Determining humidity of nitrogen and air atmospheres by means of a protonic ceramic sensor

Abstract

• An original design of a solid-state high-temperature amperometric gas sensor. • The sensor includes two electrochemical cells based on proton-conducting electrolytes. • Sc-doped barium stannate is used for the first time as the sensor’s electrolyte. The present work describes a design, fabrication, operation principle and testing of a solid-state amperometric sensor used for humidity analysis of nitrogen and air gas atmospheres. This sensor consists of two electrochemical cells (in fact, two sensors are combined into one) based on proton-conducting electrolytes, one of the cells is made of Sc-doped calcium zirconate (CaZr 0.95 Sc 0.05 O 3–δ ; CZS), while another is made of Sc-doped barium stannate (BaSn 0.75 Sc 0.25 O 3–δ ; BSS). Using two sensors in one allowed us to compare their sensing properties. The sensor was tested at 500 °C and different water vapor partial pressures (pH 2 O). The volt-ampere ( U – I ) dependencies and calibration curves (limiting current vs pH 2 O) of the fabricated sensor were obtained and analyzed. The limiting current of the BSS-based cell is reached at a lower voltage than that of the CZS-based cell. In a nitrogen-containing atmosphere, the limiting current was reached for both electrochemical cells, and it varied linearly depending on pH 2 O. In an air atmosphere, the limiting current could not be reached only for the BSS-based cell at pH 2 O values less than 0.043 atm. A possible explanation for this is proposed.