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
WS2 has been considered as a promising anode material due to its high lithium storage capacity as well as fascinating physical properties. However, the insufficient electrical and ionic conductivities deteriorate the rate per- formance of the batteries. Herein, we report a simple synthetic approach towards graphene-WS2 hybrids by rolling graphene into a hollow nanotube in which WSz nanoplates are en- capsulated. This new electrode design strategy facilitates the fabrication of integrated and binder-free lithium ion battery and sodium ion battery electrodes by combining electrospin- ning and chemical vapor deposition （CVD） methods. Bene- fiting from their confined growth and the interconnected in- situ graphitic carbon coating nanocable web, the WS2@G with nano-level WS2 dispersion not only provides an efficiently conductive and electrolyte accessible framework, but effec- tively alleviates the volume change during the cycling, en- abling a mechanically robust binder-free electrode along with the outstanding electrochemical Li＋ and Na＋ storage proper- ties.
Debin KongaXiongying QiuBin WangZhichang XiaoXinghao ZhangRuiyingGuot Yang GaoQuan-Hong YangLinjie 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 out-of-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 nan- otubes （DBNNTs） by applying radial strain and coupled ex- ternal electric field. We show that the band alignment be- tween the inner and outer walls of the DBNNTs can be tuned from type I to type II with increasing radial strain, accompa- nied with a direct to indirect band gap transition and a sub- stantial gap reduction. The band gap can be further signifi- cantly 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 re- markable 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 applica- tions 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.
Controlled growth of hexagonal boron nitride （h-BN） with desired properties is essential for its wide range of applications. Here, we systematically carried out the chemical vapor deposition of monolayer h-BN on Cu twin crystals. It was found that h-BN nucleated and grew preferentially and simultaneously on the narrow twin crystal strips present in the Cu substrates. The density functional theory calculations revealed that the introduction of oxygen could effidently ~ne the selectivity. This is because of the reduction in the dehydrogenation barrier of the precursor molecules by the introduction of oxygen. Our findings throw light on the direct growth of functional h-BN nanoribbons on nano-twinned crystal strips and switching of the growth behavior of h-BN films by oxygen.
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.
Single cobalt atom is promising non-precious metal catalyst instead of Pt in the oxygen reduction reaction(ORR).However,it is still a great challenge to develop a costeffective,ultrastable and efficent single-atom cobalt catalyst for ORR,requiring efficient fabrication strategies and robust support to stabilize the single cobalt atom.Here,we prepared a highly active and stable atomically isolated cobalt catalyst via covalent triazine framework(CTF)support with Ketjen Black(KB)hybridization in scale.The prepared single Co catalyst(Co-CTF/KB)possesses high metal loading over 4 wt%and shows superior ORR performance with a half-wave potential(E1/2)of 0.830 V and a limiting current density of 6.14 mA cm-2 as well as high tolerance of methanol in an alkaline medium,which outperforms commercial Pt/C and most non-precious-metal catalysts reported to date.Benefiting from strong stabilization of Co atoms on CTF,Co-CTF/KB shows outstanding stability with only 5 mV negative shifts after 10,000 cycles.Moreover,it also displays high catalytic activity for oxygen evolution reaction(OER),suggesting it is an efficient ORR/OER bifunctional catalyst.The present work provides a facile strategy for preparing single-atom catalysts in bulk quantity and contributes to development of catalysts for electrochemical conversion and storage devices.
