The mixed-potential NH3 sensor using BiVO4/Bi4V2O11 heterojunction sensing electrode prepared by self-phase separation

Abstract

BiVO4/Bi4V2O11 heterojunction sensing materials for the mixed-potential NH3 sensor were prepared by the hydrothermal method and sequent heat treatment, accompanying self-phase separation. The influence of the Bi3+/V5+ mole ratios on phase composition, microstructure of sensing materials and the performances of the sensor was investigated. The samples with different Bi3+/V5+(1:1–2:1) calcined at 500 °C form non-stoichiometric Bi4V2O11 and Bi2VO5.5 and further calcination at 750 °C, all samples change into BiVO4/Bi4V2O11 heterojunction materials. The mixed potential sensors based on above-mentioned heterojunction materials and Ce0.8Gd0.2O1.9 electrolyte show excellent performance. The sensor based on sensing electrode with Bi3+/V5+=1.75:1 can stably work at 450–600 °C due to good porous structure of sensing electrode, which is conducive to gas diffusion and adsorption. At 500 °C, the sensor has the highest sensitivity and the lowest detection limit. The relationship between ΔV and logarithm of NH3 concentrations is piecewise linear in the range of 1–25 ppm and 25–300 ppm, and the sensitivity is −6.9 and −38.2 mV/decade, respectively. The cross-sensitivity test of the sensor shows that co-existent gas CO2, CH4, H2 or H2S makes the response value change −3.7%, −3.0%, 0.9% and −6.8%, showing good anti-interference performance to these gases. While NO or NO2 causes serious interference, making the response value reduce by −9% and −27%. CuO instead of Pt as the reference electrode nearly eliminates the interference of NO and NO2. In addition, sensor following the mixed potential mechanism was confirmed by experiments.