Membranes for water electrolysis

Abstract

In electrolysers, AEM are in contact with hot, liquid water. Surprisingly, it is not well investigated how this changes the membrane properties. We show stress-strain tests in temperature-controlled water, analyze if and how much decreasing temperature reduces the membrane dimensions, and present a simple method to measure the true hydroxide conductivity of AEM in temperature-controlled water.[1] AEM are often reinforced to tackle the swelling in hot water, but the different swelling behavior of matrix and support leads to their delamination. This forms voids and thus increases transfer of materials across the membrane. To strengthen the matrix│support interface, we propose a method which introduces covalent bonds between matrix and support.[2] To minimize dimensional changes during cell assembly (dry membrane) and start of operation (wet membrane in contact with water, we propose to pre-swell AEM with high boiling point solvents like ethylene glycol (EG). While water evaporates quickly, it takes several hours to evaporate EG. Thus, the EG-swollen membrane can be handled easily without significant dimensional changes during cell assembly, and only swells marginally when the electrolyser is filled with water or KOH solution.[3] An alternative to AEM is the use of ion-solvating membranes. We developed porous PTFEsupported polybenzimidazole gels. In comparison to state-of-the art KOH doped PBI membranes, which fail rapidly in alkaline electrolysers, the reinforced gel PBI membranes were successfully tested for 1000 hours without failure, at a performance similar to PEM water electrolysers.[4]