Mapping frontier molecular orbitals using photocurrents

<正>In the regime of coherent transport, the conductance of a molecular junction is governed(Fig. 1a) by the probability of electron transmission between the metal electrodes, a physica property which is affected significantly by the hybridization of frontier molecular orbitals(FMOs) with the continuous band of energy levels on the electrodes.     

Organic materials for rechargeable sodium-ion batteries

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炭材料在锂金属电池中应用进展

金属锂作为下一代高能量密度电池的负极材料,具有广阔的应用前景.然而,金属锂的沉积/剥离过程常伴随着高曲折度的枝晶的形成,导致电池寿命短,甚至会诱发安全隐患.迄今为止,研究者们已开发出多种方法来抑制枝晶生长和调节固体电解质界面膜的均匀性.炭材料因其轻质、高导电、多级多孔、化学和物理稳定特性被设计成不同种类的材料来用于稳定...     

Hybrid silica-porphyrin materials with tailored pore sizes

This study is concerning about optical and morphological properties of novel porphyrin doped silica materials consisting in 5,10,15,20-tetrakis(4-allyloxyphenyl)porphyrin (TAPP) encapsulated in silica matrices, exhibiting intensive absorption of light in the red-near IR region. The silica-porphyrin materials were prepared by the sol-gel process, by using different porphyrin immobilization schemes: in situ and by impregnation. As starting materials tetraethoxysilane and isobuthyltrietoxysilane, as silica precursors, N-buthyl-3-methylpyridinium tetrafluoroborate ionic liquid, as additive, and hydrochloric acid and sodium fluoride, as catalysts, were used. The obtained hybrid porphyrin-silica materials were characterized by using BET measurements (Brunauer-Emmett-Teller analysis), thermal analysis, FT-IR, fluorescence and UV-vis spectroscopy techniques. UV-vis behavior and fluorescence emissions and excitations were evaluated in terms of synthesis stages and immobilization processes. The obtained hybrid porphyrin-silica materials presented increased fluorescence emission with maxima situated at about 655 nm and 715 nm in comparison with the porphyrin base that make these transparent materials candidates for second generation photosensitizers. BET analysis revealed that every introduction of TAPP causes decreasing on surface area of the nanomaterial. Although, when the porphyrin is immobilized by in situ method the reduction is lower than in case of using impregnation method, that is leading to the conclusion that the porphyrin is placed inside on the silica network in both studied cases, independent of the performed method of immobilization. The pore size is narrowly distributed in the range of 1.97-3.81 nm for in situ obtained materials and in the range of 3.07-4.62 for hybrids obtained by impregnation. These materials with tunable pore sizes diameter are promising for building of sensor devices.     

Electrochromic materials using mechanically interlocked molecules

Recent investigations on the design and synthesis of electrochromic materials based on switchable three-station [2]catenanes are summarized. The reasoning and preliminary experiments behind the design of electrochemically controllable red–green–blue (RGB), donor–acceptor [2]catenanes are presented. A basis for color generation is discussed in which the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), serves as the π-electron deficient ring which circumrotates between three π-electron rich recognition sites within a macrocyclic polyether, generating the three different colors (RGB) based on the different charge transfer interactions between the tetracationic cyclophane and recognition sites based on 1,5-dioxynaphthalene (R), tetrathiafulvalene (G) and benzidine (B). Issues relating to the realization of an RGB [2]catenane are raised and discussed: they include (i) color tuning, (ii) thermodynamic considerations, (iii) electrochemistry on model compounds, (iv) molecular design, (v) the electrochemical behavior of three-station [2]catenanes and (vi) electrochromism in polymer gel matrices. Finally, the challenges that need to be met in the future if the ideal RGB catenane is to be prepared, are outlined.     

Electrochromic materials using mechanically interlocked molecules

Abstract

Recent investigations on the design and synthesis of electrochromic materials based on switchable three-station [2]catenanes are summarized. The reasoning and preliminary experiments behind the design of electrochemically controllable red–green–blue (RGB), donor–acceptor [2]catenanes are presented. A basis for color generation is discussed in which the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), serves as the π-electron deficient ring which circumrotates between three π-electron rich recognition sites within a macrocyclic polyether, generating the three different colors (RGB) based on the different charge transfer interactions between the tetracationic cyclophane and recognition sites based on 1,5-dioxynaphthalene (R), tetrathiafulvalene (G) and benzidine (B). Issues relating to the realization of an RGB [2]catenane are raised and discussed: they include (i) color tuning, (ii) thermodynamic considerations, (iii) electrochemistry on model compounds, (iv) molecular design, (v) the electrochemical behavior of three-station [2]catenanes and (vi) electrochromism in polymer gel matrices. Finally, the challenges that need to be met in the future if the ideal RGB catenane is to be prepared, are outlined.     

Rational design of thermally stable polymorphic layered cathode materials for next generation lithium rechargeable batteries

Classical layered transition metal oxides have remained the preferred cathode materials for commercial lithium-ion batteries. Variation in the transition metal composition and local ordering can greatly affect the structure stability. In classical layered cathodes, high concentrations of electrochemically inert Mn elements usually act as a pillar to stabilize the structure. When excess amount of Li and Mn are present in the layered structure, the capacity of the Li-rich layered oxide (molar ratio of lithium over transition metal is larger than one by design) can exceed that expected from transition metal redox. However, the over lithiation in the classical layered structure results in safety issues, which remains challenging for the commercialization of Li-rich layered oxides. To characterize the safety performance of a series of Li-rich layered cathodes, we utilize differential scanning calorimeter and thermal gravimetric analysis; this is coupled with local structural changes using in situ temperature dependent synchrotron X-ray diffraction and X-ray adsorption spectroscopy. These methods demonstrate that the gradual decrease of the Mn–M (M = Ni, Co, Mn and Li) coordination number directly reduces structural stability and accelerates oxygen release. For safety characterization tests in practice, we evaluate the thermal runaway process through accelerating rate calorimeter in 1.0 Ah pouch cells to confirm this trend. Using the insights obtained in this work, we design a polymorphic composition to improve the thermal stability of Li-rich layered cathode material, which outperforms Ni-rich layered oxides in terms of both electrochemical and safety performances.     

Direct metal fabrication of titanium implants with tailored materials and mechanical properties using electron beam melting technology

The design of custom or tailored implant components has been the subject of research and development for decades. However, the economic feasibility of fabricating such components has proven to be a challenge. New direct metal fabrication technologies such as Electron Beam Melting (EBM) have opened up new possibilities. This paper discusses the design and fabrication of titanium implant components having tailored mechanical properties that mimic the stiffness of bone to reduce stress shielding and bone remodeling. Finite Element Analysis was used to design the tailored structures, and results were verified using mechanical testing.     

Interfacially stable MOF nanosheet membrane with tailored nanochannels for ultrafast and thermo-responsive nanofiltration

Two-dimensional nanosheet membranes with responsive nanochannels are appealing for controlled mass transfer/separation, but limited by everchanging thicknesses arising from unstable interfaces. Herein, an interfacially stable, thermo-responsive nanosheet membrane is assembled from twin-chain stabilized metal-organic framework (MOF) nanosheets, which function via two cyclic amide-bearing polymers, thermo-responsive poly(N-vinyl caprolactam) (PVCL) for adjusting channel size, and non-responsive polyvinylpyrrolidone for supporting constant interlayer distance. Owing to the microporosity of MOF nanosheets and controllable interface wettability, the hybrid membrane demonstrates both superior separation performance and stable thermo-responsiveness. Scattering and correlation spectroscopic analyses further corroborate the respective roles of the two polymers and reveal the microenvironment changes of nanochannels are motivated by the dehydration of PVCL chains.

     

Highly stable Pt3Ni ultralong nanowires tailored with trace Mo for the ethanol oxidation

Pt3Ni alloy structure is an effective strategy to accelerate ethanol oxidation reaction(EOR),while the stability in acid electrolyte is the fatal weakness and t...     

表面活性剂模板法制备中孔材料的探索

自从发现M41S系列分子筛以来,人们对中孔材料进行了很多研究工作,包括合成、应用以及机理等方面的探索。在中孔材料的制备方面,由表面活性剂作模板剂来组装的方法有着重要的地位。本文回顾了近年来中孔材料制备技术方面的进展,主要包括各种各样的形成机理。以及如何控制孔径等主题。     

Engineering the surface of LiCoO2 electrodes using atomic layer deposition for stable high-voltage lithium ion batteries

Developing advanced technologies to stabilize positive electrodes of lithium ion batteries under high-voltage operation is becoming increasingly important,owing to the potential to achieve substantially enhanced energy density for applications such as portable electronics and electrical vehicles.Here,we deposited chemically inert and ionically conductive LiAlO2 interfacial layers on LiCoO2 electrodes using the atomic layer deposition technique.During prolonged cycling at high-voltage,the LiAlO2 coating not only prevented interfacial reactions between the LiCoO2 electrode and electrolyte,as confirmed by electrochemical impedance spectroscopy and Raman characterizations,but also allowed lithium ions to freely diffuse into LiCoO2 without sacrificing the power density.As a result,a capacity value close to 200 mA·h·g-1 was achieved for the LiCoO2 electrodes with commercial level loading densities,cycled at the cut-off potential of 4.6 V vs.Li+/Li for 50 stable cycles;this represents a 40％ capacity gain,compared with the values obtained for commercial samples cycled at the cut-off potential of 4.2 V vs.Li+/Li.     

Three-dimensionally ordered,ultrathin graphitic-carbon frameworks with cage-like mesoporosity for highly stable Li-S batteries

Mesoporous carbons have been widely utilized as the sulfur host for lithium-sulfur (Li-S) batteries.The ability to engineer the porosity,wall thickness,and graphitization degree of the carbon host is essential for addressing issues that hamper commercialization of Li-S batteries,such as fast capacity decay and poor high-rate performance.In this work,highly ordered,ultrathin mesoporous graphitic-carbon frameworks (MGFs) having unique cage-like mesoporosity,derived from self-assembled Fe3O4 nanoparticle superlattices,are demonstrated to be an excellent host for encapsulating sulfur.The resulting S@MGFs exhibit high specific capacity (1,446 mAh·g-1 at 0.15 C),good rate capability (430 mAh.g-1 at 6 C),and exceptional cycling stability (～0.049％ capacity decay per cycle at 1 C) when used as Li-S cathodes.The superior electrochemical performance of the S@MGFs is attributed to the many unique and advantageous structural features of MGFs.In addition to the interconnected,ultrathin graphitic-carbon framework that ensures rapid electron and lithium-ion transport,the microporous openings between adjacent mesopores efficiently suppress the diffusion of polysulfides,leading to improved capacity retention even at high current densities.     

Graphene sheets decorated with ZnO nanoparticles as anode materials for lithium ion batteries

ZnO/graphene composites were synthesized using a facile solution-based method. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, and Raman spectra revealed that ZnO nanoparticles with a particle size of around 4 nm were densely and homogeneously deposited on graphene sheets. As the anode material for the lithium ion batteries, the ZnO/graphene composites delivered a stable capacity of 404 mAh/g after 100 cycles at a current rate of 0.5 C, which is much superior to bare ZnO nanoparticles. The battery performance result indicates the presence of graphene sheets in the composites effectively enhance the conductivity and accommodate the volume change.     

Electrospun polycaprolactone scaffolds with tailored porosity using two approaches for enhanced cellular infiltration

The impact of mat porosity of polycaprolactone (PCL) electrospun fibers on the infiltration of neuron-like PC12 cells was evaluated using two different approaches. In the first method, bi-component aligned fiber mats were fabricated via the co-electrospinning of PCL with polyethylene oxide (PEO). Variation of the PEO flow rate, followed by selective removal of PEO from the PCL/PEO mesh, allowed for control of the porosity of the resulting scaffold. In the second method, aligned fiber mats were fabricated from various concentrations of PCL solutions to generate fibers with diameters between 0.13 ± 0.06 and 9.10 ± 4.1 μm. Of the approaches examined, the variation of PCL fiber diameter was found to be the better method for increasing the infiltration of PC12 cells, with the optimal infiltration into the ca. 1.5-mm-thick meshes observed for the mats with the largest fiber diameters, and hence largest pore sizes.     

Synthesis of highly ordered and hydrothermally stable mesoporous materials using sodium silicate as a precursor

Highly ordered mesoporous silica and aluminosilicate materials with extremely high hydrothermal stability have been synthesized successfully at a high hydrothermal treatment temperature of 200 °C by using inexpensive sodium silicate and sodium aluminate as the silica source and alumina source, respectively. The resultant mesoporous materials possess a hexagonal mesostructure and extraordinary stability towards the steam treatment at 800 °C for 2 h. In addition, the direct incorporation of Al into the mesoporous framework can further enhance the hydrothermal stability of ordered mesoporous materials. Our contribution provides a commercially important approach to synthesize ordered mesoporous materials with highly hydrothermal stability, which may find potential applications for the catalytic cracking in the petroleum industry.     

S,N-codoped carbon capsules with microsized entrance: Highly stable S reservoir for Li-S batteries

Nanostructured carbon materials are extensively applied as host materials to improve the utilization rate and reversibility of elemental sulfur in lithium sulfur (Li-S) batteries. Here, S, N-codoped carbon capsules (SNCCs) with microporous walls, prepared by a self-assembly process, are used as the sulfur host material in Li-S batteries. The SNCCs provide plenty of micron-sized cavities to accommodate a high S loading, which are sealed by thick walls with microsized entrance to efficently suppress the shuttle effect of lithium polysulfides. As the cathode in Li-S battery, the SNCCs/sulfur composite with a sulfur mass loading of 70 wt% exhibits a high average reversible capacity of 1220 and 1116 mA h g^?1 at 0.5C and 1C, respectively, superior rate performance (905 and 605 mAh g^?1 at 5C and 10C, respectively) and excellent cycling stability (capacity fading rate of 0.03% per cycle in 500 cycles). Even at a high sulfur areal loading of 7.3 mg/cm², the SNCCs/0.7S electrode still deliver a high initial discharge capacity of 838 mAh g^?1 and keeps at 730 mAh g^?1 after 100 cycles, corresponding to an extraordinary capacity retention of 87.1%, showing an excellent cyclic stability. The outstanding electrochemical performance is associated with the unique capsule structure with abundant volume, microsized entrance and high conductivity. Our results provides a new strategy to prepare highly stable sulfur-carbon composites for the application in Li-S batteries.     

Cross-linked siloxane-based copolymer binder with combined hardness and softness for stable silicon anodes in Li-ion batteries

Silicon has become one of the most emerging anode materials in Li-ion batteries due to its excellent specific capacity. The incorporation of binders can significantly reduce the volume expansion of silicon during the cycling process. In this work, a novel type of cross-linked siloxane-based copolymer, poly (tert-butyl acrylate-co-vinyl tri-lactate ethyl silane) (TBA-VTLES) was designed and utilized as the binder for the silicon anode in Li-ion batteries to alleviate the inner stress of adverse volume changes and improve the electrochemical performance. The hard TBA and soft VTLES were interwoven into a 3D network to achieve the adhesive action via free radical polymerization. The soft chains in TBA-VTLES can enhance the cohesion of the copolymer to disperse residual stress, and thus avoid structural damage during lithiation. Meanwhile, the rigid chains can provide sufficient mechanical strength to maintain the integrity of silicon anode during de-lithiation. Moreover, the presence of TBA-VTLES can improve the adhesive strength between the copper collector and the binder. This novel type of siloxane-based copolymer binder with hardness and softness provides a feasible way to improve the silicon anode performance of Li-ion batteries.

Graphical abstract

The synthesized cross-linked copolymer binder can improve the interfacial interaction and electrochemical performance of Si anode-- present in Graphical abstract figure-- need or not.