Evaluation of Rate Constants for Rapid Electrode Reactions by Using Microelectrode Voltammetry: Virtues of Measurement at Lower Temperatures.

摘要

The prospects of utilizing electrochemical kinetic measurements at lower temperatures for evaluating reliably the standard rate constants, ks, of rapid redox couples in nonaqueous media, specifically using microelectrode voltammetry, have been examined by means of digital simulations along with experiment. Cyclic voltammetric measurements were made between 200 and 300K at a gold microdisk, for ferrocenium-ferrocene (Fc+/o), o-nitrotoluene 0/-, and nitromesitylene o/- redox couples in acetone, propionitrile, and butyronitrile, at a gold microdisk with scan rates from 100 to 104 V/s. The latter two couples were selected as examples of systems that exhibit rapid, yet still unambiguously measurable, ks values at ambient temperatures; the more facile fc+/o system has been suspected to yield immeasurably fast electrode kinetics using conventional techniques under these conditions. Sample simulated voltammograms were generated between 200 and 300K for a sequence of activation enthalpies for electron exchange accounting also for known temperature dependent diffusion coefficients, solution resistance, and double-layer capacitance.