Gas sensing element

A gas sensing element comprising,

• a measured gas chamber for storing a measured gas introduced from an outside of the element;
• a reference gas chamber for storing a reference gas;
• a first pump electrode positioned in said measured gas chamber and containing Au;
• a second pump electrode being in operative association with said first pump electrode;
• a pump cell constituted by said first and second pump electrodes and a solid electrolytic substrate having surfaces on which said first and second pump electrodes are provided;
• a measured gas side electrode positioned in said measured gas chamber;
• a reference electrode positioned in said reference gas chamber so as to be operatively associated with said measured gas side electrode;
• a sensor cell constituted by said measured gas side electrode, said reference electrode, and a solid electrolytic substrate having surfaces on which said measured gas side electrode and said reference electrode are formed;
• and
• a sensor circuit for detecting a concentration of NOx included in the measured gas from an electric current output from said sensor cell,
• wherein said sensor circuit gives a difference in a sensing voltage between said measured gas side electrode and said reference electrode of said sensor cell to decompose NOx of the measured gas on the measured gas side electrode and to generate an oxygen ion current in said solid electrolytic substrate due to decomposition of the NOx, and measures the electric current generated from the oxygen ion current to detect the concentration of NOx said measured gas side electrode of said sensor cell is mainly made of Pt and Rh, and said measured gas side electrode contains Au by an amount of 0.01 wt % to 2.0 wt % (external wt %) when an overall amount of said measured gas side electrode of said sensor cell is 100 wt %.