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TECHNICAL PAPERS

Novel Deposition of PtC Nanocatalysts and Nafion® Solution on Carbon-Based Electrodes via Electrophoretic Process for PEM Fuel Cells

[+] Author and Article Information
R. F. Louh, Hansen Huang, Felix Tsai

Department of Materials Science and Engineering, Feng Chia University, 100 Wenhwa Road, Taichung, Taiwan 407

J. Fuel Cell Sci. Technol 4(1), 72-78 (Apr 17, 2006) (7 pages) doi:10.1115/1.2393307 History: Received November 30, 2005; Revised April 17, 2006

Nanosized platinum particles supported on carbon black carriers (PtC) are popular for use in fabrication of proton exchange membrane fuel cells (PEMFCs). Here, an electrophoretic deposition (EPD) process is proposed to investigate the power performance of PtC nanopowders onto various carbon-based electrodes for the PEMFC applications in a better controlled and cost-effective manner. Novel deposition of PtC nanocatalysts and Nafion® solution via electrophoretic process give rise to higher deposition efficiency and a uniform distribution of catalyst and Nafion ionomer on the electrodes of PEMFCs. Preparation of an EPD suspension with good dispersivity is much desirable for an agreeable overall performance of catalyst coating in terms of types of organic solvents, milling processes, and use of pH adjusting agents and surfactants in the EPD suspension. The EPD suspension was prepared by sonication of mixture of PtC nanopowders, Nafion solution and isopropyl alcohol, the optimal pH value of which was reached by using acetic acid or ammonium hydroxide. The colloidal stability of EPD suspension was achieved at pH 10 for an EPD suspension of either PtC catalysts or mixture of PtC catalysts and Nafion ionomer. A nicely distributed deposition of PtC nanocatalysts and Nafion ionomer on both hydrophilic or hydrophobic carbon-based electrodes was successfully obtained by using PtC concentration of 1.0gl, electrical field of 300Vcm, and deposition time of 5min. Microstructural analysis results indicate that PtC nanopowders not only embrace the entire surface of carbon fibers but also infiltrate into the gaps and voids in fiber bundles such that a higher contact area of the same loading of PtC nanocatalysts through the EPD process is thus expected. At present, the EPD process can effectively save more of Pt catalyst loading on electrodes in PEMFC, as compared to conventional methods, such as screen printing, brushing, or spraying through the similar level of power performance for PEMFCs.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Process flow of electrophoretic deposition of Pt∕C nanocatalysts and Nafion® solution on carbon-based electrodes

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Figure 2

Zeta potential of (a) Pt∕C in IPA suspension and (b) Pt∕C and Nafion® in IPA suspension at different pH value

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Figure 3

Scanning electron micrographs of Pt∕C nanocatalysts and Nafion® ionomer evenly coated on the fibers of carbon-based electrodes via EPD process: (a) Pt∕C nanocatalysts was deposited singly, (b) Pt∕C nanocatalysts and Nafion® ionomer were deposited in consecutive EPD steps, and (c) both Pt∕C nanocatalysts and Nafion® ionomer were deposited simultaneously in a co-EPD process

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Figure 4

Cell potential versus current density curves of single cells prepared from Pt∕C nanocatalysts and Nafion® ionomer were deposited (∎) in consecutive EPD steps and (●) in a co-EPD process

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Figure 5

Scanning electron micrographs of the morphology of Pt∕C nanocatalysts deposited on the carbon-based electrodes under different waveform of dc applied electrical field

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Figure 6

Both (a) backscattered electron imaging and (b) energy dispersive spectroscopy analysis indicate Pt∕C nanocatalysts were evenly distributed on the surface of hydrophobic carbon cloth by EPD method with deposition time of 5min and applied electrical field of 300V∕cm

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Figure 7

EPD yield for (∎) Pt∕C nanocatalyst loading on carbon electrode by co-EPD process of Pt∕C and Nafion® and (●) Nafion ionomer loading by EPD process of Nafion solution only at different Nafion® content in the EPD suspension

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Figure 8

Cell potential versus current density curves for different Nafion® contents (wt. %) in the EPD suspension

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Figure 9

Cell potential as a function of Nafion® loading at different current densities

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Figure 10

Cell potential versus current density curves for different Pt catalyst loadings by EPD and screen printing method. The testing was carried out at cell temperature of 70°C in a humidified condition.

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