Wanlu Yang

Solvothermal One-Step Synthesis of Ni–Al Layered Double Hydroxide/Carbon Nanotube/Reduced Graphene Oxide Sheet Ternary Nanocomposite with Ultrahigh Capacitance for Supercapacitors

A Ni-Al layered double hydroxide (LDH), mutil-wall carbon nanotube (CNT), and reduced graphene oxide sheet (GNS) ternary nanocomposite electrode material has been developed by a facile one-step ethanol solvothermal method. The obtained LDH/CNT/GNS composite displayed a three-dimensional (3D) architecture with flowerlike Ni-Al LDH/CNT nanocrystallites gradually self-assembled on GNS nanosheets. GNS was used as building blocks to construct 3D nanostructure, and the LDH/CNT nanoflowers in turn separated the two-dimensional (2D) GNS sheets, which preserved the high surface area of GNSs. Furthermore, the generated porous networks with a narrow pore size distribution in the LDH/CNT/GNS composite were also demonstrated by the N2 adsorption/desorption experiment. Such morphology would be favorable to improve the mass transfer and electrochemical action of the electrode. As supercapacitor electrode material, the LDH/CNT/GNS hybrid exhibited excellent electrochemical performance, including ultrahigh specific capacitance (1562 F/g at 5 mA/cm(2)), excellent rate capability, and long-term cycling performance, which could be a promising energy storage/conversion material for supercapacitor application.

Hierarchical NiCo2O4@NiO core–shell hetero-structured nanowire arrays on carbon cloth for a high-performance flexible all-solid-state electrochemical capacitor

A hierarchical NiCo2O4@NiO core–shell nanowire hetero-nanostructure has been successfully anchored on a carbon cloth conductive substrate by the stepwise design to fabricate the NiCo2O4@NiO/CC composite for a high-performance flexible all-solid-state electrochemical capacitor. The assembled capacitor exhibits improved pseudocapacitive performance because of the synergetic effect of each component. Impressively, based on the total mass of active material on both electrodes, a high gravimetric capacitance of 1792 F g−1 at 5 mA cm−2 is achieved for the final NiCo2O4@NiO/CC flexible capacitor, along with excellent rate capability and cycle performance (with the capacity retention of 87.5% after 5000 cycling). The outstanding electrochemical performances are attributed to its superstructure with significantly enhanced active-surface area, favorable morphological stability and convenient ion transport paths. These results clearly present a cost-effective and alterable method for fabrication of various core–shell nanostructures on flexible conductive substrates, which may bring new design opportunities of device configuration for energy-storage applications in future wearable electronics.

The growth and assembly of the multidimensional hierarchical Ni3S2 for aqueous asymmetric supercapacitors

Mushroom-like Ni3S2 consisting of a thin film on nanorod arrays have been successfully synthesized via a dissolution-precipitation route, which was carried out through a hydrothermal process using the Ni foam in thioacetamide alcohol solution without the introduction of other Ni sources. The thin film played a key role in exhibiting an excellent electrochemistry performance of the mushroom-like Ni3S2 electrode. As a pseudocapacitor material, the as-obtained mushroom-like Ni3S2 electrode showed a significant specific capacitance (1190.4 F g−1 at 8 A g−1). Moreover, an asymmetric supercapacitor, with the mushroom-like Ni3S2 as the positive electrode material and activated carbon powder (AC) as the negative electrode material, exhibited a high energy density (60.3 W h kg−1) at an average power density of 3600 W kg−1 based on the mass of the active material.

Manganese dioxide core–shell nanowires in situ grown on carbon spheres for supercapacitor application

A manganese dioxide (MnO2) core–shell nanostructure has been in situ grown on carbon spheres to form a core–shell MnO2–MnO2/C composite electrode material as a supercapacitor via an effective two-step hydrothermal method. Such a nanostructure enhances the specific surface area of MnO2, and effectively decreases the ion diffusion and charge transport resistance in the electrode reaction. The morphology and structure of the as-prepared samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform IR (FT-IR) spectra. The electrochemical behavior of the as-prepared electrode was evaluated by cyclic voltammetry (CV), electrochemical impedance spectrometry (EIS) and chronopotentiometry tests in a 1 M Na2SO4 aqueous electrolyte. Results reveal that the prepared electrode exhibits good electrochemical reversibility, a high specific capacitance (225 F g−1 at 2 mA cm−2) and excellent cycling stability with a retention ratio of 90% after 5000 cycles.

Hierarchically porous MgAl mixed metal oxide synthesized by sudden decomposition of MgAl layered double hydroxide gel

In this study, a hierarchically porous MgAl mixed metal oxide has been synthesized by using MgAl layered double hydroxide gel as a precursor. During the calcination of the precursor, the explosive decomposition of the layered double hydroxide resulted in a number of interconnecting pores. To investigate the formation mechanism, the as-prepared materials were characterized by XRD, SEM, TEM, FT-IR, TG-DSC and nitrogen sorption measurements. Results revealed that the MgAl layered double hydroxide gel was a complicated mixture containing layered double hydroxide, NH4NO3, water and organic by-products. At about 188 °C, the formation of a hierarchically porous structure was complete in 3 s because of the instantaneous combustion of organic by-products. The current research provides information for understanding the assembly of the hierarchically porous material under template-free conditions.