Date of Award

Summer 1997

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry & Biochemistry

Program/Concentration

Chemistry

Committee Director

John B. Cooper

Committee Member

Frank E. Scully, Jr.

Committee Member

John R. Donat

Call Number for Print

Special Collections LD4331.C45 P36

Abstract

The electrochemical behavior of boron-doped diamond microelectrodes has been studied in acetonitrile solutions containing two redox couples using cyclic voltammetry. One test system is 1-2.5 mM ferrocene, containing 0.1 M Tetrabutyl ammonium hexafluorophosphate (TBAH). This well-known reversible redox system involves only one electron transfer with little or no change in the solvation sphere and no breakage/formation of chemical bonds. Another test system is a 1 mM S2Mo180644- solution containing 0.1 M HCIO4. This is one of the most complicated redox systems. In the presence of acid, electrons are usually transferred consecutively and reversibly in even numbers due to stabilization of these species by protonation. An interesting property of these compounds is that they can act as electron "sinks" and Fermi level "meters" since a number of well-defined reduced species can be generated in acidic solution. The above two investigations demonstrate that diamond electrodes exhibit a useful analytical response for a wide range of redox reactions in solution.

Single crystal diamond and continuous diamond films were grown on etched tungsten wires and were subsequently sealed in glass capillary tubes, The electroactive diamond was exposed either by mechanical polishing or by chemical etching of the glass. The resulting electrodes are referred to as diamond microelectrodes and macroelectrodes, respectively.

To date, over 20 diamond microelectrodes and one diamond macroelectrode have been generated with varying results. The ideal diamond microelectrodes yield a reversible steady-state response at low scan rates in both systems, while the diamond macroelectrode yields a typical diffusion limited response for a cyclic voltammogram. Some undesirable results are also obtained. One diamond microelectrode with a low level of boron doping exhibited a significant IR drop in both the Faradaic and non- Faradaic regions. Another diamond microelectrode exhibited surface fouling, presumably, resulting from a higher content of non-diamond carbon. Imperfect microelectrode fabrication may lead to an undetectable constriction separating the electrode proper from the bulk solution. The "lagoon-type" and "crack-type" microelecbodes exhibiting thin-cell behavior are also evaluated in this thesis.

Additionally, these microelectrodes offer many benefits, such as steady-state response, low charging current, low IR drop, and very fast scan rates. This work gives good insight into the advantages of making diamond microelectrodes and demonstrates a potentially powerful analytical tool. For the first time, boron-doped diamond microelectrodes have been fabricated and evaluated in this thesis.

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DOI

10.25777/rm8f-ng88

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