The measurements were carried out at room temperature and from 50 to 300 °C, with 50 °C steps, for both oxidizing and reducing gases using a self-heating system. The sensor response was defined as 𝑅 /𝑅 for oxidizing gases and 𝑅 /𝑅 for reducing ones, where 𝑅 and 𝑅 are the sensor electrical resistance in the presence of the analyte (NO2, CO, and H2) and in dry air, respectively . The response and recovery time were defined as the time required for the resistance to reach 90% of its final value in presence and removal of the analyte gas in the test chamber, respectively .