Method for preparing vertical graphene coating on surface of stainless steel bipolar plate and optimizing process

Abstract

The invention provides a method for preparing a vertical graphene coating on the surface of a stainless steel bipolar plate and optimizing a process, which comprises the following steps of: preparing the vertical graphene coating on the surface of the stainless steel bipolar plate by utilizing a plasma enhanced chemical vapor deposition technology to realize large-area growth of vertical graphene on the surface of the stainless steel bipolar plate; methane flux, plasma power, growth time and growth temperature are respectively used as independent variables to regulate and control the morphology, the structure and the required performance of the vertical graphene on the surface of the stainless steel bipolar plate, so that the purpose of optimizing the preparation process of the vertical graphene coating on the surface of the stainless steel bipolar plate within a certain range is achieved.

Description

Technical Field

[0001] The invention belongs to the field of surface modification of stainless steel bipolar plates of proton exchange membrane fuel cells, and in particular relates to a method for preparing a vertical graphene coating on the surface of a stainless steel bipolar plate and optimizing the process. Background Art

[0002] Proton exchange membrane fuel cells can generate electricity through hydrogen. They have the advantages of high energy conversion efficiency, zero pollution and sufficient raw materials. They are the current research focus in the field of hydrogen energy. However, the high cost and poor durability strictly limit their large-scale commercial production. Proton exchange membrane fuel cells are mainly composed of proton exchange membranes, catalyst layers, gas diffusion layers and bipolar plates. The bipolar plates account for about 30-40% of the total cost of the battery and 60-80% of the total weight, which is one of the key factors affecting its cost and durability. Bipolar plate materials include graphite, polymers and metals. Currently, stainless steel is the main metal material. It is worth noting that stainless steel bipolar plates are prone to corrosion and increased surface resistance when exposed to acidic environments for a long time, which seriously affects the durability and working efficiency of proton exchange membrane fuel cells. Therefore, improving the corrosion resistance and conductivity of stainless steel bipolar plates is of great significance to the further development of proton exchange membrane fuel cells, and coating with excellent conductivity and corrosion resistance is the most effective way to solve the above problems.

[0003] Vertical graphene has a unique three-dimensional structure. It has received extensive research attention as a metal corrosion barrier due to its excellent corrosion resistance, conductivity, and hydrophobicity. It has potential application prospects in the field of corrosion protection of stainless steel bipolar plates. At present, there is technology that uses PECVD to prepare vertical graphene coatings on the surface of stainless steel, but it is still in the basic stage and has not been studied in depth. There are still many key issues to be solved regarding the preparation of vertical graphene coatings on the surface of stainless steel bipolar plates: the change rules between the morphology and the preparation conditions are unclear, and it is difficult to regulate the morphology and structure of the vertical graphene coating. In addition, the morphology and structure of vertical graphene play a certain role in improving its electrochemical properties. However, there is currently no technical report on the effect of changes in preparation conditions on the electrochemical properties of vertical graphene. Therefore, it is difficult to select the optimal process parameters in the preparation process of vertical graphene. For example, the preparation of graphene on the surface of stainless steel with patent publication number CN106784915A has an overly complicated preparation process, requiring solution preparation, and has not explored the different process parameters during coating preparation, while coating growth depends on the selection of process parameters. Summary of the invention

[0004] Purpose of the invention: In order to solve the above-mentioned technical problems, the present invention proposes a method for preparing and optimizing the process of a vertical graphene coating on the surface of a stainless steel bipolar plate, and utilizes PECVD technology to prepare a vertical graphene coating on the surface of the stainless steel, so as to achieve large-area growth of vertical graphene on the surface of the stainless steel bipolar plate, and by changing the four process parameters of methane flux, plasma power, growth time and growth temperature, the morphology, structure and performance of the vertical graphene coating on the surface of the stainless steel bipolar plate are directional regulated, thereby achieving the purpose of optimizing the preparation process of the vertical graphene coating on the surface of the stainless steel bipolar plate within a certain range.

[0005] Technical solution: To achieve the above purpose, the present invention proposes a method for preparing a vertical graphene coating on the surface of a stainless steel bipolar plate and optimizing the process, the method comprising the following steps:

[0006] (1) Using stainless steel as a substrate, ultrasonically cleaning its surface with anhydrous ethanol and deionized water in sequence;

[0007] (2) After the sample is cleaned, place it in the heated quartz tube of the PECVD deposition furnace, adjust it to the middle position of the heated quartz tube, and then evacuate the reaction chamber;

[0008] (3) High-purity argon and hydrogen with a purity of 99.99% to 99.999% are introduced into the reaction chamber, and the growth temperature is set;

[0009] (4) When the temperature reaches the set growth temperature, it is kept warm. After the preset holding time, CH4 is introduced within a certain flow range;

[0010] (5) setting the plasma power and growth time, turning on the plasma source, and ionizing CH4 under the action of the plasma to generate carbon-containing plasma radicals, which are deposited on the stainless steel surface as a vertical graphene coating through radical diffusion, surface adsorption and nucleation processes;

[0011] (6) After the growth is completed, turn off the plasma source and the gas source, maintain the vacuum state, and take out the sample after the temperature naturally cools to room temperature.

[0012] Preferably, in step (1), the thickness of the stainless steel is 0.1 mm, the grade is 316L, and the ultrasonic cleaning time is 15 min.

[0013] Preferably, in step (2), the pressure of the reaction chamber is pumped down to below 5 Pa.

[0014] Preferably, in step (3), the flow rates of the high-purity argon and hydrogen are 80 sccm and 10 sccm respectively, and the growth temperature range is 500-700°C.

[0015] Preferably, the heating rate is 10°C min -1 .

[0016] Preferably, in step (4), the insulation time is 10 minutes and the CH4 flow rate range is 10-30 sccm.

[0017] Preferably, in step (5), the power range is 100-300 W, and the growth time range is 20-100 min.

[0018] Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0019] (1) The preparation process of the present invention is simple and the raw materials are simple. The vertical graphene can be grown with or without a catalyst. The obtained vertical graphene is grown in situ, so that the vertical graphene has a strong bonding force with the substrate, thereby achieving large-area growth of vertical graphene on the surface of the stainless steel bipolar plate.

[0020] (2) The morphology and structure of the vertical graphene prepared by the present invention can be controlled by changing process parameters such as methane flux, plasma power, growth time and growth temperature, and the optimal process parameters can be selected according to performance requirements.

[0021] (3) The vertical graphene coating on the surface of the stainless steel bipolar plate obtained by the present invention has a certain hydrophobicity and can significantly improve the conductivity of the stainless steel bipolar plate.

[0022] Instruction Manual

[0023] Figure 1 SEM oblique images of vertical graphene prepared in Example 1 at different CH4 flow rates, the CH4 flow rates of ae are 10 sccm, 15 sccm, 20 sccm, 25 sccm, and 30 sccm, respectively, and the magnification of a1-e1 is 1-20KX, and the magnification of a2-e2 is 2-50KX;

[0024] Figure 2 The interfacial contact resistance of the vertical graphene-coated stainless steel bipolar plate prepared in Example 1 at different CH4 flow rates under a compaction pressure of 1.4 MPa;

[0025] Figure 3 The SEM oblique images of vertical graphene prepared in Example 2 at different plasma powers, the plasma powers of ae are 100W, 150W, 200W, 250W, and 300W, respectively, and the magnification of a1-e1 is 1-20KX, and the magnification of a2-e2 is 2-50KX;

[0026] Figure 4The interface contact resistance of the vertical graphene-coated stainless steel bipolar plate prepared in Example 2 at different plasma powers and a compaction pressure of 1.4 MPa;

[0027] Figure 5 The SEM oblique images of the vertical graphene prepared in Example 3 at different growth times, and the growth times of ae are 20min, 40min, 60min, 80min, and 100min respectively, and the magnification of a1-e1 is 1-20KX, and the magnification of a2-e2 is 2-50KX;

[0028] Figure 6 The interfacial contact resistance of the vertical graphene-coated stainless steel bipolar plate prepared in Example 3 at different growth times under a compaction pressure of 1.4 MPa;

[0029] Figure 7 The SEM oblique images of vertical graphene prepared in Example 4 at different growth temperatures, and the growth temperatures of ae are 500°C, 550°C, 600°C, 650°C, and 700°C, respectively, and the magnification of a1-e1 is 1-20KX, and the magnification of a2-e2 is 2-50KX;

[0030] Figure 8 The interface contact resistance of the vertical graphene-coated stainless steel bipolar plate prepared in Example 4 at different growth temperatures under a compaction pressure of 1.4 MPa;

[0031] Fig. 9 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0032] In order to better understand the present invention, the above scheme is further described below in conjunction with specific embodiments. The preferred embodiments of the present invention are described in detail as follows:

[0033] Example 1 Preparation of vertical graphene under different CH4 fluxes

[0034] (1) Pretreatment of stainless steel substrate: Using commercial 0.1 mm 316L stainless steel as the substrate, the surface was ultrasonically cleaned with anhydrous ethanol and deionized water for 15 min in sequence;

[0035] (2) After the sample is cleaned, it is placed in the heated quartz tube of the PECVD deposition furnace and its position is adjusted to the middle position of the heated quartz tube. The reaction chamber is evacuated to below 5 Pa.

[0036] (3) 80 sccm of high-purity argon and 10 sccm of hydrogen were introduced into the reaction chamber, and the growth temperature was set to 650°C with a heating rate of 10°C min -1 .

[0037] (4) When the temperature reaches the set growth temperature, keep warm for 10 minutes and then introduce CH4 at different flow rates. The CH4 flow rates are 10 sccm, 15 sccm, 20 sccm, 25 sccm and 30 sccm respectively.

[0038] (5) Turn on the plasma source, set the plasma power to 100 W, and the growth time to 60 min.

[0039] (6) After the growth is completed, turn off the plasma source and the gas source, continue to maintain the vacuum, and take out the sample after the temperature naturally cools to room temperature.

[0040] The vertical graphene obtained in this embodiment under different CH4 flow rates was tested by scanning electron microscope oblique image, and the results are shown in Figure 1 The results show that the vertical graphene prepared under different CH4 flow rates all show the morphological characteristics of vertical orientation and exposed edges. The interface contact resistance test of the vertical graphene-coated stainless steel bipolar plate obtained in this example under different CH4 flow rates is shown in the following figure. Figure 2 The results show that after vertical graphene is deposited on the surface of 316L stainless steel, the interface contact resistance of the sample can meet the DOE standard (i.e., interface contact resistance <10mΩcm) when the compaction pressure is 1.4MPa. 2 ), in addition, with the increase of CH4 flow rate, the interfacial contact resistance of the sample gradually increases.

[0041] Example 2: Preparation of vertical graphene at different plasma powers

[0042] (1) Pretreatment of stainless steel substrate: Using commercial 0.1 mm 316L stainless steel as the substrate, the surface was ultrasonically cleaned with anhydrous ethanol and deionized water for 15 min in sequence;

[0043] (2) After the sample is cleaned, it is placed in the heated quartz tube of the PECVD deposition furnace and its position is adjusted to the middle position of the heated quartz tube. The reaction chamber is evacuated to below 5 Pa.

[0044] (3) 80 sccm of high-purity argon and 10 sccm of hydrogen were introduced into the reaction chamber, and the growth temperature was set to 650°C with a heating rate of 10°C min -1 .

[0045] (4) When the temperature reaches the set growth temperature, keep it warm for 10 minutes and then introduce 20 sccm of CH4.

[0046] (5) Turn on the plasma source, set the plasma power to 100 W, 150 W, 200 W, 250 W, and 300 W respectively, and set the growth time to 60 min.

[0047] (6) After the growth is completed, turn off the plasma source and the gas source, continue to maintain the vacuum, and take out the sample after the temperature naturally cools to room temperature.

[0048] The vertical graphene obtained in this embodiment under different plasma powers was tested by scanning electron microscope oblique image, and the results are shown in Figure 3 The results show that as the plasma power increases, the vertical graphene grows in a random distribution with different heights. When magnified, these vertical graphenes form a clustered growth morphology similar to "cabbage leaves". The interface contact resistance of the vertical graphene-coated stainless steel bipolar plate obtained in this example at different plasma powers is tested. The results are shown in Figure 4 The results show that the interfacial contact resistance of most vertical graphene-coated stainless steel bipolar plates is less than 10 mΩ cm 2 , and with the increase of power, the contact resistance shows a downward trend.

[0049] Example 3: Preparation of vertical graphene at different growth times

[0050] (1) Pretreatment of stainless steel substrate: Using commercial 0.1 mm 316L stainless steel as the substrate, the surface was ultrasonically cleaned with anhydrous ethanol and deionized water for 15 min in sequence;

[0051] (2) After the sample is cleaned, it is placed in the heated quartz tube of the PECVD deposition furnace and its position is adjusted to the middle position of the heated quartz tube. The reaction chamber is evacuated to below 5 Pa.

[0052] (3) 80 sccm of high-purity argon and 10 sccm of hydrogen were introduced into the reaction chamber, and the growth temperature was set to 650°C with a heating rate of 10°C min -1 .

[0053] (4) When the temperature reaches the set growth temperature, keep it warm for 10 minutes and then introduce 20 sccm of CH4.

[0054] (5) Turn on the plasma source, set the plasma power to 100 W, and set the growth time to 20 min, 40 min, 60 min, 80 min, and 100 min respectively.

[0055] (6) After the growth is completed, turn off the plasma source and the gas source, continue to maintain the vacuum, and take out the sample after the temperature naturally cools to room temperature.

[0056] The vertical graphene obtained in this embodiment under different growth conditions was tested by scanning electron microscope oblique images, and the results are shown in Figure 5The results show that within the growth time range of 20-80 minutes, the density of vertical graphene on the substrate surface gradually decreases with the extension of time. When the growth time is greater than 80 minutes, the density of vertical graphene on the substrate surface gradually increases with the extension of time. The interface contact resistance test of the vertical graphene-coated stainless steel bipolar plate obtained in this embodiment at different plasma powers is shown in the following figure. Figure 6 ,The results show that the interfacial contact resistance of the vertical graphene-coated stainless steel bipolar plates under a pressure of 1.4MPa meets the DOE standard and decreases with the extension of the growth time.

[0057] Example 4: Preparation of vertical graphene at different growth temperatures

[0058] (1) Pretreatment of stainless steel substrate: Using commercial 0.1 mm 316L stainless steel as the substrate, the surface was ultrasonically cleaned with anhydrous ethanol and deionized water for 15 min in sequence;

[0059] (2) After the sample is cleaned, it is placed in the heated quartz tube of the PECVD deposition furnace and its position is adjusted to the middle position of the heated quartz tube. The reaction chamber is evacuated to below 5 Pa.

[0060] (3) 80 sccm of high-purity argon and 10 sccm of hydrogen were introduced into the reaction chamber, and the growth temperatures were set to 500°C, 550°C, 600°C, 650°C, and 700°C, respectively, with a heating rate of 10°C min -1 .

[0061] (4) When the temperature reaches the set growth temperature, keep it warm for 10 minutes and then introduce 20 sccm of CH4.

[0062] (5) Turn on the plasma source, set the plasma power to 100 W, and the growth time to 60 min.

[0063] (6) After the growth is completed, turn off the plasma source and the gas source, continue to maintain the vacuum, and take out the sample after the temperature naturally cools to room temperature.

[0064] The vertical graphene obtained at different growth temperatures in this embodiment was tested by scanning electron microscope oblique images, and the results are shown in Figure 7 The results show that the vertical graphene prepared in the range of 550-600℃ is more dense and has a more uniform size distribution. The interface contact resistance test of the vertical graphene-coated stainless steel bipolar plates obtained in this embodiment under different growth conditions is carried out. The results are shown in Figure 8 ,The results show that the interfacial contact resistance of the vertical graphene-coated stainless steel bipolar plate shows an overall downward trend with the increase of growth temperature.

Claims

1. A method for preparing and optimizing a vertical graphene coating on a stainless steel bipolar plate surface, characterized in that: The method comprises the following steps: (1) Using stainless steel as a substrate, ultrasonically cleaning its surface with anhydrous ethanol and deionized water in sequence; (2) After the sample is cleaned, place it in the heated quartz tube of the PECVD deposition furnace, adjust it to the middle position of the heated quartz tube, and then evacuate the reaction chamber; (3) High-purity argon and hydrogen with a purity of 99.99% to 99.999% are introduced into the reaction chamber, and the growth temperature is set; (4) When the temperature reaches the set growth temperature, it is kept warm. After the preset holding time, CH4 is introduced within a certain flow range; (5) setting the plasma power and growth time, turning on the plasma source, and ionizing CH4 under the action of the plasma to generate carbon-containing plasma radicals, which are deposited on the stainless steel surface as a vertical graphene coating through radical diffusion, surface adsorption and nucleation processes; (6) After the growth is completed, turn off the plasma source and the gas source, maintain the vacuum state, and take out the sample after the temperature naturally cools to room temperature.

2. The method for preparing and optimizing the vertical graphene coating on the surface of a stainless steel bipolar plate according to claim 1, characterized in that: In the step (1), the thickness of the stainless steel is 0.1 mm, the grade is 316L, and the ultrasonic cleaning time is 15 min.

3. The method for preparing and optimizing the vertical graphene coating on the surface of a stainless steel bipolar plate according to claim 1, characterized in that: In the step (2), the pressure of the reaction chamber is pumped down to below 5 Pa.

4. The method for preparing and optimizing the vertical graphene coating on the surface of a stainless steel bipolar plate according to claim 1, characterized in that: In the step (3), the flow rates of the high-purity argon gas and hydrogen gas are 80 sccm and 10 sccm respectively, and the growth temperature range is 500-700°C.

5. The method for preparing and optimizing the vertical graphene coating on the surface of a stainless steel bipolar plate according to claim 1 or 4, characterized in that: Heating rate: 10℃min -1 .

6. The method for preparing and optimizing the vertical graphene coating on the surface of a stainless steel bipolar plate according to claim 1, characterized in that: In the step (4), the insulation time is 10 minutes, and the CH4 flow rate range is 10-30 sccm.

7. The method for preparing and optimizing a vertical graphene coating on a stainless steel bipolar plate surface according to claim 1, characterized in that: In the step (5), the power range is 100-300 W, and the growth time range is 20-100 min.

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