Tin‐based compounds have received much attention as anode materials for lithium/sodium ion batteries owing to their high theoretical capacity. However, the huge volume change usually leads to the pulverization of electrode, giving rise to a poor cycle performance, which have severely hampered their practical application. Herein, highly durable yolk–shell SnSe2 nanospheres (SnSe2@SeC) are prepared by a multistep templating method, with an in situ gas‐phase selenization of the SnO2@C hollow nanospheres. During this process, Se can be doped into the carbon shell with a tunable amount and form SeC bonds. Density functional theory calculation results reveal that the SeC bonding can enhance the charge transfer properties as well as the binding interaction between the SnSe2 core and the carbon shell, favoring an improved rate performance and a superior cyclability. As expected, the sample delivers reversible capacities of 441 and 406 mAh g−1 after 2000 cycles at 2 and 5 A g−1, respectively, as the anode material for a sodium‐ion battery. Such performances are significantly better than the control sample without the SeC bonding and also other metal selenide‐based anodes, evidently showing the advantage of Se doping in the carbon shell.
Because of its high theoretical capacity, MnSe has been identified as a promising candidate as the anode material for sodiumion batteries. However, its fast capacity deterioration due to the huge volume change during the intercalation/deintercalation of sodium ions severely hinders its practical application. Moreover, the sodium storage mechanism of MnSe is still under discussion and requires in-depth investigations. Herein, the unique thorn ball-like α-MnSe/C nanospheres have been prepared using manganese-containing metal organic framework (Mn-MOF) as a precursor followed by in situ gas-phase selenization at an elevated temperature. When serving as the anode material for sodium-ion battery, the as-prepared α-MnSe/C exhibits enhanced sodium storage capabilities of 416 and 405 mAh g −1 at 0.2 and 0.5 A g −1 after 100 cycles, respectively. It also shows a superior capacity retention of 275 mA h g −1 at 10 A g −1 after 2000 cycles, and a rate performance of 279 mA h g −1 at 20 A g −1 . Such sodium storage properties could be attributed to the unique structure offering a highly efficient Na + diffusion kinetics with a diffusion coefficient between 1 × 10 -11 and 3 × 10 -10 cm 2 s −1 . The density functional theory calculation indicates that the fast Na + diffusion mainly takes place on the (100) plane of MnSe along a V-shaped path because of a relatively low diffusion energy barrier of 0.15 eV.
The output power efficiency of the fuel cell system mainly depends on the required current, stack temperature, air excess ratio, hydrogen excess ratio, and inlet air humidity. Therefore, the operating conditions should be optimized to get maximum output power efficiency. In this paper, a dynamic model for the fuel cell stack was developed, which is comprised of a mass flow model, a gas diffusion layer model, a membrane hydration, and a stack voltage model. Experiments have been performed to calibrate the dynamic Polymer Electrolyte Membrane Fuel Cell (PEMFC) stack model. To achieve the maximum output power and the minimum use of hydrogen in a certain power condition, optimization was carried out using Response Surface Methodology (RSM) based on the proposed PEMFC stack model. Using the developed method, optimal operating conditions can be effectively selected in order to obtain minimum hydrogen consumption.
A new method using thermal analysis database and optimization technique has been developed to substitute the original method what was based on trial and error. First, an original vacuum furnace was manufactured according to experiences. Modified baseline vacuum furnace which can be used in high temperature was produced from the original one by using experimental data and experiences. The results in 2 different conditions of nearly vacuum and argon ambient gas were investigated in order to define the worse but necessary condition between them. By comparing the analysis results with experimental results, the unknown thermal conductivity of insulator in high temperature has been found out. The calculated thermal conductivity of insulator has been applied to the process of thermal analysis database constructing under the condition of argon ambient gas which is the worse but necessary condition. In order to check the accuracy of constructed thermal analysis database, the interpolated results using constructed thermal analysis database have been compared with computational results. Finally, optimization study has been carried out to design an energy efficient, high temperature vacuum furnace which can fully satisfy user's design requirements by using the new method. Feasible optimal design has been obtained as a final product. With negligible computational cost, a high temperature vacuum furnace which has 31.9% reduction in the total heat was designed by using the new developed method.
NOMENCLATUREC P =specific heat of ABS sheet, J/kg.K H=thickness of total sheets, m h=heat transfer coefficient, W/m 2 .K k=thermal conductivity of ABS, 0.174 W/m.K k eq =thermal conductance, W/m.K L=half of the total thickness, m N=total number of sheets q in =inputted heat flux, W/m 2 R c =contact resistance, m․ K/W T a =average temperature, K T c =center temperature, K T s =surface temperature, K T 0 =initial temperature, K T ∞ =environmental temperature, K t=time, s t h =heating time, s ρ=density of ABS sheet, 1050 kg m -3 α=thermal diffusivity of ABS, m 2 /s η n =eigen valueObtaining a uniform thickness of the final product using thermoforming is difficult, and the thickness distribution depends strongly on the distribution of the sheet temperature. In this paper, the time-dependent temperature distribution of the total sheets in the storing stage was studied because the temperature after the storing stage is the initial temperature of the heating process. An analytic solution for simulating the storing stage was derived. Using the solved analytic solution, the time-dependent temperature distribution of the total sheets was found out under the condition of assuming that the temperature-dependent specific heat of the ABS sheets was a certain constant value. Finally, the control method for a successful thermoforming using the heater power or heating time was researched in order to improve the quality of the final products. The results show that the satisfied temperature distribution can be obtained by adjusting the heater power or heating time. The method for analysis in this study will be used to improve the quality of the final products.
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