Annealing temperature-dependent structural and electrical properties of (Ta2O5)1-x - (TiO2)x thin films,x ≤ 0.11

(Ta₂O₅)_1-x- (TiO₂)_x (TTO_x) thin films, with x = 0, 0.03, 0.06, 0.08, and 0.11, were deposited using magnetron direct current (DC) sputtering method onto the P/boron-silicon (1 0 0) substrates by varying areas of Tantalum and Titanium metallic targets, in oxygen environment at ambient temperature. The as-deposited thin films were annealed at temperatures ranging from 500 to 800 °C. Generally, the formation of the Ta₂O₅ structure was observed from the X-ray diffraction measurements of the annealed films. The capacitance of prepared metal– oxide– semiconductor (MOS) structures of Ag/TTO_x/p-Si was measured at 1 MHz. The dielectric constant of the deposited films was observed altering with varying composition and annealing temperature, showing the highest value 71, at 1 MHz, for the TTO_x films, x = 0.06, annealed at 700 °C. With increasing annealing temperature, from 700 to 800 °C, the leakage current density was observed, generally decreasing, from 10^?5 to 10^?8 A cm^?2, for the prepared compositions. Among the prepared compositions, films with x = 0.06, annealed at 800 °C, having the observed value of dielectric constant 48, at 1 MHz; and the leakage current density 2.7 × 10^?8 A cm^?2, at the electric field of 3.5 × 10⁵ V cm^?1, show preferred potential as a dielectric for high-density silicon memory devices.     

Manganese oxide nanocomposites with improved surface area prepared by one-pot surfactant route for electro catalytic and biosensor applications

Braunite phase manganese oxide is naturally available in manganese–silicate rocks with minor amount of silicate content. New synthetic route is attempted to prepare the manganese oxide nanoparticle and silica incorporated manganese oxide nanocomposite in the present study. XRD patterns reveal the braunite phase formation for as synthesized manganese oxide nanocomposite and silica incorporated MnO₂ nanocomposite materials. Improved BET surface area values are achieved by one step surfactant assisted method (i.e., 82 and 151 m²/g) compared to conventional route prepared manganese oxide nanomaterial. Flaky pastry type morphology was observed for as synthesized Si–MnO₂ nanocomposites. Cyclic voltammetry studies predict the electrocatalytic activity of manganese oxide nanoparticle and Si–MnO₂ nanocomposite in presence of electroactive redox couple. Si–MnO₂ nanocomposite modified glassy carbon (GC) electrode shows the effective electroactive response in presence of Fe²⁺/Fe³⁺ redox couple at 0.69 V with current density of 0.343 × 10⁻⁵ A/cm² compared to manganese oxide nanoparticle modified GC electrode. The biosensor responses for ascorbic acid have been tested in the present study and manganese oxide nanoparticle modified GC electrode shows effective response at low concentration of (1 × 10⁻⁵ M) ascorbic acid in phosphate buffer solution. Manganese oxide nanoparticle modified electrode shows the better response with current density value of 0.115 × 10⁻⁵ A/cm² compared to Si–MnO₂ nanocomposite.     

Composite Electrodes for Electrochemical Supercapacitors

Manganese dioxide nanofibers with length ranged from 0.1 to 1 μm and a diameter of about 4–6 nm were prepared by a chemical precipitation method. Composite electrodes for electrochemical supercapacitors were fabricated by impregnation of the manganese dioxide nanofibers and multiwalled carbon nanotubes (MWCNT) into porous Ni plaque current collectors. Obtained composite electrodes, containing 85% of manganese dioxide and 15 mass% of MWCNT, as a conductive additive, with total mass loading of 7–15 mg cm⁻², showed a capacitive behavior in 0.5-M Na₂SO₄ solutions. The decrease in stirring time during precipitation of the nanofibers resulted in reduced agglomeration and higher specific capacitance (SC). The highest SC of 185 F g⁻¹ was obtained at a scan rate of 2 mV s⁻¹ for mass loading of 7 mg cm⁻². The SC decreased with increasing scan rate and increasing electrode mass.     

Composite electrodes for electrochemical supercapacitors

Manganese dioxide and Ag-doped manganese dioxide powders were prepared by a chemical precipitation method using KBH₄ as a reducing agent. The powders were studied by X-ray analysis, thermogravimetry, and electron microscopy. Composite electrodes for electrochemical supercapacitors (ES) were fabricated by impregnation of slurries of the precipitated powders and carbon black into porous nickel foam current collectors. In the composite electrodes, carbon black nanoparticles formed a secondary conductivity network within the nickel foam cells. Obtained composite electrodes, containing manganese dioxide and 20 wt% carbon black with total mass loading of 50 mg cm⁻², showed a capacitive behavior in the 0.5 M Na₂SO₄ solutions. The capacitive behavior of the composite electrodes can be improved by mixing of manganese dioxide and carbon black in solutions or using Ag-doped manganese dioxide powders. The highest specific capacitance (SC) of 150 F g⁻¹ was obtained at a scan rate of 2 mV s⁻¹. The electrodes showed good cycling behavior with no loss in SC during 1,000 cycles.     

Electrochemical preparation and properties of nanostructured Co3O4 as supercapacitor material

Nanostructured Co₃O₄ was prepared via a simple two-step process: cathodic electrodeposition of cobalt hydroxide from additive free nitrate bath and then heat treatment at 400 °C for 3 h. The prepared oxide product was characterized by powder X-ray diffraction, infrared spectroscopy, surface area measurement, scanning electron microscopy, and transmission electron microscopy. Morphological characterization showed that the oxide product was composed of porous nanoplates, and BET measurement displayed that the oxide plates have the average pore diameter and the surface area of 4.75 nm and 208.5 m² g⁻¹, respectively. The supercapacitive performance of the nanoplates was evaluated using cyclic voltammetry and charge–discharge tests. A specific capacitance as high as 393.6 F g⁻¹ at the constant current density of 1 A g⁻¹ and an excellent capacity retention (96.5% after 500 charge–discharge cycles) was obtained. These results indicate that Co₃O₄ nanoplates can be recognized as high-performance electrode materials.     

Study of electrochemical properties and the charge/discharge mechanism for Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript>/MnO<Subscript>2</Subscript>-AC hybrid supercapacitor

Spinel Li₄Mn₅O₁₂ was prepared by a sol–gel method. The manganese oxide and activated carbon composite (MnO₂-AC) were prepared by a method in which KMnO₄ was reduced by activated carbon (AC). The products were characterized by XRD and FTIR. The hybrid supercapacitor was fabricated with Li₄Mn₅O₁₂ and MnO₂-AC, which were used as materials of the two electrodes. The pseudocapacitance performance of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor was studied in various aqueous electrolytes. Electrochemical properties of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the hybrid supercapacitor has electrochemical capacitance performance. The charge/discharge test showed that the specific capacitance of 51.3 F g⁻¹ was obtained within potential range of 0–1.3 V at a charge/discharge current density of 100 mA g⁻¹ in 1 mol L⁻¹ Li₂SO₄ solution. The charge/discharge mechanism of Li₄Mn₅O₁₂ and MnO₂-AC was discussed.     

Electrochemical characteristics of manganese oxide electrodes prepared by an immersion technique

In order to control the amount of manganese oxide coated onto a graphite surface, immersion durations were varied. A maximum capacitance of 490 mF cm⁻² was obtained in 0.5 M NaCl and using an immersion time of 20 min and a current of 1 mA. In addition, for the manganese oxide electrode, the lower the current, the higher the capacitance and the higher the immersion time, the higher the resistance. Furthermore, the chronopotentiometric (CP) charge–discharge curves were symmetrical and featured similar isosceles triangles, which demonstrate high electrochemical reversibility and good stability. Cyclic voltammograms of the manganese oxide electrode demonstrate that its operational stability is high.     

Supercapacitive properties of composite electrodes consisting of polyaniline, carbon nanotube, and RuO2

Three types of composite supercapacitor electrodes were prepared; electroactive polyaniline (PANI), PANI/multi-walled carbon nanotube (CNT), and PANI/CNT/RuO₂. Specifically, the PANI and PANI/CNT were prepared by polymerization, and PANI/CNT/RuO₂ was prepared by electrochemical deposition of RuO₂ on the PANI/CNT matrix. Cyclic voltammetry between −0.2 and 0.8 V (vs. Ag/AgCl) at various scan rates was performed to investigate the supercapacitive properties in an electrolyte solution of 1.0 M H₂SO₄. The PANI/CNT/RuO₂ electrode showed the highest specific capacitance at all scan rates (e.g., 441 and 392 F g⁻¹ at 100 and 1,000 mV s⁻¹, respectively). In contrast, the PANI/CNT electrode demonstrated the best capacitance retention (66%) after 10⁴ cycles. Additional analysis including morphology and complex impedance spectroscopy suggested that with small loading of RuO₂, an increase in capacitance was observed, but dissolution and/or detachment of RuO₂ species from the electrode might occur during cycling to reduce the cycle performance.     

Electrical properties of poly(vinyl alcohol) (PVA) based on LiFePO<Subscript>4</Subscript> complex polymer electrolyte films

Li ion conducting polymer electrolyte films were prepared based on poly(vinyl alcohol) (PVA) with 5, 10, 15, 20, 25 and 30 wt% lithium iron phosphate (LiFePO₄) salt using a solution-casting technique. X-ray diffraction (XRD) was used to determine the complexation of the polymer with LiFePO₄ salt. Differential scanning (DSC) calorimetry was used to determine the melting temperatures of the pure PVA and complexed films. The maximum ionic conductivity was found to be 1.18 × 10⁻⁵ S cm⁻¹ for (PVA:LiFePO₄) (75:25) film, which increased to 3.12 × 10⁻⁵ S cm⁻¹ upon the addition of propylene carbonate (PC) plasticizer at ambient temperature. The Li⁺ ion transport number was found to be 0.40 for (PVA: LiFePO₄) (75:25) film using AC impedance and DC polarization methods. Dielectric studies were performed for these polymer electrolyte films in the frequency range of 10 Hz to 10 MHz at different temperatures. The activation energies of the complexed films were calculated from the dielectric loss tangent spectra and were found to be 0.35, 0.30, 0.27 and 0.28 eV. The cyclic voltammogram (CV) curves of (PVA: LiFePO₄) (75:25)+PC film exhibited higher specific capacities than those for other films.     

Morphology-dependent electrochemical supercapacitive characteristics of nanostructured manganese dioxide

The dependence on morphology of the supercapacitive characteristics of manganese dioxide nanospheres (NSs) and nanorods (NRs) was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and a series of electrochemical techniques. Because the nanosized pores in MnO₂ NSs resulted in high surface area, MnO₂ electrodes made of NSs had higher specific capacitance (SC) than those made of NRs at current densities less than 2.0 A g⁻¹. However, at current densities over 2.0 A g⁻¹, the power density of MnO₂ electrodes composed of NRs was better than that of NSs. The high surface area and nanosized pores in MnO₂ NSs increase the number of redox active sites, which leads to high specific capacitance. On the other hand, the small pore size in MnO₂ NSs restricts the rates of charge and discharge, thus limiting their power density.     

Temperature and processing effects on lithium ion conductivity of solution-deposited lithium zirconium phosphate (LiZr2P3O12) thin films

Lithium zirconium phosphate (LiZr₂P₃O₁₂) thin films have been prepared on platinized silicon substrates via a chemical solution deposition approach with processing temperatures between 700°C and 775°C. Films that were subject to a single high-temperature anneal were found to crystallize at temperatures above 725°C. Crystallization was observed in films annealed after each deposited layer at 700°C and above. In both cases, grain size was found to increase with annealing temperature. Ion conductivity was found to increase with annealing temperature in singly annealed films. In per-layer annealed films ion conductivity was found to initially increase then decrease with increasing annealing temperature. A maximum ion conductivity of 1.6 × 10⁻⁶ S/cm was observed for the singly annealed 775°C condition, while a maximum ion conductivity of 5.8 × 10⁻⁷ S/cm was observed for the 725°C per-layer annealed condition. These results are consistent with an increasing influence of cross-plane, internal interface resistance and vapor phase carrier loss in the per-layer annealed samples. This work demonstrates that post-deposition processing methods can strongly affect the ion conducting properties of LiZr₂P₃O₁₂ thin films.     

Influence of post-deposition annealing on electrical and optical properties of (Ta2O5)1-x - (TiO2)x thin films,x ≤ 0.08

Tantalum (Ta) and titanium (Ti) metal targets were direct current (DC) magnetron sputtered in the oxygen environment by varying its relative areas to deposit (Ta₂O₅)_1-x- (TiO₂)_x (TTO_x) thin films, with x = 0, 0.03, 0.06, and 0.08, onto the boron-doped p-silicon (1 0 0) and optically polished quartz substrates, at room temperature; and were annealed at 500, 600, 700, and 800 °C, for 1.5 h. The thin films annealed at and above 600 °C show the Ta₂O₅ structure. The leakage current density and capacitance-voltage (C–V) characteristics were measured for TTO_x, x ≤ 0.08, assisted Ag/TTO_x/p-Si metal– oxide– semiconductor (MOS) structures. The leakage current density was found minimum, for the films annealed at 800 °C, for all the prepared TTO_x films, x ≤ 0.08. The minimum leakage current density 1.6 × 10^?8 A/cm², at 3.5 × 10⁵ V/cm electric field, was observed for x = 0.03, annealed at 800 °C, among the prepared compositions. The prepared TTO_0.03 films, annealed at 700 °C show maximum dielectric constant 39, at 1 MHz. The optical parameters, viz., refractive index (n), extinction coefficient (k), and optical band gap (E_g) of the films, with x = 0.03, prepared on quartz substrates, were determined from their optical transmittance plots. The values of n and k of the crystalline films were observed increasing from 2.123 to 2.143, and 0.099 to 0.130, respectively, at 550 nm wavelength; and E_g decreasing from 3.95 to 3.89 eV with the increasing annealing temperature, from 600 to 800 °C. Ohmic emission, in the lower electric field; Schottky and space-charge- limited current conduction mechanisms, in the intermediate to higher electric fields, were generally envisaged from the current-voltage characteristics in the prepared Ag/TTO_0.03/p-Si structures.     

Designing micro-nano structure of anodized iron oxide films by metallographic adjustment on T8 steel

In this study, the anodized iron oxide films with micro-nano structure were prepared by a combination of heat treatment and anodization. The adjustment of these oxide films at the micron-scale was achieved by heat treatment on substrate to modify the position of the cementite and ferrite. The distribution and existing forms of carbon on cementite and ferrite determine the morphology of their respective anodization. It was found annealing at 300 °C can improve the crystallinity of iron oxide and maintain the original micro-nano structure. Although the crystal quality of iron oxide can be further improved with higher annealing temperature, it would result in the collapse of nanoporous structures and the reconstruction of the surface morphology. Furthermore, anodized samples made from those with lamellar ferrite and cementite show better specific capacitance. The iron oxide film on the annealed substrate obtained the highest specific capacitance of 35.3 mF/cm² at a scan rate of 20 mV/s in our samples.     

Preparation and characterization of manganese oxide/CNT composites as supercapacitive materials

Manganese oxide was synthesized and dispersed on carbon nanotube (CNT) matrix by thermally decomposing manganese nitrates. CNTs used in this paper were grown directly on graphite disk by chemical vapor deposition technique. The capacitive behavior of manganese oxide/CNT composites was investigated by cyclic voltammetry and galvanostatic charge–discharge method in 1 M Na₂SO₄ aqueous solutions. When the loading mass of MnO₂ is 36.9 μg cm^− 2, the specific capacitance of manganese oxide/CNT composite (based on MnO₂) at the charge–discharge current density of 1 mA cm^− 2 equals 568 F g^− 1. Additionally, excellent charge–discharge cycle stability (ca. 88% value of specific capacitance remained after 2500 charge–discharge cycles) and power characteristics of the manganese oxide/CNT composite electrode can be observed. The effect of loading mass of MnO₂ on specific capacitance of the electrode has also been investigated.     

Effects of adding different morphological carbon nanomaterials on supercapacitive performance of sol–gel manganese oxide films

In this study, the supercapacitive performances of manganese oxide films were investigated by adding different carbon nanomaterials, including carbon nanocapsules (CNC), multiwalled carbon nanotubes (MWCNTs) and multi-layered graphene. The manganese oxide films were prepared with manganese acetate precursor by sol–gel method, and the post-treatment effects were also examined. With a heat-treatment above 300 °C, the as-prepared amorphous films transformed to a compound of Mn₃O₄ and Mn₂O₃ phases, and the smooth surface became rough as well. Cyclic voltammogram (CV) tests showed that the manganese oxide film, which was mixed with 0.05 wt% MWCNTs and annealed at 350 °C for 1 h, exhibited the optimized specific capacitance, 339.1 F/g. During 1000CV cycles, the specific capacitances of original manganese oxide film decreased gradually from 198.7 to 149.1 (75%) F/g. After same number of cycle tests, the modified films containing 0.025 wt% CNC, 0.05 wt% MWCNTs and 0.1 wt% graphene retained 201.8 (64.2%), 267.4 (78.9%) and 193.1 (57.4%) F/g respectively. The results indicates that the supercapacitive performance of manganese oxide films were significantly modified by carbon nanomaterials; in addition, the MWCNTs additive could also reduce the decay rate.     

Supercapacitive properties of polyaniline/hydrous RuO2 composite electrode

A composite electrode based on polyaniline (PANI) and hydrous RuO₂ is prepared by electrochemical deposition of PANI onto hydrous RuO₂ (PANI/RuO₂) and its supercapacitive properties are investigated using cyclic voltammetry. The specific capacitances of PANI/RuO₂ and hydrous RuO₂ electrodes are determined to be 708 and 517 F g⁻¹ at 5 mV s⁻¹, respectively. Simple electrodeposition of PANI on the hydrous RuO₂ can achieve comparatively greater capacitance values.     

Current status of proton-conducting solid oxide fuel cells development

Solid oxide fuel cells (SOFC) are promising devices for high efficiency cogeneration. The most widely used and studied ones have an anion conducting electrolyte that requires high operating temperatures to limit ohmic losses across this electrolyte; temperatures typically range between 800 and 1,000 °C. This temperature is associated with undesirable phenomena such as material interaction and insulating phase formation that result in unsatisfactory durability and high cost for market entry. Proton conducting solid oxide fuel cells (PCFC) constitutes a promising alternative since they allow a significant decrease in operating temperature. The Ba(Zr,Ce,Ln)O_3−δ perovskite family exhibits ionic conductivities reaching 10⁻² to 10⁻¹ S cm⁻¹ at temperatures as low as 600–700 °C, these values being obtained with anion conducting SOFC between 700 and 1,000 °C. On the basis of a review of work on half cells and complete cells, this paper addresses the main parameters that control and limit PCFC behaviour. This analysis aims at proposing recommendations for designing and testing proton conducting fuel cells.     

Impact of electrolyte additives (alkali metal salts) on the capacitive behavior of NiO-based capacitors

To improve the specific capacitance and energy density of electrochemical capacitor, nanostructured NiO was prepared by high temperature solid-state method as electrode material. The crystal structure and morphology of as-parepared NiO samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Cyclic voltammetry (CV) measurement was applied to investigate the specific capacitance of the NiO electrode. Furthermore, a novel mixed electrolyte consisting of NaOH, KOH, LiOH and Li₂CO₃ was prepared for the NiO capacitor, and the component and concentration of the four different electrolytes was examined by orthogonal test. The results showed that the NiO sample has cubic structure with nano-size particles, and the optimal composition of the electrolyte was: NaOH 2 mol L⁻¹, KOH 3 mol L⁻¹, LiOH 0.05 mol L⁻¹, and Li₂CO₃ 0.05 mol L⁻¹. At a scan rate of 10 mV s⁻¹, the fabricated capacitor exhibits excellent electrochemical capacitive performance, while the specific capacitance and the energy density were 239 F g⁻¹ and 85 Wh kg⁻¹, which was higher than one-component electrolyte.     

Photoelectrochemical characterization of the synthetic crednerite CuMnO<Subscript>2</Subscript>

High quality crednerite CuMnO₂ was prepared by solid state reaction at 950 °C under argon flow. The oxide crystallizes in a monoclinically distorted delafossite structure associated to the static Jahn–Teller (J–T) effect of Mn³⁺ ion. Thermal analysis showed that it converts reversibly to spinel Cu _x Mn_3−x O₄ at ~420 °C in air and further heating reform the crednerite above 940 °C. CuMnO₂ is p-type, narrow semiconductor band gap with a direct optical gap of 1.31 eV. It exhibits a long-term chemical stability in basic medium (KOH 0.5 M), the semi logarithmic plot gave an exchange current density of 0.2 μA cm⁻² and a corrosion potential of ~−0.1 V_SCE. The electrochemical oxygen insertion/desinsertion is evidenced from the intensity–potential characteristics. The flat band potential (V _fb = −0.26 V_SCE) and the holes density (N _A  = 5.12 × 10¹⁸ cm⁻³) were determined, respectively, by extrapolating the curve C ⁻² versus the potential to the intersection with C ⁻²  = 0 and from the slope of the Mott–Schottky plot. From photoelectrochemical measurements, the valence band formed from Cu-3d wave function is positioned at 5.24 ± 0.02 eV below vacuum. The Nyquist representation shows straight line in the high frequency range with an angle of 65° ascribed to Warburg impedance originating from oxygen intercalation and compatible with a system under mass transfer control. The electrochemical junction is modeled by an equivalent electrical circuit thanks to the Randles model.     

UV-visible technique for studying powder coatings and their dissolution

UV-Visible (UVV) technique used to monitor powder coating and its dissolution processes from hard latex particles. Three sets of latex coatings were prepared from poly(methyl methacrylate) (PMMA) particles. The first set of coatings was annealed at elevated temperatures in various time intervals during which reflected photon intensity, I_rf, was measured. The second set of coatings was annealed at various temperatures in 10 min time intervals during which transmitted intensity, I_tr, was measured. I_rf first decreased and then increased as the annealing temperature was increased. Decrease in I_rf was explained with the void closure mechanism due to viscous flow. Increase in I_tr and I_rf against time and temperature were attributed to an increase in crossing density at the junction surface. The activation energy of viscous flow, ΔH, was measured and found to be around 8 kcal/mol and the back and forth activation energies (ΔE_rf and ΔE_tr) were measured and found to be around 49 and 53 kcal/mol for a reptating polymer chain across the junction surface. Diffusion of solvent molecules (chloroform) into the annealed latex coatings was followed by desorption of PMMA chains for the third set of films. Desorption of pyrene, P, labeled PMMA chains was monitored in real-time by the absorbance change of pyrene in the polymer-solvent mixture. A diffusion model with a moving boundary was employed to quantify real-time UVV data. Diffusion coefficients of desorbed PMMA chains were measured and found to be between 2 and 0.6 × 10⁻¹¹ cm² s⁻¹ in the 100 and 275°C temperature range. Presented at the 2000 Spring Meeting of the PMSE Div. of the American Chemical Society, March 26–30, 2000, San Francisco, CA. Dept. of Physics, Maslak 80626 Istanbul, Turkey. Dept. of Physics, 22030 Edirne, Turkey.