Redox Flow Battries
Redox flow batteries (RFB)
Redox
flow batteries (RFB) represent one class of electrochemical energy storage
devices. The name “redox” refers to chemical reduction and oxidation reactions
employed in the RFB to store energy in liquid electrolyte solutions which flow
through a battery of electrochemical cells during charge and discharge.
During
discharge, an electron is released via an oxidation reaction from a high
chemical potential state on the negative or anode side of the battery. The
electron moves through an external circuit to do useful work. Finally, the electron is accepted via a
reduction reaction at a lower chemical potential state on the positive or
cathode side of the battery. The direction of the current and the chemical
reactions are reversed during charging.
The
total difference in chemical potential between the chemical states of the
active elements on the two sides of the battery determines the electromotive
force (emf or voltage) generated in each cell of the battery. The voltage developed by the RFB is specific
to the chemical species involved in the reactions and the number of cells that
are connected in series. The current
developed by the battery is determined by the number of atoms or molecules of
the active chemical species that are reacted within the cells as a function of
time. The power delivered by the RFB is
the product of the total current and total voltage developed in the
electrochemical cells. The amount of
energy stored in the RFB is determined by the total amount of active chemical
species available in the volume of electrolyte solution present in the system.
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