Synthesis of sulfonated poly(arylene ether ketone) block copolymers for proton exchange membrane fuel cells Kwangjin Oh, Kriangsak Ketpang, Hasuck Kim, Sangaraju Shanmugam n Department of Energy Systems Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu 42988, South Korea article info Article history: Received 28 November 2015 Received in revised form 14 January 2016 Accepted 11 February 2016 Available online 12 February 2016 Keywords: Polymer electrolyte membrane fuel cells Sulfonated poly(arylene ether ketone) Block copolymers Membrane Proton conductivity abstract Sulfonated poly(arylene ether ketone) (SPAEK) block copolymers were synthesized through nucleophilic aromatic substitution polymerization. Compared with a Nafion (NRE-212), state-of-the-art proton con- ducting membrane, the block copolymer membrane showed a well separated phase morphology and high proton conductivity under fully hydrated condition at 80 °C. The fuel cell operated with a SPAEK membrane showed a current density of 1617 mA cm 2 at 0.6 V under 100% relative humidity (RH), whereas a NRE-212 membrane exhibited a current density of 1238 mA cm 2 , which is about 30% lower than newly prepared SPEAK membrane. In addition, the maximum power density of 1160, and 800 mW cm 2 was observed for SPAEK, NRE-212 membranes, respectively at 80 °C under 100% RH condition. The SPEAK membrane exhibited 1.4-folds enhancement in the maximum power density in comparison with NRE-212 membrane. & 2016 Elsevier B.V. All rights reserved. 1. Introduction Polymer electrolyte membranes fuel cells (PEMFCs) have con- sidered one of the promising energy conversion devices because of their high efficiencies and wide range of applications such as power stations, electric vehicles, and electronic applications [1]. Fuel cell powered electric vehicles have been commercialized. However, some technical issues for full scale commercializing PEMFCs powered vehicle still remain. The most important challenge is the cost of present fuel cell materials. The commercialized membrane such as Nafion has high production cost, low durability, low glass transition temperature and environmental concerns of fluorine pre- sent in the membrane [2–4]. To overcome these technical issues, one of the most important problems is to develop alternative membranes with enhanced proton conductivity as well as excellent fuel cell per- formance with respect to the state-of-the-art polymer electrolyte membrane (PEMs) such as perfluorosulfonic acid (PFSA) ionomer. Hydrocarbon based PEMs were investigated in the last decade because of their low gas permeability, low production cost, and good thermal-stability. Especially, non-fluorinated aromatic membranes have received considerable attention due to the en- vironmental compatibility [5,6]. Although, the hydrocarbon membranes have certain good properties, however they exhibit several drawbacks such as weak mechanical properties, low pro- ton conductivity, and low fuel cell performance [7,8]. To overcome these inferior properties, block copolymers composed of hydro- phobic and hydrophilic blocks with sulfonic acid groups were developed to achieve the well-developed phase separation with interconnected ionic channels [9–16]. Bae et al. reported block copolymers composed of rigid and robust chemical structure as a hydrophobic component to improve the proton conductivity [17]. By introducing asymmetric chemical structure into the polymer, the phase separation of the block copolymer was well established in the membrane [17]. The ether (–O–) linkage, sulfide groups (– S–), ketone groups (–C ¼ O–), and sulfoxide groups (–O ¼ S ¼ O–) were introduced for membrane flexibility and sulfonic acid groups would be attached on benzene. However, all of these groups can be easily susceptible from the oxidative degradation. Miyatake et al. synthesized block copolymers with sulfonated benzophe- none groups as hydrophilic blocks through coupling reaction to improve oxidative stability of membrane, as decreasing ether linkage [18]. In this study, we introduce the rigid and robust hydrophobic oligomer as our block copolymer component to achieve high proton conductivity. In addition, we have developed block copo- lymers composed of a new hydrophilic oligomer with bi-phenol and sulfonated difluorobenzophenone in order to improve the oxidative stability of the membrane. The synthesis and char- acteristics of the oligomer and block copolymer are presented in supporting information. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science http://dx.doi.org/10.1016/j.memsci.2016.02.027 0376-7388/& 2016 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: sangarajus@dgist.ac.kr (S. Shanmugam). Journal of Membrane Science 507 (2016) 135–142