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Research Paper

Preparation of Electrocatalysts for Polymer Electrolyte Fuel Cell Cathodes From Au-Pt Core-Shell Nanoparticles Synthesized by Simultaneous Aqueous-Phase Reduction

[+] Author and Article Information
Wataru Yamaguchi

e-mail: w.yamaguchi@aist.go.jp

Yutaka Tai

Materials Research Institute for Sustainable Development (MRISUS),
National Institute of Advanced Industrial Science and Technology (AIST),
2266-98 Anagahora, Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the Journal of Fuel Cell Science and Technology. Manuscript received April 1, 2013; final manuscript received April 16, 2013; published online June 17, 2013. Editor: Nigel M. Sammes.

J. Fuel Cell Sci. Technol 10(4), 041006 (Jun 17, 2013) (5 pages) Paper No: FC-13-1033; doi: 10.1115/1.4024574 History: Received April 01, 2013; Revised April 16, 2013

Electrocatalysts for polymer electrolyte fuel cell (PEFC) cathodes were prepared using Au-Pt core-shell nanoparticles. Polyvinylpyrrolidone (PVP)-protected core-shell nanoparticles were synthesized by simultaneous aqueous-phase reduction of Au and Pt, and they were deposited on carbon black support material. The catalyst powder was thermally processed in air to remove PVP, since the protecting polymers prevent nanoparticles from directly contacting the support material as well as reactant molecules. To avoid sintering during the thermal treatment, the effects of temperature and processing time on sintering were carefully examined. It was found that PVP was selectively oxidized and removed at 170 °C in air without notable damages to the other components of the catalyst. Stability of the core-shell catalyst in water was improved after the removal of PVP. The oxidation state of the Pt shell was found to be very close to zero. The thus-prepared Au-Pt core-shell catalyst for a PEFC cathode exhibited mass activity that was 20% higher than that of pure Pt catalyst.

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Figures

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Fig. 1

TEM images of Au-Pt bimetallic nanoparticles supported on carbon black (Vulcan XC-72) (a) before thermal treatments, (b) after thermal treatment in air at 170 °C for 144 h, (c) at 200 °C for 2 h, and (d) at 250 °C for 0.5 h

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Fig. 2

TG-DTA profiles of Au-Pt bimetallic nanoparticles supported on carbon black (a) before thermal treatment and (b) after the thermal treatment at 170 °C for 144 h, recorded in air at the heating rate of 25 °C/min

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Fig. 3

Photographs of stains on filter paper created by aqueous dispersion of Au-Pt catalyst powders (a) before and (b) after the thermal treatment at 170 °C for 144 h

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Fig. 4

Cyclic voltammograms in 0.5 M H2SO4 at a scan rate of 90 mV/s for (a) Au nanoparticles, (b) Pt nanoparticles, (c) equivalent mixture of Au and Pt nanoparticles, and (d) Au-Pt bimetallic nanoparticles treated at 170 °C for 144 h, supported on carbon black

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Fig. 5

Pt L3-edge XANES spectra of Au-Pt core-shell catalyst, Pt metal foil, and PtO2

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Fig. 6

Comparison of cathode catalyst performance in PEFC operations. (a) Cell voltage versus current density and (b) power density versus current density plots for six cathode catalysts using Au-Pt core-shell nanoparticles supported on Vulcan XC72, thermally treated in different conditions. Pt loadings for the cathode are (●) 0.167, (○) 0.189, (▴) 0.189, (△) 0.230, (▪) 0.271, and (□) 0.165 mgPt/cm2. Pt loadings for the anode are within the range 0.07 to 0.09 mgPt/cm2.

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Fig. 7

Tafel plots of cell voltage versus Pt-mass activity (A/mgPt) characteristics, for comparing cathode performances of the Au-Pt core-shell catalyst treated at 170 °C for 144 h and a commercial Pt catalyst (EC-20-PTC, ElectroChem)

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