Preparation method and application of a waste wood-derived porous carbon integrated bifunctional air electrode

Abstract

The application discloses a preparation method and application of a waste wood derived porous carbon integrated bifunctional air electrode. The chemical composition of the bifunctional air electrode is CoNiLDH@NPC. The waste wood derived nitrogen and phosphorus doped self-supporting carbon material is used as a substrate for the first time, and cobalt salt and nickel salt are used as the LDH synthesis source. The LDH catalytic material with a nanosheet structure is synthesized on the substrate through in-situ hydrothermal growth, and the integrated nitrogen and phosphorus doped carbon material bifunctional air electrode loaded with CoNi-LDH is obtained. The bifunctional air electrode retains the layered porous structure and the large specific surface area characteristics of wood itself, forms an electrochemical heterojunction interface composed of a carbon carrier and nanosheets, is beneficial to the full exposure of active sites, enriches the electron density at the interface, greatly improves the electrocatalytic performance, and the zinc air battery assembled from the bifunctional air electrode has excellent discharge power density and charge-discharge stability.

Description

Technical Field

[0001] This invention relates to a method for preparing and applying an integrated bifunctional air electrode made of porous carbon derived from waste wood, belonging to the field of electrocatalysis technology. Background Technology

[0002] Rechargeable zinc-air batteries (RZABs), as a renewable energy conversion and storage device, have attracted much attention in recent years due to their environmental friendliness, non-toxicity, and high energy density (1086 Wh / kg). However, the energy conversion efficiency of ZABs is severely limited by the slow kinetics of the four-electron transfer pathway during oxygen conversion. The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are the core processes in all metal-air batteries that occur at the cathode (air electrode) interface. During discharge and charging, although noble metal materials (Pt / C, RuO2, and IrO2) are currently the most advanced ORR and OER electrocatalysts, their scarcity and insufficient catalytic stability hinder the widespread application of RZABs.

[0003] Ion chemical engineering is an effective way to improve catalytic performance, with layered double hydroxide (LDH) nanosheets being a typical example. These nanosheets consist of a hydroxyl-coordinated metal cation as the main layer and anion or molecular water as the intermediate layer. This structure allows for precise control of the LDH layer composition to achieve good physicochemical properties, and the sheet-like morphology and layered structure expose a large number of active sites, exhibiting superior activity in OER catalysis. For example, cobalt-nickel layered double hydroxide (CoNi-LDH) has a main layer composed of a large number of divalent cobalt ions and trivalent nickel ions. These two ions, through mutual modulation of their valence band electrons, optimize the adsorption and desorption free energies of reactants and products, accelerating catalytic kinetics and thus favoring the reaction. CoNi-LDH, containing a large number of high-valence nickel ions, exhibits extremely high OER activity, but its bifunctional catalytic performance is not satisfactory due to its low conductivity and lack of ORR active sites. To address these challenges, LDH nanosheets are typically anchored to carbon substrates such as graphene, carbon nanotubes, carbon nanoframes, and carbon nanocages to achieve good conductivity and catalytic stability. However, these carbon materials still suffer from high cost, low catalytic activity, and complex preparation processes. Therefore, finding a convenient and efficient way to prepare catalysts composed of LDH and nanocarbon materials to achieve efficient and long-term stable oxygen electrocatalysis has become a key challenge and a hot topic in current research on bifunctional catalytic materials.

[0004] In addition to the development of electrocatalytic materials, the preparation of traditional air electrodes is usually achieved by spraying powdered catalysts onto a conductive substrate. This method often results in weak interaction between the catalyst and the substrate, causing the catalyst to detach during long-term reaction and seriously damaging the battery performance. Therefore, the direct construction of catalytic materials on a conductive substrate has attracted widespread attention. Summary of the Invention

[0005] The purpose of this invention is to address the technical problems existing in the prior art, such as poor conductivity of LDH, insufficient bifunctionality, cumbersome preparation process, and insufficient durability of traditional spray-applied air electrodes during long-term reactions. This invention proposes a method for preparing a high-efficiency air electrode in zinc-air batteries by converting low-cost waste wood into a self-supporting carbon composite material. This method directly converts waste wood into a self-supporting carbon composite material, fully preserving the tubular three-dimensional structure of the wood to construct a self-supporting substrate, which can effectively promote mass transfer during the catalytic reaction process. Experimental results show that the prepared electrode, when directly used in zinc-air batteries, exhibits excellent discharge power density and charge-discharge cycle performance.

[0006] To address the aforementioned technical problems, this invention provides an integrated bifunctional air electrode made of porous carbon derived from waste wood, with a chemical composition of CoNiLDH@NPC. The bifunctional air electrode uses a wood-derived nitrogen and phosphorus-doped self-supporting carbon material as a substrate, and cobalt and nickel salts as sources for LDH synthesis. An LDH catalytic material with a nanosheet structure is synthesized on the substrate through in-situ hydrothermal growth, resulting in an integrated nitrogen and phosphorus-doped carbon material loaded with CoNi-LDH, which is the bifunctional air electrode.

[0007] This invention also provides a method for preparing the above-mentioned waste wood-derived porous carbon integrated bifunctional air electrode, comprising the following steps:

[0008] Step 1): Place the wood chips in a deionized phosphoric acid aqueous solution to carry out a hydrothermal reaction;

[0009] Step 2): After the reaction is complete, the wood chips are removed, dried, mixed with urea and ammonium dihydrogen phosphate, and placed in a tube furnace for pyrolysis under an inert atmosphere to obtain a self-supporting nitrogen-phosphorus doped carbon substrate.

[0010] Step 3): Add Co(NO3)3·6H2O, Ni(NO3)2·6H2O and CO(NH2)2 to deionized water, and obtain a mixed solution after complete dissolution;

[0011] Step 4): The self-supporting nitrogen-doped carbon substrate obtained in Step 2) is added to the mixed solution obtained in Step 3) for thorough impregnation, and then transferred to a reactor for hydrothermal reaction.

[0012] Step 5): After the reaction is complete, the carbon substrate is removed, rinsed with deionized water, and freeze-dried to obtain a wood-derived porous carbon integrated bifunctional air electrode.

[0013] Preferably, in step 1), the wood chips are 20mm × 20mm × 3mm in size, and the concentration of the deionized phosphoric acid aqueous solution is 25–35 wt%.

[0014] Preferably, the temperature of the hydrothermal reaction in step 1) is 135-145°C and the time is 10-14 hours.

[0015] Preferably, the drying temperature in step 2) is 75-85°C and the drying time is 45-50 hours.

[0016] Preferably, in step 2), the mass ratio of urea to ammonium dihydrogen phosphate is 1:1, and the pyrolysis process conditions are: temperature 850-950℃, heating rate 4-6℃ / min, and time 1-3h.

[0017] Preferably, in step 3), the molar ratio of Co(NO3)3·6H2O, Ni(NO3)2·6H2O and CO(NH2)2 is 2:2:20, and the molar concentration of Co(NO3)3·6H2O is 0.02-0.03 mol / L.

[0018] Preferably, the soaking time in step 4) is 1 to 3 hours, the temperature of the hydrothermal reaction is 115 to 125°C, and the time is 7 to 9 hours.

[0019] Preferably, the freeze-drying time in step 5) is 20-30 hours.

[0020] The present invention also provides the application of the above-mentioned waste wood-derived porous carbon integrated bifunctional air electrode in zinc-air batteries.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) This invention uses cheap and readily available waste wood as the raw material for constructing a carbon substrate, and then loads CoNi-LDH on the obtained carbon substrate to prepare a self-supporting air electrode. In view of the shortcomings of CoNi-LDH such as low electronic conductivity, poor catalytic stability and poor bifunctional catalytic activity, this invention uses a wood-derived nitrogen and phosphorus doped self-supporting carbon substrate as a carrier and CoNi-LDH as a catalytic active material to prepare an integrated structure air electrode derived from waste wood. This invention overcomes the problems of active sites being masked, resistance increasing and stability being poor due to the use of binders in the traditional air electrode preparation method.

[0023] (2) In this invention, nanosheet-like CoNi-LDH is first constructed in a wood-derived carbon support using an in-situ hydrothermal growth method to construct a carbon composite material with high catalytic efficiency, forming an electrochemical heterogeneous interface composed of carbon support and nanosheets. The porous characteristics of wood ensure that it has a large specific surface area, which is conducive to gas transport during the catalytic reaction and allows it to combine with fully exposed catalytic active sites, thereby promoting the reaction. At the same time, the loading of nanosheets regulates the wettability of the air electrode surface, forming a highly efficient solid-liquid-gas three-phase interface, which improves the heterogeneous catalytic performance of the air electrode and further improves the stability of the prepared electrode during the charge and discharge process.

[0024] (3) In this invention, the nitrogen-doped carbon support and CoNi-LDH nanosheets are effectively combined, which further enriches the electron density of the electrochemical heterostructure interface, ensures the formation of a widely distributed three-dimensional electron transport network inside the air electrode, helps to reduce the material's own impedance, improve its electronic conduction performance, and greatly enhance the dual functionality of the air electrode prepared by this invention.

[0025] (4) The waste wood-derived bifunctional air electrode prepared in this invention exhibits a half-wave potential as high as 0.85V during ORR catalysis and an overpotential of only 320mV during OER. When the self-supporting electrode is directly used in a zinc-air battery, it exhibits a high efficiency of up to 263mW / cm². 2 Its peak discharge power density and charge-discharge cycle performance of up to 500 hours demonstrate great potential for commercialization. Attached Figure Description

[0026] Figure 1 SEM images of the waste wood-derived self-supporting nitrogen-doped carbon substrate (a) prepared in Comparative Example 1, the CoNi-LDH catalytic material (b) prepared in Comparative Example 2, and the waste wood-derived integrated bifunctional air electrode (c) prepared in Example 1.

[0027] Figure 2a Comparison of ORR polarization curves of materials prepared in the examples and comparative examples with Pt / C;

[0028] Figure 2b Comparison of OER polarization curves of the materials prepared in the examples and comparative examples with RuO2;

[0029] Figure 3a A comparison of the self-supporting morphology and powder morphology of the waste wood-derived integrated bifunctional air electrode prepared in Example 1 with the discharge power of Pt / C-RuO2.

[0030] Figure 3b The self-supported morphology and powder morphology of the waste wood-derived integrated bifunctional air electrode prepared in Example 1 are shown in the 10 mA / cm² range. 2Comparison of charging and discharging under constant current. Detailed Implementation

[0031] To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0032] The microstructure of the products in the embodiments of this invention was tested using a scanning transmission electron microscope (SEM, Hitachi S-4800). Half-cell performance and battery discharge performance were tested using a Chenhua CHI760 series electrochemical workstation. Charge-discharge performance was tested using a CT2001A blue battery testing system.

[0033] Example 1

[0034] This embodiment provides a method for preparing an integrated bifunctional air electrode (CoNiLDH@NPC) derived from waste wood. The specific preparation steps are as follows:

[0035] Step 1): Place the wood chips with dimensions of 20mm × 20mm × 3mm in a 30wt% deionized phosphoric acid aqueous solution;

[0036] Step 2): Transfer the phosphoric acid aqueous solution containing wood chips from Step 1) to an oven and hydrothermally react at 140°C for 12 hours. Then remove the wood chips and dry them at 80°C for 48 hours.

[0037] Step 3): Mix the completely dried wood chips with urea (2g) and ammonium dihydrogen phosphate (2g), place them in a tube furnace, use nitrogen protection, use a heating rate of 5℃ / min, maintain at 900℃ for 2h, and then cool to room temperature to obtain a self-supporting nitrogen-phosphorus doped carbon substrate.

[0038] Step 4): Add 2 mmol Co(NO3)3·6H2O, 2 mmol Ni(NO3)2·6H2O and 20 mmol CO(NH2)2 to 80 mL of deionized water and dissolve them completely to obtain a mixed solution;

[0039] Step 5): The self-supporting nitrogen-doped carbon substrate obtained in step 3) is added to the mixed solution obtained in step 4) and fully impregnated for 2 hours, and then transferred to a reactor and hydrothermally heated at 120°C for 8 hours.

[0040] Step 6): After the reaction is complete, the carbon substrate is removed, rinsed with deionized water, and freeze-dried for 24 hours to obtain an integrated bifunctional air electrode derived from waste wood. Its microstructure is as follows: Figure 1 As shown in c, after grinding, a bifunctional air electrode in powder form is obtained.

[0041] Figure 1c indicates that under the conditions of Example 1, the integrated bifunctional air electrode maintains the porous characteristics of wood, ensuring that the electrode itself has a large specific surface area, which is conducive to gas diffusion during the catalytic reaction, allowing it to combine with the fully exposed catalytic active sites to promote the reaction. At the same time, the loading of nanosheets regulates the wettability of the air electrode surface, forming a highly efficient solid-liquid-gas three-phase interface, improving the multiphase catalytic performance of the air electrode, and further improving the stability of the prepared electrode during the charge and discharge process.

[0042] Comparative Example 1

[0043] This comparative example provides a method for preparing a self-supported nitrogen-doped carbon substrate derived from waste wood. The specific preparation steps are as follows:

[0044] Step 1): Place the wood chips with dimensions of 20mm × 20mm × 3mm in a 30wt% deionized phosphoric acid aqueous solution;

[0045] Step 2): Transfer the phosphoric acid aqueous solution containing wood chips from Step 1) to an oven and hydrothermally react at 140°C for 12 hours. Then remove the wood chips and dry them at 80°C for 48 hours.

[0046] Step 3): The completely dried wood chips were mixed with urea (2g) and ammonium dihydrogen phosphate (2g), placed in a tube furnace, and heated at 900℃ for 2 hours under nitrogen protection using a heating rate of 5℃ / min. The mixture was then cooled to room temperature to obtain a self-supporting nitrogen-phosphorus doped carbon substrate, the microstructure of which is shown below. Figure 1 As shown in a.

[0047] Comparative Example 2

[0048] This comparative example provides a method for preparing CoNi-LDH catalytic materials, and the specific preparation steps are as follows:

[0049] Step 1): Add 2 mmol Co(NO3)3·6H2O, 2 mmol Ni(NO3)2·6H2O and 20 mmol CO(NH2)2 to 80 mL of deionized water, and obtain a mixed solution after complete dissolution;

[0050] Step 2): Transfer the solution prepared in Step 1) to the reaction vessel and hydrothermally heat it at 120°C for 8 hours;

[0051] Step 3): The precipitate obtained in Step 2) was collected by centrifugation, washed with deionized water, and freeze-dried for 24 hours to obtain the CoNi-LDH catalyst material, whose microstructure is as follows. Figure 1 As shown in b.

[0052] The microstructure of the bifunctional air electrode prepared in Example 1, and the self-supporting nitrogen-doped carbon substrate and CoNi-LDH catalytic material prepared in Comparative Examples 1 and 2 were examined using SEM. Figure 1 The SEM images shown in ac reveal that the wood-derived nitrogen-phosphorus doped carbon substrate exhibits a layered porous structure, while CoNi-LDH forms a layered nanostructure. Effectively combining these two materials allows for the construction of a highly efficient carbon composite material, forming an electrochemical heterogeneous interface between the carbon support and nanosheets. The porous nature of wood ensures a large specific surface area, facilitating gas diffusion during the catalytic reaction and enabling effective binding with fully exposed catalytic active sites, thereby promoting the reaction. Furthermore, the loading of nanosheets modulates the wettability of the air electrode surface, forming a highly efficient solid-liquid-gas three-phase interface, enhancing the heterogeneous catalytic performance of the air electrode, and further improving the stability of the prepared electrode during charge-discharge processes.

[0053] Example 2

[0054] 10 mg of the bifunctional air electrode in powder form prepared in Example 1, the nitrogen-phosphorus-doped carbon substrate prepared in Comparative Example 1, the CoNi-LDH catalyst prepared in Comparative Example 2, and commercial Pt / C and RuO2 powders were dissolved in 2 mL of a solution composed of ethanol and 5% Nafion. The solutions were ultrasonicated for 30 minutes to form a homogeneous slurry. The resulting slurry was then drop-coated onto the glassy carbon surface of a rotating disk electrode with a loading of 0.1 mg / cm³. 2 After thorough drying, it was used as the working electrode, forming a three-electrode system with a platinum wire counter electrode and a silver / silver chloride reference electrode. Potassium hydroxide solution was used as the alkaline electrolyte, and tests were conducted using a CHI760 series electrochemical workstation from Chenhua Company. The ORR and OER performance were investigated using a linear voltammetric scan method (scan rate of 5 mV / s).

[0055] Test results are as follows Figure 2a As shown in b, Figure 2a The ORR catalytic performance of the prepared catalytic materials in the examples and comparative examples was compared with that of commercial noble metal catalysts. It was found that the limiting current density of CoNiLDH@NPC in the ORR catalytic process was 5.58 mA / cm². 2 The half-wave potential is 0.85V, compared to 5.66mA / cm² for commercial Pt / C catalysts. 2 The ORR catalytic performance (0.89V) is very close to that of the comparative nitrogen-phosphorus doped carbon substrate and CoNi-LDH. Figure 2b The comparison of the OER catalytic performance of the prepared catalytic materials in the examples and comparative examples with commercial noble metal catalysts shows that CoNiLDH@NPC exhibits the highest limiting current density in the OER catalytic process, and also reaches the highest current density at 10 mA / cm². 2The overpotential (320mV) at the point is much smaller than that of all the comparative materials; the effective composite of the nitrogen-doped carbon support and CoNi-LDH forms a heterogeneous interface with rich electron density, which forms a widely distributed three-dimensional electron transport network inside the air electrode, which helps to reduce the material's own impedance, improve its electronic conduction performance, and greatly enhance its electrocatalytic bifunctionality. The air electrode CoNiLDH@NPC prepared in the example has the best half-cell performance.

[0056] Example 3

[0057] 10 mg of the integrated bifunctional air electrode in powder form prepared in Example 1 and Pt / C-RuO2 powder were dissolved in ethanol and 5% Nafion solution, respectively, and ultrasonicated for 30 minutes to form a uniform catalyst slurry. The slurry was then sprayed onto hydrophobic carbon paper (loading 2 mg / cm³). 2 After drying, an air electrode is obtained and used as the positive electrode. This self-supporting integrated dual-function air electrode requires no coating and can be used directly as the positive electrode material. Subsequently, a zinc sheet is used as the negative electrode, and a 6M potassium hydroxide solution is used as the electrolyte. The above components are then assembled into a zinc-air battery within a battery device. Discharge power density testing (scan rate 5 mV / s) is performed using an electrochemical workstation equipped with a current amplifier, and charge-discharge testing (current density 10 mA / cm²) is conducted using a battery testing system. 2 The cycle is 20 minutes (10 minutes of discharge, 10 minutes of charge).

[0058] Test results are as follows Figure 3a As shown in b, Figure 3a A comparison of the discharge power density of different embodiments reveals that the zinc-air battery assembled using self-supporting CoNiLDH@NPC exhibits an extremely high peak discharge power density (263 mW / cm²) during testing. 2 The integrated dual-function air electrode delivers superior power output compared to batteries assembled using powdered materials, demonstrating its excellent discharge performance. Figure 3b For the comparison of cycle charge-discharge stability in the example, at a current density of 10 mA / cm² 2 At that time, the zinc-air battery assembled by the self-supporting CoNiLDH@NPC could operate stably for 500 hours, or 1500 charge-discharge cycles, with a voltage difference of 0.79V and no significant increasing trend. This is better than the charge-discharge cycle time and charge-discharge voltage difference of batteries assembled using powdered materials.

[0059] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make several improvements and additions without departing from the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A waste wood-derived porous carbon integrated bifunctional air electrode, characterized by, Its chemical composition is CoNiLDH@NPC. The bifunctional air electrode is based on a wood-derived nitrogen and phosphorus doped self-supporting carbon material, with cobalt salt and nickel salt as the source of LDH synthesis. The LDH catalytic material with a nanosheet structure is synthesized on the substrate through in-situ hydrothermal growth, resulting in an integrated nitrogen and phosphorus doped carbon material loaded with CoNi-LDH, which is the bifunctional air electrode. The method for preparing the bifunctional air electrode includes the following steps: Step 1): Place the wood chips in a deionized phosphoric acid aqueous solution to carry out a hydrothermal reaction; Step 2): After the reaction is complete, the wood chips are removed, dried, mixed with urea and ammonium dihydrogen phosphate, and placed in a tube furnace for pyrolysis under an inert atmosphere to obtain a self-supporting nitrogen-phosphorus-doped carbon substrate. Step 3): Add Co(NO3)3·6H2O, Ni(NO3)2·6H2O and CO(NH2)2 to deionized water, and after complete dissolution, obtain a mixed solution; Step 4): The self-supporting nitrogen-doped carbon substrate obtained in Step 2) is added to the mixed solution obtained in Step 3) for thorough impregnation, and then transferred to a reactor for hydrothermal reaction; Step 5): After the reaction is complete, the carbon substrate is removed, rinsed with deionized water, and freeze-dried to obtain a wood-derived porous carbon integrated bifunctional air electrode.

2. The method for preparing waste wood-derived porous carbon integrated bifunctional air electrode according to claim 1, characterized in that, Includes the following steps: Step 1): Place the wood chips in a deionized phosphoric acid aqueous solution to carry out a hydrothermal reaction; Step 2): After the reaction is complete, the wood chips are removed, dried, mixed with urea and ammonium dihydrogen phosphate, and placed in a tube furnace for pyrolysis under an inert atmosphere to obtain a self-supporting nitrogen-phosphorus-doped carbon substrate. Step 3): Add Co(NO3)3·6H2O, Ni(NO3)2·6H2O and CO(NH2)2 to deionized water, and after complete dissolution, obtain a mixed solution; Step 4): The self-supporting nitrogen-doped carbon substrate obtained in Step 2) is added to the mixed solution obtained in Step 3) for thorough impregnation, and then transferred to a reactor for hydrothermal reaction; Step 5): After the reaction is complete, the carbon substrate is removed, rinsed with deionized water, and freeze-dried to obtain a wood-derived porous carbon integrated bifunctional air electrode.

3. The method for preparing waste wood-derived porous carbon integrated bifunctional air electrode according to claim 2, wherein, In step 1), the wood chips are 20mm × 20mm × 3mm in size, and the concentration of the deionized phosphoric acid aqueous solution is 25~35wt%.

4. The method for preparing the waste wood-derived porous carbon integrated bifunctional air electrode as described in claim 2, characterized in that, The hydrothermal reaction in step 1) is carried out at a temperature of 135~145℃ for 10~14h.

5. The method for preparing waste wood-derived porous carbon integrated bifunctional air electrode according to claim 2, wherein The drying temperature in step 2) is 75~85℃, and the time is 45~50h.

6. The method for preparing the waste wood-derived porous carbon integrated bifunctional air electrode as described in claim 2, wherein the mass ratio of urea to ammonium dihydrogen phosphate in step 2) is 1:1, and the pyrolysis process conditions are: temperature 850~950℃, heating rate 4~6℃ / min, and time 1~3h.

7. The method of producing waste wood derived porous carbon integrated bifunctional air electrode according to claim 2, wherein, In step 3), the molar ratio of Co(NO3)3·6H2O, Ni(NO3)2·6H2O and CO(NH2)2 is 2:2:20, and the molar concentration of Co(NO3)3·6H2O is 0.02~0.03mol / L.

8. The method of producing waste wood derived porous carbon integrated bifunctional air electrode according to claim 2, wherein, The soaking time in step 4) is 1~3h, and the temperature of the hydrothermal reaction is 115~125℃, and the time is 7~9h.

9. The method for preparing the waste wood-derived porous carbon integrated bifunctional air electrode as described in claim 2, characterized in that, The freeze-drying time in step 5) is 20-30 hours.

10. The application of the waste wood-derived porous carbon integrated bifunctional air electrode as described in claim 1 in a zinc-air battery.

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