A single-atom supported cobalt-based spinel electrocatalyst, preparation method and application thereof
By using a cobalt-based spinel electrocatalyst with a nano-array micro-nano structure, the electronic structure of Co3+ was adjusted and the hydrogen evolution side reaction was suppressed, which solved the problems of insufficient activity of cobalt-based catalysts and poor stability of noble metals, and achieved the effect of efficient reduction of nitrate to ammonia.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 天津仁爱学院
- Filing Date
- 2026-04-09
- Publication Date
- 2026-06-12
Smart Images
Figure CN122189692A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of catalyst technology, and in particular to a single-atom supported cobalt-based spinel electrocatalyst, its preparation method, and its application. Background Technology
[0002] The photovoltaic (PV) industry has rapidly emerged due to its unique advantages of being clean and renewable, gradually becoming an important component of the global renewable energy structure. However, the PV industry generates large amounts of waste nitric acid solution, i.e., acidic nitrate nitrogen wastewater, during processes such as texturing and polycrystalline silicon etching. With the rapid development of the PV industry, the discharge of such wastewater is increasing daily. If discharged directly without effective treatment, it will cause serious pollution to the aquatic environment, threatening ecological balance and human health.
[0003] Ammonia, as an important bulk chemical, is widely used in agricultural fertilizers and industrial chemical raw materials, with huge market demand. Currently, the technology for recovering ammonia from aqueous solutions via degassing membranes is mature and industrialized. Therefore, driven by renewable energy, the reduction of nitrate pollutants in acidic water to ammonia using electrocatalytic technology can not only effectively treat wastewater pollution but also achieve the recovery and reuse of nitrogen resources, representing a sustainable waste-to-resource strategy.
[0004] In the study of electrocatalytic reduction of nitrate, cobalt-based electrocatalysts have attracted widespread attention due to their ammonia selectivity of over 90%. Among them, cobalt-based composite oxides (AB2O4) with spinel structures can maintain good structural stability in strongly acidic and strongly oxidizing solutions, and have potential application value. However, existing cobalt-based spinel catalysts still have the following problems: (1) The high energy barrier for active hydrogen generation on the surface of metal oxides leads to insufficient supply of active hydrogen required for the catalytic reaction, which limits the improvement of catalytic efficiency; (2) Under acidic electrolyte conditions, the hydrogen evolution side reaction (HER) is highly competitive, which reduces the selectivity of nitrate reduction to ammonia; (3) Noble metal clusters / nanoparticles have poor stability and high cost in strongly oxidizing acidic environments.
[0005] While single-atom structures can solve the above problems, existing single-atom preparation methods generally suffer from drawbacks such as complex processes, low efficiency, low single-atom loading, and easy agglomeration, making it difficult to meet the needs of practical applications. Summary of the Invention
[0006] The purpose of this invention is to provide a highly efficient, stable, and easily prepared single-atom supported spinel structure metal-based composite oxide electrocatalyst for the treatment of acidic photovoltaic wastewater, thereby solving the aforementioned technical problems.
[0007] To achieve the above objectives, this invention provides a single-atom-supported cobalt-based spinel electrocatalyst, wherein the electrocatalyst is a spinel-type composite oxide modified with a noble metal single atom having a nano-array micro-nano structure, and has the chemical formula M. SA -ACo2O4, where A is a divalent transition metal ion, M SA It consists of noble metal single atoms, and the total loading of noble metal single atoms accounts for 0.1 to 5.0 wt% of the catalyst mass.
[0008] Preferably, A is Zn 2+ Cu 2+ or Ni 2+ M SA It is a single atom of Pd, Rh, or Ru.
[0009] Preferably, in the nanoarray micro / nano structure of the electrocatalyst, the height of a single nanounit is 100 nm to 2 μm, and the diameter of a single nanounit is 50 to 300 nm.
[0010] The preparation method of the above-mentioned single-atom supported cobalt-based spinel electrocatalyst includes the following steps: (1) Dissolve transition metal salts, cobalt nitrate, ammonium fluoride and urea in deionized water and carry out a solvothermal reaction at 80-120℃ for 6-18h to obtain the product; (2) After drying the product obtained in step (1), calcine it in air at 400-600℃ for 8-15h to obtain ACo2O4 catalyst powder with nano-array micro-nano structure. (3) The ACo2O4 catalyst powder from step (2) is impregnated in a noble metal salt solution, dried, and then heated to 1000-1500℃ in a mixed atmosphere of H2 and Ar by Joule heating and maintained for 0.5-3s to achieve anchoring of noble metal single atoms, thus obtaining M. SA -ACo2O4.
[0011] Preferably, in step (1), the total molar amount of transition metal salt and cobalt nitrate is 50-500 mmol, the atomic ratio of transition metal ion A in transition metal salt to Co in cobalt nitrate is 1:2, the molar amount of ammonium fluoride is 50-500 mmol, and the molar amount of urea is 100-600 mmol.
[0012] Preferably, in step (1), the transition metal salt includes one of nitrate, chloride, and sulfate.
[0013] Preferably, in step (3), the mass of the ACo2O4 catalyst powder is 50-500 mg.
[0014] Preferably, in step (3), the precious metal salt includes one of palladium chloride, rhodium chloride, and ruthenium chloride, and the concentration of the precious metal salt solution is 2-100 mmol / L.
[0015] Preferably, in step (3), the drying temperature after impregnation is 65-85℃, and the heating rate of Joule heating is greater than 10. 4 In a mixed atmosphere of H2 and Ar at K / s, H2 accounts for 3%-10% of the total volume.
[0016] The above-mentioned single-atom supported cobalt-based spinel electrocatalyst is used to treat acidic photovoltaic wastewater with a pH of 1-3, selectively converting nitrates in the acidic photovoltaic wastewater into ammonia.
[0017] Mechanism of the invention: In spinel-structured cobalt-based composite oxides (ACo2O4), octahedral coordinated Co 3+ (Co Oh The nitrate reduction site is the main active site for nitrate reduction. This invention utilizes transition metals with different electronegativity (such as Zn) 2+ Cu 2+ Ni 2+ As a tetrahedral coordination site (site A), it connects with site B (Co) through site A. Oh Electron interactions between Co and Co regulate Co's behavior. 3+ The electronic structure of the active hydrogen is modified to reduce the energy barrier for active hydrogen generation and improve the efficiency of active hydrogen supply.
[0018] In acidic media, single-atom adsorbed active hydrogen readily reacts with abundant protons in the solution via the Heyrovsky mechanism (H + H₂). + +e - →H2) coupling hydrogen evolution, the nanoarray structure can accumulate OH during electrocatalysis. - It significantly increases the local pH value on the electrode surface, changes the thermodynamic conditions of the hydrogen evolution reaction, effectively inhibits the hydrogen evolution side reaction in acidic media, and improves the selectivity of nitrate reduction to ammonia.
[0019] The preparation method of this invention employs the Joule heating method, utilizing its ultra-rapid heating rate (>10). 4 (K / s) Without damaging the nano-array micro-nano structure, it achieves rapid reduction and single-atom dispersion of metal ions, solving the problems of low single-atom loading and easy agglomeration in traditional methods; at the same time, the rapid heating and cooling process enhances the interaction between noble metal single atoms and the support, improving the stability of the catalyst.
[0020] Therefore, the present invention, employing the above-mentioned single-atom supported cobalt-based spinel electrocatalyst, its preparation method, and its application, has the following beneficial effects: (1) This invention regulates Co through A-site metal ions. 3+ The electronic structure significantly reduces the energy barrier for active hydrogen generation, while the synergistic effect of noble metal single atoms and Co active sites greatly enhances the catalytic activity for the reduction of nitrate to ammonia.
[0021] (2) The local high pH microenvironment constructed by the nanoarray microstructure of the present invention effectively suppresses the hydrogen evolution side reaction and significantly improves the selectivity of ammonia. The spinel structure has good structural stability in strong acid and strong oxidizing environment, and the single-atom high dispersion loading achieved by the Joule heating method enhances the interaction between metal atoms and the support, avoids the dissolution and aggregation of noble metals, and extends the service life of the catalyst.
[0022] (3) The present invention uses the Joule heating method to achieve high-efficiency loading of single atoms. The process steps are simple, the reaction time is short, and the repeatability is strong. The loading of noble metal single atoms can reach 0.1-5.0 wt%, which is much higher than the traditional wet chemical method and has the potential for large-scale production.
[0023] (4) This invention efficiently converts nitrate in photovoltaic wastewater into high-value ammonia products, turning waste into treasure, which is in line with the concept of green and sustainable development.
[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0025] Figure 1 This is a comparison diagram of the local pH values of the catalysts in Example 1 and Comparative Example 1 of the present invention; Figure 2 This is a comparison chart of the nitrate reduction catalytic performance of the catalysts in Example 1 and Comparative Example 2 of the present invention; Figure 3 The figure shows the test results of the effect of different noble metal loading on the catalytic performance of nitrate reduction in this invention; Figure 4 This is a SEM image of the single-atom supported cobalt-based spinel electrocatalyst of Example 1 of the present invention. Detailed Implementation
[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.
[0027] This invention provides a single-atom-supported cobalt-based spinel electrocatalyst, wherein the electrocatalyst is a spinel-type composite oxide modified with a noble metal single atom having a nano-array micro-nano structure, and has the chemical formula M.SA -ACo2O4, where A is a divalent transition metal ion, M SA It consists of noble metal single atoms, and the total loading of noble metal single atoms accounts for 0.1 to 5.0 wt% of the catalyst mass.
[0028] Preferably, A is Zn 2+ Cu 2+ or Ni 2+ M SA It is a single atom of Pd, Rh, or Ru.
[0029] Preferably, in the nanoarray micro / nanostructure of the electrocatalyst, the height of each nanounit is 100 nm to 2 μm, and the diameter of each nanounit is 50 to 300 nm. The nanoarray micro / nanostructure is used to increase the local pH value of the electrode surface to suppress the hydrogen evolution reaction.
[0030] The preparation method of the above-mentioned single-atom supported cobalt-based spinel electrocatalyst includes the following steps: (1) Dissolve transition metal salts, cobalt nitrate, ammonium fluoride and urea in deionized water and carry out a solvothermal reaction at 80-120℃ for 6-18h to obtain the product, namely the metal hydroxide / carbonate precursor.
[0031] (2) After drying the product obtained in step (1), calcine it at 400-600℃ in air for 8-15 h to obtain ACo2O4 catalyst powder with nano-array microstructure; the nano-array microstructure helps to accumulate OH during electrocatalysis. - It increases the local pH and inhibits hydrogen evolution side reactions in acidic media.
[0032] (3) The ACo2O4 catalyst powder from step (2) is impregnated in a noble metal salt solution, dried, and then heated to 1000-1500℃ in a mixed atmosphere of H2 and Ar by Joule heating and maintained for 0.5-3s to achieve anchoring of noble metal single atoms, thus obtaining M. SA -ACo2O4, i.e., a single-atom supported cobalt-based spinel electrocatalyst.
[0033] Preferably, in step (1), the total molar amount of transition metal salt and cobalt nitrate is 50–500 mmol, the atomic ratio of transition metal ion A in the transition metal salt to Co in the cobalt nitrate is 1:2 to ensure the formation of a stable spinel structure, the molar amount of ammonium fluoride is 50–500 mmol, and the molar amount of urea is 100–600 mmol. By adjusting the amounts of each component within the above range, this invention can adjust the density of the nanoarray micro / nano structure, thereby affecting the local pH value.
[0034] Preferably, in step (1), the transition metal salt includes one of nitrate, chloride, and sulfate.
[0035] More preferably, the transition metal salt includes, but is not limited to, one of zinc nitrate, copper nitrate, nickel nitrate, zinc chloride, copper chloride, nickel chloride, zinc sulfate, copper sulfate, and nickel sulfate.
[0036] Preferably, in step (3), the mass of the ACo2O4 catalyst powder is 50-500 mg.
[0037] Preferably, in step (3), the precious metal salt includes one of palladium chloride, rhodium chloride, and ruthenium chloride, and the concentration of the precious metal salt solution is 2-100 mmol / L.
[0038] This invention ensures that the loading of noble metal single atoms is 0.1 to 5.0 wt% of the mass of the cobalt-based spinel catalyst by controlling the amount of ACo2O4 catalyst powder and the concentration of the noble metal salt solution within the above-mentioned range. Insufficient noble metal will affect the catalytic efficiency of nitrate reduction, while excessive noble metal will also agglomerate during the reaction, affecting dispersibility and forming noble metal clusters or particles that are easily soluble in acid solutions.
[0039] In this invention, the role of loading noble metal single atoms is not only to stably provide the active hydrogen required for the reaction, but also to regulate the electronic structure of Co atoms at the catalytic active site, thereby synergistically improving the ability to catalyze the reduction of nitrate.
[0040] Preferably, in step (3), the drying temperature after impregnation is 65-85℃, and the heating rate of Joule heating is greater than 10. 4 In a mixed atmosphere of H2 and Ar at K / s, H2 accounts for 3%-10% of the total volume. The heating rate is greater than 10 K / s. 4 K / s avoids the sintering collapse of nanoarrays caused by prolonged heating in traditional tube furnaces, maintaining the original morphology while achieving highly dispersed single-atom loading.
[0041] This invention controls the Joule heating temperature at 1000-1500℃ and holds it for 0.5-3 seconds. Using the Joule heating method, noble metal precursors can be reduced to single atoms in milliseconds, much faster than the time required for atomic diffusion. In contrast, traditional tube furnaces heat up slowly, reducing the noble metal precursor (such as Pt) to single atoms. 2+ ,Rh 2+ There is sufficient time for them to migrate on the carrier and revert to clusters / particles.
[0042] More preferably, the present invention further includes a post-processing step, in which the product after Joule heating in step (3) is washed 3-5 times alternately with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 55-65°C for 5-7 hours to obtain the final electrocatalyst.
[0043] The above-mentioned single-atom supported cobalt-based spinel electrocatalyst is used to treat acidic photovoltaic wastewater with a pH of 1-3, selectively converting nitrates in the acidic photovoltaic wastewater into ammonia.
[0044] Example 1 This invention provides a single-atom supported cobalt-based spinel electrocatalyst, which is a spinel-type composite oxide modified with a noble metal single atom having a nano-array micro-nano structure, with the chemical formula Pd. SA -NiCo2O4. Its preparation method includes the following steps: (1) 100 mmol nickel chloride, 200 mmol cobalt nitrate, 300 mmol ammonium fluoride and 200 mmol urea were placed in 30 mL of deionized water and stirred evenly. The mixture was then subjected to a solvothermal reaction at 100 °C for 12 h to form a nickel cobalt hydroxide / carbonate precursor.
[0045] (2) After drying the nickel-cobalt hydroxide / carbonate precursor obtained in step (1), place it in a tube furnace and heat it in air at 200 mL / min. -1 NiCo2O4 catalyst powder with nano-array micro-nano structure was obtained by calcining at a gas flow rate of 500℃ for 10 hours.
[0046] (3) Weigh 200 mg of NiCo2O4 catalyst powder obtained in step (2), immerse it in 20 mmol / L palladium chloride solution, immerse it for 5 h, dry it at 75 °C, and then heat it to 1000 °C in a mixed atmosphere of 5% H2 and 95% Ar by Joule heating and maintain it for 0.5 s to achieve anchoring of noble metal single atoms.
[0047] (4) The product from step (3) was washed three times alternately with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 6 hours to obtain Pd. SA -NiCo2O4, in which the Pd single atom loading is 1wt%.
[0048] Example 2 The difference between this embodiment and Example 1 is that the concentration of the palladium chloride solution in step (3) is 10 mmol / L, and the Pd obtained in step (4) is different. SA The Pd single atom loading in NiCo2O4 is 0.5wt%, and the rest is the same as in Example 1.
[0049] Example 3 The difference between this embodiment and Example 1 is that the concentration of the palladium chloride solution in step (3) is 40 mmol / L, and the Pd obtained in step (4) is different. SA The Pd single atom loading in NiCo2O4 is 2wt%, and the rest is the same as in Example 1.
[0050] Example 4 The difference between this embodiment and Example 1 is that the concentration of the palladium chloride solution in step (3) is 2 mmol / L, and the Pd obtained in step (4) is different. SA The Pd single atom loading in NiCo2O4 is 0.1 wt%, and the rest is the same as in Example 1.
[0051] Example 5 The difference between this embodiment and Example 1 is that the concentration of the palladium chloride solution in step (3) is 100 mmol / L, and the Pd obtained in step (4) is different. SA The Pd single atom loading in NiCo2O4 is 5wt%, and the rest is the same as in Example 1.
[0052] Example 6 This invention provides a single-atom supported cobalt-based spinel electrocatalyst, which is a spinel-type composite oxide modified with a noble metal single atom having a nano-array micro-nano structure, with the chemical formula Rh SA -ZnCo2O4. Its preparation method includes the following steps: (1) 250 mmol zinc chloride, 500 mmol cobalt nitrate, 500 mmol ammonium fluoride and 600 mmol urea were placed in 30 mL of deionized water and stirred evenly. The mixture was then subjected to a solvothermal reaction at 80 °C for 10 h to form a zinc cobalt hydroxide / carbonate precursor.
[0053] (2) After drying the zinc cobalt hydroxide / carbonate precursor obtained in step (1), place it in a tube furnace and heat it in air at 500 mL / min. -1 The ZnCo2O4 catalyst powder with a nano-array micro-nano structure was obtained by calcining at a gas flow rate of 600℃ for 8 hours.
[0054] (3) Weigh 250 mg of the ZnCo2O4 catalyst powder obtained in step (2), immerse it in a 10 mmol / L rhodium chloride solution, immerse it for 8 h, dry it at 75 °C, and then heat it to 1300 °C in a mixed atmosphere of 10% H2 and 90% Ar by Joule heating and maintain it for 1 s to achieve the anchoring of noble metal single atoms.
[0055] (4) The product from step (3) was washed three times alternately with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 6 hours to obtain Rh. SA -ZnCo2O4, wherein the Rh single atom loading is 1wt%.
[0056] Example 7 This invention provides a single-atom supported cobalt-based spinel electrocatalyst, which is a spinel-type composite oxide modified with a noble metal single atom having a nano-array micro-nano structure, with the chemical formula Pd. SA-CuCo2O4. Its preparation method includes the following steps: (1) 50 mmol copper chloride, 100 mmol cobalt nitrate, 300 mmol ammonium fluoride and 300 mmol urea were placed in 30 mL of deionized water and stirred evenly. The mixture was then subjected to a solvothermal reaction at 110 °C for 6 h to form a copper cobalt hydroxide / carbonate precursor.
[0057] (2) After drying the copper-cobalt hydroxide / carbonate precursor obtained in step (1), place it in a tube furnace and heat it in air at 1500 mL / min. -1 The CuCo2O4 catalyst powder with a nano-array micro-nano structure was obtained by calcining at a gas flow rate of 500℃ for 11 hours.
[0058] (3) Weigh 50 mg of CuCo2O4 catalyst powder obtained in step (2), immerse it in 5 mmol / L palladium chloride solution, immerse it for 3 h, dry it at 75 °C, and then heat it to 1000 °C in a mixed atmosphere of 8% H2 and 92% Ar by Joule heating and maintain it for 1.5 s to achieve anchoring of noble metal single atoms.
[0059] (4) The product from step (3) was washed three times alternately with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 6 hours to obtain Pd. SA -CuCo2O4, in which the Pd single atom loading is 0.95wt%.
[0060] Comparative Example 1 A Pd SA The preparation method of NiCo2O4 nanoparticle catalyst includes the following steps: (1) 100 mmol nickel chloride, 200 mmol cobalt nitrate, 300 mmol ammonium fluoride and 200 mmol urea were placed in 30 mL of deionized water and stirred evenly. The mixture was then dropped dropwise onto the Ti plate on the heating plate and reacted at 100 °C for 12 hours to form nickel cobalt hydroxide / carbonate nanoparticle precursor.
[0061] (2) After drying the nickel-cobalt hydroxide / carbonate nanoparticle precursor from step (1) at 60°C, place it in a tube furnace and heat it in air at 500 mL / min. -1 NiCo2O4 nanoparticle catalyst powder was obtained by calcining at a gas flow rate of 500℃ for 10 hours.
[0062] (3) Weigh 200 mg of NiCo2O4 nanoparticle catalyst powder from step (2), immerse it in 20 mmol / L palladium chloride solution, immerse it for 8 h, dry it at 75 °C, put it in a reactor, and heat it to 1000 °C in a mixed atmosphere of 5% H2 and 95% Ar by Joule heating and maintain it for 0.5 seconds.
[0063] (4) The product from step (3) was washed three times alternately with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 6 hours to obtain Pd. SA -NiCo2O4 nanoparticle catalyst with a Pd loading of 20wt%, far exceeding the Pd single atom loading in Example 1, is easy to aggregate into particles.
[0064] Comparative Example 2 Pd prepared by heating in a tube furnace SA The preparation method of NiCo2O4 nanoarray catalyst includes the following steps: (1) 100 mmol nickel chloride, 200 mmol cobalt nitrate, 300 mmol ammonium fluoride and 200 mmol urea were placed in 30 mL of deionized water and stirred evenly. The mixture was then subjected to a solvothermal reaction at 100 °C for 12 h to form a nickel cobalt hydroxide / carbonate precursor.
[0065] (2) After drying the nickel-cobalt hydroxide / carbonate precursor obtained in step (1), place it in a tube furnace and heat it in air at 200 mL / min. -1 NiCo2O4 catalyst powder with nano-array micro-nano structure was obtained by calcining at a gas flow rate of 500℃ for 10 hours.
[0066] (3) Weigh 200 mg of NiCo2O4 catalyst powder obtained in step (2), immerse it in 20 mmol / L palladium chloride solution, immerse it for 6 h, dry it at 75 °C, and then heat it to 1000 °C and maintain it for 5 h in a conventional tube furnace at a heating rate of 2 °C / min in a mixed atmosphere of 5% H2 and 95% Ar.
[0067] (4) The product from step (3) was washed three times alternately with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 6 hours to obtain Pd. SA -NiCo2O4.
[0068] The catalysts of Example 1 and Comparative Example 1 were subjected to local pH testing using in-situ electrochemical Raman spectroscopy with phosphate as a probe. The local pH value was determined based on the peak positions of different phosphate species. The results are as follows: Figure 1 As shown in the figure, the catalyst with the nanoarray structure can effectively increase the local pH value of the surface, while the local pH value of the nanoparticle catalyst is lower, indicating that the nanoarray structure can accumulate OH-. - Suppress hydrogen evolution side reactions.
[0069] The nitrate reduction catalytic performance of the catalysts in Example 1 and Comparative Example 2 was tested in an acidic electrolyte of 0.5 mol / L H2SO4. The test conditions for nitrate reduction were as follows: the electrolyte required for the reaction was a mixed solution of 1M NaOH and 1M NaNO3, the working electrode was the prepared catalyst, the counter electrode was a stone rod, and the reference electrode was an Hg / HgO electrode.
[0070] The results are as follows Figure 2 As shown, the catalyst prepared by the Joule heating method can achieve a Faraday efficiency of over 85%, which is significantly higher than that of the catalyst prepared by the traditional tube furnace heating method (Faraday efficiency of about 60%). This is because the Joule heating method maintains the morphology of the nanoarray and avoids sintering and agglomeration.
[0071] The nitrate reduction catalytic performance of catalysts with different noble metal loadings in Examples 1-5 was tested under the same conditions as above. The results are as follows: Figure 3 As shown, when the loading is 0.1 wt%, the selectivity is approximately 30%, which is relatively low. When the loading is increased to 0.5 wt%, the selectivity jumps to approximately 60%, showing a significant performance improvement. At a loading of 2 wt%, the selectivity reaches its peak (approximately 80%). When the loading is increased to 5 wt%, the selectivity drops back to approximately 40%. This indicates that the optimal loading range is 0.5–2 wt%. This is because when the loading is <0.5 wt%, the supply of active hydrogen is insufficient (few single-atom sites), which cannot effectively drive nitrate reduction, resulting in low selectivity. When the loading is between 0.5 and 2 wt%, the single atoms are uniformly dispersed, and the selectivity is high. 3+ The active sites work synergistically, ensuring a sufficient supply of active hydrogen while suppressing hydrogen evolution side reactions, resulting in high selectivity. However, when the loading is greater than 2 wt%, the single atoms exceed the anchoring capacity of the support, causing aggregation and the formation of noble metal particles. This reduces the effective active sites and exacerbates hydrogen evolution side reactions, leading to a decrease in selectivity.
[0072] The microstructure of the single-atom supported cobalt-based spinel electrocatalyst of Example 1 was characterized by scanning electron microscopy (SEM), and the results are as follows: Figure 4 As shown, the electrocatalyst exhibits a densely packed array structure of nanorods (or nanoneedles). These nanounits are slender needles / rods with a height of 100 nm to 2 μm and a diameter of 50 to 300 nm. They are distributed in a bundle-like aggregate, with a smooth surface, regular morphology, and no obvious agglomeration or breakage.
[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.
Claims
1. A single-atom supported cobalt-based spinel electrocatalyst, characterized in that: The electrocatalyst is a spinel-type composite oxide modified with a noble metal single atom having a nano-array micro-nano structure, with the chemical formula M. SA -ACo2O4, where A is a divalent transition metal ion, M SA It consists of noble metal single atoms, and the total loading of noble metal single atoms accounts for 0.1 to 5.0 wt% of the catalyst mass.
2. The single-atom supported cobalt-based spinel electrocatalyst according to claim 1, characterized in that: A is Zn 2 + Cu 2+ or Ni 2+ M SA It is a single atom of Pd, Rh, or Ru.
3. The single-atom supported cobalt-based spinel electrocatalyst according to claim 1, characterized in that: In the nanoarray micro / nano structure of electrocatalysts, the height of a single nanounit is 100 nm to 2 μm, and the diameter of a single nanounit is 50 to 300 nm.
4. A method for preparing a single-atom supported cobalt-based spinel electrocatalyst according to any one of claims 1-3, characterized in that: Includes the following steps: (1) Dissolve transition metal salts, cobalt nitrate, ammonium fluoride and urea in deionized water and carry out a solvothermal reaction at 80-120℃ for 6-18h to obtain the product; (2) After drying the product obtained in step (1), calcine it in air at 400-600℃ for 8-15h to obtain ACo2O4 catalyst powder with nano-array micro-nano structure. (3) The ACo2O4 catalyst powder from step (2) is impregnated in a noble metal salt solution, dried, and then heated to 1000-1500℃ in a mixed atmosphere of H2 and Ar by Joule heating and maintained for 0.5-3s to achieve anchoring of noble metal single atoms, thus obtaining M. SA -ACo2O4.
5. The method for preparing the single-atom supported cobalt-based spinel electrocatalyst according to claim 4, characterized in that: In step (1), the total molar amount of transition metal salt and cobalt nitrate is 50-500 mmol, the atomic ratio of transition metal ion A in transition metal salt to Co in cobalt nitrate is 1:2, the molar amount of ammonium fluoride is 50-500 mmol, and the molar amount of urea is 100-600 mmol.
6. The method for preparing the single-atom supported cobalt-based spinel electrocatalyst according to claim 4, characterized in that: In step (1), the transition metal salt includes one of nitrate, chloride, and sulfate.
7. The method for preparing the single-atom supported cobalt-based spinel electrocatalyst according to claim 4, characterized in that: In step (3), the mass of ACo2O4 catalyst powder is 50-500 mg.
8. The method for preparing the single-atom supported cobalt-based spinel electrocatalyst according to claim 4, characterized in that: In step (3), the precious metal salt includes one of palladium chloride, rhodium chloride, and ruthenium chloride, and the concentration of the precious metal salt solution is 2-100 mmol / L.
9. The method for preparing the single-atom supported cobalt-based spinel electrocatalyst according to claim 4, characterized in that: In step (3), the drying temperature after impregnation is 65-85℃, and the heating rate of Joule heating is greater than 10. 4 In a mixed atmosphere of H2 and Ar at K / s, H2 accounts for 3%-10% of the total volume.
10. The application of a single-atom supported cobalt-based spinel electrocatalyst according to any one of claims 1-3, characterized in that: This method is used to treat acidic photovoltaic wastewater with a pH of 1-3, selectively converting nitrates in the wastewater into ammonia.