Potentiometric CO2 sensor using Li+ ion conducting Li3PO4 thin film electrolyte

Li+ ion conducting Li3PO4 thin film electrolytes with thickness 300nm, 650nm and 1.2 mu m were deposited on Al2O3 substrate at room temperature by thermal evaporation method. Reference and sensing electrodes were printed on Au interfaces by conventional screen printing technique. The overall dimension of the sensor was 3 x 3 mm and of electrodes were 1 x 1.5 mm each. The fabricated solid state potentiometric CO2 sensors of type: CO2, O-2, Au, Li2TiO3-TiO2\ Li3PO4 \Li2CO3, Au, CO2, O-2 have been investigated for CO2 sensing properties. The electromotive force (emf) and Delta emf/dec values of the sensors are dependent on the thickness of the electrolyte film. 1.2 mu m thickness deposited sensor has shown good sensing behavior than the sensors with less thickness. The. emf values of the sensor are linearly increased up to 460 degrees C operating temperature and became stable above 460 degrees C. Between 460-500 degrees C temperatures region the sensor has reached an equilibrium state and the experimentally obtained. emf values are about 80% of the theoretically calculated values. A Nernst's slope of -61 mV/decade has been obtained between 250 to 5000 ppm of CO2 concentration at 500 degrees C temperature. The sensor is suitable for ease of mass production in view of its miniaturization and cost effectiveness after some further improvement.