Patent ID: 8197652

Claim:
A NOx sensor composed of an oxygen ion conductive solid electrolyte, in which a NOx concentration in a measurement gas is specified on the basis of a current flowing in said solid electrolyte by decomposition of NOx, said NOx sensor comprising: an internal space to which the measurement gas is introduced from an outside; a reference gas space to which a reference gas is introduced; a pumping cell including a first electrode and a second electrode and pumping out oxygen in said internal space by applying a predetermined voltage between said first electrode and said second electrode; and a measuring cell including a third electrode and a fourth electrode and measuring a current flowing between said third electrode and said fourth electrode when a voltage is applied between said third electrode and said fourth electrode; wherein said first electrode provided on a surface of said internal space is formed of porous cermet consisting of a noble metal and an oxygen ion conductive solid electrolyte using a material in which a reduction ability for an NO component in the measurement gas is weakened or a material without a reduction ability, and the porosity of said first electrode is greater than or equal to 30% and less than or equal to 40%; said second electrode is formed in a different space from said internal space; said third electrode, which is composed of a porous cermet of a metal for resolving NOx and zirconia, is formed on the surface of said internal space, and said fourth electrode is formed in a different portion from said internal space.