Monatomic electrocatalyst of metal polyphenol network as well as preparation method and application of monatomic electrocatalyst

Abstract

The invention discloses a monatomic electrocatalyst of a metal polyphenol network as well as a preparation method and application of the monatomic electrocatalyst. The preparation method comprises the following steps: adding an alkaline solution of Pluronic F127; polyphenol and formaldehyde are added for a cross-linking reaction; dropwise adding a metal salt solution, stirring and mixing, carrying out a hydrothermal reaction, carrying out centrifugal separation to obtain a precipitate, and washing and drying to obtain the monatomic catalyst. According to the method, polyphenol containing a large number of hydroxyl groups is taken as a ligand, coordination with metal ions is realized through formaldehyde-assisted crosslinking, a reaction path is precisely regulated and controlled through hydrogen bond engineering, a CO2 reduction reaction path is changed from a traditional * CO path to a low-energy barrier formyl path, C-C chemical coupling and hydrogen evolution / deuterium evolution side reaction are synchronously inhibited, and the reaction efficiency is improved. The selectivity of methane or deuterated methane is obviously improved, the operation stability for ultra-long time is realized, and an effective solution is provided for synthesis of methane and deuterated methane with high additional value.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide regeneration technology, specifically to a single-atom electrocatalyst with a metal polyphenol network, its preparation method, and its application. Background Technology

[0002] Electroreduction of carbon dioxide (CO2) driven by renewable energy sources is a key pathway to achieving carbon neutrality. Methane (CH4), as a major component of natural gas (accounting for 24% of global energy), has a carbon dioxide content of 55.5 MJ / kg. –1 The high volumetric energy density of carbon makes it the most commercially valuable product, while its deuterated isotope (deuterated methane, CD4) has unique value in medicinal chemistry (such as enhancing drug metabolic stability), reaction mechanism research, and isotope tracing technology. The efficient electrocatalytic synthesis of CD4 faces more severe challenges than ordinary CH4, mainly due to the deuterium nucleus (D... + Or D3O + The transfer rate is significantly slower than that of hydrogen nuclei (H). + or H3O + This kinetic lag not only exacerbates the reaction energy barrier of the octet transfer pathway, but also leads to enhanced competition for the deuterium evolution side reaction (DER), resulting in lower current density and CD4 selectivity in the existing catalytic system in D2O electrolyte.

[0003] Although recent studies have confirmed that the D2O system can directly synthesize high-deuterated chemicals (such as formic acid-d2), the electrosynthesis of CD4 at industrial-grade current densities still faces fundamental bottlenecks: the slow eight-step proton-coupled electron transfer (PCET) process and the interaction with multi-carbon products (C... 2+ CD4 shares a CO intermediate pathway and exhibits kinetically dominant DER side reactions (ACS Catal. 2025, 15, 1038). CD4 commands an extremely high market premium (>76,720 USD kg). –1 (Approximately 30,000 times that of CH4), making its efficient synthesis increasingly urgent.

[0004] Traditional copper (Cu)-based catalysts in the electrosynthesis of CH4 and CD4 are limited by complex octet transfer processes and competitive hydrogen evolution (or deuteration) side reactions (HER / DER), generally exhibiting low product selectivity (<50%) and limited current density (<200 mA / cm²). –2 The core challenge lies in stabilizing key reaction intermediates and simultaneously regulating interfacial proton transfer kinetics to suppress HER / DER and promote C–H bond formation. Although Cu single-atom catalysts (Cu SACs) can suppress C–H coupling and reduce C… 2+The product is obtained, but the traditional Cu–N4 configuration has weak adsorption of the *CO intermediate, making it difficult to achieve deep hydrogenation / deuteration. Theoretical studies (Angew. Chem. Int. Ed. 2023, 62, e202301767) suggest that stabilizing the alternative *OCHO intermediate (which directly generates CH4 via the formyl pathway with a lower energy barrier than the *CO pathway) is key to improving selectivity, but this requires atomically precise control of the active site microenvironment. While hydrogen bonds, as dynamic non-covalent interactions, can regulate the reaction intermediate and local environment, their potential has not been fully explored. When electronegative groups are present in the spatial coordination microenvironment surrounding the active site, strong hydrogen bonds easily form with the reaction intermediate *OCHO; however, atomically precise hydrogen bond-mediated interface design remains a frontier of exploration.

[0005] While existing invention patent CN118910643A has achieved the preparation of high-loading Cu SACs catalysts, its Cu–N4 configuration still depends on the *CO intermediate pathway. Furthermore, the preparation process involves complexation with o-phenanthroline and multi-step calcination at 550-620℃ (first producing carbon nitride from urea, then complexing with copper salt-o-phenanthroline and undergoing secondary calcination), making the process cumbersome and lacking hydrogen bond regulation capabilities. Therefore, developing new materials that possess atomically dispersed active sites, controllable hydrogen bond microenvironment, and industrial-grade current tolerance is the core direction for overcoming the technological bottleneck of electroreduction of CO2 to CH4 / CD4. Summary of the Invention

[0006] This invention addresses the common problems of adsorption energy imbalance and low proton transfer efficiency in the electroreduction of CO2 to CH4 / CD4. It provides a method for preparing a single-atom electrocatalyst with a metal polyphenol network. This catalyst shifts the reaction pathway from the traditional *CO pathway to the lower-energy-barrier formyl pathway during the catalytic electroreduction of CO2 to CH4 / CD4, thereby fundamentally suppressing C–C chemical bond coupling and hydrogen / deuterium evolution side reactions, effectively improving catalytic efficiency and product selectivity.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a single-atom electrocatalyst based on a metal polyphenol network includes the following steps:

[0009] Step 1: Dissolve Pluronic F127 and adjust the pH to obtain an alkaline solution of Pluronic F127;

[0010] Step 2: Add polyphenols and formaldehyde to the alkaline solution from Step 1 to carry out a cross-linking reaction;

[0011] Step 3: Add a metal salt solution dropwise to the reaction solution in Step 2, stir and mix, and then carry out a hydrothermal reaction. Centrifuge to obtain a precipitate, and wash and dry it to obtain the single-atom catalyst.

[0012] The formaldehyde-assisted crosslinking and metal polyphenol coordination strategy employed in this invention can obtain M–O4 active sites with hydrogen bond regulation function across a wide process window. Its uniqueness lies in the fact that the free hydroxyl group in the coordination framework acts as a hydrogen bond donor, forming an O–H··O chemical bond with the key reaction intermediate *OCHO. This shifts the reaction pathway from the traditional *CO pathway to the lower-barrier formyl pathway, fundamentally suppressing C–C bond coupling and hydrogen / deuterium evolution side reactions. This improves the HER / DER inhibition rate. The hydrothermal crystallization strategy avoids high-temperature calcination, simplifying the preparation process and maintaining the stability of the Cu–O4 coordination structure. The minimal performance degradation after 22 hours of continuous operation demonstrates the excellent tolerance of the hydrogen bond microenvironment to the electrocatalytic CO2 reduction reaction under high current density.

[0013] The polyphenols include one or more of tannic acid, caffeic acid, protocatechuic aldehyde, and gallic acid;

[0014] The polyphenols employ phenolic ligands such as tannic acid, caffeic acid, protocatechuic aldehyde, and gallic acid, which contain a large number of phenolic hydroxyl groups, to provide coordination groups for metal ions. In this process, the hydroxyl groups of the phenolic substances act as electron donors, while metal ions with vacant electron orbitals (called coordination sites) accept electron pairs, thereby establishing coordination bonds between the phenolic hydroxyl groups and the metal ions. This allows the oxygen atoms in the metal ions and hydroxyl groups to share electron pairs, forming a metal-oxygen coordination single-atom catalyst.

[0015] Preferably, the polyphenol ligand is tannic acid; tannic acid is a natural high-molecular-weight polyphenol containing a large number of catechol and pyrogallol units in its molecular structure. Compared with small-molecule ligands such as gallic acid, protocatechuic aldehyde (or caffeic acid), tannic acid has an extremely high coordination site density. This structural characteristic allows it to act as a "multidentate" or "chelate" ligand, forming multiple coordination bonds with the same or multiple metal ions simultaneously. This multiple coordination significantly enhances the stability of the metal-polyphenol network single atom, effectively preventing the leaching or aggregation of metal ions during catalysis, thereby ensuring the structural integrity and sustained catalytic activity of the single-atom catalyst.

[0016] Furthermore, the high molecular weight and multiple flexible aromatic ring structure of tannic acid facilitate cross-linking to form extended three-dimensional network structures when coordinated with metal ions. This network structure provides ideal spatial isolation sites for metal atoms, effectively "anchoring" and separating them, which is crucial for the efficient preparation of highly loaded and highly dispersed single-atom catalysts. In contrast, small-molecule ligands (such as gallic acid) form simpler coordination structures with lower dimensionality, exhibiting weaker spatial confinement capabilities for metal atoms, and are more likely to form metal clusters or nanoparticles during the catalytic process when forming single-atom catalysts.

[0017] The molar ratio of the polyphenols to formaldehyde is 1:1 to 1:6;

[0018] The metal salt includes soluble salts of one or more metals selected from copper, iron, zinc, nickel, and cobalt; the soluble salt includes chloride salts, nitrate salts, or sulfate salts, etc.

[0019] Preferably, the metal salt is a copper salt, wherein the active center of the copper metal has a moderate *CO intermediate binding energy, thus exhibiting excellent catalytic performance in the electroreduction of CO2. It includes at least one of copper sulfate, copper nitrate, and copper chloride; preferably a sulfate, whose anion (SO4) 2– It has the least interference with hydrogen bond networks.

[0020] The mass ratio of polyphenol to metal salt is 1:0.05-0.5; preferably, the mass ratio of polyphenol to metal salt is 1:0.1-0.3. Catalysts with more active sites are obtained within this ratio range, and metal single-atom aggregation is less likely to occur.

[0021] The solvent used to dissolve Pluronic F127 in step 1 includes one or more mixed solvents selected from water, ethanol, and isopropanol; preferably, a mixed solution of water and ethanol is used to ensure the solubility of polyphenols while optimizing surfactant micelle formation. A water-to-ethanol volume ratio of 1-5:1 is further preferred, as this ratio is more conducive to the formation of micelles with excellent performance. An excessively high ethanol ratio (>5:1) will weaken hydrophilic crosslinking, while an excessively low ethanol ratio (<1:1) may reduce copper ion diffusion efficiency.

[0022] The mass ratio of Pluronic F127 to polyphenols is 1:0.5-1;

[0023] The pH of the alkaline solution is 8-10;

[0024] The crosslinking reaction is carried out at room temperature for 12-48 hours.

[0025] In step 3, the mixing is carried out continuously at room temperature for 12-48 hours;

[0026] The hydrothermal reaction temperature is 80-150℃, and the reaction time is 12-48h. Preferably, the hydrothermal reaction temperature is 90-110℃, at which temperature the catalyst crosslinking network is more complete. At low temperatures, the crosslinking network is incomplete, and the hydrogen bond donor density decreases; high temperatures lead to the thermal decomposition of uncoordinated hydroxyl groups, weakening the stabilizing effect on the *OCHO intermediate.

[0027] Preferably, the drying is carried out at 50-80℃ for 10-24 hours, which effectively removes moisture or impurities, clears mesoporous channels, increases specific surface area, and thus improves the performance of the catalyst.

[0028] The present invention also provides a single-atom electrocatalyst of a metal polyphenol network prepared by the preparation method described above.

[0029] The present invention also provides the application of the single-atom electrocatalyst as a working electrode in the electrocatalytic reduction of CO2.

[0030] The present invention also provides the application of the single-atom electrocatalyst as a working electrode in the electrocatalytic reduction of CO2 to prepare CH4 and / or CD4.

[0031] The catalyst prepared in this invention possesses a well-defined Cu–O4 coordination structure and retains uncoordinated hydroxyl groups. Compared to the traditional Cu–N4 configuration and existing Cu–O4 materials, the hydrogen bond network formed by its adjacent free hydroxyl groups can stabilize the *OCHO intermediate, thus lowering the energy barrier of the formyl pathway reaction. When applied to the electrocatalytic reduction of CO2, using an Ag / AgCl electrode as the reference electrode, nickel foam as the counter electrode, and catalyst-supported carbon paper as the working electrode, this catalyst exhibits excellent electroreduction performance for CO2 to CH4 and CD4 in 1M KOH / H2O and 1M KOH / D2O electrolytes, respectively.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] In this invention, gallic acid, containing a large number of hydroxyl groups, is used as a ligand. Through formaldehyde-assisted crosslinking and coordination with metal ions, and by precisely controlling the reaction pathway through hydrogen bond engineering, Cu–O4 active sites containing uncoordinated hydroxyl groups can be constructed at a relatively low hydrothermal reaction temperature. These hydroxyl groups act as stable hydrogen bond donors. * OCHO intermediates change the CO2 reduction reaction pathway from the traditional * The CO pathway is redirected to a low-energy-barrier formyl pathway, simultaneously suppressing C–C chemical coupling and hydrogen / deuterium evolution side reactions. This enables catalytic CO2 reduction reactions, significantly improving the selectivity for methane or deuterated methane, and exhibits extremely long-term operational stability, providing an effective solution for the synthesis of high-value-added methane and deuterated methane. Attached Figure Description

[0034] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the catalyst prepared in Example 1.

[0035] Figure 2 The image shows the Raman spectrum of the catalyst prepared in Example 1.

[0036] Figure 3 This is an aberration-corrected high-angle annular dark-field scanning transmission electron microscope (AC HAADF-STEM) image of the catalyst prepared in Example 1.

[0037] Figure 4The Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectrum of the catalyst prepared in Example 1 is shown.

[0038] Figure 5 The graph shows the performance of the catalyst prepared in Example 1 in the electroreduction of CO2 to CH4 in 1M KOH / H2O electrolyte.

[0039] Figure 6 The catalyst prepared in Example 1 was subjected to 300 mA cm⁻¹ in a 1M KOH / H₂O electrolyte. –2 Stability test curve under constant current for 22 hours.

[0040] Figure 7 The graph shows the performance of the catalyst prepared in Example 1 in the electroreduction of CO2 to CD4 in 1M KOH / D2O electrolyte.

[0041] Figure 8 The catalyst prepared in Example 1 was subjected to 300 mA cm⁻¹ in a 1M KOH / D₂O electrolyte. –2 Stability test curve under constant current for 22 hours. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0043] All raw materials used in the following specific implementation methods were purchased from the market.

[0044] Example 1

[0045] (1) Dissolve 0.6g of Pluronic F127 in a mixed solution of 96mL of deionized water and 24mL of ethanol, add 1.2mL of 25wt.% ammonia to adjust the pH to 8-9, and stir for 1h;

[0046] (2) Add 0.6g of tannic acid to the above solution, dissolve it, then inject 1.14mL of 28wt.% formaldehyde, and stir at room temperature for 24h to carry out the cross-linking reaction;

[0047] (3) Dissolve 120 mg CuSO4·5H2O in 6 mL of water, add it dropwise to the system, and stir for 24 h;

[0048] (4) Transfer the mixture into a 200mL reactor and react at 100℃ for 24h;

[0049] (5) Centrifuge at 10,000 rpm for 30 min, wash with water three times, and vacuum dry at 60℃ for 12 h to obtain the catalyst Cu-PTA (measured Cu loading 5.02 wt.%).

[0050] Figure 1 The X-ray diffraction pattern of the catalyst Cu-PTA prepared in Example 1 is shown. The 27° broad diffraction peak confirms the amorphous polymer network characteristics, and the absence of characteristic peaks of the metallic copper crystalline phase indicates atomic-level dispersion. Figure 2 The Raman spectrum of the catalyst Cu-PTA prepared in Example 1 is shown, with the value at 623 cm⁻¹. –1 The presence of Cu–O coordination characteristic peaks at the site provides evidence for the formation of active sites. Figure 3 Isolated bright spots (without clusters) in the aberration-corrected HAADF-STEM image of the catalyst directly confirm the single-atom dispersion characteristics of metallic copper; Figure 4 Fourier transform EXAFS spectra of the catalyst in Strong Cu–O coordination peak at (none) The Cu–Cu peak confirmed the Cu–O4 coordination configuration.

[0051] Example 2

[0052] Following the process of Example 1, the amount of CuSO4·5H2O in step (3) was reduced to 60 mg, while the rest remained the same as in Example 1, to obtain the catalyst Cu-PTA-2.

[0053] Example 3

[0054] Following the process of Example 1, the amount of CuSO4·5H2O in step (3) was increased to 240 mg, and the rest was the same as in Example 1, to obtain the catalyst Cu-PTA-3.

[0055] Example 4

[0056] Following the process of Example 1, CuSO4·5H2O in step (2) was replaced with an equimolar amount of Cu(NO3)2·3H2O, and the rest was the same as in Example 1, to obtain the catalyst Cu-PTA-4.

[0057] Example 5

[0058] Following the process of Example 1, CuSO4·5H2O in step (2) was replaced with an equimolar amount of CuCl·2H2O, and the rest was the same as in Example 1, to obtain the catalyst Cu-PTA-5.

[0059] Example 6

[0060] Following the process of Example 1, the tannic acid in step (2) was replaced with an equimolar amount of gallic acid, and the rest was the same as in Example 1, to prepare the catalyst Cu-PGA.

[0061] Comparative Example 1

[0062] Following the process of Example 1, CuSO4·5H2O in step (2) was replaced with an equimolar amount of FeSO4·7H2O, and the rest was the same as in Example 1, to obtain the catalyst Fe-PTA.

[0063] Comparative Example 2

[0064] Following the process of Example 1, CuSO4·5H2O in step (2) was replaced with an equimolar amount of CoSO4·7H2O, and the rest was the same as in Example 1, to obtain the catalyst Co-PTA.

[0065] Comparative Example 3

[0066] Following the process of Example 1, CuSO4·5H2O in step (2) was replaced with an equimolar amount of NiSO4·7H2O, and the rest was the same as in Example 1, to obtain the catalyst Ni-PTA.

[0067] Comparative Example 4

[0068] Following the process of Example 1, CuSO4·5H2O in step (2) was replaced with an equimolar amount of ZnSO4·7H2O, and the rest was the same as in Example 1, to obtain the catalyst Zn-PTA.

[0069] Comparative Example 5

[0070] Following the process of Example 1, with the total metal content remaining unchanged, CuSO4·5H2O in step (2) was replaced with a mixture of CuSO4·5H2O and FeSO4·7H2O (molar ratio of 1:1), and the rest was the same as in Example 1, to obtain the catalyst Cu. 0.5 Fe 0.5 -PTA.

[0071] Comparative Example 6

[0072] Following the process of Example 1, with the total metal content unchanged, CuSO4·5H2O in step (2) was replaced with a mixture of CuSO4·5H2O, FeSO4·7H2O, and CoSO4·7H2O (molar ratio of 2:1:1), and the rest was the same as in Example 1. The resulting catalyst was denoted as Cu. 0.5 Fe 0.25 Co 0.25 -PTA.

[0073] Comparative Example 7

[0074] Following the process of Example 1, the addition of formaldehyde in step (2) was omitted, and the rest was the same as in Example 1. After the reaction was completed, the product was a homogeneous brown transparent solution, and no precipitate or solid particles were observed to form. After centrifuging the solution in step (5) (10000 rpm, 30 min), no solid precipitate could be collected in the centrifuge tube, indicating that the target catalyst was not successfully prepared.

[0075] In the application example, the catalysts prepared in the examples and comparative examples were used as electrodes to catalyze the CO2 reduction reaction in order to test their performance.

[0076] (1) Electrode preparation: 10 mg of catalyst was dispersed in 970 μL of isopropanol and 30 μL of 5 wt.% Nafion solution, and ultrasonically mixed for 2 h to form a slurry. 100 μL of the slurry was then coated onto a 1×1 cm electrode. 2 Carbon paper (loading 0.44 mg cm) -2 );

[0077] (2) CO2 reduction performance test: A Shanghai Chenhua CHI 760E electrochemical workstation was used. 1M KOH / H2O and 1M KOH / D2O were used as electrolytes in the flow cell, with Ag / AgCl as the reference electrode and nickel foam as the counter electrode. The CO2 flow rate was 20 sccm, and the product distribution was measured under constant current. Gas chromatography was used to record the product concentration and calculate the Faraday efficiency of the product.

[0078] The catalysts prepared in the examples and comparative examples were tested in a 1M KOH / H2O electrolyte at a current density of 400 mA cm⁻¹. -2 The performance of electroreduction of CO2 to prepare CH4 is shown in Table 1.

[0079] Table 1 shows the single-atom electrocatalysts prepared in the examples and comparative examples at a current density of 400 mA / cm² in a 1 M KOH / H₂O electrolyte. -2 Performance of electroreduction of CO2 to produce CH4

[0080]

[0081] Figure 5 Table 2 shows the performance graphs and data of the catalyst prepared in Example 1 in the electroreduction of CO2 to CH4 in a 1M KOH / H2O electrolyte. It can be seen that in the 1M KOH / H2O electrolyte system, at 400 mA cm⁻¹... –2 At a given current density, CH4 achieves a Faraday efficiency of 75.5% and a partial current density of 302.0 mA / cm². -2 . Figure 6 The catalyst prepared in Example 1 was subjected to 300 mA cm⁻¹ in a 1M KOH / H₂O electrolyte. –2Stability test curves under constant current for 22 hours. The catalyst stability test curves show that at 300 mA cm⁻¹... -2 Under constant current density, the potential remained basically stable during continuous operation for 22 hours, and the CH4 Faraday efficiency remained above 60%.

[0082] Figure 7 Table 3 shows the performance graphs and data of the catalyst prepared in Example 1 in the electroreduction of CO2 to CD4 in a 1M KOH / D2O electrolyte. It can be seen that the catalyst in a 1M KOH / H2O electrolyte at 500 mA cm⁻¹ –2 At a given current density, the CD4 Faraday efficiency reaches 83.1%, with a partial current density of 415.6 mA cm⁻¹. –2 ; Figure 8 The catalyst prepared in Example 1 was subjected to 300 mA cm⁻¹ in a 1M KOH / D₂O electrolyte. –2 Stability test curves under constant current for 22 hours. The stability test curves confirm that at 300mA cm⁻¹… –2 Under constant current density, the potential fluctuation is small during continuous operation for 22 hours, and the CD4 Faraday efficiency remains above 80%.

[0083] Table 2 shows the performance of the electrocatalyst Cu-PTA prepared in Example 1 in the electroreduction of CO2 to CH4 at different current densities in a 1M KOH / H2O electrolyte.

[0084]

[0085] Table 3 shows the performance of the electrocatalyst Cu-PTA prepared in Example 1 in the electroreduction of CO2 to CD4 in 1M KOH / D2O electrolyte at different current densities.

[0086]

[0087] Example 1: A Cu-PTA catalyst was prepared using 120 mg CuSO4·5H2O (tannic acid / copper salt = 1:0.3) at 400 mA cm⁻¹. –2 The CH4 production selectivity reached 75.5%. When the copper loading was halved (Example 2, Cu-PTA-2), the CH4 production selectivity decreased to 72.9% due to insufficient catalytic active site density; while doubling the copper loading (Example 3, Cu-PTA-3) caused some copper agglomeration to form copper nanoparticles, promoting C–C coupling, resulting in an increase in the yield of multi-carbon products (C2H4), and the CH4 production selectivity decreased to 72.3%.

[0088] Comparative Examples 1-4 were replaced with Fe, Co, Ni, and Zn metal salts, respectively. Because these metals more readily adsorb *H at their M–O4 sites, the HER selectivity of the side reaction increased to >75%, while the CH4 selectivity decreased to <2.3%. Comparative Example 5 used a Cu / Fe bimetallic (Cu...) 0.5 Fe 0.5 In the case of Cu-PTA (as in Example 1), although the total metal content remains the same, the Cu site density is reduced to half, the existing Fe sites strongly compete for protons to generate H2 (HER efficiency > 90%), and the Cu–O4 hydrogen bond microenvironment is disrupted, resulting in a decrease in CH4 production selectivity to 46.2%. Furthermore, although Cu in Comparative Example 5... 0.5 Fe 0.5 -PTA has the same copper loading as Cu-PTA-2 in Example 2, but the CH4 Faraday efficiency differs significantly, with Cu... 0.5 Fe 0.5 The 46.2% of -PTA and 72.9% of Cu-PTA-2 further confirm the strong competitive HER of the Fe site.

[0089] Compared to Example 1, the Cu-PGA catalyst obtained using gallic acid ligands in Example 6 contains fewer uncoordinated hydroxyl groups, thus its reaction pathway during CO2 electroreduction is... * CO is the dominant component, leading to the production of a large amount of CO byproducts, thus exhibiting relatively low CH4 selectivity (65.4%, 400 mA cm⁻¹). -2 However, the overall effect is still good.

[0090] The target catalyst was not obtained through the process in Comparative Example 7, but the catalyst powder from Comparative Example 7 was obtained by freeze-drying and CO2 electroreduction experiments were conducted. Since freeze-drying cannot remove impurities from the catalyst, the CO2 electroreduction product was mainly hydrogen evolution.

[0091] It is noteworthy that the CH4 selectivity of Cu-PTA in 1M KOH / H2O electrolyte (Table 2) is within 400 mA cm⁻¹. –2 The concentration reached 75.5%, but in 1M KOH / D2O electrolyte (Table 3), it exhibited a rare reverse isotope effect, significantly promoting CD4 formation and inhibiting DER; at 500 mA cm⁻¹ –2 The Faraday efficiency of CD4 reached 83.1%, and the HER / DER side reaction kinetics were suppressed under D2O conditions (H2 yield decreased from 27.37% to 9.19% of D2).

[0092] The core reason for the significant suppression of DER when D2O is used instead of H2O in the electroreduction of CO2 lies in the kinetic energy barrier difference induced by the deuterium isotope. Specifically, in an alkaline environment, the rate-determining step of DER is the dissociation of the O–D bond in the D2O molecule, and the dissociation energy of the O–D bond is higher than that of the O–H bond (H2O). This energy difference stems from the lower zero-point vibrational energy caused by the larger mass of the deuterium atom, making the breaking of the O–D bond require a higher activation energy. The limited adsorption capacity of the Cu catalyst (located on the weak adsorption side of the HER volcano diagram) for *D further amplifies this kinetic limitation, forcing the reaction to proceed at a higher cathode overpotential, thus directly suppressing the rate of DER. In addition, the slow dissociation characteristics of D2O indirectly improve the mass transport conditions, further reducing the occurrence of DER. At high current densities, excessive water permeation in the H2O system leads to flooding of the gas diffusion layer (GDL), hindering CO2 transport and exacerbating HER; while the kinetic limitation of D2O dissociation reduces water accumulation in the cathode region, alleviating the CO2 mass transport bottleneck, thus indirectly suppressing DER.

Claims

1. A method for preparing a single-atom electrocatalyst of a metal polyphenol network, characterized in that, Including the following steps: Step 1: Dissolve Pluronic F127 and adjust the pH to obtain an alkaline solution of Pluronic F127; Step 2: Add polyphenols and formaldehyde to the alkaline solution from Step 1 to carry out a cross-linking reaction; Step 3: Add a metal salt solution dropwise to the reaction solution in Step 2, stir and mix, and then carry out a hydrothermal reaction. Centrifuge to obtain a precipitate, and wash and dry it to obtain the single-atom catalyst.

2. The method for preparing the single-atom electrocatalyst of the metal polyphenol network according to claim 1, characterized in that, The polyphenols include one or more of tannic acid, caffeic acid, protocatechuic aldehyde, and gallic acid; and / or, the molar ratio of the polyphenols to formaldehyde is 1:1 to 1:

6.

3. The method for preparing the single-atom electrocatalyst of the metal polyphenol network according to claim 1, characterized in that, The metal salt includes a soluble salt of one or more metals selected from copper, iron, zinc, nickel, and cobalt; preferably, the metal salt is a copper salt, including at least one of copper sulfate, copper nitrate, and copper chloride.

4. The method for preparing the single-atom electrocatalyst of the metal polyphenol network according to claim 1, characterized in that, The mass ratio of the polyphenol to the metal salt is 1:0.05-0.

5.

5. The method for preparing the single-atom electrocatalyst of the metal polyphenol network according to claim 1, characterized in that, The solvent used to dissolve Pluronic F127 in step 1 includes one or more mixed solvents selected from water, ethanol, and isopropanol; And / or, the mass ratio of Pluronic F127 to polyphenol is 1:0.5-1; And / or, the pH of the alkaline solution is 8-10.

6. The method for preparing the single-atom electrocatalyst of the metal polyphenol network according to claim 1, characterized in that, The crosslinking reaction is carried out at room temperature for 12-48 hours. In step 3, the mixing is carried out continuously at room temperature for 12-48 hours.

7. The method for preparing the single-atom electrocatalyst of the metal polyphenol network according to claim 1, characterized in that, The hydrothermal reaction temperature is 80-150℃, and the reaction time is 12-48h.

8. A single-atom electrocatalyst of a metal polyphenol network prepared by the preparation method according to any one of claims 1-6.

9. The application of the single-atom electrocatalyst according to claim 7 as a working electrode in the electrocatalytic reduction reaction of CO2.

10. The application of the single-atom electrocatalyst according to claim 7 as a working electrode in the electrocatalytic reduction of CO2 to prepare CH4 and / or CD4.

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