Doped-vanadium oxides as sensing materials for high temperature operative selective ammonia gas sensors

Resistive electrochemical sensors based on vanadium oxides equipped with a pair of interdigital Au electrodes can detect NH3 gas selectively at high temperature (500 °C). NH3 addition in a base gas increased the relative conductance (σ/σ0). Addition of less electronegative cation (Ce, Zr, Mg) to V2O5 increased the response and recovery rates, while electronegative cation (Al, Fe, Ni) increased sensor response magnitude. Among the samples tested, Al and Ce co-doped sample (VAlCe) was the most suitable sensor. The VAlCe sensor responded rapidly and linearly to change in concentration of NH3 in the oxygen rich gas mixture and showed high selectivity in the presence of coexisting gases (NO, CO, H2). The presence of water vapor did not markedly decrease the response magnitude but increased the response rate; the 90% response and 50% recovery times were less than 15 s. Based on the in situ UV–vis results, a possible sensing mechanism is proposed; adsorbed NH3 causes reduction of V5+ to V4+, which results in the conductivity increase. Role of surface acidity on the selective detection of NH3 as a basic molecule is also discussed.