JPWO2006109645A1 - Solid oxide fuel cell and method of operating the same - Google Patents

Abstract

A solid polymer electrolyte membrane; a cathode disposed on one surface of the solid polymer electrolyte membrane; an anode disposed on the other surface; and a cathode current collector disposed on each of the cathode and the anode And an anode current collector, a fuel supply suppression film disposed above the anode current collector and controlling supply of liquid fuel to the anode, and disposed above the fuel supply suppression film, the fuel supply A perforated plate having a plurality of holes for supplying liquid fuel to the suppression membrane, and a vent hole provided between the fuel supply suppression membrane and the perforated plate.

Description

  The present invention relates to a solid electrolyte type fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane and using liquid fuel, and an operation method thereof.

  Since solid oxide fuel cells using liquid fuel are easily reduced in size and weight, research and development as power sources for various electronic devices such as portable devices are being actively promoted today.

しかし、従来、アノードへのメタノールの供給量が水の供給量に比べて相対的に多くなると、メタノールが上記式１で表される反応に寄与することなく固体高分子電解質膜を透過してしまう「クロスオーバー」が起こり、発電容量や発電電力が低下することが知られている。クロスオーバーが大きくなると、(i)出力（電位）が下がってしまう、(ii)燃料の消費効率が悪くなってしまう、(iii)発熱量が大きくなってＭＥＡの温度が上がるため、燃料温度が必要以上に上昇してクロスオーバーがさらに加速され、更なる温度上昇を引き起こしてしまう、等の問題が生じ易くなる。A solid electrolyte fuel cell includes an electrode-electrolyte membrane assembly (MEA) having a structure in which a solid polymer electrolyte membrane is sandwiched between an anode and a cathode. A type of fuel cell that supplies liquid fuel directly to the anode is called a direct fuel cell. In the direct fuel cell, the supplied liquid fuel is decomposed on a catalyst supported on an anode to generate cations, electrons, and intermediate products. Furthermore, in this type of fuel cell, the generated cations permeate the solid polymer electrolyte membrane and move to the cathode side, and the generated electrons move to the cathode side through an external load, and these are oxygen in the air at the cathode. To generate electricity. For example, in a direct methanol fuel cell (hereinafter referred to as DMFC) using a methanol aqueous solution as a liquid fuel as it is, the reaction represented by the following formula 1 occurs at the anode, and the reaction represented by the following formula 2 occurs at the cathode. . As apparent from these formulas 1 and 2, in DMFC, 1 mol of methanol and 1 mol of water react theoretically at the anode to produce 1 mol of reaction product (carbon dioxide). At this time, since hydrogen ions and electrons are also generated, the theoretical concentration of methanol in the methanol aqueous solution as the fuel is about 70 vol% in volume%.

However, conventionally, when the supply amount of methanol to the anode is relatively larger than the supply amount of water, methanol permeates the solid polymer electrolyte membrane without contributing to the reaction represented by the above formula 1. It is known that “crossover” occurs and power generation capacity and power generation are reduced. When the crossover increases, (i) the output (potential) decreases, (ii) the fuel consumption efficiency deteriorates, (iii) the heat generation amount increases and the temperature of the MEA increases, so the fuel temperature increases. The temperature rises more than necessary, and the crossover is further accelerated, thereby causing a problem such as causing a further temperature rise.

  The above crossover mainly occurs when using a methanol aqueous solution (methanol aqueous solution having a high concentration of about 70 vol% or more) in which the molar ratio of methanol to water exceeds 1, but the same problem occurs when using high concentration methanol. Not only that, but also when a low-concentration methanol aqueous solution having a methanol concentration of, for example, less than 10 vol% is used. Although it is easy to reduce crossover by using a low-concentration methanol aqueous solution, when such a low-concentration methanol aqueous solution is used as a liquid fuel, the amount of power generation per unit mass of the liquid fuel is reduced. The problem arises that the energy density of the fuel cell cannot be increased. Therefore, in order to obtain a solid oxide fuel cell having a high energy density, it is desired to use a liquid fuel having a high concentration of raw fuel, such as a high-concentration methanol aqueous solution, while suppressing crossover.

  As a DMFC technique for suppressing crossover, for example, Japanese Patent Application Laid-Open No. 2000-106201 (Reference 1) includes a fuel vaporization layer that is laminated on an anode and supplies vaporized fuel, and a fuel vaporization layer that is laminated on the fuel vaporization layer. And a fuel permeation layer for supplying the supplied liquid fuel to the fuel vaporization layer. According to the description in Patent Document 1, “gas fuel in the fuel vaporization layer is maintained in a substantially saturated state by vaporizing and supplying the fuel in this way, so that the gas in the fuel vaporization layer by the cell reaction is maintained. Liquid fuel is vaporized from the fuel permeation layer for the amount of fuel consumed, and liquid fuel is further introduced into the cell by capillary force for the amount of vaporization, thus, the fuel supply amount is linked to the fuel consumption amount, There is almost no unreacted fuel discharged outside the cell, and unlike the conventional liquid fuel cell, there is no need for a processing system on the fuel outlet side. ”

  That is, as shown in FIG. 1, the liquid permeation layer 106 for introducing liquid fuel into the cell by capillary force, the anode 102 and the fuel permeation layer 106, and the liquid introduced into the cell A fuel vaporization layer 107 for vaporizing the fuel and supplying the fuel to the anode in the form of a gas is laminated. By stacking a plurality of the fuel permeation layer 106, the fuel vaporization layer 107, and the electromotive unit 104 via the separator 105, a stack 109 serving as a battery body is formed. The liquid fuel introduced into the liquid fuel introduction path 110 is supplied from the side surface of the stack 109 to the fuel permeation layer 106 by capillary force, further vaporized by the fuel vaporization layer 107, and supplied to the anode 102. Since the separator 105, the fuel permeation layer 106, and the fuel vaporization layer 107 also function as a current collecting plate that conducts the generated electrons, for example, the fuel permeation layer 106 is formed of a carbon conductive material.

  In this example, a 1: 1 mixture (molar ratio) of methanol and water is used as the fuel, and the liquid fuel is supplied from the fuel storage tank to the liquid fuel introduction path 110 by providing the tank above the power generation unit. The liquid fuel may be pushed out by a natural drop, an internal pressure in the tank, or the like, or the fuel may be drawn out by the capillary force of the liquid fuel introduction path 110.

  Upon further study of the configuration disclosed in Document 1, the present inventors have found that the following problems exist and stable power generation cannot be performed as it is.

  That is, in the configuration in Document 1, a 1: 1 mixture (molar ratio) of methanol and water is used, and liquid fuel can be supplied to the fuel vaporization layer 107 by an internal pressure or the like in the tank. Et al. Found that in the configuration of Patent Document 1, a stable fuel supply cannot be achieved by a product generated during a power generation operation. In other words, the reaction of the above formula 1 occurs in the anode and carbon dioxide is generated. However, the generated carbon dioxide increases the internal pressure on the anode side and prevents the supply of fuel from the fuel vaporization layer.

  Furthermore, in the structure in literature 1, it turned out that it is impossible to use a high concentration methanol solution as a fuel more than 1: 1 (molar ratio) liquid mixture of methanol and water as a fuel. That is, since the amount of methanol vaporized and supplied is larger than the required amount of water, the anode reaction of Formula 1 is not performed smoothly.

  The present invention has been made to solve the above-described problems, and the object thereof is to enable power generation using a higher concentration fuel in a DMFC comprising vaporization supply, which is advantageous for suppressing crossover. The object is to provide a solid oxide fuel cell. Another object of the present invention is to provide an efficient operation method of such a solid oxide fuel cell.

  A solid oxide fuel cell according to the present invention includes a solid polymer electrolyte membrane, a cathode disposed on one surface of the solid polymer electrolyte membrane, an anode disposed on the other surface, the cathode, A cathode current collector and an anode current collector respectively disposed on the anode; a fuel supply suppression film disposed on the anode current collector for controlling supply of liquid fuel to the anode; and the fuel supply A perforated plate disposed above the suppression membrane and having a plurality of holes for supplying liquid fuel to the fuel supply suppression membrane, and a vent hole provided between the fuel supply suppression membrane and the perforated plate And.

  According to the present invention, since the fuel supply control film is disposed on the anode current collector between the anode current collector and the perforated plate, the fuel supply control film suppresses the fuel permeation amount to the anode. The optimal amount of fuel can be supplied to the anode. Furthermore, according to the present invention, since the vent hole is provided between the solid polymer electrolyte membrane and the anode current collector, carbon dioxide generated during power generation is discharged from the vent hole to the outside. be able to. By effectively discharging carbon dioxide, the internal pressure does not increase, so that the fuel supply from the fuel supply suppression membrane to the anode can be prevented from being hindered. In addition, since the oxygen can be taken into the anode, the vent can react with the catalyst carried on the anode and store water in the anode in advance. Due to the presence of this water, there is a remarkable effect that power generation is possible even when a 100% methanol solution is used as the liquid fuel.

  The solid electrolyte fuel cell may further include a spacer having a sealing function and provided between the solid polymer electrolyte membrane and the anode current collector, and the air hole is formed in the spacer. It is desirable to be provided.

  In terms of structure, it is convenient to provide the vent hole in a spacer provided between the solid polymer electrolyte membrane and the anode current collector.

  The solid oxide fuel cell preferably further includes an evaporation suppression layer provided on the cathode current collector.

  According to this invention, since the evaporation suppression layer is provided on the cathode current collector, it is possible to prevent evaporation of water generated at the cathode. The water whose evaporation is suppressed can be back-diffused to the anode side to generate a power generation reaction with the 100% methanol solution.

  In the above solid oxide fuel cell, it is preferable that a gap is provided between the fuel supply suppressing membrane and the anode. Moreover, it is preferable that the said vent hole is provided so that the said space | gap and the exterior may be connected.

  According to the present invention, since there is a gap between the fuel supply suppression membrane and the anode, oxygen from the vent is supplied to the entire anode, and water can be efficiently generated. In addition, since heat generated in the MEA (electrode-electrolyte membrane assembly) is hardly transmitted to the fuel tank side, an effect of preventing an increase in fuel temperature can be obtained.

  In the above-described solid oxide fuel cell, it is desirable that the fuel supply suppression membrane is sandwiched and fixed between the perforated plate and the anode current collector.

  In the above solid oxide fuel cell, the liquid fuel preferably contains methanol and water, and the ratio of the number of moles of methanol (Mm) to the number of moles of water (Mw) is preferably Mm / Mw> 1.

  The reason why the liquid fuel in which the ratio of the number of moles of methanol (Mm) to the number of moles of water (Mw) is Mm / Mw> 1 can be continuously used is as follows. That is, when power generation was continued using 100% methanol, the initial generated water was consumed, but it was confirmed that stable power generation was still possible. This is presumably because water generated by the power generation reaction of the cathode is diffused back to the anode side, so that water necessary for the anode reaction is sufficiently supplied even if water is not supplied as fuel.

  A solid oxide fuel cell according to the present invention is a method for operating the above solid oxide fuel cell. A step of supplying an oxidant to the fuel cell in an initial state or a resting state, a step of starting fuel supply, and a step of starting energization to an external load after the cell potential reaches a predetermined potential.

  According to the present invention, when operating from the initial state or the resting state, water is sufficiently generated at the anode by supplying the oxidant and the fuel without first energizing. After passing the step of energizing and starting power generation thereafter, stable power generation can be continued even when a high-concentration liquid fuel exceeding the theoretical value, such as 100% methanol, is supplied.

  According to the solid oxide fuel cell of the present invention, the fuel supply control membrane acts so as to suppress the fuel permeation amount to the anode, so that an optimal amount of fuel can be supplied to the anode and stable power generation can be achieved. Can continue. Further, since the vent hole acts to discharge the carbon dioxide generated during power generation to the outside, the carbon dioxide is effectively discharged. Accordingly, it is possible to stabilize the fuel supply from the fuel supply suppression film to the anode while preventing an increase in internal pressure. Moreover, since this ventilation hole can take in oxygen to an anode, the taken-in oxygen reacts with the catalyst carry | supported by the anode, and can store water in an anode beforehand. The presence of this water in the solid oxide fuel cell of the present invention has a remarkable effect that power generation is possible even when a 100% methanol solution is used as the liquid fuel.

It is the figure which showed an example of the conventional vaporization supply type DMFC. It is a schematic cross section which shows an example of the cell structure of the solid oxide fuel cell of this invention. It is a model perspective view which shows the structure arrangement | sequence from MEA to a perforated board. It is a schematic diagram which shows the example of the air vent provided between the solid polymer electrolyte membrane and the anode electrical power collector. It is a schematic diagram which shows the example of the air vent provided between the solid polymer electrolyte membrane and the anode electrical power collector. It is a schematic diagram which shows the example of the air vent provided between the solid polymer electrolyte membrane and the anode electrical power collector. It is a graph which shows the film thickness dependence with respect to the methanol transmission rate of the fuel supply suppression film | membrane used in the Example. It is the graph which showed the electric potential-time change when it generate | occur | produces electricity for 10 hours by DMFC structure of this invention. 1 is a plan view showing a spacer that constitutes a solid oxide fuel cell of Example 1. FIG. 2 is a plan view showing a perforated plate constituting the solid oxide fuel cell of Example 1. FIG.

  Hereinafter, a solid oxide fuel cell and an operation method thereof according to the present invention will be described with reference to the drawings. FIG. 2 is a schematic cross-sectional view showing an example of the cell structure of the solid oxide fuel cell of the present invention, and FIG. 3 is a schematic perspective view showing an outline of the arrangement from the MEA to the perforated plate. 4A to 4C are schematic views showing the form of a vent hole provided between the solid polymer electrolyte membrane and the anode current collector. The present invention is not limited to these drawings and the embodiments described below.

(Solid electrolyte fuel cell)
The solid oxide fuel cell of the present invention includes a solid polymer electrolyte membrane 11, a cathode 12 disposed on and in contact with one surface of the solid polymer electrolyte membrane 11, and a surface on the other surface. A cell structure 10 (at least a cathode structure and a cathode current collector 14 and an anode current collector 15 disposed on and in contact with the anode 12 and the anode 13, respectively, and supplied with liquid fuel. Hereinafter, it is a solid oxide fuel cell having simply “cell” or “cell structure”.

  The solid polymer electrolyte membrane 11, the cathode 12 and the anode 13 constitute an MEA (electrode-electrolyte membrane assembly; Membrane and Electrode Assembly). A cathode current collector 14 and an anode current collector 15 are pressure-bonded to the upper and lower surfaces of the MEA with spacers 21 and 22 interposed therebetween, respectively. The solid polymer electrolyte membrane 11 is not particularly limited, but commercially available ones used in the examples described later can also be used. Both the cathode 12 and the anode 13 sandwiching the solid polymer electrolyte membrane 11 from both sides are produced by applying a catalyst paste containing carbon particles carrying a catalyst onto, for example, a carbon paper that is a porous substrate. The The produced cathode 12 and anode 13 are disposed and pressure-bonded so that the catalyst paste layer side is on the solid polymer electrolyte membrane 11 side, thereby producing an MEA. In FIG. 2, the solid polymer electrolyte membrane 11, the cathode 12, and the anode 13 are denoted by reference numerals as constituting the MEA, but the solid polymer electrolyte membrane 11 is shown for the cathode 12 and the anode 13. The layer on the side represents the catalyst paste layer (no symbol), and the layer on the side away from the solid polymer electrolyte membrane 11 represents the porous substrate (no symbol).

  The greatest feature of the present invention is that the anode current collector 15 has a fuel supply suppressing film 17 disposed between the anode current collector 15 and the perforated plate 16, and the solid polymer electrolyte membrane 11. A vent hole 31 (see FIGS. 4A to 4C) is provided between the anode current collector 15 and the anode current collector 15.

  In the solid oxide fuel cell of the present invention, a fuel supply suppressing film 17 is provided between the anode current collector 15 and the perforated plate 16. The fuel supply suppression film 17 is a control film that vaporizes the fuel and controls the supply thereof, and acts to suppress the fuel permeation amount to the anode 13. As a result, an optimal amount of fuel can be supplied to the anode 13, and stable power generation can be continued. The fuel is supplied from the fuel tank 18 through the perforated plate 16 to the fuel supply suppressing film 17.

  The fuel supply suppression film 17 is sandwiched and fixed by an anode current collector 15 having an opening for supplying fuel to the anode 14 without interfering with fuel and a perforated plate 16 such as a punching sheet. Therefore, it is not necessary to press and fix by a fuel holding layer called a wicking material or the like as in the prior art, and the methanol permeation rate that permeates the fuel supply suppression membrane 17 by setting the thickness according to the fuel concentration. The optimum amount of methanol can be easily supplied.

  As the fuel supply suppression film 17, an electrolyte film (styrene divinylbenzene film) is used. Further, the film thickness is set according to the fuel concentration to be used. The styrene divinyl benzene film is a styrene divinyl benzene copolymer that has been sulfonated. The amount of fuel supplied to the fuel supply suppression membrane 17 needs to be equal to or greater than the amount of methanol consumed in the MEA (electrode-electrolyte membrane assembly), and is determined by the methanol permeation rate and the opening area of the fuel supply suppression membrane 17. Is done. The opening area can be easily controlled by sandwiching the fuel supply suppression membrane 17 between, for example, two perforated plates 16.

  The perforated plate 16 is provided closer to the fuel tank 18 than the fuel supply suppressing film 17. The perforated plate 16 has a plurality of holes for supplying the fuel solution to the fuel supply suppressing film 17. As described above, the perforated plate 16 may be provided so as to sandwich the fuel supply suppressing film 17 as necessary. The perforated plate 16, together with the anode current collector 15, prevents the membrane from being greatly deformed due to swelling of the fuel supply restraining membrane 17 or an increase in internal pressure due to generation of gas at the anode, and prevents excessive stress from being applied. It works to prevent. The material of the perforated plate 16 may be any material as long as it has methanol resistance and a certain degree of hardness. For example, SUS or the like is used. By using a perforated plate, a structure in which a gap 27 is provided between the fuel supply suppressing film 17 and the anode 13 can be obtained. As a result, the heat generated by the MEA (electrode-electrolyte membrane assembly) is not easily transmitted to the fuel tank 18 side, an increase in fuel temperature can be suppressed, and stable power generation is possible.

  In the solid oxide fuel cell of the present invention, a plurality of spacers having a sealing function are provided in each part of the cell structure 10. For example, as shown in FIGS. 2 and 3, (i) a spacer 21 having a thickness substantially the same as the thickness of the cathode 12 is provided between the solid polymer electrolyte membrane 11 and the cathode current collector 14. (Ii) Between the solid polymer electrolyte membrane 11 and the anode current collector 15, a spacer 22 having substantially the same thickness as the anode 13 is provided on the periphery of the cell structure 10. (Iii) A spacer 23 having a sealing function is provided on the periphery of the cell structure 10 between the anode current collector 15 and the fuel supply suppressing film 17, and (iv) the fuel supply suppressing film 17. A spacer 24 having a sealing function is provided on the periphery of the cell structure 10 between the perforated plate 16 and the perforated plate 16, and (v) the perforated plate 16 and the fuel tank 18 made of a plastic material such as PP, for example. In between, it has a seal function. A pacer 25 is provided on the periphery of the cell structure 10. Each of these spacers is usually formed of silicon rubber or plastic having a sealing function.

The present invention is characterized in that a vent hole is provided between the solid polymer electrolyte membrane 11 and the anode current collector 15. The vent hole communicates with the outside. Although the air hole can be provided in any form as long as it is provided between the solid polymer electrolyte membrane 11 and the anode current collector 15, the effect of the present invention can be obtained. The spacer 22 provided between the molecular electrolyte membrane 11 and the anode current collector 15 is preferably provided with a vent hole 31 which is a characteristic configuration of the present invention. By providing the air holes 31 in the spacer 22, carbon dioxide generated during power generation in the catalyst paste layer of the anode 13 is porous to hold the catalyst paste layer directly or once after exiting the gap 27. It passes through the porous substrate and is discharged from the vent hole 31 of the spacer 22 arranged on the periphery of the anode 13. In the present invention, the vent hole 31 effectively discharges carbon dioxide, so that an increase in internal pressure in the cell can be prevented, and fuel supply from the fuel supply suppression film 17 to the anode 13 can be prevented. It can be prevented from being disturbed. In addition, the vent hole 31 can also take oxygen into the anode 13 from the outside. The taken-in oxygen and the supplied fuel react on the catalyst carried on the anode 13 as shown in the following formula 3, and water can be stored in the anode in advance. According to the experiments by the present inventors, it was confirmed that power generation was possible even when a 100% methanol solution was used as the liquid fuel.

  When power generation is continued using a 100% methanol solution, the initial generated water is consumed, but it has been confirmed by experiments by the present inventors that stable power generation is still possible. This is presumably because the water generated by the power generation reaction of the cathode is diffused back to the anode side, and sufficient water necessary for the anode reaction is supplied even if water is not supplied as fuel. Since the reverse diffusing water also wets the solid polymer electrolyte membrane, it can prevent a decrease in proton conductivity and contribute to stable operation.

As a result of the discovery of such a new power generation mechanism by the present inventors, the liquid fuel contains methanol, and the ratio of the number of moles of methanol (Mm) to the number of moles of water (Mw) is Mm / Mw> 1. A thing can be used suitably. In particular, as described above, even when a 100% methanol solution containing no water is used, power generation can be caused and the power generation can be continued. The vent hole 31 is preferably provided at a position where oxygen for generating water that is initially required at the anode is supplied and the generated by-product (carbon dioxide) can be efficiently removed. For example, as shown in FIGS. 4A to 4C, the spacer 22 provided between the anode current collector 15 and the solid polymer electrolyte membrane 11 may be provided by fragmentation or the like (A). A rectangular cut may be provided so as to be uneven (B), or a form (C) in which a through-hole traversing the inside of the spacer 22 is provided, and a structure that exhibits the same function can be used. If it does not specifically limit. Examples of the material of the spacer 22 that forms the vent hole 31 include silicon rubber and plastic. 4A to 4C show an example in which the vent holes 31 are formed only on the two opposite sides, the vent holes 31 may be provided on all four sides.
In order to prevent a reaction between oxygen and water in the anode during storage in an initial state before operation or in a rest state where operation is stopped, a structure in which the vent hole 31 can be opened and closed is adopted. preferable. Further, during storage, it is preferable to take measures such as providing a shutter mechanism or at least emptying the fuel flow path so that methanol does not permeate the fuel supply suppression film 17.

Conventionally, in DMFC, it is known that water leakage due to water generated on the cathode side becomes a problem, but in the present invention, it is desirable that the water generated on the cathode side is reversely diffused to the anode side. It is necessary to prevent water evaporation at the cathode 12. Therefore, it is preferable to provide the evaporation suppression layer 19 on the cathode current collector 14.
As a moisturizing method using the evaporation suppression layer 19, for example, (i) a method in which an evaporation suppression layer made of a hydrophilic material is directly attached to the cathode to moisturize, and (ii) the cathode is closed with an evaporation suppression layer made of a water repellent material. And (iii) a method of moisturizing the above (i) and (ii) in combination. Examples of the material for the evaporation suppression layer 19 suitable for the method (i) include fiber mats, hydrophilic cellulose fibers, glass fibers, and the like, and the evaporation suppression layer 19 suitable for the method (ii). Examples of the material include a meta-resistant plastic material (PTFE, ETFE, polypropylene, polyethylene, etc.), a metal mat, and the like. The material of the evaporation suppression layer 19 preferably has resistance to methanol.

  Such an evaporation suppression layer 19 has an effect of keeping the moisture by preventing evaporation of water. In addition, you may provide the cover member 20 on this evaporation suppression layer 19 (refer FIG. 2). The cover member 20 can take in air necessary for power generation by adopting a structure in which air is taken in from the side surface or a structure in which a hole is formed in the cover member 20 itself. As a result, it is possible to suppress excessive evaporation of the generated water from the cathode while restricting the air vent 31 serving as an air intake port to the minimum necessary.

In the present invention, as shown in FIG. 2, a gap 27 may be provided between the fuel supply suppression film 17 and the anode 13. Due to the presence of the gap 27, oxygen from the vent hole 31 is supplied to the entire anode, and water can be efficiently generated. Further, it is possible to make it difficult to transfer the heat generated by the MEA to the fuel tank side, and the effect of preventing the temperature rise of the fuel can be obtained.
As described above, according to the solid oxide fuel cell of the present invention, there is a remarkable effect that power generation is possible even when a 100% methanol solution is used as the liquid fuel.

(Operation method of solid oxide fuel cell)
An operation method of a solid oxide fuel cell according to the present invention is an operation method of a solid oxide fuel cell according to the present invention, wherein an oxidant is supplied to a fuel cell in an initial state or a dormant state, and a fuel supply And a step of starting energization to the external load after the cell potential reaches a predetermined potential.
First, an oxidant is supplied to the fuel cell in the initial state or the resting state. The oxidant is oxygen (including oxygen in the air; hereinafter referred to as air). When the air gap 27 is formed in advance, the air present in the air gap is supplied as the oxidant. . On the other hand, when no gap is formed, the air that has entered through the air holes 31 is supplied as an oxidant.
Next, fuel is supplied from the fuel cartridge device or the fuel tank 18. The fuel supplied from the fuel tank 18 passes through the perforated plate 16 and is vaporized by the fuel supply suppressing film 17 and supplied to the anode. In the present invention, since the oxidant is already supplied to the anode before the fuel is supplied, when the fuel is supplied to the anode, the oxidant and the fuel are expressed by the above formula on the catalyst supported on the anode. As a result of the reaction, water is generated.

  Next, the cell potential is confirmed, and energization to the external load is started after the cell potential reaches a predetermined potential. The confirmation of the cell potential is to confirm that sufficient water is generated. The cell potential is confirmed to confirm that the generated electromotive force has reached a predetermined value, and then energization to the external load is started. In the present invention, for example, when 100% methanol is supplied as fuel, power generation proceeds without supplying water as fuel, so that water generated at the cathode due to the progress of power generation is reversed to the anode side. It was thought to be spreading. As a result, power generation proceeds even if water is not supplied.

  According to such an operation method, stable power generation can be continued even when a high-concentration liquid fuel such as 100% methanol exceeding a theoretical value is supplied.

Hereinafter, the solid oxide fuel cell of the present invention will be specifically described by showing experimental examples.
FIG. 5 is a graph showing the film thickness dependence on the methanol permeation rate of the fuel supply suppression film used in this example. As the fuel supply suppression membrane, a styrene divinylbenzene membrane with a changed film thickness is used. One of the fuel supply suppression membranes is on the methanol side and the other is open to the atmosphere. Asked. The fuel consumption (methanol permeation rate) is known to be proportional to the current density. For example, in this example, when the permeation rate of methanol of MEA is 0.01 g / h / cm ² , the fuel supply The methanol permeation rate of the suppression membrane is desirably 0.02 to 0.03 g / h / cm ² which is about 2 to 3 times the methanol permeation rate of MEA. If the methanol permeation rate is too high, crossover will occur and stable power generation will not be possible, and the energy density will also decrease. On the other hand, if the methanol permeation rate is too low, the fuel supply amount is insufficient, and power generation itself cannot be performed. In the case of the styrenedivinylbenzene film used in this example, the range of 100 to 135 μm is appropriate considering the methanol permeation rate in FIG.

The cell structure used in this example will be described below. First, catalyst-supported carbon fine particles were prepared by supporting 50% by weight of platinum fine particles having a particle diameter in the range of 3 to 5 nm on carbon particles (Ketjen Black EC600JD manufactured by Lion Corporation). An appropriate amount of a 5 wt% Nafion solution (trade name; DE521, “Nafion” is a registered trademark of DuPont) manufactured by DuPont was added to 1 g and stirred to obtain a catalyst paste for cathode formation. This catalyst paste was applied at a coating amount of 8 mg / cm ² on carbon paper (TGP-H-120 manufactured by Toray Industries, Inc.) as a base material and dried to prepare a 4 cm × 4 cm cathode sheet. On the other hand, the catalyst paste for forming the cathode described above was used except that platinum (Pt) -ruthenium (Ru) alloy fine particles (Ru ratio was 50 at%) having a particle diameter in the range of 3 to 5 nm were used instead of the platinum fine particles. A catalyst paste for forming an anode was obtained under the same conditions as obtained. An anode was produced under the same conditions as the cathode, except that this catalyst paste was used.

  Next, an 8 cm × 8 cm × 180 μm thick membrane made of Nafion 117 (number average molecular weight 250,000) manufactured by DuPont is used as the solid polymer electrolyte membrane 11, and the cathode is formed on one surface in the thickness direction of the membrane. Was placed with the carbon paper facing outward, and the anode was placed on the other surface with the carbon paper facing outward, and hot pressed from the outside of each carbon paper. As a result, the cathode 12 and the anode 13 were joined to the solid polymer electrolyte membrane 11, and an MEA (electrode-electrolyte membrane assembly) was obtained.

Next, current collectors 14 and 15 made of a stainless steel (SUS316) made of stainless steel (SUS316) and having a rectangular frame shape with an outer dimension of 6 cm ² , a thickness of 1 mm, and a width of 11 mm were disposed. Further, between the solid polymer electrolyte membrane 11 and the anode current collector 15, a vent hole 31 made of a rectangular frame-shaped frame plate made of silicon rubber and having an outer dimension of 6 cm ² , a thickness of 0.3 mm, and a width of 10 mm is formed. The spacer 22 was placed. In this spacer 22, a vent hole 31 for discharging carbon dioxide was used in which a total of eight cuts with a width of 0.5 mm were provided on each side of the frame (see FIG. 7A). A spacer 21 having a sealing function between the solid polymer electrolyte 11 and the cathode current collector 14 was disposed. This spacer 21 and other spacers 23, 24, 25 (see FIG. 2) have a sealing function made of a rectangular frame-shaped frame plate made of silicon rubber and having an outer dimension of 6 cm ² , a thickness of 0.3 mm, and a width of 10 mm. A spacer was used.

An 8 cm × 8 cm × 125 μm thick fuel supply suppression membrane 17 made of the above-mentioned styrene divinylbenzene-based membrane (ion exchange capacity 1.9 mmol / g, water content 13%) is prepared, and an anode current collector through a spacer 23 Arranged on the 15th side. Furthermore, a perforated plate 16 (see FIG. 7B) of SUS316 stainless steel having an outer dimension of 6 cm ² , a thickness of 1 mm, a hole diameter of 4 mm, and an opening ratio of 60% is prepared, and is provided on the fuel supply suppression membrane 17 side via the spacer 24 Arranged. Further, a fuel tank 18 was provided adjacent to the perforated plate 16. The fuel tank 18 is a container made of PP and having an outer dimension of 6 cm ² , a height of 8 mm, an inner dimension of 44 mm ² , and a depth of 3 mm. A fuel supply port 18a for fuel supply is provided on the side surface of the container. Contains a wicking material made of urethane as a fuel retention material.

On the other hand, an evaporation suppression layer 19 made of a fiber mat was provided above the cathode. The evaporation inhibiting layer 19, which functions as a moisture retaining layer, processed cellulose fiber sheet (cotton fibers wiper member BEMCOT, manufactured by Asahi Kasei Corporation) in ² corners 35mm Place, as the cover member 20 thereon, the thickness A PTFE punching sheet having a hole diameter of 0.5% and an aperture ratio of 60% was placed thereon, and the evaporation suppression layer 19 was fixed.

  Of these members, members other than the cover member 20 are screwed to the cell frame 29 and integrated. In addition, the screw used at this time is a resin screw to prevent leakage. In this way, the MEA, the cathode current collector, the anode current collector, the fuel supply suppression film, the seal member, the evaporation suppression layer, and the like are integrated by a predetermined number of screws, and the solid oxide fuel cell having the cross-sectional structure shown in FIG. Obtained.

FIG. 6 shows a solid oxide fuel cell obtained as described above, using pure methanol (100% methanol) as a fuel, at room temperature (25 ° C.), 0.3 A (about 19 mA / cm ² ) for 10 hours. It is the graph which showed the time change of the potential when generating electricity. It can be seen from FIG. 6 that power generation is stable for 10 hours. The fuel consumption at this time was 0.185 g / h (about 0.012 g / h / cm ² ), and the energy density per weight was 0.52 Wh / g. The reason why the fuel consumption is smaller than the value of the fuel supply suppression membrane alone (corresponding to 100 μm) is that the amount of fuel permeation suppressed by MEA is also included.

Claims (8)

A solid polymer electrolyte membrane;
A cathode disposed on one surface of the solid polymer electrolyte membrane;
An anode disposed on the other surface;
A cathode current collector and an anode current collector respectively disposed on the cathode and the anode;
A fuel supply suppression membrane disposed on the anode current collector and controlling supply of liquid fuel to the anode;
A perforated plate disposed above the fuel supply suppression membrane and having a plurality of holes for supplying liquid fuel to the fuel supply suppression membrane;
A vent hole provided between the solid polymer electrolyte membrane and the perforated plate;
A solid oxide fuel cell comprising: A solid oxide fuel cell according to claim 1, comprising:
Furthermore,
A spacer having a sealing function, provided between the solid polymer electrolyte membrane and the anode current collector,
Comprising
The vent is a solid oxide fuel cell provided in the spacer. A solid oxide fuel cell according to claim 1 or 2, comprising:
Furthermore,
An evaporation suppression layer is provided on the cathode current collector. A solid oxide fuel cell according to any one of claims 1 to 3,
A solid oxide fuel cell having a gap between the fuel supply suppression membrane and the anode. A solid oxide fuel cell according to claim 4, comprising:
The vent is a solid oxide fuel cell provided to communicate the gap with the outside. A solid oxide fuel cell according to any one of claims 1 to 5,
The fuel supply suppression membrane is a solid oxide fuel cell in which the perforated plate and the anode current collector are sandwiched and fixed. A solid oxide fuel cell according to any one of claims 1 to 6,
The liquid fuel includes methanol and water,
A solid oxide fuel cell in which the ratio of the number of moles of methanol (Mm) to the number of moles of water (Mw) is Mm / Mw> 1. A method for operating a solid oxide fuel cell according to any one of claims 1 to 7,
Supplying an oxidant to the fuel cell in an initial state or a dormant state;
Starting the fuel supply;
Starting energization to an external load after the cell potential reaches a predetermined potential;
A method for operating a solid oxide fuel cell comprising:

Images