Elucidating the Synergic Effect in Nanoscale MoS\u3csub\u3e2\u3c/sub\u3e/TiO\u3csub\u3e2\u3c/sub\u3e Heterointerface for Na-Ion Storage

Interface engineering in electrode materials is an attractive strategy for enhancing charge storage, enabling fast kinetics, and improving cycling stability for energy storage systems. Nevertheless, the performance improvement is usually ambiguously ascribed to the “synergetic effect”, the fundamental understanding toward the effect of the interface at molecular level in composite materials remains elusive. In this work, a well-defined nanoscale MoS2/TiO2 interface is rationally designed by immobilizing TiO2 nanocrystals on MoS2 nanosheets. The role of heterostructure interface between TiO2 and MoS2 by operando synchrotron X-ray diffraction (sXRD), solid-state nuclear magnetic resonance, and density functional theory calculations is investigated. It is found that the existence of a hetero-interfacial electric field can promote charge transfer kinetics. Based on operando sXRD, it is revealed that the heterostructure follows a solid-solution reaction mechanism with small volume changes during cycling. As such, the electrode demonstrates ultrafast Na+ ions storage of 300 mAh g−1 at 10 A g−1 and excellent reversible capacity of 540 mAh g−1 at 0.2 A g−1. This work provides significant insights into understanding of heterostructure interface at molecular level, which suggests new strategies for creating unconventional nanocomposite electrode materials for energy storage systems

Determination of hydroxyl groups in biorefinery resources via quantitative 31P NMR spectroscopy

The analysis of chemical structural characteristics of biorefinery product streams (such as lignin and tannin) has advanced substantially over the past decade, with traditional wet-chemical techniques being replaced or supplemented by NMR methodologies. Quantitative 31P NMR spectroscopy is a promising technique for the analysis of hydroxyl groups because of its unique characterization capability and broad potential applicability across the biorefinery research community. This protocol describes procedures for (i) the preparation/solubilization of lignin and tannin, (ii) the phosphitylation of their hydroxyl groups, (iii) NMR acquisition details, and (iv) the ensuing data analyses and means to precisely calculate the content of the different types of hydroxyl groups. Compared with traditional wet-chemical techniques, the technique of quantitative 31P NMR spectroscopy offers unique advantages in measuring hydroxyl groups in a single spectrum with high signal resolution. The method provides complete quantitative information about the hydroxyl groups with small amounts of sample (~30 mg) within a relatively short experimental time (~30-120 min)

Modeling study on the secondary arc with stochastic initial positions caused by the primary arc

In the conversion process from primary arc to secondary arc, there exists stochasticness phenomenon of the initial positions of secondary arc. However, the present simulation results of the arcing time with the arc chain model are constant, which is not consistent with the test results. In reaction to the above phenomenon, the stochastic simulation model was first established to calculate the relationship between the conductivity of the air and the temperature. Furthermore, the conductivity along the radius direction of the primary arc was acquired, and then the stochastic initial length of the secondary arc with different primary current was also obtained. Results showed that with the increase of primary current, the average value and dispersion of the initial secondary arc length also increased. Finally, the stochastic model of secondary arc with different initial positions was applied into the arc chain model to calculate the arcing time with dispersion, and the simulation results were compared with the experimental results. Results showed that the simulation results of the arcing time are consistent with the test results, and the relative errors are within 10%, which shows that the stochastic model is effective and reliable

Study on Sulfide Distribution in the Operating Oil of Power Transformers and Its Effect on the Oil Quality

Corrosive sulfides in transformer oil could react with copper wire to produce cuprous sulfide, causing insulation failure. At present, both the quantitative measurement method and distribution of sulfur components in operating oil are not clear yet. In this paper, the existing types and contents of sulfides in oil samples with different alkyl groups and different voltage levels were investigated. With quantitative testing methods, the distribution of sulfur composition in the operating oil was analyzed. Results showed that the thiophene sulfide in transformer oil existed mainly in the form of benzothiophene with an unsaturation of 6 and dibenzothiophene with an unsaturation of 9. The content of monosulfide sulfide with unsaturation of 3 or 6 was the highest. The disulfide existed basically in the form of Dibenzyl disulfide (DBDS). The influence of sulfides on the oil quality were analyzed on this basis. Results showed that the existence of sulfides would increase the moisture content in oil. The absorbed moisture could cause the decrease of the breakdown voltage and rise of the dielectric loss. The above study could provide some engineering practice for understanding the sulphide distribution in transformer oils and further prevent the sulfur corrosion faults

Space Plasma Distribution Effect of Short-Circuit Arc on Generation of Secondary Arc

Secondary arc is more severe in the ultra-high voltage (UHV) power grid. However, the mechanism for the generation process of secondary arc at the extinction moment of a short-circuit arc is not yet clear. It is of great theoretical significance and technological application value to study the generation mechanism and dynamic physical characteristics of secondary arc, and further to develop effective suppression technology. In this article, an arc numerical simulation model based on the coefficient partial differential equations combining with classical drift-diffusion model was established, and the implementation method based on the finite element software COMSOL (COMSOL Multiphysics 5.2a, COMSOL Inc., Stockholm, Sweden) was given. Then, the transient analysis method was applied to simulate the generation, diffusion and dissipation phenomena of the short-circuit arc strike, and further to explore the electric field, microscopic particle spatial distribution and reaction process during the arc discharge process. The simulation results show that the development of short-circuit arc mainly includes two processes: corona discharge and arc discharge, of which the former has a very short duration and the latter is caused by short-circuit. During the discharge process, the electron density first increases and then decreases, which is different from the general characteristics of streamer discharge. Although the concentration distribution curve of the positive ions and negative ions has the same trend, there are subtle differences. The diffusion effect of space ions in the initial discharge stage is almost zero, while radial diffusion direction in the peak discharge stage and axial direction in the late discharge stage. The electric field intensity in space has an S-shaped upward trend during discharge. The time relationship of the ion source generated by the neutralization reaction and by the short-circuit arc discharge are basically the same, and the rate of neutralization reaction is lowest near the electrode. When the ionic reaction is approaching the end of the simulation, the ionic concentration is higher than the initial level, which proves that the space ionic concentration is increased due to the short-circuit discharge, and providing the necessary environmental conditions for the subsequent generation of the secondary arc

Micro‐mechanism study on synergistic degradation of the oil‐paper insulation with dibenzyl disulfide, hexadecyl mercaptan and benzothiophene

Abstract In recent years, there have been many cases of transformer failures caused by corrosive sulfides. At present, research mainly focuses on the single sulfide dibenzyl disulphide, but few research on multiple sulphur or the oil‐paper hybrid insulation. In this study, three typical sulfides dibenzyl disulfide, hexadecyl mercaptan and benzothiophene were selected to form seven sulfide‐oil‐paper models. Then relaxation calculations were carried out, and through molecular dynamics simulation, the synergistic effect of different sulfides on the properties of insulating paper and insulating oil was discussed. Results show that the coexistence of the three sulfides has the most severe weakening on the mechanical properties of cellulose, and it also causes great damage to hydrogen bonds. Hexadecyl mercaptan has a weaker effect on hydrogen bond destruction, but it will greatly aggravate the cellulose chain movement. The viscosity of insulating oil is generally increased by the influence of sulfide. Hexadecyl mercaptan is the main factor affecting the viscosity. Thiophene has little effect on the viscosity, ctive protection technology on sulphur corrosion

Rapid Identification of Main Vegetation Types in the Lingkong Mountain Nature Reserve Based on Multi-Temporal Modified Vegetation Indices

Nature reserves are among the most bio-diverse regions worldwide, and rapid and accurate identification is a requisite for their management. Based on the multi-temporal Sentinel-2 dataset, this study presents three multi-temporal modified vegetation indices (the multi-temporal modified normalized difference Quercus wutaishanica index (MTM-NDQI), the multi-temporal modified difference scrub grass index (MTM-DSI), and the multi-temporal modified ratio shaw index (MTM-RSI)) to improve the classification accuracy of the remote sensing of vegetation in the Lingkong Mountain Nature Reserve of China (LMNR). These three indices integrate the advantages of both the typical vegetation indices and the multi-temporal remote sensing data. By using the proposed indices with a uni-temporal modified vegetation index (the uni-temporal modified difference pine-oak mixed forest index (UTM-DMI)) and typical vegetation indices (e.g., the ratio vegetation index (RVI), the difference vegetation index (DVI), and the normalized difference vegetation index (NDVI)), an optimal feature set is obtained that includes the NDVI of December, the NDVI of April, and the UTM-DMI, MTM-NDQI, MTM-DSI, and MTM-RSI. The overall accuracy (OA) of the random forest classification (98.41%) and Kappa coefficient of the optimal feature set (0.98) were higher than those of the time series NDVI (OA = 96.03%, Kappa = 0.95), the time series RVI (OA = 95.56%, Kappa = 0.95), and the time series DVI (OA = 91.27%, Kappa = 0.90). The OAs of the rapid classification and the Kappa coefficient of the knowledge decision tree based on the optimal feature set were 95.56% and 0.95, respectively. Meanwhile, only three of the seven vegetation types were omitted or misclassified slightly. Overall, the proposed vegetation indices have advantages in identifying the vegetation types in protected areas