In order to develop an air electrode to be used for rechargeable metal‐air batteries, gas‐diffusion type carbon‐based electrodes have been tested for the electrochemical reduction and evolution of oxygen. The electrode, loaded with a large surface area of La0.6Ca0.4CoO3 catalyst was found to show high bifunctional performance, i.e., 3000 mA/cm2 (oxygen reduction) and 1000 mA/cm2 (oxygen evolution) at −125 and +700 mV vs. normalHg/normalHgO , respectively, in 30 w/o KOH at 25°C. The oxide catalyst is considered to decompose effectively HO2− , an intermediate appearing in both oxygen reduction and oxygen evolution reactions. The air electrode was stable for 100 cycles of charge‐discharge test at a current density of 100 mA/cm2.

A simple potentiometric CO2 sensor based upon a Na+-conducting solid electrolyte (NASICON) was found to be greatly improved in response time and water vapor-resistance by using a binary carbonate electrode of BaCO3–Na2CO3. For a wide range of CO2 concentration from 4 to 400000 ppm, the electromotive force examined at 823 K followed a Nernst’s equation excellently, with a 90% response time of as short as 8 s. Water vapor hardly affected the sensor characteristics, in contrast to the case of a pure Na2CO3 electrode.

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Electrochromic properties of the V,05 thin films prepared from a spinnable organic vanadium solution were investigated. The films heat-treated at 400 "C showed clear two-step electrochromism, deep blue F? greens yellow, with its response time for obtaining AOD = 0.5 being -2 s. The yellow and green colors showed good memory effects for more than 20 h, while the blue one was considerably degraded within 10 h.

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A novel sol-gel process was developed for preparing thin films and fine powders of lanthanum manganite (LaMnO 3 ) with perovskite-type structure. Lanthanum and manganese acetylacetonate powders could be easily dissolved in a mixed solution of methyl alcohol and ethylene glycol (or methyl alcohol and propionic acid) to give a spinnable organic solution as a starting material. Pretreatment of a substrate by poly(vinyl alcohol) (PVA) aqueous solution, a gel former, made it possible to deposit a thin film as well as to lower the sintering temperature.

A solid electrolyte CO2 sensor was developed by combining an Na+ conductor and a Li-based binary carbonate auxiliary electrode represented by Li2CO3–CaCO3 (1.8 : 1 in molar ratio: eutectic mixture). It responded to CO2 quickly and reversibly, following a Nernst equation excellently in the CO2 concentration range 102–105 ppm. In addition, Li2CO3–CaCO3 electrode was found to be stable to deliquescence even when kept under a highly humid condition at 30 °C for more than 700 h.