Blended and cross-linked ionomer membranes for application in membrane fuel cells

Differently cross-linked blend membranes were prepared from commercial arylene main-chain polymers of the poly(etherketone) and poly(ethersulfone) classes, modified with sulfonate groups, sulfinate cross-linking groups, and basic N-groups. The following membrane types have been prepared: (i) Van-der Waals/dipole-dipole blends by mixing a polysulfonate with unmodified PSU. This membrane type showed a heterogeneous morphology, leading to extreme swelling and even dissolution of the sulfonated component at elevated temperatures. (ii) Hydrogen bridge blends by mixing a polysulfonate with a polyamide or a polyetherimide. This membrane type showed a partially heterogeneous morphology, also leading to extreme swelling/dissolution of the sulfonated blend component at elevated temperatures. (iii) Acid-base blends by mixing a polysulfonate with a polymeric N-base (in-house developed/commercial). A wide range of properties could be achieved with this membrane type by variation of the different parameters. Membranes showing excellent stability and good fuel cell performance up to 100 degrees C (PEFC) and 130 degrees C (DMFC) were obtained. (iv) Covalently cross-linked (blend) membranes by either mixing a polysulfonate with a polysulfinate or by preparing a polysulfinatesulfonate, followed by reaction of the sulfinate groups in solution with a dihalogeno compound under S-alkylation. The membranes prepared showed effective suppression of swelling without a loss in the H+-conductivity. The membranes showed good PEFC (up to 100 degrees C) and DMFC (up to 130 degrees C) performance. (v) Covalent-ionically cross-linked blend membranes by mixing polysulfonates with polysulfinates and polybases or by mixing a polysulfonate with a polymer carrying both sulfinate and basic N-groups. The covalent-ionically crosslinked membranes were tested in a DMFC up to 110 degrees C and demonstrated good performance. (vi) Differently crosslinked organic-inorganic blend composite membranes via various procedures. The best results were obtained with blend membranes having a layered zirconium phosphate ZrP phase: they were transparent, and showed good H+-conductivity and stability. The application of one of these composite membranes in a PEFC yielded good performance up to T = 115 degrees C.