High-temperature water vapor sensors based on rare-earth-doped barium cerate

In this novel study, BaCe0.9Y0.1O3–δ, BaCe0.9Eu0.1O3–δ, BaCe0.9Nd0.1O3–δ, and BaCe0.9Dy0.1O3–δ powders were synthesized by the self-combustion method and processed into thick porous films (60–70% porosity) to investigate the water vapor sensing properties in the 400–700 ºC temperature range. All samples showed a stable response value to water vapor in the whole temperature range, expressed as impedance ratio in dry and wet argon (ZdryAr / ZwetAr), and were able to detect 0.03 vol% of water vapor at 550 ºC within the impedance range of 103 Ω at 100 Hz. The response values increased with the partial pressure of water and decreased with the temperature, whereas the maximal value of 3.41 reached the BaCe0.9Eu0.1O3–δ sample at 550 ºC and p(H2O) = 4.28 kPa. The average response time was several seconds and only slightly changed with the material type and experimental conditions. The recovery time depended on temperature and the ZdryAr / ZwetAr ratio, whereas the increase in the gas flow rate from 100 cm3/min to 200 cm3/min significantly reduced the recovery time for the BaCe0.9Eu0.1O3–δ sample from 230 s to 55 s at 550 ºC and p(H2O) = 2.14 kPa. All the samples exhibited stability and a high degree of reversibility after multiple exchanges of wet and dry atmospheres at different temperatures. Yet, their tendency to deteriorate in the presence of CO2 might challenge a potential application in aggressive environments.