphology of the TiO₂ nanocrystals can be controlled by tuning the pH and molar ratio of [Cl-] to [SO₄2-].The samples were characterized by means of SEM, XRD, UV-vis, XPS, EIS and so on. In order to further improve the photochemical performance under visible light illumination, the TiO₂ films we treated by electrochemical reduction.By testing the photoelectrochemical performance of samples grown under different conditions, we found that oriented anatase nanorod films exhibited the highest photocurrent, which was a consequence of the low defect density of the nanocrystals in the films. A photocurrent density of 1.2 mA?cm-2 at 1.25 V vs RHE was obtained by self-doping with Ti3+via electrochemical reduction. IPCE measurements show that the enhancement of photocurrent is due to the improved photoactivity in the UV region, as a result of the increased concentration of free carriers. These anatase TiO₂ nanorod films could serve as important materials for photoelectrochemical and photovoltaic devices in the near future.