NOx SENSOR

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 consisted of noble metal containing gold of greater than or equal to 0.01 wt % and less than or equal to 0.95 wt %, and an oxygen ion conductive solid electrolyte;
• said second electrode is formed in a different space from said internal space;
• said third electrode is formed on the surface of said internal space, and
• said fourth electrode is formed in a different portion from said internal space.