Hot microelectrodes are very small electrodes (usually 1 100 µm in diameter), which have a surface temperature much higher than the temperature in the bulk solution. In this work, the heating is achieved by applying an alternating potential of very high frequency (100 MHz 2 GHz) and of high amplitude (up to 2.8 Vrms) to the microelectrode. As a result, very fast (on the order of milliseconds) changes in the temperature of the electrolyte solution surrounding the electrode can be achieved. Due to the size of the heated microelectrodes, the hot zone in solution is small. Therefore, the solution can be easily overheated and temperatures above the boiling point can be reached.<p>
The purpose of this research was to investigate and understand the phenomena occurring at ac polarized microelectrodes and to propose new applications of these electrodes. Using both steady-state and fast-scan (10 V/s) cyclic voltammetry measurements, mass transport of redox species has been studied at ac heated microelectrodes. It has been established that the convection at hot-disk microelectrodes is driven primarily by the electrothermal flow of an electrolyte solution. In addition, other effects such as ac dielectrophoresis and Soret (nonisothermal) diffusion are also observed. Numerical simulations have been employed to predict the distribution of temperature in the hot zone, the direction and magnitude of the electrothermal force and the solution flow rate, as well as the voltammetric response of hot-disk microelectrodes. The results of the simulations agree well with the experimental observations.
Theoretical findings of this PhD work are very important for the understanding of the fundamentals of high temperature electrochemistry, particularly mass transport. The proposed explanation of the convection mechanism is most likely applicable not only to ac polarized microelectrodes, but also to the microwave heated microelectrodes, since the only difference between these two heating methods is in the way of delivering electrical energy (wired vs. wireless). The results of the studies of Soret diffusion indicate that it contributes significantly to mass transfer of redox species at hot microelectrodes. Taking into account that the magnitude of the Soret effect has been considered negligible by other electrochemists, the results obtained in this work prove the opposite and show that Soret diffusion affects both the faradaic current and the half-wave potential of the redox reaction. Therefore, the Soret effect can not be ignored if working with hot microelectrodes.<p>
Hot microelectrodes can have a number of interesting applications. The results of the initial investigations indicate that these electrodes can be successfully used in the arrangement for Scanning Electrochemical Microscopy (such a novel technique is termed Hot-Tip SECM). In addition, the observed dielectrophoretic and electrothermal convection effects can enhance the performance of the electrochemical sensors based on hot microelectrodes. This can lead to the improvement of the detection limits of many biologically important analytes, such as proteins, bacteria and viruses.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-06242010-155233 |
| Date | 02 July 2010 |
| Creators | Boika, Aliaksei |
| Contributors | Burgess, Ian, Reid, R. Stephen, Dodds, David, Gravel, Michel, Ding, Zhifeng, Baranski, Andrzej S. |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-06242010-155233/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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