Pt Based Alloy Nanoparticles for Oxygen Reduction Prepared By a Solvothermal Method

Abstract

In this study, platinum based alloy (PtNi, PtCo, PtNiCo) nanocatalysts with well controlled sizes and shapes have been synthesized using a one pot, facile and surfactant free solvothermal approach for application to the oxygen reduction reaction (ORR). Focus is on the fine-tuning of PtNi and PtNiCo nanostructure with the aim of achieving a defined particle geometry that can withstand treatment leading to a Pt-skin like structure and long electrochemical durability cycles. Effects of synthesis variables that include temperature, heating rate and the nature and ratio of metal precursor salts will be discussed. The samples were characterized using X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), high-resolution scanning transmission electron microscopy (HR-STEM), energy-dispersive x-ray spectroscopy (EDS) and thermogravimetric analysis (TGA). EDS mapping and line scans coupled with HR-STEM imaging was utilized to study the elemental distribution within individual Pt alloy nanoparticles, for as prepared samples, electrochemically activated samples and samples after electrochemical durability cycling. The as-prepared samples were subjected to an electrochemical treatment (activation) in deaerated 0.1 M HClO4 to form a Pt-skin like structure. Activated samples exhibited ~ 3-10 fold greater enhancement in ORR activity than commercially available Pt-C in terms of both specific activity and mass activity. Furthermore, most Pt alloy particles retained their activity after the course of the electrochemical durability cycling.