Reaction analysis on sensing electrode of amperometric NO2 sensor based on sodium ion conductor by using chronopotentiometry

Galvanostatic chronopotentiometry was performed to identify the reaction products formed on the sensing electrode of an amperometric NO2 sensor based on NASICON (Na+ conductor). It was indicated that the products after the sensing operation at 150 or 200°C were different, depending on the atmosphere. NaNO2 and NaNO3 were formed in the NO2-containing air, while NaOx (presumably Na2O2) was formed in the NO2-free air. It is concluded that NaOx is formed through the cathodic reaction of O2, while NaNO2 is formed as a primary product of the cathodic reaction of NO2. It is also concluded that NaNO3 is formed as a secondary product of the chemical reaction between NaOx and NaNO2 in dry condition, although the reaction between NaOx and gaseous NO2 also takes place in the humid condition as another root for NaNO3 formation.