Enzyme-Mimicking Redox-Active Vitamin B12 Functionalized MWCNT-Catalyst for Nearly 100% Faradaic Efficiency in Electrochemical CO2 Reduction

Abstract

Due to the detrimental effects of CO2 on the atmosphere, including climate change, the development of environmentally friendly electrocatalysts for CO2 reduction is crucial for mitigation. Inspired by carbon monoxide dehydrogenase (CODH) enzymes, where an active centre is surrounded by a protein scaffold, this work introduces a biomimetic system featuring a Vitamin B12 cluster protected by a matrix of multi-walled carbon nanotubes (MWCNTs). Unlike to the literature-based Vitamin B12 systems with nil redox behaviour, we have developed a multi-walled nanotubes (MWCNTs) functionalized with Vitamin B12 (MWCNT@B12) as a highly redox-active system and explored for electrocatalytic CO2 reduction reaction at room temperature in aqueous medium. The presence of Vitamin B12 in the matrix was confirmed through a series of characterizations employing FTIR, Raman spectroscopy, FESEM, EDAX, ultrapressure liquid chromatography (UPLC), scanning electrochemical microscopy (SECM) and cyclic voltammetry. This new electrocatalyst demonstrates high Faradaic efficiency (~100%), low overpotential (ηCO2=242 mV), and a significant current density (43.5 mA cm-2) for the electrocatalytic conversion of CO2 to CO in 0.5 M NaHCO3 solution. In-situ SECM reveals that clusters of Vitamin B12 embedded on the modified electrode are the active sites for the overall electrocatalytic reaction. Compared to previously reported heterogeneous molecular catalyst electrodes, this system exhibits a lower peak-reduction potential of 100-600 mV and current densities 2-40 times higher for CO2 reduction reaction. Furthermore, Vitamin B12 is a naturally occurring, non-toxic redox mediator. Therefore, the B12-modified electrode presented here is a promising development for future green CO2 reduction applications.