Synthesis of a new magnetic Y2Mn2/3Re4/3O7 with pyrochlore-like structure

A complex oxide of the Y₂Mn_2/3Re_4/3O₇ composition with pyrochlore-like structure and parameters of hexagonal unit cell _a=14.91(1) Å _c=17.53(1) Å was synthesized. The magnetic susceptibility and magnetization measurements showed that below 190 K this oxide possesses spontaneous magnetic moment. In the paramegnetic region, the magnetic susceptibility obeys the Curie-Weiss law χ=C/(T?Θ), with C=2.07 cm³ K mol^?1 and Θ=?160 K, and the effective magnetic moment corresponding to the cationic combination Mn²⁺-Re⁵⁺. The data obtained allow one to assume that the compound has a noncollinear antiferromagnetic structure.     

Evaluation of lyophility of carbon materials for electrodes of supercapacitors

Physics of the Solid State - The heats of wetting have been measured experimentally for some of the solvents used for the preparation of electrolytes of supercapacitors. For the first time, the...     

Halloysite nanotubes template-induced fabrication of carbon/manganese dioxide hybrid nanotubes for supercapacitors

Ionics - Carbon/manganese dioxide (C/MnO2) hybrid nanotubes were prepared by the successive deposition of carbon and manganese dioxide using natural halloysite nanotubes as template. The...     

Promising nitrogen-doped porous nanosheets carbon derived from pomegranate husk as advanced electrode materials for supercapacitors

Nitrogen-doped porous activated carbons (N-PHACs) have been successfully synthesized using pomegranate husk as carbon precursor via ZnCl₂-activation carbonization and subsequent urea-assisted hydrothermal nitrogen-doping method. The obtained N-PHACs possesses abundant mesoporous structure, high specific surface area (up to 1754.8 m² g^?1), pore volume (1.05 cm³ g^?1), and nitrogen-doping content (4.51 wt%). Besides, the N-PHACs-based material showed a high specific capacitance of 254 F g^?1 at a current density of 0.5 A g^?1 and excellent rate performance (73% capacitance retention ratio even at 20 A g^?1) in 2 M KOH aqueous electrolyte, which is attributed to the contribution of double-layer capacitance and pseudocapacitance. The assembled N-PHACs-based symmetric capacitor with a wide operating voltage range of 0–1.8 V exhibits a maximum energy density of 15.3 Wh kg^?1 at a power density of 225 W kg^?1 and superior cycle stability (only 6% loss after 5000 cycles) in 0.5 M Na₂SO₄ aqueous electrolyte. These exciting results suggest that the novel N-doping porous carbon material prepared by a green and low-cost design strategy has a potential application as high-performance electrode materials for supercapacitors.     

Electrochemical supercapacitors of electrodeposited PANI/H-RuO2 hybrid nanostructure

Electrodeposited mixed nanostructures composed of conducting polyaniline (PANI) and hydrous ruthenium oxide (H-RuO₂) referred as a hybrid nanostructure was synthesized. The surface morphology was investigated from the field-emission scanning electron microscopy digital photoimages. Fibrous network of PANI and spheres of H-RuO₂ were obtained. PANI embedded H-RuO₂ was confirmed from the Raman spectroscopy analysis. Cyclic-voltammetry, used to characterize the electrochemical capacitive properties of hybrid PANI/H-RuO₂ (RP 30) nanostructure, showed a specific capacitance as high as 322 F/g in 0.5 M H₂SO₄ electrolyte. The electrochemical impedance spectroscopy measurement revealed the low equivalent series resistance.     

Engineering advanced Li1.2V3O8 composite electrodes for lithium batteries

Li_1.2V₃O₈-based electrodes with a composition of 80% w/w Li_1.2V₃O₈, 12% w/w carbon black and 8% w/w poly(methyl methacrylate) can be prepared from slurries with a solid content of 30% w/w in ethyl acetate, which is a more environmentally friendly solvent than tetrahydrofuran or N-methylpyrrolidone, by adding the ethylene carbonate plasticizer at an optimum concentration of 25% w/w of dried electrode and by using ball milling. The mixing sequence of the constituents was observed to be important. Ethylene carbonate improves dispersion of the Li_1.2V₃O₈ grains and enhances the adhesion in the dry state to the current collector. A long-term cycling capacity of 250 mAh g⁻¹ was achieved. This paper was presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Characterization of Cu1.4Mn1.6O4/PPy composite electrodes

In this work, we have studied the multilayered polypyrrole(PPy)/oxide composite electrode on glassy carbon (GC) having the structure GC/PPy/PPy(Cu_1.4Mn_1.6O₄)/PPy using X-ray Photoelectron Spectroscopy and Mn K-edge and Cu K-edge XANES and EXAFS. The mixed oxide particles have been incorporated into the PPy matrix simultaneously to the electropolymerization of Py from a solution containing 0.1 M Py + 0.15 M KCl + Cu_1.4Mn_1.6O₄. The XPS data have shown that, prior to the incorporation of the oxide into the PPy matrix, it contains Cu⁺, Cu²⁺, Mn³⁺ and Mn⁴⁺. The XPS, XANES and EXAFS results have shown that when the oxide is incorporated into the PPy matrix, the Cu⁺ present in the original oxide suffers dismutation to give Cu²⁺ and metallic Cu. The metallic Cu is segregated out of the spinel structure. The Mn K-edge XANES and EXAFS data show that, after the incorporation into the PPy matrix, Mn is present as Mn³⁺ and Mn⁴⁺ occupying octahedral sites in a spinel-related structure while the Cu K-edge XANES and EXAFS data indicate that copper occupies tetrahedral sites predominantly in that structure but having a large degree of disorder in the second and higher coordination shells.     

ZrO2 coating of LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

ZrO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ materials were prepared by hydroxide precipitation. The structure and electrochemical properties of the ZrO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ were investigated using X-ray diffraction, scanning electron microscope, and charge–discharge tests, indicating that the lattice structure of LiNi_1/3Co_1/3Mn_1/3O₂ were unchanged after the coating but the cycling stability was improved. As the coating amount increased from 0.0 to 0.5 mol.%, the initial capacity of the coated LiNi_1/3Co_1/3Mn_1/3O₂ decreased slightly; however, the cycling stability increased remarkably over the cut-off voltages of 2.5~4.3 V and the capacity retention reached 99.5% after 30 cycles at the coating amount of 0.5 mol.%. ZrO₂ coating also improved the cycling stability of LiNi_1/3Co_1/3Mn_1/3O₂ over wider cut-off voltage of 2.5~4.6 V.     

TiO2 coating of LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

TiO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ materials were prepared by the hydrolyzation of Ti(OBu)₄. The impact of TiO₂ coating on the structure and electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ was investigated using X-ray diffraction, scanning electron microscope, and charge–discharge tests. The results indicated that TiO₂ coating did not affect the lattice of LiNi_1/3Co_1/3Mn_1/3O₂, but exhibited obvious effects on its discharge capacity and cycling stability. As coated TiO₂ increased from 0.0 to 2.0 mol%, the initial capacity of samples decreased slightly, but the cycling stability over 2.5∼4.3 V increased remarkably. The capacity retention reached 99.5% at the 50th cycle at a coating amount of 2.0 mol%.     

Hydrothermal synthesis and electrochemical performance studies of Al2O3-coated LiNi1/3Co1/3Mn1/3O2 for lithium-ion batteries

LiNi_1/3Co_1/3Mn_1/3O₂ nanocrystallites were synthesized by a one-step hydrothermal method, and uniform second particles were formed by a subsequent calcination process. X-ray diffraction results indicate that the as-synthesized material can be indexed by α-NaFeO₂ layered structure with R-3 m space group. The results of Rietveld refinements show the I ₀₀₃/I ₁₀₄ value of the material is 2.032, and the nanostructured material presents low cation mixing, small cell volume, and a consequent suppression of lattice strain. The rate performances of the as-synthesized material can be further improved by coating Al₂O₃. The discharging capacity of Al₂O₃-coated material reaches 154.4 mAh g^?1, and the capacity retention maintains 80.3 % after 50 cycles at 5 C in the voltage range of 2.5 to 4.5 V, while those of the bare one is only 139.0 mAh g^?1 and 71.6 %, respectively. The transmission electron microcopy observation shows no zigzag layer exists on the surface of particle after cycles for Al₂O₃-coated LiNi_1/3Co_1/3Mn_1/3O₂. Compared to bare LiNi_1/3Co_1/3Mn_1/3O₂, the de-intercalation potential difference before and after cycles of Al₂O₃-coated one is smaller. This indicates that Al₂O₃ coating can reduce the electrochemistry polarization in the electrode bulk.     

MnO2-polypyrrole conducting polymer composite electrodes for electrochemical redox supercapacitors

Redox supercapacitors using electrochemically synthesised MnO₂-polypyrrole composite electrodes have been fabricated with different electrolytes, namely polymer electrolyte film (polyvinyl alcohol, PVA-H₃PO₄ aqueous blend), aprotic liquid electrolyte (LiClO₄-propylene carbonate, PC) and polymeric gel electrolyte [poly methyl methacrylate, (PMMA)-Ethylene carbonate (EC)-Propylene carbonate (PC)-NaClO₄]. The capacitors have been characterised using galvanostatic charge-discharge methods. The cell with aqueous PVA-H₃PO₄ shows non-capacitive behaviour owing to some reversible chemical reaction of MnO₂ with water while the MnO₂-polypyrrole composite is found to be a suitable electrode material for redox supercapacitors with aprotic (non-aqueous) electrolytes. The solid state supercapacitor based on MnO₂-polypyrrole composite electrodes with gel electrolyte gives stable values of capacitance of 10.0–18.0 mF cm⁻² for different discharge current densities.     

Antiferromagnetic phase transition in garnet-type AgCa2Mn2V3O12 and NaPb2Mn2V3O12

Ferrimagnetism has been extensively studied in garnets, whereas it is rare to find the antiferromagnet. Present work will demonstrate antiferromagnetism in the two Mn–V-garnets. Antiferromagnetic phase transition in AgCa₂Mn₂V₃O₁₂ and NaPb₂Mn₂V₃O₁₂ has been found, where the magnetic Mn²⁺ ions locate only on octahedral A site. The heat capacity shows sharp peak due to antiferromagnetic order with the Néel temperature T_N=23.8 K for AgCa₂Mn₂V₃O₁₂ and T_N=14.2 K for NaPb₂Mn₂V₃O₁₂. The magnetic entropy change over a temperature range 0–50 K is 13.9 J K^?1 mol-Mn²⁺-ions^?1 for AgCa₂Mn₂V₃O₁₂ and 13.6 J K^?1 mol-Mn²⁺-ions^?1 for NaPb₂Mn₂V₃O₁₂, which are in good agreement with calculated value of Mn²⁺ ion with spin S=5/2. The magnetic susceptibility shows the Curie–Weiss behavior over the range 29–350 K. The effective magnetic moment μ_eff and the Weiss constant θ are μ_eff=6.20 μ_B Mn²⁺-ion^?1 and θ=?34.1 K (antiferromagnetic sign) for AgCa₂Mn₂V₃O₁₂ and μ_eff=6.02 μ_B Mn²⁺-ion^?1 and θ=?20.8 K for NaPb₂Mn₂V₃O₁₂.     

Characterization of Na-substituted LiNi1/3Co1/3Mn1/3O2 cathode materials for lithium-ion battery

Highly crystalline layered Li_1?xNa_xNi_1/3Co_1/3Mn_1/3O₂ (x?=?0, 0.001, 0.01, 0.03, 0.05) materials are synthesized by molten salts method and characterized by scanning electron microscopy, inductively coupled plasma (ICP), X-ray diffraction, Rietveld refinement, and electrochemical measurement, respectively. ICP, SEM, and EDS results show that Na ions are incorporated in LiNi_1/3Co_1/3Mn_1/3O₂. Rietveld refinement results show that suitable Na substitution leads to stable layered structure by full Na occupying in Li layer and further attributes to low cation mixing. Electrochemical studies demonstrate that the Na-substituted LiNi_1/3Co_1/3Mn_1/3O₂ shows improved rate capability and cycling performance compared to that of pure LiNi_1/3Co_1/3Mn_1/3O₂.     

Synthesis of spherical LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

Spherical LiNi_1/3Co_1/3Mn_1/3O₂ was successfully prepared by controlled crystallization. The preparation started with the spherical coprecipitate of Ni_1/3Co_1/3Mn_1/3CO₃ from NiSO₄, CoSO₄, MnSO₄, NH₄HCO₃, and NH₃·H₂O, followed by pyrolysis of Ni_1/3Co_1/3Mn_1/3CO₃ at 600°C for 3 h. The X-ray diffraction analysis showed that the homogeneous cubic (Ni_1/3Co_1/3Mn_1/3)₃O₄ was obtained after the pyrolysis. Spherical LiNi_1/3Co_1/3Mn_1/3O₂ was obtained by sintering of the mixture of as-obtained (Ni_1/3Co_1/3Mn_1/3)₃O₄ and LiOH·H₂O at 900°C for 6 h in air. As-prepared spherical LiNi_1/3Co_1/3Mn_1/3O₂ presented initial discharge capacity of 162.9 mA h g⁻¹ and capacity retention of 98% at 50th cycle.     

Resistance switching properties of In2O3 nanocrystals memory device with organic and inorganic hybrid structure

A memory device with In₂O₃ nanocrystals embedded in a biphenyl-tertracarboxylic dianhydride-phenylen diamine (BPDA-PDA) polyimide layer on a ZnO layer was fabricated, and its electrical properties were evaluated. Then, the transmittance efficiency in the structure of the BPDA-PDA polyimide/In₂O₃ nanocrystals/ZnO/ITO/double polishing sapphire substrate was measured to be about 80% between 440 to 800 nm by ultraviolet-visible transmittance spectroscopy. A bipolar switching current bistability by difference resistance appeared in the sweep voltage rage from −7 to 7 V. It was considered that the bipolar behavior of current-voltage may originate from a resistance fluctuation because of the electron charging effect in In₂O₃ nanocrystals by voltage sweeping, Fowler–Nordheim tunneling, space-charge-limited current, and the migration of O²⁻ ions.     

Cavitation intensifying bags improve ultrasonic advanced oxidation with Pd/Al2O3 catalyst

Advanced oxidation processes can potentially eliminate organic contaminants from industrial waste streams as well as persistent pharmaceutical components in drinking water. We explore for the first time the utilization of Cavitation Intensifying Bags (CIB) in combination with Pd/Al₂O₃ catalyst as possible advanced oxidation technology for wastewater streams, oxidizing terephthalic acid (TA) to 2-hydroxyterephthalic acid (HTA). The detailed characterization of this novel reaction system reveals that, during sonication, the presence of surface pits of the CIB improves the reproducibility and thus the control of the sonication process, when compared to oxidation in non-pitted bags. Detailed reaction kinetics shows that in the CIB reactor the reaction order to TA is zero, which is attributed to the large excess of TA in the system. The rate of HTA formation increased ten-fold from ~0.01 μM*min⁻¹ during sonication in the CIB, to ~0.10 μM*min⁻¹ for CIB in the presence of the Pd/Al₂O₃ catalyst. This enhancement was ascribed to a combination of improved mass transport, the creation of thermal gradients, and Pd/Al₂O₃ catalyst near the cavitating bubbles. Further analysis of the kinetics of HTA formation on Pd/Al₂O₃ indicated that initially the reaction underwent through an induction period of 20 min, where the HTA concentration was ~0.3 μM. After this, the reaction rate increased reaching HTA concentrations ~6 μM after 40 min. This behavior resembled that observed during oxidation of hydrocarbons on metal catalysts, where the slow rate formation of hydroperoxides on the metal surface is followed by rapid product formation upon reaching a critical concentration. Finally, a global analysis using the Intensification Factor (IF) reveals that CIB in combination with the Pd/Al₂O₃ catalyst is a desirable option for the oxidation of TA when considering increased oxidation rates and costs.     

The use of ionic liquids as solvent-free green electrolytes for hybrid supercapacitors

The aim of this paper is to demonstrate that the use of ionic liquids (ILs) in activated carbon (AC)//poly(3-methyl-thiophene) (pMeT) hybrid supercapacitors is a very promising strategy to develop high voltage supercapacitors operating above room temperature with solvent-free green electrolytes. The ILs used were 1-butyl-3-methyl-imidazolium tetrafluoroborate, 1-butyl-3-methyl-imidazolium hexafluorophosphate, N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide. We report and discuss the performance of AC and pMeT electrodes in such ILs compared to that in propylene carbonate-based electrolytes, in order to give indications for further research effort in IL-based hybrid supercapacitors. PACS 82.47.Uv; 84.60.-h     

Nano-sized Co/Co(OH)2 core-shell structure synthesized in molten salt as electrode materials for supercapacitors

Ionics - A facile and low cost molten salt method for the synthesis of Co@Co(OH)2 core-shell nanostructured material exhibiting high specific capacitances for supercapacitors was developed. In our...     

CuO nanoparticles supported on carbon microspheres as electrode material for supercapacitors

Ionics - C/CuO nanocomposites were prepared by hydrothermal treatment of copper nitrate with starch, followed by H2O2 oxidation and calcination. Structure characterizations show that high...     

First-principles study on the electronic structure and magnetism of layered oxyselenide La2Mn2Se2O3

The electronic structure and magnetism of layered oxyselenide La(2)Mn(2)Se(2)O(3) have been studied by using first-principles calculations within the generalized gradient approximation (GGA) and GGA + U methods. The G-type antiferromagnetic (AF) state is calculated to be the most stable phase among the various magnetic configurations of interest, irrespective of the choice of the functional used, which is in good agreement with the experiments. In contrast to La(2)Fe(2)Se(2)O(3) and La(2)Co(2)Se(2)O(3), in which the AF states show metallic behavior under the GGA method, we predict the ground state of La(2)Mn(2)Se(2)O(3) is a semiconductor with an indirect band gap of ～0.52 eV via the GGA calculations. This is closely related to a closed shell configuration and large exchange splitting (～3.5 eV) in the Mn 3d states. Moreover, the magnetic properties are also discussed in terms of the calculated Heisenberg spin exchange constants, suggesting that La(2)Mn(2)Se(2)O(3) is a strong two-dimensional magnetically frustrated system.