Abstract :  NOx decomposition over the electrochemical cell that involves oxygen-conducting membrane and lanthanum stannate pyrochlore catalysts has been investigated. Removal of the oxygen adsorbed on the active sites, triple-phase boundaries, was prerequisite for electrochemical NOx decomposition. NOx was decomposed only after the minimum current density was applied and its conversion increased abruptly with increasing the applied current. Decomposition activity was also strongly influenced by composition, microstructure, and configuration of the working electrode. Higher decomposition was observed for the cell composed of (La2Sn2O7+YSZ)/Pt composite electrode than the platinum electrode. Such the cell sintered at 1500 8C decomposed 87% NOx at the current density ~194 mA/cm2 in the reactant gas containing 2% O2 whereas 80.5% NOx was reduced at 325 mA/cm2 under 4% O2 condition.