Electron-donating perylene tetracarboxylic acids for dye-sensitized solar cells

Novel perylene imide derivatives with both electron-donating and bulky substituents have been synthesized for dye-sensitized solar cells. The power conversion efficiency reached 2.6%, which is the highest value among perylene-sensitized TiO2 solar cells.     

Enhanced surface sensitivity in secondary ion mass spectrometric analysis of organic thin films using size‐selected Ar gas‐cluster ion projectiles

A size‐selected argon (Ar) gas‐cluster ion beam (GCIB) was applied to the secondary ion mass spectrometry (SIMS) of a 1,4‐didodecylbenzene (DDB) thin film. The samples were also analyzed by SIMS using an atomic Ar⁺ ion projectile and X‐ray photoelectron spectroscopy (XPS). Compared with those in the atomic‐Ar⁺ SIMS spectrum, the fragment species, including siloxane contaminants present on the sample surface, were enhanced several hundred times in the Ar gas‐cluster SIMS spectrum. XPS spectra during beam irradiation indicate that the Ar GCIB sputters contaminants on the surface more effectively than the atomic Ar⁺ ion beam. These results indicate that a large gas‐cluster projectile can sputter a much shallower volume of organic material than small projectiles, resulting in an extremely surface‐sensitive analysis of organic thin films. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface properties and aggregate morphology of partially fluorinated carboxylate-type anionic gemini surfactants

Three anionic homologues of a novel partially fluorinated carboxylate-type anionic gemini surfactant, N,N′-di(3-perfluoroalkyl-2-hydroxypropyl)-N,N′-diacetic acid ethylenediamine (2 edda, where n represents the number of carbon atoms in the fluorocarbon chain (4, 6, and 8)) were synthesized. In these present gemini surfactants, the relatively small carboxylic acid moieties form hydrophilic head groups. The surface properties or structures of the aggregates of these surfactants are strongly influenced by the nonflexible fluorocarbons and small head groups; this is because these surfactants have a closely packed molecular structure. The equilibrium surface tension properties of these surfactants were measured at 298.2 K for various fluorocarbon chain lengths. The plot of the logarithm of the critical micelle concentration (cmc) against the fluorocarbon chain lengths for 2 edda (n = 4, 6, and 8) showed a minimum for n = 6. Furthermore, the lowest surface tension of 2 edda at the cmc was 16.4 mN m⁻¹. Such unique behavior has not been observed even in the other fluorinated surfactants. Changes in the shapes and sizes of these surfactant aggregate with concentration were investigated by dynamic light scattering and transmission electron microscopy (TEM). The TEM micrographs showed that in an aqueous alkali solution, 2 edda mainly formed aggregates with stringlike (n = 4), cagelike (n = 6), and distorted bilayer structures (n = 8). The morphological changes in the aggregates were affected by the molecular structure composed of nonflexible fluorocarbon chains and flexible hydrocarbon chains.     

Noble metal-free hydrazine fuel cell catalysts: EPOC effect in competing chemical and electrochemical reaction pathways

We report the discovery of a highly active Ni-Co alloy electrocatalyst for the oxidation of hydrazine (N(2)H(4)) and provide evidence for competing electrochemical (faradaic) and chemical (nonfaradaic) reaction pathways. The electrochemical conversion of hydrazine on catalytic surfaces in fuel cells is of great scientific and technological interest, because it offers multiple redox states, complex reaction pathways, and significantly more favorable energy and power densities compared to hydrogen fuel. Structure-reactivity relations of a Ni(60)Co(40) alloy electrocatalyst are presented with a 6-fold increase in catalytic N(2)H(4) oxidation activity over today's benchmark catalysts. We further study the mechanistic pathways of the catalytic N(2)H(4) conversion as function of the applied electrode potential using differentially pumped electrochemical mass spectrometry (DEMS). At positive overpotentials, N(2)H(4) is electrooxidized into nitrogen consuming hydroxide ions, which is the fuel cell-relevant faradaic reaction pathway. In parallel, N(2)H(4) decomposes chemically into molecular nitrogen and hydrogen over a broad range of electrode potentials. The electroless chemical decomposition rate was controlled by the electrode potential, suggesting a rare example of a liquid-phase electrochemical promotion effect of a chemical catalytic reaction ("EPOC"). The coexisting electrocatalytic (faradaic) and heterogeneous catalytic (electroless, nonfaradaic) reaction pathways have important implications for the efficiency of hydrazine fuel cells.     

Microfluidic devices for electrochemical measurement of photosynthetic activity of cyanobacteria microcystis cells

A microfluidic device with analytical chambers for electrochemical measurements has been employed to detect photosynthetic activity at single cell level. The flowing cells (Microcystis viridis) in a main channel are individually guided to the chamber with microelectrodes by an electrophoretic manipulation. The reduction current of oxygen was continuously monitored to determine the photosynthetic activity upon light irradiation. The average rates for oxygen generation were estimated and found to be 10(-18) mol/s level.     

LSI-based amperometric sensor for bio-imaging and multi-point biosensing

We have developed an LSI-based amperometric sensor called "Bio-LSI" with 400 measurement points as a platform for electrochemical bio-imaging and multi-point biosensing. The system is comprised of a 10.4 mm × 10.4 mm CMOS sensor chip with 20 × 20 unit cells, an external circuit box, a control unit for data acquisition, and a DC power box. Each unit cell of the chip contains an operational amplifier with a switched-capacitor type I-V converter for in-pixel signal amplification. We successfully realized a wide dynamic range from ±1 pA to ±100 nA with a well-organized circuit design and operating software. In particular, in-pixel signal amplification and an original program to control the signal read-out contribute to the lower detection limit and wide detection range of Bio-LSI. The spacial resolution is 250 μm and the temporal resolution is 18-125 ms/400 points, which depends on the desired current detection range. The coefficient of variance of the current for 400 points is within 5%. We also demonstrated the real-time imaging of a biological molecule using Bio-LSI. The LSI coated with an Os-HRP film was successfully applied to the monitoring of the changes of hydrogen peroxide concentration in a flow. The Os-HRP-coated LSI was spotted with glucose oxidase and used for bioelectrochemical imaging of the glucose oxidase (GOx)-catalyzed oxidation of glucose. Bio-LSI is a promising platform for a wide range of analytical fields, including diagnostics, environmental measurements and basic biochemistry.     

Comparison of electrode structures and photovoltaic properties of porphyrin-sensitized solar cells with TiO2 and Nb, Ge, Zr-added TiO2 composite electrodes

Electrode structures and photovoltaic properties of porphyrin-sensitized solar cells with TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were examined to disclose the effects of partial substitution of Ti atom by the other metals in the composite electrodes. The TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were prepared by sol-gel process using laurylamine hydrochloride as a template for the formation of micellar precursors yielding well-defined mesoporous nanocrystalline structures, as in the cases of the formation of silica and titania tubules and nanoparticles by the templating mechanism. The TiO2 and Nb-, Ge-, and Zr-added TiO2 composite electrodes were characterized by transmission electron microscopy, BET surface area analysis, X-ray diffraction analysis, Raman spectroscopy, and impedance measurements. The TiO2 anatase nanocrystalline structure is retained after doping a small amount (5 mol %) of Nb, Ge, or Zr into the TiO2 structure, suggesting the homogeneous distribution of the doped metals with replacing Ti atom by the doped metal. The power conversion efficiency of the porphyrin-sensitized solar cells increases in the order Zr-added TiO2 (0.8%) < Nb-added TiO2 (1.2%) < TiO2 (2.0%) < Ge-added TiO2 cells (2.4%) under the same conditions. The improvement of cell performance of the Ge-added TiO2 cell results from the negative shift of the conduction band of the Ge-added TiO2 electrode. The Ge-added TiO2 cell exhibited a maximum power conversion efficiency of 3.5% when the porphyrin was adsorbed onto the surface of the Ge-added TiO2 electrode with a thickness of 4 microm in MeOH for 1 h.     

Scavenging DPPH radicals catalyzed by binary noble metal-dendrimer nanocomposites

Catalytic activity of gold-platinum, gold-palladium, and platinum-palladium dendrimer nanocomposites for scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals was investigated. The gold-platinum and gold-palladium dendrimer nanocomposites were prepared via simultaneous reduction by sodium borohydride in the presence of poly(amidoamine) (PAMAM) dendrimers with amine or carboxyl terminal groups. The particles were not mixtures of monometallic particles but alloyed bimetallic particles. Bimetallic particles exhibited higher catalytic activity than monometallic ones.     

New dimeric and monomeric chromanones,gonytolides D–G,isolated from the fungus Gonytrichum sp.

In the course of the screening of innate immune regulators from natural resources, we isolated new dimeric and monomeric chromanones, gonytolides D–G (4–7), from Gonytrichum sp. along with a known innate immune promoter, gonytolide A (1). The structures of these compounds were determined by spectral analysis, chemical conversion, and biogenetic consideration. The compounds 4–7 were evaluated on the innate immune response, indicating that the 8,8′-linked bischromanone rings were crucial for innate immune-promoting activity.