WO2011036716A1 - Fuel cell - Google Patents

Abstract

A fuel cell system comprises: a membrane electrode assembly including an anode catalyst layer, a cathode catalyst layer, and an electrolyte membrane inserted between the anode catalyst layer and the cathode catalyst layer; a generator unit in which a first layer and an anode channel are disposed on the anode catalyst layer side of the membrane electrode assembly, the first layer including a carbon material and having porous and water-repellent properties, the anode channel having a fuel supply portion for supplying a fuel to the anode catalyst layer through the first layer and a fuel discharging portion for discharging a discharged material from the anode catalyst layer through the first layer; and a control unit electrically connected to the generator unit and electrically connectable to a load. The operation of the control unit includes a step of stopping power feeding from the generator unit to the load and a step of preventing an oxidation agent from intruding into the generator unit from the outside.

Description

Fuel cell

The present invention relates to a fuel cell.

Direct power methanol fuel cell (Direct Methanol Fuel Cell: DMFC) generates power (voltage) with time if it generates power continuously for a long time. This deterioration is not simply caused by the power generation time, but may occur significantly early depending on the power generation environment. Possible causes for this include a decrease in the activity of the anode and cathode catalyst, deterioration of the electrolyte membrane, and a decrease in the ability to diffuse fuel and oxygen at the anode and cathode.

There are Patent Documents 1 and 2 as techniques for preventing the deterioration of such fuel cells.

Patent Document 1 discloses a fuel cell that can control the operation of the fuel cell by an external operation. Patent Document 2 discloses a fuel cell system that can easily determine whether or not the supply of gas to the cathode can be interrupted after a power generation stop instruction.

JP 2009-54466 A JP 2009-4369 A

Among the causes of deterioration, deterioration that occurs at the anode occurs within 1000 hours of operation and is highly dependent on the power generation environment. In particular, in the case of a low permeate water type direct methanol supply type fuel cell, the amount of voltage decrease due to the deterioration of the anode after the first 1000 hours from the start of operation is the voltage due to the deterioration of the anode after the first 5000 hours. Accounts for about 40% of the amount of decrease. For this reason, suppression of deterioration of the anode has been a major issue.

The present invention has been made to solve such problems, and an object of the present invention is to provide a fuel cell system capable of maintaining a stable output for a long period of time by preventing a decrease in the activity of the anode catalyst of the fuel cell system. To do.

A fuel cell according to the present invention includes an anode catalyst layer, a cathode catalyst layer, a membrane electrode assembly including an electrolyte membrane interposed between the anode catalyst layer and the cathode catalyst layer, and an anode of the membrane electrode assembly A first layer containing a carbon material and having porosity and water repellency on the catalyst layer side, a fuel supply unit for supplying fuel to the anode catalyst layer via the first layer, and a fuel from the anode catalyst layer A power generation section having an anode flow path having a fuel discharge section that discharges exhaust through the first layer, and is electrically connected to the power generation section and can be electrically connected to a load A control unit, wherein the control unit stops power supply from the power generation unit to the load, and prevents an oxidant from entering the power generation unit from the outside. Characterized by having That.

The fuel cell control method according to the present invention includes an anode catalyst layer, a cathode catalyst layer, a membrane electrode assembly including an electrolyte membrane interposed between the anode catalyst layer and the cathode catalyst layer, and the membrane. A first layer containing a carbon material and having porosity and water repellency on the anode catalyst layer side of the electrode assembly, a fuel supply unit for supplying fuel to the anode catalyst layer via the first layer, and A fuel cell system control method comprising: an anode flow path having a fuel discharge section that discharges an exhaust from an anode catalyst layer through the first layer; and a control method for the fuel cell system. The method includes a step of stopping power supply from the power generation unit to a load and a step of preventing an oxidant from entering the power generation unit.

According to the above aspect, it is possible to provide a fuel cell system that maintains a stable output for a long period of time by preventing a decrease in the activity of the anode catalyst.

The fuel cell system which concerns on 1st Embodiment. The fuel cell system which concerns on 2nd Embodiment. The fuel cell system which concerns on 3rd Embodiment. A fuel cell system according to a fourth embodiment. The fuel cell system which concerns on 5th Embodiment. Sectional drawing of the electric power generation part which concerns on 1st Embodiment. Sectional drawing of the electric power generation part which concerns on the modification of 1st Embodiment. The control part of 1st Embodiment. Explanatory drawing of the estimation model of catalyst deterioration. The flowchart of the control method which concerns on 1st Embodiment. The flowchart of the control method which concerns on 4th Embodiment. The flowchart of the control method which concerns on 5th Embodiment. The example of the experimental result by the fuel cell system concerning a 1st embodiment.

Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the embodiment described below exemplifies an apparatus and a method for embodying the technical idea of the present invention, and the technical idea of the present invention includes the material, shape, structure, The arrangement is not limited to the following. The technical idea of the present invention can be variously modified within the scope of the claims.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the following description, a direct methanol fuel cell system (DMFC) using a methanol aqueous solution as a fuel will be described as an example.

FIG. 1 shows the configuration of the fuel cell system according to the first embodiment.

The fuel cell system 10 according to the first embodiment shown in FIG. 1 includes a power generation unit 4, a fuel supply unit 42, a tank 43, a fuel discharge unit 46, an oxidant supply unit 52, an oxidant discharge unit 56, a fluid. A supply unit 62, a tank 63, and a control unit 7 are included.

(Power generation part)
The power generation unit 4 will be described with reference to FIG.

The power generation unit 4 includes an anode 2 that oxidizes the fuel 41, a cathode 3 that reduces the oxidant-containing gas 51, and an electrolyte membrane (solid polymer electrolyte membrane) 1 that is sandwiched between the anode 2 and the cathode 3. The On the anode catalyst layer 21, an anode carbon dense water repellent layer 26, an anode gas diffusion layer 22, and an anode flow path plate 23 are arranged in this order. On the cathode catalyst layer 21, a cathode carbon dense water repellent layer 26, a cathode GDL 22, and a cathode flow path plate 23 are arranged in this order.

(Electrolyte membrane)
In the case of a direct methanol fuel cell system (DMFC), the electrolyte membrane 1 may be, for example, a Dupont Nafion membrane (trademark). The electrolyte membrane 1 functions as a medium for transferring protons (H ⁺ ) generated in the catalyst layer 21 of the anode 2 (hereinafter referred to as the anode catalyst layer 21) to the catalyst layer of the cathode 3 (hereinafter referred to as the cathode catalyst layer 31). .

(Anode catalyst layer / Cathode catalyst layer)
An anode catalyst layer 21 and a cathode catalyst layer 31 are disposed on both sides of the electrolyte membrane 1. When an aqueous methanol solution is used as the fuel 41, for example, a Pt—Ru catalyst can be used for the anode catalyst layer 21. Further, a noble metal catalyst such as a Pt catalyst can be used for the cathode catalyst layer 31.

The anode catalyst layer 21 is prepared by mixing a Pt-Ru catalyst with a perfluorosulfonic acid resin solution (Nafion solution (trademark)), water, and ethylene glycol, and then dispersing the mixture on a fluororesin sheet such as Teflon (trademark). The mixed solution can be applied by spraying, and then hot-pressed to be transferred onto the electrolyte membrane. As another method, it can be produced by directly applying the material onto the electrolyte membrane by spraying.

The cathode catalyst 31 is prepared by mixing a Pt catalyst with a perfluorosulfonic acid resin solution (Nafion solution (trademark)), water, and ethylene glycol, and then dispersing the mixture in a fluororesin sheet such as Teflon (trademark). Can be applied by spraying and then hot-pressed to transfer onto the electrolyte membrane. As another method, it can be produced by directly spraying on the electrolyte membrane.

(Anode MPL)
A carbon dense water repellent layer (Micro Porous Layer: MPL) is disposed on the anode catalyst layer 21. This MPL can be produced by mixing carbon particles and a water repellent (Teflon particles; Teflon is a trademark), layering them, and then heating. Since MPL has a space between the carbon particles and the water repellent, it has porosity. Moreover, since it contains a water repellent, it has water repellency. The MPL may be formed on the GDL described later.

The anode MPL 26 provides a function of adjusting the fuel used for power generation. The presence of MPL makes it possible to supply fuel to the catalyst layer in a gaseous state. In general, in a direct methanol supply type fuel cell, the concentration of methanol in the fuel supplied to the anode is about 3 to 15%. Here, when the fuel with the concentration as it is is sent to the anode catalyst layer, a low α environment described later cannot be created. That is, the presence of MPL makes it possible to supply methanol and water in the fuel not as a liquid composition ratio but as a gas composition ratio. With this function, the fuel ratio (methanol / water) supplied to the anode catalyst layer can be increased, and the fuel cell can be operated in a low α environment. By realizing a low α environment, there are advantages that the water recovery mechanism can be omitted, the performance degradation due to flooding at the cathode can be suppressed, and the amount of air supplied to the cathode can be reduced.

(Anode GDL)
A gas diffusion layer (Gas Diffusion Layer; GDL) is further disposed on the MPL. GDL has a porous substrate and a water-repellent layer formed on the substrate.

Formation of the water repellent layer on the surface of the GDL is performed by immersing a solvent in which a water repellent (particles such as PTFE) is dispersed in the base material, followed by a heat treatment to fix the water repellent to the base material. Can be formed. As the substrate, carbon paper, carbon cloth, carbon nonwoven fabric, or the like can be used.

The porosity of GDL is larger than that of MPL. Thereby, the anode GDL 22 provides a function of smoothly supplying fuel to the anode catalyst layer 21, discharging the product, and collecting current. The porosity can be determined by measuring the ratio of vacancies per unit weight of GDL and MPL by mercury porosimetry.

A water repellent layer may be separately provided on the GDL, and the surface on which the water repellent layer is formed may be opposed to a flow path 25 described later. In this case, the water repellent layer has a function of limiting the amount of fuel penetration.

(Anode channel plate)
An anode flow path plate 23 is further disposed on the anode GDL 22. The anode flow path plate 23 has anode flow paths 25 (25a, 25b, 25c). The anode channel 25 provided in the anode channel plate 23 can be, for example, a serpentine channel or a parallel channel in which a plurality of channels run in parallel.

The anode flow path 25 has a function of supplying fuel to the anode catalyst layer 21 through the anode GDL 22 and the anode MPL 26 and discharging a product (CO ₂ or the like) generated by the anode reaction (Formula 1). In addition, the function of the current collecting plate of the anode 2 can also be provided by using conductive carbon or the like for the anode flow path plate 23.

Of the region sandwiched between the anode channel plate 23 and the electrolyte membrane 1, the region excluding the anode channel plate 23 and the electrolyte membrane 1 is referred to as the anode 2. That is, in FIG. 6, the anode GDL 22, the anode MPL 26, and the anode catalyst layer 21 correspond to the anode 2.

As the anode flow path plate 25, carbon, metal, or the like can be used. As the metal, a metal having high corrosion resistance such as titanium or a metal having a surface subjected to corrosion resistance is preferable.

(Cathode MPL, Cathode GDL)
Also on the cathode catalyst layer 31, a cathode MPL 36, a cathode GDL 32, and a cathode channel plate 33 are disposed.

The cathode MPL 36 and the cathode GDL 32 can also be produced by the same method as the anode MPL 26 and the anode GDL 32.

Since the cathode MPL 36 reduces the amount of water that moves from the cathode catalyst layer 31 to the cathode GDL 32, it has the effect of suppressing flooding of the cathode 3.

The cathode GDL 32 provides a function of smoothly supplying air to the cathode catalyst layer 31, discharging a product, and collecting current.

(Cathode channel plate)
A cathode channel plate 33 is further disposed on the cathode GDL 32. The cathode channel plate 33 has a cathode channel 35 (35a, 35b, 35c) of an oxidizing agent-containing gas. The cathode channel 35 provided in the cathode channel plate 33 can be, for example, a serpentine channel or a parallel channel in which a plurality of channels run in parallel.

The cathode flow path plate 33 is used for the purpose of supplying the oxidant supply gas to the cathode catalyst layer 31 through the cathode GDL 32 and for the purpose of discharging the products (H ₂ O, etc.) generated by the cathode reaction (Formula 2). A flow path 35 is provided. The cathode channel plate 33 can be provided with the function of a cathode current collecting plate by using conductive carbon or the like.

Of the region sandwiched between the cathode channel plate 33 and the electrolyte membrane 1, the region excluding the cathode channel plate 33 and the electrolyte membrane 1 is defined as the cathode 3. That is, in FIG. 6, the cathode GDL 32, the cathode MPL 36, and the cathode catalyst layer 31 correspond to the cathode 3.

As the cathode flow path plate 35, carbon, metal or the like can be used. As the metal, a metal having high corrosion resistance such as titanium or a metal having a surface subjected to corrosion resistance is preferable.

(MEA)
A structure in which the anode 2, the electrolyte membrane 1, and the cathode 3 are sequentially laminated may be referred to as a membrane electrode assembly (MEA) 5.

Here, α is defined as a value obtained by subtracting the amount of generated water from the amount of water collected on the cathode side, and dividing that value by the amount of proton moving to the cathode, that is, the amount of entrained water per proton. Low permeated water (low α) means that the value of α is in the range of −1/6 to 1.5. Such a low αMEA has different characteristics from the conventional MEA in the management of the water of the anode 2.

In the anode 2, the MEA 5 in which the anode MPL 26 is disposed can realize a so-called low permeate MEA (low αMEA) in which the methanol crossover is small. In addition, a fuel cell using the low permeate water MEA may be referred to as a low permeate water fuel cell (low α fuel cell).

Here, the value of α can be obtained by actually manufacturing and operating a fuel cell and measuring the current-voltage characteristics of the power generation unit 4 and the material balance of water. Specifically, it is as follows.

The α value is obtained by subtracting the product water and methanol crossover product water from the water collected from the cathode and dividing the remainder by the number of protons that contributed to power generation.

When the electrode area of the single cell is S (cm ² ) and the current density at a constant load is A (A / cm ² ), the current amount at this time is S · A (A). If the Faraday constant is F,
The number of moles of electrons necessary to extract the current amount value S · A is (S · A) / F (mol). In the cathode reaction of DMFC (formula (1)), the number of moles of electrons is equal to the number of moles of protons, and 0.5 water is generated for one electron. Therefore,
(Mol number of generated water) = 0.5 × (mol number of electrons)
The water produced by methanol crossover is the carbon dioxide concentration P (vol%) in the cathode exhaust gas and the exhaust gas amount Q (mL / min). 60/100 (mL).

When calculated as a standard state, the number of moles of carbon dioxide per second is ((P · Q) / 60/100) / (22.4 × 1000).

Carbon dioxide is generated at the cathode because methanol crosses over to the cathode, and 1 mol of methanol is required per 1 mol of carbon dioxide. At that time, 2 mol of water is produced. Therefore, the water produced by methanol crossover per second is 2 × (P · Q / 60/100) / (22.4 × 1000).

Therefore, if the amount of water collected at the cathode per second is W (mol), the total amount of entrained water (mol) = W−0.5 × (S · A) / F−2 × (P · Q / 60/100 ) / (22.4 × 1000)
Therefore,
α = total amount of water entrained / ((SA) / F)
It can be asked.

The above is calculated with water generated in 1 second in a single cell, but when evaluating over 1 second in a stack, the number of stacks and time (seconds) are added to items other than W in the above formula. Multiply and calculate. Needless to say, in order to obtain W, the humidity originally contained in the air supplied to the cathode is excluded.

(Method for producing MEA)
The low αMEA5 can be produced as follows.

When producing the anode catalyst layer and the cathode catalyst layer with very thin films as in the above-described spray method, MPL and GDL are disposed on the catalyst layer. This is because the catalyst layer is thin and has good diffusivity, so that the amount of permeate cannot be reduced unless MPL is arranged. When a catalyst layer is produced by a spray method, a precursor layer of a catalyst layer is formed on a fluorine resin sheet, for example, a Teflon sheet (Teflon is a trademark) by a spray method, and this is hot-pressed on an electrolyte membrane. By transferring, a three-layer structure of catalyst layer / electrolyte membrane / catalyst layer can be produced.

Note that it is also possible to produce the catalyst layer directly on the electrolyte membrane. As a method for producing the catalyst layer, for example, a carbon-supported catalyst or a non-supported catalyst that does not use a support can be used for the catalyst layer.

Note that when a catalyst layer is prepared using a carbon-supported catalyst as the anode catalyst layer, the high water-repellent GDL and the catalyst layer replace the MPL even if there is no MPL because the catalyst layer is thick. α can be used.

FIG. 6 shows an example in which the MPL 26 and the GDL 22 are arranged on the anode 2, but the configuration and number of GDLs and MPLs are limited as long as α is within the range of −1/6 to 1.5. Not. As an example, FIG. 7 shows an example of an MEA prepared by preparing two members obtained by bonding MPL and GDL and bringing them into contact with each other back to back.

(Measuring instrument)
The power generation unit 4 includes a measuring instrument 8 that measures current, voltage, and temperature. The measuring instrument 8 is connected to the control unit 7 via a signal line E8.

(Fuel supply part)
Next, the fuel cell system 10 will be described with reference to FIG.

The tank 43 stores the fuel 41. As the fuel 41, an aqueous methanol solution adjusted to a predetermined concentration (for example, 1 to 5 mol-CH ₃ OH / L) can be used.

The tank 41 is connected to the anode 2 through the pipe L1. A fuel supply unit 42 is interposed in the pipe L1. The fuel supply unit 42 includes a valve 42a and a pump 42b.

The fuel supply unit 42 has a function of supplying, stopping, and adjusting the flow rate of the fuel 41 from the fuel container 43 in which the fuel 41 is stored to the anode flow path 25 (25a to 25c) of the anode 2.

(Oxidant supply unit)
The pipe L2 is connected to the cathode 3. An oxidant supply unit 52 is inserted in the pipe L2. The oxidant supply unit 52 includes a valve 52a and a pump 52b. The oxidant supply unit 52 has a function of supplying, stopping, and adjusting the flow rate of the oxidant-containing gas 71 to the cathode channel 35 (35a to 35c) of the cathode 3.

In the first embodiment, the pump 52b is operated to supply external air to the cathode 3. In addition, when a pressurized cylinder is used as a supply source of the oxidizing agent-containing gas, the pump 62b can be omitted.

(Fluid supply part)
The tank 63 stores the first fluid 61. The tank 61 is connected to the anode 2 via a pipe L3. A fluid supply unit 62 is inserted in the pipe L3. The fluid supply unit 62 includes a valve 62a and a pump 62b.

The fluid supply unit 62 has a function of supplying, stopping, and adjusting the flow rate of the first fluid 61 from the tank 63 in which the first fluid 61 is stored to the anode flow path 25 (25a to 25c) of the anode 2.

In the first embodiment, pure water is supplied as the first fluid to prevent the oxidant from entering the power generation unit 4 from the outside.

As the fluid other than pure water, an aqueous solution composed of the same compound as the fuel and water can be used. For example, in the case of a direct methanol supply type fuel cell, it is allowed to use an aqueous methanol solution. This is because the presence of methanol makes it possible to replace the fuel in the anode 2 in a short time at the time of restart, and to prevent contamination of MEA because it is composed of the same compound as the fuel. In particular, it is preferable to use a methanol aqueous solution having a concentration lower than that of the methanol aqueous solution used as the fuel.

As another example, since the discharge from the fuel discharge unit 46, which will be described later, contains unused fuel and water as main components, the fuel is diluted by recirculating them to the fuel supply unit 42. Can do. This liquid may be used as the first fluid.

(Fuel discharge part)
A pipe L4 is connected to the anode 2. A fuel discharge part 46 is inserted in the pipe L4. The fuel discharge part 46 has a valve 46a.

The fuel discharge unit 46 has a function of discharging the unreacted fuel and the discharged water such as water after the reaction from the anode 2.

(Oxidant discharge section)
A pipe L5 is connected to the cathode 3. An oxidant discharge part 56 is inserted in the pipe L5. The oxidant discharge part 56 has a valve 56a.

The oxidant discharge unit 55 has a function of discharging unreacted oxidant and water as a product after the reaction from the cathode 3.

(load)
A load 12 can be connected to the fuel cell system 10. The load 12 is electrically connected between the anode 2 and the cathode 3. Examples of the load provided outside the fuel cell system 10 include electronic devices (such as a personal computer) that operate using the fuel cell system 10 as a power source. Examples of the load provided in the fuel cell system 10 include power storage devices such as a secondary battery that stores the electricity of the fuel cell system 10. The load 12 is connected to the control unit 7 via a signal line E12. In addition, the current / voltage exchanged between the power generation unit 4 and the load 12 and the connection state such as short circuit / opening with the fuel cell system are monitored and controlled via signal lines E8 and E12.

(Control part)
The fuel cell system according to the present embodiment has a control unit 7. FIG. 8 shows the configuration of the control unit 7. The control unit 7 includes an input / output control unit 71, an information storage unit 72, and an arithmetic processing unit 73. The input / output control unit 71, the information storage unit 72, and the arithmetic processing unit 73 are connected so as to exchange signals with each other.

(I / O control unit)
The input / output control unit 71 has these states for controllable elements (load 12, fuel supply unit 42, fuel discharge unit 46, oxidant supply unit 52, oxidant discharge unit 56, fluid supply unit 72). A control unit for instructing a signal for controlling the signal line Ei (i is the number of each element). That is, the load control unit 711, the fuel supply unit control unit 712, the fuel discharge unit control unit 713, the oxidant supply unit control unit 714, the oxidant discharge unit control unit 715, the fluid supply unit control unit 716, and the power generation unit control unit 717 is there.

The function of each control unit in the first embodiment is as follows.

The load control unit 711 has the following functions.

Instructing the load 12 to short-circuit / open the load through the signal line E12 and monitoring the state The fuel supply unit control unit 712 has the following functions.

Instruction for opening and closing the valve 42a through the signal line E42a and monitoring the state Operation and stop instruction for the pump 42b through the signal line E42b and state monitoring The fuel discharge control unit 713 has the following functions.

The valve 46a is instructed to open and close through the signal line E46a, and the state is monitored. The oxidant supply unit control unit 714 has the following functions.

Instruction for opening and closing the valve 52a through the signal line E52a and monitoring the state Operation and stop instruction for the pump 52b through the signal line E52b and state monitoring The oxidant discharge unit control unit 715 has the following functions.

Opening / closing instruction and state monitoring for the valve 56a through the signal line E56a The fluid supply control unit 716 has the following functions.

Instruction for opening and closing the valve 62a through the signal line E62a, monitoring of the state for the pump 62b Operation and stop instruction through the signal line E62b, monitoring of the state The power generation unit control unit 717 has the following functions.

Monitoring of the operation state (current, voltage, temperature) through the signal line E8 with respect to the power generation unit 4 The input / output control unit 71 does not always need to have all of these, and has a necessary control unit according to the embodiment. What is necessary is just to comprise.

Each control unit can be configured as an independent electric circuit. Alternatively, a program for controlling each control unit may be stored in the information storage unit 72 and appropriately called by the arithmetic processing unit 73 to give instructions to each controllable element through each control unit. Is possible.

(Information storage)
The information storage unit 72 is information on the operating state (current, voltage, temperature) of the power generation unit 4 collected, processed, and processed by the input / output control unit 71 and the arithmetic processing unit 73, information on the state of elements that are controllable, and the like. , Etc. can be stored. In addition, information serving as a criterion for issuing a control signal from the input / output control unit 71 can be stored. The information storage unit 72 can be a storage medium such as a hard disk.

(Calculation processing part)
The arithmetic processing unit 74 exchanges information between the input / output control unit 71 and the information storage unit 72, arithmetic processing and processing of the information, storage in the information storage unit 72, control signal to the input / output control unit 71 The function of performing the output. The arithmetic processing unit 73 can be a CPU such as an electronic computer.

(Operation of fuel cell system)
Next, the operation of the fuel cell system shown in FIG. 1 will be described.

First, the fuel 41 (methanol aqueous solution) is supplied to the anode flow path 25 through the fuel supply unit 42 (pump 42b), and is supplied to the anode catalyst layer 21 through the anode GDL22 and the anode MPL26. In the anode catalyst layer 21 of the membrane electrode assembly 5, the above-described anode reaction (formula 1) occurs.

Based on (Formula 1), protons (H ⁺ ) generated in the anode catalyst layer 21 flow from the anode catalyst layer 21 through the electrolyte membrane 1 to the cathode catalyst layer 31. Electrons (e ⁻ ) are carried to the cathode catalyst layer 31 via the anode GDL 22, the anode MPL 26, the anode flow path plate 23, the load 12, the cathode flow path plate 33, the cathode MPL 36, and the cathode GDL 32. Carbon dioxide (CO ₂ ) generated in the anode catalyst layer 21 is discharged to the outside through the anode GDL 22, the anode MPL 26, and the anode flow path 25.

Due to the oxidant-containing gas (for example, air) 51 supplied from the oxidant gas supply means 52, protons and electrons are consumed in the cathode reaction shown in (Formula 2) described above in the cathode catalyst layer 31. In FIG. 1, the oxidant-containing gas 51 is supplied to the cathode catalyst layer 31 via the cathode channel 35, the cathode GDL 32, and the cathode MPL 36 of the cathode channel plate 33.

In general, when the cathode reaction (formula 2) occurs, methanol (CH ₃ OH) and water (H ₂ O) also move through the electrolyte membrane 1 along with the movement of protons (the former is methanol crossover and the latter is water). Called crossover (or proton-entrained water). Of these, methanol that has permeated through the electrolyte membrane 1 undergoes an oxidation reaction shown in (Equation 3) in the cathode catalyst layer 31 by the air 51 supplied from the oxidant gas supply unit 52 to generate water.

Further, the water generated in the cathode reaction (formula 2) and a part of the permeated water are back-diffused to the anode catalyst layer 21 through the electrolyte membrane 1. When all the water necessary for the reaction at the anode is covered by the water produced by the cathode, α = −1 / 6. The remaining water is discharged from the membrane electrode assembly 5 to the outside through the cathode channel plate 33.

Here, when the load 12 is released from the power generation unit 4 and the power supply to the load 12 is stopped, if left as it is, an oxidizing agent (for example, air) from the outside enters the power generation unit 4. As a result, the above-described phenomenon of catalyst deterioration starts. As described above, in the case of the low permeate type, the catalyst layer is deteriorated mainly on the anode side.

This catalyst deterioration prevention can be prevented by performing the following control via the control unit 7.

(Control method)
Hereinafter, this procedure will be described with reference to FIG. FIG. 10 is a process flow showing a procedure for preventing catalyst deterioration of the anode catalyst layer 21 in the first embodiment. As a premise for starting the process flow (Start), it is assumed that the fuel cell system 10 is in an operating state.

(Load release step: S01)
First, the load control unit 711 of the control unit 7 instructs the load 12 to release the load through the signal line E12.

(Oxidant supply stop step: S02)
The supply of the oxidant to the fuel cell system 10 is stopped. For this purpose, the oxidant supply unit control unit 714 issues an instruction to stop the oxidant supply unit 52 through the signal line E52. Specifically, the oxidant supply unit control unit 714 issues an instruction to close the valve 52a through the signal line E52a. Similarly, an instruction to stop the pump 52b is issued through the signal line E52b.

(Fuel supply stop step: S03)
The fuel supply to the fuel cell system 10 is stopped. For this purpose, the fuel supply unit control unit 712 issues an instruction to stop the fuel supply unit 42 through the signal line E42. Specifically, the fuel supply unit control unit 712 issues an instruction to close the valve 42a through the signal line E42a. Similarly, an instruction to stop the pump 42b is issued through the signal line E42b.

The valve 42a is for preventing an adverse effect caused by excessive pressure applied to the fuel supply unit 42, the tank 43, etc. during the supply of pure water described later. Therefore, when there is no such fear, the operation of closing the valve 42a can be omitted. Specifically, in the case of a stop valve, such an operation is unnecessary.

Further, the valve 42a can be omitted for a pump (for example, a tube pump) in which the pump 42b also functions as a valve.

(Pure water supply start step: S04)
Pure water is supplied to the fuel cell system 10. For this purpose, the fluid supply control unit 716 issues an instruction to supply pure water to the anode 2 to the fluid supply unit 62 via the signal line E62. Specifically, the fluid supply unit control unit 716 issues an instruction to open the valve 62a through the signal line E62a. Similarly, an instruction to operate the pump 62b is issued through the signal line E62b.

By flowing pure water through the anode 2 for a predetermined time, the amount of by-products remaining on the anode 2 can be reduced.

(Pure water supply stop step: S05)
After a predetermined time has elapsed, the fluid supply unit control unit 716 instructs the fluid supply unit 62 to stop through the signal line E62. Specifically, the fluid supply unit control unit 716 issues an instruction to close the valve 62a through the signal line E62a. Similarly, an instruction to stop the pump 62b is issued through the signal line E62b. Thereby, the supply of pure water to the power generation unit 4 is stopped.

(Fuel cell sealing step: S06)
Intrusion of the oxidant from the outside to the fuel cell system 10 is prevented. For this purpose, the fuel discharge control unit 713 issues an instruction to close the valve 46a through the signal line E46a. Further, the oxidant discharge unit control unit 715 issues an instruction to close the valve 56a through the signal line E56a.

By the above operation, since the anode 2 is filled with pure water, the possibility that an external oxidizing agent enters the anode and contacts the anode catalyst layer 21 can be reduced.

(Technical significance)
The technical significance of the first embodiment is estimated as follows.

The fuel 41 used in the anode reaction in the power generation of the fuel cell system is theoretically water: methanol = 1: 1 (mol ratio) as shown in the equation (1). However, when protons generated at the anode move to the cathode, about three waters move as entrained water. Therefore, in the fuel cell system, the water / methanol ratio (molar ratio) actually supplied to the cell is not 1, but varies from about 1 to 19 depending on the fuel control and the structure of the MEA. The excess water described above is water that moves with protons, and reducing this as much as possible is required to improve the energy efficiency and miniaturization of the fuel cell system.

As a method for reducing the amount of water that moves along with protons as much as possible, there is a low permeation type fuel cell system. As described above, the low permeate type means a fuel cell having an MEA having α of −1/6 to 1.5. On the other hand, the conventional system is sometimes referred to as a highly permeable water fuel cell system.

The fuel used in the conventional high permeation water fuel cell system is usually 1 to 2 mol-CH ₃ OH / L. On the other hand, in the low permeation water fuel cell system shown in the first embodiment, an aqueous solution of 0.8 to 2 mol CH ₃ OH / L is often used. When the GDL 22 is subjected to water repellent treatment and the catalyst layer is thick, an aqueous solution of 2 to 10 mol CH ₃ OH / L may be used.

Further, various measures have been taken, such as supplying the fuel 41 by reducing the supply amount of fuel 41 per unit time, or using a highly water-repellent carbon porous plate for the anode 2 in the MEA structure. In the first embodiment, an MPL is interposed between the anode catalyst layer 21 and the anode GDL 22 to provide a low permeation water fuel cell system.

By the way, when power supply from the power generation unit 4 to the load 12 is stopped, an aqueous solution containing a by-product (residual active material) of the anode reaction, such as formic acid, is not discharged from the anode catalyst layer 21 and around the catalyst. It is thought that it will remain. In a low α power generation environment, it is estimated that the amount of water remaining in the anode catalyst layer 21 after power generation is stopped is extremely small. This is because the amount of water supplied to the anode catalyst 21 is extremely small as compared with a high α power generation environment. Furthermore, when the supply of oxygen as an oxidant from the outside is not interrupted, it is assumed that the remaining active material present around the Pt-Ru catalyst degrades the anode catalyst by associating with oxygen in the vicinity of the catalyst. .

Therefore, to prevent catalyst deterioration,
(Condition A) By-product (residual active material) present around the anode catalyst is removed. (Condition B) Any operation of preventing entry of oxidant from the outside to the power generation unit is performed from the catalyst. Necessary for preventing elution of Ru and Pt.

In the high permeation water fuel cell system, a large amount of water is present in the vicinity of the catalyst, so the concentration of by-products remains low, and these by-products are surrounded by a large amount of water. By-products are prevented from contacting the oxidant (air). Thereby, it is estimated that the anode catalyst of the high permeation water fuel cell system was hardly deteriorated. This concept is shown in FIG. FIG. 9A shows that a large amount of water 102 exists around the catalyst particles 101 and the binder 103 that conducts protons. A by-product 114 is also present in the water 102, but the oxidant 115 cannot approach the by-product 114 due to the presence of the water 102.

On the other hand, in the low permeation water fuel cell system, since there is only a small amount of water near the catalyst, the concentration of by-products is high, and the amount of water surrounding these by-products is small. It is presumed that the contact between the by-product and air (oxidant) is easy. This concept is shown in FIG. In FIG. 9B, unlike FIG. 9A, only a small amount of water 102 exists around the catalyst particles 101 and the binder 103 that conducts protons. For this reason, the oxidizing agent 115 can easily approach the by-product 114.

Thus, the progress rate of deterioration of the anode catalyst in the low permeate fuel cell system is not negligible compared to the high permeate fuel cell system.

Therefore, in the low permeation water fuel cell system, it is considered that at least the operation of (Condition A) or (Condition B) described above is necessary after the power supply from the power generation unit to the load is stopped.

(Effects of the first embodiment)
According to the first embodiment, since the by-product of the anode reaction is removed from the anode catalyst layer 21 before the power generation unit 4 is sealed, a reliable catalyst deterioration suppressing effect can be obtained. In particular, the infiltration of the oxidant may occur not only through the piping such as the fuel supply unit and the fuel discharge unit but also through the gasket 24. In the first embodiment in which the anode 2 is filled with pure water, even if the gasket 24 is a member having a high oxygen permeability, there is an effect that the infiltration of the oxidizing agent can be suppressed. Thereby, there is an advantage that the degree of freedom in selecting the material of the gasket is increased and the degree of freedom in designing the fuel cell system 10 is increased.

Examples of the member having high oxygen permeability include silicon and EPDM.

(Example of the first embodiment)
A low permeate water fuel cell system and a high permeate water fuel cell system were produced, and the effects of the first embodiment were verified. Specifically, each fuel cell system was produced by the following procedure.

(I) Production of Low Permeate Water Fuel Cell System The electromotive part for the low permeate water fuel cell is produced by the following method.

Electromotive member used in this embodiment anode 10 mg / cm ² of Pt-Ru (1: 1) catalyst, the cathode to the electrolyte membrane of the catalyst layer prepared 3 mg / cm ² of Pt catalyst at each spray method ( Gore film) was hot pressed (130 ° C.). To this, GDL with MPL was further applied by hot pressing. Specifically, two layers of NOK2315 (manufactured by NOK Corporation) and LT2300W (manufactured by BASF) were stacked on the anode side, and LT2500W (manufactured by BASF) was used on the cathode side. In the single cell power generation test, an electromotive part having an electrode area of 12 cm ² was used.

(Ii) Production of High Permeability Water Fuel Cell System The electromotive member used for the high permeation water fuel cell is the MPL of anode and cathode among the constituent members of the electromotive member for the low permeation water fuel cell described above. It was prepared by changing the attached GDL to carbon paper.

Even when using a low permeate water fuel cell electromotive unit, it is possible to forcibly realize a high α state by increasing the amount of air supplied to the cathode during power generation (chemical stoichiometric ratio: about 4 to 10). Is not impossible.

(Iii) Verification Test FIGS. 13A and 13B show the anode for the low permeation water fuel cell system and the high permeation water fuel cell system produced as described above, with and without the operation shown in FIG. It shows changes over time of overvoltage. Curves A to D are as follows.

Curve A: When the operation of FIG. 10 is not performed for the low permeate water fuel cell system Curve B: When the operation of FIG. 10 is performed for the low permeation water fuel cell system Curve C: About the high permeation water fuel cell system When the operation of FIG. 10 is not performed Curve D: When the operation of FIG. 10 is performed for the high permeation water fuel cell system The specific test procedure is as follows.

In this experiment, the above-described low permeation water fuel cell and high permeation water fuel cell were each subjected to a power generation test using a single cell. The power generation conditions are as follows: the cell temperature is 60 ° C., the methanol aqueous solution used is 1 to 2 M, air is supplied as the oxidant, and power generation is continued for 8 to 12 hours under the condition of a constant load (150 mA / cm ² ), and then 12 to 16 hours. By repeating the step of pausing.

Experiments were performed in an environment where the air supply amount was 60 mL / min for the low-permeability fuel cell and the air supply amount was 500 mL / min for the high-permeability fuel cell.

In order to investigate the deterioration of the anode during the experiment, the change with time in the anode overvoltage was examined.

As is apparent from the curve A, the anode overvoltage increases with time, and increases by about 60 mV from 0.36 V to 0.40 V after about 1200 hours. On the other hand, in curve B, an increase of about 4 mV is suppressed from 0.345 V to 0.349 V after about 1200 hours.

In contrast, the effect of the same operation on the high permeation water fuel cell system was verified. The result is curve C and curve D. According to this, adoption of (Condition A) and (Condition B) in a highly permeable water fuel cell system has little effect on the increase in overvoltage. When the difference between the overvoltages (Δ1) of curve A and curve B after 1200 hours and the difference (Δ2) between the overvoltages of curve C and curve D are compared, Δ1 is significantly smaller than Δ2. That is, the operations of (Condition A) and (Condition B) described above do not have a special effect in suppressing the overvoltage of the highly permeable water fuel cell system. On the other hand, it is also clear from the results of FIG. 13 that the operation shown in FIG. 10 described above has a significant effect on the overvoltage suppression of the low permeation water fuel cell system.

[Second Embodiment]
Although FIG. 1 shows a mode in which the fuel supply unit 42 and the fluid supply unit 62 are provided separately, a system in which the fluid supply unit 62 for supplying pure water is shared with the fuel supply unit 42 may be employed. A specific configuration is shown in FIG. Specifically, the valves 42a and 62a are changed to valves (three-way valves) 42c, and the pump 62b is omitted.

The changes from the first embodiment are as follows.

(Fuel supply stop step: S03)
The fuel supply to the fuel cell system 10 is stopped. For this purpose, the fuel supply unit control unit 712 issues an instruction to stop the fuel supply unit 42 through the signal line E42. Specifically, the fuel supply unit control unit 712 issues an instruction to close the valve 42c through the signal line E42c. Similarly, an instruction to stop the pump 42b is issued through the signal line E42b.

(Pure water supply start step: S04)
Pure water is supplied to the fuel cell system 10. For this purpose, the fuel supply control unit 712 instructs the valve 42c to change the connection of the fuel supply unit 42 from the connection to the tank 43 to the connection to the tank 63 via the signal line E42c.

Further, the fuel supply unit control unit 712 issues an instruction to supply the pure water 61 stored in the tank 63 to the anode 2 through the signal line E42b.

By flowing pure water through the anode 2 for a predetermined time, the amount of by-products remaining on the anode 2 can be reduced.

(Pure water supply stop step: S05)
After a predetermined time has elapsed, the fuel supply unit control unit 712 instructs the fuel supply unit 42 to stop through the signal line E42. Thereby, the supply of pure water to the power generation unit 4 is stopped. Specifically, the fuel supply unit control unit 712 issues an instruction to close the valve 42a through the signal line E42c. Similarly, an instruction to stop the pump 42b is issued through the signal line E42b.

(Effect of the second embodiment)
In this case, since the number of fluid supply units 62 and valves can be reduced, the fuel cell system 10 can be downsized.

[Third Embodiment]
In FIG. 1, the first fluid is supplied only to the anode 2, but a method of supplying the second fluid to the cathode 3 can also be adopted. A specific configuration is shown in FIG. FIG. 3 illustrates a system for supplying pure water (second fluid) to the cathode 3 in addition to a mode for supplying pure water (first fluid) to the anode 2. The valve 62a in FIG. 1 is changed to a valve (three-way valve) 62c. The valve 62c is used in combination with a fluid supply unit to the anode 2 and a fluid supply unit to the cathode.

The changes from the first embodiment are as follows.

(Pure water supply start step: S04)
Pure water is supplied to the fuel cell system 10. For this purpose, the fluid supply control unit 716 instructs the fluid supply unit 62 to supply pure water to the anode 2 and the cathode 3 via the signal line E62. Specifically, the fluid supply unit control unit 716 instructs the valve 62a to connect the fluid supply unit 62 to the anode 2 and the cathode 3 through the signal line E62a. Similarly, an instruction to operate the pump 62b is issued through the signal line E62b.

By flowing pure water through the anode 2 for a predetermined time, the amount of by-products remaining on the anode 2 can be reduced.

(Pure water supply stop step: S05)
After a predetermined time has elapsed, the fluid supply unit control unit 716 instructs the fluid supply unit 42 to stop through the signal line E62. Thereby, the supply of pure water to the power generation unit 4 is stopped. Specifically, the fluid supply unit control unit 716 issues an instruction to close the valve 62a through the signal line E62c. Similarly, an instruction to stop the pump 42b is issued through the signal line E42b.

(Effect of the third embodiment)
In this case, before the power generation unit 4 is sealed, in addition to the removal of byproducts of the anode reaction from the anode catalyst layer 21, the oxidant is also removed from the cathode side. For this reason, the oxidizing agent permeate | transmitted from the cathode 3 through the electrolyte membrane 1 to the anode 2 can be reduced. As a result, it is possible to obtain a more reliable catalyst deterioration suppressing effect than in the first embodiment.

[Fourth Embodiment]
In FIG. 1, pure water is used as the first fluid, but a system using this as an inert gas can also be adopted. A specific configuration is shown in FIG. A specific configuration is shown in FIG.

In FIG. 4, an inert gas 71 is stored in the tank 71 as the first fluid. The tank 73 is connected to the anode 2 via the pipe L3. A fluid supply part 72 (valve 72a) is inserted in the pipe L3. The fluid supply part 72 has a valve 72a. The valve 72a is connected to the fluid supply unit control unit 716 via the signal line E72a.

That is, in the fourth embodiment, an inert gas (first fluid) is supplied to the power generation unit 4 in order to prevent an oxidant from entering from the outside.

Hereinafter, this procedure will be described with reference to FIG. As in the first embodiment, it is assumed that the fuel cell system 10 is in an operating state.

Since the load release step (S11), the oxidant supply stop step (S12), and the fuel supply stop step (S13) are the same as those in the first embodiment, they are omitted.

(Inert gas supply start step: 14)
An inert gas is supplied to the fuel cell system 10. For this purpose, the fluid control unit 716 issues an instruction to open the valve 72a via the signal line E72a. By flowing an inert gas through the anode 2 for a predetermined time, the amount of oxidant remaining on the anode 2 can be reduced. Further, when the by-product has volatility, the amount of the by-product remaining on the anode 2 can be reduced.

(Inert gas supply stop step: S15)
After a predetermined time has elapsed, the fluid supply control unit 716 issues an instruction to close the valve 72a through the signal line E72a. Thereby, supply of the inert gas to the power generation unit 4 is stopped.

(Effect of the fourth embodiment)
According to the fourth embodiment, the inert gas is a compressive fluid, and if a pressure vessel is used, a large volume of fluid can be transported with a small volume, and in particular, the fuel cell system for portable use can be downsized. It becomes possible to contribute to.

[Fifth Embodiment]
In FIG. 1, pure water is used as the first fluid, but a system in which the supply of the first fluid is omitted may be employed. Specifically, the tank 63 and the fluid supply unit 62 in FIG. 1 are omitted. A specific configuration is shown in FIG. In FIG. 5, the oxidant from the outside is prevented from entering the power generation unit 4 only by operating the valve without supplying the first fluid and the second fluid.

The flowchart according to the fifth embodiment is as shown in FIG. That is, the pure water supply start step (S04) and the pure water supply stop step (S05) are omitted from the flowchart of FIG. The other load release step (S21), oxidant supply stop step (S22), fuel supply stop step (S23), and fuel cell sealing step (S24) are the same as those in the first embodiment.

(Effect of 5th Embodiment)
According to the fifth embodiment, it is effective when the gasket 24 is a member having low oxygen permeability. In the fifth embodiment, pure water, inert gas, and a fluid supply unit for supplying these are not required, and the fuel cell system 10 can be downsized.

Examples of the member having low oxygen permeability include Tygon (trademark), Noprene (trademark), Viton, fluorine rubber, high nitrile rubber, butyl rubber, urethane rubber, and polysulfide rubber.

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Anode 3 ... Cathode 4 ... Power generation part 5 ... Membrane electrode assembly (MEA)
7: Control unit 8: Measuring instrument (current measuring instrument, voltage measuring instrument, temperature measuring instrument)
DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 12 ... Load 21 ... Anode catalyst layer 22, 22a, 22b ... Anode gas diffusion layer (anode GDL layer)
24 ... Gaskets 25, 25a, 25b, 25c ... Anode channel 26 ... Anode microporous layer (anode MPL layer)
31 ... Cathode catalyst layer 32 ... Cathode gas diffusion layer (cathode GDL layer)
33 ... Cathode flow path plate (cathode current collector plate)
34 ... Gaskets 35, 35a, 35b, 35c ... Cathode channel 36 ... Cathode microporous layer (cathode MPL layer)
41 ... Fuel 42 ... Fuel supply parts 42a, 42c ... Valve 42b ... Pump 43 ... Fuel container 46 ... Fuel discharge part 46a ... Valve 51 ... Gas containing oxidant (air)
52 ... Oxidant supply part 52a ... Valve 52b ... Pump 55 ... Valve (cathode discharge part)
56 ... Oxidant discharge part 56a ... Valve 61 ... Pure water (first fluid, second fluid)
62 ... Fluid supply part 63 ... Container 71 ... Inert gas (first fluid)
72 ... Fluid supply part 72a ... Valve 101 ... Catalyst particles 102 ... Water 103 ... Proton conductive binder 114 ... Active material (residual active material)
115 ・ ・ ・ Active material (oxidant)
Ei ... Signal line Li ... Piping

Claims (10)

A membrane electrode assembly including an anode catalyst layer, a cathode catalyst layer, and an electrolyte membrane interposed between the anode catalyst layer and the cathode catalyst layer, and a carbon material on the anode catalyst layer side of the membrane electrode assembly A first layer containing porosity and water repellency; a fuel supply unit that supplies fuel to the anode catalyst layer via the first layer; and an exhaust from the anode catalyst layer. An anode flow path having a fuel discharge section that discharges via a power generation section, a control section that is electrically connected to the power generation section and that can be electrically connected to a load,
A fuel cell system comprising:
The control unit includes a step of stopping power supply from the power generation unit to the load, and a step of preventing an oxidant from entering the power generation unit from the outside. Between the anode catalyst layer and the anode channel, there is further provided a second layer having a porous substrate and a water-repellent layer formed on the substrate, and the second layer The fuel cell system according to claim 1, wherein a porosity is higher than the first porosity. 3. The fuel cell system according to claim 2, wherein the step of preventing an oxidant from entering the power generation unit from outside is performed by closing the fuel supply unit and the fuel discharge unit. The fuel cell system further includes a first fluid supply unit that supplies a first fluid to the anode catalyst layer,
The step of preventing an oxidant from entering the power generation unit from the outside is performed by supplying the first fluid from the first fluid supply unit to the anode catalyst layer. Fuel cell system. 5. The first fluid includes at least one selected from the group consisting of an aqueous solution composed of the same compound as the fuel and water, pure water, and an inert gas. The fuel cell system described in 1. The fuel cell system further includes an oxidant supply unit for supplying an oxidant to the cathode catalyst layer, and an oxidant discharge unit for discharging a fluid from the cathode catalyst layer,
6. The fuel cell system according to claim 5, wherein the step of preventing an oxidant from entering the power generation unit from outside is performed by closing the oxidant supply unit and the oxidant discharge unit. The fuel cell system further includes a second fluid supply unit that supplies a second fluid to the cathode catalyst layer,
The step of preventing an oxidant from entering the power generation unit from the outside is performed by supplying the second fluid from the second fluid supply unit to the cathode catalyst layer. Fuel cell system. The fuel cell system according to claim 7, wherein the second fluid includes at least one selected from the group consisting of water and an inert gas. 9. The fuel cell system according to claim 8, wherein after the second fluid is supplied, the oxidant supply unit and the oxidant discharge unit are closed to prevent the oxidant from entering the power generation unit. . A membrane electrode assembly including an anode catalyst layer, a cathode catalyst layer, and an electrolyte membrane interposed between the anode catalyst layer and the cathode catalyst layer, and a carbon material on the anode catalyst layer side of the membrane electrode assembly A first layer containing porosity and water repellency; a fuel supply unit that supplies fuel to the anode catalyst layer via the first layer; and an exhaust from the anode catalyst layer. A fuel cell system control method including an anode flow path having a fuel discharge section that discharges via a fuel discharge section, wherein the control method stops power supply from the power generation section to a load. And a step of preventing an oxidant from entering the power generation unit.

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