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.