Formation of a Pt-Decorated Au Nanoparticle Monolayer Floating on an Ionic Liquid by the Ionic Liquid/Metal Sputtering Method and Tunable Electrocatalytic Activities of the Resulting Monolayer

Abstract

A novel strategy to prepare a bimetallic Au-Pt particle film was developed through sequential sputter deposition of Au and Pt on a room temperature ionic liquid (RTIL). Au sputter deposition onto an RTIL containing hydroxyl-functionalized cations produced a monolayer of Au particles 4.2 nm in size on the liquid surface. Subsequent Pt sputtering onto the original Au particle monolayer floating on the RTIL enabled decoration of individual Au particles with Pt metals, resulting in the formation of a bimetallic Au-Pt particle monolayer with a Pt-enriched particle surface. The particle size slightly increased to 4.8 nm with Pt deposition for 120 min. The shell layer of a bimetallic particle was composed of Au-Pt alloy, the composition of which was tunable by controlling the Pt sputter deposition time. The electrochemical surface area (ECSA) was determined by cyclic voltammetry of bimetallic Au-Pt particle monolayers transferred onto HOPG electrodes by a horizontal liftoff method. The Pt surface coverage, determined by ECSAs of Au and Pt, increased from 0 to 56 mol % with elapse of the Pt sputter deposition time up to 120 min. Thus-obtained Au-Pt particle films exhibited electrocatalytic activity for methanol oxidation reaction (MOR) superior to the activities of pure Au or Pt particles. Volcano-type dependence was observed between the MOR activity and Pt surface coverage on the particles. Maximum activity was obtained for Au-Pt particles with a Pt coverage of 49 mol %, being ca. 120 times higher than that of pure Pt particles. This method enables direct decoration of metal particles with different noble metal atoms, providing a novel strategy to develop highly efficient multinary particle catalysts.

Nanoalloy Materials for Chemical Catalysis

“…Under dry synthesis conditions without a solvent or reductant, the product is pure, thus no posttreatment is needed. Sputtering is suitable for high‐purity supported NA catalysts, e.g., Au@PtAu nanomonolayer . But it has special requirements on equipment.…”

Sputtering onto a liquid: interesting physical preparation method for multi-metallic nanoparticles

“…Sputter deposition onto IL surfaces was further developed with sequential sputtering to form either bimetallic alloy NPs or a monolayer of NPs with a metal core coated with an alloy shell structure [101][102][103][104][105][106]. Wang [101].…”

“…In 2016, Torimoto's group developed a sequential sputtering process of Au and Pt for tailoring NPs with a well-defined metal core@metal alloy shell structure as well as assembling them into a monolayer ( Figure 5(f)) [104]. They chose an IL, 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate [HyEMI][BF 4 ], containing hydroxyl functionalized cations to achieve a monolayer of 4.2 nm Au NPs on the liquid surface by first sputtering an Au target.…”

Core–Shell-Structured Low-Platinum Electrocatalysts for Fuel Cell Applications

“…And by using this technique with the ionic liquid of 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate (HyEMI-BF4), uniform Au@Pt electrocatalysts for ORR can be prepared (Fig. 17) [382]. Many other core-shell-structured electrocatalysts such as Pd@Pt and CrN@Pt have also been prepared by using sputtering deposition and are listed in Table 9.…”