WO2024014344A1 - Hydrogen production method and anode material - Google Patents

Hydrogen production method and anode material Download PDF

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WO2024014344A1
WO2024014344A1 PCT/JP2023/024661 JP2023024661W WO2024014344A1 WO 2024014344 A1 WO2024014344 A1 WO 2024014344A1 JP 2023024661 W JP2023024661 W JP 2023024661W WO 2024014344 A1 WO2024014344 A1 WO 2024014344A1
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mass
overvoltage
electrolytic solution
koh
electrolysis
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French (fr)
Japanese (ja)
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健次 川口
俊之 野平
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国立大学法人京都大学
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    • 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
    • C25B1/02—Hydrogen or oxygen
    • C25B1/04—Hydrogen or oxygen by electrolysis of water
    • 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
    • C25B11/042—Electrodes formed of a single material
    • C25B11/046—Alloys
    • 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
    • C25B15/00—Operating or servicing cells
    • C25B15/02—Process control or regulation
    • C25B15/023—Measuring, analysing or testing during electrolytic production
    • C25B15/025—Measuring, analysing or testing during electrolytic production of electrolyte parameters
    • C25B15/027—Temperature
    • 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
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features

Definitions

  • the present disclosure relates to a method for producing hydrogen and an anode material.
  • One of the water electrolysis methods is alkaline water electrolysis.
  • a potassium hydroxide (KOH) aqueous solution with a concentration of about 30% by weight is used industrially, and the operation is performed at about 80°C. has been done.
  • Electrolysis at a higher temperature is desirable in consideration of overvoltage, but this requires a pressure-sealed structure to suppress evaporation of the electrolytic solution, resulting in large-scale equipment.
  • Patent Document 1 As described in Patent Document 1, in alkaline water electrolysis, it is required to reduce oxygen overvoltage and hydrogen overvoltage from the viewpoint of energy efficiency. In order to reduce overvoltage, optimization of the material of ordinary electrodes is being considered. For example, Patent Document 1 describes that nickel (Ni) is ideal as an anode material, and platinum (Pt) is ideal as a cathode material. It is stated that.
  • Patent Documents 2 and 3 various studies have been made in recent years, and proposals have been made such as plating the surface of the base material with a Ni-based alloy.
  • the present disclosure has been made in view of this situation, and one of its objectives is to provide a method for producing hydrogen that can further reduce the total value of oxygen overvoltage and hydrogen overvoltage compared to conventional techniques. It is.
  • Aspect 1 of the present invention is A step of electrolyzing an electrolytic solution heated to a temperature of 120 ° C. or higher and between a lower limit temperature above the melting point and an upper limit temperature below the boiling point,
  • the electrolytic solution contains 52.3% by mass or more and 90% by mass or less of an alkali metal hydroxide selected from the group consisting of Li, Na, and K.
  • Aspect 2 of the present invention is The manufacturing method according to aspect 1, wherein the electrolytic solution contains 61% by mass or more and 90% by mass or less of the alkali metal hydroxide.
  • Aspect 3 of the present invention is In the electrolysis step, Ni: 25 to 95% by mass, at least one of Fe and Co, and selected from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W.
  • the manufacturing method according to aspect 1 or 2 using an anode containing at least one or more elements.
  • Aspect 4 of the present invention is The manufacturing method according to any one of aspects 1 to 3, wherein the current density in the electrolysis step is 0.5 to 3.0 A/cm 2 .
  • Aspect 5 of the present invention is The manufacturing method according to any one of aspects 1 to 4, wherein the electrolysis step is performed under a pressure of 1 ⁇ 10 5 to 2 ⁇ 10 7 Pa.
  • Aspect 6 of the present invention is Ni: 50 to 75% by mass, at least one or more of Fe and Co, and at least one or more selected from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W.
  • FIG. 1 is a binary system phase diagram of KOH-H 2 O.
  • FIG. 2 shows the relationship between KOH concentration and boiling point in a KOH aqueous solution.
  • FIG. 3 is a schematic diagram of an experimental apparatus for verifying the effects of the embodiment of the present invention.
  • FIG. 4 is a graph showing the relationship between temperature and hydrogen overvoltage when constant current electrolysis is performed at a current density of 0.5 A/cm 2 .
  • FIG. 5 is a graph showing the relationship between temperature and oxygen overvoltage when constant current electrolysis is performed at a current density of 0.5 A/cm 2 .
  • FIG. 6 is a graph showing the relationship between temperature and hydrogen overvoltage when constant current electrolysis is performed at a current density of 1.0 A/cm 2 .
  • FIG. 7 is a graph showing the relationship between temperature and oxygen overvoltage when constant current electrolysis is performed at a current density of 1.0 A/cm 2 .
  • the present inventors have realized a hydrogen production method that can lower the total value of oxygen overvoltage and hydrogen overvoltage compared to the conventional technology in which alkaline water electrolysis was performed at a KOH concentration of 30% by mass and a heating temperature of 80°C. We considered this from various angles.
  • alkaline water electrolysis for example, water is generated in a tank (electrolytic cell) filled with an electrolytic solution containing an alkali metal hydroxide, between an anode (oxygen generating electrode) and a cathode (hydrogen generating electrode), and between the anode and the cathode.
  • a diaphragm capable of separating hydrogen and oxygen and passing a direct current between the anode and the cathode.
  • reactions as shown in the following formulas (1) and (2) may occur.
  • the present inventors considered reducing overvoltage from a completely different perspective from the examination of materials for anodes and cathodes and examination of catalysts, which are normally performed for reducing overvoltage. Specifically, the present inventors considered reducing the overvoltage by promoting the electrode reactions (1) and (2) by increasing the temperature.
  • a conventional aqueous solution with a KOH concentration of 30% by mass has a boiling point of 113° C. at normal pressure, and simply increasing the temperature causes the problem that the amount of volatilization of the KOH aqueous solution increases. Therefore, the present inventors came up with the idea of increasing the KOH concentration to raise the boiling point.
  • the KOH concentration has conventionally been controlled to 30% by mass or less in order to ensure the amount of free water, etc., and increasing the KOH concentration will decrease the amount of free water, which may actually have a negative effect on the overvoltage and, in turn, on the cell voltage. It was widely known.
  • the present inventors have determined that by setting the concentration of alkali metal hydroxide such as KOH contained in the electrolyte to 52.3% by mass or more and 90% by mass or less, the boiling point of the electrolyte can be increased rapidly. Even at this concentration, if electrolysis is performed by heating above 120°C and above the melting point of the electrolytic solution, it will not have a negative effect on overvoltage, and in fact can reduce overvoltage compared to conventional technology. I found out.
  • melting point and boiling point of the electrolytic solution at normal pressure for convenience. That is, “melting point” and “boiling point” in this specification mean the melting point and boiling point at normal pressure, unless otherwise specified.
  • the embodiments of the present invention are not limited to being carried out at normal pressure; for example, it is expected that the effects of the present invention will be obtained without any problems even if carried out under pressures higher than normal pressure. Ru.
  • a method for producing hydrogen according to an embodiment of the present invention includes a step of electrolyzing an electrolytic solution heated to a temperature of 120° C. or higher and between a lower limit temperature equal to or higher than the melting point and an upper limit temperature lower than the boiling point,
  • the liquid contains 52.3% by mass or more and 90% by mass or less of an alkali metal hydroxide selected from the group consisting of Li, Na, and K.
  • the electrolyte contains 52.3% by mass or more and 90% by mass or less of an alkali metal hydroxide (MOH, M is one or more selected from the group consisting of Li, Na, and K). include. Preferably, M is at least one selected from the group consisting of Na and K.
  • the electrolytic solution contains KOH and NaOH
  • the mixing ratio of KOH and NaOH is preferably 10:90 to 90:10 in mass ratio, more preferably 20:80 to 80: 20, more preferably 30:70 to 70:30.
  • the electrolyte may be an alkaline aqueous solution, and the alkali metal hydroxide may dissociate into M + and OH ⁇ in the electrolyte.
  • the electrolytic solution may contain 10% by mass or more and 47.7% by mass or less of water.
  • the water may be, for example, ion-exchanged water, ultrafiltered water or distilled water. If the electrolytic solution contains 10% by mass or more of water, it is sufficient to reduce the overvoltage, and may also contain other substances such as metal hydroxides.
  • the electrolytic solution may contain other metal hydroxides of more than 0% by mass and less than 10% by mass, preferably more than 0% by mass and not more than 5% by mass, Other metal hydroxides include calcium hydroxide (Ca(OH) 2 ) and the like.
  • the electrolytic solution may have a concentration gradient as long as it is adjusted to a desired MOH concentration range on average.
  • the electrolytic solution may be a solidified product thereof before heating, for example, as long as it is liquid after heating (that is, when electrolyzing the electrolytic solution).
  • the electrolytic solution only needs to be adjusted to the above-mentioned desired MOH concentration range after heating (that is, when electrolyzing the electrolytic solution); for example, it is not necessarily adjusted to the above-mentioned desired MOH concentration range before heating. There's no need to be there.
  • the concentration of MOH may be adjusted continuously or intermittently by adding MOH or water.
  • the electrolytic solution (or its solidified product) before heating may be prepared by a known method, for example, by adding MOH or a hydrated product thereof such that the content of MOH is 52.3% by mass or more and 90% by mass or less. It can be prepared by adding it to water as necessary, and stirring and mixing as necessary.
  • MOH metal-oxide-semiconductor
  • a heated electrolyte one of the requirements for further reducing the total value of oxygen overvoltage and hydrogen overvoltage compared to conventional methods is to set the lower limit temperature of the heating temperature to 120°C or higher and the melting point of the electrolyte. There is a need to. Thereby, the electrode reaction can be sufficiently promoted compared to the conventional method.
  • the lower limit temperature of the heating temperature is 120° C. or higher and the melting point of the electrolytic solution +20° C. or higher. Since the higher the heating temperature is, the more the overvoltage can be reduced, the lower limit temperature of the heating temperature is preferably 130°C or higher and the melting point of the electrolytic solution or higher, and 130°C or higher and the melting point of the electrolyte + 20°C or higher. It is more preferable. Further, the lower limit temperature of the heating temperature is preferably 140° C.
  • this heating temperature can be achieved by using various types of waste heat (for example, from various factories and garbage incineration plants), so there is no need to consume extra energy for heating.
  • the melting point of the electrolytic solution can be determined by actual measurement. Specifically, the melting point of an electrolyte can be determined by placing a small amount of the electrolyte (which may be solid at room temperature depending on the MOH concentration) into a platinum sample container and measuring it at a sufficiently low temperature (solid state) using a differential scanning calorimeter (DSC). It can be determined by the rise temperature of the endothermic peak of melting when heated from .
  • DSC differential scanning calorimeter
  • FIG. 1 shows a binary phase diagram of KOH-H 2 O cited from the literature.
  • the horizontal axis of FIG. 1 is the KOH concentration (mass% KOH)
  • the vertical axis is the temperature (°C)
  • the numbers "120" on the vertical axis, "66", “83”, and "86” on the horizontal axis, and the straight lines corresponding thereto were drawn by the applicant. As can be seen from FIG.
  • the melting point of the electrolytic solution is 120° C. or less.
  • the KOH concentration is more than 66% by mass and not more than 83% by mass and more than 86% by mass and not more than 90% by mass, the melting point of the electrolytic solution is more than 120°C.
  • the upper limit temperature of the heating temperature must be lower than the boiling point. If the heating temperature is set above the boiling point, water etc. in the electrolytic solution will evaporate and a solid phase will precipitate, and there is a possibility that the total value of oxygen overvoltage and hydrogen overvoltage cannot be sufficiently reduced, or that electrolysis itself cannot be performed.
  • the upper limit of the heating temperature is lower than the boiling point of the electrolytic solution -20°C.
  • the boiling point of the electrolytic solution can be determined by actual measurement. Specifically, the boiling point of the electrolytic solution can be determined by the following method. An electrolytic solution (which may be solid at room temperature depending on the MOH concentration) is placed in a closed container, and the atmosphere is evacuated by evacuation at a low temperature where the vapor pressure is sufficiently low. Thereafter, the entire container is heated in a sealed state, and the temperature at which the internal pressure reaches 1 ⁇ 10 5 Pa can be set as the boiling point of the electrolytic solution.
  • the boiling point of the electrolyte reference may be made to literature values; for example, for the boiling point of a KOH aqueous solution, see the literature (Robert D.
  • FIG. 2 shows the relationship between KOH concentration and boiling point in a KOH aqueous solution based on the literature.
  • the values of each plot are quoted from the relevant literature, and each approximate straight line and the equation of the straight line ( The formula for the coefficient of determination R2 ) was written by the applicant.
  • the boiling point sharply increases from KOH concentration of 52.3% by mass or higher, which is indicated by the dashed line.
  • the boiling point at the KOH concentration between each plot in FIG. 2 may be determined as changing linearly between each plot (that is, may be interpolated).
  • the boiling point of the electrolytic solution may increase as the mass molar concentration of the electrolytic solution increases.
  • the electrolyte may include LiOH and/or NaOH in place of some or all of the KOH, but since LiOH and NaOH have lower molecular weights than KOH, the content is lower than that of KOH. High molarity can be obtained with Therefore, in the embodiment of the present invention, by setting the MOH concentration to at least 52.3% by mass or more, an electrolytic solution with a sufficiently high boiling point can be obtained.
  • the MOH concentration of the electrolyte is preferably 55% by mass or more, 61% by mass or more, 65% by mass or more, 70% by mass or more, or 75% by mass or more, in this order.
  • the electrolysis step may be performed at normal pressure (approximately 1 ⁇ 10 5 Pa), or may be performed under pressure in advance, considering that the obtained hydrogen will be stored under pressure later.
  • it may be 1 ⁇ 10 5 to 2 ⁇ 10 7 Pa.
  • the upper limit value of the pressure is lower.
  • the upper limit of the pressure is preferably 1 ⁇ 10 7 Pa or less, 5 ⁇ 10 6 Pa or less, 1 ⁇ 10 6 Pa or less, or 5 ⁇ 10 5 Pa or less, in this order.
  • the hydrogen obtained can be treated as a “high-pressure gas” under the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). preferable.
  • GHS Globally Harmonized System of Classification and Labeling of Chemicals
  • anode material that can be used in the above electrolysis step
  • known conductive materials can be used.
  • the Ni content is more preferably 50 to 75% by mass.
  • the content of at least one of Fe and Co (total content of Fe and Co) is preferably 1.0% by mass or more, more preferably 5.0% by mass or more.
  • At least one content selected from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W (Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, The total content of Ta and W is preferably 0.1% by mass or more, more preferably 3.0% by mass or more.
  • the anode material comprises Ni, at least one of Fe and Co, and from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta and W. and at least one selected one or more in the above content, and the remainder may be unavoidable impurities.
  • Unavoidable impurities refer to elements other than the elements specified above that are brought in depending on the circumstances of raw materials, materials, manufacturing equipment, etc., and may be, for example, 1.0% by mass or less in total.
  • the cathode material known conductive materials such as platinum, nickel, etc. can be used.
  • the diaphragm material known diaphragm materials for alkaline water electrolysis, such as porous insulating materials, can be used.
  • Known materials can be used as appropriate for other members (tank, packing, etc.).
  • fluororesin can be used for the tank and packing.
  • the current density could only be increased to, for example, about 0.2 A/cm 2 due to high oxygen overvoltage and high hydrogen overvoltage.
  • the current density can be increased and the amount of hydrogen generated can be increased.
  • the upper limit of the current density is not particularly limited, but if the current density is increased too much, voltage loss other than overvoltage may increase, so it is preferably 3.0 A/cm 2 or less, more preferably 2.0 A/cm 2 or less. It is 0A/ cm2 or less.
  • Ni-based alloys have been considered as anode materials.
  • a method is adopted in which alloy plating is applied to the surface of the electrode base material.
  • the present inventors have specifically combined Ni: 25 to 95% by mass (preferably Ni: 50 to 75% by mass), at least one of Fe and Co, Al, Ti, Cr,
  • an anode material containing at least one element selected from the group consisting of Mn, Cu, Zn, Nb, Mo, Ta, and W oxygen can be significantly reduced from room temperature to high temperature electrolysis. It was found that the overvoltage was reduced.
  • the content of at least one of Fe and Co is preferably 1.0% by mass or more, more preferably 5.0% by mass or more.
  • the total content of Ta and W is preferably 0.1% by mass or more, more preferably 3.0% by mass or more.
  • the anode material comprises Ni, at least one of Fe and Co, and from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta and W. and at least one selected one or more in the above content, and the remainder may be unavoidable impurities.
  • Unavoidable impurities refer to elements other than the elements specified above that are brought in depending on the circumstances of raw materials, materials, manufacturing equipment, etc., and may be, for example, 1.0% by mass or less in total.
  • FIG. 3 is a schematic diagram of an experimental apparatus for verifying the effects of the embodiment of the present invention.
  • a tank 1 is filled with an electrolytic solution (KOH aqueous solution) 2 having a predetermined concentration.
  • a working electrode 3, a counter electrode 4, a reference electrode 5, and a thermometer 6 are arranged in the electrolytic solution 2. Note that fluororesin was used for the tank 1 and packing (not shown).
  • a heater 7 is arranged outside the tank 1. Further, Ar gas was flowing into the tank 1, and the pressure inside the tank 1 was adjusted to 1.0 ⁇ 10 5 to 1.1 ⁇ 10 5 Pa.
  • Ni, Hastelloy (registered trademark) C-276 Ni: 57% by mass, Fe: 4 to 7% by mass, Mo: 17% by mass, Cr: 16% by mass, and W: 3 to 4.5% by mass
  • a flag electrode of one of Pt (an alloy containing % by mass, hereinafter sometimes referred to as "HC-276") and Pt was used, and the electrode area was 0.157 cm 2 in both cases.
  • a platinum wire electrode ( ⁇ 2 mm) was used as the counter electrode, and the electrode area was 1.92 cm 2 .
  • a palladium hydride (Pd-H) electrode was used as a reference electrode, and the potential was calibrated using a reversible hydrogen electrode (RHE) standard.
  • RHE reversible hydrogen electrode
  • the concentration of the KOH aqueous solution was 30% by mass, which is conventional, or 85% by mass, which satisfies the requirements of the embodiment of the present invention.
  • the heating temperature was 25°C or 80°C
  • the concentration of the KOH aqueous solution was 85% by mass
  • the heating temperature was 150°C.
  • Constant current electrolysis was performed at a current density of ⁇ 0.5 A/cm 2 or ⁇ 1.0 A/cm 2 .
  • Figure 4 shows the results of electrolysis using Ni or Pt as the working electrode and a constant current density of -0.5 A/cm 2 so that hydrogen is generated from the working electrode (that is, using the working electrode as the cathode). This is the result of measuring hydrogen overvoltage versus heating temperature. In this measurement, the electrode potential after IR correction in a steady state was determined, and the hydrogen overvoltage was calculated from the difference between the electrode potential and the equilibrium potential. Note that the equilibrium potential of hydrogen generation at each heating temperature is 0V vs. It is RHE. As shown in FIG. 4, when using either Ni or Pt for the working electrode, the KOH concentration satisfies the requirements of the embodiment of the present invention compared to the conventional KOH concentration of 30% by mass and heating temperature of 80°C.
  • the hydrogen overvoltage significantly decreased. Furthermore, as can be seen from Figure 4, the hydrogen overvoltage tends to decrease as the heating temperature increases; for example, when heated to 120°C or higher (and above the melting point of the electrolyte), which is sufficiently higher than the conventional heating temperature ( ⁇ 80°C). It can be said that hydrogen overvoltage can be further reduced compared to conventional techniques by performing electrolysis.
  • Ni, HC-276, or Pt is used for the working electrode, and the current density is kept constant at 0.5 A/ cm2 , and electrolysis is performed so that oxygen is generated from the working electrode (that is, the working electrode is used as the anode).
  • the electrode potential after IR correction in a steady state was determined, and the oxygen overvoltage was calculated from the difference between the electrode potential and the equilibrium potential. Note that the equilibrium potential for oxygen generation at each heating temperature is 1.229V vs. 25°C. RHE, 1.183V vs. 80°C. RHE, 1.155V vs. 150°C. It was set as RHE.
  • the equilibrium potential was determined by the standard theoretical decomposition voltage calculated from the standard Gibbs energy change of the water electrolysis reaction at each heating temperature.
  • the requirements of the embodiment of the present invention are When the KOH concentration was 85% by mass and the heating temperature was 150° C., the oxygen overvoltage was significantly reduced. Furthermore, as can be seen from Figure 5, the oxygen overvoltage tends to decrease as the heating temperature increases; for example, when heated to 120°C or higher (and above the melting point of the electrolyte), which is sufficiently higher than the conventional heating temperature ( ⁇ 80°C).
  • oxygen overvoltage can be further reduced compared to conventional techniques by performing electrolysis. Comparing the working electrodes (anodes), when HC-276 was used as the anode, the oxygen overvoltage was the lowest and favorable results were obtained. This is because HC-276 is made from the group consisting of Ni: 25 to 95% by mass, at least one of Fe and Co, and Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W. This is considered to be due to the fact that the selected at least one or more are included.
  • Figure 6 shows the results when electrolysis is performed using Ni or Pt as the working electrode, with a constant current density of -1.0 A/ cm2 , and hydrogen is generated from the working electrode (that is, with the working electrode as the cathode). This is the result of measuring hydrogen overvoltage versus heating temperature. In this measurement, the electrode potential after IR correction in a steady state was determined, and the hydrogen overvoltage was calculated from the difference between the electrode potential and the equilibrium potential. Note that the equilibrium potential of hydrogen generation at each heating temperature is 0V vs. It is RHE. As shown in Figure 6, regardless of whether Ni or Pt is used for the working electrode and the current density is -1.0A/ cm2 , the conventional KOH concentration is 30% by mass and the heating temperature is 80°C.
  • the hydrogen overvoltage was significantly reduced. Furthermore, as can be seen from Figure 6, even when the current density is set to -1.0 A/cm 2 , the hydrogen overvoltage tends to decrease as the heating temperature increases, and for example, the hydrogen overvoltage tends to decrease as the heating temperature increases. It can be said that by performing electrolysis by heating to a temperature of 120° C. or higher (and higher than the melting point of the electrolytic solution), the hydrogen overvoltage can be further reduced compared to the conventional technology.
  • Ni, HC-276, or Pt is used as the working electrode, and the current density is kept constant at 1.0 A/ cm2 , and electrolysis is performed so that oxygen is generated from the working electrode (that is, the working electrode is used as the anode).
  • the electrode potential after IR correction in a steady state was determined, and the oxygen overvoltage was calculated from the difference between the electrode potential and the equilibrium potential. Note that the equilibrium potential for oxygen generation at each heating temperature is 1.229V vs. 25°C. RHE, 1.183V vs. 80°C. RHE, 1.155V vs. 150°C. It was set as RHE.
  • the equilibrium potential was determined by the standard theoretical decomposition voltage calculated from the standard Gibbs energy change of the water electrolysis reaction at each heating temperature.
  • the current density is set to 1.0 A/ cm2 , compared to the conventional KOH concentration of 30 mass% and heating temperature of 80 °C, At a KOH concentration of 85% by mass and a heating temperature of 150° C., which meet the requirements of the embodiment of the present invention, the oxygen overvoltage was significantly reduced.
  • the current density is set to 1.0 A/cm 2 , the oxygen overvoltage tends to decrease as the heating temperature increases, and for example, the oxygen overvoltage tends to decrease as the heating temperature increases.
  • HC-276 is made from the group consisting of Ni: 25 to 95% by mass, at least one of Fe and Co, and Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W. This is considered to be due to the fact that the selected at least one or more are included.
  • Example 1 The KOH aqueous solution in Example 1 was changed to a mixed aqueous solution of NaOH and KOH, the mass ratio of NaOH:KOH:H 2 O was 30:43:27 (that is, the MOH concentration was 73% by mass), and the heating temperature was 130 ° C. And so. Note that the equilibrium potential of oxygen generation in this case is 1.160V vs. It was set as RHE. In other respects, constant current electrolysis was performed in the same manner as in Example 1.
  • Patent Document 1 the configuration of the prior art example in Table 1 is as follows: KOH concentration: 30% by mass, heating temperature: 80°C, anode: Ni, and cathode: Pt (as described above) , Patent Document 1 describes that Ni is ideal for the anode and Pt is ideal for the cathode).
  • Examples 1 to 4 of the present invention which meet the requirements of the embodiment of the present invention, can reduce the total value of hydrogen overvoltage and oxygen overvoltage (total overvoltage) compared to the prior art examples.
  • the preferred requirements of the embodiments of the present invention i.e., the anode contains 25 to 95% by mass of Ni, at least one of Fe and Co, Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, It can be seen that Examples 2 and 4 of the present invention, which satisfy at least one selected from the group consisting of Ta and W, can further reduce the oxygen overvoltage than Examples 1 and 3 of the present invention.

Abstract

A hydrogen production method comprising a step for electrolyzing an electrolytic solution heated to a temperature that is not lower than 120°C and that is between a lower limit temperature not lower than the melting point and an upper limit temperature lower than the boiling point, wherein the electrolytic solution contains 52.3-90 mass% of a hydroxide of an alkali metal which is at least one selected from the group consisting of Li, Na, and K.

Description

水素の製造方法および陽極材料Hydrogen production method and anode material
　本開示は水素の製造方法および陽極材料に関する。 The present disclosure relates to a method for producing hydrogen and an anode material.
　太陽光および風力などの再生可能エネルギーは間欠性電源であるため、その大量導入に伴って需給バランスの調整が困難になる。その解決策として、大量に発生する余剰電力を、水電解により水素に変換して貯蔵及び輸送し、必要な時及び場所で、燃料電池及び／又は水素タービンにより電力に再変換する、いわゆる「水素エネルギーシステム」が期待されている。 Renewable energies such as solar and wind power are intermittent power sources, so their large-scale introduction will make it difficult to balance supply and demand. As a solution to this problem, a large amount of surplus electricity is converted into hydrogen through water electrolysis, stored and transported, and then reconverted into electricity using fuel cells and/or hydrogen turbines when and where it is needed. energy system" is expected.
　水電解法の１つとして、アルカリ水電解が挙げられる。例えば特許文献１に記載されているように、従来のアルカリ水電解において、工業的には、濃度が重量比で約３０質量％の水酸化カリウム（ＫＯＨ）水溶液が使用され、約８０℃で稼動されている。過電圧を考慮すればより高い温度での電解が望ましいが、電解液の蒸発を抑制するために加圧密封構造が必要になるなど、設備が大掛かりになる問題がある。 One of the water electrolysis methods is alkaline water electrolysis. For example, as described in Patent Document 1, in conventional alkaline water electrolysis, a potassium hydroxide (KOH) aqueous solution with a concentration of about 30% by weight is used industrially, and the operation is performed at about 80°C. has been done. Electrolysis at a higher temperature is desirable in consideration of overvoltage, but this requires a pressure-sealed structure to suppress evaporation of the electrolytic solution, resulting in large-scale equipment.
　特許文献１に記載されているように、アルカリ水電解において、エネルギー効率の観点から、酸素過電圧及び水素過電圧を低減することが求められている。過電圧を低減するため、通常電極の材質の最適化が検討されており、例えば、特許文献１には、陽極の材質としてニッケル（Ｎｉ）が、陰極の材質として白金（Ｐｔ）が、それぞれ理想的であることが記載されている。 As described in Patent Document 1, in alkaline water electrolysis, it is required to reduce oxygen overvoltage and hydrogen overvoltage from the viewpoint of energy efficiency. In order to reduce overvoltage, optimization of the material of ordinary electrodes is being considered. For example, Patent Document 1 describes that nickel (Ni) is ideal as an anode material, and platinum (Pt) is ideal as a cathode material. It is stated that.
　電極材料については、近年種々の検討がなされ、基材表面にＮｉ系合金をめっきする等の提案もなされている（特許文献２および３）。 Regarding electrode materials, various studies have been made in recent years, and proposals have been made such as plating the surface of the base material with a Ni-based alloy (Patent Documents 2 and 3).
特開２０１３－１８９６９９号公報Japanese Patent Application Publication No. 2013-189699 特開２０１８－１２７６６４号公報JP2018-127664A 特開２０２３－０１１３１１号公報JP2023-011311A
　従来技術において、アルカリ水電解における酸素過電圧及び水素過電圧は依然として高く、さらなる改善が求められている。 In the prior art, the oxygen overvoltage and hydrogen overvoltage in alkaline water electrolysis are still high, and further improvements are required.
　本開示はこのような状況に鑑みてなされたものであり、その目的の１つは、従来技術と比較して酸素過電圧および水素過電圧の合計値をより低減できる、水素の製造方法を提供することである。 The present disclosure has been made in view of this situation, and one of its objectives is to provide a method for producing hydrogen that can further reduce the total value of oxygen overvoltage and hydrogen overvoltage compared to conventional techniques. It is.
　本発明の態様１は、
　１２０℃以上で且つ融点以上の下限温度と、沸点未満の上限温度と、の間の温度に加熱した電解液を電解する工程を含み、
　前記電解液は、Ｌｉ、ＮａおよびＫからなる群から選択されるいずれか一種以上であるアルカリ金属の水酸化物を５２．３質量％以上９０質量％以下含む、水素の製造方法である。 Aspect 1 of the present invention is
A step of electrolyzing an electrolytic solution heated to a temperature of 120 ° C. or higher and between a lower limit temperature above the melting point and an upper limit temperature below the boiling point,
In this method, the electrolytic solution contains 52.3% by mass or more and 90% by mass or less of an alkali metal hydroxide selected from the group consisting of Li, Na, and K.
　本発明の態様２は、
　前記電解液は、前記アルカリ金属の水酸化物を６１質量％以上９０質量％以下含む、態様１に記載の製造方法である。 Aspect 2 of the present invention is
The manufacturing method according to aspect 1, wherein the electrolytic solution contains 61% by mass or more and 90% by mass or less of the alkali metal hydroxide.
　本発明の態様３は、
　前記電解工程において、Ｎｉ：２５～９５質量％と、ＦｅおよびＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上の元素と、を含む陽極を用いる、態様１または２に記載の製造方法である。 Aspect 3 of the present invention is
In the electrolysis step, Ni: 25 to 95% by mass, at least one of Fe and Co, and selected from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W. The manufacturing method according to aspect 1 or 2, using an anode containing at least one or more elements.
　本発明の態様４は、
　前記電解工程における電流密度は０．５～３．０Ａ／ｃｍ２である、態様１～３のいずれか１つに記載の製造方法である。 Aspect 4 of the present invention is
The manufacturing method according to any one of aspects 1 to 3, wherein the current density in the electrolysis step is 0.5 to 3.0 A/cm 2 .
　本発明の態様５は、
　１×１０５～２×１０７Ｐａの圧力下で前記電解工程を行う、態様１～４のいずれか１つに記載の製造方法である。 Aspect 5 of the present invention is
The manufacturing method according to any one of aspects 1 to 4, wherein the electrolysis step is performed under a pressure of 1×10 5 to 2×10 7 Pa.
　本発明の態様６は、
　Ｎｉ：５０～７５質量％と、Ｆｅ及びＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、Ｔａ及びＷからなる群から選択される少なくとも１つ以上の元素と、を含む陽極材料である。 Aspect 6 of the present invention is
Ni: 50 to 75% by mass, at least one or more of Fe and Co, and at least one or more selected from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W. An anode material containing the elements.
　本発明の実施形態によれば、従来技術と比較して酸素過電圧および水素過電圧の合計値をより低減でき、その結果アルカリ水電解におけるエネルギー効率が向上した、水素の製造方法を提供できる。 According to the embodiments of the present invention, it is possible to provide a hydrogen production method in which the total value of oxygen overvoltage and hydrogen overvoltage can be further reduced compared to conventional techniques, and as a result, the energy efficiency in alkaline water electrolysis is improved.
図１は、ＫＯＨ－Ｈ２Ｏの二元系状態図である。FIG. 1 is a binary system phase diagram of KOH-H 2 O. 図２は、ＫＯＨ水溶液における、ＫＯＨ濃度と沸点の関係を示す。FIG. 2 shows the relationship between KOH concentration and boiling point in a KOH aqueous solution. 図３は、本発明の実施形態の効果を検証するための実験装置の模式図である。FIG. 3 is a schematic diagram of an experimental apparatus for verifying the effects of the embodiment of the present invention. 図４は、電流密度：０．５Ａ／ｃｍ２として定電流電解を行ったときの、温度と水素過電圧の関係を示すグラフである。FIG. 4 is a graph showing the relationship between temperature and hydrogen overvoltage when constant current electrolysis is performed at a current density of 0.5 A/cm 2 . 図５は、電流密度：０．５Ａ／ｃｍ２として定電流電解を行ったときの、温度と酸素過電圧の関係を示すグラフである。FIG. 5 is a graph showing the relationship between temperature and oxygen overvoltage when constant current electrolysis is performed at a current density of 0.5 A/cm 2 . 図６は、電流密度：１．０Ａ／ｃｍ２として定電流電解を行ったときの、温度と水素過電圧の関係を示すグラフである。FIG. 6 is a graph showing the relationship between temperature and hydrogen overvoltage when constant current electrolysis is performed at a current density of 1.0 A/cm 2 . 図７は、電流密度：１．０Ａ／ｃｍ２として定電流電解を行ったときの、温度と酸素過電圧の関係を示すグラフである。FIG. 7 is a graph showing the relationship between temperature and oxygen overvoltage when constant current electrolysis is performed at a current density of 1.0 A/cm 2 .
　本発明者らは、ＫＯＨ濃度３０質量％および加熱温度８０℃としてアルカリ水電解を行っていた従来技術と比較して、酸素過電圧および水素過電圧の合計値をより低くできる水素の製造方法を実現するべく、様々な角度から検討した。 The present inventors have realized a hydrogen production method that can lower the total value of oxygen overvoltage and hydrogen overvoltage compared to the conventional technology in which alkaline water electrolysis was performed at a KOH concentration of 30% by mass and a heating temperature of 80°C. We considered this from various angles.
　アルカリ水電解は、例えば、アルカリ金属水酸化物を含む電解液を充填した槽（電解槽）内に、陽極（酸素発生電極）および陰極（水素発生電極）、ならびに陽極及び陰極間に、生成する水素および酸素を分離可能な隔膜を配置し、陽極及び陰極間に直流電流を通電することにより実施され得る。陽極および陰極では、下記式（１）および（２）のような反応が起こり得る。

　陽極：４ＯＨ－→２Ｈ２Ｏ＋Ｏ２＋４ｅ－　・・・（１）
　陰極：４Ｈ２Ｏ＋４ｅ－→４ＯＨ－＋２Ｈ２　・・・（２）

　上記電解において、主に、陽極での酸素過電圧および陰極での水素過電圧等により、水の標準理論分解電圧（２５℃においては１．２２９Ｖ、８０℃においては１．１８３Ｖ）よりも電圧が高くなり、結果的にエネルギー効率が低下する。 In alkaline water electrolysis, for example, water is generated in a tank (electrolytic cell) filled with an electrolytic solution containing an alkali metal hydroxide, between an anode (oxygen generating electrode) and a cathode (hydrogen generating electrode), and between the anode and the cathode. This can be carried out by arranging a diaphragm capable of separating hydrogen and oxygen and passing a direct current between the anode and the cathode. At the anode and cathode, reactions as shown in the following formulas (1) and (2) may occur.

Anode: 4OH - → 2H 2 O+O 2 +4e -... (1)
Cathode: 4H 2 O + 4e - → 4OH - +2H 2 ... (2)

In the above electrolysis, the voltage becomes higher than the standard theoretical decomposition voltage of water (1.229V at 25℃, 1.183V at 80℃) mainly due to oxygen overvoltage at the anode and hydrogen overvoltage at the cathode. , resulting in lower energy efficiency.
　本発明者らは、過電圧低減のために通常行われる陽極および陰極の材質検討ならびに触媒検討とは全く異なる視点で、過電圧を低減することを考えた。具体的には、本発明者らは、温度上昇により（１）および（２）の電極反応を促進することで過電圧を低減させることを考えた。しかし、従来のＫＯＨ濃度が３０質量％の水溶液では、常圧における沸点が１１３℃であり、単に温度上昇させるとＫＯＨ水溶液の揮発量が増大する問題が生じる。そこで本発明者らは、ＫＯＨ濃度を増大させて沸点を上昇させることを着想した。ただし、従来ＫＯＨ濃度は自由水量の確保等のために３０質量％以下に制御されており、ＫＯＨ濃度を増大させると、自由水量が減少して、過電圧ひいてはセル電圧にむしろ悪影響を及ぼし得ることが広く知られていた。
　これらの問題に対し、本発明者らは、電解液に含まれるＫＯＨ等のアルカリ金属水酸化物の濃度を５２．３質量％以上９０質量％以下にすることにより、電解液の沸点が急上昇して揮発を抑制できること、そして当該濃度であっても、１２０℃以上且つ電解液の融点以上に加熱して電解を行えば、過電圧に悪影響を与えず、むしろ従来技術と比較して過電圧を低減できることを見出した。 The present inventors considered reducing overvoltage from a completely different perspective from the examination of materials for anodes and cathodes and examination of catalysts, which are normally performed for reducing overvoltage. Specifically, the present inventors considered reducing the overvoltage by promoting the electrode reactions (1) and (2) by increasing the temperature. However, a conventional aqueous solution with a KOH concentration of 30% by mass has a boiling point of 113° C. at normal pressure, and simply increasing the temperature causes the problem that the amount of volatilization of the KOH aqueous solution increases. Therefore, the present inventors came up with the idea of increasing the KOH concentration to raise the boiling point. However, the KOH concentration has conventionally been controlled to 30% by mass or less in order to ensure the amount of free water, etc., and increasing the KOH concentration will decrease the amount of free water, which may actually have a negative effect on the overvoltage and, in turn, on the cell voltage. It was widely known.
In order to solve these problems, the present inventors have determined that by setting the concentration of alkali metal hydroxide such as KOH contained in the electrolyte to 52.3% by mass or more and 90% by mass or less, the boiling point of the electrolyte can be increased rapidly. Even at this concentration, if electrolysis is performed by heating above 120°C and above the melting point of the electrolytic solution, it will not have a negative effect on overvoltage, and in fact can reduce overvoltage compared to conventional technology. I found out.
　以下に、本発明の実施形態が規定する各要件の詳細を示す。なお、本明細書において、電解液の融点および沸点につき、便宜上常圧時の融点および沸点を用いて、本発明の実施形態が説明される。すなわち、本明細書における「融点」および「沸点」は、特に言及しない限り、常圧時の融点および沸点を意味する。ただし、後述するように、本発明の実施形態は、常圧で実施することに限定されず、例えば常圧以上の圧力下で実施しても問題なく本発明の効果が得られることが期待される。 Details of each requirement defined by the embodiment of the present invention are shown below. In this specification, embodiments of the present invention will be described using the melting point and boiling point of the electrolytic solution at normal pressure for convenience. That is, "melting point" and "boiling point" in this specification mean the melting point and boiling point at normal pressure, unless otherwise specified. However, as will be described later, the embodiments of the present invention are not limited to being carried out at normal pressure; for example, it is expected that the effects of the present invention will be obtained without any problems even if carried out under pressures higher than normal pressure. Ru.
　本発明の実施形態に係る水素の製造方法は、１２０℃以上で且つ融点以上の下限温度と、沸点未満の上限温度と、の間の温度に加熱した電解液を電解する工程を含み、前記電解液は、Ｌｉ、ＮａおよびＫからなる群から選択されるいずれか一種以上であるアルカリ金属の水酸化物を５２．３質量％以上９０質量％以下含む。これにより、ＫＯＨ濃度３０質量％および加熱温度８０℃としてアルカリ水電解を行っていた従来技術と比較して、酸素過電圧および水素過電圧の合計値をより低減できる。 A method for producing hydrogen according to an embodiment of the present invention includes a step of electrolyzing an electrolytic solution heated to a temperature of 120° C. or higher and between a lower limit temperature equal to or higher than the melting point and an upper limit temperature lower than the boiling point, The liquid contains 52.3% by mass or more and 90% by mass or less of an alkali metal hydroxide selected from the group consisting of Li, Na, and K. As a result, the total value of oxygen overvoltage and hydrogen overvoltage can be further reduced compared to the conventional technique in which alkaline water electrolysis was performed at a KOH concentration of 30% by mass and a heating temperature of 80°C.
　本発明の実施形態において、電解液は、５２．３質量％以上９０質量％以下のアルカリ金属水酸化物（ＭＯＨ、ＭはＬｉ、ＮａおよびＫからなる群から選択されるいずれか一種以上）を含む。好ましくは、ＭはＮａおよびＫからなる群から選択されるいずれか一種以上であることである。電解液がＫＯＨおよびＮａＯＨを含む場合、ＫＯＨおよびＮａＯＨの混合比率（ＫＯＨ：ＮａＯＨ）としては、質量比で、１０：９０～９０：１０であることが好ましく、より好ましくは２０：８０～８０：２０であり、さらに好ましくは３０：７０～７０：３０である。電解液はアルカリ水溶液であり得、上記アルカリ金属水酸化物は電解液中において、Ｍ＋とＯＨ－に解離し得る。電解液は、ＭＯＨの他、水を１０質量％以上４７．７質量％以下含み得る。水は、例えば、イオン交換水、限外ろ過水又は蒸留水であってよい。電解液は、水を１０質量％以上含有していれば、過電圧を低減する上で十分であり、例えば他の金属水酸化物等の物質を含んでもよい。例えば、電解液は、水を１０質量％以上含有していれば、他の金属水酸化物を０質量％超１０質量％以下、好ましくは０質量％超５質量％以下含んでいてもよく、他の金属水酸化物としては、水酸化カルシウム（Ｃａ（ＯＨ）２）等が挙げられる。なお、本発明の実施形態において、電解液は、平均して所望のＭＯＨ濃度範囲に調整されていれば、濃度勾配を有していてもよい。 In an embodiment of the present invention, the electrolyte contains 52.3% by mass or more and 90% by mass or less of an alkali metal hydroxide (MOH, M is one or more selected from the group consisting of Li, Na, and K). include. Preferably, M is at least one selected from the group consisting of Na and K. When the electrolytic solution contains KOH and NaOH, the mixing ratio of KOH and NaOH (KOH:NaOH) is preferably 10:90 to 90:10 in mass ratio, more preferably 20:80 to 80: 20, more preferably 30:70 to 70:30. The electrolyte may be an alkaline aqueous solution, and the alkali metal hydroxide may dissociate into M + and OH − in the electrolyte. In addition to MOH, the electrolytic solution may contain 10% by mass or more and 47.7% by mass or less of water. The water may be, for example, ion-exchanged water, ultrafiltered water or distilled water. If the electrolytic solution contains 10% by mass or more of water, it is sufficient to reduce the overvoltage, and may also contain other substances such as metal hydroxides. For example, if the electrolytic solution contains 10% by mass or more of water, it may contain other metal hydroxides of more than 0% by mass and less than 10% by mass, preferably more than 0% by mass and not more than 5% by mass, Other metal hydroxides include calcium hydroxide (Ca(OH) 2 ) and the like. In the embodiment of the present invention, the electrolytic solution may have a concentration gradient as long as it is adjusted to a desired MOH concentration range on average.
　本発明の実施形態において、加熱後に（すなわち電解液を電解する際に）液体であれば、電解液は、例えば加熱前にはその凝固物等であってもよい。また、電解液は、加熱後において（すなわち電解液を電解する際に）上記所望のＭＯＨ濃度範囲に調整されていればよく、例えば加熱前においては、必ずしも上記所望のＭＯＨ濃度範囲に調整されている必要はない。例えば、電解実施下においても、ＭＯＨ又は水を添加するなどして、上記ＭＯＨの濃度を連続的又は断続的に調整してもよい。
　加熱前における上記電解液（またはその凝固物）は公知の方法で準備してよく、例えば、ＭＯＨまたはその含水物を、ＭＯＨの含有量が５２．３質量％以上９０質量％以下となるように、必要に応じて水に添加し、さらに必要に応じて攪拌混合すること等により、準備できる。
　加熱した電解液を準備する際、従来と比較して酸素過電圧および水素過電圧の合計値をより低減する要件の１つとして、加熱温度の下限温度を、１２０℃以上で且つ電解液の融点以上とする必要がある。これにより、従来と比較して電極反応を十分に促進できる。電解液の融点が１２０℃超の場合、１２０℃以下に加熱すると固相が析出し、例えば電解に悪影響を及ぼすおそれがある。好ましくは、加熱温度の下限温度は、１２０℃以上で且つ前記電解液の融点＋２０℃以上とする。
　加熱温度は高い方が過電圧をより低減できるため、加熱温度の下限温度は、１３０℃以上で且つ電解液の融点以上とすることが好ましく、１３０℃以上で且つ電解液の融点＋２０℃以上とすることがより好ましい。さらに、加熱温度の下限温度は、１４０℃以上で且つ電解液の融点以上とすることが好ましく、１４０℃以上で且つ電解液の融点＋２０℃以上とすることがより好ましい。
　なお、この加熱温度は、種々の排熱（例えば、各種工場およびごみ焼却場など）を利用できるので、加熱のために別段エネルギーを消費する必要はない。 In embodiments of the present invention, the electrolytic solution may be a solidified product thereof before heating, for example, as long as it is liquid after heating (that is, when electrolyzing the electrolytic solution). In addition, the electrolytic solution only needs to be adjusted to the above-mentioned desired MOH concentration range after heating (that is, when electrolyzing the electrolytic solution); for example, it is not necessarily adjusted to the above-mentioned desired MOH concentration range before heating. There's no need to be there. For example, even during electrolysis, the concentration of MOH may be adjusted continuously or intermittently by adding MOH or water.
The electrolytic solution (or its solidified product) before heating may be prepared by a known method, for example, by adding MOH or a hydrated product thereof such that the content of MOH is 52.3% by mass or more and 90% by mass or less. It can be prepared by adding it to water as necessary, and stirring and mixing as necessary.
When preparing a heated electrolyte, one of the requirements for further reducing the total value of oxygen overvoltage and hydrogen overvoltage compared to conventional methods is to set the lower limit temperature of the heating temperature to 120°C or higher and the melting point of the electrolyte. There is a need to. Thereby, the electrode reaction can be sufficiently promoted compared to the conventional method. When the melting point of the electrolytic solution is higher than 120°C, heating to 120°C or lower may precipitate a solid phase, which may adversely affect, for example, electrolysis. Preferably, the lower limit temperature of the heating temperature is 120° C. or higher and the melting point of the electrolytic solution +20° C. or higher.
Since the higher the heating temperature is, the more the overvoltage can be reduced, the lower limit temperature of the heating temperature is preferably 130°C or higher and the melting point of the electrolytic solution or higher, and 130°C or higher and the melting point of the electrolyte + 20°C or higher. It is more preferable. Further, the lower limit temperature of the heating temperature is preferably 140° C. or higher and the melting point of the electrolytic solution or higher, and more preferably 140° C. or higher and the melting point of the electrolytic solution +20° C. or higher.
Note that this heating temperature can be achieved by using various types of waste heat (for example, from various factories and garbage incineration plants), so there is no need to consume extra energy for heating.
　電解液の融点については、実測により求めることができる。具体的には、電解液の融点は、少量の電解液（ＭＯＨ濃度によっては室温で固体もあり得る）を白金製試料容器に入れ、示差走査熱量計（ＤＳＣ）により十分な低温（固体状態）から加熱した際の融解の吸熱ピークの立ち上がり温度により決定することができる。電解液の融点については、文献値を参照してもよく、例えばＫＯＨ水溶液の融点については、文献（W. M. Vogel, et al., "Some Physicochemical Properties of the KOH-H2O System－Range: 55 to 85 Weight % and 120℃ to 250℃－", Journal of Chemical and Engineering Data, (米), 1967, Vol.12, No.4, p.465）を参照することができる。図１に、当該文献から引用したＫＯＨ－Ｈ２Ｏの二元系状態図を示す。図１の横軸はＫＯＨ濃度（質量％ＫＯＨ）であり、縦軸は温度（℃）であり、縦軸の「１２０」、横軸の「６６」、「８３」および「８６」の数字、ならびにそれらに対応する直線は出願人が記載した。図１からわかるように、電解液がＫＯＨおよび水からなる場合であって、ＫＯＨ濃度が６６質量％以下および８３質量％超８６質量％未満の場合、電解液の融点は１２０℃以下となる。一方、ＫＯＨ濃度が６６質量％超８３質量％以下および８６質量％以上９０質量％以下の場合、電解液の融点が１２０℃超となる。 The melting point of the electrolytic solution can be determined by actual measurement. Specifically, the melting point of an electrolyte can be determined by placing a small amount of the electrolyte (which may be solid at room temperature depending on the MOH concentration) into a platinum sample container and measuring it at a sufficiently low temperature (solid state) using a differential scanning calorimeter (DSC). It can be determined by the rise temperature of the endothermic peak of melting when heated from . For the melting point of the electrolyte, reference may be made to literature values; for example, for the melting point of a KOH aqueous solution, see the literature (W. M. Vogel, et al., "Some Physicochemical Properties of the KOH-H 2 O System-Range: 55 to 85 Weight % and 120℃ to 250℃－", Journal of Chemical and Engineering Data, (US), 1967, Vol.12, No.4, p.465). FIG. 1 shows a binary phase diagram of KOH-H 2 O cited from the literature. The horizontal axis of FIG. 1 is the KOH concentration (mass% KOH), the vertical axis is the temperature (°C), and the numbers "120" on the vertical axis, "66", "83", and "86" on the horizontal axis, and the straight lines corresponding thereto were drawn by the applicant. As can be seen from FIG. 1, when the electrolytic solution consists of KOH and water and the KOH concentration is 66% by mass or less and more than 83% by mass and less than 86% by mass, the melting point of the electrolytic solution is 120° C. or less. On the other hand, when the KOH concentration is more than 66% by mass and not more than 83% by mass and more than 86% by mass and not more than 90% by mass, the melting point of the electrolytic solution is more than 120°C.
　従来と比較して酸素過電圧および水素過電圧の合計値をより低減する要件の１つとして、加熱温度の上限温度を沸点未満にする必要がある。加熱温度を沸点以上にすると、電解液の水分等が蒸発して固相が析出し、酸素過電圧および水素過電圧の合計値を十分に低減できない、もしくは電解自体ができなくなるおそれがある。好ましくは、加熱温度の上限温度は、前記電解液の沸点－２０℃未満である。 One of the requirements for further reducing the total value of oxygen overvoltage and hydrogen overvoltage compared to conventional methods is that the upper limit temperature of the heating temperature must be lower than the boiling point. If the heating temperature is set above the boiling point, water etc. in the electrolytic solution will evaporate and a solid phase will precipitate, and there is a possibility that the total value of oxygen overvoltage and hydrogen overvoltage cannot be sufficiently reduced, or that electrolysis itself cannot be performed. Preferably, the upper limit of the heating temperature is lower than the boiling point of the electrolytic solution -20°C.
　電解液の沸点については、実測により求めることができる。具体的には、電解液の沸点は、以下の方法で求めることができる。電解液（ＭＯＨ濃度によっては室温で固体もあり得る）を密閉容器に入れて、蒸気圧が十分に低い低温において真空引きにより大気を排気する。その後、密閉状態で容器全体を加熱してゆき、内部の圧力が１×１０５Ｐａとなった温度を、電解液の沸点とすることができる。電解液の沸点については、文献値を参照してもよく、例えばＫＯＨ水溶液の沸点については、文献（Robert D. Walker, Jr., "A STUDY OF GAS SOLUBILITIES AND TRANSPORT PROPERTIES IN FUEL CELL ELECTROLYTES", Research Grant NGR 10-005-022 Third Semi-Annual Report, (米), 1967, p.12）を参照することができる。図２に、当該文献に基づく、ＫＯＨ水溶液におけるＫＯＨ濃度と沸点の関係を示す。なお、図２において、各プロットの値は、当該文献から引用し、低濃度側（２０～４０質量％）および高濃度側（６０～８０質量％）のプロットの各近似直線および直線の式（決定係数Ｒ２の式含む）は、出願人が記載した。図２に示すように、一点鎖線で示すＫＯＨ濃度：５２．３質量％以上から沸点が急上昇することが分かる。本発明の実施形態において、図２における各プロット間のＫＯＨ濃度における沸点は、各プロット間で直線的に変化するものとして求めてもよい（すなわち内挿してよい）。なお、電解液の沸点は、当該電解液の質量モル濃度が高いほど上昇し得る。本発明の実施形態において、電解液は、ＫＯＨの一部または全てに代えて、ＬｉＯＨ及び／又はＮａＯＨを含み得るが、ＬｉＯＨ及びＮａＯＨは、ＫＯＨよりも分子量が低いため、ＫＯＨよりも低い含有量で高い質量モル濃度を得ることができる。従って、本発明の実施形態において、少なくともＭＯＨ濃度を５２．３質量％以上にしておくことにより、十分に高い沸点の電解液が得られる。 The boiling point of the electrolytic solution can be determined by actual measurement. Specifically, the boiling point of the electrolytic solution can be determined by the following method. An electrolytic solution (which may be solid at room temperature depending on the MOH concentration) is placed in a closed container, and the atmosphere is evacuated by evacuation at a low temperature where the vapor pressure is sufficiently low. Thereafter, the entire container is heated in a sealed state, and the temperature at which the internal pressure reaches 1×10 5 Pa can be set as the boiling point of the electrolytic solution. For the boiling point of the electrolyte, reference may be made to literature values; for example, for the boiling point of a KOH aqueous solution, see the literature (Robert D. Walker, Jr., "A STUDY OF GAS SOLUBILITIES AND TRANSPORT PROPERTIES IN FUEL CELL ELECTROLYTES", Research Grant NGR 10-005-022 Third Semi-Annual Report, (USA), 1967, p.12). FIG. 2 shows the relationship between KOH concentration and boiling point in a KOH aqueous solution based on the literature. In addition, in FIG. 2, the values of each plot are quoted from the relevant literature, and each approximate straight line and the equation of the straight line ( The formula for the coefficient of determination R2 ) was written by the applicant. As shown in FIG. 2, it can be seen that the boiling point sharply increases from KOH concentration of 52.3% by mass or higher, which is indicated by the dashed line. In an embodiment of the present invention, the boiling point at the KOH concentration between each plot in FIG. 2 may be determined as changing linearly between each plot (that is, may be interpolated). Note that the boiling point of the electrolytic solution may increase as the mass molar concentration of the electrolytic solution increases. In embodiments of the present invention, the electrolyte may include LiOH and/or NaOH in place of some or all of the KOH, but since LiOH and NaOH have lower molecular weights than KOH, the content is lower than that of KOH. High molarity can be obtained with Therefore, in the embodiment of the present invention, by setting the MOH concentration to at least 52.3% by mass or more, an electrolytic solution with a sufficiently high boiling point can be obtained.
　加熱温度の許容範囲は広い方が生産性の観点で好ましく、そのため電解液のＭＯＨ濃度は高い方が好ましい。具体的には、電解液のＭＯＨ濃度は５５質量％以上、６１質量％以上、６５質量％以上、７０質量％以上、または７５質量％以上にするのが順に好ましい。 A wider allowable range of heating temperature is preferable from the viewpoint of productivity, and therefore a higher MOH concentration in the electrolyte is preferable. Specifically, the MOH concentration of the electrolyte is preferably 55% by mass or more, 61% by mass or more, 65% by mass or more, 70% by mass or more, or 75% by mass or more, in this order.
　前記電解工程は、常圧（約１×１０５Ｐａ）で行ってもよいし、得られた水素を後に加圧して保存することを考慮して、予め加圧して行ってもよく、例えば圧力としては、１×１０５～２×１０７Ｐａとしてもよい。また、生産性の観点から、圧力の上限値は低い方が好ましい。具体的には、圧力の上限値は、１×１０７Ｐａ以下、５×１０６Ｐａ以下、１×１０６Ｐａ以下、または５×１０５Ｐａ以下であることが順に好ましい。さらに、２×１０５Ｐａ未満の圧力で電解を行うことにより、得られた水素につき、化学品の分類および表示に関する世界調和システム（ＧＨＳ）上の「高圧ガス」ではない範囲で扱えるため、より好ましい。 The electrolysis step may be performed at normal pressure (approximately 1×10 5 Pa), or may be performed under pressure in advance, considering that the obtained hydrogen will be stored under pressure later. For example, it may be 1×10 5 to 2×10 7 Pa. Further, from the viewpoint of productivity, it is preferable that the upper limit value of the pressure is lower. Specifically, the upper limit of the pressure is preferably 1×10 7 Pa or less, 5×10 6 Pa or less, 1×10 6 Pa or less, or 5×10 5 Pa or less, in this order. Furthermore, by performing electrolysis at a pressure of less than 2×10 5 Pa, the hydrogen obtained can be treated as a “high-pressure gas” under the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). preferable.
　上記電解工程に使用できる陽極材料としては、公知の導電性材料を用いることができる。本発明の実施形態において、好ましくは、Ｎｉ：２５～９５質量％と、ＦｅおよびＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上と、を含む陽極を用いることである。Ｎｉ含有量としては、より好ましくは５０～７５質量％である。ＦｅおよびＣｏの少なくとも１つ以上の含有量（ＦｅおよびＣｏの合計含有量）としては、１．０質量％以上であることが好ましく、５．０質量％以上であることがより好ましい。Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上の含有量（Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷの合計含有量）としては、０．１質量％以上であることが好ましく、３．０質量％以上であることがより好ましい。このような陽極を用いることで、より酸素過電圧を低減することができる。本発明の好ましい１つの実施形態において、陽極材料は、Ｎｉと、ＦｅおよびＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上と、を上述の含有量で含み、かつ残部が不可避不純物であり得る。不可避不純物とは、上記で特定された元素以外であって、原料、資材、製造設備等の状況によって持ち込まれる元素を指し、例えば、総量で１．０質量％以下であり得る。陰極材料としては、公知の導電性材料、例えば白金、ニッケル等を用いることができる。隔膜材料としては、公知のアルカリ水電解用隔膜材料、例えば多孔性の絶縁性物質等を用いることができる。その他の部材（槽、パッキン等など）についても、公知の材料を適宜用いることができ、例えば、槽およびパッキンには、フッ素樹脂を用いることができる。 As the anode material that can be used in the above electrolysis step, known conductive materials can be used. In an embodiment of the present invention, preferably Ni: 25 to 95% by mass, at least one of Fe and Co, and Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W. and at least one selected from the group consisting of: The Ni content is more preferably 50 to 75% by mass. The content of at least one of Fe and Co (total content of Fe and Co) is preferably 1.0% by mass or more, more preferably 5.0% by mass or more. At least one content selected from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W (Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, The total content of Ta and W is preferably 0.1% by mass or more, more preferably 3.0% by mass or more. By using such an anode, oxygen overvoltage can be further reduced. In one preferred embodiment of the invention, the anode material comprises Ni, at least one of Fe and Co, and from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta and W. and at least one selected one or more in the above content, and the remainder may be unavoidable impurities. Unavoidable impurities refer to elements other than the elements specified above that are brought in depending on the circumstances of raw materials, materials, manufacturing equipment, etc., and may be, for example, 1.0% by mass or less in total. As the cathode material, known conductive materials such as platinum, nickel, etc. can be used. As the diaphragm material, known diaphragm materials for alkaline water electrolysis, such as porous insulating materials, can be used. Known materials can be used as appropriate for other members (tank, packing, etc.). For example, fluororesin can be used for the tank and packing.
　従来のアルカリ水電解では、酸素過電圧および水素過電圧が高い等の理由により、例えば０．２Ａ／ｃｍ２程度までしか電流密度を増大させることができなかった。本発明の実施形態に係る水素の製造方法では、従来と比較して酸素過電圧および水素過電圧の合計値をより低減できるため、電流密度を増大させて水素発生量を増加させることができる。例えば、電流密度を０．５Ａ／ｃｍ２以上として電解を行うことが、本発明の実施形態の効果が顕著となり好ましい。より好ましくは、電流密度が０．７Ａ／ｃｍ２以上であり、さらに好ましくは電流密度が１．０Ａ／ｃｍ２以上である。一方、電流密度の上限値は特に制限されないが、電流密度を増大させすぎると、過電圧以外の電圧損失が大きくなり得るため、３．０Ａ／ｃｍ２以下にすることが好ましく、より好ましくは２．０Ａ／ｃｍ２以下である。 In conventional alkaline water electrolysis, the current density could only be increased to, for example, about 0.2 A/cm 2 due to high oxygen overvoltage and high hydrogen overvoltage. In the hydrogen production method according to the embodiment of the present invention, since the total value of oxygen overvoltage and hydrogen overvoltage can be further reduced compared to the conventional method, the current density can be increased and the amount of hydrogen generated can be increased. For example, it is preferable to conduct electrolysis at a current density of 0.5 A/cm 2 or more, since the effects of the embodiments of the present invention are significant. More preferably, the current density is 0.7 A/cm 2 or more, and even more preferably, the current density is 1.0 A/cm 2 or more. On the other hand, the upper limit of the current density is not particularly limited, but if the current density is increased too much, voltage loss other than overvoltage may increase, so it is preferably 3.0 A/cm 2 or less, more preferably 2.0 A/cm 2 or less. It is 0A/ cm2 or less.
　また、従来技術では、特許文献２および３に示すように、陽極材料として、Ｎｉ基合金が検討されてきた。具体的な形態としては電極基材の表面に合金めっきを施す方法が採られている。
　上記従来技術に対して、本発明者らは、特にＮｉ：２５～９５質量％（好ましくはＮｉ：５０～７５質量％）と、ＦｅおよびＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上の元素と、を含む陽極材料を用いることにより、室温から高温での電解に至るまで、顕著に酸素過電圧が低下することを見出した。この材料は、電極基材の表面にめっき法等で被覆することでも効果を奏すると考えられる。ＦｅおよびＣｏの少なくとも１つ以上の含有量（ＦｅおよびＣｏの合計含有量）としては、１．０質量％以上であることが好ましく、５．０質量％以上であることがより好ましい。Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上の含有量（Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷの合計含有量）としては、０．１質量％以上であることが好ましく、３．０質量％以上であることがより好ましい。本発明の好ましい１つの実施形態において、陽極材料は、Ｎｉと、ＦｅおよびＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上と、を上述の含有量で含み、かつ残部が不可避不純物であり得る。不可避不純物とは、上記で特定された元素以外であって、原料、資材、製造設備等の状況によって持ち込まれる元素を指し、例えば、総量で１．０質量％以下であり得る。 Furthermore, in the prior art, as shown in Patent Documents 2 and 3, Ni-based alloys have been considered as anode materials. As a specific form, a method is adopted in which alloy plating is applied to the surface of the electrode base material.
In contrast to the above-mentioned prior art, the present inventors have specifically combined Ni: 25 to 95% by mass (preferably Ni: 50 to 75% by mass), at least one of Fe and Co, Al, Ti, Cr, By using an anode material containing at least one element selected from the group consisting of Mn, Cu, Zn, Nb, Mo, Ta, and W, oxygen can be significantly reduced from room temperature to high temperature electrolysis. It was found that the overvoltage was reduced. This material is also considered to be effective when coated on the surface of the electrode base material by a plating method or the like. The content of at least one of Fe and Co (total content of Fe and Co) is preferably 1.0% by mass or more, more preferably 5.0% by mass or more. At least one content selected from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W (Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, The total content of Ta and W is preferably 0.1% by mass or more, more preferably 3.0% by mass or more. In one preferred embodiment of the invention, the anode material comprises Ni, at least one of Fe and Co, and from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta and W. and at least one selected one or more in the above content, and the remainder may be unavoidable impurities. Unavoidable impurities refer to elements other than the elements specified above that are brought in depending on the circumstances of raw materials, materials, manufacturing equipment, etc., and may be, for example, 1.0% by mass or less in total.
　以下、実施例を挙げて本発明の実施形態をより具体的に説明する。本発明の実施形態は以下の実施例によって制限を受けるものではなく、前述および後述する趣旨に合致し得る範囲で、適宜変更を加えて実施することも可能であり、それらはいずれも本発明の実施形態の技術的範囲に包含される。 Hereinafter, embodiments of the present invention will be described in more detail with reference to Examples. The embodiments of the present invention are not limited by the following examples, and can be implemented with appropriate changes within the scope that can meet the spirit described above and below, and any of them can be implemented without limiting the scope of the present invention. It is included within the technical scope of the embodiment.
　図３は、本発明の実施形態の効果を検証するための実験装置の模式図である。図３に示すように、槽１内に所定の濃度の電解液（ＫＯＨ水溶液）２が充填されている。電解液２内に、作用極３、対極４、参照極５および温度計６が配置されている。なお、槽１およびパッキン（図示せず）にはフッ素樹脂を用いた。槽１の外側には、ヒーター７が配置されている。また、槽１内にＡｒガスを流しており、槽１内の圧力は１．０×１０５～１．１×１０５Ｐａに調整された。
　作用極としては、Ｎｉ、ハステロイ（登録商標）Ｃ－２７６（Ｎｉ：５７質量％、Ｆｅ：４～７質量％、Ｍｏ：１７質量％、Ｃｒ：１６質量％、およびＷ：３～４．５質量％を含む合金、以下「ＨＣ－２７６」と称することがある）およびＰｔのいずれか１つのフラッグ電極を用い、電極面積は、いずれも０．１５７ｃｍ２とした。対極としては白金ワイヤー電極（Φ２ｍｍ）を用い、電極面積は１．９２ｃｍ２とした。参照電極としては、パラジウム水素化物（Ｐｄ－Ｈ）電極を用い、電位は可逆水素電極（ＲＨＥ）基準で較正した。なお、ＲＨＥに対するＰｄ－Ｈ電極の平衡電位は熱力学計算から決定した。ＫＯＨ水溶液の濃度は、従来の３０質量％、または本発明の実施形態の要件を満たす８５質量％とした。ＫＯＨ水溶液の濃度が３０質量％の場合、加熱温度は２５℃または８０℃とし、ＫＯＨ水溶液の濃度が８５質量％の場合、加熱温度を１５０℃とした。電流密度は±０．５Ａ／ｃｍ２または±１．０Ａ／ｃｍ２として、定電流電解を行った。 FIG. 3 is a schematic diagram of an experimental apparatus for verifying the effects of the embodiment of the present invention. As shown in FIG. 3, a tank 1 is filled with an electrolytic solution (KOH aqueous solution) 2 having a predetermined concentration. A working electrode 3, a counter electrode 4, a reference electrode 5, and a thermometer 6 are arranged in the electrolytic solution 2. Note that fluororesin was used for the tank 1 and packing (not shown). A heater 7 is arranged outside the tank 1. Further, Ar gas was flowing into the tank 1, and the pressure inside the tank 1 was adjusted to 1.0×10 5 to 1.1×10 5 Pa.
As a working electrode, Ni, Hastelloy (registered trademark) C-276 (Ni: 57% by mass, Fe: 4 to 7% by mass, Mo: 17% by mass, Cr: 16% by mass, and W: 3 to 4.5% by mass) A flag electrode of one of Pt (an alloy containing % by mass, hereinafter sometimes referred to as "HC-276") and Pt was used, and the electrode area was 0.157 cm 2 in both cases. A platinum wire electrode (Φ2 mm) was used as the counter electrode, and the electrode area was 1.92 cm 2 . A palladium hydride (Pd-H) electrode was used as a reference electrode, and the potential was calibrated using a reversible hydrogen electrode (RHE) standard. Note that the equilibrium potential of the Pd--H electrode with respect to RHE was determined from thermodynamic calculations. The concentration of the KOH aqueous solution was 30% by mass, which is conventional, or 85% by mass, which satisfies the requirements of the embodiment of the present invention. When the concentration of the KOH aqueous solution was 30% by mass, the heating temperature was 25°C or 80°C, and when the concentration of the KOH aqueous solution was 85% by mass, the heating temperature was 150°C. Constant current electrolysis was performed at a current density of ±0.5 A/cm 2 or ±1.0 A/cm 2 .
　図４は、作用極にＮｉまたはＰｔを用い、電流密度を－０．５Ａ／ｃｍ２で一定として、作用極から水素が発生するように（すなわち作用極を陰極として）電解を行ったときの、加熱温度に対する水素過電圧を測定した結果である。なお、当該測定では、定常状態におけるＩＲ補正を行った後の電極電位を求め、当該電極電位と平衡電位との差から水素過電圧を算出した。なお、各加熱温度における水素発生の平衡電位は、０Ｖｖｓ．ＲＨＥである。図４に示すように、作用極にＮｉまたはＰｔのどちらを用いた場合においても、従来のＫＯＨ濃度３０質量％、加熱温度８０℃と比較して、本発明の実施形態の要件を満たすＫＯＨ濃度８５質量％、加熱温度１５０℃では、水素過電圧が大きく減少した。また図４からわかるように、加熱温度上昇に従って水素過電圧が低下する傾向があり、例えば従来の加熱温度（～８０℃）よりも十分に高い１２０℃以上（且つ電解液の融点以上）に加熱して電解を行うことにより、従来技術と比較して水素過電圧をより低減できるといえる。 Figure 4 shows the results of electrolysis using Ni or Pt as the working electrode and a constant current density of -0.5 A/cm 2 so that hydrogen is generated from the working electrode (that is, using the working electrode as the cathode). This is the result of measuring hydrogen overvoltage versus heating temperature. In this measurement, the electrode potential after IR correction in a steady state was determined, and the hydrogen overvoltage was calculated from the difference between the electrode potential and the equilibrium potential. Note that the equilibrium potential of hydrogen generation at each heating temperature is 0V vs. It is RHE. As shown in FIG. 4, when using either Ni or Pt for the working electrode, the KOH concentration satisfies the requirements of the embodiment of the present invention compared to the conventional KOH concentration of 30% by mass and heating temperature of 80°C. At 85% by mass and a heating temperature of 150° C., the hydrogen overvoltage significantly decreased. Furthermore, as can be seen from Figure 4, the hydrogen overvoltage tends to decrease as the heating temperature increases; for example, when heated to 120°C or higher (and above the melting point of the electrolyte), which is sufficiently higher than the conventional heating temperature (~80°C). It can be said that hydrogen overvoltage can be further reduced compared to conventional techniques by performing electrolysis.
　図５は、作用極にＮｉ、ＨＣ－２７６またはＰｔを用い、電流密度を０．５Ａ／ｃｍ２で一定として、作用極から酸素が発生するように（すなわち作用極を陽極として）電解を行ったときの、加熱温度に対する酸素過電圧を測定した結果である。なお、当該測定では、定常状態におけるＩＲ補正を行った後の電極電位を求め、当該電極電位と平衡電位との差から酸素過電圧を算出した。なお、各加熱温度における酸素発生の平衡電位は、２５℃において１．２２９Ｖｖｓ．ＲＨＥ、８０℃において１．１８３Ｖｖｓ．ＲＨＥ、１５０℃において１．１５５Ｖｖｓ．ＲＨＥとした。なお、当該平衡電位は、各加熱温度における水電解反応の標準ギブスエネルギー変化から算出した標準理論分解電圧により決定した。図５に示すように、作用極にＮｉ、ＨＣ－２７６またはＰｔのいずれを用いた場合においても、従来のＫＯＨ濃度３０質量％、加熱温度８０℃と比較して、本発明の実施形態の要件を満たすＫＯＨ濃度８５質量％、加熱温度１５０℃では、酸素過電圧が大きく減少した。また図５からわかるように、加熱温度上昇に従って酸素過電圧が低下する傾向があり、例えば従来の加熱温度（～８０℃）よりも十分に高い１２０℃以上（且つ電解液の融点以上）に加熱して電解を行うことにより、従来技術と比較して酸素過電圧をより低減できるといえる。
　作用極（陽極）について比較すると、陽極に、ＨＣ－２７６を使用した場合、最も酸素過電圧が低く、好ましい結果となった。これは、ＨＣ－２７６が、Ｎｉ：２５～９５質量％と、ＦｅおよびＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上と、を含むことに起因すると考えられる。 In Figure 5, Ni, HC-276, or Pt is used for the working electrode, and the current density is kept constant at 0.5 A/ cm2 , and electrolysis is performed so that oxygen is generated from the working electrode (that is, the working electrode is used as the anode). These are the results of measuring oxygen overvoltage versus heating temperature. In addition, in this measurement, the electrode potential after IR correction in a steady state was determined, and the oxygen overvoltage was calculated from the difference between the electrode potential and the equilibrium potential. Note that the equilibrium potential for oxygen generation at each heating temperature is 1.229V vs. 25°C. RHE, 1.183V vs. 80°C. RHE, 1.155V vs. 150°C. It was set as RHE. Note that the equilibrium potential was determined by the standard theoretical decomposition voltage calculated from the standard Gibbs energy change of the water electrolysis reaction at each heating temperature. As shown in FIG. 5, when Ni, HC-276, or Pt is used for the working electrode, compared to the conventional KOH concentration of 30% by mass and heating temperature of 80°C, the requirements of the embodiment of the present invention are When the KOH concentration was 85% by mass and the heating temperature was 150° C., the oxygen overvoltage was significantly reduced. Furthermore, as can be seen from Figure 5, the oxygen overvoltage tends to decrease as the heating temperature increases; for example, when heated to 120°C or higher (and above the melting point of the electrolyte), which is sufficiently higher than the conventional heating temperature (~80°C). It can be said that oxygen overvoltage can be further reduced compared to conventional techniques by performing electrolysis.
Comparing the working electrodes (anodes), when HC-276 was used as the anode, the oxygen overvoltage was the lowest and favorable results were obtained. This is because HC-276 is made from the group consisting of Ni: 25 to 95% by mass, at least one of Fe and Co, and Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W. This is considered to be due to the fact that the selected at least one or more are included.
　図６は、作用極にＮｉまたはＰｔを用い、電流密度を－１．０Ａ／ｃｍ２で一定として、作用極から水素が発生するように（すなわち作用極を陰極として）電解を行ったときの、加熱温度に対する水素過電圧を測定した結果である。なお、当該測定では、定常状態におけるＩＲ補正を行った後の電極電位を求め、当該電極電位と平衡電位との差から水素過電圧を算出した。なお、各加熱温度における水素発生の平衡電位は、０Ｖｖｓ．ＲＨＥである。図６に示すように、作用極にＮｉまたはＰｔのどちらを用いた場合においても、電流密度を－１．０Ａ／ｃｍ２にした場合においても、従来のＫＯＨ濃度３０質量％、加熱温度８０℃と比較して、本発明の実施形態の要件を満たすＫＯＨ濃度８５質量％、加熱温度１５０℃では、水素過電圧が大きく減少した。また図６からわかるように、電流密度を－１．０Ａ／ｃｍ２にした場合においても、加熱温度上昇に従って水素過電圧が低下する傾向があり、例えば従来の加熱温度（～８０℃）よりも十分に高い１２０℃以上（且つ電解液の融点以上）に加熱して電解を行うことにより、従来技術と比較して水素過電圧をより低減できるといえる。 Figure 6 shows the results when electrolysis is performed using Ni or Pt as the working electrode, with a constant current density of -1.0 A/ cm2 , and hydrogen is generated from the working electrode (that is, with the working electrode as the cathode). This is the result of measuring hydrogen overvoltage versus heating temperature. In this measurement, the electrode potential after IR correction in a steady state was determined, and the hydrogen overvoltage was calculated from the difference between the electrode potential and the equilibrium potential. Note that the equilibrium potential of hydrogen generation at each heating temperature is 0V vs. It is RHE. As shown in Figure 6, regardless of whether Ni or Pt is used for the working electrode and the current density is -1.0A/ cm2 , the conventional KOH concentration is 30% by mass and the heating temperature is 80°C. In comparison, at a KOH concentration of 85% by mass and a heating temperature of 150° C., which meet the requirements of the embodiment of the present invention, the hydrogen overvoltage was significantly reduced. Furthermore, as can be seen from Figure 6, even when the current density is set to -1.0 A/cm 2 , the hydrogen overvoltage tends to decrease as the heating temperature increases, and for example, the hydrogen overvoltage tends to decrease as the heating temperature increases. It can be said that by performing electrolysis by heating to a temperature of 120° C. or higher (and higher than the melting point of the electrolytic solution), the hydrogen overvoltage can be further reduced compared to the conventional technology.
　図７は、作用極にＮｉ、ＨＣ－２７６またはＰｔを用い、電流密度を１．０Ａ／ｃｍ２で一定として、作用極から酸素が発生するように（すなわち作用極を陽極として）電解を行ったときの、加熱温度に対する酸素過電圧を測定した結果である。なお、当該測定では、定常状態におけるＩＲ補正を行った後の電極電位を求め、当該電極電位と平衡電位との差から酸素過電圧を算出した。なお、各加熱温度における酸素発生の平衡電位は、２５℃において１．２２９Ｖｖｓ．ＲＨＥ、８０℃において１．１８３Ｖｖｓ．ＲＨＥ、１５０℃において１．１５５Ｖｖｓ．ＲＨＥとした。なお、当該平衡電位は、各加熱温度における水電解反応の標準ギブスエネルギー変化から算出した標準理論分解電圧により決定した。図７に示すように、いずれの作用極を用いた場合においても、電流密度を１．０Ａ／ｃｍ２にした場合においても、従来のＫＯＨ濃度３０質量％、加熱温度８０℃と比較して、本発明の実施形態の要件を満たすＫＯＨ濃度８５質量％、加熱温度１５０℃では、酸素過電圧が大きく減少した。また図７からわかるように、電流密度を１．０Ａ／ｃｍ２にした場合においても、加熱温度上昇に従って酸素過電圧が低下する傾向があり、例えば従来の加熱温度（～８０℃）よりも十分に高い１２０℃以上（且つ電解液の融点以上）に加熱して電解を行うことにより、従来技術と比較して酸素過電圧をより低減できるといえる。
　作用極（陽極）について比較すると、陽極にＨＣ－２７６を使用した場合、最も酸素過電圧が低く、好ましい結果となった。これは、ＨＣ－２７６が、Ｎｉ：２５～９５質量％と、ＦｅおよびＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上と、を含むことに起因すると考えられる。 In Figure 7, Ni, HC-276, or Pt is used as the working electrode, and the current density is kept constant at 1.0 A/ cm2 , and electrolysis is performed so that oxygen is generated from the working electrode (that is, the working electrode is used as the anode). These are the results of measuring oxygen overvoltage versus heating temperature. In addition, in this measurement, the electrode potential after IR correction in a steady state was determined, and the oxygen overvoltage was calculated from the difference between the electrode potential and the equilibrium potential. Note that the equilibrium potential for oxygen generation at each heating temperature is 1.229V vs. 25°C. RHE, 1.183V vs. 80°C. RHE, 1.155V vs. 150°C. It was set as RHE. Note that the equilibrium potential was determined by the standard theoretical decomposition voltage calculated from the standard Gibbs energy change of the water electrolysis reaction at each heating temperature. As shown in FIG. 7, no matter which working electrode is used and the current density is set to 1.0 A/ cm2 , compared to the conventional KOH concentration of 30 mass% and heating temperature of 80 °C, At a KOH concentration of 85% by mass and a heating temperature of 150° C., which meet the requirements of the embodiment of the present invention, the oxygen overvoltage was significantly reduced. Furthermore, as can be seen from Fig. 7, even when the current density is set to 1.0 A/cm 2 , the oxygen overvoltage tends to decrease as the heating temperature increases, and for example, the oxygen overvoltage tends to decrease as the heating temperature increases. By performing electrolysis by heating to a high temperature of 120° C. or higher (and higher than the melting point of the electrolytic solution), it can be said that the oxygen overvoltage can be further reduced compared to the conventional technology.
When comparing the working electrodes (anodes), when HC-276 was used for the anodes, the oxygen overvoltage was the lowest and favorable results were obtained. This is because HC-276 is made from the group consisting of Ni: 25 to 95% by mass, at least one of Fe and Co, and Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W. This is considered to be due to the fact that the selected at least one or more are included.
　なお、図５および図７から明らかなように、ＨＣ－２７６を陽極に使用した場合、室温条件の電解反応でも酸素過電圧が低下していることが分かる。 As is clear from FIGS. 5 and 7, when HC-276 is used as an anode, the oxygen overvoltage is reduced even in the electrolytic reaction at room temperature.
　実施例１のＫＯＨ水溶液を、ＮａＯＨおよびＫＯＨの混合水溶液に変更し、ＮａＯＨ：ＫＯＨ：Ｈ２Ｏの質量比は３０：４３：２７（すなわちＭＯＨ濃度は７３質量％）とし、加熱温度は１３０℃とした。なお、この場合の酸素発生の平衡電位は、１．１６０Ｖｖｓ．ＲＨＥとした。その他は実施例１と同様に定電流電解を行った。 The KOH aqueous solution in Example 1 was changed to a mixed aqueous solution of NaOH and KOH, the mass ratio of NaOH:KOH:H 2 O was 30:43:27 (that is, the MOH concentration was 73% by mass), and the heating temperature was 130 ° C. And so. Note that the equilibrium potential of oxygen generation in this case is 1.160V vs. It was set as RHE. In other respects, constant current electrolysis was performed in the same manner as in Example 1.
　水素過電圧と酸素過電圧の合計値につき、本発明の実施形態の値と従来技術の値との違いを説明するために、実施例１の図４～図７および実施例２から適切な値を抜粋して表１に示す。なお、表１における従来技術例、本発明例１および２は、実施例１（ＭＯＨ＝ＫＯＨ）から抜粋したものであり、本発明例３および４は、実施例２（ＭＯＨ＝ＮａＯＨ＋ＫＯＨ）から抜粋したものである。また、表１における従来技術例の構成のとしては、特許文献１に記載のように、ＫＯＨ濃度：３０質量％、加熱温度：８０℃、陽極：Ｎｉおよび陰極：Ｐｔとした（上述したように、特許文献１には、陽極としてはＮｉが、陰極としてはＰｔが、それぞれ理想的であることが記載されている）。 Appropriate values are extracted from FIGS. 4 to 7 of Example 1 and Example 2 in order to explain the difference between the values of the embodiment of the present invention and the values of the prior art regarding the total value of hydrogen overvoltage and oxygen overvoltage. The results are shown in Table 1. In addition, the prior art examples and the invention examples 1 and 2 in Table 1 are extracted from Example 1 (MOH=KOH), and the invention examples 3 and 4 are extracted from Example 2 (MOH=NaOH+KOH). This is what I did. Further, as described in Patent Document 1, the configuration of the prior art example in Table 1 is as follows: KOH concentration: 30% by mass, heating temperature: 80°C, anode: Ni, and cathode: Pt (as described above) , Patent Document 1 describes that Ni is ideal for the anode and Pt is ideal for the cathode).
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１に示すように、本発明の実施形態の要件を満たす本発明例１～４は、従来技術例と比較して、水素過電圧と酸素過電圧の合計値（過電圧合計）を低減できることがわかる。特に、本発明の実施形態の好ましい要件（すなわち、陽極がＮｉ：２５～９５質量％と、ＦｅおよびＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上と、を含む）を満たす本発明例２および４は、本発明例１および３よりもさらに酸素過電圧を低減できることがわかる。 As shown in Table 1, it can be seen that Examples 1 to 4 of the present invention, which meet the requirements of the embodiment of the present invention, can reduce the total value of hydrogen overvoltage and oxygen overvoltage (total overvoltage) compared to the prior art examples. In particular, the preferred requirements of the embodiments of the present invention (i.e., the anode contains 25 to 95% by mass of Ni, at least one of Fe and Co, Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, It can be seen that Examples 2 and 4 of the present invention, which satisfy at least one selected from the group consisting of Ta and W, can further reduce the oxygen overvoltage than Examples 1 and 3 of the present invention.
　上記とは別に、室温においてＫＯＨの濃度が８５質量％および水の濃度が１５質量％の固体ペレットを加熱して８０℃としたが、融解せずに固体のままであったため電解できなかった。またＫＯＨ水溶液の濃度を３０質量％として加熱した場合、約１１０℃で電解液が沸騰し、それ以上の温度では電解できなかった。 Separately from the above, a solid pellet with a KOH concentration of 85% by mass and a water concentration of 15% by mass at room temperature was heated to 80°C, but it remained solid without melting, so it could not be electrolyzed. Further, when heating the KOH aqueous solution at a concentration of 30% by mass, the electrolytic solution boiled at about 110° C., and electrolysis could not be performed at a temperature higher than that.
　本出願は、出願日が２０２２年７月１３日である日本国特許出願、特願第２０２２－１１２５８３号を基礎出願とする優先権主張を伴う。特願第２０２２－１１２５８３号は参照することにより本明細書に取り込まれる。 This application claims priority to the Japanese patent application, Japanese Patent Application No. 2022-112583, whose filing date is July 13, 2022, as the basic application. Japanese Patent Application No. 2022-112583 is incorporated herein by reference.
　１　槽
　２　電解液
　３　作用極
　４　対極
　５　参照極
　６　温度計
　７　ヒーター 1 Tank 2 Electrolyte 3 Working electrode 4 Counter electrode 5 Reference electrode 6 Thermometer 7 Heater

Claims (6)

  1. 　１２０℃以上で且つ融点以上の下限温度と、沸点未満の上限温度と、の間の温度に加熱した電解液を電解する工程を含み、
    　前記電解液は、Ｌｉ、ＮａおよびＫからなる群から選択されるいずれか一種以上であるアルカリ金属の水酸化物を５２．３質量％以上９０質量％以下含む、水素の製造方法。     A step of electrolyzing an electrolytic solution heated to a temperature of 120 ° C. or higher and between a lower limit temperature above the melting point and an upper limit temperature below the boiling point,
    The method for producing hydrogen, wherein the electrolytic solution contains 52.3% by mass or more and 90% by mass or less of an alkali metal hydroxide selected from the group consisting of Li, Na, and K.
  2. 　前記電解液は、前記アルカリ金属の水酸化物を６１質量％以上９０質量％以下含む、請求項１に記載の製造方法。 The manufacturing method according to claim 1, wherein the electrolytic solution contains 61% by mass or more and 90% by mass or less of the hydroxide of the alkali metal.
  3. 　前記電解工程において、Ｎｉ：２５～９５質量％と、ＦｅおよびＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、ＴａおよびＷからなる群から選択される少なくとも１つ以上の元素と、を含む陽極を用いる、請求項１または２に記載の製造方法。 In the electrolysis step, Ni: 25 to 95% by mass, at least one of Fe and Co, and selected from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W. The manufacturing method according to claim 1 or 2, using an anode containing at least one or more elements.
  4. 　前記電解工程における電流密度は０．５～３．０Ａ／ｃｍ２である、請求項１～３のいずれか１項に記載の製造方法。 The manufacturing method according to any one of claims 1 to 3, wherein the current density in the electrolysis step is 0.5 to 3.0 A/cm 2 .
  5. 　１×１０５～２×１０７Ｐａの圧力下で前記電解工程を行う、請求項１～４のいずれか１項に記載の製造方法。 The manufacturing method according to any one of claims 1 to 4, wherein the electrolysis step is performed under a pressure of 1×10 5 to 2×10 7 Pa.
  6. 　Ｎｉ：５０～７５質量％と、Ｆｅ及びＣｏの少なくとも１つ以上と、Ａｌ、Ｔｉ、Ｃｒ、Ｍｎ、Ｃｕ、Ｚｎ、Ｎｂ、Ｍｏ、Ｔａ及びＷからなる群から選択される少なくとも１つ以上の元素と、を含む陽極材料。 Ni: 50 to 75% by mass, at least one or more of Fe and Co, and at least one or more selected from the group consisting of Al, Ti, Cr, Mn, Cu, Zn, Nb, Mo, Ta, and W. An anode material containing the elements.
PCT/JP2023/024661 2022-07-13 2023-07-03 Hydrogen production method and anode material WO2024014344A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH02153088A (en) * 1988-12-06 1990-06-12 Mitsubishi Metal Corp Solder plating method
JP2009007647A (en) * 2007-06-29 2009-01-15 Hitachi Ltd Organic hydride manufacturing apparatus and distributed power supply and automobile using the same
CN112156788A (en) * 2020-07-28 2021-01-01 中南大学 Quaternary Ni-Fe-W-Mo alloy high-efficiency oxygen evolution electrocatalyst and preparation method and application thereof

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH02153088A (en) * 1988-12-06 1990-06-12 Mitsubishi Metal Corp Solder plating method
JP2009007647A (en) * 2007-06-29 2009-01-15 Hitachi Ltd Organic hydride manufacturing apparatus and distributed power supply and automobile using the same
CN112156788A (en) * 2020-07-28 2021-01-01 中南大学 Quaternary Ni-Fe-W-Mo alloy high-efficiency oxygen evolution electrocatalyst and preparation method and application thereof

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