electrode

Abstract

An electrode (1) is provided with a substrate (2) and an electrically conductive carbon layer (3), toward one side in a thickness direction. The electrically conductive carbon layer (3) contains metal nanoparticles (5) which are dispersed in the electrically conductive carbon layer (3). An arithmetic mean roughness Ra of the electrically conductive carbon layer (3) on one surface in the thickness direction is at least equal to 0.2 nm.

Description

Technical Field

[0001] The present invention relates to an electrode.

Background Art

[0002] An electrode including a base material and a conductive carbon layer disposed on one surface in the thickness direction thereof and in which gold nanoparticles are dispersed is known (see Non-Patent Document 1 below). One surface in the thickness direction of the conductive carbon layer described in Non-Patent Document 1 is flat.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An even more excellent electrode activity is required for the electrode. However, the electrode described in Non-Patent Document 1 has limitations.

[0005] The present invention provides an electrode having excellent electrode activity.

Means for Solving the Problems

[0006] [[ID=4′5]] The present invention (1) includes an electrode including a base material and a conductive carbon layer provided in this order toward one side in the thickness direction, the conductive carbon layer contains gold nanoparticles dispersed in the conductive carbon layer, and an arithmetic mean roughness Ra of one surface in the thickness direction of the conductive carbon layer is 0.2 nm or more.

[0007] In this electrode, one side of the conductive carbon layer in the thickness direction is moderately rough. Moreover, this roughness is due to gold nanoparticles, which have particularly excellent conductivity, contained in the conductive carbon layer. Therefore, the contact area per unit area with the object to be measured on one side of the conductive carbon layer can be increased. As a result, this electrode has excellent activity with respect to the object to be measured.

[0008] (2) The present invention relates to a condition in which the exposed area (true surface area) of the gold nanoparticles from one side is such that the unit electrode area (geometric surface area of ​​the electrode is 1 cm²) is such that 2 ) 0.10cm 2 The above includes the electrode described in (1).

[0009] The present invention (3) includes the electrode according to (1) or (2), wherein the content of the gold nanoparticles in the conductive carbon layer is 3.0 atomic% or more.

[0010] Furthermore, in the present invention (4), the conductive carbon layer is sp 2 The atoms that bond and sp 3 The electrode includes any one of items (1) to (3), which includes the bonding atom. [Effects of the Invention]

[0011] The electrode of the present invention exhibits excellent electrode activity. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view of an electrode from the present invention. [Modes for carrying out the invention]

[0013] <One Embodiment> One embodiment of the electrode of the present invention will be described with reference to Figure 1.

[0014] <Electrode 1> As shown in Figure 1, the electrode 1 extends in a plane direction perpendicular to the thickness direction. The electrode 1 has one surface in the thickness direction and another surface that is spaced apart from the first surface in the thickness direction.

[0015] The electrode 1 comprises a base material 2 and a conductive carbon layer 3 disposed on one side of the base material 2 in the thickness direction. That is, the electrode 1 comprises the base material 2 and the conductive carbon layer 3 in order on one side in the thickness direction. Preferably, the electrode 1 comprises only the base material 2 and the conductive carbon layer 3.

[0016] <Base material 2> The substrate 2 forms the other surface of the electrode 1 in the thickness direction. Examples of substrate 2 include inorganic substrates and organic substrates. Examples of inorganic substrates include silicon and glass. Examples of organic substrates include polyethylene terephthalate. Other known materials can also be preferably used as the material for substrate 2. Preferably, from the viewpoint of electrode activity, an inorganic substrate is used, and more preferably, silicon is used. When the material for substrate 2 is silicon, substrate 2 is prepared, for example, as a silicon wafer.

[0017] The thickness of the base material 2 is not limited. The thickness of the base material 2 is, for example, 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, and also, for example, 1000 μm or less, preferably 500 μm or less, more preferably 100 μm or less.

[0018] <Conductive carbon layer 3> The conductive carbon layer 3 forms one surface in the thickness direction of the electrode 1. The conductive carbon layer 3 is conductive. The conductive carbon layer 3 is in contact with one surface in the thickness direction of the substrate 2.

[0019] The conductive carbon layer 3 contains a plurality of gold nanoparticles 5. The plurality of gold nanoparticles 5 are dispersed in the conductive carbon layer 3. Specifically, the conductive carbon layer 3 contains, for example, a carbon matrix 4 and a plurality of gold nanoparticles 5.

[0020] The carbon matrix 4 is the main part of the conductive carbon layer 3. The carbon matrix 4 has carbon with sp 2 bonding and carbon with sp 3 bonding. That is, the carbon matrix 4 is a microcrystalline domain having a graphite-type structure and a diamond-type structure. Thereby, the conductive carbon layer 3 can reduce background noise based on a chemically stable structure while having good conductivity. As a result, the sensitivity to the measurement target is sufficiently improved.

[0021] In the conductive carbon layer 3, the ratio of the number of atoms bonded by sp 3 to the sum of the number of atoms bonded by sp 2 and the number of atoms bonded by sp 3 (sp 3 / (sp 3 +sp 2 )) is not limited. In the conductive carbon layer 3, the ratio of the number of atoms bonded by sp 3 to the sum of the number of atoms bonded by sp 2 and the number of atoms bonded by sp 3 (sp 3 / (sp 3 +sp 2 )) is, for example, 0.05 or more, preferably 0.10 or more, more preferably 0.15 or more, still more preferably 0.20 or more, particularly preferably 0.25 or more. If the ratio of the number of atoms bonded by sp 3 (sp 3 / (sp 3 +sp 2 )) is above the above-mentioned lower limit, the potential window of the electrode 1 can be widened. In the conductive carbon layer 3, the ratio of the number of atoms bonded by sp 3 to the sum of the number of atoms bonded by sp 2 and the number of atoms bonded by sp 3 (sp 3 / (sp 3 +sp 2 )) is, for example, 0.90 or less, preferably 0.60 or less. The ratio of the number of atoms bonded by sp 3 (sp 3 / s(p 3 +sp 2The measurement method for )) will be described in a later example.

[0022] Furthermore, the carbon matrix 4 may contain trace amounts of unavoidable impurities. Examples of unavoidable impurities include oxygen, argon, and nitrogen.

[0023] The gold nanoparticles 5 are uniformly dispersed in the carbon matrix 4. The median diameter of the gold nanoparticles 5 is, for example, 0.1 nm or more, preferably 1 nm or more, and for example, 20 nm or less, preferably 10 nm or less.

[0024] Some of the multiple gold nanoparticles 5 are exposed from one side in the thickness direction of the carbon matrix 4. In this embodiment, in the conductive carbon layer 3, the leading edge (one end) of the exposed gold nanoparticles 5 is located on one side in the thickness direction.

[0025] The exposed area (true surface area) of gold nanoparticles exposed from one side in the thickness direction of the carbon matrix 4 is equal to the unit electrode area (geometric surface area of ​​the electrode, 1 cm²). 2 ) per 0.01cm 2 Preferably, 0.05 cm 2 More preferably, 0.10 cm 2 Furthermore, 0.3cm 2 More than 0.5cm 2 Above, 0.65cm 2 More than 1.0cm 2 The above is preferable, and also, for example, 10 cm 2 The following applies: If the exposed area (true surface area) of the gold nanoparticles is greater than or equal to the lower limit mentioned above, the activity of electrode 1 can be further improved. The fact that the exposed area (true surface area) of gold nanoparticles per unit of the geometric surface area of ​​electrode 1 is greater than 1 indicates that the gold is predominantly irregular.

[0026] The content of gold nanoparticles 5 in the conductive carbon layer 3 is not limited. For example, the content of gold nanoparticles 5 in the conductive carbon layer 3 is 1.0 atomic% or more, preferably 3.0 atomic% or more, more preferably 5 atomic% or more, even more preferably 10 atomic% or more, and particularly preferably 20 atomic% or more. If the content of gold nanoparticles 5 in the conductive carbon layer 3 is above the lower limit described above, electrode activity can be improved. The content of gold nanoparticles 5 in the conductive carbon layer 3 will be described in later examples.

[0027] <Arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3> The arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 is 0.2 nm or greater.

[0028] If the arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 is less than 0.2 nm, the electrode activity of electrode 1 will decrease.

[0029] In this embodiment, the arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 is 0.2 nm or more, resulting in excellent electrode activity of the electrode 1.

[0030] The arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 is preferably 0.3 nm or more, more preferably 0.5 nm or more, even more preferably 0.7 nm or more, particularly preferably 1.0 nm or more, most preferably 1.2 nm or more, and even more preferably 1.5 nm or more.

[0031] On the other hand, the upper limit of the arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 is, for example, 100 nm, or even 10 nm. If the arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 exceeds the above upper limit, background noise increases. The method for measuring the arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 will be described in a later example. Alternatively, the arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 can be measured in accordance with JIS B 0601 (2013).

[0032] To set the arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 to the range described above, increase the ion acceleration voltage (described later), increase the power of the gold target (described later), and / or decrease the power of the sintered carbon target.

[0033] <Other physical properties of conductive carbon layer 3> The thickness of the conductive carbon layer 3 is, for example, 0.1 nm or more, preferably 0.2 nm or more, and 100 nm or less, preferably 50 nm or less.

[0034] The surface resistance Rs on one side in the thickness direction of the conductive carbon layer 3 is, for example, 1.0 × 10⁻⁶ 4 Ω / □ or less, preferably 1.0 × 10 3 It is less than or equal to Ω / □.

[0035] The thickness of electrode 1 is the total thickness of the substrate 2 and the conductive carbon layer 3, and specifically, for example, is 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, and also, for example, 1000 μm or less, preferably 500 μm or less, more preferably 00 μm or less.

[0036] <Method for manufacturing electrode 1> Next, we will explain how to manufacture electrode 1.

[0037] First, in this method, base material 2 is prepared.

[0038] Next, a conductive carbon layer 3 is formed on one side of the substrate 2 in the thickness direction. A dry method is used to form the conductive carbon layer 3. Examples of dry methods include PVD (physical vapor deposition) and CVD (chemical vapor deposition). The PVD method is preferred as the dry method. Examples of PVD methods include sputtering, vacuum deposition, laser deposition, and ion plating (arc deposition). Preferably, sputtering is used.

[0039] Examples of sputtering methods include unbalanced magnetron sputtering (UBM sputtering), high-power pulsed sputtering, electron cyclotron resonance sputtering, RF sputtering, DC sputtering (DC magnetron sputtering), DC pulsed sputtering, and ion beam sputtering. More preferably, UBM sputtering is used.

[0040] Examples of targets used in sputtering include sintered carbon and gold. The targets are provided in the sputtering apparatus. Two targets are provided in the sputtering apparatus. The sputtering apparatus also includes, for example, a film-forming member. Examples of film-forming members include a film-forming plate (film-forming substrate) and a film-forming roll. The film-forming member is positioned opposite the target with a gap between them. Desired power and voltage can be applied to each of the targets and film-forming members. The power and voltage are controlled by the arithmetic mean roughness Ra of the conductive carbon layer 3, sp 3 The ratio, the content of gold nanoparticles 5, and the exposed area of ​​gold nanoparticles 5 are set as appropriate.

[0041] The arithmetic mean roughness Ra, sp of the conductive carbon layer 3 is determined by at least one of the following means (i), means (ii), and means (iii). 3 The ratio, the content of gold nanoparticles 5, and the exposed area of ​​gold nanoparticles 5 are adjusted. Note that the adjustment of each of the above physical properties is not limited to the means described above.

[0042] In method (i), the voltage applied to the film-forming member is increased. The voltage applied to the film-forming member is called the ion-accelerating voltage because it has the effect of accelerating the speed of sputtering gas ions that collide with the film-forming member. By increasing the ion-accelerating voltage while doping with gold, the arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 increases, and sp 3 The ratio of the number of atoms to bond (sp 3 / (sp 3 +way 2The )) increases, and the content of gold nanoparticles 5 in the conductive carbon layer 3 increases. Specifically, the ion acceleration voltage is, for example, 25V or higher, preferably 50V or higher, and more preferably 70V or higher.

[0043] In method (ii), the power of the gold target is increased. By increasing the power of the gold target, the arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 increases, the content ratio of gold nanoparticles 5 in the conductive carbon layer 3 increases, and the exposed area of ​​gold nanoparticles 5 increases. On the other hand, even if the power of the gold target is increased, sp 3 The ratio of the number of atoms to bond (sp 3 / (sp 3 +way 2 )) does not fluctuate substantially. Specifically, the power of the gold target is, for example, 1W or more, preferably 5W or more, and also, for example, 150W or less.

[0044] Method (iii) involves lowering the power of the sintered carbon target. By lowering the power of the sintered carbon target while doping with gold, the arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 increases, and sp 3 The ratio of the number of atoms to bond (sp 3 / (sp 3 +way 2 The )) becomes lower, and the content ratio of gold nanoparticles 5 in the conductive carbon layer 3 increases. Specifically, the power of the sintered carbon target is, for example, 50W or more, preferably 75W or more, and also, for example, 1000W or less.

[0045] Examples of sputtering gases introduced into a sputtering apparatus include inert gases. These inert gases include, for example, argon. The pressure during sputtering is, for example, 1 Pa or less.

[0046] This results in an electrode 1 having a base material 2 and a conductive carbon layer 3 arranged sequentially on one side in the thickness direction.

[0047] <Applications of Electrode 1> Electrode 1 can be used as various types of electrodes, and is preferably an electrode for electrochemical measurements to be performed using electrochemical measurement methods, specifically as a working electrode for cyclic voltammetry (CV), square wave voltammetry (SWV), anodic stripping voltammetry (ASV), and amperometry.

[0048] In particular, this electrode 1 is preferably used as an electrode (working electrode) with high sensitivity to the following target substances.

[0049] Examples of target substances include electrochemically active aromatic ring-containing compounds, lactone structure-containing compounds, alcohols, and sugars.

[0050] Examples of electrochemically active aromatic ring-containing compounds include phenol compounds, nucleic acid bases, and aromatic amino acid compounds. Examples of phenol compounds include catechol compounds and catechin compounds. Catechol compounds have a structure in which two hydroxyl groups are directly attached to one aromatic ring. Examples of catechol compounds include catechol, dopamine (DA), adrenaline, and noradrenaline. Examples of catechin compounds include catechin, epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate. Examples of nucleic acid bases include guanine, adenine, thymine, cytosine, uracil, and their derivative compounds. Examples of aromatic amino acid compounds include tryptophan compounds, phenylalanine compounds, and tyrosine. Examples of tryptophan compounds include tryptophan, 3-hydroxykynurenine (3HK), and serotonin. Examples of phenylalanine compounds include phenylalanine and phenethylamine.

[0051] An example of an alcohol is methanol.

[0052] Examples of sugars include galactose.

[0053] Among the target substances described above, preferably, are compounds containing an electrochemically active aromatic ring, more preferably, catechol compounds, and even more preferably, dopamine. In other words, preferably, this electrode 1 is used as an electrode for measuring catechol compounds, and even more preferably, as an electrode for measuring dopamine.

[0054] <Effects of one embodiment> In this electrode 1, one surface of the conductive carbon layer 3 in the thickness direction is moderately rough, with irregularities of a size similar to those of the compound being measured. Moreover, this roughness is due to the gold nanoparticles 5 contained in the conductive carbon layer 3, which have particularly excellent conductivity. Therefore, the contact area per unit area with the sample to be measured on one surface of the conductive carbon layer 3 can be increased. As a result, this electrode 1 exhibits excellent activity with respect to the sample to be measured.

[0055] Furthermore, in this electrode 1, the exposed area (true surface area) of gold nanoparticles 5 from one side of the conductive carbon layer 3 is equal to the unit electrode area (geometric surface area of ​​the electrode 1 cm²). 2 ) 0.10cm 2 If the above conditions are met, the activity of electrode 1 can be further improved.

[0056] Furthermore, if the gold nanoparticle content 5 in the conductive carbon layer 3 of electrode 1 is 3.0 atomic percent or more, the activity of electrode 1 can be further improved.

[0057] Furthermore, in this electrode 1, the conductive carbon layer 3 is sp 2 The atoms that bond and sp 3 Because it contains bonding atoms, the conductive carbon layer 3 has good conductivity, and its sensitivity to the object being measured is significantly improved.

[0058] <Variation> In the modified examples, components and processes similar to those in the first embodiment are given the same reference numerals, and their detailed descriptions are omitted. Furthermore, the modified examples can achieve the same effects and advantages as the first embodiment, unless otherwise specified. Moreover, the first embodiment and its modified examples can be combined as appropriate.

[0059] As shown in Figure 1, in one embodiment, the electrode 1 comprises one substrate 2 and one conductive carbon layer 3. In a modified example, although not shown, the electrode 1 comprises one substrate 2 and multiple (specifically, two) conductive carbon layers 3. In other words, the electrode 1 can be provided with multiple (specifically, two) conductive carbon layers 3 on one substrate 2. When the electrode 1 comprises two conductive carbon layers 3, the conductive carbon layers 3, the substrate 2, and the conductive carbon layers 3 are arranged sequentially in the thickness direction. The conductive carbon layer 3 arranged on the other side of the substrate 2 in the thickness direction is formed by the same method as the conductive carbon layer 3 arranged on one side of the substrate 2 in the thickness direction.

[0060] One or more functional layers may be further provided between the substrate 2 and the conductive carbon layer 3, or on the other side of the substrate 2 in the thickness direction (the side opposite to the conductive carbon layer 3 relative to the substrate 2). Examples of functional layers include a base layer, a gas barrier layer, a conductive layer, an adhesion layer, and a surface smoothing layer. [Examples]

[0061] The present invention will be further described below with reference to examples and comparative examples. However, the present invention is not limited in any way to the examples and comparative examples. Furthermore, specific numerical values ​​such as blending ratios (content ratios), physical properties, and parameters used in the following description may be replaced with the corresponding upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or "greater than or equal to") of the blending ratios (content ratios), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0062] <Example 1> A substrate 2 consisting of a silicon wafer with a thickness of 280 μm was prepared.

[0063] Next, the substrate 2 was placed in the sputtering apparatus. The sputtering apparatus comprises a first target, a second target, and a deposition plate, all independently. By sputtering using this apparatus, a conductive carbon layer 3 with a target thickness of 40 nm was formed on one side of the substrate 2 in the thickness direction. This produced an electrode 1 comprising the substrate 2 and the conductive carbon layer 3 in which gold nanoparticles 5 were dispersed. The sputtering conditions were as follows.

[0064] Target 1: Sintered carbon Second target: Gold Sputtering gas: Argon Pressure: 0.6 Pa Voltage applied to the film deposition plate (ion acceleration voltage): 100V Power applied to the first target: 100W Power applied to the second target: 5W

[0065] <Examples 2 to 6, Comparative Example 1> Electrode 1 was manufactured in the same manner as in Example 1. However, the voltage applied to the film deposition plate, the power applied to the first target, and the power applied to the second target were changed as shown in Table 1.

[0066] <Rating> The following aspects were evaluated for Electrode 1 in Examples 1 to 6 and Comparative Example 1.

[0067] (1) The content ratio of gold nanoparticles in the conductive carbon layer 3, and sp 3 / (sp 3 +way 2 ) The content ratio of gold nanoparticles 5 in the conductive carbon layer 3, and sp 3 / (sp 3 +way 2 The results were observed using X-ray photoelectron spectroscopy (XPS, Shimadzu Corporation).

[0068] (2) Arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 The arithmetic mean roughness Ra of one side in the thickness direction of the conductive carbon layer 3 was determined from the shape image obtained by tapping mode measurement using an atomic force microscope (AFM, Bruker).

[0069] (3) Exposed area of ​​gold nanoparticles 5 from one side in the thickness direction of the conductive carbon layer 3 (true surface area) A sample electrode with a known electrode area was prepared by attaching insulating tape with a 2 mm diameter hole to one side of the conductive carbon layer 3. This sample electrode was used as the working electrode and inserted into a 0.05 mol / L H2SO4 aqueous solution, and connected to a potentiostat (CHI Instruments, ALS900). Similarly, a reference electrode (Ag / AgCl) and a counter electrode (Pt) were also inserted into H2SO4 aqueous solutions and connected to the potentiostat. This prepared an electrochemical measurement system equipped with a working electrode, a reference electrode, and a counter electrode.

[0070] Cyclic voltammetry (CV) measurements were performed on a reference electrode within a potential sweep range of -2.4 to 2.4 V at a scanning speed of 0.1 V / sec. The current density was -500 μA / cm². 2 ~+500μA / cm 2 The CV curve was obtained by CV measurement. From the area of ​​the peak observed around 0.8V during the reduction of the Au oxide film in the obtained CV curve, the amount of electricity [μC] was determined, and this value was converted using a conversion constant: 390 [μC / cm²]. 2 By dividing by ], the unit electrode area (geometric surface area of ​​the electrode 1 cm²) in the conductive carbon layer 3 of the sample electrode is obtained. 2 The exposed surface area (true surface area) of gold nanoparticles per unit area was calculated.

[0071] (4) Oxidation peak potential (Epa) when dopamine (DA) is detected In the same manner as in (3) above, an electrochemical measurement system was prepared. As the electrolyte, 100 mmol / L phosphate buffer solution (pH 7) was used. Dopamine (DA) was added to this electrolyte to a concentration of 100 μmol / L. CV measurement was carried out at a scanning rate of 0.1 V / sec. The obtained oxidation peak potential was designated as Epa. A lower Epa means higher activity towards dopamine.

[0072]

Table 1

Industrial Applicability

[0073] The electrode is used as an electrode for electrochemical measurement for carrying out an electrochemical measurement method.

Explanation of Reference Numerals

[0074] 1 Electrode 2 Substrate 3 Conductive Carbon Layer 5 Gold Nanoparticles

Claims

1. The substrate and the conductive carbon layer are arranged sequentially toward one side in the thickness direction. The conductive carbon layer contains gold nanoparticles dispersed in the conductive carbon layer, The arithmetic mean roughness Ra of one surface in the thickness direction of the conductive carbon layer is 0.2 nm or more. An electrode in which the exposed area of ​​the gold nanoparticles from one side is 0.60 cm² or more per unit electrode area.

2. The electrode according to claim 1, wherein the content ratio of the gold nanoparticles in the conductive carbon layer is 3.0 atomic percent or more.

3. The conductive carbon layer is sp ２ The atoms that bond and sp ３ The electrode according to claim 1 or 2, comprising a bonding atom.

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