JP2016207535A - Reversible fuel cell with third electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a fuel cell is inferior in followability with respect to load variation and a secondary battery is capable of storing power, on the other hand, but electric capacity capable of storing power in the battery is limited.SOLUTION: In a reversible fuel cell with a third electrode, a first electrode containing nickel hydroxide, a second electrode containing a hydrogen-storing alloy, the third electrode containing manganese dioxide and a separator interposed among the first electrode, the second electrode and the third electrode are accommodated within a sealed container. In the reversible fuel cell that is improved in the load followability, an oxygen gas that is generated from the first electrode by an oxidation reduction reaction between the first electrode and the third electrode and a hydrogen gas that is generated from the second electrode by an oxidation reduction reaction between the second electrode and the third electrode are separately stored in an oxygen gas storage chamber and a hydrogen gas storage chamber, and power is generated by the oxygen gas and the hydrogen gas from the oxygen gas storage chamber and the hydrogen gas storage chamber.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a reversible fuel cell that can store electrical energy supplied at the time of charging as chemical energy, and convert the stored chemical energy into electrical energy for use.

  Secondary batteries and fuel cells are highly efficient and clean energy sources. In recent years, development of electric vehicles, fuel cell vehicles, and trains using such secondary batteries and fuel cells as power sources has been progressing worldwide.

  Fuel cells are attracting attention as power sources with high energy conversion efficiency and low environmental impact. The fuel cell cannot store electricity. However, it is possible to construct a kind of electric power storage system by combining a fuel cell and a hydrogen production apparatus using water electrolysis. Such a power storage system is called a reversible fuel cell (see Patent Document 1 and Patent Document 2). In such a reversible fuel cell in which a fuel cell and a water electrolyzer are combined, electrolysis of water, which is a reverse reaction of power generation, is performed using natural energy or night power when power is not generated. Thus, the power generation system using the reversible fuel cell manufactures its own fuel.

  On the other hand, the secondary battery is used as a power source for electric and electronic devices that require large current discharge such as electric tools. In particular, recently, nickel hydride secondary batteries and lithium ion secondary batteries have attracted attention as batteries for hybrid vehicles driven by engines and batteries.

  A normal secondary battery is charged by receiving supply of electric energy and can store electricity. Patent Document 3 discloses a secondary battery that can be charged using a gas. Patent Document 4 discloses a new type of fuel cell that combines a secondary battery and a fuel cell that uses manganese hydroxide as a positive electrode active material and a hydrogen storage alloy as a negative electrode active material.

JP 2002-348694 A JP 2005-65398 A JP 2010-15729 A

  The secondary battery can store electricity. In addition, the output characteristics are excellent and the load followability is good. However, the amount of the negative electrode and the positive electrode active material depends on the volume of the battery. For this reason, there is a limit to the electric capacity that can be stored in the battery. And it is difficult for a secondary battery to raise energy density significantly.

  On the other hand, the fuel cell generates power (discharges) using hydrogen gas or oxygen gas supplied from the outside. For this reason, the fuel cell does not have a problem related to the limit of energy density, which the secondary battery has. However, since the fuel cell is inferior to the load fluctuation at the time of discharge, it is difficult to apply to a use with a large load fluctuation, and it is usually used in combination with a power storage device such as a secondary battery or a capacitor. There are many. In addition, the fuel cell has a structure in which the reaction space is small because the line where gas, liquid, and solid contact at the same time, which is a gas diffusion electrode, is used as a reaction space. There are problems such as the need for such an expensive catalyst.

  Further, a fuel gas such as hydrogen gas used in the fuel cell is taken out from a hydrogen production apparatus (for example, Patent Document 1), and the generated gas is a brown gas in which the ratio of hydrogen to oxygen is 2: 1. is there. Therefore, care must be taken to ensure safety.

  The present invention has been made in consideration of such points, and an object thereof is to provide a reversible fuel cell having high energy density and excellent load followability.

In order to achieve the above-described object, a reversible fuel cell including a third electrode according to the present invention includes a first electrode containing nickel hydroxide, a second electrode containing a hydrogen storage alloy, and a standard electrode potential of the first electrode. A third electrode that is smaller than a standard electrode potential of one electrode and larger than a standard electrode potential of the second electrode; and a separator that allows ions interposed between the electrodes to pass but does not allow electrons to pass. The oxygen gas generated from the first electrode is stored by the oxidation reaction using the first electrode as an anode and the reduction reaction using the third electrode as a cathode, and the oxidation reaction using the second electrode as a cathode and the first reaction. Hydrogen gas generated from the second electrode is stored by a reduction reaction using three electrodes as an anode.
In this configuration, the third electrode is disposed between the first electrode and the second electrode. A reversible fuel cell refers to a fuel cell capable of storing electricity that can reversibly convert fuel gas and electrical energy. Oxygen is generated from the first electrode by an oxidation reaction using the fully charged first electrode as an anode, and hydrogen is generated from the second electrode by an oxidation reaction using the fully charged second electrode as a cathode. Convert electrical energy into chemical energy of oxygen and hydrogen.

The reversible fuel cell having the third electrode according to the present invention generates power by supplying the hydrogen gas to the second electrode and supplying the oxygen gas to the third electrode.
In this configuration, the reversible fuel cell according to the present invention can generate power using the oxygen gas and hydrogen gas generated by the oxidation-reduction reaction described above, and can also generate power using oxygen gas and hydrogen gas supplied from the outside. Can do.

In the reversible fuel cell including the third electrode according to the present invention, the third electrode contains manganese dioxide. In the reversible fuel cell provided with the third electrode according to the present invention, the third electrode further contains nickel hydroxide. Furthermore, in the reversible fuel cell including the third electrode according to the present invention, the electrode capacity of the third electrode is larger than the electrode capacity of the first electrode and the second electrode.
In this configuration, by using manganese dioxide as the third electrode, a reversible fuel cell can be configured at low cost. Further, by adding nickel hydroxide to the third electrode, an electrode excellent in output characteristics and life characteristics can be obtained.

In the reversible fuel cell including the third electrode according to the present invention, the distance between the first electrode, the third electrode, and the second electrode is 5 to 500 μm.
In this configuration, since the distance between the electrodes is short, a reversible fuel cell having high efficiency and excellent output characteristics can be configured.

A reversible fuel cell including a third electrode according to the present invention includes a sealed container that houses the first electrode, the second electrode, the third electrode, and the separator, and the hydrogen gas and the Each oxygen gas can be taken out from the sealed container.
In this configuration, the hydrogen gas and the oxygen gas can be individually taken out from the non-pay container without being mixed, so that no brown gas is generated. Safety is ensured.

A reversible fuel cell including a third electrode according to the present invention includes a first electrode containing nickel hydroxide, a second electrode containing a hydrogen storage alloy, and a standard electrode potential smaller than the standard electrode potential of the first electrode. And a third electrode that is larger than the standard electrode potential of the second electrode, a separator that allows ions interposed between the electrodes to pass but does not pass electrons, the first electrode, the second electrode, and the third electrode. An oxygen container which has an electrode, the separator, and a sealed container for storing an electrolyte, and is generated from the first electrode by an oxidation reaction using the first electrode as an anode and a reduction reaction using the third electrode as a cathode; Is taken out from the sealed container in a state dissolved in the electrolyte, and hydrogen generated from the second electrode is gasified by an oxidation reaction using the second electrode as a cathode and a reduction reaction using the third electrode as an anode. State in removed from the sealed container.
In this configuration, hydrogen and oxygen taken out from the sealed container are stored in the hydrogen gas storage chamber and the oxygen gas storage chamber, respectively. The stored hydrogen and oxygen can be reconverted into electrical energy for use when the battery is discharged. In particular, oxygen generated in the positive electrode is dissolved in the electrolytic solution and completely separated from hydrogen, so that the safety of handling oxygen is improved.

  In the reversible fuel cell having the third electrode according to the present invention, the electrolyte in the sealed container can flow into the buffer tank, and the pressure from the buffer tank is reduced to reduce oxygen from the electrolyte. Gas can be taken out from the buffer tank.

  In the reversible fuel cell having the third electrode according to the present invention, a salt concentration adjusting device for adjusting the concentration of the electrolytic solution is connected to the buffer tank, and the electrolytic solution is injected by injecting pure water. The salt concentration can be adjusted. In the reversible fuel cell having the third electrode according to the present invention, the sealed container is provided with an inlet and an outlet for the electrolyte, and the electrolyte flowing out from the outlet is the buffer tank. It is possible to flow into the inflow port via.

  The reversible fuel cell having the third electrode according to the present invention performs power generation by supplying the hydrogen gas to the second electrode and supplying the oxygen gas extracted from the buffer tank to the third electrode.

  As described above, according to the reversible fuel cell according to the present invention, by providing a storage chamber for separately storing hydrogen gas and oxygen gas, the electric energy supplied at the time of charging is stored as a gas and reconverted into electric energy. Can be used. For this reason, in this reversible fuel cell, the electrical energy that can be taken out is stored as chemical energy in each storage chamber, and does not depend on the amount of active material contained in the electrode material, so that high energy density is achieved. It becomes possible.

In addition, in the conventional sealed secondary battery, energy that has been discarded as heat at the time of overcharging can be reused as electric energy, so that energy utilization efficiency is improved.
Furthermore, since electric energy is input and output through the electrode reaction of the secondary battery, charging is possible and followability with respect to load fluctuations is greatly improved as compared with conventional fuel cells. Moreover, such a battery can be manufactured and supplied at low cost by adopting a simple structure that does not require an additional member or device for supplying gas.

  The reversible fuel cell provided with the third electrode of the present invention is characterized by high energy density and excellent load followability. In addition, by separating the reaction that generates oxygen and the reaction that generates hydrogen, hydrogen gas and oxygen gas are not mixed, and safety is high.

1 is a drawing schematically showing a structure of a battery unit according to a reversible fuel cell of the present invention. It is drawing which shows the structure typically about the variation of a battery unit. It is drawing which shows the structure typically about the other variation of a battery unit. It is a systematic diagram of the process which concerns on 2nd Embodiment using a reversible fuel cell. It is a systematic diagram for demonstrating the electric power generation process which concerns on 3rd Embodiment using a reversible fuel cell.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments, and various other modifications are possible.
(First embodiment)

Prior to detailed description of the reversible fuel cell according to the first embodiment, electrodes that are main components will be described, and then the reversible fuel cell will be described. For convenience of explanation, the first electrode will be referred to as the positive electrode, the second electrode will be referred to as the negative electrode, and the third electrode will be referred to as the intermediate electrode. To do.
<Positive electrode material>
The positive electrode active material is preferably nickel hydroxide. Moreover, since it is easy to achieve high capacity | capacitance, a positive electrode active material has a large bulk density, for example, a spherical thing is preferable.

<Hydrogen storage alloy>
The hydrogen storage alloy contained in the negative electrode material is not particularly limited as long as it can store and release hydrogen. For example, AB5 type that is a rare earth alloy, AB2 type that is a Laves phase alloy, AB type that is a titanium-zirconium alloy, and A2B type that is a magnesium alloy can be used.

  Among these, from the viewpoints of hydrogen storage capacity, charge / discharge characteristics, self-discharge characteristics, and cycle life characteristics, it is preferable to be an AB5 type rare earth-nickel alloy containing a MmNiCoMnAl misch metal.

<Intermediate electrode material>
The standard electrode potential of the intermediate electrode is preferably between the standard electrode potential of the positive electrode and the negative electrode. Since the standard electrode potential of the positive electrode (nickel hydroxide) is 0.480 and the standard electrode potential of the negative electrode (hydrogen storage alloy) is -0.828, the standard electrode potential of the intermediate electrode is -0.828 to 0.480. If it is in range. Examples of the active material for the intermediate electrode include cadmium, zinc, lead, and manganese dioxide. Among these, manganese dioxide is the most appropriate considering the price and environmental burden. The standard electrode potential of the intermediate electrode using manganese dioxide as an active material is 0.15, which is within the above range. Manganese dioxide has abundant reserves and is 1/5 to 1/10 the price of nickel hydroxide. As will be described later, the amount of nickel hydroxide required for the reaction can be greatly reduced by introducing the intermediate electrode.

<Binder>
Examples of the binder include polyacrylic acid soda, methyl cellulose, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), ethylene-vinyl alcohol, ethylene vinyl acetate copolymer (EVA), polyethylene ( PE), polypropylene (PP), and styrene-ethylene-butylene-styrene copolymer (SEBS).
When the total of the electrode materials such as the active material, the binder and the conductive auxiliary agent is 100% by weight, the weight ratio of the binder mixed in each electrode is 0.1 to 10% by weight. It is preferable.

<Conductive aid>
The conductive auxiliary agent may be a conductive powder. The conductive aid may be a carbon powder such as graphite powder, acetylene black, and ketjen black. When the total of the electrode materials such as the active material, the binder and the conductive auxiliary agent is 100% by weight, the weight ratio of the conductive auxiliary agent mixed in each electrode is in the range of 0.1 to 10% by weight. It is preferable.

[Positive electrode]
Nickel hydroxide was used as the active material, carbon black was used as the conductive additive, and ethylene vinyl acetate copolymer (EVA) was used as the binder, and the blending ratio was 100: 5: 5. A powdered positive electrode material was mixed and kneaded into a paste, and this paste was applied or filled on both sides of the current collector. After drying, the current collector was rolled with a roller press to produce a positive electrode. The electrode capacity was 45 mAh. Note that. Although a nickel foil having a thickness of 20 μm was used as the current collector, it may be nickel metal or platinum metal, and the shape may be a three-dimensional shape or a plate shape, and the electrodes may be formed on both sides.

[Negative electrode]
A hydrogen storage alloy was used as the active material, carbon black was used as the conductive additive, and ethylene vinyl acetate copolymer (EVA) was used as the binder, and the blending ratio was 100: 15: 10. Powdered negative electrode materials were mixed and kneaded into a paste, and this paste was applied or filled on both sides of the current collector. After drying, the current collector was rolled with a roller press to produce a negative electrode. The electrode capacity was 48 mAh. Note that. Although nickel foam as a current collector was used, nickel metal or platinum metal may be used, and the shape may be three-dimensional or plate-like, and the electrodes may be formed on both sides.

[Intermediate electrode]
Manganese dioxide was used as the active material, carbon black was used as the conductive assistant, and ethylene vinyl acetate copolymer (EVA) was used as the binder, and the blending ratio was 100: 15: 10. Powdered intermediate electrode materials were mixed and kneaded into a paste, and the paste was filled in a nickel foam current collector. After drying, the current collector was rolled with a roller press to produce an intermediate electrode. The electrode capacity was 260 mAh. Note that. Although nickel foam is used as the current collector, it may be nickel metal or platinum metal, the shape may be foil or plate, and the electrodes may be formed on both sides.

[Electrolytes]
The electrolytic solution used in the present invention is not particularly limited as long as it is an alkaline aqueous solution usually used in water electrolysis. For example, potassium hydroxide (KOH), lithium hydroxide (LiOH), sodium hydroxide (NaOH), etc. Those obtained by dissolving one alkali substance or two or more alkali substances in water are preferred. From the viewpoint of battery output characteristics, the electrolytic solution is preferably an aqueous potassium hydroxide solution. The concentration of the alkaline substance in these electrolytic solutions is preferably 1 to 10 mol / L, and more preferably 3 to 8 mol / L.

[Separator]
The separator used in the present invention is preferably a separator that does not pass electrons but allows protons to pass therethrough but hardly allows gas to pass. Examples of the shape of the separator include a microporous film, a woven fabric, a nonwoven fabric, and a green compact. Among these, a nonwoven fabric is preferable from the viewpoint of output characteristics and production cost. The material of the separator is not particularly limited, but is preferably a separator having alkali resistance, oxidation resistance, and reduction resistance. Examples thereof include materials such as polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, aramid, polyethylene, and polypropylene.
The thickness is preferably in the range of 5 to 500 μm, and more preferably in the range of 20 to 250 μm. If the thickness is less than 5 μm, the possibility of a rare short increases, and if it is 500 μm or more, the electrical resistance increases and the heat loss increases. In the examples, a polypropylene nonwoven fabric having a thickness of 120 μm was employed.

A configuration of a battery unit, which is a main component of the reversible fuel cell according to the present invention, will be described with reference to FIG.
The battery unit 20 constitutes a reversible fuel cell in which a reaction mechanism of a secondary battery is incorporated in a fuel cell that converts the chemical energy of hydrogen and oxygen into electric energy, and is opposed to the battery unit 20 via a separator 14. A positive electrode 11, an intermediate electrode 13, a negative electrode 12, and a sealed container 16 that stores these electrode groups are provided as main components.

  The positive electrode 11, the negative electrode 12, and the intermediate electrode 13 are laminated with a separator 14 that allows ions to pass therethrough but not electrons. The separator 14 prevents the electrodes 11, 12, and 13 from being electrically short-circuited and plays a role of holding the electrolytic solution 15. The electrodes with the separator 14 disposed therebetween are stacked to constitute the electrode stack 10. The scale of the reversible fuel cell can be easily adjusted by adjusting the number of electrodes.

  Each of the positive electrode 11, the negative electrode 12, and the intermediate electrode 13 has terminals 11t, 12t, and 13t for connection with external devices at the ends. The connection terminals 11t, 12t, and 13t are connected to the DC power source 21 by electric wires 22a, 22b, and 22c, respectively. The connection terminals 11t, 12t, and 13t can be selectively connected to the positive pole and the negative pole of the DC power supply 21 by a changeover switch (not shown) built in the DC power supply 21.

  The positive electrode 11 has an oxygen circulation port 17 opened on the electrode surface of the positive electrode 11. In addition, the negative electrode 12 has a hydrogen circulation port 18 opened on the electrode surface of the negative electrode 12. The oxygen circulation port 17 is connected to the oxygen gas storage chamber 23 by a pipe 25a. The hydrogen circulation port 18 is connected to the hydrogen gas storage chamber 24 by a pipe 25b. As shown in FIG. 1, the sealed container 16 is filled with an electrolytic solution 15. The electrode stack 10 is stored in the sealed container 16 in a state of being immersed in the electrolytic solution 15, and constitutes a battery unit 20.

  The battery unit 20 is provided with a replenishing water system 26 for replenishing water that has decreased due to the reaction. The makeup water system 26 has a tank 26 a for storing makeup water and a water supply line 26 b for feeding makeup water to the sealed container 16. A pump may be provided in the water supply line 26b.

  Another configuration example of the electrode group will be described with reference to FIG. The separator 14 is arranged between the electrodes in common with FIG. The positive electrode 11 -the intermediate electrode 13 -the negative electrode 12 are laminated in one set. Although two sets of electrodes are shown in FIG. 2 for convenience, the number of sets is not particularly limited. In this configuration, the number of electrodes 11, 12, 13 is the same. On the other hand, FIG. 3 shows positive electrode 11−intermediate electrode 13−negative electrode 12−intermediate electrode 13−positive electrode 11−intermediate electrode 13..., And the number of intermediate electrodes 13 is increased. As a method of adjusting the capacity of the intermediate electrode 13, the number of sheets may be adjusted as shown in FIG. 2, or the thickness of the intermediate electrode 13 may be doubled as shown in FIG. In addition, variations such as arranging the positive electrode 11 at both ends of the electrode stack 10 are conceivable.

  The positive electrode 11, the intermediate electrode 13, and the negative electrode 12 may be laminated via a separator 14 to constitute an electrode stack, or the laminated electrode may be folded in a bellows shape to constitute the electrode stack 10. In this state, the electrode stack 10 may be configured by winding in a spiral shape. Moreover, the electrolyte solution 15 may be impregnated in the separator 14, or the electrode stack 10 may be immersed in a sealed container 16 filled with the electrolyte solution 15 as shown in FIG. In short, the separator 14 may hold the electrolytic solution 15.

2 and 3, the plurality of positive terminals 11t are connected to each other and connected to the DC power source 24 through the electric wire 22a, and the plurality of negative terminals 12t are connected to each other and connected to the DC power source 24 through the electric wire 22b. The plurality of intermediate electrode terminals 13t are connected to each other and connected to the DC power source 24 through the electric wire 22c.
Similarly, the oxygen circulation port 17 of each positive electrode 11 is connected to the oxygen gas storage chamber 23 by a pipe 25a, and the hydrogen circulation port 18 of each negative electrode 11 is connected to the hydrogen gas storage chamber 24 by a pipe 25b. .

  The operation of the reversible fuel cell configured as described above will be described separately for a fuel gas generation mode, a fuel cell operation mode, and a secondary battery operation mode.

(Fuel gas generation mode)
The fuel gas generation mode is a mode in which hydrogen gas and oxygen gas are generated using an electrode reaction. In this mode, hydrogen gas is generated from the negative electrode 12, and oxygen gas is generated from the positive electrode 11. These hydrogen gas and oxygen gas are not in contact with each other, and are separately provided in the hydrogen gas storage chamber 24 and the oxygen gas storage chamber. 23, respectively.
The fuel gas generation mode will be described using a reaction formula, divided into an oxygen gas generation step and a hydrogen gas generation step.

(STEP1)
This step is an oxygen generation reaction step. The positive electrode 11 was charged by connecting the positive electrode of the DC power source 24 (hereinafter simply referred to as “positive electrode”) to the positive electrode 11 and connecting the negative electrode (hereinafter simply referred to as “negative electrode”) of the DC power source 24 to the intermediate electrode 13. In this case, the reaction formula of the positive electrode 11 is the formula (1).
Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (1)
When the positive electrode 11 is fully charged, oxygen is generated from the positive electrode 11 according to the reaction formula (2).
2OH ⁻ → 2e ⁻ + H ₂ O + 1 / 2O ₂ (2)
On the other hand, the reaction formula of the intermediate electrode is the formula (3).
MnO ₂ + H ₂ O + e ⁻ → MnOOH + OH ⁻ (3)
And the total reaction formula before full charge of the positive electrode and the intermediate electrode is
From Equation (1) and Equation (3), Equation (4) is obtained.
MnO ₂ + Ni (OH) ₂ → MnOOH + NiOOH (4)
Here, as the discharge of the intermediate electrode 13 proceeds, an irreversible manganese trioxide (Mn ₃ O ₄ ) is generated, so that the reaction is stopped before the generation of trimanganese tetraoxide. This is a measure considering the life of the intermediate electrode 13.
The total reaction formula after full charge is expressed by formulas (2) and (3) to (5).
_{2MnO 2 + H 2 O → 2MnOOH} + 1 / 2O 2 (5)

(STEP2)
This step is a hydrogen generation reaction step. When the positive electrode is connected to the intermediate electrode 13 and the negative electrode 12 is connected to the negative electrode 12 to charge the negative electrode 12, the reaction formula of the negative electrode 12 is expressed by equation (6) when the hydrogen storage alloy is represented by M.
2M + 2H ₂ O + 2e ⁻ → 2MH + 2OH ⁻ (6)
When the negative electrode 12 is fully charged and the hydrogen storage alloy does not store hydrogen, hydrogen is generated from the negative electrode 12 according to the reaction formula (7).
2MH → 2M + H ₂ (7)
At this time, the total reaction formula of the negative electrode 12 becomes the formula (8).
2H ₂ O + 2e ⁻ → 2OH ⁻ + H ₂ (8)
On the other hand, the intermediate electrode 13 is charged by taking in hydroxide ions, and the reaction equation becomes the equation (9).
2MnOOH + 2OH ⁻ → 2MnO ₂ + 2H ₂ O + 2e ⁻ (9)
When the intermediate electrode 13 is fully charged, the reaction is stopped.
At this time, the total reaction formula of the intermediate electrode 13 and the negative electrode 12 is the formula (10).
_{2MnOOH → 2MnO 2 + H 2 (} 10)
The total reaction of the positive electrode 11, the intermediate electrode 13, and the negative electrode 12 including STEP1 and STEP2 is represented by the formula (11).
H ₂ O → H ₂ + 1 / 2O ₂ (11)

Thereafter, by performing STEP 1, oxygen gas is generated from the positive electrode 11, and the generated oxygen gas is stored in the oxygen gas storage chamber 23. Next, by performing STEP 2, hydrogen gas is generated from the negative electrode 12, and the generated hydrogen gas is stored in the hydrogen gas storage chamber 24.
The characteristic of the above reaction is that oxygen and hydrogen are obtained by utilizing the oxidation-reduction reaction of the electrode without directly electrolyzing water.

  By repeating the reaction of STEP1 and STEP2, hydrogen gas and oxygen gas can be generated with a time difference. By providing a time difference, hydrogen and oxygen can be separated and collected easily and safely while maintaining high purity. It should be noted here that the generation amounts of oxygen and hydrogen are regulated by the amounts of nickel hydroxide and hydrogen storage alloy as shown in the equations (5) and (8), respectively. By repeating the above, oxygen and hydrogen can be continuously generated. That is, by introducing an inexpensive third electrode (intermediate electrode), it is possible to reduce the amount of positive electrode active material and negative electrode active material required for the reaction.

(Fuel cell operation mode)
The fuel cell operation mode is a mode in which power generation is performed using hydrogen gas and oxygen gas stored in the hydrogen gas storage chamber 24 and the oxygen gas storage chamber 23, respectively. Moreover, the mode which charges the negative electrode 12 and the positive electrode 11 with the hydrogen gas and oxygen gas which were stored in each store room, respectively is also included. As hydrogen gas and oxygen gas, hydrogen gas and oxygen gas stored in the fuel gas generation mode may be used, or fuel gas produced elsewhere may be used. Hereinafter, the fuel cell operation mode will be described using a reaction formula.

The negative electrode 12 can be charged with hydrogen gas stored in the hydrogen gas storage chamber 24. The reaction formula is shown in Formula (12).
2M + H ₂ → 2MH (12)
The intermediate electrode 13 can be charged with oxygen gas stored in the oxygen gas storage chamber 23. The reaction formula is shown in Formula (13).
4MnOOH + O ₂ → 4MnO ₂ + 2H ₂ O (13)
If the negative electrode 12 and the intermediate electrode 13 are in a charged state, the battery unit 20 can generate power as a fuel cell.
At this time, the reaction formulas of the negative electrode 12 and the intermediate electrode 13 are the formulas (14) and (15), respectively.
2MH + 2OH ⁻ → 2M + 2H ₂ O + 2e ⁻ (14)
_{2MnO 2 + 2H 2 O + 2e} - → 2MnOOH + 2OH - (15)
The oxygen reduction reaction rate is slower than the hydrogen oxidation reaction rate, and there is a difference in the reaction rate. However, in the reversible fuel cell described here, the electrode capacity of the intermediate electrode using manganese dioxide as the active material is adjusted to be larger than the electrode capacity of the negative electrode using the hydrogen storage alloy as the active material. Is balanced between the negative electrode and the intermediate electrode.

The negative electrode and the intermediate electrode are charged with hydrogen gas and oxygen gas, respectively. At the same time, the negative electrode and the intermediate electrode in a charged state are discharged, so that the fuel cell can generate power. In other words, the charging reaction of formula (12) occurs in the negative electrode, and the discharge reaction of formula (14) occurs, resulting in the reaction shown in formula (16) as the whole negative electrode.
H ₂ + 2OH ⁻ → 2H ₂ O + 2e ⁻ (16)
At this time, the hydrogen storage alloy of the negative electrode functions as a catalyst.
In addition, the charging reaction of the expression (13) occurs in the intermediate electrode, and the discharging reaction of the expression (15) occurs, so that the reaction shown in the expression (17) is performed as the whole intermediate electrode.
1 / 2O ₂ + H ₂ O + 2e ⁻ → 2OH ⁻ (17)
At this time, manganese dioxide of the intermediate electrode acts as a catalyst.

(Secondary battery operation mode)
The secondary battery operation mode is a mode for charging and discharging as a secondary battery. The battery can be charged by using an external power source such as natural energy power generation, and discharged when the amount of power generated by natural energy is reduced to be used for adjusting power supply and demand. Hereinafter, the secondary battery operation mode will be described using a reaction formula.
The positive electrode and the negative electrode can be charged by an external power source. The reaction formula of the positive electrode is shown in the formula (18), and the reaction formula of the negative electrode is shown in the formula (19).
Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (18)
2M + 2H ₂ O + 2e ⁻ → 2MH + 2OH ⁻ (19)
The positive and negative electrodes in the charged state can supply power to the external load by discharging. The reaction formula is the reverse reaction of the above formulas (18) and (19).
Further, in the state where the reaction of STEP1 in the fuel gas generation mode and the subsequent STEP2 is completed, both the positive electrode and the negative electrode are in a charged state, and power can be supplied to the external load by discharging. The reaction formula of the positive electrode at this time is shown in the formula (20), and the reaction formula of the negative electrode is shown in the formula (21).
NiOOH + H ₂ O + e ⁻ → Ni (OH) ₂ + OH ⁻ (20)
MH + OH ⁻ → M + H ₂ O + e ⁻ (21)

  In the reversible fuel cell according to the present embodiment, in addition to the energy that can be stored in the electrode by charging as a secondary battery, the electric energy supplied during overcharging is stored as gas in each gas storage chamber 23, 24. It is possible to reconvert this into electric energy and use it. Therefore, unlike the conventional secondary battery, the electric capacity of the reversible fuel cell is not limited by the amount of the active material, so the energy density of the reversible fuel cell is significantly higher than that of the conventional secondary battery. It becomes possible to improve (for example, several tens of times). Moreover, since the oxygen gas generated at the positive electrode 11 and the hydrogen gas generated at the negative electrode 12 are directly stored in the gas storage chambers 23 and 24 at the time of overcharging, it is necessary to additionally provide a gas booster or a communication path. And a simple structure can be obtained.

  Furthermore, as described above, when the reversible fuel cell is discharged, electric energy is output based on the cell reaction. For this reason, as compared with the conventional fuel cell, the followability to the load and the power are greatly improved. As a result, the reversible fuel cell can be used for applications with large load fluctuations that require instantaneous high output. In this case, the reversible fuel cell can be used alone without requiring an additional secondary battery or an electricity storage device such as a capacitor.

The hydrogen stored in the hydrogen gas storage chamber and the oxygen stored in the oxygen gas storage chamber can be reconverted to electrical energy for use when the battery is discharged. In particular, oxygen generated at the positive electrode is dissolved in the electrolytic solution and is not stored in a gas state. For this reason, the safety of handling oxygen is improved.
(Another embodiment of the intermediate electrode)

  The intermediate electrode (third electrode) may contain nickel hydroxide in addition to manganese dioxide. Specifically, when the total of manganese dioxide and nickel hydroxide is 100% by weight, 10 to 30% by weight of nickel hydroxide may be included.

Manganese dioxide changes in the discharge process as manganese dioxide MnO ₂ → manganese oxyhydroxide MnOOH → manganese hydroxide Mn (OH) ₂ . At this time, if discharge is performed until manganese hydroxide is generated, irreversible manganese tetraoxide (Mn ₃ O ₄ ) is generated. Manganese tetraoxide is difficult to conduct electricity and cannot be recharged.

Further, when manganese dioxide is charged at a high voltage, delta-type manganese dioxide is generated, which is changed to low-reactivity trimanganese tetraoxide at the time of discharge reaction, and the active material is deteriorated and cycle characteristics are lowered. Further, manganese dioxide has a problem that the electrical conductivity (10 ⁻⁷ to 10 ⁻² S / cm) is low, and it cannot cope with instantaneous output, and the output characteristics are inferior.

  By mixing manganese dioxide particles and nickel hydroxide particles, particles consisting of two types of active materials can be produced, so nickel oxyhydroxide with high electrical conductivity compensates for the disadvantages of manganese dioxide with low electrical conductivity and has excellent output characteristics. Electrode. Furthermore, since the charge / discharge voltage is regulated by nickel oxyhydroxide, the life characteristics of the intermediate electrode are improved. That is, the charging voltage of manganese dioxide is suppressed by nickel oxyhydroxide, and the crystal structure is difficult to become δ. Also, the discharge voltage of manganese dioxide is suppressed by nickel oxyhydroxide and It becomes difficult to generate. The electrode has excellent life characteristics.

(Second Embodiment)
The power generation process will be described with reference to FIG. Since the structure of the electrode stack is the same as that of the first embodiment, description thereof is omitted. The battery unit 30 is connected to the buffer tank 46 through a pipe 42a. The electrolytic solution 43 exiting from the electrolytic solution outlet 40 of the battery unit 30 flows into the buffer tank 46 via the throttle 41a disposed in the pipe 42a. The electrolytic solution 43 flowing into the buffer tank 46 is decompressed by the buffer tank 46, and oxygen dissolved in the electrolytic solution becomes a gas state and is stored in the space at the top of the buffer tank 46. An oxygen gas storage tank 47 is connected to the top of the buffer tank 46 via a gas passage 52, and oxygen in a gas state is stored in the oxygen gas storage tank 47. The oxygen gas storage tank 47 is connected to the oxygen circulation port 37 of the battery unit 30 via a shutoff valve 49 provided in the oxygen gas flow passage 51.

  The electrolytic solution 43 in the buffer tank 46 is returned to the battery unit 30 via the pipes 42b and 42c. A throttle 41b is provided in the pipe 42b. The throttles 41a and 41b serve to maintain the pressure in the battery unit 30 at a high level. In addition, a makeup water system 48 is connected in the middle of the pipe 42b, and the battery unit 30 is replenished with water deficient due to the reactions (4) to (11). The electrolytic solution 43 exiting the buffer tank 46 is pressurized by the pump 45 and returned to the battery unit 30 from the electrolytic solution inflow 50. The electrolytic solution 43 whose temperature has been increased by use as a secondary battery is cooled by a cooler 44 provided in the pipe 42c.

Next, the operation of the second embodiment will be described. By performing STEP 1 described above, oxygen is generated from the positive electrode 31, a part of the generated oxygen is dissolved in the electrolytic solution 43, and the other part is in a gas state. Next, hydrogen gas is generated from the negative electrode 32 by carrying out STEP2. The generated hydrogen gas is difficult to dissolve in the electrolytic solution 43 and is stored at the top of the sealed container 36.
If the reaction proceeds by repeating STEP 1 and STEP 2, the hydrogen gas at the top of the sealed container 36 increases and its pressure increases. If the hydrogen gas pressure is increased, the pressure of the electrolytic solution 43 is increased accordingly, and oxygen generated in STEP 1 is dissolved in the electrolytic solution 43.

  The electrolytic solution 43 in which oxygen is dissolved is decompressed in the buffer tank 46, and the generated oxygen gas is stored in the oxygen gas storage tank 47. At this time, the shut-off valve 49 is closed. A hydrogen gas outlet 60 is provided at the top of the sealed container 36, and the hydrogen gas in the sealed container 36 is sent to the hydrogen gas storage tank 64 via the open shut-off valve 63 a and the hydrogen gas storage passage 62. . This operation is the fuel gas generation mode described above.

  Next, the fuel cell operation mode will be described. The hydrogen gas in the hydrogen gas storage tank 64 is sent to the hydrogen circulation port 38 via the hydrogen gas supply passage 61 and the open shut-off valve 63b, and supplies the hydrogen gas to the negative electrode 32. The oxygen gas in the oxygen gas storage tank 47 is sent to the oxygen circulation port 37 via the oxygen gas flow passage 51 and the open shut-off valve 49 to supply the oxygen gas to the positive electrode 31. The battery unit 30 that is supplied with the hydrogen gas and the oxygen gas generates power.

(Third embodiment)
Another embodiment of the power generation process is shown in FIG. A pipe 220 is connected to the electrolyte outlet 211 of the battery unit 210. The electrolytic solution 137 deteriorated by the discharge of the battery unit 210 is carried to the first chamber 231 of the salt concentration adjusting device 230 via the pipe 220. A reverse osmosis membrane 233 is attached to the salt concentration adjusting device 230. The salt concentration adjusting device 230 is divided into a first chamber 231 and a second chamber 232 by the reverse osmosis membrane 233. The reverse osmosis membrane 233 has a function of selectively permeating moisture in the electrolytic solution 137. The permeated moisture is stored as drainage in the second chamber 232 and is discharged out of the system through the drain port 234.

  The electrolyte solution 137 of the salt concentration adjusting device 230 is carried to the buffer tank 250 via the pipe 221. The electrolytic solution 137 is depressurized in the buffer tank 250, and oxygen dissolved in the electrolytic solution becomes a gas state and is stored in the space at the top of the buffer tank 250. An oxygen storage tank 251 is connected to the top of the buffer tank 250 via an oxygen gas flow passage 252, and the oxygenated gas is stored in the oxygen storage tank 251. The oxygen gas in the oxygen storage tank 251 is connected to an oxygen circulation port (not shown) of the battery unit 210 via the oxygen gas flow passage 253 and the shutoff valve 254. In addition, throttles 224 and 225 are provided in the piping 221 and 222 at the entrance and exit of the buffer tank 250 to maintain the pressure in the battery unit 210 at a high level. A replenishment water system 280 is connected in the middle of the pipe 222 to replenish the battery unit 210 with water deficient due to the oxidation-reduction reaction.

  The electrolytic solution 137 is pressurized by the pump 270 and returned to the battery unit 210 from the electrolytic solution outlet 212 via the pipe 222. The electrolyte solution 137 whose temperature has been increased by use as a secondary battery is cooled by the cooler 260.

  In the battery unit 210, hydrogen gas and oxygen gas generated during overcharging are stored in the hydrogen gas storage tank 256 and the oxygen gas storage tank 251 respectively. The hydrogen gas and oxygen gas stored in the hydrogen gas storage tank 256 and the oxygen gas storage tank 251 are used as fuel gas when the battery unit 210 operates as a fuel cell, respectively, as a negative electrode and a positive electrode (both not shown). I) supplied.

  In this reversible fuel cell, oxygen and hydrogen obtained by the electrode reaction are stored and used at a high pressure without returning to atmospheric pressure. Thereby, high power generation efficiency is realizable.

  The reversible fuel cell of the present invention can be suitably used as an industrial and consumer fuel cell.

10 Electrode stack 11 Positive electrode (11t: connection terminal)
12 Negative electrode (12t: Connection terminal)
13 Intermediate electrode (13t: Connection terminal)
14 Separator 15 Electrolyte 16 Sealed container 17 Oxygen flow port 18 Hydrogen flow port 20 Battery unit 21 DC power source 22 Electric wire 23 Oxygen gas storage chamber 24 Hydrogen gas storage chamber 25 Piping (gas passage)
26 Supply Water System 30 Battery Unit 31 Positive Electrode 32 Negative Electrode 36 Sealed Container 37 Oxygen Flow Port 38 Hydrogen Flow Port 40 Electrolyte Outlet 41 Throttle 42 Pipe 43 Electrolyte 44 Cooler 45 Pump 46 Buffer Tank 47 Oxygen Gas Storage Tank 48 Makeup Water System 49 Shutoff valve 50 Electrolyte inlet 51 Oxygen gas passage 60 Hydrogen gas outlet 61 Hydrogen gas supply passage 62 Hydrogen gas storage passage 63 Shutoff valve 64 Hydrogen gas storage tank 210 Battery unit 230 Salt concentration adjusting device 250 Buffer tank 260 Cooling 270 Pump

JP 2002-348694 A JP 2005-65398 A JP 2010-15729 A JP 2010-15783 A

A reversible fuel cell including a third electrode according to the present invention includes a sealed container that houses the first electrode, the second electrode, the third electrode, and the separator, and the hydrogen gas and the Each oxygen gas can be taken out from the sealed container.
In this configuration, the hydrogen gas and the oxygen gas can be individually taken out from the sealed container without mixing, so that no brown gas is generated. Safety is ensured.

In order to achieve the above-described object, a reversible fuel cell including a third electrode according to the present invention includes a first electrode containing nickel hydroxide, a second electrode containing a hydrogen storage alloy, and a standard electrode potential of the first electrode. A third electrode that is smaller than a standard electrode potential of one electrode and larger than a standard electrode potential of the second electrode; and a separator that allows ions interposed between the electrodes to pass but does not allow electrons to pass. The oxygen gas generated from the first electrode is stored by the oxidation reaction using the first electrode as an anode and the reduction reaction using the third electrode as a cathode, and the reduction reaction using the second electrode as a cathode and the first reaction . Hydrogen gas generated from the second electrode is stored by an oxidation reaction using three electrodes as anodes.
In this configuration, the third electrode is disposed between the first electrode and the second electrode. A reversible fuel cell refers to a fuel cell capable of storing electricity that can reversibly convert fuel gas and electrical energy. Oxygen is generated from the first electrode by an oxidation reaction using the fully charged first electrode as an anode, and hydrogen is generated from the second electrode by a reduction reaction using the fully charged second electrode as a cathode. Convert electrical energy into chemical energy of oxygen and hydrogen.

A reversible fuel cell including a third electrode according to the present invention includes a first electrode containing nickel hydroxide, a second electrode containing a hydrogen storage alloy, and a standard electrode potential smaller than the standard electrode potential of the first electrode. And a third electrode that is larger than the standard electrode potential of the second electrode, a separator that allows ions interposed between the electrodes to pass but does not pass electrons, the first electrode, the second electrode, and the third electrode. An oxygen container which has an electrode, the separator, and a sealed container for storing an electrolyte, and is generated from the first electrode by an oxidation reaction using the first electrode as an anode and a reduction reaction using the third electrode as a cathode; the taken out of the sealed container at a state of being dissolved in the electrolyte, by oxidation reaction using the third electrode and the reducing reaction to a cathode of the second electrode and the anode, a gas of hydrogen generated from the second electrode State in removed from the sealed container.
In this configuration, hydrogen and oxygen taken out from the sealed container are stored in the hydrogen gas storage chamber and the oxygen gas storage chamber, respectively. The stored hydrogen and oxygen can be reconverted into electrical energy for use when the battery is discharged. In particular, oxygen generated in the positive electrode is dissolved in the electrolytic solution and completely separated from hydrogen, so that the safety of handling oxygen is improved.

Claims (15)

A first electrode comprising nickel hydroxide;
A second electrode containing a hydrogen storage alloy;
A third electrode having a standard electrode potential smaller than the standard electrode potential of the first electrode and larger than the standard electrode potential of the second electrode;
A separator that allows ions interposed between the electrodes to pass but does not allow electrons to pass;
Storing oxygen gas generated from the first electrode by an oxidation reaction using the first electrode as an anode and a reduction reaction using the third electrode as a cathode;
A reversible fuel cell comprising a third electrode for storing hydrogen gas generated from the second electrode by an oxidation reaction using the second electrode as a cathode and a reduction reaction using the third electrode as an anode   The reversible fuel cell having the third electrode according to claim 1, wherein power generation is performed by supplying the hydrogen gas to the second electrode and supplying the oxygen gas to the third electrode.   The reversible fuel cell provided with the 3rd electrode according to any one of claims 1 and 2 in which said 3rd electrode contains manganese dioxide.   The reversible fuel cell provided with the 3rd electrode according to claim 3 in which said 3rd electrode further contains nickel hydroxide.   The reversible fuel cell provided with the 3rd electrode according to any one of claims 1 to 4 whose electrode capacity of said 3rd electrode is larger than the electrode capacity of said 1st electrode and said 2nd electrode.   The reversible fuel cell provided with the 3rd electrode according to any one of claims 1 to 5 whose interval of said 1st electrode, said 3rd electrode, and said 2nd electrode is 5-500 micrometers.   A sealed container that houses the first electrode, the second electrode, the third electrode, and the separator, wherein the hydrogen gas and the oxygen gas can be taken out from the sealed container, respectively. The reversible fuel cell provided with the 3rd electrode as described in any one of claim | item 1 -6. A first electrode comprising nickel hydroxide;
A second electrode containing a hydrogen storage alloy;
A third electrode having a standard electrode potential smaller than the standard electrode potential of the first electrode and larger than the standard electrode potential of the second electrode;
A separator that allows ions interposed between the electrodes to pass but not electrons;
The first electrode, the second electrode, the third electrode, the separator, and a sealed container for storing an electrolyte solution,
The oxygen generated from the first electrode is taken out from the sealed container in a state of being dissolved in the electrolytic solution by an oxidation reaction using the first electrode as an anode and a reduction reaction using the third electrode as a cathode.
A reversible fuel cell comprising a third electrode for taking out hydrogen generated from the second electrode in a gas state from the sealed container by an oxidation reaction using the second electrode as a cathode and a reduction reaction using the third electrode as an anode   The reversible fuel cell provided with the 3rd electrode according to claim 8 in which said 3rd electrode contains manganese dioxide.   The reversible fuel cell provided with the 3rd electrode according to claim 9 in which said 3rd electrode further contains nickel hydroxide.   The reversible fuel cell provided with the 3rd electrode according to any one of claims 8 to 10 whose electrode capacity of said 3rd electrode is larger than the electrode capacity of said 1st electrode and said 2nd electrode.   9. The electrolytic solution in the sealed container can flow into a buffer tank, and oxygen gas can be taken out from the buffer tank from the electrolytic solution by reducing the pressure of the buffer tank. A reversible fuel cell comprising the third electrode according to any one of to 11.   The salt concentration adjusting device for adjusting the concentration of the electrolytic solution is connected to the buffer tank, and the salt concentration of the electrolytic solution can be adjusted by injecting pure water. Reversible fuel cell comprising the described third electrode   The closed container is provided with an inlet and an outlet for the electrolyte, and the electrolyte flowing out from the outlet can flow into the inlet via the buffer tank. A reversible fuel cell comprising the third electrode according to any one of 12 and 13 The reversible fuel cell having the third electrode according to claim 12, wherein power generation is performed by supplying the hydrogen gas to the second electrode and supplying the oxygen gas extracted from the buffer tank to the third electrode.

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