Silica Containing Composite Anion Exchange Membranes by Sol-Gel Synthesis: A Short Review.

Emanuela Sgreccia,Philippe Knauth,Riccardo Narducci,Maria Di Vona

doi:10.3390/polym13111874

Abstract

This short review summarizes the literature on composite anion exchange membranes (AEM) containing an organo-silica network formed by sol–gel chemistry. The article covers AEM for diffusion dialysis (DD), for electrochemical energy technologies including fuel cells and redox flow batteries, and for electrodialysis. By applying a vast variety of organically modified silica compounds (ORMOSIL), many composite AEM reported in the last 15 years are based on poly (vinylalcohol) (PVA) or poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) used as polymer matrix. The most stringent requirements are high permselectivity and water flux for DD membranes, while high ionic conductivity is essential for electrochemical applications. Furthermore, the alkaline stability of AEM for fuel cell applications remains a challenging problem that is not yet solved. Possible future topics of investigation on composite AEM containing an organo-silica network are also discussed.

Highlights

Anion exchange membranes (AEM) are important materials for applications in energy and in the environment [1,2,3,4]. They are used as ion-conducting separators between the electrode compartments physically impeding the mixture of electrolyte solutions in redox flow batteries [5,6,7,8,9,10] or gases in anion exchange membrane fuel cells (AEMFC) and water electrolyzers [11
The major requirements are a high ionic conductivity in order to reduce as much as possible the Ohmic drop during current flow; and a low permeability to reactants, i.e., electrochemically active ions in a redox flow battery or a low hydrogen and oxygen permeability in AEMFC
AEM; the largest part is devoted to diffusion dialysis, followed by electrochemical energy technologies and electrodialysis

Summary

Introduction

Anion exchange membranes (AEM) are important materials for applications in energy and in the environment [1,2,3,4]. Co-polymers formed of vinylbenzyl chloride (VBC) and MPS were quaternized and reacted with PVA by the sol–gel process as reported in Figure 3 [59] They showed excellent properties in DD compared to commercial membranes. The authors observed that during the process the power consumption decreased while the current efficiency increased with the functionalized silica content Another approach was realized preparing 2-(dimethylaminomethyl)pyridine quaternized with a long chain formed by hydroxyl alkylbromide and used as the precursor for sol–gel and cross-linking reactions with PVA and TEOS [63]. Was followed by sol–gel reaction with PVA, crosslinking, and quaternization [70] These membranes were analyzed from the point of view of different electrochemical properties including electro-osmotic drag, electrodialysis, and ionic conductivity in NaCl solution (up to 7.2 mS/cm). The resulting materials were efficiently used for the ion-chromatographic separation of inorganic anions

Membranes for Electrochemical Energy

Salient Features

Findings

Conclusions