Double-active-site modified wood charcoal catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts for zinc-air batteries, and discloses a double-active-site modified wood charcoal catalyst as well as a preparation method and application thereof. NPC is used as a carrier, and double active sites CoN and CoP2 are loaded on the carrier. The preparation method comprises the following steps: (1) cleaning and drying wood blocks, soaking the wood blocks in an NH4Cl solution with the mass fraction of 32-36%, taking out the wood blocks, drying the wood blocks, wrapping the wood blocks with NH4Cl, and pyrolyzing the wood blocks in an inert atmosphere at the temperature of 600-900 DEG C for 1-3 hours to obtain NC; (2) dipping the NC into a cobalt acetylacetonate ethanol solution, taking out the NC, placing the NC at room temperature for 12-24 hours, drying the NC, and then pyrolyzing the NC at 550-850 DEG C in an inert atmosphere for 1-3 hours to obtain CoN-coated NC; and (3) the CoN-coated NC and NaH2PO2 are kept for 0.5-1 h at the temperature of 200-550 DEG C in the inert atmosphere according to the mass ratio of 1: (1-2). The catalyst disclosed by the invention shows activity and stability superior to those of a commercial catalyst in ORR and OER; the flexible zinc air battery assembled by using the catalyst can be stably charged and discharged for 240 times, and the charging and discharging voltage difference is basically kept unchanged even at different bending angles.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts for rechargeable zinc-air batteries, and in particular relates to a double-active-site modified wood charcoal catalyst and a preparation method and application thereof. Background Art

[0002] Rechargeable zinc-air batteries (ZABs) are regarded as a promising energy storage technology due to their excellent energy density, safety, economy and environmental friendliness. The performance of oxygen electrocatalysts on the air electrode directly determines the efficiency of ZABs, especially the oxygen reduction reaction (ORR) during discharge and the oxygen evolution reaction (OER) during charge. Since both processes involve the transfer of four electrons, their slow charge transfer kinetics limit the performance of the battery. In order to improve the catalytic efficiency of ZABs and achieve high current density, it is urgent to develop efficient catalysts that can accelerate these two electrochemical processes. Currently, Pt-based materials perform well in ORR, while RuO2 and IrO2 are commonly used catalysts for OER. Although these noble metal-based catalysts are highly active, their single active site, high cost, scarce resources and poor stability limit their widespread application in rechargeable ZABs. Therefore, the development of bifunctional oxygen electrocatalysts that are both economical and efficient is crucial to promote the practical application of rechargeable ZABs.

[0003] In the research of non-precious metal electrocatalysts, metal nitrides and phosphides have attracted much attention due to their excellent catalytic performance in acidic and alkaline environments. In particular, iron and cobalt nitrides are considered to be powerful alternatives to traditional commercial catalysts. However, these metal nitrides are not sufficiently active in OER, which affects the charging efficiency of rechargeable metal-air batteries. In addition, metal-based catalysts still have certain limitations in practical applications, and their poor conductivity and low mass transfer efficiency are more prominent. Summary of the invention

[0004] In order to solve the problems of high cost, poor stability, single active site and insufficient catalytic activity of catalysts used in rechargeable zinc-air batteries in the prior art, the purpose of the present invention is to provide a double active site modified wood charcoal catalyst and its preparation method and application.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A dual-active site modified wood charcoal catalyst with the chemical formula CoN / CoP2@NPC uses nitrogen and phosphorus co-doped wood charcoal nanosheets as a carrier. The carrier is loaded with dual active sites: CoN nanoparticles and CoP2 nanoparticles, and CoN and CoP2 form a heterojunction.

[0006] The preparation method of the dual-active site modified wood charcoal catalyst comprises the following steps: (1) After cleaning and drying the wood block, immerse it in a 32-36% by mass NH4Cl solution. After being fully immersed, take it out and dry it. Then, wrap the wood block with NH4Cl and pyrolyze it at 600-900℃ for 1-3h in an inert atmosphere to obtain nitrogen-doped wood charcoal, named NC. (2) NC was immersed in a cobalt acetylacetonate ethanol solution. After being fully immersed, it was taken out and placed at room temperature for 12-24 hours, dried, and then pyrolyzed at 550-850 °C for 1-3 hours in an inert atmosphere to obtain CoN nanoparticle-modified NC, named CoN@NC. (3) CoN@NC and NaH2PO2 were mixed in a mass ratio of 1:(1-2) under an inert atmosphere at 200-550°C for 0.5-1h to obtain the target product CoN / CoP2@NPC.

[0007] Preferably, the wood blocks are oak blocks.

[0008] Preferably, in step (1), when cleaning the wood block, first use water for ultrasonic cleaning for 10 to 20 minutes, and then use ethanol for ultrasonic cleaning for 10 to 20 minutes.

[0009] Preferably, in step (1), the ethanol is anhydrous ethanol.

[0010] Preferably, in step (2), the cobalt acetylacetonate ethanol solution is prepared by dissolving 0.01-0.05 g of cobalt acetylacetonate in 3-10 mL of ethanol.

[0011] Preferably, in step (2), the ethanol is anhydrous ethanol.

[0012] Preferably, in step (2), the mass-to-volume ratio of NC: cobalt acetylacetonate ethanol solution is (0.1-0.3) g: (3-10) mL.

[0013] Application of the dual-active site modified wood charcoal catalyst in OER and / or ORR.

[0014] Application of the dual-active site modified wood charcoal catalyst in rechargeable zinc-air batteries.

[0015] The reason why the present invention chooses wood charcoal as a carrier is that: the carbon carrier can significantly reduce the diffusion resistance, improve the conductivity and specific surface area of ​​the material, and inhibit the aggregation of metal substances; it is worth noting that the carbon material itself has unique advantages. It can be used as an integral electrode catalyst, effectively avoiding the situation where the catalytic activity may be suppressed due to the presence of traditional adhesives; currently, many carbon-based catalysts are mainly derived from petroleum and coal products, such as carbon nanotubes, graphene oxide, etc., but their synthesis process is often demanding on conditions and consumes a lot of energy. In comparison, agricultural and forestry biomass-derived carbon materials have significant advantages: on the one hand, their reserves are abundant and renewable, which meets the needs of sustainable development; on the other hand, the hierarchical multi-level pore structure and continuous conductive network structure of agricultural and forestry biomass are extremely beneficial for accelerating the migration rate of ions, and at the same time can expose more active sites, which makes the carbon material prepared with forest biomass as the starting material show good performance in promoting the transport of reactants and products and electron transfer.

[0016] The CoN / CoP2@NPC catalyst of the present invention achieves efficient ORR and OER bifunctional catalytic activity in an alkaline environment through the synergistic heterogeneous interface of CoN and CoP2 and the hierarchical pore structure of the N and P co-doped carbon carrier: in the ORR process, all steps proceed spontaneously when U=0, CoN as the main active site dominates the adsorption and activation of oxygen molecules (O2), and generates key intermediates (*OOH→*O→*OH) through proton-electron coupling transfer, among which the desorption process of *O→*OH is the rate-determining step, and CoP2 provides the OH required for the alkaline environment by promoting the dissociation of water molecules (H2O→*OH+H*). - , further optimizing the generation pathway of *OOH intermediates; in the OER process, CoP2 acts as the core active site to drive the dissociation of water molecules to generate *OH, and completes the oxygen atom coupling through the oxidation pathway of *OH→*O→*OOH, where the oxygen coupling step of *O→*OOH (*O+OH - →*OOH+e - ) is the rate-determining step, and CoP2 significantly reduces its reaction energy barrier; through the synergistic effect of CoN and CoP2, the catalyst realizes a low-barrier four-electron transfer mechanism in both ORR and OER (ORR: O2+2H2O+4e - →OH - ; OER: 4OH - →O2+2H2O+4e -), whose bifunctional activity originates from the precise regulation of key intermediates (*OOH, *O, *OH) by each component and the efficient synergy of alkaline reaction pathways. It is worth noting that the N, P co-doped carbon support not only provides a large number of anchoring sites for the attachment of nanoparticles, but also its own hierarchical pore structure can effectively accelerate the transport of reactants and intermediates, thereby promoting ORR and OER reactions.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The catalyst prepared by the present invention, the synergistic effect of the dual active sites of CoN / CoP2 accurately regulates the adsorption energy of key intermediates (*OOH, *O, *OH), and the hierarchical pore structure optimizes the reaction path. Experiments have confirmed that the synergistic effect between the dual active sites and the hierarchical porous carbon co-doped with N and P greatly improves the ORR and OER electrocatalytic activity of CoN / CoP2@NPC. The catalyst exhibits superior activity and stability to commercial catalysts in both ORR and OER. The flexible zinc-air battery assembled using CoN / CoP2@NPC as the air cathode catalyst can stably charge and discharge 240 times, and the charge and discharge voltage difference remains basically unchanged even at different bending angles. (2) The present invention not only provides a low-cost preparation strategy for non-precious metal catalysts, providing new ideas for the practical application of flexible ZABs, but also promotes the application of carbon-based catalysts in the energy field and the high-value utilization of agricultural and forestry biomass. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 : X-ray diffraction patterns (XRD) of the catalysts CoN / CoP2@NPC-1, NC, CoN@NC, CoN@NPC and CoN / CoP2@NPC-2 prepared in Example 1 and Comparative Examples 1 to 4.

[0019] Figure 2 : X-ray photoelectron spectrum (XPS) of Co 2p, N 1s, P 2p and O 1s of the catalyst CoN / CoP2@NPC-1 prepared in Example 1.

[0020] Figure 3 : TEM and HRTEM images of the catalyst CoN / CoP2@NPC-1 prepared in Example 1.

[0021] Figure 4 : ORR linear sweep voltammetry (LSV) curves of the catalysts CoN / CoP2@NPC-1, NC, CoN@NC, CoN@NPC and CoN / CoP2@NPC-2 prepared in Example 1 and Comparative Examples 1 to 4.

[0022] Figure 5: OER linear sweep voltammetry (LSV) curves of the catalysts CoN / CoP2@NPC-1, NC, CoN@NC, CoN@NPC and CoN / CoP2@NPC-2 prepared in Example 1 and Comparative Examples 1 to 4.

[0023] Figure 6 :CoN / CoP2@NPC-1 based zinc-air battery at 2 mA cm -2 The charge and discharge cycle test curve under.

[0024] Figure 7 :CoN / CoP2@NPC-1 based zinc-air batteries at different angles and 2 mA cm -2 The charge and discharge cycle test curve under. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the described embodiments, all other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present invention.

[0026] Example 1

[0027] A method for preparing a double-active site modified wood charcoal catalyst, the steps are as follows: (1) An oak block of 1.5 cm*1.5 cm*0.5 cm (length*width*height) was first ultrasonically cleaned with deionized water for 10 min, then ultrasonically cleaned with anhydrous ethanol for 10 min, taken out and dried at 60 °C for 12 h, and then immersed in a 34% NH4Cl solution (15.45 g NH4Cl, 30 mL deionized water), stirred for 72 h to fully immerse it, taken out and dried at 60 °C for 24 h, and then wrapped with NH4Cl and heated at 5 °C min under nitrogen protection. -1 The temperature was raised to 900 °C and pyrolyzed for 2 h to obtain nitrogen-doped wood charcoal, named NC. (2) Immerse 0.15 g of NC in a cobalt acetylacetonate ethanol solution (0.03 g of cobalt acetylacetonate, 5 mL of anhydrous ethanol) for 6 h to fully immerse it. Take it out, place it at room temperature for 24 h, vacuum dry it for 12 h, and then incubate it at 5 °C min under nitrogen protection. -1 The temperature was raised to 650 °C and pyrolyzed for 2 h to obtain NC modified with CoN nanoparticles, named CoN@NC. (3) CoN@NC and NaH2PO2 were heated in a tube furnace at a mass ratio of 1:1 under nitrogen atmosphere at 3 °C min -1The temperature was raised to 350 °C at a rate of 0.5 h and maintained for 0.5 h to obtain the target product CoN / CoP2@NPC-1.

[0028] Comparative Example 1 Preparation method of catalyst NC: same as step (1) of Example 1.

[0029] Comparative Example 2 Preparation method of catalyst CoN@NC: (1) Same as step (1) in Example 1; (2) Same as step (2) of Example 1.

[0030] Comparative Example 3 Preparation method of catalyst CoN@NPC: (1) Same as step (1) in Example 1; (2) Same as step (2) in Example 1; (3) CoN@NC and NaH2PO2 were heated in a tube furnace at a mass ratio of 1:0.5 under nitrogen atmosphere at 3 °C min -1 The temperature was raised to 350 °C at a rate of 100 °C and maintained for 0.5 h to obtain the target product CoN@NPC.

[0031] Comparative Example 4 Preparation method of catalyst CoN / CoP2@NPC-2: (1) Same as step (1) in Example 1; (2) Same as step (2) in Example 1; (3) CoN@NC and NaH2PO2 were heated in a tube furnace at a mass ratio of 1:3 under nitrogen atmosphere at 3 °C min -1 The temperature was raised to 350 °C at a rate of 0.5 h and maintained for 0.5 h to obtain the target product CoN / CoP2@NPC-2.

[0032] Product structure characterization Figure 1 X-ray diffraction patterns (XRD) of the catalysts CoN / CoP2@NPC-1, NC, CoN@NC, CoN@NPC and CoN / CoP2@NPC-2 prepared in Example 1 and Comparative Examples 1 to 4, wherein: The crystal planes are attributed to CoN, ◆(022), ◆(032), and ◆(-213) are attributed to CoP2, and C(002) and C(101) are attributed to carbon. Figure 1It can be seen that the catalyst CoN / CoP2@NPC-1 prepared in Example 1 corresponds to the standard spectra cards CoP2 (JCPDS No. 26-0481) and CoN (JCPDS No. 16-0116). This indicates the successful synthesis of the catalyst CoN / CoP2@NPC-1.

[0033] Figure 2 X-ray photoelectron spectrum (XPS) of Co 2p, N 1s, P 2p and O 1s of the catalyst CoN / CoP2@NPC-1 prepared in Example 1. The XPS spectrum shows that the CoN / CoP2@NPC-1 catalyst was successfully prepared.

[0034] Figure 3 TEM and HRTEM characterization of the catalyst CoN / CoP2@NPC-1 prepared in Example 1. Figure 3 It can be clearly seen in the figure: the porous hierarchical structure of wood charcoal and the heterogeneous structure of CoP2 and CoN, which is consistent with the XRD results.

[0035] Catalyst performance test The performance tests of oxygen reduction reaction ORR and oxygen evolution reaction OER were both tested using a three-electrode system: the catalyst was loaded onto a glassy carbon electrode, which was the working electrode, saturated silver chloride was the reference electrode, and a platinum wire electrode was the counter electrode. Preparation of the working electrode: 4 mg of catalyst, 50 uL of Nafion solution (5 wt%) and 500 uL of anhydrous ethanol were mixed evenly to obtain a catalyst slurry; 5 uL of the catalyst slurry was added dropwise to the glassy carbon electrode (5 mm in diameter) in the rotating ring disk electrode RRDE, dried, and a working electrode was obtained. Among them, the catalysts are the catalysts CoN / CoP2@NPC-1, NC, CoN@NC, CoN@NPC, and CoN / CoP2@NPC-2 prepared in Example 1 and Comparative Examples 1 to 4, respectively. At the same time, commercial Pt / C (Pt content of 20 wt%) was used as a control for the ORR performance test, and commercial RuO2 was used as a control for the OER performance test.

[0036] 1. ORR performance test Linear sweep voltammetry (LSV) measurements were performed at 1600 rpm in an O2-saturated 0.1KOH solution.

[0037] The results are as follows Figure 4 As shown, from Figure 4 It can be seen that the onset potential of CoN / CoP2@NPC-1 catalyzed ORR was 0.95 V, and the half-wave potential ( E 1 / 2 ) is 0.86V, E 1 / 2It is better than other catalysts NC (0.76 V), CoN@NC (0.81 V), CoN@NPC (0.80 V), CoN / CoP2@NPC-2 (0.81 V) and commercial Pt / C (0.84 V). It shows that the performance of the catalyst CoN / CoP2@NPC-1 is higher than that of the comparative catalyst, indicating that the initially obtained CoN is conducive to the occurrence of ORR, and a certain proportion of phosphating can improve the catalytic rate.

[0038] 2. OER performance test Linear sweep voltammetry (LSV) measurements were performed at 1600 rpm in a 0.1KOH solution saturated with N2.

[0039] The results are as follows Figure 5 As shown, from Figure 5 It can be seen that the CoN / CoP2@NPC-1 catalyst exhibits excellent OER performance at a current density of 10 mA cm -2 When the overpotential is 260 mV, it is close to 250 mV of RuO2, which is better than NC (531 mV), CoN@NC (381 mV), CoN@NPC (298 mV) and CoN / CoP2@NPC-2 (284 mV). This shows that the catalyst CoN / CoP2@NPC-1 has fast OER kinetics.

[0040] Performance test of flexible zinc-air battery The zinc sheet was used as the anode, the carbon paper loaded with the catalyst was attached to the air electrode group as the cathode, and the electrolyte was PVA-6M KOH hydrogel. The preparation of the carbon paper loaded with the catalyst: 4 mg of the catalyst CoN / CoP2@NPC-1, 50 uL of Nafion solution (5 wt%) and 500 uL of anhydrous ethanol were mixed evenly to obtain a catalyst slurry; the catalyst slurry was applied on the carbon paper and dried to obtain the carbon paper loaded with the catalyst. The catalyst loading was 1 mg / cm 2 .

[0041] (one), Figure 6 The CoN / CoP2@NPC-1 based Zn-air battery has a high performance at 2 mA cm -2 The charge and discharge cycle test curve under Figure 6 It can be seen that the CoN / CoP2@NPC–1-based zinc-air battery has a high -2 The charge and discharge cycles were repeated for 240 times (80 h) under low temperature, and the stability was better than that of zinc-air batteries composed of most Co-based catalysts.

[0042] (II) Test the charge-discharge cycle stability of CoN / CoP2@NPC-1 based zinc-air battery in two cycles: unbending, bending at 90°, and bending at 180°. Figure 7 CoN / CoP2@NPC-1 based zinc-air batteries at different angles and 2 mA cm -2 The charge and discharge cycle test curve under Figure 7 It can be seen that at different bending degrees, the charge and discharge voltage difference remains basically unchanged, indicating that the CoN / CoP2@NPC-1-based zinc-air battery has stable charge and discharge cycle performance.

Claims

1. A double active site modified wood charcoal catalyst, characterized in that: The chemical formula is CoN / CoP2@NPC. The catalyst uses nitrogen and phosphorus co-doped wood carbon nanosheets NPC as a carrier. The carrier is loaded with dual active sites: CoN nanoparticles and CoP2 nanoparticles, and CoN and CoP2 form a heterojunction.

2. A method for preparing a double-active-site modified wood charcoal catalyst as claimed in claim 1, characterized in that: Here are the steps: (1) After cleaning and drying the wood block, immerse it in a 32-36% by mass NH4Cl solution. After being fully immersed, take it out and dry it. Then, wrap the wood block with NH4Cl and pyrolyze it at 600-900℃ for 1-3h in an inert atmosphere to obtain nitrogen-doped wood charcoal, named NC. (2) NC was immersed in a cobalt acetylacetonate ethanol solution. After being fully immersed, it was taken out and placed at room temperature for 12-24 hours, dried, and then pyrolyzed at 550-850 °C for 1-3 hours in an inert atmosphere to obtain CoN nanoparticle-modified NC, named CoN@NC. (3) CoN@NC and NaH2PO2 were mixed in a mass ratio of 1:(1-2) under an inert atmosphere at 200-550°C for 0.5-1h to obtain the target product CoN / CoP2@NPC.

3. The method for preparing the dual-active site modified wood charcoal catalyst according to claim 2, characterized in that: In step (1), the wooden block is an oak block.

4. The method for preparing the double active site modified wood charcoal catalyst according to claim 2, characterized in that: In step (1), when cleaning the wood block, first use water ultrasonic cleaning for 10 to 20 minutes, and then use ethanol ultrasonic cleaning for 10 to 20 minutes.

5. The method for preparing the double active site modified wood charcoal catalyst according to claim 4, characterized in that: In step (1), the ethanol is anhydrous ethanol.

6. The method for preparing the double active site modified wood charcoal catalyst according to claim 2, characterized in that: In step (2), the cobalt acetylacetonate ethanol solution is prepared by dissolving 0.01-0.05 g of cobalt acetylacetonate in 3-10 mL of ethanol.

7. The method for preparing a double-active-site modified wood charcoal catalyst according to claim 6, characterized in that: In step (2), the ethanol is anhydrous ethanol.

8. The method for preparing the double active site modified wood charcoal catalyst according to claim 2, 6 or 7, characterized in that: In step (2), the mass-to-volume ratio is NC: cobalt acetylacetonate ethanol solution = (0.1-0.3) g: (3-10) mL.

9. Use of the double active site modified wood charcoal catalyst according to claim 1 in OER and / or ORR.

10. Use of the double active site modified wood charcoal catalyst as claimed in claim 1 in a rechargeable zinc-air battery.

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