Faradaic

Faradaic refers to electrochemical processes in which charge transfer across the electrode–electrolyte interface is accompanied by a chemical change in the participants. In a Faradaic process, electrons are exchanged between an electrode and redox-active species in solution or on the electrode surface, producing oxidation or reduction reactions. The current arising from such processes is called Faradaic current and is proportional to the rate of the redox reaction. The overall amount of substance transformed relates to the total charge passed through the system by Q = z n F, where z is the number of electrons transferred per molecule, n is the number of moles of substance involved, and F is Faraday’s constant.

Faradaic processes contrast with non-Faradaic (or capacitive) processes, where charging of the electrical double layer occurs without net chemical change. In capacitive processes the current is due to electrostatic storage rather than electron transfer in chemical reactions. In real systems, both Faradaic and non-Faradaic currents can be present; the observed current is a combination of reaction-driven charge transfer and double-layer charging.

Applications and implications: Faradaic reactions underpin electrolysis, electrodeposition, batteries, and many electrochemical sensing techniques. The kinetics and mass transport of the reacting species, as well as the electrode material and applied potential, influence the magnitude of Faradaic current. Faradaic efficiency describes the fraction of current that drives the desired chemical transformation versus side reactions. The term honors Michael Faraday, whose laws relate electrical charge to the quantity of substance transformed during electrochemical reactions.