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 literature-based vitamin B12 systems with no redox activity, we have developed multi-walled nanotubes (MWCNTs) functionalized with vitamin B12 (MWCNT@B12) as a highly redox-active system and explored it for electrocatalytic CO₂ reduction reaction at room temperature in an aqueous medium. The presence of vitamin B12 in the matrix was confirmed through a series of characterizations by 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 (η_CO2 = 242 mV), and a significant current density (43.5 mA cm⁻²) for the electrocatalytic conversion of CO₂ to CO in a 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 the CO₂ reduction reaction. Furthermore, vitamin B12 is a naturally occurring, non-toxic redox mediator. Therefore, the B12-modified electrode presented herein is a promising development for future green CO₂ reduction applications.