Structural improvement of Sm–Mn oxides for enhanced CO sensing performance

Restricted by an insufficient understanding of the compositional and structural characteristics of the sensing materials that affect the sensing performances, the YSZ-based CO gas sensor remains in a dilemma in terms of further promoting sensitivity, selectivity and long-term stability. In this work, two bimetallic oxides with different crystal structures, perovskite SmMnO3 and mullite SmMn2O5, were prepared and adopted to elucidate the roles of the Mn3+, Mn4+ and surface oxygen vacancies. Compared with SmMnO3, the coexisting coordination modes of Mn3+ and Mn4+ in SmMn2O5 is conducive to generating oxygen vacancies. Furthermore, a SmMn2O5-based sensor with more oxygen vacancies demonstrates a relatively faster response/recovery speed and enhanced sensitivity of 2.05 times that of SmMnO3 under the same operation conditions. Such work may broaden insight into the development of efficient sensing materials that introduce oxygen vacancies through the construction of phase structures without complicated operations. Overall, the sensor attached to SmMn2O5 exhibits a low detection limit (5 ppm), a feasible response/recovery speed (24 s/28 s toward 40 ppm CO operating at 450 °C), satisfactory CO selectivity and long-term stability, highlighting its potential for CO monitoring in harsh environments.