Photodoping of doped metal oxide nanocrystals for energy storage electrodes

In an era where global warming presents significant challenges, advancing materials science is crucial to meet the collective goals of emissions reduction and the transitioning to clean energy. This PhD thesis delves into the exploration of novel heterostructures comprising Indium Tin Oxide nanocrystals (ITO NCs) and diverse NCs or chemicals, for cutting-edge light-driven optoelectronic nanodevices and energy storage systems. This research integrates the processes of energy harvesting, conversion, and storage into a singular hybrid nanomaterial. The use of Doped Metal Oxide (MO) NCs is gaining increasing attention in the realm of nano-supercapacitors, thanks to their capacity to hold additional charges within their electronic structure, achieving high values of specific capacitance. These materials are able to store charges upon illumination with light (photocharging or photodoping), via the absorption of photons and generation of photocharges. During my research, I first studied the charge accumulation process in a solution-based process, moving then to realizing MO NCs films, to work with an electrochemically functional device. The scalability of colloidal synthesis for ITO NCs was demonstrated, highlighting the consistency of material properties such as size control, optical features, and crystalline phase across different batch sizes. The transition from small-scale to larger batches was achieved with increased efficiency and minimized mechanical losses, maintaining the quality of the nanoparticles. The material obtained was then employed to test ITO NCs charge accumulation ability both in solutions and in solid state (i.e. thin films). At first, solution-dispersed ITO NCs were tested to explore the potential combination with various redox couples (e.g., TEMPO, crystal violet, and ferrocene) to act as reversible hole scavengers and enhance photodoping in ITO NCs. The findings demonstrated that ferrocene effectively increases charge density in doped metal oxide nanoparticles. ITO NCs were then employed to fabricate thin films, underscoring the critical role of fabrication protocols in achieving optimal film properties such as uniformity and thickness. Photodoping was investigated in thin films, revealing the ability of ITO NCs to undergo photo-charging even when in solid-state dispersion, preparing their use for the final application of the work. Finally, the prepared thin films were employed as photo-electrodes in a photo-electrochemical system. The research highlighted the promising role of ITO NCs/visible light-sensitizer thin films as photo-electrodes in supercapacitor applications, with capacitances reaching up to the order of 1 mF/cm2. The use of a visible light sensitizer illustrated its compatibility with ITO NCs, enhancing the system's capacitance under UV and green light. Overall, the thesis presented a work on the scalable synthesis, photodoping capabilities, thin film fabrication, and photo-electrochemical applications of ITO NCs. The potential applications in energy conversion, storage, and photo-electrocatalysis position these findings at the forefront of sustainable energy research, opening doors to new innovations in solar energy technologies.