Pt@Ag/C ELECTROCATALYST WITH AN INHOMOGENEOUS DISTRIBUTION OF METALS IN THE NANOPARTICLES
Important advantage of «Pt-shell - M-core» nanoparticles in comparison with Pt-alloy nanoparticles consists in core, protected from an aggressive environment by the shell. Usage of nanoparticles with «Pt-shell - M-core» structure allows avoid electrolyte pollution by M + cations and destruction of polymer membrane. The choice of silver as a core - material is dealt with its high thermodynamic stability in comparison, for example, with copper or nickel. Ag has a crystal lattice similar to platinum (face-centered cubic) with close value of an elementary cell parameter. Thus structure seems more suitable for growth of the platinum monolayer on the Ag-core surface. The sequential chemical reduction of silver and platinum was used to prepare Ag@Pt/C electrocatalysts that contain bimetallic nanoparticles with a high surface content of platinum. The compositions, microstructures and electrochemical behaviors of these catalysts were studied using X-ray diffraction, thermogravimetry, X-ray fluorescence analysis, TEM and cyclic voltammetry. It was shown that the combination of heat- and corrosion treatments of Pt-Ag/C material, and cyclic repetition of potential sweep didn’t result in complete dissolution of silver from bimetallic nanoparticles. It may be associated with the presence of nanoparticles with «Ag-core - Pt-shell» structure, formed during synthesis of the material.H.eat and corrosion treatment of Pt-Ag/C did not have a positive impact on the stability of microstructure of the material, although the post-treatment led to an increase in the electrochemically active surface area of from 57 to 70 m 2∙g -1 (Pt).