Multiscale modelling of the glass transition in Nafion membranes for perspective flow and fuel batteries

Prof. Dr. Alexey V. Lyulin, Technische Universität Eindhoven

Nafion is a commonly used polyelectrolyte membrane (PEM) in fuel cells and flow batteries. Nanocomposites of Nafion are used to enhance temperature resistance and proton conductivity. The properties of hydrated membranes, and the water influence on Nafion glassy behavior is very important. We first report molecular-dynamics simulations of Nafion films of different thicknesses between two potential walls of variable wettability [1]. The water cluster sizes showed an increase with film thickness for the high wettability cases, in agreement with SAXS experiments. The in-plane water diffusion was considerably enhanced for the high wettability walls. We report the modelling of the annealing effects on both structure, dynamics and electric conductivity of the membranes. We observe [2] strong antiplasticization effect and increase in the glass-transition temperature upon hydration. The hydrophilic channels evolution upon annealing and associated changes in ion diffusion and electric conductivity will be discussed. Large scale Dissipative Particle Dynamics simulations were carried out as well to study the temporal evolution of the water-PEM interface as a function of the PEM side-chain length.

Acknowledgements
This work was done as a part of the FOM-SHELL 15CSER13 research project and was carried out on the Dutch national e-infrastructure with the support of SURF Cooperative. AVL and AV both thank DUO-India Fellowship Program for the possibility to visit and work at IISER Pune and TU Eindhoven, correspondingly. Arun Venkatnathan thanks DST Nanomission Thematic Unit (SR/NM/TP-13/2016(G)).

References
[1] S. Sengupta, A. V. Lyulin, J. Phys. Chem. B, 122, 6107-6119, 2018.
[2] A. V. Lyulin S. Sengupta, A. Varghese, P. Komarov and A. Venkatnathan, ACS Appl. Polym. Mater., 2, 5058-5066, 2020.