Hydroxide ion conduction mechanism in Mg-Al Co32− layered double hydroxide

Abstract

2− 2− Ionic conduction mechanism of Mg-Al layered double hydroxides (LDHs) intercalated with CO3 (Mg-Al CO3 LDH) was studied. The electromotive force for the water vapor concentration cell using Mg-Al CO2−3 LDH as electrolyte showed water vapor partial pressure dependence and obeyed the Nernst equation, indicating that the hydroxide ion transport number of Mg-Al CO2−3 LDH is almost unity. The ionic conductivity of Mg(OH)2, MgCO3 and Al2(CO3)3 was also examined. Only Al2(CO3)3 showed high hydroxide ion conductivity of the order of 10 S cm under 80% relative humidity, sug-gesting that−4 −1Al2(CO3)3 is an ion conducting material and related to the generation of carrier by interaction with water. To 2− discuss the ionic conduction mechanism, Mg-Al CO2−3 LDH having deuterium water as interlayer water (Mg-Al CO3 LDH(D2O)) was prepared. After the adsorbed water molecules on the surface of Mg-Al CO2−3 LDH(D2O) were removed by drying, DC polarization test for dried Mg-Al CO2−3 LDH(D2O) was examined. The absorbance attributed to O-D-stretching band for Mg-Al CO2−3 LDH(D2O) powder at around the positively charged electrode is larger than that before polarization, indicating that the interlayer in Mg-Al CO2−3 LDH is a hydroxide ion conduction channel.