Co-sputtered CuPt/Ag alloy nanoparticles and comparative catalytic performance of mono-, bi-, and tri-metallic nanoparticles in the oxygen reduction reaction

Abstract

CuPt/Ag trimetallic alloy nanoparticles (NPs) were synthesized by co-sputtering onto liquid polyethylene glycol (PEG), using a CuPt alloy target and an Ag target. The fine structure analysis reveals that the obtained NPs are trimetallic solid solution alloys. Ag compositions increased with the increase of sputtering currents applied to an Ag target while keeping the sputtering currents applied to CuPt target constant. Moreover, it was found that the Cu : Pt atomic ratios of single NPs measured by energy dispersive spectroscopy (EDS) coupled with scanning transmission electron miscroscopy (STEM) were lower than the average value of the sputtered NPs dispersed in PEG. This suggests that NPs which are big enough to be checked by STEM-EDS are mainly Pt-rich NPs. The Cu, Ag, and Pt compositions of trimetallic NPs varied in a wide range, indicating random alloy formation. The sputtered trimetallic CuPt/Ag NPs were studied as catalysts in the oxygen reduction reaction (ORR), and the catalytic performance is compared with sputtered bimetallic alloy Cu/Pt and Ag/Pt NPs and monometallic Pt NPs. Trimetallic CuPt/Ag NPs showed higher ORR catalytic activities than bimetallic alloy Cu/Pt NPs owing to their better stability and dispersibility on the carbon support. However, the trimetallic alloy NPs performed worse than bimetallic Ag/Pt NPs and Pt NPs. This is caused by Cu oxidation and dissolution of Pt and Cu. Comparable ORR catalytic peformance of Ag/Pt NPs (40 atom% Ag) with Pt NPs is thought to come from the synergy between Pt and Ag in the bimetallic alloy.