Modeling the discharge behavior of a lithium-sulfur battery

In lithium-sulfur (Li-S) batteries, the discharge performance depends greatly on a number of cell design parameters because of the complex reaction mechanisms in the cathode. Electrolyte-to-sulfur (E/S) ratio and carbon-to-sulfur (C/S) ratio in the cell are key examples of these critical design factors that define the Li-S battery performance. Here, a 1-D electrochemical model is reported to calculate the dependence of the discharge behavior of a Li-S battery on the E/S and C/S ratios. Proposed model describes the complex kinetics through two electrochemical and two dissolution/precipitation reactions. Concentration variations in the cathode are also taken into account in the model. Characteristic aspects of the discharge profile of a Li-S battery -the two distinct voltage plateaus and the voltage dip in between- are captured in the predicted voltage curve. Similar trends on the discharge performance of the Li-S cell with varying E/S and C/S ratios are projected; both voltage and discharge capacity of the Li-S battery are improved substantially with increasing C/S or E/S ratio up to a certain point, whereas, the dependence of the discharge performance on these factors is less substantial at higher ratios. This model offers a mechanistic interpretation of the influence of cell design on the Li-S battery performance.     

Modeling the effect of key cathode design parameters on the electrochemical performance of a lithium‐sulfur battery

A 1D model is developed for the Li‐S cell to predict the effect of critical cathode design parameters—carbon‐to‐sulfur (C/S) and electrolyte‐to‐sulfur (E/S) ratios in the cathode—on the electrochemical performance. Cell voltage at 60% depth of discharge corresponding to the lower voltage plateau is used as a metric for calculating the cell performance. The cathode kinetics in the lower voltage plateau is defined with a single electrochemical reaction; thus, the model has a single apparent kinetic model parameter, the cathode exchange current density (i_0,pe). The model predicts that cell voltage increases considerably with increasing carbon content until a C/S ratio of 1 is attained, whereas the enhancement in the cell voltage at higher ratios is less obvious. The model can capture the effect of the C/S ratio on the cathode kinetics by expressing the electrochemically active area in the cathode in carbon volume fraction; the C/S ratio in the cathode does not affect i_0,pe in the model. On the other hand, the electrolyte amount has a significant impact on the kinetic model parameter such that increasing electrolyte amount improves the cell voltage as a result of increasing i_0,pe. Therefore, in the model, i_0,pe needs to be defined as a function of the electrolyte volume fraction, which is known to have a crucial effect on reaction kinetics.     

Biomimicking,metal-chelating and surface-imprinted polymers for the degradation of pesticides

Molecularly imprinted polymer beads (PIBs) and non-imprinted (control) polymer beads (NIBs) have been prepared from methacryloylhistidine-Co²⁺, -Ni²⁺, and -Zn²⁺ monomers and applied as catalyst in the hydrolysis of paraoxon which is an organophosphate ester and used as a pesticide. The PIBs were prepared by a molecular surface imprinting technique. The catalytic performance of these polymers having Co²⁺, Ni²⁺ and Zn²⁺ ions in their catalytic active centers was evaluated according to the enzyme kinetic model of Michaelis–Menten and their activities were compared to each other. PIBs always showed higher catalytic activities than NIBs analogues. In addition, the imprinted polymers of methacryloylhistidine-Co²⁺, -Ni²⁺, or -Zn²⁺ complexes provided hydrolysis rate enhancements by a factor of 356, 241, and 95, respectively, compared to the rate in non-catalyzed media that contains only buffer.     

An improved lumped element nonlinear circuit model for a circular CMUT cell

This paper describes a correction and an extension in the previously published large signal equivalent circuit model for a circular capacitive micromachined ultrasonic transducer (CMUT) cell. The force model is rederived so that the energy and power is preserved in the equivalent circuit model. The model is able to predict the entire behavior of CMUT until the membrane touches the substrate. Many intrinsic properties of the CMUT cell, such as the collapse condition, collapse voltage, the voltage-displacement interrelation and the force equilibrium before and after collapse voltage in the presence of external static force, are obtained as a direct consequence of the model. The small signal equivalent circuit for any bias condition is obtained from the large signal model. The model can be implemented in circuit simulation tools and model predictions are in excellent agreement with finite element method simulations.     

Pure Bending Fatigue Crack Propagation in Deep-Drawn Steel Cord Filaments

Metal Science and Heat Treatment - Wires with diameter 0.25 mm from a carbon steel with 0.70 and 0.90% C for tire cords are studied. The effect of the treatment modes, of the carbon content and of...     

Kinetic analysis of photosynthetic growth,hydrogen production and dual substrate utilization by Rhodobacter capsulatus

Rhodobacter capsulatus is purple non-sulfur (PNS) bacterium which can produce hydrogen and CO₂ by utilizing volatile organic acids in presence of light under anaerobic conditions. Photofermentation by PNS bacteria is strongly affected by temperature and light intensity. In the present study we present the kinetic analysis of growth, hydrogen production, and dual consumption of acetic acid and lactic acid at different temperatures (20, 30 and 38 °C) and light intensities (1500, 2000, 3000, 4000 and 5000 lux). The cell growth data fitted well to the logistic model and the cumulative hydrogen production data fitted well to the Modified Gompertz Model. The model parameters were affected by temperature and light intensity. Lactic acid was found to be consumed by first order kinetics. Rate of consumption of acetic acid was zero order until most of the lactic acid was consumed, and then it shifted to first order. The results revealed that the optimum light intensities for maximum hydrogen production were 5000 lux for 20 °C and 3000 lux for 30 °C and 38 °C.     

Reduction of Nickel Oxide with Ethanol

This work aims to investigate the reduction behavior of NiO powder by ethanol vapor at 600–1100 K for the reaction times up to 60 min. The products were characterized by mass measurement, x-ray diffraction, and scanning electron microscopy techniques. The reaction of NiO with ethanol essentially consisted of oxide reduction followed by C deposition. At 600 K, significant oxide reduction was attained. Full oxide reduction was observed at 650–1100 K within 10–15 min. At this temperature range, the reduction reaction was controlled by external mass transfer of gaseous species. At the lower temperature range 600–650 K, the reduction rate was sensitive to the temperature change and influenced by the total gas flow rate to a lesser degree. The temperature dependence of C uptake was explained by Boudouard reaction. The results of this study demonstrate that NiO can be completely reduced to Ni by ethanol as predicted by the thermodynamic analysis.     

Facile two-step preparation of polystyrene/anatase TiO2 core/shell colloidal particles and their potential use as an oxidation photocatalyst

Titania and materials containing titania have received considerable attention due to their technological importance in many areas. In this study, anatase crystalline titania (TiO₂) coated polystyrene (PS) colloidal particles were successfully prepared in two easy steps. First, a one pot synthesis of the colloidal particles was produced via an emulsifier-free emulsion copolymerization of styrene (S) and 2-(dimethylamino)ethyl methacrylate (DMA) at pH 4.0. In the second step, the synthesized particles were coated by titania using a sol–gel process in-situ hydrolysis and a condensation reaction of titanium(IV) isopropoxide in an acidic aqueous solution. In this way, anatase crystalline titania, rather than the usual amorphous form, was obtained as a shell on the PS colloidal particles. Both the PS colloidal particles and the polystyrene/anatase titania (PS/TiO₂) core/shell colloidal particles had monodisperse morphology and were characterized using SEM, Zetasizer, FTIR, XRD and TGA techniques or measurements. In addition, the photocatalytic activity of the PS/TiO₂ core/shell particles was tested for the first time in an oxidation reaction, in the oxidation of 4-methoxybenzyl alcohol (MBA) with O₂ in water. Much higher selectivities of the target product, p-anisaldehyde (AA), were obtained with the PS/TiO₂ core/shell particles than with a commercial anatase crystalline TiO₂.