Mixed potential NH3 sensor based on Mg-doped lanthanum silicate oxyapatite

• La10Si5MgO26 was used as electrolyte for a mixed-potential type NH3 sensor.
• Y2O3 was introduced as sintering aid to improve the sinterability of La10Si5MgO26.
• Nano-structured CoWO4 sensing electrode was fabricated by hydrothermal method.
• Good response/recovery, reproducibility and selectivity of the sensor were obtained.

A mixed-potential type NH3 sensor was fabricated using La10Si5MgO26 (LSMO) as electrolyte with both a dense layer and a porous layer and nano-structured CoWO4 as the sensing electrode. The dense LSMO electrolyte was prepared by solid state reaction method at 1500 °C via introducing Y2O3 as the sintering aid. The nano-structured CoWO4 powders were synthesized by hydrothermal method and then screen printed on the porous LSMO layer as the sensing electrode. The sensor exhibited well response-recovery characteristics to NH3 at 400–700 °C. The response and recovery time were 11 and 13 s when the NH3 concentration was changed between 200 and 300 ppm, respectively. Good linear correlations between the ΔV values of the sensor and the logarithm of the NH3 concentrations for 30–300 ppm were obtained. Compared with the sensor without LSMO porous layer, the sensor with LSMO porous layer exhibited larger ΔV values and higher sensitivity due to the enhanced TPB length. The mixed-potential-model of the sensor was identified by the polarization curves in different atmospheres. The sensitivity of the sensor decreased with increasing the sintering temperature of the CoWO4 electrode, due to the growth of the CoWO4 particles. Furthermore, the present sensor also displayed small cross-sensitivities to H2, CH4 and CO2 present in the gas mixture.