Multilayer-Structured Poly-Vanadium Acid/Polyaniline Composite: Synthesis and Properties for Humidity Sensing

Abstract

A high-performance humidity sensor based on multilayer-structured poly-vanadium acid/polyaniline (V/PANI) composite was reported in this paper. Two-layer-structured V/PANI composite was fabricated by dip-coating poly-vanadium acid and electrochemically polymerizing PANI onto the interdigitated gold electrode in sequence, and then the process could be repeated to prepare the second two-layer-structured V/PANI composite. The crystalline phase properties and structural characteristics of the poly-vanadium acid, PANI, and V/PANI composite were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and UV-visible spectroscopy, respectively. The morphological characteristics of the first two-layer-structured V/PANI composite and multilayer-structured V/PANI composite were characterized by scanning electron microscopy. Additionally, sensors based on the multilayer-structured V/PANI composite showed good humidity sensing properties. For instance, its impedance changed linearly for approximately four orders of magnitude in a wide range of 11-97% RH. Furthermore, it displayed small hysteresis (~5% RH), fast response (t90% of 8 s and 12 s for adsorption and desorption processes, respectively), good stability. The possible sensing mechanism was analyzed by considering the special multilayer structure and using complex impedance spectra and the corresponding equivalent circuit of the sensor. The measurement results highlight the multilayer-structured V/PANI composite film is a candidate material for constructing humidity sensors.