Exploring Crystal Structure Features in Proton Exchange Membranes and Their Correlation with Proton and Heat Transport.

Proton exchange membranes (PEMs) are dominated by semicrystalline structures because highly pure crystals are still challenging to produce and control. Currently, the development and application of PEMs have been hindered by a lack of understanding regarding the effects of microstructure on proton and heat transport properties. Based on an experimentally characterized perfluoro sulfonic acid membrane, the corresponding semicrystalline model and the crystal model contained therein were constructed. The water distribution, proton, and heat transport in the crystal, amorphous, and semicrystalline regions were examined using molecular dynamics simulations and energy-conserving dissipative particle dynamics simulations. The crystal structure had pronounced water connection pathways, a proton transport efficiency 5-10 times higher than that of the amorphous structure, and an in-plane covalent bonding that boosted the thermal diffusion coefficient and thermal conductivity by more than 1-3 times. The results for the semicrystalline structure were validated by the corresponding experiments. In addition, a proportionality coefficient that depended on both temperature and water content was proposed to explain how vehicle transport contributed to the proton conductivities, facilitating our understanding of the proton transport mechanism. Our findings enhance our theoretical understanding of PEMs in proton and heat transport, considering both the semicrystalline and crystalline regions. Additionally, the research methods employed can be applied to the study of other semicrystalline polymers.