High-activity and high-stability carbonized nanofiber membrane electrode and preparation method thereof

Abstract

The invention discloses a high-activity and high-stability carbonized nanofiber membrane electrode and a preparation method thereof, and the preparation method comprises the following steps: mixing water, alcohol, a catalyst and a binder according to a ratio to prepare an electrostatic spinning slurry, adopting electrostatic spinning to prepare nanofibers, and carbonizing the prepared nanofibers in a mixed atmosphere of H2 and Ar; grinding the carbonized product, preparing slurry with water, alcohol and an ionomer, uniformly attaching the slurry to a cathode and an anode of a proton exchange membrane, and drying to obtain the proton exchange membrane. According to the method, the nanofiber morphology of the catalyst layer is maintained, and the Pt utilization rate of the catalyst layer can be maintained. And the catalytic activity of the catalyst is improved by adopting H2 / Ar condition carbonization. Then, no ionomer (Nafion) is added when the nanofibers are constructed in the first step, impurities wrapping the catalyst after carbonization are reduced, the catalytic activity is improved, finally, the non-conductive binder is changed into conductive carbon through the carbonized nanofibers, and the conductivity and stability of the catalytic layer are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrode material preparation, and specifically relates to a carbonized nanofiber membrane electrode with high activity and stability and a preparation method thereof. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Fuel cells, especially hydrogen fuel cells, have attracted much attention due to their high energy density and pollution-free advantages, and are regarded as the ultimate energy source for achieving sustainable development. However, the cost of fuel cells is high, mainly due to the high price of catalysts. Therefore, it is necessary to improve the utilization rate of Pt-based catalysts. The construction of ordered membrane electrodes can effectively reduce the amount of Pt and improve the utilization rate of catalysts. Electrospinning is an effective method for constructing nanofiber ordered membrane electrodes, but the construction of ordered membrane electrodes by electrospinning requires the use of binders, which are non-conductive, non-proton-conductive and easily soluble in water, resulting in poor conductivity and stability of the membrane electrode. If the nanofiber electrode is directly carbonized under inert gas conditions, ground and sprayed on the anode and cathode, although the stability and conductivity of the catalyst layer are improved, the performance of the membrane electrode is poor. Summary of the invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a carbonized nanofiber membrane electrode with high activity and stability and a preparation method thereof.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a carbonized nanofiber membrane electrode with high activity and high stability, comprising the following steps:

[0007] Water, alcohol, a catalyst and a binder are mixed in proportion to prepare an electrospinning slurry, nanofibers are prepared by electrospinning, and the prepared nanofibers are carbonized in a mixed atmosphere of H2 and Ar;

[0008] The carbonized product is ground and mixed with Nafion or Aquivion, water and alcohol to form a slurry, and the slurry is evenly attached to the positive and negative electrodes of the proton exchange membrane. After drying, the product is obtained.

[0009] The present invention adopts the method of carbonizing nanofibers under H2 / Ar conditions to convert unstable and non-conductive binders into carbon, thereby improving the catalytic activity of the catalyst. In the first step of constructing the nanofibers, no solvents such as Nafion are added, which reduces the impurities that wrap the catalyst after carbonization and improves the catalytic activity. This not only maintains the high performance of the ordered nanofiber membrane electrode, but also improves the conductivity and stability of the membrane electrode.

[0010] The method for uniformly attaching the slurry to both sides of the proton exchange membrane may be spraying or coating, as long as uniform attachment of the slurry can be achieved.

[0011] In some embodiments, in the mixed atmosphere of H 2 and Ar, the volume ratio of H 2 to Ar is 1:9-19.

[0012] In some embodiments, in the electrospinning slurry, the mass ratio of water, alcohol, catalyst and Nafion is 4-6:4-6:1:0.006-0.008.

[0013] Preferably, the alcohol is selected from at least one of methanol, ethanol, isopropanol or n-propanol.

[0014] Preferably, the binder is selected from polyvinyl alcohol, polyacrylic acid or polyvinyl pyrrolidone.

[0015] Preferably, the catalyst is selected from at least one of a platinum-carbon catalyst, a platinum-based alloy catalyst and a non-precious metal catalyst.

[0016] Preferably, the water, alcohol, catalyst and binder are stirred and mixed in proportion for 20-30 hours to ensure uniform mixing.

[0017] In some embodiments, the carbonization temperature is 500-1000° C., and the carbonization time is 1-5 h.

[0018] In some embodiments, the ionomer is Nafion or Aquivion.

[0019] Preferably, in the slurry, the mass ratio of the carbonization product, water, alcohol and ionomer is 1:4-6:120-140:6-8.

[0020] In a second aspect, the present invention provides a carbonized nanofiber membrane electrode with high activity and high stability, which is prepared by the preparation method.

[0021] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0022] In the present invention, a method of pyrolyzing nanofibers under H2 / Ar conditions is adopted to achieve the successful preparation of carbonized nanofiber membrane electrodes. First, the method maintains the nanofiber morphology of the catalyst layer, which is conducive to maintaining the Pt utilization rate of the catalyst layer. Secondly, the catalytic activity of the catalyst is improved by carbonization under H2 / Ar conditions. Then, when constructing the nanofibers in the first step, Nafion is not added, which reduces the impurities that wrap the catalyst after carbonization and improves the catalytic activity. Finally, the carbonized nanofibers convert the non-conductive binder into conductive carbon, which improves the conductivity and stability of the catalyst layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 This is a SEM image of the nanofiber catalytic layer in Example 1 of the present invention;

[0025] Figure 2 This is a SEM image of the carbonized nanofiber catalyst layer in Example 1 of the present invention;

[0026] Figure 3 This is a SEM image of the carbonized and ground product sprayed on the cathode of the proton exchange membrane in Example 1 of the present invention;

[0027] Figure 4 Graphs showing polarization curves of the carbonized nanofiber membrane electrodes prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0028] Figure 5 This is a stability comparison diagram of the nanofiber membrane electrodes prepared in Example 1 and Comparative Example 3;

[0029] Figure 6 This is a stability comparison chart of the electrodes prepared in Example 1 and Comparative Example 4. DETAILED DESCRIPTION

[0030] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0031] The present invention will be further described below in conjunction with the embodiments.

[0032] Example 1

[0033] (1) Accurately weigh 1.5 g of EC600JD catalyst (60% Pt / C, Pt supported on activated carbon, Pt mass percentage is 60%), 7.4 g of isopropanol, and 11.8 g of deionized water, crush the cells for 10 min, shear for 20 min, and ultrasonicate for 40 min to mix them evenly, take 8.3 g of the mixed solution, add 0.12 g of PAA, and stir for 24 h;

[0034] (2) controlling the temperature to be lower than 30° C., the humidity to be lower than 50%, the positive high voltage to be 14 kV, the negative high voltage to be −2 kV, the liquid flow rate to be 0.2 mm / min, and electrospinning for 5 h to obtain the nanofiber catalyst layer;

[0035] (3) Peel off the catalyst layer and carbonize at 800 °C for 1 h under H2 / Ar (the volume ratio of H2 to Ar is 1:19);

[0036] (4) taking out the carbonized catalyst layer and grinding it into powder;

[0037] (5) Take 0.23 g of catalyst layer powder, add 1.6 g of deionized water, 0.645 g of 10% Nafion and 30.2 g of ethanol in sequence, crush the cells for 45 min, and ultrasonicate for 30 min to obtain a spray slurry;

[0038] (6) Spray the slurry on the positive and negative electrodes of the proton exchange membrane, with 0.3 mg / cm2 for the cathode 2 , anode 0.05mg / cm 2 .

[0039] SEM image of the nanofiber catalytic layer in Example 1, see Figure 1 ,Depend on Figure 1 It can be seen that the morphology of the nanofibers is good, and it can be seen that the catalyst layer can present a good nanofiber shape even without adding Nafion.

[0040] SEM image of the carbonized nanofiber catalyst layer in Example 1, see Figure 2 ,Depend on Figure 2 It can be seen that the catalytic layer still presents the shape of nanofibers after carbonization, which means that carbonization does not destroy the nanofiber structure.

[0041] The SEM image of the carbonized and ground sample sprayed on the cathode of the proton exchange membrane in Example 1 is shown in FIG. Figure 3 ,Depend on Figure 3 It can be seen that the catalytic layer formed by spraying after grinding still presents a nanofiber structure, which not only helps the transmission of substances but also improves the conductivity of the catalytic layer.

[0042] Example 2

[0043] (1) Accurately weigh 1.5 g of EC600JD catalyst (60% Pt / C), 7.8 g of isopropanol, and 12.8 g of deionized water, crush the cells for 10 min, shear for 30 min, and ultrasonicate for 40 min to mix them evenly. Take 8.3 g of the mixed solution, add 0.12 g of polyacrylic acid PAA, and stir for 24 h;

[0044] (2) controlling the temperature to be lower than 30° C., the humidity to be lower than 50%, the positive high voltage to be 15 kV, the negative high voltage to be -3 kV, the liquid flow rate to be 0.4 mm / min, and electrospinning for 5 h to obtain the nanofiber catalyst layer;

[0045] (3) Peel off the catalyst layer and carbonize at 900 °C for 1 h under H2 / Ar (the volume ratio of H2 to Ar is 1:19);

[0046] (4) taking out the carbonized catalyst layer and grinding it into powder;

[0047] (5) Take 0.25 g of catalyst layer powder, add 2 g of deionized water, 0.678 g of 10% Nafion and 30.5 g of ethanol in sequence, crush the cells for 45 min, and ultrasonicate for 30 min to obtain a spray slurry;

[0048] (6) Spray the slurry on the positive and negative electrodes of the proton exchange membrane, with 0.3 mg / cm2 for the cathode 2 , anode 0.05mg / cm 2 .

[0049] Example 3

[0050] (1) Accurately weigh 1.5 g of EC600JD catalyst (60% Pt / C), 6.5 g of isopropanol, and 11.1 g of deionized water, crush the cells for 10 min, shear for 25 min, and ultrasonicate for 30 min to mix them evenly. Take 8.5 g of the mixed solution, add 0.15 g of PAA, and stir for 25 h;

[0051] (2) controlling the temperature to be lower than 30° C., the humidity to be lower than 50%, the positive high voltage to be 14 kV, the negative high voltage to be −2 kV, the liquid flow rate to be 0.2 mm / min, and electrospinning for 5 h to obtain the nanofiber catalyst layer;

[0052] (3) Peel off the catalyst layer and carbonize it at 1000 °C for 1 h under H2 / Ar conditions;

[0053] (4) taking out the carbonized catalyst layer and grinding it into powder;

[0054] (5) Take 0.2 g of catalyst layer powder, add 1.5 g of deionized water, 0.66 g of 10% Nafion and 31.1 g of ethanol in sequence, crush the cells for 45 min, and ultrasonicate for 30 min to obtain a spray slurry;

[0055] (6) Spray the slurry on the positive and negative electrodes of the proton exchange membrane, with 0.3 mg / cm2 for the cathode 2 , anode 0.05mg / cm 2 .

[0056] Example 4

[0057] (1) Accurately weigh 1.5 g of EC600JD catalyst (60% Pt / C), 7.4 g of isopropanol, and 11.8 g of deionized water, crush the cells for 10 min, shear for 20 min, and ultrasonicate for 40 min to mix them evenly. Take 8.3 g of the mixed solution, add 0.12 g of PAA, and stir for 24 h;

[0058] (2) controlling the temperature to be lower than 30° C., the humidity to be lower than 50%, the positive high voltage to be 14 kV, the negative high voltage to be −2 kV, the liquid flow rate to be 0.2 mm / min, and electrospinning for 5 h to obtain the nanofiber catalyst layer;

[0059] (3) Peel off the catalyst layer and carbonize at 800 °C for 1 h under H2 / Ar (the volume ratio of H2 to Ar is 1:19);

[0060] (4) taking out the carbonized catalyst layer and grinding it into powder;

[0061] (5) Take 0.23 g of catalyst layer powder, add 1.6 g of deionized water, 0.258 g of 25% Aquivion and 30.2 g of ethanol in sequence, crush the cells for 45 min, and ultrasonicate for 30 min to obtain a spray slurry;

[0062] (6) Spray the slurry on the positive and negative electrodes of the proton exchange membrane, with 0.3 mg / cm2 for the cathode 2 , anode 0.05mg / cm 2 .

[0063] Comparative Example 1

[0064] (1) Accurately weigh 1.5 g of EC600JD catalyst (60% Pt / C), 4.2 g of 10% Nafion, 7.4 g of isopropanol, and 11.8 g of deionized water, crush the cells for 10 min, shear for 20 min, and ultrasonicate for 40 min to mix them evenly. Take 8.3 g of the mixed solution, add 0.12 g of PAA, and stir for 24 h;

[0065] (2) controlling the temperature to be lower than 30° C., the humidity to be lower than 50%, the positive high voltage to be 14 kV, the negative high voltage to be −2 kV, the liquid flow rate to be 0.2 mm / min, and electrospinning for 5 h to obtain the nanofiber catalyst layer;

[0066] (3) peeling off the catalyst layer and carbonizing at 800° C. for 1 h under H2 / Ar conditions (same as in Example 1);

[0067] (4) taking out the carbonized catalyst layer and grinding it into powder;

[0068] (5) Take 0.23 g of catalyst layer powder, add 1.6 g of deionized water, 0.645 g of 10% Nafion and 30.2 g of ethanol in sequence, crush the cells for 45 min, and ultrasonicate for 30 min to obtain a spray slurry;

[0069] (6) Spray the slurry on the positive and negative electrodes of the proton exchange membrane, with 0.3 mg / cm2 for the cathode 2 , anode 0.05mg / cm 2 .

[0070] Comparative Example 2

[0071] (1) Accurately weigh 1.5 g of EC600JD catalyst (60% Pt / C), 4.2 g of 10% Nafion, 7.4 g of isopropanol, and 11.8 g of deionized water, crush the cells for 10 min, shear for 20 min, and ultrasonicate for 40 min to mix them evenly. Take 8.3 g of the mixed solution, add 0.12 g of PAA, and stir for 24 h;

[0072] (2) controlling the temperature to be lower than 30° C., the humidity to be lower than 50%, the positive high voltage to be 14 kV, the negative high voltage to be −2 kV, the liquid flow rate to be 0.2 mm / min, and electrospinning for 5 h to obtain the nanofiber catalyst layer;

[0073] (3) Peel off the catalyst layer and carbonize it at 800 °C for 1 h under N2 conditions;

[0074] (4) taking out the carbonized catalyst layer and grinding it into powder;

[0075] (5) Take 0.23 g of catalyst layer powder, add 1.6 g of deionized water, 0.645 g of 10% Nafion and 30.2 g of ethanol in sequence, crush the cells for 45 min, and ultrasonicate for 30 min to obtain a spray slurry;

[0076] (6) Spray the slurry on the positive and negative electrodes of the proton exchange membrane, with 0.3 mg / cm2 for the cathode 2 , anode 0.05mg / cm 2 .

[0077] The polarization curves of the carbonized nanofiber membrane electrodes prepared in Example 1, Comparative Example 1 and Comparative Example 2 are as follows: Figure 4 As shown, the catalytic layer obtained by H2 / Ar treatment is 1A / cm 2 The voltage of the final catalytic layer increased by nearly 200mV, indicating that H2 / Ar treatment can improve the catalytic ability of the active sites. Without adding Nafion to the slurry in the first step of electrospinning, the final catalytic layer has a 1A / cm 2 The voltage increased by nearly 30mV, indicating that the carbonization treatment without adding Nafion reduced the wrapping of impurities on the catalyst and improved the catalytic activity of the catalytic layer.

[0078] Comparative Example 3

[0079] (1) Accurately weigh 1.5 g of EC600JD catalyst (60% Pt / C), 4.2 g of 10% Nafion, 7.4 g of isopropanol, and 11.8 g of deionized water, crush the cells for 10 min, shear for 20 min, and ultrasonicate for 40 min to mix them evenly. Take 8.3 g of the mixed solution, add 0.12 g of PAA, and stir for 24 h;

[0080] (2) controlling the temperature to be lower than 30° C., the humidity to be lower than 50%, the positive high voltage to be 14 kV, the negative high voltage to be −2 kV, the liquid flow rate to be 0.2 mm / min, and electrospinning for 5 h to obtain the nanofiber catalyst layer;

[0081] (3) At 150°C and 0.3 MPa, the nanofibers were transferred onto a proton exchange membrane to obtain a single-sided nanofiber membrane electrode;

[0082] (4) Spraying the anode to obtain a nanofiber membrane electrode.

[0083] The stability comparison diagram of the nanofiber membrane electrode prepared in Example 1 and Comparative Example 3 is as follows: Figure 5 As shown, the nanofiber membrane electrode prepared by direct electrospinning has a collapse of the nanofiber structure because the binder is easily dissolved during the CV treatment, while the carbonized nanofiber structure can be well maintained after CV treatment. Therefore, the stability of the nanofiber membrane electrode is improved after carbonization treatment.

[0084] Comparative Example 4

[0085] (1) Weigh 0.5 g of catalyst (60% Pt / C), add 3.5 g of water, 2.8 g of Nafion and 65.9 g of alcohol, crush the cells for 40 min, and ultrasonicate for 30 min to obtain catalyst slurry;

[0086] (2) Spraying onto both sides of the proton exchange membrane to obtain a sprayed membrane electrode.

[0087] The stability comparison diagram of the electrodes prepared in Example 1 and Comparative Example 4 is as follows: Figure 6 As shown, the stability of the membrane electrode after carbonization treatment is comparable to that of the sprayed membrane electrode, indicating that the carbonization treatment can both maintain the ordered structure of the nanofibers and improve the stability of the catalytic layer.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a highly active and stable carbonized nanofiber membrane electrode, characterized in that: The steps include: Water, alcohol, a catalyst and a binder are mixed in proportion to prepare an electrospinning slurry, nanofibers are prepared by electrospinning, and the prepared nanofibers are carbonized in a mixed atmosphere of H2 and Ar; The carbonized product is ground and mixed with ionomer, water and alcohol to form a slurry, which is evenly attached to the positive and negative electrodes of the proton exchange membrane. After drying, a membrane electrode is obtained.

2. The method for preparing the highly active and highly stable carbonized nanofiber membrane electrode according to claim 1, characterized in that: In the mixed atmosphere of H2 and Ar, the volume ratio of H2 to Ar is 1:9-19.

3. The method for preparing the highly active and highly stable carbonized nanofiber membrane electrode according to claim 1, characterized in that: In the electrospinning slurry, the mass ratio of water, alcohol, catalyst and binder is 4-6:4-6:1:0.006-0.

008.

4. The method for preparing the highly active and highly stable carbonized nanofiber membrane electrode according to claim 1, characterized in that: The alcohol is selected from at least one of methanol, ethanol, isopropanol or n-propanol.

5. The method for preparing a carbonized nanofiber membrane electrode with high activity and stability according to claim 1, characterized in that: The binder is selected from polyvinyl alcohol, polyacrylic acid or polyvinyl pyrrolidone.

6. The method for preparing a carbonized nanofiber membrane electrode with high activity and stability according to claim 1, characterized in that: The catalyst is selected from at least one of a platinum-carbon catalyst, a platinum-based alloy catalyst and a non-precious metal catalyst.

7. The method for preparing a carbonized nanofiber membrane electrode with high activity and stability according to claim 1, characterized in that: The time for stirring and mixing water, alcohol, catalyst and binder in proportion is 20-30 hours.

8. The method for preparing a carbonized nanofiber membrane electrode with high activity and stability according to claim 1, characterized in that: The carbonization temperature is 500-1000° C., and the carbonization time is 1-5 hours.

9. The method for preparing a carbonized nanofiber membrane electrode with high activity and stability according to claim 1, characterized in that: The ionomer is Nafion or Aquivion; Preferably, in the slurry, the mass ratio of the carbonization product, water, alcohol and ionomer is 1:4-6:120-140:6-8.

10. A highly active and stable carbonized nanofiber membrane electrode, characterized in that: Prepared by the preparation method described in any one of claims 1 to 9.

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