Competition between electrocatalytic CO2 reduction and H+ reduction by Cu(II), Co(II) complexes containing redox-active ligand

Abstract

A benzimidazole derivative ligand (L1) and its corresponding transition metal complexes ML1Cl2 (M = Cu (1), Co (2)) have been synthesized and characterized by a combination of X-ray crystallography, PXRD, electrochemistry, spectral (IR, UV–vis) techniques and DFT calculations. The electrocatalytic activity of the two complexes for CO2 reduction was investigated without and with proton source. Bulk electrolysis of the two compounds demonstrates that there is a competition between CO2 and H+ reduction during the electrocatalytic process, leading to a low Faradaic efficiency for CO evolution but a high FE for H2 evolution. The reason of the serious competition reaction of hydrogen generation in the process of catalytic CO2 reduction have been investigated. Studies show that the catalytic effect could be due to a synergy effect between the redox active ligand L1 and metal ions (Cu (II) (1) and Co (II) (2)), while the formation of hydride complex [M(I)L1•−H•−]1- might be the crux in the selectivity between CO2 reduction and H2 evolution, and the process of electrocatalytic reduction of CO2 could have promoted H+ reduction.