JP4606038B2 - POLYMER ELECTROLYTE FUEL CELL AND METHOD OF OPERATING THE SAME - Google Patents

Description

  The present invention relates to a polymer electrolyte fuel cell including a polymer electrolyte membrane and a method for operating the same.

  A polymer electrolyte fuel cell including a polymer electrolyte membrane includes a hydrogen-containing fuel gas supplied to a fuel electrode as an anode and an oxidant gas such as oxygen-containing air supplied to an oxygen electrode as a cathode. By making it react electrochemically, electric power and heat are generated simultaneously.

  In general, a polymer electrolyte fuel cell is composed of a battery stack including a plurality of unit cells that are basic units. In the unit cell, a fuel electrode is disposed on one surface of a polymer electrolyte membrane that selectively transports hydrogen ions, and an oxygen electrode is disposed on the other surface. A gas seal is placed around these electrodes with a polymer electrolyte membrane sandwiched between them so that fuel gas and oxidant gas supplied to each electrode do not leak to the outside and mix with each other. Materials and gaskets are arranged. In this way, a pair of electrodes and a polymer electrolyte membrane are integrated and assembled in advance, and an electrode, a polymer electrolyte membrane, a gas seal material, and a gasket are integrated into an electrode electrolyte membrane assembly (hereinafter referred to as MEA). To be described). The MEA is sandwiched between a pair of separator plates to form a single cell, and a required number of single cells are connected in series to form a battery stack.

  At present, as a polymer electrolyte membrane used for MEA, a polymer electrolyte membrane made of perfluorocarbon sulfonic acid, for example, a Nafion membrane manufactured by Du Pont, USA, is generally used because of its excellent durability.

  By the way, such a polymer electrolyte fuel cell has a problem of gas cross leak through the polymer electrolyte membrane. Specifically, in the fuel cell, it is necessary to reduce the resistance of the membrane portion from the viewpoint of the power generation efficiency of the cell, and therefore the thickness of the polymer electrolyte membrane is reduced. However, when the thickness of the polymer electrolyte membrane is reduced, not only hydrogen ions move from the fuel electrode side to the oxygen electrode side through the membrane, but also the fuel gas and oxidant gas supplied to each electrode respectively. Cross leak to the other side through. As a result, the polymer electrolyte membrane deteriorates, causing problems such as a decrease in voltage.

  As a method for suppressing such gas cross-leakage, a method of increasing the film thickness of the polymer electrolyte membrane, or providing a catalyst layer in the membrane to cross-leak fuel gas and oxidant gas in the membrane. There has been proposed a method of converting to (for example, see Patent Document 1). However, these methods have problems such as a decrease in power generation efficiency of the battery due to an increase in film thickness and an increase in cost due to the installation of a catalyst layer in the film.

  Further, a method has been proposed in which oxygen that cross leaks to the fuel electrode side is used to remove CO poisoning of the oxygen electrode (see, for example, Patent Document 2). However, in this case, there is a problem that when the fuel cell is held at a very high voltage in the vicinity of an open circuit state exceeding 0.9 V, the polymer electrolyte membrane is decomposed.

On the other hand, regarding the mechanism of deterioration of durability of the fuel cell, hydrogen peroxide generated by a side reaction at the time of oxygen reduction of the oxygen electrode serving as the cathode becomes a radical by the Fenton reaction shown in the reaction formula of FIG. It is expected that the electrolyte membrane will be decomposed (for example, see Non-Patent Document 1). In addition, Fe ion in a figure is an ion derived from the member of a catalyst or an apparatus. Although the detailed mechanism of polymer electrolyte membrane decomposition is not yet known, gas cross-leakage may have an effect.
JP-A-6-103992 JP 2001-76742 A Proceedings of the 10th Fuel Cell Symposium P261

  The present invention solves the above-described conventional problems, and an object thereof is to provide a highly durable polymer electrolyte fuel cell and a method for operating the same by suppressing decomposition and deterioration of the polymer electrolyte membrane.

  As a result of intensive studies by the inventors on the mechanism of deterioration of the durability of the fuel cell due to the decomposition of the polymer electrolyte membrane of the fuel cell, the polymer electrolyte membrane is decomposed from the oxygen electrode side serving as the cathode to the fuel electrode side serving as the anode. It became clear that the influence of cross leaking oxygen was great. The actual amount of oxygen cross-leakage cannot be measured while the fuel cell is in operation, but oxygen ions and moisture are moving through the polymer electrolyte membrane during operation of the fuel cell. The amount of leak is considered to be affected by these factors. Based on these points, the inventors arrived at the present invention described below.

  That is, the polymer electrolyte fuel cell and the operation method thereof according to the present invention include a first electrode disposed on one surface of a hydrogen ion conductive electrolyte membrane and provided with a catalytic reaction layer, and the other surface of the electrolyte membrane. A second electrode provided with a catalytic reaction layer, a fuel gas passage for supplying a fuel gas containing hydrogen and supplying the fuel gas to the first electrode, and an oxidant gas containing oxygen flowing An oxidant gas flow path for supplying the oxidant gas to the second electrode, and generating power by oxidation of the fuel gas in the catalytic reaction layer of the first and second electrodes In the battery, the pressure of the fuel gas supplied to the first electrode is higher than the pressure of the oxidant gas supplied to the second electrode.

  The fuel gas flow path includes a pair of separators sandwiching the first and second electrodes, and a recess is formed on a contact surface of the separator disposed on the first electrode side with the first electrode. And a concave portion is formed on a contact surface of the separator disposed on the second electrode side with the second electrode to form the oxidant gas flow path, and the fuel gas flow path in the fuel gas flow path The pressure of the fuel gas may be equal to or higher than the pressure of the oxidant gas in the oxidant gas flow path.

  The pressure of the fuel gas at the gas inlet of the fuel gas channel may be eight times or more the partial pressure of the oxygen in the oxidant gas at the gas inlet of the oxidant gas channel.

  The pressure of the fuel gas at the gas outlet of the fuel gas channel may be eight times or more the partial pressure of the oxygen in the oxidant gas at the gas outlet of the oxidant gas channel.

  For example, a first electrode provided on one surface of a hydrogen ion conductive electrolyte membrane and provided with a catalytic reaction layer, a second electrode provided on the other surface of the electrolyte membrane and provided with a catalytic reaction layer, A pair of separators for sandwiching the first and second electrodes, the first electrode being disposed on the first electrode side and having a recess formed on a contact surface with the first electrode to form a fuel gas flow path 1 separator and a second separator disposed on the second electrode side and provided with a recess in a contact surface with the second electrode to form an oxidant gas flow path. A fuel gas containing hydrogen is allowed to flow through the fuel gas flow path to supply the fuel gas to the first electrode, and an oxidant gas containing oxygen is supplied to the oxidant gas flow path of the second separator. Supply the oxygen to the second electrode, and In the polymer electrolyte fuel cell that generates power by oxidation of the fuel gas in the catalytic reaction layer of the first and second electrodes, the fuel gas channel length of the first separator is L1, and the fuel When the minimum flow sectional area of the gas flow path is S1, and the supply amount of the fuel gas supplied to the fuel gas flow path is V1, the pressure loss Pa of the fuel gas in the fuel gas flow path is a proportional constant. α is expressed as Pa = α × (L1 / S1) × V1, and the channel length of the oxidant gas channel of the second separator is L2, and the minimum of the oxidant gas channel When the flow path cross-sectional area is S2 and the supply amount of the oxidant gas supplied to the oxidant gas flow path is V2, the pressure loss Pc of the oxidant gas in the oxidant gas flow path is a proportional constant α. ', Pc = α' × (L2 / S 2) When the pressure loss of the oxygen gas in the oxidant gas is represented by Pc / 5, the outlet of the fuel gas channel and the outlet of the oxidant gas channel are open to the atmosphere. In this state, the fuel gas flow is such that the relationship Pa / (Pc / 5) ≧ 8 is established between the pressure loss Pa in the fuel gas channel and the pressure loss Pc in the oxidant gas channel. The channel lengths L1 and L2 of the channel and the oxidizing gas channel, the minimum channel cross-sectional areas S1 and S2, and the supply amounts V1 and V2 of the fuel gas and the oxidizing gas may be set.

  An exhaust pressure adjusting valve for adjusting the pressure of the fuel gas taken out from the outlet of the fuel gas flow path may be further provided.

  The fuel gas channel and the oxidant gas channel are provided in parallel, and the flow direction of the fuel gas from the inlet to the outlet of the fuel gas channel is the outlet from the inlet of the oxidant gas channel. It is preferable that it is the same as the flow direction of the said oxidant gas which goes to.

  The first and second electrodes each include a gas diffusion layer disposed on the outer surface of the catalytic reaction layer, and the gas diffusion layers disposed on the first electrode side and the second electrode side, respectively. It is preferable that at least one of the above is constituted with carbon paper as a base material. .

  The present invention is implemented in the form as described above, and has the following effects. That is, according to the polymer electrolyte fuel cell and the operation method thereof according to the present invention, the deterioration of the polymer electrolyte membrane can be suppressed, and the durability is high and the high voltage can be maintained over a long period of time. A molecular electrolyte fuel cell can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic perspective view showing a configuration of a polymer electrolyte fuel cell (hereinafter simply referred to as a fuel cell) according to an embodiment of the present invention. Here, a single cell (cell) is shown. . FIG. 2 is a schematic cross-sectional view of the unit cell of FIG. FIG. 3 is a schematic cross-sectional view showing a configuration of an electrode electrolyte membrane assembly (hereinafter referred to as MEA) used in the single battery of FIG. FIG. 4 is a schematic cross-sectional view for explaining the operation of the MEA during power generation by the fuel cell.

  As shown in FIGS. 1 to 4, in the unit cell 100 of the fuel cell according to the present embodiment, a surface of the membrane 11 with a hydrogen ion conductive polymer electrolyte membrane (hereinafter simply referred to as an electrolyte membrane) 11 interposed therebetween. A pair of electrodes (specifically, the fuel electrode 16 and the oxygen electrode 17) are disposed on the MEA 18. A gasket plate 19 is joined to the outer periphery of the MEA 18, and a pair of conductive separator plates 10 a and 10 b are disposed so as to sandwich the gasket plate 19 and the MEA 18, thereby constituting the unit cell 100.

  The gasket plate 19 and the separators 10a and 10b are formed with a manifold hole 24 for flowing fuel gas and oxidant gas and a manifold hole 25 for flowing cooling water. In addition, a fuel gas that is a reaction gas is supplied to the fuel electrode 16 at a portion that contacts the MEA 18 of the separator plate 10a, and a gas flow path (ie, a gas flow path for taking out a generated gas and surplus gas of a power generation reaction to the outside of the fuel cell). A fuel gas passage 26) is formed. In addition, an oxidant gas, which is a reactive gas, is supplied to the oxygen electrode 17 in a portion that contacts the MEA 18 of the separator plate 10b, and a gas flow path for taking out a generated gas or surplus gas of a power generation reaction outside the fuel cell ( That is, an oxidant gas flow path 27) is formed. The fuel gas flow channel 26 and the oxidant gas flow channel 27 can be provided separately from the separator plates 10a and 10b. However, as in the present embodiment, grooves are provided on the surfaces of the separator plates 10a and 10b to provide gas flow channels. A method of forming is generally used. In FIG. 1, striped grooves are formed on the surfaces of the separator plates 10a and 10b. However, as will be described later with reference to FIG. 5, a serpentine type in which the grooves meander is formed.

  In order to supply gas to the fuel gas channel 26 and the oxidant gas channel 27 formed in the separator plate 10a and the separator plate 10b in this way, a separator plate that uses fuel gas and oxidant gas supply pipes. A piping jig is required that branches according to the number of the plates 10a and 10b and connects the branch destinations directly to grooves formed on the surfaces of the separator plates 10a and 10b. This jig is called a manifold, and in particular, a manifold that is directly connected from a gas supply pipe is called an external manifold. In addition, there is a type of manifold called an internal manifold with a simplified structure. The internal manifold is provided with through holes (that is, manifold holes 24) at four corners of the separator 10a in which the fuel gas passage 26 is formed and the separator plate 10b in which the oxidant gas passage 27 is formed. The inlets and outlets of the flow path 26 and the oxidant gas flow path 27 are passed to the corresponding manifold holes 24, and the respective gases are supplied directly from the manifold holes 24 to the fuel gas flow path 26 and the oxidant gas flow path 27. In the present embodiment, the fuel cell has this internal manifold type configuration.

  Although not shown here, the manifold hole 24 communicating with the inlet of the fuel gas channel 26 communicates with a fuel supply pipe provided outside, and the fuel gas channel 26 is communicated via the manifold hole 24. Fuel gas is supplied to Further, the manifold hole 24 communicating with the inlet of the oxidant gas flow path 27 communicates with an oxidant supply pipe provided outside, and the oxidant gas to the oxidant gas flow path 27 via the manifold hole 24. Supply is made. The manifold hole 24 communicating with the outlet of the fuel gas passage 26 and the manifold hole 24 communicating with the outlet of the oxidant gas passage 27 are externally provided so that the generated gas and surplus gas in the power generation reaction can be taken out. Communicate.

  FIG. 5 is a schematic diagram showing the relative arrangement of the fuel gas flow path 26 and the oxidant gas flow path 27 formed in the separator plates 10a and 10b. As shown in FIG. 5, here, serpentine type, that is, separator plates 10a and 10b formed by meandering fuel gas passage 26 and oxidant gas passage 27 are used. The relative arrangement of the fuel gas flow path 26 and the oxidant gas flow path 27 of the serpentine-type separator plates 10a and 10b depends on the flow direction of the gas in the flow path. It can be divided into three types: flow type.

  As shown in FIG. 5A, when the fuel gas flow channel 26 and the oxidant gas flow channel 27 are arranged in a parallel flow type, an inlet A of the fuel gas flow channel 26 is provided at one upper end of the separator plate. The outlet B of the fuel gas channel is provided at the diagonal end of the lower part of the separator plate, and the channel from the inlet A to the outlet B is formed to meander in the horizontal direction. On the other hand, the inlet C of the oxidant gas flow path 27 is provided at the other upper end of the separator, and the outlet D of the oxidant gas flow path 27 is provided at the diagonal end of the lower part of the separator plate, from the inlet C to the outlet D. The flow path is meandering in the horizontal direction and formed in parallel with the fuel gas flow path 26.

  On the other hand, as shown in FIG. 5B, when the fuel gas passage 26 and the oxidant gas passage 27 are arranged in a cross flow type, the inlet A of the fuel gas passage 26 is at the upper end of the separator plate. In addition, the outlet B of the fuel gas passage 26 is provided at the diagonal end of the lower part of the separator plate, and the passage from the inlet A to the outlet B is meandering in the vertical direction. On the other hand, the inlet C of the oxidant gas flow path 27 is provided at the other upper end of the separator, and the outlet D of the oxidant gas flow path 27 is provided at the diagonal end of the lower part of the separator plate, from the inlet C to the outlet D. Are formed so as to meander in the horizontal direction and perpendicular to the fuel gas passage 26.

  On the other hand, as shown in FIG. 5 (c), when the fuel gas flow channel 26 and the oxidant gas flow channel 27 are arranged in a counterflow type, the inlet A of the fuel gas flow channel 26 is at the lower end of the separator plate. The outlet B of the fuel gas passage 26 is provided at the diagonal end of the upper part of the separator plate, and the passage from the inlet A to the outlet B is formed to meander in the horizontal direction. On the other hand, the inlet C of the oxidant gas passage 27 is provided at one end of the separator upper portion above the inlet A of the fuel gas passage 26, and the outlet D of the oxidant gas passage 27 is provided at the diagonal end below the separator plate. The flow path from the inlet C to the outlet D meanders in the horizontal direction and is formed in parallel with the fuel gas flow path 26.

  5A to 5C show a configuration in which one fuel gas channel 26 is formed in the separator plate 10a and one oxidant gas channel 27 is formed in the separator plate 10b. Actually, a plurality of fuel gas passages 26 and oxidant gas passages 27 are formed in the separator plates 10a and 10b, respectively. For example, a separator plate 10a, 10b having a length of 20 cm, a width of 32 cm, and a thickness of 1.3 mm, a fuel gas flow path 26 having a width of 1 to 1.5 mm and a flow path depth of 1 to 1.5 mm and an oxidizer A gas flow path 27 is formed. In the fuel gas flow path 26, 2 to 4 channels having a length of 140 to 180 cm are formed in one separator 10a. In the oxidant gas flow path 27, one separator is formed. Six to eight channels having a length of 100 to 150 cm are formed in 10b.

  Further, a groove serving as the cooling water flow path 28 is formed on the surface of the separator 10a, 10b opposite to the surface in contact with the MEA 18. The cooling water passage 28 is connected to a cooling water flow pipe (not shown) provided outside via the manifold hole 25.

Normally, a fuel cell used as a power source requires a voltage of several volts to several hundred volts, so that the unit cell 100 having the above configuration obtains a desired voltage in actual use of the fuel cell. A fuel cell stack (that is, a stacked body of unit cells 100) is configured by connecting in series as many as necessary. The fuel cell stack constitutes a fuel cell. Although not shown here, a current collector plate and an insulating plate made of an electrically insulating material are disposed at both ends of the fuel cell stack, and these are entirely composed of an end plate and a fastening block. It is fixed. As a result, when a practical current having a density of several tens to several hundreds mA / cm ² is supplied, an electromotive force of about 0.7 to 0.8 V can be generated in one unit cell 100, and the fuel cell as a whole Can generate an electromotive force of several volts to several hundred volts.

As shown in FIGS. 3 and 4, the electrolyte membrane 11 constituting the MEA 18 is configured by an ion exchange membrane capable of selectively transporting hydrogen ions (H ⁺ ) from the fuel electrode 16 side to the oxygen electrode 17 side. Has been. As the electrolyte membrane 11, a polymer electrolyte membrane made of perfluorocarbon sulfonic acid (for example, a Nafion membrane manufactured by Du Pont, USA) is generally used because of its excellent durability. A fuel electrode 16 serving as an anode is formed on a portion of the electrolyte membrane 11 excluding an edge portion on one surface, and an oxygen electrode 17 serving as a cathode is formed on a portion other than the edge portion on the other surface.

  The fuel electrode 16 and the oxygen electrode 17 are composed of catalyst reaction layers 12 and 14 and gas diffusion layers 13 and 15, respectively. The catalyst reaction layers 12 and 14 are formed on the surface of the electrolyte membrane 11, and the catalyst Gas diffusion layers 13 and 15 are formed on the outer surfaces of the reaction layers 12 and 14 to form electrodes 16 and 17. Specifically, as shown in FIG. 4, a catalyst body 104 obtained by supporting a platinum-based metal catalyst 101 on a carbon powder 102 on both surfaces of an electrolyte membrane 11, and a hydrogen ion conductive polymer electrolyte (not shown). Catalyst reaction layers 12 and 14 composed of a mixture of The outer surface of the catalytic reaction layers 12 and 14 has a gas diffusion layer 13 having both air permeability and electronic conductivity, for example, a base material 105 made of water-repellent carbon paper, carbon felt, carbon cloth or the like. , 15 are formed. The catalyst reaction layers 12 and 14 and the gas diffusion layers 13 and 15 form a fuel electrode 16 and an oxygen electrode 17. The fuel electrode 16 and the oxygen electrode 17 thus formed are connected by a circuit 110 connected to the outside.

  The gas diffusion layers 13 and 15 mainly have the following three functions. The first function is to uniformly distribute the fuel gas from the fuel gas channel 26 for supplying the fuel gas and the oxidant gas channel 27 for supplying the oxidant gas to the catalyst 101 in the catalyst reaction layer 12 and the catalyst reaction layer 14. And a function of diffusing the fuel gas and the oxidant gas in order to supply the oxidant gas. The second function is a function of quickly discharging water generated by the power generation reaction in the catalyst reaction layers 12 and 14 to the outside of the electrode. The third function is a function of conducting electrons necessary for the power generation reaction or generated electrons. From the above, the gas diffusion layers 13 and 15 are required to have good reaction gas permeability, moisture discharge property, and electronic conductivity.

  As a general technique, in order to provide gas permeability, the gas diffusion layers 13 and 15 are made of a conductive porous material such as a fine carbon powder having a developed structure, a pore former, carbon paper, or carbon cloth. The material 105 is used to give the gas diffusion layers 13 and 15 a porous structure. Further, in order to provide moisture drainage, a water-repellent polymer such as a fluororesin is dispersed in the gas diffusion layers 13 and 15. Furthermore, in order to give electronic conductivity, the gas diffusion layers 13 and 15 are made of an electronic conductive material such as carbon fiber, metal fiber, or carbon fine powder.

  On the other hand, the catalytic reaction layers 12 and 14 mainly have four functions. The first function is a function of supplying the fuel gas and the oxidant gas supplied from the gas diffusion layers 13 and 15 to the reaction site of the catalyst 101. The second function is a function of conducting hydrogen ions necessary for the reaction on the catalyst 101 or generated hydrogen ions. Furthermore, the third function is a function of conducting electrons necessary for the reaction or generated electrons. The fourth function is high catalyst performance for accelerating the reaction and its wide reaction area. From the above, the catalytic reaction layers 12 and 14 are required to have good reaction gas permeability, hydrogen ion conductivity, electronic conductivity and catalytic performance.

  As a general technique, in order to give gas permeability to the catalytic reaction layers 12 and 14, a gas having a porous structure using a fine carbon powder or a pore former having a developed structure structure as a catalyst carrier 102 is used. A flow channel 103 is formed to form a gas channel. Further, in order to make the catalyst reaction layers 12 and 14 have hydrogen ion permeability, a polymer electrolyte (not shown) is dispersed in the vicinity of the catalyst 101 in the catalyst reaction layers 12 and 14 and a hydrogen ion network is formed. Things have been done. In addition, in order to give the catalyst reaction layers 12 and 14 electron conductivity, an electron channel is formed by using an electron conductive material such as carbon fine powder or carbon fiber as the catalyst carrier 102. Further, in order to improve the catalyst performance, a metal catalyst 101 having a high reaction activity represented by platinum is supported on the fine carbon powder as the catalyst support 102 as very fine particles having a particle diameter of several nanometers. The catalyst body 104 is highly dispersed in the catalyst reaction layers 12 and 14.

The fuel cell having the above configuration is used in the following fuel cell power generation system. FIG. 6 is a schematic diagram showing a configuration of a fuel cell power generation system including the fuel cell having the above configuration.
As shown in FIG. 6, in the fuel cell power generation system, the main surface of each single cell 100 (specifically, the main surfaces of the separator plates 10a and 10b and the MEA 18) is arranged along the vertical direction, and a plurality of single cells 100 are provided. A fuel cell 200 is composed of fuel cell stacks arranged in series in a horizontal direction and connected in series, a fuel gas supply device 201 that supplies fuel gas to the fuel electrode 16 of each unit cell 100, and an oxygen electrode of each unit cell 100 17, an oxidant gas supply device 202 that supplies an oxidant gas to the power source 17, a power load 203 connected to a current collector plate (not shown) of the fuel cell 200 and supplied with electricity obtained by a power generation reaction, and a fuel gas supply A device 201, an oxidant gas supply device 202, and a control device 204 for controlling the fuel cell 200 are provided.

  The fuel electrode 16 of each unit cell 100 of the fuel cell 200 is connected to the fuel gas supply device 201 through the fuel gas supply pipe a. Specifically, the fuel gas supply pipe a is branched and connected to each fuel electrode 16 so that the fuel gas can be supplied to the fuel electrode 16 of each unit cell 100 of the fuel cell 200. A pressure sensor 205 for detecting the pressure of the fuel gas supplied to the fuel electrode 16 (hereinafter referred to as the fuel gas inlet side pressure) is disposed in the main pipe portion of the fuel gas supply pipe a.

  The fuel cell 200 is connected to a fuel gas extraction pipe b for extracting gas generated by the power generation reaction and unreacted gas from the fuel electrode 16 side. The fuel gas extraction pipe b is branched and connected to each fuel electrode 16 so that the generated gas and the unreacted gas can be extracted from the fuel electrode 16 of each unit cell 100. A pressure sensor 206 for detecting the pressure of gas taken out from the fuel electrode 16 (hereinafter referred to as fuel gas outlet side pressure) is disposed in the middle of the main pipe portion of the fuel gas take-out pipe b. An exhaust pressure adjusting valve 207 is provided in the middle of the main pipe.

  On the other hand, the oxygen electrode 17 of each unit cell 100 of the fuel cell 200 is connected to the oxidant gas supply device 202 through the oxidant gas supply pipe c. Specifically, the oxidant gas supply pipe c is branched and connected to each oxygen electrode 17 so that the oxidant gas can be supplied to the oxygen electrode 17 of each unit cell 100 of the fuel cell 200. A pressure sensor 208 for detecting the pressure of the oxidant gas supplied to the oxygen electrode 17 (hereinafter referred to as the oxidant gas inlet side pressure) is disposed in the main pipe portion of the oxidant gas supply pipe c. ing.

  The fuel cell 200 is connected to an oxidant gas extraction pipe d for extracting gas generated by the power generation reaction and unreacted gas from the oxygen electrode 17 side. This oxidant gas extraction pipe d is branched and connected to each oxygen electrode 17 so that the generated gas and the unreacted gas can be extracted from the oxygen electrode 17 of each unit cell 100. A pressure sensor 209 for detecting the pressure of the gas extracted from the oxygen electrode 17 (hereinafter referred to as the oxidant gas outlet side pressure) is disposed in the middle of the main pipe portion of the oxidant gas extraction pipe d. In addition, an exhaust pressure adjusting valve 210 is disposed in the middle of the main pipe.

  As will be described later, during operation of the fuel cell power generation system, the inlet side pressure and the outlet side pressure of the fuel gas and the oxidant gas are detected (monitored) using the respective pressure sensors 205, 206, 208, and 209. Based on each pressure, the control device 204 adjusts the fuel gas supply amount from the fuel gas supply device 201 and the oxidant gas supply amount from the oxidant gas supply device 202, and the exhaust pressure adjusting valve 207, The opening / closing of 210 is adjusted. By adjusting the supply amounts of the fuel gas and the oxidant gas, the amount of current (current density) flowing through each unit cell 100 of the fuel cell 200 is adjusted. Further, the pressure of the fuel gas and the oxidant gas is adjusted by adjusting the exhaust pressure adjusting valves 207 and 210.

  Next, the operation of the fuel cell power generation system having such a configuration will be described.

  An operation start control signal is output from the control device 204, and the operation of the fuel cell power generation system is started. Specifically, when a control signal for starting operation is output, the fuel gas is supplied from the fuel gas supply device 201 to each fuel electrode 16 of the fuel cell 200 through the fuel gas supply pipe a, and the oxidant gas supply device. The oxidant gas is supplied from 202 to each oxygen electrode 17 of the fuel cell 200 through the oxidant gas supply pipe c. Here, hydrogen-rich gas is supplied from the fuel gas supply device 201 as the fuel gas. Further, air is supplied from the oxidant gas supply device 202 as the oxidant gas.

  In each unit cell 100 of the fuel cell 200, the fuel gas supplied through the fuel gas supply pipe a is introduced into the fuel gas passage 26 of the separator plate 10 a through the manifold hole 24 and supplied to the fuel electrode 16. . On the other hand, the oxidant gas supplied through the oxidant gas supply pipe c is introduced into the oxidant gas flow path 27 of the separator plate 10 b through the manifold hole 24 and supplied to the oxygen electrode 17. Simultaneously with the supply of the fuel gas and the oxidant gas, cooling is performed through a pipe (not shown) and the manifold hole 25 in the fuel cell 200 and the cooling water passage 28 formed in the separator plates 10a and 10b. Water flows through the fuel cell 200.

  Here, as shown in FIG. 5A, when the relative arrangement of the fuel gas channel 26 and the oxidant gas channel 27 in each unit cell 100 of the fuel cell 200 is a parallel flow type, the fuel gas is From the inlet A at the upper end of the separator plate to the outlet B at the lower diagonal end, it flows in the flow path while meandering in the horizontal direction along the inner wall of the groove constituting the flow path. At this time, the oxidant gas flows in the flow path while meandering in the horizontal direction along the inner wall of the groove constituting the flow path from the inlet C at the other upper end of the separator plate toward the outlet D at the lower diagonal end. . As described above, in the case of the parallel flow type arrangement, the fuel gas and the oxidant gas both flow from the upper part of the separator toward the lower part while reciprocating in the horizontal direction of the separator.

  On the other hand, as shown in FIG. 5B, when the relative arrangement of the fuel gas channel 26 and the oxidant gas channel 27 is a cross-flow type, the fuel gas flows downward from the inlet A at the upper end of the separator plate. Toward the outlet B at the diagonal end of the channel, flowing in the channel while meandering in the vertical direction along the inner wall of the groove constituting the channel. At this time, the oxidizing gas flows in the flow path while meandering horizontally along the inner wall of the groove constituting the flow path from the inlet C at the other upper end of the separator plate to the outlet D at the lower diagonal end. Flowing. Thus, in the case of the cross flow type, the fuel gas flows from one end of the separator in the horizontal direction to the other end while reciprocating in the vertical direction of the separator, while the oxidant gas flows in the separator while reciprocating in the horizontal direction of the separator. It flows from top to bottom.

  On the other hand, as shown in FIG. 5C, when the relative arrangement of the fuel gas channel 26 and the oxidant gas channel 27 is a counter flow type, the fuel gas flows upward from the inlet A at one end of the lower part of the separator plate. Toward the outlet B at the diagonal end of the channel, flowing in the channel while meandering in the horizontal direction along the inner wall of the groove constituting the channel. At this time, the oxidant gas forms a flow path from the inlet C at the upper end of the separator plate (specifically, above the inlet A of the fuel gas flow path 26) toward the outlet D at the lower diagonal end. It flows in the flow path while meandering in the horizontal direction along the inner wall of the groove. Thus, in the case of the counter flow type, the fuel gas flows from the lower part of the separator to the upper part while reciprocating in the horizontal direction of the separator, while the oxidant gas is the flow of the fuel gas while reciprocating in the horizontal direction of the separator. It flows from the upper part of the separator toward the lower part so as to face each other.

When the fuel gas is supplied to the fuel electrode 16 and the oxidant gas is supplied to the oxygen electrode 17 as described above, in each unit cell 100 of the fuel cell 200, as shown in FIG. The supplied fuel gas reaches the catalytic reaction layer 12 through the gas diffusion layer 13, and hydrogen ions (H ⁺ ) and electrons (e ⁻ ) are generated by the action of the catalyst 101. The electrons reach the oxygen electrode 17 through the circuit 110 connected to the outside. As a result, a current flows from the fuel electrode 16 toward the oxygen electrode 17. On the other hand, hydrogen ions move through the electrolyte membrane 11 and reach the oxygen electrode 17. In the oxygen electrode 17, due to the action of the catalyst 101 in the catalyst reaction layer 12, the electrons and hydrogen ions that have moved react with oxygen in the supplied oxidant gas (that is, air) to generate water. Accordingly, in the entire fuel cell, a reaction in which water and carbon dioxide are generated from the fuel gas and oxygen is performed, and power is generated during the reaction. The electricity obtained by the fuel cell 200 in this way is supplied to the power load 203. In addition, unused fuel gas and oxidant gas that have not been used for the power generation reaction are supplied from the fuel gas passage 26 and the oxidant gas passage 27 through the fuel gas extraction pipe b and the oxidant gas extraction pipe d, respectively. It is taken out outside. At this time, the gas generated by the power generation reaction is also taken out.

  By the way, during operation of the fuel cell power generation system, the pressure side of the fuel gas and the oxidizing gas is detected by the pressure sensors 205 and 208, and the pressure of the fuel gas and the oxidizing gas is detected by the pressure sensors 206 and 209. To do. The fuel gas inlet side pressure is always greater than the oxygen partial pressure at the oxidant gas inlet side pressure and / or the fuel gas outlet side pressure is greater than the oxygen partial pressure at the oxidant gas outlet side pressure. The supply amounts of the fuel gas and the oxidant gas and the opening / closing of the exhaust pressure adjusting valves 207 and 210 are adjusted so as to increase. Specifically, the fuel gas inlet side pressure is 8 times or more the oxygen partial pressure of the oxidant gas inlet side pressure, or the fuel gas outlet side pressure is the oxygen partial pressure of 8 of the oxidant gas outlet side pressure. It is set to be at least twice, and is preferably in the range of not less than 8 times and not more than 20 times.

  Here, the opening and closing of the exhaust pressure adjusting valves 207 and 210 are automatically adjusted by the control device 204 so that the pressure on the inlet side of the fuel gas is eight times the oxygen partial pressure of the inlet side pressure of the oxidant gas. In this case, the supply amounts of the fuel gas and the oxidant gas are kept constant, and the downstream ends of the fuel gas take-out path b and the oxidant gas take-out path d are opened to the atmosphere. The pressure of the gas (that is, the outlet side pressure of the fuel gas) and the pressure of the oxidant gas at the outlet of the oxidant gas (that is, the outlet side pressure of the oxidant gas) are atmospheric pressures.

  Thus, in the fuel cell 200 of the fuel cell power generation system in which the pressure on the fuel gas inlet side is set to eight times or more than the pressure on the oxygen gas inlet side, the pressure on the fuel electrode 16 side in each unit cell 100 is the electrolyte membrane 11. Since the pressure is higher than the pressure on the oxygen electrode 17 side, the oxygen cross-leakage from the oxygen electrode 17 side to the fuel electrode 16 side through the electrolyte membrane 11 can be suppressed at low cost without reducing the battery performance. It becomes possible. As a result, it is possible to suppress the decomposition and deterioration of the electrolyte membrane 11, and thus it is possible to realize a highly durable fuel cell power generation system capable of maintaining a high voltage over a long period of time.

  The cross leak of gas in the fuel cell 200 is affected by the film thickness of the electrolyte membrane 11 in addition to the influence of the pressure of the fuel gas and the oxidant gas as described above. However, the thickness of the electrolyte membrane 11 currently used as a standard in a polymer fuel cell is about 25 to 50 μm, and within this range, the thickness of the electrolyte membrane 11 has almost no influence on the deterioration of durability. Absent. Therefore, the durability of the fuel cell is determined by the pressure of the fuel gas and the oxidant gas as described above, and therefore the effect of the present invention is effectively exhibited.

  By the way, in the fuel gas and the oxidant gas flowing in the fuel cell 200, the pressure of the gas in the flow path differs depending on each region of the fuel gas flow path 26 and the oxidant gas flow path 27. For example, since the oxygen gas in the fuel gas and the oxidant gas is consumed by the power generation reaction of the fuel cell 200, the fuel gas channel 26 and the oxidant gas channel are used for the fuel gas and the oxygen gas in the oxidant gas. The pressure on the inlet side of 27 is higher than the pressure on the outlet side. Also, the gas pressure in each region of the flow path varies depending on the configuration of the fuel gas flow path 26 and the oxidant gas flow path 27 (for example, flow path arrangement, flow path width, depth, flow path length, etc.). Come. The cross leak of oxygen gas from the oxygen electrode 17 side to the fuel electrode 16 side occurs according to the differential pressure between the fuel gas and the oxygen gas in the oxidant gas. If the pressure difference between the gas and the oxygen gas in the oxidant gas is different, the cross leak state is different in each region of the flow path. Therefore, in the present embodiment, the pressure on the inlet side of the fuel gas is 8 times or more (for example, 8 times to 20 times, for example, 8 times) the pressure on the inlet side of the oxidizing gas having the highest oxygen partial pressure. To do. According to such a configuration, it becomes possible to suppress oxygen cross-leakage at the portion with the highest oxygen partial pressure, so that the effect of preventing deterioration of the electrolyte membrane 11 is more effectively exhibited.

  In particular, when the fuel gas channel 26 and the oxidant gas channel 27 are arranged in a parallel flow type (see FIG. 5A), the flow of the fuel gas and the oxidant flowing through the fuel gas channel 26 The flow of the oxidant gas flowing through the gas flow path 27 is parallel, and the fuel gas and the oxidant gas form a flow in the same direction from the upper part of the separator to the lower part along the flow paths 26 and 27. Therefore, in the parallel flow type arrangement, the decreasing direction of the fuel gas pressure in the fuel gas channel 26 and the decreasing direction of the oxygen partial pressure in the oxidant gas pressure in the oxidant gas channel 27 are directed from the upper part to the lower part of the separator. The direction is the same. Therefore, it is possible to suppress cross leak of oxygen gas with a minimum pressure difference. In addition, the decrease in the fuel gas pressure and the oxygen gas pressure due to the consumption of the gas accompanying the power generation reaction is the same as the decrease in the pressure difference between the oxygen gas in the fuel gas and the oxidant gas. It is possible to efficiently suppress the cross leak without providing it. Therefore, in the parallel flow type arrangement, the effect of the application of the present invention is particularly effective.

  By the way, as described above, the pressure on the inlet side of the fuel gas is at least eight times the oxygen partial pressure at the inlet side pressure of the oxidant gas, and the outlet side pressure of the fuel gas and the outlet side pressure of the oxidant gas are both large. In the case of atmospheric pressure, the pressure loss from the fuel gas inlet to the outlet (hereinafter referred to as fuel electrode side pressure loss, referred to as Pa) and the pressure loss from the oxidant gas inlet to the outlet (hereinafter referred to as oxygen) The relationship of the following formula | equation (1) is materialized between electrode side pressure loss and (it represents with Pc). Here, since air is supplied as the oxidant gas and the ratio of oxygen gas in the air is 20%, the oxygen partial pressure loss in the pressure loss of the oxidant gas is represented by Pc / 5. It is.

Pa / (Pc / 5) ≧ 8 (1)
Here, the pressure loss in the gas channel is mainly caused by the channel resistance when the gas flows through the gas channel. The flow path resistance of the gas flow path is expressed by flow path resistance = L / S when the flow path length L of the gas flow path and the minimum cross-sectional area S of the flow path are used. From this, the pressure loss P in the gas channel can be expressed by the following equation (2) using the channel resistance L / S and the gas flow rate V in the channel. In the formula, α is a proportionality constant.

Pressure loss P = α × (L / S) × V (2)
For example, when attention is paid to the unit cell 100 of the fuel cell 200 of the present embodiment, the fuel electrode side pressure loss Pa ′ in the unit cell 100 is substantially the average channel length of the plurality of fuel gas channels 26 formed in the separator 10a. Based on the above equation (2), La, the minimum cross-sectional area Sa of the fuel gas passage 26, the flow rate Va of the fuel gas supplied to the fuel gas passage 26, and the proportionality constant α ′ are calculated. In addition, the oxygen electrode side pressure loss Pc ′ in the unit cell 100 is the approximate average channel length Lc of the plurality of oxidant gas channels 27 formed in the plurality of separators 10 b and the minimum cross-sectional area of the oxidant gas channel 27. Based on the above equation (2), Sc, the flow rate Vc of the oxidant gas supplied to the oxidant gas flow path 27, and the proportionality constant α ″ are calculated. Therefore, the fuel electrode side pressure loss Pa ′ and the oxygen electrode side pressure loss Pc ′ calculated in this way satisfy the relationship of the above expression (1), that is, Pa ′ / (Pc ′ / 5) ≧ 8. The configuration (specifically, the width, depth, and length of the flow path) of the fuel gas flow path 26 and the oxidant gas flow path 27 of the separator plates 10a and 10b, the fuel gas and the oxidant gas If the supply amount is set, it is possible to prevent deterioration of the electrolyte membrane 11 due to cross leak of oxygen gas.

  As described above, when the pressure on the fuel electrode 16 side is higher than the pressure on the oxygen electrode 17 side, a large stress is applied to the electrolyte membrane 11 due to the pressure difference. For this reason, it is preferable that at least one base material 105 (see FIG. 4) of the gas diffusion layers 13 and 15 is composed of carbon paper having high rigidity. With such a configuration, this stress can be absorbed by the carbon paper, so that the burden on the electrolyte membrane 11 can be reduced and the durability of the membrane can be improved. Therefore, the fuel cell 200 having a longer life can be realized.

  In the above description, the fuel gas inlet side pressure is set higher than the oxidant gas inlet side pressure. However, the fuel gas outlet side pressure is set higher than the oxidant gas outlet side pressure. It may be.

  For example, depending on the setting of the utilization rate of the oxidant gas (specifically, air), the oxygen partial pressure at the outlet side pressure of the oxidant gas may increase. The utilization factor of air is determined by the current density of the output current and the supply amount of air. If the air utilization factor is low, the oxygen partial pressure at the outlet side pressure of the oxidant gas increases and the cross There is a high possibility of leakage. Specifically, when the fuel cell power generation system is operated at a low current density, since the supply amount of fuel gas and air is small, the water generated in the fuel cell 200 due to the power generation reaction is converted into the fuel gas passage 26 and the oxidant gas. The force pushed out from the flow path 27 is weak, and therefore this water closes the fuel gas flow path 26 and the oxidant gas flow path 27, causing a voltage drop (this phenomenon is called a flooding phenomenon). Therefore, in such an operation at a low current density, in order to prevent the flooding phenomenon, in particular, the operation is often performed by reducing the utilization rate of the air that is the oxidant gas. Becomes higher. Therefore, when the oxygen partial pressure at the outlet side pressure of the oxidant gas becomes high in this way, the exhaust gas side exhaust pressure is discharged so that the oxygen partial pressure at the outlet side pressure of the oxidant gas is at least eight times the oxygen partial pressure of the outlet side pressure of the oxidant gas. It is preferable to perform pressure adjustment using the pressure adjusting valves 207 and 210. Thereby, it is possible to prevent the occurrence of cross leaks at the fuel gas and oxidant gas outlet sides of the fuel cell 200, and as a result, the durability of the fuel cell is further improved.

  The configuration of the fuel cell power generation system according to the present invention is not limited to the configuration of the above embodiment. For example, in the above, the exhaust pressure regulating valves 207 and 210 are provided in both the fuel gas take-out pipe b and the oxidant gas take-out pipe d, but the pressure of the fuel gas is higher than the pressure of oxygen in the oxidant gas. Since the above-described effect is exhibited as long as the configuration becomes, only the exhaust pressure adjustment valve 207 may be provided.

  In the above, since the perfluorocarbon sulfonic acid membrane having the highest durability among the polymer electrolyte membranes is used as the electrolyte membrane 11, the electrolyte membrane can be obtained by setting the pressure on the fuel electrode 16 side to eight times that on the oxygen electrode 17 side. 11 can be suppressed, but when a polymer electrolyte membrane having lower durability than the perfluorocarbon sulfonic acid membrane is used as the electrolyte membrane 11, it is necessary to suppress oxygen cross-leakage. Therefore, the pressure on the fuel electrode 16 side is further increased as compared with the case of using a perfluorocarbon sulfonic acid membrane.

[Example]
In the example, the MEA 18 was manufactured as follows, and the fuel cell 200 was manufactured using the MEA 18. Then, an evaluation test of the fuel cell 200 was performed.

(Production of MEA)
Carbon powder acetylene black (specifically, “Denka Black” manufactured by Denki Kagaku Kogyo Co., Ltd., particle size: 35 nm) was converted into an aqueous dispersion of polytetrafluoroethylene (hereinafter referred to as PTFE) (specifically, Were mixed with Daikin Industries, Ltd. “D1”) to prepare a water-repellent ink containing 20 wt% PTFE in dry weight. This ink is used as a carbon cloth (specifically, “Carboron GF-20-31E” manufactured by Nippon Carbon Co., Ltd.) or carbon paper (specifically, the base material 105 of the gas diffusion layers 13 and 15 (see FIG. 4). Is coated and impregnated on “TGPH060H” manufactured by Toray Industries, Inc., heat treated at 300 ° C. using a hot air dryer, and gas diffusion layers 13 and 15 having a thickness of about 200 μm (see FIG. 4). ) Was formed.

  On the other hand, on the ketjen black of carbon powder (specifically, “Ketjen Black EC” manufactured by Ketjenblack International Co., Ltd., particle size 30 nm) as the catalyst support 102 (see FIG. 4), the Pt catalyst 101 ( A catalyst body 104 (see FIG. 4) obtained by loading 50% by weight of the catalyst body 104 (see FIG. 4) is formed, and 66 parts by weight of the catalyst body 104 is a hydrogen ion conductive material and a binder. Perfluorocarbon sulfonic acid ionomer (specifically, 5 wt% Nafion dispersion manufactured by Aldrich, USA) is mixed with 33 parts by weight in dry weight, and the resulting mixture is molded to form a catalytic reaction layer having a thickness of 10 to 20 μm. 12, 14 (see FIG. 4) were formed.

  As shown in FIG. 4, the catalyst reaction layers 12 and 14 and the gas diffusion layers 13 and 15 obtained as described above are formed on an electrolyte membrane 11 (specifically, “Nafion” membrane manufactured by DuPont, USA). The both surfaces were joined in this order to produce MEA18.

  Next, as shown in FIG. 1, a rubber gasket plate 19 is joined to the outer periphery of the manufactured MEA 18 to form a manifold hole 24 for fuel gas and oxidant gas circulation and a manifold hole 25 for cooling water circulation. did.

  On the other hand, it consists of a graphite plate impregnated with a phenolic resin having an outer dimension of 10 cm × 25 cm × 1.3 mm and having a fuel gas channel 26 formed on one side and a cooling water channel 28 formed on the other side. A conductive separator plate 10a and a conductive separator 10b made of the same material having the same outer dimensions and having an oxidant gas flow path 27 formed on one surface and a cooling water flow path 28 formed on the other surface; Prepared. Here, three cooling water channels 28 having a width of 1 mm, a depth of 1 mm, and a channel length of 200 cm are formed in the separator plates 10a and 10b. Further, two fuel gas passages 26 having a width of 1.5 mm, a depth of 0.9 mm, and a passage length of 250 cm are formed in the separator plate 10a, and the separator plate 10b has a width of 1.5 mm, a depth of 0.9 mm, Six oxidant gas channels 27 having a channel length of 100 cm are formed. The fuel gas flow channel 26 and the oxidant gas flow channel 27 are formed in a serpentine type. Here, the fuel gas flow channel 26 and the oxidant gas flow channel 27 are parallel flow types shown in FIGS. Separator plates 10a and 10b that can be arranged in a cross flow type and a counter flow type were prepared.

Separator plate 10b in which oxidant gas flow path 27 is formed on one surface of MEA 18 is overlapped so that flow path 27 is in contact with MEA 18, and separator plate 10a in which fuel gas flow path 26 is formed on the other surface. Are stacked so that the flow path 26 is in contact with the MEA 18 to produce a single cell 100 (see FIG. 1). Then, as shown in FIG. 2, two unit cells 100 were stacked to produce a unit cell stack unit having a structure in which cooling water flows between the unit cells 100 through the cooling water channel 28. Furthermore, the unit cell stack unit was repeatedly stacked, a fuel cell stack in which a total of 50 unit cells 100 were stacked was manufactured, and a fuel cell 200 was manufactured. Although illustration is omitted, at this time, a stainless steel current collector plate, an insulating plate made of an electrically insulating material, and an end plate are arranged at both ends of the fuel cell stack, and the whole is fixed with a fastening rod. The fastening pressure at this time was 10 kgf / cm ² per separator area.

  The fuel cell power generation system shown in FIG. 6 was configured using the fuel cell 200 manufactured as described above. Then, this fuel cell power generation system was operated, and an evaluation test of the fuel cell 200 was performed by the following method.

[Evaluation test method]
During operation of the fuel cell system of the embodiment, a hydrogen-rich reformed gas is generated by a reforming reaction in a hydrogen generator (not shown), and the fuel gas is supplied to the fuel electrode 16 of the fuel cell 200 using this hydrogen-rich gas as a fuel gas. It supplied through the piping a. Air was supplied as an oxidant gas to the oxygen electrode 17 of the fuel cell 200 through the oxidant gas supply pipe c. Here, the fuel gas supply device 201 has a configuration having a hydrogen generator, and the hydrogen generator reforms the 13A gas that is the raw material gas to generate a hydrogen-rich reformed gas. In the fuel cell 200, a power generation reaction is performed by the supplied fuel gas and oxidant gas (air), and the generated electric power is supplied to an electric power load 203 connected to a current collector plate (not shown) of the fuel cell 200. did. Further, the fuel gas and air that were not used in the power generation reaction were taken out through the fuel gas take-out pipe b and the oxidant gas take-out pipe d, respectively.

  In the operation of such a fuel cell power generation system, the pressure on the inlet side and the outlet side of the fuel gas are detected by the pressure sensors 205 and 206, and based on the detected values, the fuel gas has a predetermined pressure described in the following embodiments. Thus, the supply amount of the fuel gas and the opening / closing of the exhaust pressure adjustment valve 207 were adjusted by the control device 204. Further, the pressure sensor 208, 209 detects the inlet side pressure and the outlet side pressure of the oxidant gas (air), and based on the detected values, the oxidant gas has a predetermined pressure described in the following examples. The control device 204 adjusted the supply amount of the oxidant gas (air) and the opening / closing of the exhaust pressure regulating valve 210. Further, the current density flowing through each unit cell 100 of the fuel cell 200 was adjusted by controlling the supply amount of the fuel gas and the oxidant gas by the control device 204.

  In the following examples, unless otherwise specified, the battery temperature during operation of the fuel cell power generation system is 70 ° C., the fuel gas utilization rate (Uf) is 75%, and the air utilization rate (Uo) is 40%. As a result, a discharge test was conducted. The fuel gas and air supplied to the fuel cell power generation system were humidified so as to have a dew point of 70 ° C., respectively.

In the evaluation test, air and fuel gas were continuously supplied to the fuel cell power generation system, and the operation for generating power at a current density of 200 mA / cm ² was continuously performed. And while measuring the degradation rate of the voltage of the fuel cell 200 after 1000 hours continuous operation, the decomposition amount of the polymer electrolyte membrane 11 was measured. Here, F contained in the fuel gas and the air has been removed from the fuel cell 200 ^- the amount of ions, and F are included in the generated by power generation reaction water ^- the amount of ions, ion chromatography (Toa DKK Ltd. " the ion analyzer IA-100 "was quantified by the use) as analyzer are detected F ^- think ions produced upon decomposition of the polymer electrolyte membrane 11, the F ^- polymer electrolyte membrane 11 a detectable amount of ions It was measured as an indicator of the amount of degradation of

Example 1
In Example 1, the relationship between the pressure difference between the fuel gas inlet side pressure and the oxidant gas (air) inlet side pressure and the deterioration of the polymer electrolyte membrane 11 was examined.

  Here, the inlet side pressure of the oxidant gas detected by the pressure sensor 208 is kept constant at 105 kPa, while the inlet side pressure of the fuel gas detected by the pressure sensor 205 is set to the depth of the groove of the fuel gas passage 26. Each of the values shown in FIG. 7 was set by using different separator plates 10a. In addition, the outlet pressure of the fuel gas detected by the pressure sensor 206 and the outlet side pressure of the oxidant gas detected by the pressure sensor 209 are both open to the atmosphere. Therefore, the outlet side of the fuel gas and the oxidant gas Both pressures were 101 kPa. Further, here, the separators 10a and 10b are arranged so that the fuel gas channel 26 and the oxidant gas channel are in a parallel flow type arrangement.

7, voltage degradation rate and F when the inlet pressure of the fuel gas was varied ^- the results obtained by examining the elution amount of ions.

As shown in FIG. 7, as the pressure on the fuel gas inlet side increases, that is, the difference between the fuel gas inlet side pressure and the air inlet side pressure increases, the voltage degradation of the fuel cell 200 decreases, and F ⁻ It was clarified that the amount of decomposition of the polymer electrolyte membrane 11 was small because the amount of ion elution was small. Further, here, since air is used as the oxidant gas, the oxygen partial pressure in the air humidified at 70 ° C. is about 14 kPa. Therefore, the pressure on the inlet side of the fuel gas is the oxygen content at the pressure on the inlet side of the air. It has been clarified that both the voltage deterioration rate of the fuel cell 200 and the F ^- ion elution amount can be reduced if the pressure is about 8 times or more of the pressure.

(Example 2)
In Example 2, the relationship between the pressure difference between the outlet side pressure of the fuel gas and the outlet side pressure of the oxidant gas (air) and the deterioration of the polymer electrolyte membrane 11 was examined.

Here, an evaluation test was performed for the case where the operation was performed with the air utilization rate being 40% and the case where the operation was performed with the air utilization rate being 10%. The air utilization rate can be adjusted by the ratio between the current density of the output current of the fuel cell 200 and the supply amount of the fuel gas and the oxidant gas supplied to the fuel cell 200. Here, the current density of the output current is set to 200 mA / The supply amount of the fuel gas was adjusted so as to achieve an air utilization rate of 40% and 10% while maintaining the cm ² . Also, here, the separator plate 10b having different oxidant gas (air) inlet side pressures and different depths of the formed oxidant gas flow paths 27 is appropriately selected in the examples 2-1 to 2-12. It was unified at 105 kPa. Further, here, the separators 10a and 10b are arranged so that the fuel gas channel 26 and the oxidant gas channel 27 are arranged in a parallel flow type.

  Specifically, in the case where the air utilization rate is 40% and the fuel gas inlet side pressure is 110 kPa, the fuel gas outlet side pressure is opened to the atmosphere (that is, the outlet side pressure is 101 kPa). -1, the fuel gas outlet was throttled by the exhaust pressure regulating valve 207, and the fuel gas outlet side pressure was set to 104 kPa and 107 kPa, and the fuel gas inlet with an air utilization rate of 40% Example 2-4 in which the side pressure was 115 kPa and the outlet side pressure of the fuel gas was released to the atmosphere (that is, the outlet side pressure was 101 kPa), the fuel gas outlet was throttled by the exhaust pressure regulating valve 207, and the fuel gas outlet side pressure was An evaluation test was performed on Example 2-5 and Example 2-6 at 104 kPa and 107 kPa.

  Further, in the case where the air utilization rate is 10% and the fuel gas inlet side pressure is 110 kPa, the fuel gas outlet side pressure is opened to the atmosphere (that is, the outlet side pressure is 101 kPa). Example 2-8 and Example 2-9 in which the fuel gas outlet was throttled by the exhaust pressure regulating valve 207 to set the fuel gas outlet side pressure to 104 kPa and 107 kPa, and the fuel gas inlet side pressure was set at an air utilization rate of 10%. Example 2-10 in which the fuel gas outlet side pressure was released to the atmosphere (that is, the outlet side pressure was 101 kPa), the fuel gas outlet was throttled by the exhaust pressure adjusting valve 207, and the fuel gas outlet side pressures were 104 kPa and 107 kPa. An evaluation test was conducted on Example 2-11 and Example 2-12.

The results of Example 2-1 to Example 2-6 are shown in FIG. 8, and the results of Example 2-7 to Example 2-12 are shown in FIG. As shown in FIGS. 8 and 9, the fuel gas outlet side pressure is large, that is, the fuel gas outlet side pressure and the oxidant gas (air) outlet side pressure, as in the first embodiment shown in FIG. as the difference between the larger, the voltage degradation rate of the fuel cell 200 and F ^- elution of ions it was found to decrease. Further, as apparent from the comparison between FIG. 8 and FIG. 9, it is clear that when the air utilization rate is small, the deterioration of the electrolyte membrane 11 is further promoted, and thus the effect of the present invention is more effectively achieved. became.

When the air utilization factor is 40%, the oxygen partial pressure at the outlet side pressure of the oxidant gas is about 9 kPa, and when the air utilization factor is 10%, the oxygen partial pressure at the outlet side pressure of the oxidant gas is about 13 kPa. It becomes. Therefore, in order to suppress the voltage deterioration rate to 4 μV / h and the F ⁻ ion elution amount to 0.1 μg / cm ² / day or less, the fuel gas outlet side pressure is set to the oxygen content at the oxidant gas outlet side pressure. It became clear that the pressure should be about 8 times the pressure.

  Further, the case of 90% air utilization was also examined. In this case, the difference in oxygen partial pressure between the inlet side and the outlet side of the oxidant gas was only about 7%, and the downstream of the oxidant gas flow path. Cross leak on the side cannot be ignored. Therefore, in this case, by adjusting the exhaust pressure regulating valve 207 and maintaining the fuel gas pressure high up to the outlet of the flow path, cross leakage on the downstream side of the oxidant gas flow path is suppressed, and the durability is further improved. It became clear that it could be increased.

(Example 3)
In Example 3, when the relative arrangement of the fuel gas flow path 26 formed in the separator plate 10a and the oxidant gas flow path 27 formed in the separator plate 10b is a parallel flow type, a cross flow type, And the evaluation test was done about the case of a counterflow type.

  Here, the inlet side pressure of the oxidant gas (air) was 105 kPa, the inlet side pressure of the fuel gas was 110 kPa, and the outlet side pressures of the oxidant gas and the fuel gas were both open to the atmosphere (that is, 101 kPa). The result is shown in FIG.

As shown in FIG. 10, most voltage degradation rate of the fuel cell 200 and F in parallel flow type ^- small amount of eluted ions, crossflow and voltage degradation rate in the order of the counter-flow and F ^- elution of ions increases It became clear to do. As described above, it is possible to suppress the deterioration of the electrolyte membrane 11 with the parallel flow type most efficiently. This is because, in the cross flow type, as shown in FIG. 5 (b), since the pressure decreasing directions of the oxidant gas and the fuel gas are different, there is a portion where the pressure difference is locally reduced. This is considered to be because the deterioration of the electrolyte membrane 11 has progressed. Although a method of increasing the initial pressure difference in accordance with the portion where the pressure difference becomes small can be considered, there are problems in terms of efficiency and noise, such as a need for a blower having a larger capacity. Further, in the counter flow type, as shown in FIG. 5C, the directions of the inlet and outlet of the oxidant gas and the fuel gas are reversed, so that the pressure of the oxidant gas at the oxidant gas inlet is higher than that of the fuel gas. Therefore, it is considered that the oxygen partial pressure at the oxidant inlet portion becomes larger than the pressure of the fuel gas, so that oxygen cross leak occurs and the electrolyte membrane 11 further deteriorates.

Example 4
In Example 4, the configuration of the gas diffusion layers 13 and 15 (see FIG. 4) was studied. Here, the gas diffusion layer 13 of the fuel electrode 16 includes a base material 105 (see FIG. 4) made of carbon paper, and the gas diffusion layer 15 of the oxygen electrode 17 includes a base material 105 made of carbon cloth. An evaluation test was performed on Example 4-1 and Example 4-2 in which the gas diffusion layer 13 of the fuel electrode 16 and the gas diffusion layer 17 of the oxygen electrode 17 were each provided with the base material 105 made of carbon cloth.

  In the case where the base material 105 of the gas diffusion layer 13 is made of carbon paper (Example 4-1) and the case where both of the gas diffusion layers 13 and 15 are made of carbon cloth (Example 4-2), FIG. As shown in FIG. 4, the degree of penetration of the base material 105 into the gas flow path 103 differs depending on the material of the base material 105, and thus the pressure loss of the fuel gas and the oxidant gas (air) also changes. Therefore, in Example 4-1, which uses carbon paper that hardly penetrates into the base material 105, by adjusting the depths of the fuel gas channel 26 and the oxidant gas channel 27 of the separators 10a and 10b, Setting was made such that the inlet pressures of the fuel gas and the oxidant gas were the same at the same fuel gas and oxidant gas supply flow rates as in Example 4-2 using carbon cloth. Further, in Example 4-1 and Example 4-2, in order to accelerate the deterioration of the mechanical durability of the electrolyte membrane 11, the inlet side pressure of the oxidant gas is 105 kPa, and the outlet side is opened to the atmosphere (that is, the outlet side pressure). On the other hand, the pressure on the inlet side of the fuel gas was set to 150 kPa, and the pressure was increased by the exhaust pressure adjusting valve 207 to set the outlet side pressure to 140 kPa, thereby setting a large pressure difference.

In each of Example 4-1 and Example 4-2, as a result of discharging the fuel cell 200 at a current density of 200 mA / cm ² , voltage degradation occurred in Example 4-1 and Example 4-2 at the initial stage of operation. Although no difference was observed, when 4000 hours passed, the unit cell 100 in which the voltage was lowered was observed in the fuel cell 200 of Example 4-2 in which the carbon diffusion was used for the gas diffusion layers 13 and 15. When the electrolyte membrane 11 of the unit cell 100 was analyzed, the electrolyte membrane 11 was broken along the grooves of the fuel gas channel 26 and the oxidant gas channel 27 formed in the separator plates 10a and 10b. On the other hand, it has become clear that the fuel cell 200 of Example 4-1 using carbon paper for the gas diffusion layer 13 can stably generate power for 5000 hours or more. This is considered to be because the gas diffusion layer 13 made of carbon paper having high rigidity suppressed deformation of the electrolyte membrane 11 and prevented mechanical deterioration.

  Since the solid polymer fuel cell and the operation method thereof according to the present invention can suppress the deterioration of the polymer electrolyte membrane due to the cross leak of oxygen gas, the solid polymer fuel cell has high durability. It is useful and can be applied to, for example, solid polymer fuel cells used in stationary cogeneration systems, electric vehicles, and the like.

1 is a schematic perspective view showing a configuration of a unit cell of a polymer electrolyte fuel cell according to the present invention. It is typical sectional drawing of the single battery of FIG. It is typical sectional drawing which shows the structure of MEA of FIG. It is a schematic diagram which shows the operation | movement in the electric power generation reaction of MEA of FIG. It is a schematic diagram which shows the relative arrangement | positioning of the fuel gas flow path and oxidant gas flow path which are formed in a separator. It is a schematic diagram which shows the structure of the fuel cell power generation system provided with the polymer electrolyte fuel cell of FIG. 2 is a table showing the results of Example 1. 10 is a table showing the results of Example 2. 10 is a table showing the results of Example 2. 10 is a table showing the results of Example 3. 3 is a reaction formula showing a mechanism of deterioration of an electrolyte membrane.

Explanation of symbols

10a, 10b Separator plate 11 Electrolyte membrane 12, 14 Catalytic reaction layer 13, 15 Gas diffusion layer 16 Fuel electrode 17 Oxygen electrode 18 MEA
26 Fuel gas flow path 27 Oxidant gas flow path 28 Cooling water flow path 100 Single cell 200 Fuel cell 201 Fuel gas supply apparatus 202 Oxidant gas supply apparatus 203 Power load 204 Controller 205, 206, 208, 209 Pressure sensors 207, 210 Exhaust pressure adjustment valve

Claims (9)

A first electrode provided on one surface of the hydrogen ion conductive electrolyte membrane and provided with a catalytic reaction layer; a second electrode provided on the other surface of the electrolyte membrane and provided with a catalytic reaction layer; and hydrogen A fuel gas flow path for supplying the fuel gas to the first electrode by flowing a fuel gas; and an oxidant gas for supplying the oxidant gas to the second electrode by flowing an oxidant gas containing oxygen. A polymer electrolyte fuel cell comprising a flow path and generating power by oxidation of the fuel gas in the catalytic reaction layer of the first and second electrodes,
The polymer characterized in that the pressure of the fuel gas at the gas inlet of the fuel gas channel is at least eight times the partial pressure of the oxygen in the oxidant gas at the gas inlet of the oxidant gas channel. Electrolytic fuel cell. A first electrode provided on one surface of the hydrogen ion conductive electrolyte membrane and provided with a catalytic reaction layer; a second electrode provided on the other surface of the electrolyte membrane and provided with a catalytic reaction layer; and hydrogen A fuel gas flow path for supplying the fuel gas to the first electrode by flowing a fuel gas; and an oxidant gas for supplying the oxidant gas to the second electrode by flowing an oxidant gas containing oxygen. A polymer electrolyte fuel cell comprising a flow path and generating power by oxidation of the fuel gas in the catalytic reaction layer of the first and second electrodes,
The polymer characterized in that the pressure of the fuel gas at the gas outlet of the fuel gas channel is at least 8 times the partial pressure of the oxygen in the oxidant gas at the gas outlet of the oxidant gas channel. Electrolytic fuel cell. A pair of separators sandwiching the first and second electrodes;
A recess is formed in a contact surface of the separator disposed on the first electrode side with the first electrode to form the fuel gas flow path, and the separator disposed on the second electrode side the oxidant gas flow passage recess is formed in the contact surface between the second electrode is constituted,
The polymer electrolyte fuel cell according to claim 1 or 2. A first electrode provided on one surface of the hydrogen ion conductive electrolyte membrane and provided with a catalytic reaction layer; a second electrode provided on the other surface of the electrolyte membrane and provided with a catalytic reaction layer; And a pair of separators sandwiching the second electrode, the first electrode being disposed on the first electrode side and provided with a recess in a contact surface with the first electrode to form a fuel gas flow path A separator and a second separator which is disposed on the second electrode side and has a recess formed on a contact surface with the second electrode to form an oxidant gas flow path. A fuel gas containing hydrogen is caused to flow through the fuel gas channel, the fuel gas is supplied to the first electrode, and an oxidant gas containing oxygen is passed through the oxidant gas channel of the second separator. And supplying the oxygen to the second electrode, and In the polymer electrolyte fuel cell that generates electricity by oxidation of the fuel gas in the catalytic reaction layer of the second electrode,
The flow length of the fuel gas flow path of the first separator is L1, the minimum flow cross-sectional area of the fuel gas flow path is S1, and the supply amount of the fuel gas supplied to the fuel gas flow path is Assuming V1, the pressure loss Pa of the fuel gas in the fuel gas flow path is expressed as Pa = α × (L1 / S1) × V1, using a proportionality constant α, and
The length of the oxidant gas flow path of the second separator is L2, the minimum flow cross-sectional area of the oxidant gas flow path is S2, and the oxidant gas supplied to the oxidant gas flow path , The pressure loss Pc of the oxidant gas in the oxidant gas flow path is expressed by Pc = α ′ × (L2 / S2) × V2 using a proportional constant α ′. When the pressure loss of oxygen gas in the oxidant gas is expressed as Pc / 5,
In a state where the outlet of the fuel gas channel and the outlet of the oxidant gas channel are opened to the atmosphere, Pa / between the pressure loss Pa in the fuel gas channel and the pressure loss Pc in the oxidant gas channel. (Pc / 5) ≧ 8 so that the relationship between the fuel gas channel and the oxidant gas channel, the channel lengths L1, L2, the channel minimum cross-sectional areas S1, S2, and the fuel gas are satisfied. And a supply amount V1 and V2 of the oxidizing gas are set. The polymer electrolyte fuel cell according to any one of claims 1 to 4 , further comprising a discharge pressure adjusting valve for adjusting a pressure of the fuel gas taken out from an outlet of the fuel gas flow path. The fuel gas channel and the oxidant gas channel are provided in parallel, and the flow direction of the fuel gas from the inlet to the outlet of the fuel gas channel is the outlet from the inlet of the oxidant gas channel. the polymer electrolyte fuel cell according to any one of claims 1 to 5 which is identical to the flow direction of the oxidizing gas toward the. The first and second electrodes each include a gas diffusion layer disposed on the outer surface of the catalytic reaction layer, and the gas diffusion layers disposed on the first electrode side and the second electrode side, respectively. The polymer electrolyte fuel cell according to any one of claims 1 to 6 , wherein at least one of the above is constituted with carbon paper as a base material. A fuel gas containing hydrogen is allowed to flow through a fuel gas flow path to a first electrode disposed on one surface of the hydrogen ion conductive electrolyte membrane and provided with a catalytic reaction layer, and the fuel gas is supplied to the first electrode. And an oxidant gas containing oxygen is allowed to flow through the oxidant gas flow path to the second electrode disposed on the other surface of the electrolyte membrane and provided with a catalytic reaction layer. And supplying the oxidant gas to the catalyst, and using the supplied fuel gas and the oxidant gas to oxidize the fuel gas in the catalytic reaction layers of the first and second electrodes to generate electricity. In the method of operating the fuel cell,
A polymer characterized in that the pressure of the fuel gas at the gas inlet of the fuel gas channel is at least eight times the partial pressure of the oxygen in the oxidant gas at the gas inlet of the oxidant gas channel. A method of operating an electrolyte fuel cell. A fuel gas containing hydrogen is allowed to flow through a fuel gas flow path to a first electrode disposed on one surface of the hydrogen ion conductive electrolyte membrane and provided with a catalytic reaction layer, and the fuel gas is supplied to the first electrode. And an oxidant gas containing oxygen is allowed to flow through the oxidant gas flow path to the second electrode disposed on the other surface of the electrolyte membrane and provided with a catalytic reaction layer. And supplying the oxidant gas to the catalyst, and using the supplied fuel gas and the oxidant gas to oxidize the fuel gas in the catalytic reaction layers of the first and second electrodes to generate electricity. In the method of operating the fuel cell,
A polymer characterized in that the pressure of the fuel gas at the gas outlet of the fuel gas channel is at least eight times the partial pressure of the oxygen in the oxidant gas at the gas outlet of the oxidant gas channel. A method of operating an electrolyte fuel cell.

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