Humidity sensing mechanism of mesoporous MgO/KCl-SiO ₂ composites analyzed by complex impedance spectra and bode diagrams

Composites of mesoporous silica SBA-15 and MgO/KCl were prepared by a simple grind method following a heat-treatment process. Their structures were characterized by X-ray diffraction (XRD). Humidity sensing properties were studied and the results indicated that, under the same preparation condition, KCl-SBA-15 composite was more suitable to be a promising humidity sensing material than MgO-SBA-15 composite. The impedance of KCl-SBA-15 composite changed more than four orders of magnitude when relative humidity changed from 11% to 95%. The response and recovery time were about 6 s and 26 s, respectively. High stability and low hysteresis were also observed. Complex impedance spectra, the corresponding equivalent circuit, and bode diagrams under different relative humidity was analyzed to explore the humidity sensing mechanism of this material.