Suitable acid groups and density in electrolytes to facilitate proton conduction

Area of Science:

• Materials Science
• Computational Chemistry
• Electrochemistry

Background:

• Proton conducting materials exhibit reduced conductivity in low relative humidity (RH) environments.
• Acid-acid interactions, facilitating proton transport without water, offer a promising solution to this limitation.

Purpose of the Study:

• To computationally identify optimal acid groups and densities for polymer design that promote acid-acid interactions.
• To guide experimental synthesis of advanced proton conducting materials.

Main Methods:

• Utilized ab initio calculations to investigate acid-acid interactions in various polymer structures.
• Employed parameters based on optimized coordination interactions of acids and water molecules for evaluation.

Main Results:

• Established an order for the propensity of polymer electrolytes to induce acid-acid interactions: hydrocarbon-based phosphonated polymers > phosphonated aromatic hydrocarbon polymers > perfluorosulfonic acid polymers ≈ perfluorophosphonic acid polymers > sulfonated aromatic hydrocarbon polymers.
• Demonstrated that closer proximity between acid groups strengthens acid-acid interactions, with a preferred distance of within 13 Å for phosphonate moieties.

Conclusions:

• Phosphonated polymers show significant potential for enhancing proton conductivity via acid-acid interactions.
• Computational screening of acid group type and density is crucial for designing high-performance proton conducting materials for low RH conditions.