Hierarchical Carbon Nanowire/Ni@MnO2 Nanocomposites for High-Performance Asymmetric Supercapacitors

A 3D hierarchical carbon cloth/nitrogen-doped carbon nanowires/Ni@MnO₂ (CC/N-CNWs/Ni@MnO₂) nanocomposite electrode was rationally designed and prepared by electrodeposition. The N-CNWs derived from polypyrrole (PPy) nanowires on the carbon cloth have an open framework structure, which greatly increases the contact area between the electrode and electrolyte and provides short diffusion paths. The incorporation of the Ni layer between the N-CNWs and MnO₂ is beneficial for significantly enhancing the electrical conductivity and boosting fast charge transfer as well as improving the charge-collection capacity. Thus, the as-prepared 3D hierarchical CC/N-CNWs/Ni@MnO₂ electrode exhibits a higher specific capacitance of 571.4 F g⁻¹ compared with those of CC/N-CNWs@MnO₂ (311 F g⁻¹), CC/Ni@MnO₂ (196.6 F g⁻¹), and CC@MnO₂ (186.1 F g⁻¹) at 1 A g⁻¹ and remarkable rate capability (367.5 F g⁻¹ at 10 A g⁻¹). Moreover, asymmetric supercapacitors constructed with CC/N-CNWs/Ni@MnO₂ as cathode material and activated carbon as anode material deliver an impressive energy density of 36.4 W h kg⁻¹ at a power density of 900 W kg⁻¹ and a good cycling life (72.8 % capacitance retention after 3500 cycles). This study paves a low-cost and simple way to design a hierarchical nanocomposite electrode with large surface area and superior electrical conductivity, which has wide application prospects in high-performance supercapacitors.     

Mixed Cu2Se Hexagonal Nanosheets@Co3Se4 Nanospheres for High-Performance Asymmetric Supercapacitors

Rational designing and constructing multiphase hybrid electrode materials is an effective method to compensate for the performance defects of the single component. Based on this strategy, Cu₂Se hexagonal nanosheets@Co₃Se₄ nanospheres mixed structures have been fabricated by a facile two-step hydrothermal method. Under the synergistic effect of the high ionic conductivity of Cu₂Se and the remarkable cycling stability of Co₃Se₄, Cu₂Se@Co₃Se₄ can exhibit outstanding electrochemical performance as a novel electrode material. The as-prepared Cu₂Se@Co₃Se₄ electrode displays high specific capacitance of 1005 F g⁻¹ at 1 A g⁻¹ with enhanced rate capability (56 % capacitance retention at 10 A g⁻¹), and ultralong lifespan (94.2 % after 10 000 cycles at 20 A g⁻¹). An asymmetric supercapacitor is assembled applying the Cu₂Se@Co₃Se₄ as anode and graphene as cathode, which delivers a wide work potential window of 1.6 V, high energy density (30.9 Wh kg⁻¹ at 0.74 kW kg⁻¹), high power density (21.0 Wh kg⁻¹ at 7.50 kW kg⁻¹), and excellent cycling stability (85.8 % after 10 000 cycles at 10 A g⁻¹).     

Structural Design and Synthesis of an SnO2@C@Co-NC Composite as a High-Performance Anode Material for Lithium-Ion Batteries

To overcome the drawbacks of the structural instability and poor conductivity of SnO₂-based anode materials, a hollow core–shell-structured SnO₂@C@Co-NC (NC=N-doped carbon) composite was designed and synthesized by employing the heteroatom-doping and multiconfinement strategies. This composite material showed a much-reduced resistance to charge transfer and excellent cycling performance compared to the bare SnO₂ nanoparticles and SnO₂@C composites. The doped heteroatoms and heterostructure boost the charge transfer, and the porous structure shortens the Li-ion diffusion pathway. Also, the volume expansion of SnO₂ NPs is accommodated by the hollow space and restricted by the multishell heteroatom-doped carbon framework. As a result, this structured anode material delivered a high initial capacity of 1559.1 mA h g⁻¹ at 50 mA g⁻¹ and an initial charge capacity of 627.2 mA h g⁻¹ at 500 mA g⁻¹. Moreover, the discharge capacity could be maintained at 410.8 mA h g⁻¹ after 500 cycles with an attenuation rate of only 0.069 % per cycle. This multiconfined SnO₂@C@Co-NC structure with superior energy density and durable lifespan is highly promising for the next-generation lithium-ion batteries.     

Hierarchical NiCo2S4 Nanotube@NiCo2S4 Nanosheet Arrays on Ni Foam for High‐Performance Supercapacitors

Hierarchical NiCo₂S₄ nanotube@NiCo₂S₄ nanosheet arrays on Ni foam have been successfully synthesized. Owing to the unique hierarchical structure, enhanced capacitive performance can be attained. A specific capacitance up to 4.38 F cm^?2 is attained at 5 mA cm^?2, which is much higher than the specific capacitance values of NiCo₂O₄ nanosheet arrays, NiCo₂S₄ nanosheet arrays and NiCo₂S₄ nanotube arrays on Ni foam. The hierarchical NiCo₂S₄ nanostructure shows superior cycling stability; after 5000 cycles, the specific capacitance still maintains 3.5 F cm^?2. In addition, through the morphology and crystal structure measurement after cycling stability test, it is found that the NiCo₂S₄ electroactive materials are gradually corroded; however, the NiCo₂S₄ phase can still be well‐maintained. Our results show that hierarchical NiCo₂S₄ nanostructures are suitable electroactive materials for high performance supercapacitors.     

Rational Construction of 2D Fe3O4@Carbon Core–Shell Nanosheets as Advanced Anode Materials for High-Performance Lithium-Ion Half/Full Cells

Transition metal oxides have vastly limited practical application as electrode materials for lithium-ion batteries (LIBs) due to their rapid capacity decay. Here, a versatile strategy to mitigate the volume expansion and low conductivity of Fe₃O₄ by coating a thin carbon layer on the surface of Fe₃O₄ nanosheets (NSs) was employed. Owing to the 2D core–shell structure, the Fe₃O₄@C NSs exhibit significantly improved rate performance and cycle capability compared with bare Fe₃O₄ NSs. After 200 cycles, the discharge capacity at 0.5 A g⁻¹ was 963 mA h g⁻¹ (93 % retained). Moreover, the reaction mechanism of lithium storage was studied in detail by ex situ XRD and HRTEM. When coupled with a commercial LiFePO₄ cathode, the resulting full cell retains a capacity of 133 mA h g⁻¹ after 100 cycles at 0.1 A g⁻¹, which demonstrates its superior energy storage performance. This work provides guidance for constructing 2D metal oxide/carbon composites with high performance and low cost for the field of energy storage.     

Polypyrrole Shell@3D‐Ni Metal Core Structured Electrodes for High‐Performance Supercapacitors

Three‐dimensional (3D) nanometal films serving as current collectors have attracted much interest recently owing to their promising application in high‐performance supercapacitors. In the process of the electrochemical reaction, the 3D structure can provide a short diffusion path for fast ion transport, and the highly conductive nanometal may serve as a backbone for facile electron transfer. In this work, a novel polypyrrole (PPy) shell@3D‐Ni‐core composite is developed to enhance the electrochemical performance of conventional PPy. With the introduction of a Ni metal core, the as‐prepared material exhibits a high specific capacitance (726 F g^?1 at a charge/discharge rate of 1 A g^?1), good rate capability (a decay of 33 % in C_sp with charge/discharge rates increasing from 1 to 20 A g^?1), and high cycle stability (only a small decrease of 4.2 % in C_sp after 1000 cycles at a scan rate of 100 mV s^?1). Furthermore, an aqueous symmetric supercapacitor device is fabricated by using the as‐prepared composite as electrodes; the device demonstrates a high energy density (≈21.2 Wh kg^?1) and superior long‐term cycle ability (only 4.4 % and 18.6 % loss in C_sp after 2000 and 5000 cycles, respectively).     

Hollow 3D Frame Structure Modified with NiCo2S4 Nanosheets and Spinous Fe2O3 Nanowires as Electrode Materials for High-Performance All-Solid-State Asymmetric Supercapacitors

Supercapacitors have attracted tremendous research interest, since they are expected to achieve battery-level energy density, while having a long calendar life and short charging time. Herein, a novel asymmetric supercapacitor has been successfully assembled from NiCo₂S₄ nanosheets and spinous Fe₂O₃ nanowire modified hollow melamine foam decorated with polypyrrole as positive and negative electrodes, respectively. Owing to the well-designed nanostructure and suitable matching of electrode materials, the assembled asymmetric supercapacitor (ASC) exhibits an extended operation voltage window of 1.6 V with an energy density of 20.1 Wh kg⁻¹ at a power density of 159.4 kW kg⁻¹. Moreover, the ASC shows stable cycling stability, with 81.3 % retention after 4000 cycles and a low internal resistance of 1.03 Ω. Additionally, a 2.5 V light-emitting diode indicator can be lit up by three ASCs connected in series; this provides evidence of the practical application potential of the assembled energy-storage system. The excellent electrochemical performances should be credited to the significant enhancement of the specific surface area, charge transport, and mechanical stability resulting from the unique 3D morphology.     

Microporous Carbon Nanofibers Derived from Poly(acrylonitrile-co-acrylic acid) for High-Performance Supercapacitors

Carbon nanofiber (CNF)-based supercapacitors have promising applications in the field of energy storage. It is desirable, but remains challenging, to develop CNF electrode materials with large specific surface area (SSA), high specific capacitance (SC), and high power density, as well as excellent cycling stability and high reliability. Herein, acrylonitrile–acrylic acid copolymer P(AN-co-AA) was synthesized for the preparation of nitrogen-doped microporous CNFs. Thermal degradation of the AA segment leads to the formation of micropores that are distributed not only on the CNF surface, but also inside the material. The microporous structure and nitrogen content can be manipulated at the molecular level by adjusting the weight ratio between AN and AA, and the SSA and SC could reach as high as 1099 m² g⁻¹ and 156 F g⁻¹, respectively. After KOH activation, the activated CNFs have an extremely high SSA of 2117 m² g⁻¹ and SC of 320 F g⁻¹, which are among the highest values ever reported for electric double-layer supercapacitors with an alkaline electrolyte. Furthermore, the capacitance retention, which can be maintained at 99 % even after 16 000 cyclic tests, reveals outstanding durability and repeatability.     

Hydrothermal Synthesis of Nickel Oxide Nanosheets for Lithium‐Ion Batteries and Supercapacitors with Excellent Performance

Nickel oxide nanosheets have been successfully synthesized by a facile ethylene glycol mediated hydrothermal method. The morphology and crystal structure of the nickel oxide nanosheets were characterized by X‐ray diffraction, field‐emission SEM, and TEM. When applied as electrode materials for lithium‐ion batteries and supercapacitors, nickel oxide nanosheets exhibited a high, reversible lithium storage capacity of 1193 mA h g^?1 at a current density of 500 mA g^?1, an enhanced rate capability, and good cycling stability. Nickel oxide nanosheets also demonstrated a superior specific capacitance of 999 F g^?1 at a current density of 20 A g^?1 in supercapacitors.     

Facile In Situ Synthesis of Hierarchical Porous Ni/Ni(OH)2 Hybrid Sponges with Excellent Electrochemical Energy‐Storage Performances for Supercapacitors

Herein, we report the in situ growth of single‐crystalline Ni(OH)₂ nanoflakes on a Ni support by using facile hydrothermal processes. The as‐prepared Ni/Ni(OH)₂ sponges were well‐characterized by using X‐ray diffraction (XRD), SEM, TEM, and X‐ray photoelectron spectroscopy (XPS) techniques. The results revealed that the nickel‐skeleton‐supported Ni(OH)₂ rope‐like aggregates were composed of numerous intercrossed single‐crystal Ni(OH)₂ flake‐like units. The Ni/Ni(OH)₂ hybrid sponges served as electrodes and displayed ultrahigh specific capacitance (SC=3247 F g^?1) and excellent rate‐capability performance, likely owing to fast electron and ion transport, sufficient Faradic redox reaction, and robust structural integrity of the Ni/Ni(OH)₂ hybrid electrode. These results support the promising application of Ni(OH)₂ nanoflakes as advanced pseudocapacitor materials.     

Hierarchical ZnCo2O4@NiCo2O4 Core–Sheath Nanowires: Bifunctionality towards High‐Performance Supercapacitors and the Oxygen‐Reduction Reaction

Increasing energy demands and worsening environmental issues have stimulated intense research on alternative energy storage and conversion systems including supercapacitors and fuel cells. Here, a rationally designed hierarchical structure of ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires synthesized through facile electrospinning combined with a simple co‐precipitation method is proposed. The obtained core–sheath nanostructures consisting of mesoporous ZnCo₂O₄ nanowires as the core and uniformly distributed ultrathin NiCo₂O₄ nanosheets as the sheath, exhibit excellent electrochemical activity as bifunctional materials for supercapacitor electrodes and oxygen reduction reaction (ORR) catalysts. Compared with the single component of either ZnCo₂O₄ nanowires or NiCo₂O₄ nanosheets, the hierarchical ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires demonstrate higher specific capacitance of 1476 F g^?1 (1 A g^?1) and better rate capability of 942 F g^?1 (20 A g^?1), while maintaining 98.9 % capacity after 2000 cycles at 10 A g^?1. Meanwhile, the ZnCo₂O₄@NiCo₂O₄ core–sheath nanowires reveal comparable catalytic activity but superior stability and methanol tolerance over Pt/C as ORR catalyst. The impressive performance may originate from the unique hierarchical core–sheath structures that greatly facilitate enhanced reactivity, and faster ion and electron transfer.     

Controllable Conversion of CdNCN Nanoparticles into Various Chalcogenide Nanostructures for Photo-driven Applications

Semiconductor nanocrystals of tunable shell/core configurations have great potential in photo-driven applications such as photoluminescence and photocatalysis, but few strategies realize a controllable synthesis with respect to both the size of the core and the shell with high crystallinity. Here, a new synthetic method based on cadmium cyanamide (CdNCN) nanoparticle anion exchange reactions was developed to access solid or hollow CdSe nanocrystals with tunable size and CdNCN@CdS heterostructures with modulated shell/core thickness. The gradual shift and narrow width of photoluminescence features demonstrate the high crystallinity and monodispersity of the resulting CdSe nanocrystals. In the CdNCN@CdS heterostructures, synergistic effects of the photocarrier separation is observed between the CdS shell and CdNCN core, which leads to great improvement in photocatalysis with optimized shell/core ratio.     

Hatted 1T/2H-Phase MoS2 on Ni3S2 Nanorods for Efficient Overall Water Splitting in Alkaline Media

A new hatted 1T/2H-phase MoS₂ on Ni₃S₂ nanorods, as a bifunctional electrocatalyst for overall water splitting in alkaline media, is prepared through a simple one-pot hydrothermal synthesis. The hat-rod structure is composed mainly of Ni₃S₂, with 1T/2H-MoS₂ adhered to the top of the growth. Aqueous ammonia plays an important role in forming the 1T-phase MoS₂ by twisting the 2H-phase transition and expanding the interlayer spacing through the intercalation of NH₃/NH₄⁺. Owing to the special “hat-like” structure, the electrons conduct easily from Ni foam along Ni₃S₂ to MoS₂, and the catalyst particles maintain sufficient contact with the electrolyte, with gaseous molecules produced by water splitting easily removed from the surface of the catalyst. Thus, the electrocatalytic performance is enhanced, with an overpotential of 73 mV, a Tafel slope of 79 mV dec⁻¹, and excellent stability, and the OER demonstrates an overpotential of 190 mV and Tafel slope of 166 mV dec⁻¹.     

Hierarchically Porous Nickel Oxide Nanosheets Grown on Nickel Foam Prepared by One‐Step In Situ Anodization for High‐Performance Supercapacitors

Porous NiO nanosheets are successfully grown on nickel foam substrate through an in situ anodization by using molten KOH as the electrolyte. High‐purity NiO is directly obtained by this one‐step method without any subsequent treatment. The obtained NiO supported on nickel foam is used as a binder‐free electrode for a supercapacitor and its pseudocapacitive behavior has been investigated by cyclic voltammetry and galvanostatic charge–discharge tests in a 6 M aqueous solution of KOH. Electrochemical data demonstrates that this binder‐free electrode possesses ultrahigh capacitance (4.74 F cm^?2 at 4 mA cm^?2), excellent rate capability, and cycling stability. After 1000 cycles, the areal capacitance value is 9.4 % lower than the initial value and maintains 85.4 % of the maximum capacitance value.     

Three‐Dimensional NiMoO4 Nanosheets Supported on a Carbon Fibers@Pre‐Treated Ni Foam (CF@PNF) Substrate as Advanced Electrodes for Asymmetric Supercapacitors

Herein, we report a nanoarchitectured nickel molybdate/carbon fibers@pre‐treated Ni foam (NiMoO₄/CF@PNF) electrode for supercapacitors. The synthesis of NiMoO₄/CF@PNF mainly consists of a direct chemical vapor deposition (CVD) growth of dense carbon fibers (CFs) onto pre‐treated Ni foam (PNF) as the substrate, followed by in situ growth of NiMoO₄ nanosheets (NSs) on the CF@PNF substrate by means of a hydrothermal process. The NiMoO₄/CF@PNF electrode exhibits a high areal capacitance (5.14 F cm^?2 at 4 mA cm^?2) and excellent cycling stability (97 % capacitance retention after 2000 cycles at 10 mA cm^?2). Furthermore, we have successfully assembled NiMoO₄ NSs//activated carbon (AC) asymmetric supercapacitors, which can achieve an energy density of 45.6 Wh kg^?1 at 674 W kg^?1, and excellent stability with 93 % capacitance retention after 2000 cycles at 5 mA cm^?2. These superior properties hold great promise for energy‐storage applications.     

Synergistic Effect of SnO2/ZnWO4 Core–Shell Nanorods with High Reversible Lithium Storage Capacity

High reversible lithium storage capacity is obtained from novel SnO₂/ZnWO₄ core–shell nanorods. At C/20 (20 h per half cycle) rate, the reversible capacity of SnO₂/ZnWO₄ core–shell nanorods is as high as 1000 mAh g^?1, much higher than that of pure ZnWO₄, SnO₂, or the traditional theoretical result of the simple mixture. Such performance can be attributed to the synergistic effect between the nanostructured SnO₂ and ZnWO₄. The distinct electrochemical activity of ZnWO₄ nanorods probably activates the irreversible capacity of the SnO₂ nanoparticles. These results indicate that high‐performance lithium ion batteries can be realized by introducing the synergistic effect of one‐dimensional core–shell nanocomposites.     

Sodium‐Doped Mesoporous Ni2P2O7 Hexagonal Tablets for High‐Performance Flexible All‐Solid‐State Hybrid Supercapacitors

A simple hydrothermal method has been developed to prepare hexagonal tablet precursors, which are then transformed into porous sodium‐doped Ni₂P₂O₇ hexagonal tablets by a simple calcination method. The obtained samples were evaluated as electrode materials for supercapacitors. Electrochemical measurements show that the electrode based on the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets exhibits a specific capacitance of 557.7 F g^?1 at a current density of 1.2 A g^?1. Furthermore, the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets were successfully used to construct flexible solid‐state hybrid supercapacitors. The device is highly flexible and achieves a maximum energy density of 23.4 Wh kg^?1 and a good cycling stability after 5000 cycles, which confirms that the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets are promising active materials for flexible supercapacitors.     

Fabrication of a Hierarchical Ni(OH)2@Ni3S2/Ni Foam Electrode from a Prussian Blue Analogue-Based Composite with Enhanced Electrochemical Capacitive and Electrocatalytic Properties

Developing high-efficiency, cost-effective, and durable electrodes is significant for electrochemical capacitors and electrocatalysis. Herein, a 3D bifunctional electrode consisting of nickel hydroxide nanosheets@nickel sulfide nanocubes arrays on Ni foam (Ni(OH)₂@Ni₃S₂/NF) obtained from a Prussian blue analogue-based precursor is reported. The 3D higher-order porous structure and synergistic effect of different compositions endow the electrode with large specific surface area, facile ion/electron transport path, and improved conductivity. As a result, the Ni(OH)₂@Ni₃S₂/NF electrode exhibits a high specific capacity of 211 mA h g⁻¹ at a current density of 1 A g⁻¹ and 73 % capacity retention after 5000 cycles at 5 A g⁻¹. Moreover, the Ni(OH)₂@Ni₃S₂/NF electrode has superior electrocatalytic activity for the hydrogen evolution reaction with low overpotentials of 140 and 210 mV at current densities of 10 and 100 mA cm⁻², respectively. The synthetic strategy for the unique higher-order porous structure can be extended to fabricate other composite materials for energy storage and conversion.     

Selected-Control Synthesis of Monodisperse Fe3O4@C Core–Shell Spheres,Chains, and Rings as High-Performance Anode Materials for Lithium-Ion Batteries

A method is reported for the first time for the selected-control, large-scale synthesis of monodispersed Fe₃O₄@C core–shell spheres, chains, and rings with tunable magnetic properties based on structural evolution from eccentric Fe₂O₃@poly(acrylic acid) core–shell nanoparticles. The Fe₃O₄@C core–shell spheres, chains, and rings were investigated as anode materials for lithium-ion batteries. Furthermore, a possible formation mechanism of Fe₃O₄@C core–shell chains and rings has also been proposed.