CN114665114A

CN114665114A - Multilayer composite carbon coating and preparation method and application thereof

Info

Publication number: CN114665114A
Application number: CN202210374433.8A
Authority: CN
Inventors: 杨敏; 周锦程; 陈福平; 万玲玉; 詹吟桥; 孙跃新
Original assignee: Shanghai Electric Group Corp
Current assignee: Shanghai Electric Group Corp
Priority date: 2022-04-11
Filing date: 2022-04-11
Publication date: 2022-06-24

Abstract

The invention discloses a multilayer composite carbon coating and a preparation method and application thereof. The multilayer composite carbon coating comprises a conductive functional layer which is formed from the surface of a base material outwards and sequentially comprises at least a metal bottom layer, a transition layer of a diamond-like carbon layer and a graphite-like layer; the carbon content of the SP3 structure in the transition layer is more than 70 at%; the carbon content of the SP2 structure in the conductive functional layer is more than 70 at%. The multilayer composite carbon coating has strong binding force and good corrosion resistance.

Description

Multilayer composite carbon coating and preparation method and application thereof

Technical Field

The invention particularly relates to a multilayer composite carbon coating and a preparation method and application thereof.

Background

A Proton Exchange Membrane Fuel Cell (PEMFC) uses hydrogen and oxygen as fuel, and is respectively introduced into two sides of a proton exchange membrane with catalysts on both sides to form a potential difference; at this time, an external circuit is connected, and oxidation-reduction reaction occurs on the electrode to generate current which can be utilized by the outside. Because the reactant is water, the environment is really protected, no pollution is caused, and in addition, the hydrogen source is wide, the working temperature is in a normal temperature range, and the efficiency is higher than that of the traditional internal combustion engine, so the application range relates to automobiles, unmanned aerial vehicles, stationary power stations and the like; is a novel power source with wide application prospect.

The bipolar plate plays an important role in the proton exchange membrane fuel cell. It has several functions, gas distribution, heat conduction and a certain supporting function, and occupies 80% of the weight of the electric pile and 45% of the electric pile cost. The current common bipolar plate materials of the proton exchange membrane fuel cell include metal/graphite/composite materials and the like. The metal bipolar plate has excellent electric and thermal conductivity and good mechanical properties, and is the first choice of the plate material of the fuel cell. However, because the proton exchange membrane is mostly made of perfluorinated sulfonic acid membrane, the inside of the fuel cell is usually in an acid working environment with pH of 3-5 (the dual functions of sulfonic acid and hydrofluoric acid), and the metal polar plate can be seriously corroded under the working condition of 80 ℃. The output properties of the fuel cell stack are greatly reduced.

There has been extensive attention and effort now due to the low cost and simple preparation of carbon-based coatings. CN112582634A uses the plasma to assist the chemical vapor deposition method to prepare the multilayer composite carbon coating and obtains better corrosion resistance, conductivity, combination property and the like, but relates to doping various non-metallic elements, needs to use various processes such as carburization, vapor deposition and the like, and has complex preparation process; CN 113206267A mentions that amorphous carbon coating is deposited by using a magnetron sputtering graphite target method, and a pure metal target and a multi-element alloy target are required to form a multi-layer coating, so that a good bonding force is obtained, and the durability of the coating under the working condition of a battery is ensured; however, the method is not suitable for mass production, and other surface treatment techniques besides the vacuum coating technique are applied, so that the process is complicated.

Therefore, in the art, a preparation process of a multilayer composite carbon coating, which is simple in process, low in cost (adopts few doping elements, low in temperature and the like) and excellent in adhesion, corrosion resistance and electrical conductivity of the prepared multilayer composite carbon coating, is still lacking.

Disclosure of Invention

The invention aims to overcome the defects that a multi-layer composite carbon coating with excellent adhesive force, corrosion resistance and electrical conductivity is still lacked, the preparation process is simple, the cost is low and the like in the prior art, and provides the multi-layer composite carbon coating and the preparation method thereof.

The invention solves the technical problems by the following scheme:

the invention provides a multilayer composite carbon coating, which comprises a conductive functional layer, a plurality of layers and a plurality of layers, wherein the conductive functional layer is formed from the surface of a base material to the outside in sequence and at least comprises a metal bottom layer, a transition layer of a diamond-like carbon layer and a graphite-like layer;

the carbon content of the SP3 structure in the transition layer is more than 70 at%;

the carbon content of the SP2 structure in the conductive functional layer is more than 70 at%.

In the present invention, the material of the metal underlayer is preferably one of Cr, Ti, W, and Ni.

In the present invention, the thickness of the metal underlayer is preferably 50 to 300 nm.

In the present invention, the thickness of the transition layer is preferably 50nm to 2 μm, more preferably 100nm to 1 μm.

In the present invention, the nano-hardness of the transition layer is preferably HV1800-HV3000, more preferably HV2000-HV3000, and most preferably HV2200-HV 3000.

In the present invention, the carbon content of the SP3 structure in the transition layer is preferably 80 at% to 100 at%, more preferably 90 at% to 100 at%.

In the present invention, the nano-hardness of the conductive functional layer is preferably HV1000-HV2000, more preferably HV1200-HV 2000.

In the present invention, the thickness of the conductive functional layer is preferably 50nm to 300nm, for example, 100nm or 200 nm.

In the present invention, the carbon content of the SP2 structure in the conductive functional layer is preferably 80 at% to 100 at%, more preferably 90 at% to 100 at%.

The invention also provides an application of the multilayer composite carbon coating as a coating in a bipolar plate.

In the present invention, the bipolar plate may be a metal bipolar plate in a proton exchange membrane fuel cell.

The invention also provides a preparation method of the multilayer composite carbon coating, which comprises the following steps:

step S1, introducing inert gas, taking one of Cr, Ti, W and Ni as a target material, and performing unbalanced magnetron sputtering on the surface of the substrate to form a metal bottom layer;

step S2, introducing carbon source gas, and depositing a transition layer of a SP3 type carbon structure on the surface of the metal bottom layer by adopting PECVD;

and step S3, introducing mixed gas of carbon source gas and inert gas, and performing unbalanced magnetron sputtering on the surface of the transition layer to form a conductive functional layer of a carbon structure in the SP2 form.

In step S1, in the unbalanced magnetron sputtering method, the process pressure is preferably in the range of 0.1 to 1 Pa.

In step S2, in the PECVD method, the DC power voltage of the ionized carbon source gas is preferably 1000-3000V, more preferably 1500-2500V, such as 2000V.

In step S2, the process pressure used in the PECVD method is preferably in the range of 0.1-10Pa, such as 1Pa or 2 Pa.

In step S2, in the PECVD method, the rf power of the ionized carbon source gas is preferably 0-500W, and is not 0, and more preferably 50-300W.

In step S2, in the PECVD method, the bias voltage of the ionized carbon source gas is preferably between 0.5KV and 10KV, more preferably between 1KV and 5KV, such as 3KV or 5 KV.

In step S2, in the PECVD method, the flow rate of the carbon source gas is preferably 0 to 1000 seem and is not 0, more preferably 50 to 500 seem, such as 100 seem or 200 seem.

In step S3, in the unbalanced magnetron sputtering method, the pressure is preferably 0.01 to 1Pa, for example, 0.1Pa or 0.2 Pa.

In step S3, in the unbalanced magnetron sputtering method, the gas flow ratio of the carbon source gas and the inert gas is preferably 1 (1-10). When the gas flow ratio is outside this range, the bonding force is typically on the order of 4-5, or even 6.

In step S3, in the unbalanced magnetron sputtering method, the sputtering target current is preferably 2A to 10A, more preferably 4A to 8A, such as 5A or 6A.

In step S3, in the unbalanced magnetron sputtering method, the bias voltage is preferably 50-500V, more preferably 100-300V, such as 150V or 200V.

In the present invention, the step S1 is generally preceded by a step of cleaning the substrate. The cleaning step generally comprises: firstly, ultrasonic cleaning is adopted, and then inert gas is adopted to carry out plasma etching on the base material. Wherein the pressure of the plasma etching is preferably lower than 3 x 10^-3Pa vacuum degree. Can remove most of oxygen on the surface of the substrateThe compound, adsorbate, eliminates particulate dust, making the bond between the treated surface and the coating tighter. The cleaning liquid adopted by the ultrasonic cleaning can be an alkaline substance aqueous solution.

Wherein, the inert gas is preferably argon.

Wherein, the time of the plasma etching is preferably 30-60 min.

In the present invention, the substrate may be a stainless steel substrate.

In the present invention, the carbon source gas may be a gas containing a carbon element, such as acetylene or methane, in step S2 and/or step S3.

In step S2, the PECVD manner may be implemented by an anode ion beam, a microwave antenna, a heating wire, a pulse bias power supply, a dual plate, or a hollow cathode.

In step S3, the target material used in the unbalanced magnetron sputtering may be a graphite target.

In the invention, the unbalanced magnetron sputtering can be radio frequency magnetron sputtering, direct current magnetron sputtering or intermediate frequency direct current magnetron sputtering.

On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.

The reagents and starting materials used in the present invention are commercially available.

The positive progress effects of the invention are as follows:

according to the multilayer composite carbon coating prepared by adopting the magnetron sputtering and PECVD methods, elements in the transition layer and the conductive function layer are only carbon elements, other elements are not doped basically, the manufacturing cost is low, the process is simple, the good binding force (maintained at 1-2 level) of the multilayer composite carbon coating can be ensured on the premise of controlling the preparation conditions, and the multilayer composite carbon coating has good corrosion resistance and good conductivity.

Detailed Description

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions, or according to the commercial instructions.

Example 1

(1) Putting the metal bipolar plate into a vacuum device, and pumping to a proper vacuum degree of less than 3 x 10^-3Pa, opening a heater in the equipment to bake the polar plate and the cavity until the vacuum degree reaches the requirement again and is lower than 3 x 10^-3Pa; then argon is introduced, a bias power supply connected with the bipolar plate is started, 800-1200V is carried out, the time is 30-60min, and the surface of the bipolar plate is cleaned (namely plasma etching);

(2) keeping introducing argon gas, keeping the process pressure at 0.1Pa, starting a magnetron sputtering target, depositing a metal bottom layer on the surface of the bipolar plate, wherein the thickness of the metal bottom layer is 100 nm;

(3) closing argon, introducing acetylene, keeping the pressure at 1Pa, keeping the voltage of a direct-current power supply at 2KV, starting a power supply at the value of 3KW of a bias voltage, carrying out PECVD (anode ion beam) deposition on a metal bottom layer to form a carbon coating, wherein the carbon source gas has the flow rate of 100sccm, the SP3 form carbon structure is taken as the main material (the carbon content of the SP3 structure in the transition layer is ensured to be 70 at%), and the nano hardness is HV 2000; the thickness is 0.5 mu m, certain corrosion resistance and conductivity are considered, the coating layer has a compact structure, and the corrosion current density is low.

(4) Adopting a magnetron sputtering graphite target direct current magnetron sputtering deposition carbon coating as a conductive functional layer on the transition layer, wherein the sputtering target current is 5A, the bias voltage is 150V, the process pressure is 0.1Pa, and simultaneously introducing mixed gas of argon and acetylene (the gas flow ratio is 1:1), the layer is mostly of a carbon structure in the form of SP2, the carbon content of the SP2 structure is 70 at%, the thickness is 100nm, and the nano hardness is HV 1200; therefore, a hardness gradient can be formed between the functional layer and the transition layer, the hardness difference is not too large, tight combination can be formed between the two layers, the final coating combination force can reach 1-2 level, and the coating performance has better durability.

Example 2

(1) Putting the metal bipolar plate into a vacuum device, and pumping to a proper vacuum degree lower than 3 x 10^-3Pa, opening a heater in the equipment to bake the polar plate and the cavity until the vacuum degree reaches the requirement again and is lower than 3 x 10^-3Pa; then argon is introduced to open the connectionThe bias power supply of the bipolar plate is 800-1200V for 30-60min, and the surface of the bipolar plate is cleaned (namely plasma etching);

(2) keeping introducing argon, keeping the process pressure at 0.2Pa, starting a magnetron sputtering target, depositing a metal bottom layer on the surface of the bipolar plate, wherein the thickness of the metal bottom layer is 200 nm;

(3) closing argon, introducing acetylene, keeping the pressure at 2Pa, keeping the power of a radio frequency power supply at 300W, starting a bias voltage point value at 5KW, performing PECVD (double-plate electrode) deposition on a metal bottom layer to form a carbon coating, wherein the flow of a carbon source gas is 200sccm, the carbon structure in the form of SP3 is mainly used (the carbon content of the SP3 structure in a transition layer is ensured to be 80 at%), and the nano hardness is HV 2000; the thickness is 0.7 μm, certain corrosion resistance and conductivity are considered, the coating structure of the layer is compact, and the corrosion current density is low.

(4) Adopting a magnetron sputtering graphite target direct current magnetron sputtering deposition carbon coating as a conductive functional layer on the transition layer, wherein the sputtering target current is 6A, the bias voltage is 200V, the process pressure is 0.2Pa, and simultaneously introducing mixed gas of argon and acetylene (the gas flow ratio is 1:1), the layer is mostly of a carbon structure in the form of SP2, the carbon content of the SP2 structure is 70 at%, the thickness is 200nm, and the nano hardness is HV 1200; therefore, a hardness gradient can be formed between the functional layer and the transition layer, the hardness difference is not too large, tight combination can be formed between the two layers, the final coating combination force can reach 1-2 level, and the coating performance has better durability.

Comparative example 1

The differences from example 1 are: in both the step S2 and the step S3, a PECVD method is adopted to deposit a carbon layer, the hardness is higher than 1500, the bonding force of the final multilayer composite carbon coating is 1-3 grade, but the outermost functional layer has poor conductivity and the resistance value is 1-2 orders of magnitude higher than the requirement (requirement in the Department of Energy, DOE).

Comparative example 2

The difference from example 1 is that: in both the step S2 and the step S3, the carbon layer is deposited by magnetron sputtering of a graphite target, and the bonding force is poor, generally 4 to 5 grades, or even 6 grades.

Effects of the embodiment

(1) Cohesion test

The multilayer composite carbon coatings prepared in the embodiment 1 and the embodiment 2 are pressed into round pits on a massive stainless steel test piece by adopting a Rockwell hardness tester, the peeling condition of the coating at the periphery of the pits is observed, and the bonding force can reach 1-2 grades according to the evaluation of the bonding force standard (VDI3198) (1-4 is qualified, and 5-6 grades are unqualified).

(2) Corrosion resistance test

The multi-layered composite carbon coatings prepared in examples 1 and 2 were subjected to potentiodynamic and potentiostatic tests, respectively, according to a method conventional in the art.

Wherein the self-corrosion current is 15.80e^-9A/cm²The self-etching potential is 287 mV.

Wherein, the constant potential test is polarized for 1h under the potential of 0.84V, the corrosion current density is 3.8e-⁹A/cm²The average value of the surface contact resistance was 3.75 m.OMEGA cm²。

Therefore, the test results of the corrosion resistance of the present application all satisfy the standards in the united states Department of Energy (DOE).

Claims

1. The multilayer composite carbon coating is characterized by comprising a conductive functional layer which is formed from the surface of a base material outwards and at least comprises a metal bottom layer, a transition layer of a diamond-like carbon layer and a graphite-like layer;

2. The multi-layer composite carbon coating of claim 1, wherein the material of the metallic underlayer is one of Cr, Ti, W, and Ni;

and/or the thickness of the metal bottom layer is 50-300 nm;

and/or the thickness of the transition layer is 50nm-2 μm, preferably 100nm-1 μm;

and/or the nano-hardness of the transition layer is HV1800-HV3000, preferably HV2000-HV3000, more preferably HV2200-HV 3000;

and/or the carbon content of the SP3 structure in the transition layer is 80 at% to 100 at%, preferably 90 at% to 100 at%.

3. The multilayer composite carbon coating according to claim 1, wherein the nano-hardness of the electrically conductive functional layer is HV1000-HV2000, preferably HV1200-HV 2000;

and/or the thickness of the conductive functional layer is 50nm to 300nm, such as 100nm or 200 nm;

and/or the carbon content of the SP2 structure in the conductive functional layer is 80 at% to 100 at%, preferably 90 at% to 100 at%.

4. Use of a multilayer composite carbon coating according to any one of claims 1 to 3 as a coating in a bipolar plate.

5. A preparation method of a multilayer composite carbon coating is characterized by comprising the following steps:

6. The method of producing a multilayer composite carbon coating of claim 5,

in step S1, in the unbalanced magnetron sputtering method, the adopted process pressure range is 0.1-1 Pa;

and/or, in step S2, in the PECVD method, the DC power voltage of the ionized carbon source gas is 1000-3000V, preferably 1500-2500V, such as 2000V;

and/or, in step S2, the process pressure used in the PECVD method ranges from 0.1Pa to 10Pa, such as 1Pa or 2 Pa.

7. The method of producing a multilayer composite carbon coating of claim 5,

in step S2, in the PECVD method, the rf power of the ionized carbon source gas is 0-500W, but not 0, preferably 50-300W;

and/or, in step S2, in the PECVD method, the ionized carbon source gas has a bias voltage between 0.5KV and 10KV, preferably between 1KV and 5KV, such as 3KV or 5 KV;

and/or, in step S2, in the PECVD method, the flow rate of the carbon source gas is 0-1000 seem and is not 0, preferably 50-500 seem, such as 100 seem or 200 seem.

8. The method of producing a multilayer composite carbon coating of claim 5,

in step S3, in the unbalanced magnetron sputtering method, the process pressure is in the range of 0.01 to 1Pa, for example, 0.1Pa or 0.2 Pa;

and/or in step S3, in the method of unbalanced magnetron sputtering, the gas flow ratio of the carbon source gas to the inert gas is 1 (1-10);

and/or, in step S3, in the method of unbalanced magnetron sputtering, the sputtering target current is 2A to 10A, preferably 4A to 8A, such as 5A or 6A;

in step S3, in the method of unbalanced magnetron sputtering, the bias voltage is 50-500V, preferably 100-300V, such as 150V or 200V.

9. The method of producing a multilayer composite carbon coating of claim 5,

in step S2 and/or step S3, the carbon source gas is a gas containing a carbon element, such as acetylene or methane.

10. The method of producing a multilayer composite carbon coating of claim 5,

in step S2, the PECVD manner is implemented by an anode ion beam, a microwave antenna, a heating wire, a pulse bias power supply, a dual plate, or a hollow cathode.