JP5332110B2 - Fuel cell and operation method thereof - Google Patents

Description

  The present invention relates to a fuel cell and an operation method thereof, and more particularly, to a fuel cell characterized by a configuration for recovering a decrease in output due to a change with time in a micro fuel cell and an operation method thereof.

  In recent years, with the remarkable progress of portable electronic devices such as mobile phones, PDAs (Personal Digital Assistants), notebook computers, etc., power consumption has increased and the use has been extended for a long time. It has been.

  However, with lithium-ion secondary batteries currently installed in most portable devices, the performance improvement is approaching the limit in terms of materials and structure. On the other hand, as a new high-capacity drive power supply, Attention has been focused on micro fuel cells, which have a large theoretical capacity and are expected to have a capacity that is several times higher than that of lithium ion batteries.

This is a fuel cell in which a polymer solid electrolyte is used as an electrolyte and an energy density is improved by supplying an organic fuel such as methanol onto an electrode, and is suitable for light weight and small size.
For example, a direct methanol fuel cell (DMFC) using methanol as a fuel supplies methanol and water to the fuel electrode in the liquid phase or gas phase, generates protons and carbon dioxide on the electrode catalyst, and the generated protons are Permeated through the polymer electrolyte membrane, transported to the air electrode and combined with oxygen to produce water. At that time, the fuel electrode and air electrode are connected to an external circuit to extract electric power. It is.

  Such a fuel supply method in the DMFC can be classified into a liquid supply type in which liquid fuel is directly supplied to the fuel electrode surface and a vaporization supply type in which the liquid fuel is vaporized and then supplied to the electrode portion (for example, (See Patent Document 1 or Patent Document 2).

  Among these, in the vaporization supply type, it is possible to increase the concentration of the fuel supplied from the tank, and the energy density is improved compared to the case where low concentration fuel is used when compared with the same fuel volume. It can be said that the vaporization supply method is a suitable method for use in portable electronic devices where high energy density is required.

  As for the above-described micro fuel cell, so far, organic fuel has been focused on methanol and research and development has been actively conducted. In this case, Pt-Ru is mainly used as a catalyst for the fuel electrode that oxidizes methanol. It is used for.

  However, such a DMFC has a problem that only a relatively low power density can be obtained at room temperature, and further, there is a problem that a crossover in which fuel methanol passes through the solid polymer electrolyte membrane is remarkable. The crossed-over fuel burns directly at the air electrode and is not converted into electrical energy.

This results in excessive heat generation at the air electrode in addition to the fact that the inherent energy of the fuel cannot be used effectively.
Furthermore, the potential drop at the air electrode is caused to lower the battery voltage and the efficiency of the battery is lowered, which is very disadvantageous for application to portable electronic device applications.

  Therefore, in order to overcome the problems in DMFC as described above, there has been proposed a fuel cell in which formic acid, which is an organic liquid, is used as fuel as well as methanol, and Pd is used as a fuel electrode catalyst. (For example, refer to Patent Document 3 or Patent Document 4).

  Such a formic acid-Pd fuel cell exhibits a power density that is 2-3 times higher at room temperature than a methanol-Pt-Ru fuel cell, and formic acid has a significantly lower crossover amount than methanol. There are features.

Therefore, compared with methanol, most of the supplied fuel can be electrochemically reacted at the fuel electrode, and the energy of the fuel can be effectively converted into electrical energy.
Further, heat generation at the air electrode is suppressed. Furthermore, the potential drop at the air electrode is small, and the efficiency of the battery is increased.

Thus, it can be said that the formic acid-Pd fuel cell is very promising when applied to a power source for portable electronic devices.
JP 2000-106201 A JP 2006-040882 A JP 2005-522015 Gazette JP 2006-093128 A

  As described above, a formic acid-Pd micro fuel cell using formic acid as a fuel and Pd as a fuel electrode catalyst shows a higher power density than DMFC, but such a formic acid-Pd micro fuel cell is continuous. There is a problem of a change with time in the characteristic that the power density gradually decreases during power generation.

  That is, there is a problem that a high output density, which is a major feature of this system, cannot be continuously maintained, and even in the above-mentioned Patent Document 4, no particular mention is made regarding means for recovering the decreasing output density.

  Therefore, an object of the present invention is to recover output reduction due to aging with a simple configuration.

FIG. 1 is a diagram illustrating the basic configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
See FIG. 1 In order to solve the above-mentioned problem, in the fuel cell according to the present invention, an air electrode 3 that reduces oxygen as an active material through an electrolyte 1 and a fuel electrode 2 that oxidizes a fuel 7 made of formic acid or a formic acid aqueous solution. And a cleaning mechanism for cleaning the fuel electrode 2 by supplying the cleaning liquid 4 directly only to the fuel electrode side, and the cleaning mechanism collects the water generated at the air electrode 3 and It has the collection | recovery mechanism used as a washing | cleaning liquid, It is characterized by the above-mentioned.

In this way, by providing a cleaning mechanism for supplying the cleaning liquid 4 only to the fuel electrode side to clean the fuel electrode 2, the power generation is interrupted before the power density drops to a practically unfavorable value. The decreased output can be recovered by cleaning the electrode 2 with the cleaning liquid 4. In particular, since the cleaning mechanism is provided with a recovery mechanism that recovers the water generated in the air electrode 3 to obtain the cleaning liquid 4, the water can be used effectively and the amount of water that must be supplied from the outside is reduced. be able to.

  The cleaning mechanism in this case preferably includes a first storage unit 5 for storing the cleaning liquid 4 and a second storage unit 6 for storing the used cleaning liquid 4, thereby using the reaction product containing the reaction product. The used cleaning liquid 4 is not released to the environment.

  As the cleaning liquid 4, water is particularly effective, and the reaction product that poisons the Pd catalyst generated during power generation can be removed by washing with water, so that the characteristics are restored to the initial values. Conceivable.

  In this case, the catalyst component of the fuel electrode 2 is typically a Pd metal or an alloy containing Pd, and the fuel 7 in that case is typically formic acid.

  The fuel supply method in this case may be either a liquid supply type or a vaporization supply type, but the liquid supply type fuel 7 is preferably a 5 to 85% by weight aqueous formic acid solution, while the vaporization supply type fuel 7 is used. Is preferably a 5 to 100% by weight aqueous formic acid solution.

Further, when operating the above-described fuel cell, when it is detected that the output has decreased to a predetermined output value determined at the time of power generation, the power generation is interrupted, and the cleaning liquid that collects the water generated at the air electrode 3 is recovered. It is desirable to perform the operation of supplying fuel 4 directly only to the fuel electrode side to wash the fuel electrode 2, whereby the power density can be restored to the initial value and the high power density can be maintained for a long time.
Further, after the power generation is completed, an operation of cleaning the fuel electrode 2 by directly supplying the cleaning liquid 4 recovered from the water generated in the air electrode 3 only to the fuel electrode side may be performed. When the is used again, the initial power density can be obtained.

Further, the amount of cleaning liquid to be flowed at the time of cleaning is preferably 0.60 cc / cm ² or more per unit electrode area of the membrane-electrode assembly, whereby a high output density can be maintained for a long time.

  According to the present invention, the reaction product is removed by washing the fuel electrode with water or the like when the output density falls below a predetermined value due to a change over time, so the feature of the formic acid-Pd fuel cell is that A certain high power density can be maintained for a long time.

See Figure 2
FIG. 2 is a conceptual configuration diagram of the power generation unit of the fuel cell according to the present invention. The power generation unit is called MEA (membrane electrode assembly), and the fuel electrode 11 and the air electrode 15 are interposed via the electrolyte layer 14 made of a solid electrolyte. Are installed opposite each other.
The fuel electrode 11 oxidizes the fuel to extract protons and electrons, and is arranged by laminating the fuel electrode catalyst layer 12 and the fuel electrode current collector 13 in this order from the electrolyte layer 14 side.
Here, for example, a Pd black catalyst (manufactured by Aldrich) is used as the fuel electrode catalyst layer 12.

On the other hand, the air electrode 15 generates water by reduction of oxygen by reaction with electrons and protons generated at the fuel electrode 11, and the air electrode catalyst layer 16, the air electrode current collector from the electrolyte layer 14 side. The layers are arranged in the order of 17.
In addition, as the air electrode catalyst layer 16 in this case, for example, a Pt-supported carbon catalyst TEC10E50E (Tanaka Kikinzoku product model number) is used.

The electrolyte layer 14 is a path for transporting protons generated in the fuel electrode 11 to the air electrode 15 and has high proton conductivity without electron conductivity. As a typical example, Nafion There is a film (trade name, manufactured by DuPont).
For example, Nafion 112 (trade name manufactured by Dupont) is used as the electrolyte constituting the electrolyte layer 14.

  In this configuration of the fuel cell, the formic acid fuel 24 stored in the fuel storage unit 18 is supplied to the fuel electrode 11 through the pipe 19 and the valve 20, continuously generates power, and is not used for power generation. The fuel is collected in the waste fuel storage unit 23 via the pipe 21 and the valve 22.

  In the present invention, a cleaning mechanism 30 is provided that includes a cleaning liquid supply system including a cleaning liquid storage unit 31, a pipe 32, and a valve 33, and a cleaning liquid recovery system including a pipe 34, a valve 35, and a used cleaning liquid storage unit 36. Pure water 37 is supplied from the cleaning liquid storage unit 31 to the fuel electrode 11 to clean the fuel electrode 11 to remove reaction products generated by power generation.

Next, a recovery scheme for the reduced output value will be described.
When the formic acid fuel 24 is supplied and power generation is started, the output decreases with time from the initial value, but when it is detected that the output value has decreased to a predetermined value, power generation is interrupted and The fuel electrode 11 is washed by controlling to switch to the path for supplying the water 37.

After washing, control is performed again to switch to a path for supplying formic acid fuel 24 from pure water 37 by valve operation, and power generation is resumed.
By doing so, it is possible to operate for a long time at a high output.
If the fuel electrode 11 is controlled to be washed with water after the power generation is completed, a high output operation can be immediately performed at the start of the next power generation.

See Figure 3
FIG. 3 is a diagram showing a change in output density over time when cleaning is performed. When the output decreases with time from the initial value and the output value decreases to a predetermined value, the cleaning of the fuel electrode 11 is repeated. By doing so, the initial value of the power density can always be recovered.

The reason why the characteristic is restored to the initial value by the method described above can be considered as follows.
Due to the reaction product generated during power generation, poisoning of the fuel electrode catalyst will occur and the characteristics will deteriorate, but it can be removed by washing with water, so it is assumed that the characteristics will be restored to their initial values. .

From the knowledge obtained from the measurement results described later, it has been confirmed that a certain amount of washing water needs to be passed in order for the characteristics to completely recover to the initial values.
Specifically, for example, the lower limit power density during the operation of the battery voltage 0.6V in case of a 80 mW / cm ² is required the washing water in the amount of the unit electrode area per 0.60 cc / cm ² of the MEA Become.

  The liquid fuel supply configuration associated with this measurement is 0.1 wt.% Using 15 wt (wt) of formic acid as the fuel, a fuel flow rate of 3 cc / min, and an air flow rate of 2 L / min. A 6 V constant voltage discharge was performed.

In the output evaluation, the lower limit output density is set to 80 mW / cm ^2, and the value of the output density after washing when water washing is performed when the lower limit output density is reached is the initial value of power generation start. Assessed as 100%.

In Example 1 of the present invention, in addition to the measurement conditions described above,
MEA electrode area: 25 cm ²
Wash water flow rate: 3 cc / min Wash time: 15 minutes Wash water volume per unit area: 1.8 cc / cm ²
The fuel cell was operated under the following conditions.

See Figure 4
FIG. 4 is a diagram showing a change with time in the output density when cleaning is performed in Example 1. When the output decreases with time from the initial value and the output value decreases to a predetermined value, the fuel electrode is changed. By repeatedly performing the cleaning, the initial value of the power density can always be recovered.

  In this case, the output density recovery rate after the first cleaning in this case is 103%, and the output density recovery rate after the 10th cleaning is 99%. In addition, it was confirmed that the initial value was recovered almost even after the 10th washing.

In Example 2 of the present invention, in addition to the measurement conditions described above,
MEA electrode area: 25 cm ²
Washing water flow rate: 3 cc / min Washing time: 5 minutes Washing water amount per unit area: 0.60 cc / cm ²
The fuel cell was operated under the following conditions.

  In this case, the output density recovery rate after the first cleaning is 97%, and the output density recovery rate after the 10th cleaning is 101%, which is almost restored to the initial value for each cleaning. It was confirmed.

In Example 3 of the present invention, in addition to the measurement conditions described above,
MEA electrode area: 25 cm ²
Washing water flow rate: 6 cc / min Washing time: 2.5 minutes Washing water amount per unit area: 0.60 cc / cm ²
The fuel cell was operated under the following conditions.

  In this case, the output density recovery rate after the first cleaning is 98%, and the output density recovery rate after the 10th cleaning is 98%, which is almost restored to the initial value for each cleaning. It was confirmed.

In Example 4 of the present invention, while reducing the MEA electrode area, in addition to the measurement conditions described above,
MEA electrode area: 5 cm ²
Wash water flow rate: 3 cc / min Wash time: 3 minutes Wash water volume per unit area: 1.8 cc / cm ²
The fuel cell was operated under the following conditions.

  In this case, the output density recovery rate after the first cleaning is 103%, and the output density recovery rate after the 10th cleaning is 101%, which is almost restored to the initial value for each cleaning. It was confirmed.

Also in Example 5 of the present invention, the MEA electrode area is reduced, and in addition to the above measurement conditions,
MEA electrode area: 5 cm ²
Washing water flow rate: 3 cc / min Washing time: 1 minute Washing water amount per unit area: 0.60 cc / cm ²
The fuel cell was operated under the following conditions.

  In this case, the output density recovery rate after the first cleaning is 98%, and the output density recovery rate after the 10th cleaning is 100%, which is almost restored to the initial value for each cleaning. It was confirmed.

Also in Example 6 of the present invention, the MEA electrode area is reduced, and in addition to the above measurement conditions,
MEA electrode area: 5 cm ²
Washing water flow rate: 1 cc / min Washing time: 3 minutes Washing water amount per unit area: 0.60 cc / cm ²
The fuel cell was operated under the following conditions.

  In this case, the output density recovery rate after the first cleaning is 99%, and the output density recovery rate after the 10th cleaning is 97%, which is almost restored to the initial value for each cleaning. It was confirmed.

Next, a comparative example for confirming the comparison effect in the embodiment of the present invention will be described.
[Comparative Example 1]
In Comparative Example 1, without washing,
MEA electrode area: 25 cm ²
Washing water flow rate: 0 cc / min Washing time: 0 minutes Washing water amount per unit area: 0 cc / cm ²
The fuel cell was operated under the following conditions.

See Figure 5
FIG. 5 is a graph showing a change with time in the output density in Comparative Example 1, and it was confirmed that the output gradually decreased with time from the initial value.

[Comparative Example 2]
In Comparative Example 2, in addition to the measurement conditions described above,
MEA electrode area: 25 cm ²
Washing water flow rate: 3 cc / min Washing time: 3 minutes Washing water amount per unit area: 0.36 cc / cm ²
The fuel cell was operated under the following conditions.

  In this case, the output density recovery rate after the first cleaning is 86%, and the output density recovery rate after the 10th cleaning is 35%, and considerable recovery is seen in the first cleaning. However, the recovery rate after the 10th washing was very low.

[Comparative Example 3]
In Comparative Example 3, while reducing the electrode area, in addition to the measurement conditions described above,
MEA electrode area: 5 cm ²
Washing water flow rate: 3cc / min Washing time: 0.5
Washing water amount per unit area: 0.3 cc / cm ²
The fuel cell was operated under the following conditions.

  In this case, the output density recovery rate after the first cleaning is 83%, and the output density recovery rate after the 10th cleaning is 29%, which is lower than that of Comparative Example 2. Met.

See FIG.
FIG. 6 summarizes the measurement results of Examples 1 to 6 above and the measurement results of Comparative Examples 1 to 3, and in order to withstand long-term use by water cleaning, It can be seen that cleaning with a total water amount of 0.60 cc / cm ² or more per unit electrode area of the MEA is required instead of the cleaning time.

Next, a gas supply type fuel cell according to Example 7 of the present invention will be described with reference to FIG.
See FIG.
FIG. 7 is a conceptual configuration diagram of a power generation unit of a gas supply type fuel cell according to Example 7 of the present invention. In the power generation unit, a fuel electrode 11 and an air electrode 15 are opposed to each other through an electrolyte layer 14 made of a solid electrolyte. Has been.
The fuel electrode 11 oxidizes the fuel to extract protons and electrons, and is arranged by laminating the fuel electrode catalyst layer 12 and the fuel electrode current collector 13 in this order from the electrolyte layer 14 side.
Here, for example, a Pd black catalyst (manufactured by Aldrich) is used as the fuel electrode catalyst layer 12.

  A gas diffusion layer 41, a fuel vaporization unit 42, and a fuel chamber 43 are sequentially provided so as to be in contact with the fuel electrode 11, and the formic acid fuel 45 stored in the liquid fuel storage unit 44 passes through a valve 46 and a pipe 47. To the fuel chamber 43.

On the other hand, the air electrode 15 generates water by reduction of oxygen by reaction with electrons and protons generated at the fuel electrode 11, and the air electrode catalyst layer 16, the air electrode current collector from the electrolyte layer 14 side. The layers are arranged in the order of 17.
In addition, as the air electrode catalyst layer 16 in this case, for example, a Pt-supported carbon catalyst TEC10E50E (Tanaka Kikinzoku product model number) is used.

The electrolyte layer 14 is a path for transporting protons generated in the fuel electrode 11 to the air electrode 15 and has high proton conductivity without electron conductivity. As a typical example, Nafion There is a film (trade name, manufactured by DuPont).
For example, Nafion 112 (trade name manufactured by Dupont) is used as the electrolyte constituting the electrolyte layer 14.

  Also in the seventh embodiment, a cleaning mechanism 30 including a cleaning liquid supply system including a cleaning liquid storage unit 31, a pipe 32, and a valve 33 and a cleaning liquid recovery system including a pipe 34, a valve 35, and a used cleaning liquid storage unit 36. And supplying pure water 37 from the cleaning liquid storage unit 31 to the fuel electrode 11 to clean the fuel electrode 11 to remove reaction products generated by power generation.

The operation method of the gas supply type fuel cell of Example 7 is exactly the same as the above liquid supply type fuel cell, for example, when the lower limit output density is set to 80 mW / cm ² and the lower limit output density is reached. The initial output is restored by washing with water in this case, and in this case as well, operation is performed by washing with a total water amount of 0.60 cc / cm ² or more per unit electrode area of the MEA.

As mentioned above, although each Example of this invention was described, this invention is not restricted to the structure, conditions, and numerical value which were shown to each Example, A various change is possible .

  In addition, the fuel electrode, air electrode, or electrolyte membrane material shown in each of the above-described embodiments is merely an example, and various modifications are possible within the scope of the known technology. For example, the fuel electrode is limited to Pd. Instead, Pd alloys such as Pd—V and Pd—Mo may be used.

  Although not particularly mentioned in each of the above embodiments, the fuel electrode may be washed separately from the output reduction state immediately after the power generation is once finished. When operating the system, it is possible to obtain a normal initial power density from the beginning.

  In each of the above embodiments, a 15% by weight aqueous formic acid solution is used as the fuel. However, the present invention is not limited to a 15% by weight aqueous formic acid solution. % Formic acid aqueous solution is desirable, and in the case of a gas supply type, 5 to 105% by weight aqueous formic acid aqueous solution is desirable.

Here, referring to FIG. 1 again, the detailed features of the present invention will be described again.
Again see Figure 1
(Supplementary note 1) A power generation part in which an air electrode 3 for reducing oxygen as an active material through an electrolyte 1 and a fuel electrode 2 for oxidizing a fuel 7 made of formic acid or a formic acid aqueous solution are disposed, and a cleaning liquid 4 only on the fuel electrode side And a cleaning mechanism for cleaning the fuel electrode 2 directly , and the cleaning mechanism has a recovery mechanism for recovering the water generated at the air electrode 3 and using it as the cleaning liquid. .
(Additional remark 2) The said washing | cleaning mechanism has the 1st storage part 5 which stores the washing | cleaning liquid 4, and the 2nd storage part 6 which stores the used washing | cleaning liquid 4. The fuel cell of Additional remark 1 characterized by the above-mentioned. .
(Supplementary note 3 ) The fuel cell according to Supplementary note 1 or 2 , wherein the fuel electrode 2 includes a Pd metal or an alloy containing Pd as a catalyst component.
(Additional remark 4 ) The fuel storage part 8 which stores the fuel 7 which consists of the said formic acid or formic acid aqueous solution, and a fuel vaporization part between the said fuel storage part 8 and the said fuel electrode 2 are provided, and the said fuel 7 is provided in the said fuel electrode 2. The fuel cell according to any one of supplementary notes 1 to 3 , wherein the fuel cell is supplied in a gas state.
(Additional remark 5 ) In the electric power generation part by which the air electrode 3 which reduces oxygen as an active material through the electrolyte 1 and the fuel electrode 2 which oxidizes the fuel 7 which consists of formic acid or formic acid aqueous solution are arrange | positioned, predetermined output predetermined at the time of electric power generation is arrange | positioned When it is detected that the fuel electrode 2 has fallen to the value, the power generation is interrupted, and the fuel electrode 2 is cleaned by directly supplying the cleaning liquid 4 collected from the air electrode 3 only to the fuel electrode side. A method for operating a fuel cell, comprising:
(Additional remark 6 ) In the electric power generation part by which the air electrode 3 which reduces oxygen as an active material through the electrolyte 1 and the fuel electrode 2 which oxidizes the fuel 7 which consists of formic acid or a formic acid aqueous solution are arrange | positioned, after completion | finish of electric power generation, the said air electrode 3 A method for operating a fuel cell, comprising: supplying the cleaning liquid 4 recovered from the water produced in step 1 directly only to the fuel electrode side to clean the fuel electrode 2.
(Additional remark 7 ) The operating method of the fuel cell of Additional remark 5 or Additional remark 6 characterized by making the amount of washing | cleaning liquids flowed at the time of the said washing | cleaning into 0.60 cc / cm < ² > or more per unit electrode area of a membrane-electrode assembly.

  As an application example of the present invention, a fuel cell is typical as a power source of a portable electronic device such as a mobile phone, a PDA, or a notebook personal computer, but is not limited to the power source of the portable electronic device, It is also used as a power source for desktop personal computers and other relatively large electronic devices.

It is explanatory drawing of the fundamental structure of this invention. It is a notional block diagram of the electric power generation part of the fuel cell of this invention. It is explanatory drawing of the time-dependent change of the output density at the time of washing | cleaning. It is explanatory drawing of the time-dependent change of the output density at the time of washing | cleaning in Example 1. FIG. It is explanatory drawing of the time-dependent change of the output density in the comparative example 1. It is explanatory drawing of the measurement result of Example 1 thru | or Example 6, and the measurement result of Comparative Example 1 thru | or Comparative Example 3. FIG. It is a notional block diagram of the electric power generation part of the gas supply type fuel cell of Example 7 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte 2 Fuel electrode 3 Air electrode 4 Cleaning liquid 5 1st storage part 6 2nd storage part 7 Fuel 8 Fuel storage part 11 Fuel electrode 12 Fuel electrode catalyst layer 13 Fuel electrode collector 14 Electrolyte layer 15 Air electrode 16 Air Electrode catalyst layer 17 Air electrode current collector 18 Fuel storage part 19 Pipe 20 Valve 21 Pipe 22 Valve 23 Waste fuel storage part 24 Formic acid fuel 30 Cleaning mechanism 31 Cleaning liquid storage part 32 Pipe 33 Valve 34 Pipe 35 Valve 36 Used cleaning liquid storage part 37 Pure water 41 Gas diffusion layer 42 Fuel vaporization section 43 Fuel chamber 44 Liquid fuel storage section 45 Formic acid fuel 46 Valve 47 Piping

Claims (5)

A power generation unit in which an air electrode that reduces oxygen as an active material through an electrolyte and a fuel electrode that oxidizes fuel made of formic acid or a formic acid aqueous solution are disposed;
A cleaning mechanism that supplies the cleaning liquid directly only to the fuel electrode side to clean the fuel electrode;
The fuel cell according to claim 1, wherein the cleaning mechanism includes a recovery mechanism that recovers water generated at the air electrode to form the cleaning liquid.   The fuel cell according to claim 1, wherein the fuel electrode includes a Pd metal or an alloy containing Pd as a catalyst component. A fuel storage unit that stores the fuel made of the formic acid or the formic acid aqueous solution; a fuel vaporization unit that is provided between the fuel storage unit and the fuel electrode; and the formic acid is supplied to the fuel electrode in a gaseous state. The fuel cell according to claim 1. It was detected that the power generation part in which the air electrode for reducing oxygen as an active material through the electrolyte and the fuel electrode for oxidizing the fuel made of formic acid or a formic acid aqueous solution were lowered to a predetermined output value predetermined during power generation was detected. At that point, power generation was interrupted,
A method of operating a fuel cell, wherein an operation for cleaning the fuel electrode is performed by directly supplying a cleaning liquid obtained by collecting water generated at the air electrode only to the fuel electrode side . In the power generation unit in which an air electrode that reduces oxygen as an active material through an electrolyte and a fuel electrode that oxidizes fuel made of formic acid or a formic acid aqueous solution are disposed,
A method of operating a fuel cell, wherein an operation for cleaning the fuel electrode is performed by directly supplying a cleaning liquid obtained by collecting water generated at the air electrode only to the fuel electrode side .

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