Êtes-vous un étudiant de l'EPFL à la recherche d'un projet de semestre?
Travaillez avec nous sur des projets en science des données et en visualisation, et déployez votre projet sous forme d'application sur GraphSearch.
Concept
Relation de Butler-Volmer
Résumé
In electrochemistry, the Butler–Volmer equation (named after John Alfred Valentine Butler and Max Volmer), also known as Erdey-Grúz–Volmer equation, is one of the most fundamental relationships in electrochemical kinetics. It describes how the electrical current through an electrode depends on the voltage difference between the electrode and the bulk electrolyte for a simple, unimolecular redox reaction, considering that both a cathodic and an anodic reaction occur on the same electrode:
The Butler–Volmer equation is:
or in a more compact form:
where:
electrode current density, A/m2 (defined as j = I/S)
exchange current density, A/m2
electrode potential, V
equilibrium potential, V
absolute temperature, K
number of electrons involved in the electrode reaction
Faraday constant
universal gas constant
so-called cathodic charge transfer coefficient, dimensionless
so-called anodic charge transfer coefficient, dimensionless
activation overpotential (defined as ).
The right hand figure shows plots valid for .
There are two limiting cases of the Butler–Volmer equation:
the low overpotential region (called "polarization resistance", i.e., when E ≈ Eeq), where the Butler–Volmer equation simplifies to:
the high overpotential region, where the Butler–Volmer equation simplifies to the Tafel equation. When , the first term dominates, and when , the second term dominates.
for a cathodic reaction, when E < Eeq, or
for an anodic reaction, when E >> Eeq
where and are constants (for a given reaction and temperature) and are called the Tafel equation constants. The theoretical values of the Tafel equation constants are different for the cathodic and anodic processes. However, the Tafel slope can be defined as:
where is the faradaic current, expressed as , being and the cathodic and anodic partial currents, respectively.
The more general form of the Butler–Volmer equation, applicable to the mass transfer-influenced conditions, can be written as:
where:
j is the current density, A/m2,
co and cr refer to the concentration of the species to be oxidized and to be reduced, respectively,
c(0,t) is the time-dependent concentration at the distance zero from the surface of the electrode.
Source officielle
À propos de ce résultat
Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.
Publications associées (1)
Cours associés (1)
ChE-407: Electrochemical engineering
This course builds upon the underlying theory in thermodynamics, reaction kinetics, and transport and applies these methods to electrosynthesis, fuel cell, and battery applications. Special focus is p