Engineering interfacial charge-transfer pathways in ionic porous organic polymer powders and flexible films for selective and reversible ammonia sensing.

Ammonia (NH3) is a toxic and corrosive gas that requires reliable detection at low concentrations for industrial safety, environmental monitoring and indoor air-quality control. Chemiresistive sensors often suffer from a trade-off in which stronger adsorption improves sensitivity but slows recovery and weakens reversibility. To address this issue, interfacial charge transfer was modulated in imidazolium-based ionic porous organic polymers with π-conjugated backbones in both powder and flexible film forms. Ionic-site regulation and polyiodide confinement were applied to powders, and Au decoration was introduced in films to improve interfacial charge transport. Polyiodide-treated I2-PAmTB showed the best powder performance, with a response value of around 35 toward 100 ppm NH3 at 50 °C with strong selectivity and stability. The PAmTB framework was further converted into a flexible device via catalyst-free in situ growth on ITO-PET followed by Au decoration. The resulting Au-PAmTB film enabled heater-free room-temperature NH3 sensing from 2 to 100 ppm with near-linear calibration and a detection limit of 0.14 ppm. It also showed negligible resistance change under repeated bending. These results provide an interfacial-engineering framework that connects ionic-site regulation with charge-transport control, enabling low-power NH3 sensing in both powder and flexible thin-film devices.