电化学阴极沉积制备氧化钴/CNTs复合电极的准电容特性

采用电化学阴极沉积还原Co(NO3)2的方法制备了具有准电容特性的氧化钴电极材料,其比容量达到280 F／g,采用CNTs作为电极基体,在其表面均匀的沉积了纳米钴化镍颗粒并由此制备了氧化钴碳纳米管复合电极材料.采用循环伏安,恒流充放电,交流阻抗及扫描电镜等方法考察了复合电极材料的容量特性、阻抗特性、自放电特性以及电极表观特征．实验表明复合电极具有良好的电化学特性,CNTs基体在明显降低氧化镍材料的阻抗的同时还提高了电极材料的电化学容量并拓宽了电极材料的有效工作电位窗,复合电极在1 mol／L KOH电解液中比容量达到322 F／g且表现了良好的电化学可逆性．并分别采用氧化钴／CNTs复合电极作为正极,活性炭纤维作为负极制备了复合型电化学电容器,其工作电压达到1．4 V,电容器质量比容量达到47 F／g．在0．1 A／cm2放电时,复合型电容器的能量密度达到10 Wh／kg,兼具高能量特性和优良的大电流放电特性．     

聚苯胺在电化学电容器中的应用

采用化学氧化聚和法制备了聚苯胺电极材料,所制备的聚苯胺具有高于420F/g的法拉第赝电容和良好的电化学特性.分别采用聚苯胺作为正极材料,高比容量活性碳作为负极,38%硫酸作为电解液制备了复合型电化学电容器.复合型电容器工作电压达到1.4V,最大电容器比容量达到57F/g,最大比能量达到15.5Wh/kg.电容器200mA/cm2放电条件下真实功率达到2.8W/g,峰值比功率达到20.4W/g.循环工作寿命超过1000次.     

电化学阴极沉积制备氧化镍/碳纳米管复合电极的准电容特性

采用催化裂解的方法制备了碳纳米管,其比容量为12F/g.采用碳纳米管作为电极基体,采用阴极电化学还原Ni(NO3)2的方法在碳纳米管基体表面均匀的沉积了纳米氧化镍颗粒并由此制备了氧化镍碳纳米管复合电极材料.采用循环伏安、恒流充放电、交流阻抗及扫描电镜等方法考察了复合电极材料的容量特性、阻抗特性、自放电特性以及电极表观特征.实验表明复合电极具有良好的电化学特性,碳纳米管基体在明显降低氧化镍材料的阻抗的同时还提高了电极材料的电化学容量并拓宽了电极材料的有效工作电位窗,复合电极在6mol/LKOH电解液中比容量达到25F/g且表现了良好的电化学可逆性.与碳纳米管基电容器相比,采用氧化镍复合电极材料组装的电容器具有较低的自放电率.     

常压干燥法制备碳气凝胶及其电极性能研究北大核心CSCD

以间苯二酚-甲醛为前驱体,通过加入P123以增强有机气骨架的方法,采用常压干燥技术制备碳气凝胶电极材料,有机凝胶在干燥过程中收缩率极大降低。通过二氧化碳活化法对常压干燥获得的碳气凝胶孔结构进行了调控。研究了不同温度对其结构的影响,获得了最高比表面积达3544m2/g的碳气凝胶。6mol/L的KOH电解液中测试表明,常压干燥碳气凝胶具有稳定的充放电性能,随着活化温度的升高,比容量逐渐增加,最高比电容可达261F/g。常压干燥技术制备的碳气凝胶电极材料在降低生产成本的同时,仍具有理想的电化学性能。     

电化学制备钛网负载聚吡咯/石墨烯复合膜及其在超级电容器中的应用

通过电化学的方法在钛网上制备了聚吡咯与石墨烯的复合物薄膜,其过程是先在钛网上通过自组装干燥膜法附着上石墨烯氧化物膜,而后采用电化学还原的方法原位还原制备得到石墨烯膜,随后加入吡咯单体,再通过电化学聚合的方法在石墨烯的表面生长聚吡咯,得到的聚吡咯开始以颗粒的形式存在,而后随着聚合的进行得到了链状的聚吡咯.得到的复合膜有高的比表面积和导电性,可以作为电极活性材料用于超级电容器中提供赝电容,结果表明,复合膜作为电极材料的超级电容器拥有高的性能,比电容达400 F/g,并且电极的充放电稳定性高,5000次复合膜充放电循环后比电容还能保留82%,说明该材料适合于超级电容器.     

石墨烯在超级电容器中的应用

正1.引言超级电容器是一种介于传统电容器和二次电池之间的新型电化学储能元件,它拥有功率密度高、充放电速率快、环境友好、温度特性好及使用寿命长等优点(表1),已在备用电源系统、便携式电子设备和电动汽车领域有广泛的应用。众所周知,电极材料是超级电容器的关键所在,它决定着电容器的主要性能指标,如能量密度、功率密度和循环稳定性等,所以制备合成具有优异性能的电极材料成为超级电容器研究的核心课题。目前,超级电容器的电极材料主要可以分为三类:碳基材料、过渡金属化合物和导电聚合物如图1     

碳气凝胶及活化碳气凝胶电极材料制备与性能

 以间苯二酚(R)-甲醛(F)为原料,制备了有机气凝胶和碳气凝胶,并对其进行二氧化碳活化。X射线衍射(XRD)测试表明,二氧化碳渗入到碳气凝胶网络结构发生反应,造成(002)峰和(100)峰减弱;扫描电子显微镜(SEM)测试表明,活化没有破坏碳气凝胶的骨架结构,而是增加了大量的nm尺度微孔,从而大大提高了碳气凝胶的比表面积和微孔比例。在1 mol/L KOH电解液中进行了循环伏安和计时电位扫描测试,电极材料电化学性能稳定,具有较好的可逆性,在1 mA/s电流密度下进行充放电测试,得到活化前电极比电容为103 F/g,活化后由于比表面积的增加,比电容达到371 F/g,是一种理想的电化学电极材料。     

糠醇辅助的聚合凝胶法制备纳米Li4Ti5O12负极材料

以硝酸锂、钛酸正丁酯和糠醇为反应物,采用糠醇聚合凝胶法制备了纳米Li₄Ti₅O₁₂粉体．利用XRD、SEM和BET比表面测试对产物进行了表征,并研究了纳米Li₄Ti₅O₁₂粉体作为锂离子电池负极材料的电化学性能．在700℃或更高温度烧结时产物为纯相的尖晶石型．通过柠檬酸、聚乙烯吡咯烷酮、十六烷基三甲基溴化铵(CTAB)表面活性剂的加入能够减少产物颗粒的团聚程度,增大粉体的比表面积,提高其电化学性能．加入0.5 g CTAB、700℃烧结12 h的Li₄Ti₅O₁₂粉体展示出最高的比容量和最佳的循环性能,10 C下充电比容量高达156.7 mAh/g．     

基于中性水凝胶/取向碳纳米管阵列高电压柔性固态超级电容器

随着科技发展和时代进步,发展质轻便携、安全环保的高性能储能器件变得日趋重要,对柔性固态超级电容器的研究也应运而生.柔性电极材料及电解质的选用是设计柔性固态超级电容器的关键因素,近年来一直是研究的热点.考虑到环境污染及实际需求问题,本文采用中性凝胶电解质对具有高比表面积、良好导电性及取向性的碳纳米管阵列进行包埋处理,所形成的柔性复合薄膜作为电极材料,设计制备三明治结构的柔性超级电容器件.通过改变凝胶电解质中所加入的无机盐电解质种类,调控器件的电化学储能性质.最终在聚乙烯醇PVA-NaCl作为凝胶电解质时,整个器件比容量最高达104.5 mF·cm~(–3),远高于有机离子凝胶与碳管阵列形成的复合器件以及无规分布的碳纳米管与水凝胶形成的复合器件,同时获得了0.034 mW·h·cm~(–3)的最大能量密度,并且具有良好的倍率性能、循环稳定性及抑制自放电的效果,并在高电压1.6 V下依然保持良好的化学稳定性.这种中性凝胶/碳管阵列复合超级电容器件不仅满足了绿色安全、柔性便携的要求,未来在医学可植入器件等领域也具有很好的应用前景.     

多孔碳纳米球的制备及其电化学性能

以三嵌段共聚物F108为软模板,通过水热法合成酚醛树脂球并在氮气氛围下碳化、KOH活化处理,最终得到多孔碳纳米球材料.通过扫描电子显微镜、透射电子显微镜和氮气吸附分析仪对样品进行表征,结果表明样品的平均粒径为120 nm,球形度高,比表面积达到1403 m~2/g,孔径分布广.通过X射线衍射研究样品的结晶度,傅里叶红外光谱分析样品表面官能团的情况,结果表明KOH处理和高温处理使得样品的微晶结构有序度提高,表面官能团含量降低.以多孔碳纳米球作为超级电容器电极的活性物质,电化学特性测试结果表明,多孔碳纳米球材料的比电容能够达到132 F/g(0.2 A/g),在10 A/g的电流密度下,经过10000次循环充放电后,电容量保留率为97.5%.本文采用水热法制备的多孔碳纳米球电化学性能良好,适用于超级电容器电极材料,研究结果表明,比表面积大、孔径分布合适(具有一定介孔含量)、结晶度高和含有少量表面官能团的理化特性的电极材料,其电化学性能更加优越.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.