Biaxially stretched anion exchange membrane with high and stable hydroxide conductivity at subzero temperature

The high flexibility is the future development trend of anion exchange membranes (AEMs) to meet the requirement of portability for anion exchange membrane fuel cell (AEMFC). This research focuses on constructing flexible AEMs with the accelerated hydroxide ions conduction even at subzero temperature. The flexible AEMs composing with quaternized poly (2,6-dimethyl-1,4-phenylene oxide) (QPPO) and polystyrene-block-poly (ethylene-ran-butylene)-block-polystyrene bromide (SEBSBr) can withstand external mechanical force owing to the highly flexible SEBSBr moieties. The prepared QPPO/N-SEBSBr membrane possesses stable microstructures even if it is folded and biaxially stretched. The rectangular membrane is folded in the width direction for 3 times and the square membrane is biaxially stretched by sequentially stretching 10 % strain in the X and Y direction for repeating thirty times. The accelerated hydroxide ions conduction behaviors are achieved in the range of −25 °C–25 °C and 30 °C–80 °C. Specifically, the QPPO/N-SEBSBr membrane exhibits the hydroxide conductivity of 2.31 mS/cm at −25 °C and 80.6 mS/cm at 80 °C. The fine alkaline stability is confirmed by the slight decrease on hydroxide conductivities during the ten-cycle of −25 °C–30 °C measurement. A single fuel cell equipped with the (Q/N-SBr)-bs membrane shows the maximum power density of 321 mW/cm2.