Block copolymer anion exchange membrane containing polymer of intrinsic microporosity for fuel cell application

Abstract

High hydroxide conductivity and good stability of anion exchange membranes (AEMs) is the guarantee that anion exchange membrane fuel cells (AEMFCs) yield high power output for a long time. Balanced conductivity and stability can be better guaranteed by adopting a relatively low ion exchange capacity (IEC) while reducing the ion transport resistance Herein, a novel block copolymer AEM was designed and synthesized, which contains hydrophobic polymer of intrinsic microporosity (PIM) blocks and hydrophilic, quaternized polysulfone (PSF) blocks. The PIM block imparts high free volume to the membrane so that the resistance of hydroxide ion transport can be reduced; meanwhile, the hydrophilic block can self-assemble more easily to produce a better developed hydrophilic microphase, which may function as efficient channels for hydroxide ion transport. Both transmission electron microscopy images and small-angle X-ray scattering patterns suggested that the resulting AEM possessed a microphase separated morphology. The membrane showed a conductivity of 52.6 mS cm-l at 80 °C with a relatively low IEC of 0.91 mmol g−1. It also exhibited a good dimensional stability, swelling ratio maintained almost constant (ca. 17%) at 25 to 80 °C. The assembled H2/O2 fuel cell yielded a peak power density of 270 mW cm−2 at 560 mA cm−2. Our work demonstrates that incorporation of PIM in an AEM by means of block polymerization is an efficient way of promoting microphase separation and facilitating ion transport.