Conductive film, manufacturing method for conductive film, and electrode

Abstract

This conductive film includes: layered material particles that include a plurality of layers; and a conductive polymer, wherein the layers comprise a layer body represented by the following formula of MmXn (in the formula, M is at least one metal of Group 3, 4, 5, 6, or 7 and includes Ti, X is a carbon atom, a nitrogen atom, or a combination thereof, n is 1 to 4, and m is greater than n and equal to or less than 5), and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body.

Description

Conductive film, method for producing conductive film, and electrode

[0001] The present disclosure relates to a conductive film, a method for manufacturing a conductive film, and an electrode.

[0002] In recent years, MXene has attracted attention as a novel conductive material. MXene is a type of so-called two-dimensional material, and more specifically, as described below, it is a two-dimensional material (layered material) having the form of one or more layers. Generally, MXene is in the form of particles (which may include powder, flakes, nanosheets, etc.) of such two-dimensional (layered) materials. Patent Document 1 discloses a bioelectrode formed from a contact material containing MXene.

[0003] International Publication No. 2019 / 055784

[0004] In Patent Document 1, a composite film of MXene and a conductive polymer is used as an electrode. However, Patent Document 1 does not specifically discuss electrodes with reduced impedance. The object of the present disclosure is to provide a conductive film with reduced impedance, a method for manufacturing the conductive film, and an electrode including the conductive film.

[0005] According to one aspect of the present disclosure, there is provided a conductive film comprising layered material particles comprising a plurality of layers and a conductive polymer, wherein the layers are represented by the following formula: M m X n (wherein M is at least one metal of Group 3, 4, 5, 6, or 7, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and a modified or terminated T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body.

[0006] According to the present disclosure, it is possible to provide a conductive film with reduced impedance, a method for manufacturing the conductive film, and an electrode including the conductive film.

[0007] 1 is a schematic cross-sectional view showing a layered material particle that can be used in one embodiment of the present disclosure, where (a) shows a single-layer MXene particle and (b) shows a multi-layer (exemplarily two-layer) MXene particle. FIG. 2 is a diagram showing an example of the aspects of a layered material particle and a conductive polymer in a conductive film of the present disclosure. FIG. 3 is a schematic cross-sectional view showing one embodiment of an electrode of the present disclosure. FIG. 4 is a schematic cross-sectional view showing another embodiment of an electrode of the present disclosure. FIG. 5 is a schematic cross-sectional view showing another embodiment of an electrode of the present disclosure. FIG. 6 is a SEM observation photograph of a cross section of a composite film of Example 1. FIG. 7 is an EDX measurement result (Ti) of a cross section of a composite film of Example 1. FIG. 8 is an EDX measurement result (C) of a cross section of a composite film of Example 1. FIG. 9 is an EDX measurement result (S) of a cross section of a composite film of Example 1. FIG. 10 is an SEM observation photograph of a cross section of a composite film of single-layer MXene and PEDOT:PSS.

[0008] (Embodiment 1: Conductive Film) Hereinafter, a conductive film according to one embodiment of the present disclosure will be described in detail, but the present disclosure is not limited to this embodiment.

[0009] The conductive film in this embodiment is a conductive film comprising layered material particles including a plurality of layers and a conductive polymer, wherein the layers are represented by the following formula: M m X n (wherein M is at least one metal of Group 3, 4, 5, 6, or 7, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and a modified or terminated T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body.

[0010] The layered material (MXene) constituting the layered material particles (MXene particles) can be understood as a layered compound, and is also referred to as "MXene." m X n T s ", where s is any number, and conventionally, x or z may be used instead of s. Typically, n can be 1, 2, 3, or 4, but is not limited thereto.

[0011] In the above formula for MXene, M may be only Ti, or may include Ti and further include one or more Group 3, 4, 5, 6, and 7 metals other than Ti. For example, M may include Ti and further include at least one element selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo, and Mn. When M includes an element other than Ti, it is more preferable that the element other than Ti is at least one element selected from the group consisting of V, Cr, and Mo.

[0012] MXene is a compound represented by the formula: M m X n However, it is known that it can be expressed as follows: Ti ２ C, Ti ２ N, (Ti, V) ２ C, (Ti, Nb) ２ C, Ti ３ C ２ , Ti ３ N ２ , Ti ３ (CN), (Ti,V) ３ C ２ , (Ti ２ Nb)C ２ , (Ti ２ Ta) C ２ , (Ti ２ Mn)C ２ , (V ２ Ti)C ２ , (Cr ２ Ti)C ２ , (Mo ２ Ti)C ２ , (W ２ Ti)C ２ , Ti ４ N ３ , (Ti, Nb) ４ C ３ , (Ti ２ Nb ２ ) C ３ , (Ti ２ Ta ２ ) C ３ , (V ２ Ti ２ ) C ３ , (Cr ２ Ti ２ ) C ３, (Mo ２ Ti ２ ) C ３ , (W ２ Ti ２ ) C ３

[0013] Typically, in the above formula, M can be titanium, or titanium and vanadium, and X can be a carbon atom or a nitrogen atom. For example, the MAX phase, which is a precursor of MXene, can be Ti ３ AlC ２ and MXene is Ti ３ C ２ T ｓ (in other words, M is Ti, X is C, n is 2, and m is 3).

[0014] In the present disclosure, MXene may contain a relatively small amount of residual A atoms, for example, 10% by mass or less of the original A atoms. The amount of residual A atoms may be preferably 8% by mass or less, more preferably 6% by mass or less. However, even if the amount of residual A atoms exceeds 10% by mass, this may not be a problem depending on the application and conditions of use of the adsorbent.

[0015] The MXene particles, which correspond to the skeleton of the conductive film according to this embodiment, will be described below with reference to FIG.

[0016] The MXene particles constituting the conductive film of this embodiment are aggregates containing multiple layers of MXene (multilayer MXene), as shown in FIG. 1(b). As shown in FIG. 1(b), examples include, but are not limited to, two-layer MXene 10b. More specifically, the individual MXene particles in FIG. 1(b) are m X n The layer body (M m X n The MXene layer 7a has a main layer 1a and modifications or terminations T3a, 5a present on the surface of the main layer 1a (more specifically, on at least one of the two opposing surfaces of each layer). m X n T s ", where s is an arbitrary number.

[0017] MXene 10a shown in FIG. 1(a) is a single layer of multilayer MXene 10b separated from one another. In this embodiment, it is preferable to separate multilayer MXene 10b into the MXene 10a shown in FIG. 1(a) and have it exist as a single layer. FIG. 2 is a schematic cross-sectional view showing a multilayer MXene (layered material particle containing multiple layers) 10c, the outermost surface of which is covered with conductive polymer 11. While FIG. 2 shows a configuration in which the entire outermost surface of multilayer MXene 10c is covered with conductive polymer 11, this is not limiting, and it is sufficient that at least a portion of the outermost surface of multilayer MXene is covered with conductive polymer. Preferably, 50% by volume or more, more preferably 80% by volume or more, and even more preferably, the entire outermost surface of multilayer MXene is covered with conductive polymer.

[0018] While FIG. 1(b) shows an example with two MXene layers, FIG. 2 illustrates an example with five MXene layers. The modifications or terminations T3a and 5a shown in FIG. 1(b) are not shown in FIG. 2. While FIG. 2 shows a configuration in which metal atoms (metal cations) 13 are present between the MXene layers, metal atoms (metal cations) 13 are not required. As shown in FIG. 2, the presence of a conductive polymer 11 around the multilayer MXene 10c ensures the strength of the conductive film while providing low impedance due to MXene. The low AC impedance of MXene is due to the large electric double layer capacitance of the MXene surface (referring to surfaces 7a and 7b in FIG. 1, including the opposing surfaces of 7a and 7b, i.e., the surfaces between the MXene flakes). By using multilayer MXene as MXene, when mixed with a conductive polymer, it is believed that at least the surfaces between the MXene flakes in the multilayer MXene (e.g., MXene surfaces 15a and 15b between MXene layers 7b and 7c in Figure 2) are not covered with conductive polymer, ensuring lower impedance compared to when the entire surface of a single layer MXene is covered with conductive polymer.

[0019] In the multilayer MXene, two adjacent MXene layers (e.g., 7a and 7b) do not necessarily need to be completely separated and may be in partial contact. The conductive film of this embodiment is primarily composed of multilayer MXene, and the ratio of multilayer MXene to the total MXene may be, for example, 80% by volume or more, or even 90% by volume or more, or even 95% by volume or more. However, it is acceptable for a portion of multilayer MXene 10b to be separated and for a small amount of single-layer MXene 10a to be present.

[0020] Although this embodiment is not limited thereto, the thickness of each MXene layer (corresponding to the above-described MXene layers 7a and 7b) is, for example, 0.8 nm to 5 nm, particularly 0.8 nm to 3 nm (this may vary mainly depending on the number of M atomic layers contained in each layer). For each of the multiple MXene stacks that may be included, the interlayer distance (or gap dimension, shown as Δd in FIG. 1(b)) may be, for example, 0.8 nm to 10 nm, particularly 0.8 nm to 5 nm, more particularly about 1 nm, and the total number of layers may be 2 to 20,000.

[0021] (Conductive Polymer) The conductive film of this embodiment is a composite film containing the above-described multilayer MXene and a conductive polymer. MXene exhibits lower AC impedance than conventional materials. While electrodes containing only MXene can be self-supporting, they have low strength. For applications such as biosensing electrodes, it is necessary to improve the strength of the MXene-containing film itself and its adhesion to substrates, etc., and thus a conductive polymer is included. By including a conductive polymer, impedance can be reduced while maintaining adhesion strength. In particular, the multilayer MXene in the conductive film of this embodiment has stronger bonds between MXene flakes than monolayer MXene, preventing conductive polymer molecules from intercalating between layers. The reason for the low AC impedance of MXene, as mentioned above, is the large electric double layer capacitance on the MXene surface (referring to surfaces 7a and 7b in Figure 1, including the opposing surfaces of 7a and 7b, i.e., the surfaces between the MXene flakes). Therefore, it is preferable to arrange the polymer so as not to cover the surface of the MXene as much as possible. By using multilayer MXene as the MXene, as mentioned above, at least the surfaces between the MXene flakes in the multilayer MXene are not covered with conductive polymer. Therefore, even if the entire outermost surface of the multilayer MXene is covered with conductive polymer, the impedance is lower than when the entire surface of a single layer MXene is covered with conductive polymer.

[0022] The polymer contained in the conductive film of this embodiment may be any conductive polymer, and any specific type is acceptable. Examples of conductive polymers include polythiophene, poly(3,4-ethylenedioxythiophene), polystyrene sulfonate, polyaniline, and polypyrrole, and one or more selected from the group consisting of these may be used. From the viewpoint of keeping the overall resistance of the electrode, particularly the DC resistance, of the conductive film of this embodiment low, it is preferable to use PEDOT:PSS (poly(3,4-ethylenedioxythiophene-polystyrene sulfonate)).

[0023] The conductive polymer preferably contains a C=O bond (carbon-oxygen double bond). The conductive polymer having a C=O bond can further reduce impedance while maintaining adhesion strength. Examples of conductive polymers containing a C=O bond include doped conductive polymers obtained by doping the above-listed conductive polymers with a dopant having a C=O bond, such as ortho-phthalic acid. The presence or absence of the C=O bond can be confirmed by FT-IR measurement.

[0024] The volume ratio of the conductive polymer to the total of MXene and the conductive polymer is preferably 20% by volume or more and 80% by volume or less.

[0025] (Metal Atoms) The layered material particles of this embodiment are preferably metal-atom-containing layered material particles containing metal atoms. By including metal atoms, the electric double layer capacitance can be further increased, thereby further reducing impedance. It is noted that if the metal atom has a divalent cation, it is difficult to sufficiently reduce impedance. Therefore, the metal atom is preferably an alkali metal atom, the cation of which is monovalent. The metal atom is preferably one or more of lithium, sodium, and potassium. The metal atom is preferably present between the MXene layers through intercalation. The metal atom is preferably present as a metal cation between the MXene layers, preferably between layers of a layered material particle containing multiple layers (multilayer MXene). That is, the metal atom is preferably present as a monovalent metal cation between the MXene layers, preferably between layers of multilayer MXene.

[0026] The metal atoms are preferably present in an amount of 6.0×10 per 1 g of metal atom-containing layered material particles. －４ By containing at least 1 mol of the compound, the impedance can be further reduced while maintaining the adhesive strength, which is preferable.

[0027] (Embodiment 3: Method for Producing Conductive Film) The method for producing a conductive film of this embodiment comprises: (a) forming a conductive film containing a compound represented by the following formula: M m AX n (b) preparing a precursor represented by the formula: (wherein M is at least one Group 3, 4, 5, 6, or 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; A is at least one Group 12, 13, 14, 15, or 16 element; n is 1 or more and 4 or less; and m is greater than n and 5 or less; －(c) performing an etching treatment to remove at least some of the A atoms from the precursor using an etching solution containing the compound (a), (b) washing the etched product obtained by the etching treatment with water to obtain layered material particles without delamination, and (d) supplying a mixture of the layered material particles and a conductive polymer onto a substrate to form a conductive film. This manufacturing method makes it possible to manufacture a conductive film with low impedance.

[0028] Each step of the above manufacturing method will be described in detail below.

[0029] Step (a) First, a predetermined precursor is prepared. The predetermined precursor that can be used in this embodiment is a MAX phase, which is a precursor of MXene, and is represented by the following formula: M m AX n (wherein M is at least one metal of Groups 3, 4, 5, 6, and 7, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; A is at least one element of Groups 12, 13, 14, 15, and 16; n is 1 or more and 4 or less; and m is greater than n and 5 or less).

[0030] The above M, X, n, and m are as explained for MXene. A is at least one Group 12, 13, 14, 15, or 16 element, and is usually a Group A element, typically Group IIIA or Group IVA, and more specifically, can include at least one element selected from the group consisting of Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, S, and Cd, and is preferably Al.

[0031] The MAX phase is M m X n (each X may have a crystal lattice in which it is located in an octahedral array of M) and a layer composed of A atoms is located between them. In the MAX phase, typically when m=n+1, one layer of X atoms is arranged between each of the n+1 layers of M atoms (these are collectively referred to as "M m X nThe repeating unit has a layer of A atoms (also referred to as an "A atom layer") arranged as the next layer after the n+1th layer of M atoms, but is not limited thereto.

[0032] The MAX phase can be produced by a known method. For example, TiC powder, Ti powder, and Al powder are mixed in a ball mill, and the resulting mixed powder is sintered in an Ar atmosphere to obtain a sintered body (a block of the MAX phase). The sintered body is then pulverized with an end mill to obtain the powdered MAX phase for the next step.

[0033] ・Process (b) F － An etching treatment is performed to remove at least a part of the A atoms from the precursor using an etching solution containing the compound.

[0034] The A atoms (and possibly some of the M atoms) are selectively etched (removed and possibly layer separated) from the MAX phase, thereby removing the A atom layer (and possibly some of the M atoms) to expose the M ｍ X ｎ The surface of the layer is modified with hydroxyl groups, fluorine atoms, chlorine atoms, oxygen atoms, hydrogen atoms, etc. present in the etching solution (usually, an aqueous solution of fluorine-containing acid is used, but this is not limited to this) to terminate the surface.

[0035] The etching is carried out by F － For example, a method using a mixed solution of lithium fluoride and hydrochloric acid, or a method using hydrofluoric acid may be used.

[0036] Step (c): The etched product (or intercalation product, if an intercalation process is performed after the etching process (b) and before the water washing (c) involves mixing the etched product with a compound containing metal atoms) obtained by the etching process is washed with water to obtain layered material particles without delamination. Specifically, after the etching (or intercalation process), decantation is performed using pure water and a centrifuge to remove any remaining acid. In this embodiment, delamination is not performed to obtain multilayer MXene, rather than single-layer or few-layer MXene. After decantation, the precipitate recovered by centrifugation is obtained as clay-like multilayer MXene, or this clay-like MXene can be freeze-dried to obtain powdered multilayer MXene.

[0037] (Intercalation Treatment) When metal atom-containing layered material particles are obtained, a metal atom intercalation treatment is carried out during the etching treatment (b), which includes mixing a compound containing a metal atom with a precursor, or a metal atom intercalation treatment is carried out after the etching treatment (b) and before the water washing (c), which includes mixing a compound containing a metal atom with the etched product.

[0038] When a metal atom intercalation treatment is performed during the etching treatment, examples of the metal compound containing a monovalent metal ion include those used in the intercalation treatment described below. The content of the metal compound containing a monovalent metal ion in the etching solution is preferably 0.001% by mass or more. The content is more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. On the other hand, from the viewpoint of dispersibility in the solution, the content of the metal compound containing a monovalent metal ion in the etching solution is preferably 10% by mass or less, more preferably 1% by mass or less.

[0039] When the metal atom intercalation treatment is carried out after the etching treatment (b) and before the water washing (c), it can be carried out, for example, as follows.

[0040] For example, a monovalent metal ion intercalation treatment may be performed, which includes a step of mixing the etched product obtained by the etching treatment with a metal compound containing a monovalent metal ion. When performing the intercalation treatment, the powder obtained through the above-mentioned washing step may be redispersed in pure water and used instead. Examples of the monovalent metal ions constituting the metal compound containing a monovalent metal ion include alkali metal ions such as lithium ions, sodium ions, and potassium ions, copper ions, silver ions, and gold ions. Examples of the metal compound containing a monovalent metal ion include ionic compounds in which the above metal ions are bonded to cations. Examples include iodides, phosphates, sulfide salts including sulfates, nitrates, acetates, and carboxylates of the above metal ions. The monovalent metal ion is preferably a sodium ion, and the metal compound containing a monovalent metal ion is preferably a metal compound containing a sodium ion, more preferably an ionic compound of a sodium ion, and even more preferably one or more of iodides, phosphates, and sulfide salts of sodium ions. It is believed that if sodium ions are used as metal ions, an ideal multilayer MXene can be obtained in which sodium is inserted between the layers but does not form a monolayer.

[0041] The content of the compound containing the metal atom in the intercalation treatment formulation is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. On the other hand, from the viewpoint of dispersibility in the solution, the content of the compound containing the metal atom is preferably 10% by mass or less, more preferably 1% by mass or less.

[0042] The specific method of intercalation treatment is not particularly limited, and for example, the compound containing the metal atom may be mixed with the MXene water medium clay, and the mixture may be stirred or left to stand. For example, stirring at room temperature may be used. Examples of the stirring method include a method using a stirring bar such as a stirrer, a method using a stirring blade, a method using a mixer, and a method using a centrifuge. The stirring time can be set depending on the production scale of the adsorbent, and may be set between 12 and 24 hours, for example.

[0043] Step (d) The mixture of layered material particles and conductive polymer is supplied onto a substrate to form a conductive film.

[0044] A mixture of layered material particles and a conductive polymer can be obtained, for example, as follows. For example, a mixture can be obtained by mixing an MXene aqueous dispersion or a dispersion of MXene in an organic medium, in which the layered material particles (MXene particles) are present in a medium liquid, or an MXene powder with the conductive polymer described above. The medium liquid of the MXene aqueous dispersion is typically water, and in some cases, it may contain a relatively small amount of other liquid substance in addition to water (for example, 30% by mass or less, preferably 20% by mass or less, based on the total). Examples of the organic medium liquid include N-methylpyrrolidone, N-methylformamide, N,N-dimethylformamide, ethanol, methanol, dimethyl sulfoxide, ethylene glycol, and acetic acid.

[0045] The layered material particles and the conductive polymer can be stirred using a dispersing device such as a homogenizer, a propeller stirrer, a thin film rotary stirrer, a planetary mixer, a mechanical shaker, or a vortex mixer.

[0046] For example, a slurry, which is a mixture of the layered material particles and a conductive polymer, may be applied to at least a portion of the surface of the substrate (for example, the surface of the silver / silver chloride electrode portion formed on the surface of the substrate, in the case of a silver / silver chloride electrode portion substrate). The application method is not limited, and examples thereof include spray application using a nozzle such as a one-fluid nozzle, a two-fluid nozzle, or an airbrush; slit coating using a table coater, comma coater, or bar coater; screen printing; metal mask printing; and application methods by spin coating, immersion, or dropping.

[0047] The formation and drying of the conductive film can be repeated as needed until the desired conductive film thickness is obtained. For example, the combination of spraying and drying can be repeated multiple times. The conductive film may contain or may be substantially free of liquid components derived from the liquid medium of the slurry.

[0048] Drying may be performed under mild conditions such as natural drying (typically, placing the precursor in an air atmosphere at room temperature and pressure) or air drying (blowing air), or under relatively active conditions such as hot air drying (blowing heated air), heat drying, and / or vacuum drying. In this embodiment, "drying" refers to removing any liquid medium that may be present in the precursor. The drying may be performed, for example, at a temperature of 400°C or less using a normal pressure oven or a vacuum oven. For example, drying may be performed at a temperature of 30°C to 200°C for 30 minutes to 24 hours.

[0049] (Embodiment 2: Electrode) The electrode according to this embodiment includes the conductive film. The electrode according to this embodiment is not limited to a specific form as long as it includes the conductive film. The electrode may be formed only from the conductive film, or may include the conductive film and, for example, a substrate. The electrode may be in a solid state or in a flexible, soft state.

[0050] In the electrode of this embodiment, the conductive film may be exposed to the outside air so as to be in direct contact with the object to be measured, or other laminates such as ion-permeable gels or films including porous membranes may be formed. The porous membrane may have a large number of fine pores and selectively transmit ions or molecules smaller than the pore diameter. The materials of these other laminates are not particularly limited and may be made of organic materials, inorganic materials, or mixtures thereof. For example, the organic material may be a polymer such as a hydrophilic polymer, the inorganic material may be ceramics, or a combination thereof. The film thickness of these other laminates may be, for example, 0.1 μm or more and 300 μm or less. The porous membrane may have an average pore diameter of, for example, 1 nm or more and 1 μm or less. The porous membrane may have, for example, an aggregated particulate porous membrane, a mesh-like porous membrane, a fibrous porous membrane, a porous membrane having a plurality of isolated and / or interconnected pores, a honeycomb-structured porous membrane, etc., depending on the pore shape.

[0051] When the electrode of this embodiment has a substrate, the conductive film and the substrate may be in direct contact. The material of the substrate is not particularly limited. The substrate may be formed of a conductive material. Examples of conductive materials include at least one of metal materials such as gold, silver, copper, platinum, nickel, titanium, tin, iron, zinc, magnesium, aluminum, tungsten, and molybdenum, and conductive polymers. The substrate may have a conductive film, such as a metal film, separate from the conductive film of this embodiment on the contact surface with the conductive film of this embodiment. Alternatively, the substrate may be formed of an organic material. Examples of the organic material include flexible organic materials, such as thermoplastic polyurethane elastomer (TPU), PET film, and polyimide film.

[0052] In one preferred embodiment, the electrode according to this embodiment comprises a substrate, a silver / silver chloride electrode portion, and the conductive film (composite film). One embodiment of the electrode according to this embodiment comprises a silver / silver chloride electrode portion disposed on at least a portion of the surface of the substrate, and a conductive film disposed on at least a portion of the surface of the silver / silver chloride electrode portion exposed to the external environment. For example, as shown in the schematic cross-sectional view of FIG. 3, an electrode 20a may be provided in which a silver / silver chloride electrode portion 23 is disposed on the surface of an electrode substrate 21, and a conductive film 25 is disposed on the surface of the silver / silver chloride electrode portion 23. As shown in FIG. 3, the substrate 21 has a tip and a longitudinal direction, the silver / silver chloride electrode portion 23 is disposed on the surface of the tip and side portions of the substrate 21, and the conductive film 25 is disposed on approximately 50% or more of the surface of the silver / silver chloride electrode portion 23 exposed to the external environment.

[0053] Another embodiment of the electrode according to the present invention is an electrode in which a conductive film is disposed on at least a portion of the surface of a substrate, and a silver / silver chloride electrode portion is disposed on at least a portion of the surface of the conductive film that is exposed to the external environment. One example of this is an electrode 20b, as shown in the schematic cross-sectional view of Figure 4, in which a conductive film 25 is disposed on the surface of an electrode substrate 21, and a silver / silver chloride electrode portion 23 is disposed on the surface of the conductive film 25. As shown in Figure 4, an example of an electrode is one in which the substrate 21 has a tip end and a longitudinal direction, the conductive film 25 is disposed on a surface including the tip end of the substrate 21, and the silver / silver chloride electrode portion 23 is disposed on approximately 50% or more of the surface of the conductive film 25 that is exposed to the external environment.

[0054] As a modification of Fig. 3, there is an electrode 20c, in which the proportion of the silver / silver chloride electrode portion 23 disposed on the surface of the electrode substrate 21 is smaller than that of Fig. 3, as shown in the schematic cross-sectional view of Fig. 5. As shown in Fig. 5, an example of an electrode is one in which the substrate 21 has a tip and a longitudinal direction, the silver / silver chloride electrode portion 23 is disposed on the surface of the substrate 21, including the tip, and the conductive film (a film containing layered material particles) 25 is disposed on the entire surface of the silver / silver chloride electrode portion 23 exposed to the external environment. An example of an electrode of this embodiment is a contact pin, for example, as shown in Fig. 5, in which the substrate has a tip and a longitudinal direction, the silver / silver chloride electrode portion 23 is configured only in the tip region 27 of the contact pin, and the conductive film 25 is disposed so as to cover the entire surface of the silver / silver chloride electrode portion 23 exposed to the external environment. In this embodiment, when used as a biosensing electrode, for example, the surface that comes into contact with the skin is a conductive film, resulting in excellent biocompatibility. Furthermore, as shown in Figure 5, by reducing the proportion of the silver / silver chloride electrode portion in the electrode and covering the silver / silver chloride electrode portion with a conductive film, it is thought that deterioration of the silver / silver chloride electrode portion can be suppressed and the life of the electrode can be extended.

[0055] In the electrode according to this embodiment, as shown in FIG. 3 and the like, it is preferable that the silver / silver chloride electrode portion and the conductive film are in direct contact at least in part.

[0056] Another aspect of the electrode according to this embodiment is a brush-shaped electrode having a support and a plurality of contact pins for contacting the measured object, in which the silver / silver chloride electrode portion is disposed on at least a portion of the surface of the base material, including the tips of the contact pins, and the conductive film is disposed on at least a portion of the surface of the silver / silver chloride electrode portion that is exposed to the external environment. For example, as shown in Fig. 6, a brush-shaped electrode 30 having a plurality of contact pins 33 connected to a support 31 can be used, and each of the plurality of contact pins 33 can have any of the aspects shown in Figs. 3 to 5.

[0057] 3 to 6 are explanatory diagrams for ease of understanding, and the shapes of the electrode substrate, silver / silver chloride electrode portion, and conductive film, the sizes of the film thicknesses, the relative sizes, the number, spacing, and arrangement of the contact pins, etc., in these figures may differ from those of an actual electrode. Furthermore, although the electrodes according to this embodiment have been described using the above drawings, the electrodes according to this embodiment are not limited to the forms shown in the above drawings. For example, the cross section of the contact pins of a brush-shaped electrode may be not only rectangular as shown in the above drawings, but also tapered triangular or tapered trapezoidal. Furthermore, the tip of the contact pin may be flat or convexly curved.

[0058] (Method for manufacturing an electrode) When the electrode according to this embodiment has a silver / silver chloride electrode substrate, for example, it can be manufactured by the method described below. However, the method for manufacturing an electrode according to this embodiment is not limited to this embodiment.

[0059] Examples of a method for manufacturing an electrode according to this embodiment include: (A) using a mixture of multilayer MXene and a conductive polymer, forming a film containing the mixture on at least a portion of the surface of a silver / silver chloride electrode portion formed on the surface of a substrate (the surface exposed to the external environment); or (B) using a mixture of multilayer MXene and a conductive polymer, forming a film containing the mixture on at least a portion of the surface of a substrate, and then forming a silver / silver chloride electrode portion on at least a portion of the surface of the film containing the mixture (the surface exposed to the external environment).

[0060] The mixture of multilayer MXene and conductive polymer is as described in the conductive film manufacturing method. In both step (A) and step (B), the silver / silver chloride electrode portion can be formed by a method similar to that used to form a conventional silver / silver chloride electrode. The mixture of multilayer MXene and conductive polymer can be applied directly or after appropriate adjustment (e.g., dilution with a medium solution or addition of a binder) to at least a portion of the surface of the silver / silver chloride electrode portion in step (A), or to at least a portion of the surface of the substrate in step (B). An example of a supplying method is coating. The coating method and drying after coating are as described in the conductive film manufacturing method.

[0061] Although the conductive film and electrode of the present disclosure have been described in detail above, various modifications are possible. Note that the conductive film and electrode of the present disclosure may be manufactured by a method different from the manufacturing method in the above-described embodiment.

[0062] The present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples, and can be implemented by making appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present disclosure.

[0063] Example 1 1. Preparation of MXene Layered material particles (MXene particles) were first obtained by carrying out the following steps in order: (1) preparation of a precursor (MAX), (2) etching of the precursor, (3) cleaning after etching, (4) Na intercalation, (5) cleaning after the intercalation treatment, and (6) powderization, as detailed below.

[0064] (1) Preparation of Precursor (MAX) TiC powder, Ti powder, and Al powder (all manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed in a molar ratio of 2:1:1 in a ball mill containing zirconia balls for 24 hours. The resulting mixed powder was sintered at 1350°C for 2 hours in an Ar atmosphere. The resulting sintered body (block-shaped MAX) was pulverized with an end mill to a maximum size of 40 μm or less. This resulted in the preparation of TiC powder as a precursor (powder-shaped MAX). ３ AlC ２ particles were obtained.

[0065] (2) Etching of precursor (MAX) Ti prepared by the above method ３ AlC ２ Using particles (powder), etching was performed under the following etching conditions to remove Ti ３ AlC ２ A solid-liquid mixture (slurry) containing solid components derived from the powder was obtained. (Etching conditions) Precursor: Ti ３ AlC ２ (Sieved through a 45 μm mesh) Etching solution composition: 49% HF 6 mL, H ２O 18 mL HCl (12 M) 36 mL Precursor input amount: 3.0 g Etching container: 100 mL Eye Boy Etching temperature: 35°C Etching time: 24 h Stirrer rotation speed: 400 rpm

[0066] (3) Post-etching cleaning The above slurry was divided into two equal parts and placed in two 50 mL centrifuge tubes. Then, after centrifuging at 3500 G for 5 minutes using a centrifuge, the supernatant was discarded. Then, (i) 35 mL of pure water was added to the remaining precipitate in each centrifuge tube, (ii) stirring by hand shaking, (iii) centrifuging at 3500 G for 5 minutes, and (iv) removing the supernatant. These steps (i) to (iv) were repeated 10 times. Finally, centrifugation at 3500 G for 5 minutes was performed to remove Ti. ３ C ２ T ｓ - Water medium clay was obtained. ３ C ２ T ｓ - The water medium clay was freeze-dried to obtain MXene powder after etching and washing.

[0067] (4) Na intercalation For sodium intercalation, 1.6 g of MXene powder after etching and cleaning was weighed out and mixed with 40 g of pure water. Separately, 2.16 g of NaCl powder and 40 g of pure water were weighed out and mixed. These two solutions were then stirred. Intercalation container: 100 mL Eye Boy. Temperature: 20°C to 25°C (room temperature). Time: 12 hours. Stirrer rotation speed: 800 rpm.

[0068] (5) Washing after intercalation The slurries obtained after intercalation were transferred to centrifuge tubes, (i) 40 mL of pure water was added, (ii) centrifuged at 3,500 G using a centrifuge, and (iii) the supernatant was separated and removed. These steps (i) to (iii) were repeated five times to remove excess Na, and an intercalation-treated product was obtained: MXene clay intercalated with Na (sodium-intercalated multilayer MXene clay).

[0069] (6) Powdering The intercalation-treated product was divided into appropriate portions in petri dishes and frozen at −18° C. or below, and then dried in a freeze dryer for 24 hours or more to obtain a powder.

[0070] 2. Preparation of Composite Slurry of MXene and Conductive Polymer 1.346 g of the powder obtained in (6) above and 3.158 g of Teikatron PSCM1 manufactured by Teika Corporation were weighed into a 105 mL wide-mouth plastic container and stirred for 60 seconds using a planetary centrifugal mixer at a revolution speed of 1340 rpm and a rotation speed of 1340 rpm to obtain a composite slurry of MXene and conductive polymer. As shown in Table 1 as "Teikatron PSCM1 (50 vol%)," the volume ratio of conductive polymer to (MXene + conductive polymer) was 50 vol%.

[0071] 3. Preparation of a composite electrode of MXene and conductive polymer [for impedance measurement] The composite slurry obtained in "2. Preparation of composite slurry of MXene and conductive polymer" above was dip-coated onto the tip of a conductive rubber brush electrode manufactured by Datwyler to form a composite film. The brush electrode was previously plasma-cleaned using oxygen plasma under desired conditions for 1 minute. The brush electrode dip-coated with the composite slurry was then dried in a normal pressure oven at 80°C for 2 hours to obtain an electrode for impedance measurement.

[0072] [For cross-cut testing] The composite slurry obtained in "2. Preparation of composite slurry of MXene and conductive polymer" above was applied to a polyimide film using a film coater to form a composite film. The polyimide film was previously plasma cleaned using oxygen plasma under desired conditions for 1 minute. After film formation, the film was dried at 80°C for 2 hours in a normal pressure oven to obtain an electrode for cross-cut testing.

[0073] [Example 2] An electrode was obtained in the same manner as in Example 1, except that Li intercalation was performed under the following conditions instead of the above Na intercalation. (Li intercalation conditions) For lithium intercalation, 1.6 g of MXene powder after etching and cleaning and 40 g of pure water were weighed and stirred. Separately, 1.6 g of LiCl powder and 40 g of pure water were weighed and stirred. These two solutions were stirred. - Intercalation container: 100 mL Eye Boy - Temperature: 20°C to 25°C (room temperature) - Time: 12 hours - Stirrer rotation speed: 800 rpm

[0074] Example 3 An electrode was obtained in the same manner as in Example 1, except that after the etching, the intercalation was not performed, and the electrode was washed by decantation with pure water using a centrifuge, and the precipitate obtained by centrifugation was recovered as multilayer MXene without intercalation.

[0075] Comparative Example 1 The process up to Li intercalation was carried out in the same manner as in Example 2. An electrode was obtained in the same manner as in Example 2, except that the Li intercalation-treated product was subjected to delamination under the following conditions.

[0076] (I) Delamination and Water Washing The slurry obtained by Li intercalation was placed in a 50 mL centrifuge tube and centrifuged at 3500 G using a centrifuge, after which the supernatant was discarded. Next, (i) 40 mL of pure water was added to the remaining precipitate, followed by stirring for 15 minutes on a shaker, (ii) centrifuging at 3500 G, and (iii) recovering the supernatant as a single-layer / sparse-layer MXene-containing solution. These steps (i) to (iii) were repeated a total of four times to obtain a single-layer / sparse-layer MXene-containing supernatant. Furthermore, this supernatant was centrifuged at 4300 G for 2 hours using a centrifuge, after which the supernatant was discarded, and MXene clay containing single and plural layers of MXene was obtained as the remaining precipitate.

[0077] (II) Powdering The delaminated MXene was divided into appropriate portions in petri dishes and frozen at −18° C. or below, and then dried in a freeze dryer for 24 hours or more to obtain a powder.

[0078] Comparative Example 2 An electrode was obtained in the same manner as in Comparative Example 1, except that the powdering step (II) above was not carried out and the slurry (water slurry) was used to form the electrode.

[0079] The manufacturing conditions for MXene in Examples 1 to 3 and Comparative Examples 1 and 2 and the conductive polymers used are shown in Table 1.

[0080]

[0081] 4. Evaluation of the Conductive Film Structure [SEM-EDX Observation] The composite film obtained in Example 1 was polished so that its cross section in the thickness direction could be observed. The cross section of the composite film in the thickness direction was then observed using SEM-EDX. The SEM photograph is shown in Figure 7. In Figure 7, the rock-like structures with low contrast are believed to be multilayer MXene, and the surrounding areas with high contrast are believed to be PEDOT:PSS. As evidence, as shown in Figure 8, EDX detected a large amount of Ti at the location of the rock-like structures, suggesting that these structures are MXene. Meanwhile, in the high-contrast areas of Figure 7, EDX detected a large amount of S and also detected C, as shown in Figures 9 and 10, where the locations of C and S are indicated by white dots, suggesting that these structures are PEDOT:PSS. Furthermore, Figure 7 shows that at least a portion of the outermost surface of the multilayer MXene (layered material particles containing multiple layers) is covered with a conductive polymer. For reference, Figure 11 shows an SEM photograph of a cross section of a composite film made of single-layer MXene (layered material particles containing one layer) and PEDOT:PSS (a different product number from the material used in this example, but with the same basic structure). Comparing Figures 7 and 11 reveals that even in the cross section of the same composite film in the thickness direction, there is a clear difference between when multilayer MXene is used and when single-layer MXene is used. Figure 7 shows that the conductive film according to this embodiment is composed of multilayer MXene (the proportion of multilayer MXene is 80% by volume or more).

[0082] The composite film obtained in Example 1 was evaluated by XRD (X-ray diffraction), and it was confirmed that the interlayer distance was wider than that of a composite film obtained without intercalation. From this, it is considered that a composite film obtained by preferably performing intercalation has metal atoms (metal cations) present between layers.

[0083] Furthermore, when the conductive film of Example 1 was measured by FT-IR (Fourier transform infrared spectroscopy), it was confirmed that it had a C═O bond (carbon-oxygen double bond).

[0084] 5. Evaluation of Characteristics Using the electrodes obtained in Examples 1 to 3 and Comparative Examples 1 and 2, impedance was measured to evaluate conductivity, and strength (adhesion strength with the substrate) was evaluated as described below.

[0085] [Impedance Measurement] A Natus gel electrode (product number: 019-415200) was placed on a WetLab biosheet (product number: OHMTS01212) as a counter electrode and a reference electrode. The impedance measurement electrode prepared in "3. Preparation of a composite electrode of MXene and conductive polymer" above was placed on the biosheet as a working electrode.

[0086] Impedance measurements were performed using a Metrohm electrochemical measuring device (product number: PGSTAT302N). Detailed conditions are shown below. For electroencephalograms, signals of around 10 Hz are basically important, but 0.1 Hz signals are also sometimes used. For example, the signal known as a slow potential, which is a clue to diagnosing epilepsy, is 0.1 Hz. Therefore, in the measurements, values ​​of 0.1 Hz and 10 Hz were used as representative values ​​for analysis. (Impedance measurement conditions) Frequency range: 0.1 to 10 ４ Hz Number of plots: 51 points Voltage: 10mVrms

[0087] [Cross-cut test] The cross-cut test was performed according to JIS K 5600-5-6:1999. Specifically, grid-like cuts were made in the composite film of the cross-cut test electrode prepared in "3. Preparation of composite electrode of MXene and conductive polymer" above. Cellophane tape was applied to the cut areas and then peeled off. It was then confirmed whether the composite film (electrode) had peeled off from the polyimide film.

[0088] The results of these measurements are shown in Table 2.

[0089]

[0090] The results in Tables 1 and 2 are considered below. The composite films (electrodes) of Examples 1 to 3 exhibited lower AC impedances than the composite films (electrodes) of Comparative Examples 1 and 2. This is thought to be because, as mentioned above, the MXene flakes in multilayer MXene are more strongly bonded to each other than in single-layer MXene, and polymer molecules do not intercalate between the layers, meaning the MXene surface between the flakes is not covered with polymer, resulting in lower impedance than when single-layer MXene was used. Among Examples 1 to 3, Examples 1 and 2, which contained metal atoms, exhibited lower impedances than Example 3. This is thought to be because the inclusion of metal atoms increases the electric double layer capacity.

[0091] On the other hand, the single-layer MXene powder used in Comparative Example 1 had a large specific surface area, which led to interactions between the polymer and the MXene flakes. The sum of the interactions between each MXene flake and the polymer manifested itself as an increase in the viscosity of the slurry. As a result, film formation was not possible, and characteristic evaluation was not possible. In Comparative Example 2, the impedance was high for two reasons: the surface of the MXene flakes was covered with polymer, making them less functional as an electrode; and because an aqueous slurry was used, the crystallization of PEDOT was disrupted by the addition of water, resulting in a decrease in conductivity.

[0092] As shown in Examples 1 to 3, by using multilayer MXene to form a composite film with a polymer, the adhesion strength to a substrate, etc. can be improved compared to when using MXene alone, and as a result, it can be applied to, for example, biosensing electrodes, etc.

[0093] This application claims priority from Japanese Patent Application No. 2023-208781, which is incorporated herein by reference.

[0094] The conductive film of the present disclosure can be used for any suitable purpose, and can be preferably used, for example, as an electrode, and further as a biosignal sensing electrode.

[0095] <1> A conductive film comprising layered material particles including a plurality of layers and a conductive polymer, wherein the layers are represented by the following formula: M m X n (wherein M is at least one metal of Group 3, 4, 5, 6, or 7, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and a modified or terminated T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body. <2> The conductive film according to <1>, wherein the conductive polymer is one or more selected from the group consisting of polythiophene, poly3,4-ethylenedioxythiophene, polystyrenesulfonic acid, polyaniline, and polypyrrole. <3> The conductive film according to <1> or <2>, wherein the conductive polymer contains a C═O bond. <4> The conductive film according to any one of <1> to <3>, wherein the layered material particles are metal-atom-containing layered material particles containing metal atoms. <5> The conductive film according to <4>, wherein the metal atoms are one or more of lithium, sodium, and potassium. <6> The conductive film according to <4> or <5>, wherein the metal atoms are present as metal cations between layers of layered material particles containing a plurality of layers. <7> The metal atoms are present in an amount of 6.0 × 10 per 1 g of metal-atom-containing layered material particles. －４<8> The conductive film according to any one of <1> to <7>, wherein the layered material particles comprising a plurality of layers account for 80 vol % or more of the layered material particles contained in the conductive film. <9> The conductive film according to any one of <1> to <8>, wherein at least a portion of the outermost surface of the layered material particles is covered with a conductive polymer. <10> An electrode comprising the conductive film according to any one of <1> to <9>. <11> The electrode according to <10>, further comprising a substrate and a silver / silver chloride electrode portion. <12> The electrode according to <10> or <11>, which is a biosignal sensing electrode. <13> (a) a compound represented by the following formula: M m AX n (b) preparing a precursor represented by the formula: (wherein M is at least one Group 3, 4, 5, 6, or 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; A is at least one Group 12, 13, 14, 15, or 16 element; n is 1 or more and 4 or less; and m is greater than n and 5 or less; － (c) performing an etching treatment to remove at least some A atoms from the precursor using an etching solution containing the compound; (c) washing the etched product obtained by the etching treatment with water to obtain layered material particles without delamination; and (d) supplying a mixture of the layered material particles and a conductive polymer onto a substrate to form a conductive film. <14> The method according to <13>, wherein during the etching treatment (b), a metal atom intercalation treatment is performed which includes mixing a compound containing a metal atom with the precursor, or after the etching treatment (b) and before the water washing (c), a metal atom intercalation treatment is performed which includes mixing a compound containing a metal atom with the etched product. <15> The method according to <13> or <14>, wherein the metal atom is one or more of lithium, sodium, and potassium.

[0096] 1a, 1b Layer main body (MmXn layer) 3a, 5a, 3b, 5b Modified or terminated T 7a, 7b, 7c, 7d, 7e MXene layer 10a, 10b, 10c MXene particle (layered material particle) 11 Conductive polymer 13 Metal atom (metal cation) 15a, 15b MXene surface between MXene layers 20a, 20b, 20c, 30 Electrode 21 Electrode substrate 23 Silver / silver chloride electrode portion 25 Conductive film 27 Tip region of contact pin 31 Support 33 Contact pin

Claims

1. A conductive film comprising layered material particles including a plurality of layers and a conductive polymer, wherein the layers are represented by the following formula: M m X n (wherein M is at least one metal of Group 3, 4, 5, 6, 7, and includes Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and a modification or termination T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on a surface of the layer body.

2. The conductive film according to claim 1, wherein the conductive polymer is one or more selected from the group consisting of polythiophene, poly3,4-ethylenedioxythiophene, polystyrenesulfonic acid, polyaniline, and polypyrrole.

3. The conductive film according to claim 1 or 2, wherein the conductive polymer contains a C=O bond.

4. The conductive film according to any one of claims 1 to 3, wherein the layered material particles are metal atom-containing layered material particles that contain metal atoms.

5. The conductive film of claim 4, wherein the metal atoms are one or more of lithium, sodium, and potassium.

6. The conductive film according to claim 4 or 5, wherein the metal atoms are present as metal cations between layers of layered material particles comprising a plurality of layers.

7. The metal atoms are 6.0×10 per gram of metal-atom-containing layered material particles. －４ The conductive film according to any one of claims 4 to 6, comprising at least 1 mol of the compound.

8. The conductive film according to any one of claims 1 to 7, wherein the proportion of layered material particles containing a plurality of layers in the layered material particles contained in the conductive film is 80 volume % or more.

9. The conductive film of any one of claims 1 to 8, wherein at least a portion of the outermost surface of the layered material particles is covered with a conductive polymer.

10. An electrode comprising the conductive film according to any one of claims 1 to 9.

11. The electrode of claim 10 further comprising a substrate and a silver / silver chloride electrode portion.

12. The electrode according to claim 10 or 11, which is a biosignal sensing electrode.

13. (a) a compound having the formula: m A.X. n (b) preparing a precursor represented by the formula: (wherein M is at least one Group 3, 4, 5, 6, 7 metal, including Ti; X is a carbon atom, a nitrogen atom, or a combination thereof; A is at least one Group 12, 13, 14, 15, 16 element; n is 1 to 4 inclusive; and m is greater than n and 5 inclusive; (b) preparing a precursor represented by the formula: － (c) washing the etched product obtained by the etching process with water to obtain layered material particles without delamination; and (d) supplying a mixture of the layered material particles and a conductive polymer onto a substrate to form a conductive film.

14. The method according to claim 13, further comprising: performing a metal atom intercalation treatment during the etching treatment (b), the metal atom intercalation treatment including mixing a compound containing a metal atom with a precursor; or performing a metal atom intercalation treatment after the etching treatment (b) and before the water washing (c), the metal atom intercalation treatment including mixing a compound containing a metal atom with the etched product.

15. The method of claim 13 or 14, wherein the metal atom is one or more of lithium, sodium, and potassium.

Images