Atomistic Simulations of Perfluoro Phosphonic and Phosphinic Acid Membranes and Comparisons to Nafion

Journal Article · Thu Mar 31 04:00:00 EDT 2011 · Journal of Physical Chemistry B, 115(12):2959-2969

DOI:https://doi.org/10.1021/jp111972h· OSTI ID:1012281

Idupulapati, Nagesh B; Devanathan, Ramaswami; Dupuis, Michel

We used classical molecular dynamics (MD) simulations to investigate the nanoscale morphology and proton transport properties of perfluoro phosphonic (FPA) and phosphinic acid (FPA-I) membranes as they are being considered for use in low temperature fuel cells. We systematically investigated these properties as a function of the hydration level. The changes in nanostructure, in transport dynamics of water and hydronium ions, and in water network percolation were extracted from MD simulations and compared with Nafion. Phosphonic and phosphinic acid moieties in FPA and FPA-I, have lower acidity than sulfonic acid in Nafion, yet the diffusion of water was observed to be faster in FPA and FPA-I than in Nafion, particularly at low hydration levels. However this did not give rise to notable differences in hydronium ion diffusion and water network percolation for these membranes over Nafion. Similar observations were also reported by our group recently in a study of perfluoro-sulfonyl imide membranes carrying stronger super-acids than sulfonic acid of Nafion. These findings together suggest no strong apparent correlation between the acidity strength of the functional acid groups and the dynamics of water and hydronium ions in hydrated polymer electrolyte membranes (PEMs) with similar fluorocarbon backbones and acidic group-carrying side chains. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1012281
• Report Number(s): PNNL-SA-76901; 40083; KC0302020
• Journal Information: Journal of Physical Chemistry B, 115(12):2959-2969, Journal Name: Journal of Physical Chemistry B, 115(12):2959-2969 Journal Issue: 12 Vol. 115; ISSN 1520-6106
• Country of Publication: United States
• Language: English

Related Subjects

30 DIRECT ENERGY CONVERSION
DIFFUSION
ELECTROLYTES
Environmental Molecular Sciences Laboratory
FUEL CELLS
FUNCTIONALS
HYDRATION
IMIDES
MEMBRANES
MORPHOLOGY
OXONIUM IONS
PH VALUE
PHOSPHINIC ACIDS
POLYMERS
PROTON TRANSPORT
Polymer electrolyte membranes
SULFONIC ACIDS
TRANSPORT
WATER
acidity
molecular dynamics
percolation