Electrochemical Cycling Induced Surface Segregation of AuPt Nanoparticles in HClO₄and 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 HClO 4 and H 2 SO 4 . The nanoparticles were electrochemically cycled in Ar-saturated HClO 4 and H 2 SO 4 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 H 2 SO 4 shows higher degree of surface segregation of Au than doing same in HClO 4 . 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.

Synthesis of Au@Pt Core—Shell Nanoparticles as Efficient Electrocatalyst for Methanol Electro-Oxidation

“…Figure 5a shows a HAADF-STEM image of Au@Pt (1:1) NPs and its corresponding line-scan plot (Figure 5b) to clarify that the signal of Au is confined to core region whereas the Pt signal is uniformly distributed throughout the entire particle, confirming the formation of a core–shell structure. These results are consistent with the previous reports, when few atomic layers are deposited on atomic core NPs with the atomic ratio Au/Pt is 1:1 [44,45]. Figure 5c shows a HAADF-STEM image of Au@Pt (1:3) NPs; as above was mentioned due to similar atomic number between Au and Pt, the HAADF-STEM image does not reveal a contrast difference between Au core and Pt shells.…”

ZSM-5 Zeolite Support for PtAu Toward Ethanol Oxidation

“…Since the surface energy of Au is lower than that of Pt, the surface composition of Pt x Au y nanoparticles can be further altered by the thermal treatment or electrochemical method. 9,40 From the average charge associated with the hydrogen adsorption and desorption, after the double layer deduction, and a charge of 210 μC cm -2 for polycrystalline Pt as well as the Pt loading of catalysts, the electrochemically active surface areas (EASAs) of 26.2 and 30.1 cm 2 g -1 (Pt) are obtained for PtAu/ ZSM-5 and PtAu/C, respectively. The results of ethanol oxidation on PtAu/ZSM-5 and PtAu/C are shown in Fig.…”