JP5271345B2 - Conductive diamond electrode, sulfuric acid electrolysis method and sulfuric acid electrolysis apparatus using the same - Google Patents

Abstract

The present invention provides an electrically conductive diamond electrode comprising an electrically conductive substrate and an electrically conductive diamond layer coated on the surface of the electrically conductive substrate, featuring that: 1) the thickness of the electrically conductive diamond layer is 1ˆ¼25µm, 2) the potential window fulfills Equation (1) and 3) the ratio (A/B) of the diamond component A and the non-diamond component B by the Raman spectroscopic analysis fulfills Equation (2). 2.1 �¢ V ‰¦ potential window ‰¦ 3.5 �¢ V 1.5 < A / B ‰¦ 6.5 A: Intensity at the wave number 1300cm -1 by the Raman spectroscopic analysis B: Intensity at the wave number 1500cm -1 by the Raman spectroscopic analysis. The present invention intends to provide an electrically conductive diamond electrode with a high durability as electrode, which achieves a high current efficiency of oxidizing agent at a low cell voltage by controlling the thickness of the electrically conductive diamond layer and crystallinity of the electrically conductive diamond, a sulfuric acid electrolysis method and an electrolysis apparatus of sulfuric acid applying the electrically conductive diamond electrode.

Description

  The present invention relates to a sulfuric acid electrolysis method and a sulfuric acid electrolysis apparatus in which sulfuric acid is directly electrolyzed using a conductive diamond electrode and a conductive diamond electrode to stably generate an oxidizing substance.

  For various manufacturing and inspection processes such as pretreatment agents and etching agents for metal electroplating, oxidants in chemical mechanical polishing treatment in semiconductor device manufacturing, organic oxidizers in wet analysis, silicon wafer cleaning agents, etc. As a drug to be used, persulfuric acid or persulfate is used. These persulfuric acid and persulfate are called “oxidizing substances”, and this “oxidizing substance” is known to be produced by electrolysis of sulfuric acid, and has already been electrolytically produced on an industrial scale.

  In the present invention, the “oxidizing substance” refers to persulfuric acid, hydrogen peroxide, which is a general term for peroxodisulfuric acid and peroxomonosulfuric acid. When using "oxidizing substances", which are electrolytic products, for cleaning or surface treatment of parts, in many cases, the higher the total concentration, the more effective the chemical solution. Is required. In addition, although the electrolysis method is used in these manufactures, reducing the power consumption calculated from the cell voltage, electrolysis current, and current efficiency and maintaining stable and high current efficiency over time In order to reduce the energy required for this, it is effective in improving productivity, and an electrode manufacturing method for realizing it is required. In addition, the high durability of the electrode used is effective because the electrode life can be extended and a clean electrolyte solution free from contamination from the electrode can be produced.

  Patent Document 1 describes a sulfuric acid electrolysis method for producing persulfuric acid by electrolyzing concentrated sulfuric acid using a conductive diamond anode, and a cleaning method for washing a silicon wafer workpiece using the produced persulfuric acid. This conductive diamond electrode is superior in efficiency of electrolytic oxidation of sulfuric acid to persulfuric acid because it has a higher overvoltage for oxygen generation than a platinum electrode that has been widely used as an electrode for generating persulfate. In addition, it has excellent chemical stability and long electrode life.

That is, the conductive diamond electrode has higher persulfuric acid generation efficiency than other electrode catalysts (Pt, PbO _2, etc.), and can produce a clean electrolyte solution that is highly durable and free from contamination from the electrode. In particular, it is being developed for cleaning liquid manufacturing applications such as semiconductor wafers.

  However, a sulfuric acid electrolysis method for producing persulfuric acid by electrolyzing concentrated sulfuric acid using the conductive diamond anode described in Patent Document 1 generates a cleaning solution containing persulfuric acid by electrolyzing sulfuric acid, and the cleaning solution is provided with a resist. This is a method in which cleaning is performed by supplying an object to be cleaned such as a silicon wafer, and the used cleaning liquid with a reduced persulfuric acid concentration is recovered and electrolyzed again to increase the persulfuric acid concentration and repeatedly use the same cleaning liquid for cleaning. There is no disclosure regarding the crystallinity of the conductive diamond electrode, the relationship between the Raman spectral characteristics and the potential window, the persulfuric acid such as peroxodisulfuric acid, the current efficiency of the oxidizing substance in the cleaning liquid, and the productivity such as the cell voltage.

  Patent Document 2 discloses a method for increasing the wear resistance of diamond by prescribing the film thickness and maintaining the high strength of the diamond by defining the film thickness, and by defining the peak intensity ratio of Raman spectroscopy. Yes. Furthermore, it is described that the diamond described in Patent Document 2 has a film thickness of 50 μm or more, and the peak ratio of diamond carbon to non-diamond carbon (non-diamond carbon / diamond carbon) by Raman spectroscopy is 2.0 or less. Has been. However, this diamond is not an electrode for electrolysis, but the correlation between the crystallinity of the conductive diamond electrode and the potential window, which is one of the electrolysis characteristics, and the presence of persulfuric acid such as peroxodisulfuric acid and oxidizing substances in the cleaning liquid. There is no disclosure about the relationship between productivity such as current efficiency and cell voltage.

Patent Document 3 discloses a conductive diamond electrode having a conductive film of conductive diamond-like carbon as an electrode for electrolysis for an ozone water production apparatus. Conductive film described in Patent Document 3, in Raman spectroscopic analysis, the integrated intensity of the peaks present in 1580 cm ^-1 ± 20 cm ^-1 and the integrated intensity Int <1340> of peaks present in 1340cm ^-1 ± 20cm ^-1 Int An ozone water production apparatus capable of producing the ozone water with high current efficiency while maintaining the durability of the electrode by the ratio of <1580> satisfying the following formula is disclosed.
Int <1340> / Int <1580> = 0.5 to 1.5

  However, diamond-like carbon indicates amorphous hard carbon, and it is clearly disclosed in Patent Document 3 that the structure is different from conductive diamond having a crystal structure.

  However, in Patent Document 3, diamond-like carbon is used as an electrode, and the relationship between the crystallinity of the conductive diamond electrode and the Raman spectral characteristics / potential window, the crystallinity of the conductive diamond electrode, and peroxodisulfuric acid. There is no disclosure about the relationship between the current efficiency of the oxidizing substance in the sulfuric acid and the cleaning liquid and the productivity such as the cell voltage.

  However, in the methods described in Patent Documents 1 to 3, the correlation between the crystallinity of the conductive diamond electrode and the Raman spectroscopic characteristics / potential window is not clear. Further, in these methods, the durability of the electrode is high, and Therefore, it was not possible to produce a conductive diamond electrode with a low cell voltage and high oxidizing substance generation efficiency.

JP 2006-278838 A JP-A-2-232106 JP 2008-266718 A

  An object of the present invention is to eliminate such problems of the prior art, and to provide a conductive diamond electrode having excellent electrode durability, low cell voltage and high oxidizing substance generation efficiency, and a sulfuric acid electrolysis method and sulfuric acid using the same. It is to provide an electrolyzer.

  As a result of intensive studies to solve the above problems, the present inventors have found that the crystallinity of conductive diamond is closely related to the electrolysis performance (electrode durability, cell voltage, current efficiency of oxidizing substances). In addition, the evaluation of crystallinity was successful in achieving the above electrolytic performance by defining from the film thickness of the conductive diamond film, the width of the potential window, and the peak intensity ratio of Raman spectroscopy.

The present invention for solving the above problems, consists coated on the conductive substrate and the surface of the conductive substrate made of a conductive silicon substrate conductive diamond layer,
1) The conductive diamond layer doping agent consists only of boron,
2) The conductive diamond layer contains 1000 to 6000 ppm of boron,
3) The thickness of the conductive diamond layer is a 1 0 ~25μm,
4 ) The potential window satisfies equation (1),
5 ) The ratio (A / B) of the diamond component A to the non-diamond component B by Raman spectroscopic analysis satisfies the formula (2),
6) To provide a conductive diamond electrode characterized in that it is used for sulfuric acid electrolysis .
2.1V ≦ potential window ≦ 3.5V (1)
3.2 ≦ A / B ≦ 6.5 (2)
A = Intensity at wave number 1300 cm ⁻¹ in Raman spectroscopic analysis B = Intensity at wave number 1500 cm ⁻¹ in Raman spectroscopic analysis

Further, the second solution according to the present invention is divided into an anode chamber and a cathode chamber by a diaphragm, a conductive diamond anode is provided in the anode chamber, a cathode is provided in the cathode chamber, and in the anode chamber and the cathode chamber, In the electrolytic method of sulfuric acid in which an electrolytic solution containing sulfate ions is supplied from the outside to perform electrolysis, and an oxidizing substance is generated in the anode electrolyte in the anode chamber, the conductive diamond electrode has a specific conductivity. Another object of the present invention is to provide a sulfuric acid electrolysis method using a diamond electrode and a solution containing a sulfate ion concentration of 2 to 14 mol / l of the electrolyte solution containing the sulfate ion.

The third solving means of the present invention is to provide a sulfuric acid electrolysis method in which the acid concentration of the electrolytic solution containing sulfate ions is 4 to 28 mol / l under the electrolysis conditions.

The fourth solution according to the present invention is divided into an anode chamber and a cathode chamber by a diaphragm, a conductive diamond anode is provided in the anode chamber, a cathode is provided in the cathode chamber, and in the anode chamber and the cathode chamber, In each of the sulfuric acid electrolysis apparatuses that perform electrolysis by supplying an electrolyte solution containing sulfate ions from the outside and generate an oxidizing substance in the anode electrolyte solution in the anode chamber, the conductive diamond electrode is used, and the diaphragm It is intended to provide a sulfuric acid electrolysis apparatus using a fluororesin cation exchange membrane or a diaphragm made of a porous fluororesin membrane subjected to hydrophilic treatment.

Further, the fifth solution according to the present invention is divided into an anode chamber and a cathode chamber by a diaphragm, a conductive diamond anode is provided in the anode chamber, a cathode is provided in the cathode chamber, and in the anode chamber and the cathode chamber, In the electrolytic method of sulfuric acid in which an electrolytic solution containing sulfate ions is supplied from the outside to perform electrolysis, and an oxidizing substance is generated in the anode electrolyte in the anode chamber, the conductive diamond is used as the conductive diamond electrode. Another object of the present invention is to provide a sulfuric acid electrolysis method that uses an electrode and electrolyzes an electrolytic solution containing sulfate ions under conditions satisfying the expressions (3) and (4).
100 ≦ X ≦ 10000 (3)
25 <Y <250 (4)
X = current value / anolyte amount (A / l)
Y = current density (A / dm ² )

The sixth solving means of the present invention is to provide a sulfuric acid electrolysis method for electrolyzing a solution containing sulfate ions under a condition satisfying the expression (5) under the above electrolysis conditions.
18000 ≦ Z ≦ 10800000 (5)
Z = amount of electricity per unit volume (C / l) = current value × electrolysis time / anolyte amount (A · s / l)

  According to the conductive diamond electrode according to the present invention, and the sulfuric acid electrolysis method and the sulfuric acid electrolysis apparatus using the same, the durability of the electrode, which could not be achieved by the prior art, is high, and a high concentration oxidizing substance solution can be obtained at a low cell voltage. It can be manufactured with high current efficiency.

The whole figure which shows an example of the electrolysis cell used for the sulfuric acid electrolysis method and sulfuric acid electrolysis apparatus by this invention. The whole figure which shows an example of the sulfuric acid electrolysis method and sulfuric acid electrolysis apparatus by this invention. The whole figure which shows the other example of the sulfuric acid electrolysis method and sulfuric acid electrolysis apparatus by this invention.

  The present invention relates to the crystallinity of a conductive diamond electrode, the durability of the electrode when the conductive diamond electrode is incorporated in an electrolytic cell and electrolysis of sulfuric acid, the cell voltage, and the oxidizing substance of the oxidizing substance solution produced. It has been found that there is a close relationship between concentration and current efficiency.

Diamond is a cubic crystal in which each constituting carbon atom is bonded by SP3 hybrid orbitals, and has a wide band gap and is an insulator.
On the other hand, the conductive diamond in the present invention refers to a diamond imparted with conductivity by containing impurities having a valence different from that of carbon. From the viewpoint of increasing the conductivity, it is preferable that the impurity concentration is high. On the other hand, if the impurity concentration is too high, the crystallinity is lost, so that an electrode having soot attached thereto is obtained, and the durability is poor.

  The crystallinity in the present invention represents the regularity of crystal arrangement and the content of impurities other than carbon. Specifically, when there are many non-diamond components, graphite components, and amorphous diamonds, the conductive diamond layer When the film thickness of the conductive diamond is small, the conductive diamond has a small particle size, or the content of impurity elements other than carbon is large, the crystallinity is low.

  As a result of many experiments by the present inventors, the film thickness of the conductive diamond layer and the ratio (A / B) of the diamond component A to the non-diamond component B by Raman spectroscopic analysis are as follows. Is a factor that expresses crystallinity, and by defining them, the electrode has high durability, can be electrolyzed at a low cell voltage, has high current efficiency of the oxidizing substance, and produces a highly concentrated oxidizing substance solution. It was revealed that a conductive diamond electrode that can be used, and a sulfuric acid electrolysis method and a sulfuric acid electrolysis device using the same can be obtained.

In the present invention, the conductive diamond layer has a film thickness of 1 to 25 μm, the potential window satisfies the formula (1), and the ratio of the diamond component A to the non-diamond component B by Raman spectroscopy (A / B) Is a conductive diamond electrode characterized by satisfying the expression (2).
2.1V ≦ potential window ≦ 3.5V (1)
1.5 <A / B ≦ 6.5 (2)
A = Intensity at wave number 1300 cm ⁻¹ in Raman spectroscopic analysis B = Intensity at wave number 1500 cm ⁻¹ in Raman spectroscopic analysis

First, the reason for limiting the film thickness of the conductive diamond electrode will be described first.
The conductive diamond layer preferably has a thickness of 1 to 25 μm, more preferably 1 to 15 μm. The thinner the conductive diamond layer is, the shorter the manufacturing time of the conductive diamond layer is, and the lower the crystallinity of the conductive diamond is. Low crystallinity is preferable because the current efficiency of the oxidizing substance is high and the cell voltage is low. However, if the film thickness is too thin and thinner than 1 μm, the durability of the electrode becomes poor, for example, the substrate is exposed due to corrosion of the substrate or the film is peeled off during electrolysis. Further, if the film thickness becomes too thick and becomes thicker than 25 μm, the crystallinity becomes high, the base material is not exposed, and the electrolyte does not penetrate into the base material. Therefore, the thickness of the conductive diamond electrode according to the present invention is preferably 1 to 25 μm.

Next, the reason for limiting the potential window will be described.
In the present invention, the potential window indicates a potential region where neither hydrogen nor oxygen is generated in the water electrolysis reaction.
When the potential window is wide, the crystallinity of the conductive diamond film is increased and the durability of the electrode is improved. However, if the potential window is wider than 3.5 V, the current efficiency of the oxidizing substance is low and the cell voltage is high. On the other hand, if the potential window is narrower than 2.1V, the durability of the electrode is lowered.

  Moreover, when the peak intensity ratio A / B of Raman spectroscopy is large, the crystallinity of the conductive diamond film is increased, and the durability of the electrode is improved. However, when the peak intensity ratio A / B of Raman spectroscopy is larger than 6.5, the current efficiency of the oxidizing substance is low and the cell voltage is high. On the other hand, when the peak intensity ratio A / B of Raman spectroscopy is small, the crystallinity of the conductive diamond film is low, the efficiency of the oxidizing substance is high, and the cell voltage is low. However, when the peak intensity ratio A / B of Raman spectroscopy is 1.5 or less, the durability of the electrode is low.

  The conductive diamond layer preferably contains 1000 to 6000 ppm of boron, more preferably 3000 to 5000 ppm of boron. The higher the boron concentration, the lower the crystallinity, the lower the cell voltage, and the higher the current efficiency of the oxidizing substance, which is preferable. However, if the boron concentration becomes too high and exceeds 6000 ppm, it becomes an electrode with soot attached, and the durability of the electrode is poor. Therefore, the conductive diamond electrode according to the present invention preferably contains 1000 to 6000 ppm of boron. .

  The conductive substrate is not particularly limited, and tantalum, tungsten, titanium, niobium, or the like can be used. However, when a silicon substrate is used, an electrode with better adhesion can be manufactured. The shape of the conductive substrate is not particularly limited, and a plate shape, a rod shape, a pipe shape, a spherical shape, or the like can be used. The conductive substrate may contain impurities such as boron and carbon.

  Hereinafter, an example of the implementation of the sulfuric acid electrolysis method and the sulfuric acid electrolysis apparatus according to the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of an electrolytic cell used in a sulfuric acid electrolysis method and a sulfuric acid electrolysis apparatus according to the present invention.
This electrolytic cell contains a conductive diamond anode 10 by a diaphragm 9, an anode chamber 3 filled with the electrolyte containing sulfate ions and a conductive diamond cathode 12, and has the same concentration as the anode chamber 3. It is partitioned into a cathode chamber 4 filled with sulfuric acid. An anolyte supply port 7 is connected to the anolyte chamber 3, and sulfuric acid as an anolyte is supplied to the anolyte chamber 3 through the anolyte supply port 7. The catholyte supply port 8 is connected to the cathode chamber 4, and the catholyte is supplied to the cathode chamber 4 through the catholyte supply port 8.
The oxidizing substance solution generated in the anode chamber 3 is discharged from the anolyte discharge port 1. The hydrogen and sulfuric acid solution generated in the cathode chamber 4 is discharged from the catholyte discharge port 2.
Reference numeral 5 denotes an anode feeding terminal, 6 denotes a cathode feeding terminal, 11 denotes a conductive substrate of the conductive diamond anode 10, 13 denotes a conductive substrate of the conductive diamond cathode 12, and 14 denotes a sealing material for the electrolytic cell. , 15 is a cooling jacket, 16 is a cooling water discharge port, and 17 is a cooling water supply port.

The conductive diamond anode 10 and the conductive diamond cathode 12 in the present invention are composed of a conductive diamond layer coated on the surfaces of the conductive substrates 11 and 13.
The method for coating the conductive diamond layer is not particularly limited, and any method can be used. As a typical method, a hot filament CVD method, a microwave plasma CVD method, a DC arc jet plasma CVD method, or the like can be selected.
As the cathode, platinum or another cathode may be used instead of the conductive diamond cathode 12.

The electrolytic solution containing sulfate ions (HSO ₄ ⁻ or SO ₄ ²⁻ ) in the present invention preferably contains ² to 14 mol / l, preferably 3 to 9 mol / l of sulfate ions.
If the sulfate ion concentration (HSO ₄ ⁻ or SO ₄ ²⁻ ) is less than 2 mol / l, the current efficiency of the oxidizing substance is low because the amount of reactants is small. On the other hand, if the sulfate ion concentration is higher than 14 mol / l, the viscosity of the electrolytic solution is increased and gas escape is poor, the bubble rate is increased, the electrical conductivity of the electrolytic solution is decreased, and the cell voltage is increased.
For this reason, in this invention, the sulfate ion concentration of the electrolyte solution containing the said sulfate ion shall be 2-14 mol / l.

The acid (H ⁺ ) concentration of the electrolyte solution containing sulfate ions in the present invention is in the range of 4 to 28 mol / l, preferably 6 to 18 mol / l.
If the acid (H ⁺ ) concentration is lower than 4 mol / l, the conductivity of the electrolyte is low and the cell voltage is high. On the other hand, when the acid concentration (H ⁺ ) is higher than 28 mol / l, the current efficiency of the oxidizing substance is low.
For this reason, in this invention, the acid concentration of the electrolyte solution containing the said sulfate ion shall be 4-28 mol / l.

In the sulfuric acid electrolysis method according to the present invention, the conductive diamond electrode is used, and the electrolyte containing the sulfate ions is X = current value / anolyte amount (A / l) is 100 ≦ X ≦ 10000, preferably 300 ≦ X ≦ 6000, and electrolysis is preferably performed under the condition that Y = current density (A / dm ² ) satisfies 25 <Y <250, preferably 50 ≦ Y ≦ 200.
It has been found that when X is less than 100, the current efficiency of the oxidizing substance is low, whereas when X is greater than 10,000, the gas generated in the cell is filled and the cell voltage becomes high. It is a thing. In the sulfuric acid electrolysis method according to the present invention, when the current density Y (A / dm ² ) is 25 or less, the current efficiency of the oxidizing substance is low. On the other hand, when Y is 250 or more, the heat generation is remarkable. Therefore, it becomes difficult to control the temperature of the electrolytic solution. In addition, gas escape is poor, the bubble rate increases, the conductivity of the electrolyte decreases, and the cell voltage becomes high.
For this reason, in this invention, it is set as the range of 100 <= X <= 10000 and 25 <Y <250.

Further, in the sulfuric acid electrolysis method according to the present invention, the conductive diamond electrode is used, and the electrolytic solution containing the sulfate ion is changed to Z = amount of electricity per unit volume (C / l) = current value × electrolysis time / anolyte. It is preferable to perform electrolysis under the condition that the amount (A · s / l) satisfies 18000 ≦ Z ≦ 1080000, preferably 100,000 ≦ Z ≦ 800000.
When Z is less than 18000, the concentration of the oxidant substance is lowered. On the other hand, when Z is greater than 10800000, the current efficiency of the oxidant substance is lowered. Therefore, the range is set to 18000 ≦ Z ≦ 1080000.

  The diaphragm 9 in the present invention defines the conductivity by partitioning the anode chamber 3 and the cathode chamber 4 while the ion exchange action or the electrolyte moves between the anode chamber 3 and the cathode chamber 4 through the holes in the diaphragm. To be expressed. Although the constituent material is not particularly limited, it is preferable to use a fluororesin cation exchange membrane or a membrane made of a porous fluororesin membrane subjected to hydrophilic treatment from the viewpoint of durability. In the present invention, if there is no diaphragm, the oxidizing substance is electrolytically reduced at the cathode, and the concentration of the oxidizing substance is lowered. Therefore, the diaphragm 9 is preferably provided.

  The constituent material of the wetted part with the sulfuric acid electrolyte such as an electrolytic cell, piping, pump, gas-liquid separation tank, etc. in the present invention is not particularly limited, but fluororesin such as PTFE and PFA having resistance to sulfuric acid, glass, Quartz is preferred.

  The electrolytic solution containing sulfate ions in the present invention may contain impurities in addition to sulfate ions. However, an electrolytic solution composed of sulfuric acid or a sulfate such as ammonium sulfate and water has a current efficiency of persulfuric acid production. Since it becomes high, it is preferable. In addition, it is preferable that the organic substance not be contained because it can react with an oxidizing substance generated by electrolysis and reduce the oxidizing substance concentration of the electrolytic solution. Further, when used as a cleaning agent or the like in the manufacture of semiconductor devices, it is preferable that the metal does not contain metal ions because it adversely affects the device as an impurity.

  Furthermore, in the present invention, the electrolysis temperature of electrolysis is preferably 0 to 50 ° C. The lower the temperature, the higher the current efficiency of the oxidizing substance. On the other hand, if the pressure is too low, the viscosity of the electrolytic solution increases, gas outflow is poor, the bubble rate increases, the conductivity of the electrolytic solution decreases, and the cell voltage increases, so the electrolysis temperature can be set to 0 to 50 ° C. preferable.

  In the present invention, the presence or absence of the electrolyte solution is not limited. However, the circulation is preferable because the electrolyte solution can be cooled efficiently. The amount of anolyte when the electrolyte is circulated means the sum of the amount of electrolyte on the anode side in the circulation system, such as the electrolytic cell, piping, gas-liquid separation tank, and pump. In the present invention, the electrolyte solution is not circulated and the electrolyte solution is circulated only once through the electrolytic cell, including the so-called one-pass case. The amount of anolyte in the one-pass case is present in the electrolytic cell. It means the amount of electrolyte solution on the anode side.

  FIG. 2-1 shows an example of a sulfuric acid electrolysis method and a sulfuric acid electrolysis apparatus according to the present invention in which sulfuric acid is electrolyzed while circulating an anolyte and a catholyte, respectively. The electrolytic solution containing sulfate ions is supplied from the anolyte supply line 18 to the anode chamber 3 of the electrolysis cell 21 using the anolyte supply pump 19 and the flow meter 20, and is electrolyzed in the anode chamber 3. The liquid is circulated to the anode chamber 3 by the anolyte circulation line 25 using the liquid circulation / discharge pump 23. At that time, the generated gas is separated from the anode-side air separator 26 and discharged from the generated gas discharge port 27. When the electrolysis is completed, the manufactured oxidizing substance solution is discharged from the oxidizing substance solution discharge line 24 using the flow meter 22 and the anolyte circulation / discharge pump 23. On the other hand, an electrolytic solution containing sulfate ions is supplied to the cathode from the catholyte supply line 28 to the cathode chamber 4 of the electrolytic cell 21 using the catholyte supply pump 29 and the flow meter 30, and is electrolyzed in the cathode chamber 4. Then, it is circulated to the cathode chamber 4 by a catholyte circulation line 34 using a flow meter 31 and a catholyte circulation / discharge pump 32. At that time, the generated gas is separated from the cathode-side air separator 35 and discharged from the generated gas discharge port 36. When the electrolysis is completed, the catholyte is discharged from the catholyte discharge line 33 using the flow meter 31 and the catholyte circulation / discharge pump 32. The electrolysis cell 21 is cooled by the cooling jacket 15 and the cooling water circulation line 37. In addition, the temperature of electrolyte solution measured the electrolyte solution temperature of the anolyte discharge port 1 of FIG.

  FIG. 2-2 shows another example of the sulfuric acid electrolysis method and the sulfuric acid electrolysis apparatus according to the present invention, in which only the catholyte is circulated and the anolyte is not circulated, and the oxidizing substance solution is manufactured in one pass. is there. FIG. 2-2 is the same process as FIG. 2-1, except that the oxidant solution is not circulated and the oxidizing substance solution is manufactured in one pass, and the same reference numerals are used. The description of the process 2-2 is omitted.

Next, the present invention will be specifically described with reference to examples and comparative examples. However, the present invention is not limited to these examples.
In addition, the Raman spectral characteristic measurement of the produced electrode in the present invention, the film thickness measurement of the conductive diamond electrode, the boron concentration measurement, the electrode durability test, the measurement of the potential window, and the production of the electrolytic solution containing sulfate ions used for electrolysis The concentration of the oxidizing substance in the manufactured oxidizing substance solution was measured by the following method.

<Raman spectral characteristics measurement>
The surface Raman measurement of the electrode was performed in order to measure whether the conductive diamond was produced and to measure the A / B intensity ratio.
・ Measuring device: Raman spectrophotometer manufactured by Thermo Fisher Scientific ・ Model: AlMEGA XR
・ Laser light: 532 nm
-Exposure time: 2.00 seconds-Number of exposures: 20
-Number of background exposures: 20
・ Grating: 672lines / mm
Measurement width: 700 to 2000 cm ^-1
・ Spectroscope aperture: 25μm slit ・ Low resolution measurement in the macro test room ・ Measurement point: Divide equally from both edges indicating the longest distance of the electrode, and measure the center point to confirm the average value did.
-Spectral correction: The intensity at 2000 cm ^-1 was subtracted from the intensity in the entire range.
Diamond components: a peak intensity in the range of wave number 1300 ± 50 cm ^-1, strength and non-diamond component of the wave number 1300 cm ^-1 If the peak is not confirmed: peak intensity in the range of wave number 1500 ± 50 cm ^-1, if the peak is not confirmed manufactured illustrates the Raman-active in the range of intensity wavenumber 1300 ± 50 cm ^-1 in wave number 1500 cm ^-1, i.e., a case where a peak or broad waveform in the wave number range of 1300 ± 50 cm ^-1 is conductive diamond electrode It was judged that it was made.

<Measurement of conductive diamond film thickness>
The conductive diamond electrode is equally divided into five equal parts from both edges indicating the longest distance of the electrode, and the whole substrate is cut. Using the scanning electron microscope (manufacturer: JEOL, trade name: JSM6490), the obtained cross section was observed and photographed at least one cross section of the entire cut sample at an acceleration voltage of 10 kV and 8000 times, and the film thickness was determined from the average value. Asked.

<Boron concentration measurement>
Using the secondary ion mass spectrometry (manufacturer: ULVAC-PHI, trade name: PHI ADEPT1010), the prepared electrode surface was primary ion O ₂ ⁺ , primary ion energy 3 keV, detection region 100 μmφ, and secondary ion polarity positive. It was measured. Concentration conversion was performed by measuring a standard concentration sample of B in the SiC composition together, obtaining a relative sensitivity coefficient, and substituting the coefficient into the sample.
<Durability test of conductive diamond electrode>
Using the electrodes prepared for both the anode and cathode, an oxidizing substance solution was manufactured under the following conditions using the sulfuric acid electrolysis apparatus shown in FIG. 2A incorporating the electrolytic cell 21 with a diaphragm shown in FIG. .
Current density: 100 A / dm ²
Electrolysis time: 12h
Anolyte volume: 200ml
Electrolyte temperature: 35 ° C
Cooling water temperature: 15 ° C
Anolyte flow rate: 1 l / min
Catholyte flow rate: 1 l / min
Anode electrolyte: 4.2 mol / l sulfuric acid (diluted sulfuric acid manufactured by Kanto Chemical Co., Ltd. for electronics industry with pure water for electronics industry)
Cathodic electrolyte: 4.2 mol / l sulfuric acid (diluted sulfuric acid manufactured by Kanto Chemical Co., Ltd. for electronics industry with pure water for electronics industry)
Diaphragm: (Poreflon (registered trademark) manufactured by Sumitomo Electric Fine Polymer Co., Ltd.)
Visual observation of the electrode after completion of electrolysis. Durability was confirmed when the conductive diamond film was not peeled. Durability was confirmed when peeling was very slight. Durability was confirmed by more than half of the area. Durability x.

<Measurement of potential window>
For the measurement of the potential window, the redox decomposition voltage was measured by a cyclic voltammogram. That is, a potential of 50 mV / s using 4.2 mol / l sulfuric acid as an electrolyte, an electrode having a conductive diamond layer formed on a base as a working electrode, a platinum wire as a counter electrode, and a mercuric sulfate reference electrode as a reference electrode. The potential when a current of ± 50 mA / dm ² was swept was measured, and the potential window was determined from the reduction and oxidative decomposition potential values.

Ｃ(g)：1l電解液を作製するのに必要な98%硫酸の質量 <Sulfuric acid mass required for electrolyte preparation>
The mass of 98% sulfuric acid necessary to produce 1 liter of electrolyte is calculated based on the formula (6), 98% sulfuric acid (manufactured by Kanto Chemical Co., Inc.) is collected in a 1 liter volumetric flask, and ultrapure water is added. In addition, a total of 1 liter of electrolyte was obtained.

C (g): Mass of 98% sulfuric acid necessary to prepare a 1 liter electrolyte

<Acid concentration>
Based on the concentration (mol / l) of the electrolyte solution containing sulfate ions to be prepared, which was adopted in Equation (6), the acid concentration was calculated from Equation (7) below.
Acid concentration = concentration of electrolyte containing sulfate ion to be prepared × 2 (7)

<Oxidizing substance concentration measurement>
0.4 ml of the manufactured oxidizing substance solution is weighed into a 100 ml Erlenmeyer flask, and ultrapure water is added to make a total of 3 ml of sample solution, and potassium iodide (manufactured by Wako Pure Chemical Industries, Ltd.) is adjusted with ultrapure water. 5 ml of a 200 g / l solution was added and colored with free iodine. The Erlenmeyer flask was filled with nitrogen and sealed with silicon rubber for 30 minutes, and then 0.02 mol / l sodium thiosulfate solution (sum) Koganei Pharmaceutical Co., Ltd.) was added dropwise until the sample solution became colorless. The number of measurement was 3 times for each sample, and the concentration of the oxidizing substance was calculated by the following formula (8) using the average value.

<Current efficiency of oxidizing substances>
The current efficiency was calculated by the following formula (9) using the value obtained by measuring the oxidizing substance concentration of the manufactured oxidizing substance solution in the concentration measurement of the oxidizing substance.

<Formation of conductive diamond layer: by hot filament CVD>
The conductive diamond electrode in the present invention was produced by the following method. Single crystal Si was used as the conductive substrate, and the substrate surface was polished, washed, nucleated with diamond particles, and then placed in the apparatus. Using hydrogen, methane, Ar + trimethylborate as the introduction gas, the pressure in the apparatus was maintained at 60 Torr while flowing through the apparatus at a rate of 5 liters / minute, and power was applied to the filament to raise the temperature to 2300 ° C. . At this time, the substrate temperature was 800 ° C.
Trimethyl borate was introduced into the apparatus by bubbling Ar into a container filled with liquid trimethyl borate.
The film quality was changed by changing the methane flow rate and the trimethyl borate flow rate.
The film thickness was changed by changing the film formation time.

<Example 1>
The sulfuric acid electrolysis apparatus shown in FIG. 2A incorporating the electrolytic cell 21 with a diaphragm using the conductive diamond electrode having an electrolytic area of 1.000 dm ² shown in FIG. While each was circulated, sulfuric acid was electrolyzed, and an oxidizing substance solution was produced under the following conditions.
Table 1 shows the characteristics of the fabricated electrodes.
Electrolytic sulfuric acid was produced under the conditions described in Table 1 and the following conditions using an electrode prepared with both an anode and a cathode and using an electrolytic cell with a diaphragm. The electrolyte solution was 403 g of 98% sulfuric acid (manufactured by Kanto Chemical Co., Ltd.) based on the formula (6) in a 1 l volumetric flask, diluted with ultrapure water to a total of 1 l, and sulfate ions of 4.2 mol / 1 was used, 300 ml of which was used as the anolyte and the remaining 300 ml was used as the catholyte. The acid concentration calculated from the formula (7) was 18.4 mol / l.
Cell current: 100A
Current density: 100 A / dm ²
Electrolysis time: 20 minutes Anolyte volume: 300 ml
Electrolyte temperature: 28 ° C
Cooling water temperature: 15 ° C
Anolyte flow rate: 1 l / min
Catholyte flow rate: 1 l / min
Anode electrolyte solution: 4.2 mol / l sulfuric acid Cathode electrolyte solution: 4.2 mol / l sulfuric acid Membrane: (Poreflon (registered trademark) manufactured by Sumitomo Electric Fine Polymer Co., Ltd.)
The results of the obtained oxidizing substance solution are shown in Table 6 and the following.
When the produced oxidizing substance solution was used for titration according to the above-mentioned oxidizing substance concentration measuring method, 44.00 ml of 0.02 mol / l sodium thiosulfate solution was dropped, and the solution became colorless. Further, when the measurement was repeated twice by the same means, the measurement results were 44.00 and 44.00 ml, respectively. Using these average values of 44.00 ml, the oxidizing substance concentration was calculated according to the formula (8) and found to be 1.10 mol / l. Further, the current efficiency was calculated by the equation (9) using the oxidizing substance concentration, and it was 53%.

<Examples 3, 4, 6, 8, 9 and Reference Examples 2, 5, 7, 10>
By changing the methane flow rate, the trimethyl borate flow rate, and the film formation time as Examples 3, 4, 6, 8, 9 and Reference Examples 2, 5, 7, and 10, conductive diamond film thickness, potential window, A / B. An oxidizing substance solution was obtained in the same manner as in Example 1 except that the electrode having the boron concentration changed as shown in Tables 1 and 2 was used for the anode.
The results of the obtained oxidizing substance solution are shown in Tables 6 and 7.

<Examples 11 to 14>
An oxidizing substance solution was obtained in the same manner as in Example 1 except that the sulfate ion concentration and the acid concentration in the electrolytic solution were changed as shown in Tables 2-3.
The result of the obtained oxidizing substance solution was shown to Tables 7-8.

<Examples 15 to 16>
The amount of the anolyte in the electrolyte, the current value / the amount of the anolyte, and the electrolysis time were changed as shown in Table 3, and the conductive diamond electrode having an electrolysis area of 1.000 dm ² shown in FIG. 1 was used for both the anode and the cathode. Using the sulfuric acid electrolysis apparatus shown in FIG. 2-2, which incorporates the electrolytic cell 21 with the diaphragm, the oxidant solution was not circulated and the oxidizing substance solution was produced in a single pass in the same manner as in Example 1. An oxidizing substance solution was obtained.
The results of the obtained oxidizing substance solution are shown in Table 8.

<Examples 17 to 24>
An oxidant solution was obtained in the same manner as in Example 1 except that the amount of anolyte, current value / anolyte amount, electrolysis time, and amount of electricity per unit volume were changed as shown in Tables 3-4. .
The result of the obtained oxidizing substance solution was shown to Tables 8-9.

< Reference Example 25>
An oxidizing substance solution was obtained in the same manner as in Example 1 except that niobium was used as the base material.
The results of the obtained oxidizing substance solution are shown in Table 9.

1) As a result of Examples 1 , 3, 4, and Reference Example 2 , as the potential window is narrower, A = ratio of intensity at wave number 1300 cm ⁻¹ in Raman spectroscopic analysis and B = intensity at wave number 1500 cm ⁻¹ in Raman spectroscopic analysis It was found that the smaller the A / B, the higher the current efficiency of the oxidizing substance and the lower the cell voltage. On the other hand, in Reference Example 2, when the electrode after the durability test of the electrode was visually confirmed, peeling of the conductive diamond film was confirmed very little.
2) As a result of Reference Example 5 , as compared with the result of Example 1, it was found that the thinner the conductive diamond layer, the higher the current efficiency of the oxidizing substance and the lower the cell voltage. This is because the thinner the conductive diamond layer, the narrower the potential window, and the smaller the ratio A / B of A = intensity at wave number 1300 cm ⁻¹ in Raman spectroscopic analysis and B = intensity at wave number 1500 cm ⁻¹ in Raman spectroscopic analysis. It is believed that there is.
On the other hand, in Example 6, compared with the result of Example 1, the current efficiency of the oxidizing substance was low and the cell voltage was high.
3) As a result of Examples 8 and 9 and Reference Examples 7 and 10, as compared with the result of Example 1, the higher the boron concentration, the higher the current efficiency of the oxidizing substance, and the higher the accompanying oxidizing substance concentration. The voltage was found to be low. This is because the higher the boron concentration, the narrower the potential window, and the smaller the ratio A / B of A = intensity at wave number 1300 cm ⁻¹ in Raman spectroscopic analysis and B = intensity at wave number 1500 cm ⁻¹ in Raman spectroscopic analysis. Conceivable.
On the other hand, in Reference Example 10, when the electrode after the electrode durability test was visually confirmed, peeling of the conductive diamond film was confirmed very little.
4) As a result of Examples 11 and 12, it was found that the lower the sulfate ion concentration, the lower the current efficiency compared to the result of Example 1. This is probably because the lower the sulfate ion concentration, the less the reactant. Further, it was found that the cell voltage was higher as the acid concentration was lower than the result of Example 1. This is thought to be due to the low acid concentration and low conductivity. As a result of Examples 13 and 14, it was found that the current efficiency was lower as the acid concentration was higher than the result of Example 1. This is considered to be because the oxidizing substance is easily decomposed as the acid concentration increases. Further, it was found that the cell voltage was higher as the sulfate ion concentration was higher than the result of Example 1. This is probably because the sulfate ion concentration was high, the viscosity was high, the outgassing was poor, the bubble rate was increased, the conductivity of the electrolyte was lowered, and the cell voltage was increased.
5) As a result of Examples 15 to 18, compared with the result of Example 1, X = current value / anolyte amount (A / l) is larger, and the current efficiency of the oxidizing substance is higher. It was found that a liquid having a high concentration can be obtained. On the other hand, the larger the X = current value / anolyte amount (A / l), the higher the cell voltage. This is presumably because the cell voltage was increased by filling the cell with gas. In Examples 17 and 18, the cell voltage was good, but the current efficiency was low.
6) As a result of Examples 19 to 20, when the current density (A / dm ² ) is lower than the result of Example 1, the current efficiency of the oxidizing substance is lowered, and accordingly the oxidizing substance concentration is lowered. I understood. On the other hand, as a result of Examples 21 and 22, when the current density (A / dm ² ) is higher than the result of Example 1, the current efficiency of the oxidizing substance is increased, but the cell voltage is increased. It was. This is presumably because the generated gas filled the cell because the current density was high.
7) As a result of Example 23, it was found that when the amount of electricity per unit volume was lower than the result of Example 1, the current efficiency of the oxidizing substance was high, and the oxidizing substance concentration was lowered accordingly. On the other hand, as a result of Example 24, it was found that when the amount of electricity per unit volume is high, the current efficiency of the oxidizing substance is low and the oxidizing substance concentration is high.
8) As a result of Reference Example 25, when the substrate material is niobium as compared with the result of Example 1, the current efficiency of the oxidizing substance and the accompanying oxidizing substance concentration are good, but the electrode after the durability test of the electrode It was confirmed by visual observation of the surface that the film was slightly peeled off.

<Comparative Examples 1-4>
Example 1 except that an electrode in which the conductive diamond film thickness, potential window, and A / B were changed as shown in Table 5 by changing the methane flow rate, the trimethyl borate flow rate, and the film formation time was used as the anode. An oxidizing substance solution was obtained in the same manner as described above. The results of the obtained oxidizing substance solution are shown in Table 10.

In Comparative Example 1, although the cell voltage and the current efficiency of the oxidizing substance were good, it was confirmed that the film was largely peeled off by visual observation of the electrode surface after the electrode durability test.
In Comparative Example 2, although the deterioration of the film in the visual observation of the electrode surface after the electrode durability test was not confirmed, the cell voltage during electrolysis was high, and the current efficiency of the obtained oxidizing substance-containing solution was low. became.
In Comparative Example 3, good cell voltage and current efficiency were obtained, but it was confirmed by visual observation of the electrode surface after the electrode durability test that the film was largely peeled off.
In Comparative Example 4, although the deterioration of the film in the visual observation of the electrode surface after the electrode durability test was not confirmed, the cell voltage during electrolysis was high, and the current efficiency of the obtained oxidizing substance-containing solution was low. became.
In Comparative Example 5, the electrode deteriorated during electrolysis, and carbon powder was visually confirmed in the electrolytic solution, so electrolysis was interrupted.

  The diamond electrode according to the present invention has an effect of stably producing an oxidizing substance, particularly when used as an anode in sulfuric acid electrolysis. However, when used as a cathode in sulfuric acid electrolysis, the effect can be improved. Furthermore, the conductive diamond electrode according to the present invention can be used as an anode and a cathode for other electrolysis.

1: anolyte outlet 2: catholyte outlet 3: anode chamber 4: cathode chamber 5: anode feeding terminal 6: cathode feeding terminal 7: anolyte feeding port 8: catholyte feeding port 9: porous PTFE diaphragm 10: Conductive diamond anode 11: conductive substrate 12: conductive diamond cathode 13: conductive substrate 14: sealing material 15: cooling jacket 16: cooling water discharge port 17: cooling water supply port 18: anolyte supply line 19: anolyte Supply pump 20: flow meter 21: electrolysis cell 22: flow meter 23: anolyte circulation / discharge pump 24: oxidizing substance solution discharge line 25: anolyte circulation line 26: anode side gas-liquid separator 27: generated gas discharge port 28: Catholyte supply line 29: Catholyte supply pump 30: Flow meter 31: Flow meter 32: Catholyte circulation / discharge pump 33: Catholyte discharge line 34: Catholyte circulation line 35: Cathode side gas-liquid separator 36 Generated gas discharge port 37: cooling water circulation line

Claims (6)

A conductive substrate composed of a conductive silicon substrate and a conductive diamond layer coated on the surface of the conductive substrate,
1) The conductive diamond layer doping agent consists only of boron,
2) The conductive diamond layer contains 1000 to 6000 ppm of boron,
3) The thickness of the conductive diamond layer is a 1 0 ~25μm,
4 ) The potential window satisfies equation (1),
5 ) The ratio (A / B) of the diamond component A to the non-diamond component B by Raman spectroscopic analysis satisfies the formula (2),
6) A conductive diamond electrode used for sulfuric acid electrolysis .
2.1V ≦ potential window ≦ 3.5V (1)
3.2 ≦ A / B ≦ 6.5 (2)
A = Intensity at wave number 1300 cm ⁻¹ in Raman spectroscopic analysis B = Intensity at wave number 1500 cm ⁻¹ in Raman spectroscopic analysis Partitioned into an anode chamber and a cathode chamber by a diaphragm, a conductive diamond anode is provided in the anode chamber, a cathode is provided in the cathode chamber, and an electrolytic solution containing sulfate ions is supplied to the anode chamber and the cathode chamber from the outside. Then, in the sulfuric acid electrolysis method for electrolyzing and generating an oxidizing substance in the anode electrolyte in the anode chamber, the conductive diamond electrode according to claim 1 is used as the conductive diamond electrode, and the sulfuric acid is used. A sulfuric acid electrolysis method, characterized in that the concentration of the electrolytic solution containing ions is a solution containing 2 to 14 mol / l of sulfate ions. 3. The sulfuric acid electrolysis method according to claim 2 , wherein the electrolytic solution containing the sulfate ion is a solution containing an acid concentration of 4 to 28 mol / l. Partitioned into an anode chamber and a cathode chamber by a diaphragm, a conductive diamond anode is provided in the anode chamber, a cathode is provided in the cathode chamber, and an electrolytic solution containing sulfate ions is supplied to the anode chamber and the cathode chamber from the outside. In the electrolysis apparatus of sulfuric acid which electrolyzes and produces an oxidizing substance in the anode electrolyte in the anode chamber, the conductive diamond electrode according to claim 1 is used as the conductive diamond electrode, and the diaphragm is used. A sulfuric acid electrolysis apparatus using a fluororesin cation exchange membrane or a diaphragm made of a porous fluororesin membrane subjected to a hydrophilization treatment. Partitioned into an anode chamber and a cathode chamber by a diaphragm, a conductive diamond anode is provided in the anode chamber, a cathode is provided in the cathode chamber, and an electrolytic solution containing sulfate ions is supplied to the anode chamber and the cathode chamber from the outside. Then, in the sulfuric acid electrolysis method for electrolyzing and generating an oxidizing substance in the anode electrolyte in the anode chamber, the conductive diamond electrode according to claim 1 is used as the conductive diamond electrode, and the sulfuric acid is used. A sulfuric acid electrolysis method characterized by electrolyzing an electrolytic solution containing ions under conditions satisfying formulas (3) and (4).
100 ≦ X ≦ 10000 (3)
25 <Y <250 (4)
X = current value / anolyte amount (A / l)
Y = current density (A / dm ² ) 6. The sulfuric acid electrolysis method according to claim 5 , wherein the solution containing sulfate ions is electrolyzed under conditions satisfying formula (5).
18000 ≦ Z ≦ 10800000 (5)
Z = amount of electricity per unit volume (C / l) = current value × electrolysis time / anolyte amount (A · s / l)

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