Mechanochemical approach for fabrication of a nano-structured NiO-sensing electrode used in a zirconia-based NO2 sensor

Highly uniform NiO nano-particles with a crystallite size of about 3 nm were obtained by room-temperature ball-milling of the parent Ni(OH)2, which was derived using a sol–gel method. The obtained nano-structured NiO precursor was then utilized for the fabrication of NiO-sensing electrodes (SEs), which were further examined in the mixed-potential-type YSZ-based planar NO2 sensor. The obtained results revealed the attractive advantages for the application of mechanochemical approach in regard to achieve high NO2 sensitivity, NO2 selectivity and reproducibility. All of the evaluated sensors attached with the nano-structured NiO-SEs, regardless of its sintering temperature, were found to exhibit high NO2 sensitivity at 800 °C under the wet condition (5 vol.% water vapor). In addition to high NO2 sensitivity, the sensor attached with 1100 °C-sintered NiO-SE showed highly selective properties towards NO2. The observed improvement in NO2-sensing characteristics as well as the attainment of highly reproducible behavior for different sensor devices is discussed based on morphological and electrochemical observations of the studied sensors.