Solid-state potentiometric H2S sensor combining NASICON with Pr6O11-doped SnO2 electrode

A compact tubular sensor based on sodium super ionic conductor (NASICON) and Pr6O11-doped SnO2 sensing electrode was designed for the detection of H2S. In order to reduce the size of the sensor, a thick film of NASICON was formed on the outer surface of a small Al2O3 tube; furthermore, a thin layer of SnO2 with nanometer size was attached on the NASICON as a sensing electrode. Compared with pure SnO2, Pr6O11-doped SnO2 was found to be more suitable for the sensing electrode. The sensor using Pr6O11-doped SnO2 gave excellent sensing properties to 5–50 ppm H2S in air at 200–400 °C. The EMF value of the sensor was almost proportional to the logarithm of H2S concentration, the sensitivity (slope) was 74 mV/decade at 300 °C. It was also seen that the sensor showed a good selectivity to H2S against SO2, NO2, CH4 and CO, and an excellent resistance to water vapor. The sensor had speedy response kinetics to H2S, the 90% response time to 5, 20 and 50 ppm H2S was 8, 6 and 4 s, respectively, and the recovery time was 12, 18 and 30 s, respectively. On the basis of XPS analysis for the H2S-adsorbed sensing electrode, a sensing mechanism involving the mixed potential at the sensing electrode was proposed.