Water Sorption Behavior in Different Aromatic Ionomer Composites Analyzed with a “New Dual-Mode Sorption” Model

A new dual-mode sorption model (NDMS) was applied to sigmoid-shaped isotherms of water vapor sorption in composites of sulfonated or nonsulfonated polysulfones with a sulfonic-modified laponite clay and in blends of sulfonated poly­(ether ether ketone) with sulfonated polyether sulfone cardo, respectively. The three NDMS parameters, <i>C</i>_<i>p</i>, <i>A</i>′, and <i>k</i>′ can be correlated to the amount of water molecules sorbed in the first hydration shell, the subsequent sorption on the sulfonic-sites and the tendency for water molecules to form clusters at very high water activities, respectively. The fitted values were used to study the relationship between sorption behaviors and component structure or organization in the composites. The analysis of the sorption–desorption cycles shows that the sorption hysteresis increases with the ionomer chain rigidity. An analytical expression for the mean cluster size (MCS) as a function of activity was deduced and validated by correlating to sorption kinetics. It has been shown that MCS increases with chain flexibility at high water activities

Water Transport Properties of Plasma-Modified Commercial Anion-Exchange Membrane for Solid Alkaline Fuel Cells

In the field of low-temperature fuel cells, solid alkaline membrane fuel cells (SAMFCs) appear to be a very promising new fuel cell technology. Nevertheless, commercial hydroxyl-exchange membranes suitable for SAMFCs suffer from some limitations, especially low retention to water at the cathode (where water is required to be reactive in the electrochemical reaction), which weakens fuel cell performances. In this study, the commercial Morgan ADP membrane by Solvay has been modified on the surface by plasma processes using argon or argon/triallylamine as gaseous phases. Plasma-treated and untreated membranes have been characterized in terms of water sorption and diffusion properties performing water vapor sorption measurements. Analysis of sorption isotherms and related modeling from Park model has shown that plasma treatments induce a decrease in water sorption and diffusion abilities without qualitatively affecting the water transport properties. Plasma modification from triallylamine leading to the deposition of a highly cross-linked film on the membrane surface is more influent than argon plasma treatment, causing surface physical cross-linking coupled to hydrophilization effect

High-Temperature Ionic-Conducting Material: Advanced Structure and Improved Performance

A new composite proton-conducting material based on the association of an ionic liquid and a porous polymer support was prepared with the aim of applying it as an electrolyte in a proton exchange membrane fuel cell (PEMFC) at elevated temperature (130 °C). The porous support was made from a high glass-transition temperature polymer (<i>T</i>g) by using the vapor-induced phase separation (VIPS) method in conditions leading to highly interconnected porous films. The ionic liquid tested was obtained by the reaction of a sulfonic acid with a tertiary amine and presents enough high-temperature stability to be used at elevated temperatures. Composite samples were prepared by immersing pieces of porous film in the ionic liquids under test. The porous support was characterized by scanning electron microscopy (SEM), gas permeation, and thermogravimetric analysis (TGA) tests, and the composite samples were characterized by mechanical and proton-conduction measurements. At 130 °C, this new material exhibits proton conductivity (20 mS cm^–1) below, but very close to, that of the pure ionic liquid (31 mS cm^–1) and presents, up to at least 150 °C, a storage modulus exceeding 200 MPa. This is very promising considering the PEMFC applications