Single atom Cu-N-C catalysts for the electro-reduction of CO_(2) to CO assessed by rotating ring-disc electrode

The electrochemical CO_(2) reduction reaction(CO_(2)RR) to controllable chemicals is considered as a promising pathway to store intermittent renewable energy. Herein, a set of catalysts based on copper-nitrogendoped carbon xerogel(Cu-N-C) are successfully developed varying the copper amount and the nature of the copper precursor, for the efficient CO_(2)RR. The electrocatalytic performance of Cu-N-C materials is assessed by a rotating ring-disc electrode(RRDE), technique still rarely explored for CO_(2)RR. For comparison, products are also characterized by online gas chromatography in a H-cell. The as-synthesized Cu-NC catalysts are found to be active and highly CO selective at low overpotentials(from -0.6 to -0.8 V vs.RHE) in 0.1 M KHCO_(3), while H_(2) from the competitive water reduction appears at larger overpotentials(-0.9 V vs. RHE). The optimum copper acetate-derived catalyst containing Cu-N_(4) moieties exhibits a CO_(2)-to-CO turnover frequency of 997 h^(-1) at -0.9 V vs. RHE with a H_(2)/CO ratio of 1.8. These results demonstrate that RRDE configuration can be used as a feasible approach for identifying electrolysis products from CO_(2)RR.

聚吡咯-过渡金属-氧配合物储锂材料的结构与性能研究

目前锂离子电池电极材料主要使用无机材料.近年来有机物电极材料虽有报道,但这些材料大都比容量低、倍率性能差.本文介绍一类新型有机金属配合物聚吡咯-过渡金属-氧储锂材料的合成、结构及电化学性能.结合扩展X-射线吸收精细结构谱分析和密度泛函理论计算,发现这类材料呈现多层结构特征,层内稳定的过渡金属-吡咯N的配位作用及循环过程中层间过渡金属-氧键的可逆断裂和结合使该类材料具有很高的储锂容量和循环稳定性,且聚吡咯导电网络使得该材料具有良好的倍率性能.这类新材料将有望成为锂离子电池的高比容量负极材料.

Surface oxidation of Ni-cermet electrodes by CO_(2) and H_(2)O and how to moderate it

The oxidation of porous Ni-yttria-stabilized zirconia(YSZ)and Ni-gadolinia-doped ceria(GDC)ceramicmetal(cermet)electrodes in H_(2)O and CO_(2)atmospheres was studied by near-ambient pressure X-ray photoelectron spectroscopy(NAP-XPS).We show that the oxidation of nickel by the two gases is not similar,as is commonly believed,but it depends on the ceramic type.Nickel is vulnerable to oxidation in H_(2)O but it resists to CO_(2)in Ni-GDC,as compared to the Ni-YSZ electrode.Inspired by this observation we conceptualize and fabricate Ni-YSZ electrodes modified by ceria nanoparticles,which show significantly higher resistance to CO_(2)oxidation as compared with conventional Ni-YSZ electrodes.The preparation of tailormade cermet electrodes with identical bulk/mechanical characteristics but very different surface properties offers a promising fabrication strategy for high-performance and durability solid oxide electrolysis cells for CO_(2)conversion.

Effect of oxygen and nitrogen functionalization on the physical and electronic structure of graphene

graphene 的共有原子价 functionalization 为定制它的性质提供机会并且是一些 graphene 合成技术的不可避免的后果。然而， functionalization 导致的变化很好没被理解。由使用原子来源控制氧和氮 functionalization 的程度，我们在原子规模在结构和性质学习了进化。虽然，原子氧 reversibly 介绍 epoxide 组，在类似的条件下面，原子氮不可逆转地创造包括的多样的功能代理， pyridinic，和 pyrrolic 氮。原子氧在迪拉克点离开费密能量(即， undoped ) ，虽然原子氮导致网做 n；然而，试验性的结果与为两是转变从的主导的电子效果一致去除到局部性的状态，和因此签名的损失 graphene 的电子结构。

X射线自由电子激光在化学与能源材料科学中的应用

在过去的十多年中,X射线自由电子激光器（X-ray Free Electron Laser,XFEL）的成功研制和快速发展,极大地推动了超快X射线光谱学实验技术的发展,并且在物理、化学和生物科学等不同研究领域获得了广泛的应用。通过飞秒激光脉冲对样品的激发,X射线可以在不同时间尺度下,跟踪固态、液态和气态等各种情况下样品的微观结构动力学过程。X射线吸收和发射光谱,衍射和散射是探测激光诱导结构变化的典型工具。文章将介绍近年来飞秒X射线技术的发展,及其在化学与能源材料领域的应用。相信随着上海X射线自由电子激光器的建成,将使得飞秒X射线技术在更多的科学领域发挥作用。

X-ray-induced radiophotodynamic therapy （RPDT） using lanthanide micelles： Beyond depth limitations

We report lanthanide-based micelles integrating hypericin （Hyp） for X-ray- triggered photodynamic therapy （PDT）. The lanthanide luminescence induced by X-ray irradiation excites the photosensitizer, which leads to the generation of singlet oxygen. This versatile approach can be extended to other photosensitizers or other types of liponanoparticles and can allow for magnetic resonance imaging （MRI） guidance.

界面工程促进雪花状Ru/RuO_(2)纳米片氢气氧化性能

近年来,贵金属钌(Ru)因其具备与铂(Pt)媲美的氢吸附能以及比铂更低的价格被认为是很有前景的氢氧化反应(HOR)和析氢反应(HER)催化剂.然而,目前钌基催化剂在HOR和HER上的大规模应用依然受限于其活性低、稳定性不高等缺点.本文采用湿化学和热处理结合策略制备了具有Ru/RuO_(2)界面的二维雪花纳米片(Ru/RuO_(2) SNSs).表征和理论计算结果表明, Ru/RuO_(2) SNSs的界面结构与热处理温度密切相关.因此,可通过改变热处理温度调控界Ru/RuO_(2)界面相互作用,并进一步调控催化剂表面的氢结合能(HBE)和氢氧根结合能(OHBE),从而提高HOR和HER的催化性能.当Ru/RuO-12 SNSs用于催化碱性HOR时,在50 mV的过电位为下,其质量活性达到了9.13 A mgRu,分别是Ru SNSs(0.14 A mg^(-1)_(Ru))、RuO_(2) SNSs(0.03 A mg^(-1)_(Ru))和商用Pt/C(0.43 A mg^(-1)_(Ru))的65倍、304倍和21倍.此外, Ru/RuO_(2) SNSs还表现出优异的碱性HER性能.在1 mol L^(-1) KOH中,当电流密度达到10 mA cm^(-2)时,过电位低至20.2 mV.这项工作不仅开发了一种高效的HOR和HER催化剂,而且对开发新型高效催化剂也起到了重要的推动作用.

A convolutional neural network for defect classification in Bragg coherent X-ray diffraction

Coherent diffraction imaging enables the imaging of individual defects,such as dislocations or stacking faults,in materials.These defects and their surrounding elastic strain fields have a critical influence on the macroscopic properties and functionality of materials.However,their identification in Bragg coherent diffraction imaging remains a challenge and requires significant data mining.The ability to identify defects from the diffraction pattern alone would be a significant advantage when targeting specific defect types and accelerates experiment design and execution.Here,we exploit a computational tool based on a three-dimensional(3D)parametric atomistic model and a convolutional neural network to predict dislocations in a crystal from its 3D coherent diffraction pattern.Simulated diffraction patterns from several thousands of relaxed atomistic configurations of nanocrystals are used to train the neural network and to predict the presence or absence of dislocations as well as their type(screw or edge).Our study paves the way for defect-recognition in 3D coherent diffraction patterns for material science.

Free electron lasers driven by plasma accelerators:status and near-term prospects

Owing to their ultra-high accelerating gradients,combined with injection inside micrometer-scale accelerating wakefield buckets,plasma-based accelerators hold great potential to drive a new generation of free-electron lasers(FELs).Indeed,the first demonstration of plasma-driven FEL gain was reported recently,representing a major milestone for the field.Several groups around the world are pursuing these novel light sources,with methodology varying in the use of wakefield driver(laser-driven or beam-driven),plasma structure,phase-space manipulation,beamline design,and undulator technology,among others.This paper presents our best attempt to provide a comprehensive overview of the global community efforts towards plasma-based FEL research and development.

Capacitive beam position monitors for the low-β beam of the Chinese ADS proton linac

Beam Position Monitors（BPMs） for the low-β beam of the Chinese Accelerator Driven Subcritical system（CADS） Proton linac are of the capacitive pick-up type.They provide higher output signals than that of the inductive type.This paper will describe the design and tests of the capacitive BPM system for the low-β proton linac,including the pick-ups,the test bench and the read-out electronics.The tests done with an actual proton beam show a good agreement between the measurements and the simulations in the time domain.

Connector theory for reusing model results to determine materials properties

The success of Density Functional Theory(DFT)is partly due to that of simple approximations,such as the Local Density Approximation(LDA),which uses results of a model,the homogeneous electron gas,to simulate exchange-correlation effects in real materials.We turn this intuitive approximation into a general and in principle exact theory by introducing the concept of a connector:a prescription how to use results of a model system in order to simulate a given quantity in a real system.In this framework,the LDA can be understood as one particular approximation for a connector that is designed to link the exchange-correlation potentials in the real material to that of the model.Formulating the in principle exact connector equations allows us to go beyond the LDA in a systematic way.Moreover,connector theory is not bound to DFT,and it suggests approximations also for other functionals and other observables.We explain why this very general approach is indeed a convenient starting point for approximations.We illustrate our purposes with simple but pertinent examples.

Visualization of the electronic phase separation in superconducting K_(x)Fe_(2−y)Se_(2)

Type-II iron-based superconductors(Fe-SCs),the alkali-metal-intercalated iron selenide A_(x)Fe_(2−y)Se_(2)(A=K,Tl,Rb,etc.)with a superconducting transition temperature of 32 K,exhibit unique properties such as high Néel temperature,Fe-vacancies ordering,antiferromagnetically ordered insulating state in the phase diagram,and mesoscopic phase separation in the superconducting materials.In particular,the electronic and structural phase separation in these systems has attracted intensive attention since it provides a platform to unveil the insulating parent phase of type-II Fe-SCs that mimics the Mott parent phase in cuprates.In this work,we use spatial-and angle-resolved photoemission spectroscopy to study the electronic structure of superconducting K_(x)Fe_(2−y)Se_(2).We observe clear electronic phase separation of K_(x)Fe_(2−y)Se_(2) into metallic islands and insulating matrix,showing different K and Fe concentrations.While the metallic islands show strongly dispersive bands near the Fermi level,the insulating phase shows an energy gap up to 700 meV and a nearly flat band around 700 meV below the Fermi energy,consistent with previous experimental and theoretical results on the superconducting K_(1−x)Fe_(2)Se_(2)(122 phase)and Fe-vacancy ordered K_(0.8)Fe_(1.6)Se_(2)(245 phase),respectively.Our results not only provide important insights into the mysterious composition of phase-separated superconducting and insulating phases of K_(x)Fe_(2−y)Se_(2),but also present their intrinsic electronic structures,which will shed light on the comprehension of the unique physics in type-II Fe-SCs.

tuning the properties of confined water in standard and lybrid nanotubes： An infrared spectroscopic study

Imogolite is a natural nanotubular aluminum silicate clay mineral found in volcanic soils. Its well-defined, tunable structure makes it a good candidate for studying water confinement in a one-dimensional （1D） structure. Water confinement in self-sustaining imogolite thin films was studied using infrared spectroscopy. Two types of synthetic imogolites were investigated： pristine imogolite （IMO-OH） with a hydrophilic inner surface covered with Si-OH groups and hybrid imogolite （IMO-CH3） with a hydrophobic inner surface covered with Si-CH3 groups. Both imogolites have an outer surface that is covered with Al-OH groups. Infrared spectra were recorded in the 20-4,000 cm^-1 spectral range as a function of relative humidity. Analysis of the O-H stretching band provides information on the H bonding of confined water molecules inside and outside the IMO-OH tubes. The scenario for water filling as a function of relative humidity is determined for both systems. Adsorption begins in the IMO-OH tubes at the lowest relative humidity （〈 10%）. The inner surface of the tubes is first covered with water molecules; then, the central part of the tubes is filled, leading to very strong H bonds and a structured spectrum. In contrast, the H bonds of water adsorbed on the outer surfaces of these tubes are weaker. A different scenario is observed for water inside IMO-CH3： Weakly H-bonded water molecules are present, similar to that observed in carbon nanotubes. Water confinement in imogolites is governed by the hydrophilicity of the inner walls. At similar partial pressures, the degree of H bonding depends on the interactions between water and the nanotube wall.

基于分子筛结构的钼钒氧化物相工程在锌离子电池中的研究

随着大规模储能需求的不断增加,水性锌离子电池在世界范围内引起了越来越多的关注.然而,基于锌离子存储的宿主材料有限,严重地阻碍了锌离子电池的商业化应用.基于此,本论文精确地构建了一系列相结构(正交、三方和四方晶系)的钼钒氧化物,研究了该钼钒氧化物电极材料在锌离子电池中的储锌性能.一系列开放的框架和隧道结构有利于锌离子的扩散动力学.通过相工程优化,正交晶系的钼钒氧化物电极材料的比容量能够达到约400 m A h g^(−1),循环稳定性达到了1000次.正交晶系的钼钒氧化物相中具有大量的六元和七元环结构,在锌离子的可逆嵌入/脱出反应方面发挥了至关重要的作用.本文提出的相工程策略为锌离子电池中正极材料的设计提供了一种新方法.

Competing magnetic states in silicene and germanene 2D ferromagnets

Two-dimension(2D)magnets have recently developed into a class of stoichiometric materials with prospective applications in ultra-compact spintronics and quantum computing.Their functionality is particularly rich when different magnetic orders are competing in the same material.Metalloxenes REX2(RE=Eu,Gd;X=Si,Ge),silicene or germanene—heavy counterparts of graphene—coupled with a layer of rare-earth metals,evolve from three-dimension(3D)antiferromagnets in multilayer structures to 2D ferromagnets in a few monolayers.This evolution,however,does not lead to fully saturated 2D ferromagnetism,pointing at a possibility of coexisting/competing magnetic states.Here,REX2 magnetism is explored with element-selective X-ray magnetic circular dichroism(XMCD).The measurements are carried out for GdSi2,EuSi2,GdGe2,and EuGe2 of different thicknesses down to 1 monolayer employing K absorption edges of Si and Ge as well as M and L edges of the rare-earths.They access the magnetic state in REX2 and determine the seat of magnetism,orbital,and spin contributions to the magnetic moment.High-field measurements probe remnants of the bulk antiferromagnetism in 2D REX2.The results provide a new platform for studies of complex magnetic structures in 2D materials.

Huge metastable axial strain in ultrathin heteroepitaxial vertically aligned nanowires

紧张工程是一个强大的工具定制协调地在取向附生的 heterostructure 叠的材料的物理性质。如此的一条途径，适用于平面 heteroepitaxy 的成熟领域，产出许多新现象和设备。最近， heteroepitaxial 垂直地排列了 nanocomposites 作为平面结构的选择出现了。由于如此的 nanoarchitectures 的古怪几何学，有效种类控制能被完成，打开到新奇功能的路。在这份报纸，我们在在一个氧化物矩阵嵌入的取向附生的转变金属 nanowires 报导一个很大的张力的轴的种类。我们证明超过 1.5% 罐头的轴的种类在有 ultrasmall 直径(36 nm ) 的取向附生的 nanowires 在大厚度(一些百纳米) 上被支撑。轴的种类取决于 nanowires 的直径，反映它的取向附生的性质和接口和有弹性的精力的平衡。而且，如此的种类是亚稳的，这试验性地被显示出，与在 Frenkel-Kontorova 模型的框架执行的计算一致。直径依赖和 metastability 提供有效方法控制种类，为功能的 nanoarchitectures 的设计的一个呼吁的特征。

Correlative optical photothermal infrared and X-ray fluorescence for chemical imaging of trace elements and relevant molecular structures directly in neurons

Alzheimer's disease(AD)is the most common cause of dementia,costing about 1%of the global economy.Failures of clinical trials targeting amyloid-βprotein(Aβ),a key trigger of AD,have been explained by drug inefficiency regardless of the mechanisms of amyloid neurotoxicity,which are very difficult to address by available technologies.Here,we combine two imaging modalities that stand at opposite ends of the electromagnetic spectrum,and therefore,can be used as complementary tools to assess structural and chemical information directly in a single neuron.Combining label-free super-resolution microspectroscopy for sub-cellular imaging based on novel optical photothermal infrared(O-PTIR)and synchrotron-based X-ray fluorescence(S-XRF)nano-imaging techniques,we capture elemental distribution and fibrillary forms of amyloid-βproteins in the same neurons at an unprecedented resolution.Our results reveal that in primary AD-like neurons,iron clusters co-localize with elevated amyloidβ-sheet structures and oxidized lipids.Overall,our O-PTIR/S-XRF results motivate using high-resolution multimodal microspectroscopic approaches to understand the role of molecular structures and trace elements within a single neuronal cell.

Vasarely painting at the nanoscale on sapphire crystals

We demonstrate that convenient thermal treatment of a specific sapphire vicinal surface can induce the formation of a fully two-dimensional(2D)ordered surface made of a periodic assembly of(006)facets.The simiarity between the resuting surface topography and pattemns represented in the hexagon series"of paintings by Vasarely is really striking!We thus propose to call these surfaces as"nanoscaled Vasarely surfaces".We also show that the self-organization process,which is driven by the minimization of the free energy of a closed system,results in a quasi-linear isothermal growth of the facets'surface area over time.

Delocalization of dark and bright excitons in flat-band materials and the optical properties of V_(2)O_(5)

The simplest picture of excitons in materials with atomic-like localization of electrons is that of Frenkel excitons,where electrons and holes stay close together,which is associated with a large binding energy.Here,using the example of the layered oxide V_(2)O_(5),we show how localized charge-transfer excitations combine to form excitons that also have a huge binding energy but,at the same time,a large electron-hole distance,and we explain this seemingly contradictory finding.The anisotropy of the exciton delocalization is determined by the local anisotropy of the structure,whereas the exciton extends orthogonally to the chains formed by the crystal structure.Moreover,we show that the bright exciton goes together with a dark exciton of even larger binding energy and more pronounced anisotropy.These findings are obtained by combining first principles many-body perturbation theory calculations,ellipsometry experiments,and tight binding modelling,leading to very good agreement and a consistent picture.Our explanation is general and can be extended to other materials.

X-ray microscopic investigation of molecular orientation in a hole carrier thin film for organic solar cells

As dipyranylidenes are excellent hole carriers, applications in organic solar cells or organic light emitting diode are envisaged. In the present study, we investigate the morphology of 2,2＇,6,6＇-tetraphenyl-4,4＇-dipyranylidene （DIPO-Ph4） deposited under vacuum on a silicon nitride （Si3N4） substrate, a paradigmatic system for the study of molecular crystal/inorganic substrate interfaces. Samples with various coating ratios and different thermal treatments were prepared. The films were characterized by atomic force microscopy and scanning transmission X-ray microscopy to gain insight into material growth. The results show a change in orientation at a molecular level depending upon the evaporation conditions. We are now able to tailor an organic layer with a specific molecular orientation and a specific electronic behavior.