Iron single-atom / cluster electrocatalysts supported on chitosan micro / nanofiber carbon aerogels: preparation and application

Abstract

Iron single-atom / cluster electrocatalysts supported on chitosan micro / nanofiber carbon aerogels, their preparation and application, include the following steps: Step 1: Dissolve chitosan in an aqueous acetic acid solution and stir magnetically in a water bath until completely dissolved to obtain a chitosan solution; Step 2: Add Fe... 3+ and Cd 2+ A metal-chitosan viscous solution was prepared by a one-pot method using a metal salt solution and the chitosan solution. Step 3: The Cs-Fe / Cd viscous solution was directionally frozen using an ice-templating method, followed by freeze-drying to obtain a 3D honeycomb-structured chitosan-Fe / Cd ion-crosslinked composite aerogel. Step 4: The CMNA-Fe / Cd aerogel was placed in a quartz boat, positioned in the center of a tube furnace, and carbonized at high temperature in an inert gas environment to synthesize an iron single-atom / cluster electrocatalyst supported on chitosan micro / nanofiber carbon aerogel. This invention aims to optimize the electronic structure and microstructure of the catalyst, accelerate the oxygen reduction reaction kinetics, and achieve rapid mass transfer and maximum exposure of active sites.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalyst materials technology, specifically relating to an iron single-atom / cluster electrocatalyst supported on chitosan micro / nanofiber carbon aerogel, its preparation and application. Background Technology

[0002] Among numerous new energy technologies, zinc-air batteries have shown promising development prospects due to their high energy density, low cost, and environmental friendliness. However, the oxygen reduction reaction (ORR) in zinc-air batteries involves a multi-electron transfer process, resulting in relatively slow reaction kinetics. Therefore, developing efficient and stable catalysts is crucial for improving the performance of zinc-air batteries. Single-atom catalysts (SACs), especially those with transition metals forming four-coordinate structures with nitrogen atoms (M-N4, M=Fe, Co, Mn, etc.), have gained widespread acceptance as novel ORR catalysts for various electrochemical energy conversion and storage devices. However, the M-N4 structure typically has highly planar D... 4h The symmetrical configuration results in unsatisfactory adsorption strength between the M-N4 structure and oxygen intermediates, thus limiting the ORR catalytic activity.

[0003] Studies have shown that co-anchoring metal single atoms (SAs) and atomic clusters (ACs) on a suitable carbon substrate can break the local charge symmetry of M-N4, thereby optimizing the adsorption strength of oxygen intermediates and reducing the energy barrier in the reaction pathway, thus synergistically optimizing ORR catalytic kinetics. It is noteworthy that although M... SA+AC -NC exhibits excellent initial activity, but its stability and durability remain insufficient for practical applications. The high surface energy of SAs and ACs may lead to their tendency to aggregate or migrate on carbon supports, and the weak interaction between the carbon support and metal sites reduces M SA+AC The catalytic performance and stability of the substrate are affected. Furthermore, conductive carbon substrates typically have a densely stacked structure, which greatly hinders the transport of reactants and can even block active sites. Summary of the Invention

[0004] To overcome the problems existing in the prior art, the present invention aims to provide an iron single-atom / cluster electrocatalyst supported on chitosan micro / nanofiber carbon aerogel, and its preparation and application. This method utilizes chitosan rich in hydroxyl and amino groups to crosslink with Fe / Cd ions and undergo fibrillation to form chitosan micro / nanofibers. A 3D honeycomb structure of chitosan crosslinked with Fe / Cd ions (CMNA-Fe / Cd) was constructed using directional freezing technology. Subsequently, a carbonization strategy was employed to prepare a chitosan micro / nanofiber carbon aerogel (CMNCA-Fe) synergistically supported on Fe-N4 single atoms and clusters. SA+ACThis method aims to optimize the electronic structure and microstructure of the catalyst, accelerate the oxygen reduction reaction (ORR) kinetics, and achieve rapid mass transfer and maximum exposure of active sites.

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

[0006] A method for preparing iron single-atom / cluster electrocatalysts supported on chitosan micro / nanofiber carbon aerogel includes the following steps:

[0007] Step 1: Dissolve chitosan in an aqueous acetic acid solution and stir magnetically in a water bath until completely dissolved to obtain a chitosan solution;

[0008] Step 2: [The text abruptly ends here, likely due to an incomplete sentence or a formatting error.] 3+ and Cd 2+ A metal-chitosan viscous solution (Cs-Fe / Cd) was prepared by a one-pot method using a metal salt solution and the chitosan solution.

[0009] Step 3: The Cs-Fe / Cd viscous solution was directionally frozen using the ice template method, and then freeze-dried to obtain a 3D honeycomb structured chitosan and Fe / Cd ion crosslinked composite aerogel (CMNA-Fe / Cd).

[0010] Step 4: Place the CMNA-Fe / Cd aerogel into a quartz boat, center it in a tube furnace, and carbonize it at high temperature in an inert gas environment to synthesize a chitosan micro / nanofiber carbon aerogel-supported iron single-atom / cluster electrocatalyst (CMNCA-Fe). SA+AC ).

[0011] In step 1, the degree of deacetylation of chitosan is ≥95%.

[0012] In step 1, 20–80 mg of chitosan is dissolved in 1–10 ml of a 1–10% (v / v) aqueous acetic acid solution, and the solution is magnetically stirred for 1–3 hours in a water bath at 40–80°C to obtain a chitosan solution. The purpose is to completely dissolve the chitosan.

[0013] In step 2, Fe is contained 3+ and Cd 2+ The metal salt solutions were ferric chloride hexahydrate and cadmium chloride hemihydrate (pentahydrate) solutions, respectively.

[0014] In step 2, the preparation process of the CS-Fe / Cd viscous solution is as follows:

[0015] a) Ferric chloride hexahydrate and cadmium chloride hemihydrate (pentahydrate) are dissolved in water at a molar ratio of 1:20 to 1:1000 to obtain a Fe / Cd metal mixed solution. Here, a large amount of cadmium salt plays a crucial role in the spatial separation of iron active sites, and at the same time acts as a pore-forming agent during pyrolysis, thereby generating a large number of micropores and defect sites in the carbon aerogel.

[0016] b) Pour the Fe / Cd metal mixed salt solution into the chitosan solution and mix and stir for 1-5 hours to obtain a Cs-Fe / Cd viscous solution; wherein the mass ratio of chitosan to Fe / Cd metal mixed solution is 1:20-20:1. This ratio is intended to ensure complete cross-linking and coordination between the metal ions and chitosan.

[0017] In step 3, the specific operation of directional freezing of the Cs-Fe / Cd viscous solution using the ice template method is as follows:

[0018] A beaker containing a Cs-Fe / Cd viscous solution was placed on a copper block cooling platform immersed in liquid nitrogen to achieve directional freezing. In the Cs-Fe / Cd viscous solution, water molecules crystallized and grew orderly along the temperature gradient. Chitosan micro / nanofibers loaded with metal ions were compressed between the ice crystals, forming a stable 3D honeycomb structure with hierarchical pores. This structure provides a large specific surface area and abundant exposed active sites for catalytic reactions.

[0019] In step 3, the freeze-drying temperature of the composite aerogel CMNA-Fe / Cd is -20 to -53°C, and the time is 24 to 72 hours.

[0020] In step 4, the inert gas used is argon.

[0021] In step 4, the carbonization temperature is 700–1000℃, the holding time is 1–4h, and the heating rate of the tube furnace is 1–10℃ / min.

[0022] The iron single-atom / atom cluster electrocatalyst supported on the chitosan micro / nanofiber carbon aerogel has a local layered network structure with a high aspect ratio and multi-scale micro / nanofiber interwoven.

[0023] On a macroscopic level, due to the directional cryogenic casting process, this material exhibits a three-dimensional honeycomb structure and ordered, abundant porous channels; CMNCA-Fe after high-temperature carbonization SA+AC The macroscopic 3D honeycomb structure and layered network structure remain intact, and are loaded with a large number of Fe-N4 single atoms and clusters. The catalyst exhibits excellent electrochemical performance in 0.1M KOH, with an onset potential of 0.99V and a half-wave potential of 0.91V.

[0024] The iron single-atom / cluster electrocatalyst supported on the chitosan micro / nanofiber carbon aerogel is used in zinc-air batteries.

[0025] Both the assembled aqueous zinc-air batteries and solid-state zinc-air batteries exhibit high power density and excellent charge-discharge cycle stability, based on CMNCA-Fe SA+AC The maximum power density of aqueous zinc-air batteries can reach 192.1 mW / cm³. -2 At 10mA / cm 2 It can operate reliably for 306 hours at the specified current density.

[0026] The beneficial effects of this invention are:

[0027] (1) This invention uses chitosan, an environmentally friendly and green source, as a nitrogen-containing carbon source. It utilizes the abundant hydroxyl and amino groups in chitosan to crosslink with Fe / Cd ions without the need for additional nitrogen sources. Chitosan micro / nanofibers are evenly distributed and interwoven to form a layered network structure, which promotes the uniform dispersion of Fe-N4 single atoms and clusters while further anchoring them strongly to the carbon substrate.

[0028] (2) The present invention utilizes Cd salt to separate iron active sites in space and act as a pore-forming agent during pyrolysis, thereby generating a large number of micropores and defect sites in carbon aerogel.

[0029] (3) The process of this invention is simple, requires no post-processing or additional nitrogen source, and meets the requirements of large-scale production.

[0030] (4) The carbon aerogel prepared by this invention has excellent ORR catalytic activity and stability as a zinc-air battery catalyst, providing a new strategy for the development and application of clean energy technology and biomass resources. Attached Figure Description

[0031] Figure 1 This is a scanning electron microscope (SEM) image of CMNA-Fe / Cd-2 obtained in Example 2 of the present invention.

[0032] Figure 2 This is a transmission electron microscope (TEM) image of CMNA-Fe / Cd-2 obtained in Example 2 of the present invention.

[0033] Figure 3 It is the CMNCA-Fe obtained in Example 2 of this invention. SA+AC Scanning electron microscope (SEM) image at -2.

[0034] Figure 4 It is the CMNCA-Fe obtained in Example 2 of this invention. SA+AC Transmission electron microscopy (TEM) image of -2.

[0035] Figure 5It is the CMNCA-Fe obtained in Example 2 of this invention. SA+AC High-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image with double spherical aberration correction at -2.

[0036] Figure 6 It is the CMNCA-Fe obtained in Example 2 of this invention. SA+AC -2, CMNCA-Fe obtained in Comparative Example 1 SA The CMNCA-Fe obtained in Comparative Example 2 NP The X-ray diffraction (XRD) patterns of CMNCA obtained in Comparative Example 3.

[0037] Figure 7 It is the CMNCA-Fe obtained in Example 2 of this invention. SA+AC -2, CMNCA-Fe obtained in Comparative Example 1 SA The CMNCA-Fe obtained in Comparative Example 2 NP Linear sweep scalar (LSV) plots of CMNCA obtained in Comparative Example 3 and commercial Pt / C catalyst.

[0038] Figure 8 It is the CMNCA-Fe obtained in Example 2 of this invention. SA+AC Chronoamperometry (it) measurement curves for -2 and commercial Pt / C.

[0039] Figure 9 It is the CMNCA-Fe obtained in Example 2 of this invention. SA+AC -2 is used as the cathode material to assemble solid zinc-air batteries in series for charging smartphones.

[0040] Figure 10 It is the CMNCA-Fe obtained in Example 2 of this invention. SA+AC Discharge polarization curves and power density curves of aqueous zinc-air cells assembled with -2 and commercial Pt / C as cathode materials.

[0041] Figure 11 It is the CMNCA-Fe obtained in Example 2 of this invention. SA+AC Charge-discharge cycle test diagram of aqueous zinc-air batteries assembled with -2 and commercial Pt / C as cathode materials. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings.

[0043] Example 1

[0044] Step 1: Dissolve 40 mg of chitosan (CS) in 2 ml of 2% (v / v) acetic acid aqueous solution, and stir magnetically in a water bath until completely dissolved to obtain a chitosan solution.

[0045] Step 2: Dissolve 0.015 mmol ferric chloride hexahydrate and 2.18 mmol cadmium chloride hemihydrate (pentahydrate) in 10 ml of water to prepare a Fe / Cd metal mixed solution. Pour the Fe / Cd mixed solution into a chitosan solution and stir magnetically for 2 h to obtain a viscous CS-Fe / Cd-1 solution.

[0046] Step 3: The beaker containing the Cs-Fe / Cd viscous solution was placed on a copper cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, it was freeze-dried at -30°C for 72 hours to prepare a 3D honeycomb structured chitosan-Fe / Cd ion crosslinked composite aerogel (CMNA-Fe / Cd-1).

[0047] Step 4: Place the CMNA-Fe / Cd aerogel into a quartz boat, center it in a tube furnace, and heat it to 700℃ at 2℃ / min in an Ar gas environment and hold it for 1 hour to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe) with synergistic support of Fe-N4 single atoms and clusters. SA+AC -1).

[0048] Example 2

[0049] Step 1: Dissolve 60 mg of chitosan (CS) in 3 ml of 4% (v / v) acetic acid aqueous solution, and stir magnetically in a water bath until completely dissolved to obtain a chitosan solution.

[0050] Step 2: Dissolve 0.015 mmol ferric chloride hexahydrate and 4.38 mmol cadmium chloride hemihydrate (pentahydrate) in 10 ml of water to prepare a Fe / Cd metal mixed solution. Pour the Fe / Cd mixed solution into a chitosan solution and stir magnetically for 3 h to obtain a viscous CS-Fe / Cd-2 solution.

[0051] Step 3: The beaker containing the Cs-Fe / Cd-2 viscous solution was placed on a copper cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, it was freeze-dried at -53°C for 48 hours to prepare a 3D honeycomb structured chitosan-Fe / Cd ion crosslinked composite aerogel (CMNA-Fe / Cd-2).

[0052] Step 4: Place the CMNA-Fe / Cd-2 aerogel into a quartz boat, center it in a tube furnace, and heat it to 800℃ at 5℃ / min in an Ar gas environment and hold it for 2 hours to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe) with synergistic support of Fe-N4 single atoms and clusters. SA+AC -2).

[0053] Example 3

[0054] Step 1: Dissolve 80 mg of chitosan (CS) in 5 ml of 6% (v / v) acetic acid aqueous solution, and stir magnetically in a water bath until completely dissolved to obtain a chitosan solution.

[0055] Step 2: Dissolve 0.015 mmol ferric chloride hexahydrate and 6.58 mmol cadmium chloride hemihydrate (pentahydrate) in 10 ml of water to prepare a Fe / Cd metal mixed solution. Pour the Fe / Cd mixed solution into a chitosan solution and stir magnetically for 3 h to obtain a viscous CS-Fe / Cd-3 solution.

[0056] Step 3: The beaker containing the Cs-Fe / Cd-3 viscous solution was placed on a copper cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, it was freeze-dried at -53°C for 36 hours to prepare a 3D honeycomb structured chitosan-Fe / Cd ion crosslinked composite aerogel (CMNA-Fe / Cd-3).

[0057] Step 4: Place the CMNA-Fe / Cd-3 aerogel into a quartz boat, center it in a tube furnace, and heat it to 1000℃ at 10℃ / min in an Ar gas environment and hold it for 3 hours to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe) with synergistic support of Fe-N4 single atoms and clusters. SA+AC -3).

[0058] Comparative Example 1

[0059] Step 1: Dissolve 60 mg of chitosan (CS) in 3 ml of 4% (v / v) acetic acid aqueous solution, and stir magnetically in a water bath until completely dissolved to obtain a chitosan solution.

[0060] Step 2: Dissolve 0.015 mmol ferric chloride hexahydrate and 4.38 mmol cadmium chloride hemihydrate (pentahydrate) in 10 ml of water to prepare a Fe / Cd metal mixed solution. Pour the Fe / Cd mixed solution into a chitosan solution and stir magnetically for 3 h to obtain a viscous CS-Fe / Cd-2 solution.

[0061] Step 3: The beaker containing the Cs-Fe / Cd-2 viscous solution was placed on a copper cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, it was freeze-dried at -53°C for 48 hours to prepare a 3D honeycomb structured chitosan-Fe / Cd ion crosslinked composite aerogel (CMNA-Fe / Cd-2).

[0062] Step 4: Place the CMNA-Fe / Cd-2 aerogel into a quartz boat, center it in a tube furnace, and heat it to 800℃ at 5℃ / min in an Ar gas environment and hold it for 2 hours to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe) with synergistic support of Fe-N4 single atoms and clusters. SA+AC -2).

[0063] Step 5: Add the CMNCA-Fe SA+AC -2 was acid-etched in 0.5 M H₂SO₄ solution at 50 °C for 24 hours. Subsequently, it was washed repeatedly with deionized water until the filtrate reached neutrality. The product was collected and freeze-dried to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe) with Fe-N₄ single-atom supported structure. SA ).

[0064] Comparative Example 2

[0065] Step 1: Dissolve 60 mg of chitosan (CS) in 3 ml of 4% (v / v) acetic acid aqueous solution, and stir magnetically in a water bath until completely dissolved to obtain a chitosan solution.

[0066] Step 2: Dissolve 0.015 mmol of ferric chloride hexahydrate in 10 ml of water to prepare an Fe metal solution. Pour the Fe metal solution into the chitosan solution and stir magnetically for 3 h to obtain a CS-Fe viscous solution.

[0067] Step 3: The beaker containing the Cs-Fe viscous solution was placed on a copper cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, it was freeze-dried at -53°C for 48 hours to prepare a 3D honeycomb structured chitosan-Fe ion crosslinked composite aerogel (CMNA-Fe).

[0068] Step 4: Place the CMNA-Fe aerogel into a quartz boat, center it in a tube furnace, and heat it to 800℃ at 5℃ / min in an Ar gas environment and hold it for 2 hours to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe) supported on Fe nanoparticles. NP ).

[0069] Comparative Example 3

[0070] Step 1: Dissolve 60 mg of chitosan (CS) in 3 ml of 4% (v / v) acetic acid aqueous solution, and stir magnetically in a water bath until completely dissolved to obtain a chitosan solution.

[0071] Step 2: Dissolve 4.38 mmol of cadmium chloride hemihydrate (pentahydrate) in 10 ml of water to prepare a Cd metal solution. Pour the Cd metal solution into a chitosan solution and stir magnetically for 3 h to obtain a CS-Cd viscous solution.

[0072] Step 3: The beaker containing the Cs-Cd viscous solution was placed on a copper cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, it was freeze-dried at -53°C for 48 hours to prepare a 3D honeycomb structured chitosan-Cd ion crosslinked composite aerogel (CMNA-Cd).

[0073] Step 4: Place the CMNA-Cd aerogel into a quartz boat, place it in the center of a tube furnace, and heat it to 800°C at 5°C / min in an Ar gas environment and keep it at that temperature for 2 hours to obtain the chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA).

[0074] Experimental Example 1

[0075] The CMNA-Fe / Cd-2 prepared in Example 2 was subjected to scanning electron microscopy (SEM) and transmission electron microscopy (TEM) tests, respectively. The obtained images are shown below. Figure 1 and 2 As shown.

[0076] like Figure 1 and Figure 2 As shown, CMNA-Fe / Cd-2 aerogel has a rich 3D honeycomb structure of interwoven micro / nanofibers, with a smooth surface and uniform size. The diameter of the microfibers is about 0.8 to 1.4 μm, and the diameter of the nanofibers is about 20 to 25 nm.

[0077] Take the CMNCA-Fe prepared in Example 2 SA+AC -2. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) with double spherical aberration correction were performed respectively. The obtained images are shown below. Figure 3 , Figure 4 and Figure 5 As shown.

[0078] like Figure 3 and Figure 4 As shown, CMNCA-Fe SA+AC -2 maintains the 3D honeycomb structure of interwoven micro / nanofibers, and the surface becomes rough after carbonization. Figure 5 This indicates that Fe exists in two forms: single atoms (shown by solid black circles) and clusters of atoms (shown by dashed black circles).

[0079] Take the CMNCA-Fe obtained in Example 2 SA+AC-2, CMNCA-Fe obtained in Comparative Example 1 SA The CMNCA-Fe obtained in Comparative Example 2 NP The CMNCA obtained in Comparative Example 3 was subjected to X-ray diffraction (XRD) tests. Figure 6 As shown, CMNCA-Fe SA+AC -2, CMNCA-Fe SA CMNCA and Fe exhibit two significant diffraction peaks at 24° and 42°, corresponding to the (002) and (100) crystal planes of graphitic carbon, respectively. In contrast, CMNCA-Fe... NP The peaks exhibited correspond to those associated with iron crystallization. This confirms that cadmium salts effectively separate iron active sites spatially, preventing the aggregation and crystallization of iron metal. Simultaneously, cadmium salts act as pore-forming agents during pyrolysis, thereby generating numerous micropores and defect sites in the carbon aerogel, ultimately leading to the formation of Fe single atoms and atomic clusters.

[0080] Take the CMNCA-Fe obtained in Example 2 SA+AC -2, CMNCA-Fe obtained in Comparative Example 1 SA The CMNCA-Fe obtained in Comparative Example 2 NP Linear sweep spectroscopy (LSV) tests were performed on the CMNCA catalyst obtained in Comparative Example 3 and the commercial Pt / C catalyst, respectively. Figure 7 As shown, CMNCA-Fe SA+AC -2 exhibits the highest half-wave potential, confirming its excellent oxygen reduction catalytic activity.

[0081] Take the CMNCA-Fe obtained in Example 2 SA+AC -2 and commercial Pt / C catalysts were measured using chronoamperometry (it). The results are as follows: Figure 8 As shown, the current decay rate was only 3.4% during the 10-hour operation period, which is significantly lower than the test results for Pt / C.

[0082] Take the CMNCA-Fe obtained in Example 2 SA+AC -2 was used as the cathode material to assemble a solid-state zinc-air battery for actual charging tests. A polished zinc plate with a thickness of 0.08 mm served as the anode; the cathode consisted of nickel foam, a conductive and waterproof layer, and a loading of 2 mg / cm³. -2 CMNCA-Fe SA+AC Catalyst layer (1cm) -2The solid electrolyte is a PVA-KOH-Zn(CH3COO)2 hydrogel, prepared as follows: 2g of polyvinyl alcohol (PVA) was dissolved in 15mL of deionized water under stirring at 90℃ to obtain solution A. Then, 2mL of a 6.0M KOH solution containing 0.2M Zn(CH3COO)2 was added dropwise to solution A, while continuously stirring for 2 hours to form a homogeneous solution. Finally, the resulting mixture was transferred to a silicone mold and cooled in a refrigerator to obtain the PVA-KOH-Zn(CH3COO)2 hydrogel polymer. Figure 9 As shown, it consists of four cascaded CMNCA-Fe SA+AC The solid-state zinc-air battery with a cathode can charge smartphones, demonstrating its considerable potential in the field of flexible wearable technology.

[0083] Take the CMNCA-Fe obtained in Example 2 SA+AC -2 and commercial Pt / C catalysts were used as cathode materials to assemble an aqueous zinc-air battery for discharge polarization and power density curve testing. A 0.5 mm thick polished zinc plate was used as the anode; the cathode consisted of nickel foam, a conductive and waterproof layer, and a loading of 2 mg cm⁻². -2 CMNCA-Fe SA+AC Catalyst layer (1cm) -2 The electrolyte is a solution of 6M KOH + 0.2M Zn(Ac)₂. Figure 10 As shown, based on CMNCA-Fe SA+AC The zinc-air cell with a cathode achieves a maximum power density of 192.1 mW / cm². -2 It surpasses the zinc-air cell based on Pt / C+RuO2 (151.9 mW cm⁻¹). -2 ).

[0084] Take the CMNCA-Fe obtained in Example 2 SA+AC -2 and commercial Pt / C catalysts were used as cathode materials to assemble an aqueous zinc-air battery for charge-discharge cycle testing. For example... Figure 11 As shown, based on CMNCA-Fe SA+AC The aqueous zinc-air battery exhibits excellent cycle stability at 10 mA / cm². 2 It can operate reliably for 306 hours at the specified current density.

[0085] like Figure 7 As shown, 5 mg of the prepared catalyst or commercial Pt / C was dispersed in 500 μL of a mixed solution containing 20 μL Nafion (5 wt%) and 480 μL ethanol. The mixture was sonicated for 1 h to form a homogeneous catalyst ink. 8 μL or 10 μL of the catalyst ink was then added at a concentration of 0.4 mg / cm³. -2The loading amount was dropped into a polishing rotating disk electrode (RDE), with a geometric area of ​​approximately 0.20 cm². 2 Or rotating ring-disk electrode (RRDE, geometric area approximately 0.25 cm²) 2 The surface of the sample was dried spontaneously. ORR electrochemical testing was performed using a rotating ring-disc electrode (DC-DSR ROTATOR, PHYCHEMI) with a standard three-electrode configuration. Pt wire and Ag / AgCl were used as the counter and reference electrodes, respectively, and the resulting electrode was used as the working electrode. The alkaline electrolyte consisted of a 0.1M aqueous solution of saturated O2.

[0086] like Figure 10 As shown, various performance tests were conducted using a CHI 760E electrochemical workstation in the zinc-air battery test. A polished zinc sheet (8 cm × 3.2 cm) was used as the anode, and a CMNCA-Fe coated anode was used. SA+AC -2 or a mixture of commercial Pt / C+RuO2 with a mass ratio of 1:1 (loading: 2 mg cm⁻²) -2 The carbon cloth is used as the cathode (air electrode), and the electrolyte consists of a mixture of 6M KOH and 0.2M zinc acetate.

Claims

1. A method for preparing iron single-atom / cluster electrocatalyst supported on chitosan micro / nanofiber carbon aerogel, characterized in that, Includes the following steps: Step 1: Dissolve chitosan in an aqueous acetic acid solution and stir magnetically in a water bath until completely dissolved to obtain a chitosan solution; Step 2: [The text abruptly ends here, likely due to an incomplete sentence or a formatting error.] 3+ and Cd 2+ A metal-chitosan viscous solution Cs-Fe / Cd was prepared by a one-pot method using a metal salt solution and the chitosan solution. Step 3: The Cs-Fe / Cd viscous solution was directionally frozen using the ice template method, and then freeze-dried to obtain a 3D honeycomb structured chitosan and Fe / Cd ion crosslinked composite aerogel CMNA-Fe / Cd. Step 4: Place the CMNA-Fe / Cd aerogel into a quartz boat, center it in a tube furnace, and carbonize it at high temperature in an inert gas environment to synthesize the chitosan micro / nanofiber carbon aerogel-supported iron single-atom / cluster electrocatalyst CMNCA-Fe. SA+AC ; In step 2, Fe is present. 3+ and Cd 2+ The metal salt solutions were ferric chloride hexahydrate and cadmium chloride half-solution, respectively. In step 2, the preparation process of the CS-Fe / Cd viscous solution is as follows: a) Ferric chloride hexahydrate and cadmium chloride half-dissolved in water at a molar ratio of 1:20 to 1:1000 to obtain a Fe / Cd metal mixed solution; b) Pour the Fe / Cd metal mixed salt solution into the chitosan solution and stir for 1 to 5 hours to obtain a Cs-Fe / Cd viscous solution; wherein the mass ratio of chitosan to Fe / Cd metal mixed solution is 1:20 to 20:

1.

2. The method for preparing the iron single-atom / cluster electrocatalyst supported on chitosan micro / nanofiber carbon aerogel according to claim 1, characterized in that, In step 1, the degree of deacetylation of chitosan is ≥95%; In step 1, 20-80 mg of chitosan is dissolved in 1-10 ml of 1-10% v / v acetic acid aqueous solution and magnetically stirred for 1-3 h in a water bath at 40-80°C to obtain a chitosan solution.

3. The method for preparing the iron single-atom / cluster electrocatalyst supported on chitosan micro / nanofiber carbon aerogel according to claim 1, characterized in that, In step 3, the specific operation of directional freezing of the Cs-Fe / Cd viscous solution using the ice template method is as follows: A beaker containing a Cs-Fe / Cd viscous solution is placed on a copper block cooling platform immersed in liquid nitrogen to achieve directional freezing.

4. The method for preparing the iron single-atom / cluster electrocatalyst supported on chitosan micro / nanofiber carbon aerogel according to claim 3, characterized in that, In step 3, the freeze-drying temperature of the composite aerogel CMNA-Fe / Cd is -20 to -53°C, and the time is 24 to 72 hours.

5. The method for preparing the iron single-atom / cluster electrocatalyst supported on chitosan micro / nanofiber carbon aerogel according to claim 1, characterized in that, In step 4, the inert gas used is argon. In step 4, the carbonization temperature is 700~1000℃, the holding time is 1~4h, and the heating rate of the tube furnace is 1~10℃ / min.

6. An iron single-atom / cluster electrocatalyst supported on chitosan micro / nanofiber carbon aerogel obtained by the method of any one of claims 1-5, characterized in that, The iron single-atom / cluster electrocatalyst supported on chitosan micro / nanofiber carbon aerogel has a local layered network structure with a high aspect ratio and multi-scale micro / nanofiber interwoven. On a macroscopic level, due to the directional cryogenic casting process, the material exhibits a three-dimensional honeycomb structure and an orderly and abundant porous channel. CMNCA-Fe after high-temperature carbonization SA+AC The macroscopic 3D honeycomb structure and layered network structure remain intact, and are loaded with a large number of Fe-N4 single atoms and clusters. The catalyst exhibits excellent electrochemical performance in 0.1M KOH, with an onset potential of 0.99 V and a half-wave potential of 0.91 V.

7. The application of the iron single-atom / cluster electrocatalyst supported on the chitosan micro / nanofiber carbon aerogel obtained by the method of any one of claims 1-5, characterized in that, Iron single-atom / cluster electrocatalysts supported on chitosan micro / nanofiber carbon aerogels are used in zinc-air batteries.

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