Crosslinked high-performance anion exchange membranes based on poly(dibenzyl N-methyl piperidine) and pentafluorobenzoyl-substituted SEBS

Abstract

The high ionic conductivity and chemical stability of poly(aryl piperidinium) (PAP) underpin its extensive use in anion exchange membranes (AEMs) for water electrolysis (WE) and fuel cell (FC) applications. Nonetheless, the limited elongation of PAP-based AEMs negatively impacts cell performance and durability. Their high ion exchange capacity (IEC), while enhancing cell performance, often causes excessively high water uptake and diminishes the mechanical properties and phase separation performance. This study developed high-performance AEMs by crosslinking two polymers with contrasting characteristics: poly(dibenzyl N-methyl piperidine) (PDB), a rigid PAP-based unit, and poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS), a flexible unit with good phase separation. Notably, the pentafluorobenzoyl group was incorporated into SEBS to enhance microphase separation. AEMs were developed with pentafluorobenzoyl contents ranging from 4 to 12% (labeled as x-PDB-m-F5-SEBS, m = 4, 8, and 12), and the results were compared with the x-PDB-0-F5-SEBS membrane without the pentafluorobenzoyl group. All x-PDB-m-F5-SEBS membranes exhibit low hydrogen permeability, excellent chemical stability, and a conductivity retention of over 99% after 1080 h. x-PDB-4-F5-SEBS demonstrated the most pronounced microphase separation, coupled with high ionic conductivity. It also achieved excellent WE cell performance (3.204 A cm⁻² at 1.8 V), significantly surpassing that of commercial membranes including FAA-3-50 and PiperION. Even when using a non-precious metal catalyst (Ni₂Fe) in place of IrO₂, the membrane exhibited a cell performance of 3.364 A cm⁻² at 1.8 V, equivalent to that achieved with precious metal catalysts. When applied to AEM-based FCs, x-PDB-4-F5-SEBS also exhibited a high-power density of 785 mW cm⁻², highlighting its significant potential as an AEM in WE and FC applications.