Potentiometric CO2 Gas Sensor Prepared from Lithium Ionic Conductors.

The properties of five kinds of lithium ionic conductors, LiLaSiO4, LiNdSiO4, LiSmSiO4, Li2Zr(PO4)2 and LiAlSi2O6, as solid electrolytes were investigated by designing the solid electrochemical cells such as (-) air, Pt|lithium ionic conductor| Au, Li2CO3, CO2, O2 (+), for the CO2 gas sensor. The electromotive force, EMF, of these sensors increased linearly with an increase in the logarithmic value of carbon dioxide partial pressure, in accordance with Nernst's law. It was suggested from the slope of Nernst's equation that the two-electron reaction associated with carbon dioxide molecule takes place at the detection electrode above 400°C. The 90% response times of EMF for all these sensors for an increase in CO2 concentration were within 2min at 450°C.