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

Abstract

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 H 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 compared to Nafion-115 (131 mS cm) at 90 °C under 100% relative humidity (RH). Among the SPAEK membranes, proton conductivity of SPAEK X9.1Y8.8 (140.7 mS cm) is higher than that of Nafion-115 (102 mS cm) 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, which is higher than that of Nafion-115 (291 mW cm) at 60 °C under 100% RH.

Effect of functionalized SiO 2 toward proton conductivity of composite membranes for PEMFC application

“…The 3,3′‐diphenyl‐4,4‐difluorodiphenylketone (DP‐DFB) was synthesized by sequential reactions of bromination and Suzuki‐Miyaura coupling reactions as described in Scheme S1 . In the first synthetic step, DFB (15.0 g), NBS (25.0 g), and H 2 SO 4 (130 mL) were put together in a 250‐mL round‐bottomed flask, and the reaction was proceeded at room temperature (RT) for 48 hours.…”

“…As shown in Scheme S2, the multiblock PAEK was synthesized via direct copolymerization of a hydrophilic precursor and hydrophobic oligomer with a molar ratio of 1:1 according to previously reported procedure . The hydrophilic precursor was prepared by DP‐DFB and 6F‐BPA via nucleophilic substitution reaction.…”

Study of morphological characteristics on hydrophilicity‐enhanced SiO 2 /Nafion composite membranes by using multimode atomic force microscopy

“…Thus, the characterization of morphology variation owing to the composition with inorganic pillar materials is crucial to the understanding of composite membranes. Many groups reported that the water uptake and proton conductivity increased because the hydrophilic ionic cluster network changes and the hygroscopic characteristics are improved by the sulfonized fillers materials . Lee et al studied the proton conductivity of SPAEK block copolymer membranes with a controlled F‐oligomer length bearing a pendant diphenyl unit.…”

“…Many groups reported that the water uptake and proton conductivity increased because the hydrophilic ionic cluster network changes and the hygroscopic characteristics are improved by the sulfonized fillers materials . Lee et al studied the proton conductivity of SPAEK block copolymer membranes with a controlled F‐oligomer length bearing a pendant diphenyl unit. According to this study, increasing the length of the hydrophilic oligomer in the main chain induces clear separation of hydrophobic and hydrophilic regions.…”

Synthesis of Sulfonated Poly(arylene ether)s in a One‐Pot Polymerization Process and Their Nafion‐Blend Membranes for Proton Exchange Membrane Fuel Cell Applications

“…In order to ensure a better comparison of the intrinsic properties of the series, the membranes were prepared in similar thickness and same manufacturing process of MEAs were carried out. As presented in Figure , all MEAs exhibited open‐circuit voltages (OCVs) exceeding 0.9 V, indicating that there was no great gas crossover . In low current region, the SPAE‐80 membrane showed the higher voltage value compared with that of blend membranes and Nafion 212 membrane, which reveals the membrane was low in Ohmic resistance .…”