A near ambient pressure photoemission electron microscope (NAP-PEEM)

Ning, Yanxiao; Fu, Qiang; Li, Yifan; Zhao, Su; Wang, Chao; Breitschaft, Martin; Hagen, Sebastian; Schaff, Oliver; Bao, Xinhe

doi:10.1016/j.ultramic.2019.02.028

Cited by 16 publications

(13 citation statements)

References 48 publications

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“…The dispersion sustains with increasing time and eventually leads to a nearly complete disappearance of AgNWs at t = 45 min. Similarly, the dispersion process was further confirmed by NAP-PEEM 42 ( Supplementary Fig. 6), which was conducted at 873 K in O 2 ambience up to 0.1 mbar.…”

Section: Ex Situ Characterization Of Oxidation-induced Dispersion Ofmentioning

confidence: 61%

In situ identification of the metallic state of Ag nanoclusters in oxidative dispersion

Zhu

et al. 2021

Nat Commun

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Oxidative dispersion has been widely used in regeneration of sintered metal catalysts and fabrication of single atom catalysts, which is attributed to an oxidation-induced dispersion mechanism. However, the interplay of gas-metal-support interaction in the dispersion processes, especially the gas-metal interaction has not been well illustrated. Here, we show dynamic dispersion of silver nanostructures on silicon nitride surface under reducing/oxidizing conditions and during carbon monoxide oxidation reaction. Utilizing environmental scanning (transmission) electron microscopy and near-ambient pressure photoelectron spectroscopy/photoemission electron microscopy, we unravel a new adsorption-induced dispersion mechanism in such a typical oxidative dispersion process. The strong gas-metal interaction achieved by chemisorption of oxygen on nearly-metallic silver nanoclusters is the internal driving force for dispersion. In situ observations show that the dispersed nearly-metallic silver nanoclusters are oxidized upon cooling in oxygen atmosphere, which could mislead to the understanding of oxidation-induced dispersion. We further understand the oxidative dispersion mechanism from the view of dynamic equilibrium taking temperature and gas pressure into account, which should be applied to many other metals such as gold, copper, palladium, etc. and other reaction conditions.

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Section: Ex Situ Characterization Of Oxidation-induced Dispersion Ofmentioning

confidence: 61%

In situ identification of the metallic state of Ag nanoclusters in oxidative dispersion

Zhu

et al. 2021

Nat Commun

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“…For reviews, single crystal studies and a recent NAP‐PEEM variant, which enables high resolution (<100 nm) imaging around 1 mbar from 150–1200 K, refer to. [ 95,187,193–198 ]…”

Section: Selected Operando Methodsmentioning

confidence: 99%

“…For reviews, single crystal studies and a recent NAP-PEEM variant, which enables high resolution (<100 nm) imaging around 1 mbar from 150-1200 K, refer to. [95,187,[193][194][195][196][197][198] Figure 6. a) Illustration of operando photoemission electron microscopy (PEEM) and kinetics by imaging: [97,[185][186][187] a) an ongoing catalytic reaction on a structurally-heterogeneous sample, for example, a polycrystalline Pd foil, is monitored simultaneously by PEEM and MS. Local data obtained from the intensity analysis of PEEM video-sequences for each individual (hkl)-domain (µm-scale) are compared with global (averaged) MS data.…”

Section: Photoemission Electron Microscopymentioning

confidence: 99%

“…[91][92][93]271,272] NAP-PEEM is still a niché, but will find more applications for sure. [197,198] Altogether, the ongoing technological development of new and more sensitive operando methods, both in timeand spatially-resolved modes, will enable new insights on active centers in catalytic systems. This is a prerequisite of catalysts improvement and finally rational design.…”

Section: Further Developmentsmentioning

confidence: 99%

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Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

Rupprechter

2021

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described as metal dispersion (number of metal surface atoms relative to the total number of metal atoms in the catalyst), whereas the support is characterized by the specific surface area (m 2 g −1). For hemispherical metal particles of ≈1.5, 2, 5, and 10 nm diameter, the dispersion is about 0.8, 0.6, 0.3, and 0.1, respectively, illustrating why the nanoscale is required not to waste precious metal inside the particles. The ultimate dispersion is, of course, provided by single metal atoms and this concept is followed in "single atom catalysis" or "single site catalysis". [10-17] However, the adsorption and reaction steps of a catalytic reaction do typically not occur on isolated single atoms, but also involve neighboring sites, for example, of the oxide support [18] or of a metal matrix (for bimetallic nanoparticles, active metal atoms may be embedded in an inert or less-active metal matrix [11,19-23]). The so-called site isolation of active atoms may prevent CC bond cleavage (coking), which requires at least two neighboring active metals. In any case, the stability of the single atoms is the key challenge, as atoms may diffuse and sinter. Furthermore, for example, Pt, Pd, Cu, or Au atoms are mobilized by CO, [24-28] forming CO-M 1 units that may eventually sinter into larger clusters. Herein, we define metal clusters as entities with less than ≈100 atoms, characterizing the so-called "non-scalable" regime (Figure 1a). [29] Their atomic and electronic structure is significantly different from that of bulk metals, for example, with respect to atom positions (icosahedral vs face centered cubic fcc), distances (lattice contraction or expansion), and band structure (semiconductor vs metal). Clearly, these properties are size-dependent ("each atom counts" [30,31]), with pronounced impact on adsorption and reaction properties. [5,32] Accordingly, nanoparticles with more than ≈100 atoms are in the "scalableregime" and start to have or exhibit bulk atomic and electronic structure. [6,32-34] Nevertheless, the relative contributions of corner, edge, step, terrace and phase boundary sites on the surface of a nanoparticle (Figure 1b,c) are still size-dependent. [35,36] Meso-scale ("black") powders of metals are clearly bulk-like and have very low dispersion (Figure 1d), but the µm-sized aggregates still consist of adjoining nanocrystals with structured surfaces, comparable to that of true nanoparticles. Operando characterization of working catalysts, requiring per definitionem the simultaneous measurement of catalytic performance, is crucial to identify the relevant catalyst structure, composition and adsorbed species. Frequently applied operando techniques are discussed, including X-ray absorption spectroscopy, near ambient pressure X-ray photoelectron spectroscopy and infrared spectroscopy. In contrast to these area-averaging spectroscopies, operando surface microscopy by photoemission electron microscopy delivers spatially-resolved data, directly visualizing catalyst heterogeneity. For thorough interpretation, the exper...

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“…First, surface science analysis is mostly done in ultrahigh vacuum (UHV), and thus it is difficult to explore electrochemical reactions occurring at liquid/solid interfaces. Nevertheless, solid-state or ionic liquid (IL) electrolytes are UHV compatible [ 6 , 7 , 9 , 10 , 19 , 20 ], and even water/solid interfaces can be probed by newly developed near ambient pressure surface techniques [ 18 , 21 , 22 ]. Second, most surface-sensitive techniques need to probe open and well-defined surfaces, but electrode surfaces in real electrochemical devices are all buried by electrolytes and current collectors which are totally inaccessible to surface probes.…”

Section: Introductionmentioning

confidence: 99%

Operando surface science methodology reveals surface effect in charge storage electrodes

Wang

Ning

Huang

et al. 2020

National Science Review

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Surface and interface play critical roles in energy storage devices, calling for operando characterization techniques to probe the electrified surfaces/interfaces. In this work, surface science methodology including electron spectroscopy and scanning probe microscopy has been successfully applied to visualize electrochemical processes at operating electrode surfaces in an Al/graphite model battery. Intercalation of anions together with cations is directly observed in surface region of the graphite electrode with tens of nanometers thickness, whose concentration is amazingly one order higher than that in bulk. An intercalation pseudocapacitance mechanism and a double specific capacity in the electrode surface region are expected based on the super-dense intercalants and anion/cation co-intercalation, which are in sharp contrast with the battery-like mechanism in the electrode bulk. The distinct electrochemical mechanism at electrode surface is well verified by performance tests of real battery devices, showing that surface-dominant nanometer thick graphite cathode outperforms bulk-dominant micrometer thick graphite cathode. Our findings highlight the important surface effect of working electrodes in charge storage systems.

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A near ambient pressure photoemission electron microscope (NAP-PEEM)

Cited by 16 publications

References 48 publications

In situ identification of the metallic state of Ag nanoclusters in oxidative dispersion

In situ identification of the metallic state of Ag nanoclusters in oxidative dispersion

Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

Operando surface science methodology reveals surface effect in charge storage electrodes

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