Carbon dioxide chemical recycling is a promising eco-sustainable alternative to fossil fuels which allows, at the same time, a decrease of greenhouse gas emissions and the energy storage by the CO₂conversion into fuels or feedstock chemicals.

The present project aims to develop efficient catalysts, based on non-precious transition metal complexes (MCs), for the photoelectro-catalytic reduction of CO₂, and to prepare nanostructured electrodes functionalized with the MCs. Indeed, recent investigations indicate that the catalytic activity could be enhanced by anchoring the complexes to nanoparticles (NPs) deposited on electrodes. In order to achieve this purpose, competences on several fields such as synthesis, characterization and computational modelling of the complexes, NPs and electrodes preparation and characterization, are required, as well as on theoretical study on NP-catalyst interactions and electron transfer. As far as the catalysts are concerned, we will prepare complexes of transition non-noble metal ions such as Ni(II), Co(II), Cu(II) and Fe(II) with dibenzotetraaza[14]annulenes (1), dioximes (2) or dithiolenes (3) as ligands. We will investigate compounds of already known ligands and others with new architectures, properly designed to improve the catalyst performance in the operating conditions. Moreover, the molecules will be suitably functionalized with anchoring groups (AGs), namely thiol, carboxylic or phosphate, enabling to bind the ligand to the NPs. The complexes will be characterized by several techniques such as elemental analysis, mass spectrometry, UV-vis-NIR, FT-IR and NMR spectroscopies, cyclic voltammetry (CV) and spectroelectrochemistry; their homogenous catalytic activity will be investigated by CV to evaluate the current enhancement under CO₂. In addition, computational studies using ab initio (AI), density functional theory (DFT) and semiclassical methods, will be performed to deeply understand the structural-electronic properties relationship and as support to design new and potentially more efficient catalysts. Calculations will also help to elucidate the catalytic cycle, by clarifying issues such as the active site on the molecule for CO₂reduction. The most promising catalysts, will be anchored onto NPs immobilized on mesoporous electrodes based on TiO₂, SiO₂ or SnO₂. We will focus mostly on TiO₂, CdS, and CdInS₂ NPs, which will be characterized as well as the electrodes, by N₂ physisorption, FT-IR and UV-vis-NIR spectroscopies, TEM, HRTEM, SEM, XRD and CV. Both the NPs and the mesoporous electrodes will be prepared accordingly to the methods reported in the literature. The complexes will be anchored on the NPs by immersion of the electrode in a solution containing the catalyst; the adsorption efficiency will be checked by UV-vis absorption and SEM. To confirm the catalytic activity and to determine the selectivity of the CO₂ reduction we will carry out electrolysis at controlled potential under CO₂ and under simulated solar light irradiation. Sample at different times will be analysed by gas chromatography (GC). In order to describe the localized electronic states present in molecules, nanoparticles, or even in extended oxide systems, we will use a beyond-standard DFT methodology developed in the past by some of us, and proven successful for a vast range of materials.