Impact of hydrogen concentrations on the impedance spectroscopic behavior of Pd-sensitized ZnO nanorods

Muhammad Kashif,Syed M Usman Ali,Md Eaqub Ali,Uda Hashim,Sharifah Bee Abd Hamid

doi:10.1186/1556-276x-8-68

Abstract

ZnO nanorods were synthesized using a low-cost sol-gel spin coating technique. The synthesized nanorods were consisted of hexagonal phase having c-axis orientation. SEM images reflected perpendicular ZnO nanorods forming bridging network in some areas. The impact of different hydrogen concentrations on the Pd-sensitized ZnO nanorods was investigated using an impedance spectroscopy (IS). The grain boundary resistance (Rgb) significantly contributed to the sensing properties of hydrogen gas. The boundary resistance was decreased from 11.95 to 3.765 kΩ when the hydrogen concentration was increased from 40 to 360 ppm. IS gain curve showed a gain of 6.5 for 360 ppm of hydrogen at room temperature. Nyquist plot showed reduction in real part of impedance at low frequencies on exposure to different concentrations of hydrogen. Circuit equivalency was investigated by placing capacitors and resistors to identify the conduction mechanism according to complex impedance Nyquist plot. Variations in nanorod resistance and capacitance in response to the introduction of various concentrations of hydrogen gas were obtained from the alternating current impedance spectra.

Highlights

While hydrogen gas has been increasingly used as a clean and green fuel in household and transportation appliances, the absence of color, odor, and taste has made it difficult to trace and detect hydrogen under complex matrices [1]
The sharp peak located at 34.5° (002) plane of the synthesized zinc oxide (ZnO) nanorods revealed their high-quality crystals and c-axis alignment
The second peak at 38.53° (211) plane confirmed the presence of palladium oxide (PdO)

Summary

Introduction

While hydrogen gas has been increasingly used as a clean and green fuel in household and transportation appliances, the absence of color, odor, and taste has made it difficult to trace and detect hydrogen under complex matrices [1]. Hydrogen is a light and diffusible gas (diffusion coefficient of 0.61 cm2/s in air) [1] with a wide ranging inflammability (4% to 75%) [2]. Even 4.65% hydrogen in air is sufficient to cause explosion [2]. The detection and leakage control of this gas is a challenging task, and there is an increasing demand in the development of methodology for the ultrasensitive detection of hydrogen. Selective H2 sensors were proposed for the detection of hydrogen leakage in solid-state fuel cells [3], proton exchange membrane fuel cells [3], hydrogen engines [4], and hydrogen storage devices [5]. Bamsaoud et al [6] used nanoparticulate tin oxide (SnO2)-based resistive films for the selective detection of hydrogen against 100 ppm of CO, isobutane, CH4, CO2, and SO2. In the forthgoing era, there is a requirement of hydrogen sensors having superior stability, sensitivity, and fast response time, along with low operating power and weight

Methods

Results

Conclusion