JP2013254685A - Redox flow cell and fuel cell system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a redox flow cell capable of preventing the mixture of a negative electrode electrolyte and a positive electrode electrolyte, and a fuel cell system using the same.SOLUTION: A redox flow cell 100 includes a first chamber 112 receiving a negative electrode electrolyte and having a first negative electrode 120 arranged, a second chamber 114 receiving hydrogen gas and having a first positive electrode 122 and a second negative electrode 124 arranged, a third chamber 116 receiving a positive electrode electrolyte and having a second positive electrode 126 arranged, an ion conductive first partition 130 for isolating the negative electrode electrolyte and the hydrogen gas, an ion conductive second partition 132 for isolating the positive electrode electrolyte and the hydrogen, and a conductor 134 for connecting the first positive electrode and the second negative electrode, and makes hydrogen generation reaction and hydrogen oxidation reaction by hydrogen gas intervene oxidation reduction reaction by the negative electrode electrolyte and the positive electrode electrolyte in charging and discharging. Thus, charging and discharging can be performed by preventing the mixture of the negative electrode electrolyte and the positive electrode electrolyte.

Description

  The present invention relates to a redox flow battery in which charging and discharging are performed by supplying each of two types of solutions containing a pair of substances to be oxidized / reduced to a negative electrode and a positive electrode of a cell, and in particular, mixing of the two types of solutions can be prevented. The present invention relates to a redox flow battery and a fuel cell system using the redox flow battery.

  A redox flow battery is a battery that supplies each of two types of solutions containing a redox pair to a negative electrode and a positive electrode by a pump, and generates electricity by a redox pair oxidation-reduction reaction, and is usually a secondary battery that can be charged. . “Redox” is a term that collectively represents reduction and oxidation. The “redox pair” refers to a substance pair (redox pair) that undergoes redox, that is, a pair of reductant (reducing agent) and oxidant (oxidant) that can change with each other. The redox flow batteries currently in practical use include iron / chromium redox flow batteries disclosed in the following non-patent document 1, vanadium redox flow batteries disclosed in the following non-patent document 2, and the like. There is.

  Referring to FIG. 1, a conventional redox flow battery includes a battery cell 900, a tank 920 containing a negative electrode electrolyte (hereinafter also referred to as negative electrode solution or anolyte), a positive electrode electrolyte (hereinafter also referred to as positive electrode solution or catholyte). , A pump 930 for circulating the negative electrode solution, and a pump 932 for circulating the positive electrode solution. The battery cell 900 includes a negative electrode chamber 902, a positive electrode chamber 904, and a diaphragm 910. A porous negative electrode (anode) 906 is disposed in the negative electrode chamber 902, and a porous positive electrode (cathode) 908 is disposed in the positive electrode chamber 904. A diaphragm 910 is disposed between the negative electrode side cell 902 and the positive electrode side cell 904. In FIG. 1, the negative electrode 906 and the positive electrode 908 are disposed on both surfaces of the diaphragm 910, but the negative electrode 906 and the positive electrode 908 may be disposed separately from the diaphragm 910.

  The pump 930 circulates the negative electrode solution between the tank 920 and the negative electrode chamber 902 through the pipe 934. The pump 932 circulates the positive electrode solution between the tank 922 and the positive electrode chamber 904 through the pipe 936. FIG. 1 shows a load 940 electrically connected to the negative electrode 906 and the positive electrode 908.

In the case of an iron-chromium redox flow battery, as an anorite, a hydrochloric acid (HCl) solution containing CrCl ₂ and CrCl _3, that is, a redox pair of chromium divalent ions (Cr ²⁺ ) and chromium trivalent ions (Cr ³⁺ ). Use hydrochloric acid solution. As the catholyte, a hydrochloric acid solution containing FeCl ₂ and FeCl _3, that is, a hydrochloric acid solution containing a redox pair of iron divalent ions (Fe ²⁺ ) and iron trivalent ions (Fe ³⁺ ) is used. An oxidation reaction (Cr ²⁺ → Cr ³⁺ + e ⁻ ) occurs on the negative electrode 906 side, and this oxidation-reduction potential is −0.41V. The generated electrons (e ⁻ ) are supplied to the load 940. A reduction reaction (Fe ³⁺ + e ⁻ → Fe ²⁺ ) occurs on the positive electrode 908 side, and this oxidation-reduction potential is 0.77V. Therefore, the theoretical electromotive force of the redox flow battery is 1.18V. In the most charged state, chromium in anolite becomes divalent ions, and iron in catholite becomes trivalent ions. In the most discharged state, chromium in anolite becomes trivalent ions, and iron in catholite becomes divalent ions.

As the diaphragm 910 that separates the negative electrode 906 and the positive electrode 908, a cation exchange membrane is usually used. In this case, as shown in FIG. 1, hydrogen ions (H ⁺ ) commonly contained in the anolyte and catholyte carry the current in the diaphragm 910. When a cation exchange membrane is used, there is a problem that chromium ions in anolite, which are cations, become ions that carry current in the diaphragm 910 and move to the positive electrode chamber 904 (catholyte side). Even when no current is passed, both chromium ions and iron ions are positive ions, so that they gradually diffuse toward the counter electrode. Regarding this problem, if an anion exchange membrane is used as the diaphragm 910, permeation of iron ions and chromium ions through the diaphragm 910 can be blocked. When an anion exchange membrane is used, unlike FIG. 1, chlorine ions (Cl ⁻ ) that are commonly contained in anolyte and catholyte bear the current in the diaphragm 910.

In fact, a cell using an anion exchange membrane as the diaphragm 910 has been studied. However, because the current performance of anion exchange membranes (anion exchange membranes) is not high (poor selectivity and some cations pass through), the iron / chromium redox flow batteries currently in practical use are Rather, after using a cation exchange membrane (cation exchange membrane), an excess acid is added to the electrolytic solution to contain a large amount of hydrogen ions (H ⁺ ), and the current in the diaphragm 910 is mainly borne by hydrogen ions. Designed. However, even in that case, it is not possible to make the iron ions move to the negative electrode chamber 902 and the chromium ions move to the positive electrode chamber 904, and the mixing of anolyte and catholite gradually proceeds (for example, one cycle of charge / discharge) About 1% each), thereby reducing battery capacity. In order to recover the battery capacity, a regular regeneration process (a process of separating iron and chromium) is required.

A type of redox flow battery that does not require a regeneration process even when mixed is also known. This is a battery using different redox pairs (redox pairs) of the same element for both electrodes. A typical example is a vanadium redox flow battery. This uses vanadium divalent ions (V ²⁺ ) and trivalent ions (V ³⁺ ) as redox pairs in anolite, and the same vanadium tetravalent ions (V ⁴⁺ ) and pentavalent as redox pairs in catholytes. It is a battery using ions (V ⁵⁺ ). In such a cell, the regeneration process is unnecessary because the components of the liquid do not change even when mixed.

  Further, a fuel cell system using the redox flow battery shown in FIG. 1 is known. For example, Non-Patent Documents 3 and 4 below disclose indirect fuel cells (Redox fuel cells) that indirectly perform a fuel oxidation reaction and an oxygen reduction reaction using a redox mediator. The redox mediator means a redox pair newly introduced for the purpose of mediating the reaction when any substance is oxidized or reduced.

  A normal fuel cell is a battery that uses an electrochemical cell that performs an oxidation reaction in which fuel is burned at the negative electrode and performs a reduction reaction that generates water from oxygen (air) at the positive electrode. In an indirect fuel cell using a redox mediator, the fuel is not directly oxidized in the cell, but is indirectly oxidized by introducing a negative side redox mediator. In addition, oxygen is not directly reduced by the cell, but is indirectly reduced by introducing a redox mediator on the positive electrode side. An indirect fuel cell using a redox mediator is configured, for example, as shown in FIG.

  Referring to FIG. 2, the redox fuel cell includes a redox flow battery 950, an anolyte regeneration reaction tank 960, and a catholyte regeneration reaction tank 962. The redox flow battery 950 corresponds to the redox flow battery shown in FIG. FIG. 2 shows only a part of the redox flow battery shown in FIG.

The combustion (oxidation) of the fuel is performed through the reduction reaction of the anolyte on the negative electrode side of the redox flow battery 950. That is, the combustion of fuel is caused by the reduction of Cr ³⁺ generated by the oxidation reaction (Cr ²⁺ → Cr ³⁺ + e ⁻ ) in the anolyte regeneration reaction tank 960 (Cr ³⁺ + e ⁻ → Cr ²⁺ ). In addition, the generation (reduction reaction) of water from oxygen (air) is performed through the oxidation reaction of catholyte on the positive electrode side of the redox flow battery 950. That is, reduction reaction ^{- Fe 2+} created by the ^{(Fe 3+ + e → Fe 2+} ) are oxidized in the catholyte regeneration reactor ^{962 (Fe 2+ → Fe 3+ +} e -) water from the oxygen (air) as a medium that Generated.

Ken Nozaki, et al., “Research and Development of Redox Flow-Type Batteries at Electronic Research Institute”, Electrochemistry and Industrial Physical Chemistry, 51: 1 (1983) 189. M. Skyllas-Kazacos et al., “NewAll-Vanadium Redox Flow Cell”, Journal of the Electrochemical Society, 133 (1986) 1057. Shinichi Tsujimura et al., “Research on Redox Fuel Cells (Part 1)”, Electrochemistry and Industrial Physical Chemistry, 31: 8 (1963) 598. D-G. Oei, “Chemically regenerative redox fuel cells”, Journal of Applied Electrochemistry, Vol. 12, No. 1 (1982) 41.

  Even in the case of redox flow batteries (vanadium-based redox flow batteries) that do not require a regeneration process even if anolyte and catholyte are mixed, the mixing itself is a chemical short (progress of useless reaction that does not contribute to power generation). There is a problem that causes a decrease in efficiency (the amount of electricity obtained by discharging is less than the amount of electricity required for charging). Therefore, in vanadium redox flow batteries and the like, it is desirable that the mixing of anolyte and catholyte be as little as possible.

In an iron-chromium-based and vanadium-based redox flow battery, anions do not contribute to the reaction, but it is practically essential to use the same anions for anolyte and catholyte. The reason is that even if a cation exchange membrane is used as the diaphragm, the selectivity of ions passing therethrough is not perfect, and anions can also diffuse, so they will eventually be mixed. That is, there is a problem that the degree of freedom in selecting anolite and catholyte is low. For example, a redox flow battery using a hydrochloric acid (HCl) solution for anolyte and a sulfuric acid (H ₂ SO ₄ ) solution for catholyte cannot be realized. Further, a redox flow battery using an acidic electrolyte for anolyte and an alkaline electrolyte for catholyte cannot be realized because neutralization proceeds rapidly.

  Therefore, an object of the present invention is to provide a redox flow battery capable of preventing mixing of anolyte and catholyte and a fuel cell system using the redox flow battery.

  The above object can be achieved by the following.

  That is, the redox flow battery according to the first aspect of the present invention contains a negative electrode electrolyte, a first chamber in which a first negative electrode is arranged, a gas, and a first positive electrode and a second negative electrode. A second chamber containing a positive electrode electrolyte, a third chamber in which the second positive electrode is disposed, and an ion conductive first diaphragm separating the negative electrode electrolyte in the first chamber and the gas in the second chamber; , An ion conductive second diaphragm that separates the positive electrode electrolyte in the third chamber and the gas in the second chamber, and a conductive member that electrically connects the first positive electrode and the second negative electrode, The second diaphragm is disposed on the second chamber side surface of the second diaphragm, and the second negative electrode is disposed on the second chamber side surface of the second diaphragm.

  Preferably, the first negative electrode is disposed on the first chamber side surface of the first diaphragm, and the second positive electrode is disposed on the third chamber side surface of the second diaphragm.

  More preferably, the second chamber is movable between the fourth chamber in which the first positive electrode is disposed, the fifth chamber in which the second negative electrode is disposed, and the gas accommodated in the fourth and fifth chambers. And a pipe connecting the fourth chamber and the fifth chamber.

  More preferably, the gas is hydrogen gas, oxygen gas, fluorine gas, chlorine gas or iodine gas.

  Preferably, the gas is hydrogen gas, and the negative electrode electrolyte and the positive electrode electrolyte are electrolytes containing hydrogen ions, and during discharge, the gas is oxidized at the second negative electrode to release electrons and generate hydrogen ions. The generated hydrogen ions pass through the second diaphragm, and the hydrogen ions contained in the negative electrode electrolyte pass through the first diaphragm and acquire electrons transmitted through the conductive member at the first positive electrode. To form hydrogen gas.

  More preferably, the gas is hydrogen gas, and the negative electrode electrolyte and the positive electrode electrolyte are aqueous solutions. At the time of discharge, the gas is oxidized at the second negative electrode to emit electrons and generate water molecules. Water molecules pass through the second diaphragm, and water molecules contained in the negative electrode electrolyte pass through the first diaphragm. At the first positive electrode, the electrons transmitted through the conductive member are acquired to generate hydrogen gas. Form.

  More preferably, ions that do not constitute a redox pair contained in the negative electrode electrolyte and the positive electrode electrolyte are different from each other.

  Preferably, one of the negative electrode electrolyte and the positive electrode electrolyte is an acidic solution, and the other is an alkaline solution.

  More preferably, one of the negative electrode electrolyte and the positive electrode electrolyte is an aqueous solution, and the other is an organic solvent solution.

  A fuel cell system according to a second aspect of the present invention includes any one of the above redox flow batteries, a fuel supply device, and an air supply device, and is included in the negative electrode electrolyte of the redox flow battery. The oxidant of the redox couple is converted into a reductant by combustion of the supplied fuel, and the reductant of the redox pair contained in the cathode electrolyte of the redox flow battery is reduced by the reduction reaction of oxygen in the supplied air. Change to oxidant.

  According to the present invention, mixing of anolyte and catholyte can be prevented in a redox flow battery. This eliminates the need for an anolyte or catholyte regeneration process.

  In addition, it is possible to independently design the electrolyte solutions most suitable for the adopted redox pair, and the degree of freedom in selecting anolyte and catholyte is increased. Therefore, the choices of the two pairs of redox pairs to be adopted are widened, and diversification of practical redox flow batteries can be realized.

  Also in the redox fuel cell, mixing of anolyte and catholyte can be prevented.

It is a block diagram which shows the structure of the conventional redox flow battery. It is a block diagram which shows the structure of the fuel cell system which applied the conventional redox flow battery. It is a block diagram which shows the structure of the redox flow battery which concerns on embodiment of this invention. FIG. 4 is a block diagram showing a case where an alkaline solution is used for catholyte in the redox flow battery of FIG. 3. It is a block diagram which shows the redox flow battery with which the chamber which accommodates gas isolate | separated into two based on embodiment of this invention. It is a block diagram which shows the structure of the fuel cell system using the redox flow battery which concerns on embodiment of this invention. It is a block diagram which shows the structure of the half cell used for the Example. It is a graph which shows the charging / discharging characteristic which is an experimental result using the half cell of FIG. It is a graph which shows the charging / discharging characteristic which is an experimental result using the redox pair different from FIG. 8 in the half cell of FIG. It is a graph which shows the charge / discharge characteristic of the redox flow battery obtained from the result of FIG.8 and FIG.9.

  In the following embodiments, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  Referring to FIG. 3, the redox flow battery 100 according to the embodiment of the present invention includes a battery cell complex 110, a negative solution tank 140, a positive solution tank 142, a negative solution circulation pump 150, and a positive solution circulation pump 152. I have. The battery cell complex 110 includes a first chamber 112, a second chamber 114, a third chamber 116, a first diaphragm 130, and a second diaphragm 132. A first diaphragm 130 is disposed between the first chamber 112 and the second chamber 114, and a second diaphragm 132 is disposed between the second chamber 114 and the third chamber 116. A first negative electrode 120 is disposed in the first chamber 112, a first positive electrode 122 and a second negative electrode 124 are disposed in the second chamber 114, and a second positive electrode 126 is disposed in the third chamber 116. The first positive electrode 122 is disposed on the surface of the first diaphragm 130, and the second negative electrode 124 is disposed on the surface of the second diaphragm 132. The first positive electrode 122 and the second negative electrode 124 are electrically connected by a conductor 134.

  In FIG. 3, the first negative electrode 120 is disposed on the surface of the first diaphragm 130, but the first negative electrode 120 may be disposed separately from the first diaphragm 130. Similarly, the second positive electrode 126 may be spaced apart from the second diaphragm 132.

  The negative electrode solution tank 140 contains anolite (negative electrode electrolyte), and the positive electrode solution tank 142 contains catholyte (positive electrode electrolyte). The negative electrode liquid circulation pump 150 circulates anolyte between the negative electrode liquid tank 140 and the first chamber 112 via the negative electrode liquid circulation path 154. The cathode solution circulation pump 152 circulates catholyte between the cathode solution tank 142 and the third chamber 116 via the cathode solution circulation path 156. FIG. 3 shows a load 190 electrically connected to the first negative electrode 120 and the second positive electrode 126.

The first diaphragm 130 and the second diaphragm 132 are, for example, cation exchange membranes. The second chamber 114 stores hydrogen gas (H ₂ ).

In FIG. 3, of the two redox pairs to be used, a reduced form and an oxidized form of a redox pair having a relatively low redox potential (for example, a redox pair contained in anolyte) are represented by Red [1] and Ox [ 1]. A reduced form and an oxidized form of a redox pair having a relatively high oxidation-reduction potential (for example, a redox pair contained in catholyte) are represented by Red [2] and Ox [2], respectively. According to this notation, the discharge reaction of the redox flow battery 100 is expressed by Equation 1 and Equation 2.
Red [1] → Ox [1] + e ⁻ (Formula 1)
Ox [2] + e ⁻ → Red [2] (Formula 2)
More specifically, in the redox flow battery 100, a hydrogen generation reaction and a hydrogen oxidation reaction by the hydrogen gas in the second chamber 114 are interposed between the reactions of Formula 1 and Formula 2. That is, at the time of discharge, in addition to the above-described reaction of Formula 1 in the first chamber 112, the reaction of Formula 3 occurs in the first positive electrode 122 of the second chamber 114 as follows.

  In addition to the reaction of the above formula 2 in the third chamber 116, the reaction of the formula 4 occurs in the second negative electrode 124 of the second chamber 114 as follows.

  Therefore, it can be said that the redox flow battery 100 has a configuration in which a cell in which the discharge reaction is represented by Formula 1 and Formula 3 and a cell in which the discharge reaction is represented by Formula 4 and Formula 2 are connected in series.

For example, a hydrochloric acid solution containing CrCl ₂ and CrCl _3, that is, a hydrochloric acid solution containing a redox pair of chromium divalent ions (Cr ²⁺ ) and chromium trivalent ions (Cr ³⁺ ) can be used as the anorite. As the catholyte, a hydrochloric acid solution containing FeCl ₂ and FeCl _3, that is, a hydrochloric acid solution containing a redox pair of iron divalent ions (Fe ²⁺ ) and iron trivalent ions (Fe ³⁺ ) can be used. In that case, during discharge, an oxidation reaction (Cr ²⁺ → Cr ³⁺ + e ⁻ ) occurs in the vicinity of the first negative electrode 120 in the first chamber 112 (see Formula 1). This redox potential is -0.41V. The generated electrons (e ⁻ ) are supplied to the load 190. On the other hand, a reduction reaction (Fe ³⁺ + e ⁻ → Fe ²⁺ ) occurs in the vicinity of the second positive electrode 126 in the third chamber 116 (see Formula 2). This redox potential is 0.77V. In the second chamber 114, hydrogen is generated in the first positive electrode 122 by the reaction of the above formula 3, and in the second negative electrode 124, hydrogen is separated into hydrogen ions and electrons by the reaction of the above formula 4. The generated electrons are supplied from the second negative electrode 124 to the first positive electrode 122 through the conductor 134 and used for generating hydrogen.

  Thus, since the anolyte and the catholyte are spatially separated, the redox flow battery 100 can prevent the anolyte and the catholyte component, which was a conventional problem, from being gradually mixed. Therefore, it is not necessary to perform a regeneration process for recovering the decrease in battery capacity due to the mixing of two pairs of redox pairs, which has been conventionally required.

Moreover, since anolyte and catholyte do not contact, the freedom degree of selection of the electrolyte solution used as anolite and catholyte spreads. For example, a pair of ions contained in anolyte and catholyte (for example, an anion in the case of an iron-chromium redox flow battery) may be different from each other. For example, a hydrochloric acid (HCl) solution can be used for anolyte, and a sulfuric acid (H ₂ SO ₄ ) solution can be used for catholyte. It is also possible to select an anionic one as a redox pair, and in that case, a pair of cations contained in anolyte and catholyte may be the same or different from each other. In addition, when any redox pair is used, a salt composed of a cation unrelated to the redox pair and an unrelated anion (such as sodium chloride) may be added to anolyte and catholyte.

  Further, as anolyte and catholyte, for example, a combination of an acidic solution and an alkaline solution, or a combination of an aqueous solution and an organic solvent solution is possible.

  As a result, it is possible to independently design the electrolytes most suitable for the adopted redox pair. As a result, the choices of the two pairs of redox pairs to be adopted are widened, and diversification of practical batteries can be realized.

The electromotive force generated by the redox flow battery 100 depends on the hydrogen generation reaction (see formula 3) and the hydrogen oxidation reaction (see formula 4) from the values expected from the oxidation-reduction potential in the reactions of formulas 1 and 2. Decreases by the amount of overvoltage (driving force to advance the reaction). As described above, when a hydrochloric acid solution containing CrCl ₂ and CrCl ₃ is used as the anorite and a hydrochloric acid solution containing FeCl ₂ and FeCl ₃ is used as the catholyte, the electromotive force of the redox flow battery 100 is the redox potential − It becomes smaller than 1.18V which is a value expected from 0.41V and 0.77V. However, since the hydrogen generation reaction and the hydrogen oxidation reaction are reactions with a small overvoltage (a highly reversible reaction), the influence on the decrease in electromotive force is small.

When anolyte and catholyte are acidic solutions, as described above (see FIG. 3), hydrogen ions pass through the first diaphragm 130 and the second diaphragm 132 and carry the current in the diaphragm. However, the ions responsible for the current in the diaphragm are not limited to hydrogen ions. When anolyte or catholyte is an alkaline solution, hydroxide ions (OH ⁻ ) and water pass through the diaphragm. For example, as shown in FIG. 4, when the catholyte is an alkaline solution and the second diaphragm 132 is an anion exchange membrane, hydroxide ions and water pass through the second diaphragm 132 (see the one-dot chain line region). . FIG. 4 is the same as FIG. 3 except that catholyte is an alkaline solution and the second diaphragm 132 is an anion exchange membrane. Therefore, repeated explanation will not be repeated.

In the redox flow battery shown in FIG. 4, the reaction of Formula 5 occurs in the second negative electrode 124 of the second chamber 114 during discharge, unlike in FIG. 3. That is, the hydrogen gas in the second chamber 114 reacts with hydroxide ions that have passed through the second diaphragm 132 to generate water (H ₂ O) and discharge electrons. Note that the reaction in the third chamber 116 is the reaction of Formula 2 above.

  In the redox flow battery shown in FIG. 4, the reverse reaction of Formula 5, that is, the reaction of Formula 6, occurs at the second negative electrode 124 during charging.

  In FIG. 3, when anolyte is an alkaline solution, if an anion exchange membrane is used as the first diaphragm 130, hydroxide ions and water pass through the first diaphragm 130 as described above. In this case, at the time of discharge, the reaction of Formula 6 occurs in the first positive electrode 122 due to the water that has passed through the first diaphragm 130. At the time of charging, the reaction of Formula 5 occurs at the first positive electrode 122.

  When anolyte or catholyte is an organic solvent, hydrogen ions may be introduced into the organic solvent in order to use hydrogen gas.

In the above, the case where the hydrogen generation reaction and the hydrogen oxidation reaction by hydrogen gas are interposed has been described, but the present invention is not limited to this. The gas stored in the second chamber 114 may be a neutral gas that is not charged, and a gas other than hydrogen can be used. For example, oxygen gas (O ₂ ), fluorine gas (F ₂ ), chlorine gas (Cl ₂ ), or iodine gas (I ₂ ) may be used. The intervening reaction is preferably a highly reversible reaction between a reaction in which one or more atoms constituting the gas are ionized and a reaction in which a gas is generated from ions that are the reverse reaction.

  With respect to the positive electrode, the negative electrode, and the diaphragm, materials used for the positive electrode, the negative electrode, and the diaphragm of a known battery (not limited to a redox flow battery) can be used.

  Although the case where one second chamber 114 includes the first positive electrode 122 and the second negative electrode 124 has been described above, the present invention is not limited to this. For example, as shown in FIG. 5, the second chamber 114 includes a portion including the first positive electrode 122 (hereinafter referred to as the fourth chamber) 172 and a portion including the second negative electrode 124 (hereinafter referred to as the fifth chamber) 174. It may be divided. In the redox flow battery 170 shown in FIG. 5, the first positive electrode 122 and the second negative electrode 124 are disposed in the fourth chamber 172 and the fifth chamber 174, respectively. The fourth chamber 172 and the fifth chamber 174 contain hydrogen gas and are connected by a pipe 176. Hydrogen gas in the fourth chamber 172 and the fifth chamber 174 can move to each other by a pipe 176. Since the other configuration of redox flow battery 170 is the same as that of redox flow battery 100 in FIG. 3, repeated description will not be repeated.

  In the above description, the single redox flow battery has been described. However, the present invention is not limited to this. For example, an indirect fuel cell system similar to that shown in FIG. 2 can be configured using the redox flow battery 100 shown in FIG.

  Referring to FIG. 6, the indirect fuel cell system 200 includes a redox flow battery 210, an anolyte regeneration reaction tank 212, and a catholyte regeneration reaction tank 214. The redox flow battery 210 corresponds to the redox flow battery 100 shown in FIG. FIG. 6 shows only a part of the redox flow battery 100 shown in FIG.

  Fuel is supplied to the anolyte regeneration reaction tank 212. As the fuel, a known fuel (such as hydrogen or methanol) used in a fuel cell can be used. The catholyte regeneration reaction tank 214 is supplied with air containing oxygen.

By the combustion (oxidation reaction) of the fuel, the oxidant in the anolyte on the negative electrode side of the redox flow battery 210 is returned to the reductant. That is, during discharge of the redox flow battery 210, the oxidant Ox [1] generated by the oxidation reaction (Red [1] → Ox [1] + e ⁻ ) is burned in the anolyte regeneration reaction tank 212 (oxidation reaction). ) Is acquired to be reduced form Red [1] (Ox [1] + e ⁻ → Red [1]). Further, the reductant in the catholyte on the positive electrode side of the redox flow battery 210 is returned to the oxidant by generation of water (reduction reaction) from oxygen (air). That is, when the redox flow battery 210 is discharged, the reductant Red [2] generated by the reduction reaction (Ox [2] + e ⁻ → Red [2]) is converted from oxygen (air) to water in the catholyte regeneration reaction tank 214. As a result of the formation (reduction reaction), electrons are released to form an oxidant Ox [2] (Red [2] → Ox [2] + e ⁻ ). In this way, the indirect fuel cell system 200 converts anolyte and catholyte changed by power generation (discharge) of the redox flow battery 210 into combustion of fuel (oxidation reaction) and generation of water (reduction reaction) from oxygen (air). It is possible to generate electric power continuously by regenerating.

  The experimental results are shown below to show the effectiveness of the present invention. As described above, the redox flow battery 100 shown in FIG. 3 can be said to have a configuration in which two cells are connected in series. In either case, the redox flow battery 100 includes an electrolyte solution containing a redox pair (redox pair) on one electrode side. And hydrogen gas is provided on the other electrode side. Therefore, the half cell shown in FIG.

The manufactured half cell (FIG. 7) includes a first chamber 300, a second chamber 302, a first electrode 304, a second electrode 306, and a diaphragm 308. The first chamber 300 contained an electrolytic solution, and the second chamber 302 contained hydrogen gas. For the diaphragm 308, Nafion (registered trademark) 117, which is a cation exchange resin film, was used. For the first electrode 304 (electrolytic solution side), a carbon cloth containing no catalyst was used. For the second electrode 306 (hydrogen side), a carbon black powder carrying platinum fine particles and a cation exchange resin coated on the surface of a carbon cloth was used. The effective electrode geometric area of the prepared half cell was 2.25 cm ² .

  In FIG. 7, the positive reaction (solid arrow) that is a combination of hydrogen oxidation and electrolyte reduction is a charging process in the cell including the first negative electrode 120, the first positive electrode 122, and the first diaphragm 130 of FIG. In the cell including the second negative electrode 124, the second positive electrode 126, and the second diaphragm 132 shown in FIG. In FIG. 7, the reverse reaction (dotted arrow), which is a combination of hydrogen generation and electrolyte oxidation, causes a discharge process in the cell including the first negative electrode 120, the first positive electrode 122, and the first diaphragm 130 of FIG. In the cell including the second negative electrode 124, the second positive electrode 126, and the second diaphragm 132 shown in FIG.

As the electrolytic solution, a 1 mol / L HCl aqueous solution containing 0.1 mol / L Fe ³⁺ was used. The redox couple is Fe ³⁺ and Fe ²⁺ . While preparing 100 mL of this electrolytic solution in a tank (not shown) and circulatingly supplying it from the tank to the first chamber 300 using a pump (not shown) at 20 mL / min, a current of 22.5 mA, that is, 10 mA / cm. ^A charge / discharge experiment was conducted at a current density of ² . The result is shown in FIG. The operating temperature of the half cell during the experiment was 40 ° C.

  In FIG. 8, the vertical axis represents electromotive force (V), and the horizontal axis represents time (hour). In FIG. 8, the charge capacity (C: Coulomb) in each charge / discharge cycle is shown enclosed by a solid line square. These charge capacities are values calculated from experimental values.

Assuming a one-electron reaction of Equation 7, the theoretical capacity under the above experimental conditions is
0.1 (mol / L) × 0.1 (L) × 96500 (C / mol) = 965 (C)
It is.

In the experiment, since the initial state of the solution was an oxidant, the reduction process was started first. In the first reduction process (the left end in FIG. 8), the electromotive force suddenly decreased after 11.5 hours and stopped. The amount of charge passed during this period is
22.5 (mA) × 11.5 (h) × 3600 (s / h) = 932 (C)
(Refer to the numerical values in the lower left square frame in FIG. 8). In the subsequent oxidation process (charge), and further in the reduction process (discharge) and oxidation process (charge) in the second and subsequent cycles, the charge / discharge capacity almost as theoretically obtained was obtained by the same calculation (the square in FIG. 8). (Refer to the number in the box.)

A similar experiment was performed using an electrolytic solution different from Example 1 using the half cell of FIG. The difference from Example 1 is that 0.5 mol / L of H ₂ SO containing 0.05 mol / L of anthraquinone-2,6-disulfonic acid (Anthraquinone-2,6-disulfonate: hereinafter referred to as AQDS) is used as an electrolytic solution. It is only the point which used ₄ aqueous solution. Redox pairs are AQDS and AQDSH _2.

Charging / discharging was performed under the same conditions as in Example 1, namely, 100 mL of electrolytic solution, circulation supply rate of 20 mL / min, current value of 22.5 mA (current density of 10 mA / cm ² ), and half-cell operating temperature of 40 ° C. The result is shown in FIG. The notation of FIG. 9 is the same as FIG.

Assuming the two-electron reaction of Equation 8, the theoretical capacity is
2 × 0.05 (mol / L) × 0.1 (L) × 96500 (C / mol) = 965 (C)
It is.

  From the values in the solid-line square frame shown in FIG. 9, it can be seen that also in Example 2, a charge / discharge capacity close to the theoretical value was obtained. Note that the capacitance value shown in the lower left of FIG. 9 is a value (996C) that is larger than the theoretical value of 965C, which is considered to be due to the occurrence of a reaction other than Equation 8.

From the results of FIGS. 8 and 9, when the combination of Fe ²⁺ and AQDS is used in the redox flow battery 100 of FIG. 3, the redox flow battery having the charge / discharge characteristics shown in FIG. 10 can be realized. The graph of FIG. 10 shows charge / discharge data in the region indicated by the one-dot chain line in FIG. 8 (oxidation data in the first cycle and reduction data in the second cycle) and charging / discharging of the region indicated in the one-dot chain line in FIG. 6 is a graph obtained by combining discharge data (reduction data and oxidation data in the second cycle).

  The present invention has been described above by describing the embodiment. However, the above-described embodiment is an exemplification, and the present invention is not limited to the above-described embodiment, and is implemented with various modifications. be able to.

100 redox flow battery 110 battery cell 112 first chamber 114 second chamber 116 third chamber 120 first negative electrode 122 first positive electrode 124 second negative electrode 126 second positive electrode 130 first diaphragm 132 second diaphragm 134 conductor 140 negative electrode liquid tank 142 Cathode Solution Tank 150 Cathode Solution Circulation Pump 152 Cathode Solution Circulation Pump 154 Cathode Solution Circulation Path 156 Cathode Solution Circulation Path 190 Load

Claims (10)

A first chamber containing a negative electrode electrolyte and in which a first negative electrode is disposed;
A second chamber containing gas and in which the first positive electrode and the second negative electrode are disposed;
A third chamber containing a positive electrode electrolyte and having a second positive electrode disposed thereon;
An ion-conductive first diaphragm that separates the negative electrode electrolyte in the first chamber and the gas in the second chamber;
An ion conductive second diaphragm that separates the positive electrode electrolyte in the third chamber and the gas in the second chamber;
A conductive member that electrically connects the first positive electrode and the second negative electrode;
The first positive electrode is disposed on a surface of the first diaphragm on the second chamber side,
The redox flow battery, wherein the second negative electrode is disposed on a surface of the second diaphragm on the second chamber side. The first negative electrode is disposed on the first chamber side surface of the first diaphragm,
The redox flow battery according to claim 1, wherein the second positive electrode is disposed on a surface of the second diaphragm on the third chamber side. The second chamber is
A fourth chamber in which the first positive electrode is disposed;
A fifth chamber in which the second negative electrode is disposed;
The pipe | tube which connects the said 4th chamber and the said 5th chamber so that the said gas accommodated in the said 4th chamber and the said 5th chamber can move mutually is provided. Redox flow battery.   The redox flow battery according to any one of claims 1 to 3, wherein the gas is hydrogen gas, oxygen gas, fluorine gas, chlorine gas, or iodine gas. The gas is hydrogen gas;
The negative electrode electrolyte and the positive electrode electrolyte are electrolytes containing hydrogen ions,
When discharging
The gas is oxidized in the second negative electrode, emits electrons to generate hydrogen ions,
The generated hydrogen ions pass through the second diaphragm,
Hydrogen ions contained in the negative electrode electrolyte pass through the first diaphragm, and acquire the electrons transmitted through the conductive member in the first positive electrode to form hydrogen gas. The redox flow battery according to any one of claims 1 to 4. The gas is hydrogen gas;
The negative electrode electrolyte and the positive electrode electrolyte are aqueous solutions,
When discharging
The gas is oxidized in the second negative electrode, emits electrons to generate water molecules,
The generated water molecules pass through the second diaphragm,
Water molecules contained in the negative electrode electrolyte pass through the first diaphragm, and acquire the electrons transmitted through the conductive member in the first positive electrode to form hydrogen gas. The redox flow battery according to any one of claims 1 to 4.   The redox flow battery according to any one of claims 1 to 6, wherein ions that do not constitute a redox pair contained in the negative electrode electrolyte and the positive electrode electrolyte are different from each other.   8. The redox flow battery according to claim 1, wherein one of the negative electrode electrolyte and the positive electrode electrolyte is an acidic solution, and the other is an alkaline solution. 9.   8. The redox flow battery according to claim 1, wherein one of the negative electrode electrolyte and the positive electrode electrolyte is an aqueous solution, and the other is an organic solvent solution. 9. The redox flow battery according to any one of claims 1 to 9,
An apparatus for supplying fuel;
A device for supplying air,
The oxidant of the redox couple contained in the negative electrode electrolyte of the redox flow battery is changed into a reductant by the combustion of the supplied fuel,
The fuel cell system according to claim 1, wherein the redox pair reductant contained in the cathode electrolyte of the redox flow battery is changed to an oxidant by a reduction reaction of oxygen in the supplied air.

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