Mark Orazem, Professor
Department of Chemical Engineering
University of Florida

Influence of Ohmic Impedance

Abstract: Electrochemical impedance spectroscopy is a transfer-function technique that is applied to electrochemical systems. The technique has a unique capability to provide valuable information that may otherwise be difficult or impossible to obtain. Unlike chemical spectroscopies for which interpretation may make use of libraries, detailed interpretation requires system-specific models. Impedance spectroscopy measurements are often confounded by electrode-geometry-induced high-frequency phenomena in the form of a frequency-dependent complex ohmic impedance. The presence of ohmic impedance can be attributed to the nonuniform current and potential distribution associated with the electrode geometry. While the influence of ohmic impedance was suggested first by numerical simulations, recent work has provided experimental verification. The experiments were performed for ferricyanide and ferrocyanide redox species (10 mM each) in a 0.5 M KCl solution. The working electrode consisted of a 5-mm-diameter Au disk rotating at 800 rpm. The process model used to fit experimental data was expressed in terms of an ohmic impedance and an expression that accounted for the influence of a local constant-phase element on the faradaic reaction and the convective diffusion impedance, expressed in terms of a series expansion.  Regressions were weighted by the experimentally determined error structure of the data, and the resulting parameters characteristic of the ohmic impedance were in excellent agreement with numerical simulations. This presentation will include a description of impedance spectroscopy and a discussion of new results concerning the ohmic impedance contribution to the overall measurement.

Bio: Mark Orazem obtained his BS and MS degrees from Kansas State University and his doctorate in 1983 from the University of California, Berkeley. In 1983, he began his career as an Assistant Professor at the University of Virginia, and in 1988 he joined the faculty of the University of Florida, where he is a Distinguished Professor of Chemical Engineering. He was recognized as a University of Florida Foundation Preeminence Professor and was the recipient of numerous University of Florida term professorships. Prof. Orazem is a Fellow of both the Electrochemical Society and the International Society of Electrochemistry, and he served as President of the International Society of Electrochemistry in 2011-2013. He has over 220 refereed publications, and he co-authored, with Bernard Tribollet of the CNRS in Paris, a textbook entitled Electrochemical Impedance Spectroscopy. This book, published by Wiley in 2008, was translated into Chinese and published by Chemical Industry Press in 2014. The second edition was published in 2017, and the Chinese translation is in preparation. His edited book on Underground Pipeline Corrosion was published by Woodhead Publishing in 2014. In 2012, Prof. Orazem received the Henry B. Linford Award of the Electrochemical Society. With his co-author Bernard Tribollet, Prof. Orazem is a 2019 recipient of the Claude Gabrielli Award for contributions to electrochemical impedance spectroscopy.
 

Mark Orazem, Professor
Department of Chemical Engineering
University of Florida

Influence of Ohmic Impedance

Abstract: Electrochemical impedance spectroscopy is a transfer-function technique that is applied to electrochemical systems. The technique has a unique capability to provide valuable information that may otherwise be difficult or impossible to obtain. Unlike chemical spectroscopies for which interpretation may make use of libraries, detailed interpretation requires system-specific models. Impedance spectroscopy measurements are often confounded by electrode-geometry-induced high-frequency phenomena in the form of a frequency-dependent complex ohmic impedance. The presence of ohmic impedance can be attributed to the nonuniform current and potential distribution associated with the electrode geometry. While the influence of ohmic impedance was suggested first by numerical simulations, recent work has provided experimental verification. The experiments were performed for ferricyanide and ferrocyanide redox species (10 mM each) in a 0.5 M KCl solution. The working electrode consisted of a 5-mm-diameter Au disk rotating at 800 rpm. The process model used to fit experimental data was expressed in terms of an ohmic impedance and an expression that accounted for the influence of a local constant-phase element on the faradaic reaction and the convective diffusion impedance, expressed in terms of a series expansion.  Regressions were weighted by the experimentally determined error structure of the data, and the resulting parameters characteristic of the ohmic impedance were in excellent agreement with numerical simulations. This presentation will include a description of impedance spectroscopy and a discussion of new results concerning the ohmic impedance contribution to the overall measurement.

Bio: Mark Orazem obtained his BS and MS degrees from Kansas State University and his doctorate in 1983 from the University of California, Berkeley. In 1983, he began his career as an Assistant Professor at the University of Virginia, and in 1988 he joined the faculty of the University of Florida, where he is a Distinguished Professor of Chemical Engineering. He was recognized as a University of Florida Foundation Preeminence Professor and was the recipient of numerous University of Florida term professorships. Prof. Orazem is a Fellow of both the Electrochemical Society and the International Society of Electrochemistry, and he served as President of the International Society of Electrochemistry in 2011-2013. He has over 220 refereed publications, and he co-authored, with Bernard Tribollet of the CNRS in Paris, a textbook entitled Electrochemical Impedance Spectroscopy. This book, published by Wiley in 2008, was translated into Chinese and published by Chemical Industry Press in 2014. The second edition was published in 2017, and the Chinese translation is in preparation. His edited book on Underground Pipeline Corrosion was published by Woodhead Publishing in 2014. In 2012, Prof. Orazem received the Henry B. Linford Award of the Electrochemical Society. With his co-author Bernard Tribollet, Prof. Orazem is a 2019 recipient of the Claude Gabrielli Award for contributions to electrochemical impedance spectroscopy.