electrode

Abstract

To provide an electrode modified for manufacturing electrolytic manganese dioxide obtained by reducing an electrolytic voltage without falling and elution of metal, even when being immersed in an electrolytic solution of sulfuric acid acidity at high temperature, while reducing an amount of attached liquid when the electrode is raised.SOLUTION: There is provided an electrode containing paraffin, that has a structure in which platinum is supported in graphite.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an electrode, and more particularly to an electrode for producing electrolytic manganese dioxide, for example, an electrode used in producing electrolytic manganese dioxide used as a positive electrode active material in manganese dry batteries, particularly alkaline manganese dry batteries. [Background technology]

[0002] Electrolytic manganese dioxide is generally produced by electrolytic oxidation deposition on the anode by passing an electric current between the anode and cathode in a sulfuric acid-based manganese sulfate electrolyte at a temperature close to 100°C. While the electrolytic manganese dioxide deposition reaction occurs on the anode, the hydrogen evolution reaction occurs on the cathode, which does not directly affect the quality of the electrolytic manganese dioxide. For this reason, the cathode has not received much attention until now, and there have been few examples of it being studied in the past.

[0003] Graphite is primarily used for the cathode, but copper and steel are also used (Patent Document 1). For example, Patent Document 2 studies a cathode in which graphite is coated with copper. However, when a copper-containing cathode is immersed in a high-temperature electrolyte containing sulfuric acid, copper dissolves into the electrolyte when no current is applied. Furthermore, in electrolysis at temperatures approaching 100°C in an acidic sulfuric acid environment, even corrosion-resistant metals such as titanium and stainless steel corrode when no current is applied. On the other hand, cathodes for salt electrolysis or water electrolysis (Patent Documents 3 and 4) are not designed for use in an acidic sulfuric acid environment at temperatures approaching 100°C. Therefore, these electrodes contain elements that may affect the quality of manganese dioxide, and are expensive to manufacture, making them difficult to use as cathodes for manganese dioxide electrolysis.

[0004] During the production of electrolytic manganese dioxide, the electrolyte is maintained at a high temperature of 93°C to 98°C. Therefore, an oil layer with a high boiling point, such as paraffin, is floated on top of the electrolyte to prevent evaporation of the electrolyte. However, because paraffin affects the product quality of electrolytic manganese dioxide, methods to remove paraffin that has been incorporated into electrolytic manganese dioxide or electrolysis methods that do not allow paraffin to be incorporated are being investigated (Patent Document 2).

[0005] Furthermore, electrodes such as cathodes and anodes are inserted and removed from the top of an electrolytic cell or a cleaning cell during electrolysis or cleaning, and when they are pulled up, the electrolyte or cleaning solution adheres to them. Because the electrolyte or other liquid adhering to the electrodes is lost, there is a need to reduce the amount of water, such as the electrolyte, adhering to the electrodes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2000 / 037714 [Patent Document 2] Japanese Patent Publication No. 2022-7926 [Patent Document 3] International Publication No. 2020 / 110527 [Patent Document 4] Patent No. 6837342 [Patent Document 5] Japanese Patent Application Laid-Open No. 2001-247987 Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure provides an electrode for producing electrolytic manganese dioxide, which has been modified for the purpose of reducing the electrolysis voltage without causing metal detachment or elution even when immersed in a high-temperature, sulfuric acid-acidic electrolyte, and which has a small amount of water attached when pulled out from an aqueous solution. [Means for solving the problem]

[0008] In this disclosure, we have focused on the performance expression and metal elution of electrodes used in the production of electrolytic manganese dioxide, and have investigated electrode modification. As a result, we have found that the inclusion of paraffin reduces the amount of moisture attached when the electrode is pulled up, and that supporting platinum on graphite prevents an increase in bath voltage during electrolysis, even under high-temperature, high-concentration sulfuric acid acidic conditions.

[0009] That is, the present invention is as defined in the claims, and the gist of the present disclosure is as follows. [1] An electrode that has a structure in which platinum is supported on graphite and contains paraffin. [2] The electrode according to the above [1], wherein the electrode is an electrode for producing electrolytic manganese dioxide. [3] The amount of platinum supported per unit area of ​​the graphite is 3 μg / cm 2 More than 500μg / cm 2 The electrode according to the above [1] or [2], which is: [4] The electrode according to any one of [1] to [3] above, wherein the content of the paraffin is 1 mg / g or more and 100 mg / g or less based on the weight of the part of the electrode immersed in the electrolyte during electrolysis. [5] The electrode according to any one of the above [1] to [4], wherein the melting point of the paraffin is 40°C or higher and 80°C or lower. [6] The electrode according to any one of the above [1] to [5], wherein the contact angle of the electrode surface with pure water is more than 90° and less than 180°. [7] A method for producing electrolytic manganese dioxide, using the electrode according to any one of [1] to [6]. [8] A method for producing an electrode according to any one of the above [1] to [6], comprising a platinum supporting step of supporting platinum on graphite to obtain platinum-supported graphite, and a paraffin-containing step of contacting the platinum-supported graphite with paraffin to incorporate paraffin into the platinum-supported graphite. [9] The method for producing an electrode according to the above [8], wherein in the platinum supporting step, platinum is supported on graphite by plating.

[10] The method for producing an electrode according to [8] above, wherein the paraffin-containing step is a method in which paraffin is applied to the surface of the platinum-supported graphite and then penetrated into the inside of the platinum-supported graphite. [Effects of the Invention]

[0010] The present disclosure provides an electrode for producing electrolytic manganese dioxide, which has been modified for the purpose of reducing the electrolysis voltage without causing metal detachment or elution even when immersed in a high-temperature, sulfuric acid-acidic electrolyte, and which exhibits a small amount of adhering water when removed from an aqueous solution. Furthermore, the electrode of the present disclosure prevents metal elution from the electrode plate into the electrolyte even when no current is applied during electrolysis in the production of manganese dioxide, further reducing the electrolysis voltage. Furthermore, the amount of liquid adhering when the electrode is removed from an electrolytic bath or cleaning bath can be reduced, enabling efficient and stable production of electrolytic manganese dioxide. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present disclosure will be described in detail below by showing an example of an embodiment thereof. Note that the present disclosure includes any combination of the configurations and parameters disclosed herein, and also any combination of the upper and lower limits of the numerical values ​​disclosed herein. <Electrode> The electrode of this embodiment has a structure in which platinum is supported on graphite and contains paraffin, i.e., an electrode containing platinum-supported graphite and paraffin. Furthermore, the electrode of this embodiment can also be considered as an electrode having a graphite substrate on which platinum is supported and containing paraffin, or even as an electrode having a graphite substrate on which platinum is supported and containing paraffin.

[0012] Graphite is the electrode substrate of the electrode of this embodiment.

[0013] The type of graphite may be, for example, one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, pyrolytic graphite, and carbon fiber, with artificial graphite being preferred from the viewpoint of ease of availability and processing.

[0014] The shape of the graphite may be any shape that can be used as an electrode for producing electrolytic manganese dioxide, and examples thereof include a plate shape and a rectangular parallelepiped shape that are also used in metal refining and plating, but the shape is not essentially limited to these. Preferred examples of the shape of graphite include a rectangular parallelepiped (columnar) and a plate shape.

[0015] Platinum is a catalyst for the electrolytic oxidation reaction in the production of electrolytic manganese dioxide. The platinum may be in a state that functions as a catalyst, and examples thereof include one or more selected from the group consisting of metallic platinum, platinum alloys, and platinum compounds. Metallic platinum is preferred as the platinum, as this allows for a further reduction in the bath voltage during the production of electrolytic manganese dioxide.

[0016] A platinum alloy is a metal containing platinum and a metal element other than platinum, and examples thereof include a metal containing platinum (Pt) and one or more elements selected from the group consisting of silver (Ag), gold (Au), cobalt (Co), copper (Cu), iron (Fe), iridium (Ir), manganese (Mn), nickel (Ni), palladium (Pd), ruthenium (Ru), titanium (Ti), and zirconium (Zr).

[0017] The platinum compound is a compound containing platinum and a non-metallic element, such as a compound containing platinum (Pt) and one or more elements selected from the group consisting of carbon (C), chlorine (Cl) and oxygen (O).

[0018] The electrode of this embodiment has a structure in which platinum is supported on graphite, and in particular, platinum is supported on the surface of the graphite. The structure is that platinum is supported on the graphite surface, that is, the electrode substrate Platinum is supported on graphite, which allows for a lower bath voltage during the production of electrolytic manganese dioxide. It can be reduced.

[0019] In the electrode of this embodiment, platinum may be supported on the portion of graphite where the electrolytic reaction of electrolytic manganese dioxide occurs, and platinum may be supported on part or all of the graphite surface. Because this allows for a reduction in the amount of platinum used, which is a precious metal, it is preferable that platinum be supported on part of the graphite surface. In other words, the graphite may have regions where platinum is supported and regions where platinum is not supported.

[0020] Platinum acts as an electrocatalyst by being present on graphite and maintaining electrical contact with it. It is known that platinum's hydrogen evolution electrocatalytic activity is superior to that of carbon, the material from which graphite is made. For example, the minimum hydrogen evolution overvoltage under 2N sulfuric acid aqueous solution conditions is 335 mV for carbon, while that of platinum is 0.002 mV. Therefore, compared to graphite, platinum exhibits superior catalytic activity at a lower hydrogen evolution overvoltage.

[0021] The graphite in the electrode of this embodiment has a platinum carrying amount per unit area (hereinafter also simply referred to as "platinum carrying amount") of 3 μg / cm 2 More than 500μg / cm 2 Preferably, it is 10 μg / cm or less. 2 More than 400μg / cm 2 Less than 20 μg / cm is more preferable. 2 More than 200μg / cm 2 The following is even more preferable: When the amount of supported platinum is within the above range, the supported metal (i.e., platinum) does not fall off even under high-temperature and high-concentration sulfuric acid acid conditions, and the bath voltage during electrolysis in the production of electrolytic manganese dioxide can be reduced.

[0022] In this embodiment, the platinum loading amount can be calculated from the following formula using a composition obtained by analyzing a solution obtained by crushing and dissolving the platinum-loaded region of an electrode sample in acid using inductively coupled plasma atomic emission spectrometry (ICP method).

[0023] G=M / A G is the platinum loading (μg / cm 2 ), M is the amount of platinum (μg) determined from the platinum concentration of the solution obtained by ICP measurement, and A is the area of ​​the region where platinum is supported in the electrode sample (cm 2 )

[0024] The ICP method may be performed using a general inductively coupled plasma emission spectrometer (for example, trade name: OPTIMA3000DV, manufactured by PERKIN ELMER).

[0025] The dissolution solution may be prepared by any known method capable of dissolving the electrode sample, such as a method in which the platinum-supported region of the electrode is crushed, the electrode sample is heated in the air at 400°C to 700°C, a mixed solution of concentrated sulfuric acid and concentrated nitric acid is added to the crushed electrode sample in the air, and the mixture is heated to evaporate and dry, and then the dried product is dissolved in aqua regia.

[0026] The electrode of this embodiment contains paraffin. By containing paraffin, the amount of liquid adhering to the electrode of this embodiment when it is removed from an electrolytic bath or a cleaning bath can be reduced. The paraffin is a hydrocarbon mixture mainly composed of linear hydrocarbons having 16 to 40 carbon atoms, and is preferably the same as that used to prevent evaporation of a manganese dioxide electrolytic bath (i.e., to prevent evaporation of the electrolyte used in the production of electrolytic manganese dioxide). To prevent evaporation, it is preferable that the paraffin becomes liquid during electrolysis and solidifies at room temperature during recovery. Therefore, the melting point of the paraffin is preferably 40°C or higher and 80°C or lower, i.e., the paraffin has a melting point of 40°C or higher and 80°C or lower, and more preferably, a melting point of 50°C or higher and 65°C or lower. A specific example of paraffin is Paraffin Wax-125 (manufactured by Nippon Seiro Co., Ltd.; melting point: 53°C).

[0027] The paraffin content is preferably 1 mg / g or more and 100 mg / g or less, more preferably 3 mg / g or more and 80 mg / g or less, and even more preferably 3 mg / g or more and 50 mg / g or less, relative to the mass (unit mass) of the portion immersed in the electrolyte (hereinafter also referred to as the "immersed portion") in the production of electrolytic manganese dioxide using the electrode of this embodiment. When the paraffin content is within the above range, the amount of moisture (amount of adhered liquid) is reduced. As long as it does not interfere with platinum loading (i.e., within a range in which platinum loading is possible), paraffin may be contained in the graphite before platinum loading, or may be impregnated into the electrode after platinum loading.

[0028] The content of paraffin in this embodiment is the mass of paraffin relative to the weighed mass (g) of the electrode of this embodiment.

[0029] The unit moisture content of the electrode of this embodiment is 0 mg / cm 2 More than 4.0mg / cm 2 Less than 0 mg / cm is preferred 2 More than 3.0mg / cm 2 Less than or equal to 0 mg / cm is more preferable. 2 More than 2.5mg / cm 2 The following is more preferable: When the unit moisture adhesion amount is within the above range, the amount of liquid adhering to the electrode of this embodiment when it is removed from the electrolytic bath or cleaning bath can be reduced, and loss of the electrolytic solution and cleaning solution can be reduced.

[0030] In this embodiment, the unit moisture content is calculated by dividing the mass difference between before and after immersion of the electrode in pure water by the surface area (cm 2 ) and the value (mg / cm 2 If the graphite has a region where platinum is not supported, the region may be masked and immersed in pure water.

[0031] The contact angle of the electrode of this embodiment is preferably more than 90° and less than 180°, more preferably 95° or more and less than 180°, and even more preferably 100° or more and less than 180°. When the contact angle exceeds 90°, the amount of liquid adhering to the electrode of this embodiment when it is removed from the electrolytic bath or cleaning bath can be reduced, and loss of the electrolytic solution and cleaning solution can be further reduced.

[0032] The contact angle in this embodiment is a value determined by the following method.

[0033] That is, using a contact angle meter (for example, DMo-501, manufactured by Kyowa Interface Science Co., Ltd.) and measurement and analysis software (for example, FAMAS1, manufactured by Kyowa Interface Science Co., Ltd.), 2.0±0.1 μL of pure water is dropped onto the platinum-supported area at room temperature (25°C±5°C). Assuming that the shape of the droplet 60 seconds after dropping is a part of a perfect circle, the contact angle (°) of the electrode with pure water is measured using the following θ / 2 method. Measurements are taken three times, and the arithmetic mean value can be used as the contact angle of the electrode of this embodiment.

[0034] Contact angle (°)=2×arctan(h / r) h: Distance from the electrode surface to the top of the droplet (mm) r: Radius of the contact surface between the electrode surface and the droplet (mm) The electrode of this embodiment can be used as a cathode for producing electrolytic manganese dioxide. When a plate-shaped electrode of this embodiment having a height of 250 mm, a width of 200 mm, and a thickness of 10 mm is used as a cathode, the voltage (hereinafter also referred to as "bath voltage") in electrolysis under the following conditions is preferably 1.23 V or more and 2.00 V or less, more preferably 1.23 V or more and 1.80 V or less, and even more preferably 1.23 V or more and 1.70 V or less.

[0035] Anode: Titanium electrode (Plate shape: 250mm high, 200mm wide, and 10mm thick) Electrode spacing: 50mm Electrolyte: 85.4g / L manganese sulfate-27.0g / L sulfuric acid mixed aqueous solution 6L and 50g of paraffin Electrolyte replenisher: 118g / L manganese sulfate aqueous solution Electrolysis temperature: 96℃ Electrolytic current density: 0.65A / dm 2 Prior to electrolysis, the cathode and anode are placed in an electrolytic cell filled with an electrolyte and paraffin and heated to 96°C, in the order anode, cathode, and anode, with their main surfaces (height x width) facing each other, with a gap of 50 mm between them. Electrolysis is then carried out for 24 hours.

[0036] During electrolysis, the concentration of manganese ions decreases due to the precipitation of electrolytic manganese dioxide as the electrolytic reaction progresses. To maintain a constant manganese ion concentration in the electrolyte, it is preferable to continuously supply an aqueous manganese sulfate solution (electrolyte replenisher) to the electrolytic cell during electrolysis. It is more preferable to supply the aqueous manganese sulfate solution while discharging the electrolyte in an amount equal to the amount of the aqueous manganese sulfate solution supplied. This allows the manganese ion concentration in the electrolyte to be maintained constant.

[0037] The electrode of this embodiment is resistant to platinum elution even when immersed in an electrolyte solution for producing electrolytic manganese dioxide. Therefore, the electrode of this embodiment has a platinum content in the sulfuric acid-manganese sulfate mixed aqueous solution (hereinafter also referred to as the "platinum elution amount") after immersion in the sulfuric acid-manganese sulfate mixed aqueous solution under the following immersion conditions, which may be 0 mg / L to 2 mg / L, 0 mg / L to 1 mg / L, 0 mg / L to 0.5 mg / L, or 0 mg / L to 0.1 mg / L.

[0038] (Immersion conditions) Electrode shape: Plate-shaped, 250mm high, 200mm wide, and 10mm thick Sulfuric acid-manganese sulfate mixed solution: 6L (Sulfuric acid concentration 27.0g / L) (Manganese sulfate concentration 85.4g / L) Heating start temperature: 86℃ Heating rate: 0.1℃ / min Soaking temperature: 96℃ Soaking time: 80min Furthermore, the electrode of this embodiment is preferably resistant to platinum elution even when no current is applied after the electrolysis reaction. After electrolysis under the following electrolysis conditions, the electrode of this embodiment preferably has a platinum concentration in the electrolyte 3 hours after the electrolysis is stopped (hereinafter also referred to as "amount of elution without current application") of 0 mg / L to 2 mg / L, 0 mg / L to 1 mg / L, 0 mg / L to 0.5 mg / L, or 0 mg / L to 0.1 mg / L.

[0039] (Electrolysis conditions) Anode: Titanium electrode (Plate shape: 250mm high, 200mm wide, and 10mm thick) Electrode spacing: 50mm Electrolyte: 85.4g / L manganese sulfate-27.0g / L sulfuric acid mixed aqueous solution 6L and 50g of paraffin Electrolyte replenisher: 118g / L manganese sulfate aqueous solution Electrolysis temperature: 96℃ Electrolytic current density: 0.65A / dm 2 Electrolysis period: 6 days When the amount of platinum eluted without applying current falls within the above range, an increase in bath voltage during electrolysis in the production of electrolytic manganese dioxide can be suppressed. Furthermore, when the amount of platinum eluted into the electrolytic solution at the end of the electrolysis falls within the above range, the life of the electrodes is extended, and electrolytic manganese dioxide can be repeatedly produced.

[0040] The electrode of this embodiment can reduce the electrolysis voltage in the electrolysis reaction using the electrode, and therefore can be used as an electrode (cathode) for producing electrolytic manganese dioxide, thereby enabling efficient production of electrolytic manganese dioxide. <Electrode manufacturing method> The electrode of this embodiment can be produced, for example, by using platinum and carrying the precious metal by electroplating or electroless plating in an electrolyte containing precious metal ions on a graphite plate as a working electrode so as to achieve the above-mentioned loading amount, or by a method for producing an electrode including a paraffin-containing step of incorporating paraffin into platinum-supported graphite. A preferred method for producing the electrode of this embodiment is an electrode production method including a platinum-supporting step of supporting platinum on graphite to obtain platinum-supported graphite, and a paraffin-containing step of contacting the platinum-supported graphite with paraffin to incorporate paraffin into the platinum-supported graphite.

[0041] The method for supporting platinum on graphite in the platinum supporting step may be any method that can support platinum on graphite, and is preferably a plating method, more preferably at least one of electroplating and electroless plating, and even more preferably electroplating.

[0042] The preferred electroplating method for supporting platinum on graphite is to use a titanium platinum electrode as the anode, graphite as the cathode, and a mixed solution of chloroplatinic acid (VI) and hydrochloric acid as the plating solution, at a temperature of 50°C to 100°C, and a current density of 0.3 A / dm 2 Above, 2.0A / dm 2Electroplating can be performed at temperatures between 60°C and 90°C, and at a current density of 0.5A / dm 2 Above, 1.5A / dm 2 It is preferable to electroplate with the following:

[0043] The longer the electroplating time, the greater the amount of platinum supported. The plating time may be any time depending on the desired amount of platinum supported and the size of the graphite (electrode substrate), and may be, for example, from 15 seconds to 2 minutes.

[0044] In order to prevent the platinum from falling off after plating, it is preferable to polish the graphite prior to supporting platinum.

[0045] After the platinum supporting step, a washing step of washing the platinum-supported graphite may be carried out prior to the paraffin-containing step. The washing step can reduce impurities such as plating solution remaining on the surface. The washing method in the washing step may be any method capable of reducing impurities, and examples thereof include washing with pure water. A preferred washing method includes immersion in warm water at 30°C or higher and 100°C or lower for 10 minutes or longer and then washing with pure water.

[0046] The washed platinum-supported graphite is preferably dried by any method. The drying conditions are arbitrary, but examples include drying in the air at 30°C to 100°C for 1 hour to 24 hours.

[0047] The paraffin-containing step is a step of contacting the platinum-supported graphite with paraffin to cause the platinum-supported graphite to contain paraffin.

[0048] The contact of the platinum-supported graphite with paraffin may be achieved by adhering paraffin to the surface of the platinum-supported graphite and then allowing the paraffin to penetrate into the interior of the platinum-supported graphite. For example, the platinum-supported graphite may be immersed in pure water having a paraffin layer on its surface at a temperature of 60°C or higher but lower than 100°C, preferably pure water at a temperature of 80°C or higher but lower than 100°C. The platinum-supported graphite passes through the paraffin layer, causing paraffin to adhere to the surface of the platinum-supported graphite. The platinum-supported graphite is then immersed in pure water at the above-mentioned temperature range, allowing the molten paraffin to penetrate the platinum-supported graphite. The thickness of the paraffin layer may be any thickness that allows the paraffin to adhere uniformly to the surface of the platinum-supported graphite, and may be, for example, 1 cm or higher but 2 cm or lower. The immersion time is optional, but may be 1 hour or higher but 24 hours or lower, and preferably 5 hours or higher but 24 hours or lower.

[0049] After the immersion, the platinum-supported graphite is preferably immersed in warm water containing no paraffin, washed with warm water, and dried, thereby removing the paraffin remaining on the outermost surface of the platinum-supported graphite. [Example]

[0050] Hereinafter, the present disclosure will be described with reference to examples, but the present disclosure is not limited to the following examples.

[0051] <Metal Loading Measurement> The amount of metal carried was measured by measuring the metal concentration in the measurement solution by inductively coupled plasma emission spectrometry (ICP method) using a general inductively coupled plasma emission spectrometer (product name: OPTIMA3000DV, manufactured by PERKIN ELMER).

[0052] The measurement solution was prepared as follows. First, a stamp mill was used to pulverize the platinum-loaded region of the electrode sample until it could pass through a 0.5 mm mesh sieve. The electrode samples were cut out from the portion immersed in the plating bath described below. Specifically, samples were used that were cut out from the bottom of a graphite rod (described below) up to 5 cm (Examples 1 and 2, Comparative Examples 1 to 4), and samples were used that were cut out from the largest surface (i.e., the height × width surface, hereinafter also referred to as the "main surface") of a graphite plate (described below) 4 cm from the bottom edge of the graphite plate, extending 2 cm to 6 cm to the right or left and 5 cm up from the center in the width direction (the point that bisects a perpendicular line drawn parallel to the width direction from the left edge to the right edge of the graphite plate) (i.e., a 5 cm high, 4 cm wide range) (Examples 3 to 8, Comparative Examples 5 to 8).

[0053] Next, the crushed electrode sample (fragments) was placed in a porcelain crucible and heated in an air atmosphere at 600°C for 70 hours. 1 mL of concentrated sulfuric acid and 2 mL of concentrated nitric acid were added in the air atmosphere, and the mixture was heated and evaporated to dryness. The mixture was then dissolved in aqua regia to obtain a solution. Pure water was added to the solution until the total volume was 1 L, and the metal concentration of the resulting solution was measured.

[0054] The metal loading amount was calculated from the metal concentration of the measurement solution obtained by ICP measurement using the following formula.

[0055] G=C×W1 / W2×V / A In the above formula, G is the metal loading (mg / cm 2 ), C is the metal concentration (mg / L) of the measurement solution obtained by ICP measurement, W1 is the mass (g) of the cut-out electrode sample, W2 is the mass (g) of the crushed electrode sample (pieces), V is the volume of the measurement solution (=1 (L), except for Example 7, which was 0.1 L), and A is the surface area (cm) of the platinum-loaded region of the cut-out platinum-loaded graphite. 2 )

[0056] <Paraffin content> The paraffin content of the electrode sample was measured by gas chromatography using a gas chromatograph (Agilent 7890A GC, manufactured by Agilent Technologies, Inc.).

[0057] 1.0 g of electrode sample (fragments) crushed in the same manner as in the metal loading measurement and 5 mL of hexane were added to a screw-cap sample tube and shaken for 15 minutes. The mixture was then centrifuged at 3000 rpm for 15 minutes and filtered using a filter (product name: MyShoridisc H-13-5, manufactured by Tosoh Corporation). The hexane layer recovered was used as the measurement sample. The measurement sample was subjected to gas chromatography, and the signal detected by the FID detector attached to the instrument was compared with the signal of a standard sample to determine the paraffin content.

[0058] The standard sample used was a hexane solution containing paraffin (trade name: Paraffin Wax-125, manufactured by Nippon Seiro Co., Ltd.) at a concentration of 10 mg / L.

[0059] <Measurement of the amount of metal eluted into the electrolyte at the start> The amount of metal eluted into the initial electrolyte from the electrode sample was measured by the ICP method using a general inductively coupled plasma emission spectrometer (product name: OPTIMA3000DV, manufactured by PERKIN ELMER).

[0060] The starting electrolyte (described below) was diluted 10 times with pure water, and the metal concentration in the diluted electrolyte was measured by ICP. The metal concentration obtained was multiplied by 10 and used as the metal concentration (mg / L) in the starting electrolyte.

[0061] <Measurement of moisture adhesion amount and unit moisture adhesion amount> The moisture content of the electrode in each Example or Comparative Example was measured by measuring the mass of the electrode before and after immersion in pure water. Specifically, a screw cap containing pure water was placed on an electronic balance. A rod-shaped electrode was immersed in the screw cap so that the entire electrode surface was immersed in pure water. After immersion for 10 seconds, the rod-shaped electrode was removed from the screw cap. The difference in the values ​​on the electronic balance before and after immersion of the electrode (i.e., the difference between the mass of the rod-shaped electrode before immersion and the mass of the rod-shaped electrode after removal) was calculated and used as the moisture content (mg).

[0062] The measurement sample used was a rod-shaped electrode with a portion above 5 cm from the bottom covered with PTFE tape.

[0063] The measurement was carried out three times, and the arithmetic mean value was taken as the amount of moisture attached (mg).

[0064] The resulting amount of water attached (mg) was then calculated based on the surface area (cm 2 ) to obtain the unit moisture content (mg / cm 2 ) was decided.

[0065] Electrode surface area (cm 2 ) is the surface area (cm) of the platinum-supported region 2 ) was decided.

[0066] <Contact angle measurement> The contact angle of the electrode was measured using a contact angle meter (device name: DMo-501, manufactured by Kyowa Interface Science Co., Ltd.) and the measurement and analysis software (FAMAS1, manufactured by Kyowa Interface Science Co., Ltd.) attached to the device. A 2.0±0.1 μL droplet of pure water was dropped onto the electrode surface in an environment at room temperature of 25°C, and the shape of the droplet 60 seconds after dropping was assumed to be a part of a perfect circle, and the contact angle (°) of the electrode with pure water was measured using the following θ / 2 method.

[0067] Contact angle (°)=2×arctan(h / r) h: Distance from the electrode surface to the top of the droplet (mm) r: Radius of the contact surface between the electrode surface and the droplet (mm) The measurement was carried out three times, and the arithmetic mean value was taken as the contact angle (°).

[0068] <Measurement of bath voltage and electrode durability> The bath voltage and electrode durability of the electrodes of each Example or Comparative Example were confirmed by electrolytically synthesizing electrolytic manganese dioxide using an electrolytic cell equipped with a graphite plate of each Example or Comparative Example as the cathode, a titanium plate as the anode, and a manganese sulfate-sulfuric acid mixed aqueous solution as the electrolyte.

[0069] First, 6 L of electrolyte and 50 g of paraffin for preventing evaporation of the electrolyte were added to an electrolytic cell, and then the temperature was raised to 86° C. A manganese sulfate-sulfuric acid mixed aqueous solution with a manganese sulfate concentration of 85.4 g / L and a sulfuric acid concentration of 27.0 g / L was used as the electrolyte.

[0070] Next, one plate electrode (cathode) from each Example or Comparative Example and two titanium plate anodes (height 250 mm, width 200 mm, thickness 5 mm) were each immersed in the electrolyte to a depth of 160 mm so that they were perpendicular to the electrolyte surface. The cathode and anode were then fixed 50 mm apart so that their main surfaces (height x width) faced each other (i.e., in the order anode, cathode, anode). The electrolyte was then heated to 96°C over 3 hours. After the temperature increase was complete, 50 mL of electrolyte was sampled (hereinafter, the electrolyte sampled after the temperature increase is also referred to as the "initial electrolyte").

[0071] Then, a DC stabilized power supply (PAN-18-10A, manufactured by Kikusui Electronics Co., Ltd.) was connected, and a current of 4.48 A (i.e., 0.65 A / dm 2 Electrolytic synthesis of electrolytic manganese dioxide was carried out at a constant current of 1000 kJ / s. During electrolysis, an aqueous manganese sulfate solution (electrolyte replenisher) with a manganese sulfate concentration of 118 g / L was continuously supplied to the electrolytic cell to prevent changes in the composition of the electrolyte, and the electrolyte was continuously removed from the electrolytic cell so that the amount of electrolyte in the cell remained constant at 6 L. 24 hours after the start of electrolysis, the voltage display on the DC stabilized power supply was read and used as the bath voltage.

[0072] Electrolysis was continued for another 6 days and stopped on the 7th day after the start of electrolysis. 3 hours after the electrolysis was stopped, 50 mL of electrolyte was collected (hereinafter, the electrolyte collected 3 hours after the electrolysis was stopped 7 days after the start of electrolysis is also referred to as the "finishing electrolyte"). Furthermore, the amount of metal eluted into the finishing electrolyte, i.e., the amount of metal eluted without current application (mg / L), was measured using the same method as in <Measurement of the amount of metal eluted into the starting electrolyte> above.

[0073] Example 1 All six surfaces of a rectangular parallelepiped (columnar) graphite rod (PSG322, manufactured by SEC Carbon Co., Ltd.) measuring 100 mm in length (height), 10 mm in width, and 10 mm in thickness were polished with #400 grit sandpaper (hereinafter, the graphite rod described above that had been polished will also be referred to as the "graphite rod"). The bottom of the rod was covered with plating masking tape (manufactured by 3M Co.) from 50 mm to 70 mm from the bottom (the portion from 50 to 70 mm in the longitudinal direction was covered).

[0074] Then, the graphite rod was immersed in an electrolyte solution of 10 g / L chloroplatinic acid (VI) and 20 g / L hydrochloric acid at 70°C, and the graphite rod was used as the anode and the titanium platinum electrode as the cathode. This plating bath was used at a cathode current density of 1.0 A / dm 2 The graphite rod was electroplated at 100° C. for 2 minutes to support platinum on the graphite rod (that is, the portion extending from the bottom surface of the graphite rod to 50 mm in the longitudinal direction).

[0075] After platinum was applied, the masking tape was removed from the graphite rod, which was then immersed in 50°C warm water for 30 minutes, washed with running water, and then dried in an air atmosphere at 50°C for 12 hours. (Hereinafter, the process from covering with masking tape to drying at 50°C will also be referred to as the "platinization process.") The electrode was then immersed overnight to a height of 6.5 cm from the bottom in a solution of 1.5 cm of melted paraffin (product name: Paraffin Wax-125, manufactured by Nippon Seiro Co., Ltd., melting point 53°C) in 97°C hot water. After being removed from the hot water with the floating paraffin, the electrode was transferred to a beaker filled with hot water at 75°C before the paraffin solidified, and further hot water at 75°C was poured over the electrode for 10 minutes to remove the paraffin from the surface. The electrode was then air-dried at room temperature for one day, and this was used as the electrode of Example 1. (Hereinafter, the process from immersion in the hot water with the floating paraffin to air-drying will also be referred to as the "paraffin-containing process.") Unit platinum loading is 140μg / cm 2 , paraffin content is 2.9 mg / g, moisture content is 41 mg, and unit moisture content is 2.0 mg / cm 2 , and the contact angle was 124°.

[0076] Example 2 An electrode of Example 2 was obtained in the same manner as in Example 1, except that the electroplating time was set to 30 seconds.

[0077] Platinum loading is 31 μg / cm 2 , paraffin content 4.5mg / g, moisture content 48mg, unit moisture content 2.3mg / cm 2 , and the contact angle was 123°.

[0078] Comparative Example 1 A graphite rod prepared in the same manner as in Example 1 was used as the electrode of Comparative Example 1 (i.e., the same operations as in Example 1 were performed except that the platinum plating step and the paraffin impregnation step were not performed).

[0079] The water adhesion amount of the electrode in this comparative example was 95 mg, and the unit water adhesion amount was 4.5 mg / cm 2 , and the contact angle was 84°.

[0080] Comparative Example 2 A comparative black electrode was prepared by the same procedure as in Example 1, except that the platinum plating step was not carried out.

[0081] No platinum was detected from this electrode (unit platinum content: 0 mg / g), the paraffin content was 18 mg / g, the water adhesion amount was 44 mg, and the unit water adhesion amount was 2.1 mg / cm 2 , and the contact angle is 113° It was.

[0082] Comparative Example 3 An electrode of Comparative Example 3 was prepared by carrying out the same procedure as in Example 1, except that the paraffin impregnation step was not carried out.

[0083] Unit platinum loading is 140μg / cm 2 , paraffin was not detected (paraffin content 0 mg / g), the moisture content was 95 mg, and the unit moisture content was 4.5 mg / cm 2 , and the contact angle was 81°.

[0084] Comparative Example 4 An electrode of Comparative Example 4 was prepared by the same procedure as in Example 2, except that the paraffin impregnation step was not carried out.

[0085] Platinum loading is 32μg / cm 2 , no paraffin was detected, and the moisture content was 110 mg and the unit moisture content was 5.2 mg / cm 2 , and the contact angle was 74°.

[0086] The results of these examples and comparative examples are shown in the table below.

[0087] [Table 1] From the table above, we can see that when paraffin is impregnated into graphite, the amount of moisture adhering to the electrode decreases. Furthermore, we can see that for electrodes containing paraffin, the contact angle of pure water increases, and the amount of moisture adhering decreases, regardless of whether or not there is metal plating and the amount of metal plating.

[0088] Example 3 A rectangular parallelepiped graphite plate (PSG322, manufactured by SEC Carbon Co., Ltd.; hereafter referred to as the "graphite plate") measuring 250 mm in height, 200 mm in width, and 10 mm in thickness was used. The area from 160 mm to 185 mm from the bottom of the graphite plate was covered with plating masking tape (manufactured by 3M). The area from the bottom to 160 mm (160 mm in height from the bottom) was then immersed in an electrolyte solution containing 10 g / L chloroplatinic acid (VI) and 20 g / L hydrochloric acid maintained at 70°C. The two largest surfaces of the graphite plate (height × width surfaces; hereafter referred to as the "main surfaces") were set facing each other, forming a plating bath with two titanium-platinum electrodes as the anode and the graphite plate as the cathode. This plating bath was used with a cathode current density of 1.0 A / dm 2Electroplating was performed at 40°C for 4 minutes to support platinum on the electrode. The masking tape was then removed, and the electrode was immersed in 50°C warm water for 30 minutes. It was then washed with running water and dried at 50°C for 12 hours. The electrode was then immersed overnight to a height of 15 cm from the bottom in 97°C warm water containing a 1.5 cm layer of paraffin (product name: Paraffin Wax-125, manufactured by Nippon Seiro Co., Ltd., melting point 53°C). After being removed from the warm water containing the floating paraffin, the electrode was immersed in a container filled with 75°C warm water before the paraffin solidified, and then 75°C warm water was poured over the container for 10 minutes to remove the paraffin from the surface. The electrode was then air-dried at room temperature for 1 day, and used as the electrode of Example 3.

[0089] Platinum loading is 400μg / cm 2 The paraffin content was 44 mg / g, the contact angle was 133°, and the bath voltage was 1.52 V. No platinum was detected in the starting or ending electrolyte, so the amount of platinum eluted and the amount of platinum eluted without current application were both 0 mg / L.

[0090] Example 4 An electrode was prepared in the same manner as in Example 3 except that the electroplating time was set to 2 minutes, and this was used as the electrode of this example.

[0091] Platinum loading is 130μg / cm 2 The paraffin content was 19 mg / g, the contact angle was 114°, and the bath voltage was 1.50 V. No platinum was detected in the initial or final electrolyte, so the amount of platinum eluted and the amount eluted without current application were both 0 mg / L.

[0092] Example 5 An electrode of Example 5 was prepared in the same manner as in Example 3, except that the electroplating time was set to 1 minute.

[0093] Platinum loading is 59μg / cm 2 The paraffin content was 9.4 mg / g, the contact angle was 107°, and the bath voltage was 1.54 V. No platinum was detected in the starting or ending electrolyte, so the amount of platinum eluted and the amount of platinum eluted without current application were both 0 mg / L.

[0094] Example 6 An electrode of Example 6 was prepared in the same manner as in Example 3, except that the electroplating time was set to 30 seconds.

[0095] Platinum loading is 21μg / cm 2 The paraffin content was 21 mg / g, the contact angle was 112°, and the bath voltage was 1.62 V. No platinum was detected in the initial or final electrolyte, so the amount of platinum eluted and the amount of platinum eluted without current application were both 0 mg / L.

[0096] Example 7 An electrode of Example 7 was prepared in the same manner as in Example 3, except that the electroplating time was set to 15 seconds.

[0097] Platinum loading: 3.5 μg / cm 2 The paraffin content was 39 mg / g, the contact angle was 115°, and the bath voltage was 1.68 V. No platinum was detected in the starting or ending electrolyte, so the amount of platinum eluted and the amount of platinum eluted without current application were both 0 mg / L.

[0098] Comparative Example 5 A graphite plate was used as the electrode of this example (that is, the same operations as in Example 3 were carried out except that the platinum plating step and the paraffin impregnation step were not carried out).

[0099] Platinum, copper, palladium, and paraffin were not detected from this electrode (unit platinum loading, unit copper loading, and unit palladium loading were 0 μg / cm 2 , and paraffin content is 0 mg / g).

[0100] The bath voltage of the electrode of this comparative example was measured, except that paraffin was not added to the electrolytic bath and the electrolyte was not analyzed.

[0101] The contact angle was 84° and the bath voltage was 1.67V.

[0102] Comparative Example 6 The same procedure as in Example 3 was carried out except that the platinum plating step was not carried out, and the graphite plate was impregnated with paraffin to prepare an electrode for Comparative Example 6.

[0103] No platinum, copper, or palladium was detected from this electrode (unit platinum loading, unit copper loading, and unit palladium loading were 0 μg / cm 2 ), the paraffin content was 48 mg / g, the contact angle was 115°, and the bath voltage was 2.09 V.

[0104] Comparative Example 7 Using the same graphite plate as in Example 3, the area from 160 mm to 180 mm from the bottom of the graphite plate was covered with masking tape for plating (manufactured by 3M), and then the area from the bottom to 160 mm was covered with copper (Cu 2+ The plate was immersed in an electrolyte containing 20 g / L of ions and 40 g / L of sulfuric acid. Two copper plate electrodes were set facing the two largest surfaces of the graphite plate, and the graphite plate was used as the cathode and the current density was 1.0 A / dm 2 The electrode was electroplated at 50°C for 10 minutes to deposit copper on both sides of the electrode. After removing the masking tape, the electrode was immersed in warm water at 50°C for 30 minutes, washed with running water, and dried at 50°C for 12 hours. After that, the same paraffin impregnation step as in Example 3 was carried out to obtain the electrode of Comparative Example 7.

[0105] The amount of copper supported per unit area on graphite is 1900 μg / cm 2 The paraffin content was 36 mg / g, the contact angle was 112°, and the bath voltage was 1.74 V. 22 mg / L and 27 mg / L of copper were detected in the initial and final electrolytes, respectively, so the copper elution amount was 22 mg / L and the non-current elution amount was 27 mg / L.

[0106] Comparative Example 8 Using the same graphite plate as in Example 3, the area from 160 mm to 180 mm from the bottom of the graphite plate was covered with masking tape for plating (manufactured by 3M), and then the area from the bottom to 160 mm was immersed in a palladium plating solution (Palabrite SST-L, Japan High Purity Co., Ltd.) maintained at 50°C. Two titanium platinum electrodes were set up facing the two largest surfaces of the graphite plate as anodes, and the graphite plate was used as the cathode, with a current density of 1.0 A / dm 2 After removing the masking tape, the electrode was immersed in hot water at 50°C for 30 minutes, then in a 5% aqueous hydrochloric acid solution at 50°C for 5 minutes, and then again in hot water at 50°C for 30 minutes. After that, it was washed with running water and dried at 50°C for 12 hours. After that, it was subjected to the same paraffin impregnation process as in Example 3, and this was used as the electrode of Comparative Example 8.

[0107] The amount of palladium supported per unit area on graphite is 47 μg / cm 2 The paraffin content was 30 mg / g, the contact angle was 126°, and the bath voltage was 1.62 V. No palladium was detected in the starting electrolyte, and 2.8 mg / L of palladium was detected in the ending electrolyte. Therefore, the amount of palladium eluted was 0 mg / L, and the amount of eluted without current application was 2.8 mg / L.

[0108] The performance of graphite electrodes that do not carry metal deteriorates when they contain paraffin. The results of the above examples and comparative examples are shown in the table below.

[0109] [Table 2] From Comparative Examples 5 and 6 in Table 2, it can be seen that the graphite electrodes containing paraffin and not plated with a metal (platinum, copper or palladium) have an increased bath voltage and a reduced electrode performance.

[0110] However, the bath voltage was reduced by including paraffin and plating a metal (platinum, copper, or palladium). Furthermore, Examples 3 to 7 showed that using platinum as the plating metal could suppress metal elution.

[0111] As described above, the electrode of this example contains paraffin, thereby reducing adhesion of moisture to the electrode, and by supporting platinum, there is no metal elution into the electrolyte even when no current is applied, even under conditions of high temperature and containing sulfuric acid, and has the effect of reducing the voltage during electrolysis.

[0112] Patent Document 3 shows that paraffin penetrates graphite and that removing the paraffin improves the performance of the graphite electrode. However, it has now been discovered that the graphite of the present invention, when containing paraffin, has the effect of reducing the amount of liquid that adheres to the electrode when it is pulled out of the liquid.

Claims

1. The graphite has a structure in which platinum is supported, and the amount of platinum supported per unit area of ​​the graphite is 50 μg / cm ２ More than 500μg / cm ２ or less, wherein the electrode surface has a contact angle with pure water of 100° or more and less than 180°, and the electrode contains paraffin.

2. 2. The electrode of claim 1, wherein said graphite is synthetic graphite.

3. 3. The electrode according to claim 1, wherein the content of the paraffin is 1 mg / g or more and 100 mg / g or less based on the weight of the portion of the electrode immersed in the electrolyte during electrolysis.

4. 3. The electrode according to claim 1, wherein the melting point of the paraffin is 40°C or higher and 80°C or lower.

5. A method for producing electrolytic manganese dioxide, using the electrode according to claim 1 or 2.

6. 3. The method for producing an electrode according to claim 1, further comprising: a platinum supporting step of supporting platinum on graphite to obtain platinum-supported graphite; and a paraffin-containing step of contacting the platinum-supported graphite with paraffin to cause the platinum-supported graphite to contain paraffin.

7. The method for producing an electrode according to claim 6, wherein the method for supporting platinum on graphite in the platinum supporting step is a plating method.

8. 7. The method for producing an electrode according to claim 6, wherein the paraffin-containing step comprises adhering paraffin to the surface of the platinum-supported graphite and then allowing paraffin to penetrate into the interior of the platinum-supported graphite.

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