Electrical conductivity in Li–Si–P–O–N oxynitride thin-films

Nitrogen-incorporated lithium silicophosphate (LiSiPON) thin-film electrolytes, which contain two glass-forming elements, are fabricated by sputtering from a (1−x)Li₃PO₄·xLi₂SiO₃ target in a nitrogen reactive plasma. The results of impedance measurements show that the activation energy for conduction decreases as the Si content increases, which leads to an increase in the ionic conductivity of the films. It is suggested that these improvements in the electrical properties of the films are due to the combined effect of the mixed former and nitrogen incorporation. It appears that the decomposition potential of the electrolyte film in contact with Pt is about 5.5 V.     

Electrochemical behavior of Mg–Li,Mg–Li–Al and Mg–Li–Al–Ce in sodium chloride solution

Mg–Li, Mg–Li–Al and Mg–Li–Al–Ce alloys were prepared and their electrochemical behavior in 0.7 M NaCl solutions was investigated by means of potentiodynamic polarization, potentiostatic current–time and electrochemical impedance spectroscopy measurements as well as by scanning electron microscopy examination. The effect of gallium oxide as an electrolyte additive on the potentiostatic discharge performance of these magnesium alloys was studied. The discharge activities and utilization efficiencies of these alloys increase in the order: Mg–Li < Mg–Li–Al < Mg–Li–Al–Ce, both in the absence and presence of Ga₂O₃. These alloys are more active than commercial magnesium alloy AZ31. The addition of Ga₂O₃ into NaCl electrolyte solution improved the discharging currents of the alloys by more than 4%, and enhanced the utilization efficiencies of the alloys by more than 6%. It also shortened the transition time for the discharge current to reach to a steady value. Electrochemical impedance spectroscopy measurements showed that the polarization resistance of the alloys decreases in the following order: Mg–Li > Mg–Li–Al > Mg–Li–Al–Ce. Mg–Li–Al–Ce exhibited the best performance in term of activity, utilization efficiency and activation time.     

Microstructure and electrochemical properties of Zr–Ti–V–Ni–Mn–LM alloys for application in Ni–MH secondary battery

A series of multi-component Zr_1−xTi_xV_0.4Ni_1.2Mn_0.4LM_y (x=0.3, 0.4; y=0.0,0.02,0.05,0.1,0.2,0.3, LM; lantanum-rich-mischmetal) alloys are prepared and their crystal structure and P–C–T curves are analyzed. The alloys have been modified by adding LM and their gaseous and electrochemical hydrogenation properties are studied to find out the effect of LM elements. Also, the second phase and initial activation performance are investigated. The Zr_1−xTi_xV_0.4Ni_1.2Mn_0.4LM_y (x=0.3,0.4; y=0.0,0.02,0.05,0.1,0.2,0.3) alloys have C14 Laves phase hexagonal structure, so the volume expansion ratio of lattice parameters with LM has increased. As the amount of LM in alloy has increased, correspondingly the second phase is also increased. The second phase is LM, Ti and V-rich. The second phase improve the activation of La-rich misch-metal, and also the concentration of elements Ti, V〉LM〉 matrix in alloys.The addition of LM in Zr_1−xTi_xV_0.4Ni_1.2Mn_0.4LM_y (x=0.3, 0.4) alloys have increased the activation rate and hydrogen storage capacity significantly, but the plateau pressure and the discharge capacity have been decreased due to the formation of second phase. For more Zr in electrode alloys, the activation of rate becomes slow.     

Preparation and performance of novel Li–Ti–Si–P–O–N thin-film electrolyte for thin-film lithium batteries

Novel Li–Ti–Si–P–O–N thin-film electrolyte was successfully fabricated by RF magnetron sputtering from a Li–Ti–Si–P–O target in N₂ atmosphere at various temperatures. XRD, SEM, EDX, XPS, and EIS were employed to characterize their structure, morphology, composition and electrochemical performances. The films were smooth, dense, uniform, without cracks or voids, and possessed an amorphous structure. Their room temperature lithium-ion conductivities were measured to be from 3.6 × 10⁻⁷ S cm⁻¹ to 9.2 × 10⁻⁶ S cm⁻¹, and the temperature dependence of the ionic conductivities fits the Arrhenius relation. This kind of electrolyte possessed good properties is a promising candidate material for solid-state thin-film lithium batteries.     

Electrochemical hydrogen storage performance of Mg–Ti–Zr–Ni alloys

Mg_1.5Ti_0.5−xZr_xNi (x = 0, 0.1, 0.2, 0.3, 0.4), Mg_1.5Ti_0.3Zr_0.1Pd_0.1Ni and Mg_1.5Ti_0.3Zr_0.1Co_0.1Ni alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. X-ray diffraction studies showed that all the replacement elements (Ti, Zr, Pd and Co) perfectly dissolved in the amorphous phase and Zr facilitated the amorphization of the alloys. When the Zr/Ti ratio was kept at 1/4 (Mg_1.5Ti_0.4Zr_0.1Ni alloy), the initial discharge capacity of the alloy increased slightly at all the ball milling durations. The further increase in the Zr/Ti ratio resulted in reduction in the initial discharge capacity of the alloys. The presence of Zr in the Ti-including Mg-based alloys improved the cyclic stability of the alloys. This action of Zr was attributed to the less stable and more porous characteristics of the barrier hydroxide layer in the presence of Zr due to the selective dissolution of the disseminated Zr-oxides throughout the hydroxide layer on the alloy surface. Unlike Co, the addition of Pd into the Mg–Ti–Zr–Ni type alloy improved the alloy performance significantly. The positive contribution of Pd was assumed to arise from the facilitated hydrogen diffusion on the electrode surface in the presence of Pd. As the Zr/Ti atomic ratio increased, the charge transfer resistance of the alloy decreased at all the depths of discharges. Co and Pd were observed to increase the charge transfer resistance of the Mg–Ti–Zr–Ni alloys slightly.     

Hydrogen absorption characteristics of mechanically alloyed Ti–Zr–Ni and Ti–V–Ni powders

A first investigation into the production of amorphous and nanostructured Ti-based alloys with nominal compositions Ti_41.5Zr_41.5Ni₁₇, Ti₆₁Zr₂₂Ni₁₇, Ti_41.5V_41.5Ni₁₇ and Ti₆₁V₂₂Ni₁₇ by mechanical alloying (MA) technique is presented. This technique was adopted to produce alloys' powders with high fresh surface area that were active for hydrogen storage. Hydrogen absorption characteristics and structure changes in the alloys after hydrogenation were investigated. Gas phase hydrogenation of the Ti–Zr–Ni alloys, at 573 K and an initial hydrogen pressure of 2 MPa, exhibited good hydriding properties and started at a maximal rate without induction period with a hydrogenation capacity up to 1.2 wt%. However, hydriding of Ti–V–Ni alloys at the same conditions exhibited slower rates. The Ti₆₁V₂₂Ni₁₇ composition showed high hydrogen absorption capacity of 1.8 wt% and exceeded 4 wt% at 345 K. In addition, the Ti–V–Ni alloys showed structure stability after hydrogenation and retained the amorphous structure.     

Alkaline composite PEO–PVA–glass-fibre-mat polymer electrolyte for Zn–air battery

An alkaline composite PEO–PVA–glass-fibre-mat polymer electrolyte with high ionic conductivity (10⁻² S cm⁻¹) at room temperature has been prepared and applied to solid-state primary Zn–air batteries. The electrolyte shows excellent mechanical strength. The electrochemical characteristics of the batteries were experimentally investigated by means of ac impedance spectroscopy and galvanostatic discharge. The results indicate that the PEO–PVA–glass-fibre-mat composite polymer electrolyte is a promising candidate for application in alkaline primary Zn–air batteries.     

Crystallographic and electrochemical characteristics of melt-spun Ti–Zr–Ni–Y alloys

Ti₄₅Zr₃₀Ni₂₅Y_x (x = 1, 3, 5 and 7) alloys were prepared by melt-spinning at wheel velocity of 20 m s⁻¹. The effect of additive Y on phase structure and electrochemical performance of melt-spun alloys was investigated. Ti₄₅Zr₃₀Ni₂₅Y_x melt-spun alloys were composed of I-phase and amorphous phase. The amorphous phase increased with increasing x value, indicating amorphous forming ability improved with increasing Y content. The maximum discharge capacity and high-rate dischargeability decreased with increasing x value, which may be ascribed to the decrease of nickel content. Cycling stability first increased with increasing x from 1 to 3, and then decreased when x increased to 7, which was resulted from the combined effect of the decrease of nickel content and the increase of amorphous phase.     

Synthesis and electrochemical properties of layered Li–Ni–Mn–O compounds

An attempt to prepare solid solutions in the system of LiNiO₂, LiMnO₂ and Li₂MnO₃ was performed by heating metal acetates. The solid solutions between end members LiNiO₂ and Li₂MnO₃ can be successfully prepared in the overall compositional ranges. Both the structure and capacity were compared based on Rietveld analysis and electrochemical investigation on solid solutions between LiNiO₂ and Li₂MnO₃. The result showed that the cationic disorder as well as capacity was closely related to the ratio of Li, Mn and Ni in formula. The investigation of chronopotentiogram and ex situ XRD on the solid solutions indicated that the complex phase transitions in LiNiO₂ during delithiation were strongly suppressed with low Mn content (Mn/(Mn+Ni) ratio was 0.1 or 0.2) and completely suppressed with the ratio more than 0.5.     

Crystallographic and electrochemical characteristics of Ti–Zr–Ni–Pd quasicrystalline alloys

Ti₄₅Zr₃₅Ni_20−xPd_x (x = 0, 1, 3, 5 and 7, at%) alloys were prepared by melt-spinning. The phase structure and electrochemical hydrogen storage performances of melt-spun alloys were investigated. The melt-spun alloys were icosahedral quasicrystalline phase, and the quasi-lattice constant increased with increasing x value. The maximum discharge capacity of alloy electrodes increased from 79 mAh/g (x = 0) to 148 mAh/g (x = 7). High-rate dischargeability and cycling stability were also enhanced with the increase of Pd content. The improvement in the electrochemical hydrogen storage characteristics may be ascribed to better electrochemical activity and oxidation resistance of Pd than that of Ni.     

Polymer Ni–MH battery based on PEO–PVA–KOH polymer electrolyte

An alkaline polymer electrolyte film has been prepared by a solvent-casting method. Poly(vinyl alcohol), PVA is added to improve the ionic conductivity of the electrolyte. The ionic conductivity increases from 10⁻⁷ to 10⁻² S cm⁻¹ at room temperature when the weight percent ratio of poly(ethylene oxide), PEO to PVA is increased from 10:0 to 5:5. The activation energy of the ionic conductivity for the PEO–PVA–KOH polymer electrolyte is 3–8 kJ mol⁻¹. The properties of the electrolyte film are characterized by a wide variety of techniques and it is found that the film exhibits good mechanical stability and high ionic conductivity at room temperature. The application of such electrolyte films to nickel–metal-hydride (Ni–MH) batteries is examined and the electrochemical characteristics of a polymer Ni–MH battery are obtained.     

An exergy–cost–energy–mass analysis of a hybrid copper–chlorine thermochemical cycle for hydrogen production

An exergoeconomic assessment using exergy–cost–energy–mass (EXCEM) analysis is reported of a copper–chlorine (Cu–Cl) thermochemical water splitting cycle for hydrogen production. The quantitative relation is identified between capital costs and thermodynamic losses for devices in the cycle. A correlation detected in previous assessments, suggesting that devices in energy systems are configured so as to achieve an overall optimal design by appropriately balancing thermodynamic (exergy-based) and economic characteristics of the overall system and its components, is observed to apply for the Cu–Cl cycle. Exergetic cost allocations and various exergoeconomic performance parameters are determined for the overall cycle and its components. The results are expected to assist ongoing efforts to increase the economic viability and to reduce product costs of potential commercial versions of this process. The impacts of these results are anticipated to be significant since thermochemical water splitting with a copper–chlorine cycle is a promising process that could be linked with nuclear reactors to produce hydrogen with no greenhouse gases emissions, and thereby help mitigate numerous energy and environment concerns.     

Tunable microstructure,de-/hydrogenation kinetics and thermodynamics performance of Mg–Ni–La–Ti–H systems

In the light of positive effects of rare earth and transition metals on the hydrogen absorption/desorption properties of magnesium, the Mg20La–5TiH₂, Mg20Ni–5TiH₂ and Mg10Ni10La–5TiH₂ composites have been prepared in this work to ameliorate the de-/hydrogenation kinetics and thermodynamic performance. The results indicate that the as-prepared composites are mainly composed of Mg, Mg₂Ni/LaH₃ and TiH₂ phases after activation, and LaH₃ and TiH₂ are stable during de-/hydrogenation cycles. The morphology observations give evidences that LaH₃ with size about ~20 nm and Mg₂Ni with size about ~1 μm are uniformly distributed in the composites. It is noted that the de-/hydriding kinetics of the as-prepared composites are significantly improved after internal and surface modification, of which the Mg10Ni10La–5TiH₂ composite can desorb as high as 5.66 wt% hydrogen within 3 min at 623 K. Moreover, the thermodynamic properties of the experimental composites have also been investigated and discussed according to the pressure-composition isothermal curves and corresponding calculation by Van't Hoff equation. The improved hydrogen storage properties of the as-prepared composites are mainly attributed to the uniformly distributed LaH₃, Mg₂Ni and TiH₂ phases, which provide a large amount of phase boundaries, diffusion paths and nucleation sites for de-/hydrogenation reactions.     

High coercive Sm–Fe–Co–N powders prepared byapplying the HDDR process

The Hydrogen Disproportionation Desorption Recrystallisation process (HDDR) isstill used to achieve high coercive fine powders of Nd₂Fe₁₄B. Here we study thesolid-gas reactions (hydrogenation and nitrogenation) on Sm₂ (Fe_1−xCo_x) ₁₇ alloys. In order to insure stoichiometry of the Sm₂M₁₇ alloysalong the thermal treatments, some iron has been substituted by cobalt (x = 0.3, 0.5) .Fine particles were achieved by using a planetary miller, and sieved up to a size less than 10 μm. Solid-gas reactions (Sm₂ (Fe_1−xCo_x) ₁₇⧸H₂, N₂) were analysed by using a thermomagnetic balance, the sample reacting under theflowing gas. Clear relationships between the particle sizes and the kinetics of reactions werefound. The HDDR process was optimised for recrystallisation rate, plateau temperature andduration. High coercive Sm₂ (Fe_1−xCo_x) ₁₇N_ypowders with H_cj up to 18 kOe were achieved.     

Fabrication–microstructure–performance relationships of reversible solid oxide fuel cell electrodes–review

Abstract

A reversible solid oxide fuel cell system can act as an energy storage device by storing energy in the form of hydrogen and heat, buffering intermittent supplies of renewable electricity such as tidal and wave generation. The most widely used electrodes for the cell are lanthanum strontium manganate–yttria stabilised zirconia and Ni–yttria stabilised zirconia. Their microstructure depends on the fabrication techniques, and determines their performance. The concept and efficiency of reversible solid oxide fuel cells are explained, along with cell geometry and microstructure. Electrode fabrication techniques such as screen printing, dip coating and extrusion are compared according to their advantages and disadvantages, and fuel cell system commercialisation is discussed. Modern techniques used to evaluate microstructure such as three-dimensional computer reconstruction from dual beam focused ion beam–scanning electron microscopy or X-ray computed tomography, and computer modelling are compared. Reversible cell electrode performance is measured using alternating current impedance on symmetrical and three electrode cells, and current/voltage curves on whole cells. Fuel cells and electrolysis cells have been studied extensively, but more work needs to be done to achieve a high performance, durable reversible cell and commercialise a system.     

The effect of hydrogen addition on premixed laminar acetylene–hydrogen–air and ethanol–hydrogen–air flames

In the present work, the laminar premixed acetylene–hydrogen–air and ethanol–hydrogen–air flames were investigated numerically. Laminar flame speeds, the adiabatic flame temperatures were obtained utilizing CHEMKIN PREMIX and EQUI codes, respectively. Sensitivity analysis was performed and flame structure was analyzed. The results show that for acetylene–hydrogen–air flames, combustion is promoted by H and O radicals. The highest flame speed (247 cm/s) was obtained in mixture with 95% H₂–5% C₂H₂ at λ = 1.0. The region between 0.95 < X_H2 < 1.0 was referred to as the acetylene-accelerating hydrogen combustion since the flame speed increases with increase the acetylene fraction in the mixture. Further increase in the acetylene fraction decreases the H radicals in the flame front. In ethanol–hydrogen–air mixtures, the mixture reactivity is determined by H, OH and O radicals. For X_H2 < 0.6, the flame speed in this regime increases linearly with increasing the hydrogen fraction. For X_H2 > 0.8, the hydrogen chemistry control the combustion and ethanol addition inhibits the reactivity and reduces linearly the laminar flame speed. For 0.6 < X_H2 < 0.8, the laminar flame speed increases exponentially with the increase of hydrogen fraction.     

DRIFTS study of Cu–Zr–Ce–O catalysts for selective CO oxidation

The effects of different components in Cu₁Zr₁Ce₉O_δ catalyst and the variations of the feed stream on the catalytic performance of selective CO oxidation were investigated by diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) technique. It is found that the active sites of Cu₁Zr₁Ce₉O_δ catalyst are mainly Cu⁺ species. Formate species is formed through the reaction between CO gas and hydroxyl groups on the reduced cerium surface. CeO₂ in the Cu₁Zr₁Ce₉O_δ catalyst facilitates the formation of Cu⁺ species and improves the amount of CO adsorption whereas it is unfavorable to the deep reduction of Cu⁺ species. ZrO₂ doped into the Cu₁Zr₁Ce₉O_δ catalyst increases the Cu coverage and CO adsorption capacity, while it decreases the adsorption of CO₂ on the catalyst surface. The adsorption capacities of oxygen and CO are associated with the catalytic performance for the selective CO oxidation at lower and higher temperatures, respectively. The presence of CO in the feed stream promotes the reduction of Ce⁴⁺ species and the production of geminal OH group on the reduced ceria surface. Hydrogen in the feed diminishes the CO adsorption ability but stimulates the CO desorption. CO₂ in the feed occupies the active sites and decreases the adsorption of the reactants, thus deteriorates the catalytic performance for the selective CO oxidation.     

Modeling oil price–US stock nexus: A VARMA–BEKK–AGARCH approach

This study adds to the existing literature on oil price–US stock nexus in three ways. First, it employs the VARMA–AGARCH model developed by McAleer et al. (2009) within the context of BEKK framework using West Texas Intermediate (WTI) and Brent as proxies for oil market and S&P stocks as a proxy for US stock market. Secondly, it modifies the model to include endogenously determined structural break using the general structure for analyzing breaks with unit roots in Perron (2006). Third, it uses the adopted model to compute optimal portfolio weight and hedge ratios between oil price and US stocks using different sample data based on the break date. On average, our empirical evidence suggests a significant positive return spillover from US stock market to oil market and bi-directional shock spillovers between the two markets. In addition, there is significant own asymmetric shock effect in both markets while volatility spillover from oil market to stock market became pronounced after the break which coincides with the period of global economic slowdown. Similarly, the results of portfolio management differ across the sample data. More importantly, we find that ignoring structural break when it exists may exaggerate hedging effectiveness.     

Evaluation of Pt–Ru–Ni and Pt–Sn–Ni catalysts as anodes in direct ethanol fuel cells

In this study, the electrooxidation of ethanol on carbon supported Pt–Ru–Ni and Pt–Sn–Ni catalysts is electrochemically studied through cyclic voltammetry at 50 °C in direct ethanol fuel cells. All electrocatalysts are prepared using the ethylene glycol-reduction process and are chemically characterized by energy-dispersive X-ray analysis (EDX). For fuel cell evaluation, electrodes are prepared by the transfer-decal method. Nickel addition to the anode improves DEFC performance. When Pt₇₅Ru₁₅Ni₁₀/C is used as an anode catalyst, the current density obtained in the fuel cell is greater than that of all other investigated catalysts. Tri-metallic catalytic mixtures have a higher performance relative to bi-metallic catalysts. These results are in agreement with CV results that display greater activity for PtRuNi at higher potentials.