High-speed electrochemistry using ultramicroelectrodes

This research investigates the use of ultramicroelectrodes in performing electrochemistry on microsecond and nanosecond time scales. Other researchers have used ultramicroelectrodes for this purpose, but their studies have centered on dissolved species and generally use cyclic voltammetry experiments. One purpose of this research was to look at new ways to apply ultramicroelectrodes to high speed experiments. Some of the aspects that are discussed in this thesis are: (a) A novel technique was developed for measuring currents on short time scales that involves conversion of the current to light using a light emitting diode and measuring the light intensity as a function of time using time correlated single photon counting (TCSPC). Computer processing of the light intensity data can convert this data back to current. The technique is capable of measurements on nanosecond time scales, but TCSPC requires tens or hundreds of millions of experiments to obtain a complete set of data and this frequently results in severe electrode fouling problems. (b) Potential step experiments were used instead of potential sweep experiments. Potential step experiments enable the separation in time of the faradaic and charging currents for chemical systems in which the faradaic impedance is greater than the uncompensated solution resistance. (c) For systems in which the faradaic impedance and uncompensated resistance are of the same order of magnitude, a computer simulation was developed which accounts for the interaction of the faradaic and double layer charging processes. (d) Application of short time scale experiments to the study of surface processes. Some processes studied in this work are the oxidation of clean platinum surfaces, electrode reactions of anthraquinone-2,6-disulfonic acid adsorbed on mercury, reductive hydrogen adsorption on platinum and double layer charging. (e) A study of the smallest available time constants was performed, taking into account non-idealities in the electrode such as stray capacitance and resistance of the electrode itself. This study indicates that time constants in the tens of nanoseconds are probably the shortest attainable using the conventional setups for ultramicroelectrode experiments. (f) A discussion of techniques for cleaning electrodes which are often necessary for repetitive experiments due to electrode fouling problems. One technique useful in cleaning platinum electrodes for hydrogen adsorption studies is to use a double pulse waveform in which the first pulse oxidizes and reduces the platinum to clean the electrode. The second pulse, which occurs microseconds or milliseconds after the first pulse, causes the hydrogen adsorption process.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Walsh, Michael Ralph

Contributors dc:contributor

• Faulkner, Larry R.

• Chemistry, Analytical

Statement dc:rights

• Copyright 1989 Walsh, Michael Ralph

Language dc:language

eng

Identifier

AAI8924964
(UMI)AAI8924964

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/20596