Composite precoating, metal bipolar plate and method of manufacture

Abstract

The application discloses a composite pre-coating, a metal bipolar plate and a preparation method. The composite pre-coating comprises a soft metal layer, a first diffusion layer, a transition metal layer, a second diffusion layer, a ceramic transition layer, a third diffusion layer and a conductive carbon layer which are sequentially stacked; the material of the soft metal layer is any one of gold, silver, tin, magnesium, indium, copper, aluminum and yttrium. The composite pre-coating has small interface contact resistance and good conductivity, can effectively resist the strain force in the stamping process, has high bonding strength, prevents the peeling and cracking of the coating due to stamping, and effectively improves the compactness and corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite precoating, metal bipolar plate and a method of manufacture. BACKGROUND

[0002] Proton exchange membrane fuel cell (PEMFC) is a new power technology that can replace traditional fossil energy, which has high power density, high efficiency, cleanness and low working temperature, and has broad application prospects in fixed and transportation fields.

[0003] In the automobile fuel cell, the bipolar plate as the core component accounts for 80%-85% of the total weight and 40% of the total cost. The bipolar plate mainly provides mechanical support for the single cell group, separates and guides the reaction gas, collects the current, discharges the product water, and manages the water inlet. Therefore, the bipolar plate must have high electrical conductivity, low permeability, high thermal conductivity and hydrophobicity. Compared with the loose structure, poor air tightness and poor mechanical strength of graphite bipolar plate, metal bipolar plate has the advantages of good electrical conductivity and thermal conductivity, easy processing and forming, etc., and is the first choice for fuel cell bipolar plate material. However, in the working environment of proton exchange membrane fuel cell, the porous passivation film formed on the metal surface cannot protect the bipolar plate and the metal ions produced by corrosion will poison the catalyst, causing the output performance of PEMFC cell to decrease. In addition, the oxide film generated on the metal surface after corrosion increases the interface contact resistance, increases the ohmic polarization loss, and further reduces the output performance of the fuel cell. Therefore, the metal bipolar plate needs to be surface modified to improve the electrical conductivity and corrosion resistance of the bipolar plate.

[0004] In the prior art, an electrically conductive corrosion-resistant coating, such as a noble metal coating, a metal nitride coating, a metal carbide coating, and a carbon-based coating, is usually deposited on the surface of a metal bipolar plate, and a metal transition layer is often deposited between the coating and the metal substrate to improve the adhesion and corrosion resistance of the coating. Chinese Patent Document CN112795886A discloses an electrically conductive corrosion-resistant pre-coating for metal bipolar plate forming and a preparation method thereof. The ion implantation layer and diffusion treatment layer prepared by the invention can effectively improve the bonding performance of the coating substrate, eliminate coating defects and improve uniformity, and avoid cracking and peeling of the coating during stamping into a plate. Chinese Patent Document CN110797545B discloses a metal bipolar plate and a preparation method thereof, as well as a fuel cell. The prepared coating has at least two carbon films, and the multiple layers of carbon films work together to overcome the defects of each layer of carbon film deposition, thereby improving the adhesion of the carbon-based coating, the corrosion resistance of the carbon-based coating, and the electrical conductivity. Although the above-mentioned prior art can protect the metal bipolar plate to some extent and enable the fuel cell to operate stably for a period of time, the interface contact resistance of these coatings increases over a long period of time due to defects on the surface of the coating, and the coating separates from the substrate. In addition, the pre-coating process causes the coating to crack and peel off during the subsequent bipolar plate forming process due to excessive strain, resulting in the penetration of corrosive solution into the substrate and accelerated corrosion.

[0005] Therefore, there is a need to develop a coating with high electrical conductivity, corrosion resistance, and strong adhesion to the metal substrate to effectively protect the metal bipolar plate for a long time and enable the fuel cell to operate stably for a long time. SUMMARY

[0006] The technical problem to be solved by the present invention is to overcome the defects of the existing metal bipolar plate coating, such as large interface contact resistance, coating separation from the substrate, coating cracking and peeling, and substrate corrosion, and to provide a composite pre-coating, a metal bipolar plate, and a preparation method. The composite pre-coating of the present invention has small interface contact resistance, good electrical conductivity, can effectively resist the strain force during stamping, has high bonding strength, prevents the coating from peeling and cracking due to stamping, and effectively improves the density and corrosion resistance.

[0007] The present invention solves the above technical problems by the following technical solutions.

[0008] The present invention provides a composite pre-coating, which comprises a soft metal layer, a first diffusion layer, a transition metal layer, a second diffusion layer, a ceramic transition layer, a third diffusion layer, and an electrically conductive carbon layer stacked in sequence.

[0009] The soft metal layer is made of any one of gold, silver, tin, magnesium, indium, copper, aluminum, and yttrium.

[0010] In the present invention, the first diffusion layer is generally a layer formed by interdiffusion of particles on the surface of the soft metal layer and particles on the surface of the transition metal layer during the preparation of the composite pre-coating.

[0011] In the present invention, the second diffusion layer is generally a layer formed by interdiffusion of particles on the surface of the transition metal layer and particles on the surface of the ceramic transition layer during the preparation of the composite pre-coating.

[0012] In the present invention, the third diffusion layer is generally a layer formed by interdiffusion of particles on the surface of the ceramic transition layer and particles on the surface of the conductive carbon layer during the preparation of the composite pre-coating.

[0013] In the present invention, the thickness of the soft metal layer can be 10-100 nm, for example, 10 nm, 12 nm, 20 nm or 50 nm.

[0014] In the present invention, the thickness of the transition metal layer can be 10-120 nm, for example, 15 nm.

[0015] In the present invention, the thickness of the ceramic transition layer can be 10-120 nm, for example, 12 nm.

[0016] In the present invention, the thickness of the conductive carbon layer can be 20-150 nm, for example, 100 nm or 70 nm.

[0017] In the present invention, the thickness of the first diffusion layer is generally 1-10 nm, for example, 5 nm.

[0018] In the present invention, the thickness of the second diffusion layer is generally 1-10 nm, for example, 5 nm.

[0019] In the present invention, the thickness of the third diffusion layer is generally 1-10 nm, for example, 5 nm.

[0020] In the present invention, the composite pre-coating is provided on at least one side of a substrate, and the soft metal layer is adjacent to the substrate. The substrate can be a conventional substrate in the art, and the thickness of the substrate can be a conventional thickness in the art. Generally, the substrate is a metal substrate, and the metal substrate can be a conventional metal substrate that can be used to prepare a metal bipolar plate, for example, stainless steel with a trade name of 316L.

[0021] In the present invention, when the composite pre-coating is provided on at least one side of a substrate, particles on the surface of the substrate and particles on the surface of the soft metal layer will generally interdiffuse to form a fourth diffusion layer (i.e., the fourth diffusion layer is located between the substrate and the soft metal layer). The thickness of the fourth diffusion layer is generally 5-50 nm, for example, 30 nm.

[0022] In the present application, the thickness of the first, second, third and fourth diffusion layers is closely related to the properties (e.g. element type) of the elements in each layer of the composite pre-coating layer and the preparation process (e.g. plating temperature) of each layer. According to the properties of the elements in each layer and the different operating conditions of the preparation process of each layer, the thickness of the first, second, third and fourth diffusion layers will also be different.

[0023] In the present application, the material of the soft metal layer is preferably copper.

[0024] In the present application, the material of the transition metal layer can be a conventional transition metal in the art, preferably any one of Cr, Ti and Nb, for example Ti.

[0025] In the present application, the material of the ceramic transition layer can be a conventional substance that can be used as a ceramic transition layer in the art, preferably a transition metal carbide and / or a transition metal nitride.

[0026] In the present application, the transition metal in the transition metal carbide is preferably one or more of Cr, Ti, Nb, Zr, Ta and Mo.

[0027] In the present application, the transition metal in the transition metal nitride is preferably one or more of Cr, Ti, Nb, Zr, Ta and Mo, for example TiN.

[0028] In the present application, the material of the conductive carbon layer can be a conventional conductive carbon material in the art, for example one or more of amorphous carbon, graphitic carbon, diamond-like carbon and hydrogenated carbon, preferably amorphous carbon.

[0029] The present application also provides a preparation method of a composite pre-coating layer, comprising the following steps:

[0030] S1. Forming a soft metal layer on at least one side of the substrate by primary deposition;

[0031] Forming a transition metal layer on the surface of the soft metal layer by secondary deposition; the material of the soft metal layer is any one of gold, silver, tin, magnesium, indium, copper, aluminum and yttrium;

[0032] Forming a ceramic transition layer on the surface of the transition metal layer by tertiary deposition;

[0033] Forming a conductive carbon layer on the surface of the ceramic transition layer by quaternary deposition; obtaining a substrate loaded with a composite pre-coating layer;

[0034] The bias voltage of the primary deposition is -50 to -200 V;

[0035] S2. Subjecting the substrate loaded with the composite pre-coating layer to vacuum heat treatment, and

[0036] The vacuum heat treatment forms: a first diffusion layer between the soft metal layer and the transition metal layer; a second diffusion layer between the transition metal layer and the ceramic transition layer; a third diffusion layer between the ceramic transition layer and the conductive carbon layer; and a fourth diffusion layer between the substrate and the soft metal layer.

[0037] In S1, the deposition mode of the first deposition, the second deposition, the third deposition and the fourth deposition can each independently be a conventional deposition mode in the art, for example the deposition mode can be reactive magnetron sputter deposition, chemical vapor deposition, vacuum magnetron sputter deposition or vacuum multi-arc ion plating deposition.

[0038] In some preferred embodiments of the present application, the deposition mode of the first deposition is vacuum multi-arc ion plating deposition.

[0039] In some preferred embodiments of the present application, the deposition mode of the second deposition is vacuum multi-arc ion plating deposition.

[0040] In some preferred embodiments of the present application, the deposition mode of the third deposition is reactive magnetron sputter deposition.

[0041] In some preferred embodiments of the present application, the deposition mode of the fourth deposition is vacuum magnetron sputter deposition.

[0042] In S1, the current of the first deposition can be 0.5-10 A, preferably 2-8 A, for example 5 A.

[0043] In S1, the bias voltage of the first deposition is preferably -55 to -180 V, for example -60 V, -70 V, -100 V or -150 V.

[0044] In S1, the pressure of the first deposition is preferably 0.03-0.1 Pa, for example 0.06 Pa or 0.08 Pa.

[0045] In S1, the temperature of the first deposition can be 100-300℃, for example 150℃, 200℃ or 250℃.

[0046] In S1, the time of the first deposition can be 1-300 min, preferably 1-100 min, for example 6 min.

[0047] In some preferred embodiments of the present application, in S1, the current of the first deposition is 5 A, the bias voltage of the first deposition is -100 V, the pressure of the first deposition is 0.06 Pa, the temperature of the first deposition is 200℃, and the time of the first deposition is 6 min.

[0048] In S1, the current for the second deposition can be 0.5-10 A, preferably 2-8 A, for example 5 A.

[0049] In S1, the bias voltage for the second deposition is preferably -15 to -100 V, for example -30 V, -50 V, -60 V, or -80 V.

[0050] In S1, the pressure for the second deposition is preferably 0.3-1 Pa, for example 0.5 Pa, 0.6 Pa, or 0.8 Pa.

[0051] In S1, the temperature for the second deposition can be 100-300 °C, for example 150 °C, 200 °C, or 250 °C.

[0052] In S1, the time for the second deposition can be 1-300 min, preferably 1-100 min, for example 10 min.

[0053] In some preferred embodiments of the present application, in S1, the current for the second deposition is 5 A, the bias voltage for the second deposition is -60 V, the pressure for the second deposition is 0.6 Pa, the temperature for the second deposition is 200 °C, and the time for the second deposition is 10 min.

[0054] In S1, the current for the third deposition can be 0.5-10 A, preferably 4-10 A, for example 7 A.

[0055] In S1, the bias voltage for the third deposition is preferably -15 to -100 V, for example -30 V, -50 V, -60 V, -70 V, or -80 V.

[0056] In S1, the pressure for the third deposition is preferably 0.3-1 Pa, for example 0.5 Pa, 0.6 Pa, or 0.8 Pa.

[0057] In S1, the temperature for the third deposition can be 150-400 °C, for example 180 °C, 200 °C, 250 °C, 300 °C, or 350 °C.

[0058] In S1, the time for the third deposition can be 1-300 min, preferably 1-100 min, for example 10 min.

[0059] In some preferred embodiments of the present application, in S1, the current for the third deposition is 7 A, the bias voltage for the third deposition is -70 V, the pressure for the third deposition is 0.6 Pa, the temperature for the third deposition is 300 °C, and the time for the third deposition is 10 min.

[0060] In S1, the current for the fourth deposition can be 0.5-10 A, preferably 4-10 A, for example 7 A.

[0061] In S1, the bias voltage of the four-time deposition is preferably -200 to -500 V, for example -250 V, -300 V, -350 V, -400 V or -450 V.

[0062] In S1, the pressure of the four-time deposition is preferably 0.3 to 1 Pa, for example 0.5 Pa, 0.6 Pa or 0.8 Pa.

[0063] In S1, the temperature of the four-time deposition can be 200 to 500 °C, for example 250 °C, 300 °C, 350 °C, 400 °C or 450 °C.

[0064] In S1, the time of the four-time deposition can be 1 to 300 min, preferably 1 to 100 min, for example 10 min.

[0065] In some preferred embodiments of the present application, in S1, the current of the four-time deposition is 7 A, the bias voltage of the four-time deposition is -300 V, the pressure of the four-time deposition is 0.6 Pa, the temperature of the four-time deposition is 400 °C, and the time of the four-time deposition is 10 min.

[0066] In S1, the thickness of the soft metal layer can be 10 to 100 nm, for example 10 nm, 12 nm, 20 nm or 50 nm.

[0067] In S1, the thickness of the transition metal layer can be 10 to 120 nm, for example 15 nm.

[0068] In S1, the thickness of the ceramic transition layer can be 10 to 120 nm, for example 12 nm.

[0069] In S1, the thickness of the conductive carbon layer can be 20 to 150 nm, for example 100 nm or 70 nm.

[0070] In S2, the thickness of the fourth diffusion layer is generally 5 to 50 nm, for example 30 nm.

[0071] In S2, the thickness of the first diffusion layer is generally 1 to 10 nm, for example 5 nm.

[0072] In S2, the thickness of the second diffusion layer is generally 1 to 10 nm, for example 5 nm.

[0073] In S2, the thickness of the third diffusion layer is generally 1 to 10 nm, for example 5 nm.

[0074] In S1, the substrate can be a substrate conventional in the art, and the thickness of the substrate can be a thickness conventional in the art. Generally, the substrate is a metal substrate, and the metal substrate can be a metal substrate conventional in the art that can be used to prepare a metal bipolar plate, for example, stainless steel with a trade designation of 316L.

[0075] In S1, the soft metal layer is preferably made of copper.

[0076] In S1, the transition metal layer is preferably made of any one of Cr, Ti and Nb, such as Ti.

[0077] In S1, the ceramic transition layer is preferably made of any one of Cr, Ti and Nb, such as Ti.

[0078] In S1, the ceramic transition layer is preferably made of any one of Cr, Ti and Nb, such as Ti.

[0079] In S1, the ceramic transition layer is preferably made of any one of Cr, Ti and Nb, such as Ti.

[0080] In S1, the ceramic transition layer is preferably made of any one of Cr, Ti and Nb, such as Ti.

[0081] In S1, the conductive carbon layer is preferably made of any one of amorphous carbon, graphitic carbon, diamond-like carbon and hydrogenated carbon.

[0082] In S1, the substrate is generally pretreated before the first deposition. The pretreatment can be performed by any method known in the art, such as cleaning. The pretreatment time can be 10-80 min, preferably 10-60 min, more preferably 10-30 min, such as 15 min.

[0083] In S1, the substrate is generally pretreated before the first deposition. The pretreatment can be performed by any method known in the art, such as cleaning. The pretreatment time can be 10-80 min, preferably 10-60 min, more preferably 10-30 min, such as 15 min.

[0084] In S1, the substrate is generally pretreated before the first deposition. The pretreatment can be performed by any method known in the art, such as cleaning. The pretreatment time can be 10-80 min, preferably 10-60 min, more preferably 10-30 min, such as 15 min.

[0085] In S1, the substrate is generally pretreated before the first deposition. The pretreatment can be performed by any method known in the art, such as cleaning. The pretreatment time can be 10-80 min, preferably 10-60 min, more preferably 10-30 min, such as 15 min.

[0086] In S1, the substrate is generally pretreated before the first deposition. The pretreatment can be performed by any method known in the art, such as cleaning. The pretreatment time can be 10-80 min, preferably 10-60 min, more preferably 10-30 min, such as 15 min.

[0087] When the cleaning method is plasma cleaning, the bias voltage of the plasma cleaning can be -500 to -1000 V, for example -700 V.

[0088] When the cleaning method is plasma cleaning, the pressure of the plasma cleaning can be -0.01 to 10 Pa, for example 2.0 Pa.

[0089] In some preferred embodiments of the present application, in S1, before the first deposition, the pretreatment comprises the following steps: sequentially ultrasonic cleaning the substrate in acetone, anhydrous ethanol and deionized water for 15 min each; and then placing the dried metal substrate into a vacuum coating device, and performing plasma cleaning at a bias voltage of -700 V and a pressure of 2.0 Pa for 30 min.

[0090] In S2, the temperature of the vacuum heat treatment can be 200 to 700 ℃, for example 450 ℃.

[0091] In S2, the pressure of the vacuum heat treatment can be 0.01 to 5000 Pa, preferably 100 to 3000 Pa, for example 2000 Pa.

[0092] In S2, the time of the vacuum heat treatment can be 1 to 100 min, preferably 30 to 60 min, for example 60 min.

[0093] In S2, the rate of temperature rise to the temperature of the vacuum heat treatment can be 1 to 30 ℃·min -1 , for example 8 ℃·min -1 .

[0094] In S2, the vacuum heat treatment generally comprises a cooling step. The rate of cooling can be 2 to 40 ℃·min -1 , for example 5 ℃·min -1 .

[0095] The present application also provides a composite pre-coating prepared by the method for preparing a composite pre-coating as described above.

[0096] The present application also provides a metal bipolar plate comprising a composite pre-coating as described above.

[0097] In the present application, "first", "second", "third" and "fourth" are only used to distinguish the diffusion layers, and have no special meaning.

[0098] In the present application, "first", "second", "third" and "fourth" are only used to distinguish the diffusion layers, and have no special meaning.

[0099] On the basis of common sense in the art, the above-mentioned preferred conditions can be combined arbitrarily, i.e. to obtain each preferred example of the present application.

[0100] The reagents and raw materials used in the present application are commercially available.

[0101] The positive progress effect of the present application is that:

[0102] (1) The composite pre-coating layer of the present application has small interface contact resistance, good electrical conductivity, can effectively resist the strain force in the stamping process, has high bonding strength, can prevent the coating from peeling and cracking due to stamping, and effectively improves the compactness and corrosion resistance.

[0103] (2) The composite pre-coating layer of the present application can effectively protect the metal bipolar plate for a long time.

[0104] (3) The metal bipolar plate of the present application can make the fuel cell run stably for a long time. BRIEF DESCRIPTION OF DRAWINGS

[0105] Figure 1 is a schematic diagram of the structure of the modified composite coating of the present application.

[0106] Figure 2 is a schematic diagram of the flow field plate contact resistance test method.

[0107] REFERENCE NUMERALS:

[0108] Metal substrate 1

[0109] Soft metal layer 2

[0110] Transition metal layer 3

[0111] Ceramic transition layer 4

[0112] Conductive carbon layer 5

[0113] Fourth diffusion layer 6

[0114] First diffusion layer 7

[0115] Second diffusion layer 8

[0116] Third diffusion layer 9 DETAILED DESCRIPTION

[0117] The present application will be further described by way of examples below, but the present application is not limited in the scope of the examples described. The experimental methods in the following examples are not specified, which are selected according to conventional methods and conditions, or according to the instructions of the goods.

[0118] Unless otherwise specified, the reagents, raw materials used in the present application are commercially available.

[0119] The present application will be further described by way of examples below, but the present application is not limited in the scope of the examples described. The experimental methods in the following examples are not specified, which are selected according to conventional methods and conditions, or according to the instructions of the goods. Figure 1 The present application will be further described by way of examples below, but the present application is not limited in the scope of the examples described. The experimental methods in the following examples are not specified, which are selected according to conventional methods and conditions, or according to the instructions of the goods.

[0120] Example 1

[0121] A composite pre-coating, which has a structure as shown in the figure: a fourth diffusion layer 6, a soft metal layer 2, a first diffusion layer 7, a transition metal layer 3, a second diffusion layer 8, a ceramic transition layer 4, a third diffusion layer 9 and a conductive carbon layer 5 are sequentially stacked on a metal substrate 1; Figure 1 The thickness of the soft metal layer 2 is 12 nm; the thickness of the transition metal layer 3 is 15 nm; the thickness of the ceramic transition layer 4 is 12 nm; the thickness of the conductive carbon layer 5 is 70 nm;

[0122] The thickness of the first diffusion layer 7 is 5 nm; the thickness of the second diffusion layer 8 is 5 nm; the thickness of the third diffusion layer 9 is 5 nm; the thickness of the fourth diffusion layer 6 is 30 nm;

[0123] The material of the soft metal layer 2 is Cu; the material of the transition metal layer 3 is Ti; the material of the ceramic transition layer 4 is TiN; the material of the conductive carbon layer 5 is amorphous carbon.

[0124] Preparation process:

[0125] (1) The metal substrate 1 (stainless steel, grade 316L) is sequentially ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 15 min each to remove surface oil stains and oxide films, and is dried by blowing N2 in a dust-free environment to remove water film and avoid re-oxidation and pollution of the substrate;

[0126] (2) The cleaned and dried metal substrate 1 is placed into a vacuum coating device, and plasma cleaning is performed at a bias voltage of -700 V and a pressure of 2.0 Pa for 30 min, and the temperature of the plasma cleaning is 450℃ to remove the oxide film on the surface of the metal substrate 1 and increase the adhesion of the coating;

[0127] (3) The vacuum multi-arc ion plating deposition method is adopted to sequentially form the fourth diffusion layer 6 and the soft metal layer 2 on one surface of the pretreated metal substrate 1 by one-time deposition, the temperature of one-time deposition is 200℃, the bias voltage of one-time deposition is -100 V, the pressure of one-time deposition is 0.06 Pa, the thickness of the Cu soft metal layer 2 is 10 nm; the time of one-time deposition is 6 min, and the current of one-time deposition is 5 A;

[0128] (4) The vacuum multi-arc ion plating deposition method is adopted to sequentially form the first diffusion layer 7 and the transition metal layer 3 on the surface of the soft metal layer 2 by two-time deposition, the temperature of two-time deposition is 200℃, the bias voltage of two-time deposition is -60 V, the pressure of two-time deposition is 0.6 Pa, the thickness of the Ti transition layer 3 is 15 nm; the time of two-time deposition is 10 min, and the current of two-time deposition is 5 A;

[0129]

[0130] ​(5) The second diffusion layer 8 and the ceramic transition layer 4 are formed on the surface of the transition metal layer 3 by three times of deposition by the reactive magnetron sputtering deposition method, the temperature of the three times of deposition is 300℃, the bias voltage of the three times of deposition is -70V, the pressure of the three times of deposition is 0.6Pa, the thickness of the TiN ceramic transition layer 4 is 12nm; the time of the three times of deposition is 10min, the current of the three times of deposition is 7A;

[0131] (6) The third diffusion layer 9 and the conductive carbon layer 5 are formed on the surface of the ceramic transition layer 4 by four times of deposition by the vacuum magnetron sputtering deposition method, the temperature of the four times of deposition is 400℃, the bias voltage of the four times of deposition is -300V, the pressure of the four times of deposition is 0.6Pa, the thickness of the conductive carbon layer 5 is 70nm; the time of the four times of deposition is 10min, the current of the four times of deposition is 7A;

[0132] (7) The metal substrate loaded with the composite pre-coating layer is subjected to vacuum heat treatment for 1h (at a pressure of 2000Pa), the temperature of the heat treatment is 700℃, the heating rate of the heat treatment is 8℃·min -1 , the cooling rate is 5℃·min -1 ; and the metal sheet loaded with the composite pre-coating layer is obtained.

[0133] The main process parameters involved in the above embodiment 1 are shown in Table 1.

[0134] Table 1

[0135]

[0136] Embodiment 2

[0137] Except that the deposition bias voltage in (3) is changed to -60V and the thickness of the Cu metal layer is also increased to 12nm accordingly, the other steps are the same as those in embodiment 1. It is possible that due to the decrease of the negative bias voltage, the bombardment effect of the deposition ions on the substrate is weakened, thus leading to the decrease of the substrate temperature and the weakening of the bombardment, stirring and implantation on the substrate surface, the diffusion process of the deposition particles is reduced, and the formation and widening of the pseudo-diffusion transition zone are reduced, thus increasing the thickness of the Cu layer.

[0138] Comparative Example 1a (without deposition of Cu soft metal layer)

[0139] Compared with embodiment 1, the step of depositing the Cu soft metal layer is omitted in comparative example 1.

[0140] Comparative Example 1b (without vacuum high-temperature treatment)

[0141] Compared with embodiment 1, the step of vacuum high-temperature treatment is omitted in comparative example 1b.

[0142] Comparative Example 2a

[0143] The step (3) is changed to deposition bias of -30V, other steps are same as example 2, and the thickness of Cu soft metal layer is same as example 2.

[0144] Comparative example 2b

[0145] The step (3) is changed to deposition bias of -300V, other steps are same as example 2, and the thickness of Cu soft metal layer is 5nm same as example 2.

[0146] Effect example

[0147] (1) Interface contact resistance test

[0148] Test object: The metal sheet loaded with composite pre-coating prepared in example 1, and comparative examples 1 and 2.

[0149] Test method: The interface contact resistance (ICR) is an important parameter for evaluating the interface conductivity of the bipolar plate. The ICR value of the composite pre-coating sample and carbon paper is determined according to the method of GB / T 20042.6-2011. According to the formula shown in the following, the sample is loaded on the test device, and a carbon paper used as the diffusion layer of the fuel cell is placed between the two gold-plated copper electrodes and a certain pressure is applied. The resistance value is measured by a low resistance meter, and the measuring electrode is the gold-plated copper electrode. Figure 2

[0150] During the test, a resistance value is recorded every time the pressure increases by 0.1 MPa, until the change rate of the current resistance test value and the previous resistance test value is ≤5%, and then the minimum resistance value is considered to be reached, and the test is stopped. The resistance values under different pressures are recorded.

[0151] The measurement pressure range is 0.3-1.6 MPa, and the resistance value under the pressure of 1.5 MPa is selected.

[0152] Under the conventional pressure (1.5 MPa), the ICR between the carbon paper and the coating sample can be calculated by the following formula.

[0153] R1 = RSS + 2Rcp / coating + 2Rcp + 2Rcp / Au + 2RAu (1)

[0154] R2 = Rcp + 2Rcp / Au + 2RAu (2)

[0155] R1 - R2 = RSS + Rcp + 2Rcp / coating ≈ 2Rcp / coating (3)

[0156] ICR = (R1 - R2 ) / 2× Ac (4)

[0157] ​In formula (1) and formula (2), R1, R2 are respectively steps 1, 2 (as shown in Figure 2 The specific operation is: placing the sample to be tested between the upper and lower copper plates, placing Toray carbon paper between the copper plate and the sample to simulate the contact between the bipolar plate and the diffusion layer, then applying a constant current between the copper plates by an external power supply, finally pressing the two sides of the copper plate, recording the voltage value between the two copper plates, and calculating the value of the contact resistance ICR by formula (4) above) The total resistance of the resistance. RSS is the resistance of the substrate, Rcp is the resistance of the carbon paper, RAu is the resistance of the gold-plated copper plate, Rcp / coating is the contact resistance between the carbon paper and the coating sample, Rcp / ss is the contact resistance between the carbon paper and the substrate, and Rcp / Au is the contact resistance between the carbon paper and the gold-plated copper plate. In formula (3), since the resistances of RSS and Rcp are much smaller than Rcp / coating, their values can be ignored. In formula (4), Ac is the effective contact area between the carbon paper and the test sample.

[0158] Test results: as shown in Table 1.

[0159] (2) Hydrophobicity test

[0160] Test object: metal sheets loaded with composite pre-coating prepared in Example 1, and Comparative Examples 1a-1b and 2a-2b.

[0161] Test method:

[0162] An SDC-350 full-automatic contact angle measuring instrument produced by Dongguan Shengding Precision Instrument Co., Ltd. was used to measure the static water contact angle on the surface of the sample by the sessile drop method. Under room temperature and atmospheric pressure, the hydrophilic or hydrophobic property of the sample surface was evaluated by measuring the size of the static contact angle between the surface of each sample and 2 μL of water (i.e. the water droplet amount for measuring the water contact angle was 2 μL).

[0163] During the experiment, the contact angle values at three different positions of each sample were measured, and the average value was finally taken as the final contact angle value of the sample surface. Generally, a larger water contact angle value (greater than 90°) indicates that the hydrophobicity of the sample surface is better, while a smaller water contact angle value (less than 90°) indicates that the hydrophilicity of the sample is better.

[0164] Test results: as shown in Table 2.

[0165] (3) Corrosion resistance test

[0166] Test object: metal sheets loaded with composite pre-coating prepared in Examples 1-2 and Comparative Examples 1a-1b and 2a-2b.

[0167] Test method: The corrosion resistance test method is according to GBT 20042.6-2011. The main test requirements are as follows:

[0168] The metal sheets loaded with the composite pre-coating prepared in Examples 1-2, Comparative Examples 1a-1b, 2a-2b were respectively used as working electrodes, a saturated calomel electrode (SCE) was used as a reference electrode, and a platinum mesh was used as an auxiliary electrode in a three-electrode system for testing. In the actual test process, a Gamry 3000 electrochemical workstation was used, and a conventional three-electrode test system was used to test the potentiodynamic polarization curve. Considering that the environment on the cathode side of the fuel cell is more likely to cause corrosion of the material compared to the anode side in the actual operating conditions, therefore, in this test, the corrosion resistance of the carbon-based coating sample was evaluated by mainly simulating the corrosion environment on the cathode side. Air was introduced into the 0.5 mol / L H2SO4 corrosion solution at a temperature of 80°C and with a F - concentration of 5×10 -6 mol / L at a flow rate of 50 sccm to simulate the cathode environment. First, the sample was stabilized at the open circuit potential for 30 min, and then linear potential scanning was performed at a scanning rate of 2 mV / s, with a potential range of -0.4 V to 0.9 V (vs. SCE). The Tafel fitting was performed on the measured polarization curve, and the current corresponding to the intersection of the Tafel straight line was the corrosion current of the test object.

[0169] Test results: as shown in Table 2.

[0170] (4) Coating life test (stability test)

[0171] Test object: metal sheets loaded with the composite pre-coating prepared in Examples 1-2, Comparative Examples 1a-1b, 2a-2b.

[0172] Test method: In order to test the life of the composite pre-coating obtained by different processes, an accelerated electrochemical test was performed on the metal sheets loaded with the composite pre-coating. A conventional three-electrode test system was used to test the potentiodynamic polarization curve by an electrochemical workstation Gamry 3000. Air was introduced into the 0.5 mol / L H2SO4 corrosion solution at a temperature of 80°C and with a F - concentration of 5×10 -6 mol / L at a flow rate of 50 sccm to simulate the cathode environment. First, the sample was stabilized at the open circuit potential for 30 min, and then linear potential scanning was performed at a scanning rate of 2 mV / s, with a constant potential of 0.8 V (the fuel cell basically operates in the range of 0.6-0.65) for 10 hours. The Tafel fitting was performed on the measured polarization curve, and the current corresponding to the intersection of the Tafel straight line was the corrosion current of the test object.

[0173] Test results: see Table 2.

[0174] Table 2

[0175]

[0176] Note: "I corr " represents the corrosion current density. The corrosion current is a reflection of the compactness of the coating, the lower the corrosion current, the more compact the coating.

[0177] From the data of the interface contact resistance, the interface contact resistance of Example 1 is the lowest, followed by Example 2, and the interface contact resistance of Comparative Examples 1a and 1b is equal, and the interface contact resistance of Comparative Examples 2a and 2b is significantly increased, being 5.87 mΩ·cm 2 and 6.16 mΩ·cm 2 , respectively, which may be caused by the poor contact between the collector and the soft metal layer interface due to the too low (-30V) or too high (-300V) bias voltage during the deposition of the soft metal layer.

[0178] From the data of the contact angle, the contact angle of Example 2 is the largest, followed by Example 1, which is close to Example 2, and the contact angles of Comparative Examples 1a and 1b are comparable. The contact angles of Comparative Examples 2a and 2b are both low. Specifically, the water contact angle of Example 1 can reach 112.3°, and the contact angles of Comparative Example 1a and Comparative Example 1b are 107.5° and 105.6°, respectively, which may be related to the reduction of the coating surface roughness caused by the addition of Cu soft metal and the vacuum post-treatment in Example 1. The increase of the contact angle is more conducive to the water management of the fuel cell stack, and is also an important reason for its good corrosion resistance. The contact angle of Example 2 is 114.1°, which is close to Example 1, and the contact angles of Comparative Examples 2a and 2b are smaller than those of other samples, being 100.5 and 101.7°, respectively, which is presumably caused by the change of the substrate / soft metal layer interface, which leads to the change of the surface roughness of the subsequent coating.

[0179] From the data of the corrosion current density, the corrosion current density of Example 1 is the smallest (the compactness is the best), the corrosion current density of Example 2 is close to that of Example 1, and the corrosion current densities of Comparative Examples 1a and 1b are larger. The corrosion current values of Example 1, Example 2, and Comparative Examples 1a and 1b can all reach the target value of the U.S. Department of Energy for the corrosion current density of fuel cell bipolar plates in 2025, which is <1 μA / cm 2 . However, the corrosion current data of Comparative Examples 2a and 2b are both higher (the compactness is poorer), being 5.87 μA / cm 2 and 5.36 μA / cm 2 , respectively. Specifically:

[0180] The amorphous carbon coating uniformly covers the surface of the stainless steel, which effectively avoids direct contact between the base metal and the acidic corrosion solution, and greatly improves the corrosion resistance of the bipolar plate. The corrosion resistance (cathode) of the amorphous carbon coating formed by different processes was analyzed, and Example 1 had the smallest corrosion current of 0.48 μA / cm 2 , indicating that the amorphous carbon coating formed by adding a soft metal Cu layer and vacuum post-treatment has the best performance. The corrosion current density of Comparative Example 1a is lower than that of Comparative Example 1b, indicating that the diffusion layer between the layers formed by vacuum post-treatment has a greater effect on improving the corrosion resistance of the coating than adding a soft metal Cu layer. The corrosion current data of Comparative Examples 2a and 2b cannot meet the requirements, which also indicates that the corrosion resistance of the coating prepared by improper selection of bias is poor, and although there is subsequent vacuum heat treatment, it still cannot compensate for the defects caused by the interface between the substrate / soft metal layer.

[0181] From the corrosion current density after 10 hours of constant potential 0.8 V test, the corrosion current of Examples 1 and 2 did not change after 10 hours of continuous test, and still maintained at 0.48 μA / cm 2 and 0.493 μA / cm 2 . It can be seen that the corrosion resistance of the composite pre-coating prepared in Examples 1 and 2 is good, and the stability is good, which can meet the service life requirement of the coating. The corrosion current of Comparative Examples 1a and 1b increased by about 40% and 10%, respectively, which increased slightly; the corrosion current of Comparative Examples 2a and 2b increased by about 10 times, the compactness decreased significantly, the stability was poor, and it could not meet the service life requirement of the coating.

Claims

1. A composite pre-coat characterized in that, It comprises a soft metal layer, a first diffusion layer, a transition metal layer, a second diffusion layer, a ceramic transition layer, a third diffusion layer and a conductive carbon layer which are sequentially stacked; The material of the soft metal layer is copper; The material of the transition metal layer is Ti; The material of the ceramic transition layer is TiN; The thickness of the soft metal layer is 10-100 nm; The thickness of the transition metal layer is 10-120 nm; The thickness of the ceramic transition layer is 10-120 nm; The thickness of the conductive carbon layer is 20-150 nm.

2. The composite pre-coat of claim 1, wherein, It meets one or more of the following conditions a-d; a. The thickness of the first diffusion layer is 1-10 nm; b. The thickness of the second diffusion layer is 1-10 nm; c. The thickness of the third diffusion layer is 1-10 nm; d. The composite pre-coating layer is arranged on at least one side of the substrate, and a fourth diffusion layer is formed between the substrate and the soft metal layer.

3. The composite pre-coat of claim 2, wherein, The composite pre-coating layer meets the conditions a-d in claim 2 at the same time.

4. The composite pre-coat of claim 2, wherein, It meets one or more of the following conditions a-g; a. The thickness of the soft metal layer is 10 nm, 12 nm, 20 nm or 50 nm; b. The thickness of the transition metal layer is 15 nm; c. The thickness of the ceramic transition layer is 12 nm; d. The thickness of the conductive carbon layer is 100 nm or 70 nm; e. The thickness of the first diffusion layer is 5 nm; f. The thickness of the second diffusion layer is 5 nm; g. The thickness of the third diffusion layer is 5 nm.

5. The composite pre-coat of claim 2, wherein, The substrate is a metal substrate.

6. The composite pre-coat of claim 2, wherein, The substrate is 316L stainless steel.

7. The composite pre-coat of claim 2, wherein, The thickness of the fourth diffusion layer is 5-50 nm.

8. The composite pre-coat of claim 1, wherein, The material of the conductive carbon layer is one or more of amorphous carbon, graphite-like carbon, diamond-like carbon and hydrogenated carbon.

9. The composite pre-coat of claim 8, wherein, The material of the conductive carbon layer is amorphous carbon.

10. A method of preparing a composite pre-coat layer, characterized in that, It comprises the following steps: S1. Forming a soft metal layer on at least one side of a substrate by once deposition; Forming a transition metal layer on the surface of the soft metal layer by twice deposition, the material of the transition metal layer is Ti, and the material of the soft metal layer is copper; Forming a ceramic transition layer on the surface of the transition metal layer by thrice deposition; the material of the ceramic transition layer is TiN; Forming a conductive carbon layer on the surface of the ceramic transition layer by four times deposition; a substrate loaded with a composite pre-coating layer is obtained; The bias voltage of the once deposition is -50~-200 V; S2. Vacuum heat treatment is performed on the substrate loaded with the composite pre-coating layer, and the process is completed; After the vacuum heat treatment, the following layers are formed: a first diffusion layer between the soft metal layer and the transition metal layer; a second diffusion layer between the transition metal layer and the ceramic transition layer; a third diffusion layer between the ceramic transition layer and the conductive carbon layer; and a fourth diffusion layer between the substrate and the soft metal layer.

11. The method of claim 10, wherein the composite pre-coat is prepared by, It meets one or both of the following conditions a-b; a. The deposition mode of the once deposition, the twice deposition, the thrice deposition and the four times deposition is reactive magnetron sputtering deposition, chemical vapor deposition, vacuum magnetron sputtering deposition or vacuum multi-arc ion plating deposition; b. The material of the conductive carbon layer is one or more of amorphous carbon, graphite-like carbon, diamond-like carbon and hydrogenated carbon.

12. The method of claim 11, wherein the composite pre-coat is prepared by, The material of the conductive carbon layer is amorphous carbon.

13. The method of claim 11, wherein the composite pre-coat is prepared by, The deposition mode of the first deposition is vacuum multi-arc ion plating deposition.

14. The method of claim 11, wherein the composite pre-coat is prepared by, The deposition mode of the second deposition is vacuum multi-arc ion plating deposition.

15. The method of claim 11, wherein the composite pre-coat is prepared by the steps of: a) providing a first layer of a first material; b) providing a second layer of a second material; and c) providing a third layer of a third material. 15 The deposition mode of the third deposition is reactive magnetron sputtering deposition.

16. The method of claim 11, wherein the composite pre-coat is prepared by the steps of: a) providing a first layer of a first material; b) providing a second layer of a second material; and c) providing a third layer of a third material. 16 The deposition mode of the fourth deposition is vacuum magnetron sputtering deposition.

17. The method for preparing the composite pre-coating as described in claim 10, characterized in that, It meets one or more of the following conditions a-j; a. The current of the first deposition is 0.5-10A; b. The bias voltage of the first deposition is -55~-180V; c. The pressure of the first deposition is 0.03-0.1Pa; d. The temperature of the first deposition is 100-300℃; e. The time of the first deposition is 1-300min; f. The current of the second deposition is 0.5-10A; g. The bias voltage of the second deposition is -15~-100V; h. The pressure of the second deposition is 0.3-1Pa; i. The temperature of the second deposition is 100-300℃; j. The time of the second deposition is 1-300min.

18. The method of claim 17, wherein the composite pre-coat is prepared by, It meets one or more of the following conditions a-j; a. The current of the first deposition is 2-8A; b. The bias voltage of the first deposition is -60V, -70V, -100V or -150V; c. The pressure of the first deposition is 0.06Pa or 0.08Pa; d. The temperature of the first deposition is 150℃, 200℃ or 250℃; e. The time of the first deposition is 1-100min; f. The current of the second deposition is 2-8A; g. The bias voltage of the second deposition is -30V, -50V, -60V or -80V; h. The pressure of the second deposition is 0.5Pa, 0.6Pa or 0.8Pa; i. The temperature of the second deposition is 150℃, 200℃ or 250℃; j. The time of the second deposition is 1-100min.

19. The method of claim 18, wherein the composite pre-coat is prepared by, It meets one or more of the following conditions a-d; a. The current of the first deposition is 5A; b. The time of the first deposition is 6min; c. The current of the second deposition is 5A; d. The time of the second deposition is 10min.

20. The method of claim 17, wherein the composite pre-coat is prepared by, The current of the first deposition is 5A, the bias voltage of the first deposition is -100V, the pressure of the first deposition is 0.06Pa, the temperature of the first deposition is 200℃, and the time of the first deposition is 6min.

21. The method of claim 17, wherein the composite precoat is prepared by the steps of: The current of the first deposition is 5A, the bias voltage of the first deposition is -100V, the pressure of the first deposition is 0.06Pa, the temperature of the first deposition is 200℃, and the time of the first deposition is 6min.

22. The method of claim 10, wherein the composite precoat is prepared by the steps of: It meets one or more of the following conditions a-j; a. The current of the third deposition is 0.5-10A; b. The bias voltage of the third deposition is -15~-100V; c. The pressure of the third deposition is 0.3-1Pa; d. The temperature of the third deposition is 150-400℃; e. The time of the third deposition is 1-300min; f. the current of the four depositions is 0.5-10 A; g. the bias voltage of the four depositions is -200 - -500 V; h. the pressure of the four depositions is 0.3-1 Pa; i. the temperature of the four depositions is 200-500℃; j. the time of the four depositions is 1-300 min.

23. The method of claim 22, wherein the composite pre-coat is prepared by, which satisfies one or more of the following conditions a-j; a. the current of the three depositions is 4-10 A; b. the bias voltage of the three depositions is -30 V, -50 V, -60 V, -70 V or -80 V; c. the pressure of the three depositions is 0.5 Pa, 0.6 Pa or 0.8 Pa; d. the temperature of the three depositions is 180℃, 200℃, 250℃, 300℃ or 350℃; e. the time of the three depositions is 1-100 min; f. the current of the four depositions is 4-10 A; g. the bias voltage of the four depositions is -250 V, -300 V, -350 V, -400 V or -450 V; h. the pressure of the four depositions is 0.5 Pa, 0.6 Pa or 0.8 Pa; i. the temperature of the four depositions is 250℃, 300℃, 350℃, 400℃ or 450℃; j. the time of the four depositions is 1-100 min.

24. The method of claim 23, wherein the composite pre-coat is prepared by, which satisfies one or more of the following conditions a-d; a. the current of the three depositions is 7 A; b. the time of the three depositions is 10 min; c. the current of the four depositions is 7 A; d. the time of the four depositions is 10 min.

25. The method of claim 22, wherein the composite precoat is prepared by the steps of: the current of the three depositions is 7 A, the bias voltage of the three depositions is -70 V, the pressure of the three depositions is 0.6 Pa, the temperature of the three depositions is 300℃, and the time of the three depositions is 10 min.

26. The method of claim 22, wherein the composite precoat is prepared by the steps of: the current of the four depositions is 7 A, the bias voltage of the four depositions is -300 V, the pressure of the four depositions is 0.6 Pa, the temperature of the four depositions is 400℃, and the time of the four depositions is 10 min.

27. The method of making a composite pre-coat according to any one of claims 10-26, wherein, which satisfies one or more of the following conditions a-f; a. the substrate is pretreated before the one deposition is performed; b. the temperature of the vacuum heat treatment is 200-700℃; c. the gas pressure of the vacuum heat treatment is 0.01-5000 Pa; d. the time of the vacuum heat treatment is 1-100 min; e. the rate of temperature increase to the temperature of the vacuum heat treatment is 1-30°C min -1 ; f. the vacuum heat treatment comprises a cooling step; the cooling rate is 2-40°C·min -1 .

28. The method of claim 27, wherein the composite precoat is prepared by the steps of: the method for preparing the composite pre-coating layer simultaneously satisfies the conditions a-f in claim 27.

29. The method of claim 27, wherein the composite pre-coat is prepared by, which satisfies one or more of the following conditions a-e; a. the temperature of the vacuum heat treatment is 450℃; b. the gas pressure of the vacuum heat treatment is 100-3000 Pa; c. the time of the vacuum heat treatment is 30-60 min; d. the rate of temperature increase to the temperature of the vacuum heat treatment is 8°C / min -1 ; e. the rate of cooling is 5°C min -1 .

30. The method of claim 29, wherein the composite precoat is prepared by the steps of: which satisfies one or more of the following conditions a-b; a. the gas pressure of the vacuum heat treatment is 2000 Pa; b. the time of the vacuum heat treatment is 60 min.

31. A composite pre-coat, characterized in that, which is prepared by the method for preparing the composite pre-coating layer according to any one of claims 10-30.

32. A metal bipolar plate characterized by which comprises the composite pre-coating layer according to any one of claims 1-9 and claim 31.

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