Preparation and Evaluation of Membrane Electrode Assemblies for Electrochemical CO2 Reduction

Kurzfassung

The research on electrochemical CO2 reduction is dominated by catalyst materialtesting and investigations on selectivity controls. The focus is shifting from the H-cell research design towards a membrane electrode assembly (MEA) cell designs which are more suitable for industrial applications. A MEA cell using H2O anolyte is the desired configuration. Compared to other anolyte systems the H2O usage presents the characteristics of less utilisation costs, fewer security efforts as well as the prevention of salt formation. In order to study selectivities of specific CO2 reduction products (CO2RP) the preparation process of this thesis included the assembly of a 25 cm2 MEA setup that realises the electrochemical CO2 reduction reaction (CO2RR). Therefore, the basic element is a graphite flow field MEA cell construction. When preparated, the cell offered the conduction of continuative studies on electrochemical CO2RR performance and selectivity. In this thesis, the studies focussed on the influence of the anolyte material, the catalyst loading and the reduction reaction stability. First, the anolyte variation was tested for low concentrated 0.1 M KOH and 0.5 M KHCO3 in comparison to ultrapure water. The results with the Fumasep® AEM show performance differences depending on the anolyte concentrations. Nonetheless, it is illustrated that there is no selectivity deficit using the H2O anolyte. The AEM reveals less and the PEM shows no CO2RR selectivity. Each anolyte system presents a high selectivity of C2H4 (15-20% FE) and CO (up to 34% FE). The 90 min stability measurement at 80 mA/cm2 reveals no loss in the Faradaic efficiency results. Second, the Cu2O sprayed catalyst loading was varied from 1-2.5 mg/cm2 to optimise selectivities and performance, achieving current densities up to 400 mA/cm 2. Third, a Sustainion™membrane AEM and a Nafion® PEM material where tested. One measurement presents the high potential of water anolyte systems reaching 76% FE (Faradaic efficiency) CO2RR products including 55% FE ethylene.