In-situ self-crosslinked sulfonated poly(arylene ether ketone) with alkyl side chain for enhanced performance

Synthesis and Characterization of Poly(5'-hexyloxy-1',4-biphenyl)-b-poly(2',4'-bispropoxysulfonate-1',4-biphenyl) with High Ion Exchange Capacity for Proton Exchange Membrane Fuel Cell Applications

Proton exchange membrane (PEM) is pivotal for proton exchange membrane fuel cells (PEMFCs). In the present work, a block copolymer with hydrophilic alkyl sulfonated side groups and hydrophobic flexible alkyl ether side groups, poly(5'-hexyloxy-1',4-biphenyl)-b-poly(2',4'-bispropoxysulfonate-1',4-biphenyl) (HBP-b-xBPSBP), is designed and synthesized by copolymerization of the hydrophilic and hydrophobic oligomers. The oligomers are synthesized via a Pd-catalyzed Suzuki cross-coupling of 1,3-dibromo-5-hexyloxybenzene, and 3,3'-[(4,6-dibromo-1,3-phenylene)bis(oxy)]bis(propane-1-sulfonate) or 1,4-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene. The good solubility and film-forming characteristics are achieved via the introduction of flexible hexyloxy side groups, and high ion exchange capacity (IEC) is achieved via the introduction of high density of alkyl sulfonated side groups. The HBP-b-0.5BPSBP has the highest IEC of 3.17 mmol/g, the highest proton conductivity of 43.5 mS/cm at 95 °C and 90% relative humidity (RH) and low methanol permeability of 6.45×10^-7  cm² /s. Meanwhile, crosslinked HBP-b-xBPSBP exhibits promising water uptake, swelling ratio and low methanol permeability. These characteristics are attributed to the crosslinked structure and the hydrophilic/hydrophobic nanophase separation morphology promoted by the poly(m-phenylene) main chains, flexible alkyl ether groups, and alkyl sulfonated side groups.

Enhanced Performance of a Sulfonated Poly(arylene ether ketone) Block Copolymer Bearing Pendant Sulfonic Acid Groups for Polymer Electrolyte Membrane Fuel Cells Operating at 80% Relative Humidity

The series of sulfonated poly(arylene ether ketone) (SPAEK) block copolymers with controlled F-oligomer length bearing pendant diphenyl unit were synthesized via a polycondensation reaction. Sulfonation was verified by ¹H NMR analysis to introduce sulfonic acid group selectively and intensively on the pendant diphenyl unit of polymer backbones. The SPAEK membranes fabricated by the solution casting approach were very transparent and flexible with the thickness of ∼50 μm. These membranes with different F-oligomer lengths were investigated to the physiochemical properties such as water absorption, dimensional stability, ion exchange capacity, and proton conductivity. As a result, the SPAEK membranes (X4.8Y8.8, X7.5Y8.8, and X9.1Y8.8) in accordance to increasing the length of hydrophilic oligomer showed excellent proton conductivity in range of 131-154 mS cm^-1 compared to Nafion-115 (131 mS cm^-1) at 90 °C under 100% relative humidity (RH). Among the SPAEK membranes, proton conductivity of SPAEK X9.1Y8.8 (140.7 mS cm^-1) is higher than that of Nafion-115 (102 mS cm^-1) at 90 °C under 80% RH. The atomic force microscopy image demonstrated that number of ion transport channels is increased with increase in the length of hydrophilic oligomer in the main chains, and the morphology is proved to be related to the proton conductivity. The synthesized SPAEK membrane exhibited a maximum power density of 324 mW cm^-2, which is higher than that of Nafion-115 (291 mW cm^-2) at 60 °C under 100% RH.

Facile construction of crosslinked anion exchange membranes based on fluorenyl-containing polysulfone via click chemistry

Crosslinked fluorenyl-containing polysulfone based anion exchange membranes have been successfully synthesized via click chemistry with improved properties by controlling the crosslinking degree and micro-phase structure.