PBI nanofiber mat-reinforced anion exchange membranes with covalently linked interfaces for use in water electrolysers

Anion exchange membranes (AEM) are key components in anion exchange membrane water electrolysers. Recently developed materials are less susceptible to the alkaline degradation of the polymer backbone and quaternary ammonium groups. A remaining challenge is the mechanical stability in contact with hot water and dimensional stability when the temperature of the feed solution changes. One solution is to reinforce membranes with a porous support. Since support materials like PEEK or PTFE have a different swelling behavior than the matrix and no strong interactions with the matrix, voids can form, and gas crossover increases. In this work, we approach this issue by pore filling polybenzimidazole nanofiber mats with the bromomethylated precursor of mTPN, an ultra-stable AEM material. During drying, a covalent interaction between support (PBI amine groups) and matrix (-CH₂Br) is established. After quaternization, the optimized PBI/mTPN-50.120 composite membrane still shows a high conductivity of 62 mS cm⁻¹, but 37% reduced length swelling in comparison to the non-reinforced membrane. Tensile strength and Young modulus increase 17% and 56% to 49 MPa and 680 MPa, respectively. In an electrolyser, a stable voltage of 1.98V at 0.25 A cm⁻² was achieved, and no change in membrane resistance was observed over the test time of 200 h (50 °C, 1 M KOH, catalysts based on Ni/Fe and Mo).