The Evolution of Hydrogen Bond Network in Nafion via Molecular Dynamics Simulation

The hydrogen bond network (HBN) is of primary importance to the proton transport in Nafion. However, the evolution of the HBN in Nafion with water content and the underlying thermodynamics have not been revealed. In this study, the free energy of hydrogen bond formation is calculated based on an information-theoretic approach, indicating the formation of HBN in Nafion is a thermodynamically favorable process as the water content increases. In addition, the evolution of HBN in Nafion with water content including the topology and basic building blocks has been visualized and quantified by a ring statistics approach based on graph theory. Finally, the rearrangement dynamics and heterogeneity of HBN are also disclosed. This study provides a fundamental and comprehensive understanding of HBN in Nafion including the formation thermodynamics, topology, and rearrangement dynamics, which is useful for the design of high-performance proton exchange membranes.