KR100864957B1 - A membrane electrode assembly including a catalyst layer having a thickness gradient, a manufacturing method thereof, a fuel cell including the membrane electrode assembly, and an operating method thereof - Google Patents

Abstract

The present invention relates to a fuel cell MEA, a method of manufacturing the same, a fuel cell including the MEA, and a method of operating the same, wherein the cathode catalyst layer of the MEA is operated under a non-humidized or low humidified condition coated with a thickness gradient. According to the present invention, by eliminating the humidifier itself, the humidification level of the reactants is lowered to solve all the problems associated with the installation of the humidifier, and by using a catalyst loading amount gradient, it is possible to effectively use the water produced even under no humidification or low humidification conditions. Cell performance improvement.

Membrane Electrode Assembly, Fuel Cell, Humidification, Thickness Gradient

Description

A membrane electrode assembly including a catalyst layer having a thickness gradient, a method of manufacturing the same, a fuel cell including the membrane electrode assembly, and a method of operating the same about}

1A to 1D are schematic diagrams showing a cathode catalyst layer coating of Comparative Examples (FIGS. 1A and 1C) and Examples 1B and 1D of the present invention, respectively, and FIG. 1E shows air (oxygen) flow in the cathode. Schematic diagram.

2A-2B are graphs showing polarization curves under fully humidified hydrogen and air conditions (FIG. 2A) and fully humidified hydrogen and oxygen conditions (FIG. 2B) of membrane electrode assemblies of the comparative examples and embodiments of the present invention. Here, the catalyst loading amount of the anode is 0.3 mg / cm ^2, respectively.

3A to 3B are graphs showing polarization curves under unhumidified hydrogen and air conditions (FIG. 3A) and unhumidified hydrogen and oxygen conditions (FIG. 3B) of MEAs of Comparative Examples and Examples of the present invention. Here, the catalyst loading amount of the anode is 0.3 mg / cm ^2, respectively.

4A to 4B are graphs showing voltages at 0.8 A / cm ² under unhumidified hydrogen and air conditions of the MEA of the Comparative Examples and Examples of the present invention.

FIG. 5 is a graph showing polarization curves when temperature is changed under unhumidified hydrogen and air conditions of the MEA of Example 2 of the present invention. FIG.

B. Yang, A. Manthiram, J. Electrochem. Soc. 151 (2004) A 2120-A 2125.

2. N.H. Jalani, K. Dunn, R. Datta, Electrochimica Acta, 51 (2005) 553.

3.F. Liu, B. Yi, D. Xing, J. Yu, Z. Hou, Y. Fu, J. Power Sources, 124 (2003) 81.

The present invention relates to a membrane electrode assembly (hereinafter referred to as "MEA") comprising a catalyst layer having a thickness gradient, a method of manufacturing the same, a fuel cell including the membrane electrode assembly, and a method of operating the same.

In the present invention, the low humidification condition means a humidification condition when the humidity is in the range of more than 0 and 20% or less, and the non-humidification condition means that the humidity is 0%.

The proton exchange membrane fuel cell (hereinafter referred to as "PEMFC") is an electrochemical device in which chemical energy of fuel is converted into electrical energy, which is environmentally friendly and has high energy efficiency as compared to conventional power generation systems. I am getting it.

PEMFC typically uses a Nafion type perfluorosulfonic acid polymer as an electrolyte membrane. The Nafion electrolyte membrane must be humidified to maintain proton conductivity, and for this purpose, a separate humidifier must be installed in the PEMFC.

However, in order to install the humidifier, a separate space is required, thereby inhibiting the space utilization of the entire fuel cell. The use of humidifiers is not particularly suitable for power supplies where the use of auxiliary components, such as mobile power supplies, should be minimized.

Furthermore, when a humidifier is mounted, a large amount of water is supplied to the fuel cell. However, when an excessive amount of water is supplied, a certain cell performance is impaired, which causes inconvenience to be removed from the fuel cell.

The most appropriate way to solve this problem of mounting the humidifier is to remove the humidifier itself, ie to allow the fuel cell to operate under low or no humidification conditions without external humidification. Operation of the PEMFC without external humidification can simplify the entire fuel cell system and significantly reduce costs.

In order to operate a PEMFC without external humidification, several components must be modified in the fuel cell. These techniques are known.

For example, the operation of PEMFC using a magnetic humidifying membrane in which an inorganic material is added to an ion exchange membrane has been developed (see prior art documents 1 and 2). Furthermore, platinum is dispersed in the center of Nafion and PTFE composite membranes to dry conditions. It is also known to improve the cell performance (see the prior art document 3).

However, in order to operate PEMFC under no-humidity or low-humidity conditions, the produced water must be used efficiently during fuel cell operation. Most of the water will diffuse from the cathode reaction site into the gas channel. Thus, even when a large amount of water is produced, the membrane cannot be sufficiently hydrated, resulting in a decrease in cell performance.

Accordingly, the present invention is to solve the above problems, an object of the present invention, in the membrane electrode assembly or the fuel cell, by removing the humidifier itself to lower the level of humidification of the reactant to solve the problems associated with the installation of the humidifier. In addition, it is possible to effectively use the water produced under no humidification or low humidification conditions to achieve cell performance improvement.

The object of the present invention as described above is achieved by a fuel cell MEA, characterized in that the cathode catalyst layer of the MEA is coated to have a thickness gradient as a fuel cell MEA operated under no humidification or low humidification conditions.

An object of the present invention as described above is a method for manufacturing a fuel cell MEA that is operated under no humidification or low humidification conditions, the method of manufacturing a fuel cell MEA characterized in that the cathode catalyst layer of the MEA is coated to have a thickness gradient. Is achieved.

The object of the present invention as described above is achieved by a fuel cell including the MEA in a fuel cell operated under no humidification or low humidification conditions.

An object of the present invention as described above is a method of operating a fuel cell that is operated under a condition of no humidification or low humidification, the fuel cell operating method characterized in that for driving to increase the current density during operation. Is achieved. At this time, the current density 0.8A / cm ² is less than the lower the operating temperature 0.8A / cm ² or more is preferred to increase the operating temperature.

In the above, the MEA preferably forms a gradient such that the catalyst layer thickness at the air or oxygen inlet side is larger than the catalyst layer thickness at the air or oxygen outlet side.

Hereinafter, the present invention will be described in detail by explaining preferred embodiments. However, the present invention is not limited to the following examples, and various forms of embodiments can be implemented within the scope of the appended claims, and the following examples are only common in the art while making the disclosure of the present invention complete. It is intended to facilitate the implementation of the invention to those with knowledge.

In the present invention, the humidifier is removed, but to effectively use the water produced in the operation process to obtain efficient cell performance under no humidification or low humidification conditions. To this end, in the present invention, the catalyst layer thickness has a gradient when coating the catalyst layer, unlike the conventional catalyst layer is formed in a uniform thickness throughout the catalyst layer. For example, the present invention allows the cathode inlet reaction site to produce a larger amount of water at the cathode inlet reaction site by having a larger thickness of the catalyst bed than the outlet reaction site, thereby reducing the difference in concentration of water and thus reducing the humidification or low humidification bath. Even under dry conditions, the membrane can be fully hydrated and the cell performance can be improved.

[Manufacture of MEA]

Specifically, MEA was prepared as follows, for example. A catalyst ink was prepared by mixing carbon supported catalyst powder (40 wt%, Pt / C, E-Tek), Nafion solution (EW 1100, 5 wt%, DuPont) and isopropyl alcohol (Baker, HPLC). The catalyst ink was sonicated and sprayed directly onto a Nafion 111 membrane to prepare a MEA (active area: 5 × 5 cm ² ). MEA was dried at 60 ° C. for 10 hours. When the catalyst ink is sprayed, the coating thickness is uniform or has a gradient as in the following examples.

FIG. 1A shows the catalyst coating of Comparative Example 1, wherein the cathode was coated such that the catalyst had an overall uniform loading amount (0.3 mg / cm ² ). FIG. 1 c shows the catalyst coating of Comparative Example 2, wherein the cathode was coated such that the catalyst had an overall uniform loading amount (0.4 mg / cm ² ).

FIG. 1 b shows the catalyst coating of Example 1 wherein the cathode has a gradient (loading amount of 0.2 mg / cm ² to 0.4 mg / cm ² ) of the catalyst layer from air or oxygen inlet side to outlet side Coated. FIG. 1D shows the catalyst coating of Example 2 wherein the cathode has a gradient (loading amount of 0.3 mg / cm ² to 0.5 mg / cm ² ) of catalyst layer from air or oxygen inlet side to outlet side Coated.

As can be seen from the above, Comparative Example 1 and Example 1, Comparative Example 2 and Example 2 have the same average catalyst loading amount (0.3 mg / cm ² or 0.4 mg / cm ² ), but there is a difference in the thickness gradient is formed.

In the prepared Comparative Examples and Examples of MEA, an oxidant of air or oxygen was flowed as shown in FIG. 1E.

[Performance test]

For performance testing, a low porosity is used in the selection of the MEA, gas diffusion medium (Sigracet 10BC, SGL Carbon Inc .; GDM), which has a higher water retention and is therefore better than having a high porosity. Performance), and a single cell was assembled into a graphite plate with PTFE gasket and serpentine channel. Prior to cell performance testing for testing under humidification conditions, the single cell was activated for 24 hours with a constant current mode (0.8 A / cm ² ) and fully humidified fuel and oxidant at 50 ° C. The single cell was operated under 50 ° C. no humidification conditions for 24 hours prior to cell performance testing for testing under no humidification conditions.

[result]

2A-2B show polarization curves under fully humidified hydrogen and air conditions (FIG. 2A) and fully humidified (humidity 100%) hydrogen and oxygen conditions (FIG. 2B) of membrane electrode assemblies of the comparative examples and embodiments of the present invention. A graph representing.

The MEA of the embodiments having a coating thickness gradient when the fully humidified hydrogen and air were injected had lower cell performance than the MEA of the comparative examples having a uniform coating thickness. This difference was better understood in the high current region. On the other hand, it was also found that the difference is relatively insignificant when fully humidified hydrogen and oxygen. These results show that MEAs with gradients in coating thickness are internally vulnerable to mass transfer when operated with humidified hydrogen and air. That is, near the inlet side, where the coating thickness is large, more water is formed, which impedes the transfer of air to the reaction site in the entire active area.

3A to 3B are graphs showing polarization curves under unhumidified hydrogen and air conditions (FIG. 3A) and unhumidified hydrogen and oxygen conditions (FIG. 3B) of MEAs of the comparative examples and examples of the present invention. 4A to 4B are graphs showing voltages at the case of 0.8 A / cm ² under the non-humidified hydrogen and air conditions of the MEA of the Comparative Examples and Examples of the present invention.

As can be seen from FIG. 3 and FIG. 4, unlike in the case of FIG. 2, in the non-humidified condition, the MEA of the embodiments having the coating thickness gradient was much higher than the MEA of the comparative examples having the uniform coating thickness. In particular, in the case of the non-humidified conditions, the catalyst loading amounts of 0.3 mg / cm ² and 0.4 mg / cm ² showed 11% and 17% improvement in cell performance at current densities of 0.8 A / cm ² , respectively.

The improvement in cell performance in this case is rather significant for high current densities, which supports the fact that having a gradient of catalyst thickness in the coating of the catalyst is well suited for managing the produced water.

On the other hand, the above results were the same in the non-humidity condition of 0% humidity as well as the low humidification condition in which the humidity ranges from 0% to 20% or less. In such low humidification conditions, the capacity and volume of the humidification system can be reduced in correspondence with the amount of humidity.

FIG. 5 is a graph showing polarization curves when the temperature is varied under unhumidified hydrogen and air conditions of the MEA of Example 2 of the present invention. FIG.

As can be seen in FIG. 5, the cell performance is lower in the case of the high temperature compared to the case of the low temperature because the water evaporation is severe. However, in the case of the high current density region above the current density of 0.8 A / cm ^2, the cell performance is reversed. This is related to the increased mass transfer loss due to the low saturated steam pressure of 35 ° C.

According to the present invention, by eliminating the humidifier itself, it is possible to lower the humidification level of the reactants to solve all the problems associated with the humidifier, and to improve the cell performance by effectively using the water produced under the no humidification or low humidification conditions. have.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications or variations without departing from the spirit and scope of the invention. Accordingly, the appended claims will cover such modifications and variations as fall within the spirit of the invention.

Claims (7)

MEA for fuel cells operated under a non-humidifying condition or a low humidification condition in which the humidity is more than 0% and 20% or less, The cathode catalyst layer of the MEA is a fuel cell MEA, characterized in that the coating having a thickness gradient. The method of claim 1, The MEA is a fuel cell MEA, characterized in that the catalyst layer thickness of the air or oxygen inlet side is larger than the catalyst layer thickness of the air or oxygen outlet side. A method of manufacturing a MEA for a fuel cell operated under low humidity conditions where no humidification or humidity is greater than 0% and less than or equal to 20%, Method for producing a fuel cell MEA characterized in that the coating of the cathode catalyst layer of the MEA has a thickness gradient. The method of claim 3, wherein Wherein the MEA is coated such that the thickness of the catalyst layer on the air or oxygen inlet side is greater than the thickness of the catalyst layer on the air or oxygen outlet side. In a fuel cell operated under low humidity conditions where no humidification or humidity is greater than 0% and less than 20%, A fuel cell comprising the MEA according to claim 1. A method of operating a fuel cell under no humidification or low humidification conditions in which humidity is greater than 0% and less than 20%, Method of operating a fuel cell, characterized in that for operating the fuel cell according to claim 5. The method of claim 6, Method of operating a fuel cell characterized in that to increase the operating temperature, an electric current density during the operation of the fuel cell 0.8A / cm ² is less than the lower the operating temperature 0.8A / cm ² or more.

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