KR20120020499A - Method and apparatus for controlling operation of direct methanol fuel cell system - Google Patents

Abstract

PURPOSE: A driving method of direct methanol type fuel cell system is provided to recover the performance of the catalyst contaminated by by-product like carbon monoxide through simple method, thereby maintaining the output electricity stably. CONSTITUTION: A driving method of direct methanol type fuel cell system comprises a step of operating a fuel cell system in the state the connection of load and the supply of air and fuel are discontinued for specific time. The direct methanol fuel cell system comprises a stack(100), a mixing tank(110) collecting and storing unreacted fuel and air, a fuel tank(120) supplying fuel to the mixing tank, and a fuel pump(121) supplying mixed fuel to the stack, and a control part(130) operating the system for specific time, and operating the system in the state the connection of load and the supply of air and fuel are discontinued for specific time.

Description

Operation Control Method of Direct Methanol Fuel Cell System and Direct Methanol Fuel Cell System Employing the Method {Method and Apparatus for Controlling Operation of Direct Methanol Fuel Cell System}

The present invention relates to an operation control method of a direct methanol fuel cell system and a direct methanol fuel cell system employing the same. More specifically, the output power is stably restored by recovering the performance of a catalyst poisoned by carbon monoxide in a simple manner. The present invention relates to an operation control method of a sustainable direct methanol fuel cell system and a direct methanol fuel cell system employing the same.

A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrogen or hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy.

This fuel cell is a clean energy source that can replace fossil energy, and has a merit that can produce a wide range of outputs by stacking unit cells, and has an energy density of 4 to 10 times that of a small lithium battery. It is attracting attention as a compact and mobile portable power source.

The fuel cell may be classified into a phosphate fuel cell, a molten carbonate fuel cell, a solid oxide fuel cell, a polymer electrolyte fuel cell, an alkaline fuel cell, and the like according to the type of electrolyte used. Each of these fuel cells basically operates on the same principle, but differs in the type of fuel used, operating temperature, catalyst, and electrolyte.

The polymer electrolyte fuel cell has an advantage of having a high energy density and a high output, but requires attention to handling hydrogen gas and reforms fuel for reforming methane, methanol, natural gas, etc. to produce hydrogen as fuel gas. There is a problem that requires additional equipment such as a device.

Direct Methanol Fuel Cell (DMFC) is a fuel cell that uses a polymer membrane that conducts hydrogen ions as an electrolyte and methanol as a fuel directly to the anode. DMFC is operated at operating temperature below 100 ℃ without using fuel reformer, so it is suitable for portable or small fuel cell structure.

In general, a direct methanol fuel cell includes a stack, a fuel tank, a fuel pump, and the like for system configuration. The stack is a part that generates electricity by receiving fuel, and is a membrane electrode assembly (MEA) and a separator ( It has a structure in which a unit cell consisting of a separator) is stacked in a number to several tens. On the other hand, the membrane-electrode assembly is composed of a polymer electrolyte membrane and an anode electrode and a cathode electrode bonded to both surfaces thereof.

The direct methanol type fuel cell has a problem in that the performance of the catalyst gradually decreases with its use, because by-products such as carbon monoxide generated during the operation of the fuel cell poison the catalyst. Therefore, in order to stably maintain the performance of the direct methanol fuel cell and to enable long-term use, it is necessary to prevent the poisoning of the catalyst or to continuously restore the poisoned catalyst to its original state to maintain the performance of the catalyst.

It is an object of the present invention to recover the performance of a catalyst poisoned by by-products such as carbon monoxide in a simple manner, and to control the operation of a direct methanol fuel cell system capable of stably maintaining output power for a long time, and a direct methanol type employing the same. It is to provide a fuel cell system.

In order to achieve the above object, the present invention provides a method for intervening operation (S1) in a state in which a fuel and air supply and load are disconnected for a predetermined time during a normal operation of a methanol fuel cell system. Provided is an operation control method for a direct methanol fuel cell system, characterized in that. According to the operation control method, the normal operation step and the S1 step are repeated during long term operation.

It is preferable that the operation of the fuel and air supply and the load are interrupted is performed when the normal operation of the system is performed for 2 to 120 minutes.

Preferably, the operation of the fuel and air in a state in which the connection between the load and the load is stopped is performed for 5 to 30 seconds.

The present invention also provides a direct methanol fuel comprising the step (S2) of operating in a state in which the supply of air and the load are interrupted for a predetermined time during the normal operation of the direct methanol fuel cell system. An operation control method of a battery system is provided. According to the operation control method, the normal operation step and the S2 step are repeated during long term operation.

Operation of the air supply and the load (load) is interrupted is preferably performed when the normal operation of the system for 2 to 120 minutes.

Operation of the air supply and the load (load) in the interrupted state is preferably performed for 5 to 30 seconds.

The present invention also provides a stack comprising an electrolyte membrane and at least one membrane-electrode assembly including an anode electrode and a cathode electrode positioned on both sides of the electrolyte membrane; A mixing tank for recovering and storing unreacted fuel and water discharged from the stack; A fuel tank for supplying high concentration fuel to the mixing tank; And a fuel pump for supplying the mixed fuel stored in the mixing tank to the stack, the direct methanol type fuel cell system operating the system normally for a predetermined time and supplying fuel and air for a predetermined time and connecting the rod. It provides a direct methanol fuel cell system further comprising a control unit for operating the system in a stopped state.

The present invention also provides a stack comprising an electrolyte membrane and at least one membrane-electrode assembly including an anode electrode and a cathode electrode positioned on both sides of the electrolyte membrane; A mixing tank for recovering and storing unreacted fuel and water discharged from the stack; A fuel tank for supplying high concentration fuel to the mixing tank; And a fuel pump for supplying the mixed fuel stored in the mixing tank to the stack, the direct methanol fuel cell system operating the system normally for a predetermined time and stopping the supply of air and the connection of the rod for a predetermined time. It provides a direct methanol fuel cell system characterized in that it further comprises a control unit for operating the system in the state.

According to the operation control method of the direct methanol fuel cell system of the present invention, the process of operating the direct methanol fuel cell system in a state in which the supply of fuel and air and the load are interrupted for a predetermined time during normal operation is performed. By intervening, not only can the performance of the catalyst poisoned by carbon monoxide or the like be restored, so that the performance of the system can be stably maintained, and the system can be used for a long time.

In addition, there is an advantage that the cost and time can be reduced by restoring the performance of the catalyst in a simple manner through the control of the operation method without the use of additional equipment or materials.

1 is a schematic diagram of a direct methanol fuel cell system according to an embodiment of the present invention.
Figure 2 is a graph showing the experimental results of the dynamic response of the DMFC stack occurs when the constant current 2.4A through the four abnormal operating modes during normal operation.
Figure 3 is a graph showing the results of successfully performing long-term operation of 10000 hours in load-methanol-air on-off mode.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the embodiments according to the present invention, detailed descriptions of related well-known configurations or functions will be omitted. In addition, in adding the reference numerals to the components of each drawing, the same reference numerals are added to the same components as much as possible.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary meanings and should be construed in accordance with the technical meanings and concepts of the present invention.

The embodiments described in the specification and the configuration shown in the drawings are preferred embodiments of the present invention, and do not represent all of the technical idea of the present invention, various equivalents and modifications that can replace them at the time of the present application are There may be.

1 is a schematic diagram of a direct methanol fuel cell system according to an embodiment of the present invention.

Referring to FIG. 1, a direct methanol fuel cell system according to an embodiment of the present invention includes a stack 100, a mixing tank 110, a fuel tank 120, a fuel injection device 111, and an oxidant supply device 160. ), The fuel injection device (111) 130 and the control unit (130).

In more detail, the stack 100 electrochemically reacts the fuel supplied to the anode electrode and the oxidant supplied to the cathode electrode to generate electricity and heat. The stack 100 includes an anode electrode and a cathode electrode together with an electrolyte membrane that electrically separates the anode electrode and the cathode electrode and selectively transmits protons obtained from the fuel from the anode electrode to the cathode electrode.

In addition, the stack 100 includes an anode inlet for fuel inflow to the anode electrode and an anode outlet for exhausting reaction products such as unreacted fuel and carbon dioxide from the anode electrode, and for inflow of an oxidant to the cathode electrode. And a cathode outlet for discharging reaction products such as water and unreacted oxidant from the cathode inlet and the cathode electrode.

The mixing tank 110 supplies the mixed fuel to the anode electrode of the stack 100. In addition, the mixing tank 110 receives and stores the high concentration fuel from the fuel tank 120, and recovers and stores unreacted fuel and water from the fluid discharged through the anode outlet and the cathode outlet of the stack 100. In this case, the mixing tank 110 is coupled to a heat exchanger for depriving the thermal energy of the fluid discharged from the stack 100, it is preferable to have an exhaust port for discharging the unwanted gas in the fluid. As the aforementioned mixing tank 110, a recycling apparatus having various existing shapes and structures may be easily used.

The fuel tank 120 supplies a high concentration of fuel to the mixing tank 110. The amount of fuel supplied from the fuel tank 120 may be controlled using the pump 121 or the like. The high concentration fuel is an aqueous methanol solution having a concentration of at least 6 moles or includes pure methanol.

The fuel injection device 111 supplies the mixed fuel stored in the mixing tank 110 to the anode electrode of the stack 100 and controls the supply amount of the mixed fuel. The fuel injection device 111 may be implemented as a fuel injection device 111 or a compression device.

The oxidant supply device 160 supplies the oxidant to the cathode electrode of the stack 100. As the oxidizing agent, it is preferable to use a material that appropriately reduces protons at the cathode electrode, such as oxygen-containing air or pure oxygen, and does not generate substances harmful to humans or the environment as reaction products. The oxidant supply device 160 described above may be implemented as an air fuel injection device 111 or a blower.

The controller 130 controls the supply of fuel and air and the connection of the rod.

According to an operation control method of a direct methanol fuel cell system according to an embodiment of the present invention, the fuel and air supply and load are connected for a predetermined time during the normal operation of the direct methanol fuel cell system. The step S1 of operating in the stopped state is intervened.

Here, 'normal operation' refers to a state in which fuel and air supply and load are normally connected, and 'predetermined time' refers to a time according to a predetermined value and is not specified as a single value. It may be arbitrarily determined in consideration of various elements of.

On the other hand, intervening the step (S1) for operating in a state in which the connection of the fuel and air and the load (load) is interrupted for a predetermined time during the normal operation, the normal operation, S1 stage, normal operation, S1 stage, normal operation This means that the normal operation and the step S1 are continuously repeated in the same manner as the step S1.

In repeating the normal operation and the step S1, the normal operation and the progression of the step S1 may be performed for a predetermined time, it is preferable that the normal operation proceeds for 2 to 120 minutes and the S1 step is performed for 5 to 30 seconds. When the normal operation time is less than the lower limit of the range, it is difficult for the fuel cell stack constituting the system to reach the steady state, and when the upper limit of the range is exceeded, the effect of intervening the S1 step is reduced, which is undesirable. In addition, when the progress time of the step S1 is less than the lower limit of the above range, it is difficult to ensure sufficient time to induce a voltage drop in the state of interrupting the supply of fuel and air and the load, exceeding the upper limit of the above range In this case, the capacity of the battery for power supply during the system down time may be too large, which is not preferable.

In the above-described embodiment, the connection between the fuel and air supply and the rod is stopped together during the normal operation, but by simplifying this, a method of stopping the supply of the air and the connection between the rod and the fuel supply as it is may be applied. While stopping the supply of fuel and air and the connection of the rods together can achieve the most desirable effect, the method of stopping only the supply of air and the connection of the rods can also provide a significant recovery of system performance.

Figure 2 is a graph showing the experimental results of the dynamic response of the DMFC stack that occurs when a constant voltage of 2.4V through four abnormal operating modes during normal operation. The four abnormal operating modes are load on-off mode (A), load-methanol on-off mode (B), load-air on-off mode (C), load-methanol-air on-off mode (D) to be. These modes of operation have an off time of 10s equal to on time 120s. In only turning off the load, the rod and fuel, the rod and fuel, the rod and the air and the fuel, the load on time means the normal operation time, the load-off time is the time when the connection of the load is interrupted.

The data in FIG. 2A shows that stack performance and response behavior are affected by each abnormal mode of operation. When the DMFC stack is operated in load on-off mode and load-methanol on-off mode, the stack has an output power of 5.11W. On the other hand, when operated by the load-air on-off mode and the load-methanol-air on-off mode, the stack performance increases above 6W. This improvement in performance is also related to the effective removal of water from the cathode by an air on-off process, but it is not just for this reason that a 1 W difference in performance occurs during a short cycling time. In other words, complex electrochemical reactions in catalysts such as catalyst poisoning, da-poisoning and catalyst utility can be seen to be affected by rapid voltage changes in each abnormal mode of operation. This assumption is supported by the dynamic reaction behavior following these abnormal modes of operation.

As shown in Figures 2B and 2C, the stack current produced varies with each abnormal operating mode. In addition, each abnormal operating mode exhibits different currents (FIG. 2B) and voltage response behavior (FIG. 2C). With respect to the stack current response, when the stack is operated in load on-off mode and load-methanol on-off mode, the current reaches a steady state without a transient stage. Conversely, when operated by the load-air on-off mode and the load-methanol-air on-off mode, the stack undergoes overshooting and relaxation. The load-methanol-air on-off mode and load-air on-off gradually increase the current at an early stage, after which the stack returns to normal. Current can be increased by detoxification of the electrode surface through oxidation of a material such as CO, and can also increase the free surface site for the methanol oxidation reaction. Therefore, the load-air on-off mode and the load-methanol-air on-off mode are very effective for increasing the active site of the catalyst.

These phenomena are more evident from the stack voltage behavior during the load off state. When the stack is off in load on-off mode, load-methanol on-off mode, the voltage returns to an open circuit value. Conversely, in the off state of the load-air on-off mode and the load-methanol-air, it drops to 0.5V (see FIG. 2C). At high amounts of potential, the oxidation of platinum forms a platinum oxide layer or corrosion of the carbon carrier, which reduces the number of platinum active sites. On the other hand, the low potential at the cathode reduces the surface oxide layer of the platinum catalyst and quickly consumes oxygen at the cathode. Then, the performance of the DMFC cathode is restored. Therefore, the voltage drop in the load off state promotes detoxification of the catalyst surface, and this phenomenon increases the stack performance in the load-air on-off mode and the load-methanol-air on-off mode.

When the load-air on-off mode and the load-methanol-air on-off mode are applied, the stack maintains a low voltage for 2-3 seconds in the load-on phase. In addition, the air supply at the cathode is delayed for 2-3 seconds when the load-air on-off mode and the load-methanol-air on-off mode are used. Therefore, the immediate lack of air at the cathode can lower the cathode potential required for the reduction of surface oxides. In addition, the stack produces high currents even if the air supply flow to the stack is delayed. This phenomenon can occur because residual air in the stack layer or the porous layer of the electrode participates in the reaction and because it discharges higher current in the electrical double layer at both electrodes.

2D shows the voltage response of the DMFC stack in the on-off state. Measurements were made during a short sampling time of 0.02 s to observe more detailed voltage behavior. Although the stack is operated at a constant voltage of 2.4V, transient overshooting behavior (about 16-18s) occurs in the voltage response. This transient behavior is due to the high overpotential that oxidizes the absorbed poisoning material. And overshooting results from excessive poisoning of the catalyst surface. This result indicates that the load on-off mode and the load-methanol on-off mode during the off state cause poisoning of the catalyst, while the load air on-off mode and the load-methanol-air on-off mode cause catalyst detoxification. Indicates that Therefore, all data in FIG. 2 indicate that the load-air on-off mode and the load-methanol-air on-off mode are much better operating modes for the DMFC stack compared to the load on-off mode and load-methanol on-off mode. Prove that.

Long-term operation was performed for 10,000 hours through the load-methanol-air on-off mode to confirm how effectively the performance of the system was maintained during the long-term operation when the load-methanol-air on-off mode was intervened. In the above experiment, the normal operation time (load on time) was 30 minutes and the abnormal operation time (load off time) was 10 seconds, and the normal operation and abnormal operation were repeated.

Figure 3 is a graph showing the results of the above experiment, it can be seen that through the load-methanol-air on-off mode can maintain the performance of the system continuously.

Claims (12)

Operation control method of the direct methanol fuel cell system characterized in that the step of operating in a state in which the supply of fuel and air and the load (load) is interrupted for a predetermined time during the normal operation of the direct methanol fuel cell system. .
The method of claim 1,
The operation control method of the direct methanol fuel cell system, characterized in that the operation of the fuel and air supply and the load (load) is stopped when the normal operation of the system proceeds for 2 to 120 minutes .
The method of claim 2,
And operating in a state in which the fuel and air supply and the load are interrupted, the operation of the direct methanol fuel cell system according to claim 5, wherein the operation is performed for 5 to 30 seconds.
A method of controlling the operation of a direct methanol fuel cell system, characterized in that the step of operating in a state in which the supply of air and the connection of the load (load) is interrupted for a predetermined time during the normal operation of the direct methanol fuel cell system.
The method of claim 4, wherein
Operating in a state in which the supply of air and the connection of the loads are interrupted, wherein the normal operation of the system is performed for 2 to 120 minutes.
The method of claim 5,
Operating in a state in which the supply of air and the connection of the load (load) is stopped operating method of the direct methanol fuel cell system, characterized in that performed for 5 to 30 seconds.
A stack comprising an electrolyte membrane and at least one membrane-electrode assembly comprising an anode electrode and a cathode electrode positioned on both sides of the electrolyte membrane;
A mixing tank for recovering and storing unreacted fuel and water discharged from the stack;
A fuel tank for supplying high concentration fuel to the mixing tank; And
In the direct methanol fuel cell system comprising a fuel pump for supplying the mixed fuel stored in the mixing tank to the stack,
And a control unit for operating the system in a state in which the system is normally operated for a predetermined time and the connection between the fuel and air supply and the load is stopped for a predetermined time.
The method of claim 7, wherein
The control unit is a direct methanol fuel cell system, characterized in that for operating the system for 2 to 120 minutes after the normal operation of the fuel and air supply and the load (load) is disconnected.
The method of claim 8,
And the control unit operates the system for 5 to 30 seconds after the normal operation of the system and the connection of the fuel and air to the load and the load are interrupted.
A stack comprising an electrolyte membrane and at least one membrane-electrode assembly comprising an anode electrode and a cathode electrode positioned on both sides of the electrolyte membrane;
A mixing tank for recovering and storing unreacted fuel and water discharged from the stack;
A fuel tank for supplying high concentration fuel to the mixing tank; And
In the direct methanol fuel cell system comprising a fuel pump for supplying the mixed fuel stored in the mixing tank to the stack,
And a control unit for operating the system in a state in which the system is normally operated for a predetermined time and the supply of air and the load are interrupted for a predetermined time.
The method of claim 10,
The control unit is a direct methanol fuel cell system, characterized in that for operating the system in a state in which the supply of the air and the load (load) is stopped after the normal operation of the system for 2 to 120 minutes.
The method of claim 11,
The control unit is a direct methanol fuel cell system, characterized in that for operating the system for 5 to 30 seconds in a state in which the supply of air and the load (load) is stopped after the normal operation of the system.

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