Flexible, Breathable and Hydrophobic SnO₂–SnS₂–SiO₂/SiO₂ All‐Inorganic Self‐Supporting Nanofiber Membrane for Ultralow‐Concentration NO₂ Sensing Under High Humidity

Abstract Inorganic semiconductor gas sensors, being widely utilized in gas‐sensing applications, face significant challenges in attaining mechanical flexibility and humidity resistance in wearable sensing fields. Herein, a highly flexible, breathable, and hydrophobic all‐inorganic self‐supporting nanofiber (NF) gas sensor is developed using electrospinning combined with thermal sulfidation approach. This innovative sensor features a bilayer configuration, with an amorphous SiO 2 nanofiber substrate layer and an interwoven SiO 2 and SnO 2 –SnS 2 nanofiber active layer. The relatively low elastic modulus of the amorphous SiO 2 nanofibers, combined with the three‐dimensional network interwoven structure, endow the SnO 2 –SnS 2 –SiO 2 /SiO 2 sensor with superior mechanical flexibility. The sensor exhibits excellent sensitivity, selectivity, moisture resistance, and cycling stability (>10 000 cycles at 140° bending) to both high and low concentration NO 2 . Notably, an excellent flexible detecting capability of the sensor to NO 2 , an asthma‐related biomarker, is demonstrated at ultralow concentrations (≈25 ppb) in simulated exhaled breath environments. The enhanced moisture resistance is attributed to the effective inhibition of hydrogen bond formation from H 2 O molecules by the Sn─S bonds formed through sulfidation of SnO 2 nanofibers. This work represents a substantial advancement in the universal fabrication of flexible, breathable and moisture‐resistant inorganic semiconductor sensors for wearable breath sensing applications.