Confining TiO_2 Nanotubes in PECVD-Enabled Graphene Capsules Toward Ultrafast K-Ion Storage: In Situ TEM/XRD Study and DFT Analysis

Titanium dioxide(TiO2) has gained burgeoning attention for potassium-ion storage because of its large theoretical capacity,wide availability,and environmental benignity.Nevertheless,the inherently poor conductivity gives rise to its sluggish reaction kinetics and inferior rate capability.Here,we report the direct graphene growth over TiO2 nanotubes by virtue of chemical vapor deposition.Such conformal graphene coatings effectively enhance the conductive environment and well accommodate the volume change of TiO2 upon potassiation/depotassiation.When paired with an activated carbon cathode,the graphene-armored TiO2 nanotubes allow the potassium-ion hybrid capacitor full cells to harvest an energy/power density of 81.2 Wh kg-1/3746.6 W kg-1.We further employ in situ transmis sion electron microscopy and ope rando X-ray diffraction to probe the potassium-ion storage behavior.This work offers a viable and versatile solution to the anode design and in situ probing of potassium storage technologies that is readily promising for practical applications.

Tunable and highly sensitive temperature sensor based on graphene photonic crystal fiber

Optical fiber temperature sensors have been widely employed in enormous areas ranging from electric power industry,medical treatment,ocean dynamics to aerospace.Recently,graphene optical fiber temperature sensors attract tremendous attention for their merits of simple structure and direct power detecting ability.However,these sensors based on transfer techniques still have limitations in the relatively low sensitivity or distortion of the transmission characteristics,due to the unsuitable Fermi level of graphene and the destruction of fiber structure,respectively.Here,we propose a tunable and highly sensitive temperature sensor based on graphene photonic crystal fiber(Gr-PCF)with the non-destructive integration of graphene into the holes of PCF.This hybrid structure promises the intact fiber structure and transmission mode,which efficiently enhances the temperature detection ability of graphene.From our simulation,we find that the temperature sensitivity can be electrically tuned over four orders of magnitude and achieve up to~3.34×10^(-3) dB/(cm·℃)when the graphene Fermi level is~35 meV higher than half the incident photon energy.Additionally,this sensitivity can be further improved by~10 times through optimizing the PCF structure(such as the fiber hole diameter)to enhance the light–matter interaction.Our results provide a new way for the design of the highly sensitive temperature sensors and broaden applications in all-fiber optoelectronic devices.

Direct insight into sulfiphilicity-lithiophilicity design of bifunctional heteroatom-doped graphene mediator toward durable Li-S batteries

The practical applications of lithium-sulfur(Li-S)battery have been greatly hindered by the severe polysulfide shuttle at the cathode and rampant lithium dendrite growth at the anode.One of the effective solutions deals with concurrent management of both electrodes.Nevertheless,this direction remains in a nascent stage due to a lack of material selection and mechanism exploration.Herein,we devise a temperature-mediated direct chemical vapor deposition strategy to realize the controllable synthesis of three-dimensional boron/nitrogen dual-doped graphene(BNG)particulated architectures,which is employed as a light-weighted and multi-functional mediator for both electrodes in Li-S batteries.Benefiting from the“sulfiphilic”and“lithiophilic”features,the BNG modified separator not only enables boosted kinetics of polysulfide transformation to mitigate the shuttle effect but also endows uniform lithium deposition to suppress the dendritic growth.Theoretical calculations in combination with electro-kinetic tests and operando Raman analysis further elucidate the favorable sulfur and lithium electrochemistry of BNG at a molecular level.This work offers direct insight into the mediator design via controllable synthesis of graphene materials to tackle the fundamental challenges of Li-S batteries.

Theoretical investigations on the growth of graphene by oxygenassisted chemical vapor deposition

Recently,graphene has drawn considerable attention in the field of electronics,owing to its favorable conductivity and high carrier mobility.Crucial to the industrialization of graphene is its high-quality microfabrication via chemical vapor deposition.However,many problems remain in its preparation,such as the not fully understood cracking mechanism of the carbon source,the mechanism of its substrate oxidation,and insufficient defect repair theory.To help close this capability gap,this study leverages density functional theory to explore the role of O in graphene growth.The effects of Cu substrate oxidation on carbon source cracking,nucleation barriers,crystal nucleus growth,and defect repairs are discussed.OCu was found to reduce energy change during dehydrogenation,rendering the process easier.Moreover,the adsorbed O in graphene or its Cu substrate can promote defect repair and edge growth.

二维材料最新研究进展

Research on two-dimensional(2D) materials has been explosively increasing in last seventeen years in varying subjects including condensed matter physics, electronic engineering, materials science, and chemistry since the mechanical exfoliation of graphene in 2004. Starting from graphene, 2D materials now have become a big family with numerous members and diverse categories. The unique structural features and physicochemical properties of 2D materials make them one class of the most appealing candidates for a wide range of potential applications. In particular, we have seen some major breakthroughs made in the field of 2D materials in last five years not only in developing novel synthetic methods and exploring new structures/properties but also in identifying innovative applications and pushing forward commercialisation. In this review, we provide a critical summary on the recent progress made in the field of 2D materials with a particular focus on last five years. After a brief backgroundintroduction, we first discuss the major synthetic methods for 2D materials, including the mechanical exfoliation, liquid exfoliation, vapor phase deposition, and wet-chemical synthesis as well as phase engineering of 2D materials belonging to the field of phase engineering of nanomaterials(PEN). We then introduce the superconducting/optical/magnetic properties and chirality of 2D materials along with newly emerging magic angle 2D superlattices. Following that, the promising applications of 2D materials in electronics, optoelectronics, catalysis, energy storage, solar cells, biomedicine, sensors, environments, etc. are described sequentially. Thereafter, we present the theoretic calculations and simulations of 2D materials. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future outlooks in this rapidly developing field.

Biomass Template Derived Boron/Oxygen Co-Doped Carbon Particles as Advanced Anodes for Potassium-Ion Batteries

Among various anode candidates for potassium-ion batteries,carbonaceous materials have attracted significant attention due to their overwhelming advantages including cost-effectiveness and environmental benignity.However,the inferior specific capacity and the sluggish reaction kinetics hinder the further development in this realm.Herein,we report biomass templated synthesis of boron/oxygen heteroatom co-doped carbon particles(BO-CPs)via direct plasma-enhanced chemical vapor deposition.With the combined advantages of abundant active sites,large accessible surface area,and functional groups,BO-CP anode exhibits high reversible specific capacity(426.5 mAh g^(-1)at 0.1 A g^(-1))and excellent rate performance(166.5 mAh g^(-1)at 5 A g^(-1)).The K-ion storage mechanism is probed by operando Raman spectroscopy,ex situ X-ray photoelectron spectroscopy/electrochemical impedance spectroscopy,galvanostatic intermittent titration technique measurements,and theoretical simulations.The synergistic effect of boron and oxygen co-doping greatly facilitates the performance of carbon-based anode,wherein boron dopant improves the conductivity of carbon framework and the oxygen dopant affords ample active sites and thus harvests additional specific capacity.This work is anticipated to propel the development of high-performance anode materials for emerging energy storage devices.

Simultaneously enhanced interfacial shear strength and tensile strength of heterocyclic aramid fiber by graphene oxide

Heterocyclic aramid fibers,a typical kind of high-performance fibers,have been widely used in aerospace and protection fields because of their excellent mechanical properties.However,the application of heterocyclic aramid fibers as a reinforcement is hindered by the weak interfacial combination with matrix materials,especially epoxy.Traditional strategies enhancing the interfacial shear strength(IFSS)usually decrease the tensile strength.Therefore,simultaneous enhancement of both mechanical properties remains a challenge.Herein,we report a novel heterocyclic aramid fiber with high interfacial shear strength(49.3 MPa)and tensile strength(6.27 GPa),in which 4,4′-diamino-2′-chlorobenzanilide(DABA-Cl)and a small amount of graphene oxide(GO)are introduced through in-situ polymerization.Hydrogen bonds andπ–πinteraction between GO and polymer chains trigger the enhancement in crystallinity,orientation,and lateral interaction of the fibers,thus improving the tensile strength and interfacial shear strength of the fibers.Moreover,the interfacial interaction between fiber and epoxy is enhanced due to the improvement of the surface polarity of the fibers caused by DABA-Cl.Therefore,a method to improve both tensile strength and interfacial shear strength of heterocyclic aramid fibers was found by introducing GO and DABA-Cl,which may provide guidance for the design and preparation of other high-performance fibers.

Confining MOF-derived SnSe nanoplatelets in nitrogen-doped graphene cages via direct CVD for durable sodium ion storage

Tin-based compounds are deemed as suitable anode candidates affording promising sodium-ion storages for rechargeable batteries andhybrid capacitors.However,synergistically tailoring the electrical conductivity and structural stability of tin-based anodes to attain durablesodium-ion storages remains challenging to date for its practical applications.Herein,metal-organic framework(MOF)derived SnSe/C wrappedwithin nitrogen-doped graphene(NG@SnSe/C)is designed targeting durable sodium-ion storage.NG@SnSe/C possesses favorable electricalconductivity and structure stability due to the"inner"carbon framework from the MOF thermal treatment and"outer"graphitic cage from thedirect chemical vapor deposition synthesis.Consequently,NG@SnSe/C electrode can obtain a high reversible capacity of 650 mAh·g^-1 at 0.05 A·g^1,a favorable rate performance of 287.8 mAh·g^1 at 5 A·g^1 and a superior cycle stability with a negligible capacity decay of 0.016%percycle over 3,200 cycles at 0.4 A·g^1.Theoretical calculations reveal that the nitrogen-doping in graphene can stabilize the NG@SnSe/Cstructure and improve the electrical conductivity.The reversible Na-ion storage mechanism of SnSe is further investigated by in-situ X-raydiffraction/ex-s/tu transmission electron microscopy.Furthermore,assembled sodium-ion hybrid capacitor full-cells comprising our NG@SnSe/Canode and an active carbon cathode harvest a high energy/power density of 115.5 Wh·kg^-1/5,742 W·kg^-1,holding promise for next-generationen ergy storages.

Fast-chargingand dendrite-free lithiummetal anodeeenabledby partial lithiation ofgraphene aerogel

The development of deeply cyclable lithium metal batteries with fast-charging capability offers a promising solution to relieve the“range anxiety”in driving electric vehicles.Conventional lithium metal anodes suffered from low operating current densities and shallow charge/discharge depths,owing to the intrinsic dendrite growth governed by Sand’s law.Herein,we come up with a novel design of heavy-duty lithium metal anode fabricated by partially infusing the three-dimensional(3D)porous graphene aerogel with molten Li.Both electroanalytical measurements and simulations show that the unique electrode architecture brings notable advantages in mediating smooth Li plating/stripping,including reduced local current density,inhibited dendrite growth,buffered volume fluctuation,as well as more efficient Li utilization.Consequently,a remarkable cycling performance in symmetric cells for over 400 cycles(800 h)with an ultrahigh cycling capacity of 15 mAh·cm^(−2) at 15 mA·cm^(−2) is achieved,which,to our best knowledge,has been never seen in literature.LiFePO4 full cells demonstrate a superb rate capability up to 10 C and a prolonged cycling of 1,600 cycles at 2 C with the per-cycle capacity decay of only 0.023%.This study paves the way for the ultimate deployment of lithium metal batteries in real-world applications that require fast charging and deep cycling.

Preparation and application of graphene-based wearable sensors

With the development of digital healthcare technology,the demand for non-invasive monitoring of human health is rapidly increasing.In recent years,the research and application of timely,economical,and easy-to-operate wearable sensing devices have attracted much attention.Among recent studies,graphene has been widely used to improve the sensing performance of wearable sensors due to its advantages in mechanical,electrical,and thermal properties.This review mainly focuses on summarizing graphene and its derivative-based wearable sensors and their latest developments in personal health monitoring.We will first introduce the novel structure and sensing mechanism of different types of graphene sensors.Then,we summarize the latest applications of the graphene wearable sensors in human health monitoring,including human activity,heart rate,pulse,electrophysiological signal,and electronic skin.Finally,the future challenges and prospects of graphene wearable devices will be discussed.

Graphene-driving strain engineering to enable strain-free epitaxy of AlN film for deep ultraviolet light-emitting diode

The energy-efficient deep ultraviolet(DUV)optoelectronic devices suffer from critical issues associated with the poor quality and large strain of nitride material system caused by the inherent mismatch of heteroepitaxy.In this work,we have prepared the strain-free AlN film with low dislocation density(DD)by graphene(Gr)-driving strain-pre-store engineering and a unique mechanism of strain-relaxation in quasi-van der Waals(QvdW)epitaxy is presented.The DD in AlN epilayer with Gr exhibits an anomalous sawtooth-like evolution during the whole epitaxy process.Gr can help to enable the annihilation of the dislocations originated from the interface between AlN and Gr/sapphire by impelling a lateral two-dimensional growth mode.Remarkably,it can induce AlN epilayer to pre-store sufficient tensile strain during the early growth stage and thus compensate the compressive strain caused by hetero-mismatch.Therefore,the low-strain state of the DUV light-emitting diode(DUV-LED)epitaxial structure is realized on the strain-free AlN template with Gr.Furthermore,the DUV-LED with Gr demonstrate 2.1 times enhancement of light output power and a better stability of luminous wavelength compared to that on bare sapphire.An in-depth understanding of this work reveals diverse beneficial impacts of Gr on nitride growth and provides a novel strategy of relaxing the vital requirements of hetero-mismatch in conventional heteroepitaxy.

Graphene: A promising candidate for charge regulation in high-performance lithium-ion batteries

The development of rechargeable lithium-ion batteries (LIBs) is being driven by the ever-increasing demand for high energy density and excellent rate performance. Charge transfer kinetics and polarization theory, considered as basic principles for charge regulation in the LIBs, indicate that the rapid transfer of both electrons and ions is vital to the electrochemical reaction process. Graphene, a promising candidate for charge regulation in high-performance LIBs, has received extensive investigations due to its excellent carrier mobility, large specific surface area and structure tunability, etc. Recent progresses on the structural design and interfacial modification of graphene to regulate the charge transport in LIBs have been summarized. Besides, the structure-performance relationships between the structure of the graphene and its dedicated applications for LIBs have also been clarified in detail. Taking graphene as a typical example to explore the mechanism of charge regulation will outline ways to further understand and improve carbon-based nanomaterials towards the next generation of electrochemical energy storage devices.

Oxygen-assisted direct growth of large-domain and high-quality graphene on glass targeting advanced optical filter applications

Growing high quality graphene films directly on glass by chemical vapor deposition(CVD)meets a growing demand for constructing high-performance electronic and optoelectronic devices.However,the graphene synthesized by prevailing methodologies is normally of polycrystalline nature with high nucleation density and limited domain size,which significantly handicaps its overall properties and device performances.Herein,we report an oxygen-assisted CVD strategy to allow the direct synthesis of 6-inch-scale graphene glass harvesting markedly increased graphene domain size(from 0.2 to 1.8μm).Significantly,as-produced graphene glass attains record high electrical conductivity(realizing a sheet resistance of 900Ω·sq^(-1)at a visible-light transmittance of 92%)amongst the state-of-the-art counterparts,readily serving as transparent electrodes for fabricating high-performance optical filter devices.This work might open a new avenue for the scalable production and application of emerging graphene glass materials with high quality and low cost.

Batch synthesis of transfer-free graphene with wafer-scale uniformity

Scalable synthesis of transfer-free graphene over insulators offers exciting opportunity for next-generation electronics and optoelectronics.However,rational design of synthetic protocols to harvest wafer-scale production of directly grown graphene still remains a daunting challenge.Herein we explore a batch synthesis of large-area graphene with wafer-scale uniformity by virtue of direct chemical vapor deposition(CVD)on quartz.Such a controllable CVD approach allows to synthesize 30 pieces of 4-inch graphene wafers in one batch,affording a low fluctuation of optical and electrical properties.Computational fluid dynamics simulations reveal the mechanism of uniform growth,indicating thermal field and confined flow field play leading roles in attaining the batch uniformity.The resulting wafer-scale graphene enables the direct utilization as key components in optical elements.Our method is applicable to other types of insulating substrates(e.g.,sapphire,SiO2/Si,Si3N4),which may open a new avenue for direct manufacture of graphene wafers in an economic fashion.

Vertical graphene nanosheetsmodiBed Al current collectors for high-performance sodium-ion batteries

Rechargeable sodium-ion batteries(SIBs)are promising candidates for large-scale energy storage owing to their excellent high-power performance.However,Al-based current collectorsat both anodes and cathodes of SIBs,which widely influence the power properties of a variety of electrodes in SIBs,have rarely been investigated.Here,we demonstrate that vertical graphene nanosheets grown on commercial Al foil by the plasma-enhanced chemical vapor deposition(PECVD)method,form a robust connection with the carbon-based conductive network of the electrode,thereby significantly reducing the electrode current collector interfacial resistance.For sodium vanadium phosphate(NVP)anodes with vertical graphenenanosheetmodified Al foil(G-AI)current collectors,the interfacial resistance between the electrode and current collector is reduced 20-fold compared with that in the case of Al foil.The G-AI current collector reduces the polarization and improves the rate capability compared with that of Al current collectors within both cathodes and anodes of SIBs.At a high rate of 5 C,the capacity retention of NVP cathode with G-AI current collector is 74%,which is much higher than that with AI foil(22%).We believe that the obtained results support the prospect for the widespread use of G-AI current collectors in the further improvement of high-power profiles of SIBs.

Vertical graphene-coated Cu wire for enhanced tolerance to high current density in power transmission

Cu wires(CuWs)are widely used as electric transmission lines.However,their limited thermal and chemical stabilities become challenges under the high-power and harsh environment.Graphene is regarded as an ideal protective barrier for CuW benefiting from its impermeability to all atoms and molecules.Particularly,the excellent hydrophobicity of vertical graphene(VG)will strengthen its protective capability as a corrosion and oxidation barrier.Herein,VG is directly synthesized on CuW by plasmaenhanced chemical vapor deposition method.The hydrophobic VG coating with a high water contact angle can effectively exclude the corrosive liquid and moisture from CuW surface and prevent their further penetration.Consequently,the electrochemical corrosion rate of VG-CuW is reduced by~13,8,and 2 times,compared with bare CuW,VG-CuW with hydrophilic treatment,and CuW coated with thick horizontal graphene layers,respectively.Negligible oxidation occurs on VGCuW after the long-time exposure to humid air at~200℃ along with the largely enhanced tolerance under high-current operating condition.This study reveals the impressive potentials of hydrophobic VG as a robust corrosion and oxidation barrier for metal wires used in high-power cables and electronic devices in harsh environment.

Carbon nanotube fibers with excellent mechanical and electrical properties by structural realigning and densification

Floating catalysis chemical vapor deposition(FCCVD)direct spinning process is an attractive method for fabrication of carbon nanotube fibers(CNTFs).However,the intrinsic structural defects,such as entanglement of the constituent carbon nanotubes(CNTs)and inter-tube gaps within the FCCVD CNTFs,hinder the enhancement of mechanical/electrical properties and the realization of practical applications of CNTFs.Therefore,achieving a comprehensive reassembly of CNTFs with both high alignment and dense packing is particularly crucial.Herein,an efficient reinforcing strategy for FCCVD CNTFs was developed,involving chlorosulfonic acid-assisted wet stretching for CNT realigning and mechanical rolling for densification.To reveal the intrinsic relationship between the microstructure and the mechanical/electrical properties of CNTFs,the microstructure evolution of the CNTFs was characterized by cross-sectional scanning electron microscopy(SEM),wide angle X-ray scattering(WAXS),polarized Raman spectroscopy and Brunauer–Emmett–Teller(BET)analysis.The results demonstrate that this strategy can improve the CNT alignment and eliminate the inter-tube voids in the CNTFs,which will lead to the decrease of mean distance between CNTs and increase of inter-tube contact area,resulting in the enhanced inter-tube van der Waals interactions.These microstructural evolutions are beneficial to the load transfer and electron transport between CNTs,and are the main cause of the significant enhancement of mechanical and electrical properties of the CNTFs.Specifically,the tensile strength,elastic modulus and electrical conductivity of the high-performance CNTFs are 7.67 GPa,230 GPa and 4.36×10^(6)S/m,respectively.It paves the way for further applications of CNTFs in high-end functional composites.

碳纳米管提升氧化亚硅负极稳定性的起源

高容量的SiO (SO)合金基材料是最有希望的下一代锂离子电池负极之一.使用碳纳米管(CNTs)导电添加剂,虽然可以有效地解决SO较差的循环寿命这一难题,然而除了动力学因素之外,其它潜在的作用机理目前仍不明确.在本工作中,一系列的测试结果表明CNTs可以使电极在循环后依然维持完整的导电网络,确保均匀的电化学反应.CNTs也使得电极局部的体积膨胀得到了抑制,从而避免了固态电解质界面的不断生长,活性材料从集流体剥离,甚至析锂.得益于CNTs的上述作用, SO-CNTs负极在0.5 C (1 C=1600 mA g^(-1))下可以稳定循环200次,其容量保持率为96.2%. CNTs的作用机理也进一步地在商业化的SO/石墨复合负极(SO650-CNTs, 1 C=650 mA g^(-1))中得到了验证,SO650-CNTs在1 C下循环400次后容量保持率为80.6%.本工作为导电添加剂的作用机理提出了新的见解,并将有助于加速合金类负极的商业化进程.

Two-dimensional material-assisted remote epitaxy and van der Waals epitaxy: a review

Heteroepitaxy can reduce the cost and widen the application range of semiconductor film synthesis and device fabrication.However,the lattice and thermal expansion coefficient mismatches between epilayers and substrates limit the improvement of crystal quality and device performance.Two-dimensional(2D)material-assisted heteroepitaxy offers an effective solution to these challenges.The weak interaction at the interface between films and substrates facilitates the subsequent exfoliation and transfer of epilayer for the fabrication of flexible or high-power electronics.Herein,we summarize the modes of 2D material-assisted epitaxy,which can be classified into remote epitaxy,pinhole epitaxy and van der Waals epitaxy based on the interfacial interaction between the epilayers and substrates.Furthermore,we discuss in detail the improved crystal quality and functional applications,such as flexible devices,wavelength-modulated optoelectronic devices,and thermal management in high-power devices.Moreover,we highlight the challenges and prospects of 2D material-assisted epitaxy,providing roadmaps for lateral research and semiconductor production.

Substrate screening for superclean graphene growth using firstprinciples calculations

Suppressing the formation of amorphous surface carbon and contaminants during the preparation of graphene by chemical vapor deposition remains an ongoing issue.Herein,we analyzed how substrate characteristics affect graphene quality by simulating margin extension,the nucleation process,and defect pegging configurations on mono-crystalline oriented metal substrates with the aim of enhancing graphene cleanliness.Defect formation energy and nucleation potential,which are indirect substrate–graphene interaction features,were found to appropriately evaluate graphene quality.The crystallographic orientation of the metal substrate was discovered to be critical for producing superclean graphene.A low graphene defect density and high nucleation rate on the Cu(100)facet guarantee growth of high-quality graphene,especially in terms of suppressing the formation of amorphous carbon.In addition,rapid kink growth and self-healing on the Cu(100)facet facilitate rapid graphene synthesis,which is also promoted by rapid kink splicing and margin self-repair on this facet.This study provides theoretical insight useful for the synthesis of superclean graphene.