Unravelling Surface Composition of Bimetallic Nanoparticles

Accurately determining the surface composition of bimetallic nanoparticles (bi-MNPs) is crucial in assessing their catalytic potential for energy applications and surface-enhanced Raman scattering (SERS). Despite its importance, characterizing the surface composition of bi-MNPs is still extremely difficult with existing techniques. Here, we show that the challenge is approached by combining extended Xray absorption fine structure (EXAFS) analyses and modeling calculations. A generally applicable methodology using an ethylene glycol-assisted redox transmetallation (EG-RTM) strategy has been used to deduce the surface Pt composition of various Pt-Ru bi-MNPs to facilitate discussion of their electrochemical catalytic efficiency. Further discussion is fo-cused on SERS, related to the surface Ag content of various Ag-Pt bi-MNPs formed in ethylene glycol solutions at controlled pH values. Although the present methodology is demonstrated on fcc structured bi-MNPs it should be transferable to bi-MNP structures with different shapes and also to ternary nanoparticles. The proposed methodology enables us to deduce the surface composition of bi-MNPs from experimental data directly and to estimate the surface composition under real conditions, when compared to simulation. The ability of the present combined modeling and experimental approach makes it a unique tool in our quest to understand the physical and chemical properties of NPs.