Study of a Flexible ZnO/MWCNTs Thin Film Sensor for Hydrogen Peroxide Vapor Detection by Impedance Spectroscopy

The growing demand for sensors capable of detecting hydrogen peroxide vapor (HPV) in industrial and medical applications has led to increased research activity in this field. Despite significant progress, there remains a strong need for the development of new HPV-sensitive materials as well as for improving the performance of existing sensor systems. This work presents a flexible hydrogen peroxide vapor sensor employing a ZnO/MWCNTs (multi-walled carbon nanotubes) thin film as the sensing layer and provides a detailed impedance-based analysis.

The frequency dependence of the real and imaginary components of the complex impedance was measured in air and under exposure to HPV at operating temperatures ranging from room temperature to 200 °C. The influence of ultraviolet (UV) irradiation on the impedance response of the ZnO/MWCNTs sensor was also examined. The structural, morphological, and compositional characteristics of the ZnO/MWCNTs composite were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS).

Analysis of the impedance spectra enabled the proposal of an equivalent electrical circuit describing the sensor structure. The parameters of the circuit elements were determined, and the calculated impedance curves showed good agreement with the experimental data. A linear increase in sensor sensitivity was observed with increasing temperature up to 175 °C. Ultraviolet (UV) irradiation resulted in an approximately twofold enhancement of sensor sensitivity at room temperature.

It was demonstrated that the flexible polyimide substrate with platinum interdigitated electrodes makes a significant contribution to the overall impedance of the ZnO/MWCNTs sensor structure. In the equivalent circuit, this contribution is represented by a parallel parasitic capacitance (C₀ ≈ 1.67 × 10^-11 F). Exposure to hydrogen peroxide vapor mainly affects the resistance of the ZnO/MWCNTs sensing film. The validity of the proposed equivalent electrical circuit is confirmed by the close correspondence between the calculated Nyquist plots and the experimental impedance data.