JP2009179871A - Electrolytic cell and hydrogen producing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic cell provided with an electrode using a metal oxide to be inexpensive than platinum and having a lower overvoltage than that of a metal such as nickel or iron of a platinum substitute material and a hydrogen producing apparatus. <P>SOLUTION: In an electrolytic cell electrolyzing alkali water 2 by applying a prescribed voltage from a power source part 6 to an oxygen electrode 3 and a hydrogen electrode 4 dipped in the alkali water 2 housed in a water bath 1, a voltage applied part where the prescribed voltage is applied is constituted of an oxide having a perovskite type structure to produce hydrogen in the hydrogen producing apparatus A. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrolysis cell and a hydrogen production apparatus.

Reduction of CO ₂ generation is screamed as a global warming prevention measure. The generation of CO ₂ is largely caused by the generation of energy by burning fossil fuel. In particular, the combustion of gasoline fuel in automobiles is the best, and in recent years, there is an increasing expectation for a clean fuel that will replace fossil fuel.

Hydrogen gas is drawing attention as a clean fuel. Since hydrogen gas does not generate CO ₂ when burned, it generates only water and is therefore environmentally friendly, and is expected to be a fuel for the next generation of automobiles.

  As an apparatus for generating this hydrogen gas, an electrolyzer utilizing electrolysis of water is known. The electrolysis apparatus includes an electrolytic cell containing water, two metal electrodes immersed in the water in the electrolytic cell, a separator, and a voltage application device that applies a predetermined voltage between the two electrodes. Yes.

  Then, when generating hydrogen gas, a voltage application device applies a predetermined voltage between the two metal electrodes to electrolyze water, and oxygen gas is supplied from one metal electrode (anode electrode) side. While generating, hydrogen gas was generated from the other metal electrode (cathode electrode) side.

  In addition, in this type of electrolyzer, attempts have been made to generate hydrogen gas by electrolyzing alkaline water instead of water. Thus, hydrogen gas can be generated more efficiently when electrolyzing alkaline water than when electrolyzing water.

As this type of electrolysis apparatus, Patent Document 1 discloses that metals such as Pt (platinum) and Ni (nickel) having high electrical conductivity and low overvoltage when generating hydrogen gas are used for the anode electrode and the cathode electrode. There has been disclosed an electrolyzer that uses it to improve the generation efficiency of hydrogen gas. (For example, refer to Patent Document 1).
JP 2006-118202 A

  However, in the above conventional electrolysis apparatus, expensive Pt, which is a noble metal, is used for the anode electrode and the cathode electrode, so that it is difficult to mass-produce at a low cost. There was a problem of low.

  Therefore, in the present invention according to claim 1, an electrolytic cell for electrolyzing the alkaline water by applying a predetermined voltage by immersing in alkaline water, the voltage application to which the predetermined voltage is applied. The portion is made of an oxide having a perovskite structure.

  Further, in the present invention according to claim 2, in the hydrogen production apparatus for electrolyzing alkaline water to produce hydrogen, the oxygen electrode on the oxygen generation electrode side on the anode side immersed in the alkaline water tank and the alkaline water tank And a hydrogen electrode on the hydrogen generation electrode side on the cathode side to be immersed, wherein the hydrogen electrode is composed of an oxide having a perovskite structure.

  According to a third aspect of the present invention, in the hydrogen production apparatus according to the second aspect, the oxygen electrode is composed of an oxide having the perovskite structure.

  According to the present invention, the voltage application unit to which a predetermined voltage is applied when the alkaline water is electrolyzed by immersing in alkaline water and applying a predetermined voltage is constituted by an oxide having a perovskite structure. In an electrolysis cell that electrolyzes alkaline water to which this technology is applied and a hydrogen production apparatus that electrolyzes alkaline water to produce hydrogen, it is manufactured in comparison with those using a metal electrode such as Pt as the voltage application unit The price can be kept low, and the electrolysis of alkaline water can be performed with a high efficiency equal to or higher than that of Pt, and the hydrogen generation efficiency can be greatly improved. Furthermore, since the crystal structure is a perovskite structure and the lattice energy is stable and large, it does not cause metal oxide alteration due to reduction on the hydrogen generation electrode side despite the metal oxide, and the electrolysis performance of alkaline water can be improved. There is an effect that does not hinder.

  The electrolysis cell according to the present embodiment is an electrolysis cell that electrolyzes the alkaline water by immersing it in alkaline water and applying a predetermined voltage, and a voltage application unit to which the predetermined voltage is applied. Is made of an oxide having a perovskite structure.

  Further, in a hydrogen production apparatus that electrolyzes alkaline water to produce hydrogen, an oxygen electrode on the oxygen generation electrode side on the anode side immersed in the alkaline water tank, and a hydrogen generation electrode side on the cathode side that is also immersed in the alkaline water tank The hydrogen electrode is composed of an oxide having a perovskite structure in the crystal structure.

  The oxygen electrode is composed of an oxide having the perovskite structure.

  An embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram of a hydrogen production apparatus A according to this embodiment. As shown in FIG. 1, the hydrogen production apparatus A includes a water tank 1, alkaline water 2, an oxygen electrode 3, a hydrogen electrode 4, a porous polymer film 5, and a power supply unit 6. Alkaline water 2 is accommodated in the water tank 1. In the alkaline water 2, an oxygen electrode 3 (hereinafter referred to as electrode 3) serving as an oxygen generation electrode on the anode side and a hydrogen electrode 4 (hereinafter referred to as electrode 4) serving as a hydrogen generation electrode on the cathode side are immersed. A porous polymer film 5 such as polypropylene is interposed between the electrodes 3 and 4 as a separator. Reference numeral 6 denotes a power supply unit for performing electrolysis. The power supply unit 6 applies a predetermined voltage between the electrodes 3 and 4 as a voltage application unit.

  In the hydrogen production apparatus A of the present embodiment, the electrodes 3 and 4 and the porous polymer film 5 therebetween are arranged at predetermined intervals. An integrated electrolysis cell may be formed by bringing the conductive polymer film 5 into close contact. Further, the electrodes 3 and 4 and the porous polymer film 5 between them can be formed in a thin film shape, and the electrolysis cell can be of a thin film type.

  Next, oxides of materials used for the electrodes 3 and 4 will be described. The present inventor has paid attention to the fact that the electrolysis reaction of water that obtains hydrogen and oxygen by flowing electricity into water and the power generation reaction in the fuel cell that obtains electricity from hydrogen and oxygen are opposite to each other. The idea of using the perovskite oxide, which has been used as the electrode catalyst for the cathode electrode on the cathode reaction side, as the electrode catalyst for the hydrogen generation electrode on the cathode reaction side in alkaline water electrolysis, has been reached.

  Usually, in the hydrogen production apparatus A, when a metal oxide is used for the electrode 4 on the hydrogen generation electrode side, the electrode 4 on the hydrogen generation electrode side is expected to be reduced during electrolysis and the electrolysis efficiency is expected to decrease. Until now, there has been no technical idea to use metal oxide for the electrode 4 on the hydrogen generation electrode side of the hydrogen production apparatus A. Therefore, as a result of intensive research, the inventor of the present invention did not change the physical properties even when the metal oxide was used for the electrode 4 on the hydrogen generation electrode side, and was stable, low overvoltage, excellent energy efficiency, and electrolysis. It has been found that the present invention can perform alkaline water electrolysis with energy efficiency equal to or higher than Pt without using expensive Pt or the like.

A metal oxide having a perovskite structure is generally represented by ABO ₃ . In particular, each of the electrodes 3 and 4 of this embodiment has an element such as La (lanthanum) arranged at the A site, and further, an element such as Sr (strontium) is doped into the element such as La constituting the A site. ing. Further, an element such as Co (cobalt) is arranged at the B site. Since this perovskite type crystal structure has a stable and large lattice energy, even if it is used as the electrode 4 for the hydrogen generation electrode on the cathode side, the metal oxide is not reduced and deteriorated. The A site is not limited to La, and any rare earth element can be used.

  Since different atoms are doped at the A site, charge carriers are generated due to the effect of the doped different atoms, and the electrical conductivity is improved. Therefore, each of the electrodes 3 and 4 is used as an electrode having a highly active electrode catalyst. Can be configured.

  Further, in this embodiment, the oxygen electrode 3 on the oxygen generation electrode side and the hydrogen electrode 4 on the hydrogen generation electrode side are manufactured using the same perovskite structure metal oxide, so the other electrode is manufactured in a separate process. There is no need to mix up the materials. Therefore, since each electrode 3 and 4 can be mass-produced simultaneously, the cheap and highly efficient hydrogen production apparatus A can be provided.

  In the present embodiment, both the oxygen electrode 3 on the oxygen generation electrode side and the hydrogen electrode 4 on the hydrogen generation electrode side are made of an oxide having a perovskite structure, but only the hydrogen electrode 4 has a crystal structure. You may comprise with the oxide of a perovskite type structure.

  Next, a method for producing a metal oxide having a perovskite structure in this embodiment will be described.

  First, as shown in FIG. 2, as a preparation stage, La acetate, Sr acetate, and Co acetate are prepared, and dissolved and stirred so as to be uniformly mixed.

  Here, each acetate is weighed so that La, Sr, and Co have a predetermined ratio, and dissolved in pure water to prepare an aqueous solution. By stirring the prepared aqueous solution, each acetate is mixed so as to be uniform (step 101, dissolution stirring step). Here, the ratio of La, Sr, and Co is (La: Sr: Co) = (0.6: 0.4: 1).

  Next, the aqueous solution prepared in step 101 is heated in an electric furnace to evaporate moisture and obtain a sample in which each acetate salt is uniformly mixed (step 102, firing preparation step).

  The sample obtained in step 102 is pre-baked at 400 ° C. for 2 hours, and a generated gas such as acetic acid gas is discharged (step 103, pre-baking step).

  Subsequently, the sample calcined in step 103 is subjected to main baking at 1000 ° C. for 6 hours (step 104, main baking step).

  The sample fired in Step 104 is pulverized with a pestle and a mortar, and further fired at 1200 ° C. for 6 hours (Step 105, finishing process).

  Whether or not the sample obtained in Step 105 is a metal oxide having a perovskite structure is analyzed and confirmed by an X-ray diffractometer.

  In this embodiment, the ratio of La, Sr, and Co in the metal oxide having a perovskite structure is (La: Sr: Co) = (0.6: 0.4: 1). However, if at least La, Sr and Co are contained, the blending ratio can be arbitrarily changed.

  As a characteristic of the metal oxide of the present embodiment, since the crystal structure is a perovskite structure and stable, the lattice energy is stable and large. There is no reduction.

A metal oxide having a perovskite structure in the present embodiment is represented by ABO ₃ . La is arranged at the A site, and Co is arranged at the B site. Further, partial substitution is performed by doping Sr of different atoms into the A site as an additive, generating electron holes and improving electrical conductivity. As the ratio, (La: Sr) = (1: 9) to (9: 1) can be considered, but preferably the ratio is (La: Sr) = (6: 4) to (7: 3). By doing so, an excellent electrode can be configured. In this way, a highly active electrode catalyst can be obtained by optimally doping the metal at the A site of the perovskite-type metal oxide with a different atom as an additive. The additive is not limited to Sr as long as it has a low valence, and similar effects can be obtained with alkaline earth metals such as Ca (calcium) and Ba (barium) and alkali metals such as Na (sodium). However, Sr close to the ion radius La exhibits the best effect.

  Here, a method for manufacturing an electrode using a metal oxide having a perovskite structure will be described. First, a polymer compound is mixed as a molding binder with the perovskite metal oxide produced by the above-described method. At this time, for example, they are mixed at a ratio of (metal oxide: polymer compound = 98: 2 (weight ratio)).

  Next, an electrode is formed by spreading the metal oxide mixed with the molding binder as described above so that the current collecting mesh is surrounded by the center. At this time, it is formed so as to be sandwiched with the metal oxide mixed with the molding binder as described above, with the current collecting mesh as the center.

  After the electrode is formed, the electrode is manufactured by hot pressing at a temperature, a time, and a pressure of, for example, 120 ° C., 5 minutes, 1 MPa, then 120 ° C., 5 minutes, 2 MPa.

  As described above, the electrodes 3 and 4 of the present embodiment are made of stainless steel that becomes a powder metal oxide and an electrode body by mixing a polymer compound with a metal oxide and allowing the polymer compound to function as a molding binder. The connection with the current collector mesh is improved, and the contact resistance between the metal oxide and the current collector mesh is reduced. Therefore, the electrolytic characteristics of the hydrogen production apparatus A are improved. In the present embodiment, the electrolytic characteristics are further improved by mixing the polymer compound, for example, Nafion (registered trademark) powder at the aforementioned ratio.

  The electrolytic characteristics of the electrodes 3 and 4 will be described. FIG. 3 shows electrolytic characteristics when each metal oxide is used as an electrode for alkaline water electrolysis. The vertical axis represents current density and the horizontal axis represents potential.

  In FIG. 3, the relationship between the potential of the hydrogen generation electrode on the cathode side and the current density is shown on the left side from the center, and the relationship between the potential and the current density of the oxygen generation electrode on the anode side is shown on the right side.

  Here, a comparison is made by changing the types of metals at the A site and the B site of a metal oxide having a perovskite type crystal structure.

  The present invention is characterized in that a metal oxide is used for the electrode 4, and as an object for comparison, the electrolytic characteristics of a carbon electrode carrying platinum that is usually used for electrolysis of alkaline water are also shown. . In the electrolysis of alkaline water, the electrolytic characteristics of the electrolysis cell are determined by comprehensively determining the characteristics of the electrodes of both electrodes. For example, even if only the hydrogen generation electrode on the cathode side has good electrolysis efficiency, if the electrolysis efficiency on the oxygen generation electrode side on the anode side is not good, the electrolysis characteristics of the electrolysis cell as a whole are not very good.

As shown in FIG. 3, the carbon electrode carrying Pt showing a high current density at a low voltage has the best electrolysis efficiency at the hydrogen generation electrode on the cathode side. However, when the potential is around −1.0 V, Pt is supported. Since the retained carbon electrode and the La _0.6 Sr _0.4 CoO ₃ electrode show substantially the same electrolysis efficiency, it can be seen that a perovskite metal oxide is used for the electrode 4 on the cathode side hydrogen generation electrode side.

Further, as shown in FIG. 3, at the oxygen generation electrode on the anode side, it can be seen that the La _0.6 Sr _0.4 CoO ₃ electrode and the La _0.6 Sr _0.4 FeO ₃ electrode showing high current density at a low voltage have the best electrolysis efficiency. . In addition, Ag and AgCl are used as electrodes as standard electrodes for potential measurement.

FIG. 4 shows the electrolysis characteristics of the electrolysis cell in which the characteristics of the electrodes of both electrodes in the electrolysis of alkaline water are combined as described above. The vertical axis represents current density and the horizontal axis represents potential. As the electrode of the alkaline water electrolysis cell, the carbon electrode carrying Pt and the La _0.6 Sr _0.4 CoO ₃ electrode show substantially the same electrolysis efficiency. From this, it can be seen that an inexpensive and highly efficient electrode for an alkaline water electrolysis cell can be provided by using a metal oxide for both electrodes without using expensive Pt for the electrode.

FIG. 5 shows impedance measurement results in alkaline water electrolysis of a La _0.6 Sr _0.4 CoO ₃ electrode having particularly good electrolysis efficiency and a carbon electrode carrying platinum used in normal alkaline water electrolysis. . FIG. 5A shows that the impedance plot trajectory of the La _0.6 Sr _0.4 CoO ₃ electrode extends in the horizontal axis direction when the La _0.6 Sr _0.4 CoO ₃ electrode and the Pt-supported C electrode are compared. From this, the La _0.6 Sr _0.4 CoO ₃ electrode has a larger diffusion overvoltage because the metal oxide particles constituting the electrode are larger than the Pt-supported C electrode, that is, the surface area of the metal oxide particles is small. I understand.

Further, from FIG. 5B, when comparing the La _0.6 Sr _0.4 CoO ₃ electrode and the Pt-carrying C electrode, the Pt-carrying C electrode shows a slightly complicated impedance plot trajectory. It can be seen that the locus of the impedance plot extends in the direction. From this, it can be seen that there is almost no difference in the decrease in electrolytic efficiency of the La _0.6 Sr _0.4 CoO ₃ electrode and the Pt-supported C electrode due to the activation overvoltage.

Thus, from FIGS. 5 (a) and 5 (b), there is almost no difference in the decrease in electrolytic efficiency due to the activation overvoltage of the La _0.6 Sr _0.4 CoO ₃ electrode and the Pt-supported C electrode. Is used as an electrode for alkaline water electrolysis, metal oxide particles are made fine, and the surface area of the particles is increased to reduce the diffusion overvoltage as much as possible. A decomposition electrode can be produced at low cost.

FIG. 6 shows the production rate of hydrogen and oxygen when the metal oxide in the electrolysis of alkaline water is used for the cathode-side hydrogen generation electrode and the anode-side oxygen generation electrode. The vertical axis represents the generation rate, and the horizontal axis represents the current density. The measured values plotted in FIG. 6 are the values of the La _0.6 Sr _0.4 CoO ₃ electrode that showed excellent electrolysis efficiency among the metal oxides used in the electrode for alkaline water electrolysis.

  As can be seen from FIG. 6, the measured value is close to the theoretical value according to Faraday's law, and even in the electrolysis of alkaline water, even if the metal oxide is used for both electrodes, particularly the hydrogen generation electrode on the cathode side, it is highly efficient. It can be seen that decomposition can be performed.

FIG. 7 is a graph showing the results of X-ray diffraction of a La _0.6 Sr _0.4 CoO ₃ electrode showing excellent electrolysis efficiency among the metal oxides used for the electrode for alkaline water electrolysis. Is strength, and the horizontal axis is angled. Also, a in FIG. 7) shows the composition of La _0.6 Sr _0.4 CoO ₃ before alkaline water electrolysis, b) the composition of La _0.6 Sr _0.4 CoO ₃ oxygen generating electrode at the anode side after alkaline water electrolysis C) shows the composition of La _0.6 Sr _0.4 CoO ₃ of the hydrogen generation electrode on the cathode side after alkaline water electrolysis.

  Since peaks a), b), and c) in FIG. 7 are at substantially the same positions and the heights thereof are also approximately the same, metal oxides are used for both electrodes in alkaline water electrolysis. It can also be seen that the electrode composition does not change before and after electrolysis.

FIG. 8 is a graph showing the long-term stability of a La _0.6 Sr _0.4 CoO ₃ electrode showing excellent electrolysis efficiency among metal oxides used for an electrode for alkaline water electrolysis. The horizontal axis takes time. The locus of data when electrolysis is performed for a long time at a current density of 25 mA / cm ² is shown. Since the potential value gradually increases until 100 hours after electrolysis and the current density is constant, it can be seen that the electrolysis efficiency decreases due to the increase in resistance. However, since the electric potential value does not increase, that is, the resistance does not increase after that, the metal oxide is particularly formed on the cathode side hydrogen generating electrode, which is a feature of the present invention. It can be seen that electrolysis can be carried out stably over a long period of time without reducing and deteriorating even when using.

  From the above, in the present embodiment, the metal oxide, which is conventionally considered to be reduced when used for the electrode 4 on the hydrogen generation electrode side, can also be used on the hydrogen generation electrode side on the cathode side. It can be seen that highly efficient alkaline water electrolysis can be performed without reducing the electrode 4.

  As described above, by forming the electrodes 3 and 4 of the alkaline water electrolysis cell using a metal oxide, a highly efficient and inexpensive hydrogen production apparatus can be provided without using Pt.

  Furthermore, in order to provide a highly efficient hydrogen production apparatus, it is necessary to construct an electrolytic cell for low resistance alkaline water.

  In the hydrogen production apparatus A, by reducing the distance between the electrodes, the IR loss of the cell can be reduced and the electrolysis efficiency can be improved. Furthermore, by using a porous polymer film such as polypropylene as a separator, a thin-film alkaline water electrolytic decomposition cell can be constructed, and the hydrogen production apparatus can be downsized. In this embodiment, a Nafion (registered trademark) film can be used as a separator.

  FIG. 9 is a schematic view of a thin film type electrolysis cell. As shown in FIG. 9, the thin-film electrolysis cell is constructed by adhering a hydrogen generation electrode 4 on the cathode side, an oxygen generation electrode 3 on the anode side, and a porous polymer film 5. When electrolysis is performed, alkaline water as an electrolyte is immersed in the porous polymer film 5, a predetermined voltage is applied to the electrodes 3 and 4, and the thin film electrolysis cell is energized, whereby the alkaline water is discharged. Decomposition can be performed.

  By interposing the separator between the electrodes as described above, the internal resistance can be reduced by arranging the electrodes by shortening the distance between the electrodes. In addition, since the electrolytic cell can be made into a thin film type, a small hydrogen production apparatus can be configured. Also, by conducting impedance analysis, creating an equivalent circuit, and measuring and evaluating the circuit, a three-phase interface where the gas phase, the electrolyte liquid phase, and the catalyst phase in the electrolysis of alkaline water are in contact with each other By analyzing the progress in and reflecting the analysis result, a more efficient and small alkaline water electrolysis cell can be constructed. In addition, by increasing the operating temperature of the electrolyzer, a more efficient and compact hydrogen production apparatus can be obtained.

  The hydrogen production apparatus itself can be mounted on an automobile using hydrogen gas as fuel.

  Moreover, when mounting the hydrogen production apparatus A which concerns on this embodiment in a motor vehicle, the alkaline water pressurized previously in the water tank 1 of the hydrogen production apparatus A is thrown in. Thus, since the pressurized hydrogen gas can be obtained even if it does not use a compressor by using the alkaline water pressurized beforehand in the water tank 1, the enlargement of an apparatus can be prevented. .

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims.・ Change is possible.

It is the schematic diagram which showed the hydrogen production apparatus which concerns on this Embodiment. It is the flowchart which showed the preparation procedures of each electrode which concerns on this Embodiment. It is the figure which showed the electrolysis characteristic at the time of using each metal oxide for each electrode which concerns on this Embodiment. It is the figure which showed the electrolysis characteristic of the electrolysis cell which integrated the characteristic of each electrode which concerns on this Embodiment. Each electrode according to the present embodiment is a diagram showing the impedance measurement results in the alkaline water electrolysis when the C electrodes carrying the La _0.6 Sr _0.4 CoO ₃ electrodes or Pt. Each electrode according to the present embodiment is a view showing a hydrogen and oxygen generation rate when using the La _0.6 Sr _0.4 CoO _3. Each electrode according to the present embodiment is a graph showing the results of X-ray diffraction before and after electrolysis when using the La _0.6 Sr _0.4 CoO _3. Each electrode according to the present embodiment is a view showing a long-term stability of the electrode when using an La _0.6 Sr _0.4 CoO _3. It is a schematic diagram of the thin film type electrolysis cell of the hydrogen production device concerning this embodiment.

Explanation of symbols

A Hydrogen production equipment 1 Water tank 2 Alkaline water 3 Oxygen electrode 4 Hydrogen electrode 5 Porous polymer membrane 6 Power supply

Claims (3)

An electrolysis cell for electrolyzing the alkaline water by immersing it in alkaline water and applying a predetermined voltage,
An electrolysis cell, wherein the voltage application section to which the predetermined voltage is applied is made of an oxide having a perovskite structure. In a hydrogen production device that produces hydrogen by electrolyzing alkaline water,
An oxygen electrode on the oxygen generation electrode side on the anode side immersed in the alkaline water tank;
Also having a hydrogen electrode on the hydrogen generation electrode side on the cathode side immersed in the alkaline water tank,
An apparatus for producing hydrogen, wherein the hydrogen electrode is composed of an oxide having a perovskite structure.   The hydrogen production apparatus according to claim 2, wherein the oxygen electrode is made of an oxide having the perovskite structure.

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