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Enhanced Oxygen Reduction Reaction Activity and Characterization of Pt–Pd/C Bimetallic Fuel Cell Catalysts with Pt-Enriched Surfaces in Acid Media
journal contribution
posted on 2012-11-08, 00:00 authored by Licheng Liu, Gabor Samjeske, Shin-ichi Nagamatsu, Oki Sekizawa, Kensaku Nagasawa, Shinobu Takao, Yoshiaki Imaizumi, Takashi Yamamoto, Tomoya Uruga, Yasuhiro IwasawaThree types of bimetallic Pt–Pd nanoparticles
with different
core–shell structures besides Pt and Pd nanoparticles were
synthesized by coreduction and sequential reduction methods in ethylene
glycol. The synthesized nanoparticles were supported on carbon to
prepare five different electrocatalysts Pt/C, Pd/C, PdPt alloy/C,
Pd(core)–Pt(shell)/C, and Pt(core)–Pd(shell)/C for oxygen
reduction reaction (ORR) in fuel cells. The nanoparticles and supported
catalysts were characterized by means of transmission electron microscopy
(TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray powder
diffraction (XRD), extended X-ray absorption fine structure (EXAFS),
and cyclic voltammetry (CV). It was proposed by these characterizations
that the PdPt alloy/C, Pd(core)–Pt(shell)/C, and Pt(core)–Pd(shell)/C
catalysts constituted Pd4Pt1(core)–Pt(two-layers
shell), Pd (core)–Pd2Pt1(three-layers)–Pt(three-layers
shell), and Pt(core)–Pt2Pd1(two-layers)–Pd
(microcrystal shell), respectively. The Pt surface-enriched catalysts
were more stable than the Pd surface-enriched catalysts in long-term
CV scanning in acid electrolyte. The Pt/C, PdPt alloy/C, and Pd(core)–Pt(shell)/C
catalysts with Pt-enriched surfaces showed much higher ORR specific
activity than the Pd/C and Pt(core)–Pd(shell)/C catalysts with
Pd-enriched surfaces. The Pt surface-enriched bimetal catalysts with
core–shell structures showed the higher Pt-based mass activity
than the Pt monometal catalyst. The PdPt catalysts with Pd/Pt = 2
and 4 in an atomic ratio were also prepared by the coreduction method.
The Pt-enriched surfaces formed also with these samples, but the ORR
specific activity and (Pd + Pt)-based mass activity decreased with
increasing Pd/Pt ratios (1, 2, and 4). The present study provided
core–shell catalysts with better ORR activity, which may be
useful for understanding key issues to develop next-generation fuel-cell
cathode catalysts.
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Keywords
EXAFSPt monometal catalystfuel cellscyclic voltammetryCV scanningPdPt catalystsethylene glycolXRDoxygen reduction reactionacid electrolyteAcid MediaThree typesPd nanoparticlesTEMEnhanced Oxygen Reduction Reaction Activitytransmission electron microscopyORR activitysequential reduction methodscoreduction method
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