Ammonium gas sensor

Abstract

An ammonium gas sensor is provided. The ammonium gas sensor includes: 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 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; and the protection layer includes the oxide that is in an amount smaller than a content of the oxide included in the selective reaction layer.

What is claimed is: 
     
         1 . An ammonium gas sensor comprising:
 a solid electrolyte layer having oxygen ion conductivity;   a reaction electrode formed on one surface of the solid electrolyte layer;   a reference electrode that is a counter electrode of the detection electrode; and   a protection layer covering the reaction electrode and made from a porous material;   wherein   the reaction electrode includes 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; and   the protection layer includes the oxide that is in an amount smaller than a content of the oxide included in the reaction electrode.   
     
     
         2 . The ammonium gas sensor according to  claim 1 ,
 wherein   in A x M y O z  representing the oxide, A is one or more kind (s) selected from the group consisting of bismuth, lanthanum, strontium, calcium, copper, gadolinium, neodymium, yttrium, samarium, and magnesium.   
     
     
         3 . The ammonium gas sensor according to  claim 1 ,
 wherein   the oxide is represented by BiVO 4 .   
     
     
         4 . The ammonium gas sensor according to  claim 1 ,
 wherein   the oxide content in the protection layer in the vicinity of an interface between the protection layer and the reaction electrode is 10 mol % or less.   
     
     
         5 . The ammonium gas sensor according to  claim 1 ,
 wherein   the oxide content in the protection layer is smaller in the vicinity of a surface of the protection layer as compared to that in the vicinity of an interface between the protection layer and the reaction electrode.   
     
     
         6 . The ammonium gas sensor according to  claim 1 ,
 wherein   the oxide content in the protection layer in the vicinity of an interface between the protection layer and the reaction electrode is 0.1 mol % or more.   
     
     
         7 . The ammonium gas sensor according to  claim 1 ,
 wherein   a thickness of a part of the protection layer that includes the oxide content of 0.1 to 10 mol % is equal to or less than a thickness of the reaction electrode.   
     
     
         8 . The ammonium gas sensor according to  claim 1 ,
 wherein   the ammonium gas sensor comprises a second protection layer covering the reference electrode, and   the second protection layer does not contain the oxide included in the reaction electrode.   
     
     
         9 . The ammonium gas sensor according to  claim 1 ,
 wherein   the reaction electrode comprises at least one of A x O z  and M y O z , where A is one or more kind (s) of metal, M is vanadium, tungsten, or molybdenum, and x, y, and z are atomic ratios.