Unique Yolk-shell Structure Research Articles

High performance of yolk-shell structured MnO@nitrogen doped carbon microspheres as lithium ion battery anode materials and their in operando X-ray diffraction study

The MnO@nitrogen doped carbon microspheres with a yolk-shell structure (YS-MnO@NC) is reported. As an anode for lithium ion battery, the YS-MnO@NC exhibits a very high reversible capacity (1280 mA h g−1 at 0.1 A g−1), superior rate capability (capacities of 1090, 860, 700, 545, and 390 mA h g−1 at 0.2, 0.5, 1.0, 2.0, and 5.0 A g−1, respectively), and stable cycling performance (880 mA h g−1 at 1.0 A g−1 after 1000 cycles). The reversible capacity and cyclability of YS-MnO@NC is higher than MnO based materials reported previously. Its remarkable performance is attributable to the unique yolk-shell structure and the presence of the NC shell. Specifically, the yolk-shell structure improves its structural stability during the repeated cycles due to the presence of the internal void between the core and shell, while the NC shell increases its electric conductivity and wettability toward the electrolyte solution. Additionally, the nitrogen doped structure also promotes a strong electronic coupling between MnO and NC. The in operando X-ray diffraction studies show that the MnO core and hollow NC microsphere play comparatively equal contributions on the high performance of the YS-MnO@NC. Both the NC shell and MnO microsphere exhibit high reversibility in lithiation and delithiation.

Constructing of hierarchical yolk-shell structure Li4Ti5O12-SnO2 composites for high rate lithium ion batteries

High performance Li-ion batteries require materials with well-designed and controlled structures on nano and micrometre scales, and electrochemical properties can be enhanced by manipulating structure and morphology. Here a hierarchical yolk-shell structure Li4Ti5O12-SnO2 (LTO-SnO2) composites for application of lithium-ion batteries are successfully prepared by controlling the reaction temperature of hydrothermal process. The experimental results demonstrate that the LTO-SnO2 composites prepared at 130 °C (Marked as LS-130) have a well hierarchical yolk-shell structure and a good electrochemical property. The LS-130 electrode exhibits the first discharge specific capacity of 556.4 mAh g−1 at 1 C, and a stable capacity of 253.2 mAh g−1 still maintained even after 200 cycles. Moreover, when the current rate increase to 10 C, the average discharge specific capacities of LS-130 electrode also show 154.6 mAh g−1, indicating an excellent rate performance. The excellent electrochemical performance is mainly ascribed to the stability of unique yolk-shell structure and composition involved with the numerous ultrathin LTO nanosheets. The work described here shows that the hierarchical yolk-shell structure LTO-SnO2 composite is a promising anode material for high power and long life lithium ion batteries.

Metal-organic frameworks derived yolk-shell ZnO/NiO microspheres as high-performance anode materials for lithium-ion batteries

Smart design and rational fabrication of novel anode materials with high specific capacity and long cycling stability are of significant importance for high-performance lithium-ion batteries (LIBs). Herein, nanostructured ZnO/NiO microspheres with a nanorods-composed shell and a microsphere yolk were synthesized by a controlled calcination treatment of the bimetallic organic frameworks in air. The obtained yolk-shell ZnO/NiO microspheres are observed to have an average diameter of 2 μm with uniform microsphere morphology from field-emission scanning electron microscopy and high-resolution transmission electron microscopy. Benefitting from the unique yolk-shell structure inherited from the bimetallic organic frameworks and the synergistic effect from ZnO and NiO, the as-prepared yolk-shell ZnO/NiO displays excellent lithium storage performance, including high specific capacity (1008.6 mAh g−1 at 0.1 A g−1 after 200 cycles), superior rate capability (437.1 mAh g−1 at 2 A g−1) and outstanding long-term cycling stability (592.4 mAh g−1 at 0.5 A g−1 after 1000 cycles), which demonstrates its promising potential as high-performance anode material for LIBs.

Metal-Organic-Framework-Derived Yolk-Shell-Structured Cobalt-Based Bimetallic Oxide Polyhedron with High Activity for Electrocatalytic Oxygen Evolution.

The development of inexpensive, efficient, and environmentally friendly catalysts for oxygen evolution reaction (OER) is of great significant for green energy utilization. Herein, binary metal oxides (MxCo3-xO4, M = Zn, Ni, and Cu) with yolk-shell polyhedron (YSP) structure were fabricated by facile pyrolysis of bimetallic zeolitic imidazolate frameworks (MCo-ZIFs). Benefiting from the synergistic effects of metal ions and the unique yolk-shell structure, MxCo3-xO4 YSP displays good OER catalytic activity in alkaline media. Impressively, ZnxCo3-xO4 YSP shows a comparable overpotential of 337 mV at 10 mA cm-2 to commercial RuO2 and exhibits superior long-term durability. The high activity and good stability reveals its promising application.

Interface-modulated fabrication of hierarchical yolk–shell Co3O4/C dodecahedrons as stable anodes for lithium and sodium storage

Transition-metal oxides (TMOs) have gradually attracted attention from researchers as anode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) because of their high theoretical capacity. However, their poor cycling stability and inferior rate capability resulting from the large volume variation during the lithiation/sodiation process and their low intrinsic electronic conductivity limit their applications. To solve the problems of TMOs, carbon-based metal-oxide composites with complex structures derived from metal–organic frameworks (MOFs) have emerged as promising electrode materials for LIBs and SIBs. In this study, we adopted a facile interface-modulated method to synthesize yolk–shell carbon-based Co3O4 dodecahedrons derived from ZIF-67 zeolitic imidazolate frameworks. This strategy is based on the interface separation between the ZIF-67 core and the carbon-based shell during the pyrolysis process. The unique yolk–shell structure effectively accommodates the volume expansion during lithiation or sodiation, and the carbon matrix improves the electrical conductivity of the electrode. As an anode for LIBs, the yolk–shell Co3O4/C dodecahedrons exhibit a high specific capacity and excellent cycling stability (1,100 mAh·g−1 after 120 cycles at 200 mA·g−1). As an anode for SIBs, the composites exhibit an outstanding rate capability (307 mAh·g−1 at 1,000 mA·g−1 and 269 mAh·g−1 at 2,000 mA·g−1). Detailed electrochemical kinetic analysis indicates that the energy storage for Li+ and Na+ in yolk–shell Co3O4/C dodecahedrons shows a dominant capacitive behavior. This work introduces an effective approach for fabricating carbonbased metal-oxide composites by using MOFs as ideal precursors and as electrode materials to enhance the electrochemical performance of LIBs and SIBs.

Multiple Interfaces Structure Derived from Metal-Organic Frameworks for Excellent Electromagnetic Wave Absorption

Hierarchical yolk–shell nanostructure (NiO/Ni/GN@Air@NiO/Ni/GN) derived from Ni-based metal–organic frameworks (Ni-MOFs) is synthesized by solvothermal reactions. After successive carbonization and oxidation treatments, hierarchical NiO/Ni nanocrystals covered with a graphene shell are obtained with the yolk–shell nanostructure intact. The NiO/Ni/GN@Air@NiO/Ni/GN composites are characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that the NiO/Ni/GN@Air@NiO/Ni/GN composites exhibit superior electromagnetic wave absorption properties. A minimum reflection loss (RLmin) of −34.5 dB is obtained at 17.2 GHz with the thin thickness of 1.7 mm. In addition, the best microwave absorption properties are achieved with a 2.0 mm absorber layer (RLmin = −22.5 dB, bandwidth of 6.0 GHz). The outstanding absorption ability may arise from the unique yolk–shell structure and nanoporous carbon, which can tune the dielectric of the NiO/Ni/GN@Air@NiO/Ni/GN composites to acquire good impedance matching. Moreover, the interspaces can induce interfacial polarization and multiple reflections.

Na–Mn–O@C yolk–shell nanorods as an ultrahigh electrochemical performance anode for lithium ion batteries

By virtue of its unique yolk–shell structure and composition, the as-built Na0.55Mn2O4·1.5H2O@C electrode endows LIBs with attractive electrochemical performances.

Yolk-Shell Ni@SnO2 Composites with a Designable Interspace To Improve the Electromagnetic Wave Absorption Properties.

In this study, yolk-shell Ni@SnO2 composites with a designable interspace were successfully prepared by the simple acid etching hydrothermal method. The Ni@void@SnO2 composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results indicate that interspaces exist between the Ni cores and SnO2 shells. Moreover, the void can be adjusted by controlling the hydrothermal reaction time. The unique yolk-shell Ni@void@SnO2 composites show outstanding electromagnetic wave absorption properties. A minimum reflection loss (RLmin) of -50.2 dB was obtained at 17.4 GHz with absorber thickness of 1.5 mm. In addition, considering the absorber thickness, minimal reflection loss, and effective bandwidth, a novel method to judge the effective microwave absorption properties is proposed. On the basis of this method, the best microwave absorption properties were obtained with a 1.7 mm thick absorber layer (RLmin= -29.7 dB, bandwidth of 4.8 GHz). The outstanding electromagnetic wave absorption properties stem from the unique yolk-shell structure. These yolk-shell structures can tune the dielectric properties of the Ni@air@SnO2 composite to achieve good impedance matching. Moreover, the designable interspace can induce interfacial polarization, multiple reflections, and microwave plasma.

Yolk-Shell MnO@ZnMn2 O4 /N-C Nanorods Derived from α-MnO2 /ZIF-8 as Anode Materials for Lithium Ion Batteries.

Manganese oxides (MnOx ) are promising anode materials for lithium ion batteries, but they generally exhibit mediocre performances due to intrinsic low ionic conductivity, high polarization, and poor stability. Herein, yolk-shell nanorods comprising of nitrogen-doped carbon (N-C) coating on manganese monoxide (MnO) coupled with zinc manganate (ZnMn2 O4 ) nanoparticles are manufactured via one-step carbonization of α-MnO2 /ZIF-8 precursors. When evaluated as anodes for lithium ion batteries, MnO@ZnMn2 O4 /N-C exhibits an reversible capacity of 803 mAh g-1 at 50 mA g-1 after 100 cycles, excellent cyclability with a capacity of 595 mAh g-1 at 1000 mAg-1 after 200 cycles, as well as better rate capability compared with those non-N-C shelled manganese oxides (MnOx ). The outstanding electrochemical performance is attributed to the unique yolk-shell nanorod structure, the coating effect of N-C and nanoscale size.

Highly Active and Stable Pt-Loaded Ce0.75Zr0.25O2 Yolk-Shell Catalyst for Water-Gas Shift Reaction.

Multishelled, Pt-loaded Ce0.75Zr0.25O2 yolk-shell microspheres were prepared by a simple spray pyrolysis process for use in the water-gas shift (WGS) reaction. The Pt-loading was optimized, obtaining highly active Pt/Ce0.75Zr0.25O2 yolk-shell nanostructures for the WGS. Of the prepared catalysts, a 2% Pt loading of the Ce0.75Zr0.25O2 yolk-shell microspheres showed the highest CO conversion. The high catalytic activity of the 2% Pt/Ce0.75Zr0.2O2 catalyst was mainly due to its easier reducibility and the maintenance of active catalytic Pt species. The Pt-loaded Ce0.75Zr0.25O2 catalyst microspheres were highly resistant to Pt sintering because of their unique yolk-shell structure. Spray pyrolysis was found to be highly efficient for the production of precious-metal-loaded, multicomponent metal oxide yolk-shell microspheres for catalytic applications.

Improved electrochemical performance of yolk-shell structured SnO2@void@C porous nanowires as anode for lithium and sodium batteries

Various yolk-shell structured particles designed for large volume expansion materials for lithium-ion storage have been reported, the cycle stability and coulombic efficiency can be effectively improved through such structure design. SnO2 has high theoretical capacity of 1494 mA h g−1 and 1378 mA h g−1 for lithium and sodium storage, respectively. The large volume expansion problem of SnO2 has long been considered as the primary reason for the capacity fading of SnO2 based anode materials. In this paper, the yolk-shell structured SnO2 porous nanowire has been designed, and this unique yolk-shell structure is reported as anode materials for lithium and sodium-ion storage for the first time. The yolk-shell structured porous nanowires deliver significantly improved cycle stability and coulombic efficiency as active material for both lithium and sodium-ion storage compared with that of pure SnO2 porous nanowires. It exhibits a high and stable capacity of 1150 mA h g−1 at current density of 200 mA g−1 for lithium-ion storage, and a capacity of 401 mA h g−1 at current density of 50 mA g−1 after 50 cycles for sodium-ion storage.

Resorcinol-formaldehyde resin based porous carbon materials with yolk-shell structure for high-performance supercapacitors

Novel yolk-shell structure of resorcinol-formaldehyde resin (YRF) is formed via the condensation polymerization of resorcinol and formaldehyde at 0°C without any template. After carbonized and activated with KOH at 700°C, the YRF based porous carbon materials are obtained and the unique yolk-shell structure is remained. The specific surface area of the porous carbon materials is up to 1218m2g−1 through the N2 adsorption-desorption method and many micropores and mesopores are formed in the carbonized materials which are beneficial for electrolyte transport. The specific capacitance of porous carbon material YRFC700-1:3 reaches 397.4Fg−1 at the current density of 0.5Ag−1 and the capacitance retention is 91.2% after 10,000 charge-discharge processes at large current density of 20Ag−1. The strategy developed in this work provides a good example for making full use of polymer-based carbon materials. The good electrochemical performance demonstrates that the polymer-based carbon materials may have promising applications in high-performance of energy-storage devices.

Large-scale aerosol-assisted synthesis of biofriendly Fe₂O₃ yolk-shell particles: a promising support for enzyme immobilization.

Multiple-shelled Fe2O3 yolk-shell particles were synthesized using the spray drying method and intended as a suitable support for the immobilization of commercial enzymes such as glucose oxidase (GOx), horseradish peroxidase (HRP), and laccase as model enzymes. Yolk-shell particles have an average diameter of 1-3 μm with pore diameters in the range of 16 to 28 nm. The maximum immobilization of GOx, HRP, and laccase resulted in the enzyme loading of 292, 307 and 398 mg per g of support, respectively. After cross-linking of immobilized laccase by glutaraldehyde, immobilization efficiency was improved from 83.5% to 90.2%. K(m) and V(max) values were 41.5 μM and 1722 μmol min(-1) per mg protein for cross-linked laccase and those for free laccase were 29.3 μM and 1890 μmol min(-1) per mg protein, respectively. The thermal stability of the enzyme was enhanced up to 18-fold upon cross-linking, and the enzyme retained 93.1% of residual activity after ten cycles of reuse. The immobilized enzyme has shown up to 32-fold higher stability than the free enzyme towards different solvents and it showed higher efficiency than free laccase in the decolorization of dyes and degradation of bisphenol A. The synthesized yolk-shell particles have 3-fold higher enzyme loading efficiency and lower acute toxicity than the commercial Fe2O3 spherical particles. Therefore, the use of unique yolk-shell structure Fe2O3 particles with multiple-shells will be promising for the immobilization of various enzymes in biotechnological applications with improved electrochemical properties. To the best of our knowledge, this is the first report on the use of one pot synthesized Fe2O3 yolk-shell structure particles for the immobilization of enzymes.

Mesoporous yolk-shell structure Bi2MoO6 microspheres with enhanced visible light photocatalytic activity

Mesoporous yolk-shell structure Bi2MoO6 (BMO-YS) microspheres were successfully synthesized via a facile solvothermal route in Bi2MoO6 precursor solution. The morphology, structure and photocatalytic performance of the BMO-YS in the degradation of Rhodamine B (RhB) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption–desorption, UV–vis absorption spectroscopy and electrochemical impedance spectra, respectively. The as-prepared BMO-YS mainly consists of microspheres with diameters of about 1.5μm. The photocatalytic studies reveal that the BMO-YS not only exhibits optimum photocatalytic performance, which may be attributed to the excellent charge separation characteristics and the enhanced light absorption offered by its unique yolk-shell structure, but also possesses excellent recyclability for photocatalysis.

Silver-loaded nitrogen-doped yolk-shell mesoporous TiO2 hollow microspheres with enhanced visible light photocatalytic activity.

Silver-loaded nitrogen-doped yolk-shell mesoporous TiO2 hollow microspheres (Ag-N-TiO2-YSM) were prepared by employing acetic acid as the hollowing controller and triethanolamine as the N source for the first time. Ag nanoparticles (NPs) were uniformly deposited by a simple in situ photo-reduction method, which can prevent the aggregation of Ag NPs. The efficiency of the as-prepared samples was investigated by monitoring the degradation of rhodamine B and ciprofloxacin under visible light irradiation. The experimental results indicate that N-doped yolk-shell mesoporous TiO2 hollow microspheres show higher photocatalytic activity than P25 TiO2 under visible light irradiation because of N doping and the unique yolk-shell structure. In addition, Ag-N-TiO2-YSM shows enhanced activity compared with N-TiO2-YSM due to the SPR absorption of silver NPs and the fast generation, separation and transportation of the photogenerated carriers. Moreover, the Ag contents can affect the photocatalytic activity of the Ag-N-TiO2-YSM composite. A suitable amount of Ag deposition gives the highest photocatalytic activity. A higher loading does not improve the photocatalytic activity of N-TiO2-YSM further. The active species generated in the photocatalytic system were also investigated. Based on our experimental results, a possible photocatalytic mechanism was proposed. The strategy presented here gives a promising route towards the development of delicate metal@hollow semiconductor composites for many applications in photocatalysis.

Synthesis of small yolk–shell Fe3O4@TiO2 nanoparticles with controllable thickness as recyclable photocatalysts

Core–shell nanophotocatalysts consisting of superparamagnetic cores and functional shells are intriguing in environmental remediation and biology. A few Fe3O4@TiO2 particles have been developed in previous research studies, while most of them show a submicron-scale size and thick SiO2 interlayers. Herein, we present a facile approach to prepare small Fe3O4@TiO2 with a unique yolk–shell structure below 50 nm, in which most of the SiO2 interlayers have been simultaneously etched off during synthesis. The prepared photocatalysts have been characterized by TEM, XRD, BET and VSM, and a formation mechanism is proposed. Controllable thickness of the TiO2 shell has been achieved and its effect on their photocatalytic activities has also been investigated. These small yolk–shell Fe3O4@SiO2 nanoparticles are expected to be applied in a variety of fields due to their low density, high surface area, superparamagnetic behavior and good photocatalytic activity.

Generalized synthesis of yolk–shell metal oxide spheres

Abstracts Varieties of yolk–shell metal oxide spheres, including SnO 2 , CeO 2 and Tb 4 O 7 , with high yield have been successfully prepared via a general solvothermal method by using carbon spheres as sacrificial templates. The creation of yolk–shell structure is achieved after the removal of carbon templates by annealing. The results show that the typical products of yolk–shell SnO 2 spheres exhibit excellent textural properties, which makes them good candidates for use in gas-sensing, energy storage, and so on. Many more metal oxides with such a unique yolk–shell structure can be easily prepared through the present approach, and they may show great application potentials.

Hierarchical Fe3O4@TiO2 Yolk–Shell Microspheres with Enhanced Microwave‐Absorption Properties

A facile and efficient strategy for the synthesis of hierarchical yolk-shell microspheres with magnetic Fe3O4 cores and dielectric TiO2 shells has been developed. Various Fe3O4@TiO2 yolk-shell microspheres with different core sizes, interstitial void volumes, and shell thicknesses have been successfully synthesized by controlling the synthetic parameters. Moreover, the microwave absorption properties of these yolk-shell microspheres, such as the complex permittivity and permeability, were investigated. The electromagnetic data demonstrate that the as-synthesized Fe3O4@TiO2 yolk-shell microspheres exhibit significantly enhanced microwave absorption properties compared with pure Fe3O4 and our previously reported Fe3O4@TiO2 core-shell microspheres, which may result from the unique yolk-shell structure with a large surface area and high porosity, as well as synergistic effects between the functional Fe3O4 cores and TiO2 shells.

A performance study of enhanced visible-light-driven photocatalysis and magnetical protein separation of multifunctional yolk–shell nanostructures

Synthesis of functional yolk–shell nanostructures (YSNs) containing SiO2 nanoparticle yolk and a mesoporous shell of NiTiO3 is reported. SiO2@TiO2 core–shell spheres were first prepared via a sol–gel approach, and then a Ni(OH)2 nanowhisker was deposited on the surface of a TiO2 layer and SiO2 nanoparticle-core etching took place simultaneously in a H2O–ethanol–ammonia solution reaction, and then a SiO2@void@TiO2@Ni(OH)2 structure was obtained. Finally, the TiO2@Ni(OH)2 shell was transformed into the NiTiO3 shell via calcination treatment, and the SiO2@NiTiO3 YSNs were achieved. The chemical composition and photoresponsive properties of the SiO2@NiTiO3 yolk–shell material can be easily tailored by adjusting the molar ratio of the Ni/Ti precursors. Their visible-light-induced photocatalytic activities were evaluated by the degradation of methylene blue. The SiO2@NiTiO3 YSNs exhibited enhanced and stable photocatalytic performance due to the unique yolk–shell structure, large surface area, fast diffusion of reactants, and multiple reflections of visible light within the sphere interior voids. Furthermore, the present synthesis method can be extended to the preparation of other functional YSNs, such as magnetic YSNs consisting of SiO2-coated Fe3O4 yolk and a Ni(OH)2-coated TiO2 shell, for the application of magnetic separation of proteins.

Facile one-pot synthesis of Eu, N-codoped mesoporous titania microspheres with yolk-shell structure and high visible-light induced photocatalytic performance

A new type of Eu, N-codoped mesoporous TiO2 microspheres with yolk–shell structure (TiO2@void@TiO2) was successfully synthesized by a facile one-pot hydrothermal method at low temperature (180°C). The physical and chemical properties of as-synthesized samples, such as morphology, crystal phase, surface elements composition, porous structure, specific surface area and optical response, were characterized in detail. The resultant samples were porous microspheres with a diameter of about 1–3μm, and were composed of a large number of smaller nanoparticles. An interior circular cavity in each microsphere was formed between core and shell to construct a special yolk–shell structure, and a large number of pores were produced in shell and yolk by CO2 gas bubbles resulting from hydrothermal decomposition of the urea molecules, which tremendously increased the specific surface area and the pore volume of as-obtained samples. The absorption edges of Eu, N-codoped TiO2 were extended to longer wavelength, which led to notable absorption in the visible-light region. The photocatalytic performances of all samples were evaluated by photocatalytic decoloration of rhodamine B and methyl orange under visible light irradiation (λ>420nm). Eu, N-codoped TiO2 with 0.1at.% Eu dopant showed the highest photocatalytic activity, the efficiency of which was 5 times higher than that of Degussa P25. The enhanced photocatalytic performance could be attributed to the synergic effects of many factors, such as high specific surface area, large pore volume and strong absorption to visible light, which were created by the Eu, N-codoping and the unique yolk–shell structure. Based on the above results, the mechanism of enhanced photocatalysis on Eu, N-codoped TiO2 under visible light was proposed.