Insights into Hydration Dynamics and Cooperative Interactions in Glycerol-Water Mixtures by Terahertz Dielectric Spectroscopy.

We report relaxation dynamics of glycerol-water mixtures as probed by megahertz-to-terahertz dielectric spectroscopy in a frequency range from 50 MHz to 0.5 THz at room temperature. The dielectric relaxation spectra reveal several polarization processes at the molecular level with different time constants and dielectric strengths, providing an understanding of the hydrogen-bonding network in glycerol-water mixtures. We have determined the structure of hydration shells around glycerol molecules and the dynamics of bound water as a function of glycerol concentration in solutions using the Debye relaxation model. The experimental results show the existence of a critical glycerol concentration of ∼7.5 mol %, which is related to the number of water molecules in the hydration layer around a glycerol molecule. At higher glycerol concentrations, water molecules dispersed in a glycerol network become abundant and eventually dominate, and four distinct relaxation processes emerge in the mixtures. The relaxation dynamics and hydration structure in glycerol-water mixtures are further probed with molecular dynamics simulations, which confirm the physical picture revealed by the dielectric spectroscopy

Novel Electrospun Anatase/Poly(3,4-Ethylenedioxythiophene) Polystyrene Sulfonate-based Li-ion Battery Anodes and their Electrochemical Performances

Among the common batteries, LIBs as one of the pioneers in rechargeable batteries has become an intrinsic part of almost all the electronic devises. However, there are lots of rooms for improvement in terms of safety, working life, and charging pace. Using fibrous electrodes can improve the electrochemical behavior thanks to the enhancement of connection of the electrolyte with active material by increasing voids to facilitate the Li+ transference. Electrospining as a simple, scalable, and cost-effective technique can build up the fibrous electrodes used in LIBs. In this study, for the first time, highly conductive poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) polymer was used as a carrier of electrospun TiO2/CB-based anode. Due to the low viscosity of PEDOT:PSS solution, another carrier polymer with high molecular weight, PEO, was added to electrospinning ink to increase the viscosity and make the electrospinning process practical. A systematic and laborious optimizing work was performed to achieve the homogeneous ink composition and finally fibers with homogeneous particle distribution. The parameters include sonication type and time, PEO/PEDOT:PSS ratio, ink solid ratio, dispersants ratio (DMF/Water), PEO polymer ratio, and PEO molecular weight besides the operational parameters like operational voltage, needle to collector distant, polymer feeding rate and relative humidity. TGA, XRD, RAMAN, FTIR, and FE-SEM techniques were used to characterize the electrodes. After electrode fabrication, electrochemical tests including galvanostatic charge/discharge, cyclic voltammetry, and electrochemical impedance spectroscopy were performed. Presence of PEDOT:PSS assists the anode performance by: i) improving the conductivity and ii) increasing capacity due to the electrochemical activity of the polymer. Not only the achieved areal capacity (1.67 mAh.cm-2) was comparable to the other studies, but also the gravimetric capacity (300 mAh.g-1) was much higher than similar studies. These results are very promising for the next generation electrospun LIB electrodes fabricated using PEDOT: PSS as a binder/carrier

Electrospun nanotubular titania and polymeric interfaces for high energy density li-ion electrodes

In the current study, for the first time, electrospinning of nanotubular structures was developed for Li-ion battery high energy density applications. For this purpose, titania-based nanotubular materials were synthesized and characterized. Before electrospinning with PVDF to obtain a self-standing electrode, the nanotubes were modified to obtain the best charge-transferring structure. In the current study, for the first time, the effects of various thermal treatment temperatures and durations under an Ar-controlled atmosphere were investigated for Li+ diffusion. Electrochemical impedance spectroscopy, cyclic voltammograms, and galvanostatic intermittent titration technique showed that the fastest charge transfer kinetics belongs to the sample treated for 10 h. After optimization of electrospinning parameters, a fully nanotube-embedded fibrous structure was achieved and confirmed by scanning electron microscopy and transmission electron microscopy. The obtained flexible electrode was pressed at ambient and 80 °C to improve the fiber volume fraction. Finally, the galvanostatic charge/discharge tests for the electrospun electrode after 100 cycles illustrated that the hot-pressed sample showed the highest capacity. The polymeric network enabled the omission of metallic current collectors, thus increasing the energy density by 14%. The results of electrospun electrodes offer a promising structure for future high-energy applications

Titania-based freestanding electronically conductive electrospun anodes with enhanced performance for Li-Ion batteries

A conductive composite binder made of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) and polyethylene oxide is utilized in a freestanding electrospun anode, loaded with high amounts of TiO2 for Li-ion batteries (LIBs). This kind of conductive binder polymer which enhances the performance of the cell is used for the first time. To prove the superior characteristics of these PEDOT:PSS binder-based electrodes, the polyvinylidene fluoride-based fibrous anode was also prepared by electrospinning. The electrospinning condition was thoroughly investigated and optimized to reach a robust fully covered fibrous network. The performed electrochemical characterizations show that PEDOT:PSS is electrochemically active and leads to an increased gravimetric capacity up to about 302 mA h/g at 0.2 C. After 100 cycles, PEDOT:PSS-based anodes showed a stable cycling performance which is comparable with commercial titanate-based electrodes. The outstanding performance of the electrodes is attributed to the improved titania loading and the electronically conductive highly porous network which contributed to charge-transfer kinetics. This study shows the potential of PEDOT:PSS as a conductive binder for other active materials in LIBs and self-standing electrodes for lower resistance and higher specific capacity

Electrodeposition of Co-P coatings reinforced by MoS2 + Y2O3 hybrid ceramic nanoparticles for corrosion-resistant applications: influences of operational parameters

During recent decades, Co-P alloy deposits have gained enormous attention primarily owing to their favorable tribomechanical properties; therefore, they are regarded as a potential alternative to hard chromium coatings. The previous works on these systems usually addressed the approaches to improve their tribomechanical characteristics. However, to increase the industrial applications, especially in marine environments, enhancement of corrosion performance should also be considered. The focus of this investigation is improving the corrosion properties of Co-P deposits through the incorporation of hybrid nanoparticles, i.e., MoS2 and Y2O3, as well as controlling the applied current density. Microstructural and morphological aspects of the coatings were characterized by XRD, EDS, FE-SEM, and AFM. While the surface morphology of the Co-P alloy deposit contains several surface defects, MoS2 + Y2O3 reinforced ones are compact and composed of nodular grains. Although there is no change in morphology of the nodular grains with current density variation, the surface roughness increases by increasing the current density from 15 to 25 A dm−2. Influences of both nanoparticle loadings in the electrolyte and the applied current density on the corrosion performance of the deposits are addressed in detail. Overall, the results confirmed that the Co-P-4 g/L MoS2 + Y2O3 nanocomposite coating electrodeposited at 25 A dm−2 has the highest corrosion resistance against 3.5 pct NaCl solution, ≈ 10 times higher than that of Co-P

Insights into Hydration Dynamics and Cooperative Interactions in Glycerol-Water Mixtures by Terahertz Dielectric Spectroscopy.

We report relaxation dynamics of glycerol-water mixtures as probed by megahertz-to-terahertz dielectric spectroscopy in a frequency range from 50 MHz to 0.5 THz at room temperature. The dielectric relaxation spectra reveal several polarization processes at the molecular level with different time constants and dielectric strengths, providing an understanding of the hydrogen-bonding network in glycerol-water mixtures. We have determined the structure of hydration shells around glycerol molecules and the dynamics of bound water as a function of glycerol concentration in solutions using the Debye relaxation model. The experimental results show the existence of a critical glycerol concentration of ∼7.5 mol %, which is related to the number of water molecules in the hydration layer around a glycerol molecule. At higher glycerol concentrations, water molecules dispersed in a glycerol network become abundant and eventually dominate, and four distinct relaxation processes emerge in the mixtures. The relaxation dynamics and hydration structure in glycerol-water mixtures are further probed with molecular dynamics simulations, which confirm the physical picture revealed by the dielectric spectroscopy