Investigation of zinc powder modified by ultrasonic impregnation of rare earth lanthanum

Different lanthanum conversion films coated directly on zinc particles are prepared by ultrasonic impregnation with the variable concentration of lanthanum nitrate solution and the adjusted ultrasonic time to modify zinc powder, and the characterization as well as electrochemical behavior of zinc are analyzed using scanning electron microscopy, energy dispersion spectrometry, potentiodynamic polarization, cyclic voltammetry. The lanthanum conversion films are found to enhance the property of corrosion resistance, suppress the dendritic growth and reduce the capacity loss for zinc electrode made of such modified zinc powder. Furthermore, the particle size of zinc powder immersed in lanthanum nitrate solution becomes thin and slim under the effect of ultrasound, which is beneficial to improve the electrochemical reaction activity of zinc powder at the assurance of high corrosion resistance for zinc electrode.     

A novel method for the modification of zinc powder by ultrasonic impregnation in cerium nitrate solution

This work is devoted to an extensive study of cerium deposits distributed directly on zinc particles by simple impregnation or ultrasonic impregnation for the modification of zinc powder. Meantime, the characterization of modified zinc powder and the influence of ultrasound parameters in the modification process upon the dendritic growth, the corrosion behavior and the cyclic performance of zinc are investigated using scanning electron microscopy, energy dispersion spectrometry, potentiostatic polarization, potentiodynamic polarization and cyclic voltammetry. Compared with simple impregnation, the assistance of ultrasonic irradiation is found to have a significant effect on the sedimentary state and favorable properties of cerium deposits in a protective way. Besides the cyclic voltammetry measurements display that the application of ultrasound also improves the cyclic performance of zinc electrode containing modified zinc powder mainly because the cerium deposits formed under ultrasonic irradiation can greatly hinder the dissolution and diffusion of the oxidation product of zinc in the electrolyte and effectively favor the capacity maintenance of zinc electrode.     

Effects of lithium phosphorous oxynitride film coating on electrochemical performance and thermal stability of graphite anodes

In this study, we investigated the effects of lithium phosphorus oxynitride (LiPON) solid electrolyte thin-film deposition on the electrochemical performance and thermal stability of pristine graphite and carbon-coated graphite composite anodes. The LiPON film was deposited by radio frequency (rf) magnetron sputtering. We studied the thermal stability of the lithiated electrodes when immersed in the presence of a liquid electrolyte by differential scanning calorimetry (DSC).The LiPON thin-film coating suppressed the impedance growth during the cycling process and inhibited the reaction between the lithiated electrode and the electrolyte, thus improving the cycle performance and thermal stability of the graphite electrode. However, for the carbon-coated graphite electrode, the heat evolution below 250 °C decreased, whereas that below 300 °C increased. We attributed this phenomenon to the low thermal stability of the LiPON thin-film coating owing to an exothermic reaction between the LiPON film and the electrolyte that occurs at approximately 290 °C.     

Characterizations of octahedral zinc oxide synthesized by sonochemical method

The ultrasonic reaction of zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine (C₆H₁₂N₄) was investigated by varying the concentration of the reactants, the irradiation time, and the type of sonicator. The morphology, composition, and phase structure of the products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopy. Octahedral zinc oxide (ZnO) micropowders were formed at low concentrations, 0.05 M, of Zn(NO₃)₂·6H₂O and C₆H₁₂N₄ in both lab-made sonicator and commercial ultrasonic bath. However, at concentrations between 0.1 and 1.0 M Zn(NO₃)₂-C₆H₁₂N₄ mainly plate-like zinc hydroxide nitrate hydrate (Zn₅(OH)₈(NO₃)₂(H₂O)₂) resulted with only a small fraction of ZnO, irrespective of the irradiation time employed, highlighting the sensitivity of the system to the concentration of the starting materials. Heat treatment of Zn₅(OH)₈(NO₃)₂(H₂O)₂ at 350 °C in air affords a ZnO phase of irregular morphology. Octahedral ZnO is found to exhibit slightly lower IR absorption and similar UV absorption to that of commercial prismatic hexagonal ZnO, although an extra peak due to small quantities of Zn₅(OH)₈(NO₃)₂(H₂O)₂ is observed.     

Process and performance of hot dip zinc coatings containing ZnO and Ni-P under layers as barrier protection

A new coating system of under layer for hot dip zinc coating was explored as an effective coating for steel especially for application in relatively high aggressive environments. The influence of different barrier layers formed prior to hot dip galvanization was investigated to optimize high performance protective galvanic coatings. The deposition of ZnO and Ni-P inner layers and characteristics of hotdip zinc coatings were explored in this study. The coating morphology was characterized by scanning electron microscope (SEM) analysis. The hot dip zinc coatings containing under layer showed substantial improvement in their properties such as good adhesion, and high hardness. In addition, a decrease in the thickness of the coating layer and an enhancement of the corrosion resistance were found. Open circuit potential (OCP) of different galvanized layers in different corrosive media viz. 5% NaCl and 0.5 M H₂SO₄ solutions at 25 ± 1 °C was measured as a function of time. A nobler OCP was exhibited for samples treated with ZnO and Ni than sample of pure Zn; this indicates a dissolution process followed by passivation due to the surface oxide formation. The high negative OCP can be attributed to the better alloying reaction between Zn and Fe and to the sacrificial nature of the top pure zinc layer.     

Ultrasonic irradiation effect in the impregnation-reduction process of preparing Pt/Nafion NH(4)(+) sensor

A systematic study on the ultrasonic irradiation effect in the impregnation-reduction (I-R) process for preparing a Pt/Nafion electrode was carried out in a flow-injection system of ammonium ion detection. Both the impregnation and the reduction stages were affected by ultrasonic irradiation which increased the sensing currents of electrodes. Moreover, the effect of ultrasonic irradiation was found more significant in the reduction process than in the impregnation process. The relationship between sensing current and power of ultrasonic irradiation was also obtained. The specific active surface area of the Pt/Nafion electrodes were evaluated by the cyclic voltametric technique. Meanwhile, the surfaces of the electrodes were characterized by XRD and SEM.     

Electrochemical capacitance from carbon nanotubes decorated with titanium dioxide nanoparticles in acid electrolyte

The electrochemical activity of an electrode of carbon nanotubes (CNTs) attached with TiO₂ nanoparticles was investigated. A chemical-wet impregnation was used to deposit different TiO₂ particle densities onto the CNT surface, which was chemically oxidized by nitric acid. Transmission electron microscopy showed that each TiO₂ nanoparticle has an average size of 30-50 nm. Nitrogen physisorption measurement indicated that the porosity of CNTs is partially hindered by some titania aggregations at high surface coverage. Cyclic voltammetry measurements in 1 M H₂SO₄ showed that (i) an obvious redox peak can be found after the introduction of TiO₂ and (ii) the specific peak current is proportional to the TiO₂ loading. This enhancement of electrochemical activity was attributed to the fact that TiO₂ particles act as a redox site for the improvement of energy storage. According to our calculation, the electrochemical capacitance of TiO₂ nanocatalysts in acid electrolyte was estimated to be 180 F/g. Charge-discharge cycling demonstrated that the TiO₂-CNT composite electrode maintains stable cycleability of over 200 cycles.     

Spray pyrolysis deposition of ZnO thin films on FTO coated substrates from zinc acetate and zinc chloride precursor solution at different growth temperatures

ZnO thin films were fabricated using zinc chloride and zinc acetate precursors by the spray pyrolysis technique on FTO coated glass substrates. The ZnO films were grown in different deposition temperature ranges varying from 400 to 550 °C. Influences of substrate temperature and zinc precursors on crystal structure, morphology and optical property of the ZnO thin films were investigated. XRD patterns of the films deposited using chloride precursor indicate that (1 0 1) is dominant at low temperatures, while those deposited using acetate precursor show that (1 0 1) is dominant at high temperatures. SEM images show that deposition temperature and type of precursor have a strong effect on the surface morphology. Optical measurements show that ZnO films are obviously influenced by the substrate temperatures and different types of precursor solutions. It is observed that as temperature increases, transmittance decreases for ZnO films obtained using zinc chloride precursor, but the optical transmittance of ZnO films obtained using zinc acetate precursor increases as temperature increases.     

Novel chemical synthetic route and characterization of zinc selenide thin films

Zinc selenide (ZnSe) thin film have been deposited using chemical bath method on non-conducting glass substrate in a tartarate bath containing zinc sulfate, ammonia, hydrazine hydrate, sodium selenosulfate in an aqueous alkaline medium at 333 K. The deposition parameter of the ZnSe thin film is interpreted in the present investigation. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical absorption, electrical measurements, atomic absorption spectroscopy (AAS). The ZnSe thin layers grown with polycrystalline zinc blende system along with some amorphous phase present in ZnSe film. The direct optical band gap ‘E_g’ for the film was found to be 2.81 eV and electrical conductivity in the order of 10⁻⁸(Ω cm)⁻¹ with n-type conduction mechanism.     

Intercalation of lithium ions into bulk and powder highly oriented pyrolytic graphite

The electrochemical reactions of highly oriented pyrolytic graphite (HOPG) bulk and powder electrodes in 1 M LiPF₆ 1:1 EC/DMC solution were investigated and the results show that the intercalation reaction of lithium ion into HOPG electrode occurs only at the edge plane and SEI formation reaction on the basal plane is negligible in comparison with that on the edge plane. The active surface area of HOPG powder electrode could be deduced by comparing the peak area (consumed charge for SEI formation) at potential of 0.5 V on voltammograms with that of bulk HOPG edge electrode. The diffusion coefficients of lithium ion in HOPG bulk layers and in HOPG powder was for the first time measured by use of electrochemical impedance spectra and potential step chronamperameter methods. It was found that the diffusion coefficients of lithium in HOPG were in the range of 10⁻¹¹-10⁻¹² cm² s⁻¹ for the lithium-HOPG intercalation compounds at potentials from 0.2 (vs. Li/Li⁺) to 0.02 V, decreasing with the increase of lithium intercalation degree. A good agreement was obtained between the results from bulk and powder HOPG electrodes by electrochemical impedance spectra method.     

An atypical coordination in hexacyanometallates: Structure and properties of hexagonal zinc phases

In hexacyanometallates, the involved transition metals are usually found with octahedral coordination. The exception corresponds to the hexagonal zinc phases where this metal appears tetrahedrally coordinated to N ends from the CN ligands. Those zinc hexacyanometallates where such atypical coordination appears were identified and for four of them the crystal structure was refined from X-ray diffraction powder patterns using the Rietveld method. Zinc hexacyanoferrates (III), hexacyanocobaltate (III), hexacyanoiridate (III) and the mixed zinc-cesium hexacyanoferrate (II) were found to be dimorphic, cubic (Fm-3m) and hexagonal (R-3c), related to the zinc atom in octahedral or tetrahedral coordination, respectively. In the absence of an exchangeable cation, the hexagonal phases result anhydrous. This last feature was attributed to a low polar character for the pores surface. The Mössbauer spectrum of hexagonal zinc hexacyanoferrate (III) is an unresolved quadrupole splitting doublet (Δ=0.18 mm/s). The iron nucleus is sensing a weak electric field gradient related to a relatively high symmetry for its ligands and charge environment. The IR spectrum appears to be an excellent sensor to identify the coordination for the zinc atom in a given sample. For the tetrahedral coordination, the CN stretching absorption was found at least 8 cm⁻¹ above the frequency observed for this vibration in the octahedral one. For hydrated phases, the crystal water evolves on heating preserving the material porous framework. The temperature at which the material becomes anhydrous parallels the polarizing power of the charge balancing cation sited within the channels. Hexagonal Zn-Cs ferrocyanide becomes anhydrous at 100 °C, while for the Zn-Na analogue a heating close to 200 °C is required. The stability temperature range for the anhydrous phases depends on the nature of the engaged hexacyanometallate anion; the higher stability was observed for hexacyanoferrates (II). Zinc ferricyanide shows the weaker magnetic interaction for the hexagonal modification due to an unfavourable geometry for the overlapping path between the unpaired electrons on the iron(III) atoms. The open 3D porous network is formed by relatively large ellipsoidal cavities, three per cell, communicated through elliptical openings (windows), six per cavity. For dimorphic zinc hexacyanometallates (III), the most compact structure (higher density) corresponds to the hexagonal modification, however, it has the largest cavity windows and cavity (pore) size, and also the higher thermal stability.     

Template-free preparation and characterization of nanocrystalline ZnO in aqueous solution of [EMIM][EtSO4] as a low-cost ionic liquid using ultrasonic irradiation and photocatalytic activity

A fast, template-free, and environmentally benign green route for the preparation of nanocrystalline ZnO in aqueous solution of 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM][EtSO₄], room-temperature ionic liquid (RTIL), via ultrasonic irradiation is proposed. The X-ray diffraction (XRD) studies display that the products are excellently crystallized in the form of wurtzite hexagonal. Energy-dispersive X-ray spectroscopy (EDX) investigations reveal the products are extremely pure. The morphology of as-prepared nanocrystalline ZnO was characterized by scanning electron microscopy (SEM). Diffuse reflectance spectra (DRS) of the products with absorption maxima at 359 nm show blue shift relative to the bulk ZnO with absorption at 384 nm that can be attributed to quantum confinement effect of nanocrystalline ZnO. A possible formation mechanism of the nanocrystalline ZnO using ultrasonic irradiation in aqueous solution of the RTIL is presented. The results demonstrate that photocatalytic activity of the nanocrystalline ZnO prepared in the presence of the RTIL is higher than the prepared sample in water.     

Preparation, characterization and electrochemical property of Sn-Fe-Mo-Al2O3 multi-phase composites

A novel technique has been developed to synthesize Sn-Fe-Mo-Al₂O₃, while nanoscale dispersion of a highly active tin phase was finely distributed in a stable inert multi-phase. The precursor was prepared by co-precipitation method with SnCl₄, FeCl₃, AlCl₃ and (NH₄)₆Mo₇O₂₄ as the raw materials. Sn-Fe-Mo-Al₂O₃ mixture was produced by reducing the precursor with H₂. The product was characterized by X-ray diffraction (XRD), ICP and scanning electron microscopy (SEM). The performance of the electrode was investigated. The Sn-Fe-Mo-Al₂O₃ electrode was found to have an initial charge capacity of over 461 mAh/g, and a reversible volumetric capacity of 2090 mAh/cm³, which is two times larger than that of graphite electrode (800 mAh/cm³). The coulomb efficiency in the first cycle was over 55%, but its cyclability was not improved significantly. In order to enhance the cycle performance, we investigated the anode after heat treated at 270 °C for 12 h. Under the same condition, the first charge-discharge characteristics were almost equivalent to the as-coated anode, and the retention capacity ratio after 20 cycles was improved from 41.1% to 86.5%. The heat-treated Sn-Fe-Mo-Al₂O₃ electrode exhibited better cycle life. The electrochemical reaction of the Sn-Fe-Mo-Al₂O₃ electrode with Li may obey the alloying-dealloying mechanism of Li_xSn(x?4.4) formation in the other tin-based electrodes.     

Efficient passively Q-switched operation of a diode-pumped Nd:GGG laser with a Cr:YAG saturable absorber

The continuous-wave (cw) and passive Q-switching operation of a diode-end-pumped gadolinium gallium garnet doped with neodymium (Nd:GGG) laser at 1062 nm was realized. A maximum cw output power of 6.9 W was obtained. The corresponding optical conversion efficiency was 50.9%, and the slope efficiency was determined to be 51.4%. By using Cr⁴⁺:YAG crystals as saturable absorbers, Q-switching pulse with average output power of 1.28 W, pulse width of 4 ns and repetition rate of 6.2 kHz were obtained. The single-pulse energy and peak power were estimated to be 206 μJ and 51.6 kW, respectively. The conversion efficiency of the output power from cw to Q-switching operation was as high as 84.7%.     

Layered nanocomposite of zinc sulfide covered reduced graphene oxide and their implications for electrocatalytic applications

Herein, we have synthesized zinc sulfide nanospheres (ZnS NPs) encapsulated on reduced graphene oxide (RGO) hybrid by an ultrasonic bath (50 kHz/60 W). The physical and structural properties of ZnS NPs@RGO hybrid were analyzed by TEM, XRD, EIS and EDS. As-prepared ZnS NPs@RGO hybrid was applied towards the electrochemical determination of caffeic acid (CA) in various food samples. The ZnS NPs@RGO hybrid modified electrode (GCE) exhibited an excellent electrocatalytic performance towards caffeic acid detection and determination, when compared to other modified electrodes. Therefore, the electrochemical sensing performance of the fabricated and nanocomposite modified electrode was significantly improved owing to the synergistic effect of ZnS NPs and RGO catalyst. Furthermore, the hybrid materials provide highly active electro-sites as well as rapid electron transport pathways. The proposed electrochemical caffeic acid sensor produces a wide linear range of 0.015–671.7 µM with a nanomolar level detection limit (3.29 nM). In addition, the real sample analysis of the proposed sensor has applied to the determination of caffeic acid in various food samples.     

Effects of seed layer on the structure and property of zinc oxide thin films electrochemically deposited on ITO-coated glass

ZnO films with different morphologies were deposited on the ITO-coated glass substrate from zinc nitrate aqueous solution at 65 °C by a seed-layer assisted electrochemical deposition route. The seed layers were pre-deposited galvanostatically at different current densities (i_sl) ranging from −1.30 to −3.0 mA/cm², and the subsequent ZnO films had been done using the potentiostatic technique at the cathode potential of −1.0 V. Densities of nucleation centers in the seed layers varied with increasing the current density, and the ZnO films on them showed variable morphologies and optical properties. The uniform and compact nanocrystalline ZnO film with (0 0 2) preferential orientation was obtained on seed layer that was deposited under the current density (i_sl) of −1.68 mA/cm², which exhibited good optical performances.     

Study on the electrochemical behavior of vanadium nitride as a promising supercapacitor material

Vanadium nitride (VN) powder was synthesized by calcining V₂O₅ xerogel in a furnace under an anhydrous NH₃ atmosphere at 400 °C. The structure and surface morphology of the obtained VN powder were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The supercapacitive behavior of VN in 1 M KOH electrolyte was studied by means of cyclic voltammetry (CV), constant current charge-discharge cycling (CD) and electrochemical impedance spectroscopy (EIS). The XRD result indicates that the obtained VN belongs to the cubic crystal system (Fm3m [2 2 5]) with unit-cell parameter 4.15 Å. SEM images show the homogeneous surface of the obtained VN. The CV diagrams illustrate the existence of fast and reversible redox reactions on the surface of VN electrode. The specific capacitance of VN is 161 F g⁻¹ at 30 mV s⁻¹. Furthermore, the specific capacitance remains 70% of the original value when the scan rate increases from 30 to 300 mV s⁻¹. CD experiments show that VN is suitable for CD at high current density, and the slow and irreversible faradic reactions exist during the charge-discharge process of the VN electrode. The experimental results indicate that VN is a promising electrode material for electrochemical supercapacitors.     

Improved performance of TiO2 electrodes coated with NiO by magnetron sputtering for dye-sensitized solar cells

TiO₂ electrodes are coated with NiO by DC magnetron sputtering, and their structural, optical and electrochemical performance has been investigated. X-ray diffractometry (XRD), UV-vis spectrophotometry, scanning electron microscopy (SEM), AC impedance, and linear sweep voltammetry (LSV) are used to characterize the TiO₂/NiO electrodes. Their performance is evaluated with a computer controlled electrochemical workstation in combination with three conventional electrodes. The experimental results indicate that the surface modification of TiO₂ electrodes with sputtered NiO reduces trap sites on TiO₂ and improves the electrochemical performance of dye-sensitized solar cells (DSSCs). Sputtering NiO for 7 min, which is about 21 nm thick, on 6.5 μm thick TiO₂ greatly improves the DSSC parameters, and the conversion efficiency increases from 3.21 to 4.16%. Mechanisms of the influence of the NiO coating on electrochemical performance are discussed.     

Synthetic antibacterial agent assisted synthesis of gold nanoparticles: Characterization and application studies

In this study, we report synthesis of water-soluble gold nanoparticles (Au-NPs), having an average diameter of ca. ∼20 nm, using ciprofloxacin (CF) as a reducing/stabilizing agent. The synthesized Au-NPs have been characterized by scanning electron microscopy (SEM), EDX, TEM, UV-visible spectroscopy (UV-vis), X-ray diffraction and cyclic voltammetry. TEM and SEM combined with EDX analysis confirmed that spherical-shaped Au-NPs were formed. UV-vis spectra of the Au-NPs showed two absorption bands corresponding to the capping agent ciprofloxacin and surface plasmon absorption bands at 274 and 527 nm, respectively. The synthesized Au-NPs are used to modify a glassy carbon electrode (GCE) and its electrochemical and electrocatalytic properties are investigated. The Au-NPs modified electrode showed excellent electrocatalytic activity towards the oxidation of methanol at +0.33 V in alkaline solution, which was not observed on the unmodified GCE. Further, electrocatalytic reduction of oxygen was also studied using the Au-NPs modified electrode at lower potential. Here, CF was used as a reducing agent for the preparation of Au-NPs dispersion. This Au-NPs dispersion is highly stable, and can be stored for more than three months in air at room temperature.     

Effects of Ag layer and ZnO top layer thicknesses on the physical properties of ZnO/Ag/Zno multilayer system

Two groups of transparent conductive ZnO/Ag/ZnO, ZAZ, multilayer coatings were successively deposited by direct current (DC) magnetron sputtering. Sputtering was carried out from zinc (Zn) and silver (Ag) metallic targets. The effects of Ag layer thickness and ZnO top layer thickness on the properties of the ZAZ multilayer system were examined using different analytical methods. The influences of the Ag layer thickness and ZnO top layer thickness on structural properties were studied using X-ray diffraction. The thicknesses of ZAZ multilayer system were determined using X-ray reflectometry. A sheet resistance of 2.3 Ω/sq at an Ag layer thickness of 17.7 nm was obtained. The sheet resistance changes slightly with ZnO top layer thickness. The optical properties of the films were analyzed. Both Ag layer thickness and ZnO top layer thickness affect transmittance. The optical constants of the ZAZ multilayer system were calculated from transmittance and reflectance measurements. The figure of merit was applied on the ZAZ coatings and the most suitable films for the application as transparent conductive electrodes were determined.