Electrochemical potentials from first principles
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ORIGINAL PAPER
Electrochemical potentials from first principles Stephen Fletcher 1 Received: 18 June 2020 / Revised: 21 June 2020 / Accepted: 22 June 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The electrochemical potential is the fundamental parameter in the theory of electrochemistry. Not only does it determine the position of electrochemical equilibria but also it acts as the driving force for electron transfer reactions, diffusion-migration phenomena, and phase transformations of all kinds. In the present work, the electrochemical potential is defined as the total work done in transferring a single particle of a substance from a universal reference state to a specified location, at constant temperature and pressure. It is the sum of two scalar fields: the electrostatic potential energy and the chemical potential energy. The electrochemical potential is widely underutilized within the fields of solid-state science and electrochemical engineering. For historical reasons, many authors prefer to analyze driving forces in terms of electrode potentials, concentration gradients, or Gibbs free energies. In this paper, the author provides a short introduction to the electrochemical potential and then shows how some of the major branches of electrochemistry can benefit from using it. Topics examined include the Volta potential difference, the membrane potential difference, the scanning Kelvin probe microscope, the electromotive force, the proton motive force, and the activation of electron transfer. Keywords Electrochemical potential . Vacuum scale . Volta potential difference . Membrane potential difference . Electromotive force . Proton motive force . Activation of electron transfer
Introduction During my lifetime, no one has done more to classify and clarify the terminology of electrochemistry than Prof. Dr. Fritz Scholz. He is one of those rare individuals who is at once a lexicographer, a historian, and a scientist. It is therefore a particular pleasure for me to present him with a self-consistent set of definitions which, I hope, will fit with his own profound knowledge of the field, while at the same time helping the next generation of scientists to disambiguate electrochemical potentials, electrode potentials, and electromotive forces. Many of the definitions discussed in the present work have long histories. They are the product of decades of thought by dozens of talented researchers. Unfortunately, in the limited space available, it has proved impossible to provide a narrative account of the history of each term or even to summarize the This article is dedicated to Prof. Dr. Fritz Scholz on the occasion of his 65th birthday. * Stephen Fletcher [email protected] 1
The Fletcher Consultancy, Loughborough, Leicestershire LE11 3LU, UK
dialectics of each case. Instead, what I have attempted to do is juxtapose the definitions in ways that emphasize the interlocking character of the various sub-fields of electrochemistry. How far I have succeeded in this task must be left
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