1. Field of the Invention
This invention relates to improvements in an electrocatalyst for electrolytic reduction of carbon dioxide gas (CO.sub.2).
2. Description of the Prior Art
Attention is being paid to researches and developments relating to reduction fixation and recovery of carbon dioxide gas, which are disclosed for example in Japanese Patent Provisional Publication No. 65-15388. These researches and developments include ones relating to electrochemical reduction of carbon dioxide gas in which a reduction by using an electrolysis catalyst is used for the purpose of improving selectivity in reaction and decreasing over voltage. The reduction catalyst is used in the state to modify the surface of an electrode of metal, or to be added in an electrolyte solution. It is known that examples of such a reduction catalyst are metallopthanine complexes and nickel microcyclic polyamine.
Additionally, it is disclosed that nickel cyclam (1,4,8,11-tetraazatetradecane) serves as an electrocatalyst for reducing carbon dioxide to carbon monoxide with a high reaction selectivity even in an aqueous solution, in "Journal of the American Chemical Society", 1986, 108, 7461-7467.
However, the following difficulties have been encountered in the conventional electrocatalyst of nickel cyclam: (a) An effect of decreasing the overvoltage is low, thereby increasing energy consumption. (b) The turnover number for the catalyst is low. (3) The stability of the catalyst is low. (4) In the aqueous electrolyte solution, a hydrogen gas generation reaction and a carbon dioxide reduction reaction compete with each other, so that the selectivity of reactions is insufficient. Thus, the conventional electrocatalyst of nickel cyclam is insufficient for practical use in electrolytic reduction of carbon dioxide gas in an aqueous solution.