Anhydrous proton-conducting polymeric electrolytes for fuel cells

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• High-temperature fuel cells (≥120°C) require advanced proton-conducting electrolytes.
• Existing electrolytes often rely on water, limiting high-temperature performance.
• Development of "water-free" polymeric materials is crucial for anhydrous operation.

Purpose of the Study:

• To investigate the properties of "water-free" proton-conducting membranes based on polymeric organic amine salts.
• To evaluate the performance of these membranes over a wide temperature range (25-180°C).
• To explore the potential of nanocomposites with hydroxylated silica for enhanced conductivity.

Main Methods:

• Synthesis and characterization of poly-2-vinylpyridine (P2VP), poly-4-vinylpyridine (P4VP), and polyvinylimidazoline (PVI) salts (bisulfates and dihydrogenphosphates).
• Proton conductivity measurements across a temperature range of 25-180°C.
• Proton Nuclear Magnetic Resonance (NMR) spectroscopy to assess polymer mobility and proton ionization.

Main Results:

• The investigated polymers (P2VP, P4VP, PVI salts) exhibit stability and proton conductivity up to 200°C.
• Phosphate-based polymers demonstrate higher conductivity than bisulfate counterparts.
• Ionic conduction activation energy decreases with increasing temperature, linked to polymer mobility and proton ionization, confirmed by NMR.
• Conductivity correlates with the difference in pKa values between the polymer amine and the mineral acid.

Conclusions:

• Anhydrous polymer systems based on acid-base polymer salts are promising for high-temperature proton conduction.
• Combining these polymer salts with nanoparticulate silica can enhance proton conductivity over a broad temperature range.
• The findings provide a basis for designing novel water-free acid-base polymer electrolytes for fuel cell applications.