Preparation of Visible Light-Active Dual-Layer Photoelectrode by Sputtering and Its Application in Hydrogen Production via Photocatalytic Water Splitting
Date Issued
2014
Date
2014
Author(s)
Liao, Chi-Hung
Abstract
Hydrogen is the ideal fuel for the future because it is clean, energy efficient and abundant in nature. Recently, solar hydrogen via photocatalytic water splitting has attracted tremendous attention due to its great potential for low-cost and clean hydrogen production. One of the technologies for improving the efficiency of photocatalytic water splitting is the adoption of an H-type reactor system that allows separate evolution of hydrogen and oxygen during the reaction, preventing the backward reaction to form water. The key components of an H-type reactor system are reactor, photoelectrode and proton exchange membrane. In this study, visible light-absorbing TiO2 (vis-TiO2) and WO3 (vis-WO3) thin films as the photoelectrode materials were prepared by radio-frequency magnetron sputtering at high temperature and used to carry out photocatalytic water splitting in an H-type reactor system. Instrumental analyses such as XRD, FESEM, AFM, EDS, XPS, and UV-Vis were performed to reveal the crystallinity, surface morphology, chemical composition, and light absorption of the prepared photocatalytic thin films. It is believed that the shift of the absorption spectra towards the visible-light region for the prepared thin films is resulted from the increase of their metal-to-oxygen ratio due to high-temperature sputtering. To further extend the light absorption spectrum of the photoelectrode, a dual-layer photocatalyst (DLP) that consists of both vis-TiO2 and vis-WO3 was prepared. The photoactivities of single-layer and dual-layer photocatalysts were examined first by photovoltammetry followed by conducting water-splitting reactions in an H-type reactor under both UV and visible-light irradiations. It was demonstrated that H2 and O2 yields obtained from water-splitting reaction are consistent with the photocurrent results (from photovoltammetry); showing that DLP is more active than single-layer photocatalyst. The enhanced performance of DLP comparing with single-layer photocatalyst is mainly attributed to the improved charge separation of the dual-layer structure. Later on, the effect of adding a thin layer of MgO on TiO2 was investigated. From the photocurrent measurement results, it was found that coating a very thin layer of MgO on TiO2 may have the benefit to improve TiO2’s photoactivity. Finally, MgO modified DLP was prepared and its photoactivity was demonstrated by carrying out water-splitting reaction in the H-type reactor system under visible-light irradiation. Comparing with DLP, the MgO modified DLP show improved H2 and O2 yield. It is believed that the improvement is resulted from the hygroscopic nature of MgO, which can increase the concentration of water molecules on the photocatalyst surface to perform water oxidation, consequently, reducing the probability of electron-hole recombination. Moreover, the inclusion of MgO may also suppress current leakage of the photoelectrode by preventing electrons from diffusing toward the TiO2-water interface.
Subjects
光催化
水分解
氫氣
SDGs
Type
thesis
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