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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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