Electrochemical Cycling Induced Surface Segregation of AuPt Nanoparticles in HClO4 and H2SO4

Abstract

The surface composition of bimetallic nanoparticles is critical to their electrochemical performance. The most effective existing approach for changing surface composition is the thermal treatment, which induces the surface segregation of the metal with low surface energy. Some studies have shown that the surface segregation in bimetallic nanoparticles may also occur under the electrochemical conditions. However, the effect of the electrolyte in this process has not been investigated. This article presents a comparative study on the difference between cycling AuPt nanoparticles in HClO4 and H2SO4. The nanoparticles were electrochemically cycled in Ar-saturated HClO4 and H2SO4 and the electrochemical surface composition of nanoparticles was analyzed by cyclic voltammetry method. The size evolution was investigated by transition electron microscope (TEM). Energy-dispersive X-ray spectroscopy (EDX) mapping analysis confirmed no phase separation on AuPt nanoparticles. It is found that cycling in H2SO4 shows higher degree of surface segregation of Au than doing same in HClO4. The enhanced surface segregation of Au is believed due to the stronger adsorption of bi-sulfate anions on Au. In addition, the cycled nanoparticles with various surface composition exhibited different activities toward electrooxidation of methanol. This work indicates that electrolytes may affect the surface segregation of bimetallic nanoparticles.