L. Pasquini

Effects of anion substitution on hydration, ionic conductivity and mechanical properties of anion-exchange membranes

Anion-conducting ionomers were synthesized by the chloromethylation of polysulfone (PSU) followed by the formation of quaternary ammonium groups by a reaction with trimethylamine (TMA) or 1,4-diazabicyclo[2.2.2]octane (DABCO). The degree of functionalization was determined by 1H NMR and titration. Anions (F−, Cl−, Br−, SO42−, NO3−, CO32−, HCO3−, CH3CO2−, and OH−) were substituted by ion exchange in aqueous solution. Water uptake, ionic conductivity and mechanical properties of various ionomers were determined. Hydration has a large influence on both ionic conductivity and mechanical properties: ionic conductivity increases with water uptake, whereas the Young’s modulus decreases. Hydroxide and fluoride containing ionomers present a particularly large ionic conductivity.

Fluoride-ion-conducting Polymers: Ionic Conductivity and Fluoride Ion Diffusion Coefficient in Quaternized Polysulfones

We describe the three-step synthesis of a new polymeric fluoride ion conductor based on the fully aromatic polymer polysulfone (PSU). In the first step, PSU is chloromethylated (CM-PSU) using reagents (i.e., stannic chloride, paraformaldehyde, and trimethylchlorosilane) that are less toxic than those used in the standard procedure. In the second step, CM-PSU reacts with a tertiary amine (trimethylamine or 1,4-diazabicyclo[2.2.2]octane) to form quaternary ammonium groups fixed on the PSU backbone and mobile chloride counter-anions. The chloride ions can, in a third step, be exchanged with fluoride ions by immersion of the ionomer in NaF solution. The fluoride ion conductivity reaches 3-5 mS cm(-1) at 25 °C and 5-10 mS cm(-1) at 40 °C. We determined the F(-) diffusion coefficient in these ionomers by pulsed gradient spin-echo (PGSE) high-resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) spectroscopy and by impedance spectroscopy using the Nernst-Einstein relation. The diffusion coefficients determined by the two methods are in good agreement, ranging from 2 to 4×10(-10)  m(2)  s(-1) . The porosity and tortuosity of the ionomer membranes can be estimated.

Anion-conducting sulfaminated aromatic polymers by acid functionalization

A simple synthesis technique for the preparation of anionic conducting membranes is presented. In the first step, poly-ether-ether-ketone (PEEK) reacts with chlorosulfonic acid to produce chlorosulfonated PEEK, which in a second step is transformed by reaction with a secondary amine, dimethyl- or diethylamine, into sulfaminated PEEK. The sulfaminated PEEK is cast and the membranes are functionalized in a last step by reaction with various aqueous acid solutions, including HCl, HBr, HNO3, H2SO4, and H3PO4. The spectroscopic, thermal, mechanical, permeability and electrical properties of the membranes are determined and discussed. The combination of appealing properties, such as high elastic modulus (∼1300 MPa), high thermal stability, low cation permeability, respectable anionic conductivity (2–4 mS cm−1), and a relatively simple and inexpensive synthesis make these new ionomers very promising for applications especially in acidic media, like in vanadium redox flow batteries.

Stabilized sulfonated aromatic polymers by in situ solvothermal cross-linking

The cross-link reaction via sulfone bridges of sulfonated polyetheretherketone (SPEEK) by thermal treatment at 180 °C in presence of dimethylsulfoxide (DMSO) is discussed. The modifications of properties subsequent to the cross-linking are presented. The mechanical strength as well as the hydrolytic stability increased with the thermal treatment time, i.e., with the degree of cross-linking. The proton conductivity was determined as function of temperature, IEC, degree of cross-linking and hydration number. The memory effect, which is the membrane ability to “remember” the water uptake reached at high temperature also at lower temperature, is exploited in order to achieve high values of conductivity. Membranes swelled at 110 °C can reach a conductivity of 0.14 S/cm at 80°C with a hydration number () of 73.