Tsutomu Ioroi

Iridium Oxide/Platinum Electrocatalysts for Unitized Regenerative Polymer Electrolyte Fuel Cells

To improve the water electrolysis performance of unitized regenerative fuel cells, ultrafine powder was synthesized from colloidal precursors, and an active electrode for oxygen evolution and reduction was prepared by mixing the powder and Pt black. Analysis showed that the surface area of the synthesized was higher than that of high‐surface‐area Pt black. During fuel cell operation, increased the overpotential slightly; however during water electrolysis, the mixed electrocatalyst had a considerably higher activity for oxygen evolution. The addition of only a small amount of to the oxygen electrode was sufficient for the unitized regenerative fuel cell.

Preparation of Perovskite‐Type La1 − x Sr x MnO3 Films by Vapor‐Phase Processes and Their Electrochemical Properties II. Effects of Doping Strontium to on the Electrode Properties

Complex alternating current impedance and steady-state polarization measurements have been conducted on dense and thin LaMnO{sub 3} and La{sub 0.85}Sr{sub 0.15}MnO{sub 3} film electrodes and porous-sintered LaMnO{sub 3} and La{sub 0.85}Sr{sub 0.15}O{sub 3} electrodes in air at elevated temperatures between 873 and 1,273 K, in order to study the reaction mechanism of oxygen reduction at the La{sub 1{minus}x}Sr{sub x}MnO{sub 3} electrode of a solid oxide fuel cell. By fitting impedance spectra to an appropriate equivalent circuit, the chemical diffusion coefficient of oxygen and interfacial reaction resistance of the LaMnO{sub 3} and La{sub 0.85}Sr{sub 0.15}MnO{sub 3} film electrodes were determined. The chemical diffusion coefficient was scarcely affected by Sr doping, while the interfacial reaction resistance considerably decreased by Sr doping. Steady-state polarization behavior of the porous-sintered La{sub 1{minus}x}Sr{sub x}MnO{sub 3} was dramatically improved by doping Sr, while those of the dense La{sub 1{minus}x}Sr{sub x}MnO{sub 3} film were almost unchanged by Sr doping. These results suggested that the electrochemical reduction of oxygen at the porous La{sub 1{minus}x}Sr{sub x}MnO{sub 3} electrode takes place around the triple phase boundary (TPB), and the reaction rate is controlled by the surface reactions close to the triple phase boundary region.

Growth rate of yttria-stabilized zirconia thin films formed by electrochemical vapour-deposition using NiO as an oxygen source II. Effect of the porosity of NiO substrate

Abstract Yttria-stabilized zirconia (YSZ) thin films were formed at 1000°C by a modified electrochemical vapour-deposition (EVD) using NiO as an oxygen source, and ZrCl4 and YCl3 as metal sources. Growth rate kinetics were examined using NiO pellet substrates with different pore structures. The thickness of YSZ film increased linearly with deposition time, and the growth rate increased with increasing the porosity of the substrate. The pore size as well as the porosity affected the growth rate. In addition, the observed growth rate was much slower than the theoretical one assuming that the electrochemical transportation of the charged species across the growing film is rate limiting. From these results, it was concluded that the rate-determining step is not the bulk electrochemical transport, but the mass transport of dissociated oxygen in the substrate pore.

Stability of Corrosion-Resistant Magnéli-Phase Ti4O7-Supported PEMFC Catalysts

Corrosion of carbonaceous catalyst support materials such as carbon black has been recognized as one of the cause for the performance degradation of PEMFC under repeated start-stop cycles or high potential conditions [1,2]. Therefore, a more oxidation-resistant catalyst support at high potentials (> 1.0 V) is desired for practical fuel cell, especially for automotive applications. Sub-stoichiometric titanium oxide of the general formula TinO2n-1 (4 1.2 V, stability of ECA is completely different depending on the support material; Pt/Ti4O7 shows better stability than Pt/XC72 catalyst at high potentials. The results of potential cycling and long-term fuel cell tests will be discussed at the meeting.

Kinetics of Vapor‐Phase Electrolytic Deposition of Yttria‐Stabilized Zirconia Thin Films

The kinetic aspects of the vapor-phase electrolytic deposition (VED) process are discussed. This new technology, which is similar to the electrochemical vapor deposition process, is based on electrolytic deposition using a glow-discharge plasma as the conductive medium. After reaction for 2 h at a dc current density of 2.82 mA cm -2 , a uniform cubic fluorite yttria-stabilized zirconia (YSZ) layer containing about 8 mol % Y 2 O 3 about 7 μm thick was deposited. The thickness of the deposited layer was directly proportional to the reaction time, indicating that the VED process is consistent with Faradays law. In VED, the deposition rate of YSZ depends on the O -2 flux (the dc current density) through the YSZ layer.