Detecting CO₂ at ppm level in synthetic air using mixed conducting double perovskite-type metal oxides

Here, we report a novel double perovskite-type BaCa_0.33Nb _0.34Fe_0.33O_3-δ (Fe-BCN) as a CO ₂ sensor at ppm level in a mixture of 21% O₂ in N ₂ (dry synthetic air) working at 500-700 °C. Powder X-ray diffraction (PXRD) was used to confirm the formation of cubic double perovskite-type structure. In situ PXRD measurement under CO₂ showed excellent chemical stability in the temperature range of 25-800 °C. A significant decrease in total impedance (resistance) was observed upon exposure to CO₂ (ppm level) in synthetic air using AC impedance spectroscopy. Fe-BCN showed a fast response (t₉₀ ∼ 4 min) when 1500 ppm CO ₂ was introduced. The sensor response was found to be linear over the investigated range in the log I vs. log pCO₂. Fe-substitution in BaCa_0.33Nb_0.67O₃ (BCN) is critical for the observed CO₂ sensor properties since BCN exhibited a poor response under the identical sensor measurement conditions. The CO₂ sensor mechanism was established using mass spectrometry (MS) in combination with DC measurements. The long-term sensor performance was studied for Fe-BCN and re-assured high sensitivity, stability and reliability.