Nanostructured PEFC Electrode Catalysts Prepared via In-situ Colloidal Impregnation
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Nanostructured PEFC Electrode Catalysts Prepared via In-situ Colloidal Impregnation Kazunari Sasaki1,2, Kenji Shinya1, Shuhei Tanaka1, Yuudai Kawazoe1, Takashi Kuroki1, Kouhei Takata1, Hajime Kusaba1, and Yasutake Teraoka1 1
Kyushu University, Interdisciplinary Graduate School of Engineering Sciences, Kasuga-Koen 6-1, Kasuga-shi, Fukuoka 816-8580, JAPAN 2 Kyushu University, Hydrogen Technology Research Center, Fukuoka, JAPAN
ABSTRACT Nanostructured Platinum-based electrode catalysts were prepared via in-situ colloidal impregnation for polymer electrolyte fuel cells. Crystallite size, grain size, and distribution of Pt nanoparticles on carbon support materials were characterized by XRD, TEM, high-resolution FESEM, and STEM. Effective surface area and kinetically-controlled current density of Pt electrode catalysts were analyzed by cyclic and hydrodynamic voltammetry using rotating disk electrodes. PEFCs with these electrode catalysts were also prepared and their I-V characteristics were examined at 80oC. We have succeeded to develop Pt electrode catalysts with a diameter of a few nm, supported on carbon nanofibers with different structures (including herringbone-type fibers, platelet-type fibers, and highly-conductive vapor-grown fibers), carbon nanotubes, as well as carbon black. The dependencies of nanostructure and electrochemical properties on crystallographic structure of carbon support materials and preparation conditions of electrode catalysts are analyzed and discussed. Nanostructural design of PEFC electrode catalyst layers using carbon nanofibers as catalyst supports and electrode fillers is also discussed. H2PtCl 6・ 6H2O NaHSO3 Distilled water
INTRODUCTION Polymer electrolyte fuel cells (PEFCs) are promising energy conversion systems. However, further improvement of electrochemical performance and a considerable reduction of noble metal loading are essential for their commercialization. It is therefore of technological interest to develop high-performance electrode catalysts by applying nanostructured alternative materials. In this study, various types of carbon materials (especially carbon nanofibers) are applied as catalyst supports or electrode fillers. A colloidal impregnation procedure is developed to prepare nanocrystalline Pt-based electrode catalysts.
Carbon support H２O２
Pt colloids In-situ colloidal impregnation
Filtration
Drying, Calcination
Figure 1. Preparation procedure of electrode catalysts via in-situ colloidal impregnation.
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EXPERIMENTAL Pt catalysts (20wt%Pt/C) were impregnated via an in-situ colloidal procedure using H2PtCl6, NaHSO3 and H2O2 as schematically shown in Fig. 1, as well as via a conventional (evaporation-to-dryness) impregnation process. In the in-situ impregnation process, Pt colloids were prepared in the dispersion of carbon support materials. Pt-based electrode catalysts were obtained after calcination in H2 atmosphere at 200oC for 2h. Nanostructure of the electrode catalysts was mainly observed by high-resolution FESEM coupled with STEM. Crystall
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