B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Diamond Proposal Number(s):
[26045]
Open Access
Abstract: Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) was employed to investigate the effect of applied potential on the interface of TiO2(110) with 0.1 M HCl. The study, which involved operando electrochemical characterization, enabled real-time monitoring and analysis of electrochemical processes. There is a significant influence on the interface composition; in particular, the surface Cl– surface coverage varies with electrochemical potential. Moreover, there appears to be a reaction of evolved Cl with adventitious carbon to form C–Cl and C–Cl2 species.
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Nov 2024
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I06-Nanoscience (XPEEM)
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M.
Lowe
,
A.
Al-Mahboob
,
D.
Ivarsson
,
M.
Armbrüster
,
J.
Ardini
,
G.
Held
,
F.
Maccherozzi
,
A.
Bayer
,
V.
Fournee
,
J.
Ledieu
,
J. T.
Sadowski
,
R.
Mcgrath
,
H. R.
Sharma
Open Access
Abstract: The intermetallic compound ZnPd has been found to have desirable characteristics as a catalyst for the steam reforming of methanol. The understanding of the surface structure of ZnPd is important to optimize its catalytic behavior. However, due to the lack of bulk single-crystal samples and the complexity of characterizing surface properties in the available polycrystalline samples using common experimental techniques, all previous surface science studies of this compound have been performed on surface alloy samples formed through thin-film deposition. In this study, we present findings on the chemical and atomic structure of the surfaces of bulk polycrystalline ZnPd studied by a variety of complementary experimental techniques, including scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), low energy electron microscopy (LEEM), photoemission electron microscopy (PEEM), and microspot low-energy electron diffraction (𝜇-LEED). These experimental techniques, combined with density functional theory (DFT)-based thermodynamic calculations of surface free energy and detachment kinetics at the step edges, confirm that surfaces terminated by atomic layers composed of both Zn and Pd atoms are more stable than those terminated by only Zn or Pd layers. DFT calculations also demonstrate that the primary contribution to the tunneling current arises from Pd atoms, in agreement with the STM results. The formation of intermetallics at surfaces may contribute to the superior catalyst properties of ZnPd over Zn or Pd elemental counterparts.
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Oct 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
I10-Beamline for Advanced Dichroism - scattering
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Diamond Proposal Number(s):
[33639, 34919, 36558]
Open Access
Abstract: Spinel ferrites exhibit significant promise in photocatalysis and other applications due to their compositional diversity and favourable electronic structure, magnetism, and partially tuneable cation distribution. However, their complex properties, for example, the different behaviour of bulk and nanostructured materials, are not well understood. Here, we combine advanced computational and experimental methods with reactivity measurements to explore the inversion degrees, electronic structures, and photocatalytic activities of MFe2O4 spinels (M = Co, Cu, Zn). X-ray diffraction and anomalous X-ray scattering measurements determined bulk inversion degrees of 0.81, 0.91, and 0.26 for CoFe2O4, CuFe2O4, and ZnFe2O4, respectively. Photocatalytic tests showed that only ZnFe2O4 is active in the oxygen evolution reaction (OER), which correlates with its favourable band alignment, as determined through electronic structure simulations. Surface-sensitive X-ray Absorption Spectroscopy (XAS) measurements provided insights into the cation distributions at the surfaces, showing significant deviations from bulk properties, particularly in ZnFe2O4 in which 52% of the near-surface tetrahedral sites are occupied by Fe cations, compared to 26% in the bulk. DFT simulations of ZnFe2O4 illustrated how the surface terminations can alter the thermodynamic preference for cation distribution in comparison with the bulk. Our findings illustrate the complex interplay between surface and bulk properties in spinel ferrites.
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Sep 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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F.
Bassato
,
S.
Mauri
,
L.
Braglia
,
A. Yu.
Petrov
,
E.
Dobovičnik
,
F.
Tavani
,
A.
Tofoni
,
P.
Ferrer
,
D.
Grinter
,
G.
Held
,
P.
D'Angelo
,
P.
Torelli
Diamond Proposal Number(s):
[33111]
Abstract: A-site doped SrTiO3 is considered as a promising substitute for traditional anodic metals in solid oxide fuel cells (SOFCs). In this study, we present the reactivity of La0.2Sr0.25Ca0.45TiO3 (LCSTO), La0.2Sr0.7TiO3 (LSTO), and SrTiO3 (STO) toward H2 by operando ambient pressure NEXAFS spectroscopy and theoretical spectra simulation with FDMNES code. The samples were synthesized by MBE (molecular beam epitaxy), hydrothermal, and modified-Pechini routes. We found that the reducibility of the samples depends not only on their stoichiometry but also on the morphology, which is determined by the synthetic method. The results of these experiments give insight into the reducibility of Ti4+ in perovskites as well as the opportunity to further optimize the synthesis of these materials to obtain the best performance for SOFC applications.
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Aug 2024
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
E01-JEM ARM 200CF
I09-Surface and Interface Structural Analysis
I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Xuze
Guan
,
Rong
Han
,
Hiroyuki
Asakura
,
Bolun
Wang
,
Lu
Chen
,
Jay Hon Cheung
Yan
,
Shaoliang
Guan
,
Luke
Keenan
,
Shusaku
Hayama
,
Matthijs A.
Van Spronsen
,
Georg
Held
,
Jie
Zhang
,
Hao
Gu
,
Yifei
Ren
,
Lun
Zhang
,
Zhangyi
Yao
,
Yujiang
Zhu
,
Anna
Regoutz
,
Tsunehiro
Tanaka
,
Yuzheng
Guo
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[23759, 24450, 29092, 31852]
Open Access
Abstract: Single-atom catalysts have garnered significant attention due to their exceptional atom utilization and unique properties. However, the practical application of these catalysts is often impeded by challenges such as sintering-induced instability and poisoning of isolated atoms due to strong gas adsorption. In this study, we employed the mechanochemical method to insert single Cu atoms into the subsurface of Fe2O3 support. By manipulating the location of single atoms at the surface or subsurface, catalysts with distinct adsorption properties and reaction mechanisms can be achieved. It was observed that the subsurface Cu single atoms in Fe2O3 remained isolated under both oxidation and reduction environments, whereas surface Cu single atoms on Fe2O3 experienced sintering under reduction conditions. The unique properties of these subsurface single-atom catalysts call for innovations and new understandings in catalyst design.
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Jul 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Ioanna
Itskou
,
Andreas
Kafizas
,
Irena
Nevjestic
,
Soranyel
Gonzalez Carrero
,
David C.
Grinter
,
Hassan
Azzan
,
Gwilherm
Kerherve
,
Santosh
Kumar
,
Tian
Tian
,
Pilar
Ferrer
,
Georg
Held
,
Sandrine
Heutz
,
Camille
Petit
Diamond Proposal Number(s):
[30777]
Open Access
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Jul 2024
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Diamond Proposal Number(s):
[32832]
Abstract: The conversion of CO2-H2 mixtures on Ni-based catalysts can proceed through either the reverse water gas shift reaction (RWGS) path to produce CO or the CO2 methanation path to produce CH4. The balance between these competing reactions depends on both the reaction conditions and catalyst structure. In this study, using surface-sensitive infrared and ambient pressure X-ray photoelectron spectroscopies, we investigate the effect of reaction conditions on the interaction between CO2 and H2 on a Ni(111) model catalyst. Our findings highlight the occurrence of RWGS, involving direct dissociation of CO2 to CO and atomic oxygen, followed by oxygen reacting with hydrogen to form H2O, and CO and H2O desorption. Hydrogen affects the distribution of CO between hollow and top sites by displacing oxygen from the energetically preferred hollow sites. The overall balance between oxygen production from CO2 dissociation and oxygen removal by hydrogen governs the oxygen coverage and consequently the distribution of CO between top and hollow sites. This balance is significantly influenced by the reaction temperature and the H2/CO2 partial pressures.
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Jun 2024
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Diamond Proposal Number(s):
[32763, 33640]
Open Access
Abstract: Suitable reaction cells are critical for operando near ambient pressure (NAP) soft X-ray photoelectron spectroscopy (XPS) and Near-edge X-ray absorption fine structure (NEXAFS) studies. They enable tracking the chemical state and structural properties of catalytically active materials under realistic reaction conditions, and thus allow a better understanding of charge transfer at the liquid-solid interface, activation of reactant molecules, and surface intermediate species. In order to facilitate such studies, we have developed a top-side illuminated operando spectro-electrochemical flow cell for synchrotron-based NAP-XPS and NEXAFS studies. Our modular design uses a non-metal (PEEK) body, and replaceable membranes which can be either of X-ray transparent silicon nitride (SiNx) or of water permeable polymer membrane materials (e.g., NafionTM). The design allows rapid sample exchange and simultaneous measurements of total electron yield (TEY), Auger electron yield (AEY) and fluorescence-yield (TFY). The developed system is highly modular and can be used in the laboratory or directly at the beamline for operando XPS/ X-ray absorption spectroscopy (XAS) investigations of surfaces and interfaces. We present examples to demonstrate the capabilities of the cell. These include an operando NEXAFS study of the Cu-redox chemistry using a SiNx membrane/Ti-Au/ Cu working electrode assembly (WEA) and a NAP-XPS and -NEXAFS study of water adsorption on a NafionTM polymer membrane based working electrode assembly (NafionTM/C/IrOx catalyst).
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Jun 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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David C.
Grinter
,
Pilar
Ferrer
,
Federica
Venturini
,
Matthijs A.
Van Spronsen
,
Alexander I.
Large
,
Santosh
Kumar
,
Maximilian
Jaugstetter
,
Alex
Iordachescu
,
Andrew
Watts
,
Sven L. M.
Schroeder
,
Anna
Kroner
,
Federico
Grillo
,
Stephen M.
Francis
,
Paul B.
Webb
,
Matthew
Hand
,
Andrew
Walters
,
Michael
Hillman
,
Georg
Held
Open Access
Abstract: The beamline optics and endstations at branch B of the Versatile Soft X-ray (VerSoX) beamline B07 at Diamond Light Source are described. B07-B provides medium-flux X-rays in the range 45–2200 eV from a bending magnet source, giving access to local electronic structure for atoms of all elements from Li to Y. It has an endstation for high-throughput X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) measurements under ultrahigh-vacuum (UHV) conditions. B07-B has a second endstation dedicated to NEXAFS at pressures from UHV to ambient pressure (1 atm). The combination of these endstations permits studies of a wide range of interfaces and materials. The beamline and endstation designs are discussed in detail, as well as their performance and the commissioning process.
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May 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
B18-Core EXAFS
E02-JEM ARM 300CF
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Longxiang
Liu
,
Liqun
Kang
,
Jianrui
Feng
,
David G.
Hopkinson
,
Christopher S.
Allen
,
Yeshu
Tan
,
Hao
Gu
,
Iuliia
Mikulska
,
Veronica
Celorrio
,
Diego
Gianolio
,
Tianlei
Wang
,
Liquan
Zhang
,
Kaiqi
Li
,
Jichao
Zhang
,
Jiexin
Zhu
,
Georg
Held
,
Pilar
Ferrer
,
David
Grinter
,
June
Callison
,
Martin
Wilding
,
Sining
Chen
,
Ivan
Parkin
,
Guanjie
He
Diamond Proposal Number(s):
[30614, 32058, 32035, 32117, 33466, 29271]
Open Access
Abstract: Electrochemical hydrogen peroxide (H2O2) production (EHPP) via a two-electron oxygen reduction reaction (2e- ORR) provides a promising alternative to replace the energy-intensive anthraquinone process. M-N-C electrocatalysts, which consist of atomically dispersed transition metals and nitrogen-doped carbon, have demonstrated considerable EHPP efficiency. However, their full potential, particularly regarding the correlation between structural configurations and performances in neutral media, remains underexplored. Herein, a series of ultralow metal-loading M-N-C electrocatalysts are synthesized and investigated for the EHPP process in the neutral electrolyte. CoNCB material with the asymmetric Co-C/N/O configuration exhibits the highest EHPP activity and selectivity among various as-prepared M-N-C electrocatalyst, with an outstanding mass activity (6.1 × 105 A gCo−1 at 0.5 V vs. RHE), and a high practical H2O2 production rate (4.72 mol gcatalyst−1 h−1 cm−2). Compared with the popularly recognized square-planar symmetric Co-N4 configuration, the superiority of asymmetric Co-C/N/O configurations is elucidated by X-ray absorption fine structure spectroscopy analysis and computational studies.
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May 2024
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