Mechanism of monovalent and divalent ion mobility in Nafion membrane: An atomistic simulation study

Polymer cation exchange membranes (CEMs) are widely used in water treatment processes. The fundamental factors that control the separation and selectivity of cations with different valences in CEMs are not fully understood. In this study, we use atomistic molecular dynamics simulations to investigate the underlying molecular mechanisms that control the mobility of cations with different valences in Nafion membranes. Our results indicate structural differences in binding of monovalent and divalent cations, which gives rise to differences in ion diffusion in Nafion. Monovalent cations are shown to be territorially bound, i.e., bound while partially hydrated, to the fixed charge groups whereas divalent cations are shown to be site bound, i.e., bound while fully dehydrated, to the charge groups on the polymer. This difference in binding structure gives rise to differences in transport characteristics of cations in Nafion.

Automated summary

In this study, atomistic molecular dynamics simulations were used to investigate the molecular mechanisms that control the mobility of cations with different valences in Nafion membranes. The results showed that monovalent and divalent cations have structural differences, leading to differences in ion diffusion in Nafion. Monovalent cations are territorially bound while partially hydrated to the fixed charge groups, whereas divalent cations are site bound while fully dehydrated to the charge groups on the polymer. This difference in binding structure results in differences in the transport characteristics of cations in Nafion.