Electrocatalytic CO2 to CO and Methanol Conversion Using a Molecular Cobalt Corrole Complex

Abstract

Triphenylcorrole (Cor)Co^III(DMSO) (Cat 1) was investigated for its electrochemical CO₂ reduction catalysis, facilitating 2-, 4-, and 6-electron transfer processes. Cat 1 was identified as an active molecular catalyst for the conversion of CO₂ to CO (2e^–, 2H⁺) under homogeneous conditions in CH₃CN, using water as the proton source. Under heterogeneous conditions, Cat 1@E (Cat 1 immobilized on multiwalled carbon nanotubes (MWCNTs) and coated on carbon paper) demonstrated CO₂-to-CO conversion with a near-perfect Faradaic efficiency (FE_CO) of ∼97% and high stability at near-neural pH in a single-cell setup. When the electrode was transitioned to a flow-cell configuration, the j_CO significantly improved to 47.5 ± 0.5 mA cm^–2 while maintaining a high FE_CO of ∼95%. Applying a higher j_tot of −200 mA cm^–2 led to the formation of CH₃OH (6e^–, 6H⁺) with an FE_CH3OH of ∼2%, representing a 7-fold increase compared to the single-cell configuration (FE_CH3OH ∼0.34%) and j_CH3OH of ∼3.84 mA cm^–2 with trace amounts of HCHO (4e^–, 4H⁺) in parallel. Metal-bound CO, i.e., [Mⁿ⁺–CO], was identified as a key intermediate for CH₃OH formation, as replacing CO₂ with CO in the feed gas further promotes the FE of the liquid products, reaching ∼4 to 5% for both CH₃OH and HCHO under a single-cell configuration. The demonstration that simple Co-corrole can drive the CO₂RR up to 6 electrons illustrates that multi proton–electron activation with molecular catalysts is a more general possibility than anticipated.