Nobuyuki Serizawa

EQCM Measurement of Ag ( I ) ∕ Ag Reaction in an Amide-Type Room-Temperature Ionic Liquid

Electrodeposition of silver was investigated using an impedance technique (separately excited, passive technique) electrochemical quartz crystal microbalance (EQCM) in a room-temperature ionic liquid. The mass changes during silver deposition and dissolution were observed with the current efficiencies of nearly 100% during potential sweep, constant potential step, and constant current step experiments. The product of the viscosity and density of the electrolyte near the electrode, η L ρ L , can be estimated by the resonance resistance, which can be monitored simultaneously with the resonance frequency. The change in the η L ρ L value during silver deposition was consistent with the change in the calculated concentration of Ag(I) near the electrode. During the outer-sphere electron-transfer reaction between ferrocenium and ferrocene, no significant changes in the mass and the η L ρ L value were observed.

Static and Transport Properties of Alkyltrimethylammonium Cation-Based Room-Temperature Ionic Liquids

We have measured physicochemical properties of five alkyltrimethylammonium cation-based room-temperature ionic liquids and compared them with those obtained from computational methods. We have found that static properties (density and refractive index) and transport properties (ionic conductivity, self-diffusion coefficient, and viscosity) of these ionic liquids show close relations with the length of the alkyl chain. In particular, static properties obtained by experimental methods exhibit a trend complementary to that by computational methods (refractive index ∝ [polarizability/molar volume]). Moreover, the self-diffusion coefficient obtained by molecular dynamics (MD) simulation was consistent with the data obtained by the pulsed-gradient spin-echo nuclear magnetic resonance technique, which suggests that computational methods can be supplemental tools to predict physicochemical properties of room-temperature ionic liquids.

Effects of Lithium Salts on Shear Relaxation Spectra of Pyrrolidinium-Based Ionic Liquids

The shear relaxation spectra of the solutions of lithium salts in ionic liquids composed of N-methyl-N-propylpyrrolidinium cation paired with bis(trifluoromethanesulfonyl)amide (TFSA(-)) or bis(fluorosulfonyl)amide (FSA(-)) anions are determined from 5 to 205 MHz at various concentrations of lithium salts. The addition of lithium salt retards the shear relaxation, together with the increase in the shear viscosity. The normalized spectra reduce to a single curve when plotted against the product of the frequency and zero-frequency shear viscosity, which indicates that the increase in the shear viscosity by lithium salts is ascribed to the increase in the relaxation time. The difference in the shear viscosity of TFSA- and FSA-based ionic liquids is also elucidated in terms of the shear relaxation time. The relationship with previous studies on ionic mobility and liquid structure is also discussed.

Effects of non-equimolar lithium salt glyme solvate ionic liquid on the control of interfacial degradation in lithium secondary batteries

Control of interfacial properties between the electrode and electrolyte is important for obtaining long life-cycle lithium-ion secondary batteries. To control interfacial degradation, we investigated the effect of changing the composition ratio of lithium salt (LiN(SO2CF3)2) and low-molecular-weight ether (CH3–O–(C2H4O)3–CH3) in the system. A highly electrochemically stable lithium salt glyme solvated ionic liquid electrolyte was realized, with long-lived, robust lithium solvation complexes by increasing the lithium salt composition ratio. Lithium secondary batteries using the electrolyte show notable suppression of the degradation of interfacial resistance at the interface of the electrolyte and the positive electrode (high oxidation state), which leads to a longer life-cycle of the batteries.

Evaluation of SrTi1−xCoxO3 Perovskites (0 ≤ x ≤ 0.2) as Interconnect Materials for Solid Oxide Fuel Cells

The compatibility of SrTi1− x Cox O3 perovskites (0 ≤ x ≤ 0.2) was evaluated for use as interconnect materials in solid oxide fuel cells (SOFCs). Although SrTi1− x Cox O3 perovskites have a single perovskite phase in the range of 0 ≤ x ≤ 0.2, it was observed for SrTi0.8 Co0.2 O3 that Co element agglomerated at the grain boundary during sintering. The dense SrTi0.8 Co0.2 O3 sample was destroyed and included Sr2 TiO4 as a secondary phase after reducing treatment at 1000 °C. As a result of Co doping, the linear thermal expansion coefficient (TEC) increased remarkably with increasing Co content, but the TEC of SrTi0.9 Co0.1 O3 was comparable with those of SOFC cathodes and anodes. Co doping of SrTiO3 effectively increased electrical conductivity in air, whereas the conductivity of Co-doped SrTiO3 in a reducing atmosphere was much lower than that in air. This suggests that the Co ions3+/4+ in the perovskites were earlier reduced into Co2+ ions, compared to Ti4+ ions.

CHAPTER 14:Design and New Energy Application of Ionic Liquids

New electrochemical application using room-temperature ionic liquids (ILs) are introduced, such as lithium secondary batteries, electrochemical double layer capacitors, and novel types of electrical devices for sustainable and renewal energy society. ILs have so many combinations, owing to many cation/anion species. In this chapter, we introduce properties from fundamental (general and special physicochemical properties) to electrochemical applications of ILs. We also discuss importance of molecular design and application target of ILs.