Hydroxide ion Conduction Mechanism in Mg-Al CO32- Layered Double Hydroxide

Ionic conduction mechanism of Mg-Al layered double hydroxides (LDHs) intercalated with CO32- (Mg-Al CO32- LDH) was studied. The electromotive force for the water vapor concentration cell using Mg-Al CO32- LDH as electrolyte showed water vapor partial pressure dependence and obeyed the Nernst equation, indicating that the hydroxide ion transport number of Mg-Al CO32- LDH is almost unity. The ionic conductivity of Mg(OH)(2), MgCO3 and Al-2(CO3)(3) was also examined. Only Al-2(CO3)(3) showed high hydroxide ion conductivity of the order of 10(-4) S cm(-1) under 80% relative humidity, suggesting that Al-2(CO3)(3) is an ion conducting material and related to the generation of carrier by interaction with water. To discuss the ionic conduction mechanism, Mg-Al CO32- LDH having deuterium water as interlayer water (Mg-Al CO32-LDH(D2O)) was prepared. After the adsorbed water molecules on the surface of Mg-Al CO32- LDH(D2O) were removed by drying, DC polarization test for dried Mg-Al CO32- LDH(D2O) was examined. The absorbance attributed to O-Dstretching band for Mg-Al CO32- LDH(D2O) powder at around the positively charged electrode is larger than that before polarization, indicating that the interlayer in Mg-Al CO32- LDH is a hydroxide ion conduction channel