Application of the Koutecký-Levich Method to the Analysis of Steady State Voltammograms with Ultramicroelectrodes.

We demonstrate a new experimental approach to measure heterogeneous electron transfer rates. We adapted the classical Koutecký-Levich model for a rotating disk electrode (RDE) to a general heterogeneous electrochemical kinetic study with ultramicroelectrodes (UMEs) even for fast redox systems, where different sizes of UMEs are used to modulate the mass transfer rate (m). Subsequently, a linear plot of (1/current density) vs 1/m at different potentials can be created from the obtained steady state voltammograms, which is analogous to the traditional Koutecký-Levich plot. A simple numerical treatment with a slope and y-intercept from a linear plot allows for extracting kinetic parameters. A unifying treatment is presented for the steady state quasi-reversible, irreversible, and reversible voltammograms for a simple electron transfer reaction at UMEs. This new experimental approach with submicrometer to ∼ micrometer sized UMEs exceeds the mass transfer rates achieved by conventional electrochemical methods using rotating electrodes or solely tens of micrometer sized electrodes, thus enables us to study much faster heterogeneous electron transfer kinetics with simple instrumentation. The method should be particularly useful in studying particle size and structure effects.