Electrocatalytic CO<sub>2</sub> to CO and Methanol Conversion Using a Molecular Cobalt Corrole Complex
Afridi Zamader, Ajeet Singh, Bishnubasu Giri, Marcello Caruso, W. Ryan Osterloh, Nicolas Desbois, Claude P. Gros, Marc Robert
Abstract
Triphenylcorrole (Cor)Co III (DMSO) (Cat 1) was investigated for its electrochemical CO 2 reduction catalysis, facilitating 2-, 4-, and 6-electron transfer processes. Cat 1 was identified as an active molecular catalyst for the conversion of CO 2 to CO (2e –, 2H + ) under homogeneous conditions in CH 3 CN, 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 CO 2 -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 CH 3 OH (6e –, 6H + ) with an FE CH 3 OH of ∼2%, representing a 7-fold increase compared to the single-cell configuration (FE CH 3 OH ∼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., [M n + –CO], was identified as a key intermediate for CH 3 OH formation, as replacing CO 2 with CO in the feed gas further promotes the FE of the liquid products, reaching ∼4 to 5% for both CH 3 OH and HCHO under a single-cell configuration. The demonstration that simple Co-corrole can drive the CO 2 RR up to 6 electrons illustrates that multi proton–electron activation with molecular catalysts is a more general possibility than anticipated.