Comparison of photocatalytic and transport properties of TiO₂ and ZnO nanostructures for solar-driven water splitting

Abstract

Titanium dioxide (TiO2) and zinc oxide (ZnO) nanostructures have been widely used as photo-catalysts due to their low-cost, high surface area, robustness, abundance and non-toxicity. In this work, four TiO2 and ZnO-based nanostructures, i.e. TiO2 nanoparticles (TiO2 NPs), TiO2 nanotubes (TiO2 NTs), ZnO nanowires (ZnO NWs) and ZnO@TiO2 core-shell structures, specifically prepared with a fixed thickness of about 1.5 μm, are compared for the solar-driven water splitting reaction, under AM1.5G simulated sunlight. Complete characterization of these photo-electrodes in their structural and photo-electrochemical properties was carried out. Both TiO2 NPs and NTs showed photo-current saturation reaching 0.02 and 0.12 mA cm(-2), respectively, for potential values of about 0.3 and 0.6 V vs. RHE. In contrast, the ZnO NWs and the ZnO@TiO2 core-shell samples evidence a linear increase of the photocurrent with the applied potential, reaching 0.45 and 0.63 mA cm(-2) at 1.7 V vs. RHE, respectively. However, under concentrated light conditions, the TiO2 NTs demonstrate a higher increase of the performance with respect to the ZnO@TiO2 core-shells. Such material-dependent behaviours are discussed in relation with the different charge transport mechanisms and interfacial reaction kinetics, which were investigated through electrochemical impedance spectroscopy. The role of key parameters such as electronic properties, specific surface area and photo-catalytic activity in the performance of these materials is discussed. Moreover, proper optimization strategies are analysed in view of increasing the efficiency of the best performing TiO2 and ZnO-based nanostructures, toward their practical application in a solar water splitting device.

Probing the charge recombination in rGO decorated mixed phase (anatase-rutile) TiO2 multi-leg nanotubes

“…However, the major bottle necks such as limited absorption of the visible light and higher recombination of the photo-generated charges are addressed through several strategies including doping, 4 decoration with metal and semiconductor nano-particles 5 and composite formation using other semiconductor materials. 6,7 In recent times, graphene and its derivatives (reduced graphene oxide-rGO) are also being investigated for improving the photo-catalytic/photovoltaic properties by forming composite with TiO 2 . [8][9][10] It is reported that excellent electronic conductivity of this 2D material helps in the separation of photo-generated charges which, in turn, improves the catalytic activities.…”

Photocatalytic Water Oxidation on ZnO: A Review

“…Despite possessing higher electron mobility, several studies have shown that ZnO demonstrated a lower photo-conversion efficiency compared to TiO 2 [17,18]. This observation has been attributed to the higher rate of recombination in ZnO compared to TiO 2 [17].…”

Studi Dinamika Molekular dan Kinetika Reaksi pada Pembelahan Molekul Air untuk Produksi Gas Hidrogen

“…Proses pembelahan air meliputi tiga tahapan utama; (a) absorpsi foton; (b) pemisahan dan migrasi pembawa muatan yang tereksitasi; dan (c) reaksi permukaan antara pembawa muatan dengan molekul air (2).…”