PBI-Blended Membrane Evaluated in High Temperature SO2 Electrolyzer

Wednesday, 16 May 2018: 10:50
Room 617 (Washington State Convention Center)
R. Peach (NWU, Focus Area: Chemical Resource Beneficiation, Institute of Chemical Process Engineering, Stuttgart), H. Krieg (NWU, Focus Area: Chemical Resource Beneficiation), A. Kruger, D. Bessarabov (NWU HySA Infrastructure), and J. A. Kerres (University of Stuttgart, Institute of Chem. Proc. Eng.)
It has been shown that hydrogen, which can be used for energy storage, can be produced efficiently by the membrane based Hybrid Sulfur (HyS) process. During the HyS electrolysis step, SO2 and H2O are converted to H2 and H2SO4. The proton exchange membrane (PEM) used for this process should have both a high proton conductivity and acid stability. Since the widely used perfluorosulfonic type materials are restricted by their humidification requirements, materials such as polybenzimidazole (PBI) has been found to be promising in blends with partially fluorinated polyaromatic polymers at operating temperatures of 80 and 95 °C within the SO2 electrolyser. Operation at higher temperatures (>100 °C) however holds many advantages such as improved reaction kinetics and simplified water management. For this study a cross-linked partially fluorinated polyaromatic PBI blended membrane was evaluated at 120 °C. Humidified SO2 was supplied to the anode to produce sulfuric acid while hydrogen was formed at the cathode. The SO2:H2O feed was managed at the applied current densities until a constant voltage was obtained, and there after increased accordingly with increasing current density. Polarisation curves (Figure 1) recorded for the blended PBI membrane were comparable with reported s-PBI in literature values in the lower current density region (< 0.5 A/cm2). A maximum current density of 1.1 A/cm2 was reached in comparison to the 0.5 A/cm2 for s-PBI at a temperature of 110 °C. Voltage stability was monitored at a current density of 0.3 and 0.6 A/cm2 for a duration of 6 hours or until the maximum voltage had been reached. The lower current density (0.3 A/cm2) was more constant over the course of the measurement, with a standard deviation of 3 mV, when compared to the higher applied current density. These results are promising for further testing and optimization of the blended PBI membranes for higher temperature SO2 electrolysis.