LiMn2O4 electrode prepared by gold–titanium codeposition with improved cyclability

An LiMn₂O₄ electrode was prepared based on mixed-metals (gold–titanium) codeposition method. By this method, titanium oxide is also incorporated into the electroactive film formed on substrate electrode. Formation of titanium oxide on the spinel surface avoids dissolution of Mn from the spinel at elevated temperatures. TiO₂can act as a bridge between the spinel particles to reduce the interparticle resistance and as a good material for the Li intercalation/deintercalation. Thus, electrochemical performance of the LiMn₂O₄ spinel can be improved by the surface modification with TiO₂. This action improves cyclability for lithium battery performance and reduces capacity fades of LiMn₂O₄ at elevated temperatures.     

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.     

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.     

A screen-printed Ce0.8Sm0.2O1.9 film solid oxide fuel cell with a Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathode

Screen-printing technology was developed to fabricate Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte films onto porous NiO–SDC green anode substrates. After sintering at 1400 °C for 4 h, a gas-tight SDC film with a thickness of 12 μm was obtained. A novel cathode material of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ was subsequently applied onto the sintered SDC electrolyte film also by screen-printing and sintered at 970 °C for 3 h to get a single cell. A fuel cell of Ni–SDC/SDC (12 μm)/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ provides the maximum power densities of 1280, 1080, 670, 370, 180 and 73 mW cm⁻² at 650, 600, 555, 505, 455 and 405 °C, respectively, using hydrogen as fuel and stationary air as oxidant. When dry methane was used as fuel, the maximum power densities are 876, 568, 346 and 114 mW cm⁻² at 650, 600, 555 and 505 °C, respectively. The present fuel cell shows excellent performance at lowered temperatures.     

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.     

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.     

Cycle characterizations of LiMxMn2−xO4 (M=Co, Ni) materials for lithium secondary battery at wide voltage region

LiM_xMn_2−xO₄ (M=Co, Ni) materials have been synthesized by a melt-impregnation method using γ-MnOOH as the manganese source. Highly crystallized LiM_xMn_2−xO₄ compounds were synthesized at a calcination temperature of 800°C for 24 h in air. All compounds show a single phase except for LiNi_0.5Mn_1.5O₄ based on the X-ray diffraction (XRD) diagram. With the increase of the doping content from 0.1 to 0.5, the capacity of doping materials decreases mainly in the 4 V region.

Although LiM_0.5Mn_1.5O₄ (M=Co, Ni) compound shows a small capacity in the (3+4) V region compared with parent LiMn₂O₄, it is a very effective material in reducing capacity loss in the 3 V region that is caused by the Jahn–Teller distortion. The doping of Co and Ni ions in the LiMn₂O₄ cathode material promotes the stability of this structure and provides an excellent cyclability.     

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.     

High-temperature superconductor, YBa2Cu307-x as all- solid-state lithium cell

The utility of the high-temperature superconductor, YBa₂Cu₃O_7-itx, as the cathode material for an all-solid-state lithium cell has been examined. The capacity of YBa₂Cu₃O₇-x, is 223 mA h g⁻¹ and the discharge efficiency is> 92%. Measurements of a.c. impedance show that the charge-transfer resistance at the interface of the electrolyte/cathode is very low and increases with the depth-of-discharge of the battery. Studies using X-ray photoelectron spectroscopy (XPS) reveal that the cathode becomes doped with Li⁺ ions as the cell discharges.     

Structural and electrochemical properties of Li1+xNi0.5Mn0.5O2+δ (0 ≤ x ≤ 0.7) cathode materials for lithium-ion batteries

A comparative analysis of the properties of LiNi_0.5Mn_0.5O₂ and Li_1+xNi_0.5Mn_0.5O₂ (0.2 ≤ x ≤ 0.7) powders, obtained by the freeze drying method, was performed. Lattice parameters of Li_1+xNi_0.5Mn_0.5O₂ decreased considerably with growing amounts of Li until x = 0.3; at x > 0.5 trace amounts of Li₂MnO₃ are observed by X-ray diffraction (XRD) patterns. X-ray photoelectron spectroscopy (XPS) analysis displayed an increase of Ni³⁺/Ni²⁺ ratio at 0.3 < x < 0.5, while Mn 2p spectra were almost identical in all samples. Rechargeable capacity values (V = 2.5–4.6 V) increased systematically with x reaching its maximum (185–190 mAh g⁻¹) at x = 0.5. Samples with superstoichiometric lithium content also demonstrated good C rate characteristics.     

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.     

Electrochemical supercapacitor behavior of nanoparticulate rutile-type Ru1−xVxO2

Rutile-type Ru_1−xV_xO₂ nanoparticles possessing high surface area were prepared by a polymerizable-complex method and its electrochemical supercapacitor behavior was studied. X-ray diffractometry, energy-dispersive X-ray analysis, and N₂ adsorption/desorption measurements were used to characterize the structure of the products. The electrochemical supercapacitor behavior of thick and thin films was studied by cyclic voltammetry in various acidic, neutral, and alkaline electrolytes. Ru_1−xV_xO₂ exhibited extremely enhanced supercapacitive properties compared to pure RuO₂. The highest surface redox activity was achieved with an acidic electrolyte. Ru_1−xV_xO₂ showed negligible surface redox activity in neutral electrolytes.     

Electrochemical behaviour of amorphous V2O5(-P2O5) cathodes for lithium secondary batteries

The electrochemical behaviour of amorphous vanadium oxides (a-V₂O₅ and a-V₂O₅-P₂O₅) cathodes in lithium cells has been investigated. The reversibility of the cathodes is superior to that Of c-V₂O₅ and the cathodes can operate for> 300 cycles. The relationship between cathode composition and cycle performance has been determined, and P₂O₅, as a network-former, has been found not to harm the reversibility of cathodes. The degradation in capacity with cycling of the Li/a-V₂O₅(-P₂O₅) system is due to deterioration of the anode, i.e., an increased polarization on discharge.     

Environmental assessment and extended exergy analysis of a “zero CO2 emission”, high-efficiency steam power plant

Aim of this paper is to analyze the performance of an innovative high-efficiency steam power plant by means of two “life cycle approach” methodologies, the life cycle assessment (LCA) and the “extended exergy analysis” (EEA).

The plant object of the analysis is a hydrogen-fed steam power plant in which the H₂ is produced by a “zero CO₂ emission” coal gasification process (the ZECOTECH^© cycle). The CO₂ capture system is a standard humid-CaO absorbing process and produces CaCO₃ as a by-product, which is then regenerated to CaO releasing the CO₂ for a downstream mineral sequestration process.

The steam power plant is based on an innovative combined-cycle process: the hydrogen is used as a fuel to produce high-temperature, medium-pressure steam that powers the steam turbine in the topping section, whose exhaust is used in a heat recovery boiler to feed a traditional steam power plant.

The environmental performance of the ZECOTECH^© cycle is assessed by comparison with four different processes: power plant fed by H₂ from natural gas steam reforming, two conventional coal- and natural gas power plants and a wind power plant.     

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.     

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.     

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%。     

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.     

Methane-fueled IT-SOFCs with facile in situ inorganic templating synthesized mesoporous Sm0.2Ce0.8O1.9 as catalytic layer

Mesoporous Ce_0.8Sm_0.2O_1.9 (SDC) oxide with high surface area was prepared by a novel glycine-nitrate combustion process with in situ created nickel oxide as template, and applied as the catalytic layer for methane-fueled solid-oxide fuel cells (SOFCs) operated at reduced temperatures. The weight ratio of nickel oxide to SDC in the synthesis process was found to have significant effect on both the crystallite size and the textural properties of the resulted SDC powder. In particular, when it was at 9, the thermally stable and well-crystallized SDC powder showed a mesoporous structure with narrow pore-size distribution, high surface area (77 m² g⁻¹) and large pore volume (0.2276 cm³ g⁻¹), even after the calcination at 700 °C for 3 h. The mesoporous SDC was found to favor free gas diffusion with no gas diffusion polarization occurred even at high current density both for hydrogen and methane fuels. The SOFC with Ru impregnated mesoporous SDC catalytic layer displayed promising performance with a peak power density of 462 mW cm⁻² at 650 °C.     

Characterization of Ni porous electrode covered by a thin film of LiMg0.05Co0.95O2

A porous electrode of nickel covered by a thin film of lithium cobaltite doped with magnesium (LiMg_0.05Co_0.95O₂) was prepared in order to protect nickel cathode against dissolution into the molten carbonate. A sol impregnation technique was used to deposit gel precursors on the porous surface of the substrate; the covered substrate was submitted to thermal treatments, which produced a lithium cobaltite layer. The cathode was characterized by the following measurements: biaxial bending test, SEM/EDX analysis, which demonstrated the uniformity of the lithium cobaltite layer and the presence of cobalt homogeneously distributed over the nickel particles, electrical conductivity.

To test the cathodic performance of the material under study a cell was assembled and tested in a 10 cm × 10 cm electrodes area plant. The cell performance during the time was studied carrying out polarization curves for many hours (more than 1000 h). To determine the influence of the cathodic gas composition on the electrode performance the atmosphere was changed maintaining alternatively at a constant value the partial pressure of CO₂ and O₂. In such a way the kinetic effect of the single gas was studied. By the technique of IR interruption the internal resistance of the cell was measured.