Blended and Cross‐Linked Ionomer Membranes for Application in Membrane Fuel Cells

Abstract

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.

Acid–base blend membranes consisting of sulfonated poly(ether ether ketone) and 5-amino-benzotriazole tethered polysulfone for DMFC

“…Compared to some blend membrane systems based on acid-base interactions that have been investigated in the literature [18,19,31,32], the SPEEK/PSf-BTraz blend membranes presented here show higher proton conductivity than plain SPEEK membrane despite a decrease in the IEC values due to acid-base interactions. We believe this is mainly due to the insertion of the heterocyclic groups of PSf-BTraz into the ionic clusters formed by the sulfonic acid groups of SPEEK as indicated by the SAXS data and the consequent widening of the ionic cluster size compared to that in plain SPEEK.…”

“…The brittleness is possibly caused by the inflexibility of the covalent networks [12][13][14][15]. Because of this reason, more attention is being directed towards the development of ionomer networks containing ionically cross-linked blend systems such as SPPO (poly(2,6-dimethyl-1,4-phenylene oxide))/PBI (polybenzimidazole respectively), SPEEK/PBI, and SPSf/aminated PSf, which are more flexible [16][17][18][19]. Our group reported recently [20][21][22][23] that blend membranes based on acid-base interactions between the sulfonic acid groups of SPEEK and the N-heterocycle groups (benzimidazole (BIm), amino-benzimidazole (ABIm), nitrobenzimidazole (NBIm), and 1H-perimidine (PImd)) tethered to PSf show improved DMFC performance compared to plain SPEEK membranes due to both suppressed methanol crossover and enhanced proton conductivity.…”

Acid–base blend membranes based on 2-amino-benzimidazole and sulfonated poly(ether ether ketone) for direct methanol fuel cells

“…Cross-linked ionomers have been pursued to overcome this problem, but they usually lead to a sacrifice in fuel cell performance and microphase-separation is easy to occur in such blends due to different, incompatible acidic (aromatic) and basic (polybenzimidazole) polymer structures [14,15].…”

“…Tethering of N-heterocycles to a polymer backbone followed by its blending with a sulfonic acid polymer is an attractive strategy to achieve high proton conduction through acid-base interactions involving the sulfonic acid groups in one polymer (acidic polymer) and the basic Ncontaining groups in the other polymer (basic polymer) [14][15][16][17]. However, this strategy has been pursued with basic polymers having only one or two nitrogen atoms acting as proton donors or acceptors (e.g.…”

Cross‐Linking of Sulfonated Poly(ether ether ketone) by Thermal Treatment: How Does the Reaction Occur?

“…Cross-linking (XL) reactions are among the most powerful ways to control and improve the properties of polymeric materials, such as swelling and mechanical behavior [18][19][20]. However, the reticulation often relies on the introduction of cross-linker species, which requires special procedures, such as grafting by irradiation [21][22][23][24].…”