Nanostructure-Informed Multiscale Modeling of Degradation Effects on Proton Conductivity in Nafion Membranes

Abstract

The objective of this study is to establish a comprehensive multiscale modeling framework capable of accurately predicting the nanostructure properties and proton conductivity of Nafion membranes under varying hydration levels, temperatures, and chemical degradation conditions. Initially, we constructed a coarse-grained molecular dynamics (CGMD) model to simulate structural evolution in Nafion membranes, systematically incorporating membrane degradation─an aspect rarely explored in prior studies. The resulting CGMD-derived nanostructures were subsequently analyzed using advanced numerical techniques, including the finite difference method (FDM) for vehicle-mechanism (VM) proton transport and a collective random walk model (RWM) to capture Grotthuss-mechanism (GM) hopping dynamics. To our knowledge, this integrated modeling approach to quantify both proton conduction mechanisms─is unprecedented. Key nanostructured properties, such as porosity, tortuosity factor, and pore size distribution, were evaluated to understand their influence on proton transport pathways at different degradation levels. Our results reveal that chemical degradation significantly affects proton conductivity, particularly via alterations in the membrane's water retention capacity and nanostructured heterogeneity, highlighting the complex interplay between hydration, temperature, and degradation process. By comparing our findings with available theoretical and experimental data, our multiscale framework not only deepens the fundamental understanding of nanostructure-property relationships in proton exchange membranes but also provides essential insights for the molecular-level design and optimization of more durable, high-performance polymer electrolyte fuel cell membranes.

Keywords: degradation; membrane; multiscale modeling; polymer electrolyte membrane fuel cells; proton conduction.