The properties of RuO_2 |YSZ| Pd cell and Pd |YSZ| for NO decomposition in the presence of O_2 were studied. The results have proved that, the NO was decomposed via the electrocatalysis mechanism other than electrolysis mechanism at the reaction temperature between 650 ～ 700 ℃ on the both cells at applied voltages in the range of 1 ～ 4 V. Namely, the O~(2-) produced from NO decomposition and ionization of O_2 on the surface of the cathode was transported through YSZ to the anode by DC voltage and then given off in the form of O_2 so as to maintain the active states of the cathode and the catalyst being coated on the cathode. On the Pd |YSZ| Pd cell, the palladium metal surface is the active site for NO decomposition and on the RuO_2 |Pd|YSZ| Pd cell, the partially reduced RuO_x (0 < x < 2) is the main active site for NO decomposition. In the reaction temperature range of 650 ～ 700 ℃, NO is selectively decomposed in the presence of O_2 at suitable voltages between 0 V and 4 V on the RuO_2 |Pd|YSZ| Pd cell.

Key words: ELECTRO-CATALYSIS, NO, DECOMPOSITION, ELECTROLYTE, RUTHENIUM OXIDE, PLATINUM, ELECTROLYSIS