Influence of Radiation‐Induced Grafting Process on Mechanical Properties of ETFE‐Based Membranes for Fuel Cells

Abstract

The mechanical stability is, in addition to thermal and chemical stability, a primary requirement of polymer electrolyte membranes in fuel cells. In this study, the impact of grafting parameters and preparation steps on stress–strain properties of ETFE‐based proton conducting membranes, prepared by radiation‐induced grafting and subsequent sulphonation, was studied. No significant change in the mechanical properties of the ETFE base film was observed below an irradiation dose of 50 kGy. It was shown that the elongation at break decreases with increasing both the crosslinker concentration and graft level (GL). However, the tensile strength was positively affected by the crosslinker concentration. Yield strength and modulus of elasticity are almost unaffected by the introduction of crosslinker. Interestingly, yield strength and modulus of elasticity increase gradually with GL without noticeable change of the inherent crystallinity of grafted films. The most brittle membranes are obtained via the combination of high GL and crosslinker concentration. The optimised ETFE‐based membrane (GL of ∼25%, 5% DVB v/v), shows mechanical properties superior to those of Nafion® 112 membrane. The obtained results were correlated qualitatively to the other ex situ properties, including crystallinity, thermal properties and water uptake of the grafted membranes.

Proton Conducting Membranes Based on Poly(2,2′‐imidazole‐5,5′‐bibenzimidazole)

“…Polymer electrolyte membrane fuel cells (PEMFCs) have attracted a lot of attention these years due to their eco-friendliness and high efficiency of energy conversion [1][2][3][4][5]. The widely used proton exchange membranes (PEMs) for PEMFCs are perfluorosulfonic acid polymers, such as Nafion ® and Flemion ® [6][7][8][9][10].…”

Grafting design: a strategy to increase the performance of radiation‐grafted membranes

“…Membranes of type A have been synthesized and thoroughly investigated at the Paul Scherrer Institute over the last decade . The optimized reaction conditions for styrene grafting were found to be a mixture of 70 vol% isopropanol, 10 vol% ultrapure water and 20 vol% styrene monomer at temperatures between 55 and 60 °C .…”

“…As the ETFE in the 30/50/7 system is exposed to a higher dose, which might lead to a greater number of chain scissions compared to the 3 kGy system, this might also contribute to this result. However, ETFE is known to be a material that is very stable against irradiation, its mechanical properties not being markedly affected until doses of above 50 kGy …”

“…After stirring for 5 h at room temperature the sulfonated films were removed from the reaction mixture and repeatedly washed with ultrapure water (3 × 800 mL). Hydrolysis of the functionalized films to sulfonic acid groups was performed in ultrapure water (800 mL) at 80 °C for 15 h. More information can be found elsewhere …”

“…In contrast to the mentioned ATRP studies, the magnitude of compared numbers of repeat units is most likely not in the range of 10 to 120, but can be assumed to be in a higher range due to the nature of the radiation grafting approach. Unfortunately, it is not possible to determine the exact chain lengths due to the insolubility of the resulting polymer membrane (ETFE‐ g ‐PSSA) . Nevertheless, an estimation of the graft length of type A and B membranes was made based on dose‐dependent radical concentrations and the level of grafting of the membranes.…”