Electrochemical production of hydrocarbons from carbon dioxide and water

Electrocatalytic reduction of CO2 is one possibility to solve the electrical energy storage problem and decrease the amount of CO2. Copper is the only metal that has been reported to produce hydrocarbons in the electrochemical CO2 reduction at ambient pressure and temperature. External parameters (potential, temperature and electrolyte), copper catalyst morphology and purity and newly designed carbon-based electrodes were investigated. The highest Faraday efficiency towards hydrocarbons at 22°C was obtained at a fixed potential of -2.50 V vs. Ag/AgCl reference electrode. The best electrolyte solution is 0.1 M KHCO3. Methane is the dominant product. FE towards ethylene maximizes at -2.25 V. Up to 40°C, the total Faraday efficiency towards hydrocarbons is not influenced by temperature, but ethylene amount increases with increasing temperature. Above 40°C hardly any hydrocarbons are formed. Altering the surface structure of the copper catalyst by electrodeposition give different results for the electrocatalytic CO2 reduction. The rougher the surface, the less methane and the more ethylene was formed. The macroscopic smooth surfaces are related to the (001) orientation and a rough macroscopic surface is related to the (111) orientation. To increase the surface area, carbon-based catalyst supports (graphite plates, carbon nanofibers and carbon xerogels) were tested. They show promising results.