title: Ab initio molecular dynamics simulation of proton hopping in a model polymer membrane.
abstract: We report the results of ab initio molecular dynamics simulations of a model Nafion polymer membrane initially equilibrated using classical molecular dynamics simulations. We studied three hydration levels (λ) of 3, 9, and 15 H2O/SO3(-) corresponding to dry, hydrated, and saturated fuel cell membrane, respectively. The barrier for proton transfer from the SO3(-)-H3O(+) contact ion pair to a solvent-separated ion pair decreased from 2.3 kcal/mol for λ = 3 to 0.8 kcal/mol for λ = 15. The barrier for proton transfer between two water molecules was in the range from 0.7 to 0.8 kcal/mol for the λ values studied. The number of proton shuttling events between a pair of water molecules is an order of magnitude more than the number of proton hops across three distinct water molecules. The proton diffusion coefficient at λ = 15 is about 0.9 × 10(-5) cm(2)/s, which is in good agreement with experiment and our previous quantum hopping molecular dynamics simulations.
authors: Physical Sciences Division, MS K2-01, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors: Ram
authors: R
authors: Devanathan
authors: Nagesh
authors: N
authors: Idupulapati
authors: Marcel D
authors: MD
authors: Baer
authors: Christopher J
authors: CJ
authors: Mundy
authors: Michel
authors: M
authors: Dupuis
mesh_terms: D005465:Fluorocarbon Polymers / Q000737:chemistry*; D008567:Membranes, Artificial; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011522:Protons; D013455:Sulfur / Q000737:chemistry
chemical_list: D005465:Fluorocarbon Polymers; D008567:Membranes, Artificial; D011522:Protons; C040402:perfluorosulfonic acid; D013455:Sulfur