Scalable Synthesis of Carbon-Supported Platinum–Lanthanide and −Rare-Earth Alloys for Oxygen Reduction

Abstract

Platinum–rare-earthalloys have proven to be both active and stable under accelerated stability tests in their bulk polycrystalline form. However, a scalable method for the synthesis of a high-surface-area supported catalyst of these alloys has so far not been presented. Herein we discuss the thermodynamics relevant for the reduction conditions of the rare earths to form alloys with platinum. We show how the tolerance for water and oxygen severely limits the synthesis parameters and how under certain conditions the thermal reduction of YCl3 with H2 is possible from 500 °C. From the insight gained, we synthesized a PtxY/C catalyst by modifying a Pt/C catalyst and confirmed alloy formation by both X-ray diffraction and X-ray photoelectron spectroscopy measurements.These reveal crystalline intermetallic phases and the metallic state of yttrium. Without any optimization of the method, the catalyst has an improved mass activity in comparison to the unmodified catalyst,proving the viability of the method. Initial work based on thermodynamic equilibrium calculations on reduction time show promise in controlling the phase formed by tuning the parameters of time, temperature, and gas composition.