Effect of phosphorus and copper additions on the structure of Pt and Pt–Cu nanoparticles in a radiation-induced reduction method

The effects of phosphorus (PH₂O₂ ⁻) and copper (Cu²⁺) additions to the aqueous precursor solution on the structure of Pt–Cu nanoparticles were investigated for a radiation-induced reduction method. Addition of PH₂O₂ ⁻ in the precursor solution reduced the diffraction intensity of Pt or Pt–Cu crystallites due to smaller size and/or lower crystallinity. Both the diffraction intensity and the particle size (measured by an electron microscope) were minimized when Cu/Pt ratio was 0.05–0.25, which was attributed to the effects of copper and phosphorus to stabilize crystallites and particles through the negative heat of mixing. The concomitant increase in phosphorus content suggested that PH₂O₂ ⁻ is partly reduced and taken into the Pt lattice. Further increase of copper content caused larger particles and decrease in phosphorus content. These trends were also consistent with electrochemical surface area and oxidation/reduction behavior of Pt surface. The radiation-induced reduction method is suited to produce small Pt–Cu particles uniformly distributed on carbon support, which are potentially served for heat treatment for improved oxygen reduction performance.