To counteract global warming, triggered by the rising levels of anthropogenic greenhouse gas CO2 in the atmosphere, carbon capture and utilisation technology (CCU), which includes the electroreduction of CO2, is a promising strategy. This technology not only valorises an otherwise harmful gas but also enables the closing of the anthropogenic carbon cycle, which could help to reduce the CO2 levels in the atmosphere. Gas diffusion electrodes (GDE) play a central role in investigating the electroreduction of CO2, as they ensure optimal contact between the catalyst, CO2, and the electrolyte/ions, thereby defining an optimal reaction environment. To advance the technical maturity of the electroreduction of CO2 to formate, this thesis investigates factors influencing the optimal reaction environment, i.e., wettability, degradation mechanisms, and cell structure, based on the electrode architecture. This dissertation emphasises the importance of a microporous layer (MPL) for achieving relevant current densities and Faradaic Efficiencies (FE). The MPL influences the focus of the catalyst layer on the GDE surface, the wetting, and the electrical conductivity, leading to an improved interface between the catalyst, the electrolyte and CO2. This improved catalyst interface enables obtaining relevant current densities and FEFormate >80%. The effects of the improved catalyst inter-face can only be exceeded by a high through-plane conductivity. In this context, the high through-plane conductivity even enables GDEs without MPL to achieve the highest FEs of all investigated GDEs (>90%), hence surpassing the obtained FE of GDEs with MPL. In addition to the MPL, the extent of the hydrophobic treatment is also decisive, as it determines the electrode wetting and the extent of the GDE/electrolyte interface. Hereby, in the case of GDEs without MPL, a lower hydrophobic treatment (10 % vs 30 % PTFE) was particularly advantageous for achieving high FEs. Regarding the influence of the hydrophobic treatment on the GDE’s durability and performance, early-stage performance changes were already apparent after 1 hour of CO2 electroreduction. These changes manifested in catalyst ag-glomeration and loss of hydrophobicity. The latter is most probably triggered by structural changes of the binder’s side chains and/or sulfonic groups, indicating the unsuitability of the binder in the investigated setup. Interestingly, the increase of the catalyst loading improved the electrode performance only to a certain point, with a medium catalyst loading of 2.3 mg.cm−2 showing the best performance. Various ion exchange ionomers were tested for their suitability to investigate further the influence of the loss of hydrophobicity and its prevention. The outcome indicates a relationship between the structural composition of the binder and the obtained cathodic current densities at –1.15 VRHE and FEFormate. The imidazolium-based binder Sustainion obtained stable FEsFormate >90% during repeated cycling due to the CO2 affinity of the imidazolium structure. The stable FEs >90% obtained with Sustainion as a binder would possibly enable the transition from a gas-fed batch cell to a flow cell. However, in preceding tests with the flow cell, the increasing HER and the premature electrode flooding over time demonstrated its detrimental use. With certain adaptations to the GDE architecture, the addition of an MPL, and a change of binder to a mixture of Aemion + Nafion, comparable results were obtained between the gas-fed batch cell and the flow cell. This engineered GDE architecture was furthermore stable during a 6-hour operation.
Verena Theussl (Wed,) studied this question.