Anthropogenic climate change presents an unrivalled threat to environmental stability and the prosperity of future generations. Utilising abundant, renewable resources in energy generation and storage will be essential to halt climate change and its effects. Solar water splitting is an excellent tool in the renewable energy arsenal for countering climate change, as it utilises both sunlight and water, two of the most abundant resources available on earth. Furthermore, the direct formation of a chemical fuel, hydrogen, is thought to be more practical for storing in large quantities than electricity. Work in this thesis covers the investigation of a variety of materials, fabricated by aerosol assisted chemical vapour deposition (AACVD), for their ability to carry out photoelectrochemical water splitting. In one project, thin films of Bi2Ti2O7 (BTO), specifically of the pyrochlore crystal structure, are fabricated by AACVD and analysed for their photoelectrochemical properties. The resulting thin films are found to be phase pure with a band gap of 2.88 eV, which is 0.32 eV smaller than TiO2. Efforts to dope the BTO thin films are further investigated through the addition of iron. Significant modification to the band gap is observed, leading to a confirmed pyrochlore thin film exhibiting a band gap of 2.5 eV, a reduction of 0.38 eV from undoped BTO. The resulting thin film had a photocurrent 5 times higher than that of undoped BTO. Finally, efforts to fabricate Fe2Ti2O7 are outlined. It is discovered that a stable phase of Fe2TiO5 is preferentially formed over the pyrochlore phase, even with dramatic modification to the deposition parameters and precursor stoichiometry. The high stability of this phase, coupled with the limiting features of the glass substrates, highlights the challenges with forming certain pyrochlore thin films. In a second project, the effect of depositing titanium nanoclusters onto the surface of bismuth vanadate is investigated. Nanoclusters are of huge interest because their properties lie between those of atoms and bulk materials. Additionally, nanoscale clusters can be fabricated with incredible precision, allowing one to select discrete diameter particles for deposition on surfaces. Ti nanoclusters over a range of sizes are deposited onto BiVO4 photoanodes. It is discovered that the deposition of ultralow loadings of Ti2000 clusters results in an 80 % enhancement in the photocurrent of the BiVO4 substrates. Further experimentation highlights that the photocurrent enhancement is linked to the size of the nanocluster and the density of the clusters on the surface. A mechanism is outlined, whereby the Ti nanoclusters partially reduce the surface of the BiVO4, leading to enhanced electron transport within the thin films due to the presence of oxygen vacancies. In a final project, polycrystalline InN, GaN and systematically controlled InxGa1-xN composite thin films are fabricated on FTO glass by a facile, low-cost and scalable aerosol assisted chemical vapor deposition technique. Variation of the indium content in the composite films leads to a dramatic shift in the optical absorbance properties, which correlates with the band edges shifting between those of GaN to InN. Moreover, the photoelectrochemical properties are shown to vary with indium content, with the 50 % indium composite having an external quantum efficiency of around 8 %. Whilst the overall photocurrent is found to be low, the photocurrent stability is shown to be excellent, with little degradation seen over 1 hour. Subsequent attempts to modify the morphology by conducting vertical-AACVD are also outlined. Thin films fabricated using vertical-AACVD are found to grow via a different mechanism, leading to undesired split phase growth, where two different compositions form on the same substrate.

An electrochromic (EC) material is able to change colour under the influence of an electric potential. The development of energy efficient smart windows for architectural applications is at present the subject of intense research for both economic and environmental reasons. Thus there is now a considerable research effort to develop smart windows with natural colour switching properties, i.e. shades of grey. In this regard, a promising metal oxide with a brown-black anodic colouring state is NiO or hydrated nickel oxide (also called nickel hydroxide , Ni(OH)2). The present work outlines the preparation and optimisation of EC nickel oxide-based ceramic precursor films onto various conducting substrates towards smart window applications. The literature review chapter outlines the different methods used for generating ceramic materials, a review of electrochromism and history of nickel oxide-based EC materials are also provided. Thins films have been deposited by an electrochemical cathodic deposition and by aerosol assisted chemical vapour deposition (AACVD) technique. For hydrated NiO films prepared by electrochemical cathodic deposition, various deposition factors at small-scale area (30 x 7 mm) have been investigated in order to optimise the films properties towards EC applications. With deposition on fluorine-doped tin oxide (SnO2:F, FTO) on glass, use of nickel nitrate (0.01 mol dm-3) solution at an applied current of -0.2 mA (-0.1 mA cm-2) for 800 s was optimal for preparing uniform deposits with a porous interconnecting flake-like structure, which is generally regarded as favourable for the intercalation/deintercalation of hydroxide ions during redox cycling. The as-deposited hydrated NiO films showed excellent transmittance modulation (Δ%T = 83.2 at 432 nm), with average colouration efficiency (CE) of 29.6 cm2 C-1 and low response times. However, after 50 voltammetric cycles, the cycle life was found to fade by 17.2% from charge measurements, and 28.8 % from in-situ transmittance spectra measurements. In an attempt to prepare films with improved durability, AACVD has been used for the first time in the preparation of thin-film EC nickel(II) oxide (NiO). The as-deposited films were confirmed to be cubic NiO from analysis of powder X-ray diffraction data, with an optical band gap that decreased from 3.61 to 3.48 eV with an increase in film thickness (in the range 330 820 nm). The EC properties of the films were investigated as a function of film thickness, following 50, 100 and 500 conditioning oxidative voltammetric cycles in aqueous KOH (0.1 mol dm-3). Light modulation of the films increased with the number of conditioning cycles. EC response times were < 10 s and generally longer for the colouration than the bleaching process. The films showed excellent stability when tested for up to 10000 colour/bleach cycles. Using a calculation method based on the integration of experimental spectral power distributions derived from in-situ visible region spectra over the CIE 1931 colour-matching functions, the colour stimuli of the NiO-based films, and the changes that take place on reversibly switching between the bleached and coloured forms have been calculated. Films prepared by both deposition techniques gave positive a* and b* values to produce orange. However, in combination with low L* values, the films were perceived as brown-grey. Hydrated NiO prepared via electrochemical cathodic deposition suffers from two well-known limitations; firstly, it shows catalytic properties towards the oxygen evolution reaction (OER), which is a process very close to the Ni(II)/Ni(III) redox process. Secondly, hydrated NiO shows poor cycling durability in alkaline solution. The co-deposition of single or bimetallic additives is an effective way to overcome these problems. Electrochemical studies revealed that the combination of cobalt (10%) with lanthanum (5%) was found to be the optimal composition for preparing hydrated NiO films with improved film durability. Finally, the emphasis of this work was on scale-up of deposition. Therefore, optimised deposition conditions from small scale (3.0 x 0.7 cm) have been used to successfully deposit films on two different sized large-area (10 x 7.5 and 30 x 30 cm) conducting substrates.

The doping of rhenium into molybdenum disulfide was achieved by Aerosol Assisted Chemical Vapour Deposition (AACVD) from single source precursors. Rhenium can be studied as a model for immobilization of radioactive technetium-99 (99Tc) in MoS2. The metals Mo(IV), Re(IV), and Tc(IV) have similar ionic radii 0.65, 0.63 and 0.65 Å respectively, and their Shannon-Prewitt crystal radii 0.79, 0.77 and 0.79 Å Hence demonstrating the potential storage of nuclear waste in geologic like formations in of groundwater may be possible. The interaction between the nuclear waste forms and groundwater, which could lead to release and transport low concentrations or vapour of radionuclides to the near field, as a result, decomposition of engineered barriers. The molecular precursors [Mo(S2CNEt2)4], [Re3(μ-SiPr)3(SiPr)6], [Re(S2CC6H5)(S3CC6H5)2], and [Re2(μ-S)2(S2CNEt2)4] have been used to deposit Re-doped MoS2 thin films. Mo-doped ReS2 alloyed, polycrystalline thin films were synthesised using [Re(S2CC6H5)(S3CC6H5)2], [Mo(S2CNEt2)4] via AACVD, adding with a low concentration of Mo source for the first time . We reported as well a new way for production of ultrathin ReS2 nanosheets by coupling bottom up processing AACVD with top-down LPE. This is important in synthetic pathways for the production of rare transition dichalcogenide, also, our processing methodology is potentially scalable and thus could be a way to commercial exploitation. Characterisation of produced materials performed by pXRD, SEM, TEM, STEM, EDX, ICP and Raman spectroscopy.

In this thesis complexes of acylchalcogoureas with cadmium (II), lead (II) and nickel (II) have been synthesised and investigated as single source precursors for the formation of metal chalcogenide thin films viaaerosol assisted chemical vapour deposition (AACVD). Routes to binary thin films have been explored using homoleptic complexes of the general structure bis(N,N-diethyl-N'-naphthoylchalcogoureato)metal(II). Analysis of the thin films produced showed the successful deposition of the binary materials from the synthesised complexes when characterised by powder XRD, ICP-OES, SEM and EDX. Routes to ternary thin films with the general structure MExE'1-x, where M represents a metal (Cd, Ni and Pb); and E chalcogen (S or Se) have been investigated using heteroleptic metal complexes of cadmium, nickel or lead including different chalcogen containing N,N-diethyl-N'-naphthoylchalcogoureato ligands and diethyldithiocarbamate. The precursors were fully characterised and novel compounds had their crystal structures determined. The heteroleptic complexes were thermolysed by AACVD forming the MExE'1-x thin films. In the cases of lead, nickel and cadmium the thin films produced showed that the composition of the film tended heavily towards the metal selenide. Ternary films of type MS1-xSex was prepared by mixing their binary precursors of type bis(N,N-diethyl-N'-naphthoylselenoureato)metal(II) and bis(N,N-diethyl-N'-naphthoylthioureato)metal(II) [metal = Cd, Ni and Pb]. In the case of lead and cadmium chalcogenide films variation of the ratio of sulphur and selenium containing precursors allowed for the full transition in composition between metal sulphide and metal selenide. In the case of CdS1-xSexthe band gap of the films was determined from UV-visible spectroscopy to vary from 2.4 eV (CdS) to 1.7 eV(CdSe). In the case of NiS1-xSex the movement from sulphide to selenide was less simple with multiple phases of nickel chalcogenides produced.

Photoelectrodes and photovoltaic devices have been prepared via multiple thin film deposition methods. Aerosol assisted chemical vapour deposition (AACVD), electrodeposition (ED), chemical bath deposition (CBD) and doctor blade technique (DB) have been used to deposit binary and ternary metal oxide films on FTO glass substrates. The prepared thin films were characterised by a combination of SEM (Scanning Electron Microscopy), powder X-ray diffraction, mechanical strength tests and photochemical measurements. Nickel oxide (NiO) thin films prepared by AACVD were determined to have good mechanical strength . with a photocurrent of 7.6 μA cm-2 at 0 V and an onset potential of about 0.10 V. This contrasted with the dark current density of 0.3 μA cm-2 at 0 V. These NiO samples have very high porosity with crystalline columns evidenced by SEM. In comparison with the AACVD methodology, NiO films prepared using a combination of ED and DB show good mechanical strength but a higher photocurrent of 24 μA cm-2 at 0 V and an onset potential of about 0.10 V with a significantly greater dark current density of 7 μA cm-2 at 0 V. The characteristic features shown in the SEM are smaller pores compared to the AACVD method. Copper (II) oxide (CuO) and copper (I) oxide (Cu2O) films were fabricated by AACVD by varying the annealing temperature between 100-325°C in air using a fixed annealing time of 30 min. It was shown by photocurrent density (J-V) measurements that CuO produced at 325 °C was most stable and provided the highest photocurrent of 173 μA cm-2 at 0 V with an onset potential of about 0.23 V. The alignment of zinc oxide (ZnO) nano-rods and nano-tubes fabricated by CBD have been shown to be strongly affected by the seed layer on the FTO substrate. SEM images showed that AACVD provided the best seed layer for aligning the growth of the nano-rods perpendicular to the surface. Nano-rods were successfully altered into nano-tubes using a potassium chloride bath etching method. NiO prepared by both AACVD and the combined ED/DB method were sensitized to absorb more of the solar spectrum using AACVD to deposit CuO over the NiO. A large increase in the photocurrent was observed for the p-type photoelectrode. These p-type photoelectrode showed a photocurrent density of approximately 100 μA cm-2 at 0 V and an onset potential of 0.3 V. This photocathode was then used as a base to produce a solid state p-type solar cell. For the construction of the solid state solar cells several n-type semiconductors were used, these were ZnO, WO3 and BiVO4. WO3 and BiVO4 were successfully produced with BiVO4 proving to be the optimum choice. This cell was then studied more in depth and optimised by controlling the thickness of each layer and annealing temperatures. The best solid state solar cell produced had a Jsc of 0.541 μA cm-2 (541 nA) and a Voc of 0.14 V, TX146 made up of NiO 20 min, CuFe2O4 50 min, CuO 10 min, BiVO4 27 min, using AACVD and then annealed for 30 min at 600°C.