Langmuir 2005, 21, 8487-8494
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Single-Wall Carbon Nanotube-Based Proton Exchange Membrane Assembly for Hydrogen Fuel Cells G. Girishkumar,† Matthew Rettker,†,‡ Robert Underhile,†,‡ David Binz,§ K. Vinodgopal,*,†,‡ Paul McGinn,§ and Prashant Kamat*,†,§ Radiation Laboratory and Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, and Department of Chemistry, Indiana University Northwest, Gary, Indiana 46408 Received June 6, 2005 A membrane electrode assembly (MEA) for hydrogen fuel cells has been fabricated using single-walled carbon nanotubes (SWCNTs) support and platinum catalyst. Films of SWCNTs and commercial platinum (Pt) black were sequentially cast on a carbon fiber electrode (CFE) using a simple electrophoretic deposition procedure. Scanning electron microscopy and Raman spectroscopy showed that the nanotubes and the platinum retained their nanostructure morphology on the carbon fiber surface. Electrochemical impedance spectroscopy (EIS) revealed that the carbon nanotube-based electrodes exhibited an order of magnitude lower charge-transfer reaction resistance (Rct) for the hydrogen evolution reaction (HER) than did the commercial carbon black (CB)-based electrodes. The proton exchange membrane (PEM) assembly fabricated using the CFE/SWCNT/Pt electrodes was evaluated using a fuel cell testing unit operating with H2 and O2 as input fuels at 25 and 60 °C. The maximum power density obtained using CFE/SWCNT/Pt electrodes as both the anode and the cathode was ∼20% better than that using the CFE/CB/Pt electrodes.
Introduction High surface area carbon materials such as activated carbon, carbon nanofibers, and carbon nanotubes as new electrode materials have drawn significant interest in recent years for improving the performance of fuel cells.1-4 Unique electrical and electronic properties, wide electrochemical stability windows, and high surface area set single wall carbon nanotubes (SWCNTs) apart from the rest.5-7 It is this expected improvement in conductivity and charge transfer at the electrode interfaces that has prompted a number of groups to use these carbon nanotubes as electrode materials for both oxidation and reduction reactions in fuel cells.8-11 The expectation is that the enhanced electrocatalytic properties of CNTs would reduce the amount of precious metal catalyst such as platinum (Pt) that would substantially increase the commercial viability of fuel cells. * To whom correspondence should be addressed. E-mail:
[email protected];
[email protected]; tel.: 574-631-5411; fax: 574631-8068. † Radiation Laboratory, University of Notre Dame. ‡ Indiana University Northwest. § Department of Chemical and Biomolecular Engineering, University of Notre Dame. (1) Serp, P.; Corrias, M.; Kalck, P. Appl. Catal., A 2003, 253, 337. (2) Li, W. Z.; Liang, C. H.; Zhou, W. J.; Qiu, J. S.; Zhou, Z. H.; Sun, G. Q.; Xin, Q. J. Phys. Chem. B 2003, 107, 6292. (3) Liu, Z. L.; Lin, X. H.; Lee, J. Y.; Zhang, W.; Han, M.; Gan, L. M. Langmuir 2002, 18, 4054. (4) Steigerwalt, E. S.; Deluga, G. A.; Lukehart, C. M. J. Phys. Chem. B 2002, 106, 760. (5) Baughman, R. H.; Zakhidov, A. A.; de Heer, W. A. Science 2002, 297, 787. (6) Wang, J.; Deo, R. P.; Poulin, P.; Mangey, M. J. Am. Chem. Soc. 2003, 125, 14706. (7) Rajesh, B.; Thampi, K. R.; Bonard, J. M.; Mathieu, H. J.; Xanthopoulos, N.; Viswanathan, B. Chem. Commun. 2003, 2022. (8) Rajesh, B.; Thampi, K. R.; Bonard, J. M.; Xanthopoulos, N.; Mathieu, H. J.; Viswanathan, B. J. Phys. Chem. B 2003, 107, 2701. (9) Li, W. Z.; Liang, C. H.; Zhou, W. J.; Qiu, J. S.; Li, H. Q.; Sun, G. Q.; Xin, Q. Carbon 2004, 42, 436. (10) Matsumoto, T.; Komatsu, T.; Nakano, H.; Arai, K.; Nagashima, Y.; Yoo, E.; Yamazaki, T.; Kijima, M.; Shimizu, H.; Takasawa, Y.; Nakamura, J. Catal. Today 2004, 90, 277. (11) He, Z. B.; Chen, J. H.; Liu, D. Y.; Tang, H.; Deng, W.; Kuang, W. F. Mater. Chem. Phys. 2004, 85, 396.
Anchoring the carbon nanotubes on the conducting surface is the crucial step in constructing a robust electrode-catalyst assembly with low resistivity. Past efforts to employ SWCNTs as a nanostructured carbon support in proton exchange membrane fuel cells have involved either casting a film with a polymer binder or growing the carbon nanotubes directly onto the carbon paper or cloth.12-15 Although the use of binders provides a convenient method to cast SWCNT films, they often pose the problem of increased resistivity. Recently Wang and co-workers have grown multiwalled carbon nanotubes (MWCNTs) on carbon paper through chemical vapor deposition with Co as a catalyst support.16 Electrophoretic deposition is another effective and comparatively facile approach for assembling SWCNTs on the desired electrode surface. In our earlier work, we have made use of the asymmetric charging effects of SWCNTs in tetrahydrofuran (THF) suspensions to assemble them as linear bundles and deposit them on a conducting electrode surface under the influence of an applied dc field.17,18 The electrodes cast on conducting glass and carbon electrodes showed excellent electrochemical activity toward methanol oxidation.18 Electrophoretic deposition is gaining increasing attention as a simple technique for fabricating a fuel cell electrode assembly.19-21 The advantages of electrophoretic deposition include uniform deposition of charged particles (12) Sun, X.; Li, R.; Stansfield, B.; Dodelet, J. P.; Desilets, S. Chem. Phys. Lett. 2004, 394, 266. (13) Sun, X.; Li, R.; Villers, D.; Dodelet, J. P.; Desilets, S. Chem. Phys. Lett. 2003, 379, 99. (14) Sun, X.; Stansfield, B.; Dodelet, J. P.; Desilets, S. Chem. Phys. Lett. 2002, 363, 415. (15) Choi, W.-B.; Chu, J.-U.; Pak, C.-H.; Chang, H. Method of fabrication of carbon nanotubes for fuel cells. In U.S. Pat. Appl. Publ.; Samsung SDI Co., Ltd.: South Korea, 2004; Vol. 01; pp A1. (16) Wang, C.; Waje, M.; Wang, X.; Tang, J. M.; Haddon, R. C.; Yan, Y. S. Nano Lett. 2004, 4, 345. (17) Kamat, P. V.; George Thomas, K.; Barazzouk, S.; Girishkumar, G.; Vinodgopal, K.; Meisel, D. J. Am. Chem. Soc. 2004, 126, 10757. (18) Girishkumar, G.; Vinodgopal, K.; Kamat, P. V. J. Phys. Chem. B 2004, 108, 19960. (19) Hayashi, K.; Furuya, N. J. Electrochem. Soc. 2004, 151, A354. (20) Teranishi, T.; Hosoe, M.; Tanaka, T.; Miyake, M. J. Phys. Chem. B 1999, 103, 3818.
10.1021/la051499j CCC: $30.25 © 2005 American Chemical Society Published on Web 07/28/2005
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Langmuir, Vol. 21, No. 18, 2005
Scheme 1. SWCNT-Based Proton Exchange Membrane Assembly for a H2/O2-Based Fuel Cell
and control of film morphology by modulating the applied electric field.22-24 The pristine catalyst particles (e.g., Ptloaded carbon particles) when suspended in a solvent become charged under the influence of a dc electric field and migrate toward the oppositely charged electrode. The film cast on the electrode surface is robust, and the amount of deposition can be controlled by changing the duration of the applied field. Similarly, the SWCNTs suspended in THF when subjected to a low dc field of
