Hydrogen characteristics and ordered structure of mono-mesogen type liquid-crystalline epoxy polymer Shuji Kawamoto a , Hirotada Fujiwara b , Shin Nishimura c,* a Department of Hydrogen Energy Systems, Graduate School of Engineering, Kyushu University, Japan b Research Center for Hydrogen Industrial Use and Storage, Kyushu University, Japan c Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan article info Article history: Received 12 October 2015 Received in revised form 7 March 2016 Accepted 20 March 2016 Available online 10 April 2016 Keywords: Epoxy Polymer Crystallization Liquid crystal Thermal conductivity Hydrogen properties abstract Fuel cell systems, such as those used in electric vehicles require lightweight hydrogen fuel storage. Polymer composites are candidate materials for storage vessels requiring high fracture resistance for high pressure cycling, as well as high thermal conductivity. Here, we investigate 4,4 0 -diglycidyloxybiphenyl (DGOBP) epoxy for such applications, and clarified the relationship between the hydrogen penetration properties and the ordered structure of the epoxy. We controlled the ordered structure of the DGOBP polymer by adjusting the curing temperature of a 4,4 0 -diaminodiphenyl methane (DDM) curing system. We obtained a series of cured DGOBP with DDM samples with crystallinity values of 19%, 27%, 32%, and 36%, corresponding to curing temperatures of 130, 120, 110, and 100  C, respectively. The thermal conductivities of these samples were 0.26e0.31 Wm 1 K 1 . Cured DGOBP showed hydrogen contents of 403e1271 ppm (25e75% smaller than that of conventional epoxies). Liquid crystalline epoxy polymers can be a candidate material for hydrogen storage sys- tems requiring well-controlled hydrogen penetration properties. Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Introduction Hydrogen energy systems are being investigated for next- generation clean energy systems. However, safety is a pri- mary concern for commercial application and must be considered in the design of hydrogen energy systems. For hydrogen energy to be feasible and widely implemented in transport and stationary technologies, it needs to be safely and efficiently stored [1]. Compressed gas is currently the preferred solution for storing hydrogen in fuel cell vehicles (FCV). To satisfy the desired driving range and convenience of FCVs, hydrogen should be stored at 70 MPa and filled at a rapid rate, reaching its storage pressure within 3 min. To avoid thermal damage to the storage vessel, the hydrogen gas needs to be pre-cooled to 40  C at the hydrogen filling station. Because the compression can greatly elevate the temperature of the gas [2], vessel materials must effectively radiate heat. Moreover, hydrogen storage vessels installed in FCVs need to be lightweight [3] in order to achieve high fuel efficiency. * Corresponding author. Tel.: þ81 92 802 3248. E-mail address: nishimura.shin.691@m.kyushu-u.ac.jp (S. Nishimura). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 41 (2016) 7500 e7510 http://dx.doi.org/10.1016/j.ijhydene.2016.03.124 0360-3199/Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.