Preparation method and application of zinc air battery catalyst derived based on poplar-MOFs precursor

Abstract

The invention discloses a preparation method of a zinc air battery catalyst based on poplar-MOFs precursor derivation, and belongs to the field of electrocatalysis. The method comprises the following steps: adding deionized water and poplar without lignin into Co (NO3) 3.6 H2O, stirring, adding 2-methylimidazole, adding deionized water, fully stirring, carrying out suction filtration, and carrying out vacuum drying to obtain a wood-based precursor; the wood-based precursor and boric acid are subjected to high-temperature carbonization, grinding, suction filtration and drying, and the catalyst is obtained. The wood-derived carbon-based composite material co-doped with B and N and loaded with MOFs is used as the air cathode electrocatalyst of the zinc-air battery. The wood-derived carbon-based composite material disclosed by the invention has abundant pore diameters and relatively large specific area and defect degree, so that more active sites are exposed, and O2 diffusion and electron transfer are facilitated; co-coated CoO serves as a catalytic center and is uniformly coated with a carbon shell, excellent oxygen reduction and oxygen evolution catalytic activity is shown, extremely high charging and discharging stability is shown, and an assembled zinc-air battery shows excellent specific capacity and stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon-based catalysts and electrocatalysis, and relates to a preparation method and application of a poplar-MOFs precursor-derived zinc-air battery catalyst. BACKGROUND

[0002] Wood-derived carbon is widely used as an oxygen electrocatalyst due to its low cost, renewability and tunable hierarchical porous structure. However, the intrinsic conductivity of wood-derived carbon-based catalysts is insufficient and the active sites are limited, which makes it difficult for the electrocatalytic performance to meet the actual demand. How to simultaneously improve the conductivity and bifunctional activity of carbon-based catalysts through material design and component regulation is still a core problem to be solved in this field. The active center catalysts of various metal compounds loaded in conventional wood-derived carbon materials may cause the shedding of metal compounds or single-atom active centers during the use of electrocatalysis, especially at high current oxidation potential, which hinders the stability of the catalyst. On the other hand, the graphitization degree of the porous carbon skeleton directly derived from wood materials is limited, which is not conducive to the transmission of electrons in the subsequent catalytic reaction process.

[0003] In contrast, the catalytic material obtained by in-situ growth of MOFs on the surface of wood and then carbonization can not only maintain the original rich ion channels and porous structure of the wood substrate, but also realize stable loading by virtue of the carbon coating effect in the formation process of metal compounds. Moreover, the graphitized carbon skeleton formed by MOFs at high temperature can further improve the electron transmission rate of the carbon substrate, realizing efficient electron transmission in the catalytic process. SUMMARY

[0004] The application provides a preparation method of a boron-nitrogen co-doped MOF-loaded wood-based zinc-air battery catalyst, in order to solve the problems of high cost and poor stability of the current zinc-air battery catalyst. The wood-derived carbon-based composite material has a rich three-dimensional porous structure and a large specific surface area, and the doping of heteroatoms effectively promotes electron transfer, thereby exposing a large number of active sites. The carbon shell serves as an active center, and the catalyst has excellent bifunctional electrocatalytic activity.

[0005] To achieve the above object, the application provides the following scheme: The application aims to provide a preparation method of a poplar-MOFs precursor-derived zinc-air battery catalyst, comprising the following steps: Step 1, adding deionized water and delignified poplar to Co(NO3)3·6H2O, stirring, adding 2-methylimidazole, adding deionized water, fully stirring, filtering, vacuum drying, and obtaining a wood-based precursor; Step 2: The wood-based precursor and boric acid are subjected to high-temperature carbonization, grinding, filtration and drying to obtain the catalyst.

[0006] Further, in step 1, the molar ratio of Co(NO3)3·6H2O to 2-methylimidazole in the MOFs aqueous solution is 1:7; the mass ratio of Co(NO3)3·6H2O to lignin-free poplar wood is 1:0.5; and the metal ion concentration is 0.069 mol / L. -1 .

[0007] Furthermore, the vacuum drying temperature in step 1 is 60°C, and the time is 12 hours.

[0008] Further, the delignified poplar wood was prepared according to the following steps: 400 mL of deionized water was added to 27 g of anhydrous sodium acetate, the pH was adjusted to 4.6 with acetic acid, and then the volume was brought up to 500 mL. 100 mL of the solution was taken out, 12.5 g of sodium chlorite was added, and the previously taken-out solution was added to make the total mass of the solution 500 g. The mixture was stirred thoroughly. 27 g of poplar wood was added to the solution, and the mixture was reacted in an oven for 12 h. Finally, the poplar wood was taken out, washed, and dried.

[0009] Furthermore, the reaction is carried out in a 60°C oven.

[0010] Furthermore, in step 2, the mass ratio of the wood-based precursor to boric acid is 0.5:0.3.

[0011] Furthermore, high-temperature carbonization was carried out under an argon atmosphere at a temperature of 5°C for 1 minute. -1 The temperature is increased to 900℃ at a rapid rate and held for 2 hours.

[0012] Furthermore, the vacuum drying temperature in step 2 is 60°C, and the time is 12 hours.

[0013] Furthermore, magnetic boats containing boric acid and wood-based precursors are placed upstream and downstream of a tube furnace, respectively. Argon gas is introduced to fill the tube furnace, and the upstream boron vapor is blown into the downstream wood-based precursor using the argon gas flow to achieve boron doping.

[0014] This invention also provides the application of the catalyst prepared by any of the above methods in the cathode oxygen reduction reaction of a standard three-electrode system, wherein the reference electrode is an Ag / AgCl electrode; the working electrode is a disk electrode loaded with an electrocatalyst; and the counter electrode is a Pt mesh electrode.

[0015] This invention also provides the application of the catalyst prepared by any of the methods described above in the anodic oxygen evolution reaction in a standard three-electrode system; the reference electrode is an Ag / AgCl electrode; the working electrode is a 1 cm electrode loaded with an electrocatalyst. 2 Carbon paper; counter electrode is a Pt mesh electrode.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes lignin-free wood-based materials as the carbon substrate, 2-methylimidazole as the nitrogen source, cobalt nitrate hexahydrate as the Co source, and boric acid as the B source to prepare a B / N co-doped wood-based bifunctional electrocatalyst. A standard three-electrode electrochemical platform for supporting the catalyst was constructed to detect the ORR and OER catalytic performance of the catalyst. The key feature of this invention is the use of abundant, readily available, and inexpensive poplar wood as a raw material instead of expensive precious metals, thus reducing manufacturing costs. Simultaneously, the B / N co-doping strategy effectively improves the ORR / OER catalytic performance of the wood-based carbon material and greatly simplifies the fabrication process, demonstrating broad application prospects in the field of electrocatalysis. Attached Figure Description

[0017] Figure 1 These are SEM, TEM, and corresponding element mapping images of Co@CoO / BNC from Example 1; Figure 2 These are the XRD spectra of Embodiment 1, Embodiment 2, and the comparative example of the present invention; Figure 3 These are the CV curves of Embodiment 1, Embodiment 2, and the comparative example of the present invention under N2 and O2 gases; Figure 4 This is a comparison chart of the LSV polarization curves of Embodiment 1, Embodiment 2, and the comparative example of the present invention at 1600 rpm. Figure 5 These are the ORR Tafel curves for Examples 1 and 2; Figure 6 This is a comparison chart of the LSV polarization curves of the oxygen evolution reaction in Examples 1, 2, and the comparative example. Figure 7 The figures show the RRDE curves, electron transfer number, and H2O2 yield of Co@CoO / BNC at 1600 rpm in Example 1. Figure a shows the LSV curve of the Co@CoO / BNC ring-disk electrode at 1600 rpm, and Figure b shows the electron transfer number and H2O2 yield of the oxygen reduction reaction catalyzed by Co@CoO / BNC. Figure 8 This is the it curve of Co@CoO / BNC in Example 1 after approximately 30,000 seconds; Figure 9 This is a comparison chart of LSV before and after 3000 cycles of Co@CoO / BNC in Example 1; Figure 10These are the test comparison curves related to Co@CoO / BNC and the zinc-air battery assembled with Pt / C+RuO2 in Example 1. Figure a is a schematic diagram of the zinc-air battery; Figure b is a comparison of open-circuit voltage curves; Figure c is a comparison of battery polarization curves and power density curves; Figure d is a comparison of charge-discharge rate curves; Figure e is a specific capacity test curve; Figure f is a photo of the assembled zinc-air battery lighting an LED light at a charge-discharge cycle; Figure g is a photo of the battery at a current density of 2 mA / cm². -2 The constant current cyclic charge and discharge curves at that time. Detailed Implementation

[0018] Example 1: The preparation method of the zinc-air battery catalyst derived from poplar-MOF precursor in this example is carried out according to the following steps: Step 1: Add 25 mL of deionized water and 0.3 g of delignin-free poplar wood to 1 g of Co(NO3)3·6H2O, stir for 12 h, add 1.97 g of 2-methylimidazole, add 25 mL of deionized water, stir thoroughly for 12 h, filter, and vacuum dry at 60 °C for 12 h to obtain the wood-based precursor. Step 2: Place 0.5g of wood-based precursor and 0.3g of boric acid in a tube furnace. Place magnetic boats containing boric acid and wood-based precursor upstream and downstream of the tube furnace, respectively. Introduce argon gas to fill the tube furnace. Use the argon gas flow to blow boron vapor from the upstream to the downstream wood-based precursor to achieve boron doping. After high-temperature carbonization, grinding, filtration, and vacuum drying at 60°C for 12 hours, the catalyst is obtained. Among them, high-temperature carbonization is carried out under an argon atmosphere at 5°C for 5 minutes. -1 The temperature is increased to 900℃ at a rapid rate and held for 2 hours.

[0019] In this embodiment, the delignified poplar wood was prepared according to the following steps: 400 mL of deionized water was added to 27 g of anhydrous sodium acetate, the pH was adjusted to 4.6 with acetic acid, and then the volume was brought up to 500 mL. 100 mL of the solution was taken out, 12.5 g of sodium chlorite was added, and the previously taken-out solution was added to make the total mass of the solution 500 g. The mixture was stirred thoroughly. 27 g of poplar wood was added to the solution, and the mixture was reacted in an oven for 12 h. Finally, the poplar wood was taken out, washed, and dried.

[0020] Example 2: The preparation method of the zinc-air battery catalyst derived from poplar-MOF precursor in this example is carried out according to the following steps. The preparation method and process are the same as in Example 1, except that 0.3g of boric acid is not added and placed in a tube furnace: Step 1: Add 25 mL of deionized water and 0.5 g of delignin-free poplar wood to 1 g of Co(NO3)3·6H2O, stir for 12 h, add 1.97 g of 2-methylimidazole, add 25 mL of deionized water, stir thoroughly for 12 h, filter, and vacuum dry at 60 °C for 12 h to obtain the wood-based precursor. Step 2: Place 0.5g of wood-based precursor in a tube furnace, place the magnetic boat containing the wood-based precursor in the tube furnace, and introduce argon gas to fill the tube furnace. After high-temperature carbonization, grinding, filtration, and vacuum drying at 60°C for 12 hours, the catalyst is obtained. Among them, high-temperature carbonization is carried out under an argon atmosphere at 5°C for 5 minutes. -1 The temperature is increased to 900℃ at a rapid rate and held for 2 hours.

[0021] In this embodiment, the delignified poplar wood was prepared according to the following steps: 400 mL of deionized water was added to 27 g of anhydrous sodium acetate, the pH was adjusted to 4.6 with acetic acid, and then the volume was brought up to 500 mL. 100 mL of the solution was taken out, 12.5 g of sodium chlorite was added, and the previously taken-out solution was added to make the total mass of the solution 500 g. The mixture was stirred thoroughly. 27 g of poplar wood was added to the solution, and the mixture was reacted in an oven for 12 h. Finally, the poplar wood was taken out, washed, and dried.

[0022] Comparative Example Step 1: Place the delignified poplar wood in a tube furnace, place the magnetic boat containing the delignified poplar wood in the tube furnace, and fill the tube furnace with argon gas. After high-temperature carbonization, grinding, filtration, and vacuum drying at 60°C for 12 hours, the catalyst is obtained. Among them, high-temperature carbonization is carried out under an argon atmosphere at 5°C for 5 minutes. -1 The temperature is increased to 900℃ at a rapid rate and held for 2 hours.

[0023] In this embodiment, the delignified poplar wood was prepared according to the following steps: 400 mL of deionized water was added to 27 g of anhydrous sodium acetate, the pH was adjusted to 4.6 with acetic acid, and then the volume was brought up to 500 mL. 100 mL of the solution was taken out, 12.5 g of sodium chlorite was added, and the previously taken-out solution was added to make the total mass of the solution reach 500 g. The mixture was stirred thoroughly. 27 g of poplar wood was added to the solution, and the mixture was reacted in an oven for 12 h. Finally, the poplar wood was taken out, washed, and dried.

[0024] A 5 mg / mL carbon slurry was prepared for the electrochemical detection of the catalyst. The preparation method was as follows: 10 mg of catalyst (Co@CoO / BNC, Co@CoO / NC, WC) was placed in a 5 mL centrifuge tube, 2 mL of isopropanol and 40 μL of naphthol were added, and the mixture was sonicated for 90 min until it was evenly dispersed and dissolved to obtain the slurry for later use.

[0025] 1) Phase analysis The surface crystal structure of the samples from Examples 1, 2, and the comparative example was detected using X-ray diffraction. Figure 2 As shown, according to X-ray diffraction spectroscopy analysis and comparison with the PDF standard card, the main phase of Co@CoO / BNC is Co, and the main phase of Co@CoO / NC is Co. No obvious crystal peaks appeared in WC, indicating that the Co metal element in Examples 1 and 2 was successfully encapsulated in carbon materials.

[0026] 2) SEM, TEM and corresponding element mapping analysis Observe the SEM image of Co@CoO / BNC in Example 1, such as Figure 1 As shown, the preservation of the natural porous structure of wood effectively ensures the electrocatalytic performance of oxygen; TEM images of Co@CoO / BNC in Example 1 are observed as follows... Figure 1 As shown, Co is encapsulated within a carbon shell, protecting it from electrolyte corrosion and effectively ensuring the catalyst's stability. Observing the elemental mapping spectrum of Co@CoO / BNC in Example 1, as shown... Figure 1 As shown, the carbonized wood-derived carbon contains Co, B, N, and O elements, indicating that these four elements were successfully incorporated into the wood-derived carbon. The uniform distribution of Co indicates that there was no severe agglomeration of the metal phase during the preparation process, and it was highly dispersed. This effectively promotes electron transfer, increases the active sites of the carbon shell, and improves the oxygen electrocatalytic performance of the material.

[0027] 3) Analysis of scanning voltammetry and linear voltammetry curves for oxygen reduction reaction The oxygen reduction electrocatalytic performance of Examples 1, 2, and the comparative example was tested using a standard three-electrode system and an electrochemical workstation. Figure 3 This proves that the reaction occurring in the workstation is an oxygen reduction reaction; such as Figure 4 As shown, the maximum diffusion current for oxygen reduction gradually increases with increasing rotational speed. Furthermore, comparing the LSV curves of Examples 1, 2, and the comparative example reveals that Co@CoO / BNC exhibits better ORR kinetic activity compared to other catalysts. This indicates that Co@CoO / BNC demonstrates the best oxygen reduction catalytic performance.

[0028] 4) Analysis of Faraday efficiency of oxygen reduction reaction Tafel slope analysis of the oxygen reduction reaction was performed on Examples 1 and 2. Figure 5 It can be seen that Co@CoO / BNC exhibits a lower Tafel slope, further indicating that Co@CoO / BNC exhibits better ORR kinetic activity compared to other catalysts.

[0029] 5) Analysis of linear voltammetric curves of oxygen evolution The electrocatalytic performance of oxygen evolution in Examples 1, 2, and the comparative example was tested using a standard three-electrode system and an electrochemical workstation. Figure 6 As shown, when the current density reaches 10 mA cm⁻¹ -2 The Co@CoO / BNC catalyst exhibited the lowest overpotential, indicating that the introduction of boron doping significantly improved the OER catalytic performance of the Co@CoO / BNC catalyst compared to other catalysts. 6) Analysis of electron transfer number and H2O2 yield The number of transferred electrons and the H2O2 yield of Co@CoO / BNC in Example 1 were detected using a rotating ring-disk electrode and an electrochemical workstation. Figure 7 As shown, Co@CoO / BNC maintains an extremely low hydrogen peroxide conversion rate throughout the entire potential range, exhibiting high selectivity. Furthermore, calculations indicate that the average number of electrons transferred during the reaction is 3.6, proving that the reaction occurs via a highly efficient four-electron reaction pathway throughout the entire potential range.

[0030] 7) Stability analysis of oxygen reduction reaction and oxygen evolution reaction The stability of the Co@CoO / BNC in Example 1 for oxygen reduction and oxygen evolution reactions was tested using a three-electrode system and an electrochemical workstation. Figure 8 Co@CoO / BNC exhibits excellent oxygen reduction reaction stability, maintaining a high current density even after 30,000 seconds of continuous operation; according to Figure 9 Comparing the linear scan curves of Co@CoO / BNC before and after 3000 cyclic scans, when the current density reaches 10 mA cm⁻¹ -2 At that time, the electrode potential showed only a slight increase of less than 14 mV. This demonstrates that the Co@CoO / BNC catalyst possesses a certain degree of stability in the OER reaction.

[0031] 8) Performance analysis of zinc-air batteries To verify whether the catalytic performance of Co@CoO / BNC in Example 1 could be used in practical applications, it was assembled into a zinc-air battery for testing. At 6 mol L... -1 KOH solution and 0.2 mol L -1 Zinc acetate was used as the electrolyte, and Co@CoO / BNC loaded carbon paper was used as the air cathode (carbon paper area 1 cm²). 2 Catalyst loading 1 mg cm -2 The zinc sheet is polished smooth to serve as the metal anode. Figure 10 (a) is a schematic diagram of an aqueous zinc-air battery. To further verify the performance of the assembled zinc-air battery, this paper tested its polarization curve and open-circuit voltage during operation, and calculated its power density curve.Figure 10 As shown in (b) and (c), the maximum power density of the Co@CoO / BNC zinc-air battery is 115.72 mW / cm². -2 It also possesses a high open-circuit voltage (1.431 V). It passed the rate charge / discharge test (…). Figure 10 (d) It can be seen that as the current density increases exponentially, the voltage remains stable. When the current density decreases to 0, the discharge voltage can recover to its initial state, indicating that the assembled Co@CoO / BNC zinc-air battery has good rate performance. The zinc-air battery loaded with Co@CoO / BNC was discharged at a current density of 2 mA cm⁻¹. -2 Below, its specific capacity was measured to be 958.3 mA hg. -1 (like Figure 10 (e) shows that the battery has a large specific capacity. Connecting the light-emitting diode (LED) in series with the two assembled zinc-air batteries, the LED successfully lights up (as shown in [example]). Figure 10 (f) shows that the assembled battery can provide power to the LED. To further confirm whether the assembled Co@CoO / BNC zinc-air battery has the ability to be used for a long time, its stability was tested. Figure 10 As shown in (g), the battery can operate stably for more than 200 hours after a short activation period, with the charging potential stabilizing at around 2.02 V and the discharging voltage stabilizing at around 1.22 V, demonstrating excellent charging and discharging efficiency and stability.

[0032] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a zinc-air battery catalyst derived from poplar-MOF precursor, characterized in that, Includes the following steps: Step 1: Add deionized water and delignin-free poplar wood to Co(NO3)3·6H2O, stir, add 2-methylimidazole, add deionized water, stir thoroughly, filter, and vacuum dry to obtain wood-based precursor; Step 2: The wood-based precursor and boric acid are subjected to high-temperature carbonization, grinding, filtration and drying to obtain the catalyst.

2. The method according to claim 1, characterized in that, The molar ratio of Co(NO3)3·6H2O to 2-methylimidazole in the MOF aqueous solution was 1:7; the mass ratio of Co(NO3)3·6H2O to lignin-free poplar wood was 1:0.5; and the metal ion concentration was 0.069 mol / L. -1 .

3. The method according to claim 1, characterized in that, Delignified poplar wood was prepared according to the following steps: 400 mL of deionized water was added to 27 g of anhydrous sodium acetate, the pH was adjusted to 4.6 with acetic acid, and then the volume was brought up to 500 mL. 100 mL of the solution was taken out, and 12.5 g of sodium chlorite was added. The total mass of the solution was brought up to 500 g, and the mixture was stirred thoroughly. 27 g of poplar wood was added to the solution, and the mixture was reacted in an oven for 12 h. Finally, the poplar wood was taken out, washed, and dried.

4. The method according to claim 3, characterized in that, React in an oven at 60℃.

5. The method according to claim 1, characterized in that, In step 2, the mass ratio of the wood-based precursor to boric acid is 0.5:0.

3.

6. The method according to claim 1, characterized in that, High-temperature carbonization is carried out under an argon atmosphere at a temperature of 5°C for 1 minute. -1 The temperature is increased to 900℃ at a rapid rate and held for 2 hours.

7. The application of a catalyst prepared by the method according to any one of claims 1 to 6 in the cathode oxygen reduction reaction of a standard three-electrode system.

8. The application according to claim 7, characterized in that, The reference electrode is an Ag / AgCl electrode; the working electrode is a disk electrode loaded with an electrocatalyst; and the counter electrode is a Pt sheet electrode.

9. The application of a catalyst prepared by the method according to any one of claims 1 to 6 in the anodic oxygen evolution reaction in a standard three-electrode system.

10. The application according to claim 7, characterized in that, The reference electrode is an Ag / AgCl electrode; the working electrode is a 1 cm electrode loaded with an electrocatalyst. 2 Carbon paper; counter electrode is a Pt sheet electrode.

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