U.S. patent application number 15/396897 was filed with the patent office on 2018-07-05 for method of enhancing efficiency of carbon felts in flow battery through sonication.
The applicant listed for this patent is Institute of Nuclear Energy Research, Atomic Energy Council, Executive Yuan, R.O.C.. Invention is credited to Heng-Wei Chiang, Yi-Sin Chou, Ning-Yih Hsu, Chao-Yen Kuo.
Application Number | 20180187368 15/396897 |
Document ID | / |
Family ID | 62708952 |
Filed Date | 2018-07-05 |
United States Patent
Application |
20180187368 |
Kind Code |
A1 |
Chou; Yi-Sin ; et
al. |
July 5, 2018 |
Method of Enhancing Efficiency of Carbon Felts in Flow Battery
through Sonication
Abstract
A method is provided to enhance efficiency of carbon felts in a
flow battery. The carbon felts are directly immersed in a mixed
acid solution. The carbon felts with the solution are heated at a
low temperature and processed through sonication. On surface
defects of the carbon felts, --OH and C.dbd.O functional groups are
efficiently generated. The functional groups catalyze the redox
reaction of vanadium ions. More active positions are obtained on
the carbon felts through the activation treatment. Both of valence
exchange and redox velocity of the vanadium ions are enhanced.
Thus, the present invention has simple and fast processes with
easily regulated experimental parameters for good modification
without high temperature treatment but low cost.
Inventors: |
Chou; Yi-Sin; (New Taipei
city, TW) ; Chiang; Heng-Wei; (Taoyuan city, TW)
; Kuo; Chao-Yen; (Taoyuan city, TW) ; Hsu;
Ning-Yih; (Keelung city, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Institute of Nuclear Energy Research, Atomic Energy Council,
Executive Yuan, R.O.C. |
Taoyuan City |
|
TW |
|
|
Family ID: |
62708952 |
Appl. No.: |
15/396897 |
Filed: |
January 3, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 8/188 20130101;
Y02E 60/50 20130101; D06M 10/02 20130101; D06M 2101/40 20130101;
H01M 8/0234 20130101; D06M 11/55 20130101; D06M 10/06 20130101;
D06M 11/64 20130101; Y02E 60/528 20130101 |
International
Class: |
D06M 10/02 20060101
D06M010/02; H01M 8/18 20060101 H01M008/18; H01M 4/96 20060101
H01M004/96; D06M 11/55 20060101 D06M011/55; D06M 11/65 20060101
D06M011/65 |
Claims
1. A method of enhancing efficiency of carbon felts in a flow
battery through sonication, comprising steps of: (a) immersing a
plurality of carbon felts in a mixed acid solution; processing
heating and sonication; and, then, washing said carbon felts with
ultrapure water and drying said carbon felts; (b) obtaining said
carbon felts after being processed with said sonication to be made
into a positive electrode and a negative electrode; and assembling
a cell stack with said positive electrode and said negative
electrode; (c) filling an electrolyte into said cell stack by two
pumps, said electrolyte comprising 1 mole (M) to 3M of vanadyl
sulfate and an aqueous solution of 1M to 5M of inorganic acid;
under a flow rate controlled between 20 and 100 milliliters per
minute (mL/min), flowing said electrolyte through an anode inlet
and a cathode inlet to be uniformly in contact with said positive
electrode and said negative electrode which are made of said carbon
felts; flowing said electrolyte through an anode outlet and a
cathode outlet and said anode inlet and said cathode inlet to be
collected in a positive electrolyte container and a negative
electrolyte container; recycling said electrolyte to be pumped into
said cell stack again through said anode inlet and said cathode
inlet until air in said cell stack is completely expelled; and (d)
connecting an external power supply to said positive electrode and
said negative electrode; conducting a current of 1.about.2 amperes
(A) under a constant-current mode with a cut-off voltage of 1.6
volts (V); processing charging and discharging operations in said
cell stack; and repeating said charging and discharging operations
until charge ends.
2. The method according to claim 1, wherein, in step (a), said
mixed acid solution has a volume ratio of 3:1 of sulfuric acid to
nitric acid.
3. The method according to claim 1, wherein, in step (a), said
heating is processed to a temperature of 55.about.85.degree. C.
and, then, said sonication is processed for 10.about.90 min.
4. The method according to claim 1, wherein, in step (b), said cell
stack comprises a proton exchange membrane; two gaskets, said two
gaskets clipping said proton exchange membrane; two electrodes,
said two electrodes clipping said two gaskets, said two electrodes
being said positive electrode and said negative electrode, said two
electrodes being made of said carbon felt; two flow plates, said
two flow plate clipping said two electrodes, one of said two flow
plates having an anode inlet and a cathode inlet, another one of
said two flow plates having an anode outlet and a cathode outlet;
and two end plates, said two end plates clipping said two flow
plates.
5. The method according to claim 1, wherein, in step (c), said
inorganic acid is selected from a group consisting of sulfuric
acid, hydrochloric acid, nitric acid and phosphoric acid.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to carbon felt; more
particularly, relates to directly immersing carbon felts in a mixed
acid solution to be heated at a low temperature and processed
through sonication, where --OH and C.dbd.O functional groups are
efficiently generated on surface defects of the carbon felts during
modification.
DESCRIPTION OF THE RELATED ARTS
[0002] Electrochemical flow battery, also known as redox flow
battery, is an electrochemical energy storage device. Therein,
those which use vanadium salt solution for positive and negative
electrodes are called vanadium redox flow battery. The vanadium
redox flow battery is ideal as a green-energy storage device
because it has excellent charge and discharge performance, low cost
and long life and its manufacture, use and dispose do not generate
harmful material.
[0003] A general flow of its electrochemical reactions is shown in
FIG. 5, where a three-electrode configuration is used for redox
reaction with voltage conducted, comprising the following
steps:
[0004] (1) Step 51: An unmodified carbon felt is obtained as a
negative electrode; a titanium plate (or a graphite plate) is
obtained as a positive electrode; a solution of 1 mole (M) sulfuric
acid is obtained as an electrolyte; and a voltage or a current is
conducted for processing electrochemical oxidation.
[0005] (2) Step 52: The reactions are processed for a few minutes
to an hour.
[0006] (3) Step 53: After processing washing with deionized water,
vacuum drying is processed at a temperature of 120 celsius degrees
(.degree. C.) for 5 hours.
[0007] (4) Step 54: The electrodes are used for assembling a cell
stack of the flow battery.
[0008] (5) Step 55: A new solution is pumped into the flow battery,
where the solution contains 1M to 3M of vanadyl sulfate and 1M to
5M of sulfuric acid (or hydrochloric acid or nitric acid or
phosphoric acid.) The solution flows in through an anode inlet and
a cathode inlet to be uniformly in contact with the unmodified
carbon felt at a flow rate controlled between 20 and 100
milliliters per minute (mL/min). The solution flows out through an
anode outlet and a cathode outlet to be collected with electrolyte
containers. Then, the solution flows back to the cell stack through
the anode inlet and the cathode inlet to be recycled repeatedly
until air in the cell stack is completely expelled out.
[0009] (6) Step 56: The positive and negative electrodes are
connected with an external power supply to conduct a current in a
constant-current mode for charging the cell stack through repeated
charging and discharging operations.
[0010] However, the prior art uses the noble metal titanium, whose
cost is high. A long time (about 6 hours) is required to process
the above step 51 to step 53 for obtaining a single cell. If 10
pieces of single cells are used for assembling the cell stack, the
above steps need to be repeated for 10 times--it is time-consuming.
Because this method is used for single cell only, each single cell
obtained through the repeated procedure may be inconsistent owing
to external environment and the procedure is too complicated to be
effectively commercialized. In addition, the carbon felts used in
this traditional electrochemical oxidation method can not be fully
in contact with the electrolyte. Hydrogen and oxygen bubbles may be
generated as byproducts on surfaces of the electrodes made of the
carbon felts when they are immersed in the electrolyte. Because the
carbon felts are porous, there will be some areas that are not
uniformly in contact with the electrolyte for processing the
electrochemical reaction and, therefore, efficiency of the flow
battery can not be effectively improved. Moreover, the traditional
acid treatment method needs to set up equipments for heating,
refluxing and condensing; the reaction time may take up to several
hours or more; the procedure is complicated and needs to be
operated at a high temperature and a high pressure; and, the energy
consumption required for production is relatively high.
[0011] Besides, the traditional method of electrochemical oxidation
for modifying carbon felts uses three-electrode configuration,
where voltage is conducted for processing redox reaction to form
functional groups on surfaces of the carbon felts. After the
modification of the carbon felts is completed, a flow battery is
assembled with the modified carbon felts followed by charging and
discharging operations of the battery. The traditional
electrochemical oxidation method can not make the carbon felts
sufficiently and fully in contact with the electrolyte. It is
because that, when the carbon felts are immersed in the
electrolyte, side reactions of the electrolyte may happen to
generate hydrogen and oxygen bubbles on surfaces of the electrodes.
Because the carbon felts are porous, there will be some areas that
are not uniformly in contact with the electrolyte for processing
the electrochemical reaction and, therefore, efficiency of the flow
battery can not be effectively improved. Another electrochemical
oxidation method directly puts carbon felts in a flow battery. A
voltage is conducted through a mixed acid solution to modify the
carbon felts. After the modification is finished, the mixed acid
solution is replaced by a vanadium electrolyte to obtain a vanadium
flow battery. Thus, the electrochemical oxidation method for
directly modifying the carbon felts is simple, but extra power is
required while graphite plates may be easily worn out. Sonication
is another method for modifying carbon felts. After the carbon
felts is modified through sonication at first, a flow battery is
assembled with the modified carbon felts. Although the procedure is
a little complicated, the carbon felts are sufficiently and fully
in contact with the electrolyte to obtain a better performance.
Under a current density of 80 milliamperes per square centimeters
(mA/cm.sup.2), cycles of charging and discharging a single cell of
flow battery with carbon felts modified through the above two
methods are processed. The charging and discharging operations
using the carbon felts modified through sonication has an energy
efficiency of 80%; and, those using the carbon felts modified
through electrochemical oxidation has an energy efficiency of 70%
only.
[0012] Hence, the prior arts do not fulfill all users' requests on
actual use.
SUMMARY OF THE INVENTION
[0013] The main purpose of the present invention is to directly
immerse carbon felts in a mixed acid solution to be heated at a low
temperature and processed through sonication, where --OH and
C.dbd.O functional groups are efficiently generated on surface
defects of the carbon felts during modification.
[0014] Another purpose of the present invention is to obtain simple
and fast processes with easily regulated experimental parameters
for good modification without high temperature treatment but with
low cost.
[0015] Another purpose of the present invention is to increase
efficiencies (coulomb efficiency, energy efficiency and voltage
efficiency) of a flow battery by modifying carbon felts through
sonication.
[0016] To achieve the above purposes, the present invention is a
method of enhancing efficiency of carbon felts in a flow battery
through sonication, comprising steps of: (a) immersing a plurality
of carbon felts in a mixed acid solution; processing heating and
sonication; and, then, washing the carbon felts with ultrapure
water and drying the carbon felts; (b) obtaining the carbon felts
after being processed with the sonication to be made into a
positive electrode and a negative electrode; and assembling a cell
stack with the positive electrode and the negative electrode; (c)
filling an electrolyte into the cell stack by two pumps, the
electrolyte comprising 1 mole (M) to 3M of vanadyl sulfate and an
aqueous solution of 1M to 5M of inorganic acid; under a flow rate
controlled between 20 and 100 milliliters per minute (mL/min),
flowing the electrolyte through an anode inlet and a cathode inlet
to be uniformly in contact with the positive electrode and the
negative electrode which are made of the carbon felts; flowing the
electrolyte through an anode outlet and a cathode outlet and the
anode inlet and the cathode inlet to be collected in a positive
electrolyte container and a negative electrolyte container;
recycling the electrolyte to be pumped into the cell stack again
through the anode inlet and the cathode inlet until air in the cell
stack is completely expelled; and (d) connecting an external power
supply to the positive electrode and the negative electrode;
conducting a current of 1.about.2 amperes (A) under a
constant-current mode with a cut-off voltage of 1.6 volts (V);
processing charging and discharging operations in the cell stack;
and repeating the charging and discharging operations until charge
ends. Accordingly, a novel method of enhancing efficiency of carbon
felts in a flow battery through sonication is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The present invention will be better understood from the
following detailed description of the preferred embodiment
according to the present invention, taken in conjunction with the
accompanying drawings, in which
[0018] FIG. 1 is the flow view showing the preferred embodiment
according to the present invention;
[0019] FIG. 2 is the structural view showing the cell stack;
[0020] FIG. 3 is the view showing the architecture using the cell
stack.
[0021] FIG. 4 is the SEM view showing the surfaces of the carbon
felts; and
[0022] FIG. 5 is the view of the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] The following description of the preferred embodiment is
provided to understand the features and the structures of the
present invention.
[0024] Please refer to FIG. 1.about.FIG. 4, which are a flow view
showing a preferred embodiment according to the present invention;
a structural view showing a cell stack; a view showing an
architecture using the cell stack; and a SEM view showing surfaces
of the carbon felts. As shown in the figures, the present invention
is a method of enhancing efficiency of carbon felts in a flow
battery through sonication, comprising the following steps:
[0025] (a) Fabricating carbon felts 11: A plurality of carbon felts
(5 centimeters (cm).times.5cm) are immersed into a mixed acid
solution of sulfuric acid and nitric acid. The solution is heated
to 55.about.85 celsius degrees (.degree. C.) and sonication is
processed for 10.about.90 minutes (min). Then, the carbon felts are
washed with ultrapure water and dried. Therein, the mixed acid
solution has a volume ratio of 3:1 of sulfuric acid to nitric
acid.
[0026] (b) Assembling cell stack 12: The carbon felts obtained
after being processed through the sonication is made into a
plurality of electrodes; and a cell stack is assembled with the
electrodes. As shown in FIG. 2, the cell stack 2 comprises a proton
exchange membrane 21, two gaskets 22,23, two electrodes 24,25, two
flow plates 26,27 and two end plates 28,29. Therein, the two
gaskets 22,23 clips the proton exchange membrane 21; the two
electrodes 24,25 clips the two gaskets 22,23; the two electrodes
24,25 are a positive electrode 24 and a negative electrode 25; the
two electrodes 24,25 are made of the carbon felts; the two flow
plate 26,27 clips the two electrodes 24,25; one of the two flow
plates 26 has an anode inlet 261 and a cathode inlet 262; another
one of the two flow plates 27 have an anode outlet 271 and a
cathode outlet 272; and, the two end plates 28,29 clips the two
flow plates.
[0027] (c) Filling electrolyte 13: An electrolyte is filled into
the cell stack by two pumps 31,32, where the electrolyte comprise 1
mole (M) to 3M of vanadyl sulfate and an aqueous solution of 1M to
5M of inorganic acid. Under a flow rate controlled between 20 and
100 milliliters per minute (mL/min), the electrolyte is flown
through the anode inlet 261 and the cathode inlet 262 to be
uniformly in contact with the carbon felts (i.e. the positive
electrode 24 and the negative electrode 25). The electrolyte flows
through an anode outlet 271 and a cathode outlet 272 along with the
anode inlet 261 and the cathode inlet 262 to be collected in a
positive electrolyte container 33 and a negative electrolyte
container 34. The electrolyte is recycled to be pumped into the
cell stack 2 again through the anode inlet 261 and the cathode
inlet 262 until air in the cell stack 2 is completely expelled.
Therein, the inorganic acid is sulfuric acid, hydrochloric acid,
nitric acid or phosphoric acid
[0028] (d) Charging cell stack 14: An external power supply 35 is
connected to the positive electrode 24 and the negative electrode
25. A current of 1.about.2 amperes (A) is conducted under a
constant-current mode with a cut-off voltage of 1.6 volts (V).
Charging and discharging operations are processed in the cell stack
2 of a flow battery 3 and the charging and discharging operations
are repeated until charge ends.
[0029] The present invention modifies carbon felts through
sonication to efficiently generate --OH and C.dbd.O functional
groups on surface defects of the carbon felts. The --OH and C.dbd.O
functional groups catalyze redox reaction of vanadium ions. It
means that, through an activation treatment, the carbon felts
obtains more active positions to enhance valence exchange of
vanadium ions and increase efficiency of the redox reaction. The
general method of acid treatment needs to set up a reflux condenser
with reaction time up to several hours or more. In contrast, the
present invention is simple and uses sonication with no need for a
high pressure environment. A plurality of 5 cm.times.5 cm carbon
felts are immersed into a mixed acid solution having a volume ratio
of 3:1 of sulfuric acid to nitric acid. Under a temperature of
70.degree. C., the sonication is processed for 30, 60 and 90 min,
respectively, followed by washing with ultrapure water and drying
to be used for subsequent detection and cell testing.
[0030] A scanning electron microscope (SEM) is used to detect
surfaces of the carbon felts. As shown in FIG. 4, the picture of
notation 41 shows an unmodified carbon felt; and the other pictures
of notation 42,43 and 44 show modified carbon felts obtained
through 30, 60 and 90 minutes of sonication, respectively. From the
results, it is known that the surface of the unmodified carbon felt
is smooth and the surfaces of the modified carbon felts become
rougher and more uneven as the reaction time increases. Defects are
generated on the surfaces of the modified carbon felts.
[0031] The above four carbon felts are examined. Nafion 117 is
obtained as a proton exchange membrane. An industrial-grade vanadyl
sulfate is obtained as an electrolyte, whose concentration is 1.6M.
Under a flow rate of 50 mL/min, a current of 2 A is conducted in a
constant-current mode with a cutoff voltage of 1.6V for charging
and discharging a flow battery with the electrolyte. The charging
and discharging operations keep repeating until charge ends. Table
1 shows a result obtained after 50 rounds of charging and
discharging operations. It shows that the carbon felt modified
through sonication for 60 min has the best voltage efficiency and
energy efficiency, which obtains about 3% improvement as compared
to the unmodified carbon felt. The results show that sonication
with acid treatment can effectively modify carbon felts and
significantly shorten reaction time, and thus enhance the overall
energy efficiency of single cell.
TABLE-US-00001 TABLE 1 Coulomb Energy Voltage Time efficiency
efficiency efficiency unmodified 94.89% 76.30% 80.41% carbon felt
Sonication 30 min 95.80% 78.08% 81.51% Sonication 60 min 95.96%
80.14% 83.51% Sonication 90 min 96.40% 77.38% 80.28%
[0032] Thus, the present invention directly immerses carbon felts
in a mixed acid solution to be heated at a low temperature and
processed through sonication for efficiently generating --OH and
C.dbd.O functional groups on surface defects of the carbon felts.
The --OH and C.dbd.O functional groups catalyze redox reaction of
vanadium ions for obtaining more active positions on the carbon
felts to enhance valence exchange of vanadium ions and increase
efficiency of the redox reaction. Thereby, the present invention
has simple and fast processes with easily regulated experimental
parameters for good modification without high temperature treatment
but with low cost.
[0033] To sum up, the present invention is a method of enhancing
efficiency of carbon felts in a flow battery through sonication,
where carbon felts are modified through sonication to generate --OH
and C.dbd.O functional groups on surface defects of the carbon
felts; and the present invention has simple and fast processes with
easily regulated experimental parameters for good modification
without high temperature treatment but with low cost.
[0034] The preferred embodiment herein disclosed is not intended to
unnecessarily limit the scope of the invention. Therefore, simple
modifications or variations belonging to the equivalent of the
scope of the claims and the instructions disclosed herein for a
patent are all within the scope of the present invention.
* * * * *