N, S-doped TiO2 anode effect on performance of dye-sensitized solar cells

The modification of non-metallic elements N and S to nanocrystalline TiO₂ anode results in the energy gap is reduced to 2.63 eV and a strong redshift to the visible region occurred in the UV–visible spectrum. Poly (3-decylthiophene) (P3DT) is synthesized. Ultraviolet–visible spectra (UV–vis) shows that the light absorption of P3DT (Poly (3-decylthiophene)) and N719 (RuL2(NCS)2:2TBA (L=2,2′-bipyridyl-4, 4′-dicarboxylic acid)) are complementary to cover the entire visible region. Solar cell based on N–S/TiO₂ is co-sensitized by P3DT and N719. The photoelectric conversion efficiency of co-sensitized solar cell increases 56.8% comparing with the single dye-sensitized solar cell.     

Effect of carbon nanotubes on the anode performance of natural graphite for lithium ion batteries

A comparative investigation was carried out on carbon black and multiwalled carbon nanotubes as conductive additives in spherical natural graphite for lithium ion batteries. Scanning electron microscopy images showed that carbon nanotubes interlaced graphite particles in series to form a three-dimensional network. The constant current charge-discharge experiments showed that carbon nanotubes were more effective in improving reversible capacity and cycle stability. The reversible capacity was improved to 366 mAh/g and the cycle stability was improved effectively when carbon nanotubes were used. The research is of potential interest to the application of carbon nanotubes as conductive additives in anode materials for high-power lithium ion batteries.     

Influence of morphology on the emissive properties of dye-doped PVP nanofibers produced by electrospinning

Dye-doped polymer micro- and nanofibers with tailored light emission properties have great potential for applications in optical, optoelectronic, or photonic devices. In this study, these types of structures were obtained by electrospinning rhodamine 6 G-doped polyvinylpyrrolidone (PVP) using a polymer solution of 10% (mass) concentration in ethanol. Polymer nanofibers with different morphologies (smooth and beaded) and diameters of about 500 nm were obtained using different electrospinning conditions with the same solutions. Fluorescence optical microscopy observations showed that the dye was distributed uniformly in the doped PVP nanofibers. Different shifts were observed when we compared the wavelength of the dye emission band peak of the smooth nanofibers (566 nm) and the wavelength of the dye emission band peak of the beaded fibers (561.5 nm) produced by electrospinning in different conditions with the wavelength of the emission band peak for transparent thin films produced by spin coating (558 nm) using the same polymer solution. This demonstrates that it is possible to tune the optical properties of electrospun dye-doped polymer nanofibers simply by modifying the morphology of the material, i.e., the parameters of the electrospinning process.     

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.     

Electrochemical properties of carbon-coated LiFePO4 synthesized by a modified mechanical activation process

Carbon-coated lithium iron phosphate (LiFePO₄/C) composites were synthesized by conventional mechanical activation (MA) process and also by a modified MA process. Phase-pure particles were obtained of ∼100 nm size with a nano-meter thick web of carbon surrounding the particles. The composite prepared by the modified MA process shows good performance as cathode material in lithium cells at room temperature. A high performance was achieved at 0.1 C-rate with >96% utilization of the active material. A stable cycle performance even at higher C-rates was achieved with a cathode that has a total carbon content of only 12 wt%. The use of the modified MA process to synthesize LiFePO₄/C has promise to be an efficient process to decrease the total carbon content of the cathode, resulting in the enhanced energy density.     

Application of TiO2 nano-particles on the electrode of dye-sensitized solar cells

In this study, nano-TiO₂ thin film electrode and solar cell have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible absorption spectra, contact angle, X-ray photoelectron spectroscopy (XPS), and current-voltage characteristics analyses. X-ray diffraction patterns show that the best sintering temperature of a nano-TiO₂ film is 600 °C, at which TiO₂ anatase phase forms best and the particle size of 8-10 nm can be obtained. The SEM images of a nano-TiO₂ thin film show that the surface of the film is smooth and porous, and the thickness of the nano-TiO₂ film is 4 μm. The measurements of contact angle between nano-TiO₂ film and deionized water (DI water) reveal that the nano-TiO₂ film is super-hydrophilic when solarized under ultraviolet. The electrode of dye-sensitized solar cell is used as a free-base porphyrin with carboxyl group, 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (TCPP) as the sensitizer to adsorb onto the TiO₂ thin film. From the results of ultraviolet-visible absorption spectra and XPS analyses of the electrode, the effects of nano-TiO₂ particles’ addition to the electrode of dye-sensitized solar cell can improve the absorption of visible light (400-700 nm) and increase electrons transferred from TCPP to the conduction band of TiO₂, resulting in the enhancement of efficiency for dye-sensitized solar cells.     

Structures and photovoltaic properties of copper oxides/fullerene solar cells

Copper oxide (CuO_x) thin films were produced by spin-coating and electrodeposition methods, and their microstructures and photovoltaic properties were investigated. Thin film solar cells based on the Cu₂O/C₆₀ and CuO/C₆₀ heterojunction or bulk heterojunction structures were fabricated on F-doped or In-doped SnO₂, which showed photovoltaic activity under air mass 1.5 simulated sunlight conditions. Microstructures of the CuO_x thin films were examined by X-ray diffraction and transmission electron microscopy, which indicated the presence of Cu₂O and CuO nanoparticles. The energy levels of the present solar cells were also discussed.     

Fabrication and characterization of fullerene/porphyrin bulk heterojunction solar cells

Fullerene/porphyrin bulk heterojunction solar cells were fabricated and, the electronic and optical properties were investigated. Effects of exciton-diffusion blocking layer of perylene derivative on the solar cells between active layer and metal layer were also investigated. Optimized structures with the exciton-diffusion blocking layer improved conversion efficiencies. Energy levels of the molecules were calculated and discussed. Nanostructures of the solar cells were investigated by X-ray and electron diffraction, which indicated formation of fullerene/porphyrin mixed crystals. Electronic structures of the molecules were investigated by molecular orbital calculation, and energy levels of the solar cells were discussed.     

Improvement of ZnO nanorod-based dye-sensitized solar cell efficiency by Al-doping

The current study investigates the performance of dye-sensitized solar cells (DSSCs) based on Al-doped and undoped ZnO nanorod arrays synthesized by a simple hydrothermal method. Current density-voltage (J-V) characterizations indicate that Al-doping in ZnO crystal structure can significantly improve current densities and the energy conversion efficiency (η) of ZnO nanorod-based DSSCs. The maximum η, 1.34%, was achieved in DSSC when Al-doped ZnO nanorod arrays were grown in 0.04 M zinc acetate dihydrate solution with 5 mM aluminum nitrate nonahydrate. This result represents a large increase of η in Al-doped ZnO nanorod-based DSSCs as compared to undoped (0.05%). The improved DSSC photovoltaic performance can be attributed to two main factors: (1) increased light harvesting efficiency due to a large amount of N719 adsorbed on the large surface area of Al-doped ZnO nanorod arrays, and (2) increased electrical conductivity due to A1³⁺ ion doped into the ZnO lattice at the divalent Zn²⁺ site, allowing electrons to move easily into the Al-doped ZnO conduction band.     

Stable cycle-life properties of Ti-doped LiFePO4 compounds synthesized by co-precipitation and normal temperature reduction method

Submicron-sized LiFePO₄ and Ti-doped LiFePO₄ cathode materials were synthesized by a reformative co-precipitation and normal temperature reduction method, for which Ti ions were added in the process of preparing precursors to pursue a kind of sufficient and homogenous doping way. ICP and XRD analyses indicate that Ti ions were sufficiently doped in LiFePO₄ and did not alter its crystal structure. It is noted that higher Ti ions doping levels are conducive to electrochemical performance of LiFePO₄, especially on the aspect of stable cycle-life at higher C rates. The sample doped with 3 at% Ti shows the most impressive cycling performance, even after 100 cycles, discharge capacity of 133 mAh g⁻¹ was obtained (102.3% of its initial value) at 1C rate, and the discharge decreased little from 124 to 120 mAh g⁻¹ (96.8% of its initial value) at 2C rate.     

Controllable synthesis and characterization of CuO, β-Ni(OH)2 and Co3O4 nanocrystals in the MCln-NH4VO3-NaOH system

In this study, we demonstrate a general but efficient solution-phase approach for preparing CuO, β-Ni (OH)₂ and Co₃O₄ nanocrystals selectively by simply adjusting the amount of NaOH in the reaction system of MCl_n-NH₄VO₃-NaOH. The experimental results revealed that the amount of NaOH is crucial in the formation of desirable products. The as-obtained nanocrystals were characterized by means of X-ray powder diffraction, transmission electron microscope, high resolution transmission electron microscope, selected area electron diffraction and electrochemical techniques. The as-prepared CuO are nanorods with 15 nm in diameter and 50 nm in length. The as-prepared Ni (OH)₂ nanocrystals have the flocculent feature and Co₃O₄ nanocrystals are composed of irregular particles. It should be pointed out that some traditional metal vanadates occur in these reaction systems, which were usually prepared by the solid-state routes. On the other hand, the electrochemical properties of the obtained products were studied in brief. Electrochemical performances of CuO, β-Ni (OH)₂ and Co₃O₄ nanocrystals were measured with Li metal as the reference anode, which indicates their excellent capacities of Li-deposited for Li-ion batteries.     

Model design on calculations of microwave permeability and permittivity of Fe/SiO2 particles with core/shell structure

Fe/SiO₂ particles with core/shell structure were prepared by coating silica on the surface of a commercial spherical carbonyl iron via the hydrolysis process of tetraethyl orthosilicate (TEOS). The electromagnetic performance of commercial carbonyl iron and as-prepared Fe/SiO₂ particles was studied theoretically and experimentally. As predicted by the theoretical calculation based on the Bruggeman formula and the Landau–Lifshitz–Gilbert (LLG) theory, the insulating surface layer of silica was effective to reduce the permittivity parameters of pure carbonyl iron. The measured results showed good agreement with the theoretical prediction. Although there was a little decrease in the permeability of the Fe/SiO₂ core/shell particles, a better impedance match especially at higher frequency range was obtained when used as a microwave absorber. The reflection loss (RL) curves show that the lowest reflection loss of Fe/Epoxy composite (−20.5 GHz) was obtained corresponding to the frequency of 8.5 GHz when the thickness of the absorber was 3 mm. A different trend was observed in Fe/SiO₂/Epoxy composite. The reflection loss value got lower by decreasing the thickness of absorbers. At the thickness of 2.2 mm, a relative low reflection loss (−17 GHz) corresponding to the frequency of 13.6 GHz was obtained. Compared with the Fe/Epoxy composite, the improvement on shifting the reflection loss peak to higher frequency and on reducing the optimal thickness of absorbers was made by Fe/SiO₂/Epoxy composite.     

Self-discharge performance of Ni-MH battery by using electrodes with hydrophilic/hydrophobic surface

The polytetrafluoroethylene (PTFE) and carboxymethyl cellulose (CMC) film is separately coated on the surface of the metal hydride (MH) and Ni(OH)₂ electrodes to obtain the electrodes with hydrophobic or hydrophilic surface. The effects of the surface treatment on the oxygen and hydrogen evolution from the electrodes are studied by using cyclic voltammetry tests. Although the positive and negative active materials of the Ni-MH batteries show a lower self-decomposition rate after the CMC treatment, the self-discharge rate of the batteries show little change. On the contrary, the self-discharge rate of the batteries decreases from 35.9% to 27.1% by using the PTFE-treated Ni(OH)₂ electrodes, which might be related to the suppression of the reaction between NiOOH and H₂ by the hydrophobic film.     

Effect of sulfur additive on density of localized states in nanostructures chalcogenide Se95−xSxZn5 thin films

This paper reports the measurement of space charge limited conduction (SCLC) on the fabricated thin films of Se_95−xS_xZn₅ (0.2≤x≤10) in temperature range 313–353 K for the first time. At high electric fields (E∼10⁴ V/cm), the current could be fitted into the theory of space charge limited conduction, in case of uniform distribution of localized states in mobility gap. The homogeneity and surface morphology of thin films were assessed by scanning electron microscopy. The crystalline nature of the thin films was confirmed by powder XRD and the crystallite size was calculated using Scherer's formula. The crystallite size and density of localized states were found to increase with the increase of sulfur concentration. DC conductivity and activation energy were calculated and found to decrease and increase respectively, with the increase of sulfur concentration.     

Inter-collisional cutting of multi-walled carbon nanotubes by high-speed agitation

High-speed agitation by a mixing blade has efficiently achieved the cutting of a large diameter (100-150 nm) of multi-walled carbon nanotubes. The cutting process is caused by an inter-collision of the nanotubes with high transfer energy. The collision-induced cutting allows for the shortening of the nanotubes without serious damage of the original graphitic layers due to the cutting effect being limited to the collision points. Furthermore, the operation under ambient atmosphere introduces oxygen-containing functional groups to the cut nanotubes. The estimated length distribution has indicated that high-speed agitation achieves a large cutting effect during a short duration of several minutes.     

Porous SnO2 nanoflakes with loose-packed structure: Morphology conserved transformation from SnS2 precursor and application in lithium ion batteries and gas sensors

Porous SnO₂ nanoflakes with loose-packed structure were synthesized by calcination of SnS₂ precursors that were obtained through solvothermal method at low temperature. The as-obtained SnO₂ product had a three-dimensional porous structure with relatively high specific surface area. It was found that the SnO₂ nanoflakes inherited the morphology of precursor while numerous pores were formed after the annealing process. The combined techniques of X-ray diffraction, energy-dispersive spectrum, field emission scanning electron microscopy, and (high-resolution) transmission electron microscopy were used for characterization of the as-prepared SnO₂ product. Moreover, the porous SnO₂ nanoflakes with loose-packed structure could be used as gas sensors for detecting ethanol and acted as anode for lithium ion batteries. Our study shows that the as-prepared SnO₂ nanoflakes not only exhibit good response and reversibility to ethanol gas but also display enhanced Li-ion storage capability.     

In-situ current-voltage characteristics of the n-type GaAs substrate in HF:Et-OH electrolyte

In-situ characterisation of the n⁺-GaAs/HF:Et-OH interface is studied by current-voltage, J(V). The experimental current-potential exhibits the presence of three potential regions, which are attributed to different reaction mechanisms between HF and n⁺-type GaAs surface. Depending on HF concentration a current peak appears in the J(V) characteristics. Scanning electron microscopy (SEM) images of samples at different point of the J(V) characteristic exhibits different surface morphologies which depend strongly on the electrochemical anodization conditions.     

Optical properties of sol-gel fabricated Ni/SiO2 glass nanocomposites

Nickel nanoparticles were grown in silica glass by annealing of the sol-gel prepared silicate matrices doped with nickel nitrate. TEM characterization of Ni/SiO₂ glass proves the formation of isolated spherical nickel nanoparticles with mean sizes 6.7 and 20 nm depending on annealing conditions. The absorption and photoluminescence spectra of Ni/SiO₂ glasses were measured. In the absorption spectra, we observed the band related to the surface plasmon resonance (SPR) in Ni nanoparticles. The broadening of SPR was observed with decrease of Ni nanoparticle size. The width of the surface plasmon band decreases 1.5 times at the lowering of temperature from 293 to 2 K because of strong electron-phonon interaction. The spectra proved the creation of nickel oxide NiO clusters and Ni²⁺ ions in silica glass as well.     

Effect of Gd2O3 on the hydrogen evolution property of nickel–cobalt coatings electrodeposited on titanium substrate

The effect of rare earth compound, Gd₂O₃, on the microstructure and the hydrogen evolution property of Ni–Co alloy electrode was studied. The morphology and microstructure were characterized by SEM and XRD, respectively, and the electrocatalytic efficiency was evaluated on the basis of electrochemical data obtained from steady-state polarization curves, Tafel curves and electrochemical impedance spectroscopy measurements carried out in 0.50 M Na₂SO₄+0.10 M H₂SO₄ solution. It was found that the embedded Gd₂O₃ particles largely enhanced the electrocatalytic activity of Ni–Co alloy electrode to hydrogen evolution reaction.     

Systematic investigation on the properties of carbon nanotube electrodes with different chemical treatments

The functionalization of carbon nanotubes (CNTs) was carried out by using different chemical treatment methods. These functionalized CNTs were characterized by TEM image and FT-IR spectra. The CNT electrodes are measured by thermal resistivity and cyclic voltammetry experiments. The results showed that two important factors controlled the electrochemical properties of the CNT film electrode: one is the active functional group; another is activation energy of the CNT film. From our experiments, we have found the electrode of 10 min nitric acid treated CNTs have the optimal peaks in relation to carboxylic acids, the highest redox peak currents, the biggest value of k⁰ and well-defined quasi-reversible voltammograms for redox of iron couples, in which the two factors best match.