Magnesium-air secondary battery-based carbon dioxide conversion hybrid power system and seawater desalination system using same

Abstract

The present invention relates to a magnesium-air secondary battery-based carbon dioxide conversion hybrid power system capable of generating power through an oxygen reduction reaction (ORR) in a discharge process of a magnesium-air secondary battery and simultaneously generating carbonate by a carbonation reaction of carbon dioxide.

Description

A carbon dioxide conversion hybrid power system based on a magnesium-air secondary battery and a seawater desalination system using the same.

[0001] The present invention relates to an eco-friendly battery technology for power generation and carbon dioxide reduction, and more specifically, to a technology for generating power and directly reducing carbon dioxide by utilizing a magnesium-carbon dioxide battery based on a magnesium-air electrode.

[0002] Carbon dioxide utilization (CCU) technology is a technology that can convert carbon dioxide into various chemical raw materials, energy sources, and building materials using chemical or electrochemical methods. Carbon dioxide resource utilization technology using concentrated seawater is a technology that uses calcium ions (Ca) that are abundant in concentrated seawater. 2+ ) and magnesium ions (Mg 2+ ) is used to spontaneously dissolve HCO3 in seawater. - This is a technology that uses mineralization technology. This is because a process has already been developed to convert calcium ions and magnesium ions contained in concentrated seawater from desalination facilities into economically viable carbonate minerals. Korea Electric Power Corporation has developed a technology to produce sodium bicarbonate (NaHCO3) by reacting carbon dioxide in the exhaust gas of thermal power plants with sodium hydroxide produced by electrolysis of brine, and plans to install a demonstration plant with Lotte Chemical that will reduce carbon dioxide by 20,000 tons per year. LG Chem plans to build a pilot plant that produces 1,000 tons of plastic using carbon dioxide and methane, a by-product gas, which will have the effect of reducing carbon dioxide emissions by 50%. In 2019, the Korea Institute of Geoscience and Mineral Resources developed a technology to reduce greenhouse gases by dissolving carbon dioxide in seawater and carbonating metal ions.

[0003] In 2021, UNIST also developed a technology to carbonate carbon dioxide in seawater using an electrochemical reaction. The electrode material used was iridium oxide (IrO2), a precious metal. While precious metals like iridium oxide were able to generate electrochemical reactions when using a basic electrolyte containing sodium chloride (NaCl), their performance deteriorated significantly when using pure seawater.

[0004] As mentioned above, there have been several studies conducted domestically on technologies for reducing carbon dioxide by directly injecting it into concentrated seawater. However, these previous studies required a pretreatment process to adjust the pH of the seawater, which resulted in significant costs for the pretreatment when constructing facilities for large-scale CO2 treatment. Furthermore, electrochemical cells typically require the use of precious metal catalysts. However, precious metal catalysts are prone to deterioration due to strong chloride ion adsorption in seawater. Furthermore, they often lack sufficient activity in high-salt waters, such as concentrated seawater, making them difficult to use in practice.

[0005] The Mg-CO2HER battery, a technology that indirectly converts carbon dioxide into resources, has been developed overseas. Because the Mg-CO2HER battery converts carbon dioxide into carbonate in the electrolyte, it can not only convert carbon dioxide into carbonate, but also use the produced hydrogen as fuel. However, the Mg-HER battery system's cathode requires an expensive platinum (Pt) catalyst. Furthermore, the presence of impurities such as NOx and SOx significantly reduces performance. Therefore, the Mg-HER system is subject to the inherent impact of the purity of the carbon dioxide input, making the carbon dioxide process indispensable.

[0006] Accordingly, the present invention proposes a technology for converting carbon dioxide using a magnesium-air secondary battery. To overcome existing technological limitations, the present invention introduces a non-precious metal catalyst to reduce costs and prevent deterioration caused by the adsorption of chloride ions in seawater. Simultaneously, a system has been developed that effectively reduces and recycles carbon dioxide by dissolving it in concentrated seawater and converting it into magnesium and calcium carbonate.

[0007] One object of the present invention is to provide a hybrid power system that produces electricity by converting carbon dioxide through a carbonate reaction based on a magnesium-air secondary battery and simultaneously produces carbonate.

[0008] Another object of the present invention is to provide a system for desalinating seawater using the hybrid power system.

[0009] In one aspect, the present invention comprises a reaction tank containing an electrolyte solution; a magnesium electrode positioned within the reaction tank; an air electrode positioned within the reaction tank for inducing an oxygen reduction reaction (ORR); a connecting portion connecting the magnesium electrode and the air electrode; and a gas injection device for injecting a gas containing carbon dioxide into the electrolyte solution, wherein bicarbonate (HCO3) is produced by a carbonation reaction within the electrolyte solution. - ) or carbonate (CO3 2-) can be a carbon dioxide conversion hybrid power system based on a magnesium-air secondary battery, characterized in that a material is generated. The reactor contains an electrolyte solution and provides a space where an electrochemical reaction occurs. The magnesium electrode immersed in the electrolyte solution in the reactor acts as an anode in the system, and magnesium is oxidized during a discharge process to release magnesium ions and electrons. The air electrode immersed in the electrolyte solution in the reactor acts as a cathode in the system, and the air electrode can be a catalytic electrode that promotes the reduction reaction of oxygen in the air (ORR reaction), which is an important part in producing power through the discharge process of the battery. The connecting part may be a wire or a conductor, etc., and may serve to produce and supply power through an external circuit, and is not limited as long as it can move electrons between the magnesium electrode and the air electrode. The gas injection device is not limited as long as it corresponds to a device capable of injecting carbon dioxide gas. The above gas injection device serves to supply carbon dioxide from an external source and inject it into the electrolyte solution. The carbon dioxide injected into the electrolyte solution undergoes a carbonation reaction to produce bicarbonate or carbonate, effectively converting and fixing the carbon dioxide. The combination of the above components effectively reduces carbon dioxide and generates electricity, maximizing the performance and efficiency of the battery.

[0010] In one embodiment, the electrolyte solution may include concentrated seawater. Concentrated seawater refers to seawater with a higher salt and mineral concentration than normal seawater. Typically, concentrated seawater contains a salt concentration of at least 7 wt.%, which is more than twice the salt concentration of standard seawater (approximately 3.5 wt.%). Using concentrated seawater as the electrolyte solution in the present invention can help improve ionic conductivity and accelerate reaction rates. Furthermore, because concentrated seawater contains more cations, it can produce more carbonate or bicarbonate-based substances.

[0011] In one embodiment, the air electrode may include a non-precious metal catalyst. Non-precious metal catalysts are less expensive and more abundant than precious metal catalysts, and are used in various chemical reactions and systems. Representative examples include iron (Fe), nickel (Ni), and cobalt (Co). Using a non-precious metal catalyst as the air electrode in the present invention can help maximize power generation performance by being less expensive and exhibiting high catalytic activity in the oxygen reduction reaction (ORR) compared to precious metal catalysts such as platinum (Pt).

[0012] In one embodiment, the non-precious metal catalyst may include an iron-bonded nitrogen-doped carbon (Fe-NC) catalyst. The Fe-NC catalyst is a composite coated on a conductive carbon support doped with iron (Fe) atoms and nitrogen (N), which provides high catalytic activity and stability in the oxygen reduction reaction (ORR). The iron (Fe) atoms act as active sites in the oxygen reduction reaction (ORR) and can contribute to maximizing the catalytic performance by lowering the activation energy of the ORR reaction by optimizing the electronic environment of the Fe active center. In addition, since nitrogen acts as a coordinating member that stabilizes the iron atoms in a coordination structure, doping with nitrogen changes the chemical properties of the carbon structure, thereby allowing chloride ions (Cl) to form. -) can help maintain stable performance for a long period of time by suppressing the adsorption of the catalyst and preventing deterioration of the catalyst.

[0013] In one embodiment, the pH of the electrolyte solution may be maintained at 7.0 to 9.0 by the oxygen reduction reaction (ORR) and the carbonation reaction. This pH range corresponds to the typical pH range of seawater. The pH can be maintained by balancing the hydrogen ion consumption due to the oxygen reduction reaction and the hydrogen ion dissociation due to the carbonation reaction.

[0014] In one embodiment, the gas injection device may further include a device for controlling the inflow of gas containing carbon dioxide to maintain the pH of the electrolyte solution. This control device may monitor the pH of the electrolyte solution in real time and, as necessary, adjust the inflow of carbon dioxide to maintain an optimal pH range. Since the amount of carbon dioxide injected must be linked to the amount of hydrogen ions removed in the oxygen reduction reaction, it may be adjusted according to the discharge amount.

[0015] In one embodiment, the generated bicarbonate (HCO3 - ) or carbonate (CO3 2- ) may additionally include a device for separating the substance. The generated bicarbonate (HCO3 - ) or carbonate (CO3 2- ) The device for separating the substance may be a microfiltration filter device, a sedimentation tank, a membrane separation system, and an electrodialysis device. Through this, the bicarbonate and carbonate substances generated in the electrolyte solution can be efficiently separated, thereby contributing to the continuous operation of the battery system and maximizing resource utilization.

[0016] In one embodiment, the gas injected into the gas injection device may be an exhaust gas containing carbon dioxide and oxygen, and may be characterized in that the exhaust gas can additionally supply oxygen to the air electrode. This can effectively utilize the exhaust gas to improve the performance of the battery and make it environmentally friendly.

[0017] In one embodiment, the magnesium-air secondary battery-based carbon dioxide conversion hybrid power system may be a power generation facility installed near the coast. Power generation facilities installed near the coast have the advantage of easily securing seawater resources, such as concentrated seawater, and can be combined with various renewable energy sources.

[0018] In another aspect, the present invention may be a seawater desalination system comprising: a desalination tank containing a high-concentration seawater electrolyte; an oxidation electrode positioned within the desalination tank; a reduction electrode positioned within the desalination tank; and means for applying power generated from a magnesium-air secondary battery-based carbon dioxide conversion hybrid power system to the oxidation electrode and the reduction electrode. Seawater to be desalinated is introduced into the desalination tank, where it separates freshwater and salt. Power generated from the magnesium-air secondary battery-based carbon dioxide conversion hybrid power system is supplied to the oxidation electrode and the reduction electrode. When voltage is applied, anions from the seawater move to the oxidation electrode and are vaporized, and cations move to the reduction electrode and are precipitated as metals. This system can effectively remove salt from seawater to produce high-quality freshwater, and can maximize energy efficiency by utilizing the power generated from the battery.

[0019] The carbon dioxide conversion hybrid power system based on a magnesium-air secondary battery according to the present invention has a dual function of reducing carbon dioxide and producing electricity at the same time, thereby processing carbon dioxide economically and efficiently to produce eco-friendly electricity.

[0020] The seawater desalination system according to the present invention can economically and environmentally desalinate seawater by using power produced from the magnesium-air secondary battery-based carbon dioxide conversion hybrid power system.

[0021] FIG. 1 is a diagram illustrating a concept of a continuous carbon dioxide conversion process utilizing a magnesium-carbon dioxide concentrated seawater battery technology according to one embodiment of the present invention.

[0022] Figure 2a is a graph showing the cell voltage and pH changes of a magnesium-air secondary battery at a specific current density or open circuit voltage.

[0023] Figure 2b is a graph showing the solubility of various metal hydroxides according to pH.

[0024] Figure 3a is a schematic diagram showing the carbonation reaction of carbon dioxide in actual seawater.

[0025] Figure 3b is a graph showing the carbonate ratio according to the pH of water.

[0026] Figure 3c is a graph showing the solubility of carbon dioxide according to pH value.

[0027] Figure 4a is a schematic diagram showing a solution plasma synthesis method for synthesizing the catalyst electrode of the present invention.

[0028] FIG. 4b is a photograph showing a plasma reactor prepared for synthesizing a catalyst electrode of the present invention and a photograph showing a plasma synthesis setup.

[0029] FIG. 4c is a photograph showing a catalyst coated on carbon felt according to one embodiment of the present invention.

[0030] Figure 4d shows a cell frame according to one embodiment of the present invention.

[0031] Figure 4e shows a cell assembly photograph according to one embodiment of the present invention.

[0032] FIG. 4f is a photograph of a three-electrode cell system according to one embodiment of the present invention.

[0033] Figure 4g is a photograph showing a VSP for electrochemical experiments used in one embodiment of the present invention.

[0034] FIG. 5a is a photograph showing a scene of injecting carbon dioxide into a magnesium-carbon dioxide ORR concentrated seawater battery system according to one embodiment of the present invention.

[0035] FIG. 5b is a photograph showing a magnesium-carbon dioxide ORR concentrated seawater battery system according to one embodiment of the present invention.

[0036] FIG. 5c is a graph of voltage over time showing the durability of a magnesium-carbon dioxide ORR concentrated seawater battery system according to one embodiment of the present invention.

[0037] FIG. 5d is a graph showing a performance evaluation according to the concentration of concentrated seawater in a magnesium-carbon dioxide ORR concentrated seawater battery system according to one embodiment of the present invention.

[0038] Figure 6a shows a graph showing the performance evaluation of a magnesium-carbon dioxide secondary battery depending on the presence or absence of carbon dioxide.

[0039] Figure 6b shows a graph showing EIS analysis to evaluate the resistance of the battery with and without carbon dioxide.

[0040] Figure 6c shows a graph to demonstrate the electrochemical performance of the battery even under carbon dioxide conditions.

[0041] Figure 6d shows an X-ray diffraction graph that can identify reaction byproducts by comparing XRD patterns with and without carbon dioxide.

[0042] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. The present invention is susceptible to various modifications and variations, and thus specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention. Throughout the description of each drawing, similar reference numerals have been used to designate similar components.

[0043] The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, step, operation, component, part, or combination thereof described in the specification, but do not preclude the possibility of the presence or addition of one or more other features, steps, operations, components, parts, or combinations thereof.

[0044] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0045]

[0046] The magnesium-air secondary battery, which is the basis of the present invention, is a battery that generates electricity by utilizing the electrochemical reaction between magnesium and oxygen in the air. The electrons generated during the discharge process move through an external circuit to supply electricity, and the magnesium ions released from the anode during this process can react with oxygen in the air to form stable magnesium hydroxide (Mg(OH)2). The present invention proposes a continuous carbon dioxide conversion hybrid system utilizing magnesium-carbon dioxide concentrated seawater battery technology based on this magnesium-air secondary battery technology. Here, "hybrid" means that electricity can be generated by the magnesium-air battery reaction while simultaneously producing carbonate or bicarbonate minerals by the carbon dioxide conversion reaction in concentrated seawater.

[0047] Figure 1 is a conceptual diagram illustrating a continuous carbon dioxide conversion system and seawater desalination system utilizing magnesium-carbon dioxide enrichment seawater battery technology according to one embodiment of the present invention. The system device of Figure 1 comprises a reactor, a magnesium electrode, an air electrode, a wire connecting the magnesium electrode and the air electrode as a connecting part, and a gas injection device containing carbon dioxide. During the discharge process of this battery, the anode electrode made of magnesium metal is oxidized to release magnesium ions and electrons. The released electrons move along the wire to the cathode air electrode, causing a discharge. The cathode air electrode receives electrons during the discharge process and causes an ORR reaction that reduces oxygen molecules in the air. Here, the ORR reaction (oxygen reduction reaction) is a reaction in which oxygen molecules receive electrons and are reduced to produce water. The chemical reaction equation for the oxidation-reduction reaction occurring at the anode and cathode is as follows.

[0048] Magnesium electrode (anode): 2Mg → 2Mg 2+ + 4e -

[0049] Air electrode (cathode): O2+ 4e -+ 4H + → 2H2O

[0050] The electrons generated during the discharge process move through the external circuit to produce and supply electricity, and during this process, the magnesium ions released from the anode exist in the form of magnesium ions in the electrolyte in the form of magnesium hydroxide (Mg(OH)2).

[0051] At this time, when exhaust gas generated from factories, automobiles, etc. is injected into the electrolyte solution in the reactor through a gas injection device, carbon dioxide gas reacts with water in the electrolyte solution to form bicarbonate (HCO3). - ) and carbonate (CO3 2- ) occurs, and a carbonation reaction occurs to acidify the electrolyte solution containing the concentrated seawater. The bicarbonate (HCO3 - ) and carbonate (CO3 2- ) reacts with magnesium ions released from the anode or other cations contained in the concentrated seawater to precipitate carbonate minerals such as Mg(HCO3)2 or MgCO3. The chemical reaction equations for the carbon dioxide conversion reaction and carbonate reaction are as follows.

[0052] Carbon dioxide conversion reaction (acid-base reaction): 4CO2+ 4H2O → 4HCO3 - + 4H + (bicarbonate production) or 2CO2+ 2H2O → 2CO3 2- + 4H + (carbonate production)

[0053] Carbonate reaction (precipitation reaction): 2Mg 2+ + 4HCO3 - → 2Mg(HCO3)2 (bicarbonate mineral formation) or 2Mg 2+ + 2CO3 2- → 2MgCO3 (carbonate mineral formation)

[0054] The seawater desalination system of the present invention is illustrated in the upper left corner of Figure 1. Seawater desalination can be achieved by supplying power generated by the hybrid power system according to the present invention to the seawater desalination system. The power supply causes oxidation-reduction reactions and electrolysis to occur at the electrodes included in the seawater desalination system, and the water can be separated into pure water and brine through a membrane that selectively allows only specific ions to pass through.

[0055] Figures 2 and 3 are drawings explaining the theoretical background of carbon dioxide conversion technology using a magnesium-carbon dioxide power device based on concentrated seawater.

[0056] Figure 2a is a diagram showing the pH change and solubility of the electrolyte solution during the actual operation of a magnesium-air secondary battery, and Figure 2b shows the solubility of various substances, including magnesium hydroxide, according to pH. Referring to the four graphs in Figure 2a, as a result of experiments at various current densities, it can be confirmed that the pH of the electrolyte solution rises to about 10 to 11 over time and then becomes constant. This shows that the pH rises to a certain level and is maintained during the operation of the battery. Figure 2b shows the solubility limit of magnesium hydroxide, which explains why the pH is maintained at a certain level. When the pH is 10 to 11, magnesium hydroxide reaches its solubility limit and can be precipitated. Due to this precipitation process, the pH of the electrolyte can be maintained, as shown in Figure 2a.

[0057] Figures 2a and 2b illustrate the process by which the pH of the electrolyte solution increases and stabilizes during battery operation. This leads to the continuous carbonation reaction of carbon dioxide in the concentrated seawater described in Figure 3.

[0058] Figure 3a is a schematic diagram showing the carbonation reaction of carbon dioxide in actual seawater. First, carbon dioxide reacts with water to form carbonic acid (H2CO3). This carbonic acid is converted into bicarbonate (HCO3) through the first dissociation reaction. - ) and hydrogen ions (H + ) is released. The bicarbonate is released through the second dissociation reaction as carbonate (CO3 2- ) and hydrogen ions (H + ) is released. Since the presence of hydrogen ions in an aqueous solution indicates the acidity of the solution, carbon dioxide in the atmosphere can acidify seawater. The two dissociation reactions of carbonic acid are as follows.

[0059] First dissociation reaction of carbonic acid: H2CO3→ H + + HCO3 -

[0060] Second dissociation reaction of carbonic acid: HCO3 - → H + + CO3 2-

[0061] Figure 3b shows the carbonate ratio according to the pH of water, respectively. Referring to Figure 3b, it can be seen that the higher the pH of the aqueous solution, the more active the dissociation reaction occurs by reacting with carbon dioxide, and the higher the carbonate and bicarbonate ratios. Since carbon dioxide does not dissolve in water above its maximum solubility (approximately 1.5 g / l at 1 atm) unless the gas pressure is increased, HCO3 is required to continuously dissolve carbon dioxide in the electrolyte solution at the reaction equilibrium. - and H + must be consumed continuously.

[0062] Figure 3c shows the measured pH value and the expected pH fluctuation range near pH 8 of typical seawater. During the discharge process of a magnesium-secondary battery, oxygen reacts with hydrogen ions in the solution to produce water, so the solution becomes alkaline and the pH increases. In the magnesium-air battery reaction, H+ Because carbon dioxide must be continuously consumed, the elevated pH during the discharge process allows carbon dioxide to continuously dissolve in the concentrated seawater. As carbon dioxide dissolves in seawater, H + Because the carbon dioxide is continuously dissociated, the pH of the electrolyte solution does not change significantly. At this time, the dissolved carbon dioxide is converted to carbonate or bicarbonate, which reacts with the metal in the seawater and the magnesium ions of the magnesium electrode to form carbonated minerals, which can be stored and separated. In addition, because the magnesium electrode continuously provides metal, it can additionally contribute to the process of converting carbon dioxide.

[0063] Synthesis of Fe-NC catalytic air electrode materials and catalyst electrode coating

[0064] The Fe-NC catalyst air electrode was synthesized using a solution plasma synthesis method, as shown in Fig. 4a. A precursor solution was prepared by adding 100 mg of graphene nanoplatelets and 100 mg of iron phthalocyanine to 100 mL of 1-methyl-2-pyrrolidone (NMP) solution and magnetically stirring for 2 hours to ensure sufficient mixing. The prepared precursor solution was placed in a plasma reactor, and a pair of graphite electrodes for plasma generation were positioned facing each other with a gap of approximately 1 mm. As shown in Fig. 4b, the electrodes were insulated with ceramic tubes, and only the 1 mm ends were exposed to the solution to concentrate energy. A high-voltage bipolar pulse generator (voltage 1 kV, current 1 A) was used in the prepared reactor to apply pulse current to both electrodes to carry out catalyst synthesis. The applied voltage, pulse width, and frequency were precisely maintained at 10 kV, 1.0 μs, and 25 kHz, respectively, and the process was performed for 20 minutes. The solution after plasma synthesis was filtered through a polytetrafluoroethylene (PTFE) filter with a pore size of 0.45 μm and washed several times with ethanol and distilled water to remove residual precursors. The filtered powder was dried in an oven at 80°C for 24 hours. The dried Fe-NC catalyst powder was evenly ground using a mortar and pestle.

[0065] In the present invention, the carbon felt used as the substrate of the catalyst air electrode was prepared by heat treatment at 500°C for 3 hours (heating temperature: 2°C / min) in an air atmosphere for hydrophilic treatment. The catalyst ink was prepared by mixing distilled water (200 μL), ethanol (780 μL), and Nafion 117 solution (20 μL) per catalyst powder (4 mg) and ultrasonicating for 30 minutes. As the coating area changed, the ratio of the ink composition was maintained, but the amounts of the catalyst and solution introduced were adjusted by decreasing or increasing them. As shown in Fig. 4c, the catalyst ink was applied to the carbon felt using a spray coater at a concentration of 2 mg / cm. 2 was coated. The coated electrode was dried in an oven at 80°C for 24 hours. Through this process, the catalytic air electrode of the present invention can be manufactured.

[0066] Cell assembly and electrochemical performance evaluation

[0067] Seawater or concentrated seawater was prepared by adding sea salt to distilled water. Seawater was prepared by adding sea salt at a concentration of 34 ppt, and concentrated seawater was prepared by adding sea salt at a concentration of 68 ppt or higher. AZ-31 was used as the magnesium-based metal. The catalyst electrode was assembled into an acetal frame, as shown in Fig. 4d. The metal electrode was positioned at a distance of approximately 1 cm from the catalyst electrode, as shown in Fig. 4e, and assembled.

[0068] As shown in Fig. 4f, a three-electrode cell system was constructed with the catalyst electrode as the working electrode, the metal electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode. Electrochemical experiments were conducted using a VSP multi-potentiostat / galvanostat from BioLogic, as shown in Fig. 4g. Electrochemical experiments were conducted with sufficient carbon dioxide gas injected.

[0069] FIG. 5a and FIG. 5b are photographs showing a scene of injecting carbon dioxide into a hybrid power system according to an embodiment of the present invention and a scene of lighting an LED bulb using the hybrid power system, respectively. In one embodiment of the present invention, a non-precious metal (Fe-NC) was applied as a catalyst for the cathode air electrode. Here, NC is nitrogen-doped carbon, and Fe-NC is a complex of iron atoms and NC carbon, which is a catalyst that provides high efficiency and stability in the oxygen reduction reaction (ORR reaction). Thanks to the chlorine-preventing function provided by NC, deterioration can be minimized, so that carbon dioxide can show a conversion efficiency of 0.8 g / Wh and the battery can be operated for more than 50 hours in concentrated seawater (7 wt.% NaCl).

[0070] Referring to Figure 5c, there is a section where the voltage starts at around 1.65 V and then suddenly drops to near 1.0 V in the very beginning. This is due to rapid electrochemical changes within the battery and the activation of initial reactions on the electrode surface, and is a common phenomenon that can occur during the battery stabilization process. Excluding that section, the voltage is continuously maintained at around 1.0 V for over 50 hours, indicating stable battery performance. In other words, since the battery provides consistent voltage for a long period of time after the initial stabilization process, the long-term durability of the battery can be assessed as good.

[0071] According to Figure 5d, in the case where concentrated seawater with a salinity concentration of 1.2 M, which is one embodiment of the present invention, was used as an electrolyte solution, the maximum output was 36.15 mW / cm. 2 You can see that it can show the highest output.

[0072] The four drawings in FIG. 6 show the results of comparing the performance in concentrated seawater and the performance when using carbon dioxide using a hybrid power system according to one embodiment of the present invention.

[0073] Referring to Fig. 6a, the battery was sufficiently discharged using concentrated seawater, and in particular, the discharge current and battery voltage increased when carbon dioxide was injected. This is thought to be because carbon dioxide dissolved in concentrated seawater forms ions, which enhances the ionic conductivity of the concentrated seawater until the solubility limit of the substance is reached, thereby reducing the resistance of the electrolyte. In particular, the pH of the electrolyte is lowered as carbon dioxide is dissolved, which improves the voltage of the battery.

[0074] Referring to Figure 6b, EIS analysis confirmed that the resistance of the battery significantly decreased when carbon dioxide was injected compared to when carbon dioxide was not injected. This decrease in battery resistance is thought to indicate increased electrolyte conductivity and enhanced electrode surface reactivity.

[0075] Referring to Figure 6c, although the values ​​vary depending on the current density, the voltage remains nearly constant over time at the same current density. This confirms that the hybrid power system of the present invention can respond stably for several hours or more even when carbon dioxide is injected.

[0076] Figure 6d shows the XRD graph when the discharge process was performed with and without carbon dioxide injection. Specifically, the "*" marked on the red line only shows the peak corresponding to Mg(OH)2, a by-product generated during the discharge of the Mg-air battery, but it can be confirmed that the black line not only shows the "*" mark but also the "red circle" mark corresponding to sodium carbonate. In the case of magnesium carbonate, since the experimental measurement was in the early stage of discharge, the relatively abundant Na in seawater was precipitated as carbonate first, and if the reaction continues, the by-product Mg(OH)2 can be converted to magnesium carbonate and then precipitated. Through this difference in XRD peaks, it was confirmed that the actual CO2 was ultimately converted into a carbonate or bicarbonate substance through the developed Mg-CO2 secondary battery system.

[0077]

[0078] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below.

Claims

1. A reactor containing an electrolyte solution; A magnesium electrode positioned within the above reactor; An air electrode for inducing an oxygen reduction reaction (ORR) located within the above reactor; a connecting portion connecting the magnesium electrode and the air electrode; and A gas injection device for injecting a gas containing carbon dioxide into the above electrolyte solution is included. Bicarbonate (HCO3) is produced by carbonation reaction in the above electrolyte solution. - ) or carbonate (CO3 2- ) characterized by the production of a system substance, Carbon dioxide conversion hybrid power system based on magnesium-air secondary batteries.

2. In paragraph 1, The above electrolyte solution contains concentrated seawater, Carbon dioxide conversion hybrid power system based on magnesium-air secondary batteries.

3. In paragraph 1, The above air electrode comprises a non-precious metal catalyst, Carbon dioxide conversion hybrid power system based on magnesium-air secondary batteries.

4. In paragraph 3, The above non-precious metal catalyst comprises an iron-bonded nitrogen-doped carbon (Fe-NC) catalyst. Carbon dioxide conversion hybrid power system based on magnesium-air secondary batteries.

5. In paragraph 1, Characterized in that the pH of the electrolyte solution is maintained at 7.0 to 9.0 by the oxygen reduction reaction (ORR) and the carbonation reaction. Carbon dioxide conversion hybrid power system based on magnesium-air secondary batteries.

6. In paragraph 5, The above gas injection device further includes a device for controlling the amount of gas containing carbon dioxide to maintain the pH of the electrolyte solution. Carbon dioxide conversion hybrid power system based on magnesium-air secondary batteries.

7. In paragraph 1, The bicarbonate (HCO3) produced above - ) or carbonate (CO3 2- ) additionally including a device for separating the system material, Carbon dioxide conversion hybrid power system based on magnesium-air secondary batteries.

8. In paragraph 1, The gas injected into the above gas injection device is exhaust gas containing carbon dioxide and oxygen, characterized in that oxygen can be additionally supplied to the air electrode by the exhaust gas, Carbon dioxide conversion hybrid power system based on magnesium-air secondary batteries.

9. In paragraph 1, The above magnesium-air secondary battery-based carbon dioxide conversion hybrid power system is a power generation facility installed near the coast. Carbon dioxide conversion hybrid power system based on magnesium-air secondary batteries.

10. Desalination tank containing high concentration seawater electrolyte; An oxidation electrode positioned within the above desalination tank; A reduction electrode located within the desalination tank; and Comprising a means for applying power produced by a carbon dioxide conversion hybrid power system based on a magnesium-air secondary battery according to any one of claims 1 to 9 to the oxidation electrode and the reduction electrode. Seawater desalination system.

Images