Molecular dynamics simulation of Keggin HPA doped Nafion® 117 as a polymer electrolyte membrane

Abstract

Heteropoly acids (HPAs) are important conductive materials with numerous potential applications in fuel cells. Keggin HPAs, as a promising example, have frequently been used as a doping agent in fuel cell membranes. A molecular-level understanding of morphological alteration caused by HPAs is very important for designing membranes with high proton conductivity at elevated temperatures. In the present study, a morphological insight is gained by means of molecular dynamics (MD) simulation of three different HPAs as doping components, i.e. [Xⁿ⁺W₁₂O₄₀]⁸⁻ⁿ (X ≡ P⁵⁺, Si⁴⁺, and Al³⁺), at various degrees of hydration. Moreover, the influence of the anionic charge of HPA on the dynamic properties of protons is investigated. In addition to water cluster analysis, this study presents the activation energies for diffusion of water molecules and hydronium ions through the composite membranes. The results show the advantage of using HPAs as a dopant in fuel cell membranes.