CN113675418A - Method for preparing graphene conductive polymer coating on surface of bipolar plate by adopting electrodeposition method - Google Patents
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 89
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- ZAJAQTYSTDTMCU-UHFFFAOYSA-N 3-aminobenzenesulfonic acid Chemical compound NC1=CC=CC(S(O)(=O)=O)=C1 ZAJAQTYSTDTMCU-UHFFFAOYSA-N 0.000 description 1
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- 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
- H01M8/0204—Non-porous and characterised by the material
- H01M8/0223—Composites
- H01M8/0228—Composites in the form of layered or coated products
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
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- C25D9/00—Electrolytic coating other than with metals
- C25D9/02—Electrolytic coating other than with metals with organic materials
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- C25D9/00—Electrolytic coating other than with metals
- C25D9/04—Electrolytic coating other than with metals with inorganic materials
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- 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
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- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
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Abstract
The invention provides a method for preparing a graphene conductive polymer coating on the surface of a bipolar plate by adopting an electrodeposition method, which comprises the following steps: step one, chemically modifying graphene oxide, grafting an anionic functional group, and preparing a modified graphene oxide aqueous dispersion; step two, mixing the modified graphene aqueous dispersion and the conductive polymer monomer aqueous dispersion according to a ratio to obtain an electrolyte; step three, pretreating the metal-based bipolar plate, soaking the metal-based bipolar plate in sulfuric acid solution, and removing a surface passivation film of the metal-based bipolar plate; step four, taking the metal-based bipolar plate as an anode and a platinum sheet as a cathode, and performing electrodeposition on the metal-based bipolar plate by using a direct current power supply; and fifthly, drying the deposited wet film to obtain the graphene conductive polymer composite coating. According to the invention, the doping effect of the functional group on the surface of the anionic modified graphene on the conductive polymer is utilized, so that pi electron delocalization of the conductive polymer is promoted, and the conductivity of the composite coating is improved.
Description
Technical Field
The invention relates to the technical field of graphene coatings and the field of metal-based bipolar plate materials for proton exchange membrane fuel cells, in particular to a method for preparing a graphene conductive polymer coating on the surface of a bipolar plate by adopting an electrodeposition method.
Background
Proton Exchange Membrane Fuel Cells (PEMFCs) are gaining attention for their great potential in the zero-pollution transformation of energy problems. Bipolar Plates (BPs) account for 60-80% of the total mass of the fuel cell, 70-80% of the total volume, and 30-45% of the total cost, and are an important material in PEMFCs, whose main functions in fuel cells include: 1. the reaction gas is uniformly distributed in the active region through the gas flow channel on the polar plate; 2. providing mechanical support for the membrane electrode assembly; 3. passing current between the battery components; 4. removing water generated at the cathode; 5. preventing leakage of reaction gas; 6. heat generated by gas reaction is eliminated; therefore, the bipolar plate needs to withstand high humidity, high potential, high temperature (80 ℃ C.) and other working environments. The performance indexes of the bipolar plate in 2020 of the U.S. department of energy are as follows: 1. corrosion current density (Icor)<1μA/cm2(ii) a 2. Contact Resistance (ICR)<10mΩ/cm2(ii) a 3. Electrical conductivity of>100S/cm; 4. thermal conductivity>10W/m.K; 5. gas permeability<2×10–6cm3/s·cm2(ii) a 6. Bending strength>50 MPa; 7. shore hardness>40。
Metal-based bipolar plates have become a major development trend for bipolar plate materials due to their excellent electrical and thermal conductivity, mechanical properties, gas tightness, workability, and low cost. However, the metal bipolar plate is very easy to corrode under the working environment of high temperature, high humidity and high potential in the fuel cell, a passivation film is formed, the contact resistance between the bipolar plate and the membrane electrode is increased, and the working efficiency of the fuel cell is reduced. Therefore, the preparation of the conductive corrosion-resistant coating on the surface of the metal-based bipolar plate is the key to realizing the application of the conductive corrosion-resistant coating.
Coating materials commonly used on the surface of metal-matrix bipolar plates include three major classes: carbon materials, noble metals and cermets. These coatings are usually deposited on metal substrates by chemical vapor deposition or physical vapor deposition, which is expensive, energy-consuming and inefficient. In addition, the standard electrode potentials of carbon materials and noble metals are generally higher than those of metal substrates. Once the electrolyte penetrates the interface between the coating and the substrate, the coating becomes cathodic and the metal substrate becomes anodic, possibly resulting in accelerated corrosion of the substrate metal. The electrodeposition method provided by the invention is more efficient and more suitable for industrial production, and the composite coating of the modified graphene and the conductive polymer has the conductive performance, the barrier performance and the corrosion inhibition performance, and can meet the requirements of the PEMFC bipolar plate.
The conductive polymer has been applied to the surface of a metal substrate bipolar plate because of simple preparation method, easy film formation, small pollution, good corrosion resistance and high conductivity. The main corrosion-resistant protection mechanism comprises: 1. barrier action 2, anode protection action 3, corrosion inhibition action. However, micro-defects in the coating formed during the synthesis of a single conductive polymer coating still cause electrolyte permeation and are difficult to withstand the harsh operating environment of PEMFCs. Therefore, it is important to improve the structural defects of the conductive polymer coating and to improve the compactness thereof.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention aims to provide a method for preparing a graphene conductive polymer coating on the surface of a bipolar plate by using an electrodeposition method, which is used for preparing a modified graphene conductive polymer composite coating with low contact resistance and high corrosion resistance, and the coating is used on the surface of a metal-based bipolar electrode in a proton exchange membrane fuel cell.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a method for preparing a graphene conductive polymer coating on the surface of a bipolar plate by adopting an electrodeposition method, which comprises the following steps:
the method comprises the following steps:
step one, chemically modifying graphene oxide, grafting an anionic functional group, and preparing a modified graphene oxide aqueous dispersion;
step two, mixing the modified graphene aqueous dispersion and the conductive polymer monomer aqueous dispersion according to a ratio to obtain an electrolyte;
step three, pretreating the metal-based bipolar plate, soaking the metal-based bipolar plate in sulfuric acid solution, and removing a surface passivation film of the metal-based bipolar plate;
step four, taking the metal-based bipolar plate as an anode and a platinum sheet as a cathode, and performing electrodeposition on the metal-based bipolar plate by using a constant-voltage direct-current power supply;
and fifthly, drying the deposited wet film to obtain the graphene conductive polymer composite coating.
In a preferred embodiment, in the first step, the anionic functional group includes a sulfonic acid group, a benzenesulfonic acid group, a sulfuric acid group, and a phosphoric acid group.
As a preferred technical solution, in the second step, the conductive polymer monomer includes polypyrrole, polyaniline, and polythiophene.
Preferably, in the second step, the electrolyte further includes an initiator, a dispersion aid, and a surfactant.
Preferably, in the second step, the concentration of the modified graphene aqueous dispersion is 1mg/ml to 4mg/ml, and the concentration of the conductive polymer monomer is 0.01mol/L to 0.15 mol/L.
In the third step, the metal-based bipolar plate is a stainless steel bipolar plate or a titanium alloy bipolar plate, the surface of the metal-based bipolar plate is polished by using sand paper to remove a surface passivation film, oil stains and fingerprints on the surface of the metal-based bipolar plate are removed by using acetone, and excess solvent is removed by using ethanol.
As a preferable technical scheme, in the fourth step, the deposition voltage is 1-5V, and the deposition time is 10-20 min.
In the fifth step, the wet film is dried by heating at a temperature ranging from 40 ℃ to 80 ℃.
As a preferred technical scheme, the deposited wet film is placed in a vacuum oven and dried for 3 hours at the constant temperature of 40 ℃, and after the surface film layer of the sample is dried, the drying is carried out for 10 hours at the temperature of 80 ℃.
As a preferable technical scheme, the anionic functional group of the modified graphene oxide is a sulfonic acid group, and the preparation method of the sulfonated graphene aqueous dispersion specifically comprises the following steps:
step a, mixing a graphene oxide aqueous dispersion (1mg/ml) with a sodium borohydride solution (1.05mol/L), and stirring in a water bath at 80 ℃ to obtain a pre-reduced graphene oxide dispersion;
step b, mixing aminobenzenesulfonic acid and sodium nitrite in an acid environment under an ice bath condition to obtain a diazonium salt solution;
step c, adding a freshly prepared diazonium salt solution into the pre-reduced graphene oxide dispersion liquid, and stirring under an ice bath condition for 3-5 hours;
and d, performing centrifugal cleaning on the mixed solution obtained in the step c for multiple times to remove redundant reactants to obtain the sulfonated graphene aqueous dispersion, wherein the preparation concentration of the sulfonated graphene aqueous dispersion is 1-4 mg/ml.
As a preferred technical scheme, the anionic functional group of the modified graphene oxide is a phosphoric acid group, and the phosphorylated graphene aqueous dispersion comprises the following steps:
step a, slowly dropping sodium hydroxide into hydroxyethylidene diphosphonic acid (60%) until the pH value is equal to 9-10;
step b, mixing the graphene oxide aqueous dispersion (1mg/ml) with the solution obtained in the step a, and stirring for 7 hours in a water bath at the temperature of 80 ℃;
and c, performing centrifugal cleaning on the mixed solution obtained in the step b for multiple times to remove redundant reactants to obtain the phosphorylated graphene aqueous dispersion.
In the invention, the modified graphene plays three roles: a. physical barrier effect; b. the composite coating is used as a template for conductive polymer deposition, so that the appearance of the composite coating is smoother and more compact; c. the functional group on the surface of the modified graphene plays a doping role on the conductive polymer and promotes pi electron delocalization of the conductive polymer.
The modified graphene surface anionic functional group is hydrolyzed to generate negative charges and the conductive polymer reaching the oxidation potential is subjected to self-assembly; moving towards the substrate under the action of electric field force, and aligning in parallel with the surface of the metal substrate; in addition, the modified graphene has a two-dimensional shape and an oversized specific surface area, and can be used as a template for the growth of a conductive polymer, and the functional group on the surface of the modified graphene can be used for carrying out anion doping on the conductive polymer to promote pi electron delocalization of the conductive polymer. The composite coating comprises a high-orientation modified graphene lamellar layer, a flat and compact composite coating and a high-doping-degree conductive polymer, and can obtain the high-conductivity and high-corrosion-resistance modified graphene conductive polymer composite coating under the combined action of the high-orientation modified graphene lamellar layer, the flat and compact composite coating and the high-doping-degree conductive polymer. After the metal base bipolar plate is deposited on the surface of the metal base bipolar plate, the corrosion resistance and the interface contact resistance both meet the performance requirements of the bipolar plate of the proton exchange membrane fuel cell
As described above, the present invention has the following advantageous effects:
(1) under the action of an electric field force, the modified graphene two-dimensional sheet layers are arranged on the surface of the metal-based bipolar plate in parallel, so that the physical barrier property of the composite coating is improved.
(2) In the electrodeposition process of the conductive polymer material, the modified graphene two-dimensional sheet layer is used as a template, so that the appearance of the composite coating is smoother and more compact.
(3) According to the invention, the doping effect of the functional group on the surface of the anionic modified graphene on the conductive polymer is utilized, so that pi electron delocalization of the conductive polymer is promoted, and the conductivity of the composite coating is improved.
(4) Compared with physical vapor deposition and chemical vapor deposition, the electrodeposition method provided by the invention has the advantages of low energy consumption and remarkable production efficiency, and is more suitable for the requirement of industrialization.
(5) The solvent used in the electrolyte is mainly water, and the production process is green and environment-friendly.
Drawings
Fig. 1 shows the morphology of the modified graphene polypyrrole composite coating under a scanning electron microscope.
Fig. 2 shows the results of measuring the interface contact resistance of the modified graphene polypyrrole composite coating, the sulfuric acid doped polypyrrole coating, and the graphene oxide polypyrrole composite coating.
Fig. 3 shows the potentiodynamic polarization test results of the modified graphene polypyrrole composite coating, the sulfuric acid doped polypyrrole coating and the oxidized graphene polypyrrole composite coating.
Detailed Description
The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure.
Example 1
The embodiment provides a method for preparing a graphene conductive polymer coating on the surface of a bipolar plate by adopting an electrodeposition method, which comprises the following steps:
step one, preparing modified graphene;
step 1.1, dispersing 1g of graphene oxide in 1L of water, stirring to uniformly mix the graphene oxide and the water, and then stirring and dispersing the graphene oxide dispersion liquid at the rotating speed of 600rpm to obtain 1mg/mL of graphene oxide dispersion liquid well dispersed in an aqueous solution;
step 1.2, adjusting the PH of the dispersion to be alkaline (PH 9-10) by using sodium hydroxide, preparing a sodium borohydride aqueous solution (1.05mol/L), mixing the prepared sodium borohydride aqueous solution and the dispersion, stirring at 80 ℃, pre-reducing the graphene oxide dispersion, and centrifuging the pre-reduced graphene oxide.
And step 1.3, carrying out sulfonation modification on the pre-reduced graphene oxide.
The step 1.3 comprises the following specific steps:
step a, adding 0.65g of sulfanilic acid and 0.24g of sodium nitrite into hydrochloric acid aqueous solution with the pH value of 3 under the condition of ice bath at the temperature of 0 ℃, mixing, and reacting for 1 hour to obtain diazonium salt solution;
step b, adding the diazonium salt solution obtained in the step a into the pre-reduced graphene oxide aqueous dispersion, and continuously stirring and reacting for 4 hours at the temperature of 0 ℃ under the ice bath condition to obtain sulfonated graphene dispersion;
and c, centrifuging the sulfonated graphene dispersion liquid obtained in the step b at the rotating speed of 20000rpm, washing the obtained solid with deionized water to remove redundant reactants to obtain sulfonated graphene, and dispersing the obtained sulfonated graphene in water.
Step two, preparing a graphene conductive polymer coating;
step 2.1, the metal-based bipolar plate material is SS304, the stainless steel surface is polished by sand paper (200 meshes and 1000 meshes), and surface dullness is removedFilm formation; removing oil stain and fingerprint on the surface by using acetone, removing excessive solvent by using ethanol, and putting the polished sample into a container with the volume of 1mol/L H2SO4Further removing the surface passivation film and increasing the binding sites of the surface;
step 2.2, preparing a 3mg/ml sulfonated graphene aqueous solution, adding pyrrole (0.05mol/L) to obtain a mixed electrolyte, stirring the mixed solution at a rotating speed of 600rmp for 10min, performing ultrasonic treatment at 150Hz for 10min (the ultrasonic temperature is 24 ℃), and obtaining a uniformly mixed electrolyte;
step 2.3, installing the polished and cleaned SS304 on an electrode clamp to be used as a working electrode, and using a platinum sheet as a counter electrode; performing electrodeposition on the sample by using a constant-voltage direct-current power supply, wherein the deposition voltage is 1.2V, and the deposition time is 10 min;
2.4, placing the deposited wet film in a vacuum oven, drying for 3 hours at the constant temperature of 40 ℃, and after drying the surface film layer of the sample, drying for 10 hours at 80 ℃;
and 2.5, characterizing the metal-based bipolar plate containing the modified graphene, wherein an electron microscope photo shows that the thickness of the prepared graphene coating is about 9 μm, as shown in figure 1. The contact resistance of the bipolar plate is 5m omega cm2(the contact resistance test condition is 1.5MPa), and the electrochemical test result shows that the corrosion current is 0.5 mu A/cm2(potentiodynamic polarization test conditions were H2SO4 solution at pH 3, 80 ℃). The corrosion resistance and the contact resistance of the graphene conductive polymer composite coating prepared by the method are shown to meet the requirements of a bipolar plate of a proton exchange membrane fuel cell.
Example 2
The embodiment provides a method for preparing a graphene conductive polymer coating on the surface of a bipolar plate by adopting an electrodeposition method, which comprises the following steps:
step 1, grinding the surface of stainless steel by using sand paper (200 meshes and 1000 meshes) to remove a surface passive film, wherein the metal-based bipolar plate material is SS 304; removing oil stain and fingerprint on the surface by using acetone, removing excessive solvent by using ethanol, and putting the polished sample into a container with the volume of 1mol/L H2SO4Further removing the surface passivation film and increasing the binding sites of the surface;
step 4, placing the deposited wet film in a vacuum oven, drying for 3 hours at the constant temperature of 40 ℃, and after drying the surface film layer of the sample, drying for 10 hours at the temperature of 80 ℃;
and 5, characterizing the metal-based bipolar plate containing the modified graphene, wherein the contact resistance of the bipolar plate is 16m omega cm2(the test condition is 1.4 MPa), the electrochemical test result shows that the corrosion current is 18.729 mu A/cm2(potentiodynamic polarization test conditions of H with PH 3 ═ H2SO4Solution, 80 ℃). The test result shows that the contact resistance and the corrosion resistance of the metal-based bipolar plate can be influenced by changing the proportion of the modified graphene in the electrolyte, and the contact resistance of the composite coating can be effectively reduced by improving the concentration of the sulfonic acid group in the electrolyte.
Comparative example 1
The comparative example provides a method for preparing a conductive polymer coating doped with sulfuric acid, comprising the following steps:
step 1, grinding the surface of stainless steel by using sand paper (200 meshes and 1000 meshes) to remove a surface passive film, wherein the metal-based bipolar plate material is SS 304; removing oil stain and fingerprint on the surface by using acetone, removing excessive solvent by using ethanol, and putting the polished sample into a container with the volume of 1mol/L H2SO4Further removing the surface passivation film and increasing the binding sites of the surface;
step 4, placing the deposited wet film in a vacuum oven, drying for 3 hours at the constant temperature of 40 ℃, and after drying the surface film layer of the sample, drying for 10 hours at the temperature of 80 ℃;
and 5, characterizing the metal-based bipolar plate containing the graphene, wherein the contact resistance of the bipolar plate is 15.61m omega cm as shown in figure 22(test condition 1.4 MPa), the electrochemical test result shows that the corrosion current is 26.31 mu A/cm as shown in figure 32(potentiodynamic polarization test conditions were H2SO4 solution at pH 3, 80 ℃).
The test result shows that the corrosion resistance of the composite coating is effectively enhanced by the large lamellar structure of the graphene (compared with the corrosion current density of the modified graphene conductive polymer composite coating reduced by nearly two orders of magnitude compared with that of a sulfuric acid sample in comparative example 1 and comparative example 1). In addition, the sulfonic acid group is grafted on the surface of the modified graphene, so that the conductive polymer can be doped, and the contact resistance of the composite coating is reduced (as shown in fig. 2).
Comparative example 2
The comparative example provides a preparation method of a graphene oxide conductive polymer conductive corrosion-resistant composite coating, which comprises the following steps:
step 1, grinding the surface of stainless steel by using sand paper (200 meshes and 1000 meshes) to remove a surface passive film, wherein the metal-based bipolar plate material is SS 304; removing oil stain and fingerprint on the surface by using acetone, removing excessive solvent by using ethanol, and putting the polished sample into a container with the volume of 1mol/L H2SO4Further removing the surface passivation film and increasing the binding sites of the surface;
step 4, placing the deposited wet film in a vacuum oven, drying for 3 hours at the constant temperature of 40 ℃, and after drying the surface film layer of the sample, drying for 10 hours at the temperature of 80 ℃;
and 5, characterizing the metal-based bipolar plate containing the graphene, wherein the contact resistance of the bipolar plate is 40m omega cm2(the test condition is 1.4 MPa), the electrochemical test result shows that the corrosion current is 17.67 mu A/cm2(potentiodynamic polarization test conditions of H with PH 3 ═ H2SO4Solution, 80 ℃). Test results show that the oxygen-containing groups on the surface of the graphene oxide can not effectively dope the conductive polymer, so that the contact resistance of the composite coating is high.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (9)
1. A method for preparing a graphene conductive polymer coating on the surface of a bipolar plate by adopting an electrodeposition method is characterized by comprising the following steps:
step one, chemically modifying graphene oxide, grafting an anionic functional group, and preparing a modified graphene oxide aqueous dispersion;
step two, mixing the modified graphene aqueous dispersion and the conductive polymer monomer aqueous dispersion according to a ratio to obtain an electrolyte;
step three, pretreating the metal-based bipolar plate, soaking the metal-based bipolar plate in sulfuric acid solution, and removing a surface passivation film of the metal-based bipolar plate;
step four, taking the metal-based bipolar plate as an anode and a platinum sheet as a cathode, and performing electrodeposition on the metal-based bipolar plate by using a constant-voltage direct-current power supply;
and fifthly, drying the deposited wet film to obtain the graphene conductive polymer composite coating.
2. The method for preparing a graphene conductive polymer coating on a surface of a bipolar plate according to claim 1, wherein in the first step, the anionic functional group comprises a sulfonic acid group, a benzenesulfonic acid group, a sulfuric acid group, and a phosphoric acid group.
3. The method for preparing the graphene conductive polymer coating on the surface of the bipolar plate by using the electrodeposition method according to claim 1, wherein in the second step, the conductive polymer monomer comprises polypyrrole, polyaniline and polythiophene.
4. The method for preparing the graphene conductive polymer coating on the surface of the bipolar plate by using the electrodeposition method according to claim 1, wherein in the second step, the electrolyte further comprises an initiator, a dispersion aid and a surfactant.
5. The method for preparing the graphene conductive polymer coating on the surface of the bipolar plate by using the electrodeposition method according to claim 1, wherein in the second step, the concentration of the modified graphene aqueous dispersion is 1mg/ml to 4mg/ml, and the concentration of the conductive polymer monomer is 0.01mol/L to 0.15 mol/L.
6. The method for preparing the graphene conductive polymer coating on the surface of the bipolar plate by using the electrodeposition method according to claim 1, wherein in the third step, the metal-based bipolar plate is a stainless steel bipolar plate or a titanium alloy bipolar plate, the surface of the metal-based bipolar plate is polished by using sand paper to remove a surface passivation film, oil stains and fingerprints on the surface of the metal-based bipolar plate are removed by using acetone, and excess solvent is removed by using ethanol.
7. The method for preparing the graphene conductive polymer coating on the surface of the bipolar plate by using the electrodeposition method according to claim 1, wherein in the fourth step, the deposition voltage is 1-5V, and the deposition time is 10-20 min.
8. The method for preparing the graphene conductive polymer coating on the surface of the bipolar plate by using the electrodeposition method according to claim 1, wherein in the fifth step, the wet film is dried by heating at a temperature ranging from 40 ℃ to 80 ℃.
9. The method for preparing the graphene conductive polymer coating on the surface of the bipolar plate by using the electrodeposition method according to claim 8, wherein the wet film obtained by deposition is placed in a vacuum oven and dried at a constant temperature of 40 ℃ for 3 hours, and after the surface film layer of the sample is dried, the drying is changed to 80 ℃ for 10 hours.
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