Nanomaterials for photoelectrochemical and photocatalytic conversion of solar energy

In the 21st century, the quest for sustainable sources of renewable energy is expecting several challenges: the growing global population will require not only energy, but also nutrition, and both will have to be attained without further endangering an already precarious environmental situation. Therefore, in order to decrease the carbon footprint and increase the sustainability of energy production, sources must be widely available, fabricated through means that do not cause any negative consequence on the environment, and they should prove to be durable enough to be worth the financial impact. Photocatalytic and photoelectrochemical phenomena are regarded as attractive options for harnessing solar energy in a chemical form: this would alleviate some of the challenges related to storage and transportation, while also compensating for the differences in solar irradiation across the planet. These phenomena are also applicable to photocatalytic reduction of CO2, water reformation, and CO2 conversion to biomass, with a significant impact in solving environmental issues. This thesis presents advanced fabrication strategies for semiconductor nanomaterials conducive to  water splitting, photodeposition and water reformation applications: the main goal of the present work is to improve the efficiency of as-prepared materials through doping, disordering, surface decoration and interface engineering, and finally to explore fabrication processes that have a low energetic consumption. Novel techniques for extrinsic doping of hematite thin films are presented, and interface engineering for favoring the transport of photogenerated charge carriers from semiconductor to electrolyte, on both α-Fe2O3-TiO2 and III-V semiconductors, is also explored in this thesis. Photodeposition of metal and metal oxide nanoparticles is then highlighted and discussed as a technique for the electrically unassisted growth of catalyst nanoparticle, under different illumination and chemical conditions, with versatile outcomes and with applications to pollutant degradation in water. Finally, this thesis advances the technoeconomic assessment of a system that combines photoelectrochemical water splitting with the growth of hydrogenotrophic bacteria, in comparison with existing technologies for the cultivation of microalgae. The results of this thesis provide new insight into the improvement of the water splitting performance of nanomaterials through doping, disordering and interface engineering. The outcomes are novel modification strategies for tuning the valence and conduction bands towards optima in proximity of the semiconductor-electrolyte interface, fabrication methods with low environmental impact, and a comprehensive real-life evaluation of a practical solution based on solar water splitting.