A method for scalably preparing a trifunctional electrocatalyst for oxygen reduction, oxygen evolution, and hydrogen evolution, as well as its products and applications

Abstract

The present invention discloses a method for scalably preparing a trifunctional electrocatalyst of oxygen reduction-oxygen evolution-hydrogen evolution, wherein graphite is first subjected to oxidation treatment to obtain expandable graphite powder having a significantly increased specific surface area; the expandable graphite powder is then mixed with ammonium carbonate and subjected to high-energy ball milling treatment, wherein ammonium carbonate, as an intercalating agent, further weakens the interaction between graphites during the ball milling process, and ethylene glycol is added as an abrasive, and the ball milling treatment produces a large amount of flake graphite; the cobalt phthalocyanine added thereafter continues to be broken into small fragments after ball milling and is fixed to the surface of the flake graphite; and dicyandiamide is added and subjected to high-temperature pyrolysis treatment to obtain a nitrogen-doped graphite-loaded and carbon-nitrogen complex-coated cobalt nanoparticle composite. This composite simultaneously has excellent electrocatalytic activity and stability for oxygen reduction, oxygen evolution, and hydrogen evolution. The preparation process of this composite of the present invention is simple, easy to implement large-scale production, and has important practical significance.

Description

Technical Field

[0001] The present invention belongs to the field of water electrolysis and electrochemical energy materials. Specifically, it provides a method for scalably preparing a trifunctional electrocatalyst for oxygen reduction-oxygen evolution-hydrogen evolution, as well as a product and application thereof. Background Art

[0002] The development of new electrocatalysts for oxygen reduction, oxygen evolution, and hydrogen evolution reactions (RE) is of great practical significance for the research of new electrochemical energy sources and water electrolysis. The RE is an essential cathode process in new electrochemical energy sources such as fuel cells and metal-air batteries. The development of corresponding high-efficiency electrocatalysts is crucial for their practical application. Currently, platinum or Pt-based catalysts are the most effective electrocatalysts for the RE, but the limited resources and high cost of Pt severely restrict their practical application in new electrochemical energy sources. Similarly, in the water electrolysis process, both oxygen evolution at the anode and hydrogen evolution at the cathode require efficient electrocatalysts. Currently, Pt or Pt-based catalysts are the most efficient electrocatalysts for hydrogen evolution; iridium oxide is also a highly efficient electrocatalyst for oxygen evolution. In summary, currently effective electrocatalysts for the RE, OER, and HER are still based on precious metals. Therefore, the development of non-precious metal electrocatalysts is of great practical significance for the widespread application of new electrochemical energy sources and water electrolysis.

[0003] In order to develop non-precious metal electrocatalysts, people have conducted a lot of research and proposed various preparation methods. However, in general, since these electrocatalysts are all in the form of nanoparticle dispersion, their preparation process is usually relatively cumbersome, which makes it difficult to produce them on a large scale. Therefore, the development of non-precious metal electrocatalysts with simple preparation process, easy industrial-scale application, and high electrocatalytic activity has a practical effect on the large-scale practical application of new electrochemical energy and water electrolysis. The present invention uses expandable graphite with a large specific surface area as the basic raw material and adopts a simple method combining high-energy ball milling with a pyrolysis process to prepare nitrogen-doped graphite-loaded cobalt nanoparticle composite materials, which show excellent electrocatalytic activity and high stability for oxygen reduction, oxygen evolution and hydrogen evolution. The process of the present invention is simple and easy to achieve large-scale production. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for scalably preparing a trifunctional electrocatalyst for oxygen reduction-oxygen evolution-hydrogen evolution, as well as a product and application thereof.

[0005] To achieve the above object, the embodiment of the present invention is: a method for scalably preparing a trifunctional electrocatalyst for oxygen reduction-oxygen evolution-hydrogen evolution, comprising the following steps:

[0006] (1) adding graphite to concentrated sulfuric acid and stirring evenly, then adding 60% hydrogen peroxide, stirring the mixture evenly, placing it in a 40°C constant temperature water bath, letting it stand, and after sufficient reaction, filtering and washing with water until the pH is 5-6. The obtained solid is dried at 50°C and then fully ground to obtain expanded graphite powder;

[0007] (2) The expandable graphite powder and ammonium carbonate are mixed in a mass ratio of 1:20, and then an appropriate amount of ethylene glycol is added to ensure that the ethylene glycol completely immerses the solid mixture, and then sufficient ball milling is performed, and then cobalt phthalocyanine is added and the ball milling is continued to be sufficient. The obtained mixed solid is a ball milling product containing ethylene glycol; the ball milling product is mixed with an appropriate amount of anhydrous ethanol, stirred evenly and allowed to stand, and then the upper ethanol solution is poured out, and the obtained solid is repeatedly treated with anhydrous ethanol to obtain Precursor-1;

[0008] The mass ratio of the cobalt phthalocyanine to the expandable graphite powder is 1:2; the total mass of the agate balls used in the ball milling process is 10 to 15 times the mass of ammonium carbonate;

[0009] (3) Precursor-1 and dicyandiamide were mixed at a mass ratio of 1:(0.5-5), and then an appropriate amount of anhydrous ethanol was added and the mixture was thoroughly ground. The resulting mixture was dried at 40°C and then fully ground again to obtain Precursor-2;

[0010] (4) The above-mentioned precursor-2 was heated at 4°C·min in a nitrogen atmosphere. -1 The reaction mixture was heated to 152°C and maintained for 0.5 h, then continued to heat to 800°C and maintained for 2 h. After cooling to room temperature, the resulting solid was collected and fully ground to obtain a trifunctional electrocatalyst for oxygen reduction-oxygen evolution-hydrogen evolution.

[0011] A scalable trifunctional electrocatalyst for oxygen reduction-oxygen evolution-hydrogen evolution prepared according to the method.

[0012] The invention relates to a scalable trifunctional electrocatalyst for oxygen reduction-oxygen evolution-hydrogen evolution prepared by the method and its application in oxygen reduction, oxygen evolution and hydrogen evolution.

[0013] The present invention first oxidizes graphite to produce expandable graphite powder with a significantly increased specific surface area. The expandable graphite powder is then mixed with ammonium carbonate and subjected to high-energy ball milling. The ammonium carbonate acts as an intercalating agent, further weakening the interactions between the graphite particles during the milling process. With the addition of ethylene glycol as a grinding agent, the milling produces a large amount of flake graphite. Cobalt phthalocyanine is then added, further ball milling breaks it down into small fragments that are fixed to the surface of the flake graphite. Dicyandiamide is then added and subjected to high-temperature pyrolysis to produce a nitrogen-doped graphite-supported cobalt nanoparticle composite coated with a carbon-nitrogen complex. This composite exhibits excellent electrocatalytic activity and stability for oxygen reduction, oxygen evolution, and hydrogen evolution. The composite is simple to prepare and readily scalable, possessing significant practical significance in the fields of electrochemical new energy and water electrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the preparation mechanism of the catalyst product;

[0015] Figure 2 This is an SEM image of the catalyst product prepared in Example 1;

[0016] Figure 3 This is the SEM image of the catalyst product prepared in Example 2.

[0017] Figure 4 The electrocatalytic activity diagram of the catalyst product prepared in Example 1 for oxygen reduction (ORR), oxygen evolution (OER) and hydrogen evolution (HER).

[0018] Figure 5 The electrocatalytic activity diagram of the catalyst product prepared in Example 2 for oxygen reduction (ORR), oxygen evolution (OER) and hydrogen evolution (HER). DETAILED DESCRIPTION

[0019] Example 1

[0020] A method for scalably preparing a trifunctional electrocatalyst for oxygen reduction, oxygen evolution, and hydrogen evolution comprises the following steps:

[0021] (1) According to the prior art (Zhao Guogang, Ma Jiyang, Wu Yan, Preparation of expandable graphite by hydrogen peroxide oxidation, Journal of Heilongjiang University of Science and Technology, 2014, 24(2):173-176), expandable graphite powder was prepared, specifically by the following steps: 10 g of graphite was added to 28 mL of concentrated sulfuric acid, stirred evenly, and then 1 mL of 60% hydrogen peroxide was added. After the mixture was fully stirred until uniform, stirring was stopped, and the mixture was placed in a 40°C constant temperature water bath and allowed to stand for 1 hour. After the reaction was completed, the mixture was filtered and washed with water until the pH was 5-6. The obtained solid was dried at 50°C for 4 hours and then fully ground to obtain expandable graphite powder.

[0022] (2) 0.2 g of expandable graphite powder and 4 g of ammonium carbonate were mixed and transferred to a high-energy ball mill. An appropriate amount of ethylene glycol was added to ensure that the mixture solid was completely immersed in the ethylene glycol. A 5 mm diameter agate ball was added and ball milled at 500 rpm for 8 hours. Subsequently, 0.4 g of cobalt phthalocyanine was added to the ball mill and high-energy ball milling was continued for 8 hours. The resulting mixed solid was a ball milling product containing ethylene glycol. The ball milling product was mixed with an appropriate amount of anhydrous ethanol, stirred evenly, and allowed to stand. The upper ethanol solution was then poured off and the resulting solid was repeatedly treated with anhydrous ethanol to obtain Precursor-1.

[0023] (3) The above-mentioned precursor-1 was mixed with 2 g of dicyandiamide, and then an appropriate amount of anhydrous ethanol was added, and the mixture was thoroughly ground in a mortar. The resulting mixture was dried at 40°C for 6 hours; then, the mixture was thoroughly ground to obtain precursor-2.

[0024] (4) Transfer the above-mentioned precursor-2 into a tube furnace and heat it at 4℃·min under nitrogen atmosphere. -1 The reaction mixture was heated to 152°C at a rate of 1000 ℃ and maintained for 0.5 h, and then continued to be heated to 800°C and maintained for 2 h. After cooling to room temperature, the solid was collected and thoroughly ground to obtain the catalyst product.

[0025] (5) The above catalyst product was mixed with an appropriate amount of ethanol, and then Nafion solution was added. The slurry formed after ultrasonic mixing was coated on the surface of the hydrophobic treated carbon cloth. After drying, an air electrode was obtained. It was used as a working electrode, a carbon rod as a counter electrode, and a HgO / Hg electrode as a reference electrode to form a three-electrode system. The polarization curves of hydrogen evolution (HER) and oxygen evolution (OER) reactions were tested in 1M KOH solution, and the polarization curve of oxygen reduction reaction (ORR) was tested in 0.1M KOH solution. For comparison, the polarization curves of hydrogen evolution (HER) of Pt / C catalyst and oxygen evolution (OER) reaction of IrO2 catalyst in 1M KOH solution were tested; the polarization curve of oxygen reduction reaction (ORR) of Pt / C catalyst in 0.1M KOH solution was tested. At 10mA / cm 2 At the current density of 50 mA / cm, the difference between the potential corresponding to OER and the potential corresponding to HER is ΔV=1.76V (catalyst product), ΔV=1.70V (Pt / C / IrO2 system). 2 At the current density of 10 mA / cm, the difference between the potential corresponding to OER and the potential corresponding to HER is ΔV=1.98V (catalyst product) and ΔV=1.98V (Pt / C / IrO2 system). 2The difference ΔE between the potential corresponding to OER and the half-wave potential of ORR at the current density is: ΔE = 0.76V (catalyst product) and ΔE = 0.59V (Pt / C / IrO2 system).

[0026] Example 2

[0027] A method for scalably preparing a trifunctional electrocatalyst for oxygen reduction, oxygen evolution, and hydrogen evolution comprises the following steps:

[0028] (1) According to the prior art (Zhao Guogang, Ma Jiyang, Wu Yan, Preparation of expandable graphite by hydrogen peroxide oxidation, Journal of Heilongjiang University of Science and Technology, 2014, 24(2):173-176), expandable graphite powder was prepared, specifically by the following steps: 10 g of graphite was added to 28 mL of concentrated sulfuric acid, stirred evenly, and then 1 mL of 60% hydrogen peroxide was added. After the mixture was fully stirred until uniform, stirring was stopped, and the mixture was placed in a 40°C constant temperature water bath and allowed to stand for 1 hour. After the reaction was completed, the mixture was filtered and washed with water until the pH was 5-6. The obtained solid was dried at 50°C for 4 hours and then fully ground to obtain expandable graphite powder.

[0029] (2) 0.2 g of expandable graphite powder and 4 g of ammonium carbonate were mixed and transferred to a high-energy ball mill. An appropriate amount of ethylene glycol was added to ensure that the mixture solid was completely immersed in the ethylene glycol. A 5 mm diameter agate ball was added and ball milled at 500 rpm for 8 hours. Subsequently, 0.4 g of cobalt phthalocyanine was added to the ball mill and high-energy ball milling was continued for 8 hours. The resulting mixed solid was a ball milling product containing ethylene glycol. The ball milling product was mixed with an appropriate amount of anhydrous ethanol, stirred evenly, and allowed to stand. The upper ethanol solution was then poured off and the resulting solid was repeatedly treated with anhydrous ethanol to obtain Precursor-1.

[0030] (3) The above-mentioned precursor-1 was mixed with 4 g of dicyandiamide, and then an appropriate amount of anhydrous ethanol was added, and the mixture was thoroughly ground in a mortar. The resulting mixture was dried at 40°C for 6 hours; then, the mixture was thoroughly ground to obtain precursor-2.

[0031] (4) Transfer the above-mentioned precursor-2 into a tube furnace and heat it at 4℃·min under nitrogen atmosphere. -1 The reaction mixture was heated to 152°C at a rate of 1000 ℃ and maintained for 0.5 h, and then continued to be heated to 800°C and maintained for 2 h. After cooling to room temperature, the solid was collected and thoroughly ground to obtain the catalyst product.

[0032] (5) The above catalyst product was mixed with an appropriate amount of ethanol, and then Nafion solution was added. The slurry formed after ultrasonic mixing was coated on the surface of the hydrophobic treated carbon cloth. After drying, an air electrode was obtained. It was used as a working electrode, a carbon rod as a counter electrode, and a HgO / Hg electrode as a reference electrode to form a three-electrode system. The polarization curves of hydrogen evolution (HER) and oxygen evolution (OER) reactions were tested in 1M KOH solution, and the polarization curve of oxygen reduction reaction (ORR) was tested in 0.1M KOH solution. For comparison, the polarization curves of hydrogen evolution (HER) of Pt / C catalyst and oxygen evolution (OER) reaction of IrO2 catalyst in 1M KOH solution were tested; the polarization curve of oxygen reduction reaction (ORR) of Pt / C catalyst in 0.1M KOH solution was tested. At 10mA / cm 2 At the current density of 50 mA / cm, the difference ΔV between the potential corresponding to OER and the potential corresponding to HER is: ΔV = 1.79 V (catalyst product), ΔV = 1.70 V (Pt / C / IrO2 system); 2 At the current density of 10 mA / cm, the difference between the potential corresponding to OER and the potential corresponding to HER is ΔV=1.95V (catalyst product) and ΔV=1.98V (Pt / C / IrO2 system). 2 The difference ΔE between the potential corresponding to OER and the half-wave potential of ORR at the current density is: ΔE = 0.763V (catalyst product), ΔE = 0.59V (Pt / C / IrO2 system).

Claims

1. A method for scalably preparing a trifunctional electrocatalyst for oxygen reduction, oxygen evolution and hydrogen evolution, characterized in that: The following steps are involved: (1) Add graphite to concentrated sulfuric acid and stir evenly. Then add 60% hydrogen peroxide and stir the mixture thoroughly. Place the mixture in a 40°C constant temperature water bath and allow it to stand for a long time. After sufficient reaction, filter and wash with water until the pH value is 5-6. The obtained solid is dried at 50°C and then fully ground to obtain expanded graphite powder. (2) The expanded graphite powder and ammonium carbonate are mixed in a mass ratio of 1:20, and then an appropriate amount of ethylene glycol is added to ensure that the ethylene glycol completely immerses the solid mixture, and then sufficient ball milling is performed. Subsequently, cobalt phthalocyanine is added and the ball milling is continued. The resulting mixed solid is a ball milling product containing ethylene glycol; the ball milling product is mixed with an appropriate amount of anhydrous ethanol, stirred evenly, and then allowed to stand. Subsequently, the upper ethanol solution is poured out, and the resulting solid is repeatedly treated with anhydrous ethanol to obtain Precursor-1; The mass ratio of the cobalt phthalocyanine to the expandable graphite powder is 1:2; the total mass of the agate balls used in the ball milling process is 10 to 15 times the mass of ammonium carbonate; (3) The above-mentioned precursor-1 and dicyandiamide were mixed in a mass ratio of 1: (0.5~5), and then an appropriate amount of anhydrous ethanol was added and fully ground. The resulting mixture was dried at 40°C and then fully ground again to obtain precursor-2; (4) The above-mentioned precursor-2 was heated at 4 ℃·min in a nitrogen atmosphere. -1 The catalyst was heated to 152 °C at a rate of 1000 °C and maintained for 0.5 h, then continued to be heated to 800 °C and maintained for 2 h. After cooling to room temperature, the obtained solid was collected and fully ground to obtain a trifunctional electrocatalyst for oxygen reduction-oxygen evolution-hydrogen evolution.

2. A scalable trifunctional electrocatalyst for oxygen reduction-oxygen evolution-hydrogen evolution prepared according to the method of claim 1.

3. Application of a scalable trifunctional electrocatalyst for oxygen reduction, oxygen evolution and hydrogen evolution prepared by the method of claim 1 in oxygen reduction, oxygen evolution and hydrogen evolution.

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