High theoretical capacitance of MnO2 nanoparticles were successfully electrodeposited on the conductive graphene/activated carbon (GN/AC) composite film, and the urchin type MnO2 microspheres were controlled by adjusting the electro-deposition reaction times. The GN/AC/MnO2-1200s composite electrodes exhibited a maximum specific capacitance of 1231 mF/cm2 (MnO2 loading mass of 7.65 mg/cm2 and the mass specific capacitance of 123 F/g) at a current density of 0.5 mA/cm2. The assembled flexible solid-state symmetric supercapacitor had a good mechanical flexibility (about 88.6% of its original capacitance after 500 bending times) and prominent cycling stability (about 82.8% retention in capacitance over 10000 cycles). More importantly, the device could possess a maximum energy density of 0.27 mW h/cm3 and a maximum power density of 0.02 W/cm3. These results well demonstrate a great potential for applications of GN/AC/MnO2 composite electrodes in flexible energy storage devices.

A ternary composite of graphene/activated carbon/polypyrrole (GN/AC/PPy) used as an electrode active material for supercapacitors has been synthesized via vacuum filtration and anodic constant current deposition methods. The ACs sandwiched between GN sheets can be used as flexible substrates for PPy nanoparticles, and the microscopic morphologies and electrochemical performances of GN/AC/PPy electrodes were synthesized and designed through regulating different deposition current densities and deposition times. The GN/AC/PPy 15 -200 s electrode exhibits a maximum areal specific capacitance of 906 mF cm À2 with a PPy loading mass of 2.75 mg cm À2 (specific capacitance of 178 F g À1 ) at a current density of 0.5 mA cm À2 . Its capacitance retention still remained at 64.4% after 5000 charge-discharge cycles and 83.6% after 500 stretching-bending cycles at a current density of 3 mA cm À2 . The flexible, free-standing and binder-free GN/AC/PPy electrodes have a broad prospect in flexible energy storage devices. Fig. 4 (a) GCD curves of all samples at the current density of 1 mA cm À2 ; (b) CV curves of samples at the scan rate of 10 mV s À1 ; (c) areal specific capacitances of all samples at different current densities; (d) Nyquist plot of all samples.This journal is

In this paper, litchi-like microspheres structures of NiCo 2 Se 4 @carbon microspheres (NCSC) hybrids were successfully synthesized via a simple two-step hydrothermal method. The effects of the content of NiCo 2 Se 4 on the structure of NCSC composites are investigated. The morphology and nanostructure of the as-obtained NCSC hybrids were examined by XRD, XPS, FESEM and TEM. The results indicate that the carbon microspheres (CM) were uniformly covered with NiCo 2 Se 4 and with the increase of NiCo 2 Se 4 content, the superficies of NCSC also exhibits homogeneous rough nanoparticles and regular spheres connect with each other. Meanwhile, the electrochemical tests indicate a suitable mass ratio of NiCo 2 Se 4 and carbon microspheres (2:3) showed the highest specific capacitance value (1394 F g −1 at the current density of 0.5 A g −1 , 766 F g −1 even at the current density of 50 A g −1 ), excellent rate property and outstanding cycling stability (80.093% of the initial value after 10000 cycles at the current density of 5 A g −1 ). Benefiting from the above integrated advantages, asymmetric supercapacitors (ASC) fabricated with NCSC composites as the positive electrode and porous activated carbon as negative electrode operating at the voltage window of 0-2 V deliver a high energy density of 101 Wh kg −1 at a power density of 0.749 kW kg −1 , with the specific capacitance retention of 81.095% after 10000 cycles at the current density of 10 A g −1 , superior to most of reported supercapacitors.

Free-standing, binder-free and flexible activated carbon/reduced graphene oxide (AC/rGO) composite films with various ratios were fabricated via a facile vacuum-filtration process.

A novel layered transparent Er:CaF 2 composite ceramic was proposed in the present study. Er:CaF 2 nanoparticles were synthesized by a chemical coprecipitation method. The crystal structures and morphologies of synthesized nanoparticles were performed by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) measurements, respectively. Transparent composite ceramic was fabricated by the combination of multistep dry pressing and hot-pressed sintering method without any sintering aids or binders. The average grain size of 2% Er-doped and 5% Er-doped layers were about 30 and 55 μm, respectively. The thickness of interfacial between two different Er-doped layers was 150-200 μm. For a 1.5 mm thickness transparent Er:CaF 2 composite ceramic, the optical transmittance reached 44.9% at 500 nm and 53.6% at 1200 nm. The luminescence spectra and thermal conductivities of transparent ceramic specimens were also discussed.