Electrochemical Conversion of CO₂ to CO by a Competent Fe^I Intermediate Bearing a Schiff Base Ligand

Iron complexes with a N₂ O₂ -type N,N'-bis(salicylaldehyde)-1,2-phenylenediamine salophen ligand catalyze the electrochemical reduction of CO₂ to CO in acetonitrile with phenol as the proton donor, giving rise to 90-99 % selectivity, faradaic efficiency up to 58 %, and turnover frequency up to 10³  s^-1 at an overpotential of 0.65 V. This novel class of molecular catalyst for CO₂ reduction operate through a mononuclear Fe^I intermediate, with phenol being involved in the process with first-order kinetics. The molecular nature of the catalyst and the low cost, easy synthesis and functionalization of the salophen ligand paves the way for catalyst engineering and optimization. Competitive electrodeposition of the coordination complex at the electrode surface results in the formation of iron-based nanoparticles, which are active towards heterogeneous electrocatalytic processes mainly leading to proton reduction to hydrogen (faradaic efficiency up to 80 %) but also to the direct reduction of CO₂ to methane with a faradaic efficiency of 1-2 %.