Youichi Shimizu

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 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. , respectively, in 30 w/o at 25°C. The oxide catalyst is considered to decompose effectively , 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.

Abstract 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.

A NASICON-basic CO = sensor was improved considerably when it was fitted with a Ba-Na binary carbonate electrode (Ba content: 46 atom percent). It responded to CO = very quickly with a 90 % response time of less than 8 s, at 550 ~ without being affected by water vapor. The electromotive force responses followed perfectly aNernst equation corresponding to a 2-electron reaction for CO = over a wide CO = concentration range at 450-600 ~ The sensor performance was stable for the test period of 200 days. X-ray diffraction analysis revealed that no free Na~.CO3 remained in the binary carbonate electrode, while scanning electron microscopy observation of the electrode revealed eposits of micro-needles containing both Ba and Na. It was concluded that the disappearance of free NasCO3 to form needle-like deposits gave rise to a resistance to water vapor and the quick response rates of the sensor element. Similar improvements were also observed for other bi-nary carbonate systems, such as Sr-Na and Ca-Na. CO2 emissions are a global issue. In addition, CO2 moni-toring and control in offices, homes, agricultural fields, and bio-related processes are of growing importance. Therefore, there are ever increasing needs for solid-state CO = sensors which are reliable, inexpensive, and compact.

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.