Fractal diffusion in high temperature polymer electrolyte fuel cell membranes

Area of Science:

• Materials Science
• Electrochemistry
• Condensed Matter Physics

Background:

• Fuel cell performance relies heavily on proton diffusion within the proton conducting membrane.
• High-temperature polymer electrolyte fuel cells utilize polymer membranes swollen with phosphoric acid as the electrolyte.

Purpose of the Study:

• To investigate proton diffusion dynamics in phosphoric acid-swollen polymer membranes.
• To understand the mechanism of proton conduction relevant to fuel cell operation.

Main Methods:

• Neutron scattering techniques, specifically time-of-flight and backscattering spectroscopy, were employed.
• Isotopic substitution (hydrogen vs. deuterium in phosphoric acid) was used to selectively probe proton diffusion.
• Data analysis involved subtracting scattering data from different samples to isolate proton contributions.

Main Results:

• Subdiffusive proton diffusion behavior was observed in the polymer electrolyte membranes.
• A new scattering function for fractal diffusion was developed to model the observed behavior.
• The fractal diffusion dimension (dw) and Hausdorff dimension (df) were determined.

Conclusions:

• Proton diffusion in these fuel cell membranes exhibits fractal characteristics.
• The developed fractal diffusion model provides insights into ion transport mechanisms.
• Neutron scattering is a powerful tool for studying proton dynamics in fuel cell electrolytes.