title: Atomistic simulation of water percolation and proton hopping in Nafion fuel cell membrane.
abstract: We have performed a detailed analysis of water clustering and percolation in hydrated Nafion configurations generated by classical molecular dynamics simulations. Our results show that at low hydration levels H(2)O molecules are isolated and a continuous hydrogen-bonded network forms as the hydration level is increased. Our quantitative analysis has established a hydration level (λ) between 5 and 6 H(2)O/SO(3)(-) as the percolation threshold of Nafion. We have also examined the effect of such a network on proton transport by studying the structural diffusion of protons using the quantum hopping molecular dynamics method. The mean residence time of the proton on a water molecule decreases by 2 orders of magnitude when the λ value is increased from 5 to 15. The proton diffusion coefficient in Nafion at a λ value of 15 is about 1.1 × 10(-5) cm(2)/s in agreement with experiment. The results provide quantitative atomic-level evidence of water network percolation in Nafion and its effect on proton conductivity.
authors.affiliation: Chemical & Materials Sciences Division, MS K2-01, Pacific Northwest National Laboratory, Richland, Washington 99352, USA. ram.devanathan@pnl.gov
authors.forename: Ram
authors.initials: R
authors.lastname: Devanathan
authors.forename: Arun
authors.initials: A
authors.lastname: Venkatnathan
authors.forename: Roger
authors.initials: R
authors.lastname: Rousseau
authors.forename: Michel
authors.initials: M
authors.lastname: Dupuis
authors.forename: Tomaso
authors.initials: T
authors.lastname: Frigato
authors.forename: Wei
authors.initials: W
authors.lastname: Gu
authors.forename: Volkhard
authors.initials: V
authors.lastname: Helms
mesh_terms: D005465:Fluorocarbon Polymers / Q000737:chemistry*; D057446:Hydrodynamics; D008567:Membranes, Artificial; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011522:Protons; D014867:Water / Q000737:chemistry*
chemical_list: D005465:Fluorocarbon Polymers; D008567:Membranes, Artificial; D011522:Protons; D014867:Water; C040402:perfluorosulfonic acid