Mass transport effects on product distribution during electrochemical CO2 reduction in a custom-designed rotating cylindrical electrode cell

Abstract

As the global energy demand is rising continuously and the fossil fuel depletion is advancing, new technologies are needed to meet the challenges the energy industry is facing. Progress in the field of renewable energies has grown steadily. However, it is still critical to accelerate progress in the economic viability of these technologies. In the near future, no single renewable technology will be able to compete with fossil fuels. The task is to establish an infrastructure to jointly utilize energy from many different areas of renewable energy in a sustainable manner. In this work a promising field of research - the electrochemical reduction of carbon dioxide (CO2RR) - will be discussed. This reaction can potentially produce various C2+ carbohydrates, oxygenates and other carbon moieties that can be used as fuels or as basic chemicals needed in the chemical industry. The input required for this reduction is simply electricity and the reactants carbon dioxide and water. Carbon dioxide (CO2) is a major greenhouse gas that contributes to climate change and rising temperatures and exhibits an increasing concentration in the atmosphere. The local removal of CO2 from industrial exhaust gases or the direct extraction from the air not only generates the main reactant of this reaction but also contributes in reducing its occurrence in the atmosphere to a moderate level. The second reactant, water, is abundant. The aim would be to minimize the overpotential required for this reaction and to convert excess electricity fromrenewable energy sources such as solar and wind into chemicals with a high energy density. This thesis focuses on mass transfer effects during electrochemical CO2 reduction in a successfully designed gas-tight electrochemical cell with an integrated rotating cylindrical electrode. The application of the reduction of potassium ferricyanide was used to quantify the hydrodynamics of the rotation cell. By conducting experiments on CO2RR at different rotation speeds and electrolyte concentrations a deeper understanding of the reaction mechanism and the influence of mass transport effects on product selectivity was gained. A mathematical model was developed to rationalize that obtained data. The insights helped to further develop an advantageous experimental set-up that will add to achieve the goal of lowering overpotentials, and thus, reduce the electricity input needed. This will lead to lower costs of this technology making it more competitive in the field of energyalternatives on the road to replace fossil resources.