Hierarchical Yolk Shell Research Articles

Hierarchical Yolk-Shell Porous Ionic Liquids with Lower Viscosity for Efficient C3H6/C3H8 Adsorption and Separation.

Yolk-shell metal-organic framework (YS-MOF) liquids are candidate materials in large-size species with high-efficiency separation, owing to their hierarchical porosity, faster mass transfer, better compatibility, and higher solution processability than MOF liquids with micropores. Nevertheless, facile synthesis strategies of yolk-shell porous ionic liquids (YSPILs) with regulations of size and morphology are an ongoing challenge. Herein, we propose a general strategy to construct YSPILs based on Z67@PDA with tunable core sizes and morphologies. Benefiting from the unique hierarchical yolk-shell structure, as-prepared YSPILs exhibit promise in C3H6/C3H8 capture and separation with the increased sizes of core in yolk-shell ZIF-67@PDA. Advanced YS-MOF liquids have improved the adsorption properties and increased our ability to tailor chemical composition and pore architecture. Impressively, the adsorption capacity of C3H6 and C3H8 of YSPILs exhibits an approximately 3-fold enhancement compared with that of the neat ILs, confirming that the accessible porosities are retained. Effective C3H6/C3H8 separation performance of YSPILs over PILs based on ZIF-67, revealing the hierarchical porosity of YS-Z67@PDA liquids, benefits larger-size gas separation. Therefore, we believe that this work can not only help us to rationally design novel hierarchically porous ionic liquids but also promote candidate applications in large-size species separation, catalysis, and nanoreactors.

Yolk–Shell Cu2O@CuO‐decorated RGO for High‐Performance Lithium‐Ion Battery Anode

Based on the great advantages of an inner hollow structure and excellent solid counterpart capacity, complex hierarchical structures have been widely used as electrodes for lithium‐ion batteries. Herein, hierarchical yolk–shell Cu2O@CuO‐decorated RGO (YSRs) was designed and synthesized via a multi‐step approach. Octahedron‐like Cu2O‐decorated RGO was firstly produced, in which GO was reduced slightly while cuprous oxide was synthesized. Subsequently, the controlled oxidation of Cu2O@RGO led to the synthesis of special YSRs, which were composed of a solid Cu2O core, spur‐CuO, CuO shell, and RGO covered. As anode materials, YSRs could provide considerable capacity density. Meanwhile, the void existed between shells and solid active materials retaining the advantages of inner hollow structure. As a result, the unique architecture of the materials renders the composites with enhanced electronic and ionic diffusion kinetics, high specific capacity (~894 mAh g‐1, 0.1C), and an excellent rate capability.

Bio-alcohol induced self-assembly of heterojunctioned TiO2/WO3 composites into a hierarchical yolk-shell structure for photocatalysis.

In the fabrication of efficient multicomponent semiconductors for photocatalysis, well-defined hierarchical structures and high-quality heterojunctions are still highly desired. A general preparation method was developed for a series of hierarchical TiO2-based heterojunctions with tailored interior space from solid, core-shell and yolk-shell to fully hollow structures.

Design and construction of bi-metal MOF-derived yolk–shell Ni2P/ZnP2 hollow microspheres for efficient electrocatalytic oxygen evolution

Hierarchical yolk–shell Ni2P/ZnP2 hollow microspheres are smartly synthesized, and exhibit exceptional OER performance, benefiting from their unique compositional/structural merits.

Synthesis of cobalt-doped V2O3with a hierarchical yolk–shell structure for high-performance lithium-ion batteries

Co-V2O3-24 yolk–shell nanospheres were synthesizedviaa solvothermal treatment and subsequent calcination. The electrochemical performance of Co-V2O3-24 is greatly improved because of Co-doping and the novel hierarchical yolk–shell structure.

Construction of hierarchical yolk-shell nanospheres organized by ultrafine Janus subunits for efficient overall water splitting.

Although the bimetal sulfide is intensively pursued in catalytic systems, synthesis of ultrafine sized bimetal sulfide Janus subunits is still a great challenge. In this work, ultrafine NiS2/MoS2 Janus subunits organized on yolk-shell nanospheres (NSs) are synthesized by a novel and facile approach. The greatly reduced particle size of both two-dimensional MoS2 and one-dimensional NiS2 on the ultrafine NiS2/MoS2 Janus subunits endows the yolk-shell NSs with numerous intimate interfaces of bimetal sulfide hybrids greatly promoting the intimate electronic interaction and dissociation of water molecules. Benefiting from the ultrafine NiS2/MoS2 Janus subunits, abundant edge sites and the high density of interfaces, the as-prepared NiS2/MoS2 yolk-shell NSs exhibit high electrocatalytic activity with a low η10 value of 135 and 293 mV for the HER and OER, respectively. In addition, a low cell voltage (1.58 V) is achieved by using NiS2/MoS2 yolk-shell NSs as both anode and cathode. This study has significant indications in exploring the ultrafine nanoparticles for the water splitting reaction, fuel cells and organic synthesis.

Interfacial Charge Field in Hierarchical Yolk–Shell Nanocapsule Enables Efficient Immobilization and Catalysis of Polysulfides Conversion

AbstractInhibiting the shuttle effect of lithium polysulfides and accelerating their conversion kinetics are crucial for the development of high‐performance lithium–sulfur (Li–S) batteries. Herein, a modified template method is proposed to synthesize the robust yolk–shell sulfur host that is constructed by enveloping dispersive Fe2O3 nanoparticles within Mn3O4 nanosheet‐grafted hollow N‐doped porous carbon capsules (Fe2O3@N‐PC/Mn3O4‐S). When applied as a cathode for Li–S batteries, the as‐prepared Fe2O3@N‐PC/Mn3O4‐S can deliver capacities as high as 1122 mAh g−1 after 200 cycles at 0.5 C and 639 mAh g−1 after 1500 cycles at 10 C, respectively. Remarkably, even as the areal sulfur loading is increased to 5.1 mg cm−2, the cathode can still maintain a high areal specific capacity of 5.08 mAh cm−2 with a fading rate of only 0.076% per cycle over 100 cycles at 0.1 C. By a further combination analysis of electron holography and electron energy loss spectroscopy, the outstanding performance is revealed to be mainly traced to the oxygen‐vacancy‐induced interfacial charge field, which immobilizes and catalyzes the conversion of lithium polysulfides, assuring low polarization, fleet redox reaction kinetics, and sufficient utilization of sulfur. These new findings may shed light on the dependence of electrochemical performance on the heterostructure of sulfur hosts.

Yolk–shell-structured manganese oxide/nitride composite powders comprising cobalt-nanoparticle-embedded nitrogen-doped carbon nanotubes as cathode catalysts for long-life-cycle lithium–oxygen batteries

An air-electrode catalyst material with a hierarchically porous structure and efficient chemical composition can improve the performances of lithium–oxygen (Li–O2) batteries. In this study, hierarchically yolk–shell structured manganese oxide/manganese nitride composite powders comprising Co-nanoparticle-embedded N-doped carbon nanotubes (yCo–NCNT–Mn) are successfully fabricated as O2-electrode catalysts for Li–O2 batteries. The as-prepared yCo–NCNT–Mn powders exhibit high electrocatalytic activities toward both oxygen reduction and evolution. The Li–O2 battery with yCo–NCNT–Mn exhibits a high capacity (22,344 mA h g−1 at 200 mA g−1), low charge overpotential (0.25 V), and long cycling life (227 cycles at 200 mA g−1 and cut-off capacity of 500 mA h g−1). Experimental analyses reveal that the improved electrochemical performance can be attributed to the synergistic advantages of the electrically conductive NCNTs and excellent catalytic activity of the bifunctional catalyst as the composite form of Co, NCNT, MnO, and Mn4N. Moreover, the unique hierarchical yolk–shell structure increases the capacity by providing a sufficient space to accommodate Li2O2.

Yolk–Shell Structured Assembly of Bamboo‐Like Nitrogen‐Doped Carbon Nanotubes Embedded with Co Nanocrystals and Their Application as Cathode Material for Li–S Batteries

AbstractDespite their high theoretical specific capacity (1675 mA h g−1), the practical application of Li–S batteries remains limited because the capacity rapidly degrades through severe dissolution of lithium polysulfide and the rate capability is low because of the low electronic conductivity of sulfur. This paper describes novel hierarchical yolk–shell microspheres comprising 1D bamboo‐like N‐doped carbon nanotubes (CNTs) encapsulating Co nanoparticles (Co@BNCNTs YS microspheres) as efficient cathode hosts for Li–S batteries. The microspheres are produced via a two‐step process that involves generation of the microsphere followed by N‐doped CNTs growth. The hierarchical yolk–shell structure enables efficient sulfur loading and mitigates the dissolution of lithium polysulfides, and metallic Co and N doping improves the chemical affinity of the microspheres with sulfur species. Accordingly, a Co@BNCNTs YS microsphere‐based cathode containing 64 wt% sulfur exhibits a high discharge capacity of 700.2 mA h g−1 after 400 cycles at a current density of 1 C (based on the mass of sulfur); this corresponds to a good capacity retention of 76% and capacity fading rate of 0.06% per cycle with an excellent rate performance (752 mA h g−1 at 2.0 C) when applied as cathode hosts for Li–S batteries.

Scalable and general synthesis of spinel manganese-based cathodes with hierarchical yolk–shell structure and superior lithium storage properties

Hierarchical yolk–shell structured cathodes with controllable composition are potentially attractive materials for the fabrication of lithium-ion batteries, but they are difficult to synthesize. In this work, we present a simple, scalable, and general morphology-inheritance strategy to synthesize spinel manganese cathodes with a hierarchical yolk–shell structure. Starting from uniform Mn carbonate spheres prepared by an ultrafast and scalable microwave-assisted method, we show that the subsequent sintering results in the formation of Mn2O3 precursors with a yolk–shell structure, which can be effectively transferred to spinel manganese cathodes via simple impregnation and solid-state reaction. Owing to the simple and scalable nature of the present strategy, materials prepared through this approach have great potential as cathodes of lithium-ion batteries, where they can lead to high specific capacity, outstanding cyclability, and superior rate capability. In particular, both LiMn2O4 and LiNi0.5Mn1.5O4 with hierarchical yolk–shell structure achieved nearly theoretical capacity, without any apparent decay after 100 cycles at 1 C. Moreover, 80% of the initial discharge capacities of both samples can be maintained for up to 500 cycles at a high rate of 10 C.

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.

From zinc-cyanide hybrid coordination polymers to hierarchical yolk-shell structures for high-performance and ultra-stable lithium-ion batteries

Uniform zinc-cyanide hybrid coordination polymer microspheres were successfully synthesized by a coprecipitation method. Then hierarchical yolk-shell structured and carbon coated ZnO microspheres (YC-ZnO) composed of ZnO@C nanocrystals were prepared by consecutive post annealing processes of these microspheres in argon and air atmosphere. Such micro-nano porous structures have the advantages of large specific surface area, good charge transport kinetics, and large cavity to accommodate the volume change and maintain the mechanical integrity of the electrode material. When evaluated as anode materials of lithium ion batteries, these ZnO yolk-shell spheres exhibited excellent battery performance with a high rate capacity and ultra-stable cycling stability.

In Situ Confined Growth Based on a Self-Templating Reduction Strategy of Highly Dispersed Ni Nanoparticles in Hierarchical Yolk-Shell Fe@SiO2 Structures as Efficient Catalysts.

Ni-based magnetic catalysts exhibit moderate activity, low cost, and magnetic reusability in hydrogenation reactions. However, Ni nanoparticles anchored on magnetic supports commonly suffer from undesirable agglomeration during catalytic reactions due to the relatively weak affinity of the magnetic support for the Ni nanoparticles. A hierarchical yolk-shell Fe@SiO2 /Ni catalyst, with an inner movable Fe core and an ultrathin SiO2 /Ni shell composed of nanosheets, was synthesized in a self-templating reduction strategy with a hierarchical yolk-shell Fe3 O4 @nickel silicate nanocomposite as the precursor. The spatial confinement of highly dispersed Ni nanoparticles with a mean size of 4 nm within ultrathin SiO2 nanosheets with a thickness of 2.6 nm not only prevented their agglomeration during catalytic transformations but also exposed the abundant active Ni sites to reactants. Moreover, the large inner cavities and interlayer spaces between the assembled ultrathin SiO2 /Ni nanosheets provided suitable mesoporous channels for diffusion of the reactants towards the active sites. As expected, the Fe@SiO2 /Ni catalyst displayed high activity, high stability, and magnetic recoverability for the reduction of nitroaromatic compounds. In particular, the Ni-based catalyst in the conversion of 4-nitroamine maintained a rate of over 98 % and preserved the initial yolk-shell structure without any obvious aggregation of Ni nanoparticles after ten catalytic cycles, which confirmed the high structural stability of the Ni-based catalyst.

Constructing graphite-like carbon nitride modified hierarchical yolk–shell TiO2 spheres for water pollution treatment and hydrogen production

Here we present a new visible light active composite based on porous graphitic carbon nitride decorated hierarchical yolk–shell TiO2 spheres for water pollution treatment and H2 evolution.

Novel hollow SnO2 nanosphere@TiO2 yolk–shell hierarchical nanospheres as anode material for high-performance lithium-ion batteries

Hollow SnO2 nanosphere@TiO2 yolk–shell hierarchical nanospheres (h-SnO2@TiO2 YSHNSs) have been synthesized for the first time and evaluated as a high-performance anode material in lithium-ion batteries (LIBs). The h-SnO2@TiO2 YSHNS anode exhibited high reversible capacity (~520mAhg−1 at a current density of 100mAg−1 after 100 charge/discharge cycles), superior cyclic stability (capacity retention of ~63.3% after 100 cycles) and good rate performance (~172mAhg−1 at 2400mAg−1) due to the unique hierarchical yolk–shell nanostructure, comprised of a TiO2 shell surrounding an interspace and the hollow SnO2 yolk. These results suggest that the h-SnO2@TiO2 YSHNS should be a promising anode candidate for next-generation LIBs.

Cobalt-Doped MnO2Hierarchical Yolk–Shell Spheres with Improved Supercapacitive Performance

Cobalt-doped MnO2 with a hierarchical yolk–shell spherical structure has been prepared by a light-assisted method. The hierarchical spheres obtained are characterized by X-ray diffraction, nitrogen...

Self-assembled hierarchical yolk–shell structured NiO@C from metal–organic frameworks with outstanding performance for lithium storage

A facile generic environmental strategy is employed to prepare hierarchical yolk-shell hybrid NiO@C materials viz. metal-organic frameworks. The intrinsic yolk-shell nature as well as the multi-element characteristics of active components of the unique nanostructures contributes greatly to the outstanding electrochemical performance.

A fast synthesis of hierarchical yolk–shell copper hydroxysulfates at room temperature with adjustable sizes

Hierarchical 3D yolk–shell copper hydroxysulfate microspheres were successfully synthesized by a fast synthesis method at room temperature. Both the core and the shell of the yolk–shell microspheres were assembled from 2D nanoplates or tiny nanoplatelets. The as-synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectrometry (XPS), atomic absorption spectrophotometry (AAS) and thermogravimetric analysis (TG). The diameter of the yolk–shell microspheres can be tuned by simply adjusting the concentration of the chelating agent, 1,3-propanediamine. This reaction can be scaled up by a factor of 1000 with almost no loss in yield. An Ostwald ripening controlled formation mechanism was proposed. Furthermore, the yolk–shell copper hydroxysulfates were evaluated as catalysts for the oxidation of styrene to benzaldehyde.

Trimodel hierarchical yolk–shell porous materials TS-1@mesocarbon: Synthesis and catalytic application

Abstract Trimodal hierarchical yolk–shell materials consisting of TS-1 core and mesoporous carbon shell (YS-TS-1@MC) was successfully synthesized by using TS-1@mesosilica as hard template, sucrose as carbon source and organic base tetrapropylammonium hydroxide (TPAOH) as silica etching agent. The resultant YS-TS-1@MC contains the micropores (0.51 nm) in TS-1 core, the mesopores (2.9 nm) in carbon shell as well as a void or a stack pore between TS-1 fragements (TS-1 intercrystal mesopores, ∼18.4 nm). Under the rigorous etching conditions, the crystalline structure of TS-1core was well retained. The YS-TS-1@MC served as a good support for palladium nano-particles (Pd NPs) or Rh(OH)x species, giving rise to efficient bifunctional catalysts for the tandem reactions including one-pot synthesis of propylene oxide or amides.