1. A preparation method of a polyaniline-based composite coating applied to a stainless steel bipolar plate is characterized by comprising the following steps:

(1) preparing aniline-pyrrole mixed solution

Dissolving doping acid, aniline monomer and pyrrole monomer in deionized water, and performing dispersion treatment to obtain aniline-pyrrole solution; wherein, 0.1-1mol of doping acid, 0.1-0.3mol of aniline monomer and 0.01-0.1mol of pyrrole monomer are prepared in every 1L of deionized water;

(2) preparing an electrolyte

Adding nano titanium dioxide particles into an aniline-pyrrole solution, adding a surfactant, sealing, and performing dispersion treatment to obtain an electrolyte; wherein, 0.1-5g of nano titanium dioxide particles and 20-500mg of surfactant are prepared in each 1L of aniline-pyrrole solution;

(3) pretreatment of stainless steel substrate

Polishing one surface of the cut stainless steel sheet by using abrasive paper, ultrasonically cleaning the stainless steel sheet by using a mixed solution of acetone and ethanol in a volume ratio of 1: 1 for 10min, and then sequentially pickling the surface by using a hydrochloric acid solution and a sulfuric acid solution; the other side is connected with a copper wire and then sealed to obtain a metal base material;

(4) composite electrodeposition

And (2) placing the metal substrate, the reference electrode and the auxiliary electrode in electrolyte, externally connecting an electrochemical workstation to build a three-electrode system, placing the system in a magnetic stirring environment, carrying out composite electrodeposition, and forming a polyaniline-based composite coating on the surface of the metal substrate.

2. The method for preparing a polyaniline-based composite coating as described in claim 1, wherein in the step (1), the doping acid is one selected from sulfuric acid, oxalic acid or sulfonic acid; in the step (2), the particle size of the nano titanium dioxide particles is 5-100nm, and the surfactant is alkyl sulfonate; the dispersion treatment mode is one or the combination of ultrasonic dispersion and stirring dispersion; in the step (3), the stainless steel is one of 304, 316 and 316L stainless steel.

3. The method for preparing a polyaniline-based composite coating as described in claim 1, wherein the polishing process in step (3) is specifically, sequentially polishing with 600 mesh, 1200 mesh, 2400 mesh, 4000 mesh silicon carbide sandpaper until the scratches are consistent and the mirror effect is achieved; the pickling process specifically comprises soaking the stainless steel sheet in 10% hydrochloric acid solution and 20% sulfuric acid solution for 3min, and then washing with deionized water.

4. The method for preparing polyaniline-based composite coating as described in claim 1, wherein the compound electrodeposition in step (4) is performed by magnetic stirring at a speed of 300r/min and cyclic voltammetry, the reference electrode is a saturated calomel electrode, the auxiliary electrode is a platinum sheet electrode, and the cyclic scanning process specifically comprises: setting the scanning range to be-0.2-1.2V, the scanning speed to be 10mV/s and the cycle number to be 1; the scanning range is set to be-0.2-1V, the scanning speed is 50mV/s, and the cycle times are set to be 10-20 times.

Background

The development of a hydrogen energy technology is beneficial to energy conservation and emission reduction, energy utilization is improved, and the dependence on fossil energy is reduced, the proton exchange membrane fuel cell is an important terminal for hydrogen energy utilization, has the advantages of high power density, high starting speed, low working temperature, relatively high overall efficiency, zero emission and the like, is widely applied to various fields of traffic, electric power and the like, and is vigorously researched and supported by various countries.

The bipolar plate is a core component of the proton exchange membrane fuel cell, plays roles of blocking and conveying reactants and reaction products, collecting and conducting generated electric energy, supporting a membrane electrode and radiating in a single cell, and plays a key skeleton supporting role in the whole cell stack. The bipolar plate has a large weight and cost of the stack, and its various properties have a great influence on the output and life of the stack. Metal bipolar plates represented by stainless steel have advantages of excellent workability, high strength, and low manufacturing cost, and are considered as a new generation of bipolar plate material. It is susceptible to corrosion damage in the operating environment, passivation results in reduced electrical conductivity and hence reduced fuel cell performance, and balancing corrosion resistance with electrical conductivity is a major problem faced by metallic bipolar plates. The most effective method is to use corrosion-resistant and conductive materials as the coating of the stainless steel bipolar plate, including metal and its oxide coating, and carbon-based coating, but the corrosion product of the metal-based coating may reduce the activity of the catalyst, and the carbon-based coating has the problem of poor durability.

Conductive polymers such as polyaniline, polypyrrole, polythiophene and the like have unique properties in the aspects of conductivity, electrochemical performance, mechanical strength, chemistry, electrochemical synthesis and the like, and are widely applied in the fields of electrochemical sensors, capacitors, corrosion prevention and the like. The PANI has the advantages of good chemical stability, high conductivity, processability, easy polymerization, low monomer cost and the like, can protect metal from corrosion by catalyzing the surface of the metal to form a passivation oxide layer, and is a promising metal protection material. Joseph et al deposited PANI on the stainless steel surface separately by cyclic voltammetry, and found that the corrosion current density of the coated stainless steel decreased and decreased with the increase of the number of cycles (deposition thickness); meanwhile, the contact resistance of the coated stainless steel deposited by three cycles is very close to that of a graphite plate under a certain pressure (Joseph S, McClure J C, Chianelli R, et al. reduction Polymer-coated stainless steel plates for a Proton Exchange Membrane Fuel Cells (PEMFC) [ J ]. International Journal of Hydrogen Energy, 2005, 30 (12): 1339-. Compared with a chemical oxidation method, the conductive polymer coating prepared by electrodeposition is simpler, more convenient and more efficient, and the deposition process is more controllable, but the surface of the prepared PANI coating often has micron-sized holes, so that the shielding effect on corrosive ions is reduced, and the durability of the PANI coating is weakened.

The PANI is combined with various organic and inorganic materials to prepare the composite coating so as to reduce the pore defects in the structure of the composite coating, for example, the composite coating is formed by introducing high molecular materials and various nano particles, and the advantages of the high molecular materials and the nano particles can be fully exerted. Deyab (Deyab MA, Mel G.Stainless Steel bipolar plate coated with polyurethane/Zn-Porphyrin composites coatings for proton exchange membrane cell [ J]Scientific reports, 2020, 10 (1): 3277-3277.) et al added zinc-Porphyrin (Zn-Porphyrin) to the PANI coating at 1M H₂5O₄The effect of PANI/Zn-Pr composite coatings on improving PEMFC performance and protecting stainless steel bipolar plates from corrosion was studied in solution. The research surface shows that the novel PANI coating added with Zn-Pr has excellent anti-corrosion performance and simultaneously improves the output density of the PEMFC. When the addition amount of Zn-Pr is 1.0%, the corrosion resistance activity of the PANI/Zn-Pr composite material can reach 99.41 percent at most.

The titanium dioxide is known for its unique carrier, oxidation ability, non-toxicity, chemical and light stability, and the nano titanium dioxide particles can fill the pores in the coating, reducing the porosity of the conductive polymer, thereby reducing the diffusion of corrosive ions and enhancing the corrosion resistance of the conductive polymer.

Disclosure of Invention

In view of the defects of the prior art, the invention aims to provide a preparation method of a polyaniline-based composite coating for a stainless steel bipolar plate of a proton exchange membrane fuel cell, wherein the polyaniline-based composite coating has the advantages of high corrosion resistance and electric conductivity, and the preparation method has the advantages of simple process and low raw material cost.

The technical scheme of the invention is as follows:

a preparation method of a polyaniline-based composite coating applied to a stainless steel bipolar plate is characterized by comprising the following steps:

(1) preparing aniline-pyrrole mixed solution

Dissolving doping acid, aniline monomer and pyrrole monomer in deionized water, and performing dispersion treatment to obtain aniline-pyrrole solution; wherein, in every 1L of deionized water, 0.1-1mol of doping acid, 0.1-0.3mol of aniline monomer and 0.01-0.1mol of pyrrole monomer are prepared:

(2) preparing an electrolyte

Adding nano titanium dioxide particles into an aniline-pyrrole solution, adding a surfactant, sealing, and performing dispersion treatment to obtain an electrolyte; wherein, 0.1-5g of nano titanium dioxide particles and 20-500mg of surfactant are prepared in each 1L of aniline-pyrrole solution;

(3) pretreatment of stainless steel substrate

Polishing one surface of the cut stainless steel sheet by using abrasive paper, ultrasonically cleaning the stainless steel sheet by using a mixed solution of acetone and ethanol in a volume ratio of 1: 1 for 10min, and then sequentially pickling the surface by using a hydrochloric acid solution and a sulfuric acid solution; the other side is connected with a copper wire and then sealed to obtain a metal base material;

(4) composite electrodeposition

And (2) placing the metal substrate, the reference electrode and the auxiliary electrode in electrolyte, externally connecting an electrochemical workstation to build a three-electrode system, placing the system in a magnetic stirring environment, carrying out composite electrodeposition, and forming a polyaniline-based composite coating on the surface of the metal substrate.

The preparation method of the polyaniline-based composite coating comprises the following steps of (1), wherein doping acid is one of sulfuric acid, oxalic acid or sulfonic acid; in the step (2), the particle size of the nano titanium dioxide particles is 5-100nm, and the surfactant is alkyl sulfonate; the dispersion treatment mode is one or the combination of ultrasonic dispersion and stirring dispersion; in the step (3), the stainless steel is one of 304, 316 and 316L stainless steel.

The preparation method of the polyaniline-based composite coating comprises the following steps of (1) grinding by using 600-mesh, 1200-mesh, 2400-mesh and 4000-mesh silicon carbide sand paper in sequence until scratches are consistent and a mirror surface effect is achieved; the pickling process specifically comprises soaking the stainless steel sheet in 10% hydrochloric acid solution and 20% sulfuric acid solution for 3min, and then washing with deionized water.

The preparation method of the polyaniline-based composite coating comprises the following steps of (1) carrying out composite electrodeposition in the step (5), wherein the magnetic stirring speed is 300r/min, the electrodeposition is carried out by adopting cyclic voltammetry, the reference electrode is a saturated calomel electrode, the auxiliary electrode is a platinum sheet electrode, and the cyclic scanning process specifically comprises the following steps: setting the scanning range to be-0.2-1.2V, the scanning speed to be 10mV/s and the cycle number to be 1; the scanning range is set to be-0.2-1V, the scanning speed is 50mV/s, and the cycle times are set to be 10-20 times.

Has the advantages that: the polyaniline-polypyrrole-nano titanium dioxide composite coating prepared by the method has lower surface contact resistance and excellent corrosion resistance and durability, can reduce the internal resistance of a proton exchange membrane fuel cell, and provides excellent corrosion protection performance for a stainless steel bipolar plate, so that the service life and the output power of the fuel cell are improved, and meanwhile, the preparation method can also reduce the preparation cost of the stainless steel bipolar plate composite coating. In addition, the coating is also applied to the general corrosion protection field of other metal materials with the conductive requirement, and has wide application prospect.

Drawings

FIG. 1 is a schematic structural diagram of the composite electrodeposition of polyaniline-based composite coating according to the present invention;

FIG. 2 is a graph showing the contact resistance of the polyaniline-polypyrrole-nano titanium dioxide composite coating according to the embodiment of the present invention as a function of pressure;

FIG. 3 is H at pH 3 for a polyaniline-polypyrrole-nano titanium dioxide composite coating in an embodiment of the invention₂SO₄+2ppm potentiodynamic potential and potentiostatic polarization test results in HF solution;

Detailed Description

The invention is further illustrated and described below with reference to the drawings and the specific examples, without limiting the scope of protection of the invention. In the present invention, the starting materials used are all commercially available products well known in the art, unless otherwise specified.

Implementation example: a preparation method of a polyaniline-polypyrrole-nano titanium dioxide composite coating with high corrosion resistance and high conductivity specifically comprises the following steps:

(1) putting 0.3mol of anhydrous oxalic acid, 0.1mol of aniline monomer and 0.04mol of pyrrole monomer into 1L of deionized water to obtain aniline-pyrrole solution; adding 1g of nano titanium dioxide particles with the particle size of 5-10nm into aniline-pyrrole solution, adding 100mg of sodium dodecyl sulfate, putting into a magnetic stirrer, and then sealing the container by using adhesive tapes; performing ultrasonic treatment for 10min, then performing dispersion treatment in a magnetic stirring manner, and stirring for 3h to obtain an electrolyte;

(3) cutting a 316L stainless steel sheet into a size of 10cm multiplied by 10cm, sequentially polishing by 600-mesh, 1200-mesh and 2400-mesh silicon carbide abrasive paper until scratches are consistent and a mirror surface effect is achieved, and then ultrasonically cleaning for 10min by using a mixed solution of acetone and ethanol with the volume ratio of 1: 1; cutting the polished 316L stainless steel sheet to a size of 1cm multiplied by 1cm, connecting the non-polished surface with a copper conductor to obtain a stainless steel substrate sample, placing the polished surface of the sample downwards in a cold-insert die, mixing and stirring resin powder and a curing agent uniformly, pouring the mixture into the die, and taking the sample out of the die after the liquid is completely cured and cooled. Keeping the polished surface of the sample clean and complete as the surface to be plated, sequentially placing the sample in a 10% hydrochloric acid solution and a 20% sulfuric acid solution for soaking for 3min, and carrying out acid pickling and activating treatment on the surface to be plated to obtain a stainless steel substrate sample.

(4) And (3) placing the stainless steel substrate sample, the reference electrode and the auxiliary electrode in electrolyte, externally connecting an electrochemical workstation to build a three-electrode system, and carrying out composite electrodeposition. In the composite electrodeposition process, the magnetic stirring rate is 300r/min, cyclic voltammetry is adopted for electrodeposition, a reference electrode is a saturated calomel electrode, an auxiliary electrode is a platinum sheet electrode, and the cyclic scanning process specifically comprises the following steps: setting the scanning range to be-0.2-1.2V, the scanning speed to be 10mV/s and the cycle number to be 1; the scanning range is set to be-0.2-1V, the scanning speed is 50mV/s, and the cycle number is 10 times.

According to the national standard proton exchange membrane fuel cell part 6: the surface contact resistance of the composite coated stainless steel bipolar plate is tested by the contact resistance test method in the bipolar plate characteristic test method GB/T20042.6-2011, and the result is shown in figure 2, and it can be seen that the contact resistance is reduced along with the increase of pressure, is 28.4m omega under 1.4MPa and is far lower than that of 316L stainless steel bipolar plates under the protection of 316L stainless steel bare steel and PANI coatings.

The self-corrosion potential and the corrosion current density of the composite coating modified bipolar plate are tested according to the test standard suggested by DOE, a sample is taken as a working electrode, an Ag/AgCl electrode is taken as a reference electrode, a platinum sheet electrode is taken as an auxiliary electrode to form a three-electrode system, and H with pH of 3 is used₂SO₄+2ppm HF solution (80 ℃, N feed)₂) In order to simulate the working environment of the proton exchange membrane fuel cell, the test result is shown in fig. 3, and it can be seen that the polyaniline-polypyrrole-nano titanium dioxide composite coating can provide a good protection effect for a 316L stainless steel bipolar plate, the potentiodynamic polarization test shows that the self-corrosion potential reaches 0.14V, the corrosion current density under the long-time constant potential test is lower than 1 mua, and the requirements of DOE are met.