CN116314853A - Gradient microporous layer gas diffusion layer for carbon dioxide reduction and preparation method thereof - Google Patents
Gradient microporous layer gas diffusion layer for carbon dioxide reduction and preparation method thereof Download PDFInfo
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- 238000013461 design Methods 0.000 description 1
- HTXDPTMKBJXEOW-UHFFFAOYSA-N dioxoiridium Chemical compound O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 description 1
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- HQQADJVZYDDRJT-UHFFFAOYSA-N ethene;prop-1-ene Chemical group C=C.CC=C HQQADJVZYDDRJT-UHFFFAOYSA-N 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/88—Processes of manufacture
- H01M4/8803—Supports for the deposition of the catalytic active composition
- H01M4/8807—Gas diffusion layers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/8605—Porous electrodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/023—Porous and characterised by the material
- H01M8/0234—Carbonaceous material
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- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Life Sciences & Earth Sciences (AREA)
- Sustainable Development (AREA)
- Sustainable Energy (AREA)
- Inert Electrodes (AREA)
Abstract
The invention relates to a gradient microporous layer gas diffusion layer for carbon dioxide reduction and a preparation method thereof. The gas diffusion layer comprises a basal layer and a gradient microporous layer; the gradient microporous layer comprises a plurality of microporous sublayers having different hydrophilicity and hydrophobicity along the thickness direction thereof; the hydrophobicity of each microporous sublayer tends to decrease in a gradient in a direction away from the substrate layer. The gradient microporous layer gas diffusion layer provided by the invention is suitable for the technical field of carbon dioxide reduction, microporous layers with hydrophobicity gradient change are constructed by utilizing microporous sublayers with different hydrophobes, pores smaller than 0.1 mu m are formed by mutually filling carbon materials among different microporous sublayers, and the preparation operation of the gradient microporous layer gas diffusion layer is simple and repeatable and has high application value.
Description
Technical Field
The invention relates to a gradient microporous layer gas diffusion layer for carbon dioxide reduction and a preparation method thereof, in particular to a multilayer microporous layer gas diffusion layer with hydrophobicity gradient change and a preparation method thereof.
Background
The renewable electric driven carbon dioxide reduction technology opens up the possibility of converting the main component of greenhouse gases carbon dioxide into value-added chemical raw materials or fuels, and is considered as an effective measure for achieving the national carbon neutralization and carbon peak "two carbon" strategy. In addition, the use of carbon dioxide as a feedstock for chemical production can reduce reliance on fossil fuel resources, with both environmental and economic benefits.
The diffusion path of carbon dioxide through the gas diffusion layer to the catalyst surface (-50 nm) is about 3 orders of magnitude smaller than the diffusion path through the bulk electrolyte to the catalyst surface (-50 μm) for a gas diffusion electrode employing a gas diffusion layer as compared to a planar metal electrode immersed in a liquid electrolyte. The improvement in carbon dioxide transport enables the cell with the gas diffusion layer to achieve a greater current density, which is more advantageous for scaling up the reduction of carbon dioxide to industrially relevant levels.
The Gas Diffusion Electrode (GDE) is composed of a basal layer (CFS), a microporous layer (MPL) and a Catalyst Layer (CL), wherein the gas diffusion layer is a complex porous structure of electric conduction, gas conduction, heat conduction and water conduction. More specifically, the microporous layer reduces the contact resistance between the substrate layer and the catalyst layer by forming a flat and strong fill layer, and is critical to maintaining efficient transport of the liquid and vapor phases. The ideal microporous layer needs to have proper pore size distribution and hydrophilicity and hydrophobicity to avoid the permeation of liquid electrolyte into the gas diffusion layer to block the gas transportation channel, enhance the effectiveness of carbon dioxide transportation to active catalyst sites and thus improve the carbon dioxide reduction performance.
CN114481184a discloses a gas diffusion layer for electrochemical reduction of carbon dioxide and a preparation method thereof, and a general hydrophobizing agent regulates a basal layer and a microporous layer, forms proper hydrophobicity, porosity and pore size distribution in the gas diffusion layer, promotes mass transfer of carbon dioxide and shows higher running current density.
CN113308707a discloses a gas diffusion electrode for electrochemical reduction of carbon dioxide to prepare hydrocarbon fuel, which is subjected to hydrophobic treatment and enhanced in conductivity by spray gun spraying method to prevent overflow of electrolyte to form an ideal gas-liquid-solid three-phase interface for carbon dioxide reduction reaction.
In the prior art of carbon dioxide reduction, most of the carbon dioxide reduction adopts an indiscriminate gas diffusion layer structure for water/gas management, and no report on a gradient diffusion electrode is found yet. Thus, we constructed a gradient microporous layer gas diffusion layer. And forming a double-layer or three-layer microporous sub-layer with the concentration of the hydrophobic agent sequentially reduced from one side adjacent to the basal layer to one side adjacent to the catalytic layer. The design ensures that the catalyst layer has certain moisture retention capacity and can timely discharge redundant electrolyte so as to ensure that enough transportation channels are not blocked by the electrolyte and effectively transport carbon dioxide. The invention provides a gradient microporous layer gas diffusion layer with a novel structure, which can improve the running current density and the water management capability and has important significance.
Disclosure of Invention
The invention relates to a gradient microporous layer gas diffusion layer for carbon dioxide reduction and a preparation method thereof. The gradient microporous layer with the concentration of the hydrophobe sequentially reduced from one side adjacent to the basal layer to one side adjacent to the catalytic layer is prepared, has good water/gas management capability, and can obviously improve the performance of the carbon dioxide reduction gas diffusion electrode.
The invention aims at realizing the following technical scheme:
the invention provides a gradient microporous layer gas diffusion layer for carbon dioxide reduction, which consists of a basal layer and a gradient microporous layer; the gradient microporous layer comprises a plurality of microporous sublayers having different hydrophilicity and hydrophobicity along the thickness direction thereof; the hydrophobicity of each microporous sublayer tends to decrease in a gradient in a direction away from the substrate layer.
As one embodiment of the invention, the gradient microporous layer gas diffusion layer is provided with a microporous layer with gradient change of hydrophobicity, the hydrophobicity gradually decreases along the direction of the substrate to the catalyst layer, and capillary pressure difference formed by the gradient change of hydrophobicity in the direction drives liquid water to be discharged from the catalyst layer to the substrate layer, so that the catalytic sites are prevented from being covered by electrolyte; meanwhile, small holes smaller than 0.1 mu m are formed in the gas diffusion electrode, and the pore volume of the hydrophobic holes accounts for more than 95% of the total pore volume. Since the critical pressure of liquid water entering the larger pores is lower than the critical pressure entering the smaller pores, liquid water will preferentially penetrate the larger hydrophobic pores. The hydrophobic pores (less than 0.1 μm) formed are advantageous in maintaining free transport of carbon dioxide.
Each micropore sublayer consists of a conductive material and a hydrophobic agent.
As one embodiment of the present invention, the substrate layer is one of carbon cloth, carbon paper, foamed nickel, foamed titanium, and titanium fiber sintered felt.
As one embodiment of the invention, the hydrophobic agent is micro powder, solution or emulsion formed by mixing one or more of polytetrafluoroethylene, vinylidene fluoride, polyvinylidene fluoride, fluorinated ethylene propylene and ethylene/tetrafluoroethylene copolymer in any proportion.
As one embodiment of the invention, the conductive material is a mixture formed by mixing one or more of conductive carbon black, carbon powder, carbon fiber, carbon nano tube, carbon nano fiber, graphene, nano graphite powder and the like in any proportion.
The number of the microporous sublayers is double or triple.
The invention also provides a preparation method of the gas diffusion layer, which comprises the following steps:
s1, immersing a substrate layer into a hydrophobic agent emulsion and drying to constant weight to obtain the substrate layer;
s2, mixing conductive materials with different contents, hydrophobic agent emulsion and dispersing agent, and fully stirring to obtain emulsion I, emulsion II and emulsion III;
s3, sequentially depositing at least two emulsions of the emulsion I, the emulsion II and the emulsion III in the S2 to one side of the substrate layer obtained in the S1 according to the sequence of the emulsion I, the emulsion II and the emulsion III; drying at 50-80 ℃ to constant weight after each slurry is deposited, so as to obtain a precursor of the gas diffusion layer of the double-layer or three-layer gradient microporous layer;
and S4, performing heat treatment on the precursor of the gradient microporous layer gas diffusion layer in the step S3 to obtain the gradient microporous layer gas diffusion layer.
In the step S2, the mass ratio of the conductive material to the hydrophobic agent in the emulsion I is 1:0.66-1:1.5; the mass ratio of the conductive material to the hydrophobic agent in the emulsion II is 1:0.12-1:0.66; the mass ratio of the conductive material to the hydrophobic agent in the emulsion III is 1:0.05-1:0.12. Too high a proportion of the hydrophobizing agent in the emulsion I can reduce the conductivity of the electrode, and too low a proportion can enable the electrode to be easily submerged by liquid water to prevent gas transmission.
As one embodiment of the invention, when preparing the gas diffusion layer of the double-layer gradient microporous layer, the carrying capacity of the conductive agent deposited on the basal layer is the same for any two of emulsion I, emulsion II and emulsion III; when the three gradient microporous layer gas diffusion layers are prepared, the carrying capacity of the conductive agents deposited on the substrate layers by emulsion I, emulsion II and emulsion III is the same.
As one embodiment of the invention, the total loading of the conductive material in the gradient microporous layer of the gas diffusion layer is 0.03-5 mg cm -2 。
As one embodiment of the present invention, the dispersant is a mixture of one or more of absolute ethyl alcohol, isopropyl alcohol and ultrapure water mixed in an arbitrary ratio.
As an embodiment of the present invention, the deposition method is selected from any one of screen printing, air spraying, electrostatic spraying, ultrasonic spraying, dip coating, knife coating, roll pressing.
As one embodiment of the invention, the heat treatment is to heat up from room temperature to 245 ℃ for 30-60 min; preserving the temperature at 245 ℃ for 30-60 min; heating from 245 ℃ to 345 ℃ for 30-60 min; preserving heat for 30-60 min at 345 ℃; cooling to room temperature for 60-120 min.
Compared with the prior art, the invention has the following beneficial effects:
(1) The invention provides a gradient microporous layer gas diffusion layer for carbon dioxide reduction and a preparation method thereof. The capillary pressure difference formed by the gradient change of hydrophobicity drives liquid water to be discharged from the catalytic layer to the basal layer, so that catalytic sites are prevented from being covered by electrolyte, and the water management capability of carbon dioxide reduction is improved.
(2) Compared with the prior art, the gradient microporous layer gas diffusion layer for carbon dioxide reduction and the preparation method thereof can form more small holes, and particularly further comprise a certain number of hydrophobic micropores with the pore diameter smaller than 0.1 mu m, so that free gas transportation under high current density is ensured, and the gas transportation capacity of carbon dioxide reduction is improved.
(3) The gradient microporous layer gas diffusion layer for carbon dioxide reduction provided by the invention has the advantages of simple preparation method, high repeatability and low raw material cost, and is beneficial to large-scale production.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
FIG. 1 is a schematic diagram of the structure of a three-layer gradient microporous layer gas diffusion layer for carbon dioxide reduction in example 2;
FIG. 2, comparative example 1, example 1 and example 2 shows pore size distribution diagrams of gradient microporous layer gas diffusion layers for carbon dioxide reduction;
FIG. 3, carbon monoxide partial current density for converting carbon dioxide to carbon monoxide at different voltages using the gradient microporous layer gas diffusion layers obtained in comparative example 1 and example 1 in a carbon dioxide reduction cell.
FIG. 4, carbon monoxide partial current density for converting carbon dioxide to carbon monoxide at different voltages using the gradient microporous layer gas diffusion layers obtained in comparative example 1 and example 2 in a carbon dioxide reduction cell.
FIG. 5, carbon monoxide partial current density for converting carbon dioxide to carbon monoxide at different voltages, using the gradient microporous layer gas diffusion layers obtained in comparative example 2 and example 1 in a carbon dioxide reduction cell.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.
The following examples provide a gradient microporous layer gas diffusion layer for carbon dioxide reduction comprising a hydrophobe treated substrate layer and a gradient microporous layer comprising a plurality of microporous sublayers of different hydrophilicity and hydrophobicity; the hydrophobicity of each microporous sublayer tends to decrease in a gradient in a direction away from the substrate layer.
The microporous sublayer comprises a conductive material and a hydrophobic agent.
The substrate layer is one of carbon cloth, carbon paper, foam nickel, foam titanium and titanium fiber sintered felt.
The hydrophobic agent is micropowder, solution or emulsion formed by mixing one or more of polytetrafluoroethylene, vinylidene fluoride, polyvinylidene fluoride, fluorinated ethylene propylene, ethylene/tetrafluoroethylene copolymer and the like in any proportion.
The conductive material is a mixture formed by mixing one or more of conductive carbon black, carbon powder, carbon fiber, carbon nano tube, carbon nano fiber, graphene, nano graphite powder and the like according to any proportion.
The preparation method of the gradient microporous layer gas diffusion layer comprises the following steps:
1) Immersing the substrate layer into the hydrophobizing agent emulsion and drying to constant weight to obtain the substrate layer;
2) Mixing conductive materials with different contents, hydrophobic agent emulsion and dispersing agent, and fully stirring to obtain microporous layer mixed emulsion I, emulsion II and emulsion III; the mass ratio of the conductive material to the hydrophobic agent in the emulsion I is 1:0.66-1:1.5; the mass ratio of the conductive material to the hydrophobic agent in the emulsion II is 1:0.12-1:0.66; the mass ratio of the conductive material to the hydrophobic agent in the emulsion III is 1:0.05-1:0.12;
3) Sequentially depositing at least two emulsions of the emulsion I, the emulsion II and the emulsion III in the 2) to one side of the substrate layer obtained in the 1) according to the sequence of the emulsion I, the emulsion II and the emulsion III; drying at 50-80 ℃ to constant weight after each slurry is deposited, so as to obtain a precursor of the gas diffusion layer of the double-layer or three-layer gradient microporous layer; the deposition method is selected from any one of screen printing method, air spraying, electrostatic spraying, ultrasonic spraying, dip coating, knife coating method and rolling method; when preparing the double-layer gradient microporous layer gas diffusion layer, the carrying capacity of the conductive agent deposited on the basal layer is the same for any two of emulsion I, emulsion II and emulsion III; when preparing three gradient microporous layer gas diffusion layers, the carrying capacity of the conductive agents deposited on the basal layer by emulsion I, emulsion II and emulsion III is the same;
4) Performing heat treatment on the precursor of the gradient diffusion electrode layer in the step 3) to obtain a gradient microporous layer gas diffusion layer; the high-temperature sintering treatment comprises the following steps: heating from room temperature to 245 ℃ for 30-60 min; preserving the temperature at 245 ℃ for 30-60 min; heating from 245 ℃ to 345 ℃ for 30-60 min; preserving heat for 30-60 min at 345 ℃; cooling to room temperature for 60-120 min.
The loading capacity of the conductive material in the microporous layer of the gas diffusion layer is 0.03-5 mg cm -2 。
The carbon dioxide reduced gas diffusion layer can be prepared under the conditions of the parameters.
Example 1
The embodiment relates to a gas diffusion layer for carbon dioxide electrolytic reduction and a preparation method thereof, and the steps are as follows:
1) The W0S1009 carbon cloth produced by taiwan carbon energy CeTech company was soaked in 5wt% polytetrafluoroethylene emulsion for 30 seconds, taken out, and dried in a vacuum to a constant weight in a drying oven at 60 ℃. Repeating the steps until the weight difference between the carbon cloth before impregnation and the carbon cloth after drying is 30 weight percent of the total weight of the carbon cloth after impregnation and drying.
2) Mixing 0.25g of Vulcan XC-72 conductive carbon black, 3.33g of 5wt% polytetrafluoroethylene emulsion and 2.5g of ethanol, and fully stirring to uniformly mix the components to obtain emulsion I; 0.25g of Vulcan XC-72 conductive carbon black, 0.56g of 5wt% polytetrafluoroethylene emulsion and 2.5g of absolute ethyl alcohol are mixed and fully stirred to be uniformly mixed, so as to obtain emulsion III.
3) Screen printing the emulsion I obtained in the step 2) on the substrate layer obtained in the step 1) to form a microporous layer 1, drying at 60 ℃ for 30min, screen printing the emulsion III obtained in the step 2) on the microporous layer 1 to form a microporous layer 2, drying at 60 ℃ for 30min, heating from 60 ℃ to 245 ℃ for 30min, heating to 345 ℃ for 30min, heating to 30min, and cooling to room temperature.
4) The total loading of the conductive carbon black of the microporous layer in the gradient microporous layer gas diffusion layer obtained in the step 3) is 0.7mg cm -2 The total thickness of the gas diffusion layer was 0.33mm.
Example 2
A gradient microporous layer gas diffusion layer for carbon dioxide electrolytic reduction and a preparation method thereof are provided, and the steps are as follows:
1) The W0S1009 carbon cloth produced by taiwan carbon energy CeTech company was soaked in 5wt% polytetrafluoroethylene emulsion for 30 seconds, taken out, and dried in a vacuum to a constant weight in a drying oven at 60 ℃. Repeating the steps until the weight difference between the carbon cloth before impregnation and the carbon cloth after drying is 30 weight percent of the total weight of the carbon cloth after impregnation and drying.
2) Mixing 0.17g of Vulcan XC-72 conductive carbon black, 2.22g of 5wt% polytetrafluoroethylene emulsion and 1.67g of absolute ethyl alcohol, and fully stirring to uniformly mix the components to obtain emulsion I; mixing 0.17g of Vulcan XC-72 conductive carbon black, 1.14g of 5wt% polytetrafluoroethylene emulsion and 1.67g of absolute ethyl alcohol, and fully stirring to uniformly mix the components to obtain emulsion II; 0.17g of Vulcan XC-72 conductive carbon black, 0.37g of 5wt% polytetrafluoroethylene emulsion and 1.67g of absolute ethyl alcohol are mixed and fully stirred to be uniformly mixed, so as to obtain emulsion III.
3) As shown in fig. 1, the emulsion i obtained in step 2) is screen-printed on the substrate layer obtained in step 1) to form a microporous layer 1, dried at 60 ℃ for 30min, the emulsion ii obtained in step 2) is screen-printed on the microporous layer 1 to form a microporous layer 2, dried at 60 ℃ for 30min, the emulsion iii obtained in step 2) is screen-printed on the microporous layer 2 to form a microporous layer 3, dried at 60 ℃ for 30min, heated from 60 ℃ to 245 ℃ for 30min, heated to 345 ℃ for 30min, and heat-preserved for 30min, and finally cooled to room temperature.
4) The total loading of the conductive carbon black of the microporous layer in the gradient microporous layer gas diffusion layer obtained in the step 3) is 0.7mg cm -2 The total thickness of the gas diffusion layer was 0.33mm.
Comparative example 1
A conventional commercial carbon cloth W1S1010 with a microporous layer manufactured by taiwan carbon energy CeTech company was used as comparative example 1.
Comparative example 2
The carbon dioxide electrolytic reduction gradient microporous layer gas diffusion layer with the mass ratio of the conductive material to the hydrophobizing agent exceeding the technical scheme is taken as comparative example 2. The method comprises the following steps:
1) The W0S1009 carbon cloth produced by taiwan carbon energy CeTech company was soaked in 5wt% polytetrafluoroethylene emulsion for 30 seconds, taken out, and dried in a vacuum to a constant weight in a drying oven at 60 ℃. Repeating the steps until the weight difference between the carbon cloth before impregnation and the carbon cloth after drying is 30 weight percent of the total weight of the carbon cloth after impregnation and drying.
2) Mixing 0.25g of Vulcan XC-72 conductive carbon black, 9.3g of 5wt% polytetrafluoroethylene emulsion and 2.5g of ethanol, and fully stirring to uniformly mix the components to obtain emulsion I (the mass ratio of conductive material to hydrophobic agent in the emulsion I is 1:1.86); 0.25g of Vulcan XC-72 conductive carbon black, 0.56g of 5wt% polytetrafluoroethylene emulsion and 2.5g of absolute ethyl alcohol are mixed and fully stirred to be uniformly mixed, so as to obtain emulsion III.
3) Screen printing the emulsion I obtained in the step 2) on the substrate layer obtained in the step 1) to form a microporous layer 1, drying at 60 ℃ for 30min, screen printing the emulsion III obtained in the step 2) on the microporous layer 1 to form a microporous layer 2, drying at 60 ℃ for 30min, heating from 60 ℃ to 245 ℃ for 30min, heating to 345 ℃ for 30min, heating to 30min, and cooling to room temperature.
4) The total loading of the conductive carbon black of the microporous layer in the gradient microporous layer gas diffusion layer shown in the figure 1 and obtained in the step 3) is 0.7mg cm -2 The total thickness of the gas diffusion layer was 0.33mm.
Effect testing
1. Hydrophobic pore volume ratio and pore size distribution
The hydrophobic pore volume ratios and pore size distributions of examples 1 and 2 and comparative example 1 are shown in table 2, fig. 2, illustrating: the gradient gas diffusion electrode can greatly improve the volume ratio of the hydrophobic holes, and the number of the holes smaller than 0.1 mu m is obviously increased.
2. Electrochemical performance test
In a zero-gap electrolytic cell, 80sccm of dry carbon dioxide was introduced into a cathode, 60℃ultrapure water was introduced into an anode, X37-50 RT produced by Sustainion was used as a separator, cobalt phthalocyanine slurry was sprayed on the gas diffusion layers of comparative example 1 and the gas diffusion layers prepared in comparative example 2 and examples 1 and 2 to form a cathode, and iridium oxide slurry was sprayed on a nickel screen to form an anode. The electrochemical performance curves shown in fig. 3, 4, and 5 were obtained. The electrochemical performance curve shows that: the gradient microporous layer gas diffusion layers prepared in examples 1 and 2 have better gas transport and water management capabilities, and are capable of significantly reducing the operating current density and conversion rate of electrochemical reduction of carbon dioxide.
The previous description of the embodiments is provided to facilitate a person of ordinary skill in the art in order to make and use the present invention. It will be apparent to those skilled in the art that various modifications can be readily made to these embodiments and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments, and those skilled in the art, based on the present disclosure, should make improvements and modifications without departing from the scope of the present invention.
Claims (10)
1. A gradient microporous layer gas diffusion layer for carbon dioxide reduction, wherein the gas diffusion layer comprises a substrate layer and a gradient microporous layer; the gradient microporous layer comprises a plurality of microporous sublayers having different hydrophilicity and hydrophobicity along the thickness direction thereof; the hydrophobicity of each microporous sublayer tends to decrease in a gradient in a direction away from the substrate layer.
2. The gradient microporous layer gas diffusion layer for carbon dioxide reduction of claim 1, wherein the microporous sublayer comprises a conductive material and a hydrophobic agent composition.
3. The gradient microporous layer gas diffusion layer for carbon dioxide reduction of claim 1, wherein the base layer is one of carbon cloth, carbon paper, foamed nickel, foamed titanium, titanium fiber sintered felt.
4. The microporous sublayer of a gas diffusion layer according to claim 2, wherein the conductive material is a mixture of one or more of conductive carbon black, carbon powder, carbon fiber, carbon nanotube, carbon nanofiber, graphene, and nano-graphite powder mixed in any ratio.
5. The microporous sublayer of a gas diffusion layer according to claim 2, wherein the hydrophobic agent is a micropowder, solution or emulsion of one or more of polytetrafluoroethylene, vinylidene fluoride, polyvinylidene fluoride, fluorinated ethylene propylene, ethylene/tetrafluoroethylene copolymer mixed in any ratio.
6. The gradient microporous layer of a gas diffusion layer according to claim 1, wherein the number of microporous sublayers is two or three.
7. A method of preparing a gradient microporous layer gas diffusion layer for carbon dioxide reduction according to claim 1, comprising the steps of:
s1, immersing a substrate layer into a hydrophobic agent emulsion and drying to constant weight to obtain the substrate layer;
s2, mixing conductive materials with different contents, hydrophobic agent emulsion and dispersing agent, and fully stirring to obtain emulsion I, emulsion II and emulsion III;
s3, sequentially depositing at least two emulsions of the emulsion I, the emulsion II and the emulsion III in the S2 to one side of the substrate layer obtained in the S1 according to the sequence of the emulsion I, the emulsion II and the emulsion III; drying at 50-80 ℃ to constant weight after each slurry is deposited, so as to obtain a precursor of the gas diffusion layer of the double-layer or three-layer gradient microporous layer;
and S4, performing heat treatment on the precursor of the gradient microporous layer gas diffusion layer in the step S3 to obtain the gradient microporous layer gas diffusion layer.
8. The preparation method according to claim 7, wherein the mass ratio of the conductive material to the hydrophobic agent in the emulsion I is 1:0.66-1:1.5; the mass ratio of the conductive material to the hydrophobic agent in the emulsion II is 1:0.12-1:0.66; the mass ratio of the conductive material to the hydrophobic agent in the emulsion III is 1:0.05-1:0.12.
9. The method according to claim 7, wherein the carrying amount of the conductive agent deposited on the base layer is the same for any two of emulsion i, emulsion ii, and emulsion iii when the gas diffusion layer of the double-layered gradient microporous layer is prepared; when the three gradient microporous layer gas diffusion layers are prepared, the carrying capacity of the conductive agents deposited on the substrate layers by emulsion I, emulsion II and emulsion III is the same.
10. The method of claim 7, wherein the heat treatment is: heating from room temperature to 245 ℃ for 30-60 min; preserving the temperature at 245 ℃ for 30-60 min; heating from 245 ℃ to 345 ℃ for 30-60 min; preserving heat for 30-60 min at 345 ℃; cooling to room temperature for 60-120 min.
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