Improved sensing performances of NO2 sensors based on YSZ and porous sensing electrode prepared by MnCr2O4 admixed with phenol-formaldehyderesin microspheres

The phenol-formaldehyde (PF) resin microspheres were firstly used as the template in the sensing electrode (SE) preparation process of sensors based on Y2O3 stabilized ZrO2 (YSZ). The PF resin microspheres were synthesized by a facile hydrothermal method. The high char yield and the few morphological changes of PF resin microspheres before and after sintering at 900 °C indicated the perfect thermal stability at high temperature. The sensors using MnCr2O4 admixed with various contents PF microspheres (0 wt%, 5 wt%, 10 wt%, and 20 wt%) were fabricated and their sensing performances on NO2 gas were also investigated. The sensor with sensing electrode prepared by MnCr2O4 with 10 wt% PF showed the best NO2 sensing performance with a response of 110.8 mV to 100 ppm NO2 as well as the higher sensitivity (87.4 mV/decade) with the NO2 concentration ranging from 10 to 500 ppm at 550 °C. According to the mixed-potential mechanism, the porous electrode is good for gas penetration, so the gas can easily reach the MnCr2O4/YSZ/gas triple phase boundary (TPB) to participate in the electrochemical reactions. Additionally, the sensor exhibited excellent selectivity and repeatability, which indicated its potential application in the NO2 detection.