The role of nucleation in the electrochemistry of organic conducting salt electrodes

Author

Kristian Michael Scaboo

Date of Award

5-1999

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

James Q. Chambers

Abstract

Organic conducting salts in the TCNQ family exhibit unique electrochemical characteristics when used as working electrodes in the presences of aqueous electrolyte solutions. The surface redox reactions of these electrodes involve a rearrangement of the solid state crystal lattice accompanied by electrolyte ion ingress or egress to achieve charge balance. These processes give rise to atypical responses when investigated using the classical electrochemical techniques of cyclic voltammetry (CV) and chronoamperometry. The CV response of these compounds is characterized by very large peak separations, narrow peak widths, and a large apparent double layer charging, while the potential step experiment results in peaked current transients.

This thesis presents the results of an investigation of two different organic conducting salt electrodes composed of: i) polycrystalline films of 9AAH⁺[(TCNQ)2]^- mechanically applied to glassy carbon substrates and ii) single crystal electrodes of TTF-TCNQ exposed to aqueous electrolyte solutions. The electrochemical responses of these electrode systems were studied using conventional cyclic voltammetry and chronoamperometry as well as a novel technique combining derivative chronopotentiometry and quartz crystal microgravimetry. An attempt to explain these responses in the context of previous mechanistic interpretations of these processes, invoking the square scheme, failed to account for the experimental results.

A detailed analysis of the voltammetric and chronoamperometric data using existing models of nucleation controlled processes revealed that the experimental data matched an instantaneous-diffusional, nucleation-controlled mechanism. While this theory accounted for the kinetics of electron transfer, it did not account for the large energy difference between the reduction and oxidation processes which manifested itself in the form of significantly different formal potentials for the two processes.

An attempt is made to explain the nucleation behavior in the context of thermodynamic energy gaps caused by a solid state immiscibility between the reduced and oxidized forms of the conducting salt phases.

Recommended Citation

Scaboo, Kristian Michael, "The role of nucleation in the electrochemistry of organic conducting salt electrodes. " PhD diss., University of Tennessee, 1999.
https://trace.tennessee.edu/utk_graddiss/8928