Molecular dynamics revelations of structures and dynamics of H3O+, Cu+ and Cu2+ ions within a model polymeric Nafion membrane

A Vaidyanathan and P Sahu and B Chakraborty and SM Ali, JOURNAL OF CHEMICAL SCIENCES, 137, 90 (2025).

DOI: 10.1007/s12039-025-02403-9

The microscopic understanding of the morphology and ion/proton dynamics in hydrated Nafion systems is extremely essential for optimizing the efficiency of thermochemical/electrochemical processes like the Cu-Cl thermodynamic cycle for hydrogen generation. The present study addresses the gap in theoretical investigations on the structure and proton dynamics in aqueous Nafion systems, focusing on Cu+/Cu2+ and proton dynamics using robust MD simulations. We report a systematic investigation of the structure, transport and dynamics of protons and copper ions by varying water content, temperature and copper ion concentration. The present study captures the formation of continuous water channels within the hydrophobic Nafion matrix as observed in many experimental findings. Simulations are also conducted with 10% hydrated Nafion in contact with 11 N HCl and 1 M copper ions to represent the real composition of Cu-Cl electrolyzer. The MD analyses demonstrated that the highly acidic environment (11 N HCl) of the Cu-Cl electrolyzer would boost the swelling of Nafion membrane with reduced water-water interactions. On the other hand, the pairing of Cu-Cl ions would enhance the Nafion-hydronium ion interactions in the presence than in the absence of acid. The augmented interaction of hydronium ions with the sulfonic acid group of Nafion, would in due course, assist in faster transport of hydronium ions following Grotthuss mechanism. The hydrogen- bond life time of Nafion hydrated water was higher than that of bulk water due to the formation of separate water clusters within the Nafion membrane. The pores of Nafion allows only the transport of hydronium ions and water molecules whereas copper and chloride ions are restricted. The present findings on the structure and proton dynamics of the polymeric Nafion membranes might contribute towards the optimization of Cu-Cl electrolyzer for efficient and trouble free hydrogen production.Graphical abstractThe effects of water content, temperature, presence of Cu+/Cu2+ ions and acidity in Nafion membrane were investigated. The increasing water content led to the formation of water channels within the membrane. Swelling, formation of channels and enhanced hydrogen bonding were observed at higher water content.

Return to Publications page