Diagnostic criteria of electrochemical reaction mechanisms using cyclic square wave voltammetry

Abstract

An electrode reaction is an electron transfer that occurs at the surface of the working electrode in a typical three electrode cell. The electron transfer may be reversible or it may be complicated by sluggish electron transfer kinetics, preceding chemical reactions, and/or following chemical reactions. Furthermore, the species within the reaction may be adsorbed to the electrode surface. This thesis investigates reversible electron transfers that are coupled to chemical reactions, kinetically controlled electron transfers (both diffusional and adsorbed on the electrode surface), and kinetically controlled electron transfers that are coupled to chemical reactions. Each chapter explores a specific mechanism to determine its diagnostic criteria using cyclic square wave voltammetry. The reactions for each mechanism are written containing both the electroactive and electroinactive species. From these reactions and appropriate diffusion equations and boundary conditions, the expressions of concentrations of each specie can be formulated. Using these expressions, an equation that evaluates current as a function of time and potential is derived and subsequently coded in MATLAB. Systematic variation of empirical parameters is performed, and the impact on peak parameters is analyzed. Diagnostic trends in peak parameters can be used for qualitative mechanism assignment then quantitatively determine reaction kinetics. Subsets of mechanisms are compared to one another so that the experimentalist can discern between mechanisms. All results are summarized in a table for each mechanism so that the information is rapidly available to the experimentalist. By following a set of recommended experiments and subsequently generating plots, experimenters will be able to compare their results to those presented for each mechanism investigated. The significant results within this thesis prove that both kinetically controlled and chemically coupled mechanisms can be identified and that rates can be determined using cyclic square wave voltammetry. Furthermore, this thesis exemplifies that the cyclic square wave waveform has added benefits over other electrochemical techniques. This work broadly impacts both the electrochemistry and non-electrochemistry communities as it intended for both the expert and non-expert to rapidly, easily, and most importantly, correctly interpret data.