Sulfonated poly(ether sulfone)/sulfonated polybenzimidazole blend membrane for fuel cell applications N. Nambi Krishnan a , Hye-Jin Lee a , Hyoung-Juhn Kim a, * , Ju-Yong Kim b , Inchul Hwang c , Jong Hyun Jang a , Eun Ae Cho a , Soo-Kil Kim a , Dirk Henkensmeier a , Seong-Ahn Hong a , Tae-Hoon Lim a a Fuel Cell Center, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Sungbuk-gu, Seoul 136-791, South Korea b Energy Lab, Corporate R&D Center, Samsung SDI, 575 Shin-dong, Yeongtong-gu, Suwon-si, Gyeonggi-do 443-731, South Korea c Fuel Cell Vehicle Team, Hyundai Motor Company & Kia Motors Corp., 104 Mabuk-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-912, South Korea article info Article history: Received 7 November 2009 Received in revised form 25 February 2010 Accepted 7 March 2010 Available online 11 March 2010 Keywords: Polymer electrolyte fuel cells Polymer blends Proton exchange membrane Sulfonated poly(ethersulfone) Sulfonated polybenzimidazole abstract Polymer blending is used to modify or improve the dimensional and thermal stability of any two different polymers or copolymers. In this study, both sulfonated polybenzimidaz- ole homopolymer (MS-p-PBI 100) and sulfonated poly(aryl ether benzimidazole) copoly- mers (MS-p-PBI 50, 60, 70, 80, 90) were successfully synthesized from commercially available monomers. The chemical structure and thermal stability of these polymers was characterized by 1 H NMR, FT-IR and TGA techniques. Blend membranes (BMs) were pre- pared from the salt forms of sulfonated poly(ether sulfone) (PES 70) and MS-p-PBI 100 using dimethylacetamide (DMAc). These blend membranes exhibited good stability in boil- ing water. The blending of 1 wt.% of MS-p-PBI 100 and 99 wt.% of PES 70 to produce the blend membrane BM 1 reduced membrane swelling, thus leading to good dimensional sta- bility and comparable proton conductivity. Hence, BM 1 was chosen for the fabrication of a membrane electrode assembly (MEA) for proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) applications. This paper reports on PEMFC and DMFC performance under specific conditions. Ó 2010 Published by Elsevier Ltd. 1. Introduction Polymer electrolyte fuel cells (PEFCs) are one of the most promising worldwide alternative power sources for applications in stationary, automotive, and portable de- vices. PEFCs are electrochemical energy converters which directly transform chemical energy into electricity using a series of electrochemical redox reactions. To date, perflu- orosulfonic acid polymer membranes, produced by Du- Pont, have been the most widely studied polymer electrolytes in the fuel cells. Although they show high pro- ton conductivity and excellent chemical stability, their high cost and the environmental hazards they pose have led scientists to search for lower cost and more environ- mentally friendly membranes. Therefore, various alterna- tive polymer electrolytes have been studied and reported for fuel cell applications [1–4]. Aromatic polybenzimidazoles (PBIs) have received con- siderable attention in the past decade due to their potential application in PEFCs [5–21]. Recently, phosphoric acid- doped sulfonated PBI membranes have shown higher proton conductivities than the corresponding phosphoric acid- doped non-sulfonated PBI membranes [22]. Especially, the synthesis and characterization of sulfonated PBIs from sul- fonated monomers have been studied widely. The direct polymerization method from the sulfonated monomers has proved to be better at precisely controlling the degree 0014-3057/$ - see front matter Ó 2010 Published by Elsevier Ltd. doi:10.1016/j.eurpolymj.2010.03.005 * Corresponding author. Tel.: +82 2 958 5299; fax: +82 2 958 5199. E-mail address: hjkim25@kist.re.kr (H.-J. Kim). European Polymer Journal 46 (2010) 1633–1641 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj