Structural and electrochromic properties of nanosized Fe/V-oxide films with FeVO4 and Fe2V4O13 grains: comparative studies with crystalline V2O5

Various mixed Fe/V-oxides can be used as anodes in Li⁺ rocking chair batteries, however, their small optical modulation during the insertion/extraction of Li⁺ ions makes them candidates for the counter electrodes in electrochromic (EC) devices. The sol–gel route in combination with dip-coating deposition was used for the preparation of Fe/V-oxide films with molar ratios Fe:V=0.1:1, 1:2, 1:1 and 2:1. X-ray diffraction combined with Fourier transform infrared (FT-IR) spectroscopy studies of films and powders reveal that heating of xerogel films at 400°C produces films with nanosized FeVO₄ (Fe:V=1:1) and Fe₂V₄O₁₃ (Fe:V=1:2) grains, while the corresponding crystalline powders were obtained at 500°C (8 h). Charge capacities (Q) of Fe/V-oxide films (300 and 400°C) were determined using cyclic voltammetry (CV) from 1.5 to −1.5 V vs. Ag/AgCl (4.8 to 1.8 V vs. Li) in 1 M LiClO₄/propylene carbonate (PC) electrolyte. Our results revealed that Q values of Fe/V-oxide films are up to 20 mC cm⁻² depending on the thickness (40–100 nm), temperature of heating and the Fe:V molar ratio (1:2, 1:1). During the first 300 cycles the cycling stability of the Fe-containing films is better than that of V₂O₅ crystalline films. UV-visible spectra of charged/discharged films revealed that these films, similar to V₂O₅ films, exhibit a mixed anodic/cathodic electrochromism. It was established that with regard to the colouring/bleaching changes of V₂O₅ crystalline films, the Fe/V-oxide films exhibit smaller cathodic colouring at wavelengths λ>600 nm and higher visible transmittance. IR spectroscopy of charged/discharged Fe/V-oxide films confirmed that the reduction of Fe³⁺ prevents the overreduction of V⁵⁺ to V³⁺, which takes place in V₂O₅ films cycled in the same potential range.     

Ag/Al2O3(Li2O)/g-C3N4光催化乙醇制取环氧乙烷

本文制备了一系列Ag/Al₂O₃(Li₂O)/g-C₃N₄复合催化剂,考察了其可见光催化乙醇制取环氧乙烷的性能。Li₂O可调变Al₂O₃表面的酸性,从而降低了主要副产物乙醛的选择性。Ag/Al₂O₃(Li₂O) 在g-C₃N₄上的负载量对产物环氧乙烷的选择性有较大影响,当Ag/Al₂O₃(Li₂O) 负载量为5wt%时,乙醇具有较高的转换率,且环氧乙烷的选择性高达100%。     

Enhancing the elevated temperature performance of Li/LiMn2O4 cells by reducing LiMn2O4 surface area

Lithium-rich spinels were obtained with the same structure but different surface area by two different synthesis routes, namely the “once-annealed” and the “twice-annealed” methods. The elevated temperature performance of Li/Li_1+xMn₂O₄ cell is significantly improved using a spinel cathode with a small surface area: the cell at 50°C lost 5% of the initial capacity over the first 100 cycles based on a spinel cathode with the small surface area of 1.2 m²/g compared to 8% based on a large one of 6.2 m²/g. Also the mechanism responsible for the reaction of LiMn₂O₄ with LiOH to form lithium-rich spinel has been investigated.     

A highly active catalyst, Ni/Ce–ZrO2/θ-Al2O3, for on-site H2 generation by steam methane reforming: pretreatment effect

The steam treatment effect has been investigated over the doubly impregnated catalyst, Ni/Ce–ZrO₂/θ-Al₂O₃, in steam methane reforming (SMR). The catalyst was remarkably deactivated by steam treatment but reversibly regenerated by H₂-reduction. XRD results showed that the steam treatment resulted in the formation of NiAl₂O₄ which is inactive for SMR but it was reversibly converted to Ni by the reduction. The reversible oxidation-reduction of Ni state was also evidenced by XPS and it was observed that the formation of NiAl₂O₄ is more favorable at higher temperature. It is most likely that the alumina support is only partially covered with Ce–ZrO₂ and most Ni directly interacts with θ-Al₂O₃ which would probably make easy formation of NiAl₂O₄ in the presence of steam alone. The results imply that, during the start-up procedure in SMR, too high concentration of steam could deactivate seriously Al₂O₃ supported Ni catalysts.     

Effect of Bi2O3 content on characteristics of Bi2O3–GDC systems for direct methane oxidation

Ceramic systems of Bi₂O₃ and gadolinia-doped ceria (GDC) solid mixture were prepared as catalysts for direct methane oxidation. These systems were characterized by temperature-programmed reduction using hydrogen and carbon monoxide, temperature-programmed reaction of methane, fixed-temperature direct methane oxidation, and X-ray diffraction analysis. Adding Bi₂O₃ to GDC promotes both hydrogen and CO oxidation activities, because of the presence of surface Bi₂O₃ and the high content of mobile oxygen in Bi₂O₃. The reactivity of CO with surface lattice oxygen is enhanced to a higher extent than that of H₂, and this enhanced extent shows a maximum in Bi₂O₃ content. Such a maximum also exists for the catalytic activity of direct methane oxidation. A synergistic effect occurs due to a combination of the high methane reactivity of GDC and the high content of mobile oxygen in Bi₂O₃. The CO₂ selectivity of direct methane oxidation can be modulated by varying the Bi₂O₃ content. The mixing of Bi₂O₃ with GDC also increases the self-de-coking capability of the catalyst during direct methane oxidation, which stabilizes the activity.     

Energy-efficient conversion of propane to propylene and ethylene over a V2O5/CeO2/SA5205 catalyst in the presence of limited oxygen

Oxidative conversion of propane to propylene and ethylene over a V₂O₅/CeO₂/SA5205 (V:Ce=1:1) catalyst, with or without steam and limited O₂, has been studied at different temperatures (700–850 °C), C₃H₈/O₂ ratio (4.0), H₂O/C₃H₈ ratio (0.5) and space velocity (3000 cm³ g⁻¹ h⁻¹). The propane conversion, selectivity for propylene and net heat of reaction (ΔHr) are strongly influenced by the reaction temperature and presence of steam in the reactant feed. In the presence of steam and limited O₂, the process involves a coupling of endothermic thermal cracking and exothermic oxidative conversion reactions of propane which occur simultaneously. Because of the coupling of exothermic and endothermic reactions, the process operates in an energy-efficient and safe manner. The net heat of reaction can be controlled by the reaction temperature and concentration of O₂. The process exothermicity is found to be reduced drastically with increasing temperature. Due to the addition of steam in the feed, no coke formation was observed in the process.     

Reduction of NiAl2O4 containing catalysts for steam methane reforming reaction

Reducibility of a NiAl₂O₄ containing catalyst was studied. On a measurement of NiAl₂O₄ concentration in a catalyst, a peak area ratio of NiAl₂O₄ in XRD analysis was verified to express the NiAl₂O₄ concentration. The reducibility of NiAl₂O₄ was confirmed to be dependent on the calcining temperature to form NiAl₂O₄, not dependent on the calcining time. The catalyst containing NiAl₂O₄ was ascertained to be reduced under convenient conditions to actual plant operations; H₂/N₂ = 30/70 at 1023K for 1 h + steam/CH₄ = 6 at 1023K for 17 h.     

Combustion wave speeds of nanocomposite Al/Fe2O3: the effects of Fe2O3 particle synthesis technique

Combustion wave speeds of nanoscale aluminum (Al) powders mixed with iron oxide (Fe₂O₃) were measured as a function of Fe₂O₃ synthesis technique and fuel/oxidizer composition. Three reactant synthesis techniques were examined; two focus on sol–gel processing of nanoscale Fe₂O₃ particles and the third utilizes commercially available nanoscale Fe₂O₃ powder. Nanoscale aluminum particles (52 nm in diameter) were combined with each oxidizer in various proportions. Flame propagation was studied by igniting low-density mixtures and taking data photographically with a high-speed camera. Both open and confined burning were examined. Results indicate that the combustion wave speed is a strong function of the stoichiometry of the mixture and a slightly fuel-rich mixture provides an optimum combustion wave speed regardless of oxidizer synthesis technique. Oxidizers processed using sol–gel chemistry originally contained impurities which retarded the combustion wave speeds. When the same oxidizers are annealed at moderate temperatures, the new heat-treated oxidizer shows a dramatic improvement, with combustion wave speeds on the order of 900 m/s.     

Preparation and properties of V2O5 thin films for energy-efficient selective-surface applications

Thin V₂O₅ films have been prepared by thermal evaporation onto glass substrates at a pressure of about 1.99×10⁻³ Pa. The temperature dependence of electrical measurements exhibits an anomaly in resistivity at a temperature around 329 K. Temperature co-efficient of resistance (TCR) studies show positive values, so indicating semi-metallic behaviour up to a temperature of 363 K and the negative thereafter so indicating semi-conducting behaviour. Thickness-dependent resistivity measurement follows the Fuchs-Sordheimer size-effect theory. X-ray diffraction studies show that the material is amorphous. Optical studies show the material is highly transparent both in the visible and infrared regions. The integrated value of T_lum and T_sol is high, so indicating that the material is a potential candidate for selective surface applications.     

Interfacial charge transfer and photocatalytic activity in a reverse designed Bi2O3/TiO2 core-shell

In this study, the electronic and photocatalytic properties of core-shell heterojunctions photocatalysts with reversible configuration of TiO₂ and Bi₂O₃ layers were studied. The core-shell nanostructure, obtained by efficient control of the sol-gel polymerization and impregnation method of variable precursors of semiconductors, makes it possible to study selectively the role of the interfacial charge transfer in each configuration. The morphological, optical, and chemical composition of the core-shell nanostructures were characterized by high-resolution transmission electron microscopy, UV-visible spectroscopy and X-ray photoelectron spectroscopy. The results show the formation of homogenous TiO₂ anatase and Bi₂O₃ layers with a thickness of around 10 and 8 nm, respectively. The interfacial charge carrier dynamic was tracked using time resolved microwave conductivity and transition photocurrent density. The charge transfer, their density, and lifetime were found to rely on the layout layers in the core-shell nanostructure. In optimal core-shell design, Bi₂O₃ collects holes from TiO₂, leaving electrons free to react and increase by 5 times the photocatalytic efficiency toward H₂ generation. This study provides new insight into the importance of the design and elaboration of optimal heterojunction based on the photocatalyst system to improve the photocatalytic activity.     

Rb掺杂Li4Ti5O12作为锂离子电池负极材料的合成及电化学性能

合成了不同Rb掺杂量的钛酸锂（Li_4-xRb_xTi₅O₁₂; x = 0.010, 0.015, 0.020）作为锂离子电池的负极材料。测试结果显示,Rb离子掺杂有效增强了钛酸锂的电子电导率。相同的测试条件下,相比于未掺杂样品和高Rb含量掺杂样品（x = 0.015, 0.020）,适量的Rb掺杂钛酸锂（Li_3.99Rb_0.01Ti₅O₁₂; x = 0.010）表现出最优的电化学性能。Li_3.99Rb_0.01Ti₅O₁₂材料表现出161.2 mA∙h/g的初始容量,且在1 C下经过1000次循环后容量保持率可达90.9%。此外,全电池Li_3.99Rb_0.01Ti₅O₁₂ // LiFePO₄在0.5 C条件下首次放电容量为144 mA∙h/g,经过150次循环后,容量保持率为78.8%。     

钛酸锂基锂离子电池及其健康状态研究进展

锂离子电池的高功率密度和高能量密度等特性使其成为电动汽车能源和新能源电网储能的重要载体。功率性能和安全特性是锂离子电池发展的两个主要挑战。钛酸锂Li₄Ti₅O₁₂材料因具有良好的结构稳定性、安全性能、长循环寿命、高功率特性和高低温放电性能,被认为是锂电池负极材料的良好备选。综述了以钛酸锂材料为负极的锂离子电池的相关工作,介绍了钛酸锂材料的结构、电化学特性、制备方法和作为电池负极材料面临的主要问题,重点介绍了钛酸锂负极电池的全电池性能和健康状态研究等方面。     

Electrochemical performance of Nd0.6Sr0.4Co0.5Fe0.5O3−δ–Ag composite cathodes in intermediate temperature solid oxide fuel cells

The electrochemical performances of Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag composite cathodes have been investigated in intermediate temperature solid oxide fuel cells. The Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag cathodes prepared by ball milling followed by firing at 920 °C show the maximum performance (power density: 0.15 W cm⁻² at 800 °C) at 3 wt.% Ag. On the other hand, the Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag composite cathodes with 0.1 mg cm⁻² (0.5 wt.%) Ag that were prepared by an impregnation of Ag into Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ followed by firing at 700 °C (but the electrolyte–Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ assembly was prepared first by firing at 1100 °C) exhibit much better performance (power density: 0.27 W cm⁻² at 800 °C) than the composite cathodes prepared by ball milling, despite a much smaller amount of Ag due to a better dispersion and an enhanced adhesion. AC impedance analysis indicates that the Ag catalysts dispersed in the porous Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ cathode reduce the ohmic and the polarization resistances due to an increased electronic conductivity and enhanced electrocatalytic activity.     

Sm0.5Sr0.5CoO3 + Sm0.2Ce0.8O1.9 composite cathode for cermet supported thin Sm0.2Ce0.8O1.9 electrolyte SOFC operating below 600 °C

The cathode is a key component in low temperature solid oxide fuel cells. In this study, composite cathode, 75 wt.% Sm_0.5Sr_0.5CoO₃ (SSC) + 25 wt.% Sm_0.2Ce_0.8O_1.9 (SDC), was applied on the cermet supported thin SDC electrolyte cell which was fabricated by tape casting, screen-printing, and co-firing. Single cells with the composite cathodes sintered at different temperatures were tested from 400 to 650 °C. The best cell performance, 0.75 W cm⁻² peak power operating at 600 °C, was obtained from the 1050 °C sintered cathode. The measured thin SDC electrolyte resistance R_s was 0.128 Ω cm² and total electrode polarization R_p(a + c) was only 0.102 Ω cm² at 600 °C.     

Preliminary attempt to enhance the hydrogenation of carbon dioxide to methane on cobalt oxide catalyst by adding CuO---ZnO---Cr2O3

Hydrogenation of carbon dioxide (CO₂) was carried out on cobalt oxide catalyst (Co₃O₄) at atmospheric pressure. The hydrogenation proceeded even at 473K. Total conversion reached a maximum (ca 55%) at 573K. Methane (ca 50%) and small amounts of CO (3–5%) were produced during the hydrogenation. It is indicated that the reaction proceeds on partially reduced Co₃O₄. An attempt to enhance the hydrogenation of CO₂ was carried out by adding CuO---ZnO---Cr₂O₃ as a cocatalyst and as a result, the yield of methane was selectively increased.     

Ti4O7 supported IrOx for anode reversal tolerance in proton exchange membrane fuel cell

Fuel starvation can occur and cause damage to the cell when proton exchange membrane fuel cells operate under complex working conditions. In this case, carbon corrosion occurs. Oxygen evolution reaction (OER) catalysts can alleviate carbon corrosion by introducing water electrolysis at a lower potential at the anode in fuel shortage. The mixture of hydrogen oxidation reaction (HOR) and unsupported OER catalyst not only reduces the electrolysis efficiency, but also influences the initial performance of the fuel cell. Herein, Ti₄O₇ supported IrO_x is synthesized by utilizing the surfactant-assistant method and serves as reversal tolerant components in the anode. When the cell reverse time is less than 100 min, the cell voltage of the MEA added with IrO_x/Ti₄O₇ has almost no attenuation. Besides, the MEA has a longer reversal time (530 min) than IrO_x (75 min), showing an excellent reversal tolerance. The results of electron microscopy spectroscopy show that IrO_x particles have a good dispersity on the surface of Ti₄O₇ and IrO_x/Ti₄O₇ particles are uniformly dispersed on the anode catalytic layer. After the stability test, the Ti₄O₇ support has little decay, demonstrating a high electrochemical stability. IrO_x/Ti₄O₇ with a high dispersity has a great potential to the application on the reversal tolerance anode of the fuel cell.     

Synthesis and electrochemical studies on Al2O3 coated LiNi0.5Co0.44Fe0.06VO4 for lithium ion batteries

LiNi_0.5Co_0.44Fe_0.06VO₄ cathode material has been synthesized by a citric acid:polyethylene glycol polymeric method at 723 K for 5 h in air. The surface of the LiNi_0.5Co_0.44Fe_0.06VO₄ was coated with various wt.% of Al₂O₃ by a wet chemical procedure and heat treated 873 K for 2 h in air. The samples were characterized by XRD, FTIR, SEM, and TEM techniques. XRD patterns expose that the complete crystalline phase occurred at 723 K and there was no indication of new peaks for the coated samples. FTIR spectra show that the complete removal of organic residues and the formation of LiNi_0.5Co_0.44Fe_0.06VO₄. TG/DTGA results reveal that the formation of LiNi_0.5Co_0.44Fe_0.06VO₄ occurred between 480 and 670 K and the complete crystalline occurred at 723 K. SEM micrographs show the various morphological stages of the polymeric intermediates. TEM micrographs of the pristine LiNi_0.5Co_0.44Fe_0.06VO₄ reveal that the particle size ranged from 130 to 150 nm and Al₂O₃ coating on the fine particles was compact and had an average thickness of about 15 nm. The charge–discharge experiments were carried out between 2.8 and 4.9 V (versus Li) at a current rate of 0.15 C. The 1.0 wt.% Al₂O₃ coated sample had the best electrochemical performance, with an initial capacity of 65 mAh g⁻¹ and capacity retention of 60% after 50 cycles. The electrochemical impedance behavior suggests that the failure of pristine cathode performance is associated with an increase in the impedance growth on the surface of the cathode material upon continuous cycling.     

Layered alkali titanates (A2TinO2n+1): possible uses for energy/environment issues

Uses of layered alkali titanates (A₂Ti_nO_2n+1; Na₂Ti₃O₇, K₂Ti₄O₉, and Cs₂Ti₅O₁₁) for energy and environmental issues are summarized. Layered alkali titanates of various structural types and compositions are regarded as a class of nanostructured materials based on titanium oxide frameworks. If compared with commonly known titanium dioxides (anatase and rutile), materials design based on layered alkali titanates is quite versatile due to the unique structure (nanosheet) and morphological characters (anisotropic particle shape). Recent development of various synthetic methods (solid-state reaction, flux method, and hydrothermal reaction) for controlling the particle shape and size of layered alkali titanates are discussed. The ion exchange ability of layered alkali titanate is used for the collection of metal ions from water as well as a way of their functionalization. These possible materials design made layered alkali titanates promising for energy (including catalysis, photocatalysts, and battery) and environmental (metal ion concentration from aqueous environments) applications.     

Electrochemical characteristics and cycle performance of LiMn2O4/a-Si microbattery

A LiMn₂O₄ thin film and an amorphous Si (a-Si) thin film were prepared by radio-frequency (rf) magnetron sputtering. Each thin film was electrochemically evaluated by cyclic voltammetry (CV) and galvanostatic cycling. The rate of capacity fade on cycling was monitored as a function of the voltage window and current density. This was compared with the cycle performance of cathode and anode using two kinds of electrolyte, 1 M LiPF₆ in EC/DMC and PC, for 100 cycles. It was found that the discharge capacity of optimized LiMn₂O₄/a-Si full-cell reached 24 μAh/(cm²-μm) in the first cycle, and a reversible capacity of about 16 μAh/(cm² μm) was still maintained after 100 cycles. In a voltage window of 3.0–4.2 V, LiMn₂O₄/a-Si full-cell exhibits relatively stable cycle performance compared to a voltage window of 2.75–4.2 V.     

Selective removal of CO from hydrogen-rich stream over CuO/CexSn1−xO2–Al2O3 catalysts

The solid solutions of Ce_xSn_1−xO₂ incorporated with alumina to form Ce_xSn_1−xO₂–Al₂O₃ mixed oxides, by the suspension/co-precipitation method, were used to prepare CuO/Ce_xSn_1−xO₂–Al₂O₃ catalysts for the selective oxidation of CO in excess hydrogen. Incorporating Al₂O₃ increased the dispersion of Ce_xSn_1−xO₂, but did not change their main structures and did not weaken their redox properties. Doping Sn⁴⁺ into CeO₂ increased the mobility of lattice oxygen and enhanced the activity of the 7%CuO/Ce_xSn_1−xO₂–Al₂O₃ catalyst in the selective oxidation of CO. The selective oxidation of CO was weakened as the doped fraction of Sn⁴⁺ exceeded 0.5. Incorporating appropriate amounts of Sn⁴⁺ and Al₂O₃ could obtain good candidates 7%CuO/Ce_xSn_1−xO₂–Al₂O₃(20%), 1–x=0.1–0.5, for a preferential oxidation (PROX) unit in a polymer electrolyte membrane fuel cell system for removing CO. Its activity was comparable with, and its selectivity was much larger than, that of the noble catalyst 5%Pt/Al₂O₃.