The anodic behaviors of bare nickel, nickel-based composite, and carbon electrodes in molten fluorides containing HF such as NH4F·2HF and NH4F·KF·mHF (m=3 and 4) at 100°C are described from the viewpoints of NF3 formation, the oxidized layer formation, and the anodic dissolution. Although the anodic dissolution of the nickel based composite electrodes was smaller than that of the nickel electrode, the current efficiency for NF3 formation decreased slightly on the nickel-oxide composite electrode, because of water formed through the reaction of the oxides with HF in the melt. Addition of LiF to the melt was effective for increasing the current efficiency for NF3 formation and decreasing the anode consumption of the nickel and nickel-based composite electrodes. Fluorine-graphite intercalation compounds (GICs) having stage numbers higher than three were detected on the surface of carbon electrode after pre-electrolysis at 2.3 V and then 4 V, and the presence of the GIC layer suppressed the occurrence of the anode effect during electrolysis for NF3 production. Boron-doped Diamond (BDD) anodes were developed and their anode performance for electrochemical synthesis was investigated. The anode potential even at 1000 mA cm−2 on a BDD electrode was much lower than those at 100 or 30 mA cm−2 on a nickel and a pristine carbon FE-5 electrode and no anode effect took place up to 1000 mA cm−2. That is, the electrolysis with the BDD anode can be conducted at a high current density for long duration. The current efficiency for NF3 formation on the BDD anode was the highest among these anodes and its maximum value was 72.4%. Therefore, BDDs are promising candidates for anode materials in electrolytic production of NF3.
The physical and chemical properties of the rust film are quite significant for the corrosion resistance of weathering steel. The investigations of the ion-selective permeability and the ion-permeation resistance (film resistance) are necessary to characterize the rust film. In the present paper, the membrane potential and the electrochemical impedance of the rust film, which was fabricated by the precipitation of Fe(III) from the solution, were measured. The rust film showed the anion-selective permeability in the neutral solution, indicating that the pore wall in the rust film has a positive fixed charge. The measurements of electrochemical impedance of the rust film membrane were performed by four-electrode method. The working and reference electrodes were platinum wire and silver/silver chloride electrode, respectively. The current between two working electrodes was measured by controlling the alternative voltage between two reference electrodes. The electrochemical impedance showed an apparent capacitive loop on the complex plane, and the diameter of the capacitive loop corresponds to the film resistance. The ion-selective permeability and the film resistance were changed depending on the adsorption of metallic ions on the rust film.
The Japanese spacecraft, HAYABUSA, was launched on May 9, 2003 and spent more than 2.5 years approaching the asteroid ITOKAWA. This spacecraft used 13.2 Ah lithium-ion secondary cells. After HAYABUSA touched down on ITOKAWA in December 2005, it could not communicate for seven weeks due to a malfunction of the attitude control. During this period, four of 11 lithium-ion secondary cells were over-discharged, and solar power was unavailable due to the spacecraft’s tumbling motion. However, the battery power was still indispensable for sealing the container with the asteroid sample. The seven remaining healthy cells were slowly recharged using minimum current. During this time, ground simulation tests using similarly-built and intentionally short-circuited cells were carried out to evaluate the battery’s operational safety. After its safety was confirmed, the lithium-ion secondary battery was used to transfer, latch, and successfully seal the sample container into the reentry capsule. The necessary power for these actions was supplied by the battery.
One of the poly (aminoquinoxaline) compounds series, poly (2,3-dithienyl-5-aminoquinoxaline), P(AQX-06) has high potential as an electrochemical capacitor electrode materials. In the tetraethylammonium tetrafluoroborate (TEABF4) acetonitrile media, P(AQX-06)/carbon felt electrode showed electrochemical redox activity at potential window between −1.8 and 1.5 V vs. Ag wire. First, specific capacity of P(AQX-06) was lower level, but it gradually rose to reach at 134 Ah kg−1 (210 Fg−1) after 3,600 cycling. Such high capacity was maintained after further 2,000 cycling. The charge utilization of P(AQX-06)/carbon felt electrode showed 62%, which is higher level than other conductive polymer materials. By SEM analysis, a lot of pores are observed on the surface of the electrode after the cycling.
A ligand compound with strong coordinating property, 2-(1H-pyrrole-3-yl) pyrazine (pz-Py), was synthesized to increase the density of active sites for oxygen reduction. The obtained compound was coordinated with cobalt (II) ions strongly. It was revealed that the metal complex could be used as a cathode catalyst in fuel cells. The potential for oxygen reduction was positive (Ep=0.27 V vs SCE) for the catalyst prepared by refluxing the corresponding compound, cobalt acetate tetrahydrate, and the carbon particles. This activity was superior to CoPy/C which was synthesized by refluxing pyrrole, cobalt acetate tetrahydrate, and the carbon particles, and it was shown that nitrogen atoms of pyrazine type contribute accumulation of cobalt ions. The activity of the catalyst was improved after heat treatment under Ar gas. These results show the potential use of the present catalyst as a novel cathode catalyst in fuel cells.
In this paper, experimental and theoretical attempts have been made to evaluate the reduction ability of polyols. The experimental evaluations were carried out using voltammetric measurements. In voltammetry measurements, the potential difference between polyols at higher temperature was marginal and also the measurement at boiling temperature was difficult. Thus reducing ability of polyol was evaluated assuming that it depended on the energy gap between the HOMO of polyol and LUMO of the metal ion to be reduced. The HOMO energy levels of polyols were evaluated fixing the LUMO energy level of metal. It became clear that a polyol has many conformers with different energy states and orbital energies, and the prominence of any conformer depended on their corresponding thermal energy barrier. Therefore, the reduction potential of polyol was a function of temperature and their increase was ascribed to transformation of the polyol’s conformers. The theoretically estimated hierarchy of reducing ability of polyol was experimentally verified.