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

Abstract

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)(N-3)(2)](2) and [Co(acac)(2-pic)(N-3)(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.