Carbon dioxide has been selectively reduced to ethylene with a CuCl-confined Cu-mesh electrode. In this system, the CO2 reduction is performed at the three-phase (gas/liquid/solid) interface, and CO2 is supplied to the electrode surface from the gas phase, permitting us to maintain a high concentration of CO2 irrespective of the solubility of CO2 in the solution. A maximum faradaic efficiency (69.5%) for C2H4 was obtained at -1.8 V vs. Ag/AgCl, and the selectivity estimated on the basis of carbon content was 74%. The selective reduction of CO2 to ethylene is attributed to the ability of CuCl to reversibly combine with CO and C2H4. First, CO2(g) is electrochemically reduced to CO(g) at the three-phase interface, and then CO is adsorbed on CuCl with its p bond perpendicular to the surface. Further electrochemical reduction of CO leads to the generation of CH2 and the coupling of methylene radicals to C2H4. The ethylene thus formed may be stabilized by being adsorbed on CuCl with its pi bond parallel to the surface. (C) 2003 The Electrochemical Society.