JP2009021113A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase a surface area of a power generation part, to improve removability of gas components generated on the fuel electrode side by power generation reaction, and to improve power generation efficiency and timewise stability. <P>SOLUTION: A fuel cell 1 comprises an electromotive part 3 equipped with a plurality of single cells 2; a fuel supply part 4; and a housing chamber 5 of a liquid fuel. A plurality of single cells 2 are arranged separately from each other along the main face of an electrolyte membrane 8 in a shape of the cross-sectional waveform where bending is alternately repeated. At the bending part of the electrolyte membrane 8 between respective single cells 2, a degassing hole 8a is installed so that the gas components formed on the anode 6 side escape toward the cathode 7 side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell using liquid fuel.

  In recent years, attempts have been made to use a fuel cell as a power source for portable electronic devices such as notebook computers and mobile phones so that they can be used for a long time without being charged. A fuel cell is characterized in that it can generate electric power simply by supplying fuel and air, and can generate electric power continuously for a long time if fuel is replenished. For this reason, if the fuel cell can be reduced in size, it can be said that the system is extremely advantageous as a power source for portable electronic devices.

  A direct methanol fuel cell (DMFC) is promising as a power source for portable electronic devices because it can be miniaturized and the fuel can be easily handled. As a fuel supply method in the DMFC, there are known an active method such as a gas supply type and a liquid supply type, and a passive method such as an internal vaporization type in which the liquid fuel in the fuel container is vaporized inside the cell and supplied to the fuel electrode. It has been.

  Among these, a passive system such as an internal vaporization type is particularly advantageous in terms of downsizing the DMFC. In the passive type DMFC, for example, a structure in which a membrane electrode assembly (MEA) having a fuel electrode, an electrolyte membrane, and an air electrode is arranged on a fuel storage portion formed of a box-like container has been proposed (for example, , See Patent Document 1).

  And since a single cell (single cell) made of the membrane electrode assembly (MEA) cannot obtain practically sufficient power, a plurality of single cells are connected via a separator to form a stack structure. Things have been proposed. There are also known fuel cells having a structure in which a plurality of single cells are arranged in a plane of one electrolyte membrane at a predetermined interval and are electrically connected (see, for example, Patent Document 2 and Patent Document 3). ).

  However, the former fuel cell with the stack structure has a problem that the entire device becomes large and heavy. Also in the latter fuel cell, it is required to increase the surface area of the portion related to power generation and improve the output without increasing the size as much as possible. Therefore, it has been studied to form a single cell in a zigzag shape (see, for example, Patent Document 4 and Patent Document 5).

  Further, when high-concentration methanol fuel or the like introduced directly from the fuel storage part or through the flow path is vaporized and supplied to the fuel electrode, the gasified fuel is confined on the fuel electrode side of the MEA and the power generation reaction is performed. It is necessary to release gas components such as carbon dioxide gas and water vapor generated based on the outside of the system. With respect to such a point, in a conventional passive type DMFC, it has been studied to provide a gas vent hole on the side surface of the container on the fuel electrode side to release a gas component out of the system (for example, see Patent Document 6). .

However, when the gas vent hole is provided on the side surface of the DMFC container, the generated gas component will escape from the peripheral portion, so the gas component generated near the center of the MEA cannot be sufficiently removed, There was a problem that stable power generation characteristics could not be obtained. Moreover, since the temperature of the peripheral part of the MEA is lower than that of the central part, there is a problem that the gas vent hole is easily clogged due to condensation of water vapor, so that stable output characteristics cannot be obtained over time.
International Publication No. 2005/112172 Pamphlet JP 2002-015763 A JP 2007-026873 A JP 2003-331860 A JP 2006-156223 A JP 2006-108028 A

  An object of the present invention is to provide a compact and improved fuel cell output by increasing the surface area of the power generation unit without increasing the volume of the entire apparatus as much as possible. Another object of the present invention is to provide a fuel cell capable of improving the efficiency of the power generation reaction and the stability over time by enhancing the removability of the gas component generated on the fuel electrode side of the MEA with the power generation reaction.

  A fuel cell according to an aspect of the present invention includes an electrolyte membrane and a membrane electrode assembly each having a fuel electrode and an air electrode provided to face each other with the electrolyte membrane interposed therebetween. An electromotive part having a plurality of single cells arranged separately from each other along the main surface, and a fuel supply mechanism for supplying fuel to the fuel electrode of the membrane electrode assembly constituting the single cell, The electrolyte membrane has a cross-sectional corrugated shape or zigzag shape in which a mountain fold and a valley fold are alternately repeated between the arrangement portions of the single cells, and the membrane electrode joint is formed on the bent portion of the electrolyte membrane. It is characterized in that a gas vent hole for releasing the gas component generated on the fuel electrode side of the body to the air electrode side is provided.

  Since the fuel cell according to the aspect of the present invention has a structure in which a plurality of single cells are separated from each other at a predetermined interval along the main surface of a corrugated or zigzag electrolyte membrane. Compared to a fuel cell in which a plurality of single cells are arranged in the plane of a planar electrolyte membrane, a larger number of single cells can be arranged in a limited space (volume) to increase the surface area of the power generation unit. . Therefore, the power generation output can be improved without increasing the size of the entire fuel cell.

  In addition, gas components such as carbon dioxide and water vapor generated on the fuel electrode side of the membrane electrode assembly based on the power generation reaction can be efficiently released to the air electrode side from the vent holes provided in the bent portion of the electrolyte membrane. Therefore, it is possible to improve the efficiency of power generation reaction, stability over time, etc., and maintain high power continuous power generation.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a configuration of an embodiment of a fuel cell of the present invention. FIG. 2 is an exploded perspective view showing the configuration of the electromotive unit of the fuel cell shown in FIG.

  A fuel cell 1 shown in FIG. 1 includes an electromotive unit 3 including a plurality of single cells 2, a fuel supply unit 4 that supplies fuel to the electromotive unit 3, and a fuel storage chamber that stores liquid fuel F. 5 mainly.

  Each single cell 2, 2... Has an anode (fuel electrode) 6 having an anode catalyst layer and an anode gas diffusion layer, and a cathode (air electrode / oxidant electrode) 7 having a cathode catalyst layer and a cathode gas diffusion layer, And a membrane electrode assembly (MEA) comprising a proton (hydrogen ion) conductive electrolyte membrane 8 sandwiched between a catalyst layer (anode catalyst layer) of the anode 6 and a catalyst layer (cathode catalyst layer) of the cathode 7 have.

  Here, examples of the catalyst contained in the anode catalyst layer and the cathode catalyst layer include a simple substance of a platinum group element such as Pt, Ru, Rh, Ir, Os, and Pd, and an alloy containing the platinum group element. For the anode catalyst layer, it is preferable to use Pt—Ru, Pt—Mo or the like having strong resistance to methanol, carbon monoxide, or the like. It is preferable to use Pt, Pt—Ni or the like for the cathode catalyst layer. However, the catalyst is not limited to these, and various substances having catalytic activity can be used. These catalysts may be either a supported catalyst using a conductive support such as a carbon material or an unsupported catalyst.

  Examples of the proton conductive material constituting the electrolyte membrane 8 include fluorine-based resins (Nafion (trade name, manufactured by DuPont) and Flemion (trade name, manufactured by Asahi Glass Co., Ltd.) such as a perfluorosulfonic acid polymer having a sulfonic acid group. Etc.), organic materials such as hydrocarbon resins having sulfonic acid groups, or inorganic materials such as tungstic acid and phosphotungstic acid. However, the proton conductive electrolyte membrane 8 is not limited to these.

  The anode gas diffusion layer laminated on the anode catalyst layer serves to uniformly supply fuel to the anode catalyst layer and at the same time has a current collecting function of the anode catalyst layer. The cathode gas diffusion layer laminated on the cathode catalyst layer serves to uniformly supply air as an oxidant to the cathode catalyst layer and at the same time has a current collecting function of the cathode catalyst layer. The anode gas diffusion layer and the cathode gas diffusion layer are made of a porous base material having conductivity such as carbon paper.

  An anode current collector 9 is laminated outside the anode gas diffusion layer, and a cathode current collector 10 is laminated outside the cathode gas diffusion layer. These current collectors 9 and 10 have through holes through which fuel, oxidant (air), and the like circulate. For example, a mesh or a porous film made of a conductive metal material such as Au is used. The anode current collector 9 and the cathode current collector 10 are not shown in FIG.

  The plurality of single cells 2, 2... Share the electrolyte membrane 8 in common. The single cell 2, 2... Common electrolyte membrane 8 has a cross-sectional waveform or zigzag shape in which mountain-fold and valley-fold bends are alternately repeated. Along the main surface of the common electrolyte membrane 8. A plurality of single cells are arranged separately from each other at a predetermined interval. That is, the common electrolyte membrane 8 has a cross-sectional waveform or a zigzag shape in which a mountain fold and a valley fold are alternately repeated between the arrangement portions (separation portions) of the single cells 2, 2. A plurality of single cells 2, 2... Are respectively disposed in the inclined portions between the bent portions.

  The angle of the bent portion (mountain fold portion and valley fold portion), that is, the bend angle (θ) is preferably the same in each bend portion in the range of 30 to 150 degrees. A more preferable bending angle is 60 degrees in that it is more compact in terms of space but has high uniform supply and diffusibility of fuel, and can improve output. If the bending angle is less than 30 degrees, it is difficult to supply fuel uniformly to the entire anode 6 in each single cell 2, 2,.

  Further, a gas vent hole 8a is provided through the electrolyte membrane 8 in a bent portion of the electrolyte membrane 8 located between the single cells 2, 2,. The gas vent 8a is for letting a gas component generated on the anode 6 side accompanying the power generation reaction escape to the cathode 7 side. The gas vent hole 8a can be disposed in a mountain fold or valley fold or both of the bent portions of the electrolyte membrane 8, but is preferably disposed in the mountain fold. The structure in which the gas vent hole 8a is disposed in the mountain fold portion has an advantage that the gas component released to the cathode 7 side through the gas vent hole 8a has less adverse effect on the cathode 7.

  The diameter of the vent hole 8a is preferably 50 μm or more and 2 mm or less, and more preferably 1 mm or less. When the hole diameter of the gas vent hole 8a is 50 μm or less, clogging or the like due to water vapor aggregation occurs, making it difficult to achieve a sufficient gas venting effect. On the other hand, when the hole diameter of the gas vent hole 8a is 2 mm or more, the amount of fuel that permeates directly to the cathode 7 side through this hole increases, and a local heating state is likely to occur. Etc. may be reduced. Further, the number of the vent holes 8a is preferably 1 to 4 per each bent portion, and is preferably arranged at an equal interval.

  In the plurality of single cells 2, 2... Arranged on the main surface of the electrolyte membrane 8, the adjacent single cells 2 are connected in series by the anode current collector 9 and the cathode current collector 10 described above. ing. An example of the current collector plate 11 for connecting the single cells 2, 2... In series is shown in FIG. In this connection current collector plate 11, a plurality of anode current collectors 9, 9... Corresponding to a plurality of single cells and a plurality of cathode current collectors 10, 10,. In the central folded portion, wiring portions 12, 12... For electrically connecting the corresponding anode current collector 9 and cathode current collector 10 are formed. The connecting current collecting plate 11 is folded from the center, and the MEAs of the single cells 2, 2,... Are sandwiched between the anode current collectors 9, 9,. It is contacted and arranged.

  Further, the electromotive unit 3 having a plurality of single cells 2, 2,... Has an undulating shape having a cross-sectional waveform or a zigzag shape like the electrolyte membrane 8, and an anode having a through hole through which fuel or air flows. The side support 13 and the cathode support 14 are sandwiched and held from both sides. A space between the electromotive unit 3 and the anode-side support 13 and the cathode-side support 14 is sealed by a sealing member 15 such as an O-ring, thereby causing fuel leakage or oxidant leakage from the electromotive unit 3 (MEA). Is prevented. The cathode support 14 can be omitted.

  Thus, the anode side of the electromotive unit 3 held by the anode side support 13 is disposed on the fuel storage chamber 5 in which the liquid fuel F is stored via the fuel supply unit 4. That is, the gas-liquid separation layer 16 is disposed so as to cover the opening of the fuel storage chamber 5, and the electromotive unit 3 held by the anode side support 13 is disposed on the gas-liquid separation layer 16. The vaporized component of the liquid fuel F that has passed through the gas-liquid separation layer 16 from the fuel storage chamber 5 is supplied to the anodes 6 of the single cells 2, 2. The gas-liquid separation layer 16 separates the vaporized component of the liquid fuel F and the liquid fuel F and allows the vaporized component to permeate the anode 6 side, and is made of a material such as silicone rubber or fluororesin. Note that the gas-liquid separation layer 16 may be interposed between the anode current collector 9 and the anode side support 13 of the electromotive unit 3. In this structure, the gas-liquid separation layer 16 provided on the opening of the fuel storage chamber 5 can be omitted.

  The liquid fuel F stored in the fuel storage chamber 5 is a methanol aqueous solution having a concentration exceeding 50 mol% or pure methanol. The purity of pure methanol is preferably 95% by weight or more and 100% by weight or less. The vaporized component of the liquid fuel F means vaporized methanol when liquid methanol is used as the liquid fuel, and the vaporized component of methanol and the vaporized component of water when an aqueous methanol solution is used as the liquid fuel. Means an air-fuel mixture consisting of

  A cover having a moisture retaining layer disposed on the cathode side support 14 disposed on the cathode side of the electromotive unit 3 as necessary, and having an opening 17a for taking in air as an oxidant thereon. Plates 17 are stacked. The moisturizing layer is impregnated with a part of the water produced in the cathode catalyst layer to suppress the transpiration of water and promote uniform diffusion of air to the cathode catalyst layer. Consists of. The cover plate 17 is formed of a metal such as SUS304, for example.

  Thus, the passive DMFC 1 of the embodiment is configured by arranging the electromotive unit 3, the cover plate 17, and the like in order on the fuel storage chamber 5 via the gas-liquid separation layer 16 to hold the whole. Yes.

In the fuel cell 1 of the embodiment configured as described above, the fuel supplied from the fuel storage chamber 5 to the anode 6 of each single cell 2 via the gas-liquid separation layer 16 diffuses in the anode gas diffusion layer in the MEA. And supplied to the anode catalyst layer. When methanol fuel is used as the liquid fuel F, an internal reforming reaction of methanol shown in the following formula (1) occurs in the anode catalyst layer. When pure methanol is used as the methanol fuel, the water generated in the cathode catalyst layer or the water in the electrolyte membrane 8 is reacted with methanol to cause the internal reforming reaction of the formula (1). Alternatively, the internal reforming reaction is caused by another reaction mechanism that does not require water.
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)

Electrons (e ⁻ ) generated by this reaction are guided to the outside via the anode current collector 9, and after operating a portable electronic device or the like as so-called electricity, the cathode 7 via the cathode current collector 10. Led to. Protons (H ⁺ ) generated by the internal reforming reaction of the formula (1) are guided to the cathode 7 through the electrolyte membrane 8. Air is supplied to the cathode 7 as an oxidant. Electrons (e ⁻ ) and protons (H ⁺ ) that have reached the cathode 7 react with oxygen in the air in the cathode catalyst layer according to the following formula (2), and water is generated with this reaction.
6e ⁻ + 6H ⁺ + (3/2) O ₂ → 3H ₂ O (2)

  In the power generation reaction of the fuel cell 1 described above, in order to increase the power generated by the fuel cell 1 having the plurality of single cells 2, 2..., The electrode (anode 6) of the electromotive unit 3 (MEA) where the power generation reaction is performed. It is important to increase the total surface area of the cathode 7). In the embodiment, since the plurality of single cells 2, 2... Are separated from each other along the main surface of the corrugated or zigzag electrolyte membrane 8, the plurality of single cells are arranged. Compared to the fuel cell arranged in the plane of the electrolyte membrane, more single cells are arranged in a limited space, and the total surface area of the electrode is increased. Therefore, the output of power generation is improved.

  For example, when comparing the output of a fuel cell having six rectangular single cells (power density per projected plane area), the output density of a fuel cell in which a single cell is arranged in the plane of a planar electrolyte membrane is 1 In this case, in the fuel cell of the embodiment in which the single cell is arranged in the main surface of the electrolyte membrane having a cross-sectional waveform at a bending angle of 150 degrees, the output density is 1.036 times. In the fuel cell in which the bending angle of the electrolyte membrane is 30 degrees in the embodiment, the output density is 3.86 times, and an extremely high output can be obtained.

  Further, in order to supply fuel uniformly to the MEA having a plurality of single cells 2, 2, and increase the generated power of the fuel cell 1, gases such as carbon dioxide and water vapor generated by the power generation reaction It is also important to quickly remove components and allow the supplied fuel to uniformly reach the reaction section. Since gas components such as carbon dioxide and water vapor are generated on the anode 6 side of the MEA, the gas components generated by the power generation reaction increase the internal pressure on the anode 6 side. Furthermore, the gas component itself becomes a factor that inhibits the supplied fuel from reaching the reaction section.

  In the fuel cell 1 of the embodiment, the gas vent hole 8a is provided through the electrolyte membrane 8 in the bent portion of the electrolyte membrane 8 between the single cells 2, 2,. The gas component is released to the cathode 7 side through the gas vent hole 8a, and further released to the outside of the system. Thus, gas components can be uniformly removed from the surface of the MEA, and the fuel supplied thereby can be stably and uniformly supplied to each single cell 2, 2. It becomes possible to generate a power generation reaction efficiently and continuously in the entire electromotive unit 3.

  As a specific example, a conventional structure fuel cell that discharges internal pressure to the atmosphere by providing a gas vent hole on the anode side surface of the DMFC container, and a gas vent hole in the bent portion of the electrolyte membrane 8 between each single cell 2, 2. In each of the fuel cells of the embodiment configured to provide the gas component to the cathode 7 side by providing a constant voltage at room temperature, the fuel cell of the embodiment is a conventional fuel cell. The output reduction rate has increased by about 10%. In the structure in which no vent hole is provided on the anode side surface, the pressure on the anode side increased to 0.3 MPa in 4 hours, and methanol fuel could not be delivered, making continuous output difficult.

  In the embodiment described above, a direct methanol fuel cell using an aqueous methanol solution or pure methanol as the liquid fuel F has been described. However, the liquid fuel F is not limited to these. For example, ethanol fuel such as ethanol aqueous solution or pure ethanol, propanol fuel such as propanol aqueous solution or pure propanol, glycol fuel such as glycol aqueous solution or pure glycol, dimethyl ether, formic acid, or other liquid fuel may be used.

  In the above embodiment, the passive DMFC has been described as an example. However, the present invention is not limited to the passive type, but is also an active type fuel cell, and further to a semi-passive type fuel cell using a pump or the like for a part of fuel supply. In contrast, the present invention can be applied, and the same effect as that obtained when a passive fuel cell is used can be obtained.

  In the semi-passive type fuel cell, the fuel supplied from the fuel storage part to the membrane electrode assembly is used for the power generation reaction, and is not circulated thereafter and returned to the fuel storage part. The semi-passive type fuel cell is different from the conventional active method because it does not circulate the fuel, and does not impair the downsizing of the device. In addition, the fuel cell uses a pump for supplying fuel, and is different from a pure passive system such as a conventional internal vaporization type. Therefore, this type of fuel cell is referred to as a semi-passive method as described above. In this semi-passive type fuel cell, a fuel cutoff valve may be arranged in place of the pump as long as fuel is supplied from the fuel storage portion to the membrane electrode assembly. In this case, the fuel cutoff valve is provided to control the supply of liquid fuel through the flow path.

  That is, the present invention can be applied to various fuel cells using liquid fuel. In addition, the specific configuration of the fuel cell, the supply state of the fuel, and the like are not particularly limited, and all of the fuel supplied to the MEA is liquid fuel vapor, all is liquid fuel, or part is liquid state. The present invention can be applied to various forms such as a vapor of supplied liquid fuel. In the implementation stage, the constituent elements can be modified and embodied without departing from the technical idea of the present invention. Furthermore, various modifications are possible, such as appropriately combining a plurality of constituent elements shown in the above embodiments, or deleting some constituent elements from all the constituent elements shown in the embodiments. Embodiments of the present invention can be expanded or modified within the scope of the technical idea of the present invention, and these expanded and modified embodiments are also included in the technical scope of the present invention.

It is sectional drawing which shows the structure of one Embodiment of the fuel cell of this invention. It is a disassembled perspective view which shows the structure of the electromotive part of the fuel cell shown in FIG. In the fuel cell shown in FIG. 1, it is a figure which shows an example of the current collection board for a connection for connecting a single cell in series.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell, 2 ... Single cell, 3 ... Electromotive part, 4 ... Fuel supply part, 5 ... Fuel storage chamber, 6 ... Anode, 7 ... Cathode, 8 ... Electrolyte membrane, 8a ... Gas vent hole, 9 ... Anode Current collector, 10 ... cathode current collector, 11 ... current collector for connection, 13 ... anode side support, 14 ... cathode side support, 16 ... gas-liquid separation layer, 17 ... cover plate.

Claims (4)

It consists of a membrane electrode assembly having an electrolyte membrane and a fuel electrode and an air electrode provided opposite to each other with the electrolyte membrane interposed therebetween, and is arranged separately from each other along the main surface of the electrolyte membrane provided in common. An electromotive unit having a plurality of unit cells provided, and a fuel supply mechanism for supplying fuel to the fuel electrode of the membrane electrode assembly constituting the unit cell,
The electrolyte membrane has a cross-sectional corrugated shape or a zigzag shape in which bending of a mountain fold and a valley fold is alternately repeated between the arrangement portions of the single cells,
The fuel cell is characterized in that a bent part of the electrolyte membrane is provided with a gas vent hole for escaping a gas component generated on the fuel electrode side of the membrane electrode assembly to the air electrode side.   The fuel cell according to claim 1, wherein the fuel supply mechanism includes a gas-liquid separation layer.   3. The fuel cell according to claim 1, wherein the single cells are electrically connected through current collecting layers provided on the fuel electrode side and the air electrode side, respectively.   The fuel cell according to any one of claims 1 to 3, wherein the fuel is methanol fuel.

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