Chitosan micro / nanofiber carbon aerogel loaded iron monatomic / atomic cluster electrocatalyst as well as preparation and application thereof

Abstract

The invention discloses a chitosan micro / nanofiber carbon aerogel loaded iron monatomic / atomic cluster electrocatalyst and preparation and application thereof, and the preparation method comprises the following steps: step 1, dissolving chitosan in an acetic acid aqueous solution, and magnetically stirring under a water bath condition until the chitosan is completely dissolved to prepare a chitosan solution; 2, preparing a metal-chitosan viscous solution from a metal salt solution containing Fe < 3 + > and Cd < 2 + > and the chitosan solution through a one-pot method; 3, directionally freezing the Cs-Fe / Cd viscous solution through an ice template method, and then freeze-drying to obtain chitosan and Fe / Cd ion cross-linked composite aerogel with a 3D honeycomb structure; and 4, putting the CMNA-Fe / Cd aerogel into a quartz boat, putting the quartz boat in the center of a tubular furnace, and performing high-temperature carbonization in an inert gas environment to synthesize the chitosan micro / nanofiber carbon aerogel loaded iron monatomic / atomic cluster electrocatalyst. The invention aims to optimize the electronic structure and microstructure of the catalyst, accelerate oxygen reduction reaction kinetics, and realize rapid mass transfer and maximum exposure of active sites.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalyst materials, and in particular relates to a chitosan micro / nano fiber carbon aerogel-supported iron single atom / atom cluster electrocatalyst and its preparation and application. Background Art

[0002] Among many new energy technologies, zinc-air batteries have shown good 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 a relatively slow reaction kinetics. Therefore, the development of efficient and stable catalysts has become the key to improving the performance of zinc-air batteries. Single atom catalysts (SACs), especially catalysts in which transition metals form a four-coordinate structure with nitrogen atoms (M-N4, M=Fe, Co, Mn, etc.), have been widely recognized as new ORR catalysts for various electrochemical energy conversion and storage devices. However, the D-type ions in the M-N4 structure are usually highly planar. 4h The symmetrical configuration results in unsatisfactory adsorption strength of the M-N4 structure with oxygen intermediates, thus limiting the ORR catalytic activity.

[0003] The study showed that the synergistic anchoring of metal single atoms (SAs) and atomic clusters (ACs) on appropriate carbon substrates can break the local charge symmetry of M-N4, thereby optimizing the adsorption strength of oxygen intermediates and reducing the energy barriers in the reaction pathway, thereby synergistically optimizing the ORR catalytic kinetics. SA+AC -NCs have excellent initial activity, but their stability and durability are still 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 carbon supports and metal sites reduces the M SA+AC In addition, the conductive carbon substrate usually has a densely stacked structure, which poses a great obstacle to the transport of reactants and even blocks the active sites. Summary of the invention

[0004] In order to overcome the problems existing in the above prior art, the purpose of the present invention is to provide a chitosan micro / nanofiber carbon aerogel-loaded iron single atom / atom cluster electrocatalyst and its preparation and application. The method utilizes chitosan rich in hydroxyl and amino groups to crosslink with Fe / Cd ions and fibrillate into chitosan micro / nanofibers. Through directional freezing technology, a 3D honeycomb structured composite aerogel (CMNA-Fe / Cd) of chitosan and Fe / Cd ions crosslinking is constructed. Subsequently, a carbonization strategy is adopted to prepare a chitosan micro / nanofiber carbon aerogel (CMNCA-Fe SA+AC). This approach aims to optimize the electronic structure and micromorphology of the catalyst, accelerate the oxygen reduction reaction (ORR) kinetics, and achieve fast mass transfer and maximum active site exposure.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The preparation method of the iron single atom / atom cluster electrocatalyst supported by chitosan micro / nano fiber carbon aerogel comprises the following steps:

[0007] Step 1: dissolving chitosan in an acetic acid aqueous solution, and stirring magnetically in a water bath until the chitosan is completely dissolved to obtain a chitosan solution;

[0008] Step 2: Add Fe 3+ and Cd 2+ The metal salt solution and the chitosan solution are prepared by a one-pot method to obtain a metal-chitosan viscous solution (Cs-Fe / Cd);

[0009] Step 3: Directionally freezing the Cs-Fe / Cd viscous solution by ice template method, and then freeze-drying to obtain a 3D honeycomb structured composite aerogel (CMNA-Fe / Cd) of chitosan and Fe / Cd ions cross-linked;

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

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

[0012] 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 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 3+ and Cd 2+ The metal salt solutions are ferric chloride hexahydrate and cadmium chloride hemi(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 hemi(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 vital role in spatially separating the iron active sites and acts as a porogen during the pyrolysis process, 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 stir and react for 1 to 5 hours to obtain a Cs-Fe / Cd viscous solution; wherein the mass ratio of chitosan to the Fe / Cd metal mixed solution is 1:20 to 20:1. The purpose of this ratio is to ensure that the metal ions and chitosan are completely cross-linked and coordinated.

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

[0018] The beaker containing the 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 direction. Chitosan micro / nanofibers loaded with metal ions were compressed between ice crystals to form a stable 3D honeycomb structure and multi-level pores. This structure provides a large specific surface area and abundant exposed active sites for catalytic reactions.

[0019] In the 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° C., the holding time is 1-4 hours, and the heating rate of the tubular furnace is 1-10° C. / min.

[0022] The chitosan micro / nano fiber carbon aerogel-supported iron single atom / atom cluster electrocatalyst is a local layered network structure of multi-scale micro / nano fibers interwoven with high aspect ratio;

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

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

[0025] The assembled aqueous zinc-air battery and solid-state zinc-air battery have high power density and excellent charge-discharge cycle stability. SA+AC The maximum power density of aqueous zinc-air batteries can reach 192.1 mW cm -2 , at 10mA / cm 2 The device can operate reliably for 306 hours at a current density of 1.58kWh.

[0026] Beneficial effects of the present invention:

[0027] (1) The present invention uses environmentally friendly and green chitosan as a nitrogen-containing carbon source, and utilizes its rich hydroxyl and amino groups to crosslink with Fe / Cd ions without the need to add an additional nitrogen source. The chitosan micro / nanofibers are evenly distributed and intertwined to form a layered network structure, which promotes the uniform dispersion of Fe-N4 single atoms and atomic clusters and further strongly anchors them on the carbon substrate.

[0028] (2) The present invention utilizes Cd salts to spatially separate the iron active sites and simultaneously act as porogens during the pyrolysis process, thereby generating a large number of micropores and defect sites in the carbon aerogel.

[0029] (3) The process of the present invention is simple, does not require any post-treatment and does not require the addition of an additional nitrogen source, and thus meets the requirements of large-scale production.

[0030] (4) The carbon aerogel prepared by the present 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. BRIEF DESCRIPTION OF THE DRAWINGS

[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 The CMNCA-Fe obtained in Example 2 of the present invention SA+AC -2 scanning electron microscope (SEM) image.

[0034] Figure 4 The CMNCA-Fe obtained in Example 2 of the present invention SA+AC -2 transmission electron microscope (TEM) image.

[0035] Figure 5The CMNCA-Fe obtained in Example 2 of the present invention SA+AC -2 double spherical aberration corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image.

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

[0037] Figure 7 The CMNCA-Fe obtained in Example 2 of the present invention SA+AC -2, CMNCA-Fe obtained in Comparative Example 1 SA , CMNCA-Fe obtained in Comparative Example 2 NP , the linear scan curve (LSV) diagram of the CMNCA obtained in Comparative Example 3, and the commercial Pt / C catalyst.

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

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

[0040] Fig.10 The CMNCA-Fe obtained in Example 2 of the present invention SA+AC Discharge polarization curve and power density curve of aqueous zinc-air battery assembled with -2 and commercial Pt / C as cathode materials.

[0041] Fig.11 The CMNCA-Fe obtained in Example 2 of the present invention SA+AC -2 and commercial Pt / C as cathode materials assembled into an aqueous zinc-air battery charge and discharge cycle test diagram. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below in conjunction with 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 the mixture is completely dissolved to prepare a chitosan solution.

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

[0046] Step 3: Place the beaker of the Cs-Fe / Cd viscous solution on a copper block cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, freeze-drying is performed at -30°C for 72 hours to prepare a 3D honeycomb structure of a composite aerogel (CMNA-Fe / Cd-1) of chitosan and Fe / Cd ions cross-linked.

[0047] Step 4: Place the CMNA-Fe / Cd aerogel in a quartz boat, place it in the center of a tube furnace, heat it to 700°C at 2°C / min in an Ar gas environment and keep it warm for 1 hour to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe 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 the mixture is completely dissolved to prepare a chitosan solution.

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

[0051] Step 3: Place the beaker of the Cs-Fe / Cd-2 viscous solution on a copper block cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, freeze-drying is performed at -53°C for 48 hours to prepare a 3D honeycomb structure of a composite aerogel (CMNA-Fe / Cd-2) cross-linked with chitosan and Fe / Cd ions.

[0052] Step 4: Place the CMNA-Fe / Cd-2 aerogel in a quartz boat, place it in the center of a tube furnace, heat it to 800°C at 5°C / min in an Ar gas environment and keep it warm for 2 hours to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe 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 the mixture is completely dissolved to prepare a chitosan solution.

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

[0056] Step 3: Place the beaker of the Cs-Fe / Cd-3 viscous solution on a copper block cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, freeze drying is performed at -53°C for 36 hours to prepare a 3D honeycomb structure of a composite aerogel (CMNA-Fe / Cd-3) cross-linked with chitosan and Fe / Cd ions.

[0057] Step 4: Place the CMNA-Fe / Cd-3 aerogel in a quartz boat, place it in the center of a tube furnace, heat it to 1000°C at 10°C / min in an Ar gas environment and keep it warm for 3 hours to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe 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 the mixture is completely dissolved to prepare a chitosan solution.

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

[0061] Step 3: Place the beaker of the Cs-Fe / Cd-2 viscous solution on a copper block cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, freeze drying is performed at -53°C for 48 hours to prepare a 3D honeycomb structure of a composite aerogel (CMNA-Fe / Cd-2) cross-linked with chitosan and Fe / Cd ions.

[0062] Step 4: Place the CMNA-Fe / Cd-2 aerogel in a quartz boat, place it in the center of a tube furnace, heat it to 800°C at 5°C / min in an Ar gas environment and keep it warm for 2 hours to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe 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 h. Subsequently, it was washed with deionized water several times until the filtrate reached neutrality. The product was collected and freeze-dried to obtain chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe 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 the mixture is completely dissolved to prepare 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: Place the beaker of the Cs-Fe viscous solution on a copper block cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, freeze-drying is performed at -53°C for 48 hours to prepare a 3D honeycomb structure of a composite aerogel (CMNA-Fe) cross-linked with chitosan and Fe ions.

[0068] Step 4: Place the CMNA-Fe aerogel in a quartz boat, place it in the center of a tube furnace, heat it to 800°C at 5°C / min in an Ar gas environment and keep it warm for 2 hours to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA-Fe 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 the mixture is completely dissolved to prepare a chitosan solution.

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

[0072] Step 3: Place the beaker of the Cs-Cd viscous solution on a copper block cooling platform immersed in liquid nitrogen to achieve directional freezing. Subsequently, freeze-drying is performed at -53°C for 48 hours to prepare a 3D honeycomb structure of chitosan and Cd ion cross-linked 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, heat it to 800°C at 5°C / min in an Ar gas environment and keep it warm for 2 hours to obtain a chitosan micro / nanofiber-based carbon aerogel electrocatalyst (CMNCA).

[0074] Test Example 1

[0075] The CMNA-Fe / Cd-2 prepared in Example 2 was tested by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the images obtained were as follows: Figure 1 and 2 shown.

[0076] like Figure 1 and Figure 2 As shown, the CMNA-Fe / Cd-2 aerogel is a 3D honeycomb structure with abundant micro / nano fibers interwoven with each other, a smooth surface, and uniform size. The diameter of the microfiber is about 0.8-1.4 μm, and the diameter of the nanofiber is about 20-25 nm.

[0077] Take the CMNCA-Fe prepared in Example 2 SA+AC -2, respectively, the scanning electron microscope (SEM), transmission electron microscope (TEM) and double spherical aberration corrected high angle annular dark field scanning transmission electron microscope (HAADF-STEM) tests were carried out, and the measured images were as follows Figure 3 , Figure 4 and Figure 5 shown.

[0078] like Figure 3 and Figure 4 As shown, CMNCA-Fe SA+AC -2 maintains a 3D honeycomb structure of interwoven micro / nano fibers, and the surface becomes rough after carbonization. Figure 5 It shows that Fe exists in two forms: single atom (shown by black solid circle) and atomic cluster (shown by black dashed circle).

[0079] Take the CMNCA-Fe obtained in Example 2 SA+AC-2, CMNCA-Fe obtained in Comparative Example 1 SA , CMNCA-Fe obtained in Comparative Example 2 NP , and the CMNCA obtained in Comparative Example 3 were subjected to X-ray diffraction (XRD) tests respectively. Figure 6 As shown, CMNCA-Fe SA+AC -2.CMNCA-Fe SA and CMNCA show two significant diffraction peaks at 24° and 42°, corresponding to the (002) and (100) crystal planes of graphitic carbon, respectively. NP The characteristic peaks corresponding to the crystalline phase of iron are shown. This confirms that the cadmium salt effectively separates the iron active sites in space, avoiding the aggregation and crystallization of iron metal, and acts as a porogen during the pyrolysis process, thereby generating a large number of micropores and defect sites in the carbon aerogel, and then generating 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 , CMNCA-Fe obtained in Comparative Example 2 NP The CMNCA and commercial Pt / C catalyst obtained in Example 3 were subjected to linear sweep curve (LSV) tests. Figure 7 As shown, CMNCA-Fe SA+AC -2 exhibited 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 by chronoamperometry (it). The results are shown in Figure 8 As shown, within 10 hours of operation, the current decay rate is only 3.4%, which is significantly lower than the test result of 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 test. A polished zinc plate with a thickness of 0.08 mm was used as the anode; the cathode included nickel foam, a conductive waterproof layer and a loading of 2 mg cm -2 CMNCA-Fe SA+AC Catalytic layer of catalyst (1cm -2); the solid electrolyte is PVA-KOH-Zn(CH3COO)2 hydrogel, and its preparation method is as follows: 2g of polyvinyl alcohol (PVA) is dissolved in 15mL of deionized water under stirring at 90°C to obtain solution A. Subsequently, 2ml of 6.0M KOH solution containing 0.2M Zn(CH3COO)2 is added dropwise to solution A, while continuously stirring for 2 hours to form a uniform solution. Finally, the resulting mixture is transferred to a silicone mold, and after cooling in a refrigerator, a PVA-KOH-Zn(CH3COO)2 hydrogel polymer is obtained. Fig. 9 As shown, it consists of four series-connected CMNCA-Fe SA+AC The solid-state zinc-air battery with a cathode can charge a smartphone, 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 catalyst as cathode materials were assembled into aqueous zinc-air batteries for discharge polarization curve and power density curve tests. A polished zinc plate with a thickness of 0.5 mm was used as the anode; the cathode included nickel foam, a conductive waterproof layer and a loading of 2 mg cm -2 CMNCA-Fe SA+AC Catalytic layer of catalyst (1cm -2 ); the electrolyte is a solution of 6M KOH + 0.2M Zn(Ac)2. Fig.10 As shown, based on CMNCA-Fe SA+AC The maximum power density of the zinc-air battery with a cathode is as high as 192.1 mW cm -2 , exceeding the zinc-air battery based on Pt / C+RuO2 (151.9 mW cm -2 ).

[0084] Take the CMNCA-Fe obtained in Example 2 SA+AC -2 and commercial Pt / C catalyst as cathode materials were assembled into aqueous zinc-air batteries for charge-discharge cycle tests. Fig.11 As shown, based on CMNCA-Fe SA+AC The aqueous zinc-air battery showed excellent cycling stability at 10 mA / cm 2 The device can operate reliably for 306 hours at a current density of 1.58kWh.

[0085] like Figure 7 As shown in Figure 2, 5 mg of the prepared catalyst or commercial Pt / C was dispersed in 500 μL of a mixed solution containing 20 μL of Nafion (5 wt%) and 480 μL of ethanol. The mixture was ultrasonicated for 1 h to form a uniform catalyst ink. 8 μL or 10 μL of the catalyst ink was added at 0.4 mg cm -2The loading amount was dropped onto a polished rotating disk electrode (RDE, with a geometric area of ​​about 0.20 cm 2 ) or a rotating ring disk electrode (RRDE, with a geometric area of ​​about 0.25 cm 2 ) on the surface of a 200 μm thick layer and allowed to dry spontaneously. ORR electrochemical tests were performed using a rotating ring disk electrode (DC-DSR ROTATOR, PHYCHEMI) with a conventional three-electrode configuration. Pt wire and Ag / AgCl were used as counter and reference electrodes, respectively, and the resulting electrode was used as the working electrode. The alkaline electrolyte consisted of an aqueous 0.1 M KOH solution saturated with O2.

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

Claims

1. A method for preparing a chitosan micro / nano fiber carbon aerogel-supported iron single atom / atom cluster electrocatalyst, characterized in that: The following steps are involved: Step 1: dissolving chitosan in an acetic acid aqueous solution, and stirring magnetically in a water bath until the chitosan is completely dissolved to prepare a chitosan solution; Step 2: Add Fe 3+ and Cd 2+ The metal salt solution and the chitosan solution are prepared by a one-pot method to obtain a metal-chitosan viscous solution (Cs-Fe / Cd); Step 3: Directionally freezing the Cs-Fe / Cd viscous solution by ice template method, and then freeze-drying to obtain a 3D honeycomb structured composite aerogel (CMNA-Fe / Cd) of chitosan and Fe / Cd ions cross-linked; Step 4: Place the CMNA-Fe / Cd aerogel in a quartz boat, place it in the center of a tube furnace, and perform high-temperature carbonization in an inert gas environment to synthesize the chitosan micro / nanofiber carbon aerogel-supported iron single atom / atom cluster electrocatalyst (CMNCA-Fe SA+AC ).

2. The method for preparing the chitosan micro / nano fiber carbon aerogel-supported iron single atom / atom cluster electrocatalyst according to claim 1, characterized in that: In the step 1, the deacetylation degree of chitosan is ≥ 95%; In the 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 hours in a water bath at 40-80° C. to obtain a chitosan solution.

3. The method for preparing the chitosan micro / nano fiber carbon aerogel-supported iron single atom / atom cluster electrocatalyst according to claim 1, characterized in that: In step 2, Fe 3+ and Cd 2+ The metal salt solutions are ferric chloride hexahydrate and cadmium chloride hemi(pentahydrate) solutions respectively.

4. The method for preparing the chitosan micro / nano fiber carbon aerogel-supported iron single atom / atom cluster electrocatalyst according to claim 3, characterized in that: In step 2, the preparation process of the CS-Fe / Cd viscous solution is as follows: a) dissolving ferric chloride hexahydrate and cadmium chloride hemi(pentahydrate) in water at a molar ratio of 1:20 to 1:1000 to obtain a Fe / Cd metal mixed solution; b) pouring the Fe / Cd metal mixed salt solution into the chitosan solution and mixing and stirring for 1 to 5 hours to obtain a Cs-Fe / Cd viscous solution; wherein the mass ratio of chitosan to the Fe / Cd metal mixed solution is 1:20 to 20:

1.

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

6. The method for preparing the chitosan micro / nano fiber carbon aerogel-supported iron single atom / atom cluster electrocatalyst according to claim 5, characterized in that: In the 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.

7. The method for preparing the chitosan micro / nano fiber carbon aerogel-supported iron single atom / atom cluster electrocatalyst 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° C., the holding time is 1-4 hours, and the heating rate of the tubular furnace is 1-10° C. / min.

8. The iron single atom / atom cluster electrocatalyst supported by chitosan micro / nano fiber carbon aerogel obtained by the method according to any one of claims 1 to 7, characterized in that: The iron single atom / atom cluster electrocatalyst supported by chitosan micro / nanofiber carbon aerogel is a local layered network structure of multi-scale micro / nanofiber interweaving with high aspect ratio; On a macroscopic level, the material exhibits a three-dimensional honeycomb structure and ordered and abundant porous channels due to the directional freeze casting process; the CMNCA-Fe SA+AC The macroscopic 3D honeycomb structure and layered network structure remain intact, and a large number of Fe-N4 single atoms and atomic clusters are loaded. The catalyst exhibits excellent electrochemical performance in 0.1 M KOH, with an onset potential of 0.99 V and a half-wave potential of 0.91 V.

9. The use of the chitosan micro / nano fiber carbon aerogel-supported iron single atom / atom cluster electrocatalyst obtained by the method according to any one of claims 1 to 7, characterized in that: Chitosan micro / nanofibrous carbon aerogel-supported iron single atom / atom cluster electrocatalysts for zinc-air batteries.

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