A PEM water electrolysis membrane electrode based on modified Nafion ionomer and its preparation method

Abstract

The present invention belongs to the field of energy material technology, specifically a PEM water electrolysis membrane electrode based on modified Nafion ionomer and its preparation method. The modified Nafion ionomer provided by the present invention is obtained by doping and modifying Nafion ionomer or solid membrane, denoted as FOH n ‑Nafion ionomer, doped with CF3(CF2) n CH2OH; The present invention modifies the Nafion solution by heating and stirring, and modifies the Nafion membrane by impregnation; the modified ionomer is mixed with the anode catalyst to form a slurry, and the membrane electrode is sprayed to prepare a membrane electrode with better stability than the original Nafion; The present invention effectively improves the stability and use value of the non-precious metal catalyst membrane electrode, and is expected to replace precious metal catalysts, thereby reducing the application cost of PEM. In the PEM test, 1A cm ‑2 The voltage is 1.84V under the current density, and good stability is maintained, and the stable operation is 40 hours, which is 10 times of the original. The modification method of the present invention is simple and suitable for mass production.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy materials, and in particular relates to a PEM water electrolysis membrane electrode and a preparation method thereof. Background Art

[0002] As an efficient and environmentally friendly method of hydrogen production, water electrolysis technology has the potential to dominate the future hydrogen production market. This technology converts intermittent energy sources such as solar and wind power into storable hydrogen resources. When needed, this technology, through the flexible application of fuel cell technology, enables on-demand power generation, ensuring zero carbon emissions throughout the entire process, demonstrating its significant advantages in energy conversion and storage.

[0003] To further improve the efficiency of hydrogen production from water electrolysis, researchers are developing new electrolyzers and catalysts. For example, new electrolyzer technologies such as solid oxide electrolyzers (SOECs) and proton exchange membrane electrolyzers (PEMs) show great potential in increasing current density and reducing energy consumption. PEM water electrolysis, with its more compact system design, lower ohmic losses, wider load range, and faster system response, has already entered the market. PEMs rely on traditional ionomers, such as perfluorosulfonic acid resins (Nafion), to conduct protons and bind catalysts. However, catalysts struggle to maintain good stability under these acidic conditions, limiting catalyst selection. To achieve large-scale application of PEM water electrolysis, non-precious metal catalysts are needed to replace precious metal catalysts. Past efforts have focused on developing advanced catalysts, overlooking the role of ionomers on the catalytic interface. Therefore, optimizing ionomers may be another path to improving the overall stability of PEMs.

[0004] The anode reaction in PEM water electrolysis is the oxygen evolution reaction (OER), a reaction step involving the breaking of hydrogen-oxygen bonds and the transfer of protons. Excessive protons cause localized acidity to increase, which can easily lead to the collapse of the catalyst structure. At the same time, sulfonate groups may coordinate with the catalyst surface at high potentials, further reducing stability. Therefore, strategies such as optimizing the hydrogen-bonded water network, increasing hydrophilic channels, and inhibiting sulfonate coordination can help improve the stability of water splitting, especially when applied to non-precious metal catalysts.

[0005] Unfortunately, most current Nafion modifications are based on applications in electrolyte membranes, which require extremely high mechanical strength, while ionomers do not. Some dopants, such as silica nanoparticles, easily block catalytic sites and are not suitable for ionomer modification. Small molecules are easily lost during the reaction, resulting in poor stability. Therefore, choosing a small molecule that strongly interacts with Nafion is an excellent strategy. CF3 (CF2) is the choice here. nThe CH2OH series, with its hydrophobic carbon-fluorocarbon structure and hydrophilic tail hydroxyl groups, can act like a surfactant, building a bridge between the hydrophilic and hydrophobic regions of Nafion polymers through self-assembly, thereby optimizing water channels. The hydroxyl groups can also coordinate with sulfonic acid groups, improving the hydrogen-bonded water network while inhibiting the coordination of sulfonic acid groups with catalysts, thereby achieving multifunctional optimization of PEM performance. Summary of the Invention

[0006] The purpose of the present invention is to provide a PEM water electrolysis model electrode based on modified Nafion ionomer and a preparation method thereof, so as to improve the stability of the catalyst in the practical application of PEM water electrolysis.

[0007] The present invention first provides a modified Nafion ionomer obtained by doping commercial Nafion ionomer (or solid membrane), denoted as FOH. n -Nafion ionomer, the structural formula of which is shown in the following formula (I):

[0008]

[0009] Where, for a Nafion membrane with an equivalent weight (EW) of 1100 g / eq, x is 6;

[0010] Among them, the dopant is CF3 (CF2) n CH2OH, n is 2-10.

[0011] In the present invention, the mass ratio of the dopant to the Nafion ionomer (or solid membrane) is 0.2-4.0; preferably, the doping mass ratio is 0.5-2.

[0012] The present invention also provides FOH n -The preparation method of Nafion ionomer, that is, the Nafion modification method, specifically comprises the following steps:

[0013] (1) According to the doping mass ratio, weigh the doping molecules CF3 (CF2) n CH2OH and Nafion ionomer solution or solid membrane;

[0014] (2) Modification of ionomer solution: CF3(CF2) n CH2OH is dissolved in the Nafion ionomer solution, placed in a sealed container, heated and stirred to obtain a mixed solution; for the modification of the solid membrane: the solid membrane is directly immersed in the corresponding amount of doping molecules for 0.5-6 hours, and then dried at 40-80°C.

[0015] Further:

[0016] The doping mass ratio is 0.2-4.0; preferably the doping mass ratio is 0.5-2;

[0017] The mass fraction of the Nafion ionomer solution used is 5-20%; the preferred mass fraction of the solution is 5-10%;

[0018] The heating temperature is 40-80°C; preferably the heating temperature is 60-70°C;

[0019] The heating time is 0.5-6 hours; the preferred heating time is 2-4 hours;

[0020] The present invention provides a method for preparing a PEM water electrolysis model electrode based on modified Nafion ionomer, and the specific steps are as follows:

[0021] (1) According to the mass ratio of Nafion and catalyst, weigh FOH n -Nafion and catalyst are added to ethanol or isopropanol and uniformly dispersed by ultrasonication to obtain catalyst slurry;

[0022] (2) placing the Nafion membrane on a vacuum adsorption hot table, and evenly coating the prepared catalyst slurry on the Nafion membrane by ultrasonic spraying or doctor blade coating;

[0023] (3) First perform hot pressing and fixing, then perform cold pressing and plasticization to obtain a PEM electrolytic water model electrode.

[0024] In step (1):

[0025] The catalyst can be a cobalt tetroxide type, a manganese dioxide type, or a ruthenium oxide type catalyst, and the loading is controlled at 1.5-3 mg / cm 2 ;

[0026] The mass ratio of the Nafion to the catalyst is 0.2-0.4.

[0027] The mass fraction of the ethanol or isopropanol is 70-99%, the volume is 1-5 ml, and the oscillation ultrasonic time is 5-60 min.

[0028] The Nafion membrane models may be Nafion 212, Nafion 211, Nafion 117 and Nafion 115.

[0029] In step (3), the hot pressing pressure is 1-4 MPa, the temperature is 60-100°C, and the time is 3-10 min. The cold pressing is at room temperature, and the other parameters are the same as those of the hot pressing.

[0030] The present invention also provides a method for testing the performance of the ionomer membrane electrode, which comprises the following specific steps:

[0031] (1) Prepare cathode catalyst slurry. Specifically, use 20-60% Pt / C, and weigh FOH, n -Nafion and catalyst are ultrasonically mixed with appropriate amount of ethanol or isopropanol to form catalyst slurry, and then sprayed on carbon paper or the cathode side of the membrane electrode, with the loading controlled at 0.2-0.4 mg Pt / cm 2 ;

[0032] (2) Platinum-coated titanium felt was used as the gas diffusion layer on the anode side of the membrane electrode, and titanium plates on both sides were used as current collectors to build a PEM electrolyzer; the water inlet rate was 30-80 ml / min and the temperature was 60-90 °C;

[0033] (3) First, the current density is 20mA / cm 2 Activate for 2-10 hours, then increase the current density stepwise to 1000mA / cm 2 .

[0034] The technical features and functional advantages of the present invention mainly include:

[0035] The modified FOH of the present invention n -Nafion ionomers have higher electrolytic cell stability than commercial Nafion ionomers. The modification method of the present invention is simple and applicable to a variety of syntheses. The modified molecules are easily available and can be easily mass-produced at low cost. The modified Nafion ionomer can be used with a variety of PEMWE anode catalysts. Without changing the catalyst, the stability can be significantly improved by simply optimizing the reaction interface. It has certain universality, especially for cobalt tetroxide catalysts. At a PEMWE current density of 1A cm -2 The PEMWE catalyst operated stably for 40 hours, a tenfold increase from its original current density. The voltage was only 1.84V, while a commercial Nafion ionomer at the same current density achieved a voltage of 1.87V and deactivated after 4 hours of operation. The superior performance of PEMWE is attributed to the incorporation of amphiphilic molecules. The carbon-fluorine chains are well compatible with the hydrophobic backbone of Nafion, while the hydroxyl groups interact with sulfonate groups to optimize the hydrogen-bonded water network and draw water molecules into the hydrophobic side, expanding the water transfer space. Combined, these effects enhance the stability of non-precious metal catalysts and are expected to promote the widespread application of PEMWE. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The corresponding values ​​of Example 1 (FOH2-Nafion) and Comparative Example 1 (Nafion) are 1 H NMR spectrum.

[0037] Figure 2This is a high-resolution transmission electron microscopy (HRTEM) image of Example 1 (FOH2-Nafion) of the present invention.

[0038] Figure 3 This is a high-resolution transmission electron microscope (HRTEM) image of Comparative Example 1 (Nafion) of the present invention.

[0039] Figure 4 Graph showing proton conductivity changes with temperature for Example 7 of the present invention and Comparative Example 2.

[0040] Figure 5 These are the AC impedance spectra of Example 1 (FOH2-Nafion) of the present invention and Comparative Example 1 (Nafion).

[0041] Figure 6 This is the PEM test of Example 1 (FOH2-Nafion), Example 4 (FOH4-Nafion) and Comparative Example 1 (Nafion) of the present invention. DETAILED DESCRIPTION

[0042] The present invention is further described below through embodiments with reference to the accompanying drawings.

[0043] Example 1:

[0044] CF3CF2CF2CH2OH and 5% Nafion solution were weighed at a doping mass ratio of 0.5. CF3CF2CF2CH2OH was added to the Nafion solution, placed in a sealed container, and heated with stirring for 1 hour at 60°C to obtain a modified ionomer solution.

[0045] Example 2:

[0046] CF3CF2CF2CH2OH and 10% Nafion solution were weighed separately at a doping mass ratio of 1.0. CF3CF2CF2CH2OH was added to the Nafion solution, placed in a sealed container, and heated with stirring for 3 hours at 60°C to obtain a modified ionomer solution.

[0047] Example 3:

[0048] CF3CF2CF2CH2OH and 5% Nafion solution were weighed separately at a doping mass ratio of 3.0. CF3CF2CF2CH2OH was added to the Nafion solution, placed in a sealed container, and heated with stirring for 2 hours at 80°C to obtain a modified ionomer solution.

[0049] Example 4:

[0050] CF3CF2CF2CF2CF2CH2OH and 5% Nafion solution were weighed at a doping mass ratio of 0.5. CF3CF2CF2CF2CF2CH2OH was added to the Nafion solution, placed in a sealed container, and heated with stirring for 3 hours at 60°C to obtain a modified ionomer solution.

[0051] Example 5:

[0052] CF3CF2CF2CF2CF2CF2CF2CH2OH and 5% Nafion solution were weighed at a doping mass ratio of 0.5. CF3CF2CF2CF2CF2CF2CH2OH was added to the Nafion solution, placed in a sealed container, and heated with stirring for 1 hour at a heating temperature of 40°C to obtain a modified ionomer solution.

[0053] Example 6:

[0054] CF3CF2CF2CF2CF2CF2CF2CF2CF2CH2OH and 5% Nafion solution were weighed at a doping mass ratio of 0.5. CF3CF2CF2CF2CF2CF2CH2OH was added to the Nafion solution, placed in a sealed container, and heated with stirring for 1 hour at a heating temperature of 40°C to obtain a modified ionomer solution.

[0055] Example 7:

[0056] The doping molecules CF3CF2CF2CH2OH and Nafion membrane were weighed separately at a doping mass ratio of 1.0. The membrane was immersed in a corresponding amount of doping molecule solvent for 1 hour and then dried at 40°C to obtain a modified membrane.

[0057] Example 8:

[0058] The doping molecules CF3CF2CF2CF2CF2CH2OH and Nafion membrane were weighed at a doping mass ratio of 1.0, and the membrane was immersed in a corresponding amount of doping molecule solvent for 1 hour, and then dried at 60°C to obtain a modified membrane.

[0059] Comparative Example 1:

[0060] Weigh 5% Nafion solution, place the Nafion solution in a sealed container, heat and stir for 1 hour, and the heating temperature is 60°C.

[0061] Comparative Example 2:

[0062] Ethanol and Nafion membrane were weighed separately at a doping mass ratio of 1.0, the Nafion membrane was immersed in ethanol for 1 hour, and then dried at 60° C. to obtain a modified membrane.

[0063] Structural characterization of the modified ionomers of Examples 1-6 and Comparative Example 1.

[0064] use 1 H NMR was used to characterize Example 1 and Comparative Example 1. Figure 1 The original hydrogen peak of the sulfonic acid group and the CF3CF2CF2CH2OH hydroxyl hydrogen peak disappeared and merged into a broad peak in the middle position, indicating that the hydroxyl group reacted with the sulfonic acid group, as shown in its structural formula.

[0065] The microscopic morphology of Example 1 and Comparative Example 1 was obtained by HRTEM. Figure 2 , Figure 3 .contrast Figure 2 and Figure 3 , it can be found that Nafion has dark circular areas, which are clusters of sulfonate groups. n The circular areas in Nafion are larger and lighter in color, indicating that the sulfonate clusters are dispersed, the hydrophilic areas are expanded, and they are intertwined with the hydrophobic areas.

[0066] The structural characterization results of Examples 2-6 are similar to those of Example 1 and are not repeated here.

[0067] Membrane electrode preparation, according to the mass ratio of ionomer to cobalt tetroxide catalyst of 0.3, FOH n -Nafion and catalyst are added to ethanol or isopropanol and ultrasonically dispersed to obtain catalyst slurry. The Nafion membrane is placed on a vacuum adsorption hot table and the prepared catalyst slurry is evenly coated on the Nafion membrane by ultrasonic spraying or doctor blade coating. The loading is controlled at 1.5-3 mg / cm 2 The membrane electrode was obtained by hot pressing at 80°C and 1 MPa for 5 minutes, and then cold pressing to plasticity and cold pressing to room temperature.

[0068] Proton conductivity tests of the modified membranes of Examples 7-8 and Comparative Example 2:

[0069] Since it is impossible to directly measure the proton conductivity of the ionomer, the modified membrane was selected as the object of qualitative research. The membrane to be tested was first immersed in ultrapure water for 10 hours. Then, the two-electrode four-probe method was used to perform AC impedance spectroscopy on the membrane to be tested in pure water. The temperature ranged from 18 to 50°C, and each temperature was stabilized for 15 minutes before testing. The frequency ranged from 10 6 to 1, with an amplitude of 5mV.

[0070] The test results of Example 8 are similar to those of Example 7. The proton conductivity is significantly improved compared to that of Comparative Example 2, showing good proton transfer ability. Figure 4 .

[0071] For membrane electrode testing, a cathode catalyst slurry was prepared, with 40% Pt / C, and Nafion ionomer at a mass ratio of 0.3 was added. The catalyst slurry was ultrasonically mixed with an appropriate amount of ethanol or isopropanol and then sprayed on carbon paper or the cathode side of the membrane electrode. The loading was controlled at 0.2-0.4 mg. Pt / cm 2 On the anode side, platinum-plated titanium felt was selected as the gas diffusion layer, and titanium plates on both sides were used as current collectors to build a PEM electrolyzer. The water inlet rate was 30-80 ml / min and the temperature was 60-90 ° C. First, the PEM was allowed to flow at a current density of 20 mA / cm 2 Activate for 2-10 hours, then increase the current density stepwise to 1000mA / cm 2 For the AC impedance spectrum test in PEM, the voltage is 1.6V and the frequency range is 10 5 to 0.01, with an amplitude of 10mV.

[0072] In the PEMWE, AC impedance test, the results of Examples 2-6 are similar to those of Example 1. The charge transfer resistance at a voltage of 1.6 V is less than that of Comparative Example 1. Figure 5 In the PEMWE stability test, the results of Examples 2-3 are similar to those of Example 1. The results of Examples 5-6 are similar to those of Example 4. Figure 6 Example 1 in PEMWE 1A / cm 2 It can work continuously for 40 hours under working conditions, with better stability than comparative example 1, showing outstanding water electrolysis performance.

[0073] In summary, the present invention presents a method for doping and modifying Nafion ionomer and Nafion membrane and a method for preparing and testing membrane electrodes. n CH2OH regulates the distribution of the hydrophilic and hydrophobic phases of Nafion, making the cobalt tetroxide catalyst 1A / cm 2 Under normal working conditions, it can work continuously for 40 hours, showing good stability. This ionomer gives non-precious metal catalysts higher activity and has certain industrial application prospects. It is expected to replace precious metal catalysts, reduce production costs, and promote the popularization of PEM water electrolysis.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a PEM water electrolysis model electrode based on modified Nafion ionomer, characterized in that: The modified Nafion ionomer is obtained by doping and modifying the Nafion ionomer or solid membrane, and is denoted as FOH. n -Nafion ionomer, the structural formula of which is shown in the following formula (I): ； Where, for Nafion membrane with an equivalent EW of 1100 g / eq, x is 6; Among them, the dopant is CF3 (CF2) n CH2OH, n is 2-10; The mass ratio of dopant to Nafion ionomer or solid membrane is 0.2-4.0; The specific steps of the preparation method are as follows: (1) Preparation of modified Nafion ionomer, the specific steps are: (1) According to the doping mass ratio, weigh the doping molecules CF3 (CF2) n CH2OH and Nafion ionomer solution or solid membrane; (2) Modification of ionomer solution: CF3(CF2) n CH2OH is dissolved in the Nafion ionomer solution, placed in a sealed container and heated and stirred to obtain a mixed solution; Modification of solid membrane: directly immerse the solid membrane in the corresponding amount of doping molecules for 0.5-6 hours, and then dry it at 40-80℃; the modified Nafion ionomer is recorded as FOH n -Nafion; (2) Preparation of PEM water electrolysis model electrodes, (1) According to the mass ratio of Nafion and catalyst, weigh FOH n -Nafion and catalyst are added to ethanol or isopropanol and uniformly dispersed by ultrasonication to obtain catalyst slurry; (2) Place the Nafion membrane on a vacuum adsorption hot plate, and evenly coat the prepared catalyst slurry on the Nafion membrane by ultrasonic spraying or doctor blade coating; (3) First perform hot pressing and then perform cold pressing to obtain the PEM electrolysis water model electrode.

2. The preparation method according to claim 1, characterized in that Modification of the ionomer solution in step (1): The mass fraction of the Nafion ionomer solution used is 5-20%; the heating temperature is 40-80° C.; and the heating time is 0.5-6 hours.

3. The preparation method according to claim 2, characterized in that In step (2): The catalyst is a cobalt tetroxide type, a manganese dioxide type, or a ruthenium oxide type catalyst, with a loading of 1.5-3 mg / cm 2 ; The mass ratio of Nafion to catalyst is 0.2-0.4; The ethanol or isopropanol has a mass fraction of 70-99% and a volume of 1-5 ml; the oscillation ultrasonic time is 5-60 min; The hot pressing pressure is 1-4 MPa, the temperature is 60-100°C, and the time is 3-10 min; the cold pressing is at room temperature, and the other parameters are the same as those of the hot pressing.

4. A PEM water electrolysis model electrode based on modified Nafion ionomer obtained by the preparation method according to any one of claims 1 to 3.

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