Unique Yolk-shell Structure Research Articles

Encapsulating Fe2 O3 Nanotubes into Carbon-Coated Co9 S8 Nanocages Derived from a MOFs-Directed Strategy for Efficient Oxygen Evolution Reactions and Li-Ions Storage.

The development of high-efficiency, robust, and available electrode materials for oxygen evolution reaction (OER) and lithium-ion batteries (LIBs) is critical for clean and sustainable energy system but remains challenging. Herein, a unique yolk-shell structure of Fe2 O3 nanotube@hollow Co9 S8 nanocage@C is rationally prepared. In a prearranged sequence, the fabrication of Fe2 O3 nanotubes is followed by coating of zeolitic imidazolate framework (ZIF-67) layer, chemical etching of ZIF-67 by thioacetamide, and eventual annealing treatment. Benefiting from the hollow structures of Fe2 O3 nanotubes and Co9 S8 nanocages, the conductivity of carbon coating and the synergy effects between different components, the titled sample possesses abundant accessible active sites, favorable electron transfer rate, and exceptional reaction kinetics in the electrocatalysis. As a result, excellent electrocatalytic activity for alkaline OER is achieved, which delivers a low overpotential of 205mV at the current density of 10mA cm-2 along with the Tafel slope of 55mV dec-1 . Moreover, this material exhibits excellent high-rate capability and excellent cycle life when employed as anode material of LIBs. This work provides a novel approach for the design and the construction of multifunctional electrode materials for energy conversion and storage.

Yolk-Shell-Structured Nanospheres with Goat Pupil-Like S-Doped SnSe Yolk and Hollow Carbon-Shell Configuration as Anode Material for Sodium-Ion Storage.

Rationally nanostructured electrode materials exhibit excellent sodium-ion storage performance. In particular, yolk-shell configurations of metal chalcogenide@void@C are introduced in various synthetic strategies for use as superior anode materials. Herein, yolk-shell-structured nanospheres, with goat pupil-like configuration of S-doped SnSe yolks and hollow carbon shells, are synthesized by salt-infiltration and a simple post-treatment procedure. Impressively, the co-infiltration of thiourea and selenium oxide enables the doping of sulfur into SnSe (SnSeS) and carbon shells, as well as the formation of a goat pupil-like yolk-shell architecture. High-reactivity thiourea-derived H2 S gas forms nanocrystals inside the carbon nanospheres. The nanocrystals act as seeds for the crystal growth of SnSeS through Ostwald ripening. The unique yolk-shell structure and composition with a heterointerface provide not only structural stability but also fast electrode reaction kinetics during repeated cycling. The SnSeS@C electrode shows an excellent cycle life (186mA h g-1 for 1000 cycles at 0.5 A g-1 ) and rate capability (112mA h g-1 at 5.0 A g-1 ).

Fabrication of yolk-shell NiCo alloy@C composites derived from trimetallic metal–organic frameworks as light-weight and high-performance electromagnetic wave absorbers

Developing the high-performance electromagnetic wave (EMW) absorbers with the characteristics of thin thickness, broad bandwidth and strong absorption against the increasingly serious electromagnetic pollution was still a great challenge. In this work, NiCo alloy@C (NCC) composites were fabricated through high-temperature pyrolysis of trimetallic NiCoZn metal-organic framework. Results showed that the NCC composites displayed a unique yolk-shell structure, and the carbonization temperature had a great influence on the crystal structure, graphitization degree and micromorphology. Moreover, the electromagnetic parameters and absorption capacity could be regulated by adjusting the carbonization temperature and filler contents. Significantly, the obtained NCC composite presented the integrated optimal absorption capacity, including the minimum reflection loss of −61.9 dB under an ultrathin thickness of 1.5 mm and a wide absorption bandwidth of 6.0 GHz at 1.7 mm. Additionally, the underlying absorption mechanisms were revealed. Our results could offer a new approach to fabricate light-weight and high-efficiency EMW absorbers.

Enhanced catalytic performance of Nix-V@HSS catalysts for the DRM reaction: The study of interfacial effects on Ni-VOx structure with a unique yolk-shell structure

A series of Nix-V@HSS catalysts were prepared via a facile one-pot microemulsion method and evaluated in the dry reforming of methane reaction. The influence of interfacial effects of the Ni-VOx structure on the catalysts’ performance was investigated by comparing them to Ni@HSS-V. Ni9.6-V@HSS catalyst exhibited the best activity, with a methane TOF of 12.7 S−1, which was two-times higher than Ni@HSS and Ni@HSS-V. The possible promotion mechanism by V species was proposed based on temperature-programmed surface reaction (TPSR) and in situ infrared spectroscopy of CO, and CO2 adsorption. The activity was strongly related to the interfacial effects of the Ni-VOx structure, over which VOx species interacted with adjacent Ni particles and supplied electrons to Ni to activate CH4. In addition, more oxygen vacancies formed in VOx species due to the formation of a Ni-VOx structure, which accelerated the dissociation of CO2 to generate reactive oxygen species and suppressed carbon deposition. Combined with the enhanced anti-sintering ability caused by the strong interactions between Ni and V promoter, Ni9.6-V@HSS catalyst also exhibited the best stability in long-term test.

Ex-situ XPS analysis of yolk-shell Sb2O3/WO3 for ultra-fast acetone resistive sensor

The preparation of fast, highly responsive and reliable gas sensing devices for the detection of acetone gas is considered to be a key challenge for the development of accurate disease diagnosis systems through exhaled respiratory gases. In the paper, yolk shell Sb2O3/WO3 is synthesized and its gas sensing performance was studied by static test system. Special, the maximum response value of 1:1 Sb2O3/WO3 yolk-shell (WO3-1 YSL) sensor to 100 ppm acetone can reach as high as 50.0 at 200 ℃. And it also exhibits excellent response/recover time (4 s/5 s), low detection limit (2 ppm) and superior selectivity towards acetone. More importantly, in mixed selective gas test, the sensor shows high selectivity towards acetone. And the mechanism is analyzed by ex-situ XPS. The excellent gas-sensing performance can be attributed to unique yolk-shell structure, which facilitates the rapid transport of charge carriers from the surface to the bulk and provides more active sites for gas adsorption and desorption; the heterojunction between of Sb2O3 and WO3, which promotes oxygen pre-adsorption on the surface and increasing the interfacial potential; the increased oxygen vacancies which allowing more chemisorbed oxygen to form.

Yolk-shell Si@void@C composite with Chito-oligosaccharide as a C–N precursor for high capacity anode in lithium-ion batteries

The yolk-shell structure of Si@void@C anode for lithium ion batteries with Chito-oligosaccharide (COS) as carbon and nitrogen source was successfully prepared by using a newly designed method. As a low-molecular-weight precursor, COS is completely soluble in an aqueous solution to make the composite more homogeneous. The COS derived carbon has a higher porosity than macromolecules derived carbon, providing reliable channels for ions to shuttle. In addition, amino groups from COS effectually promote the wettability of electrode interface. For the yolk-shell structure of Si@void@C composite, the outer carbon shell is not only conducive to the rapid transmission of electrons and lithium ions, but also to the reduction of charge transfer resistance and effective protection of the silicon core ball from electrolyte corrosion. Furthermore, the void layer between silicon core and carbon shell can adapt to huge volume expansion of Si and stabilize the electrode structure. Therefore, Si@void@C exhibits superior cycle stability and high rate performance. At a current density of 420 mA g−1, after 200 cycles, the Si@void@C maintains a high capacity of 1038.5 mAh g−1. In this experiment, the innovative synthesis of a unique yolk-shell structure of Si@C composites is an effective way to obtain high-performance anode materials.

Fabrication for improved photocatalytic H2 production using γ-ray irradiation: Yolk-shell and hollow structures derived from MIL-125

The yolk-shell MIL-125/TiO2/ Pt/CdS and hollow TiO2/Pt/CdS visible-light catalysts were successfully synthesized from MIL-125 by γ-ray irradiation. During the reduction process by γ-ray irradiation, metal organic frameworks are partially or completely hydrolyzed to TiO2 nanosheets, forming the unique yolk-shell or hollow structure. The hydrogen production rate is 2.9835 mmol·g−1·h−1 for yolk-shell structures and 1.9342 mmol·g−1·h−1 for hollow structures under visible-light illumination, which is 7.9 and 5.1 times higher than that of CdS, respectively. The excellent properties of these photocatalysts may be attributed to the effective absorption and utilization of the light, the porous yolk-shell or hollow structure derived from MIL-125 to facilitate mass transfer, and close contact among CdS nanoparticles, TiO2 nanosheets and Pt nanoparticles to improve the separation of electron-hole pairs. This research can provide a simple and new method for the construction of high efficiency photocatalysts derived from MOFs using the γ-ray irradiation.

Ultrathin Metal–Organic Framework Nanosheets-Derived Yolk–Shell Ni 0.85 Se@NC with Rich Se-Vacancies for Enhanced Water Electrolysis

We present a controlled fabrication of selective ultrathin metal–organic framework (MOF) nanosheets as preassembling platforms, yolk–shell structured with a few-layered N-doped carbon (NC) shell-en...

A Li-S battery with ultrahigh cycling stability and enhanced rate capability based on novel ZnO yolk-shell sulfur host

Shuttle effect is still a challenging issue for Li-S batteries. Here, we synthesize the yolk-shell ZnO structure as sulfur host, which effectively suppresses lithium polysulfides shuttling effect and enhances the electrochemical performance of Li-S batteries. Currently, lithium-sulfur (Li-S) batteries still suffer from fast capacity decay, poor coulombic efficiency (CE) and short cycling lifespan, which result from the severe shuttle effect issue caused by high solubility and rapid diffusion of lithium polysulfides (LiPSs) in organic electrolytes. Here, yolk-shell zinc oxide (YS-ZnO) spheres are synthesized and for the first time, applied as a host for Li-S batteries to tackle this challenge. The polar ZnO exhibits high chemical anchoring ability toward LiPSs while the unique yolk-shell structure not only provides an additional physical barrier to LiPSs but also enables much more uniform sulfur distribution, thus significantly suppressing LiPSs shuttling effect meanwhile promoting sulfur conversion reactions. As a result, the YS-ZnO enables the Li-S battery to display an initial specific capacity of 1355 mAh g −1 and an outstanding capacity retention capability (~89.44% retention rate) even after 500 cycles with the average CE of ~99.46% at the current of 0.5 C. By contrast, the capacity of conventional-ZnO-nanoparticles based battery severely decays to 472 mAh g −1 after cycling for 500 times. More impressively, the S/YS-ZnO based Li-S battery can maintain a low decay rate of 0.040% every cycle and high average CE of 98.82% over 1000 cycles at 3 C.

Synthesis of SnO2/yolk-shell LaFeO3 nanocomposites as efficient visible-light photocatalysts for 2,4-dichlorophenol degradation

Herein, yolk-shell LaFeO3 (YS-LFO) microsphere has been successfully prepared by a carbon microsphere (CMS) template-adsorption-calcination method. It was confirmed that the YS-LFO microspheres showed high visible-light photoactivities for 2,4-dichlorophenol degradation as compared to bare LaFeO3 (LFO) nanoparticles, attributing to the unique yolk-shell structure and the increased surface area. The visible-light photocatalytic activities of YS-LFO microspheres could be further promoted by coupling with SnO2 (SO) nanoparticles. Based on the surface photovoltage spectra, photoelectrochemical measurements and other characterization, it was demonstrated that the coupled SO afforded a thermodynamically suitable platform for accepting the high-level energy electrons from LaFeO3 so as to enhance the charge separation. Compared with YS-LFO microspheres and LFO nanoparticles, the amount optimized (10SO/YS-LFO) nanocomposites displayed 1.6 and 4.7-time enhancement for 2,4-dichlorophenol degradation under visible-light irradiation, respectively. This efficient strategy of morphology controlling and photoelectron modulating could pave the approach to design high-activity visible-light driven photocatalysts.

Yolk-shell nanovesicles endow glutathione-responsive concurrent drug release and T1 MRI activation for cancer theranostics

The effort of incorporating therapeutic drugs with imaging agents has been one of the mainstreams of nanomedicine, which holds great promise in cancer treatment in terms of monitoring therapeutic drug activity and evaluating prognostic index. However, it is still technically challenging to develop nanomedicine endowing a spatiotemporally controllable mechanism of drug release and activatable imaging capability. Here, we developed a yolk-shell type of GSH-responsive nanovesicles (NVs) in which therapeutic drug (Doxorubicin, DOX) and magnetic resonance imaging (MRI) contrast agent (ultrasmall paramagnetic iron oxide nanoparticles, USPIO NPs) formed complexes (denoted as USD) and were encapsulated inside the NVs. The formation of USD complexes is mediated by both the electrostatic adsorption between DOX and poly(acrylic acid) (PAA) polymers and the DOX-iron coordination effect on USPIO NPs. The obtained USD NVs showed a unique yolk-shell structure with restrained drug activity and quenched T1 MRI contrast ability which, on the other hand, can respond to glutathione (GSH) and lead to drug release and T1 contrast activation in a spatiotemporally concurrent manner. Furthermore, the USD NVs exhibited great potential to kill HCT116 cancer cells in vitro and effectively inhibit the tumor growth in vivo. This study may shed light on the design of sophisticated nanotheranostics in precision nanomedicine.

Magnetic yolk-shell structure of ZnFe2O4 nanoparticles for enhanced visible light photo-Fenton degradation towards antibiotics and mechanism study

Constructing yolk-shell structure is a promising strategy for creating much more active sites and enhancing relative light absorption. Yolk-shell ZnFe2O4 has been well used in the areas of electrocatalysis, sensor, etc., but no corresponding application in photo-Fenton reaction. In this work, yolk-shell ZnFe2O4 was firstly employed as photo-Fenton catalyst to investigate its advantage for antibiotics degradation. Interestingly, the yolk-shell ZnFe2O4 showed much improved photo-Fenton catalytic performance with magnetic recycling property, which is 5 times and 23 times higher than the ZnFe2O4 normal particles and α-Fe2O3, respectively, for degradation of contaminants under visible light irradiation. The superiority was mainly attributed to its relatively large surface area and much enhanced light absorption as well as effective charge separation, induced by unique yolk-shell structure. Besides, from the practical application view, the effect of reaction conditions, co-existing cations and anions were systematically investigated for the tetracycline (TC) photo-Fenton degradation. The TC degradation intermediate products were analyzed by HPLC-MS and a possible degradation pathway was proposed to illustrate the mechanism of TC degradation. The as-employed yolk-shell structure of ZnFe2O4 in this work probably provides a new method for designing high efficiency of photo-Fenton catalyst towards the decontamination of refractory pollutants in aqueous solution.

Synthesis of yolk-shell structure Fe3O4/P(MAA-MBAA)-PPy/Au/ void/TiO2 magnetic microspheres as visible light active photocatalyst for degradation of organic pollutants

Yolk-shell magnetic Fe3O4/P(MAA-MBAA)-PPy/Au/void/TiO2 microspheres have been prepared as visible light active photocatalyst. In this structure, the Fe3O4/P(MAA-MBAA)-PPy core-shell support provides magnetic properties for the catalyst and a large number of binding sites for the Au nanoparticles. In addition, coupling TiO2 with Au nanoparticles can extend the range of absorbable sunlight and enhance electron hole separation. The test of degrading rhodamine B (RhB) under simulated visible light was used to verify the photocatalytic activity of the photocatalyst. The results showed that the photocatalyst exhibited favorable catalytic properties within 90 min in the case of using 4 mg itself. The improved performances were ascribed to the unique yolk-shell structure, which on the one hand greatly improves the light utilization, on the other hand favors full contact of the dye because of the porous appearance of the outer shell. Furthermore, the existence of magnetic core was beneficial to the recycling of the photocatalyst. And the recycling results demonstrated that the catalyst efficiency was maintained at 70.2% even after six recycling experiments. This work not only displays a new material for the degradation of organic dyes, but also provides a new approach for the synthesis of yolk-shell structure photocatalysts.

Yolk-shell CdS@void@TiO2 composite particles with photocorrosion resistance for enhanced dye removal and hydrogen evolution

Yolk-shell CdS@void@TiO2 (cadmium sulfide@void@titanium dioxide) composite particles (CPs), consisting of three parts: core (CdS) synthesized by solvent thermal reaction, void generated by polypyrrole (PPy) sacrificed layers and porous shell (TiO2) by sol-gel method, were innovatively fabricated. The actual yolk-shell structure and chemical composition of the resultant CdS@void@TiO2 were verified by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffraction analyses (XRD), and X-ray photoelectron spectroscopy (XPS). CdS@void@TiO2 CPs possessed enhanced visible light response due to its narrower energy gap (2.9 eV) than TiO2 (3.2 eV). With the support of photocatalytic performance test results, CdS@void@TiO2 exhibits much higher hydrogen evolution rate up to 1893.5 μmol h−1 g−1 as well as dye removal efficiency both under visible and UV light irradiation than pristine TiO2. The covering of TiO2 shell remarkably promotes the photocorrosion resistance of CdS. The unique yolk-shell structure promotes striking photocatalytic performance in dye removal and hydrogen evolution. A possible photocatalytic mechanism about enhanced photocatalytic activity and robust photostability is also proposed.

Yolk–Shell Structured FeP@C Nanoboxes as Advanced Anode Materials for Rechargeable Lithium‐/Potassium‐Ion Batteries

AbstractMaintaining structural stability and alleviating the intrinsic poor conductivity of conversion‐type reaction anode materials are of great importance for practical application. Introducing void space and a highly conductive host to accommodate the volume changes and enhance the conductivity would be a smart design to achieve robust construction; effective electron and ion transportation, thus, lead to prolonged cycling life and excellent rate performance. Herein, uniform yolk–shell FeP@C nanoboxes (FeP@CNBs) with the inner FeP nanoparticles completely protected by a thin and self‐supported carbon shell are synthesized through a phosphidation process with yolk–shell Fe2O3@CNBs as a precursor. The volumetric variation of the inner FeP nanoparticles during cycling is alleviated, and the FeP nanoparticles can expand without deforming the carbon shell, thanks to the internal void space of the unique yolk–shell structure, thus preserving the electrode microstructure. Furthermore, the presence of the highly conductive carbon shell enhances the conductivity of the whole electrode. Benefiting from the unique design of the yolk–shell structure, the FeP@CNBs manifests remarkable lithium/potassium storage performance.

Resorcinol-Formaldehyde Resin-Coated Prussian Blue Core-Shell Spheres and Their Derived Unique Yolk-Shell FeS2@C Spheres for Lithium-Ion Batteries.

The practical applications of transition metal sulfides as electrode materials for lithium-ion batteries (LIBs) is greatly hindered by the fast capacity fading owing to the large volume expansion. To address this issue, construction of transition metal sulfide and carbon nanocomposites with unique yolk-shell structures is an effective strategy but also remains a great challenge. In this work, we reported a facile approach to synthesize the unique yolk-shell FeS2@carbon (FeS2@C) spheres via calcination treatment of the resorcinol-formaldehyde (RF) resin-coated Prussian blue (FeFe PB) core-shell spheres in Ar atmosphere and a subsequent sulfidation treatment. The synthetic method herein was quite simple and convenient. Such unique structure design could effectively prevent the large volume expansion and dissolution of the active materials in the electrolytes during lithiation. As expected, the yolk-shell FeS2@C spheres exhibited good electrochemical performance as anode materials for LIBs, which displayed a high discharge capacity of 560 mA h g-1 at 100 mA g-1 for 100 cycles. When the current density increased to 1000 mA g-1, a reversible discharge capacity of 269 mA h g-1 was still retained after 500 cycles. The present work demonstrated an extraordinary synthetic strategy to construct transition metal sulfide and carbon nanocomposites with unique yolk-shell structure. In addition, this RF resin coating strategy can be further extended to synthesize other RF resin-coated PB analogue (PBA) core-shell nanostructures, demonstrating the generality of this RF resin coating strategy.

Lignosulfonate-Directed Synthesis of Consubstantial Yolk–Shell Carbon Microspheres with Pollen-Like Surface from Sugar Biomass

The carbon materials with diverse morphologies and structures have attracted much interest for various applications. In this work, by introducing lignosulfonate with PEO-PPO-PEO triblock copolymer P123 as soft templates, unique yolk–shell structure with pollen-like surface of carbon microspheres were innovatively synthesized using xylose as the carbon precursor under hydrothermal carbonization. A mechanism for the yolk–shell carbon microspheres formation was proposed. The associations between lignosulfonate and P123 led to the formation of mixed micelles. Owing to the highly branched structure and steric hindrance effect of lignosulfonate, lignosulfonate preferentially assembled at the outer position of double layers of micelles, while linear structure P123 located at the inner position. The xylose assembly process depended on the hydrogen bond interactions between xylose and P123/lignosulfonate soft templates, which do provide appropriate nucleation and growth sites for the assembled particles and affect...

Z-Scheme Au@Void@g-C3N4/SnS Yolk-Shell Heterostructures for Superior Photocatalytic CO2 Reduction under Visible Light.

Au@g-C3N4/SnS yolk-shell Z-scheme photocatalysts are fabricated by a simple template-assisted strategy. Thel-cysteine can offer the amine groups and meanwhile anchor on the surface of g-C3N4 during solvothermal reaction and thus contributes greatly to the enhanced carbon dioxide adsorption capability. This Z-scheme photocatalytic reduction mechanism of Au@g-C3N4/SnS performs valuable functions in the reaction, leading to CH4 generation much earlier and higher concentration than that of Au@g-C3N4. Meanwhile, the unique yolk-shell structure can make the light bounce back and forth in the cavity and thus enhances the availability ratio of light. The application of small amount of noble metal cocatalysts and the large Brunauer-Emmett-Teller surface areas are also benefited for the enhanced photocatalytic activities. Hence, this novel material exhibits a distinguished reduction performance for CO2 reduction under visible light. The highest yields of CH4 (3.8 μmol g-1), CH3OH (5.3 μmol g-1), and CO (17.1 μmol g-1) can be obtained for the sample of Au@g-C3N4/SnS (SnS 41.5%), whichis higher than other latest reported g-C3N4-based photocatalysts for CO2 photoreduction including coupled with semiconductors and noble metal cocatalysts. This strategy might represent a novel way for the effective transition of CO2 to clean fuels and can also be enormous feasible utilization in the photocatalytic field.

Optimizing the Electromagnetic Wave Absorption Performances of Designed Co3Fe7@C Yolk-Shell Structures.

Due to the increasing demand for military and commercial applications, magnetic metal-based core@shell nanostructures have attracted extensive attention in the field of electromagnetic wave (EMW) absorption materials. To further improve the overall performance, herein, an effective strategy is designed to fabricate Co3Fe7@C yolk-shell structures by using (Co0.9Fe0.1)Fe2O4@phenolic resin core@shell structures as precursors. The structure parameters, including the size of the CoFe alloy cores, the thickness of the carbon shell, and the void between the core and the shell, can be tailored by controlling the reaction conditions. It is demonstrated that the EMW absorption properties of the as-prepared Co3Fe7@C yolk-shell structures are closely related to their structure parameters. The optimized Co3Fe7@C yolk-shell structure shows excellent EMW absorption performance, the strongest reflection loss (RL) is up to -35.3 dB at 9.1 GHz with the matching thickness of 2.0 mm, and the effective bandwidth (RL < -10 dB) can reach 8.4 GHz (9.6-18 GHz) with a thickness of only 1.5 mm. It is revealed that the excellent performances stem from the unique yolk-shell structure as well as the complementarities and synergies between the dielectric loss and the magnetic loss. By rational designing, the magnetic metal alloy@carbon yolk-shell structures will be convinced to have the potential as novel high-efficiency EMW absorption materials with lightweight, low thickness, wide absorption frequency, high stability, and strong absorption characteristics.

Uniform yolk-shell Fe3O4@nitrogen-doped carbon composites with superior electrochemical performance for lithium-ion batteries

The practical application of metal oxides (e.g., Fe3O4) as anode materials for lithium-ion batteries is hindered by their poor electrical conductivity and severe volume change in spite of their high theoretical capacities and abundance nature. In this work, uniform yolk-shell Fe3O4@nitrogen-doped carbon composites are synthesized by combining polymerization of o-phenylenediamine (oPD) with core-shell Fe3O4@SiO2 nanospheres, followed by pyrolysis of poly (o-phenylenediamine) (PoPD) and removal of silica. This novel composites exhibit superior lithium storage capacity and cycling stability due to their unique yolk-shell structure and nitrogen-doped carbon shell, which provide ample space to accommodate the volume expansion of Fe3O4 nanoparticles, prevent the aggregation of Fe3O4 nanoparticles, and enhance the electron conductivity during cycling. This newly developed method can be employed in other yolk-shell structural design of hybrids with high-performance for lithium-ion or lithium-sulfur batteries.