Morphology and proton transport in sulfonated poly(ether ether ketone) membranes: a molecular dynamics and DFT study

Area of Science:

• Materials Science
• Polymer Chemistry
• Computational Chemistry

Background:

• Sulfonated poly(ether ether ketone) (SPEEK) is a key material for proton exchange membranes (PEMs).
• SPEEK performance is influenced by water content (λ) and degree of sulfonation (DS).
• Understanding the interplay between λ and DS is crucial for optimizing PEMs.

Purpose of the Study:

• To investigate the synergistic effects of water content and degree of sulfonation on SPEEK membrane properties.
• To determine the optimal hydration and sulfonation levels for enhanced proton transport in SPEEK.
• To provide quantitative guidelines for designing advanced SPEEK-based proton exchange membranes.

Main Methods:

• Molecular dynamics simulations (MD) were employed to model SPEEK behavior.
• Density functional theory (DFT) was utilized for detailed electronic structure analysis.
• Key analyses included hydrogen bond counting, transport kinetics, and radial distribution functions.

Main Results:

• Membrane density and hydrophilic-hydrophobic interface stabilization occurred at an optimal swelling of λ = 10.
• Optimal hydration level was identified at λ = 10, with increasing DS enhancing proton transport up to a point.
• Maximized hydronium ion diffusion was observed at DS = 60-70%, indicating well-developed proton transport channels.

Conclusions:

• The optimal parameter range for SPEEK membranes is λ = 10 and DS = 60-70%.
• This study elucidates the intrinsic correlation between hydration and sulfonation in SPEEK.
• Findings offer quantitative guidance for optimizing proton exchange membrane architectures for improved performance.