Synthesis of nitrogen-sulfur co-doped Ti_(3)C_(2)Tx MXene with enhanced electrochemical properties

Through material innovation,nanoscale structural design and hybrid manufacturing methods,great efforts have been made in developing high-performance energy storage systems.These devices can be comprised of twodimensional(2D)nanomaterials,such as MXene,and show promise for use in energy storage devices.In order to achieve better electrochemical properties of MXene,one crucial technique is to modify its structure by introducing defects or heteroatom dopants,which may expand the interlayer spacing and increase the ion transfer kinetics during the charge/discharge process.Here,a modified two-step multi-element strategy is explored utilizing ammonium citrate as intercalant and nitrogen source to enhance the level of heteroatom doping during annealing of MXene with sulfur.The resulting nitrogen/sulfur co-doped MXene displayed enhanced gravimetric capacitance(495 F g^(-1) at 1 A g^(-1)),outstanding rate capability(180 F g^(-1) at 10 A g^(-1))and excellent cycle stability(98%retention after 6000 charge/discharge cycles).The synthesis of NS-MXene reveals a novel and facile multiheteroatom pathway for functionalizing Ti_(3)C_(2)Tx MXene and demonstrates the potential variety of this family of modified MXenes that has yet to be explored,as well as unveils great promise for use in applications such as high performance supercapacitors.

Systematic characterization of transport and thermoelectric properties of a macroscopic graphene fiber

Graphene, a two-dimensional material with extraordinary electrical, thermal, and elastic performance, is a potential candidate for future technologies. However, the superior properties of graphene have not yet been realized for graphenederived macroscopic structures such as graphene fibers. In this study, we systematically investigated the temperature （T ）-dependent transport and thermoelectric properties of graphene fiber, including the thermal conductivity （A）, electrical conductivity （o）, and Seebeck coefficient （S）. A increases from 45.8 to 149.7 W·m^-1·K^-1 and then decreases as T increases from 80 to 290 K, indicating the boundary-scattering and three-phonon Umklapp scattering processes. σ increases with T from 7.1 × 10^4 to 1.18 × 10^5 S·m^-1, which can be best explained by the hopping mechanism. S ranges from -3.9 to 0.8 μV·K^-1 and undergoes a sign transition at approximately 100 K.

High energy storage performance for dielectric film capacitors by designing 1D SrTiO_(3)@SiO_(2) nanofillers

The development of advanced dielectric film materials with high energy storage performance is of critical significance for pulsed power capacitor applications.Nevertheless,the low discharged energy density(Ue)of current dielectric film material restricts their further application.In this work,core-shell structured SrTiO_(3)@SiO_(2) nanowires(ST@SiO_(2) NWs)fillers are fabricated based on interface engineering for high Ue.The optimized SiO2 insulating layer could effectively confine the mobility of space charge carriers in the interfacial zone between ST NWs and thick SiO2 insulating layer,thus reducing the interfacial polarization between the interface of nanofillers/polymer,which could be used to optimize the electric field strength and electric displacement of the corresponding nanocomposite.As a result,this nanocomposite film simultaneously exhibits enhanced maximum applied electric field(Emax)and(Dmax-Pr)values,thus releasing an ultrahigh discharged energy density of 14.7 J/cm^(3) at 390 MV/m,which is 99%higher than that of the conventional ST/P(VDF-CTFE)(without SiO2 coating)nanocomposite,and it is almost 2.5 times that of pure P(VDF-CTFE).This work demonstrates the superiority of the core-shell structured paraelectric nanowire in enhancing the energy storage performance of dielectric film capacitors,which is expected to guide the design of advanced energy-storage nanocomposites.

A Poriferous Nanoflake-Assembled Flower-Like Ni_(5)P_(4) Anode forHigh-Performance Sodium-Ion Batteries

Sodium-ion batteries(SIBs)have been regarded as one of the most competitive alternatives for lithium-ion batteries(LIBs)due to the abundance of sodium and comparable electrochemical characteristics of sodium to that of lithium.However,while highly desired,developing stable anode materials remains a critical challenge.In this work,the development of a stable anode for SIBs is reported,a poriferous nanoflake-assembled flower-like nickel tetraphosphide(PNAF-NP)with high surface area and typical mesoporous property.Due to the unique structure,the PANF-NP anode exhibits excellent reversible capacity of 648.34mAhg^(-1) at 0.2Ag^(-1) with a Coulombic efficiency of 98.67%,and superior cycling stability at 0.2Ag^(-1) with high retention capacity of 456.34 mAhg^(-1) and average Coulombic efficiency of 99.19%after 300 cycles.Moreover,the high reversible capacity of 614.43,589.49,512.66,and 432.23mAhg^(-1) is achieved at 0.5,1,2,and 5Ag^(-1),respectively,indicating the superior rate capability of the PNAF-NP anode.This work represents a great advancement in the field of SIBs by reporting a high-performance anode material.

Reduction in thermal conductivity of monolayer WS_(2) caused by substrate effect

Understanding the substrate and temperature effect on thermal transport properties of transition metal dichalcogenides(TMDs)monolayers are crucial for their future applications.Herein,a dual-wavelength flash Raman(DF-Raman)method is used to measure the thermal conductivity of monolayer WS_(2) at a temperature range of 200–400 K.High measurement accuracy can be guaranteed in this method since the influence of both the laser absorption coefficient and temperature-Raman coefficient can be eliminated through normalization.The room-temperature thermal conductivity of suspended and supported WS_(2) are 28.5±2.1(30.3±2.0)and 15.4±1.9(16.9±2.1)W/(m·K),respectively,with a~50%reduction due to substrate effect.Molecular dynamics(MD)simulations reveal that the suppression of acoustic phonons is mainly responsible for the striking reduction.The behaviors of optical phonons are also unambiguously investigated using Raman spectroscopy,and the in-plane optical mode,E(Γ),is surprisingly found to be slightly enhanced while out-of-plane mode,A1g(Γ),is suppressed due to substrate interaction,mutually verified with MD results.Our study provides a solid understanding of the phonon transport behavior of WS_(2) with substrate interaction,which provides guidance for TMDs-based nanodevices.

Experimental research on thermal transport properties of crystallized palladium-based alloys

Palladium-based alloy is a kind of material with a high glass forming ability and can be easily formed into an amorphous state. After an annealing process, it can also be maintained at a crystallized state. To study the thermal and electrical transport properties of crystallized palladium-based alloys, the steady-state T-type method, standard four-probe method, and AC heating-DC detecting T-type method were used to measure the thermal conductivity, electrical conductivity, and Seebeck coeffi- cient of crystallized Pd4oNiloCu3oP2o and Pd43Nilo- Cu27P2o alloys respectively. The results show that compared to amorphous samples, the thermal conductivity and electrical conductivity of crystallized palladium-based alloys are significantly higher, while the Seebeck coeffi- cient is lower. The ratio of crystallized and amorphous thermal conductivity is higher for Pd43Ni10Cu27P2o alloy fiber which has a higher glass forming ability, while the ratio of electronic thermal conductivity almost remains constant for both alloy fibers. The results also show that the slope of electrical resistivity to temperature is a function of elemental composition for crystallized quaternary palla- dium-based alloy fibers. The sensitivity of thermal conductivity and electrical conductivity to the composition is high, while the correlation between Seebeck coefficient and composition is relatively weak.

Progress and perspective of high strain NBT-based lead-free piezoceramics and multilayer actuators

In this review,the evolution of high strain Na_(0.5)Bi_(0.5)TiO_(3)-based lead-free piezoceramics and their multilayer actuators has been explored.First,in terms of Na_(0.5)Bi_(0.5)TiO_(3)-based ceramic materials,the origin of high strain,the typical chemical modification methods of obtaining large strain and extrinsic factors affecting the large strain are discussed.Then it briefly summarizes the problems existing in Na_(0.5)Bi_(0.5)TiO_(3)-based ceramics for multilayer actuator applications.Strategies to optimize strain performance by means of microstructure control and phase structure design are also discussed.Thereafter,in terms of multilayer actuator,we describe its characteristics,applications and preparation process systematically,as well as the recent development of Na_(0.5)Bi_(0.5)TiO_(3)-based multilayer actuator.At last,perspectives on directions of following work and promising fields for the applications of the materials and their devices are presented.

一种测量单个纳米颗粒比热的焦耳加热-针尖增强拉曼闪光法

纳米颗粒在复合材料及纳米器件中有广泛的应用,研究单个纳米颗粒的性能对纳米科技的发展有至关重要的作用.然而,受限于传统测量方法的空间分辨率,目前尚未报道有效的测量单个纳米颗粒热物性的方法.本文利用焦耳加热和针尖增强拉曼闪光法,设计了一种测量单个纳米颗粒比热的方法.将单个纳米颗粒放置在基底上,使用镀铂的探针作为加热器和温度探测器,探针接触纳米颗粒,通过稳态方法测量抽真空前后探针在同一温度下不同的发热量,即可通过比较求得纳米颗粒的对流换热系数;通过针尖增强拉曼散射方法,使用激光加热纳米颗粒,可获得纳米颗粒温度随时间变化曲线,结合稳态方法测定的对流换热系数,即可测定纳米颗粒的比热容和激光吸收率.分析可知,1 ns左右的激光脉冲分辨率即可满足常规状况下直径为100 nm的纳米颗粒比热的测量要求.

Low-temperature sintered(Na_(1/2)Bi_(1/2))TiO_(3)-based incipient piezoceramics for co-fired multilayer actuator application

Low-temperature sintered(Na_(1/2)Bi_(1/2))_(0.935)Ba_(0.065)Ti_(0.975)(Fe_(1/2)Nb_(1/2))_(0.025)O_(3)(NBT-BT-0.025FN)lead-free incipient piezoceramics were investigated using high-purity Li_(2)CO_(3) as sintering aids.With the ≤0.5 wt%Li_(2)CO_(3) addition,the introduced Li^(+) cations precede to enter the A-sites of the perovskite lattice to compensate for the A-site deficiencies.Once the addition exceeds 0.5 wt%,the excess Lit cations will occupy B-sites and give rise to the generation of oxygen vacancies,which accelerate the mass transport and thus lower the sintering temperature effectively from 1100℃ down to 925℃.It was also found that a small amount of Lit addition has little effect on the phase structure and electromechanical properties of the system,but overweight seriously disturbs these characteristics because of the large lattice distortion.The sintered NBT-BT-0.025FN incipient piezoceramics with 1.25 wt%Li_(2)CO_(3) addition at 925℃ provides a large strain of 0.33% and a corresponding large signal piezoelectric coefficient d_(33)^(*) of 550 pm/V at 60 kV/cm,indicating this system is a very promising candidate for lead-free co-fired multilayer actuator application.

Silkworm Silk Fibers with Multiple Reinforced Properties Obtained through Feeding Ag Nanowires

Silkworm silk fbers have been woven into textiles for thousands of years,because of their attractive luster,good mechanical properties,excellent biocompatibility,and large-scale production.With the development of human society,preparation of silk fbers with modifed or enhanced properties are highly desirable for potential applications in structural materials and smart textiles.Herein,we realized the reinforcement of multiple properties of silk fbers by feeding silkworms with Ag nanowire(Ag NW)modifed diets.The obtained silk fbers show obviously enhanced comprehensive mechanical properties,including improved tensile strength,elongation at break,tensile modulus,and toughness,which are increased by 37.2%,37.6%,68.3%,and 69.8%,respectively.Furthermore,compared with unmodifed silk,the electrical conductivity and thermal conductivity of modifed silk fbers are improved by 246.4%and 32.1%,respectively.The analysis on the components and structure shows that the incorporated Ag NWs lead to increased content of random coil/α-helix,improved orientation of crystallites,and increased content of Ag compared to pristine silk fbers,which may contribute to the enhanced mechanical,electrical,and thermal properties.