Electrochemical carbon dioxide reduction on rough copper surfaces

Abstract

Sustainable development and climate change is considered to be one of the top challenges of humanity. Electrochemical carbon dioxide (CO2) reduction to fuels or fuel precursor using renewable electricity is a very promising way to recycle CO2 and store the electricity. This would also provide renewable fuel to the transportation which heavily relies on liquid hydrocarbons. In this thesis, the formation of fuel or fuel type of molecules by CO2 electroreduction was investigated and discussed. The primary aims were to decrease the required overpotential which will be reflected as a lower consumption of electricity in any industrial electrochemical process and understanding of formation of different products such as CO, ethylene and methane on nanostructured copper electrodes which is very essential to improve the efficiency of the electrochemical process. We uncovered that the selectivity of electrochemical carbon dioxide reduction is dramatically influenced by the catalyst loading, roughness, surface area and applied process conditions. High surface area electrodes produce mostly C2 hydrocarbons in contrast to smooth polycrystalline electrodes. Ethylene is formed as a result of a high local pH and pressure, whereas ethane is formed by further hydrogenation of ethylene. One of the most original and intriguing results we obtained is the deactivation of copper when methane is produced on the electrode. It was very important to discover that a CO dimerization pathway does not lead to poisonous species on the electrode surface, which are most likely associated with a C1 pathway. Rough surfaces not only result in selective hydrocarbon formation, but also in formation of carbon monoxide. By improving the mass transfer either by elevated pressure or use of gas diffusion electrodes, a high selectivity towards carbon monoxide (≈75%) can be obtained at low overpotentials (200-400 mV).