Toshikatsu Kojima

Indigo carmine: An organic crystal as a positive-electrode material for rechargeable sodium batteries

Using sodium, instead of lithium, in rechargeable batteries is a way to circumvent the lithiums resource problem. The challenge is to find an electrode material that can reversibly undergo redox reactions in a sodium-electrolyte at the desired electrochemical potential. We proved that indigo carmine (IC, 5,5′-indigodisulfonic acid sodium salt) can work as a positive-electrode material in not only a lithium-, but also a sodium-electrolyte. The discharge capacity of the IC-electrode was ~100u2005mAh g−1 with a good cycle stability in either the Na or Li electrolyte, in which the average voltage was 1.8u2005V vs. Na+/Na and 2.2u2005V vs. Li+/Li, respectively. Two Na ions per IC are stored in the electrode during the discharge, testifying to the two-electron redox reaction. An X-ray diffraction analysis revealed a layer structure for the IC powder and the DFT calculation suggested the formation of a band-like structure in the crystal.

Long-term operation of small-sized single molten carbonate fuel cells

Abstract Single molten carbonate fuel cells (MCFCs), with an effective electrode area of 256 cm 2 and state-of-the-art components, are run at 150 mA cm −2 under atmospheric pressure for 15u2008000 and 40u2008000 h, then the components are analyzed for material degradation. Cell output is reduced due to a short-circuit induced by dissolution of the NiO cathode, increase of IR-drop, and increase of anode and cathode polarization. It is concluded that the main factors that limit the life of the materials are dissolution of the NiO cathode and the degradation of LiAlO 2 matrix.

Density, molar volume, and surface tension of molten Li2CO3-Na2CO3 and Li2CO3-K2CO3 containing alkaline earth (Ca, Sr, and Ba) carbonates

The density, molar volume, and surface tension of binary, ternary, and quaternary molten carbonate mixtures of Li 2 CO 3 -Na 2 CO 3 and Li 2 CO 3 -K 2 CO 3 containing alkaline earth (Ca, Sr, and Ba) carbonates were measured using a maximum bubble pressure technique. The addition of alkaline earth carbonates resulted in increases in the density and surface tension of the molten carbonate mixtures. The apparent molar volume of a component carbonate in mixtures can be derived from the density data, assuming additivity, and inversely be used to estimate the molar volume and density of mixtures within an error of 1 %. The surface tensions of alkali-alkaline earth carbonates were proportional to the mole fraction of the added alkaline earth carbonate.

XAFS Analysis of Pt and Pt‐Ru Catalysts for PEFCs by In‐Situ Measurements under Operating Conditions in the Fluorescence Mode

In‐situ X‐ray absorption fine structure (XAFS) is one of powerful spectroscopic techniques to analyze valence state and chemical bonding in Pt and Pt‐Ru electrocatalysts under fuel cell operating conditions. We measured Pt L3 and Ru K‐XAFS of Pt and Pt‐Ru electrocatalysts in fluorescence mode under different operation voltages using pure H2 or 97 ppm CO containing H2 as fuel gases that were fed to the anode. The radial structure functions that derived from the obtained XAFS spectra showed that the local structure around Pt and Ru atoms in the electrocatalysts changes depending on the operation voltage and shows difference with the existence of CO in the fuel gas.