SO2-sensing characteristics of Nasicon sensors with Na2SO4–BaSO4 auxiliary electrolytes

SO2-sensing characteristics of the Nasicon cells with Na2SO4–xBaSO4 (x=0–40 mol%) auxiliary electrolytes have been investigated in 5–95 ppm SO2 concentration range at 400–550 °C. The cell Na2SO4 alone and Na2SO4–xBaSO4 auxiliary electrolytes exhibit stable behaviors above 450 °C in dry SO2 atmosphere. Long-term stabilities for the cell with Na2SO4–10 mol% BaSO4 auxiliary electrolyte are obtained at 550 °C for 30 days. Response time is the shortest for the cell with Na2SO4–10 mol% BaSO4 auxiliary electrolyte, which is due to the porous, needle-like surface. Increase of BaSO4 content in Na2SO4 leads to decrease in moisture effect of these cells under SO2 atmosphere containing 4.242 kPa water vapor. Slight decrease in emf is inevitable because the inlet SO2 gas and water vapor react to form H2SO4 and then the gas composition is reduced by the degree of dissociation.