3D-Printable Ionogels Based on Protic Ionic Liquids for Energy Applications

Abstract

In light of the well-known challenges regarding the global energy economy and climate issues fuel cells are widely discussed for their benefits and potential applications in the future. One of the main problems of PEM-fuel cells is that Nafion®-membranes have a limited application temperature window of ≤ 80 °C at ambient pressure due to dehydration and corresponding loss of conductivity at higher temperatures. [1] As a result there is a significant need for new membranes of a precise and defined size and geometry exhibiting significant ion mobilities far above 100 °C. Based on their highly useful properties like thermal stability, non-flammability, and high ionic conductivities ionic liquids (ILs) are promising components in energy devices such as batteries, solar cells or fuel cells. For proper function of, for example, fuel cell membranes, it is, however, necessary to immobilize the ILs in a polymer matrix, resulting in ionogels (IGs) combining the characteristics of the respective IL with e. g. the mechanical stability of the polymer. [2] The combination of 3D-printing with suitable polymer scaffolds and suitable ILs enables the design of membrane materials with precisely controlled sizes, shapes and geometries along with the necessary electrochemical performance. [3] The aim of this work therefore is the synthesis and characterization of protic amine-based ILs for proton conduction. All compounds are ILs at room temperature. Their ionic conductivities range between 10-2 – 10-4 S/cm. Moreover, with wide electrochemical and thermal stability windows (ΔE up to 3 V, Tg around -90 °C and Td over 200 °C) these ILs are promising for ion transport in fuel cell membranes above 100 °C. The corresponding transparent and flexible IGs display promising thermal and mechanical stability and reach ionic conductivities of up to 10-3 S/cm at elevated temperatures. Moreover, this study also demonstrates that the IGs can be obtained and structured using 3D-printing; this clearly enables the design of many materials with different requirements by simply adapting the size and shape. [1] A. Martinelli, A. Matic, P. Jacobsson, L. Börjesson, A. Fernicola, S. Panero, B. Scrosati, H. Ohno, J. Phys. Chem. B, 2007, 111, 12462. [2] Y.-S. Ye, J. Rick, B.-J. Hwang, J. Mater. Chem. A, 2013, 1, 2719. [3] K. Zehbe, A. Lange, A. Taubert, Sustainable Energy Fuels, submitted.