OH− and H3O+ Diffusion in Model AEMs and PEMs at Low Hydration: Insights from Ab Initio Molecular Dynamics

Fuel cell-based anion-exchange membranes (AEMs) and proton exchange membranes (PEMs) are considered to have great potential as cost-effective, clean energy conversion devices. However, a fundamental atomistic understanding of the hydroxide and hydronium diffusion mechanisms in the AEM and PEM enviro...

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Veröffentlicht in:Membranes (Basel) Jg. 11; H. 5; S. 355
Hauptverfasser: Zelovich, Tamar, Tuckerman, Mark E.
Format: Journal Article
Sprache:Englisch
Veröffentlicht: Basel MDPI AG 12.05.2021
MDPI
Schlagworte:
ab initio molecular dynamics
Anion exchanging
anion-exchange membrane
Anions
Aqueous solutions
Cations
Clean energy
Confined spaces
Diffusion
Electrolytes
Energy conversion
Fuel cells
Fuel technology
Hydration
hydronium diffusion mechanisms
Hydronium ions
hydroxide diffusion mechanisms
low hydration
Molecular dynamics
Motivation
Oxygen
Polymers
Proton exchange membrane fuel cells
proton exchange membranes
Solvation
Sulfur
Transport phenomena
ISSN:2077-0375, 2077-0375
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Zusammenfassung:Fuel cell-based anion-exchange membranes (AEMs) and proton exchange membranes (PEMs) are considered to have great potential as cost-effective, clean energy conversion devices. However, a fundamental atomistic understanding of the hydroxide and hydronium diffusion mechanisms in the AEM and PEM environment is an ongoing challenge. In this work, we aim to identify the fundamental atomistic steps governing hydroxide and hydronium transport phenomena. The motivation of this work lies in the fact that elucidating the key design differences between the hydroxide and hydronium diffusion mechanisms will play an important role in the discovery and determination of key design principles for the synthesis of new membrane materials with high ion conductivity for use in emerging fuel cell technologies. To this end, ab initio molecular dynamics simulations are presented to explore hydroxide and hydronium ion solvation complexes and diffusion mechanisms in the model AEM and PEM systems at low hydration in confined environments. We find that hydroxide diffusion in AEMs is mostly vehicular, while hydronium diffusion in model PEMs is structural. Furthermore, we find that the region between each pair of cations in AEMs creates a bottleneck for hydroxide diffusion, leading to a suppression of diffusivity, while the anions in PEMs become active participants in the hydronium diffusion, suggesting that the presence of the anions in model PEMs could potentially promote hydronium diffusion.
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ISSN:2077-0375
2077-0375
DOI:10.3390/membranes11050355