Time Course of Product Selectivity by Ag Nanoparticle Modification on Metal Cathode Electrodes for Electrochemical CO₂ Reduction

Global warming is a major issue in modern society. The most significant cause of global warming is the increase in the concentration of carbon dioxide in the atmosphere. One of the technologies to reduce the concentration of carbon dioxide in the atmosphere is carbon dioxide reduction. Carbon dioxide reduction is a technology that uses electrical energy to electrochemically reduce carbon dioxide to formic acid, methane, ethylene, ethanol, and other substances. Current problems with electrochemical carbon dioxide reduction include the lack of product selection and the inability to operate for long periods of time. It is known that the selectivity of products varies with the material used for the CO₂-reduced cathode electrode and the cathode potential during the reaction. Especially for the electrode material, the metal type and crystal surface affect the products. The copper cathode has attracted much because of its high efficiency in generating ethylene, which is an industrially useful substance such as a raw material for plastics. However, the products have not yet been fully controlled. In addition, there is a problem in that the surface of copper changes after prolonged operation, making it decrease the ethylene reduction efficiently.<br/>It is known that CO is produced as an intermediate product in the reaction process of CO₂ to ethylene. Therefore, spray coating the Cu electrode with Ag, which reduces CO₂ to CO well, is expected to improve the CO₂ reduction capability. The Ag nanoparticles were sprayed on the Cu electrode surface using a spray coating machine to modify the electrodes in this report. The evaluations were performed with electrochemical cyclic voltammetry and chronopotentiometry. The reduced products were evaluated by gas chromatography. The surface condition of the electrode before and after the reaction was also evaluated.<br/>It was found that the metal cathode electrode modified with Ag nanoparticles improved the CO₂ reduction ability to ethylene compared with the bare Cu metal electrode. It was also confirmed that the potential during the reaction was stabilized by modification with Ag nanoparticles. The surface evaluation results showed that the surface showed dispersed Ag nanoparticles on the metal surface, and it has the possibility of the improvement of CO₂ reduction.