Tuning interface mechanism of FeCo alloy embedded N,S-codoped carbon substrate for rechargeable Zn-air battery

The interface mechanism between catalyst and carbon substrate has been the focus of research.In this paper,the FeCo alloy embedded N,S co-doped carbon substrate bifunctional catalyst(FeCo/S-NC)is obtained by a simple one-step pyrolysis strategy.The experimental results and density functional theory(DFT)calculation show that the formation of FeCo alloy is conducive to promoting electron transfer,and the introduction of S atom can enhance the interaction between FeCo alloy and carbon substrate,thus inhibiting the migration and agglomeration of particles on the surface of carbon material.The FeCo/SNC catalysts show outstanding performance for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).FeCo/S-NC shows a high half-wave potential(E_(1/2)=0.8823 V)for ORR and a low overpotential at 10 mA cm^(-2)(E_(j=10)=299 mV)for OER.In addition,compared with Pt/C+RuO_(2) assembled Zn-air battery(ZAB),the FeCo/S-NC assembled ZAB exhibits a larger power density(198.8 mW cm^(-2)),a higher specific capacity(786.1 mA h g_(zn)~(-1)),and ultra-stable cycle performance.These results confirm that the optimized composition and the interfacial interaction between catalyst and carbon substrate synergistically enhance the electrochemical performance.

Rational construction and decoration of Li_(5)Cr_(7)Ti_(6)O_(25)@Cnanofibers as stable lithium storage materials

Li_(5)Cr_(7)Ti_(6)O_(25) is regarded as a promising anode material for Li-ion batteries(LIBs)because of its low cost and high theoretical capacity.However,the inherently poor conductivity significantly limits the enhancement of its rate capability and cycling stability,especially at high current densities.In this work,we construct one-dimensional Li_(5)Cr_(7)Ti_(6)O_(25)/C nanofibers by electrospinning method to enhance the kinetic,which realizes high cycling stability.Carbon coating enhances the structure stability,insertion/extraction reversibility of Li-ions and electrochemical reaction activity,and facilitates the transfer of Li-ions.Benefited from the unique architecture and component,the Li_(5)Cr_(7)Ti_(6)O_(25)/C(6.6 wt%)nanofiber shows an excellent rate capability with a reversible de-lithiation capacity of 370.8,290.6,269.2,254.3 and 244.9 m Ah g^(-1) at 200,300,500,800 and 1000 m A g^(-1),respectively.Even at a higher current density of 1 A g^(-1),Li_(5)Cr_(7)Ti_(6)O_(25)/C(6.6 wt%)nanofiber shows high cycling stability with an initial de-lithiation capacity of 237.8 m Ah g^(-1) and a capacity retention rate of about 84%after 500 cycles.The density functional theory calculation result confirms that the introduction of carbon on the surface of Li_(5)Cr_(7)Ti_(6)O_(25) changes the total density of states of Li_(5)Cr_(7)Ti_(6)O_(25),and thus improves electronic conductivity of the composite,resulting in a good electrochemical performance of Li_(5)Cr_(7)Ti_(6)O_(25)/C nanofibers.Li_(5)Cr_(7)Ti_(6)O_(25)/C nanofibers indicate a great potential as an anode material for the next generation of high-performance LIBs.

Regulating the electrochemical activity of Fe-Mn-Cu-based layer oxides as cathode materials for high-performance Na-ion battery

Fe-Mn based layer oxides cathode materials have attracted widespread attention as a potential candidate for sodium-ion batteries(SIBs)owing to the earth abundance,cost-effectiveness and acceptable specific capacity.However,the irreversible phase transition often brings rapid capacity decay,which seriously hinders the practical application in large-scale energy storage.Herein,we design a nickel-doped Na_(0.70)Fe_(0.10)Cu_(0.20)Ni_(0.05)Mn_(0.65)O_(2)(NFCNM-0.05)cathode material of SIBs with activated anionic redox reaction,and then inhibit the harmful phase transition.The ex-situ X-ray diffraction patterns demonstrate the NFCNM-0.05 always keeps the P2 phase during the sodiation/desodiation process,indicating a high structure stability.The ex-situ X-ray photoelectron spectroscopy implies the redox reactions between O2-and O-occur in the charging process,which offers extra specific capacity.Thus,the NFCNM-0.05 electrode delivers a high initial discharge capacity of 148 mA h g-1and remains a prominent cycling stability with an excellent capacity retention of 95.9%after 200 cycles at 1 C.In addition,the electrochemical impedance spectroscopy and galvanostatic intermittent titration technique show the NFCNM-0.05 electrode possesses fast ion diffusion ability,which is beneficial for the enhancement of rate performance.Even at 10 C,the NFCNM-0.05 can offer a reversible discharge capacity of 81 mA h g-1.DFT calculation demonstrates the doping of appropriate amount of Ni ions is benefit for the enhancement of the electrochemical performance of the layer oxides.This work provides an effective strategy to enhance the electrochemical performance of Fe-Mn based cathode materials of SIBs.

Understanding of the charge storage mechanism of MnO_(2)-based aqueous zinc-ion batteries:Reaction processes and regulation strategies

Though secondary aqueous Zn ion batteries(AZIBs)have been received broad concern in recent years,the development of suitable cathode materials of AZIBs is still a big challenge.The MnO_(2) has been deemed as one of most hopeful cathode materials of AZIBs on account of some extraordinary merits,such as richly natural resources,low toxicity,high discharge potential,and large theoretical capacity.However,the crystal structure diversity of MnO_(2) results in an obvious various of charge storage mechanisms,which can cause great differences in electrochemical performance.Furthermore,several challenges,including intrinsic poor conductivity,dissolution of manganese and sluggish ion transport dynamics should be conquered before real practice.This work focuses on the reaction mechanisms and recent progress of MnO_(2)-based materials of AZIBs.In this review,a detailed review of the reaction mechanisms and optimal ways for enhancing electrochemical performance for MnO_(2)-based materials is proposed.At last,a number of viewpoints on challenges,future development direction,and foreground of MnO_(2)-based materials of aqueous zinc ions batteries are put forward.This review clarifies reaction mechanism of MnO_(2)-based materials of AZIBs,and offers a new perspective for the future invention in MnO_(2)-based cathode materials,thus accelerate the extensive development and commercialization practice of aqueous zinc ions batteries.

Advancement of technology towards high-performance non-aqueous aluminum-ion batteries

Al-ion batteries(AIBs) have been identified as one of the most hopeful energy storage systems after Li-ion batteries on account for the ultrahigh volumetric capacity,high safety and low cost from the rich abundance of Al.Nonetheless,some inevitable shortcomings,such as the formation of passive oxide film,hydrogen side reactions and anode corrosion,finally limit the large-scale application of aqueous AIBs.The nonaqueous AIBs have been considered as one of most hopeful alternatives for high-powered electrochemical energy storage devices.Nonetheless,various technical and scientific obstacles should be resolved because nonaqueous AIBs are still nascent.Some significant efforts have aimed to resolve these issues towards large-scale applications,and some important advancement has been made.In the present review,we mainly intended to offer an overview of non-aqueous AIBs systems,and we comprehensively reviewed the recent research advancement of the cathode materials,anode materials electrolyte and collectors as well as the fundamental understanding of the functional mechanisms.In addition,we have also analyzed several technical challenges and summarized the strategies used for overcoming the challenges in improving the electrochemical properties,including morphology control,surface engineering,doping and construction of composite electrodes as well as the charge storage mechanisms of the materials with different crystal structures.At last,future research orientation and development prospect of the AIBs are proposed.

Structure and electrochemical properties of LiLa_xMn_(2-x)O_4 cathode material by the ultrasonic-assisted sol-gel method

Powders of spinel LiLaxMn2-xO4 were successfully synthesized by the ultrasonic-assisted sol-gel （UASG） method. The structure and properties of LiLaxMn2-xO4 were examined by X-ray diffraction （XRD）, Fourier transform infrared （FT-IR） spectroscopy, scanning electronic microscopy （SEM）, galvanostatic charge-discharge test, and cyclic voltammetry （CV）. XRD results show that the La^3＋ can partially reptace Mn^3＋ in the spinel and the doped materials with La^3＋ have a larger lattice constant compared with pristine LiMn2O4. FT-IR indicates that the absorption peak of Mn^3＋-O and Mn^4＋- O bonds has a red and blue shift with the increase of doping lanthanum in LiLaxMn2-xO4, respectively. The charge-discharge test exhibits that the initial discharge capacity of LiLaxMn2-xO4 drops off, and the capacity retention increases gradually at C/5 discharge rate with the increase of doping lanthanum, and LiLa0.01Mn1.99O4 has a higher discharge capacity and a better cycling performance at 1C discharge rate. CV reveals that the doping La^3＋ is beneficial to the reversible extraction and intercalation of Li^＋ ions.

Towards high-performance anodes:Design and construction of cobalt-based sulfide materials for sodium-ion batteries

Sodium-ion batteries are increasingly becoming important in the energy storage field owing to their low cost and high natural abundance of sodium.Cobalt-based sulfide materials have been extensively studied as anode materials owing to their remarkable Na storage capability.Nevertheless,the application of cobalt-based sulfides is hampered by their serious capacity degradation and unsatisfactory cycling stability due to severe structural changes during cycling.Therefore,it is important to comprehensively summarize advances in the understanding and modification of cobalt-based sulfides from various perspectives.In the present review,recent advances on various cobalt-based sulfides,such as CoS,CoS_(2),Co_(3)S_(4),Co_(9)S_(8),NiCo_(2)S_(4),CUCo_(2)S_(4),and SnCoS_(4),are outlined with particular attention paid to strategies that improve their sodium storage performance.First,the mechanisms of charge storage are introduced.Subsequently,the key barriers to their extensive application and corresponding strategies for designing high-performance cobalt-based sulfide anode materials are discussed.Finally,key developments are summarized and future research directions are proposed based on recent advancements,aiming to offer possible fascinating strategies for the future promotion of cobalt-based sulfides as anode materials applied in sodium-ion batteries.

Quasi-periodic Oscillation Analysis for the BL Lacertae Object 1823+568

We studied the optical band periodic variability of 1823+568 using the Jurkevich method,the Lomb-Scargle periodogram and the REDFIT38 software,and found evidence of quasi-periodic oscillation.An unprecedented variability with period P=283^(+17)_(-13) days was identified by three different analysis methods.This quasi-periodic variability most likely results from nonballistic helical jet motion driven by the orbital motion in a binary black hole system.Considering the light-travel time effect,the real physical period is P_(d)=67.1 yr.Moreover,we estimated that the primary black hole mass is M■1.92×10^(9) M_(⊙)to 3.43×10^(9) M_(⊙).

The broadband spectral energy distributions of SDSS blazars

We compiled the radio, optical and X-ray data of blazars from the Sloan Digital Sky Survey database, and presented the distribution of luminosities and broadband spectral indices. The distribution of luminosities shows that the averaged luminosity of flat spectrum radio quasars（FSRQs） is larger than that of BL Lacertae（BL Lac） objects. On the other hand, the broadband spectral energy distribution reveals that FSRQs and low energy peaked BL Lac objects have similar spectral properties,but high energy peaked BL Lac objects have a distinct spectral property. This may be due to the fact that different subclasses of blazars have different intrinsic environments and are at different cooling levels. Even so, a unified scheme is also revealed from the color-color diagram, which hints that there are similar physical processes operating in all objects under a range of intrinsic physical conditions or beaming parameters.

The spectral properties of Fermi blazars:the spectral sequence and unification of blazars

Using a large sample of blazars of the Fermi observations presented by Abdo et al., we constructed a sample of blazars including high energy peaked BL Lac objects （HBLs）, low energy peaked BL Lac objects （LBLs） and flat-spectral ra- dio quasars （FSRQs）. These unique characteristics make it possible to unambiguously address the question of how HBLs, LBLs and FSRQs are related. In this paper, we investigated the relationship between X-ray and 7-ray spectral indices （~^-aT）, as well as the relationship between the broadband spectral indices （~ro--ar~, ~ro--~ox, OZro--O^x7 and ~r^-~xT） for this sample. The color-color diagram shows that there is a significant correlation between both quantities when all three subclasses of blazars are considered, which suggests that there is a unified scheme for blazars. On the other hand, the a^-~7 diagram reveals that three kinds of blazars have different spectral energy distributions： the trend of HBLs is different from that of FSRQs and LBLs, whereas FSRQs and LBLs have a similar trend, which hints that FSRQs and LBLs have similar spectral properties, but HBLs have distinct spectral properties. In addi- tion, the broadband energy distributions also reveal the similar spectral properties with that of the Cx-C7 diagram. The spectral properties revealed from the Fermi sample do not support the blazar sequence reported by Fossati et al. and Ghisellini et al.

Improving the stability,lithium diffusion dynamics,and specific capacity of SrLi_(2)Ti_(6)O_(14)via ZrO_(2)coating

SrLi_(2)Ti_(6)O_(14)(SLTO)coated with different amount of ZrO_(2)was successfully prepared.The as-obtained composites are stacked by a series of particles with a pure phase structure and a good crystallinity.Furthermore,ZrO_(2)coating not only enhances the structural stability of the materials but also facilitates the diffusion of lithium through the SEI film.As a result,the redox polarization was reduced,and the reversibility of the electrochemical reaction was enhanced.Particularly,SLTO-ZrO_(2)-2 sample delivers a high initial lithiation capacity of 283.6 mA h g^(-1),and the values maintain at 251.7,228.0,207.4,175.3,and 147.7 mA h g^(-1)at the current densities of 0.13,0.26,0.54,1.31,and 2.62 A g^(-1),respectively.Our experiment also confirmed that SLTO materials coated with ZrO_(2)are suitable for high power density applications,and the lithiation specific energy efficiency of SLTO-ZrO_(2)-2 is 200%as high as that of pure SLTO at a power density of 1257 W kg^(-1).

Comprehensive Study of the Blazars from Fermi-LAT LCR: The Log-Normal Flux Distribution and Linear rms–Flux Relation

Fermi-LAT LCR provides continuous and regularly sampled gamma-ray light curves, spanning about 14 yr, for a large sample of blazars. The log-normal flux distribution and linear rms–flux relation of the light curves for a few Fermi blazars have been examined in previous studies. However, the probability that blazars exhibit the log-normal flux distribution and linear rms–flux relation in their gamma-ray light curves has not been systematically explored.In this study, we comprehensively research the distribution of γ-ray flux and the statistical characteristics on a large sample of 1414 variable blazars from the Fermi-LAT LCR catalog, including 572 FSRQs, 477 BL Lacs, and 365BCUs, and statistically compare their flux distributions with normal and log-normal distributions. The results indicate that the probability of not rejecting log-normal is 42.05% for the large sample, and there is still a 2.05%probability of not rejecting normality, based on the joint of Kolmogorov–Smirnov, Shapiro–Wilk, and Normality tests. We further find that the probability that BL Lacs conform to the log-normal distribution is higher than that of FSRQs. Besides, after removing sources with less than 200 data points from this large sample, a sample of 549blazars, which is still a large sample compared to the previous studies, was obtained. Based on dividing the light curves into segments every 20 points(or 40 points, or one year), we fitted the linear rms–flux relation of these three different sets and found that the Pearson correlation coefficients are all close to 1 for most blazars. This result indicates a strong linear correlation between the rms and the flux of these 549 blazars. The log-normal distribution and linear rms–flux relation indicate that the variability of the γ-ray flux for most blazars is a non-linear and multiplicative process.

Highly variable γ-ray emission of CTD 135 and implications for its compact symmetric structure

Theγ-ray emission properties of CTD 135,a typical compact symmetric object(CSO),are investigated with-11-year Fermi/LAT observations.We show that it has bright and significantly variable GeV emission,with theγ-ray luminosity of L_(γ)-10^(47) erg s^(-1) and a variation index of TS_(var)=1002.A quasi-periodic oscillation(QPO)with a periodicity of-460 days is detected in the global 95%false-alarm level.Theseγ-ray emission features are similar to that of blazars.Its broadband spectral energy distribution(SED)can be attributed to the radiations of the relativistic electrons accelerated in the core region and the extended region.The SED modeling shows that theγ-rays are from the core region,which has a Doppler boosting factor ofδ-10.8 and relativistically moves with a small viewing angle,being similar to blazar jets.On the base of the analysis results,we propose that the episodic activity of the central engine in CTD135 results in a blazar-like jet and the bubble-like lobes as the Fermi bubbles in the Galaxy.The strong 7-ray emission with obvious variability is from the jet radiations and the symmetric radio structure is attributed to the bubbles.The jet radiation power and disk luminosity in units of Eddington luminosity of CTD 135 follow the same relation as other young radio sources,indicating that its jet radiation may also be driven by the Eddington ratio.

Flux and spectral variation characteristics of 3C 454.3 at the GeV band

We analyze the long-term lightcurve of 3C 454.3 observed with Fermi/LAT and investigate its relation to flux in the radio,optical and X-ray bands.By fitting the 1-day binned Ge V lightcurve with multiple Gaussian functions（MGF）,we propose that the typical variability timescale in the Ge V band is 1–10 d.The Ge V flux variation is accompanied by the spectral variation characterized as fluxtracking,i.e.,＂harder when brighter.＂The Ge V flux is correlated with the optical and X-ray fluxes,and a weak correlation betweenγ-ray flux and radio flux is also observed.Theγ-ray flux is not correlated with the optical linear polarization degree for the global lightcurves,but they show a correlation for the lightcurves before MJD 56000.The power density spectrum of the global lightcurve shows an obvious turnover at^7.7 d,which may indicate a typical variability timescale of 3C 454.3 in theγ-ray band.This is also consistent with the derived timescales by fitting the global lightcurve with MGF.The spectral evolution and an increase in the optical linear polarization degree along with the increase inγ-ray flux may indicate that the radiation particles are accelerated and the magnetic field is ordered by the shock processes during the outbursts.In addition,the nature of 3C 454.3 may be consistent with a self-organized criticality system,similar to Sagittariusand thus the outbursts could be from plasmoid ejections driven by magnetic reconnection.This may further support the idea that the jet radiation regions are magnetized.

Evidence of Quasi-periodic Oscillation in the Optical Band of the Blazar 1ES 1959+650

We analyzed the optical monitoring data in the R band of Te V blazar 1ES 1959+650 from 2002 to 2018,and provided evidence of a quasi-periodic oscillation in this object.The light curve shows a stable and persistent periodicity at~540 days,detected by the Lomb–Scargle periodogram,Jurkevich and weighted wavelet z-transform techniques.The red noise power spectrum was estimated using the PSRESP method,and this period was found to be at>3σsignificance level.There are also two possible periodicities at~268 and~1100 days detected by all three methods.However,their significance levels are relatively low,and thus these two periods cannot be verified by the present data.We discuss several possible physical models that could explain the periodic variability in this object.

A Close Correlation between the Spectral Lags and Redshifts of Gamma-Ray Bursts

Based on nine BATSE GRBs with known redshifts, we found that the maximum spectral lag of all the pulses in a gamma-ray burst （GRB） appears to be anti-correlated with the redshift of the burst. In order to confirm this finding, we analyzed 10 GRBs detected by HETE-2 with known redshifts and found a similar relation. Using the relation, we estimated the redshifts of 878 long GRBs in the BATSE catalog, then we investigated the distributions of the redshifts and 869 Eiso of these GRBs. The distribution of the estimated redshifts is concentrated at z = 1.4 and the distribution of Eiso peaks at 10^52.5 erg. The underlying physics of the correlation is unclear at present.

Possible properties of Te V spectra in PKS 2155–304

We present a one-zone homogeneous lepton-hadronic model and obtain steady-state spectra by solving the time-dependent equations to study a plausible origin of hard TeV spectra in PKS 2155-304.In this model,we assume a steady electron and proton injection rate in the source and solve the non-linear time-dependent kinematic equations that self-consistently consist of proton-photon interaction,synchrotron radiation of electron/positron pairs and proton,inverse Compton scattering,and synchrotron self-absorption.We employ this model to reproduce the multi-wavelength spectrum of PKS 2155-304,then find that the possible bump located at E~1 TeV which may originate from the synchrotron radiation of secondary electrons produced by Bethe-Heitler pair production,resulting in the hard TeV spectrum.

The Relationship between the Rise Width and the Full Width of γ-ray Burst Pulses and Its Implications

We investigate the relationship between the rise width and the full width of gamma-ray burst pulses. Theoretical analysis shows that either width is proportional to Г^-2△τθ,FWHMRc/c（Г the Lorentz factor of the bulk motion, △τθ,FWHM a local pulse＇s width, Rc the radius of fireballs and c the velocity of light）. We study the relationship for four samples of observed pulses. We find： （1） merely the curvature effect could reproduce the relationship between the rise and full widths with the same slope as derived from the model of Qin et al.; （2） gamma-ray burst pulses, selected from both the short and long GRBs, follow the same sequence in the rise width vs. full width diagram, with the shorter pulses at one end; （3） all GRBs may intrinsically result from local Gaussian pulses. These features place constraints on the physical mechanism（s） for producing long and short GRBs.

Rapid lithium-ion insertion/extraction and migration behavior of Na_(2)WO_(4)-encapsulated lithium-rich layered oxide cathode

Due to the low cost,high working voltage and high storage capacity,Li-rich Mn-based layered compounds show promise as the cathode materials for lithiumion batteries(LIBs).However,the side reactions at the solid-liquid interface of the cathode will lead to rapid capacity decay and inferior rate performance.Herein,this article proposes a liquid-phase dispersion strategy to introduce a Na_(2)WO_(4)layer on the Li_(1.2)Ni_(0.13)-Co_(0.13)Mn_(0.54)O_(2) cathode,which can reduce the side effects between raw materials and electrolyte and promote the insertion/extraction rate of Li^(+),thus enhancing the material stability and rate performance.As a result,the capacity retention rate is 96.9%after 200 cycles under 2C.Moreover,the capacities are 177.5,149.5,111.1 and58.3 mAh·g^(-1)at 1C,2C,5C and 10C,implying a superior fast charging performance.The exceptional performance can be ascribed to both the increased conductivity and enhanced structural stability of the cathode material.What's more,based on the investigation of ion insertion/extraction behavior in electrode materials and the ion migration kinetics in the electrolyte,this study suggests that coating Li-rich Mn-based materials with Na_(2)WO_(4)can be a promising strategy to improve their performance in LIBs.

Well-dispersed Sb particles embedded on N-doped carbon nanofibers toward high-performance Li-ion battery

The alloy-type material Sb is widely used in the anode materials of lithium-ion batteries(LIBs)due to its high theoretical specific capacity.However,its serious volume expansion problem during alloying/dealloying of Li~+limits its practical application.In this work,C-Sb composite was constructed as anode material of LIBs by electrospinning route for the first time,Sb was introduced into the polyacrylonitrile-based hard carbon and coal tar pitch-based soft carbon composite amorphous carbon fiber with a diameter of 300-600 nm,which realized high cycling stability.The C-Sb-2(the mass ratio of polyacrylonitrile to Sb source is 1:2)electrode displayed charge capacities of 1098.5,930.3,841.7,753.5,643.9 and 545.8 mAh·g^(-1)at 0.1,0.2,0.3,0.5,1 and 2 A·g^(-1),respectively.And when the current density returned to 0.1 A·g^(-1),the charge capacity was 939.3 mAh·g^(-1),revealing good stability and reversibility.The introduction of Sb into the amorphous carbon improved its conductivity and addressed the volume expansion issue of high specific capacity Sb during charge/discharge.Ex-situ XRD analysis confirmed the high reversibility of the C-Sb-2 during charging and discharging.Density functional theory(DFT)calculations revealed the gradual enhancement of the interface interaction between Sb_(x)Li_(y) and amorphous carbon(AMC)with increasing lithium content,contributing to the anchoring of alloy nanoparticles on the AMC surface and buffering the volume change of the alloy.Moreover,the gradual lithiation of Sb facilitated the electron transfer from Sb_(x)Li_(y) to AMC.These findings hold promise for designing lithium storage materials with exceptional performance,highlighting the potential of C-Sb composites as anode materials for efficient next-generation lithium storage.