Application of Ionized Intrinsic Microporous Poly(phenyl-alkane)s as Alkaline Ionomers for Anion Exchange Membrane Water Electrolyzers

Alkaline ionomers used in anion exchange membrane water electrolyzers (AEMWEs) require fast mass transport to maximize the activity of the catalytic reaction at the three-phase boundary. Taking advantage of the high free volume of polymers of intrinsic microporosity (PIMs), herein we propose a new strategy to apply ionized PIMs in the preparation of high-performance alkaline ionomers. A series of novel intrinsic microporous poly(phenyl-alkane) alkaline ionomers were synthesized by acid-catalyzed Friedel–Crafts polycondensation of electron-rich single-benzene/multi-benzene derivatives and trifluoromethyl/cyanide-substituted benzaldehydes. By adjusting the structure of aromatic monomers and aldehydes and the proportion of comonomers, the structures of the ionomer skeletons were systematically regulated. By evaluating the microporosities, ion transport properties, and device properties, we found that introducing a twisted spirobisindane unit and a trifluoromethyl substituent to the poly(phenyl-alkane) skeleton promoted the formation of more micropore structures. Increased microporosity is beneficial for the construction of efficient and stable mass transfer channels, facilitating improved AEMWE performance (1685 mA cm–2 at 1.8 V with a circulating 1 M NaOH solution at 80 °C) and excellent durability (>180 h at a high current density of 1000 mA cm–2). This work provides insights into the structure–property relationships of intrinsic microporous poly(phenyl-alkane) alkaline ionomers and demonstrates that ionic intrinsic microporous polymers are very promising candidates for the preparation of high-performance alkaline ionomers for AEMWEs.