Electrochemical reduction of carbon dioxide was studied with various series of copper single crystal electrodes in 0.1 M KHCO3 aqueous solution at constant current density 5 mA cm(-2); the electrodes employed are Cu(S)-[n(1 0 0) x (1 1 1)], Cu(S)-[n(1 0 0) x (1 1 0)], Cu(S)-[n(1 1 1) x (1 0 0)], Cu(S)-[n(1 1 1) x (1 1 1)] and Cu(S)-[n(1 1 0) x (1 0 0)]. The electrodes based on (1 0 0) terrace surface give ethylene as the major product. The ethylene formation is further promoted by the introduction of (1 1 1) or (1 1 0) steps to the (1 0 0) basal plane. The highest C2H4 to CH4 formation ratio amounts to 10 in terms of the current efficiency for the (7 1 1) (=4(1 0 0) - (1 1 1)) surface as compared with the value 0.2 for the (I 11) electrode. The n (1 1 1) - (1 1 1) surfaces favor the formations of acetic acid, acetaldehyde and ethyl alcohol with the increase of the (1 1 1) step atom density. CH4 formation at the n (1 1 1) - (1 1 1) electrodes decreases with the increase of the (111) step atom density. The n (1 1 1) - (1 0 0) surfaces give higher gaseous products; the major product is CH4 with lower fraction of C-2+ compounds. (C) 2003 Elsevier Science B.V. All rights reserved.