Design and Fabrication of Electrochemical Gas Sensor

Abstract

This thesis manifests the fabrication of electrochemical gas sensor by chemically modifying copper based interdigitated electrodes (IDEs) with various nanomaterials. Five electrochemical sensors for ammonia (NH3) gas sensing and five electrochemical sensors for carbon dioxide (CO2) gas sensing have been prepared. A simple, fast and low-cost method of fabricating copper based interdigitated electrodes (IDEs) is presented. The fabrication process employed, involves fewer processing steps and cheap materials. Layout of the circular interdigitated electrode with diameter of 17.5mm is designed using CAD software and scanned onto a transparent film to make a positive mask of it. This positive mask is used to impose the design on a screen used in screen printing technique and the design is transferred onto the copper clad board by using PVC black printing ink. The ink acts as an etch resist in a ferric chloride solution. The layout design of the obtained IDE is observed under an optical microscope and is found same as in the CAD layout. Co-precipitation route has been employed for the successful synthesis of nickel magnesium ferrite (Ni0.5Mg0.5Fe2O4) and it’s composite with reduced graphene oxide (rGO) has been obtained through physical method by ultrasonication technique. Electrochemical gas sensors for investigating the electrochemical response towards various concentrations of NH3 and CO2 gases were developed by the modification of IDEs with Ni0.5Mg0.5Fe2O4 nanoparticles, graphene oxide (GO), rGO and Ni0.5Mg0.5Fe2O4/rGO nanocomposite. The modifiers (sensing materials) were characterized by using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) for their structural and morphological studies. The SEM results of Ni0.5Mg0.5Fe2O4 nanoparticles confirmed the spherical morphology of nanoparticles with the average particle size to be 20nm without any agglomeration and SEM micrograph of nanocomposite showed that these spherical nanoparticles are homogenously distributed on graphene sheets. The XRD results showed that all the relevant peaks are present, thus justifying the formation of required sensing materials. iv . The electrochemical response of the chemically modified IDEs exposed to different concentrations of NH3 and CO2 gases in 0.1M NaOH electrolyte has been established through cyclic voltammetry. The cyclic voltammograms obtained reveal that all the modified IDEs show considerable change in current before and after exposure to the gases (analyte). The maximum response towards various gas concentrations of NH3 and CO2 was shown by the Ni0.5Mg0.5Fe2O4/rGO nanocomposite modified IDE while as bare electrode showed very limited change in the response followed by Ni0.5Mg0.5Fe2O4 nanoparticles modified IDE. The sensitivity and limit of detection (LOD) of Ni0.5Mg0.5Fe2O4/rGO nanocomposite modified IDE towards various concentrations of NH3 gas have been calculated. The sensitivity achieved by using Ni0.5Mg0.5Fe2O4/rGO nanocomposite as a sensing element was found to be 0.000713023 A ppm-1 and limit of detection (LOD) obtained was 17.1 ppm, which is below the threshold limit of 25ppm set by the world health organization (WHO).