Carbon-based coating for fuel cell metal bipolar plates and method of making

Abstract

The application discloses a carbon-based coating of a fuel cell metal bipolar plate and a preparation method thereof. The carbon-based structure coating of the metal bipolar plate comprises, from top to bottom, a conductive functional amorphous carbon layer, a compact amorphous carbon corrosion barrier layer and a flexible metal Ti transition layer. The flexible metal Ti transition layer is prepared by a magnetron sputtering process, the sputtering target material is pure metal Ti, and the thickness of the flexible metal Ti transition layer is 100 nm. The carbon material is used as the main body of the coating, so that the preparation cost of the protective coating can be effectively reduced. The amorphous carbon coating prepared by the magnetic filtering cathode vacuum arc technology and the cathode vacuum arc technology can effectively shorten the deposition time and improve the production efficiency. After the prepared carbon-based protective coating is subjected to constant potential corrosion at 0.6 V for 7200 min, the surface morphology of the coating does not change, and the contact resistance of the coating still meets the use standard.

Description

Technical Field

[0001] This invention relates to the field of fuel cell metal bipolar plate technology, and more particularly to a carbon-based coating for fuel cell metal bipolar plates and its preparation method. Background Technology

[0002] Bipolar plates, as the core component of proton exchange membrane fuel cells (PEMFCs), primarily function to separate reactants (H2 and O2), collect current, support electrodes, and connect individual cells in series. While traditional graphite bipolar plates maintain good conductivity and resist corrosion in the harsh internal environment of PEMFCs, their poor machinability actually increases manufacturing costs. In contrast, stainless steel offers higher strength, is easier to process and form, has lower permeability, and is less expensive, making it a preferred material for fuel cell stacks. However, in the acidic, high-temperature operating environment of fuel cells, while the passivation film formed on the stainless steel surface can resist corrosion ions, it increases the contact resistance between the stainless steel and the gas diffusion layer. Furthermore, metal ions deposited from stainless steel can contaminate the catalyst, all of which reduce fuel cell efficiency and lifespan.

[0003] Currently, to address the problems existing in stainless steel bipolar plates, major enterprises and universities have proposed solutions such as conductive and corrosion-resistant protective coatings. These coatings mainly include noble metal coatings, nitride coatings, carbide coatings, and inorganic non-metallic carbon coatings. However, current modified coating solutions for metal bipolar plates still suffer from problems such as coating peeling during long-term use, increased coating contact resistance, and high coating preparation costs. Therefore, this patent proposes a low-cost method for preparing a carbon-based composite coating for fuel cell metal bipolar plates, primarily composed of amorphous carbon coatings.

[0004] Amorphous carbon materials possess excellent electrical conductivity and strong chemical stability, meeting the technical requirements for conductive and corrosion-resistant coatings in metal bipolar plates, making them one of the preferred materials for protective coatings in fuel cell metal bipolar plates. Currently, commonly used amorphous carbon coating preparation technologies primarily utilize magnetron sputtering based on PVD processes and cathode arc evaporation. Magnetron sputtering has relatively low deposition efficiency and struggles to guarantee the absence of numerous pore defects in the prepared film. Cathode arc evaporation, on the other hand, offers fast deposition rates and dense film structures, but inevitably introduces large carbon particles that penetrate the amorphous carbon coating. The presence of these large carbon particles reduces the longitudinal resistance of the coating, and when in contact with the gas diffusion layer, the conductive carbon particles embedded in the gas diffusion layer also increase the contact area between the metal bipolar plate and the gas diffusion layer, maintaining a low contact resistance. While the presence of carbon particles in amorphous carbon coatings prepared by cathode arc evaporation is advantageous in reducing contact resistance, the presence of large carbon particles inevitably becomes a channel for corrosive solutions during long-term testing under simulated fuel cell operating conditions, leading to coating perforation and reduced corrosion resistance. Summary of the Invention

[0005] The technical problem solved by this invention is that the deposition efficiency of magnetron sputtering for preparing amorphous carbon in related technologies is relatively low, and it is difficult to ensure that the prepared film will not have many pore defects. While amorphous carbon coatings prepared by cathodic arc evaporation technology have the characteristics of fast deposition rate and dense film structure, large carbon particles inevitably appear penetrating the amorphous carbon coating. The presence of large carbon particles reduces the longitudinal resistance of the coating, and the conductive carbon particles embedded in the gas diffusion layer also increase the contact area between the metal bipolar plate and the gas diffusion layer, thus maintaining a low contact resistance between the coating and the gas diffusion layer. In terms of reducing contact resistance, the carbon particles present in the amorphous carbon coating prepared by cathodic arc evaporation technology are advantageous. However, in long-term testing under simulated fuel cell operating conditions, the presence of large carbon particles inevitably becomes a channel for corrosive solutions, leading to coating perforation and reduced corrosion resistance.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a carbon-based coating for a fuel cell metal bipolar plate, comprising a conductive amorphous carbon layer, a dense amorphous carbon corrosion barrier layer, and a flexible metal Ti transition layer, which are arranged from top to bottom.

[0007] As a preferred embodiment of the carbon-based coating for the metal bipolar plate of the fuel cell described in this invention, the flexible metal Ti transition layer is prepared by magnetron sputtering, the sputtering target is pure metal Ti, and the thickness of the flexible metal Ti transition layer is 100 nm.

[0008] As a preferred embodiment of the carbon-based coating for the metal bipolar plate of the fuel cell described in this invention, the dense amorphous carbon corrosion barrier layer is prepared by a filtered cathode vacuum arc technology, the target material is pure graphite, and the thickness of the dense amorphous carbon corrosion barrier layer is 200 nm.

[0009] As a preferred embodiment of the carbon-based coating for the metal bipolar plate of the fuel cell described in this invention, the conductive amorphous carbon layer is prepared by cathode arc evaporation technology, the target material is pure graphite, and the thickness of the conductive amorphous carbon layer is 100 nm.

[0010] As a preferred embodiment of the carbon-based coating for the metal bipolar plate of the fuel cell described in this invention, the preparation conditions of the magnetron sputtering process include: an output power of 2 kW for the DC magnetron power supply, an air pressure of 0.5 Pa, and a bias voltage of -100 V.

[0011] As a preferred embodiment of the carbon-based coating for the metal bipolar plate of the fuel cell described in this invention, the preparation conditions of the filtered cathode vacuum arc technology include: a magnetic filtering arc source current of 100A, a bias voltage of -2000V, a back vacuum of 5MPa, and no gas deposition.

[0012] As a preferred embodiment of the carbon-based coating for the metal bipolar plate of the fuel cell described in this invention, the preparation conditions of the cathode arc evaporation technology include: a current of 100A, a bias voltage of -300V to -400V, an argon atmosphere, and a gas pressure of 0.2Pa.

[0013] As a preferred embodiment of the method for preparing carbon-based coatings for metal bipolar plates of fuel cells according to the present invention, the step 1 is: substrate pretreatment;

[0014] Step 2: First, a flexible metal Ti transition layer is prepared on the upper surface of the metal bipolar plate substrate obtained in Step 1. Then, a dense amorphous carbon corrosion barrier layer is prepared on the upper surface of the flexible metal Ti transition layer. Finally, a conductive amorphous carbon layer is prepared on the upper surface of the dense amorphous carbon corrosion barrier layer to obtain the carbon-based coating of the fuel cell metal bipolar plate.

[0015] The preparation of the conductive amorphous carbon layer on a dense amorphous carbon corrosion barrier layer includes: under the conditions of a cathode arc evaporation arc source with a current of 100A, bias voltages of -300V / -350V / -400V, an argon atmosphere, and a pressure of 0.2Pa, a conductive amorphous carbon coating with carbon particles on its surface is prepared, thus realizing the preparation of a carbon-based composite coating for a metal bipolar plate. The conductive amorphous carbon layer with carbon particles prepared under the three bias voltage conditions of -300V / -350V / -400V can meet the requirement of a contact resistance of less than 10mΩ·cm under a pressure of 1.4MPa. 2The requirements are as follows: A flexible metallic Ti transition layer is used to improve the adhesion of the coating; a dense amorphous carbon corrosion barrier layer is used to block the erosion of corrosion ions by virtue of the dense structure of the coating and its own corrosion resistance; a conductive functional layer uses graphite carbon particles embedded in the coating to improve the conductivity of the coating and reduce the contact resistance.

[0016] First, a flexible metallic Ti transition layer is prepared on the surface of a 304 stainless steel substrate using magnetron sputtering. Then, a dense amorphous carbon corrosion barrier layer is prepared on the metallic Ti transition layer using magnetically filtered cathode vacuum arc technology under the conditions of 100A arc source current, 5mPa background vacuum, and -2000V bias. Finally, a conductive amorphous carbon layer is prepared on the dense amorphous carbon corrosion barrier layer using cathode vacuum arc technology under the conditions of 100A arc source current, 0.2Pa Ar atmosphere, and -300V / -350V / -400V bias. This provides a low-cost method for preparing carbon-based coatings for fuel cell metal bipolar plates.

[0017] The beneficial effects of this invention are as follows: using carbon materials as the coating body can effectively reduce the preparation cost of the protective coating; and the amorphous carbon coating prepared by magnetic filtering cathode vacuum arc technology and cathode vacuum arc technology can effectively shorten the deposition time and improve production efficiency; secondly, after the prepared carbon-based protective coating is etched at a constant potential of 0.6V for 7200 minutes, the coating does not show any surface morphology change, and the contact resistance of the coating still meets the usage standards. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a carbon-based composite coating for a metal bipolar plate with a carbon particle conductive layer, which is used in the preparation method of the carbon-based coating for a fuel cell metal bipolar plate.

[0019] Figure 2 This is a schematic diagram of the contact resistance of a carbon-based composite structure coating with different conductive functions on the surface of a carbon-based coating for a fuel cell metal bipolar plate after corrosion.

[0020] Figure 3 This is a potentiodynamic polarization curve of the carbon-based coating and preparation method for a fuel cell metal bipolar plate.

[0021] Figure 4 a is a schematic diagram of the surface morphology of the carbon particle conductive functional layer in the carbon-based coating and preparation method of the metal bipolar plate of the fuel cell. Figure 4 b is a schematic diagram of the cross-sectional morphology of the single-layer carbon particle conductive functional layer in the carbon-based coating and preparation method of the fuel cell metal bipolar plate. Figure 4 c is a schematic diagram of the surface morphology of the single-layer dense amorphous carbon corrosion barrier layer in the carbon-based coating and preparation method of the metal bipolar plate of the fuel cell. Figure 4d is a schematic diagram of the cross-sectional morphology of a single-layer dense amorphous carbon corrosion barrier layer in the carbon-based coating and preparation method of fuel cell metal bipolar plates. Detailed Implementation

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] Example 1

[0024] Reference Figure 1 As one embodiment of the present invention, it includes:

[0025] 1. Matrix pretreatment

[0026] (1) Mechanical grinding and polishing of 304 stainless steel substrate to achieve mirror effect.

[0027] (2) Solvent cleaning treatment was performed on the 304 stainless steel substrate with mirror effect. First, it was ultrasonically cleaned for 10 minutes with metal cleaner and deionized water, then ultrasonically cleaned for 10 minutes with alcohol solution with volume fraction >99.8%, and then ultrasonically cleaned for 3 minutes with ultrapure water.

[0028] (3) Glow Glow Cleaning Treatment. The substrate was cleaned for 30 minutes using an Ar gas ion source to remove stains from the substrate surface. The furnace pressure was 1.5 Pa; the substrate bias voltage was -900 V; and the duty cycle was 70%.

[0029] 2. A composite process was used to prepare a carbon-based composite structure coating for metal bipolar plates.

[0030] (1) First, a Ti target with a purity of 99.9% was sputtered onto the pretreated substrate using magnetron sputtering technology. The magnetron power supply was 2KW, the argon atmosphere pressure was 0.5pa, and the bias voltage was -100V to prepare a Ti transition coating. The deposition time was 8min, and the thickness of the Ti coating was controlled at 100nm.

[0031] (2) Then, magnetic filter cathode arc evaporation technology is used, with graphite target material of 99.9% purity, arc source current of 100A, back vacuum of 5mPa, bias voltage of -2000V, to build a dense amorphous carbon corrosion barrier layer on the surface of metal Ti layer, deposition time of 30min, and control of the thickness of dense amorphous carbon corrosion barrier coating at 200nm.

[0032] (3) Finally, the cathode arc evaporation technology was used, with a graphite target of 99.9% purity, an arc source current of 100A, and a deposition time of 3min in an Ar atmosphere of 0.2Pa. The thickness of the conductive amorphous carbon coating was controlled at 100nm, and the amorphous carbon coating with excellent conductivity was deposited at a bias voltage of -300V to obtain the product.

[0033] Figure 1 This is a schematic diagram of a carbon-based composite coating for a metal bipolar plate with a conductive carbon particle layer. The composite structure consists of a Ti metal transition layer, a dense amorphous carbon corrosion barrier layer, and an amorphous carbon conductive surface layer. The Ti metal is primarily used to balance the difference in thermal expansion coefficients between the 304 stainless steel substrate and the amorphous carbon layer, thereby improving the adhesion of the amorphous carbon coating. The dense amorphous carbon corrosion barrier layer utilizes the chemical stability of amorphous carbon materials and magnetic filtering cathodic arc evaporation technology to prepare the dense amorphous carbon coating, protecting the stainless steel substrate from corrosion ions. The amorphous carbon conductive surface layer uses conductive carbon particles penetrating the coating to reduce the surface contact resistance between the coating and the gas diffusion layer. However, cracks or small pores inevitably exist around the carbon particles, allowing corrosive solutions to penetrate the surface conductive layer.

[0034] Example 2

[0035] 1. Matrix pretreatment

[0036] (1) Mechanical grinding and polishing of 304 stainless steel substrate to achieve mirror effect.

[0037] (2) Solvent cleaning treatment of the 304 stainless steel substrate with mirror effect. First, use metal cleaner + deionized water for ultrasonic cleaning for 10 min, then use alcohol solution with volume fraction >99.8% for ultrasonic cleaning for 10 min, take it out and then use ultrapure water for ultrasonic cleaning for 3 min.

[0038] (3) Glow Glow Cleaning Treatment. The substrate was cleaned for 30 minutes using an Ar gas ion source at a furnace pressure of 1.5 Pa; the substrate bias voltage was -900 V and the duty cycle was 70%.

[0039] 2. A composite process was used to prepare a carbon-based composite structure coating for metal bipolar plates.

[0040] (1) First, a Ti target with a purity of 99.9% was sputtered using magnetron sputtering technology. The magnetron power supply was 2KW, the argon atmosphere pressure was 0.5pa, and the bias voltage was -100V to prepare a Ti transition coating. The deposition time was 8min, and the thickness of the Ti coating was controlled at 100nm.

[0041] (2) Then, magnetic filter cathode arc evaporation technology is used, with graphite target material of 99.9% purity, arc source current of 100A, back vacuum of 5mPa, bias voltage of -2000V, to build a dense amorphous carbon corrosion barrier layer on the surface of metal Ti layer, deposition time of 30min, and control of the thickness of dense amorphous carbon corrosion barrier coating at 200nm.

[0042] (3) Finally, the cathode arc evaporation technology was used, with a graphite target of 99.9% purity, an arc source current of 100A, and a deposition time of 3min in an Ar atmosphere of 0.2Pa. The thickness of the conductive amorphous carbon coating was controlled at 100nm, and the amorphous carbon coating with excellent conductivity was deposited at a bias voltage of -350V to obtain the product.

[0043] Figure 2 The corrosion potential, corrosion current density, and contact resistance before corrosion of carbon-based composite coatings with different conductive surfaces in a solution of H₂SO₄ + 2ppmHF at 80℃, pH 3, were measured. The contact resistance after corrosion for 7200 min at a constant potential of 0.6V in a standard solution was also evaluated. Most importantly, the carbon-based composite coating not only met the corrosion current density standard for metal bipolar plate coatings proposed by the US DOE 2025, but also maintained the acceptable contact resistance after 7200 min of corrosion at a constant potential of 0.6V.

[0044] Example 3

[0045] 1. Matrix pretreatment

[0046] (1) Mechanical grinding and polishing of 304 stainless steel substrate to achieve mirror effect.

[0047] (2) Solvent cleaning treatment of the 304 stainless steel substrate with mirror effect. First, use metal cleaner + deionized water for ultrasonic cleaning for 10 min, then use alcohol solution with volume fraction >99.8% for ultrasonic cleaning for 10 min, take it out and then use ultrapure water for ultrasonic cleaning for 3 min.

[0048] (3) Glow Glow Cleaning Treatment. The substrate was cleaned for 30 minutes using an Ar gas ion source at a furnace pressure of 1.5 Pa; the substrate bias voltage was -900 V and the duty cycle was 70%.

[0049] 2. A composite process was used to prepare a carbon-based composite structure coating for metal bipolar plates.

[0050] (1) First, a Ti target with a purity of 99.9% was sputtered using magnetron sputtering technology. The magnetron power supply was 2KW, the argon atmosphere pressure was 0.5pa, and the bias voltage was -100V to prepare a Ti transition coating. The deposition time was 8min, and the thickness of the Ti coating was controlled at 100nm.

[0051] (2) Then, magnetic filter cathode arc evaporation technology is used, with graphite target material of 99.9% purity, arc source current of 100A, back vacuum of 5mPa, bias voltage of -2000V, to build a dense amorphous carbon corrosion barrier layer on the surface of metal Ti layer, deposition time of 30min, and control of the thickness of dense amorphous carbon corrosion barrier coating at 200nm.

[0052] (3) Finally, the cathode arc evaporation technology was used, with a graphite target of 99.9% purity, an arc source current of 100A, and a deposition time of 3min in an Ar atmosphere of 0.2Pa. The thickness of the conductive amorphous carbon coating was controlled at 100nm, and the amorphous carbon coating with excellent conductivity was deposited at a bias voltage of -400V to obtain the product.

[0053] Comparative Example 1

[0054] 1. Matrix pretreatment

[0055] (1) Mechanical grinding and polishing of 304 stainless steel substrate to achieve mirror effect.

[0056] (2) Solvent cleaning treatment of the 304 stainless steel substrate with mirror effect. First, use metal cleaner + deionized water for ultrasonic cleaning for 10 min, then use alcohol solution with volume fraction >99.8% for ultrasonic cleaning for 10 min, take it out and then use ultrapure water for ultrasonic cleaning for 3 min.

[0057] (3) Glow Glow Cleaning Treatment. The substrate was cleaned for 30 minutes using an Ar gas ion source at a furnace pressure of 1.5 Pa; the substrate bias voltage was -900 V and the duty cycle was 70%.

[0058] 2. A composite process was used to prepare a carbon-based composite structure coating for metal bipolar plates.

[0059] (1) First, a Ti target with a purity of 99.9% was sputtered using magnetron sputtering technology. The magnetron power supply was 2KW, the argon atmosphere pressure was 0.5pa, and the bias voltage was -100V to prepare a Ti transition coating. The deposition time was 8min, and the thickness of the Ti coating was controlled at 100nm.

[0060] (2) Then, using magnetic filter cathode arc evaporation technology, a graphite target with a purity of 99.9% is used, the arc source current is 100A, the back vacuum is 5mPa, the bias voltage is -2000V, a dense amorphous carbon corrosion barrier layer is constructed on the surface of the metal Ti layer, the deposition time is 30min, and the thickness of the dense amorphous carbon corrosion barrier coating is controlled at 200nm to obtain the product.

[0061] Comparative Example 2

[0062] 1. Matrix pretreatment

[0063] (1) Mechanical grinding and polishing of 304 stainless steel substrate to achieve mirror effect.

[0064] (2) Solvent cleaning treatment of the 304 stainless steel substrate with mirror effect. First, use metal cleaner + deionized water for ultrasonic cleaning for 10 min, then use alcohol solution with volume fraction >99.8% for ultrasonic cleaning for 10 min, take it out and then use ultrapure water for ultrasonic cleaning for 3 min.

[0065] (3) Glow Glow Cleaning Treatment. The substrate was cleaned for 30 minutes using an Ar gas ion source at a furnace pressure of 1.5 Pa; the substrate bias voltage was -900 V and the duty cycle was 70%.

[0066] 2. A composite process was used to prepare a carbon-based composite structure coating for metal bipolar plates.

[0067] (1) First, a Ti target with a purity of 99.9% was sputtered using magnetron sputtering technology. The magnetron power supply was 2KW, the argon atmosphere pressure was 0.5pa, and the bias voltage was -100V to prepare a Ti transition coating. The deposition time was 8min, and the thickness of the Ti coating was controlled at 100nm.

[0068] (2) Then, magnetic filtering cathode arc evaporation technology is used, with graphite target material of 99.9% purity, arc source current of 100A, back vacuum of 5mPa, bias voltage of -2000V, to build a dense amorphous carbon corrosion barrier layer on the surface of the metal Ti layer, with a deposition time of 30min, and the thickness of the dense amorphous carbon corrosion barrier coating is controlled at 200nm.

[0069] (3) Finally, the cathode arc evaporation technology was used, with a graphite target of 99.9% purity, an arc source current of 100A, and a deposition time of 3min in an Ar atmosphere of 0.2Pa. The thickness of the conductive amorphous carbon coating was controlled at 100nm, and the amorphous carbon coating with excellent conductivity was deposited at a bias voltage of -450V to obtain the product.

[0070] Comparative Example 3

[0071] 1. Matrix pretreatment

[0072] (1) Mechanical grinding and polishing of 304 stainless steel substrate to achieve mirror effect.

[0073] (2) Solvent cleaning treatment of the 304 stainless steel substrate with mirror effect. First, use metal cleaner + deionized water for ultrasonic cleaning for 10 min, then use alcohol solution with volume fraction >99.8% for ultrasonic cleaning for 10 min, take it out and then use ultrapure water for ultrasonic cleaning for 3 min.

[0074] (3) Glow Glow Cleaning Treatment. The substrate was cleaned for 30 minutes using an Ar gas ion source at a furnace pressure of 1.5 Pa; the substrate bias voltage was -900 V and the duty cycle was 70%.

[0075] 2. A composite process was used to prepare a carbon-based composite structure coating for metal bipolar plates.

[0076] (1) First, a Ti target with a purity of 99.9% was sputtered using magnetron sputtering technology. The magnetron power supply was 2KW, the argon atmosphere pressure was 0.5pa, and the bias voltage was -100V to prepare a Ti transition coating. The deposition time was 8min, and the thickness of the Ti coating was controlled at 100nm.

[0077] (2) Then, magnetic filter cathode arc evaporation technology is used, with graphite target material of 99.9% purity, arc source current of 100A, back vacuum of 5mPa, bias voltage of -2000V, to build a dense amorphous carbon corrosion barrier layer on the surface of metal Ti layer, deposition time of 30min, and control of the thickness of dense amorphous carbon corrosion barrier coating at 200nm.

[0078] (3) Finally, the cathode arc evaporation technology was used, with a graphite target of 99.9% purity, an arc source current of 100A, and a deposition time of 3min in an Ar atmosphere of 0.2Pa. The thickness of the conductive amorphous carbon coating was controlled at 100nm, and the amorphous carbon coating with excellent conductivity was deposited at a bias voltage of -250V to obtain the product.

[0079] Comparative Example 4

[0080] 1. Matrix pretreatment

[0081] (1) Mechanical grinding and polishing of 304 stainless steel substrate to achieve mirror effect.

[0082] (2) Solvent cleaning treatment of the 304 stainless steel substrate with mirror effect. First, use metal cleaner + deionized water for ultrasonic cleaning for 10 min, then use alcohol solution with volume fraction >99.8% for ultrasonic cleaning for 10 min, take it out and then use ultrapure water for ultrasonic cleaning for 3 min.

[0083] (3) Glow Glow Cleaning Treatment. The substrate was cleaned for 30 minutes using an Ar gas ion source at a furnace pressure of 1.5 Pa; the substrate bias voltage was -900 V and the duty cycle was 70%.

[0084] 2. A composite process was used to prepare a carbon-based composite structure coating for metal bipolar plates.

[0085] (1) First, a Ti target with a purity of 99.9% was sputtered using magnetron sputtering technology. The magnetron power supply was 2KW, the argon atmosphere pressure was 0.5pa, and the bias voltage was -100V to prepare a Ti transition coating. The deposition time was 8min, and the thickness of the Ti coating was controlled at 100nm.

[0086] (2) Then, magnetic filter cathode arc evaporation technology is used, with graphite target material of 99.9% purity, arc source current of 100A, back vacuum of 5mPa, bias voltage of -1500V, to build a dense amorphous carbon corrosion barrier layer on the surface of metal Ti layer, deposition time of 30min, and control of the thickness of dense amorphous carbon corrosion barrier coating at 200nm.

[0087] (3) Finally, the cathode arc evaporation technology was used, with a graphite target of 99.9% purity, an arc source current of 100A, and a deposition time of 3min in an Ar atmosphere of 0.2Pa. The thickness of the conductive amorphous carbon coating was controlled at 100nm, and the amorphous carbon coating with excellent conductivity was deposited at a bias voltage of -350V to obtain the product.

[0088] Comparative Example 5

[0089] 1. Matrix pretreatment

[0090] (1) Mechanical grinding and polishing of 304 stainless steel substrate to achieve mirror effect.

[0091] (2) Solvent cleaning treatment of the 304 stainless steel substrate with mirror effect. First, use metal cleaner + deionized water for ultrasonic cleaning for 10 min, then use alcohol solution with volume fraction >99.8% for ultrasonic cleaning for 10 min, take it out and then use ultrapure water for ultrasonic cleaning for 3 min.

[0092] (3) Glow Glow Cleaning Treatment. The substrate was cleaned for 30 minutes using an Ar gas ion source at a furnace pressure of 1.5 Pa; the substrate bias voltage was -900 V and the duty cycle was 70%.

[0093] 2. A composite process was used to prepare a carbon-based composite structure coating for metal bipolar plates.

[0094] (1) First, a Ti target with a purity of 99.9% was sputtered using magnetron sputtering technology. The magnetron power supply was 2KW, the argon atmosphere pressure was 0.5pa, and the bias voltage was -100V to prepare a Ti transition coating. The deposition time was 8min, and the thickness of the Ti coating was controlled at 100nm.

[0095] (2) Then, magnetic filter cathode arc evaporation technology is used, with graphite target material of 99.9% purity, arc source current of 100A, back vacuum of 5mPa, bias voltage of -2500V, to build a dense amorphous carbon corrosion barrier layer on the surface of metal Ti layer, deposition time of 30min, and control of the thickness of dense amorphous carbon corrosion barrier coating at 200nm.

[0096] (3) Finally, the cathode arc evaporation technology was used, with a graphite target of 99.9% purity, an arc source current of 100A, and a deposition time of 3min in an Ar atmosphere of 0.2Pa. The thickness of the conductive amorphous carbon coating was controlled at 100nm, and the amorphous carbon coating with excellent conductivity was deposited at a bias voltage of -350V to obtain the product.

[0097] Figure 2 The figures show the potentiodynamic polarization curves of carbon-based composite coatings with different conductive functional surfaces in the examples at 80°C, pH=3, and in a solution of H2SO4 + 2ppmHF. It can be seen that as the bias voltage for preparing the conductive functional surface increases, the corrosion current density of the coating tends to increase continuously. This is because with the increase of bias voltage, the ion backsputtering effect is enhanced, and the density of the conductive functional surface decreases. However, the corrosion current density of the carbon-based composite coating is still less than 1 μA / cm². 2 It still meets the 2025 standard for metal bipolar plate coating proposed by the US DOE.

[0098] Figure 3 The above are the potentiodynamic polarization curves of carbon-based composite coatings with different conductive surface layers and different corrosion-blocking layers in a solution of H2SO4 + 2ppm HF at 80℃, pH 3, and in a comparative example. It can be seen that the corrosion current density of the dense amorphous carbon corrosion-blocking coating prepared with a bias voltage of -2000V meets the DOE2025 standard, while the corrosion current density of the dense amorphous carbon corrosion-blocking layer sample prepared with a bias voltage of -1500V... 3 The proportion of hybrid carbon is higher and the corrosion current density is lower. However, due to the amplified bombardment effect, the density of the amorphous carbon corrosion barrier layer sample prepared by biasing at -2500V is reduced. The amorphous carbon corrosion barrier layer can no longer protect the substrate, and the increased corrosion current density no longer meets the DOE2025 standard.

[0099] Figure 4 a represents the surface morphology of the carbon particle conductive functional layer; Figure 4 b shows the cross-sectional morphology of the single-layer carbon particle conductive functional layer, where conductive carbon particles that penetrate the entire amorphous carbon coating can be clearly observed. Figure 4 c represents the surface morphology of a single-layer dense amorphous carbon corrosion barrier layer. It can be observed that the magnetic filter bend in the magnetic filter cathode arc evaporation process filters out most of the neutral carbon particles, and the coating surface is smooth and flat. Figure 4d represents the cross-sectional morphology of a single-layer dense amorphous carbon corrosion barrier layer, showing a glassy, ​​dense amorphous carbon corrosion barrier layer structure.

[0100] Table 1 shows the potentiodynamic polarization curves of the carbon-based composite coatings with different conductive functional surfaces in Examples 1-3 at 80°C, pH=3, and H2SO4+2ppm HF solution. It can be seen that as the bias voltage for preparing the conductive functional surface increases, the corrosion current density of the coating tends to increase continuously. This is because with the increase of bias voltage, the ion backsputtering effect is enhanced, and the density of the conductive functional surface decreases. However, the corrosion current density of the carbon-based composite coating is still less than 1 μA / cm². 2 It still meets the 2025 standard for metal bipolar plate coating proposed by the US DOE.

[0101] Table 1: Potentiodynamic polarization curves of carbon-based composite coatings with different conductive functions.

[0102]

[0103] The dense amorphous carbon corrosion barrier layers used in Examples 1-3 were all prepared using the same process (bias voltage -2000V; bias voltage adjustment is the most direct way to change the carbon structure of the coating). The variation in bias voltage adjustment of the corrosion barrier layer is shown in Comparative Examples 1-5, where bias voltages of -1500V and -2500V were compared. The difference between Examples 1-3 lies in the change in the bias voltage of the conductive amorphous carbon layer. In Examples 1-3, as the bias voltage changed from -300V to -400V, the carbon structure in the coating changed from sp... 3 Hybridization towards sp 2 Hybridization transformation (amorphous carbon coating is sp) 3 Hybridized carbon and sp 2 Hybrid carbon mixtures, based on the growth mechanism of amorphous carbon, will exhibit relaxation phenomena when carbon ion energy is too high, leading to sp in the coating. 3 Hybrid carbon structures will move towards sp 2 Hybridization transition) due to sp 3 Hybridized carbon has higher bond energies, making it more resistant to corrosion ions, but carbon's sp bond energy is lower. 3 The hybrid structure is not conductive, sp 3 Excessive content will improve the corrosion resistance of the coating, but will decrease its conductivity; conversely, it will increase the SP content. 2 The content of a certain substance will increase the conductivity of the coating but decrease its corrosion resistance.

[0104] Although the designed coating primarily relies on a dense amorphous carbon layer as a barrier against corrosive ions, variations in the structure of the conductive amorphous carbon surface layer can also affect the overall corrosion resistance of the coating. According to the potential kinetics results in Table 1, as the bias voltage for preparing the conductive amorphous carbon surface layer increases, the spt in the conductive surface layer...2 Increasing the proportion of hybrid carbon slightly increased the measured corrosion current density (a higher corrosion current density indicates the worst corrosion resistance of the coating; the standard given by the U.S. Department of Energy is less than 1 μA / cm). 2 Examples 1-3 all meet the requirements, but considering the contact resistance before and after corrosion, sp 2 The increased proportion of hybrid carbon significantly reduced the contact resistance, and both before and after corrosion, the contact resistance remained less than 10 mΩ·cm under a pressure of 1.4 MPa. 2 Therefore, based on the test results, Examples 1-3 meet the requirements. Under the condition of preparing the corrosion barrier layer at a bias voltage of -2000V, the preparation bias voltage of the conductive amorphous carbon layer can meet the usage requirements within the range of -300V to -400V.

[0105] Table 2 shows the corrosion potential, corrosion current density, and contact resistance before corrosion of carbon-based composite coatings with different conductive functional layers in Comparative Examples 1-5 at 80℃, pH=3, H2SO4+2ppm HF solution, and the contact resistance after corrosion for 7200 min at a potential of 0.6V in standard solution. It can be seen that the samples in the Comparative Examples without the added carbon particle conductive functional layer have a relatively high contact resistance, which does not meet the DOE 2025 requirement of a contact resistance less than 10 mΩ·cm. 2 The sample with a carbon particle conductive functional layer prepared under a bias of -450V had a contact resistance that did not meet the usage standards after 7200 minutes of etching with a standard solution due to the excessive porosity of the coating. The sample prepared under a bias of -250V... 3 The high proportion of hybrid carbon, although the corrosion current density decreases, results in a high contact resistance that no longer meets the usage requirements.

[0106] Table 2: Comparison of contact resistance of carbon-based composite coatings with different conductive functions.

[0107]

[0108] Comparative Examples 1-5 included control experiments with the absence of a conductive amorphous carbon layer, and with excessively high or low bias voltages used to prepare dense amorphous carbon corrosion barrier layers and conductive amorphous carbon layers, respectively. In Comparative Example 1, the preparation process of the dense amorphous carbon corrosion barrier layer in Examples 1-3 was kept unchanged, but no conductive amorphous carbon layer was added. Although the corrosion current density of the coating did not increase sharply, the increased contact resistance due to the absence of the conductive amorphous carbon layer did not meet the usage requirements. (The principle behind the reduced contact resistance of the conductive amorphous carbon layer is that, in addition to the excellent conductivity of the coating itself, the conductive graphite particles embedded within and penetrating the coating reduce the longitudinal resistance of the coating. In actual testing, under pressure, the graphite particles embedded in the gas diffusion layer increase the contact area between the coating and the gas diffusion layer. Therefore, the contact resistance is reduced after adding the conductive amorphous carbon layer.)

[0109] In Comparative Example 2, the same corrosion barrier layer fabrication process as in the Example was maintained, and the bias voltage for fabricating the conductive amorphous carbon layer was further increased. Although the increased bias voltage further increased the sp in the coating... 2 The proportion of hybrid carbon is increased, but the bombardment effect of higher ion energy on the coating is intensified, making the coating more porous. The contact area between the corrosion solution and the conductive amorphous carbon layer increases. After long-term constant potential testing, the contact resistance of the coating changes significantly and no longer meets the requirements (the oxygen dissolved in the corrosion solution combines with carbon to form compounds, which will cause the contact resistance to increase. Although the conductive amorphous carbon layer prepared in the bias range of -300V to -400V has large particles penetrating the coating, the rest of the coating still exhibits a dense glassy structure).

[0110] In Comparative Example 3, the fabrication process of the dense amorphous carbon corrosion barrier layer was kept unchanged, but the bias voltage for fabricating the conductive amorphous carbon layer was reduced, and the sp in the coating... 3 An increase in the proportion of hybrid carbon, after analyzing the potentiodynamic testing results, revealed a decrease in corrosion current density. However, due to the increased conductivity of the amorphous carbon layer, sp... 2 With the reduction of the proportion of hybrid carbon, the conductivity of the coating decreases, and the contact resistance no longer meets the requirements for use.

[0111] In Comparative Example 4, the bias voltage for preparing the dense amorphous carbon corrosion barrier layer was reduced to -1500V. The reason for the large negative bias voltage in the preparation of the corrosion barrier layer is that the corrosion barrier layer uses a magnetic filter cathode vacuum arc process. Because of the presence of this air filter bend, the distance between the target and the substrate is greater, requiring a larger bias voltage to maintain the energy of the carbon ions.

[0112] The conductive amorphous carbon layer was prepared using the process described in Example 2. As the bias voltage of the corrosion barrier layer decreased, the sp in the coating... 3 An increase in the proportion of hybrid carbon reduces the corrosion current density of the coating and increases its corrosion resistance, but the amount of sp in the corrosion barrier layer...2 If the proportion of hybrid carbon is reduced too much, the conductivity of the coating will decrease sharply, and the overall resistance of the composite coating will increase. Even if there is a conductive functional layer, the contact resistance of the coating will still increase, which will not meet the requirements for use.

[0113] In Comparative Example 5, the bias voltage for preparing the dense amorphous carbon corrosion barrier layer was increased to -2500V, and the conductive amorphous carbon layer was prepared using the process described in Example 2. With the increase of the bias voltage for preparing the corrosion barrier layer, although the sp in the coating increased... 2 The proportion of hybrid carbon is reduced, but under the bombardment of high-energy particles, the density of the corrosion barrier layer structure decreases. This results in the fact that although the contact resistance of the coating decreases, corrosion ions penetrate the corrosion barrier layer, the corrosion current density increases, and the corrosion resistance of the coating decreases, no longer meeting the requirements for use.

[0114] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A carbon-based coating for a fuel cell metal bipolar plate, characterized in that, include: The carbon-based structure coating of the metal bipolar plate consists of, from top to bottom, a conductive amorphous carbon layer, a dense amorphous carbon corrosion barrier layer, and a flexible metal Ti transition layer. The flexible metal Ti transition layer is prepared by magnetron sputtering, with pure metal Ti as the sputtering target and a thickness of 100 nm. The dense amorphous carbon corrosion barrier layer is prepared by filtered cathode vacuum arc technology, the target material is pure graphite, and the thickness of the dense amorphous carbon corrosion barrier layer is 200 nm. The conductive amorphous carbon layer is prepared by cathodic arc evaporation technology, the target material is pure graphite, and the thickness of the conductive amorphous carbon layer is 100 nm. The preparation conditions for the filtered cathode vacuum arc technology include: a magnetic filtering arc source with a current of 100A, a bias voltage of -2000V, a back vacuum of 5MPa, and no gas deposition. The corrosion current density of the carbon-based composite coating is less than 1 μA / cm. 2 ; Before and after corrosion, the contact resistance was less than 10 mΩ·cm under a pressure of 1.4 MPa. 2 The standard.

2. The carbon-based coating for the metal bipolar plate of a fuel cell as described in claim 1, characterized in that, The preparation conditions for the magnetron sputtering process include: an output power of 2 kW for the DC magnetron power supply, an air pressure of 0.5 Pa, and a bias voltage of -100 V.

3. The carbon-based coating for the metal bipolar plate of a fuel cell as described in claim 1, characterized in that, The preparation conditions of the cathode arc evaporation technology include: a current of 100A, a bias voltage of -300V to -400V, an argon atmosphere, and a gas pressure of 0.2Pa.

4. The method for preparing the carbon-based coating of the fuel cell metal bipolar plate according to claim 1 includes: Step 1: Matrix pretreatment; Step 2: First, a flexible metal Ti transition layer is prepared on the upper surface of the metal bipolar plate substrate obtained in Step 1. Then, a dense amorphous carbon corrosion barrier layer is prepared on the upper surface of the flexible metal Ti transition layer. Finally, a conductive amorphous carbon layer is prepared on the upper surface of the dense amorphous carbon corrosion barrier layer to obtain the carbon-based coating of the fuel cell metal bipolar plate.

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