Cobalt complex pre-catalyst for electrocatalytic oxygen evolution and preparation method thereof

Abstract

The invention discloses a cobalt complex pre-catalyst for electrocatalytic oxygen evolution and a preparation method thereof, and relates to the technical field of functional complexes. The structure of the cobalt complex pre-catalyst (CotPBA-anion) is formed by coordination of a cobalt coordination cation unit chelated by tPBA and an anion; the structure of the catalyst is CoOOH / tPBA, and the catalyst is characterized in that the catalyst is cobalt oxyhydroxide loaded by an organic ligand. Wherein the CoOOH / tPBA reconstructed by using the CotPBA-Cl shows the optimal electrochemical activity and stability. The pre-catalyst is simple in preparation process and mild in reaction condition, and shows good electro-catalytic oxygen evolution reaction activity and electrochemical stability after simple reconstruction.

Description

Technical Field

[0001] This invention relates to the field of functional complex technology, specifically to a cobalt complex precatalyst for electrocatalytic oxygen evolution and its preparation method. Background Technology

[0002] Through water electrolysis technology, intermittent electrical energy is converted into high energy density (120 MJ kg). –1 Hydrogen from water electrolysis is beneficial for achieving sustainable energy. The efficiency of water electrolysis largely depends on the oxygen evolution reaction (OER), whose slow, multi-step proton-coupled electron transfer process limits the energy conversion efficiency of electrocatalytic devices. Although noble metals such as ruthenium and iridium are widely used as benchmark catalysts for OER, their high cost and scarcity make large-scale industrial application difficult. In this direction, significant efforts have been devoted to developing abundant transition metal catalysts to improve OER efficiency. Simultaneously, organic ligands are used to modulate the electronic and coordination structures of transition metals, improving their OER kinetics and thermodynamics, thereby positively adjusting the catalytic reaction pathway and lowering the energy barrier required for the reaction. Therefore, complexes constructed from organic ligands and transition metals are considered potential candidate materials.

[0003] During the OER process, coordination compounds undergo dynamic reconstruction, which alters the local electronic and stereochemical structures of their metal centers, thereby enhancing their electrochemical activity and kinetic properties. Therefore, coordination compounds are often used as precatalysts for constructing highly active OER catalysts. However, the complex reconstruction process makes it difficult to directionally design the coordination compound structure. Some studies have shown that designing ligand structures and coordination interactions can facilitate the effective reconstruction of coordination compounds into highly active catalysts. In particular, constructing coordination compound precatalysts with weak metal-ligand interactions can induce deep reconstruction of their coordination and framework structures during the OER process. In short, the partial dissolution of ligands on the surface of the coordination compound precatalyst promotes the effective exposure of metal sites and the asymmetric modulation of electronic structures, leading to the effective generation of the OER active phase. Therefore, a thorough and comprehensive understanding of the surface microenvironment changes of coordination compound precatalysts during the reconstruction process is beneficial for better controlling their positive transformation into the active phase. Summary of the Invention

[0004] To address the shortcomings of the aforementioned background technology, this invention provides a cobalt complex precatalyst for electrocatalytic oxygen evolution and its preparation method. This method uses an electrochemical approach to convert the cobalt complex precatalyst into a metal-organic hybrid catalyst that can be used to catalyze the OER reaction.

[0005] The first objective of this invention is to provide a cobalt complex precatalyst for electrocatalytic oxygen evolution, wherein the structure of the cobalt complex precatalyst is composed of a cobalt cation unit chelated by tPBA and coordinated with an anion; Wherein, tPBA is tris((1-(pyridin-4-methyl)-1H-benzo[d]imidazol-2-yl)methyl)amine; the anion is chloride ion, formate ion or nitrate ion; The cobalt complex precatalyst is triclinic.

[0006] Preferably, the cobalt complex precatalyst is transformed into a metal-organic hybrid catalyst through electrochemical activation.

[0007] Preferably, the molecular formula of the cobalt complex precatalyst includes [Co(tPBA)Cl]·Cl, [Co(tPBA)FA]·NA, or [Co(tPBA)NA]·NA; Wherein, Cl represents chloride ions, FA represents formate ions, and NA represents nitrate ions.

[0008] The second objective of this invention is to provide a method for preparing a cobalt complex precatalyst for electrocatalytic oxygen evolution, comprising the following steps: After dissolving cobalt salt and tPBA in an organic solution, they are mixed evenly with deionized water and then sealed to obtain a mixed solution. The mixed solution was reacted at 80~100℃ for 60~80h to obtain the reaction solution; The reaction solution was collected, washed, dried, and ground sequentially to obtain a cobalt complex precatalyst for electrocatalytic oxygen evolution.

[0009] Preferably, the cobalt salt is cobalt chloride hexahydrate or cobalt nitrate hexahydrate; The molar ratio of the cobalt salt to tPBA is 1:0.5~1.5.

[0010] Preferably, the organic solvent is N,N-dimethylacetamide or N,N-dimethylformamide; The volume ratio of the organic solvent to deionized water is 1:1 to 10.

[0011] The third objective of this invention is to provide an application of a cobalt complex precatalyst for electrocatalytic oxygen evolution in the preparation of organometallic hybrid catalysts.

[0012] The fourth objective of this invention is to provide a metal-organic hybrid catalyst, employing a cobalt complex precatalyst in 1M KOH at a rate of 10 mA / cm⁻¹. 2 The catalyst was prepared by constant current density activation for 30 minutes; the structure of the metal-organic hybrid catalyst is tPBA-supported cobalt hydroxyoxide.

[0013] The fifth objective of this invention is to provide an application of a cobalt complex precatalyst for electrocatalytic oxygen evolution in electrocatalytic oxygen evolution.

[0014] The sixth objective of this invention is to provide an application of a metal-organic hybrid catalyst in electrocatalytic oxygen evolution.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a cobalt complex precatalyst for electrocatalytic oxygen evolution and its preparation method. The cobalt complex precatalyst of this invention uses tPBA as a ligand, Cl, FA, or NA as coordinating anions, and Co as the metal center. It features low raw material cost, low metal usage with high utilization rate, avoids the use of precious metals, and has a simple preparation method suitable for large-scale industrial use. Through simple electrochemical reconstruction, it can be transformed into a highly active and stable OER electrocatalyst. This effectively solves the problems of poor OER stability of complex materials and low OER activity of pure transition metal materials. Attached Figure Description

[0016] Figure 1 Synthetic route diagram for CotPBA-anion; Figure 2 A three-dimensional structural diagram of CotPBA-anion; Figure 3 XRD and microscope images of CotPBA-anion powder; Figure 4 Constant current reconstruction for CotPBA-anion; Figure 5 TEM image of CoOOH / tPBA; Figure 6 The energy spectrum of CoOOH / tPBA is shown below. Figure 7 XRD pattern of CoOOH / tPBA powder; Figure 8 OER performance testing of CoOOH / tPBA; Figure 9 The OER Faraday efficiency of CoOOH / tPBA; Figure 10 OER stability test of CoOOH / tPBA; Figure 11 This is a single-crystal structure model of CotPBA-anion. Detailed Implementation

[0017] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0018] This invention aims to provide a cobalt complex precatalyst for electrocatalytic oxygen evolution and its preparation method. The complex precatalyst is CotPBA-anion, where tPBA represents tris((1-(pyridin-4-methyl)-1H-benzo[d]imidazol-2-yl)methyl)amine, and anion represents the coordinating anion Cl, FA, or NA, where Cl is chloride ion, FA is formate ion, and NA is nitrate ion. The structural feature of CotPBA-anion is that cobalt ions and organic ligands form a stable three-dimensional supramolecular framework through co-coordination with anion. The catalyst derived from CotPBA-anion through in-situ electrochemical reconstruction has the structure CoOOH / tPBA, characterized by cobalt hydroxyl oxide supported on organic ligands. Among them, CoOOH / tPBA reconstructed with CotPBA-Cl exhibits the best electrochemical activity and stability. The preparation process of this precatalyst is simple, the reaction conditions are mild, and it exhibits good electrocatalytic oxygen evolution reaction activity and electrochemical stability after simple reconstruction.

[0019] To achieve the above objectives, the first aspect of the present invention provides a cobalt complex precatalyst for electrocatalytic oxygen evolution, wherein the structure of the cobalt complex precatalyst is composed of a cobalt cation unit chelated by tPBA and coordinated with an anion; Wherein, tPBA is tris((1-(pyridin-4-methyl)-1H-benzo[d]imidazol-2-yl)methyl)amine; the anion is chloride ion, formate ion or nitrate ion; The cobalt complex precatalyst is triclinic.

[0020] The cobalt complex precatalyst is transformed into a metal-organic hybrid catalyst through electrochemical activation.

[0021] The molecular formula of the cobalt complex precatalyst includes [Co(tPBA)Cl]·Cl, [Co(tPBA)FA]·NA, or [Co(tPBA)NA]·NA; wherein Cl is chloride ion, FA is formate ion, and NA is nitrate ion.

[0022] In this invention, cobalt complex precatalysts with the molecular formulas [Co(tPBA)Cl]·Cl, [Co(tPBA)FA]·NA, or [Co(tPBA)NA]·NA are named CotPBA-Cl, CotPBA-FA, and CotPBA-NA, respectively. The single-crystal structure model of this complex precatalyst is shown in [link to relevant documentation]. Figure 11 As shown.

[0023] A second aspect of this invention provides a method for preparing a cobalt complex precatalyst for electrocatalytic oxygen evolution, comprising the following steps: After dissolving cobalt salt and tPBA in an organic solution, they are mixed evenly with deionized water and then sealed to obtain a mixed solution. The mixed solution was reacted at 80~100℃ for 60~80h to obtain the reaction solution; The reaction solution was collected, washed, dried, and ground sequentially to obtain a cobalt complex precatalyst for electrocatalytic oxygen evolution.

[0024] The preparation process of this invention is essentially a self-assembly of metal ions and organic ligands driven by coordination reactions. Its core mechanism lies in the initial interaction between cobalt ions and the tripod-tetradentate chelate ligand tPBA in an organic / water mixed solvent system to construct [CotPBA]. 2+ The cation-coordinating unit, characterized by a remaining single coordination site, can further coordinate with different anions generated from the decomposition of cobalt salts or solvents, especially chloride, formate, and nitrate ions, to form a complex precatalyst. The type of solvent, reaction temperature, and the type of metal salt and its molar ratio with the organic ligand are key parameters controlling the final product type and crystallinity. For example, by adjusting the appropriate solvent type and reaction temperature, stable single-crystal complex precatalysts can be synthesized; while adjusting the type of metal salt and organic solvent can generate precatalysts with different anion coordination; adjusting the molar ratio of reactants is crucial for generating a single-phase, high-purity product.

[0025] The cobalt salt is cobalt chloride hexahydrate or cobalt nitrate hexahydrate; The molar ratio of the cobalt salt to tPBA is 1:0.5~1.5.

[0026] The organic solvent is N,N-dimethylacetamide or N,N-dimethylformamide; The volume ratio of the organic solvent to deionized water is 1:1 to 10.

[0027] For example, in the preparation of CotPBA-Cl, the metal salt is cobalt chloride hexahydrate, the organic solution is N,N-dimethylacetamide, the molar ratio of metal salt to tPBA is 1:1, and the volume ratio of organic solution to deionized water is 3:4.

[0028] For example, in the preparation of CotPBA-FA, the metal salt is cobalt nitrate hexahydrate, the organic solution is N,N-dimethylformamide, the molar ratio of metal salt to tPBA is 1:1, and the volume ratio of organic solution to deionized water is 0.5:4.5.

[0029] For example, in the preparation of CotPBA-NA, the metal salt is cobalt nitrate hexahydrate, the organic solution is N,N-dimethylacetamide, the molar ratio of metal salt to tPBA is 1:1, and the volume ratio of organic solution to deionized water is 3:4.

[0030] A third aspect of the present invention provides the application of a cobalt complex precatalyst for electrocatalytic oxygen evolution in the preparation of organometallic hybrid catalysts.

[0031] A fourth aspect of the present invention provides a metal-organic hybrid catalyst, which employs a cobalt complex precatalyst in 1 MKOH at a speed of 10 mA / cm². 2 The catalyst was prepared by activation at a constant current density for 30 minutes; the structure of the metal-organic hybrid catalyst is tPBA-supported cobalt hydroxyoxide, i.e., CoOOH / tPBA. The fifth aspect of the present invention provides the application of a cobalt complex precatalyst for electrocatalytic oxygen evolution in electrocatalytic oxygen evolution.

[0032] The sixth aspect of this invention provides the application of a metal-organic hybrid catalyst in electrocatalytic oxygen evolution.

[0033] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0034] Example 1 The preparation method of CotPBA-Cl is as follows: Cobalt chloride hexahydrate (23.79 mg, 0.1 mmol) and tPBA (68.08 mg, 0.1 mmol) were dissolved in 3 mL of DMA and placed in a 10 mL pressure-resistant reaction flask. Then, 4 mL of deionized water was added to the flask, and the mixture was sonicated for 30 minutes until fully mixed. The flask was then incubated at 90 °C for 72 hours. After natural cooling and filtration, purple CotPBA-Cl block crystals were obtained. The crystals were washed three times with a 1:3 mixture of ethanol and water and then dried at 45 °C for 5 hours.

[0035] Example 2 The preparation method of CotPBA-FA is as follows: Cobalt nitrate hexahydrate (29.10 mg, 0.1 mmol) and tPBA (68.08 mg, 0.1 mmol) were dissolved in 0.5 mL of DMF and placed in a 10 mL pressure-resistant reaction flask. Then, 4.5 mL of deionized water was added to the flask, and the mixture was sonicated for 30 minutes until fully mixed. The flask was then incubated at 90 °C for 72 hours. After natural cooling and filtration, red CotPBA-FA block crystals were obtained. The crystals were washed three times with a 1:3 mixture of ethanol and water and then dried at 45 °C for 5 hours.

[0036] Example 3 The preparation method of CotPBA-NA is as follows: Cobalt nitrate hexahydrate (29.10 mg, 0.1 mmol) and tPBA (68.08 mg, 0.1 mmol) were dissolved in 3 mL of DMA and placed in a 10 mL pressure-resistant reaction flask. Then, 4 mL of deionized water was added to the flask, and the mixture was sonicated for 30 minutes until fully mixed. The flask was then incubated at 90 °C for 72 hours. After natural cooling and filtration, magenta-red CotPBA-NA block crystals were obtained. The crystals were washed three times with a 1:3 mixture of ethanol and water and then dried at 45 °C for 5 hours.

[0037] Example 4 The electrochemical reconstruction method is as follows: Electrochemical reconstruction was performed using a three-electrode system on a CHI 760E electrochemical workstation. A carbon rod electrode and Hg / HgO were used as the counter and reference electrodes, respectively. The working electrode was prepared by ink deposition on a conductive carbon paper substrate, with a working area of ​​1 × 1 cm⁻¹. 2 The loading capacity was 0.2 mg / cm³. -2 To prepare the ink, 5 mg of powder, 700 μL of deionized water, 30 μL of 5% Nafion solution, and 270 μL of ethanol were mixed and sonicated at room temperature for 30 minutes until the mixture was uniformly suspended. Before preparing the ink, the CotPBA anion was ground in an agate mortar for 20 minutes.

[0038] Working electrodes prepared from CotPBA-Cl, CotPBA-FA, and CotPBA-NA respectively, as provided in Examples 1-3, were subjected to oxidation in 1 M KOH at 10 mA / cm⁻¹. 2 The reconstructed CoOOH / tPBA catalyst was prepared by constant current density activation for 30 minutes.

[0039] To illustrate the cobalt complex precatalyst for electrocatalytic oxygen evolution provided by this invention, the following description is provided in conjunction with the accompanying drawings. It should be noted that CotPBA-anion includes CotPBA-Cl, CotPBA-FA, and CotPBA-NA.

[0040] Figure 1The synthetic route for CotPBA anions is shown below, involving the reaction of tPBA ligands with cobalt nitrate in N,N-dimethylacetamide (DMA) to yield cobalt-coordinated CotPBA-NA molecules. Replacing DMA with N,N-dimethylformamide (DMF), which has lower thermal stability, causes DMF to decompose into FA, which then competes for coordination with NA, forming CotPBA-FA molecules. Using cobalt chloride as the metal source and reacting it in DMA yields Cl-coordinated CotPBA-Cl. SC-XRD analysis indicates that all three CotPBA anions are in the triclinic crystal system. Crystallized within a space group. Single-crystal structural models show that its structural units consist of [CotPBA]. 2+ The coordinating cation is formed together with a monodentate anion ligand NA, FA, or Cl, and the coordinating cation contains a tripentate ligand. κ The 4-tPBA ligand chelates a cobalt metal center.

[0041] Figure 2 The three-dimensional structural model of CotPBA-anion shows that the constructed CotPBA-anion molecule can assemble into hexagonal units through π-stacking interactions between the benzimidazole and pyridine rings, forming different open cavities. These hexagonal units can then assemble into a two-dimensional supramolecular structure. Further assembly into a three-dimensional supramolecular framework is possible through π-stacking interactions between pyridine rings (CotPBA-FA and CotPBA-NA), or through atypical CH···Cl / π hydrogen bonding interactions (CotPBA-Cl).

[0042] Figure 3 The XRD and microscopic images of CotPBA-anion powder confirm the phase purity and crystallinity of the material.

[0043] Figure 4 The galvanostatic activation curves for the three complex precatalysts are shown. In the first 5 minutes, CotPBA-Cl exhibits a faster potential decrease rate (~2.2 mV min). -1 The descent rate of CotPBA-FA is approximately ~0.8 mV min. -1 Between 10 and 30 minutes, the potential decrease rates of CotPBA-Cl and CotPBA-FA tended to be consistent (approximately 0.3 mV min). -1 [CotPBA] coordinates with NA. 2+ A significant potential drop (approximately 0.6 mV min) was observed only in the first 5 minutes. -1 This phenomenon is attributed to the blocking effect of its internal microstructure. The figure confirms that CotPBA-Cl can be electrochemically reconstituted into the OER active phase CoOOH / tPBA more quickly and efficiently.

[0044] Figure 5 Transmission electron microscopy (TEM) images of CoOOH / tPBA reconstructed from CotPBA-Cl show a wrinkled, uniformly distributed nanosheet structure (a). High-resolution transmission electron microscopy (HRTEM) reveals observable short-range ordered regions in the wrinkled areas of the reconstructed CotPBA-Cl (b), a phenomenon further validated by selected area electron diffraction (SAED) results (c).

[0045] Figure 6 Energy dispersive spectroscopy (EDS) analysis of CoOOH / tPBA after CotPBA-Cl reconstruction showed that the Cl species signal disappeared after reconstruction, the O / Co element signal in the folded region was enhanced, while the C / N elements remained uniformly distributed on the substrate, indicating the formation of an active mixed phase composed of tPBA and cobalt oxide.

[0046] Figure 7 The P-XRD diffraction pattern of CoOOH / tPBA after CotPBA-Cl reconstruction is shown. The characteristic diffraction peaks of CotPBA-Cl gradually disappear over time, while diffraction peaks belonging to tPBA appear. This confirms that CotPBA-Cl evolves into the pure tPBA crystalline phase during the cobalt species rearrangement process.

[0047] Experiment Example 5: Electrochemical Testing Electrochemical performance and Faraday efficiency were tested using a three-electrode system on a CHI 760E electrochemical workstation, while stability was tested using a two-electrode system. A carbon rod electrode (platinum-carbon supported on carbon paper for stability testing) and Hg / HgO were used as the counter and reference electrodes, respectively. The working electrode was fabricated by ink deposition on a conductive carrier, nickel foam, with a working area of ​​1 × 1 cm⁻¹. 2 (0.2 mg cm) -2 To prepare the ink, 5 mg of CotPBA-Cl, 700 μL of deionized water, 30 μL of 5% Nafion solution, and 270 μL of ethanol were mixed and sonicated at room temperature for 30 minutes until the mixture was uniformly suspended. Before preparing the ink, CotPBA-Cl was ground in an agate mortar for 20 minutes. Linear sweep voltammetry was performed at 5 mV s. -1 The rate was recorded. 95% iR compensation was performed using the resistance value measured at open circuit potential. The Faraday efficiency of CoOOH / tPBA was tested using the water displacement method.

[0048] Figure 8 OER performance testing of CoOOH / tPBA after CotPBA-Cl reconstruction. η 10 The overpotential is only 289 mV.

[0049] Figure 9 The OER Faradaic efficiency of CoOOH / tPBA after CotPBA-Cl reconstruction, determined by the water displacement method, is stable at ~98.6%.

[0050] Figure 10 The stability of the CoOOH / tPBA reconstituted with CotPBA-Cl as the anode electrode was tested for complete water splitting. This electrolytic cell achieved 100 mA cm⁻¹ at a cell voltage of 1.61 V. -2 Current density. Furthermore, this electrolytic cell operates at 100 to 500 mA cm⁻¹. -2 At a stepped current density, continuous water electrolysis operation can be achieved for more than 150 hours.

[0051] Although embodiments of the present invention have been shown and described above, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cobalt complex precatalyst for electrocatalytic oxygen evolution, characterized in that, The structure of the cobalt complex precatalyst consists of a cobalt cation unit chelated with tPBA and coordinated with an anion. Wherein, tPBA is tris((1-(pyridin-4-methyl)-1H-benzo[d]imidazol-2-yl)methyl)amine; the anion is chloride ion, formate ion or nitrate ion; The cobalt complex precatalyst is triclinic.

2. The cobalt complex precatalyst for electrocatalytic oxygen evolution according to claim 1, characterized in that, The cobalt complex precatalyst is transformed into a metal-organic hybrid catalyst through electrochemical activation.

3. The cobalt complex precatalyst for electrocatalytic oxygen evolution according to claim 1, characterized in that, The molecular formula of the cobalt complex precatalyst includes [Co(tPBA)Cl]·Cl, [Co(tPBA)FA]·NA, or [Co(tPBA)NA]·NA; Wherein, Cl represents chloride ions, FA represents formate ions, and NA represents nitrate ions.

4. A method for preparing a cobalt complex precatalyst for electrocatalytic oxygen evolution according to any one of claims 1 to 3, characterized in that, Includes the following steps: After dissolving cobalt salt and tPBA in an organic solution, they are mixed evenly with deionized water and then sealed to obtain a mixed solution. The mixed solution was reacted at 80~100℃ for 60~80h to obtain the reaction solution; The reaction solution was collected, washed, dried, and ground sequentially to obtain a cobalt complex precatalyst for electrocatalytic oxygen evolution.

5. The method for preparing the cobalt complex precatalyst for electrocatalytic oxygen evolution according to claim 4, characterized in that, The cobalt salt is cobalt chloride hexahydrate or cobalt nitrate hexahydrate; The molar ratio of the cobalt salt to tPBA is 1:0.5~1.

5.

6. The method for preparing the cobalt complex precatalyst for electrocatalytic oxygen evolution according to claim 4, characterized in that, The organic solvent is N,N-dimethylacetamide or N,N-dimethylformamide; The volume ratio of the organic solvent to deionized water is 1:1 to 10.

7. The use of a cobalt complex precatalyst for electrocatalytic oxygen evolution as described in any one of claims 1 to 3 in the preparation of organometallic hybrid catalysts.

8. A metal-organic hybrid catalyst, characterized in that, Using the cobalt complex precatalyst according to any one of claims 1 to 3 in 1 M KOH at 10 mA / cm 2 The catalyst was prepared by constant current density activation for 30 minutes; the structure of the metal-organic hybrid catalyst is tPBA-supported cobalt hydroxyoxide.

9. The application of the cobalt complex precatalyst for electrocatalytic oxygen evolution as described in any one of claims 1 to 3 in electrocatalytic oxygen evolution.

10. The application of the metal-organic hybrid catalyst of claim 8 in electrocatalytic oxygen evolution.

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