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Langmuir 2005, 21, 9386-9389
Carbon Nanotube Film by Filtration as Cathode Catalyst Support for Proton-Exchange Membrane Fuel Cell Wenzhen Li, Xin Wang, Zhongwei Chen, Mahesh Waje, and Yushan Yan* Department of Chemical and Environment Engineering and College of Engineering - Center for Environmental Research and Technology (CE-CERT), University of California, Riverside, California 92521 Received April 27, 2005. In Final Form: June 18, 2005 A simple filtration method is developed to prepare a partially oriented superhydrophobic film of carbon nanotubes (CNTs) that have been catalyzed with uniform small Pt nanoparticles (2.8 nm) at high metal loading (30 wt %). A proton-exchange membrane fuel cell with the oriented CNT film as the cathode achieves higher single-cell performance than those with carbon black and a disordered CNT-film-based cathode probably because of the enhanced electrocatalytic activity of Pt/CNT and improved mass transport within the oriented film.
Carbon nanotubes (CNTs) have been studied as an electrocatalyst support for proton-exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs).1-10 Some early investigations found that by using the normal paste method and simply replacing carbon black particles with disordered multiwalled CNTs as the support for Pt catalyst nanoparticles higher PEMFC and DMFC performances were achieved.1-5 There was also an effort to form a single-walled carbon nanotube (SWNT) film via the electrophoretic method for studying the effect of SWNTs as a catalyst support in fuel cells.6 It is believed that an oriented CNT film may offer much improved fuel cell performance over that of disordered CNTs because of its unique microstructure. First, the electronic conductivity of CNTs is much higher along the tubes than across the tubes, and there is no energy loss when electrons transfer along the tubes.11,12 Second, higher gas permeability is expected with the oriented CNT film. Third, an oriented film may also exhibit superhydrophobicity,13 which can greatly facilitate water removal within the electrode, thereby improving mass transport in a PEMFC or DMFC. In our previous studies, we proposed the idea of growing an aligned multiwalled carbon nanotube (MWNTs) film * Corresponding author. E-mail:
[email protected]. (1) Li, W.; Liang, C.; Qiu, J.; Zhou, W.; Han, H.; Wei, Z.; Sun, G.; Xin, Q. Carbon 2002, 40, 791-794. (2) Li, W.; Liang, C.; Zhou, W.; Qiu, J.; Zhou, Z.; Sun, G.; Xin, Q. J. Phys. Chem. B 2003, 107, 6292-6299. (3) Liu, Z.; Lee, J.; Chen, W.; Han, M.; Gan, L. Langmuir 2004, 20, 181-187. (4) Matsumoto, T.; Komatsu, T.; Arai, K.; Yamazaki, T.; Kijima, M.; Shimizu, H.; Takasawa, Y.; Nakamura, Chem. Commun. 2004, 7, 840841. (5) Kim, C.; Kim, Y. J.; Kim, Y. A.; Yanagisawa, T.; Park, K. C.; Endo, M.; Dresselhaus, M. S. J. Appl. Phys. 2004, 96, 5903-5905. (6) Girishkumar, G.; Vinodgopal, K.; Kamat, P. V. J. Phys. Chem. B 2004, 108, 19960-19966. (7) Sun, X.; Li, R.; Villers, D.; Dodelet, J.; Desilets, S. Chem. Phys. Lett. 2003, 379, 99-104. (8) Sun, X.; Stansfield, B.; Dodelet, J.; Desilets, S. Chem. Phys. Lett. 2002, 363, 415-421. (9) Wang, C.; Waje, M.; Wang, X.; Tang, J.; Haddon, R.; Yan, Y. Nano Lett. 2004, 4, 345-348. (10) Wang, X.; Waje, M.; Yan, Y. S. Electrochem. Solid State Lett. 2005, 8, 42-44. (11) Frank, S.; Poncharal, P.; Wang, Z.; de Heer, W. Science 1998, 280, 1744-1746. (12) Liang, W.; Bockrath, M.; Bozovic, D.; Hafner, J.; Tinkham, M.; Park, H. Nature 2001, 411, 665-669. (13) Li, H. J.; Wang, X. B.; Song, Y. L.; Liu, Y. Q.; Li, Q. S.; Jiang, L.; Zhu, D. B. Angew. Chem., Int. Ed. 2001, 40, 1743-1746.
directly on a carbon paper substrate by the chemical vapor deposition (CVD) method with subsequent deposition of Pt nanoparticles on the MWNTs to form the composite electrode. The unique advantage of this approach is that the deposited Pt nanoparticles are almost guaranteed to be in electrical contact with the external circuit9,10 and much improved Pt utilization (e.g., 60%) has been achieved.10 With the aforementioned direct CVD method, however, it has been difficult thus far to prepare Pt catalyst nanoparticles with a uniform small diameter (e.g.,
