一种无粘结剂的柔性正极材料用于可充电的钠空气电池

随着全球环保意识的加强,开发具有环保可持续且高能量密度的能源逐渐成为人们关注的焦点.近年来,金属-空气电池凭借其高的能量密度作为能源存储器件已经引起了人们的广泛关注.最重要的是,此类电池的反应物为空气中的氧气,并不需要辅助设备对其储存,使得无论在质量和体积方面均优于其他二次电池.尤其锂空气电池凭借其高的理论比容量11140 Wh/kg,比现有锂离子电池高出1–2个数量级,且有质量轻便等优势,成为近几年的研究热点.然而,考虑到金属锂资源的短缺和金属钠与其具有相似的物理化学性质,因此呼吁用金属钠取代金属锂,钠-空气电池作为未来的储能器件引起了广大研究者的兴趣.但是,钠空气电池目前的实际应用仍存在很多问题：充放电过程中产生过高的过电位,循环寿命低,电解液不稳定,粘结剂的不稳定性,空气正极的结构以及外界操作环境条件等.解决这些问题的一种重要途径就是寻找合适的催化剂和设计合理的电极结构.催化剂的加入既可以增强其氧还原(ORR)及氧析出(OER)活性又可以通过调控电极的结构,为氧气、电子和离子的运输提供更多的通道,从而加速 ORR和 OER进程.基于粘结剂的不稳定性,需设计一体化的正极材料.由于碳纤维布作为柔性集流体具有高的机械强度和电化学稳定性好的优点,因此本文使用水热处理和热处理两步法在碳纤维布上原位生长 Co3O4纳米线(Co3O4 NWs),制备柔性、无粘结剂的一体化正极材料(COCT)用于钠空气电池.本实验以硝酸钴为主盐,尿素为矿化剂,氟化铵为络合剂,通过120°C热处理5 h在碳纤维布上生长 Co3O4 NWs的前驱体,然后经过400°C热处理2 h得到一体化柔性电极材料并用于钠空气电池,该材料表现出优异的电化学性能：充放电过程产生较低的过电位;高的放电比容量4687 mAh/g,碳纤维布作为正极放电容量是1113.7 mAh/g;能稳定循环62圈(碳纤维布作为正极循环16圈).这些优异的性能可归功于 Co3O4 NWs高的催化性能和多孔性效应：(1)由于 Co3O4 NWs紧密地附着在碳纤维布表面,形成了快速的电子传导通道,因而具有优异的电子传导性;(2) Co3O4 NWs之间的空隙以及多孔结构增加了反应的活性面积和活性位点,这种结构有利于氧气和离子的运输以及电解液的扩散,从而加速 ORR和 OER进程;(3) COCT电极结构能为放电产物和反应物提供更多的存储位置,从而提高了放电容量和倍率性能.结果证实,钠空气电池的放电产物是过氧化钠和超氧化钠的混合物.加入催化剂后,放电产物的形貌发生了变化：当碳纤维布作为正极材料时,放电产物的形貌是片状的; COCT电极作为正极材料时,放电产物沿着 Co3O4 NWs生长.这种柔性一体化正极材料的应用,为柔性钠空气电池器件的发展起到了巨大的推动作用.     

Isolated Co single atoms in nitrogen-doped graphene for aluminum-sulfur batteries with enhanced kinetic response

Al-S batteries are promising next generation energy storage devices due to their high theoretical energy density (1340 Wh kg^-1),low cost,and safe operation.However,the electrochemical performance of Al-S batteries suffers poor reversibility owing to slow kinetic processes determined by the difficulty of reversible conversion between Al and S.Here,we proposed a single-atom catalysts comprising Co atoms embedded in a nitrogen-doped graphene (Co NG) as an electrochemical catalyst in the ...     

Recent progress on two-dimensional materials confining single atoms for CO2 photoreduction

Photoreduction of CO₂ into value-added products offers a promising approach to overcome both climate change and energy crisis. However, low conversion efficiency, poor product selectivity, and unclear mechanism limit the further advancement of CO₂ photoreduction. The development of two-dimensional (2D) materials and construction of single atom sites are two frontier research fields in catalysis. Combining the advantages of 2D materials and single atom sites is expected to make a breakthrough in CO₂ photoreduction. In this review, we summarized the design and application, proposed challenges and opportunities, and laid a foundation for further research and application of 2D materials confining single atoms (SACs@2D) for CO₂ photoreduction.     

Excitation temperatures of atoms and ions in a hollow cathode discharge

Excitation temperatures have been measured in a hollow cathode discharge from intensities of Ar I, Ar II, Ti I, Ti II, AI I, Mg I, Mg II, Cu I and Pb I lines. The differences between values derived from the species listed are discussed.     

Distribution of metastable argon atoms in the modified Grimm-type electrical discharge

The absorbance by metastable argon atoms of the Ar 696.543 nm line in the modified Grimm-type electrical discharge source was measured at different discharge conditions and at distances varying from 0.25 to 6 mm from the cathode. A uranium/argon hollow cathode lamp was used as primary source, which gave an argon gas temperature of 850 K when run at 12 mA. A maximum absorbance of 0.57 was found 3 mm from the cathode at 600 V, 80 mA. The magnitude of absorbance increases with discharge current while the position of maximum absorbance shifts away from the cathode with increase in discharge voltage. The quenching of metastable atoms by nitrogen is demonstrated.The spatial distribution of the intensity of four different types of spectral lines is shown. The approximate number densities of the different particles are 10¹²cm^?3 for metastable argon atoms, 10¹⁶cm^?3 for neutral argon atoms, 10¹³ cm^?3 for sputtered copper atoms and 10¹⁴cm^?3for electrons.     

Tuning the charge distribution and crystal field of iron single atoms via iron oxide integration for enhanced oxygen reduction reaction in zinc-air batteries

Metal-air batteries face a great challenge in developing efficient and durable low-cost oxygen reduction reaction(ORR) electrocatalysts. Single-atom iron catalysts embedded into nitrogen doped carbon(Fe-N-C) have emerged as attractive materials for potential replacement of Pt in ORR, but their catalytic performance was limited by the symmetrical electronic structure distribution around the single-atom Fe site.Here, we report our findings in significantly enhancing the ORR performance of Fe-N-C b...     

二维材料限域单原子催化剂研究进展

近年来,单一原子或单一位点催化剂因其独特的结构和电子特性受到催化研究人员的广泛关注.目前,多种无机固体材料被用作限域该类单原子催化剂,包括传统的金属氧化物、沸石分子筛以及金属有机框架配合物等.载体的性质会显著地影响单原子的催化性能,因此具有独特物理化学性质的二维材料无疑是限域单原子的一类理想介质,并逐渐引起了人们在该领域的研究兴趣.二维材料兴起于石墨烯的成功剥离,随后其他类似物如氮化硼、氮化碳以及二硫化钼等蓬勃发展起来.结构简单明确且性质独特的二维材料自身就是一类新颖的催化剂,其与单原子的结合将会为催化带来更多新的可能.二维材料限域单原子催化剂的潜在优势如下:(1)二维材料独特的电子结构对单原子中心的电子特性有显著的调变作用,使其催化性能更为独特;(2)二维材料通常具有巨大的比表面积,这允许其锚定更多的单原子从而显著提高其活性位密度;(3)单原子层二维材料有利于反应物分子从双向接触其表面限域的单原子位点,增加碰撞几率并降低传质阻力;(4)二维材料限域单原子催化剂可被视为理想的模型催化剂,其结构均一的活性中心有利于催化剂构效关系的研究;(5)二维材料限域的单原子能够反过来促进或激活二维材料的本征催化活性.在这里,我们总结了二维材料限域单原子催化剂的最新进展,其中二维材料主要涉及石墨烯、氮化碳和硫化钼.我们围绕在二维材料限域单原子催化剂中什么是真正的活性位点及其如何协同催化等问题进行了讨论,进而展望了二维材料限域单原子催化剂的应用前景和挑战.     

How the electrolyte limits fast discharge in nanostructured batteries and supercapacitors

Solid state and interfacial processes are not necessarily the principal rate limiting process during fast discharge of LiFePO₄ composite electrodes with particle size less than 1 μm. A simple model based on salt diffusion to a sharp discharge front explains the observed dependence of discharge rate on electrode thickness, electrolyte concentration, lithium transference number, and dilution of the active material. The effect of changing the electrolyte is dramatic, e.g. discharge to 25% capacity was obtained on a 40 μm thick electrode after only 4 s in an optimised electrolyte, aqueous Li₂SO₄, showing a rate of 900 C as compared with less than 10 C for a similar cell with an ionic liquid as the electrolyte.     

Direct detection of discharge products in lithium-oxygen batteries by solid-state NMR spectroscopy

A closer look: Solid-state (7) Li and (17) O?NMR spectroscopy is a valuable tool in the characterization of products formed in the lithium-oxygen battery, a necessary step in the development of a viable cell. Since lithium peroxide, the desired discharge product, has a unique (17) O?NMR signature, it can be clearly identified.     

A mechanistic study of selective propane dehydrogenations on MoS2 supported single Fe atoms

On-purpose propane dehydrogenation (PDH) has emerged as a profitable alternative to the traditional cracking of oil products for propylene production. By means of density functional theory (DFT) calculations, the present work demonstrates that Fe atoms may atomically disperse on MoS₂ (Fe₁/MoS₂) and serve as a promising single-atom catalyst (SAC) for PDH. The catalytic activity of Fe₁/MoS₂ is attributed to the highly exposed d orbitals of single Fe atoms, while the propylene selectivity is originated from the kinetic inhibition of propylene dehydrogenation resulting from fast propenyl hydrogenation. The unique catalytic selectivity of Fe₁/MoS₂ may inspire further investigations of on-purpose dehydrogenations of propane on SACs.     

Recoil spectrometer for the detection of single atoms

Kinetic decay of paramagnetic species formed in the radiolysis of tetracycline hydrochloride in powder form, at 77 K, shows that most of the H· is not able to migrate. Geminate recombination between H· and its partner is the main reaction: H·+TC· TCH, although a few H· succeed in diffusing slowly. But when H· acquires enough kinetic energy to migrate, it reacts preferentially with species different from its partner. The e^– is not observed by ESR, at 77 K, although tetracycline hydrochloride is a chemical trap for e^– in methanol, benzyl alcohol and alkaline aqueous solutions. In the radiolysis of tetracycline hydrochloride in powder form, the dimethylammonium group blocks H· abstraction reaction at 77 K.From a thesis submitted by S. M. L. G. to the University of São Paulo in partial fulfillment of the requirements for a Doctor of Science in Nuclear Technology.     

Gas-phase CO2 activation with single electrons,metal atoms,clusters,and molecules

In this review,the history and outlook of gas-phase CO2 activation using single electrons,metal atoms,clusters (mainly metal hydride clusters),and molecules are...     

The polarization characteristics of lithium-ion batteries under cyclic charge and discharge

Journal of Solid State Electrochemistry - A high-fidelity electrochemical-thermal coupling was established to study the polarization characteristics of power lithium-ion battery under cycle charge...     

A comparison study on single metal atoms (Fe,Co, Ni) within nitrogen-doped graphene for oxygen electrocatalysis and rechargeable Zn-air batteries

Single atom catalysts (SACs) with atomically dispersed transition metals on nitrogen-doped carbon supports have recently emerged as highly active non-noble metal electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), showing great application potential in Zn-air batteries. However, because of the complex structure-performance relationships of carbon-based SACs in the oxygen electrocatalytic reactions, the contribution of different metal atoms to the catalytic activity of SACs in Zn-air batteries still remains ambiguous. In this study, SACs with atomically dispersed transition metals on nitrogen-doped graphene sheets (M-N@Gs, M = Co, Fe and Ni), featured with similar physicochemical properties and M-N@C configurations, are obtained. By comparing the on-set potentials and the maximum current, we observed that the ORR activity is in the order of Co-N@G > Fe-N@G > Ni-N@G, while the OER activity is in the order of Co-N@G > Ni-N@G > Fe-N@G. The Zn-air batteries with Co-N@G as the air cathode catalysts outperform those with the Fe-N@G and Ni-N@G. This is due to the accelerated charge transfer between Co-N@C active sites and the oxygen-containing reactants. This study could improve our understanding of the design of more efficient bifunctional electrocatalysts for Zn-air batteries at the atomic level.     

基于氮杂Mn咔咯二维纳米材料的单原子Mn中心催化氧化烷烃制醇

咔咯是由四个吡咯共轭相连而形成的具有芳香性的新型卟啉类大环化合物,但咔咯分子中存在一个直接连结两个吡咯环的C?C键,与卟啉相比,仅仅是少了一个“meso”位置的C原子.因此,在结构上,咔咯含有三个“吡咯型”氮原子和一个“吡啶型”氮原子,当咔咯失去三个内氢原子后变成了三价阴离子,易与金属形成高价态的稳定配合物.氮杂咔咯是一种咔咯的meso位上的C被取代为N的咔咯衍生物.与正常的咔咯相比,它更易于与过渡金属形成稳定配合物.正是由于这些独特的结构特点,使其在金属催化、染料敏化太阳能电池、光敏剂、金属传感器、甚至在医学上都有很好的应用前景.金属有机大环均相催化剂的非均相化,是改进反应产物分离和实现催化剂循环使用的最简单有效方法之一.环境友好的Mn氮杂咔咯催化剂,在温和条件下可以利用氧气直接将有机底物氧化.本文选用Mn氮杂咔咯催化剂作为基本构建单元,通过理论计算,构建了一种新型的具有高催化活性的含Mn氮杂咔咯环结构单元的二维纳米催化材料.我们分别使用高斯软件(Gaussian 09)和维也纳从头算模拟软件包(VASP)对孤立分子和周期性体系进行结构优化以及性质的计算.在这种二维材料中,每一个Mn原子作为相对独立的金属单原子中心(SAC),保留了单环中Mn金属中心的高催化活性.在温和的光照条件下,Mn金属中心可以直接活化氧气生成类自由基[Mn]-O-O中心,随后[Mn]-O-O中心可以有效地通过夺取有机底物中的H和紧接着新生自由基的偶合反应,选择性氧化C?H键为C?OH键.另外,通过沿[Mn]-O-O反应轴施加不同强度的外电场,可对此二维纳米材料的催化反应活性进行精细调控.本文为实验上制备基于Mn氮杂咔咯的非均相催化剂以及单原子Mn基催化剂提供了理论依据.     

Anchoring Ni single atoms on sulfur-vacancy-enriched ZnIn2S4 nanosheets for boosting photocatalytic hydrogen evolution

Structure manipulation of photocatalysts at an atomic scale is a promising way to improve its photocatalytic performance.Herein,we realize the anchoring of sing...     

Potential active sites of Mo single atoms for electrocatalytic reduction of N2

Single atom catalysts(SACs) with isolated metal atoms dispersed on supports exhibit distinctive performances for electrocatalysis reactions.The designable realization of well-dispersed single metal atoms is still a great challenge owing to their ease of aggregation.Here,Mo single atomic sites(Mo-N₃C)combined with some ultrasmall Mo₂C/MoN clusters(Mo-SA/Mo₂C-MoN-Cs,mean diameter <2 nm) on nitrogen-doped porous carbon were synthesized via a simple pyrolysis of bimetallic Zn/Mo metalorganic frameworks.X-ray absorption near edge spectra(XANES) in combination with various characterizations show that most of Mo species in sample exist in the form of single sites and the exact structure is Mo-N₃C.Density functional theory(DFT) calculation further shows that as the number of Ncoordination in the Mo-NxC moieties increases,the positive cha rge of Mo atoms increases.The single Mo atoms in Mo-N₃C have the best capability of N₂ adsorption,which may serve as main active sites for further electrochemical N2 reduction.     

Specific incorporation of chalcogenide bridge atoms in molybdenum/tungsten-iron-sulfur single cubane clusters

An extensive series of heterometal-iron-sulfur single cubane-type clusters with core oxidation levels [MFe(3)S(3)Q](3+,2+) (M = Mo, W; Q = S, Se) has been prepared by means of a new method of cluster self-assembly. The procedure utilizes the assembly system [((t)Bu(3)tach)M(VI)S(3)]/FeCl(2)/Na(2)Q/NaSR in acetonitrile/THF and affords product clusters in 30-50% yield. The trisulfido precursor acts as a template, binding Fe(II) under reducing conditions and supplying the MS(3) unit of the product. The system leads to specific incorporation of a μ(3)-chalcogenide from an external source (Na(2)Q) and affords the products [((t)Bu(3)tach)MFe(3)S(3)QL(3)](0/1-) (L = Cl(-), RS(-)), among which are the first MFe(3)S(3)Se clusters prepared. Some 16 clusters have been prepared, 13 of which have been characterized by X-ray structure determinations including the incomplete cubane [((t)Bu(3)tach)MoFe(2)S(3)Cl(2)(μ(2)-SPh)], a possible trapped intermediate in the assembly process. Comparisons of structural and electronic features of clusters differing only in atom Q at one cubane vertex are provided. In comparative pairs of complexes differing only in Q, placement of one selenide atom in the core increases core volumes by about 2% over the Q = S case, sets the order Q = Se > S in Fe-Q bond lengths and Q = S > Se in Fe-Q-Fe bond angles, causes small positive shifts in redox potentials, and has an essentially nil effect on (57)Fe isomer shifts. Iron mean oxidation states and charge distributions are assigned to most clusters from isomer shifts. ((t)Bu(3)tach = 1,3,5-tert-butyl-1,3,5-triazacyclohexane).