For the isotopic labelling experiments with 13 CO2, the 13 CO2 capture was performed by stirring the 1 M TEA solution in water or 1 M NaOH solution in EG for 2 h under CO2 atmosphere. The obtained solutions were purged with N2 for 15 min to remove physically dissolved CO2 and were then used for electrochemical reduction as per standard electrochemical conditions. The product gas mixture generated in the cathode after 2 h (at -0.7 V vs. RHE, TEA/H2O system) or 20 h (at -1.85 V vs. Fc/Fc + , NaOH/EG system) of CPE were analysed by IR spectroscopy to determine the isotopic abundance in the product CO.