Li–air batteries:air stability of lithium metal anodes

Aprotic rechargeable lithium–air batteries(LABs) with an ultrahigh theoretical energy density(3,500 Wh kg^-1) are known as the‘holy grail’ of energy storage systems and could replace Li-ion batteries as the next-generation high-capacity batteries if a practical device could be realized. However, only a few researches focus on the battery performance and reactions in the ambient air environment, which is a major obstacle to promote the practical application of LABs. Here, we have summar...     

Monolayers of γ-globulin at the air–water interface

Monolayer formation, of γ-globulin at the air–water interface has been investigated under varying subphase compositions. At pH 7.4, it is found that a stable monolayer is obtained only when the ionic strength is greater than 0.5 M. The magnitude of the collapse pressure increases with increasing ionic strength of the subphase. These data are analyzed in comparison to the literature data. Received: 2 March 1999 Accepted in revised form: 16 June 1999     

Selection of hydrogel electrolytes for flexible zinc–air batteries

Flexible zinc–air batteries attract more attention due to their high energy density, safety, environmental protection, and low cost. However, the traditional aqueous electrolyte has the disadvantages of leakage and water evaporation, which cannot meet application demand of flexible zinc–air batteries. Hydrogels possessing good conductivity and mechanical properties become a candidate as the electrolytes of flexible zinc–air batteries. In this work, advances in aspects of conductivity, mechanical toughness, environmental adaptability, and interfacial compatibility of hydrogel electrolytes for flexible zinc–air batteries are investigated. First, the additives to improve conductivity of hydrogel electrolytes are summarized. Second, the measures to enhance the mechanical properties of hydrogels are taken by way of structure optimization and composition modification. Third, the environmental adaptability of hydrogel electrolytes is listed in terms of temperature, humidity, and air composition. Fourth, the compatibility of electrolyte–electrode interface is discussed from physical properties of hydrogels. Finally, the prospect for development and application of hydrogels is put forward.     

Experiments of the secondary ignition of gasoline–air mixture in a confined tunnel

In this article, a special phenomenon of secondary ignition, which is caused when a gasoline–air mixture comes in contact with a local heat source after the first explosion or fire in a confined tunnel, is studied through experiments carried out in a cylinder tunnel with a solid heating device. Based on the analysis of the experimental results of secondary thermal ignition in the confined tunnel, the mode, critical ignition temperature, and critical concentration of the secondary thermal ignition’s occurrence of the gasoline–air mixture in the confined tunnel are discussed. The results indicate that the mode of secondary thermal ignition of gasoline–air mixture in the confined tunnel includes burning, slow deflagration, and rapid deflagration. Compared to the first thermal ignition, the burning intensity of the secondary thermal ignition is stronger and the ignition delay is much shorter. The relationship between critical ignition temperature and gas mixture temperature follows a cubic polynomial. Experiments also indicate that whether the secondary thermal ignition occur or not is determined by critical gasoline vapor and oxygen concentration even if the temperature is maintained in a reasonable scope. When the concentration of the gas vapor is as low as 0.45 % and the oxygen as low as 10.4 %, the secondary thermal ignition still can be triggered.     

Properties of lipophilic nucleoside monolayers at the air–water interface

The capability of self-assembly and molecular recognition of biomolecules is essential for many nanotechnological applications, as in the use of alkyl-modified nucleosides and oligonucleotides to increase the cellular uptake of DNA and RNA. In this study, we show that a lipophilic nucleoside, which is an isomer mixture of 2′-palmitoyluridin und 3′-palmitoyluridin, forms Langmuir monolayers and Langmuir–Blodgett films as a typical amphiphile, though with a smaller elasticity. The nucleoside may be incorporated into dipalmitoyl phosphatidyl choline (DPPC) monolayers that serve as a simplified cell membrane model. The molecular-level interactions between the nucleoside and DPPC led to a remarkable condensation of the mixed monolayer, which affected both surface pressure and surface potential isotherms. The morphology of the mixed monolayers was dominated by the small domains of the nucleoside. The mixed monolayers could be deposited onto solid substrates as a one-layer Langmuir Blodgett film that displayed UV–vis absorption spectra typical of aggregated nucleosides owing to the interaction between the nucleoside and DPPC. The formation of solid films with DNA building blocks in the polar heads may open the way for devices and sensors be produced to exploit their molecular recognition properties.     

Interfacial behaviour of wheat puroindolines: monolayers of puroindolines at the air–water interface

Puroindolines are among the major basic and cysteine-rich lipid binding proteins of wheat seeds. The interfacial properties of puroindoline-a (PIN-a) and puroindoline-b (PIN-b) are important both from a biological and a technological point of view. In the work reported here, the interfacial characteristics of spread monolayers of wheat puroindolines at the air–water interface were studied at varying subphase compositions using a Langmuir–Blodgett film balance. The compression isotherms (π–A _Sp) were recorded at constant barrier speed (3.3 cm/min). It was observed that both PIN-a and PIN-b form stable monolayers at the air–water interface. The stability of the monolayers was found to be dependent on the subphase composition as well as on the concentration of protein in the spreading solution. When the ionic strength of the subphase is below 0.50, the compression isotherms of both PIN-a and PIN-b remains unaffected with the change in the ionic strength of the subphase; however, when the ionic strength is above 0.50, the compression isotherms of both PIN-a and PIN-b undergo significant change with an increase in the ionic strength of the subphase. A gradual increase in the values of the collapse pressure (π_C) and the limiting area (A ₀) was observed due to an increase in the ionic strength of the subphase from 0.5 to 4.0, which may be correlated with the salt-induced conformational changes of the protein molecule. The presence of NaCl and KCl (ionic strength 1.0) in the subphase has a comparable effect on the compression isotherms of both PIN-a and PIN-b; however, the presence of CaCl₂ (ionic strength 1.0) in the subphase leads to an increase in the values of π_C and A ₀. A change in the pH of the subphase from 3.0 to 7.2 was to have a significant effect on the values of π_C and A ₀, which may be due to the pH-induced alteration of the protein conformation. Received: 8 August 2000 Accepted: 15 December 2000     

Formation of calcium in the products of iron oxide–aluminum thermite combustion in air

The composition of condensed products resulting from the combustion of thermite mixtures (Al + Fe₂O₃) in air is studied by precise methods. It is shown that during combustion, calcium is formed and stabilized in amounts of maximal 0.55 wt %, while is missing from reactants of 99.7 wt % purity. To explain this, it is hypothesized that a low-energy nuclear reaction takes place alongside the reactions of aluminum oxidation and nitridation, resulting in the formation of calcium (Kervran–Bolotov reaction).     

Determination of methylmercury fluxes across the air–water and air–soil interfaces by gas chromatography with electron capture detection

A method for the determination of methylmercury (MeHg) fluxes across the air–water and air–soil interfaces was developed using an in situ chamber. The MeHg in the air coming out of the chamber was captured by a column containing sulfhydryl cotton fiber adsorbent. MeHg was then desorbed from the column by using 2 mol L^–1 HCl. The MeHg in the effluent was extracted with benzene, and determined by gas chromatography with electron capture detection. Finally, the MeHg flux was calculated using the chamber. The method was applied to simulated experiments, and the results showed that the MeHg fluxes in the air–water system were higher than those in the air–soil–water system. The method was also successfully applied to the field measurements of an environment polluted by a chemical factory, and the results showed that the MeHg fluxes across the air–soil and air–water interfaces were 0.21–3.09 and 0.14–0.79 ng m^–2 h^–1, respectively. The method will be a useful tool in the environmental study of MeHg.     

Infrared and Raman spectroscopies of monolayers at the air–water interface

Infrared and Raman spectroscopies are now currently used to obtain molecular information (orientation, conformation, organization) on monolayers at the air–water interface. In the past year, several original studies were performed on peptides and proteins and their interaction with phospholipidic monolayers.     

Development of hydrogen–air fuel cells with membranes based on sulfonated polyheteroarylenes

Proton-conducting membranes based on sulfonated polynaphthoyleneimide (PNI) and polytriazole (PTA) are synthesized that can be used in portable hydrogen–air fuel cells (HAFC). Membrane–electrode assemblies (MEAs) based on sulfonated PNI and PTA membranes in individual HAFC manifested power and voltammetric characteristics exceeding the characteristics of MEA based on the commercial Nafion-212 membrane. Thus, the current density of 320 mA cm^–2 and the power density of 160 mW cm^–2 are obtained at the room temperature with no pressure or gas humidification at the voltage of 0.5 V. Also activity of the oxygen electroreduction Pt–Fe/C (30 wt % of metals in total) catalyst synthesized on the basis of coordination compounds is tested in MEA HAFC. It is shown that the values of power for MEAs with the cathodic Pt–Fe/C catalyst at the voltage of 0.5 V, at the room temperature, without additional pressure and gas humidification considerably exceed the corresponding values for MEAs with the commercial E-TEK 20% Pt/C catalyst.     

M?ssbauer study of transformation mechanism of Fe cations in olivine after thermal treatments in air

The transformation mechanism of Fe cations in natural olivine after thermal treatments in air has been studied using mainly⁵⁷Fe Mössbauer spectroscopy. -Fe₂O₃ nanoparticles appear as the primary Fe³⁺ phase in Mössbauer spectra of olivine samples heated at 600-900 °C. These nanoparticles are thermally unstable and they are transformed to -Fe₂O₃ with the increase of heating time. Another transformation mechanism of iron related with the complete decomposition of olivine structure has been observed at temperatures of 1000 °C and higher. The mixed oxide MgFe₂O₄ with the spinel structure and enstatite MgSiO₃ were identified as iron-bearing decomposition products.     

Micellization study and adsorption properties of an ionic surfactant synthesized from hydrogenated cardanol in air–water and in air–brine interfaces

A sulfonate (2,4-sodium dissulfonate-5-n-pentadecylphenol) was synthesized from hydrogenated cardanol and the micellization study was carried out using temperature and electrolyte concentration as variables. The adsorption parameters were obtained using surface tension data by the Frumkin adsorption model and the Simplex Nelder–Mead method. Values of critical micelle concentration (cmc) and surface excess (Γ) were obtained in three different temperatures (303 K, 313 K, and 323 K) and two electrolyte concentrations (NaCl solution—0.1 M and 0.25 M). It was verified that cmc decreased with increasing electrolyte concentration and temperature. The Gibbs free energy showed that the micellization process was spontaneous for all studied systems and temperatures, and also that the presence of several CH₂ groups was significant for micelle formation.     

Fruit Tree model for uptake of organic compounds from soil and air†

The current European risk assessment for chemicals considers only tap water, while in reality other beverages play an important role. A good part of beverages are made from fruits, for example apple juice and vine. A mathematical model was developed to predict uptake of neutral organic chemicals from soil and air into fruits. The new fruit tree model considers eight compartments, i.e. two soil compartments, fine roots, thick roots, stem, leaves, fruits, and air. Chemical equilibrium, advective transport in xylem and phloem, diffusive exchange to soil and air and growth dilution are the main processes. The parameterization is for a square-meter of an apple orchard. The model predicts that polar, non-volatile compounds will effectively be transported from soil to fruits, while lipophilic compounds will preferably accumulate from air into fruits. Results from various experiments show no disagreement with the model predictions.     

STS study of TiO_2 film and Pt-deposited TiO_2 film in air

Direct investigation of the electronic structure of catalyst surfaces on the near-atomic scale in general has not been impossible in the past. However, with the advent of the scanning tunneling microscope (STM), the opportunity arises for incorporating the scanning tunneling spectroscopy (STS) for correlation in-situ surface electronic structure with topography on a sub-nanometer scale. In this paper, we report the STS results of thin film TiO2 and Pt-deposited TiO2 annealed at 450℃. It…     

The effect of UV irradiation on air/water interfacial activity of Tween 20–coumarin conjugates

In order to obtain photo-sensitive surfactants, coumarin derivatives were covalently attached, through either ester bond or ether bond, to hydroxyl groups located at the ends of PEO segments of Tween 20. The molar ratios of Tween 20 to coumarin residues in both Tween 20–coumarin conjugate having ester bond (TCES) and ether bond (TCET) were about 1:1 despite the excess coumarin in the reaction mixture. The photo-dimerization degree was in the order of TCET?>?TCES?>?a free coumarin derivative. And the air/water interfacial activity was in the order of TCET?>?Tween 20?>?TCES. The interfacial activities of TCES and TCET increased with the UV irradiation time. This is possibly because the coumarin residues of TCES and TCET are photo-dimerized to produce Gemini surfactant-like dimeric surfactants. The photo-induced change in the interfacial activity of TCES was slightly greater than that of TCET, probably due to the difference in the length, the polarity, and the flexibility of the linker between two monomeric conjugates of Gemini-like dimeric surfactants.     

Synthesis of amphiphilic V-type silica nanogels and study of their self-assembling at the air–water interface

The methods for the synthesis of silica nanogels and a modifying agent, as well as related amphiphilic V-type silica nanogels are presented. Self-assembly of the synthesized amphi philic nanogels during the formation of Langmuir monolayers at the air–water interface is considered. Aggregate structures were revealed to form during ordering of the silica V-type nanogels at the air–water interface after collapse of the Langmuir monolayer. For the low-molecular-weight fraction of the silica nanogels, the aggregates do not completely decompose upon the expansion of the Langmuir layer since are formed by mutually penetrating macromolecules. For the highmolecular- weight fraction, they are reversibly formed and decompose in consecutive compression– expansion cycles, which is characteristic of Langmuir layers of nanoparticles.     

Alkaline methanol–air system

Methanol is a promising fuel for power devices such as fuel cells because it has a high theoretical capacity per volume and weight, is relatively easy to handle and is easy to store. Many studies on the alkaline methanol fuel cell system were made in the 1960s and 1970s. The article gives a brief summary of these studies and shows some results of the new work started recently at the TU Graz, AustriaDedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday in recogniton of his numerous contributions to interfacial electrochemistry.     

Estimation of the uncertainty components associated with the measurement of radionuclides in air filters using γ-ray spectrometry

This paper discusses and assesses the major sources of uncertainty arising in measurement of radionuclide activity concentrations in air. Besides counting statistics, the main contributors to the overall uncertainty of the activity concentration of long-lived radionuclides are the heterogeneities of the calibration source and the test samples (approximately 4%). In addition, in the case of radionuclides with half-lives of the order of days or shorter, a significant uncertainty results from the variability of the source term because the peak concentration of the radionuclide might occur either at the beginning or at the end of the sampling period. For¹³¹I (T_1/28 days), for instance, the relative standard uncertainty was estimated as 17% owing to this effect. In addition, the uncertainty introduced by the software used for evaluation of the -ray spectra is discussed. Details of the uncertainty components, including their assessed probability distributions and degrees of freedom, and the conversion into standard uncertainties are reported in this paper, following the ISO Guide to the expression of uncertainty in measurement. A standard form for documenting and reporting the uncertainty budged is proposed and illustrated with an example.     

Paper like free-standing hybrid single-walled carbon nanotubes air electrodes for zinc–air batteries

Flexible electrode architectures based on non-functionalized (P2) and functionalized (P3) single-walled carbon nanotubes (SWNTs) were fabricated via a simple vacuum filtration process. A hybrid layer of various compositions of P2- and P3-SWNTs forms free-standing membranes (~80 μm in thickness), and their electrochemical performance was evaluated as an air electrode AEP_2/P3 in zinc–air batteries. Such bifunctionalized air electrodes showed uniform surface morphology with interconnected micron-sized porous structure with high porosity (~70%). The N₂ adsorption isotherms at 77 K are of type IV with BET-specific surface areas of AE_(60/40) and AE_(80/20) to be 130.54 and 158.76 m² g⁻¹, respectively, thus facilitates high active surface area for active oxygen reduction/evolution reactions. BJH pore size distribution of AE_(60/40) and AE_(80/20) shows maximum pores with diameter <15 nm. The zigzag interlaying of the SWNTs imparts mechanical stability and flexibility in zinc–air batteries. Zinc–air batteries with optimized compositions of P2- and P3-SWNTs in air electrode AE_(60/40) had ionic conductivity ~1 × 10⁻² S cm⁻¹ and delivered higher discharge capacity ~300 mAh g⁻¹ as compared to AE_(80/20) composition. The unique properties of AE_(P2/P3) studied in this work would enable flexible air electrode architectures in future metal–air batteries.