Stacking of various flow-cells for the CO$_{2}$-to-CO electrolysis

Based on the highly selective and stable electrocatalyst Ag, the aqueous CO$_2$-to-CO electrolysis has emerged as a promising prospect for replacing fossil resources in the production chain of various chemical products. However, despite encouraging performances of single flow-cells in lab-scale size operating with gas-diffusion-electrodes (GDEs) at industrially relevant conditions, the discussion around the scaling of CO$_2$-to-CO electrolysis systems is underrepresented. In this work, studies are performed concerning the stacking of the most promising flow-cell concepts, which is a key enabling step in scaling electrolysis processes. In an initial study, a GDE-flow-cell with a proton exchange membrane and a flow-cell with a membrane electrode assembly (MEA) containing an anion exchange membrane (AEM) were singled out as the most promising cell designs. To the first one mentioned, performance-enhancing modifications on the media flow compartments were carried out.A gas flow-field was implemented, leading to an enhanced selectivity at diluted feed gas supply. An ionically conductive spacer was introduced in the catholyte chamber, which enhanced the process stability. To demonstrate, that the combination of the two modifications results in stackability, a two-cell short-stack is tested.While a general stackability of the concept is demonstrated, a limitation of the stack design regarding the investigation of stack-specific challenges becomes evident. Building upon the experience gained, a modular short-stack design and its operation as a three-cell short-stack with the MEAs is presented. Due to temperature effects, the short-stack surpassed its equivalent single-cell in cell voltage. Benefiting from the modular characteristic, temperature gradients, which led to a position-dependent behavior of the individual cells in the stack, could be observed. Furthermore, the presented design enabled the quantification of shunt currents, which were identified to be negligible in the examined system. Once again, the modularity was exploited in a study concerning the anodic catalyst surface area, which was increased by the implementation of catalyst-coated flow-fields. While the functionality of two-material Bipolar-Plates was demonstrated, the impact of the catalyst surface increase was considered to be negligible.