Solution-processed In₂Se₃ nanosheets for ultrasensitive and highly selective NO₂ gas sensors

In this work, we demonstrate that solution-processed In₂Se₃ nanosheets exhibit exceptional selectivity and sensitivity to NO₂ gas, making them a promising candidate for gas detection systems. Theoretical simulations and surface-science experiments reveal the unique surface properties of In₂Se₃ nanosheets, which prevent physisorption of oxygen, carbon monoxide, and carbon dioxide, making them remarkably stable towards oxidation and CO-poisoning. Moreover, we show that NO₂ molecules adsorb stably on In₂Se₃ nanosheets, particularly on Se vacancies, even at high temperatures. The coadsorption of water further enhances NO₂ sticking on the In₂Se₃ surface, making it an ideal material for gas sensing applications in humid and harsh environments. The fabricated In₂Se₃ gas sensors exhibit excellent and reversible sensing response to NO₂ gas, with a limit of detection of 5 ppb at 300 °C, and a highly selective response to NO₂ compared to other gases and volatile organic compounds. Our sensors outperform other two-dimensional (2D) semiconductors, metal oxides, and their heterostructures, thanks to the unique surface properties of In₂Se₃ nanosheets. Importantly, the number of layers and termination of the surface almost have no impact on the sensing performance of In₂Se₃, which is advantageous for practical applications. The high sensitivity, selectivity, and stability of In₂Se₃ nanosheets make them an exciting platform for the fabrication of high-performance gas sensors, particularly in harsh environments, such as industrial settings or outdoor monitoring. Moreover, our solution processing approach enables scalable production of the sensors. Additionally, their unique surface properties make them an attractive candidate for developing complex composite nanostructures with tailored gas sensing characteristics for various applications.