Patent ID: 8366893

Claim:
A pump electrode provided in an inner space of a gas sensor that measures a concentration of a gas component in a measurement gas by a current-limiting method, the gas sensor including an electrochemical pump cell for adjusting an oxygen partial pressure in said inner space, said pump electrode being composed of a cermet of a noble metal and an oxide having oxygen ion conductivity, wherein said noble metal comprises: a first noble metal having a catalytic activity, a second noble metal having a catalytic activity suppressing ability to suppress the catalytic activity of said first noble metal with respect to an oxide gas except for oxygen, and wherein an abundance ratio of said second noble metal with respect to said first noble metal in a particle surface of said first noble metal existing in said pump electrode is 0.01 to 0.3, wherein said abundance ratio is an area ratio of a part covered with said second noble metal with respect to a part not covered with said second noble metal where particles of said first noble metal itself are exposed in a particle surface of said first noble metal in said pump electrode, and wherein said first noble metal is platinum and said second noble metal is gold.