NOx concentration-measuring apparatus

A NOx concentration-measuring apparatus for measuring a NOx concentration of a measurement gas, comprising:

• an oxygen pump cell having a first internal space into which a measurement gas is introduced, said oxygen pump cell including at least one pump electrode in communication with said first internal space, said pump electrode exhibiting substantially no or low decomposing/reducing ability with respect to NOx;
• another electrochemical cell having a second internal space and at least a NOx-decomposing electrode in communication with said second internal space, said NOx-decomposing electrode comprising an Rh-containing cermet electrode alloyed with Pt such that a weight ratio of Pt:Rh ranges from 25:75 to 50:50,
• wherein the Pt suppresses oxidation of the Rh-containing cermet electrode;
• and
• a fluid communication path within said apparatus for providing fluid communication between said first and second internal spaces;
• wherein said oxygen pump cell controls an oxygen concentration in the measurement gas within said first internal space to have a predetermined value at which NO is not substantially decomposed, and said NOx-decomposing electrode decomposes NOx within said second internal space to measure the NOx concentration of the measurement gas.