Partially cross-linked sulfonated PBT-b-PBI block copolymers enabling wide-temperature proton exchange membrane fuel cells

This research was dedicated to the development of high-performance proton exchange membranes (PEMs) via the synthesis of two sulfonated poly(benzothiazole)-b-poly(benzimidazole) (sPBTx-PBI) block copolymers.The structural difference between them is primarily in the length of their hydrophilic chains. Excellent solubility was achieved through the incorporation of hexafluoroisopropyl and phenylphosphine oxide units. Partially cross-linked PEMs (sPBTx-PBI-y) were subsequently fabricated via thermal cross-linking of the hydrophobic PBI segments. The elongation of the hydrophilic block was found to promote water uptake, swelling, and proton conductivity at the expense of oxidative stability. Cross-linking effectively mitigated swelling and greatly improved durability while preserving high proton conductivity. The proton conductivity of the sPBT12-PBI-20% membrane reached 0.115 S cm −1 at 80 °C and 100% RH—exceeding Nafion 117—and maintained a stable operating voltage of 0.79 V over 20 h. Under anhydrous 200 °C conditions, single-cell power densities reached up to 510 mW cm −2 . These results demonstrate that partially cross-linking of sPBT-PBI block copolymers provides a promising pathway toward mechanically robust and highly conductive PEMs for wide-temperature fuel cell applications.