Method for preparing non-precious metal catalyst for oxygen reduction reaction using lotus pods and industrial waste acid

Abstract

The present invention belongs to the field of new materials for preparing oxygen reduction catalysts, and discloses a method for preparing a non-precious metal catalyst for oxygen reduction reaction using industrial waste acid and lotus pods. Industrial waste acid is used as an iron source, lotus pods are used as carbon and nitrogen sources, and NaCl is used as a pore-forming agent. Porous iron-nitrogen doped carbon is obtained by freeze drying and high-temperature pyrolysis, and finally a non-precious metal catalyst is obtained by acid washing and etching. Salt addition to form pores ensures that the catalyst has a large specific surface area and an optimizable pore size distribution, while multi-element doping is beneficial to improving the performance of the catalyst. Electrochemical tests have shown that the non-precious metal catalyst prepared by the present invention has better oxygen reduction performance than traditional commercial Pt / C. It is used as a catalyst material in zinc-air battery oxygen reduction catalysis, and has the advantages of simple experimental operation, mild reaction conditions, and short cycle, as well as high catalytic activity, low cost, and no pollution to the product.

Description

Technical Field

[0001] The invention relates to the preparation of an oxygen electrocatalyst, in particular to a method for preparing a non-precious metal catalyst for oxygen reduction reaction by utilizing industrial waste acid and lotus pods. Background Art

[0002] Zinc-air battery (Zn-Air Battery) is a device that generates electricity mainly through oxygen reduction reaction between metal zinc sheets and oxygen in the air. It has the advantages of being environmentally friendly, safe operation, low cost, and non-polluting reaction products. Zinc-air battery has attracted worldwide attention as a new type of clean energy. However, the widespread application of zinc-air battery is limited by the slow kinetics of its cathode oxygen reduction reaction (ORR), which often requires a catalyst to catalyze its reaction. Currently, the catalysts used to catalyze the oxygen reduction reaction are mainly divided into metal catalysts and non-metal catalysts, and carbon-supported platinum and platinum alloy catalysts are the most widely used and the best catalytic metal catalysts. However, their limited resources, high prices, and poor resistance to methanol poisoning cannot meet the long-term cycle use of zinc-air batteries. This requires us to find non-precious metal catalysts that can replace precious metal catalysts. Transition metals such as iron, cobalt, nickel, and copper among non-precious metals have low costs and high reserves, so transition metal-nitrogen-doped carbon catalysts are considered to be one of the most promising non-precious metal catalysts due to their high electrocatalytic activity and catalytic stability.

[0003] Research in recent years has found that biomass-based carbon materials have the advantages of rich variety, low price, and controllable structure. They have excellent tolerance in acidic or alkaline media, and they contain heteroatoms such as N, P, S, and O, which can regulate the electronic structure and charge distribution of carbon materials and change the physical and chemical properties of carbon materials.

[0004] Lotus seeds are people's favorite food, but lotus seed pods (lotus pods) as waste are usually discarded at will, which not only pollutes the environment but also causes waste of resources. The surface of lotus pods has many scattered honeycomb holes, rich porous structure and large specific surface area, so we consider using it as a biomass-based carbon material to prepare non-precious metal catalysts for oxygen reduction reaction.

[0005] In the process of industrial production, mining, smelting, etc., inorganic acids (hydrochloric acid, sulfuric acid, nitric acid, etc.) are often used to clean metal surfaces or dissolve ores. As a result, a large amount of waste acid solutions containing various metal ions are produced, including iron-containing waste acid obtained by factories using acid to clean the surface of steel equipment. If it is discharged directly without treatment, it will not only waste natural resources, but also pollute the environment, soil and water sources. Therefore, it is considered to use iron-containing waste acid as the iron source in oxygen electrocatalysts. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a non-precious metal catalyst for oxygen reduction reaction by using lotus pods and industrial waste acid, and to use the prepared non-precious metal catalyst for cathode oxygen reduction reaction in a zinc-air battery.

[0007] A method for preparing a non-precious metal catalyst for oxygen reduction reaction using lotus pods and industrial waste acid, comprising the following steps:

[0008] (1) Using lotus pods as carbon and nitrogen sources, iron in industrial waste acid as iron source, and NaCl as active agent, lotus pod powder, industrial waste acid and NaCl are mixed and stirred at room temperature for 12 to 24 hours at a speed of 350 r / min; then put in a refrigerator and freeze until solidified;

[0009] (2) placing the sample frozen in step (1) into a freeze dryer for freeze drying for 12 to 24 hours until a dry solid is obtained;

[0010] (3) The freeze-dried sample in step (2) is placed in a quartz tube, placed in a tubular furnace under nitrogen protection, and subjected to a first high-temperature pyrolysis carbonization treatment at 800-1000°C for 2 hours, then immersed in an acidic solution for 8-12 hours, centrifuged, washed with distilled water until neutral, and then dried, and then subjected to a second high-temperature pyrolysis at 900°C to obtain a sample with a specific surface area of ​​1000-1400 m 2 / g of non-precious metal catalyst (Fe / N / C) for oxygen reduction reaction.

[0011] In step (1), the ratio of the lotus seed pod powder, sodium chloride and industrial waste acid is 2g:6g:15-25mL. The lotus seed pod is obtained by harvesting the lotus seed pod when the fruit is ripe, removing the fruit and drying it; the industrial waste acid comes from the pickling of steel in the factory, and its main components are ferric chloride and hydrochloric acid.

[0012] The acidic solution is a hydrochloric acid solution, and the concentration of the acidic solution is 1-5 mol / L.

[0013] The non-noble metal catalyst prepared by the invention is used for cathode oxygen reduction catalysis in zinc-air batteries.

[0014] The beneficial effects of the present invention are:

[0015] The lotus pod raw material of the present invention contains a relatively rich nitrogen source. The prepared biomass non-precious metal catalyst has good ORR catalytic activity compared with the traditional commercial Pt / C catalyst, can be used as a catalyst material for zinc-air battery oxygen reduction catalysis, and has the advantages of high catalytic activity, low cost, clean and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a TEM image of the non-precious metal catalyst prepared in the present invention.

[0017] Figure 2 This is a Raman comparison chart of the non-precious metal catalyst prepared by the present invention and the non-metal catalyst prepared without adding waste acid.

[0018] Figure 3 This is a diagram of the oxygen reduction polarization curve of the non-precious metal catalyst prepared in the present invention. DETAILED DESCRIPTION

[0019] The method for preparing a novel biomass non-precious metal catalyst using lotus pods of the present invention is further described below through specific examples.

[0020] Example 1

[0021] Weigh 2g of lotus powder, add 15ml of industrial waste acid and 6g of NaCl (the mass ratio of lotus powder to NaCl is 1:3), stir for 24h, put it in a refrigerator to freeze it into a solid and then freeze-dry it. Take 1.0g of the dried sample, grind it and carbonize it at 900℃ for 2h, then soak it in 3mol / L HCl for 12h, take it out, wash it with distilled water until it is neutral, put it in an oven at 80℃ to dry, grind it and place it in a tubular furnace, under argon protection, and graphitize it at 900℃ for 2h to obtain a biomass-based non-precious metal catalyst.

[0022] Through oxygen reduction testing, it was found that the half-wave potential of the oxygen reduction reaction of the biomass non-precious metal catalyst was positively shifted by 9 mV compared with the Pt / C catalyst.

[0023] Example 2

[0024] Weigh 2g of lotus powder, add 20ml of industrial waste acid and 6g of NaCl (the mass ratio of lotus powder to NaCl is 1:3), stir for 24h, put it in the refrigerator to freeze into a solid and then freeze-dry it. Take 1.0g of the dried sample, grind it and carbonize it at 900℃ for 2h, then soak it in 3mol / L HCl for 12h, take it out, wash it with distilled water until neutral, put it in an oven at 80℃ to dry, grind it and place it in a tubular furnace, under argon protection, and graphitize it at 900℃ for 2h to obtain a biomass-based non-precious metal catalyst.

[0025] Through oxygen reduction testing, it was found that compared with the Pt / C catalyst, the half-wave potential of the oxygen reduction reaction of the biomass-based non-precious metal catalyst was positively shifted by 23 mV.

[0026] Example 3

[0027] Weigh 2g of lotus powder, add 25ml of industrial waste acid and 6g of NaCl (the mass ratio of lotus powder to NaCl is 1:3), stir for 24h, put it in a refrigerator to freeze it into a solid and then freeze-dry it. Take 1.0g of the dried sample, grind it and carbonize it at 900℃ for 2h, then soak it in 3mol / L HCl for 12h, take it out, wash it with distilled water until it is neutral, put it in an oven at 80℃ to dry, grind it and place it in a tubular furnace, under argon protection, and graphitize it at 900℃ for 2h to obtain a biomass-based non-precious metal catalyst.

[0028] Through oxygen reduction testing, it was found that the half-wave potential of the oxygen reduction reaction on the biomass-based non-precious metal catalyst electrode was shifted positively by 3 mV compared with Pt / C.

[0029] Example 4

[0030] Weigh 2g of lotus powder, add 20ml of industrial waste acid and 6g of NaCl (the mass ratio of lotus powder to NaCl is 1:3), stir for 24h, put it in a refrigerator to freeze into a solid and then freeze-dry it. Take 1.0g of the dried sample, grind it and carbonize it at 800℃ for 2h, then soak it in 3mol / L HCl for 12h, take it out, wash it with distilled water until neutral, put it in an oven at 80℃ to dry, grind it and place it in a tubular furnace, under argon protection, graphitize it at 800℃ for 2h to obtain a biomass-based non-precious metal catalyst.

[0031] Through oxygen reduction testing, it was found that the half-wave potential of the oxygen reduction reaction on the biomass non-precious metal catalyst electrode shifted positively by 14 mV compared with Pt / C.

[0032] Example 5

[0033] Weigh 2g of lotus powder, add 20ml of industrial waste acid and 6g of NaCl (the mass ratio of lotus powder to NaCl is 1:3), stir for 24h, put it in a refrigerator to freeze it into a solid and then freeze-dry it. Take 1.0g of the dried sample, grind it and carbonize it at 1000℃ for 2h, then soak it in 3mol / L HCl for 12h, take it out, wash it with distilled water until neutral, put it in an oven at 80℃ to dry, grind the dry powder and place it in a tubular furnace. Under argon protection, graphitize it at 1000℃ for 2h to obtain a biomass-based non-precious metal catalyst.

[0034] Through oxygen reduction testing, it was found that the half-wave potential of the oxygen reduction reaction of the biomass-based non-precious metal catalyst was shifted positively by 2 mV compared with Pt / C.

[0035] Example 6

[0036] Weigh 2g of lotus powder, add 15ml of industrial waste acid and 6g of NaCl (the mass ratio of lotus powder to NaCl is 1:3), stir for 12h, put it in a refrigerator to freeze into a solid and then freeze-dry it. Take 1.0g of the freeze-dried sample, grind it and carbonize it at 900℃ for 2h, then soak it in 3mol / L HCl for 12h, take it out, wash it with distilled water until neutral, put it in an oven at 80℃ to dry, grind it and place it in a tubular furnace, under argon protection, and graphitize it at 900℃ for 2h to obtain the biomass-based non-precious metal catalyst Fe / N / C.

[0037] Electrochemical tests revealed that the half-wave potential of the oxygen reduction reaction of the biomass-based non-precious metal catalyst was negatively shifted by 5 mV compared with the Pt / C catalyst.

[0038] Example 7

[0039] Weigh 2g of lotus powder, add 15ml of industrial waste acid and 6g of NaCl (the mass ratio of lotus powder to NaCl is 1:3), stir for 16h, put it in a refrigerator to freeze into a solid and then freeze-dry it. Take 1.0g of the freeze-dried sample, grind it and carbonize it at 900℃ for 2h, then soak it in 3mol / L HCl for 12h, take it out, wash it with distilled water until neutral, put it in an oven at 80℃ to dry, grind it and place it in a tubular furnace, under argon protection, and graphitize it at 900℃ for 2h to obtain the biomass-based non-precious metal catalyst Fe / N / C.

[0040] Electrochemical tests revealed that the half-wave potential of the oxygen reduction reaction of the biomass-based non-precious metal catalyst was negatively shifted by 3 mV compared with the Pt / C catalyst.

[0041] Example 8

[0042] Weigh 2g of lotus powder, add 15ml of industrial waste acid and 6g of NaCl (the mass ratio of lotus powder to NaCl is 1:3), stir for 20h, put it in a refrigerator to freeze into a solid and then freeze-dry it. Take 1.0g of the freeze-dried sample, grind it and carbonize it at 900℃ for 2h, then soak it in 3mol / L HCl for 12h, take it out, wash it with distilled water until neutral, put it in an oven at 80℃ to dry, grind it and place it in a tubular furnace, under argon protection, and graphitize it at 900℃ for 2h to obtain the biomass-based non-precious metal catalyst Fe / N / C.

[0043] Electrochemical tests revealed that the half-wave potential of the oxygen reduction reaction of the biomass-based non-precious metal catalyst shifted negatively by 1 mV compared with the Pt / C catalyst.

[0044] The raw material lotus seed pod powder in the above examples is the product of dried and ground lotus seed pods.

[0045] The structure and performance of the non-precious metal catalyst prepared by the present invention are analyzed and tested below.

[0046] Figure 1 This is a TEM image of the non-precious metal catalyst prepared in Example 2 of the present invention. Figure 1 It can be seen that the biomass non-precious metal catalyst contains iron particles.

[0047] Figure 2 This is a Raman comparison chart of the non-precious metal catalyst prepared in Example 2 of the present invention. Figure 2 It can be seen that at 1295cm -1 and 1594cm -1 The characteristic peaks of carbon materials appeared near the D / I G The value of is the smallest, which is 0.98, indicating that the waste acid improves the graphitization degree of carbon materials.

[0048] Figure 3 Polarization curves of the oxygen reduction reaction catalyzed by the non-precious metal catalyst prepared in the present invention and the commercial Pt / C catalyst. Figure 3 A is the non-precious metal catalyst prepared in Example 2, Example 4 and Example 5, Figure 3 B is the non-precious metal catalyst prepared in Example 1, Example 2 and Example 3; Figure 3 It can be seen intuitively that compared with the commercial Pt / C catalyst, the starting potential and half-wave potential of the oxygen reduction reaction on the non-precious metal catalyst electrode prepared by the present invention have an obvious positive shift, and the half-wave potential reaches a maximum of 0.87V, which is much larger than the half-wave potential of the commercial platinum carbon electrode (0.85V), indicating that this material exhibits better oxygen reduction performance than the traditional commercial Pt / C catalyst.

Claims

1. A method for preparing a non-precious metal catalyst for oxygen reduction reaction using lotus pods and industrial waste acid, characterized in that: The following steps are involved: (1) Weigh a certain amount of lotus seed pod powder and sodium chloride in proportion, add them to a certain volume of industrial waste acid, stir to form a mixed solution; then put it in a refrigerator and freeze it until it solidifies; The lotus pod is obtained by harvesting the lotus pod when the fruits are ripe, removing the fruits and drying them in the sun; The industrial waste acid comes from steel pickling in the factory, and its main components are ferric chloride and hydrochloric acid; (2) placing the sample frozen in step (1) into a freeze dryer for freeze drying until a dry solid is obtained; (3) taking a certain mass of the sample after freeze-drying in step (2), placing it in a quartz tube, placing it in a tube furnace under argon protection, performing a first high-temperature pyrolysis, then soaking it in an acidic solution, centrifuging it, washing it with distilled water until it is neutral, and then drying it, and then performing a second high-temperature pyrolysis to obtain a non-precious metal catalyst for cathode oxygen reduction reaction in a zinc-air battery; In step (1), the ratio of lotus seed powder, sodium chloride and industrial waste acid is 2g:6g:15-25mL; In step (3), the temperature of the first high-temperature pyrolysis is 800-1000°C for 2 hours; the temperature of the second high-temperature pyrolysis is 900°C.

2. The method for preparing a non-precious metal catalyst for oxygen reduction reaction using lotus pods and industrial waste acid according to claim 1, characterized in that: In step (1), the stirring conditions are: a rotation speed of 350 r / min, and stirring at room temperature for 12 to 24 hours.

3. The method for preparing a non-precious metal catalyst for oxygen reduction reaction using lotus pods and industrial waste acid according to claim 1, characterized in that: In step (2), the freeze-drying treatment time is 12 to 24 hours.

4. The method for preparing a non-precious metal catalyst for oxygen reduction reaction using lotus pods and industrial waste acid according to claim 1, characterized in that: In step (3), the acidic solution is a hydrochloric acid solution with a concentration of 1-5 mol / L; and the soaking time is 8-12 h.

5. A method for preparing a non-precious metal catalyst for oxygen reduction reaction using lotus pods and industrial waste acid, which is obtained by the method of any one of claims 1 to 4, characterized in that: The catalyst has a developed pore structure with a specific surface area of ​​1000-1400m 2 / g.

6. Use of the non-precious metal catalyst for oxygen reduction reaction according to claim 5 for oxygen reduction catalysis in zinc-air batteries.

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