Fengrui Zhou

Flexible Asymmetrical Solid-State Supercapacitors Based on Laboratory Filter Paper

In this study, a flexible asymmetrical all-solid-state supercapacitor with high electrochemical performance was fabricated with Ni/MnO2-filter paper (FP) as the positive electrode and Ni/active carbon (AC)-filter paper as negative electrode, separated with poly(vinyl alcohol) (PVA)-Na2SO4 electrolyte. A simple procedure, such as electroless plating, was introduced to prepare the Ni/MnO2-FP electrode on the conventional laboratory FP, combined with the subsequent step of electrodeposition. Electrochemical results show that the as-prepared electrodes display outstanding areal specific capacitance (1900 mF/cm(2) at 5 mV/s) and excellent cycling performance (85.1% retention after 1000 cycles at 20 mA/cm(2)). Such a flexible supercapacitor assembled asymmetrically in the solid state exhibits a large volume energy density (0.78 mWh/cm(3)) and superior flexibility under different bending conditions. It has been demonstrated that the supercapacitors could be used as a power source to drive a 3 V light-emitting diode indicator. This study may provide an available method for designing and fabricating flexible supercapacitors with high performance in the application of wearable and portable electronics based on easily available materials.

Hierarchical architectures of monodisperse porous Cu microspheres: synthesis, growth mechanism, high-efficiency and recyclable catalytic performance

Novel hierarchical architectures of porous copper (Cu) microspheres assembled with nanoparticles have been successfully synthesized by ingeniously selecting the precursor and complexant through a facile wet chemical reduction method. The resultant porous Cu microspheres have a size distribution of 700 ± 50 nm and have excellent monodispersity. The synergistic effect between the precursor of slightly soluble copper hydroxide and the complexants of polyacrylic acid and ethanol amine exactly induces the generation of unique porous hierarchical architectures. The obtained porous Cu microspheres were applied to reduce and degrade different organic dyes with high concentrations (4-nitrophenol, methylene blue, and rhodamine B) in the presence of NaBH4. Compared with solid Cu particles that have the same size, these porous Cu microspheres exhibit more excellent catalytic activity due to their hierarchical structures. Moreover, the catalyst with universal applicability could be easily separated from the catalytic system and sustainedly possess high stability in recycled reactions.

Copper salts mediated morphological transformation of Cu2O from cubes to hierarchical flower-like or microspheres and their supercapacitors performances.

Monodisperse Cu2O of different microstructures, such as cubes, flower-like, and microspheres, have been extensively synthesized by a simple polyol reduction method using different copper salts, i.e. (Cu(acac)2, Cu(OH)2, and Cu(Ac)2·H2O). The effects of copper salts on the morphology of Cu2O were investigated in details through various characterization methods, including X-ray diffraction, transmission electron microscopy, scanning electron microscopy and UV-Vis absorption spectra. The effects of morphology on the electrochemical properties were further studied. Among the different structures, Cu2O with the microspheric morphology shows the highest specific capacitance and the best cycling stability compared with those of the other two structures, thus bear larger volume charge during the electrochemical reaction due to the microspheres of small nanoparticles.

Comparative study of LiMnPO4 cathode materials synthesized by solvothermal methods using different manganese salts

The effects of anions on the particle size, phase impurity, crystal structural, and crystal growth orientation of olivine LiMnPO4 prepared via the solvothermal synthesis method are systematically studied. LiMnPO4 cannot be obtained for the precursor containing NO3− anions due to its strong oxidizing ability in acid environment. The SO42− anion may facilitate the growth of high-index planes of the LiMnPO4 crystals owing to its higher charge number. The Ac− anion with larger volume may have a significant atomic-scale template effect, thus the particle size of LiMnPO4 is greatly limited and the crystal growth is inclined to the equilibrium state. The LiMnPO4 samples, prepared from MnSO4, MnCl2 and Mn(Ac)2, deliver an initial capacity of 145, 129 and 81 mAh g−1, respectively. Among them, the sample synthesized from MnCl2 can maintain 91% of its initial capacity after 200 cycles at 2 C, due to its high purity and crystal orientation growth with ac planes.

Spherical and flake-like BN filled epoxy composites: morphological effect on the thermal conductivity, thermo-mechanical and dielectric properties

Epoxy composites, with boron nitride spheres (s-BN) and flakes (f-BN) as fillers were prepared. The effect of filler morphology, content, and crystallization of BN particles on the thermal conductivity, thermo-mechanical and dielectric properties of the composites were investigated. At the same loading level, s-BN with smaller size and larger surface area led to much more significant increase in the glass transition temperature (Tg), reduction in the coefficient of thermal expansion and lower storage modulus (E′), while much higher thermal conductivities were observed in epoxy composites containing f-BN, owing to the larger aspect ratio and better crystallization. In addition, the introduction of BN fillers only did slightly increase on the dielectric constant and dielectric loss of the epoxy resin. We believe, the BN enhanced epoxy composites, with significantly improved thermal conductivity and thermo-mechanical properties, yet maintaining low dielectric constant and dielectric loss at the same time, have great application potential in the microelectronic insulation industry.

Synergistic effect for the preparation of LiMn2O4 microspheres with high electrochemical performance

Under the synergistic promotion of chemical reactions, MnO2 microspheres are successfully prepared using MnCO3 precursor as self-template, with maximum use of the raw materials, and are then converted into spinel LiMn2O4 microspheres via a solid-state reaction. When applied as cathode materials for rechargeable lithium-ion batteries, the LiMn2O4 microspheres deliver a discharge capacity of 133.2 mA h g−1 and 109.8 mA h g−1 at 0.1 C and 10 C rates, respectively. More than 91.3% of the initial storage capacity is maintained after 1000 cycles at a 1 C charge and 10 C discharge rate. Furthermore, even when cycled at elevated temperature (55 °C) at a 1 C charge and 10 C discharge rate, this material showes 86.2% capacity retention after 100 cycles, which reveals a high reversible capacity, superior rate capability and excellent cycling stability under high rates both at room temperature and high temperature. The performance is comparable to the best results shown in the literature so far. This structured LiMn2O4 microspheres in the present work are very promising for large-scale commercialization of high-power lithium ion batteries.

Low cost, high performance flexible asymmetric supercapacitor based on modified filter paper and an ultra-fast packaging technique

A flexible all-solid-state asymmetric supercapacitor (FAAS) was prepared via a low-cost method with commonly used paper fibers as the substrate and a modified polymer-based hydrogel as the electrolyte. In the designed structure of the positive electrode, a three dimensional network of stacked thin film based on paper fibers (PFs), chemically reduced graphene oxide (RGO) and the electro-polymerization of polyaniline (PANI) nanorods was prepared via an extended filtration assisted method. The fabricated PF–RGO–PANI electrodes exhibit large specific capacitance of 587 F g−1 at the current density of 0.8 A g−1 and excellent cycling stability (99.6% retention of initials specific capacitance even after 5000 cycles). PF–RGO film was introduced as the negative electrode for the designed asymmetric supercapacitor. During the preparation process of FAAS, a glutaraldehyde (GA) cross-linked PVA–H2SO4 hydrogel was not only used as the electrolyte but also explored as a separator and external packaging material prepared by a fast layer-by-layer assembly technique within one minute. The resulted FAAS exhibits a maximum energy density and power density of 175 W h kg−1 and 9200 W kg−1. Moreover, superior mechanical stability of the FAAS has been demonstrated by testing its bending and folding performance, which retains over 84% of its original specific capacitance even after 2000 cycles of bending and folding. The simple and low-cost preparation process of electrodes, the ultra-fast flexible supercapacitor assembling and the efficient packaging technique proposed in this study provide a good contribution to the development of FAAS for the next generation flexible energy storage devices.

Laboratory filter paper as a substrate material for flexible supercapacitors

In this study, a flexible asymmetrical solid-state filter paper-based supercapacitor was fabricated. Common laboratory filter paper (FP) provides toughness and flexibility to the whole device. Simply, traditional electroless Ni plating and electro-deposition were introduced to change the electrical conductivity of FP as a flexible and conductive substrate material. Then, the electrochemical active material Co(OH)2 and active carbon (AC) were respectively coated on the conductive Ni paper through electro-deposition and physical coating methods to prepare Ni/Co(OH)2-FP as a positive electrode and Ni/AC-FP as a negative electrode. Moreover, they were separated by a piece of FP coated with an ionic gel electrolyte to assemble the flexible asymmetrical solid-state supercapacitors. This supercapacitor exhibits superior flexibility, large volume energy density (0.64 mW h cm−3), and good bending cycle performance (95.89% capacitance retention after 500 bending cycles). It has been demonstrated that the assembled supercapacitor can still power a red light-emitting diode (LED) indicator normally regardless of the bending state and bending frequency. This study may provide promising insights for the design and fabrication of a flexible asymmetrical solid-state supercapacitor in a flexible power supply for wearable and portable applications.

Facile synthesis of water soluble reduced graphene oxide with a high concentration and its application in printable micro-supercapacitors

Direct printing techniques have generated significant research interest in fabricating flexible and scalable micro-supercapacitors (MSCs). In this study, we report a facile and cost-effective way to synthesize water soluble reduced graphene oxide (WSG) with a high concentration by decoration with aminobenzenesulfonic acid (ABS) and reduction with ascorbic acid. The WSG possesses excellent electrical conductivity (360 S m−1), good water dispersion stability as well as a high zeta potential value (−62 mV at pH 11), and the concentration of the as-prepared WSG could reach 5 mg mL−1, nearly as great as the highest value from previous reports. Then, using this high-concentration WSG dispersion directly as an electrochemically active ink material, micro-supercapacitor electrodes could be facilely fabricated via a direct printing technique on common printing paper, and the all-solid-state flexible MSCs could be further assembled. The results show that these flexible MSCs exhibit high area and volume specific capacitances of 2.67 mF cm−2 and 6.75 F cm−3, maintaining 94.8% of their initial specific capacitance after 5000 cycles at a scan rate of 50 mV s−1. More importantly, the capacitance and potential can be expanded by connecting a WSG-MSC device in parallel and in series, and the assembled devices are further demonstrated to be capable of lighting a liquid crystal display with three WSG-MSCs in series. These findings not only provide a simple way to synthesize WSG with a high concentration, but also facilitate its applications in printable and flexible MSCs with high performance.

Multi-Dimensional Ternary Hybrids with Synergistically Enhanced Electrical Performance for Conductive Nanocomposites and Prosthetic Electronic Skin

Graphene and silver nanowires (AgNWs) are ideal fillers for conductive polymer composites, but they tend to aggregate in the polymer matrix due to the lack of surface functional groups and large specific surface area, which is hard for the polymer composites filled with them to reach their full potential. Here, ternary hybrids with multidimensional architectures including 3D polystyrene (PS) microspheres, 2D reduced graphene oxide (RGO) nanosheets, and 1D AgNWs are obtained using a simple, but effective, electrostatic attraction strategy. The electrical conductivity (136.25 S m-1) of the ternary hybrid conductive nanocomposites filled with RGO and AgNWs is significantly higher than that of the nanocomposites containing only RGO (3.255 S m-1) at the same total filler loading due to the synergistic effect of RGO and AgNWs. The conductive nanocomposites simultaneously present a low percolation threshold of 0.159 vol % and a maximum electrical conductivity of 1230 S m-1 at 3.226 vol % filler loading. Moreover, a flexible electronic skin based on the multidimensional ternary hybrids is presented, and it exhibits large stretchability, high gauge factor, and excellent cyclic working durability, which is successfully demonstrated in monitoring prosthetic finger motions.