Tetrazole-Substituted isomeric ruthenium polypyridyl complexes for low overpotential electrocatalytic CO2 reduction

Abstract

Introducing tetrazole moiety to the ligand framework of two isomeric ruthenium catalysts, cis/trans-[Ru(tpy)(mtzp)(CH3CN)]2+ (tpy = 2,2′:6′,2′'-terpyridine, mtzp = 2-(1-methyl-1H-tetrazol-5-yl)pyridine), for the electrochemical reduction of CO2 to CO has altered the catalytic pathway with significantly low overpotential (0.37 V) compared to its analogous catalysts. Without manipulating steric effects, only the electronic nature of tetrazole moiety enables CO2 binding to ruthenium center to form metallocarboxylate intermediate just after one-electron reduction. This is the first synthesized isomeric pair of ruthenium complex follow ECE (E = electron transfer, C = chemical reaction) mechanism for electrocatalytic reduction of CO2. By successful characterization of the Ru–CO intermediate with the help of 13C NMR, spectro-electrochemical studies and analysis of byproducts formed during the electrocatalysis, a mechanism of CO2 reduction has been established in presence of water and anhydrous conditions which is further supported by density functional theory (DFT).