A platinum-cobalt phosphate catalyst for selective electro-oxidation of ethylene glycol to glycolic acid and its preparation method and application

Abstract

This invention discloses a platinum-cobalt phosphate catalyst for the selective electrooxidation of ethylene glycol to glycolic acid, its preparation method, and its application. The preparation method includes: S1, pretreating nickel foam (NF); S2, dissolving disodium hydrogen phosphate dodecahydrate and hexadecyltrimethylammonium bromide in a mixture of water and ethylene glycol, adding cobalt nitrate and stirring to obtain a precursor; S3, immersing the nickel foam in the precursor solution and refrigerating it overnight at low temperature; S4, transferring it to a reaction vessel and hydrothermally heating it at 160 °C for 10 hours to obtain cobalt phosphate (CoPO / NF); S5, using CoPO / NF as the working electrode, electrochemically depositing platinum in an H2PtCl6 and KOH electrolyte using cyclic voltammetry; S6, washing and vacuum drying to obtain the final product. This invention is the first to prepare a platinum-cobalt phosphate catalyst for the selective electrooxidation of ethylene glycol to glycolic acid at 100 mA cm⁻¹. ‑2 With a working potential of only 0.67 V at current density (relative to RHE) and a Faraday efficiency of 100% for glycolic acid, it has significant advantages and application potential in the highly selective production of glycolic acid in the electro-oxidation reaction of ethylene glycol.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysts, and more specifically to a platinum-cobalt phosphate catalyst for the selective electrooxidation of ethylene glycol to glycolic acid, its preparation method, and its application. Background Technology

[0002] Against the backdrop of a escalating global energy crisis and environmental problems, electrocatalytic water splitting for hydrogen evolution has garnered significant attention due to its ability to convert renewable electricity into clean hydrogen energy, and is considered a crucial pathway to achieving a sustainable energy system. However, in traditional water electrolysis hydrogen production systems, the oxygen evolution reaction (OER) at the anode involves a complex four-electron transfer process, resulting in a lengthy reaction path and sluggish kinetics, becoming a key bottleneck restricting overall energy conversion efficiency. To overcome this limitation, thermodynamically more favorable small-molecule oxidation reactions have been introduced into the anode system to assist water electrolysis hydrogen production technology. By using anodic oxidation reactions of biomass-derived molecules (such as glycerol, methanol, and ethylene glycol) to replace traditional OER, the problems of high overpotential and slow kinetics of OER are effectively avoided. Furthermore, while reducing hydrogen evolution energy consumption, the co-production of high-value-added chemicals at the anode can be achieved, thus realizing synergistic effects between cathode hydrogen production and anode resource utilization, providing a new approach for green hydrogen production and biomass conversion.

[0003] Currently, industrial production of glycolic acid mainly relies on the carbonylation reaction of formaldehyde with syngas or the alkaline hydrolysis process of chloroacetic acid. The former requires harsh conditions of high temperature (50~400 ℃) and high pressure (0.1~100 MPa), while the latter involves the use of highly corrosive raw materials and complex separation processes, resulting in high energy consumption and significant environmental burden. In contrast, the selective electro-oxidation of ethylene glycol (EGOR) to produce glycolic acid can be carried out at ambient temperature and pressure, and the conversion is driven by renewable electricity, exhibiting advantages such as mild conditions, green process, and low energy consumption, thus becoming a promising alternative route. The key challenge in the electrocatalytic oxidation of ethylene glycol to glycolic acid lies in the precise control of the degree of oxidation. An ideal reaction pathway requires the catalyst to selectively activate the hydroxyl groups in ethylene glycol, oxidizing them only to aldehyde or carboxyl groups, while avoiding the breaking of C–C bonds. However, most current electrocatalysts (such as Fe, Ni, and Co-based materials) tend to deeply oxidize ethylene glycol to CO2 or formic acid during the reaction, resulting in limited selectivity for the target product, glycolic acid. In recent years, noble metal-based catalysts, especially Pt and Pd, have attracted widespread attention in the selective oxidation of ethylene glycol to glycolic acid due to their excellent oxidation activity and stability against hydroxyl oxidation intermediates. However, current electrocatalysts for ethylene glycol generally suffer from problems such as high operating potentials, slow reaction kinetics, and insufficient long-term stability. Therefore, developing electrocatalysts with high catalytic activity, high selectivity, and good stability to achieve efficient conversion of ethylene glycol to glycolic acid under mild conditions has significant research value and practical implications. Thus, developing EGOR catalysts with good catalytic activity and C2 selectivity is an urgent need.

[0004] Significant progress has been made in the selective oxidation of ethylene glycol to formic acid; however, reports on C2 products remain relatively limited. The two hydroxyl groups in ethylene glycol possess both structural symmetry and high reactivity. Therefore, precisely controlling the oxidation process of individual hydroxyl groups to avoid C-C bond breakage or over-oxidation is a key challenge for achieving efficient electrochemical conversion. The formation and adsorption of the glycolaldehyde intermediate are crucial steps in the subsequent generation of C2 products and enhancing their selectivity. Therefore, efforts should be focused on developing electrocatalysts that possess low potential, high activity, and high stability, and can control the adsorption / desorption behavior of reactants and intermediates on the catalyst surface, enabling the highly selective conversion of ethylene glycol into the higher-value C2 product (glycolic acid), thereby further improving the overall economic efficiency and application potential of biomass electrocatalytic conversion. Summary of the Invention

[0005] The purpose of this invention is to provide a platinum-cobalt phosphate catalyst for the selective electro-oxidation of ethylene glycol to glycolic acid, its preparation method and application, thereby solving the problem of the lack of an ethylene glycol electro-oxidation catalyst with low operating potential, high glycolic acid selectivity and high stability in the prior art.

[0006] According to a first aspect of the present invention, a method for preparing a catalyst for the selective electro-oxidation of platinum-cobalt phosphate ethylene glycol to glycolic acid is provided, comprising the following steps: S1, placing nickel foam sequentially in a mixed solution of acetone:HCl in a volume ratio of 1:1, ethanol, and deionized water, ultrasonically cleaning each solution for 5 minutes, and then drying at 60 °C for 10-14 hours to remove surface impurities; S2, dissolving disodium hydrogen phosphate dodecahydrate and hexadecyltrimethylammonium bromide in a molar ratio of 3:1 in a mixed solvent of 12 mL deionized water and 8 mL ethylene glycol, and magnetically stirring to ensure complete dissolution; then adding cobalt nitrate hexahydrate and continuing stirring to obtain a blue precursor solution; S3, immersing the nickel foam treated in step S1 into the above blue precursor solution and allowing it to stand overnight at a low temperature to allow cobalt phosphate to rapidly crystallize on the surface of the nickel foam, forming a nanoflower-like structure; S4, transferring the mixture containing nickel foam obtained in step S3 to a hydrothermal reactor lined with polytetrafluoroethylene, and heating at 140-170 °C. The reaction was carried out at a constant temperature of ℃ for 8-12 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The nickel foam was removed, thoroughly rinsed with deionized water, and finally dried in an oven to obtain the cobalt phosphate (CoPO / NF) electrocatalyst. In step S5, the CoPO / NF obtained in step S4 and the NF obtained in step S1 were used as working electrodes, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolyte was a solution containing H2PtCl6 and KOH in a volume ratio of 2:3. Electrochemical deposition of 6wt%~12wt% Pt was performed within a potential window of -1.42 V to -0.9 V. In step S6, the Pt-CoPO / NF electrode obtained in step S5 was vacuum dried at 30-40 ℃ for 6-12 hours.

[0007] Preferably, step S1 includes: placing the nickel foam in a 1:1 mixture of acetone and 1 M HCl, ethanol, and deionized water, ultrasonically cleaning each for 5 minutes, and finally drying at 60 °C for 10-14 hours.

[0008] Preferably, in step S2, the molar ratio of disodium hydrogen phosphate dodecahydrate to hexadecyltrimethylammonium bromide is 3:1, and the amount of cobalt nitrate hexahydrate is 3 mmol.

[0009] Preferably, step S3 includes: refrigerating overnight at a low temperature of 0~5 ℃.

[0010] Preferably, in step S4, the reaction mixture is placed in a sealed reaction vessel and heated to react at a set temperature and pressure to synthesize cobalt phosphate (CoPO / NF).

[0011] Preferably, in step S5, a three-electrode system is used, with CoPO / NF and the NF obtained in step S1 as the working electrodes, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolyte is a solution containing 10~14 mM H2PtCl6 and 1 M KOH in a volume ratio of 2:3. Using cyclic voltammetry (CV), Pt with a content of 6 wt%~12 wt% is electrochemically deposited within a potential window of -1.42 V to -0.9 V.

[0012] Preferably, step S6 includes: vacuum drying at 30~40 ℃ for 6~12 hours.

[0013] According to the preparation method provided by the present invention, step S1 aims to remove surface oxide impurities, which is a common method for treating nickel foam and has been reported in academic papers; step S2 aims to prepare a blue precursor solution to facilitate the subsequent preparation of platinum-cobalt phosphate; step S3 aims to rapidly crystallize cobalt phosphate on the surface of nickel foam at low temperature to grow nanoflower crystals; step S4 aims to synthesize cobalt phosphate CoPO / NF by heating a closed reaction vessel under specific temperature and pressure conditions; step S5 aims to synthesize platinum-cobalt phosphate (Pt-CoPO / NF) and Pt / NF by depositing platinum on CoPO / NF and NF under specific parameters using cyclic voltammetry; step S6 aims to place the electrodeposited electrode in a vacuum drying oven and dry it at 30-40 °C for 6-12 hours to remove residual solvent on the surface and prevent the platinum component from oxidizing in the air, thus ensuring the activity and stability of the catalyst.

[0014] According to a second aspect of the present invention, a Pt-CoPO / NF ethylene glycol electrooxidation catalyst prepared according to the above preparation method is provided, which can achieve oxidation at 100 mA cm⁻¹. -2 At current densities, the operating potential is as low as 0.67 V (relative to RHE).

[0015] According to a third aspect of the invention, there is an application of a platinum-cobalt phosphate catalyst for the selective electro-oxidation of ethylene glycol to glycolic acid.

[0016] Preferably, Co generated by electrochemical reconstruction of Pt-CoPO / NF 3+ Able to convert OH at lower potentials - Oxidation results in the formation of an active hydroxyl species (*OH). *OH not only promotes the breaking of the OH / CH bond in the ethylene glycol molecule, accelerating the dehydrogenation process, but also rapidly converts the carbonyl intermediate into the target product, glycolic acid. Simultaneously, the in-situ alloy structure formed by Pt and Co, under the synergistic regulation of the interface, leads to… dThe downward shift of the center promotes the rapid desorption and transfer of glycolic acid from the active Pt site, effectively inhibiting the breaking of C-C bonds.

[0017] According to a preferred embodiment of the present invention, a method for preparing a platinum-cobalt phosphate catalyst for the selective electrooxidation of ethylene glycol to glycolic acid is provided, comprising the following steps: Step 1: Removing impurities from the surface of nickel foam: First, using an acetone:1 M HCl = 1:1 solution, ethanol, and deionized water respectively to clean (1×2 cm) 2 The process involved five steps: 1) Sonicating the nickel foam for 5 minutes and drying it at 60°C for 12 hours. 2) Dissolving 3 mmol of disodium hydrogen phosphate dodecahydrate and 1 mmol of hexadecyltrimethylammonium bromide in a mixture of 12 mL of water and 8 mL of ethylene glycol and stirring magnetically for 3 minutes. Then, adding 0.873 g (3 mmol) of cobalt nitrate hexahydrate to the solution and stirring for another 20 minutes yielded a blue precursor solution. 3) Immersing the pre-cleaned nickel foam in the above mixture and refrigerating it overnight at 0–5°C. 4) Transferring the mixture to a 50 mL Teflon hydrothermal reactor and maintaining it at 160°C for 10 hours. After naturally cooling to room temperature, thoroughly rinsing the sample with deionized water and then drying it in a 60°C oven for 12 hours yielded CoPO / NF. 5) Using a three-electrode system, CoPO / NF and NF were used as working electrodes, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolyte was a solution containing 12.6 mM H₂PtCl₆ and 1 M KOH in a volume ratio of 2:3. A certain amount of Pt (6 wt%~12 wt%, depending on the specific application) was electrochemically deposited using cyclic voltammetry (CV) within a potential window of -1.42 V to -0.9 V. The sixth step involved vacuum drying the electrodeposited electrode at 30~40 ℃ for 6~12 hours.

[0018] As described in the background section of this invention, on the one hand, noble metal-based catalysts (such as Pt and Pd) exhibit good stabilization capabilities for hydroxyl oxidation intermediates in the selective oxidation of ethylene glycol to glycolic acid. However, their application is still limited by problems such as high operating potential, slow reaction kinetics, and insufficient long-term stability, making it difficult to achieve efficient conversion under low energy consumption conditions. On the other hand, although non-noble metal-based electrocatalysts (such as Fe, Ni, and Co-based materials) have cost advantages and can drive the ethylene glycol oxidation reaction under specific conditions, they tend to excessively break C-C bonds, resulting in low selectivity for the target product glycolic acid. Furthermore, they usually require a high operating potential (>1.5 V relative to RHE) to achieve industrial-grade current density, which restricts their practical application potential for high-selectivity generation of C2 products under mild conditions.

[0019] To address the shortcomings of existing ethylene glycol electrooxidation catalysts, such as high operating potential, poor ethylene glycol selectivity, and poor stability, this invention provides a platinum-cobalt phosphate catalyst for the selective electrooxidation of ethylene glycol to glycolic acid, along with its preparation method and application. First, a cobalt phosphate support is synthesized via a hydrothermal method. Then, platinum is controllably loaded onto the surface of the cobalt phosphate using cyclic voltammetric electrodeposition. By adjusting the electrodeposition parameters (number of scans), the platinum loading can be controlled, thereby optimizing its electrocatalytic performance for the ethylene glycol electrooxidation reaction. Through corresponding electrochemical tests, we found that a specific amount of platinum in the cobalt phosphate can lower the operating potential while simultaneously improving the selectivity and stability of the glycolic acid electrooxidation reaction.

[0020] The key inventive points of this invention are as follows: 1) This invention demonstrates a significant performance improvement by electrodepositing a certain amount of platinum (Pt) into cobalt phosphate (CoPO / NF). Specifically, the Pt-CoPO / NF electrocatalyst exhibits improved performance at 100 mA cm⁻¹. -2 At a current density of 0.67 V, the operating potential is 0.67 V (relative to RHE). Pt-CoPO / NF exhibits both excellent glycolic acid selectivity and stability: at 50 mA cm⁻¹ -2 Operating at current densities of 100 and 150 mA cm⁻¹ for 24 hours, the Faraday efficiency of glycolic acid remained above 90%; at current densities of 100 and 150 mA cm⁻¹... -2 Under current densities of 8 hours, the glycolic acid Faraday efficiency was greater than 85% in both cases. 2) This invention provides a simpler method for preparing an ethylene glycol electrooxidation catalyst by electrodepositing a certain amount of Pt into CoPO, specifically by electrochemically depositing 6 wt% to 12 wt% Pt within a potential window of -1.42 V to -0.9 V using cyclic voltammetry. This promotes the widespread application of ethylene glycol electrooxidation technology in industrial settings. Conversely, excessive or insufficient Pt content will lead to a decrease in the electrochemical performance of the prepared ethylene glycol electrooxidation catalyst, specifically reaching 100 mA cm⁻¹. -2 The required voltage has increased, but the demand cannot be met; 3) The Pt-CoPO / NF catalyst prepared according to the method of this invention was verified by in-situ Raman spectroscopy to generate Co through electrochemical reconstruction. 3+ Able to convert OH at lower potentials - Oxidation to active hydroxyl species (*OH) accelerates the dehydrogenation process. Theoretical calculations show that the in-situ alloy structure formed by Pt and Co, under the synergistic regulation of the interface, leads to... d The downward shift of the center promotes the rapid desorption and transfer of glycolic acid from the active Pt site, effectively inhibiting the breaking of C-C bonds.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) Compared with other noble metal catalysts, the Pt-CoPO / NF composite material prepared in this invention exhibits significantly improved electrocatalytic performance in the electro-oxidation reaction of ethylene glycol. At a current density of 100 mA·cm⁻¹ -2 At this point, its operating potential is as low as 0.67 V (relative to RHE), overcoming the problems of high operating potential, poor glycolic acid selectivity, and insufficient stability commonly found in non-noble metal-based catalysts during ethylene glycol oxidation. Furthermore, Pt-CoPO / NF exhibits excellent product selectivity and operational stability: at 50 mA·cm⁻¹ -2 After 24 hours of continuous operation at a current density, the glycolic acid Faradaic efficiency remained above 90% at 100 mA·cm⁻¹. -2 and 150 mA·cm -2 Under high current density, the glycolic acid Faraday efficiency was higher than 85% after 8 hours of operation. 2) Addressing the issues of high operating potential and insufficient stability of noble metal-based catalysts in existing technologies, and poor selectivity of non-noble metal-based catalysts for glycolic acid and difficulty in achieving industrial current densities at low potentials, this invention proposes modifying cobalt phosphate through electrodeposition of platinum to optimize its catalytic performance in the selective electro-oxidation of ethylene glycol to glycolic acid. This significantly improves the current density at low potentials, the selectivity of the target product, and the operational stability. Compared to other solutions, such as introducing complex nanostructure modifications, the preparation method of this invention is simpler, allowing for in-situ alloy formation, thus making the highly efficient electro-oxidation of ethylene glycol to glycolic acid technology more feasible for industrial applications. 3) The divalent cobalt-oxygen bond (Co) in cobalt phosphate tetrahydrate (Co3(PO4)2·4H2O) prepared by hydrothermal synthesis. 2+ During the selective electro-oxidation of ethylene glycol, -O tends to reconstruct tetravalent cobalt-oxygen bonds (Co-O) to form tetravalent cobalt-oxygen bonds. 4+ -O) bonds; however, when cobalt phosphate is deposited on platinum, a cobalt-platinum alloy is formed in situ, and the Co generated by electrochemical reconstruction... 3+ Able to convert OH at lower potentials - Oxidation to active hydroxyl species (*OH) accelerates the dehydrogenation process. Theoretical calculations show that the in-situ alloy structure formed by Pt and Co, under the synergistic regulation of the interface, leads to... d The downward shift of the bond center promotes the rapid desorption and transfer of glycolic acid from the active Pt site, effectively inhibiting C / C bond breakage. This invention is the first to discover that Pt can form a CoPt alloy in situ with Co via electrodeposition, which is beneficial for optimizing the adsorption energy of intermediates during the electro-oxidation of ethylene glycol, enabling selective oxidation to glycolic acid.

[0022] In summary, this invention, by electrodepositing a certain amount of Pt into CoPO / NF during the synthesis process, with the Pt content controlled at 6 wt%~12 wt%, for the first time prepares a platinum-cobalt phosphate catalyst for the selective electrooxidation of ethylene glycol to glycolic acid, at 100 mA cm⁻¹. -2 At current densities, the operating potential is as low as 0.67 V (relative to RHE). The relatively low operating potential broadens the practical application of the glycolic acid electro-oxidation catalyst in the electrosynthesis of glycolic acid, making the platinum-cobalt phosphate catalyst of this invention have significant advantages and application potential in the selective electro-oxidation of ethylene glycol to glycolic acid. Attached Figure Description

[0023] Figure 1 Scanning electron microscope images of the Pt-CoPO / NF electrocatalyst (a) and the prepared CoPO electrocatalyst (b) prepared in Example 1 of the present invention; Figure 2 Linear sweep voltammetry curves of electrocatalysts Pt-CoPO / NF, CoPO / NF, Pt / NF, and NF as controls; Figure 3 The double-layer capacitance curves are for the electrocatalysts Pt-CoPO / NF, CoPO / NF, Pt / NF, and NF as controls. Figure 4 Chronopotential curves of the electrocatalyst Pt-CoPO / NF (a) and its Faradaic efficiency of glycolic acid at different current densities (b). Figure 5 Cyclic voltammetry curves of electrocatalysts Pt-CoPO / NF, CoPO / NF, and Pt / NF are shown. Figure 6 The in-situ Raman spectrum of the CoPO / NF electrocatalyst is shown below. Figure 7 The in-situ Raman spectra of Pt-CoPO / NF (a) and Pt / NF (b) electrocatalysts are shown. Figure 8 The density of states diagrams for the electrocatalysts Pt-CoPO / NF and Pt / NF are shown. Figure 9 The in-situ infrared spectrum of the electrocatalyst Pt-CoPO / NF is shown. Figure 10 The Faraday efficiency of Pt-CoPO / NF, CoPO / NF, and Pt / NF electrocatalysts for glycolic acid and formic acid; Figure 11 Linear sweep voltammetry curves of electrocatalysts Pt-CoPO / NF-L, Pt-CoPO / NF, and Pt-CoPO / NF-H. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, the techniques used in the embodiments are conventional practices in the art, or experimental methods recommended by the instrument manufacturer. Unless otherwise specified, the reagents and materials used in the embodiments are commercially available. Example

[0025] All reagents used in the preparation of the platinum-cobalt phosphate catalyst in this invention are of analytical grade and were purchased from Sinopharm Chemical Reagent Co., Ltd. The specific preparation process of a platinum-cobalt phosphate catalyst for the selective electrooxidation of ethylene glycol to glycolic acid is as follows.

[0026] 1. Place the nickel foam in a 1:1 mixture of acetone and 1 M HCl, ethanol, and deionized water in sequence, and ultrasonically clean each solution for 5 minutes. Finally, dry it at 60 °C for 10-14 hours.

[0027] 2. Disodium hydrogen phosphate dodecahydrate (1.074 g) and hexadecyltrimethylammonium bromide (0.364 g) were dissolved in a mixed solvent of 12 mL deionized water and 8 mL ethylene glycol at a molar ratio of 3:1. The mixture was magnetically stirred for 3 minutes to ensure complete dissolution. Then, 0.873 g (3 mmol) of cobalt nitrate hexahydrate was added, and the mixture was stirred for another 5 minutes to obtain a blue precursor solution.

[0028] 3. Immerse the pre-cleaned nickel foam in the above mixed solution and refrigerate overnight at 0-5°C.

[0029] 4. Transfer the mixture into a 50 mL Teflon hydrothermal reactor and maintain it at 160 °C for 10 hours. After naturally cooling to room temperature, thoroughly rinse the sample with deionized water, and then dry it in an oven at 60 °C for 12 hours to obtain cobalt phosphate (denoted as CoPO / NF).

[0030] 5. A three-electrode system was used, with CoPO / NF and NF as working electrodes, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolyte was a solution containing 12.6 mM H₂PtCl₆ and 1 M KOH in a volume ratio of 2:3. Cyclic voltammetry (CV) was used, with a scan rate of 1 mV / s within a potential window from -1.42 V to -0.9 V. -1 With 25 scan cycles, Pt was electrochemically deposited to obtain platinum-cobalt phosphate (denoted as Pt-CoPO / NF) and Pt / NF.

[0031] 6. Dry the electrodeposited Pt-CoPO / NF under vacuum at 30~40 ℃ for 6~12 hours.

[0032] Electrochemical Testing and Product Analysis of Ethylene Glycol Electrooxidation Catalyst: Electrolysis was conducted using a single-cell electrolyzer. The ethylene glycol electrooxidation reaction was tested in a three-electrode system using a CHI electrochemical workstation (type 660e). The platinum-cobalt phosphate electrode was used as the working electrode, with alcohols dissolved in an alkaline aqueous solution as the electrolyte. A platinum sheet electrode served as the counter electrode, and an Ag / AgCl electrode was used as the reference electrode. The electrocatalytic selective oxidation reaction was carried out at room temperature (25-30 °C) to produce high-value-added glycolic acid. Cyclic voltammetry was performed at 50 mV / s. -1 The scanning rate is adjusted to activate the material and achieve a stable working state. Linear scanning voltammetry is performed at 5 mV / s. -1 The scan rate was used for testing. All recorded polarization curves were not iR corrected and were converted to the reversible hydrogen electrode scale using the following equation: E (relative to RHE) = E + 0.059 × pH + E Ag / AgCl Where E Ag / AgCl The relative value of RHE was 0.1976 V, and the pH was 14.

[0033] The formula for calculating the Tafel slope is as follows: η = a + b × log(j) Where η, b, and j represent overpotential, Tafel slope, and current density, respectively.

[0034] Double-layer capacitor (C dl The calculation formula for ) is as follows: C dl =∆ j / 2 / V Where ∆j is the difference between the anode and cathode current densities at open-circuit voltage.

[0035] Electrochemical impedance spectroscopy was performed at open-circuit voltage. The frequency range was 0.01 Hz to 100 kHz, and the amplitude was 10 mV. Chorometric potentiometry was used to evaluate the long-term performance of the electrocatalyst.

[0036] In-situ Raman spectroscopy: In-situ Raman spectroscopy was performed on a Horiba LabRAM HR Raman spectrometer. A platinum wire was used as the counter electrode, and Ag / AgCl as the reference electrode. The experiment was conducted in situ using a K004 in-situ Raman cell from Tianjin Aida. The excitation wavelength was 532 nm, and a 50× microscope objective with a numerical aperture of 0.55 was used. Spectra of the pretreated electrode were collected at each applied potential for 60 seconds.

[0037] Originally for infrared testing: The experiment employed a typical three-electrode system, using a silicon wafer with a deposited gold nanofilm as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum mesh as the counter electrode. During testing, infrared light was coupled into the silicon wafer from the back side at an incident angle of approximately 45°, undergoing total internal reflection at the silicon / gold film interface, thus selectively detecting species on the gold film surface and in its adjacent areas. An electrochemical workstation was responsible for applying the potential and measuring the response current. Infrared spectra were simultaneously acquired at each set stable potential. Each data point was typically obtained by averaging the interferogram signals from 32 cumulative scans, with a single spectrum acquisition time of approximately 25 seconds.

[0038] Theoretical calculations: Density functional theory (DFT) simulations were performed using the Vienna Atomic-Level Simulation Package (VASP). The Projected Enhanced Wave (PAW) method was employed to describe the core electron interaction. The Pedwer-Burke-Enzehoff (PBE) form of the generalized gradient approximation (GGA) was chosen to account for exchange-correlation effects. Furthermore, Grimm's DFT-D3 empirical correction was integrated to accurately describe the van der Waals (vdW) interaction. A plane-wave basis set with a kinetic energy cutoff of 450 eV was implemented, and the Brillouin zone was sampled using a gamma-centered Monkhorst-Parker k-point grid.

[0039] The content of products from the ethylene glycol oxidation reaction was analyzed using nuclear magnetic resonance (NMR, Avance III 400 instrument (Bruker)). First, a series of products at different concentrations (0.5 mmol L⁻¹) were prepared. -1 1 mmol L -1 2 mmol L -1 3 mmol L -1 5 mmol L -1 A mixed solution of formic acid and glycolic acid was prepared. 0.5 mL of this mixed solution and 0.1 mL of heavy water were added to an NMR tube and thoroughly mixed before NMR testing. A standard curve was plotted based on the ratio of the integrated intensity of the ion signal peak to the ion concentration. To analyze the products in the electrolyte, 0.5 mL of electrolyte and 0.1 mL of heavy water were added to an NMR tube and thoroughly mixed. NMR testing was then performed to obtain the overall intensity of the synthesized ion signal. The glycolic acid content was calculated based on the standard curve. The Faraday efficiency is calculated as follows: The Faraday efficiency of glycolic acid = N × F × n / Q = N × F × n / (I × t) Where N is the number of moles of the product, N is the number of moles of glycolic acid produced, F is the Faraday constant, I is the applied current, and t is the electrolysis time.

[0040] The morphology of the Pt-CoPO / NF and CoPO electrodes prepared above was characterized.

[0041] like Figure 1 CoPO / NF exhibits a disordered stacked nanosheet structure (see [link]). Figure 1 In section a), the nanosheets are relatively tightly packed, with some areas exhibiting agglomeration. However, after Pt electrodeposition modification, the microstructure of the material undergoes a significant transformation: the originally disordered CoPO nanosheets form a regular three-dimensional flower-like structure through the CV process (see section a). Figure 1 (b) In this section, the flower-like structure is composed of a large number of interwoven ultrathin nanosheets that uniformly cover the three-dimensional porous surface of the NF substrate. This unique three-dimensional nanoflower-like structure not only effectively inhibits the aggregation of nanosheets but also significantly increases the specific surface area of ​​the material, providing abundant active sites for electrochemical reactions, while also facilitating electrolyte penetration and rapid charge transport.

[0042] Electrochemical tests were performed on the Pt-CoPO / NF, CoPO / NF, and Pt / NF electrodes prepared above.

[0043] like Figure 2 In a 1 M KOH electrolyte containing 1 M EG, at 100 mA cm⁻¹ -2 At current densities of 0.67 V, Pt-CoPO / NF exhibits the lowest potential compared to CoPO / NF (1.52 V), Pt / NF (0.75 V), and bare NF (1.6 V), and also shows significantly reduced onset and overpotentials at high current densities. Pt-CoPO / NF requires only a low potential of 1.0 V to achieve a potential up to 400 mA cm⁻¹. -2 High current density.

[0044] like Figure 3 We measured the electrochemical double-layer capacitance (Cf) in the non-Radida region. dl To compare the performance of Pt-CoPO / NF, CoPO / NF, and Pt / NF, we can use the following method: Pt-CoPO / NF has a C0... dl Value (28.83 mF cm) -2 The value is much greater than Pt / NF (8.77 mF cm⁻¹). -2 ) and undoped CoPO (1.65 mF cm⁻¹) -2 ) and naked NF (1.35 mF cm -2This indicates that the introduction of Pt effectively increases the exposure density of active sites and optimizes the charge transport efficiency at the electrode-electrolyte interface. This implies the existence of more active sites on the Pt-CoPO / NF electrode. Based on these experimental results, we can infer that the improved activity of the ethylene glycol electrooxidation reaction is mainly due to two factors. First, the electrochemically active interface generated by the alloy structure between Pt and Co on the Pt-CoPO / NF electrode plays a crucial role in catalysis. Second, the increased electrochemical specific surface area of ​​the Pt-CoPO / NF electrode leads to the generation of more active sites.

[0045] Selective ethylene glycol electro-oxidation reaction of Pt-CoPO / NF, CoPO / NF and Pt / NF was tested using chronopotentiometric method.

[0046] like Figure 4 We used a chronopotentiometric method to test the selectivity of Pt-CoPO / NF for ethylene glycol electrooxidation. The results showed that Pt-CoPO / NF exhibited selectivity at 50 mA cm⁻¹. -2 It operated for at least 24 hours at the specified current density (see [reference]). Figure 4 (a) In this study, the oxidation potential of the electrode increased by only 200 mV, demonstrating its excellent long-term stability. Furthermore, we periodically collected electrolyte samples and measured the selectivity of glycolic acid by NMR analysis. During the electro-oxidation of ethylene glycol, the Faraday efficiency of glycolic acid was greater than 90%. Even at higher current densities (e.g., 100 mA cm⁻¹), this selectivity remained stable. -2 or 150 mA cm -2 Pt-CoPO / NF can still maintain a Faradaic efficiency of more than 85% for glycolic acid (see [link]). Figure 4 (b) in the middle.

[0047] like Figure 5 To further quantitatively evaluate the interfacial adsorption characteristics of the material, we employed CV analysis. A significant oxidation peak observed around 0.40 V corresponds to the -OH adsorption region on the electrode surface. Comparative experiments showed that the oxidation current density of Pt-CoPO / NF in this region was significantly higher than that of CoPO / NF and Pt / NF. This indicates that the introduction of Pt and its electronic synergistic effect with the support greatly enhances the adsorption efficiency of the catalyst for -OH species, thus providing sufficient reaction intermediates for the EGOR process and accelerating the entire EGOR process.

[0048] like Figure 6 We performed in-situ Raman spectroscopy analysis on CoPO. Under open-circuit potential (OCPT) conditions, at 518 cm⁻¹... -1 Nearby, belonging to Co 2+ -O key F 2gRaman peaks of the vibrational mode. With increasing potential, CoPO reaches a peak at 463 cm⁻¹. -1 New characteristic peaks gradually appear at this point, which is consistent with Co. 4+ The Co-O vibrational characteristics of the species are consistent, further confirming that CoPO undergoes a Co-O vibration during the reaction. 2+ →Co 3+ →Co 4+ The gradual oxidation process.

[0049] like Figure 7 Raman spectra of the Pt-CoPO / NF catalyst (see...) Figure 7 (a) 690 cm -1 and 780 cm -1 The Raman band at the potential gradually increases with increasing potential, corresponding to the bending and stretching vibration modes of oxygen-containing species adsorbed on the surface, which can be attributed to adsorption on Co. 3+ Hydroxylated species at the site (Co) 3+ Characteristic vibrations of -OH. Driven by the reaction potential, electron loss and structural reorganization occur on the catalyst surface, resulting in the formation of more Co. 3+ The substance. The resulting Co. 3+ -OH active species can effectively promote the oxidative dehydrogenation step of EGOR. Meanwhile, in the in-situ Raman spectrum of Pt / NF (see...), Figure 7 b) No obvious adsorption peaks related to OH were observed, further indicating that the close contact between the CoPt alloy and the cobalt oxide layer in Pt-CoPO / NF can synergistically promote the adsorption and activation of OH substances.

[0050] like Figure 8 Density functional theory (DFT) calculations show that Pt-CoPO / NF d center of the band (ε) d Compared to Pt / NF, it has shifted significantly downward, from -2.306 eV to -2.274 eV. d The moderate downward shift of the orbital center reduces the adsorption strength of intermediates, thereby accelerating product desorption and regeneration of active sites, while ensuring effective activation of reactant molecules. This optimized adsorption / desorption kinetic equilibrium is the reason for the high selectivity of Pt-CoPO / NF for glycolic acid.

[0051] like Figure 9 To verify the hypothesis that the adsorption of intermediates by Pt-CoPO / NF is weakened during the electro-oxidation reaction of ethylene glycol, we obtained dynamic evolution information during the reaction process using in-situ surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). The results show that with increasing potential, the adsorption of intermediates decreases at approximately 1100 cm⁻¹. -1The stretching vibration peak of the aldehyde group (-CHO) gradually increases at approximately 1630 cm⁻¹. -1 The broad peak at [location] can be attributed to the overlap of the bending vibration signal of the key intermediate 2-hydroxyacetyl (*OC-CH2OH) with the interfacial water molecule. Additionally, at approximately 1382 cm⁻¹... -1 and 1570 cm -1 The characteristic signals at these locations correspond to the asymmetric stretching vibration of the carboxylate group (OCO) and the characteristic absorption peak of the product glycolic acid, respectively. These results confirm that during the oxidation of ethylene glycol, the adsorption of intermediates is weakened, thereby avoiding deep oxidation and the formation of C1 byproducts.

[0052] like Figure 10 We used chronopotentiometric assays to perform a 24-hour electro-oxidation selectivity test on Pt-CoPO / NF, CoPO / NF, and Pt / NF. CP testing and quantitative analysis of product distribution were performed on CoPO / NF and Pt / NF. 1 Quantitative results from HNMR showed that the CoPO / NF formate exhibited a Faradaic efficiency as high as 60%, while the target product, glycolic acid, had a Faradaic efficiency of only 5%. This extremely low selectivity indicates that, in the presence of Pt centers, CoPO alone readily leads to deep oxidation of ethylene glycol and C / C bond cleavage. In contrast, Pt / NF achieved Faradaic efficiencies of 57% and 14% for formate and glycolic acid, respectively, significantly better than CoPO, but still far lower than Pt-CoPO / NF (>90%). These results suggest that CoPO and Pt / NF cannot achieve a balance between high current density, long-term stability, and product selectivity. The superior performance of Pt-CoPO / NF is attributed to the synergistic effect between the metal and the support, achieving efficient and stable directional conversion of ethylene glycol to glycolic acid by optimizing the adsorption barrier of the intermediate, enhancing the chemical stability of the active site, and suppressing deep oxidation pathways. Example

[0053] In the cyclic voltammetric electrodeposition of Pt, platinum-cobalt phosphate ethylene glycol electro-oxidation catalysts were prepared using different numbers of cycles: the specific method was the same as in Example 1, except that the number of cycles was set to 15 and 35 respectively in the cyclic voltammetric electrodeposition of Pt to obtain Pt-CoPO / NF-L and Pt-CoPO / NF-H, while the other steps remained unchanged.

[0054] The electrochemical performance of the electrocatalyst prepared in Example 2 in the electrooxidation reaction of ethylene glycol was tested using the same method as in Example 1, and the test results are as follows: Figure 11 The electrochemical activity of the electrocatalysts prepared using different electrodeposition cycles was not significantly different from that of the platinum-cobalt phosphate electrocatalyst prepared in Example 1.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. All simple and equivalent changes and modifications made in accordance with the claims and description of this application fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A method for preparing a platinum-cobalt phosphate catalyst for the selective electrooxidation of ethylene glycol to glycolic acid, characterized in that, Includes the following steps: S1. To remove impurities from the surface of nickel foam (NF), it was ultrasonically cleaned in sequence with a mixture of acetone-hydrochloric acid (volume ratio 1:1), ethanol, and deionized water. After cleaning, it was dried for later use. S2, disodium hydrogen phosphate dodecahydrate and hexadecyltrimethylammonium bromide in a molar ratio of 3:1 are dissolved in a mixed solvent of deionized water and ethylene glycol. The mixture is thoroughly mixed and dissolved under magnetic stirring. Then, cobalt nitrate hexahydrate is added and stirred to obtain a blue precursor solution. S3, the pre-cleaned nickel foam is immersed in a blue precursor solution and left to stand overnight at a low temperature to induce cobalt phosphate to rapidly crystallize and grow on the nickel foam substrate to form a nano-flower-like crystal structure. S4. Transfer the reaction mixture obtained in step S3 to a Teflon-lined hydrothermal reactor and react at a constant temperature of 140-170 °C for 9-12 hours. After the reaction is complete, allow it to cool naturally to room temperature. Remove the product, rinse it repeatedly with deionized water, and then dry it in an oven to obtain cobalt phosphate (CoPO / NF). In step S5, the CoPO / NF obtained in step S4 and the NF obtained in step S1 are used as working electrodes, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolyte is a solution containing H2PtCl6 and KOH in a volume ratio of 2:

3. Using cyclic voltammetry (CV), platinum (Pt) with a content of 6 wt% to 12 wt% is electrochemically deposited within a potential window of -1.42 V to -0.9 V. S6. The material deposited in step S5 is thoroughly washed with distilled water and vacuum dried at 30~40 °C overnight to obtain platinum-cobalt phosphate (Pt-CoPO / NF) catalyst and Pt / NF catalyst.

2. The preparation method according to claim 1, characterized in that, Step S1 includes: placing the nickel foam in a 1:1 mixture of acetone and 1 M HCl, ethanol, and deionized water in sequence, ultrasonically cleaning each solution for 5 minutes, and finally drying it at 60 °C for 10-14 hours.

3. The preparation method according to claim 1, characterized in that, In step S2, the molar ratio of disodium hydrogen phosphate dodecahydrate to hexadecyltrimethylammonium bromide is 3:1, and the amount of cobalt nitrate hexahydrate is 3 mmol.

4. The preparation method according to claim 1, characterized in that, Step S3 includes: refrigerating overnight at a low temperature of 0~5 ℃.

5. The preparation method according to claim 1, characterized in that, In step S4, the reaction mixture is placed in a sealed reaction vessel and heated to react at a set temperature and pressure to synthesize cobalt phosphate CoPO / NF.

6. The preparation method according to claim 1, characterized in that, In step S5, a three-electrode system was used, with CoPO / NF and NF as working electrodes, a graphite rod as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolyte was a solution containing 10–14 mM H₂PtCl₆ and 1 M KOH in a volume ratio of 2:

3. Cyclic voltammetry (CV) was used to electrochemically deposit Pt with a content of 6–12 wt% within a potential window of -1.42 V to -0.9 V.

7. The preparation method according to claim 1, characterized in that, In step S6, vacuum dry at 30~40 ℃ for 6~12 hours.

8. A platinum-cobalt phosphate ethylene glycol electrooxidation catalyst prepared by the method according to any one of claims 1-7, at 100 mA cm⁻¹ -2 At current densities, the operating potential is as low as 0.67 V (relative to RHE), and the Faraday efficiency of glycolic acid can reach 100%.

9. The application of the platinum-cobalt phosphate electro-oxidation catalyst as described in claim 8 in the selective electro-oxidation of ethylene glycol to glycolic acid.

10. The application according to claim 9, characterized in that, Co generated by electrochemical reconstruction of platinum-cobalt phosphate 3+ Able to convert OH at lower potentials - Oxidation results in the formation of an active hydroxyl species (*OH). *OH not only promotes the breaking of the OH / CH bond in the ethylene glycol molecule, accelerating the dehydrogenation process, but also rapidly converts the carbonyl intermediate into the target product, glycolic acid. Simultaneously, the in-situ alloy structure formed by Pt and Co, under the synergistic regulation of the interface, leads to… d The downward shift of the center promotes the rapid desorption and transfer of glycolic acid from the active Pt site, effectively inhibiting the breaking of C-C bonds.

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