B18-Core EXAFS
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Diamond Proposal Number(s):
[22152]
Abstract: Fe–N–C aerogel catalysts were prepared by sol–gel polycondensation of resorcinol, melamine and formaldehyde precursors in the presence of FeCl3 salt, followed by supercritical drying and thermal treatments. The effect of the mass ratio of precursors on the microstructure, iron speciation and oxygen reduction reaction (ORR) performance of the Fe–N–C aerogels was investigated by N2 sorption, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, X-ray absorption spectroscopy, CO chemisorption and rotating disk electrode in acidic medium. The best ORR performance (activity and mass transport) was obtained by an optimum balance between pore structure and active Fe-Nx species. Through acid washing, the durability of the catalyst was further improved by eliminating unstable and inactive species, particularly iron nanoparticles and iron carbide. From the CO chemisorption and turnover-frequency value, the surface sites were comparable with the highest values reported in literature. Finally, Fe–N–C aerogel catalyst was implemented a in membrane–electrode assembly with an active area of 25 cm2 and tested in single cell, emphasizing the importance of the ink formulation on the performance.
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Dec 2021
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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E.
Arias-Egido
,
M. A.
Laguna-Marco
,
C.
Piquer
,
P.
Jimenez-Cavero
,
I.
Lucas
,
L.
Morellon
,
F.
Gallego
,
A.
Rivera-Calzada
,
M.
Cabero
,
J.
Santamaría
,
G.
Fabbris
,
D.
Haskel
,
R.
Boada
,
S.
Diaz-Moreno
Diamond Proposal Number(s):
[17266]
Open Access
Abstract: A metal–insulator transition is observed in spin–orbit-coupled IrO2 thin films upon reduction of the film thickness. In the epitaxially grown samples, the critical thickness (t ∼ 1.5–2.2 nm) is found to depend on growth orientation (001), (100) or (110). Interestingly from the applied point of view, the insulating behavior is found even in polycrystalline ultrathin films. By analyzing the experimental electrical response with various theoretical models, we find good fits to the Efros–Shklovskii-VRH and the Arrhenius-type behaviors, which suggests an important role of electron correlations in determining the electrical properties of IrO2. Our magnetic measurements also point to a significant role of magnetic order. Altogether, our results would point to a mixed Slater- and Mott-type of insulator.
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Oct 2021
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Open Access
Abstract: Perovskite-inspired materials aim to replicate the optoelectronic performance of lead-halide perovskites, while eliminating issues with stability and toxicity. Chalcohalides of group IV/V elements have attracted attention due to enhanced stability provided by stronger metal-chalcogen bonds, alongside compositional flexibility and ns2 lone pair cations – a performance-defining feature of halide perovskites. Following the experimental report of solution-grown tin-antimony sulfoiodide (Sn2SbS2I3) solar cells, with power conversion efficiencies above 4%, we assess the structural and electronic properties of this emerging photovoltaic material. We find that the reported centrosymmetric Cmcm crystal structure represents an average over multiple polar Cmc21 configurations. The instability is confirmed through a combination of lattice dynamics and molecular dynamics simulations. We predict a large spontaneous polarisation of 37 μC cm−2 that could be active for electron–hole separation in operating solar cells. We further assess the radiative efficiency limit of this material, calculating ηmax > 30% for film thicknesses t > 0.5 μm.
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Oct 2021
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I19-Small Molecule Single Crystal Diffraction
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Guopeng
Han
,
Andrij
Vasylenko
,
Alex R.
Neale
,
Benjamin B.
Duff
,
Ruiyong
Chen
,
Matthew S.
Dyer
,
Yun
Dang
,
Luke
Daniels
,
Marco
Zanella
,
Craig
Robertson
,
Laurence J.
Kershaw Cook
,
Anna-Lena
Hansen
,
Michael
Knapp
,
Laurence J.
Hardwick
,
Frédéric
Blanc
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Diamond Proposal Number(s):
[21726]
Open Access
Abstract: Extended anionic frameworks based on condensation of polyhedral main group non-metal anions offer a wide range of structure types. Despite the widespread chemistry and earth abundance of phosphates and silicates, there are no reports of extended ultraphosphate anions with lithium. We describe the lithium ultraphosphates Li3P5O14 and Li4P6O17 based on extended layers and chains of phosphate, respectively. Li3P5O14 presents a complex structure containing infinite ultraphosphate layers with 12-membered rings that are stacked alternately with lithium polyhedral layers. Two distinct vacant tetrahedral sites were identified at the end of two distinct finite Li6O1626– chains. Li4P6O17 features a new type of loop-branched chain defined by six PO43– tetrahedra. The ionic conductivities and electrochemical properties of Li3P5O14 were examined by impedance spectroscopy combined with DC polarization, NMR spectroscopy, and galvanostatic plating/stripping measurements. The structure of Li3P5O14 enables three-dimensional lithium migration that affords the highest ionic conductivity (8.5(5) × 10–7 S cm–1 at room temperature for bulk), comparable to that of commercialized LiPON glass thin film electrolytes, and lowest activation energy (0.43(7) eV) among all reported ternary Li–P–O phases. Both new lithium ultraphosphates are predicted to have high thermodynamic stability against oxidation, especially Li3P5O14, which is predicted to be stable to 4.8 V, significantly higher than that of LiPON and other solid electrolytes. The condensed phosphate units defining these ultraphosphate structures offer a new route to optimize the interplay of conductivity and electrochemical stability required, for example, in cathode coatings for lithium ion batteries.
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Oct 2021
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[26551]
Open Access
Abstract: For sodium-ion batteries, two pressing issues concerning electrolytes are flammability and compatibility with hard carbon anode materials. Non-flammable electrolytes that are sufficiently stable against hard carbon have—to the authors’ knowledge—previously only been obtained by either the use of high salt concentrations or additives. Herein, the authors present a simple, fluorine-free, and flame-retardant electrolyte which is compatible with hard carbon: 0.38 m sodium bis(oxalato)borate (NaBOB) in triethyl phosphate (TEP). A variety of techniques are employed to characterize the physical properties of the electrolyte, and to evaluate the electrochemical performance in full-cell sodium-ion batteries. The results reveal that the conductivity is sufficient for battery operation, no significant self-discharge occurs, and a satisfactory passivation is enabled by the electrolyte. In fact, a mean discharge capacity of 107 ± 4 mAh g−1 is achieved at the 1005th cycle, using Prussian white cathodes and hard carbon anodes. Hence, the studied electrolyte is a promising candidate for use in sodium-ion batteries.
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Oct 2021
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E02-JEM ARM 300CF
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Jingjing
Liu
,
Zhichao
Gong
,
Christopher
Allen
,
Wen
Ge
,
Haisheng
Gong
,
Jiangwen
Liao
,
Jianbin
Liu
,
Kang
Huang
,
Minmin
Yan
,
Rui
Liu
,
Guanchao
He
,
Juncai
Dong
,
Gonglan
Ye
,
Huilong
Fei
Diamond Proposal Number(s):
[27260]
Abstract: Metal- and nitrogen-coordinated nanocarbons (M-N/Cs) represent the most promising nonprecious catalysts for the oxygen reduction reaction (ORR), but it remains challenging to simultaneously achieve high intrinsic activity, fast mass transport, and efficient utilization of active sites in a single catalyst. Herein, we design an Fe-N/C catalyst consisting of edge-hosted Fe-N3 sites dispersed on multiscale porous carbon frameworks (eFe-N3/PCF). The low coordination and edge effect of the Fe-N3 moieties endow eFe-N3/PCF with high intrinsic activity, while the enriched nanopores enable improved mass transport and atom utilization efficiency. When evaluated by a rotating disk electrode in the base, eFe-N3/PCF presents early-onset and half-wave potentials of 1.090 and 0.934 V versus the reversible hydrogen electrode, respectively. Furthermore, when employed as gas diffusion electrodes, eFe-N3/PCF displays excellent mass-transport efficiency that enables high-rate/power capabilities at practically high current densities. This work opens up opportunities for designing high-performance ORR electrocatalysts toward applications in diverse energy conversion and storage technologies.
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Oct 2021
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I07-Surface & interface diffraction
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Shuai
Yuan
,
Lin-Song
Cui
,
Linjie
Dai
,
Yun
Liu
,
Qing-Weii
Liu
,
Yu-Qi
Sun
,
Florian
Auras
,
Miguel
Anaya
,
Xiaopeng
Zheng
,
Edoardo
Ruggeri
,
You-Jun
Yu
,
Yang-Kun
Qu
,
Mojtaba
Abdi-Jalebi
,
Osman M.
Bakr
,
Zhao-Kui
Wang
,
Samuel D.
Stranks
,
Neil C.
Greenham
,
Liang-Sheng
Liao
,
Richard H.
Friend
Diamond Proposal Number(s):
[17223]
Open Access
Abstract: Metal halide perovskite semiconductors have demonstrated remarkable potentials in solution-processed blue light-emitting diodes (LEDs). However, the unsatisfied efficiency and spectral stability responsible for trap-mediated non-radiative losses and halide phase segregation remain the primary unsolved challenges for blue perovskite LEDs. In this study, it is reported that a fluorene-based π-conjugated cationic polymer can be blended with the perovskite semiconductor to control film formation and optoelectronic properties. As a result, sky-blue and true-blue perovskite LEDs with Commission Internationale de l'Eclairage coordinates of (0.08, 0.22) and (0.12, 0.13) at the record external quantum efficiencies of 11.2% and 8.0% were achieved. In addition, the mixed halide perovskites with the conjugated cationic polymer exhibit excellent spectral stability under external bias. This result illustrates that π-conjugated cationic polymers have a great potential to realize efficient blue mixed-halide perovskite LEDs with stable electroluminescence.
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Sep 2021
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B18-Core EXAFS
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Abstract: The recent report of P2–Na2/3Mg0.28Mn0.72O2 (P2-NMM) demonstrated the possibility of utilizing the oxygen redox couple in a layered oxide cathode without the need for alkali ions or vacancies in the transition metal layer. In this work, we report the synthesis of a new P2-type compound, Na2/3Mg1/4Mn7/12Co1/6O2 (P2-NMMC), which exhibits reversible specific capacities as high as 173 mAh g−1 and an improvement of the first cycle voltage hysteresis over P2-NMM. The material was characterised using a combination of ex-situ and operando techniques including X-ray diffraction (XRD), differential electrochemical mass spectrometry (DEMS) and X-ray spectroscopy (XAS) to identify potential sources for this improvement.
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Sep 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[23125]
Open Access
Abstract: In modern Li-based batteries, alloying anode materials have the potential to drastically improve the volumetric and specific energy storage capacity. For the past decade silicon has been viewed as a “Holy Grail” among these materials; however, severe stability issues limit its potential. Herein, we present amorphous substoichiometric silicon nitride (SiNx) as a convertible anode material, which allows overcoming the stability challenges associated with common alloying materials. Such material can be synthesized in a form of nanoparticles with seamlessly tunable chemical composition and particle size and, therefore, be used for the preparation of anodes for Li-based batteries directly through conventional slurry processing. Such SiNx materials were found to be capable of delivering high capacity that is controlled by the initial chemical composition of the nanoparticles. They exhibit an exceptional cycling stability, largely maintaining structural integrity of the nanoparticles and the complete electrodes, thus delivering stable electrochemical performance over the course of 1000 charge/discharge cycles. Such stability is achieved through the in situ conversion reaction, which was herein unambiguously confirmed by pair distribution function analysis of cycled SiNx nanoparticles revealing that active silicon domains and a stabilizing Li2SiN2 phase are formed in situ during the initial lithiation.
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Sep 2021
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I14-Hard X-ray Nanoprobe
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Sofiia
Kosar
,
Andrew J.
Winchester
,
Tiarnan A. S.
Doherty
,
Stuart
Macpherson
,
Christopher E.
Petoukhoff
,
Kyle
Frohna
,
Miguel
Anaya
,
Nicholas S.
Chan
,
Julien
Madéo
,
Michael K. L.
Man
,
Samuel D.
Stranks
,
Keshav M.
Dani
Diamond Proposal Number(s):
[19023]
Open Access
Abstract: With rapidly growing photoconversion efficiencies, hybrid perovskite solar cells have emerged as promising contenders for next generation, low-cost photovoltaic technologies. Yet, the presence of nanoscale defect clusters, that form during the fabrication process, remains critical to overall device operation, including efficiency and long-term stability. To successfully deploy hybrid perovskites, we must understand the nature of the different types of defects, assess their potentially varied roles in device performance, and understand how they respond to passivation strategies. Here, by correlating photoemission and synchrotron-based scanning probe X-ray microscopies, we unveil three different types of defect clusters in state-of-the-art triple cation mixed halide perovskite thin films. Incorporating ultrafast time-resolution into our photoemission measurements, we show that defect clusters originating at grain boundaries are the most detrimental for photocarrier trapping, while lead iodide defect clusters are relatively benign. Hexagonal polytype defect clusters are only mildly detrimental individually, but can have a significant impact overall if abundant in occurrence. We also show that passivating defects with oxygen in the presence of light, a previously used approach to improve efficiency, has a varied impact on the different types of defects. Even with just mild oxygen treatment, the grain boundary defects are completely healed, while the lead iodide defects begin to show signs of chemical alteration. Our findings highlight the need for multi-pronged strategies tailored to selectively address the detrimental impact of the different defect types in hybrid perovskite solar cells.
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Sep 2021
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