Corrosion-resistant high-conductivity stainless steel bipolar plate semiconductor film, method for preparing same, and use thereof

Abstract

The application discloses a kind of corrosion-resistant high-conductive stainless steel bipolar plate semiconductor film and preparation method and application thereof, belong to the stainless steel bipolar plate semiconductor film preparation technical field for PEMFC.The preparation steps of the corrosion-resistant high-conductive stainless steel bipolar plate semiconductor film include: the stainless steel bipolar plate is immersed into passivation liquid, under the condition that passivation potential is 1.1~1.3V, passivation temperature is 40~60 DEG C, passivation time is 0.5~1h, electrochemical passivation is carried out, and the corrosion-resistant high-conductive stainless steel bipolar plate semiconductor film is obtained;Wherein, the content of Cr in the stainless steel bipolar plate is 16~20wt%, and the total content of Cr and Fe is not less than 87.2wt%.The corrosion-resistant high-conductive stainless steel bipolar plate semiconductor film prepared by the application has working condition corrosion current density ≤1 μA / cm 2 , contact resistance ≤2 mΩ·cm 2 , contact angle ≥110 DEG, with good corrosion resistance, conductivity and hydrophobicity.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel bipolar plate semiconductor film preparation technology for PEMFC, specifically relating to a corrosion-resistant and highly conductive stainless steel bipolar plate semiconductor film, its preparation method, and its application. Background Technology

[0002] As the global energy structure continues its transformation towards a green and low-carbon direction, hydrogen energy, as a green and renewable energy source, has become an important development direction in the new energy field. Proton exchange membrane fuel cells (PEMFCs), a key technology for hydrogen energy utilization, are electrochemical devices that generate electricity through non-combustible electrochemical reactions. They can directly convert the chemical energy of fuel (hydrogen) and oxidant (oxygen or air) into electrical energy. Due to their environmental friendliness and high utilization rate, they are widely used and researched. Bipolar plates are important multifunctional components in PEMFCs. They provide channels for the flow of reactant gases and uniformly disperse active gases in the active region, isolate cathode and anode reactants, collect electrons generated by the electrochemical reaction and conduct output current, support the membrane electrode assembly, and remove heat and water produced by the reaction from the fuel cell system. For safe operation of fuel cells, bipolar plates require high mechanical strength and excellent corrosion resistance, conductivity, and hydrophobicity. Bipolar plates account for approximately 60-80% of the weight and 30-40% of the cost of the fuel cell stack. Developing low-cost, high-performance bipolar plates with high corrosion resistance and conductivity is one of the key challenges for the large-scale application of PEMFCs.

[0003] Among metal bipolar plates, stainless steel is an ideal material due to its low cost, wide availability, and ease of processing. Although stainless steel bipolar plates significantly reduce the volume and cost of the stack, they are subject to varying degrees of corrosion and dissolution when operating in the acidic environment of PEMFCs (pH 2–3, 80°C), leading to increased interfacial contact resistance, reduced conductivity, and even shortened service life.

[0004] To protect the structural integrity and service life of bipolar plates and improve the stability of PEMFCs, it is necessary to develop anti-corrosion and conductive coatings for bipolar plate surfaces. Currently, bipolar plate coatings include graphite coatings, metal coatings, metal nitride coatings, metal carbide coatings, metal oxide coatings, polymer coatings, and composite coatings. These coatings face challenges such as uneven dispersion of nanofillers, complex preparation processes, operational difficulties, environmental issues, and high costs.

[0005] Overall, issues such as corrosion resistance and cost-effectiveness of PEMFC stainless steel bipolar plates urgently need to be addressed. Summary of the Invention

[0006] The purpose of this invention is to provide a corrosion-resistant, highly conductive stainless steel bipolar plate semiconductor film, its preparation method, and its applications. This invention utilizes stainless steel of a specific composition and adjusts the electrochemical passivation process conditions to prepare a low-cost semiconductor film with high corrosion resistance and high conductivity on the surface of a PEMFC stainless steel bipolar plate. The preparation process is simple and can replace the complex and costly PEMFC battery bipolar plate coating.

[0007] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is: a method for preparing a corrosion-resistant, highly conductive stainless steel bipolar plate semiconductor film, comprising the following steps: A stainless steel bipolar plate is immersed in a passivation solution and electrochemically passivated under the conditions of a passivation potential of 1.1–1.3 V, a passivation temperature of 40–60 °C, and a passivation time of 0.5–1 h to obtain the corrosion-resistant and highly conductive stainless steel bipolar plate semiconductor film; the Cr content in the stainless steel bipolar plate is 16–20 wt%, and the total content of Cr and Fe is not less than 87.2 wt%.

[0008] Preferably, the stainless steel bipolar plate further includes a pretreatment step of cleaning and polishing before electrochemical passivation.

[0009] More preferably, the polishing is performed until the surface roughness of the stainless steel bipolar plate is 80-500 nm.

[0010] Preferably, the passivation potential is 1.3V.

[0011] Preferably, the passivation temperature is 60°C.

[0012] Preferably, the passivation time is 1 hour.

[0013] Preferably, the passivation solution is a sulfuric acid or nitric acid solution with a mass fraction of 5-20%.

[0014] The second technical solution of the present invention provides a corrosion-resistant, high-conductivity stainless steel bipolar semiconductor film prepared according to the above-mentioned method for preparing a corrosion-resistant, high-conductivity stainless steel bipolar semiconductor film.

[0015] The corrosion-resistant and highly conductive stainless steel bipolar semiconductor film prepared by this invention has a thickness of 2.0–5.0 nm. Its inner layer is rich in Cr₂O₃, and its outer layer is rich in Fe oxides. The Cr₂O₃ content is 32.2–38.7%, the Fe oxide content is 30.9–40.2%, and the Fe content is 16.6–24.9%, achieving a synergistic improvement in corrosion resistance and conductivity. The resulting semiconductor film has a contact angle of not less than 110°, excellent hydrophobicity, and a surface contact resistance not exceeding 2 mΩ·cm. 2It has good electrical conductivity, and the corrosion current density under operating conditions does not exceed 1 μA / cm. 2 The self-corrosion potential in a simulated PEMFC cathode service environment can reach 180mV. Ag / AgCl The above exhibits good corrosion resistance.

[0016] The third technical solution of the present invention provides an application of the above-mentioned corrosion-resistant and highly conductive stainless steel bipolar plate semiconductor membrane in the preparation of stainless steel bipolar plates for proton exchange membrane fuel cells.

[0017] The fourth technical solution of the present invention provides an application of the above-mentioned corrosion-resistant and highly conductive stainless steel bipolar semiconductor membrane in the preparation of proton exchange membrane fuel cells.

[0018] The beneficial technical effects of the present invention are as follows: The corrosion-resistant and highly conductive stainless steel bipolar plate semiconductor film provided by this invention can be used as a semiconductor film for PEMFC stainless steel bipolar plates, and its preparation process is simple.

[0019] The corrosion-resistant, high-conductivity stainless steel bipolar semiconductor film provided by this invention has a corrosion current density of ≤1μA / cm² under operating conditions. 2 Contact resistance ≤ 2mΩ·cm 2 It has a contact angle ≥110° and good corrosion resistance, electrical conductivity and hydrophobicity.

[0020] The corrosion-resistant and highly conductive stainless steel bipolar semiconductor film preparation process provided by this invention uses simple and low-cost equipment, overcoming the problems of complex and high-cost existing processes for preparing PEMFC stainless steel bipolar semiconductor films. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The diagram shows the cyclic potentiodynamic polarization curves of Comparative Example 1 and Example 18 under a simulated PEMFC working environment.

[0023] Figure 2 The images shown are a cross-sectional TEM annular dark field image (a) and a Fourier transform image (b) of the semiconductor film layer of the stainless steel bipolar plate obtained in Example 18.

[0024] Figure 3 This is a schematic diagram of the structure of a semiconductor film and a stainless steel bipolar plate substrate.

[0025] Figure 4 The semiconductor film Cr 2p prepared in Example 18 3 / 2 and Fe 2p 3 / 2 XPS fitting results (a) and atomic ratios of Cr and Fe elements under XPS depth analysis (b).

[0026] Figure 5 MS curves (a) and carrier concentration bar graphs (b) of the stainless steel bipolar plates finally obtained in Example 18 and Comparative Example 1 under simulated PEMFC cathode service environment.

[0027] Figure 6 This is a schematic diagram of the water contact angle of the stainless steel bipolar plates obtained in Comparative Example 1 and Example 18.

[0028] Figure 7 The bar chart shows the contact resistance of the stainless steel bipolar plates obtained in Example 18 and Comparative Examples 1-7. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0030] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0031] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0032] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] In this invention, room temperature refers to a temperature of 20±10℃.

[0035] In the embodiments and comparative examples of this invention, "%" refers to mass percentage. Examples 1-18 Preparation of stainless steel bipolar plate semiconductor film: S1. Pretreatment: First, clean the ferritic stainless steel bipolar plate (C 0.02%, Si 0.08%, Cr 18%, Mn 0.3%, Ni 1.9%, Cu 0.3%, Mo 2.5%, Nb 0.1%, Ti 0.2%, with the balance being Fe and impurities with a total content not exceeding 0.35%) with a specification of 10mm×10mm×3mm to remove surface foreign matter. Then, use 60-800 grit sandpaper to polish off the oxide layer, controlling the surface roughness of the stainless steel bipolar plate to be within the range of 80-500nm after polishing. Clean and degrease, and blow dry.

[0036] S2. Electrochemical passivation: The pretreated stainless steel bipolar plate is immersed in an electrochemical cell containing a passivation solution (10% nitric acid solution by mass) and electrochemical passivation is performed at a specific passivation potential, passivation temperature and passivation time.

[0037] S3. Post-processing: After electrochemical passivation, the stainless steel bipolar plate is removed, excess passivation solution is cleaned off the surface, and it is left to dry in a drying oven to obtain a stainless steel bipolar plate semiconductor film.

[0038] The specific passivation potential, passivation temperature and passivation time in step S2 of Examples 1 to 18 are shown in Table 1.

[0039] Table 1 The corrosion resistance of the stainless steel bipolar plates containing semiconductor films prepared in Examples 1-18 was tested using a conventional three-electrode system. The self-corrosion potential of each semiconductor film was tested under simulated acidic working environment of a PEMFC cathode (80°C, pH=3 sulfuric acid solution) at operating conditions (0.4–0.6V). Ag / AgCl The corrosion current density of each semiconductor film was tested to see if it was less than 1 μA / cm. 2 The results are shown in Table 2.

[0040] Table 2 Table 2 shows that the corrosion current densities under operating conditions in Examples 1–18 all meet the 2025 standards of the U.S. Department of Energy (cathodic corrosion current density <1 μA / cm). 2 Example 18 has the highest self-corrosion voltage and the lowest operating corrosion current density.

[0041] Example 19 Compared with Example 18, the stainless steel bipolar plate used was made of austenitic stainless steel (C 0.08%, Cr 18%, Ni 10%, Mn 0.5%, Si 0.5%, with the remainder being Fe and impurities with a total content not exceeding 0.35%), and other conditions were the same as in Example 18.

[0042] Example 20 Compared with Example 18, the stainless steel bipolar plate used was precipitation hardening stainless steel (C 0.06%, Cr 16%, Ni 4%, Cu 3.5%, Nb 0.2%, the remainder being Fe and impurities with a total content not exceeding 0.35%), and other conditions were the same as in Example 18.

[0043] Example 21 Compared to Example 18, the stainless steel bipolar plate used was made of duplex stainless steel (C 0.03%, Cr 22%, Ni 5%, Mo 3%, N 0.2%, with the remainder being Fe and impurities with a total content not exceeding 0.35%), and other conditions were the same as in Example 18.

[0044] Example 22 Compared to Example 18, the passivation solution used was a 10% sulfuric acid solution, and other conditions were the same as in Example 18.

[0045] Comparative Example 1 Example 18 is an unpassivated stainless steel bipolar plate.

[0046] Comparative Example 2 Compared to Example 18, the passivation voltage was 0.8V, and all other conditions were the same.

[0047] Comparative Example 3 Compared to Example 18, the passivation voltage was 1.8V, and all other conditions were the same.

[0048] Comparative Example 4 Compared to Example 18, the passivation temperature was 25°C, and all other conditions were the same.

[0049] Comparative Example 5 Compared to Example 18, the passivation temperature was 85°C, and all other conditions were the same.

[0050] Comparative Example 6 Compared with Example 18, the passivation time was 0.005 h, and other conditions were the same.

[0051] Comparative Example 7 Compared with Example 18, the passivation time was 2.5 hours, and other conditions were the same.

[0052] The corrosion resistance of the stainless steel bipolar plates obtained in Examples 19-22 and Comparative Examples 1-7 was tested using the same method as in Examples 1-18. The test results are shown in Table 3.

[0053] Table 3 Table 3 shows that the semiconductor films obtained by electrochemical passivation using the method provided in this invention on various types of stainless steel exhibit excellent corrosion resistance. However, outside the parameter conditions specified in this invention, the obtained semiconductor films do not provide good corrosion resistance.

[0054] At room temperature, the water contact angle of the stainless steel bipolar plate surface obtained in Example 18 and Comparative Examples 1-7 was measured using a contact angle meter with a 5 μL water droplet. The average value was obtained from at least three parallel positions. The results are shown in Table 4.

[0055] Referring to standard GB / T 20042.6-2011, the contact resistance of the stainless steel bipolar plates finally obtained in Example 18 and Comparative Examples 1-7 was tested, and the material resistance was recorded at 150 N / cm. 2 The contact resistance values ​​were measured, and the test results are shown in Table 4.

[0056] Table 4 Table 4 shows that the electrochemical passivation conditions specified in this invention can yield semiconductor films with better hydrophobicity.

[0057] The thickness of the semiconductor films prepared in each embodiment and comparative example, as well as the content of Cr2O3, Fe oxides, and Fe in the semiconductor films, were statistically analyzed, and the results are shown in Table 5.

[0058] Table 5 Figure 1 The diagram shows the cyclic potentiodynamic polarization curves of Comparative Example 1 and Example 18 under a simulated PEMFC working environment.

[0059] Depend on Figure 1 It is evident that after preparing a semiconductor film on the surface, the self-corrosion potential of the stainless steel bipolar plate increases, the corrosion current density at the same potential decreases, and the corrosion resistance is significantly improved. Therefore, this invention, by rationally adjusting the electrochemical passivation preparation method of the PEMFC stainless steel bipolar plate, can optimize the corrosion resistance of the stainless steel bipolar plate.

[0060] Figure 2 The images shown are a cross-sectional TEM annular dark field image (a) and a Fourier transform image (b) of the semiconductor film layer of the stainless steel bipolar plate obtained in Example 18.

[0061] Figure 2 The results show that the semiconductor film is continuously and uniformly distributed above the stainless steel substrate, with a thickness of approximately 2–3 nm. Surface scan analysis of the semiconductor film composition reveals that Cr is enriched in the central region, while Fe is uniformly distributed throughout the entire thickness of the film. The Cr element exhibits a stronger signal and binds tightly with O, forming a crystalline semiconductor film dominated by Cr₂O₃. Figure 3 This is a schematic diagram of the structure of a semiconductor film and a stainless steel bipolar plate substrate.

[0062] The semiconductor film Cr 2p prepared in Example 18 3 / 2 and Fe 2p 3 / 2 The XPS fitting results are shown in Figure 4 (a) The elemental valence states and contents of the semiconductor film prepared in Example 18 were collected using XPS (XPS depth profiling, 15 etching passes, approximately 0.5 nm each). The variation patterns of metal element valence states and contents in different thickness regions of the semiconductor film were analyzed. The results are shown in Figure 18. Figure 4 (b)

[0063] Figure 4 The data shows that Cr 2p 3 / 2 Fine spectra are divided into Cr 0 (Metallic state) and Three characteristic peaks were observed. Cr₂O₃ is the main form of Cr in the semiconductor film, with a content of approximately 32.2%–38.7%. A peak appears at a film thickness of approximately 2 nm, indicating that the Cr content is slightly higher in the middle region of the film, further proving that Cr₂O₃ is the dominant substance constituting the inner semiconductor film. Fe 2p 3 / 2 Fine spectrum divided into Fe 0 (Metallic state) , and Four characteristic peaks, among which Metallic Fe is the main form in which Fe exists. 0 The signal is enhanced as the depth of the semiconductor film increases.

[0064] Figure 5 MS curves (a) and carrier concentration bar graphs (b) of the stainless steel bipolar plates finally obtained in Example 18 and Comparative Example 1 under simulated PEMFC cathode service environment.

[0065] Figure 5 As shown in Figure (a), Comparative Example 1 (bare sample) and Example 18 mainly exhibit n-type semiconductor characteristics. Example 18 also shows certain p-type semiconductor characteristics, which is related to the high content of Cr(OH)3 (exhibiting p-type semiconductor characteristics) in the outer layer of the semiconductor film, which can effectively inhibit anions (such as F) in the solution. -The intrusion of n-type semiconductors improves the corrosion resistance of stainless steel in cathode service environments. The characteristics of n-type semiconductors correspond to the inner layer of semiconductor films, mainly related to the film... The properties exhibited in the n-type semiconductor are related to the doped metallic Fe.

[0066] Figure 5 As shown in (b), N in Example 18 D The decrease in the carrier concentration value compared to the bare sample indicates that the semiconductor film prepared by the present invention has fewer overall defects and higher density, which means its protective performance is improved, further enhancing the corrosion resistance of stainless steel in the cathode service environment.

[0067] Furthermore, in practical applications of fuel cells, the good hydrophobicity of the bipolar plates is crucial, directly affecting fuel cell performance, efficiency, and lifespan. Hydrophobic surfaces prevent liquid water from spreading and remaining, causing it to tend to form easily rolling droplets that are quickly carried out of the flow channel by the reactant gas flow. This ensures that the reactant gas can reach the catalyst reaction sites unimpeded, avoiding insufficient reactant supply due to "flooding." Table 4 shows that the contact angle of Example 18 (111.2°) is greater than that of Comparative Examples 1–7, exhibiting good hydrophobicity, which facilitates liquid flow and gas reaction, and can improve the service durability of the stainless steel bipolar plates. Figure 6 This is a schematic diagram of the water contact angle of the stainless steel bipolar plates obtained in Comparative Example 1 and Example 18.

[0068] The semiconductor film prepared by this invention exhibits a crystalline crystal structure and its conductivity is higher than that of traditional amorphous passivation films. In the semiconductor film... (30.9–40.2%), exhibiting good electronic conductivity, and the overall doping with a high content of metallic Fe (16.6–24.9%) further enhances the electronic conductivity of the semiconductor film. Lower contact resistance means more chemical energy is converted into electrical energy output, increasing the battery's voltage and power density, and resulting in better conductivity. Table 4 shows that the contact resistance of Example 18 is lower than that of Comparative Examples 1–7, and meets the US Department of Energy's 2025 standard (contact resistance <20 mΩ·cm). 2 ). Figure 7 This is a bar chart showing the contact resistance. This specific gradient composite structure enables the semiconductor film to simultaneously achieve good corrosion resistance and conductivity.

[0069] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a corrosion-resistant, highly conductive stainless steel bipolar semiconductor film, characterized in that, Includes the following steps: A stainless steel bipolar plate is immersed in a passivation solution and electrochemically passivated under the conditions of a passivation potential of 1.1–1.3 V, a passivation temperature of 40–60 °C, and a passivation time of 0.5–1 h to obtain the corrosion-resistant and highly conductive stainless steel bipolar plate semiconductor film; the Cr content in the stainless steel bipolar plate is 16–20 wt%, and the total content of Cr and Fe is not less than 87.2 wt%.

2. The method for preparing the corrosion-resistant, high-conductivity stainless steel bipolar semiconductor film according to claim 1, characterized in that, The stainless steel bipolar plate also includes a pretreatment step of cleaning and polishing before electrochemical passivation.

3. The method for preparing the corrosion-resistant, highly conductive stainless steel bipolar semiconductor film according to claim 2, characterized in that, The grinding process involves grinding the stainless steel bipolar plate until the surface roughness is 80–500 nm.

4. The method for preparing the corrosion-resistant, highly conductive stainless steel bipolar semiconductor film according to claim 1, characterized in that, The passivation potential is 1.3V.

5. The method for preparing the corrosion-resistant, high-conductivity stainless steel bipolar semiconductor film according to claim 1, characterized in that, The passivation temperature is 60°C.

6. The method for preparing the corrosion-resistant, highly conductive stainless steel bipolar semiconductor film according to claim 1, characterized in that, The passivation time is 1 hour.

7. The method for preparing the corrosion-resistant, highly conductive stainless steel bipolar semiconductor film according to claim 1, characterized in that, The passivation solution is a sulfuric acid or nitric acid solution with a mass fraction of 5-20%.

8. A corrosion-resistant, high-conductivity stainless steel bipolar semiconductor film prepared by the method of preparing the corrosion-resistant, high-conductivity stainless steel bipolar semiconductor film according to any one of claims 1 to 7.

9. The application of the corrosion-resistant, high-conductivity stainless steel bipolar semiconductor membrane of claim 8 in the preparation of stainless steel bipolar plates for proton exchange membrane fuel cells.

10. The application of the corrosion-resistant, high-conductivity stainless steel bipolar semiconductor membrane of claim 8 in the preparation of a proton exchange membrane fuel cell.

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