Key Engineering Materials Vols. 512-515

Abstract: Because of the features of photonic localization in photonic bandgap(PBG), the photonic crystals can be coupled to DSSC to increase the conversion efficiency. In this paper, through exploring the preparation of large inverse opal structure of ZnO, we attempt to apply the photonic crystals to the Dye-Sensitized Solar Cells (DSSC) to improve its efficiency. The colloidal crystal template is prepared by self-assembled on FTO substrates, and three-dimensional ZnO inverse opal is synthesized via an electrochemical deposition method in zinc nitrate solution. Then we study the inflations of its surface morphology and photonic bandgap on the solar cell’s photoelectric conversion efficiency.

Abstract: Dye-sensitized solar cell is gradually becoming a strong competitor to Si-based solar cells, attracting much attention both from research and industry. Organic dyes used in dye-sensitized solar cells usually resemble dyes found in plants, fruits, and other natural products. In the present study, trollius pigment was extracted from a natural flower named trollius petals to serve as the sensitizer of the cells. UV-Vis absorption measurement revealed that the extracted pigment had a stronger absorbance under acid condition than that under basic condition. Devices were assembled with this trollius pigment, by systematically correlating the photovoltaic performance with the pH value of dye solution, film thickness and the sensitization time of the photoanode. The power conversion efficiency was increased by 37.9% when the pH of the dye solution was changed from alkaline (pH=9) to acidic (pH=4.3). The optimized efficiency of 0.254% was obtained when the film thickness was 13μm and the sensitization time was 3h under acidic condition.

Abstract: Glass frit sealant was prepared under different conditions, including the ratios of each composition, grinding method of the sealants drying temperature, and sintering process. When the ratio of glass frit, terpineol and ethyl cellulose was fixed at 5:4:1, a uniform sealant film without any pore or crack was obtained. The rates of weight loss for the cells filled with water and electrolyte sealed with the glass frit films were investigated. The drying temperature of 25°C and sintering at 560°C with temperature gradients led to the smallest rate of weight loss both for water and electrolyte. Furthermore, the optimized sealant was fabricated into solar cells, which exhibited best stability by retaining 80% of their initial conversion efficiency, accompanying an electrolyte leakage rate as small as 0.12% after 800 hours tracking test at room temperature.

Abstract: In this research, aerogels were synthesized by a two-step sol-gel process without supercritical conditions. During the process, tetraethoxysilane (TEOS) was used as precursor, and different surfactants, i.e. cetyltrimethyl ammonium bromide (CTAB) and polyethylene glycol–600 (PEG–600), were used as dopants respectively. In order to minimize the drying shrinkage and preserve the high porosity structure, the surface of the gels was modified by trimethylchlorosilane (TMCS) before the ambient pressure drying (APD). The effect of surfactent on the structure of the resulting aerogels was investigated. The aerogels which involved surfactants exhibited resistance to cracking during the APD of the alcogels. The modification by TMCS has been confirmed using Infrared (IR) spectroscopy. The porous structure of aerogels was investigated by Brunauer-Emmett- Teller (BET) instrument, differential scanning calorimeter (DSC) and scanning electron micrograph (SEM). The results indicated that surfactants as dopants could significantly affect the structure and optical property of aerogels and be beneficial for obtaining crack-free silica aerogels via ambient pressure drying process.

Abstract: Methods of manufacturing Niobium oxide electrolytic capacitor were studied in this work. Some phenomena were found and the reasons or mechanisms were studied by using SEM(scanning electron microscope), EDS. In experiment, comparing with the type 6.3V/47μF tantalum capacitor, NbO powder were pressed to pellet as the capacitor anode, then the NbO capacitor was manufactured through the following processes: sintering, welding, anode oxidation, MnO₂ decomposition and cathode coating. Its capacitance, leakage current, ESR(equivalent series resistance) and tgδ were measured and compared with that of the simily type of tantalum capacitor, and the suitable technical parameters were chosen

Abstract: For energy storage devices such as capacitances, pulsed power applications and other any electronic systems, high permittivity and high breakdown strength (BDS) are necessary for dielectric materials used in high energy storage capacitors. Ba_0.4Sr_0.6TiO₃ nano-powders were directly synthesized from solution and then wrapped by a thin surrounding shell with composition of zinc oxides dopants in aluminum oxides. This core-shell structure was characterized by a conjunction of XRD, and TEM analysis. The core-shell nanoparticles were pressed into pellets with 10 mm diameter and then sintered at different temperature in air. The specimen coated with 2.0wt% compounds of aluminum oxides doped with zinc oxides showed the maximum breakdown strength of 475kV/cm and the energy storage density of 4.7J/cm3 while the tanδ was only 0.002, whereas the uncoated Ba_0.4Sr_0.6TiO₃ was only 86.9kV/cm, 0.23J/cm3 and 0.005, respectively. And the energy storage density and the BDS decreased when the shell content was more than 2.0wt%.

Abstract: In this work, a facile approach combining polymerization-induced phase separation and starch-templating is presented to synthesize hierarchically macro/mesoporous carbons. The obtained porous carbons have bimodal macropores with pore diameters of 10~60 μm and 3~5 μm and 3D interconnected mesopores with pore diameters of 5~40 nm. The large macropores and the small macropores are obtained by the thermal decomposition and the closely stacking of starch particles, respectively. The 3D interconnected mesopores are developed through polymerization-induced phase separation between ethylene glycol and phenolic resin via spinodal decomposition mechanism. These as-prepared hierarchically macro/mesoporous carbons may have great potential for applications as electrodes materials for batteries, fuel cells, and supercapacitors due to their facile synthesis, unique hierarchical porous structure, and large BET surface areas (~ 610 m2/g).

Abstract: A series of n-type BiTeSe/ZnAlO composites were prepared by zone melting method. Thermoelectric properties, including the electrical conductivity σ, Seebeck coefficient α and thermal conductivity κ, were measured in the temperature range of 300-550K. Results show that the electrical properties have been slightly lowered due to the reduced carrier concentration by ZnAlO addition. However, the low-temperature-shifted peak α, resulting from the prematurely happened intrinsic excitation, have shifted peak ZT to lower temperatures. As a result, the ZT values at 300 K were significantly enhanced for BiTeSe/ZnAlO composites compared to that of BiTeSe, making more attractive for cooling applications at ambient temperature.

Abstract: P-type BiSbTe/RuO₂ composite was fabricated using a combined process of melting and spark plasma sintering. The XRD patterns showed that RuO₂ reacted with the matrix for the RuO₂ content of 1.0 wt% and 4.0 wt% samples. The measured thermoelectric properties showed that the highest electrical conductivity was obtained for the sample with 2.0 wt% RuO₂. The power factor (α²σ/κ) decreased with the increase of RuO₂ below 450 K. The lattice thermal conductivity was lower than that of BiSbTe over the whole temperature range for BiSbTe/2.0 wt% RuO₂.

Abstract: During oil-water separation process, the influence of the operational parameters such as transmembrane pressure, crossflow velocity and feed temperature on the oil-water separation efficiency of TiO₂ modified α-alumina microfiltration membrane was studied. The results show that the permeation flux of the membrane is 371.68 L•m^-2•h^-1 and the oil content in the permeation is 9.63 mg•L^-1 when the TMP is 0.15 MPa, the crossflow velocity is 5.89 m•s^-1 and the feed temperature is 30°C.