Fabrication of carbon nanotube(CNT) - epoxy electrodes

Abstract

Carbon nanotubes (CNTs) have been widely used as electrochemical sensor due to its excellent electrical, thermal, mechanical and chemical properties. It is generally accepted that the CNT tips have much better electrochemical properties than the sidewall of CNTs. In order to make use of CNT tips, CNT arrays were encapsulated in dielectric epoxy by degassing, and then the CNT tips were exposed by mechanical grinding and polishing. The aim of this final year project is to optimize the fabrication process to improve the performance of the CNT-based electrodes, in particular to reduce background current and increase electron transfer rate. Different parameters have been investigated. These include the mixing ratio of Epoxies, vacuum duration, vacuum pressure, Oxygen plasma duration, types of Epoxies used (Epolam 5015 and EpoFix), polishing processes and different curing processes. The CNT-Epoxy electrodes were then characterized by Cyclic Voltammetry using two different electrolytes. The results of background current and the peak potential difference, ∆Ep, were analysed and compared. The different background currents obtained and the current densities calculated have a co-relation with the area of exposed CNT tips during Cyclic Voltammetry, while the peak potential differences, ∆Ep, signify the electron mass transfer rate at the surfaces of the CNT-Epoxy electrodes during electrochemical reaction at the electrode.

The experimental results conclude that air plasma can significantly increase the electron transfer rate: the longer the plasma duration, the better the electron transfer rate. Moreover, the 30% hardener/resin mixing ratio is the best as it has the smallest ∆Ep. The 3 hours vacuum duration sample gave the smallest background current and vacuum pressure has an effect on the background current. With the use of additional polishing steps, more tips of CNT array are exposed, resulting in more active sites for better electron transfer, thus smaller ∆Ep values. In addition, the first curing process – room temperature curing for 24 hours followed by curing it further at a temperature, Tc°C generally has the lowest set of ∆Ep and background current, with Tc at 90°C as the best curing temperature in curing process 1. In the comparative study between polymer types, Epolam epoxy produced electrodes with smaller ∆Ep thus better electron transfer rate, as compared to EpoFix epoxy.

It is concluded that the fabrication of the CNT-Epoxy electrodes is indeed process dependent whereby any fabrication parameter can have a direct effect on the background current and ∆Ep results obtained. Some of the CNT-Epoxy electrodes fabricated have small background current and small ∆Ep values. This good sensitivity characteristic can be used in the development of electrochemical sensors in the field of bioscience and nanotechnology.