Yoshinobu Shiokawa

Electron-Transfer Kinetics of Np3 + ∕ Np4 + , NpO2 + ∕ NpO2 2 + , V2 + ∕ V3 + , and VO2 + ∕ VO2 + at Carbon Electrodes

Like vanadium redox couples (V 2 + /V 3 + and VO 2 + /VO + 2 ), neptunium is a good candidate for the active materials of a redox-flow battery because it possesses two isostructural and reversible redox couples (Np 3 + /Np 4 + and NpO + 2 /NpO 2 + 2 ). The standard rate constants k 0 of the neptunium electrode reactions were first determined at four types of carbon electrodes. The k 0 values for Np 3 + /Np 4 + and NpO + 2 /NpO 2 + 2 are 1.9 X 10 - 2 and 1.5 X 10 - 2 cm s - 1 , respectively, at the c plane of pyrolytic graphite [PG(c plane)] and also 1.4 × 10 - 2 and 2.1 × 10 - 2 cm s - 1 , respectively, at plastic formed carbon (PFC). The standard rate constants for the V 2 + /V 3 + and VO 2 + /VO + 2 electrode reactions were also first determined at PG(c plane) and PFC electrodes. The determined k 0 values are larger at the PFC electrode, k 0 = 5.3 × 10 - 4 and 8.5 × 10 - 4 cm s - 1 for V 2 + /V 3 + and VO 2 + /VO + 2 , respectively, than at the PG(c plane) electrode. There is about a 10 2 order of difference between the k 0 values of neptunium and vanadium ions, and this difference was discussed in reference to the homogeneous electron-exchange rate constants of these redox couples.

Electrochemical investigation of uranium β-diketonates for all-uranium redox flow battery

Abstract The redox flow battery using uranium as the negative and the positive active materials in polar aprotic solvents was proposed. In order to establish the guiding principle for the uranium compounds as the active materials, the investigation of uranium β-diketonate complexes was conducted on (i) the solubility of active materials, (ii) the electrode reaction of U(VI) and U(IV) β-diketonate complexes and (iii) the estimation of the open circuit voltage of the battery. The solubilities of higher than 0.8 mol dm −3 of U(VI) complexes and higher than 0.4 mol dm −3 of a U(IV) complex were obtained in the solvents. The electrode reactions of U(pta) 4 , UO 2 (dpm) 2 , UO 2 (fod) 2 and UO 2 (pta) 2 were first studied and the redox potentials of uranium β-diketonates were thermodynamically discussed. The open circuit voltage is estimated more than 1 V by using Hacac or Hdpm. The larger open circuit voltage is expected when a ligand with the larger basicity is used.

Single Crystal Growth and Anisotropic Superconducting Property of PuRhGa5

We grew a single crystal of the transuranium superconductor PuRhGa 5 with the tetragonal structure by the Ga-flux method, and measured its magnetic susceptibility, magnetization and AC susceptibili...

Magnetic and Electrical Properties of NpTGa5 (T=Fe, Rh and Ni)

We grew high-quality single crystals of NpTGa 5 (T = Fe, Rh, and Ni) with a tetragonal structure by the Ga-flux method and measured their electrical resistivity, specific heat, magnetic susceptibility, and magnetization. All the investigated compounds undergo magnetic ordering. NpFeGa 5 orders antiferromagnetically at T N =118 K and shows another magnetic transition at T * =78 K. A relatively large electrical resistivity indicates that NpFeGa 5 might be a low-carrier compound. NpRhGa 5 also orders antiferromagnetically at T N1 =36 K. Below another magnetic transition at T N2 =32 K, the antiferromagnetic easy-axis is most likely changed from [001] to the (001) plane. On the other hand, NpNiGa 5 undergoes ferromagnetic ordering at T C =30 K, where the magnetic moment of Np is directed along the [001] direction. Furthermore, below another magnetic transition at T * =18 K, the ordered moment is discontinuously enlarged and a change of the magnetic structure occurs. The electronic specific heat coefficients ar...

First Observation of the de Haas–van Alphen Effect in NpNiGa5

We succeeded in observing the de Haas–van Alphen (dHvA) oscillations in NpNiGa 5 single crystals, which were grown by the Ga-flux method. This is the first dHvA observation in transuranium compound...

Two Kinds of Cylindrical Fermi Surface Determined by de Haas–van Alphen Experiments in NpCoGa5

We succeeded in observing de Haas–van Alphen (dHvA) oscillations in an antiferromagnet NpCoGa 5 with a tetragonal structure. The dHvA signal was significantly enhanced at higher fields than the metamagnetic transition field H m (=43 kOe for H ∥[001]), where the antiferromagnetic state is changed into the field-induced ferromagnetic (paramagnetic) state. In the paramagnetic state, the Fermi surface was found to consist of two kinds of cylindrical main Fermi surface and small pocket Fermi surfaces. The cyclotron masses of the main Fermi surfaces were considerably large, ranging from 6 to 12 m 0 . This is the first case where the Fermi surface was determined experimentally in transuranium compounds.

An application of actinide elements for a redox flow battery

The electrochemical properties of U, Np, Pu and Am were discussed from the viewpoint of cell active materials. From the thermodynamic properties and the kinetics of electrode reactions, it is found that neptunium in the aqueous system can be utilized as an active material of the redox flow battery for the electric power storage. A new neptunium redox battery is proposed in the present article: the galvanic cell is expressed by The neptunium battery is expected to have more excellent charge and discharge performance than the current vanadium battery, whereas the thermodynamic one of the former is comparable to the latter. For the development of a uranium redox flow battery, the application of the redox reactions in the non-aqueous solvents is essential.

Itinerant 5f electrons and the fermi surface properties in an enhanced pauli paramagnet NpGe3

We succeeded in growing a high-quality single crystal of an enhanced Pauli paramagnet, NpGe 3 , by the Bi-flux method, and observed the de Haas–van Alphen (dHvA) effect. The topology of a Fermi surface is well explained by the relativistic linear augmented-plane-wave (LAPW) band calculations based on the 5 f itinerant band model. The Fermi surface consists of a nearly spherical electron-Fermi surface with necks along the direction, forming a hollow ball, centered at the R point, which is derived from the single band. The cyclotron effective mass is in the range from 2.6 to 16 m 0 , which is enhanced approximately 3.5 times from the corresponding band mass.

New Evidence for Spin Glass States in U2TSi3 (T=Pd, Pt and Au): AC Susceptibility and Electrical Resistivity

The uranium intermetallic compounds U 2 T Si 3 ( T =Pd, Pt and Au), which crystallize in a disordered derivative of the hexagonal AlB 2 -type structure, have been studied by means of ac susceptibil...

First observation of de Haas-van Alphen effect in PuIn3

We observed de Haas–van Alphen (dHvA) oscillation in a paramagnetic plutonium compound, PuIn 3 . In the present paper, we report the first observation of dHvA effect in plutonium compounds. One det...