Method for synthesizing ethylene glycol through electrocatalysis of formaldehyde

Abstract

The invention provides a method for synthesizing ethylene glycol through electrocatalysis of formaldehyde, and belongs to the field of electrocatalysis, ethylene glycol is synthesized through electrocatalysis of formaldehyde reduction coupling, a flowing electrolytic tank with a double-liquid-chamber structure is adopted, an aqueous solution containing formaldehyde and supporting electrolyte is used as a cathode electrolyte, an integrated electrode is used as a cathode, and electrolyte / cathode surface hydrophobic modification is carried out. The cathode is contacted with the catholyte or immersed in the catholyte, the temperature of the catholyte is raised and is continuously circulated, a certain potential or current is applied, and ethylene glycol is generated on the cathode side. The method can achieve higher ethylene glycol Faraday efficiency as well as electrolytic stability in excess of 1000 hours.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic conversion of carbon-containing small molecules, and more specifically, to a method for the electrocatalytic synthesis of ethylene glycol from formaldehyde. Background Technology

[0002] Ethylene glycol is an important raw material in the polyester industry and is widely used as an antifreeze. Traditional petroleum-based ethylene glycol production processes (i.e., ethylene oxide hydration processes) require high temperatures (~200°C) and high pressures (2.0 MPa). Coal-based ethylene glycol production processes using syngas (carbon monoxide and hydrogen) and syngas derivatives (dimethyl oxalate) as feedstocks can be carried out at atmospheric pressure, but the required reaction temperatures are still very high (e.g., 160°C), leading to significant carbon emissions. With the continuous development of renewable electricity, electrocatalytic formaldehyde reduction coupling provides a green and sustainable pathway for ethylene glycol production at ambient temperature and pressure.

[0003] Currently, the reported electrocatalytic reduction coupling of formaldehyde to ethylene glycol is mainly achieved on carbon materials. Weinberg et al. (J. Appl. Electrochem. 1991, 21, 895-901) used a graphite rod as the cathode in a formaldehyde electrolyte containing tetramethylformate at 90°C, achieving a reaction at 1000 mA / cm². 2 A high Faraday efficiency of 91% was achieved at a given current density. Xia et al. (Nat. Commun. 2023, 14, 4570) reported that the XC-72R carbon material can achieve a high Faraday efficiency of 91% at 50 °C and 50 mA / cm². 2 A 92% Faradaic efficiency for ethylene glycol formation was achieved. These results demonstrate that achieving high Faradaic efficiencies in ethylene glycol over a relatively wide range of current densities is feasible in this field.

[0004] In existing reports on the electrocatalytic reduction coupling of formaldehyde to ethylene glycol, long-term stability at higher current densities remains poor. For example, the research by Weinberg et al. (J. Appl. Electrochem. 1991, 21, 895-901) showed that the Faradaic efficiency of ethylene glycol rapidly decreased to below 50% within 2 hours. Xia et al. (Nat. Commun. 2023, 14, 4570) only reported the XC-72R carbon material at 100 mA / cm². 2 Stability data over 10 hours under certain conditions. Patent CN109487298A discloses a method for electrocatalytically producing ethylene glycol from formaldehyde, which utilizes a polytetrafluoroethylene hydrophobic modifier to treat the surface of carbon materials to improve the stability of electrocatalytic hexanediol, and can maintain a high ethylene glycol Faradaic efficiency (60%) for 10 hours.

[0005] Furthermore, in the field of electrocatalysis, ionomer binders (such as Nafion) are commonly used in catalyst loading processes to achieve effective contact between catalyst particles and conductive supports. However, these binders are prone to swelling and delamination after prolonged immersion in high-concentration ethylene glycol solutions. To further realize the industrial application of electrocatalytic formaldehyde reduction coupling to ethylene glycol, it is essential to significantly improve long-term operational stability. Currently, no research has reported using an integrated electrode as the cathode, with hydrophobic treatment of the electrolyte / cathode surface, to improve the long-term electrolytic stability of electrocatalytic formaldehyde reduction coupling to ethylene glycol at high current densities.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for the electrocatalytic synthesis of ethylene glycol from formaldehyde. This method achieves highly stable electrocatalytic reduction and coupling of formaldehyde to ethylene glycol. It employs an integrated electrode as the cathode and performs hydrophobic treatment on the cathode surface and electrolyte. This method can achieve high ethylene glycol selectivity over a wide range of current densities and maintain a high ethylene glycol Faraday efficiency over 1000 hours of electrolysis.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A method for the electrocatalytic synthesis of ethylene glycol from formaldehyde, comprising the following steps: Step (1) Assemble the electrolytic cell: The flow electrolytic cell adopts a "dual liquid chamber" structure. The flow electrolytic cell includes an anode chamber and a cathode chamber, and is equipped with an anode, a diaphragm, and a cathode; the cathode is an integrated electrode that has been modified by hydrophobicity. Step (2) Prepare the cathode electrolyte and anolyte, and add them to the electrolytic cell; Step (3) Heat the cathode electrolyte and anolyte and circulate them continuously in the electrolytic cell; Step (4) Apply a certain potential or current to generate ethylene glycol on the cathode side.

[0009] Further, the anode in step (1) is at least one of platinum sheet, nickel sheet, titanium sheet, and graphite sheet.

[0010] Furthermore, the integral electrode described in step (1) is composed of at least one of silicon, carbon, or silicon carbide.

[0011] Further, the membrane mentioned in step (1) is at least one of anion exchange membrane, cation exchange membrane or bipolar membrane.

[0012] Further, in step (2), the cathode is in contact with the cathode electrolyte or the cathode is placed in the cathode electrolyte.

[0013] Further, the cathode electrolyte in step (2) is an aqueous solution containing formaldehyde and cathode supporting electrolyte; the formaldehyde concentration in the cathode electrolyte is 1~52wt%; and the cathode supporting electrolyte concentration is 0.1~3mol / L.

[0014] Furthermore, the anolyte in step (2) is an aqueous solution containing an anolyte supporting electrolyte and does not contain formaldehyde; the concentration of the anolyte supporting electrolyte is 0.1~3 mol / L.

[0015] Furthermore, the integrated electrode comprises high-purity elemental silicon, high-purity elemental carbon, or high-purity silicon carbide, and / or derivative materials of high-purity elemental silicon, high-purity elemental carbon, or high-purity silicon carbide.

[0016] Furthermore, the preparation method of the integrated electrode includes at least one of crystallization, sintering, die casting, casting, and 3D printing.

[0017] Furthermore, the cathode supporting electrolyte is at least one selected from sodium acetate, potassium acetate, lithium acetate, sodium formate, potassium formate, and lithium formate.

[0018] Furthermore, the anode supporting electrolyte is at least one of sodium hydroxide and potassium hydroxide.

[0019] Furthermore, the hydrophobic modification method for the integrated electrode is as follows: hydrophobic modification of the integrated electrode with electrolyte and / or hydrophobic modification of the cathode surface.

[0020] Further, the method for hydrophobic modification of the electrolyte is as follows: adding a hydrophobic ionic liquid or an ionic liquid linear polymer containing hydrophobic functional groups to the cathode electrolyte; the concentration of the hydrophobic ionic liquid added to the cathode electrolyte is 0.1wt%~5wt%; the concentration of the ionic liquid linear polymer containing hydrophobic functional groups added to the cathode electrolyte is 0.1~5wt%.

[0021] Furthermore, the method for hydrophobic modification of the cathode surface is as follows: covering the surface of the integral electrode with a linear polymer of an ionic liquid containing hydrophobic functional groups or a cross-linked polymer of an ionic liquid containing hydrophobic functional groups.

[0022] Furthermore, the hydrophobic ionic liquid is at least one of tetramethylammonium chloride, n-butyltrimethylammonium chloride, n-octyltrimethylsodium chloride, dodecyltrimethylammonium chloride, and hexadecyltrimethylammonium chloride.

[0023] Furthermore, the coating method is at least one of spraying, dripping, scraping, spin coating, and in-situ polymerization.

[0024] Furthermore, the integrated electrode undergoes pretreatment before hydrophobic modification. The pretreatment method involves calcining the electrode in a hydrogen atmosphere for a period of time to obtain the pretreated integrated electrode.

[0025] Furthermore, the hydrogen concentration in the hydrogen atmosphere during pretreatment is 1.5~100 vol.

[0026] Furthermore, the calcination temperature is 200~600℃.

[0027] Furthermore, the calcination time is 2-5 hours.

[0028] Furthermore, the temperature of the cathode electrolyte and the temperature of the anode electrolyte in step (3) are 30~90℃.

[0029] Further, the circulation flow rate of the anolyte and the circulation flow rate of the cathode electrolyte in step (3) are 0.1~500mL / min.

[0030] Furthermore, the electrolysis method in step (4) by applying potential or current is constant current electrolysis.

[0031] Furthermore, the circulation flow rate of the anolyte and the circulation flow rate of the cathode electrolyte in step (3) are 1~75 mL / min.

[0032] Furthermore, the current density of the constant current electrolysis in step (4) is 50~1000 mA / cm². 2 .

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention provides a method for the electrocatalytic synthesis of ethylene glycol from formaldehyde, using an integrated silicon electrode, an integrated carbon electrode, or an integrated silicon carbide electrode as the cathode for the electrocatalytic reduction coupling of formaldehyde to prepare ethylene glycol. Compared with the traditional supported cathode, it does not use ionomer binders and can withstand long-term immersion in high-concentration ethylene glycol solutions.

[0034] 2. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde in this invention modifies the surface of the integrated cathode with hydrophobicity of the electrolyte / cathode, which can achieve high ethylene glycol selectivity under a wide current density and maintain a high ethylene glycol Faraday efficiency during an electrolysis process of more than 1000 hours.

[0035] 3. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde in this invention employs a flow electrolytic cell with a "two-compartment" structure. An aqueous solution containing formaldehyde and a supporting electrolyte is used as the cathode electrolyte. An integrated electrode is used as the cathode, and the electrolyte / cathode surfaces are hydrophobically modified. The cathode is in contact with or immersed in the cathode electrolyte, causing the electrolyte to heat up and circulate continuously. A specific potential or current is applied, resulting in the generation of ethylene glycol on the cathode side. This method achieves higher ethylene glycol Faradaic efficiency and electrolytic stability exceeding 1000 hours. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the components of the flow electrolyzer of the present invention; Figure 2 This is an X-ray diffraction pattern of the doped silicon wafer used in Embodiment 1 of the present invention; Figure 3 This is the X-ray photoelectron spectrum of the doped silicon wafer used in Embodiment 1 of the present invention. Detailed Implementation

[0038] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0039] A method for the electrocatalytic synthesis of ethylene glycol from formaldehyde, comprising the following steps: Step (1) Assemble the electrolytic cell: The flow electrolytic cell adopts a "dual liquid chamber" structure. The flow electrolytic cell includes an anode chamber and a cathode chamber, and is equipped with an anode, a diaphragm, and a cathode; the cathode is an integrated electrode that has been modified by hydrophobicity. Step (2) Prepare the cathode electrolyte and anolyte, and add them to the electrolytic cell; Step (3) Heat the cathode electrolyte and anolyte and circulate them continuously in the electrolytic cell; Step (4) Apply a certain potential or current to generate ethylene glycol on the cathode side.

[0040] Preferably, in step (1), the anode is at least one of platinum sheet, nickel sheet, titanium sheet, and graphite sheet.

[0041] Preferably, the preparation of the integral electrode in step (1) does not depend on the adhesive, and the integral electrode is composed of at least one of silicon, carbon or silicon carbide; preferably, it is a silicon electrode.

[0042] Preferably, the integral electrode comprises high-purity elemental silicon, high-purity elemental carbon, or high-purity silicon carbide, and / or derivative materials of high-purity elemental silicon, high-purity elemental carbon, or high-purity silicon carbide; the derivative materials of high-purity elemental silicon, high-purity elemental carbon, or high-purity silicon carbide are derivative materials formed by modifying, for example, doping high-purity elemental silicon, high-purity elemental carbon, or high-purity silicon carbide; preferably, it is doped and modified silicon.

[0043] Preferably, the preparation method of the integral electrode includes at least one of crystallization, sintering, die casting, casting, and 3D printing.

[0044] Preferably, the hydrophobic modification method for the integrated electrode is: to perform electrolyte hydrophobic modification and / or cathode surface hydrophobic modification on the integrated electrode.

[0045] Preferably, the integrated electrode undergoes pretreatment before hydrophobic modification. The pretreatment method involves calcining the electrode in a hydrogen atmosphere for a period of time to obtain the pretreated integrated electrode.

[0046] Preferably, the hydrogen concentration in the hydrogen atmosphere during pretreatment is 1.5~100 vol% (including but not limited to 1.5 vol%, 5 vol%, 10 vol%, 15 vol%, 20 vol%, 30 vol%, 40 vol%, 50 vol%, 60 vol%, 70 vol%, 80 vol%, 90 vol%, 100 vol%), the calcination temperature is 200~600℃ (including but not limited to 200℃, 300℃, 400℃, 50℃, 600℃), and the calcination time is 2~5h (including but not limited to 2h, 3h, 4h, 5h).

[0047] Preferably, the method for hydrophobic modification of the electrolyte is to add a hydrophobic ionic liquid or an ionic liquid linear polymer containing hydrophobic functional groups to the cathode electrolyte.

[0048] Preferably, the concentration of the hydrophobic ionic liquid added to the cathode electrolyte is 0.1 to 5 wt%, including but not limited to 0.1 wt%, 0.2 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, and preferably 2 wt%.

[0049] Preferably, the hydrophobic ionic liquid is at least one of tetramethylammonium chloride, n-butyltrimethylammonium chloride, n-octyltrimethylsodium chloride, dodecyltrimethylammonium chloride, and hexadecyltrimethylammonium chloride.

[0050] Preferably, the hydrophobic ionic liquid is dodecyltrimethylammonium chloride or hexadecyltrimethylammonium chloride, and the concentration added to the cathode electrolyte is 2 wt%.

[0051] Preferably, the concentration of the linear polymer containing hydrophobic functional groups added to the cathode electrolyte is 0.1~5wt%, preferably 2wt%.

[0052] Preferably, the hydrophobic functional group in the linear polymer of the ionic liquid is at least one of the following segments: butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, and hexadecyl.

[0053] Preferably, the linear polymer containing hydrophobic functional groups of the ionic liquid added to the cathode electrolyte is an allyl dodecyl dimethyl ammonium chloride linear polymer.

[0054] Preferably, the method for hydrophobic modification of the cathode surface is as follows: coating the surface of the integral electrode with a linear polymer of an ionic liquid containing hydrophobic functional groups or a cross-linked polymer of an ionic liquid containing hydrophobic functional groups.

[0055] Preferably, the coating method is at least one of spraying, dripping, scraping, spin coating, or in-situ polymerization. Spraying and in-situ polymerization are preferred.

[0056] Preferably, the hydrophobic functional group in the linear polymer of the ionic liquid is at least one of the following segments: butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, and hexadecyl. More preferably, allyl dimethyl butyl ammonium chloride-divinylbenzene copolymer, allyl dimethyl octyl ammonium chloride-divinylbenzene copolymer, allyl dimethyl dodecyl ammonium chloride-divinylbenzene copolymer, and allyl dimethyl hexadecyl ammonium chloride-divinylbenzene copolymer are also preferred.

[0057] Preferably, the hydrophobic functional group in the ionic liquid crosslinked polymer containing the hydrophobic functional group is at least one of the following segments: butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, and hexadecyl.

[0058] Preferably, the membrane in step (1) is at least one of anion exchange membrane, cation exchange membrane, or bipolar membrane.

[0059] Preferably, the cation exchange membrane is a Nafion 117 proton exchange membrane; the anion exchange membrane is a FuMAKS anion exchange membrane, preferably the FAB-PK-130 or FAA-PK-130 type FuMAKS anion exchange membrane.

[0060] Preferably, in step (2), the cathode electrolyte is an aqueous solution containing formaldehyde and cathode supporting electrolyte; the formaldehyde concentration in the cathode electrolyte is 1~52wt% (including but not limited to 1wt%, 5wt%, 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 52wt%), preferably 37~52wt%; the cathode supporting electrolyte concentration is 0.1~3mol / L (including but not limited to 0.1mol / L, 0.5mol / L, 1mol / L, 2mol / L, 3mol / L).

[0061] Preferably, the cathode supporting electrolyte is at least one selected from sodium acetate, potassium acetate, lithium acetate, sodium formate, potassium formate, and lithium formate. Sodium acetate, sodium formate, and potassium formate are preferred.

[0062] Preferably, the cathode supporting electrolyte is sodium acetate, and the concentration of sodium acetate in the cathode electrolyte is 1 mol / L.

[0063] Preferably, in step (2), the anolyte is an aqueous solution containing an anolyte supporting electrolyte and does not contain formaldehyde; the concentration of the anolyte supporting electrolyte is 0.1~3 mol / L (including but not limited to 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L); preferably, the concentration of the anolyte supporting electrolyte is 3 mol / L.

[0064] Preferably, the anode supporting electrolyte is at least one of sodium hydroxide and potassium hydroxide.

[0065] Preferably, the cathode is in contact with the cathode electrolyte or is placed in the cathode electrolyte.

[0066] Preferably, the temperature of the cathode electrolyte and the temperature of the anode electrolyte in step (3) are 30~90℃, including but not limited to 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, and 90℃; preferably 40~70℃.

[0067] Preferably, in step (3), the circulation flow rate of the anolyte and the circulation flow rate of the cathode electrolyte are 0.1~500 mL / min, including but not limited to 0.1 mL / min, 0.2 mL / min, 0.5 mL / min, 1 mL / min, 5 mL / min, 10 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min, and 500 mL / min; more preferably, the circulation flow rate of the anolyte and the circulation flow rate of the cathode electrolyte are 1~75 mL / min, and more preferably 20~75 mL / min.

[0068] Preferably, the electrolysis method in step (4) by applying potential or current is constant current electrolysis, with a current density of 50~1000 mA / cm². 2 including but not limited to 50mA / cm 2 100mA / cm 2 200mA / cm 2 500mA / cm 2 800mA / cm 2 1000mA / cm 2 .

[0069] Example 1 Integrated silicon electrode based on doped silicon wafer (purchased from Guangzhou Fangdao Semiconductor Co., Ltd., 0.001~0.005Ω) -1 The pretreatment and electrocatalytic reduction coupling of formaldehyde (hereinafter the same) to ethylene glycol testing are as follows: (1) Pretreatment: The doped silicon wafer was thoroughly washed three times with anhydrous ethanol and deionized water respectively; then dried overnight at 60°C in a vacuum drying oven; subsequently, it was calcined at 500°C for 5 hours in a tube furnace under a 1.5% hydrogen atmosphere to obtain the treated doped silicon wafer, which can be directly used as an integrated silicon electrode for subsequent electrolysis.

[0070] (2) Electrocatalytic test: The integrated silicon electrode based on the doped silicon wafer was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anolyte. The cathode electrolyte contained 37 wt% formaldehyde, and the supporting electrolyte was sodium acetate with a concentration of 1 mol / L. The flow rate of the cathode electrolyte was 15 mL / min. The anolyte was an aqueous solution of sodium hydroxide with a concentration of 3 mol / L. The flow rate of the anolyte was 15 mL / min. An external water bath was used to maintain the cathode electrolyte and anolyte at a constant temperature of 50 °C. The electrolysis method was constant current electrolysis with a current density of 200 mA / cm². 2 400mA / cm 2 600mA / cm2 800mA / cm 2 1000mA / cm 2 .

[0071] (3) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faraday efficiency under the corresponding conditions was calculated. In this embodiment, the integrated silicon electrode based on a doped silicon wafer achieved an efficiency of 200 mA / cm². 2 400mA / cm 2 600mA / cm 2 800mA / cm 2 1000mA / cm 2 The Faraday efficiencies were 89.8%, 87.1%, 82.4%, 79.7%, and 72.0%, respectively.

[0072] like Figures 2-3 As shown, the peak positions of the doped silicon wafer in the X-ray diffraction pattern are at 28.5°, 47.4°, 56.2°, 69.3° and 76.5°, corresponding to the Si (111) plane, while the X-ray photoelectron spectroscopy shows that the doped silicon wafer is mainly composed of elemental silicon and silicon oxide.

[0073] Example 2 The pretreatment and electrocatalytic formaldehyde reduction coupling synthesis of ethylene glycol based on integrated carbon electrodes and silicon carbide electrodes are described in the following steps: (1) Pretreatment: The carbon sheet and silicon carbide sheet were thoroughly washed three times with anhydrous ethanol and deionized water respectively; then, they were dried overnight at 60°C in a vacuum drying oven; subsequently, they were calcined at 400°C for 5 hours in a tube furnace under a 1.5% hydrogen atmosphere to obtain the treated carbon sheet and the treated silicon carbide sheet, which can be directly used as integrated carbon electrode and integrated silicon carbide electrode for subsequent electrolysis.

[0074] (2) Electrocatalytic test: The integrated carbon electrode and integrated silicon carbide electrode were used as cathodes, and platinum sheets were used as anodes. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and anolyte. The cathode electrolyte contained 37 wt% formaldehyde, and the supporting electrolyte was sodium acetate at a concentration of 1 mol / L. The flow rate of the cathode electrolyte was 15 mL / min. The anolyte was a potassium hydroxide aqueous solution at a concentration of 3 mol / L, and the flow rate was 15 mL / min. An external water bath was used to maintain the cathode electrolyte and anolyte at a constant temperature of 50°C. The electrolysis method was constant current electrolysis with a current density of 200 mA / cm². 2 .

[0075] (3) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR spectroscopy to obtain the content of ethylene glycol, and then the ethylene glycol Faraday efficiency under the corresponding conditions was calculated. In this embodiment, the integrated carbon electrode and the integrated silicon carbide electrode based on carbon sheet and silicon carbide sheet were at 200 mA / cm 2 The Faraday efficiencies were 80.7% and 84.5%, respectively.

[0076] Example 3 The specific steps for pretreatment and electrocatalytic formaldehyde reduction coupling to ethylene glycol testing of an integrated silicon electrode based on a high-purity silicon wafer are as follows: (1) Pretreatment: Wash the high-purity silicon wafer three times with anhydrous ethanol and deionized water; then dry it overnight at 60°C in a vacuum drying oven; then calcine it at 300°C for 3 hours in a tube furnace under a 10% hydrogen atmosphere to obtain the treated high-purity silicon wafer, which can be directly used as an integrated silicon electrode for subsequent electrolysis.

[0077] (2) Electrocatalytic test: The integrated silicon electrode based on the high-purity silicon wafer was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anolyte. The cathode electrolyte contained 37 wt% formaldehyde, and the supporting electrolyte was sodium acetate with a concentration of 1 mol / L. The flow rate of the cathode electrolyte was 15 mL / min. The anolyte was an aqueous solution of sodium hydroxide with a concentration of 3 mol / L. The flow rate of the anolyte was 15 mL / min. An external heating device was used to heat the cathode electrolyte and the anolyte in a water bath to maintain a constant temperature of 50 °C. The electrolysis method was constant current electrolysis with a current density of 50 mA / cm². 2 .

[0078] (3) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faraday efficiency under the corresponding conditions was calculated. In this embodiment, the integrated silicon electrode based on a high-purity silicon wafer achieved an efficiency of 50 mA / cm². 2 The Faraday efficiency is 84.6%.

[0079] Example 4 The electrocatalytic reduction coupling of formaldehyde to ethylene glycol using an integrated silicon electrode based on a doped silicon wafer under hydrophobic modification conditions, with the addition of different hydrophobic ionic liquids, is tested. The specific steps are as follows: (1) Hydrophobic modification of the cathode electrolyte: The cathode electrolyte contains 37 wt% formaldehyde and the supporting electrolyte is sodium acetate with a concentration of 1 mol / L. Different hydrophobic ionic liquids with a mass fraction of 2 wt% are added to the cathode electrolyte for hydrophobic modification, namely tetramethylammonium chloride, n-butyltrimethylammonium chloride, n-octyltrimethylammonium chloride, dodecyltrimethylammonium chloride, and hexadecyltrimethylammonium chloride.

[0080] (2) Electrocatalytic testing: A monolithic silicon electrode based on a doped silicon wafer was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anolyte. The cathode electrolyte flow rate was 15 mL / min; the anolyte was an aqueous sodium hydroxide solution with a concentration of 3 mol / L, and the anolyte flow rate was 15 mL / min. An external heating device was used to heat the cathode electrolyte and the anolyte in a water bath to maintain a constant temperature of 50°C. The electrolysis method was constant current electrolysis, with a specific current density parameter of 200 mA / cm². 2 .

[0081] (3) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faraday efficiency under the corresponding conditions was calculated. In this embodiment, with the addition of 2 wt% tetramethylammonium chloride, n-butyltrimethylammonium chloride, n-octyltrimethylammonium chloride, dodecyltrimethylammonium chloride, and hexadecyltrimethylammonium chloride to the cathode electrolyte, the integrated silicon electrode based on the doped silicon wafer achieved an efficiency of 200 mA / cm². 2 The Faraday efficiencies were 93.4%, 94.2%, 94.6%, and 95.8%, respectively.

[0082] (4) Long-term stability: In the long-term stability test, after a single electrolysis cycle (generally when the formaldehyde mass fraction in the cathode electrolyte decreases to below 2 wt%), a new electrolyte is replaced for cyclic electrolysis. In the stability test without the addition of hydrophobic ionic liquid, after two cycles of electrolysis, the overall ethylene glycol Faraday efficiency of a single cycle decreased from 80% to 50%, and the formaldehyde conversion rate decreased from 90% to 60%, at which point the long-term stability was 40 h. In the long-term stability test with the addition of 2 wt% dodecyltrimethylammonium chloride, the average ethylene glycol Faraday efficiency was 80% and the average formaldehyde conversion rate was 90% in a stability test lasting up to 1500 h, with virtually no degradation.

[0083] Example 5 The electrocatalytic reduction coupling of formaldehyde to ethylene glycol using an integrated silicon electrode based on a doped silicon wafer under hydrophobic modification conditions, with different mass fractions of hydrophobic ionic liquids added, was tested. The specific steps are as follows: (1) Hydrophobic modification of the cathode electrolyte: The cathode electrolyte contains 37wt% formaldehyde and sodium acetate as the supporting electrolyte with a concentration of 1mol / L. Different mass fractions of dodecyltrimethylammonium chloride are added to the cathode electrolyte, with mass fractions of 0.1wt%, 1wt%, and 3wt%, respectively.

[0084] (2) Electrocatalytic testing: A monolithic silicon electrode based on a doped silicon wafer was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anolyte. The cathode electrolyte flow rate was 15 mL / min; the anolyte was an aqueous sodium hydroxide solution with a concentration of 3 mol / L, and the anolyte flow rate was 15 mL / min. An external heating device was used to heat the cathode electrolyte and the anolyte in a water bath to maintain a constant temperature of 50°C. The electrolysis method was constant current electrolysis, with a specific current density parameter of 200 mA / cm². 2 .

[0085] (3) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by nuclear magnetic resonance (NMR) to obtain the content of ethylene glycol, and then the ethylene glycol Faraday efficiency under the corresponding conditions was calculated. In this embodiment, under the conditions of adding 0.1 wt%, 1 wt%, and 3 wt% dodecyltrimethylammonium chloride by mass fraction in cathode electrolysis, the integrated silicon electrode based on the doped silicon wafer achieved an efficiency of 200 mA / cm². 2 The Faraday efficiencies were 90.2%, 93.4%, and 94.4%, respectively.

[0086] Example 6 The electrocatalytic reduction coupling of formaldehyde to ethylene glycol using an integrated silicon electrode based on a doped silicon wafer under hydrophobic modification conditions with the addition of allyl dodecyl dimethyl ammonium chloride linear polymer is described in the following steps: (1) Hydrophobic modification of the cathode electrolyte: Allyl dimethyl dodecyl ammonium chloride was placed in a 50 mL three-necked flask, and azobisisobutyronitrile (ANOVA) was added as the initiator. After heating at 90 °C for 48 hours, a linear polymer of allyl dimethyl dodecyl ammonium chloride was obtained. The cathode electrolyte contained 37 wt% formaldehyde, and the supporting electrolyte was sodium acetate with a concentration of 1 mol / L. 2 wt% of the linear polymer of allyl dimethyl dodecyl ammonium chloride was added.

[0087] (2) Electrocatalytic testing: A monolithic silicon electrode based on a doped silicon wafer was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anolyte. The cathode electrolyte flow rate was 15 mL / min; the anolyte was an aqueous sodium hydroxide solution with a concentration of 3 mol / L, and the anolyte flow rate was 15 mL / min. An external heating device was used to heat the cathode electrolyte and the anolyte in a water bath to maintain a constant temperature of 50°C. The electrolysis method was constant current electrolysis, with a specific current density parameter of 200 mA / cm². 2 .

[0088] (3) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faradaic efficiency under the corresponding conditions was calculated. In this embodiment, under the condition of adding 2 wt% allyl dimethyl dodecyl ammonium chloride linear polymer to the cathode electrolyte, the integrated silicon electrode based on the doped silicon wafer achieved an efficiency of 200 mA / cm². 2 The Faraday efficiency is 93.8%.

[0089] (4) Long-term stability: In the long-term stability test, after a single electrolysis cycle (generally when the formaldehyde mass fraction in the cathode electrolyte drops below 2wt%), a new electrolyte is replaced for cyclic electrolysis. In this embodiment, after five cycles of electrolysis, the overall ethylene glycol Faraday efficiency of a single cycle decreased from 80.5% to 62.8%, and the formaldehyde conversion rate decreased from 91% to 72%. At this point, the long-term stability was 100h.

[0090] Example 7 The application of allyl dimethyl dodecyl ammonium chloride-divinylbenzene copolymer to an integrated silicon electrode based on a doped silicon wafer for electrocatalytic formaldehyde reduction coupling to ethylene glycol under hydrophobic modification of the cathode surface is described in the following steps: (1) Hydrophobic modification of cathode surface: Allyl dimethyl dodecyl ammonium chloride and divinylbenzene were placed in a 50 mL three-necked flask, and azobisisobutyronitrile (ANOVA) was added as an initiator. After heating and reacting at 90 °C for 48 hours, an allyl dimethyl dodecyl ammonium chloride-divinylbenzene copolymer was obtained. The copolymer was then coated onto the surface of an integral silicon electrode based on a doped silicon wafer using a spray coating method.

[0091] (2) Electrocatalytic testing: A monolithic silicon electrode with hydrophobic surface modification was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anolyte. The cathode electrolyte contained 37 wt% formaldehyde, and the supporting electrolyte was sodium acetate with a concentration of 1 mol / L. The flow rate of the cathode electrolyte was 15 mL / min. The anolyte was an aqueous solution of sodium hydroxide with a concentration of 3 mol / L. The flow rate of the anolyte was 15 mL / min. An external heating device was used to heat the cathode electrolyte and the anolyte in a water bath to maintain a constant temperature of 50 °C. The electrolysis method was constant current electrolysis, with a specific current density parameter of 200 mA / cm². 2 .

[0092] (3) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faraday efficiency under the corresponding conditions was calculated. In this embodiment, after spraying allyl dimethyl dodecyl ammonium chloride-divinylbenzene copolymer to modify the surface of the integrated silicon electrode based on the doped silicon wafer for hydrophobic modification, the ethylene glycol Faraday efficiency was obtained at 200 mA / cm². 2 The Faraday efficiency is 95.8%.

[0093] (4) Long-term stability: In the long-term stability test, after a single electrolysis is completed (generally when the formaldehyde mass fraction in the cathode electrolyte decreases to below 2wt%), a new electrolyte is replaced for cyclic electrolysis. In this embodiment, during the stability test of up to 800 hours, the average ethylene glycol Faraday ratio and the average formaldehyde conversion rate showed almost no decay.

[0094] Example 8 The electrocatalytic reduction coupling of formaldehyde to ethylene glycol using an integrated silicon electrode based on a doped silicon wafer under hydrophobic modification conditions, with the application of allyl ionic liquids of different alkyl chain lengths-divinylbenzene copolymers, was tested. The specific steps are as follows: (1) Hydrophobic modification of cathode surface: Allyl ionic liquids with different alkyl chain lengths and divinylbenzene were placed in a 50 mL three-necked flask, and the initiator azobisisobutyronitrile was added. After heating and reacting at 90 °C for 48 hours, allyl ionic liquid-divinylbenzene copolymers with different alkyl chain lengths were obtained, namely allyl dimethyl butyl ammonium chloride-divinylbenzene copolymer, allyl dimethyl octyl ammonium chloride-divinylbenzene copolymer, and allyl dimethyl hexadecyl ammonium chloride-divinylbenzene copolymer. The above copolymers were coated on the surface of an integral silicon electrode based on a doped silicon wafer by spraying.

[0095] (2) Electrocatalytic testing: A monolithic silicon electrode with hydrophobic surface modification was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anolyte. The cathode electrolyte contained 37 wt% formaldehyde, and the supporting electrolyte was sodium acetate with a concentration of 1 mol / L. The flow rate of the cathode electrolyte was 15 mL / min. The anolyte was an aqueous solution of sodium hydroxide with a concentration of 3 mol / L. The flow rate of the anolyte was 15 mL / min. An external heating device was used to heat the cathode electrolyte and the anolyte in a water bath to maintain a constant temperature of 50 °C. The electrolysis method was constant current electrolysis, with a specific current density parameter of 200 mA / cm². 2 .

[0096] (3) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faraday efficiency under the corresponding conditions was calculated. In this embodiment, allyl dimethyl butyl ammonium chloride-divinylbenzene copolymer, allyl dimethyl octyl ammonium chloride-divinylbenzene copolymer, and allyl dimethyl hexadecyl ammonium chloride-divinylbenzene copolymer were used to modify the cathode surface of the integrated silicon electrode based on the doped silicon wafer for hydrophobic modification, and the efficiency was achieved at 200 mA / cm 2 The Faraday efficiencies were 93.5%, 95.8%, and 95.9%.

[0097] Example 9 The electrocatalytic reduction coupling of formaldehyde to ethylene glycol using an integrated silicon electrode based on a doped silicon wafer under different ion exchange membrane conditions is tested. The specific steps are as follows: (1) Electrocatalytic test: A monolithic silicon electrode based on a doped silicon wafer was used as the cathode, and a platinum sheet was used as the anode. Different ion exchange membranes were used as separators to separate the cathode electrolyte and the anode electrolyte, including FuMAKS anion exchange membranes (FAB-PK-130, FAA-PK-130) and cation exchange membranes (Nafion 117). The cathode electrolyte contained 37 wt% formaldehyde, and the supporting electrolyte was sodium acetate with a concentration of 1 mol / L. The flow rate of the cathode electrolyte was 15 mL / min. The anode electrolyte was an aqueous solution of sodium hydroxide with a concentration of 3 mol / L. The flow rate of the anode electrolyte was 15 mL / min. An external heating device was used to heat the cathode electrolyte and the anode electrolyte in a water bath to control the temperature at a constant 50°C. The electrolysis method was constant current electrolysis, and the specific current density parameter was 200 mA / cm². 2 .

[0098] (2) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faraday efficiency under the corresponding conditions was calculated. In this embodiment, FAB-PK-130, FAA-PK-130, and Nafion 117 proton exchange membranes were used as separators, and the integrated silicon electrode based on the doped silicon wafer was used at 200 mA / cm². 2 The Faraday efficiencies were 90.2%, 88.7%, and 89.8%, respectively.

[0099] Example 10 The electrocatalytic reduction coupling of formaldehyde to ethylene glycol using an integrated silicon electrode based on a doped silicon wafer at different formaldehyde mass fractions is tested. The specific steps are as follows: (1) Electrocatalytic test: A monolithic silicon electrode based on a doped silicon wafer was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anolyte. The cathode electrolyte contained different mass fractions of formaldehyde, namely 52wt%, 37wt%, 20wt%, and 10wt%, respectively. The supporting electrolyte was sodium acetate with a concentration of 1mol / L, and the cathode electrolyte flow rate was 15mL / min. The anolyte was an aqueous solution of sodium hydroxide with a concentration of 3mol / L, and the anolyte flow rate was 15mL / min. An external heating device was used to heat the cathode electrolyte and the anolyte in a water bath to control the temperature at a constant 50℃. The electrolysis method was constant current electrolysis, and the specific current density parameter was 200mA / cm. 2 .

[0100] (2) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faradaic efficiency under the corresponding conditions was calculated. In this embodiment, cathode electrolytes with formaldehyde mass fractions of 52wt%, 37wt%, 20wt%, and 10wt% were used respectively. The integrated silicon electrode based on the doped silicon wafer was used at 200 mA / cm². 2 The Faraday efficiencies were 90.2%, 89.8%, 88.7%, and 87.8%, respectively.

[0101] Example 11 The electrocatalytic reduction coupling of formaldehyde to ethylene glycol using an integrated silicon electrode based on a doped silicon wafer under different supporting electrolyte conditions in the cathode electrolyte is tested. The specific steps are as follows: (1) Electrocatalytic test: A monolithic silicon electrode based on a doped silicon wafer was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anode electrolyte. The cathode electrolyte contained 37 wt% formaldehyde and different supporting electrolytes were added, namely sodium acetate, potassium acetate, lithium acetate, sodium formate, lithium formate, and potassium formate, with a concentration of 1 mol / L. The flow rate of the cathode electrolyte was 15 mL / min. The anode electrolyte was an aqueous solution of sodium hydroxide with a concentration of 3 mol / L and a flow rate of 15 mL / min. An external heating device was used to heat the cathode electrolyte and the anode electrolyte in a water bath to control the temperature at a constant 50°C. The electrolysis method was constant current electrolysis, with a specific current density parameter of 200 mA / cm². 2 .

[0102] (2) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faradaic efficiency under the corresponding conditions was calculated. In this embodiment, under the conditions of adding sodium acetate, potassium acetate, lithium acetate, sodium formate, and potassium formate as supporting electrolytes respectively, the integrated silicon electrode based on the doped silicon wafer achieved an efficiency of 200 mA / cm². 2 The Faraday efficiencies were 89.8%, 87.2%, 85.4%, 90.5%, and 90.8%, respectively.

[0103] Example 12 The electrocatalytic reduction coupling of formaldehyde to ethylene glycol using an integrated silicon electrode based on a doped silicon wafer under different cathode electrolyte circulation rates was tested. The specific steps are as follows: (1) Electrocatalytic test: A monolithic silicon electrode based on a doped silicon wafer was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anode electrolyte. The cathode electrolyte contained 37 wt% formaldehyde, and the supporting electrolyte was sodium acetate with a concentration of 1 mol / L. Different cathode electrolyte circulation rates were used: 1 mL / min, 35 mL / min, 55 mL / min, and 75 mL / min. The anode electrolyte was an aqueous sodium hydroxide solution with a concentration of 3 mol / L, and the anode electrolyte flow rate was 15 mL / min. An external heating device was used to heat the cathode electrolyte and the anode electrolyte in a water bath to maintain a constant temperature of 50 °C. The electrolysis method was constant current electrolysis, and the specific current density parameter was 200 mA / cm². 2 .

[0104] (2) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faraday efficiency under the corresponding conditions was calculated. In this embodiment, the cathode electrolyte circulation flow rate was controlled at 1 mL / min, 35 mL / min, 55 mL / min, and 75 mL / min, respectively. The integrated silicon electrode based on the doped silicon wafer was tested at 200 mA / cm². 2 The Faraday efficiencies were 63.5%, 89.8%, 90.2%, 91.4%, and 92.5%, respectively.

[0105] Example 13 The electrocatalytic reduction coupling of formaldehyde to ethylene glycol using an integrated silicon electrode based on a doped silicon wafer at different cathode and anolyte temperatures was tested. The specific steps are as follows: (1) Electrocatalytic test: A monolithic silicon electrode based on a doped silicon wafer was used as the cathode, and a platinum sheet was used as the anode. A Nafion 117 proton exchange membrane was used as a separator to separate the cathode electrolyte and the anolyte. The cathode electrolyte contained 37 wt% formaldehyde, and the supporting electrolyte was sodium acetate with a concentration of 1 mol / L. The circulating flow rate of the cathode electrolyte was 15 mL / min. The anolyte was an aqueous solution of sodium hydroxide with a concentration of 3 mol / L. The anolyte flow rate was 15 mL / min. An external heating device was used to heat the cathode electrolyte and the anolyte in a water bath to control them at different constant temperatures, namely 30℃, 70℃, and 90℃. The electrolysis method was constant current electrolysis, and the specific current density parameter was 200 mA / cm². 2 .

[0106] (2) Electrocatalytic performance: After electrolysis for a period of time, 1 mL of the cathode electrolyte was taken for quantitative analysis by 1H NMR to obtain the content of ethylene glycol, and then the ethylene glycol Faraday efficiency under the corresponding conditions was calculated. In this embodiment, the cathode electrode liquid and anolyte temperature were controlled at 30℃, 70℃ and 90℃ respectively. The integrated silicon electrode based on the doped silicon wafer achieved an efficiency of 200 mA / cm². 2 The Faraday efficiencies were 58.7%, 92.2%, and 94.8%, respectively.

Claims

1. A method for the electrocatalytic synthesis of ethylene glycol from formaldehyde, comprising the electrocatalytic reduction coupling of formaldehyde to ethylene glycol, characterized in that, Includes the following steps: Step (1) Assemble the electrolytic cell: The flow electrolytic cell adopts a "dual liquid chamber" structure. The flow electrolytic cell includes an anode chamber and a cathode chamber, and is equipped with an anode, a diaphragm, and a cathode; the cathode is an integrated electrode that has been modified by hydrophobicity. Step (2) Prepare the cathode electrolyte and anolyte, and add them to the electrolytic cell; Step (3) Heat the cathode electrolyte and anolyte and circulate them continuously in the electrolytic cell; Step (4) Apply a certain potential or current to generate ethylene glycol on the cathode side.

2. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde according to claim 1, characterized in that, Includes at least one of the following technical features: A. The anode mentioned in step (1) is at least one of platinum sheet, nickel sheet, titanium sheet, and graphite sheet; B. The integral electrode described in step (1) is composed of at least one of silicon, carbon, or silicon carbide; C. The membrane mentioned in step (1) is at least one of anion exchange membrane, cation exchange membrane or bipolar membrane; D. In step (2), the cathode is in contact with the cathode electrolyte or the cathode is placed in the cathode electrolyte; E. The cathode electrolyte in step (2) is an aqueous solution containing formaldehyde and cathode supporting electrolyte; the formaldehyde concentration in the cathode electrolyte is 1~52wt%; the concentration of the cathode supporting electrolyte is 0.1~3mol / L. F. The anolyte in step (2) is an aqueous solution containing an anolyte supporting electrolyte and does not contain formaldehyde; the concentration of the anolyte supporting electrolyte is 0.1~3 mol / L.

3. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde according to claim 2, characterized in that, Includes at least one of the following technical features: A. The integrated electrode comprises high-purity elemental silicon, high-purity elemental carbon, or high-purity silicon carbide, and / or derivative materials of high-purity elemental silicon, high-purity elemental carbon, or high-purity silicon carbide. B. The preparation method of the integrated electrode includes at least one of crystallization, sintering, die casting, casting, and 3D printing; C. The cathode supporting electrolyte is at least one of sodium acetate, potassium acetate, lithium acetate, sodium formate, potassium formate, and lithium formate; D. The anode supporting electrolyte is at least one of sodium hydroxide and potassium hydroxide.

4. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde according to claim 3, characterized in that, The hydrophobic modification method for the integrated electrode is as follows: hydrophobic modification of the integrated electrode with electrolyte and / or hydrophobic modification of the cathode surface.

5. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde according to claim 4, characterized in that, Includes at least one of the following technical features: A. The method for hydrophobic modification of the electrolyte is as follows: adding a hydrophobic ionic liquid or a linear polymer of an ionic liquid containing hydrophobic functional groups to the cathode electrolyte; the concentration of the hydrophobic ionic liquid added to the cathode electrolyte is 0.1wt%~5wt%; the concentration of the linear polymer of an ionic liquid containing hydrophobic functional groups added to the cathode electrolyte is 0.1~5wt%. B. The method for hydrophobic modification of the cathode surface is as follows: covering the surface of the integral electrode with a linear polymer of ionic liquid containing hydrophobic functional groups or a cross-linked polymer of ionic liquid containing hydrophobic functional groups.

6. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde according to claim 5, characterized in that, Includes at least one of the following technical features: A. The hydrophobic ionic liquid is at least one of tetramethylammonium chloride, n-butyltrimethylammonium chloride, n-octyltrimethylsodium chloride, dodecyltrimethylammonium chloride, and hexadecyltrimethylammonium chloride; B. The coating method is at least one of spraying, dripping, scraping, spin coating, and in-situ polymerization.

7. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde according to claim 4, characterized in that, The integrated electrode undergoes pretreatment before hydrophobic modification. The pretreatment method involves calcining the electrode in a hydrogen atmosphere for a period of time to obtain the pretreated integrated electrode.

8. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde according to claim 7, characterized in that, Includes at least one of the following technical features: A. The hydrogen concentration in the hydrogen atmosphere during pretreatment is 1.5~100 vol%. B. The calcination temperature is 200~600℃; C. Calcination time is 2~5 hours.

9. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde according to claim 1, characterized in that, Includes at least one of the following technical features: A The temperature of the cathode electrolyte and the temperature of the anolyte in step (3) are 30~90℃; B. The circulation flow rate of the anolyte and the circulation flow rate of the cathode electrolyte in step (3) are 0.1~500mL / min; C. The electrolysis method in step (4) by applying potential or current is constant current electrolysis.

10. The method for electrocatalytic synthesis of ethylene glycol from formaldehyde according to claim 9, characterized in that, Includes at least one of the following technical features: A The circulation flow rate of the anolyte and the circulation flow rate of the cathode electrolyte in step (3) are 1~75 mL / min; B. The current density of constant current electrolysis in step (4) is 50~1000 mA / cm². 2 .

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