JP2013076130A - Conductive diamond electrode and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the manufacturing cost of a conductive diamond electrode, and to improve the detection sensitivity of the conductive diamond electrode.SOLUTION: A conductive diamond electrode 1 is manufactured by depositing BDD ink 6 containing conductive diamond powder and insulating binder on a carbon paste 5 (a collector). The conductive diamond powder is constituted by forming a diamond layer with boron being doped therein on a surface of diamond particles. The conductive diamond powder is mixed in the BDD ink 6 so that the volume ratio of the conductive diamond powder to the insulating binder may be ≥20% and ≤90%.

Description

  The present invention relates to a conductive diamond electrode containing conductive diamond particles and a manufacturing method thereof.

  It is known that when insulating diamond is doped with boron at a high concentration, holes are formed (p-type semiconductor) and metallic conductivity is imparted. Boron Doped Diamond (BDD), which is highly doped with boron in diamond, has features such as a wide potential window, small background current, and high physical and chemical stability derived from diamond. As a functional electrode material effective for electrochemical analysis and electrolysis, it is attracting attention compared to other electrode materials. A conductive diamond electrode using boron-doped diamond as an electrode material is expected to be applied to oxygen reduction electrodes for fuel cells, detection electrodes for gas sensors, and the like. Furthermore, since the conductive diamond electrode has electrochemical characteristics such as a wide potential window and a small background current, it is used for a highly sensitive electrochemical sensor or a highly efficient electrode for electrolysis (for example, water treatment). Use as an electrode for electrolysis is expected.

  Boron-doped diamond is produced mainly by chemical vapor deposition (CVD: Chemical Vapor Deposition) (for example, Patent Document 1). In this case, the boron-doped diamond is formed in a thin film on a flat growth substrate. Therefore, the shape of the conductive diamond electrode is limited. Further, since the size of the boron-doped diamond thin film depends on the size of the CVD apparatus, there is a problem that it is difficult to increase the size of the conductive diamond electrode. Furthermore, since the growth of the boron-doped diamond crystal requires a high temperature condition of 800 ° C. or higher, the problem of melting the base material on which the boron-doped diamond crystal is grown and the thermal expansion coefficient between the boron-doped diamond crystal and the base material Due to this difference, there was a problem that the boron-doped diamond crystal peeled off from the base material during cooling. As a result, materials that can be used as the base material are very limited, such as Si and Mo. These substrates are relatively expensive and difficult to process after the formation of boron-doped diamond crystals.

  In order to solve these problems, research on methods for producing powdery boron-doped diamond and growing boron-doped diamond under low temperature conditions has been conducted in recent years (for example, Patent Document 2, Non-Patent Document). 1, 2). In particular, if a powdery boron-doped diamond can be produced, the processing after the boron-doped diamond is produced is easy, leading to an expansion of the field of application of boron-doped diamond. Furthermore, by forming boron-doped diamond in powder form, high efficiency due to an increase in specific surface area and production of a highly functional catalyst by combining with metal fine particles are expected.

  Further, in recent years, microelectrodes having a small electrode size have been used in micromeasurements in fields such as environmental analysis, clinical examination, and food inspection in order to improve response speed and S / N ratio. The response behavior of the microelectrode depends on the size of the electrode, and the response speed and the S / N ratio improve as the electrode size decreases. However, when the electrode diameter is reduced, the obtained current value itself is also reduced. Therefore, in order to improve the reliability of the measurement value (in order to increase the current value), a microelectrode array in which the number of electrodes is increased to form an array is used (for example, Patent Documents 3 and 4). In this microelectrode array, an insulating polymer is screen-printed on an electrode, and after the polymer is cured, the pattern of the electrode or the mask is formed by using a method (for example, Patent Document 3) or a photolithographic technique. It takes time and effort to make the method.

JP 2006-9147 A Special table 2007-528495 gazette Special table 2007-535670 gazette JP 2004-285405 A JP 11-319530 A

Anne E. Fischer, 1 other, "Preparation and Characterization of Boron-Doped Diamond Powder", J. Electrochem. Soc., August 2005, Volume 152, 9, p.B369-B375 Ayten Ay, two others, "The Physicochemical and Electrochemical Properties of 100 and 500 nm Diameter Diamond Powders Coated with Boron-Doped Nanocrystalline Diamond", J. Electrochem. Soc., August 2008, Volume 155, 10, p. B1013- B1022 Y. G. Wang, 3 others, “Resonant Raman scattering studies of Fano-type interference in boron doped diamond”, J. Appl. Phys., 2002, Volume 92, 12, p.7253

  In order to apply the conductive diamond electrode to an apparatus such as a sensor, the production cost of the conductive diamond electrode can be reduced, the conductive diamond electrode can be easily manufactured for mass production, There is a need to improve detection sensitivity.

  Therefore, an object of the present invention is to provide a technique that contributes to a reduction in manufacturing cost of a conductive diamond electrode and contributes to an improvement in detection sensitivity of the conductive diamond electrode.

  The conductive diamond electrode of the present invention that achieves the above object comprises a current collector, and conductive diamond particles disposed on the current collector and electrically connected to the current collector. An electrode is characterized in that an insulating binder is provided between the conductive diamond particle groups, and a conductive diamond array is formed on the current collector.

  Another embodiment of the conductive diamond electrode of the present invention that achieves the above object is a conductive diamond electrode formed by depositing a conductive diamond ink containing conductive diamond particles and an insulating binder. The volume of the conductive diamond particles relative to the volume of the insulating binder is 20% or more and 90% or less.

  The method for producing a conductive diamond electrode of the present invention that achieves the above object is a method for producing a conductive diamond electrode using conductive diamond particles, comprising dissolving an insulating binder. The conductive diamond particles containing the conductive diamond particles are mixed with the solvent so that the volume of the conductive diamond particles with respect to the volume of the insulating binder is 20% to 90%. A step of obtaining an ink, and a step of depositing the conductive diamond ink on a current collector to obtain a conductive diamond electrode.

  According to the above invention, it can contribute to reducing the manufacturing cost of the conductive diamond electrode and can contribute to the improvement of the detection sensitivity of the conductive diamond electrode.

(A) A perspective view of a conductive diamond electrode according to an embodiment of the present invention, (b) an exploded perspective view of a conductive diamond electrode according to an embodiment of the present invention. It is a schematic diagram of the BDD ink which concerns on embodiment of this invention, (a) The figure which shows before drying, (b) The figure which shows after drying. It is the schematic of the MPCVD apparatus for manufacturing the boron dope diamond particle (BDDP) which concerns on embodiment of this invention. It is a characteristic view which shows the Raman measurement result of BDDP. It is a characteristic view which shows the Raman measurement result of DP. It is a figure which shows the measurement result of the particle size distribution of DP and BDDP. It is a flowchart explaining the preparation method of BDD ink. It is a flowchart explaining the preparation process of an electroconductive diamond electrode. It is a CV figure in the 0.5 mol / L sodium sulfate aqueous solution of the electroconductive diamond electrode which concerns on an Example, (a) CV figure of Example 1, 2 and (b) CV figure of Example 3, 7. . It is a CV figure in the 0.5 mol / L sodium sulfate aqueous solution of the electroconductive diamond electrode which concerns on a reference example. It is the figure which compared the background current which flows in the 0.5 mol / L sodium sulfate aqueous solution of the electroconductive diamond electrode which concerns on an Example and a reference example. It is a CV figure in the 0.5 mmol / L potassium ferricyanide-0.5 mol / L sodium sulfate aqueous solution of the electroconductive diamond electrode which concerns on an Example. It is a CV figure in the 0.5 mmol / L potassium ferricyanide-0.5 mol / L sodium sulfate aqueous solution of the electroconductive diamond electrode which concerns on a reference example. The characteristic view which shows the relationship between the BDDP volume ratio with respect to the volume of the insulating binder of the conductive diamond electrode which concerns on an Example and a reference example, and the S / B ratio of the oxidation reduction reaction of Fe [(CN) ₆ ] ^{3- / 4-} . It is. (A) Explanatory drawing of the conductive diamond electrode which concerns on a prior art, (b) It is explanatory drawing of the conductive diamond electrode which concerns on embodiment of this invention. It is a CV figure in 0.5 mmol / L ascorbic acid-0.1 mol / L phosphate buffer (pH 7.4) of the electroconductive diamond electrode which concerns on the Example of this invention. It is the figure which compared the S / B ratio of the oxidation reaction of ascorbic acid of the electroconductive diamond electrode which concerns on the Example of this invention. It is a characteristic view which shows the difference in the potential window by the difference in the kind of electrode material.

  A conductive diamond electrode according to an embodiment of the present invention and a method for manufacturing a conductive diamond electrode according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1A is a perspective view of a conductive diamond electrode according to an embodiment of the present invention. As shown in FIG. 1 (a), a conductive diamond electrode 1 according to an embodiment of the present invention includes a paste (hereinafter referred to as BDD (BDD)) in which conductive diamond powder (BDDP) and an insulating binder are mixed. Boron Doped Diamond) ink 6) is deposited on a current collector in which the silver paste 3 is coated with the carbon paste 4.

  FIG. 1B shows an exploded perspective view of the conductive diamond electrode 1. As shown in FIG. 1B, when producing the conductive diamond electrode 1, a silver paste 3 is printed on the polyimide substrate 2, and a carbon paste 4 is printed on the silver paste 3. Further, an insulating resin 5 is printed so as to cover the silver paste 3 on which the carbon paste 4 is printed. At this time, the insulating resin 5 is printed so that the insulating resin 5 does not cover at least a part of the carbon paste 4. That is, a portion of the carbon paste 4 that is not covered with the insulating resin 5 is a current collector, and this portion is an apparent electrode area. Moreover, by providing the connection part 3a which is not covered with the insulating resin 5 at one end part of the silver paste 3, the connection part 3a becomes a connection part between the conductive diamond electrode 1 and a measuring device (detection device) such as a potentiostat. . A BDD ink 6 is printed on the carbon paste 4.

  As the conductive diamond powder, for example, diamond particles (DP: Diamond Powder) are used as a base material, and conductive diamond particles in which a boron-doped diamond (BDD: Boron Doped Diamond) layer is formed on the surface of the diamond particles. The thing which consists of is mentioned.

  As the diamond particles, natural diamond powder such as insulating diamond powder commercially available as an abrasive or artificially produced diamond powder can be used. Artificial diamond powder can be produced by CVD such as thermal CVD, RF plasma, hot filament CVD, PVD such as ion beam or ionized vapor deposition, and high temperature and high pressure. The particle diameter (average particle diameter) and shape of the diamond particles are not particularly limited, but are appropriately set in consideration of the workability of the BDD ink 6 and the thickness of the BDD layer after the BDD ink 6 is dried. Is done. For example, when the particle diameter of diamond particles is 5 nm to 100 μm, and more preferably 50 nm to 10 μm, sufficient workability can be secured to produce the conductive diamond electrode 1 by printing the BDD ink 6. In the conductive diamond electrode 1, the conductive diamond particles and the current collector are electrically connected.

When the BDD layer is formed on the surface of the diamond particles, the amount of boron doped into the diamond is at least 10 ppm, more preferably 1000 ppm, and even more preferably 10,000 ppm of boron with respect to the carbon constituting the diamond. (In other words, the boron concentration ratio in the crystal is 10 ²⁰ to 10 ²² cm ⁻³ ) Conductive diamond particles having sufficient conductivity can be obtained.

  The conductive diamond particles mixed in the BDD ink 6 are added so that the volume of the conductive diamond particles is 20% to 90% with respect to the volume of the insulating binder. As shown in FIG. 2A, the BDD ink 6 to which the conductive diamond particles 6a are added is printed on the carbon paste 4 so that the volume of the conductive diamond particles is 90% or less with respect to the volume of the insulating binder. At this time, the conductive diamond particles 6a aggregate to form a conductive diamond particle group 6b. In general, it is known that many conductive particles such as carbon black are often aggregated into a lump (for example, Patent Document 5), and the conductive diamond particles 6a of the present invention are also agglomerated in the same manner. It is thought that it forms a collection. When the BDD ink 6 is dried, as shown in FIG. 2B, the solvent is volatilized from the BDD ink 6, so that the film thickness of the BDD ink 6 becomes thin. As a result, the distance in the vertical direction of the BDD ink 6 film between the conductive diamond particles 6a is shortened, and the conductive diamond particles 6a constituting the conductive diamond particle group 6b are in close contact with each other, so that the BDD ink 6 It is considered that the conductive diamond particles 6a exposed from the surface of the portion and the current collector 4 form a conductive diamond particle group 6b electrically connected by the conductive diamond particles 6a. In addition, since an insulating binder exists between the conductive diamond particle groups 6b in the planar direction of the BDD layer, the conductive diamond particle groups 6b surrounded by the insulating binder are dispersed at a low density. Form (pseudo microelectrode).

  On the other hand, in the BDD layer obtained by drying the BDD ink 6, as the volume ratio of the conductive diamond particles 6a with respect to the volume of the insulating binder exceeds 90% and the volume ratio of the conductive diamond particles 6a increases, conductive diamond The tendency that the particle groups 6b are electrically connected to each other increases. Therefore, the diamond particle group 6b electrically connected to the carbon paste 4 on the surface of the conductive diamond electrode 1 does not have a form as a pseudo microelectrode existing at a low density. Further, when the volume of the conductive diamond particles 6a with respect to the volume of the insulating binder is smaller than 20%, the ratio of the conductive diamond particles 6a that are surrounded by the insulating binder and cannot be electrically connected to the carbon paste 4 in the BDD layer. Increases and the Faraday current flowing through the conductive diamond electrode 1 decreases.

  The insulating binder is preferably various polyester resins which are polycondensates of polycarboxylic acid (dicarboxylic acid) and polyalcohol (diol) from the viewpoint of adhesion to the current collector. The insulating binder is not limited to a polyester resin, but includes various modified polyester resins such as urethane-modified polyester resin, epoxy-modified polyester resin, and acrylic-modified polyester, polyether urethane resin, polycarbonate urethane resin, polyethylene, Polyolefin resins such as polypropylene, ethylene vinyl acetate polymer, maleated polyolefin, vinyl chloride / vinyl acetate polymer, epoxy resin, phenol resin, polyamideimide, nitrocellulose, cellulose acetate acetate butyrate (CAB), cellulose acetate acetate Modified celluloses such as propionate (CAP) may be used.

  Next, with reference to specific examples, the conductive diamond electrode according to the embodiment of the present invention and the method for manufacturing the conductive diamond electrode according to the embodiment of the present invention will be described in more detail.

(Example)
[Method for producing boron-doped diamond powder (BDDP)]
FIG. 3 shows a schematic diagram of a microwave plasma CVD apparatus (MPCVD apparatus 7) for producing boron-doped diamond powder. In Examples (and Reference Examples), boron-doped diamond powder was prepared using an MPCVD apparatus manufactured by ASTeX.

  As diamond powder (DP) which is a base material for growing the BDD layer, pulverized natural diamond powder (manufactured by Element Six, Micron + SND, particle size 0 to 0.5 μm) was used.

First, diamond powder contains metal components and various sp ² carbons as impurities, and these impurities adversely affect the final product. Therefore, in order to remove these impurities, it was treated with aqua regia heated to 60 ° C. for 30 minutes and similarly with 30% hydrogen peroxide solution heated to 60 ° C. for 30 minutes to remove impurities contained in the diamond powder. . The washed diamond powder was ultrasonically cleaned in ultrapure water, 2-propanol, and acetone and dried.

  1.0 g of the diamond powder whose surface was cleaned was stored as a base material in the storage container 8 in the MPCVD apparatus 7, and a diamond layer doped with boron was grown on the surface layer of the diamond powder.

As the carbon source, an acetone / methanol mixed solution in which trimethoxyborane (B (OCH ₃ ) ₃ ) was dissolved so that the boron concentration ratio (B / C) was 20000 ppm was used. In a state where the diamond powder stored in the storage container 8 is irradiated with microwaves from a quartz window, trimethoxyborane and hydrogen are supplied to the storage container 8 to grow a diamond layer doped with boron on the surface of the diamond powder. Boron doped diamond powder was obtained. The microwave output was fixed at 1300 W, and the growth time was 8 hours. Detailed reaction conditions are shown in Table 1.

  After the growth of the BDD layer, the muffle furnace was heated in air at 425 ° C. for 5 hours to remove graphite impurities generated during the growth of the BDD layer. Thereafter, a hydrogen termination treatment was performed on the surface oxidized by the heat treatment. The hydrogen termination treatment was performed under the conditions of a hydrogen flow rate of 100 sccm, a pressure of 20 Torr, a microwave output of 500 W, and a stage temperature of 800 ° C. for 1 hour.

[Raman measurement]
Raman measurement of the obtained BDDP was performed using a Raman spectrometer (NSR-3200, manufactured by JASCO). The measurement results are shown in FIG. As a reference example, FIG. 5 shows the Raman measurement result of diamond powder (DP). In the above Raman measurement, the measurement conditions were as follows: measurement range: 1100 to 1800 cm ⁻¹ , laser wavelength: 532 nm, integration number: 5 times.

The peak near 1332 cm ^{−1 of the} Raman spectrum (peak corresponding to diamond (sp ³ )) correlates with the boron concentration, and this peak position shifts at a low wavenumber as the boron concentration in boron-doped diamond increases. Is known (for example, Non-Patent Document 3).

Comparing the BDDP Raman measurement result (shown in FIG. 4) with the DP Raman measurement result (shown in FIG. 5), the BDDP measurement result has a diamond (sp ³ ) peak near 1332 cm ^−1. On the other hand, in DP, it can be confirmed that there is a peak of diamond (sp ³ ) near 1336 cm ⁻¹ . That is, in the BDDP after the CVD process, the peak corresponding to diamond (sp ³ ) is shifted to the low wave number side, and from the result of this Raman measurement, the DP is processed by the MPCVD apparatus 7 to be on the DP. It was confirmed that the BDD layer was growing.

[BDDP particle size distribution measurement]
In FIG. 6, the measurement result of the particle size distribution of DP used as the base material and the measurement result of the particle size distribution of the obtained BDDP are shown. The particle size distribution was measured by a laser diffraction scattering method. The relative particle amount is based on volume.

  As shown in FIG. 6, since DP has a particle size distribution in the range of 0.1 to 1 μm in particle size, the particle size distribution of BDDP shows a particle size distribution having almost the same tendency. In BDDP, a distribution is also present in the vicinity of a particle diameter of 5 to 50 μm, which is considered to be due to aggregation of BDDP particles. Thus, even before mixing of the BDDP and the binder, BDDP aggregates already exist. In addition, the formation of this aggregate is promoted by using BDDP as the BDD ink, and more electrical connection (energization path) structures between the BDDP and the carbon paste are easily formed. It is considered to be a suitable conductive diamond particle.

[Method for producing conductive diamond electrode]
1. Preparation of Boron Doped Diamond (BDD) Ink FIG. 7 shows a flow diagram of a method for preparing BDD ink. Based on this figure, the preparation method of the BDD ink whose BDDP volume ratio with respect to the volume of the polyester resin (insulating binder) is 89% will be described. First, 40 mg of polyester resin (trade name: Byron GK-140, manufactured by Toyobo Co., Ltd.) as an insulating binder was weighed into a beaker.

Next, 5 drops (63.0 mg) of methyl ethyl ketone with a Pasteur pipette and 5 drops (79.4 mg) of isophorone with a Pasteur pipette were added to 40 mg of the polyester resin to dissolve the polyester resin. At this time, methyl ethyl ketone was easily added because it easily volatilizes. After dissolving the polyester resin, 100 mg of BDDP was added and sufficiently dispersed to prepare a BDD ink. A BDD ink in which the ratio of BDDP and polyester resin was changed was prepared in the same manner. Table 2 shows the ratio of the polyester resin and BDDP in the BDD inks according to Examples 1 to 7, and Table 3 shows the ratio of the polyester resin and BDDP in the BDD ink according to Reference Example 1. In Tables 2 and 3, the BDDP volume ratio (%) to the polyester resin volume was calculated from the polyester resin / BDDP mass ratio based on the diamond density of 3.5 g / cm ³ and the polyester resin density of 1.25 g / cm ³ . .

2. Screen printing The production of the conductive diamond electrode was performed using a screen printer (manufactured by NEW LONG, LS-150TV). Screen printing is a type of stencil printing, and is a printing method in which holes are made in the plate itself and ink is rubbed from there. In screen printing, screen eyes woven with chemical fibers such as polyamide fibers and polyarylate fibers are generally used to manufacture many electronic components such as ceramics, circuit boards, printed circuit boards, and film circuit boards. It's being used. Screen printing can print on a wide range of materials and can print on curved surfaces as well as flat surfaces. In addition, there are various features such as excellent reproducibility and productivity, printing with a film thickness of about several tens to several hundreds of μm, and a variety of inks.

  With respect to a method for producing a conductive diamond electrode by a screen printer, an external view of the conductive diamond electrode 1 shown in FIG. 1 (a) (and an exploded view shown in FIG. 1 (b)) and a conductive diamond shown in FIG. This will be described with reference to a production flow diagram of the electrode 1.

  The conductive diamond electrode 1 uses the BDD ink according to Examples 1 to 7 shown in Table 2 and the BDD ink according to Reference Example 1 shown in Table 3 above. A diamond electrode and a conductive diamond electrode according to Reference Example 1 were produced.

  In the description of the flow chart for producing the conductive diamond electrode 1 in FIG. 8, a method for producing the conductive diamond electrode according to Example 1 will be described as an example. About the manufacturing method of the conductive diamond electrode which concerns on another Example and a reference example, since it can manufacture by the method similar to the manufacturing method of the conductive diamond electrode of Example 1 except that the BDDp volume ratio in BDD ink differs. The description is omitted to avoid duplication.

  As shown in FIG. 8, first, silver paste 3 (ECM-100 AF5000, manufactured by Taiyo Ink Co., Ltd.) was printed on polyimide substrate 2 (trade name: Kapton Film, manufactured by Toray DuPont Co., Ltd.) (step S1).

  Next, carbon paste 4 (JELCON CH-10, manufactured by Jujo Chemical Co., Ltd.) was printed on the printed silver paste 3 (step S2).

  Furthermore, the insulating resin 5 (TF-200FR1, manufactured by Taiyo Ink Co., Ltd.), which is a kind of resist ink, was printed so as to cover the silver paste 3 (step S3). At this time, the insulating resin 5 is printed so as not to cover at least a part of the carbon paste 4 formed in Step 2. The carbon paste 4 on which the insulating resin 5 is not printed functions as a current collector for the conductive diamond electrode 1.

  And the BDD ink 6 of Example 1 shown in Table 2 was printed on the carbon paste 4 (step S4). After printing the BDD ink 6, the conductive diamond electrode 1 was produced by heating at 120 ° C. for 30 minutes (step S5).

[Evaluation of conductive diamond electrode]
1. Electrochemical characteristics in aqueous sodium sulfate solution As an evaluation of the conductive diamond electrode, cyclic voltammetry (hereinafter, CV measurement) was performed in an aqueous sodium sulfate solution. CV measurement was performed with a three-electrode system using a potentiostat (HZ-5000, manufactured by Hokuto Denko Corporation). The configuration of the measurement apparatus and measurement conditions are shown below.
Working electrode: Conductive diamond electrode Counter electrode: Platinum wire measurement solution: Sodium sulfate aqueous solution (0.5 mol / L)
Reference electrode: Silver / silver chloride (Ag / AgCl) saturated potassium chloride electrode Sweep speed: 10 mV / s
The measurement results with the conductive diamond electrodes of Examples 1 and 2 are shown in FIG. 9A, the measurement results with the conductive diamond electrodes of Examples 3 and 7 are shown in FIG. 9B, and the conductivity of Reference Example 1 is shown. The measurement results at the diamond electrode are shown in FIG. Further, the value of the current that flows when a potential of 0.3 V (vs Ag / AgCl) was applied to the conductive diamond electrode was measured as the background current. The measurement results of the background current measured with the conductive diamond electrodes of Examples 1 to 7 and Reference Example 1 are shown in FIG.

  As shown in FIG. 11, when the volume ratio of the conductive diamond particles to the volume of the insulating binder is in the range of 20% to 90%, the conductive diamond electrode has a background current value as compared with Reference Example 1. It can be seen that it can be reduced.

2. Electrochemical properties in aqueous solution of potassium ferricyanide (K ₃ [Fe (CN) ₆ ]) Potassium ferricyanide, which is a redox species used to evaluate general electrochemical properties as a further evaluation of conductive diamond electrodes CV measurement was carried out with a sodium sulfate aqueous solution containing. The configuration of the measuring apparatus and the measurement conditions are as follows.
Working electrode: conductive diamond electrode Counter electrode: platinum wire measurement solution: potassium ferricyanide (0.5 mmol / L) -sodium sulfate aqueous solution (0.5 mol / L)
Reference electrode: Silver / silver chloride (Ag / AgCl) saturated potassium chloride electrode Sweep speed: 10 mV / s
The CV measurement result with the conductive diamond electrode of Examples 1, 2, 3, and 7 is shown in FIG. 12, and the CV measurement result with the conductive diamond electrode of Reference Example 1 is shown in FIG.

  In addition, in CV measured in an aqueous solution containing potassium ferricyanide, the current value when the potential was swept in the negative direction was defined as a signal current including a background current, and similarly measured in an aqueous sodium sulfate solution as a background current. The maximum value of the ratio between the signal current and the background current was calculated as the signal / background current ratio (S / B ratio). The S / B calculation result in Examples 1-7 and the conductive diamond electrode of Reference Example 1 is shown in FIG.

  Table 4 shows S / B ratios calculated for the conductive diamond electrodes of Examples 1 to 7, and Table 5 shows S / B ratios calculated for the conductive diamond electrode of Reference Example 1.

As shown in FIG. 13, in the conductive diamond electrode of Reference Example 1, a current peak caused by the oxidation-reduction reaction of Fe [(CN) ₆ ] ^{3− / 4−} can be confirmed as in the case of the flat plate electrode. This is because the conductive diamond particles do not form an "array" and as a result, the conductive diamond particles are continuously present on the electrode surface and the conductive diamond electrode has no microelectrode-like properties. It is thought that.

As shown in FIG. 12, even in the conductive diamond electrode according to Example 1, although the current peak due to the oxidation-reduction reaction of Fe [(CN) ₆ ] ^{3− / 4−} can be confirmed, it is related to Example 1. The conductive diamond electrode has also been recognized as a pseudo microelectrode (such as an improved S / B ratio), and is conductive using a BDD ink having a BDDP volume of 90% or less with respect to the volume of the insulating binder. If a conductive diamond electrode is prepared, it is considered that a conductive diamond electrode having a pseudo-microelectrode-like characteristic can be obtained.

  As shown in FIG. 14, the conductive diamond electrodes of Examples 1 to 7 had a higher S / B ratio than the conductive diamond electrode of Reference Example 1. Moreover, the peak of S / B ratio can be confirmed when the BDDP volume ratio is around 40%, and preferably the background current is small and the S / B ratio is large when the volume ratio of BDDP is 20% or more and 90% or less. The result was obtained. Therefore, when the volume ratio of BDDP is 20% or more and 90% or less in the conductive diamond electrode, an electrode having high detection sensitivity required for application to a measuring device such as a sensor can be obtained. In particular, when the BDDP volume ratio is 30% or more and 55% or less, the S / B ratio is 6000 or more, and an electrode having higher detection sensitivity can be obtained.

  Here, the difference in the S / B ratio due to the difference in the BDDP volume ratio will be described with reference to FIG. As shown in FIG. 15A, when the volume ratio of BDDP is large (when it exceeds 90%), the conductive diamond particles constituting the conductive diamond electrode are in contact with each other and diffuse to the conductive diamond electrode. The redox species will diffuse linearly with respect to the conductive diamond electrode. On the other hand, as shown in FIG. 15B, when the BDDP volume ratio is small (90% or less), an insulating binder is interposed between the current collector and the conductive diamond particle group electrically connected. Thus, a structure in which a plurality of conductive diamond particle groups (microelectrodes) surrounded by an insulating binder exists is obtained. That is, a conductive diamond array in which conductive diamond particles are aggregated is formed on the electrode surface, and a so-called pseudo microelectrode is configured. As a result, the diffusion of the redox species into the individual microelectrodes (conductive diamond particle group) becomes hemispherical diffusion, and it is considered that the S / B ratio is increased due to the microelectrode array effect.

  In addition, the S / B ratio decreases as the BDDP volume ratio decreases, with the BDDP volume ratio peaking at 40% to 55%. One reason for this is considered that the exposure of the current collector affects the background current. That is, it can be considered that as the BDDP volume ratio decreases, the volume decrease during drying of the BDD ink increases, and accordingly, the exposure of the current collector increases and the background current increases.

  From the above, it is considered that when the BDDP volume ratio is 30% or more and 55% or less, a conductive diamond array can be formed and a conductive diamond electrode coated with a current collector can be obtained.

3. Comparison of signal current / background current ratio (S / B ratio) in ascorbic acid aqueous solution As an evaluation of conductive diamond electrodes, analysis of ascorbic acid, a representative substance of electrochemically active species present in vivo, went. CV measurement was performed using the conductive diamond electrode according to Examples 2 and 3 with 0.5 mmol / L ascorbic acid-0.1 mol / L phosphate buffer (pH 7.4). CV measurement was performed with a three-electrode system using a potentiostat (HZ-5000, manufactured by Hokuto Denko Corporation). The configuration of the measurement apparatus and measurement conditions are shown below.
Working electrode: conductive diamond electrode Counter electrode: platinum wire measurement solution: ascorbic acid (0.5 mmol / L) -phosphate buffer (pH 7.4) (0.1 mol / L)
Reference electrode: Silver / silver chloride (Ag / AgCl) saturated potassium chloride electrode Sweep speed: 10 mV / s
FIG. 16 shows the results of CV measurement with ascorbic acid-phosphate buffer (pH 7.4). In addition, the current value that flows when a potential of 1.2 V (vs Ag / AgCl) is applied to the conductive diamond electrode is measured as a signal current, and 1.2 V (vs Ag / AgCl) is applied to the conductive diamond electrode in an aqueous sodium sulfate solution. ) Was applied as a background current. And the ratio (S / B ratio) of this signal current and background current was calculated. FIG. 17 shows the calculated S / B ratio.

Also in the result of calculating the signal current / background current ratio (S / B ratio) in the ascorbic acid aqueous solution using the conductive diamond electrodes according to Examples 2 and 3, “2. Potassium ferricyanide (K ₃ [Fe (CN The same tendency as the relationship between the volume ratio of BDDP and the S / B ratio in “ ₆ ) Electrochemical characteristics in aqueous solution” was obtained.

  As described above, according to the conductive diamond electrode of the present invention and the method of manufacturing the conductive diamond of the present invention, it is possible to produce a pseudo microelectrode having an electrode surface with minute conductive regions exposed at a low density. Such an electrode configuration exhibits characteristics as a microelectrode array, such as a high signal current / background current ratio and high-sensitivity electrochemical measurement, and a stationary or quasi-stationary current. Furthermore, since the conductive diamond electrode of the present invention has a small current flowing through each pseudo microelectrode constituting the pseudo microelectrode array, the contribution of the charging current of the electric double layer is small, and the IR drop (uncompensated solution resistance) is low. It becomes smaller and measurement accuracy improves.

  In the conductive diamond electrode of the present invention, BDD ink to which conductive diamond particles are added so as to be 20% or more and 90% or less, more preferably 30% or more and 55% or less with respect to the volume of the insulating binder is printed. Thus, a pseudo microelectrode can be easily produced. In other words, by using BDD ink in which the content ratio of an insulating binder that does not contribute to electrical conduction and electrode reaction is increased, a pseudo microelectrode can be easily produced, and the electrochemical response of a conventional conductive diamond electrode is the same. A conductive diamond electrode exhibiting a moderate response can be obtained.

  If the content ratio of the insulating binder is increased (the content ratio of the conductive diamond particles is reduced), the value of the current flowing through the electrode becomes small, so that the response of the electrochemical reaction becomes worse from the viewpoint of the current value. However, when comparing the S / B ratio, which is an index combining the two data of the signal current and the background current, the conductive diamond electrode of the present invention has higher sensitivity than the conventional conductive diamond electrode. Yes. That is, it can be seen that the conductive diamond electrode of the present invention has a high S / B ratio and is useful for a sensor for detecting a low-concentration sample.

  In addition, the conductive diamond electrode can be produced by printing ink containing conductive diamond particles and an insulating binder, thereby reducing the manufacturing cost and easily producing the conductive diamond electrode. Mass production of diamond electrodes becomes possible. Moreover, the production cost of the conductive diamond electrode can be reduced by reducing the amount of conductive diamond particles in the BDD ink when producing the conductive diamond electrode. As a result, the conductive diamond electrode can be supplied in a large amount at a low cost, so that the conductive diamond electrode of the present invention can be used as an electrode for conducting screening experiments for conditions in the development of a modified electrode. Further, when the conductive diamond electrode of the present invention is used as a disposable electrode, it is possible to avoid contamination and infection when used for biological component analysis.

  As shown in FIG. 18, the conductive diamond electrode has a very wide potential window in an aqueous solution as compared with other metal electrodes and carbon electrode materials. The width of the potential window depends on the magnitude of hydrogen and oxygen overvoltage in the aqueous solution. Since the conductive diamond electrode has an extremely wide potential window, electrochemical detection and electrolytic synthesis of a substance having an oxidation potential / reduction potential in a potential region that cannot be used with conventional electrode materials is possible.

The conductive diamond electrode of the present invention has a very small residual current density. The residual current density depends on the current density that flows to move as many carriers as necessary to form the electric double layer to the electrode surface, that is, the capacitance of the electrode surface. The conductive diamond electrode has a capacitance of several μFcm ⁻² on the electrode surface, which is two orders of magnitude smaller than that of glassy carbon (GC). Therefore, the residual current density of the conductive diamond electrode is on the order of 100 nAcm ⁻² , compared to platinum (in the order of several μAcm ⁻² ), gold (in the order of μAcm ⁻² ), and GC (in the order of 100 μAcm ⁻² ). Remarkably small. Therefore, the S / B ratio with respect to the Faraday current due to the electrochemical reaction is increased, and a smaller current can be detected. That is, even if the amount of redox species in the solution is extremely small, effective detection is possible.

  Furthermore, the conductive diamond electrode of the present invention is excellent in physical and chemical stability and durability. Diamond is physically very stable because it is made of only the strongest covalent bond among atoms. The fact that it is made of a covalent bond greatly affects the chemical stability. Therefore, the conductive diamond electrode does not need to be etched with chemicals or abrasive paper before measurement like a metal electrode or a GC electrode, and is used as an electrode for a sensor or electrolysis as an electrode that is easy to use. be able to.

  In addition, the conductive diamond electrode of the present invention has a fast electron transfer relative to the redox system and is selective in electrode reaction. Therefore, when the conductive diamond electrode of the present invention is used as a detection electrode of a trace element sensor, trace elements can be measured with high sensitivity and speed.

  As described above, the conductive diamond electrode and the method for manufacturing the conductive diamond electrode of the present invention have been described in detail only for the specific examples described. However, the conductive diamond electrode of the present invention and the method for manufacturing the conductive diamond electrode are as follows. It will be apparent to those skilled in the art that various modifications and corrections are possible within the scope of the technical idea of the present invention. Such modifications and corrections are not limited to the conductive diamond electrode of the present invention and the conductivity of the present invention. It goes without saying that it belongs to a method of manufacturing a diamond electrode.

  For example, the conductive diamond particles used in the conductive diamond electrode of the present invention may be diamond particles having conductivity, and is not limited to forming a boron-doped diamond layer on the diamond particles. That is, the substance doped into diamond is not limited to boron, but may be doped with a substance that can impart conductivity to diamond, such as nitrogen or phosphorus.

  Further, the configuration of the conductive diamond particles is not limited to forming a conductive diamond layer on the diamond particles (base material), and as a base material, silicon (Si), molybdenum (Mo) particles, etc. A known base material capable of forming a conductive diamond layer may be used. Alternatively, a conductive diamond crystal may be used as the conductive diamond particles without using a base material.

  Also, the method for producing conductive diamond particles is not limited to MPCVD, and other known CVD methods such as high-temperature and high-pressure methods, hot filament CVD, and PVD methods can be used for the conductive diamond electrode of the present invention. It can be applied to the manufacturing method.

  Further, the printing method of the conductive diamond electrode is preferably screen printing capable of easily controlling the film thickness and patterning, but the powder spray coating method, spray coating method, spin coating method, gravure printing method, offset printing method, A normal printing method such as an inkjet printing method can be used. The film thickness of the BDD ink formed by printing is not particularly limited, but it was confirmed that it acts as a conductive diamond electrode with a film thickness of several to several hundred μm, more preferably 10 to 50 μm.

  Moreover, the solvent used for BDD ink can melt | dissolve an insulating binder, and can use the known solvent which has a high boiling point. That is, as the solvent, a solvent having good compatibility with the binder resin is used, and the solvent may be a solvent composed of one kind of solvent or a solvent in which plural kinds of solvents are mixed. As a specific example, when a polyester resin is used as the binder resin, ethyl carbitol acetate (boiling point 217 ° C.) and butyl cellosolve acetate (boiling point 188 ° C.) having good compatibility with the polyester resin are 75/25 (mass ratio). A blend of a mixed solvent and a high boiling point solvent such as methyl ether, ethyl ether, propyl ether, polypropylene glycol monomethyl ether having a boiling point of 250 ° C. or higher, and trimellitic acid tri (2-ethylhexyl) can be used. .

  In the description of the embodiment, a polyimide substrate having high mechanical strength and excellent heat resistance and chemical resistance is used as a substrate for producing a conductive diamond electrode. A known substrate may be appropriately used depending on conditions such as corresponding mechanical strength and heat resistance (heat resistance of about a temperature (for example, 120 ° C.) necessary for ink drying). For example, a known substrate such as a paper phenol substrate, a paper epoxy substrate, a glass composite substrate, a glass epoxy substrate, a glass polyimide substrate, a fluorine substrate, a glass PPO substrate, a metal substrate, or a ceramic substrate may be used.

  Further, in the description of the embodiment, the hydrogen termination treatment is performed on the conductive diamond particles, but a necessary surface treatment may be performed according to the measurement target. For example, oxygen termination treatment, halogenation treatment, ferrocene modification treatment, sulfo group modification treatment, quaternary ammonia group termination treatment, treatment by chemical modification such as carboxylic acid termination treatment (other organic functional group modification treatment), Furthermore, thermal treatment may be performed. Furthermore, in order to impart electrochemical characteristics to the conductive diamond particles, the conductive diamond particles may be mixed (or added / bonded) with one or more types of redox catalysts or one or more types of mediators. . Examples of the redox catalyst include chemical substances such as enzymes, antibodies, and metals.

  Since the conductive diamond electrode of the present invention has high chemical stability and high detection sensitivity, it can be used as a detection electrode for various sensors. For example, by arranging glucose oxidoreductase on conductive diamond particles, it can be used as a detection electrode of a blood glucose monitoring device. In addition, the conductive diamond electrode of the present invention has a high S / B ratio and can detect a very small amount of a substance. It can be used as a detection electrode of a sensor that detects a substance that has been detected by electrochemical measurement.

  In addition, since the conductive diamond electrode of the present invention can be produced easily and in large quantities, when used as a disposable electrode, dopamine in blood or urine, protein (cancer marker), oxalic acid, glucose, insulin, The detection of histamine and the like can be performed rapidly with high sensitivity by electrochemical measurement, and the risk of contamination and infection can be avoided.

  In the conductive diamond electrode of the present invention, the current collector for printing the BDD ink may be a known current collector material, and the current collector and the lead may be integrally formed.

  In addition, a detection electrode unit is manufactured by printing the conductive diamond electrode (working electrode) of the present invention together with a counter electrode and a reference electrode on the same substrate, or the conductive diamond electrode of the present invention is used as a working electrode. Thus, a plurality of working electrodes can be formed on the same substrate, and the effects of the present invention can be obtained.

DESCRIPTION OF SYMBOLS 1 ... Conductive diamond electrode 2 ... Polyimide substrate 3 ... Silver paste 3a ... Connection part 4 ... Carbon paste (current collector)
DESCRIPTION OF SYMBOLS 5 ... Insulating resin 6 ... BDD ink 6a ... Conductive diamond particle 6b ... Conductive diamond particle group 7 ... MPCVD apparatus 8 ... Containment container

Claims (9)

A current collector,
Conductive diamond particles disposed on the current collector and electrically connected to the current collector;
A conductive diamond electrode having
An electrically conductive diamond electrode, wherein an insulating binder is provided between the electrically conductive diamond particles, and an electrically conductive diamond array is formed on the current collector. Conductive diamond particles;
An insulating binder;
A conductive diamond electrode formed by depositing a conductive diamond ink containing
The volume of the conductive diamond particles with respect to the volume of the insulating binder is 20% or more and 90% or less. The conductive diamond electrode according to claim 2, wherein the conductive diamond ink is printed on a current collector. The conductive diamond electrode according to any one of claims 1 to 3, wherein the conductive diamond particles are formed by forming a conductive diamond layer on a substrate surface. 4. The conductive diamond electrode according to claim 1, wherein the conductive diamond particles are conductive diamond crystals. 5. The conductive diamond electrode according to any one of claims 1 to 5, wherein the surface of the conductive diamond particles is subjected to a hydrogen termination treatment or a chemical modification treatment. 7. The conductive diamond electrode according to claim 1, wherein a particle diameter of the conductive diamond particles is 5 nm to 100 μm. A method for producing a conductive diamond electrode using conductive diamond particles to produce a conductive diamond electrode,
The conductive diamond particles are mixed with a solvent in which the insulating binder is dissolved so that the volume of the conductive diamond particles with respect to the volume of the insulating binder is 20% to 90%. Obtaining a conductive diamond ink containing:
Depositing the conductive diamond ink on a current collector to obtain a conductive diamond electrode;
A method for producing a conductive diamond electrode, comprising: The method for producing a conductive diamond electrode according to claim 8, wherein the conductive diamond particles are formed by forming a conductive diamond layer on a surface of the diamond particles.

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