Electro-oxidation reaction of NO in phosphate buffer solution (0.1 M (1 M= 1 mol dm-3), pH 7.2) containing its oxidized species, electroactive NO2-, has been investigated using cyclic and linear sweep voltammetry with electrochemically pretreated Au, Pt, and glassy carbon electrodes. Well-separated oxidation peaks for NO and NO2- could be observed at these pretreated electrodes. Thus the values of saturated concentration (CNO) and diffusion coefficient (DNO) of NO were simultaneously determined to be 1.7±0.1 mM and (1.3±0.1)×10-5 cm2 S-l, respectively, using hydrodynamic chronocoulometry. The values obtained are briefly discussed on the basis of comparison with those previously reported.
Electrochemical behavior of lead was investigated using EQCM technique at Au electrode in alkaline aqueous solutions. The interfacial mass at Au electrode modified with Pb monolayer remarkably decreases by the oxidation and dissolution of Pb in the range 0.25 to 0.6 V. A Pb thin film deposited on the electrode is easily oxidized and dissolved in the range 0.25 to 1.0 V.
An aramid resin, poly(p-phenylene terephtalamide) (PPTA) was available on an ITO electrode as a stable matrix film. Electrochromic iridium oxide was electrodeposited on the electrode. In the oxidized state, original iridium oxide without PPTA film showed blue, while the PPTA / iridium oxide film showed greenish blue: the maximum absorption wavelength of the original iridium oxide film was about 650 nm, while that of the PPTA / iridium oxide film was about 600 nm. The XPS-biding energy of Ir 4f5/2 and Ir 4f7/2 electrons was shifted to about 2 eV higher energy, meaning that the color change was probably due to donating of the lone pair electrons of PPTA to the indium. The electrodeposition of Au on the PPTA / iridium oxide film was carried out. The obtained Au-electrodeposited PPTA / iridium oxide film showed quite different electrochromic properties. New redox current peaks appeared in the CV of the film. The film was colored vermilion in the reduced state and greenish blue in the oxidized state. The XPS-biding energy of Ir 4f5/2 and Ir 4f7/2 electrons was shifted to about 2 eV lower energy, implying that the electrodeposition of Au transformed the electronic state and structure of iridium oxide, suggesting the formation of a -Au-CI-Ir- binuclear Cl-bridged complex and/or the plasmon absorption of the Au microparticles dispersed in the PPTA film.
Dye-sensitized solar cells were fabricated by using water-based electrolytes for the purpose to realize environmentally benign, green solar cells in which electrolyte solvent, water, can serve as a recyclable medium. Mesoporous TiO2 electrode was treated with ozone and UV light for hydrophilic conversion of the TiO2 mesopore and was dyesensitized with Ru(bipy)2 (SCN)2 in the presence of 4-tert-butylpyridine. These processes for surface activation highly improved photocurrent density and voltage of the electrode in contact with aqueous electrolytes that contain iodide/iodine as redox agents. Replacement of a portion of water with ethanol in the electrolyte composition further enhanced photovoltaic performance. With aqueous electrolyte containing 35% ethanol, photocell achieved power conversion efficiency of 2.2% under exposure to simulated solar light of 100 mW/cm2.
A composite-type optical waveguide was applied to a gas sensor using a thin film of siloxane polymer which absorbs NO2 gas. The waveguide was prepared by using ion exchange (K+-doped base layer, about 2 μm thick) and sputtering (TiO2 top layer, about 20 nm thick, with slopes on both sides). A highly sensitive interferometer was constructed on the basis of the difference in cutoff thickness for TE and TM modes. Changes in thickness or refractive index taking place in the polymer film coated on to the TiO2 part induce phase shifts (Δϕ) of the propagating lightwave. NO2 gas with concentration less than 1 ppb was detected by measuring changes in Δϕ as a function of time. The response was reversible for low concentration, and irreversible for high concentration. The irreversible changes were attributed to the ion-pair formation in the film.
Carbon dioxide was reduced by the surface modified carbon fiber electrodes impregnated with indium to form formic acid which is expected to be available for the chemiluminescent application. The PAN (polyacrylonitrile) based carbon fiber (800°C pre-heated) was baked with aluminum chloride and water in nitrogen atmosphere oven to introduce oxygen atoms and to increase the degree of crystallization, which results in the improvement in hydrogen overvoltage and some electrochemical reactivities. Indium was electrodeposited to the surface modified carbon fibers for the working electrode. The current efficiency of carbon dioxide conversion to formic acid was close to 100%, and trace of by-products such as folmaldehyde and carbon monooxide were detected under the optimum electrochemical conditions. The cell technologies of flow coulometric detectors and redox flow batteries were applied to the design of the electrolytic cells for carbon dioxide reduction.
New paste-type positive electrodes with Ni- or Co(OH)2-coated Ni(OH)2 for nickel/metal-hydride (Ni/MH) battery were prepared using low-cost punching metal as substrate. Their charge-discharge properties were evaluated using non-sealed battery. Electrodes with Ni- and Co(OH)2-coated Ni(OH)2 showed higher discharge capacity than those with Ni and CoO as conductive agents, respectively. SEM observation and resistance of these Ni(OH)2 materials suggest formation of fine conductive network by homogeneous Ni and Co(OH)2 coating. The capacities of these coated electrodes faded by 25% after 50 charge-discharge cycles. Their swelling rate during cycles was larger than those of the conventional Ni-foam electrodes, and the cycle degradation was mainly attributable to decrease in current collectivity by the swelling. Sealed battery with Co(OH)2-coated Ni(OH)2 showed utilization efficiency of 77% (vs. 0.2 C) at 3 C rate, which was comparable to that of conventional Ni-foam electrode.