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The Unique Features of the "Squirrel" Design
Comparison with Lead-Acid Batteries
Comparison with Other Vanadium Batteries
Preparation of the Electrolyte
Basic Principle of the Vanadium Fuel Cell
A vanadium fuel cell is an electrochemical cell divided into two compartments
by an ionic membrane with acid vanadium sulfate electrolytes in each
compartment. The electrolytes are pumped through the compartments
from two separate electrolyte tanks. The oxidation states of the vanadium
are V2+ to V3+
in the negative electrolyte and V5+ to
V4+ in the positive electrolyte. When
the electrodes of the cell are connected to an external load the differing
oxidation states of the vanadium cause an electrical current to flow
in the circuit (see Fig. 1). The electrodes, which are made of carbon,
do not participate in the chemical reactions. |
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Fig.1. A vanadium fuel cell. An electric current is produced by the
reactions V2+
--> V3+ + e- on the negative side
and V5+ + e- --> V4+
on the positive side.
These reactions are reversed when the electrolytes are recharged. |
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In the fully charged state (V2+ in the
negative electrolyte and V5+ in the positive
electrolyte) the potential across the cell is 1.6 V. In the discharged
state (V3+ and V4+)
the potential is 1.1 V. By connecting stacks of cells electrically
in series any larger voltage can be obtained
The conventional way of assembling a stack of cells is shown in Fig.
2. The cells are connected electrically in series, and the electrolytes
are fed to the cells in a parallel flow arrangement. The cells are
placed vertically and the stack extends in a horizontal direction.
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Fig.2. A conventional horizontal stack
of vertical cells. The cells are connected electrically in series.
The electrolytes are fed to the cells in parallel. |
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The storage capacity (kilowatt-hours) is determined by the quantity
of electrolytes used. The power rating (kilowatts) is determined by
the area of the electrochemical cells.
These two parameters can be sized independently over wide ranges (watts
to megawatts).
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