Method for synthesizing Ir-Co heteronuclear single-atom catalysts by one-step annealing and its application

Abstract

The present invention relates to the field of metal single-atom catalysts, and discloses a method for synthesizing Ir-Co heteronuclear single-atom catalysts by a one-step annealing method, comprising the following steps: S1, weighing 5g of dicyandiamide and adding it to a beaker, slowly adding 40mL of water and 4.4mL of formaldehyde, adding a certain amount of IrCl3·3H2O and different amounts of Co(NO3)2·6H2O, transferring the beaker to an oil bath and heating it to 80°C, stirring for 24h, and then placing it in a 60°C oven to dry. After the sample is completely dried, it is calcined at 900°C for 2h in a tube furnace under an N2 atmosphere, and the black block product is fully ground to obtain Ir-Co heteronuclear single-atom catalysts with different atomic ratios. The present invention fixes the content of Ir and modulates the content of Co to obtain heteronuclear single-atom catalysts with different atomic ratios. The nitrogen-doped carbon material has a good anchoring effect, so that the single atoms do not agglomerate. Thanks to the synergistic effect between the Ir and Co components, the obtained Ir-Co catalyst has excellent electrocatalytic formic acid oxidation performance.

Description

Technical Field

[0001] The present invention relates to the field of metal single-atom catalysts, and in particular to a method for synthesizing Ir-Co heteronuclear single-atom catalysts by a one-step annealing method and application thereof. Background Art

[0002] Direct formic acid fuel cells (DFAFCs) offer advantages such as high energy density, rapid chemical kinetics, safety, and low toxicity, making them promising energy conversion devices. Furthermore, formic acid molecules consist of only one carbon atom, requiring only the breakage of two hydrogen atoms during oxidation, resulting in fast reaction kinetics and favorable for faster discharge. Furthermore, the low permeability of Nafion® in formic acid fuel cells is unmatched by other small molecules, ensuring their stability under operating conditions and demonstrating great development potential and application potential.

[0003] At present, the catalyst for the formic acid oxidation reaction at the anode focuses on Pt and Pd-based metal particles. For example, the patent application number "CN202210758470.9" provides a cerium oxide-palladium / carbon catalyst for formic acid electrooxidation and its preparation method. The cerium oxide-palladium / carbon catalyst is Pd and CeO2 loaded on a C carrier. CeO2 is a spherical particle with a size of ≤10nm. The spherical nano-CeO2 not only increases the uniformity of Pd loading, thereby increasing the electrochemical active area of the catalyst; at the same time, nano-CeO2 and Pd synergistically improve the activity, resistance to CO poisoning and stability of the catalyst.

[0004] However, in the existing technology, as proposed in patent application number "CN202210758470.9", Pt, Pd-based metal particles not only have low mass activity, but also face the problems of high price and small reserves, which restricts the development of formic acid fuel cells. Secondly, precious metal particles are prone to indirect oxidation pathways during the catalytic oxidation of formic acid. The generated CO intermediates occupy the active sites, causing the catalyst to deactivate, resulting in low activity and poor stability. Summary of the Invention

[0005] In order to address the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide a preparation method and application of Ir-Co heteronuclear single-atom catalysts with different atomic ratios having high catalytic activity and stability.

[0006] The object of the present invention can be achieved by the following technical solution: A method for synthesizing an Ir-Co heteronuclear single-atom catalyst by a one-step annealing method comprises the following steps:

[0007] S1. Add 250 mg of IrCl3·3H2O to 20 mL of deionized water to prepare a 12.5 mg / mL aqueous solution of iridium trichloride. At the same time, add 1000 mg of Co(NO3)2·6H2O reagent to 20 mL of deionized water to prepare a 50 mg / mL aqueous solution of cobalt nitrate.

[0008] S2. Weigh 5 g of dicyandiamide and add it to a beaker with a magnet. Then, add 40 mL of water and 4.4 mL of formaldehyde. Then, add 400 μL of an aqueous solution of edsyl chloride and 50-400 μL of an aqueous solution of cobalt nitrate dropwise to obtain a precursor solution.

[0009] S3. The precursor solution was transferred to an oil bath and heated to 80°C, stirred for 24 hours, cooled to room temperature, and then transferred to an oven at 60°C and dried for 24 hours to obtain a pink solid sample.

[0010] S4. The pink solid obtained above was transferred to a ceramic ark and annealed at 900 °C for 2 h in a tube furnace under N2 conditions to obtain a black block sample. After the temperature dropped to room temperature, the black block sample was ground into a uniformly dispersed black powder to obtain an Ir-Co heteronuclear single atom catalyst.

[0011] In step S1, the prepared aqueous solution of iodine trichloride and aqueous solution of cobalt nitrate are ultrasonically shaken for 30 minutes to ensure complete dissolution of the solution, and the shaken and dissolved solution is stored in a refrigerator to facilitate subsequent precise control of the addition of the precursor.

[0012] In step S2, the formaldehyde and the precursor solution are added dropwise, and the solution containing water and dicyandiamide is continuously stirred during the addition process.

[0013] In step S2, a pipette is used to add an aqueous solution of edible trichloride and an aqueous solution of cobalt nitrate to achieve precise control of the volume of the precursor solution. The volume of the added aqueous solution of cobalt nitrate is 50 μL, 100 μL, 200 μL or 400 μL.

[0014] In step S4, the temperature of the tube furnace is raised to 900° C. at a rate of 5° C. / min, and the temperature is maintained at 900° C. for 2 hours before being cooled to room temperature.

[0015] In the step S4, the annealed bulk sample is ground using a mortar for 10 minutes to obtain uniformly dispersed black powder.

[0016] A one-step annealing method for synthesizing an Ir-Co heteronuclear single-atom catalyst is disclosed. The prepared Ir-Co heteronuclear single-atom catalyst is used in the electrocatalytic formic acid oxidation reaction.

[0017] Beneficial effects of the present invention:

[0018] The present invention obtains heteronuclear single-atom catalysts with different atomic ratios by fixing the Ir content in the precursor source and changing the Co content. The nitrogen-doped carbon material has a good anchoring effect, and the strong interaction between the metal and the support prevents single atoms from agglomerating, which is the key to obtaining Ir-Co heteronuclear single-atom catalysts with different atomic ratios. The introduction of Co in inactive sites brings about a significant improvement in performance, indicating that the synergistic effect between Ir and Co is the key to the performance improvement. The method of the present invention can universally prepare single-atom catalysts with different contents.

[0019] The Ir-Co heteronuclear single-atom catalyst prepared by the method of the present invention realizes efficient single-atom catalytic formic acid oxidation, has not only excellent atomic activity but also extremely good stability, and also has good resistance to CO poisoning. The single-atom catalyst not only reduces the amount of precious metals used, reduces the cost of the catalyst, and improves the atomic utilization rate, thereby achieving efficient catalytic performance, but also the introduction of non-precious metal Co effectively regulates the electronic structure of Ir. The synergistic effect between the Ir-Co heteronuclear single atoms effectively improves the performance of the catalyst, makes the adsorption of reactants and reaction intermediates more favorable, has a faster kinetic process, and thus achieves higher current density and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0021] Figure 1 The X-ray diffraction patterns of Comparative Example 1 and Examples 1, 2, 3, and 4 are shown;

[0022] Figure 2 is a TEM image of Comparative Example 1;

[0023] Figure 3 is a TEM image of Example 1;

[0024] Figure 4 is a TEM image of Example 2;

[0025] Figure 5 is a TEM image of Example 3;

[0026] Figure 6 is a TEM image of Example 4;

[0027] Figure 7is the Fourier transform X-ray fine structure absorption spectrum of the Ir element in Examples 1, 2, 3, 4 and Irfoil;

[0028] Figure 8 is the Fourier transform X-ray fine structure absorption spectrum of the Co element in Examples 1, 2, 3, 4 and Cofoil;

[0029] Figure 9 This is a bar chart comparing the performance of Comparative Example 1 and Examples 1, 2, 3, and 4;

[0030] Figure 10 This is a performance comparison chart before and after the stability test of Example 2;

[0031] Figure 11 This is a comparison chart of the performance and stability of commercial Pt / C and commercial Pd / C in Example 2. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0033] Comparative Example 1

[0034] Add 250 mg of IrCl3·3H2O reagent to 20 mL of deionized water to prepare a 12.5 mg / mL aqueous solution of iridium trichloride and store it in a refrigerator until use.

[0035] Weigh 5 g of dicyandiamide and add it to a beaker with a magnet. First add 40 mL of water and then add 4.4 mL of formaldehyde dropwise. Then use a pipette to transfer 400 uL of an aqueous solution of edsyl trichloride and slowly add it dropwise to the stirring beaker to obtain a precursor solution. Transfer the precursor solution to an oil bath and heat it to 80°C. Stir continuously for 24 hours. After cooling to room temperature, transfer it to a 60°C oven and dry it for 24 hours to obtain a light yellow solid sample.

[0036] The light yellow solid sample obtained above was transferred to a ceramic ark, and then heated to 900°C at a heating rate of 5°C / min in a tube furnace under N2 conditions and annealed for 2 hours. After the temperature dropped to room temperature, the block sample was collected, transferred to a mortar and fully ground for 10 minutes to obtain a uniformly dispersed black powder, which is the Ir single-atom catalyst.

[0037] Example 1

[0038] Add 250 mg of IrCl3·3H2O reagent to 20 mL of deionized water to prepare a 12.5 mg / mL aqueous solution of iridium trichloride. Use this solution as a precursor solution. Simultaneously, add 1000 mg of Co(NO3)2·6H2O reagent to 20 mL of deionized water to prepare a 50 mg / mL aqueous solution of cobalt nitrate. Store both solutions in a refrigerator until ready for use.

[0039] Weigh 5 g of dicyandiamide and add it to a beaker with a magnet. First add 40 mL of water and then add 4.4 mL of formaldehyde dropwise. Then use a pipette to transfer 400 μL of an aqueous solution of edible trichloride and 50 μL of an aqueous solution of cobalt nitrate and slowly add them dropwise to the stirring beaker to obtain a precursor solution. Transfer the precursor solution to an oil bath and heat it to 80°C. Continue stirring for 24 hours. After cooling to room temperature, transfer it to a 60°C oven and dry it for 24 hours to obtain a pink solid sample.

[0040] The pink solid sample obtained above was transferred to a ceramic ark, and then heated to 900°C in a tube furnace under N2 conditions at a heating rate of 5°C / min and maintained for 2 hours. After the temperature dropped to room temperature, the block sample was collected, transferred to a mortar and fully ground for 10 minutes to obtain a uniformly dispersed black powder, which is the Ir-Co heteronuclear single-atom catalyst.

[0041] Example 2

[0042] Add 250 mg of IrCl3·3H2O reagent to 20 mL of deionized water to prepare a 12.5 mg / mL aqueous solution of iridium trichloride. Use this solution as a precursor solution. Simultaneously, add 1000 mg of Co(NO3)2·6H2O reagent to 20 mL of deionized water to prepare a 50 mg / mL aqueous solution of cobalt nitrate. Store both solutions in a refrigerator until ready for use.

[0043] Weigh 5 g of dicyandiamide and add it to a beaker with a magnet. First add 40 mL of water and then add 4.4 mL of formaldehyde dropwise. Then use a pipette to transfer 400 μL of an aqueous solution of edsyl chloride and 100 μL of an aqueous solution of cobalt nitrate and slowly add them dropwise to the stirring beaker to obtain a precursor solution. Transfer the precursor solution to an oil bath and heat to 80°C. Continue stirring for 24 hours. After cooling to room temperature, transfer to a 60°C oven and dry for 24 hours to obtain a pink solid sample.

[0044] The pink solid sample obtained above was transferred to a ceramic ark, and then heated to 900°C at a heating rate of 5°C / min in a tube furnace under N2 conditions and annealed for 2 hours. After the temperature dropped to room temperature, the block sample was collected, transferred to a mortar and fully ground for 10 minutes to obtain a uniformly dispersed black powder, which is the Ir-Co heteronuclear single-atom catalyst.

[0045] Example 3

[0046] Add 250 mg of IrCl3·3H2O reagent to 20 mL of deionized water to prepare a 12.5 mg / mL aqueous solution of iridium trichloride. Use this solution as a precursor solution. Simultaneously, add 1000 mg of Co(NO3)2·6H2O reagent to 20 mL of deionized water to prepare a 50 mg / mL aqueous solution of cobalt nitrate. Store both solutions in a refrigerator until ready for use.

[0047] Weigh 5 g of dicyandiamide and add it to a beaker with a magnet. First add 40 mL of water and then add 4.4 mL of formaldehyde dropwise. Then use a pipette to transfer 400 μL of an aqueous solution of edsyl chloride and 200 μL of an aqueous solution of cobalt nitrate and slowly add them dropwise to the stirring beaker to obtain a precursor solution. Transfer the precursor solution to an oil bath and heat to 80°C. Continue stirring for 24 hours. After cooling to room temperature, transfer to a 60°C oven and dry for 24 hours to obtain a red solid sample.

[0048] The red solid sample obtained above was transferred to a ceramic ark, and then heated to 900°C at a heating rate of 5°C / min in a tube furnace under N2 conditions and annealed for 2 hours. After the temperature dropped to room temperature, the block sample was collected, transferred to a mortar and fully ground for 10 minutes to obtain a uniformly dispersed black powder, which is the Ir-Co heteronuclear single-atom catalyst.

[0049] Example 4

[0050] Add 250 mg of IrCl3·3H2O reagent to 20 mL of deionized water to prepare a 12.5 mg / mL aqueous solution of iridium trichloride. Use this solution as a precursor solution. Simultaneously, add 1000 mg of Co(NO3)2·6H2O reagent to 20 mL of deionized water to prepare a 50 mg / mL aqueous solution of cobalt nitrate. Store both solutions in a refrigerator until ready for use.

[0051] Weigh 5 g of dicyandiamide and add it to a beaker with a magnet. First add 40 mL of water and then add 4.4 mL of formaldehyde dropwise. Then use a pipette to transfer 400 uL of an aqueous solution of edsyl chloride and 400 μL of an aqueous solution of cobalt nitrate and slowly add them dropwise to the stirring beaker to obtain a precursor solution. Transfer the precursor solution to an oil bath and heat to 80°C. Continue stirring for 24 hours. After cooling to room temperature, transfer to a 60°C oven and dry for 24 hours to obtain a purple solid sample.

[0052] The purple solid sample obtained above was transferred to a ceramic ark, and then heated to 900°C at a heating rate of 5°C / min in a tube furnace under N2 conditions and annealed for 2 hours. After the temperature dropped to room temperature, the block sample was collected, transferred to a mortar and fully ground for 10 minutes to obtain a uniformly dispersed black powder, which is the Ir-Co heteronuclear single-atom catalyst.

[0053] Structural inspection

[0054] Depend on Figure 1 From the XRD results, it can be seen that the samples of Comparative Example 1 and Examples 1, 2, 3, and 4 do not have the relevant diffraction peaks of Ir and Co metal particles, indicating that the Ir and Co atoms do not aggregate to form a crystal structure of nanoparticles at high temperature.

[0055] Depend on Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 and Figure 6 From the high-resolution TEM images, it can be seen that no obvious Ir and Co particles were found in the samples of Comparative Example 1 and Examples 1, 2, 3, and 4. Even if the Co content was increased, no Co particles were found. Combined with the XRD results, it was proved that no Ir and Co particles or small clusters appeared, which were considered to be single-atom sites. This shows that this method effectively prepares Ir and Co heteronuclear single-atom catalysts.

[0056] In order to further confirm the influence of the existence form and coordination environment of Ir in Examples 1, 2, 3 and 4 on the formic acid oxidation performance, we used Fourier transform X-ray fine structure absorption spectroscopy (FT-EXAFS, Figure 7 and Figure 8 ) The materials were characterized, and it can be seen that Examples 2, 3, 4, and 5 all have non-metallic coordination of Ir-N, and no Ir-Ir metal coordination peak appears. At the same time, the Co element in Examples 2, 3, 4, and 5 also shows a Co-N coordination peak, but no Co-Co metal coordination peak. No Co-Co metal coordination peak is found in the sample of Example 5 with the highest Co content. Combined with the conclusions of the aforementioned XRD and electron microscopy, it is judged that the existence form of Ir and Co are both single-atom forms, which effectively confirms that this method can be used to synthesize heteronuclear single-atom catalysts with different contents of Ir and Co.

[0057] Performance testing

[0058] In order to evaluate the activity and stability of formic acid oxidation of the Ir metal catalysts in Comparative Example 1 and Examples 1, 2, 3, and 4, we conducted performance evaluations under the same test conditions. The specific test steps and results are as follows:

[0059] (1) 0.49 mL of isopropanol, 0.49 mL of deionized water, 5 mg of catalyst, 2 mg of carbon powder, and 20 μL of Nafion solution were mixed and ultrasonicated in an ice-water bath for 2 h to disperse into an ink-like state.

[0060] (2) Add 27.2 mL of analytically pure concentrated H2SO4 solution and 19.2 mL of 98% formic acid solution to deionized water, and then transfer to a 1000 mL volumetric flask to prepare an electrolyte solution of 0.5 MH2SO4 + 0.5 MHCOOH.

[0061] (3) Measure 80 mL of the prepared reaction solution and add it to the test bottle. Select a carbon rod, Ag / AgCl electrode, and glassy carbon electrode as the counter electrode, reference electrode, and working electrode, respectively. Drop the prepared ink onto the glassy carbon electrode and let it dry naturally to form a film to obtain the working electrode for testing.

[0062] like Figure 9 and Figure 11 After the introduction of Co, the performance of Examples 1, 2, 3, and 4 was significantly improved compared to the comparative example 1 without the introduction of Co. The experiment proved that Co was an inactive site, indicating that the synergistic effect between the active site Ir and the inactive site Co effectively promoted the catalytic performance of the Ir single atom. At the same time, with the increase of Co content, a volcano-shaped curve was found in the performance graph. The Ir-Co heteronuclear single atom catalyst prepared in Example 2 showed the best electrocatalytic activity, indicating that the introduction of an appropriate amount of Co effectively controlled the electronic structure of Ir, thereby obtaining the optimal structure for catalytic formic acid oxidation, with a mass activity of 35.29 A / mgIr. -1 , which are 69 times and 43 times that of commercial Pt / C and commercial Pd / C, respectively. Figure 10 The Ir-Co heteronuclear single-atom catalyst prepared in Example 2 was subjected to stability cycling at a certain voltage. After the stability test, its activity was still maintained at 98% of the initial activity, indicating that the introduction of Co not only improved the activity of the catalyst, but also effectively improved the stability of the catalyst, which further illustrates the important influence of the atomic ratio of the inactive site on the active site. In summary, the Ir-Co heteronuclear single-atom catalyst prepared in the present invention has excellent electrocatalytic formic acid oxidation activity and stability.

[0063] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for synthesizing Ir-Co heteronuclear single-atom catalysts by a one-step annealing method, characterized in that: The following steps are involved: S1. Add 250 mg of IrCl3•3H2O to 20 mL of deionized water to prepare a 12.5 mg / mL aqueous solution of iodine trichloride. At the same time, add 1000 mg of Co(NO3)2•6H2O reagent to 20 mL of deionized water to prepare a 50 mg / mL aqueous solution of cobalt nitrate. S2. Weigh 5 g of dicyandiamide and add it to a beaker with a magnet. Then, add 40 mL of water and 4.4 mL of formaldehyde. Then, add 400 μL of an aqueous solution of edsyl chloride and 50-400 μL of an aqueous solution of cobalt nitrate dropwise to obtain a precursor solution. S3. The precursor solution was transferred to an oil bath and heated to 80°C, stirred for 24 hours, cooled to room temperature, and then transferred to an oven at 60°C and dried for 24 hours to obtain a pink solid sample. S4. The pink solid obtained above was transferred to a ceramic ark and annealed in a tube furnace under N2 conditions at 900°C for 2 h to obtain a black block sample. After the temperature dropped to room temperature, the black block sample was ground into a uniformly dispersed black powder to obtain an Ir-Co heteronuclear single atom catalyst; In step S2, the formaldehyde and the precursor solution are added dropwise, and the solution containing water and dicyandiamide is continuously stirred during the addition process; In step S4, the temperature of the tube furnace is raised to 900° C. at a rate of 5° C. / min, and the temperature is maintained at 900° C. for 2 hours before being cooled to room temperature.

2. The method for synthesizing Ir-Co heteronuclear single-atom catalyst by one-step annealing method according to claim 1, characterized in that: In step S1, the prepared aqueous solution of iodine trichloride and aqueous solution of cobalt nitrate are ultrasonically shaken for 30 minutes to ensure complete dissolution of the solution, and the shaken and dissolved solution is stored in a refrigerator to facilitate subsequent precise control of the addition of the precursor.

3. The method for synthesizing Ir-Co heteronuclear single-atom catalyst by one-step annealing method according to claim 1, characterized in that: In step S2, a pipette is used to add an aqueous solution of edible trichloride and an aqueous solution of cobalt nitrate to achieve precise control of the volume of the precursor solution. The volume of the added aqueous solution of cobalt nitrate is 50 μL, 100 μL, 200 μL or 400 μL.

4. The method for synthesizing Ir-Co heteronuclear single-atom catalyst by one-step annealing method according to claim 1, characterized in that: In the step S4, the annealed bulk sample is ground using a mortar for 10 minutes to obtain uniformly dispersed black powder.

5. The method for synthesizing an Ir-Co heteronuclear single-atom catalyst by a one-step annealing method according to any one of claims 1 to 4, wherein the prepared Ir-Co heteronuclear single-atom catalyst is used in an electrocatalytic formic acid oxidation reaction.

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