SOLID-STATE ELECTROCHEMICAL CO2 GAS SENSORS BASED ON SODIUM IONIC CONDUCTORS

The sensing characteristics of a solid-state electrochemical CO2 gas sensor, expressed as Pt\O2, Na2O\\ Na ionic conductor \\Na2CO3\CO2, O2\Pt were investigated in terms of a two-electron electrochemical reaction. The number of electrons for the cell reaction was higher than 2 and approached 2 with an increase in the operating temperature up to about 500-degrees-C. The introduction of water vapour induced a lowering of the e.m.f. and a prolongation of the response time. The formation of sodium oxides in the Na2CO3 layer was considered as a possible cause of these water effects. The sensing characteristics recovered completely after the water vapour was cutoff. The e.m.f. reduction due to water sorption was depressed by using a densified Na3Zr2Si2PO12. A densified Na3Zr2Si2PO12-based electrolyte is preferable for use as a gas sensor with a fast response and high stability for detection of CO2 in air.