A new graphene-modified protic ionic liquid-based composite membrane for solid polymer electrolytes† Yun-Sheng Ye, a Chi-Yung Tseng, a Wei-Chung Shen, a Jing-Shiuan Wang, a Kuan-Jung Chen, a Ming-Yao Cheng, a John Rick, a Yao-Jheng Huang, b Feng-Chih Chang b and Bing-Joe Hwang * a Received 17th March 2011, Accepted 14th April 2011 DOI: 10.1039/c1jm11152c The production of a solid polymer electrolyte with high ionic conductivity and mechanical properties is the main fabrication challenge in application of polymer electrolyte membranes. This paper describes a novel polymer electrolyte membrane using protic ionic liquids (PILs) with ionic liquid polymer modified graphene (G) sheets [denoted PIL(NTFSI)-G] that exhibit dramatic enhancements in ionic conductivity (257.4%) and mechanical properties (345% improvement in tensile strength and a near 25-fold increase in modulus were achieved at 150  C) with a minimal loading of PIL(NTFSI)-G (0.5 wt %). The addition of graphene, by sparing the high-cost PIL addition, gives a 20% cost-saving. The homogeneous distribution of graphene sheets as a 3D network through the polymer matrix in the composite membrane provides a high degree of continuous and interconnected transfer channels to facilitate ion transfer and enhance nanofiller–matrix adhesion to reinforce mechanical properties. This newly developed material provides a potential route toward the design and fabrication of polymer electrolytes. 1. Introduction Graphene, which comprises a one-atom-thick two-dimensional honeycomb carbon lattice, has attracted increasing attention in recent years, mainly due to its: superior thermal and electrical conductivity, excellent mechanical properties, large specific surface area, and low cost. 1–3 The use of graphene has been explored for various applications such as: electronic and energy storage devices, 4–6 sensors, 7,8 transparent electrodes, 9,10 and nanocomposites. 11,12 Polymer nanocomposites comprising combinations of carbon black, carbon nanotubes (CNTs) and graphene sheets have been seen as potential candidate materials offering the potential to combine several properties, such as: mechanical strength, thermal stability and electrical conduc- tivity. However, graphene sheets provide a more approachable option for forming functional nanocomposites due to the unre- solved issues that affect CNTs such as: the tendency of CNTs to agglomerate during processing, the limited availability of high- quality CNTs in large quantities and the high cost of their production. 13,14 The combination of their extraordinary inherent physical properties, combined with their ability to disperse in various polymer matrices, together with their low manufacturing cost (graphite) has led to the creation of cost-effective and high- performance polymer nanocomposites. Protic ionic liquids (PILs) have attracted considerable atten- tion in recent years due to their interesting and potentially useful physicochemical properties, including their: high ionic conduc- tivities, high polarities, high densities, high heat capacities, and their high thermal and chemical stabilities. 15,16 PILs with these sought after characteristics have been pursued as replacements for liquid electrolytes, which are: toxic, flammable and subject to leaching. One of the main issues needing to be addressed with respect to the development of polymer electrolyte membrane fuel cells (PEMFCs) is the development of membrane materials with high operating temperatures (>100  C) that show: high reaction kinetics at both electrodes, less poisoning at the anode, and easy heat and water management of the stacks. 17,18 Recently, many studies have been carried out to develop IL-based membranes with high ionic conductivities that can operate at higher temperatures (100–200  C) in anhydrous conditions. 19–23 It is well-known that incorporating inorganic fillers into the polymer electrolytes can alter and improve the physical and chemical properties of polymers. In previous studies, membranes modified with nanosized inorganic fillers have exhibited excellent performance and encouraging results. 22,24,25 In addition, the approach of using carbon nanofillers in the polymer electrolyte fuel cells membrane 26,27 has shown a remarkable improvement in membrane performance such as proton conductivity, mechanical properties and methanol permeability, due to the increased sulfonic acid content and better channel-like network for proton transport. 27 Although there have been some recent reports a Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan. E-mail: bjh@mail.ntust.edu.tw b Institute of Applied Chemisty, National Chiao-Tung University, Hsin- Chu, Taiwan † Electronic supplementary information (ESI) available. See DOI: 10.1039/c1jm11152c 10448 | J. Mater. Chem., 2011, 21, 10448–10453 This journal is ª The Royal Society of Chemistry 2011 Dynamic Article Links C < Journal of Materials Chemistry Cite this: J. Mater. Chem., 2011, 21, 10448 www.rsc.org/materials PAPER Published on 17 June 2011. Downloaded by National Chiao Tung University on 25/04/2014 02:49:08. View Article Online / Journal Homepage / Table of Contents for this issue