JP2011054307A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell having improved operating stability under low-temperature environment. <P>SOLUTION: The fuel cell includes a fuel cell body using liquid fuel for generating power, a fuel supply part for supplying fuel to the fuel cell body, a temperature sensor for detecting the temperature of the fuel cell body, a supply speed determining part for determining the speed of the fuel to be supplied by the fuel supply part in accordance with the measurement result of the temperature sensor, and a fuel supply control part for controlling the fuel to be supplied by the fuel supply part in accordance with the determined supply speed while restricting the supply of the fuel when the temperature is lower than a predetermined reference value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell.

  Electronic devices such as mobile phones and portable information terminals are being downsized. Along with miniaturization of electronic equipment, attempts have been made to use fuel cells for power supplies. Fuel cells have the advantage that they can generate electricity simply by supplying fuel and air, and can continuously generate electricity if only the fuel is replaced or replenished. Therefore, if the fuel cell can be miniaturized, it is effective as a power source for small electronic devices.

  As a fuel cell, a direct methanol fuel cell (hereinafter referred to as DMFC (Direct Methanol Fuel Cell)) has attracted attention (for example, see Patent Document 1). Such DMFCs are classified according to the liquid fuel supply method, such as an active method such as a gas supply type and a liquid supply type, and an internal vaporization type that vaporizes the liquid fuel in the fuel storage section inside the battery and supplies it to the fuel electrode. There is a passive type. Of these, the passive type is advantageous for downsizing the DMFC.

JP 2008-243732 A

  Here, it is necessary to control the fuel supply to the DMFC. For example, the fuel cell temperature (cathode temperature) is monitored, and the fuel supply is controlled so that the temperature falls within an appropriate range.

  However, it was found that when the external environment (outside temperature) is low, the operation of the DMFC tends to become unstable.

  An object of the present invention is to provide a fuel cell in which the stability of operation at a low temperature is improved.

  A fuel cell according to an aspect of the present invention includes a fuel cell body that generates power using liquid fuel, a fuel supply unit that supplies fuel to the fuel cell body, a temperature sensor that detects the temperature of the fuel cell body, and the temperature A supply rate determination unit for determining a supply rate of fuel by the fuel supply unit based on a measurement result of the sensor; a control of the supply of fuel by the fuel supply unit based on the determined supply rate; and A fuel supply control unit that restricts fuel supply when the temperature is lower than a predetermined reference value.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell which aimed at the improvement of the stability of operation | movement under low temperature can be provided.

1 is a block diagram showing a schematic configuration of a fuel cell system according to an embodiment of the present invention. 1 is a cross-sectional view of a fuel cell main body 1. 3 is a perspective view of a fuel distribution mechanism 105. FIG. It is a flowchart showing an example of the operation | movement procedure of a fuel cell.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The fuel cell shown in FIG. 1 includes a fuel cell main body (DMFC) 1, a pump drive unit 2, a DC-DC converter 3, a control unit 4, a temperature sensor SS1, and a current sensor SS2.

  The fuel cell main body 1 includes a power generation unit 101, a fuel storage unit 102, a flow path 103, a pump 104, and a temperature sensor SS1. The power generation unit (cell) 101 generates power by burning fuel and constitutes an electromotive unit of the fuel cell system. The fuel storage unit 102 stores liquid fuel used in the power generation unit 101. The flow path 103 connects the fuel storage unit 102 and the power generation unit (cell) 101. The pump 104 is a fuel supply unit that transfers liquid fuel from the fuel storage unit 102 to the power generation unit (cell) 101.

  As shown in FIG. 2, the power generation unit 101 includes an anode (fuel electrode) 13 having an anode catalyst layer 11 and an anode gas diffusion layer 12, and a cathode (air electrode) having a cathode catalyst layer 14 and a cathode gas diffusion layer 15. / Oxidant electrode) 16 and a membrane electrode assembly (MEA) composed of a proton (hydrogen ion) conductive electrolyte membrane 17 held between the anode catalyst layer 11 and the cathode catalyst layer 14. Have.

  Here, examples of the catalyst contained in the anode catalyst layer 11 and the cathode catalyst layer 14 include a simple substance of a platinum group element such as Pt, Ru, Rh, Ir, Os, and Pd, and an alloy containing the platinum group element. It is done. The anode catalyst layer 11 is preferably made of Pt—Ru or the like having strong resistance to methanol, carbon monoxide and the like. It is preferable to use Pt, Pt—Co or the like for the cathode catalyst layer 14. However, the catalyst is not limited to these, and various substances having catalytic activity can be used. The catalyst may be either a supported catalyst using a conductive support such as a carbon material or an unsupported catalyst.

  Examples of the proton conductive material constituting the electrolyte membrane 17 include a fluorine-based resin (Nafion (trade name, manufactured by DuPont) or Flemion (trade name, manufactured by Asahi Glass Co., Ltd.) such as a purple sulfonic acid polymer having a sulfonic acid group. ), Etc.), organic materials such as hydrocarbon resins having sulfonic acid groups, or inorganic materials such as tungstic acid and phosphotungstic acid. However, the proton conductive electrolyte membrane 17 is not limited to these.

  The anode gas diffusion layer 12 laminated on the anode catalyst layer 11 serves to uniformly supply fuel to the anode catalyst layer 11 and also serves as a current collector for the anode catalyst layer 11. The cathode gas diffusion layer 15 laminated on the cathode catalyst layer 14 serves to uniformly supply the oxidant to the cathode catalyst layer 14 and also serves as a current collector for the cathode catalyst layer 14. The anode gas diffusion layer 12 and the cathode gas diffusion layer 15 are made of a porous substrate.

  A conductive layer is laminated on the anode gas diffusion layer 12 and the cathode gas diffusion layer 15 as necessary. These conductive layers include, for example, a porous layer (for example, a mesh) made of a conductive metal material such as Au or Ni, a porous film, a foil body, or a conductive metal material such as stainless steel (SUS) or Cu. A composite material coated with a highly conductive material such as carbon or carbon is used. A rubber 0-ring 19 is interposed between the electrolyte membrane 17 and a fuel distribution mechanism 105 and a cover plate 18 which will be described later, thereby preventing fuel leakage and oxidant leakage from the power generation unit 101. Yes.

  The cover plate 18 has an opening (not shown) for taking in air as an oxidant. A moisture retaining layer and a surface layer are disposed between the cover plate 18 and the cathode 16 as necessary. The moisturizing layer is impregnated with a part of the water produced in the cathode catalyst layer 14 to suppress the transpiration of water and promote the uniform diffusion of air to the cathode catalyst layer 14. The surface layer is for adjusting the amount of air taken in, and has a plurality of air inlets whose number and size are adjusted according to the amount of air taken in.

  A fuel distribution mechanism 105 is disposed on the anode (fuel electrode) 13 side of the power generation unit 101. A fuel storage unit 102 is connected to the fuel distribution mechanism 105 via a liquid fuel flow path 103 such as a pipe.

  Liquid fuel corresponding to the power generation unit 101 is stored in the fuel storage unit 102. Examples of the liquid fuel include methanol fuels such as aqueous methanol solutions of various concentrations and pure methanol. The liquid fuel is not necessarily limited to methanol fuel. The liquid fuel may be, for example, an ethanol fuel such as an ethanol aqueous solution or pure ethanol, a propanol fuel such as a propanol aqueous solution or pure propanol, a glycol fuel such as a glycol aqueous solution or pure glycol, dimethyl ether, formic acid, or other liquid fuel. In any case, liquid fuel corresponding to the power generation unit 101 is stored in the fuel storage unit 102.

  Fuel is introduced into the fuel distribution mechanism 105 from the fuel storage portion 102 via the flow path 103. The flow path 103 is not limited to piping independent of the fuel distribution mechanism 105 and the fuel storage unit 102. For example, when the fuel distribution mechanism 105 and the fuel storage unit 102 are stacked and integrated, a fuel flow path connecting them may be used. The fuel distribution mechanism 105 only needs to be connected to the fuel storage unit 102 via the flow path 103.

  As shown in FIG. 3, the fuel distribution mechanism 105 includes at least one fuel inlet 21 through which fuel flows in through the flow path 103 and a plurality of fuel outlets 22 through which fuel and vaporized components thereof are discharged. A fuel distribution plate 23 is provided. As shown in FIG. 2, a gap 24 serving as a fuel passage led from the fuel injection port 21 is provided inside the fuel distribution plate 23. The plurality of fuel discharge ports 22 are directly connected to gaps 24 that function as fuel passages.

  The fuel introduced into the fuel distribution mechanism 105 from the fuel inlet 21 enters the gap portion 24 and is led to the plurality of fuel discharge ports 22 through the gap portion 24 functioning as the fuel passage. For example, a gas-liquid separator (not shown) that transmits only the vaporized component of the fuel and does not transmit the liquid component may be disposed in the plurality of fuel discharge ports 22. As a result, the vaporized component of the fuel is supplied to the anode (fuel electrode) 13 of the power generation unit 101. The gas-liquid separator may be installed as a gas-liquid separation membrane or the like between the fuel distribution mechanism 105 and the anode 13. The vaporized component of the fuel is discharged from a plurality of fuel discharge ports 22 toward a plurality of locations on the anode 13.

A plurality of fuel discharge ports 22 are provided on the surface of the fuel distribution plate 23 in contact with the anode 13 so that fuel can be supplied to the entire power generation unit 101. The number of the fuel discharge ports 22 may be two or more, but 0.1 to 10 / cm ² fuel discharge ports 22 exist in order to equalize the fuel supply amount in the plane of the power generation unit 101. It is preferable to form as follows.

  A pump 104 as a fuel transfer control means is inserted into a flow path 103 that connects between the fuel distribution mechanism 105 and the fuel storage unit 102. The pump 104 is not a circulation pump that circulates fuel, but is a fuel supply pump that transfers fuel from the fuel storage portion 102 to the fuel distribution mechanism 105. By supplying the fuel when necessary with such a pump 104, the controllability of the fuel supply amount is improved. In this case, as the pump 104, a rotary vane pump, an electroosmotic pump, a diaphragm pump, a squeezing pump, etc. should be used from the viewpoint that a small amount of fuel can be sent with good controllability and can be reduced in size and weight. Is preferred. A rotary vane pump feeds liquid by rotating a wing with a motor. The electroosmotic flow pump uses a sintered porous material such as silica that causes an electroosmotic flow phenomenon. The diaphragm pump is a pump that feeds liquid by driving a diaphragm with an electromagnet or piezoelectric ceramics. The squeezing pump presses a part of the flexible fuel flow path and squeezes the fuel. Among these, it is more preferable to use an electroosmotic pump or a diaphragm pump having piezoelectric ceramics from the viewpoints of driving power and size.

The fuel stored in the fuel storage unit 102 is transferred through the flow path 103 by the pump 104 and supplied to the fuel distribution mechanism 105. The fuel discharged from the fuel distribution mechanism 105 is supplied to the anode (fuel electrode) 13 of the power generation unit 101.
The fuel storage unit 102 may be disposed between the pump 104 and the fuel distribution mechanism 105, and the fuel storage unit 102 may be pressurized by the pump 104 to transfer the liquid fuel.

In the power generation unit 101, the fuel diffuses through the anode gas diffusion layer 12 and is supplied to the anode catalyst layer 11. When methanol fuel is used as the fuel, an internal reforming reaction of methanol shown in the following formula (1) occurs in the anode catalyst layer 11. When pure methanol is used as the methanol fuel, the water generated in the cathode catalyst layer 14 or the water in the electrolyte membrane 17 is reacted with methanol to cause the internal reforming reaction of the formula (1). Alternatively, the internal reforming reaction is caused by another reaction mechanism that does not require water.
_{CH 3 OH + H 2 O →} 6H + + CO 2 tens ^6e - ... (1)

Electrons (e ⁻ ) generated by this reaction are led to the outside via a current collector, supplied as so-called output to the load side, and then led to the cathode (air electrode) 16. Further, protons (H ⁺ ) generated by the internal reforming reaction of the formula (1) are guided to the cathode 16 through the electrolyte membrane 17. Air is supplied to the cathode 16 as an oxidant. Electrons (e ⁻ ) and protons (H ⁺ ) that have reached the cathode 16 react with oxygen in the air in accordance with the following equation (2) in the cathode catalyst layer 14, and water is generated along with this reaction.
6H ⁺ + (3/2) O ₂ + 6e ⁻ → 3H ₂ 0 (2)

  The pump drive unit 2 controls the drive of the pump 104. The pump drive unit 2 controls on / off of the pump 104 based on an instruction from the control unit 4.

  The DC-DC converter 3 has a switching element and an energy storage element (not shown). The DC-DC converter 3 stores / releases the electric energy generated by the fuel cell body 1 by the switching element and the energy storage element, A relatively low output voltage is boosted to a sufficient voltage and output.

  The temperature sensor SS1 is a sensor that is disposed in the vicinity of the cathode 16 and measures the temperature of the cathode 16 (DMFC temperature), such as a thermistor or a thermocouple. A signal (temperature signal) representing the temperature measurement result from the temperature sensor SS1 is sent to the control unit 4 and used for fuel supply control.

  Note that the fuel cell according to the present embodiment does not use an external temperature for control and does not require measurement of the external temperature, so that the device configuration can be simplified. For example, it becomes unnecessary to expose a sensor for measuring the external temperature to the outside.

  The control unit 4 includes a supply speed determination unit 41 and a fuel supply control unit 42.

The supply speed determination unit 41 determines the fuel supply speed (Duty ratio D) so that the temperature T becomes the target temperature Tt.
Here, it is assumed that the pump drive unit 2 controls whether or not the pump 104 supplies fuel to the power generation unit 101. That is, the pump drive unit 2 does not directly control the fuel supply speed itself. The pump drive unit 2 temporally controls whether or not fuel is supplied by the pump 104, and as a result, the amount of fuel supplied within a certain time can be controlled.

At this time, the fuel supply speed V [g / sec] is represented by the duty ratio D as follows.
V = Av * D
D = ton / (ton + toff)
= Ton / tal ...... Formula (15)
Av: proportional constant ton: time during which pump 104 supplies fuel (ON time)
toff: time when pump 104 is not supplying fuel (OFF time)
tal = ton + toff: Sum of ON time and OFF time

The supply speed determination unit 41 can determine the Duty ratio D using the following equation (15).
D = Kp · (T−Tt) + Ki · B∫ (T−Tt) dt (16)

  Expression (16) represents so-called PI (Proportional Integral) control, where a proportional term (Kp · (T−Tt)) and an integral term (Ki · B∫) of the deviation (T−Tt) between the current temperature T and the target temperature Tt. Based on (T−Tt) dt), the Duty ratio D is determined. Note that PID (Proportional Integral Differential) control may be used instead of PI control.

  The fuel cell can be controlled so that the temperature T matches the target temperature Tt by periodically determining the duty ratio D using the equation (16) and controlling the fuel supply speed by the pump 104. it can.

The fuel supply control unit 42 controls the pump 104 via the pump drive unit 2 so that fuel is supplied at the duty ratio D determined by the supply speed determination unit 41.
Here, the fuel supply control unit 42 fixes the upper limit of the fuel supply speed (upper limit of the Duty ratio D) when the temperature (cathode temperature) T continues to be equal to or lower than the minimum temperature Tmin (DutyLock). With this DutyLock, the operation of the fuel cell can be stabilized without measuring the external temperature. When the temperature (cathode temperature) T exceeds the target temperature Tt (T> Tt), the DutyLock is released.

As described above, in principle, the fuel supply control unit 42 controls the supply of fuel so that the temperature T becomes the target temperature Tt.
However, it has been found that when the external temperature is greatly decreased (for example, 45 → 5 ° C.), the operation of the fuel cell may become unstable. When the external temperature decreases, the water generated by the reaction (2) aggregates on the surface of the cathode 16 and the supply of oxygen to the cathode 16 becomes insufficient (cathode oxygen deficient state). If the target temperature Tt is to be maintained in this oxygen-deficient state, the amplitude of the temperature T increases. Further, the output from the power generation unit 101 when the temperature T rises decreases. Furthermore, there is a risk that the fuel is excessively supplied to maintain the target temperature Tt, the anode catalyst layer 11 and the cathode catalyst layer 14 are dissolved, and the fuel cell body (DMFC) 1 is irreversibly deteriorated.

  When the temperature (cathode temperature) T continues to be below the minimum temperature Tmin, turning on DutyLock (DutyLock setting) prevents excessive fuel supply. This means that the achievement of the target temperature Tt is once abandoned. In this case, the fuel cell is maintained in a temporary stable state, and the output from the power generation unit 101 is also relatively low.

  When the external temperature rises, the temperature (cathode temperature) T gradually rises and reaches the target temperature Tt (T> Tt) even if the DutyLock is ON. Thus, when the temperature (cathode temperature) T reaches the target temperature Tt, the DutyLock is turned OFF (DutyLock is released).

  As described above, when the state where the temperature T is equal to or lower than the minimum temperature Tmin continues, the DutyLock is turned on, and when the temperature T reaches the target temperature Tt, the DutyLock is turned off. By doing so, it becomes possible to stably operate the fuel cell in response to a shortage of oxygen supply caused by a decrease in the external temperature without measuring the external temperature.

(Operation of fuel cell)
FIG. 4 is a flowchart showing an example of the operation procedure of the fuel cell.

A. Determination of Duty ratio D
The duty ratio D is periodically determined (step S11). That is, the duty ratio D is determined by the equation (16). In principle, the pump 104 is controlled based on the determined duty ratio D (step S13).

  The duty ratio D used for controlling the pump 104 is stored as the duty ratio D0 (step S12). As will be described later, when the duty ratio D is adjusted and the pump 104 is controlled based on this value, the adjusted duty ratio D is stored as the duty ratio D0. The duty ratio D0 is used in the later-described DutyLock.

B. Adjustment of Duty Ratio D In some cases, the Duty ratio D is adjusted based on temperature conditions and the like, and the pump 104 is controlled based on the adjusted Duty ratio D.
1) Setting of DutyLock (Steps S41 to S45)
When the following conditions a to c are satisfied, DutyLock is set (DutyLock ON), and an increase in Duty ratio D is prohibited (Steps S41 to S43). That is, if the duty ratio D determined in the current cycle is larger than the duty ratio D0 used in the previous cycle (step S44), the duty ratio D0 used in the previous cycle is substituted into the duty ratio D ( Step S45). As a result, the Duty ratio D is set to a value less than or equal to the Duty ratio D0.
As will be described later, when the duty lock is set, an increase in the duty ratio D is prohibited even if the conditions a to c are not satisfied.

a. Temperature T is lower than minimum temperature Tmin (T <Tmin)
b. Temperature is falling (Temperature differential coefficient dT / dt <0)
c. Current I decreasing (current differential coefficient dI / dt <0)

  Note that when conditions a to c are satisfied a predetermined number of times (for example, three times), DutyLock is set, and erroneous setting of DutyLock due to noise or the like can be prevented.

2) Processing when setting DutyLock (steps S31, S44, S45)
When setting DutyLock, even if the conditions a to c are not satisfied, an increase in the Duty ratio D is prohibited. That is, if the duty ratio D determined in the current cycle is larger than the duty ratio D0 used in the previous cycle (step S44), the duty ratio D0 used in the previous cycle is substituted into the duty ratio D ( Step S45).

3) Canceling DutyLock (Steps S21 and S22)
When conditions d and e are satisfied, DutyLock is released (DutyLock OFF).
d. Temperature T1 is higher than target temperature (T1> Tt)
e. Temperature T is rising (Temperature differential coefficient dT / dt> 0)

(Other embodiments)
Embodiments of the present invention are not limited to the above-described embodiments, and can be expanded and modified. The expanded and modified embodiments are also included in the technical scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell main body, 101 ... Electric power generation part, 102 ... Fuel accommodating part, 103 ... Flow path, 104 ... Pump, 105 ... Fuel distribution mechanism, 2 ... Pump drive part, 3 ... Converter, 4 ... Control part, 11 ... Anode Catalyst layer, 12 ... anode gas diffusion layer, 13 ... anode, 14 ... cathode catalyst layer, 15 ... cathode gas diffusion layer, 16 ... cathode, 17 ... electrolyte membrane, 18 ... cover plate, 19 ... ring, 21 ... fuel inlet , 22 ... Fuel discharge port, 23 ... Fuel distribution plate, 24 ... Gap, 41 ... Supply speed determination unit, 42 ... Fuel supply control unit

Claims (6)

A fuel cell body that generates power from liquid fuel;
A fuel supply unit for supplying fuel to the fuel cell body;
A temperature sensor for detecting the temperature of the fuel cell body;
A supply rate determination unit that determines a supply rate of fuel by the fuel supply unit based on a measurement result of the temperature sensor;
A fuel supply control unit that controls the supply of fuel by the fuel supply unit based on the determined supply rate and restricts the fuel supply when the temperature is lower than a predetermined reference value;
A fuel cell comprising: The supply speed determining unit continuously determines the supply speed;
The fuel supply control unit continuously controls the fuel supply based on the continuously determined supply speed;
The fuel cell according to claim 1. When the temperature is lower than the predetermined reference value, the fuel supply control unit controls the supply of fuel based on a supply speed equal to or lower than the supply speed used in the previous control;
The fuel cell according to claim 2. 4. The fuel cell according to claim 1, wherein the supply speed determination unit determines the supply speed of the fuel based on a comparison between the temperature and a target temperature. 5. The fuel supply control unit controls whether or not fuel is supplied from the fuel supply unit to the fuel cell body;
The fuel cell according to any one of claims 1 to 4, wherein: The ratio of the operation time to the sum of the operation time for supplying the fuel from the fuel supply unit to the fuel cell main body and the stop time for not supplying the fuel cell main body from the fuel supply unit. The fuel cell according to claim 5, wherein the fuel supply speed is determined.

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