001] The present disclosure broadly relates to a method of preparing vanadium
electrolyte and particularly refers to an electrochemical method of preparing
5 vanadium electrolyte suitable for use in all-vanadium redox flow battery (VRFB)
systems.
BACKGROUND OF INVENTION
[002] Redox flow batteries (RFBs) have received extraordinary attention due to
10 their simple operating conditions (room temperature and atmospheric pressure),
decoupled scale-up for power and energy capacity, longer cycle life than normal
secondary batteries, reduced self-discharging, excellent reliability, and safety.
vanadium redox flow battery (VRFB) is a very special kind of secondary redox
flow battery (RFB) that utilizes vanadium as an active material on the positive and
15 negative side of the electrodes, which eliminates the issue of electrolyte
contamination due to crossover of ionic species. VRFBs employ the redox couples
VO2
+
/VO2+ as catholyte and V2+/V3+ as anolyte in aqueous acid solutions stored
in two external tanks. These batteries preferably require vanadium electrolyte in
+3.5 oxidation state as a fuel for energy generation and storage operated through
20 a charge-discharge cycle.
[003] Most of the vanadium precursor materials are quite expensive. In
particular, the vanadium electrolyte constitutes a major portion of a VRFB cost.
For example, 40% to 41% of the total cost of a system of 10kW/120kWh accounts
for the cost of vanadium and electrolyte production cost (Noack, Jens, et al.
25 "Techno-economic modeling and analysis of redox flow battery
systems." Energies 9.8 (2016): 627).
[004] Generally, the hydrated form of vanadium sulphate VOSO4.xH2O is used
for preparing vanadium electrolyte for the VRFB system. Many methods, such as
electrolytic process, chemical reduction, and addition of reducing agents have
30 been proposed for synthesizing vanadium electrolyte solution for VRFB systems
3
which involve complex ways of separation of mixed electrolyte solution along
with other chemical impurities.12047319A1
[005] KR20190124865A discloses a method for preparing vanadium electrolyte
by phase transformation of ammonium metavanadate (AMV) to ammonium
polyvanadate (PMV) by carrying out a heat treatment at 230-280o
5 C temperature.
US5587132A discloses a combined route of purification and reduction of V2O5
and ammonium metavanadate (NH4NO3) followed by successive purification
steps at a temperature of 400oC-700oC to prepare a vanadium electrolyte solution.
[006] The present research in the development of vanadium electrolyte is
10 associated with many setbacks with respect to high temperature requirements,
multiple purification steps, cell damage issues, and high cost of vanadium
precursors used which further make VRFB systems an expensive option for
commercial applications. Thus, in order to address the above said problems, there
is a dire need to develop an economically viable and high-performance vanadium
15 electrolyte production process to achieve a broader acceptance of VRFBs.
SUMMARY OF THE INVENTION
[007] In first aspect of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte, the method
20 comprising: (a) contacting at least one vanadium precursor with aqueous sulfuric
acid to obtain a solution; and (b) introducing the solution into a part of an
electrochemical reactor and allowing a reaction to complete to form the vanadium
electrolyte, wherein the reactor has an operating voltage in the range of 200 mV
to 1700 mV.
25 [008] In second aspect of the present disclosure, there is provided a vanadium
redox flow battery comprising: (a) a positive half-cell containing a positive halfcell solution comprising the vanadium electrolyte; and (b) a negative half-cell
containing a negative half-cell solution comprising the vanadium electrolyte,
wherein the vanadium electrolyte is prepared by an electrochemical preparation
30 method, the method comprising: (1) contacting at least one vanadium precursor
with aqueous sulfuric acid to obtain a solution; and (2) introducing the solution
4
into a part of an electrochemical reactor and allowing a reaction to complete to
form the vanadium electrolyte, wherein the reactor has an operating voltage in the
range of 200 mV to 1700 mV.
[009] In third aspect of the present disclosure, there is provided a vanadium
5 redox flow battery comprising: (a) a positive half-cell containing a positive halfcell solution comprising the vanadium electrolyte; and (b) a negative half-cell
containing a negative half-cell solution comprising the vanadium electrolyte,
wherein the vanadium electrolyte is prepared by an electrochemical preparation
method, the method comprising: (1) contacting at least one vanadium precursor
10 with aqueous sulfuric acid to obtain a solution; and (2) introducing the solution
into a part of an electrochemical reactor and allowing a reaction to complete to
form the vanadium electrolyte, wherein the reactor has an operating voltage in the
range of 200 mV to 1700 mV, and wherein the positive half-cell solution has
vanadium concentration in the range of 1 M - 2 M and the negative half-cell
15 solution has a vanadium concentration in the range 1 M to 2 M.
[0010] These and other features, aspects, and advantages of the present subject
matter will be better understood with reference to the following description and
appended claims. This summary is provided to introduce a selection of concepts
in a simplified form. This summary is not intended to identify key features or
20 essential features of the claimed subject matter, nor is it intended to be used to
limit the scope of the claimed subject matter.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0011] The following drawings form a part of the present specification and are
included to further illustrate aspects of the present disclosure. The disclosure may
be better understood by reference to the drawings in combination with the detailed
25 description of the specific embodiments presented herein.
[0012] Figure 1 depicts the scheme of an electrochemical reactor for preparing
vanadium electrolyte, in accordance with an embodiment of the present disclosure.
5
[0013] Figure 2 depicts the scheme of a conventional vanadium redox flow battery
(VRFB) system used to utilize vanadium electrolyte, in accordance with an
embodiment of the present disclosure.
[0014] Figure 3 depicts the plot for applied voltage (V) vs time (min) data of the
5 experiment conducted in the electrochemical reactor for conversion of vanadium
pentoxide (V2O5) to V3.5+ vanadium electrolyte, in accordance with an embodiment
of the present disclosure.
[0015] Figure 4 depicts the potential (V) vs. time (h) data plot describing the
charge-discharge cycle of the conventional vanadium redox flow battery (VRFB)
10 system, in accordance with an embodiment of the present disclosure.
[0016] Figure 5 depicts the potential (V) vs capacity (Ah) data plot describing the
charge storing capacity of the conventional vanadium redox flow battery (VRFB)
system, in accordance with an embodiment of the present disclosure.
15 DETAILED DESCRIPTION OF THE INVENTION
[0017] Those skilled in the art will be aware that the present disclosure is subject
to variations and modifications other than those specifically described. It is to be
understood that the present disclosure includes all such variations and
modifications. The disclosure also includes all such steps, features, compositions,
20 and compounds referred to or indicated in this specification, individually or
collectively, and any and all combinations of any or more of such steps or features.
Definitions
[0018] For convenience, before further description of the present disclosure,
25 certain terms employed in the specification, and examples are delineated here.
These definitions should be read in the light of the remainder of the disclosure and
understood as by a person of skill in the art. The terms used herein have the
meanings recognized and known to those of skill in the art, however, for
convenience and completeness, particular terms and their meanings are set forth
30 below.
6
[0019] The articles “a”, “an” and “the” are used to refer to one or to more than
one (i.e., to at least one) of the grammatical object of the article.
[0020] The terms “comprise” and “comprising” are used in the inclusive, open
sense, meaning that additional elements may be included. It is not intended to be
5 construed as “consists of only”.
[0021] Throughout this specification, unless the context requires otherwise the
word “comprise”, and variations such as “comprises” and “comprising”, will be
understood to imply the inclusion of a stated element or step or group of element
or steps but not the exclusion of any other element or step or group of element or
10 steps.
[0022] The term “including” is used to mean “including but not limited to”.
“Including” and “including but not limited to” are used interchangeably.
[0023] Ratios, concentrations, amounts, and other numerical data may be
presented herein in a range format. It is to be understood that such range format is
15 used merely for convenience and brevity and should be interpreted flexibly to
include not only the numerical values explicitly recited as the limits of the range,
but also to include all the individual numerical values or sub-ranges encompassed
within that range as if each numerical value and sub-range is explicitly recited.
For example, a concentration range of about 1M to 2M should be interpreted to
20 include not only the explicitly recited limits of about 1M to about 2M, but also to
include sub-ranges, such as 1.1M to 1.9M, 1.3 to 1.7M, and so forth, as well as
individual amounts, including fractional amounts, within the specified ranges,
such as 1.15M, 1.24M, and 1.625M.
[0024] The term “electrolyte” used herein refers to a solid, liquid, or less
25 frequently a gaseous substance that conducts electricity by the movement of ions.
[0025] The term “trivalent vanadium” used herein refers to vanadium in +3
oxidation state.
[0026] The term “tetravalent vanadium” used herein refers to vanadium in +4
oxidation state.
30 [0027] The term “pentavalent vanadium” used herein refers to vanadium in +5
oxidation state.
7
[0028] The term “vanadium concentration” used herein refers to concentration of
vanadium in +3.5 oxidation state.
[0029] The term “carbon paper” used herein refers to flat sheets consisting of
carbon microfibers. It is a porous layer that lays between the catalyst coating layer
5 and fed gas layer.
[0030] The term “graphite felt” used herein refers to rayon or polyacrylonitrile
based soft, flexible and high temperature resistible material comprising carbon
content in the form of graphite.
[0031] The term “solid electrolyte membrane” used herein refers to a solid sheet
10 like dense porous material with proton conduction and cation exchanging
properties generally used in fuel cells. Examples include nafion 117, nafion 115,
etc.
[0032] The term “Ah” used herein refers to ampere-hour which is a unit for
specifying the storage capacity of a battery. For example, a battery of 1 Ah
15 capacity can provide a current of 1 ampere for 1 hour. 1 Ah also corresponds to
3,600 coloumbs of electric charge.
[0033] The term “coulombic efficiency” used herein refers to charge efficiency
with which electrons are transferred in batteries. It is calculated as :
ηc = (Qout/Qin) * 100
20 wherein, ηc is the coulombic efficiency %, Qout is the amount of charge that exits
a battery during a discharge cycle, and Qin is the amount of charge that enters the
battery during the charge cycle.
[0034] The term “at most 200mA/cm2
” used herein refers to any current density
more than 0 and less than 200.0. It includes current densities selected from the
range of 0.1-199.9mA/cm2
, 5-195mA/cm2
, 50-150mA/cm2
25 etc.
[0035] Ratios, concentrations, amounts, and other numerical data may be
presented herein in a range format. It is to be understood that such range format is
used merely for convenience and brevity and should be interpreted flexibly to
include not only the numerical values explicitly recited as the limits of the range,
30 but also to include all the individual numerical values or sub-ranges encompassed
within that range as if each numerical value and sub-range is explicitly recited.
8
[0036] Unless defined otherwise, all technical and scientific terms used herein
have the same meaning as commonly understood by one of ordinary skill in the
art to which this disclosure belongs. Although any methods and materials similar
or equivalent to those described herein can be used in the practice or testing of the
5 disclosure, the preferred methods, and materials are now described. All
publications mentioned herein are incorporated herein by reference.
[0037] The present disclosure is not to be limited in scope by the specific
embodiments described herein, which are intended for the purposes of
exemplification only. Functionally-equivalent products, compositions, and
10 methods are clearly within the scope of the disclosure, as described herein.
[0038] As discussed in the background of the present disclosure, vanadium
electrolyte for VRFB systems can be produced by an electrolytic process and/or a
chemical reduction process, and/or a process requiring the addition of reducing
compounds, however, such methods are energy intensive, time taking and
15 complicated. Most of the processes result in a mixed electrolyte that requires
further processing before it is used in a VRFB. Some of the conventionally used
methods also require additional liquid and/or solid chemical/reducing agent,
which circulates in the VRFB system as an impurity even after purification. In
other processes, high temperature operation is also needed along with liquid/solid
20 chemicals/reducing agents which make the reactant synthesis process more
complicated and costlier for synthesizing vanadium electrolyte solution using
V2O5 for VRFB system.
[0039] To address the problems mentioned above, the present disclosure provides
an electrochemical preparation method for a vanadium electrolyte, the method
25 comprising: (a) contacting at least one vanadium precursor with aqueous sulfuric
acid to obtain a solution; and (b) introducing the solution into a part of an
electrochemical reactor and allowing a reaction to complete to form the vanadium
electrolyte, wherein the reactor has an operating voltage in the range of 200 mV
to 1700 mV.
30 [0040] The present disclosure discloses a simple one-step electrochemical
preparation method, which uses vanadium pentoxide (V2O5) in sulphuric acid
9
solution. Since the cost of conventionally used VOSO4.xH2O is much higher than
vanadium pentoxide (V2O5) powder, preparation of low-cost vanadium electrolyte
from V2O5 powder strengthens the practical use of VRFB system of the present
disclosure. Moreover, the major disadvantage related to the low solubility of V2O5
5 which prevents direct production of its high concentration solutions has been
overcome in the present disclosure by employing an electrochemical preparation
methodto achieve maximum dissolution of V2O5. The reaction involved in the
reduction of vanadium precursor V2O5 having vanadium in +5 oxidation state to
VO2+ and V3+ having vanadium in +4 and +3 oxidation states respectively is as
10 below:
V2O5 + 2H+
2VO2
+ + H2O
VO2
+ + 2H+ + e-
VO2+ + H2O
VO2+ + 2H+ + e- V
3+ + H2O
[0041] The reactions (ii) and (iii) are fine tuned in order to obtain VO2+ and V3+
15 aqueous solution in equimolar concentrations so to account for the formation of
pure V3.5+ electrolyte. The vanadium (V
3.5+) electrolyte solution obtained in the
process does not need any separation or purification step as the process does not
require any liquid and/or solid chemical/reducing agent to be added. The obtained
V
3.5+ can directly be used in all-vanadium redox flow battery or hybrid vanadium
20 redox flow battery systems. The process does not require any elevated temperature
and is energy efficient. The present disclosure substantiates the efficiency of
electrochemical preparation method of vanadium electrolyte in terms of a less
complicated, cost efficient, easily scalable, energy feasible due to low
overpotential, minimized electrode etching, as well as a less time taking process
25 due to fast reaction.
[0042] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte, the method
comprising: (a) contacting at least one vanadium precursor with aqueous sulfuric
acid to obtain a solution; and (b) introducing the solution into a part of an
30 electrochemical reactor and allowing a reaction to complete to form the vanadium
10
electrolyte, wherein the reactor has an operating voltage in the range of 200 mV
to 1700 mV.
[0043] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte, the method
5 comprising: (a) contacting at least one vanadium precursor with aqueous sulfuric
acid to obtain a solution; and (b) introducing the solution into a part of an
electrochemical reactor and allowing a reaction to complete to form the vanadium
electrolyte, wherein the reactor has an operating voltage in the range of 200 mV
to 1700 mV, and wherein the vanadium electrolyte is an equimolar mixture of
10 trivalent vanadium and tetravalent vanadium in sulfuric acid.
[0044] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte, the method
comprising: (a) contacting at least one vanadium precursor with aqueous sulfuric
acid to obtain a solution having pentavalent vanadium; and (b) introducing the
15 solution into a part of an electrochemical reactor and allowing a reaction to
complete to form the vanadium electrolyte, wherein the reactor has an operating
voltage in the range of 200 mV to 1700 mV. In another embodiment of the present
disclosure, the pentavalent vanadium is provided by V2O5 powder.
[0045] In an embodiment of the present disclosure, there is provided an
20 electrochemical preparation method for a vanadium electrolyte as described
herein, wherein the at least one vanadium precursor is V2O5 powder. In another
embodiment of the present disclosure, V2O5 powder has a maximum particle size
of 500 microns.
[0046] In an embodiment of the present disclosure, there is provided an
25 electrochemical preparation method for a vanadium electrolyte, the method
comprising: (a) contacting at least one vanadium precursor with aqueous sulfuric
acid to obtain a solution is carried out at a temperature in the range of 15 to 30 oC
and at atmospheric pressure of 1.01 bar; and (b) introducing the solution into a
part of an electrochemical reactor and allowing a reaction to complete to form the
30 vanadium electrolyte, wherein the reactor has an operating voltage in the range of
200 mV to 1700 mV.
11
[0047] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte, the method
comprising: (a) contacting at least one vanadium precursor with aqueous sulfuric
acid to obtain a solution is carried out at a temperature in the range of 15 to 30 oC
5 and at atmospheric pressure of 1.01 bar, wherein at least one vanadium precursor
is vanadium pentoxide powder; and (b) introducing the solution into a part of an
electrochemical reactor and allowing a reaction to complete to form the vanadium
electrolyte, wherein the reactor has an operating voltage in the range of 200 mV
to 1700 mV.
10 [0048] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte, the method
comprising: (a) contacting at least one vanadium precursor with aqueous sulfuric
acid to obtain a solution is carried out at a temperature in the range of 15 to 30 oC
and at atmospheric pressure of 1.01 bar, wherein at least one vanadium precursor
15 is vanadium pentoxide powder, and wherein the aqueous sulfuric acid has a
concentration in the range of 4 M – 8 M; and (b) introducing the solution into a
part of an electrochemical reactor and allowing a reaction to complete to form the
vanadium electrolyte, wherein the reactor has an operating voltage in the range of
200 mV to 1700 mV. In another embodiment of the present disclosure, the
20 aqueous sulfuric acid has a concentration in the range of 4 M – 6 M. In another
embodiment of the present disclosure, the aqueous sulfuric acid has a
concentration in the range of 4 M – 5 M.
[0049] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
25 herein, wherein the at least one vanadium precursor has a weight percentage in the
range of 7 % - 14 % with respect to the solution.
[0050] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
herein, wherein introducing the solution into a part of the electrochemical reactor
30 and allowing a reaction to complete to form the vanadium electrolyte is carried
out a temperature in the range of 40-50oC.
12
[0051] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
herein, wherein the reactor is operated at a current density of at most 200mA/cm2
.
[0052] In an embodiment of the present disclosure, there is provided an
5 electrochemical preparation method for a vanadium electrolyte as described
herein, wherein the electrochemical reactor comprises: (i) a catalyst coated anode
made up of carbon paper; (ii) a cathode made up of a material selected from carbon
paper/felt or graphite felt; and (iii) a solid electrolyte membrane, wherein the
cathode is fed with the solution and the catalyst coated anode is fed with hydrogen
10 gas.
[0053] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
herein, wherein the electrochemical reactor comprises: (i) a catalyst coated anode
made up of carbon paper; (ii) a cathode made up of graphite felt with a pore size
15 in the range of 10-100 micrometers; and (iii) a solid electrolyte membrane,
wherein the cathode is fed with the solution and the catalyst coated anode is fed
with hydrogen gas.
[0054] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
20 herein, wherein the electrochemical reactor comprises: (i) a catalyst coated anode
made up of carbon paper; (ii) a cathode made up of a material selected from carbon
paper/felt or graphite felt; and (iii) a solid electrolyte membrane, wherein the
cathode is fed with the solution and the catalyst coated anode is fed with hydrogen
gas at a pressure of 1 atm.
25 [0055] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
herein, wherein the electrochemical reactor comprises: (i) a catalyst coated anode
made up of carbon paper, wherein the catalyst is selected from platinum-based
catalyst, ruthenium-based catalyst, or palladium-based catalyst; (ii) a cathode
30 made up of a material selected from carbon paper/felt or graphite felt; and (iii) a
13
solid electrolyte membrane, wherein the cathode is fed with the solution and the
catalyst coated anode is fed with hydrogen gas.
[0056] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
5 herein, wherein the electrochemical reactor comprises: (i) a catalyst coated anode
made up of carbon paper; (ii) a cathode made up of a material selected from carbon
paper/felt or graphite felt; and (iii) a solid electrolyte membrane selected from a
group consisting of nafion 117, nafion 115, and combinations thereof, wherein the
cathode is fed with the solution and the catalyst coated anode is fed with hydrogen
10 gas.
[0057] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
herein, wherein the electrochemical reactor comprises: (i) a catalyst coated anode
made up of carbon paper, wherein the catalyst is selected from platinum-based
15 catalyst, ruthenium-based catalyst, or palladium-based catalyst; (ii) a cathode
made up of a material selected from carbon paper/felt or graphite felt with a pore
size in the range of 10-100 micrometers; and (iii) a solid electrolyte membrane
selected from a group consisting of nafion 117, nafion 115, and combinations
thereof, wherein the cathode is fed with the solution and the catalyst coated anode
20 is fed with hydrogen gas at a pressure of 1 atm.
[0058] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
herein, wherein the vanadium electrolyte is suitable for use in a vanadium redox
flow battery without further reduction.
25 [0059] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
herein, wherein the electrochemical reactor comprises: (i) a catalyst coated anode
made up of carbon paper; (ii) a cathode made up of a material selected from carbon
paper/felt or graphite felt with a pore size in the range of 10-100 micrometers; and
30 (iii) a solid electrolyte membrane, wherein the cathode is fed with the solution and
the catalyst coated anode is fed with hydrogen gas, and wherein the vanadium
14
electrolyte is suitable for use in a vanadium redox flow battery without further
reduction.
[0060] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
5 herein, wherein the electrochemical reactor comprises: (i) a catalyst coated anode
made up of carbon paper; (ii) a cathode made up of a material selected from carbon
paper/felt or graphite felt with a pore size in the range of 10-100 micrometers; and
(iii) a solid electrolyte membrane, wherein the cathode is fed with the solution and
the catalyst coated anode is fed with hydrogen gas, and wherein the vanadium
10 electrolyte has a total vanadium concentration in the range of 1 M to 2 M with
respect to the vanadium electrolyte. In another embodiment of the present
disclosure, the vanadium electrolyte has a total vanadium concentration in the
range of 1.3 M to 1.7 M with respect to the vanadium electrolyte.
[0061] In an embodiment of the present disclosure, there is provided an
15 electrochemical preparation method for a vanadium electrolyte as described
herein, wherein the vanadium electrolyte has a total vanadium concentration in
the range of 1 M to 2 M with respect to the vanadium electrolyte. In another
embodiment of the present disclosure, the vanadium electrolyte has a total
vanadium concentration in the range of 1.3 M to 1.7 M with respect to the
20 vanadium electrolyte.
[0062] In an embodiment of the present disclosure, there is provided an
electrochemical preparation method for a vanadium electrolyte as described
herein, wherein the vanadium electrolyte is prepared in a time period in the range
80 – 150 minutes. In another embodiment of the present disclosure, the vanadium
25 electrolyte is prepared in a time period in the range 82 – 110 minutes. In another
embodiment of the present disclosure, the vanadium electrolyte is prepared in a
time period in the range 83 – 90 minutes.
[0063] In an embodiment of the present disclosure, there is provided a vanadium
redox flow battery comprising: (a) a positive half-cell containing a positive half30 cell solution comprising the vanadium electrolyte prepared by the method as
described herein; and (b) a negative half-cell containing a negative half-cell
15
solution comprising the vanadium electrolyte prepared by the method as described
herein.
[0064] In an embodiment of the present disclosure, there is provided a vanadium
redox flow battery comprising: (a) a positive half-cell containing a positive half5 cell solution comprising the vanadium electrolyte prepared by the method as
described herein, wherein the positive half-cell solution has vanadium
concentration in the range of 1 M - 2 M; and (b) a negative half- cell containing a
negative half-cell solution comprising the vanadium electrolyte prepared by the
method as described herein, wherein the negative half-cell solution has a
10 vanadium concentration in the range 1 M to 2 M.
[0065] Although the subject matter has been described in considerable detail with
reference to certain examples and implementations thereof, other implementations
are possible.
15 EXAMPLES
[0066] The disclosure will now be illustrated with working examples, which is
intended to illustrate the working of disclosure and not intended to take
restrictively to imply any limitations on the scope of the present disclosure. Unless
defined otherwise, all technical and scientific terms used herein have the same
20 meaning as commonly understood to one of ordinary skill in the art to which this
disclosure belongs. Although methods and materials similar or equivalent to those
described herein can be used in the practice of the disclosed methods and
compositions, the exemplary methods, devices and materials are described herein.
It is to be understood that this disclosure is not limited to particular methods, and
25 experimental conditions described, as such methods and conditions may apply.
[0067] The working examples as depicted in the forthcoming sections highlight
the process to the reduction of vanadium precursor V2O5 having vanadium in +5
to V3.5+ electrolytic solution in an electrochemical reactor and further evaluates
the performance of a conventional VRFB system utilizing the prepared vanadium
30 electrolyte of the present disclosure.
16
Materials and Methods
[0068] For the purpose of the present disclosure, vanadium pentoxide (V2O5)
powder was procured from of up to 99.9% purity. The sulfuric acid solution used
for dissolving V2O5 powder was obtained from. The objectives and benefits of the
5 present method of the disclosure are made clear with the help of accompanying
Figures 1 and 2. Figure 1 depicts an electrochemical reactor that is used for
preparing the vanadium electrolyte of the present disclosure. Figure 2 depicts a
conventional vanadium redox flow battery (VRFB) system which further utilizes
the prepared vanadium electrolyte for electrical energy storing purpose.
10
Scheme for the electrochemical reactor for preparing vanadium electrolyte
[0069] Figure 1 reveals a labelled scheme of an electrochemical reactor employed
for preparing a vanadium electrolyte in a continuous manner by reduction of a
vanadium precursor solution. The labelled scheme is described using the
15 following designators : 1: dissolution vessel; 2: pump; 3: membrane; 4: catalyst
coated gas diffusion layer; 5, 6, 7, 8: gaskets; 9: anodic graphite plate; 10: cathodic
graphite plate; 11: hydrogen gas inlet; 12: hydrogen gas outlet; 13: feed inlet; 14:
electrolyte outlet; 15: carbon electrode; and 16: cathode chamber of the
electrochemical cell.
20 [0070] Vanadium precursor solution was prepared by dissolving a definite
amount of V2O5 powder in sulphuric acid solution. The dissolved vanadium
pentoxide solution was sent to the electrochemical reactor having an anode,
cathode, and a solid electrolyte membrane. The anode was made up of carbon
paper with a platinum catalyst coated hydrogen gas diffusion layer positioned in
25 close proximity with the Nafion-117 solid electrolyte membrane. The cathode was
made up of thermally treated graphite felt having a pore size in the range of 10-
100 micrometers. It was separated from the membrane by a cathode chamber to
accommodate the flow of the precursor solution. The dissolved solution
containing V2O5 precursor was circulated through the cathode chamber of the
30 electrochemical cell with the help of a pump. The continuous circulation was done
in order to collect vanadium electrolyte having vanadium in +3.5 oxidation state
17
in a pure form so that it can directly be used in a VRFB system without further
reduction or purification.
Scheme of a conventionally used vanadium redox flow battery (VRFB)
5 system for utilizing the prepared vanadium electrolyte
[0071] Figure 2 reveals a labelled scheme of a conventionally used vanadium
redox flow battery system employed to utilize the prepared vanadium electrolyte
in order to substantiate its performance in electrical energy storage for the purpose
of the present disclosure. The labelled scheme is described using the following
10 designators: 17, 18: graphite felt electrode; 19: positive electrolyte tank; 20:
negative electrolyte tank; 21, 22: pumping device; 23: membrane; 24: source/load.
The prepared vanadium V
3.5+ electrolyte was stored in the positive and negative
electrolyte tanks from where it was pumped through the pumping device to act as
a reactant at both cathode and anode. The concentration of the fed vanadium
15 electrolyte remained 1.5M at all times in the process. The VRFB was then
operated in charging mode and discharging mode, as generally done in any
secondary battery. The synthesized energy was stored in the source/load in the
form of electrical energy which can be utilized for further applications.
[0072] The efficiency of the electrochemical reactor in producing vanadium
20 electrolyte is depicted in Example 1. Example 2 and 3 depict the performance of
produced vanadium electrolyte in terms of stored voltage in charge-discharge
cycle and charge storing capacity of the VRFB system respectively.
EXAMPLE 1
25 Method for preparation of vanadium electrolyte
[0073] Vanadium precursor solution was prepared by dissolving vanadium
pentoxide (V2O5) powder in sulfuric acid solution at ambient conditions of 15-
30oC temperature and 1.01 bar pressure. V2O5 powder (~13.77 g) was dissolved
in a suitable volume (~ 95 mL) of 4.0 M H2SO4 to prepare 100 mL of total solution
30 comprising pentavalent vanadium. The total concentration of vanadium in the 100
mL solution was 1.5 M which contributes to 13.77% (w/v) in the vanadium
18
electrolyte. The reduction of pentavalent vanadium was carried out in the
electrochemical reactor operated at 40-50oC temperature. A constant current was
applied at the DC source at a current density of 200 mA/cm2
and with a voltage
window of 200 mV to 1700 mV. It can be derived from the voltage vs time data
5 as revealed in Figure 3 that the experiment was completed within 84 minutes of
increasing the potential starting from 200 mV up to 1700 mV. A vanadium
electrolyte containing vanadium in 3.5+ oxidation state in a total concentration of
1.5M was obtained.
10 EXAMPLE 2
Utilization of vanadium electrolyte in a conventional vanadium redox flow
battery (VRFB) system
[0074] The vanadium electrolyte prepared in Example 1 was subjected to a
conventional VRFB system as provided in Figure 2. Figure 4 reveals the charging15 discharging cycle observed in the VRFB system with 1.5M vanadium electrolyte
in the potential limit of 1000 mV to 1700 mV. In the beginning, charging of VRFB
with an opening voltage of 1470 mV up to 1700 mV was observed. Thereafter,
the portion of the curve represents the discharging of VRFB with an opening
voltage of 1290 mV which falls with the course of discharging to a limit of 1000
20 mV. Figure 5 reveals potential (V) vs. capacity (Ah) data of VRFB as recorded
with 1.5M vanadium electrolyte substantiating the charge storage capacity of the
battery. The upper curve represents charging of VRFB to a potential limit of 1700
mV, where the battery achieves a capacity of 0.92Ah. On discharging this battery
with the lower potential window of 1000 mV (represented by the bottom curve),
25 the battery discharges to a capacity of 0.85Ah. The battery operates with a
coulombic efficiency of ~93%.
[0075] In light of the examples as described herein, the selection of present
disclosure is to provide a simple one-step electrochemical preparation method to
prepare low-cost vanadium electrolyte without using reducing agents while
30 avoiding electrolytic etch or corrosion of the electrodes in use. It is also an object
of the present disclosure to provide a vanadium electrolyte solution that can be
19
further applied in all-vanadium redox flow battery or hybrid vanadium redox flow
battery systems to efficiently generate electrical energy for storage purposes.
[0076] However, the example has been shown and described with reference to
certain preferred embodiments, it is obvious for a person skilled in the art to arrive
5 at various modifications and changes with respect to some or all mentioned
embodiments without deviating from the spirit and scope of the invention and
compromising on the advantageous aspects of the present disclosure.
Advantages of the present disclosure
10 [0077] The present disclosure discloses an electrochemical preparation method
for a vanadium electrolyte wherein the vanadium electrolyte is prepared by the
one-step process of subjecting the vanadium precursor solution to the
electrochemical reactor. The vanadium precursor selected is a low-cost vanadium
pentoxide powder in comparison to conventionally used vanadium sulphate
15 precursor. In electrochemical systems, high purity is important, therefore,
vanadium pentoxide powder taken was of 99.9% purity. Owing to its
electrochemical nature, the vanadium electrolyte preparation method achieves
maximum dissolution of vanadium pentoxide without applying elevated
temperatures, which makes it a safer and an energy efficient process in comparison
20 to processes at high temperature. The main advantage of the present disclosure
lies in the complete elimination of any successive purification or separation steps
as the reduction process is carried without including the addition of reducing
agents. Moreover, H2 reduction is a thermodynamically more favorable process
than water electrolysis and does not need high potentials. Since carbon-based
25 material generally corrodes over 1700 mV, the present disclosure operates at much
lower potential difference, which is a safe operating voltage window for electrode
health. Further, at the anodic side of the electrochemical reactor, platinum with
carbon paper is used to facilitate a fast splitting reaction of H2 gas. It is a
continuous process and can be scaled up very easily. The present disclosure also
30 discloses appreciable energy storage capacity and coulombic efficiency of the
20
prepared vanadium electrolyte when employed in the vanadium flow redox battery
system.

We Claim:

1) An electrochemical preparation method for a vanadium electrolyte, the
method comprising:
(a) contacting at least one vanadium precursor with aqueous sulfuric acid
5 to obtain a solution; and
(b) introducing the solution into a part of an electrochemical reactor and
allowing a reaction to complete to form the vanadium electrolyte,
wherein the reactor has an operating voltage in the range of 200 mV to
1700 mV.
10 2) The method as claimed in claim 1, wherein the vanadium electrolyte is an
equimolar mixture of trivalent vanadium and tetravalent vanadium in
sulfuric acid.
3) The method as claimed in claim 1, wherein the solution has pentavalent
vanadium.
15 4) The method as claimed in claim 1, wherein contacting at least one
vanadium precursor with aqueous sulfuric acid to obtain a solution is
carried out at a temperature in the range of 15 to 30 oC and at atmospheric
pressure of 1.01 bar.
5) The method as claimed in claim 1, wherein the at least one vanadium
20 precursor is vanadium pentoxide powder.
6) The method as claimed in claim 1, wherein the aqueous sulfuric acid has
a concentration in the range of 4 M – 8 M.
7) The method as claimed in claim 1, wherein the at least one vanadium
precursor has a weight percentage in the range of 7 % - 14 % with respect
25 to the solution.
8) The method as claimed in claim 1, wherein introducing the solution into a
part of the electrochemical reactor and allowing a reaction to complete to
form the vanadium electrolyte is carried out a temperature in the range of
40-50oC.
30 9) The method as claimed in claim 1, wherein the reactor is operated at a
current density of at most 200mA/cm2
.
22
10) The method as claimed in claim 1, wherein the electrochemical reactor
comprises:
(i) a catalyst coated anode made up of carbon paper;
(ii) a cathode made up of a material selected from carbon paper/felt
5 or graphite felt; and
(iii) a solid electrolyte membrane,
wherein the cathode is fed with the solution and the catalyst coated anode
is fed with hydrogen gas.
11) The method as claimed in claim 9, wherein the graphite felt has a pore size
10 in the range of 10-100 micrometers.
12) The method as claimed in claim 9, wherein hydrogen gas is fed at a
pressure of 1 atm.
13) The method as claimed in claim 9, wherein the catalyst is selected from
platinum-based catalyst, ruthenium-based catalyst, or palladium-based
15 catalysts.
14) The method as defined in any one of the claim 1 – 12, wherein the
vanadium electrolyte is suitable for use in a vanadium redox flow battery
without further reduction.
15) The method as claimed in any one of the claims 1 – 12, wherein the
20 vanadium electrolyte has a total vanadium concentration in the range of 1
M to 2 M with respect to the vanadium electrolyte.
16) The method as claimed in any one of the claims 1 – 12, wherein the
vanadium electrolyte is prepared in a time period in the range 80 – 150
minutes.
25 17) A vanadium redox flow battery comprising:
(a) a positive half-cell containing a positive half-cell solution comprising
the vanadium electrolyte prepared by the method as claimed in any one
of the claims 1- 15; and
(b) a negative half-cell containing a negative half-cell solution comprising
30 the vanadium electrolyte prepared by the method as claimed in any one
of the claims 1- 15.
23
18) A vanadium redox flow battery as claimed in claim 16, wherein the
positive half-cell solution has vanadium concentration in the range of 1 M
- 2 M and the negative half-cell solution has a vanadium concentration in
the range 1 M to 2 M.