Use of isotopically labelled compounds for the in situ IR study of the electroreduction of CO2 in aqueous hydrogencarbonate and buffered phosphate solutions

Subtractively normalised FTIR spectroscopy studies on the electroreduction of CO, at a Cu electrode, using isotopically labelled CO2 and HCO3- in H2O and D2O, indicate that as the applied potential is varied in the staircase mode from -0.6 to -1.5 V (vs. SCE), aqueous CO2 is first transformed to hydrogencarbonate and then to carbonate rather than undergoing a reduction process. This result confirms that the 'carbonate route' introduces a major obstacle in the electrochemical reduction of CO2 in aqueous systems. The use of isotopically labelled CO2 and HCO3- confirms unequivocally, that the carbonate ions formed at the electrode originate from the dissolved CO2 and not from the bulk electrolyte. Studies performed using other electrodes (Ni and Pt) show the same behaviour although in different potential ranges. Comparison with similar studies reported in recent literature suggests that the history of the electrode and pretreatment are very critical. An important isotope fractionation effect was observed which can be attributed to the different rates of hydration and ensuing reactions of (CO2)-C-12 and (CO2)-C-13.