Electrochemical performance of sulfur composite cathode materials for rechargeable lithium batteries

The structure and characteristic of carbon materials have a direct influence on the electrochemical performance of sulfur-carbon composite electrode materials for lithium-sulfur battery. In this paper, sulfur composite has been synthesized by heating a mixture of elemental sulfur and activated carbon, which is characterized as high specific surface area and microporous structure. The composite, contained 70% sulfur, as cathode in a lithium cell based on organic liquid electrolyte was tested at room temperature. It showed two reduction peaks at 2.05 V and 2.35 V, one oxidation peak at 2.4 V during cyclic voltammogram test. The initial discharge specific capacity was 1180.8 mAh g-1 and the utilization of electrochemically active sulfur was about 70.6% assuming a complete reaction to the product of Li2S. The specific capacity still kept as high as 720.4 mAh g^-1 after 60 cycles retaining 61% of the initial discharge capacity.

Study on High Power MH/Ni Battery for Hybrid Electric Vehicles

Metal hydride-nickel cell is one of the best choices for hybrid electric vehicle for its high specific energy density,security,reliability and renewability.However,its poor capability under high temperature and low specific power restrict its applications.Our studies on the metal hydride-nickel cell with different loading densities show that Ni（OH） 2 with CoOOH has good oxidation and reduction properties and proton spread rate when the loading density is 0.617 kg/m2.The power density and energy density can be as high as 1 250 W/kg and 49.4 W·h/kg respectively when Ni（OH） 2 with CoOOH was used in high power battery with the nickel foam.

Preparation and characterization of Pt-WO_3/C catalysts for direct ethanol fuel cells

Three co-impregnation/chemical reduction methods in acidic solutions of pH 〈 1,including ethylene glycol （EG）,NaBH4,and HCOOH,were compared for Pt-WO3/C catalysts.Pt-WO3/C catalysts containing 10 wt.% and 20 wt.% platinum per carbon were prepared by the three methods; their morphology and electrocatalytic activities were characterized.The 20 wt.% Pt-WO3/C catalyst prepared by the co-impregnation/EG method presented the optimal dispersion with an average particle size of 4.6 nm and subsequently the best electrocatalytic activity,and so,it was further characterized.Its anodic peak current density for ethanol oxidation from linear sweep voltammetry （LSV） is 7.9 mA·cm^-2,which is 1.4 and 5.2 times as high as those of the catalysts prepared by co-impregnation/NaBH4 and co-impregnation/ HCOOH reduction methods,2.1 times as high as that of the 10 wt.% Pt-WO3/C catalyst prepared by co-impregnation/EG method,respectively.

Compliant semiconductor scaffolds: building blocks for advanced neural interfaces

Neuroscience,neuroprosthetics and neural regeneration would benefit from more adequate interfacing devices.To understand how neurons communicate,process information and control behavior,researchers need to monitor nerve cell activity with high specifity and high spatio-temporal resolution.Neural prostheses require minimally invasive-implantable devices to re- place lost function, and bypass dysfunctional pathways in the nervous system. Devices built to repair damaged nerves have to support and promote regeneration of host neurons through an injured area. Finally, as neuromodulation is being elevated from last resort to first choice treatment for an increasing number of conditions, implantable devices able to perform targeted regu- lation of neural activity are needed. Recent advances in device miniaturization, materials engineering, and nanotechnology are enabling development of an increasing number of devices that effectively interface with neural circuits. Wireless spinal cord and deep brain stimulators, retinal and cochlear implants, high density electrodes arrays for neural recording have already proven to significantly impact fundamental research in neuro- science, as well as individuals＇ quality of life.

Microstructure and electrochemical performances of LiF-coated spinel LiMn_2O_4

LiF-coated LiMn2O4 samples were prepared via a chemical method. X-ray diffraction(XRD) patterns show that the bare LiMn2O4 and the LiF-coated LiMn2O4 samples are all spinel structure in Fd 3mspace group. The apparent morphologies,the spectroscopic properties and the LiF distributions of the as-prepared samples were studied by scanning electronic microscopy(SEM),Fourier infrared spectroscopy(FTIR),transmission electronic microscopy(TEM),selected area electron diffractometry(SAED) respectively. The LiF-coated LiMn2O4 gets a more stable surface than bare LiMn2O4,and changes the interaction between the cathode material and the electrolyte. Therefore,it can endure overcharge in the secondary lithium batteries,and achieve better electrochemical performances even when charged to 4.7 V and 4.9 V.

Nickel boride alloys as catalysts for successive hydrogen generation from sodium borohydride solution

Nickel boride alloys,Ni-B,were prepared using chemical reduction method by the reaction of metal chloride with sodium borohydride,and heat-treated at various temperatures. The structures of the as-prepared alloys were studied using X-ray diffractometry(XRD),scanning electronic microscopy(SEM) and nitrogen adsorption-desorption analysis. When being adopted as the catalysts for successive hydrogen generation from sodium borohydride solution,the Ni-B alloy treated at 90 ℃ achieves a maximum hydrogen generation rate of 15.4 L/(min·g),and an average hydrogen generation rate of 13.6 L/min,which can give successive hydrogen supply to a 2.2 kW PEMFC at a hydrogen utilization of 100%.

Nanostructure and Formation Mechanism of Pt-WO_3/C Nanocatalyst by Ethylene Glycol Method

Pt-WO3 nanoparticles uniformly dispersed on Vulcan XC-72R carbon black were prepared by an ethylene glycol method.The morphology,composition,nanostructure,electrochemical characteristics and electrocatalytic activity were characterized,and the formation mechanism was investigated.The average particle size was 2.3 nm,the same as that of Pt/C catalyst.The W/Pt atomic ratio was 1/20,much lower than the design of 1/3.The deposition of WO3·xH2O nanoparticles on Vulcan XC-72R carbon black was found to be very difficult by TEM.From XPS and XRD,the Pt nanoparticles were formed in the colloidal solution of Na2WO4,the EG insoluble Na2WO4 resulted in the decreased relative crystallinity and increased crystalline lattice constant compared with those of Pt/C catalyst and,subsequently,the higher specific electrocatalytic activity as determined by CV.The Pt-mass and Pt-electrochemically-active-specific-surface-area based anodic peak current densities for ethanol oxidation were 422.2 mA·mg-1Pt and 0.43 mA·cm-2Pt,1.2 and 1.1 times higher than those of Pt/C catalyst,respectively.

Preparation and characterization of a mixing soft-segment waterborne polyurethane polymer electrolyte

混合软片断的 WPU (水运的聚氨酯) 聚合物电解质被使用 PEO 综合(poly (乙烯氧化物)) 并且 PDMS (polydimethylsiloxane ) 作为软片断。这些聚合物电解质展出好热、电气化学的稳定性。胶化聚合物电解质的传导性是 2.52 ×；在 25 ° 的 10 −3 S/cm；有 LiTFSI/( 直接数字控制 + EC ) 的 C 130% 的内容。

Synthesis and characterization of mixing soft-segmented waterborne polyurethane polymer electrolyte with room temperature ionic liquid

Composite polymer electrolytes based on mixing soft-segment waterborne polyurethane （WPU） and 1-butyl-3-methylimidazolium bis[（trifluoromethyl）sulfonyl]imide （BMImTFSI） have been prepared and characterized. The addition of BMImTFSI results in an increase of the ionic conductivity. At high BMImTFSI concentration （BMImTFSI/WPU = 3 in weight ratio）, the ionic conductivity reaches 4.27 × 10^-3 S/cm at 30 ℃. These composite polymer electrolytes exhibit good thermal and electrochemical stability, which are high enough to be applied in lithium batteries.

Nd^(3+)-doped Li_3V_2(PO_4)_3 cathode material with high rate capability for Li-ion batteries

A series of Nd^3＋-doped LiNdxV2-x（PO4）3（x = 0.00, 0.02, 0.05, 0.08 or 0.1） composites are synthesized by the rheological phase reaction method. The XRD results indicate that Nd3＋ions have been successfully merged into a lattice structure. Doped samples show good electrochemical performance in high discharge rate and long cycle. In the potential range of 3.0–4.3 V, Li3Nd0.08V1.92（PO4）3exhibits an initial discharge capacity of 115.8 m Ah/g at 0.2 C and retain 80.86% of capacity retention at 2 C in the 51 st cycle.In addition, Li3Nd0.05V1.95（PO4）3holds at 100.4 m Ah/g after 80 cycles at 0.2 C with a capacity retention of92.4%. Finally, the CV test proves that the potential polarization of Li3Nd0.08V1.92（PO4）3decreased compared with the un-doped one.

Femtosecond Degenerate Four-Wave-Mixing in ZnO Microcrystallite Thin Films

Transient third-order optical nonlinearityχ^(3)of ZnO microcrystallite thin films is measured at various temperatures by using femtosecond degenerate four-wave-mixing.Room-temperature excitonic enhancement of is observed.The magnitude ofχ^(3)ranges between 10^(-4)to 10^(-6)esu from 4.2K to room temperature.The measuredχ^(3)response time ranging from 200 to 300 fs ultrafast for temperature down to 4.2K.

Preparation and performance of novel LLTO thin film electrolytes for thin film lithium batteries

We prepared a series of lithium lanthanum titanate(LLTO) thin film electrolytes by radio frequency(RF) magnetron sputtering using LLTO targets in a N2 atmosphere.We also deposited the LLTO thin films in an Ar atmosphere under a same condition as references for comparison.The microstructure morphology and the composition of the thin films were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS),respectively.Results show that the thin film has an amorphous structure with a uniform surface and it is free of pinholes and cracks.Impedance measurements reveal that the ionic conductivity of the electrolytes is beneficial for all solid lithium batteries dependent on the lithium content at room temperature.We found that the amorphous LLTO thin film performs well and it has potential application in microbatteries for use in microelectronic devices.

Dynamic and nonlinear properties of epitaxial quantum dot lasers on silicon for isolator-free integration

This work investigates the dynamic and nonlinear properties of quantum dot(QD) lasers directly grown on silicon with a view to isolator-free applications. Among them, the chirp parameter, also named the αHfactor,is featured through a thermally insensitive method analyzing the residual side-mode dynamics under optical injection locking. The αHat threshold is found as low as 0.32. Then, the nonlinear gain is investigated from the gain compression factor viewpoint. The latter is found higher for epitaxial QD lasers on silicon than that in heterogeneously integrated quantum well(QW) devices on silicon. Despite that, the power dependence of the αHdoes not lead to a large increase of the chirp coefficient above the laser’s threshold at higher bias. This effect is confirmed from an analytical model and attributed to the strong lasing emission of the ground-state transition, which transforms into a critical feedback level as high as-6.5 d B, which is ~19 d B higher than a comparable QW laser.Finally, the intensity noise analysis confirms that QD lasers are overdamped oscillators with damping frequencies as large as 33 GHz. Altogether, these features contribute to fundamentally enhancing the reflection insensitivity of the epitaxial QD lasers. This last feature is unveiled by the 10 Gbit/s error-free high-speed transmission experiments. Overall, we believe that this work is of paramount importance for future isolator-free photonics technologies and cost-efficient high-speed transmission systems.

Uncovering recent progress in nanostructured light-emitters for information and communication technologies

Semiconductor nanostructures with low dimensionality like quantum dots and quantum dashes are one of the best attractive and heuristic solutions for achieving high performance photonic devices.When one or more spatial dimensions of the nanocrystal approach the de Broglie wavelength,nanoscale size effects create a spatial quantization of carriers leading to a complete discretization of energy levels along with additional quantum phenomena like entangled-photon generation or squeezed states of light among others.This article reviews our recent findings and prospects on nanostructure based light emitters where active region is made with quantum-dot and quantum-dash nanostructures.Many applications ranging from silicon-based integrated technologies to quantum information systems rely on the utilization of such laser sources.Here,we link the material and fundamental properties with the device physics.For this purpose,spectral linewidth,polarization anisotropy,optical nonlinearities as well as microwave,dynamic and nonlinear properties are closely examined.The paper focuses on photonic devices grown on native substrates(InP and GaAs)as well as those heterogeneously and epitaxially grown on silicon substrate.This research pipelines the most exciting recent innovation developed around light emitters using nanostructures as gain media and highlights the importance of nanotechnologies on industry and society especially for shaping the future information and communication society.

Dynamic performance and reflection sensitivity of quantum dot distributed feedback lasers with large optical mismatch

This work reports on a high-efficiency In As/Ga As distributed feedback quantum dot laser.The large optical wavelength detuning at room temperature between the lasing peak and the gain peak causes the static,dynamic,and nonlinear intrinsic properties to all improve with temperature,including the lasing efficiency,the modulation dynamics,the linewidth enhancement factor,and consequently the reflection insensitivity.Results reported show an optimum operating temperature at 75°C,highlighting the potential of the large optical mismatch assisted single-frequency laser for the development of uncooled and isolator-free high-speed photonic integrated circuits.

Characterization of Yb-doped ZBLAN fiber as a platform for radiation-balanced lasers

Recent advances in power scaling of fiber lasers are hindered by the thermal issues,which deteriorate the beam quality.Anti-Stokes fluorescence cooling has been suggested as a viable method to balance the heat generated by the quantum defect and background absorption.Such radiation-balanced configurations rely on the availability of cooling-grade rare-earth-doped gain materials.Herein,we perform a series of tests on an ytterbium-doped ZrF4–BaF2–LaF3–AlF3–Na F(ZBLAN)optical fiber to extract its laser-cooling-related parameters and show that it is a viable laser-cooling medium for radiation balancing.In particular,a detailed laser-induced modulation spectrum test is performed to highlight the transition of this fiber to the cooling regime as a function of the pump laser wavelength.Numerical simulations support the feasibility of a radiation-balanced laser,but they highlight that practical radiation-balanced designs are more demanding on the fiber material properties,especially on the background absorption,than solid-state laser-cooling experiments.

High-capacity free-space optical link in the midinfrared thermal atmospheric windows using unipolar quantum devices

Free-space optical communication is a very promising alternative to fiber communication systems,in terms of ease of deployment and costs.Midinfrared light has several features of utter relevance for free-space applications:low absorption when propagating in the atmosphere even under adverse conditions,robustness of the wavefront during long-distance propagation,and absence of regulations and restrictions for this range of wavelengths.A proof-of-concept of high-speed transmission taking advantage of intersubband devices has recently been demonstrated,but this effort was limited by the short-distance optical path(up to 1 m).In this work,we study the possibility of building a long-range link using unipolar quantum optoelectronics.Two different detectors are used:an uncooled quantum cascade detector and a nitrogen-cooled quantum well-infrared photodetector.We evaluate the maximum data rate of our link in a back-to-back configuration before adding a Herriott cell to increase the length of the light path up to 31 m.By using pulse shaping,pre-and post-processing,we reach a record bitrate of 30 Gbit s−1 for both two-level(OOK)and four-level(PAM-4)modulation schemes for a 31-m propagation link and a bit error rate compatible with error-correction codes.

Reflection sensitivity of dual-state quantum dot lasers

This work experimentally and theoretically demonstrates the effect of excited state lasing on the reflection sensitivity of dual-state quantum dot lasers,showing that the laser exhibits higher sensitivity to external optical feedback when reaching the excited state lasing threshold.This sensitivity can be degraded by increasing the excited-to-ground-state energy separation,which results in a high excited-to-ground-state threshold ratio.In addition,the occurrence of excited state lasing decreases the damping factor and increases the linewidth enhancement factor,which leads to a low critical feedback level.These findings illuminate a path to fabricate reflectioninsensitive quantum dot lasers for isolator-free photonic integrated circuits.

A new composite polymer electrolyte based on poly(ethyleneoxide)/ polysiloxane/BMImTFSI/organomontmorillonite

合成聚合物电解质基于(乙烯氧化物) poly， polysiloxane/1-butyl-3-methylimidazolium 二度(trifluoromethanesulfonyl ) imide/organomontmorillonite (PEOPDMS/IL/OMMT ) 被准备并且描绘。到 PEOPDMS 的聚合物底的离子的液体和 OMMT 的增加导致了离子的电导率的增加。在房间温度，样品 PPB100OMMT4 的离子的传导性是 2.19 ? 牰 ' 要棙 M 杮愠摮瘠牡慩汢? 敳敬瑣潩吗？

Preparation of Pt/C Nanocatalysts by Ethylene Glycol Method in Weakly Acidic Solutions

Pt/C catalysts were prepared by ethylene glycol （EG） method in weakly acidic solutions adjusted by sodium citrate （NasCit）, sodium acetate （NaAc） and sodium hydroxide （NaOH）, separately. The effects of alkalizing agent, pH and temperature were investigated by transmission electron microscopy （TEM） and CV. The composition and structure of Pt/C catalyst prepared at optimal conditions of 140℃ and pH=6.7 adjusted by NasCit was further characterized by X-ray photoelectron microscopy （XPS） and X-ray diffraction （XRD）, respectively. The average particle size of Pt/C catalyst prepared using Na3Cit is 2.1 nm, smaller than that of Pt/C catalyst （2.9 nm） prepared using NaAc, much smaller than that of Pt/C catalyst （100 nm） prepared using NaOH. The electrocatalytic activity of Pt/C catalysts prepared using Na3Cit and NaAc for ethanol oxidation are 456.6 and 419.2 mA/mgPt, comparative to those of Pt/C catalyst prepared by typical EG method and commercial E-TEK Pt/C catalyst. Finally, the size control mechanism of Pt nanoparticles was discussed.