|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1995 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1994 : ¥1,400,000 (Direct Cost : ¥1,400,000)
1 Electrochemical reduction of carbon dioxide in aqueous media yields various kinds of products, the distribution of which depends greatly upon metal electrodes. Metal electrodes are thus divided into four groups in accordance with the product selectivity in CO_2 reduction. (1) Ni, Fe and Pt etc. can hardly reduce carbon dioxide and only hydrogen is evolved as a result of water reduction (H_2 metals). (2) Au and Ag etc. give CO from CO_2 (CO metals). (3) Formic acid is produced at Hg and Pb etc. electrodes (FA metals). (4) Cu electrode exclusively yields hydrocarbons, such as methane and ethylene, and alcohols (HC metal). The distinct metal groups indicate different adsorbate on the metal surface. Infrared spectroscopy gives informetions about adsorbed species and its circumstances. The present investigator observed adsorbed species and revealed the inetermediate of thesereac tions over various metal electrodes by infrared spectroscopy.
2 Four metal electrodes in three groupes were inve
stigated ; (1) Ni and Fe, as H_2 metals, (2) Au, as, CO metal, and (3) Cu, as HC metal.
(1) H_2 metal : Ni reduces CO_2 or CO to a small amounts of hydrocarbons besides a large amounts of hydogen. Infrared spectroscopy revealed that CO is formed and adsorbed on the surface during Co_2 duction and that hydrocarbons are formed from the adsorbed CO.The metals in this group produce CO but adsorbed CO disturb CO_2 reduction and adsorbed CO can reduce to hydrocarbons, but its reduction rate is slow.
(2) CO metal : Infrared spectra of adsorbed CO was deteted at Au electrode after CO_2 reduction, but CO adsorbs at limited potentials and does not adsorb the potentials which CO_2 reduces.
HC metal : During CO_2 reduction at Cu, adsorbad CO was obserbed by IR spectroscopy. The reaction rate of adsorbad CO is fast. The reason of high reactivity of CO adsorbad on Cu will be next thema.
3 From above infrared spectroscopic results, CO is formed at H_2 metals and HC metal, and then (1), (2) and (3) metal groups are considered as (expanded) CO metal group. The selection to CO and formic acid is important. CO_2^- anion radical is proposed as the key intermediate of the selection. Investigation of the nature of CO adsorbed on Cu electrode and the detection of CO_2^- is importanta and will be next thema. Less