E01-JEM ARM 200CF
|
Diamond Proposal Number(s):
[33314]
Open Access
Abstract: Rigorous comparisons between single site- and nanoparticle (NP)-dispersed catalysts featuring the same composition, in terms of activity, selectivity, and reaction mechanism, are limited. This limitation is partly due to the tendency of single metal atoms to sinter into aggregated NPs at high loadings and elevated temperatures, driven by a decrease in metal surface free energy. Here, we have developed a unique two-step method for the synthesis of single Cu sites on ZSM-5 (termed CuS/ZSM-5) with high thermal stability. The atomic-level dispersion of single Cu sites was confirmed through scanning transmission electron microscopy, X-ray absorption fine structure (XAFS), and electron paramagnetic resonance spectroscopy. The CuS/ZSM-5 catalyst was compared to a CuO NP-based catalyst (termed CuN/ZSM-5) in the oxidation of NH3 to N2, with the former exhibiting superior activity and selectivity. Furthermore, operando XAFS and diffuse reflectance infrared Fourier transform spectroscopy studies were conducted to simultaneously assess the fate of the Cu and the surface adsorbates, providing a comprehensive understanding of the mechanism of the two catalysts. The study shows that the facile redox behavior exhibited by single Cu sites correlates with the enhanced activity observed for the CuS/ZSM-5 catalyst.
|
Jul 2024
|
|
B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
B18-Core EXAFS
E02-JEM ARM 300CF
|
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.
|
May 2024
|
|
E02-JEM ARM 300CF
I11-High Resolution Powder Diffraction
|
Kan
Ma
,
Thomas
Blackburn
,
Johan P.
Magnussen
,
Michael
Kerbstadt
,
Pedro A.
Ferreiros
,
Tatu
Pinomaa
,
Christina
Hofer
,
David G.
Hopkinson
,
Sarah J.
Day
,
Paul A. J.
Bagot
,
Michael P.
Moody
,
Mathias C.
Galetz
,
Alexander J.
Knowles
Diamond Proposal Number(s):
[32708, 32309]
Open Access
Abstract: Chromium alloys are being considered for next-generation concentrated solar power applications operating > 800 °C. Cr offers advantages in melting point, cost, and oxidation resistance. However, improvements in mechanical performance are needed. Here, Cr-based body-centred-cubic (bcc) alloys of the type Cr(Fe)-NiAl are investigated, leading to ‘bcc-superalloys’ comprising a bcc-Cr(Fe) matrix (β) strengthened by ordered-bcc NiAl intermetallic precipitates (β’), with iron additions to tailor the precipitate volume fraction and mechanical properties at high temperatures. Computational design using CALculation of PHAse Diagram (CALPHAD) predicts that Fe increases the solubility of Ni and Al, increasing precipitate volume fraction, which is validated experimentally. Nano-scale, highly-coherent B2-NiAl precipitates with lattice misfit ∼ 0.1% are formed in the Cr(Fe) matrix. The Cr(Fe)-NiAl A2-B2 alloys show remarkably low coarsening rate (∼102 nm3/h at 1000 °C), outperforming ferritic-superalloys, cobalt- and nickel-based superalloys. Low interfacial energies of ∼ 40/20 mJ/m2 at 1000/1200 °C are determined based on the coarsening kinetics. The low coarsening rates are principally attributed to the low solubility of Ni and Al in the Cr matrix. The alloys show high compressive yield strength of ∼320 MPa at 1000 °C. The Fe-modified alloy exhibits resistance to age softening, related to the low coarsening rate as well as the relatively stable Orowan strengthening as a function of precipitate radius. Microstructure tailoring with Fe additions offers a new design route to improve the balance of properties in “Cr-superalloys”, accelerating their development as a new class of high-temperature materials.
|
Jul 2023
|
|
B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
E02-JEM ARM 300CF
|
Longxiang
Liu
,
Liqun
Kang
,
Arunabhiram
Chutia
,
Jianrui
Feng
,
Martyna
Michalska
,
Pilar
Ferrer
,
David
Grinter
,
Georg
Held
,
Yeshu
Tan
,
Fangjia
Zhao
,
Fei
Guo
,
David
Hopkinson
,
Christopher
Allen
,
Yanbei
Hou
,
Junwen
Gu
,
Ioannis
Papakonstantinou
,
Paul
Shearing
,
Dan
Brett
,
Ivan P.
Parkin
,
Guanjie
He
Diamond Proposal Number(s):
[29340, 32501, 30614, 29809, 32058]
Open Access
Abstract: The electrochemical synthesis of hydrogen peroxide (H2O2) via a two-electron (2e-) oxygen reduction reaction (ORR) process provides a promising alternative to replace the energy-intensive anthraquinone process. However, the development of efficient electrocatalysts is still facing lots of challenges like insufficient understanding of active sites. Herein, we develop a facile template-protected strategy to synthesize a highly active quinone-rich porous carbon catalyst (PCC) for H2O2 electrochemical production. The optimized PCC900 exhibits unprecedented activity and selectivity, of which the onset potential reaches 0.83 V vs. reversible hydrogen electrode in 0.1 M KOH and the H2O2 selectivity is over 95 % in a wide potential range. Comprehensive synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) spectroscopy combined with electrocatalytic characterizations reveals the positive correlation between quinone content and 2e- ORR performance. The effectiveness of chair-form quinone groups as the most efficient active sites is highlighted by the molecule-mimic strategy and theoretical analysis.
|
Mar 2023
|
|
E02-JEM ARM 300CF
|
Yi-Chao
Zou
,
Lucas
Mogg
,
Nick
Clark
,
Cihan
Bacaksiz
,
Slavisa
Milanovic
,
Vishnu
Sreepal
,
Guang-Ping
Hao
,
Yi-Chi
Wang
,
David G.
Hopkinson
,
Roman
Gorbachev
,
Samuel
Shaw
,
Kostya S.
Novoselov
,
Rahul
Raveendran-Nair
,
Francois M.
Peeters
,
Marcelo
Lozada-Hidalgo
,
Sarah
Haigh
Diamond Proposal Number(s):
[21981, 21597]
Abstract: The physical properties of clays and micas can be controlled by exchanging ions in the crystal lattice. Atomically thin materials can have superior properties in a range of membrane applications, yet the ion-exchange process itself remains largely unexplored in few-layer crystals. Here we use atomic-resolution scanning transmission electron microscopy to study the dynamics of ion exchange and reveal individual ion binding sites in atomically thin and artificially restacked clays and micas. We find that the ion diffusion coefficient for the interlayer space of atomically thin samples is up to 104 times larger than in bulk crystals and approaches its value in free water. Samples where no bulk exchange is expected display fast exchange at restacked interfaces, where the exchanged ions arrange in islands with dimensions controlled by the moiré superlattice dimensions. We attribute the fast ion diffusion to enhanced interlayer expandability resulting from weaker interlayer binding forces in both atomically thin and restacked materials. This work provides atomic scale insights into ion diffusion in highly confined spaces and suggests strategies to design exfoliated clay membranes with enhanced performance.
|
Aug 2021
|
|
E02-JEM ARM 300CF
|
Diamond Proposal Number(s):
[19315, 21597]
Abstract: Suspended specimens of 2D crystals and their heterostructures are required for a range of studies including transmission electron microscopy (TEM), optical transmission experiments and nanomechanical testing. However, investigating the properties of laterally small 2D crystal specimens, including twisted bilayers and air sensitive materials, has been held back by the difficulty of fabricating the necessary clean suspended samples. Here we present a scalable solution which allows clean free-standing specimens to be realized with 100% yield by dry-stamping atomically thin 2D stacks onto a specially developed adhesion-enhanced support grid. Using this new capability, we demonstrate atomic resolution imaging of defect structures in atomically thin CrBr3, a novel magnetic material which degrades in ambient conditions.
|
Aug 2020
|
|
E02-JEM ARM 300CF
|
Astrid
Weston
,
Yichao
Zou
,
Vladimir
Enaldiev
,
Alex
Summerfield
,
Nicholas
Clark
,
Viktor
Zólyomi
,
Abigail
Graham
,
Celal
Yelgel
,
Samuel
Magorrian
,
Mingwei
Zhou
,
Johanna
Zultak
,
David
Hopkinson
,
Alexei
Barinov
,
Thomas H.
Bointon
,
Andrey
Kretinin
,
Neil R.
Wilson
,
Peter H.
Beton
,
Vladimir I.
Fal’ko
,
Sarah J.
Haigh
,
Roman
Gorbachev
Diamond Proposal Number(s):
[19315, 21597]
Abstract: Van der Waals heterostructures form a unique class of layered artificial solids in which physical properties can be manipulated through controlled composition, order and relative rotation of adjacent atomic planes. Here we use atomic-resolution transmission electron microscopy to reveal the lattice reconstruction in twisted bilayers of the transition metal dichalcogenides, MoS2 and WS2. For twisted 3R bilayers, a tessellated pattern of mirror-reflected triangular 3R domains emerges, separated by a network of partial dislocations for twist angles θ < 2°. The electronic properties of these 3R domains, featuring layer-polarized conduction-band states caused by lack of both inversion and mirror symmetry, appear to be qualitatively different from those of 2H transition metal dichalcogenides. For twisted 2H bilayers, stable 2H domains dominate, with nuclei of a second metastable phase. This appears as a kagome-like pattern at θ ≈ 2°, transitioning at θ → 0 to a hexagonal array of screw dislocations separating large-area 2H domains. Tunnelling measurements show that such reconstruction creates strong piezoelectric textures, opening a new avenue for engineering of 2D material properties.
|
May 2020
|
|
E02-JEM ARM 300CF
|
Jonas
Bekaert
,
Ekaterina
Khestanova
,
David G.
Hopkinson
,
John
Birkbeck
,
Nick
Clark
,
Mengjian
Zhu
,
Denis
Bandurin
,
Roman
Gorbachev
,
Simon
Fairclough
,
Yichao
Zou
,
Matthew
Hamer
,
Daniel J.
Terry
,
Jonathan J. P.
Peters
,
Ana M.
Sanchez
,
Bart
Partoens
,
Sarah
Haigh
,
Milorad
Milosevic
,
Irina V.
Grigorieva
Diamond Proposal Number(s):
[19315, 21597]
Abstract: When approaching the atomically thin limit, defects and disorder play an increasingly important role in the properties of two-dimensional materials. While defects are generally thought to negatively affect superconductivity in 2D materials, here we demonstrate the contrary in the case of oxygenation of ultrathin tantalum disulfide (TaS2). Our first-principles calculations show that incorporation of oxygen into the TaS2 crystal lattice is energetically favourable and effectively heals sulfur vacancies typically present in these crystals, thus restoring the electronic band structure and the carrier density to the intrinsic characteristics of TaS2. Strikingly, this leads to a strong enhancement of the electron-phonon coupling, by up to 80% in the highly-oxygenated limit. Using transport measurements on fresh and aged (oxygenated) few-layer TaS2, we found a marked increase of the superconducting critical temperature (Tc) upon aging, in agreement with our theory, while concurrent electron microscopy and electron-energy loss spectroscopy confirmed the presence of sulfur vacancies in freshly prepared TaS2 and incorporation of oxygen into the crystal lattice with time. Our work thus reveals the mechanism by which certain atomic-scale defects can be beneficial to superconductivity and opens a new route to engineer Tc in ultrathin materials.
|
Apr 2020
|
|
E02-JEM ARM 300CF
|
David G.
Hopkinson
,
Viktor
Zólyomi
,
Aidan P.
Rooney
,
Nick
Clark
,
Daniel J.
Terry
,
Matthew
Hamer
,
David J.
Lewis
,
Christopher S.
Allen
,
Angus I.
Kirkland
,
Yury
Andreev
,
Zakhar
Kudrynskyi
,
Zakhar
Kovalyuk
,
Amalia
Patanè
,
Vladimir I.
Fal'Ko
,
Roman
Gorbachev
,
Sarah
Haigh
Diamond Proposal Number(s):
[16892, 17837]
Abstract: GaSe and InSe are important members of a class of 2D materials, the III-VI metal monochalcogenides, which are attracting considerable attention due to their promising electronic and optoelectronic properties. Here an investigation of point and extended atomic defects formed in mono-, bi-, and few-layer GaSe and InSe crystals is presented. Using state-of-the-art scanning transmission electron microscopy (STEM), it is observed that these materials can form both metal and selenium vacancies under the action of the electron beam. Selenium vacancies are observed to be healable; recovering the perfect lattice structure in the presence of selenium or enabling incorporation of dopant atoms in the presence of impurities. Under prolonged imaging, multiple point defects are observed to coalesce to form extended defect structures, with GaSe generally developing trigonal defects and InSe primarily forming line defects. These insights into atomic behavior could be harnessed to synthesize and tune the properties of 2D post transition metal monochalcogenide materials for optoelectronic applications.
|
Apr 2019
|
|
