Slide 1Department of Physics and Energy
Materials and Surface Science Institute
University of Limerick
sources (e.g., wind, ocean, solar)
• Separate sizing of power and energy
•Vanadium redox system
• Negative (VII/VIII): V2+ = V3+ + e–
• Typically 1.5 mol dm-3 Vanadium or greater
• Separated by proton-conducting membrane
Traditional Method 1: Open-circuit Voltage
Positive: Eo(VV/VIV) = 1.00 V vs SHE
Negative: Eo(VIII/VII) = -0.26 V vs SHE
− Small offsets and drifts in electrodes potentials
can be equivalent to the effect of a significant
change in mixture ratio (especially for mixture
ratios close to 50%)
Traditional Method 2: Coulometry
charge is estimated
− Unequal half cell efficiencies are not
accounted for so SoC imbalance is not
detected
5
Traditional Method 3: Conductivity
− Other effects such as electrolyte dilution
and impurity levels also alter conductivity
6
Traditional Method 4: UV-visible spectroscopy
Each of the vanadium species has a
characteristic absorption spectrum
vanadium species at low concentration
− In-situ (high concentration) measurements of
vanadium IV/V mixtures display spectra that do
not correspond to the predicted values
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VIII
0.5
1.0
VII
Each of the vanadium species has a characteristic absorption spectrum
Accurate determination of concentration of each vanadium species at low concentration
8
VIV VV
200 400 600 800 0
1
2
3
min
VIV VV
200 400 600 800 0
1
2
3
−In-situ (high concentration) measurements of vanadium IV/V mixtures display spectra that
do not correspond to the predicted values
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Instantaneous measurement of SoC and vanadium concentration without knowing past operation;
Possible in-situ measurement (i.e. at high vanadium concentration) without the need for electrolyte dilution;
Easy to connect to existing systems without need for electrodes;
Greater accuracy than other techniques (e.g. conductivity and potential measurement);
Separate readings for the SoC and concentration of anolyte and catholyte;
Measurement is independent of system’s electrochemistry;
The technique does not require knowledge of concentration of vanadium.
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& Vanadium Concentration
VII+VIII Conc.
two probes.
analyse electrolyte at any
Typically for use during
vanadium redox flow battery
Concentration To be used in vehicles that store their energy
in a vanadium redox flow battery
An optical fibre probe could be placed in each
of the two ‘fuel’ tanks or in the ‘fuel’ lines
Two needles on a gauge (or some other type
of display) could show the remaining charge
so that the operator would know when to refill
Also, if the operator refilled before ‘zero
charge’ they would know how much charge
was in the electrolyte they exchange at the
filling station
of the fuel being exchanged
E