Hydrolysis of the Nafion® precursor studied by X-ray scattering and in-situ atomic force microscopy

Abstract

The hydrolysis of Nafion ® † precursor material to a perfluorosulfonate ion exchange membrane has been studied in situ at the surface of a sample using atomic force microscopy (AFM), and in the bulk using a combination of small and wide-angle X-ray scattering. The AFM results show that there is a rapid and significant change in the surface morphology of the sample during the first 12 min after the introduction of aqueous hydroxyl ions, provided that an appropriate swelling agent is used. After this point there is little change in surface morphology, although bulk swelling of the sample continues. The wide-angle X-ray scattering results indicate a significant drop in the degree of crystallinity of fluorocarbon matrix from 14±1% to 7±1% on hydrolysis, as a result of the bulk structural reordering necessary to accommodate the formation of ionic clusters. Ionic clustering is confirmed by the appearance of a characteristic small-angle X-ray peak. However, the peak forms towards the end of the hydrolysis process, and subsequently coarsens, suggesting that the formation of ionic clusters is a slow process compared to the rate of hydrolysis. It is confirmed that an appropriate water/solvent mixture is necessary to achieve an efficient conversion of precursor to membrane. AFM images of the precursor surface, when water alone is used, show no signs of structural change.

Impact of Heating on the Structure of Perfluorinated Polymer Electrolyte Membranes: A Positron Annihilation Study

“…This sharp peak can be indexed as the 100 reflection of the hexagonal structure of PTFE-like crystallites. [25][26][27] The crystalline peak is caused by regular intermolecular spacings and the broad peak over a range of 2u ¼ 25-558 consists of several diffraction peaks from intramolecular correlations. [23] The crystalline reflection around 178 and the broad peak are strengthened after heating at 160 8C, suggesting enhanced crystallinity and distinct ordering of the amorphous regions in both Nafion NR212 and Aquivion E8705.…”

A review on durability issues and restoration techniques in long-term operations of direct methanol fuel cells

“…An increase in crystallinity of the membrane implies the change in the physical properties of Nafion ® 117 after being subjected to long-term test. For instance, the hydrophilic ionic zone (sulfonic zone) in the net structure of Nafion ® , which is considered to be amorphous and proton conductive, might have become shrunk [155].…”

Complex Impedance Studies of Electrosprayed and Extruded Nafion Membranes

“…In Nafion 10 117, there is approximately one side chain for every 13 CF 2 in the polymer backbone. 7,8 In the acid form, these side chains end in a sulfonate group. Water clusters about the sulfonate and solvates the proton.…”