Hyphenated techniques in dynamic electrochemistry. 1. Mechanistic diagnosis for redox switching of electroactive films using nonelectrochemical population probes

The use of hyphenated electrochemical techniques to study electroactive films has two aspects. First, there is an electrochemical control function that drives fluxes of film mobile species and may trigger film structural changes. Second, there are two responses, one characteristic of the probe and the other the conventional electrochemical response. We present a quantitative theory relating changes in electroactive film mobile species populations to different electrochemical control functions. This theory identifies the coulostatic and potentiostatic step methods as optimal for separation of the elementary steps in the redox switching of electroactive films. Combinations of the population changes to the coulostatic and potentiostatic control functions predict the population changes to all other electrochemical control functions. Although the theory is general, we discuss it specifically with regard to a model for redox switching of electroactive films that incorporates three elementary steps. These elementary steps are exemplified by coupled electron/ion transfer, solvent transfer, and film structural change. A simple procedure qualitatively identifies the rate-controlling step and quantitatively determines the rate constants. A scheme-of-cubes representation simplifies visualization of the many mechanistic possibilities for film redox switching.