Photoelectrochemical water splitting and gas ionisation sensing using metal oxide nanostructures

摘要

Energy harvesting directly from sunlight has attracted tremendous attention owing to its great potential for low-cost and clean hydrogen production. However, the current photoconversion efficiency from nanostructured metal oxides remains low due to a number of factors, such as low surface area, limited light absorption, poor electron mobility and high electron-hole recombination. In this research, a number of approaches have been carried out to overcome these difficulties.ududFirstly, changing the morphology of nanomaterials will help to increase the effective surface area of the photoanodes. ZnO nanotubes were prepared and the photoelectrochemical measurements revealed an efficiency of 3 times higher than their nanorod counterparts. In addition, the combination of ZnO nanorods with a 3D metal substrate, stainless steel mesh, showed a further enhancement in the water splitting efficiency by two-fold when compared with that on a planar substrate.ududSecondly, the hybridisation of two different metal oxides was studied by creating a heterojunction to improve the charge separation, extending the light absorption and increasing the total surface area of the electrode. In this work, both urchin-like ZnO nanorod arrays on TiO2 hollow hemispheres and 1D BiVO4/ZnO nanorod films displayed synergistic enhancement in photoelectrochemical water splitting efficiency.ududThirdly, doped ZnO nanostructures with different optical and/or electrical properties were tailored for photoelectrochemical water splitting and gas ionisation sensing applications. The photoelectrochemical water splitting performances of the doped ZnO nanostructures was improved by at least 27% due to increased light absorption. Conductive Y-doped ZnO nanorods were prepared and applied in gas ionisation sensor application. The measurements revealed that both the selectivity and sensitivity of Y-doped ZnO nanorods were enhanced with respect to undoped ZnO nanorods. Furthermore, the effect of UV illumination on gas sensitivity was also investigated.ududIn summary, different approaches and namomaterials have been adapted and demonstrated in this thesis, for the design of specific photoanodes/electrodes for specific applications.