Molecular Modeling in Anion Exchange Membrane Research: A Brief Review of Recent Applications

Anion Exchange Membrane (AEM) fuel cells have attracted growing interest due to their encouraging advantages, including high power density and relatively low cost. AEM is a polymer matrix, which has positively charged head groups (mainly quaternary ammonium (QA) groups) covalently bound to the polymer backbone, conducts hydroxide ($\mathrm{OH^{-}}$) ions, and prevents physical contact of electrodes. The chemical instability of the quaternary ammonium (QA) based head groups at alkaline pH and elevated temperature is a significant threshold in AEMFC technology. This review work aims to introduce recent studies on the chemical stability of various QA-based head groups and transportation of $\mathrm{OH^{-}}$ ion in AEMFC via modeling and simulation techniques at different scales. It starts by introducing the fundamental theories behind AEM-based fuel cell technology. In the main body of this review, we present selected computational studies that dealt with the effects of various parameters on AEMs via a variety of multi-length and multi-time scale modeling and simulation methods. Such methods include electronic structure calculations via the quantum Density Functional Theory (DFT), ab initio, classical all-atom Molecular Dynamics (MD) simulations, and coarse-grained MD simulations. The explored processing and structural parameters include temperature, hydration levels, several QA-based head groups, various types of QA-based head groups and backbones, etc. Nowadays, many methods and software packages for molecular and materials modeling are available. Applications of such methods may help to understand transportation mechanisms of $\mathrm{OH^{-}}$ ions, chemical stability of functional head groups, and many other relevant properties, leading to a performance-based molecular and structure design and ultimately improved AEM-based fuel cell performances. This contribution aims to introduce those molecular modeling methods and their recent applications to the research community on AEM-based fuel cells.