Protons and Sodium Ions Interacting With Nafion Confined Water

Abstract

Proton transport in aqueous media, using structural diffusion, is known to be anomalously fast com- pared to that of other cations, using mass diffusion. While proton transport is believed to involve the interconversion between the Eigen complex and the Zundel complex, details of this mechanism are still under debate. Using a frequency domain coaxial line reflectometric method and time domain THz-pulse spectroscopy, it is shown experimentally that pro- ton transport in Nafion membranes is equally slowed down by the Nafion environment as the transport of sodium ions, even at low water contents. The results suggest that structural diffusion is equally influenced by the nanoporous Nafion as mass diffusion, and that the Grotthuss mechanism holds in the Nafion envi- ronment, even at these low water contents. These results are anticipated to be a starting point for fur- ther research on the behavior of ions, and especially protons, in nanoporous aqueous media, as this plays a crucial role in many processes in biological systems, such as energy transport and acid-base reactions, and industrial electrochemical systems, such as the pro- ton exchange membrane (PEM) fuel cells.