In Operando Investigation of the Concentration Dependent NO2 Sensing Mechanism of Bi2S3 Nanorods at Low Temperatures and the Interference of O3

The demand for gas sensors that can detect gases selectively at low temperatures has increased steadily over recent years. Most devices use semiconducting metal oxides as sensing materials which often require high operation temperatures and suffer from a lack of selectivity. Semiconducting metal sulfides were found to be a reasonable alternative for the application in sensing devices at low temperatures. Since metal sulfides are a relatively new class of materials applied in gas sensors, there is little work on sensing mechanisms and overall sensing characteristics of these materials. In this work, the authors investigated the sensing performance of Bi2S3 nanorods operated at 50 °C in the presence of several target gases and found a selective response to oxidizing gases. With the help of DC resistance measurements, diffuse reflectance infrared Fourier transform spectroscopy and work function measurements in a Kelvin Probe setup, the NO2 and O3 sensing mechanisms of Bi2S3 nanorods were revealed. While initially sulfur vacancies were the predominant reaction sites, the formation of nitrates became the key reaction in higher NO2 concentrations. Additionally, it was found that the reaction with O3 healed sulfur vacancies effectively inhibiting the reaction with NO2.