Impact of the Solid Interface on Proton Conductivity in Nafion Thin Films

Area of Science:

• Materials Science
• Electrochemistry
• Physical Chemistry

Background:

• Proton conductivity in polyelectrolytes is critical for polyelectrolyte fuel cell performance.
• Understanding interfacial effects is essential for optimizing these devices.

Purpose of the Study:

• To investigate proton conductivity in Nafion thin films.
• To examine conductivity variations with film thickness and direction (normal/parallel to interface).
• To elucidate the role of the solid-polyelectrolyte interface on proton transport.

Main Methods:

• Neutron reflectivity measurements to characterize interfacial structure.
• Proton conductivity measurements in both out-of-plane and in-plane directions.
• Fabrication of laminated Nafion films to vary interface-to-volume ratio.

Main Results:

• A water-containing multilamellar structure forms at the Nafion-substrate interface.
• The interfacial layer suppresses out-of-plane proton conductivity.
• The interfacial layer enhances in-plane proton conductivity, forming a 2D conductive pathway.
• Proton transport mechanism at the interface differs from bulk (Grotthuss mechanism).

Conclusions:

• Proton conductivity in Nafion thin films is strongly dependent on the interface-to-volume ratio.
• Interfacial engineering can tune proton conductivity for device optimization.
• Findings are crucial for designing advanced polyelectrolyte-based devices.