Acetylacetonate Derived Cobalt(III) Complexes as Photocatalysts and Electrocatalysts for Energy Conversion

Developing systems that facilitate the conversion of solar energy into fuel by reducing carbon dioxide and producing hydrogen could bridge the gap between production and consumption. In this work, a new method to study the reaction intermediates of carbon dioxide reduction reaction (CO₂RR) and hydrogen elimination reaction (HER) catalyzed by Cobalt(III) catalysts with high photocatalytic activity in a water/acetonitrile solvent system is proposed. The optimization of the cobalt catalysts ([Co(acac)(bpy)(N₃)₂].H₂O 1, [Co(acac)(en)(N₃)₂] 2 and [Co(acac)(2-pic)(N₃)₂] 3) for photocatalytic activities in visible light irradiation (>420 nm) is performed by varying solvents systems (v/v) (CH₃COCH₃/H₂O, CH₃CN/H₂O, DMF/H₂O, EtOH/H₂O and H₂O), sacrificial electron donors (1-benzyl-1,4-dihydronicotinamide (BNAH), diethanolamine (DEOA), triethylamine (TEA), and triethanolamine (TEOA), photosensitizers (Eosin Y, Erythrosin B, Fluorescein (Fl), Rose Bengal, Rhodamine-B, and Ru(bpy)₃ (Ru)), pH (7–12.5) and different catalyst concentrations (0–2 mM). The arrangement around the Cobalt(III) ion is an octahedral coordination geometry. A combination of experimental characterization and density functional theory (DFT) is used to identify the mechanism of the photocatalytic CO₂ reduction reaction. DFT calculations and experimental results for the photocatalytic activity of the catalysts 1–3 reveal the involvement of multi-electron metal-ligand exchange coupling in promoting CO₂RR and HER, and provide a starting point for the integration of these strategies into catalyst design.