Patent ID: 8828206

Claim:
A gas sensor element comprising: a solid electrolyte body having oxygen ion conductivity and an opposite pair of first and second surfaces; a measurement electrode provided on the first surface of the solid electrolyte body so as to be exposed to a measurement gas; a reference electrode provided on the second surface of the solid electrolyte body so as to be exposed to a reference gas; a porous diffusion-resistant layer through which the measurement gas is introduced to the measurement electrode, the diffusion-resistant layer having an outer surface via which the measurement gas flows into the diffusion-resistant layer; and a catalyst layer that is formed on the outer surface of the diffusion-resistant layer and contains Pt, Pd and Rh, wherein in the catalyst layer, the percentage content of Pt is in the range of 2.5 to 12 mass %, the percentage content of Pd is in the range of 0.4 to 2 mass %, and the percentage content of Rh is in the range of 0.06 to 1.5 mass %, the catalyst layer includes catalytic noble metal particles each of which is made of a Pt-Pd alloy, a Pt-Rh alloy or a Pt-Pd-Rh alloy, each of the catalytic noble metal particles has a core portion and an outer peripheral portion that surrounds the core portion, and the percentage content of Pt at the outer peripheral portion is lower than that at the core portion.