An AlFFIVE-1-Ni-Based Humidity Sensor with Fast Response-Recovery Speed

Humidity sensors based on porous materials have demonstrated broad application prospects in the field of relative humidity (RH) monitoring due to their unique advantages. In this work, a high-performance resistance-type humidity sensor was successfully fabricated using the MOF-type humidity-sensitive material AlFFIVE-1-Ni. Systematic studies reveal that the straight-through and ordered pore structure, abundant fluorine (F) atoms, and open metal sites (Ni²⁺) inherent in the AlFFIVE-1-Ni endow it with exceptional hydrophilicity and excellent cycling stability. Benefiting from these features, the AlFFIVE-1-Ni-based humidity sensor exhibits outstanding sensing performance. For instance, within the low-frequency range (40-100 Hz), the total impedance modulus of the AlFFIVE-1-Ni-based sensor changes by more than two orders of magnitude over the RH interval of 11-95%, demonstrating its ability to generate a highly sensitive response to humidity variations across a wide humidity range. Meanwhile, above 33% RH, the sensor shows a good linear correlation between impedance modulus and RH, confirming the reliability and consistency of its response under different humidity levels. Impressively, the AlFFIVE-1-Ni-based humidity sensor exhibits rapid response-recovery speeds (6 s/3 s), low hysteresis (3% RH), and excellent long-term stability across a wide RH range (11-95%). Furthermore, the intrinsic mechanism underlying the exceptional sensing performance of the AlFFIVE-1-Ni-based sensor has been thoroughly elucidated through complex impedance curve (CIC) and equivalent circuit (EC) analysis, density functional theory (DFT) calculations, and Grand Canonical Monte Carlo (GCMC) simulations. These results collectively highlight the tremendous potential of the AlFFIVE-1-Ni-based humidity sensor for highly sensitive and rapid RH detection.