Ag / MnO2 alkaline oxygen evolution catalyst as well as preparation method and application thereof

Abstract

The invention discloses an Ag / MnO2 alkaline oxygen evolution catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The preparation method of the catalyst comprises the following steps: (1) co-dissolving a manganese salt, a silver salt and an anionic surfactant in a solvent, and carrying out a hydrothermal reaction to prepare an Ag / MnO2 precursor; and (2) calcining the Ag / MnO2 precursor to prepare the Ag / MnO2 alkaline oxygen evolution catalyst. The catalyst is made of non-noble metal materials, the raw materials are rich in source and low in cost, and the production cost of the catalyst can be reduced; in addition, the preparation method of the catalyst is simple to operate and easy for large-scale production. In the catalyst, Ag nanoparticles are anchored on the surface of MnO2, so that the specific surface area of the composite catalyst is increased, an electrochemical reaction region is expanded, and the catalyst has good OER catalytic activity and stability in an alkaline electrolyte.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to an Ag / MnO2 alkaline oxygen evolution catalyst and a preparation method and application thereof. Background Art

[0002] With the development of industry, fossil energy has been overexploited and environmental pollution has worsened. There is an urgent need to find new and sustainable alternative energy sources. Hydrogen energy is considered to be the best choice to replace traditional fossil fuels due to its high combustion calorific value and environmentally friendly combustion products. As part of the future hydrogen economy, water electrolysis has been studied in depth as an economically feasible and environmentally friendly hydrogen production technology. Water electrolysis consists of two half reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The HER reaction involves a two-electron transfer process. However, the OER reaction involves four-electron transfer and oxygen-oxygen bond formation, and its slow reaction kinetics are the main reason affecting the efficiency of water electrolysis. The development of efficient OER reaction catalysts is the 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 thoroughly studied. However, the low electrical conductivity limits the electron transfer rate during the MnO2 catalytic reaction. Ag is considered to be an attractive conductive modifier due to its high conductivity, acceptable cost and excellent OER catalytic activity. However, in the prior art, Ag and MnO2 are often used in combination for acidic electrocatalytic oxygen evolution reaction, but there are no reports on the use of Ag and MnO2 in combination for alkaline electrocatalytic oxygen evolution reaction. Summary of the invention

[0004] In order to solve the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a Ag / MnO2 alkaline oxygen evolution catalyst and a preparation method and application thereof. The catalyst raw material source is abundant and the cost is low. The catalyst can be used for alkaline electrocatalytic oxygen evolution reaction, and the catalyst can be synthesized by a one-step method. The preparation process is simple and easy to mass produce.

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

[0006] (1) dissolving manganese salt, silver salt and anionic surfactant in a solvent, and preparing Ag / MnO2 precursor through hydrothermal reaction;

[0007] (2) The Ag / MnO2 precursor is calcined to obtain an Ag / MnO2 alkaline oxygen evolution catalyst.

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

[0009] In the present invention, by adding anionic surfactants, the surface tension in the hydrothermal system can be significantly reduced, the wettability of the system is enhanced, and the raw material Ag nanoparticles are better dispersed in the solvent to avoid agglomeration, thereby improving the uniformity and efficiency of the reaction. In other words, by adding anionic surfactants, Ag is evenly distributed on the surface of MnO2, which is beneficial to the catalytic reaction.

[0010] In the Ag / MnO2 catalyst prepared by the present invention, Ag nanoparticles are anchored on the surface of MnO2, and there is a strong interaction between the two, so it can help to increase the specific surface area of ​​the composite catalyst and expand the electrochemical reaction area. At the same time, the high conductivity of the Ag nanoparticles helps to build an electron transmission channel between MnO2 particles, thereby realizing the rapid transfer of electrons during the reaction process, improving the electrochemical activity, and making the catalyst have good OER catalytic activity and stability in alkaline electrolyte.

[0011] On the basis of the above technical solution, the present invention can also be improved as follows:

[0012] Furthermore, 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° C., and the reaction time is 8-12 h; preferably, the temperature during the hydrothermal reaction is 130° C., and the reaction time is 10 h.

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

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

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

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

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

[0021] The MnO2 in the present invention is an α-MnO2 crystal structure, which is a crystal with a layered structure, and its basic structural unit is a [MnO6] octahedron. These octahedrons are interconnected by sharing oxygen atoms to form a layered crystal structure, which makes α-MnO2 have a high specific surface area and good ion exchange performance, which is conducive to the catalytic reaction.

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

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

[0024] The catalyst of the present invention is made of non-precious metal materials, and the raw material source is abundant and low in cost, which can reduce the production cost of the catalyst; in addition, the preparation method of the catalyst is simple to operate and easy to mass produce. The catalyst prepared by the present invention has good OER catalytic activity and stability in alkaline electrolyte. The oxygen evolution reaction is measured in 1M KOH at a current density of 10mA cm -2 When the overpotential is 535mV, the Tafel slope is 81mV dec. -1 , the ohmic impedance value is 2.010Ω at @1.724V vs.RHE. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure 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 the SEM image of Ag / MnO2-S1 (Example 1) of the present invention;

[0028] Figure 4 Linear sweep voltammetry (LSV) graphs 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) graphs of MnO2-D1 (Comparative Example 1), Ag / MnO2-S4 (Example 4) and Ag / MnO2-S1 (Example 1) in 1M KOH electrolyte. DETAILED DESCRIPTION

[0031] The following examples are only used to explain the present invention and are not intended to limit the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0032] Embodiment 1:

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

[0034] (1) According to the molar ratio of Ag to Mn of 5:95, weigh silver nitrate (0.054g) and potassium permanganate (0.960g) respectively and place them in a clean beaker, add sodium dodecyl sulfate (0.096g), and then add 70ml of deionized water and stir magnetically for 1h. Pour the mixed solution into the lining of a 100ml stainless steel reactor, place the reactor in an oven and heat treat it at 130℃ for 10h, and then cool it naturally to room temperature in the air. Pour the black precipitate in the reactor lining into a suction filtration bottle for suction filtration, and wash it with anhydrous ethanol and deionized water for 2-3 times in turn. Place the filtered precipitate sample in a drying oven and dry it at 100℃ for 6h, then grind it for 1h to obtain Ag / MnO2 precursor;

[0035] (2) The Ag / MnO2 precursor was heated in air at 3°C ​​min -1The temperature was raised to 700°C at a heating rate of 1.5 °C and annealed for 6 h to obtain Ag / MnO2 catalyst, which was named Ag / MnO2-S1.

[0036] Embodiment 2:

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

[0038] (1) According to the molar ratio of Ag to Mn of 5:95, weigh silver nitrate (0.054g) and potassium permanganate (0.960g) respectively and place them in a clean beaker, add sodium dodecyl sulfate (0.096g), and then add 70ml of deionized water and stir magnetically for 1h. Pour the mixed solution into the lining of a 100ml stainless steel reactor, place the reactor in an oven and heat treat it at 100℃ for 10h, and then cool it naturally to room temperature in the air. Pour the black precipitate in the reactor lining into a suction filtration bottle for suction filtration, and wash it with anhydrous ethanol and deionized water for 2-3 times in turn. Place the filtered precipitate sample in a drying oven and dry it at 80℃ for 8h, then grind it for 1h to obtain Ag / MnO2 precursor;

[0039] (2) The Ag / MnO2 precursor was heated at 2°C min in air atmosphere. -1 The temperature was raised to 600°C at a heating rate and annealed for 6 hours to obtain Ag / MnO2 catalyst, which was named Ag / MnO2-S2.

[0040] Embodiment 3:

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

[0042] (1) According to the molar ratio of Ag to Mn of 5:95, weigh silver nitrate (0.054g) and potassium permanganate (0.960g) respectively and place them in a clean beaker, add sodium dodecyl sulfate (0.096g), and then add 70ml of deionized water and stir magnetically for 1h. Pour the mixed solution into the lining of a 100ml stainless steel reactor, place the reactor in an oven and heat treat it at 150℃ for 10h, and then cool it naturally to room temperature in the air. Pour the black precipitate in the reactor lining into a suction filtration bottle for suction filtration, and wash it with anhydrous ethanol and deionized water for 2-3 times in turn. Place the filtered precipitate sample in a drying oven and dry it at 120℃ for 4h, then grind it for 1h to obtain Ag / MnO2 precursor;

[0043] (2) The Ag / MnO2 precursor was heated at 4°C min in air atmosphere. -1 The temperature was raised to 800°C at a heating rate and annealed for 6 hours to obtain Ag / MnO2 catalyst, which was named Ag / MnO2-S3.

[0044] Embodiment 4:

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

[0046] (1) According to the molar ratio of Ag to Mn of 10:90, weigh silver nitrate (0.114g) and potassium permanganate (0.960g) respectively and place them in a clean beaker, add sodium dodecyl sulfate (0.096g), and then add 70ml of deionized water and stir magnetically for 1h. Pour the mixed solution into the lining of a 100ml stainless steel reactor, place the reactor in an oven and heat treat it at 130℃ for 10h, and then cool it naturally to room temperature in the air. Pour the black precipitate in the reactor lining into a suction filtration bottle for suction filtration, and wash it with anhydrous ethanol and deionized water for 2-3 times in turn. Place the filtered precipitate sample in a drying oven and dry it at 100℃ for 6h, then grind it for 1h to obtain Ag / MnO2 precursor;

[0047] (2) The Ag / MnO2 precursor was heated in air at 3°C ​​min -1 The temperature was raised to 700°C at a heating rate and annealed for 6 hours to obtain Ag / MnO2 catalyst, which was named Ag / MnO2-D2.

[0048] Comparative Example 1:

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

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

[0051] (2) The MnO2 precursor was heated at 3 °C min in air atmosphere. -1 The temperature was raised to 700°C at a heating rate and annealed for 6 hours to obtain a 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 is taken as an example to illustrate it.

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

[0055] 2. The Ag / MnO2 alkaline oxygen evolution catalyst in Example 1 was subjected to SEM analysis. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the nanorod structure is MnO2 particles, and the spherical particles on the surface of the nanorods are Ag nanoparticles. The anchoring of Ag nanoparticles on the surface of MnO2 helps to increase the specific surface area of ​​the composite catalyst and expand the electrochemical reaction area. The high conductivity of Ag nanoparticles helps to build electron transmission channels between MnO2 particles, thereby achieving rapid electron transfer during the reaction and improving its catalytic performance.

[0056] 3. Take 10 mg of each of the alkaline oxygen evolution catalysts prepared in Example 1, Example 4, and Comparative Example 1, mix them with 10 mg of Super P Li, and then disperse them in a mixture of 1 ml of anhydrous ethanol and 0.100 ml of Nafion, ultrasonicate for 60 min to form a uniform slurry, and take 0.100 ml of the catalyst slurry and drop them evenly on a 1 cm 2 The carbon paper was used as the working electrode.

[0057] Electrochemical test: The electrochemical test uses DH7000 electrochemical workstation (Jiangsu Donghua Analytical Instrument Co., Ltd.), adopts three-electrode system, carbon paper loaded with catalyst is working electrode, reference electrode is Hg / HgO (1M KOH), and counter electrode is platinum wire. All tests are carried out in 1M KOH solution saturated with O2. Before the test, O2 needs to be passed into 1M KOH solution for 30 minutes in advance to ensure saturation of 1M KOH electrolyte. Oxygen is continuously passed during the test until the end of the test. The linear sweep voltammetry (LSV) of the OER reaction is obtained at room temperature (25°C) with a voltage of 10mV s -1 The electrode potentials obtained from the electrochemical test relative to Hg / HgO (1M KOH) were converted to reversible hydrogen electrode potentials, and the conversion formula is:

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

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

[0060] Figure 4 is the polarization curve of 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 -2 When , the corresponding overpotentials of MnO2-D1, Ag / MnO2-S4 and Ag / MnO2-S1 are 599, 579 and 535 mV respectively.

[0061] Figure 5 The Tafel plots of MnO2-D1, Ag / MnO2-S4 and Ag / MnO2-S1 in 1M KOH are 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 spectra of MnO2-D1, Ag / MnO2-S4 and Ag / MnO2-S1 in 1M KOH; it can be seen from the figure 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 2.010Ω respectively.

[0063] Depend on Figure 4-Figure 6 It can be seen that the more Ag is added, the better the catalytic performance is. When the molar ratio of Ag and Mn is 10:90, the catalytic performance decreases compared to when the molar ratio of Ag and Mn is 5:95. This is because as the Ag content increases, the Ag particles will agglomerate during the sintering synthesis of the catalyst, resulting in a decrease in their specific surface area and a decrease in catalytic activity. Therefore, when the molar ratio of Ag and Mn is 5:95, the effect is best.

[0064] In addition, in an alkaline environment, the requirements of the oxygen evolution reaction for the catalyst mainly relate to the activity and stability of the catalyst. Under alkaline conditions, the catalyst needs to have a high catalytic activity, can effectively reduce the overpotential of the oxygen evolution reaction, and increase the reaction rate. In addition, the catalyst also needs to have good stability, can maintain catalytic activity for a long time in an alkaline environment, and is not easily corroded or ineffective. The catalyst provided by the present invention can have a high catalytic activity in an alkaline environment and can be well applied to alkaline electrocatalytic oxygen evolution reaction.

[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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a Ag / MnO2 alkaline oxygen evolution catalyst, characterized in that: The following steps are involved: (1) dissolving manganese salt, silver salt and anionic surfactant in a solvent, and preparing Ag / MnO2 precursor through hydrothermal reaction; (2) The Ag / MnO2 precursor is calcined to obtain an Ag / MnO2 alkaline oxygen evolution catalyst.

2. The method for preparing the Ag / MnO2 alkaline oxygen evolution catalyst according to claim 1, characterized in that: 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.

3. The method for preparing the Ag / MnO2 alkaline oxygen evolution catalyst according to claim 1, characterized in that: In step (1), the manganese salt is KMnO4 or Mn(CH3COO)2; the silver salt is AgNO3; the anionic surfactant is sodium dodecyl sulfonate, fatty acid salt or sodium alkylbenzene sulfonate; and the solvent is water.

4. The method for preparing the Ag / MnO2 alkaline oxygen evolution catalyst according to claim 1, characterized in that: The temperature during the hydrothermal reaction in step (1) is 100-150° C. and the reaction time is 8-12 h.

5. The method for preparing the Ag / MnO2 alkaline oxygen evolution catalyst according to claim 4, characterized in that: The temperature during the hydrothermal reaction in step (1) is 130° C. and the reaction time is 10 h.

6. 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 obtain an Ag / MnO2 precursor.

7. The method for preparing the Ag / MnO2 alkaline oxygen evolution catalyst according to claim 1, characterized in that: In step (2), the calcination is carried out at 2-4°C min in air atmosphere. -1 The Ag / MnO2 precursor is heated to 600-800°C at a heating rate and annealed for 4-6 hours.

8. The method for preparing the Ag / MnO2 alkaline oxygen evolution catalyst according to claim 1, characterized in that: The MnO2 in the Ag / MnO2 alkaline oxygen evolution catalyst is an α-MnO2 crystal structure.

9. An Ag / MnO2 alkaline oxygen evolution catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the Ag / MnO2 alkaline oxygen evolution catalyst according to claim 9 in an alkaline electrocatalytic oxygen evolution reaction.

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