Soft landing of bare PtRu nanoparticles for electrochemical reduction of oxygen

Abstract

Magnetron sputtering of two independent Pt and Ru targets coupled with inert gas aggregation in a modified commercial source has been combined with soft landing of mass-selected ions to prepare bare 4.5 nm diameter PtRu nanoparticles on glassy carbon electrodes with controlled size and morphology for electrochemical reduction of oxygen in solution. Employing atomic force microscopy (AFM) it is shown that the nanoparticles bind randomly to the glassy carbon electrode at a relatively low coverage of 7 × 10(4) ions μm(-2) and that their average height is centered at 4.5 nm. Scanning transmission electron microscopy images obtained in the high-angle annular dark field mode (HAADF-STEM) further confirm that the soft-landed PtRu nanoparticles are uniform in size. Wide-area scans of the electrodes using X-ray photoelectron spectroscopy (XPS) reveal the presence of both Pt and Ru in atomic concentrations of ∼9% and ∼33%, respectively. Deconvolution of the high energy resolution XPS spectra in the Pt 4f and Ru 3d regions indicates the presence of both oxidized Pt and Ru. The substantially higher loading of Ru compared to Pt and enrichment of Pt at the surface of the nanoparticles is confirmed by wide-area analysis of the electrodes using time-of-flight medium energy ion scattering (TOF-MEIS) employing both 80 keV He(+) and O(+) ions. The activity of electrodes containing 7 × 10(4) ions μm(-2) of bare 4.5 nm PtRu nanoparticles toward the electrochemical reduction of oxygen was evaluated employing cyclic voltammetry (CV) in 0.1 M HClO4 and 0.5 M H2SO4 solutions. In both electrolytes a pronounced reduction peak was observed during O2 purging of the solution that was not evident during purging with Ar. Repeated electrochemical cycling of the electrodes revealed little evolution in the shape or position of the voltammograms indicating high stability of the nanoparticles supported on glassy carbon. The reproducibility of the nanoparticle synthesis and deposition was evaluated by employing the same experimental parameters to prepare nanoparticles on glassy carbon electrodes on three occasions separated by several days. Surfaces with almost identical electrochemical behavior were observed with CV, demonstrating the highly reproducible preparation of bare nanoparticles using physical synthesis in the gas-phase combined with soft landing of mass-selected ions.

In situ solid-state electrochemistry of mass-selected ions at well-defined electrode–electrolyte interfaces

“…Of note is that ORR on Pt follows a four-electron pathway in both protic IL and aqueous acidic electrolyte (e.g., Nafion) (32) and the intrinsic ORR activity should not change between protic IL and Nafion electrolyte. Approximately 2 × 10 12 bare anionic Pt clusters produced by magnetron sputtering and gas aggregation (33,34) are uniformly deposited onto both variants of cell 2 and characterized by CV under a N 2 or O 2 atmosphere (Fig. 4).…”

“…In this study, in-source CID was achieved by increasing the rf of both ion funnels and adjusting the potential difference between the end plate of the second ion funnel and the dc offset of the collisional quadrupole. In the second instrument, SL of bare anionic Pt clusters was achieved using the modified commercial Nanogen-Trio cluster source and Q-Prep 500 deposition system (Mantis Deposition Ltd.) (33,34). The bare anionic Pt clusters were produced by dc magnetron sputtering of a circular Pt target in a controlled flow of ultra high-purity argon and helium and deposited onto cell 2 without mass selection.…”

From Isolated Ions to Multilayer Functional Materials Using Ion Soft Landing

“…In ar elated study,l iquid-phase CV measurements on size-selected Pt n clusters soft landed on glassy carbon electrodes without exposure to the ambient environment were performed by using au nique vacuumbased electrochemical cell. [70] In af ollowing publication, the same authors described an approach that involved seeding the sputtering gas with asmall amount of volatile hydrocarbons to synthesize TaCnanoparticles that surprisingly exhibited ORR activity reminiscent of precious metals such as Pt. Theu nusual behavior of Pt 4 clusters provides important mechanistic insight into corrosion of the carbon support-one of the major degradation modes in PEMFCs.A commercial magnetron sputter gas aggregation source was employed to prepare bare Pt x Yn anoparticles larger than 1nmi nd iameter,w hich were found to be highly electrochemically active toward the ORR.…”

Understanding ligand effects in gold clusters using mass spectrometry

“…155 The same group later deposited polyatomic ions onto surfaces complete with retention of charge. 156 In the intervening years a range of ions have been soft landed including peptides, 157-160 proteins, [161][162][163][164][165][166][167] viruses, 168 nanoparticles, [169][170][171][172][173][174][175][176] clusters, 132,142,154,[177][178][179][180][181][182][183] dyes, 184,185 graphene, 186 and organometallic complexes. [187][188][189][190][191][192] For example, we have investigated the charge reduction, neutralization, and desorption behavior of ionic peptides, [193][194][195][196] organometallic complexes, [187][188][189][197][198]…”