Mixed-potential type NH3 sensor based on TiO2 sensing electrode with a phase transformation effect

Mixed-potential type NH 3 sensors were fabricated using La 10 Si 5.5 Al 0.5 O 27 (LSAO) consisting of a porous layer and a dense layer as solid electrolyte and TiO 2 as the sensing electrode. The effect of a LSAO porous layer and TiO 2 phase transformation on sensor performances was investigated. The porous layer of LSAO electrolyte obviously enhanced sensor performance. Compared with the sensor without a LSAO porous layer, the sensor with LSAO porous layer exhibited larger responding potential values and higher sensitivity due to the enhanced three phase interface length. Anatase-TiO 2 (a-TiO 2 ) based sensor exhibited better sensing performance than rutile-TiO 2 (r-TiO 2 ) based sensor at the examined temperature range. A-TiO 2 transformation toward r-TiO 2 resulted in poor sensing performances of the sensor. The best sensing characteristics were achieved for the NH 3 sensor with a-TiO 2 sensing electrode calcined at 900   °C for 3   h. The potential values of the sensor response to NH 3 linearly depended on the logarithm of NH 3 concentrations at 450–600   °C and the sensitivity reached 169.7   mV/decade in the range of 50–400   ppm at 500   °C. At the same time, the sensor exhibited well anti-interference capability to H 2 , NO, CH 4 and CO 2 , but a little cross-sensitivity toward NO 2 was observed. High temperature treatment (>900   °C) caused a-TiO 2 transformation into r-TiO 2 and V 2 O 5 additions were conducive to TiO 2 phase transformation.