Dielectric and energy storage properties of barium strontium titanate based glass–ceramics prepared by sol–gel method

Ba_0.6Sr_0.4TiO₃ based glass–ceramics were prepared by sol–gel process. Influences of B–Si–O glass content on the microstructure, dielectric, and energy storage properties of the BST based glass–ceramics have been investigated. Perovskite barium strontium titanate phase was found at annealing temperature 800 °C. A secondary phase Ba₂TiSi₂O₈ was detected and lowered by declining the mole ratio of element Si (from 50 to 25 mol%) in glass additive. Microstructural observation indicated that the microstructure homogeneity can be improved by glass addition till 2 mol%, while worsened by excessive glass concentrations. Due to relatively homogeneous microstructure, the maximum discharged energy density and breakdown strength were also obtained in samples with 2 mol% glass additive, which were found to be 0.553 J/cm³ and 43.2 kv/mm, respectively. Microscopic observation of the breakdown area was performed and the mechanical failure, including the formation and accumulation of micro-cracks during the dielectric breakdown process, was considered to be the main cause of dielectric breakdown. Results of the charging and discharging energy densities show that the BST based glass–ceramics prepared by sol–gel method has a potential for pulse power applications.     

One-pot synthesis of porous nickel–manganese sulfides with tuneable compositions for high-performance energy storage

Mixed-metal compounds, especially for the sulfides, have been investigated as a very attractive type of electroactive materials for supercapacitors. In this work, we demonstrate nickel?manganese (Ni?Mn) sulfides are very attractive for supercapacitors with promising electrochemical performance. The Ni?Mn sulfides with different Ni to Mn ratios have been synthesized via a facile one-pot hydrothermal method, which show a similar structure of interconnected particles and are very porous in microstructure. And then, the Ni?Mn sulfides are investigated by three-electrode measurements and demonstrate strong synergy between Ni and Mn. The Ni?Mn sulfide with a Ni to Mn ratio of 2:1 demonstrates superior performance of 1068?F?g^?1 at 1?A?g^?1. Lastly, The Ni?Mn sulfide with a Ni to Mn ratio of 2:1 are used as positive electrode for two-electrode test, and the asymmetric supercapacitor shows both high energy and power densities combined with excellent cycling stability. Our work demonstrates that the Ni?Mn sulfides are also very electrochemical active for supercapacitors and their performance can be tuned by changing the Ni to Mn ratio.

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Nd-doped barium titanate ceramics with various Ti/Ba ratios prepared by sol-gel method

The Nd-doped BaTiO3 nanocrystalline powders and ceramics with different Ti/Ba ratios were prepared by sol-gel method. Phases and microstructures of the Nd-doped BaTiO3 based powders and ceramics were characterized by XRD, SEM and TEM methods. The results revealed that the powders synthesized by sol-gel method were nanometer scale (30-60 nm) and were mainly composed of cubic BaTiO3 with a small amount of BaCO3. After sintering at high temperature, both cubic BaTiO3 and BaCO3 were transformed into tetrahedron BaTiO3 phase. The dielectric properties of the ceramics were also determined and the influence of Ti/Ba ratio on the dielectric properties was discussed. The Tc did not change with the variation of Ti/Ba ratio, while theεmax increased firstly and then decreased. The excess TiO2 is benefit for the modification of ceramics' microstructure and dielectric properties.     

A novel nanocomposite matrix based on graphene oxide and ferrocene-branched organically modified sol–gel/chitosan for biosensor application

A novel platform for the fabrication of a glucose biosensor was successfully constructed by entrapping glucose oxidase (GOD) in a ferrocene (Fc)-branched organically modified silica material (ormosil)/chitosan (CS)/graphene oxide (GO) nanocomposite. The morphology, structure, and electrochemistry of the nanocomposite were characterized by transmission electron microscopy, X-ray powder diffraction, UV–vis spectroscopy, Fourier transform infrared spectroscopy, and electrochemical techniques. Results demonstrated that the proposed electrochemical platform not only provided an excellent microenvironment to maintain the bioactivity of the immobilized enzyme, but also effectively prevented the leakage of both the enzyme and mediator from the matrix and retained the electrochemical activity of Fc. Furthermore, dispersing GO within the Fc-branched ormosil/CS matrix could significantly improve the stability of GO and make it exhibit a positive charge, which was more favorable for the further immobilization of biomolecules, such as GOD, with higher loading. Moreover, it could also improve the conductivity of the matrix film and facilitate the electron shuttle between the mediator and electrode. Under optimal conditions, the designed biosensor to glucose exhibited a wide and useful linear range of 0.02 to 5.39 mM with a low detection limit of 6.5 μM. The value of K _M ^app was 4.21 mM, indicating that the biosensor possesses higher biological affinity to glucose. The present approach could be used efficiently for the linkage of other redox mediators and immobilize other biomolecules in the process of fabricating novel biosensors.     

CuO–Fe2O3 nanoparticles embedded onto reduced graphene oxide nanosheets: a high-performance nanocomposite anode for Li-ion battery

Journal of Solid State Electrochemistry - The development of safe, fast charging, and long-lasting Li-ion batteries has been taking major steps forward through novel combinations of nanomaterials....     

C-PCM based calculation of energy profiles for proton transfer in phosphorus-containing acid–N,N-dimethylformamide complexes

Proton transfer along the hydrogen bond in complexes of DMF with Н₃РО₄, Н₃РО₃, СН₃Н₂РО₃, and their dimers has been investigated by the B3LYP/6-31++G** method in combination with the C-PCM model. When the О_acid···О_DMF distance (R) in the scanning procedure is not fixed, the energy profile in all cases has a single well. When this distance is fixed, there can be a proton transfer in all of the complexes in the gas phase at R > 2.6 Å; if solvation is taken into account, proton transfer can take place at R > 2.4 Å (R > 2.5 Å for DMF complexes with СН₃Н₂РО₃ and its dimer). The height of the energy barrier to proton transfer increases with increasing R. Proton transfer is energetically most favorable in the DMF–phosphoric acid complexes. The structural and energetic characteristics of the hydrogen-bonded complexes calculated on the basis of the solvation model are compared with the same parameters for the complexes in the gas phase.     

CuO/NiOx thin film–based photocathodes for photoelectrochemical water splitting

Journal of Solid State Electrochemistry - Copper oxides are considered to be very promising materials for promoting a hydrogen evolution reaction (HER). However, some CuO features, such as the...     

Porous electrospun nanocomposite mats based on chitosan–cellulose nanocrystals for wound dressing: effect of surface characteristics of nanocrystals

Randomly oriented fiber mats of chitosan–polyethylene oxide matrix reinforced with cellulose nanocrystals (CNCs) were prepared by electrospinning technique. The cellulose nanocrystals used were isolated using hydrochloric acid (CNC_HCl) or sulphuric acid (\({\text{CNC}}_{{{\text{H}}_{ 2} {\text{SO}}_{ 4} }}\)) and the concentration of CNCs was 50 wt% in the electrospun mats. The surface characteristics of the nanocrystals were found to affect the dispersion, viscosity, conductivity and zeta-potential of the respective spinning solutions and resulted in better spinnability, homogeneity as well as crosslinking of CNC_HCl based nanocomposite fiber mats compared to \({\text{CNC}}_{{{\text{H}}_{ 2} {\text{SO}}_{ 4} }}\) ones. The microscopy studies showed that the diameter of the electrospun fibers decreased with the inclusion of both types of nanocrystals and that crosslinking decreased the porosity of the mats. The tensile strength and tensile modulus of the mats increased with the addition of nanocrystals and increased further for the CNC_HCl based mats (58 MPa, 3.1 GPa) after crosslinking. The as-spun CNC_HCl based mats had average pore diameters of 1.6 μm and porosity of 38 %. The water vapor permeability and the O₂/CO₂ transmission increased with the addition of CNC_HCl. The used nanocrystals as well as electrospun mats showed non-cytotoxic impact on adipose derived stem cells (ASCs), which was considered favorable for wound dressing.     

Synergistic enhancement of vinyltriethoxysilane and layered Mg–Al double hydroxide on the tracking and erosion resistance of silicone rubber

It is of great significance and challenge to efficiently improve the tracking and erosion resistance of silicone rubber along with the growing requirements in the field of outdoor high voltage insulation. In this work, we herein proposed an effective way to address this issue by incorporating vinyltriethoxysilane (ViTES) and layered Mg–Al double hydroxide (LDH) into high temperature vulcanized silicone rubber (HTVSR). ViTES/LDH notably enhanced the tracking and erosion resistance of HTVSR. With addition of 3.33 phr ViTES and 5.00 phr LDH, the anti-tracking performance of HTVSR reached the 1A 4.5 level, and the eroded mass was merely 0.3%. The results of scanning electron microscopy and equilibrium swelling showed that ViTES substantially improved the interfacial interaction between HTVSR and LDH and the crosslinking density of HTVSR, and enhanced the dispersion of LDH sheets in the HTVSR matrix. The possible synergistic suppression mechanism of ViTES/LDH on the tracking and erosion of HTVSR was further studied and demonstrated by the plasma irradiation analysis, thermogravimetry and thermogravimetry-Fourier transform infrared spectrometry. It was indicated that under the high voltage arcing discharge, LDH facilitated the formation of a dense barrier layer consisting of bimetal mixed oxides on the HTVSR surface, exerting outstanding lamellar barrier effect. The further degradation and the generation as well as development of electrical tracking were efficiently suppressed. Our findings provided a new approach to fabricate silicone rubber with excellent tracking and erosion resistance.     

Novel core–shell SDC/amorphous Na2CO3 nanocomposite electrolyte for low-temperature SOFCs

Novel core–shell SDC (Ce_0.8Sm_0.2O_1.9)/amorphous Na₂CO₃ nanocomposite was prepared for the first time. The core–shell nanocomposite particles are smaller than 100 nm with amorphous Na₂CO₃ shell of 4–6 nm in thickness. The nanocomposite electrolyte shows superionic conductivity above 300 °C, where the conductivity reaches over 0.1 S cm⁻¹. Such high conductive nanocomposite has been applied in low-temperature solid oxide fuel cells (LTSOFCs) with an excellent performance of 0.8 W cm⁻² at 550 °C. A new potential approach of designing and developing superionic conductors for LTSOFCs was presented to develop interface as ‘superionic highway’ in two-phase materials based on coated SDC.     

Microwave-assisted sol-gel synthesis of CeO2–NiO nanocomposite based NO2 gas sensor for selective detection at lower operating temperature

The progress in the development of gas sensors has considerably grown using some novel nanomaterials of metal, metal oxide and composite. In the current study, we intended and evaluated the properties of nanomaterials like CeO₂, NiO, and CeO₂–NiO composite and its application as NO₂ gas sensor. Sensing of low concentration of NO₂ gas at optimum functional temperature was succeeded using CeO₂–NiO nanocomposites (NCs) film. The working temperature ranges in between 100 and 225 ?°C. Highly crystalline nanomaterials (CeO₂, NiO and CeO₂–NiO) have been prepared by applying microwave-assisted sol-gel route. The as-prepared nanomaterials are characterized for their structure, size, morphology and constitution by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis. XRD studies of nanoparticles reveal the formation of nanoscale CeO₂ and NiO with crystallite size 26, 23 ?nm, respectively. Both are having a face centered cubic structure. The nanocomposite (NC) Ce:Ni ?= ?60:40 has crystallite size of 13 ?nm. XRD study of NCs shows assimilation of Ni metal into the ceria and proves physical similarities of two phases. It can be observed from SEM that prepared NC has a porous surface which enables more surface active sites for adsorbing oxygen. The optical properties are measured with the help of UV–Vis. Spectroscopy. Optical band gaps of 3.19, 3.41 and 2.9 ?eV were observed for CeO_2, NiO nanoparticles (NPs) and CeO₂–NiO NC, respectively. Gas sensing properties state that the NC material shows a higher gas response % of 67.34% for NO₂ gas (25 ?ppm) at comparatively low operating temperature (125 ?°C). It gives response time as (～28 ?s) and the recovery (～54 ?s). NiO incorporation in CeO₂ results in a decline of operating temperature of NC and improves the sensing features.     

Sol–gel-based silver nanoparticles-doped silica – Polydiphenylamine nanocomposite for micro-solid-phase extraction

A nanocomposite of silica-polydiphenylamine doped with silver nanoparticles (Ag–SiO₂-PDPA) was successfully synthesized by the sol–gel process. For its preparation, PDPA was mixed with butanethiol capped Ag nanoparticles (NPs) and added to the silica sol solution. The Ag NPs were stabilized as a result of their adsorption on the SiO₂ spheres. The surface characteristic of nanocomposite was investigated using scanning electron microscopy (SEM). In this work the Ag–SiO₂-PDPA nanocomposite was employed as an efficient sorbent for micro-solid-phase extraction (μ-SPE) of some selected pesticides. An amount of 15 mg of the prepared sorbent was used to extract and determine the representatives from organophosphorous, organochlorine and aryloxyphenoxy propionic acids from aqueous samples. After the implementation of extraction process, the analytes were desorbed by methanol and determined using gas chromatography–mass spectrometry (GC–MS). Important parameters influencing the extraction and desorption processes such as pH of sample solution, salting out effect, type and volume of the desorption solvent, the sample loading and eluting flow rates along with the sample volume were experimentally optimized. Limits of detection (LODs) and the limits of quantification (LOQs) were in the range of 0.02–0.05 μg L⁻¹ and 0.1–0.2 μg L⁻¹, respectively, using time scheduled selected ion monitoring (SIM) mode. The relative standard deviation percent (RSD %) with four replicates was in the range of 6–10%. The applicability of the developed method was examined by analyzing different environmental water samples and the relative recovery (RR %) values for the spiked water samples were found to be in the range of 86–103%.     

Molten salt synthesis of α-MnO2/Mn2O3 nanocomposite as a high-performance cathode material for aqueous zinc-ion batteries

Thanks to low cost,high safety,and large energy density,aqueous zinc-ion batteries have attracted tremendous interest worldwide.However,it remains a challenge to develop high-performance cathode materials with an appropriate method that is easy to realize massive production.Herein,we use a molten salt method to synthesize nanostructured manganese oxides.The crystalline phases of the manganese oxides can be tuned by changing the amount of reduced graphene oxide added to the reactant mixture.It is found that the α-MnO₂/Mn₂O₃ nanocomposite with the largest mass ratio of Mn₂O₃ delivers the best electrochemical performances among all the products.And its rate capability and cyclability can be significantly improved by modifying the Zn anode with carbon black coating and nanocellulose binder.In this situation,the nanocomposite can deliver high discharging capacities of 322.1 and 213.6 mAh g^-1 at 0.2 and 3 Ag^-1,respectively.After 1000 cycles,it can retain 86.2% of the capacity at the 2 nd cycle.Thus,this nanocomposite holds great promise for practical applications.     

Preparation of yolk-shell sulfur/carbon nanocomposite via an organic solvent route for lithium–sulfur batteries

A yolk-shell sulfur/carbon (S/C) composite for the cathode of lithium–sulfur batteries was successfully prepared by an accessible method with tetrahydrofuran as solvent. The as-prepared composites are characterized by thermal gravimetric, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption and desorption. In this composite, sulfur particle is encapsulated in the carbon shell even entering into the micropores of carbon Bp2000. The electrochemical performance of the S/C composites is evaluated. The results indicate that the S/C composite with 50 wt% sulfur content shows good reversibility, excellent rate capability, and slow degradation. It delivers an initial capacity of 784.4 mAh g^?1 (based on sulfur weight) and preserves at 598.3 mAh g^?1 after 195 cycles at 1C. It achieves a high-capacity retention of 76.27 % from the 5th to 200th cycle, and as high as 91.19 % during the latter 150 cycles. The improvement is mainly attributed to the favorable structure of the S/C composite, in which the carbon cannot only facilitate transport of electrons and Li⁺ ions but also trap polysulfides and retard the shuttle effect during charge/discharge process.     

Designer uniform Li plating/stripping through lithium–cobalt alloying hierarchical scaffolds for scalable high-performance lithium-metal anodes

Lithium metal anodes are of great interest for advanced high-energy density batteries such as lithiumair, lithium-sulfur and solid-state batteries, due to their low electrode potential and ultra-high theoretical capacity. There are, however, several challenges limiting their practical applications, which include low coulombic efficiency, the uncontrollable growth of dendrites and poor rate capability. Here, a rational design of 3D structured lithium metal anodes comprising of in-situ growth of cobalt-decorated nitrogen-doped carbon nanotubes on continuous carbon nanofibers is demonstrated via electrospinning.The porous and free-standing scaffold can enhance the tolerance to stresses resulting from the intrinsic volume change during Li plating/stripping, delivering a significant boost in both charge/discharge rates and stable cycling performance. A binary Co-Li alloying phase was generated at the initial discharge process, creating more active sites for the Li nucleation and uniform deposition. Characterization and density functional theory calculations show that the conductive and uniformly distributed cobalt-decorated carbon nanotubes with hierarchical structure can effectively reduce the local current density and more easily absorb Li atoms, leading to more uniform Li nucleation during plating. The current work presents an advance on scalable and cost-effective strategies for novel electrode materials with 3D hierarchical microstructures and mechanical flexibility for lithium metal anodes.     

Plasmonic CsPbBr3–Au nanocomposite for excitation wavelength dependent photocatalytic CO2 reduction

The optoelectronic performance of CsPbBr_3 nanocrystal(NC) has been dramatically limited by the severe charge carrier recombination and its narrow light absorption range,which are anticipated to be resolved via coupling with plasmonic Au nanoparticle(NP).In view of this,CsPbBr_3-Au nanocomposite is fabricated and further employed as a concept model to study the electronic interaction between perovskite NC and Au NP for the first time.It has been found that the excitation-wavelength dependent carrier transfer behavior exists in CsPbBr_3-Au nanocomposite.Upon illumination with visible light(λ>420 nm),photo-generated electrons in CsPbBr_3 can inject into Au with an electron injection rate and efficiency of 2.84×10~9 s^-1 and 78%,respectively.The boosted charge separation is further translated into a 3.2-fold enhancement in CO_2 photocatalytic reduction activity compared with pristine CsPbBr_3.On the other hand,when solely exciting Au NP with longer wavelength light(λ>580 nm),the localized surface plasmon resonance(LSPR) induced hot electrons in Au NPs can transfer to CsPbBr_3 NC and further participate in photocatalytic reaction towards CO_2 reduction.The present study provides new insights into preparing plasmonic nanostructure to enhance the performance of perovskite based optoelectronic devices.