A membrane electrode and a method for manufacturing the same

Abstract

This invention belongs to the field of electrochemical technology, specifically relating to a membrane electrode and its preparation method. The membrane electrode preparation method provided by this invention includes the following steps: (1) activating an ion exchange membrane and then depositing a conductive coating on the surface of the ion exchange membrane to obtain a pretreated ion exchange membrane; (2) using the pretreated ion exchange membrane as the working electrode, placing it, along with a counter electrode and a reference electrode, in an electrolyte containing a metal salt catalyst, and growing a catalyst layer in situ on the surface of the pretreated ion exchange membrane through electrochemical deposition; (3) coating the surface of the catalyst layer with an ionomer and then drying it. This method uses an ion exchange membrane as a substrate to grow a catalyst in situ, directly obtaining a three-layer structure of catalyst layer / ion exchange membrane / catalyst layer, reducing the loss of catalyst raw materials during preparation, improving the bonding strength between the catalyst and the ion exchange membrane, and thus significantly improving the electrochemical performance and stability of the membrane electrode system.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a membrane electrode and its preparation method. Background Technology

[0002] Since the Industrial Revolution, human society and the economy have developed rapidly. However, with the large-scale use of fossil fuels, environmental problems have become increasingly severe, making a global energy transition imperative. Against this backdrop, the direct use of fossil fuels has been restricted, while the proportion of renewable energy power generation has been rising, promoting the process of "re-electrification" and advancing the development of electrochemical devices.

[0003] The membrane electrode assembly (MEA) is a core component of proton exchange membrane fuel cells and proton / anion exchange membrane electrolyzers. It plays a crucial role in mass transfer and energy exchange during electrochemical reactions, and its performance significantly impacts the overall performance of electrochemical devices. Therefore, improving the electrochemical performance of the MEA is of paramount importance. Summary of the Invention

[0004] This invention is based on the inventor's discoveries and understanding of the following facts and problems:

[0005] Membrane electrode assemblies mainly consist of three key materials: a proton exchange membrane, a catalyst, and a gas diffusion layer, along with a frame. The bonding between the catalyst layer and the ion exchange membrane plays a crucial role in the electrochemical performance of the membrane electrode assembly. Currently, membrane electrodes are primarily prepared using either a five-in-one CCS (catalyst-coated substrate) or a three-in-one CCM (catalyst-coated membrane) method. Although the CCM method improves the adhesion between the catalyst layer and the ion exchange membrane compared to the CCS method, its preparation process remains complex and susceptible to various environmental factors, resulting in instability and inconsistent membrane electrode formation. Therefore, further research is needed to determine the optimal preparation methods for membrane electrodes.

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for preparing a membrane electrode. This method uses an ion exchange membrane as a substrate to grow a catalyst in situ, directly obtaining a three-layer structure of catalyst layer / ion exchange membrane / catalyst layer. This reduces the loss of catalyst raw materials during preparation, improves the bonding strength between the catalyst and the ion exchange membrane, and, by changing experimental parameters, allows for control over the physicochemical properties of the catalyst, such as thickness and particle size. This avoids the complex processes of traditional membrane electrode preparation and significantly improves the electrochemical performance and stability of the membrane electrode system.

[0007] The method for preparing the membrane electrode according to an embodiment of the present invention includes the following steps:

[0008] (1) The ion exchange membrane is activated and then a conductive coating is deposited on the surface of the ion exchange membrane to obtain a pretreated ion exchange membrane.

[0009] (2) Using the pretreated ion exchange membrane obtained in step (1) as the working electrode, place it, the counter electrode and the reference electrode in an electrolyte containing a metal salt catalyst, and grow a catalyst layer in situ on the surface of the pretreated ion exchange membrane by electrochemical deposition.

[0010] (3) The surface of the catalyst layer obtained in step (2) is coated with ionomer and dried.

[0011] The advantages and technical effects of the membrane electrode preparation method of this invention are as follows: 1. The conductive coating deposited on the surface of the ion exchange membrane by the method of this invention can improve the conductivity of the ion exchange membrane and serve as a template on the ion exchange membrane for elemental substitution with the catalyst, thereby enabling the catalyst to be better deposited on the surface of the ion exchange membrane; 2. The method of this invention uses the ion exchange membrane as a substrate and employs electrochemical deposition to grow the catalyst in situ, which improves the bonding strength between the catalyst layer and the ion exchange membrane, thereby enhancing the electrochemical performance and stability of the membrane electrode; 3. The method of this invention simplifies the preparation process, is easy to operate, and is convenient for promotion and application in industrial production.

[0012] In some embodiments, in step (1), the activation treatment includes immersing the ion exchange membrane in a salt solution or an alkaline solution.

[0013] In some embodiments, in step (1), the conductive coating is deposited by vacuum sputtering; and / or, the thickness of the conductive coating is 10 to 500 nm.

[0014] In some embodiments, in step (1), the conductive coating includes at least one of platinum, palladium, nickel, iron, aluminum, and copper.

[0015] In some embodiments, in step (2), the reference electrode is Ag / AgCl, and the counter electrode is a platinum sheet or a graphite sheet; and / or, the metal salt catalyst comprises at least one of H2PtCl4, Ni(NO3)2, NiSO4, AgNO3, Zn(NO3)2, Co(NO3)2, CoCl2, Pb(ClO4)2, and Bi(CH3COO)3.

[0016] In some embodiments, in step (2), the concentration of metal ions of the metal salt catalyst in the electrolyte is 0.01 to 0.1 mol / L; and / or, the electrolyte is 0.05 to 1 mol / L H2SO4 or 0.1 to 2 mol / L HClO4.

[0017] In some embodiments, in step (2), the scanning potential range during electrochemical deposition is 0.2 to 0.9 V, the scanning speed is 1 to 100 mV / s, and the number of scans is 5 to 100.

[0018] In some embodiments, step (2) further includes cleaning the conductive coating on the surface of the pretreated ion exchange membrane before electrochemically depositing the catalyst layer; and / or, step (3) further includes cleaning the catalyst layer before coating the ionomer.

[0019] In some embodiments, in step (3), the content of the ionomer is 5 to 30 wt% of the catalyst content.

[0020] This invention also provides a membrane electrode, which is prepared using the method described above.

[0021] The membrane electrode provided by the embodiments of the present invention has advantages and technical effects. The membrane electrode prepared by the above method has a better bonding strength between the catalyst layer and the ion exchange membrane, which makes the membrane electrode have better electrochemical performance and stability. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the fabrication of a membrane electrode with in-situ catalyst growth;

[0023] Figure 2 These are scanning electron microscope images of the in-situ grown platinum@copper film electrodes prepared in Examples 1-3;

[0024] Figure 3 This is a comparison curve of the water electrolysis performance of the membrane electrodes prepared in Example 1 and Comparative Examples 1-2;

[0025] Figure 4 This is a comparison curve of the water electrolysis performance of the membrane electrodes prepared in Examples 1 and 4-5. Detailed Implementation

[0026] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] The method for preparing the membrane electrode according to an embodiment of the present invention includes the following steps:

[0028] (1) The ion exchange membrane is activated and then a conductive coating is deposited on the surface of the ion exchange membrane to obtain a pretreated ion exchange membrane.

[0029] (2) Using the pretreated ion exchange membrane obtained in step (1) as the working electrode, place it, the counter electrode and the reference electrode in an electrolyte containing a metal salt catalyst, and grow a catalyst layer in situ on the surface of the pretreated ion exchange membrane by electrochemical deposition.

[0030] (3) The surface of the catalyst layer obtained in step (2) is coated with ionomer and dried.

[0031] The advantages and technical effects of the membrane electrode preparation method of this invention are as follows: 1. The method of this invention, by depositing a metal conductive coating on the surface of the ion exchange membrane, can improve the conductivity of the ion exchange membrane and, on the other hand, serve as a template on the ion exchange membrane to perform elemental substitution with the catalyst, thereby enabling the catalyst to be better deposited on the surface of the ion exchange membrane; 2. The method of this invention, using the ion exchange membrane as a substrate, employs electrochemical deposition to grow the catalyst in situ, which improves the bonding strength between the catalyst layer and the ion exchange membrane, thereby enhancing the electrochemical performance and stability of the membrane electrode; 3. The method of this invention simplifies the preparation process, is simple and easy to operate, and is convenient for promotion and application in industrial production.

[0032] In some embodiments, preferably, in step (1), the activation treatment involves immersing the ion exchange membrane in a salt solution or an alkaline solution. More preferably, when the ion exchange membrane is an anion exchange membrane, the salt solution is at least one of 0.1–1 mol / L KCl, NaCl, K₂CO₃, and Na₂CO₃, and the alkaline solution is at least one of 0.1–1 mol / L KOH and NaOH; when the ion exchange membrane is a cation exchange membrane, the salt solution is at least one of 0.1–0.5 mol / L KCl and NaCl. Even more preferably, when the ion exchange membrane is a cation exchange membrane, the activation treatment further includes sequentially boiling the ion exchange membrane at 80°C for 30 min using 0.5 mol / L H₂SO₄ and 30 wt% H₂O₂ solutions, respectively.

[0033] In this embodiment of the invention, the ion exchange membrane is activated by soaking it in a salt solution or an alkaline solution, which can convert the anion exchange membrane into anion exchange membrane with OH-. — The ions are in a conductive form, converting the cation exchange membrane into H+. + Ions are conductive.

[0034] In some embodiments, preferably, in step (1), the conductive coating is deposited by vacuum sputtering; and / or, the thickness of the conductive coating is 10–500 nm. More preferably, the conductive coating comprises at least one of platinum, palladium, nickel, iron, aluminum, and copper.

[0035] In this embodiment of the invention, the thickness of the conductive coating is further optimized so that a portion of the conductive coating can undergo elemental replacement with the catalyst, promoting the deposition of the catalyst on the ion exchange membrane, while the remaining conductive coating ensures the conductivity of the ion exchange membrane. If the thickness of the conductive coating is too small, such as less than 10 nm, it will all be replaced, reducing the conductivity of the ion exchange membrane. If the thickness of the conductive coating is too large, it is easy to cause the coating to peel off, resulting in performance degradation of the membrane electrode.

[0036] In some embodiments, preferably, in step (2), the reference electrode is Ag / AgCl, and the counter electrode is a platinum sheet or a graphite sheet; and / or, the metal salt catalyst comprises at least one selected from H2PtCl4, Ni(NO3)2, NiSO4, AgNO3, Zn(NO3)2, Co(NO3)2, CoCl2, Pb(ClO4)2, and Bi(CH3COO)3. More preferably, in step (2), the concentration of metal ions of the metal salt catalyst in the electrolyte is 0.01–0.1 mol / L; and / or, the electrolyte is 0.05–1 mol / L H2SO4 or 0.1–2 mol / L HClO4.

[0037] In this embodiment of the invention, the composition of the catalyst layer can be directly controlled by selecting the type of catalyst. For example, selecting H2PtCl4 or CoCl2 can prepare a PtCo catalyst layer, thereby enabling better regulation of the catalytic performance of the catalyst layer.

[0038] In some embodiments, preferably, in step (2), the scanning potential range in the electrochemical deposition is 0.2 to 0.9 V, the scanning speed is 1 to 100 mV / s, and the number of scans is 5 to 100.

[0039] In this embodiment of the invention, the thickness and particle size of the catalyst layer can be controlled by setting the electrochemical deposition parameters, which avoids the catalyst loss problem and complex process in the existing process, and further improves the electrochemical performance and stability of the membrane electrode.

[0040] In some embodiments, preferably, step (2) further includes cleaning the conductive coating on the surface of the pretreated ion exchange membrane before electrochemically depositing the catalyst layer; and / or, step (3) further includes cleaning the catalyst layer before coating the ionomer. More preferably, the cleaning process in step (2) includes: using the pretreated ion exchange membrane as the working electrode, a platinum sheet or graphite sheet as the counter electrode, Ag / AgCl as the reference electrode, and 0.5 mol / L H2SO4 or 1 mol / L HClO4 as the electrolyte, performing 3 to 10 cyclic voltammetric scans at a scan rate of 10 mV / s in a potential range of 0.2 to 1.2 V; the cleaning process in step (3) includes rinsing the catalyst layer with deionized water after maintaining a constant potential for 60 s, wherein the constant potential range is 0.9 to 1.0 V.

[0041] In this embodiment of the invention, cleaning the surface conductive metal coating before catalyst deposition removes impurity particles from the surface of the conductive metal coating, making the surface more uniform and smooth, and further improving the bonding strength between the catalyst layer and the ion exchange membrane. Scanning at a constant potential activates the surface atoms of the conductive coating, facilitating metal deposition. Rinsing the catalyst layer with deionized water cleans the surface of the catalyst layer, reduces the impact of impurities on the membrane electrode, and further improves the electrochemical performance and stability of the membrane electrode.

[0042] In some embodiments, preferably, in step (3), the content of the ionomer is 5 to 30 wt% of the catalyst content. More preferably, the ionomer includes at least one of Nafion, FAA3-SOLUT-10, PiperION-A5, and SustainionXA-9.

[0043] In this embodiment of the invention, the amount of ionomer is preferred. The ionomer not only serves as an ion exchange membrane for transferring protons and water to the cathode, but more importantly, it also acts as a binder, gas transporter, and proton transferer in the catalyst layer. When the amount of ionomer is within a suitable range, it is beneficial to further improve the overall performance of the membrane electrode. If the content of ionomer is too low, it is easy to cause poor conductivity of the membrane electrode and catalyst shedding. If the content of ionomer is too high, it will cause insufficient exposure of active sites on the catalyst surface, resulting in the degradation of membrane electrode performance.

[0044] This invention also provides a membrane electrode, which is prepared using the above method.

[0045] The membrane electrode provided in this embodiment of the invention has a good bonding strength between the catalyst layer and the ion exchange membrane, which makes the membrane electrode have better electrochemical performance and stability.

[0046] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0047] Example 1

[0048] (1) First, the FAA3-50 anion exchange membrane was used as a substrate and immersed in 1M KOH solution for 24 hours. Then, the membrane was replaced with a new 1M KOH solution and immersed for another 24 hours for activation treatment. A 200nm thick copper film was deposited on its surface by vacuum sputtering.

[0049] (2) Figure 1 The assembled electrolytic cell uses 1 mol / L HClO4 as the electrolyte and the anion exchange membrane side as the working electrode, with an effective working area of ​​10 cm². 2 Using Pt as the counter electrode and Ag / AgCl as the reference electrode, the scanning range was set to 0.2–1.2 V, the scanning speed to 10 mV / s, and the cyclic voltammetry scans to 10 times to clean the copper thin film.

[0050] (3) Replace the electrolyte with 0.05mol / L H2PtCl4 / 1mol / L HClO4 solution, set the scan range to 0.38~0.66V, the scan rate to 10mV / s, and the number of cyclic voltammetry scans to 60.

[0051] (4) Maintain a constant potential of 0.95V for 60s, remove the anion exchange membrane, and clean the Pt cathode surface with deionized water.

[0052] (5) Invert the anion exchange membrane and repeat step (2) in 11 mol / L HClO4 solution;

[0053] (6) Replace the electrolyte with 0.1M Ni(NO3)2 / 1M HClO4 solution, set the scan range to 0.4~0.8V, the scan rate to 10mV / s, and the number of cyclic voltammetry scans to 60.

[0054] (7) Hold at a constant voltage of 0.9V for 60s, remove the anion exchange membrane, and rinse the Ni anode surface with deionized water;

[0055] (8) Coat the Pt cathode / Ni anode surface with 100 mg of FAA3-SOLUT-10 ionomer solution (10 wt%) and dry for later use.

[0056] Example 2

[0057] The preparation method of this embodiment is the same as that of Example 1, except that the scanning speed in step (3) is 2mV / s and the scanning speed in step (6) is 2mV / s.

[0058] Example 3

[0059] The preparation method of this embodiment is the same as that of Example 1, except that the scanning speed in step (3) is 50mV / s and the scanning speed in step (6) is 50mV / s.

[0060] Example 4

[0061] The preparation method of this embodiment is the same as that of Example 1, except that in step (3), the number of cyclic voltammetric scans is 10.

[0062] Example 5

[0063] The preparation method of this embodiment is the same as that of Example 1, except that in step (3), the number of cyclic voltammetric scans is 100.

[0064] Comparative Example 1

[0065] Pt / C and IrO2 catalyst inks with a concentration of 20 mg / mL were prepared separately (the solution was a mixture of isopropanol and water, in which the mass ratio of isopropanol to water was 3-1, and 20 wt% of FAA3-SOLUT-10 ionomer was added). After ultrasonic dispersion for 0.5-1 h, the cation and anion catalysts were sprayed onto both sides of the anion exchange membrane using ultrasonic spraying, and then dried for later use.

[0066] Comparative Example 2

[0067] Pt / C and IrO2 catalyst inks with a concentration of 20 mg / mL were prepared separately (the solution was a mixture of isopropanol and water, in which the mass ratio of isopropanol to water was 3-1, and 20 wt% of FAA3-SOLUT-10 ionomer was added). After ultrasonic dispersion for 0.5-1 h, the anion and cation catalysts were sprayed onto the surface of nickel foam using ultrasonic spraying. After drying, they were hot-pressed with anion exchange membranes to form a sandwich structure.

[0068] Comparative Example 3

[0069] The preparation method of this embodiment is the same as that of Example 1, except that: in step (1), a thin copper film is not deposited on the surface of the anion exchange membrane.

[0070] Comparative Example 4

[0071] The preparation method of this embodiment is the same as that of Example 1, except that: in step (1), no activation treatment is performed.

[0072] Experimental Example

[0073] 1. Scanning electron microscope

[0074] All samples were dried in a forced-air drying oven at 50°C for 12 hours, and gold was sputtered onto the samples for 100 seconds at a current of 20 mA. The surface morphology and cross-sectional morphology of the diaphragm were observed using an electron field emission scanning electron microscope (SEM, Regulus 8100, Hitachi, Japan).

[0075] SEM images of the membrane electrodes prepared in Examples 1-3 are shown below. Figure 2 As shown, from Figure 2 As can be seen, the particle size of the catalyst layer in the membrane electrode prepared in Example 1 is about 50 nm; the particle size of the catalyst layer in the membrane electrode prepared in Example 2 is about 20 nm; and the particle size of the catalyst layer in the membrane electrode prepared in Example 3 is about 100 nm.

[0076] 2. Hydrogen production by water electrolysis

[0077] Using 1M KOH solution as the electrolyte, the electrolyte was circulated at a rate of 100 mL / min, and the test temperature was 60℃. The test was conducted in a micro-electrolytic cell test system. After activation using cyclic voltammetry and chronoamperometry, the membrane electrode current-potential curve was recorded using linear cyclic voltammetry (scan rate 10 mV / s, range 1.2–2.2 V).

[0078] Various membrane electrodes at 0.5 A / cm 2 The potential values ​​corresponding to the current density are shown in Table 1. The comparison diagram of the water electrolysis hydrogen production performance of the membrane electrode in Example 1 and the membrane electrodes in Comparative Examples 1-2 is shown in the figure below. Figure 3 As shown in the figure, the water electrolysis performance comparison of the membrane electrodes prepared in Examples 1 and 4-5 is as follows. Figure 4 As shown.

[0079] 3. Electrochemical performance and durability

[0080] As in Experimental Example 2, the membrane electrodes in Examples 1-5 and Comparative Examples 1-4 were respectively subjected to a constant current method at 0.5 A / cm. 2 The stability test was carried out at the current density corresponding to the current for 24 hours. The mass of the membrane electrode was compared before and after the reaction, and the amount of catalyst loss is shown in Table 1.

[0081] Test results:

[0082] Table 1

[0083]

[0084] The test results above show that, compared with Example 1, Example 2 used a smaller scanning speed, resulting in smaller particle size and relatively low coverage. Compared with Example 1, Example 3 used a higher scanning speed, resulting in larger particle size and improved coverage. However, catalyst stacking may occur, making the surface layer easy to detach, thus reducing the performance compared with Example 1.

[0085] Compared with Example 1, Examples 4 and 5 differ in that the number of scans was changed, resulting in different coverage of the ion exchange membrane by the catalyst. Compared with Example 1, Example 4 had fewer scans and lower coverage, resulting in fewer active sites and a decrease in membrane electrode performance. Compared with Example 1, Example 5 had a higher number of scans and higher coverage, resulting in catalyst stacking and the formation of a mesoporous structure. The membrane electrode performance was lower than that of Example 1.

[0086] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0087] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing a membrane electrode, characterized by, Includes the following steps: (1) The ion exchange membrane is activated and then a conductive coating is deposited on the surface of the ion exchange membrane to obtain a pretreated ion exchange membrane; the thickness of the conductive coating is 10~500nm and the conductive coating includes at least one of platinum, palladium, nickel, iron, aluminum and copper. (2) Using the pretreated ion exchange membrane obtained in step (1) as the working electrode, place it, along with the counter electrode and the reference electrode, in an electrolyte containing a metal salt catalyst, and grow a catalyst layer in situ on the surface of the pretreated ion exchange membrane by electrochemical deposition; wherein, the conductive coating is provided on the side of the ion exchange membrane away from the counter electrode and the reference electrode; a portion of the conductive coating undergoes elemental substitution with the catalyst, and the remaining conductive coating ensures the conductivity of the ion exchange membrane; the metal salt catalyst contains at least one of H2PtCl4, Ni(NO3)2, NiSO4, AgNO3, Zn(NO3)2, Co(NO3)2, CoCl2, Pb(ClO4)2, and Bi(CH3COO)3; the scanning potential range in the electrochemical deposition is 0.2~0.9V, the scanning speed is 1~100mV / s, and the number of scans is 5~100; (3) The surface of the catalyst layer obtained in step (2) is coated with ionomer and dried.

2. The method for producing a membrane electrode according to claim 1, characterized by, In step (1), the activation treatment includes immersing the ion exchange membrane in a salt solution or an alkaline solution.

3. The method of claim 1, wherein the membrane electrode is prepared by the steps of: In step (1), the conductive coating is deposited using a vacuum sputtering method.

4. The method of claim 1, wherein the membrane electrode is prepared by the steps of: In step (2), the reference electrode is Ag / AgCl, and the counter electrode is a platinum sheet or a graphite sheet.

5. The method for producing a membrane electrode according to claim 1 or 4, characterized by, In step (2), the concentration of metal ions of the metal salt catalyst in the electrolyte is 0.01~0.1 mol / L; and / or, the electrolyte is 0.05~1 mol / L H2SO4 or 0.1~2 mol / L HClO4.

6. The membrane electrode preparation method according to claim 1, wherein Step (2) further includes cleaning the conductive coating on the surface of the pretreated ion exchange membrane before electrochemically depositing the catalyst layer; and / or, step (3) further includes cleaning the catalyst layer before coating the ionomer.

7. The method for preparing a membrane electrode according to claim 1, characterized in that, In step (3), the content of the ionomer is 5 to 30 wt% of the catalyst content.

8. A membrane electrode, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

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