Electrocatalytic Activity for Oxygen Reduction Reaction of Au Core/Pt Shell Catalysts

摘要

We succeeded in preparing Au nanoparticles-loaded carbon black (Au/CB) catalyst by using Au colloidal solutions, which were prepared by just bubbling CO gas in KAuCl_4 aqueous solutions including polyvinyl alcohol. After CO bubbling, the color of the solutions changed from light yellow to red-brown, and UV-VIS absorption spectra showed surface plasmon resonance (SPR) band due to the formation of Au colloid. The SPR peak shifted to lower wavelengths with decreasing KAuCl_4 concentration, indicating the formation of smaller Au particles. Transmission electron microscopy revealed that the Au nanoparticles loaded with CB have a mean size of 3.3 nm with a standard deviation of 0.7 nm; this mean particle size agrees with that estimated by X-ray diffraction. Pt monolayers were deposited on the Au/CB nanoparticles (Pt_x/Au/CB (x = number of monolayers)) by underpotential deposition. Cyclic voltammograms of the Pt_1/Au/CB nanoparticles indicate that 75% of the Au surface is covered with Pt. The activity per unit mass of Pt (mass activity) for the oxygen reduction reaction (ORR) for the Pt_1/Au/CB at 0.9 V was 5.1 times higher than that of commercial Pt/CB. In durability tests in which the potential was cycled between 0.6-1.0 V, Pt_1/Au/CB had a higher durability than commercial Pt/CB.