Atomistic simulation of water percolation and proton hopping in Nafion fuel cell membrane.
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.
Devanathan
Ram
R
Chemical & Materials Sciences Division, MS K2-01, Pacific Northwest National Laboratory, Richland, Washington 99352, USA. ram.devanathan@pnl.gov
Venkatnathan
Arun
A
Rousseau
Roger
R
Dupuis
Michel
M
Frigato
Tomaso
T
Gu
Wei
W
Helms
Volkhard
V
D005465:Fluorocarbon Polymers / Q000737:chemistry*; D057446:Hydrodynamics; D008567:Membranes, Artificial; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011522:Protons; D014867:Water / Q000737:chemistry*
D005465:Fluorocarbon Polymers; D008567:Membranes, Artificial; D011522:Protons; D014867:Water; C040402:perfluorosulfonic acid