Monodispersed PtCo nanoparticles on hexadecyltrimethylammonium bromide treated graphene as an effective oxygen reduction reaction catalyst for proton exchange membrane fuel cells Kwan-Woo Nam a , Jongchan Song b , Keun-Hwan Oh a , Min-Ju Choo b , Hyunah Park a , Jung-Ki Park a,b , Jang Wook Choi a, * a Graduate School of EEWS (WCU), KAIST Institute NanoCentury, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak- ro, Yuseong-gu, Daejeon 305-701, Republic of Korea b Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea ARTICLE INFO Article history: Received 1 January 2012 Accepted 30 March 2012 Available online 5 April 2012 ABSTRACT We report hexadecyltrimethylammonium bromide (CTAB)-functionalized graphene as a carbon support for Pt or PtCo nanoparticle (NP) catalysts for fuel cell cathodes. The CTAB treatment plays several critical roles in improving the cell performance: CTAB is non-cova- lently bound on the graphene surfaces and also functionalizes NP surfaces, thus minimiz- ing aggregation between graphene sheets as well as between NPs with extremely small dimensions down to 1–2 nm for a large number of cycles. Also, unlike covalent bonding based treatments, the CTAB treatment preserves intrinsic electronic and structural proper- ties of graphene. The increased dispersion and decreased dissolution of NP catalysts using the CTAB functionalization are reflected in various electrochemical measurements such that the CTAB-treated samples exhibit higher values in oxygen reduction reaction activity, electrochemical active surface area, and long-term durability compared to commercial cat- alysts and control cases with no such treatment. Finally, for the same CTAB-treated graph- ene, PtCo catalyst shows a higher catalytic activity than does Pt catalyst, thus confirming the known improved activities of the alloyed catalysts. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Proton exchange membrane fuel cells (PEMFCs) have received considerable attention because they are technologically and economically one of the most viable options for generating electricity from hydrogen [1]. PEMFC based hydrogen technol- ogy could also represent a critical means in addressing future energy issues as most reserves of fossil fuels are predicted to dwindle further in the near future [2]. Also, PEMFCs are ex- pected to play an important role in resolving various environ- mental issues [1] because they enable the emergence of carbon dioxide-free transportation as well as the replacement of other internal combustion systems [3]. Despite the future potential opportunities, there are critical obstacles in PEMFC performance that inhibit their broad propagation. In particu- lar, technological bottlenecks such as low catalytic activity and limited long-term stability are still difficult to address [4]. Currently, the most commonly used cathode catalysts 0008-6223/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2012.03.048 * Corresponding author: Fax: +82 42 350 1719. E-mail address: jangwookchoi@kaist.ac.kr (J.W. Choi). CARBON 50 (2012) 3739 – 3747 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon