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

摘要

Resistive electrochemical sensors based on vanadium oxides equipped with a pair of interdigital Au electrodes can detect NH_3 gas selectively at high temperature (500℃). NH_3 addition in a base gas increased the relative conductance (σ/σ_0). Addition of less electronegative cation (Ce, Zr, Mg) to V_2O_5 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 (VAICe) was the most suitable sensor. The VAICe sensor responded rapidly and linearly to change in concentration of NH_3 in the oxygen rich gas mixture and showed high selectivity in the presence of coexisting gases (NO, CO, H_2). 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 V~(5+) to V~(4+), which results in the conductivity increase. Role of surface acidity on the selective detection of NH_3 as a basic molecule is also discussed.