Electrocatalytic urea synthesis from CO2 and nitrate co-reduction on natural vitamin B12 coupled carbon nanotubes

Abstract

The synthesis of urea from CO2 and nitrate co-electrolysis is highly attractive for the sustainable production of nitrogen-containing fertilizers such as urea. However, this process requires electrocatalysts that are not only highly active but also selective. In this study, we present a remarkable approach wherein Vitamin B12 is immobilized on the surface of carbon nanotubes to catalyze the co-electroreduction to urea under ambient conditions. This unique hybrid system, incorporating a naturally abundant molecular catalyst, exhibits exceptional selectivity and maintains a constant current density in CO2-saturated 0.1 M KNO3. Remarkably, we achieved a Faradaic efficiency (FE) of 26.04% at −0.5 V versus the reversible hydrogen electrode (RHE), resulting in a production yield of 164.04 μg h−1 mg−1 and an impressive turnover number (TON) reaching up to 830.53 while demonstrating excellent stability and durability over a period of 50 hours. Our experimental findings are further supported by density functional theory (DFT) studies that shed light on the influence exerted by the covalently attached and redox-active benzimidazole unit within Vitamin B12 molecule itself when immobilized onto conductive surfaces like carbon nanotubes. This work represents an unprecedented example where naturally abundant vitamin has been successfully immobilized on a conductive surface for achieving highly efficient electroproduction of urea.