Effects of B-Site Modification of Bi-Ru Based Oxide on Catalytic Activity for Oxygen Reactions

摘要

An aqueous air secondary battery uses oxygen in air as the active mass of the air electrode, at which the reactions are oxygen reduction during discharge and oxygen evolution during charge. The polarization of the air electrode is known to be large and a highly active bi-functional oxygen catalyst is needed to reduce the polarization. We have been developing a metal hydride/air secondary battery using KOH solutions and have found that bismuth and ruthenium based oxide (BRO) can suppress the polarization of oxygen reactions. Although BRO has a good bi-functionality, there is still an issue that the polarization of oxygen reduction is ca. 100 mV larger than that of oxygen evolution. In this work, we aimed to improve the catalytic activity of BRO with modification of B-site element by substituting ruthenium with manganese. Then, the modified BRO (MBRO) was examined by titanium disk method (TDM) developed by our group, which is very useful to know the activity of oxygen catalyst, because no oxygen reactions on titanium occur in the examined potential range so that no oxygen current from the substrate is excluded. The electrochemical polarization data was analyzed to obtain some kinetic parameters such as Tafel slope and exchange current density.