(701a) XANES Modeling of the Time-Resolved Metal-Ligand Bonding During Pt-SnCl3- Complex Reduction to Form Pt-Sn Core-Shell Nanoparticles

Single-crystal studies have previously demonstrated that Pt surface poisoning by intermediates produced during the ethanol oxidation reaction (EOR) can be mitigated by the presence of Sn atoms.  We have developed an aqueous-based synthesis method to produce Pt nanoparticles reduced and stabilized by SnCl₃^– surface ligands.  These ligands are intrinsic to our synthesis approach and do not need to be incorporated ex-situ by post-synthesis processing methods such electrochemical adsorption. The SnCl₃^– can be readily converted in-situ to surface-adsorbed Sn(IV) for improved ethanol oxidation reaction activity. We show how our synthesis approach can be extended to other metals such as Bi, which are difficult to disperse but have also been shown to promote mass-specific EOR activity in association with Pt.

Here we are able to observe the nature of the Pt-Sn metal-ligand bond by modeling time-resolved, in situ x-ray absorption near-edge spectroscopy (XANES) data collected at the Pt L_2,3 edges and Sn K edge. Additionally, DFT calculations illustrate metal-ligand charge transfer from the Pt to the surface adsorbed SnCl₃^–. Metal-ligand bonding is shown to play a key role in regulating the kinetics of nanoparticle growth. We have previously presented results concerning the structural evolution of the Pt-SnCl₃^– core-shell nanoparticle structure using small-angle x-ray scattering (SAXS) data. The new XANES observations on bonding behavior are shown to be complementary to this structural information via SAXS, as well as more recent ¹¹⁹Sn Mössbauer data we are in the process of gathering.