No abstract

Aqueous solutions have attracted considerable attention for use in aqueous-based energy-conversion devices such as aqueous lithium-ion batteries. While aqueous solutions have some desirable properties as electrolyte solutions, one drawback is the narrow potential window of water due to the electrolysis reactions of water (oxygen/hydrogen evolution reaction, OER/HER). Recently, it has been reported that the potential windows were expanded in concentrated electrolyte solutions. In this study, we investigated the potential windows in aqueous concentrated electrolyte solutions with various salts at different concentrations. A neutral pH solution with the lowest water concentration showed the largest potential window, and the potential windows were not affected by the electrolyte salts. In addition, we observed an asymmetric expansion of potential windows: the upper potential limits were shifted more than the lower limits. This can be explained by the local pH change in the vicinity of electrodes caused by OER/HER and the decrease in the rate of OER due to the reduced water concentrations.

No abstract

We investigated the catalytic activities of three perovskite oxide (LaMnO 3 , La 0.8 Sr 0.2 MnO 3 , and La 0.8 Sr 0.2 CoO 3 ) thin films grown by pulsed laser deposition when they were used as oxygen electrodes for aqueous rechargeable metal-air batteries. The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on perovskite oxide thin films in alkaline solution were observed by linear sweep voltammetry using a rotating disk electrode. Although we confirmed that the resultant perovskite oxide thin films were sufficiently electroconductive to facilitate the ferricyanide reduction reaction on themselves, the ORR activities of perovskite oxide thin films were much lower than those of conventional composite electrodes, which consist of perovskite oxide powder and carbon black. In contrast, the OER activities of thin films and their activity order (La 0.8 Sr 0.2 CoO 3 > LaMnO 3 ≥ La 0.8 Sr 0.2 MnO 3 ) were almost the same as those of conventional composite electrodes. We discuss the catalytic roles of perovskite oxides and carbon powder in oxygen electrodes and propose possible reaction paths for the ORR and OER.

New electrolyte solutions for rechargeable magnesium metal batteries were studied. The electrolyte solution composed of triethylene glycol dimethyl ether (triglyme) and butyl methyl triglyme as solvents and magnesium(II) bis(trifluoromethanesulfonyl)amide as a magnesium salt. The reversible deposition and dissolution of magnesium metal was achieved in these electrolyte solutions at ambient temperature. The electrochemical stability of triglyme-based electrolyte solutions showed high stability toward oxidation.