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.