B18-Core EXAFS
E01-JEM ARM 200CF
|
Ruoyu
Xu
,
Liqun
Kang
,
Konstantinos G.
Papanikolaou
,
Bolun
Wang
,
Sushila
Marlow
,
Qian
He
,
Peng
Zhang
,
Jianfang
Wang
,
Dan J. I.
Brett
,
Michail
Stamatakis
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[20643, 19318, 19246, 19072, 20629]
Open Access
Abstract: Proton exchange membrane fuel cells require oxygen reduction catalysts with high activity and stability. Pt based alloy materials are most widely applied ORR catalyst due to its high intrinsic activity, but usually suffer from rapid deactivation as a result of particle agglomeration, detachment, Ostwald ripening and/or Pt dissolution. Here we investigate the degradation of the PdPt alloys via in situ X-ray absorption fine structure, Δμ analysis, identical location-electron microscopy and DFT calculations. We conclude that the origin of high activity and stability of the PdPt catalyst stems from the oxidation resistance of metallic Pt, forming mainly surface adsorbed O species at high potentials. Two stage degradation process are observed, showing an evolution of dynamic surface dependent ORR performance along with the deactivation process. The careful design of Pt alloy structure leads to controlled surface oxygen behaviours. This opens a new way to increase the lifespan of fuel cells and improve the Pt utilization efficiency.
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Nov 2022
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
B18-Core EXAFS
E01-JEM ARM 200CF
|
Xuze
Guan
,
Rong
Han
,
Hiroyuki
Asakura
,
Zhipeng
Wang
,
Siyuan
Xu
,
Bolun
Wang
,
Liqun
Kang
,
Yiyun
Liu
,
Sushila
Marlow
,
Tsunehiro
Tanaka
,
Yuzheng
Guo
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[23759, 24450, 29094, 24197]
Open Access
Abstract: Surface oxidation chemistry involves the formation and breaking of metal–oxygen (M–O) bonds. Ideally, the M–O bonding strength determines the rate of oxygen absorption and dissociation. Here, we design reactive bridging O2– species within the atomic Cu–O–Fe site to accelerate such oxidation chemistry. Using in situ X-ray absorption spectroscopy at the O K-edge and density functional theory calculations, it is found that such bridging O2– has a lower antibonding orbital energy and thus weaker Cu–O/Fe–O strength. In selective NH3 oxidation, the weak Cu–O/Fe–O bond enables fast Cu redox for NH3 conversion and direct NO adsorption via Cu–O–NO to promote N–N coupling toward N2. As a result, 99% N2 selectivity at 100% conversion is achieved at 573 K, exceeding most of the reported results. This result suggests the importance to design, determine, and utilize the unique features of bridging O2– in catalysis.
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Nov 2022
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B18-Core EXAFS
E01-JEM ARM 200CF
|
Zhangxiang
Hao
,
Jie
Chen
,
Xuekun
Lu
,
Liqun
Kang
,
Chun
Tan
,
Ruoyu
Xu
,
Lixia
Yuan
,
Dan J.l.
Brett
,
Paul R.
Shearing
,
Feng Ryan
Wang
,
Yunhui
Huang
Diamond Proposal Number(s):
[19072, 19246]
Open Access
Abstract: Despite progress of functionalized separator in preventing the shuttle effect and promoting the sulfur utilization, the precise and non-destructive investigation of structure-function-performance associativity remains limited so far in Li-S batteries. Here, we build consecutive multiscale analysis via combining X-ray absorption fine structure (XAFS) and X-ray computational tomography (CT) techniques to precisely visit the structure-function-performance relationship. XAFS measurement offers the atomic scale changes in the chemical structure and environment. Moreover, a non-destructive technique of X-ray CT proves the functionalized separator role for microscopic scale, which is powerful chaining to bridge the chemical structures of the materials with the overall performance modulation of cells. Benefiting from this consecutive multiscale analysis, we report that the uniform doping of Sr2+ into the perovskite LaMnO3-δ material changes the Mn oxidation states and conductivity (chemical structure), leading to effective lithium polysulfide trapping and accelerated sulfur redox (separator function), and resulting in outstanding cell performance.
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Apr 2022
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B18-Core EXAFS
E01-JEM ARM 200CF
E02-JEM ARM 300CF
|
Diamond Proposal Number(s):
[16966, 17559, 18909, 19246, 19318, 20643, 20847, 17377, 15151, 14239]
Abstract: First discovered in the 19th century, RuII compounds are widely used in catalysis, photocatalysis, and medical applications. They are
usually obtained in a reductive environment, as molecular oxygen can oxidise RuII to RuIII and RuIV. Researchers designed an air‐stable
II
Ru site that is coordinated on the polyphenylene-bipyridine (PPhen-bipy) based system. The team used the electron Physical Science
Imaging Centre (ePSIC) at Diamond Light Source to confirm the presence of Ru single-site. They performed their study at atomic resolution with High Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM). X-ray Absorption Spectroscopy (XAS) at Ru K-edge carried out at beamline B18 followed the evolution of the geometric structures of the Ru single-site during CO oxidation.
In addition, the HAADF-STEM study confirmed the successful synthesis of eight other metal single-sites coordinated with the PPhen-bipy framework. Those single-sites have well-defined geometric and electronic structures for catalytic applications. Such single-site catalysts exhibit great potential in life sciences and the pharmaceutical industry. The PPhen-bipy framework also enables the study of coordination chemistry at solid/gas interface, helping to understand structure-performance relationship of the surface single-sites.
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Jul 2021
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
E01-JEM ARM 200CF
|
Zhangxiang
Hao
,
Junrun
Feng
,
Yiyun
Liu
,
Liqun
Kang
,
Bolun
Wang
,
Junwen
Gu
,
Lin
Sheng
,
Ruoyu
Xu
,
Sushila
Marlow
,
Dan J.l.
Brett
,
Yunhui
Huang
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[22572, 21641, 22604, 26717, 29407]
Abstract: Polymer materials offer controllable structure-dependent performances in separation, catalysis and drug release. Their molecular structures can be precisely tailored to accept Li+ for energy storage applications. Here the design of sp2 carbon-based polyphenylene (PPH) with high lithium-ion uptakes and long-term stability is reported. Linear-PPH (L-PPH) exceeds the performance of crosslink-PPH (C-PPH), due to the fact that it has an ordered lamellar structure, promoting the Li+ intercalation/deintercalation channel. The L-PPH cell shows a clear charge and discharge plateau at 0.35 and 0.15 V vs. Li+/Li, respectively, which is absent in the C-PPH cell. The Li+ storage capacity of L-PPH is five times that of the C-PPH. The reversible storage capacity is further improved to 261 mAh g−1 by functionalizing the L-PPH with the –SO3H groups. In addition, the Li-intercalated structures of C-PPH and L-PPH are investigated via near-edge X-ray absorption fine structure (NEXAFS), suggesting the high reversible Li+ - C=C bond interaction at L-PPH. This strategy, based on new insight into sp2 functional groups, is the first step toward a molecular understanding of the structure storage-capacity relationship in sp2 carbon-based polymer.
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Jul 2021
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B18-Core EXAFS
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Siyu
Zhao
,
Ruikuan
Xie
,
Liqun
Kang
,
Manni
Yang
,
Xingyu
He
,
Wenyao
Li
,
Ryan
Wang
,
Dan J. L.
Brett
,
Guanjie
He
,
Guoliang
Chai
,
Ivan P.
Parkin
Diamond Proposal Number(s):
[19850]
Open Access
Abstract: It remains a challenge to develop efficient electrocatalysts in neutral media for hydrogen evolution reaction (HER) due to the sluggish kinetics and switch of the rate determining step. Although metal phosphides are widely used HER catalysts, their structural stability is an issue due to oxidization, and the HER performance in neutral media requires improvement. Herein, a new material, i.e., grapevine‐shaped N‐doped iron phosphide on carbon nanotubes, as an efficient HER catalyst in neutral media is developed. The optimized catalyst shows an overpotential of 256 mV at a large current density of 65 mA cm−2, which is even 10 mV lower than that of the commercial 20% Pt/C catalyst. The excellent performance of the catalyst is further studied by combined computational and experimental techniques, which proves that the interaction between nitrogen and iron phosphides can provide more efficient active structures and stabilize the metal phosphide electrocatalysts for HER.
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May 2021
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|
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Liqun
Kang
,
Bolun
Wang
,
Andreas T.
Güntner
,
Siyuan
Xu
,
Xuhao
Wan
,
Yiyun
Liu
,
Sushila
Marlow
,
Yifei
Ren
,
Diego
Gianolio
,
Chiu C.
Tang
,
Vadim
Murzin
,
Hiroyuki
Asakura
,
Qian
He
,
Shaoliang
Guan
,
Juan J.
Velasco-Vélez
,
Sotiris E.
Pratsinis
,
Yuzheng
Guo
,
Feng Ryan
Wang
Open Access
Abstract: Electronic metal‐support interaction (EMSI) describes the electron flow between metal sites and a metal oxide support. It is generally used to follow the mechanism of redox reactions. In the study of CuO‐CeO2 redox, an additional flow of electron from metallic Cu to surface carbon species is observed via a combination of operando X‐ray absorption spectroscopy, synchrotron X‐ray powder diffraction, near ambient pressure‐near edge X‐ray absorption fine structure, and diffuse reflectance infrared Fourier transform spectroscopy. An electronic metal‐support‐carbon interaction (EMSCI) is proposed to explain the reaction pathway of CO oxidation. The EMSCI provides a complete picture of the mass and electron flow, which will help predict and improve the catalytic performance in the selective activation of CO2 , carbonate or carbonyl species in C1 chemistry.
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Mar 2021
|
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E01-JEM ARM 200CF
|
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
E02-JEM ARM 300CF
|
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
|
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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