JP2012109072A - Fuel battery, fuel battery system, and method for operation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel battery which can keep an output and durability even with a fuel gas containing high-density CO introduced into a fuel electrode.SOLUTION: A fuel battery according to an embodiment includes: a fuel electrode; an oxidant electrode; a polymer electrolyte membrane disposed between the fuel electrode and the oxidant electrode; and a fuel electrode separator and an oxidant electrode separator which are disposed outside the fuel electrode and the oxidant electrode respectively. In the fuel battery, the fuel electrode includes: a fuel electrode diffusion layer on a side of the fuel electrode separator; and a fuel electrode catalyst layer on a side of the polymer electrolyte membrane. The fuel electrode catalyst layer includes a fuel electrode catalyst having a carrier carrying metal particles. The metal particles contain platinum and a second metal other than platinum. The effective reaction area of the metal particles is 70-150 cmper square centimeter in the plane direction of the fuel electrode catalyst layer. The fuel gas supplied to the fuel electrode contains 100-500 ppm of carbon monoxide.

Description

  Embodiments described herein relate generally to a fuel cell, a fuel cell system, and an operation method thereof.

  A fuel cell system is a power generator that supplies a fuel cell such as hydrogen and an oxidant such as air to the fuel cell and reacts them electrochemically, thereby converting the chemical energy of the fuel directly into electrical energy and taking it out. is there. This fuel cell system is highly efficient and environmentally friendly despite its relatively small size. In addition, it can be applied as a cogeneration system by collecting the heat generated by power generation as hot water or steam. Therefore, it is expected to be used for a wide range of applications such as business use (factories, hospitals, etc.), general home use, and automobile use.

  When a hydrocarbon fuel is used as a raw fuel, the fuel cell system includes a fuel reforming system that reforms the raw fuel into a hydrogen-rich gas by a reforming reaction using steam. In such a fuel cell system, hydrogen rich gas (hereinafter also referred to as fuel gas) produced by the fuel reforming system is introduced into a fuel electrode and reacted with oxygen to generate power. The introduced fuel gas contains carbon monoxide (hereinafter also referred to as CO). It is known that when CO contained in the fuel gas is adsorbed on the metal particles in the fuel electrode, there arises a problem that the output of the fuel cell is greatly reduced. It is also known that CO accelerates the deterioration of the fuel cell and reduces the durability of the fuel cell. Therefore, various devices have been devised so far in order to suppress such influence by CO.

  Generally, in order to reduce CO contained in fuel gas, the fuel reforming system includes a CO selective oxidation reactor. However, incorporating the CO selective oxidation reactor into the fuel reforming system is not preferable from the viewpoint of cost. On the other hand, when the CO selective oxidation reactor is omitted for cost reduction, the CO concentration in the fuel gas increases, causing problems such as a decrease in output, deterioration, and durability of the fuel cell.

JP 2008-66186 A

  Provided is a fuel cell capable of maintaining output and durability even when a fuel gas containing a high concentration of CO is introduced into a fuel electrode.

According to the embodiment, the fuel electrode, the oxidant electrode, the polymer electrolyte membrane disposed between the fuel electrode and the oxidant electrode, and the fuel electrode and the oxidant electrode are disposed on the outside. A fuel cell comprising a fuel electrode separator and an oxidant electrode separator is provided. In the fuel cell, the fuel electrode includes a fuel electrode diffusion layer on the fuel electrode separator side and a fuel electrode catalyst layer on the polymer electrolyte membrane side. The fuel electrode catalyst layer includes a fuel electrode catalyst in which metal particles are supported on a carrier, the metal particles include platinum and a second metal other than platinum, and the effective reaction area of the metal particles is the fuel electrode catalyst. a planar direction of the area of 1 cm ² per 70～150Cm ² layers, the fuel gas supplied to the fuel electrode comprises a carbon monoxide 100 to 500 ppm.

FIG. 1 is a cross-sectional view of a fuel cell according to an embodiment. FIG. 2 is a diagram showing a cyclic voltammogram of the fuel electrode. FIG. 3 is a conceptual diagram of the fuel cell system according to the embodiment. FIG. 4 is a diagram showing the relationship between the effective reaction area Z of the catalyst per unit area and the cell voltage drop amount in Test 1. FIG. FIG. 5 is a diagram showing the relationship between the effective reaction area Z of the catalyst per unit area and the relative ratio of the cross leak amount. FIG. 6 is a graph showing the relationship between the effective reaction area Z of the catalyst per unit area and the cell voltage drop amount in Test 3. FIG. FIG. 7 is a diagram showing the relationship between the battery temperature and the cell voltage drop amount. FIG. 8 is a diagram showing the relationship between the ruthenium content in the metal particles and the cell voltage drop. FIG. 9 is a diagram showing the time change of the unit cell voltage when the high concentration CO supply continuous power generation test is performed on the fuel cell to which the fuel electrode diffusion layer having different Gurley numbers is applied. FIG. 10 is a diagram comparing the cell voltage drop amount of the fuel cell in the case of using the operation method of Example 2 and the case of using the conventional operation method.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a fuel cell according to an embodiment.

  The fuel cell 1 has a structure in which a membrane electrode assembly in which a fuel electrode 2 and an oxidant electrode 3 are bonded to both surfaces of a polymer electrolyte membrane 4 is sandwiched between a fuel electrode separator 9 and an oxidant electrode separator 10.

  The fuel electrode 2 is formed by laminating the fuel electrode catalyst layer 5 and the fuel electrode diffusion layer 6 in this order from the side in contact with the electrolyte membrane 4. On the other hand, the oxidant electrode 3 is formed by laminating the oxidant electrode catalyst layer 7 and the oxidant electrode diffusion layer 8 in this order from the side in contact with the electrolyte membrane 4.

  In actual power generation, a fuel cell stack is generally used in which a plurality of the fuel cells 1 that are single cells are stacked in the thickness direction.

  Hereinafter, each member of the fuel cell shown in FIG. 1 will be described in detail.

  The fuel electrode catalyst layer 5 and the oxidant electrode catalyst layer 7 are layers in which the reaction actually proceeds. Specifically, a hydrogen oxidation reaction proceeds in the fuel electrode catalyst layer 5, and an oxygen reduction reaction proceeds in the oxidant electrode catalyst layer 7. Each of the fuel electrode catalyst layer 5 and the oxidant electrode catalyst layer 7 contains a catalyst and an electrolyte having proton conductivity.

  As the fuel electrode catalyst, a supported catalyst in which metal particles are supported on a carbon support is used. The metal particles include platinum and a second metal other than platinum, and it is preferable to use ruthenium, nickel, or the like as the second metal. Use of platinum is preferable from the viewpoint of hydrogen oxidation reaction activity, heat resistance, and the like.

In the fuel electrode catalyst layer 5 of the present embodiment configured as described above, the catalytic effective reaction area is 70 cm ² or more and 150 cm ² or less per 1 cm ² of the planar area of the fuel electrode catalyst layer 5. Here, the effective reaction area of a catalyst means the sum total of the surface area of the metal particle which is a catalyst. Further, the area in the planar direction of the fuel electrode catalyst layer means the area of the fuel electrode catalyst layer in the direction parallel to the stacking surface of the layers of the fuel cell.

  When a fuel gas having a high CO concentration is introduced into the fuel electrode, the amount of CO adsorbed on the metal particles in the catalyst layer increases, and the area of the catalyst that reacts effectively decreases. This causes a problem that the output of the fuel cell is significantly reduced. Furthermore, as described above, when the effective reaction area of the catalyst is reduced, the amount of hydrogen peroxide produced increases during the reduction reaction of oxygen that permeates the polymer electrolyte membrane from the oxidant electrode and reaches the fuel electrode. As a result, the deterioration of the polymer electrolyte membrane is accelerated by hydrogen peroxide, which causes a problem that the durability of the fuel cell is lowered.

However, by setting the effective reaction area of the catalyst to 70 cm ² or more per 1 cm ² of the planar area of the fuel electrode catalyst layer, it is possible to sufficiently ensure a catalyst that reacts effectively in the fuel electrode catalyst layer. For this reason, even if a fuel gas containing high concentration CO is supplied to the fuel electrode, the catalyst reaction is normally performed due to the presence of a catalyst having no CO adsorbed on the surface, so that the output of the fuel cell is reduced. It is difficult to maintain resistance. Moreover, by ensuring a sufficient effective reaction area of the catalyst, an increase in the amount of hydrogen peroxide produced by the oxygen reduction reaction is suppressed, and water is produced instead. As a result, deterioration of the polymer electrolyte membrane can be suppressed. On the other hand, when the effective reaction area of the catalyst is less than 70 cm ² , the ratio of the catalyst having CO adsorbed on the surface to the entire catalyst increases, and as a result, the catalytic reaction is not performed normally, resulting in a decrease in the output of the fuel cell. . Further, if the effective reaction area of the catalyst is increased, the amount of decrease in the output of the fuel cell is reduced. However, if the effective reaction area of the catalyst exceeds 150 cm ² , the amount of decrease in the output of the fuel cell is hardly changed. In order to increase the effective reaction area of the catalyst, it is necessary to use a large amount of metal particles. Therefore, it is not preferable to increase the effective reaction area of the catalyst to more than 150 cm ² from the viewpoint of cost.

  When the metal particles are an alloy containing platinum and ruthenium, the ratio of ruthenium in the metal particles is preferably 66 to 75 at% in terms of molar ratio. By setting the ruthenium content in the metal particles to 66 at% or more in terms of molar ratio, the CO adsorption energy on the metal particles is reduced, and the cell voltage drop due to high concentration CO can be suppressed. On the other hand, if the ruthenium content in the metal particles exceeds 75 at%, a problem may arise in the stability of the catalyst. Here, the cell voltage drop means that the cell voltage decreases compared to when no CO is supplied.

  Here, a method for calculating the effective reaction area of the catalyst will be described with reference to FIG.

FIG. 2 is a diagram showing a cyclic voltammogram of the fuel electrode. Here, the current flowing when the potential of the fuel electrode with respect to the oxidant electrode was changed was measured. Specifically, nitrogen is supplied to the fuel electrode, hydrogen is supplied to the oxidizer electrode, and the fuel electrode potential is set to 0.08 V to 0.7 V with respect to the oxidizer electrode potential at a scanning speed of 10 mV / sec for 3 cycles. The current value generated at the third cycle was measured by scanning. The temperature of the fuel cell during the potential scan of the fuel electrode was 30 ° C., the dew point of nitrogen and hydrogen was 30 ° C., and the supply flow rates of nitrogen and hydrogen were both 4 NmL / min / cm ² . In the obtained cyclic voltammogram, the current value when the potential of the fuel electrode is 0.4 V is defined as the baseline (A). Surrounded by a baseline (A), a straight line (B) perpendicular to the horizontal axis indicating a potential of 0.1 V, and a current curve (C) of a reduction current in a cyclic voltammogram of 0.1 V to 0.4 V The area of the region (S) is calculated using the formula [1]. Subsequently, using S and the potential scanning speed (dV / dt), Q is obtained by Equation [2]. Q is the quantity of electricity, and the unit is coulomb [C]. Q in this potential region is related to the amount of hydrogen adsorbed on platinum, and the surface area X of the metal particles can be calculated using the obtained Q value and Equation [3]. X represents the surface area of the entire metal particles contained in the fuel electrode catalyst layer, that is, the effective reaction area of the catalyst in the entire fuel electrode catalyst layer, and the unit is [cm ² ]. When the area in the planar direction of the fuel electrode catalyst layer is Y [cm ² ], the effective reaction area Z [cm ² ] of the catalyst per 1 cm ^{2 in} the planar direction of the fuel electrode catalyst layer is represented by the formula [4]. .

  As the oxidant electrode catalyst, a noble metal of at least one element or an alloy catalyst of the noble metal can be used. Examples thereof include metals such as platinum, ruthenium and palladium, and alloys such as platinum-cobalt alloy, platinum-iron alloy, and platinum-nickel alloy. Only one type of catalyst component may be included in the catalyst layer, or two or more types of catalyst components may be included. The catalyst components contained in the fuel electrode catalyst layer 5 and the oxidant electrode catalyst layer 7 may be the same or different. From the viewpoints of oxygen reduction reaction activity, heat resistance, etc., those containing platinum are preferably used, but the oxidant electrode catalyst is not particularly limited, and various substances having catalytic activity can be used. The oxidant electrode catalyst may be either a supported catalyst in which metal particles are supported on a conductive carrier, or an unsupported catalyst consisting only of metal particles, but a supported catalyst is preferably used. As the conductive carrier, particulate carbon such as activated carbon or graphite, or fibrous carbon can be used.

  For the electrolyte contained in the fuel electrode catalyst layer 5 and the oxidant electrode catalyst layer 7, an organic material or an inorganic material capable of transporting protons can be used. The electrolyte contained in the catalyst layer plays a role of improving the mobility of protons moving from the fuel electrode catalyst layer 5 to the polymer electrolyte membrane 4 and the oxidant electrode catalyst layer 7 as power generation proceeds. Examples of the electrolyte having proton conductivity include fluorine-based resins such as perfluorocarbon polymers having sulfonic acid groups, organic materials such as hydrocarbon resins having sulfonic acid groups, or organic-inorganic composite materials. . Specifically, the electrolyte includes Nafion (manufactured by DuPont), Flemion (manufactured by Asahi Glass Co., Ltd.), Aciplex (manufactured by Asahi Kasei Kogyo Co., Ltd.), and the like. The electrolyte having proton conductivity is not limited to these. For example, a copolymer of a trifluorostyrene derivative, polybenzimidazole impregnated with phosphoric acid, aromatic polyether ketone sulfonic acid, or aliphatic It can be comprised with the electrolyte which can transport protons, such as hydrocarbon resin. The catalyst layer does not need to have a single layer structure as shown in FIG. 1, and may have a multilayer structure having two or more layers.

  Next, components other than the catalyst layer will be described.

  The polymer electrolyte membrane 4 is a proton conductive membrane disposed between the fuel electrode catalyst layer 5 and the oxidant electrode catalyst layer 7. The polymer electrolyte membrane 4 has a function of selectively transmitting protons generated in the fuel electrode catalyst layer 5 to the oxidant electrode catalyst layer 7 along the film thickness direction. The polymer electrolyte membrane 4 also has a function as a partition wall that prevents mixing of the fuel gas supplied to the fuel electrode side and the oxidant gas supplied to the oxidant electrode side. As the electrolyte contained in the polymer electrolyte membrane 4, electrolytes having proton conductivity as mentioned above can be used.

  The fuel electrode diffusion layer 6 and the oxidant electrode diffusion layer 8 are respectively arranged outside the catalyst layer so as to sandwich the electrolyte membrane and the catalyst layer. That is, the fuel electrode diffusion layer 6 is laminated on the surface of the fuel electrode catalyst layer 5 opposite to the polymer electrolyte membrane 4 side. On the other hand, the oxidant electrode diffusion layer 8 is laminated on the surface of the oxidant electrode catalyst layer 7 opposite to the polymer electrolyte membrane 4.

  The fuel electrode diffusion layer 6 plays a role of uniformly supplying fuel to the fuel electrode catalyst layer 5 and also functions as a current collector of the fuel electrode catalyst layer. The oxidant electrode diffusion layer 8 serves to uniformly supply the oxidant to the oxidant electrode catalyst layer 7 and also functions as a current collector for the oxidant electrode catalyst layer.

  The diffusion layer is generally made of a porous material. The fuel electrode diffusion layer 6 and the oxidant electrode diffusion layer 8 are made of a sheet material made of carbon paper, carbon cloth, nonwoven fabric, carbon woven fabric, paper-like paper body, felt, or the like.

  The diffusion layer preferably exhibits functions such as electron conductivity and water repellency. When the diffusion layer has excellent electron conductivity, electrons generated by the power generation reaction are effectively transported, and the power generation performance of the fuel cell is improved. Further, when the diffusion layer has excellent water repellency, the generated water is efficiently discharged. In order to ensure high water repellency, a technique for repelling the material constituting the diffusion layer has also been proposed. For example, there is a method in which a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) is applied to a material constituting a gas diffusion layer such as carbon paper and dried in the air or an inert gas such as nitrogen. At this time, carbon powder may be mixed in the solution in order to further improve the water repellency.

  The Gurley number of the fuel electrode diffusion layer 6 is preferably 18 sec or less. Since the Gurley number is small, the gas diffusibility of the fuel electrode is improved. Therefore, if a fuel electrode diffusion layer with a small Gurley number is used, the gas diffusibility in the vicinity of the metal particles is improved even if the area of the catalyst that normally functions due to CO adsorption is reduced, thereby suppressing a decrease in the cell voltage. Is done. On the other hand, a gas diffusion layer such as carbon paper is necessary for sandwiching and holding the fuel electrode catalyst layer, the polymer electrolyte membrane, and the oxidant electrode catalyst layer, and cannot be omitted. Further, the Gurley number becomes larger than 0 by providing the gas diffusion layer. From the above, the Gurley number of the fuel electrode diffusion layer 6 is preferably larger than 0 sec and not longer than 18 sec.

  The seal portion 11 is disposed on the outer periphery of the fuel electrode diffusion layer 6 and the oxidant electrode diffusion layer 8 and has a function of preventing leakage of supplied fuel gas or oxidant gas from the catalyst layer and the diffusion layer.

  The material constituting the seal portion 11 is not particularly limited as long as it is a material that does not allow gas, particularly oxygen or hydrogen to permeate. For example, a rubber material such as fluorine rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, Polymer materials such as polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVdF) can be used.

  The separator is a porous member made of carbon or metal as a constituent material, and is disposed outside the membrane electrode assembly including the fuel electrode 2, the oxidant electrode 3, and the polymer electrolyte membrane 4. A fuel electrode separator 9 is disposed on the fuel electrode side, and an oxidant electrode separator 10 is disposed on the oxidant electrode side. The fuel electrode separator 9 is provided with a fuel gas flow path 9a for introducing fuel gas and a refrigerant body flow path 9b through which the refrigerant passes, and the oxidant electrode separator 10 has an oxidant gas flow for introducing oxidant gas. A passage 10a and a refrigerant passage 10b through which the refrigerant passes are provided.

  As described above, a fuel cell is generally composed of a stack formed by stacking a plurality of unit cells each having a structure as shown in FIG. The separator has a function of flowing fluids such as a fuel gas, an oxidant gas and a refrigerant, and a function of maintaining the mechanical strength of the stack, in addition to the function of electrically connecting the single cells in series. Further, a fuel gas (or oxidant gas) that flows through the separator, and an oxidant gas (or fuel gas) that flows through the separators of other cells disposed adjacently through the separator, It also has a reactive gas blocking function to prevent mixing through the separator. Furthermore, the heat generated by the cell power generation can be removed by flowing the coolant through the coolant channel provided in the separator.

  The material of the fuel electrode separator 9 and the oxidant electrode separator 10 is not particularly limited as long as it has conductivity. For example, a carbon material such as dense carbon graphite and a carbon plate, and a metal material such as stainless steel are used. Can do. More preferably, it is made of a porous material.

  The method for producing the fuel cell shown in FIG. 1 described above is not particularly limited, and can be produced by a method known in the art.

  Next, a fuel cell system including the fuel cell will be described with reference to FIG. FIG. 3 is a conceptual diagram of the fuel cell system according to the embodiment.

  The fuel cell system 100 includes a fuel cell 1 that generates power by reacting fuel gas and air, a fuel reforming system 12, an air blower 13, a cooling water supply system 16, and a control system 17 connected to the fuel cell 1. It comprises. As the fuel cell 1, the fuel cell shown in FIG. 1 described above is used. The fuel reforming system 12 for supplying the fuel gas to the fuel electrode 2 of the fuel cell 1 is connected to the upstream end of the fuel gas supply path 18, and the fuel gas supply path 18 is a fuel gas flow path provided in the fuel electrode separator. Its downstream end is in communication. An air blower 13 for supplying air to the oxidant electrode 3 of the fuel cell 1 is connected to the upstream end of the oxidant gas supply path 19, and the oxidant gas supply path 19 is an oxidant gas provided in the oxidant electrode separator. The downstream end communicates with the flow path. A coolant supply system 16 that supplies a coolant to the fuel cell 1 is connected to a coolant flow path provided in a separator of the fuel cell 1 via a coolant supply path 20. The control system 17 is connected to the fuel cell 1 and controls the operation of the fuel cell system 100.

  The fuel reforming system 12 is a system for reforming a hydrocarbon-based gas such as city gas into a gas containing hydrogen, and the produced fuel gas is provided in the separator of the fuel cell 1 through the fuel gas supply path 18. Supplied to the fuel gas flow path. The fuel reforming system 12 generally comprises at least a reformer, a CO converter and a CO selective oxidation reactor. However, in the fuel reforming system 12 in this embodiment, the CO selective oxidation reactor is omitted.

The CO selective oxidation reactor is a device having a function of reducing CO concentration in fuel gas by converting CO contained in fuel gas into CO ₂ by reacting with air. Therefore, if the CO selective oxidation reactor is omitted, the CO concentration in the fuel gas supplied to the fuel electrode of the fuel cell is as high as 100 to 500 ppm. When a fuel gas having a high CO concentration is introduced into the fuel electrode, various problems as described above occur.

  However, as described above, in the fuel cell described in the above embodiment used here, the metal particles having a catalytic action in the fuel electrode have a predetermined effective reaction area, so that fuel gas containing high concentration CO is used as fuel. Even if it is supplied to the pole, it is possible to maintain the output and tolerance. Therefore, in the fuel cell system using this fuel cell, the CO selective oxidation reactor can be omitted. As a result of omitting the CO selective oxidation reactor in this way, the fuel cell system can be simplified and the cost can be reduced.

  Next, the operation method of the fuel cell described above will be described with reference to FIG. 1 and FIG.

The fuel gas reformed in the fuel reforming system 12 passes through the fuel gas channel 9 a of the fuel electrode separator 9, diffuses in the fuel electrode diffusion layer 6, and reaches the fuel electrode catalyst layer 5. Hydrogen in the fuel gas generates protons and electrons by a hydrogen oxidation reaction on the metal particles of the fuel electrode catalyst layer 5. Protons reach the oxidant electrode catalyst layer 7 via the polymer electrolyte membrane 4, and electrons flow to the external load device 14. The fuel reforming system 12 in the present fuel cell system is simplified by eliminating the CO selective oxidation reactor. Therefore, the CO concentration in the fuel gas supplied to the fuel electrode 2 is as high as 100 ppm to 500 ppm. However, since the metal particles of the fuel electrode catalyst layer 5 have an effective reaction area of 70 cm ² or more, the hydrogen oxidation reaction Is not disturbed. That is, even if CO is adsorbed on the surface of the metal particles in the fuel electrode catalyst layer 5, a sufficient effective reaction area remains, so that the hydrogen oxidation reaction is not hindered.

A small amount of oxygen may be additionally supplied to the fuel electrode 2 for the purpose of oxidizing and removing CO adsorbed on the metal particles. The fuel electrode oxidant additional supply device 15 mixes the fuel gas with a minute amount of air to supply air to the fuel electrode, and oxidizes and removes CO adsorbed to the metal particles in the fuel electrode catalyst layer 5 to CO _2. It has a function. As the fuel electrode oxidant additional supply device 15, an air blower 13 that supplies air to the oxidant electrode 3 may be used. Air is supplied to the oxidizer electrode 3 from the air blower 13. The air passes through the oxidant gas channel 10 a of the oxidant electrode separator 10, diffuses in the oxidant electrode diffusion layer 8, and reaches the oxidant electrode catalyst layer 7. Oxygen in the air, protons supplied from the fuel electrode catalyst layer 5 via the polymer electrolyte membrane 4, and electrons supplied from the fuel electrode catalyst layer 5 via the external load device 14 Oxygen reduction reaction occurs on the metal particles of the electrode catalyst layer 7 to generate water.

  As for the additional air flow rate supplied from the fuel electrode oxidant additional supply device 15, the larger the amount, the lower the cell voltage drop due to the high concentration CO. However, if the air in the fuel electrode becomes excessive, it may cause a direct combustion reaction with hydrogen in the fuel gas, which may cause a shortage of hydrogen gas locally by increasing the hydrogen utilization rate in the fuel electrode. Therefore, the additional air flow rate is preferably 0.5 to 3 v / v% with respect to the fuel gas.

  The pressure of the refrigerant passing through the refrigerant passages provided in the fuel electrode separator 9 and the oxidant electrode separator 10 is the same as that of the fuel gas and the oxidation passing through the fuel gas passage 9a and the oxidant gas passage 10a provided in the separator. The pressure is preferably lower than the pressure of the agent gas. This is because the fuel electrode separator 9 and the oxidant electrode separator 10 suck out excess water in the polymer electrolyte membrane, the catalyst layer, the diffusion layer, and the gas flow path into the cooling water flow path due to the pressure difference between the gas and the refrigerant body, This is because inhibition of gas diffusion caused by excess water is suppressed. As a result, the gas diffusibility of the fuel electrode is improved, and even if the effective reaction area of the catalyst is reduced by the adsorption of CO, the decrease in the cell voltage is suppressed by improving the gas diffusibility in the vicinity of the metal particles. The

  Specifically, it is preferable that the pressure of the refrigerant body is −5 kPa to −50 kPa with respect to the gas pressure. This is because if the pressure difference is too small, excess water in the battery cannot be sucked, and if the pressure difference is too large, the gas used for the reaction is sucked into the cooling water flow path.

  In addition, the temperature of the coolant inlet in the coolant channel (hereinafter also referred to as battery temperature) is preferably 60 ° C. or higher and lower than 100 ° C. The higher the battery temperature, the smaller the battery voltage drop due to CO. In particular, by setting the battery temperature to 60 ° C. or higher, the output and durability of the fuel cell can be maintained even when high concentration CO is supplied to the battery. On the other hand, when the battery temperature is 100 ° C. or higher, the cooling water boils when water is used as the refrigerant, making it difficult to continue the operation of the fuel cell. The battery temperature is more preferably 60 to 80 ° C.

<Example 1>
A fuel cell was prepared as shown below.

  The fuel electrode diffusion layer is obtained by mixing a carbon paper and an ink obtained by mixing carbon powder and polytetrafluoroethylene having an average particle diameter of 0.3 μm in a solid content weight ratio of 6: 4 with a doctor blade method after drying. It produced by apply | coating so that thickness might be set to 20 micrometers.

  The fuel electrode catalyst layer is a mixed solution of a catalyst in which a platinum-ruthenium alloy (platinum to ruthenium molar ratio of 1: 2), which is metal particles having a particle diameter of 1 to 5 nm, is supported on carbon, and Nafion D520 (manufactured by DuPont). Ink was formed and applied by applying the ink on the fuel electrode diffusion layer by a doctor blade method. The weight ratio of catalyst to Nafion was 2: 1.

  The oxidant electrode diffusion layer is obtained by drying, using a doctor blade method, an ink obtained by mixing carbon paper and polytetrafluoroethylene having an average particle diameter of 0.3 μm in a solid content weight ratio of 6: 4. It was produced by coating so that the thickness of the film became 20 μm.

  The oxidant electrode catalyst layer creates an ink composed of a mixed solution of a catalyst in which platinum, which is a metal particle having a particle diameter of 1 to 8 nm, is supported on carbon, and Nafion D520 (manufactured by DuPont). It was formed by applying a doctor blade method on the pole diffusion layer. The weight ratio of catalyst to Nafion was 2: 1.

As the polymer electrolyte membrane, NR211 (manufactured by DuPont) was used. The electrolyte membrane, the fuel electrode, and the oxidant electrode were overlapped so that the fuel electrode catalyst layer and the oxidant electrode catalyst layer were on the electrolyte membrane side, and these were integrated by thermocompression bonding. The thermocompression bonding was performed at a temperature of 135 ° C. and a pressure of 20 kgfcm ⁻² for 2 minutes.

  The membrane electrode assembly produced as described above was sandwiched between a fuel electrode separator and an oxidant electrode separator in which a gas channel and a refrigerant channel were formed, to obtain a fuel cell (single cell). Also, 50 unit cells were stacked to form a fuel cell stack.

(Test Example 1)
For the fuel cell of Example 1, the amount of cell voltage drop when the effective reaction area Z of the catalyst in the fuel electrode catalyst layer was changed was measured. The catalytic effective reaction area Z was adjusted by changing the particle size of the metal used, the metal concentration in the catalyst, the amount of catalyst, and the like. In Test Example 1, the temperature of the refrigerant supplied to the fuel cell 1 was 65 ° C., and the CO concentration contained in the fuel gas supplied to the fuel electrode was 100 ppm.

FIG. 4 is a diagram showing the relationship between the effective reaction area Z of the catalyst per unit area and the cell voltage drop amount in Test 1. FIG. The effective reaction area Z of the catalyst per unit area means the effective reaction area of the catalyst per 1 cm ^{2 in} the planar direction of the fuel electrode catalyst layer. The amount of cell voltage drop is the difference between the cell voltage when CO is not supplied and the cell voltage when CO is supplied. The larger the cell voltage drop amount, the lower the CO tolerance of the fuel cell, and the lower the output of the fuel cell. Hereinafter, when the terms “effective reaction area of the catalyst per unit area” and “cell voltage drop amount” are used, they have the same meaning as described above.

When Z is less than 70 cm ^{2, the} amount of cell voltage decrease is significantly large, and the output decreases to the extent that power generation by the fuel cell cannot be continued. On the other hand, when Z is larger than 150 cm ^{2, the} amount of cell voltage decrease decreases as Z increases, but the amount of decrease is small, so that the increased performance of the metal particles can be fully exhibited. However, the cost increases due to the increase in metal particles.

(Test Example 2)
With respect to the fuel cell of Example 1, the effective reaction area Z of the catalyst in the fuel electrode catalyst layer was changed, and the relative ratio of the cross leak amount after the high concentration CO supply continuous power generation test was measured. Adjustment of the effective reaction area of the catalyst was carried out in the same manner as in Test Example 1. The result is shown in FIG.

FIG. 5 is a diagram showing the relationship between the effective reaction area Z of the catalyst per unit area and the relative ratio of the cross leak amount. An increase in the amount of cross leak indicates that the deterioration of the polymer electrolyte membrane is progressing. It can be seen that the fuel cell with a Z smaller than 70 cm ² significantly increases the amount of cross leak. This is caused by the fact that high concentration of CO is adsorbed on the catalyst in the fuel electrode catalyst layer, that is, the metal particles, and the surface area of the metal particles is reduced, and the fuel electrode passes through the polymer electrolyte membrane from the oxidant electrode. This is because the amount of hydrogen peroxide generated increases when oxygen diffused in the gas causes a reduction reaction on the metal particles in the fuel electrode catalyst layer. Hydrogen peroxide is known as a substance that promotes deterioration of the polymer electrolyte membrane. On the other hand, in the fuel cell in which Z is 70 cm ² or more, the cross leak amount is not increased.

From Test Examples 1 and 2, the fuel electrode catalyst layer has an effective reaction area of the catalyst per unit area of 70 cm ² or more, so that even if fuel gas containing a high concentration of CO is supplied, It can be said that a decrease in output is suppressed and durability can be maintained. Therefore, when the effective reaction area of the catalyst is within the above range, the CO selective oxidation reactor can be omitted from the fuel reforming system. As a result, the system can be simplified and the cost can be reduced. In addition, by setting the effective reaction area of the catalyst in the fuel electrode catalyst layer to 150 cm ² or less per 1 cm ² of the area in the plane direction of the fuel electrode catalyst layer, excessive metal particles are not used, thereby reducing extra cost. be able to.

(Test Example 3)
In Test Example 1, the power generation condition of the fuel cell was changed, and the amount of cell voltage drop when the effective reaction area Z of the catalyst in the fuel electrode catalyst layer was changed was measured. Specifically, the cell temperature was 80 ° C., the CO concentration in the fuel gas supplied to the fuel electrode was 500 ppm, and additional air was supplied at a flow rate of 3 v / v% with respect to the fuel gas. Other test conditions were the same as in Test Example 1. The results are shown in FIG.

FIG. 6 is a graph showing the relationship between the effective reaction area Z of the catalyst per unit area and the cell voltage drop amount in Test 3. FIG. It is known that the amount of cell voltage drop due to CO remarkably depends on the temperature of the fuel cell and the additional supply air flow rate. FIG. 6 shows that even under the power generation conditions of Test Example 3, when the effective reaction area Z of the catalyst is smaller than 70 cm ^{2, the} amount of cell voltage drop increases significantly. It can be seen that when Z is larger than 150 cm ² , the change in the cell voltage drop is small, and the effect of increasing the metal particles as the catalyst is small. From this, it can be seen that even if the power generation conditions of the fuel cell are changed, the dependence of the cell voltage drop amount due to CO on the catalytic effective reaction area Z does not change.

(Test Example 4)
Regarding the fuel cell of Example 1, the correlation between the coolant inlet temperature of the fuel electrode separator, that is, the cell temperature, and the cell voltage drop amount was examined. As power generation conditions, a fuel gas containing 500 ppm of CO was supplied to the battery, and additional air at a flow rate of 3 v / v% was supplied to the fuel gas. Measurements effective reaction area Z per unit area of the catalyst in the anode catalyst layer is performed on the single cells of 70cm ² and 150 cm ^2. The results are shown in FIG.

  FIG. 7 is a diagram showing the relationship between the battery temperature and the cell voltage drop amount. Assuming that the maximum allowable value of the cell voltage drop when supplying 500 ppm of CO is 50 mV, it can be said from FIG. 7 that the battery temperature is preferably 60 ° C. or higher.

(Test Example 5)
In Test Example 5, the influence on the fuel cell when the content of ruthenium contained in the metal particles of the fuel electrode catalyst was changed was examined. As a comparative example, a fuel cell in which the ruthenium content in the metal particles was 75 at%, 66 at%, and 60 at% in a molar ratio was produced in the same manner as in Example 1. About these fuel cells, the cell temperature was measured when the cell temperature was 80 ° C. and the fuel gas containing 500 ppm of CO was supplied to the fuel electrode. The results are shown in FIG.

  FIG. 8 is a diagram showing the relationship between the ruthenium content in the metal particles and the cell voltage drop. In the order of 75 at% Ru, 66 at% Ru, and 60 at% Ru, it can be said that the cell voltage decrease amount is small and the CO resistance is high. This is due to the fact that the CO adsorption energy of the metal particles has decreased due to the large amount of Ru. From the above, it can be said that it is preferable that the ruthenium content in the metal particles is 66 to 75 at% in terms of molar ratio in that it constitutes a fuel electrode catalyst layer with high CO resistance and suppresses a decrease in output due to CO.

(Test Example 6)
In Test Example 6, the influence on the fuel cell when the anode diffusion layer having different Gurley numbers was applied was examined. A fuel cell using a fuel electrode diffusion layer having Gurley numbers of 18 sec and 35 sec was produced in the same manner as in Example 1. About these fuel cells, the time change of the cell voltage when the fuel gas containing high concentration CO was introduced was measured. The Gurley number was measured by a method generally used in this field. The results are shown in FIG.

  FIG. 9 is a diagram showing the time change of the unit cell voltage when the high concentration CO supply continuous power generation test is performed on the fuel cell to which the fuel electrode diffusion layer having different Gurley numbers is applied. Regarding the fuel cell to which the fuel electrode diffusion layer having the Gurley number of 18 sec is applied, it can be seen that the cell voltage drop is small.

<Example 2>
A fuel cell system as shown in FIG. 3 was constructed using the fuel cell of Example 1. When operating this fuel cell, the pressure of the refrigerant passing through the refrigerant passage provided in the separator was maintained lower than the pressure of the fuel gas and the oxidant gas passing through the fuel gas passage and the oxidant gas passage. . Specifically, the pressure of the refrigerant body was set to −14 kPa with respect to the gas pressure. In addition, water was used as the refrigerant body.

(Test Example 5)
Regarding the fuel cell system of Example 2, the influence on the fuel cell when a fuel gas containing a high concentration of CO was supplied was examined. The cell temperature was 80 ° C., and the amount of cell voltage drop was measured when fuel gas containing 500 ppm of CO was supplied to the fuel electrode. The results are shown in FIG.

  FIG. 10 is a diagram comparing the cell voltage drop amount of the fuel cell in the case of using the operation method of Example 2 and the case of using the conventional operation method. In the operation method of Example 2, the amount of cell voltage drop due to CO was smaller than in the conventional operation method.

  According to the above-described embodiment or example, it is possible to provide a fuel cell capable of maintaining output and durability even when a fuel gas containing high-concentration CO is introduced into the fuel electrode. Further, since the CO selective oxidation apparatus in the fuel reforming system can be omitted, the fuel cell system can be simplified and the cost can be reduced.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell, 2 ... Fuel electrode, 3 ... Oxidant electrode, 4 ... Polymer electrolyte membrane, 5 ... Fuel electrode catalyst layer, 6 ... Fuel electrode diffusion layer, 7 ... Oxidant electrode catalyst layer, 8 ... Oxidant electrode Diffusion layer, 9 ... Fuel electrode separator, 9a ... Fuel gas flow path, 9b ... Refrigerant body flow path, 10 ... Oxidant electrode separator, 10a ... Oxidant gas flow path, 10b ... Refrigerant body flow path, 11 ... Seal part, DESCRIPTION OF SYMBOLS 12 ... Fuel reforming system, 13 ... Air blower, 14 ... External load apparatus, 15 ... Fuel electrode oxidant additional supply apparatus, 16 ... Refrigerant body supply system, 17 ... Control system, 18 ... Fuel gas supply path, 19 ... Oxidation Agent gas supply path, 20 ... refrigerant supply path, 100 ... fuel cell system.

Claims (7)

An anode,
An oxidizer electrode;
A polymer electrolyte membrane disposed between the fuel electrode and the oxidant electrode;
A fuel cell comprising a fuel electrode separator and an oxidant electrode separator disposed respectively outside the fuel electrode and the oxidant electrode;
The fuel electrode includes a fuel electrode diffusion layer on the fuel electrode separator side and a fuel electrode catalyst layer on the polymer electrolyte membrane side, and the fuel electrode catalyst layer is a fuel electrode catalyst in which metal particles are supported on a carrier. wherein the said metallic particles comprise a second metal other than platinum and platinum, the effective reaction area of the metal particles is a planar direction of the area of 1 cm ² per 70～150Cm ² of the fuel electrode catalyst layer, the fuel The fuel gas supplied to the electrode includes 100 to 500 ppm of carbon monoxide.   2. The fuel cell according to claim 1, wherein the metal particles are composed of platinum and ruthenium, and a ratio of ruthenium in the metal particles is 66 to 75 at% in a molar ratio.   The fuel cell according to claim 1, wherein the fuel electrode diffusion layer has a Gurley number of 18 sec or less. The fuel cell according to any one of claims 1 to 3,
A fuel reforming system for reforming raw fuel to generate a fuel gas, and supplying the fuel gas to the fuel electrode through a fuel gas flow path provided in the fuel electrode separator;
A fuel cell system comprising an air blower for supplying air as an oxidant gas to the oxidant electrode through an oxidant gas flow path provided in the oxidant electrode separator,
The fuel reforming system does not include a CO selective oxidation reactor that selectively oxidizes and removes carbon monoxide (CO) contained in the fuel gas.   5. The fuel electrode separator and the oxidant electrode separator are porous, and a refrigerant body flow path through which a refrigerant body passes is provided in at least one of the fuel electrode separator and the oxidant electrode separator. In the fuel cell separator, in the fuel electrode separator, the pressure of the coolant passing through the coolant flow path is lower than the pressure of the fuel gas passing through the fuel gas flow path, and the oxidant electrode In the separator, the pressure of the refrigerant passing through the refrigerant passage is lower than the pressure of the oxidant gas passing through the oxidant gas passage.   6. The method of operating a fuel cell system according to claim 5, wherein the temperature of the coolant inlet of the coolant channel is 60 ° C. or higher and lower than 100 ° C.   The method of operating a fuel cell system according to claim 5 or 6, wherein 0.5 to 3 v / v% of additional air with respect to the fuel gas is supplied to the fuel electrode.

Images