Role of (Li2-Sr)CO3 bi-auxiliary electrolyte in protecting potentiometric CO2 sensor against moisture

A series of bi-auxiliary solid state poteDtiometric CO2 sensors of type, O-2, CO2, Li2CO3-SrCO3, Au vertical bar Li3PO4 vertical bar Au, Li2TiO3-TiO2, CO2, O-2 were fabricated using Li2CO3-SrCO3 mixed carbonates (different mol%) as bi-auxiliary sensing electrodes, Li3PO4 mixed with SiO2 as a solid electrolyte and Li2TiO3 mixed with TiO2 as a reference electrode. The measured electromotive force (emf) of the sensors was found to be linear with the logarithm Of CO2 partial pressure in the test range from 500 to 5000 ppm at 500 degrees C working temperature. The sensors with 10 and 20 mol% SrCPO3 showed not only a good Nernstian behavior but also a high emf value. The experimentally obtained Delta emf/dec value for 10 mol% SrCO3 loaded Li2CO3 sensor was in close accord with the theoretical value, and a two-electron reaction (n = 2.22) of CO2 was obtained for various CO2 concentrations. The performance of the sensor was found to be highly stable in dry as well as humid atmospheres in the overall test range. A new phase containing Li(4)siO(4), Sr2SiO4 and Sr2P2O7 forming between the sensing electrode and the electrolyte interface is proposed as playing a significant role in the improved stability of the sensor against moisture.