(477j) Design Insights into Anion Exchange Membranes for Eco-Friendly Applications: Perspectives on Molecular Modeling Approaches

Anion exchange membranes (AEMs) are considered a cost-effective alternative for green hydrogen technologies, such as fuel cells and water electrolyzers, which traditionally rely on proton exchange membranes. AEMs operate under alkaline conditions and enable the use of non-precious metal catalysts. However, these conditions also accelerate chemical degradation of membranes, which limits long-term performance. To support the development of next-generation AEM-based systems, a better understanding of how membrane properties are affected by polymer structure and operating conditions is required, especially at the interfaces.

Key transport properties of AEMs, including hydroxide conductivity and water diffusion, are strongly influenced by the nanoscale morphology of ionomers. This morphology is affected by polymer composition and changes with water content, which is determined by ion exchange capacity and the structure of cationic side chains. Molecular modeling techniques are used to analyze these structure–property relationships. Atomistic simulations help reveal local transport mechanisms near charged groups, while coarse-grained simulations are applied to predict equilibrium membrane morphology and bulk transport behavior.

A modeling framework has been developed using the dissipative particle dynamics (DPD) method to study the mesoscopic behavior of AEMs. This approach captures relevant effects such as water percolation, hydroxide transport, and polymer dynamics in phase-separated domains. The simulation method has been applied to investigate the influence of side chain structures in commonly used AEMs, including functionalized PPO and SEBS. New membrane designs have also been proposed by introducing tapering and crosslinking in triblock copolymers to improve phase morphology and control hydroxide ion pathways.
(Ref. [1], [2])

Recent efforts have been made to improve the coarse-grained model for AEM design. A swelling protocol has been introduced to estimate equilibrium water uptake, which is closely related to ion conductivity. The force field has been refined to better describe polymer chain dynamics, which affects ion mobility near functional groups. In addition, slip-spring models and associative interactions have been added to represent crosslinking and relaxation behavior, which are important for predicting mechanical properties of AEMs. Future directions for coarse-grained model development will also be discussed.

References:
[1] Ming-Tsung Lee, Functionalized Triblock Copolymers with Tapered Design for Anion Exchange Membrane Fuel Cells, Polymers 2024, 16(16), 2382. https://doi.org/10.3390/polym16162382
[2] Ming-Tsung Lee, Designing Highly Conductive Block Copolymer-Based Anion Exchange Membranes by Mesoscale Simulations, J. Phys. Chem. B 2021, 125(10), 2729–2740. https://doi.org/10.1021/acs.jpcb.0c10909