Reducing hydroxide transport resistance by introducing high fractional free volume into anion exchange membranes

The efficiency of ion transport in solid polyelectrolytes is significantly hindered by tight polymer chain entanglement compared to that in liquids. In this study, a series of hyperbranched poly(aryl piperidinium) anion exchange membranes (AEMs) with 1,3,5-triacetylbenzene as a branching point were synthesized. The hyperbranched structure results in weaker chain entanglement and a larger interchain correlation distance, leading to a higher fractional free volume, thereby greatly reducing ion transport resistance. Consequently, a remarkably higher OH- conductivity of the as-prepared hyperbranched AEM (296 mS cm-1) is achieved compared to that of non-hyperbranched AEMs (180 mS cm-1). Furthermore, the hyperbranched AEMs exhibit excellent fuel cell and water electrolysis performance, with a peak power density of 1.53 W cm-2 in AEMFCs and a current density of 1 A cm-2 at a voltage of 2 V in AEMWEs, respectively.