Fuel cell system

Abstract

To improve the energy efficiency of fuel cells during startup. [Solution] The fuel cell system 1 has a fuel cell stack 2 that is an internal reforming type in which multiple power generation units are stacked and supplied with fuel gas and oxidizer gas to generate electricity, and the supplied fuel gas can be reformed internally using a reforming catalyst. When a power generation request occurs, the fuel cell system 1 determines whether or not to generate electricity in the fuel cell stack 2 based on the electrical resistance value of the fuel cell stack 2 obtained. The fuel cell system 1 can start generating electricity at an appropriate timing and can suppress the starting energy to the minimum necessary.

Description

Technical Field

[0001] The present invention relates to a fuel cell system.

Background Art

[0002] For example, Patent Document 1 discloses a technique for controlling the temperature of a fuel cell by the heat generation of partial oxidation reforming of a fuel cell stack based on the temperature of an oxidant gas discharged from a cell stack having a reforming catalyst.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in Patent Document 1, the oxidation state and reduction state of the reforming catalyst in the cell stack when starting power generation in the fuel cell are unknown. Therefore, in Patent Document 1, the partial oxidation reforming of the cell stack is carried out for a longer time than necessary, and there is a risk that extra energy is consumed for the partial oxidation reforming of the cell stack and the performance deteriorates.

Means for Solving the Problems

[0005] The fuel cell system of the present invention is characterized by including: an internally reforming type fuel cell stack in which a plurality of power generation units that supply fuel gas and oxidant gas to generate power are stacked and the supplied fuel gas can be reformed internally using a reforming catalyst; a control unit that controls the amount of fuel gas and the amount of oxidant gas supplied to the fuel cell stack; a resistance detection unit that detects the electrical resistance of the fuel cell stack; and a power generation availability determination unit that determines the availability of power generation in the fuel cell stack based on the electrical resistance value of the fuel cell stack obtained when a predetermined power generation request occurs.

Effects of the Invention

[0006] According to the present invention, the timing at which the reduction of the anode electrode is completed and fuel reforming is sufficiently performed can be accurately determined from the electrical resistance value of the fuel cell stack. Therefore, the fuel cell system can start generating power at the appropriate time and suppress the startup energy to the minimum necessary. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram illustrating the outline of a fuel cell system according to the first embodiment of the present invention. [Figure 2] A schematic diagram illustrating the configuration of a power generation unit. [Figure 3] A characteristic diagram showing an example of the change in the resistance value (electrical resistance value) of the anode electrode of a fuel cell. [Figure 4] A schematic diagram illustrating the correlation between the weight and resistance of the anode electrode. [Figure 5] A timing chart showing an example of how various parameters change when a fuel cell stack is warmed up. [Figure 6] A flowchart illustrating the control flow when a power generation request is received by a fuel cell system. [Figure 7] A schematic diagram illustrating the outline of a fuel cell system according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0008] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Figure 1 is a schematic diagram illustrating the outline of a fuel cell system 1 according to a first embodiment of the present invention.

[0009] The fuel cell system 1 is installed as a power source in vehicles such as automobiles, and generates electricity by supplying fuel gas and oxidizer gas (e.g., air). Here, the fuel gas includes, for example, hydrocarbons. The fuel cell system 1 can also be applied to power sources other than vehicles.

[0010] The fuel cell system 1 comprises a so-called internal reforming type fuel cell stack 2, a GPU (Gas Processing Unit) 3, a fuel supply device 4, a blower 5, and a control unit 6.

[0011] The fuel cell stack 2 is a solid oxide fuel cell stack (SOFC stack) composed of multiple sheet-shaped power generation units 21 (described later) stacked with separators 22 (described later) in between. In the fuel cell stack 2, by stacking (stacking) multiple power generation units 21, anode channels 28 (described later) through which fuel gas flows and cathode channels 29 (described later) through which oxidizer gas flows are alternately formed in the stacking direction of the power generation units 21. In addition, in the fuel cell stack 2, anode channels 28 through which fuel gas flows and cathode channels 29 through which oxidizer gas flows are formed with separators 22 in between in the stacking direction of the power generation units 21. The fuel cell stack 2 has separators 22. The fuel cell stack 2 can generate electricity by supplying fuel gas and oxidizer gas to these anode channels 28 and cathode channels 29, respectively.

[0012] Figure 2 is a schematic diagram illustrating the configuration of the power generation unit 21. As shown in Figure 2, the power generation unit 21 has a metal support layer 23, a reforming catalyst layer 24, an anode electrode layer (anode electrode) 25, an electrolyte layer 26, and a cathode electrode layer (cathode electrode) 27. The anode electrode layer 25 and the cathode electrode layer 27 are electrode layers for power generation. In a fuel cell stack 2 formed by stacking multiple power generation units 21, the anode electrode layer 25 of the power generation unit 21 faces the anode flow path 28 and is exposed to the flow (fuel gas) in the anode flow path 28. In a fuel cell stack 2 formed by stacking multiple power generation units 21, the cathode electrode layer 27 of the power generation unit 21 faces the cathode flow path 29 and is exposed to the flow (oxidizer gas) in the cathode flow path 29.

[0013] The metal support layer 23 is made of a porous metal material, and its surface is covered with platinum as a reforming catalyst. In other words, a reforming catalyst is placed in the metal support layer 23. The base metal material of the metal support layer 23 can be, for example, iron, chromium, nickel, titanium, or ferritic stainless steel.

[0014] The metal support layer 23 has a modified catalyst layer 24, an anode electrode layer 25, an electrolyte layer 26, and a cathode electrode layer 27 stacked in that order on one surface 23a, and a separator 22 is placed on the other surface 23b.

[0015] The reforming catalyst layer 24 is made of, for example, platinum. The platinum in the reforming catalyst layer 24 corresponds to the reforming catalyst. The reforming catalyst layer 24 faces one side of the metal support layer 23 and is positioned on the surface of the anode electrode layer 25 located on one side of the metal support layer 23. In other words, the reforming catalyst layer 24 is sandwiched between the metal support layer 23 and the anode electrode layer 25.

[0016] The anode electrode layer 25 is made of a porous metal material and has platinum added as a reforming catalyst. In other words, a reforming catalyst is placed in the anode electrode layer 25. The base metal material of the anode electrode layer 25 is, for example, nickel, cobalt, etc.

[0017] The electrolyte layer 26 is made of solid oxide ceramic and has the function of separating fuel gas and oxidant gas.

[0018] The cathode electrode layer 27 is made of a metal material. The metal material serving as the base material of the cathode electrode layer 27 is, for example, lanthanum, strontium, manganese, cobalt, etc.

[0019] Reference numeral 22 in FIG. 2 is the separator described above. The separator 22 is a corrugated plate-shaped member made of a conductive metal material. In the fuel cell stack 2, the power generation unit 21 is laminated so that the other surface of the metal support layer 23 and the cathode electrode layer 27 face each other with the separator 22 interposed therebetween. In the fuel cell stack 2, in the stacking direction of the power generation unit 21, the anode flow path 28 and the cathode flow path 29 are formed on both sides thereof with the separator 22 interposed therebetween. One surface of the separator 22 forming the anode flow path 28 is covered with platinum as a reforming catalyst. That is, a reforming catalyst is disposed on the separator 22. The reforming catalyst reforms the fuel gas in the fuel cell stack 2 to generate hydrogen.

[0020] The GPU 3 is configured by integrating a combustor 3a that catalytically burns the fuel gas (anode off-gas) that has passed through the fuel cell stack 2 and a heat exchanger 3b (not shown) that heats the oxidant gas supplied to the fuel cell stack 2 with the heat obtained by burning the fuel gas in the combustor 3a.

[0021] The fuel supply device 4 is a supply source of fuel gas. The fuel supply device 4 includes, for example, a fuel tank (not shown), an injector capable of adjusting the supply amount of fuel gas, and the like.

[0022] The fuel supply device 4 can directly supply fuel gas to the combustor 3a of the GPU 3 via the second fuel supply path 8, described later, before power generation starts (during warm-up) when a predetermined power generation request occurs from the fuel cell stack 2. A power generation request occurs, for example, when the charge amount (battery SOC) of the battery, which is charged with electricity generated by the fuel cell system 1, falls below a predetermined amount. When the fuel supply device 4 supplies fuel gas to the fuel cell stack 2, for example, it may stop supplying fuel from the fuel supply device 4 to the GPU 3. Also, when the fuel supply device 4 supplies fuel gas to the GPU 3, for example, it may stop supplying fuel from the fuel supply device 4 to the fuel cell stack 2.

[0023] Blower 5 pumps oxidizing gas towards the cathode flow path 29, and the flow rate of the oxidizing gas is adjustable.

[0024] The control unit 6 is a well-known digital computer equipped with a CPU, ROM, RAM, and input / output interfaces. The control unit 6 controls the amount of fuel gas supplied to the fuel cell stack 2 by controlling the fuel supply device 4. The control unit 6 also controls the flow rate of oxidizer gas by controlling the operation of the blower 5. In other words, the control unit 6 corresponds to a control unit that controls the amount of fuel gas and oxidizer gas supplied to the fuel cell stack 2.

[0025] The gas flow paths of the fuel cell system 1 are a first fuel supply path 7, a second fuel supply path 8, an anode off gas path 9, an air supply path 10, a cathode gas path 11, a cathode off gas path 12, a combustion gas supply path 13, an exhaust path 14, and a POx path 15.

[0026] The first fuel supply line 7 corresponds to the anode line and is a passage connecting the fuel supply device 4 to the inlet of the anode flow path 28 in the fuel cell stack 2, supplying fuel gas to the fuel cell stack 2. The fuel gas supplied to the fuel cell stack 2 from the first fuel supply line 7 is reformed within the fuel cell stack 2.

[0027] The second fuel supply passage 8 is a passage connecting the fuel supply device 4 and the combustion gas flow path (not shown) of the combustor 3a in the GPU 3, and directly supplies fuel gas to the combustor 3a. Fuel gas is supplied to the GPU 3 via the second fuel supply passage 8, for example, before the fuel cell stack 2 starts generating power (during warm-up).

[0028] The anode off-gas passage 9 is a passage that connects the outlet of the anode flow path 28 in the fuel cell stack 2 to the combustion gas supply passage 13.

[0029] The air supply passage 10 is a passage that sends outside air as an oxidizing gas to the air passage (not shown) inside the GPU 3 via the blower 5, thereby supplying the oxidizing gas to the GPU 3. As described above, the oxidizing gas supplied to the GPU 3 is heated through heat exchange with the combustion gas burned inside the GPU 3.

[0030] The cathode gas passage 11 corresponds to the first cathode line and is a passage connecting the outlet of the air passage of the GPU 3 to the inlet of the cathode passage 29 in the fuel cell stack 2. The cathode gas passage 11 supplies the oxidizer gas heated by the GPU 3 to the fuel cell stack 2. That is, the fuel cell stack 2 is supplied with fuel gas from the first fuel supply passage 7 and with oxidizer gas from the cathode gas passage 11. This enables the fuel cell stack 2 to generate electricity.

[0031] The cathode-off gas passage 12 is a passage that connects the outlet of the cathode flow path 29 in the fuel cell stack 2 to the combustion gas supply passage 13. The cathode-off gas passage 12 supplies the cathode-off gas discharged from the fuel cell stack 2 to the combustion gas supply passage 13.

[0032] The combustion gas supply passage 13 is a passage that connects the anode-off gas passage 9 and the cathode-off gas passage 12 to the inlet of the combustion gas flow path (not shown) of the GPU3. Within the combustion gas supply passage 13, the anode-off gas (fuel gas) supplied from the anode-off gas passage 9 and the cathode-off gas (oxidizer gas) supplied from the cathode-off gas passage 12 are mixed. The mixed gas in the combustion gas supply passage 13 is supplied as combustion gas to the combustion gas flow path of the GPU3. The combustion gas supplied to the GPU3 from the combustion gas supply passage 13 burns within the GPU3 and becomes harmless exhaust gas, which is discharged to the outside via the exhaust passage 14.

[0033] When power generation begins in the fuel cell system 1, a combustion gas mixture of fuel gas and an oxidizer gas for burning the fuel gas is supplied to the combustion gas flow path of the GPU 3 from the combustion gas supply path 13.

[0034] Furthermore, when the fuel cell system 1 starts generating power, the fuel gas and oxidizer gas may be supplied to the GPU 3 using the anode-off gas passage 9 and the cathode-off gas passage 12. Alternatively, a separate gas passage connected to the combustion gas supply passage 13 may be provided, and the gas may be supplied to the GPU 3 from this gas passage via the combustion gas supply passage 13.

[0035] The exhaust passage 14 is a passage that connects the outlet of the combustion gas flow path of the GPU 3 to the outside of the fuel cell system 1, and discharges the exhaust gas emitted from the GPU 3 to the outside.

[0036] The POx channel 15 corresponds to the second cathode line and is a passage that branches off from the air supply channel 10 and connects to the inlet of the anode channel 28 in the fuel cell stack 2. For example, before power generation starts when a power generation request arises from the fuel cell stack 2 (during warm-up), it supplies oxidizer gas for the partial oxidation reaction (POx) to the anode channel 28 of the fuel cell stack 2 via the first fuel supply channel 7. Since the partial oxidation reaction is an exothermic reaction, when oxidizer gas is supplied from the POx channel 15 to the fuel gas flowing through the anode channel 28 of the fuel cell stack 2 and the partial oxidation reaction begins, the warm-up of the fuel cell stack 2 is accelerated.

[0037] In Figure 1, reference numeral 16 denotes a POx flow channel valve located in the POx flow channel 15. The POx flow channel valve 16 is a solenoid valve and opens, for example, in response to a command from the control unit 6 before power generation starts (during warm-up) when a power generation request is made by the fuel cell stack 2.

[0038] In fuel cell system 1, if the anode electrode layer 25 or other components oxidize due to oxidation of the reforming catalyst, fuel reforming becomes insufficient. In this case, the electrical resistance of the fuel cell stack 2 increases as the anode electrode layer 25 oxidizes.

[0039] The electrical resistance of the fuel cell stack 2 is detected by applying a predetermined voltage or a predetermined current to the fuel cell stack 2. Alternatively, the electrical resistance of the fuel cell stack 2 is detected by the control unit 6, which acts as a resistance detection unit.

[0040] Figure 3 is a characteristic curve showing an example of the change in the resistance (electrical resistance) of the anode electrode of a fuel cell. The solid characteristic line R1 in Figure 3 represents an example of the change in electrical resistance in a reducing atmosphere when the anode electrode temperature is high (activated state). The dashed characteristic line R2 in Figure 3 represents an example of the change in electrical resistance in a reducing atmosphere when the anode electrode temperature is low (inactivated state). In Figure 3, times t1 to t2 represent the period when hydrogen gas for reduction was supplied to the anode electrode, and the anode electrode was in a reducing atmosphere. Before time t1 and after time t2 in Figure 3 represent the period when nitrogen gas and a very small amount of oxygen gas were supplied to the anode electrode, and the anode electrode was in an oxidizing atmosphere.

[0041] As shown in Figure 3, the anode electrode of a fuel cell decreases in resistance at higher temperatures due to reduction in a reducing atmosphere, but at lower temperatures, reduction does not progress even in a reducing atmosphere, and the resistance remains almost unchanged.

[0042] Furthermore, as shown in Figure 4, the resistance of the material used for the anode electrode of a fuel cell increases as it oxidizes and its weight increases. The electrical resistance of a fuel cell also changes depending on the specifications (material) of the anode electrode. Figure 4 is a schematic diagram illustrating the correlation between the weight and resistance of the anode electrode. The characteristic lines S1, S2, and S3 in Figure 4 show the correlation between the weight and resistance of anode electrodes with different specifications (materials). In a fuel cell, the electrical resistance (resistance) increases as the anode electrode oxidizes, but the electrical resistance value corresponding to the weight (degree of oxidation) differs depending on the material of the anode electrode.

[0043] In other words, the state of the anode electrode layer 25 of the fuel cell stack 2 can be estimated from the electrical resistance value by conducting experiments beforehand to understand the relationship between the surrounding atmosphere, electrode temperature, and electrical resistance value, provided that the specifications (material) of the anode electrode layer 25 are known. That is, the temperature state and oxidation / reduction state of the anode electrode layer 25 can be estimated from the electrical resistance value of the fuel cell stack 2.

[0044] Figure 5 is a timing chart showing an example of changes in various parameters when the fuel cell stack 2 is warmed up. The characteristic line T1, shown as a solid line in Figure 5, shows the change in oxidant gas temperature at the inlet of the cathode channel 29 of the fuel cell stack 2. The characteristic line T2, shown as a dashed line in Figure 5, shows the change in oxidant gas temperature at the outlet of the cathode channel 29 of the fuel cell stack 2 when the partial oxidation reaction is started on the anode channel 28 side from time t1 in Figure 5. The characteristic line T3, shown as a dashed line in Figure 5, shows the change in oxidant gas temperature at the outlet of the cathode channel 29 of the fuel cell stack 2 when the partial oxidation reaction is not started on the anode channel 28 side. The characteristic line Rp, shown as a thick solid line in Figure 5, shows the change in the electrical resistance value of the fuel cell stack 2 when the partial oxidation reaction is started on the anode channel 28 side during the warm-up of the fuel cell stack 2.

[0045] In the fuel cell system 1, when the partial oxidation reaction is initiated on the anode channel 28 side during warm-up, the temperature of the oxidizer gas at the outlet of the cathode channel 29 of the fuel cell stack 2 rises more rapidly compared to when the partial oxidation reaction is not initiated on the anode channel 28 side. Furthermore, if the anode electrode side of the fuel cell stack 2 is oxidized, initiating the partial oxidation reaction on the anode channel 28 side during warm-up allows for rapid reduction of the anode electrode layer 25 side.

[0046] In Figure 5, time t1 indicates the start of the partial oxidation reaction on the anode channel 28 side of the fuel cell stack 2. In Figure 5, time t2 indicates the time when the temperature of the oxidizer gas at the outlet of the cathode channel 29 of the fuel cell stack 2 reaches a predetermined temperature. In Figure 5, time t3 indicates the time when the electrical resistance value on the anode electrode layer 25 side of the fuel cell stack 2 reaches the state where reduction is complete.

[0047] For example, when estimating the oxidation / reduction state inside a fuel cell based on the temperature of the oxidizer gas immediately after it passes through the fuel cell, it is determined that the inside of the fuel cell has been reduced from an oxidized state when a predetermined time has elapsed after the temperature of the oxidizer gas immediately after it passes through the fuel cell reaches a predetermined temperature (a predetermined warm-up completion temperature set in advance). In this case, the predetermined time is set with a certain margin to ensure that the inside of the fuel cell is sufficiently reduced. Therefore, even if the fuel cell continues to warm up after the inside has been reduced and is in a state where power generation can begin, there is a risk that power generation will not be performed by the fuel cell.

[0048] On the other hand, the fuel cell system 1 according to the present invention estimates the oxidation / reduction state on the anode electrode layer 25 side based on the electrical resistance value of the fuel cell stack 2.

[0049] Specifically, the fuel cell system 1, in the control unit 6, determines whether the fuel cell stack 2 is in an oxidized or reduced state based on the electrical resistance value of the fuel cell stack 2 obtained when a predetermined power generation request occurs. If the fuel cell stack 2 is in a reduced state, power generation in the fuel cell stack 2 is permitted. If the fuel cell stack 2 is in an oxidized state, power generation is permitted only after the inside of the fuel cell stack 2 has been reduced. In other words, the control unit 6 corresponds to a power generation feasibility determination unit that determines whether or not power generation in the fuel cell stack 2 is permitted.

[0050] When a power generation request arises for the fuel cell stack 2, if the electrical resistance of the fuel cell stack 2 is high and the anode electrode layer 25 side of the fuel cell stack 2 is oxidized, the fuel cell system 1 supplies combustion gas from the second fuel supply passage 8 to the combustor 3a to burn it, warms up the oxidizer gas passing through the heat exchanger 3b to warm up the fuel cell stack 2, and also performs reduction of the reforming catalyst which is placed on the anode electrode layer 25 side of the power generation unit 21 to reform the fuel gas.

[0051] Figure 6 is a flowchart showing the control flow when a power generation request is made to the fuel cell system 1.

[0052] Step S1 determines whether there is a power generation request. If it is determined in Step S1 that there is a power generation request, the process proceeds to Step S2. If it is determined in Step S1 that there is no power generation request, the routine ends.

[0053] In step S2, the blower 5 is turned on. In step S3, the heater of the combustor 3a is turned on to raise the catalyst temperature of the combustor 3a.

[0054] In step S4, it is determined whether the temperature of the combustor 3a is above a predetermined first temperature. The first temperature is, for example, the temperature at which catalytic combustion becomes possible when fuel gas is supplied to the combustor 3a. If it is determined in step S4 that the combustor 3a is above the first temperature, the process proceeds to step S5. If it is determined in step S4 that the combustor 3a is below the first temperature, the process proceeds to step S3.

[0055] In step S5, combustion gas is supplied to the combustor 3a from the second fuel supply passage 8.

[0056] In step S6, it is determined whether the temperature of the combustor 3a is above a predetermined second temperature. The second temperature is, for example, the temperature of the fuel cell stack 2 at which power generation becomes possible. If it is determined in step S6 that the combustor 3a is above the second temperature, the process proceeds to step S7. If it is determined in step S6 that the combustor 3a is below the second temperature, the process proceeds to step S5.

[0057] In step S7, measurement of the electrical resistance of the fuel cell stack 2 begins. In step S8, the POx flow channel valve 16, which was closed, is opened.

[0058] In step S9, fuel is supplied to the fuel cell stack 2 from the first fuel supply line 7.

[0059] In step S10, the electrical resistance value of the fuel cell stack 2 is used to determine whether the reduction of the fuel cell stack 2 is complete. Specifically, in step S10, the electrical resistance value of the fuel cell stack 2 is used to determine whether the reduction of the anode electrode layer 25 side of the fuel cell stack 2 is complete. In particular, in step S10, for example, if the electrical resistance value of the fuel cell stack 2 falls below a predetermined resistance threshold, it is determined that the reduction of the fuel cell stack 2 is complete.

[0060] In step S10, it may be determined that the reduction of the fuel cell stack 2 is complete if the electrical resistance value of the fuel cell stack 2 remains below the above resistance threshold for a predetermined period of time. If it is determined in step S10 that the reduction of the anode electrode layer 25 side of the fuel cell stack 2 is complete, proceed to step S11. If it is determined in step S10 that the reduction of the anode electrode layer 25 side of the fuel cell stack 2 is not complete, proceed to step S9.

[0061] In step S11, the measurement of the electrical resistance of the fuel cell stack 2 is completed. In step S12, the POx flow channel valve 16, which was open, is closed.

[0062] In the flowchart of Figure 6, steps S3 to S6 are steps related to warming up the combustor 3a when a power generation request arises. Also, in the flowchart of Figure 6, steps S9 to S10 are steps related to the POx and warming up of the fuel cell stack 2 when a power generation request arises. Specifically, steps S9 to S10 are steps to introduce fuel gas and oxidizer gas from the first fuel supply passage 7 and the POx passage 15 to the anode electrode layer 25 side until the electrical resistance value of the fuel cell stack 2 falls below a predetermined resistance threshold, warming up the fuel cell stack 2 by a partial oxidation reaction, and reducing the reforming catalyst located on the anode electrode layer 25 side of the power generation unit 21.

[0063] The fuel cell system 1 starts generating electricity in the fuel cell stack 2 after the warm-up and reduction of the fuel cell stack 2 is complete and the POX flow channel valve 16 is closed.

[0064] The fuel cell system 1 of the first embodiment described above can determine the temperature on the anode electrode layer 25 side and the reduction state on the anode electrode layer 25 side based on the electrical resistance value of the fuel cell stack 2 obtained when a power generation request occurs.

[0065] The fuel cell system 1 can accurately determine the timing when reduction on the anode electrode layer 25 side is complete and sufficient fuel reforming can be performed, based on the electrical resistance value of the fuel cell stack 2.

[0066] Therefore, the fuel cell system 1 can start generating power at the appropriate time and suppress the startup energy to the minimum necessary.

[0067] Furthermore, the fuel cell system 1 performs a partial oxidation (POx) reaction on the anode electrode layer 25 side of the fuel cell stack 2, and a reforming reaction on the anode electrode layer 25 side. The fuel cell system 1 can reduce the anode electrode layer 25 side by generating hydrogen through the partial oxidation (POx) reaction on the anode electrode layer 25 side. In addition, the temperature when the anode electrode layer 25 side is reduced is expressed as a resistance value, so the temperature inside the fuel cell stack 2 and the reduction state can be determined.

[0068] Other embodiments of the present invention will be described below. Note that components identical to those in the embodiments described above are denoted by the same reference numerals, and redundant descriptions are omitted.

[0069] A second embodiment of the present invention will be described using Figure 7. Figure 7 is a schematic explanatory diagram showing the outline of a fuel cell system 41 according to the second embodiment of the present invention. The fuel cell system 41 of the second embodiment has substantially the same configuration as the fuel cell system 1 of the first embodiment described above, but as shown in Figure 7, the fuel cell stack 2 consists of a first fuel cell stack 2a and a second fuel cell stack 2b. That is, the fuel cell system 41 of the second embodiment has a second fuel cell stack 2b to which fuel gas that has passed through the anode electrode layer 25 side of the first fuel cell stack 2a is supplied. The first fuel cell stack 2a and the second fuel cell stack 2b have substantially the same configuration as the fuel cell stack 2 of the first embodiment. The second fuel cell stack 2b corresponds to a second fuel cell stack.

[0070] In the fuel cell system 41, the oxidizer gas that has passed through the second fuel cell stack 2b is supplied to the first fuel cell stack 2a, and the fuel gas that has passed through the first fuel cell stack 2a is supplied to the second fuel cell stack 2b. In other words, the fuel cell system 41 has a second fuel cell stack 2b to which the fuel gas that has passed through the first fuel cell stack 2a is supplied.

[0071] More specifically, in the fuel cell system 41, the first fuel supply passage 7 and the POx passage 15 are connected to the anode passage 28 of the first fuel cell stack 2a, and the cathode-off gas passage 12 is connected to the cathode passage 29 of the first fuel cell stack 2a.

[0072] Furthermore, in the fuel cell system 41, the anode off-gas passage 9 is connected to the anode flow path 28 of the second fuel cell stack 2b, and the cathode gas passage 11 is connected to the cathode flow path 29 of the second fuel cell stack 2b.

[0073] Furthermore, the anode channel 28 of the first fuel cell stack 2a is connected to the anode channel 28 of the second fuel cell stack 2b via the third fuel supply channel 42. The cathode channel 29 of the first fuel cell stack 2a is connected to the cathode channel 29 of the second fuel cell stack 2b via the second cathode channel 43. In other words, the fuel cell system 41 is configured such that the first fuel cell stack 2a and the second fuel cell stack 2b are connected so that the oxidizer gas that has passed through the cathode electrode layer 27 side of the second fuel cell stack 2b is supplied to the cathode electrode layer 27 side of the first fuel cell stack 2a.

[0074] Furthermore, the second fuel cell stack 2b has fewer reforming catalysts than the first fuel cell stack 2a. For example, in the second fuel cell stack 2b, the power generation unit 21 does not need to have a reforming catalyst.

[0075] In the fuel cell system 41 of the second embodiment, the feasibility of generating electricity in the fuel cell stack 2 is determined based on the electrical resistance value of the first fuel cell stack 2a.

[0076] In this second embodiment of the fuel cell system 41, the same effects and advantages as those of the first embodiment of the fuel cell system 1 described above can be achieved.

[0077] Furthermore, the fuel cell system 41 of the second embodiment can improve power generation efficiency by having a second fuel cell stack 2b, and can suppress cost increases by reducing the amount of reforming catalyst placed in the second fuel cell stack 2b.

[0078] Although specific embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0079] For example, in the power generation unit 21, the reformed catalyst layer 24 may be omitted.

[0080] For example, instead of using the total electrical resistance value of the fuel cell stack 2 or the first fuel cell stack 2a, the representative value may be the electrical resistance value of one of the multiple power generation units 21 that make up the fuel cell stack 2 or the first fuel cell stack 2a.

[0081] For example, the reforming catalyst may be placed in at least one of the following locations: on the surface of the separator 22 facing the anode electrode layer 25, within the metal support layer 23, within the anode electrode layer 25, or on the surface of the anode electrode layer 25.

[0082] For example, to determine whether the reduction of the fuel cell stack 2 is complete, the electrical resistance value of the fuel cell stack 2 when a power generation request is made and the electrical resistance value of the fuel cell stack 2 (2a) after the fuel gas and oxidizer gas have been introduced to the anode electrode layer 25 side of the fuel cell stack 2 after the power generation request are made can be used, and it may be determined that the reduction is complete when the difference between these values ​​exceeds a predetermined threshold.

[0083] For example, to determine whether the reduction of fuel cell stack 2 is complete, the reduction may be determined when the electrical resistance value of the fuel cell stack remains below a resistance threshold for a predetermined period of time. In this case, the determination of whether the reduction of fuel cell stack 2 is complete ensures that the detected electrical resistance value of fuel cell stack 2 is not a value that could have been instantaneously. [Explanation of Symbols]

[0084] 1…Fuel cell system 2…Fuel cell stack 3…GPU 4…Fuel supply device 5... Blower 6…Control Unit 7…1st fuel supply path 8…Second fuel supply path 9... Anode off-gas passage 10…Air supply path 11… Cathode gas passage 12... Cathode-off gas passage 13…Combustion gas supply line 14… Exhaust passage 15…POx channel 16…POx flow valve 21... Power generation unit 22... Separator 23...Metal support layer 23a... one side 23b...the other side 24…Reformed catalyst layer 25... Anode electrode layer 26...Electrolyte layer 27... Cathode electrode layer 28... Anode channel 29... Cathode channel

Claims

1. Multiple power generation units are stacked to generate electricity by supplying fuel gas and oxidizer gas, and the supplied fuel gas can be internally reformed using a reforming catalyst. A control unit that controls the amount of fuel gas and oxidizer gas supplied to the fuel cell stack, A resistance detection unit for detecting the electrical resistance of the fuel cell stack, A fuel cell system characterized by having a power generation feasibility determination unit that determines whether or not power generation can be performed in the fuel cell stack based on the electrical resistance value of the fuel cell stack obtained when a predetermined power generation request occurs.

2. The fuel cell system according to claim 1, characterized in that the resistance detection unit detects an electrical resistance value by applying a predetermined voltage or passing a predetermined current through the fuel cell stack.

3. The fuel cell stack described above includes a first cathode line that supplies oxidant gas to the cathode electrode, an anode line that supplies fuel gas to the anode electrode, and a second cathode line that supplies oxidant gas to the anode electrode. The fuel cell system according to claim 1, characterized in that an oxidizing agent gas and fuel gas are introduced to the anode electrode until the electrical resistance value of the fuel cell stack detected by the resistance detection unit is below a predetermined resistance threshold, the fuel cell stack is warmed up by a partial oxidation reaction, and a reducing catalyst, which is placed on the anode electrode side of the power generation unit to reform the fuel gas, is reduced.

4. The above-mentioned power generation unit has an anode electrode layer, an electrolyte layer, and a cathode electrode layer supported on one side of a metal support layer, and adjacent power generation units are stacked via a separator located on the other side of the metal support layer. The fuel cell system according to claim 1, characterized in that platinum as a reforming catalyst is disposed at least at one of the following locations: the separator, within the metal support layer, within the anode electrode layer, or on the surface of the anode electrode layer facing one surface of the metal support layer.

5. The fuel cell system according to claim 4, characterized in that it has a second fuel cell stack to which the fuel gas that has passed through the above fuel cell stack is supplied.

6. The fuel cell stack and the second fuel cell stack are connected so that the oxidizer gas that has passed through the second fuel cell stack is supplied to the fuel cell stack. The fuel cell system according to claim 5, characterized in that the second fuel cell stack has fewer reforming catalysts arranged in it than the fuel cell stack described above.

7. The fuel cell system according to claim 1 or 2, characterized in that the power generation feasibility determination unit determines that power generation can be started in the fuel cell stack when the electrical resistance value of the fuel cell stack detected by the resistance detection unit falls below a predetermined resistance threshold.

8. The above fuel cell stack is capable of introducing an oxidizer gas and fuel gas to the anode electrode side to perform warm-up by a partial oxidation reaction and reduction of a reforming catalyst to reform the fuel gas. The fuel cell system according to claim 1 or 2, characterized in that the power generation feasibility determination unit uses the electrical resistance value of the fuel cell stack when a power generation request is made and the electrical resistance value of the fuel cell stack after introducing oxidant gas and fuel gas to the anode electrode side of the fuel cell stack after a power generation request is made, and determines that power generation can be started in the fuel cell stack when the difference between these values ​​exceeds a predetermined determination threshold.

9. The fuel cell system according to claim 7, characterized in that the power generation feasibility determination unit determines that power generation can be started in the fuel cell stack if the electrical resistance value of the fuel cell stack detected by the resistance detection unit remains below the resistance threshold for a predetermined period of time.

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