KR102294549B1 - Composite comprising post-transition metal and porous carbon, Preparation method thereof and Redox flow cell comprising the same - Google Patents

Abstract

The present invention relates to a composite comprising a metal and porous carbon after the transition, a method for preparing the same, and a redox flow battery including the same, and has a structure in which the metal and porous carbon are combined after the transition, the composite is evenly deposited on an electrode, , The redox flow battery comprising an electrode containing the composite has the advantage of excellent capacity retention and energy efficiency.

Description

Composite comprising post-transition metal and porous carbon, manufacturing method thereof, and redox flow battery including same

The present invention relates to a composite comprising a metal and porous carbon after transition, a method for preparing the same, and a redox flow battery comprising the same.

In order to alleviate the environmental problems caused by the use of fossil fuels, research for using new and renewable energy as an energy source is being actively conducted. Accordingly, the importance of an energy saving system (ESS), a new and renewable energy storage device, is emerging, and a lithium secondary battery is currently used as an energy storage system battery.

However, due to the characteristics of lithium secondary batteries, many accidents related to safety, such as fire and explosion accidents, occur. Therefore, a redox flow battery with secured stability is being discussed as a substitute for lithium secondary batteries for energy storage systems. The redox flow battery has the advantage that it is easy to increase the capacity because the output part and the active material storage part are separated so that the output and capacity can be freely set. However, in the case of a water-based redox flow battery, there is a problem in that the energy efficiency is lowered due to the generation of hydrogen as a side reaction at the negative electrode during charging and the capacity is reduced due to ion imbalance. To prevent this, bismuth is deposited on the electrode by dissolving the bismuth (Bi) additive in the electrolyte. There is a problem in that it is difficult, and bismuth has a problem in that the reactivity to the active material is poor due to the relatively low electrical conductivity.

Republic of Korea Patent Publication No. 10-2016-0037826

An object of the present invention is to provide a composite in which porous carbon having excellent electrical conductivity and a post-transition metal inhibiting hydrogen generation are combined to increase the capacity retention rate and energy efficiency of the redox flow battery, a manufacturing method thereof, and a redox flow battery will do

In one embodiment, the present invention provides a composite comprising a post-transition metal and a porous carbon, wherein the post-transition metal is bonded to the porous carbon.

In addition, the present invention, in one embodiment, provides a manufacturing method for manufacturing the composite.

In addition, the present invention, in one embodiment, provides a redox flow battery comprising the complex.

The composite according to the present invention has a structure in which metal and porous carbon are combined after transition, the composite is evenly deposited on the electrode, and the redox flow battery including the electrode containing the composite has excellent capacity retention and energy efficiency There is this.

1 is a TEM (Transmission Electron Microscopy) analysis photograph for confirming the shape of a porous carbon composite to which bismuth is bonded as an embodiment according to the present invention.
2 is a TEM-EDS (Energy Dispersive x-ray Spectroscopy) analysis photograph for confirming the form of a porous carbon hybrid catalyst bound to bismuth as an embodiment according to the present invention.
3 is a cyclic voltammetry (CV) method to confirm the redox reactivity of chromium, which is an anode active material, in an iron-chromium redox flow battery including a composite prepared as an embodiment according to the present invention. This is a graph showing the results.
4 is an iron-chromium redox flow battery comprising a composite prepared as an embodiment according to the present invention to confirm the overvoltage for the hydrogen evolution reaction, hydrogen generation through a linear sweep voltammetry (LSV) It is a graph measuring potential change.
5 is a graph measuring the coulombic efficiency of the iron-chromium redox flow battery including the composite prepared as an embodiment according to the present invention.
6 is a graph measuring the voltage efficiency of an iron-chromium redox flow battery including a composite prepared as an embodiment according to the present invention.
7 is a graph measuring the energy efficiency of an iron-chromium redox flow battery including a composite prepared as an embodiment according to the present invention.
8 is a graph measuring the discharge capacity of an iron-chromium redox flow battery including a composite prepared as an embodiment according to the present invention.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and will be described in detail in the detailed description.

However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

In the present invention, terms such as "comprises" or "have" are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Therefore, the configuration shown in the embodiment described in this specification is only the most preferred embodiment of the present invention and does not represent all the technical spirit of the present invention, so various equivalents that can be substituted for them at the time of the present application and variations.

The present invention provides a composite having excellent dispersibility including a metal and porous carbon after transition, having high chemical resistance in an acidic electrolyte, excellent electrical conductivity, and improved reactivity to an active material.

As an example, the composite of the present invention may have a form in which a post-transition metal and porous carbon are combined.

The form in which the metal and the porous carbon are combined after the transition may be a form in which the metal is evenly dispersed after the transition on the surface of the porous carbon. As an example, the bond between the metal and the porous carbon after the transition may be a bond formed by reducing the precursor of the metal after the transition by a reducing agent, and precipitating the metal after the transition on the surface and inside of the porous carbon.

In general, post-transition metals are metallic elements located between transition metals and metalloids, and their electronegativity is smaller than that of transition metals and larger than those of alkali metals or alkaline earth metals. It has lower melting and boiling points than transition metals, and is soft.

The metal after the transition is aluminum (Aluminium, Al), gallium (Gallium, Ga), indium (Indium, In), tin (Tin, Sn), thallium (Thallium, Tl), lead (Lead, Pb), bismuth (Bismuth) , Bi), pololium (Polonium, Po), germanium (Germanium, Ge) and antimony (Antimon, Sb) may be one or more selected.

The post-transition metal may be at least one selected from the group consisting of antimony, lead, thallium and bismuth, and more specifically, bismuth.

When the composite containing the metal after the transition is used in the battery, there is an effect of suppressing the hydrogen reaction generated at the negative electrode during charging.

In the porous carbon of the present invention, in order to compensate for the relatively low electrical conductivity of the metal after the transition and to improve the dispersibility of the metal after the transition, it is preferable to use carbon having high electrical conductivity and a large surface area.

As an index capable of predicting the electrical conductivity and surface area of the porous carbon, the pore volume, porosity, DBP (dibutyl phthalate) oil absorption, or BET specific surface area of the porous carbon may be used.

The DBP oil absorption refers to the amount of dibutyl phthalate absorbed per unit weight of carbon, and refers to the degree of structural development of porous carbon.

The higher the DBP oil absorption value, the more branched the structure, the larger the specific surface area of the porous carbon, and thus excellent electrical conductivity.

The pore volume of the porous carbon suitable for the present invention is more than 0.8cm ³ / g or more, 1.0cm ³ / g or more, 1.2cm ³ / g or more than 1.3cm ³ / g, the pore volume by the gas adsorption method (BET) it is measured

The porosity of the porous carbon suitable for the present invention is 40% or more, 50% or more, 60% or more, or 70% or more.

In addition, DBP oil absorption of porous carbon suitable for the present invention is 200ml/100g or more, 300ml/100g or more, 400ml/100g or more, or 500ml/100g or more, and the DBP oil absorption is a value measured according to ASTM D 2414. .

The BET specific surface area suitable for the present invention is 700 m 2 /g or more, 800 m 2 /g or more, 900 m 2 /g or more, or 1,000 m 2 /g or more, and the BET specific surface area is a value measured according to ASTM D 3037.

When the porous carbon of the present invention has the pore volume, porosity, DBP oil absorption, or BET specific surface area as described above, it has many pores, a large specific surface area, and a developed structure to have excellent electrical conductivity.

When the composite of the present invention containing the porous carbon is applied to a battery, the reactivity of the metal and the active material after the transition of the present invention is improved due to excellent electrical conductivity, and due to the large surface area of the porous carbon of the present invention, the dispersion of the metal after the transition is reduced It has the advantage of being easy.

Examples of the porous carbon include carbon black, activated carbon, carbon nanotubes, carbon fibers, fullerene and graphene, and carbon black is preferable in order to satisfy the conditions of porous carbon disclosed in the present invention.

As carbon black, commercially available products such as Ketjenblack or Acetylene black can be used, and Ketjen Black having excellent surface area and electrical conductivity is preferable.

In addition, the present invention provides a method for preparing a composite including a metal and porous carbon after the transition.

The method for preparing the composite includes a preparation step of preparing a mixed solution in which a metal precursor, a porous carbon and a solvent are mixed after the transition, and a bonding step of combining the metal and the porous carbon after the transition by adding a reducing agent to the mixed solution.

The post-transition metal precursor is not limited as long as the post-transition metal is uniformly precipitated and bound on the porous carbon by reduction, for example, nitrides, sulfides, hydroxides, halides, oxides, hydrates, and these metals after the transition. It may be any one selected from the group consisting of a combination of.

The metal after the transition is aluminum (Aluminium, Al), gallium (Gallium, Ga), indium (Indium, In), tin (Tin, Sn), thallium (Thallium, Tl), lead (Lead, Pb), bismuth (Bismuth) , Bi), pololium (Polonium, Po), germanium (Germanium, Ge) and antimony (Antimon, Sb) may be one or more selected.

The post-transition metal may be at least one selected from the group consisting of antimony, lead, thallium and bismuth, and more specifically, bismuth.

The precursor of bismuth may include bismuth nitrate, bismuth chloride, bismuth sulfate or bismuth fluoride, for example, bismuth nitrate pentahydrate.

In the porous carbon of the present invention, in order to compensate for the relatively low electrical conductivity of the metal after the transition and to improve the dispersibility of the metal after the transition, it is preferable to use carbon having high electrical conductivity and a large surface area.

As an index capable of predicting the electrical conductivity and surface area of the porous carbon, the pore volume, porosity, DBP (dibutyl phthalate) oil absorption, or BET specific surface area of the porous carbon may be used.

The pore volume of the porous carbon suitable for the present invention is more than 0.8cm ³ / g or more, 1.0cm ³ / g or more, 1.2cm ³ / g or more than 1.3cm ³ / g, the pore volume by the gas adsorption method (BET) it is measured

The porosity of the porous carbon suitable for the present invention is 40% or more, 50% or more, 60% or more, or 70% or more.

In addition, DBP oil absorption of porous carbon suitable for the present invention is 200ml/100g or more, 300ml/100g or more, 400ml/100g or more, or 500ml/100g or more, and the DBP oil absorption is a value measured according to ASTM D 2414. .

The BET specific surface area suitable for the present invention is 700 m 2 /g or more, 800 m 2 /g or more, 900 m 2 /g or more, or 1,000 m 2 /g or more, and the BET specific surface area is a value measured according to ASTM D 3037.

When the porous carbon of the present invention has the pore volume, porosity, DBP oil absorption, or BET specific surface area as described above, it has many pores, a large specific surface area, and a developed structure to have excellent electrical conductivity.

When the composite of the present invention containing the porous carbon is applied to a battery, the reactivity of the metal and the active material after the transition of the present invention is improved due to excellent electrical conductivity, and due to the large surface area of the porous carbon of the present invention, the dispersion of the metal after the transition is reduced It has the advantage of being easy.

Examples of the porous carbon include carbon black, activated carbon, carbon nanotubes, carbon fibers, fullerene and graphene, and carbon black is preferable in terms of satisfying the conditions of porous carbon of the present invention.

As carbon black, commercially available products such as Ketjenblack or Acetylene black can be used, and Ketjen Black having excellent surface area and electrical conductivity is preferable.

As an example, the preparation step of preparing the mixed solution is bismuth nitrate pentahydrate (Bi(NO ₃ ) ₃ ·5H) of porous carbon, Ketjenblack, and a metal precursor of 0.5M to 1.5M after transition. ₂ O) may be mixed with a solvent, stirred at a temperature of 50° C. to 100° C., and irradiated with ultrasonic waves. Specifically, the solvent may be distilled water.

The method for preparing the complex of the present invention may further include adjusting the pH of the mixed solution after the step of preparing the mixed solution. In the step of adjusting the pH of the mixed solution, the pH of the mixed solution may be adjusted to exhibit weak alkalinity.

As a method of adjusting the pH, a known method can be used, for example, by adding and dissolving sodium hydroxide (NaOH) powder to the mixed solution, the mixed solution can be adjusted to exhibit weak alkalinity.

It is preferable that the weak alkalinity has a pH of 8 to 10.

The bonding step of combining the metal and the porous carbon after the transition by adding a reducing agent to the mixed solution is a step of bonding the metal and the porous carbon after the transition by a method of chemical reduction using a reducing agent.

Specifically, the binding step may be performed by adding a reducing agent to the mixed solution and reacting for 10 to 15 hours. The reducing agent is not particularly limited as long as it is a material capable of reducing the metal precursor after the transition, but sodium borohydride (NaBH ₄ ) may be used.

In addition, the step of washing and drying the complex of the present invention bound after the binding step may be further included, and the washing and drying step may be performed by sufficiently washing the complex with distilled water and drying the complex.

In addition, the present invention provides an electrode comprising the above-described composite. For example, the electrode may be a negative electrode.

As the material of the electrode, a known electrode may be used, and as an example, carbon felt may be used. The carbon felt electrode has a large surface area and excellent fluidity of the electrolyte.

Specifically, the electrode may be in a form in which a composite is included on the electrode. More specifically, the electrode may be in a form in which a composite including a metal and porous carbon after transition is dispersed on a carbon felt electrode. For example, the electrode may be in a form in which a composite including a metal and porous carbon is deposited on a carbon felt electrode after the transition.

In addition, the present invention provides a redox flow battery comprising an electrode including the composite.

A redox flow battery is a battery that performs charging and discharging by supplying a positive electrolyte and a negative electrolyte to a cell having positive and negative electrodes and a diaphragm interposed between the positive electrodes, and is an all-vabadium redox flow battery. , VRFB), zinc-bromine redox flow battery (ZBRFB), iron-chromium redox flow battery (ICRFB), polysulfide-bromine redox flow battery (PSBRFB), etc. It can have various forms used in pairs.

As an example, the redox flow battery may be an iron-chromium redox flow battery. The iron-chromium redox flow battery is economically superior in terms of the low cost of the electrolyte.

As a result of observing the change in the chromium redox reaction using cyclic voltammetry (CV), the electrode including the composite may exhibit an improved chromium redox response compared to the electrode not using the composite.

In addition, in the redox flow battery, the electrode on which the composite is deposited on one side is a result of measuring the hydrogen generation potential change according to the electrode change using a linear sweep voltage (LSV), after the transition metal and Simultaneous inclusion of porous carbon may result in overpotential shifts for hydrogen reactions.

Through this, it can be seen that by including the composite according to the present invention, the redox flow battery of the present invention inhibits or inhibits hydrogen reaction and improves energy efficiency.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention. These Examples and Comparative Examples are merely presented by way of example in order to explain the present invention in more detail, and the scope of the present invention is not limited thereto.

[Production Example]

A DBP oil absorption of 510mg / 100g, the pore volume is 1.3cm ³ / g, BET is a specific surface area of 1,270, a porous carbon in the 70% porosity (Ketjen black (Ketjenblack) ®, LION社) metal precursor and after 0.2 g I 30 ml of (0.1M bismuth nitrate pentahydrate, Bi(NO ₃ ) ₃ ·5H ₂ O) in distilled water at 80 °C and sufficiently stirred at 1,000 rpm until the bismuth nitrate pentahydrate appears milky ( A mixed solution was prepared by dispersing it by means of Miseong Machinery Co., Ltd.) and ultrasonic waves (Hwashin Machinery Co., Ltd.).

To the mixed solution, 0.4 g of sodium hydroxide (NaOH) was added to adjust the pH to 9. To this mixed solution, sodium borohydride (NaBH ₄ , Daejeong Hwageum), a reducing agent, was added and reacted for about 12 hours to reduce bismuth to Ketjen Black. The product was sufficiently washed with distilled water and dried to prepare a composite in which bismuth and carbon were bonded.

[Comparative Example 1]

A mixture in which bismuth and porous carbon were simply mixed was prepared.

[Example 1]

Composite ink was prepared by mixing 10 mg of the complex prepared in Preparation Example, 1 ml of isopropyl alcohol, and 10 ul of 5 wt% Nafion (Sigma-aldrich). 1ul of the prepared composite ink was pipetted onto a 0.5 cm diameter glass carbon (Glassy Carbon, BioLogic) electrode and dried at 25° C. for at least 10 minutes to prepare an electrode containing the composite prepared by Preparation Example.

[Comparative Example 2]

Glassy carbon (Glassy Carbon, BioLogic Co.) electrodes were prepared.

[Comparative Example 3]

An electrode was prepared in the same manner as in Example 1, except that the mixture of Comparative Example 1 was used instead of the composite of Preparation Example 1.

[Example 2]

A complex solution was prepared by mixing 60 mg of the complex prepared in Preparation Example, 10 ml of ethanol, and 100 ul of 5 wt% Nafion (Sigma-aldrich). A carbon felt (XF-30A, Toyobo Co.) electrode having a size of 2 cm x 3 cm was immersed in the prepared complex solution, and then dispersed in an ultrasonic disperser for 20 minutes. Then, the electrode was taken out of the composite solution and dried in a vacuum oven at 60° C. for 12 hours or more to prepare an electrode. An iron-chromium redox flow battery using the prepared electrode as a negative electrode was prepared.

[Comparative Example 4]

An iron-chromium redox flow battery using only carbon felt electrodes was prepared.

[Comparative Example 5]

Ketjen Black was loaded onto a carbon felt (XF-30A, Toyobo Co., Ltd.) electrode having a size of 2 cm x 3 cm to prepare an iron-chromium redox flow battery.

In order to confirm the shape of the composite of Preparation Example and Comparative Example 1, TEM (Transmission Electron Microscope, transmission electron microscope) photographs are shown in FIGS. 1 and 2 . Unlike the TEM photograph of Comparative Example 1 in which a small amount of bismuth particles were non-uniformly distributed in the dense porous carbon particles, the TEM and TEM-EDS photographs of Preparation Example showed that fine bismuth particles of about 1 μm were evenly distributed between the dense porous carbon particles. there seems to be

This is a result of the bismuth precursor being reduced to bismuth by a reducing agent in a state in which it is evenly mixed with the porous carbon and uniformly bonded to the surface of the porous carbon.

Cyclic voltammetry (CV) was performed to confirm the redox reactivity of chromium, which is an anode active material, of the iron-chromium redox flow batteries of Examples 1, 2 and 3 above.

The measurement was performed in a standard 3-electrode electrochemical cell (BioLogic) having a Pt wire counter electrode and an Ag/AgCl reference electrode with a potentiostat (VSP, BioLogic), and measured with EC-Lab V11.20 software.

At this time, the experiment was conducted in a voltage range of -0.2 to -0.9 V (vs. Ag/AgCl) from -0.2 to -0.9 V (vs. Ag/AgCl) at a scanning speed of ^{20 mV s -1} through cyclic voltammetry in a solution _{of 0.1 M CrCl 3 in 2.0 M HCl.} It proceeded by measuring the current change. The results are shown in FIG. 3 .

In Comparative Examples 2 and 3, although the chromium redox reaction did not occur or the reaction occurred, the current density value was shown, but the value was small. On the other hand, in the case of Example 1, it can be seen that the current density value significantly increased around -0.5 V and -0.65 V, and through this, it can be seen that the oxidation-reduction reaction of chromium divalent and trivalent is improved.

In particular, in Comparative Example 3, it is difficult to distinguish the reduction current density value of chromium trivalent due to the interference of hydrogen reduction current as the measured voltage approaches -1 V, which is the hydrogen generation potential, whereas in Example 1, chromium despite the hydrogen reduction current The peak of the trivalent reduction current density was separated and appeared clearly.

The above result is presumed to be because the porous carbon provides an active site for the chromium redox reaction, and the bismuth evenly distributed inside the complex inhibits the hydrogen evolution reaction.

In order to know the overvoltage for the hydrogen evolution reaction of Examples 1 and 3, the change in the hydrogen evolution potential was measured through a linear sweep voltammetry (LSV), and the results are shown in FIG. 4 .

The measurement was performed in a standard 3-electrode electrochemical cell (BioLogic) having a Pt wire counter electrode and an Ag/AgCl reference electrode with a potentiostat (VSP, BioLogic), and measured with EC-Lab V11.20 software.

At this time, the experiment is a method of measuring the current change in the voltage range from -0.5 to -1.2 V (vs. Ag/AgCl) at a scanning speed of ^{10 mV s -1 through the linear scanning potential method in 2.0M HCl solution.} proceeded.

At the inflection point (x, y) of the LSV curve, the x value means the onset potential value, and the overvoltage value for the hydrogen reaction can be known through this value. As can be seen in FIG. 4 , it can be confirmed that the overvoltage for the hydrogen reaction has a more negative value in the case of Example 1 compared to Comparative Example 3 . Specifically, Comparative Example 3 showed an onset potential value of -1.026 V and Example 1 of -1.042 V. Since the more negative the overvoltage value means the more difficult it is to generate hydrogen, it can be determined that the case of Example suppresses the hydrogen reaction compared to Comparative Example 3.

The performance of the iron-chromium redox flow battery of Example 2, Comparative Example 4 and Comparative Example 5 was evaluated, and the results are shown in FIGS. 5 to 8 .

5 to 8 , Comparative Example 4 showed the lowest results in terms of efficiency and capacity. In the case of Comparative Example 5, it was confirmed that the efficiency and capacity decreased as the charge/discharge cycle progressed while showing high efficiency and capacity at the beginning. This is because the porous carbon provides an active site for the redox reaction of chromium, the active material, and promotes the redox reaction of chromium, thereby showing high efficiency and capacity at the beginning. It seems that this is because it also promotes the phosphorus hydrogen evolution reaction, and as the cycle progresses, it has the effect of inhibiting the oxidation-reduction reaction of chromium. In the case of Example 2, the highest coulombic efficiency (FIG. 5) and high and stable voltage efficiency (FIG. 6) are shown, and even at the 50th cycle, the highest energy efficiency of 85.26% (FIG. 7) and a relatively high discharge capacity retention rate of 55.13% (Fig. 8) was shown. This result is considered to be due to the synergistic effect of the effect of porous carbon as an active site and the hydrogen suppression effect of bismuth.

Through the above experimental results, by applying the bismuth-bound porous carbon composite of the present invention to an iron-chromium redox flow battery, the energy efficiency and capacity retention of the battery can be improved by not using the composite or by simply mixing metal and porous carbon after transition. It can be seen that the improvement compared to the mixture by

Claims (15)

bismuth (Bi) and porous carbon;
The porous carbon has a BET specific surface area of 700 m 2 /g or more, and a DBP oil absorption of 200 ml/100g or more,
The bismuth is a composite for a redox flow battery, characterized in that bonded to the porous carbon.
delete In claim 1,
The porous carbon is a composite for a redox flow battery, characterized in that the pore volume (Pore volume) is 0.8cm ^{3 /g or more.}
delete delete A preparation step of preparing a mixed solution in which a bismuth (Bi) precursor, porous carbon, and a solvent are mixed; and
a binding step of combining bismuth and porous carbon by adding a reducing agent to the mixed solution;
The porous carbon has a BET specific surface area of 700 m 2 /g or more, and a DBP oil absorption amount of 200 ml/100 g or more.
In claim 6,
The method of manufacturing a composite for a redox flow battery, characterized in that it further comprises the step of adjusting the pH of the mixed solution to 8 to 10 after the preparation step.
In claim 6,
The method of manufacturing a composite for a redox flow battery, characterized in that it further comprises the step of washing and drying after the bonding step.
In claim 6,
The method for manufacturing a composite for a redox flow battery, characterized in that the bismuth precursor is any one selected from the group consisting of nitrides, hydroxides, sulfides, halides, oxides, hydrates, and combinations thereof of bismuth.
delete In claim 6,
The porous carbon has a pore volume of 0.8 cm ³ /g or more.
In claim 6,
The solvent is distilled water,
The reducing agent is a method of manufacturing a composite for a redox flow battery, characterized in that sodium borohydride (sodium borohydride).
An electrode comprising the composite for a redox flow battery of claim 1 or 3.
A redox flow battery comprising the electrode of claim 13 .
15. In claim 14,
The redox flow battery is an iron-chromium redox flow battery, characterized in that the redox flow battery.

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