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Unformatted text preview: III. Reaction Kinetics Lecture 1 3 : Butler-Volmer equation Notes by ChangHoon Lim (and MZB) 1. Interfacial Equilibrium At lecture 11, the reaction rate R for the general Faradaic half-cell reaction was derived. where =Reduced state =Oxidized state Here s i is the stochiometric coefficient of species i (positive for reduced state and negative for oxidized state), R i (O i ) is a symbol for chemical formula and Z i is the charge number of species i . where , , = electrode potential- solution potential, and is symmetry factor (transfer coefficient). [Note] The ratio of anode reaction rate to cathode reaction rate does not depend on or any properties of the transition state. In equilibrium, the net reaction rate R is zero. That is, where This is the Nernst equation. And, is a kinetic definition of the standard potential, related to microscopic reaction rates. - 2. Activation Overpotential In electrochemistry, it is more common to use (activation) overpotential rather than Overpotential is This is the extra voltage which drives a Faradaic current. In terms of overpotential, the reaction rate is ....
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