Electrochemical performance of Sn-doped δ-MnO<Subscript>2</Subscript> hollow nanoparticles for supercapacitors

Sn-doped δ-MnO₂ (Sn-MnO₂) hollow nanoparticles have been synthesized via chemical process at room temperature. Many characterizations have been carried out to fully identify the intrinsic information of the as-prepared samples and investigate their electrochemical properties. The results indicate that the morphologies of the samples can be adjusted by changing the concentration of Sn while the capacitance of Sn-MnO₂ nanoparticles increased corresponded with that of the undoped δ-MnO₂ nanoparticles. The specific capacitance of Sn(1 at.%)-MnO₂ is up to 258.2 F g^??1 at a current density of 0.1 A g^??1. What’s more, over 90% of the initial specific capacitance still remains after 1000 cycles at a current density of 2.0 A g^??1, displaying excellent cycling stability.     

Electrochemical preparation and energy storage properties of nanoporous Co(OH)<Subscript>2</Subscript> via pulse current deposition

Nanoporous Co(OH)₂ films are electrochemically deposited on Ni foams by pulse current deposition for supercapacitor application. The pore size and density are controlled by reaction conditions including frequency modulation and reaction time. The morphology of the films is monitored by SEM, and the chemical composition and crystal structure are confirmed by XPS and XRD, respectively. The electrochemical performance of the Co(OH)₂ film is characterized by cyclic voltammetry and charge–discharge tests. The charge-transfer resistances of the electrodes are examined by electrochemical impedance spectroscopy. The Co(OH)₂ film exhibits an excellent specific capacity of 1681 F g^?1 at a current density of 2 A g^?1 in a potential range of ?0.1 to 0.4 V from the charge/discharge test; this specific capacity is much higher than that obtained by direct current deposition (623 F g^?1 at the same condition) due to the highly porous structure.     

A promising mechanical ball-milling method to synthesize carbon-coated Co<Subscript>9</Subscript>S<Subscript>8</Subscript> nanoparticles as high-performance electrode for supercapacitor

A Co₉S₈/C nanocomposite has been prepared using a solid-state reaction followed by a facile mechanical ball-milling treatment with sucrose as the carbon source. The phases, morphology, and detailed structures of Co₉S₈/C nanocomposite are well characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. Our experimental results show that not only a process of particle size reduction, the ball-milling treatment also promotes the carbon and Co₉S₈ combining with each other more effectively to form an ultrafine nanocomposite. When used as an electrode material in supercapacitor, Co₉S₈/C nanocomposite exhibits a high initial specific capacitance of 756.2 F g^?1 at 1 A g^?1 and excellent cycling stability with 73.4% retention after 2000 cycles. Its outstanding electrochemical properties are mainly attributed to the nanosize of particles and amorphous carbon layer coating on its surface.     

Ordered mesoporous carbon-supported CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> composite with enhanced lithium storage properties

A high and stable reversible specific capacity (1277.7 mAh g^?1) was successfully achieved by the CoFe₂O₄/ordered mesoporous carbon nanohybrids (CFO/CMK-3) composite anode at the current density of 0.1 A g^?1 after 100 cycles. CFO/CMK-3 electrode also exhibited a stable capacity up to 733.2 and 482.6 mAh g^?1 at the current densities of 0.5 and 1 A g^?1 after 500 cycles, respectively. The CFO particles were found to be uniformly distributed inside the pore channels of CMK-3. Structure characterization before and after 100 tests revealed that the specific CMK-3 mesoporous structure and CFO crystallites remained unchanged. The stability of the anode composite stability and the rapid redox capability of CFO gave rise to superior lithium storage capacity and excellent cycling stability. CFO/CMK-3 showed a great promise to serve as anode for high-performance lithium-ion battery.     

Enhanced electrochemical performance of Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>F<Subscript>3</Subscript> for Na-ion batteries with nanostructure and carbon coating

Carbon-coating Na₃V₂(PO₄)₂F₃ nanoparticles (NVPF@C NP) were prepared by a hydrothermal assisted sol–gel method and applied as cathode materials for Na-ion batteries. The as-prepared nanocomposites were composed of Na₃V₂(PO₄)₂F₃ nanoparticles with a typical size of ~?100 nm and an amorphous carbon layer with the thickness of ~?5 nm. Cyclic voltammetry, rate and cycling, and electrochemical impedance spectroscopy tests were used to discuss the effect of carbon coating and nanostructure. Results display that the as-prepared NVPF@C NP demonstrates a higher rate capability and better long cycling performance compared with bare Na₃V₂(PO₄)₂F₃ bulk (72 mA h g^?1 at 10 C vs 39 mA h g^?1 at 10 and 1 C capacity retention of 95% vs 88% after 50 cycles). The remarking electrode performance was attributed to the combination of nanostructure and carbon coating, which can provide short Na-ion diffusion distance and rapid electron migration.     

Facial synthesis of MnO<Subscript>2</Subscript>/three dimensional graphene composite and its application in supercapacitors

MnO₂ nanoparticle/three dimensional graphene composite (MnO₂/3DG) was synthesized by a hydrothermal template-free method and subsequent ultrasonic treatment in KMnO₄ solution. The MnCO₃/3DG particles can be detected after the hydrothermal process, which may be produced through the reaction between Mn²⁺ and \({\text{C}}{{\text{O}}_{\text{3}}}^{{\text{2}} - }\) due to the decarboxylation of GO under the hydrothermal condition. The final product MnO₂/3DG displayed high specific capacitance (324 F g^??1 at 0.4 A g^?1) and good cycle stability (91.1% capacitance retention after 5000 cycles). Furthermore, the asymmetric supercapacitor assembled with MnO₂/3DG and activated carbon (AC) exhibits an energy density of 33.78 Wh kg^?1 at the powder density of 380 W kg^?1. The excellent supercapacitance of the MnO₂/3DG composite may be due to the high pseudocapacitance of the dispersed MnO₂ nanoparticles and the conductive graphene with three dimensional porous microstructure.     

Cr-doped MnO<Subscript>2</Subscript> nanostructure: morphology evolution and electrochemical properties

Cr-doped MnO₂ nanostructure has been fabricated via a facile hydrothermal method and its morphology and electrochemical properties was discussed systematically. In this process, flower-like MnO₂ transforms into the self-assembled orchid structure under the influence of Cr-doped. Moreover, electrochemical behaviors of the Cr-doped MnO₂ nanostructure electrode were clarified by cyclic voltammograms, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy, which shows a high specific capacitance of 202.5 F g^?1 and superior cycling stability (6.8 % capacitance decay after 1000 cycling test). These remarkable and excellent results prove it has a great potential of application in future energy storage device.     

Effects of rare-earth Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> addition on relaxation behavior and electric properties of 0.5PNN-0.5PZT ceramics

Rare-earth Sm₂O₃-doped Pb(Ni_1/3Nb_2/3)_0.5(Zr_0.3Ti_0.7)_0.5O₃ (0.5PNN-0.5PZT + xSm) piezoelectric ceramics were prepared by a two-step solid-state reaction method. The effects of Sm₂O₃ doping on phase structure, electric properties and dielectric relaxation of 0.5PNN-0.5PZT ceramics were investigated. The results showed that Sm³⁺ tended to occupy the B-site of Zr⁴⁺. The XRD patterns showed that all ceramics had a pure perovskite phase structure. With the increasing of Sm₂O₃ addition, Curie temperature moved towards low temperatures obviously and dispersion coefficient γ first increased and then decreased gradually. When x = 0.2 wt%, the γ reaches at maximum (1.998), it was indicated that a nearly complete diffuse phase transition existed and relaxation behaviors enhanced. But the ceramics with x = 0.2 wt% exhibited terrible electric properties: d₃₃ = 605 pC/N, k_p = 0.55, ε_r ~ 5020, tanδ ~ 2.20 %. It showed that the relaxation behaviors have relationships with electric properties to some extent.     

Vertically-aligned Mn(OH)<Subscript>2</Subscript> nanosheet films for flexible all-solid-state electrochemical supercapacitors

The arrangement of the electrode materials is a significant contributor for constructing high performance supercapacitor. Here, vertically-aligned Mn(OH)₂ nanosheet thin films were synthesized by cathodic electrodeposition technique on flexible Au coated polyethylene terephthalate substrates. Morphologies, microstructures, chemical compositions and valence state of the nanosheet films were characterized systematically. It shows that the nanosheets arranged vertically to the substrate, forming a porous nanowall structures and creating large open framework, which greatly facilitate the adsorption or diffusion of electrolyte ions for faradaic redox reaction. Electrochemical tests of the films show the specific capacitance as high as 240.2 F g^?1 at 1.0 A g^?1. The films were employed to assemble symmetric all-solid-state supercapacitors with LiCl/PVA gel severed as solid electrolyte. The solid devices exhibit high volumetric capacitance of 39.3 mF?cm^?3 at the current density 0.3 mA cm^?3 with robust cycling stability. The superior performance is attributed to the vertically-aligned configuration.     

Improvement of hydrothermally synthesized MnO2 electrodes on Ni foams via facile annealing for supercapacitor applications

Nanostructured manganese dioxide (MnO₂) is deposited on nickel foams by a hydrothermal synthesis route. As-deposited MnO₂ thin films are largely amorphous. Facile post-deposition annealing significantly improves the electrochemical performance of the MnO₂ thin films via changing their morphology, phase, and crystallinity. The specific capacitance of the MnO₂ electrode increases with the annealing temperature and reaches an optimal value of 244 F g^?1 (at the current density of 1 A g^?1) in a neutral 1 M Na₂SO₄ electrolyte for a specimen annealed at 500 °C. Furthermore, when an alkaline 5 M KOH electrolyte is used, an exceptionally high capacitance of 950 F g^?1 is achieved at the current density of 2 A g^?1. The cost-effective facile synthesis, high specific capacitance, and good cycle stability of these MnO₂-based electrodes enable their applications in high-performance supercapacitors.     

Light weight RGO/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocomposite for efficient electromagnetic absorption coating in X-band

Reduced graphene oxide (RGO)/magnetite (Fe₃O₄) nanocomposite has been synthesized by an in-situ facile hydrothermal method. The XRD pattern reveals the development of nanocomposite in which both phases are coexistent. Raman Spectroscopy shows the main characteristics peaks of D and G bands at 1349 cm^?1 and 1595 cm^?1 for graphitic structures. The intensity ratio (I_D/I_G) is also calculated, which indicate the degree of defects in the material. This ratio (I_D/I_G), increases from 0.84 for GO to 0.91 for RGO/Fe₃O₄ nanocomposite and promotes the defects which are beneficial for electromagnetic (EM) absorption. The SEM image depicts that, Fe₃O₄ spherical nanoparticles are dispersed over the surface of graphene sheets and provide a thermal conducting path for heat dissipation between different layers of graphene. The EM absorption properties have been analyzed at 2–18 GHz of RGO and RGO/Fe₃O₄. The addition of proper content of Fe₃O₄ magnetic nanoparticles in RGO sheets improved the Reflection Loss (RL) from ??13.5 dB to ??20 dB at a frequency of 9.5 GHz. Moreover, due to magnetic loss and interfacial polarization, the effective bandwidth increases from 2.5 GHz to 3.8 GHz at a coating thickness of 1.5 mm. Hence this light weight nanocomposite is an excellent material for strong EM absorption in X-band.     

Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles embedded in 3D reduced graphene oxide network as anode for high-performance lithium ion batteries

Mn₃O₄ nanoparticles were in-situ synthesized in the 3D framework of reduced graphene oxide (RGO) by a facile one-step hydrothermal method. In the reduced graphene-Mn₃O₄ (RGM) composite, the RGO network not only serves as a mechanical support to construct a self-supported and binder-free electrode, but also offers 3D continuous conductive network for effective electron transfer. The Mn₃O₄ nanoparticles anchored uniformly across the RGO framework, which provided high capacity and prevented the restacking of the RGO thin sheets. Based on the unique composite structures, strong synergistic effect was achieved between Mn₃O₄ and RGO, resulting in superior specific capacity, enhanced rate capability, stable cycling performance and nearly 100% Coulombic efficiency in the RGM2 composites. With an optimal Mn₃O₄ composition of 44% by weight (similarly hereinafter), the composite exhibits high specific capacities of 696–795 mAh g¹ based on the overall weight of the electrode in 60 cycles at 200 mA g^?1, with a large coulombic efficiency of around 98%. Even at a high current density of 10,000 mA g^?1, the composite can still deliver a capacity of 383 mAh g^?1, demonstrating its excellent rate performance. The outstanding performances of the composites are attributed to the synergistic effect of both components and the hierarchical structure of the composite.     

Preparation and electrochemical properties of nanorods and nanosheets structural Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> as anode for lithium ion batteries

In this study, nanorods and nanosheets structure of Li₄Ti₅O₁₂ (LTO) with higher capacity and cycle performance are prepared by hydrothermal synthesis. We can obtain different nanostructural LTO by changing heating time in autoclave and molar ratio between lithium (Li) and titanium (Ti). Precursor was calcined at 600 °C for 6 h in air after heating to 180 °C with the holding time of 12 and 24 h in Teflon-lined PTFE autoclave vessel, nanorods and nanosheets structure of LTO were prepared successfully, respectively. Specially, when the molar ratio between Li and Ti was 4.2:5, the discharge capacities were 177.7 and 230.7 mAh g^?1 at 20 mA g^?1, respectively. When the holding time was 24 h as well as molar ratio between Li and Ti was 4.2:5, the band gap was least, and this pure LTO reversible capacities reached 90.36 and 73.12% after 200 and 3000 cycles at 100 mA g^?1 and 1 A g^?1, respectively.     

High-power and long-life supercapacitive performance of hierarchical, 3-D urchin-like W<Subscript>18</Subscript>O<Subscript>49</Subscript> nanostructure electrodes

We report the facile, one-pot synthesis of 3-D urchin-like W₁₈O₄₉ nanostructures (U-WO) via a simple solvothermal approach. An excellent supercapacitive performance was achieved by the U-WO because of its large Brunauer–Emmett–Teller (BET) specific surface area (ca. 123 m²·g^–1) and unique morphological and structural features. The U-WO electrodes not only exhibit a high rate-capability with a specific capacitance (Csp) of ~235 F·g^–1 at a current density of 20 A·g^–1, but also superior long-life performance for 1,000 cycles, and even up to 7,000 cycles, showing ~176 F·g^–1 at a high current density of 40 A·g^–1.

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Controllable synthesis of triangular Ni(HCO<Subscript>3</Subscript>)<Subscript>2</Subscript> nanosheets for supercapacitor

Triangular Ni(HCO₃)₂ nanosheets were synthesized via a template-free solvothermal method. The phase transition and formation mechanism were explored systematically. Further investigation indicated that the reaction time and pH have significant effects on the morphology and size distribution of the triangular Ni(HCO₃)₂ nanosheets. More interestingly, the resulting product had an ultra-thin structure and high specific surface area, which can effectively accelerate the charge transport during charge–discharge processes. As a result, the triangular Ni(HCO₃)₂ nanosheets not only exhibited high specific capacitance (1,797 F·g^-1 at 5 A·g^-1 and 1,060 F·g^-1 at 50 A·g^-1), but also showed excellent cycling stability with a high current density (~80% capacitance retention after 5,000 cycles at the current density of 20 A·g^-1).

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Building an interpenetrating network of Ni(OH)<Subscript>2</Subscript>/reduced graphene oxide composite by a sol–gel method

Herein, a facile sol–gel strategy for building the ordered interpenetrating network of Ni(OH)₂ and reduced graphene oxide (rGO) was proposed. In this strategy, rGO nanosheets were homogeneously fixed inside composite utilizing the pores of Ni(OH)₂ gel as template, forming rGO-interpenetrated gel network. It was found that the rGO nanosheets could effectively reduce the internal resistant of composites and provide mechanical support for the gel network of Ni(OH)₂. Therefore, the composite presented high electrochemical performance, especially high-rate performance, due to the interpenetrating of rGO nanosheets plus the supplementary role of acetylene black. It had high specific capacitance of 2163 F g^?1 at low current density of 2.9 A g^?1 and 733 F g^?1 at high current density of 86.8 A g^?1.     

Impact of CTAB on morphology and electrochemical performance of MoS<Subscript>2</Subscript> nanoflowers with improved lithium storage properties

The search for high capacity, low-cost electrode materials for lithium-ion batteries is a significant challenge in energy research. Among the numerous potential candidates, layered compounds such as MoS₂ (Molybdenum Disulfide) have attracted increasing attention. A facile hydrothermal reduction process using hexadecyltrimethy ammonium bromide (CTAB) as surfactant was developed for the synthesis of lithium-ion battery anode material MoS₂ nanoflowers. The impact of CTAB on morphology and electrochemical performance of MoS₂ has been investigated. With the increase of CTAB content, MoS₂ ultrathin nanosheets with high specific surface area and more active sites have been successfully synthesized. Electrochemical measurements demonstrated that MoS₂ nanoflowers synthesized with 1% content of CTAB have better electrochemical performance than others as anode materials for Li-ion batteries, which yield a high discharge capacity of 1245 mAh g^?1 at a current density of 50 mA g^?1 and a stable capacity retention of 740 mAh g^?1 until 100 electrochemical cycles.     

Successful synthesis of interconnected Co<Subscript>0.85</Subscript>Se nanosheets with high pore volume and its electrochemical performance in supercapacitors

Interconnected Co_0.85Se nanosheets have been prepared by a facile hydrothermal method via tuning reaction time to control the chemical constitution and the morphology. The nanosheets morphology of Co_0.85Se offers sufficient electron transfer and short ion diffusion pathway, which can favor the fast transfer of electrolyte ions. The Co_0.85Se electrode exhibits specific capacitance of 980 F g^??1 at 10 A g^??1 with high cycling life stability (8.3% loss after 5000 cycles) and good conductivity. The assembled Co_0.85Se//AC asymmetric supercapacitor (ASC) device exhibits a high energy density of 46.2 Wh kg^??1 at a power density of 807.4 W kg^??1 and still maintained 29.3 Wh kg^??1 at a power density of 15981.8 W kg^??1 with excellent cycling performance (90.01% capacitance retention over 5000 cycles). The impressive results indicate that such unique interconnected Co_0.85Se nanosheets are promising electrode materials for high-performance supercapacitors.     

High-performance flexible supercapacitors based on C/Na<Subscript>2</Subscript>Ti<Subscript>5</Subscript>O<Subscript>11</Subscript> nanocomposite electrode materials

A new solution method to synthesize Na₂Ti₅O₁₁ with titanium powder is presented, and the C/Na₂Ti₅O₁₁ nanocomposite with high specific surface area and tunnel structure as the electrode material has excellent electrochemical performance. The single electrode composed of the C/Na₂Ti₅O₁₁ nanocomposite based on carbon fiber fabric (CFF) has the highest area capacitance of 1066 mF cm^?2 at a current density of 2 mA cm^?2, which is superior to other titanates and Na-ion materials for supercapacitors (SCs). By scan-rate dependence cyclic voltammetry analysis, the capacity value shows both capacitive and faradaic intercalation processes, and the intercalation process contributed 81.7% of the total charge storage at the scan rate of 5 mV s^?1. The flexible symmetric solid-state SCs (C/Na₂Ti₅O₁₁/CFF//C/Na₂Ti₅O₁₁/CFF) based on different C/Na₂Ti₅O₁₁ mass were fabricated, and 7 mg SCs show the best supercapacitive characteristics with an area capacitance of 309 mF cm^?2 and a specific capacitance of 441 F g^?1, it has a maximum energy density of 22 Wh kg^?1 and power density of 1286 W kg^?1. As for practical application, three SCs in series can power 100 green light-emitting diodes (LEDs) to light up for 18 min, which is much longer than our previous work by Wang et al. lighting 100 LEDs for 8 min. Thus, the C/Na₂Ti₅O₁₁ nanocomposite has promising potential application in energy storage devices.     

Preparation of amorphous cobalt/carbon nanofibers composite as binder-free and conductive-free electrode materials for high supercapacitor

One dimensional carbon nanofibers embedded amorphous cobalt oxide with high electrochemical performances were successfully prepared by electrospinning Co(NO₃)₂ in PAN/DMF solution followed by a high-temperature heat treatment process. The different molar ratio of AN/Co(NO₃)₂ were synthesis. The optimized Co/CNFs(30), in which the molar ratio of AN/Co(NO₃)₂ was 30/1, exhibited a specific capacitance of 1096 F g^?1 at 1 A g^?1 and almost no decay in specific capacitance after cycling 2500 times at 5 A g^?1. The Co/CNFs were characterized by scanning electron microscopy, X-ray diffraction, Raman, transmission electron microscopy, X-ray photoelectron spectroscopy, thermal-gravity-analysis and the N₂ adsorption–desorption. The result showed that cobalt element was successfully dispersed in the carbon nanofibers with an amorphous state.