Preparation method and application of monodisperse heteropoly acid-based Pt atomic catalyst based on double confinement strategy

Abstract

The application aims to provide a preparation method of monodisperse heteropoly acid-based Pt atomic catalyst constructed based on a double-limiting field strategy and application thereof, and belongs to the technical field of functional materials. The double-limiting field refers to anchoring active metal Pt atoms in the four-fold hollow (4-H site) of a keggin-type heteropoly acid, and isolating the heteropoly acid by using a substrate with a suitable pore size. Compared with the prior art, the unique oxygen sites of POMs can effectively capture Pt single atoms through metal-O tetrahedral coordination, and improve proton transmission. At the same time, the multi-shell structure of POMs can provide abundant hydrogen transmission sites for the anchored metal atoms. PC can not only significantly improve the conductivity of the material, but also stabilize the structure of POMs through the limiting effect. Therefore, by limiting Pt atoms on POM clusters and using sub-nanopore PC for secondary limiting, an efficient and stable hydrogen transmission channel can be constructed, which significantly promotes the hydrogen evolution reaction, and provides a new direction for the development of future efficient electrocatalysts.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of functional materials, and particularly relates to a preparation method of a monodisperse heteropoly acid-based Pt atomic catalyst constructed based on a double-limiting strategy and application thereof. BACKGROUND

[0002] Water electrolysis for hydrogen evolution has attracted extensive attention as an effective way to produce and store clean energy using renewable energy. Among them, Pt-based catalysts are considered to be the most efficient catalyst type in the hydrogen evolution reaction (HER) under alkaline conditions. Due to the high cost and scarcity of metal Pt, a large number of researchers have reduced metal Pt to atomic scale to increase the dispersion of Pt on the support. The formation of atomic-level dispersed metal Pt (Pt SAs) is mainly anchored by adjacent strong electronegative atoms (O / N / S) to form HER active sites (Pt-O / Pt-N / Pt-S). In the catalytic system, Pt SAs catalysts have unique geometric and electronic properties, the highest atomic utilization efficiency and uniform active sites, and are highly concerned. However, highly dispersed metal atoms are either moved and aggregated due to high surface energy, resulting in poor stability, or are fixed immovably due to strong interaction with the support, leading to passivation of the active sites.

[0003] In recent years, in order to solve this problem, researchers have developed various Pt single-atom catalysts, one of the important strategies of which is to combine Pt with polyoxometalate (POM). Polyoxometalate has excellent electron transport capacity, and its surface is rich in O active sites, especially the four-fold hollow sites, which exhibit strong adsorption capacity for metal single atoms. Some studies have loaded polyoxometalate on commercial carbon materials and then loaded Pt, and the results show that when the interaction between Pt and the polyoxometalate support is stronger than the cohesive energy of Pt atoms, Pt can remain atomic dispersion; otherwise, aggregation occurs. Based on this, scholars have further studied the limitation of polyoxometalate and chloroplatinic acid in the MOF framework to form a structure in which Pt atoms are dispersed on the four-fold hollow sites of phosphomolybdic acid limited by MOF. However, high-energy electron beams can easily destroy the MOF structure, resulting in inaccurate positioning of metal atoms. In addition, MOF materials have poor stability and conductivity, limiting their application in the field of electrochemistry. Therefore, developing an efficient and stable Pt single-atom-POM catalyst, especially a strategy for industrial electrocatalytic applications, has become a key problem to be solved at present. SUMMARY

[0004] The present application aims at the problems of active site aggregation and poor conductivity in the existing Pt-POM composite material, and provides a preparation method and application of a monodisperse heteropoly acid-based Pt atomic catalyst constructed based on a double confinement strategy, and a general strategy for constructing a stable double confinement atomic level catalyst. The so-called double confinement refers to anchoring the active metal Pt atom in the four-fold hollow site (4-H site) of the Keggin type POM, and isolating the POM by using a porous carbon (PC) with a suitable pore size, so as to realize a double confinement effect. The unique oxygen site of POM can effectively capture Pt single atoms through a metal-O four-coordination structure, and improve proton transmission. At the same time, the multi-shell structure (such as Pt-O-Mo-O…) of POM can provide a rich hydrogen transmission site for the anchored metal atom. The PC can not only significantly improve the conductivity of the material, but also stabilize the structure of the POM through the confinement effect. Therefore, by confining the Pt atom on the POM cluster and using sub-nanopore PC for secondary confinement, an efficient hydrogen transmission channel can be constructed, which can significantly promote the hydrogen evolution reaction (HER).

[0005] The present application adopts the following technical scheme:

[0006] The difficulty of confinement lies in accurately placing the Pt single atom on the isolated heteropoly acid and needing a simple system to anchor the Pt single atom. Therefore, the present application is expected to adopt a "two-step method", first, the heteropoly acid is accurately confined in the substrate microporous carbon with a pore size matching the heteropoly acid, which can not only stabilize the confined guest molecules, but also further optimize the electronic state of the active center of the heteropoly acid; then, thanks to the four-fold hollow site of the Keggin type heteropoly acid for accurate anchoring of the Pt single atom, by controlling the content of the Pt precursor, the goal of dispersing one Pt single atom on each heteropoly acid is achieved. In this way, by layer-by-layer confinement, a supported single-atom catalyst with unique structure and electronic properties can be obtained.

[0007] The specific steps are as follows:

[0008] S1, preparation of monomodal ultramicroporous carbon PC: the main micropore size of sucrose-derived carbon is about 0.75-2 nm, close to the size of Keggin type heteropoly acid anion. Therefore, sucrose is selected as the precursor to prepare ultramicroporous carbon by a typical carbonization and activation method. Sucrose and sodium bicarbonate are mixed in a mass ratio of 4 / 1, and are thoroughly ground in an agate mortar. Then, the mixture is heated to 400 ℃ and 900 ℃ at a heating rate of 10 ℃ / min in a tube furnace under an argon atmosphere for 1 h each. The obtained product is stirred in hydrochloric acid aqueous solution (v / v=1:1), the solution is filtered, and the product is dried at 70 ℃ to obtain monomodal ultramicroporous carbon PC;

[0009] S2, single confinement material PMo 12Preparation of PC: 25 mg of PC was mixed with 10 mL of 0.01 M aqueous phosphomolybdate (PMo 12 ) solution, and the corresponding solid product was recovered after stirring for 3 h and filtration. Subsequently, the sample was washed by suction filtration until the pH of the filtrate reached 7.0 and dried overnight to obtain the single-confined material PMo 12 @PC.

[0010] S3, double-confined material Pt1@PMo 12 @PC. 12 @PC (25 mg) sample was dispersed in 10 mL of ultrapure water, followed by magnetic stirring for 20 min to obtain a uniform suspension. Next, 260 μL of an aqueous solution of H2PtCl6·6H2O (20 mg / mL) was slowly added. After stirring at 60 °C for 16 h, the suspension was centrifugally separated. The precipitate was washed several times with ultrapure water and then dried under vacuum at 60 °C overnight. As a control, pure PC and commercial activated carbon (AC) supported PMo 12 @PC were also used to support Pt, denoted as Pt1@PC and Pt-PMo 12 / AC, respectively.

[0011] Advantages of the present application are as follows:

[0012] The present application proposes a double-confined strategy to construct a highly efficient and stable Pt single atom-POM catalyst. The isolated Pt atom is confined in PMo 12 , while PMo 12 is further confined by micropores below 1 nm in the carbon support. The resulting Pt1@POMs@PC series of catalysts have excellent HER activity and stability. This design can construct an efficient hydrogen transport channel, significantly promoting the progress of the hydrogen evolution reaction (HER). Thanks to the double-confined design, the catalyst and stability are also significantly improved, providing a new way for efficient energy conversion. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a TEM image of the precursor PC;

[0014] Figure 2 is a TEM image of the precursor PMo 12 @PC;

[0015] Figure 3 is a TEM image of Pt1@PMo 12 @PC;

[0016] Figure 4 is a HAADF-STEM image of Pt1@PMo 12 @PC;

[0017] Figure 5 TEM image of Pt1@PC;

[0018] Figure 6 TEM image of Pt1-PMo 12 @AC;

[0019] Figure 7 PMo 12 @PC, Pt1@PC, Pt1@PMo 12 HER polarization curves and corresponding Tafel plots of Pt1@PC and 20% Pt / C;

[0020] Figure 8 Chronoamperometric tests under acidic conditions. DETAILED DESCRIPTION

[0021] The application is further illustrated in connection with examples.

[0022] 1. Preparation of double-confined atomically dispersed catalyst (Pt1@PMo 12 @PC)

[0023] (1) Preparation of monomodal ultramicroporous carbon (PC): The main micropore size of sucrose-derived carbon is about 0.75-2 nm, which is close to the size of Keggin-type heteropolyanion. Therefore, sucrose was chosen as the precursor to prepare ultramicroporous carbon by the typical carbonization-activation method. Sucrose and sodium bicarbonate were mixed with a mass ratio of 4 / 1 and ground thoroughly in an agate mortar. Subsequently, the mixture was heated to 400 °C and 900 °C at a heating rate of 10 °C / min in a tube furnace under argon atmosphere for 1 h, respectively. The obtained product was stirred in hydrochloric acid aqueous solution (v / v = 1:1), the solution was filtered and dried at 70 °C to obtain PC. From Figure 1 It can be seen that the TEM image of PC mainly presents a light and thin silk-like structure, and a large number of micropores are presented on the surface, which is conducive to the confinement of PMo 12 .

[0024] (2) Preparation of single-confined material (PMo 12 @PC): 25 mg of PC was mixed with 10 mL of PMo 12 (0.01 M) aqueous solution, and the corresponding solid product was recovered after stirring for 3 h and filtration. Subsequently, the sample was washed by suction filtration until the pH value of the filtrate reached 7.0, and dried overnight. From Figure 3 It can be seen that after loading PMo 12 , its TEM image also retains the silk-like amorphous structure of PC. However, no micropores and nanoparticles or clusters are observed in PMo 12 @PC, which may be due to the uniform dispersion of small-sized phosphomolybdate.

[0025] (3) Dual-confined materials (Pt1@PMo) 12 Preparation of @PC

[0026] Then PMo 12 @PC (25 mg) sample was dispersed in 10 mL of ultrapure water and then magnetically stirred for 20 min to obtain a homogeneous suspension. Next, 260 μL of H₂PtCl₆·6H₂O aqueous solution (20 mg / mL) was slowly added. After stirring at 60 °C for 16 h, the suspension was centrifuged. The precipitate was washed several times with ultrapure water and then dried overnight under vacuum at 60 °C. As controls, pure PC and PMo supported on commercial activated carbon (AC) were compared. 12 It is also used to support Pt, denoted as Pt1@PC and Pt-PMo respectively. 12 / AC. From Figure 3 The Pt1@PMo shown in the image 12 TEM observations using PC show that no particles are present and the carbon framework remains intact, proving the presence of Pt and PMo. 12 The monodisperse state. Figure 4 Further aberration-corrected electron microscopy images revealed isolated, uniformly distributed clusters (75–0.8 nm) loaded on the double-confined PC material, with each bright Pt site located at the corresponding PMo site. 12 On the "island," these experiments demonstrated the successful synthesis of dual-confined materials. In contrast, from... Figure 5 It can be seen that Pt1@PC also retains the silk-like structure of PC, indicating the atomic state distribution of Pt. However, it should be noted that the randomly distributed anchorages of Pt on PC are random, and the binding may be unstable. Moreover, from... Figure 6 It can be seen that in Pt-PMo 12 Larger nanoparticles formed in @AC indicate confined PMo 12 It plays a very important role in the secondary confinement of Pt atoms.

[0027] 2. Electrochemical performance testing of HER under alkaline conditions

[0028] The performance of electrochemical hydrogen evolution reaction (HER) was tested on a conventional three-electrode system of CHI 760E electrochemical workstation. The catalyst-coated L-shaped glassy carbon electrode (diameter 3 mm) was used as the working electrode, saturated calomel electrode (SCE) as the reference electrode, and graphite rod as the counter electrode. All polarization curves were corrected with 90% iR compensation to eliminate the ohmic drop on the electrolyte. 2 mg of catalyst powder and 5 μL of Nafion (20 wt%) were dispersed in 550 μL of deionized water and 180 μL of isopropyl alcohol, ultrasonicated for 1 h to form a uniform catalyst ink. 3.5 μL of well-dispersed catalyst ink was dropped onto a pre-polished glassy carbon electrode (0.07 cm 2 ) and dried in a room temperature environment for measurement. Linear sweep voltammetry (LSV), Tafel slope, and electrochemical impedance spectroscopy (EIS) tests were performed on the catalyst using the electrochemical workstation to evaluate its electrocatalytic performance.

[0029] First, the reference electrode was calibrated with a reversible hydrogen electrode (RHE). In a 0.5 M H2SO4 solution saturated with high-purity H2, two Pt foils were used as the working electrode and the counter electrode, respectively, while the saturated calomel electrode was used as the reference electrode. Cyclic voltammetry (CV) was performed at a scan rate of 2 mV s -1 in the potential range of -0.2 to -0.4 V, and the average of the two potentials at which the current was zero was taken as the thermodynamic potential of the hydrogen electrode reaction. The CV results of the RHE calibration of mercury / mercury oxide in 0.5 M H2SO4 can be described as E vs. RHE) = E vs. saturated calomel electrode) + 0.2636 V.

[0030] Subsequently, the three-electrode system was placed in 0.5 M H2SO4 solution for LSV experiments, with potential test ranges of -0.15~-0.42 V and -0.85~-1.2 V, respectively, and a scan rate of 5 mV s -1 . The Tafel slope was determined by plotting the logarithm of the current density and overpotential (log |j|).

[0031] EIS performance was tested in the frequency range of 0.01 Hz to 100 kHz. The CP experiment was tested at a constant current of 0.0007 A (i.e., 10 mA cm -2 ). The solution resistance R s was obtained from the impedance spectrum, and then the LSV curve was corrected for liquid resistance using E = E RHE - 90%iR s . The different-0.034 V (E vs.Impedance testing was performed at the RHE potential. The solution resistance R can be obtained from the impedance spectrum. s Then use E = E RHE - 90%iR s To perform liquid resistance correction on the LSV curve.

[0032] 3. Electrocatalytic hydrogen evolution test: First, following the method shown in step 2, synthesize Pt1@PMo... 12 @PC catalyst was uniformly coated onto a platinum-carbon electrode to prepare the working electrode for electrochemical testing. Subsequently, the hydrogen evolution reaction (HER) activity of the sample under alkaline conditions was measured using an electrochemical workstation in a three-electrode system. LSV, EIS, and CV tests were performed sequentially according to the same electrochemical testing method as in step 2. Following the method shown in step 2, the R value obtained from the EIS was... s Perform liquid resistance correction on the LSV curve.

[0033] Multiple impedance tests were performed on the samples, and the average solution resistance of the catalyst in the acidic electrolyte was found to be 7.5 Ω. Based on this result, the LSV curve was corrected for liquid resistance.

[0034] Figure 7 For Pt1@ PMo 12 Electrochemical performance tests were conducted on Pt1@POMs@PC, the precursor, and a control system. The results showed that Pt1@POMs@PC exhibited the lowest overpotential and the lowest Tafel slope under acidic conditions. This demonstrates the effectiveness of confined PMo. 12 The presence of PMo can create a highly efficient hydrogen transport channel, significantly promoting the hydrogen evolution reaction (HER). In addition, PMo... 12 The surface contains abundant oxygen, which can increase the high coverage of H* on Pt atoms, providing a rich local H-rich microenvironment for Pt atoms and promoting the HER reaction.

[0035] from Figure 8 It can be seen that Pt1@PMo 12 The @PC catalyst exhibited high HER catalytic durability, showing no significant degradation even after a prolonged period of 100 h. This is attributed to the stable reaction environment provided by the dual confinement strategy.

[0036] Based on the above test results, it can be seen that the dual-confined atomic-level Pt1@PMo constructed in this invention 12 The @PC catalyst exhibits excellent electrocatalytic HER activity and stability under acidic conditions. This catalyst not only utilizes confined PMo 12 This study provides a rich, locally H-rich microenvironment for Pt atoms and constructs an efficient hydrogen transport channel, effectively enhancing the hydrogen evolution reaction rate. In summary, this research develops a highly efficient and stable dual-confined atomic-level Pt1@PMo method.12 @PC catalyst provides an effective way to improve the efficiency of electrocatalytic HER, and has potential application prospects.

[0037] The present application aims at the problems of active site aggregation and poor conductivity in the existing Pt-POM composite material, and proposes a general strategy for constructing a stable double-limited atomic-level dispersed catalyst. The so-called double limitation refers to anchoring the active metal Pt atom in the four-fold hollow site (4-H site) of the Keggin type POM, and isolating the POM by using a porous carbon (PC) with a suitable pore size, so as to realize the double limitation effect. Compared with the prior art, the unique oxygen site of POM can effectively capture Pt single atom through metal-O tetrahedral coordination structure, and improve the proton transmission. At the same time, the multi-shell structure of POM (such as Pt-O-Mo-O…) can provide rich hydrogen transmission sites for the anchored metal atom. PC can not only significantly improve the conductivity of the material, but also stabilize the structure of POM through the limitation effect. Therefore, by limiting the Pt atom on the POM cluster and using sub-nanoporous PC for secondary limitation, an efficient hydrogen transmission channel can be constructed, which can significantly promote the hydrogen evolution reaction (HER), and this innovative design provides a new direction for the development of future high-efficiency electrocatalysts.

[0038] The above embodiments are only used to illustrate the content of the present application, but this is not a limitation of the present application, and those skilled in the art can make corresponding adjustments and modifications without departing from the scope of the present application, therefore all equivalent replacements or equivalent modifications form technical solutions within the protection scope of the present application.

Claims

1. A method for preparing monodisperse heteropoly acid-based Pt atomic catalysts based on a double confinement strategy, characterized by: Comprising the following steps: S1, preparation of single-peak super-microporous carbon PC: sucrose and sodium bicarbonate were mixed and ground thoroughly in an agate mortar, then the mixture was heated to 400 ℃ and 900 ℃ for 1 h at a heating rate of 10 ℃ / min in a tube furnace under argon atmosphere, the obtained product was stirred in a 1:1 volume ratio hydrochloric acid aqueous solution, the solution was filtered and dried at 70 ℃ to obtain single-peak super-microporous carbon PC; S2, confined material PMo 12 @Preparation of PC: PC was mixed with aqueous phosphomolybdic acid solution. After stirring for 3 h, the corresponding solid product was recovered by filtration. Subsequently, the sample was washed by suction filtration until the pH of the filtrate reached 7.0 and dried overnight to obtain the confined material PMo 12 @PC; S3, Pt1@PMo 12 @PC was prepared: PMo 12 @PC sample was dispersed in ultrapure water, then magnetic stirring for 20 min, get uniform suspension, second, slowly add H2PtCl6·6H2O aqueous solution, stirring at 60 ℃ for 16 h, centrifugal separation of suspension, the separated precipitate was washed several times with ultrapure water, then dried at 60 ℃ under vacuum overnight, get Pt1@PMo 12 @PC.

2. The preparation method of monodisperse heteropoly acid-based Pt atomic catalysts based on the double confinement strategy according to claim 1, characterized in that: In S1, the mass ratio of sucrose to sodium bicarbonate was 4:

1.

3. The preparation method of monodisperse heteropoly acid-based Pt atomic catalysts based on the double confinement strategy according to claim 1, characterized in that: In S2, the dosage ratio of PC to phosphomolybdic acid was 25 mg:10 mL, wherein the concentration of phosphomolybdic acid was 0.01 M.

4. The preparation method of the monodisperse heteropoly acid-based Pt atomic catalyst based on the double confinement field strategy according to claim 1, characterized in that: S3, PMo 12 @PC, ultrapure water, H2PtCl6·6H2O aqueous solution in a ratio of 25 mg: 10 mL: 260 μL, wherein the concentration of H2PtCl6·6H2O aqueous solution is 20 mg / mL.

5. The preparation method of monodisperse heteropoly acid-based Pt atomic catalysts based on the double confinement strategy according to claim 1, characterized in that: The so-called double confinement refers to anchoring active metal Pt atoms in the four-fold hollow sites of Keggin-type POMs, and isolating POMs with porous carbon PC with a suitable pore size, thereby realizing a double confinement effect.

6. A monodisperse heteropoly acid-based Pt atomic catalyst constructed based on a double confinement strategy for hydrogen evolution reaction, which is prepared by the preparation method of claim 1.

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