Controlling morphology and structure of Pt₃Sn sponges using magnetron based cluster beam for hydrogen oxidation

Platinum-tin (PtSn) nanoparticles (NPs) were grown in a magnetron-based gas aggregation source and deposited on a silicon substrate inside a secondary plasma (SP). The biasing of the substrate holder led to the formation of this SP in the vicinity of the substrate. Without the SP, the deposition consists of a homogeneous film of densely packed 2.6 nm in diameter NPs. When the SP was ignited, a porous thin-film constituted of sponge-like structures, with an average diameter of 29 nm, is formed. Without SP, the alloy phase (A1) for Pt _x Sn_1-x was observed, while the formation of an additional ordered intermetallic Pt₃Sn (L1₂) phase was observed with SP. Selected area electron diffraction showed that the A1 phase corresponds to the smaller NPs, while the L1₂ phase is for sponges. Without SP, the overall atomic composition of PtSn NPs consist of three quarters of Pt atoms and one quarter of Sn ones. The Pt atomic content decreases to 70% in sponges with SP. The electrochemical studies revealed that PtSn NPs (with a nominal total loading close to 1.2 ± 0.3 mg cm^-2) suffered from limited hydrogen adsorption/desorption, probably because Sn blocks the Pt active sites. But the formation of Pt₃Sn sponges using SP exhibit markedly enhanced kinetics for both CO oxidation and the hydrogen oxidation reaction.