Haruyuki Nakanishi

Layered perovskite oxide: a reversible air electrode for oxygen evolution/reduction in rechargeable metal-air batteries.

For the development of a rechargeable metal-air battery, which is expected to become one of the most widely used batteries in the future, slow kinetics of discharging and charging reactions at the air electrode, i.e., oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively, are the most critical problems. Here we report that Ruddlesden-Popper-type layered perovskite, RP-LaSr3Fe3O10 (n = 3), functions as a reversible air electrode catalyst for both ORR and OER at an equilibrium potential of 1.23 V with almost no overpotentials. The function of RP-LaSr3Fe3O10 as an ORR catalyst was confirmed by using an alkaline fuel cell composed of Pd/LaSr3Fe3O10-2x(OH)2x·H2O/RP-LaSr3Fe3O10 as an open circuit voltage (OCV) of 1.23 V was obtained. RP-LaSr3Fe3O10 also catalyzed OER at an equilibrium potential of 1.23 V with almost no overpotentials. Reversible ORR and OER are achieved because of the easily removable oxygen present in RP-LaSr3Fe3O10. Thus, RP-LaSr3Fe3O10 minimizes efficiency losses caused by reactions during charging and discharging at the air electrode and can be considered to be the ORR/OER electrocatalyst for rechargeable metal-air batteries.

Temperature measurement using a gallium-filled carbon nanotube nanothermometer

We report here temperature measurement by means of a Ga-filled C nanotube thermometer with diameter <150 nm and length ∼12 μm. The method relies on the initial identification and calibration of a nanothermometer in a transmission electron microscope (TEM), followed by placing it into an air-filled furnace whose temperature is to be measured, and final TEM reading of a postmeasurement gradation mark visible inside the tubular channel. The mark originates from the fact that, at high temperature, the Ga column tip exposed to the air through the open C nanotube end oxidizes, and a thin Ga oxide layer sticks to the nanotube walls upon cooling. The temperature according to this gradation mark coincides closely with nominal furnace temperature controlled by standard means. The method paves the way for practical temperature measurements using a C nanothermometer in air and within spatially localized regions (e.g., dimensions of tens of micrometers).

Aminated Perfluorosulfonic Acid Ionomers to Improve the Triple Phase Boundary Region in Anion-Exchange Membrane Fuel Cells

We propose an approach to improve the triple phase boundary (TPB) of catalyst layers in anion-exchange membrane fuel cells by using aminated Nafion ionomers with amine molecules of ethylenediamine (EDA) and diethylenetriamine (DETA) as anion conductor. Aminated Nafion ionomers were characterized and clarified by Fourier transform IR spectroscopy, Raman spectroscopy, and transference number measurements. The transference number of the aminated Nafion ionomers with DETA (DETA-modified Nafion, t_ = 0.89) was larger than that of the EDA-modified Nafion (t_ = 0.81). Pt/C catalyst layers with EDA- and DETA-modified Nafion ionomers were constructed, and their oxygen reduction currents were evaluated under the same conditions as in anion-exchange membrane fuel cells. Electrochemical measurements of oxygen reduction currents showed that the order of electrode performance was DETA-modified > EDA-modified > K-form Nafion (neutralized Nafion with KOH). We effectively improved the TPB region in catalyst layers by introducing aminated Nafion ionomers and revealed the relationship between the conductivity of OH- ion in the aminated Nafion ionomers and the number of amine functional groups in an amine molecule.