Patent ID: 8465636

Claim:
An ammonium gas sensor comprising: a solid electrolyte layer having oxygen ion conductivity; a detection electrode formed on one surface of the solid electrolyte layer; a reference electrode that is a counter electrode of the detection electrode; a selective reaction layer covering the detection electrode; and a protection layer covering the selective reaction layer and made from a porous material; wherein the detection electrode includes a noble metal as a main component; the selective reaction layer includes an oxide represented by A x M y O z as a main component, where A is one or more kind(s) of metal, M is vanadium, tungsten, or molybdenum and x, y, z are atomic ratios; the protection layer includes the oxide of the selective reaction layer in an amount smaller than a content of the oxide included in the selective reaction layer, and contains at least one selected from the group consisting of MgAl 2 O 4 , SiO 2 , SiO 2 /Al 2 O 3 , zeolite and SiC as a main component; and the detection electrode is exposed to the gas to be measured.