High areal capacitance of FeOOH-carbon nanotube negative electrodes for asymmetric supercapacitors

The relatively low capacitance of negative electrodes, as compared to the capacitance of advanced positive electrodes, poses a serious problem, since this limits the development of asymmetric supercapacitor (SC) devices with a large voltage window and enhanced power-energy characteristics. We fabricate negative SC electrodes with a high capacitance that match the capacitance of advanced positive electrodes at similar active mass loadings, as high as 37?mg?cm^?2. Cyclic voltammetry, impedance spectroscopy, galvanostatic charge-discharge data and the power-energy characteristics of the asymmetric SC device exhibit good electrochemical performance for a voltage window of 1.6?V. Our approach involves the development and application of particle extraction through liquid-liquid interface (PELLI) methods, new extraction mechanisms and efficient extractors to synthesize α-FeOOH and β-FeOOH electrode materials. The use of PELLI allows agglomerate-free processing of powders, which facilitates their efficient mixing with multiwalled carbon nanotubes (MWCNT) and allows improved electrolyte access to the particle surface. Experiments to determine the properties of FeOOH-MWCNT composites provided insight into the influence of the electrode material and the structure of extractor molecules on the composite properties. The highest capacitance of 5.86?F?cm^?2 for negative electrodes and low impedance were achieved using α-FeOOH-MWCNT composites and a 16-phosphonohexadecanoic acid (PHDA) extractor. This extractor allows adsorption on particles, not only at the liquid-liquid interface, but also in the bulk aqueous phase and can potentially be used as a capping agent for particle synthesis and as an extractor in the PELLI method.     

Microwave dielectric properties of ultra-low loss Li2MgTi0.7(Mg1/3Nb2/3)0.3O4 ceramics sintered at low temperature by LiF addition

In this work, ultra-low loss Li₂MgTi_0.7(Mg_1/3Nb_2/3)_0.3O₄ ceramics were successfully prepared via the conventional solid-state method. X-ray photoelectron spectroscopy (XPS), thermally stimulated depolarization current (TSDC) and bond energy were used to determine the distinction between intrinsic and extrinsic dielectric loss in (Mg_1/3Nb_2/3)⁴⁺ ions substituted ceramics. The addition of (Mg_1/3Nb_2/3)⁴⁺ ions enhances the bond energy in unit cell without changing the crystal structure of Li₂MgTiO₄, which results in high Q·f value as an intrinsic factor. The extrinsic factors such as porosity and grain size influence the dielectric loss at lower sintering temperature, while the oxygen vacancies play dominant role when the ceramics densified at 1400?°C. The Li₂MgTi_0.7(Mg_1/3Nb_2/3)_0.3O₄ ceramics sintered at 1400?°C can achieve an excellent combination of microwave dielectric properties: ε_r =?16.19, Q·f?=?160,000?GHz and τ_f =??3.14?ppm/°C. In addition, a certain amount of LiF can effectively lower the sintering temperature of the matrix, and the Li₂MgTi_0.7(Mg_1/3Nb_2/3)_0.3O₄-3?wt% LiF ceramics sintered at 1100?°C possess balanced properties with ε_r?=?16.32, Q·f?=?145,384?GHz and τ_f =??16.33?ppm/°C.     

Tuning of ferrimagnetic nature and hyperfine interaction of Ni2+ doped cobalt ferrite nanoparticles for power transformer applications

Ferrites may contain single domain particles which gets converted into super-paramagnetic state near critical size. To explore the existence of these characteristic feature of ferrites, we have performed magnetization(M-H loop) and Mössbauer spectroscopic studies of Ni²⁺ substitution effect in Co_1-xNi_xFe₂O₄ (where x?=?0, 0.25, 0.5, 0.75 and 1) nanoparticles were fabricated by solution combustion route using mixture of carbamide and glucose as fuels for the first time. As prepared samples exhibit spinel cubic structure with lattice parameters which decreases linearly with increase in Ni²⁺ concentration. The M-H loops reveals that saturation magnetization(M_s), coercive field(H_c) remanence magnetization(M_r) and magnetron number(η_B) decreases significantly with increasing Ni²⁺ substitution. The variation of saturation magnetization has been explained on the basis of Neel's molecular field theory. The coercive field(H_c) is found strongly dependent on the concentration of Ni²⁺ and decrease of coercivity suggests that the particles have single domain and exhibits superparamagnetic behavior. The Mössbauer spectroscopy shows two ferrimagnetically relaxed Zeeman sextets distribution at room temperature. The dependence of Mössbauer parameters such as isomer shift, quadru pole splitting, line width and hyperfine magnetic field on Ni²⁺ concentration have been discussed. Hence our results suggest that synthesized materials are potential candidate for power transformer application.     

Electromechanical analytical model of shape memory alloy based tunable cantilevered piezoelectric energy harvester

International Journal of Mechanics and Materials in Design - The resonant frequency of electromechanical energy harvester should be tuned to ambient frequency so as to maximize the harvester power....     

Studying the Effect of Cobalt Doping on Optical and Magnetic Properties of Zinc Oxide Nanoparticles

Silicon - Nano-crystalline powders of Zn1−xCoxO with $\left (0.0\le x\le 0.07 \right )$ have been synthesized by sol-gel method. X-ray diffraction patterns of the prepared samples confirm the...     

Long-Term Changes in the Course of Ice Phenomena on the Oder River along the Polish–German Border

Ice phenomena are a major component of the hydrological regime of east-central and northern European rivers. However, their occurrence disturbs inland water transportation, particularly affecting the major rivers of the Central European Plain that are part of Europe’s international waterways. The Oder is one of these rivers, and is located on the boundary between the much warmer and the much colder part of the temperate climatic zone. This makes the course of ice phenomena on the river difficult to predict. The main purpose of this work is to document and analyse the dynamic of changes occurring for over 60 years (1956–2015) in the ice phenomena of a river that demonstrates a transitional ice regime. It was found that the duration of all ice phenomena decreased (by up to 0.58 days·year^?1) and so did the duration of ice cover (by up to 0.46 days·year^?1). The rates and trends of the two parameters were, however, different in different parts of the lower stretch of the river. This fact is especially important in the context of climate changes whose characteristics include an increased incidence of extreme weather situations, both meteorological and hydrological. There was also found to be a strong correlation (R² from 0.69 to 0.81) between the duration of ice phenomena and the mean air temperature in winter (December to February) and a much weaker correlation between the duration of ice phenomena and the NAO index (R² from 0.42 to 0.48). Such a little correlation of ice phenomena with NAO is likely to result from the pollution of the Oder River (in particular in the second half of the twentieth century) and icebreaking operations on the river.