▎ 摘　　要

A naturally occurring water-soluble cobalt-complex cyanocobalamin (Vitamin B12) has been identified as a new and efficient electrocatalyst for the CO2-to-CO reduction reaction in aqueous solution. Heterogeneous B12-electrocatalysts prepared by a simple electrochemical immobilization technique on graphene-oxide (GO)-modified glassy carbon and carbon paper (CP) electrodes, without any non-degradable polymer-binders, showed a highly stable and well-defined surface-confined redox peak atE'=-0.138 V vs. RHE with a surface-excess value,Gamma(B12)=4.28 nmol cm(-2). This new electrocatalyst exhibits 93 % Faradaic efficiency for CO2-to-CO conversion at an electrolysis potential, -0.882 V vs. RHE (an optimal condition) with a high current density, 29.4 mA cm(-2)and turn-over-frequency value, 5.2 s(-1), without any surface-fouling problem, in 0.5 mKHCO(3). In further, it follows an eco-friendly, sustainable and water-based approach with the involvement of biodegradable and non-toxic chemicals/materials like B12, GO and CP.