O-Bong Yang

Novel preparation of anatase TiO2@reduced graphene oxide hybrids for high-performance dye-sensitized solar cells.

An effective method was developed to prepare hybrid materials of TiO2 nanoparticles on reduced graphene oxide (RGO) sheets for application in solar cells. The morphology, size, and crystal phase of the TiO2 nanoparticles and TiO2@reduced graphene oxide (TiO2@RGO) hybrids were investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), Raman, and UV-vis diffuse reflectance spectroscopy. A possible growth mechanism of TiO2@RGO hybrids is proposed based on observations of the TiO2 nanoparticles obtained from the hydrolysis process under different conditions. The effects of different reduced graphene oxide contents on the energy conversion efficiency of the dye-sensitized solar cells (DSSCs) based on J-V and incident photon-to-current conversion efficiency (IPCE) spectra are also discussed. DSSCs based on TiO2@RGO hybrid photoanodes with a graphene content of 1.6 wt % showed an overall light-to-electricity conversion efficiency of 7.68%, which is much higher than that of pure anatase nanoparticles (4.78%) accompanied by a short-circuit current density of 18.39 mA cm(2), an open-circuit voltage of 0.682 V, and a fill factor of 61.2%.

The role of lanthanum oxide on Pd‐only three‐way catalysts prepared by co‐impregnation and sequential impregnation methods

The effect of lanthanum oxides on the catalytic performance and the physicochemical properties of Pd‐only three‐way catalysts prepared by co‐impregnation and sequential impregnation methods was studied by using hydrogen chemisorption, BET surface area, X‐ray diffraction and X‐ray photoelectron spectroscopy. It was found that the roles of La closely depended on the order of La introduction in the preparation of the Pd catalysts. Pd–La/Al2O3 prepared by co‐impregnation of La and Pd, kept its superior activity in spite of the significant loss of surface area of the alumina support after thermal aging at 1273 K, indicating that the primary role of La was a Pd stabilizer through the intimate interaction between La and Pd. However, on Pd/La/Al2O3, in which Pd was consecutively impregnated after the impregnation of La, La preferentially interacted with the alumina support as a form of LaxAlyO2, resulting in the stabilization of the alumina support during thermal aging. XPS results indicated that lanthanum oxide suppressed the formation of PdO interacting with alumina during thermal aging. In the case of Pd/La–Ce/Al2O3, the formation of the solid solution of (CexLa1−x)O2 was not strong enough to maintain the high activity and the good textural property after thermal aging.

Smart copper oxide nanocrystals: Synthesis, characterization, electrochemical and potent antibacterial activity

We report herein the synthesis and characterization of novel CuO nanocrystals and their electrochemical and potent antibacterial activity. The utilized CuO nanocrystals were prepared by wet chemical method using copper acetate and hexamethylenetetramine (HMTA) as precursors. The physicochemical properties of the synthesized CuO nanocrystals having size ~6 nm were determined by X-ray diffractometer (XRD), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM) and ultra violet-visible (UV-Vis) spectroscopy. The antibacterial study was carried out by minimum inhibitory concentration (MIC) using E. coli as model organism. The MIC of the CuO nanocrystals was found to be 2.5 μg/ml and the TEM analysis reveals that CuO nanocrystals caused disturbance to the cell wall which led to the irreversible damage to the cell envelope eventually leading to cell death. Furthermore, mechanism of bactericidal action of novel CuO nanocrystals is discussed in the light of our findings. Additionally, the synthesized CuO nanocrystals were applied as electrode material for supercapacitor. The specific capacitance of CuO nanocrystals measured at a potential scan rate of 5 mV/s was as high as 164.9 F g(-1).

Effect of chelating agents on the properties of TiO2–SiO2 mixed oxide for photocatalytic water decomposition

High band-gap energy and large contribution of Ti–O–Si linkage were found on the catalyst synthesized with acetyl acetone as a chelating agent in a sol–gel process. Meanwhile, when acetic acid as a chelating agent was employed, it promoted the formation of TiO2–SiO2 mixed oxide with relatively high specific surface area and high photocurrent density. Low charge transfer resistance as well as wide space charge region in TiO2–SiO2 particles prepared with acetic acid gave rise to high photocurrent density, which might result in the superior photocatalytic water decomposition for hydrogen production.

Morphological and Electrochemical Properties of Crystalline Praseodymium Oxide Nanorods

Highly crystalline Pr6O11 nanorods were prepared by a simple precipitation method of triethylamine complex at 500°C. Synthesized Pr6O11 nanorods were uniformly grown with the diameter of 12–15 nm and the length of 100–150 nm without any impurities of unstable PrO2 phase. The Pr6O11 nanorod electrodes attained a high electrical conductivity of 0.954 Scm−1 with low activation energy of 0.594 eV at 850°C. The electrochemical impedance study showed that the resistance of electrode was significantly decreased at high temperature, which resulted from its high conductivity and low activation energy. The reduced impedance and high electrical conductivity of Pr6O11 nanorod electrodes are attributed to the reduction of grain boundaries and high space charge width.

ZnO Nanorod–TiO2-Nanoparticulate Electrode for Dye-Sensitized Solar Cells

Highly dense ZnO nanorods were synthesized on TiO2-nanoparticulate coated fluorine-doped tin oxide (FTO) substrates by the chemical vapor deposition method for dye-sensitized solar cells (DSSCs). The uniformly grown ZnO nanorod layer has a thickness of ~4 µm on the TiO2-nanoparticulate layer with a wurtzite structures as confirmed by the X-ray diffraction pattern. The DSSC fabricated with a ZnO nanorod/TiO2-nanoparticulate electrode had an overall light-to-electricity conversion efficiency η of 3.7% with a short-circuit current density JSC of 8.12 mA/cm2, open-circuit voltage VOC of 0.76 V, and fill factor FF of 0.59, whereas ZnO nanowire/TiO2-nanoparticulate-electrode-based DSSCs exhibited a low η of 1.1% with JSC of 2.14 mA/cm2 and slightly high VOC of 0.79 V. It is expected that the enhanced photovoltaic performance of the ZnO nanorod/TiO2-nanoparticulate electrode can be attributed to high dye loading and high light harvesting through large surface areas of ZnO nanorods incorporated with TiO2-nanoparticulate as compared with the ZnO nanowire/TiO2-nanoparticulate electrode.

Electrocatalytic behavior of calcium doped LaFeO3 as cathode material for solid oxide fuel cell.

La(1-x)Ca(x)FeO3 (X = 0.0, 0.2, 0.4, abbreviated as LCF) as cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC) was synthesized by new route of glycine nitrate method. LCF materials were characterized by X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), electrical and electrochemical impedance spectroscopy (EIS). The powder LCFs exhibited single phase with orthorhombic structure, highly porous and small nanoparticles with average size of 200-300 nm. The electrical conductivities of LCFs increased as increasing the Ca content and achieved the maximum electrical conductivity of 148 Scm(-1) for La0.6Ca0.4FeO3 (X = 0.4) at 550 degrees C. The improved conductivity of LCFs could be a promising cathode material for IT-SOFCs. In the impedance analysis of fabricated symmetry cell with the optimized La0.6Ca0.4FeO3 cathode and Ce0.8Sm0.2O3 (SDC) electrolyte, the minimum area specific resistance (ASR) of 0.15 omegacm2 was observed at 850 degrees C, which may due to the lowest activation energy (1.55 eV), resulting from the reduction of oxygen molecules into oxygen ions. It was found that calcium doping was essential to increase the charge carrier concentration of lanthanum iron oxide materials, resulting in the high conductivity at intermediate temperature.

Quasi-Solid State Dye Sensitized Solar Cell Based on Poly (Acrylonitrile-co-Methacrylonitrile)-Silica Gel Electrolyte

The solid state dye-sensitized solar cells (DSSCs) are shown low conversion efficiencies as compare to liquid based DSSCs due to incomplete wetting of photoelectrode by solid electrolyte and poor contact of the solid state materials with the surface of dye coated TiO 2 surface. In current work, poly (acrylonitrile-co-methacrylonitrile)/silica based gel electrolytes have been successfully employed to fabricate quasi-solid state DSSC with the overall energy conversion efficiency of 3.0%, open-circuit voltage of 0.784 V and short circuit current of 7.33 mA/cm2 at 1 sun irradiance (100 mW/cm2). The introduction of silica filler into the copolymer [poly(acrylonitrile-co-methacrylonitrile)] matrix reduces the crystallinity of the copolymer, which increases the mobility of iodide/triiodide couple. The optimized experimental conditions such as gelation time, composition of SiO2 nanoparticles and thickness of TiO2 have been discussed in detail at this work

Charge storage and transfer in dye-sensitized solar cells: a study by electrochemical impedance spectroscopy

AC impedance measurement was found as an efficient tool to elucidate the charge storage and transfer in dye-sensitized solar cells. The imaginary impedance of the apparent space charge region at the dye adsorbed TiO/sub 2//electrolyte interface was inversely dependent on the density of photoexcited electrons. For a given TiO/sub 2/ material, the thicker the thickness of the substrate, the higher the charge storage and the slower the charge transfer of the resulting DSC. Accordingly, the existence of an optimized thickness of TiO/sub 2/ substrate is inherent for the highest overall conversion efficiency of a DSC fabricated with a given TiO/sub 2/ material. The combination of the charge storage or the density of photoexcited electrons in the porous TiO/sub 2/ film and the prompt charge transfer between it and TiO/sub 2//TCO glass interface was worthwhile to note for improvement on the overall conversion efficiency of DSC.

Variation in the Optical Properties of the SiC-SiO2 Composite Antireflection Layer in Crystalline Silicon Solar Cells by Annealing

This study showed the effects of annealing on a sol–gel-derived SiC-SiO2 composite antireflection (AR) layer and investigated the optical and photovoltaic properties of crystalline silicon (Si) solar cells. The SiC-SiO2 composite AR coating showed a considerable decrease in reflectance from 7.18% to 3.23% at varying annealing temperatures of 450–800°C. The refractive indices of the SiC-SiO2 composite AR layer were tuned from 2.06 to 2.45 with the increase in annealing temperature. The analysis of the current density–voltage characteristics indicated that the energy conversion efficiencies of the fabricated Si solar cells gradually increased from 16.99% to 17.73% with increasing annealing temperatures of 450–800°C. The annealing of the SiC-SiO2 composite AR layer in Si solar cells was crucial to improving the optical, morphological, and photovoltaic properties.