SUMMARY
The anticipated end of inexpensive fossil fuels and the environmental concerns caused by their usage has motivated development of renewable energy technologies. Examples such as solar photovoltaic (PV) systems have had some limited effectiveness for stationary systems, yet no viable carbon neutral method for the production of dense fuels (i.e., solar-to-chemical energy conversion) for transportation has been developed. As a promising option, titanium dioxide (TiO2) based semiconductor photocatalyst systems for hydrogen generation have attracted attention due to their cost advantage compared to silicon PV systems, and environmental neutrality. Despite initial promise, and considerable research efforts spanning four decades, a high band gap (3+ eV), low charge carrier mobility, poor control of charge carrier separation, and semiconductor-metal support (electrode) durability have stymied performance. Individual aspects of the TiO2 problem have been solved, in particular the doping with anions to narrow the band gap to increase solar energy absorption. Additionally, the utilization of the anatase phase of TiO2 has increased carrier mobility by an order of magnitude vs. the standard rutile phase. Despite these advances, no reports exist in the literature which combines these modifications into a durable electrode structure, which maintains a sub-micron layer thickness of the photocatalyst coating, which is essential for efficient charge carrier separation. In this PhD project a novel hybrid electrode interface structure is proposed, which synergistically implements these modifications to the standard TiO2 photocatalysts. The proposed material processing approach exploits thermally-softened nanostructured metal supports to embed the photocatalyst nanoparticles via spray-coating and flash evaporation of the carrier solvent. The resulting composite metal-semiconductor interface forms a new electrode configuration, demonstrating the once mutually exclusive durable, sub-micrometer thick layer of highly-doped anatase TiO2. The new electrode interface shows an improved photocatalytic reaction rate density as compared to similar systems, along with simple fabrication and increased durability as compared to dip- and spin- coated electrodes. An in-depth investigation of the relevant electrode material and processing parameters which result in optimum photocatalytic performance is proposed through complimentary experiments and theoretical analysis.