(220a) Kinetic Mechanism of Electrochemical Reactions In a Microfluidic Cell

We propose a novel kinetic mechanism of electrochemical reactions at solid electrode – water electrolyte interface. We assume fast formation of electron donors and electron acceptors (mediators) by thermal fluctuations in the electrode matter. Product of surface concentrations of these mediators is considered to be a constant due to thermal equilibrium. The electron mediators at an electrode can interact with oxidized or reduced forms of electrochemically active substances. In this study, we focus on a simple reversible electrochemical reaction – oxidative dissolving of a metal and its reductive deposition. Two electrodes from the same material immersed into an electrolyte form an electrochemical cell. The electrolyte contains the oxidized form of the metal (monovalent), counter-ion and auxiliary co-ion. The mathematical model consists of molar balances of the ionic components and the Poisson equation. Electric charge concentration on the electrodes is also computed. Concentrations of the electron mediators are then described as functions of the electric charge concentrations. The developed mathematical model enables dynamical and stationary analysis of behavior of the electrochemical cell.

                For example, dynamics of the electrochemical cell without electric current load is studied. Dissolution of the electrode metal is observed together with decrease of the electric potential at the electrodes. We also studied behavior of the system under the electric current load. Here we identified a shift of the system from electrochemically limited regime to the transport limited regime. Phenomenon called an “ionic gate” was observed at an electrode. The obtained current-voltage characteristics are in good agreement with predictions given by the classical Frumkin-Butler-Volmer reaction description.

                The developed model can be used for investigation various electrochemical systems and microsystems. For example, performance of ac electroosmotic micropumps is significantly affected by electrochemical interactions. Detail and comprehensive studies on this problem is still missing.