Nafion Structural Phenomena at the Platinum and Carbon Interfaces

Journal Article · Thu Jan 01 04:00:00 EST 2009 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja9033928· OSTI ID:1023343

WoodIII, David L ^[1]; Chlistunoff, Jerzy ^[1]; Majewski, Jaroslaw ^[1]; Borup, Rodney ^[1]

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1. Los Alamos National Laboratory (LANL)

Neutron Reflectometry (NR) was used to examine the interactions of Polymer Electrolyte Fuel Cell (PEFC) materials that comprise the triple-phase interface. Smooth, idealized layers of Nafion on glassy carbon (GC) and Pt surfaces were used to experimentally model the PEFC electrode interfaces. Different multilayer structures of Nafion were found in contact with the Pt or GC surfaces. These structures showed separate hydrophobic and hydrophilic domains formed within the Nafion layer when equilibrated with saturated D2O vapor. A hydrophobic Nafion region was formed adjacent to a Pt film. However, when Nafion was in contact with a PtO surface, the Nafion at the Pt interface became hydrophilic. The adsorbed oxide layer caused a long-range restructuring of the perfluorosulfonic acid (PFSA) polymer chains that comprise Nafion . The thicknesses of the hydrophobic and hydrophilic domains changed to the same magnitude when the oxide layer was present compared to a thin hydrophobic domain in contact with Pt. A three-layer Nafion structure was formed when Nafion was in direct contact with GC. The findings in this research are direct experimental evidence that both the interfacial and long-range structural properties of Nafion are affected by the material with which it is in contact. Evidence of physical changes of aged Nafion films was obtained, and the results showed a permanent increase in the thickness of the Nafion film and a decrease in scattering length density (SLD), which are attributed to irreversible swelling of the Nafion film. The aging also resulted in a decrease in SLD of the GC substrate, which is likely due to either an increase in surface oxidation of the carbon or loss of carbon mass at the GC surface.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: EE USDOE - Office of Energy Efficiency and Renewable Energy (EE)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1023343
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 50 Vol. 131; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

30 DIRECT ENERGY CONVERSION
AGING
CARBON
CHAINS
Carbon- Nafion Interface
ELECTRODES
Electrocatalyst Layer
Electrode Structure
NEUTRONS
Neutron Reflectometry
OXIDATION
OXIDES
PLATINUM
POLYMERS
PROTON EXCHANGE MEMBRANE FUEL CELLS
Platinum-Nafion Interface
Polymer Electrolyte Fuel Cell
SCATTERING LENGTHS
SWELLING
THICKNESS
Triple-Phase Interface