CN114622234A

CN114622234A - Flexible gas diffusion electrode structure and application thereof in electrochemical reduction of carbon dioxide

Info

Publication number: CN114622234A
Application number: CN202011435376.7A
Authority: CN
Inventors: 邱艳玲; 李先锋; 姚鹏飞; 郑琼; 张华民
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2020-12-10
Filing date: 2020-12-10
Publication date: 2022-06-14
Anticipated expiration: 2040-12-10
Also published as: CN114622234B

Abstract

The invention provides a flexible gas diffusion electrode which comprises a substrate layer, a catalyst layer, a polymer layer and an interface layer which are sequentially combined, wherein the substrate layer is mainly composed of a porous high polymer film. Flexible gas diffusion cellThe electrode can be bent and extruded, can bear the pressure difference formed by rapid gas generation in the flowing electrolytic cell, ensures the integrity and gas permeability of the gas diffusion electrode, and overcomes the defect that the graphite-based gas diffusion electrode is easy to crack under a certain pressure difference; a polymer layer grafted with SO 3-group and introduced from one side of the flexible gas diffusion electrode close to the electrolyte, CO₂The in-plane diffusion coefficient (D) of the layer is greater than the diffusion coefficient (D0) in the catholyte, thereby causing CO to form₂The gas flows in the layer until the CO₂Reduction takes place at the catalytically active sites, dissolving the CO in the catholyte₂The amount is reduced, and most of CO is generated₂Three-phase interface on the surface of catalyst reacts without CO₂The restriction of solubility in aqueous solution, thereby increasing the reaction rate of ERC.

Description

Flexible gas diffusion electrode structure and application thereof in electrochemical reduction of carbon dioxide

Technical Field

The invention belongs to the technical field of carbon dioxide electrochemical reduction, and particularly relates to a flexible gas diffusion electrode structure and a preparation technology and application thereof.

Background

Electrochemical reduction of CO₂(ERC) technique is the use of electrical energy to convert CO₂Reducing to a target product to realize CO₂A technique of transformation and efficient utilization. With other CO₂Compared with the conversion technology, the ERC technology has the outstanding advantages of simple operation and low cost, can utilize water as the protonation hydrogen source, and can realize CO at normal temperature and normal pressure₂The high-efficiency conversion is realized, so that the energy consumption caused by hydrogen production, heating and pressurization required by a chemical conversion technology is not required, and the equipment investment is low.

During the ongoing development of ERC technology, researchers have found that the electrocatalytic performance of these catalysts can be evaluated by using a Gas Diffusion Electrode (GDE) with a flowing catholyte, without concern for mass transfer limitations and local pH effects. I.e. so-called flow cells are constructed instead of static H-cells in the conventional sense. In a flow cell, CO₂Enters the cathode of the cell from the back of the gas diffusion layer, reacts with H + from the electrolyte in the cathode catalytic layer to be reduced, and the reduced product is discharged out of the cell through the gas diffusion layer. Flow cell not only can mitigate CO₂Polarization of mass transfer due to low solubility in water, and inhibition of hydrogen evolution side reactions and reduction of CO due to the use of mobile electrolytes₂Activation of energy barrier and enhanced CC coupling between COs, thereby increasing C₂Selectivity of the product.

However, it is not limited toIn the process of exploring the structure of a Gas Diffusion Electrode (GDE) for a flow-type electrolytic cell in the previous period, we find that the GDE constructed by taking a porous graphite-based material as a gas diffusion substrate has the problems of low pressure resistance, easy flooding of microporous channels by electrolyte under the action of capillary force and the like, so that mass transfer polarization is serious, the catalytic stability of the electrode is very low, and particularly under the condition of pressurization operation, the most outstanding problems are that the GDE is creased and/or broken along the cross section direction to cause GDE failure, CO failure and CO₂It is first dissolved in the catholyte before the reduction reaction can take place, thus converting the flow cell into a conventional H-type cell.

Disclosure of Invention

In order to solve the problems of the GDE constructed by taking a porous graphite-based material as a gas diffusion substrate, the invention provides a method for constructing a Flexible Gas Diffusion Electrode (FGDE) by taking a porous high-molecular film as a substrate.

The invention provides a gas diffusion electrode, which comprises a substrate layer, a catalyst layer, a polymer layer and an interface layer which are sequentially arranged, wherein the substrate layer comprises a porous high polymer film; the thickness of the porous high molecular polymer film is any value between 5 mu m and 100 mu m. The porous high molecular polymer is not limited to a hydrophobic structure or a hydrophilic structure, and can be used for supporting an electrode, and a person skilled in the art can select a specific kind according to actual conditions.

Preferably, the pore diameter of the porous high molecular polymer film is any value between 0.1 μm and 5 μm; the porosity is anywhere between 60% and 90%.

Preferably, the skeleton material of the porous high polymer film is one of Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), Polyethylene (PE) and polypropylene (PP);

the polymerization degree of the porous high molecular polymer in the porous high molecular polymer film is more than or equal to 10³。

The conductive microporous layer, the catalyst layer and the polymer interface layer are prepared by one of blade coating and spraying.

According to a preferable technical scheme, the thickness of the catalyst layer is 5 nm-500 nm, the thickness of the polymer layer is 2 nm-50 nm, and the thickness of the interface layer is 5 nm-200 nm;

preferably, the catalyst layer comprises a nanomaterial having electrocatalytic activity to ERC reaction and a binder;

preferably, the nano-catalyst in the catalyst layer is one of nano-metal particles, supported nano-metal particles, a carbon material doped with strong electronegativity elements or a single atom metal catalyst;

preferably, the binder is one of polyvinylidene fluoride (PVDF) and perfluorinated sulfonic acid resin;

preferably, the mass ratio of the catalyst to the binder is 8: 1-2: 1;

preferably, the polymer layer includes a porous high molecular polymer resin I.

As a preferred technical scheme, a micropore conducting layer is arranged between the substrate layer and the catalyst layer, and the thickness of the micropore conducting layer is 10 nm-1000 nm;

preferably, the conductive microporous layer comprises highly conductive carbon and a binder;

preferably, the high-conductivity carbon in the conductive microporous layer is one of graphite powder and activated carbon, and the particle size is 0.5-2 μm; the binder is one of Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) and perfluorinated sulfonic acid resin; the mass ratio of the high-conductivity carbon to the binder is 9: 1-2: 1.

Preferably, the interface layer comprises porous polymer resin II and catalyst particles as main components;

in the interface layer, the mass ratio of the polymer resin to the catalyst particles is 9:1 to 5: 1.

The porous resins of the present invention are of the type commonly used in the art for polymer layers.

Preferably, the polymer resin I in the polymer layer is an organic polymer resin containing hydrophilic groups; the hydrophilic group is preferably an acrylic group, a sulfonic group, a propenyl sulfonic group, or a quaternary amine group.

Preferably, the catalyst particles in the interface layer are the same as the catalyst particles in the catalyst layer in terms of elements; the polymer resin II in the interface layer is the same as the polymer resin I in the polymer layer.

As a preferred embodiment, CO₂The gas diffusion coefficient in the interfacial layer is greater than the diffusion coefficient in the catholyte. CO2₂The gas diffusion coefficient (D) of the gas in the interface layer is greater than the diffusion coefficient in the catholyte, i.e. it is ensured that the majority of the CO₂The reduction reaction takes place within the gas diffusion electrode, rather than into the catholyte.

The flexible gas diffusion electrode can be applied to CO2 electrochemical reduction, and is particularly suitable for CO2 electrochemical reduction technology using a flow electrolytic cell, wherein the pH value of electrolyte in the electrolytic cell is 6-14.

The invention also provides a carbon dioxide electrochemical reduction electrolytic cell, which comprises any one of the gas diffusion electrodes and C obtained by electrolysis₂The volume ratio of the product to the total reaction product is 60-80 percent, and the component C is₂The product comprises C₂H₄、C₂H₅OH。

Advantageous effects

Compared with the existing gas diffusion electrode based on porous graphite, the flexible gas diffusion electrode prepared by the method has the following characteristics:

(1) the flexible gas diffusion electrode can be bent and extruded, can bear the pressure difference formed by rapid gas generation in the flowing electrolytic cell, ensures the integrity and gas permeability of the gas diffusion electrode, and overcomes the defect that the graphite-based gas diffusion electrode is easy to crack under a certain pressure difference.

(2) Grafting SO introduced from one side of the flexible gas diffusion electrode close to the electrolyte₃ ^-Polymer layer of radicals, CO₂The in-plane diffusion coefficient (D) in the layer is greater than the diffusion coefficient (D) in the catholyte₀) Thereby making CO₂The gas flows in the layer until the CO₂The reduction is carried out in the presence of a catalyst to dissolve CO in the catholyte₂The amount is reduced, and most of CO is generated₂Three-phase interface on the surface of catalyst reacts without CO₂The restriction of solubility in aqueous solution, thereby increasing the reaction rate of ERC.

(3) In the interface layer of the flexible gas diffusion electrode, catalyst particles and polymer are mixed to obtain a 3D morphology with catalyst and polymer permeation pathways. Such FGDE will maximize the three-phase reaction interface over an extended three-dimensional (3D) morphology, enabling ERC reactions to be carried out under higher current conditions.

(4) The polymer layer can prolong the residence time of carbon dioxide on the surface of the catalytic layer and increase the conversion rate of carbon dioxide, but when the thickness is too high, the proton transfer rate is reduced, the hydrogenation reduction rate of carbon dioxide is delayed, the reduction rate of carbon dioxide is reduced, and the generation rate and the selectivity of products are influenced.

Drawings

Fig. 1 is a schematic structural diagram of a flexible gas diffusion electrode according to the present invention, in which an FGDE structure using a porous polymer film as a substrate and its interface characteristics in ERC reaction are shown.

1. A porous polymer film; 2. a conductive microporous layer; 3. a catalytic layer; 4. a polymer layer; 5. an interfacial layer.

Detailed Description

A Flexible Gas Diffusion Electrode (FGDE) is prepared by using porous high-molecular polymer film as substrate and sequentially constructing a conductive microporous layer, a catalyst layer, a polymer layer and an interface layer. The conductive microporous layer comprises highly conductive carbon and a binder; the catalyst layer comprises a nano material with electrocatalytic activity to the ERC reaction and a binder. The polymer layer is a high molecular polymer resin layer, the skeleton of the polymer resin has the same chemical composition with the substrate material, and contains hydrophobic groups, and the side chain is grafted with hydrophilic groups, so that the liquid-solid interface layer has hydrophobic and hydrophilic functions; the interface layer is mainly made of porous high molecular polymer resin and is added with a small amount of catalyst particles.

Comparative example 1

(1) Pretreatment of graphite-based porous carbon paper: the porosity is 82%, the thickness is 190 micrometers, and the area is 10cm²Carbon paper (TGP-H-030, manufactured by Toray Japan Co., Ltd.) as a base material, firstFirstly, soaking the glass fiber in acetone at room temperature for 10min to remove surface grease, and then blowing the glass fiber with high-purity argon;

(2) preparation of graphite-based Gas Diffusion Electrode (GDE): mixing Cu particles with the particle size of 20nm, a perfluorinated sulfonic acid resin (Nafion) solution and isopropanol, wherein the mass ratio of the Cu particles to the perfluorinated sulfonic acid resin is 7:3, the mass ratio of the isopropanol to the perfluorinated sulfonic acid resin solution is 8:1, performing ultrasonic dispersion on the mixture for 30min, spraying the mixture on the surface of the porous carbon paper subjected to the first step of grease removal, and controlling the surface density of the nano Cu particles to be 5mg cm^-2And drying in a vacuum oven at 60 ℃ under the vacuum degree of-0.1 MPa, wherein the thickness of the dried catalyst layer is about 200 nm.

(3) Electrochemical reduction treatment of the gas diffusion electrode: first, analytically pure sodium bicarbonate was used as a raw material, ultrapure water having a resistivity of 18.2M Ω was used as a solvent, and NaHCO was prepared at a concentration of 0.1M₃200ml of aqueous solution; then high-purity N is introduced₂And (3) taking the GDE prepared in the step (2) as a working electrode, a Pt sheet as a counter electrode and a saturated calomel electrode as a reference electrode for 1 h. At-2 mAcm^-2And after electrochemical reduction is carried out for 120min under the condition, the mixture is taken out, washed by a large amount of deionized water, dried by high-purity argon, and stored in an inert environment for later use.

(4) Electrochemical catalytic reduction of CO₂: in the flow type electrolytic cell, 20ml of 1.0M KOH aqueous solution was added to each of the anode and cathode chambers, and NF115 manufactured by DuPont was used as a separator of the anode and cathode chambers. The electrode in 3 is used as a working electrode, Ag/AgCl (saturated KCl) is used as a reference electrode, and a Pt sheet is used as a counter electrode. Controlling the flow rate of the cathode and anode electrolyte to be 3ml min^-1CO with a purity of 99.995%₂Gas enters the cathode chamber from the catalyst-free surface of the GDE, CO₂The flow rate of (2) was controlled to 20 sccm. Carrying out electrochemical reduction reaction for 35min under-1.4V working voltage, introducing reaction tail gas into gas chromatography for quantitative detection of gas products, and carrying out quantitative analysis on liquid products by adopting ion chromatography.

After the reaction proceeded for 30min, the GDE was destroyed and the ERC reaction was terminated.

The product analysis results within 30min were: c₂H₄The Faraday efficiency of the device is 40 percent, and the current is dividedThe density is 15mA cm-2; the faradaic efficiency of CO is 21%; the faradaic efficiency of HCOOH is 2%; h₂The faradaic efficiency of (a) was 38%, and the total faradaic efficiency of these four products was 99%, indicating that the other undetected products were produced in very small amounts.

Comparative example 2

(1) Pretreatment of the flexible substrate: cutting a porous polytetrafluoroethylene membrane with the thickness of 40 mu m, the porosity of 75% and the pore diameter of 0.22 mu m into 4cm by 4cm, soaking the membrane in deionized water, spreading the membrane completely, paving the membrane on the surface of clean filter paper, and sucking water.

(2) Preparing a microporous conducting layer: preparing slurry from Vulcan X-72 activated carbon with the particle size of 1 mu m, polyvinylidene fluoride (PCDF) and N, N-dimethyl pyrrolidone, controlling the mass ratio of the activated carbon to the PVDF to be 8:2, and controlling the viscosity of the slurry to be 1000 MPas; spreading the porous polytetrafluoroethylene film in the step 1 on a clean glass plate, uniformly spraying the slurry on the surface of the porous PTFE, and controlling the surface density of the active carbon to be 1.0mg cm^-2And drying the sprayed combination in a 120 ℃ oven to obtain a sprayed layer with the thickness of about 100 nm.

(3) Preparing a catalytic layer: mixing Cu particles with the particle size of 20nm, a perfluorinated sulfonic acid resin (Nafion) solution and isopropanol, wherein the mass ratio of the Cu particles to the perfluorinated sulfonic acid resin is 7:3, the mass ratio of the isopropanol to the perfluorinated sulfonic acid resin solution is 8:1, ultrasonically dispersing the mixture for 30min, spraying the mixture on the surface of the microporous conductive layer prepared in the step 2, and controlling the surface density of the nano Cu particles to be 5mg cm^-2And drying in a vacuum oven at 60 ℃ under the vacuum degree of-0.1 MPa, wherein the thickness of the dried catalyst layer is about 200 nm.

(4) Electrochemical catalytic reduction of CO₂: in the flow type electrolytic cell, 20ml of 1.0M KOH aqueous solution was added to each of the anode and cathode chambers, and NF115 manufactured by DuPont was used as a separator of the anode and cathode chambers. The electrode in 3 is used as a working electrode, Ag/AgCl (saturated KCl) is used as a reference electrode, and a Pt sheet is used as a counter electrode. Controlling the flow rate of the cathode and anode electrolyte to be 3ml min^-1CO with a purity of 99.995%₂Gas enters the cathode cavity from the GDE catalyst-free surface, CO₂The flow rate of (2) was controlled to 20 sccm. at-1.4V working voltageCarrying out electrochemical reduction reaction for 5h, introducing reaction tail gas into a gas chromatograph to carry out quantitative detection on a gas product, and carrying out quantitative analysis on a liquid product by adopting NMR.

Within 5h of reaction, the ERC reaction current is stable, and the appearance of the flexible gas diffusion electrode is intact.

The product analysis results are: c₂H₄The Faraday efficiency of the device is 43 percent, and the current density is 29mA cm^-2B, carrying out the following steps of; the faradaic efficiency of CO is 12%; c₂H₅Faradaic efficiency of OH 6.3%; the faraday efficiency of HCOOH is 3%; h₂The faradaic efficiency of (a) was 35.1%, and the total faradaic efficiency of these four products was 99.4%, indicating that the other undetected products were produced in very small amounts.

In this comparative example, the gas diffusion electrode containing no interface layer and no polymer layer had no expansion of the reaction area, a small number of reactive sites, and no CO interaction₂The increase of the in-plane diffusion coefficient enables CO2 to easily enter the electrolyte, and the ERC reaction rate is low.

Comparative examples 3 to 7, the preparation and testing procedures are similar to comparative example 2, and the relevant main parameters are detailed in table 1.

Example 1

(1) Pretreatment of the flexible substrate: cutting a porous polytetrafluoroethylene membrane with the thickness of 40 mu m, the porosity of 75 percent and the pore diameter of 0.22 mu m into 4 cm-4 cm, soaking the membrane in deionized water, spreading the membrane completely, paving the membrane on the surface of clean filter paper, and sucking water to dry.

(3) Preparing a catalytic layer: mixing Cu particles with particle diameter of 20nm, perfluorosulfonic acid resin (Nafion) solution, and isopropanol, mixing the Cu particles with perfluoroThe mass ratio of the sulfonic acid resin is 7:3, the mass ratio of the isopropanol to the perfluorinated sulfonic acid resin solution is 8:1, the mixture is subjected to ultrasonic dispersion for 30min, and then the mixture is sprayed on the surface of the microporous conductive layer prepared in the step 2, and the surface density of the nano Cu particles is controlled to be 5mg cm^-2And drying in a vacuum oven at 60 ℃ under the vacuum degree of-0.1 MPa, wherein the thickness of the dried catalyst layer is about 200 nm.

(4) Preparation of the polymer layer: spraying 1% perfluorosulfonic acid resin solution with exchange equivalent of 1100 on the surface of the catalyst layer prepared in step 3, and controlling the surface density of the perfluorosulfonic acid resin to be 0.2mg cm^-2Corresponding to a thickness of about 20 nm.

(5) Preparing an interface layer: and (4) spraying an interface layer on the surface of the polymer layer prepared in the step (3). The mass ratio of the Cu particles to the perfluorinated sulfonic acid resin is controlled to be 1:5, and the surface density of the nano Cu particles is 1mg cm^-2The thickness of the interfacial layer after drying was about 100 nm.

(6) Electrochemical catalytic reduction of CO₂: in the flow type electrolytic cell, 20ml of 1.0M KOH aqueous solution was added to each of the anode and cathode chambers, and NF115 manufactured by DuPont was used as a separator of the anode and cathode chambers. The electrode in 5 is used as a working electrode, Ag/AgCl (saturated KCl) is used as a reference electrode, and a Pt sheet is used as a counter electrode. Controlling the flow rate of the cathode and anode electrolyte to be 3ml min^-1CO with a purity of 99.995%₂Gas enters the cathode cavity from the GDE catalyst-free surface, CO₂The flow rate of (2) was controlled to 20 sccm. Carrying out electrochemical reduction reaction for 5h under the working voltage of-1.4V, introducing reaction tail gas into a gas chromatograph to carry out quantitative detection on a gas product, and carrying out quantitative analysis on a liquid product by adopting NMR.

Within 5h of reaction, the ERC reaction current is stable, and the flexible gas diffusion electrode is intact.

The product analysis results are: c₂H₄The Faraday efficiency of (A) was 65% which was 1.7 times that of comparative example; the current distribution density is 150mA cm^-210 times that of the comparative example; the faradaic efficiency of CO is 9%; c₂H₅Faradaic efficiency of OH 13.8%; h₂The faradaic efficiency of (a) was 12%, and the total faradaic efficiency of these four products was 99.8%, indicating other undetected productsThe amount of the product produced is very small.

By comparing with the test results of the comparative examples, the test results of the examples show that by adopting the electrode structure of the invention, the reaction rate of the ERC is obviously improved under the condition of taking 20nmCu particles as the catalyst, and meanwhile, the selectivity of the C2(+) product is improved from 38% to 77%, and the improvement range is up to 1 time.

Example 2

(1) Pretreatment of the flexible substrate: cutting a porous polyvinylidene fluoride membrane with the thickness of 100 mu m and the pore diameter of 0.1 mu m into 4cm by 4cm, soaking the membrane in deionized water, spreading the membrane on the surface of clean filter paper after completely spreading, and sucking water.

(2) Preparing a microporous conducting layer: preparing slurry from graphite powder with the particle size of 2 mu m, polytetrafluoroethylene and N, N-dimethyl pyrrolidone, controlling the mass ratio of the graphite powder to the PTFE to be 9:1, and controlling the viscosity of the slurry to be 1500 MPas; spreading the porous polytetrafluoroethylene film in the step 1 on a clean glass plate, uniformly spraying the slurry on the surface of the porous PVDF, and controlling the surface density of the active carbon to be 3.0mg cm^-2The sprayed composite was dried in an oven at 70 ℃ to give a sprayed layer having a thickness of about 500 nm.

(3) Preparing a catalytic layer: mixing 40 wt% Cu/C particles with the particle size of 5nm, a perfluorinated sulfonic acid resin (Nafion) solution and isopropanol, wherein the mass ratio of the Cu/C particles to the perfluorinated sulfonic acid resin is 2:1, the mass ratio of the isopropanol to the perfluorinated sulfonic acid resin solution is 10:1, ultrasonically dispersing the mixture for 30min, and spraying the mixture on the surface of the microporous conductive layer prepared in the step 2, wherein the surface density of the nano Cu/C particles is controlled to be 5mg cm^-2And drying in a vacuum oven at 60 ℃ under the vacuum degree of-0.1 MPa, wherein the thickness of the dried catalyst layer is about 500 nm.

(4) Preparation of the polymer layer: spraying perfluorosulfonic acid resin solution with exchange Equivalent Weight (EW) of 900 and concentration of 1% on the surface of the catalyst layer prepared in step 3, and controlling the surface density of the perfluorosulfonic acid resin to be 0.5mg cm^-2Corresponding to a thickness of about 50 nm.

(5) Preparing an interface layer: and (4) spraying an interface layer on the surface of the polymer layer prepared in the step (3). The mass ratio of Cu/C particles to the perfluorinated sulfonic acid resin is controlled to be 1:7, and the particle size is nanometerThe areal density of the Cu/C particles was 0.5mg cm^-2The thickness of the interfacial layer after drying was about 200 nm.

The product analysis results are: c₂H₄The Faraday efficiency of (A) was 60%, which was 1.58 times that of comparative example; the current distribution density is 120mA cm^-28 times as much as the comparative example; the faradaic efficiency of CO is 13%; c₂H₅Faraday efficiency of OH 11%; h₂The faradaic efficiency of (a) was 15%, and the total faradaic efficiency of these four products was 99%, indicating that the other non-detected products were produced in very small amounts. Wherein, the proportion of the C2(+) product in the total C product is up to 84.52%.

Example 3

(1) Pretreatment of the flexible substrate: cutting a porous polyethylene film with thickness of 5 μm and pore diameter of 0.5 μm to 4cm by 4cm, soaking in deionized water, spreading completely, spreading on the surface of clean filter paper, and sucking water.

(2) Preparing a microporous conducting layer: preparing ink slurry from KJ-300 with the particle size of 0.5 mu m, perfluorinated sulfonic acid resin and isopropanol, controlling the mass ratio of carbon black to the perfluorinated sulfonic acid resin to be 4:1, and controlling the viscosity of the slurry to be 500 MPas; spreading the porous polyethylene film in the step 1 on a clean glass plate, uniformly spraying the slurry on the surface of the porous PE, and controlling the surface density of the active carbon to be 2.0mg cm^-2Assembly after sprayingAfter drying in an oven at 60 ℃ the thickness of the spray coating was approximately 700 nm.

(3) Preparing a catalytic layer: mixing Zn particles with the particle size of 30nm, 20% of PTFE emulsion and isopropanol, wherein the mass ratio of the Zn particles to the PTFE is 8:1, the mass ratio of the isopropanol to the PTFE emulsion is 8:1, ultrasonically dispersing the mixture for 30min, and spraying the mixture on the surface of the microporous conductive layer prepared in the step 2, wherein the surface density of the nano Zn particles is controlled to be 2.5mg cm^-2And drying in a vacuum oven at 60 ℃ under the vacuum degree of-0.1 MPa, wherein the thickness of the dried catalyst layer is about 50 nm.

(4) Preparation of the polymer layer: spraying perfluoro sulfonic acid resin solution with exchange equivalent of 900 and concentration of 5% on the surface of the catalyst layer prepared in step 3, and controlling the surface density of perfluoro sulfonic acid resin to be 0.5mg cm^-2Corresponding to a thickness of about 50 nm.

(5) Preparing an interface layer: and (4) spraying an interface layer on the surface of the polymer layer prepared in the step (3). The mass ratio of the Zn particles to the perfluorinated sulfonic acid resin is controlled to be 1:9, and the surface density of the nano Zn particles is 0.2mg cm^-2The thickness of the interfacial layer after drying was about 20 nm.

(6) Electrochemical catalytic reduction of CO₂: in the flow type electrolytic cell, 20ml of 1.0M KOH aqueous solution was added to each of the anode and cathode chambers, and NF115 manufactured by DuPont was used as a separator of the anode and cathode chambers. The electrode in 5 is used as a working electrode, Ag/AgCl (saturated KCl) is used as a reference electrode, and a Pt sheet is used as a counter electrode. Controlling the flow rate of the cathode and anode electrolyte to be 3ml min^-1CO with a purity of 99.995%₂Gas enters the cathode cavity from the GDE catalyst-free surface, CO₂The flow rate of (2) was controlled to 20 sccm. Carrying out electrochemical reduction reaction for 5h under the working voltage of-1.7V, introducing reaction tail gas into a gas chromatograph to carry out quantitative detection on a gas product, and carrying out quantitative analysis on a liquid product by adopting NMR.

Within 5h of reaction, the ERC reaction current is stable, and the flexible gas diffusion electrode is intact. The product analysis results are: c₂H₄The Faraday efficiency of (2) is 4%; CH (CH)₄The Faraday efficiency of the anode is 20 percent, and the divided current density is 30mA cm^-2(ii) a The faradaic efficiency of CO is 60%; c₂H₅Faraday efficiency of OH 2％；H₂The faradaic efficiency of (a) was 12%, and the total faradaic efficiency of these five products was 99%, indicating that the other undetected products were produced in very small quantities.

The test results of example 3 demonstrate that with the electrode structure of the present invention, the ERC reaction rate was significantly improved with the 30nm Zn particles as the catalyst, the sum of the partial current densities of the C1 products was 120mA cm "2, and the proportion of the C1 product in the total C product was as high as 93%.

Example 4

(1) Pretreatment of the flexible substrate: cutting a porous polypropylene film with the thickness of 50 microns and the aperture of 0.1 micron into 4cm by 4cm, soaking the film in deionized water, spreading the film on the surface of clean filter paper after completely spreading, and sucking water.

(2) Preparing a microporous conducting layer: KJ-600 carbon black with the particle size of 1.5 mu m, polyvinylidene fluoride and N, N-dimethyl pyrrolidone are used for preparing slurry, the mass ratio of active carbon to PVDF is controlled to be 2:1, and the viscosity of the slurry is 1000 MPas; spreading the porous polypropylene film in the step 1 on a clean glass plate, uniformly spraying the slurry on the surface of the porous PP, and controlling the surface density of the active carbon to be 2.0mg cm^-2The sprayed composite is dried in a 60 ℃ oven, and the thickness of the sprayed layer is about 1000 nm.

(3) Preparing a catalytic layer: mixing nitrogen-doped hollow carbon spheres (N-HC) with the particle size of 5nm, a perfluorinated sulfonic acid resin (Nafion) solution and isopropanol, wherein the mass ratio of Cu particles to the perfluorinated sulfonic acid resin is 6:1, the mass ratio of the isopropanol to the perfluorinated sulfonic acid resin solution is 8:1, ultrasonically dispersing the mixture for 30min, spraying the mixture on the surface of the microporous conductive layer prepared in the step 2, and controlling the surface density of the nano N-HCS particles to be 0.2mg cm^-2And drying in a vacuum oven at 60 ℃ under the vacuum degree of-0.1 MPa, wherein the thickness of the dried catalyst layer is about 20 nm.

(4) Preparation of the polymer layer: spraying perfluoro sulfonic acid resin solution with exchange equivalent of 900 and concentration of 1% on the surface of the catalyst layer prepared in step 3, and controlling the surface density of perfluoro sulfonic acid resin to be 0.1mg cm^-2Corresponding to a thickness of about 10 nm.

(5) Preparing an interface layer: prepared according to the method in 3, at 4And spraying an interface layer on the surface of the polymer layer. The mass ratio of the Cu particles to the perfluorosulfonic acid resin is controlled to be 1:8, and the surface density of the N-HC particles is controlled to be 0.4mg cm^-2The thickness of the interfacial layer after drying was about 50 nm.

(6) Electrochemical catalytic reduction of CO₂: in the flow type electrolytic cell, 20ml of 1.0M KOH aqueous solution was added to each of the anode and cathode chambers, and NF115 manufactured by DuPont was used as a separator of the anode and cathode chambers. The electrode in 5 is used as a working electrode, Ag/AgCl (saturated KCl) is used as a reference electrode, and a Pt sheet is used as a counter electrode. Controlling the flow rate of the cathode and anode electrolyte to be 3ml min^-1CO with a purity of 99.995%₂Gas enters the cathode cavity from the GDE catalyst-free surface, CO₂The flow rate of (2) was controlled to 20 sccm. Carrying out electrochemical reduction reaction for 5h under the working voltage of-1.2V, introducing reaction tail gas into a gas chromatograph to carry out quantitative detection on a gas product, and carrying out quantitative analysis on a liquid product by adopting NMR.

Within 5h of reaction, the ERC reaction current is stable, and the flexible gas diffusion electrode is intact. The product analysis results are: the Faraday efficiency of CO is 88%, and the divided current density of CO is 50mA cm^-2；H₂The faradaic efficiency of (a) was 10%, and the total faradaic efficiency of both was 98%, indicating that the formation of other undetected products was extremely small.

The test results of example 4 show that the sum of the partial current densities of the CO products using the electrode structure of the invention in the presence of 50nm N-hollow carbon spheres as the catalyst is 50mA cm^-2Its Faraday efficiency is up to 88%.

Example 5

(1) Pretreatment of the flexible substrate: cutting a porous polytetrafluoroethylene membrane with the thickness of 5 microns and the pore diameter of 0.1 micron into 4cm by 4cm, soaking the membrane in deionized water, spreading the membrane on the surface of clean filter paper after completely spreading, and sucking water.

(2) Preparing a microporous conducting layer: preparing slurry from KJ-300 carbon black with the particle size of 0.5 mu m, polyvinylidene fluoride and N, N-dimethyl pyrrolidone, controlling the mass ratio of active carbon to PVDF to be 3:1, and controlling the viscosity of the slurry to be 1000 MPas; spreading the porous polytetrafluoroethylene film in the step 1 on a clean glass plate, and uniformly spraying the slurry on the porous PControlling the surface density of the activated carbon to be 0.1mg cm on the surface of TFE^-2The sprayed composite is dried in an oven at 120 ℃ to obtain a sprayed layer with a thickness of about 10 nm.

(3) Preparing a catalytic layer: monodisperse ZnN with the particle size of 30nm₄-C, perfluorosulfonic acid resin (Nafion) solution, isopropanol, ZnN₄The mass ratio of the-C particles to the perfluorinated sulfonic acid resin is 5:1, the mass ratio of the isopropanol to the perfluorinated sulfonic acid resin solution is 8:1, the mixture is subjected to ultrasonic dispersion for 30min and then is sprayed on the surface of the microporous conductive layer prepared in the step 2, and the nano ZnN is controlled₄The areal density of the-C particles was 0.3mg cm^-2And drying in a vacuum oven at 60 ℃ under the vacuum degree of-0.1 MPa, wherein the thickness of the dried catalyst layer is about 5 nm.

(4) Preparation of the polymer layer: spraying 1% perfluorosulfonic acid resin solution with exchange equivalent of 1100 on the surface of the catalyst layer prepared in step 3, and controlling the surface density of the perfluorosulfonic acid resin to be 0.05mg cm^-2Corresponding to a thickness of about 2 nm.

(5) Preparing an interface layer: and (4) spraying an interface layer on the surface of the polymer layer prepared in the step (3). Control of ZnN₄The mass ratio of the-C particles to the perfluorinated sulfonic acid resin is 1:5, and the nano ZnN is₄The areal density of the-C particles was 0.1mg cm^-2The thickness of the interfacial layer after drying was about 5 nm.

(6) Electrochemical catalytic reduction of CO₂: in the flow type electrolytic cell, 20ml of 1.0M KOH aqueous solution was added to each of the anode and cathode chambers, and NF115 manufactured by DuPont was used as a separator of the anode and cathode chambers. And (3) taking the electrode in the step (5) as a working electrode, Ag/AgCl (saturated KCl) as a reference electrode and a Pt sheet as a counter electrode. Controlling the flow rate of the cathode and anode electrolyte to be 3ml min^-1CO with a purity of 99.995%₂Gas enters the cathode cavity from the GDE catalyst-free surface, CO₂The flow rate of (2) was controlled to 20 sccm. Carrying out electrochemical reduction reaction for 5h under the working voltage of-1.5V, introducing reaction tail gas into a gas chromatograph to carry out quantitative detection on a gas product, and carrying out quantitative analysis on a liquid product by adopting NMR.

The product analysis results were: CH (CH)₄The Faraday efficiency is 75 percent, and the divided current density is 60mA cm^-2(ii) a Faraday efficiency of CO is 12%, that of HCOOH is 3%, and that of H₂The faradaic efficiency of (a) was 8%, and the total faradaic efficiency of these three products was 99%, indicating that the other non-detected products were produced in very small amounts.

The test results of example 5 demonstrate that C1 (CH) using the electrode structure of the invention in the presence of a catalyst of 30nm, ZnN4-C₄+ CO + HCOOH) product has a total Faraday efficiency of up to 91%, the main product CH₄The current distribution density of the power distribution unit is up to 60mA cm^-2。

TABLE 1 Effect of the Primary control parameters on the ERC reaction Rate and Primary product Selectivity

According to the data, comparative analysis:

1. among the electrodes of the carbon-based support structure, the electrodes are easily damaged under the action of pressure; and does not contain an interface layer and a polymer layer, the reaction area is not expanded, and CO is not treated₂Increase of in-plane diffusion coefficient, CO₂The hydrogen evolution catalyst is easy to enter into electrolyte, the ERC reaction rate is low, and the hydrogen evolution side reaction is serious;

2. in the flexible electrode, if an interface layer and a polymer layer are not constructed, the reaction area is not expanded, the number of reaction active sites is small, and CO is not reacted₂The in-plane diffusion coefficient is improved, CO2 easily enters the electrolyte, and the ERC reaction rate is low;

3. in the flexible electrode structure, if the thickness of the catalytic layer is too high, catalyst particles positioned inside cannot be used as a place for electrochemical reduction, so that the catalytic action is lost, the number of catalytic activity bits participating in the ERC reaction is reduced, and the ERC reaction rate is reduced; the thickness of the polymer layer is too high, so that the proton transfer speed can be reduced, the hydrogenation reduction speed of carbon dioxide can be delayed, the reduction speed of the carbon dioxide is reduced, and the generation speed and the selectivity of a product are influenced; the thickness of the interface layer is too high, and due to insufficient density of catalyst particles in the interface layer, on one hand, the number of active sites can be reduced, on the other hand, the proton transfer rate can also be reduced, the hydrogenation reduction rate of carbon dioxide is delayed, the reduction rate of carbon dioxide is reduced, and the generation rate and selectivity of products are influenced.

Claims

1. A gas diffusion electrode comprises a substrate layer, a catalyst layer, a polymer layer and an interface layer which are sequentially arranged, wherein the substrate layer comprises a porous high polymer film;

the thickness of the porous high molecular polymer film is any value between 5 mu m and 100 mu m.

2. The gas diffusion electrode according to claim 1, wherein the porous high molecular polymer thin film has a pore size of any value between 0.1 μm and 5 μm and a porosity of any value between 60% and 90%.

3. The gas diffusion electrode of claim 1, wherein the porous polymer film comprises a skeleton material selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and polypropylene;

4. The gas diffusion electrode of claim 1, wherein the catalyst layer has a thickness of 5nm to 500nm, the polymer layer has a thickness of 2nm to 50nm, and the interface layer has a thickness of 5nm to 200 nm;

the catalyst layer comprises a nano material with electrocatalytic activity for electrochemical reduction of carbon dioxide and a binder;

the nano material in the catalyst layer is selected from at least one of nano metal particles, supported nano metal particles, a carbon material doped with strong electronegative elements or a single atom metal catalyst;

the binder is one of polyvinylidene fluoride or perfluorosulfonic acid resin;

the mass ratio of the nano material to the binder is 8: 1-2: 1;

the polymer layer includes a porous high molecular polymer resin I.

5. The gas diffusion electrode of claim 1, wherein a microporous conductive layer is disposed between the substrate layer and the catalytic layer, the microporous conductive layer having a thickness of 10nm to 1000 nm;

the conductive microporous layer includes highly conductive carbon and a binder;

the high-conductivity carbon in the conductive microporous layer is one of graphite powder and active carbon, and the particle size is 0.5-2 mu m; the binder is at least one of polytetrafluoroethylene, polyvinylidene fluoride or perfluorosulfonic acid resin; the mass ratio of the high-conductivity carbon to the binder is 9: 1-2: 1.

6. Gas diffusion electrode according to claim 1,

the interface layer comprises porous high molecular polymer resin II and catalyst particles;

in the interface layer, the mass ratio of the polymer resin II to the catalyst particles is 9: 1-5: 1;

preferably, the catalyst particles in the interface layer are the same element as the catalyst particles in the catalytic layer;

preferably, the polymer resin II in the interface layer is the same as the polymer resin I in the polymer layer.

7. The gas diffusion electrode according to claim 6,

the polymer resin I in the polymer layer is organic polymer resin containing hydrophilic groups; the hydrophilic group includes at least one of an acrylic group, a sulfonic group, a propenyl sulfonic group, or a quaternary amine group.

8. The gas diffusion electrode of claim 1, wherein CO₂The gas diffusion coefficient of the gas in the interface layer is larger than that in the cathodeDiffusion coefficient in the electrode electrolyte.

9. A carbon dioxide electrochemical reduction cell comprising a gas diffusion electrode according to any one of claims 1 to 8.

10. The carbon dioxide electrochemical reduction cell of claim 9, electrolyzing the resulting C₂The volume ratio of the product to the total reaction product is 60-80%.