Preparation method and application of asphalt-based oxygen reduction electrocatalyst

Abstract

This invention discloses a method for preparing a pitch-based oxygen reduction electrocatalyst. Pitch and potassium citrate are used as raw materials, uniformly mixed and annealed in a tube furnace to convert them into porous carbon nanosheets. These are then subjected to typical nitrogen and sulfur atom doping to obtain nitrogen-sulfur co-doped porous carbon nanosheets, i.e., the pitch-based oxygen reduction electrocatalyst. This invention also discloses the application of the pitch-based oxygen reduction electrocatalyst prepared by the above method. The method for preparing the pitch-based oxygen reduction electrocatalyst of this invention is simple, has high pitch utilization, and produces a pitch-based oxygen reduction electrocatalyst with excellent performance, environmental friendliness, and significantly reduced preparation costs. The application of the pitch-based oxygen reduction electrocatalyst of this invention enables its use in the electrode preparation of zinc-air batteries, greatly improving the oxygen reduction capability of the motor.

Description

Technical Field

[0001] This invention relates to the field of new energy material preparation and electrocatalysis technology, specifically to a method for preparing and applying an asphalt-based oxygen reduction electrocatalyst. Background Technology

[0002] In recent years, with the increasing depletion of petroleum resources, the demand for electrochemical energy storage and conversion in the economic market has been continuously increasing. Among them, zinc-air batteries (ZABs) have enormous market potential due to their fast reaction speed, safe and readily available electrolytes, and ease of storage and transportation, attracting a large amount of scientific research. Currently, the main problem with ZABs is attributed to the slow oxygen reduction (ORR) and oxygen evolution reaction (OER) on the catalytic layer of the positive electrode air membrane. Since both ORR and OER reactions involve four-electron transfer processes, their kinetic activity is very slow, thus greatly limiting the reaction rate on the electrode and requiring the use of catalysts to accelerate the reaction. The oxygen reduction reaction (ORR) occurring at the cathode of ZABs determines the discharge rate performance; it plays a crucial role in both electron and mass transfer processes in ZABs. Therefore, compared to the anode metal, the cathode oxygen reduction reaction dominates in terms of system power density and durability, making the development of high-performance ORR electrode materials more challenging.

[0003] For a long time, researchers have focused on the study of transition metal-nitrogen-carbon (MNC) catalysts, exploring new metal elements, designing multi-atom metal centers, and optimizing coordination structures to promote the activity of individual active sites. However, the influence of individual carbon structures on catalytic performance has received less attention. Most of the reported studies have shown that the carbon sources used in the above catalysts are indirectly synthesized, rather than using raw materials directly. The choice of metal sources is also limited, with most using Fe, Co, etc., which is not conducive to the current environmentally friendly research. However, there are no reports of metal-free ORR catalysts synthesized directly from industrial byproduct pitch using a simple and pollution-free strategy. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing and applying an asphalt-based oxygen reduction electrocatalyst, in order to solve the above-mentioned defects.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a pitch-based oxygen reduction electrocatalyst involves using pitch and potassium citrate as raw materials, uniformly mixing them and annealing them in a tube furnace to convert them into porous carbon nanosheets, and then subjecting them to typical nitrogen and sulfur atom doping to obtain nitrogen and sulfur co-doped porous carbon nanosheets; the nitrogen and sulfur co-doped porous carbon nanosheets are the pitch-based oxygen reduction electrocatalyst.

[0007] Preferably, the procedure specifically includes the following steps:

[0008] S1. A certain amount of industrial asphalt and potassium citrate powder are uniformly mixed in a grinding mortar, 95% alcohol is added and ground into a single-color powder, and then placed in a tube furnace for calcination. The calcination conditions are: heating to 300℃ at a heating rate of 5℃ per minute and holding for 2 hours, then heating to 800℃ at the same heating rate and holding for 2 hours. After the calcination and holding are completed and the sample is cooled to room temperature, it is taken out and placed in a sufficient amount of 1M HCl solution and stirred for 6 hours. Finally, the obtained sample solution is filtered and dried at 60℃ for 2 hours to obtain porous carbon nanosheet material.

[0009] S2. The above porous carbon nanosheet material is mixed with thiourea and then calcined. The calcination is carried out in a tube furnace and the temperature is raised to 800°C at a rate of 5°C per minute and held for 2 hours, and then cooled naturally. The calcination is completed when the cooling is finished, thereby obtaining nitrogen and sulfur co-doped porous carbon nanosheet material, namely the pitch-based oxygen reduction electrocatalyst.

[0010] Preferably, in steps S1 and S2, the calcination conditions are: the tubular furnace is filled with an N2 atmosphere and is under a standard atmospheric pressure.

[0011] Preferably, the industrial asphalt is one or more of coal tar pitch or petroleum pitch, the mass ratio of the industrial asphalt to potassium citrate powder is 1:4, and the ratio of the mass of the industrial asphalt in grams to the volume of 95% alcohol in milliliters is (1-3):5.

[0012] Preferably, in step S1, the sample solution obtained after stirring with a sufficient amount of HCl solution is filtered, centrifuged with deionized water and ethanol until neutral, and then dried at 60°C to obtain porous carbon nanosheet material.

[0013] Preferably, in step S2, the porous carbon nanosheet material and thiourea are in a mass ratio of 1:5 and are placed together in a corundum crucible for annealing in a tube furnace.

[0014] Preferably, the application of an asphalt-based oxygen reduction electrocatalyst involves using the prepared asphalt-based oxygen reduction electrocatalyst in the preparation of electrodes for zinc-air batteries, and participating in the oxygen reduction electrocatalytic reaction of the electrodes, thereby giving the electrodes excellent oxygen reduction capabilities.

[0015] Preferably, the electrode preparation process is as follows: the prepared pitch-based oxygen reduction electrocatalyst is ground into powder and uniformly dispersed in deionized water and Nafion alcohol solution, and then ultrasonically treated. The above mixed solution is then coated on the surface of a glassy carbon electrode to prepare a working electrode; the half-wave potential of the oxidation peak of the obtained pitch-based oxygen reduction electrocatalyst is 0.83V.

[0016] The beneficial effects of this invention are as follows:

[0017] This invention discloses a method for preparing a pitch-based oxygen reduction electrocatalyst. Pitch, an industrial byproduct, is transformed into a high-value-added electrocatalyst through simple modification. This method avoids the use of harmful carbon, nitrogen, and sulfur source materials, achieves high pitch utilization, requires no special treatment of the pitch, is environmentally friendly, and reduces manpower and material resources, making it suitable for large-scale industrial production. The prepared pitch-based oxygen reduction electrocatalyst exhibits excellent catalytic performance, with catalytic activity comparable to platinum-based noble metal catalysts and frequently reported transition metal-doped electrocatalysts. However, the preparation method is simple, requiring no secondary modification or synthetic treatment to obtain nitrogen and sulfur doped materials, significantly reducing the preparation cost of high-activity catalysts. Furthermore, the prepared pitch-based oxygen reduction electrocatalyst offers great potential for application in energy conversion and energy storage technologies (metal-air batteries, supercapacitors, etc.). Attached Figure Description

[0018] Figure 1 The LSV curves of the pitch-based oxygen reduction electrocatalyst prepared in Example 1 and the commercial platinum-based electrocatalyst in an O2-saturated 0.1 mol / L KOH solution are shown.

[0019] Figure 2 The CV curves of the pitch-based oxygen reduction electrocatalyst prepared in Example 1 and the commercial platinum-based electrocatalyst in 0.1 mol / L KOH solution saturated with O2 and N2 are shown.

[0020] Figure 3 The LSV curves of the pitch-based oxygen reduction electrocatalyst prepared in Example 1 at different rotation speeds in a 0.1 mol / L KOH solution saturated with O2 and Ar.

[0021] Figure 4 This is a scanning electron microscope image of the pitch-based oxygen reduction electrocatalyst prepared in Example 1.

[0022] Figure 5 This is a schematic diagram of a liquid zinc-air battery; where 1 is the zinc electrode, 2 is the liquid electrolyte, and 3 is the air electrode.

[0023] Figure 6 The graph shows a comparison of open-circuit voltage and battery capacity for zinc-air batteries assembled using asphalt-based oxygen reduction electrocatalysts and platinum-based electrocatalysts, respectively.

[0024] Figure 7 The discharge curves and power comparison diagrams of zinc-air batteries assembled using pitch-based oxygen reduction electrocatalysts and platinum-based electrocatalysts, respectively.

[0025] Figure 8 The graph shows a comparison of the cycle stability curves of zinc-air batteries assembled using asphalt-based oxygen reduction electrocatalysts and platinum-based electrocatalysts, respectively. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments. It should be noted that these are merely examples and descriptions of the inventive concept. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the inventive concept or exceed the scope defined in the claims, they should all be considered to fall within the protection scope of the present invention.

[0027] Example 1:

[0028] I. Preparation of pitch-based oxygen reduction electrocatalysts.

[0029] A method for preparing a pitch-based oxygen reduction electrocatalyst involves using pitch and potassium citrate as raw materials. The mixture is uniformly mixed and annealed in a tube furnace to convert it into porous carbon nanosheets. Following typical nitrogen and sulfur atom doping, nitrogen-sulfur co-doped porous carbon nanosheets are obtained. The prepared nitrogen-sulfur co-doped porous carbon nanosheets are the pitch-based oxygen reduction electrocatalyst. The specific steps include:

[0030] S1. A certain amount of industrial asphalt and potassium citrate powder are uniformly mixed in a grinding mortar, and 95% alcohol is added to grind into a single-color powder. The powder is then placed in a tube furnace for calcination. The calcination conditions are as follows: the tube furnace is filled with N2 atmosphere and maintained at one standard atmosphere; the temperature is increased to 300℃ at a rate of 5℃ per minute and held for 2 hours; then the temperature is increased to 800℃ at the same rate and held for 2 hours. After the calcination and holding are completed and the sample cools to room temperature, it is removed and placed in a sufficient amount of 1M HCl solution and stirred for 6 hours. Finally, the resulting sample solution is filtered, centrifuged with deionized water and ethanol until neutral, and then dried at 60℃ for 2 hours to obtain porous carbon nanosheets.

[0031] In step S1, the industrial asphalt is one or more of coal tar pitch or petroleum pitch, the mass ratio of the raw industrial asphalt to potassium citrate powder is 1:4, and the ratio of the mass of the raw industrial asphalt in grams to the volume of 95% alcohol in milliliters is (1-3):5.

[0032] S2. The above-mentioned porous carbon nanosheet material and thiourea are mixed at a mass ratio of 1:5 and then placed together in a corundum crucible for calcination and annealing in a tube furnace. The calcination is carried out in a tube furnace filled with N2 atmosphere and under standard atmospheric pressure. The temperature is then increased to 800℃ at a rate of 5℃ per minute and held for 2 hours, followed by natural cooling. The calcination is complete after cooling, thus obtaining the nitrogen-sulfur co-doped porous carbon nanosheet material, namely the pitch-based oxygen reduction electrocatalyst, and finally obtaining the pitch-based oxygen reduction electrocatalyst material.

[0033] II. Application of asphalt-based oxygen reduction electrocatalysts and preparation of sample electrodes for electrocatalytic testing.

[0034] Application of pitch-based oxygen reduction electrocatalyst: The prepared pitch-based oxygen reduction electrocatalyst is used in the preparation of electrodes for zinc-air batteries and participates in the oxygen reduction electrocatalytic reaction of the electrodes, giving the electrodes excellent oxygen reduction capabilities.

[0035] The specific process for preparing the electrode for the electrocatalytic test sample is as follows: 5 mg of the prepared asphalt-based oxygen reduction electrocatalyst was weighed, ground into powder, and then added to a mixed solution of 1 ml of isopropanol aqueous solution (volume ratio of isopropanol to deionized water = 2:8) and 10 μL of perfluorosulfonic acid Nafion solution (DuPont, 5 wt.%). After ultrasonic treatment for 1 h, 8.5 μL of the above mixed solution was drop-coated onto a surface with an area of ​​0.19625 cm². 2 The working electrode of the electrocatalytic test sample was obtained by placing the sample on the glassy carbon electrode surface. Its ORR activity was then tested using an electrochemical workstation with an O2-saturated 0.1 mol / L KOH solution as the electrolyte and a scan rate of 5 mV / s. The half-wave potential of the oxidation peak of the obtained asphalt-based oxygen reduction electrocatalyst was 0.83 V.

[0036] Figure 1 The LSV curves of the pitch-based oxygen reduction electrocatalyst prepared in Example 1 and the commercial platinum-based electrocatalyst in an O2-saturated 0.1 mol / L KOH solution are shown. Specifically, the potential and current density curves of the prepared pitch-based oxygen reduction electrocatalyst and the commercial platinum-based electrocatalyst in an O2-saturated 0.1 mol / L KOH solution were obtained using linear cyclic voltammetry.

[0037] Figure 2 This is a CV curve of the asphalt-based oxygen reduction electrocatalyst prepared in Example 1 and a commercial platinum-based electrocatalyst in a 0.1 mol / L KOH solution saturated with O2 and N2. Specifically, it is a curve obtained by linear cyclic voltammetry in a 0.1 mol / L KOH solution saturated with O2 and N2, comparing the prepared asphalt-based oxygen reduction electrocatalyst and the commercial platinum-based electrocatalyst.

[0038] Figure 3 The LSV curves of the pitch-based oxygen reduction electrocatalyst prepared in Example 1 at different rotational speeds in a 0.1 mol / L KOH solution saturated with O2 and Ar are shown. Specifically, the curves of the prepared pitch-based oxygen reduction electrocatalyst at different rotational speeds in a 0.1 mol / L KOH solution saturated with O2 and Ar were obtained using a linear potential scanning chronoamperometry method.

[0039] Figure 4The asphalt-based oxygen reduction electrocatalyst prepared in Example 1 exhibits a clear nanosheet-like morphology under a scanning electron microscope.

[0040] III. Application, assembly, and performance testing of zinc-air batteries based on pitch-based oxygen reduction electrocatalysts.

[0041] Liquid zinc-air battery:

[0042] Figure 5 This is a schematic diagram of the structure of a liquid zinc-air battery. Figure 5 As shown, 1 is the zinc electrode, 2 is the liquid electrolyte, and 3 is the air electrode.

[0043] Zinc sheets with a thickness of 0.3-0.5 mm are cut into strips with a length and width of 2-3 cm and used as metal electrodes (i.e., zinc electrode 1); hydrophobic carbon cloth is cut into strips of the same size and used as air electrodes 3 (i.e., oxygen electrodes); finally, the prepared zinc electrode 1 and air electrode 3 are placed in the prepared liquid electrolyte 2, thereby obtaining the desired result. Figure 5 The water-based zinc-air battery shown.

[0044] Sandwich structure:

[0045] A pure zinc sheet with a thickness of 0.3-0.5 mm was cut into rectangles 2-3 cm long and 1-2 cm wide. After removing oxides by sanding, a zinc electrode was prepared and used as the anode. The prepared air electrode was also cut into strips 2-3 cm long and 1-2 cm wide, and 100 μL of asphalt-based oxygen reduction electrocatalyst was dropped onto its hydrophobic layer as an electrocatalytic test sample, forming the cathode. Subsequently, the zinc electrode, electrolyte, and air electrode were successfully assembled using a sandwich structure. Figure 5 As shown, 1 is the anode, 2 is the electrolyte, and 3 is the cathode.

[0046] The assembled zinc-air battery was tested for capacity and discharge using the Shanghai Chenhua Electrochemical Workstation 760e.

[0047] Figure 6 This is a comparison of the open-circuit voltage and battery capacity of zinc-air batteries assembled using asphalt-based oxygen reduction electrocatalysts and platinum-based electrocatalysts, respectively. It can be concluded that... Figure 5 As shown, the open-circuit voltage of the zinc-air battery was measured to be 1.442V using a multimeter, and the capacity of the battery assembled with the asphalt-based oxygen reduction electrocatalyst exceeded that of the battery assembled with the platinum-based oxygen reduction electrocatalyst.

[0048] Figure 7 The graph shows a comparison of discharge curves and power outputs for zinc-air batteries assembled using pitch-based oxygen reduction electrocatalysts and platinum-based electrocatalysts, respectively. Figure 6As shown in the discharge power curve, the limiting power density (109 mV / cm²) of the zinc-air battery assembled with the asphalt-based oxygen reduction electrocatalyst is... -2 It also exceeds the limiting power density of zinc-air batteries assembled with Pt / C (68mVcm-). 2 )

[0049] A comparative test was conducted using the Wuhan Landian Battery Testing System CT2001A to compare liquid aqueous zinc-air batteries assembled with asphalt-based oxygen reduction electrocatalysts and commercially available Pt / C liquid electrolytes. Figure 7 This is a comparison of the cycle stability curves of zinc-air batteries assembled using asphalt-based oxygen reduction electrocatalysts and platinum-based electrocatalysts, respectively. Figure 8 As shown, this battery can withstand 10mA. -2 The stable cycling time of up to 100 hours at the current density far exceeds the cycling time (44 hours) of zinc-air batteries assembled with Pt / C electrocatalysts at the same current density.

[0050] The application assembly and performance testing of the zinc-air battery based on the asphalt-based oxygen reduction electrocatalyst demonstrate that the preparation method of the asphalt-based oxygen reduction electrocatalyst of this invention transforms industrial byproduct asphalt into a high-value-added electrocatalyst through simple modification. It avoids the use of harmful carbon, nitrogen, and sulfur source materials, achieves high asphalt utilization, requires no special asphalt treatment, is environmentally friendly, and reduces manpower and material resources, making it suitable for large-scale industrial production. The prepared asphalt-based oxygen reduction electrocatalyst exhibits excellent catalytic performance, with catalytic activity comparable to platinum-based noble metal catalysts and frequently reported transition metal-doped electrocatalysts. However, the preparation method is simple, requiring no secondary modification or synthetic treatment to obtain nitrogen and sulfur doped materials, significantly reducing the preparation cost of high-activity catalysts. Furthermore, the prepared asphalt-based oxygen reduction electrocatalyst offers great potential for application in energy conversion and energy storage technologies (metal-air batteries, supercapacitors, etc.).

[0051] The above is an exemplary description of the invention. Obviously, the specific implementation of the invention is not limited to the above-described manner. Any non-substantial improvement made using the inventive concept and technical solution of the invention, or the direct application of the inventive concept and technical solution to other situations without modification, is within the protection scope of the invention.

Claims

1. A method for preparing a pitch-based oxygen reduction electrocatalyst, characterized in that, Asphalt and potassium citrate are used as raw materials. They are uniformly mixed and annealed in a tube furnace to convert them into porous carbon nanosheets. Then, they are subjected to typical nitrogen and sulfur atom doping to obtain nitrogen and sulfur co-doped porous carbon nanosheets. The nitrogen and sulfur co-doped porous carbon nanosheets are asphalt-based oxygen reduction electrocatalysts. Specifically, the following steps are included: S1. A certain amount of industrial asphalt and potassium citrate powder are uniformly mixed in a grinding mortar, 95% alcohol is added and ground into a single-color powder, and then placed in a tube furnace for calcination. The calcination conditions are: heating to 300℃ at a rate of 5℃ per minute and holding for 2 hours, then heating to 800℃ at the same rate and holding for 2 hours. After the calcination and holding are completed and the sample is cooled to room temperature, it is taken out and placed in a sufficient amount of 1M HCl solution and stirred for 6 hours. Finally, the obtained sample solution is filtered and dried at 60℃ for 2 hours to obtain porous carbon nanosheet material. S2. The above porous carbon nanosheet material is mixed with thiourea and then calcined. The calcination is carried out in a tube furnace and the temperature is raised to 800°C at a rate of 5°C per minute and held for 2 hours, and then cooled naturally. The calcination is completed when the cooling is finished, thereby obtaining nitrogen and sulfur co-doped porous carbon nanosheet material, namely the pitch-based oxygen reduction electrocatalyst. In steps S1 and S2, the calcination conditions are: the tubular furnace is filled with an N2 atmosphere and is under a standard atmospheric pressure; The industrial asphalt is one or more of coal tar pitch or petroleum pitch, the mass ratio of the industrial asphalt to potassium citrate powder is 1:4, and the ratio of the mass of the industrial asphalt in grams to the volume of 95% alcohol in milliliters is (1-3):

5. In step S1, the sample solution obtained after stirring with sufficient HCl solution is filtered, centrifuged with deionized water and ethanol until neutral, and then dried at 60°C to obtain porous carbon nanosheet material. In step S2, the porous carbon nanosheet material and thiourea are in a mass ratio of 1:5 and are placed together in a corundum crucible for annealing in a tube furnace.

2. The application of the pitch-based oxygen reduction electrocatalyst prepared by the method of claim 1, characterized in that, The prepared pitch-based oxygen reduction electrocatalyst was applied in the preparation of electrodes for zinc-air batteries and participated in the oxygen reduction electrocatalytic reaction of the electrodes, giving the electrodes excellent oxygen reduction capabilities.

3. The application of the pitch-based oxygen reduction electrocatalyst according to claim 2, characterized in that, The electrode preparation process is as follows: the prepared pitch-based oxygen reduction electrocatalyst is ground into powder and uniformly dispersed in a mixed solution of isopropanol aqueous solution and perfluorosulfonic acid Nafion solution. After ultrasonic treatment, the mixed solution is coated on the surface of a glassy carbon electrode to prepare a working electrode. The oxygen reduction peak half-wave potential of the obtained pitch-based oxygen reduction electrocatalyst is 0.83V.

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