Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/21—Manganese oxides
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/052—Electrodes comprising one or more electrocatalytic coatings on a substrate
  • C25B11/053—Electrodes comprising one or more electrocatalytic coatings on a substrate characterised by multilayer electrocatalytic coatings
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/054—Electrodes comprising electrocatalysts supported on a carrier
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
  • C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
  • C25B11/065—Carbon
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
  • C25B11/081—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the element being a noble metal

Definitions

• the present disclosure relates to an electrode and more specifically to an electrode used for the production of electrolytic manganese dioxide, such as an electrode used for producing electrolytic manganese dioxide used as a positive electrode active material in manganese dry cells, particularly in alkali manganese dry cells.
• electrolytic manganese dioxide is produced by passing a current between an anode and a cathode in a sulfuric acid-acidic manganese sulfate electrolyte solution at a temperature close to 100°C and thereby causing electrolytic oxidative deposition on the anode.
• the cathode, on which a hydrogen evolution reaction occurs, in comparison with the anode on which a deposition reaction of electrolytic manganese dioxide occurs, does not directly affect the quality of the electrolytic manganese dioxide. Therefore, attention has not been paid to the cathode, and there have been few examples examined in the past.
• the cathode is composed primarily of graphite and also includes copper and steel (Patent Document 1).
• Patent Document 2 examines a cathode including graphite coated with copper.
• a cathode containing copper is immersed in a high-temperature electrolyte solution containing sulfuric acid, copper elutes into the electrolyte solution during a non-electrolytic period.
• metals having corrosion resistance such as titanium and stainless steel, undergo corrosion during a non-electrolytic period.
• cathodes for electrolysis of brine or water are not designed in consideration of use under sulfuric acid acidity and at a temperature close to 100°C. Therefore, these electrodes contain elements that may affect the quality of manganese dioxide and have high manufacturing costs. This makes it difficult to use them as cathodes for electrolysis of manganese dioxide.
• electrodes such as cathodes and anodes are taken in and out from upper portions of an electrolytic bath and a cleaning tank during electrolysis and cleaning, and an electrolyte solution and a cleaning solution adhere to the electrodes during withdrawal. Because the electrolyte solution and the like adhering to the electrodes result in loss, a reduction in the amount of water such as the electrolyte solution adhering to the electrodes has been anticipated.
• the present disclosure provides an electrode for the production of electrolytic manganese dioxide, the electrode being modified for the purpose of reducing the amount of water adhering to the electrode during withdrawal from an aqueous solution and for preventing detachment or elution of the metals even when immersed in a high-temperature and sulfuric acid-acidic electrolyte solution, thereby reducing an electrolytic voltage.
• the present invention is as defined in the claims, and a gist of the present disclosure is as follows.
• an electrode for the production of electrolytic manganese dioxide the electrode being modified for the purpose of reducing the amount of water adhering to the electrode during withdrawal from an aqueous solution and for preventing detachment or elution of the metals even when immersed in a high-temperature and sulfuric acid-acidic electrolyte solution, thereby reducing an electrolytic voltage, can be provided.
• the electrode according to the present disclosure does not cause elution of metals from the electrode plate into an electrolyte solution during a non-electrolytic period of electrolysis for producing manganese dioxide. This further reduces an electrolytic voltage.
• the amount of liquid adhering to the electrode during withdrawal from an electrolytic bath or a cleaning tank can be reduced. This enables efficient and consistent production of electrolytic manganese dioxide.
• An electrode according to this embodiment is an electrode comprising a structure including graphite and platinum supported on the graphite and further comprising paraffin, that is, an electrode containing graphite on which platinum is supported and paraffin.
• the electrode according to this embodiment can also be regarded as an electrode containing a graphite base material on which platinum is supported and paraffin, or even further, as an electrode including a graphite base material on which platinum is supported and further containing paraffin.
• Examples of the types of the graphite include one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, pyrolytic graphite and carbon fibers. Artificial graphite is preferable from the viewpoint of availability and ease of processing.
• Platinum serves as a catalyst for the electrolytic oxidation reaction in the production of electrolytic manganese dioxide.
• Any form of platinum which functions as a catalyst may be used. Examples include one or more selected from the group consisting of metallic platinum, a platinum alloy and a platinum compound.
• the platinum is preferably metallic platinum because it further reduces the bath voltage during the production of electrolytic manganese dioxide.
• a platinum alloy is a metal containing platinum and one or more metal elements other than platinum.
• metal elements 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).
• the electrode according to this embodiment has a structure in which platinum is supported on graphite, and in particular, a structure in which platinum is supported on the surface of the graphite. Supporting platinum on the surface of the graphite, that is, in a state in which platinum is supported on the graphite serving as the electrode base material, makes it possible to further reduce the bath voltage during the production of electrolytic manganese dioxide.
• platinum is supported on a portion of the graphite on which the electrolytic reaction for electrolytic manganese dioxide occurs, and platinum may be supported on either a part or the entirety of the surface of the graphite. It is preferable that platinum be supported on only a part of the graphite surface in order to reduce the amount of platinum used, which is a noble metal. In other words, the graphite may have a region on which platinum is supported and a region on which platinum is not supported.
• Platinum acts as an electrode catalyst by being present on the graphite and maintaining electrical contact with the graphite. It is known that the catalytic activity of platinum at the hydrogen evolution electrode is superior to that of carbon, which is the material of the graphite. For example, under conditions of a 2N aqueous sulfuric acid solution, the minimum hydrogen overvoltage is 335 mV for carbon, whereas it is 0.002 mV for platinum. Accordingly, platinum exhibits excellent catalytic activity with a lower hydrogen overvoltage than graphite.
• the amount of platinum supported on the graphite per unit area is preferably 3 ⁇ g/cm 2 or more and 500 ⁇ g/cm 2 or less, more preferably 10 ⁇ g/cm 2 or more and 400 ⁇ g/cm 2 or less, and further preferably 20 ⁇ g/cm 2 or more and 200 ⁇ g/cm 2 or less. Maintaining the amount of platinum supported within the above range prevents detachment of the supported metal (i.e., platinum) even under high-temperature, high-concentration sulfuric acid-acidic conditions, and reduces the bath voltage during electrolysis in the production of electrolytic manganese dioxide.
• the supported metal i.e., platinum
• the amount of platinum supported may be determined, according to the following equation, using the composition obtained by compositional analysis, by inductively coupled plasma emission spectroscopy (ICP method), of a solution obtained by pulverizing and acid-dissolving the region of an electrode sample in which platinum has been supported.
• G M / A
• G represents the amount of platinum supported ( ⁇ g/cm 2 )
• M represents the amount of platinum ( ⁇ g) determined from the platinum concentration in the solution obtained by the ICP measurement
• A represents the area (cm 2 ) of the region of the electrode sample in which platinum has been supported.
• the ICP method may be conducted using a common inductively coupled plasma emission spectrometer (e.g., trade name: OPTIMA 3000 DV, manufactured by PerkinElmer).
• a common inductively coupled plasma emission spectrometer e.g., trade name: OPTIMA 3000 DV, manufactured by PerkinElmer.
• the solution may be prepared by any known method capable of dissolving the electrode sample.
• An example includes a method in which the region of the electrode in which platinum has been supported is pulverized, the resulting electrode sample is heated at 400°C or more and 700°C under an air atmosphere, a mixed solution of concentrated sulfuric acid and concentrated nitric acid is then added under an air atmosphere, followed by heating to evaporate to dryness, and the residue is dissolved in aqua regia.
• the electrode according to this embodiment contains paraffin. Because the electrode according to this embodiment contains paraffin, the amount of liquid adhering to the electrode when the electrode is withdrawn from an electrolytic bath or a cleaning tank can be reduced.
• the paraffin is a mixture of hydrocarbons composed primarily of straight-chain hydrocarbons having 16 to 40 carbon atoms and preferably the same as that used for preventing evaporation in manganese dioxide electrolytic baths (i.e., for preventing evaporation of the electrolyte solution in the production of electrolytic manganese dioxide). In order to prevent evaporation, it is preferable that the paraffin be in a liquid state during electrolysis and in a solid state at normal temperature during recovery.
• the melting point of the paraffin is 40°C or more and 80°C or less. That is, the paraffin is preferably a paraffin having a melting point of 40°C or more and 80°C or less, further preferably a paraffin having a melting point of 50°C or more and 65°C or less. Specific examples of the paraffin include Paraffin Wax-125 (manufactured by Nippon Seiro Co., Ltd.; melting point: 53°C).
• the content of paraffin 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 further preferably 3 mg/g or more and 50 mg/g or less, relative to the mass (unit mass) of a portion of the electrode according to this embodiment which is immersed in an electrolyte solution (hereinafter, the above portion is also referred to as "immersed portion") in the production of electrolytic manganese dioxide using the electrode. Maintaining the paraffin content within the above range reduces the amount of adhering water (amount of adhering liquid).
• the paraffin may be contained in the graphite prior to the support of platinum, or the electrode may be impregnated with paraffin subsequent to the support of platinum.
• the unit amount of adhering water of the electrode according to this embodiment is preferably 0 mg/cm 2 or more and 4.0 mg/cm 2 or less, more preferably 0 mg/cm 2 or more and 3.0 mg/cm 2 or less, and further preferably 0 mg/cm 2 or more and 2.5 mg/cm 2 or less. Maintaining the unit amount of adhering water within the above range reduces the amount of liquid adhering to the electrode according to this embodiment when it is withdrawn from an electrolytic bath or a cleaning tank, thereby reducing the loss of the electrolyte solution and the cleaning solution.
• the contact angle of the electrode according to this embodiment is preferably more than 90° and less than 180°, more preferably 95° or more and less than 180°, and further preferably 100° or more and less than 180°.
• a contact angle exceeding 90° reduces the amount of liquid adhering to the electrode according to this embodiment when it is withdrawn from an electrolytic bath or a cleaning tank, thereby facilitating a further reduction in the loss of the electrolyte solution and the cleaning solution.
• the contact angle is a value determined by the following method.
• a contact angle meter e.g., device name: DMo-501, manufactured by Kyowa Interface Science Co., Ltd.
• measurement/analysis software e.g., FAMAS1, manufactured by Kyowa Interface Science Co., Ltd.
• the contact angle (°) of the electrode with respect to pure water is measured according to the ⁇ /2 method, using the following equation. The measurement is conducted three times, and the arithmetic average of the results is used as the contact angle of the electrode according to this embodiment.
• Contact angle ° 2 ⁇ arctan h / r
• the electrode according to this embodiment can be used as a cathode for producing electrolytic manganese dioxide. It is preferable that the voltage in electrolysis performed under the following conditions using a plate-shaped electrode according to this embodiment having a height of 250 mm, a width of 200 mm, and a thickness of 10 mm as a cathode (hereinafter, this voltage is also referred to as "bath voltage”) be 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 further preferably 1.23 V or more and 1.70 V or less.
• electrolysis Prior to electrolysis, the electrolyte solution and paraffin are charged into an electrolytic bath, which is then heated to 96°C.
• the cathode and anodes are installed in the bath in the order of anode, cathode and anode at intervals of 50 mm, with the principal faces (height ⁇ width faces) of the electrodes facing one another. Subsequently, electrolysis may be performed for 24 hours.
• the concentration of manganese ions decreases as a result of deposition of electrolytic manganese dioxide with the progress of the electrolytic reaction.
• an aqueous manganese sulfate solution electrolytic feed solution
• the electrode according to this embodiment is characterized in that, when the electrode is immersed in a mixed aqueous solution of sulfuric acid and manganese sulfate under the following immersion conditions, the platinum content in the mixed aqueous solution of sulfuric acid and manganese sulfate (hereinafter, this platinum content is also referred to as "amount of platinum eluted") after immersion is, for example, 0 mg/L or more and 2 mg/L or less, 0 mg/L or more and 1 mg/L or less, 0 mg/L or more and 0.5 mg/L or less, or 0 mg/L or more and 0.1 mg/L or less.
• the electrode according to this embodiment be unlikely to cause platinum elution even during a non-electrolytic period after the electrolytic reaction. It is more preferable that, when electrolysis is performed under the following electrolysis conditions using the electrode according to this embodiment, the platinum concentration in the electrolyte solution which is measured 3 hours after the electrolysis is stopped (hereinafter, this platinum concentration is also referred to as "amount of non-electrolytic elution”) be 0 mg/L or more and 2 mg/L or less, 0 mg/L or more and 1 mg/L or less, 0 mg/L or more and 0.5 mg/L or less, or 0 mg/L or more and 0.1 mg/L or less.
• the electrode according to this embodiment makes it possible to reduce the electrolytic voltage in an electrolytic reaction using the electrode. Accordingly, the electrode according to this embodiment can be used as an electrode (cathode) for producing electrolytic manganese dioxide. This enables efficient production of electrolytic manganese dioxide.
• a method for producing the electrode according to this embodiment includes, for example, supporting a noble metal by performing electroplating or electroless plating in an electrolyte solution containing noble metal ions using platinum with a graphite plate serving as a working electrode such that the above-described supported amount is achieved.
• the method for producing the electrode also includes a paraffin-containing step in which paraffin is incorporated into the platinum-modified graphite.
• a preferable method for producing the electrode according to this embodiment includes a platinum-modifying step in which platinum is supported on graphite to obtain platinum-modified graphite, and a paraffin-containing step in which the platinum-modified graphite is brought into contact with paraffin to incorporate the paraffin into the platinum-modified graphite.
• the method for supporting platinum on graphite in the platinum-modifying step is not particularly limited and may be any method capable of supporting platinum on graphite.
• the method is preferably a plating method, more preferably at least one of electroplating and electroless plating, and further preferably electroplating.
• electroplating may be performed using a titanium-platinum electrode as an anode, graphite as a cathode, and a mixed solution of chloroplatinic acid (VI) and hydrochloric acid as a plating solution, at a temperature of 50°C or more and 100°C or less and a current density of 0.3 A/dm 2 or more and 2.0 A/dm 2 or less. It is preferable to perform the electroplating at a temperature of 60°C or more and 90°C or less and a current density of 0.5 A/dm 2 or more and 1.5 A/dm 2 or less.
• VI chloroplatinic acid
• hydrochloric acid as a plating solution
• the plating time may be set appropriately in accordance with the intended amount of platinum supported and the size of the graphite (electrode base material). For example, the plating time may be 15 seconds or more and 2 minutes or less.
• the method may further include a cleaning step in which the platinum-modified graphite is cleaned subsequent to the platinum-modifying step and prior to the paraffin-containing step.
• the cleaning step reduces impurities such as the plating solution remaining on the surface.
• the cleaning method used in the cleaning step may be any method capable of reducing impurities.
• An example includes a cleaning method using pure water.
• a preferable cleaning method includes immersion in warm water at 30°C or more and 100°C or less for 10 minutes or more and 60 minutes or less, followed by cleaning with pure water.
• drying conditions may be set appropriately. For example, drying may be performed at 30°C or more and 100°C or less under an air atmosphere for 1 hour or more and 24 hours or less.
• the paraffin-containing step is a step in which the platinum-modified graphite is brought into contact with paraffin to incorporate the paraffin into the platinum-modified graphite.
• the contact between the platinum-modified graphite and paraffin may be any method capable of causing paraffin to adhere to the surface of the platinum-modified graphite and to permeate into the inside of the platinum-modified graphite.
• the platinum-modified graphite may be immersed in pure water at a temperature of 60°C or more and less than 100°C, having a paraffin layer on the surface.
• the pure water is preferably at a temperature of 80°C or more and less than 100°C.
• the thickness of the paraffin layer may be any thickness that allows paraffin to uniformly adhere to the surface of the platinum-modified graphite, and may be, for example, 1 cm or more and 2 cm or less.
• the immersion time may be set appropriately and is, for example, 1 hour or more and 24 hours or less, preferably 5 hours or more and 24 hours or less.
• the platinum-modified graphite is preferably immersed in warm water not containing paraffin, followed by cleaning with warm water and drying. This removes paraffin remaining on the uppermost surface of the platinum-modified graphite.
• the measurement of the amount of metal supported was conducted by measuring the metal concentration in a measurement solution by inductively coupled plasma emission spectroscopy (ICP method) using a common inductively coupled plasma emission spectrometer (trade name: OPTIMA 3000 DV, manufactured by PerkinElmer).
• ICP method inductively coupled plasma emission spectroscopy
• OPTIMA 3000 DV common inductively coupled plasma emission spectrometer
• the measurement solution was prepared by the following method. First, the region of an electrode sample in which platinum had been supported was pulverized using a stamp mill until it passed through a sieve with an opening of 0.5 mm. Note that, as the electrode sample, a portion immersed in the plating bath described below was cut out.
• the pulverized electrode sample (fragments) was charged into a magnetic crucible and then heated at 600°C under an air atmosphere for 70 hours. Subsequently, 1 mL of concentrated sulfuric acid and 2 mL of concentrated nitric acid were added under an air atmosphere. The resulting mixture was heated and evaporated to dryness. Subsequently, aqua regia was added to dissolve the residue to form a solution. Pure water was added to the solution until the volume of the solution reached 1 L. Thus, a measurement solution was obtained. The metal concentration in the measurement solution was measured.
• G represents the amount of metal supported (mg/cm 2 )
• C represents the metal concentration (mg/L) in the measurement solution obtained by the ICP measurement
• W1 represents the mass (g) of the electrode sample after cutting out
• W2 represents the mass (g) of the pulverized electrode sample (fragments)
• A represents the surface area (cm 2 ) of the region of the platinum-modified graphite which was cut out and in which platinum had been supported.
• the paraffin content in the electrode sample was determined by gas chromatography using a gas chromatograph (Agilent 7890A GC, manufactured by Agilent Technologies, Inc.).
• a hexane solution containing paraffin (trade name: Paraffin Wax-125, manufactured by Nippon Seiro Co., Ltd.) at a concentration of 10 mg/L was used.
• the amount of metal eluted from the electrode sample into the initial electrolyte solution was measured by the ICP method using a common inductively coupled plasma emission spectrometer (trade name: OPTIMA 3000 DV, PerkinElmer).
• the metal concentration in a diluted electrolyte solution which was obtained by diluting the initial electrolyte solution (described below) tenfold with pure water, was measured by the ICP measurement. The measured metal concentration was multiplied by ten, and the resulting value was used as the metal concentration (mg/L) in the initial electrolyte solution.
• the amount of water in the electrode in each of the examples and the comparative examples was determined by measuring the mass of the electrode before and after immersion in pure water. Specifically, a screw-cap bottle containing pure water was placed on an electronic balance. A rod-shaped electrode was immersed in the screw-cap bottle such that entire electrode surface was immersed in pure water. After immersion for 10 seconds, the rod-shaped electrode was taken out of the screw-cap bottle. The difference between the values of the electronic balance before and after the immersion of the electrode (i.e., the difference between the mass before immersion of the rod-shaped electrode and the mass after taking out the rod-shaped electrode) was calculated and used as the amount of adhering water (mg).
• a rod-shaped electrode As the measurement sample, a rod-shaped electrode, a portion located above 5 cm from the bottom face of which was covered with a PTFE tape, was used.
• the measurement was conducted three times, and the arithmetic average of the results was used as the amount of adhering water (mg).
• the amount of adhering water (mg) was divided by the surface area (cm 2 ) of the electrode, and the resulting value was used as the unit amount of adhering water (mg/cm 2 ).
• the surface area (cm 2 ) of the electrode was defined as the surface area (cm 2 ) of the region in which platinum had been supported.
• the measurement was conducted three times, and the arithmetic average of the results was used as the contact angle (°).
• the bath voltage and electrode durability of the electrode in each of the examples and the comparative examples were determined by electrolytically synthesizing electrolytic manganese dioxide using an electrolytic bath including the graphite plate of each of the examples and the comparative examples serving as a cathode, a titanium plate serving as an anode, and a mixed aqueous solution of manganese sulfate and sulfuric acid serving as an electrolyte solution.
• the electrolyte solution used was a mixed aqueous solution of manganese sulfate and sulfuric acid having a manganese sulfate concentration of 85.4 g/L and a sulfuric acid concentration of 27.0 g/L.
• One plate-shaped electrode (cathode) of each of the examples and the comparative examples and two titanium plate anodes (height: 250 mm, width: 200 mm, thickness: 5 mm) were immersed 160 mm in the electrolyte solution so as to be perpendicular to the liquid surface of the electrolyte solution.
• the cathode and the anodes were fixed at intervals of 50 mm such that their principal faces (the height ⁇ width faces) faced one another (i.e., in the order of anode, cathode and anode).
• the temperature of the electrolyte solution was increased to 96°C over 3 hours. After completion of the temperature rise, 50 mL of the electrolyte solution was collected (hereinafter, the electrolyte solution collected after completion of the temperature rise is also referred to as "initial electrolyte solution").
• a DC stabilized power supply (PAN-18-10A, manufactured by Kikusui Electronics Corporation) was connected, and electrolytic synthesis of electrolytic manganese dioxide was conducted at a constant current of 4.48 A (i.e., 0.65 A/dm 2 with respect to the cathode).
• an aqueous manganese sulfate solution (electrolyte feed solution) having a manganese sulfate concentration of 118 g/L was continuously supplied to the electrolytic bath.
• the electrolyte solution was continuously withdrawn from the electrolytic bath such that the amount of the electrolyte solution in the electrolytic bath was maintained at 6 L. 24 hours after the start of electrolysis, the voltage displayed on the DC stabilized power supply was read and used as the bath voltage.
• Electrolysis was further continued for six days and stopped on the seventh day from the start of electrolysis.
• 50 mL of the electrolyte solution was collected 3 hours after stopping the electrolysis (hereinafter, the electrolyte solution collected 3 hours after stopping the electrolysis 7 days after the start of electrolysis is referred to as "final electrolyte solution").
• the amount of metal eluted into the final electrolyte solution that is, the amount of non-electrolytic elution (mg/L) was measured in the same manner as described above in ⁇ Measurement of Amount of Metal Eluted into Initial Electrolyte Solution>.
• All 6 surfaces of a rectangular parallelepiped (columnar) graphite (PSG322, manufactured by SEC Carbon, Ltd.) having a length (height) of 100 mm, a width of 10 mm, and a thickness of 10 mm were polished with 400-grit abrasive paper (hereinafter, the above-described graphite subjected to the polishing is also referred to as "graphite rod").
• the portion of the graphite rod extending from 50 mm to 70 mm from the bottom face was covered with a masking tape for plating (manufactured by 3M Japan Limited) (the portion from 50 mm to 70 mm in the longitudinal direction from the bottom face was covered).
• the portion of the graphite rod extending up to 60 mm from the bottom face (60 mm in the height direction from the bottom face of the graphite rod) and a titanium-platinum electrode were immersed in an electrolyte solution containing 10 g/L of chloroplatinic acid (VI), and 20 g/L of hydrochloric acid, which was maintained at 70°C, to form a plating bath including the titanium-platinum electrode serving as an anode and the graphite rod serving as a cathode.
• VI chloroplatinic acid
• electroplating was performed at cathode current density of 1.0 A/dm 2 for 2 minutes to support platinum on the graphite rod (i.e., the portion extending up to 50 mm in the longitudinal direction from the bottom face of the graphite rod).
• the graphite rod with the masking tape removed was immersed in warm water at 50°C for 30 minutes, washed with running water, and then dried at 50°C under an air atmosphere for 12 hours (hereinafter, the steps from covering with a masking tape to drying at 50°C are also referred to as "platinum plating step").
• the electrode was immersed overnight up to a height of 6.5 cm from the bottom face in a liquid in which paraffin (trade name: Paraffin Wax-125, manufactured by Nippon Seiro Co., Ltd., melting point: 53°C) melted in warm water at 97°C was floated to a thickness of 1.5 cm.
• paraffin trade name: Paraffin Wax-125, manufactured by Nippon Seiro Co., Ltd., melting point: 53°C
• the electrode was transferred to a beaker filled with warm water at 75°C. Then, warm water at 75°C was further poured over it for 10 minutes to remove the paraffin from the surface. Subsequently, the electrode was air-dried at room temperature for one day.
• the resulting electrode was used as an electrode of Example 1 (hereinafter, the steps from immersion in the warm water with floating paraffin to air-drying are also referred to as "paraffin-containing step").
• the unit amount of platinum supported was 140 ⁇ g/cm 2 , the paraffin content was 2.9 mg/g, the amount of adhering water was 41 mg, the unit amount of adhering water was 2.0 mg/cm 2 , and the contact angle was 124°.
• An electrode of Example 2 was obtained in the same manner as in Example 1, except that the electroplating time was changed to 30 seconds.
• the unit amount of platinum supported was 31 ⁇ g/cm 2 , the paraffin content was 4.5 mg/g, the amount of adhering water was 48 mg, the unit amount of adhering water was 2.3 mg/cm 2 , and the contact angle was 123°.
• a graphite rod prepared in the same manner as in Example 1 was used as an electrode of Comparative Example 1 (i.e., the same procedure as in Example 1 was conducted, except that the platinum plating step and the paraffin impregnation step were not conducted).
• the amount of adhering water of the electrode of this comparative example was 95 mg, the unit amount of adhering water was 4.5 mg/cm 2 , and the contact angle was 84°.
• An electrode of black this comparative example was prepared by conducting the same procedure as in Example 1, except that the platinum plating step was not conducted.
• An electrode of Comparative Example 3 was prepared by conducting the same procedure as in Example 1, except that the paraffin impregnation step was not conducted.
• the unit amount of platinum supported was 140 ⁇ g/cm 2 , no paraffin was detected (the paraffin content was 0 mg/g), the amount of adhering water was 95 mg, the unit amount of adhering water was 4.5 mg/cm 2 , and the contact angle was 81°.
• An electrode of Comparative Example 4 was prepared by conducting the same procedure as in Example 2, except that the paraffin impregnation step was not conducted.
• the unit amount of platinum supported was 32 ⁇ g/cm 2 , no paraffin was detected, the amount of adhering water was 110 mg, the unit amount of adhering water was 5.2 mg/cm 2 , and the contact angle was 74°.
• a rectangular parallelepiped graphite (PSG322, manufactured by SEC Carbon, Ltd., hereinafter, also referred to as "graphite plate") having a height of 250 mm, a width of 200 mm, and a thickness of 10 mm was used.
• the portion of the graphite plate extending from 160 mm to 185 mm from the bottom face was covered with a masking tape for plating (manufactured by 3M Japan Limited).
• the portion of the graphite plate extending up to 160 mm from the bottom face was immersed in an electrolyte solution containing 10 g/L of chloroplatinic acid (VI) and 20 g/L of hydrochloric acid, which was maintained at 70°C.
• VI chloroplatinic acid
• hydrochloric acid hydrochloric acid
• electroplating was performed at a cathode current density of 1.0 A/dm 2 for 4 minutes to support platinum on the electrode. Then, the electrode with the masking tape removed was immersed in warm water at 50°C for 30 minutes, followed by washing with running water and drying at 50°C for 12 hours. Subsequently, the electrode was immersed overnight up to a height of 15 cm from the bottom face in warm water at 97°C, on which paraffin (trade name: Paraffin Wax-125, manufactured by Nippon Seiro Co., Ltd., melting point: 53°C) was floated to a thickness of 1.5 cm.
• paraffin trade name: Paraffin Wax-125, manufactured by Nippon Seiro Co., Ltd., melting point: 53°C
• the electrode After being withdrawn from the warm water with floating paraffin, and before the paraffin solidified, the electrode was immersed in a container filled with warm water at 75°C. Then, warm water at 75°C was further poured over it for 10 minutes to remove the paraffin from the surface. Subsequently, the electrode was air-dried at room temperature for one day. The resulting electrode was used as an electrode of Example 3.
• the unit amount of platinum supported was 400 ⁇ g/cm 2 , the paraffin content was 44 mg/g, the contact angle was 133°, and the bath voltage was 1.52 V. Since no platinum was detected in either the initial electrolyte solution or the final electrolyte solution, both the amount of platinum eluted and the amount of non-electrolytic elution were 0 mg/L.
• An electrode was prepared in the same manner as in Example 3, except that the electroplating time was changed to 2 minutes, and was used as an electrode of this example.
• the unit amount of platinum supported was 130 ⁇ g/cm 2 , the paraffin content was 19 mg/g, the contact angle was 114°, and the bath voltage was 1.50 V. Since no platinum was detected in either the initial electrolyte solution or the final electrolyte solution, both the amount of platinum eluted and the amount of non-electrolytic elution were 0 mg/L.
• An electrode was prepared in the same manner as in Example 3, except that the electroplating time was changed to 1 minute, and was used as an electrode of Example 5.
• the unit amount of platinum supported was 59 ⁇ g/cm 2 , the paraffin content was 9.4 mg/g, the contact angle was 107°, and the bath voltage was 1.54 V. Since no platinum was detected in either the initial electrolyte solution or the final electrolyte solution, both the amount of platinum eluted and the amount of non-electrolytic elution were 0 mg/L.
• An electrode was prepared in the same manner as in Example 3, except that the electroplating time was changed to 30 seconds, and was used as an electrode of Example 6.
• the unit amount of platinum supported was 21 ⁇ g/cm 2 , the paraffin content was 21 mg/g, the contact angle was 112°, and the bath voltage was 1.62 V. Since no platinum was detected in either the initial electrolyte solution or the final electrolyte solution, both the amount of platinum eluted and the amount of non-electrolytic elution were 0 mg/L.
• An electrode was prepared in the same manner as in Example 3, except that the electroplating time was changed to 15 seconds, and was used as an electrode of Example 7.
• the unit amount of platinum supported was 3.5 ⁇ g/cm 2 , the paraffin content was 39 mg/g, the contact angle was 115°, and the bath voltage was 1.68 V. Since no platinum was detected in either the initial electrolyte solution or the final electrolyte solution, both the amount of platinum eluted and the amount of non-electrolytic elution were 0 mg/L.
• the graphite plate was used as an electrode of this example (i.e., the same procedure as in Example 3 was conducted, except that the platinum plating step and the paraffin impregnation step were not conducted).
• the bath voltage of the electrode of this comparative example was measured. Note that the measurement was conducted without adding paraffin to the electrolytic bath, and no analysis of the electrolyte solution was conducted.
• the contact angle was 84°, and the bath voltage was 1.67 V.
• An electrode of Comparative Example 6 was prepared by impregnating the graphite plate with paraffin by conducting the same procedure as in Example 3, except that the platinum plating step was not conducted.
• a graphite plate similar to that used in Example 3 was used.
• the portion of the graphite plate extending from 160 mm to 180 mm from the bottom face was covered with a masking tape for plating (manufactured by 3M Japan Limited). Subsequently, the portion of the graphite plate extending up to 160 mm from the bottom face was immersed in an electrolyte solution containing 20 g/L of copper (Cu 2+ ) ions and 40 g/L of sulfuric acid, which was maintained at 70°C.
• Electroplating was performed at a current density of 1.0 A/dm 2 for 10 minutes, using two copper plate electrodes, which were arranged to face the two largest faces of the graphite plate, as anodes and the graphite plate as a cathode, to support copper on both surfaces of the electrode. Then, the electrode with the masking tape removed was immersed in warm water at 50°C for 30 minutes, followed by washing with running water and drying at 50°C for 12 hours. Subsequently, the same paraffin impregnation step as in Example 3 was conducted, and the resulting electrode was used as an electrode of Comparative Example 7.
• the amount of copper supported per unit area on the graphite was 1900 ⁇ g/cm 2 , the paraffin content was 36 mg/g, the contact angle was 112°, and the bath voltage was 1.74 V. Because copper was detected in the initial electrolyte solution and the final electrolyte solution at 22 mg/L and 27 mg/L, respectively, the amount of copper eluted was 22 mg/L, and the amount of non-electrolytic elution was 27 mg/L.
• a graphite plate similar to that used in Example 3 was used.
• the portion of the graphite plate extending from 160 mm to 180 mm from the bottom face was covered with a masking tape for plating (manufactured by 3M Japan Limited). Subsequently, the portion of the graphite plate extending up to 160 mm from the bottom face was immersed in a palladium plating solution (PALLABRIGHT SST-L, manufactured by Japan Pure Chemical Co., Ltd.), which was maintained at 50°C.
• PALLABRIGHT SST-L manufactured by Japan Pure Chemical Co., Ltd.
• Electroplating was performed at a current density of 1.0 A/dm 2 for 15 seconds, using two titanium-platinum electrodes, which were arranged to face the two largest faces of the graphite plate, as anodes and the graphite plate as a cathode, to support palladium on both surfaces of the electrode. Then, the electrode with the masking tape removed was immersed in hot water at 50°C for 30 minutes. Subsequently, the electrode was immersed in a 5% aqueous hydrochloric acid solution at 50°C for 5 minutes, and again immersed in hot water at 50°C for 30 minutes, followed by washing with running water and drying at 50°C for 12 hours. Subsequently, the same paraffin impregnation step as in Example 3 was conducted, and the resulting electrode was used as an electrode of Comparative Example 8.
• the amount of palladium supported per unit area on the graphite was 47 ⁇ g/cm 2 , the paraffin content was 30 mg/g, the contact angle was 126°, and the bath voltage was 1.62 V. Because palladium was not detected in the initial electrolyte solution and was detected in the final electrolyte solution at 2.8 mg/L, the amount of palladium eluted was 0 mg/L, and the amount of non-electrolytic elution was 2.8 mg/L.
• the electrode of the examples reduces the adhesion of water to the electrode by containing paraffin.
• the electrode prevents metal elution into an electrolyte solution during a non-electrolytic period and reduces the voltage during electrolysis, even when the electrolyte solution is at a high temperature and contains sulfuric acid.
• Patent Document 3 discloses that paraffin permeates into graphite and that removing the paraffin improves the performance of a graphite electrode. It has been found that the graphite according to the present invention, by containing paraffin, reduces the amount of liquid adhering to the electrode when it is withdrawn from the liquid.

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