Date of Award

1-1-2019

Language

English

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Chemistry

Content Description

1 online resource (vi, 47 pages) : illustrations (some color)

Dissertation/Thesis Chair

Gerd-Uwe Flechsig

Keywords

continuous heating, directly heated electrode, heated micro-wire electrode, high temperature electrochemistry, pressurized flow cell, thermoelectrochemistry, Microelectrodes, Electric wire, Electrochemistry, Gold, teocuitlatl

Subject Categories

Analytical Chemistry

Abstract

Heated micro-wire electrodes offer lots of advantages, such as, accurate temperature control, enhanced diffusion and accelerated reaction kinetics through micro-stirring effect, easy cleaning, and low cost, etc. Its application in high temperature electrochemistry has gained lots of interests since its debut in the mid-1990s. A maximum of 250 °C has been reported using heating pulses in duration of 5 ms. For various applications, permanently heating would be more useful. In this study, two types of micro-wire electrodes were successfully developed for electrochemistry above the boiling point with acetaminophen as model compound and a continuous heating time of at least 2 mins. Thermoelectrochemical behavior of acetaminophen in neutral pH = 7.4 at directly heated fork-type gold micro-wire electrodes (1 – 115 °C and atmosphere pressure) revealed two linear regions of activation energy corresponding to diffusion control with 14.5 kJ/mol at high temperatures and rate control with 33 kJ/mol at very low temperatures, while the two regions were not very distinctive in acidic condition of pH = 1 with activation energies of 16 kJ/mol at high temperatures and 22 kJ/mol at very low temperatures. The results using directly heated flow-cell-type gold micro-wire electrodes (24 – 136 °C and 50 bar) in neutral pH = 7.4 confirmed the similar two linear regions of activation energy with 14 kJ/mol at high temperature as a result of diffusion control and 59 kJ/mol in a very narrow low temperature range due to reaction rate control. Both types of micro-wire electrodes showed a very good precision of temperature control. Consistent calibrations have been achieved with both open-circuit potentiometry and resistivity thermometer methods for the flow-cell-type electrodes at 50 bar, 0.5 mL/min and up to 160 °C. The ultimate goal of the pressurized flow cell approach is to reach supercritical conditions and enable a calibration-free analysis of trace metals.

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