The total analysis of gaseous and soluble products was carried out in the electrochemical reduction of CO2 (current density 5 mA cm−2) on various electrode metals. HCOO− was predominantly produced at Cd, In, Sn, and Pb cathodes. Ag and Au principally gave CO. CH4 was formed in an appreciable amount at Cu cathode.

The electrochemical reduction of CO2 was studied with galvanostatic (5 mA cm−2) electrolysis at a copper electrode between 0 and 40 °C. The production of CH4 and C2H4 was confirmed by GC with 4 different columns. The faradaic efficiency of CH4 formation was about 65% at 0 °C and dropped with an increase of temperature, whereas that of C2H4 formation rose to ca. 20% at 40 °C.

C02 is electrochemically reduced to CO in 0.5 M aqueous KHCOB solution at a gold electrode a t 18 "C, the reaction proceeding with markedly low overvoltage, starting at -0.8 V vs. normal hydrogen electrode (N.H.E.); the faradaic efficiency for CO formation is 91% a t -1.10 V vs. N.H.E. with a partial current of 3.7 mA cm-2, and the reaction probably proceeds via adsorbed intermediates.The cathodic reduction of C 0 2 at metal electrodes (Hg, Pb, Zn, Cd, Sn, and In) exclusively yields HC02-with high overvoltages in aqueous inorganic salt solutions. 1 We previously reported the electroreduction of C02 at various metal cathodes in KHC03 aqueous solution.2 Au and Ag cathodes gave CO as the major product. CH4 and C2H4 were produced at Cu cathodes with high current efficiencies of 5-10 mA cm-2. We now describe the effective electroreduction of C02 to CO at an Au cathode.An Au electrode (99.99% purity), size 20 X 20 x 0.5 mm, welded to a gold wire (0.5 mm diameter), was etched with aqua regia for 1 min at ambient temperature, and then rinsed three times with doubly distilled water in an ultrasonic cleaning bath. A three-compartment Pyrex cell was employed in which two anode compartments faced each side of the cathode. The cathode compartment (36 mm inner diameter) was separated from the two anodes with sheets of cation exchange membrane (Selemion). The cathode was placed roughly at the centre of the electrolyte. The potential of the cathode was measured with respect to an Ag/AgCl electrode. The electrode potential was corrected for the IR drop between the Luggin capillary tip and the cathode. The aqueous electrolyte (0.5 M KHC03) was purified by pre-electrolysis with a 30 x 20 mm Pt black cathode at 2 X 10-2 mA cm-2

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