Photo-induced electrochemical functionality of the TiO2 nanoscale films

Titanium(IV) oxide semiconducting thin films were deposited in the environment of chemically active plasma by means of the PVD hollow cathode plasma jet sputtering, PVD magnetron sputtering and the PECVD technique (surfatron produced plasma discharge as a jet type). In parallel the sol-gel process carried out in the reverse micelle environment was utilized as a purely chemical procedure. Prepared films were described by a series of characterization methods involving atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and ultraviolet-visible spectroscopy (UV-vis). All layers were tested then for their photo-induced electrochemical properties based on evaluation of polarization curves and corresponding photocurrents. These experiments were carried out in the opto-electrical apparatus supplemented with a system of highly precious spectral filters. The differences among photocurrent values were discussed.     

Sol-Gel Synthesis of Fine Gd2CuO4 Particles: Influence of Synthesis Variables

Fine particles of Gd₂CuO₄ were prepared by a sol-gel reaction of an aqueous solution of metal nitrates in the presence of urea, which leads to high-homogeneity polycrystalline powders of Gd₂CuO₄. We have studied the synthesis conditions, demonstrating the existence of a relationship between the calcination temperature and the heating time needed to attain the pure phase. Gd₂CuO₄ was obtained at temperatures of the order of 650°C, lower than temperatures employed in the conventional ceramic technique. The influence of the [urea]/[salts] ratio and an excess of Cu(II) in the starting solution was also studied and discussed. X-ray powder diffraction, inductively coupled plasma atomic emission spectroscopy (ICPAES), photon correlation spectroscopy (PCS), and transmission electron microscopy (TEM) were used to characterize the Gd₂CuO₄ samples obtained.     

A comparative study on IrO2-Ta2O5 coated titanium electrodes prepared with different methods

The electrodes of IrO₂-Ta₂O₅ coated titanium were prepared using conventionally thermal decomposition procedure and polymer sol-gel (Pechini) method, respectively. The microstructure and electrochemical properties of the electrodes were studied with scanning electron microscope (SEM), energy dispersive X-ray (EDX), atomic force microscope (AFM), potentiodynamic polarization, cyclic voltammetry, electrochemical impedance spectroscopy and accelerated life test. As compared with the electrode formed using the traditional method of thermal decomposition, the oxide electrode prepared by Pechini method presents morphology of higher nano-scale roughness and more uniform surface composition with little precipitates. It also has larger electrochemically active surface area, better electrocatalytic activity for oxygen evolution and higher stability.     

Nanostructured sol-gel coatings doped with cerium nitrate as pre-treatments for AA2024-T3: Corrosion protection performance

Nanostructured hybrid sol-gel coatings doped with cerium ions were investigated in the present work as pre-treatments for the AA2024-T3 alloy. The sol-gel films have been synthesized from tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) precursors. Additionally the hybrid sol was doped with zirconia nanoparticles prepared from hydrolyzed tetra-n-propoxyzirconium (TPOZ). Cerium nitrate, as corrosion inhibitor, was added into the hybrid matrix or into the oxide nanoparticles.The chemical composition and the structure of the hybrid sol-gel films were studied by XPS (X-ray photoelectron spectroscopy) and AFM (atomic force microscopy), respectively. The evolution of the corrosion protection properties of the sol-gel films was studied by EIS (electrochemical impedance spectroscopy), which can provide quantitative information on the role of the different pre-treatments. Different equivalent circuits, for different stages of the corrosion processes, were used in order to model the coating degradation. The models were supported by SEM (scanning electron microscopy) measurements.The results show that the sol-gel films containing zirconia nanoparticles present improved barrier properties. Doping the hybrid nanostructured sol-gel coatings with cerium nitrate leads to additional improvement of the corrosion protection. The zirconia particles present in the sol-gel matrix seem to act as nanoreservoirs providing a prolonged release of cerium ions. The nanostructured sol-gel films doped with cerium nitrate can be proposed as a potential candidate for substitution of the chromate pre-treatments for AA2024-T3.     

锂离子电池正极材料磷酸钒锂制备方法研究进展

单斜结构的磷酸钒锂[Li₃V₂（PO₄）₃]材料与其他锂离子电池正极材料相比具有较高的工作电压（3.0~4.8 V）、良好的离子迁移率和优良的热稳定性,是一种具有竞争优势和发展前景的大功率锂离子电池正极材料,成为了近年来研究的热点。综述了锂离子电池正极材料磷酸钒锂的结构特点及其充放电机理。磷酸钒锂的常用合成方法有碳热还原法、水热法、溶胶-凝胶法及流变相法等,着重阐述了磷酸钒锂的不同合成方法对所制备样品的形貌和电化学性能的影响。分析总结了不同合成方法的改进方法,以改善磷酸钒锂正极材料电子导电性和锂离子扩散系数较低的问题。最后,针对磷酸钒锂正极材料在锂离子电池的应用中所存在的问题展望了该材料未来可能的发展方向和研究热点。指出需要优化材料的制备方法以改善材料的颗粒形貌、提高电子导电率和扩散系数等,进而改善材料的循环性能、倍率性能和充放电性能等;需要改进制备流程、提高实验的安全性、简化反应流程和减少制备成本等,以实现磷酸钒锂正极材料的工业化应用。     

Hydrothermally synthesized FeCo2O4 nanostructures: Structural manipulation for high-performance all solid-state supercapacitors

The exploration of high performance supercapacitors has received emerging the worldwide research interests in satisfying the gradually increased energy consumption. In this paper, we adopt a facile hydrothermal strategy to synthesize ternary FeCo₂O₄ directly on nickel foam. A series of structure such as nanowires, nanoflake@nanowire hetero-structure and hierarchical nanospheres have been achieved via modulating the synthetic time. The morphology and structure of the as-prepared samples are characterized by using scanning electron microscopy and X-ray diffraction spectroscopy. The relationship between the detail processing parameters and electrochemical performance are also revealed by cyclic voltammetry, galvanostatic charge-discharge measurements, cycle stability tests and electrochemical impedance spectroscopy. Notably, the as-prepared nanoflake@nanowire hetero-structure exhibits a high specific capacitance of about 969 F g^?1 at 2 A g^?1 in alkaline aqueous solution and a remarkable cycling stability (91% capacity retention after 2000 cycles). The excellent supercapacitors performance of nanoflake@nanowire hetero-structure can be attributed to the high conductivity, large active area as well as robust architectures that derive from structural synergetic effects. Furthermore, a symmetric all solid-state supercapacitor has been fabricated by using nanoflake@nanowire hetero-structure as both the anode and cathode electrodes. The as-fabricated supercapacitor delivers excellent electrochemical performance. It's anticipated that FeCo₂O₄ would be a promising material for electrochemical energy storage applications.     

Synthesis of C60 Fullerene-Silica Hybrid Nano Structures

We have recently demonstrated a procedure for the synthesis of silica nanometer and micrometer particles under modest conditions. Here we report the synthesis of C₆₀ fullerene-silica hybrid nanometer sized materials via sol-gel processing at neutral pH and under ambient conditions. The C₆₀ fullerene, when functionalized, was water-soluble and also able to facilitate the formation of silica structures from an aqueous silica precursor. This C₆₀ fullerene had similar functionality to the cationically charged polymers, which have been reported earlier to act as catalysts/templates for silicification. The resulting organic-inorganic hybrid was studied using SEM, EDS and UV/Vis spectroscopy. These hybrid materials may have applications in areas such as optical devices, semiconductors, chemical sensors, catalysis and in the medical field. The results presented in this study may be useful in developing a process for the synthesis of novel organic-inorganic nanometer sized materials and for the biomimetic synthesis of silica.     

Synthesis, characterization and electrochemical properties of the V2O5·nH2O/AlO(OH)·nH2O xerogel composite

In this work, we report the synthesis, characterization and electrochemical properties of a new multicomponent material obtained from the polymerization of vanadium pentoxide in an inorganic matrix (alumina xerogel), forming a xerogel composite. The material has been characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, electron microscopy, energy dispersive X-ray spectrometry, cyclic voltammetry and impedance spectroscopy. It was found that the V₂O₅ xerogel is dispersed in the alumina matrix, but its lamellar structure is not strongly affected, thus, its conductivity properties are maintained. Moreover, the electrochemical behaviour of the V₂O₅ xerogel dispersed in the alumina matrix is quite similar to that found for the V₂O₅ xerogel alone and the inorganic matrix leads to stabilization of V₂O₅ xerogel structure.     

Nanostructured silicon sol-gel surface treatments for Al 2024-T3 protection

Current coatings for aircraft corrosion protection are based on chromate surface treatments, primers, and topcoats. One approach to developing a chromate-free surface treatment is through the use of sol-gel materials that interact strongly with both the substrate and the subsequent polymer layers. Results are reported here on a new sol-gel technique using a pre-formed, self-assembled, nano-phase particle (SNAP) sol-gel system. SNAP films have been investigated by infrared spectroscopy, atomic force microscopy, and electrochemical methods. Potentiodynamic polarization and electrochemical impedance spectroscopy demonstrated that the SNAP system generates high quality, defect-free, durable films. Formulation parameters, including crosslink density and coupling agent application, were optimized based on experimental results. Presented at the 78th Annual Meeting of the Federation of Societies for Coatings Technology, on October 18–20, 2000, in Chicago, IL Materials and Manufacturing Directorate, Nonmetallic Materials Division, Coatings Research Group, Wright-Patterson AFB, OH 45433-7750.     

Synergistic effect in structural and supercapacitor performance of well dispersed CoFe2O4/Co3O4 nano-hetrostructures

Herein, we report a facile homogeneous urea – assisted hydrothermal approach for the design of CoFe₂O₄/Co₃O₄ nano hetrostructure. A variation in Co concentration leads to smartly designed composite material namely CFC-11 and CFC-12 where CFC-12 appreciates the benefits of both CoFe₂O₄ and Co₃O₄ nanoparticles. The physico – chemical properties of as developed materials were investigated by X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron microscopy (XPS) and Raman spectroscopy. The specific surface area and pore size distribution was determined by Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halendo (BJH) respectively. Magnetic measurements via. vibrating sample magnetometer (VSM) demonstrate that saturation magnetization decreases with the incorporation of Co₃O₄ antiferromagnetic nanoparticles. To explore the utility of as designed nano-hetrostructures as supercapacitor electrodes, we employed cyclic voltammetry (CV) and electrochemical impedence spectroscopy (EIS) measurements. A high specific capacitance of 761.1?F?g^?1 at 10?mV?s^?1, admirable cyclic durability of 92.2% and a low resistance value obtained from impedence measurements was observed for CFC-12. The favorable performance demonstrates the synergistic effect of CoFe₂O₄ and Co₃O₄ nanoparticles and thus promise an excellent material for energy storage devices.     

PLA-TiO2 nanocomposites: Thermal,morphological, structural,and humidity sensing properties

In this paper, the effect of TiO₂ ceramic nanoparticles on the thermal stability, morphology, molecular mass, structure and electrical properties of the polylactic acid-Titanium dioxide (PLA-TiO₂) composites, aimed for relative humidity (RH) sensing have been reported. PLA-TiO₂ nanocomposites films were developed through a spin coating process. The developed films were characterized by X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and electrochemical impedance spectroscopy analysis (EIS). To investigate the RH-dependent characteristics, the devices were prepared on pre-patterned ITO substrates. The capacitive and resistive response of the nanocomposite films were studied under RH levels ranging from 20–90%. The PLA-TiO₂ nano-sensing films, having modified surface by acetone etching, exhibited superior morphological and electrical performance when compared to PLA-TiO₂ pristine samples.     

Carbon-Coated SnO2 Nanorod Array for Lithium-Ion Battery Anode Material

Carbon-coated SnO₂ nanorod array directly grown on the substrate has been prepared by a two-step hydrothermal method for anode material of lithium-ion batteries (LIBs). The structural, morphological and electrochemical properties were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical measurement. When used as anodes for LIBs with high current density, as-obtained array reveals excellent cycling stability and rate capability. This straightforward approach can be extended to the synthesis of other carbon-coated metal oxides for application of LIBs.     

Novel carbazole/pyridine-based host material for solution-processed blue phosphorescent organic light-emitting devices

3,6-Bis(3,5-di(pyridin-3-yl)phenyl)-9-phenyl-9H-carbazole, a novel host material for solution-processed blue phosphorescent organic light-emitting devices was synthesized by a Suzuki coupling reaction. The optical, electrochemical and thermal properties of this novel crabazole have been characterized. The compound exhibits a high glass-transition temperature (Tg = 161 °C) and high triplet energy (E_T = 2.76 eV). Additionally, atomic force microscopy measurements indicate that high-quality amorphous films of this novel compound can be prepared by spin-coating. Solution-processed blue phosphorescent organic light-emitting devices were obtained using the carbazole as the host material for the phosphorescence emitter iridium(III) bis(4,6-difluorophenylpyridinato)- picolinate and their electroluminescence properties were evaluated.     

Electrochemical performances of poly(3,4-ethylenedioxythiophene)-NiFe2O4 nanocomposite as electrode for supercapacitor

Poly 3,4-ethylenedioxythiophene (PEDOT)-based NiFe₂O₄ conducting nanocomposites were synthesized and their electrochemical properties were studied in order to find out their suitability as electrode materials for supercapacitor. Nanocrystalline nickel ferrites (5-20 nm) have been synthesized by sol-gel method. Reverse microemulsion polymerization in n-hexane medium for PEDOT nanotube and aqueous miceller dispersion polymerization for bulk PEDOT formation using different surfactants have been adopted. Structural morphology and characterization were studied using XRD, SEM, TEM and IR spectroscopy. Electrochemical performances of these electrode materials were carried out using cyclic voltammetry at different scan rates (2-20 mV/s) and galvanostatic charge-discharge at different constant current densities (0.5-10 mA/cm²) in acetonitrile solvent containing 1 M LiClO₄ electrolyte. Nanocomposite electrode material shows high specific capacitance (251 F/g) in comparison to its constituents viz NiFe₂O₄ (127 F/g) and PEDOT (156 F/g) where morphology of the pore structure plays a significant role over the total surface area. Contribution of pseudocapacitance (C_FS) arising from the redox reactions over the electrical double layer capacitance (C_DL) in the composite materials have also been investigated through the measurement of AC impedance in the frequency range 10 kHz-10 mHz with a potential amplitude of 5 mV. The small attenuation (∼16%) in capacitance of PEDOT-NiFe₂O₄ composite over 500 continuous charging/discharging cycles suggests its excellent electrochemical stability.     

Study of the lithium insertion–deinsertion mechanism in nanocrystalline γ-Fe2O3 electrodes by means of electrochemical impedance spectroscopy

Lithium intercalation hosts are a key point to the energy density of the largely used LiCoO₂ (even if of high cost and toxicity) as well as of manganese oxides which have been investigated most extensively. Iron oxides are attractive electrode materials for low-voltage rechargeable lithium batteries from both cost and environmental standpoints. However, search for iron oxides of conventional crystalline structures and micrometer particle sizes as lithium intercalation cathodes, has been greeted with disappointing results. Here we report on the synthesis, characterizations, electrochemical study and electrochemical impedance spectroscopy (EIS) of a nanocrystalline γ-Fe₂O₃ that simultaneously exhibits high lithium insertion capacity and good capacity retention upon cycling. These properties reveal thermodynamics of the nanocrystalline material inherently different from those of its microcrystalline counterpart. Moreover, EIS showed that the intercalation process of the lithium ion occurs according to two processes involving first the reduction of the surface Fe³⁺ with concomitant charge neutralization by Li⁺ ions onto the surface defects of the nanoparticle followed by the reduction of the core Fe³⁺ with insertion of the Li⁺ deeper in the particle.     

Preparation and electrochemical behaviour of {[Ru(bipy)4Cl2Ag]NO3(CHCl3)·6H2O}n obtained from the self-assembly of trans-Ru(bipy)4Cl2 and AgNO3

The synthesis and characterization of Ru(II) and Ru(II)-Ag(I) compounds are described, in view of their potential use in on/off switchable metal-ridge-metal nanodevices. The compound trans-Ru(bipy)₄Cl₂ (1) [bipy, 4,4′-bipyridine] has been prepared by Ru(DMSO)₄Cl₂ (2) (DMSO, dimethylsufoxide) and an excess of bipy. The compound has been fully characterised by physico-chemical, spectroscopic and single crystal X-ray determinations. trans-Ru(bipy)₄Cl₂ has been employed as building block in a self-assembly reaction with AgNO₃ obtaining the inorganic polymer {[Ru(bipy)₄Cl₂Ag]NO₃ (CHCl₃)·6H₂O}_n (3). The self-assembled Ru-Ag compound has been investigated by infrared (IR), ultraviolet (UV) and visible (vis) spectroscopy, elemental analyses, inductively coupled plasma optical emission spectroscopy (ICP-OES) and thermogravimetric analysis coupled with infrared detector (TGA-IR). The electrochemical behaviour of 1 and 3 have been studied by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). 1 and 3 have been tested both as soluble species in non-aqueous solvents and as self-assembled molecules on gold electrodes in aqueous medium. The electrochemical behaviour of the parent compounds trans-Ru(pyz)₄Cl₂ (4) [pyz, pyrazine] and {[Ru(pyz)₄Cl₂Ag]NO₃}_n (5) have been also investigated for comparison.     

An efficient and non-precious anode electrocatalyst of NiO-modified carbon nanofibers towards electrochemical urea oxidation in alkaline media

Non-precious NiO nanoparticles were combined with carbon fibers (CFs) to design the novel electrode material; NiO-CFs. The as-synthesized NiO-CFs material was investigated in terms of Field emission scanning electron microscope (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) surface area, Energy-dispersive X-ray spectroscopy (EDX), UV–vis spectra, Transmission electron microscope (TEM), selected area diffraction (SAED) pattern and X-ray diffraction (XRD) techniques. These analyses indicate the successful synthesis of a nanocomposite of NiO-CFs. Cyclic voltammetry (CV) in addition to chronoamperometric (CA) and electrochemical impedance spectroscopy (EIS) methods were studied in the 3-electrodes system to examine the electrochemical performance of NiO-CFs material for urea oxidation in KOH medium. The synthesized nanocomposite showed improved electrochemical oxidation of urea at various urea concentrations up to 1.5 M. The decreasing of both charge transfer impedance and series resistance indicates the enhanced transfer of electrons in the occurrence of urea which could be related to the high electrochemical performance of NiO-CFs material as an electrocatalyst. The superior electrochemical activity can be due to the assembly of C-structure with NiO nanoparticles during the synthesis steps which enhance electrocatalysis, charge transfer, and structural defects.     

Hollow porous carbon microspheres obtained by the pyrolysis of TiO2/poly(furfuryl alcohol) composite precursors

Disordered carbon materials with high porosity were prepared through the pyrolysis of TiO₂/poly(furfuryl alcohol) composites, obtained by the sol-gel method. The composites were prepared starting from titanium tetra-isopropoxide (TTIP) and furfuryl alcohol (FA) as precursors. Two different synthetic procedures for our composites were carried out, based on the addition of furfuryl alcohol (FA) before or after the TiO₂ nanoparticles formation. Also, different TTIP/FA ratio was tested. The hybrid materials obtained by both synthetic routes were pyrolyzed, under argon flow, at 900 °C producing novel TiO₂/carbon composites. All samples were characterized by XRD, FT-IR, DR-FTIR, Raman spectroscopy and TEM. Results indicated the effective FA polymerization on TiO₂ (anatase) nanoparticles, and polymer conversion to disordered carbon after the pyrolysis, simultaneously with TiO₂ anatase-rutile phase transition. The resulting TiO₂/carbon composites were treated with HF solution aiming the oxide dissolution, yielding an extremely porous carbon material as insoluble fraction. The morphology of these porous carbon materials is strongly dependent on the synthetic route adopted for the composite precursor, varying from carbon foam to highly ordered hollow microspheres.     

General synthesis and morphology control of LiMnPO4 nanocrystals via microwave-hydrothermal route

Olivine structure LiMnPO₄ has been considered as one of the very promising electrodes for lithium-ion batteries because of their low cost, low toxicity and high voltage plateau compared with LiFePO₄. In order to improve the electrochemical performance a key challenge in the field of lithium-ion battery, is to explore and invent suitable synthetic route to control the size and morphology of LiMnPO₄. Here a detailed study exploring the novel route of microwave-hydrothermal (MH) synthesis for successfully obtaining LiMnPO₄ crystals within few minutes is reported and the reaction process discussed in detail. Variation of the synthetic parameters show that a decrease in reactant concentration could lead to LiMnPO₄ nano-platelets orientated in the ac plane with a very high electrochemical performance. The effect of the starting precursor (like, Mn) concentration as a means to tailor LiMnPO₄ electrochemical performance is discussed. The effect of alteration of size, morphology, lattice parameters and crystal structure induced by addition of additives like citric acid (H₃cit) and sodium dodecyl benzene sulfonate (SDBS) is further described and an example of the first reversible discharge of a product treated with H3cit obtained by MH route as high as 89.0 mAh/g, is shown. The general investigation demonstrates that there is a relationship among microwave irradiation condition, crystal structure, morphology and electrochemical performance that can be exploited for the design of next generation lithium batteries.     

A study on the N-, S- and Cl-modified nano-TiO2 coatings for corrosion protection of stainless steel

Nano-titania coatings doped with anions of nitrogen, sulfur and chlorine have been supplied on the surface of 316L stainless steel by a sol-gel process and dip-coating technique. The measurements of XRD, SEM, ATR-IR, Raman and XPS were carried out to characterize the chemical composition and structure for the prepared samples. The corrosion performances of the coating in 0.5 M NaCl were evaluated by electrochemical impedance spectroscopy (EIS) and polarization measurements. According to the measurements of EIS and electrochemical polarization, the N-modified TiO₂ nano-coatings show a highest corrosion resistance among the prepared coatings. It is revealed, from the SEM, XRD and Raman characterizations, that the surface of N-modified TiO₂ nano-coatings are more compact and uniform, relatively well-crystallized and able to act as an optimal barrier layer to metallic substrates. The XPS analysis confirms the presence of low concentration of N element in two forms, atomic β-N (interstitial state) and chemisorbed γ-N₂ on the surface of TiO₂ nano-coatings. It is suggested that the addition of nitrogen is beneficial to improve the compact structure and enhance the hydrophobic property.