B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Jack E. N.
Swallow
,
Elizabeth S.
Jones
,
Ashley R.
Head
,
Joshua S.
Gibson
,
Roey
Ben David
,
Michael W.
Fraser
,
Matthijs A.
Van Spronsen
,
Shaojun
Xu
,
Georg
Held
,
Baran
Eren
,
Robert S
Weatherup
Diamond Proposal Number(s):
[25834]
Open Access
Abstract: The reactions of H2, CO2, and CO gas mixtures on the surface of Cu at 200 °C, relevant for industrial methanol synthesis, are investigated using a combination of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and atmospheric-pressure near edge X-ray absorption fine structure (AtmP-NEXAFS) spectroscopy bridging pressures from 0.1 mbar to 1 bar. We find that the order of gas dosing can critically affect the catalyst chemical state, with the Cu catalyst maintained in a metallic state when H2 is introduced prior to the addition of CO2. Only on increasing the CO2 partial pressure is CuO formation observed that coexists with metallic Cu. When only CO2 is present, the surface oxidizes to Cu2O and CuO, and the subsequent addition of H2 partially reduces the surface to Cu2O without recovering metallic Cu, consistent with a high kinetic barrier to H2 dissociation on Cu2O. The addition of CO to the gas mixture is found to play a key role in removing adsorbed oxygen that otherwise passivates the Cu surface, making metallic Cu surface sites available for CO2 activation and subsequent conversion to CH3OH. These findings are corroborated by mass spectrometry measurements, which show increased H2O formation when H2 is dosed before rather than after CO2. The importance of maintaining metallic Cu sites during the methanol synthesis reaction is thereby highlighted, with the inclusion of CO in the gas feed helping to achieve this even in the absence of ZnO as the catalyst support.
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Mar 2023
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I11-High Resolution Powder Diffraction
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Bixian
Ying
,
Jack R.
Fitzpatrick
,
Zhenjie
Teng
,
Tianxiang
Chen
,
Tsz Woon Benedict
Lo
,
Vassilios
Siozios
,
Claire A.
Murray
,
Helen E. A.
Brand
,
Sarah
Day
,
Chiu C.
Tang
,
Robert S.
Weatherup
,
Peter
Nagel
,
Stefan
Schuppler
,
Martin
Winter
,
Karin
Kleiner
,
Michael
Merz
Diamond Proposal Number(s):
[19772]
Open Access
Abstract: The syntheses of Ni-poor (NCM111, LiNi1/3Co1/3Mn1/3O2) and Ni-rich (NCM811 LiNi0.8Co0.1Mn0.1O2) lithium transition-metal oxides (space group R3̅m) from hydroxide precursors (Ni1/3Co1/3Mn1/3(OH)2, Ni0.8Co0.1Mn0.1(OH)2) are investigated using in situ synchrotron powder diffraction and near-edge X-ray absorption fine structure spectroscopy. The development of the layered structure of these two cathode materials proceeds via two utterly different reaction mechanisms. While the synthesis of NCM811 involves a rock salt-type intermediate phase, NCM111 reveals a layered structure throughout the entire synthesis. Moreover, the necessity and the impact of a preannealing step and a high-temperature holding step are discussed.
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Jan 2023
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[25807]
Open Access
Abstract: Understanding the chemical composition and morphological evolution of the solid electrolyte interphase (SEI) formed at the interface between the lithium metal electrode and an inorganic solid-state electrolyte is crucial for developing reliable all-solid-state lithium batteries. To better understand the interaction between these cell components, we carry out X-ray photoemission spectroscopy (XPS) measurements during lithium plating on the surface of a Li6PS5Cl solid-state electrolyte pellet using an electron beam. The analyses of the XPS data highlight the role of Li plating current density on the evolution of a uniform and ionically conductive (i.e., Li3P-rich) SEI capable of decreasing the electrode∣solid electrolyte interfacial resistance. The XPS findings are validated via electrochemical impedance spectrsocopy measurements of all-solid-state lithium-based cells.
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Nov 2022
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B07-B-Versatile Soft X-ray beamline: High Throughput
I10-Beamline for Advanced Dichroism
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Jack E. N.
Swallow
,
Michael W.
Fraser
,
Nis-Julian H.
Kneusels
,
Jodie F.
Charlton
,
Christopher G.
Sole
,
Conor M. E.
Phelan
,
Erik
Bjorklund
,
Peter
Bencok
,
Carlos
Escudero
,
Virginia
Perez-Dieste
,
Clare P.
Grey
,
Rebecca J.
Nicholls
,
Robert S
Weatherup
Diamond Proposal Number(s):
[25647, 29213, 30816]
Open Access
Abstract: The solid electrolyte interphase (SEI) that forms on Li-ion battery anodes is critical to their long-term performance, however observing SEI formation processes at the buried electrode-electrolyte interface is a significant challenge. Here we show that operando soft X-ray absorption spectroscopy in total electron yield mode can resolve the chemical evolution of the SEI during electrochemical formation in a Li-ion cell, with nm-scale interface sensitivity. O, F, and Si K-edge spectra, acquired as a function of potential, reveal when key reactions occur on high-capacity amorphous Si anodes cycled with and without fluoroethylene carbonate (FEC). The sequential formation of inorganic (LiF) and organic (-(C=O)O-) components is thereby revealed, and results in layering of the SEI. The addition of FEC leads to SEI formation at higher potentials which is implicated in the rapid healing of SEI defects and the improved cycling performance observed. Operando TEY-XAS offers new insights into the formation mechanisms of electrode-electrolyte interphases and their stability for a wide variety of electrode materials and electrolyte formulations.
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Oct 2022
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[21995, 26285]
Abstract: Ni-rich lithium nickel manganese cobalt (NMC) oxide cathode materials promise Li-ion batteries with increased energy density and lower cost. However, higher Ni content is accompanied by accelerated degradation and thus poor cycle lifetime, with the underlying mechanisms and their relative contributions still poorly understood. Here, we combine electrochemical analysis with surface-sensitive X-ray photoelectron and absorption spectroscopies to observe the interfacial degradation occurring in LiNi0.8Mn0.1Co0.1O2–graphite full cells over hundreds of cycles between fixed cell voltages (2.5–4.2 V). Capacity losses during the first ∼200 cycles are primarily attributable to a loss of active lithium through electrolyte reduction on the graphite anode, seen as thickening of the solid-electrolyte interphase (SEI). As a result, the cathode reaches ever-higher potentials at the end of charge, and with further cycling, a regime is entered where losses in accessible NMC capacity begin to limit cycle life. This is accompanied by accelerated transition-metal reduction at the NMC surface, thickening of the cathode electrolyte interphase, decomposition of residual lithium carbonate, and increased cell impedance. Transition-metal dissolution is also detected through increased incorporation into and thickening of the SEI, with Mn found to be initially most prevalent, while the proportion of Ni increases with cycling. The observed evolution of anode and cathode surface layers improves our understanding of the interconnected nature of the degradation occurring at each electrode and the impact on capacity retention, informing efforts to achieve a longer cycle lifetime in Ni-rich NMCs.
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Feb 2022
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[25807]
Abstract: The key charge transfer processes in energy storage devices occur at the electrode-electrolyte interface, which is typically buried making it challenging to access the interfacial chemistry. In the case of Li-ion batteries, metallic Li electrodes hold promise for increasing energy and power densities, and when used in conjunction with solid electrolytes adverse safety implications associated with dendrite formation in organic liquid electrolytes can potentially be overcome. To better understand the stability of solid electrolytes when in contact with alkali metals and the reactions that occur, here we consider the deposition of thin (~10 nm) alkali metal films onto solid electrolyte surfaces, that are thin enough that X-ray photoelectron spectroscopy can probe the buried electrode-electrolyte interface. We highlight the importance of in situ alkali metal deposition, by assessing the contaminant species that are present after glovebox handling and the use of ‘inert’ transfer devices. Consequently, we compare and contrast three available methods for in situ alkali-metal deposition; Li sputter deposition, Li evaporation, and Li plating induced by e− flood-gun irradiation. Studies on both a sulphide solid electrolyte (Li6PS5Cl), and a single-layer graphene probe surface reveal that the more energetic Li deposition methods such as sputtering can induce surface damage and interfacial mixing that is not seen with thermal evaporation. This indicates that appropriate selection of the Li deposition method for in situ studies is required to observe representative behaviour, and the results of previous studies involving energetic deposition may warrant further evaluation.
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Jan 2022
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Abstract: X-ray photoelectron and absorption spectroscopies can provide valuable interface-sensitive chemical information; however, they are traditionally performed under ultra-high vacuum conditions to maximize the inelastic mean free path of photoelectrons and attenuation lengths of X-rays. Developments in the field, including electron analyzers coupled with sophisticated differentially pumped lenses, have made it possible to extend these techniques to liquid and gas environments (up to tens of mbar). Enclosed environmental cells are an alternative approach that promises access to atmospheric pressures and above, and the potential for low-cost and widespread deployment by incorporation into standard X-ray photoelectron spectroscopy systems. In this chapter we discuss the progress made in the development of such enclosed environmental cells for X-ray spectroscopies. We focus on the main requirements to perform these measurements, including discussion of the implementation of X-ray and photoelectron transparent membranes, common reaction cell designs and materials, and the methods of detection typically employed. We also present some landmark examples which mark progress in this area up to now, before providing an outlook for the topic as a whole.
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Nov 2021
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Diamond Proposal Number(s):
[21925]
Abstract: Rechargeable Mg-ion batteries typically suffer from either rapid passivation of the Mg anode or severe corrosion of the current collectors by halogens within the electrolyte, limiting their practical implementation. Here, we demonstrate the broadly applicable strategy of forming an artificial solid electrolyte interphase (a-SEI) layer on Mg to address these challenges. The a-SEI layer is formed by simply soaking Mg foil in a tetraethylene glycol dimethyl ether solution containing LiTFSI and AlCl3, with Fourier transform infrared and ultraviolet–visible spectroscopy measurements revealing spontaneous reaction with the Mg foil. The a-SEI is found to mitigate Mg passivation in Mg(TFSI)2/DME electrolytes with symmetric cells exhibiting overpotentials that are 2 V lower compared to when the a-SEI is not present. This approach is extended to Mg(ClO4)2/DME and Mg(TFSI)2/PC electrolytes to achieve reversible Mg plating and stripping, which is not achieved with bare electrodes. The interfacial resistance of the cells with a-SEI protected Mg is found to be two orders of magnitude lower than that with bare Mg in all three of the electrolytes, indicating the formation of an effective Mg-ion transporting interfacial structure. X-ray absorption and photoemission spectroscopy measurements show that the a-SEI contains minimal MgCO3, MgO, Mg(OH)2, and TFSI–, while being rich in MgCl2, MgF2, and MgS, when compared to the passivation layer formed on bare Mg in Mg(TFSI)2/DME.
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May 2021
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Ye
Fan
,
Kenichi
Nakanishi
,
Vlad P.
Veigang-Radulescu
,
Ryo
Mizuta
,
J. Callum
Stewart
,
Jack E. N.
Swallow
,
Alice E.
Dearle
,
Oliver J.
Burton
,
Jack A.
Alexander-Webber
,
Pilar
Ferrer
,
Georg
Held
,
Barry
Brennan
,
Andrew J.
Pollard
,
Robert S
Weatherup
,
Stephan
Hofmann
Diamond Proposal Number(s):
[22123]
Open Access
Abstract: We find that the use of Au substrate allows fast, self-limited WS2 monolayer growth using a simple sequential exposure pattern of low cost, low toxicity precursors, namely tungsten hexacarbonyl and dimethylsulfide (DMS). We use this model reaction system to fingerprint the technologically important metal organic chemical vapour deposition process by operando X-ray photoelectron spectroscopy (XPS) to address the current lack of understanding of the underlying fundamental growth mechanisms for WS2 and related transition metal dichalcogenides. Au effectively promotes the sulfidation of W with simple organosulfides, enabling WS2 growth with low DMS pressure (<1 mbar) and a suppression of carbon contamination of as-grown WS2, which to date has been a major challenge with this precursor chemistry. Full WS2 coverage can be achieved by one exposure cycle of 10 minutes at 700 °C. We discuss our findings in the wider context of previous literature on heterogeneous catalysis, 2D crystal growth, and overlapping process technologies such as atomic layer deposition (ALD) and direct metal conversion, linking to future integrated manufacturing processes for transition metal dichalcogenide layers.
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Oct 2020
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Diamond Proposal Number(s):
[19299]
Abstract: Methanol is a promising chemical for the safe and efficient storage of hydrogen, where methanol conversion reactions can generate a hydrogen-containing gas mixture. Understanding the chemical state of the catalyst over which these reactions occur and the interplay with the adsorbed species present is key to the design of improved catalysts and process conditions. Here we study polycrystalline Cu foils using ambient pressure X-ray spectroscopies to reveal the Cu oxidation state and identify the adsorbed species during partial oxidation (CH3OH + O2), steam reforming (CH3OH + H2O), and autothermal reforming (CH3OH + O2 + H2O) of methanol at 200 °C surface temperature and in the mbar pressure range. We find that the Cu surface remains highly metallic throughout partial oxidation and steam reforming reactions, even for oxygen-rich conditions. However, for autothermal reforming the Cu surface shows significant oxidation towards Cu2O. We rationalise this behaviour on the basis of the shift in equilibrium of the CH3OH* + O* ⇌ CH3O* + OH* caused by the addition of H2O.
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Mar 2020
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