Method for manufacturing transparent conductive films

Abstract

This invention provides a method for manufacturing a transparent conductive film, which allows for the electrochemical reduction of a GO film formed on a non-conductive substrate to convert it into a transparent and conductive graphene oxide reduction product (rGO). [Solution] The present invention provides a method for manufacturing a transparent conductive film, comprising: Step 1: Forming a graphene oxide (GO) film containing graphene oxide (GO) on a non-conductive substrate (S) to obtain a graphene oxide (GO) film-attached non-conductive substrate (GO-S); and Step 2: Applying a voltage to the graphene oxide (GO) film-attached non-conductive substrate (GO-S) obtained in Step 1 to reduce the graphene oxide (GO) film, thereby forming a graphene oxide reduced product (rGO) film containing the graphene oxide reduced product (rGO) to obtain a graphene oxide reduced product (rGO) film-attached non-conductive substrate (rGO-S). The transparent conductive film contains graphene oxide reduced product (rGO).

Description

[Technical Field]

[0001] The present invention relates to a method for producing a transparent conductive film consisting of a reduced graphene oxide (rGO) film on a non-conductive substrate. [Background technology]

[0002] Graphene and its multilayer films are expected to have industrial applications as transparent conductive films (TCF) and heat dissipation materials, replacing indium tin oxide (ITO) films. However, forming graphene and its multilayer films on non-conductive substrates such as polymer materials (polyethylene terephthalate) or glass inexpensively and over large areas remains a challenging task. As a method to solve these problems, a method using graphene oxide (GO) as an intermediate is being investigated. Graphene oxide (GO) has various oxygen functional groups on its surface and exhibits electrical insulation and proton conductivity, making it a subject of active research in a wide range of fields. Furthermore, the reduced graphene oxide product obtained by reducing graphene oxide (GO) (rGO, also called reduced graphene oxide) exhibits sp² ionization as the oxygen functional groups decrease. 2 The carbon region increases, resulting in high electrical conductivity. Reduced graphene oxide (rGO) exhibits good electrical conductivity while possessing excellent optical transparency, making it suitable for use as a TCF (transparency-curing fiber) alternative to ITO (isopropyl alcohol). However, obtaining a TCF with low resistance comparable to that of graphene films required methods involving the use of extremely strong reducing agents that corrode polymer films, or methods involving thermal reduction treatment at temperatures exceeding 700°C, which surpasses the heat resistance of the polymer films. Furthermore, graphene oxide (GO), which was used in conventional reduction processes, is known to have a high-density pore structure on its sheet surface, resulting in significantly lower electrical resistance after reduction compared to graphene. Moreover, forming films on the surfaces of these materials with complex surface shapes was impossible with previously reported techniques.

[0003] As an alternative reduction method that does not require reducing agent treatment or high-temperature heat treatment, electrochemical reduction methods have been reported conventionally. For example, Patent Document 1 states that in the electrochemical reduction treatment of graphene oxide, it is preferable to use a silver / silver chloride electrode or the like as a reference electrode, a platinum or carbon electrode as a counter electrode, and a carbon electrode, diamond electrode, or metal electrode with a wide potential window as the working electrode, in an aqueous solution in which a supporting electrolyte is dissolved, and that a smaller work function makes it easier to reduce the hydrazine-treated graphene oxide (GO). Due to the vacancy structure present in graphene oxide (GO), its electronic conductivity is significantly inferior to that of graphene, so in the method of Patent Document 1, it is necessary to use a conductive material for the substrate used when reducing graphene oxide (GO). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5836866 [Overview of the project] [Problems that the invention aims to solve]

[0005] As shown in Patent Document 1, graphene oxide (GO) films formed on electrically conductive substrates are easily reduced. However, when a general graphene oxide (GO) film is formed on a non-conductive substrate such as a polymer material or glass, and the substrate is subjected to electrochemical treatment, the graphene oxide (GO) on the insulating substrate is not reduced because the substrate itself does not have electrical conductivity.

[0006] The object of the present invention is to provide a method for producing a transparent conductive film, which can electrochemically reduce a graphene oxide (GO) film formed on a non-conductive substrate to convert it into a transparent and electrically conductive reduced graphene oxide (rGO). [Means for solving the problem]

[0007] The gist of the present invention is as follows: [1] A method for producing a transparent conductive film on a non-conductive substrate (S), The transparent conductive film contains reduced graphene oxide (rGO), Step 1 involves forming a graphene oxide (GO) film containing graphene oxide (GO) on the non-conductive substrate (S) to obtain a graphene oxide (GO) film-coated non-conductive substrate (GO-S), A method for producing a transparent conductive film, comprising: step 2, applying a voltage to the graphene oxide (GO) film-coated nonconductive substrate (GO-S) obtained in step 1 to reduce the graphene oxide (GO) film, thereby forming a graphene oxide reduced product (rGO) film containing the graphene oxide reduced product (rGO), and obtaining a graphene oxide reduced product (rGO) film-coated nonconductive substrate (rGO-S). [2] The method for producing a transparent conductive film according to [1], wherein the nonconductive substrate is a polymer material or glass. [3] The infrared absorption spectrum of the graphene oxide (GO) film is 1600-1800 cm⁻¹ -1 A method for producing a transparent conductive film according to [1] or [2], wherein the region does not have an absorption spectrum originating from surface oxygen functional groups. [4] The method for producing a transparent conductive film according to any one of [1] to [3], wherein the graphene oxide (GO) has 10 or fewer pores in a 500 nm × 500 nm region when observed on the surface with a transmission electron microscope (TEM) at 500,000x magnification. [5] The method for producing a transparent conductive film according to any one of [1] to [4], wherein the graphene oxide (GO) is graphene oxide synthesized according to the Brodie method. [6] A method for manufacturing a transparent conductive film according to any one of [1] to [5], wherein the sheet resistance of the reduced graphene oxide (rGO) film formed on the nonconductive substrate is 1 to 30,000 Ω / sq. [7] A method for producing a transparent conductive film according to any one of [1] to [6], wherein the light transmittance of the reduced graphene oxide (rGO) film formed on the nonconductive substrate is 60 to 98%. [8] A method for producing a transparent conductive film according to any one of [1] to [7], wherein the graphene film thickness of the graphene oxide (GO) film is 0.5 to 30 nm. [9] The method for producing a transparent conductive film according to any one of [1] to [8], wherein the graphene oxide (GO) film is obtained by the LbL method.

[10] Step 1 comprises Step 1-1 of forming a film on the non-conductive substrate (S) using a dispersion containing graphene oxide (GO) and a dispersion medium, A method for producing a transparent conductive film according to any one of [1] to [9], comprising step 1-2 of removing the dispersion medium from the dispersion.

[11] Step 2 comprises step 2-1 of placing the graphene oxide (GO) film-coated nonconductive substrate (GO-S) in the electrolyte, which is permeated with nitrogen, in an electrochemical cell comprising a working electrode, a counter electrode and an electrolyte, Step 2-2 involves electrically connecting the graphene oxide (GO) film of the graphene oxide (GO) film-coated nonconductive substrate (GO-S) to the working electrode, A method for producing a transparent conductive film according to any one of [1] to

[10] , comprising step 2-3 of carrying out the electrochemical reduction of the graphene oxide (GO) film.

[12] In step 2, the electrochemical cell further includes a reference electrode, The aforementioned reference electrode is a silver / silver chloride reference electrode, A method for manufacturing a transparent conductive film according to

[11] , wherein a voltage of -0.1 to -5V is applied to the working electrode, which is electrically connected to the graphene oxide (GO) film, relative to a reference electrode.

[13] The method for producing a transparent conductive film according to

[11] or

[12] , wherein the electrolyte is at least one selected from the group consisting of an aqueous sulfuric acid solution, hydrochloric acid solution, aqueous nitric acid solution, aqueous iron(III) chloride solution, aqueous zinc nitrate solution, aqueous aluminum nitrate solution, aqueous zirconium chloride solution, aqueous cerium nitrate solution, sodium sulfate, aqueous potassium hydroxide solution, aqueous lithium hydroxide solution, lithium perchlorate-containing acetonitrile solution, lithium perchlorate-containing propylene carbonate solution, etc.

[14] A method for manufacturing a transparent conductive film according to any one of

[11] to

[13] , wherein the working electrode is at least one selected from the group consisting of a nickel electrode, a gold electrode, a platinum electrode, a glassy carbon electrode, etc.

[15] Further including step 3, The method for manufacturing a transparent conductive film according to any one of

[11] to

[14] , wherein step 3 is a step of applying a voltage to the non-conductive substrate (rGO-S) with a reduced graphene oxide (rGO) film obtained in step 2 in an electrolyte containing a metal salt to form a metal salt-containing reduced graphene oxide (M-rGO) film by inserting the metal salt between the layers of the reduced graphene oxide (rGO), thereby obtaining a metal salt-containing reduced graphene oxide (MrGO) film on a non-conductive substrate (MrGO-S).

[16] Step 3 comprises step 3-1, in which a non-conductive substrate (rGO-S) with a graphene oxide reduction (rGO) film obtained in step 2 is placed in the second electrolyte, which is permeated with nitrogen, in an electrochemical cell comprising a working electrode, a counter electrode and a second electrolyte, Step 3-2 involves electrically connecting the graphene oxide reduced product (rGO) film of the non-conductive substrate (rGO-S) with the graphene oxide reduced product (rGO) film to the working electrode, A method for producing a transparent conductive film according to

[15] , comprising step 3-3 of carrying out electrochemical oxidation-reduction of the graphene oxide reduced product (rGO) film.

[17] The method for producing a transparent conductive film according to

[15] or

[15] , wherein the content of the metal salt in the second electrolyte is 0.1 to 10 M.

[18] The metal salt is a metal chloride, A method for producing a transparent conductive film according to any one of

[15] to

[17] , wherein the metal is at least one selected from the group consisting of Fe, Cu, Mo, and Sb.

[19] In step 3, the electrochemical cell further includes a reference electrode, The aforementioned reference electrode is a silver / silver chloride reference electrode, A method for manufacturing a transparent conductive film according to any one of

[16] to

[17] , wherein a voltage of +1 to +3V is applied to the working electrode, which is electrically connected to the graphene oxide reduced product (rGO) film, relative to a reference electrode.

Advantages of the Invention

[0008] According to the present invention, there is provided a method for manufacturing a transparent conductive film, which can electrochemically reduce a graphene oxide (GO) film formed on a non-conductive substrate and change it into a reduced graphene oxide (rGO) having transparency and electrical conductivity.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a conceptual diagram showing an example of the molecular structure of a graphene oxide (GO) film according to an embodiment of the present invention. [Figure 2] FIG. 2 is an infrared absorption spectrum of graphene oxide (GO) according to an embodiment of the present invention. a: Graphene oxide (GO) prepared by the Brodie method. b: Graphene oxide (GO) synthesized by the Hummers method. [Figure 3A] FIG. 3A is a conceptual diagram showing a graphene oxide (GO) film on a non-conductive material according to an embodiment of the present invention. [Figure 3B] FIG. 3B is a conceptual diagram showing a reduced graphene oxide (rGO) film on a non-conductive material according to an embodiment of the present invention. [Figure 4] FIG. 4 is a conceptual diagram of an electrochemical reduction cell according to an embodiment of the present invention. [Figure 5] FIG. 5 is a diagram showing the relationship between sheet resistance and light transmittance in the number of LbL trials of the transparent film obtained in Example 1. [Figure 6] FIG. 6 is a conceptual diagram of an electrochemical cell according to an embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing the sheet resistance (before and after insertion of iron (III) chloride) in the number of LbL trials of the transparent films obtained in Examples 1 and 2. A: Example 1, 0.005 M sulfuric acid, -1.7 V vs. Ag / AgCl, 2400 sec (before insertion of iron chloride). B: Example 2, 9 M iron (III) chloride, 1.7 V vs. Ag / AgCl, 400 sec (after insertion of iron chloride). [Figure 8]Figure 8 shows a transmission electron microscope (TEM) image of an example of graphene oxide prepared by the Hummers method. [Figure 9] Figure 9 shows a transmission electron microscope (TEM) image of an example of graphene oxide prepared by the Brodie method. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described in detail below with reference to the drawings. Note that, for convenience, the drawings used in the following description may show enlarged versions of key features to make the features of the present invention easier to understand. Therefore, the dimensional ratios of each component may differ from those of the actual components.

[0011] (Method for manufacturing transparent conductive film) The method for manufacturing a transparent conductive film of the present invention will be described using the following first and second embodiments. However, it is not limited to them.

[0012] (First Embodiment) The method for manufacturing a transparent conductive film according to this embodiment is a method for manufacturing a transparent conductive film on a non-conductive substrate (S). The transparent conductive film contains reduced graphene oxide (rGO). The content of reduced graphene oxide (rGO) in the transparent conductive film may be 0.1% by weight or more, 1% by weight or more, or 10% by weight or more. It may also be 0.99% by weight or less, 9.99% by weight or less, or 99.9% by weight or less. The range of the content of reduced graphene oxide (rGO) may be any combination of the above upper and lower limits. Furthermore, the content of reduced graphene oxide (rGO) in the transparent conductive film may be 100%. Furthermore, the transparent conductive film may be a reduced graphene oxide (rGO) film. The method for manufacturing the transparent conductive film of this embodiment includes the following steps 1 and 2. Step 1: A step to form a graphene oxide (GO) film containing graphene oxide (GO) on the non-conductive substrate (S) to obtain a graphene oxide (GO) film-coated non-conductive substrate (GO-S). Step 2: A step to obtain a non-conductive substrate (rGO-S) with a graphene oxide (GO) film attached, obtained in Step 1, by applying a voltage to the graphene oxide (GO) film and reducing the graphene oxide (GO) film to form a graphene oxide reduced product (rGO) film containing the graphene oxide reduced product (rGO), thereby obtaining a graphene oxide reduced product (rGO) film attached to a non-conductive substrate (rGO-S). The following steps will be explained in detail.

[0013] [Process 1] "Method for forming graphene oxide (GO) film" In step 1, the method for forming the graphene oxide (GO) film on the non-conductive substrate (S) is not particularly limited, and known film formation methods can be used. Examples of such film formation methods include spin coating, layer-by-layer (LbL) method, Langmuir-Bludget method (LB method), and chemical vapor deposition (CVD method). Among these, the LbL method and LB method are preferred from the viewpoint of easy control of the uniformity of the prepared graphene oxide (GO) film and the number of graphene layers. The LbL method may also be used from the viewpoint of ease of operation. The LB method may also be used from the viewpoint of not having to use adhesives or the like.

[0014] In the LbL method, a dispersion containing graphene oxide (GO) and a dispersion medium may be used, and if necessary, an adhesive (binder) may be used for interlayer bonding. The dispersion medium may be water or an aqueous solvent containing water, or a non-aqueous solvent such as an organic solvent. From an environmental standpoint, water or an aqueous solvent is preferred. The aqueous solvent may include, for example, an organic solvent such as alcohol. The adhesive is used for interlayer bonding of graphene. The adhesive is not particularly limited, and known adhesives, binders, etc., can be used. Examples of the adhesive include polydiallyldimethylammonium (PDDA) and polyethyleneimine (PEI). For example, in a LbL method using an adhesive such as polydiallyldimethylammonium (PDDA), a film can be formed on the surface of the non-conductive substrate (S) by alternately depositing a solution of the adhesive and a dispersion of graphene oxide (GO), thereby forming a graphene oxide (GO) film having a single layer or two or more layers of graphene.

[0015] When using a dispersion of graphene oxide (GO), as in the LbL method described above, step 1 of the manufacturing method of this embodiment may include the following steps (1-1) and 1-2. Step 1-1: A step of forming a film on the non-conductive substrate (S) using a dispersion containing graphene oxide (GO) and a dispersion medium. Step 1-2: A step to remove the dispersion medium from the dispersion.

[0016] [Non-conductive base material (S)] The non-conductive substrate (S) in this embodiment refers to a material that does not possess the electrical conductivity necessary for electrode materials used in electrochemical reactions. For example, it does not include electrically conductive materials such as metals or carbon. Examples of the non-conductive substrate (S) include semiconductor materials and insulating materials. It is preferable that the non-conductive substrate (S) is an insulating material. Examples of the insulating material include inorganic insulating materials and polymer (resin) materials. Examples of the inorganic insulating material include glass such as sword glass and quartz glass, and crystals such as sapphire. Examples of the polymer (resin) material include PET, polycarbonate, polyolefin, acrylic resin, fluororesin, and polyimide resin.

[0017] The shape of the non-conductive substrate (S) according to this embodiment is not particularly limited. It is sufficient that a graphene oxide (GO) film can be formed on at least a part of its surface (including the back surface). Examples of such shapes include any three-dimensional shape such as a flat plate, a substantially spherical shape, a tubular shape, or a helical shape. One of the features of the manufacturing method of this embodiment is that if a graphene oxide (GO) film can be formed on a part of the surface of the non-conductive substrate (S) of any shape, the film can be electrochemically reduced in step 2 described later. The film-forming surface of the non-conductive substrate (S) may be surface-treated using known surface treatment methods as needed. Examples include ozone / UV treatment and hydrophilization treatment using reagents.

[0018] [Graphene oxide (GO) film] The graphene oxide (GO) film according to this embodiment is not particularly limited, but it is preferable to have good crystallinity and few vacancies. Known methods can be used to evaluate crystallinity, the presence or absence of vacancies, etc. For example, crystallinity can be evaluated by the full width at half maximum or the intensity ratio of the D and G bands of the Raman spectrum. Vacancies can be evaluated by a transmission electron microscope (TEM). It is preferable to have 0 to 10 vacancies in a 500 nm × 500 nm region. For example, the vacancy evaluation method using a transmission electron microscope (TEM) may involve observing the surface of the graphene oxide at a magnification of 500,000 to 50,000,000. The size of the target vacancies may be, for example, 0.2 nm or more and 50 nm or less. The graphene oxide (GO) film according to this embodiment, for example, has an infrared absorption spectrum of 1600-1800 cm⁻¹. -1 It is preferable that the region does not have an absorption spectrum originating from surface oxygen functional groups. The range of the said region is 1600 to 2000 cm⁻¹. -1 But often, 1550-1850cm -1 However, this is also acceptable. In that case, the surface oxygen functional groups of the graphene oxide (GO) film are controlled to epoxy groups. "Having no absorption spectrum" means that, as shown in Figure 2, normal graphene oxide (GO) has an absorption spectrum of 1600-1800 cm⁻¹. -1This means that, while an absorption spectrum originating from surface oxygen functional groups is present in the region, no such absorption peak is observed. "Surface oxygen functional groups are controlled by epoxy groups" may mean that, as shown in Figure 1, the surface of graphene oxide (GO) has a considerably smaller number of surface oxygen functional groups other than epoxy groups, such as hydroxyl groups, carbonyl groups, and carboxylic acid groups, compared to epoxy groups. "Surface oxygen functional groups are controlled by epoxy groups" may also mean that hydroxyl groups, carbonyl groups, carboxylic acid groups, etc., cannot be detected using infrared absorption spectroscopy. For example, the molar proportion of epoxy groups in the total surface oxygen functional groups may be 60 mol% or more, 70% or more, 80% or more, 90% or more, or 95% or more. Alternatively, other surface oxygen functional groups such as hydroxyl groups and carboxylic acid groups may be 30 mol% or less, 20% or less, 10% or less, or 5% or less.

[0019] The graphene oxide (GO) in this embodiment is not particularly limited as long as it is obtained by oxidizing graphene by a known method. Examples of the graphene oxide (GO) include that synthesized according to Non-Patent Document A (hereinafter referred to as Hummers method graphene oxide (HGO)), that synthesized according to Non-Patent Document B (hereinafter referred to as Brodie method graphene oxide (BGO)), and so on. Figure 8 is a transmission electron microscope (TEM) image of an example of graphene oxide prepared by the Hummers method (graphene oxide synthesized according to Non-Patent Literature A). Figure 9 is a transmission electron microscope (TEM) image of an example of graphene oxide prepared by the Brodie method (graphene oxide synthesized according to Non-Patent Literature B).

[0020] [Non-patent Literature A] WS Hummers et al., J. Am. Chem. Soc., 1958, Vol. 80, p. 149. [Non-patent document B] (BC Brodie, Philos. Trans. R. Soc. Lond. 1859, vol. 149, para. 249.

[0021] The graphene film thickness of the graphene oxide (GO) film according to this embodiment may be 0.5 nm or more, 5 nm or more, or 30 nm or more. It may also be 4.9 nm or less, 29 nm or less, or 100 nm or less. The range of the film thickness may be any combination of the above upper and lower limits. From the viewpoint of transparency, the wavelength is preferably 10 nm or less, and more preferably 20 nm or less. From the viewpoint of sheet resistance, it is preferably 2 nm or more, and more preferably 11 nm or more. Among these, from the viewpoint of achieving both transparency and sheet resistance, it is preferably 2 to 10 nm, and more preferably 11 to 20 nm.

[0022] The graphene oxide (GO) film according to this embodiment may or may not contain the adhesive. If the adhesive is included, the content of the adhesive in the graphene oxide (GO) film may be 0.1% or more, 1% or more, or 10% or more. It may also be 0.99% or less, 9.99% or less, or 80% or less. The range of the adhesive content may be any combination of the above upper and lower limits.

[0023] As shown in Figure 8, graphene oxide (GO) produced by the Hummers method has many voids in the plane due to oxidation during the production process, but GO produced by the Brodie method has almost no voids and possesses very high crystallinity. Furthermore, there are various methods for reducing graphene oxide (GO), such as thermal reduction, photoreduction, electrochemical reduction, and chemical reduction, and the degree of reduction of GO can be controlled by the reduction method and time. In this embodiment, the manufacturing method reduces the graphene oxide (GO) film deposited on a non-conductive substrate by an electrochemical reduction method, so it is preferable that the graphene oxide (GO) in this embodiment has few or almost no voids. It is especially preferable that the graphene oxide (GO) is produced by the Brodie method.

[0024] Graphene oxide (GO) produced by the Brodie method differs from graphene oxide produced by other methods, as shown in Figure 9, in that its surface oxygen functional group is a single epoxy group, and it has few or no vacancies, which are usually numerous within the sheet surface (Figure 1). For example, the graphene oxide (GO) used in Example 1 described later has its surface oxygen functional group controlled to an epoxy group, and its infrared absorption spectrum is 1600-1800 cm⁻¹. -1 It is characterized by having almost no absorption spectra originating from surface oxygen functional groups in this region (Figure 2-a). On the other hand, graphene oxide (GO) synthesized by the Hummers method has an absorption spectrum of 1600-1800 cm⁻¹. -1 Two distinct absorption spectra are observed in this region (Figure 2-b). It has been reported that graphene oxide (GO) produced by the Brodie method exhibits different chemical properties from graphene oxide produced by the Hummers method (e.g., Non-Patent Document C below). Conventional graphene oxide exhibits excellent electrical conductivity through annealing at 700°C or higher, UV irradiation, or reduction using hydrazine or hydroiodic acid. On the other hand, graphene oxide (GO) produced by the Brodie method undergoes reduction at a relatively low temperature (300°C) and has higher electron mobility compared to conventional graphene oxide (e.g., Non-Patent Document D below).

[0025] [Non-patent literature C] T. Tsugawa et al. Bull. Chem. Soc. Jpn., 2021, Vol. 94, pp. 2195-2201. [Non-patent Literature D] T. Taniguchi et al., Carbon, 2023, Vol. 202, pp. 26-35.

[0026] [Process 2] In step 2, it is preferable to apply a voltage to the graphene oxide (GO) film-coated nonconductive substrate (GO-S) in the solution. The solution is preferably an ionic conductive solution. Examples of ionic conductive solutions include the electrolyte for electrochemical cells described later. The aforementioned step 2 may specifically include steps 2-1 to 2-3 using an electrochemical cell. The electrochemical cell may, for example, include a working electrode, a counter electrode, and an electrolyte. Step 2-1: A step of placing the graphene oxide (GO) film-coated nonconductive substrate (GO-S) in the electrolyte that has been permeated with nitrogen in the electrochemical cell. Step 2-2: The graphene oxide (GO) film of the graphene oxide (GO) film-coated nonconductive substrate (GO-S) is electrically connected to the working electrode. Step 2-3: The graphene oxide (GO) film is subjected to electrochemical reduction.

[0027] In step 2, the electrochemical cell may further include a reference electrode. The reference electrode is not particularly limited and includes, for example, a silver / silver chloride reference electrode (Ag / AgCl), a saturated calomel electrode (SCE), a mercury-mercury(I) sulfate electrode (Hg / Hg2SO4), a hydrogen electrode (SHE), and the like. When the reference electrode is a silver / silver chloride reference electrode, a constant voltage may be applied to the working electrode electrically connected to the graphene oxide (GO) film relative to the reference electrode. The applied voltage is not particularly limited and, for example, a range that does not decompose the electrolyte may be selected. Alternatively, as a method for selecting the applied voltage, for example, the optimal applied voltage range for electrochemical reduction of the graphene oxide (GO) film may be determined by a conventional method before the manufacturing process, and that applied voltage range may be used. With respect to the silver / silver chloride reference electrode (Ag / AgCl), the voltage may be -5V or higher, -2.5V or higher, or -1.7V or higher. It may also be -2.6V or lower, -1.8V or lower, or -0.8V or lower. The voltage may be any combination of the above upper and lower limits.

[0028] The electrolyte is not particularly limited. For example, it is sufficient that the necessary current flows between the working electrode and the counter electrode. Furthermore, it is sufficient that no by-products are generated within the range of the applied voltage. Examples include aqueous sulfuric acid solution, aqueous nitric acid solution, aqueous hydrochloric acid solution, aqueous iron(III) chloride solution, aqueous zinc nitrate solution, aqueous aluminum nitrate solution, aqueous zirconium chloride solution, aqueous cerium nitrate solution, sodium sulfate, aqueous potassium hydroxide solution, aqueous lithium hydroxide solution, lithium perchlorate-containing acetonitrile solution, lithium perchlorate-containing propylene carbonate solution, and the like. Among these, nitric acid and hydrochloric acid are preferred, potassium hydroxide and perchlorate-containing acetonitrile solution are more preferred, and aqueous sulfuric acid solution is most preferred. The concentrations may be, for example, 0.0005 M or higher, 0.01 M or higher, or 0.1 M or higher. They may also be 0.0099 M or lower, 0.099 M or lower, or 1 M or lower. The range of these concentrations may be any combination of the above upper and lower limits. The electrolyte may contain a solvent. The solvent may be water or an aqueous solvent containing water, or a non-aqueous solvent such as an organic solvent. From an environmental standpoint, water or an aqueous solvent is preferred. Water is also acceptable. Examples of aqueous solvents include mixed solvents containing water and an organic solvent. Examples of organic solvents included in the aqueous solvent include alcohols such as methanol and ethanol; carbonyl compounds such as formaldehyde and acetone; and amines such as formamide and N,N-dimethylformamide. Non-aqueous solvents are preferred because they eliminate the need to consider the electrolysis of water and allow the use of high voltages. Examples of non-aqueous solvents include acetonitrile and propylene carbonate.

[0029] The working electrode and the counter electrode may be the same or different. Examples of the working electrode include nickel electrodes, gold electrodes, platinum electrodes, and glassy carbon electrodes.

[0030] [Graphene oxide reduced product (rGO) film] The reduced graphene oxide (rGO) film obtained in the step 2 has a lower electrical resistance than graphene oxide (GO) as its precursor before electrochemical reduction. As a reason for the decrease in electrical resistance, for example, it is presumed that as the oxygen functional groups on the surface of graphene oxide decrease, the sp 2 carbon region increases and shows high electrical conductivity. The transparent carbon film obtained by the manufacturing method of the present embodiment may be the reduced graphene oxide (rGO) film. Its sheet resistance may be 1 Ω / sq. or more, 1 MΩ / sq. or more, or 100 MΩ / sq. or more. Also, it may be 999 kΩ / sq. or less, 99.9 MΩ / sq. or less, or 200 MΩ / sq. or less. The range of the sheet resistance may be any combination of the above upper limit value and lower limit value. On the other hand, the transparent carbon film obtained by the manufacturing method of the present embodiment may have a light transmittance of 60% or more, 80% or more, or 90% or more. Also, it may be 79% or less, 89% or less, or 98% or less. The range of the light transmittance may be any combination of the above upper limit value and lower limit value. In particular, when the graphene oxide (GO) which is the precursor of the reduced graphene oxide (rGO) film is graphene oxide (GO) with few pores, for example, when it is graphene oxide (GO) synthesized according to the Brodie method, the reduced graphene oxide (rGO) film obtained in the step 2 has better light transmittance and lower sheet resistance. For example, in that case, the transparent carbon film obtained by the manufacturing method of the present embodiment may have a sheet resistance of 1 Ω / sq. or more, 1 kΩ / sq. or more, or 10 kΩ / sq. or more. Also, it may be 999 Ω / sq. or less, 9.99 kΩ / sq. or less, or 30 kΩ / sq. or less. The range of the sheet resistance may be any combination of the above upper limit value and lower limit value. Its light transmittance may be 70% or more, 80% or more, or 90% or more. Also, it may be 79% or less, 89% or less, or 98% or less. The range of the light transmittance may be any combination of the above upper limit value and lower limit value.

[0031] The reduced graphene oxide (rGO) film obtained in step 2 has the same number of graphene layers as the graphene oxide (GO) from step 1, which serves as its precursor. Furthermore, if the graphene oxide (GO) in step 1, which serves as the precursor, contains an adhesive, the reduced graphene oxide (rGO) film obtained in step 2 also contains an adhesive.

[0032] Furthermore, if the graphene oxide (GO) that serves as the precursor to the reduced graphene oxide (rGO) film is graphene oxide (GO) with few (or no) voids, for example, if it is graphene oxide (GO) synthesized according to the Brodie method, then the reduced graphene oxide (rGO) film obtained in step 2 will also have few (or no) voids. Therefore, a transparent conductive film made of reduced graphene oxide (rGO) has superior light transmittance and low void density.

[0033] [Specific example of the manufacturing method of the first embodiment] Figure 3(B) shows an example of the cross-sectional configuration of the transparent conductive film and non-conductive substrate (S) according to the first embodiment. As shown in Figure 3(B), the transparent conductive film 1B is a graphene oxide reduced product (rGO) film comprising several layers of conductive graphene oxide reduced product (rGO) on a non-conductive polyethylene terephthalate (PET) substrate (non-conductive substrate (S)). In addition to polyethylene terephthalate (PET), quartz glass may also be used as the non-conductive substrate (S) for the transparent conductive film 1B.

[0034] <Process 1> First, prepare polyethylene terephthalate (PET). For example, attach Kapton tape to one side of a 5cm square, 1mm thick piece of PET, and treat the other side with ozone / UV for 5 minutes to make it hydrophilic. Next, several layers of graphene oxide (GO) film 1A are formed on polyethylene terephthalate 2A by alternately coating a cationic polymer such as polydiallyldimethylammonium (PDDA) with negatively charged graphene oxide (GO) using the Layer by Layer method (sometimes called the "LbL method") (see Figure 3A). For example, PDDA is prepared by adding an aqueous solution of tetrabutylammonium hydroxide (TBA) to an aqueous solution adjusted to a concentration of 100 mg / L and adjusting the pH to 9.1. Similarly, graphene oxide (GO) is prepared by adding an aqueous solution of TBA to an aqueous solution adjusted to a concentration of 0.6 g / L and adjusting the pH to 9.1. PET 2A is immersed in a PDDA preparation solution, left to stand for 5 minutes, then washed with water and dried by nitrogen spraying. Next, it is immersed in a graphene oxide preparation solution, left to stand for 5 minutes, then washed with water and dried by nitrogen spraying. By repeating this process 1 to 5 times, several layers of graphene oxide film (GO) 1A are fabricated on PET 2A.

[0035] <Process 2> As shown in Figure 4, an electrochemical reduction cell 100 is used, which includes a glassy carbon electrode (working electrode) 20, a glassy carbon electrode (counter electrode) 40, a silver / silver chloride reference electrode 60, an electrolyte 80, and a nitrogen vent 90. As the electrolyte 80, an aqueous solution of sulfuric acid or the like with a concentration of 0.001 to 0.010 mol / L is used. In this solution, the non-conductive substrate (GO-S) 10A with a graphene oxide film (GO) as shown in Figure 3A is subjected to a silver / silver chloride reference electrode 60 with -1.0 to -2.0 V for 1000 to 10000 seconds, and an electrochemical reduction reaction is performed to obtain the non-conductive substrate (rGO-S) 10B with a reduced graphene oxide (rGO) film as shown in Figure 3B.

[0036] (Second Embodiment) "Method for manufacturing a transparent conductive film containing a metal salt" The method for manufacturing a transparent conductive film according to this embodiment is a method for manufacturing a metal salt-containing transparent conductive film on a non-conductive substrate. The manufacturing method of this embodiment includes the following steps 1 to 3. Step 1: A step to obtain a graphene oxide (GO) film on the non-conductive substrate (S) using graphene oxide (GO), thereby obtaining a graphene oxide (GO) film-coated non-conductive substrate (GO-S). Step 2: A step to obtain a non-conductive substrate (rGO-S) with a graphene oxide (GO) film attached, obtained in Step 1, by applying a voltage to the graphene oxide (GO) film and reducing the graphene oxide (GO) film to form a reduced graphene oxide (rGO) film. Step 3: A step in which a voltage is applied to the non-conductive substrate (rGO-S) with a reduced graphene oxide (rGO) film obtained in Step 2 to form a metal salt-containing reduced graphene oxide (M-rGO) by inserting a metal salt into the reduced graphene oxide (rGO), thereby obtaining a metal salt-containing reduced graphene oxide (MrGO) non-conductive substrate (MrGO-S).

[0037] [Process 1] This is the same as [Step 1] of the first embodiment described above, and the description of [Step 1] of the first embodiment will be incorporated herein by reference.

[0038] [Process 2] This is the same as [Step 2] of the first embodiment described above, and the description of [Step 2] of the first embodiment will be incorporated herein by reference.

[0039] [Process 3] The aforementioned step 3 preferably includes the following steps 3-1 to 3-3. Step 3-1: In an electrochemical cell comprising a working electrode, a counter electrode, and a second electrolyte, the non-conductive substrate (rGO-S) with the graphene oxide reduction product (rGO) film obtained in Step 2 is placed in the second electrolyte, which is permeated with nitrogen. Step 3-2: A step of electrically connecting the graphene oxide reduced product (rGO) film of the non-conductive substrate (rGO-S) with the graphene oxide reduced product (rGO) film to the working electrode. Step 3-3: A step to carry out electrochemical oxidation-reduction of the graphene oxide reduced product (rGO) film.

[0040] Examples of the metal salt being a metal chloride include FeCl3, CuCl2, MoCl5, and SbCl5. Among these, FeCl3 is preferred. If the reference electrode is a silver / silver chloride reference electrode, a voltage of +1 to 3V relative to the reference electrode may be applied to the working electrode electrically connected to the reduced graphene oxide (rGO) film. The voltage may be 1V or higher, 1.7V or higher, or 2.4V or higher. It may also be 1.6V or lower, 2.3V or lower, or 3V or lower. The voltage range may be any combination of the above upper and lower limits.

[0041] The content of the metal salt in the second electrolyte may be 0.1M or higher, 1M or higher, or 5M or higher. It may also be 0.99M or lower, 4.99M or lower, or 10M or lower. The range of the metal salt content in the second electrolyte may be any combination of the above upper and lower limits. The metal salt is not particularly limited and may be any metal salt that dissolves in the second electrolyte. It is preferable that the metal salt is a metal chloride. Furthermore, it is preferable that the metal is at least one selected from the group consisting of Fe, Cu, Mo, and Sb.

[0042] The transparent conductive film obtained in the second embodiment is a metal salt-containing transparent conductive film in which a metal salt such as FeCl3 is inserted (intercalated) between the layers of graphene. From the results of Example 2, the FeCl3-containing transparent conductive film formed on a non-conductive substrate showed reduced sheet resistance while maintaining transmittance compared to a transparent conductive film without FeCl3. Non-patent literature E below discloses metal salt-containing graphite sheets such as FeCl3, CuCl2, MoCl5, and SbCl5. However, it does not describe a method for producing a metal salt-containing transparent conductive film by inserting a metal salt such as FeCl3 between layers of reduced graphene oxide (rGO) formed on a non-conductive substrate using an electrochemical method.

[0043] [Non-patent Document E] R. Matsumoto, Y. Okabe: Electrical conductivity and air stability of FeCl3, CuCl2, MoCl5, and SbCl5graphite intercalation compounds prepared from flexible graphite sheets, Synthetic Metals, Volume 212, February 2016, Pages 62-68.

[0044] [Specific example of the manufacturing method of the second embodiment] <Process 1> This is the same as Step 1 of the specific example of the manufacturing method of the first embodiment described above, and the description of Step 1 of the specific example of the first embodiment will be incorporated here.

[0045] <Process 2> This is the same as Step 2 of the specific example of the manufacturing method of the first embodiment described above, and the description of Step 1 of the specific example of the first embodiment will be incorporated here.

[0046] <Process 3> As shown in Figure 6, an electrochemical cell 200 is used, which includes a glassy carbon electrode (working electrode) 20, a glassy carbon electrode (counter electrode) 40, a silver / silver chloride reference electrode 60, a second electrolyte 85, and a nitrogen vent 90. As the second electrolyte 85, an aqueous solution such as a 9 mol / L iron(III) chloride aqueous solution is used. In this solution, the graphene reduced product (rGO) film-coated nonconductive substrate (rGO-S) 10B obtained in step 2 (Figure 3B) is subjected to a silver / silver chloride reference electrode 60 with a voltage of 1.0 to 2.0 V for 200 to 700 seconds to obtain an iron chloride-containing graphene reduced product (rGO) film-coated nonconductive substrate (rGO-S) by electrochemical reaction (not shown).

[0047] <Applications of transparent carbon electrodes> The transparent conductive films obtained by the manufacturing methods of the first and second embodiments described above have low sheet resistance and high light transmittance, and can therefore be used as, for example, transparent electrodes, heat dissipation materials, anti-fogging materials, sensor materials, etc. [Examples]

[0048] The following describes embodiments of the present invention. The present invention is not limited to the following embodiments.

[0049] (Reagents and materials) Polyethylene terephthalate (PET): Manufactured by AS ONE Corporation, Product name: Thickness: 1mm Kapton Tape: Manufactured by AS ONE Corporation, Product Name: Kapton Tape Polydiallyldimethylammonium (PDDA): Manufactured by Sigma-Aldrich, trade name: Poly(diallyldimethylammonium chloride) solution

[0050] (Device) Ozone / UV device: Manufactured by Sen Special Light Source Co., Ltd., Product name: Tabletop UV Ozone Cleaning and Modification Device PL16-110 Electrochemical cell: Manufactured by BAS Corporation, Product name: Voltammetry cell SVC-3 Each electrode: Reference electrode (manufactured by BAS, aqueous reference electrode (Ag / AgCl RE-1B)), counter electrode (gold, platinum, or glassy carbon electrode), working electrode (non-conductive substrate and conductive electrode such as nickel, gold, platinum, or glassy carbon) Power supply: BAS-manufactured, potentiostat (Gaming Interface 1010) Voltage measurement method: Chronoamperometry (constant voltage measurement)

[0051] Infrared absorption spectrometer: Manufactured by JASCO Corporation, product name: V-550 (Evaluation method) [Method for evaluating sheet resistance] Measurements were taken using a Tektronix Model 2450 Keithle source meter. The resistance was measured by applying a 4-terminal probe vertically to the sample. Five measurements were taken for each sample, and the average value was used as the measurement value.

[0052] [Method for evaluating light transmittance] Using a V-550 UV-Vis spectrophotometer manufactured by JASCO Corporation, a non-conductive substrate without graphene oxide (GO) was set as the reference sample, and a non-conductive substrate containing reduced graphene oxide (rGO) was set as the measurement sample. The samples were set perpendicular to the laser for measurement.

[0053] [Method for evaluating film thickness] After hydrophilic treatment of a silicon wafer with ozone / UV, graphene oxide (GO) was laminated using the LbL method and reduced to reduced graphene oxide (rGO) by electrochemical reduction. Next, cross-sectional drilling was performed using a Hitachi High-Technologies Corporation FIB-SEM NB-5000. At this time, osmium was deposited on the reduced graphene oxide (rGO) film. Subsequently, the thickness of the reduced graphene oxide (rGO) film was evaluated by observing the silicon oxide coating layer and the deposited osmium layer on the silicon wafer using a JEOL Ltd. atomic-resolution analytical electron microscope NEO-ARM JEM-AEM200F.

[0054] (Synthesis Example 1) "Synthesis of graphene oxide (GO) aqueous dispersion" 1 g of graphite powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 40 mL of fuming nitric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed in an ice bath. The resulting mixture was washed seven times with pure water at 3000 rpm using a centrifuge (3700; manufactured by Kubota). The final precipitate was dried in an oven at 50°C to obtain graphite oxide powder. The oxygen content (O / (C+O)) of the graphite oxide was 0.25 or higher as a function of the amount of oxidizing agent and oxidation time. 500 mL of ammonia aqueous solution adjusted to pH 12.5 using 25% ammonia aqueous solution (Fujifilm Wako Pure Chemical Industries, Ltd.) and 500 mg of graphite oxide were added and mixed in a 500 mL plastic container. Using a shaker (manufactured by AS ONE, Shaker SRR-2), the mixture was shaken at room temperature (e.g., 25°C) for more than 5 days (100 rpm). The mixture was then separated and sealed into 50 mL glass containers, and each container was subjected to ultrasonic treatment for 30 minutes in an ultrasonic treatment tank (manufactured by SND, US-30NS). The resulting dispersions were centrifuged at 8000 rpm for 30 minutes using a centrifuge (manufactured by Bechman Coulter, Avanti J-26S XP) to separate them into two or more layers of graphene oxide (GO) and a single layer of graphene oxide (GO). Finally, the obtained graphene oxide (GO) dispersions were washed three times with pure water using a centrifuge at 15000 rpm for 30 minutes to obtain the aqueous graphene oxide (GO) dispersion for this synthesis example.

[0055] (Example 1) "Process 1" First, Kapton tape was applied to one side of a 5cm square, 1mm thick piece of polyethylene terephthalate (PET), and the other side was treated to make it hydrophilic using ozone / UV for 5 minutes. Next, several layers of graphene oxide (GO) films were formed on polyethylene terephthalate (PET) by alternately coating polydiallyldimethylammonium (PDDA) and negatively charged graphene oxide (GO) using the Layer by Layer method, as shown below. A PDDA preparation solution was prepared by adding an aqueous solution of tetrabutylammonium hydroxide (TBA) to an aqueous solution adjusted to a concentration of 100 mg / L and adjusting the pH to 9.1. Similarly, a graphene oxide preparation solution was obtained by adding an aqueous solution of TBA to an aqueous solution of graphene oxide (GO) obtained in Synthesis Example 1, adjusted to a concentration of 0.6 g / L, and adjusting the pH to 9.1. The PET sample was immersed in a PDDA preparation solution, left to stand for 5 minutes, then washed with water and dried by nitrogen spraying. Next, it was immersed in a graphene oxide preparation solution, left to stand for 5 minutes, then washed with water and dried by nitrogen spraying. This process was repeated 1 to 5 times to produce graphene oxide films (GO) No. 1 to 5 on the PET sample. The thickness of graphene oxide film (GO) No. 3, as measured by the above film thickness evaluation method, was 15 nm.

[0056] "Process 2" As shown in Figure 4, an electrochemical reduction cell 100 was used, which included a glassy carbon electrode (working electrode) 20, a glassy carbon electrode (counter electrode) 40, a silver / silver chloride reference electrode 60, an electrolyte 80, and a nitrogen vent 90. The PET with graphene oxide films (GO) No. 1 to 5 obtained in step 1 was electrically connected to the glassy carbon electrode (working electrode) 20. Specifically, using a plate electrode AE-10 manufactured by EC Frontier Co., Ltd., the glassy carbon electrode (working electrode) 20 was connected to the PET with graphene oxide films (GO) No. 1-5 by overlapping and sandwiching them. As shown in Figure 4, the glassy carbon electrode (working electrode) was placed at the upper end of the PET with graphene oxide films (GO) No. 1-5 so that it could be sandwiched between the plate electrodes. Furthermore, when immersing in the electrolyte solution, the glassy carbon electrode (working electrode) was partially immersed so that the plate electrode was not fully immersed. In addition, it is preferable that the width of the glassy carbon electrode (working electrode) be smaller than that of the PET with graphene oxide films (GO) No. 1-5 so that the contact area between the electrolyte and the graphene oxide film (GO) is increased.

[0057] A 0.005 mol / L aqueous sulfuric acid solution was used as electrolyte 80. In this solution, a working electrode 20 equipped with PET with graphene oxide films (GO) No. 1 to 5 obtained in step 1 was subjected to a silver / silver chloride reference electrode 60 at -1.7 V for 2400 seconds. By electrochemical reduction reaction, graphene reduced product (rGO) films No. 1 to 5 were obtained on the PET, respectively.

[0058] A higher number of graphene oxide (GO) layers results in a lower sheet resistance and therefore a faster reduction rate. Consequently, in sample No. 5, reduction is almost complete in about 1-2 minutes. However, since the best sheet resistance was observed at 2400 seconds, all samples No. 2-5 were subjected to a unified 2400-second test. However, in the case of sample No. 1, it is possible that the graphene oxide (GO) film did not completely coat the PET. In fact, in the case of sample No. 1, reduction may not be completely complete even at 2400 seconds, but it has been confirmed that complete reduction occurs if three or more sets of 2400-second tests are performed. The sheet resistances of graphene reduced product (rGO) films No. 1 to 5 on PET, measured using the sheet resistance evaluation method described above, are shown in Table 1 and Figure 5. Table 1 and Figure 5 show the light transmittances measured by the light transmittance evaluation method for graphene reduced product (rGO) films No. 1 to 5 on PET.

[0059] [Table 1]

[0060] (Example 2) Graphene oxide films (GO) No. 1 to 5 were fabricated on PET using the same method as in Step 1 and Step 2 of Example 1. <Process 3> As shown in Figure 6, an electrochemical cell 200 was used, which included a glassy carbon electrode (working electrode) 20, a glassy carbon electrode (counter electrode) 40, a silver / silver chloride reference electrode 60, a second electrolyte 85, and a nitrogen vent 90. The PET with graphene reduced product (rGO) membranes No. 1 to 5 obtained in step 2 was electrically connected to the glassy carbon electrode (working electrode) 20. As the second electrolyte 85, an aqueous solution such as a 9 mol / L iron(III) chloride aqueous solution was used. In this solution, a working electrode 20 equipped with graphene reduced product (rGO) films No. 1-5 was subjected to a silver / silver chloride reference electrode 60 with a voltage of 1.7 V for 400 seconds, and iron chloride-containing graphene reduced product (rGO) films No. 1-5 were obtained on the PET by electrochemical reaction. Figure 7 shows the sheet resistances of iron chloride graphene reduction (rGO) films No. 1 to 5 on PET, as measured by the sheet resistance evaluation method described above.

[0061] (Example 3) In PET coated with graphene oxide (HGO) film, which was synthesized using the conventional Hummers method (average sheet size: 2 μm) in LbL 5 sets, electrochemical reduction treatment was performed in a 0.005 mol / L sulfuric acid aqueous solution at -1.7 V for 2400 seconds. The reduction occurred only near the electrode of the glassy carbon electrode (working electrode), and when the glassy carbon electrode (working electrode) was removed and the sheet resistance was measured, it was found to be very high, ranging from 59 to 145 MΩ / sq. Furthermore, when graphene oxide manufactured by Nippon Shokubai Co., Ltd. (average sheet size: 5 μm or more) was used, reduction proceeded throughout after 24 hours, while the sheet resistance of the sample treated with electrochemical reduction at -1.7 V for 2400 seconds was a high value of 310 kΩ / sq.

[0062] (Consideration) As shown in the examples, even if the substrate does not have electrical conductivity, it was possible to reduce the graphene oxide (GO) on it by an electrochemical method and form a transparent conductive film. It is thought that the reduction reaction proceeded sequentially at the primary interface of the graphene oxide film, and a reduced graphene oxide film was formed on the non-conductive material. In particular, as shown in Example 1, in the case using graphene oxide synthesized according to the Brodie method, the graphene oxide film has few pores (or no pores), resulting in low resistance when electricity flows from the conductive part. This allows the reduction reaction to proceed sequentially at the primary interface of the graphene oxide film at a rapid rate, and the reduced graphene oxide region can expand in a short time. [Industrial applicability]

[0063] The transparent conductive film produced using the method for producing transparent conductive films of the present invention is a graphene-reduced product (rGO) film formed on a non-conductive substrate by an electrochemical method. Since its sheet resistance is comparable to that of single-layer graphene produced by conventional chemical vapor phase methods, it can be used as a transparent electrode, a transparent heater electrode, or a heat dissipation material. [Explanation of symbols]

[0064] 1A: Layers in which PDDA and epGO are stacked alternately. 1B: Layers of alternating PDDA and rGO (transparent conductive film) 2A, 2B: Insulating substrates (non-conductive substrates) such as PET and glass. 10A: Graphene oxide (GO) coated substrate 10B: Substrate coated with reduced graphene (rGO) film 15: Substrate coated with reduced graphene (rGO) film 20: Glassy carbon electrode (working electrode) 40: Glassy carbon electrode (counter electrode) 60: Silver / silver chloride reference electrode 80: Electrolyte: 0.005M sulfuric acid 85: Second electrolyte: 9M iron(III) chloride aqueous solution 90: Nitrogen vent 100: Electrochemical reduction cell 200: Electrochemical cell

Claims

1. A method for producing a transparent conductive film on a non-conductive substrate (S), The transparent conductive film contains reduced graphene oxide (rGO), Step 1 involves forming a graphene oxide (GO) film containing graphene oxide (GO) on the non-conductive substrate (S) to obtain a graphene oxide (GO) film-coated non-conductive substrate (GO-S), A method for producing a transparent conductive film, comprising: step 2, applying a voltage to the graphene oxide (GO) film-coated nonconductive substrate (GO-S) obtained in step 1 to reduce the graphene oxide (GO) film, thereby forming a graphene oxide reduced product (rGO) film containing the graphene oxide reduced product (rGO), and obtaining a graphene oxide reduced product (rGO) film-coated nonconductive substrate (rGO-S).

2. The method for producing a transparent conductive film according to claim 1, wherein the non-conductive substrate is a polymer material or glass.

3. The infrared absorption spectrum of the graphene oxide (GO) film is 1600–1800 cm⁻¹. －１ A method for producing a transparent conductive film according to claim 1, wherein the region does not have an absorption spectrum originating from surface oxygen functional groups.

4. The method for producing a transparent conductive film according to claim 1, wherein the graphene oxide (GO) has 10 or fewer pores in a 500 nm × 500 nm region when observed on the surface with a transmission electron microscope (TEM) at 500,000x magnification.

5. The method for producing a transparent conductive film according to claim 1, wherein the graphene oxide (GO) is graphene oxide synthesized according to the Brodie method.

6. The method for manufacturing a transparent conductive film according to claim 1, wherein the sheet resistance of the graphene oxide reduced product (rGO) film formed on the nonconductive substrate is 1 to 30,000 Ω / sq.

7. The method for producing a transparent conductive film according to claim 1, wherein the light transmittance of the reduced graphene oxide (rGO) film formed on the non-conductive substrate is 60 to 98%.

8. The method for producing a transparent conductive film according to claim 1, wherein the graphene film thickness of the graphene oxide (GO) film is 0.5 to 30 nm.

9. The method for producing a transparent conductive film according to claim 1, wherein the graphene oxide (GO) film is obtained by the LbL method.

10. Step 1 comprises Step 1-1, in which a film is formed on the non-conductive substrate (S) using a dispersion containing graphene oxide (GO) and a dispersion medium, A method for producing a transparent conductive film according to claim 1, comprising the steps 1-2 of removing the dispersion medium from the dispersion.

11. Step 2 is a step 2-1 in which, in an electrochemical cell including a working electrode, a counter electrode, and an electrolyte, the graphene oxide (GO) film-coated nonconductive substrate (GO-S) is placed in the electrolyte that is permeated with nitrogen, Step 2-2 involves electrically connecting the graphene oxide (GO) film of the graphene oxide (GO) film-coated nonconductive substrate (GO-S) to the working electrode, A method for producing a transparent conductive film according to claim 1, comprising step 2-3 of performing electrochemical reduction of the graphene oxide (GO) film.

12. In step 2, the electrochemical cell further includes a reference electrode, The aforementioned reference electrode is a silver / silver chloride reference electrode, A method for manufacturing a transparent conductive film according to claim 11, wherein a voltage of -0.8 to -5V is applied to the working electrode, which is electrically connected to the graphene oxide (GO) film, relative to a reference electrode.

13. The method for producing a transparent conductive film according to claim 11, wherein the electrolyte is at least one selected from the group consisting of an aqueous sulfuric acid solution, hydrochloric acid, aqueous nitric acid solution, aqueous iron(III) chloride solution, aqueous zinc nitrate solution, aqueous aluminum nitrate solution, aqueous zirconium chloride solution, aqueous cerium nitrate solution, sodium sulfate, aqueous potassium hydroxide solution, aqueous lithium hydroxide solution, lithium perchlorate-containing acetonitrile solution, and lithium perchlorate-containing propylene carbonate solution.

14. The method for manufacturing a transparent conductive film according to claim 11, wherein the working electrode is at least one selected from the group consisting of a nickel electrode, a gold electrode, a platinum electrode, a glassy carbon electrode, and the like.

15. Further including step 3, The method for manufacturing a transparent conductive film according to claim 1, wherein step 3 is a step of applying a voltage to the non-conductive substrate (rGO-S) with a reduced graphene oxide (rGO) film obtained in step 2 in a second electrolyte containing a metal salt to form a metal salt-containing reduced graphene oxide (M-rGO) film by inserting the metal salt between the layers of the reduced graphene oxide (rGO), thereby obtaining a non-conductive substrate (MrGO-S) with a metal salt-containing reduced graphene oxide (MrGO) film.

16. Step 3 is a step 3-1 in which, in an electrochemical cell comprising a working electrode, a counter electrode, and a second electrolyte, the non-conductive substrate (rGO-S) with the graphene oxide reduction product (rGO) film obtained in step 2 is placed in the second electrolyte which is permeated with nitrogen, Step 3-2 involves electrically connecting the graphene oxide reduced product (rGO) film of the non-conductive substrate (rGO-S) with the graphene oxide reduced product (rGO) film to the working electrode, A method for producing a transparent conductive film according to claim 15, comprising step 3-3 of performing electrochemical oxidation-reduction of the graphene oxide reduced product (rGO) film.

17. The method for producing a transparent conductive film according to claim 15, wherein the content of the metal salt in the second electrolyte is 0.1 to 10 M.

18. The aforementioned metal salt is a metal chloride, The method for producing a transparent conductive film according to claim 15, wherein the metal is at least one selected from the group consisting of Fe, Cu, Mo, and Sb.

19. In step 3, the electrochemical cell further includes a reference electrode, The aforementioned reference electrode is a silver / silver chloride reference electrode, A method for manufacturing a transparent conductive film according to claim 16, wherein a voltage of +1 to 3V is applied to the working electrode, which is electrically connected to the graphene oxide reduced product (rGO) film, relative to a reference electrode.

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