Design Rules for Membranes from Polymers of Intrinsic Microporosity for Crossover-free Aqueous Electrochemical Devices

Abstract

Summary Here, we lay the design rules for linking microporous polymer membrane architecture and pore chemistry to membrane stability, conductivity, and transport selectivity in aqueous electrolytes over a broad range of pH. We tie these attributes to prospects for crossover-free electrochemical cell operation. These guiding principles are applied to two emerging cell chemistries for grid batteries: specifically, Zn–TEMPO-4-sulfate and Zn–K4Fe(CN)6 cells. Key to our success is the placement of ionizable amidoxime functionalities, which are stable at high pH, within the pores of microporous ladder polymer membranes, yielding a family of charge-neutral and cation exchange membranes at low and high pH, respectively—which we call AquaPIMs. Their notably high conductivity (up to 21.5 mS cm−1 in 5.0 M aqueous KOH) and high transport selectivity (up to 104 reduction in active-material permeability through the membrane) suggest exciting opportunities for battery development, even beyond those presently demonstrated.