An Ag / MnO2 alkaline oxygen evolution catalyst, its preparation method and application

Abstract

This invention discloses an Ag / MnO2 alkaline oxygen evolution catalyst, its preparation method, and its application, belonging to the field of catalyst technology. The catalyst preparation method includes: (1) dissolving manganese salt, silver salt, and anionic surfactant in a solvent and obtaining an Ag / MnO2 precursor via a hydrothermal reaction; (2) calcining the Ag / MnO2 precursor to obtain the Ag / MnO2 alkaline oxygen evolution catalyst. The catalyst of this invention is made from non-precious metal materials, with abundant and inexpensive raw material sources, which can reduce the production cost of the catalyst; in addition, the catalyst preparation method is simple to operate and easy to mass-produce. In this invention, Ag nanoparticles anchored on the MnO2 surface help increase the specific surface area of ​​the composite catalyst, which helps to expand the electrochemical reaction region, and it exhibits good OER catalytic activity and stability in alkaline electrolytes.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to an Ag / MnO2 alkaline oxygen evolution catalyst, its preparation method, and its application. Background Technology

[0002] With industrial development, fossil fuels have been overexploited, leading to increasingly severe environmental pollution and an urgent need to find new, sustainable alternative energy sources. Hydrogen energy, due to its high calorific value and environmentally friendly combustion products, is considered the optimal choice to replace traditional fossil fuels. As part of the future hydrogen economy, water electrolysis, as an economically feasible and environmentally friendly hydrogen production technology, has been extensively studied. Water electrolysis consists of two half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The HER reaction involves a two-electron transfer process. However, the OER reaction involves a four-electron transfer and oxygen-oxygen bond formation, resulting in slow reaction kinetics, which is the main reason affecting the efficiency of water electrolysis. Developing efficient OER reaction catalysts is key to overcoming the OER reaction barrier and thus increasing the OER reaction rate.

[0003] Manganese oxides are attractive materials in various fields due to their low price, natural abundance, and low toxicity. Among them, MnO2 is the most extensively studied. However, its low electrical conductivity limits the electron transfer rate in the MnO2-catalyzed reaction process. Ag is considered an attractive conductive modifier due to its high conductivity, acceptable cost, and excellent OER catalytic activity. However, in the current technology, Ag and MnO2 are often combined for acidic electrocatalytic oxygen evolution reactions, but there are no reports on the use of Ag and MnO2 combined for alkaline electrocatalytic oxygen evolution reactions. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide an Ag / MnO2 alkaline oxygen evolution catalyst, its preparation method, and its application. This catalyst has abundant and inexpensive raw materials, can be used for alkaline electrocatalytic oxygen evolution reactions, and can be synthesized in a one-step process. The preparation process is simple and easy for large-scale production.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing an Ag / MnO2 alkaline oxygen evolution catalyst is provided, comprising the following steps:

[0006] (1) Manganese salt, silver salt and anionic surfactant are co-dissolved in a solvent and then subjected to a hydrothermal reaction to obtain Ag / MnO2 precursor;

[0007] (2) The Ag / MnO2 precursor was calcined to prepare the Ag / MnO2 alkaline oxygen evolution catalyst.

[0008] The beneficial effects of this invention are as follows: This invention grows Ag nanoparticles on MnO2 in one step using a hydrothermal method, that is, it prepares Ag / MnO2 catalyst in one step. The preparation process is simple and easy to mass-produce.

[0009] In this invention, the addition of anionic surfactants can significantly reduce the surface tension in the hydrothermal system, enhance the wettability of the system, and help the Ag nanoparticles be better dispersed in the solvent, avoiding agglomeration, thereby improving the uniformity and efficiency of the reaction. In other words, the addition of anionic surfactants makes Ag uniformly distributed on the MnO2 surface, which is beneficial to the catalytic reaction.

[0010] In the Ag / MnO2 catalyst prepared by this invention, Ag nanoparticles are anchored on the MnO2 surface, and there is a strong interaction between the two. Therefore, this helps to increase the specific surface area of ​​the composite catalyst and expand the electrochemical reaction region. Simultaneously, the high electrical conductivity of the Ag nanoparticles helps to construct electron transport channels between MnO2 particles, thereby achieving rapid electron transfer during the reaction, improving electrochemical activity, and resulting in good OER catalytic activity and stability of the catalyst in alkaline electrolytes.

[0011] Based on the above technical solution, the present invention can be further improved as follows:

[0012] Further, in step (1), the molar ratio of manganese salt to silver salt is 90-99:1-10, and the mass ratio of manganese salt to anionic surfactant is 5-15:1-3; preferably, the molar ratio of manganese salt to silver salt is 95:5, and the mass ratio of manganese salt to anionic surfactant is 10:1.

[0013] Furthermore, in step (1), the manganese salt is KMnO4 or Mn(CH3COO)2; the silver salt is AgNO3; and the solvent is water.

[0014] Furthermore, in step (1), the anionic surfactant is sodium dodecyl sulfonate, fatty acid salt, or sodium alkylbenzene sulfonate.

[0015] Furthermore, in step (1), the temperature during the hydrothermal reaction is 100-150℃ and the reaction time is 8-12h; preferably, the temperature during the hydrothermal reaction is 130℃ and the reaction time is 10h.

[0016] Further, after the hydrothermal reaction in step (1) is completed, the reaction product is filtered, washed and dried to obtain the Ag / MnO2 precursor.

[0017] Furthermore, in step (1), the washing process involves rinsing with anhydrous ethanol and deionized water 2-3 times in sequence.

[0018] Furthermore, in step (1), the drying is carried out at 80-120℃ for 4-8 hours; preferably, the drying is carried out at 100℃ for 6 hours.

[0019] Furthermore, in step (2), calcination is carried out in an air atmosphere at 2-4°C for 1 minute. -1 The Ag / MnO2 precursor was heated to 600-800℃ and annealed for 4-6 hours at a heating rate; preferably at 3℃ / min in an air atmosphere. -1 The Ag / MnO2 precursor was heated to 700℃ and annealed for 6 hours at a certain heating rate.

[0020] Furthermore, the MnO2 in the Ag / MnO2 alkaline oxygen evolution catalyst has an α-MnO2 crystal structure.

[0021] The MnO2 in this invention has an α-MnO2 crystal structure. α-MnO2 is a layered crystal with a basic structural unit of [MnO6] octahedron. These octahedrons are interconnected by sharing oxygen atoms, forming a layered crystal structure. This structure gives α-MnO2 a high specific surface area and good ion exchange performance, which is beneficial for catalytic reactions.

[0022] The above-prepared Ag / MnO2 alkaline oxygen evolution catalyst is used in alkaline electrocatalytic oxygen evolution reaction.

[0023] The present invention has the following beneficial effects:

[0024] The catalyst of this invention is made of non-precious metal materials, which are abundant and inexpensive, thus reducing the production cost of the catalyst. Furthermore, the preparation method of the catalyst is simple and easy to scale up. The catalyst prepared by this invention exhibits good OER catalytic activity and stability in alkaline electrolytes. In 1M KOH, the oxygen evolution reaction was measured to be stable at a current density of 10 mA cm⁻¹. -2 At that time, the corresponding overpotential is 535mV, and the Tafel slope is 81mV dec. -1 At 1.724V vs. RHE, the ohmic impedance is 2.010Ω. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation process of the Ag / MnO2 alkaline oxygen evolution catalyst of the present invention;

[0026] Figure 2 XRD patterns of MnO2-D1 (Comparative Example 1), Ag / MnO2-S4 (Example 4), and Ag / MnO2-S1 (Example 1);

[0027] Figure 3 This is a SEM image of Ag / MnO2-S1 (Example 1) of the present invention;

[0028] Figure 4 Linear sweep voltammetry (LSV) curves of oxygen evolution reaction of MnO2-D1 (Comparative Example 1), Ag / MnO2-S4 (Example 4) and Ag / MnO2-S1 (Example 1) in 1M KOH electrolyte;

[0029] Figure 5 Tafel plots of MnO2-D1 (Comparative Example 1), Ag / MnO2-S4 (Example 4), and Ag / MnO2-S1 (Example 1) in 1M KOH electrolyte;

[0030] Figure 6 Electrochemical impedance spectroscopy (EIS) spectra of MnO2-D1 (Comparative Example 1), Ag / MnO2-S4 (Example 4), and Ag / MnO2-S1 (Example 1) in 1M KOH electrolyte. Detailed Implementation

[0031] The examples given below are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, conditions in the examples are performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0032] Example 1:

[0033] A method for preparing an Ag / MnO2 alkaline oxygen evolution catalyst is shown in the schematic diagram below. Figure 1 The specific process includes the following steps:

[0034] (1) Weigh silver nitrate (0.054 g) and potassium permanganate (0.960 g) in a clean beaker according to the molar ratio of Ag to Mn of 5:95. Add sodium dodecyl sulfonate (0.096 g) and then add 70 ml of deionized water and stir magnetically for 1 h. Pour the mixed solution into a 100 ml stainless steel reactor liner. Place the reactor in an oven and heat-treat at 130 °C for 10 h, then allow it to cool naturally to room temperature in air. Pour the black precipitate in the reactor liner into a vacuum filtration flask and filter it. Wash the precipitate 2-3 times with anhydrous ethanol and deionized water. Place the filtered precipitate sample in a drying oven and dry it at 100 °C for 6 h, then grind it for 1 h to obtain the Ag / MnO2 precursor.

[0035] (2) The Ag / MnO2 precursor was subjected to an air atmosphere at 3°C ​​for 3 min. -1The temperature was increased to 700℃ and annealed for 6 hours to obtain the Ag / MnO2 catalyst, which was named Ag / MnO2-S1.

[0036] Example 2:

[0037] A method for preparing an Ag / MnO2 alkaline oxygen evolution catalyst includes the following steps:

[0038] (1) Weigh silver nitrate (0.054 g) and potassium permanganate (0.960 g) in a clean beaker according to the molar ratio of Ag to Mn of 5:95. Add sodium dodecyl sulfonate (0.096 g) and then add 70 ml of deionized water and stir magnetically for 1 h. Pour the mixed solution into a 100 ml stainless steel reactor liner. Place the reactor in an oven and heat-treat at 100 °C for 10 h, then allow it to cool naturally to room temperature in air. Pour the black precipitate in the reactor liner into a vacuum filtration flask and filter it. Wash the precipitate 2-3 times with anhydrous ethanol and deionized water. Place the filtered precipitate sample in a drying oven and dry it at 80 °C for 8 h, then grind it for 1 h to obtain the Ag / MnO2 precursor.

[0039] (2) The Ag / MnO2 precursor was subjected to an air atmosphere at 2℃ for 2 min. -1 The temperature was increased to 600℃ and annealed for 6 hours to obtain the Ag / MnO2 catalyst, which was named Ag / MnO2-S2.

[0040] Example 3:

[0041] A method for preparing an Ag / MnO2 alkaline oxygen evolution catalyst includes the following steps:

[0042] (1) Weigh silver nitrate (0.054 g) and potassium permanganate (0.960 g) in a clean beaker according to the molar ratio of Ag to Mn of 5:95. Add sodium dodecyl sulfonate (0.096 g) and then add 70 ml of deionized water and stir magnetically for 1 h. Pour the mixed solution into a 100 ml stainless steel reactor liner. Place the reactor in an oven and heat-treat at 150 °C for 10 h, then allow it to cool naturally to room temperature in air. Pour the black precipitate in the reactor liner into a vacuum filtration flask and filter it. Wash the precipitate 2-3 times with anhydrous ethanol and deionized water. Place the filtered precipitate sample in a drying oven and dry it at 120 °C for 4 h, then grind it for 1 h to obtain the Ag / MnO2 precursor.

[0043] (2) The Ag / MnO2 precursor was subjected to an air atmosphere at 4℃ for 4 min. -1 The temperature was increased to 800℃ and annealed for 6 hours to obtain the Ag / MnO2 catalyst, which was named Ag / MnO2-S3.

[0044] Example 4:

[0045] A method for preparing an Ag / MnO2 alkaline oxygen evolution catalyst includes the following steps:

[0046] (1) Weigh silver nitrate (0.114 g) and potassium permanganate (0.960 g) in a clean beaker according to the molar ratio of Ag to Mn of 10:90. Add sodium dodecyl sulfonate (0.096 g) and then add 70 ml of deionized water and stir magnetically for 1 h. Pour the mixed solution into a 100 ml stainless steel reactor liner. Place the reactor in an oven and heat-treat at 130 °C for 10 h, then allow it to cool naturally to room temperature in air. Pour the black precipitate in the reactor liner into a vacuum filtration flask and filter it. Wash the precipitate 2-3 times with anhydrous ethanol and deionized water. Place the filtered precipitate sample in a drying oven and dry it at 100 °C for 6 h, then grind it for 1 h to obtain the Ag / MnO2 precursor.

[0047] (2) The Ag / MnO2 precursor was subjected to an air atmosphere at 3°C ​​for 3 min. -1 The temperature was increased to 700℃ and annealed for 6 hours to obtain the Ag / MnO2 catalyst, which was named Ag / MnO2-D2.

[0048] Comparative Example 1:

[0049] A method for preparing a basic MnO2 oxygen evolution catalyst includes the following steps:

[0050] (1) Dissolve 0.960 g of potassium permanganate and 0.096 g of sodium dodecyl sulfate in 70 ml of deionized water and stir to form a homogeneous solution. Pour the solution into a 100 ml stainless steel reactor liner, place the reactor in an oven and heat-treat at 130 °C for 10 h, then allow it to cool naturally to room temperature in air. Pour the black precipitate in the reactor liner into a vacuum filtration flask and filter it, washing it 2-3 times with anhydrous ethanol and deionized water. Place the filtered precipitate sample in a drying oven and dry it at 100 °C for 6 h, then grind it for 1 h to obtain the MnO2 precursor;

[0051] (2) The MnO2 precursor was subjected to an air atmosphere at 3°C ​​for 3 min. -1 The temperature was increased to 700℃ and annealed for 6 hours to obtain the MnO2 catalyst, which was named MnO2-D1.

[0052] Experimental Example

[0053] The Ag / MnO2 alkaline oxygen evolution catalysts prepared in Examples 1-4 have similar structures and functions. The Ag / MnO2 alkaline oxygen evolution catalyst prepared in Example 1 will be used as an example for illustration.

[0054] 1. The Ag / MnO2 alkaline oxygen evolution catalyst prepared in Example 1 was analyzed by XRD, and the results are as follows: Figure 2 As shown. The characteristic peaks of MnO2 in the sample correspond to the (003), (104), (113), (024) and (125) crystal planes, and Ag corresponds to the (111), (200) and (220) crystal planes.

[0055] 2. SEM analysis was performed on the Ag / MnO2 alkaline oxygen evolution catalyst in Example 1, and the results are as follows: Figure 3 As shown. By Figure 3 It is known that the nanorod structure consists of MnO2 particles, and the spherical particles on the surface of the nanorods are Ag nanoparticles. The anchoring of Ag nanoparticles on the MnO2 surface helps to increase the specific surface area of ​​the composite catalyst, which in turn helps to expand the electrochemical reaction region. The high electrical conductivity of Ag nanoparticles helps to construct electron transport channels between MnO2 particles, thereby enabling rapid electron transfer during the reaction and improving its catalytic performance.

[0056] 3. Take 10 mg each of the alkaline oxygen evolution catalysts prepared in Example 1, Example 4 (Example 1), and Comparative Example 1, mix them with 10 mg of Super P Li, and then disperse them in a mixture of 1 ml anhydrous ethanol and 0.100 ml Nafion solution. Sonicate for 60 min to form a homogeneous slurry. Take 0.100 ml of the catalyst slurry and drop it evenly onto a 1 cm² surface. 2 It is used as a working electrode on carbon paper.

[0057] Electrochemical tests were conducted using a DH7000 electrochemical workstation (Jiangsu Donghua Analytical Instruments Co., Ltd.). A three-electrode system was employed, with catalyst-supported carbon paper as the working electrode, Hg / HgO (1M KOH) as the reference electrode, and platinum wire as the counter electrode. All tests were performed in an O2-saturated 1M KOH solution. Before each test, O2 was bubbled into the 1M KOH solution for 30 minutes to ensure saturation. Oxygen was continuously bubbled into the solution during the test until its completion. The linear sweep voltammetry (LSV) curves of the OER reaction were obtained at room temperature (25℃) at 10 mV s⁻¹. -1 The electrode potentials obtained from the scan rate test are all converted to reversible hydrogen electrode potentials from the electrochemical test relative to Hg / HgO (1M KOH). The conversion formula is as follows:

[0058] E RHE =E Hg / HgO +0.098+0.059pH (1)

[0059] Electrochemical impedance spectroscopy (EIS) of working electrodes prepared with different catalysts was tested at 1.724 V vs. RHE potential, with an amplitude of 10 mV and a frequency range of 100 kHz–0.1 Hz. Specific test results are available in [link to relevant documentation]. Figures 4-6 .

[0060] Figure 4 The graph shows the polarization curves of the oxygen evolution reaction of MnO2-D1, Ag / MnO2-S4, and Ag / MnO2-S1 in 1M KOH; Figure 4 It can be seen that at a current density of 10 mA cm⁻¹ -2 At that time, the overpotentials corresponding to MnO2-D1, Ag / MnO2-S4 and Ag / MnO2-S1 were 599, 579 and 535 mV, respectively.

[0061] Figure 5 The figures show the Tafel plots of MnO2-D1, Ag / MnO2-S4, and Ag / MnO2-S1 in 1M KOH. As shown in Figure 5, the Tafel slopes of MnO2-D1, Ag / MnO2-S4, and Ag / MnO2-S1 are 149, 84, and 81 mV dec, respectively. -1 .

[0062] Figure 6 Electrochemical impedance spectroscopy (EIS) spectra of MnO2-D1, Ag / MnO2-S4, and Ag / MnO2-S1 in 1M KOH are shown. The figures indicate that at 1.724V vs. RHE, the ohmic resistances of MnO2-D1, Ag / MnO2-S4, and Ag / MnO2-S1 are 1.706, 1.885, and 2.010 Ω, respectively.

[0063] Depend on Figures 4-6 It is known that more Ag does not necessarily mean better catalytic performance. When the molar ratio of Ag to Mn is 10:90, the catalytic performance decreases compared to when the molar ratio of Ag to Mn is 5:95. This is because with an increased Ag content, Ag particles will agglomerate during the catalyst sintering process, resulting in a decrease in their specific surface area and reduced catalytic activity. Therefore, the best effect is achieved when the molar ratio of Ag to Mn is 5:95.

[0064] Furthermore, in an alkaline environment, the requirements for catalysts in the oxygen evolution reaction (OER) mainly concern their activity and stability. Under alkaline conditions, the catalyst needs to possess high catalytic activity to effectively reduce the overpotential of the OER and increase the reaction rate. In addition, the catalyst also needs to exhibit good stability, maintaining catalytic activity for extended periods in an alkaline environment and being resistant to corrosion or degradation. The catalyst provided by this invention exhibits high catalytic activity under alkaline conditions and can be well applied to alkaline electrocatalytic OER.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an Ag / MnO2 alkaline oxygen evolution catalyst, characterized by, Comprise the following steps: (1) manganese salt, silver salt, anionic surfactant are dissolved in solvent, through hydrothermal reaction to prepare Ag / MnO2 precursor; The anionic surfactant is sodium dodecyl sulfonate, fatty acid salt or sodium alkyl benzene sulfonate;Wherein, the molar ratio of manganese salt and silver salt is 95:5, the mass ratio of manganese salt and anionic surfactant is 5-15:1-3;Manganese salt is KMnO4 or Mn (CH3COO) 2;Silver salt is AgNO3;The temperature in the hydrothermal reaction process is 100-150 ℃, and the reaction time is 8-12 h; (2) calcining the Ag / MnO2 precursor to obtain an Ag / MnO2 alkaline oxygen evolution catalyst; the calcining is to heat the Ag / MnO2 precursor to 600-800 ℃ at a heating rate of 2-4 ℃ min -1 under an air atmosphere, and annealing for 4-6 h; the MnO2 in the Ag / MnO2 alkaline oxygen evolution catalyst is in an α-MnO2 crystal structure.

2. The method for preparing the Ag / MnO2 alkaline oxygen evolution catalyst according to claim 1, characterized in that, The solvent in step (1) is water.

3. The method for preparing the Ag / MnO2 alkaline oxygen evolution catalyst according to claim 1, characterized in that, The temperature in the hydrothermal reaction process in step (1) is 130 ℃, and the reaction time is 10 h.

4. The method for preparing the Ag / MnO2 alkaline oxygen evolution catalyst according to claim 1, characterized in that, After the hydrothermal reaction in step (1) is completed, the reaction product is filtered, washed and dried to prepare Ag / MnO2 precursor.

5. The Ag / MnO2 basic oxygen evolution catalyst prepared by the preparation method of any one of claims 1-4.

6. The application of the Ag / MnO2 basic oxygen evolution catalyst in claim 5 in the basic electrocatalytic oxygen evolution reaction.

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