Understanding reactions that either precede or follow electron transfer is of primary interest in a wide range of applications, ranging from electrosynthesis to energy storage in redox flow batteries. It is critical to determine the rate at which these chemical steps occur. However, chemical steps can span a wide range of time scales which poses difficulty for measurement. Techniques such as cyclic voltammetry (CV) and rotating-disk electrode (RDE) methods have been widely used to determine the characteristic time of these chemical steps. However, these methods often fall short in measuring rapid steps (e.g. sub-ms) or slow steps (e.g. above an hr). Alternative strategies rely on two-electrode generation-collection methods to generate a redox active species at one electrode, and ‘collect’ it by applying a potential of opposite polarity at another electrode after some characteristic time. The ratio of collector current to generator current gives a collection efficiency, which indicates the extent of the reaction during the characteristic time.<br/> <br/>In this work we have microfabricated a device containing multiple interdigitated arrays (IDAs) of various separation lengths, thereby providing a means to control diffusional time-of-flight, which is the characteristic time in these experiments. We observed that the natural logarithm of collection efficiency is linear with respect to separation distance. The slope of this curve can be used to determine the chemical rate constant through a relationship uncovered by finite-element simulations and machine learning. This technique offers the capability of measuring kinetics over a wider range than is accessible with common techniques such as CV and RDE. In addition, we demonstrate how this method can be automated, allowing for use in high-throughput experiments that are necessary to study large libraries of samples.

Arrays of arrays: Microfabrication to control characteristic time in electroanalysis

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ACS Fall 2022

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