Abstract

Perovskite barium zirconate titanate nanoparticles (25–20 nm in diameter) were synthesized at low temperatures and under ambient pressure using titanium alkoxide, zirconium alkoxide and barium hydroxide as the starting materials. Microstructural analyses by X-ray diffraction and transmission electron microscopy indicated that the powders were nano-scaled, well crystallized, and had a perovskite phase. It is proposed that an acid–base neutralization reaction is the key mechanism behind the formation of such nanoparticles.

Chemical stability of (Bi_1/2Na_1/2)TiO₃ (BNT) ceramics against water was studied through a comparison experiment. Immersion of BNT in 0.01 M NaOH solution showed no noticeable influence, while BNT ceramics were seriously affected when hydrogen was deposited on them through the electrolysis of water in the solution: the capacitance was obviously decreased and the dielectric loss was dramatically increased in the low-frequency range. X-ray diffraction analysis indicated that hydrogen was first dissolved into BNT and then caused decomposition, with some other phases formed. As water-induced degradation is an important cause of degradation for piezoelectric devices, it is important to ensure that the chemical stability of BNT is not decreased when using doping and/or the formation of a solid-state solution with other perovskite-type oxides in order to improve the piezoelectric properties of BNT-based ceramics.

Abstract

NiCo₂S₄ spheres with granular core were designed and fabricated via an easy two-step hydrothermal reation: carbon sphere clusters were used as templates to obtain NiCo₂(OH)₆/C precursor, which reacted with sodium sulfide to synthesize granular NiCo₂S₄ and then, the precursor of NiCo₂S₄ was grown on the periphery of granular NiCo₂S₄ to form the unique structure. The NiCo₂S₄ spheres with granular core specific surface area reaches 26.61 m² g⁻¹, which is about twofold of granular NiCo₂S₄ (11.41 m² g⁻¹). Electrochemical performance of the electrodes has been investigated. The electrode of NiCo₂S₄ spheres with granular core displays high specific capacitance of 1156 F g⁻¹ at a current density of 1 A g⁻¹, which increases by 71% compared to that of granular NiCo₂S₄ (675 F g⁻¹). Upon 1000 charge/discharge cycles, the NiCo₂S₄ spheres with granular core electrode exhibits excellent cycling stability with 82% capacitance retention at 5 A g⁻¹. In view of the low cost and superior electrochemical performance, the NiCo₂S₄ spheres with granular core synthesized using carbon sphere clusters as templates could be a promising electrode material for supercapacitors.

Abstract

In this paper, Cu₂O/CoO nanoneedle arrays (Cu₂O/CoO-NNAs) are vertically grown on nanoporous Cu/Co (NPs-Co/Cu) conductive substrate through a facile dealloying and oxidation method. Benefiting from their intriguing structural features, the NPs-Cu/Co alloy based Cu₂O/CoO-NNAs hybrid possesses fascinating electrochemical performance as an integrated binder-free electrode for symmetric supercapacitors (SSCs). High areal capacitances of 0.21 F cm⁻² can be achieved at a current densities of 5 mA cm⁻². Moreover, electrode has an excellent long-term cycling stability with 100% capacitance retention after 10000 cycles. A maximum of volumetric energy density (0.81 mW h cm⁻³) and volumetric power density (3 W cm⁻³) were achieved for the as-fabricated SSCs device. Therefore, the present work holds a great promise for future design and large-scale production of high volumetric energy density and volumetric energy density electrodes by dealloying and oxidation method for energy storage devices.

Abstract

Synthesis of electrode materials with desirable morphology and size for supercapacitor applications is an important and challenging research topic. In this work, four types of Co₃O₄ nanostructures, namely hexagonal-shaped nanosheets, nanoflake arrays, nanoflowers and oval-shaped nanospheres were synthesized via a facile in-situ dealloying method. Applied as electrode material for supercapacitiors, the Co₃O₄ nanospheres achieves highest areal capacitance of 16.58 F cm⁻² at current density of 10 mA cm⁻². The Co₃O₄ nanoflowers exhibited promising capacitive properties and excellent retention. Its areal capacitance can reach 9.27 F cm⁻² at the current density of 10 mA cm⁻² and retain 98.5% of its initial capacitance at the current density of mA cm⁻² after 1000 charge–discharge cycles. This work could provide a deeper understanding of the morphology effect on the supercapacitive performance, and also suggests the importance of rational design and synthesis of electrode materials with desirable morphology and size for high performance supercapacitor applications.

Abstract

In the report, we explore a two-step efficient synthetic to purposefully fabricate three-dimensional (3D) NiCo₂S₄ nanosheets for advanced electrochemical supercapacitors. They were characterized for their structural, morphological and electrochemical properties by using XRD, SEM, TEM, cyclic voltammetry and charge discharge methods. The unique designed nanostructure exhibits a high specific capacitance (1257.1 F g⁻¹ at current density 1 A g⁻¹), good rate performance (75.7% retention for current increases around 20 times) and excellent cycling stability (80% retention at 5 A g⁻¹ after 1000 cycles). We are the first step in the synthesis of 3D NiCo₂S₄ flowers, which have a specific capacitance of 700.7 F g⁻¹ at the current density of 1 A g⁻¹ and exhibit excellent cycling stability with 95% capacitance retention. The S-NiCo₂S₄//activated carbon asymmetric supercapacitor is can deliver a maximum energy density of 47.3 W h kg⁻¹ at a power density of 477.3 W kg⁻¹. Therefore, according to our investigation it can be concluded that the low cost and environmental friendly two-step approach from 3D NiCo₂S₄ nanoflowers to the 3D NiCo₂S₄ nanosheets could be used to deposit efficient 3D NiCo₂S₄ nanosheets for supercapacitor application.

Abstract

In the present work, mesoporous NiCo₂O₄ nanorod/graphene oxide (NiCo₂O₄/GO) composite was prepared by a facile and cost-effective hydrothermal method and meanwhile, N-doped graphene (N-G) was fabricated also by a hydrothermal synthesis process. NiCo₂O₄/GO composite and N-G were used as positive and negative electrodes for the supercapacitor, respectively, which all displayed excellent electrochemical performances. The NiCo₂O₄/GO composite electrode exhibited a high specific capacitance of 709.7 F g⁻¹ at a current density of 1 A g⁻¹ and excellent rate capability as well as good cycling performance with 84.7% capacitance retention at 6 A g⁻¹ after 3000 cycles. A high-voltage asymmetric supercapacitor (ASC) was successfully fabricated using NiCo₂O₄/GO composite and N-G as the positive and negative electrodes, respectively, in 1 M KOH aqueous electrolyte. The ASC delivered a high energy density of 34.4 Wh kg⁻¹ at a power density of 800 W kg⁻¹ and still maintained 28 Wh kg⁻¹ at a power density of 8000 W kg⁻¹. Furthermore, this ASC showed excellent cycling stability with 94.3% specific capacitance retained at 5 A g⁻¹ after 5000 cycles. The impressive results can be ascribed to the positive synergistic effects of the two electrodes. Evidently, our work provides useful information for assembling high-performance supercapacitor devices.

Abstract

Ti–10Fe–6Al alloy was rapidly solidified using single roller melt-spinning technique to obtain ribbons, which was developed and used for supercapacitor electrode materials for the first time through facile oxidation. After oxidation at 680 °C for 100 h, TiO₂/Fe₂O₃/Al₂O₃ nanocomposite on Ti–10Fe–6Al alloy ribbons consisting of numerous nanoparticles with average diameter of 90 nm was formed, which directly served as current collectors. For Ti–10Fe–6Al alloy foils cut from alloy ingot, oxidation product also showed particle shape but the diameter was far larger than that on oxided Ti–10Fe–6Al alloy ribbons. The ribbon electrode exhibited excellent electrochemical performance with areal capacitance of 10,500 µF cm⁻² at current density of 40 µA cm⁻² as well as long-term cycling stability of about 79.9% capacitance enhancement after 5000 cycles.

Abstract

In the present paper, 10 vol%TiC/Ti–6Al–3Sn–3.5Zr–0.4Mo–0.75Nb–0.35Si composite produced via in situ casting technique was tested in the temperature range from room temperature to 900 °C and much attention was paid on the microstructural evolution during high-temperature tensile test. It was found that the variation of microstructures in deformation zones with strain exhibited different trends at different temperatures. Below 600 °C, dislocation density increased with strain over the entire strain range. As temperature increased to 700 °C, dislocations proliferated rapidly in the initial deformation and then dislocation annihilated through dynamic recovery. Above 800 °C, the variation of microstructures in deformation zones with strain was similar to that at 700 °C at the beginning but at higher strain, dynamic recrystallization (DRX) occurred, leading to the formation of equiaxed microstructure. Microstructural evolution in deformation zones corresponded to the variation of tensile stress–strain characteristics with temperature, reflecting the hardening or softening feature of matrix. Dynamic recovery ascribed to the flow softening of the composite at 700 °C, while flow softening is owing to dynamic recovery and DRX above 800 °C. In addition, matrix softening should show different trends in different temperature ranges.