Hierarchical Core-shell Structure Research Articles

Polyaniline‐Modified Hierarchical Graphene Fiber for Ultrahigh‐Performance Electrochemical Supercapacitor with Carbon Fiber in Core as Current Collector

As the demand for portable and wearable energy‐storage devices increases, fiber‐type supercapacitors have rapidly developed. Herein, a two‐step synthesis method is developed to fabricate polyaniline‐modified hierarchical graphene fibers (GFs) with carbon fiber as the core. Using these fibers as the electrode of the supercapacitor, the highly conductive graphene sheets in these fibers can accelerate the transfer of electrolyte ions and fully enhance the Faraday redox transition of polyaniline on the fiber surface, thus realizing the volume capacitance of 2053 F cm−3. The core–shell hierarchical structures contribute to the high robustness and flexibility of the fibers, which are beneficial to their application in wearable or flexible systems. Moreover, large‐scale production of the core–shell fibers as supercapacitor electrodes without metal wires can be easily realized by a simple bonding technique, which opens up a promising opportunity for practical flexible devices.

In Situ Encapsulating Metal Oxides into Core-Shell Hierarchical Hybrid Fibers for Flexible Zinc-Ion Batteries toward High Durability and Ultrafast Capability for Wearable Applications.

Rechargeable aqueous Zn-ion batteries are promising power sources for the advanced electronics because of their low cost, high safety, environmental friendliness, etc. However, their practical applications are severely restricted by the low energy density, poor rate capability, and low mass loading. In this work, a new type of the core-shell hierarchical structured hybrid fiber with encapsulated metal oxide nanoparticles is reported, which is used as a flexible cathode for aqueous Zn-ion batteries. The hierarchical hybrid fibers, consisting of one-dimensional (1D) central hollow shell and inside carbon network, build bicontinuous conductive pathways and highly porous networks for the in situ formed metal oxide nanoparticles. The core-shell hierarchical structure facilitates fast electron/ion transport and high mass loading; moreover, the 1D structure ensures good pliability and high flexibility. Two transition metal oxides, i.e., Zn2V2O7 and V2O5, are employed to construct the hybrid fibers. Both hybrid fibers exhibit excellent electrochemical properties and superior high rate capabilities. They achieve the capacities of 162 mAh g-1 (for Zn2V2O7) and 409 mAh g-1 (for V2O5) even at a high current density of 8 A g-1. Moreover, the flexible Zn-ion batteries are fabricated on the basis of the hybrid fibers. The superior energy/power density and good long-term cycling stability demonstrate their good energy storage capability and fast charge/discharge capability. Especially, the well-retained performance under high degree of outside deformations further promotes their applications in wearable electronics.

Rationally designed CuCo2O4@Ni(OH)2 with 3D hierarchical core-shell structure for flexible energy storage

Composite electrodes that possess both rational structures and appropriate integration are needed to deliver high electrochemical performance in energy storage devices. In this paper, a flexible and binder-free electrode material based on a heterogeneous core-shell structure of CuCo2O4@Ni(OH)2 nanosheets grown on carbon cloth was fabricated by a simple method. The unique three-dimensional hierarchical structure gives the electrode a large specific surface area, which enables rapid response and increases of specific capacitance. The CuCo2O4@Ni(OH)2/carbon fiber cloth (CFC) composite electrode exhibited a specific capacitance of 2160 F g−1 at 1 A g−1 and a good rate capability energy of 82.7% at 20 A g−1. A flexible all-solid-state asymmetric supercapacitor (FAASC) was assembled with the CuCo2O4@Ni(OH)2/CFC electrode as the positive electrode, and activated carbon (AC)/CFC as the negative electrode. This device showed both a high energy density and power density (58.9 W h kg−1 at a power density of 400 W kg−1), and good long-term cycling stability. Furthermore, the assembled CuCo2O4@Ni(OH)2/CFC//AC/CFC devices were capable of driving a blue light-emitting diode after a short charge. The remarkable performance of this CuCo2O4@Ni(OH)2/CFC electrode indicates that this heterogeneous structure has great potential for applications in flexible high-performance energy storage devices.

Hierarchical NiCoP/Co (OH)2 nanoarrays for high-performance asymmetric hybrid supercapacitors

Recently, researchers have shown increasing interest in transition metal phosphides (TMPs) for their outstanding performance on electrochemical energy storage. Herein, we take a simple hydrothermal route to prepare NiCoP/Co (OH)2 nanoarrays. The constructing of 3D hierarchical core-shell structure endows the material with enlarged contact area, reduced ion diffusion distance and better mechanical stability. Therefore, NiCoP/Co (OH)2 electrode combining NiCoP with high electrochemical activity and Co (OH)2 with superior stability exhibits remarkable electrochemical performance with specific capacity of 304 mAh g−1 at 1 A g−1 and retains 80% of the initial capacity at 20 A g−1. Furthermore, the as-fabricated asymmetric supercapacitors display outstanding long-term cycle life with 87% retention after 6000 cycles at 10 A g−1 and high energy density/power density. The above results suggest that the NiCoP/Co (OH)2 electrode holds considerable application potential for hybrid supercapacitors.

Ion-exchange synthesis of high-energy-density prussian blue analogues for sodium ion battery cathodes with fast kinetics and long durability

Prussian blue and its analogues are regarded as promising cathodes for sodium ion batteries. However, the structural stability and interfacial compatibility of Prussian blue cathode are major issues for achieving superior performance. Sodium copper hexacyanoferrate is synthesized by an ion-exchange method, with large specific surface area and hierarchical core-shell structure. When used as cathode for half-cell, the material delivers an initial capacity of ~90 mAh g−1 and maintain more than 81% capacity retention after 1000 cycles. Even at a high rate of 20C, an impressive capacity of ~50 mAh g−1 is retained. Especially, a full-cell assembled by sodium copper hexacyanoferrate cathode and NaTi2(PO4)3@C anode shows a high capacity of more than 80 mA h g−1 for 400 cycles. A series of electrochemical techniques and in situ tests are carries out to confirm the advantages of stable structure and high conductivity after dopping copper ions. Furthermore, the low adsorption energy of Na+ on cathode surfaces is revealed by the first principle calculation.

Monodispersed Silica@Nickel Silicate Hydroxide Core–Shell Spheres for Supercapacitor Electrodes

Monodispersed silica@nickel silicate hydroxide core–shell microspheres are prepared using a hydrothermal method. The core–shell microsphere with an average diameter of 525 nm displays a hierarchical structure. The shell with an average thickness of about 40 nm consists of Ni3Si2O5(OH)4 nanosheets yielding porous surface. Surface‐dependent electrochemical property exhibits a specific capacitance of 356.7 F g−1 at 0.5 A g−1 and a good rate performance, which is attributed to the special core–shell hierarchical structures not only providing abundant electroactive sites for redox reaction but also shortening ion/electron transportation path. The current study provides a simple and efficient way to design low‐cost electrodes for supercapacitors.

Constructing ZnCo2O4@LDH Core–Shell hierarchical structure for high performance supercapacitor electrodes

Abstract In this article, ZnCo 2 O 4 nanowires deposited with two kinds of typical layered double hydroxides (Ni–Al,Co–Al LDH) are developed via scalable method. Two materials all display core–shell hierarchical structure. High specific capacitance of 2041 F g −1 and 1586 F g −1 are obtained for ZnCo 2 O 4 @Co–Al LDH and ZnCo 2 O 4 @Ni–Al LDH,respectively. Combining with active surface and synergistic effect, the role of hierarchical structure in enhancing performance is revealed. Moreover, two all solid state supercapacitors based on fabricated materials as positive electrodes, activated carbon as negative electrodes and PVA–KOH as polymer electrolyte are assembled. The maximum power and energy densities of ZnCo 2 O 4 @Co–Al LDH//AC are 6200 W kg −1 and 50.1 Wh kg −1 , respectively. While the power and energy densities of ZnCo 2 O 4 @Ni–Al LDH//AC are 3400 W kg −1 and 27.8 Wh kg −1 . At last, an energy storage–conversion system, based on solar cell as input device and assembled asymmetric supercapacitor ZnCo 2 O 4 @Co–Al LDH//AC as output device, is integrated as a self–sustaining power device, indicating its potential in practical applications.

Fabrication of hierarchical Co(OH)2@Ni(OH)2 core-shell nanosheets on carbon cloth as an advanced electrocatalyst for oxygen evolution reaction

Transition metal-based layered double hydroxides have been reported as cost-effective and efficient oxygen evolution reaction (OER) catalysts due to their layered structure and unique redox properties. Moreover, the electrochemical performance can be greatly enhanced by rational design of nanostructures. Herein, the hierarchical Co(OH)2@Ni(OH)2 core-shell nanosheets on flexible carbon cloth (CC) were designed and prepared as advanced OER catalysts. Compared with the commercial RuO2, the Co(OH)2/CC and the Ni(OH)2/CC, the Co(OH)2@Ni(OH)2/CC hybrid electrode exhibits outstanding OER electrocatalytic activity with only ~330 mV at a current density of 10 mA cm−2. Moreover, the Co(OH)2@Ni(OH)2/CC catalyst shows long-term durability without obvious degradation over 10 h. The outstanding electrochemical performance of the Co(OH)2@Ni(OH)2/CC could be attributed to the unique 3D hierarchical core-shell structure and the synergistic effect between Co(OH)2 and Ni(OH)2. Our work offers an effective strategy to prepare advanced electrode materials for OER electrocatalysts.

Hierarchical NiCo2S4@NiCoP core-shell nanocolumn arrays on nickel foam as a binder-free supercapacitor electrode with enhanced electrochemical performance

A novel hierarchical core-shell nanocolumn array, with NiCo2S4 hollow nanowire (NiCo2S4 H-NW) as the core and NiCoP nanosheet (NiCoP NS) as the shell, has been directly synthesized on nickel foam (NF) as self-supported, binder-free electrode for high-performance supercapacitors. The morphological characterizations reveal that the diameter of NiCo2S4 H-NW core is ∼100 nm and the diameter of single NiCo2S4@NiCoP core-shell nanocolumn is ∼250 nm. Through a series of electrochemical tests and the analysis of charge storage kinetics, hierarchical NiCo2S4@NiCoP/NF electrode presents high areal specific capacitance of 5.98 F/cm2 at 1 mA/cm2, outstanding rate capability (70.29% capacitance retention with the current density increased from 1 to 50 mA/cm2) and superior cycling stability (92.94% of original capacity is retained after 5000 cycles at 10 mA/cm2). The prominent performance of NiCo2S4@NiCoP/NF electrode could be resulted from their unique hierarchical core-shell nanocolumn structure, which could offer abundant active sites near the interface for fast electrochemical reaction, and validly avoid the collapse of internal structure for the stability of whole structure in the repeated electrochemical measurement. The novel NiCo2S4@NiCoP/NF electrode offers a new method for future electrochemical energy storage devices with high-stability.

Electrothermal regeneration by Joule heat effect on carbon cloth based MnO2 catalyst for long-term formaldehyde removal

Carbon-based materials (e.g., activated carbon) have been widely used as contaminant removal media due to their unique adsorption properties. However, some of their other characteristics, such as electrothermal properties, have been greatly ignored in the field of environmental remediation. Herein, a kind of carbon cloth (CC)-supported MnO2 composite (MnO2-CC) was prepared and investigated for catalytic oxidation of gaseous formaldehyde (HCHO) under the assistance of electric power. The MnO2-CC composite exhibited unique Joule heat property and could efficiently convert electrical energy into heat energy. The surface temperature of MnO2-CC composite could be increased to as high as 138 °C within 20 s when 8 V input voltage was imposed. In addition, porous MnO2 nanosheets dispersed uniformly on the surface of CC surface, forming a kind of hierarchical core-shell structure. The close contacted interface could reduce energy loss during heat transfer. As a result, the used MnO2-CC composite could exhibit long-term HCHO removal efficiency by highly effective electrothermal regeneration. This work represents a convenient and fast approach that allows direct utilization of electric power to accelerate the complete mineralization of HCHO. The in-situ fast electric heating process along with the uniform dispersion of porous MnO2 on CC make the MnO2-CC fabric an excellent material for indoor HCHO abatement.

Growth of TiO2 nanostructures exposed {001} and {110} facets on SiC ultrafine fibers for enhanced gas sensing performance

In situ detection of toxic and combustible gases in harsh environments is much more desired in the fields of aerospace and chemical industries, etc. Herein, we have successfully grown {001} facets-exposed TiO2 nanosheets (TNS001) and {110} facets-exposed TiO2 nanorods (TNR110) on the surface of macro-meso-microporous SiC fibers (MMM-SFs). The received hierarchical TNS001@MMM-SFs sensor possesses a core-shell hierarchical structure, and exhibits a high response of 19.2 at the temperature of 450 °C towards acetone, which is 1.2 and 1.8 times as high as those of TNR110@MMM-SFs and bare TNS001, respectively. Besides, the TNS001@MMM-SFs also present good stability, fascinating selectivity and low response time to acetone. This excellent gas detecting ability is mainly contributed to the exposing of high-energy {001} crystal facets of TiO2 and the synergetic effect of TiO2/SiC heterojunctions as well as the core-shell hierarchical architectures. This work gives a general strategy of exposing high-index energy facet combined with constructing hierarchical heterojunctions structure to fabricate gas sensors.

High-performance solid-state flexible supercapacitor based on reduced graphene oxide/hierarchical core-shell Ag nanowire@NiAl layered double hydroxide film electrode

All-solid-state flexible supercapacitor (AFSC) is a promising energy storage device due to its high flexibility, security, and environmental friendliness. However, high electrical resistance and low specific capacitance of electrodes limit its application for potential portable electronic devices. In this study, we design a novel hybrid film electrode composed of reduced graphene oxide (rGO)/silver nanowire (Ag NW)@nickel aluminum layered double hydroxide (NiAl LDH; herein, GAL) possessing high electrochemical performance by using hydrothermal and vacuum filtration techniques. The Ag NW@NiAl LDH (AL) composites with hierarchical core-shell structure are utilized to increase electroactive surface area and improve electrical conductivity, while the rGO nanosheets serve as a prominent carbon material with outstanding electrical conductivity and mechanical flexibility. The freestanding GAL electrode shows high specific capacitance of 1148 F g−1 at 1 A g−1 compared with rGO/NiAl LDH (GL) of 765.2 F g−1 at 1 A g−1. Furthermore, the bind-free symmetric AFSC device is successfully prepared using GAL hybrid film as electrodes and PVA-KOH as solid-state gel electrolyte. The GAL//GAL AFSC device delivers a superior specific capacitance of 127.2 F g−1 at 1 A g−1, a high energy density of 35.75 mWh cm−3 at a power density of 1.01 W cm−3, and great cycling ability of 83.2% over 10,000 cycles at 5 A g−1. This study introduces a novel design of flexible electrode structure for advanced energy storage applications.

Trifunctional C@MnO Catalyst for Enhanced Stable Simultaneously Catalytic Removal of Formaldehyde and Ozone

The key challenge for controlling low concentration volatile organic compounds (VOCs) is to develop technology capable of operating under mild conditions in a cost-effective manner. Meanwhile, ozone (O3) is another dangerous air pollutant and byproducts of many emerging air quality control technologies, such as plasma and electrostatic precipitators. To address these multiple challenges, we report here a design strategy capable of achieving the following trifunctions (i.e., efficiently VOCs adsorption enrichment, ozone destruction, and stable VOCs degradation) from the synergistic effect of adsorption center encapsulation and catalytic active sites optimization using 2D manganese(II) monoxide nanosheets decorated carbon spheres with hierarchical core–shell structure. Carbonous residues in the as-synthesized MnOx matrices played a key role for in situ generating homogeneous dispersed unsaturated MnO during the annealing of the as-synthesized C@MnOx in the flow of argon under a proper calcination temperatur...

Cu2O templating strategy for the synthesis of octahedral Cu2O@Mn(OH)2 core–shell hierarchical structures with a superior performance supercapacitor

We demonstrate the design and fabrication of novel Cu2O@Mn(OH)2 core–shell hierarchical structures using octahedral Cu2O as a template.

Achieving highly practical capacitance of MnO2 by using chain-like CoB alloy as support.

The practical performance of MnO2 as a capacitor material is limited mainly by its poor electronic conductivity. Arranging MnO2 on the conductive backbone to form a unique hierarchical nanostructure is an efficient way to enhance its capacitor performance. Herein, a hierarchically core-shell structure, in which thin γ-MnO2 sheets are grown on amorphous CoB alloy nano-chains (CoB@MnO2), is produced via a simple and scalable solution-phase procedure at room temperature. A specific capacitance of 612.0 F g-1 is obtained for the CoB@MnO2 capacitor electrode at a discharge current density of 0.5 A g-1, a value higher than those obtained for other conductive materials supported MnO2 electrodes reported in the literature. A rate retention value of 60.9% of its initial capacitance is obtained when the discharge current density increased by 12-fold. It is found that after 6000 charge-discharge cycles at 2 A g-1, the specific performance of CoB@MnO2 is 86.5%. The excellent capacitor performance of CoB@MnO2 is explained to be due to the hierarchical core-shell structure, in which the CoB alloy nano-chain backbone provides a transport pathway for the electron, and the porous MnO2 outer layers provide the channel for mass transfer, hence allowing further exposure to active sites. The combination of high capacitor performance and low-cost synthesis makes the core-shell CoB@MnO2 a promising cathode material for alkaline electrolyte supercapacitors.

From 1D nanotube arrays to 2D nanosheet networks on silver-coated textiles: new insights into the factors determining the performance of a core–shell hierarchical structure for wearable supercapacitors

Investigating the factors that determine the performance of the electrodes with different sub-structure helps to extend the application of wearable energy storage devices.

Hierarchical core-shell structures of P-Ni(OH)2 rods@MnO2 nanosheets as high-performance cathode materials for asymmetric supercapacitors.

The hierarchical porous structure with phosphorus-doped Ni(OH)2 (P-Ni(OH)2) rods as the core and MnO2 nanosheets as the shell is fabricated directly by growth on a three-dimensional (3D) flexible Ni foam (NF) via a two-step hydrothermal process. As a binder-free electrode material, this unique hybrid structure exhibits excellent electrochemical properties, including an ultrahigh areal capacitance of 5.75 F cm-2 at a current density of 2 mA cm-2 and great cyclic stability without capacitance loss at a current density of 20 mA cm-2 after 10 000 cycles. Moreover, an all-solid-state asymmetric supercapacitor (AAS) based on a P-Ni(OH)2@MnO2 hybrid structure on Ni foam as the cathode and activated carbon (AC) as the anode is successfully assembled to enhance value the electrochemical properties. The AAS device also shows excellent electrochemical properties including a large potential window of 0∼1.6 V, an areal capacitance is 911.3 mF cm-2 at a current density of 1 mA cm-2 and long-term cycling performance. Meanwhile, the AAS device also delivers a high energy density of 0.324 mW h cm-2 at a power density of 0.8 mW cm-2; and can easily light colorful light-emitting diode (LED) lights, suggesting that 3D P-Ni(OH)2@MnO2 hybrid composite has promising potential for practical use in high-performance supercapacitors.

Hierarchical Core-Shell Nickel Cobaltite Chestnut-like Structures as Bifunctional Electrocatalyst for Rechargeable Metal-Air Batteries.

Nano-engineered hierarchical core-shell nickel cobaltite chestnut-like structures were successfully synthesized as a bifunctionally active electrocatalyst for rechargeable metal-air battery applications. Both the morphology and composition of the catalyst were optimized by a facile hydrothermal reaction, resulting in a 10 h reacted sample demonstrating significantly enhanced activity toward both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in 0.1 m KOH. Specifically, the catalyst demonstrated -0.28 and 0.60 V versus SCE (saturated calomel electrode) at the ORR half-wave potential and an OER current density of 10 mA cm-2 , respectively. The resulting ORR/OER potential difference of 0.90 V was the smallest compared to the catalysts synthesized using 2, 6, and 12 h of hydrothermal reaction time. The excellent bifunctional activity of the catalyst is attributed to the nanoscale porous morphology and the spinel nickel cobaltite composition, which improved the active site exposure and transport of reactants and charges during the oxygen reactions.

A Self-Supported Porous Hierarchical Core–Shell Nanostructure of Cobalt Oxide for Efficient Oxygen Evolution Reaction

Increasing the active surface area of an electrocatalyst is crucial for effective oxygen evolution reaction (OER). Here, a sophisticated electrode that uses the advantages of porous/hollow nanostructure, hierarchical nanostructure, and self-supported structure simultaneously is demonstrated for the first time. A self-supported porous hierarchical core–shell structure (PHCS) of cobalt oxide is synthesized by the combination of electrochemical deposition and electrochemical treatment. The treatment introduces numerous pores into the core of a core–shell structure, and it decreases the particle size of cobalt oxide to <5 nm, markedly increasing the surface area of the resultant structures. The electrochemical surface area of PHCS is 1.6 greater than that of hierarchical core–shell cobalt oxide, and is ∼20 times greater than that of cobalt oxide nanowires. The PHCS is extremely active in the OER, with the overpotential required for a current density of 100 mA cm–2 being as small as 300 mV. The Tafel slope is ...

High-performance asymmetric supercapacitor with ultrahigh energy density based on hierarchical graphene sheets@NiO core-shell nanosheets and 3D drilled graphene sheets hydrogel

In this work, we have successfully developed an advanced asymmetric supercapacitor (ASC) based on hierarchical graphene sheets@NiO (GN@NiO) core-shell nanosheets as positive electrode and 3D drilled graphene sheets (DGNs) hydrogel as negative electrode for the first time. The anode materials were synthesized by an efficient chemical bath deposition method followed by thermal annealing, and the resulting GN@NiO electrode shows an ultrahigh specific capacitance of 1092 F g−1 at 1 A g−1. Additionally, the cathode materials were fabricated via a two-step process: chemical reduction at a low temperature and cost-effective cobalt catalyzed gasification strategy. Thanks to the mesoporous hydrogel structure, the porous DGNs electrode displays a specific capacitance up to 268 F g−1 at 1 A g−1 and the value is higher than that of major carbon-based materials. The optimized GN@NiO//DGNs ASC device provides a specific capacitance of 122.5 F g−1 at 0.5 A g−1 and an maximum energy density of 43.2 Wh kg−1 and even retains 19.5 Wh kg−1 at 20,000 W kg−1, in addition, an excellent cycling stability with 95.5% capacitance retention after 5000 cycles at 6 A g−1. Our ASC device has great prospect for high energy density storage systems applications and expands the design space for graphene-based materials used in supercapacitors. Keywords: graphene; nickel oxide; porous hydrogel; hierarchical core-shell structure; asymmetric supercapacitor.