FeSe₂/Hematite n-n heterojunction with oxygen spillover for highly efficient NO₂ gas sensing

Increasing the efficiency of nitrogen dioxide (NO₂) sensing has been researched in-depth owing to the destructive and pernicious impacts of the gas on both the environment and human health. In this work, a novel n-n FeSe₂/hematite heterojunctions have been constructed through the controllable surface oxidation of FeSe₂ nanoparticles and used for NO₂ detection. Theoretical calculations suggest that the FeSe₂/Fe₂O₃ interface can facilitate the electron and mass transfer through the n-n junction and oxygen spillover effect, energetically contributing to enhanced NO₂ adsorption. In terms of NO₂ sensing, the FeSe₂/Fe₂O₃ nanocomposite exhibits a higher response (14.1–100 ppm) and faster sensing kinetics (10–30 s) than its FeSe₂ and Fe₂O₃ counterparts. Such a heterostructure also demonstrates a ppb-level detection capacity, outstanding stability and selectivity to NO₂ gas against other interfering gases at low temperatures (110 ℃). In situ Raman and Mott-Schottky measurements were further conducted to analyze the interface electronic properties and NO₂ gas adsorption behaviors. The results from this investigation suggest that the NO₂ gas could be reversibly chemi-adsorbed and desorbed on the surface of the FeSe₂/Fe₂O₃ heterostructure for fast sensing response and recovery. This study presents fundamental insights into the rational design and implementation of highly efficient NO₂ sensing materials through oxide/chalcogenide interface coupling.