Durability of Carbon Nanofiber & Carbon Nanotube as

1. Durability of Carbon Nanofiber & Carbon Nanotube as • Catalyst Support for Proton Exchange Membrane Fuel Cells • Shuang Ma Andersen1, Peter Lund2, Yli-Rantala Elina3, Antti Pasanen3Pertti Kauranen3 and Eivind M. Skou1 • 1Institute of Chemical Engineering, Biotechnology and Environmental Technology, University of Southern Denmark • 2 IRD Fuel Cells A/S, Svedberg, Denmark, 3VTT Technical Research Centre of Finland, Tampere, Finland • Corresponding author: mashu@kbm.sdu.dk Introduction Carbon Nanotube (CNT) and Carbon Nanofiber (CNF) demonstrate huge potentials in fuel cell developments [1, 2]. In this work, thermal and electrochemical durabilities of CNT and CNF as PEMFC catalyst support were studied and compared to conventional commercial catalyst supports based on both ex-situ and in–situ experiments. Experiment & Results Carbon thermal corrosion properties were tested at 200oC. Samples were packed individually in aluminum foil, whose weight was proven to be stable during the treatment. The weights of the small packages were examined via a digital balance. The samples were pre-heated at 80oC to eliminate adsorption water. The weight loss corresponds to carbon thermal corrosion, as shown in fig. 1. Fig. 1 Carbon thermal corrosion Carbon thermal decomposition was studied by thermalgravimetry TGA 92-12. Mixing of carbon or catalyst powder and Nafion ionomer solution can be found in our earlier work [3]. About 3-4 mg pretreated powder was transported into Al2O3 crucible for TG analysis. The experiment was performed under argon and oxygen of ratio 3 to 1, total pressure of one atmosphere. Data are summarized in fig.2. The detailed experiment condition of platinum dissolution in acidic media can be found in our early work [4]. The electrodes were prepared by IRD Fuel Cells. Comparison of carbon nanofiber and carbon black is shown in fig. 3. Fig. 3 Platinum (of different carbon support) dissolution in acidic media Fig. 2 TG pattern of catalyst and Nafion ionomer mixture Electrochemical stability under high voltage cyclic treatment was performed with a single cell of dimension 1.5*1.5cm2, MEA was cycled between 0.04 and 1.6 V v.s. RHE. Single cell performance was carried out with pure hydrogen and lab air were used as fuel and oxidant. The gas was humidified with 1kw humidifier (FumaTech). The system was steered with electrochemical workstation IM6 (ZAHNER). Electrochemical active surface area of the MEA before and after the treatment are shown in fig. 4. Other data are summarized in tab. 1. Fig. 4 Examples of ESA determined by hydrogen adsorption Tab. 1 Summary for electrode electrochemical stability under high potential cycling Conclusions Based on above studies, both carbon nanofiber and carbon nanotube demonstrate outstanding better stability comparing to traditional carbon black (Vulcan). Carbon nanofiber showed better performance than carbon nanotube materials Optimization and activation of membrane electrode assembly – electrode structure is the key point to gain better cell performance for carbon nanofiber based materials. [1] M. Okada et al, J. Power Sources 185 (2008), 711–716. [2] G.W. Yang et al, Carbon 45 (2007), 3036–304. [3] S. Ma, et al., Solid State Ionics 178 (2007), 1568-1575. [4] S. M. Andersen et al., Solid State Ionics, in Press, 2010.