Our scientists’ new work on finding a solution to the parallax problem in X-ray scattering/diffraction experiments has been published in a new paper, “DLSR: a solution to the parallax artefact in X‐ray diffraction computed tomography data,” published in the Journal of Applied Crystallography.
The work was performed in collaboration with the creator of the TOPAS software Alan Coelho, DESY, UCL Chemistry, ESRF and SciML.
A new tomographic reconstruction algorithm is presented, termed direct least‐squares reconstruction (DLSR), which solves the well known parallax problem in X‐ray‐scattering‐based experiments. The parallax artefact arises from relatively large samples where X‐rays, scattered from a scattering angle 2gθ, arrive at multiple detector elements. This phenomenon leads to loss of physico‐chemical information associated with diffraction peak shape and position (i.e. altering the calculated crystallite size and lattice parameter values, respectively) and is currently the major barrier to investigating samples and devices at the centimetre level (scale‐up problem). The accuracy of the DLSR algorithm has been tested against simulated and experimental X‐ray diffraction computed tomography data using the TOPAS software.
This will allow upscaling chemical tomography techniques to study large samples.
Read the full article at https://doi.org/10.1107/S1600576720013576
The research was carried out in collaboration with Dr Thomas Heenan from the Electrochemical Innovation Lab (EIL) at UCL Chemical Engineering, UCL Chemistry and ESRF.
The solid oxide fuel cell (SOFC) anode is often composed of nickel (Ni) and yttria-stabilized zirconia (YSZ). The yttria is added in small quantities (e.g., 8 mol %) to maintain the crystallographic structure throughout the operating temperatures (e.g., room-temperature to >800 °C). The YSZ skeleton provides a constraining structural support that inhibits degradation mechanisms such as Ni agglomeration and thermal expansion miss-match between the anode and electrolyte layers. Within this structure, the Ni is deposited in the oxide form and then reduced during start-up; however, exposure to oxygen (e.g., during gasket failure) readily re-oxidizes the Ni back to NiO, impeding electrochemical performance and introducing complex structural stresses. In this work, we correlate lab-based X-ray computed tomography using zone plate focusing optics, with X-ray synchrotron diffraction computed tomography to explore the crystal structure of a partially re-oxidized Ni/NiO-YSZ electrode. These state-of-the-art techniques expose several novel findings: non-isotropic YSZ lattice distributions; the presence of monoclinic zirconia around the oxidation boundary; and metallic strain complications in the presence of variable yttria content. This work provides evidence that the reduction–oxidation processes may destabilize the YSZ structure, producing monoclinic zirconia and microscopic YSZ strain, which has implications upon the electrode’s mechanical integrity and thus lifetime of the SOFC.
Read the article at https://www.mdpi.com/2073-4352/10/10/941
Our latest work on the characterisation of NMC electodes used in Li-ion batteries at the PCCP has been published in a new paper, “Exploring cycling induced crystallographic change in NMC with X-ray diffraction computed tomography” in the journal Physical Chemistry Chemical Physics.
The research was carried out in collaboration with the Electrochemical Innovation Lab (EIL) from the UCL Chemical Engineering, Johnson Matthey, the Faraday Institution, NREL, UCL Chemistry and ESRF.
This study presents the application of X-ray diffraction computed tomography for the first time to analyze the crystal dimensions of LiNi0.33Mn0.33Co0.33O2 electrodes cycled to 4.2 and 4.7 V in full cells with graphite as negative electrodes at 1 μm spatial resolution to determine the change in unit cell dimensions as a result of electrochemical cycling. The nature of the technique permits the spatial localization of the diffraction information in 3D and mapping of heterogeneities from the electrode to the particle level. An overall decrease of 0.4% and 0.6% was observed for the unit cell volume after 100 cycles for the electrodes cycled to 4.2 and 4.7 V. Additionally, focused ion beam-scanning electron microscope cross-sections indicate extensive particle cracking as a function of upper cut-off voltage, further confirming that severe cycling stresses exacerbate degradation. Finally, the technique facilitates the detection of parts of the electrode that have inhomogeneous lattice parameters that deviate from the bulk of the sample, further highlighting the effectiveness of the technique as a diagnostic tool, bridging the gap between crystal structure and electrochemical performance.
Read the full article at https://doi.org/10.1039/D0CP01851A
Synchrotron X-ray diffraction computed tomography (XRD-CT) is a marriage between powder diffraction and computed tomography using a “pencil” beam approach. The spatially-resolved signals obtained with XRD-CT can reveal information that would otherwise be lost in bulk measurements, which opens up new possibilities in functional material characterization.
In this webinar, our research scientist Dr. Antony Vamvakeros presented results from key case studies where he and the team applied XRD-CT to track the evolving solid-state chemistry of complex functional materials and devices under operating conditions. The webinar also focussed on the recent technical advances in data acquisition, treatment and handling strategies, as well as bottlenecks/limitations of the technique and the potential routes to overcome them.
For more information and to watch the webinar visit – https://www.dectris.com/landing-pages/dectris-application-webinar-series-2020/
You can see our latest work on X-ray tomographic diffraction imaging of operating dense ceramic hollow-fibre catalytic membrane reactors (CMRs) – “Real-time tomographic diffraction imaging of catalytic membrane reactors for the oxidative coupling of methane” in Catalysis Today. The paper is a result of a collaboration between scientists at UCL Chemistry, Finden, ESRF, VITO and ISIS Neutron and Muon Source.
- Synchrotron X-ray diffraction computed tomography applied to three packed bed catalytic membrane reactors.
- The solid-state evolution of catalysts and membranes is tracked under operating conditions.
- A new crystal structure model of BaCo0.4Fe0.4Zr0.2O3-δ (BCFZ) is suggested and used for the diffraction data analysis
Catalytic membrane reactors have the potential to render the process of oxidative coupling of methane economically viable. Here, the results from operando XRD-CT studies of three different catalytic membrane reactors, employing BaCo0.4Fe0.4Zr0.2O3-δ (BCFZ) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) perovskite membranes with Mn-Na-W/SiO2 and La-promoted Mn-Na-W/SiO2 catalysts, are presented. It is shown that synchrotron X-ray tomographic diffraction imaging allows the extraction of spatially-resolved diffraction information from the interior of these working catalytic membrane reactors and makes it possible to capture the evolving solid-state chemistry of their components under various operating conditions (i.e. temperature and chemical environment).
Read the paper at https://doi.org/10.1016/j.cattod.2020.05.045
Our Chief Scientific Officer Prof. Andrew Beale gave a webinar for the UK Catalysis Hub discussing opportunities for studying catalytic materials with intense radiation sources; what, where, when and how.
It was in 1836 that Jöns Jacob Berzelius provided the first, basic description of a catalyst and its properties. Both the breadth and depth of our understanding of catalysts and catalytic processes has clearly progressed a lot since then – to a large extent this has been enabled by catalyst characterisation, performed increasingly in real time as the catalyst performs its function. Despite these developments, designing a catalyst/catalytic process from scratch is still incredibly difficult. Fortunately, characterisation methods, particularly those using bright light sources (i.e. X-rays, Lasers etc.) and ways in which catalysts & catalytic process can be interrogated are constantly evolving. In this webinar Prof. Andrew Beale discussed some recent exciting studies performed by his group and others and explained how the wider catalysis community can engage with and benefit from such developments. He concluded with an overview of some of the planned technical developments on the horizon and suggested where there might be future possibilities for researchers on the quest to unravel the secrets behind what makes a catalyst work?
The webinar featured a presentation from Prof. Andrew Beale of 40 minutes, followed by a Q & A session. Visit https://ukcatalysishub.co.uk/webinar-prof-andrew-beale-professor-of-inorganic-chemistry-dept-of-chemistry-ucl-finden-ltd/ to watch this webinar for free now.
Our latest work using multi-length scale chemical tomography to study fixed bed reactors during the oxidative coupling of methane reaction has just been published at the Journal of Catalysis. “Real-time multi-length scale chemical tomography of fixed bed reactors during the oxidative coupling of methane reaction” is a result of a collaboration between scientists at UCL, Finden, ESRF, Diamond Light Source, Research Complex at Harwell, ISIS Neutron and Muon Source, University of Manchester, Boreskov Institute of Catalysis SB RAS and VITO.
In this work, we present the results from multi-length-scale studies of a Mn-Na-W/SiO2 and a La-promoted Mn-Na-W/SiO2 catalyst during the oxidative coupling of methane reaction. The catalysts were investigated from the reactor level (mm scale) down to the single catalyst particle level (μm scale) with different synchrotron X-ray chemical computed tomography techniques (multi-modal chemical CT experiments). These operando spatially-resolved studies performed with XRD-CT (catalytic reactor) and multi-modal μ-XRF/XRD/absorption CT (single catalyst particle) revealed the multiple roles of the La promoter and how it provides the enhancement in catalyst performance. It is also shown that non-crystalline Mn species are part of the active catalyst component rather than crystalline Mn2O3/Mn7SiO12 or MnWO4.
Our scientists’ new work on the evolving solid-state chemistry in secondary LiMn2O4 (LMO) particles during lithiation and its impact on the performance of the electrode has been published in a new paper, “Spatial quantification of dynamic inter and intra particle crystallographic heterogeneities within lithium ion electrodes” in Nature Communications.
The work was performed with Donal Finegan from the National Renewable Energy Laboratory and in collaboration with a team from the Electrochemical Innovation Lab (EIL) from UCL Chemical Engineering using ESRF’s ID15A beamline.
The performance of lithium ion electrodes is hindered by unfavorable chemical heterogeneities that pre-exist or develop during operation. Time-resolved spatial descriptions are needed to understand the link between such heterogeneities and a cell’s performance. Here, operando high-resolution X-ray diffraction-computed tomography is used to spatially and temporally quantify crystallographic heterogeneities within and between particles throughout both fresh and degraded LixMn2O4 electrodes. This imaging technique facilitates identification of stoichiometric differences between particles and stoichiometric gradients and phase heterogeneities within particles. Through radial quantification of phase fractions, the response of distinct particles to lithiation is found to vary; most particles contain localized regions that transition to rock salt LiMnO2 within the first cycle. Other particles contain monoclinic Li2MnO3 near the surface and almost pure spinel LixMn2O4 near the core. Following 150 cycles, concentrations of LiMnO2and Li2MnO3 significantly increase and widely vary between particles.
Finegan, D.P., Vamvakeros, A., Tan, C. et al. Spatial quantification of dynamic inter and intra particle crystallographic heterogeneities within lithium ion electrodes. Nat Commun 11, 631 (2020).
Read the full article at https://doi.org/10.1038/s41467-020-14467-x
A new paper by our former PhD student Dorota Matras and partners from MEMERE project has been accepted in the Faraday Discussions.
In this study, we investigate the effect of thermal treatment/calcination on the stability and activity of a Na-Mn-W/SiO2 catalyst for the oxidative coupling of methane reaction. The catalyst performance and characterisation measurements suggest that the W species are directly involved in the catalyst active site responsible for CH4 conversion. Under operating conditions, the active components, present in the form of Na-W-O-Mn molten state, are highly mobile and volatile. By varying the parameters of the calcination protocol, it was shown that these molten components can be partially stabilised, resulting in a catalyst with lower activity (due to loss of surface area) but higher stability even for long duration OCM reaction experiments.
Read the full paper at https://doi.org/10.1039/C9FD00142E
Our scientists’ new work on Si-graphite electrodes used for Li-ion battery applications with high resolution in situ X-ray chemical imaging has been published in a new paper, “Spatially Resolving Lithiation in Silicon–Graphite Composite Electrodes via in Situ High-Energy X-ray Diffraction Computed Tomography” in Nano Letters. The work was performed with Donal Finegan from the National Renewable Energy Laboratory and in collaboration with a team from the Electrochemical Innovation Lab (EIL) from UCL Chemical Engineering using ESRF’s ID15A beamline.
Optimizing the chemical and morphological parameters of lithium-ion (Li-ion) electrodes is extremely challenging, due in part to the absence of techniques to construct spatial and temporal descriptions of chemical and morphological heterogeneities. In this work, we present the first demonstration of combined high-speed X-ray diffraction (XRD) and XRD computed tomography (XRD-CT) to probe, in 3D, crystallographic heterogeneities within Li-ion electrodes with a spatial resolution of 1 μm. The local charge-transfer mechanism within and between individual particles was investigated in a silicon(Si)−graphite composite electrode. High-speed XRD revealed charge balancing kinetics between the graphite and Si during the minutes following the transition from operation to open circuit. Subparticle lithiation heterogeneities in both Si and graphite were observed using XRD-CT, where the core and shell structures were segmented, and their respective diffraction patterns were characterized.
Read more about it at https://www.esrf.eu/home/news/spotlight/content-news/spotlight/spotlight346.html
Read the article at https://pubs.acs.org/doi/full/10.1021/acs.nanolett.9b00955
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