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

Here, we report a novel double perovskite-type BaCa0.33Nb0.34Fe0.33O3−δ (Fe–BCN) as a CO2 sensor at ppm level in a mixture of 21% O2 in N2 (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 CO2 was introduced. The sensor response was found to be linear over the investigated range in the log I vs. log pCO2. Fe-substitution in BaCa0.33Nb0.67O3 (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.