F-doped orthorhombic Nb_(2)O_(5) exposed with 97% (100) facet for fast reversible Liþ-Intercalation

Orthorhombic Nb_(2)O_(5)(T-Nb_(2)O_(5))is attractive for fast-charging Li-ion batteries,but it is still hard to realize rapid charge transfer kinetics for Li-ion storage.Herein,F-doped T-Nb_(2)O_(5) microflowers(F-Nb_(2)O_(5))are rationally synthesized through topotactic conversion.Specifically,F-Nb_(2)O_(5) are assembled by single-crystal nanoflakes with nearly 97%exposed(100)facet,which maximizes the exposure of the feasible Li^(+)transport pathways along loosely packed 4g atomic layers to the electrolytes,thus effectively enhancing the Li^(+)-intercalation performance.Besides,the band gap of F-Nb_(2)O_(5) is reduced to 2.87 eV due to the doping of F atoms,leading to enhanced electrical conductivity.The synergetic effects between tailored exposed crystal facets,F-doping,and ultrathin building blocks,speed up the Li^(+)/electron transfer kinetics and improve the pseudocapacitive properties of F-Nb_(2)O_(5).Therefore,F-Nb_(2)O_(5) exhibit superior rate capability(210.8 and 164.9 mAh g^(-1) at 1 and 10 C,respectively)and good long-term 10 C cycling performance(132.7 mAh g^(-1) after 1500 cycles).

Conduction Properties and Scattering Mechanisms in F-doped Textured Transparent Conducting SnO_2 Films Deposited by APCVD

Transparent conducting F-doped texture SnO2 films with resistivity as low as 5× 10-4 Ω ·cm,with carrier concentrations between 3.5 × 1020 and 7× 1020 cm-3 and Hall mobilities from 15.7 to 20.1 cm2/(V/s) have been prepared by atmosphere pressure chemical vapour deposition (APCVD). These polycrystalline films possess a variable preferred orientation, the polycrystallite sizes and orientations vary with substrate temperature. The substrate temperature and fluorine flow rate dependence of conductivity, Hall mobility and carrier conentration fOr the resultingfilms have been obtained. The temperature dependence of the mobiity and carrier concentrationhave been measured over a temperature range 16～400 K. A systematically theoretical analysis on scattering mechanisms for the highly conductive SnO2 films has been given. Both theoretical analysis and experimental results indicate that for these degenerate, polycrystalline SnO2 ：F films in the low temperature range (below 100 K), ionized impurity scattering is main scattering mechanism. However, when the temperature is higher than 100 K, the lattice vibration scattering becomes dominant. The grain boundary scattering makes a small contribution to limit the mobility of the films.

Tuning F-doped degree of rGO:Restraining corrosion-promotion activity of EP/rGO nanocomposite coating

Given that graphene features high electrical conductivity,it is a kind of material with corrosion-promotion activity.This study aimed to inhibit the corrosion-promotion activity of graphene in coatings.Here,we report an exciting application of epoxy matrix(EP)/F-doped reduced graphene oxide(rGO)coatings for the long-term corrosion protection of steel.The synthesized F-doped rGO(FG)did not reduce the utilization of rGO by a wide margin and possessed distinctive electrically insulating nature.The electrical conductivity of rGO was approximately 1500 S/m,whereas those of FG-1,FG-2 and FG-3 were 1.17,5.217×10^−2 and 3.643×10^-11 S/m,respectively.FG and rGO were then dispersed into epoxy coatings.The chemical structures of rGO and FG were investigated by transmission electron microscopy(TEM),scanning probe microscopy(SPM),X-ray photoelectron spectroscopy(XPS),Fourier-transform infrared spectroscopy(FTIR),and X-ray diffraction(XRD).EP/FG coatings exhibited outstanding corrosion protection in comparison with blank EP and EP/rGO coatings mainly because the corrosion-promotion effect of rGO was eliminated.The anticorrosion ability of EP/FG coatingswasimproved with increased F-doped degree of FG.In addition,electrochemical impendance spectroscopy(EIS)results indicated that the Rc values of EP/FG-2 and EP/FG-3 were four orders of magnitude higher than those of EP/rGO in diluent NaCl solution(3.5 wt.%)after immersion for 90 days.

Electronic structure and optical properties of F-doped β-Ga_2O_3 from first principles calculations

The effects of F-doping concentration on geometric structure, electronic structure and optical property of β-GaOwere investigated. All F-doped β-GaOwith different concentrations are easy to be formed under Ga-rich conditions, the stability and lattice parameters increase with the F-doping concentration. F-doped β-GaOmaterials display characteristics of the n-type semiconductor, occupied states contributed from Ga 4s, Ga 4p and O 2p states in the conduction band increase with an increase in F-doping concentration. The increase of F concentration leads to the narrowing of the band gap and the broadening of the occupied states. F-doped β-GaOexhibits the sharp band edge absorption and a broad absorption band. Absorption edges are blue-shifted, and the intensity of broad band absorption has been enhanced with respect to the fluorine content. The broad band absorption is ascribed to the intra-band transitions from occupied states to empty states in the conduction band.

Preparation and Superconducting Properties of F-doped SmO_(1-x)F_xFeAs

Here we report the fabrication and superconductivity of the iron-based arsenic oxide SmO1-xFxFeAs compound. X-ray diffraction （XRD） results prove that the lattice parameters a and c decrease systematically with increasing x in between 0〈x≤0.35, but when x〉0.35 the a and c increase with the decrease of x in the SmO1-xFxFeAs. The critical temperature （To） increases with increasing x in between 0.15≤x≤0.3, while x〉0.3 the Tc decreases with the increase ofx. It is found that at x=0.3 SmO0.7F0.3FeAs has the highest onset resistivity transition temperature of 55.5 K. The critical current density （Jc） value at 10 K for the obtained SmO0.TF0.3FeAs is 1.3×10^5 A/cm^2 （0 T）. Meanwhile one can estimates Hc2（0） from the slope of the Hc2（T） curve at T=-Tc （Hc2 is the upper critical field）, and for the 90% normal-state resistivity （Pn） criterion （Tc=55 K）, Hc2（0） is determined to be -253 T.

Enhancing the Activity of N/C Catalyst for Oxygen Reduction Reaction by Fluorination

The synthesis of non-metal carbon catalysts with high catalytic activity for ORR(oxygen reduction reaction)in acidic media is a great challenge in the field of PEMFC(proton exchange membrane fuel cells).In this research,N-and F-codoped carbon catalyst with high performance was synthesized from ZIF-8 and NH4F,which are easily prepared structure and common chemical,respectively.The as-prepared catalyst has a high surface area of 789 m2/g and micro-porosity of~2 nm,facilitating more active sites to the ORR and O2 mass transfer in the diffusion of the catalyst matrix,respectively.The prepared N/C(NH4F)catalyst exhibited an onset potential of 0.94 V(vs.RHE)and a half-wave potential of 0.65 V in 0.1 M HClO4 solution.It also showed excellent durability in the cycling test of 10,000 times and a degradation shift of half-wave potential 70 mV was observed.Its diffusion-limiting current reached 5.85 mA/cm2 next to the theoretic value of 6 mA/cm2,suggesting that it has plenty of active sites for ORR,which could be attributed to fluorine introduction into the N/C catalyst.It proved that the introduction of fluorine into the structure of the N/C catalyst fine-tunes the Lewis basic sites of the carbon atoms adjacent to pyridinic and graphitic nitrogen species,facilitating the adsorption of oxygen molecules in the initial step of the ORR.The correlation between the N/C catalyst activity and the fluorination provides new insight into the ORR catalyst design.

Tuning the nucleation and decomposition of Li2O_(2) by fluorine-doped carbon vesicles towards high performance Li-O_(2) batteries

Li-O_(2) batteries provide an attractive and potential strategy for energy conversion and storage with high specific energy densities.However,large over-potential in oxygen evolution reactions (OER) caused by the decomposition obstacles of Li_(2)O_(2) seriously impedes its electrochemical performances.Herein,a novel N,O,S and F co-doping vesicular carbon was prepared by self-template pyrolysis method and used in LiO_(2) battery to tune the nucleation and decomposition of Li_(2)O_(2).The introduction of F in the carbon matrix with suitable content can regulate the adsorption of intermediates,through which the morphology of Li_(2)O_(2) can be controlled to film,favorable to its decomposition in charge process.The cathode based on the optimized F doped carbon vesicle exhibits improved electrochemical performances including a low over-potential,large capacity and a long-term stability.Density functional theory (DFT) results show that F and C in C–F bond hasve a strong interaction to Li and O in Li_(2)O_(2),respectively,which can enhance the transfer of electrons from Li_(2)O_(2) to the carbon matrix to generate hole polaron and thus accelerate the delithiation and decomposition of Li_(2)O_(2).This work provides a new sight into understanding the mechanism of nucleation and decomposition of Li_(2)O_(2) for the development of high-performance Li-O_(2) batteries.

The Loss of Optical Fiber with Pure Quartz Core and Fluorine—Doped Glass Cladding

The optical fiber with pure quartz core and Fluorine-doped glass cladding was made by POD (plasma outside deposition) technique in some corporations, while we used the creative technique of “overcladding F-doped tube onto quartz rod in high temperature” to make the optical fiber which has the same structure as that from POD, in order to research and compare the influence factors on the loss of the fiber, our research work includes contrast experiments on coating polymers with different refractive index and the concentricity error of the fiber core and cladding. The measurement results show us that there are great differences in the loss spectra between the different fiber samples. We made analysis of it.

半离子C-F键在钾离子电池碳负极中诱导快速离子储存和电子转移

氟(F)杂原子功能化的碳负极可以形成更多的缺陷位点,从而有效提高钾的存储容量.然而,提高电化学性能的机制尚不清楚,尤其是对何种C-F键深入影响钾储存性能仍缺乏基本认识.本文报道了一系列F掺杂的碳,并证明了C-F是半离子键而不是离子键;碳化温度对缺陷程度有显著影响.并且,高比例半离子C-F键诱导的丰富缺陷可以作为活性位点来吸附大量与电容行为相关的钾离子,不仅有利于长循环寿命,而且提升了在高电流密度下的倍率容量.密度泛函理论计算证实半离子C-F键的存在可以提高碳基体对钾离子的吸附能力并同时提高电子电导率,有利于高容量和倍率.此外,通过耦合半离子C-F键和吡啶N键,钾吸附能和电导率被进一步提升,这使得半电池实现了优异的容量(245.2 mA h g^(-1))和倍率,并且组装的全电池具有高能量密度(143.9 W h kg^(-1)).

Electrochemical performance of Li-rich cathode material,0.3Li_2MnO_3-0.7LiMn_(1/3)Ni_(1/3)Co_(1/3)O_2 microspheres with F-doping

Layered F-doped cathode materials 0.3 Li_2 MnO_3-0.7 LiMn_(1/3)Ni_(1/3)CO_(1/3))O_(2-x)F_x(x = 0, 0.01, 0.02, 0.03, 0.04,0.05) microspheres made up of nanosized primary grains were prepared through co-precipitation method. The sample of x = 0.02 demonstrates a large discharge capacity of226 mAh g^(-1) over 100 cycles at 0.1 C and excellent rate performance with discharge capacity of 96 mAh g-1 at 5.0 C and room temperature. Particularly, this material shows much enhanced electrochemical performances even at high temperature of 55 ℃. It delivers a quite high discharge capacity of 233.7 mAh·g^(-1) at 1.0 C with capacity retention as high as 97.9% after 100 cycles. The results demonstrate that the fluorine incorporation stabilizes the cathode structure and maintains stable interfacial resistances.