NOx-decomposing electrode and 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;
• an 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 a cermet electrode composed of a Pt—Rh alloy having a weight ratio of Pt:Rh in a range of from 20:80 to 1:99 and a ceramic component, and further comprising a porous layer over the NOx decomposing electrode;
• 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 remains, and said NOx decomposing electrode decomposes NOx within said second internal space to measure the NOx concentration of the measurement gas.