Optimization and gas sensing mechanism of n-SnO₂-p-Co₃O₄ composite nanofibers

Abstract

Although the employment of n-p heterojunctions is among the most popular strategies to increase the performance of gas sensors, there have been a few systematic studies to determine the optimal composition in n-p heterojunctions. This paper reports the results of a systematic study of (n) xSnO₂-(p) (1-x) Co₃O₄ composite nanofibers (NFs) for gas sensing applications. Composite NFs were synthesized by the electrospinning method followed by annealing at 600 °C. For gas sensing studies, several gases at optimal working temperature (350 °C) were tested. Depending on the nominal composition, the sensors showed either n-or p-type behavior as well as different responses to the target gases. Furthermore, for all gases tested, the 0·5SnO₂-0·5Co₃O₄ sensor (nominal composition) showed the best gas sensing characteristics. The underlying gas sensing mechanism was examined in detail. The highest response observed in the 0·5SnO₂-0·5Co₃O₄ NFs sensor was primarily attributed to the major role of the p-Co₃O₄ nanograins as electron reservoir. In addition, the possible substitution of Co⁺²/Co⁺³ in Sn⁺⁴ sites, the catalytic effect of Co₃O₄ and generation of defects were likely to be the secondary reasons. This highlights the importance of the optimal composition for achieving the maximum gas-sensing performance in n-p composite NFs.