Hollow cobalt tetraoxide / n-rGO composite material and application thereof

Abstract

This invention belongs to the field of nanomaterial electrode manufacturing, specifically relating to a hollow cobalt tetroxide / N-rGO composite material and its applications. The preparation process of the composite material includes the following steps: (1) preparing a linear diblock polymer containing hydrophilic and hydrophobic ends; (2) using ε-Co obtained by thermal decomposition of a cobalt source, attaching ε-Co to the hydrophilic end of the linear diblock polymer to obtain an intermediate material; (3) combining the Kirkendall effect to transform the intermediate material into hollow Co3O4 nanoparticles; (4) combining the hollow Co3O4 nanoparticles with nitrogen-doped redox graphene at high temperature to obtain the hollow cobalt tetroxide / N-rGO composite material. The Co3O4 / N-rGO provided by this invention has excellent performance and has great application potential and industrial value in the field of electrochemistry.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial electrode manufacturing, specifically relating to a hollow cobalt tetroxide / N-rGO composite material and its application. Background Technology

[0002] The extensive use of fossil fuels generates various toxic gases and particulate matter, accelerating environmental degradation and leading to a series of environmental problems such as global warming and rising sea levels. Wind and solar energy are widely recognized as major renewable energy sources; however, the energy provided by these technologies is overly dependent on external environmental factors. Currently, zinc-air battery technology offers advantages such as high efficiency, cleanliness, low cost, safety, and sustainability, representing the future of sustainable energy.

[0003] Nanoscale hollow materials are a special class of materials with internal spaces or voids. Their excellent structural characteristics, such as high specific surface area to volume ratio, low mass density, high porosity, and good strain regulation, have made them a favorite among researchers. Nanoscale hollow materials can provide higher reactive sites for surface-catalyzed heterogeneous reactions; furthermore, they enable maximum material utilization. In recent years, this novel and unique functional material has been widely applied in catalysis, energy storage, biomedicine, environmental protection, sensing, and optics. Several impressive methods have been developed to synthesize hollow structures, such as sacrificial templates, Ostwald ripening, Kikendall effect, and electrochemical substitution. However, these methods lack precise control over material size and avoidance of aggregation, which can hinder the full utilization of energy. It is worth noting the aggregation characteristics of organic materials, which can also prevent the full utilization of energy.

[0004] Co3O4 is a spinel-type transition metal oxide material with excellent electrocatalytic performance. Compared to the precious metals platinum group oxide and iridium and ruthenium-based compounds, which suffer from resource scarcity, high cost, and poor stability, transition metals are abundant, inexpensive, and exhibit only minor differences in catalytic activity. However, Co3O4 has poor electrical conductivity and poor stability as a catalyst. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a hollow cobalt tetroxide / N-rGO composite material and its application.

[0006] In one aspect, the present invention provides a hollow cobalt tetroxide / N-rGO composite material, the preparation process of which includes the following steps:

[0007] (1) Preparation of linear diblock polymers containing hydrophilic and hydrophobic ends;

[0008] (2) Using ε-Co obtained by thermal decomposition of cobalt source, the ε-Co is attached to the hydrophilic end of a linear diblock polymer to obtain an intermediate material;

[0009] (3) Combine the Kirkendall effect to transform the intermediate material into hollow Co3O4 nanoparticles;

[0010] (4) Hollow Co3O4 nanoparticles were combined with nitrogen-doped redox graphene at high temperature to obtain hollow cobalt tetroxide / N-rGO composite material.

[0011] Preferably, the preparation process of the linear diblock polymer containing hydrophilic and hydrophobic ends includes the following steps:

[0012] (1-1) The first polymer was prepared by initiating polymerization of the catalyst cuprous bromide, the ethyl 2-bromoisobutyrate initiator, the ligand, and the tert-butyl acrylate monomer using an atom transfer radical polymerization method.

[0013] (1-2) Styrene monomer is used as the second block monomer and is polymerized again with the first polymer by ATRP to obtain the second polymer.

[0014] (1-3) The tert-butyl acrylate monomer has an ester group, and the second polymer obtained is hydrolyzed to hydrophilic carboxyl groups by hydrolysis.

[0015] Preferably, the ligand is any one of bipyridine, tris[2-(dimethylamino)ethyl]amine, or pentamethyldiethylenetriamine, with pentamethyldiethylenetriamine being the most preferred.

[0016] Preferably, the molar ratio of cuprous bromide, ethyl 2-bromoisobutyrate initiator, ligand and tert-butyl acrylate monomer is (1-10):1:(1-5):(15-120), the molecular weight of the first polymer is 2k-8k g / mol; the molar ratio of ethyl 2-bromoisobutyrate initiator and styrene is 1:(100-500), and the molecular weight of the second polymer is 6k-20k g / mol.

[0017] In step (1-1), after the polymerization reaction, the resulting solution is dispersed in acetone, filtered through alumina, evaporated, washed, and dried to finally obtain the first polymer. The washing process involves a mixture of a good solvent and a poor solvent. For example, the good solvent can be any of methanol, ethanol, isopropanol, etc., with methanol being the most preferred.

[0018] In steps (1-2), the molecular weight of the polymer, i.e. its length, can be controlled by controlling the reaction time.

[0019] In steps (1-2), after the polymerization reaction, the resulting solution is dispersed in tetrahydrofuran, filtered through alumina, evaporated, washed, dried, and finally the second polymer is obtained.

[0020] The neutral alumina mentioned above is 100-300 mesh, for example, it can be 100-200 mesh or 200-300 mesh.

[0021] Preferably, in step (2), the linear diblock polymer containing hydrophilic and hydrophobic ends is dissolved to obtain solution one, and the cobalt source cobalt octacarbonylcobalt Co2(CO)8 is dissolved to obtain solution two. Solution one is heated to 100-300°C, and under the protection of an inert gas, solution two is rapidly injected into the heated solution one and reacted to obtain an intermediate material. The inert gas is argon or nitrogen.

[0022] Preferably, in step (2), the post-treatment process of the reaction solution is as follows: the reaction solution is ultrasonically dispersed, centrifuged at low speed, the lower layer of large particles is discarded, and a precipitant is added to precipitate the intermediate material. Preferably, the precipitant is n-hexane, at a concentration of 20-50 times that of the original solution, for example, 20, 30, 40, or 50 times. The centrifuge speed is 500-1000 rpm / min, for example, 500 rpm / min, 800 rpm / min, or 1000 rpm / min.

[0023] Preferably, in step (3), the reaction is carried out in an O2 atmosphere at a temperature of 100-300℃, most preferably 175℃, and the reaction time is 3-168 h, for example, 3h, 24h, 48h, 72h, 96h, 120h, 144h or 168h.

[0024] Preferably, in step (4), monolayer GO is prepared by the Hummers method; N / rGO is obtained by nitriding GO with any one of urea, ammonia, hydrazine hydrate, ammonia, or nitrogen.

[0025] Preferably, in step (4), the composite temperature of the hollow Co3O4 nanoparticles and nitrogen-doped reduced graphene is 100-300℃, preferably 120℃, and the reaction time is 0.5-48 h, for example, 2 h, 3 h, or 12 h. The mass ratio of the hollow Co3O4 nanoparticles to the nitrogen-doped reduced graphene is 1:0.5-2, for example, 2:1, 1:2, or 2:1.

[0026] Preferably, in step (4), the post-processing is as follows: centrifugation, washing, and drying. The drying temperature is 25-250℃, for example, 25℃, 50℃, 100℃, or 200℃.

[0027] A second aspect of the invention provides the application of the hollow cobalt tetroxide / N-rGO composite material as described above as an electrocatalyst.

[0028] A third aspect of the present invention provides the application of the hollow cobalt tetroxide / N-rGO composite material as described above in the preparation of a positive electrode for a liquid-phase zinc-air battery.

[0029] The beneficial effects of the present invention are as follows: 1. The present invention uses ATRP polymerization to synthesize blocks with different molecular weights. Co2(CO)8 is thermally decomposed at high temperature into ε-Co which is attached to the hydrophilic end. The length of the block polymer determines the size of the inorganic nanoparticles, and well-defined inorganic nanoparticles can be synthesized.

[0030] 2. The polymer hydrophobic terminal PS of this invention can prevent the spontaneous aggregation of inorganic nanoparticles due to their high surface free energy. The prepared nanoparticles can fully exert their own activity.

[0031] 3. This invention combines the Kirkendall effect to transform into a hollow structure, and the prepared Co3O4 has an ultra-large specific surface area ratio. The internal cavity can also shorten the electron / charge transport path, providing more active sites for subsequent electrocatalytic oxygen production and evolution, thereby increasing catalytic activity.

[0032] 4. This invention employs a combination of N / rGO and Co3O4. On one hand, N-doped graphene can adjust the electron configuration of carbon materials, generating active sites for oxygen adsorption or cleavage and improving stability. On the other hand, graphene can enhance the overall electrical conductivity of the material, accelerate electron transport, and improve catalytic performance.

[0033] 5. Under near-infrared laser irradiation, the Co3O4 / N-rGO composite electrocatalyst exhibits excellent oxygen reduction (ORR) and oxygen evolution (OER) activities. The half-wave potential of ORR increases to 0.84 V, and the limiting current density is significantly increased; at 10 mAcm⁻¹... -2 Under the current density standard, the overpotential of OER decreased to 270 mV, the Tafel slope decreased, and the kinetics accelerated. The power density of ZABs composed of Co3O4 / N-rGO composite material reached 225 mW cm⁻¹ under NIR laser. -2 With a specific capacity of up to 806 mAhg -1 Furthermore, the battery can stably cycle charge and discharge for 186 hours, demonstrating good stability; as a novel battery, it can enable light-emitting diodes to emit light, indicating that the material has potential practical value. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0035] Figure 1 For PAA- b -PS-Co3O4 / N-rGO hybridization flowchart;

[0036] Figure 2 For EBIB-PtBA 1 HNMR spectrum;

[0037] Figure 3 GPC curves for different tBA feed rates;

[0038] Figure 4 For PtBA-b-PS 1 H NMR spectrum;

[0039] Figure 5 GPC spectra of PtBA-b-PS at different reaction times;

[0040] Figure 6 In the middle, (ab) TEM images of graphene oxide nanosheets at different magnifications, (cd) TEM images of hollow Co3O4 / N-rGO composites at different magnifications, and (e) HAADF image and elemental mapping of hollow Co3O4 / N-rGO composites.

[0041] Figure 7 In the image, (a) XPS full spectrum of hollow Co3O4 / N-rGO composite material, (b) Co 2p spectrum, (c) O 1s spectrum, (d) N 1s spectrum, (e) C 1s spectrum, (f) XPS atomic content diagram;

[0042] Figure 8 In the image, (a) is the XRD pattern of the Co3O4 / N-rGO composite material, and (b) is the Raman pattern of the GO and Co3O4 / N-rGO composite material (inset: 300-750 cm⁻¹ of Co3O4). -1 (c) Thermogravimetric spectrum of Co3O4 / N-rGO composite material, (d) N2 adsorption-desorption curve and pore size distribution of Co3O4 / N-rGO composite material (inset).

[0043] Figure 9(a) UV-Vis absorption spectrum of Co3O4 / N-rGO composite material; (b) Temperature-time curve of electrode material under NIR light at 808 nm; (c) Near-infrared image of composite material in alkaline electrolyte.

[0044] Figure 10 In the figure, (a) cyclic voltammetry curves of the Co3O4 / N-rGO composite material under O2 and Ar saturation, and (b) ORR linear scan curves of the composite material with and without near-infrared irradiation and with commercial Pt / C catalyst.

[0045] Figure 11 The oxygen reduction properties of hollow Co3O4 / N-rGO composites under oxygen saturation were tested. (a) LSV curves of the composites at different rotational speeds, (b) KL equation fitting curves, (c) RRDE test, and (d) the number of transferred electrons and the percentage of H2O2 calculated from the RRDE data. The scan rate was 5 mV / s.

[0046] Figure 12 Oxygen reduction performance of hollow Co3O4 / N-rGO composite material under oxygen saturation. (a) Tafel slope diagram, (b) electrochemical impedance diagram, (c) methanol resistance diagram of composite material and commercial Pt / C, (d) cyclic stability diagram of 10h chronoamperometry test;

[0047] Figure 13 OER testing of hollow Co3O4 / N-rGO composite material under and without illumination. (a) LSV curve, (b) Tafel slope. Scan rate 5 mV / s, rotation speed 1600 rpm / min;

[0048] Figure 14 Tests for Faraday capacitance: (a) Hollow Co3O4 / N-rGO composite material, (b) Hollow Co3O4 / N-rGO composite material under illumination, (c) RuO2, (d) Faraday capacitance fitting graph;

[0049] Figure 15 Stability curves of hollow Co3O4 / N-rGO composite material and RuO2 under light and no illumination.

[0050] Figure 16 Performance comparison of zinc-air batteries using hollow Co3O4 / N-rGO composite material and Pt / C-RuO2 material under near-infrared illumination. (a) Polarization curves, (b) Power density;

[0051] Figure 17Performance comparison of zinc-air batteries using hollow Co3O4 / N-rGO composite material and Pt / C-RuO2 material under near-infrared irradiation. (a) Rate performance at different current densities, (b) Discharge specific capacity;

[0052] Figure 18 In the figures, (a) compare the charge-discharge cycle stability of zinc-air batteries made of hollow Co3O4 / N-rGO composite material and Pt / C-RuO2 material under near-infrared irradiation, (b) voltage diagrams of two zinc-air batteries composed of composite catalysts, and (c) diagrams of two series-connected zinc-air batteries driven by light-emitting diodes based on composite catalysts. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0054] A method for preparing a hollow Co3O4 / N-rGO composite material includes the following steps:

[0055] (a) Pretreatment of experimental reagents:

[0056] (a) Pretreatment of CuBr. Add 1 g of CuBr to a round-bottom flask, add glacial acetic acid, and stir on a magnetic stirrer for 7 h. Then add an appropriate amount of ethanol and stir for 3 h. Wash with ethanol until the solution is clear. Place the resulting white substance in a vacuum oven and dry at room temperature. Store in an inert gas atmosphere.

[0057] (b) tert-butyl acrylate ( tBA Pretreatment was performed by adding 100 mL of tBA to a 250 mL round-bottom flask, adding 1 g of calcium hydride, stirring for 24 h, and then filtering under reduced pressure. The mixture was then sealed and stored in a refrigerator for later use, protected from light.

[0058] (c) Pretreatment of styrene (St). Add 100 mL of St to a 250 mL round-bottom flask, add 1 g of calcium hydride, stir for 24 h, and filter under reduced pressure. Seal and store in a refrigerator for later use.

[0059] (II) Specific synthesis steps of EBIB-PtBA:

[0060] According to the molar ratio of ethyl 2-bromoisobutyrate (EBIB):CuBr: pentamethyldiethylenetriamine (PMDETA): tert-butyl acrylate (tBA) of 1:1:2:X (X=30, 37.5, 45, 60), the corresponding reagents were weighed and quickly added to a 25 mL round-bottom flask, along with 8 mL of methyl ethyl ketone (MEK) solvent. High-purity argon was bubbled through the flask, and the mixture was kept in an ice-water bath for 20 min. The mixture was then transferred to an oil bath at 600 rpm / min and 60 °C for 24 h for polymerization. (All experiments were conducted using rubber stoppers to isolate oxygen). The flask was then removed and placed in ice water, and the reaction was terminated by opening the rubber stopper. CuBr was removed by column chromatography using neutral alumina and acetone. The filtered solution was then subjected to rotary evaporation to remove excess acetone. A 1:1 volumetric mixture of methanol and water was used to precipitate the desired sample via reverse precipitation. The sample was then vacuum dried and washed three times. The synthesis schematic is shown below.

[0061]

[0062] (III) Specific synthesis steps of PtBA-b-PS:

[0063] The molar ratio of EBIB-PtBA:CuBr:PMDETA:Styrene (St) was 1:1:2:300. The corresponding reagents were weighed into a 25 mL round-bottom flask, and high-purity argon was bubbled through at low temperature for 20 min to remove internal oxygen. The mixture was then transferred to an oil bath at 600 rpm / min and 90 °C, with the polymerization time controlled. The round-bottom flask was removed and placed in ice water. The reaction was terminated by opening the rubber stopper. CuBr was removed by column chromatography using neutral alumina and tetrahydrofuran. The filtered solution was subjected to rotary evaporation to remove excess tetrahydrofuran solution; the sample was precipitated with pure methanol in reverse evaporation, vacuum dried, and repeatedly washed and dried three times to obtain the final pure sample. A schematic diagram of the synthesis is shown below.

[0064]

[0065] (iv) Specific synthesis steps of PAA-b-PS:

[0066] The PtBA-b-PS copolymer was dissolved in 30 mL of CHCl3 solution, and 4 mL of trifluoroacetic acid (TFA) was slowly added at 1200 rpm / min. The mixture was stirred in the dark at room temperature for 24 h. After the reaction was completed, the copolymer was rotary evaporated. An appropriate amount of DMF was used to redissolve the copolymer, and the solution was added dropwise to a methanol solution at high speed to precipitate the solid. The solid was then dried under vacuum, and the washing and drying process was repeated 3-4 times to obtain the final product. The synthesis diagram is shown below.

[0067]

[0068] (v) PAA- bSpecific experimental steps for PS-Co3O4 / N-rGO hybridization:

[0069] First, 10 mg of PAA-b-PS polymer was weighed into a 25 mL three-necked flask, sonicated to dissolve and mix thoroughly, and then heated to 175 °C. 150 mg of Co₂(CO)₈ was weighed as a precursor and sonicated to dissolve in 2 mL of o-dichlorobenzene. This solution was rapidly injected into the 175 °C reaction solution, where it underwent thermal decomposition to elemental ε-Co. The temperature was then adjusted to 160 °C, and the reaction was carried out for 30 min (under Ar gas protection throughout the hybridization process). Post-treatment involved sonication, low-speed centrifugation, and discarding the lower layer of large particles. PAA-b-PS-Co was precipitated in 500 mL of n-hexane, washed twice with DMF, and dispersed in 4 mL of o-dichlorobenzene solution under argon protection for later use.

[0070] Secondly, hollow cobalt oxide structures were synthesized using the Kirkendall effect. The above PAA-b-PS-Co material was then purged with oxygen and heated to 175 °C for 3 h. Post-treatment involved ultrasonic dispersion, precipitation with n-hexane, and two centrifugal washings with DMF to obtain clean PAA-b-PS-Co3O4 material.

[0071] Finally, a 1 mg / mL monolayer GO was prepared using the Hummers method. 30 mL of the GO dispersion was sonicated for 2 h, 2 mL of ammonia solution was added, and the mixture was placed in a 50 mL Teflon reactor and reacted at 150 °C for 3 h to obtain N-rGO. PAA-b-PS-Co3O4 / N-rGO was weighed at a mass ratio of 2:1, and an appropriate amount of DMF was added. The mixture was sonicated until homogeneous and reacted at 120 °C for 2 h. Post-treatment: centrifugation, washing, and drying were performed to obtain the final product, hollow PAA- b -PS-Co3O4 / N-rGO (hollow Co3O4 / N-rGO composite material); Figure 1 ).

[0072] The following is the characterization of the polymer ligands:

[0073] 1. Characterization of EBIB-PtBA: such as Figure 2 As shown, δ=4.10 ppm represents the hydrogen proton peak in the methylene group, and δ=1.45 ppm represents the peak of (CH3)3. - The hydrogen proton peaks in the image; by integrating the surface area ratios of the hydrogen characteristic peaks at positions 6 and 2, and then based on... The number of repeating units in the sample was calculated.

[0074] The 1H NMR spectrum results were largely consistent with the gel permeation chromatography (GPC) results, further confirming the accuracy of the molecular weight determination. Furthermore, under otherwise identical conditions, by controlling... tBAThe effect of monomer content on the molecular weight of the copolymer was studied by varying the monomer input. The molecular weight (Mn) and dispersion index (PDI) were determined using GPC, as shown in Table 1 below. tBA With increasing monomer input, the molecular weight of PtBA gradually increases; the dispersion coefficient is approximately 1.2, indicating good dispersion. Figure 3 The GPC test curve also confirmed the above conclusions. The larger the molecular weight, the earlier the peak elution, and the GPC curve did not have obvious tailing phenomenon. The peak shape was also a smooth single peak with a narrow peak shape, indicating that the polymerization process can be controlled.

[0075] Table 1 Regulation tBA The molecular weight and dispersity index of copolymers synthesized with different monomer contents

[0076]

[0077] 2. Characterization of PtBA-b-PS diblock polymers

[0078] like Figure 4 As shown, δ Characteristic peaks in the range of 6.5~7.3 ppm are attributed to H on the benzene ring and labeled as b; δ=1.3~ 1.5 ppm The peaks within the range are characteristic peaks of the tert-butyl group in the PtBA copolymer, labeled as a; by integrating the areas of the two sets of characteristic peaks a and b in the PtBA-b-PS copolymer, according to Find the number of repeating units in PS.

[0079] The PtBA-b-PS copolymer was further characterized using GPC. As shown in Table 2 below, by controlling the molar ratio of EBIB-PtBA:CuBr:PMDETA:St=1:1:2:300 and keeping other conditions constant, the longer the polymerization time, the larger the molecular weight (Mn) of the copolymer, the lower the PDI is (below 1.2), and the better the copolymer dispersion. Figure 5 The GPC curves more intuitively reveal that as the response time increases, the peak time is earlier and the molecular weight is larger.

[0080] Table 2. Molecular weight and dispersion coefficient of copolymers synthesized with different reaction times.

[0081]

[0082] The following are the morphology, composition, and structure of the hollow Co3O4 / N-rGO composite material:

[0083] 1. From Figure 6(ab) It can be seen that the synthesized GO exhibits a two-dimensional nanosheet structure with good uniformity. The number of layers, approximately 4-6, can be clearly seen under high resolution. Figure 6(c) shows that hollow Co3O4 is well dispersed on the two-dimensional N-rGO with a large specific surface area. Furthermore, the high-resolution TEM image in Figure 6(d) shows that the hollow Co3O4 nanomaterial synthesized by the ligand method has an outer size of approximately 25±5 nm and an inner diameter of approximately 15±5 nm. Measurements show that the lattice spacing is 0.244 nm, corresponding to the (311) plane of the Co3O4 material. The small-sized hollow structure is beneficial for maximizing material utilization and providing more active sites, which is conducive to the electrocatalytic reaction activity. Figure 6 As shown in the elemental mapping of (e), nitrogen has been successfully doped onto the graphene nanosheets, and Co, O, C, and N are well distributed. This hollow composite material synthesized with polymer as ligand provides strong assurance in terms of catalytic stability.

[0084] Depend on Figure 7 (ab) shows that the two characteristic peaks at 780.14 eV and 796.70 eV represent and Two valence states. (From) Figure 7 (a) As can be seen from the full spectrum of the Co3O4 / N-rGO composite material, the peak at 399.0 eV is a characteristic peak of the N 1s element, indicating that the N element has been successfully introduced into the composite material, which corresponds well with the TEM results. Figure 7 As shown in (c), the peaks at 531.2 eV and 532.3 eV in the O 1s spectrum are typical distributions of surface adsorbed hydroxyl groups and the presence of oxygen vacancies. These two types of peaks will be beneficial to the application of composite materials in the field of electrocatalysis and enhance catalytic activity. Figure 7 (d) The XPS spectrum of N 1s shows that 398.8 eV, 400.13 eV and 401.58 eV correspond to three types: pyrrole-N, pyridine-N and graphitized-N, respectively. Graphitized-N has been shown to efficiently increase oxygen reduction catalytic activity. Figure 7 (e) is the high-resolution spectrum of the fitted C 1s spectrum, where the four peaks at 284.5 eV, 284.8 eV, 286 eV, and 288.5 eV represent sp, respectively. 2 Hybridized graphitization (CC sp) 2 ), sp 3 Hybridized diamond-like carbon (CC sp) 3 ), CO and OC=O functional groups. Figure 7As shown in (f), the content analysis diagram of various element atoms obtained by XPS test shows that the C atom content is the most abundant in the hollow Co3O4 / N-rGO composite material, which is about 64.54%, Co atoms account for 7.95%, O atoms account for 20.51%, and N atoms account for 7.00%.

[0085] To further characterize the structure of the hollow Co3O4 / N-rGO composite material, crystal X-ray diffraction (XRD) was used to obtain... Figure 8 (a) A relatively strong diffraction peak appears at around 36.91°, corresponding to the (311) crystal plane of Co3O4 (PDF#43-1003-Co3O4). The four weaker peaks are located at 31.39°, 44.80°, 59.35° and 65.23°, corresponding to the (200), (400), (511) and (440) crystal planes of Co3O4, respectively. The above XRD data analysis proves that Co3O4 nanoparticles have been successfully synthesized; the weak diffraction peaks are attributed to the small particle size and the large amount of carbon material, which is consistent with the TEM and XPS data analysis. Figure 8 (b) Comparison of Raman spectral data of GO and Co3O4 / N-rGO composites. (Inset 300-750 cm⁻¹) -1 Characteristic vibrational modes of Co3O4 were observed within the range, indicating the presence of a Co3O4 structure. Notably, at 1355 cm⁻¹... -1 and 1595 cm -1 The two peaks on the left and right are characteristic of graphite and are named the D peak (caused by sp3 defects) and the G peak (caused by sp2 defects). I D and I G The values ​​represent the intensities of two peaks. The graph clearly shows the properties of the Co3O4 / N-rGO composite material. ID / IG The ratio is greater than that of GO, indicating that we have successfully converted GO in the material into rGO, which is more stable than GO. As shown in the thermogravimetric analysis in 8(c), with a temperature program of 5°C / min to 600°C, the temperature plateaus around 600°C, and the remaining material is 76.42 wt% spinel-structured Co3O4 nanomaterials. The specific surface area and pore size distribution of the Co3O4 / N-rGO composite material were obtained by N2 adsorption-desorption isotherms, as shown in the figure. Figure 8 As shown in (d), a distinct type IV hysteresis loop appears in the range of 0.0-1.0 P / P0, indicating that the composite material has a mesoporous and microporous structure (1-10 nm) and a specific surface area of ​​73.67 m². 2 g -1The pore sizes are concentrated between 3±4 nm, and the large specific surface area and mesoporous structure can provide more active sites for the composite material. These data demonstrate the excellent activity of the catalyst during the catalytic process.

[0086] The following are the catalytic performance of the hollow Co3O4 / N-rGO composite material:

[0087] Depend on Figure 9 (a) It can be seen that the composite material has a wide ultraviolet absorption range, enabling it to absorb and convert near-infrared light into heat. NIR light is irradiated onto the surface of the composite material covered with electrolyte, and the temperature change of the material surface is observed in real time using an infrared thermal imager. Figure 9 (bc) Compared to the empty electrode, the electrode with the composite material dripped on it heats up rapidly, reaching 53.9 ℃ within 5 seconds. As time progresses, the surface temperature of the material remains constant at around 70 ℃. Notably, due to the high specific heat capacity of water, the temperature is mainly concentrated on the material surface, while the electrolyte temperature changes very little, which also indirectly proves that the experiment used a localized heating method. The above experimental data clearly demonstrate that the composite material exhibits a strong photothermal effect.

[0088] To investigate the ORR catalytic activity of the hollow Co3O4 / N-rGO composite material, a three-electrode system was used for testing. Cyclic voltammetry (CV) tests were performed on the samples under saturated oxygen and Ar atmospheres. Figure 10 (a) It can be seen that, when tested in 0.1 M KOH electrolyte at a scan rate of 5 mV / s, only O 2 Under the given conditions, a distinct reduction peak appeared, revealing that the composite material possesses oxygen reduction properties, which will help in further exploring other properties of ORR. Figure 10 (b) The linear sweep scalar projection (LSV) curves show that under NIR laser irradiation, the composite material's initial potential increased from 0.920 V to 0.951 V. The half-wave potential also significantly increased, from 0.82 V to 0.84 V. Not only did the initial and half-wave potentials show marked increases, but the limiting current density of the composite material also increased considerably under NIR laser irradiation. This increase in limiting current density indicates accelerated electron transport on the composite material surface.

[0089] To test the oxygen reduction kinetics of the hollow Co3O4 / N-rGO composite material, linear sweep voltammetry (CV) curves of the composite material at different rotational speeds were measured under oxygen saturation conditions, as follows: Figure 11 As shown in (a), the limiting current density increases systematically with the square of the rotational speed. Based on the Koutecky-Levich equation, plotting the LSV curves for different rotational speeds yields a curve with good linear fit, indicating an electron transfer number of approximately 4. Figure 11 As shown in (b), this indicates that the ORR of the composite material is 4e. - The transfer process, and diffusion as a first-order kinetic process. The rotating ring-disk electrode (RRDE) can also measure the electron transfer number of the ORR. For example... Figure 11 As shown in (cd), within a voltage range of 0.3–0.7 V, the number of transferred electrons in the composite material ranges from 3.98 to 4.00, and the hydrogen peroxide yield is less than 6%. The electron transfer numbers calculated by fitting the KL equation and direct RRDE testing show a good agreement, indicating that the ORR process of the composite material tends towards 4e- electrons. - It exhibits reaction selectivity and outstanding ORR performance.

[0090] To understand the reasons for the improved performance of materials under the photothermal effect, we analyzed the Tafel slope and Nyquist plot of ORR with and without laser irradiation. Figure 12 As shown in (a), under illumination, the Tafel slope of the composite material changes from 139 mV dec -1 Reduced to 134 mV dec -1 This study reveals that composite materials effectively convert light energy into heat energy under illumination, thereby mitigating the slow oxygen reduction kinetics and accelerating electron transfer. Furthermore, it also demonstrates... Figure 12 (b) Impedance testing showed that the impedance of the composite material under photothermal effect was significantly lower than that without photothermal exposure. This further illustrates that the photothermal effect promotes charge transfer, thereby accelerating the entire oxygen reduction reaction process.

[0091] Stability is an important indicator for evaluating ORR catalytic activity. Figure 12 (c) shows the methanol resistance performance of the composite material and the commercial Pt / C catalyst. The methanol resistance test is primarily conducted because the ORR reaction is the cathode rate-determining reaction in a methanol fuel cell, and methanol shuttling in the electrolyte can easily poison the catalyst, limiting the large-scale application of fuel cells. The figure shows that adding 3 M methanol solution at 1000 s did not change the current density of the composite material, while the current density of the commercial Pt / C catalyst increased instantaneously, indicating that the commercial Pt / C catalyst dominates the methanol oxidation reaction. This also demonstrates the excellent methanol resistance of the composite material. Figure 12 (d) shows the stability of the composite material under constant voltage (it) testing. Analysis of the figure shows that after 10 hours of stability testing at 1600 rpm / min, the composite material maintained 87% and 84% stability under no light and light exposure, respectively, while the commercial Pt / C decreased to 62%. This indicates that the composite material exhibits good stability.

[0092] OER catalysis was performed using LSV in an oxygen-saturated 1 M KOH solution, such as... Figure 13As shown in (a). With a current density of 10 mA cm⁻¹ -2 Using this as a standard reference, the OER overpotential of the unilluminated composite material is 320 mV, which decreases to 270 mV after irradiation with an 808 nm NIR laser. In contrast, the overpotential of the commercial RuO2 catalyst, commonly used for OER catalytic activity comparison, is 310 mV. It is worth noting that... Figure 13 (b) The corresponding OER data and Tafel fitting data of the composite material show that, under no light illumination, the Tafel of the composite material is 90 mVdec. -1 Under near-infrared light irradiation, the Tafel of the composite material is 74 mVdec. -1 The Tafel value of the RuO2 catalyst is 83 mV dec. -1 The adsorption of hydroxyl groups by the composite catalyst is reduced under photothermal assistance. These data indicate that light irradiation can effectively promote the kinetics of the OER reaction in hollow Co3O4 / N-rGO composite materials and improve the activity of OER catalysis.

[0093] like Figure 14 As shown, we conducted CV tests at different scan rates on the hollow Co3O4 / N-rGO composite material under room temperature and NIR laser irradiation, and compared it with commercial RuO2 material, to calculate the double-layer capacitance (also known as Faraday capacitance or pseudocapacitance). CV tests were performed at different scan rates of 2, 5, 10, 15, 20, and 30 mV / s. The obtained data were processed and extracted, and the slope of the fitted curve is the Faraday capacitance (CdI). The electrochemically active surface area (ECSA) is directly proportional to the double-layer capacitance; therefore, the higher the double-layer capacitance, the larger the electrochemically active surface area, and the better the catalytic activity of the material. Therefore, under NIR laser irradiation, the CdI of the composite material is 10.20 mF cm⁻¹. -2 The Faraday capacitance of the composite material is higher than that of the unilluminated material (CdI = 7.44 mF cm⁻¹). -2 The commercial RuO2 Faraday capacitance is the lowest (CdI = 1.61 mF cm-). 2 This indicates that the composite material we synthesized has greater advantages in OER, especially under NIR laser irradiation, the composite material can effectively increase the electrochemical active surface area, and further proves that the photothermal effect can improve the activity of OER catalyst.

[0094] Stability testing is one of the important indicators of electrocatalyst performance. We used IT to test the stability of hollow Co3O4 / N-rGO composite materials under NIR laser light and at room temperature, and compared them with commercial RuO2 catalysts. The test was conducted at 1600 rpm / min for 10 h. Figure 15As shown, the stability of the hollow Co3O4 / N-rGO composite material remained at 87% after 10 h at room temperature, with only a 13% decrease. Under NIR laser irradiation, the stability of the hollow Co3O4 / N-rGO composite material was 85%, with a 15% decrease. Although the oxygen production rate of this composite catalyst increased under NIR laser irradiation, the stability values ​​were not significantly different, indicating good stability of the composite material. In contrast, the commercial RuO2 catalyst, as a comparison material, showed a significant decrease in current retention, with only 32% retention after 10 h. These data fully demonstrate that the polymer, as a ligand, can maintain the stability of the catalysis.

[0095] This embodiment utilizes a polymer ligand method to synthesize an amphiphilic PAA-b-PS diblock polymer. The PS in this polymer can undergo π-π conjugation with N-rGO, increasing the stability of the hollow Co3O4 / N-rGO composite material as a catalyst and improving the dispersibility of the nanoparticles. Through continuous modification of the material, a catalyst exhibiting both ORR and OER activities was successfully synthesized. Electrochemical characterization confirmed that the composite material possesses a four-electron transfer pathway, methanol resistance, and excellent ORR characteristics, including a hydrogen peroxide yield of less than 10%. Under NIR laser irradiation, both catalytic properties were significantly improved (the ORR half-wave potential increased by 20 mV at j = 10 mA cm⁻¹). -2 The OER overpotential at the specified current density decreased by 50 mV. Under illumination, the Tafel slopes of both the ORR and OER of the composite material decreased significantly, confirming that the photothermal effect on the composite material can accelerate electron transport on the catalyst surface, lower the chemical reaction energy barrier, and improve catalytic activity. Furthermore, the catalytic stability remained strong under illumination during catalytic stability testing (it). Additionally, the photothermal conversion properties of the hollow Co3O4 / N-rGO composite material were analyzed.

[0096] Example 2: Application of hollow Co3O4 / N-rGO composite material in zinc-air batteries:

[0097] Weigh 6 mg of hollow Co3O4 / N-rGO composite material and disperse it in 1 mL of anhydrous ethanol. Then add 50 μL of 5wt% Nafion as a binder and ultrasonically disperse for 30 minutes. Evenly drop the catalyst material onto a 5*8 mm area of ​​composite carbon paper (inner layer: carbon paper; middle layer: waterproof layer; outer layer: nickel foam), so that the final catalyst loading is 1 mg cm⁻¹. -2The cathode material was used as the battery material. A sandpaper-polished zinc sheet was used as the anode material. For comparison, the commercial Pt / C-RuO2 material was prepared in the same manner as our synthesized material. To ensure long-term battery operation, an electrolyte solution of 6 M KOH solution and 0.2 M zinc acetate was added externally and cyclically mixed. Battery performance was tested and evaluated using the Shanghai Chenhua electrochemical workstation and the Xinwei battery testing system; furthermore, comparisons were made under near-infrared light irradiation and without irradiation, while all other experimental conditions remained the same.

[0098] Under NIR irradiation, the activities of both catalytic activities were significantly enhanced, as shown in Table 3. Ej=10 represents the OER at 10 mV cm⁻¹. -2 overpotential, E 1 / 2 This represents the half-wave potential of the ORR. Potential difference ΔE = Ej - E 1 / 2 ΔE is used to evaluate the reversibility of the composite material's ORR and OER bifunctional catalysis, as well as its performance as the anode and cathode of ZABs. The smaller the ΔE value, the higher the activity and the better the reversibility of the bifunctional catalyst. This also helps to explain the excellent performance of assembled ZABs under NIR irradiation.

[0099] Table 3 Summary of potential difference values ​​for several catalysts under different conditions

[0100]

[0101] like Figure 16 As shown in (a), under NIR laser irradiation, the charge-discharge overpotentials of the polarization curves of the rechargeable ZABs of hollow Co3O4 / N-rGO composite material are lower than those of the unirradiated composite material and the Pt / C-RuO2 electrode, showing a lower charge-discharge voltage difference. This indicates that photothermal effect can reduce the polarization degree of ZABs and accelerate the rapid transport of electrons. Figure 16 (b) is a graph showing the power density of ZABs. It is clear from the graph that the composite material has the highest power under NIR illumination (225 mW cm⁻¹). -2 It is twice that of the unilluminated composite material (113 mW cm⁻¹). -2 The power density of Pt / C-RuO2 is 115 mW / cm². -2 .

[0102] Considering the discharge voltage of ZABs under high current density, discharge tests were conducted using different current densities. For example... Figure 17 As shown in (a), under NIR laser irradiation, the composite material at a current density of 1 mA cm⁻¹ -2 2 mA cm -2 5 mA cm -2 10mA cm -2and 20 mA cm -2 Discharge voltage stability tests were conducted under the specified conditions. The figures clearly show that the voltage under illumination decreased only slightly (corresponding to 1.34 V, 1.33 V, 1.312 V, 1.295 V, and 1.27 V, respectively); while the voltages of ZABs composed of unilluminated composite materials were 1.314 V, 1.302 V, 1.282 V, 1.261 V, and 1.228 V, respectively, showing a significant voltage decrease. For ZABs composed of Pt / C-RuO2, the voltage drop increased more and more with increasing current density (1.31 V, 1.292 V, 1.256 V, 1.204 V, and 1.114 V), indicating very poor performance of air batteries under high current.

[0103] Figure 17 (b) shows the discharge specific capacity under different conditions. At 10 mA cm⁻¹ -2 Under constant current density, long-term discharge tests (specific capacity calculated based on the mass of Zn consumed at the anode) showed that the composite material under illumination exhibited a smaller voltage drop and a discharge specific capacity of 806 mAh g⁻¹. -1 The specific capacity of the unilluminated composite material is 798 mAh g. -1 Both are superior to the discharge specific capacity of commercial Pt / C-RuO2 (766 mAh g). -1 These results reveal that light-assisted composite-assembled ZABs exhibit excellent stability and a large discharge specific capacity at high current densities.

[0104] To ensure the long-term operation of the battery, an external circulation pump is used to continuously add a large amount of electrolyte (6 M KOH + 0.2 M zinc acetate) to the device, flushing away newly generated carbonates and maintaining the battery's long-term operation. Figure 18 As shown in (a), we performed a charge and discharge cycle of 10 minutes each, with a current density of 10 mA / cm². 2In the charge-discharge cycle tests, the material irradiated by NIR laser showed no voltage decay during 186 h (500 cycles). Under illumination, the charging voltage was 1.96 V, the discharging voltage was 1.20 V, and the charge-discharge efficiency was 61.2%. Without illumination, the charging voltage was 2.10 V, the discharging voltage was 1.165 V, and the charge-discharge efficiency was 55.4%. The zinc-air battery composed of Pt / C-RuO2 exhibited poor long-term cycle performance, with a sharp performance degradation after 38 h, possibly attributed to agglomeration and pulverization of the material during operation, leading to the shedding of active material and resulting in performance degradation. The excellent stability of our composite material is attributed to the π-π composite of the polymer ligand PS terminal with graphene oxide, which firmly anchors the hollow Co3O4 material onto the two-dimensional graphene nanosheets, preventing material shedding and pulverization during charge-discharge processes. Figure 18 (bc) To evaluate the practicality of our prepared composite material, two liquid-phase batteries were connected in series with a voltage of approximately 2.830 V. When connected to a light-emitting diode, the diode lit up, indicating that our prepared composite material has great application potential.

[0105] The hollow Co3O4 / N-rGO composite material prepared in this invention not only exhibits outstanding ORR and OER catalytic activity, but also demonstrates excellent performance in ZABs. Especially under NIR laser irradiation, the composite material shows the smallest voltage difference in its charge-discharge polarization curve, indicating that the photo-assisted composite material possesses good charge-discharge performance; its power density is twice that of the un-illuminated composite material, ensuring sufficient long-term battery operation. Under high current density discharge with NIR laser assisted by NIR laser, voltage decay is minimal, promising rapid charge-discharge performance. More importantly, the composite material exhibits extremely high stability in continuous cyclic charge-discharge tests, while the Pt / C-RuO2 catalyst shows early voltage decay. This superior stability is attributed to the π-π composite of the polymer ligand PS terminal and graphene oxide, which firmly anchors the hollow Co3O4 material onto the graphene two-dimensional nanosheets. Furthermore, the assembled zinc-air battery can drive a light-emitting diode, indicating that the composite material designed in this invention has significant practical application potential and will be widely used in energy storage and conversion in the future.

[0106] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A hollow cobalt tetroxide / N-rGO composite material, characterized in that, Its preparation process includes the following steps: (1) Preparation of linear diblock polymers containing hydrophilic and hydrophobic ends; (2) Using ε-Co obtained by thermal decomposition of cobalt source, the ε-Co is attached to the hydrophilic end of a linear diblock polymer to obtain an intermediate material; (3) Combine the Kirkendall effect to transform the intermediate material into hollow Co3O4 nanoparticles; (4) Hollow Co3O4 nanoparticles were combined with nitrogen-doped redox graphene at high temperature to obtain hollow cobalt tetroxide / N-rGO composite material.

2. The hollow cobalt tetroxide / N-rGO composite material according to claim 1, characterized in that: The preparation process of linear diblock polymers containing hydrophilic and hydrophobic ends includes the following steps: (1-1) The first polymer was prepared by initiating polymerization of the catalyst cuprous bromide, the ethyl 2-bromoisobutyrate initiator, the ligand, and the tert-butyl acrylate monomer using an atom transfer radical polymerization method. (1-2) Styrene monomer, as the second block monomer, is polymerized again with the first polymer via ATRP to obtain the second polymer; (1-3) The tert-butyl acrylate monomer has an ester group, and the second polymer obtained is hydrolyzed to hydrophilic carboxyl groups by hydrolysis.

3. The hollow cobalt tetroxide / N-rGO composite material according to claim 2, characterized in that: The ligand is any one of bipyridine, tris[2-(dimethylamino)ethyl]amine, or pentamethyldiethylenetriamine.

4. The hollow cobalt tetroxide / N-rGO composite material according to claim 2, characterized in that: The molar ratio of cuprous bromide, ethyl 2-bromoisobutyrate initiator, ligand and tert-butyl acrylate monomer is (1-10):1:(1-5):(15-120), and the molecular weight of the first polymer is 2k-8k g / mol; the molar ratio of ethyl 2-bromoisobutyrate initiator and styrene is 1:(100-500), and the molecular weight of the second polymer is 6k-20k g / mol.

5. The hollow cobalt tetroxide / N-rGO composite material according to claim 1, characterized in that: In step (2), the linear diblock polymer containing hydrophilic and hydrophobic ends is dissolved to obtain solution one, and the cobalt source octacarbonyl cobalt Co2(CO)8 is dissolved to obtain solution two. Solution one is heated to 100-300℃, and under the protection of an inert gas, solution two is rapidly injected into the heated solution one and reacted to obtain the intermediate material.

6. The hollow cobalt tetroxide / N-rGO composite material according to claim 1, characterized in that: In step (3), the conversion reaction is carried out in an O2 atmosphere at a temperature of 100-300℃ for a reaction time of 3-168 h.

7. The hollow cobalt tetroxide / N-rGO composite material according to claim 1, characterized in that: In step (4), monolayer GO is prepared by the Hummers method; N / rGO is obtained by nitriding GO with any one of urea, ammonia, hydrazine hydrate, ammonia, or nitrogen.

8. The hollow cobalt tetroxide / N-rGO composite material according to claim 1, characterized in that: In step (4), the composite temperature of hollow Co3O4 nanoparticles and nitrogen-doped redox graphene is 100-300℃, and the reaction time is 0.5-48 h.

9. The application of the hollow cobalt tetroxide / N-rGO composite material as described in any one of claims 1-8 as an electrocatalyst.

10. The application of the hollow cobalt tetroxide / N-rGO composite material as described in any one of claims 1-8 in the preparation of the positive electrode for a liquid-phase zinc-air battery.

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