Enhanced Chemical Stability of Tetramethylammonium Head Groups via Deep Eutectic Solvent: A Computational Study

Area of Science:

• Materials Science
• Computational Chemistry
• Electrochemistry

Background:

• Tetramethylammonium (TMA) head groups are crucial in anion exchange membranes (AEMs).
• Understanding the chemical stability of TMA head groups is essential for AEM performance and longevity.
• Degradation mechanisms, such as ylide formation (YF) and nucleophilic substitution (SN2), can limit the operational lifetime of AEMs.

Purpose of the Study:

• To investigate the impact of a choline chloride and ethylene glycol-based deep eutectic solvent (DES) on the chemical stability of TMA head groups.
• To elucidate the influence of DES on key degradation mechanisms (YF and SN2) under varying hydration levels and temperatures.
• To assess the potential of DES as a stabilizing agent for TMA-based materials in AEMs.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to determine transition state energetics for degradation reactions.
• Ab initio Molecular Dynamics (MD) simulations were performed across a range of hydration levels (HLs 1-5).
• The effects of temperature on degradation mechanisms were examined in the presence and absence of DES.

Main Results:

• DFT calculations indicated that DES enhances the stability of TMA head groups by lowering activation energies for degradation.
• Ab initio MD simulations revealed that YF is the dominant degradation pathway at low hydration levels without DES.
• In the presence of DES, both YF and SN2 mechanisms were significantly suppressed across all studied hydration levels and temperatures.

Conclusions:

• The presence of DES demonstrably improves the chemical stability of tetramethylammonium head groups.
• DES effectively inhibits major degradation pathways, suggesting a protective role.
• These findings highlight the potential of DES to enhance the durability and performance of anion exchange membranes containing TMA functionalities.