JP2014165109A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance power generation efficiency by promoting fuel supply to an anode while preventing crossover.SOLUTION: A fuel cell 1 includes an anode 6 and a cathode 7 arranged oppositely to each other, an electrolyte membrane 5 provided between the anode 6 and cathode 7, and isolating a first fuel chamber 3 where the anode 6 is arranged and a first fuel X of reductive liquid is supplied, from a second fuel chamber 4 where the cathode 7 is arranged and a second oxidizing fuel Y is supplied, and electroosmotic flow generation means 8 generating an electroosmotic flow E, from the electrolyte membrane 5 side toward the anode 6, in the first fuel chamber 3.

Description

  The present invention relates to a fuel cell.

  2. Description of the Related Art Conventionally, there has been known a fuel cell in which power generation efficiency is improved by promoting supply of fuel to an anode using an electroosmotic flow pump (see, for example, Patent Document 1).

Japanese Patent No. 4922933

  However, in the fuel cell described in Patent Document 1, the fuel supplied toward the anode by the electroosmotic flow pump collides with the electrolyte membrane positioned forward in the flow direction after passing through the anode, so that the fuel is electrolyte membrane. The phenomenon of crossover flowing through the cathode and flowing out to the cathode side is promoted. As a result of this crossover, the anode fuel undergoes an oxidation reaction at the cathode, which causes a problem that the electromotive force is lowered and power generation is hindered.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a fuel cell capable of improving the power generation efficiency by promoting the supply of fuel to the anode while preventing crossover. .

In order to achieve the above object, the present invention provides the following means.
The present invention provides an anode and a cathode disposed opposite to each other, and a first fuel provided between the anode and the cathode, to which the anode is disposed and a liquid first fuel having a reducing property is supplied. An electrolyte membrane separating the chamber and the second fuel chamber to which the second fuel having oxidizing properties is supplied, and electricity flowing from the electrolyte membrane side to the anode in the first fuel chamber Provided is a fuel cell comprising electroosmotic flow generating means for generating an osmotic flow.

  According to the present invention, the first fuel is oxidized at the anode to release electrons from the first fuel, and the second fuel is reduced at the cathode using the electrons. At this time, electrons moving from the anode to the cathode can be taken out as electric energy.

  In this case, in the first fuel chamber, the first fuel flows from the electrolyte membrane side to the anode by the electroosmotic flow generated by the electroosmotic flow generating means. Thereby, supply of the 1st fuel to an anode can be promoted and power generation efficiency can be improved. Further, since the electroosmotic flow and the flow direction of the first fuel generated thereby are opposite to the flow direction of the first fuel that promotes crossover, the crossover of the first fuel can be prevented. it can.

In the above invention, the electroosmotic flow generating means includes a pair of porous electrodes arranged in the arrangement direction of the anode and the electrolyte membrane, and a porous dielectric material interposed between the pair of electrodes. And an electroosmotic flow pump that generates the electroosmotic flow between the pair of electrodes.
By doing in this way, an electroosmotic flow can be generated with a simple configuration.

In the above invention, the pair of electrodes may be arranged with the anode interposed therebetween.
By doing in this way, the electroosmotic flow which crosses an anode can be generated, and the supply efficiency of the 1st fuel to an anode can further be improved.

In the above invention, one of the electrodes of the electroosmotic flow pump may be disposed in the first fuel chamber, and the other electrode may be disposed in the second fuel chamber.
By doing in this way, the member interposed between an anode and an electrolyte membrane can be reduced, and the delivery of the ion between an anode and an electrolyte membrane can be performed efficiently.

Moreover, in the said invention, the said anode may be arrange | positioned at intervals between the inner surfaces of the said 1st fuel chamber.
In this way, a flow path for the first fuel to flow around the anode is secured, and the first fuel returns to the electrolyte membrane side of the anode along the outer surface of the anode after passing through the anode from the electrolyte membrane side. Can be promoted.

In the above invention, the electrolyte membrane may be an anion exchange membrane.
By doing in this way, it can be suitable for an anion transfer type in which the second fuel chamber is filled with an alkaline electrolyte.

  According to the present invention, it is possible to improve the power generation efficiency by promoting the supply of fuel to the anode while preventing the crossover.

It is sectional drawing which shows the whole structure of the fuel cell which concerns on one Embodiment of this invention. It is sectional drawing which shows the whole structure of the 1st modification of the fuel cell of FIG. It is sectional drawing which shows the whole structure of the 2nd modification of the fuel cell of FIG. It is sectional drawing which shows the whole structure of the 3rd modification of the fuel cell of FIG. It is sectional drawing which shows the whole structure of the 4th modification of the fuel cell of FIG. It is sectional drawing which shows the whole structure of the 5th modification of the fuel cell of FIG.

Below, fuel cell 1 concerning one embodiment of the present invention is explained with reference to drawings.
As shown in FIG. 1, the fuel cell 1 according to the present embodiment is opposed to a container 2, an electrolyte membrane 5 that partitions the inside of the container into two chambers 3, 4, and the electrolyte membrane 5 interposed therebetween. The anode 6 and the cathode 7 are provided, and an electroosmotic flow pump (electroosmotic flow generating means) 8 is provided in the first chamber 3 where the anode 6 is located.

  The container 2 has a rectangular tube shape or a cylindrical shape, and an internal space is partitioned by an electrolyte membrane 5 into a first chamber 3 on one end side and a second chamber 4 on the other end side.

  The first chamber (first fuel chamber) 3 is a space sealed by one end wall, a side wall, and the electrolyte membrane 5 of the container 2. The first chamber 3 is filled with a fuel liquid (first fuel) X containing molecules having reducing properties, which serves as fuel for the anode 6. Examples of the reducing molecule include alcohols such as methanol, ethanol, ethylene glycol, and glycerol, or sugars such as glucose and galactose. The fuel liquid X may further contain an acidic electrolyte such as sulfuric acid or hydrochloric acid.

  The second chamber (second fuel chamber) 4 is a space surrounded by the side wall of the container 2 and the electrolyte membrane 5 and opened to the outside at the other end of the container 2, and the fuel of the cathode 7 from the outside of the container 2. Air is supplied.

  The anode 6 and the cathode 7 have a flat plate shape and are arranged substantially parallel to the electrolyte membrane 5. Further, the cathode 7 is disposed in the second chamber 4 so as to be in close contact with the inner surface of the electrolyte membrane 5 and the side wall of the container 2 so as to seal the second chamber 4, and on the surface opposite to the electrolyte membrane 5. At least a part of the container 2 is exposed to the outside. The anode 6 and the cathode 7 are electrically connected to each other by a wiring 9 that passes outside the container 2.

  The anode 6 is an electrode that oxidizes the fuel liquid X, and includes a porous base material made of a conductive material and metal particles that are supported on the base material and that serve as a catalyst that promotes the oxidation reaction of the fuel liquid X. ing. As the material for the substrate, carbon is preferably used, but a material obtained by mixing a conductive material such as carbon with an oxide such as zirconia or ceria may be used. As the material of the metal particles, noble metals such as platinum, ruthenium, rhodium, gold and silver, base metals such as cobalt, nickel, copper, iron, manganese, niobium and lead, or oxides of these noble metals and base metals are suitable. Used. Binary or higher metals combining these metals and oxides, or alloys containing two or more types may be used. Alternatively, an enzyme and a mediator may be used as a catalyst.

  The cathode 7 is an electrode that reduces oxygen (second fuel) Y contained in the air, and is supported on the porous base material made of a conductive material and promotes the reduction reaction of oxygen Y. And metal particles as a catalyst. Carbon is suitably used as the base material. Platinum is preferably used as the material of the metal particles.

  The electrolyte membrane 5 is a proton exchange membrane having a property of selectively permeating hydrogen ions, and transmits hydrogen ions generated by the oxidation reaction of the fuel liquid X at the anode 6 from the first chamber 3 to the cathode 7. .

  The electroosmotic pump 8 includes a pair of plate-like electrodes 8a and 8b arranged to face each other, a pair of plate-like dielectrics 8c and 8d arranged to face each other between these electrodes 8a and 8b, and a pair of electrodes 8a. , 8b, and a power source 8e for applying a voltage.

The electrodes 8a and 8b and the dielectrics 8c and 8d are arranged along the arrangement direction of the anode 6 and the electrolyte membrane 5, and the anode 6 is sandwiched between the pair of dielectrics 8c and 8d. The electrodes 8a and 8b and the dielectrics 8c and 8d are made of a porous material through which the fuel liquid X can pass.
The electroosmotic pump 8 applies a voltage from the power source 8e to the pair of electrodes 8a and 8b, so that the other electrode 8a and 8d and the anode 6 cross the other electrode 8a located on the electrolyte membrane 5 side. An electroosmotic flow E toward the electrode 8b is generated.

  Here, the unit including the anode 6, the electrodes 8 a and 8 b and the dielectrics 8 c and 8 d is disposed with a space between one end wall of the container 2 and the inner surface of the side wall. As a result, a flow path through which the fuel liquid X can easily flow is secured around the unit, and along the inner surface of the container 2 after passing through the anode 6 from the electrolyte membrane 5 side, as indicated by a broken line arrow. A circulation path of the fuel liquid X returning to the electrolyte membrane 5 side is formed in the first chamber 3.

  As materials for the electrodes 8a and 8b, conductive materials such as platinum, gold, silver, carbon, and stainless steel are preferably used. In particular, the electrodes 8a and 8b are preferably made of a porous material made of carbon that does not interfere with the fuel liquid X, such as carbon paper.

  The dielectrics 8c and 8d are made of a porous body or a packed layer of fibers or particles. Materials for the dielectrics 8c and 8d include silica, alumina, titania, zirconia, cerium oxide, lanthanum oxide, yttrium oxide, hafnium oxide, magnesium oxide, tantalum oxide, silicon nitride, borosilicate, bicol, plastic and gypsum. Either one or a mixture thereof is preferably used. The pore diameters of the dielectrics 8c and 8d are preferably 0.1 μm to 8.0 μm, and the average porosity of the dielectrics 8c and 8d is preferably 25% to 52%. The dielectrics 8c and 8d may be subjected to hydrophilic treatment as necessary.

The power source 8e is disposed outside the container 2 and applies a voltage of preferably 30 V or less between the pair of electrodes 8a and 8b. As the power source 8e, a secondary battery such as a lithium ion battery, a fuel cell, or a dedicated power source such as a stabilized power source is used.
In order to generate the electroosmotic flow E, the fuel liquid X needs to have appropriate electrical properties. Therefore, the fuel liquid X is adjusted so as to have an appropriate pH and conductivity that can obtain the zeta potential of the dielectrics 8c and 8d, and may include a buffer solution.

Next, the operation of the fuel cell 1 configured as described above will be described below.
In the fuel cell 1 according to the present embodiment, molecules such as alcohol or sugar contained in the fuel liquid X are oxidized at the anode 6, whereby electrons are released from the molecules and hydrogen ions are generated. The emitted electrons move from the anode 6 to the cathode 7 through the wiring 9. On the other hand, the generated hydrogen ions move to the cathode 7 through the electrolyte membrane 5. At the cathode 7, the oxygen Y in the air is reduced using electrons from the anode 6. At this time, electrons moving from the anode 6 to the cathode 7 via the wiring 9 can be taken out as electric energy at a midway position of the wiring 9.

  In this case, according to the present embodiment, the fuel liquid X returns to the anode 6 along the inner surface of the container 2 through the anode 6 by the electroosmotic flow E generated by the electroosmotic flow pump 8 in the thickness direction. A circulating flow of is generated. As a result, the supply of the fresh fuel liquid X to the anode 6 and the removal of the reaction product generated at the anode 6 are continuously performed, so that there is an advantage that the power generation efficiency can be improved. Further, since the electroosmotic flow E and the circulating flow of the fuel liquid X flow from the electrolyte membrane 5 side toward the anode 6 in the vicinity of the electrolyte membrane 5, the fuel liquid X flowing from the anode 6 side toward the electrolyte membrane 5 is pushed back. . Thereby, there exists an advantage that the crossover which the fuel liquid X flows out into the 2nd chamber 4 through the electrolyte membrane 5 can be prevented.

  Although the direction of the electroosmotic flow E is opposite to the direction of movement of hydrogen ions in the electrolyte membrane 5, the hydrogen ions balance the charges on both sides of the electrolyte membrane 5 accompanying the power generation of the fuel cell 1. Since the electroosmotic flow E moves regardless of the presence or absence of the electroosmotic flow E, the electroosmotic flow E does not affect the movement of hydrogen ions.

Next, a modification of the fuel cell 1 according to this embodiment will be described.
(First modification)
As shown in FIG. 2, the fuel cell 101 according to the first modification of the present embodiment includes the protective member 10 provided at the corner in the first chamber 3. Is different. The protective member 10 has a curved surface 10a that smoothly connects two adjacent surfaces that form a corner.
By doing in this way, in the 1st chamber 3, the fuel liquid X can be made to flow smoothly also in a corner | angular part, the fuel liquid X can be circulated more smoothly, and electric power generation efficiency can further be improved.

(Second modification)
The fuel cell 102 according to the second modification of the present embodiment is different from the fuel cell 1 in that it includes two other electroosmotic pumps 81 and 82 as shown in FIG. The other two electroosmotic pumps 81 and 82 apply a voltage between the pair of electrodes 8a and 8b, a single dielectric 8c disposed between the electrodes 8a and 8b, and the pair of electrodes 8a and 8b. Power supply 8e. These electroosmotic pumps 81 and 82 are arranged between the anode 6 and the side wall of the container 2 and generate an electroosmotic flow E toward the anode 6 along the flow direction of the circulating flow.
By doing so, the flow direction of the fuel liquid X can be further adjusted, and the fuel liquid X can be supplied to the anode 6 more efficiently.

(Third Modification)
As shown in FIG. 4, in the fuel cell 103 according to the third modification of the present embodiment, the cathode 7 is disposed with a space between the electrolyte membrane 5 and the second chamber 4 has water. The fuel cell 1 is different in that it is filled with an alkaline electrolyte Z such as sodium oxide or potassium hydroxide. In this configuration, hydroxide ions generated by the reduction reaction of oxygen Y at the cathode 7 move to the first chamber 3 through the electrolyte membrane 5. Therefore, in this modification, an anion exchange membrane that selectively permeates hydroxide ions is used as the electrolyte membrane 5 instead of the proton exchange membrane.

  In this way, in the anion conduction type structure in which hydroxide ions move between the anode 6 and the cathode 7, the hydroxide ions are moved by the electroosmotic flow E from the electrolyte membrane 5 toward the anode 6. By promoting the consumption of hydroxide ions in the anode 6, it is possible to improve the power generation efficiency.

  In the anion conduction type fuel cell 103, as the fuel liquid X, a liquid further containing an alkaline electrolyte such as sodium hydroxide in addition to the alcohol or sugar described above may be used. Further, manganese oxide may be used as the catalyst supported on the cathode 7 instead of the above-described platinum.

(Fourth modification)
The fuel cell 104 according to the fourth modification example of the present embodiment is a further modification example of the fuel cell 103 according to the third modification example. As shown in FIG. One electrode 8a and the dielectric 8c are arranged in the second chamber 4.

  Even if it does in this way, it can operate | move similarly to the fuel cell 103 of a 3rd modification. Further, since the anode 6 and the electrolyte membrane 5 are disposed adjacent to each other, it is possible to improve the efficiency of power generation by increasing the transmission efficiency of hydroxide ions to the anode 6. When the cathode 7 and the electrode 8a of the electroosmotic pump 8 are arranged adjacent to each other as in this modification, the cathode 7 and the electrode are electrically insulated from each other in order to electrically insulate the cathode 7 and the electrode 8a from each other. An insulating member (not shown) is disposed between 8a and a gap is secured.

(Fifth modification)
The fuel cell 105 according to the fifth modification example of the present embodiment is a further modification example of the fuel cell 104 according to the fourth modification example, and as shown in FIG. 6, one dielectric 8 c is the electrolyte membrane 5. And is common. When the surface potential necessary for the generation of the electroosmotic flow E can be obtained by the electrolyte membrane 5, the electrolyte membrane 5 also serves as the dielectric 8c of the electroosmotic flow pump, thereby reducing the number of components and reducing the size. In addition, cost reduction can be achieved.

  In addition, in this embodiment and its modification, what consists of a single member is shown as the electrodes 8a and 8b of the electroosmotic pump 8, but the electrodes 8a and 8b are composed of a plurality of members. It may be. The dimensions of the electrodes 8a and 8b may be smaller or larger than the dimensions of the anode 6 and the cathode 7. In addition, the electrodes 8a and 8b may be arranged so as to be shifted from each other in the radial direction. In order to promote the passage of the fuel liquid X, the anode 6, the electrodes 8a and 8b, and the dielectrics 8c and 8d may be provided with through holes penetrating in the thickness direction.

1, 101, 102, 103, 104, 105 Fuel cell 2 Container 3 First chamber (first fuel chamber)
4 Second chamber (second fuel chamber)
5 Electrolyte membrane 6 Anode 7 Cathode 8 Electroosmotic flow pump (electroosmotic flow generating means)
8a, 8b Electrode 8c, 8d Dielectric 8e Power supply 9 Wiring 10 Protection member 10a Curved surface E Electroosmotic flow X Fuel liquid (first fuel)
Y Oxygen (second fuel)
Z Alkaline electrolyte

Claims (6)

An anode and a cathode disposed opposite to each other;
A first fuel chamber provided between the anode and the cathode, in which the anode is disposed and supplied with a liquid first fuel having a reducing property, and the cathode is disposed and has a second oxidizing property. An electrolyte membrane that isolates the second fuel chamber to which the fuel is supplied;
A fuel cell comprising: an electroosmotic flow generating means for generating an electroosmotic flow from the electrolyte membrane side toward the anode in the first fuel chamber.   The electroosmotic flow generating means has a pair of porous electrodes arranged in the arrangement direction of the anode and the electrolyte membrane, and a porous dielectric interposed between the pair of electrodes, The fuel cell according to claim 1, further comprising an electroosmotic flow pump that generates the electroosmotic flow between a pair of electrodes.   The fuel cell according to claim 2, wherein the pair of electrodes are disposed with the anode interposed therebetween.   4. The fuel cell according to claim 3, wherein one of the electrodes of the electroosmotic flow pump is disposed in the first fuel chamber, and the other electrode is disposed in the second fuel chamber.   The fuel cell according to any one of claims 1 to 4, wherein the anode is disposed with a space between the anode and an inner surface of the first fuel chamber.   The fuel cell according to any one of claims 1 to 5, wherein the electrolyte membrane is an anion exchange membrane.

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