A2B2O7 (A= La, Pr, Nd, Sm, Gd and B Ti, Zr, Sn) ceramics for mild-temperature NO2 sensing and reduction

Abstract

Abstract The present work demonstrates the design and synthesis of A2B2O7 (A = La, Pr, Nd, Sm, Gd and B = Ti, Zr, Sn) ceramics to fabricate NO2 sensors for efficient NO2 sensing and reduction at mild temperature. To clarify the sensing mechanism of NO2 sensor, the electron layer mechanism of rare-earth cations at A site and different ionic radius of B-site cations are investigated to discuss the difference from the NO2 sensing and reduction. The unique electronic structure of Pr3+([Xe]4f2) endows the different band structure and the variable valence in nature with +3 and + 4 oxidation states, which would induce different electronic transport, resulting in enhanced NO2 sensing performances and reduction reaction. According to A2B2O7 structure, the activation energy of oxygen hopping is clarified through comparing different ionic radius of B cations, and the surface oxygen species providing a transfer station for oxygen hopping of solid electrolyte are analyzed by various characterization techniques. The results show that high sensitivity obtained over pure Pr2Sn2O7 without any doping at A or B site is as high as 124 nA/ppm towards 25–100 ppm NO2 at 500 °C, which is significantly better than commercial YSZ sensor. This work makes a significant progress in solid electrolytes and gas sensor.