Interconnected Ion Transport Channels Enabled by Enhanced Microphase-Separated Anion-Conductive Polymers for Anion Exchange Membrane Fuel Cells

Abstract

The performance of anion exchange membrane fuel cells (AEMFCs) is severely constrained by the low OH^-conductivity of anion-conductive polymers. Although increasing the ion exchange capacity of these polymers through microstructural design effectively improves the OH^-conductivity, it often compromises the mechanical strength. To address this issue, we report enhanced microphase-separated structures in poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS)-based anion-conductive polymers, achieved through the synergy of hydrophilic quaternary ammonium (QA) groups and hydrophobic fluorinated side chains. Specifically, by precisely tuning the fluorine grafting degree of the polymer side chains, highly interconnected nanoscale ion-conducting domains are created, forming a three-dimensional (3D) pathway for efficient ion transport in anion exchange membranes (AEMs). Additionally, the mechanical stability of AEMs is strengthened by minimizing swelling. As a result, the QA- and fluorine-grafted AEM with a molar proportion of 4-fluorophenethylamine-modified blocks to styrene blocks of 30% (denoted as QSEBS-FPh 30) achieves a high OH^-conductivity of 100.86 mS/cm at 80 ℃ and a moderate tensile strength of 19.89 MPa in a fully hydrated state. The AEMFC utilizing QSEBS-FPh 30 exhibits a peak power density of 204.31 mW/cm²at a current density of 737.29 mA/cm²and 80 ℃, which is 1.4 times that of QA-grafted SEBS (QSEBS). These findings underscore the significant role of microphase separation coupled with maximized ionic domain connectivity in enhancing the OH^-conductivity of anion-conductive polymers, offering valuable insights for the rational design of high-performance AEMs.

Keywords

fuel cell / anion exchange membrane (AEM) / microphase separation / interconnected ionic domain

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