Rapid and facile preparation of freestanding dense polymer membranes from high-boiling-point solvents for anion exchange membrane water electrolyzers

Transparent, dense, and freestanding polymer membranes are typically prepared by solution casting (SC). However, SC is a time-consuming (>24 h) multi-step process that requires high-temperature vacuum treatment. Here, we report a rapid and facile method—nonsolvent-induced film formation (NIFF)—for preparing dense, freestanding membranes by immersing a polymer solution in a nonsolvent, using two types of poly(arylene piperidinium) (PAP) and their quaternized versions. Thermodynamic, kinetic, and molecular dynamics analyses of polymer/solvent/nonsolvent ternary systems reveal that the PAP polymers have high affinities for the nonsolvent (water), yielding a gel between homogeneous and heterogeneous regions. The protective gel layer at the polymer/solvent–nonsolvent interface averts penetration of the nonsolvent and permits withdrawal of the solvent from the polymer solution, forming a nonporous dense membrane. The physicochemical, mechanical, morphological, and electrochemical characteristics of NIFF- and conventional-SC-derived membranes are comparable. Moreover, the alkaline water electrolysis cell performance is evaluated using the membranes and platinum group metal-free catalyst. Both NIFF- and SC-derived membrane-based cells achieve an equivalent current density of 910 mA cm−2 at 2.0 V, which is 20 % higher than commercial FAA-3-50 membrane-based cells. This study establishes an innovative strategy to facilely fabricate freestanding polymer films with a time- and energy-saving process for ion-conducting membranes.