New Anion Exchange Membranes Tailored to Address Problems in Energy Conversion and Water Purification

Abstract

Anion exchnge membranes (AEMs) are the weak link in low-cost versatile fuel cells and electrolyzers and in electrochemically driven water purification systems. The potential of anion exchange membrane (AEM) fuel cells to provide inexpensive compact power from a wider variety of fuels than is possible with a proton exchange membrane (PEM) fuel cell, has continued to drive the research interest in this area. Alkaline catalysis in fuel cells has been demonstrated with non-precious metal catalysts, and with a variety of fuels beyond H2 and methanol. Alkaline fuel cells (AFCs), based on aqueous solutions of KOH, have serious drawbacks associated with system complexity and carbonate formation. Anion exchange membrane (AEMs) fuel cells have a number of advantages over both PEM fuel cells and traditional AFCs; however, although anionic conductivity in AEMs can be comparable to PEMs the chemical stability of membrane attached cations in hydroxide is still not always sufficient for practical applications. Recently, it has been recognized that a number of advanced cations, may give AEMs the needed chemical stability for practical applications. Inspired by this we have attached C6 N-heterocyclic cations to a novel tri-block polymer that may be lightly cross-linked. In this way we have fabricated a processable scalable material with a more stable cation that has desirable mechanical properties. We can fabricate these polymers as large area <20 μm films. As an unexpected benefit the material also has low water uptake and high hydroxide conductivity. In this presentation we will discuss the materials properties in terms of its physical chemistry, morphology and ion transport, investigated by PFGSE NMR, SAXS and electrochemical impedance spectroscopy. We will also present some preliminary data on the membranes performance in fuel cells, electrolyzers, and in elecrodialysis for water purification.