E01-JEM ARM 200CF
E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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Diamond Proposal Number(s):
[19641, 23232, 26303]
Open Access
Abstract: Synchrotron Fe‐K X‐ray absorption spectroscopy and transmission electron microscopy have been used to investigate the mineralogy and Fe‐redox variations in the space‐weathered (SW) rims of asteroidal samples. This study focuses on the FIB lift‐out sections from five Itokawa grains, returned by the Hayabusa spacecraft, including samples RB‐QD04‐0063, RB‐QD04‐0080, RB‐CV‐0011, RB‐CV‐0089, and RB‐CV‐0148. Each of the samples featured partially amorphized SW rims, caused by irradiation damage from implanted low mass solar wind ions, and the impacting of micrometeorites. Using bright‐field and HAADF‐STEM imaging, vesicular blistering and nanophase Fe metal (npFe0) particles were observed within grain rims, and solar flare tracks were observed in the substrate host grain, confirming the presence of SW zones. We use Fe‐K XANES mapping to investigate Fe‐redox changes between the host mineral and the SW zones. All SW zones measured show some increases in the ferric‐ferrous ratio (Fe3+/ΣFe) relative to their respective host grains, likely the result of the implanted solar wind H+ ions reacting with the segregated ferrous Fe in the surface material.
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Jan 2021
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E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[20643]
Abstract: The magnesium–sulfur (Mg-S) battery may be a safer alternative for the lithium-sulfur battery because Mg plating usually proceeds without dendrite formation. Here, we correlate the thermal runaway of Mg-S battery with the associated change of electrolyte vapour pressure via battery testing calorimetery. Over-pressure builds up along with the programmed heating of the cell, and as a result, the thermal runaway is triggered at 20 to 45 K over the electrolyte boiling point, corresponding to 70 to 150 kPa pressure difference between the cell and the environment. The distinct performance-safety-cost behaviours of three ether type of electrolytes stems from the different CH2CH2O chain lengths. Such molecular insight will serve as a fundamental guideline in choosing and designing the desired electrolyte that simultaneously achieves a high explosion limit and good electrochemical performance.
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Jan 2021
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E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[26190]
Open Access
Abstract: The oxidation of cyclohexane via the in-situ production of H2O2 from molecular H2 and O2 offers an attractive route to the current industrial means of producing cyclohexanone and cyclohexanol (KA oil), key materials in the production of Nylon. The in-situ route has the potential to overcome the significant economic and environmental concerns associated with the use of commercial H2O2, while also allowing for the use of far lower reaction temperatures than those typical of the purely aerobic route to KA oil. Herein we demonstrate the efficacy of a series of bi-functional Pd-based catalysts, which offer appreciable concentrations of KA oil, under conditions where limited activity is observed using O2 alone. In particular the introduction of V into a supported Pd catalyst is seen to improve KA oil concentration by an order of magnitude, compared to the Pd-only analogue. In particular we ascribe this improvement in catalytic performance to the development of Pd domains of mixed oxidation state upon V incorporation as evidenced through X-ray photoelectron spectroscopy.
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Jan 2021
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E01-JEM ARM 200CF
E02-JEM ARM 300CF
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Jian
Guo
,
Liqun
Kang
,
Xuekun
Lu
,
Siyu
Zhao
,
Jianwei
Li
,
Paul R.
Shearing
,
Ryan
Wang
,
Dan J. L.
Brett
,
Guanjie
He
,
Guoliang
Chai
,
Ivan P.
Parkin
Diamond Proposal Number(s):
[22572, 20847]
Abstract: Developing cost-effective and durable air-cathodes is crucial for improving metal-air batteries. Most reports of cathode formulation involve preparing bi-functional electrocatalysts from wet chemistry or solid-state synthesis, followed by pasting onto a substrate. In this work, the cathodes generated from electrochemical activation of normal carbon paper substrates were directly used in Zn-air batteries. The self-activated carbon paper substrate without any additional electrocatalysts exhibits an impressive cycling stability (more than 165 hours for 1,000 cycles) and a small discharge-charge voltage gap. After the activation, the maximum power density and electrochemical surface area were increased by over 40 and 1,920 times respectively. It is discovered that substrates after activation can be directly used as a cathode. The new method is scalable, inexpensive and produces near best in class performance. The mechanism behind this enhancement is due to the creation of oxygen functional groups within the cathode, which overcame slow kinetics, enhanced wettability and enabled optimum three-phase boundaries.
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Dec 2020
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B18-Core EXAFS
E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[15151, 21370, 19246, 22572]
Abstract: Selective transformation of biomass feedstocks to platform molecules is a key pursuit for sustainable chemical production. Compared to petrochemical processes, biomass transformation requires the defunctionalization of highly polar molecules at relatively low temperatures. As a result, catalysts based on functional organic polymers may play a prominent role. Targeting the hydrogenolysis of the platform chemical 5-hydroxymethylfurfural (5-HMF), here, we design a polyphenylene (PPhen) framework with purely sp2-hybridized carbons that can isolate 5-HMF via π–π stacking, preventing hemiacetal and humin formation. With good swellability, the PPhen framework here has successfully supported and dispersed seven types of metal particles via a newly developed swelling-impregnation method, including Ru, Pt, Au, Fe, Co, Ni, and Cu. Ru/PPhen is studied for 5-HMF hydrogenolysis, achieving a 92% yield of 2,5-dimethylfuran (DMF) under mild conditions, outperforming the state-of-the-art catalysts reported in the literature. In addition, PPhen helps perform a solventless reaction, achieving direct 5-HMF to DMF conversion in the absence of any liquid solvent or reagent. This approach in designing support–reactant/solvent/metal interactions will play an important role in surface catalysis.
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Nov 2020
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B18-Core EXAFS
E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[23723, 17198]
Abstract: The general and cost-effective synthesis of single atom electrocatalysts (SAECs) still remains a great challenge. Herein, we report a general synthetic protocol for the synthesis of SAECs via a simple condensation–carbonization process, in which furfural and cyanamide were condensation polymerized in the presence of polystyrene nanospheres and metal ions, followed by a pyrolysis to N-doped carbon nanosheet (NCNS) supported SAECs. Six types of SAECs containing platinum, palladium, gold, nickel, cobalt and iron were synthesized to demonstrate the generality of the synthesis protocol. This methodology affords a facile solution to the trade-off between support conductivity and metal loading of SAECs by optimizing the ratio of carbon/nitrogen precursors, i.e., furfural and cyanamide. The presence of single metal atoms was confirmed by high-angle annular dark field scanning transmission electron microscopy and X-ray absorption fine structure measurements. The three-dimensional distribution of single platinum atoms was vividly revealed by depth profile analysis using a scanning transmission electron microscope. The resulting SAECs showed excellent performance for glycerol electro-oxidation and water splitting in alkaline solutions. Notably, Pt/NCNSs possessed an unprecedent mass-normalized current density of 5.3 A per milligram of platinum, which is 32 times that of the commercial Pt/C catalyst. Density functional theory calculations were conducted to reveal the adsorption behavior of glycerol over the SAECs. Using Ni/NCNSs and Co/NCNSs as anodic and cathodic electrocatalysts, we constructed a solar panel powered electrolytic cell for overall water splitting, leading to an overall energy efficiency of 8.8%, which is among the largest solar-to-hydrogen conversion efficiencies reported in the literature.
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Nov 2020
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E01-JEM ARM 200CF
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Yiding
Jiao
,
Liqun
Kang
,
Jasper
Berry-gair
,
Kit
Mccoll
,
Jianwei
Li
,
Haobo
Dong
,
Hao
Jiang
,
Ryan
Wang
,
Furio
Corà
,
Dan J. L.
Brett
,
Guanjie
He
,
Ivan
Parkin
Diamond Proposal Number(s):
[24450]
Open Access
Abstract: The primary issue faced by MnO2 cathode materials for aqueous Zn-ion batteries (AZIBs) is the occurrence of structural transformations during cycling, resulting in unstable capacity output. Pre-intercalating closely bonded ions into the MnO2 structures has been demonstrated as an effective approach to combat this. However, mechanisms of the pre-intercalation remain unclear. Herein, two distinct δ-MnO2 (K0.28MnO2·0.1H2O and K0.21MnO2·0.1H2O) are prepared with varying amounts of pre-intercalated K+ and applied as cathodes for AZIBs. The as-prepared K0.28MnO2·0.1H2O cathodes exhibit relatively high specific capacity (300 mA h g−1 at 100 mA g−1), satisfactory rate performance (35% capacity recovery at 5 A g−1) and competent cyclability (ca. 95% capacity retention after 1000 cycles at 2 A g−1), while inferior cyclability and rate performance are observed in K0.21MnO2·0.1H2O. A stable δ-MnO2 phase is observed upon cycling, with the reversible deposition of Zn4SO4(OH)6·5H2O (ZSH), ion migration between electrodes and synchronous transition of Mn valence states. This work firstly and systematically reveals the role of the pre-intercalated ions via density functional theory simulations and show that above a threshold K/Mn ratio of ca. 0.26, the K ions suppress structural transformations by stabilizing the δ phase. To demonstrate its commercial potential, AZIBs with high-loading active materials are fabricated, which deliver adequate energy and power densities compared with most commercial devices.
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Nov 2020
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E01-JEM ARM 200CF
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Ruoyu
Xu
,
Jingwei
Xiang
,
Junrun
Feng
,
Xuekun
Lu
,
Zhangxiang
Hao
,
Liqun
Kang
,
Ming
Li
,
Yunsong
Wu
,
Chun
Tan
,
Yiyun
Liu
,
Guanjie
He
,
Dan J. L.
Brett
,
Paul R.
Shearing
,
Lixia
Yuan
,
Yunhui
Huang
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[17559, 19318, 19246, 20643]
Abstract: The lithium-sulfur (Li-S) batteries have high theoretical energy density, exceeding that of the lithium-ion batteries. However, their practical applications are hindered by the capacity decay due to lithium polysulfide shuttle effect and sulfur volume expansion. Here, we design a S@hollow carbon with porous shell/MnOx (S@HCS/MnOx) cathode to accommodate and immobilize sulfur and polysulfides, and develop a non-destructive technique X-ray computed tomography (X-ray CT) to in situ visualize the volume expansion of Li-S cathode. The designed cathode achieves a specific capacity of ~1100 mAh g-1 at 0.2 C with a fade rate of 0.18% per cycle over 300 cycles. The X-ray CT shows that only 16% volume expansion and 70% volume fraction of solid sulfur remaining in the S@HCS/MnOx cathode, superior to the commercial cathode with 40% volume expansion and 5% volume remaining of solid sulfur particles. This is the first reported visualization evidence for the effectiveness of hollow carbon structure in accommodating cathode volume expansion and immobilizing sulfur shuttling. X-ray CT can serve as a powerful in situ tool to trace the active materials and then feedback to the structure design, which helps develop efficient and reliable energy storage systems.
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Oct 2020
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B18-Core EXAFS
E01-JEM ARM 200CF
E02-JEM ARM 300CF
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Liqun
Kang
,
Bolun
Wang
,
Adam
Thetford
,
Ke
Wu
,
Mohsen
Danaie
,
Qian
He
,
Emma
Gibson
,
Ling-dong
Sun
,
Hiroyuki
Asakura
,
Richard
Catlow
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[16966, 17559, 18909, 19246, 19318, 20643, 20847, 17377, 15151, 14239]
Open Access
Abstract: Ru(II) compounds are widely used in catalysis, photocatalysis and medical applications. They are usually obtained in reductive environment as molecular O 2 can oxidize Ru(II) to Ru(III) and Ru(IV). Here we report the design, identification and evolution of an air‐stable surface ‐[bipy‐Ru(II)(CO) 2 Cl 2 ] site that is covalently mounted onto a polyphenylene framework. Such Ru(II) site was obtained by reduction of ‐[bipy‐Ru(III)Cl 4 ] ‐ with simultaneous ligand exchange from Cl ‐ to CO. This structural evolution was witnessed by a combination of in situ X‐ray and infrared spectroscopy studies. The ‐[bipy‐Ru(II)(CO) 2 Cl 2 ] site enables oxidation of CO with a turnover frequency of 0.73 × 10 ‐2 s ‐1 at 462 K, while the Ru(III) site is completely inert. This work contributes to the studies of structure‐activity relationship by demonstrating a practical control over both geometric and electronic structures of single‐site catalysts at molecular level, which can be further applied in other single site catalyst researches.
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Sep 2020
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E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[23221]
Open Access
Abstract: Supported bimetallic nanoparticles (BNPs) are promising catalysts, but study on their compositional and structural changes under reaction conditions remains a challenge. In this work, the structure of PtNi BNPs supported on UiO-67 metal-organic framework (MOF) catalyst (i.e., PtNi@UiO-67) was investigated by in situ by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). The results showed differences in the reduction behaviour of Ni species in PtNi BNPs and monometallic Ni supported on UiO-67 catalysts (i.e., PtNi@UiO-67 and Ni@UiO-67), suggesting charge transfer between metallic Pt and Ni oxides in PtNi@UiO-67. Under CO oxidation conditions, Ni oxides segregated to the outer surface of the BNPs forming a thin layer of NiOx on top of the metallic Pt (i.e., a NiOx-on-Pt structure). This resulted in a core-shell structure which was confirmed by high-resolution scanning transmission electron microscopy (HR-STEM). Accordingly, the layer of NiOx on PtNi BNPs, which is stabilised by charge transfer from metallic Pt, was proposed as the possible active phase for CO oxidation, being responsible for the enhanced catalytic activity observed in the bimetallic PtNi@UiO-67 catalyst.
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Sep 2020
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