Electrospun In₂O₃-WO₃-Pd heterojunction nanofibers for ultralow-concentration NO₂ detection at low-temperature

We report on the design and fabrication of electrospun one-dimensional In₂O₃-WO₃-Pd heterojunction nanofibers (NFs) and their outstanding NO₂ sensing performance at low operating temperatures. Comprehensive morphological, structural and compositional analyses (FESEM, XRD, HRTEM, EDX, XPS) confirmed the successful synthesis of uniform, heteronanofibers with well-defined interfaces. The optimized sensor, based on In₂O₃-WO₃ (90:10) decorated with 0.01 wt% Pd, exhibited an exceptional response of 441.3 to 1 ppm NO₂ at 150 °C and 30% RH, corresponding to 19- and 25-fold enhancements over pristine In₂O₃-WO₃ and pure In₂O₃, respectively. Remarkably, the limit of detection reached 73 ppt, ranking among the best reported to date. The improved performance is attributed to the synergistic effects of In₂O₃-WO₃ heterojunctions, which facilitate charge transfer, and the Pd catalytic sites, which promote NO₂ adsorption and reaction kinetics. In addition to ultrahigh response and selectivity, the sensors demonstrated rapid response/recovery dynamics, excellent humidity tolerance, and long-term stability. These results highlight the potential of electrospun In₂O₃-WO₃-Pd nanofibers as highly reliable platforms for next-generation NO₂ sensors operating at low temperature with ultralow detection limits.