Papers by Author: Takeshi Chuma

Abstract: Two series of compositions, BaCe0.8-xGd0.2RuxO3-δ (BCGRx, x=0-0.8) and BaGd1-yRuyO3-δ (BGRy, y=0.5-1.0), were synthesized and their crystal phases were examined. The BCGR0.15 and BGR0.5 oxides were a single phase of perovskite solid solution, while BCGR0.67 and BGR0.67 were a perovskite-related superstructure phase. The onset voltage (Vo) of the reduction current and the efficiency (E4) of the 4-electron reduction of oxygen were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. In the BCGRx series, the activities for electrochemical oxygen reduction (EOR) increased with increasing Ru content. In the BGRy series, the BGR0.67 superstructure phase showed a higher EOR activity than the perovskite BGR0.5 and the hexagonal(4H) BaRuO3. This indicates that the EOR activity depends on the crystal phase. The BGR0.67 exhibited the best EOR activity of all the samples. The Vo value was 0.80 V vs. reversible hydrogen electrode and the E4 value was almost 100 %.

Abstract: The O2-gas electrode (OGE) properties of the perovskite-related oxides SrFe1-x-yCoyRuxO3 (SFCR) were examined with the solid-state cells of the type (SFCR | Ba0.975Ce0.8Gd0.2O3 | SFCR) below 300°C. The SrFe0.7Co0.2Ru0.1O3 electrode showed the best OGE properties of the other SrFe1-x-yCoyRuxO3 (x
0.2) electrodes prepared here. An oxide-ion current of 200 μA/cm2 was allowed to flow through the cell with the SFCR electrode at 225°C. The SFCR electrodes including some other compositions can be used instead of conventional Pt electrodes in solid-state cells at temperatures below 300°C.

Abstract: The O2-gas electrode (OGE) properties of the pyrochlores Pb2Ru2-XMXO7-δ(M=Mn,Fe,Co,Ni) [PRMx] were examined below 300°C with the cell of the type (PRMx | Ba0.975Ce0.8Gd0.2O3 (BCG) | PRMx). The PRMn electrodes showed good OGE properties comparable to those of Pb2Ru2O6.5 and superior to those of a Pt-paste electrode and the La0.6Sr0.4Co0.98Ni0.02O3 electrode, which are well-known representative OGEs. The results indicate that the PRMn electrodes can be used for OGEs in low-temperature applications including oxygen sensors.