USE OF ISOTOPICALLY LABELED COMPOUNDS FOR THE IN-SITU IR STUDY OF THEELECTROREDUCTION OF CO2 IN AQUEOUS HYDROGENCARBONATE AND BUFFERED PHOSPHATE SOLUTIONS

Subtractively normalised FTIR spectroscopy studies on the electroreduc tion of CO, at a Cu electrode, using isotopically labelled CO2 and HCO 3- 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 firs t transformed to hydrogencarbonate and then to carbonate rather than u ndergoing a reduction process. This result confirms that the 'carbonat e route' introduces a major obstacle in the electrochemical reduction of CO2 in aqueous systems. The use of isotopically labelled CO2 and HC O3- confirms unequivocally, that the carbonate ions formed at the elec trode originate from the dissolved CO2 and not from the bulk electroly te. Studies performed using other electrodes (Ni and Pt) show the same behaviour although in different potential ranges. Comparison with sim ilar studies reported in recent literature suggests that the history o f the electrode and pretreatment are very critical. An important isoto pe fractionation effect was observed which can be attributed to the di fferent rates of hydration and ensuing reactions of (CO2)-C-12 and (CO 2)-C-13.