Solid-state electrochemical cells with two cathode layers were designed for effective NO., decomposition, It was found that covering of the cathode by a mixed oxide electrode increased NO decomposition even in the presence of excess oxygen. A strong correlation between the microstructure of the working electrode and conversion rate of NO, gas was observed and studied, It was shown that there was a linear dependence of the NO conversion on the value of the current passed through the electrochemical cell with a nano-porous working electrode and that the value of current efficiency depended on the NO and 02 gas concentrations only. A mechanism for the process of NO decomposition on nano-porous ceramics electrode was proposed and the theoretical value of the current efficiency was calculated. A good numerical correlation between the calculated and measured characteristics of the electrochemical cell were observed.