Abstract
Abstract In this dissertation, TiO2 nanoparticle aggregates (NPGs), TiO2 xerogels, graphene aerogels (GAs), Cu2O/TiO2, and Cu2O/CdS composites with mesoporous structure are produced and applied in dye-sensitized solar cells (DSSCs) and hydrogen production through photocatalytic water splitting. For the DSSC, TiO2 NPGs and GAs are used as the photoanode and counter electrode, respectively. The Cu2O decorated composites, possessing excellent charge separation and suitable band structures, are applied in hydrogen generation through photocatalytic water splitting. The relevant properties of the synthesized mesoporous materials and the performance of DSSCs and photocatalytic water splitting are investigated and discussed in this study. TiO2 NPGs with high specific surface areas and of sub-micron sized are produce by a one-step, template-less, surfactant-free hydrothermal process. With these NPGs, a new form of composite photoanode, consisting of the mesoporous TiO2 NPGs and xerogels, is proposed for high efficiency dye-sensitized solar cells (DSSCs). TiO2 xerogels are incorporated into the TiO2 NPGs layer with an impregnation process to form the TiO2 NPGs/xerogels composite. A high power conversion efficiency of 8.41% is achieved for the DSSCs based on the TiO2 NPGs/xerogels composite photoanode, representing a 38% efficiency boost over the efficiency of 6.11 % achieved with a P25 TiO2 based cell. GAs prepared with an organic sol-gel process, possessing a high specific surface area of 814 m2/g and a high electric conductivity of 850 S/m, are applied as a counter electrode (CE) material for DSSCs. The performance of the GA as the CE material is found to be dependent on its film thickness. At an optimum GA film thickness of 4.9 μm, a power conversion efficiency of 96% of that achieved with a Pt CE based DSSC is obtained. In addition, a thinner GA film of 1.7 μm, when loaded with Pt of 1 mol.% through a photo-reduction process, achieves a power conversion efficiency of 98% of that obtained with a Pt CE based DSSC. The excellent performances of the GA-based CEs are manifested with electrochemical impedance analyses and cyclic voltammetry catalytic activity analyses. Mesoporous TiO2 NPGs with a high specific surface area are decorated with nontoxic, band structure matched Cu2O nanocrystals through a simple, fast, and low cost chemical bath deposition process. The Cu2O nanocrystals serve as an electron-hole separation center to promote hydrogen productions. By tuning the concentration of the Cu2O precursor, the loading of Cu2O can be controlled. At preferred operation conditions, an ultrahigh specific hydrogen production rate of 223 mmol/hr．g is achieved. The Cu2O decorated TiO2 NPGs are found to possess high transmittances at low wavelengths where the TiO2 materials are photocatalytically active. With the advantages of high specific surface areas, improved electron-hole separations, and better light utilization of the Cu2O decorated TiO2 NPGs, the hydrogen production rate achieved is one order of magnitude higher than that by commercial P25 TiO2. Crystalline CdS nanobeads (NBs), nanoparticles (NPs), and nanowires (NWs) are prepared with hydrothermal and solvothermal methods. These three CdS nanostructures are applied for hydrogen productions under visible light illumination. CdS NPs show a hydrogen production rate of 9.6 μmol/hr which is higher than that of CdS NBs, attributable to the higher specific surface area of the CdS NPs. The one dimensional structure and single crystallinity of CdS NWs, both beneficial for charge transport, lead to a higher hydrogen production rate of 12.4 μmol/hr. In order to boost the hydrogen production rate, these CdS nanostructures are modified with p-type Cu2O using a simple, fast, and low cost chemical bath deposition process. The composite photocatalysts of Cu2O decorated CdS nanostructures acquire significant improvements on the hydrogen production rate, resulting from the enhancements in charge separation. A high hydrogen production rate of 238.3 μmol/hr is achieved with Cu2O decorated CdS NBs, which is 74 folds of that of plain CdS NBs.