KR102329873B1 - High-concentration nafion-based hydrogen sensor for fuel-cell electric vehicles - Google Patents

Abstract

The present invention relates to a high-concentration Nafion-based hydrogen sensor for a fuel cell, comprising a substrate, a counter electrode provided in contact with the substrate, a Nafion membrane provided on the counter electrode, and an upper portion of the Nafion membrane By including a working electrode in contact with hydrogen gas, and a sealing film for sealing the counter electrode, Nafion film, and the working electrode except for a contact region in which the working electrode is in contact with the hydrogen gas, high-concentration hydrogen gas can be accurately detected in a wide detection range. can be detected.

Description

HIGH-CONCENTRATION NAFION-BASED HYDROGEN SENSOR FOR FUEL-CELL ELECTRIC VEHICLES for fuel cell

The present invention provides high-concentration or high-concentration hydrogen gas for fuel cells that can precisely detect high-concentration hydrogen gas in a wide detection range by forming membrane electrode assemblies (MEA) with working electrodes and counter electrodes attached to the upper and lower portions of the Nafion membrane on a substrate. It relates to a pion-based hydrogen sensor.

As is well known, the demand for sensor technology in the automotive industry is increasing with the expansion of the new car market, and fuel cell electric vehicles require various types of sensors, such as high-concentration hydrogen sensors, in addition to the conventional sensors used in general combustion engine vehicles. have.

Here, it is known that hydrogen is a clean fuel, that is, does not generate environmental pollutants during combustion, but requires careful consideration for production, storage and distribution because of its explosive reaction with oxygen. A hydrogen sensor that detects the presence and leakage of hydrogen is considered a key factor in the development of fuel cell electric vehicles.

In addition to safety aspects, hydrogen sensors can help to improve fuel efficiency by precisely monitoring the concentration of hydrogen gas supplied and recycled to the fuel cell stack. For example, catalysts, thermal conductivity-based, electrochemical, resistance-based, work function-based, optics, and acoustics are being developed in various ways.

However, since most of the conventional hydrogen sensors have a detection range of up to 4 vol.% (explosive limit), they are not suitable for monitoring and controlling high concentration hydrogen gas used in fuel cell electric vehicles. development is urgently needed.

1. Korea Patent Publication No. 10-2008-0072850 (published on August 7, 2008)

The present invention provides a high-concentration Nafion-based hydrogen sensor for fuel cells that can precisely detect high-concentration hydrogen gas in a wide detection range by forming a membrane electrode assembly (MEA) with a working electrode and a counter electrode attached to the upper and lower portions of the Nafion membrane on a substrate. would like to provide

In addition, the present invention includes a substrate, a counter electrode, a Nafion film and a working electrode, and a sealing film for sealing the counter electrode, Nafion film, and the working electrode except for a contact region in which the working electrode is in contact with hydrogen gas. Based on a concentration cell containing an exposed high-concentration working electrode and a low-concentration counter electrode isolated from the external atmosphere, using the electromotive force between the two electrodes generated by the difference in proton activity according to the partial pressure of hydrogen, high concentration in a wide detection range An object of the present invention is to provide a high-concentration Nafion-based hydrogen sensor for fuel cells that can precisely detect hydrogen gas and secure a very short response time.

The purpose of the embodiments of the present invention is not limited to the above-mentioned purpose, and other objects not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the description below. .

According to an embodiment of the present invention, a substrate, a counter electrode provided in contact with the substrate, a Nafion film provided on the counter electrode, and a working electrode provided on the Nafion film and in contact with hydrogen gas And, a high concentration Nafion-based hydrogen sensor for a fuel cell including a sealing film for sealing the counter electrode, the Nafion film, and the working electrode except for a contact region in which the working electrode is in contact with the hydrogen gas may be provided.

Further, according to an embodiment of the present invention, the substrate may include polypropylene, polyester, thermoplastic polyurethane, polyethylene, polybutylene terephthalate, polyamide, polyethylene terephthalate, polyphenylene sulfide, Teflon and polyether ether ketone. A high concentration Nafion-based hydrogen sensor for fuel cells in which conductive particles made of at least one or more hydrophobic polymers selected from among carbon black, carbon nanotubes, and carbon materials selected from graphene are dispersed therein may be provided.

Further, according to an embodiment of the present invention, the counter electrode and the working electrode include a carbon material and metal nanoparticles, and the metal nanoparticles include Pd, Pt, Al, Ni, Mn, Mo, Mg and V A high concentration Nafion-based hydrogen sensor for a fuel cell comprising at least one selected from the group consisting of may be provided.

In addition, according to an embodiment of the present invention, the Nafion membrane is a high-concentration Nafion-based hydrogen sensor for fuel cells manufactured to have hydroxyl groups (OH-) on the surface or inside by acid-treating a membrane made of Nafion, which is a hydrophilic polymer. may be provided.

In addition, according to an embodiment of the present invention, the sealing film may be provided with a high concentration Nafion-based hydrogen sensor for fuel cells made of epoxy or Teflon.

In addition, according to an embodiment of the present invention, the counter electrode, the Nafion membrane and the working electrode may be provided with a high concentration Nafion-based hydrogen sensor for a fuel cell manufactured by a hot pressing method.

According to the present invention, a high concentration hydrogen gas can be precisely detected in a wide detection range by forming a membrane electrode assembly (MEA) having a working electrode and a counter electrode attached to the upper and lower portions of the Nafion film on a substrate.

In addition, the present invention includes a substrate, a counter electrode, a Nafion film and a working electrode, and a sealing film for sealing the counter electrode, Nafion film, and the working electrode except for a contact region in which the working electrode is in contact with hydrogen gas. Based on a concentration cell containing an exposed high-concentration working electrode and a low-concentration counter electrode isolated from the external atmosphere, using the electromotive force between the two electrodes generated by the difference in proton activity according to the partial pressure of hydrogen, high concentration in a wide detection range Not only can hydrogen gas be detected accurately, but also a very short response time can be ensured.

1 is a diagram illustrating a high-concentration Nafion-based hydrogen sensor for a fuel cell according to an embodiment of the present invention;
2 is a diagram illustrating a sensor measurement system of a high-concentration Nafion-based hydrogen sensor for a fuel cell according to an embodiment of the present invention;
3 to 9 are views for explaining a result of manufacturing and characteristic analysis of a high concentration Nafion-based hydrogen sensor for a fuel cell according to an embodiment of the present invention.

Advantages and features of embodiments of the present invention, and methods of achieving them, will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the art to which the present invention pertains It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

In describing the embodiments of the present invention, if it is determined that a detailed description of a well-known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, the terms to be described later are terms defined in consideration of functions in an embodiment of the present invention, which may vary according to intentions or customs of users and operators. Therefore, the definition should be made based on the content throughout this specification.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a high-concentration Nafion-based hydrogen sensor for a fuel cell according to an embodiment of the present invention.

Referring to FIG. 1 , a high concentration Nafion-based hydrogen sensor for a fuel cell according to an embodiment of the present invention has a substrate 110 , a counter electrode 120 , a Nafion film 130 , a working electrode 140 , and a sealing film 150 . ) and the like.

The substrate 110 is, for example, at least one selected from polypropylene, polyester, thermoplastic polyurethane, polyethylene, polybutylene terephthalate, polyamide, polyethylene terephthalate, polyphenylene sulfide, Teflon, and polyether ether ketone. It may be made of a hydrophobic polymer, and conductive particles made of a carbon material selected from carbon black, carbon nanotubes, and graphene may be dispersed therein.

The substrate 110 serves as a pseudo reference electrode and includes hydrophobic pores therein, thereby pushing moisture generated from the counter electrode 120 in the direction of the working electrode 140 when hydrogen is detected. In this case, the moisture discharged from the counter electrode 120 can be discharged to the outside through the Nafion membrane 130 , and moisture can be continuously supplied to the Nafion membrane 130 , so that the conductivity of the hydrogen sensor can be improved. In addition, it is possible to prevent performance degradation due to long-term use.

Here, the substrate 110 may have a porosity of 5 to 15%, and the hydrophobic pores may have a size of about 5 to 150 μm.

For example, by mixing a hydrophobic polymer such as Teflon and carbon black with an alcohol solvent and heat-treating, hydrophobic pores are formed therein, and the substrate 110 in which conductive particles, carbon black, are dispersed can be manufactured.

The counter electrode 120 is provided in contact with the substrate 110, and includes a carbon material and metal nanoparticles, the carbon material may be selected from carbon black, carbon nanotubes, and graphene, and the metal nanoparticles are , Pd, Pt, Al, Ni, Mn, Mo, may include at least one selected from the group consisting of Mg and V.

These metal nanoparticles can detect hydrogen through the change of electrical properties by adsorbing hydrogen, and can absorb a relatively large amount of hydrogen, and can be supported in the form of dispersed particles on the surface of a porous carbon powder carrier, It can be deposited by sputtering, thermal evaporation, electron beam deposition, electroplating, a method of spraying an aqueous metal solution on the sample surface, or a method of growing Pd and Pt into nanowires in an aqueous solution.

The Nafion film 130 is provided on the counter electrode 120 and may be manufactured to have hydroxyl groups (OH-) on the surface or inside by acid-treating a film made of Nafion, which is a hydrophilic polymer.

The Nafion membrane 130 may be pretreated by immersing the Nafion membrane in 10% sulfuric acid, thereby improving the ionic conductivity of the membrane.

The working electrode 140 is provided on the Nafion film 130 and is in contact with hydrogen gas, and includes a carbon material and metal nanoparticles, wherein the carbon material is selected from carbon black, carbon nanotubes, and graphene. The metal nanoparticles used as a detection material for hydrogen gas to improve adsorption and reaction properties for hydrogen include at least one selected from the group consisting of Pd, Pt, Al, Ni, Mn, Mo, Mg, and V. may include

These metal nanoparticles can detect hydrogen through the change of electrical properties by adsorbing hydrogen, and can absorb a relatively large amount of hydrogen, and can be supported in the form of dispersed particles on the surface of a porous carbon powder carrier, It can be deposited by sputtering, thermal evaporation, electron beam deposition, electroplating, a method of spraying an aqueous metal solution on the sample surface, or a method of growing Pd and Pt into nanowires in an aqueous solution.

The sealing film 150 seals the counter electrode 120 , the Nafion film 130 , and the working electrode 140 except for a contact region where the working electrode 140 comes into contact with hydrogen gas, and may be made of epoxy or Teflon. . That is, the sealing film 150 extends from the upper portion of the substrate 110 to cover the side surfaces of the counter electrode 120 , the Nafion film 130 , and the working electrode 140 , and then a portion of the upper edge of the working electrode 140 . It may be formed to surround.

As described above, the high concentration Nafion-based hydrogen sensor for a fuel cell according to an embodiment of the present invention is a concentration cell including a high concentration working electrode 140 exposed to hydrogen gas and a low concentration counter electrode 120 isolated from the external atmosphere. By using the electromotive force between the two electrodes generated by the difference in proton activity according to the partial pressure of hydrogen based on seconds) can be obtained.

Here, the membrane electrode assembly (MEA) including the counter electrode 120 , the Nafion film 130 , and the working electrode 140 may be manufactured by a hot pressing method. By sequentially arranging the 130 and the working electrode 140, heating and pressing through a heating member (eg, a hot plate, etc.) and a pressing member (eg, a weight, a press machine, etc.) , this membrane electrode assembly (MEA) can improve the ionic conductivity of the hydrogen sensor by improving problems such as contact resistance.

Such hot pressing may be performed by pressing at 1 to 20 MPa while heating to a temperature of about 140 to 200°C. There is a problem in that contact resistance increases because it does not lose strength, and when hot pressing is performed in excess of 200° C., deterioration (deformation) of the Nafion film 130 made of polymer may be caused. Preferably, the hot pressing is carried out at a temperature of less than 180° C., particularly preferably at a temperature of 140 to 160° C.

When the hot pressing temperature is high, the mechanical adhesion is excellent, but the Nafion is dehydrated and the electrical properties are poor. decreases and a lot of moisture is absorbed during sensor operation, causing expansion, and eventually the Nafion membrane and the electrode are separated.

On the other hand, the effect of temperature, relative humidity, pressure, hydrogen concentration, etc. on the hydrogen sensor by manufacturing a high concentration Nafion-based hydrogen sensor for a fuel cell according to the embodiment of the present invention as described above will be described.

2 is a diagram illustrating a sensor measurement system of a high-concentration Nafion-based hydrogen sensor for a fuel cell according to an embodiment of the present invention, and FIGS. 3 to 9 are a high-concentration Nafion-based hydrogen sensor for a fuel cell according to an embodiment of the present invention. It is a drawing for explaining the manufacturing and characteristic analysis result.

2 to 9 , the Nafion membrane having a thickness of 177 μm was converted into an ion conductor having abundant protons by performing a predetermined pretreatment.

The proton conductor film of the Nafion membrane pretreated in this way was cut into 2.0*2.0cm2 pieces, and the conductivity was measured using a 4-probe technique. The standard deviation at /cm increased from 0.021S/cm to 1.353±0.129S/cm after pretreatment.

This shows that pretreatment with 10% sulfuric acid significantly increases the ionic conductivity of the Nafion membrane, which _{results from the hopping of protons to the sulfonic acid (SO 3} H) groups of the membrane, such as sulfuric acid and nitric acid. Since the strong acid provides protons to replace other cations electrostatically bound to the dissociated sulfonic acid site (-SO3-), the ionic conductivity of the membrane can be improved by pretreatment with sulfuric acid.

Next, a membrane electrode assembly (MEA) was prepared by hot pressing by attaching an anode and a cathode to a hydrated Nafion membrane. Based on the trade-off between the mechanical and electrical properties of MEAs, 150 °C was determined.

And, it was found that high temperature resulted in good mechanical adhesion, but electrolysis was observed due to dehydration, and low temperature required an increase in high temperature compression pressure, which substantially reduced the film thickness after high temperature compression.

On the other hand, the more water absorbed by the Nafion membrane, the greater the expansion of the membrane and the faster the water absorption of the thin sample. The stress is caused by this expansion mismatch between the membrane and the electrode, which leads to the separation of the membrane and the electrode, which preferentially expands as water is produced through cathodic reaction with oxygen during sensor operation. It can be seen that the electrode is separated.

The hydrogen sensor manufactured as described above may have a multilayer structure of Pt-C electrode / Nafion film / Pt-C electrode / Teflon substrate, and the membrane electrode assembly (MEA) except for a part of the surface of the upper Pt-C electrode sealed with epoxy resin.

This hydrogen sensor is based on a concentration cell including a high concentration working electrode exposed to hydrogen gas and a low concentration counter electrode isolated from the external atmosphere, and an electromotive force is generated between the two electrodes due to the difference in proton activity depending on the partial pressure of hydrogen. , the glove box was purged with nitrogen gas to prevent oxygen permeation, and high-purity hydrogen and nitrogen gas were supplied to the sensor measurement system as shown in FIG. 2 through each supply port.

Here, the gas mixing system was used to obtain a gas mixture with different concentrations of hydrogen gas diluted in nitrogen, high concentration hydrogen gas (20-99.99%) was injected into the test room, and the discharge gas was discharged out of the glove box.

As described above, the effect of sensor electromotive force (EMF) on hydrogen concentration was investigated through the sensor measurement system of FIG. was injected for 2 minutes at a total flow of It can be seen that it increases to 80.87 mV.

Here, the theoretical value of the electromotive force (EMF) can be calculated from the Nernst equation as in Equation 1 below.

where R is the gas constant, F is the Faraday constant, T is the temperature (K), Ps is the partial gas pressure of the sample gas mixture (proportional to the hydrogen concentration), Pc is the reference partial pressure, and n is the basic electrochemical reaction of the sensor. It means the number of electrons involved (n=2 hydrogen), and in general, the sensing electrode potential represents a logarithmic function of the hydrogen concentration in air.

And, as shown in FIG. 5, it can be seen that the calculated EMF difference between 20% and 99.99% of hydrogen concentration is 20.76mV, which is almost identical to that obtained in the actual measurement (18.07mV), and similarly, 20 and 60% of It was found that the theoretical and experimental values of the difference in electromotive force (EMF) for the two concentrations showed good agreement. The small discrepancy between these theoretical and experimental electromotive force (EMF) values can be attributed to the inaccuracy of the hydrogen concentration determined by the gas mixing system.

4(b) shows the sensor response to hydrogen gas, which increases in concentration with 20% increase in each step, and this result clearly shows that the manufactured hydrogen sensor operates properly in the entire range of 0-99.99%. The change in output voltage could be estimated to be less than 1% through three repeated measurements.

And, the response time of the hydrogen sensor was measured after exposure to pure nitrogen gas for 2 minutes and then injection of hydrogen gas. indicates that an electromotive force (EMF) was generated 1 second after the Could know.

Here, the reaction time was determined as the time required to reach 90% of the steady-state voltage. It can be confirmed that as α increases from 20 to 99.99%, it decreases from 3.77 to 2.73 seconds.

Meanwhile, in the present invention, the effect of humidity, pressure, and temperature on the reliability of the sensor was investigated in order to confirm the applicability of the hydrogen sensor for monitoring the hydrogen concentration in a fuel cell electric vehicle. Reliability tests were performed to alternately inject each for 2 minutes.

Through these experiments, changes in the output characteristics of the sensor were investigated after being immersed in a chamber with constant temperature and humidity at 20% RH or 90% RH for 2 hours. It can be seen that the output voltage characteristic of the sensor appears almost constant before and after immersion, and it can be seen that a relatively large change occurs at 90% RH as shown in FIG. 7B. However, it was found that the repetitive sensing operation was well maintained while the overall output voltage fluctuation was limited to within 6%.

As described above, membrane expansion is due to water absorption, which can increase the stress of the sensor, so a high-humidity environment can degrade the sensor performance due to the mechanical instability of the Nafion membrane, and as the relative humidity increases, Nafion As the proton conductance of , high humidity itself will not be detrimental to proton conduction, and the effect of humidity on sensor performance can be considered as a limiting factor.

And, the change in the output characteristic of the sensor was measured at 100 kPa or 30 kPa for 2 hours after being put into the vacuum chamber. Although it was expected to lead to a decrease in sensor performance, as shown in Fig. 8, it was found that decreasing the pressure did not appear to affect the sensor stability, and dehydration was accelerated with increasing temperature, whereas the experiment at room temperature can be performed, and through these experimental results, it was found that reducing the pressure to 30 kPa at room temperature did not affect the membrane dehydration of the sensor.

Finally, the change in the output characteristics of the sensor was investigated after being put in a constant temperature and humidity chamber at -10°C or 80°C for 2 hours. It can be seen that the curve appears almost identical to the response curve of the raw sensor, and it can be seen that the sensor response changes rapidly when wet at 80°C, as shown in FIG. knew it wasn't.

Since this result is due to the dehydration of the Nafion membrane at 80°C or higher, in order to apply the manufactured hydrogen sensor to a high-temperature environment above 80°C, a heat-sealing structure with a small opening for gas flow must be designed to humidify the Nafion membrane. was found, and the introduction of inorganic nanoparticles into the Nafion membrane can be considered as another effective way to increase the operating temperature of the sensor.

It was found that the hydrogen sensor manufactured as described above operates in the hydrogen concentration range of 20-99.99% and exhibits a very short response time (less than 5 seconds), and environmental changes in relative humidity and pressure affect the stability of the sensor. It can be seen that the response curve of the wet sensor at -10℃ is almost the same as that of the raw sensor, but the sensor response is drastically changed when wet at 80℃. It was confirmed that it was caused by dehydration of the Pion membrane, and it was found that this could be prevented by using a sealing structure for the sensor. It can be seen that the gas can be monitored.

Therefore, the present invention can precisely detect high concentration hydrogen gas in a wide detection range by forming a membrane electrode assembly (MEA) having a working electrode and a counter electrode attached to the upper and lower portions of the Nafion film on a substrate.

In addition, the present invention includes a substrate, a counter electrode, a Nafion film and a working electrode, and a sealing film for sealing the counter electrode, Nafion film, and the working electrode except for a contact region in which the working electrode is in contact with hydrogen gas. Based on a concentration cell containing an exposed high-concentration working electrode and a low-concentration counter electrode isolated from the external atmosphere, using the electromotive force between the two electrodes generated by the difference in proton activity according to the partial pressure of hydrogen, high concentration in a wide detection range Not only can hydrogen gas be detected accurately, but also a very short response time can be ensured.

In the above description, various embodiments of the present invention have been presented and described, but the present invention is not necessarily limited thereto. It will be readily appreciated that branch substitutions, transformations and alterations are possible.

110: substrate
120: counter electrode
130: Nafion membrane
140: working electrode
150: sealing film

Claims (6)

board and
a counter electrode provided in contact with the substrate;
a Nafion film provided on the counter electrode;
a working electrode provided on the Nafion membrane and in contact with hydrogen gas;
and a sealing film for sealing the counter electrode, the Nafion film, and the working electrode except for a contact region in which the working electrode is in contact with the hydrogen gas,
The counter electrode and the working electrode include carbon materials and metal nanoparticles,
The metal nanoparticles include at least one selected from the group consisting of Pd, Pt, Al, Ni, Mn, Mo, Mg and V,
Using the electromotive force between the two electrodes generated by the difference in proton activity according to the partial pressure of hydrogen based on a concentration cell including the working electrode of high concentration exposed to hydrogen gas and the counter electrode of low concentration isolated from the external atmosphere A high concentration Nafion-based hydrogen sensor for fuel cells, characterized in that it detects hydrogen gas.
The method of claim 1,
The substrate is made of at least one hydrophobic polymer selected from polypropylene, polyester, thermoplastic polyurethane, polyethylene, polybutylene terephthalate, polyamide, polyethylene terephthalate, polyphenylene sulfide, Teflon and polyether ether ketone, , a high-concentration Nafion-based hydrogen sensor for fuel cells in which conductive particles made of carbon materials selected from carbon black, carbon nanotubes, and graphene are dispersed therein.
delete 3. The method of claim 2,
The Nafion membrane is a high concentration Nafion-based hydrogen sensor for fuel cells manufactured to have hydroxyl groups (OH-) on the surface or inside by acid-treating a membrane made of Nafion, a hydrophilic polymer.
5. The method of claim 4,
The sealing film is a high concentration Nafion-based hydrogen sensor for fuel cells made of epoxy or Teflon.
6. The method of any one of claims 1, 2, 4 and 5, wherein
The counter electrode, the Nafion membrane and the working electrode are a high concentration Nafion-based hydrogen sensor for a fuel cell manufactured by a hot pressing method.

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