Selective deposition of gold onto Pt sites in Pt/C catalysts: Electron microscopy and electrochemical characterization

This work aims to study the selective deposition of gold onto the faces of Pto in Pt/C catalyst. The preparation of monometallic Pt/C catalyst was carried out by means of the impregnation of platinum over graphite. The bimetallic catalyst Pt–Au/C was prepared by selectively depositing Au on supported monometallic Pt/C catalyst by means of the reduction “in-situ” of AuCl4−. The surface redox method used in this work was the Refilling method (RE), which consisted in adsorbing hydrogen first on the metal (Pt), and subsequently reducing the AuCl4− species by contact with the Pt–H interface at low temperature. The catalysts were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), whereas for the electrochemical tests the catalysts were supported on Vulcan XC-72 carbon and they were evaluated by linear and cyclic voltammetry as well as rotating disk electrode (RDE) measurements. The composition of the individual metal particles of the solids indicated the presence of both metals, Pt and Au. The results indicated that a partial Au coating of certain Pt facets is possible, which indicates that the coating mechanism is selective and could influence the catalytic properties of the bimetallic Pt–Au/C catalysts. As a result of this blockage we observed a reduction of the catalytic activity of the bimetallic catalyst with respect to the Pt/C catalyst. The electrochemical characterization showed a Tafel slope of −94 mV dec−1 for the Pt–Au/C sample, with a 0.62 transfer coefficient, showing the effect of the blockage of the active platinum sites.

► Au was used to selectively blocked Pt active sites on Pt/C catalysts.
► Surface redox method led to the reduction “in-situ” of AuCl4− species.
► The preferential interaction of Au with Pt was verified by HRTEM techniques.
► The electrochemical results showed the decrease of the activity of Pt–Au/C.