Effect of the Nanostructuration on the Performance of Conducting Polymer-Based Gas Sensors

Details

Supervisors

Hackens, Benoît

Faculty

Ecole polytechnique de Louvain

Degree label

Master de spécialisation en nanotechnologies

Abstract

This work builds on a series of studies on polypyrrole (Ppy)-based ammonia (NH3) gas sensors. Polypyrrole is a conductive polymer widely used for its operation at room tem perature, its simple electrochemical synthesis, and its sensitivity toNH3 via a reversible dedoping mechanism.While nanostructuring is generally presented in the literature as a means of improving the sensitivity of polypyrrole sensors, few studies actually com pare a bulk polypyrrole film with nanostructured morphologies on the same substrate and under identical test conditions. Three types of sensors were synthesized on identical gold interdigitated electrodes, doped solely with lithium perchlorate (LiClO4) : a bulk polypyrrole film, a reverse opal structure templated by polystyrene (PS) nanospheres (510 nm in diameter), and a network of nanotubes templated by methyl orange (MO). The three morphologies were obtained using reproducible synthesis protocols. The film thick ness increases linearly with the chronoamperometric deposition time for the bulk Ppy and Ppy/PS sensors, or with the number of cyclic voltammetry cycles for the Ppy/MO sensors, confirming control over the amount of material deposited. SEM characterization confirms three distinct textures: a compact globular morphology for bulk Ppy, an ordered pore net work for Ppy/PS, and a network of nanotubes for Ppy/MO, the density of which increases with the number of cycles. NH3 detection tests for increasing concentrations (5, 10, 20, and 50 ppm) at room temperature reveal that the two nanostructured sensor families exhibit a relatively lower response than that of the bulk polypyrrole sensor (70% for the bulk Ppy-10 s sensor, compared to 20.5% for the Ppy/PS-2.5 s sensor and 11.6 % for the Ppy/MO-10 cycles sensor). In contrast, these two nanostructured families achieve a bet ter limit of detection LOD (0.077 ppm for the Ppy/MO-10 cycles sensor versus 0.21 ppm for the bulk Ppy-10 s sensor). The kinetic study confirms that these three morphologies follow the same physical model (double-exponential dependence on NH3 concentration), but exhibit contrasting behaviors depending on the morphology. The nanostructured Ppy sensors exhibit faster kinetics compared to the bulk Ppy sensor. Finally, aging tests also reveal contrasting behaviors depending on morphology and thickness.