Development of Aurivillius-based photoelectrodes for the photoelectrochemical CO2 reduction

In recent years, Bismuth-based photocatalysts have received increasing attention in the field of photocatalysis, due to their appropriate bandgap and tunable surface structure, which make them suitable also for the photocatalytic reduction of CO2. However, their performance is still limited by the rapid charge carriers recombination. Recently, the exploitation of piezo/ferro-electric potentials in photo-active semiconductors, known as the piezophototronic effect, has emerged as an effective strategy to modulate the charge transfer properties within semiconducting materials. In this context, Bismuth-based Aurivillius compounds, owing to their usually strong spontaneous ferroelectric polarization, represent a promising option as photo-electrodes in photoelectrochemical cells, allowing the increase of cell efficiency by the application of an external electric field. In addition, thanks to their unique layered structure, this peculiar class of perovskites enables the migration of photo-generated holes and electrons within different areas of the materials, thus intrinsically facilitating charge separation. Within this framework, this Ph.D. thesis investigates the utilization of different Aurivillius compounds, specifically Bi4Ti3O12 (BiTO), and Bi2MoO6 (BiMO), as photo-electrode materials for the photoelectrochemical CO2 reduction (PEC-CO2RR). The use of BiTO and BiMO for the photocatalytic reduction of CO2 has recently been documented in the literature, but their utilisation as photoelectrodes materials for the PEC-CO2RR together with the development of photoelectrodes for this purpose remains largely unexplored. On this basis, BiTO and BiMO photo-electrodes were fabricated and accurately optimized to obtain both hierarchically oriented nanostructures with different morphologies, including nanosheets and nanorods arrays, as well as thin-film layers. A comprehensive characterization of the photoelectrodes including structural, morphological, optical, electrochemical and photoelectrochemical analyses was carried out. Various strategies, comprising metal doping, heterojunction construction and co-catalysts depositions, were explored to enhance their performance in PEC-CO2RR, as well as the possibility of exploiting their ferroelectric behaviours to tune the associated charge transfer properties. Finally, the most promising systems displaying suitable characteristics were used to assemble complete PEC cells and tested for the production of solar fuels from CO2.