A new electrolysis system has been developed for the selective conversion of CO2 to ethylene in which the electrochemical reduction takes place at the three-phase (gas/liquid/solid) interface on a Cu-mesh electrode mediated with copper(I) halide in an aqueous solution of potassium halide. The conversion percentage Of CO2 (initial volume: 577 cm(3)) reaches about 90% by the electrolysis with the electric charge of 8.9 kC, and the selectivity for C2H4 formation is about 75%. The selective conversion of CO2 to C2H4 is attributed to the immobilized copper(I) halide which operates as a heterogeneous catalyst by offering adsorption sites for reduction intermediates such as CO and carbene. (C) 2004 Elsevier B.V. All rights reserved.