Durability and performance of polystyrene‐b‐poly(vinylbenzyl trimethylammonium) diblock copolymer and equivalent blend anion exchange membranes

Abstract

Anion exchange membranes (AEM) are solid polymer electrolytes that facilitate ion transport in fuel cells. In this study, a polystyrene-b-poly(vinylbenzyl trimethylammonium) diblock copolymer was evaluated as potential AEM and compared with the equivalent homopolymer blend. The diblock had a 92% conversion of reactive sites with an IEC of 1.72 6 0.05 mmol g 21 , while the blend had a 43% conversion for an IEC of 0.80 6 0.03 mmol g 21 . At 50 C and 95% relative humidity, the chloride conductivity of the diblock was higher, 24-33 mS cm 21 , compared with the blend, 1-6 mS cm 21 . The diblock displayed phase separation on the length scale of 100 nm, while the blend displayed microphase separation ($10 lm). Mechanical characterization of films from 40 to 90 microns thick found that elasticity and elongation decreased with the addition of cations to the films. At humidified conditions, water acted as a plasticizer to increase film elasticity and elongation. While the polystyrene-based diblock displayed sufficient ionic conductivity, the films' mechanical properties require improvement, i.e., greater elasticity and strength, before use in fuel cells.

Effect of hydration on the mechanical properties and ion conduction in a polyethylene-b-poly(vinylbenzyl trimethylammonium) anion exchange membrane

“…The PE-b-PVBTMA[Br] membrane had good strength at dry conditions, 28 74 MPa, and strength was only reduced by 29% to 207 4 MPa when fully saturated. The strength of the PE-b-PVBTMA is lower than Nafion s [29], but better than many AEMs [9,13,15,37], and the narrow change between dry to hydrated conditions is promising for stable performance in an electrochemical device. Elongation of the PE-b-PVBTMA[Br] film was 150 720% at dry conditions and 220 720% at saturated conditions.…”

“…Polystyrene based diblocks have been synthesized previously that organized into various morphologies including spheres, cylinders, and lamellae depending on the ratio of the polymer blocks [12]. While polystyrene based diblocks have showed good ionic conductivity and ordered morphologies [12,13], the high T g polystyrene in an cationic membrane results in stiff, brittle films that do not have adequate mechanical durability for use in electrochemical devices. Replacing the hydrophobic block with a rubbery polymer, such as poly(methyl butylene), produced films with better elasticity and flexibility [14].…”

“…Limiting the dimensional swelling of an AEM will improve mechanical durability [20], but the ionic nature of the polymer and the fact that water is required to facilitate ion conduction makes swelling inevitable. Functionalization of a polymer with cations reduces elasticity and elongation [13], making it difficult to produce AEMs that maintain adequate mechanical durability. Additionally, water sorption in AEMs can severely soften and weaken AEMs when they are hydrated [25].…”

Polybenzimidazole-crosslinked poly(vinylbenzyl chloride) with quaternary 1,4-diazabicyclo (2.2.2) octane groups as high-performance anion exchange membrane for fuel cells

“…5cef); 3) in the surface and cross-sectional SEM images ( Fig. 5g and h), the PBI-c-PVBC/OH membrane showed a uniform and homogeneous morphology, whereas obvious component separation (if any) can be observed in semi-IPN membranes or blend membranes by SEM [18,19,45]. It is believed that crosslinking was an essential factor in the formation of membrane with homogeneity, because lack of interaction between two polymers will cause phase separation, even severe nonuniformity, as shown in our controlled experiments (Fig.…”

Anion exchange membranes based on carbazole-containing polyolefin for direct methanol fuel cells

“…On the other hand, polyolefin AEMs, such as polystyrene and poly (ethylene-co-tetrafluoro ethylene)-based membranes have been synthesized recently due to their intensified fuel resistance, enhanced dimensional stability, and excellent alkaline stability [22,23]. However, most of the reported AEMs are not satisfactory.…”