Carbon nanofibers(CNFs)and MnOX@CNF nanocomposites(MCNFs)are fabricated by electrospinning and investigated as free-standing electrodes for supercapacitor.This work presents the effect of heating rate during carbonization on the electrochemical behavior of the as-prepared MCNFs electrodes in 6 mol/L KOH electrolyte.Results show that the MCNFs electrodes carbonized by relatively slower heating rate exhibit higher specific capacitance.The electronic conductivity of the slow heated MCNFs electrodes is better than that of the fast heated electrodes due to the better crystallinity of the MnOXnanoparticles and the graphitic carbon layers forming on the surface of the Mn-loaded CNFs.These MCNFs electrodes demonstrate elevated rate capability and improved cycling performance without adding any polymer binder or electronic conductor.
Lin ShiHaiyong HeYan FangYuying JiaBin LuoLinjie Zhi
Analytical solutions for the elastic properties of a variety of binary nanotubes with arbitrary chirality are obtained through the study of systematic molecular mechanics. This molecular mechanics model is first extended to chiral binary nanotubes by introducing an additional outof-plane inversion term into the so-called stick-spiral model,which results from the polar bonds and the buckling of binary graphitic crystals. The closed-form expressions for the longitudinal and circumferential Young's modulus and Poisson's ratio of chiral binary nanotubes are derived as functions of the tube diameter. The obtained inversion force constants are negative for all types of binary nanotubes, and the predicted tube stiffness is lower than that by the former stick-spiral model without consideration of the inversion term, reflecting the softening effect of the buckling on the elastic properties of binary nanotubes. The obtained properties are shown to be comparable to available density functional theory calculated results and to be chirality and size sensitive. The developed model and explicit solutions provide a systematic understanding of the mechanical performance of binary nanotubes consisting of Ⅲ–Ⅴ and Ⅱ–Ⅵ group elements.
We report on a first-principles study of a novel band modulation in zigzag double-walled boron nitride nanotubes (DBNNTs) by applying radial strain and coupled external electric field. We show that the band alignment between the inner and outer walls of the DBNNTs can be tuned from type I to type II with increasing radial strain, accompanied with a direct to indirect band gap transition and a substantial gap reduction. The band gap can be further significantly reduced by applying a transverse electric field. The coupling of electric field with the radial strain makes the field-induced gap reduction being anisotropic and more remarkable than that in undeformed DBNNTs. In particular, the gap variation induced by electric field perpendicular to the radial strain is the most remarkable among all the modu-lations. These tunable properties by electromechanical cou- pling in DBNNTs will greatly enrich their versatile applications in future nanoelectronics.
An electrochemically stable two-dimensional covalent organic framework,PI-COF,has been synthesized by a scalable solvothermal method.PI-COF possesses a highly crystalline structure,well-defined pores,high specific surface area,and cluster macrostructure.Thanks to these features,PI-COF can work as electrode materials in organic supercapacitors,exhibiting a specific capacitance of 163 F/g at 0.5 A/g over a wide potential window of 0-2.5 V.Moreover,PI-COF shows excellent rate performance,which can deliver 96 F/g even at a high current density of 40 A/g.Because of the high capacitance and wide potential window,PI-COF has achieved a superior energy density of 35.7 W h/kg at a power density of 250 W/kg.Most importantly,due to the remarkable electrochemical stability,the PI-COF based device shows outstanding cycling stability with 84.1%capacitance maintained(137 F/g)after 3.0×10^4 charged/discharged cycles at 1 A/g.This work should shed light on designing new COF-based electrode materials for and other electrochemical devices.
In this paper, the bacterial celluloses(BCs) were pyrolysed in nitrogen and then activated by KOH to form a porous three- dimension-network electrode material for supercapacitor applications. Activated pyrolysed bacterial cellulose(APBC) samples with enlarged specific surface area and enhanced specific capacitances were obtained. In order to optimize electrochemical properties, APBC samples with different alkali-to-carbon ratios of 1, 2 and 3 were tested in two electrodes symmetrical capacitors. The optimized APBC sample holds the highest specific capacitance of 241.8 F/g, and the energy density of which is 5 times higher than that of PBC even at a current density of 5 A/g. This work presents a successful practice of preparing electrode material from environment-friendly biomass, bacterial cellulose.
Herein, a facile strategy for the synthesis of sandwich pyrolyzed bacterial cellulose(PBC)/graphene oxide(GO) composite was reported simply by utilizing the large-scale regenerated biomass bacterial cellulose as precursor. The unique and delicate structure where three-dimensional interconnected bacterial cellulose(BC) network embedded in two-dimensional GO skeleton could not only work as an effective barrier to retard polysulfide diffusion during the charge/discharge process to enhance the cyclic stability of the Li–S battery, but also offer a continuous electron transport pathway for the improved rate capability.As a result, by utilizing pure sulfur as cathodes, the Li–S batteries assembled with PBC/GO interlayer can still exhibit a capacity of nearly 600 mAh·g^(-1) at 3C and only 0.055% capacity decay per cycle can be observed over 200 cycles. Additionally, the cost-efficient and environmentfriendly raw materials may enable the PBC/GO sandwich interlayer to be an advanced configuration for Li–S batteries.
