Niobium doped lithium titanate as a high rate anode material for Li-ion batteries

Niobium doped lithium titanate with the composition of Li₄Ti_4.95Nb_0.05O₁₂ has been prepared by a sol-gel method. X-ray diffraction (XRD) and scanning electron microscope (SEM) are employed to characterize the structure and morphology of Li₄Ti_4.95Nb_0.05O₁₂. The Li₄Ti_4.95Nb_0.05O₁₂ electrode presents a higher specific capacity and better cycling performance than the Li₄Ti₅O₁₂ electrode prepared by the similar process. The Li₄Ti_4.95Nb_0.05O₁₂ exhibits an excellent rate capability with a reversible capacity of 135 mAh g⁻¹ at 10 C, 127 mAh g⁻¹ at 20 C and even 80 mAh g⁻¹ at 40 C. Electrical resistance measurement and electrochemical impedance spectra (EIS) reveal that the Li₄Ti_4.95Nb_0.05O₁₂ exhibits a higher electronic conductivity and faster lithium-ion diffusivity than the Li₄Ti₅O₁₂, which indicates that niobium doped lithium titanate (Li₄Ti_4.95Nb_0.05O₁₂) is promising as a high rate anode for the lithium-ion batteries.     

Hollow lithiated metal oxide particles as lithium-ion battery cathode materials

We report the synthesis and characterization of the hollow micrometer-sized (Mn_0.5Ni_0.4Co_0.1)CO₃ precursor, and one of its promising lithium-enriched phases. The chemical composition of the resulting lithiated final material was Li_1.2(Mn_0.5Ni_0.4Co_0.1)O_2+y. Lithium half cells with cathodes comprised of these hollow particles as the active intercalation material showed a reversible capacity of 183 mAh/g when cycled between 2.0 V and 4.6 V. X-ray diffraction patterns and the electrochemical data of Li_1.2(Mn_0.5Ni_0.4Co_0.1)O_2+y were consistent with the existence of the Li₂MnO₃-type integrated component that was activated during the initial charging of the cells. The results presented herein demonstrate a method to synthesize multicomponent, multiphase materials with hollow internal morphologies that can reversibly and stably be cycled with high gravimetric capacities as the active cathode material in lithium-ion batteries.     

Mixed oxides as catalysts for the selective reduction of nitrobenzene

The catalytic behaviour of the PbO-Mn₃O₄ and the Bi₂O₃-MoO₃ systems was investigated in the selective reduction of nitrobenzene to nitrosobenzene. Lead compounds appeared to be good catalysts, and co-catalysts when used with Mn₃O₄. Different from oxidations by di-oxygen, Bi₃O₃ alone is a good catalyst and formation of mixed Bi-Mo-O compounds does not enhance the catalytic activity. It is suggested that the difference between these catalysts in the mentioned reaction is related to the way in which the oxygen vacancy is represented by the oxygen donor.     

Preparation and electrochemical performance studies on Cr-doped Li3V2(PO4)3 as cathode materials for lithium-ion batteries

Cr-doped Li₃V_2−xCr_x(PO₄)₃/C (x = 0, 0.05, 0.1, 0.2, 0.5, 1) compounds have been prepared using sol–gel method. The Rietveld refinement results indicate that single-phase Li₃V_2−xCr_x(PO₄)₃/C with monoclinic structure can be obtained. Although the initial specific capacity decreased with Cr content at a lower current rate, both cycle performance and rate capability have excited improvement with moderate Cr-doping content in Li₃V_2−xCr_x(PO₄)₃/C. Li₃V_1.9Cr_0.1(PO₄)₃/C compound presents an initial capacity of 171.4 mAh g⁻¹ and 78.6% capacity retention after 100 cycles at 0.2C rate. At 4C rate, the Li₃V_1.9Cr_0.1(PO₄)₃/C can give an initial capacity of 130.2 mAh g⁻¹ and 10.8% capacity loss after 100 cycles where the Li₃V₂(PO₄)₃/C presents the initial capacity of 127.4 mAh g⁻¹ and capacity loss of 14.9%. Enhanced rate and cyclic capability may be attributed to the optimizing particle size, carbon coating quality, and structural stability during the proper amount of Cr-doping (x = 0.1) in V sites.     

Chromium Oxide Supported on Mesoporous SBA-15 as Propane Dehydrogenation and Oxidative Dehydrogenation Catalysts

The catalytic activity and selectivity of Cr₂O₃ supported on mesoporous SBA-15 for non-oxidative and oxidative dehydrogenation of propane by O₂ and CO₂ have been studied and compared with those of Cr₂O₃/ZrO₂ and Cr₂O₃/-Al₂O₃ catalysts. Cr₂O₃/SBA-15 and Cr₂O₃/ZrO₂/SBA-15 are more selective to propene and more resistant to coking in comparison with Cr₂O₃/ZrO₂ and Cr₂O₃/-Al₂O₃ for non-oxidative dehydrogenation of propane. In oxidative dehydrogenation of propane by O₂ and CO₂, Cr₂O₃/SBA-15 also displays better activity, selectivity and stability than the other two supported catalysts. The propane conversion and propene yield on Cr₂O₃/SBA-15 catalyst for oxidative dehydrogenation of propane by CO₂ at 823 K reach 24.2 and 20.3%, respectively. XPS and TG/DTA have been used to characterize the catalysts before and after reaction. The differences in catalytic behavior of various supported Cr₂O₃ catalysts in the reactions have been discussed on the basis of the characterization results.     

NOx reduction performance of lean NOx catalyst and lean NOx adsorber using DME as reducing agent

The deactivation of a commercial Selective Catalytic Reduction (SCR) catalyst, of V₂O₅−WO₃/TiO₂ type, has been studied through comparisons with results from a full-scale biomass combustion plant to that with laboratory experiments. In the latter, the catalyst was exposed to KCl and K₂SO₄ by both wet impregnation with diluted salt solutions and deposition of generated submicrometer aerosol particles by means of an electrostatic field. The reactivity of fresh and deactivated samples was examined in the SCR reaction. Chemical and physical characterizations were focusing on internal structures and chemical composition. Deposition of submicrometer sized particles on the monolithic SCR catalyst was shown to induce deactivation with characteristics resembling those obtained in a commercial biomass combustion plant.     

CoFe2O4@SiO2/PrNH2 nanoparticles as highly efficient and magnetically recoverable catalyst for the synthesis of 1,3-thiazolidin-4-ones

An efficient three-component synthesis of 1,3-thiazolidin-4-ones is described by one-pot condensation of aldehydes, aromatic amine and thioglycolic acid with nano-CoFe₂O₄@SiO₂/PrNH₂ as a robust heterogeneous catalyst. The significant advantages of this protocol are the use of magnetically recoverable catalyst, high to excellent product yields, operational simplicity and the use of CoFe₂O₄@SiO₂/PrNH₂ nanoparticles as an environment-friendly catalyst.     

Nanoporous gold as non-enzymatic sensor for hydrogen peroxide

Nanoporous gold (NPG) fabricated by dealloying Au–Ag film was investigated for the non-enzymatic detection of H₂O₂. The apparent activation energy of H₂O₂ electrochemical reduction on NPG was found to be as low as ∼30 kJ mol⁻¹. The reduction currents at −0.4 V vs. SCE demonstrated a strict linear dependence in a wide H₂O₂ concentration region from 10 μM to 8 mM with a detection limit 3.26 μM. Furthermore, the biosensor based on NPG exhibited high selectivity, good reproducibility, and long-term stability. These results indicate that NPG could be a promising electrochemical material for H₂O₂ detection.     

Nb2O5 as efficient and recyclable photocatalyst for indigo carmine degradation

Heterogeneous photocatalysis is a significant green technology for application in water purification. The application of Nb₂O₅ catalyst for the photodegradation of contaminants is few reported in the literature. Thus, the Nb₂O₅ catalyst was characterized by SEM, FTIR, surface area and charge surface density. This catalyst was applied to degrade indigo carmine dye, which was compared with degradation catalyzed by TiO₂ and ZnO. Almost 100% of dye degradation occurred at 20, 45 and 90 min for TiO₂, ZnO and Nb₂O₅, respectively. The effect of Nb₂O₅ catalyst concentration, pH and ionic strength (μ) was investigated. The Nb₂O₅ activity increased at 0.7 g/L and for higher catalyst concentrations the degradation was kept constant. Degradation of indigo carmine dye catalyzed by Nb₂O₅ was improved at pH < 4.0 and μ = 0.05 mol/L. TiO₂, ZnO and Nb₂O₅ were recovered and re-applied in other nine reaction cycles. While TiO₂ and ZnO have an abrupt loss of their catalytic activity, Nb₂O₅ maintained 85% of catalytic activity after 10 reaction cycles.     

Mixed oxides Ca2Fe2O5 and Ca2Co2O5 as anode materials for Li-ion batteries

The electrochemical performance of mixed oxides, Ca₂Fe₂O₅ and Ca₂Co₂O₅ for use in Li-ion batteries was studied with Li as the counter electrode. The compounds were prepared and characterized by X-ray diffraction and SEM. Ca₂Fe₂O₅ showed a reversible capacity of 226 mAh/g at the 14th cycle and retained 183 mAh/g at the end of 50 cycles at 60 mA/g in the voltage window 0.005-2.5 V. A reversible capacity in the range, 365-380 mAh/g, which is stable up to 50 charge-discharge cycles is exhibited by Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V and at 60 mA/g. This corresponds to recycleable moles of Li of 3.9±0.1 (theoretical: 4.0). Significant improvement in the cycling performance and attainable reversible capacity were noted for Ca₂Co₂O₅ on cycling to an upper cut-off voltage of 3.0 V as compared to 2.5 V. Coulombic efficiency for both compounds is >98%. Electrochemical impedance spectroscopy (EIS) data clearly indicate the reversible formation/decomposition of polymeric surface film on the electrode surface of Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V. Cyclic voltammetry results compliment the galvanostatic cycling data.     

Characterization Of C60/Bi2TiO4F2 as a Potential Visible Spectrum Photocatalyst for The Depolymerization of Lignin

Effects of a photocatalyst, C₆₀-modified Bi₂TiO₄F₂, on pine kraft lignin under visible light irradiation were investigated, along with those of Bi₂TiO₄F₂ and C₆₀/TiO₂ as references. The influences of pH, C₆₀ mass fraction, and the initial lignin concentration on lignin conversion and yields of mono-phenolic products were investigated. Seven products were determined by GC/MS, including phenol, 2-methoxyphenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-vinylphenol, vanillin, acetovanillone, and homovanillic acid. The yields of products and lignin conversion were higher by C₆₀/Bi₂TiO₄F₂ than Bi₂TiO₄F₂ and C₆₀/TiO₂. C₆₀/Bi₂TiO₄F₂ and C₆₀/TiO₂ were more stable than Bi₂TiO₄F₂ upon repetitive recycling of catalyst. The effectiveness of C₆₀/Bi₂TiO₄F₂ declines 25%, whereas that of Bi₂TiO₄F₂ declines 56.4% after being recycled five times. FTIR and HRTEM indicated that the deactivation of photocatalysts might be caused by lignin adsorbed on the surface of photocatalysts and the change in the crystal structure.     

Catalyst’s Sulfur Displacement by Thiophene, as Monitored by Exchange of 35S Radiotracer

The isotopic exchange has been studied between catalyst radiosulfur and H₂S, formed in thiophene hydrodesulfurization (HDS) (named S-displace) on alumina supported molybdena, on CoMoO_x, PdMoO_x, PtMoO_x and on silica–alumina supported NiWO_x. S-displace was compared with radiosulfur exchange data between catalyst radiosulfur and gas phase H₂S (S^exc) determined previously. The extent of S^exc was higher than that of the S-displace for Mo, CoMo in and NiW, whereas the extent of S-displace from PdMoO and PtMoO was significantly higher, than that of S^exc. Thiophene HDS product distribution data are discussed in terms of increased C=C hydrogenation and C–C hydrogenolysis activity, explained by increasing H₂S production with longer circulation time of the thiophene/H₂ mixture, The C₁/C₃<1 ratios among C₄-hydrogenolysis products indicate some coke formation. The decrease of thiophene HDS activity is presumably a consequence of increasing site-blocking with the formation of more H₂S and coke with longer duration of thiophene treatment.     

Mechanistic study of the reduction of oxygen in air electrode with manganese oxides as electrocatalysts

Electrochemical reduction of oxygen (O₂) in air electrode with manganese oxides (MnOx) as electrocatalysts was studied with MnOx/Nafion-modified gold (Au) electrodes using cyclic voltammetry, potential-controlled amperometry and rotating ring-disk electrode (RRDE) voltammetry in alkaline aqueous solution. At Nafion-modified (MnOx free) Au electrode, O₂ reduction undergoes two successive two-electron processes with HO₂⁻ as intermediate. The presence of MnOx, including Mn₂O₃, Mn₃O₄, Mn₅O₈ and MnOOH, on Nafion-modified Au electrodes obviously increases the first reduction peak current of O₂ to hydrogen peroxide (HO₂⁻ in this case) and decreases the second one of HO₂⁻ to OH⁻, while does not shift the reduction potential. MnOx was found to show catalytic activity for the disproportionation reaction of HO₂⁻ to O₂ and OH⁻ and thus, the O₂ reduction in air electrode was considered to include an initial two-electron reduction of O₂ to HO₂⁻ followed by a disproportionation reaction of HO₂⁻ into O₂ and OH⁻ catalyzed by MnOx. The excellent activity of MnOx for the follow-up disproportionation reaction substantially results in an overall four-electron reduction of O₂ at MnOx/Nafion-modified Au electrodes in the first reduction step, depending on potential scan rate and the kind of MnOx. The present work provides a scientific significance of the mechanism of O₂ reduction in air electrode using MnOx as electrocatalysts to effect a four-electron reduction of O₂ to OH⁻.     

Pyrolysis of pine wood in a slowly heating fixed-bed reactor: Potassium carbonate versus calcium hydroxide as a catalyst

Catalytic pyrolysis of pine wood was carried out in a fixed-bed reactor heated slowly from room temperature to 700 °C under a stream of purging argon to examine the effects of the physically mixed K₂CO₃ or Ca(OH)₂ on the pyrolysis behaviors. K₂CO₃ demonstrated a stronger catalysis for decomposition of hemicellulose, cellulose and lignin constituents, leading to the reduced yield of liquid product in conjunction with the increased yields of gaseous and char products because of the promoted secondary reactions of liquid product. With the addition of 17.7 wt.% of K₂CO₃, none of saccharides, aldehydes and alcohols was formed and the formation of acids, furans and guaiacols was substantially reduced, whereas the yields of alkanes and phenols were increased. Potassium led to an increase in the cumulative yields of H₂, CO₂ and CO at 700 °C. Ca(OH)₂ somewhat promoted the decomposition of cellulose and lignin constituents, and the effect of Ca(OH)₂ on the yields of liquid and char was opposite to that of K₂CO₃. With the addition of 22.2 wt.% Ca(OH)₂, some groups of liquid product such as acids and aldehydes disappeared completely and the yields of saccharides, furans and guaiacols were somewhat reduced, while the yield of alcohols was remarkably increased in contrast to the result of K₂CO₃. The addition of Ca(OH)₂ did not significantly change the total yield of gaseous product at 700 °C but enhanced the yield of H₂.     

Evaluation of some cobalt and nickel based perovskites prepared by freeze-drying as combustion catalysts

A series of cobalt and nickel based perovskite type catalysts with high specific surface area (8–20 m² /g) was prepared by spray-freezing/freeze-drying method. The catalytic activity of all samples in methane combustion was evaluated by measuring the light-off temperature, the conversion at 823 K and the temperature of the end of the reaction. The experimental data suggest higher activity than reported in literature for similar or other perovskites, and confirm its strong dependence on the specific surface area. Among eleven tested catalysts, including seven new compositions four of which showed excellent activity, La_0.66Sr_0.34Ni_0.3Co_0.7O₃ was the best performing.     

Hydrothermal synthesis and rate capacity studies of Li3V2(PO4)3 nanorods as cathode material for lithium-ion batteries

It is an effective method by synthesizing one-dimensional nanostructure to improve the rate performances of cathode materials for Li-ion batteries. In this paper, Li₃V₂(PO₄)₃ nanorods were successfully prepared by hydrothermal reaction method. The structure, composition and shape of the prepared were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scan electron microscope (SEM) and transmission electron microscope (TEM), respectively. The data indicate the as-synthesis powders are defect-rich nanorods and the sizes are the length of several hundreds of nanometers to 1 μm and the diameter of about 60 nm. The preferential growth direction of the prepared material was the [1 2 0]. The electrodes consisting of the Li₃V₂(PO₄)₃ nanorods show the better discharge capacities at high rates over a potential range of 3.0-4.6 V. These results can be attributed to the shorter distance of electron transport and the fact that ion diffusion in the electrode material is limited by the nanorod radius. All these results indicate that the resulting Li₃V₂(PO₄)₃ nanorods are promising cathode materials in lithium-ion batteries.     

Synthesis and Characterization of New Bivalent Agents as Melatonin- and Histamine H3-Ligands

Melatonin is an endogenous molecule involved in many pathophysiological processes. In addition to the control of circadian rhythms, its antioxidant and neuroprotective properties have been widely described. Thus far, different bivalent compounds composed by a melatonin molecule linked to another neuroprotective agent were synthesized and tested for their ability to block neurodegenerative processes in vitro and in vivo. To identify a novel class of potential neuroprotective compounds, we prepared a series of bivalent ligands, in which a prototypic melatonergic ligand is connected to an imidazole-based H₃ receptor antagonist through a flexible linker. Four imidazolyl-alkyloxy-anilinoethylamide derivatives, characterized by linkers of different length, were synthesized and their binding affinity for human MT₁, MT₂ and H₃ receptor subtypes was evaluated. Among the tested compounds, 14c and 14d, bearing a pentyl and a hexyl linker, respectively, were able to bind to all receptor subtypes at micromolar concentrations and represent the first bivalent melatonergic/histaminergic ligands reported so far. These preliminary results, based on binding affinity evaluation, pave the way for the future development of new dual-acting compounds targeting both melatonin and histamine receptors, which could represent promising therapeutic agents for the treatment of neurodegenerative pathologies.     

Long-term cyclability and high-rate capability of Li3V2(PO4)3/C cathode material using PVA as carbon source

The Li₃V₂(PO₄)₃/C composite cathode material is synthesized via a simple carbothermal reduction reaction route using polyvinyl alcohol (PVA) as both reduction agent and carbon source. The XRD pattern shows that the as-prepared Li₃V₂(PO₄)₃/C composite has a monoclinic structure with space group P2₁/n. The result of XPS shows the oxidation state of V in the Li₃V₂(PO₄)₃/C composite is +3. The Raman spectrum reveals that the coating carbon has a good structure with a low I_D/I_G ratio. The high-quality carbon can not only enhance the electronic conductivity of the Li₃V₂(PO₄)₃/C composite but also prevent the growth of the particle size. The electrochemical performance, which is especially notable for its high-rate performance, is excellent. It delivers an initial discharge capacity of 105.3 mAh/g at 5 C, which is retained as high as 90% after 2000 cycles. No capacity loss can be observed up to 300 cycles under 20 C rate condition. Our experimental results suggest that this compound can be a candidate as cathode materials for the power batteries of hybrid electric vehicles (HEVs) and electric vehicles (EVs) in the future.     

Preparation and characterization of ramsdellite Li2Ti3O7 as an anode material for asymmetric supercapacitors

Ramsdellite Li₂Ti₃O₇ was first synthesized via sol-gel process with good crystallity of an average particle size of 0.175 μm. The product was thoroughly investigated as a lithium intercalation compound, and as an active anode material in asymmetric supercapacitors coupling with activated carbon as cathode. Lithium intercalation reactions were found occurring at 1.32 and 1.62 V versus Li/Li⁺, respectively. A reversible specific capacity of 150 mA h g⁻¹ at 1C was obtained on Li₂Ti₃O₇ electrode in a nonaqueous electrolyte. The charge current was found to strongly influence the anodic discharge capacity in the asymmetric cell. The capacity retention at 10C charge-discharge rate was found to be 75.9% in comparison with that at 1C.     

Cs2.5H0.5PWO40/SiO2 as addition self-humidifying composite membrane for proton exchange membrane fuel cells

In this paper, we first reported a novel self-humidifying composite membrane for the proton exchange membrane fuel cell (PEMFC). Cs_2.5H_0.5PWO₄₀/SiO₂ catalyst particles were dispersed uniformly into the Nafion^® resin, and then Cs_2.5H_0.5PWO₄₀-SiO₂/Nafion composite membrane was prepared using solution-cast method. Compared with the H₃PWO₄₀ (PTA)_, the Cs_2.5H_0.5PWO₄₀/SiO₂ was steady due to the substitute of H⁺ with Cs⁺ and the interaction between the Cs_2.5H_0.5PWO₄₀ and SiO₂. And compared with the performance of the fuel cell with commercial Nafion^® NRE-212 membrane, the cell performance with the self-humidifying composite membrane was obviously improved under both humidified and dry conditions at 60 and 80 °C. The best performance under dry condition was obtained at 60 °C. The self-humidifying composite membrane could minimize membrane conductivity loss under dry conditions due to the presence of catalyst and hydrophilic Cs_2.5H_0.5PWO₄₀/SiO₂ particles.