JP2010225430A - Fuel cell power generation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent hydrogen density from falling due to nitrogen as inert gas mixing into a fuel side in a fuel cell power generation system, maintain cell voltage high, and heighten a dew point of exhaust gas through reuse of product water inside a fuel cell. <P>SOLUTION: The system includes a fuel cell including a membrane-electrode assembly structured by pinching an electrolyte film between an anode and a cathode, and a unit cell containing an anode-side separator with a fuel flow channel, a cathode-side separator with an oxidant flow channel, and structured by pinching the membrane-electrode assembly between the anode-side separator and the cathode-side separator, a fuel supply channel supplying fuel to the fuel cell, an oxidant supply channel supplying an oxidant containing oxygen to the fuel cell, and an oxygen concentrator for enhancing concentration of oxygen. A dew point of oxidant exhaust gas exhausted from the fuel cell is to be above an operation temperature of the fuel cell. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell power generation system.

  A polymer electrolyte fuel cell using a reformed fuel of hydrogen or an organic compound has features such as low noise and low operating temperature (about 70 to 80 ° C.). Therefore, a wide range of uses are expected as a portable power source, a power source of an electric vehicle, an electric motorcycle or an assist type bicycle, and a power source for a light vehicle such as a medical care wheelchair or a senior car.

  In the future, it is expected that sunlight or wind power will be converted into electric energy, and water will be electrolyzed to produce water that can be transported. If hydrogen production becomes widespread, it is likely that energy systems using hydrogen will be highlighted as the ultimate clean energy system. Solar energy, etc. is renewable and clean and inexhaustible, making it the most powerful energy source to break out of the current fossil energy society.

  If hydrogen is stored at a high density using a hydrogen storage alloy or the like, energy can be transported more efficiently than the energy stored in the secondary battery. If renewable energy such as sunlight can be used, it is expected that a sustainable energy society that can significantly reduce carbon dioxide will be built. In such a future society, there is a great expectation for a polymer electrolyte fuel cell that can reconvert hydrogen into electricity with high efficiency.

  A polymer electrolyte fuel cell is an electrochemical device that uses an electrolyte membrane that moves protons and directly converts the recombination reaction between hydrogen and oxygen into electrical energy. The electrolyte membrane that moves protons has electrodes formed on both sides thereof. This is called a membrane-electrode assembly (hereinafter abbreviated as MEA). A unit cell made of a separator is provided so as to face each of the electrodes. The separator is formed with a flow path (channel) for circulating fuel or oxidant.

  It is well known that when water is not contained in the electrolyte membrane, the proton (hydrogen ion) movement speed in the electrolyte membrane is extremely slow. Therefore, water is added to the fuel or oxidant in advance and supplied to the fuel cell. This operation of adding moisture is called humidification. As a result, drying of the electrolyte membrane can be suppressed, and water generated by oxidation of hydrogen is further added to keep the electrolyte membrane wet. Therefore, in the prior art, an improvement has been demanded in that the polymer electrolyte fuel cell cannot be operated without humidification.

  Patent Document 1 discloses a fuel cell system including a fuel cell, and an oxidant gas supply unit for supplying an oxidant gas to a cathode electrode of the fuel cell, and a fuel gas to an anode electrode of the fuel cell. A fuel gas supply unit for controlling the inflow of the oxidizing gas into the fuel cell, a second valve for controlling the outflow of cathode exhaust gas from the fuel cell, and the fuel cell system A control unit for controlling the operation, wherein the control unit (a) fills the fuel cell with the oxidizing gas with at least the first valve opened; and (b) the first And a step of closing the second valve and (c) a step of opening the first and second valves after performing predetermined power generation with the first and second valves closed. A fuel cell system characterized by Temu is disclosed. Patent Document 1 discloses a fuel cell system having an oxygen-nitrogen separator and a humidifier using a membrane separation method using a bundle of hollow fiber membranes, a PSA method (adsorption method), or a cryogenic separation method. .

  On the other hand, there is a case in which humidification becomes excessive, and the water formed inside the cell adheres to the separator channel or the electrode surface, thereby causing a phenomenon that inhibits the reaction of hydrogen oxidation or oxygen reduction. For example, when fuel or an oxidant is circulated through the separator channel and power generation is started, water may adhere to the separator channel and the MEA electrode surface in contact with the separator. This water is formed on both the anode and cathode surfaces.

  If a phenomenon such as clogging of the flow path or excessive wetting of the MEA occurs due to this water, the supply of fuel or oxidant to the catalyst is hindered. As a result, the cell voltage decreases and the output of the fuel cell decreases. In particular, if water adheres to the interior and surface of the catalyst layer, which interferes with the contact between the catalyst and the fuel or oxidant, a significant voltage drop results. Such a decrease in output is often significant during power generation at a high current density.

  In Patent Document 2, the cathode catalyst layer is compared with a portion that reduces oxygen and a portion that reduces oxygen for the purpose of preventing flooding phenomenon even during high-current operation and enhancing generated water dissipation and output. Thus, there is disclosed a fuel cell having a feature of having a portion exhibiting high water repellency, and the portion exhibiting high water repellency being unevenly distributed when observed on the surface of the cathode catalyst layer.

  Further, Patent Document 3 discloses a fuel cell in which a gas flow path forming member is formed of a porous material and a moisture maintenance body is disposed.

JP 2008-41516 A JP 2004-171847 A JP 2006-40563 A

  An object of the present invention is to prevent nitrogen, which is an inert gas, from entering the fuel side and lowering the hydrogen concentration, to keep the cell voltage high, and to reuse the generated water inside the fuel cell, Is to raise the dew point.

  The fuel cell power generation system of the present invention includes a membrane-electrode assembly having an electrolyte membrane sandwiched between an anode and a cathode, an anode side separator having a fuel flow path, and a cathode side separator having an oxidant flow path. A fuel cell including a unit cell having a configuration in which the membrane-electrode assembly is sandwiched between the anode-side separator and the cathode-side separator, and a fuel supply path for supplying fuel to the fuel cell, An oxidant supply path for supplying an oxidant containing oxygen to the fuel cell; and an oxygen concentrator for increasing the concentration of the oxygen, and operating the fuel cell with a dew point of exhaust gas discharged from the fuel cell. It is characterized by being above the temperature.

  According to the present invention, nitrogen, which is an inert gas, is prevented from being mixed into the fuel side and the hydrogen concentration is reduced, the cell voltage is maintained high, and the produced water is reused inside the fuel cell, The dew point of can be increased.

  Further, according to the present invention, the oxygen concentration of the oxidant can be increased and the flow rate of the oxidant can be reduced.

It is sectional drawing which shows the structure of the cell of the Example by this invention. It is a top view which shows the structure of the separator of the Example by this invention. It is sectional drawing which shows the structure of the cell stack of the Example by this invention. 1 is a schematic configuration diagram illustrating a fuel cell power generation system according to an embodiment of the present invention. It is a top view which shows the structure of the separator of the modification by this invention. It is a schematic block diagram which shows the fuel cell power generation system of the other Example by this invention. It is sectional drawing which shows the structure of the cell of the other Example by this invention. It is a graph which shows the relationship between the hydrogen concentration and the cell voltage in the fuel cell of the Example by this invention. It is a graph which shows the relationship between the oxidizing agent utilization factor and the dew point of exhaust gas in the fuel cell of the Example by this invention.

  The present invention relates to a highly efficient fuel cell power generation system.

  In view of the prior art, we examined the configuration necessary to provide a highly efficient fuel cell power generation system. And in order to construct a highly efficient power generation system, it is important to suppress the cell voltage drop due to a decrease in the hydrogen concentration in the fuel while the cell voltage is high while the supply amount of the oxidant is small. I thought.

  In the following, technical items that are problematic in realizing a highly efficient power generation system will be described in detail.

  FIG. 1 shows a single cell structure of a fuel cell targeted by the present invention.

  An MEA is provided at the center of the cross section of the single cell. This MEA has a three-layer structure in which an electrolyte membrane 103 is sandwiched between an anode 101 and a cathode 102.

  The fuel-side separator 104 has a porous flow path plate 105 through which fuel flows, and is disposed so that one surface of the porous flow path plate 105 is in contact with the anode 101. The porous flow path plate 105 has pores that allow gas to pass therethrough and has conductivity. In addition, since the other surface of the porous flow path plate 105 is in close contact with the separator 104, electrons in which fuel is oxidized on the anode 101 can flow to the separator 104 via the porous flow path plate 105. .

  The oxidant side separator 106 has a porous flow path plate 107 through which an oxidant flows, and one surface of the porous flow path plate 107 is in contact with the cathode 102. The porous flow path plate 107 also has pores and has conductivity. Electrons that reduce the oxidant flow from the separator 106 to the cathode 102 via the porous flow path plate 107.

  Gaskets are provided on the outer peripheral portions of the fuel side separator 104 and the oxidant side separator 106 so that the fuel and the oxidant do not leak to the outside and one reactant does not enter the flow path of the other reactant. 108 and 109 are provided. Note that a fuel manifold for supplying or discharging fuel to the porous flow path plate 104 is formed so as to penetrate the gaskets 108 and 109 and overlaps in the cross-sectional view, and thus is omitted in FIG. For the same reason, the oxidant manifold for supplying or discharging the oxidant to the porous flow path plate 107 is also omitted in FIG.

  Further, instead of the porous flow path plates 105 and 107 in FIG. 1, it is also possible to form grooves serving as flow paths in the fuel side separator 104 and the oxidant side separator 106 and omit the porous flow path plates. . An example of the cell cross-sectional structure in this case is shown in FIG.

  In FIG. 7, the MEA has a three-layer structure in which an anode 701 is laminated on the upper surface of an electrolyte membrane 703 and a cathode 702 is laminated on the lower surface. The fuel-side separator 704 has a flow path 705 through which fuel flows, and is disposed so that the flow path surface is in contact with the anode 701. The oxidant side separator 706 has a flow path 707 through which the oxidant flows, and the flow path surface is in contact with the cathode 702. Gaskets 708 and 709 are provided on the outer peripheral portion of the separator so that fuel and oxidant do not leak to the outside and one reactant does not enter the flow path of the other reactant. The width and depth of the flow path can be selected as desired, and the pattern can be selected as an arbitrary shape.

  The fuel used in the present invention is a gas containing a hydrogen molecule or a compound containing a hydrogen atom in the molecule. It is desirable that the fuel is hydrogen having a concentration of 100% in order to obtain high output or high power generation efficiency. However, the fuel may be a mixed gas containing an inert gas such as nitrogen as long as it does not deteriorate the catalyst of the anode 101 in FIG. 1 (701 in FIG. 7). A gas containing hydrogen obtained from natural gas, kerosene, or the like by catalytic reforming treatment may be supplied to the battery as fuel.

  Air is generally used as the oxidizing agent. As will be described later, in the present invention, a gas having purified air and an oxygen concentration higher than 21% is used. The reason for increasing the oxygen concentration will be described later.

  In a fuel cell using hydrogen as a fuel, the reaction represented by the following reaction formula (1) occurs at the anode and the reaction represented by the following reaction formula (2) occurs at the cathode, and the reaction for generating water from hydrogen and oxygen progresses as a whole. To do.

H ₂ → 2H ⁺ + 2e ⁻ (1)
2H ⁺ + 1/2 O ₂ + 2e ⁻ → H ₂ O (2)
In order for the above reaction to proceed promptly in the fuel cell, it is necessary to remove water formed on the catalyst or water that has passed through the electrolyte membrane from the vicinity of the catalyst. This is because when excess water is present, the supply of fuel and oxidant is hindered and the cell voltage becomes unstable.

  In addition, when the moisture in the vicinity of the catalyst is insufficient, the movement resistance of hydrogen ions that move inside the electrolyte binder increases, and the cell voltage decreases. This is measured as the reaction resistance of the MEA by impedance measurement or the like.

  Thus, in the vicinity of the catalyst, a three-phase interface composed of a catalyst (solid phase), an electrolyte binder (electrolyte), and a reactant phase (gas phase or liquid phase) is formed. It works effectively, resulting in an increase in cell voltage and an increase in output. That is, there is an appropriate amount of water for forming an effective three-phase interface in the vicinity of the catalyst, and its management is important.

  The “three-phase interface” described below is defined as a three-phase interface composed of a catalyst-electrolyte-reactant phase. The reactant phase in a fuel cell using hydrogen as a fuel means a gas phase composed of a fuel gas containing hydrogen or a gas phase composed of an oxidant gas containing oxygen.

  A typical situation where the moisture in the vicinity of the catalyst is insufficient is when the oxidant (for example, air) is supplied to the fuel cell without being humidified. It is known that when air that is not humidified is supplied to the fuel cell, the generated water is not generated on the MEA in the early stage of startup, so that the amount of humidification is significantly insufficient on the upstream side of the oxidant, and the cell voltage drops rapidly. Yes. This is the same even when the flow path pattern is adjusted so that the upstream of the oxidant flow path is aligned with the downstream of the fuel flow path via the MEA. This is because the generated water is not formed in the vicinity of the MEA at the initial stage of power generation, and particularly when air is used as the oxidant, the flow rate of gas flowing through the cathode channel is large, so that the stability of the voltage is remarkably deteriorated. .

  When a sudden voltage drop occurs in the early stage of startup, an excessive current flows in the MEA containing a relatively large amount of water downstream of the oxidant, and the MEA catalyst layer rapidly deteriorates due to heat generation.

  As a countermeasure, if a humidifier is provided upstream of the oxidant, the electrolyte membrane will not be locally dried, so that the cell voltage is stabilized from the beginning of startup. In this case, the pressure loss generated when the oxidant passes through the humidifier causes an increase in power consumption of the oxidant supply device (for example, a compressor, a blower, etc.), and the power generation efficiency of the system is lowered. Become.

  Moreover, if the exhaust gas from the oxidant outlet of the fuel cell has a circulation structure that returns to the oxidant inlet using a pipe, the generated water can be recycled. However, there is a problem that piping for the circulation is necessary and the system becomes large.

  On the other hand, another problem is found when looking at the fuel side. That is, when pure hydrogen (100% hydrogen) is supplied to the fuel side and power generation is continued, nitrogen molecules in the oxidant gradually permeate the electrolyte membrane, and the hydrogen concentration in the fuel flow path decreases. If the hydrogen concentration is sufficiently high, for example, if it is at least 20% or more, a high cell voltage can be obtained without rapidly decreasing the cell voltage.

  However, if the nitrogen gas is mixed into the fuel side until the hydrogen concentration is less than 20%, the cell voltage rapidly decreases. This is because nitrogen, which is an inert gas, inhibits the diffusion of hydrogen and reduces the diffusion rate of hydrogen to the anode.

  In order to prevent mixing of nitrogen gas, an oxygen cylinder may be provided in the fuel cell system, and a gas containing pure oxygen or high-concentration oxygen gas as an oxidant gas may be supplied to the fuel cell. With this configuration, it is possible to prevent nitrogen from being mixed from the oxidant side to the fuel side, and to suppress a decrease in cell voltage.

  However, there is a problem that a large amount of oxygen cylinders cannot be installed or frequent cylinder replacement cannot be avoided. As a result, the size of the fuel cell power generation system becomes very large, becomes overweight, and becomes unusable.

  Since the installation of an oxygen cylinder is not practical, when the hydrogen concentration drops, a part of the fuel is discharged or purged, and new hydrogen is added to avoid a decrease in the hydrogen concentration in the fuel. The method to be taken is taken. However, even if such a method is adopted, since hydrogen is wasted, the efficiency of power generation is reduced.

  The technical issues described above are organized into two items.

  The first problem is to provide a cell structure and system configuration in which sufficient water can exist from the start-up and operating conditions.

  In the conventional cell, the case where air is used as the oxidant is the mainstream, and since the nitrogen content is high, the exhaust gas flow rate of the oxidant is large. For this reason, the amount of generated water taken up as water vapor increases, and unless the fuel cell is humidified in advance, the cell voltage drops rapidly and power generation cannot be performed. This is due to the drying of the electrolyte membrane.

  If the exhaust gas flow rate of the oxidizing agent is lowered, the amount of water released as exhaust gas can be reduced. However, the inventors have found that this requires a significant increase in oxidant utilization.

  For example, air at room temperature is supplied to the fuel cell so that the dew point of the exhaust gas is equal to the temperature of the fuel cell (assumed to be 72 ° C.) and the balance between the amount of generated water and the amount of discharged water focused only on the cathode. Estimated conditions. In order to achieve such an equilibrium state, the oxidant utilization must be approximately 100%. Considering that the oxidant utilization rate in the current separator is around 60%, it can be said that the non-humidifying operation is practically impossible. The contents of this problem will be described in detail again in the embodiment of FIG. 9 described later.

  The second problem is a system configuration and an operation method that can omit an operation of periodically replacing the anode gas with a fresh fuel (discharge or purge of a part of the fuel) when the hydrogen concentration on the anode side decreases. Is to provide.

  According to the conventional technology, not only fuel discharge causes fuel loss but also releases hydrogen to the atmosphere, so it is necessary to dilute to the explosion limit or to burn hydrogen using a catalyst etc. There wasn't. There is a problem in that a special device is required when discharging the fuel.

  Further, since hydrogen is supplied to the anode side, the hydrogen concentration does not decrease as long as hydrogen is supplied to the fuel cell as much as hydrogen is consumed. However, nitrogen permeates the electrolyte membrane from the cathode side of the fuel cell and gradually leaks to the anode side, and the hydrogen concentration on the anode side decreases. As a result, inert nitrogen remains on the anode side, and hydrogen cannot be pushed into the anode side.

  In particular, when the hydrogen concentration is 20% or less, the potential of the anode starts to increase, resulting in a decrease in cell output. This situation means that when the air is supplied to the cathode, the nitrogen concentration in the air is 79%, and therefore, considering the equilibrium theory, the nitrogen concentration in the anode reaches a maximum of 79%. To do. Therefore, as long as air is used as the oxidant, it is inevitable to purge the anode with fuel gas or purify hydrogen.

  In order to solve the two technical problems described above at the same time, the inventors have intensively studied to arrive at the present invention.

  A fuel cell system according to the present invention includes a separator through which fuel is circulated, a separator through which an oxidant is circulated, and a membrane-electrode assembly (MEA) having an electrolyte membrane sandwiched between an anode and a cathode. The MEA has a fuel cell having a cell sandwiched between the two separators, means for supplying a fuel gas containing hydrogen to the fuel cell, an oxygen concentrator for concentrating oxygen in the atmosphere, and the oxygen concentration And means for continuously supplying the oxidant that has passed through the vessel to the fuel cell, and means for continuously discharging the oxidant that has passed through the fuel cell.

  The first solution is to adopt a configuration in which the concentration of oxygen supplied to the fuel cell is higher than 21% and the concentration of oxygen discharged from the fuel cell is lower than 21%.

  A second solution is to use a device having a molecular separation function using a porous fiber or a porous membrane as the oxygen concentrator.

  The third solution is to adopt a configuration in which the concentration of oxygen contained in the oxidant that has passed through the oxygen concentrator is 40% or more.

  A fourth solution is to provide an exhaust gas treatment device that recovers hydrogen from exhaust gas after the fuel gas has passed through the fuel cell and discharges nitrogen gas.

  A fifth solution is to employ a configuration in which the oxidant is humidified by generated water generated inside the fuel cell.

  Sixth solution means that in the fuel cell, a part of the upstream of the flow path through which the fuel passes and a part of the downstream of the flow path through which the oxidant pass can exchange heat, or the fuel Heat exchange between a part of the downstream of the flow path through which the oxidant passes and a part of the upstream of the flow path through which the oxidizing agent passes.

  The seventh solving means is characterized in that a mixture containing cellulose and conductive powder is applied to the surface of the separator used in the fuel cell.

  The eighth solution is to use an oxidant such that the dew point calculated from the flow rate of exhaust gas discharged from the fuel cell and the discharge rate of moisture contained in the exhaust gas is higher than the cell temperature of the fuel cell. The driving method is to control the rate.

  Below, the structure of the cell of this invention and a fuel cell is demonstrated.

  First, a method for manufacturing an electrode and an MEA, and a configuration of a fuel cell using the MEA of the present invention will be described.

  As the catalyst for the anode 101 and the cathode 102 in FIG. 1, a powder in which platinum fine particles are supported on a carbonaceous powder conductive material was used. In the present invention, TEC10E50E manufactured by Tanaka Kikinzoku Co., Ltd. was selected. However, the present invention is not limited to this as long as the reaction of the fuel cell can proceed. The composition of platinum contained in the catalyst powder is 46.5% (weight percentage).

  As the electrolyte binder, a Napon solution manufactured by DuPont was used. The addition amount of the electrolyte binder was 40% with respect to the above catalyst weight.

  A paste using water as a solvent was prepared from these mixtures. This paste was mixed with a kneader so as to be sufficiently uniform. There is no particular limitation on the method, and any means can be selected as long as it is a method capable of preparing a homogeneous paste without destroying the material.

These pastes were applied to the surface of a PTFE sheet (polytetrafluoroethylene sheet) using a blade coater to prepare an electrode layer (wet state) having a predetermined thickness. The electrode was a 10 cm square (area 100 cm ² ). This was air dried and the solvent was evaporated.

  Next, an electrolyte membrane (manufactured by DuPont, Nafion 112, thickness of 50 μm) was placed on the electrode layer, and the laminate was inserted between two metal plates and subjected to hot pressing. As a result, the electrode layer on the PTFE sheet is transferred to the electrolyte membrane.

The weight increase of the electrolyte membrane was measured after the transfer. From the value, the amount of platinum (Pt) used per electrode unit area was calculated. Pt amount in the present embodiment, 0.5~0.9mg / cm ² at the anode, the cathode in was 0.1~0.8mg / cm ^2.

  On the surface of the anode and cathode catalyst layers, a carbonaceous porous sheet was used for the gas diffusion layer. A PTFE dispersion was added to the carbonaceous porous sheet to impart water repellency. The thickness of the carbonaceous porous sheet was 0.2 mm.

  50 MEAs were prepared by the process described above.

  FIG. 2 is a plan view showing the structure of the separator according to the embodiment of the present invention.

  2A shows a separator 210 (anode-side separator) in contact with the anode, and FIG. 2B shows a separator 220 (cathode-side separator) in contact with the cathode.

  The fuel is supplied from the fuel supply manifold 211 of the separator 210. The fuel first reaches the porous flow path surface 214 via the flow path delimited by the ribs (or also referred to as convex portions) 212. The porous flow path surface 214 is a porous carbon sheet, and is a conductive material having a thickness of 0.5 mm and a porosity of 70%. Any material can be selected as long as it has corrosion resistance. In addition, as for the thickness and the porosity, an optimum dimension or the like can be selected according to the current flowing through the cell and the gas flow rate. The porous flow path surface 214 is housed in a recess 213 provided in the center of the separator 210 and is in close contact with the bottom surface of the recess 213.

  The rib 212 is for preventing the gaskets 108 and 109 in FIG. 1 from sagging toward the separator and blocking the space through which the gas flows. The interval between the ribs 212 is desirably set in the range of 0.5 to 5 mm.

  The porous flow path surface 214 is in contact with the anode 101 of FIG. 1 and functions to uniformly supply hydrogen consumed by the anode 101 to the entire electrode.

  The fuel is completely oxidized in the porous flow path surface 214, and the periodic discharge process of the fuel can be omitted, so the manifold for discharging the fuel is omitted.

  On the other hand, the separator 210 is formed with a manifold 215 that supplies an oxidizing agent, a manifold 216 that discharges the oxidizing agent, a manifold 217 that supplies cooling water, and a manifold 218 that discharges cooling water.

  The anode side of the separator 210 and the cathode side of the separator 220 are opposed to each other so as to sandwich the MEA.

  In this embodiment, the separators 210 and 220 are shown as separate objects, but the cathode side of the separator 220 is formed on the surface opposite to the anode side of the separator 210, and the functions of the separators 210 and 220 are given to one separator. May be.

  In the separator 220, the oxidant is supplied from the oxidant supply manifold 215 and reaches the porous flow path surface 224 via the flow path partitioned by the ribs 225. The porous flow path surface 224 is housed in a recess 223 formed in the separator, and is in close contact with the bottom surface of the recess 223. The porous flow path surface 224 is in contact with the cathode 102 in FIG. 1 and functions to supply oxygen to the cathode 102. The oxidant gas that has not been consumed is discharged out of the cell from the oxidant discharge manifold 216 through a flow path partitioned by ribs 221.

  The separator 220 is provided with a fuel supply manifold 211, a cooling water supply manifold 217, and a cooling water discharge manifold 218 so as to correspond to FIG. The cooling water channel can be formed in any shape on the back surface of FIG. 2 (a) or FIG. 2 (b).

  The gaskets 108 and 109 shown in FIG. 1 have the same outer dimensions as the separators 210 and 220 shown in FIG. Also, the recesses 213 and 223, the recesses in which the ribs 212, 225, and 221 are formed (not numbered), the manifolds 211, 215, 216, and 218 are cut out, and these portions are the openings. It has become a shape. This was inserted between the separator and the electrolyte membrane as shown in the cross-sectional view of FIG.

  The separators 210 and 220 use the porous flow path plates 214 and 224, but the flow paths may be formed from the fuel supply manifold 211 and the manifold 215 that supplies the oxidizing agent toward the center of the separators 210 and 220. . It is desirable that the shape of the flow path is uneven, the groove width is 0.5 to 5 mm, and the depth is 0.3 to 2 mm. Moreover, 0.5-2 mm is suitable for the width | variety of the convex part (rib) formed in the both sides of a groove | channel. The groove may be linear, meandering or bent. In the cathode separator 220, a flow path can be formed so as to connect the ribs 221 and 225.

  The fuel supplied from the fuel supply manifold 211 is oxidized in the process of flowing inside the porous flow path surface 214, and the composition of water vapor is increased. The water vapor is supplied from the oxidant side separator 220 facing the separator 210 via the MEA. The oxidant is supplied from the oxidant supply manifold 215 to the inside of the porous flow path surface 224, and the amount of generated water increases downstream of the oxidant. This downstream side faces the upstream side of the fuel on the fuel side separator. Therefore, water moves from the oxidant side to the fuel side. Further, the fuel downstream of the porous flow path surface 214 (at a diagonal position as viewed from the manifold 211) exchanges heat with the low temperature oxidant upstream via the MEA. Further, the fuel is cooled by the low-temperature oxidant flowing in the vicinity of the oxidant supply manifold 215, and the water vapor in the fuel gas is condensed into liquid water. This water diffuses the MEA and moves upstream of the oxidant.

  On the other hand, the oxidizing agent supplied from the oxidizing agent supply manifold 215 is consumed in the process of flowing inside the porous flow path surface 224. The remaining oxidant is discharged from the manifold 216 along with water vapor evaporated from the MEA in contact with the porous flow path surface 224. The water vapor is supplied from the porous flow path surface 214 of the fuel side separator 210 facing the separator 220. In particular, heat and water are exchanged via the fuel and MEA flowing inside the porous flow path surface 214, and more moisture is placed upstream of the fuel at the downstream of the oxidant (the porous flow path surface 224 close to the manifold 216). Can be granted.

  As described above, the water vapor generated inside the fuel cell is cooled by the supplied oxidant or fuel and stays inside the fuel cell. Further, moisture is supplied from the downstream of the fuel upstream of the oxidant and from the downstream of the oxidant upstream of the fuel, and the generated water is recycled as a whole. Thus, the wet state of the MEA is maintained without humidification, and the power generation can be continued while maintaining the cell voltage.

  In the above configuration, heat and water are transferred between the fuel flowing in the fuel flow path of the separator 210 (anode separator) of the adjacent unit cells and the oxidant flowing in the oxidant flow path of the separator 220 (cathode side separator). In other words, it can be exchanged.

  The water vapor that flows out of the fuel cell together with the remaining oxidant without being condensed by the heat exchange (cooling) described above is condensed and recovered by a condenser installed on the downstream side (outside of the fuel cell). Alternatively, the fuel cell may be recirculated into the fuel cell. The refluxed water may flow into the fuel supply manifold 211 or may flow into the oxidant supply manifold 215. By combining this with water recycling inside the battery, it becomes possible to circulate the water with higher efficiency. As a result, even if the humidifier is omitted, efficient power generation is possible.

  A 1 kW class PEFC cell stack was manufactured using the above separator and MEA. FIG. 3 shows the cross-sectional structure.

  The MEA 302 manufactured by the above-described method was sandwiched between two graphite separators 304 (single cell separators) per MEA, and the single cell 301 was assembled.

  The anode side of the graphite separator 304 has the structure shown in FIG. 2A, and the cathode side of the graphite separator 304 has the structure shown in FIG.

  When the MEA 302 is sandwiched between two graphite separators 304, the gasket 305, the electrolyte membrane portion of the MEA 302, and the gasket 305 are stacked in order and pressed to prevent leakage of fuel and oxidant. .

  Both the anode and the cathode are configured to include a catalyst layer and a gas diffusion layer. The catalyst layer of this example may be applied to the electrolyte membrane, or may be substituted by applying heat compression to the electrolyte membrane after being applied to the gas diffusion layer.

  A plurality of single cells 301 are connected in series, current collector plates 313 and 314 are installed at both ends, and further, tightened with an end plate 309 from the outside via an insulating plate 307. If the end plate is an insulating material, the insulating plate 307 can be omitted. Bolts 316, springs 317, and nuts 318 are used as fastening parts. The current collecting plates 313 and 314 can be made of a conductive material such as a metal plate or a graphite plate.

  In the separator having the cooling water flow path, the cooling water flows with the flow path surfaces facing each other. This is referred to as a cooling cell 308. One cooling cell 308 is provided for every two single cells 301. In FIG. 3, a cooling water flow path is formed in the terminal separator in contact with the current collector plates 313 and 314. Therefore, a graphite plate 303 (a flat plate component in contact with the cooling water flow path) was inserted so that the cooling water flow path and the current collecting plate were in direct contact and the current collecting plate was not corroded.

  The fuel is supplied from a supply connector 310 provided on the left end plate 309, passes through each single cell 301, and is oxidized at the surface of the MEA anode. In this embodiment, since the separator of FIG. 2 is used, the fuel discharge connector 322 is unnecessary. When the separator of FIG. 6 to be described later is used, the fuel exhaust gas that has passed through the single cell 301 needs to be discharged from the discharge connector 322 provided on the opposite end plate 309. Therefore, the discharge connector 322 is also used in this embodiment. I left it. In this example, pure hydrogen was used as the fuel. However, if the concentration of hydrogen is higher than 20% and the diluent gas is an inert nitrogen gas or the like, a low concentration hydrogen gas can be used.

  Similarly, the oxidant is supplied from the supply-side connector 311 provided on the left end plate 309 shown in FIG. 3 and discharged from the discharge-side connector 323 of the opposite end plate 309. As the oxidant, a gas having a higher oxygen concentration (21%) in the air is used. If the oxygen in the oxidizer is set to a high concentration of 30% or more, the hydrogen concentration of the fuel does not become 30% or less. For this reason, since the fall of a cell voltage can be suppressed, it is still more desirable.

  The cooling water is supplied from a supply-side connector 312 provided on the end plate 309 and flows to the cooling cell 308 or a cooling cell adjacent to the current collector plate. After passing through the cooling cell and taking heat away, the cooling water is discharged from the discharge side connector 324 of the opposite end plate 309. The cooling water discharged from here is removed by cold water in a heat exchanger (not shown) and supplied again to the pipe connector 312. A pump was used to circulate the cooling water.

With such a component structure, a cell stack in which 50 single cells 301 were stacked was manufactured. In FIG. 3, when components for 50 cells are described, the components are too fine, and the number of cells is displayed to avoid this. In the cell stack (solid polymer fuel cell) of this example, pure hydrogen and air were passed through separate external humidifiers and then humidified to the fuel supply side connector 310 and the oxidant supply side connector 311. Fuel and oxidant were supplied and initial aging operation was performed. The dew point of the humidified gas was 70 ° C. The current density was 0.2 A / cm ² and power generation was performed for 3 hours. After confirming that the cell voltage was stable, the initial aging was terminated. In this way, the MEA was previously brought into a state capable of generating power, and then incorporated into the system (FIGS. 4 and 6 described later). The cell stack after the initial aging is set to S1. In addition, initial aging is not required after the system is incorporated, and the water once held in the MEA of the cell stack is prevented from being dried by recycling the water generated by power generation.

  The cell stack S1 can draw power lines 319 from current collecting terminals 313 and 314 and supply power to an external load 321 via a converter 320 formed of a DC-DC converter or a DC-AC converter.

  FIG. 4 is a schematic configuration diagram showing a fuel cell power generation system according to an embodiment of the present invention.

  In the figure, a cell stack 430 incorporates the cell stack S1 described above.

  Fuel is supplied to the cell stack 430 from the fuel supply means 431 via the fuel supply amount regulator 432. The fuel supply means 431 (fuel storage facility) may be any device such as a hydrogen cylinder, a liquefied hydrogen storage container, or a hydrogen storage / supply device using a hydrogen storage alloy. The fuel supply amount regulator 432 is a mass flow meter that controls the hydrogen flow rate calculated from the amount of electricity output from the cell stack 430 in addition to the pressure adjustment valve that supplies fuel so that the anode gas pressure of the cell stack 430 is constant. Or a flow rate controller such as The flow rate is controlled from the outside by a microcomputer having a calculation function.

  The oxidant takes in air from an oxidant supply means 433 (air supply means) for supplying air, and is supplied to the cell stack 430 via the oxygen concentrator 434. The outside air taken into the oxygen concentrator 434 is supplied from the air supply means 433. The temperature of the outside air is usually 0 to 40 ° C., and outside air having a temperature higher than 40 ° C. may be taken in. Further, even if the outside air temperature becomes a low temperature below freezing point, if the oxygen concentrator 434 does not freeze water, low temperature freezing air may be supplied. Desirably, heating to 0 ° C. or higher and then supplying to the oxygen concentrator 434 provides an advantage of avoiding poor distribution due to freezing.

  The relative humidity of the atmosphere supplied to the oxygen concentrator 434 is usually 40 to 80%. However, the relative humidity may deviate from this range depending on the season and geographical environment. In some cases, it is assumed that air at a temperature below freezing point is supplied. However, it is sometimes necessary to raise the temperature to a temperature at which the oxygen concentrator can be activated. In this manner, the oxygen concentrator 434 can supply an oxidant having a higher oxygen concentration than air, and can reduce the flow rate of the oxidant. As the air supply means 433, a general blower such as a blower, a compressor, or a fan can be used. The oxygen concentrator 434 is a device having a molecular sieve using a difference in molecular size and molecular motion speed. For the molecular sieve, a porous plate or a hollow fiber is used.

  In addition, when an oxidant having a predetermined oxygen concentration is filled in a container in advance and the oxidant can be supplied from the container, the oxygen concentrator 434 is omitted and only the air supply means 433 is used. An oxidant may be supplied to the fuel cell 430. Even if it does in this way, it is the same as a result that the function of the oxygen concentrator 434 was implemented.

  Here, if the oxygen concentration is higher than 21%, the dew point of the oxidant exhaust gas discharged from the cell stack 430 can be made higher than the cell temperature of the cell stack. Desirably, the oxygen concentration is 30% or more, and more desirably 40% or more. This is preferable because the nitrogen concentration coexisting with oxygen is 70% or less, and nitrogen permeates through the electrolyte membrane of the cell stack 430, so that the hydrogen concentration on the anode side is not diluted below 30%. .

  If the oxygen concentration is 30% or more, more preferably 40% or more, the oxidant utilization rate of the cell stack 430 can be in the range of 60 to 80%, and the operation near the limit of 100% oxidant utilization rate is possible. It can be avoided. Under such conditions, the dew point of the cathode exhaust gas can be made higher than the cell temperature, the generated water can be recycled independently in the cell, and the humidifier can be omitted.

  If the oxidant supply system of the present invention is adopted, an oxidant containing a high concentration of oxygen can be continuously supplied to the fuel cell, avoiding the addition of an oxygen cylinder, and nitrogen as an inert gas. It is possible to prevent the hydrogen concentration from being mixed into the fuel side and to avoid a decrease in output accompanying this.

  In the system of FIG. 4, the oxidant is discharged from the fuel cell 430 to the outside, but the exhaust gas of the oxidant is circulated to a known device such as a heat exchanger or a condenser to recover water and heat. good.

  Returning to FIG. 2, the influence of the oxygen concentration of the oxidant on the recycling of the generated water inside the cell will be described. The generated water is formed on the surface of the cathode, and gradually increases from the upstream of the cathode (the electrode surface in contact with the porous flow path plate 224 at a position close to the manifold 215), and downstream (to the manifold 216) by the flow of the oxidant. It is made to flow to the electrode surface in contact with the porous flow path plate 224 at a close position. Therefore, the amount of generated water downstream is high, and the vapor pressure in the gas is also high.

  On the other hand, the surface of the anode is in a dry state at a position facing the downstream side of the cathode (an electrode surface in contact with the porous flow path plate 214 at a position close to the manifold 211), and the generated water is taken in from the cathode. The generated water moves downward in FIG. 2A along the fuel flow. As a result, the generated water tends to increase in the lower part of FIG.

  Since the amount of generated water increases below the anode, water is taken up again upstream of the oxidant in contact with the generated water, and the oxidant is humidified.

  Here, when the oxygen concentration in the oxidizing agent is higher than 21%, the dew point at the outlet of the oxidizing agent tends to be higher than the cell temperature. That is, the dew point of the oxidant exhaust gas increases from the time of startup. Therefore, since the power is generated in a state where water is constantly condensed, the cell voltage does not become unstable from the time of startup. This phenomenon will be described in detail in the description of FIG.

  In this way, the generated water moves from the downstream of the oxidant to the upstream of the fuel and is taken again from the downstream of the fuel to the upstream of the oxidant, thereby further increasing the oxygen concentration to more than 21%. Water recycling is realized. As a result, the humidifier can be omitted.

  According to the prior art, the generated water cannot be recycled in principle because the oxidant utilization rate cannot be increased and the oxidant flow rate is large (the oxygen concentration is as low as 21%). In the present invention, by increasing the oxygen concentration, the dew point of the oxidant on the downstream side becomes higher than the cell temperature, so that the water is in an excess state and the water can be easily moved upstream of the anode. Very different from technology.

  FIG. 5A shows a separator 510 (fuel side separator) in contact with the anode, and FIG. 5B shows a separator 520 (oxidant side separator) in contact with the cathode.

  The fuel is supplied from the fuel supply manifold 511 of the separator 510. The fuel first reaches the porous flow path surface 514 through the flow path partitioned by the ribs (convex portions) 512. The porous flow path surface 514 is a porous carbon sheet, and is a conductive material having a thickness of 0.5 mm and a porosity of 70%. Any material can be selected as long as it has corrosion resistance. In addition, as for the thickness and the porosity, an optimum dimension and the like can be selected according to the current flowing through the cell and the gas flow velocity. The porous flow path surface 514 is accommodated in a recess 513 provided in the center of the separator 510 and is in close contact with the bottom surface.

  The ribs 512 are provided so that the gaskets 108 and 109 in FIG. 1 sag toward the separator and do not block the space through which the gas flows. The interval between the ribs 512 is preferably set in the range of 0.5 to 5 mm.

  The porous flow path surface 514 is in contact with the anode 101 in FIG. 1 and functions to uniformly supply hydrogen consumed by the anode 101 to the entire electrode.

  The fuel is almost entirely oxidized on the flow path surface 514, and a part of the remaining gas is discharged from the discharge manifold 519. Most of the residual gas is occupied by water vapor or water permeated from the cathode to the anode upstream of the fuel. These moisture moves with the hydrogen ions from the anode to the cathode and is used for humidifying the oxidant.

  The separator 510 is formed with a manifold 515 that supplies an oxidizing agent, a manifold 516 that discharges the oxidizing agent, a manifold 517 that supplies cooling water, and a manifold 518 that discharges cooling water.

  The anode side of the separator 510 is opposed to the cathode side of the oxidant side separator 520 through the MEA. The separator 520 is a separator having a cathode channel, and may be formed on the back surface of the separator 510 or may be manufactured as an independent component.

  In the separator 520, the oxidant is supplied from the oxidant supply manifold 515 and introduced into the flow path surface 524 through the rib 525. The channel surface 524 is housed in a recess 523 formed in the separator and is in close contact with the bottom surface. The flow path surface 524 is in contact with the cathode 102 in FIG. 1 and functions to supply oxygen to the cathode 102. The oxidant gas that has not been consumed is discharged out of the cell through the oxidant discharge manifold 516 via the rib 521.

  The separator 520 is provided with a fuel supply manifold 511, a fuel discharge manifold 519, a cooling water supply manifold 517, and a cooling water discharge manifold 518 so as to correspond to FIG.

  The cooling water channel can be formed in an arbitrary shape on the back surface of FIG. 5 (a) or FIG. 5 (b).

  The cell stack shown in FIG. 3 was manufactured using the separator of FIG. This cell stack is called a cell stack S2. In addition, the same initial aging process as S1 was performed also about this cell stack.

  FIG. 6 is a schematic configuration diagram showing a fuel cell power generation system according to another embodiment of the present invention.

  The cell stack 630 in this figure is the cell stack S2.

  Fuel is supplied to the cell stack 630 from the fuel supply means 631 via the fuel supply amount regulator 632. The fuel supply means 631 (fuel storage facility) may be any device such as a hydrogen cylinder, a liquefied hydrogen storage container, or a hydrogen storage / supply device using a hydrogen storage alloy. The fuel supply amount regulator 632 is a mass flow meter that controls the hydrogen flow rate calculated from the amount of electricity flowing to the cell stack 630 in addition to the pressure adjustment valve that supplies fuel so that the anode gas pressure of the cell stack 630 is constant. Such a flow rate controller may be used. The flow rate is controlled from the outside by a microcomputer having a calculation function.

  The oxidant takes in air from the air supply means 633 for supplying air, and the oxidant having an oxygen concentration higher than that of air is supplied to the cell stack 630 via the oxygen concentrator 634. As the air supply means 633, general blower equipment such as a blower, a compressor, and a fan can be used. The oxygen concentrator 634 is a device having a molecular sieve using a difference in molecular size and molecular motion speed. For the molecular sieve, a porous plate or a hollow fiber is used.

  Here, the fuel exhaust gas is processed by a nitrogen separator 635 to separate and discharge nitrogen, and the on-off valve 636 is operated to release only nitrogen to the outside. The nitrogen separator 635 may be provided with a bypass that returns a part of the hydrogen to the fuel supply amount regulator 631. That is, a flow path may be provided for recirculating fuel exhaust gas from which nitrogen is separated and the hydrogen concentration is increased. The nitrogen separator 635 can be a nitrogen purifier using hollow fibers.

  Thereby, the hydrogen remaining in the exhaust gas can be recovered and used.

  In addition, although fuel exhaust gas was demonstrated here, it is the same also when exhaust gas is oxidizing agent exhaust gas. Similarly, when the oxidant exhaust gas is mixed with the fuel exhaust gas and discharged, hydrogen can be similarly separated and recovered using the nitrogen separator 635. That is, the definition of exhaust gas includes fuel exhaust gas and oxidant exhaust gas.

  Here, the result of the operation test of the system to which the cell stack S1 is applied in the fuel cell power generation system of the present invention shown in FIG. 4 will be described.

Hydrogen (hydrogen concentration 100%) was used as the fuel. As the oxidizing agent, air was passed through the air concentrator 434, and a gas having an oxygen concentration of 40% was supplied to the fuel cell 430. The current density was 0.3 A / cm ² , the fuel utilization rate was 100%, the oxidant utilization rate was 75%, and the cell temperature was controlled at 70 to 75 ° C. The cell voltage was a high value of 750 mV or higher, and high-efficiency power generation was possible.

  Here, the oxygen concentrator 434 was removed, and the configuration was changed so that air was directly supplied to the fuel cell 430, and a comparative test was performed. As a result, it was found that the cell voltage suddenly dropped to 0.3 V or less from the beginning of the start-up, and power generation was not practically possible. From this, it became clear that the system having the oxygen concentrator 434 is excellent.

Similarly, an operation test of a system to which the cell stack S2 was applied in the fuel cell power generation system of the present invention shown in FIG. 6 was performed. Hydrogen (hydrogen concentration 100%) was used as the fuel. As the oxidant, air was passed through the oxygen concentrator 634, and a gas having an oxygen concentration of 60% was supplied to the fuel cell 630. The current density was 0.3 A / cm ² , the fuel utilization rate was 100%, the oxidant utilization rate was 80%, and the cell temperature was controlled at 70 to 75 ° C. The cell voltage was a high value of 740 mV or higher, and high-efficiency power generation could be realized despite the high oxidant utilization rate.

  Finally, an embodiment in which the separator having the porous flow path plate shown in FIGS. 1 and 2 is changed to a separator having a flow path will be described.

  FIG. 7 is a cross-sectional view showing the cell structure of this example.

  First, the fuel flow path 705 formed in the fuel-side separator 704 has a groove depth of 0.5 mm and a groove width of 1 mm, and the width of a convex portion 711 (hereinafter referred to as a rib or rib portion) in contact with the anode 701 is 1 mm. did. On the other hand, the oxidant channel 707 formed in the oxidant side separator 706 has a groove depth of 0.8 mm and a groove width of 1 mm, and the width of the convex portion 712 (rib) in contact with the cathode 702 is 1 mm.

Next, a mixture containing cellulose acetate, acetylene black and 1-methyl-2-pyrrolidone was applied to the grooves 705 and ribs 711 of the fuel side separator 704 and the grooves 707 and ribs 712 of the oxidant side separator 706. The amount of 1-methyl-2-pyrrolidone added may be more than the amount necessary to dissolve the total amount of cellulose acetate, diluted to an appropriate concentration to control the coating film thickness. Can be used. The mixture is a mixture of cellulose acetate and acetylene black at a weight mixing ratio of 80:20, mixed in a solvent of 1-methyl-2-pyrrolidone, and sufficiently kneaded with a kneader (generally called slurry). . This slurry was applied to the inner walls and ribs of the separator grooves in the form of an ultrathin film by a spray method, a coater method, a dip method or the like. The concentration of cellulose acetate was adjusted so that the coating amount was 5 to 7 mg / cm ² as the weight of cellulose acetate per unit area.

  The application amount is not limited to the above-mentioned numerical value, and the application amount may be increased or decreased as long as the voltage loss due to the contact resistance between the rib and the electrode is relatively smaller than the cell voltage. The contact resistance can be adjusted by the mixing ratio of a conductive agent such as acetylene black.

Cellulose acetate is one of polymer materials in which cyclic carbon chains (glucose) are connected in a straight chain. In this method, an alcohol group (—CH ₂ OH) is introduced into a cyclic carbon chain and then reacted with acetic acid (CH ₃ COOH) to form an ester bond (—CH ₂ OCOCH ₃ ). The oxygen atom of this ester bond shows affinity with water, and since the whole cellulose molecule has hydrophobicity, it provides a surface state specific to water. That is, it forms both hydrophilic and hydrophobic surfaces with respect to water.

When the above alcohol groups are reacted with other carboxylic acids (CH ₃ CH ₂ COOH, organic carboxylic acids such as C ₆ H ₅ COOH, and substituted products such as CF ₃ COOH), cellulose other than cellulose acetate is synthesized. can do. In the present invention, any cellulose can be used as long as it is chemically and thermally stable in the use environment of the fuel cell.

  Further, by mixing acetylene black with cellulose acetate, electrical conductivity can be imparted to the coating film, and the contact resistance between the rib and the electrode can be prevented from increasing. Cellulose acetate itself is electrically insulating.

  Here, the conductive material to be added to cellulose acetate is not limited to acetylene black, and graphite fine powder, amorphous carbon fine powder, and nanotubes or carbon fibers cut into short fibers can be substituted. May be. Further, a semiconductor material made of a metal oxide powder such as titanium or silicon can also be used.

  In this example, a coating film of a mixture of cellulose acetate and acetylene black was formed on both the fuel channel and the oxidant channel. You may form a coating film only in any one flow path.

  The arrangement of the manifold of the separator is as shown in FIG.

  In the present embodiment, since the separator with flow path of FIG. 7 is used, the porous flow path plates 514 and 524 of FIG. 5 are deleted. The manifolds at the diagonal positions were connected with each other by a flow path pattern having a serpentine structure.

  The fuel-side separator in FIG. 5A will be further described. After the five flow paths from the fuel supply manifold 511 advance in the downward direction in the drawing, they are bent to the left and further turned upward. Next, after bending to the left, it proceeds in parallel downward and communicates with the fuel discharge manifold 519.

  The flow path pattern of the oxidant side separator in FIG. 5B also has a serpentine structure. A cell stack shown in FIG. 3 was manufactured using the separator having such a structure. This cell stack is called S3. In addition, the same initial aging process as S1 was performed also about this cell stack.

  The cell stack S3 was incorporated into the fuel cell power generation system shown in FIG. 6, and a power generation test was performed under the same conditions as the cell stack S2 described above. Hydrogen (hydrogen concentration 100%) was used as the fuel. As the oxidant, air was passed through the air concentrator 634, and a gas whose oxygen concentration was increased to 60% was supplied to the fuel cell 630.

The current density was 0.3 A / cm ² , the fuel utilization rate was 100%, the oxidant utilization rate was 80%, and the cell temperature was controlled at 70 to 75 ° C. The cell voltage was a high value of 745 mV or higher, and high-efficiency power generation could be realized despite the fact that the oxidant utilization rate was high. The reason why the voltage of S3 is higher than that of S2 is presumed to be that the surface treatment with cellulose acetate further increased the amount of water recycled. That is, it is considered that the action of cellulose acetate improves the drainage of the flow path and facilitates the recycling of water.

  FIG. 8 is a graph showing the relationship between the hydrogen concentration and the cell voltage in the fuel cell of the example according to the present invention. The horizontal axis represents the hydrogen concentration, and the vertical axis represents the cell voltage. The oxygen concentration is taken as a parameter. The cell average temperature was 72 ° C. and the current density was 0.5 A / cm 2.

  From this figure, it can be seen that the cell voltage increases as the oxygen concentration increases. It can also be seen that when the oxygen concentration is 21% (the oxygen concentration in the atmosphere), the cell voltage is significantly reduced when the hydrogen concentration is reduced to 30%. As a result, it can be seen that, under the condition where the oxygen concentration is 50% or more, even if the hydrogen concentration is reduced to 30%, the cell voltage does not decrease and power generation is possible. Furthermore, from this figure, it can be estimated that under the condition where the oxygen concentration is 50% or more, even if the hydrogen concentration becomes 25%, the cell voltage does not decrease and power generation is possible.

  As the current density increases, the hydrogen concentration at which the cell voltage starts to drop at an oxygen concentration of 21% tends to shift slightly from 50% to a higher concentration side. In such a case, if the concentration capability of the oxygen concentrator 434 in FIG. 4 or the oxygen concentrator 634 in FIG. 6 is increased so that the oxygen concentration becomes high, a high voltage can be maintained.

Moreover, since the amount of hydrogen crossover of MEA (membrane-electrode assembly) used in this example is extremely small and 1 mA / cm ² (current conversion) or less, the problem of crossover does not occur. As a result, the phenomenon of voltage instability due to hydrogen crossover was not observed.

  From the above, it can be seen that the cell voltage can be increased by increasing the oxygen concentration of the oxidant using the oxygen concentrator.

  FIG. 9 is a graph showing the relationship between the oxidant utilization rate and the dew point of the exhaust gas in the fuel cell of the example according to the present invention. The horizontal axis represents the oxidant utilization rate, and the vertical axis represents the dew point of the exhaust gas. The oxygen concentration is taken as a parameter.

  From this figure, it can be seen that the higher the oxygen concentration, the higher the dew point of the exhaust gas. Thereby, the dew point of exhaust gas can be made higher than the operating temperature of the fuel cell (for example, 70 ° C. or higher), and the water inside the battery can be recycled. That is, the discharge amount of water or water vapor can be reduced. Further, an oxidizer humidifier can be dispensed with.

  As described above, the dew point of the exhaust gas can be increased by increasing the oxygen concentration of the oxidant using the oxygen concentrator.

  101: anode, 102: cathode, 103: electrolyte membrane, 104: fuel (anode) side separator, 105: porous channel plate, 106: oxidant (cathode) side separator, 107: porous channel plate, 108: Anode side gasket, 109: cathode side gasket, 210: fuel (anode) side separator, 211: fuel supply manifold, 212: rib (convex part), 213: concave part, 214: porous flow path plate, 215: oxidant supply Manifold, 216: Oxidant discharge manifold, 217: Coolant supply manifold, 218: Coolant discharge manifold, 220: Oxidant (cathode) side separator, 221: Rib (convex part), 223: Concave part, 224: Porous flow Road plate, 225: rib (convex portion), 301: single cell, 302: MEA, 303: graphite plate, 304: Lead separator, 305: Gasket, 307: Insulating plate, 308: Cooling cell, 309: End plate, 310: Connector for fuel piping, 311: Connector for oxidant piping, 312: Connector for cooling water piping, 313: Current collector 314: current collector plate, 316: bolt, 317: spring, 318: nut, 319: external power line, 320: converter, 321: external load, 322: connector for fuel piping, 323: connector for oxidant piping, 324: Connector for cooling water piping, 430: Cell stack, 431: Fuel supply means, 432: Fuel flow rate regulator, 433: Oxidant supply means, 434: Oxygen concentrator, 510: Fuel (anode) side separator, 511: Fuel supply manifold, 512: rib, 513: recess, 514: porous flow path plate, 515: oxidant supply manifold, 516: acid Agent discharge manifold, 517: Coolant supply manifold, 518: Coolant discharge manifold, 519: Oxidant discharge manifold, 520: Oxidant (cathode) side separator, 521: Rib, 523: Recess, 524: Porous flow path plate 525: Rib, 630: Cell stack, 631: Fuel supply means, 632: Fuel flow controller, 633: Oxidant supply means, 634: Oxygen concentrator, 635: Nitrogen separator, 634: On-off valve, 701: Anode 702: cathode, 703: electrolyte membrane, 704: fuel side separator, 705: fuel channel, 706: oxidant side separator, 707: oxidant channel, 708: anode side gasket, 709: cathode side gasket, 711: Convex part (rib), 712: Convex part (rib).

Claims (8)

  A membrane-electrode assembly having a configuration in which an electrolyte membrane is sandwiched between an anode and a cathode; an anode-side separator having a fuel channel; and a cathode-side separator having an oxidant channel, and the membrane-electrode junction A fuel cell including a unit cell having a structure in which a body is sandwiched between the anode separator and the cathode separator, a fuel supply path for supplying fuel to the fuel cell, and an oxidant containing oxygen in the fuel cell And an oxygen concentrator for increasing the oxygen concentration, wherein the dew point of the oxidant exhaust gas discharged from the fuel cell is set to be equal to or higher than the operating temperature of the fuel cell. Fuel cell power generation system.   The fuel cell power generation system according to claim 1, wherein the oxygen concentrator includes a porous fiber or a porous membrane having a molecular sieving function.   3. The fuel cell power generation system according to claim 1, wherein the concentration of oxygen contained in the oxidant that has passed through the oxygen concentrator is 40% or more. 4.   The fuel cell power generation system according to any one of claims 1 to 3, further comprising a nitrogen separator for separating nitrogen from the exhaust gas.   5. The fuel cell power generation system according to claim 4, further comprising a flow path for recirculating the exhaust gas separated from nitrogen and having a high hydrogen concentration.   Heat exchange is possible between the fuel flowing through the fuel flow path of the anode-side separator of the unit cells adjacent to each other and the oxidant flowing through the oxidant flow path of the cathode-side separator. The fuel cell power generation system according to any one of claims 1 to 5.   The fuel cell power generation system according to any one of claims 1 to 6, wherein a mixture containing cellulose and conductive powder is applied to the anode separator or the cathode separator.   A membrane-electrode assembly having a configuration in which an electrolyte membrane is sandwiched between an anode and a cathode; an anode-side separator having a fuel channel; and a cathode-side separator having an oxidant channel, and the membrane-electrode junction A fuel cell including a unit cell having a structure in which a body is sandwiched between the anode separator and the cathode separator, a fuel supply path for supplying fuel to the fuel cell, and an oxidant containing oxygen in the fuel cell A method of operating a fuel cell power generation system including an oxidant supply path for supplying oxygen and an oxygen concentrator for increasing the concentration of oxygen, the flow rate of exhaust gas discharged from the fuel cell, and the exhaust gas Calculating the dew point of the exhaust gas from the amount of water contained in the gas, and supplying the dew point of the exhaust gas to the fuel cell in order to make the dew point of the exhaust gas higher than the operating temperature of the fuel cell The method of operating a fuel cell power generation system which comprises a step of controlling the utilization rate of the serial oxidizing agent.

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