Unlocking superior NO₂ sensitivity and selectivity: the role of sulfur abstraction in indium sulfide (InS) nanosheet-based sensors

To advance gas sensor technologies, it is essential to identify materials that exhibit both high selectivity and sensitivity. Here, we unravel the gas-sensing capabilities of indium sulfide (InS) nanosheets, particularly in relation to nitrogen dioxide (NO₂) detection. Utilizing a synergistic approach that combines in situ and operando experimental methodologies with density functional theory calculations, we demonstrate that these nanosheets offer outstanding sensitivity toward NO₂, characterized by a remarkably low detection threshold of 180 ppb at an operational temperature of 350 °C. This remarkable sensitivity is ascribed to the electronic charge redistribution around the Fermi level, facilitated by an oxygen-deficient In₂O_3−x surface layer that forms naturally when the InS surface is exposed to ambient conditions. A pivotal aspect of our investigation was the exploration of the influence of sulfur abstraction on these surface modifications. We demonstrate that sulfur abstraction plays a critical role in the formation and operational efficacy of the In₂O_3−x layer, thereby acting as a key element in the sensor mechanism. This unique surface chemistry not only amplifies the sensitivity to NO₂ but also confers unparalleled selectivity over other gases and volatile organic compounds. Notably, this level of performance exceeds that of other 2D semiconductors and metal oxides, thus establishing InS nanosheets as an ideal platform for high-performance gas sensors suitable for demanding environments. Moreover, unlike many state-of-the-art sensor materials, InS-based sensors can withstand a wider variety of environmental conditions due to their superior water adsorption resistance.