The Role of Alkali Cation Intercalates on the Electrochemical Characteristics of Nb2CTX MXene for Energy Storage

The intercalation of cations into layered-structure electrode materials has long been studied in depth for energy storage applications. In particular, Li⁺-, Na⁺-, and K⁺-based cation transport in energy storage devices such as batteries and electrochemical capacitors is closely related to the capacitance behavior. We have exploited different sizes of cations from aqueous salt electrolytes intercalating into a layered Nb₂CT_x electrode in a supercapacitor for the first time. As a result, we have demonstrated that capacitive performance was dependent on cation intercalation behavior. The interlayer spacing expansion of the electrode material can be observed in Li₂SO₄, Na₂SO₄, and K₂SO₄ electrolytes with d-spacing. Additionally, our results showed that the Nb₂CT_x electrode exhibited higher electrochemical performance in the presence of Li₂SO₄ than in that of Na₂SO₄ and K₂SO₄. This is partly because the smaller-sized Li⁺ transports quickly and intercalates between the layers of Nb₂CT_x easily. Poor ion transport in the Na₂SO₄ electrolyte limited the electrode capacitance and presented the lowest electrochemical performance, although the cation radius follows Li⁺>Na⁺>K⁺. Our experimental studies provide direct evidence for the intercalation mechanism of Li⁺, Na⁺, and K⁺ on the 2D layered Nb₂CT_x electrode, which provides a new path for exploring the relationship between intercalated cations and other MXene electrodes.     

Momentane Temperaturen in Halbleiter-Leistungsbauelementen

Ohne Zusammenfassung     

σ-Porosity is separably determined

We prove a separable reduction theorem for σ-porosity of Suslin sets. In particular, if A is a Suslin subset in a Banach space X, then each separable subspace of X can be enlarged to a separable subspace V such that A is σ-porous in X if and only if A∩V is σ-porous in V. Such a result is proved for several types of σ-porosity. The proof is done using the method of elementary submodels, hence the results can be combined with other separable reduction theorems. As an application we extend a theorem of L. Zají?ek on differentiability of Lipschitz functions on separable Asplund spaces to the nonseparable setting.     

Luminescent cellulose fibers activated by Eu3+-doped nanoparticles

UV- active cellulose fibers were obtained by dry-wet method spinning an 8?% by weight α-cellulose solution in N-methylomorpholine-N-oxide (NMMO) modified by europium-doped gadolinium oxyfluoride Gd₄O₃F₆:Eu³⁺ containing 5?mol (%) of the dopant. Photoluminescent nanoparticles were introduced in the in powder form into a polymer matrix during the process of cellulose dissolution in NMMO. The dependencies of emission intensity on excitation energy and the concentration of Gd₄O₃F₆:Eu³⁺ nanoparticles in the final cellulosic products were examined by photoluminescence spectroscopy (excitation and emission). The fiber structure was studied by X-ray powder diffraction analysis. The size and dispersity of the nanoparticles in the polymer matrix were evaluated using scanning electron microscopy and X-ray microanalysis. The influence of different concentration particles (in the range from 0.5 to 5?% by weight) on the mechanical properties of the fibers, such as tenacity and elongation at break, were determined.     

Effect of the Initiator Anion and of the Polarity of the Medium on the Intra-Intermolecular Growth in the Cationic Polymerization of 2,5-DimethyM, 5-hexadiene

The influence of solvents and catalysts on the formation of soluble and insoluble polymer during cationic polymerization of 2,5-dimethyl-l,5-hexadiene was studied. In nonpolar medium (n-heptane or without solvent) the amount of the insoluble part is dependent on the catalyst used and increases as follows: BF₃ ? AlBr₃ < TiCl₄. Especially soluble polymers are obtained in a solution of methylene chloride or in a mixture of methylene chloride-nitrobenzene. The temperature range studied, -30° to -78°, did not show any important influence on the polymer composition. It was found that the bulky anion of the initiator and the polarity of the medium considerably influenced cyclization during intra-intermolecular propagation of the polymer chain.     

The Initiating Effect of Vinyl Aromatic and Diene Monomers on the Polymerization of Isobutylene with VCl4

The polymerization of isobutylene with VCl₄ in n-heptane or in the bulk does not proceed in the dark at temperatures lower than -20°C, yet it may be induced by the addition of styrene, α-methylstyrene, p-divinylbenzene, 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene. In these cases the polymerizations proceed with variously long induction periods depending on the type of comonomer used. The shortest induction period was observed after the addition of p-divinylbenzene and 2, 3-dimethyl-1, 3-butadiene. In a nonpolar medium the copolymerization of isobutylene with isoprene or butadiene in the dark gives rise to copolymers insoluble in heptane, benzene, and CCl₄, while co-polymers formed with the effect of light are soluble. Unlike polymerizations carried out in a nonpolar solution, the polymerization of isobutylene with VCl₄ in methyl chloride proceeds spontaneously in the absence of protonic coinitiators. Also, soluble copolymers of isobutylene with isoprene or butadiene arise in the copolymerization in methylchloride solution irrespective of the procedure used when the copolymerization is carried out (in the dark or with the effect of light). Polymerizations and copolymerizations carried out both in nonpolar and in polar solutions are inhibited by the presence of oxygen.     

Selective Reduction of the N-O Bond in Heteroaromatic N-Oxides by TiCl4/SnCl2

Heteroaromatic N-oxides bearing various functionalities are readily and selectively converted under mild conditions into the corresponding bases using TiCl₄/SnCl₂.     

Fuzzy identification of cutting acoustic emission with extended subtractive cluster analysis

This paper presents fuzzy acoustic emission identification in high precision hard turning process based on extended subtractive cluster analysis combined with the least-square estimation method. The fuzzy identification method provides a simple way to arrive at a definite conclusion based upon the information obtained with the difficulty in understanding the exact physics of the machining process. The experimental results prove that the proposed method is efficient and feasible.