Development of highly conductive anion exchange membranes based on crosslinked PIM-SEBS with high free volume

Abstract

Polyarylene-based anion exchange membranes (AEMs) have been extensively researched in anion exchange membrane fuel cells (AEMFCs) and anion exchange membrane water electrolysis (AEMWE) due to their high conductivity and output performance. Proposed strategies to achieve high-output cell performance include developing AEMs with desirable ion exchange capacities (IECs) and optimized microstructures that involve microphase separation between hydrophilic and hydrophobic domains. In this study, novel AEMs with microphase separation, achieved through the presence of free volume in the polymer structure, are developed. A polymer of intrinsic microporosity (PIM) is incorporated as the backbone to induce a rigid twist and, thus, increase the free volume. The PIM is chemically crosslinked to varying degrees with poly(styrene-b-ethylene-co-butylene-b-styrene), or SEBS, a triblock copolymer with excellent microphase separation morphology and flexibility, resulting in x-PIM-SEBS membranes with enhanced chemical and physical stability. Among them, the 30x-PIM-SEBS membrane, with a crosslinking degree of 30%, yields the highest ionic conductivity (67.65–147.66 mS cm⁻¹) and the most pronounced microphase separation. The membrane also demonstrates impressive alkaline stability, with conductivity retention of over 98% in 1 M KOH at 80 °C after 1080 hours; excellent thermal stability under the AEMWE operating conditions; and remarkable oxidative stability due to its polymeric free volume coupled with enhanced microphase separation. Finally, AEMWE single-cell test results confirm that 30x-PIM-SEBS outperforms the commercial FAA-3-50 membrane by 176%, achieving a current density of 1.905 A cm⁻² (compared to 1.083 A cm⁻² for FAA-3-50) at 2.0 V.