B18-Core EXAFS
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Nivetha
Jeyachandran
,
Wangchao
Yuan
,
Xiang
Li
,
Akshayini
Muthuperiyanayagam
,
Stefania
Gardoni
,
Jiye
Feng
,
Qingsheng
Gao
,
Martin
Wilding
,
Peter
Wells
,
Devis
Di Tommaso
,
Cristina
Giordano
Diamond Proposal Number(s):
[29721]
Open Access
Abstract: The rising levels of CO2 have spurred growing concerns for our environment, and curbing CO2 emissions may not be practically viable with the expanding human population. One attractive strategy is the electrochemical CO2 reduction (CO2RR) into value added chemicals but because of the chemical inertness of the CO2 molecule, the electrochemical reduction requires a suitable catalyst. Cu-based catalysts have been largely investigated for CO2RR, however, the difficulty achieving a high selectivity and faradaic efficiency towards specific products, especially hydrocarbons, is still a challenge, alongside the concern over cost, stability and scarcity of the metal catalyst. The present research focuses on tuning the crystallinity of Cu nanoparticles via a green, cost-friendly, and facile method, called the urea glass route. Remarkably, the incorporation of a selected nitrogen-carbon rich source (namely, 4,5 dicyanoimidazole) at low temperatures allow the formation of an oxidized derived amorphous Cu system, whilst a second thermal treatment enables the transformation to crystalline Cu0. We found that the combination of surface Cu0 and Cu1+ (observed via XPS studies) present in our amorphous and crystalline Cu nanoparticles leads to interesting differences in the final catalytic activity when tested under CO2 reaction conditions. The combination of extended X-ray absorption fine structure (EXAFS) experiments and molecular dynamics simulations provides compelling evidence for the amorphous and metallic nature of Cu nanoparticles.
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Dec 2024
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[20568]
Open Access
Abstract: Nanostructured materials can be utilised as potential catalysts for the production of platform chemicals and renewable biofuels from biomass derived molecules. The formation of hierarchical meso-microporous zeolites LTL and FAU via the surfactant assisted tandem acid-base post-synthesis treatment has been investigated by time-resolved in situ synchrotron SAXS and WAXS, providing a new insight into the mechanism of the mesostructuring treatment. Based on the results of TEM and in situ synchrotron measurements, a model for the formation of the core-shell structure of LTL zeolite crystals is proposed. Complementary evaluation using FTIR, NMR and nitrogen adsorption, in conjunction with reaction studies on mesostructured zeolites, demonstrated a potential for enhanced catalytic performance of these materials owing to the increased accessibility of the active sites and reduced transport limitations.
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Oct 2024
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Biao
He
,
Pouya
Hosseini
,
Daniel
Escalera-López
,
Jonas
Schulwitz
,
Olaf
Rudiger
,
Ulrich
Hagemann
,
Markus
Heidelmann
,
Serena
Debeer
,
Martin
Muhler
,
Serhiy
Cherevko
,
Kristina
Tschulik
,
Tong
Li
Diamond Proposal Number(s):
[28433]
Open Access
Abstract: An atomic-scale understanding of how electrocatalyst surfaces reconstruct and transform during electrocatalytic reactions is essential for optimizing their activity and longevity. This is particularly important for the oxygen evolution reaction (OER), where dynamic and substantial structural and compositional changes occur during the reaction. Herein, a multimodal method is developed by combining X-ray fine structure absorption and photoemission spectroscopy, transmission electron microscopy, and atom probe tomography with electrochemical measurements to interrogate the temporal evolution of oxidation states, atom coordination, structure, and composition on Co2MnO4 and CoMn2O4 cubic spinel nanoparticle surfaces upon OER cycling in alkaline media. Co2MnO4 is activated at the onset of OER due to the formation of ≈2 nm Co-Mn oxyhydroxides with an optimal Co/Mn ratio of ≈3. As OER proceeds, Mn dissolution and redeposition occur for the CoMn oxyhydroxides, extending the OER stability of Co2MnO4. Such dynamic dissolution and redeposition are also observed for CoMn2O4, leading to the formation of less OER-active Mn-rich oxides on the nanoparticle surfaces. This study provides mechanistic insights into how dynamic surface reconstruction and transformation affect the activity and stability of mixed CoMn cubic spinels toward OER.
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Oct 2024
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I14-Hard X-ray Nanoprobe
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Open Access
Abstract: Background: Electrochemical devices such as fuel cells and electrolysers enable chemical and energy transformations that are required to help achieve net-zero targets by 2050. One of the emerging technologies is electrochemical reduction of CO2 into value-added products, such as carbon monoxide, formic acid and ethylene. [1] The best performing cathode catalyst for producing ethylene and other C2+ products in a CO2 electrolyser is oxide-derived copper (OD-Cu), which is metallic coper formed in situ via reduction of a copper oxide-based electrode in the electrolyser. The activity of OD-Cu tends to be significantly higher than that of similar Cu catalysts that have been reduced ex situ prior to being incorporated into the electrolyser, which suggests that additional or superior active sites are generated during the in situ electrochemical reduction [2]. In addition, the catalyst can experience significant structural changes under CO2 electroreduction conditions [3]. Obtaining structure- performance relationships of copper requires in situ characterization, which is due to the surface oxidation and possible restructuring the metal experiences when exposed to open circuit potential and air during disassembly of the electrochemical cell. In situ characterisation imaging techniques such as XAS and XRF are therefore a crucial step to capture the active catalyst formation and the morphology dynamics under electrochemical conditions. These techniques suffer from lower spatial resolution, which limits the level of understanding of the underlaying dynamics for reactions involving gases or liquids. This motivated our investigation of the hypothesis that specific conditions of thermal reduction experiments can led to the Cu structures formed under electrochemical conditions. In this way, a higher spatially-resolved analysis could be done by extrapolation from gas-phase investigation. Methods: In this work we present in-situ TEM gas phase thermal reduction experiments of CuO samples and correlate them with in-situ liquid phase electrochemical reduction of CuO samples carried out on the i14 nanoprobe beamline (Diamond Light Source). Synchrotron-based spectroscopy techniques, such as X-ray absorption spectroscopy (XAS) and X-ray fluorescence spectroscopy (XRF) are very powerful methods to study the chemical nature of the catalyst under relevant conditions [4]. Combining the i14 nanoprobe beamline(down to 50 nm resolution) with aberration corrected electron microscopy (Å resolution) allows to use spatially resolved XRF imaging to study morphology and dynamics in a liquid biasing environment and link it to gas-phase experiments on the nanoscale. Results/Conclusion: We will show the benefit of combining these techniques to reveal the effect of the thermal reduction on the CuO particles (morphology / oxidation state) through a combination of in- situ STEM imaging and EELS versus the electrochemical reduction as revealed by the in-situ liquid cell i14 XRF/XANES experiment (Figure 1). We will also address the challenges with liquid biasing experiments such as beam-induced damage, especially to the ionomer that is commonly present in catalyst layers (e.g. Nafion), and challenges involved with sample preparation.
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Oct 2024
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I14-Hard X-ray Nanoprobe
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Kyle
Frohna
,
Cullen
Chosy
,
Amran
Al-Ashouri
,
Florian
Scheler
,
Yu-Hsien
Chiang
,
Milos
Dubajic
,
Julia E.
Parker
,
Jessica M.
Walker
,
Lea
Zimmermann
,
Thomas A.
Selby
,
Yang
Lu
,
Bart
Roose
,
Steve
Albrecht
,
Miguel
Anaya
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[30427, 31964]
Open Access
Abstract: Microscopy provides a proxy for assessing the operation of perovskite solar cells, yet most works in the literature have focused on bare perovskite thin films, missing charge transport and recombination losses present in full devices. Here we demonstrate a multimodal operando microscopy toolkit to measure and spatially correlate nanoscale charge transport losses, recombination losses and chemical composition. By applying this toolkit to the same scan areas of state-of-the-art, alloyed perovskite cells before and after extended operation, we show that devices with the highest macroscopic performance have the lowest initial performance spatial heterogeneity—a crucial link that is missed in conventional microscopy. We show that engineering stable interfaces is critical to achieving robust devices. Once the interfaces are stabilized, we show that compositional engineering to homogenize charge extraction and to minimize variations in local power conversion efficiency is critical to improve performance and stability. We find that in our device space, perovskites can tolerate spatial disorder in chemistry, but not charge extraction.
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Oct 2024
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B18-Core EXAFS
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Diamond Proposal Number(s):
[29913]
Open Access
Abstract: To bridge the gap between oxygen reduction electrocatalysts development and their implementation in real proton exchange membrane fuel cell electrodes, an important aspect to be understood is the interaction between the carbon support, the active sites, and the proton conductive ionomer as it greatly affects the local transportations to the catalyst surface. Here we show that three Pt/C catalysts, synthesized using the polyol method with different carbon supports (low surface area Vulcan, high surface area Ketjenblack, and biomass-derived highly ordered mesoporous carbon), revealed significant variations in ionomer-catalyst interactions. The Pt/C catalysts supported on ordered mesoporous carbon derived from biomass showed the best performance under the gas diffusion electrode configuration. Through a unique approach of operando X-ray Absorption Spectroscopy combined with gas sorption analysis, we were able to demonstrate the beneficial effect of mesopore presence for optimal ionomer-catalyst interaction at both molecular and structural level.
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Oct 2024
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Abstract: Hydrocarbons such as gasoline and short olefins are among the most important chemical raw materials in industry. They are used as energy sources and to power most means of transport and machines worldwide. For a long time, these chemicals were produced almost exclusively in the petrochemical industry. However, the over-exploitation of these resources has led to various environmental problems and has been shown to play a crucial role in greenhouse gas emissions into the atmosphere. As a possible environmentally friendly alternative, hydrocarbons can also be synthesized through the catalytic reduction of CO2 with green H2. This process has the great advantage that the CO2 can be used as a raw material. It is particularly attractive if the CO2 is extracted directly from the atmosphere in order to generate a neutral CO2 cycle.
This work deals with the characterization of iron-based catalysts for the hydrogenation of CO2 to hydrocarbons. In particular, a combination of real catalysts (powder catalysts) and flat model catalysts (planar catalysts) is used. The advantage of such an approach is that surface science tools and methods can be used in addition to the conventional methods commonly used to characterize catalysts. The reason for this work is the numerous contradictions regarding the parameters controlling the catalytic performance of CO2 hydrogenation with Fe-based catalysts. My goal is to gain a better understanding of the fundamental behavior of the active catalytic Fe phase for the CO2 hydrogenation reaction. For this purpose, a combination of operando, in situ and ex situ characterizations are carried out and correlated with the catalytic performance of the various catalysts produced. Particular attention was paid to in situ surface characterization using X-ray photoelectron spectroscopy (NAP-XPS) and operando characterization using X-ray absorption spectroscopy (XAS).
The first part of this work addresses the role of the oxide support in the catalytic performance of Fe-based nanoparticles. It is shown how the traditionally considered inert substrates (Al2O3 and SiO2) alter the selectivity of small Fe nanoparticles during CO2 hydrogenation. The selectivity changes depending on the substrate are associated with the interaction and influence of the carrier on the Fe nanoparticles and how the carrier defines the chemical state of the active Fe phase. The second section focuses on how the size of Fe nanoparticles affects the catalytic performance in CO2 hydrogenation. In particular, the size of the Fe nanoparticles influences the reducibility of the Fe precursors during the activation of the catalyst and thus directly affects the chemical state of the Fe under the reaction conditions. In this way, it determines the observed catalytic performance. This work ends by linking both effects in Fe-based catalysts (size and support effects) as they are coupled with each other. In summary, my work shows that the catalytic performance of Fe-based materials is highly dependent on parameters such as their support and the size of the nanoparticles. This results in a deeper understanding of the complex behaviors of these Fe-based systems described in the literature.
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Oct 2024
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[30315]
Open Access
Abstract: Thin-film solar cells based on Cu2Zn(Sn1−X,GeX)S4 (CZTGS) absorbers are emerging technologies for solar energy conversion with low-cost, nontoxic components. In this work, we investigated CZTGS-based solar cells with varying Ge contents and an alternative buffer layer of Zn1–XSnXOY (ZTO) by atomic layer deposition. The results are compared to those of devices with the traditional CdS buffer layer. Overall, higher efficiency and open-circuit voltage (VOC) are observed for the devices with ZTO compared to those with the CdS buffer layer. Moreover, the results show that the CZTGS/ZTO device performance may further be improved by varying the ZTO properties (band gap or thickness) or by applying a surface treatment on the CZTGS absorber. An air annealing treatment of the chemically etched absorber surface improved the CZTGS device performance; however, nonetched devices show poor efficiency due to the presence of secondary phases (GeO2) at the absorber/buffer interface, shown by hard X-ray photoelectron spectroscopy measurements, as previously reported for the full-germanium Cu2ZnGeS4-based devices.
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Oct 2024
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[30461]
Abstract: Pushed and pulled by competing interactions, molecules can self-assemble into complex structures. Using supramolecular self-assembly, we can synthesise materials with unique structures and function. However, predicting how molecules will assemble themselves, and controlling the reaction conditions to nudge them into forming a desirable structure, is challenging. Using porous cage molecules as building blocks for larger structures is an attractive prospect. Using a hierarchical approach embeds cage molecules and their useful properties into more complex structures with new functions. However, predicting and controlling the synthesis process becomes increasingly difficult. A team of researchers from the University of Liverpool, Herriot-Watt University, Imperial College London, the University of Southampton and East China University of Science and Technology has developed a hierarchical cage molecule that can adsorb other molecules, like carbon dioxide and sulfur hexafluoride. A key aspect of the project was using computer modelling to accurately predict how the precursor molecules would self-assemble into a new material. Their work, recently published in Nature Synthesis, suggests that computational predictions backed up by experimental studies could be a successful strategy for yielding more complex and interesting materials in the future.
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Oct 2024
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B18-Core EXAFS
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Abstract: The increasing population and the global warming are motivating the transition from fossil fuel-based energy supply chain to a renewable sources-based one. Hydrogen production plays a major role in technologies for renewable energy. Urea oxidation reaction (UOR) has garnered significant attention in recent years as a promising and sustainable clean-energy technology. Urea-containing wastewater poses severe threats to the environment and human health. Numerous studies hence focus on developing UOR as a viable process for simultaneously remediating wastewater and produce hydrogen. Moreover, UOR, which has a thermodynamic potential of 0.37 V (Vs reversible hydrogen electrode, RHE), shows great promise in replacing the energy- intensive oxygen evolution reaction (OER, 1.23 Vs RHE). Since UOR entails a complex intermediate adsorption/desorption process, many studies are devoted to designing cost-effective and efficient catalysts. Notably, Nickel-based materials have demonstrated significant potential for the UOR process. In this thesis work, nickel hydroxide has been chosen as catalyst with the objective of preparing it from Ni-containing wastewater in the future in collaboration with Circular Materials s.r.l. In this thesis, however, the materials have been synthetized in the laboratory to better control their properties and be able to extract more consistent conclusions. Manganese (1.55) and molybdenum (2.16) have been selected as doping elements, considering their different electronegativity respect to nickel (1.91), and their effect on the UOR performance has been studied. Manganese is less expensive and more ecofriendly than the commonly used cobalt (1.88). Iron (1.83) is even cheaper than Mn but it was not selected since it is known that improves the OER but not the UOR. Molybdenum was selected for its high electronegativity since it was found that, in metal fluoride, the strong electronegativity of F makes the metal in the electron deficiency state, which can promote the high valence state of metal species and, therefore, promote urea oxidation. This materials were characterized with techniques such as, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray absorption (XAS) and X-ray photoelectron spectroscopy (XPS). They have been tested as UOR catalysts in alkaline solution. Nickel phosphide-based catalysts have been also obtained from the phosphorization of the nickel-based hydroxide materials. The nickel phosphide-based catalysts have been characterized using the same techniques previously mentioned. These materials have been then tested as HER and UOR catalysts. In general for all the materials, the presence of the second metal increased the activity. In UOR and OER measurements, Nickel phosphide-based samples reached higher current densities than the corresponding nickel hydroxide-based materials. For the nickel-hydroxide based-materials, the samples containing molybdenum showed a better performance during UOR than the ones containing manganese. While for the nickel-phosphide based materials it was the opposite. The foreign element did not have any effects on the activity towards the HER for the NiP-based samples. More negative on set values and low current densities were obtained.
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Oct 2024
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