Polypyrrole-modified hydrophobic carbon nanotubes as promising electrocatalyst supports in polymer electrolyte membrane fuel cells Hyung-Suk Oh, Kwanghyun Kim, Hansung Kim* Dept. of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, 120-749 Seoul, Republic of Korea article info Article history: Received 16 May 2011 Received in revised form 11 June 2011 Accepted 14 June 2011 Available online 18 July 2011 Keywords: Carbon nanotube Polypyrrole PEM fuel cell Carbon corrosion Carbon supports abstract As an alternative to oxidative acid treatment, a hydrophobic graphitized carbon nanotube (CNT) was functionalized with 1e4 nm thick polypyrrole (PPy) prior to application as catalyst supports in polymer electrolyte membrane (PEM) fuel cells. Unlike oxidative acid treatment, the PPy coating method converts the hydrophobic surface of a CNT to a hydrophilic one without creating defects on the surface of the CNT. As a result, Pt nanoparticles deposited on the PPy-coated CNTs showed an improved distribution, which significantly enhanced the fuel cell performance while preserving the intrinsic properties of the CNTs, i.e., resistance to electrochemical carbon corrosion. An additional advantage of PPy coating is that it prevents Pt nanoparticles from agglomerating on the CNT surface. These results indicated that PPy-coated CNTs are a promising catalyst support to improve both the performance and durability of PEM fuel cells. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction In recent years, graphitized carbon such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have attracted signifi- cant attention as catalyst support materials for polymer electrolyte membrane (PEM) fuel cells, mainly because of their high resistance to electrochemical carbon corrosion [1e3]. Many studies have reported that electrochemical carbon corrosion occurring during fuel cell start-up and shut-down is one of the major contributors to performance degradation [4e7]. Thus, a reduction in carbon corrosion is essential to increasing the overall lifetime of fuel cells. In use of graphitized carbon as catalyst supports, however, it is difficult to load Pt nanoparticles on these supports effec- tively. The hydrophobic nature of their surfaces hinders dispersion in a polar solvent and prevents uniform distribution of Pt nanoparticles on the carbon support. Thus, to control their hydrophobic properties, the surface of graphitized carbon has to be functionalized prior to their use as catalyst supports. The most common functionalization method is to chemically treat carbon in HNO 3 or H 2 SO 4 /HNO 3 acid solutions [8e11]. The acidic treatment generates oxygen- containing functional groups on the carbon surface, which gives the surface of the carbon with hydrophilic properties. This effect contributes to improvements in Pt loading and distribution on the carbon support. However, our previous study revealed that such a chemical oxidation method increases the number of defects, resulting in an increase in the electrochemical carbon corrosion [12]. Therefore, it is necessary to find alternative ways to load Pt nanoparticles on graphitized carbon supports without sacrificing the resistance to electrochemical corrosion. Another drawback of using * Corresponding author. Tel.: þ82 2 2123 5753; fax: þ82 2 312 6401. E-mail address: elchem@yonsei.ac.kr (H. Kim). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 36 (2011) 11564 e11571 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.06.079