Y.S. Shi, Y.L. Shang, Y.Y. Yang, C.S. Li, Y. Wang, L.X. Ni, B.N. Fu, Z.-S. Wu and L. Feng *

Advanced Functional Materials, 2025, accepted.

Chemiresistor sensors are essential for real-time environmental monitoring, yet conventional devices suffer from persistent limitations: high operating temperatures, insufficient sensitivity, poor selectivity, and long-term instability. To overcome these challenges, an atomic-level built-in electric field (BIEF) strategy is proposed through Fe-doped BiOCl (Fe-BOC), which drives directional electron migration within a single-component material with hierarchical nanoflower structures. This atomic-level BIEF, generated by asymmetric Fe─O─Bi sites, synergizes with dynamic Fe2+/Fe3+ valence transitions to construct an “electric field engine”. This engine promotes cyclic electron flow and enhances oxygen activation, achieving ultra-sensitive NO2 detection at 117 ppt with a rapid response time (<10 and="" outstanding="" stability="">6 months) at room temperature. The universality of this design is demonstrated by extending it to Cu and Sn dopants, providing a scalable platform for next-generation gas sensors. A wireless sensing system further validates its real-world applicability.