Photocatalytic water splitting has attracted significant interest in recent decades as it offers a clean and environmentally friendly route for the production of hydrogen. A key challenge remains the development of systems that employ abundant, non-toxic and inexpensive materials to dissociate water efficiently using sunlight. Titanium dioxide (TiO2), tungsten trioxide (WO3) and hematite (α-Fe2O3) are among the most studied photoanodes employed during water splitting because of the position of their valence band which is suitable for oxidising water to oxygen, and their low costs. However reported efficiencies for these materials are below the reported theoretical maximum values. A good understanding of the factors that are limiting the efficiency of these photoanodes is therefore desirable if improvements in the photocatalytic activity are to be achieved. This thesis is divided in four main sections. Chapters 3 and 4 describe transient absorption spectroscopy (TAS) studies in the microsecond-second timescales carried out on WO3 photoelectrodes and TiO2 nanowires respectively. TAS has been employed to follow the charge carriers dynamics in WO3 highlighting the presence of relatively long-lived holes (30 ms), which have been described as a requirement for the water oxidation reaction to take place. The electrons also appear to be long-lived (0.1 s), and this has been proposed to be due to slow electron transport through the film. TAS measurements have also been carried out on oxygen-deficient hydrogen-treated TiO2 nanowires, highlighting a more efficient suppression of the electron/hole recombination process in comparison with conventional anatase TiO2 photoanodes. Chapter 5 describes TAS and sum frequency generation (SFG) studies on TiO2 films which are designed to investigate the surface mechanisms of water oxidation. The dependence of the hole lifetime on the pH of the electrolytes employed has been examined by TAS and substantially faster decay rates have been found in highly alkaline solutions suggesting a change in the mechanism of water oxidation. Consequently, SFG has been employed in order to detect any possible intermediate at the interface TiO2/water. Initial measurements have provided the evidence of physisorbed and chemisorbed methanol (model probe) on the TiO2 surface and further studies at the TiO2/water interface have been carried out. Chapter 6 describes the development of a hybrid solar fuel reactor coupling a α-Fe2O3 based photoelecrochemical cell with luminescent solar concentrator plates. Initial tests have been carried out on a proof of principle prototype providing encouraging results.
|Creators||Pesci, Federico M.|
|Publisher||Imperial College London|
|Source Sets||Ethos UK|
|Type||Electronic Thesis or Dissertation|
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