Atomic distribution and structural evolution of mesostructured PtRu nanoparticles electrodeposited on a microemulsion lyotropic liquid-crystalline template probed using EXAFS and XANES

Abstract

Mesostructured PtRu nanoparticles were electrochemically reduced from their metallic salts directed by a hexagonally packed microemulsion lyotropic liquid-crystalline (MLLC) template. We investigated the structural evolution and atomic distribution of the MLLC-templated mesoporous PtRu nanoparticles (NPs) after electroreduction for varied duration using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy, complemented by energy-dispersive X-ray spectroscopy (EDS) and field-emission transmission electron microscopy (FE-TEM). The XANES data at the Ru L_2,3 and Pt L₃ edges show predominantly metallic states of Ru and Pt in the PtRu NPs upon electroreduction. The reduction of Ru³⁺ ions in RuCl₃ into Ru atoms involves intermediate RuCl-containing complexes. A more rapid reduction of Pt precursors and a release of Ru atoms from Ru precursors in two steps upon electroreduction resulted in aggregation into PtRu nanoparticles, featuring a Pt-rich core, a Ru-rich shell and a varied alloy extent of Ru, deduced from EXAFS data. The complementary results provide insight into the mechanism of growth and atomic distribution of mesostructured PtRu bimetallic nanoparticles from the use of the MLLC-type templates.