Synthesis and Characterization of Protogenic Liquid Crystals

Supacharee Roddecha and Mitchell Anthamatten. Chemical Engineering, University of Rochester, 206 Gavett Hall RC 270166, Rochester, NY 14627-0166

This paper presents a nanoscale approach to engineering anhydrous proton conducting materials. Fuel cells are electrochemical devices that convert stored chemical energy directly to electrical energy. They potentially offer a means to clean, reliable and efficient energy generation. The proton exchange membrane is the heart of a fuel cell serving to block fuel gases and electrons, while permitting proton transport. The majority of fuel cells employ perfluorinated ionomer membranes such as NafionŽ. These membranes require hydration and are limited to low temperature (~80oC) operation. At low temperature, fuel cell catalysts are readily poisoned, lowering their activity. Imidazole has been recently investigated as a novel anhydrous proton conducting functional group, capable of high operating temperature [1,2,3]. Its amphoteric behavior can support Grotthuss-like proton transport. However, it is a liquid that cannot be easily incorporated into a proton exchange membrane. Also, imidazole functional groups must be concentrated and mobile (in a liquid-like state) to provide a platform for proton transport. To enhance mobility and overcome the difficulty in incorporating liquid imidazole, imidazole functionalized liquid crystals are considered. Our hypothesis is that liquid crystal ordering can be used to facilitate proton transport. The objective of this study is to determine whether liquid crystal ordering can promote proton conductivity. Two imidazole-terminated liquid crystal molecules were designed and synthesized (Fig. 1). The targeted liquid crystal molecules contain rigid diacylhydrazine core, a flexible hydrocarbon spacer and a terminal imidazole group. Together, the spacer and the core are designed to stabilize liquid crystal mesophase. In particular, smectic mesophase may be useful in confining imidazole groups into 2D planes to promote proton transport. Terminal imidazole- group are intended to promote Grothuss-like proton transfer. Moreover, its high thermal and chemical stability will be useful in fuel cell membrane. This poster will focus on the synthesis approach and characterization of liquid crystal molecules. References [1] M. Schuster, T. Rager, A. Noda, K.D. Kreuer, J. Maier Fuel Cells 2005, 5, 355. [2] G. Scharfenberger, W. H. Meyer, G. Wegner, M. Schuster, K.-D. Kreuer, and J. Maier Fuel Cells 2006, 6, 237. [3] S. Li, Z. Zhou, M. Liu, W. Li, J. Ukai, K. Hase, M.Nakahishi Electrochemica Acta 2006, 51, 1351.