•The Sn@C yolk-shell NPs can bear hundreds of cycles with ultrafast reversible lithiation-delithiation without rupture.•Finite element analysis demonstrates that the yolk-shell structure improves the chemomechanical durability of the Sn@C NPs.•The constraint effects of C coating on Sn core were investigated by TEM and front-tracking finite element analysis.Surface coating has become an effective method to stabilize solid-electrolyte interphase (SEI), extend the cycle life, and improve rate performance of anode materials for lithium ion batteries (LIBs). However, owing to the incompatible volumetric changes between the core and the shell, core-shell structures with fully filled active materials are prone to fracture upon electrochemical cycling, leading to fast capacity fading. Here, we synthesize partially filled Sn@C yolk-shell nanoparticles (NPs) by chemical vapor deposition (CVD) as anode materials for LIBs. Our in situ transmission electron microscope (TEM) studies demonstrate that the yolk-shell NPs can lithiate and delithiate hundreds of cycles with ultrafast (2 s per cycle) reversible cycling without rupture. Front-tracking finite element analysis of the coupled chemical reaction, diffusion, and stress generation upon lithiation reveals improved chemomechanical durability of the yolk-shell NPs, in comparison to naked SnNPs and fully filled Sn@C core-shell NPs. Our results provide rational guidance to the development and optimization of yolk-shell NPs as high-performance anode materials for LIBs.The Sn@C yolk-shell NPs can lithiate and delithiate hundreds of cycles with ultrafast (2 s per cycle) reversible cycling without rupture that was demonstrated by in situ TEM investigation. Compared to the naked SnNPs and fully filled Sn@C core-shell NPs, the chemomechanical durability of the yolk-shell NPs was improved through the coupled chemical reaction, diffusion, and stress generation upon lithiation that was proved by front tracking finite element analysis.TOC Graphic: (left two) a partially filled Sn@C yolk-shell NP before and after lithiation, the relationship of volume changes of the Sn core as the applied rectangle voltages are shown in the inset images; (right) the phase changes of the Sn core before (or after delithiation) and after lithiation that is verified by the selected area electron diffraction patterns.Download high-res image (357KB)Download full-size image

The co-deformation of face centered cubic-face centered cubic and face centered cubic-body centered cubic systems were investigated using the cold drawn Cu-6 wt% Fe-4 wt% Ag alloys. Ag and Fe precipitates were introduced in the Cu matrix simultaneously and bonded together. Ag precipitates were successfully refined to nanofibers after heavy cold drawing while the Fe precipitates are hardly deformed. In-situ tensile test was performed in transmission electron microscope to reveal the dynamic interaction between Cu dislocations and Fe precipitates. Cu dislocations bowed out and bypassed the Fe precipitates while some residual segments were pinned at the Cu/Fe interface. Few dislocation pileups were found around the Fe precipitates. The different flow stress and slip system between Fe nanoprecipitates and Cu matrix are main reason for the poor co-deformation capability. The co-deformation of face centered cubic-body centered cubic system should be scale dependent.

•Amorphous Fe2O3 nanotube arrays are prepared via layer-by-layer assembly.•Pyrite FeS2 nanotube arrays are obtained by sulfurizing Fe2O3 nanotube arrays.•Various electrochemical properties are characterized.•A comparison between FeS2 nanotube and nanoparticle films is conducted.•Nanotube arrays show enhanced corrosion resistance and photoresponse.Well-aligned one-dimensional iron pyrite FeS2 nanotube arrays have been fabricated via layer-by-layer assembly technique on ZnO nanorod arrays in combination with subsequent sulfurization. The as-prepared products were confirmed to be pure phase pyrite FeS2 with Fe/S ratio approaching 1/2. Typical nanotube structure was observed for the FeS2 with average outer diameter of 150 ± 20 nm and wall thickness of 50 ± 5 nm. Comparisons of photoelectrochemical properties between FeS2 nanotubes and FeS2 nanoparticles were conducted. Tafel polarization curves and electrochemical impedance spectroscopy indicate that FeS2 nanotubes possess high corrosion resistance and electrochemical stability. The J–V curves show that the photocurrent at 1.0 V for FeS2 nanotubes is more than five times larger than that of FeS2 nanoparticles, indicating enhanced photoresponse and rapid charge transfer performances of 1-D nanotube structure. The enhanced photoelectrochemical properties mainly benefit from the unique architecture features of nanotube array structure.

A facile solution-based approach has been developed for the preparation of mackinawite FeS microsheet networks directly on Fe foil. It is found that sulfur sources significantly impact the uniformity and purity of the products, while ethylenediamine as a strong donor ligand plays an important role in the formation of FeS microsheet networks. For comparison, numerous FeS microspheres are obtained in the absence of ethylenediamine. The FeS microsheet networks deliver a promising Li storage capacity (772 mA h g−1 at the 1st cycle and 697 mA h g−1 at the 20th cycle), much higher than that of the FeS microspheres. The enhanced electrochemical performance of the FeS microsheet networks can be attributed to their layered structure and unique morphology, which possess a larger electrode–electrolyte contact area, shorter diffusion length of the ions and easier transportation of the electrons.

•Pd nanocubes enclosed by {200} facets were obtained.•A 7e reaction was realized on Pd nanocubes at 3.26 M borohydride for the first time.•DBFC using Pd nanocubes had higher power density than using Pd/C.•DBFC using Pd nanocubes had much better stability than that using commercial Pd/C.Pd nanocubes enclosed by {200} facets are synthesized and used as an anode catalyst in direct borohydride fuel cell (DBFC) to study the electrocatalytic activity of Pd towards borohydride oxidation reaction (BOR) by modifying its surface atomic structure. A 7e reaction towards BOR is implemented on Pd nanocubes with a borohydride concentration as high as 3.26 M. The cell using Pd nanocubes as anode catalyst exhibits an obvious higher power density than the cell using commercial Pd/C, and maintained 99% of its voltage after 50 h stability test. It suggests that the Pd nanocubes could be a promising anode catalyst for the DBFC application.A 7e reaction is realized on the Pd nanocubes enclosed by {200} facets at a high borohydride concentration of 3.26 M. The direct borohydride fuel cells using Pd nanocubes as anode catalyst have higher power density and much better stability than commercial Pd/C.

FeS2-sensitized ZnO/ZnS nanorod arrays were fabricated and used as the photoanodes for quantum-dot-sensitized solar cells (QDSSCs). The cell performance of the ZnO/ZnS nanorod arrays after sensitization was better than that of ZnO-based nanorod arrays without sensitizing treatment. Pyrite FeS2 was found to be an effective photosensitizer for QDSSCs. Various QDSSCs were assembled using different counter electrodes, such as Pt, FeS2 nanorods and FeS2 nanoparticles, and comparisons of cell performance as well as catalytic activity were made among them.

•Average length of Copper oxide nanowires as a function of time was obtained.•Cu2O lumps decomposed into several small nanoparticles after e-beam irradiation.•No detectable mass transmission was observed in CuO nanowires after irradiation.•No phase change was detected for Cu2O lumps or CuO nanowires after irradiation.Cu2O nanoparticles and CuO nanowires were prepared by a thermal oxidation method. The high-energy e-beam in a transmission electron microscope was used to study the anti-radiation properties of the Cu2O and CuO nanomaterials. The morphology of Cu2O nanoparticles greatly changed during irradiating. Notable mass transmission was observed and new grains formed away the irradiated region. By contrast, neither mass transmission was detected nor new grains were formed when CuO nanowires were irradiated at similar situation. No phase transition was detected whether for Cu2O nanoparticles or CuO nanowires during irradiation. The chemical and mechanical stabilities of CuO and Cu2O under e-beam irradiation were discussed.

High strength and high conductivity Cu-based materials are key requirements in high-speed railway and high-field magnet systems. Cu-Fe alloys represent one of the most promising candidates due to the cheapness of Fe compared to Cu-Ag and Cu-Nb alloys. The high strength of Cu-Fe alloys primarily relies on the high density of the Cu/Fe phase interface, which is controlled by the co-deformation of the Cu matrix and Fe phase. In this study, our main attention was focused on the deformation behavior of the Fe phase using different scales. Cu-2.5% Fe-0.2% Cr (in weight) and Cu-6% Fe alloys were cast, annealed, and cold drawn into wires to investigate their microstructure and properties evolution. Cu-6% Fe contains Cu matrix and Fe, which become the primary particles in the micrometer scale after solution treatment. Cu-2.5% Fe-0.2% Cr contains Cu matrix and Fe precipitate particles in a nanometer scale after solution and aging treatment. The Fe primary particles were elongated and evolved into ribbons in a nanometer scale while the Fe precipitate particles were hardly deformed even at a drawing strain of 6. The reason for the unchanging characteristics of Fe precipitate particles is due to the size effect and incoherent phase interface of Cu matrix and Fe precipitate particles. The strength of both Cu-6% Fe and Cu-2.5% Fe-0.2% Cr alloys increases with the increase in the drawing strain. The electrical resistivity of Cu-6% Fe gradually increases and that of Cu-2.5% Fe-0.2% Cr keeps almost constant with the increase in the drawing strain.探索Cu-Fe 合金中纳米尺寸和微米尺寸的Fe 相的变形行为及区别。1. 通过热处理在Cu-2.5% Fe-0.2% Cr 合金中得到纳米级的Fe 析出相, 在Cu-6% Fe 中得到微米级的Fe 析出相; 2. 通过冷拉拔手段使铜合金从棒状逐步变形成线材; 3. 使用光学显微镜、扫描电镜和透射电镜观察微观组织, 并用万能电子试验机测量抗拉强度, 用标准四点法测量电阻率。1. 通过热处理在Cu-6% Fe 合金中得到尺寸约5 μm 的初生Fe 颗粒, 在Cu-2.5% Fe-0.2% Cr 合金中得到尺寸约50 nm 的次生Fe 颗粒; 2. 初生Fe 颗粒在冷拉拔过程中转变成丝带状纤维, Cu/Fe 相界面密度随变形量增加而增加, 从而使Cu-6% Fe 合金的强度和电阻率都随之增大; 3. 次生Fe 颗粒即使在η=6 的时候也难以变形, 保持着球形的形貌, 同时高密度的位错环绕着Fe 颗粒; Cu-2.5% Fe-0.2% Cr 合金的强度随变形量增加而增大, 遵循Orowan 强化机制; Cu-2.5%Fe-0.2% Cr 合金的电阻率几乎保持不变, 因为Cu/Fe 相界面密度在冷拉拔过程中几乎不变; 4. 尺寸效应和Fe 析出颗粒与Cu 基体的非共格界面对Fe 析出颗粒在冷拉拔过程中不变形起到重要作用。

Excellent reversibility is crucial for the storage capacity and the cycle life of anode materials in high-performance lithium ion batteries, which has not been observed in alloy-type materials such as Si or Ge. In situ transmission electron microscopy reveals a sequential phase transformation in individual Sn nanowires during Li insertion, which is in a reverse order during Li extraction. Both the bright field image and the electron diffraction show a two-step reversible crystalline–crystalline phase transformation. It is noted that the crystalline tin has a more open lattice to readily accommodate Li up to the Li2Sn5 phase while retaining the crystallinity, which distinguishes Sn from its metalloid counterparts. The connected interstices along [001] inside lattice form a helix pipe for fast Li diffusion, indicating the openness of the Sn lattice. The ab initio simulations reveal facile Li diffusion along [001] with a low migration barrier of 0.014 eV. No phase boundary is visible in this step. In the second step, the LixSny phases, including the Li22Sn5 phase, nucleated with grain refinement and enormous volume expansion. The broaden phase boundary indicates that the further alloying is rate-limited not by the diffusion of Li but by the interfacial conversion reaction. The pulverization occurs during delithiation by agglomeration of regular-shape voids, showing a different mechanism from the cracking-dominated fracture in Si. These results elucidate the structural evolution and the phase transformation during the electrochemical cycling, which sheds light on engineering Sn anode materials.

A high solar conversion efficiency is the key characteristic required for any semiconductor material to be a candidate for photovoltaic applications. Although pyrite (FeS2) is considered a promising candidate because of its extremely high light absorption coefficient, its solar conversion efficiency still remains below 3%. We report here the design of a novel one-dimensional pyrite nanostructure to enhance the photoresponsive properties of pyrite. Well-aligned pyrite nanorod arrays were successfully grown on a transparent and conductive glass substrate of fluorine-doped tin oxide using a template-directed method. ZnO nanorod arrays were used as the initial template to produce Fe(OH)3 nanotube arrays and then the Fe(OH)3 nanotube arrays were used as a template to produce pyrite nanorod arrays. The pyrite nanorods had an average diameter of 130 nm and a length of 600 nm. The prepared pyrite nanorod films showed outstanding light absorption and enhanced photocurrents compared with nanoparticle FeS2 films. The excellent optical and photoelectrical performance of FeS2 nanorod films is attributed to the unique one-dimensional ordered architecture, which has large surface areas for light harvest and provides a direct and short pathway for charge transport, reducing the combination loss of photoelectrons. The method offers a new strategy for designing nanostructured materials with one-dimensional ordered architectures for high-performance photovoltaic devices.

•A simple new method was introduced to evaluate the alignment of ZnO arrays.•Well-aligned ZnO nanorod arrays were prepared.•A growth mechanism was proposed for the growth of ZnO nanorods.ZnO nanorod arrays (ZNAs) were prepared via a two-step seeding and solution hydrothermal growth process. Effects of preparing parameters such as seed layer, colloid concentration, substrate and precursor concentration, on the alignment control of ZNAs were systematically investigated. The deviation angle of ZnO nanorods was measured to evaluate the alignment of arrays. Results show that seed layer not only controls the vertical orientation of ZNAs, but also the compactness of ZNAs. Altering colloid concentration and substrate can influence the microstructure of ZnO seed layer and affect the ordered alignment of ZNAs. The precursor concentration has an insignificant effect on the alignment of ZNAs but has great impact on the morphology of ZNAs. Alignment-controlled and well-aligned ZnO nanorods with different diameter and aspect ratio can be obtained by properly controlling the preparing parameters. A growth mechanism was proposed for the growth of ZnO nanorods.ZnO nanorod arrays (ZNAs) were prepared via a two-step seeding and solution hydrothermal growth process. A simple new method was introduced to evaluate the alignment of arrays based on the orientation angle distribution. Effects of preparing parameters, such as seed layer, colloid concentration, substrate and precursor concentration, on the alignment control of ZNAs were systematically investigated. A growth mechanism was proposed for the growth of ZnO nanorods.

Cu-12% Fe (in weight) composite was prepared by casting, pretreating, and cold drawing. The microstructure was observed and Vickers hardness was measured for the composite at various drawing strains. Cu and Fe grains could evolve into aligned filaments during the drawing process. X-ray diffraction (XRD) was used to analyze the orientation evolution during the drawing process. The axial direction of the filamentary structure has different preferred orientations from the radial directions. The strain of Fe grains linearly increases with an increase in the drawing strain up to 6.0, and deviates from the linear relation when the drawing strain is higher than 6.0. With an increase in the drawing strain, the microstructure scales of Fe filaments exponentially decrease. The density of the interface between Cu and Fe phases exponentially increases with an increase in the aspect ratio of Fe filaments. There is a similar Hall-Petch relationship between the hardness and Fe filament spacing. The refined microstructure from drawing deformation at drawing strains lower than 3.0 can induce a more significant hardening effect than that at drawing strains higher than 3.0.

A high solar conversion efficiency is the key characteristic required for any semiconductor material to be a candidate for photovoltaic applications. Although pyrite (FeS2) is considered a promising candidate because of its extremely high light absorption coefficient, its solar conversion efficiency still remains below 3%. We report here the design of a novel one-dimensional pyrite nanostructure to enhance the photoresponsive properties of pyrite. Well-aligned pyrite nanorod arrays were successfully grown on a transparent and conductive glass substrate of fluorine-doped tin oxide using a template-directed method. ZnO nanorod arrays were used as the initial template to produce Fe(OH)3 nanotube arrays and then the Fe(OH)3 nanotube arrays were used as a template to produce pyrite nanorod arrays. The pyrite nanorods had an average diameter of 130 nm and a length of 600 nm. The prepared pyrite nanorod films showed outstanding light absorption and enhanced photocurrents compared with nanoparticle FeS2 films. The excellent optical and photoelectrical performance of FeS2 nanorod films is attributed to the unique one-dimensional ordered architecture, which has large surface areas for light harvest and provides a direct and short pathway for charge transport, reducing the combination loss of photoelectrons. The method offers a new strategy for designing nanostructured materials with one-dimensional ordered architectures for high-performance photovoltaic devices.

A facile solution-based approach has been developed for the preparation of mackinawite FeS microsheet networks directly on Fe foil. It is found that sulfur sources significantly impact the uniformity and purity of the products, while ethylenediamine as a strong donor ligand plays an important role in the formation of FeS microsheet networks. For comparison, numerous FeS microspheres are obtained in the absence of ethylenediamine. The FeS microsheet networks deliver a promising Li storage capacity (772 mA h g−1 at the 1st cycle and 697 mA h g−1 at the 20th cycle), much higher than that of the FeS microspheres. The enhanced electrochemical performance of the FeS microsheet networks can be attributed to their layered structure and unique morphology, which possess a larger electrode–electrolyte contact area, shorter diffusion length of the ions and easier transportation of the electrons.