Molecular dynamics analysis of effects of Ca2+ contaminant concentrations on proton exchange membrane transport performance for proton exchange membrane fuel cells

Components of proton exchange membrane fuel cells (PEMFCs), such as bipolar plates, gaskets, etc., may undergo deterioration and generate metal ions during long-term operation. Metal ion contaminants can damage PEMFCs. This study uses molecular dynamics (MD) simulation to explore the impact of metal ion (i.e. calcium ion) and its concentrations on transportation performance of proton exchange membrane (PEM). Six levels of Ca²⁺ concentrations (i.e. 0 %, 10 %, 20 %, 25 %, 30 % and 35 %）are used in this work. Six molecular dynamics simulation models containing Nafion212 membrane polymer chains, water molecules, hydronium ions and calcium ions are built corresponding to the six concentrations of calcium ion for MD simulations. Then, the radial distribution functions (RDFs), coordination numbers (CNs), mean square displacements (MSDs) and diffusion coefficients (Ds), relative concentration distributions (RCs) of water molecules (H₂O), hydronium ions (H₃O⁺) and Ca²⁺ in Nafion212 membrane are analyzed to study the effects of Ca²⁺ and its concentrations on PEM performance by MD simulation methods. Results show that compared with protons, calcium ions have a stronger interaction with sulfonic acid groups and are more easily attracted to sulfonic acid groups. Calcium ion significantly weakens transport of protons and water molecules in Nafion membrane, and the effect becomes more serious as Ca²⁺ concentration increases.