JP2009228041A - Electrolytic apparatus and electrolytic method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To smoothly discharge a by-product gas formed between electrodes in an electrolytic cell generating the by-product gas by the electrolysis and to dispenses with the pressure to the electrodes preliminary to passing a liquid by pressure transporting with a pump. <P>SOLUTION: The electrolytic apparatus is provided with an electrolyte tank 1 storing an electrolyte and the electrolytic cell 10 arranged in the electrolyte tank 1 and dipped in the electrolyte 2. The electrolytic cell 10 is provided with a pair of the electrodes 25, 25 comprising an anode and a cathode and in the arrangement, the upper part and the lower part between the electrodes are opened and the sides of the electrodes are shielded. Because the liquid is passed between the electrodes with natural convection by the action of the gas generated by the electrolysis, preliminary to pressure transporting with a pump, the pressure to the electrodes can be dispensed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrolysis apparatus for electrolyzing an electrolytic solution, and more particularly to an electrolysis apparatus capable of electrolysis at a high current density using a diamond electrode. Further, the present invention relates to an electrolysis method in which an electrolytic solution containing a large amount of active ingredients obtained by electrolyzing the electrolytic solution with an electrolytic device is to be effectively used.

Conventionally, in the semiconductor industry, for example, an electrolytic cell as shown in FIG. 9 has been proposed as an electrolytic cell used in a process of cleaning and peeling a coating (resist or the like) on a substrate such as a silicon wafer with a high-concentration sulfuric acid solution ( Patent Document 1).
The electrolytic cell 100 is intended to improve the pressure resistance of the electrode plate 101 of the electrolytic cell against the liquid flow through an external pump, and to reduce the contact resistance between the electrode plate 101 and the current-carrying body (copper plate) 102. A current-carrying body (copper plate) is pressed against the outermost electrode plate 101 from the outside by a compression spring 103. Further, a spacer 104 is provided on the back surface so that the outermost electrode plate 101 is not damaged by the compressive force from the outside of the spring. Furthermore, the contact area between the outermost electrode plate 101 and the current-carrying body 102 (copper plate) is made as wide as possible.
JP 2007-262531 A

However, the conventional electrolytic cell has the following problems due to its structure.
1) A spacer was used between the electrodes in order to give the electrodes pressure resistance to withstand pumping. However, this spacer creates a non-uniform state in the electrolysis performance on the electrode surface, lowering the electrolysis efficiency, It is the starting point for local wear.
2) Bubbles of gas (hydrogen, oxygen, etc.) generated on the electrode surface are not easily removed, and a gas pool is generated in the upper part of the cell, reducing the effective electrolysis area.
3) When increasing the concentration of the reaction solution generated by electrolysis, the concentration is increased while circulating the same solution, but it is necessary to perform a circulation action by an external pump.
4) In order to separate the gas (hydrogen and oxygen, etc.) generated on the electrode surface and the liquid, it is necessary to install a gas-liquid separator for discharging the gas to the gas treatment process after the cell.

  The present invention has been made against the background of the above circumstances, and an object thereof is to provide an electrolysis apparatus and an electrolysis method capable of performing electrolysis with high efficiency while having a simple and safe structure.

  That is, among the electrolytic devices of the present invention, the first present invention includes an electrolytic solution storage tank that stores an electrolytic solution, and an electrolytic cell that is disposed in the electrolytic solution storage tank and is immersed in the electrolytic solution. The electrolysis cell includes at least one pair of electrodes including an anode and a cathode, and an upper portion and a lower portion between the electrodes are opened in the arrangement state, and a side between the electrodes is shielded by a peripheral wall. It is characterized by that.

  In the electrolysis apparatus according to a second aspect of the present invention, in the first aspect of the present invention, an energization body for energizing the electrode is sealed in a chamber without contacting the electrolyte stored in the electrolyte storage tank. It is stored.

  The electrolysis apparatus according to a third aspect of the present invention is characterized in that, in the first or second aspect of the present invention, an electrode holding portion for holding the electrode is provided on the peripheral wall.

  The electrolysis apparatus according to a fourth aspect of the present invention is the electrolysis apparatus according to any one of the first to third aspects of the present invention, wherein the upper part in the electrolytic solution storage tank is an open system, and the electrolytic gas generated on the electrode surface and the electrolytic solution are electrolyzed. It is characterized by being configured to separate in the liquid storage tank.

  The electrolysis apparatus according to a fifth aspect of the present invention is characterized in that in any one of the first to fourth aspects of the present invention, at least an anode of the electrodes is a diamond electrode.

  In the electrolysis method of the sixth aspect of the present invention, the electrolysis apparatus described in the first to fifth aspects of the present invention energizes the electrolysis cell and performs electrolysis while allowing the electrolytic solution to pass between the electrodes by natural convection. Features.

  The electrolysis method according to a seventh aspect of the present invention is characterized in that, in the sixth aspect of the present invention, a current density applied to the electrolysis cell is 0.5 to 250 A / dm2.

  An electrolysis method according to an eighth aspect of the present invention is characterized in that, in the sixth or seventh aspect of the present invention, the electrolytic solution is a sulfuric acid solution having a concentration of 8 to 18M.

That is, according to the present invention, bubbles are generated by electrolysis and a difference in gas-liquid ratio occurs inside and outside the electrolysis cell, so that the electrolyte flows from the bottom of the electrolysis cell. Therefore, the electrolytic solution circulates in the electrolytic solution storage tank by natural convection and the flow rate in the electrolytic cell can be kept high, and the electrolytic gas that causes the conduction failure is quickly accumulated outside the electrolytic cell without accumulating in the electrolytic cell. To discharge.
In addition, it is preferable that the distance between each electrode of the both-ends electrode and bipolar electrode which comprises an electrolytic cell is 3 mm-50 mm. If the distance between the electrodes is too large, the electrolysis efficiency decreases and the electrolysis cell becomes large. However, if the distance between the electrodes is too small, the escape of the electrolysis gas to the outside of the electrolysis cell will be worsened, which will hinder electrolysis.

  The present invention is particularly suitable in the semiconductor industry for a process of cleaning and peeling a coating (resist, etc.) on a substrate such as a silicon wafer with a high-concentration sulfuric acid solution, and omits a pretreatment step such as an ashing process. In order to enhance the resist stripping and oxidation effect, persulfuric acid solution is produced on-site by electrolytic reactor in the temperature range of 10 ° C to 90 ° C, and chemicals such as hydrogen peroxide and ozone are added from outside by repeatedly using sulfuric acid solution. Can be applied to cleaning systems that do not require However, the present invention is not limited to a specific application, and can be applied to various applications in which gas is generated by electrolysis and problems occur due to gas retention.

  An outline of the cleaning system will be described below. 1) Electrolytic device for producing persulfuric acid solution from high concentration sulfuric acid solution, 2) Cleaning device for cleaning electronic material substrate such as silicon wafer, glass substrate for liquid crystal, photomask substrate, 3) Pump for circulating high concentration sulfuric acid solution, It is equipped with a circulation line composed of piping, and 4) a heat exchanger that exchanges the heat of the feed liquid from the electrolyzer and the return liquid from the washing tank, and 5) gas-liquid separation of the gas generated in the electrolyzer, if desired. And a catalyst processing apparatus for burning hydrogen. In the present invention, by making the upper part in the electrolytic solution storage tank an open system, the electrolytic gas and the electrolytic solution can be easily gas-liquid separated at the gas-liquid interface.

  The concentration of sulfuric acid used as a cleaning solution greatly affects the persulfuric acid production efficiency by electrolysis and the resist removal effect. When the sulfuric acid concentration is about 4 to 7M, the persulfuric acid production efficiency by electrolysis is improved, but the resist peeling and dissolving effect is lowered. Therefore, the inventors repeated various experiments and found that a sulfuric acid concentration in the range of 8 to 18M was appropriate.

In the electrolyzer, persulfuric acid is generated by electrolyzing a high-concentration sulfuric acid solution to enhance the cleaning effect. Since the persulfuric acid production efficiency is higher as the solution temperature is lower, the electrolysis temperature when producing persulfuric acid is 10 to 90 ° C., preferably 40 to 80 ° C. When a platinum electrode is used as an anode as an electrode material in such an electrolysis apparatus, there is a problem that persulfuric acid cannot be continuously produced because platinum is eluted. Thus, it has been reported that persulfuric acid is produced from sulfuric acid using a conductive diamond electrode when the current density is about 0.2 A / cm 2 (Ch. Cominellis et al., Electrochemical and Solid-State Letters). , Vol.3 (2) 77-79 (2000), Special Table 2003-511555). In the case of an electrode having a diamond thin film supported on a metal substrate or the like, there is a problem in that the diamond film peels off and the action effect may disappear in a short period of time, so the substrate is removed after being deposited on the substrate. A self-supporting conductive diamond electrode or a substrate-coated diamond electrode in which a 20-100 μm diamond layer is coated on the entire surface of the substrate is desirable. In addition, the conductive diamond thin film is obtained by doping a predetermined amount of boron or nitrogen at the time of synthesis to impart conductivity, and generally boron doped. If the doping amount is too small, technical significance does not occur. If the doping amount is too large, the doping effect is saturated. Therefore, a doping amount in the range of 50 to 20,000 ppm with respect to the carbon amount of the diamond thin film is suitable. .
In the electrolytic treatment in the electrolytic apparatus, it is desirable that the current density on the electrode surface is 0.5 to 250 A / dm2.

  As described above, according to the electrolytic device or the electrolytic method of the present invention, the electrolytic solution storage tank that stores the electrolytic solution, and the electrolytic cell that is disposed in the electrolytic solution storage tank and is immersed in the electrolytic solution. The electrolytic cell includes at least one pair of electrodes composed of an anode and a cathode, and the upper and lower portions between the electrodes are opened and the sides between the electrodes are shielded in the arrangement state. Since air bubbles are generated by electrolysis and a difference in gas-liquid ratio occurs inside and outside the electrolytic cell, the electrolytic solution flows from the lower part of the electrolytic cell. Therefore, the electrolytic solution circulates in the electrolytic solution storage tank by natural convection and the flow rate in the electrolytic cell can be kept high, and the electrolytic gas that causes the conduction failure is quickly accumulated outside the electrolytic cell without accumulating in the electrolytic cell. Can be discharged.

Below, one Embodiment of this invention is described based on FIGS.
The electrolysis cell 10 has a bottomed cylindrical cell case 11 as shown in FIGS. 1 and 2, and the cell case 11 is divided into two in a direction perpendicular to the axis line and has the same structure. It consists of
As shown in FIG. 3, the cell case portion 12 has a round hole energizing body housing recess 13 formed around the axis, and an electric wire introduction hole 13 a communicating with the energizing body housing recess 13 extends to the upper part of the cylinder wall. Is formed. A ring-shaped flat surface is formed on the outer peripheral side of the current-carrying member recess 13, an O-ring mounting groove 14 is formed on the flat surface, and a step portion 15 having an inclined surface on the outer peripheral side of the flat surface. A ring-shaped cylindrical wall end face 12a is located through the gap.

  In the cell case portion 12, a disk-shaped electric current body 20 having a diameter substantially equal to the hole diameter is accommodated in the electric current body accommodating recess 13, and an external electric wire 21 is introduced from the electric wire introduction hole 13 a to the electric current body 20. They are connected in a conductive state. Coil springs 22 are arranged at predetermined angular intervals on the inner side in the axial direction of the current-carrying body 20 (only one is shown in FIG. 1), and a disk-shaped second current-carrying body 23 is disposed on the inner side in the axial direction of the coil spring 22. It arrange | positions so that it may accommodate in the electrically-conductive body accommodation recessed part 13. As shown in FIG. An O-ring 24 is mounted in the O-ring mounting groove 14. A disk-shaped diamond electrode 25 that is accommodated inside the step portion 15 is disposed so that one surface thereof is in contact with the O-ring 24. A seal ring mounting groove 15a is formed on the circumference of the inclined surface of the step portion 15. The seal ring has rigidity so as to contact the seal ring mounting groove 15a on the inner surface side in the axial direction of the diamond electrode 25. 26 is attached. The diamond electrode 25 is pressed axially outward by the seal ring 26, whereby the inner peripheral side of the O-ring 24 is sealed by the O-ring 24 and the diamond electrode 25. That is, the current-carrying body 20 and the second current-carrying body 23 are stored in a sealed space (chamber) without being in contact with the electrolytic solution. Further, the diamond electrode 25 is urged by the coil spring 22 so that the second current-carrying body 23 is surely brought into contact therewith to ensure a conductive state. This step portion 15 corresponds to an electrode holding portion of the diamond electrode 25 of the present invention.

  Furthermore, as shown in FIG. 4, the central vertical axis of the electrolytic cell 10 is placed between the cylindrical wall end faces 12 a, 12 a of the cell case parts 12, 12 on the upper side with the electrolytic cell 10 installed. Two columnar electrode support members 27, 27 are arranged on both sides in the circumferential direction so as to sandwich the electrode, and the lower portion in the state where the electrolytic cell 10 is installed is also provided in the central vertical axis. Two columnar electrode support members 27, 27 are arranged on both sides in the circumferential direction with a gap therebetween. The both ends in the axial direction of the electrode support members 27... 27 are tightly fixed to the cylindrical wall end faces 12 a and 12 a when the cell case portions 12 and 12 are assembled. Further, between the electrode support member 27 located on the upper side and the electrode support member 27 located on the lower side on the same left and right sides, the same thickness as the electrode support member 27 is formed along the cylindrical wall end surface 12a. The surrounding walls 16 and 16 are disposed and are held and fixed by the electrode support members 27 and 27 positioned above and below.

  As a result, the upper opening 16a is formed along the vertical direction between the two electrode support members 27, 27 on the upper side in the portion on the upper side with the electrolytic cell 10 installed, and the lower portion in the installed state. A lower opening 16b is formed along the vertical direction between the two lower electrode support members 27 and 27 in the lower portion. As a result, in a state where the two cell case parts 12 and 12 are combined, only the upper opening 16a and the lower opening 16b are opened, and the periphery of these openings is shielded by the peripheral walls 16 and 16 and the electrode support members 27. The obtained cell case 11 is obtained. Accordingly, each electrode support member 27 also functions as the peripheral wall of the present invention.

  In addition, although the said surrounding walls 16 and 16 were demonstrated as what is arrange | positioned between the cell case parts 12 and 12 and hold | maintained and fixed by the electrode supporting member 27, even if fixed to the cylinder wall end surface 12a of the cell case part 12. Moreover, it may be configured integrally with the cell case portion 12. In this embodiment, the peripheral wall 16 and the electrode support member 27 are described as separate members. However, they may be configured integrally.

  On the inner side in the circumferential direction of the electrode support member 27, three electrode holding grooves 27a into which a part of the periphery of the bipolar diamond electrode 25a having the same size as the diamond electrode 25 is inserted on the circumferential surface are spaced apart in the axial direction. Is formed. The electrode holding groove 27a corresponds to an electrode holding portion for the bipolar diamond electrode 25a of the present invention. Although there are three electrode holding grooves 27a in the figure, it can be appropriately set according to the number of bipolar diamond electrodes 25a.

The bipolar diamond electrodes 25a... 25a are accommodated in the electrode holding grooves 27a, respectively, and both cell case portions pass through the axial centers of the electrode support members 27 and the through holes provided in the axial direction of the cylindrical walls of the cell case portions 12 and 12, respectively. By passing bolts 28 between 12 and 12 and fastening both ends of the bolts with nuts 29 and fixing the cell case parts 12 and 12, the electrolytic cell 10 holding each electrode as shown in FIG. 4 is obtained.
The electrolytic cell 10 having the above-described configuration is configured such that one of the external wires 21 and 21 connected to each cell case portion 12 is a positive electrode of an external power source and the other is a negative electrode, so that one of the diamond electrodes 25 and 25 is an anode and the other. Becomes the cathode.

  As shown in FIG. 1, the electrolytic cell 10 is disposed in an electrolytic solution storage tank 1 and immersed in an electrolytic solution 2 accommodated in the electrolytic solution storage tank 1. The electrolytic solution 2 is located at a predetermined height in the electrolytic solution storage tank 1, and the upper part is a space, and the upper part is provided with a storage tank lid 3. An exhaust pipe (not shown) is connected. The electrolysis apparatus of this invention is comprised by the said structure.

The operation of the electrolyzer will be described below.
An external power source (not shown) is connected to the external electric wires 21 and 21 and energized.
In the electrolytic cell 10, the applied voltage is transmitted to the diamond electrodes 25, 25 at both ends of the electrolytic cell 10 through the conductive body 20 and the second conductive body 23. By applying this voltage, the bipolar diamond electrodes 25a... 25a inside the diamond electrodes 25 and 25 are polarized, and an anode and a cathode appear at predetermined intervals. As a result, an electrolytic reaction occurs between the diamond electrodes 25 and 25a and between the bipolar diamond electrodes 25a and 25a. For example, when a sulfuric acid solution is used as an electrolytic solution, sulfate ions in the electrolytic solution are oxidized to generate persulfate ions. In addition, a by-product gas such as hydrogen is generated along with the electrolytic reaction. As bubbles of hydrogen gas and oxygen gas are generated on the electrode surface, the liquid in contact with the electrode surface rises, and at the same time, an unelectrolyzed liquid is drawn upward from the bottom toward the electrode surface. As a result, the electrolyte solution between the electrodes rises through the upper opening 16a as shown in the schematic diagram of FIG. The electrolytic solution 2 is introduced between the electrodes through the lower opening 16b, and electrolytic gas is smoothly discharged out of the electrolytic cell 10 as bubbles 30 by natural convection.

  Further, the bubbles 30 discharged out of the electrolytic cell 10 together with the electrolytic solution continue to rise in the electrolytic solution 2 and are separated into the liquid electrolyte 2 by the gas-liquid interface 2a. The separated gas such as hydrogen can be exhausted by an exhaust pipe or the like connected to the storage tank lid 3 and can be appropriately treated outside the electrolyte storage tank 1.

According to the electrolytic cell of the embodiment described above, the following advantages are obtained.
1) The electrolytic cell structure that opens the upper part of the electrolytic cell and does not hinder the flow of electrolytic gas bubbles generated during electrolysis to the upper part improves the escape of the electrolytic gas, and the gas is collected in the upper part of the electrolytic cell. lost.
2) Since the electrolytic gas and the electrolytic solution generated on the electrode surface can be gas-liquid separated in the electrolytic solution storage tank (upper part), it is no longer necessary to install a separate gas-liquid separator.
3) When used for sulfuric acid electrolytic persulfuric acid production, the sulfuric acid solution circulates in the electrolytic solution storage tank by natural convection, so that it is possible to concentrate the persulfuric acid without external power, and it can also serve as the concentrated solution storage tank. it can.
4) Since the electrolytic cell is simply immersed in an open electrolyte storage tank, pressure from the pump is not applied to the cell electrode, so there is no need to provide pressure resistance, and a reinforcing spacer is not required. As a result, the entire electrode surface became an electrolytic surface, and the current distribution became uniform, and the electrolysis efficiency was improved.

Next, a more preferred embodiment of the present invention will be described as follows.
As shown in FIG. 6A, when an electrolytic cell 40 in which bipolar electrodes 43... 43 are disposed between an anode 41 and a cathode 42 is immersed in an electrolytic solution, both end electrodes (anode 41, cathode 42) are used. It was observed that the inner bipolar electrode 43 generated less electrolysis gas than the inner bipolar electrode 43 (that is, the bipolar electrode had less electrolysis). This occurs when one or more bipolar electrodes 43 are arranged inside both end electrodes, but this is particularly noticeable when there are three or more bipolar electrodes. The reason for this phenomenon is presumed as follows.

When such an electrolytic cell 40 is energized, not only the direct transmission current flowing between the opposing electrodes sandwiching the electrolyte solution, but also the outside of the cell from the ends of both ends to the ends of the bipolar electrodes jumping over the adjacent bipolar electrode 43 facing each other A current that bypasses the liquid is also generated. And in the electrolytic cell structure tested this time, the electric resistance of the bypass current is smaller than the current resistance of the direct transmission current, so it seems that the bypass current flowed preferentially.
When an electrolysis cell having such a structure is actually used and operated with 5 electrodes (3 bipolar electrodes), the electrolysis efficiency is about half of the electrolysis efficiency with 2 electrodes (0 bipolar electrodes). It has been confirmed that it is lower.

In order to solve the above problem, the electrical resistance of the bypass current may be made larger than the electrical resistance of the direct transmission current. Here, the electrical resistance of the bypass current depends on (1) the flow path length of the bypass portion and (2) the flow path area of the bypass portion.
Therefore, as shown in FIG. 6B, the outer peripheral surfaces of the bipolar electrodes 43... 43 are covered with an insulating material 44, and openings 45 and 46 penetrating the electrolysis cell and the outside are provided. As a result, the flow path length of the bypass portion is increased and the flow path area of the bypass portion is reduced, so that the electrical resistance of the bypass current can be made larger than the electrical resistance of the direct transmission current. Thereby, it is possible to preferentially energize the direct transmission current while suppressing the bypass current.

7 and 8 show a specific structure of the electrolytic cell having the above configuration. Note that the description of the same configuration as in the above embodiment is omitted.
In this embodiment, the insulating material 44 is formed in a ring shape, and has ring-shaped electrode storage grooves 44a and 44a for storing electrodes on the front and back surfaces. In addition, as shown in FIG. 8, the insulating material 44 has a plurality of lower openings 45 penetrating the insulating material 44 in the radial direction at the lower position when installed, In this position, a plurality of upper openings 46 penetrating the insulating material 44 in the radial direction are formed.
In the installation of the electrodes, in FIG. 7, three bipolar electrodes 43 are used, and between the anode 41 and one bipolar electrode 43, between the bipolar electrodes 43 and 43, one bipolar electrical wall 43 and the cathode. Insulating material 44 is disposed between each electrode 42 and the electrode is accommodated in the electrode housing groove of the insulating material 44.
Thus, the electrolytic solution flows between the electrodes through the lower opening 45 and effectively moves together with the electrolytic gas from the upper opening 46 to the outside of the electrolytic cell through the electrodes. Further, the arrangement of the insulating material 44 covers the periphery of the electrode, and the entrance / exit through which the current flows is limited to the opening provided in the insulating material 44, so that the detour current is reduced and the electrolysis efficiency is improved.

  Although the electrolysis cell structure can be improved as described above, the electrolysis efficiency can be further improved. However, the improvement can be made so that the end face portion where the diamond electrode is likely to be peeled off is sealed so that the electrolyte does not enter. Therefore, it is possible to obtain a secondary effect that the diamond electrode is hardly peeled off and the life can be extended.

  Although the present invention has been described based on the above embodiments and examples, the present invention is not limited to the above description, and can naturally be modified without departing from the scope of the present invention. It is.

It is a front sectional view showing an electrolysis device of one embodiment of the present invention. Similarly, it is a side view. It is a figure which shows a part of cell case which comprises the electrolytic cell of this invention. It is the IV-IV sectional view taken on the line of FIG. It is a schematic explanatory drawing which shows the electrolysis condition in embodiment of this invention. It is a schematic explanatory drawing which shows the electrolysis condition in an electrolytic cell. It is front sectional drawing which shows the structure of the electrolytic cell in other embodiment of this invention. Similarly, it is a side view. It is the exploded view and front sectional drawing which show the structure of the conventional electrolytic cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte storage tank 2 Electrolyte 2a Gas-liquid interface 10 Electrolysis cell 11 Cell case 12 Cell case part 13 Current carrying part accommodation recessed part 15 Step part 16 Peripheral wall 16a Upper opening part 16b Lower opening part 25 Diamond electrode 25a Bipolar diamond electrode 27 Electrode Support member 27a Electrode holding groove

Claims (8)

  An electrolytic solution storage tank for storing an electrolytic solution, and an electrolytic cell disposed in the electrolytic solution storage tank and immersed in the electrolytic solution, the electrolytic cell having at least one pair of an anode and a cathode And an upper portion and a lower portion between the electrodes are opened in the arrangement state, and a side wall between the electrodes is shielded by a peripheral wall.   The electrolyzer according to claim 1, wherein an energizing body for energizing the electrode is stored in a sealed chamber without contacting the electrolyte stored in the electrolyte storage tank.   The electrolysis apparatus according to claim 1, wherein an electrode holding portion that holds the electrode is provided on the peripheral wall.   The upper part in the said electrolyte solution storage tank is made into an open system, It was set as the structure which isolate | separates the electrolytic gas and electrolyte solution which generate | occur | produced in the electrode surface in the said electrolyte solution storage tank. The electrolyzer described.   The electrolytic apparatus according to claim 1, wherein at least an anode of the electrodes is a diamond electrode.   6. An electrolysis method characterized in that the electrolysis apparatus according to any one of claims 1 to 5 is energized in an electrolysis cell and electrolysis is performed while the electrolyte is passed between electrodes by natural convection. The electrolysis method according to claim 6, wherein a current density for energizing the electrolysis cell is 0.5 to 250 A / dm ² .   The electrolytic method according to claim 6 or 7, wherein the electrolytic solution is a sulfuric acid solution having a concentration of 8 to 18M.

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