JP2014049215A - Polymer electrolyte fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer electrolyte fuel cell system which allows for cost reduction by reducing the number of components, and for enhancement of output density by making the system compact.SOLUTION: A polymer electrolyte fuel cell system includes a fuel cell stack laminating a plurality of unit cells generating power by using a liquid organic compound as fuel. At least some of a plurality of membrane electrode assemblies and separators constituting a fuel cell stack are provided with a through hole 107 interconnecting the laminated membrane electrode assembly and separator. A flow path and a through hole formed in the separator are separated by a sealant, and a space formed by the through hole 107 serves as a tank for storing liquid fuel or water.

Description

  The present invention relates to a polymer electrolyte fuel cell system using a liquid organic compound as a fuel.

With recent advances in electronic technology, portable electronic devices such as telephones, notebook computers, audio-visual devices, camcorders, and personal information terminal devices are rapidly spreading.
Conventionally, such portable electronic devices are systems driven by secondary batteries, and the emergence of new high energy density secondary batteries from lead-acid batteries to Ni / Cd batteries, Ni / hydrogen batteries, and even Li-ion secondary batteries. As a result, mobile devices have become smaller and lighter. On the other hand, higher functionality of portable devices has been attempted. In order to further increase the energy density of various secondary batteries, especially Li-ion secondary batteries, the development of battery active materials and the development of high-capacity battery structures have been promoted, realizing a power source that lasts longer in one charge. Efforts have been made.

  However, secondary batteries always require a charging operation after using a certain amount of power, and charging equipment and a relatively long charging time are required. There are many problems left to drive. In the future, portable devices are moving toward a direction that requires a higher power density and higher energy density power source, that is, a power source with a longer continuous drive time, in response to the increasing amount of information and its higher speed and higher functionality . Therefore, there is an increasing need for a small generator that does not require charging, that is, a small generator that can be easily refueled.

  From such a background, a fuel cell power supply can be considered as one that can meet the above-mentioned demand. A fuel cell is a generator that consists of at least a solid or liquid electrolyte and two electrodes that induce a desired electrochemical reaction, namely an anode and a cathode, and converts the chemical energy of the fuel directly into electrical energy with high efficiency. is there. As the fuel, pure hydrogen, hydrogen chemically converted from fossil fuel or water, methanol which is a liquid or solution in a normal environment, alkali hydride, hydrazine or dimethyl ether which is a pressurized liquefied gas are used. Air or oxygen gas is used as the oxidant gas. The fuel is electrochemically oxidized at the anode and oxygen is reduced at the cathode, resulting in a difference in electrical potential between the electrodes. At this time, if a load is applied between the two electrodes as an external circuit, ion migration occurs in the electrolyte, and electric energy is extracted from the external load. For this reason, various types of fuel cells are highly expected to be used as large-scale power generation systems for thermal power equipment, compact distributed cogeneration systems, and electric vehicle power supplies for engine generators.

  Among such fuel cells, a polymer electrolyte fuel cell is a membrane / electrode assembly (MEA: Membrane Electrode Assembly) in which a polymer-like solid electrolyte membrane is composed of a carbon electrode carrying a catalyst such as platinum. ) Is the main feature. A pair of separators having a flow path for supplying fuel and oxidant gas to this MEA and having a current collecting action sandwiching the MEA through a sealing material that prevents leakage of fuel and oxidant gas It is called a single cell, and the fuel cell stack is formed by stacking a plurality of such single cells. Among polymer electrolyte fuel cells, fuel cells that use liquid organic compounds, such as direct methanol fuel cells, as fuel are small in size because they do not require a reformer or hydrogen cylinder to generate hydrogen gas. It can be reduced in weight and is suitable as a small generator.

  In order to adapt a polymer electrolyte fuel cell that uses such a liquid organic compound as a fuel as a small generator, it must be as compact and lightweight as a conventional secondary battery, or it can be competitive in price. Indispensable. In direct methanol fuel cell systems, gas stacks and fuel tanks, fuel pumps, air pumps, gas-liquid separators for separating carbon dioxide discharged from the fuel discharge side, and water discharged from the air discharge side are used. Many peripheral parts such as a water tank for storage are required, but it is required to reduce these to a simple structure. As described above, improvement in energy density by reducing the size and weight of the system and cost reduction by reducing the number of parts used are important issues.

  Conventionally, for example, Patent Document 1 proposes a fuel cell system having a structure in which a cell stack is immersed in a fuel tank for the purpose of downsizing a direct methanol fuel cell system.

JP 2004-335236 A

  Patent Document 1 proposes a configuration in which a fuel cell stack is disposed in a fuel tank. The fuel cell stack is immersed in the fuel, and a separator channel is opened in the fuel tank, whereby the fuel is supplied to the fuel cell. A configuration has been proposed that can be supplied to the stack without a pump.

  With the configuration proposed in Patent Document 1, the system can be made compact. However, in the case of a so-called passive type that does not use a liquid feed pump as in Patent Document 1, since fuel is supplied by natural diffusion, if the output current is increased in order to further improve the output density, there is insufficient fuel supply. The output voltage may become unstable. Therefore, it is necessary to reduce the size of the system with a configuration that can be applied to an active type that uses a liquid feed pump for fuel supply that can handle high current output.

  An object of the present invention is to provide a polymer electrolyte fuel cell system capable of reducing the cost by reducing the number of parts and improving the power density by making the system compact.

  In order to solve the above problems, the inventors have constructed a novel configuration in which the fuel cell stack has the function of a container for storing fuel.

  A polymer electrolyte fuel cell system of the present invention includes a fuel cell stack in which a plurality of single cells that generate power using a liquid organic compound as a fuel are stacked, and a plurality of membrane electrode assemblies and separators constituting the fuel cell stack. A flow path for supplying a liquid fuel and an oxidant gas formed in the separator to the membrane electrode assembly, at least partially including a through-hole communicating with the laminated membrane electrode assembly and the separator; The through hole is separated by a sealing material, and the space formed by the through hole is a tank for storing liquid fuel or water.

  According to the present invention, it is possible to provide a polymer electrolyte fuel cell system capable of reducing the cost by reducing the number of parts and improving the output density by making the system compact.

It is a disassembled perspective view which shows the structure of the polymer electrolyte fuel cell of this invention. It is the figure which showed the structure of the separator in one form of the polymer electrolyte fuel cell of this invention. It is the figure which showed an example of the structure in one form of the polymer electrolyte fuel cell of this invention. It is the figure which abbreviate | omitted the upper collector plate and end plate of the structure shown in FIG. It is the figure which showed an example of the structure of the system of the polymer electrolyte fuel cell of this invention. It is the figure which showed the structure of the separator in one form of the polymer electrolyte fuel cell of this invention. It is the figure which showed an example of the structure in one form of the polymer electrolyte fuel cell of this invention. It is the figure which showed an example of the structure of the system of the polymer electrolyte fuel cell of this invention.

Embodiments according to the present invention will be described below, but the present invention is not limited to the following embodiments.
(First embodiment)
FIG. 1 shows an example of the configuration of the polymer electrolyte fuel cell according to the first embodiment of the present invention.
The MEA 102 includes an anode that oxidizes fuel and a cathode that reduces oxidant gas via an ion conductive solid polymer membrane. Here, a gas diffusion layer for diffusing fuel or oxidant gas in the surface may be provided on the surfaces of the anode and the cathode.
A pair of separators 103 for supplying fuel to the anode side of the MEA 102 and oxidant gas to the cathode side are arranged so as to sandwich the MEA 102. Further, a gasket 104 is disposed between the MEA 102 and the separator 103 in order to ensure a sealing property. The MEA 102, a pair of separators 103 that sandwich the MEA 102, and the gasket 104 constitute a unit cell. A plurality of unit cells are stacked to form a fuel cell stack.

The separator 103 has a flow path constituted by a groove or the like for supplying fuel or oxidant gas to the anode or the cathode, and circulates fuel or oxidant gas between a plurality of separators and also supplies fuel to the flow path of each separator. Or the through-hole which forms the manifold for distributing and supplying oxidizing gas is formed. In FIG. 2, an example of a structure of the separator of this embodiment is shown. The separator 103 has a fuel flow path for supplying fuel to the anode on one surface, and an oxidant gas flow path for supplying oxidant gas to the cathode on the other surface. A through hole is provided as a manifold for distributing and supplying fuel and oxidant gas to the passages. In this embodiment, the through hole 105 a and the through hole 105 b are connected to the fuel flow path, and the through hole 106 a and the through hole 106 b are connected to an oxidant gas flow path (not shown) provided on the back surface of the separator 103. doing. In the present invention, independent through-holes that are not connected to the flow path are different from through-holes that are connected to the fuel flow path or the oxidant flow path, such as the through holes 105a, 105b, 106a, and 106b serving as the manifold. 107. As will be described later, the through hole 107 serves as a tank for storing liquid fuel or water. Note that the MEA 102 is also provided with through holes 105 a, 105 b, 106 a, 106 b serving as a manifold, and independent through holes 107 at positions corresponding to the separator 103.
A gasket 104 is disposed on the surface of the separator 103 and is sealed by the gasket 104 so that fuel and oxidant gas are not mixed. The through hole 107 is surrounded by a gasket 104 so as to be separated from the flow path of the separator 103, and is sealed so that the fluid in the through hole 107 cannot move to the power generation surface where the flow path is formed. In FIG. 1, the configuration in which one gasket 104 is disposed between the MEA 102 and the separator 103 and sealed is described. However, the sealing material is not limited to such a gasket. What is necessary is just the structure which can seal a fluid, such as what was integrally molded.

  FIG. 3 shows a configuration of a fuel cell formed by stacking a plurality of the cells shown in FIG. The fuel cell stack includes current collector plates 108 and end plates 109 at both ends of a laminate in which unit cells are laminated. In addition, the current collector plate 108 and the end plate 109 are provided with a supply port or a discharge port connected to the manifold and the through hole 107, and a pipe is connected to the supply port or the discharge port to connect to the fuel cell stack. Fuel and oxidant gas are supplied and discharged. In FIG. 3, openings 115, 116, and 117 provided on the upper end plate 109 are connected to through holes 106b, 105b, and 107, respectively, and fuel and oxidant gas are supplied and discharged. Similarly, the lower end plate 109 is provided with an opening serving as a supply port or a discharge port.

  Although omitted in FIG. 3, in the fuel cell stack, it is necessary to circulate electrons generated by the reaction in the unit cell or circulate without leaking fuel or air. The laminated body in which the cells are laminated is sandwiched and fastened with a predetermined pressure. The method for fastening the fuel cell is not particularly limited as long as the surface pressure is uniformly applied to the MEA, such as using a bolt or a band as disclosed in the prior art.

  4 is the same as the configuration of the fuel cell shown in FIG. 3, but does not show the upper end plate and current collector plate. As shown in FIG. 4, the through-hole 107 is provided so as to communicate a plurality of MEAs and separators, and by stacking a plurality of unit cells, a space that can store a liquid such as fuel can be formed. . Since it is only necessary to secure a space necessary for storing the liquid, it is not essential to provide the through holes 107 in all of the MEAs and separators constituting the fuel cell stack, and at least some of the MEAs and separators penetrate. A hole 107 may be provided.

  FIG. 5 shows an example of the system configuration of the fuel cell of the present embodiment. As shown in FIG. 5, the fuel cell 110 has been described with reference to FIGS. 1 to 4, and includes a fuel storage portion 113 formed by laminating an anode 111, a cathode 112, and a through hole 107. The liquid fuel is filled in the fuel reservoir 113 and circulated and supplied to the anode 111 via the fuel circulation pump 202. Here, the fuel reservoir 113 and the anode 111 are connected to the supply port or discharge port of the end plate 109 connected to the fuel supply manifold and the fuel discharge manifold connected to the fuel flow path, and to the through hole 107. This is performed by connecting the supply port or the discharge port of the end plate 109 with a pipe. Moreover, the circulation pump 202 can be provided in the middle of this piping. When the concentration of methanol stored in the fuel storage unit 113 becomes lower than a predetermined concentration, the fuel tank 201 storing a high-concentration methanol aqueous solution is supplied to the fuel storage unit 113 via the fuel supply pump 203. The methanol in the fuel storage unit 113 is supplied and adjusted so as to be in a predetermined range. The methanol stored in the fuel tank 201 may be 100% methanol, but in this embodiment, an aqueous methanol solution diluted with water to a methanol concentration of 50% is used. Further, the fuel cell 110 can generate electric power by supplying air in the atmosphere as the oxidant gas to the cathode 112 via the oxidant gas supply pump 204. Carbon dioxide generated by the reaction and unreacted fuel return to the fuel storage unit 113, and carbon dioxide, which is a gas, is discharged out of the fuel cell system via the gas-liquid separation mechanism 208. In order to prevent dust and the like in the atmosphere from entering the fuel cell 110, a filter 207 is installed on the upstream side of the oxidant supply pump.

  In a polymer electrolyte fuel cell using a liquid organic compound as a fuel, an adjustment tank for adjusting the fuel concentration is required in addition to the fuel tank. The reason for this is as follows. When a direct methanol fuel cell is described as an example, there is a problem (methanol crossover phenomenon) in which methanol supplied to the anode permeates to the cathode through the electrolyte membrane. It is known that this methanol crossover phenomenon depends on the concentration of aqueous methanol solution supplied to the anode. For the problem of methanol crossover, the methanol crossover phenomenon is more diluted than the methanol concentration required for power generation. A countermeasure is taken by supplying a methanol aqueous solution having a predetermined concentration range to the anode. Further, the methanol and water are consumed by the power generation reaction and the methanol crossover phenomenon, so that the concentration of the methanol aqueous solution circulated changes with the operation time. For this reason, an adjustment tank for adjusting the methanol concentration is essential.

In the fuel cell of the present embodiment, a fuel storage unit for adjusting the fuel concentration is provided in the fuel cell stack by forming a through hole independent of the flow path in the separator and the MEA. Thus, it is possible to omit the fuel concentration adjusting mixing tank that has been provided outside the fuel cell stack in the past, which can contribute to cost reduction and compactness by reducing the number of system components. That is, in the fuel cell of the present embodiment, the separator and the MEA may be formed with a through hole for the fuel storage unit together with the through hole for the manifold by a method such as die molding or punching, and new parts and manufacturing No process is required. Therefore, it is possible to reduce the cost by reducing the number of parts by omitting the parts of the mixing tank. In addition, since the piping path for transporting fuel or water from the container to the fuel cell can be shortened as compared with the prior art, there is an effect of contributing to a compact system. Furthermore, since the liquid fuel having a relatively large specific heat can be contacted by the same type of member as the fuel cell, the thermal resistance can be lowered, and the surface area of the fuel storage part, the recovered water storage part, and the fuel cell can be reduced. The amount of heat can be reduced. As a result, the system temperature rise time after startup can be shortened, so that the effect of improving startup can be obtained.
(Second embodiment)
FIG. 6 shows an example of the configuration of the separator of the fuel cell according to the second embodiment of the present invention. The through holes serving as the flow paths and the manifolds have the same configuration as that shown in FIG. 2, but in this embodiment, two independent through holes are provided (107a and 107b). FIG. 7 is a perspective view of a fuel cell in which a plurality of layers are stacked using the separator shown in FIG. As shown in FIG. 7, the through holes 107 a and 107 b can each form a space in which a liquid such as fuel can be stored by stacking a plurality of cells. As in the present embodiment, by manipulating the shape of the through hole, the configuration of the space that can be formed during cell stacking can be changed. For example, by using a separator that does not have the through-holes 107a and / or 107b near the center in the cell stacking direction, it is possible to divide the communication space during cell stacking. FIG. 8 shows an example of a system configuration using the fuel cell shown in FIG. 7 of the present embodiment. The fuel cell 110 includes a fuel reservoir 113 formed by communicating an anode 111, a cathode 112, and a through hole 107a, and a recovered water reservoir 114 formed by communicating a through hole 107b. Liquid fuel is filled in the fuel reservoir 113 and circulated and supplied to the anode 111 via the fuel circulation pump 202. When the concentration of methanol stored in the fuel storage unit 113 becomes lower than a predetermined concentration, the fuel tank 201 storing a high-concentration methanol aqueous solution is supplied to the fuel storage unit 113 via the fuel supply pump 203. The methanol in the fuel storage unit 113 is supplied and adjusted so as to be in a predetermined range. In this embodiment, 100% methanol is used as the methanol stored in the fuel tank 201. Further, the fuel cell 110 can generate electric power by supplying air in the atmosphere as the oxidant gas to the cathode 112 via the oxidant gas supply pump 204. Carbon dioxide or unreacted fuel generated on the anode 111 by the reaction returns to the fuel storage unit 113, and carbon dioxide, which is a gas, is discharged out of the fuel cell system via the gas-liquid separation mechanism 208. Further, the water vapor generated on the cathode 112 by the power generation reaction is condensed by the water recovery mechanism 205 and stored in the recovered water storage unit 114. Unreacted air is discharged out of the fuel cell system via the gas-liquid separation mechanism 210. In order to unify the exhaust system, a gas path to the gas-liquid separation mechanism 208 may be provided. When the liquid level of the aqueous methanol solution stored in the fuel storage unit 113 falls below a predetermined value, water is supplied from the recovered water storage unit 114 to the fuel storage unit 113 via the water supply pump 209, and a certain amount of water is supplied. Configure to keep the liquid level.

With the fuel cell of this embodiment, it is possible to achieve cost reduction and downsizing by reducing the number of system components as in the first embodiment. Further, by providing a recovered water storage section in addition to the fuel storage section in the fuel cell stack, further cost reduction, compactness and high functionality can be achieved.

101 Fuel cell 102 MEA
103 Separator 104 Gasket 105a, 105b, 106a, 106b, 107, 107a, 107b Through hole 108 Current collector plate 109 End plate 110 Fuel cell 111 Anode 112 Cathode 113 Fuel reservoir 114 Recovered water reservoir 115, 116, 117 Opening 201 Fuel tank 202 Fuel circulation pump 203 Fuel supply pump 204 Oxidant supply pump 205 Water recovery mechanism 206 Cooling fan 207 Filter 208 Gas-liquid separation mechanism 209 Water supply pump 301 Mixing tank

Claims (3)

In a polymer electrolyte fuel cell system including a fuel cell stack in which a plurality of single cells that generate power using a liquid organic compound as a fuel are stacked,
At least a part of the plurality of membrane electrode assemblies and separators constituting the fuel cell stack includes a through-hole that communicates the stacked membrane electrode assemblies and the separators,
The flow path for supplying the liquid fuel and oxidant gas formed in the separator to the membrane electrode assembly and the through hole are separated by a sealing material,
A solid polymer fuel cell system characterized in that the space formed by the through holes is a tank for storing liquid fuel or water.   2. The liquid fuel is stored in the tank, the fuel supply manifold and the fuel discharge manifold of the fuel cell stack are connected to the tank, and the liquid fuel in the tank is circulated and supplied to the fuel cell stack. A polymer electrolyte fuel cell system. The water recovery mechanism according to claim 1, further comprising a water recovery mechanism for recovering water contained in the oxidant gas discharged from the fuel cell stack.
A polymer electrolyte fuel cell system, wherein water collected by the water recovery mechanism is stored in the tank.