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[en] Claims have emerged recently, of high hydrogen storage capacities at room temperature and above, for carbons such as single-wall and multi-walled nanotubes. We have been unable to verify any claims of high capacities at room temperature and low pressure. For (10,10) single wall carbon nanotubes, we used a computer controlled Sievert's apparatus to measure an adsorption at RT of 0.07 wt% gravimetric density at 1 bar, typical of what is expected on the basis of BET surface area measurements for carbons. At high pressures of > 60 bar and temperatures of 80K gravimetric densities up to ∼ 8 wt% are obtained, but more typically ∼ 7 wt% after a few adsorption desorption cycles. These values and isotherm shapes can be attributed to rearrangement of the rope structure that is formed by condensed nanotubes. Certain fullerites can also exhibit adsorption/desorption cycle dependent capacity, ranging from 2.5 to 4 wt% at 80K and 120 bar. (author)
[en] Lithium metal phosphate materials are the newest generation of active materials. With the limited number of cathode materials available at present and the prevalence of transition metal oxide cathodes, phosphates are able to answer the rising safety concerns surrounding the oxide chemistry. These inherent safety limitations have until now prevented lithium ion batteries in general from entering the large format applications markets such as electric and hybrid electric vehicles. Iron-based olivine phosphate has been the focus of extensive research: intrinsic thermal stability and continual improvement of its performance characteristics have geared the industry to a fast track adoption of this chemistry for the larger format applications. Recently developed vanadium-based phosphates possess operating voltages of 3.65 V for Li3V2(PO4)3 and 4.05 V for LiVPO4F, both of which are higher than the iron-based phosphate. The high power capability of Li3V2(PO4)3 makes it ideal for applications that require power; LiVPO4F on the other hand has high energy and a desirable cycling characteristic that makes it ideal for energy-demanding applications such as PHEV and EV. These materials are the best fit for the ever-increasing demand for energy, power and thermal stability that is essential in the large format arena. (author)
[en] Development of fuel cell (FC) and hydrogen metal-hydride storage (MH) technologies continuously demonstrate higher efficiency rates and higher safety, as hydrogen is stored at low pressures of about 2 bar in a bounded state. A combination of a FC/MH system with an electrolyser, powered with a renewable source, allows creation of an almost fully autonomous power system, which could potentially replace a diesel-generator as a back-up power supply. However, the system must be extended with an electro-chemical battery to start-up the FC and compensate the electric load when FC fails to deliver the necessary power. Present paper delivers the results of experimental and theoretical investigation of a hybrid energy system, including a proton exchange membrane (PEM) FC, MH- accumulator and an electro-chemical battery, development methodology for such systems and the modelling of different battery types, using hardware-in-the-loop approach. The economic efficiency of the proposed solution is discussed using an example of power supply of a real town of Batamai in Russia. (paper)
[en] Used as low-cost anode in the majority of lithium ion batteries, layered graphite has got critical issues. Owing to its low voltage operation, they reduce electrolyte by stealing lithium from cathode to form an SET (Solid Electrolyte Interphase), and pose fire risk from dendrite based short-circuit likely at times of fast charging or erroneous over-lithiation towards end of discharge. In this talk we are addressing this problems
[en] This paper gives a brief overview of battery packaging concepts, their specific advantages and drawbacks, as well as the importance of packaging for performance and cost. Production processes, scaling and automation are discussed in detail to reveal opportunities for cost reduction. Module standardization as an additional path to drive down cost is introduced. A comparison to electronics and photovoltaics production shows 'lessons learned' in those related industries and how they can accelerate learning curves in battery production
[en] Highlights: ► Electrospun binary fatty acid eutectics/PET ultrafine composite fibers were prepared. ► Fatty acid eutectics had appropriate phase transition temperature and heat enthalpy. ► Their morphological structures and thermal properties were different from each other. ► Composite fibers could be innovative form-stable PCMs for thermal energy storage. - Abstract: The ultrafine composite fibers based on the composites of binary fatty acid eutectics and polyethylene terephthalate (PET) with varied fatty acid eutectics/PET mass ratios (50/100, 70/100, 100/100 and 120/100) were fabricated using the technique of electrospinning as form-stable phase change materials (PCMs). The five binary fatty acid eutectics including LA–MA, LA–PA, MA–PA, MA–SA and PA–SA were prepared according to Schrader equation, and then were selected as an innovative type of solid–liquid PCMs. The results characterized by differential scanning calorimeter (DSC) indicated that the prepared binary fatty acid eutectics with low phase transition temperatures and high heat enthalpies for climatic requirements were more suitable for applications in building energy storage. The structural morphologies, thermal energy storage and thermal stability properties of the ultrafine composite fibers were investigated by scanning electron microscope (SEM), DSC and thermogravimetric analysis (TGA), respectively. SEM images revealed that the electrospun binary fatty acid eutectics/PET ultrafine composite fibers possessed the wrinkled surfaces morphologies compared with the neat PET fibers with cylindrical shape and smooth surfaces; the grooves or ridges on the corrugated surface of the ultrafine composite fibers became more and more prominent with increasing fatty acid eutectics amount in the composite fibers. The fibers with the low mass ratio maintained good structural morphologies while the quality became worse when the mass ratio is too high (more than 100/100). DSC measurements suggested that the heat enthalpies of melting and crystallization of the ultrafine composite fibers increased gradually with increasing fatty acid eutectics amounts, but their phase transition temperatures had almost no obvious variation as relative to the corresponding fatty acid eutectics. Meanwhile, the characteristic temperatures and heat enthalpies of the ultrafine composite fibers varied with the different types of binary fatty acid eutectics. TGA results indicated that the degradation of electrospun binary fatty acid eutectics/PET ultrafine composite fibers with representative mass ratio of 100/100 had two steps and corresponded respectively to the degradations of binary fatty acid eutectics and PET polymer chains; and the charred residue at 700 °C of the composite fibers was lower than that of the neat PET fibers. It could be envisioned that the electrospun binary fatty acid eutectics/PET composite fibers would be extensively used for latent heat storage in the field of building energy conservation.
[en] We have studied the sorption of hydrogen by 8 different carbon materials at pressures up to 11 MPa (1600 psi) and temperatures from -80oC to +500oC. Our samples include graphite flakes, Aldrich activated carbon, graphitized PYROGRAF vapor-grown carbon fibers (VGCF), etched PYROGRAF fibers, Showa-Denko VGCF, filaments grown from a FeNiCu alloy, and nanotubes from MER Corp. and Rice University. The results so far have been remarkably similar: very little hydrogen sorption. In fact, the sorption is so small that we must pay careful attention to calibration to get reliable answers. The largest sorption observed is less than 0.1 weight percent hydrogen at room temperature and 3.5 MPa. Furthermore, our efforts to activate these materials by reduction at high temperatures and pressures were also futile. These results cast serious doubts on any claims for large hydrogen sorption in carbon materials. (author)
[en] This paper presents an experimental investigation of the performance of water-phase change material (PCM) storage for use with conventional solar water heating systems. Paraffin wax contained in small cylindrical aluminum containers is used as the PCM. The containers are packed in a commercially available, cylindrical hot water storage tank on two levels. The PCM storage advantage is firstly demonstrated under controlled energy input experiments with the aid of an electrical heater on an isolated storage tank, with and without the PCM containers. It was found that the use of the suggested configuration can result in a 13-14 deg. C advantage in the stored hot water temperature over extended periods of time. The storage performance was also investigated when connected to flat plate collectors in a closed-loop system with conventional natural circulation. Over a test period of 24 h, the stored water temperature remained at least 30 deg. C higher than the ambient temperature. The use of short periods of forced circulation was found to have minimum effect on the performance of the system. Finally, the recovery effect and the storage performance of the PCM was analyzed under open-loop operation patterns, structured to simulate daily use patterns.
[en] Phase change material (PCM) can store large amount of thermal energy at phase change temperature. Determination of thermophysical properties of PCM plays an important role in estimation of energy stored or released in storage device. Properties of PCM are key factors for designing a latent heat thermal energy storage system. This paper deals with the study of effect of heating/cooling rate on thermophysical properties, especially on melting temperature and latent heat of fusion /solidification. Results indicate that latent heat of fusion has more dependence on heating/cooling rate than onset, peak and end temperature. (author)
[en] Carbon, as a technologically important material, is attracting much attention due to its application in electrochemical devices based on energy storage/conversion. Carbon has the unique characteristics that comes from the fact that the simple change in its surface or local bonding give rise to a new type of carbon with entirely different performance. Carbon materials have a remarkable range of electrical, optical, and electrochemical properties which primarily depends on the texture and surface chemistry. Among carious carbon materials Graphene is attracting much attention in energy storage devices especially supercapacitors where charge storage takes place by accumulation of ionic charges at the surface and pseudo capacitance