Simple Preparation of Au Nanoparticles and Their Application to Au Core/Pt Shell Catalysts for Oxygen Reduction Reaction

Au nanoparticle-loaded carbon black (Au/CB) was prepared simply by bubbling CO as a reducing agent in a KAuCl4 aqueous solution containing polyvinyl alcohol as a stabilizer and then mixing Ketjen black as carbon black. X-ray diffraction spectra and transmission electron micrographs exhibited that the Au nanoparticles loaded on CB had the mean size of 3.3 nm which was scarcely increased even by the heat-treatment at 400 A degrees C. For the Au/CB heat-treated at 400 A degrees C (Au/CB-HT400), the modification of the Au nanoparticles with a Pt monolayer shell was performed by underpotential deposition of Cu and the following galvanic displacement with Pt. Cyclic voltammograms of Au-Pt-1/CB-HT400 and Au-Pt-2/CB-HT400 electrodes, which mean a Pt monolayer shell was deposited once and twice on Au/CB-HT400, indicated that 73 % and 97 % of the Au core nanoparticle surface were covered with the Pt shell, respectively. Koutecky-Levich plots made from hydrodynamic voltammograms of the Au-Pt (x) /CB-HT400 (x = 1, 2) electrodes exhibited that oxygen reduction reaction at both electrodes proceeded in four-electron mechanism like commercial Pt/CB. The mass activity at 0.9 V vs. RHE for Au-Pt-1/CB-HT400 and Au-Pt-2/CB-HT400 was ca. 5.1 and 4.4 times as high as that for the commercial Pt/CB, respectively. Moreover, in durability tests in which the square-wave potential cycling between 0.6 and 1.0 V vs. RHE was repeated 10(4) times, both catalysts were equivalent or superior to the commercial Pt/CB.