Zong-Huai Liu

Three-Dimensional Tubular MoS2/PANI Hybrid Electrode for High Rate Performance Supercapacitor

By using three-dimensional (3D) tubular molybdenum disulfide (MoS2) as both an active material in electrochemical reaction and a framework to provide more paths for insertion and extraction of ions, PANI nanowire arrays with a diameter of 10-20 nm can be controllably grown on both the external and internal surface of 3D tubular MoS2 by in situ oxidative polymerization of aniline monomers and 3D tubular MoS2/PANI hybrid materials with different amounts of PANI are prepared. A controllable growth of PANI nanowire arrays on the tubular MoS2 surface provides an opportunity to optimize the capacitive performance of the obtained electrodes. When the loading amount of PANI is 60%, the obtained MoS2/PANI-60 hybrid electrode not only shows a high specific capacitance of 552 F/g at a current density of 0.5 A/g, but also gives excellent rate capability of 82% from 0.5 to 30 A/g. The remarkable rate performance can be mainly attributed to the architecture with synergistic effect between 3D tubular MoS2 and PANI nanowire arrays. Moreover, the MoS2/PANI-60 based symmetric supercapacitor also exhibits the excellent rate performance and good cycling stability. The specific capacitance based on the total mass of the two electrodes is 124 F/g at a current density of 1 A/g and 79% of its initial capacitance is remained after 6000 cycles. The 3D tubular structure provides a good and favorable method for improving the capacitance retention of PANI electrode.

Creation of nanopores on graphene planes with MgO template for preparing high-performance supercapacitor electrodes

Creation of nanopores on graphene planar sheets is of great significance in promoting the kinetic diffusion of electrolyte and enhancing the utilization efficiency of graphene planar sheets. Herein, we developed a facile chemical vapor deposition strategy to prepare highly porous graphene with flake-like MgO as template and ferrocene as the carbon precursor. The graphene layers show a highly porous structure with small mesopores of 4-8 nm, large mesopores of 10-20 nm and additional macropores of 100-200 nm. These nanopores on graphene sheets provide numerous channels for fast ion transport perpendicular to the 2D basal plane, while the good powder conductivity ensures an effective electron propagation within the 2D graphene plane. As a result, a specific capacitance of 303 F g(-1), an areal capacitance up to 17.3 μF cm(-2) and a nearly tenfold shorter time constant were achieved when compared with those of nonporous and stacked graphene electrodes. The method demonstrated herein would open up an opportunity to prepare porous graphene for a wide applications in energy storage, biosensors, nanoelectronics and catalysis.

Effects of Li content on the phase structure and electrical properties of lead-free (K0.46−x∕2Na0.54−x∕2Lix)(Nb0.76Ta0.20Sb0.04)O3 ceramics

Lead-free (K0.46−x∕2Na0.54−x∕2Lix)(Nb0.76Ta0.20Sb0.04)O3 piezoelectric ceramics were prepared by the conventional solid state sintering method without cold-isostatic pressing process. The x-ray diffraction and Raman scattering results show that the phase structure of the ceramics undergoes a transition from pseudocubic to tetragonal phase with increasing x from 0 to 0.10. Significantly enhanced electrical properties (d33=259pC∕N, kp=0.42, er=1653, and tan δ=0.027) were obtained in the ceramics with x=0.04 near the morphotropic phase boundary, and only the tetragonal-cubic phase transition was observed above the room temperature in the er-T curve. The temperature stability of the ceramics with x=0.04 was also investigated.

Phase transitional behavior, microstructure, and electrical properties in Ta-modified [(K0.458Na0.542)0.96Li0.04] NbO3 lead-free piezoelectric ceramics

Lead-free [(K0.458Na0.542)0.96Li0.04] (Nb1−xTax)O3 ceramics were prepared by ordinary sintering technique. The effects of Ta content on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics were investigated. X-ray diffraction results indicate that the phase structure undergoes a transition from orthorhombic to tetragonal phase with the increase in x. The small and large peaks observed in the Raman spectra can all be attributed to the internal modes of the NbO6 octahedron, and both ν5 and ν1 modes slightly shift to lower frequency numbers by increasing x. Ta substitution for Nb leads to the disappearance of the abnormal grain growth behavior, inhibits the grain growth, and improves the density of the ceramics. Increasing x leads to the different variations of dielectric constants before and after poling and makes the ceramics more relaxorlike. The proper substitution of Ta shifts the polymorphic phase transition (at To-...

Multiferroic properties of Aurivillius phase Bi6Fe2−xCoxTi3O18 thin films prepared by a chemical solution deposition route

The magnetic and ferroelectric properties of Co-doped Bi6Fe2Ti3O18 thin films Bi6Fe2−xCoxTi3O18 (BFCTO) (0 ≤x≤ 1) are investigated. The coexistence of room-temperature ferromagnetism and ferroelectricity is observed in BFCTO thin films. The x = 0.6 sample exhibits a higher remnant magnetization Mr of 8.41 emu/cm3 and a remnant polarization Pr of 17.6 μC/cm2 compared with other BFCTO thin films. The ferromagnetism can be ascribed to the spin canting of Fe- and Co-based sublattices via the Dzyaloshinskii-Moriya interaction [I. Dzyaloshinsky, J. Phys. Chem. Solids 4, 241 (1958); T. Moriya, Phys. Rev. 120, 91 (1960)]. The change in the remnant polarization is discussed in terms of the variation of grain size and oxygen vacancies caused by Co-doping.

Phase coexistence and high electrical properties in (KxNa0.96−xLi0.04)(Nb0.85Ta0.15)O3 piezoelectric ceramics

(KxNa0.96−xLi0.04)(Nb0.85Ta0.15)O3 lead-free piezoelectric ceramics were produced by conventional solid-state reaction method. The effects of K/Na ratio on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics have been investigated. The phase structure of the ceramics undergoes a transition from orthorhombic to tetragonal phase with increasing x. A double-degenerate symmetric O–Nb–O stretching vibration v1 and a triply degenerate symmetric O–Nb–O bending vibration v5 are detected as relatively strong scattering in the Raman spectra. The peak shifts of v5 and v1 modes all have a discontinuity with x between 0.42 and 0.46, which may suggest the coexistence of orthorhombic and tetragonal phases in this range. Properly modifying x reduces the sintering temperature, promotes the grain growth behavior, and improves the density of the ceramics. The polymorphic phase transition (at To-t) is shifted to near room temperature by ...

Tellurium-Assisted Epitaxial Growth of Large-Area, Highly Crystalline ReS2 Atomic Layers on Mica Substrate.

Anisotropic 2D layered material rhenium disulfide (ReS2 ) with high crystal quality and uniform monolayer thickness is synthesized by using tellurium-assisted epitaxial growth on mica substrate. Benefit from the lower eutectic temperature of rhenium-tellurium binary eutectic, ReS2 can grow from rhenium (melting point at 3180 °C) and sulfur precursors in the temperature range of 460-900 °C with high efficiency.

Functional graphene nanocomposite as an electrode for the capacitive removal of FeCl3 from water

Capacitive deionization (CDI) is a promising desalination technology which has attracted enormous interest in recent years due to its economic advantages over traditional technologies. In this paper, the facilely synthesized graphene and resol (RGO–RF) nanocomposite was proposed as a CDI electrode for the removal of ferric ions. The addition of resol led to less aggregation of the graphite oxide, while after calcination the structure collapsed and the pore size distribution widened. This was confirmed by Brunauer–Emmett–Teller (BET) techniques. The electrode’s performances, involving the adsorption isotherm and kinetics, were investigated through batch mode experiment. It was found that the electrosorptive capacity of the RGO–RF electrode was 3.47 mg g−1 with an electrical voltage of 2.0 V and initial solution concentration of 40 mg L−1. This is higher than the corresponding activated carbon and graphene electrode due to the presence of resol which is beneficial in restricting the aggregation of graphene, resulting in a high specific surface area and therefore a high electrosorption capacity. Further, the electrosorption of ferric ions onto RGO–RF follows the Langmuir isotherm, implying monolayer adsorption. Meanwhile, regardless of the electrical voltage, the kinetic analysis illustrated that the pseudo-first-order model can describe the electrosorption behaviour of the RGO–RF electrode very well.

Platelet CMK-5 as an excellent mesoporous carbon to enhance the pseudocapacitance of polyaniline.

A high-performance supercapacitor electrode consisting of platelet ordered mesoporous carbon CMK-5 and polyaniline (PANi) was prepared by chemical oxidative polymerization of aniline in the presence of CMK-5. The PANi with uniform size of 2-5 nm was primarily confined in the mesochannels of CMK-5 at low PANi loadings (40 and 51 wt %), whereas at a high loading of 64 wt %, additional PANi thin films with thicknesses of 5-10 nm were coated on the surface of the CMK-5 particles. Such CMK-5-PANi composites afforded a high electrochemical active surface area for surface Faradic redox reactions, leading to a more than 50% utilization efficiency when considering the theoretical capacitance of PANi of about 2000 F/g. As a result, a specific capacitance of 803 F/g and an energy density of 27.4 Wh/kg were achieved for CMK-5-PANi composite electrode with 64 wt % PANi, showing substantial improvement as compared with symmetric capacitors configured with CMK-5 electrodes (10.1 Wh/kg) or pure PANi electrodes (16.4 Wh/kg). Moreover, an excellent rate capability and a substantially enhanced electrochemical stability with 81% capacitance retention as compared with 68% of pure PANi were also observed over 1000 charge-discharge cycles at a constant current density of 4.0 A/g.

MnO2 nanoflakes grown on 3D graphite network for enhanced electrocapacitive performance

Free-standing 3D graphite (3DG) with an interconnected porous network and a highly conductive backbone was prepared by a chemical vapor deposition technique with Ni foam as the sacrificial template and styrene as the carbon precursor. The 3D graphite network serves as an excellent scaffold to grow MnO2 nanoflakes through a hydrothermal reaction between 3DG and KMnO4 aqueous solution. The interconnected and conductive 3D graphite network offers a pathway for fast electron and ion transport, while the MnO2 nanoflakes that emanate from the backbone surface of 3DG minimize the interfacial contact resistance between 3DG and MnO2, favoring the effective electron transport from the 3DG skeleton to MnO2 nanoflakes. As a result, the 3DG–MnO2 composite electrode with 13% MnO2 nanoflakes exhibited a specific capacitance of 210 F g−1 at a constant discharge current density of 2.0 A g−1, which still remained at 202 F g−1 at a high current density of 15 A g−1. Moreover, a good capacitance retention of 75% and an outstanding coulombic efficiency of 97.8% were achieved after 4000 cycles of galvanostatic charge–discharge. These superior capacitive properties make the 3DG–MnO2 composite one of the promising electrodes for electrochemical energy storage.