KR101105364B1 - Sensor and method for sensing fuel concentration, method and system apparatus for fuel recirculation of fuel cell using the same, fuel cell usage apparatus using the same - Google Patents

Abstract

Opening of a unit cell or a stack of the unit cells including an electrolyte membrane, a reference electrode present on one side of the electrolyte membrane, and a measurement electrode present on the other side of the electrolyte membrane, and a stack of the unit cells or the stack of the unit cells stacked A reference circuit having a set fuel concentration, a reference material having a set fuel concentration flows, a measurement target material for measuring a fuel concentration flows, and the unit cell or the unit cell The open-circuit voltage value of the stacked stack is provided with an open-circuit voltage type fuel concentration sensor and a sensing method which vary according to the fuel concentration in the measurement target material, a fuel recycling system device and method using the same, and a fuel cell using device.

Description

Sensor and method for sensing fuel concentration, method and system apparatus for fuel recirculation of fuel cell using the same, fuel cell usage apparatus using the same}

The present specification describes a fuel concentration sensor and a sensing method, an apparatus and method for recirculating a fuel cell using the same, and a fuel cell using the same. Specifically, an open circuit voltage type fuel concentration sensor and a sensing method, a fuel recycling system apparatus and method of the fuel cell using the same, and a fuel cell using the same will be described. The sensor may be usefully applied to a fuel recycling system of a fuel cell, such as a fuel recycling system of a fuel cell used in an automobile.

A fuel cell is a device that generates electricity by using fuel oxidation of an anode and oxygen reduction reaction of a cathode.

For example, the polymer electrolyte fuel cell is designed to cause electrochemical oxidation of fuel at the anode and reduction of oxygen at the cathode. In this case, the fuel is generally injected more than the amount of fuel required for current production so that the power generation reaction occurs smoothly.

As a result, an unreacted fuel is generated at the anode. When the fuel is directly discharged, fuel efficiency decreases and safety problems occur.

In order to solve this problem, in particular, a vehicle using a fuel cell as a power source can improve fuel efficiency (fuel efficiency) and safety by using a fuel recycling system that recycles and utilizes unreacted fuel again.

However, when a fuel recycle system is used, gas permeation through the electrolyte membrane and dilution of the anode fuel may occur.

For example, in the case of using a gaseous fuel, the electrolyte membrane of the fuel cell also serves as a separator that prevents mixing of the anode fuel (for example, hydrogen, hydrocarbons, etc.) and the air of the cathode, but in the actual fuel cell system oxygen and nitrogen The back light penetrates the polymer membrane and moves toward the anode. The permeated oxygen is removed by chemical reaction with hydrogen, while the residual material such as nitrogen gradually reduces the fuel concentration in the material supplied to the anode (eg hydrogen concentration in the mixture of hydrogen, nitrogen, etc.). When the fuel (eg hydrogen) is continuously recycled in the recycle system, the effect of this permeate nitrogen accumulates and consequently the fuel concentration in the material supplied to the anode is continuously lowered.

The decrease in the fuel concentration in the anode material may act as a cause of permanent performance degradation along with the performance degradation of the fuel cell. Therefore, when the fuel concentration in the anode material drops below a certain level in the fuel recirculation system, a purging operation for releasing the anode material to the outside is required.

However, in order to control proper purging, it is necessary to know the fuel concentration value in the anode material.

For this purpose, process sensors can be used to control the fuel concentration in each process of the process. Process sensors for this purpose must operate over approximately the entire concentration range (1 to 100%), so concentration accuracy and reproducibility are important. Do.

However, according to the researches of the present inventors, the process sensor is expensive and used by the engineer for a special use, which is not only difficult to use, but also has a difficulty in constructing a system with a fuel cell stack.

On the other hand, a method of estimating the anode nitrogen concentration from the operating state by calculation, a method using a wave application type concentration sensor, a method using a fuel cell type current sensitive hydrogen sensor, and the like are known.

Among them, the fuel cell type current sensitive hydrogen sensor produces electricity in the same way as the fuel cell and measures current.

However, according to the researches of the present inventors, in the case of the current-type sensor as described above, the output characteristics are sensitively dependent on the characteristics of the initial electrolyte membrane and the catalyst layer, and the current characteristics due to the deterioration of the electrolyte membrane and the catalyst layer generated in connection with the long time operation. This will not remain stable.

It is a sensor that can measure the concentration of fuel in the anode material supplied to the anode in the fuel recirculation system, which is adopted to improve the efficiency of fuel cell systems such as fuel cell vehicles. Open-circuit voltage type fuel concentration sensor and sensing method capable of preventing deterioration of the sensor due to oxidation reaction and designing integrally with the fuel cell stack, apparatus and method for fuel recycling system of fuel cell using same, and fuel using the same A battery using device is provided.

In embodiments of the present invention, an electrolyte membrane; A reference electrode on one side of the electrolyte membrane; And an open circuit voltage meter for measuring an open circuit voltage of the unit cell including the unit cell or the stack of the unit cells including the measuring electrode present on the other side of the electrolyte membrane, and the stack of the unit cell or the stack of the unit cells. The reference electrode flows a reference material having a set fuel concentration, a measurement target material flows through the measurement electrode, and an open circuit voltage value of the unit cell or the stack in which the unit cells are stacked is measured. Provided is a fuel concentration sensor characterized in that it changes in accordance with the fuel concentration in the target material.

Embodiments of the present invention also provide a reference material having a fuel concentration set on a reference electrode present on one side of an electrolyte membrane; Providing a measurement target substance to measure fuel concentration to a measurement electrode present on the other side of the electrolyte membrane; And measuring the open circuit voltage of the unit cell including the electrolyte membrane, the reference electrode, and the measurement electrode, or the stack of the unit cells stacked therein, and the open circuit voltage of the unit cell or the stack of the unit cells stacked thereon. The numerical value is changed according to the fuel concentration in the measurement target material, and provides a fuel concentration sensing method.

Embodiments of the invention also include a fuel cell; An anode material recycling flow path for recycling an anode material including an unreacted fuel flowing out of the anode to the fuel cell to the anode; A fuel concentration sensor configured to measure a fuel concentration in the anode material which is installed and recycled in the recirculation flow path, wherein the fuel concentration sensor comprises: an electrolyte membrane; A reference electrode on one side of the electrolyte membrane; And an open circuit voltage meter for measuring an open circuit voltage of the unit cell including the unit cell or the stack of the unit cells including the measuring electrode present on the other side of the electrolyte membrane, and the stack of the unit cell or the stack of the unit cells. A reference material having a set fuel concentration flows through the reference electrode, and a recycling anode material for measuring fuel concentration flows through the measurement electrode, and an open circuit voltage value of the unit cell or the stack in which the unit cells are stacked is the recycle A fuel recirculation system device is provided that varies with fuel concentration in the anode material.

Embodiments of the present invention also provide a fuel cell using device comprising the fuel recycling system device.

Embodiments of the invention also include recycling an anode material comprising unreacted fuel flowing out of the anode of a fuel cell to the anode; Measuring the concentration of the fuel in the anode material recycled during the fuel recycling process, wherein the measurement of the concentration of the fuel in the recycled anode material, the reference material having a fuel concentration set on the reference electrode present on one side of the electrolyte membrane Providing a; Providing a recycle anode material for measuring fuel concentration to a measurement electrode present on the other side of the electrolyte membrane; And measuring the open circuit voltage of the unit cell including the electrolyte membrane, the reference electrode, and the measurement electrode, or the stack of the unit cells stacked therein, wherein the open circuit voltage of the unit cell or the stack of the unit cells is stacked. The numerical value varies with the fuel concentration in the recycle anode material.

The open-circuit voltage type fuel concentration sensor according to the embodiments of the present invention is a method of measuring the open-circuit voltage, which is a thermodynamic value, so that stable operation is possible without depending on the characteristics of the catalyst layer and the electrolyte membrane, and the fuel cell unit cell (or its unit). Unlike the stack of cells), oxygen and air are not supplied, so that the system does not degrade due to oxidation.

In addition, the open-circuit voltage fuel concentration sensor according to the embodiments of the present invention is measured in the open circuit state that does not produce a current, it is possible to use a variety of materials with low catalytic reaction activity other than expensive platinum as an electrode catalyst. . In addition, various materials having low conductivity may be used as the electrolyte membrane material. In addition, it has the advantage of increasing the strength by increasing the thickness of the electrolyte membrane.

In addition, the open-circuit voltage fuel concentration sensor according to the embodiments of the present invention has a form similar to that of a fuel cell (for example, a polymer electrolyte fuel cell), so that the sensor is integrally integrated with the fuel cell stack through the design of the fuel cell stack. It can be positioned and has components similar to a fuel cell stack, which is advantageous in terms of maintenance.

1 schematically shows the structure of an open circuit voltage type fuel concentration sensor in an exemplary embodiment of the invention.
Fig. 2 is a schematic diagram showing a configuration of a recirculation system of a fuel cell to which an open circuit voltage type fuel concentration sensor is applied in an exemplary embodiment of the present invention.
FIG. 3A shows the open circuit voltage measured at a temperature of 25 ° C. in comparison with the theoretical open circuit voltage value in Experiment 1. FIG. FIG. 3B is an enlarged view of the initial section of FIG. 3A. In FIG. 3, the X axis is nitrogen concentration (%) and the Y axis is open circuit voltage change (V).
FIG. 4A shows the open-circuit voltage measured at a temperature of 65 ° C. in comparison with the theoretical open-circuit voltage value. FIG. 4B is an enlarged view of the initial section of FIG. 4A. In FIG. 4, the X axis is nitrogen concentration (%) and the Y axis is open circuit voltage change (V).
FIG. 5A shows the open circuit voltage measured at a temperature of 80 ° C. in comparison with the theoretical open circuit voltage value in Experiment 1. FIG. FIG. 5B is an enlarged view of the initial section of FIG. 5A. In FIG. 5, the X axis is nitrogen concentration (%) and the Y axis is open circuit voltage change (V).
FIG. 6A shows the open-circuit voltage measured at a temperature of 65 ° C. in comparison with the theoretical open-circuit voltage value. FIG. 6B is an enlarged view of the initial section of FIG. 6A. In FIG. 6, the X axis is nitrogen concentration (%) and the Y axis is open circuit voltage change (V).
FIG. 7A shows the open-circuit voltage measured at the temperature of 65 ° C. in comparison with the theoretical open-circuit voltage value. FIG. 7B is an enlarged view of the initial section of FIG. 7A. In FIG. 7, the X axis is nitrogen concentration (%) and the Y axis is open circuit voltage change (V).

Hereinafter, exemplary embodiments of the present invention will be described.

In the present specification, the fuel refers to a material that participates in the electrochemical reaction of the fuel cell, and the non-fuel means a material that does not participate in the electrochemical reaction of the fuel cell. The fuel and non-fuel may be liquid or gas, respectively.

In the present specification, the anode material means a material including a fuel supplied to the anode, and may be a liquid or a gas.

In the present specification, the measurement target material means a target material for which a fuel concentration in the material is to be measured.

As used herein, the reference substance means a substance known by setting a concentration of a fuel contained in the substance in advance.

In the present specification, the fuel concentration means a concentration or a ratio of fuel included in the anode material, the measurement target material, or the reference material, and may also be expressed by the concept of fuel activity. Such fuel concentrations to ratios can also be expressed, for example, in concentrations for liquids and partial pressures for gases.

In the present specification, the recycle anode material is a material including unreacted fuel flowing out of the anode in the fuel cell system, and means a material that is supplied to the anode and recycled. Such anode material may be unreacted fuel itself or a mixture of unreacted fuel and non-fuel material. The anode material may be an anode gaseous material, which may include fuel gas (eg, hydrogen, etc.) and non-fuel gas (eg, nitrogen, argon, etc.). In addition, the anode material may be an anode liquid material, which may include fuel liquids (eg, methanol, formic acid, etc.) and non-fuel liquids (eg, water, etc.).

In the present specification, the fuel flow that is initially supplied to the anode of the fuel cell is not the fuel flow that is recycled and supplied to the anode of the fuel cell again, but refers to the fuel flow that is first supplied to the anode.

In the present specification, the open circuit voltage type means that the fuel concentration sensor is a type for measuring the open circuit voltage.

In the present specification, the device using a fuel cell refers to various devices such as an automobile, a laptop, a robot, and the like using power generated from the fuel cell.

The fuel concentration sensor according to the exemplary embodiments of the present invention has a structure similar to that of the fuel cell unit cell or the stack of the unit cell (for example, the polymer electrolyte fuel cell unit cell or the stack thereof), and the fuel concentration is applied to the reference electrode. A known reference material (e.g., a gaseous fuel such as hydrogen, or a liquid fuel such as methanol or formic acid) is supplied, and a recycling anode material (e.g., a gaseous recycling anode material including hydrogen and nitrogen, etc.) to be measured for the fuel concentration to the measurement electrode, or Open-circuit voltage fuel concentration sensor supplied with methanol and water or a liquid recycle anode material including formic acid and water.

The fuel concentration sensor measures the open circuit voltage according to the fuel concentration in the recycle anode material to which the fuel concentration is to be measured. Since the open circuit voltage changes in response to the fuel concentration in the recycle anode material, it is possible to easily grasp the change in the fuel concentration in the recycle anode material by measuring the change in the open circuit voltage.

1 is a schematic diagram illustrating a fuel concentration sensor measuring an open circuit voltage in an exemplary embodiment of the present invention. 1 exemplarily shows that a reference substance having a known fuel concentration is pure hydrogen, and a substance to be measured is a mixture of hydrogen and nitrogen.

As shown in FIG. 1, the open-circuit voltage type fuel concentration sensor 100 is provided with a reference electrode 13 and a measurement electrode 15 on one side of the electrolyte membrane 10, like a unit cell of a fuel cell. An open circuit voltage meter V (for example, voltametry) for measuring the open circuit voltage of the unit cell is provided.

The reference electrode 13 has a set concentration, i.e., a reference substance which already knows the concentration (FIG. 1 illustrates pure hydrogen), and a measurement target substance to measure fuel concentration through the measurement electrode 15. (FIG. 1 illustrates hydrogen and nitrogen). As will be described later, the fuel concentration in the recycle anode material can be measured by using the measurement target material as the recycle anode material.

Here, the fuel concentration in the measurement target material such as hydrogen and nitrogen mixtures corresponding to the hydrogen concentration in the mixture (or, for example, if the mixture of methanol and water, the methanol concentration in the mixture, or the formic acid concentration in the mixture if the mixture of formic acid and water) Since the open circuit voltage is changed, the concentration of the fuel in the material to be measured can be grasped by measuring the open circuit voltage.

Calculating or grasping the concentration of fuel in the measurement target material by the open-circuit voltage measurement can be, for example, as follows.

That is, a measurement target material (where each fuel concentration is known in advance) having various fuel concentrations is provided to the measurement electrode, and the open circuit voltage data according to the fuel concentration in the measurement target material is calculated from the open circuit voltage value measured accordingly. Build. By utilizing this data, it is possible to calculate the fuel concentration in the measurement target material by comparing the open circuit voltage value obtained in the subsequent measurement with the data. For this processing, the fuel concentration sensor may include a microprocessor for performing the calculation process.

Alternatively, the measured concentration of the open circuit voltage may be substituted into a Nernst equation, such as Equation 1, to calculate or determine the fuel concentration. This can be done because, in the embodiments of the present invention, the relationship between the actual open circuit voltage value and the fuel concentration is in good agreement with the theoretical value indicated by the Nernst equation (see Experimental Examples below).

Here, a _{fuel of the reference material, reference electrode} is the activity of the fuel in the reference material known to the fuel concentration at the reference electrode (set to a fixed value for the sensor operation), a _{fuel of the measurement target material, the measuring electrode} at the measurement electrode The activity of the fuel in the material to be measured. Here, the fuel in the reference material may be 100% fuel of the reference material itself.

Herein, the activity (a) may be expressed in concentration units in the case of liquids and in pressure units, that is, partial pressures in the case of gases.

Where R is a gas constant and T is the operating temperature of the unit cell (or stack if unit cells are stacked as described below) (this operating temperature can be set, thus assigning the set value). The temperature is used as absolute temperature and the unit is K), F is the Faraday constant, and E ^OCV is the open circuit voltage. n is the number of electrons associated with the reaction of the fuel (for example, 2 when hydrogen is a fuel gas; see Equation 3 below), and varies depending on the type of fuel. For example, n is 6 when methanol is a fuel liquid and n is 2 when formic acid is a fuel liquid.

Equation 2 is a representation of Equation 1 above when the fuel is a gas.

Here, the _{fuel gas and the reference electrode of the} P _{reference material are} the partial pressures of the fuel gas which knows the partial pressure at the reference electrode in advance, and the _{fuel gas and the measurement electrode} of the P _{measurement material are the fuel gases} of the measurement target material at the measurement electrode. Partial pressure.

Equation 3 is a representation of Equation 2 when the fuel gas is hydrogen. In the case of hydrogen, n is 2.

Here, P _{hydrogen and the reference electrode} are hydrogen partial pressures (for example, pure hydrogen as the partial pressure is known) among the reference materials supplied to the reference electrode, and P _{hydrogen and the measurement electrode} are hydrogen (for example, nitrogen, etc.) in the measurement target material at the measurement electrode. Partial pressure of the reaction gas, i.e., hydrogen, which is diluted by the non-fuel gas and does not know the partial pressure.

Likewise, in order to calculate fuel concentration using the Nernst equation, the fuel concentration sensor may include a microprocessor for calculating a fuel concentration from the equation based on the open circuit voltage measurement value.

In an exemplary embodiment of the present invention, the concentration sensing method using the sensor as described above, the step of providing a reference material having a fuel concentration set on the reference electrode present on one side of the electrolyte membrane, the measurement present on the other side of the electrolyte membrane Providing a measurement target material for measuring a fuel concentration to an electrode, and measuring an open circuit voltage of the unit cell including the electrolyte membrane, the reference electrode, and the measurement electrode or a stack in which the unit cells are stacked. . As mentioned above, since the open circuit voltage value of the unit cell changes according to the fuel concentration in the material to be measured, the fuel concentration in the material to be measured can be measured by measuring it.

Meanwhile, under actual fuel cell operating conditions, a constant background potential may exist between the reference electrode and the measurement electrode in addition to the voltage difference due to the difference in the activity of the fuel (partial pressure difference in the fuel gas and difference in concentration in the fuel liquid). Since the background potential becomes equal to the potential value measured under the condition that the fuel activities of the reference electrode and the measurement electrode are the same, the background potential can be corrected by using the background potential.

In the exemplary embodiments of the present invention, the open-circuit voltage sensor may not only be used in the unit cell form of FIG. 1, but also in the form of stacking unit cells of FIG. 1. In the case of stacking, the reference material and the measurement target material flow through the reference electrode and the measurement electrode of each stacked unit cell, and the open circuit voltage is measured for the entire stacked cells. In this case, the open circuit voltage signal measured is amplified by the number of unit cells to be stacked.

2 is a schematic diagram showing a configuration of a recirculation system of a fuel cell to which a fuel concentration sensor is applied in an exemplary embodiment of the present invention.

As shown in FIG. 2, the fuel cell recirculation system includes a membrane electrode assembly having an anode and a cathode on each side of the electrolyte membrane, and air is supplied to the cathode, and fuel is supplied to the anode (FIG. 2 illustrates hydrogen). It is to include a general fuel cell 200. The anode material including the unreacted fuel flowing out of the anode is recycled and provided back to the anode side via the recycle passage R. Such a device 300 for recirculation, such as a valve, is known and thus will not be described in detail.

The recycle anode material passing through the recycle passage R flows into the fuel concentration sensor 100 as described with reference to FIG. 1 and the fuel concentration in the anode material is measured by the open circuit voltage measurement.

As such, in the exemplary embodiments of the present invention, the fuel recycling method, while recycling the anode material including the unreacted fuel flowing out from the anode of the fuel cell 200 to the anode, during the recycling process Measuring the fuel concentration in the anode material to be measured by the sensor 100.

Here, the fuel concentration measurement in the recycled anode material, as described above, in the sensor 100 to provide a reference material having a fuel concentration set on the reference electrode present on one side of the electrolyte membrane, the other side of the electrolyte membrane The process of providing a recycle anode material to measure the concentration of the present measuring electrode and the open-circuit voltage of the unit cell consisting of the electrolyte membrane, the reference electrode and the measurement electrode or a stack of the unit cells are measured.

On the other hand, since the fuel flow initially supplied to the anode of the fuel cell 200 knows its concentration, as shown in FIG. 2, some of the flow H is used as a reference material of the fuel concentration sensor 100. It is desirable to provide.

During the fuel recirculation operation, the external discharge flow path is closed by the recirculation device 300, the operation is performed only with the recycling flow path opened, and when the concentration of fuel in the recycle anode material is lowered below a predetermined level (set level), the external discharge flow path is opened. And discharge the recycle anode material (ie, the anode material whose fuel concentration is below a certain level as a mixture of fuel and non-fuel) to the outside.

For example, it is common to supply fuel in excess of the required flow rate required for current production in actual operation of a fuel cell (eg, a fuel cell for an automobile). For example, if 50% excess fuel (hydrogen) is supplied, the actual amount of fuel supplied corresponds to 150% of the required amount, which can be expressed as an equivalence ratio of 1.5. However, even when continuously supplying a gas having a flow rate equivalent to 1.5 to the anode of the fuel cell, if the anode gas is composed of 80% hydrogen and 20% nitrogen, the actual hydrogen supply is 120% of the required amount, which is equivalent to 1.2 Correspondence (1.5 × 80% = 1.2). Thus, for example, when operating a fuel cell system in which the performance decreases rapidly at a fuel equivalent ratio of 1.2 or less, if the flow rate corresponding to the equivalent ratio 1.5 is fixedly supplied, the fuel (hydrogen) ratio of the recycle gas drops to 80%. Start the system to discharge the recycle gas to the outside.

Sensor according to the embodiments of the present invention can be measured simple compared to the application of the conventionally developed sensors to the fuel cell system and can see the change in fuel concentration in real time. In addition, the design of the fuel cell stack allows the sensor to be integrally located on the fuel cell stack and has the same components as the fuel cell stack, which is advantageous in terms of maintenance.

In addition, since the open circuit voltage sensor according to the embodiments of the present invention measures the open circuit voltage, which is a thermodynamic value, stable operation is possible without depending on the characteristics of the catalyst layer and the electrolyte membrane, and a fuel cell unit cell (or a unit thereof). Unlike a stack of cells, oxygen and air are not supplied, so that the system does not degenerate due to oxidation.

In addition, the open circuit voltage sensor according to the embodiments of the present invention is measured in the open circuit state that does not produce a current, as can be seen from the experimental examples described later, in addition to expensive platinum as an electrode catalyst catalytic reaction The advantage is that a variety of low activity materials can be utilized. In addition, various materials having low conductivity may be used as the electrolyte membrane material, and the electrolyte membrane may have an advantage of increasing strength by increasing the thickness of the electrolyte membrane.

In addition, the open-circuit voltage sensor according to the embodiments of the present invention has a form and operating conditions similar to those of a fuel cell (for example, a polymer electrolyte fuel cell), so that the open circuit voltage sensor may be included in the fuel cell stack through the design of the fuel cell stack. The sensor can be located integrally and has components similar to the fuel cell stack, which is advantageous in terms of maintenance.

Open circuit voltage sensor according to embodiments of the present invention is a polymer electrolyte fuel cell (PEMFC), direct methanol fuel cell (DMFC), direct formic acid fuel cell (DFAFC), molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), phosphoric acid fuel cell (PAFC), alkaline fuel cell (AFC) and the like can be usefully used for the fuel gas analysis of a variety of fuel cells, fuel recycling system apparatus according to embodiments of the present invention is an automobile, a robot, It can be used in various fuel cell using apparatus including a fuel cell such as a notebook.

Hereinafter, exemplary embodiments of the present invention will be described in more detail with reference to non-limiting and exemplary embodiments.

[Experiment 1: Fabrication of fuel (hydrogen) concentration sensor using open circuit voltage]

Membrane electrode  Bonding and Fuel (Hydrogen) Concentration Sensor

First, the membrane electrode assembly was prepared as follows. That is, the catalyst layer was prepared by spraying directly onto the polymer electrolyte membrane (direct injection method).

The catalyst ink was prepared by dispersing a carbon supported platinum catalyst (Tanaka Kikinzoku Kogyo, Pt 45.5 wt.%) And a Nafion ionomer solution (DuPont) in a mixed solvent of isopropyl alcohol (Baker Analyzed HPLC Reagent) and deionized water.

NRE-212 membrane (DuPont) was used as the polymer electrolyte membrane. The active area was 25 cm ² . The Nafion ionomer content of both electrode layers was fixed at 30% by weight, and the platinum catalyst loading was 0.4 mg / cm ^{2, which} is the same as that of a general polymer electrolyte fuel cell.

A gas diffusion medium (Sigracet 10BC, SGL carbon Inc.), a Teflon gasket and a graphite block were fastened to the membrane electrode assembly to manufacture a fuel (hydrogen) concentration sensor having the same structure as that of a fuel cell unit cell (see FIG. 1).

One electrode of the fuel (hydrogen) concentration sensor is supplied with pure hydrogen to the reference electrode (13 in FIG. 1), and the other electrode (15 in FIG. 1) acts as a sensor electrode so that the gas to be measured to measure the hydrogen concentration is Supplied.

analysis

The temperature of the open-circuit voltage fuel (hydrogen) concentration sensor was adjusted to 25 ° C, humidified hydrogen was supplied to the reference electrode and the sensor electrode, and the open-circuit voltage was measured. After that, a mixture of hydrogen and nitrogen was supplied to the sensor electrode, and the change in the open circuit voltage was measured.

The same experiment was repeated as follows. The temperature of the fuel (hydrogen) concentration sensor was 65 degreeC, the same open circuit voltage measurement experiment was performed, and the change of the open circuit voltage was measured. In the same manner, the same open circuit voltage measurement experiment was performed at 80 ° C., and the change of the open circuit voltage was measured by measuring the open circuit voltage.

result

3A and 4A and 5A are graphs showing the experimental results of the open-circuit voltage type fuel (hydrogen) concentration sensor in the present experiment 1, respectively. 3B, 4B, and 5B show enlarged initial sections of FIGS. 3A, 4A, and 5A, respectively.

The difference between the open-circuit voltage values when supplying pure hydrogen to the sensor electrode and when supplying a nitrogen gas mixture was measured to remove voltage errors that may occur due to unevenness of the membrane electrode assembly.

The results of three repeated measurements at each temperature were plotted against the nitrogen concentration, with the standard deviation indicated with a vertical bar.

The theoretical curve indicated by the solid line and the experimental results are in good agreement with each other. In particular, it can be seen that it works well in the region of low nitrogen concentration, which is important for fuel cell vehicle applications.

[Experiment 2: Open Circuit Voltage Fuel (Hydrogen) Concentration Sensor with Reduced Platinum Usage]

In Experiment 2, we measured the characteristics of the open-circuit voltage fuel (hydrogen) sensor that greatly reduced the platinum consumption to 0.05 mg / cm ² .

Membrane electrode  Bonding and Fuel (Hydrogen) Concentration Sensor

The membrane electrode assembly was prepared as follows. That is, the catalyst layer was prepared by spraying directly onto the polymer electrolyte membrane (direct injection method).

The catalyst ink was prepared by dispersing a carbon supported platinum catalyst (Tanaka Kikinzoku Kogyo, Pt 45.5 wt.%) And a Nafion ionomer solution (DuPont) in a mixed solvent of isopropyl alcohol (Baker Analyzed HPLC Reagent) and deionized water.

NRE-212 membrane (DuPont) was used as the polymer electrolyte membrane. The active area was 25 cm ² . The Nafion ionomer content of both electrode layers was fixed at 30 wt%, and the platinum catalyst loading was 0.05 mg / cm ^{2, which} was 1/8 lower than that of a general polymer electrolyte fuel cell.

A gas diffusion medium (Sigracet 10BC, SGL carbon Inc.), Teflon gasket and graphite blocks were fastened to the membrane electrode assembly to manufacture a fuel (hydrogen) concentration sensor having the same structure as that of a fuel cell unit cell. One electrode of the fuel (hydrogen) concentration sensor is supplied with pure hydrogen as a reference electrode, and the other electrode is supplied with a gas for measuring hydrogen concentration by acting as a sensor site.

analysis

The temperature of the open-circuit voltage fuel (hydrogen) concentration sensor was adjusted to 65 ° C, humidified hydrogen was supplied to the reference electrode and the sensor electrode, and the open-circuit voltage was measured. After that, a mixture of hydrogen and nitrogen was supplied to the sensor electrode, and the change in the open circuit voltage was measured.

result

FIG. 6A is an experimental result of an open-circuit voltage fuel (hydrogen) concentration sensor in Experiment 2. FIG. FIG. 6B is an enlarged view of the initial section of FIG. 6A.

The difference between the open-circuit voltage values when supplying pure hydrogen to the sensor electrode and when supplying a nitrogen gas mixture was measured to remove voltage errors that may occur due to unevenness of the membrane electrode assembly. The theoretical curve indicated by the solid line and the experimental results are in good agreement with each other. In particular, it can be seen that it works well in the region of low nitrogen concentration, which is important for fuel cell vehicle applications.

[Experiment 3: Open-circuit voltage type fuel (hydrogen) concentration sensor reducing platinum usage and increasing polymer electrolyte membrane thickness]

In Experiment 3, we measured the characteristics of the open-circuit voltage fuel (hydrogen) concentration sensor that significantly reduced the platinum consumption to 0.05 mg / cm ² and increased the thickness of the polymer electrolyte membrane.

Membrane electrode  Bonding and Fuel (Hydrogen) Concentration Sensor

The membrane electrode assembly was prepared as follows.

That is, the catalyst layer was prepared by spraying directly onto the polymer electrolyte membrane (direct injection method). The catalyst ink was prepared by dispersing a carbon supported platinum catalyst (Tanaka Kikinzoku Kogyo, Pt 45.5 wt.%) And a Nafion ionomer solution (DuPont) in a mixed solvent of isopropyl alcohol (Baker Analyzed HPLC Reagent) and deionized water.

As the polymer electrolyte membrane, N115 membrane (DuPont) was used to increase the thickness to about 127 micrometers. The active area was 25 cm ² . The Nafion ionomer content of both electrode layers was fixed at 30% by weight, and the platinum catalyst loading was 0.05 mg / cm ^{2, which} was 1/8 lower than that of a general polymer electrolyte fuel cell.

A gas diffusion medium (Sigracet 10BC, SGL carbon Inc.), Teflon gasket and graphite blocks were fastened to the membrane electrode assembly to manufacture a fuel (hydrogen) concentration sensor having the same structure as that of a fuel cell unit cell. One electrode of the fuel (hydrogen) concentration sensor is supplied with pure hydrogen as a reference electrode, and the other electrode is supplied with a gas for measuring hydrogen concentration by acting as a sensor site.

analysis

The temperature of the open-circuit voltage fuel (hydrogen) concentration sensor was adjusted to 65 ° C, humidified hydrogen was supplied to the reference electrode and the sensor electrode, and the open-circuit voltage was measured. After that, a mixture of hydrogen and nitrogen was supplied to the sensor electrode, and the change in the open circuit voltage was measured.

result

FIG. 7A is an experimental result of an open-circuit voltage fuel (hydrogen) concentration sensor in Experiment 3. FIG. FIG. 7B is an enlarged view of the initial section of FIG. 7A.

The difference between the open-circuit voltage values when supplying pure hydrogen to the sensor electrode and when supplying a nitrogen gas mixture was measured to remove voltage errors that may occur due to unevenness of the membrane electrode assembly.

The theoretical curve shown by the solid line and the experimental results are in good agreement with each other. In particular, it can be seen that it works well in the low nitrogen concentration region, which is important for fuel cell vehicle applications.

For reference, the experimental conditions of Examples 1, 2 and 3 are summarized in the following table.

Example 1 Example 2 Example 3 Platinum loading 0.4 mg / cm ² 0.05 mg / cm ² 0.05 mg / cm ² Polymer electrolyte membrane NRE-212
(About 51 micrometers) NRE-212
(About 51 micrometers) N115
(About 127 micrometers) Experimental temperature 25 ° C, 65 ° C and 80 ° C 65 ℃ 65 ℃

Claims (18)

Electrolyte membrane;
A reference electrode on one side of the electrolyte membrane;
A unit cell or a stack in which the unit cells are stacked, including a measuring electrode existing on the other side of the electrolyte membrane;
An open circuit voltage meter for measuring the open circuit voltage of the unit cell or the stack in which the unit cells are stacked;
A reference material having a set fuel concentration flows through the reference electrode, and a measurement target material through which a fuel concentration is to be measured flows through the measurement electrode.
The open circuit voltage value of the unit cell or the stack in which the unit cells are stacked varies according to the fuel concentration in the measurement target material. The method of claim 1,
And the reference material is a liquid or gas phase fuel, and the material to be measured is a mixture of fuel and non-fuel material as liquid or gas phase. The method of claim 1,
The reference substance is methanol or formic acid, and the measurement target substance is water and methanol; Or water and formic acid; Fuel concentration sensor comprising a. The method of claim 1,
The reference substance is hydrogen, and the substance to be measured includes hydrogen and nitrogen. The method of claim 1,
The sensor further comprises a microprocessor for calculating the fuel concentration from the open circuit voltage measurement,
The microprocessor supplies an anode material containing a fuel having a set concentration to the measurement electrode, and substitutes the actually measured open circuit voltage value into the fuel concentration and open circuit voltage value data constructed from the measured open circuit voltage value. A fuel concentration sensor which calculates a fuel concentration. The method of claim 1,
The sensor further comprises a microprocessor for calculating the fuel concentration from the open circuit voltage measurement,
The microprocessor calculates fuel activity by substituting the measured open circuit voltage value into [Equation 1].
[Equation 1]

(a _{fuel of the reference material and reference electrode} are the activity of the fuel in the reference material known fuel concentration at the reference electrode, a fuel of the _{material to be measured , the measurement electrode} is the activity of the fuel of the material to be measured at the measurement electrode. T is the gas constant, T is the operating temperature of the unit cell or stack of unit cells, F is the Faraday constant, E ^OCV is the open-circuit voltage, and n is the number of electrons associated with the reaction of the fuel.) Providing a reference material having a fuel concentration set on the reference electrode present on one side of the electrolyte membrane;
Providing a measurement target substance to measure fuel concentration to a measurement electrode present on the other side of the electrolyte membrane; And
Measuring an open circuit voltage of a unit cell consisting of the electrolyte membrane, a reference electrode, and a measurement electrode or a stack of stacked unit cells;
The open circuit voltage value of the unit cell or the stack in which the unit cells are stacked varies according to the fuel concentration in the measurement target material. The method of claim 7, wherein
The method further comprises calculating a fuel concentration from the open circuit voltage measurement,
The calculating of the fuel concentration may include an anode material including a fuel having a set concentration to the measurement electrode, and the actual measured open circuit voltage value to the fuel concentration and open circuit voltage value data constructed from the measured open circuit voltage value. The fuel concentration sensing method, characterized in that for calculating the fuel concentration. The method of claim 7, wherein
The method further comprises calculating a fuel concentration from the open circuit voltage measurement,
The calculating of the fuel concentration may include calculating the fuel activity by substituting the measured open circuit voltage value into [Equation 1].
[Equation 1]

(a _{fuel of the reference material and reference electrode} are the activity of the fuel in the reference material known fuel concentration at the reference electrode, a fuel of the _{material to be measured , the measurement electrode} is the activity of the fuel of the material to be measured at the measurement electrode. T is the gas constant, T is the operating temperature of the unit cell or stack of unit cells, F is the Faraday constant, E ^OCV is the open-circuit voltage, and n is the number of electrons associated with the reaction of the fuel.) Fuel cell;
An anode material recycling flow path for recycling an anode material including an unreacted fuel flowing out of the anode to the fuel cell to the anode;
And a fuel concentration sensor configured to measure a fuel concentration in the anode material installed and recycled in the recirculation flow path.
The fuel concentration sensor includes a unit cell or a stack in which the unit cell including an electrolyte membrane, a reference electrode present on one side of the electrolyte membrane, and a measurement electrode present on the other side of the electrolyte membrane, and the unit cell or the unit cell are stacked. An open circuit voltage meter for measuring an open circuit voltage of the stacked stack,
A reference material having a set fuel concentration flows through the reference electrode, and a recycle anode material for measuring fuel concentration flows through the measurement electrode, and an open circuit voltage value of the unit cell or the stack in which the unit cells are stacked is the recycle anode. A fuel recirculation system apparatus, characterized by varying fuel concentrations in a substance. The method of claim 10,
And the fuel cell is a unit cell or a stack of unit cells. The method of claim 10,
And a portion of the fuel flow initially supplied to the anode of the fuel cell is provided as a reference material of the fuel concentration sensor. The method of claim 10,
And when the concentration of the fuel in the recycle anode material is lowered below the set level, releasing the recycle anode material to the outside of the recycle passage. A fuel cell utilization apparatus comprising a fuel recycle system device according to any one of claims 10 to 13. The method of claim 14,
The fuel cell using device is a fuel cell, characterized in that the vehicle. Recycling an anode material including the unreacted fuel flowing out of the anode of the fuel cell to the anode;
Measuring the concentration of fuel in the anode material that is recycled during the fuel recycle process;
The measurement of the concentration of fuel in the recycled anode material,
Providing a reference material having a fuel concentration set on the reference electrode present on one side of the electrolyte membrane;
Providing a recycle anode material for measuring fuel concentration to a measurement electrode present on the other side of the electrolyte membrane; And
And measuring an open circuit voltage of a unit cell consisting of the electrolyte membrane, a reference electrode, and a measurement electrode, or a stack of unit cells stacked thereon, wherein the open circuit voltage value of the unit cell or a stack of unit cells is stacked. Is dependent on the fuel concentration in the recycle anode material. 17. The method of claim 16,
And a portion of the fuel flow initially supplied to the anode of the fuel cell as the reference material. 17. The method of claim 16,
And when the concentration of the fuel in the recycle anode material is lowered below a predetermined level, the recycle anode material is discharged to the outside of the recycle passage.

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