Characteristics of NiO-YSZ Gas Sensor Employing YSZ Solid Electrolyte Prepared by Thermal Spray Coating Method

A mixed potential-type NiO-YSZ (yttria stabilized zirconia) gas sensor employing 8YSZ solid electrolyte film was fabricated using a thermal spray coating method, and tested in a NO2 atmosphere at various operating temperatures. The thermal spray coating method is useful for mass producing solid electrolytes without a forming, sintering or bonding process. In this study, the characteristics of the solid electrolyte made by thermal spray coating were examined and its potential application to a NO2 gas sensor was evaluated with mixed sensing materials. The 8YSZ solid electrolyte film exhibited a single phase of ZrO2 and had a constant conductivity in a wide range of oxygen partial pressures, even though the microstructure was rough-columnar type. In addition, it can be suggested that the lower ion conductivity and activation energy of the 8YSZ solid electrolyte film, which resulted from the rough microstructure, increased as much as that of the dense and smooth electrolyte layer prepared by the tape casting method. It produced a denser coating film after using finer granule powders. In particular, the NiO-YSZ mixed sensing material exhibited significantly improved response and recovery characteristics compared to pure NiO. This enhancement is attributed to the smaller NiO particles produced by the grain growth inhibitor YSZ, and the increased triple phase boundary between the sensing material, NO2 gas and solid electrolyte.