Cristina Iojoiu

Proton Conducting Ionic Liquid Organization as Probed by NMR: Self-Diffusion Coefficients and Heteronuclear Correlations

The structure and local organization of new proton conducting ionic liquids (PCILs) obtained by reacting alkylamine with various acids were deciphered by complementary 1- and 2-D heteronuclear NMR experiments. One the one hand, PFG NMR yielded the self-diffusion coefficients of the PCIL components (and thus information on their possible concerted translational motions), while on the other hand, 13C, 1H, and 15N, 1H correlation and intermolecular Overhauser experiments gave insight into the nature of protonic species and ion-pairing behavior.

Synthesis and photocrosslinking of benzyl acrylate substituted polydimethylsiloxanes

This article deals with the synthesis of polydimethylsiloxanes (PDMSs) substituted with chain or end benzyl acrylate groups by the hydrosilation of appropriate hydro-siloxanes, followed by phase transfer catalysed reaction of chloromethylated aromatic groups with the sodium salt of acrylic acid. Differential scanning photocalorimetry (DPC) was used to study the crosslinking behaviour of the mentioned functional PDMSs in the presence of different photoinitiators. The reaction rate, the final conversion and the inhibition period characterizing the crosslinking were found to be dependent on reaction atmosphere, light intensity, nature and concentration of photoinitiator and on polymer functional groups content.

Polysulfone-based Ionomers for Fuel Cell Applications

This paper is a review that is focused on ionomers based on aromatic polysulfone backbone and intended to be used in proton exchange membrane fuel cells or in direct methanol fuel cells. Emphasis is placed on the different chemical routes to prepare the ionomers. Special attention is given to the impact of the ionomer structure on the conductivity performance and on the dimensional stability of the membranes at high temperatures.

Effects of Block Length and Membrane Processing Conditions on the Morphology and Properties of Perfluorosulfonated Poly(arylene ether sulfone) Multiblock Copolymer Membranes for PEMFC.

Perfluorosulfonated poly(arylene ether sulfone) multiblock copolymers have been shown to be promising as proton exchange membranes. The commonly used approach for preparation of the membrane is solvent casting; the properties of the resulting membranes are very dependent on the membrane processing conditions. In this paper, we study the effects of block length, selectivity of the solvent, and thermal treatment on the membrane properties such as morphology, water uptake, and ionic conductivity. DiMethylSulfOxide (DMSO), and DiMethylAcetamide (DMAc) were selected as casting solvents based on the Flory-Huggins parameter calculated by inversion gas chromatography (IGC). It was found that the solvent selectivity has a mild impact on the mean size of the ionic domains and the expansion upon swelling, while it dramatically affects the supramolecular ordering of the blocks. The membranes cast from DMSO exhibit more interconnected ionic clusters yielding higher conductivities and water uptake as compared to membranes cast from DMAc. A 10-fold increase in proton conductivity was achieved after thermal annealing of membranes at 150 °C, and the ionomers with longer block lengths show conductivities similar to Nafion at 80 °C and low relative humidity (30%).

Preparation and Characterization of Sulfonated Polyphenylquinoxalines

Poly(phenylquinoxaline)s.(PPQs) are a family of aromatic condensation polymers known for their outstanding thermal and chemical stability. The pendant phenyl groups and chains isomerism improve the solubility and processing characteristics of these polymers. PPQs have also been shown to possess excellent thermo-oxidative stability and thermohydrolytic stability. This stability makes these polymers candidates for development as proton exchange membranes (PEMs) to be used in fuel cells. In addition to thermohydrolytic stability, PEMs require high protonic conductivity and, in order to achieve this they also require high water uptake. Aromatic condensation polymers do not possess these properties, but ionomers derived from them may. The usual method to derivatiziting these polymers is through sulfonation. In the frames of the present investigation we have carried out sulfonation of two PPQs using an H2SO 4—oleum mixture (4 : 1) as sulfonating agent at 125 3C. As a quinoxaline ring is readily formed in acidic medium synthesis of sulfonated PPQs (SPPQs) was also carried out directly from monomers using an H 2SO4—oleum mixture as solvent, catalyst and as sulfonating agent. Depending on the conditions of the reaction (temperature, duration, and the ratio of components in a sulfonating mixture) the polymers containing 0.2—6.7% S were prepared. SPPQs are soluble in polar organic solvents1 from the solutions of SPPQs high strength films (3 = 80—100 MPa) were cast. On the basis of sulfonated PPQs new cation-exchange membranes were prepared and investigated. Among the cation-exchange membranes developed those of the greatest interest are proton-exchanging membranes for fuel cells. Proton conductivity of the membranes prepared strongly depends on relative humidity and comparable with the conductivity of Nafion 117.

Extruded Proton Exchange Membranes Based on Sulfonated Polyaromatic Polymers for Fuel Cell Application

A global approach of membranes elaboration in environmentally friendly conditions and at a moderate cost, for applications in the fuel cells industry is proposed here. New elaboration methods of polysulfones proton exchange membranes have been developed. Extrusion has been used to produce homogeneous films for PEMFC. Different routes are reported: chemical modification of extruded membranes, and for the first time, extrusion of acid and alkaline forms of modified polysulfone. An electrochemical study shows that extruded films exhibited a promising proton‐conductivity.

Controlling Microstructure–Transport Interplay in Highly Phase-Separated Perfluorosulfonated Aromatic Multiblock Ionomers via Molecular Architecture Design

Proton-conducting multiblock polysulfones bearing perfluorosulfonic acid side chains were designed to encode nanoscale phase-separation, well-defined hydrophilic/hydrophobic interfaces, and optimized transport properties. Herein, we show that the superacid side chains yield highly ordered morphologies that can be tailored by best compromising ion-exchange capacity and block lengths. The obtained microstructures were extensively characterized by small-angle neutron scattering (SANS) over an extended range of hydration. Peculiar swelling behaviors were evidenced at two different scales and attributed to the dilution of locally flat polymer particles. We evidence the direct correlation between the quality of interfaces, the topology and connectivity of ionic nanodomains, the block superstructure long-range organization, and the transport properties. In particular, we found that the proton conductivity linearly depends on the microscopic expansion of both ionic and block domains. These findings indicate that neat nanoscale phase-separation and block-induced long-range connectivity can be optimized by designing aromatic ionomers with controlled architectures to improve the performances of polymer electrolyte membranes.

Electrolyte Based on Easily Synthesized, Low Cost Triphenolate–Borohydride Salt for High Performance Mg(TFSI)2-Glyme Rechargeable Magnesium Batteries

A new class of electrolyte based on TFSI- and triphenolate-borohydride anions was designed and produced which fulfill all requirements of easy synthesis, high ionic conductivity, wide potential window, and noncorrosion of Al current collector. The electrolyte composed of magnesium triphenolate borohydride and Mg(TFSI)2 in glyme simultaneously displays a high conductivity of 5.5 mS cm-1 at 25 °C and a reversible Mg plating/stripping with high current density and Coulombic efficiency at room temperature. By addition of a slight amount of MgCl2 to this electrolyte, a Coulombic efficiency of 90% in an SS/Mg cell, stable cycling performance, and a wide anodic potential of 3.4 V vs Mg2+/Mg on Al current collector can be reached. Reversible and efficient Mg insertion/deinsertion with a high capacity of 94 mAh g-1 and 96% Coulombic efficiency was obtained in a Mo6S8 Chevrel cathode phase.

Magnesium Anthracene System-Based Electrolyte as a Promoter of High Electrochemical Performance Rechargeable Magnesium Batteries

The development of efficient, inexpensive, and safe rechargeable batteries for large-scale environmentally benign cells is one of the key requirements to accommodate and satisfy various technological applications. To date, the development of magnesium battery as a promising candidate for next-generation battery systems has been hindered by the lack of high performance and stable electrolyte. In this work, we have developed an original, safe, and high-performance class of electrolytes based on a simple mixture of commercially available compounds, that is, Mg(TFSI)2, anthracene, MgCl2, and diglyme solvent. We have proven that anthracene induces stabilization of the reduced form of magnesium involving reversible magnesium plating/stripping with very high current density. The electrolyte investigated exhibits an unprecedented electrochemical stability window of up to 3.1 V, whereas MgCl2 addition allows the improvement of the Mg/electrolyte interface properties and enables a large cyclability of Mg/Mo6S8 Chevrel phase cell, allowing one to reach high performances.

Ionic Liquids and Polymers for Battery and Fuel Cells

The electrolyte component in rechargeable batteries and fuel cells [proton exchange membrane fuel cell (PEMFC)] is one of the main compounds as it conditions both the electrochemical performances and the safety of the system. The fluorine atom is omnipresent in the definition of a performant electrolyte for the systems; in this chapter, attention will be focused on fluorinated polymer and ionic liquid used as electrolyte component in the frame of lithium-ion battery and PEMFC.