Research of ZnMn spinel electrode material for aqueous secondary batteries

ZnMn complex oxides have been prepared by the organic acid complex method. X-ray diffraction (XRD) analyses show that the major product is a ZnMn spinel phase. The capacity of the sample is above 200 mAh g⁻¹ on cycling in aqueous LiOH electrolyte, but deep-discharge has great influence on the cycling property of the sample. XRD analysis shows that Li⁺ ions are intercalated into and extracted from the ZnMn spinel lattice during the discharge and charge process.     

Simulation of the behaviour of a set of Cu2SCdS unit photocells

With the help of a general simulation program (the Spice II program from the University of California, Berkeley), adapted to photocell modelling, we studied the behaviour of a large solar photocell consisting of smaller Cu₂SCdS unit solar cells in parallel. In particular we examined a theoretical set of photocells identical with the best cell made in the laboratory, a set of 30 real photocells characterized individually and the effect of introducing low efficiency cells.We indicate the role of each parameter characterizing the photocells in order to improve the behaviour of photovoltaic panels of larger dimensions.     

Investigation of a carbon-supported quaternary PtRuSnW catalyst for direct methanol fuel cells

An investigation was carried out in the electro-oxidation of methanol on a carbon-supported quaternary PtRuSnW catalyst prepared by a liquid-phase reduction method. As derived by X-ray diffraction and X-ray photoelectron spectroscopy, the catalyst was composed of metallic Pt, microcrystalline RuO₂ and SnO₂ phases and amorphous WO₃/WO₂ species. The electrochemical analysis was carried out in half-cell containing sulfuric acid electrolyte as well as in a liquid methanol-fed solid polymer electrolyte single-cell. The activity of catalyst in the half-cell varied as a function of the methanol concentration, it increased with CH₃OH molarity in the activation-controlled region and showed a maximum in 2 M CH₃OH at high currents. IR-free polarization curves showed that the activity of the quaternary catalyst was superior to Pt metal/C samples having the same Pt amount. The presence of semi-insulating metal oxides such as RuO₂, SnO₂ and WO₃ on the electrode surface exhibited a significant uncompensated resistance. The single-cell performance was lower than that predicted by the half-cell experiments mainly due to the methanol cross-over through the Nafion membrane.     

Simulation of a supersonic hydrogen–air autoignition-stabilized flame using reduced chemistry

A three-step mechanism for H₂-air combustion (Boivin et al., Proc. Comb. Inst. 33 (2010)) was recently designed to reproduce both autoignition and flame propagation, essential in lifted flame stabilization. To study the implications of the use of this reduced chemistry in the context of a turbulent flame simulation, this mechanism has been implemented in a compressible explicit code and applied to the simulation of a supersonic lifted co-flowing hydrogen–air flame. Results are compared with experimental measurements (Cheng et al., C&F (1994)) and simulations using detailed chemistry, showing that the reduced chemistry is very accurate. A new explicit diagnostic to readily identify autoignition regions in the post-processing of a turbulent hydrogen flame simulation is also proposed, based on variables introduced in the development of the reduced chemical mechanism.     

Elaboration and electrochemical characterization of Mg–Ni hydrogen storage alloy electrodes for Ni/MH batteries

Mg–Ni hydrogen storage alloy electrodes with composition of Mg–33, 50, 67 Ni at. % in amorphous phase were prepared by means of mechanical alloying (MA) process using a planetary ball mill. The electrochemical hydrogen storage characteristics and mechanisms of these electrodes were investigated by electrochemical measurements, X–ray diffraction (XRD) and scanning electron microscope (SEM) analyses. The relationship between alloy composition and electrochemical properties was evaluated. In addition, optimum milling time and composition of Mg–Ni hydrogen storage alloy with acceptable electrochemical performance were determined. XRD results show that the alloys exhibit dominatingly amorphous structures after milling of 20 h. The electrochemical measurements revealed that the discharge capacity of Mg₃₃Ni₆₇ and Mg₆₇Ni₃₃ alloy electrodes reached a maximum when alloys were prepared after 20 h of milling time (260 and 381 mAhg^?1, respectively). The maximum discharge capacity of Mg₅₀Ni₅₀ alloy was observable after 40 h milling (525 mAhg^?1). It was also found that the cyclic stability of the alloys increased with increasing Ni content. Among these alloys, the amorphous Mg₅₀Ni₅₀ alloy presents the best overall electrochemical performance. In this paper, electrode process kinetics of Mg₅₀Ni₅₀ alloy electrode was also studied by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The impedance spectra of electrodes were measured at different depths of discharge (DODs). The observed spectra were fit well with the equivalent circuit model used in the paper. The electrochemical parameters calculated from electrochemical impedance were also compared. The electrochemical discharge and cyclic performance of 20, 40 and 60 h milled Mg₅₀Ni₅₀ alloy electrodes were demonstrated by the fitted charge transfer resistance and Warburg impedance obtained at various DODs. It was further observed that the controlling-step of the discharge process changed from a mixed rate-determining process at lower DODs to a mass-transfer controlled process at higher DODs. The fitted results demonstrated that charge–transfer resistance (R_ct) increased with DOD. The R_ct of 40 h milled Mg₅₀Ni₅₀ alloy (29.27 Ω) was lower than that of 20 h (41.89 Ω) and 60 h milled alloys (92.43 Ω) at fully discharge state.     

A novel parameter for evaluation on power performance of Ni–MH rechargeable batteries

In the work, two novel conceptions of “capacity quality” (CQ) and “capacity quality coefficient” (λ) were defined to evaluate cycling power capabilities of Ni–MH rechargeable batteries when considering the effect of the kinetic limitation. For convenient comparison, the capacity quality coefficient (λ) and the efficiency of charge/discharge (η) were in parallel applied to characterize cycling capabilities based on the data from BYD H-3/4AAA800 Ni–MH batteries at 1C–3.5C. The results show that there is an obvious difference between λ and η which served as evaluation indexes for rechargeable batteries, and that the secondary battery with good capacity quality also has a good cycling capability and rate capability, especially at high rate. The introduced capacity quality not only subtly covered kinetic information of the rechargeable batteries but also factually reflected stability of the electrode materials.     

Internal Flow Simulation of High-Performance Solid Rockets using a k-ω Turbulence Model

For technological reasons many high-performance solid rocket motors are made from segmented propellant grains with non-uniform port geometry. In this paper parametric studies have been carried out to examine the geometric dependence of transient flow features in solid rockets with non-uniform ports. Numerical computations have been carried out in an inert simulator of solid propellant rocket motor with the aid of a standard k-ωturbulence model. It was seen that the damping of the temperature fluctuation is faster in solid rocket with convergent port than with divergent port geometry. We inferred that the damping of the flow fluctuations using the port geometry is a meaningful objective for the suppression and control of the instability and/or pressure/thrust oscillations during the starting transient of solid rockets.     

Internal Flow Simulation of High-Performance Solid Rockets using a k-ω Turbulence Model

For technological reasons many high-performance solid rocket motors are made from segmented propellant grains with non-uniform port geometry. In this paper parametric studies have been carried out to examine the geometric dependence of transient flow features in solid rockets with non-uniform ports. Numerical computations have been carried out in an inert simulator of solid propellant rocket motor with the aid of a standard k-ω turbulence model. It was seen that the damping of the temperature fluctuation is faster in solid rocket with convergent port than with divergent port geometry. We inferred that the damping of the flow fluctuations using the port geometry is a meaningful objective for the suppression and control of the instability and/or pressure/thrust oscillations during the starting transient of solid rockets.     

Zn4Sb3(C7) powders as a potential anode material for lithium-ion batteries

The electrochemical properties of β-Zn₄Sb₃ and Zn₄Sb₃C₇ as new lithium-ion anode materials were investigated. The reversible capacities of the pure Zn₄Sb₃ alloy electrode and 100 h milled Zn₄Sb₃ in the first cycle reached 503 and 566 mA h/g, respectively, but the cycle stability of Zn₄Sb₃ whether milled or not were obviously bad. It was demonstrated that cycle stability of Zn₄Sb₃ could be largely improved by milling after mixing with graphite. It was shown that Zn₄Sb₃C₇ composite has a lithium-ion extraction capacity of 581 mA h/g at the first cycle and 402 mA h/g at 10th cycle.     

A simplified equivalent circuit model for simulation of Pb–acid batteries at load for energy storage application

Three main types of battery chemistries in consideration for vehicle applications are Pb–acid, nickel–metal hydride, and lithium-ion batteries. Lead–acid batteries are widely used in traditional automotive applications for many years. Higher voltage, high-rate discharge capability, good specific energy, lower temperature performance, lower thermal management requirement, and low-cost in both manufacturing and recycling are the advantages of the rechargeable battery. Disadvantages of the lead–acid battery are: weight concerns of lead metal (lower energy density and lower power density) and limited cycle-life (especially in deep-cycle duties). If two major disadvantages have been significantly changed to a proper state to compete with other battery chemistries, the Pb–acid battery is still a good candidate in considering of cost/performance ratio. The lead–acid battery is always a good power source for fast starting of cold vehicles, for recharging from either a stop-start braking system, or for a charge from the engine itself, which consumes battery energy or stores electricity back into chemical energy. The main reasons for reexamining this battery chemistry are cost-savings and life-cycling considerations upon advances in electrode structure design and enhancement of capacitance behavior inside the battery pack. Several Pb–acid batteries were evaluated and tested through a unique method, i.e., the electrochemical impedance method at different loads, in order to characterize and further understand the improved electrode processes and mechanisms in performance enhancement. The impedance data at loads were collected from these lead–acid batteries at load for further analysis. Battery electrode behaviors are evaluated through impedance data simulation using a proper equivalent circuit model. A defective battery and a failed Pb–acid battery were used in non-destructive analysis. The recent Pb–acid battery advancement in structures and designs and its potential application are also discussed for power reserve in energy-efficient vehicles and sustainable electricity storage.     

Simulation of Thermocapillary Convection in a Two—Layer Immiscible Fluid System using a Boundary Element Method

A boundary element method for simulating thermocapillary convection in a two-layer immiscible fluid systemwith flat and free interface has been developed.The divergence theorem is applied to the non-linear convectivevolume integral of the boundary element formulation with the pressure penalty function.Consequently,velocitygradients are eliminated and the complete formulation is written in terms of velocity.This avoids the difficultyof convective discretizations and provides considerable reductions in storage and computational requirementswhile improving accuracy.In this paper,we give the influence of different parameters(Marangoni number,Reynolds number)on thermocapillary convection in cavity with two-layer immiscible fluids.As shown by thenumerical results,when the physical parameters between liquid encapsulant and melt are chosen appropriately,the detrimental flow in the bottom melt layer can be greatly suppressed.The influence of the free interface onthermocapillary convection is also shown.     

Properties of mechanically alloyed Mg–Ni–Ti ternary hydrogen storage alloys for Ni-MH batteries

MgNiTi_x, Mg_1−xTi_xNi and MgNi_1−xTi_x (with x varying from 0 to 0.5) alloys have been prepared by high energy ball milling and tested as hydrogen storage electrodes. The initial discharge capacities of the Mg–Ni–Ti ternary alloys are inferior to the MgNi electrode capacity. However, an exception is observed with MgNi_0.95Ti_0.05, which has an initial discharge capacity of 575 mAh/g compared to 522 mAh/g for the MgNi electrode. The Mg–Ni-Ti ternary alloys show improved cycle life compared to Mg–Ni binary alloys with the same Mg/Ni atomic ratio. The best cycle life is observed with Mg_0.5Ti_0.5Ni electrode which retains 75% of initial capacity after 10 cycles in comparison to 39% for MgNi electrodes, in addition to improved high-rate dischargeability (HRD). According to the XPS analysis, the cycle life improvement of the Mg_0.5Ti_0.5Ni electrode can be related to the formation of TiO₂ which limits Mg(OH)₂ formation. The anodic polarization curve of Mg_0.5Ti_0.5Ni electrode shows that the current related to the active/passive transition is much less important and that the passive region is more extended than for the MgNi electrode but the corrosion of the electrode is still significant. This suggests that the cycle life improvement would be also associated with a decrease of the particle pulverization upon cycling.     

Influence of Pd addition on the electrochemical performance of Mg–Ni–Ti–Al-based metal hydride for Ni–MH batteries

Amorphous Mg_0.9Ti_0.1NiAl_0.05 and Mg_0.9Ti_0.1NiAl_0.05Pd_0.1 alloys were prepared by high energy ball milling and evaluated as metal hydride electrodes for Ni–MH batteries. The Mg_0.9Ti_0.1NiAl_0.05Pd_0.1 alloy showed a much higher cycle life with a capacity retention of 72% after 100 cycles (C_100th = 288 mAh g⁻¹) compared to 26% for the Pd-free alloy (C_100th = 117 mAh g⁻¹). This was mainly attributed to the improvement of the alloy oxidation resistance in KOH electrolyte with Pd addition, as confirmed by cyclic voltammetry experiments and X-ray diffraction analyses on cycled electrodes. In addition, in situ acoustic emission (AE) measurements revealed that the energy of the AE signals related to the particle cracking is lower for the Mg_0.9Ti_0.1NiAl_0.05Pd_0.1 electrode, suggesting that the cracks are smaller in size than with the Pd-free alloy. The Mg_0.9Ti_0.1NiAl_0.05Pd_0.1 electrode also displayed a higher discharge rate capability than the Mg_0.9Ti_0.1NiAl_0.05 electrode. On the basis of their respective electrochemical pressure–composition isotherm, it was shown that the presence of Pd in the alloy decreases the thermodynamic stability of the metal hydride. Through a comparative analysis of discharge polarization curves, it was also shown that Pd addition decreases substantially the H-diffusion resistance in the alloy whereas its positive effect on the charge-transfer resistance is limited.     

Comparison of a Reaction Front Model and a Finite Difference Model for the Simulation of Solid Absorption Process

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Optimization of synthesis parameters for catalytic performance of Ni–B catalysts using response surface methodology

Hydrogen production through hydrolysis of sodium borohydride (NaBH₄) by using metal catalysts is promising for fuel cell applications. Nickel (Ni) and its alloys are favorable due to their high catalytic activity, relatively low cost and availability. In present study, the effects of temperature, pH, reduction rate and reducing agent concentration, which significantly affect the catalyst performance, were investigated using the response surface methodology (RSM). A mathematical model was derived according to results which were obtained from four-level orthogonal Taguchi L16 (4⁴) experimental design used for the optimization of multiple parameters in the process. From the RSM analyses, that compatible with the predicted experimental results, maximum hydrogen generation rate (HGR) 49.81 L min^?1 g_cat^?1 was obtained temperature of 278.12 K, pH of 5.52, reducing agent concentration of 85.96 NaBH₄.water^?1 and reduction rate of 6.82 mL min^?1. Analysis of variance reveals that both pH and rate of reduction have significant effect than the temperature on the HGR.     

A kinetic model for air-steam reforming of bio-oil over Rh–Ni/γ-Al2O3 catalyst: Acetol as a model compound

A new kinetic model is proposed for catalytic reforming of acetol to synthesis gas over a Rh–Ni/γ-Al₂O₃ catalyst. Acetol is one of the most important bio-oil model compounds formed under reactive flash volatilization reaction conditions. The model was implemented in the Aspen Plus simulation package and used to predict the product gas composition at different reaction temperatures and steam and oxygen ratios. The contributions of the reactions both in the reactor freeboard and the catalytic bed were assessed using CSTR and PFR reactor models, respectively. The reaction scheme included decomposition, steam reforming, and water-gas shift reactions. The results from the model predicted the product distribution within an acceptable degree of tolerance. This study confirms that thermal decomposition and partial oxidation of acetol precede the catalytic reactions involving steam. The effects of temperature, oxygen concentration in the feed, the volume of the freeboard, and the catalyst bed height can all be evaluated with this new kinetic model. This work suggests that bio-oil decomposed into different fractions of molecules like acetol can be successfully modelled by a series of decomposition reactions followed by partial oxidation and catalytic steam conversion. The heat transfer within the catalyst bed is found to be critical for achieving a good match with the experimental results.     

Charge–discharge behaviour of VRLA batteries: model calibration and application for state estimation and failure detection

The dynamic behaviour of batteries can be predicted using theoretical cell model for basic processes. In this paper, this model is calibrated for two types of valve regulated lead acid (VRLA) batteries, and is applied for viewing unobservable processes in battery by observable processes. It is shown that unobservable parameters like overpotential, reaction rate, porosity, acid concentration, and other parameters of electrode can be evaluated by total current, terminal voltage and temperature of surrounding atmosphere of battery. The calibrated model is applied to distinguish between outwardly equal batteries with different backup time and cut-off time. It is shown that difference in morphology of electrodes, thickness of electrodes and quantity of electrolyte in separator are the main distinguishing parameters between batteries. These parameters can be tested online by current–voltage measurements using fast calculation method proposed in this paper.     

Chemical,structural and optical characterization of NiP chemical conversion coatings for photothermal absorption of solar energy

The solar optical properties of a material can be modified by creating a rough surface. I describe the investigation of a nickel-phosphorus thin film produced by chemical deposition. Its absorbing properties are enhanced for wavelengths within the visible and near-infrared spectral regions by modification of its surface state during chemical etching. The prepared layers show, by themselves, noteworthy structural properties that influence the chemical etching; because of them, it is possible to obtain highly solar selective optical properties under some conditions.Initially, the nickel-phosphorus layer presents a rough surface resulting from the presence of numerous nodules. When the sample is etched in a nitric acid solution, its absorptance increases during the etching by the formation of numerous holes between and on the nodules. At the same time, the emittance of the sample increases slightly.The as-prepared material is characterized by its physical and chemical properties, which influence the effect of the chemical etching. This study also represents a way to optimize the deposition process. The effect of thermal treatment on these properties has been studied. The coating can withstand temperatures up to 300°C in air with only minor property variation caused by oxidation.Finally, the use of a statistical model of roughness shows that it is possible to correctly simulate the optical properties of the sample. I propose an interpretation of the attack phenomenon by taking into account kinetics with two reaction rates that depend on the microgranular structure of the as-prepared nickel-phosphorus layer.     

Desorption of hydrogen from Ti–Zr–Ni hydrides using a mass spectrometer

We have performed thermogravimetry (TG) and mass-spectrometry measurements of hydrogen desorbed from fully and partially hydrided ternary Ti–Zr–Ni amorphous, quasicrystalline and crystalline alloys, with four different initial compositions, where the Ti/Zr ratio ranged from 1 to 2.4. The icosahedral, quasicrystalline Ti–Zr–Ni samples were obtained using the melt-spinning technique, and with subsequent annealing of these ribbons at 700 °C for 2 h in vacuum we were able to obtain a mixture of crystalline C14 Laves and α/β solid-solution phases. In addition, using subsequent mechanical alloying we produced amorphous powders of Ti–Zr–Ni from the as-spun ribbons. These various samples were then hydrided and analyzed by TG and mass spectrometry. The TG measurements provided us with the mass% of desorbed hydrogen, whereas the mass-spectrometry revealed information about the hydrogen desorption temperatures in the material. Despite the fact that the amorphous and icosahedral samples undergo some crystallization during the desorption measurements, the resulting mass spectra were different and were closely related to the alloy's structure. In contrast, the shapes of mass spectra were less affected by the composition, the total amount of desorbed hydrogen and the loading pressure.     

Renewable and low carbon hydrogen for California – Modeling the long term evolution of fuel infrastructure using a quasi-spatial TIMES model

This paper describes the development and use of a hydrogen infrastructure optimization model using the TIMES modeling framework, H2TIMES, to analyze hydrogen development in California to 2050. H2TIMES is a quasi-spatial model that develops the infrastructure to supply hydrogen fuel in order to meet demand in eight separate California regions in a least cost manner subject to various resource, technology and policy constraints. A Base case, with a suite of hydrogen policies now in effect or proposed in California (renewable hydrogen mandate, fuel carbon intensity constraint and prohibition on using coal without carbon capture and sequestration) leads to hydrogen fuel with significant reductions in carbon intensity (85% below gasoline on an efficiency-adjusted basis, 75% below on a raw energy basis) and competitive hydrogen costs (∼$4.00/kg in 2025–2050). A number of sensitivity scenarios investigate the cost and emissions implications of altering policy constraints, technology and resource availability, and modeling decisions. The availability of biomass for hydrogen production and carbon capture and sequestration are two critical factors for achieving low-cost and low-emission hydrogen.