Abstract
A series of anion exchange membranes composed of partially fluorinated poly(arylene ether sulfone)s (PAESs) multiblock copolymers bearing quaternary ammonium groups were synthesized with controlled lengths of the hydrophilic precursor and hydrophobic oligomer via direct polycondensation. The chloromethylation and quaternization proceeded well by optimizing the reaction conditions to improve hydroxide conductivity and physical stability, and the fabricated membranes were very flexible and transparent. Atomic force microscope images of quaternized PAES (QN-PAES) membranes showed excellent hydrophilic/hydrophobic phase separation and distinct ion transition channels. An extended architecture of phase separation was observed by increasing the hydrophilic oligomer length, which resulted in significant improvements in the water uptake, ion exchange capacity, and hydroxide conductivity. Furthermore, the open circuit voltage (OCV) of QN-PAES X10Y23 and X10Y13 was found to be above 0.9 V, and the maximum power density of QN-PAES X10Y13 was 131.7 mW cm−2 at 60 °C under 100% RH.
Highlights
Fuel cells are energy conversion devices that convert chemical energy into electrical energy while being supplied with fuel and oxidant
The polymer lengths of the Poly(arylene sulfone) (PAS) hydrophilic precursors were determined by GPC data and an integral ratio between the proton peaks of the polymer backbone and the terminal end groups were determined from 1 H NMR spectra (Figure S1)
The tensile behavior, Young’s modulus, and elongation at break of QN-poly(arylene ether sulfone)s (PAESs) membranes were in the 60.5–77.6 MPa, 0.9–3.4 GPa, and 1.8−10.9% ranges, respectively. These results show that quaternized PAES (QN-PAES) membranes are malleable for applications in membrane electrolyte assembly (MEA)
Summary
Fuel cells are energy conversion devices that convert chemical energy into electrical energy while being supplied with fuel and oxidant. A high ion exchange capacity (IEC) value is essential to obtaining high ionic conductivity and fuel cell performance for applications in AEM. Micro phase-separated block copolymers with controlled hydrophilic and hydrophobic oligomer lengths exhibited improved ionic conductivity and thermal stability. –CF3 structure can control the permeation of fuel by increasing the free volume in the polymer and reinforcing the flexibility of the membrane due to having a sp hybrid structure In line with these facts, partially fluorinated PAES block copolymers were synthesized with different lengths of hydrophilic precursor and hydrophobic oligomer. The block copolymers containing a fluorinated hydrophobic portion were designed for the purpose of improved ionic conductivity, physicochemical stability, and flexibility of the membrane. Characterizations of the prepared AEMs including thermal stability, mechanical properties, dimensional stabilities, hydroxide conductivity, and alkaline stabilities were studied in detail
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