Tunable p–n transition behaviour of a p-La0.67Sr0.33MnO3/n-CeO2 nanofibers heterojunction for the development of selective high temperature propane sensors

Abstract

High temperature hydrocarbon sensors are of paramount importance to provide precise control of various combustion processes and directly evaluate the efficiency of catalytic converters. In this study, both p-type La_0.67Sr_0.33MnO₃ (LSMO) and n-type CeO₂ nanofibers (NFs) were prepared by electrospinning followed by facile two-step calcination. p-LSMO NFs/n-CeO₂ NFs composites with different weight ratios (CeO₂ NFs wt%: 0%, 25%, 50%, 70%, 75%, 80%, 90% and 100%) were then prepared by physical mixing with the help of sonication and further were employed as sensing elements to systematically investigate their response to carbon monoxide (CO) and propane (C₃H₈) at 800 °C. Clear p–n transition behaviour was observed from p-LSMO NFs dominated composites to n-CeO₂ NFs dominated composites in the presence of targeting gases. At the specific p-LSMO NFs/n-CeO₂ NFs composition (CeO₂ NFs wt% = 70%), the sensor exhibited an opposite response direction to CO and C₃H₈ which offers a simple way to differentiate them. Moreover, the p-LSMO NFs/n-CeO₂ NFs composite with the CeO₂ NFs content of 80% showed good sensitivity and selectivity to C₃H₈ over other reducing gases such as CO and CH₄ at a high operation temperature of 800 °C. The mechanisms of enhanced selectivity and p–n transition behaviour are also proposed based on the observed experimental results. This study opens an avenue for tailoring the selectivity of high temperature gas sensors by simply tuning the p–n heterojunction.