Iridium single atom supported on cobalt oxide-graphene aerogel self-supporting material, preparation method and application thereof
A cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms was prepared by solvothermal method and freeze drying, which solved the problems of scarce iridium-based catalyst reserves and instability of single-atom catalysts, and achieved high efficiency and stability of oxygen reduction performance, which is suitable for commercial application as a water electrolysis catalyst.
Patent Information
- Application Number
- CN202411779185.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-05
- Publication Date
- 2026-02-24
- Estimated Expiration
- 2044-12-05
AI Technical Summary
The scarcity of existing iridium-based catalysts, the instability of active sites in traditional single-atom catalysts, and the challenges of pore control and metal oxide stacking in the synthesis of graphene aerogel composite catalysts have limited the commercialization of water electrolysis catalysts.
A cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms was prepared by combining solvothermal method and freeze-drying. Metal defect sites were formed by solvothermal method, and iridium metal ions were added and anchored in graphene aerogel to form a sandwich structure, which improved catalytic activity and stability.
It achieves efficient dispersion and stable anchoring of iridium single atoms, improves the oxygen reduction performance of the catalyst in alkaline media, has higher onset potential, current density and durability, and reduces the amount of precious metals used.
Smart Images
Figure CN119710813B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrolytic water catalytic materials technology, specifically relating to cobalt oxide-graphene aerogel self-supporting materials loaded with iridium single atoms, their preparation methods and applications. Background Technology
[0002] Hydrogen energy is one of the most ideal clean energy sources and has attracted widespread attention. Water electrolysis, due to its abundant raw materials and compatibility with solar, wind, and tidal power generation systems, has become a promising clean energy conversion technology. Among its components, the electrocatalytic oxygen reduction reaction (ORR) is a core technology that has hindered the large-scale commercialization of water electrolysis. The ORR reaction is significantly influenced by catalyst performance, and the development of universal catalysts suitable for acidic, alkaline, and neutral conditions is urgently needed. Traditional iridium-based catalysts exist as alloys or iridium oxides. However, these precious metals are scarce in nature. Single-atom catalysts, on the other hand, are composed of a single atom, promoting atomic dispersion and abundant surface transition states, exhibiting higher catalytic performance and selectivity compared to traditional catalysts. Therefore, the development of single-atom catalysts is urgently needed to reduce iridium consumption and further advance the development of water electrolysis.
[0003] Anchoring iridium to the catalyst support surface in single-atom form maximizes the utilization of expensive iridium. Simultaneously, the strong interaction between the oxide support and the iridium single atoms results in unique catalytic performance. Metal oxides (TiO2, ZnO, Co3O4, Mn3O4) are the most common electrochemically stable catalyst supports, characterized by low raw material costs, no environmental pollution, and high safety. However, these supports still suffer from poor conductivity and low volumetric activity, limiting their commercialization. Moreover, most commercially available single-atom catalysts currently utilize iridium atoms adsorbed on the surface or anchored at oxygen vacancies. The interaction between the active atoms and the metal oxide support in these systems is relatively weak, and the active sites are relatively unstable, prone to ripening and aggregation, leading to poor catalyst activity and stability.
[0004] Currently, graphene aerogel (3DNG) has shown potential as a novel catalyst support in oxygen reduction catalysts using non-noble metal oxide nanoparticles. Graphene aerogel possesses high conductivity, large specific surface area, chemical stability, and good adhesion, offering significant advantages over traditional supports. Furthermore, the three-dimensional porous network structure of graphene aerogel is beneficial for increasing the active surface area and mass transfer efficiency of the catalyst, thereby enhancing its performance.
[0005] However, the synthesis of graphene aerogel composite catalysts still faces challenges, such as controlling the number, size, and hardness of pores, as well as the stacking of metal oxides and supports. Furthermore, synergistic effects play a crucial role in performance enhancement, but their construction methods and mechanisms require further investigation. Therefore, how to effectively utilize graphene aerogels as catalyst supports and achieve successful applications remains a key issue that needs to be explored. Summary of the Invention
[0006] To address the problems of the prior art, the first objective of this invention is to provide a method for preparing a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms. This method features mild process conditions and simple operation, enabling the preparation of a novel self-supporting catalyst material composed of graphene aerogel (3DNG) and Ir-Co3O4. This method synergistically enhances the electrocatalytic activity and catalytic stability of the catalyst, making it suitable for the preparation and application of electrocatalytic oxygen reduction catalysts.
[0007] A second objective of this invention is to provide a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms prepared by the above-described preparation method.
[0008] A third objective of this invention is to provide the application of the aforementioned cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms.
[0009] One of the objectives of this invention, and the technical solution adopted, is:
[0010] A method for preparing a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms includes the following steps:
[0011] Step (1): Mix the soluble cobalt salt in glycerol to obtain a mixed slurry; subject the mixed slurry to a solvothermal reaction at 170–190°C to obtain a cobalt oxide precursor;
[0012] Step (2): Mix chloroiridic acid, the cobalt oxide precursor, and polyvinyl alcohol aqueous solution, and further add graphene and mix to obtain a hydrogel; replace the unreacted ions in the hydrogel, and then freeze-dry to obtain an aerogel precursor; wherein, the mass ratio of chloroiridic acid, cobalt oxide precursor, and graphene is (18-25):(40-60):(5-10);
[0013] Step (3): Calcine the aerogel precursor to obtain a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms.
[0014] As an improvement, in step (1), the soluble cobalt salt is one or more of cobalt acetate, cobalt oxalate, and cobalt chloride. More preferably, the soluble cobalt salt is cobalt acetate. As a further improvement, the amount of soluble cobalt salt used is 0.5–2.0 g per 30 mL of glycerol.
[0015] As an improvement, in step (1), the solvothermal reaction time is 1–3 hours. Here, solvothermal reaction refers to a reaction carried out in a closed, high-temperature, high-pressure reactor as conventionally understood in the art. In this invention, a solvable cobalt salt is subjected to a solvothermal reaction in a reactor in the presence of glycerol, thereby preparing a uniformly dispersed cobalt oxide precursor that facilitates the construction of metal defect sites.
[0016] As an improved solution, in step (2), the mass concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 15-20 mg / mL; and the relative molecular mass of the polyvinyl alcohol is 50,000-100,000.
[0017] As an improved scheme, the ratio of chloroiridic acid, cobalt oxide precursor, and polyvinyl alcohol aqueous solution is (18-25) mg: (40-60) mg: (600-800) μL.
[0018] As a further improvement, in step (2), when preparing the hydrogel, the graphene added is specifically an aqueous solution of graphene, which is prepared using the Hummers method; the concentration of graphene in the aqueous solution of graphene is 1.8 to 2.2 mg / mL.
[0019] As an improved solution, in step (2), the replacement is carried out by adding a water-methanol mixture; in the water-methanol mixture, the volume percentage of methanol is 5% to 20%, more preferably 10%; the freeze-drying time is 15 to 30 hours.
[0020] As an improved solution, in step (3), the calcination is carried out in a hydrogen / argon mixture; the calcination temperature is 500-700℃ and the calcination time is 8-15h.
[0021] The second objective of this invention is achieved through the following technical solution:
[0022] The above preparation method yields a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms.
[0023] The material prepared by the above-mentioned preparation method in this invention uses cobalt oxide with metal defects as a metal support, and Ir is dispersed in the metal defect sites in the form of single atoms; at the same time, the graphene aerogel forms a robust three-dimensional porous network, which avoids the recombination of graphene and provides a large number of active centers for ORR reaction, thereby maximizing the catalytic performance.
[0024] As a further improved technical solution, in the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, the loading amount of iridium single atoms is 1wt% to 4wt%.
[0025] The third objective of this invention is achieved through the following technical solution:
[0026] The aforementioned cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms is used as a catalyst in the oxygen reduction reaction of the catalytic water electrolysis process.
[0027] Compared with the prior art, the main advantages of the present invention are:
[0028] The present invention provides a method for preparing a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms. First, a solvothermal reaction is performed between soluble cobalt salt and glycerol to form a metal compound with multi-glycerol coordination, thereby creating an oxygen-rich environment. Then, iridium metal ions are added to impregnate the interlayer of the organometallic compound. Next, graphene is added to form an aerogel precursor, and finally, calcination is performed. This process anchors nano-sized single-atom iridium at the defect vacancies of the metal oxide support during the in-situ formation of metal defects, forming a lattice-confined single-atom iridium electrocatalyst material. The above-mentioned synthesis strategy employed in this invention, combining solvothermal self-assembly with freeze-drying, successfully prepared a self-supporting oxygen reduction catalyst material composed of 3DNG and Ir-Co3O4. This catalyst material exhibits a higher onset potential in alkaline media than three-dimensional nitrogen-doped graphene aerogel and nitrogen-doped graphene / cobalt tetroxide composite catalyst (Co3O4 / NG), meaning that the catalyst can effectively promote the oxygen reduction reaction at a lower voltage, exhibiting higher catalytic activity.
[0029] The method described in this invention involves preparing a support precursor via a solvothermal method, loading Ir atoms using an impregnation method, and finally adding graphene to form a hydrogel followed by calcination, thereby obtaining a sandwich-shaped cobalt oxide-graphene aerogel self-supporting electrode material. This catalyst material uses an oxide with metal defect sites as a support, with Ir dispersed in single-atom form within these sites. Furthermore, this invention achieves single-atom-level dispersion of Ir by strictly controlling each reaction condition. Simultaneously, the metal defects in this invention effectively anchor the Ir single atoms, further improving the catalytic stability of the material. In alkaline media, the catalyst exhibits a higher onset potential, electron transfer number, and limiting current density compared to three-dimensional nitrogen-doped graphene aerogels, with a lower hydrogen peroxide yield, and better durability than commercial Pt / C catalysts.
[0030] Furthermore, the metal defect oxide precursor used in this invention has strong designability, is easy to anchor and disperse single atoms, and is conducive to the large-scale preparation of metal oxide-supported iridium single-atom electrocatalysts; and the impregnation solution involved can be collected by centrifugation and reused, which helps to reduce the cost of large-scale production.
[0031] Finally, this invention successfully prepared a sandwich-shaped cobalt oxide-graphene aerogel self-supporting electrode material by creating metal defects through glycerol end-capping and then anchoring single atoms. The single-atom synthesis method successfully developed in this invention effectively overcomes the instability of single-atom catalysts in existing technologies and has high industrial application value. Furthermore, the material provided by this invention exhibits a high half-wave potential, a high electron transfer number, and a low H₂O₂ yield in alkaline media.
[0032] The superior oxygen reduction performance of the catalytic material of this invention is attributed to its excellent structure: 1) 3DNG acts as an electron donor, continuously supplying electrons to Co3O4, providing the necessary conditions for oxygen reduction; 2) The robust three-dimensional porous network prevents the recombination of graphene, provides a large number of active centers for the ORR reaction, maximizes the catalytic activity of the catalyst, and allows for a high diffusion rate of the electrolyte; 3) 3DNG not only maximizes the active sites of the catalyst but also effectively inhibits the aggregation and desorption of catalyst particles, thereby synergistically improving the electrocatalytic activity and catalytic stability of the catalyst, and has strong prospects for industrial application in the field of oxygen reduction catalyst preparation. Attached Figure Description
[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments and test examples are briefly described below; it should be understood that the following drawings only show some test examples of the present invention and should not be regarded as a limitation on the scope of protection of the rights.
[0034] Figure 1 The above are XRD patterns of the cobalt oxide-graphene aerogel self-supporting materials loaded with iridium single atoms in Examples 1-5 of this invention.
[0035] Figure 2 This is an electronic image of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms in Example 1 of the present invention.
[0036] Figure 3 This is a SEM image of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms in Example 1 of the present invention.
[0037] Figure 4 This is a spherical aberration diagram of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms in Example 1 of the present invention.
[0038] Figure 5 The image shows the LSV performance of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms in Example 1 of this invention.
[0039] Figure 6 The image shows the CV performance of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms in Example 1 of this invention.
[0040] Figure 7 This is a graph showing the percentage of peroxide and the number of electrons transferred relative to the potential of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms in Example 1 of the present invention. Detailed Implementation
[0041] To make the technical objectives, solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of protection of this invention. Unless otherwise specified, the raw materials or reagents involved in the following embodiments are all conventional materials or reagents that can be obtained through commercial channels.
[0042] This invention provides a method for preparing a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, comprising the following steps:
[0043] Step (1): Mix the soluble cobalt salt in glycerol to obtain a mixed slurry; subject the mixed slurry to a solvothermal reaction at 170–190°C to obtain a cobalt oxide precursor;
[0044] Step (2): Mix chloroiridic acid, the cobalt oxide precursor, and polyvinyl alcohol aqueous solution, and further add graphene and mix to obtain a hydrogel; replace the unreacted ions in the hydrogel, and then freeze-dry to obtain an aerogel precursor; wherein, the mass ratio of chloroiridic acid, cobalt oxide precursor, and graphene is (18-25):(40-60):(5-10);
[0045] Step (3): Calcine the aerogel precursor to obtain a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms.
[0046] In this invention, there is no particular limitation on the soluble cobalt salt in step (1), and any cobalt salt that is soluble in glycerol and is well known to those skilled in the art can be used. Specifically, the soluble cobalt salt is one or more of cobalt acetate, cobalt oxalate, and cobalt chloride; more preferably, the soluble cobalt salt is cobalt acetate.
[0047] In this invention, for every 30 mL of glycerol, the corresponding amount of soluble cobalt salt is 0.5–2.0 g, more preferably 1 g.
[0048] This invention involves a solvothermal reaction of a soluble cobalt salt in a reaction vessel in the presence of glycerol. The solvothermal reaction is carried out in a sealed, high-temperature, high-pressure reaction vessel. This invention uses a solvothermal reaction to prepare a uniformly dispersed cobalt oxide precursor that facilitates the formation of metal defect sites. Preferably, in step (1), the solvothermal reaction time is 1–3 hours.
[0049] Preferably, step (1) further includes washing and drying the product obtained after the solvothermal reaction. This invention does not impose specific limitations on the washing method; those skilled in the art can use well-known washing methods, as long as they meet the washing requirements of the reactants. For example, the washing method specifically uses alcohol washing, and the solvent used for alcohol washing can be one or more of ethanol, methanol, and isopropanol. In the following examples, alcohol washing is used, and the solvent used for alcohol washing is specifically isopropanol. Furthermore, this invention does not impose specific limitations on the drying method; those skilled in the art can use well-known drying conditions, as long as they meet the drying requirements of the reactants. For example, the drying temperature is 60–90°C, and the drying time is 10–48 hours. In the following examples, the drying temperature is specifically 75°C, and the drying time is specifically 24 hours.
[0050] In this invention, in step (2), the mass concentration of polyvinyl alcohol in the aqueous solution is 15-20 mg / mL; more preferably, the relative molecular mass of polyvinyl alcohol is 50,000-100,000.
[0051] In this invention, in step (2), the ratio of chloroiridic acid, cobalt oxide precursor, and polyvinyl alcohol aqueous solution is (18-25) mg: (40-60) mg: (600-800) μL.
[0052] This invention does not impose any particular limitation on the form of graphene used in the preparation method; any graphene source well known to those skilled in the art can be used. In the following examples, the graphene is specifically added as an aqueous solution; the aqueous solution is prepared using the Hummers method, and the concentration of graphene in the aqueous solution is 1.8–2.2 mg / mL. In other examples, commercially available solid graphene can also be used, which is then prepared into an aqueous solution for use.
[0053] In this invention, in step (2), the graphene is added and mixed evenly by vigorous shaking to form a hydrogel.
[0054] In this invention, in step (2), the displacement is performed by adding a water-methanol mixture; the volume percentage of methanol in the water-methanol mixture is 5% to 20%, more preferably 10%; the freeze-drying time is 15 to 30 hours. This invention does not specifically limit the number of displacements, only requiring that the displacement effect be ensured; preferably, the number of displacements is 2 to 5.
[0055] In this invention, in step (3), calcination is carried out in a hydrogen / argon mixture; the calcination temperature is 500–700°C, and the calcination time is 8–15 h. This invention uses a calcination temperature of 500–700°C, which effectively ensures that the obtained material is a single-atom catalyst material. However, if a temperature below 500°C is used, such as calcination at 400°C, phase analysis shows that the precursor cannot decompose, thus a single-atom catalyst cannot be obtained. Furthermore, if a temperature above 700°C is used, such as calcination at 800°C, phase analysis shows that single atoms overflow and agglomerate to form metal particles, also resulting in the inability to obtain a uniformly dispersed single-atom catalyst.
[0056] In step (3), the present invention does not impose any particular limitation on the calcination atmosphere. In preliminary experiments, the present invention has verified that calcination in air, oxygen, argon, and nitrogen atmospheres does not affect the phase composition of the single-atom catalyst, and therefore will not affect the preparation effect of the material of the present invention. Preferably, in the embodiments of the present invention, calcination is carried out in a hydrogen / argon mixture, wherein the volume percentage of hydrogen in the mixture is 10%.
[0057] Example 1
[0058] This embodiment provides a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, the preparation method of which includes the following steps:
[0059] (1) Add 1g of cobalt acetate to 30mL of glycerol and stir magnetically for 5h to obtain a mixed slurry; transfer the mixed slurry to a reaction vessel with a polytetrafluoroethylene liner, keep the reaction vessel at 180℃ for 2h and then cool it naturally to room temperature; centrifuge, wash with alcohol, dry and collect the obtained reactants to obtain cobalt oxide precursor;
[0060] (2) Dissolve 0.02034 g of chloroiridium acid and 50 mg of the cobalt oxide precursor obtained in step (1) in 625 μL of polyvinyl alcohol (PVA) aqueous solution (concentration 16 mg / mL) to obtain a mixture; then mix the mixture with 3 mL of graphene aqueous solution (2 mg / mL) prepared by Hummers method, and shake vigorously to form a hydrogel; then add water-methanol mixture (methanol volume ratio of 10%) to the hydrogel and soak for 24 h to displace unreacted ions in the hydrogel, and change the replacement solution 3 times during the period; then use the hydrogel as a precursor to obtain an aerogel precursor by freeze drying (24 h);
[0061] (3) The aerogel precursor obtained in step (2) is placed in a mold and calcined at 600°C with a flow rate of 10% H2 / Ar for 12 hours to obtain a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, denoted as Ir-Co3O4-3DNG-PVA aerogel.
[0062] Examples 2-5
[0063] Examples 2-5 each provide a self-supporting material, the preparation method of which is the same as that of Example 1, the only difference being that: in Example 2, the amount of chloroiridium acid is adjusted to 0.00406g, in Example 3, the amount of chloroiridium acid is adjusted to 0.01220g, in Example 4, the amount of chloroiridium acid is adjusted to 0.02848g, and in Example 5, the amount of chloroiridium acid is adjusted to 0g, and the other conditions are the same as those of Example 1.
[0064] Example 6
[0065] This embodiment provides a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, the preparation method of which includes the following steps:
[0066] (1) Add 1g of cobalt acetate to 30mL of glycerol and stir magnetically for 5h to obtain a mixed slurry; transfer the mixed slurry to a reaction vessel with a polytetrafluoroethylene liner, keep the reaction vessel at 180℃ for 2h and then cool it naturally to room temperature; centrifuge, wash with alcohol, dry and collect the obtained reactants to obtain cobalt oxide precursor;
[0067] (2) Dissolve 0.02034 g of chloroiridium acid and 50 mg of the cobalt oxide precursor obtained in step (1) in 720 μL of PVA solution (concentration 16 mg / mL) to obtain a mixture; then mix the mixture with 3 mL of graphene aqueous solution (2 mg / mL) prepared by Hummers method, and shake vigorously to form a hydrogel; then add water-methanol mixture (methanol volume ratio of 10%) to the hydrogel and soak for 24 h to displace unreacted ions in the hydrogel, and change the replacement solution 3 times during the period; then use the hydrogel as a precursor to obtain an aerogel precursor by freeze drying (24 h);
[0068] (3) The aerogel precursor obtained in step (2) is placed in a mold and calcined at 600°C with a flow rate of 10% H2 / Ar for 12 hours to obtain a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, denoted as Ir-Co3O4-3DNG-PVA aerogel.
[0069] Example 7
[0070] This embodiment provides a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, the preparation method of which includes the following steps:
[0071] (1) Add 1g of cobalt acetate to 30mL of glycerol and stir magnetically for 5h to obtain a mixed slurry; transfer the mixed slurry to a reaction vessel with a polytetrafluoroethylene liner, keep the reaction vessel at 180℃ for 2h and then cool it naturally to room temperature; centrifuge, wash with alcohol, dry and collect the obtained reactants to obtain cobalt oxide precursor;
[0072] (2) Dissolve 0.02034 g of chloroiridium acid and 50 mg of the cobalt oxide precursor obtained in step (1) in 625 μL of PVA solution (concentration 16 mg / mL) to obtain a mixture; then mix the mixture with 5 mL of graphene aqueous solution (2 mg / mL) prepared by Hummers method, and shake vigorously to form a hydrogel; then add water-methanol mixture (methanol volume ratio of 10%) to the hydrogel and soak for 24 h to displace unreacted ions in the hydrogel, and change the replacement solution 3 times during the period; then use the hydrogel as a precursor to obtain an aerogel precursor by freeze drying (24 h);
[0073] (3) The aerogel precursor obtained in step (2) is placed in a mold and calcined at 600°C with a flow rate of 10% H2 / Ar for 12 hours to obtain a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, denoted as Ir-Co3O4-3DNG-PVA aerogel.
[0074] Example 8
[0075] This embodiment provides a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, the preparation method of which includes the following steps:
[0076] (1) Add 1g of cobalt acetate to 30mL of glycerol and stir magnetically for 5h to obtain a mixed slurry; transfer the mixed slurry to a reaction vessel with a polytetrafluoroethylene liner, keep the reaction vessel at 180℃ for 2h and then cool it naturally to room temperature; centrifuge, wash with alcohol, dry and collect the obtained reactants to obtain cobalt oxide precursor;
[0077] (2) Dissolve 0.02034 g of chloroiridium acid and 40 mg of the cobalt oxide precursor obtained in step (1) in 625 μL of PVA solution (concentration 16 mg / mL) to obtain a mixture; then mix the mixture with 3 mL of graphene aqueous solution (2 mg / mL) prepared by Hummers method, and shake vigorously to form a hydrogel; then add water-methanol mixture (methanol volume ratio of 10%) to the hydrogel and soak for 24 h to displace unreacted ions in the hydrogel, and change the replacement solution 3 times during the period; then use the hydrogel as a precursor to obtain an aerogel precursor by freeze drying (18 h);
[0078] (3) The aerogel precursor obtained in step (2) is placed in a mold and calcined at 600°C with a flow rate of 10% H2 / Ar for 12 hours to obtain a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, denoted as Ir-Co3O4-3DNG-PVA aerogel.
[0079] Experimental Example 1: Material Structure Analysis
[0080] X-ray diffraction (XRD) analysis was performed on the self-supporting materials prepared in Examples 1-5 of this invention. Furthermore, the cobalt oxide-graphene aerogel loaded with iridium single atoms prepared in Example 1 was analyzed by electronic appearance, scanning electron microscopy (SEM), and spherical aberration electron microscopy. The results are as follows: Figures 1-5 As shown. Among them, Figure 1 The XRD patterns are of the self-supporting materials prepared in Examples 1-5 of this invention. Figure 2 The image shows the electronic appearance of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms prepared in Example 1. Figure 3 This is a SEM image of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms prepared in Example 1. Figure 4 The image shows the spherical aberration of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms prepared in Example 1.
[0081] from Figure 1As can be seen from the XRD patterns, the materials prepared in Examples 1 to 5 of this invention all have a cobalt tetroxide crystal structure, and no diffraction peaks of other impurity phases appear.
[0082] Depend on Figure 2 As can be seen from the electronic images, the self-supporting material obtained after calcination in the mold in Example 1 has a rich macroporous structure inside.
[0083] Depend on Figure 3 The SEM images show that Co3O4 nanoparticles are uniformly embedded within the graphene aerogel, a structure with significant advantages. Unlike surface-supported catalysts, this structure effectively increases the loading mass of metal oxides. The graphene sheets act like armor, encasing the octahedral nanoparticles between the layers, increasing the contact area between Co3O4 and graphene and preventing the aggregation of metal oxides. Furthermore, this robust three-dimensional porous network structure provides a large number of active centers that can participate in the reaction, thereby maximizing the activity of the ORR catalyst.
[0084] Depend on Figure 4 The aberration diagram shows that atoms in different phases are regularly and uniformly distributed, with Ir atoms exhibiting a single-atom distribution, which can reduce the noble metal loading and improve atom utilization.
[0085] Experimental Example 2: Material Property Testing
[0086] This experimental example tests the performance of the cobalt oxide-graphene aerogel self-supporting material (Ir-Co3O4-3DNG-PVA) loaded with iridium single atoms prepared in Example 1. The LSV performance was tested using linear voltammetry with a scan potential range of 0-1.2V and a scan rate of 10mV / s under alkaline conditions. The CV performance was tested using cyclic voltammetry with a scan potential range of 0-1.2V and a scan rate of 10mV / s. To further quantify the oxygen reduction electron transfer pathway of the aerogel, this invention employs rotating ring-disk electrode (RRDE) technology to measure the H2O2 yield generated on the ring-disk electrode. The ratio of the ring current to the total measured current was normalized by a calibrated collection efficiency (0.37) to estimate the fraction of peroxides generated. The peroxide percentage and electron transfer number were tested at a rotation speed of 1600 rpm.
[0087] in, Figure 5 The LSV performance spectrum of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms in Example 1 is shown. Figure 6 The CV performance spectrum of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms in Example 1 is shown. Figure 7The graph shows the percentage of peroxide and the number of electrons transferred relative to the potential of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms in Example 1.
[0088] Figure 5 In the sample, “3DNG” is a sample of nitrogen-doped graphene aerogel without iridium loading, which is a commercially available product; “Co3O4-3DNG-PVA” is prepared according to the preparation method of Example 1, but without adding iridium compounds, that is, iridium chloride in step (2) of Example 1 is omitted during preparation, and other conditions and process parameters remain unchanged. The resulting catalyst is Co3O4-3DNG-PVA. Figure 6 In this context, "3DNG" has the same meaning as above. The preparation method of "Co3O4-3DNG" is based on Example 1, except that the iridium chloride and PVA solution in step (2) are omitted, and only 50 mg of the cobalt oxide precursor obtained in step (1) is mixed with 3 mL of graphene solution. Other conditions and process parameters remain unchanged, and the material is obtained.
[0089] Depend on Figure 5 The LSV spectra show that the Ir-Co3O4-3DNG-PVA catalyst prepared in Example 1 of this invention has a higher onset potential compared to 3DNG and Co3O4-3DNG-PVA catalysts, effectively promoting the oxygen reduction reaction at lower voltages and exhibiting higher catalytic activity. Furthermore, the LSV curve of the catalyst in Example 1 exhibits a typical S-shaped curve, with the oxygen reduction reaction initiating at 0.91V, followed by the generation of an oxygen reduction current. Subsequently, as the potential shifts negatively, the oxygen reduction current increases significantly until a very obvious gentle slope appears. When the potential drops below 0.70V, the oxygen reduction reaction enters the diffusion-controlled region, and a current plateau appears in the polarization curve, but the plateau region still has a relatively weak current slope.
[0090] Depend on Figure 6 It can be seen that the cyclic voltammetric curve of the catalyst material prepared in Example 1 of this invention has more obvious peaks, indicating that it has better redox performance. The peaks of the other two catalyst materials (3DNG and Co3O4-3DNG) are not obvious, especially 3DNG, which has no obvious redox peaks.
[0091] Depend on Figure 7 The results show that the cobalt oxide-graphene aerogel self-supporting material with iridium single atoms loaded in Example 1 had a peroxide fraction of less than 20% in the range of 0.1-0.9V and an electron transfer number of about 3.8 during the test, which proves that the catalyst has very good electron selectivity.
[0092] In summary, the method for preparing a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms provided by this invention utilizes a solvothermal reaction between soluble cobalt salt and glycerol to form a metal-organic compound with multiple glycerol coordination to create an oxygen-rich environment. Iridium metal ions are then added to impregnate the interlayer of the metal-organic compound. Graphene is then added to form an aerogel precursor, followed by calcination. This process anchors nano-sized single-atom iridium at the defect vacancies of the metal oxide support during the in-situ formation of metal defects, forming a lattice-confined single-atom iridium electrocatalyst material. The method of this invention achieves single-atom-level dispersion of Ir, and the metal defects effectively anchor the Ir single atoms. The graphene aerogel forms a robust three-dimensional porous network, thereby synergistically improving electrocatalytic activity and catalytic stability, making it suitable for the preparation and application of oxygen reduction catalysts.
Claims
1. A method for preparing a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, characterized in that, Includes the following steps: Step (1): Mix the soluble cobalt salt in glycerol to obtain a mixed slurry; subject the mixed slurry to a solvothermal reaction at 170~190℃ to obtain a cobalt oxide precursor; Step (2): Mix chloroiridic acid, the cobalt oxide precursor, and polyvinyl alcohol aqueous solution, and further add graphene and mix to obtain a hydrogel; replace the unreacted ions in the hydrogel, and then freeze-dry to obtain an aerogel precursor; wherein, the mass ratio of chloroiridic acid, cobalt oxide precursor, and graphene is (18~25):(40~60):(5~10); Step (3): The aerogel precursor is calcined to obtain a cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms; the calcination is carried out in a hydrogen / argon mixed gas; the calcination temperature is 500~700℃ and the calcination time is 8~15h.
2. The method for preparing the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms according to claim 1, characterized in that, In step (1), the soluble cobalt salt is one or more of cobalt acetate, cobalt oxalate, and cobalt chloride; for every 30 mL of glycerol, the amount of soluble cobalt salt used is 0.5~2.0 g.
3. The method for preparing the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms according to claim 1, characterized in that, In step (1), the solvothermal reaction takes 1 to 3 hours.
4. The method for preparing the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms according to claim 1, characterized in that, In step (2), the polyvinyl alcohol aqueous solution contains a polyvinyl alcohol concentration of 15~20 mg / mL; the relative molecular mass of the polyvinyl alcohol is 50,000~100,000.
5. The method for preparing the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms according to any one of claims 1 to 4, characterized in that, The ratio of chloroiridic acid, cobalt oxide precursor, and polyvinyl alcohol aqueous solution is (18~25) mg: (40~60) mg: (600~800) μL.
6. The method for preparing the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms according to any one of claims 1 to 4, characterized in that, In step (2), the displacement is carried out by adding a water-methanol mixture; the volume percentage of methanol in the water-methanol mixture is 5%~20%; the freeze-drying time is 15~30h.
7. A cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, prepared by the preparation method according to any one of claims 1 to 6.
8. The cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms according to claim 7, characterized in that, In the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms, the loading amount of iridium single atoms is 1wt%~4wt%.
9. An application of the cobalt oxide-graphene aerogel self-supporting material loaded with iridium single atoms as described in claim 7, characterized in that, Application of catalysts in the oxygen reduction reaction of catalytic water electrolysis process.