Rare earth oxide based polypyrrole composite: An efficient room temperature reliant humidity sensor

Having a competent and efficient humidity sensing material is important for vivid applications. In the present work, holmium oxide, a well-known rare-earth oxide, has been composited with Polypyrrole (PPy) to form polypyrrole/holmium oxide (PPHO) composites. The composites were prepared by chemical polymerization reactions in 10 (PPHO-1), 30 (PPHO-2), and 50 wt% (PPHO-3) of holmium oxide in PPy matrix. These composites were characterized by Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectra, and Transmission electron microscopy (TEM) to study the structural and morphological changes in the PPy and PPHO composites. Humidity sensing behavior of the composites was investigated in the relative humidity range (RH) of 11 to 97%. Among all the composites, PPHO-3 has shown a maximum sensing response of 93% with response and recovery times of 30 s and 40 s respectively, furthermore, the composite has exhibited an appreciable limit of detection (LOD) of 4.98 % RH, good linearity (0.9981), real sensitivity (27.72 MΏ-cm / %RH) and stability. Based on Grotthus' reaction, the sensing mechanism has been discussed.