Electrochemical reduction of CO 2 at copper single crystal Cu(S)-[ n(111)×(111)] and Cu(S)-[ n(110)×(100)] electrodes

Abstract

Electrochemical reduction of CO 2 was studied using two series of single-crystal electrodes, Cu(S)-[ n(111)×(111)] and Cu(S)-[ n(110)×(100)] at a constant current density of 5 mA cm −2 in 0.1 M KHCO 3 aqueous solution. Copper single crystals were grown from 99.999% copper metal in a graphite crucible, and the crystal orientation was determined by the X-ray back reflection method. The surface treatment of the copper single crystal electrodes was studied in detail, and the reproducibility of the CO 2 reduction was greatly improved. The product distribution of the CO 2 reduction varies greatly with the crystal orientation. CO 2 reduction at the Cu(110) (=Cu(S)-[2(111)×(111)]) electrode gives a current yield of 20% of CH 3COOH; the formation of CH 3COOH in CO 2 reduction has not been reported previously. The yield of CH 4 was very low (6%) at the Cu(110) electrode. The formation of CH 4 and CH 3COOH changes significantly with the crystal orientation. A decrease of the step atom density in the Cu(S)-[ n(111)×(111)] series reduces the yield of CH 3COOH and enhances that of CH 4. Introduction of the (100) step to the Cu(110) basal plane, leading to the Cu(S)-[ n(110)×(100)] series with kink sites, diminishes the feature of the Cu(110). The Cu(210) (=Cu(S)-[2(110)×(100)]), which has the highest number of dangling bonds of fcc metals, gives a high yield of CH 4 with a product distribution similar to that of Cu(111) which has the lowest density of dangling bonds.