A porous transition metal-nitrogen-carbon catalyst, and a preparation method and application thereof

Abstract

The application discloses a kind of porous transition metal-nitrogen-carbon catalyst and its preparation method and application, it is related to catalyst technical field, the present application is by the cyanethylation and amine oxime reaction of wood in alkaline condition, make that lignin in wood is dissolved, simultaneously part cellulose on pore wall is stripped, further produces crosslinked pore structure, to make wood can obtain integrated carbon material with interlinked pore structure after pyrolysis;And the method presented in the application is prepared, with cellulose in wood as grafting site, amidoxy group is grafted to wood precursor, provides abundant surface anchoring site for metal species, to realize the efficient loading of different kinds of metal species on wood-derived carbon.The present application gradually forms zinc oxide or zinc nanoparticles during pyrolysis process and then evaporates, this process inhibits the large-scale aggregation of target metal species, ensures the high dispersion state of target metal species.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a porous transition metal-nitrogen-carbon catalyst, its preparation method, and its application. Background Technology

[0002] Metal-air batteries are an important class of electrochemical energy conversion devices, whose performance is mainly limited by the slow-kinetic oxygen reduction reaction (ORR) at the cathode. Currently, platinum-based materials are considered ideal catalysts for the highly efficient ORR process, but the high cost of platinum, a precious metal, limits its large-scale application. Therefore, the development of low-cost non-precious metal catalysts has become a research hotspot in the field of metal-air batteries. Transition metal-nitrogen-carbon (MNC) materials have become a highly anticipated non-precious metal electrode catalyst due to their large specific surface area, excellent conductivity, and good stability. Because of their high ORR catalytic activity, MNCs are expected to replace platinum-based catalysts as electrode materials for the cathode of metal-air batteries. The main preparation method for MNCs is high-temperature pyrolysis, which involves high-temperature treatment of a mixture containing carbon, nitrogen, and transition metal precursors in an inert gas atmosphere. In this material, highly dispersed metal species are considered to be highly efficient catalytic active sites; therefore, the key to preparing highly active MNCs lies in how to avoid the aggregation of transition metal species and achieve their high dispersion.

[0003] Traditional MNC catalysts are mostly powdered materials, requiring complex electrode preparation processes in practical applications, including powder dispersion, coating, and drying. Furthermore, ionically conductive binders and suitable electrode substrates must be selected. The activity of electrocatalytic reactions depends not only on the activity of the catalyst itself but also significantly on the state of the electrode and catalyst on the electrode surface. Inappropriate electrode preparation processes can lead to a reduction in the active surface area of ​​the catalyst, excessive dead volume, and poor catalytic interfaces, thereby hindering electron and mass transport and increasing contact resistance. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention provides a porous transition metal-nitrogen-carbon catalyst rich in mesopores and micropores, which can be directly used as an electrode in actual electrocatalytic reactions without the need for additional binders, conductive agents, and current collectors, as well as its preparation method and application.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0006] A method for preparing a porous transition metal-nitrogen-carbon catalyst is provided, comprising the following steps:

[0007] S1: Immerse the wood block in a 10wt.% sodium hydroxide aqueous solution and let it stand at room temperature for 0.5-5 hours to obtain wood blocks with lignin removed;

[0008] S2: Immerse the wood block obtained in step S1 in acrylonitrile, and add 10 wt.% sodium hydroxide aqueous solution to adjust the pH of the reaction system to alkaline. After stirring the reaction continuously at room temperature for 3 to 10 hours, neutralize the reaction solution with 1 wt.% acetic acid solution, take out the wood block, rinse it, and freeze-dry it to obtain cyanoethylated wood block.

[0009] S3: Place cyanoethylated wood blocks in a mixed aqueous solution of hydroxylamine hydrochloride and sodium hydroxide, heat and stir for 5-12 hours. After the reaction is complete, remove the wood blocks, rinse them, and freeze-dry them to obtain amine oxime-modified wood blocks.

[0010] S4: Soak the amylopyridine wood block in a mixed aqueous solution containing transition metal salts and zinc salts for 6-72 hours. After standing for reaction, remove the wood block, rinse it, and freeze-dry it to obtain amylopyridine wood block that simultaneously chelates transition metal ions and zinc ions.

[0011] S5: The ammoniated wood block chelated with transition metal ions and zinc ions is placed in an inert atmosphere for thermal stabilization treatment, and then pyrolyzed to obtain a porous transition metal-nitrogen-carbon catalyst.

[0012] Furthermore, in step S2, an aqueous sodium hydroxide solution is added dropwise to adjust the pH of the reaction system to 8–12.

[0013] Furthermore, in step S2, the concentration of hydroxylamine hydrochloride in the mixed aqueous solution of hydroxylamine hydrochloride and sodium hydroxide is 0.5–5 mol / L, and the concentration of sodium hydroxide is 0.5–5 mol / L; and the heating temperature during the heating and stirring reaction is 50–90 °C.

[0014] Furthermore, the transition metal salt is one or a combination of manganese nitrate, manganese chloride, manganese sulfate, cobalt nitrate, cobalt chloride, cobalt sulfate, nickel nitrate, nickel chloride, nickel sulfate, copper nitrate, copper chloride, and copper sulfate, and the zinc salt is zinc nitrate, zinc chloride, or zinc sulfate.

[0015] Furthermore, the total concentration of transition metal ions and zinc ions is 0.02–2 mol / L, and the proportion of transition metal ions to the total metal ion concentration is 0.005–0.5%.

[0016] Furthermore, in step S5, the pyrolysis temperature is 900–1200℃.

[0017] Furthermore, the wood blocks are made of balsa wood, pine, linden, cedar, or birch.

[0018] The present invention also provides a porous transition metal-nitrogen-carbon catalyst prepared by the above-described preparation method.

[0019] The present invention also provides the application of the above-mentioned porous transition metal-nitrogen-carbon catalyst in the preparation of metal-air battery electrodes.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention involves cyanoethylation and ammonium oxime reactions in wood under alkaline conditions, which dissolves the lignin in the wood and removes some cellulose from the pore walls, thereby generating a cross-linked pore structure. This allows the wood to be pyrolyzed into an integral carbon material with an interconnected pore structure. Furthermore, the method proposed in this invention uses cellulose in the wood as grafting sites to graft ammonium oxime groups onto the wood precursor, providing abundant surface anchoring sites for metal species, thus achieving efficient loading of different types of metal species onto wood-derived carbon.

[0022] This invention utilizes the pyrolysis process where zinc ions gradually form zinc oxide or zinc nanoparticles and then evaporate. This process inhibits the large-scale aggregation of target metal species, ensuring their high dispersion and facilitating the formation of abundant mesoporous and microporous structures in the monolithic carbon material. This increases the number of catalytically active sites, resulting in metal-air battery electrodes with higher oxygen reduction reaction catalytic activity, and batteries with higher voltage and peak power density. Attached Figure Description

[0023] Figure 1 A scanning electron microscope image of the catalyst prepared in Example 1;

[0024] Figure 2 The nitrogen adsorption-desorption isotherm of the catalyst prepared in Example 1;

[0025] Figure 3 This is a schematic diagram of the pore size distribution of the catalyst prepared in Example 1;

[0026] Figure 4 A comparative schematic diagram of the X-ray diffraction patterns of the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0027] Figure 5 A schematic diagram comparing the ORR polarization curves of the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0028] Figure 6 This is a schematic diagram comparing the ORR polarization curves of the catalysts prepared in Examples 2, 3, and 4.

[0029] Figure 7 The polarization curve of an aluminum-air battery prepared using the catalyst prepared in Example 1. Detailed Implementation

[0030] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0031] Example 1

[0032] This embodiment uses the following steps to prepare the manganese-nitrogen-carbon catalyst:

[0033] S1: The dimensions are 30×10×2mm 3 The balsa wood blocks were immersed in a 10 wt.% sodium hydroxide aqueous solution and left to stand at room temperature for 1 hour to remove the lignin from the balsa wood blocks. In practice, it was impossible to completely remove the lignin, and the remaining lignin did not affect the subsequent preparation.

[0034] S2: The balsa wood blocks from S1 with some lignin removed were immersed in 30 mL of acrylonitrile. 1 mL of 10 wt.% sodium hydroxide aqueous solution was added dropwise to adjust the pH of the reaction system to 10. After stirring at room temperature for 7 h, the reaction solution was neutralized with 1 wt.% acetic acid solution. The wood blocks in the neutralized reaction solution were removed, rinsed with ultrapure water, and then freeze-dried to obtain cyanoethylated wood blocks.

[0035] S3: The cyanoethylated wood block was placed in a mixed aqueous solution containing 3.45 mol / L hydroxylamine hydrochloride and 3.45 mol / L sodium hydroxide, and the mixture was heated and stirred for 6 hours. The reacted wood block was rinsed with ultrapure water and then freeze-dried to obtain the amylated wood block.

[0036] S4: The amylopyridine wood block was soaked in a mixed aqueous solution containing 40 mmol / L manganese nitrate and 160 mmol / L zinc nitrate for 48 h, rinsed with deionized water, and then freeze-dried to obtain amylopyridine wood block chelated with both manganese and zinc ions.

[0037] S5: Ammoniated wood blocks chelated with manganese and zinc ions were subjected to thermal stabilization treatment at 250°C for 1 hour in a nitrogen atmosphere, followed by pyrolysis at 1000°C for 2 hours in a nitrogen atmosphere to obtain a manganese-nitrogen-carbon catalyst, labeled as m-Mn. 0.2 NC, with the subscript 0.2, represents the proportion of manganese ions to the total number of manganese and zinc ions during the chelation process.

[0038] Example 2

[0039] The difference between this embodiment and Example 1 is that: the amylopyridine-oxidized wood block was soaked in a mixed aqueous solution containing 40 mmol / L cobalt nitrate and 160 mmol / L zinc nitrate for 48 hours, rinsed with deionized water, and then freeze-dried to obtain amylopyridine-oxidized wood block chelated with both cobalt and zinc ions. After undergoing the same thermal stabilization and pyrolysis, a cobalt-nitrogen-carbon catalyst, labeled m-Co, was obtained. 0.2 NC.

[0040] Example 3

[0041] The difference between this embodiment and Example 1 is that: the amylopyridine-oxime-treated wood block was soaked in a mixed aqueous solution containing 40 mmol / L nickel nitrate and 160 mmol / L zinc nitrate for 48 hours, rinsed with deionized water, and then freeze-dried to obtain amylopyridine-oxime-treated wood block simultaneously chelated with nickel and zinc ions. After undergoing the same thermal stabilization and pyrolysis, a nickel-nitrogen-carbon catalyst, labeled m-Ni, was obtained. 0.2 NC.

[0042] Example 4

[0043] The difference between this embodiment and Example 1 is that: the amylopyridine-oxidized wood block was soaked in a mixed aqueous solution containing 40 mmol / L copper nitrate and 160 mmol / L zinc nitrate for 48 hours, rinsed with deionized water, and then freeze-dried to obtain amylopyridine-oxidized wood block chelated with both copper and zinc ions. After undergoing the same thermal stabilization and pyrolysis, a copper-nitrogen-carbon catalyst, labeled m-Cu, was obtained. 0.2 NC.

[0044] Comparative Example 1

[0045] The difference between this embodiment and Example 1 is that: the amylopyridine wood block was soaked in an aqueous solution containing 200 mmol / L manganese nitrate for 48 h, rinsed with deionized water, and then freeze-dried to obtain amylopyridine wood block chelated with manganese ions. After undergoing the same thermal stabilization and pyrolysis, a manganese-nitrogen-carbon catalyst was obtained, labeled as m-Mn1NC.

[0046] Comparative Example 2

[0047] The difference between this embodiment and Example 1 is that: balsa wood blocks with some lignin removed were directly soaked in a mixed aqueous solution containing 40 mmol / L manganese nitrate and 160 mmol / L zinc nitrate for 48 hours. After rinsing with deionized water, they were freeze-dried to obtain balsa wood blocks impregnated with both manganese and zinc ions. These blocks were then subjected to the same thermal stabilization and pyrolysis to obtain a manganese-nitrogen-carbon catalyst, labeled m-Mn. 0.2 NC-i.

[0048] Comparative Example 3

[0049] The difference between this embodiment and Example 1 is that: the amylopyridine wood block was soaked in an aqueous solution containing 200 mmol / L zinc nitrate for 48 h, rinsed with deionized water, and then freeze-dried to obtain amylopyridine wood block chelated with zinc ions. After undergoing the same thermal stabilization and pyrolysis, a nitrogen-carbon catalyst was obtained, labeled as m-NC.

[0050] Example 5 Catalyst morphology and X-ray diffraction detection

[0051] The catalyst m-Mn prepared in Example 1 0.2 NC used a scanning electron microscope to perform the scan, and the results are as follows: Figure 1 As shown, where, Figure 1 The left side shows the catalyst m-Mn 0.2 Cross-sectional scanning electron microscope image of NC. Figure 1 The right side shows the catalyst m-Mn 0.2 Longitudinal cross-sectional scanning electron microscope image of NC; by Figure 1 It can be seen that m-Mn 0.2 NC retains the transversely arranged and longitudinally extended micron-sized channels in wood, while also generating a partially cross-linked channel structure.

[0052] The catalyst m-Mn prepared in Example 1 0.2 NC performed nitrogen adsorption-desorption tests to obtain the following results: Figure 2 The nitrogen adsorption-desorption isotherm is shown; statistical analysis of catalyst m-Mn is performed. 0.2 The aperture distribution of NC is obtained as follows Figure 3 The pore size distribution diagram is shown; the catalyst m-Mn was obtained based on the BET method. 0.2 The specific surface area of ​​NC is 130 m². 2 / g, from which we can know that the catalyst m-Mn 0.2 NC has a large number of active sites, which can improve catalytic efficiency.

[0053] The m-Mn prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 0.2 NC, m-Mn1NC, m-Mn 0.2 X-ray diffraction analysis was performed on NC-i and m-NC, and the results are as follows: Figure 4 As shown, by Figure 4 It can be seen that m-Mn0 .2 The XRD pattern of NC showed no obvious metal or metal oxide diffraction peaks, only graphite diffraction peaks. In contrast, the XRD pattern of m-Mn1NC showed significant metal or metal oxide diffraction peaks. This indicates that using amine-oxime-treated wood as a precursor can simultaneously chelate target metal ions and zinc ions, which is beneficial for the high dispersion of target metal ions. Meanwhile, m-Mn... 0.2The XRD pattern of NC-i also showed obvious diffraction peaks of metals or metal oxides. This result indicates that when metals are introduced into the wood precursor by conventional impregnation methods, metal species are difficult to maintain high dispersion during pyrolysis. In contrast, amine-oxime-treated wood can efficiently anchor metal ions, thereby significantly limiting their aggregation during pyrolysis and achieving high dispersion of metal species in the electrode.

[0054] Example 6 Catalyst Performance Test

[0055] ORR polarization curves of the catalysts prepared in Examples 1-4 and Comparative Examples 1-3 were acquired using a rotating disk assay in an O2-saturated 0.1 mol / L potassium hydroxide solution. The electrode rotation speed was 1600 rpm, the potential range was 0.05–1.1 V vs RHE, and the scan rate was 10 mV·s. -1 .

[0056] m-Mn prepared in Examples 1, 2, and 3 0.2 NC, m-Mn1NC, m-Mn 0.2 The oxygen reduction polarization curves of NC-i, m-NC, and commercial platinum-carbon (Pt / C) catalysts are shown in the figure. Figure 5 As shown, by Figure 5 It can be seen that m-Mn 0.2 The half-wave potential of the oxygen reduction reaction in NC is significantly higher than that in m-NC, indicating that the introduction of metal species can efficiently catalyze the oxygen reduction reaction process. Although m-Mn1NC and m-Mn... 0.2 NC-i all contain Mn species, but their half-wave potential is much lower than that of m-Mn. 0.2 NC. This is due to m-Mn1NC and m-Mn 0.2 The large aggregation of Mn species in NC-i results in fewer actual catalytic active sites; while m-Mn 0.2 Mn species in NC are highly dispersed, resulting in a large number of actual catalytic sites.

[0057] Catalyst m-Mn prepared in Example 1 0.2 A performance comparison was made between NC and common powdered Mn-NC catalysts. Regarding half-wave potential, an important indicator for evaluating the oxygen reduction reaction activity of catalysts, m-Mn... 0.2The half-wave potential of NC reaches 0.89V, which is significantly higher than that of the powdered Mn-NC catalyst in the existing literature "H.-Y. Kim, Y.-W. Ju, Fabrication of Mn-NC catalyst for oxygen reduction reactions using Mn-embedded carbon nanofiber, Energies, 13(2020)2561." and the commercial Pt / C catalyst. Therefore, the monolithic Mn-NC electrode for oxygen reduction reactions with high metal dispersion, prepared by pyrolyzing a metallo-oxime-treated wood block that simultaneously chelates manganese and zinc ions, provided by this invention, can efficiently catalyze oxygen reduction reactions.

[0058] m-Co prepared in Examples 2, 3 and 4 0.2 NC, m-Ni 0.2 NC and m-Cu 0.2 The ORR polarization curve of NC is as follows Figure 6 As shown. By Figure 6 It is known that the method proposed in this invention can be used to prepare monolithic electrodes containing different metal species, and these electrodes all exhibit high ORR activity.

[0059] The m-Mn prepared in Example 1 0.2 NC and aluminum sheets are placed on either side of a potassium hydroxide gel electrolyte to form an aluminum-air battery. The polarization curve is shown in the figure. Figure 7 As shown. By Figure 7 It can be seen that the battery's open-circuit voltage can reach 2.3V, and its peak power density reaches 11.25mW / cm³. 2 This demonstrates that the monolithic electrode prepared by this invention can be directly used as a cathode electrode catalyst in the construction of metal-air batteries.

Claims

1. Use of a porous transition metal-nitrogen-carbon catalyst in the preparation of a metal-air battery electrode, characterized in that, The preparation method of the porous transition metal-nitrogen-carbon catalyst comprises the following steps: S1: immersing wood blocks in a 10wt.% sodium hydroxide aqueous solution, and standing at room temperature for 0.5-5h to obtain wood blocks from which lignin is removed; S2: immersing the wood blocks obtained in step S1 in acrylonitrile, and adding 10wt.% sodium hydroxide aqueous solution dropwise to adjust the pH value of the reaction system to alkaline, continuously stirring the reaction at room temperature for 3-10h, then neutralizing the reaction solution with 1wt.% acetic acid solution, taking out the wood blocks, rinsing and freeze-drying to obtain cyanoethylated wood blocks; S3: placing the cyanoethylated wood blocks in a mixed aqueous solution of hydroxylamine hydrochloride and sodium hydroxide, heating and stirring the reaction for 5-12h, taking out the wood blocks after the reaction is completed, rinsing and freeze-drying to obtain amidoxime-converted wood blocks; S4: immersing the amidoxime-converted wood blocks in a mixed aqueous solution containing manganese salt and zinc salt for 6-72h, standing the reaction, taking out the wood blocks, rinsing and freeze-drying to obtain amidoxime-converted wood blocks which are simultaneously chelated with transition metal ions and zinc ions; the concentration of the manganese salt is 40mmol / L, and the concentration of the zinc salt is 160mmol / L; S5: placing the amidoxime-converted wood blocks chelated with transition metal ions and zinc ions in an inert atmosphere for thermal stabilization treatment, and then pyrolyzing to obtain the porous transition metal-nitrogen-carbon catalyst.

2. Use according to claim 1, characterized in that, In step S2, the sodium hydroxide aqueous solution is added dropwise to make the pH value of the reaction system 8-12.

3. Use according to claim 2, characterized in that, In step S2, in the mixed aqueous solution of hydroxylamine hydrochloride and sodium hydroxide, the concentration of hydroxylamine hydrochloride is 0.5-5mol / L, and the concentration of sodium hydroxide is 0.5-5mol / L; and the heating temperature during the heating and stirring reaction is 50-90℃.

4. Use according to claim 3, characterized in that, The transition metal salt is one or a combination of several of manganese nitrate, manganese chloride and manganese sulfate, and the zinc salt is zinc nitrate, zinc chloride or zinc sulfate.

5. Use according to claim 4, characterized in that, In step S5, the pyrolysis temperature is 900-1200℃.

6. Use according to claim 5, characterized in that, The wood blocks are balsa wood, pine wood, linden wood, fir wood or birch wood.

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