Cyclodextrin modified, multication cross-linked high performance anion exchange membranes for fuel cell application

Abstract

The anion exchange membranes (AEMs) with high hydroxide ion conductivity and stability are in an urgent need for alkaline membrane fuel cell applications. High ionic exchange capacity (IEC) is necessary to improve conductivity but detrimental to stability. In this work, a series of novel AEMs modified with bulky rigid β-cyclodextrin (CD) and long flexible multiple quaternary ammonium (MQ) are designed and prepared. The resulting AEM with a relatively low IEC of 1.50 mmol g-1 shows a good hydroxide ion conductivity of 112.4 mS cm-1 at 80 oC, whereas its counterpart without CD modification exhibits 83.0 mS cm-1 despite a similar IEC (1.60 mmol g-1); this is because the large CD units can impart high free volume to the membrane, reducing the ion transport resistance, and meanwhile, the hydrophilicity of CD’s external surface may promote formation of ion transport channels across the long flexible MQ cross-links. The CD modified AEM also imparts the membrane a better alkali- and swelling resistance as well as a higher tensile strength, without sacrificing its hydroxide ion conduction properties, than the un-modified membrane. The H2–O2 fuel cell yields a high peak power density of 288 mW cm-2 at 60 oC. Our work implies that the CD enabled free volume strategy is effective to balance conductivity and stability, which may pave the way to fabrication of AEMs with further improved performance.