Preparation method of vertical graphene-carbon titanium composite coating on surface of 316L stainless steel bipolar plate

Abstract

The invention provides a preparation method of a vertical graphene-carbon titanium composite coating on the surface of a 316L stainless steel bipolar plate, which comprises the following steps: depositing a Ti layer and a C layer on the surface of an SS316L stainless steel bipolar plate through magnetron sputtering / electron beam evaporation, and growing a VG layer by using a plasma enhanced chemical vapor deposition (PECVD) technology. The vertical graphene / amorphous carbon / titanium (VG / C / Ti) gradient composite coating is constructed, and collaborative optimization of the comprehensive performance of the bipolar plate is achieved. The thickness of a VG / C layer in the composite coating is 37 + / -5 nm, Ti and a substrate form a Ti-Fe mixed layer of 75 + / -10 nm, the interface bonding force is improved to 924.26 mu N through a C-C bond and a metal bond, the corrosion current density is reduced to 0.03 mu A / cm < 2 >, the ICR value is 1.82 m omega.cm < 2 >, and an efficient modification scheme is provided for the fuel cell bipolar plate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of surface modification of key components of proton exchange membrane fuel cells, and particularly relates to a preparation method of a vertical graphene-carbon-titanium transition layer composite coating on the surface of a 316L stainless steel bipolar plate. BACKGROUND

[0002] As a high-efficiency clean energy conversion device, one of the core challenges of the commercial application of proton exchange membrane fuel cells (PEMFC) is the performance optimization of key components, bipolar plates. The bipolar plate in PEMFC bears multiple functions of conducting current, separating reaction gas and leading out reaction water, and therefore needs to meet the strict requirements of high electrical conductivity, excellent corrosion resistance, good interface stability and cost economy. Stainless steel 316L (SS316L) is widely used as the bipolar plate substrate due to its low cost and high mechanical strength, but its surface is prone to form a passivation film, resulting in insufficient electrical conductivity, and it is easy to release metal ions to pollute the proton exchange membrane in the fuel cell working condition, affecting the performance of the cell.

[0003] The in-situ growth of a vertical graphene (VG) coating on the surface of SS316L through plasma-enhanced chemical vapor deposition (PECVD) process can significantly improve the electrical conductivity and hydrophobicity of the surface, but the existing technology has two major problems: first, the plasma etching and high temperature cause damage to the surface of SS316L, and the corrosion resistance of VG / SS316L is insufficient; second, the interface bonding force between graphene and metal substrate is poor, and the VG coating is easy to fall off, resulting in short service life. The existing transition layer technology, such as metal transition layer or carbon-based transition layer, also has defects such as poor electrical conductivity, insufficient corrosion resistance or limited improvement of bonding force.

[0004] Titanium (Ti) and carbon (C) can form a chemical bond, which can effectively enhance the interface adhesion, and metal Ti has a high passivation potential, which can improve the corrosion resistance of the material, but how to build a dense and uniform C / Ti transition layer between VG and SS316L and achieve synergistic enhancement with the VG coating is still a technical problem to be solved in the field. Based on this, the present application proposes to prepare a dense C / Ti transition layer between VG and SS316L to make up for the insufficient corrosion resistance of VG / SS316L, improve the interface bonding force, and explore the influence of the C / Ti transition layer on the micro-morphology, structure quality, bonding force, corrosion resistance and electrical conductivity of VG / SS316L. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of a vertical graphene-carbon-titanium transition layer composite coating on the surface of a stainless steel bipolar plate, which solves the problems of insufficient corrosion resistance and poor interface bonding force of VG / SS316L by building a C / Ti transition layer, and at the same time improves the electrical conductivity to meet the practical application requirements of PEMFC bipolar plates.

[0006] The technical scheme is to realize the above-mentioned purposes, and the application provides a preparation method of a 316L stainless steel bipolar plate surface vertical graphene-carbon titanium composite coating, which comprises the following steps:

[0007] (1) first preparing a Ti layer on the surface of SS316L;

[0008] (2) then preparing a C layer on the Ti / SS316L surface to obtain a C / Ti / SS316L transition structure;

[0009] (3) growing a vertical graphene VG coating on the C / Ti / SS316L surface by a PECVD process to obtain a VG / C / Ti / SS316L composite coating, wherein the PECVD process parameters are as follows: CH4 flow rate 20 sccm, Ar flow rate 80 sccm, H2 flow rate 10 sccm, plasma power 100 W, substrate temperature 550 DEG C, heating rate 10 DEG C / min, growth time 60 min-70 min, and vacuum natural cooling after the growth is completed.

[0010] Further, in step (1), the deposition method of the Ti layer is magnetron sputtering or electron beam evaporation, and the thickness of the Ti layer is 50-100 nm.

[0011] Further, in step (2), the preparation method of the C layer is thermal evaporation or PECVD, the thickness of the C layer is 20-50 nm, and the material is amorphous carbon.

[0012] Further, in the VG / C / Ti / SS316L composite coating, the total thickness of the VG / C layer is 37±5 nm, and the Ti layer and the SS316L substrate form a Ti-Fe mixed layer with a thickness of 75±10 nm through atomic diffusion.

[0013] In addition, the application provides a VG / C / Ti / SS316L composite coating prepared by any one of the above-mentioned methods, wherein the VG in the composite coating grows in a petal-shaped or semi-circular sheet shape perpendicular to the substrate, the VG and the C / Ti transition layer are combined through C-C bonds, and the C / Ti transition layer and the SS316L substrate are combined through metal bonds.

[0014] Further, the corrosion resistance, electrical conductivity and interface bonding force of the bipolar plate meet the following requirements: the corrosion current density is less than or equal to 0.17 mu A / cm 2 under 0.6 V, the interface contact resistance is less than or equal to 1.82 m omega cm 2 under 1.4 MPa pressure, and the interface bonding force is greater than or equal to 850 mu N.

[0015] Compared with the prior art, the technical scheme of the application has the following beneficial technical effects:

[0016] (1) Interface bonding force is significantly improved: scratch test shows that the interface bonding force of VG / C / Ti / SS316L is improved from 414.08 μN of VG / SS316L to 924.26 μN, with an increase of more than 2 times;

[0017] (2) Corrosion resistance is improved: potentiodynamic polarization curve shows that the corrosion current density at 0.6V is reduced from 0.17 μA / cm 2 to 0.03 μA / cm 2 , with a decrease of one order of magnitude;

[0018] (3) Conductivity is optimized: the interface contact resistance (ICR) under 1.4MPa pressure is reduced from 4.84mΩ·cm 2 to 1.82mΩ·cm 2 , meeting the DOE standard.

[0019] Drawings

[0020] Figure 1 is a schematic diagram for preparing VG / C / Ti / SS316L composite coating, showing the three-step process from Ti layer deposition to VG growth.

[0021] Figure 2 is a SEM image of the inclined plane: (a) is the vertical growth structure of VG / SS316L, (b) is the petal-shaped growth of VG in VG / C / Ti / SS316L.

[0022] Figure 3 is the FIB-TEM cross-sectional thickness and the corresponding EDS element test curve: (a1) cross-sectional thickness of C / Ti / SS316L, (a2) line scan curve of C / Ti / SS316L; (b1) cross-sectional thickness of VG / C / Ti / SS316L, (b2) line scan curve of VG / C / Ti / SS316L.

[0023] Figure 4 is the bonding force test result: (a) VG / SS316L, (b) VG / C / Ti / SS316L.

[0024] Figure 5 is the potentiodynamic polarization curve in the simulated PEMFC environment solution.

[0025] Figure 6 is the interface contact resistance (ICR) test result. DETAILED DESCRIPTION

[0026] In order to better understand the present application, the above-mentioned scheme will be further described in combination with specific examples, and the preferred embodiments of the present application are described in detail as follows:

[0027] Example 1: Magnetron sputtering Ti layer + thermal evaporation C layer + PECVD growth VG

[0028] (1) Substrate pretreatment: The SS316L plate was ultrasonically cleaned with acetone and ethanol for 15 min in sequence, dried with nitrogen, and then subjected to Ar plasma etching for 5 min to remove the surface oxide layer and contaminants and improve the surface activity of the substrate.

[0029] (2) Ti layer deposition: A magnetron sputtering process was used, with a pure Ti target (99.99%) as the source, a power of 100 W, and a deposition time of 20 minutes under a vacuum of 1×10-3 Pa. A Ti layer with a thickness of approximately 75 nm was obtained. This process allows for precise control of the Ti layer thickness, and the deposited Ti layer is tightly bonded to the substrate.

[0030] (3) Preparation of C layer: Using thermal evaporation process, high-purity graphite (purity > 99.99%, 4N) was used as the source, and the vacuum degree was 1×10 -4 Pa, evaporation temperature 1200 ℃, deposition time 10min, formed an amorphous carbon layer with a thickness of 30nm. The C layer prepared by thermal evaporation method has good uniformity and provides a stable substrate for subsequent VG growth.

[0031] (4) VG layer growth: PECVD equipment was used to grow VG according to the following parameters: CH4 flow rate 20 sccm, Ar flow rate 80 sccm, H2 flow rate 10 sccm, plasma power 100 W, substrate temperature 550 °C, growth time 60 min, heating rate 10 °C / min, and vacuum was maintained during the cooling stage to room temperature.

[0032] like Figure 1 As shown in FIG, this embodiment prepares the Ti layer and the C layer by magnetron sputtering and thermal evaporation respectively, and further adopts PECVD process to grow vertically oriented graphene VG coating on the surface of C / Ti / SS316L to obtain VG / C / Ti / SS316L composite coating. The process has high stability and strong repeatability. SEM observation shows that VG stands upright on the surface of C layer in the shape of petals (see FIG. Figure 2 (b)), the total thickness of the VG / C layer is about 37nm, and the thickness of the Ti(Fe) layer is about 75nm (see Figure 3 (b1)); the scratch test shows that the interface bonding strength reaches 924.26μN (see Figure 4 ); The potentiodynamic polarization curve shows that the corrosion current density at 0.6V is 0.03μA / cm 2 , one order of magnitude lower than VG / SS316L (see Figure 5 ); ICR value at 1.4MPa is 1.82mΩ·cm 2 (See Figure 6 ), meeting the performance requirements of fuel cell bipolar plates.

[0033] Example 2: Ti layer by electron beam evaporation + C layer by PECVD + VG layer by PECVD

[0034] (1) Substrate pretreatment: After the SS316L plate was cleaned by ultrasonic cleaning with acetone and ethanol, it was polished by sandpaper to a surface roughness Ra<0.5μm, and then etched by Ar plasma for 10min to further activate the surface.

[0035] (2) Ti layer deposition: Using electron beam evaporation process, pure Ti raw material was heated to 1600℃ under a vacuum degree of 5×10 -4 Pa, and deposited at a rate of 0.5nm / s to obtain a Ti layer with a thickness of 50nm. Electron beam evaporation can achieve high-precision deposition of Ti layer, and the film layer has high density.

[0036] (3) C layer preparation: Using PECVD process, CH4 was used as carbon source, flow rate 15sccm, Ar flow rate 100sccm, plasma power 80W, substrate temperature 450℃, deposition time 8min, to prepare a C layer with a thickness of 20nm. The C layer prepared by PECVD is more firmly combined with the Ti layer, and the structure of the C layer can be controlled by adjusting the process parameters.

[0037] (4) VG layer growth: Using PECVD equipment, VG was grown according to the following parameters: CH4 flow rate 20sccm, Ar flow rate 80sccm, H2 flow rate 10sccm, plasma power 100W, substrate temperature 550℃, growth time 60min, heating rate 10℃ / min, and vacuum cooling to room temperature.

[0038] In this example, the combination of Ti layer by electron beam evaporation and C layer by PECVD enhances the bonding force of the transition layer with the substrate and the VG layer. Scratch test shows that the interfacial bonding force reaches 850.64μN (see Figure 4 ). The corrosion current density of the composite coating is 0.17μA / cm 2 at 0.6V, which is an order of magnitude lower than that of VG / SS316L (see Figure 5 ), meeting the performance requirements of fuel cell bipolar plates.

Claims

1. A method for preparing a vertical graphene-carbon-titanium composite coating on the surface of a 316L stainless steel bipolar plate, characterized by, The method comprises the following steps: (1) first preparing a Ti layer on the surface of SS316L; (2) then preparing a C layer on the surface of Ti / SS316L to obtain a C / Ti / SS316L transition structure; (3) growing a vertical graphene VG coating on the surface of C / Ti / SS316L by PECVD process to obtain a VG / C / Ti / SS316L composite coating, wherein the PECVD process parameters are as follows: CH4 flow rate 20 sccm, Ar flow rate 80 sccm, H2 flow rate 10 sccm, plasma power 100 W, substrate temperature 550 DEG C, heating rate 10 DEG C / min, growth time 60-70 min, and vacuum natural cooling after growth.

2. The preparation method of the vertical graphene-carbon-titanium composite coating on the surface of a 316L stainless steel bipolar plate according to claim 1, characterized in that, In step (1), the deposition method of the Ti layer is magnetron sputtering or electron beam evaporation, and the thickness of the Ti layer is 50-100 nm.

3. The method according to claim 1, wherein the method is characterized by the following steps: 1) preparing a 316L stainless steel bipolar plate; 2) cleaning the bipolar plate; 3) coating the bipolar plate with a titanium layer; 4) coating the bipolar plate with a vertical graphene-carbon layer; and 5) coating the bipolar plate with a titanium layer. In step (2), the preparation method of the C layer is thermal evaporation or PECVD, the thickness is 20-50 nm, and the material is amorphous carbon.

4. The method according to claim 1, wherein the method is characterized by, In the VG / C / Ti / SS316L composite coating, the total thickness of the VG / C layer is 37±5 nm, the Ti layer and the SS316L substrate form a Ti-Fe mixed layer with a thickness of 75±10 nm through atomic diffusion.

5. A composite coating of VG / C / Ti / SS316L prepared by the method according to any one of claims 1 to 4, characterized in that, In the composite coating, the VG grows in petal or semicircular sheet shape perpendicular to the substrate, the VG and the C / Ti transition layer are combined through C-C bond, and the C / Ti transition layer and the SS316L substrate are combined through metal bond.

6. Use of the composite coating according to claim 5 in a proton exchange membrane fuel cell bipolar plate, characterized in that, The corrosion resistance, electrical conductivity and interface bonding force of the bipolar plate satisfy: corrosion current density under 0.6 V ≤ 0.17 μA / cm 2 , interface contact resistance under 1.4 MPa pressure ≤ 1.82 mΩ·cm 2 , interface bonding force ≥ 850 μN.

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