All‐carbon hybrids for high performance supercapacitors

A hybrid nanostructure with partially reduced graphene oxide (rGO) and carbon nanofibers (CNFs) was fabricated and used as supercapacitor electrodes. A straightforward, environmentally friendly, and low‐cost microwave‐assisted reduction process was developed for the synthesis of rGO/CNF hybrid structures. The fabricated supercapacitor devices showed a specific capacitance of 95.3 F g^?1 and a superior long‐term cycling stability. A capacitance retention of more than 97% after 11 000 galvanostatic charge discharge cycles was obtained. These and other results reported in this paper indicate that high‐rate, all‐carbon, rGO/CNF hybrid nanostructures are highly promising supercapacitor electrode materials.     

Measurements of thermal conductivity of 1‐butyl‐3‐methylimidazolium tetrafluoroborate at high pressure

Ionic liquids are salts that are liquid at room temperature. They have attracted considerable attention as new materials. In this study, a transient short‐hot‐wire apparatus was prepared, and the thermal conductivity of 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim] [BF₄]) was measured. The experimental temperatures were from 294 to 334 K, and the pressures were from 0.1 to 20 MPa. It was found that the thermal conductivity of an ionic liquid has a very small temperature and pressure dependence. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(6): 361–372, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20166     

Amorphous and ‘micromorph’ silicon tandem cells with high open-circuit voltage

For amorphous and ‘micromorph’ silicon multi-junction solar cells, we have developed tunnel recombination junctions consisting of two microcrystalline doped layers with a defect-rich interface. While the solar cells performed reasonably well under AM 1.5 light, we found in spectral response measurements that the first deposited cell of tandem structures in nip and pin configuration was apparently leaking under low light conditions. Insertion of a thin protection layer of n-type amorphous silicon solved this issue, and led to an increase in open-circuit voltage. Voltages as high as 1.76 V have been obtained for a-Si/a-Si pinpin tandem cells.     

A high performance lead–acid battery for EV applications

Some recent work in the development of a high energy density lead–acid battery for electric vehicle application is described. Two separate methods are used to achieve this objective. Significant total cell weight savings can be achieved by the use of an electrolyte management system. This minimises the quantity of water used in the electrolyte. The second feature concerns the form and utilization of the lead–paste active materials. The positive and negative pastes are carried as a slurry and are agitated during the charge/discharge cycle. This maximises the utilisation of the active materials and reduces premature sulphation.     

Properties of high density polyethylene and its behaviour under ‘Galisol’ heat storage conditions

High density polyethylene (HDPE), crosslinked by electron beams in air, is presented as a latent heat storage material for energy storage applications at a temperature level of about 120°C. The study includes thermal investigations before and after the irradiation, investigations of the form stability, gel content determinations and microscopic investigations of HDPE. An electron energy of 0.4 MeV and a radiation dosage of 200 kGy were found to be the optimum conditions for the irradiation of the investigated HDPE in air. The pellets obtained were form-stable owing to the formation of a thin crosslinked surface layer (about 0.5 mm thickness). In spite of the presence of oxygen during irradiation, the melting enthalpy of the initial state was retained almost quantitatively. Apart from that, a quasicomplete irradiation of the pellets in volume in air, with a higher electron energy, is also possible. In this case about 95% of the initial melting enthalpy is obtained, providing a maximum gel content of 50%. Moreover, the paper offers a possibility of overcoming the low heat transfer power of HDPE by applying it in form of modified pellets in a ‘Galisol’ model storage unit with water as the heat transfer liquid. Owing to the large heat transfer area connected to boiling and condensation of water, excellent values of heat transfer power of 100–114 W/kg HDPE (ΔT=16 K) are obtained. These are comparable to those of salt hydrates, provided there is sufficient form stability. The significant influence of somewhat lower form stability on the heat output is shown.     

The integrity of materials in high temperature components; Performance and life assessment

Engineering components operating under conditions where time dependent degradation processes occur (creep, corrosion, oxidation, microstructural degradation, embrittlement etc.) have generally been designed on a relatively simplistic basis: the best available experimentally determined mechanical property data characterising the long term properties (creep and rupture strength, oxidation and corrosion rates etc.) are assembled and lower bound properties from the data sets adopted as the relevant values. These are then combined with conservatively calculated values for the operating conditions (temperature, stress etc.) and a suitable engineering safety factor to define dimensions which should, if the assumed properties and conditions are realised during the operational lifetime of the component, lead to a satisfactory and safe behaviour. The designer must therefore be vigorous in his application of the relevant design codes, confident he can properly determine the operating conditions of stress, temperature and environment and sure that the materials properties on which his design is based will in fact be realised in practice. Unfortunately, for a wide variety of reasons, it has been the case that one or other of these criteria has not been met in practice and the resultant failures have led to very significant, and occasionally catastrophic, financial penalties. Very often the loss of production costs are greater than those involved in replacement. Such events have attracted the wide interest of the metallurgical fraternity and the investigations initiated after these incidents have greatly improved the understanding of both high temperature material properties and the impact of operating factors. This knowledge, when appropriately applied, can certainly reduce the incidence of similar failures in future.

It is important to note that, for the majority of remaining life assessments of plant of all types operating at elevated temperatures, the life limiting process is rarely controlled simply by the creep behaviour of the parent material. More usually it is the effects of factors not considered in the original design, for example weldments, stress concentrators, environmental attack and so forth, which lead to premature failure. It is invaluable, therefore, to have a prior knowledge of the consequences of these factors derived from failure investigations in detecting the early stages of failure and the component remaining life.     

Super cold chain—a high quality,energy‐efficient,and environment‐friendly method

Because of the lack of understanding of microcosmic mechanisms of energy and mass transport, the current cold chain consumes too much energy and cannot guarantee the perfect quality of food, which is against to the sustainable development of environment. The key objective of this perspective article is to put forward the concept of super cold chain starting from the study of microscopic mechanism. In addition, the necessity and advantages of developing super cold chain are also emphasized. Finally, the development direction is expounded. Copyright © 2017 John Wiley & Sons, Ltd.     

Size design of lithium-ion battery with high mass specific energy ——Battery mass formula

提出了一种质量比能量型锂离子电池型号设计思路,推导出了以正极片数量和正极片长宽比为自变量的电池质量公式,并对公式的正确性和准确性进行了验证,通过实例阐述了电池质量公式的应用方法和实际意义。研究结果表明,电池质量公式在定义域内存在最小值点,可以通过求解电池质量公式的最小值为高质量比能量电池型号设计提供理论依据。     

Design and validation of the high performance and low noise CQU‐DTU‐LN1 airfoils

This paper presents the design and validation of the high performance and low noise Chong Qing University and Technical University of Denmark LN1 (CQU‐DTU‐LN1) series of airfoils for wind turbine applications. The new design method uses target characteristics of wind turbine airfoils in the design objective, such as airfoil lift coefficient, drag coefficient and lift‐drag ratio, and minimizes trailing edge noise as a constraint. To express airfoil shape, an analytical expression is used. One of the main advantages of the present design method is that it produces a highly smooth airfoil shape that can avoid the problem of curvature discontinuity. An airfoil profile with discontinuous curvature can produce a discontinuous pressure gradient (i.e., local flow acceleration or deceleration), which enhances flow separation and thus decreases the airfoil performance. By combining the design method with the blade element momentum theory, the viscous‐inviscid xfoil code and an airfoil self‐noise prediction model, an optimization algorithm has been developed for designing the high performance and low noise CQU‐DTU‐LN1 series of airfoils with targets of maximum power coefficient and low noise emission. To validate the airfoil design, CQU‐DTU‐LN118 airfoil has been tested experimentally in the acoustic wind tunnel located at the Virginia Polytechnic Institute and State University (Virginia Tech), USA. To show the superiority of the CQU‐DTU‐LN1 airfoils, comparisons on aerodynamic performance and noise emission between the CQU‐DTU‐LN118 airfoil and the National Advisory Committee for Aeronautics (NACA) 64618 airfoil, which is used in modern wind turbine blades, are carried out. Copyright © 2013 John Wiley & Sons, Ltd.     

Soft‐template synthesis of high surface area mesoporous titanium dioxide for dye‐sensitized solar cells

In the present work, 10 to 14 nm titania nanoparticles with high‐packing density are synthesized by the soft‐template method using a range of cationic surfactants including cetyl trimethylammonium bromide (CTAB), Sodium dodecyl sulfate (SDS), and dodecyl trimethylammonium bromide (DTAB). The synthesized nanoparticles are used as a photoanode material in dye solar cells. Density functional theory (DFT) simulations reproduce our experimental results of charge transfer and strong interaction between the TiO₂ and N719. N719‐TiO₂ complex establishes strong electrostatic bonding through H of the dye with the O of TiO₂ surface. Solar cell efficiency of 6.08% with 12.63 mA/cm², 793 mV, and 48.5% for short circuit current density, open circuit voltage, and fill factor, respectively, are obtained under 1 sun illumination for the dye‐sensitized solar cell (DSSC) using a film of mesoporous TiO₂ synthesized from the SDS surfactant. On the other hand, the 21 nm commercial TiO₂ powder (P25) device results in 4.60% efficiency under similar conditions. Electrochemical impedance spectroscopic studies show that the SDS device has lesser charge transport resistance than the other devices because of its higher surface area, packing density, and dye loading capacity. Our results show that employing high packing density‐based TiO₂ nanoparticles represents a commercially viable approach for highly beneficial photoanode development for future DSSC applications.     

Direct carbon solid oxide Fuel Cell—a potential high performance battery

Tubular cone-shaped Ni-based anode-supported solid oxide fuel cells (SOFCs), with yttria-stabilized zirconia (YSZ) electrolyte and La_0.8Sr_0.2MnO₃ (LSM) cathode, were investigated with Fe catalyst-loaded activated carbon directly filled in as fuel. Three identical single cells were operated at different current and it turned out that larger current resulted in shorter operation life and smaller carbon utilization. A 3-cell-stack, with the segmented cone-shaped cells connected in series, was assembled and tested. A peak power density of 465 mW cm⁻² and a volumetric power density of 710 mW cm⁻³ were achieved at 850 °C. The degradation performance was analyzed according to the electrochemical characterization and SEM-EDX measurement. Based on the experimental results, the potential of developing such direct carbon SOFC into a high performance battery was proposed.     

Sugarcane hybrids with original low lignin contents and high field productivity are useful to reach high glucose yields from bagasse

Five sugarcane hybrids plus a reference material were evaluated according to the glucose yields obtained after alkaline-sulfite pretreatment and enzymatic hydrolysis. Sugarcane hybrids with varied original chemical compositions were used to assess how contrasting samples might influence the integrated pretreatment and hydrolysis process. The hydrolysis efficiency of six samples treated at three different chemical loads, suggested that lignin and hemicellulose removals during the pretreatment were not the single factor necessary to reach high cellulose conversion levels in the enzymatic hydrolysis step. Pretreated samples with the highest total acid contents (mainly sulfonic acids) were also the most digestible materials. The glucose yields were heavily dependent not only on the digestibility of the pretreated materials but also on the field productivity of the plants. One of the hybrids, presenting high glucan yields after pretreatment and high digestibility, produced low glucose yields because it presented very low biomass productivity. In contrast, one of the hybrids that presented low glucan yield after pretreatment, but was highly digestible and presented high biomass productivity, provided the highest glucose yields in the data set, producing 4192 and 5629 kg of glucose per hectare after enzymatic hydrolysis for 24 h and 72 h, respectively.     

Development of a Sievert apparatus for characterization of high pressure hydrogen sorption materials

A volumetric gas absorption (Sievert) apparatus has been developed to measure hydrogen absorption and desorption at pressures up to 700 bar and temperatures between 240 K and 320 K. The apparatus is designed to reduce uncertainty for high pressure measurements while maintaining proper temperature control in the sample. Pressure-composition isotherms (PCI) and kinetics measurements of a well-studied material, LaNi₅ have been obtained for validation of the apparatus. Measurements of both absorption and desorption PCI curves as well as full absorption kinetics data have been obtained for TiCrMn to examine the performance at high pressures, as well as to examine the thermodynamic hysteresis effect in TiCrMn for applications in metal hydride system design. Due to this hysteresis, the thermodynamics of the absorption reaction differ significantly from those of the desorption reaction, which must be accounted for when considering thermal design of a metal hydride reactor and the suitability of the metal hydride for energy storage applications.     

Investigation of hydrogen production using wood pellets gasification with steam at high temperature over 800 °C to 1435 °C

A fixed-bed gasifier was developed to study the effects of steam flow rate and temperature on the hydrogen production during biomass gasification at high temperature over 800 °C to 1435 °C. An optimum steam flow rate for peak of hydrogen yield was found. As temperature increases, amount of hydrogen increases first, subsequently decreases and then increases again with a maximum peak of hydrogen yield at 917 °C. In the temperatures of 1018 °C through 1435 °C post the peak hydrogen production increases with temperature. The maximum volume fraction of hydrogen and hydrogen production ratio are 60% and 76%, respectively. Chemical equilibrium calculation was also done using ASPEN software, which demonstrates that the more the steam flow rate, the lower the temperature for maximum hydrogen yield; the higher the temperature, the lower the effect of steam flow rate. The results are expected to develop high temperature gasification technology.     

Enhanced hetero‐elements doping content in biomass waste‐derived carbon for high performance supercapacitor

Betel nut wastes are firstly modified with nitric acid/thiourea to fabricate hetero‐element doping carbon (C‐H‐T) for energy storage. C‐H‐T exhibits improved content of O (12.27%), N (2.52%), and S (2.88%) compared with that of purely carbonized carbon with O (9.2%) and N (1.76%). Without nitric acid heat treatment, the carbon materials prepared by hydrothermal treatment with thiourea only get increasing hetero‐elements content of O (10.46%), N (2.9%), and S (0.53%). The similar results have been obtained using urea and melamine as dopants. Due to the synergistic effects of the hetero‐elements containing functional groups, C‐H‐T get a significant enhancement in its electrochemical properties with a high capacitance (423 F g^?1 at 0.5 A g^?1) in KOH electrolyte. C‐H‐T based coin‐type symmetric supercapacitors display maximum energy density of 61.7 Wh kg^?1 and considerate cycling ability with 94% capacitance retention after 10 000 cycles. The fabricated two‐step method can inspire the increase of hetero‐elements content in carbon materials to develop its application in energy storage.     

Experimental evidence of very high open-circuit voltages of inversion–layer silicon solar cells

In this paper the first experimental evidence of the high V_oc-potential of inversion-layer silicon solar cells is given. Minority-carrier lifetime measurements on inversion-layer emitters have been performed and the diffused p–n contact of PN-IL silicon solar cells has been optimized for high open-circuit voltages. PN-IL silicon solar cells with open-circuit voltages of 693 mV have been fabricated on 0.2 and 0.5-Ω cm FZ p-Silicon wafers. These values are the highest ever reported V_oc's for inversion-layer silicon solar cells on p-Silicon. This demonstrates that inversion-layer silicon solar cells exhibit a similar potential for achieving high open-circuit voltages as silicon solar cells with a diffused p–n junction.     

The influence of ångström parameters on calculated direct solar spectral irradiances at high turbidity

This work analyzes the influence of ångström parameters on modeled spectral solar irradiance data. The ångström parameters are obtained in the same way as in the Volz method but using continuous record of spectral direct solar irradiance measures in the 400–1000 nm spectral range. Different pairs of α-β values are obtained depending on the two selected wavelengths. The comparison between the calculated irradiance data with these different α-β pairs and experimental data show important differences that may be taken into account in irradiance models.