Space‐Confined Atomic Clusters Catalyze Superassembly of Silicon Nanodots within Carbon Frameworks for Use in Lithium‐Ion Batteries

Incorporating nanoscale Si into a carbon matrix with high dispersity is desirable for the preparation of lithium‐ion batteries (LIBs) but remains challenging. A space‐confined catalytic strategy is proposed for direct superassembly of Si nanodots within a carbon (Si NDs?C) framework by copyrolysis of triphenyltin hydride (TPT) and diphenylsilane (DPS), where Sn atomic clusters created from TPT pyrolysis serve as the catalyst for DPS pyrolysis and Si catalytic growth. The use of Sn atomic cluster catalysts alters the reaction pathway to avoid SiC generation and enable formation of Si NDs with reduced dimensions. A typical Si NDs?C framework demonstrates a remarkable comprehensive performance comparable to other Si‐based high‐performance half LIBs, and higher energy densities compared to commercial full LIBs, as a consequence of the high dispersity of Si NDs with low lithiation stress. Supported by mechanic simulations, this study paves the way for construction of Si/C composites suitable for applications in future energy technologies.     

Pt-Cu合金纳米枝晶的合成及其氧还原催化性能

纳米材料的结构和化学成分对其催化性能的显著影响已经得到验证. 因此,本文通过一种简易的蚀刻方法,合成出具有均匀合金结构且尺寸和形貌均一的Pt-Cu纳米枝晶（NDs）作为高效氧还原（ORR）催化剂. 其树枝状形貌的形成得益于由Br^-/O₂氧化蚀刻剂引起的蚀刻效应. 通过改变Pt/Cu前驱体的比例可以容易地调节Pt-Cu NDs的Pt/Cu原子比,而不会使其树枝状形貌发生改变. 活性最高的碳载Pt₁Cu₁ NDs（Pt₁Cu₁ NDs/C）的面积比活性为1.17 mA·cm^-2@0.9V（vs. RHE）,约为商业Pt/C的5.32倍. 此外,Pt₁Cu₁ NDs/C还具有卓越的电化学耐久性,即使在经过加速衰减实验的12000个电势循环后仍保持其优异的ORR催化活性. Pt₁Cu₁ NDs/C优异的ORR催化活性和电化学耐久性得益于由其合金结构和枝晶形貌产生的电子效应和结构效应.     

一步法高效制备纳米Si/C复合材料及其在高性能锂离子电池中的应用

开发了一种一步高效合成纳米硅/碳复合材料的新方法, 该方法通过球磨SiCl₄、 Mg₂Si和商业碳片, 使SiCl₄自下而上还原, 原位形成的纳米硅均匀生长在碳片上, 高效制备了纳米硅与碳片均匀复合物(Nano-Si/C). 该Nano-Si/C用作锂离子电池负极材料展现出高的可逆储锂容量(2450 mA·h/g)、 良好的倍率性能及优异的长循环稳定性, 在2 A/g电流密度下, 经过600次循环后, 容量仍然稳定在1400 mA·h/g. 其突出的电化学性能主要归因于小尺寸纳米硅与碳片均匀复合的纳米结构, 在循环嵌锂/脱锂过程中仍能保持结构和电化学性质的稳定性.     

Yolk-shell Si/C composites with multiple Si nanoparticles encapsulated into double carbon shells as lithium-ion battery anodes

The conceptual design of yolk-shell structured Si/C composites is considered to be an effective way to improve the recyclability and conductivity of Si-based anode materials. Herein, a new type of yolk-shell structured Si/C composite(denoted as TSC-PDA-B) has been intelligently designed by rational engineering and precise control. In the novel structure, the multiple Si nanoparticles with small size are successfully encapsulated into the porous carbon shells with double layers benefiting from the strong etching effect of HF. The TSC-PDA-B product prepared is evaluated as anode materials for lithium-ion batteries(LIBs).The TSC-PDA-B product exhibits an excellent lithium storage performance with a high initial capacity of 2108 mAh g~(-1) at a current density of 100 mA g~(-1) and superior cycling performance of 1113 mAh g~(-1) over 200 cycles. The enhancement of lithium storage performance may be attributed to the construction of hybrid structure including small Si nanoparticles, high surface area, and double carbon shells, which can not only increase electrical conductivity and intimate electrical contact with Si nanoparticles, but also provide built-in buffer voids for Si nanoparticles to expand freely without damaging the carbon layer.The present findings can provide some scientific insights into the design and the application of advanced Si-based anode materials in energy storage fields.     

用于锂离子电池负极材料的锡/碳复合材料研究

采用分散聚合的方法在氧化锡的表面包覆聚对位二乙烯基苯,再热解制备了锡基颗粒在碳基体中均匀分散的锡/碳复合材料.该复合材料具有良好的循环性能.在该复合材料中无定形碳起到了至关重要的作用,它一方面保证了复合材料的导电性能,另一方面有效地抑制了锡基颗粒的团聚与粉化.只有当小尺寸的锡基颗粒均匀地分散在碳基体中时,锡/碳复合材料才具有稳定的电化学性能.     

Pt nanodendrites with (111) crystalline facet as an efficient,stable and pH-universal catalyst for electrochemical hydrogen production

High-performance nanomaterial catalysts for hydrogen evolution reaction via electrochemical water splitting are significant to the development of hydrogen energy. In this work, we report a robust and highly active catalyst fabricated through direct electrochemical deposition of Pt nanodendrites at the surface of activated carbon (Pt NDs). Owing to the large electrochemically active area and the exposed (111) facet of Pt, Pt NDs exhibits outstanding activity towards hydrogen evolution reaction with a low requiring overpotential of 0.027 V at 10 mA/cm² and Tafel slope of ≈ 22 mV/dec in acidic media. In addition, the hydrogen yield of Pt NDs is 30%–45% larger than that of commercial Pt/C at the same Pt loadings. Moreover, Pt NDs exhibits excellent long-term durability whose hydrogen production efficiency remains unchanged after six-hour hydrogen production, while the efficiency of commercial Pt/C catalyst decayed 9% under the same circumstance. Considering the superiority of catalytic activity and stability, this Pt NDs present great potentiality towards practical hydrogen production application.     

Density functional theory study on the possibility of Si‐, Ge‐, and Sn‐doped carbon nanotubes as efficient support materials for platinum

PBEPBE‐D3 calculations were performed to investigate how platinum (Pt) interacts with the internal and external surfaces of single‐walled pristine, Si‐, Ge‐, and Sn‐doped (6,6) carbon nanotubes (CNTs). Our calculations showed that atomic Pt demonstrates stronger binding strength on the external surfaces than the internal surface adsorption for the same type of nanotube. In cases of external surface adsorptions, Si‐, Ge‐, and Sn‐doped CNTs show comparable binding energies for Pt, at least 1.40 eV larger than pristine CNT. This enhancement can be rationalized by the strong covalent interactions between Pt and X? C (X = Si, Ge, and Sn) pairs based on structural and projected density of states analysis. In terms of internal surface adsorptions, Ge and Sn doping could significantly enhance the binding of Pt. Pt atom shows much more delocalized and bonding states inside Ge‐ and Sn‐doped CNTs, indicating multiple‐site interaction pattern when atomic Pt is confined inside the nanotubes. However, the internal surface of Si‐doped CNT presents limited enhancement in Pt adsorption with respect to that of pristine CNT because of their similar binding geometries. © 2016 Wiley Periodicals, Inc.     

Group IVB organometallic compounds of furan: 13C, 29Si and 119Sn n.m.r. Spectra

The ¹³C, ²⁹Si and ¹¹⁹Sn chemical shifts of 2- and 2,5-substituted organometallic (M=C, Si, Ge, Sn, Pb) derivatives of furan were measured. The most important factors, determining the specific features of the studied spectra, are d-orbital availability and atomic radius of the central atom M, as well as the relatively higher (as compared with benzene) energies of the π-electron energy levels of the furan ring.     

Engineering the Distribution of Carbon in Silicon Oxide Nanospheres at the Atomic Level for Highly Stable Anodes

The application of high‐performance silicon‐based anodes, which are among the most prominent anode materials, is hampered by their poor conductivity and large volume expansion. Coupling of silicon‐based anodes with carbonaceous materials is a promising approach to address these issues. However, the distribution of carbon in reported hybrids is normally inhomogeneous and above the nanoscale, which leads to decay of coulombic efficiency during deep galvanostatic cycling. Herein, we report a porous silicon‐based nanocomposite anode derived from phenylene‐bridged mesoporous organosilicas (PBMOs) through a facile sol–gel method and subsequent pyrolysis. PBMOs show molecularly organic–inorganic hybrid character, and the resulting hybrid anode can inherit this unique structure, with carbon distributed homogeneously in the Si‐O‐Si framework at the atomic scale. This uniformly dispersed carbon network divides the silicon oxide matrix into numerous sub‐nanodomains with outstanding structural integrity and cycling stability.     

水热法制备锂电池Si@C负极材料的工艺优化研究

水热法是广泛应用于锂离子电池Si@C电极材料的一种制备方法,其反应条件是影响产物最终形貌和性能的重要因素, 采取最佳的反应工艺可以大大提升材料的电化学性能。本研究中, 使用葡萄糖作为碳源, 光伏切割废料硅为硅源, 探究了水热法制备核壳结构Si@C电极材料的最优工艺, 分别研究了温度、 原料浓度、 反应时间和原料比例对产物的形貌、 性能的影响以及相互之间的关系, 并得到最佳反应条件。在该条件下(葡萄糖浓度为0.5 mol·L^-1, 硅与葡萄糖重量比为0.3:1, 反应温度190 ^oC, 反应时间9 h), 得到了包覆完整、 粒径适中的Si@C电极材料(CS190-3), 对以该样品为负极的扣式半电池进行电化学测试, 在655 mA·g^-1的电流密度下, 其首圈放电比容量为3369.5 mAh·g^-1, 经过500次循环剩余容量为1405.0 mAh·g^-1。倍率测试中, 在6550 mA·g^-1的电流密度下,其剩余容量为937.1 mAh·g^-1,当电流密度恢复至655 mA·g^-1时,电池放电比容量仍可恢复至1683.0 mAh·g^-1。     

Derivatization of tributyltin with sodium tetrakis(4-fluorophenyl)-borate for sensitivity improvement of tandem mass spectrometry.

Derivatization of tributyltin for tandem mass spectrometry is described. Tributyltin (TBT) and triphenyltin (TPT) were derivatized with sodium tetrakis(4-fluorophenyl)borate. After optimization of their MS/MS conditions, derivatization conditions were examined. Under the optimum conditions using in-situ derivatization, the calibration curves for the TBT and TPT were linear in the ranges of 0.4 - 200 and 1.2 - 200 pg of Sn, respectively. The detection limits for TBT and TPT were 0.07 and 0.43 pg of Sn, respectively. In the case of TBT, the detection limit with 4-fluorophenylation was improved about five times compared with that with pentylation (0.35 pg). This improvement is ascribed to the bond-dissociation energy of Sn-aryl being stronger than that of Sn-alkyl. Namely, the selective fragmentation of 4-fluorophenyl TBT resulted in high sensitivity. The relative recoveries of TBT and TPT from seawater were 99 and 109%, respectively. The method was successfully applied to the seawater samples.     

Rational Design of Anode Materials Based on Group IVA Elements (Si,Ge, and Sn) for Lithium‐Ion Batteries

Lithium‐ion batteries (LIBs) represent the state‐of‐the‐art technology in rechargeable energy‐storage devices and they currently occupy the prime position in the marketplace for powering an increasingly diverse range of applications. However, the fast development of these applications has led to increasing demands being placed on advanced LIBs in terms of higher energy/power densities and longer life cycles. For LIBs to meet these requirements, researchers have focused on active electrode materials, owing to their crucial roles in the electrochemical performance of batteries. For anode materials, compounds based on Group IVA (Si, Ge, and Sn) elements represent one of the directions in the development of high‐capacity anodes. Although these compounds have many significant advantages when used as anode materials for LIBs, there are still some critical problems to be solved before they can meet the high requirements for practical applications. In this Focus Review, we summarize a series of rational designs for Group IVA‐based anode materials, in terms of their chemical compositions and structures, that could address these problems, that is, huge volume variations during cycling, unstable surfaces/interfaces, and invalidation of transport pathways for electrons upon cycling. These designs should at least include one of the following structural benefits: 1) Contain a sufficient number of voids to accommodate the volume variations during cycling; 2) adopt a “plum‐pudding”‐like structure to limit the volume variations during cycling; 3) facilitate an efficient and permanent transport pathway for electrons and lithium ions; or 4) show stable surfaces/interfaces to stabilize the in situ formed SEI layers.     

Theoretical investigation of the mechanisms for the reaction of fused tricyclic dimetallenes containing highly strained E═E (E = C, Si, Ge, Sn, and Pb) double bonds

The potential energy surfaces for the reactions of fused tricyclic dimetallenes that feature a highly strained E═E double bond, Rea-E═E, where E = C, Si, Ge, Sn, and Pb, were studied using density functional theory (B3LYP/LANL2DZ). Three types of chemical reactions (i.e., a self-isomerization reaction, a [2 + 2] cycloaddition with a ketone and a methanol 1,2-addition reaction) were used to determine the reactivity of the Rea-E═E molecules. The theoretical findings reveal that the smaller the singlet-triplet splitting of the Rea-E═E, the lower are its activation barriers and, in turn, the more rapid are its chemical reactions with other chemical molecules. Theoretical observations suggest that the relative reactivity increases in the following order: C═C ? Si═Si < Ge═Ge < Sn═Sn < Pb═Pb. Namely, the smaller the atomic weight of the group 14 atom (E), the smaller is the atomic radius of E and the more stable is its fused tricyclic Rea-E═E to chemical reaction. It is thus predicted that the fused tricyclic Rea-C═C and Rea-Si═Si molecules should be stable and readily synthesized and isolated at room temperature. The computational results show good agreement with the available experimental observations. The theoretical results obtained from this work allow a number of predictions to be made.     

A Hierarchical Tin/Carbon Composite as an Anode for Lithium‐Ion Batteries with a Long Cycle Life

Tin is a promising anode candidate for next‐generation lithium‐ion batteries with a high energy density, but suffers from the huge volume change (ca. 260 %) upon lithiation. To address this issue, here we report a new hierarchical tin/carbon composite in which some of the nanosized Sn particles are anchored on the tips of carbon nanotubes (CNTs) that are rooted on the exterior surfaces of micro‐sized hollow carbon cubes while other Sn nanoparticles are encapsulated in hollow carbon cubes. Such a hierarchical structure possesses a robust framework with rich voids, which allows Sn to alleviate its mechanical strain without forming cracks and pulverization upon lithiation/de‐lithiation. As a result, the Sn/C composite exhibits an excellent cyclic performance, namely, retaining a capacity of 537 mAh g^?1 for around 1000 cycles without obvious decay at a high current density of 3000 mA g^?1.     

Non-isothermal pyrolysis of used lubricating oil and the catalytic effect of carbon-based nanomaterials on the process performance

Pyrolysis is a commonly used method for the recovery of used lubricating oil (ULO), which should be kinetically improved by a catalyst, due to its high level of energy consumption. In this research, the catalytic effects of carbon nanotube (CNT) and graphene nanoplatelets on the pyrolysis of ULO were studied through thermogravimetric analysis. First, the kinetic parameters of ULO pyrolysis including activation energy were calculated to be 170.12 and 167.01 kJ mol^?1 by FWO and KAS methods, respectively. Then, the catalytic effects of CNT and graphene nanoplatelets on pyrolysis kinetics were studied. While CNT had a negligible effect on the pyrolysis process, graphene nanoplatelets significantly reduced the temperature of maximum conversion during pyrolysis from 400 to 350 °C, due to high thermal conductivity and homogenous heat transfer in the pyrolysis process. On the other hand, graphene nanoplatelets maximized the rate of conversion of highly volatile components at lower temperatures (<?100 °C), which was mainly due to the high affinity of these components toward graphene nanoplatelets and also the effect of nanoplatelets’ edges which have free tails and can bond with other molecules. Moreover, graphene nanoplatelets decreased the activation energy of the conversion to 154.48 and 152.13 kJ mol^?1 by FWO and KAS methods, respectively.

     

Interdispersed silicon–carbon nanocomposites and their application as anode materials for lithium-ion batteries

As an anode material for lithium-ion batteries (LIBs), silicon offers among the highest theoretical storage capacity, but is known to suffer from large structural changes and capacity fading during electrochemical cycling. Nanocomposites of silicon with carbon provide a potential material platform for resolving this problem. We report a spray-pyrolysis approach for synthesizing amorphous silicon–carbon nanocomposites from organic silane precursors. Elemental mapping shows that the amorphous silicon is uniformly dispersed in the carbon matrix. When evaluated as anode materials in LIBs, the materials exhibit highly, stable performance and excellent Coulombic efficiency for more than 150 charge discharge cycles at a charging rate of 1 A/g. Post-mortem analysis indicates that the structure of the Si–C composite is retained after extended electrochemical cycling, confirming the hypothesis that better mechanical buffering is obtained when amorphous Si is embedded in a carbon matrix.     

A Truxenone-based Covalent Organic Framework as an All-Solid-State Lithium-Ion Battery Cathode with High Capacity

All-solid-state lithium ion batteries (LIBs) are ideal for energy storage given their safety and long-term stability. However, there is a limited availability of viable electrode active materials. Herein, we report a truxenone-based covalent organic framework (COF-TRO) as cathode materials for all-solid-state LIBs. The high-density carbonyl groups combined with the ordered crystalline COF structure greatly facilitate lithium ion storage via reversible redox reactions. As a result, a high specific capacity of 268 mAh g⁻¹, almost 97.5 % of the calculated theoretical capacity was achieved. To the best of our knowledge, this is the highest capacity among all COF-based cathode materials for all-solid-state LIBs reported so far. Moreover, the excellent cycling stability (99.9 % capacity retention after 100 cycles at 0.1 C rate) shown by COF-TRO suggests such truxenone-based COFs have great potential in energy storage applications.     

Metal–Organic Frameworks-Derived Mesoporous Si/SiOx@NC Nanospheres as a Long-Lifespan Anode Material for Lithium-Ion Batteries

Silicon (Si)-based anode materials with suitable engineered nanostructures generally have improved lithium storage capabilities, which provide great promise for the electrochemical performance in lithium-ion batteries (LIBs). Herein, a metal–organic framework (MOF)-derived unique core–shell Si/SiO_x@NC structure has been synthesized by a facile magnesio-thermic reduction, in which the Si and SiO_x matrix were encapsulated by nitrogen (N)-doped carbon. Importantly, the well-designed nanostructure has enough space to accommodate the volume change during the lithiation/delithiation process. The conductive porous N-doped carbon was optimized through direct carbonization and reduction of SiO₂ into Si/SiO_x simultaneously. Benefiting from the core–shell structure, the synthesized product exhibited enhanced electrochemical performance as an anode material in LIBs. Particularly, the Si/SiO_x@NC-650 anode showed the best reversible capacities up to 724 and 702 mAh g⁻¹ even after 100 cycles. The excellent cycling stability of Si/SiO_x@NC-650 may be attributed to the core–shell structure as well as the synergistic effect between the Si/SiO_x and MOF-derived N-doped carbon.     

High‐Rate Oxygen Electroreduction over Graphitic‐N Species Exposed on 3D Hierarchically Porous Nitrogen‐Doped Carbons

Nitrogen‐doped species (NDs) are theoretically accepted as a determinant of the catalytic activity of metal‐free N‐doped carbon (NC) catalysts for oxygen reduction reaction (ORR). However, direct relationships between ND type and ORR activity have been difficult to extract because the complexity of carbon matrix impairs efforts to expose specific NDs. Herein, we demonstrate the fabrication of a 3D hierarchically porous NC catalyst with micro‐, meso‐, and macroporosity in one structure, in which sufficient exposure and availability of inner‐pore catalytic sites can be achieved due to its super‐high surface area (2191 cm² g^?1) and interconnected pore system. More importantly, in‐situ formation of graphitic‐N species (GNs) on the surface of NC stimulated by KOH activation enables us to experimentally reveal the catalytic nature of GNs for ORR, which is of great significance for the design and development of advanced metal‐free NC electrocatalysts.     

Design of pyrite/carbon nanospheres as high-capacity cathode for lithium-ion batteries

Transition metal sulfides are emerging as promising electrode materials for energy storage and conversion. In this work, hierarchical FeS_2/C nanospheres are synthesized through a controllable solvothermal method followed by the annealing process. Spherical FeS_2 core is homogeneously coated by thin carbon shell. The hierarchical nanostructure and carbon coating can enhance electron transfer and accommodate the stress originated from the volume change as well as suppress the shuttle effect of polysulfide. Consequently, as the cathode material of lithium ion batteries(LIBs), the FeS_2/C nanospheres exhibit high reversible capacity of 676 m Ahg~(-1) and excellent cycling life with the capacity retention of 97.1% after100 cycles. In addition, even at the high current density of 1.8 C, a reversible capacity of 437 m Ahg~(-1) is obtained for the FeS_2/C nanospheres, demonstrating its great prospect for practical applications in highperformance LIBs.