Sensor element

A sensor element for detecting NOx in a measurement-object gas, the sensor element comprising:

• a base part in an elongated plate shape, including a plurality of oxygen-ion-conductive solid electrolyte layers stacked;
• a measurement-object gas flow part for introduction and flow of the measurement-object gas through a gas inlet formed in one end part in a longitudinal direction of the base part;
• an inner oxygen pump electrode disposed on an inner surface of the measurement-object gas flow part;
• and
• a measurement electrode disposed on the inner surface of the measurement-object gas flow part,
• wherein
• the inner oxygen pump electrode has a predetermined length (L) in the longitudinal direction and includes:
• a region (A) including an electrode end close to the gas inlet and having a predetermined length (LA) in the longitudinal direction, and
• a region (B) including an electrode end far from the gas inlet and having a predetermined length (LB) in the longitudinal direction;
• the inner oxygen pump electrode comprises a metal material, the metal material including an activity reducing metal that reduces catalytic activity of decomposing NOx;
• a content of the activity reducing metal in the metal material in the region (A) is higher than a content of the activity reducing metal in the metal material in the region (B);
• and
• a ratio (LA/L) of the length (LA) in the longitudinal direction of the region (A) of the inner oxygen pump electrode to the length (L) in the longitudinal direction of the inner oxygen pump electrode is 15% to less than or equal to 60%, and wherein
• the content of the activity reducing metal in the metal material in the region (A) is 1.0% by weight to 2.0% by weight.