Method for forming film of conductive polymer

Abstract

A test piece 14 and a counter electrode 13 having a shape conforming to the shape of a film formation surface 14A of the test piece 14 are arranged close to each other, and a film of a conductive polymer is formed on the test piece 14 by electrolytic polymerization. The method involves preliminarily obtaining conditions of the voltage and integrated current value under which a desired film thickness is obtained by electrolytic polymerization, and conducting electrolytic polymerization until the integrated value of current flowing between the counter electrode 13 and the test piece 14 reaches the integrated current value, while keeping a constant voltage between the counter electrode 13 and the test piece 14.

Description

Conductive polymer film formation method

[0001] The present disclosure relates to a method for forming a film of a conductive polymer.

[0002] In metal structures installed outdoors, such as infrastructure facilities, hydrogen generated by corrosion reactions can penetrate into the metal, causing fracture due to hydrogen embrittlement. In real-world environments, metals placed in crevice corrosion environments, such as bolts and rebar in concrete utility poles, can sometimes fracture due to hydrogen embrittlement. The more hydrogen that penetrates into the metal due to corrosion reactions, the higher the probability of fracture. Therefore, quantifying the extent and degree of hydrogen penetration into steel is important in assessing the risk of hydrogen embrittlement in crevice corrosion environments.

[0003] Non-Patent Document 1 discloses a method for detecting hydrogen that penetrates into metals using the conductive polymer polyaniline. Specifically, after plating a metal member with Ni, a polyaniline (PANI) film is formed by electrolytic polymerization to serve as a hydrogen detection section. Hydrogen that penetrates into the metal member diffuses through the steel material. When hydrogen reaches the PANI on the opposite side, it reduces the PANI. The reduced portion discolors, and hydrogen penetration can be detected on the side opposite the discolored portion.

[0004] Hiroshi Kakinuma, Saya Ajito, Tomohiko Hojo, Motomichi Koyama, Sachiko Hiromoto, and Eiji Akiyama, “In situ 2D mapping of hydrogen entry into an Fe sheet under a droplet of NaCl solution using a hydrogenochromic sensor,” International Journal of Hydrogen Energy, 2022, Volume 47, pp. 38468-38476

[0005] By using metal components equipped with hydrogen detection elements coated with the conductive polymer PANI in infrastructure structures, hydrogen intrusion into infrastructure structures can be detected. If the coating is uneven and there are irregularities in the coating, it is necessary to compare the hydrogen detection element with its initial state to determine whether discoloration is due to hydrogen intrusion. If PANI can be coated uniformly over a large area on metal components, it will be easy to determine on-site areas with high and low hydrogen intrusion by the shade of the hydrogen detection element.

[0006] However, in a typical electropolymerization set, the distance between the metal member and the counter electrode is not uniform, which causes uneven electric fields, making it difficult to form a uniform conductive polymer film over a large area. This uneven electric field becomes even more pronounced with metal members of complex shapes.

[0007] The present disclosure has been made in view of the above, and has an object to form a conductive polymer film uniformly over a large area.

[0008] A method for forming a conductive polymer film according to one aspect of the present disclosure includes arranging a metal member and a counter electrode having a shape corresponding to the surface shape of the metal member on which the conductive polymer film is to be formed in close proximity, and forming a conductive polymer film on the metal member by electrolytic polymerization.

[0009] According to the present disclosure, a conductive polymer film can be formed uniformly over a large area.

[0010] Fig. 1 is a diagram showing an example of the configuration of an apparatus for carrying out a method for forming a conductive polymer film. Fig. 2 is a diagram showing an example of the configuration of an apparatus for carrying out a method for forming a conductive polymer film. Fig. 3 is a diagram showing the integrated current value when a polyaniline film is formed by electrolytic polymerization.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0012] 1 and 2 are diagrams showing an example of the configuration of an apparatus for carrying out the method for forming a conductive polymer film according to this embodiment. The apparatus shown in the figures includes an electrochemical device 11, a reference electrode 12, a counter electrode 13, a specimen 14, and a cell 21.

[0013] The electrochemical device 11 is a measuring device that uses electrochemical techniques to generate a chemical reaction and evaluates the chemical reaction from the response signal. A potentiostat is used as the electrochemical device 11, and current is measured while maintaining a constant potential between the counter electrode 13 and the test piece 14.

[0014] The reference electrode 12 is an electrode that serves as a reference for maintaining a constant potential and is controlled by the electrochemical device 11. The reference electrode 12 is made of, for example, Ag or AgCl.

[0015] The counter electrode 13 is an electrode that receives current from the electrochemical device 11 and supplies current to the specimen 14. For example, platinum is used for the counter electrode 13. The counter electrode 13 has a shape that conforms to the shape of a film formation surface 14A of the specimen 14 on which a film of a conductive polymer is formed.

[0016] In the example of FIG. 1, the film formation surface 14A is flat, so the counter electrode 13 is a flat plate electrode.

[0017] 2, the specimen 14 is a triangular prism, and a conductive polymer film is formed on two side surfaces of the triangular prism. The counter electrode 13 is an electrode having a shape obtained by bending a flat plate along the two side surfaces (film formation surfaces 14A) of the triangular prism.

[0018] The shapes of the film formation surface 14A and the counter electrode 13 are not limited to those described above. If the film formation surface 14A is curved, the counter electrode 13 is shaped to follow the curvature of the film formation surface 14A. For example, if a conductive polymer film is formed on the surface of a sphere with a radius R, the counter electrode 13 is shaped as a concave surface with a radius R+ΔR that follows the surface of the sphere. Here, ΔR is the distance between the counter electrode 13 and the specimen 14. By shaping the counter electrode 13 to conform to the shape of the film formation surface 14A, it is possible to reduce electric field unevenness.

[0019] The counter electrode 13 may have a mesh structure conforming to the shape of the film formation surface of the specimen 14. By forming the counter electrode 13 into a mesh structure, it becomes possible to visually observe the specimen 14 during electropolymerization. In addition, the surface area of ​​the counter electrode 13 can be increased.

[0020] The specimen 14 is a metal member where an electrolytic reaction occurs (working electrode) and on which a conductive polymer film is formed. A film-forming surface 14A of the specimen 14 is plated with Ni.

[0021] The bottom surface 21A of the cell 21 is removable, allowing the bottom surface to be opened. The cell 21 is made of acrylic or glass. The specimen 14 is placed in the opening of the bottom surface of the cell 21 with the film-forming surface 14A facing the inside of the cell 21. A sealing material 22 is placed between the specimen 14 and the peripheral edge of the cell 21, and the cell 21 and the bottom surface 21A are fastened with bolts 23 to prevent leakage of the electrolyte 15. In other words, the film-forming surface 14A of the specimen 14 becomes the bottom surface inside the cell 21.

[0022] The counter electrode 13 and the specimen 14 are arranged in close proximity with the counter electrode 13 and the film formation surface 14A parallel to each other. For example, the counter electrode 13 may be arranged in close proximity to the specimen 14 so that the distance between the counter electrode 13 and the specimen 14 is 1 cm or less and the counter electrode 13 and the specimen 14 do not come into contact with each other. A structure for holding the counter electrode 13 may be provided near the bottom surface inside the cell 21. By arranging the counter electrode 13 and the specimen 14 in close proximity and parallel to each other, unevenness in the electric field can be reduced, allowing the conductive polymer to be uniformly formed into a film.

[0023] As long as the counter electrode 13 and the specimen 14 can be arranged close to each other within the cell 21, the arrangement of the counter electrode 13 and the specimen 14 is not important.

[0024] When forming a conductive polymer film, an electrolyte 15 is placed in a cell 21, and a reference electrode 12 is placed therein. For example, when forming a polyaniline film, an electrolyte 15 containing a mixture of 0.5 M sulfuric acid and 0.5 M aniline is used.

[0025] The reference electrode 12, the counter electrode 13, and the test piece 14 are electrically connected to the electrochemical device 11, and a voltage is applied between the counter electrode 13 and the test piece 14 by the electrochemical device 11, causing an electrolytic polymerization reaction to occur on the surface of the test piece 14, forming a film of a conductive polymer.

[0026] Next, the conditions for electropolymerization will be described. Typically, the conditions for electropolymerization are controlled by "voltage and time." For example, in Non-Patent Document 1, electropolymerization was performed at +1 V for 200 seconds to form a polyaniline film. In this embodiment, the counter electrode 13 and the specimen 14 are arranged close to each other, reducing the solution resistance between the counter electrode 13 and the specimen 14, resulting in a more excessive current flow than in a typical arrangement of a counter electrode and a working electrode. In the method of this embodiment, if electropolymerization is performed under the same conditions as in Non-Patent Document 1, a thick film will be formed, making it impossible to detect hydrogen.

[0027] Therefore, in this embodiment, the conditions for electrolytic polymerization are defined by "voltage and integrated current value." Specifically, a small area (for example, 1 cm ) is previously subjected to electrolytic polymerization. 2 A conductive polymer film of the desired thickness is formed on a surface (approximately 1000 kJ / cm2), and the amount of charge (integrated current) flowing from the counter electrode to the working electrode during electropolymerization is calculated to obtain the "voltage and integrated current" condition. Electropolymerization here can be performed with a standard counter electrode and working electrode arrangement. For example, if electropolymerization is performed at +1 V for 200 seconds, the "voltage and integrated current" condition of 5.74 C at +1 V is obtained.

[0028] Thereafter, in the method of this embodiment, the counter electrode 13 and the test piece 14 are placed close to each other, and based on the obtained conditions of "voltage and integrated current value," electrolytic polymerization is carried out while maintaining a constant voltage between the counter electrode 13 and the test piece 14 until the integrated value of the current flowing between the counter electrode 13 and the test piece 14 reaches the integrated current value of the condition.

[0029] 3 shows the integrated current values ​​when polyaniline films were formed under different conditions. For conditions 1 to 3, electrolytic polymerization was carried out several times under each condition to form polyaniline films.

[0030] Condition 1 is a small area (1 cm 2 Electropolymerization was carried out on a test piece (approximately 1000 kJ / cm2) under the voltage and time conditions (+1V, 200 seconds). The average cumulative current was 5.74 C. A polyaniline film with an appropriate thickness was formed, enabling hydrogen detection.

[0031] Condition 2 is a large area (10 cm 2Electropolymerization was carried out on a specimen of 1000kJ / cm2 or higher under the same voltage and time conditions (+1V, 200 seconds) as in Condition 1. The average cumulative current was 59.6C. Hydrogen detection was impossible because the polyaniline film was too thick.

[0032] Condition 3 is a large area (10 cm 2 Electropolymerization was carried out on a test specimen (of a thickness of 10 ...

[0033] In this way, by changing the "voltage and time" conditions that resulted in the desired film thickness to "voltage and integrated current value" conditions and performing electrolytic polymerization, a conductive polymer film having a desired film thickness can be formed in the conductive polymer film formation method of this embodiment.

[0034] As described above, the conductive polymer film forming method of this embodiment involves closely arranging the specimen 14 and the counter electrode 13, which has a shape corresponding to the shape of the film formation surface 14A of the specimen 14, and forming a conductive polymer film on the specimen 14 by electrolytic polymerization. By arranging the counter electrode 13 and the specimen 14 in parallel and closely, it is possible to reduce electric field unevenness and form a conductive polymer film uniformly over a large area. By uniformly forming a polyaniline film over a large area on a metal member, hydrogen detection can be performed over a large area, and localized hydrogen penetration locations in infrastructure structures, for example, can be identified over a wider area.

[0035] REFERENCE SIGNS LIST 11 Electrochemical device 12 Reference electrode 13 Counter electrode 14 Test piece 14A Film formation surface 15 Electrolyte 21 Cell 21A Bottom surface 22 Sealing material 23 Bolt

Claims

1. A method for forming a conductive polymer film, comprising: arranging a metal member and a counter electrode having a shape corresponding to the surface shape of the metal member on which a conductive polymer film is to be formed, in close proximity to each other; and forming a conductive polymer film on the metal member by electrolytic polymerization.

2. A method for forming a conductive polymer film according to claim 1, comprising determining in advance the conditions for voltage and integrated current value that will result in a desired film thickness by electrolytic polymerization, and carrying out electrolytic polymerization while maintaining said voltage between said counter electrode and said metal member until the integrated value of the current flowing between said counter electrode and said metal member reaches said integrated current value.

3. The method for forming a conductive polymer film according to claim 1, wherein the counter electrode has a mesh structure.

4. The method for forming a conductive polymer film according to claim 1, wherein the distance between the metal member and the counter electrode is set to 1 cm or less.

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