A room-temperature ionic liquid (RTIL) consisting of hydrophobic cations and anions forms a two-phase system with water (W). The interface between the RTIL and W is inevitably electrified because of the dissolution of cations and anions constituting the RTIL into the W phase and the two-phase system should, hence, be considered as a new electrochemical system where the phase-boundary potential across the RTIL|W interface plays a key role in determining physicochemical properties of the two-phase system, notably the interfacial charge transfer and the structure of the electrical double layers at the interface. When the solubility of the RTIL in W is on the order of a few mmol dm⁻³ or higher, the RTIL|W interface behaves as an electrochemically nonpolarized interface; the phase-boundary potential is determined by the composition of the two phases. At the opposite extreme where the solubility is a few tens µmol dm⁻³ or lower, the interface can be taken as an electrochemically polarized interface, since the phase-boundary potential can be controlled by externally applying a voltage across the two terminals of the cell that comprises the RTIL|W interface. This electrochemical polarizability allows us to employ a variety of electrochemical techniques for studying the RTIL|W interface. Electrochemical view points as well as electrochemical techniques are powerful in clarifying the unique properties of this new electrified interface. Conversely, this two-phase system poses us intriguing problems, which can in turn widen the scope of electrochemistry.

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A concept of chemical potential pumping effect was introduced to describe the NO_x sensing mechanism of oxide catalysts with high electronic conductivity and large carrier density. When NO_x gas in a gas-stream decomposed on the surface of the catalyst oxides continuously, the high oxygen potential released by the decomposition of NO_x stationarily covered the whole surface of the oxide. Then, the bulk oxide was equilibrated with the steady-state high oxygen potential of the surface, which was much larger than that determined by the oxygen pressure of the surrounding gas-phase. This effect was confirmed by the conductivity enhancement of La₂CuO₄ and La_0.5Sr_0.5FeO₃ with NO₂ as well as nonstoichiometry variation of La_0.5Sr_0.5CoO₃ and EMF of galvanic cell with La_0.6Sr_0.4CoO_3−d. It was shown that the chemical potential pumping effect appears essentially on dense materials while the effect is hardly observed on porous material with large surface relative. On La_0.5Sr_0.5FeO₃ as well as on La₂CuO₄, NO₂ was found to decompose into NO and O₂, while NO was almost inactive on these oxides.

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Orange network polysilanes; (MeSi)_n, (BuSi)_n, and (OctSi)_n, were obtained by electrochemical reduction of methyltrichlorosilane, butyltrichlorosilane, and octyltrichlorosilane, respectively, in 1,2-dimethoxyethane using lithium perchlorate as the supporting electrolyte and careful isolation process to exclude linear-rich polymers. These orange polymers should have wider σ-conjugated systems than the previously reported yellow polymers. TEM observation of the resulting polymer revealed the existence of extremely large molecules as large as 0.1 to 2 µm in diameter.

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We investigated the dependence of the properties, crystal structure and electrode characteristics on the heat-treatment of Li_1.052Co_1/3Ni_1/3Mn_1/3O_y. The crystal structure was determined by X-ray and neutron diffractions and Rietveld analysis. The electron density images were calculated by MEM/Rietveld analysis using X-ray diffraction. The discharge capacity increased, but the cycle performance was not good after a high P_O2 heat treatment (450°C, P_O2 2.03 MPa, 48 h, annealed). On the other hand, the cycle performance was improved by a reduced heat treatment (450°C, Ar, 48 h, annealed). Based on the crystal structural analysis, the bond length between 3b (transition metal site) and 6c (oxygen site) decreased with heat treatment in the reduction direction. From the distributions of the electron density, the (Li,Ni)[3a] site was localized and the covalent bond of (Co,Ni,Mn,Li)[3b]–O[6c] was weak due to the high P_O2 heat treatment.

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