Method for manufacturing manganese oxide-supported electrode, and redox flow battery

Abstract

The present invention relates to: a method for manufacturing a permanganate solution-supported electrode as an electrode for a redox flow battery; and an electrode. An electrode is manufactured by preparing a permanganate solution according to the concentration of permanganate, immersing a porous carbon electrode for a predetermined time, drying same, and then allowing manganese oxide to be supported on the surface of the porous carbon electrode through a heat treatment process, and the electrode is used for an electrode for a redox flow battery.

Description

Method for manufacturing manganese oxide-supported electrodes and redox flow batteries

[0001] The present invention relates to a method for manufacturing a carbon electrode applied to an electrode of a redox flow battery, and relates to a method for manufacturing a manganese oxide-supported electrode and a redox flow battery including the same.

[0002] Vanadium Redox Flow Batteries (VRFBs) are electrochemical energy storage devices primarily used as renewable energy storage devices. VRFBs are attracting attention as grid-scale energy storage systems due to their stability, long life, and high scalability.

[0003] When charging a vanadium redox flow battery, the tetravalent vanadium ions at the positive electrode are converted to pentavalent vanadium ions, and the trivalent vanadium ions are converted to divalent vanadium ions at the negative electrode. When discharging, the oxidation number of the vanadium ions changes in the opposite direction, and charging and discharging proceed.

[0004] Redox flow batteries have the advantage of being able to be stacked by laminating multiple electrodes, can be designed to separate output and energy, and have excellent safety, making them expected to be used as long-life energy storage systems (ESS). On the other hand, ESS (Energy Storage System) using vanadium redox flow batteries has the advantage of having a low current density of the stack (<120 mA / cm). 2 ) and low energy density (17Wh / L) and low energy efficiency due to BOP power loss, so despite the above advantages, its utilization is low.

[0005] In order to increase the output of a vanadium redox flow battery, it is necessary to improve the output of the stack, and for this, a technology that fundamentally maximizes the activation of the electrode under high current density conditions is required.

[0006] In general, in order to improve the activity of vanadium redox flow battery electrodes, methods such as heat treatment of porous carbon electrodes (carbon felt, carbon paper, etc.), acid treatment, and electrochemical treatment are widely used to improve the surface functional groups and to improve the curvature of the electrode surface. In particular, the method of modifying the carbon felt surface through heat treatment is the most widely used method.

[0007] Conventional heat treatment methods are about 400 to 500 o A method for improving electrode reaction characteristics by improving hydrophilicity and reaction characteristics through the introduction of oxygen functional groups on the surface through heat treatment for 1 to 5 hours under C conditions has been widely used.

[0008] To improve energy efficiency and electrode activation, various metal oxide catalyst introduction electrode technologies have been developed, and among them, low-cost manganese oxide introduction electrode technologies have been developed, but their applicability is still not high due to problems such as performance and complexity of the manufacturing process (hydrothermal synthesis).

[0009] Therefore, the manufacturing process is simple and high current density (>120 mA / cm 2 ) There is a need for a new method for manufacturing a manganese oxide electrode to improve electrochemical reaction characteristics and energy efficiency under these conditions.

[0010] The present invention aims to provide a simple method for manufacturing a manganese oxide-supported electrode using permanganate on a porous carbon electrode, using a conventional heat treatment process.

[0011] The present invention aims to provide a method for manufacturing an electrode, which enables manganese oxide loading, surface area enhancement, oxygen functional group introduction, and heteroatom doping in a single process, and which improves the affinity between an electrolyte and a porous carbon electrode and promotes oxidation and reduction reactions of vanadium, thereby improving overall battery efficiency at high current densities, and an electrode thereof. Furthermore, the present invention aims to provide a vanadium redox flow battery and a stacked secondary battery comprising the same.

[0012] To achieve the above object, the present invention provides a method for manufacturing a manganese oxide-supported electrode, comprising the steps of immersing a carbon electrode in a permanganate solution; and drying and heat-treating the immersed electrode.

[0013] Preferably, the permanganate solution is a phosphorus-based organic permanganate cation salt solution or an ammonium-based organic permanganate cation salt solution.

[0014] Preferably, the concentration of the permanganate solution is 0.01 mg / mL to 100 mg / mL.

[0015] Preferably, the immersion time is 15 to 30 minutes.

[0016] Preferably, the drying is 150 o Drying is done at a temperature below C for 1 to 10 hours.

[0017] Preferably, the heat treatment process may adopt one or more gases among Air, Ar, N2, and CO2, and the heat treatment temperature is 100 to 1,500 o C, and the heat treatment time is 0.5 to 48 hours.

[0018] Preferably, the above method can be performed as a continuous process.

[0019] The present invention provides a manganese oxide-supported electrode manufactured by the above method.

[0020] Preferably, the electrode supports manganese oxide having an oxidation number of +2 to +4 on its surface, in the form of MnO, Mn3O4, or MnO2.

[0021] Preferably, the manganese oxide is in the form of nanoparticles having a size of 10 to 500 nm.

[0022] The present invention provides a redox flow battery including the manganese oxide-supported electrode.

[0023] Preferably, the redox flow battery is a vanadium redox flow battery.

[0024] The electrode manufacturing method of the present invention has the advantage of being able to support manganese oxide on the electrode surface through a heat treatment process after supporting an organic permanganate cation salt, and since the organic cation can be removed through the heat treatment process, an additional post-treatment process is unnecessary, thereby increasing the efficiency of the process. In addition, the high oxidizing power of permanganate allows for the oxidation of the carbon electrode surface, thereby enabling an increase in the electrode surface area and the introduction of oxygen functional groups. In addition, since various organic cations of the organic permanganate cation salt can be utilized, doping with heterogeneous elements such as nitrogen or phosphorus that can promote electrode activity is possible during the manganese oxide supporting process.

[0025] Figure 1 is a schematic diagram of a method for manufacturing a manganese oxide-supported electrode according to one embodiment of the present invention.

[0026] Figure 2 shows the results of the room temperature storage stability evaluation of methyl triphenyl phosphonium permanganate (MTPMnO4) solution.

[0027] Figure 3 is a scanning electron microscope (SEM) photograph of the electrode surface of the examples and comparative examples.

[0028] Figure 4 shows the results of energy dispersive X-ray spectroscopy (EDS) analysis of the electrode surfaces of Examples 6 and 8.

[0029] Figure 5 shows the results of X-ray diffraction analysis (XRD) of the electrode of Example 6.

[0030] Figure 6 shows the results of surface area and pore analysis of the electrodes of Example 6 and Comparative Examples 1 and 2.

[0031] Figure 7 shows the results of surface Mn 2p and P 1s XPS analysis of the electrode of Example 8.

[0032] Figure 8 shows the results of surface O 1s XPS analysis of the electrodes of Example 6 and Comparative Examples 1 and 2.

[0033] Figure 9 shows the results of the catholyte-anolyte CV evaluation of the electrodes of Examples 6 and 8 and Comparative Examples 1 and 2.

[0034] Figures 10 and 11 are charge and discharge voltage curves of a vanadium redox flow battery using electrodes of Examples 6 and 8 and Comparative Examples 1 and 2.

[0035] The present invention provides a method for manufacturing an electrode having manganese oxide supported on a carbon electrode surface, and an electrode thereof. This can effectively improve the voltage efficiency and energy efficiency of a redox flow battery at high current densities by enhancing the electrochemical reaction characteristics of the redox flow battery.

[0036] The present invention improves the surface area of ​​a carbon electrode by supporting manganese oxide on a porous carbon electrode using a permanganate solution and then heat-treating the same. The permanganate is preferably an organic cation permanganate, such as a phosphorus-based organic cation permanganate or an ammonium-based organic cation permanganate. Specifically, various phosphonium permanganates or alkylammonium permanganates can be used.

[0037] As phosphonium permanganate, benzylalkylphosphonium permananate, such as benzylmethylphosphonium permanganate, benzylethylphosphonium permanganate, benzylmethyldiphenylphosphonium permanganate, benzyltrybuthylphosphonium permanagnate, benzylpropylphosphonium permanganate; as alkylphosphonium permanganate, such as methylphosphonium permanganate, ethylphosphonium permanganate, butylphosphonium permanganate, hexylphosphonium permanganate; or S-methyl benzylphosphonium permanganate can be used. The alkylphosphonium permanganate can be prepared by dissolving an alkylphosphonium salt and a potassium permanganate salt in water and causing a precipitation reaction.

[0038] As alkylammonium permanganate, tetrabutylammonium permanganate, tetrabutylammonium permanganate, and tetradecyltrimethylammonium permanganate can be used.

[0039] In addition, the present invention provides a vanadium redox flow battery and a layered secondary battery including a manganese oxide-supported porous carbon electrode.

[0040] Schematic diagram 1 of the manufacturing process of Fig. 1 illustrates a method for manufacturing an electrode having a porous electrode surface supporting manganese oxide according to the present invention. A porous carbon electrode is immersed in an organic cation permanganate solution using a permanganate solution, dried, and then subjected to a heat treatment process to manufacture a manganese oxide-supported electrode.

[0041] In the production of existing manganese oxide-supported electrodes, a hydrothermal synthesis method was used. However, the hydrothermal synthesis process has the disadvantage of being a difficult continuous process and the limitation of having to perform an additional process of washing and drying alkali ions after producing manganese oxide.

[0042] The present invention can support manganese oxide on the surface of a porous carbon electrode by immersing the porous carbon electrode in a permanganate solution and then performing a heat treatment process. After the heat treatment process, a post-treatment (washing and drying) process for removing additional organic cations can be omitted, thereby improving process efficiency and further enabling a continuous process (manufacturing process schematic diagram 2 of Fig. 1).

[0043] The formed manganese oxide can form small nano-sized particles due to the organic cation salt, and the oxidation state of the manganese oxide can be controlled by controlling the heat treatment temperature. In particular, the high oxidizing power of permanganate can induce changes in the shape of the carbon electrode surface and changes in the oxygen functional groups. In addition, by applying various organic cations including phosphorus as a pairing agent for permanganate, it is possible to dope with various heterogeneous elements that can improve the reactivity characteristics, such as phosphorus, in the manganese oxide loading process.

[0044] It has been confirmed that the carbon electrode loaded with manganese oxide according to the present invention has a high surface area, thereby dramatically improving the vanadium oxidation / reduction reaction characteristics. Therefore, by applying the carbon electrode loaded with manganese oxide according to the present invention to a vanadium redox flow battery and a layered secondary battery, it is possible to improve energy efficiency at high current densities due to the improved reactivity of the electrode.

[0045] In one embodiment of the present invention, potassium permanganate, which is a permanganate salt, is dissolved in water to prepare a potassium permanganate solution, which is then added to a solution of a phosphorus-containing organic cation salt (e.g., methyl triphenyl phosphonium chloride) dissolved in water to obtain a phosphorus-containing organic cation salt as a precipitate through a precipitation reaction.

[0046] The prepared phosphorus-containing organic permanganate cation salt is dissolved again in water to prepare a permanganate organic cation salt solution. Next, the porous carbon electrode is immersed in the phosphorus-containing organic permanganate cation salt solution for 15 to 30 minutes, and then 150 o Dry for 1 to 10 hours at a temperature below C and then 100 o C ~ 1500 o A manganese oxide-supported electrode with phosphorus introduced can be obtained through heat treatment in air or various atmospheres such as CO2, Ar, and N2 at a temperature of C for 0.5 to 48 hours.

[0047]

[0048] The present invention provides a manganese oxide-supported electrode manufactured using the above manufacturing method. The electrode includes manganese oxide on its surface having a manganese oxidation number of +2 to +4. Specifically, the manganese oxide is in the form of MnO, Mn3O4, or MnO2. Furthermore, the manganese oxide exists in the form of nanoparticles measuring 10 to 500 nm.

[0049]

[0050] The present invention provides a redox flow battery comprising the manganese oxide-supported electrode. The redox flow battery is preferably a vanadium redox flow battery.

[0051]

[0052] The present invention is described in more detail through the following examples. However, the present invention should not be considered limited thereto.

[0053]

[0054] Manufacturing example: Preparation of methyl triphenyl phosphonium permanganate (MTPMnO4) solution

[0055] Potassium permanganate (KMnO4) was dissolved in water to prepare a permanganate solution (KMnO4 3.16 g, water 200 mL), which was then added to a solution of methyl triphenyl phosphonium chloride (MTPCl), a phosphorus-containing organic cation salt, dissolved in water (MTPCl 6.44 g, water 200 mL), and a precipitation reaction was performed for 1 hour to obtain a phosphorus-containing organic permanganate precipitate. The obtained precipitate was washed with water and vacuum-treated at 40 o Methyl triphenyl phosphonium permanganate (MTPMnO4), an organic cation salt of permanganate containing phosphorus, was obtained by drying at C.

[0056] Figure 2 shows the results of the room temperature storage stability evaluation of a methyl triphenyl phosphonium permanganate (MTPMnO4) solution (concentration of 0.05 mg / mL), confirming stability without any change in the color of the solution for one month.

[0057]

[0058] Examples 1 to 8

[0059] After immersing 5 cm x 5 cm heat-treated carbon felt in a permanganate solution (concentration: 0.05 mg / mL) as shown in Table 1 below for 15 minutes, 80 oAfter drying for 4 hours at C, a manganese oxide-supported electrode was manufactured by heat-treating it in an air atmosphere at a temperature as shown in Table 1 for 2 hours.

[0060]

[0061] Comparative Example 1

[0062] A commercial carbon felt electrode (JNTG) was used as a porous carbon electrode.

[0063]

[0064] Comparative Example 2

[0065] The carbon felt electrode of Comparative Example 1 was heated at 500°C in air atmosphere. o C was heat treated for 5 hours.

[0066]

[0067] Sample Felt Type Permanganate Treatment Temperature Treatment Atmosphere Comparative Example 1 Bare---Comparative Example 2 Heat Treatment-500 Ar Example 1 Heat Treatment KMnO 4 500 Ar Example 2 Heat Treatment KMnO 4 500 Air Example 3 Heat Treatment KMnO 4 800 Air Example 4 Heat Treatment TBA MnO 4 500 Ar Example 5 Heat Treatment TBA MnO 4 500 Air Example 6 Heat Treatment TBA MnO 4 800 Air Example 7 Heat Treatment TBA MnO 4 1000 Air Example 8 Heat Treatment MTP MnO 4 800 Air

[0068] *TBAMnO4: tetrabutylammonium permanganate

[0069] *Examples 1 and 2, and Examples 4 and 5 have different heat treatment gas atmospheres of Ar and Air, respectively.

[0070]

[0071] Measurement and Evaluation

[0072] The BET surface area of ​​the electrode surfaces of the examples and comparative examples was measured. The results show that the specific surface area of ​​the electrode treated with the organic cation salt of permanganate solution increased by 8-10 times or more compared to the electrode before pretreatment (Comparative Example 1) and by 6-8 times compared to the heat-treated electrode (Comparative Example 2).

[0073] Electrode surface area (m2 / g) Comparative example 11.092 Comparative example 21.319 Example 33.410 Example 68.902 Example 810.341

[0074]

[0075] Scanning electron microscope (SEM) images of the electrode surfaces of the examples and comparative examples were taken (Fig. 3). SEM surface analysis revealed roughness on the carbon fiber surface of the example electrodes and the presence of very small particles measuring 10–100 nm. These particles are presumed to be manganese oxide.

[0076]

[0077] For the electrode surfaces of Examples 6 and 8, the C, O, P, and Mn elements on the surface of the cargon felt fiber were analyzed using energy dispersive X-ray spectroscopy (EDS) (Fig. 4). As a result of the EDS analysis, Mn and O elements were observed, so the formed particles are presumed to be manganese oxides. In addition, since phosphorus (P) was clearly observed, it can be confirmed that phosphorus (P) was introduced through the manufacturing method of the present invention.

[0078]

[0079] Example 6 X-ray diffraction (XRD) analysis was performed to analyze the crystal structure of the electrode. The results are shown in Fig. 5. It was confirmed that the material supported on the carbon felt surface was manganese oxide. The Mn3O4 crystal structure was observed at a heat treatment temperature of 500-800°C, and the MnO crystal structure was observed from 1000°C. Depending on the heat treatment temperature, changes in the crystallinity and size of manganese oxide, as well as the oxidation number of manganese, can be confirmed, indicating that the shape and oxidation number of manganese oxide can be controlled using the manufacturing method of the present invention.

[0080]

[0081] For the specific surface area and pore analysis of the electrodes of Comparative Examples 1, 2, and Example 6, a specific surface area analyzer (Brunauer Emmett Teller, BET) was performed (Fig. 6). It was confirmed that the manganese oxide of the manganese oxide-supported electrode manufactured by the method of applying the permanganate organic cation salt in the present invention maintained a particle size of about 100 nm even after undergoing a high-temperature heat treatment process.

[0082]

[0083] In Example 8, X-ray photoelectron spectroscopy (XPS) analysis of Mn 2p and P 1s of the high surface area manganese oxide electrode was performed (Fig. 7). Here, the manganese oxide formed on the carbon electrode surface had an oxidation number of Mn 2+ Wow Mn 3+ It can be confirmed that 2H2O3 is observed simultaneously, and it can be seen that the manganese oxide formed from this is in the form of Mn3O4. In addition, it can be confirmed that phosphorus is introduced to the carbon electrode surface through the P 1s XPS analysis results.

[0084]

[0085] XPS analysis of O 1s of the electrodes of Comparative Example and Example 6 was performed (Fig. 8). It was confirmed that the -COOH ratio increased in the heat-treated carbon felt electrode (Comparative Example 2) compared to the carbon felt before pretreatment (Comparative Example 1). Comparative Example 2 was heat-treated in an air atmosphere to impart hydrophilicity. The heat treatment increases the C=O groups on the surface, thereby improving the hydrophilicity.

[0086] In particular, in the case of the manganese oxide-supported electrode, it can be confirmed that the ratio of -C=O and -COOH increases compared to the heat-treated carbon felt electrode (Comparative Example 2). It can be confirmed that the surface oxygen functional groups are better developed in the manganese oxide-supported electrode compared to the heat-treated electrode. This is thought to be the result of oxidation of surface carbons by the reduction reaction of permanganate. In addition, it can be clearly seen that manganese oxide is developed on the surface of the porous carbon electrode as Mn-O-Mn is observed in the O 1s XPS analysis results.

[0087]

[0088] Comparative Example and Example 6 Cyclic voltammetry (CV) analysis of the electrode [reference electrode: saturated calomel electrode, counter electrode: Pt mesh, electrolyte: 0.1 M VOSO4 in 2.5 M H2SO4 solution, scan rate 5 mV / sec] V 4+ ↔ V 5+ The degree of oxidation / reduction reaction was compared (Fig. 9(a)). In the same way, the V of the high surface area manganese oxide electrode (Example 8) was introduced. 4+ ↔ V 5+ The oxidation / reduction reaction characteristics were measured (Fig. 9 (b)). The decrease in oxidation / reduction peak separation (ΔE) and the oxidation / reduction peak current ratio (I red / I ox ) can be confirmed to have the best characteristics.

[0089] Next, V 2+ ↔ V 3+ The degree of oxidation / reduction reaction was compared, and the V of the manganese oxide electrode (Example 8) with phosphorus introduction 2+ ↔ V 3+ The oxidation / reduction reaction characteristics are characterized by a decrease in oxidation / reduction peak separation (ΔE) and oxidation / reduction peak current ratio (Ired / I ox ) can be confirmed to have the best characteristics (Fig. 9 (c) and (d)).

[0090]

[0091] Comparative examples and examples 6 and 8 were used to evaluate vanadium redox flow battery single cells (Figs. 10 and 11). The electrolyte used was 1.7 M VOSO4 in 2.5 M H2SO4, the electrode area was 5 cm x 5 cm, the electrode compression ratio was approximately 26%, and the battery charge / discharge cut-off voltage range was 0.8 to 1.7 V.

[0092] The vanadium redox flow battery single cell using the electrodes of Examples 6 and 8 showed improved voltage efficiency characteristics (reduced overvoltage) compared to the electrodes of Comparative Examples 1 and 2, and in particular, at a current density of 200 mA / cm 2 Under high current density conditions, the overvoltage improvement effect was significantly observed. This is believed to be due to the improvement in electrode reaction characteristics in the previous electrochemical characteristic analysis.

[0093]

[0094] In addition, as shown in Table 3 below, the vanadium redox flow batteries using the electrodes of Examples 6 and 8 exhibited high electrolyte utilization characteristics due to their excellent electrolyte utilization characteristics under high current density conditions. This is believed to be due to the increased coulombic efficiency and consequently increased electrolyte utilization due to the rapid electrode reaction characteristics under low concentration conditions.

[0095] Comparative Example 1 Comparative Example 2 Example 6 Example 8 Current (mA / cm2) CE (%) VE (%) EE (%) CE (%) VE (%) EE (%) CE (%) VE (%) EE (%) CE (%) VE (%) EE (%)8092.777.772.593.791.085.293.492.786.691.592.584.812094.571.267.694.986.382.295.389.284.793.289.183.1160---95.882.278.796.185.982.193.986.180.8200---96.478.375.395.883.179.694.283.078.2300---96.767.866.497.773.671.994.875.471.5

[0096]

[0097] The present invention is being filed with the support of the tasks described below.

[0098] - Assignment ID: RS-2024-00407015

[0099] - Ministry name: Ministry of Science and ICT

[0100] - Project Management (Professional) Organization Name: National Research Foundation of Korea

[0101] - Research Project Name: Source Technology Development Project

[0102] - Research Project Name: (C) Development of Advanced Technology for 120 Wh / kg Ultra-Long-Life Aqueous Zinc Secondary Battery Based on Multielectron Iodine Reaction

[0103] - Project implementation organization name: Korea Electrotechnology Research Institute

[0104] Research period: April 1, 2024 - December 31, 2028

Claims

1. A step of immersing a carbon electrode in a permanganate solution; and A method for manufacturing a manganese oxide-supported electrode, comprising the steps of drying and heat treating the above-mentioned immersed electrode.

2. In paragraph 1, A method for manufacturing a manganese oxide-supported electrode, characterized in that the above-mentioned permanganate solution is a phosphorus-based organic permanganate cation salt solution or an ammonium-based organic permanganate cation salt solution.

3. In paragraph 1, A method for manufacturing a manganese oxide-supported electrode, characterized in that the concentration of the permanganate solution is 0.01 mg / mL to 100 mg / mL.

4. In paragraph 1, A method for manufacturing a manganese oxide-supported electrode, characterized in that the immersion time is 15 to 30 minutes.

5. In paragraph 1, The above drying is 150 o A method for manufacturing a manganese oxide-supported electrode, characterized by drying at a temperature of C or lower for 1 to 10 hours.

6. In paragraph 1, The above heat treatment process can adopt one or more gases among Air, Ar, N2, and CO2, and the heat treatment temperature is 100 to 1,500 o C, and a heat treatment time of 0.5 to 48 hours, characterized by a method for manufacturing a manganese oxide-supported electrode 7. In paragraph 1, A method for manufacturing a manganese oxide-supported electrode, characterized in that the above method is performed as a continuous process.

8. A manganese oxide-supported electrode characterized by being manufactured by the method of any one of claims 1 to 7.

9. In paragraph 8, The above electrode is a manganese oxide-supported electrode, characterized in that it supports manganese oxide having an oxidation number of +2 to +4.

10. In Article 9, A manganese oxide-supported electrode, characterized in that the manganese oxide is in the form of nanoparticles having a size of 10 to 500 nm.

11. A redox flow battery comprising a manganese oxide-supported electrode of clause 8.

12. In paragraph 11, A redox flow battery, characterized in that the above redox flow battery is a vanadium redox flow battery.

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