Carrier gas-driven compositional variations of platinum-tungsten nanoparticles generated by spark ablation

Abstract

Bimetallic nanoparticles are of interest in various catalytic applications as cost-effective replacements for precious metal catalysts. Ongoing research is aimed at developing new techniques to produce nanoparticles with precise control of their composition, size, and structure. In this study, we investigated the tuning of the composition of platinum–tungsten bimetallic nanoparticles by spark ablation. Using pure electrodes, the spark ablation method offers the possibility of forming mixed nanoparticles and adjusting their size and composition by modifying the carrier gas mixture. Morphological, structural, and compositional characterizations by High-Angle Annular Dark-Field (HAADF) and Bright Field (BF) imaging in Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive X-ray (EDX) microanalysis were used to evaluate the nanoparticle size distribution and the ratio of Pt to W, whereas interlayer d-spacings were quantified using the Selected Area Electron Diffraction (SAED) technique. Similar to previous studies that have demonstrated homogeneous internal nanoparticle mixing with different electrodes, we observed that the nanoparticles generated from the monometallic electrodes were mixed mostly homogeneously. Additionally, we demonstrate that the use of platinum as the initial anode and tungsten as the initial cathode in a nitrogen atmosphere can promote the formation of core-shell nanostructures. A theoretical model of electrode ablation was developed using the current and voltage discharge profiles to estimate the composition of the synthesized nanoparticles. The modeling revealed a longer period between platinum electrode evaporation and tungsten electrode evaporation during spark discharges as a potential reason for core-shell formation.