Carbon-containing coating for bipolar plate of fuel cell as well as preparation method and application of carbon-containing coating

Abstract

The invention relates to a carbon-containing coating for a fuel cell bipolar plate as well as a preparation method and application of the carbon-containing coating. The carbon-containing coating for the fuel cell bipolar plate comprises a transition layer and a carbon composite layer, the transition layer is located on at least one side surface of the bipolar plate, and the side surface, away from the bipolar plate, of the transition layer comprises a carbon composite layer; the carbon composite layer comprises a corrosion-resistant carbon layer and a conductive carbon layer which are stacked, the corrosion-resistant carbon layer is close to the transition layer, and the conductive carbon layer is far away from the transition layer; and the corrosion-resistant carbon layer is a low-bias-voltage carbon layer. The overall performance of the carbon-containing coating is improved through the synergistic effect of all the functional layers, the interlayer bonding strength is enhanced through the transition layer, then the corrosion-resistant carbon layer is prepared under low bias voltage, structural stability is facilitated, high stress is avoided, then the conductive carbon layer is stacked, the conductive carbon layer has high conductivity and content gradient transition, stress concentration can be further relieved, and the service life of the carbon-containing coating is prolonged. The carbon-containing coating and the bipolar plate are strong in binding force, the problems of deformation and the like of the bipolar plate are avoided, and the carbon-containing coating can have good corrosion resistance and high conductivity.

Description

Technical Field

[0001] This invention relates to the field of fuel cell electrode coating technology, and in particular to a carbon-containing coating for fuel cell bipolar plates, its preparation method, and its application. Background Technology

[0002] Carbon-containing coatings play a crucial role in fuel cell bipolar plates. On the one hand, they can reduce contact resistance and improve conductivity; on the other hand, they can act as an anti-corrosion layer to enhance corrosion resistance; and they can also be tuned to adapt to complex operating conditions, thereby improving stability. Therefore, to meet the demands of higher-level applications and further improve their conductivity, corrosion resistance, and stability, performance can be improved by optimizing the structure and preparation process of the carbon-containing coating.

[0003] sp in C layer of carbon-containing coating 3 The higher the proportion of hybrid bonds, the better the corrosion resistance. 2 A higher proportion of hybrid bonds results in better conductivity. The preparation of carbon-containing coatings mainly includes vapor deposition or magnetron sputtering. Among these, high-power pulsed magnetron sputtering (HiPIMS), which drives the magnetron sputtering process with a high-power pulsed power supply, can significantly improve film performance and is widely used in material surface modification and functional coating preparation. However, its application in actual preparation still faces the following problems: 1) Simply relying on adjusting process parameters... 2 / sp 3 The hybrid bond ratio still has limitations, making it difficult to balance the coating's corrosion resistance and conductivity; 2) High sp 3 Hybridized coatings typically rely on high temperature or high bias voltage deposition, which limits the choice of substrate material; 3) Carbon-containing coatings have high internal stress, which can easily lead to a decrease in bonding strength and affect long-term stability.

[0004] Therefore, how to further optimize the HiPIMS process and combine it with gradient structure design and post-processing technology to balance the conductivity, corrosion resistance, and mechanical stability of carbon-containing coatings is currently the main problem. At present, the methods commonly used to balance the conductivity and corrosion resistance of carbon-containing coatings include the following: 1) Increasing the deposition temperature. Using a magnetron sputtering system, the coating equipment is evacuated to the coating vacuum value, and then the system is heated to the required deposition temperature (e.g., room temperature, 200℃, 300℃, 400℃, or 500℃), and the vacuum is maintained at the coating vacuum value. Then, high-purity Ar gas is introduced for coating experiments. The underlying principle is: firstly, to control the columnar structure of the carbon-containing coating by changing the deposition temperature during the magnetron sputtering process; secondly, to achieve the desired columnar structure in the coating through a high deposition temperature. 3 Hybridized bond to sp 2The transformation of hybrid bonds, thereby improving conductivity, can be observed through Raman spectroscopy and XPS results. Increasing the deposition temperature is beneficial for the sp(s) in carbon-containing coatings. 3 Hybridized bond to sp 2 The transformation of hybrid bonds increases the degree of graphitization of carbon-containing coatings and improves their conductivity; 2) Vacuum heat treatment, using a magnetron sputtering system, the coating experiment is carried out at room temperature. After the coating is completed, the prepared coating is placed in a vacuum furnace and vacuum heat treatment is carried out at different temperatures. The principle and method 1) of this method are consistent with increasing the deposition temperature, and both can achieve the goal of increasing the degree of graphitization of carbon-containing coatings and improving their conductivity.

[0005] While the above process can improve conductivity, it still results in some loss in corrosion resistance. Overall heating will cause most of the sps in the carbon-containing coating's entire layer structure to deteriorate. 3 Hybrid bond transformation inevitably reduces corrosion resistance to some extent. At the same time, overall heating inevitably causes the substrate material (such as bipolar plate) to be heated as well, which can lead to thermal damage to the substrate. The substrate material may also be damaged due to thermal expansion, phase transformation or deformation, affecting subsequent use. In practice, in order to avoid thermal damage to the substrate material, the actual heating temperature is often reduced, which in turn limits the modification effect of carbon-containing coatings.

[0006] Therefore, how to provide a structure and preparation method for a carbon-containing coating for fuel cell bipolar plates that can simultaneously achieve excellent corrosion resistance and high conductivity has become an urgent technical problem to be solved. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a carbon-containing coating for fuel cell bipolar plates, its preparation method, and its application. This invention improves the overall performance of the carbon-containing coating through the synergistic effect of various functional layers. First, a transition layer is used to enhance the interlayer bonding strength, and then a corrosion-resistant carbon layer (high sp) is prepared under low bias voltage. 3 The hybrid bond content is beneficial to structural stability and avoids high stress, followed by the stacking of conductive carbon layers (high sp). 2 The high hybrid bond content, with its high conductivity and gradient transition, can further alleviate stress concentration, resulting in a strong bond between the carbon coating and the bipolar plate, avoiding problems such as bipolar plate deformation. At the same time, the carbon coating can also achieve good corrosion resistance and high conductivity.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a carbon-containing coating for a fuel cell bipolar plate, the carbon-containing coating for a fuel cell bipolar plate comprising a transition layer and a carbon composite layer;

[0010] The transition layer is located on at least one surface of the bipolar plate, and the side surface of the transition layer away from the bipolar plate includes a carbon composite layer;

[0011] The carbon composite layer includes a corrosion-resistant carbon layer and a conductive carbon layer stacked together, wherein the corrosion-resistant carbon layer is close to the transition layer and the conductive carbon layer is far from the transition layer;

[0012] The corrosion-resistant carbon layer is a low-bias carbon layer.

[0013] This invention improves the overall performance of carbon-containing coatings through the synergistic effect of various functional layers. First, a transition layer is used to enhance interlayer bonding strength, and then a corrosion-resistant carbon layer (high sp) is prepared under low bias voltage. 3 The hybrid bond content is beneficial to structural stability and avoids high stress, followed by the stacking of conductive carbon layers (high sp). 2 The high hybrid bond content, with its high conductivity and gradient transition, can further alleviate stress concentration, resulting in a strong bond between the carbon coating and the bipolar plate, avoiding problems such as bipolar plate deformation. At the same time, the carbon coating can also achieve good corrosion resistance and high conductivity.

[0014] In this invention, the low bias in the low bias carbon layer refers to the carbon layer prepared at a bias voltage of -50V to -400V.

[0015] As a preferred technical solution of the present invention, the thickness of the corrosion-resistant carbon layer is 10nm to 500nm, such as 10nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm or 500nm, preferably 300nm to 500nm.

[0016] Preferably, the corrosion-resistant carbon layer contains sp 3 Hybrid bond content greater than sp 2 Hybrid bond content.

[0017] Preferably, the corrosion-resistant carbon layer contains sp 3 The hybrid bond content is 51% to 80%, for example, 51%, 55%, 60%, 65%, 70%, 75% or 80%.

[0018] It should be noted that in this invention, sp 3 Hybridization content refers to the number of carbon atoms that have sp bonds. 3 The proportion of hybridized chemical bonds in the total carbon-carbon bonds.

[0019] As a preferred technical solution of the present invention, the thickness of the conductive carbon layer is 10nm to 500nm, such as 10nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm or 500nm, preferably 300nm to 400nm.

[0020] Preferably, the conductive carbon layer contains sp 2 The hybrid bond content is 30% to 80%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%, etc.

[0021] It should be noted that in this invention, sp 2 Hybridization content refers to the number of carbon atoms that have sp bonds. 2 The proportion of hybridized chemical bonds in the total carbon-carbon bonds.

[0022] As a preferred technical solution of the present invention, the conductive carbon layer is obtained by surface annealing of the obtained corrosion-resistant carbon layer.

[0023] Preferably, in the thickness direction of the conductive carbon layer, the sp in the conductive carbon layer 2 The hybrid bond content increases in a gradient from near the corrosion-resistant carbon layer to far away from the corrosion-resistant carbon layer.

[0024] In this invention, along the thickness direction of the conductive carbon layer, the sp in the conductive carbon layer... 2 The hybrid bond content increases in a gradient from near the corrosion-resistant carbon layer to far away from the corrosion-resistant carbon layer, due to the sp bond content in the carbon layer. 3 The internal stress of the hybridized bonds in the coating is extremely high, potentially reaching GPa levels. 2 The internal stress of the hybridized bonds in the coating is relatively small, on the order of MPa, thus reducing the gradient of sp. 3 Hybrid bond content, gradient increases sp 2 The amount of hybrid bonds can alleviate the effects of sp 3 Transform to sp 2 The stress changes afterward reduce the risk of peeling and delamination of the carbon-containing coating due to stress concentration, and further enhance the adhesion of the carbon-containing coating.

[0025] Preferably, the surface annealing process includes laser treatment.

[0026] Preferably, the laser used in the laser processing includes any one of femtosecond laser, picosecond laser or nanosecond laser, and is preferably a femtosecond laser.

[0027] As a preferred embodiment of the present invention, the transition layer includes a metal layer and a metal-carbon composite layer stacked together, wherein the metal layer is close to the bipolar plate and the metal-carbon composite layer is far from the bipolar plate.

[0028] Preferably, the metal element used in the metal layer is the same as the metal element used in the metal-carbon composite layer.

[0029] Preferably, the material of the metal layer includes any one or a combination of at least two of Nb, Ti, Au, Cr, Cu, Al or TiTa composite materials.

[0030] As a preferred technical solution of the present invention, the thickness of the metal layer is 1nm to 1000nm, such as 1nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm or 1000nm, etc., preferably 200nm to 300nm.

[0031] Preferably, the thickness of the metal-carbon composite layer is 1nm to 1000nm, such as 1nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm or 1000nm, and more preferably 100nm to 300nm.

[0032] Preferably, based on the total mass of the metal-carbon composite layer being 100wt%, the mass percentage of the metal material is 1wt% to 99wt%, for example, 1wt%, 10wt%, 30wt%, 50wt%, 80wt%, or 99wt%.

[0033] Preferably, based on the total mass of the metal-carbon composite layer being 100wt%, the mass percentage of carbon material is 1wt% to 99wt%, for example, 1wt%, 10wt%, 30wt%, 50wt%, 80wt%, or 99wt%.

[0034] In a second aspect, the present invention also provides a method for preparing a carbon-containing coating for a fuel cell bipolar plate according to the first aspect, the method comprising the following steps:

[0035] A transition layer is prepared on at least one side surface of the bipolar plate, and then a corrosion-resistant carbon layer and a conductive carbon layer are sequentially prepared on the surface of the transition layer to form a carbon composite layer, thereby obtaining a carbon-containing coating for fuel cell bipolar plates.

[0036] The corrosion-resistant carbon layer is a carbon layer prepared under low bias voltage.

[0037] In this invention, the corrosion-resistant carbon layer is a carbon layer prepared under low bias voltage (bias voltage -50V to -400V). That is, after obtaining the transition layer, the bias power supply is turned on to apply a negative pulse bias voltage to the bipolar plate containing the transition layer. The bias voltage of the bias power supply is -50V to -400V, thereby obtaining a corrosion-resistant carbon layer with stable structure and low stress.

[0038] As a preferred technical solution of the present invention, before preparing the transition layer, a pretreatment step is further included to obtain the bipolar plate.

[0039] Preferably, the pretreatment includes surface pretreatment and cleaning.

[0040] Preferably, the surface pretreatment method includes: sequentially ultrasonically cleaning and drying the bipolar plate to be treated to obtain a surface-pretreated bipolar plate.

[0041] Preferably, the ultrasonic cleaning time is 10 min to 30 min, such as 10 min, 12 min, 15 min, 18 min, 20 min, 22 min, 25 min, 28 min or 30 min.

[0042] Preferably, the cleaning method includes: placing the surface-pretreated bipolar plate in an inert environment, evacuating the vacuum chamber, introducing inert gas to reach the working pressure, and turning on the bias power supply to apply a negative pulse bias to the surface-pretreated bipolar plate for cleaning, thereby obtaining the bipolar plate.

[0043] Preferably, the distance between the bipolar plate and the target surface after surface pretreatment is 50mm to 200mm, such as 50mm, 80mm, 100mm, 120mm, 150mm, 180mm or 200mm.

[0044] Preferably, the inert gas in the inert environment includes argon.

[0045] Preferably, the vacuum level in the vacuum chamber is ≤5×10⁻⁶. -3 Pa, for example 5 × 10 -3 Pa, 4×10 -3 Pa, 3×10 -3 Pa, 2×10 -3 Pa, 1×10 -3 Pa or 0.5×10 -3 Pa, etc.

[0046] Preferably, the inert gas includes argon.

[0047] Preferably, the working air pressure is 1 Pa to 3 Pa, for example, 1 Pa, 1.5 Pa, 2 Pa, 2.5 Pa or 3 Pa.

[0048] Preferably, the bias voltage during the cleaning process is -500V to -700V, such as -500V, -550V, -600V, -650V, or -700V.

[0049] Preferably, the frequency during the cleaning process is 20kHz to 100kHz, such as 20kHz, 30kHz, 40kHz, 50kHz, 60kHz, 70kHz, 80kHz, 90kHz or 100kHz.

[0050] Preferably, the duty cycle during the cleaning process is 20% to 80%, such as 20%, 30%, 40%, 50%, 60%, 70%, or 80%.

[0051] Preferably, the cleaning time is 20 min to 40 min, for example, 20 min, 25 min, 30 min, 35 min or 40 min.

[0052] As a preferred technical solution of the present invention, the method for preparing the transition layer includes: turning on the metal target power supply to apply a pulse current to the metal target, turning on the bias power supply to apply a negative pulse bias to the bipolar plate, performing a first sputtering deposition on at least one side surface of the bipolar plate to form a metal layer; subsequently turning on the carbon target power supply to apply a pulse power supply to the carbon target, performing a second sputtering deposition on the surface of the metal layer to form a metal-carbon composite layer, thereby obtaining the transition layer.

[0053] Preferably, the deposition gas pressure of the first sputtering deposition is 0.1 Pa to 1 Pa, such as 0.1 Pa, 0.2 Pa, 0.3 Pa, 0.4 Pa, 0.5 Pa, 0.6 Pa, 0.7 Pa, 0.8 Pa, 0.9 Pa or 1 Pa.

[0054] Preferably, the revolution speed of the bipolar plate is 3 rpm to 20 rpm, such as 3 rpm, 5 rpm, 10 rpm, 12 rpm, 15 rpm, 18 rpm or 20 rpm.

[0055] Preferably, the pulse current of the metal target power supply is 0.5A to 2A, such as 0.5A, 0.8A, 1A, 1.2A, 1.5A, 1.8A or 2A.

[0056] Preferably, the pulse frequency of the metal target power supply is 20Hz to 100Hz, such as 20Hz, 30Hz, 40Hz, 50Hz, 60Hz, 70Hz, 80Hz, 90Hz or 100Hz.

[0057] Preferably, the pulse duty cycle of the metal target power supply is 40% to 90%, such as 40%, 50%, 60%, 70%, 80%, or 90%.

[0058] Preferably, the bias voltage of the bias power supply is -50V to -400V, such as -50V, -100V, -150V, -200V, -250V, -300V, -350V, or -400V.

[0059] Preferably, the pulse frequency of the bias power supply is 20Hz to 100Hz, such as 20Hz, 30Hz, 40Hz, 50Hz, 60Hz, 70Hz, 80Hz, 90Hz or 100Hz.

[0060] Preferably, the pulse duty cycle of the bias power supply is 20% to 80%, such as 20%, 30%, 40%, 50%, 60%, 70%, or 80%.

[0061] Preferably, the first sputtering deposition time is 10s to 300s, such as 10s, 50s, 100s, 150s, 200s, 250s or 300s.

[0062] Preferably, the deposition pressure of the second sputtering deposition is 0.1 Pa to 1 Pa, for example, 0.1 Pa, 0.2 Pa, 0.3 Pa, 0.4 Pa, 0.5 Pa, 0.6 Pa, 0.7 Pa, 0.8 Pa, 0.9 Pa or 1 Pa.

[0063] Preferably, the pulse voltage of the carbon target power supply is 500V to 700V, such as 500V, 550V, 600V, 650V or 700V.

[0064] Preferably, the pulse frequency of the carbon target power supply is 50Hz to 200Hz, such as 50Hz, 80Hz, 100Hz, 120Hz, 150Hz, 180Hz or 200Hz.

[0065] Preferably, the pulse duty cycle of the carbon target power supply is 1% to 2%, such as 1%, 1.2%, 1.5%, 1.8% or 2%.

[0066] Preferably, the second sputtering deposition time is 10s to 300s, for example, 10s, 50s, 100s, 150s, 200s, 250s or 300s.

[0067] As a preferred technical solution of the present invention, the method for preparing the carbon composite layer includes: turning on the carbon target power supply to apply a pulse current to the carbon target material, performing a third sputtering deposition on the surface of the transition layer to form a corrosion-resistant carbon layer, and performing a surface annealing treatment on the corrosion-resistant carbon layer to form a conductive carbon layer, thereby obtaining the carbon composite layer.

[0068] As a preferred technical solution of the present invention, the third sputtering deposition time is 10 min to 100 min, for example, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min or 100 min.

[0069] Preferably, the surface annealing process includes laser treatment.

[0070] Preferably, the laser used in the laser processing includes any one of femtosecond laser, picosecond laser or nanosecond laser, and is preferably a femtosecond laser.

[0071] In this invention, annealing the surface of the corrosion-resistant carbon layer using a femtosecond laser with a wavelength of 1030nm has three major advantages: ① By adjusting the appropriate pulse energy and pulse width, the annealing depth and temperature can be controlled, and slow scanning ensures uniform heating of the surface layer; ② Annealing is performed only on a certain depth range of the surface of the corrosion-resistant carbon layer, thus partially removing sp... 3 Hybrid bonds are converted to sp 2 Hybridized bonds form a layer of sp 2 A conductive carbon layer with a gradient content of hybrid bonds can also retain a deeper layer with high sp bond content. 3 ③ Corrosion-resistant layer of hybrid bonds; femtosecond laser surface annealing can perform high-temperature annealing only on the surface, avoiding annealing of the entire structure, and further avoiding phase transformation or deformation of the matrix itself caused by excessive temperature during the overall structure annealing, which would affect performance and application.

[0072] Preferably, the energy density of the femtosecond laser is 0.6 J / cm² to 1.2 J / cm², such as 0.6 J / cm², 0.7 J / cm², 0.8 J / cm², 0.9 J / cm², 1.0 J / cm², 1.1 J / cm², or 1.2 J / cm².

[0073] In this invention, by controlling the energy density of the femtosecond laser to be between 0.6 J / cm² and 1.2 J / cm², the surface annealing temperature can be controlled within a reasonable range, achieving a sufficient amount of sp. 3 Convert to sp 2 The carbon-containing coating combines good corrosion resistance with high conductivity. However, if the energy density is too low, the energy will be insufficient to break the recombination of hybrid bonds, thus failing to achieve sp...3 To sp 2 If the conversion is insufficient or inadequate, the carbon-containing coating exhibits excessive corrosion resistance but poor conductivity; conversely, excessively high energy density can lead to sp... 3 A large amount was converted into sp 2 Excessive conversion can cause carbon-containing coatings to become overly conductive and lose their corrosion resistance.

[0074] Preferably, the pulse width of the femtosecond laser is 300fs to 800fs, such as 300fs, 400fs, 500fs, 600fs, 700fs or 800fs.

[0075] Preferably, the repetition frequency of the femtosecond laser is 20kHz to 100kHz, such as 20Hz, 30Hz, 40Hz, 50Hz, 60Hz, 70Hz, 80Hz, 90Hz or 100Hz.

[0076] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0077] (1) Cleaning: Provide the bipolar plate to be treated, and perform ultrasonic cleaning and drying on the bipolar plate for 10 min to 30 min in sequence. Place the pre-treated bipolar plate in an inert environment and evacuate the vacuum chamber to ≤5×10. -3 Pa, inert gas is introduced to reach the working pressure of 1Pa to 3Pa, and the bias power supply is turned on to apply a negative pulse bias to the pretreated bipolar plate for 20min to 40min to clean it, thus obtaining the bipolar plate;

[0078] The distance between the bipolar plate and the target surface after surface pretreatment is 50mm to 200mm; the voltage during the cleaning process is -500V to -700V, the frequency is 20kHz to 100kHz, and the duty cycle is 20% to 80%.

[0079] (2) Transition layer deposition: A metal target power supply is turned on to apply a pulsed current to the metal target material. The pulsed current of the metal target power supply is 0.5A to 2A, the pulse frequency is 20Hz to 100Hz, and the pulse duty cycle is 40% to 90%. A bias power supply is turned on to apply a negative pulsed bias to the bipolar plate. The bias power supply is -50V to -400V, the pulse frequency is 20Hz to 100Hz, and the pulse duty cycle is 20% to 80%. A first sputtering deposition is performed on at least one side of the surface of the bipolar plate for 10s to 300s to form a metal layer. Subsequently, a carbon target power supply is turned on to apply a pulsed current to the carbon target material. The pulse voltage of the carbon target power supply is 500V to 700V, the pulse frequency is 50Hz to 200Hz, and the pulse duty cycle is 1% to 2%. A second sputtering deposition is performed on the surface of the metal layer for 10s to 300s to form a metal-carbon composite layer, thus obtaining the transition layer.

[0080] The bipolar plate revolves at a speed of 3 rpm to 20 rpm; the deposition gas pressure of the first sputtering deposition is 0.1 Pa to 1 Pa; the deposition gas pressure of the second sputtering deposition is 0.1 Pa to 1 Pa.

[0081] (3) Deposition of the carbon composite layer: A carbon target power supply is turned on to apply a pulsed current to the carbon target material. The pulse voltage of the carbon target power supply is 500V–700V, the pulse frequency is 50Hz–200Hz, and the pulse duty cycle is 1%–2%. A bias power supply is then turned on to apply a negative pulsed bias to the bipolar plate containing the transition layer. The bias voltage of the bias power supply is -50V–-400V, the pulse frequency is 20Hz–100Hz, and the pulse duty cycle is 20%–80%. A third sputtering deposition is then performed on the surface of the transition layer for 10 min–10 minutes. A corrosion-resistant carbon layer is formed within 0 min. The corrosion-resistant carbon layer is then subjected to femtosecond laser surface annealing treatment. The energy density of the femtosecond laser is 0.6 J / cm2 to 1.2 J / cm2, the pulse width is 300 fs to 800 fs, and the repetition frequency is 20 kHz to 100 kHz, forming a conductive carbon layer. This results in a carbon composite layer, which comprises a corrosion-resistant carbon layer and a conductive carbon layer stacked together. The corrosion-resistant carbon layer is close to the transition layer, and the conductive carbon layer is far from the transition layer, thus obtaining a carbon-containing coating for fuel cell bipolar plates.

[0082] Thirdly, the present invention also provides an application of a carbon-containing coating for a fuel cell bipolar plate, wherein the carbon-containing coating for a fuel cell bipolar plate described in the first aspect, or the carbon-containing coating for a fuel cell metal bipolar plate prepared according to the preparation method described in the second aspect, is applied to a fuel cell.

[0083] Compared with the prior art, the present invention has at least the following beneficial effects:

[0084] This invention improves the performance of carbon-containing coatings through the synergistic effect of various functional layers. First, a transition layer is used to enhance interlayer bonding strength, and then a corrosion-resistant carbon layer (high sp) is prepared under low bias voltage. 3 The hybrid bond content is beneficial to structural stability and avoids high stress. Furthermore, by annealing the corrosion-resistant carbon layer to a certain depth, part of the corrosion-resistant carbon layer is transformed into a conductive carbon layer (high sp). 2 (hybridization content), which has high conductivity and the resulting conductive carbon layer contains sp 2 A gradient transition in hybrid bond content can alleviate stress concentration and improve bonding strength, while the underlying layer remains high sp. 3 Even with a high hybrid bond content, the corrosion-resistant carbon layer still exhibits good corrosion resistance. Therefore, this invention can achieve both superior corrosion resistance and high electrical conductivity in carbon-containing coatings. Attached Figure Description

[0085] Figure 1 This is a schematic diagram of the structure of the carbon-containing coating for the fuel cell bipolar plate provided in Embodiment 1 of the present invention.

[0086] Among them, 1-stainless steel bipolar plate; 2-Nb layer; 3-Nb-C layer; 4-corrosion resistant carbon layer; 5-conductive carbon layer.

[0087] Figure 2 This is an XPS image of the corrosion-resistant carbon layer obtained before femtosecond laser surface annealing in step (3) of Embodiment 1 of the present invention.

[0088] Figure 3 This is an XPS image of the surface conductive carbon layer obtained after femtosecond laser surface annealing in step (3) of Embodiment 1 of the present invention. Detailed Implementation

[0089] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0090] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0091] In the specific embodiments of this invention, the sputtering deposition method adopts high-power pulsed magnetron sputtering (HiPIMS) technology, using Beijing Danpu Surface Technology Co., Ltd. AS1400DMTX coating equipment and Newport Corporation Spirit One 1040-8 femtosecond laser.

[0092] Example 1

[0093] This embodiment provides a carbon-containing coating for fuel cell bipolar plates and its preparation method. A schematic diagram of the structure of the carbon-containing coating for fuel cell bipolar plates is shown below. Figure 1 As shown, from bottom to top, it includes a stainless steel bipolar plate 1 (0.1 mm), an Nb layer 2 (200 nm), an Nb-C layer 3 (200 nm, Nb mass percentage 50 wt%, C mass percentage 50 wt%), a corrosion-resistant carbon layer 4 (400 nm), and a conductive carbon layer 5 (400 nm) stacked together. The corrosion-resistant carbon layer is a low bias carbon layer. The corrosion-resistant carbon layer 4 and the conductive carbon layer 5 constitute a carbon composite layer. The arrow at point A indicates the thickness direction.

[0094] The preparation method includes the following steps:

[0095] (1) Cleaning: Provide the stainless steel bipolar plate to be treated. Clean the surface of the stainless steel bipolar plate with anhydrous ethanol using ultrasonic cleaning for 15 minutes. After drying, install it into the vacuum chamber and connect it to the negative terminal of the bias power supply. Place the pre-treated bipolar plate in an argon atmosphere, 100mm away from the target surface, and evacuate the vacuum chamber to 5×10⁻⁶. -3 Pa, Ar gas was introduced and the gas flow rate was adjusted to make the vacuum degree of the vacuum chamber 1.5Pa (working gas pressure). The bias power supply was turned on and a negative pulse bias was applied to the stainless steel bipolar plate. The bias power supply parameters were: voltage -600V, frequency 60kHz, duty cycle 80%. The cleaning was completed in 30 minutes, and the stainless steel bipolar plate was obtained.

[0096] (2) Transition layer deposition: Reduce the Ar gas flow rate and adjust the gas pressure in the vacuum chamber to 0.4 Pa (the deposition pressure of the first sputtering deposition). Keep the stainless steel bipolar plate rotating on its own axis while revolving within the chamber. The revolution speed is 18 rpm. Turn on the Nb target power supply to apply a pulsed current to the Nb target material. The Nb target power supply parameters are: pulse current 1A, pulse frequency 60Hz, duty cycle 80%. At the same time, turn on the bias power supply to apply a negative pulse bias to the stainless steel bipolar plate. The bias power supply parameters are: bias voltage -100V, pulse frequency 60kHz, duty cycle 80%. Perform the first sputtering deposition on the surface of the stainless steel bipolar plate for 300s to form an Nb layer.

[0097] Ar was continued to be introduced, and the gas flow rate in the vacuum chamber was adjusted to bring the gas pressure to 0.4 Pa. The carbon target power supply was turned on to apply a pulsed power supply to the C target material. The parameters of the carbon target power supply were: pulse voltage of 700 V, pulse frequency of 100 Hz, and duty cycle of 1%. At the same time, the Nb target power supply was turned on to apply a pulsed current to the Nb target material. The parameters of the Nb target power supply were: pulse current of 1 A, pulse frequency of 60 Hz, and duty cycle of 80%. At the same time, the bias power supply was turned on to apply a negative pulse bias to the stainless steel bipolar plate containing the Nb layer. The parameters of the bias power supply were: bias voltage of -100 V, pulse frequency of 60 kHz, and duty cycle of 80%. A second sputtering deposition was performed on the surface of the Nb layer for 300 s to form an Nb-C layer, thus obtaining a transition layer.

[0098] (3) Deposition of carbon composite layer: Turn off the Nb target power supply and continue to turn on the carbon target power supply to apply a pulse power supply to the C target material. The carbon target power supply parameters are: pulse voltage of 700V, pulse frequency of 100Hz, and duty cycle of 1%. At the same time, continue to turn on the bias power supply to apply a negative pulse bias to the stainless steel bipolar plate containing the transition layer. The bias power supply parameters are: bias voltage of -100V, pulse frequency of 60kHz, and duty cycle of 80%. Perform third sputtering deposition on the surface of the transition layer for 90 minutes to form a corrosion-resistant carbon layer.

[0099] The corrosion-resistant carbon layer was surface-annealed using a femtosecond laser with a wavelength of 1030 nm (annealing depth of 400 nm). The energy density of the femtosecond laser was 0.6 J / cm². 2 With a pulse width of 300 fs, a repetition frequency of 20 kHz, and a surface annealing temperature of 350 ℃, a 400 nm corrosion-resistant carbon layer is converted into a conductive carbon layer to obtain a carbon composite layer (a 400 nm conductive carbon layer on the surface and a 400 nm corrosion-resistant carbon layer on the inner layer), thereby obtaining a carbon-containing coating for fuel cell bipolar plates.

[0100] Figure 2 The figure shows an XPS image of the corrosion-resistant carbon layer obtained before femtosecond laser surface annealing in step (3) of Embodiment 1 of the present invention. As can be seen from the figure, the corrosion-resistant carbon layer obtained before annealing has a high sp 2 and sp 3 The hybrid bond contents are 34% and 66%, respectively. Figure 3 The figure shows an XPS image of the surface conductive carbon layer obtained after femtosecond laser surface annealing in step (3) of Embodiment 1 of the present invention. As can be seen from the figure, the conductive carbon layer (surface layer) obtained after annealing contains sp 2 and sp 3 The hybrid bond ratios were 44.5% and 55.5%, respectively, with sp in the surface layer. 2 The hybrid bond content has increased significantly, resulting in a marked improvement in electrical conductivity, while also maintaining good corrosion resistance.

[0101] Example 2

[0102] This embodiment provides a carbon-containing coating for fuel cell bipolar plates and its preparation method. The layer structure, thickness and other parameters of the carbon-containing coating for fuel cell bipolar plates are consistent with those in Embodiment 1.

[0103] The difference between the preparation method described above and Example 1 is that the energy density of the femtosecond laser is 1 J / cm². 2 The surface annealing temperature was 420℃, and the rest of the preparation methods and parameters remained unchanged from Example 1.

[0104] Example 3

[0105] This embodiment provides a carbon-containing coating for fuel cell bipolar plates and its preparation method. The layer structure, thickness and other parameters of the carbon-containing coating for fuel cell bipolar plates are consistent with those in Embodiment 1.

[0106] The difference between the preparation method described above and Example 1 is that the energy density of the femtosecond laser is 1.2 J / cm². 2 The surface annealing temperature was 600℃, and the rest of the preparation methods and parameters remained unchanged from Example 1.

[0107] Example 4

[0108] This embodiment provides a carbon-containing coating for fuel cell bipolar plates and its preparation method. The layer structure, thickness and other parameters of the carbon-containing coating for fuel cell bipolar plates are consistent with those in Embodiment 1.

[0109] The difference between the preparation method described above and Example 1 is that the energy density of the femtosecond laser is 1.5 J / cm². 2 The surface annealing temperature was 800℃, and the rest of the preparation methods and parameters remained unchanged from Example 1.

[0110] Example 5

[0111] This embodiment provides a carbon-containing coating for fuel cell bipolar plates and its preparation method. The layer structure, thickness and other parameters of the carbon-containing coating for fuel cell bipolar plates are consistent with those in Embodiment 1.

[0112] The difference between the preparation method described above and Example 1 is that the energy density of the femtosecond laser is 0.3 J / cm². 2 The surface annealing temperature was 200℃, and the rest of the preparation methods and parameters remained unchanged from Example 1.

[0113] Comparative Example 1

[0114] This comparative example provides a carbon-containing coating for a fuel cell bipolar plate and its preparation method. The carbon-containing coating for the fuel cell bipolar plate includes, from bottom to top, a stainless steel bipolar plate (0.1 mm), an Nb layer (200 nm), an Nb-C layer (200 nm, Nb mass percentage 50 wt%, C mass percentage 50 wt%), and a carbon layer (i.e., a corrosion-resistant carbon layer, 800 nm).

[0115] The difference between the preparation method described above and Example 1 is that, in step (3), the process of surface annealing of the corrosion-resistant carbon layer by a femtosecond laser with a wavelength of 1030 nm is omitted, while the rest of the preparation methods and parameters remain the same as in Example 1.

[0116] Comparative Example 2

[0117] This comparative example provides a carbon-containing coating for a fuel cell bipolar plate and its preparation method. The carbon-containing coating for the fuel cell bipolar plate comprises, from bottom to top, a stainless steel bipolar plate (0.1 mm), an Nb layer (200 nm), an Nb-C layer (200 nm, with Nb mass percentage of 50 wt% and C mass percentage of 50 wt%), and a carbon layer (800 nm) stacked together.

[0118] The difference between the preparation method and Example 1 is that in step (3), after obtaining the corrosion-resistant carbon layer, heating is started to raise the overall structure (including stainless steel bipolar plate, Nb layer, Nb-C layer and corrosion-resistant carbon layer) to 500°C, keep it at that temperature for 1 hour, and then cool it to room temperature to obtain a carbon-containing coating for fuel cell bipolar plate. That is, the surface annealing treatment by femtosecond laser is replaced by heat treatment of the overall structure, and the rest of the preparation methods and parameters are consistent with Example 1.

[0119] Comparative Example 3

[0120] This comparative example provides a carbon-containing coating for fuel cell bipolar plates and its preparation method. The difference between the carbon-containing coating for fuel cell bipolar plates and Example 1 is that the corrosion-resistant carbon layer is a high-bias carbon layer, while the structure, thickness and other parameters of the remaining layers are consistent with those of Example 1.

[0121] The difference between the preparation method and Example 1 is that, in step (3) during the deposition of the carbon composite layer, the bias voltage of the corresponding bias power supply is -450V, while the other preparation methods and parameters remain unchanged from Example 1.

[0122] The performance of the carbon-containing coatings for fuel cell bipolar plates provided in Examples 1-5 and Comparative Examples 1-3 was evaluated, including:

[0123] 1) Sp-tests were performed on the surface (conductive carbon layer) and inner (corrosion-resistant carbon layer) of the carbon composite layers of Examples 1-5 and Comparative Example 3, and on the surface (the layer structure corresponding to the region perpendicularly inward from the surface of the carbon layer to 400 nm) and inner (the layer structure corresponding to the region in the carbon layer other than the surface layer) of the carbon composite layers of Comparative Examples 1-2. 2 and sp 3 Detection of hybrid bond content.

[0124] 2) The contact resistance and corrosion current of the carbon composite layers in Examples 1-5 and Comparative Example 3, and the carbon layers in Comparative Examples 1-2 were tested. DOE standard: contact resistance < 5 mΩ·cm 2 Corrosion current < 1 μA / cm 2 .

[0125] 3) Observe whether the stainless steel bipolar plate is deformed.

[0126] The specific test results are shown in Tables 1 and 2.

[0127] Table 1

[0128]

[0129] Table 2

[0130]

[0131]

[0132] The test results in Tables 1 and 2 show that:

[0133] (1) As can be seen from Examples 1-3, the present invention improves the overall performance of the carbon-containing coating through the synergistic effect of each functional layer. First, a transition layer is used to enhance the interlayer bonding strength, and then a corrosion-resistant carbon layer (high sp) is prepared under low bias voltage. 3 The hybrid bond content is beneficial to structural stability and avoids high stress, followed by the stacking of conductive carbon layers (high sp). 2 The high hybrid bond content, with its high conductivity and gradient transition, can further alleviate stress concentration, resulting in a strong bond between the carbon coating and the bipolar plate, avoiding problems such as bipolar plate deformation. At the same time, the carbon coating can achieve both good corrosion resistance and high conductivity. The contact resistance and corrosion current of the carbon coating both meet the DOE standard.

[0134] (2) As can be seen from Examples 1 and 4-5, by adjusting the energy density of the femtosecond laser to 0.6 J / cm² to 1.2 J / cm², the surface annealing temperature can be controlled within a reasonable range to achieve a sufficient amount of sp. 3 Convert to sp 2The carbon-containing coating combines good corrosion resistance with high electrical conductivity.

[0135] (3) As can be seen from Example 1 and Comparative Example 1, the carbon-containing coating prepared by deposition at room temperature has extremely high contact resistance and corrosion current, and the performance of the carbon-containing coating is extremely poor.

[0136] (4) As can be seen from Example 1 and Comparative Example 2, when annealing is performed by increasing the overall temperature, it can be found that the overall temperature increase will cause sp 3 Hybrid bonds are converted to sp 2 Although it can reach 4.5 mΩ·cm at 500℃ 2 Below DOE standard (contact resistance < 5 mΩ·cm) 2 However, the increased temperature led to an overall increase in the temperature of the carbon coating, causing deformation of the stainless steel bipolar plate, which affected the performance of the carbon coating and its subsequent use.

[0137] (5) As can be seen from Example 1 and Comparative Example 3, if the corrosion-resistant carbon layer is a high bias carbon layer, it will lead to stress concentration and poor bonding, which will in turn lead to an increase in the contact resistance of the carbon-containing coating.

[0138] In summary, this invention improves the overall performance of the carbon-containing coating through the synergistic effect of various functional layers. First, a transition layer is used to enhance the interlayer bonding strength, and then a corrosion-resistant carbon layer (high sp) is prepared under low bias voltage. 3 The hybrid bond content is beneficial to structural stability and avoids high stress, followed by the stacking of conductive carbon layers (high sp). 2 The high hybrid bond content, with its high conductivity and gradient transition, can further alleviate stress concentration, resulting in a strong bond between the carbon coating and the bipolar plate, avoiding problems such as bipolar plate deformation. At the same time, the carbon coating can also achieve good corrosion resistance and high conductivity.

[0139] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A carbon-containing coating for a fuel cell bipolar plate, characterized in that, The carbon-containing coating for the fuel cell bipolar plate includes a transition layer and a carbon composite layer; The transition layer is located on at least one surface of the bipolar plate, and the side surface of the transition layer away from the bipolar plate includes a carbon composite layer; The carbon composite layer includes a corrosion-resistant carbon layer and a conductive carbon layer stacked together, wherein the corrosion-resistant carbon layer is close to the transition layer and the conductive carbon layer is far from the transition layer; The corrosion-resistant carbon layer is a low-bias carbon layer.

2. The carbon-containing coating for fuel cell bipolar plates according to claim 1, characterized in that, The thickness of the corrosion-resistant carbon layer is 10nm to 500nm, preferably 300nm to 500nm; Preferably, the corrosion-resistant carbon layer contains sp 3 Hybrid bond content greater than sp 2 Hybrid bond content; Preferably, the corrosion-resistant carbon layer contains sp 3 The hybrid bond content is 51%–80%.

3. The carbon-containing coating for fuel cell bipolar plates according to claim 1 or 2, characterized in that, The thickness of the conductive carbon layer is 10nm to 500nm, preferably 300nm to 400nm; Preferably, the conductive carbon layer contains sp 2 The hybrid bond content is 30%–80%.

4. The carbon-containing coating for fuel cell bipolar plates according to any one of claims 1 to 3, characterized in that, The conductive carbon layer is obtained by surface annealing of the resulting corrosion-resistant carbon layer. Preferably, in the thickness direction of the conductive carbon layer, the sp in the conductive carbon layer 2 The hybrid bond content increases in a gradient from near the corrosion-resistant carbon layer to far away from the corrosion-resistant carbon layer; Preferably, the surface annealing treatment includes laser processing; Preferably, the laser used in the laser processing includes any one of femtosecond laser, picosecond laser or nanosecond laser, and is preferably a femtosecond laser.

5. The carbon-containing coating for fuel cell bipolar plates according to any one of claims 1 to 4, characterized in that, The transition layer includes a stacked metal layer and a metal-carbon composite layer, wherein the metal layer is close to the bipolar plate and the metal-carbon composite layer is away from the bipolar plate; Preferably, the metal element used in the metal layer is the same as the metal element used in the metal-carbon composite layer; Preferably, the material of the metal layer includes any one or a combination of at least two of Nb, Ti, Au, Cr, Cu, Al or TiTa composite materials.

6. The carbon-containing coating for fuel cell bipolar plates according to claim 5, characterized in that, The thickness of the metal layer is 1 nm to 1000 nm, preferably 200 nm to 300 nm; Preferably, the thickness of the metal-carbon composite layer is 1 nm to 1000 nm, and more preferably 100 nm to 300 nm; Preferably, based on a total mass of 100 wt% for the metal-carbon composite layer, the mass percentage of the metal material is 1 wt% to 99 wt%. Preferably, based on a total mass of 100 wt% for the metal-carbon composite layer, the mass percentage of carbon material is 1 wt% to 99 wt%.

7. A method for preparing a carbon-containing coating for a fuel cell bipolar plate according to any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: A transition layer is prepared on at least one side surface of the bipolar plate, and then a corrosion-resistant carbon layer and a conductive carbon layer are sequentially prepared on the surface of the transition layer to form a carbon composite layer, thereby obtaining a carbon-containing coating for fuel cell bipolar plates. The corrosion-resistant carbon layer is a carbon layer prepared under low bias voltage.

8. The preparation method according to claim 7, characterized in that, Before preparing the transition layer, the process also includes a pretreatment step for the bipolar plate to be processed, thereby obtaining the bipolar plate; Preferably, the pretreatment includes surface pretreatment and cleaning; Preferably, the cleaning method includes: placing the surface-pretreated bipolar plate in an inert environment, evacuating the vacuum chamber, introducing inert gas to reach the working pressure, turning on the bias power supply to apply a negative pulse bias to the surface-pretreated bipolar plate for cleaning, thereby obtaining the bipolar plate; Preferably, the method for preparing the transition layer includes: turning on the metal target power supply to apply a pulse current to the metal target, turning on the bias power supply to apply a negative pulse bias to the bipolar plate, performing a first sputtering deposition on at least one side surface of the bipolar plate to form a metal layer; subsequently turning on the carbon target power supply to apply a pulse power supply to the carbon target, performing a second sputtering deposition on the surface of the metal layer to form a metal-carbon composite layer, thereby obtaining the transition layer. Preferably, the method for preparing the carbon composite layer includes: turning on the carbon target power supply to apply a pulsed current to the carbon target material, performing a third sputtering deposition on the surface of the transition layer to form a corrosion-resistant carbon layer, and performing a surface annealing treatment on the corrosion-resistant carbon layer to form a conductive carbon layer, thereby obtaining the carbon composite layer.

9. The preparation method according to claim 8, characterized in that, The first sputtering deposition time is 10s to 300s; Preferably, the second sputtering deposition time is 10s to 300s; Preferably, the third sputtering deposition time is 10 min to 100 min; Preferably, the surface annealing treatment includes laser processing; Preferably, the laser used in the laser processing includes any one of femtosecond laser, picosecond laser or nanosecond laser, preferably a femtosecond laser; Preferably, the energy density of the femtosecond laser is 0.6 J / cm². 2 ~1.2J / cm 2 ; Preferably, the pulse width of the femtosecond laser is 300 fs to 800 fs; Preferably, the repetition frequency of the femtosecond laser is 20 kHz to 100 kHz.

10. An application of a carbon-containing coating for a fuel cell bipolar plate, characterized in that, The carbon-containing coating for fuel cell bipolar plates according to any one of claims 1 to 6, or the carbon-containing coating for fuel cell metal bipolar plates prepared by the preparation method according to any one of claims 7 to 9, is applied to a fuel cell.

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