Synthesis Of PtAgAu Hollow Nanoparticles Via Galvanic Replacement With Enhanced Electric Catalytic Activity

Hollow polymetallic nanocrystals with large specific surface area, good atom economy, and unique electronic effects within one particle have received extensive attention in a variety of applications, such as biomedical imaging, photothermal therapy, and energy storage. Particularly, hollow Pt-base nanometerials have very important applications in fuel cell. Currently, galvanic replacement is the widely used method for the synthesis of hollow Pt-base nanometerials. Au nanoparticles are rich in morphology, but Au nanoparticles are stable in many chemical environments and difficult to be oxidated by other metal salts. Therefore, the Au@Ag core-shell nanoparticles are selected as templates for the formation of hollow Pt-base nanometerials. The charge transfer between Au core and Ag reduces the electron density in Au, which makes Au active and promotes its oxidation. The different morphologies of PtAgAu hollow nanoparticles were synthesized via galvanic replacement. The reaction process and reaction mechanism are discussed in this paper, and we study their electric catalytic properties via formic acid oxidation. The details are as follow:1. High-quality PtAgAu nanotubes are synthesized by galvanic replacement between core-shell Au@Ag nanorods and K2PtCl4 in the presence of CTAB. Both Ag shell and Au core are demonstrated to be involved in the galvanic replacement with K2PtCl4. The products experience a structural evolution from nanorattles, to tip-empty nanorods, and eventually to porous nanotubes, which can be observed by TEM images. A series of contrast experiments prove that the oxidant is K2PtCl4 rather than oxygen dissolved in the solution. The presence of Ag shell and the close contact between Au and Ag play a vital role in the galvanic replacement. XPS spectra were collected to demonstrate an electron transfer from Au to Ag in the Au@Ag nanorods, which reduces the electrode potential of Au and accelerates the etching of Au. This result is also supported by the contrast experiments. The electro-catalyticproperties of PtAgAu nanotubes were tested by the electrooxidation reaction of formic acid.2. Taking advantage of electron transfer from Au to Ag in the Au@Ag nanparticles, high-quality PtAgAu hollow nanospheres are synthesized by galvanic replacement between core-shell Au@Ag nanospheres and K2PtCl4. in the presence of CTAB. The reaction process was characterizated by TEM images. The ratio of the elements was controlled by changing the size of Au nanospheres. The electro-catalytic properties for formic acid oxidation of PtAgAu hollow nanospheres are different, as the ratio of the elements varies. But their electro-catalytic activities are higher than that of Commercial Pt/C catalyst.