Morphology of MIL-101(Cr) and improvement of humidity sensing performance by introducing FeCl3

A series of FeCl₃ doped MIL-101(Cr)/silicon nanoporous pillar array (FeCl₃/MIL-101(Cr)/Si-NPA) humidity sensors were prepared by growing FeCl₃ doped MIL-101(Cr) on Si-NPA via a facile spin-coating method. Systematically evaluation of capacitive sensing performance demonstrated that FeCl₃ incorporation significantly enhanced humidity sensitivity. This improvement can be attributed to the increased hydrophilicity of the MIL-101(Cr)/Si-NPA composite membranes induced by FeCl₃, as confirmed by the water contact angle test results. Notably, the 8 wt.% FeCl₃/MIL-101(Cr)/Si-NPA humidity sensor exhibited the best comprehensive sensing properties, with excellent linearity (R² = 0.991) in the 11–75% relative humidity (RH) range. The capacitance of the humidity sensor increased by nearly three orders of magnitude from 11% RH to 75% RH at 300 Hz. Additionally, the humidity sensor displayed fast response (46 s) and recovery (6 s) times, as well as excellent reproducibility. The sensing mechanism was explored through the analysis of complex impedance curves. These finding indicate that the 8 wt.% FeCl₃/MIL-101(Cr)/Si-NPA sensor holds considerable promise for humidity sensing applications.