Papers by Author: Haruhiko Toda

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 BaCe1-xGd0.2RuxO3-δ(BCGRx, x=0-0.45) oxides and the BaGd1-yRuyO3-δ(BGRy, y=0.5-1.0) oxides were examined with the cell of the type solid-state cell (OGE|BaCe0.8Gd0.2O3|OGE) below 300°C. Two single perovskite phases, BCGR0.15 in the BCGR series and BGR0.5 in the BGR series, exhibited OGE properties superior to those of known OGEs of Pt electrodes and La0.6Sr0.4Co0.98Ni0.02O3. Oxide-ion currents of the order of over one hundred μAcm-2 not yet reported were allowed to pass through the solid-state cell at low temperatures of ∼200°C.

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.