Comparative performance of LiMn2O4 spinel compositions with carbon nanotubes and graphite in Li prototype battery

We reported previously the superiority of electrochemical characteristics of the mechanical mixtures of micrometer LiMn₂O₄ spinel with multiwall carbon nanotubes (MCNT) over those of spinel compositions with natural graphite in the prototypes of the Li-ion batteries. In the presented work, we extended the investigation of the kinetic and interfacial characteristics of the spinel in the redox reaction with the Li ion. Slow-rate scan cyclic voltammetry and impedance spectroscopy were used. Carbon electroconductive fillers, their nature, and particle sizes play the key role in the efficiency of the electrochemical transformation of spinel in Li-ion batteries. Electrodes based on the composition of the spinel and MCNT show a good cycling stability and efficiency at the discharge rate of 2C. Chemical diffusion coefficients of Li ion, which were determined in spinel composite with MCNT and graphite near potentials of peak activity in deintercalation/intercalation processes, change within one order of 10^?12 cm² s^?1. The value of this chemical diffusion coefficient for the composition of the spinel with MCNT and with graphite change within one order of 10^?12 cm² s^?1. The data of the impedance spectroscopy shows that the resistance of surface films on the spinel (R _s) is low and does not considerably differ from R _s in composites of the spinel with MCNT and graphite. The investigation shows that the resistance of charge transport (R _ct) through the boundary of surface film/spinel composite is dependent on the conductive filler. Value of R _ct in spinel electrode decreases by the factor of thousand in the presence of carbon filler. Exchange current of spinel electrode increases from the order of 10^?7 to 10^?4 A cm^?2 under the influence of MCNT. At the potentials of maximum activity in deintercalation processes, exchange current of spinel composite electrode with MCNT is 2.2–3.0 times more than one of the composite with graphite. Determining role of the resistance of charge transport in electrode processes of spinel is established. The value of R _ct is dependent on the resistance in contacts between spinel particles and also between particles and current collectors. Contact resistance decreases under the influence of MCNT with more efficiency than under the influence of graphite EUZ-M because of small the size of its particles with high surface area of the MCNT.     

Ion transport in Ca2+, Sr2+, Ba2+, and Pb2+ beta″ aluminas

Single crystals of Ca²⁺, Sr²⁺, Ba²⁺, and Pb²⁺ beta″ alumina were prepared from sodium beta″ alumina by ion exchange. The ionic conductivities of Ca²⁺, Sr²⁺, and Ba²⁺ beta″ alumina are comparable, about 3 × 10^?2 (ohm-cm)^?1 at 300°C. Surprisingly, Pb²⁺ beta″ alumina is much more conductive, 1.5 × 10^?1 (ohm-cm)^?1 at 300°C and 4.6 × 10^?3 (ohm-cm)^?1 at 40°C. Its conductivity approaches that of sodium beta″ alumina at temperatures below 25°C. The diffusion coefficient for Sr²⁺ in beta″ alumina at 600°C was estimated from radiotracer experiments. It is consistent with that expected from conductivity measurements.     

Adsorption of toluene-soluble polymers at the toluene–water interface

The adsorption of several toluene-soluble polymers at the toluene–water interface has been investigated by using the duNouy ring method of measuring interfacial tension γT /W . Polystyrene and poly(ethylene-co-vinyl acetate) (11.1 mole-% vinyl acetate) have little affinity for this interface at 29°C, but poly(methyl methacrylate) (PMMA) (M?_n = 420,000) and ethyl cellulose (EC) (M?_n = 50,100; 49.1% ethoxyl) adsorb significantly at concentrations as low as 1.0 × 10^?4 g/100ml. A plot of interfacial tension lowering versus initial logarithm of initial bulk phase polymer concentration is linear from 1.0 × 10^?4 to 1.0 × 10^?1 g/100 ml for EC and 1.0 × 10^?4 to 1.0 × 10^?2 g/100 ml for PMMA. When the PMMA concentration increases to 1.15 × 10^?1 g/100 ml, its adsorption behavior changes markedly. Prolonged time effects occur and adsorption becomes dependent upon dissolved water content of the toluene prior to formation of the toluene/water interface. Such effects are not observed with the other solutions studied. Increasing temperatures have variable effects on values of γT /W for the polymer solutions studied. Experiments with various polymer mixtures indicate that the polymer lowering T /W the most is preferentially adsorbed at the toluene–water interface and rapidly displaces less strongly adsorbed polymers.     

Synthesis,crystal structure,and properties of a new lanthanide tartrate coordination polymer

A new coordination polymer of terbium tartrate [Tb(H₂O)₃(C₄H₅O₆)(C₄H₄O₆)] has been synthesized and crystallizes in the polar space group P4₁ with cell constants a = 6.0415(9), b = 6.0415(9), c = 36.516(7) Å, V = 1332.8(4) ų, Z = 4. The terbium(III) ion of title complex is nine-coordinate through oxygen donors. Four different coordination modes of tartrate occur. This Tb(III) complex exhibits a characteristic luminescence in the visible region upon excitation at 353 nm. The temperature-dependent magnetic properties of the Tb(III) complex were investigated in the temperature range of 2–300 K. Title compound exhibits significant ferroelectric properties at room temperature (remnant polarization 2P _r = 0.160 μC cm^?2, coercive field 2E _c = 44.5 kV cm^?1, saturation of the spontaneous polarization P _s = 0.176 μC cm^?2).     

Performance of CeO2–TiO2-admixed photoelectrode for natural dye-sensitized solar cell

Extracts from roots of Beta vulgaris were used as natural sensitizers of a wide-bandgap semiconductor (CeO₂–TiO₂) in photoelectrochemical solar cells. The natural dye, adsorbed onto the semiconductor surface, absorbs visible light and promotes electron transfer across the dye/semiconductor interface. We have applied CeO₂–TiO₂ to natural dye sensitizer solar cells as a photoelectrode to reduce the charge recombination rate by providing energy barrier at the interface between the photoanode and electrolyte which offers an improvement of photovoltaic efficiency. Short-circuit current density (J _sc) and open-circuit voltages (V _oc) of 9.0 mA cm^?2 and 680 mV, respectively, were obtained, and an effective energy conversion efficiency of 3.5?% was achieved. This simple and cheap technique of cell preparation opens up a perspective of commercial feasibility for inexpensive and environment-friendly dye cells.     

Noise and ac impedance analysis of ion transfer kinetics at the micro liquid/liquid interface

Fluctuation analysis was utilized to determine the TEA ion transfer kinetics across the water/1,2-dichloroethane interface. The obtained data were compared with those derived from electrochemical impedance spectroscopy experiments using the same electrolytic cell. The apparent standard rate constants k_s determined by these two techniques have a similar value. The average value k_s = 0.37 cm s^− 1 is comparable with the previously reported value k_s = 0.2 cm s^− 1. The experimental approach utilizing a thick wall glass micro-capillary to fix the interface exhibits a very small stray capacitance value, proving this system to be suitable for determining the kinetics of the fast ion transfer across a liquid/liquid interface. Application of a method employing a small perturbation signal prevents polarization of the inner capillary surface by current flowing through the cell. The induced polarization of the capillary can affect ion concentration at the interface due to electroosmosis and thus make the kinetic data evaluation difficult or erroneous.     

Potential energy curves for ground and excited states of NaLi from ab initio calculations with effective core polarization potentials

Sixteen low-lying electronic states of NaLi are investigated by SCF/valence Cl calculations including core polarization effects by means of an effective potential. Spectroscopic constants are obtained with estimated uncertainties of ΔR_e ? 0.01 Å, Δω_e ? 0.6 cm^?1 and ΔD_e ? 80 cm^?1. From a comparison of experimental and theoretical G(υ) values, we suggest a ground-state dissociation energy of 7093 ± 5 cm^?1. Using our rovibrational energies and recently measured excitation lines, we are able to improve the T_e values and dissociation energies of five excited states to an accuracv of ±8 cm^?1.     

Transport of U(VI) from sulphuric acid medium across supported liquid membrane (SLM) containing di-(2-ethylhexyl) phosphoric acid (D2EHPA)/n-dodecane as a carrier

This paper reports on the supported liquid membrane (SLM) based transport studies of U(VI) from sulphate medium using di-(2-ethylhexyl) phosphoric acid/n-dodecane as carrier. Polytetrafluoroethylene membrane was used as solid support and H₂SO₄ as receiver phase. The effects of various parameters such as receiver phase concentration, feed acidity, carrier concentration, U(VI) concentration, membrane thickness and membrane pore size on U(VI) transport had been investigated. With increase in H₂SO₄ concentrations and pH of feed solution there is an increase in U(VI) transport across the SLM. Similarly with increase in membrane thickness the U(VI) transport decrease whereas in case of pore size variation reverse results are obtained. The membrane thickness variation results showed that the U(VI) transport across the SLM is entirely diffusion controlled and the diffusion coefficient the D _(o) was calculated as 1.36 × 10^?7 cm² s^?1. Based on optimized condition, a scheme had been tested for selective recovery of U(VI) from ore leach solution containing a large number of other metal ions.     

Ion-Molecule reactions in methylamine and dimethylamine and trimethylamine systems

Fourier transform ion cyclotron resonance mass spectrometry has been used to measure the reaction rates for ions derived from methylamine with dimethylamine or trimethylamine. The use of the selective ion ejection technique greatly simplifies the elucidation of the ion-molecule reaction channels. The rate constants for proton transfer from protonated metwlamine, CH₃NH ₃ ⁺ (m/z 32), to dimethylamine and trimethylamine are 16.1 ± 1.6 × 10^?10 and 9.3 ± 0.9 × 10^?10 cm³ molec^?1s^?1, respectively. The rate constants for charge transfer from methylamine molecular ion, CH₃NH ₂ ⁺ (m/z 31), to dimethylamine and trimethylamine are 9.3 ± 1.8 x 10^?10 and 15.0 ± 5 × 10^?10 cm³molec^?1s^?1, respectively.     

Cyclic voltammetry of FAD adsorbed on graphite,glassy carbon,platinum and gold electrodes

The electrochemical properties of FAD adsorbed on graphite were studied with cyclic voltammetry. A film with a surface coverage of up to 2×10^?8 mol cm^?2 was formed after 4 h. The film-covered electrodes were stable for long times and they were investigated in buffers without any FAD. A single well-behaved wave was observed, k⁰≌1 s^?1. The pH dependence of E_1/2 was studied. On glassy carbon, platinum and gold much less FAD was adsorbed and it was removed with one rinse.     

The double layer at the interface between two immiscible electrolyte solutions: Part II. Structure of the water/nitrobenzene interface in the presence of 1:1 and 2:2 electrolytes

From fast galvanostatic pulse measurements at 25°C the capacitance of the water/nitrobenzene interface was evaluated as a function of the interfacial potential difference Δ_o^w? for systems consisting of NaBr, LiCl or MgSO₄ in water and tetrabutylammonium tetraphenylborate, tetraphenylarsonium tetraphenylborate or tetraphenylarsonium dicarbollylcobaltate in nitrobenzene. The modified Verwey—Niessen model, in which an inner layer of solvent molecules separates two space-charge regions (the diffuse double layer), describes the structure of the water/nitrobenzene interface well at electrolyte concentrations above ca. 0.02 mol dm^?3, provided that the ions are allowed to penetrate into the inner layer over some distance. For all the systems studied the zero-charge potential difference was found at Δ^w_o?_pzc ≈ 0 on the basis of the standard potential difference Δ^w_o?⁰_TMA + = 0.035 V for tetramethylammonium cation which was used as a reference ion. At zero surface charge a comparison was made with the theoretical capacitance calculated using the mean spherical approximation for a model consisting of two ion and dipole mixtures facing each other. The effect of ion penetration on the interfacial capacitance was estimated from the solution of the linearized Poisson-Boltzmann equation for a triple dielectric model with a continuous distribution of the point ions. The concentration-independent inner layer potential difference and capacitance can only be inferred from the capacitance data if the ion size effect is taken into account. A non-iterative procedure based on the hypernetted-chain equation was used for the evaluation of the potential drop across the diffuse double layer. The extend of the penetration into the inner layer appears to be a function of ion solvation, e.g. the more hydrated ion the less extensive ion penetration is likely.     

Graphitic Carbon Nitride (g‐C3N4): An Interface Enabler for Solid‐State Lithium Metal Batteries

Solid‐state Li metal batteries (SSLMBs) have attracted considerable interests due to their promising energy density as well as high safety. However, the realization of a well‐matched Li metal/solid‐state electrolyte (SSE) interface remains challenging. Herein, we report g‐C₃N₄ as a new interface enabler. We discover that introducing g‐C₃N₄ into Li metal can not only convert the Li metal/garnet‐type SSE interface from point contact to intimate contact but also greatly enhance the capability to suppress the dendritic Li formation because of the greatly enhanced viscosity, decreased surface tension of molten Li, and the in situ formation of Li₃N at the interface. Thus, the resulting Li‐C₃N₄|SSE|Li‐C₃N₄ symmetric cell gives a significantly low interfacial resistance of 11 Ω cm² and a high critical current density (CCD) of 1500 μA cm^?2. In contrast, the same symmetric cell configuration with pristine Li metal electrodes has a much larger interfacial resistance (428 Ω cm²) and a much lower CCD (50 μA cm^?2).     

Ba1.03Ce0.8 Ho0.2O3-α固体电解质的制备和电性能

采用高温固相反应法制备了非化学计量组成的Ba1.03Ce0.8 Ho0.2O3-α 固体电解质,用XRD和SEM对其相组成和表面及断面形貌进行了表征。用气体浓差电池方法测定了材料在600～1000 ℃温度范围内,干燥空气、湿润空气和湿润氢气气氛中的离子迁移数;用交流阻抗谱技术测定了它们在各实验气氛中的电导率。研究了材料的离子导电特性,并与BaCe0.8Ho0.2O3-α 和Ba0.97Ce0.8Ho0.2O3-α 的性能进行了比较。结果表明：该材料为单相钙钛矿型斜方晶结构。在600～1000 ℃温度范围内、干燥空气中,是氧离子与电子空穴的混合导体,氧离子迁移数为0.10～0.36;在湿润空气中,是质子、氧离子与电子空穴的混合导体,质子迁移数为0.11～0.01,氧离子迁移数为0.34～0.30;在湿润氢气气氛中,是纯质子导体,质子迁移数为1。在600～1000 ℃温度范围内,干燥空气、湿润空气和湿润氢气气氛中,非化学计量组成材料(x = 1.03,0.97)的电导率高于化学计量组成材料(x = 1)的电导率,其中,Ba1.03Ce0.8 Ho0.2O3-α的电导率最高 (1000 ℃时、在干燥空气气氛中：3.92×10-2 S·cm-1;在湿润空气气氛中：3.46×10-2 S·cm-1;在湿润氢气气氛中：2.10×10-2 S·cm-1)。Ba1.03Ce0.8 Ho0.2O3-α材料的离子导电性优于BaCe0.8Ho0.2O3-α 和Ba0.97Ce0.8Ho0.2O3-α。     

Electrochemical polymerization of aromatic amines: IR,XPS and PMT study of thin film formation on a Pt electrode

Films resulting from the anodic oxidation of various monosubstituted aromatic amines have been grafted on Pt electrodes in a CH₃CN?NaClO₄-pyridine medium. An in situ polaromicrotribometric study of changes occurring on the electrode surface during polarization indicates that these deposits have a stable friction coefficient of 1.3f_o. Their analysis by multiple-reflection IR spectroscopy and by X-ray photoelectron spectroscopy shows that these films are organic polymers of emeraldine basic structure and that they probably result from the coupling of electrochemically formed NH^. radicals with the monomer. These films are homogeneous, very adherent, thermally stable and free of ionic impurities. In the dry state they display a conductivity of 5×10^?13 Ω^?1 cm^?1 which is characteristic of insulators.     

Kalorimetrische messungen zur ermittlung der spezifischen grenzflächenenergie einer zweiphasigen Cu-7,5 At.-% In-legierung

With the help of a commercial heat-flux calorimeter the enthalpy change was measured as a function of the interlamellar spacing for lamellar precipitated Cu-In samples. This is related to the replacement of the two-phase structure (α + δ) by the homogeneous solid solution (α₀. From this, the specific interfacial enthalpy of the α-δ interface was determined to be ΔH^δ = 1100 ± 550 mJ m^?2. A value of ΔH^c = 1320 ± 60 J mol^?1 results for the chemical part of the total measured transformation enthalpy. A value of ΔS^δ = 0.66 mJ m^?2 K^?1 was estimated for the specific interfacial entropy and using the Gibbs-Helmholtz equation the specific interfacial free energy was calculated as ΔG^δ = 700 ± 400 mJ m^?2 at 600 K.     

Electronic transport properties and electrically induced p-n junction in ZrO2 + 10 m/o Y2O3

Through the application of voltages to cubic ZrO₂, stabilized by 10 m/o Y₂O₃, using a nitrogen/Ag and an air/Pt electrode, concentration gradients of the electronic species and p-n junctions in the sample have been created. The transient relaxation of the voltage is investigated and is interpreted in terms of the mobilities of both excess and defect electrons between 700 and 900°C. The movement of the p-n junction is characterized by a shoulder-type voltage-time relation. At 900°C the mobilities of the electrons and holes are 2.3 × 10^?2 and 1.5 × 10^?4 cm²/Vsec, respectively. The activation energy of transport is much smaller for the excess electrons than the holes. The electronic conductivities are determined from the steady-state polarization current.     

Surfactant-assisted transport of lead ion through a bulk liquid membrane containing dicyclohexyl-18-crown-6: efficient removal of lead from blood serum and sea water

The selective and efficient surfactant assisted transport of Pb²⁺ ions using a bulk liquid membrane composed of dicyclohexyl-18-crown-6, as a highly selective carrier, in chloroform solution is reported. In the presence of 6.0 × 10^?2 M P₂O₇ ^4? ions and 10^?3 M sodium dodecylsulfate, as suitable stripping agent and membrane/receiving phase interface modifier, respectively, in the receiving phase and 2.4 × 10^?3 M picric acid, as a counter ion in the source phase, the amount of lead transported across the liquid membrane after 5 h is 100.0 ± 1.1. The designed transport system was successfully applied to the removal of lead from sea water and blood serum samples.     

The kinetics of chlorine evolution and reduction on glassy carbon in molten tetrachloroaluminate at 175°C

The chlorine electrode reaction on glassy carbon in sodium tetrachloroaluminate melt (AlCl₃+NaCl) with near equimolar compositions was investigated at 175°C with voltammetric techniques. The kinetic parameters (Tafel slope and exchange current density) measured as functions of chloride ion activity and partial pressure of chlorine, and the reaction orders with respect to Cl^? and Cl₂ have been collected extensively, being compared with the theoretical kinetic derivatives deduced from the rate equations solved under three different kinds of adsorption isotherms: Langmuir, non-activated Temkin and activated Temkin isotherms. All the evidence collected in this study indicates that the reaction mechanism for both evolution and dissolution of chlorine consists of a fast electron transfer (Cl^?→Cl_ad+e) followed (or preceded) by a slow Heyrovsky-type reaction (Cl^?+Cl_ad→Cl₂+e) on glassy carbon surfaces where the adsorbed intermediate obeys the activated Temkin isotherm. The exchange current density was found as 8.6±0.8 μA cm^?2 at 175°C in the melt of pCl=1.1 under an atmospheric pressure of Cl₂, and its electrode potential (E°_CΓ/Cl2) was determined as 2.182±0.005 V vs. Al.     

Surface Charges at the CaF2/Water Interface Allow Very Fast Intermolecular Vibrational‐Energy Transfer

We investigate the dynamics of water in contact with solid calcium fluoride, where at low pH, localized charges can develop upon fluorite dissolution. We use 2D surface‐specific vibrational spectroscopy to quantify the heterogeneity of the interfacial water (D₂O) molecules and provide information about the sub‐picosecond vibrational‐energy‐relaxation dynamics at the buried solid/liquid interface. We find that strongly H‐bonded OD groups, with a vibrational frequency below 2500 cm^?1, display very rapid spectral diffusion and vibrational relaxation; for weakly H‐bonded OD groups, above 2500 cm^?1, the dynamics slows down substantially. Atomistic simulations based on electronic‐structure theory reveal the molecular origin of energy transport through the local H‐bond network. We conclude that strongly oriented H‐bonded water molecules in the adsorbed layer, whose orientation is pinned by the localized charge defects, can exchange vibrational energy very rapidly due to the strong collective dipole, compensating for a partially missing solvation shell.     

Lifetime and collisional depopulation of the metastable 5D 3/2-state of Yb+

The lifetime and collisional depopulation rates of the metastable 5D _3/2 state of Yb⁺ have been determined in a radiofrequency ion trap by observation of the fluorescence count rate after ion excitation by a short laser pulse. From measurements using He, N₂ and H₂ as buffer gases between 10^?8 and 10^?6 mbar pressure and linear extrapolation to zero pressure we obtain a lifetime of τ=52.15±1.00 ms and rate constants ofR(H₂)=(1.02±0.10)×10^?9 cm³/s andR(N₂)=(1.78±0.19)×10^?10 cm³/s. The lifetime is in fair agreement with a calculated value of 74 ms.