Theoretical and experimental aspects of intermolecular and intramolecular electron-transfer kinetics of Ru-modified proteins and metal substituted cytochrome c are briefly discussed in the first part. In the second part, spectroelectro-chemical (electroreflectance) studies of horse heart cytochrome c electrostatically immobilized on carboxylic acid-terminated alkanethiol self-assembled monolayers on a well-defined gold electrode are discussed. It was found that intermolecular electron-transfer between cytochrome c and the carboxylic acid terminus is dynamically gated by configurational changes in the cytochrome c at the surface of alkanethiol self-assembled monolayers: transformation from the thermodynamically stable configuration to the electron-transfer complex, which features an efficient electron transfer channel, ultimately limits the rate of electron transfer. Kinetic measurements were carried out on horse heart cytochrome c and a recombinant rat cytochrome c (RC9-K13A), in which lysine 13 was replaced by alanine. The results revealed that the association of lysine 13 with the carboxylic acid terminus forms the electron transfer channel. A potential application of electrochemical techniques to mechanistic studies of biological intra- and intermolecular electron transfer processes is discussed as a concluding remark.
The decomposable slurry composed of Mn(NO3)2/MnO2/H2O has been developed. The solution was prepared by the addition of aqueous KMnO4 to aqueous Mn(NO3)2 solution. It was a viscous solution containing dispersed fine γ-MnO2 particle with a black color. The manganese oxide layer prepared from the dispersion showed several interesting properties; dense and uniform structure. The application of the dispersion to the tantalum solid electrolytic capacitors provided highly performed electrical characteristics of the capacitors.
Polyvinylimidazoline (PVI)-based electrolytes containing lithium perchlorate (LiClO4) were prepared and their characterizations were performed. Conductivities of PVI-based electrolytes, (PVI150)a(LiClO4)b(EtOH)d complexes, were 1.93 × 10−5 S cm−1 (a = 3.7, b = 1.0, d = 3.0), and 3.49 × 10−4 S cm−1 (a =1.5, b = 1.0, d = 1.2) at 70°C. However, their conductivities at 30°C were ca. 10−6-10−7 S cm−1. Addition of cascade nitrile compound, [-CH2-N(CH2CH2CN)2]2, ED4CN, to the PVI-based electrolytes enhanced their conductivities about one order. Conductivity of (PVI150)1.5(LiClO4) 1(ED4CN)1(EtOH) 6.11 complex was 5.00 × 10−5 S cm−1 at 30°C and it was about one order higher than that of the ED4CN-free PVI-based electrolyte. Conductivity enhancement mechanism by addition of ED4CN was investigated with X-ray diffraction, DSC, and solid state NMR measurements. Predominant coordination of ED4CN to lithium ions separated the strong coupling between lithium ion and imine-nitrogen in vinylimidazoline ring, and then increased mobility of lithium ions in the matrix. Therefore, conductivities of the PVI-based electrolytes were enhanced by addition of ED4CN to their matrix.
The local structure of LixMg2Ge, which is a candidate for anode materials of lithium secondary batteries, was investigated using both X-ray diffraction (XRD) and neutron diffraction. It was found that the nearest interatomic distance of the Ge-Mg increases slightly in electrochemically lithiated Mg2Ge, (or LixMg2Ge), although any other large structural change was not obvious. The evidences suggest that lithium atoms (or ions) accommodate at interstitial sites of the Mg2Ge lattice to form a solid solution. From the Li-Ge correlation factors observed in the radial distribution functions, furthermore, lithium atoms in the lithiated Mg2Ge were supposed to occupy the sites equivalent to those of hydrogen atoms in Mg2NiH3.9 with an anti-fluorite structure.
In order to improve durability of phosphoric acid fuel cells (PAFC), it is essential to suppress the corrosion rate of carbon, a major PAFC material. In this study, we examined the factors which influence on corrosion rates of carbon material in hot phosphoric acid. The carbon corrosion rate can be suppressed by lowering the oxygen content and reducing impurity of the content. The higher the level of graphitization carbon is used, the lesser the corrosion rate is. The fluorination of carbon surface is effective improving the corrosion resistance in case of using the sample with lower graphitization level. Among several factors affecting the durability of carbon fiber/carbon composite, the crystallite orientation of carbon fiber greatly influence the corrosion condition of carbon fiber/carbon composite. Also, a binder will influence on corrosion condition. As to what kind of material should be used for carbon fiber/carbon composite, our study revealed that the onion folded carbon fiber bound with phenol resin seems more effective in term of their durability.
High-speed removal of nitrate from aqueous solution by electrolytic method was developed. The conversion of nitrate ion to nitrogen gas was 90% after 50 minutes of reaction. The concentration of chlorite ion and nitrate ion in the initial reaction solution was 300 mg L−1 and 200 mgL−1, respectively. In this method, the highly-activated electrodes were used as a Cu-Zn cathode and a Pd anode. The main electrolytic reaction of nitrate removal involved cathodic reduction of NO3− to NH3 (NO3− + 6H2O + 8e− → NH3 + 9OH−) and anodic oxidation of Cl− to HCIO (2Cl− → Cl2 + 2e−, Cl2 + H2O → HClO + HCl), and finally got N2 by redox reaction (2NH3 + 3HClO → N2 ↑ + 3HCl + 3H2O). The performance of electrocatalysts was investigated by cyclic voltammetry.
Complex oxides LiMO2 (M = transition metal) have been used as cathode materials for lithium ion secondary batteries. To improve the performance of these materials, we should control the composition without non-stoichiometric phases that are inactive on the lithium intercalation. Therefore, it is very important that the ratio of lithium to transition metals in the complex oxide have to be controlled accurately. Spectroscopic methods such as ICP-AES (induced coupled plasma atomic emission spectroscopy) and AAS (atomic absorption spectroscopy) are generally used for the quantitative analysis of metal cations. Fatal interference between cations included in composite oxides, however, often produces erroneous data in some cases. On the other hand, IC (ion chromatography) is very useful technique for cation analytical method that equipped with a carboxylate-type separation column designed for alkali and alkaline earth metal cations. It can separate simultaneously both alkali metal ions and transition metals ions by using the mixed eluent of nitric acid and oxalic acid. In this study, we investigated the composition analysis of cathode materials using the IC technique. The data by IC had sufficient reliability and reproducibility compared with those by ICP-AES. The relationship between the heat treatment temperature and the ratio of lithium to transition metals in lithium nickel oxides showed that the fluctuation of the composition increased with increasing temperature and was larger in air atmosphere than that in oxygen. Such findings agreed well with the previous report.
The electrochemical behavior of deuteride ion on a nickel electrode in LiF-NaF-KF eutectic melt at 773 K was studied by means of cyclic voltammetry, chronopotentiometry and chronoamperometry. The observed anodic currents are considered due to the oxidation of deuteride ion to heavy hydrogen gas: D− → 1/2 D2 + e−. This anodic process is a reversible one-electron reaction governed by diffusion transport. The voltammetric half-wave potential for the oxidation of deuteride ion was obtained as 0.38 V vs. M+/M (M = alkali metal), which was almost equal to that of hydride ion. The diffusion coefficient of deuteride ion in the melt at 773 K was estimated as 0.8(± 0.2) × 10−5 cm2 s−1, 0.5(± 0.2) × 10−5 cm2 s−1 and 0.5(± 0.1) × 10−5 cm2 s−1 by means of cyclic voltammetry, chronopotentiometry and chronoamperometry, respectively.