A comparative study of three different membrane electrode assemblies for electrochemical CO2 reduction is performed in a flowcell setup utilizing gaseous CO2 as a reagent. The membrane electrode assembly consists of a bipolar or exchange membrane, an Ag-mesh catalyst and a gas di
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A comparative study of three different membrane electrode assemblies for electrochemical CO2 reduction is performed in a flowcell setup utilizing gaseous CO2 as a reagent. The membrane electrode assembly consists of a bipolar or exchange membrane, an Ag-mesh catalyst and a gas diffusion layer. The counterreaction occurring on the opposite of the electrode assembly is oxygen evolution performed in a 1 M KOH anolyte. While using a fixed cell potential of 2.5 V, it was found that the bipolar membrane configuration produces 4 to 6 times more current versus an anion exchange membrane assembly due to the low local pH enabled at the cathode due to the bipolar membrane. This difference comparatively benefitted both CO2 reduction and the competing H2 evolution. It was further found that the surrounding infrastructure, namely the titanium sample holder, was almost exclusively performing H2 evolution, both inhibiting reactions on the Ag-mesh and preventing the formed products from being transported to the cathodic gas phase. Instead, all formed products were detected in the anolyte compartment. To circumvent these issues the sample holder was removed, and ionomer solution was applied to the Ag-mesh increase conductivity between the bipolar membrane and the Ag catalyst. During operation the membrane ultimately delaminated due to internal gas accumulation. The main conclusions from this work are that the examined membrane electrode assemblies using Ag-mesh as a cathode are unable to perform CO2 reduction while the Ag-mesh is located too far from the gas diffusion layer. Even with layer compression between all components, only trace amounts of CO were produced, implying that contact between the CO2 reduction catalyst and the CO2 source was not sufficiently present. Membrane electrode assemblies might then be improved by utilising a layer of conductive liquid between the membrane and Ag-mesh. In an alternative approach a gas diffusion electrode was produced through the sputtering of Ag directly onto the gas diffusion layer. Even without optimisation this system outperformed all produced membrane electrode assemblies in terms of CO2 reduction.