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 H2O 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 H2O/SO3- 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 two 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 1.1x10-5 cm2/s in agreement with experiment. The results provide quantitative atomic-level evidence of water network percolation in Nafion and its effect on proton conductivity.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1000112
- Report Number(s):
- PNNL-SA-71730; 24811; 40083; KC0302020; TRN: US201024%%309
- Journal Information:
- Journal of Physical Chemistry B, 114(43):13681-13690, Vol. 114, Issue 43; ISSN 1520-6106
- Country of Publication:
- United States
- Language:
- English
Similar Records
Atomistic Simulation of Nafion Membrane: 2. Dynamics of Water Molecules and Hydronium Ions
Molecular Structure and Transport Dynamics in Perfluoro Sulfonyl Imide Membranes