6860
J. Phys. Chem. C 2010, 114, 6860–6868
Enhanced Durability of Au Cluster Decorated Pt Nanoparticles for the Oxygen Reduction Reaction Ye Zhang,†,‡ Qinghong Huang,† Zhiqing Zou,† Jinfei Yang,‡ Walter Vogel,§ and Hui Yang*,† Energy Science and Technology Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China, College of Chemistry and EnVironmental Science, Nanjing Normal UniVersity, Nanjing 210097, China, and Department of Chemistry, National Central UniVersity, Taiwan 32001, China ReceiVed: January 20, 2010; ReVised Manuscript ReceiVed: March 1, 2010
A low temperature approach via alcohol reduction has been employed to prepare Au cluster decorated carbonsupported Pt nanoparticles for the oxygen reduction reaction (ORR). X-ray diffraction at wide angles (WAXS) shows that both metallic Pt and Au exhibit their respective face-centered cubic structures, indicative of no alloy formation between Pt and Au. Both WAXS and transmission electron microscopy characterizations demonstrate that no major change in mean particle size for bimetallic catalysts was observed even after heat treatment at 600 °C, providing evidence for an enhanced thermal stability of the bimetallic catalysts. An ORR activity comparison proves that the initial ORR activity on the PtAu/C catalysts is comparable with that on the Pt/C. Moreover, the modification of carbon-supported Pt nanoparticles by Au clusters leads to a significant enhancement in the long-term durability of the catalyst. Thus, such a Pt-Au bimetallic electrocatalyst may be the more promising cathode catalyst for proton exchange membrane fuel cells. 1. Introduction Proton exchange membrane fuel cells (PEMFCs) have received considerable attention for applications in transportation, portable and residential power sources, etc., due to their high power density, high energy-conversion efficiency, zero or low emission of pollutants, and minimal corrosion problems.1-3 However, the commercial viability of PEMFCs is still hindered by several challenging issues such as the poor kinetics of the cathodic reaction, the high costs of both polymer electrolyte membrane and Pt-based catalysts, and the limited life. The limited lifetime of PEMFCs has been recently recognized as one of the major issues to be addressed before its widespread commercialization.4,5 It is believed that the degradation of cathode catalysts plays a critical role in decreasing the lifetime of a PEMFC.6,7 Thus, the durability of cathode catalysts is of significance not only for prolonging PEMFC lifetime but also for enhancing the reliability and reducing the total lifetime cost. However, the search for more active and less expensive oxygen reduction reaction (ORR) catalysts with better durability than Pt catalyst still remains a big challenge. Carbon-supported Pt or its alloy nanoparticles in the particle diameter range of ca. 2-6 nm are commonly used as the cathode catalysts in a PEMFC. Generally, metal nanoparticles inherently tend to aggregate due to their high specific surface energy.7,8 As a result, Pt nanoparticles agglomerating/sintering or even falling off from carbon support, dissolution of catalyst component, and carbon support corrosion all contribute to the degradation of cathode catalysts.9-14 Thus, several strategies have been developed to improve the durability of cathode catalysts: alloying of Pt with other transition metals,15-17 modification of Pt nanoparticles by other species,18,19 develop* Corresponding author: tel and fax, +86-21-32200534; e-mail,
[email protected] and
[email protected]. † Shanghai Institute of Microsystem and Information Technology. ‡ Nanjing Normal University. § National Central University.
ment of new durable catalyst supports20-23 and utilization of Pt-based catalysts with new morphologies.24 Gold is a special metal in view of its inertness in its bulk state and its high catalytic activity for both oxidation and reduction reactions in its nanoscale. When Au nanoparticles (
