First, we systematically evaluated the stability of V 2 + , V 3 + , V 4 + ,
and V 5 + sulfates in H 2 SO 4 solutions. We found that the limited
stability of the vanadium sulfate solutions ( < 1.7 M V) was
determined by the low solubility of VOSO 4 at low temperatures
(−5 ° C) and the precipitation of V 2 O 5 at high temperatures
(40 ° C), which is consistent with previous studies. [13–16]
We also
studied the effect of a wide range of organic and inorganic additives.
We were not able to identify any agent that could simultaneously
stabilize all the four different vanadium cations at both
the high and low temperature boundaries.
Such conclusions led us to explore mixed electrolyte systems
in which different anions can help stabilize different cations. To
achieve this goal, we studied the stability of V 2 + , V 3 + , V 4 + , and
V 5 + chlorides in HCl solutions in a temperature range of −5 to
40 ° C. Up to 2.3 M V 2 + , V 4 + , and V 5 + chlorides were stable (i.e.,
without crystallization or precipitation) in 6 M HCl over 10 days
at all the designated temperatures. The overall stability of the
chloride solutions was determined by the solubility of V 3 + at
low temperatures. At −5 ° C, a mixture of VOCl and VCl 3 precipitated
out from 6 M HCl solutions with > 1.5 M V 3 + .
First, we systematically evaluated the stability of V 2 + , V 3 + , V 4 + ,and V 5 + sulfates in H 2 SO 4 solutions. We found that the limitedstability of the vanadium sulfate solutions ( < 1.7 M V) wasdetermined by the low solubility of VOSO 4 at low temperatures(−5 ° C) and the precipitation of V 2 O 5 at high temperatures(40 ° C), which is consistent with previous studies. [13–16] We alsostudied the effect of a wide range of organic and inorganic additives.We were not able to identify any agent that could simultaneouslystabilize all the four different vanadium cations at boththe high and low temperature boundaries.Such conclusions led us to explore mixed electrolyte systemsin which different anions can help stabilize different cations. Toachieve this goal, we studied the stability of V 2 + , V 3 + , V 4 + , andV 5 + chlorides in HCl solutions in a temperature range of −5 to40 ° C. Up to 2.3 M V 2 + , V 4 + , and V 5 + chlorides were stable (i.e.,without crystallization or precipitation) in 6 M HCl over 10 daysat all the designated temperatures. The overall stability of thechloride solutions was determined by the solubility of V 3 + atlow temperatures. At −5 ° C, a mixture of VOCl and VCl 3 precipitatedout from 6 M HCl solutions with > 1.5 M V 3 + .
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