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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 °C (PEFC) and 130 °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 °C) and DMFC (up to 130 °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 cross‐linked membranes were tested in a DMFC up to 110 °C and demonstrated good performance. (vi) Differently cross‐linked 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 °C.

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