KR101201937B1 - Design method of Internal Die Structure and Slit Coating Die Apparatus for Uniform Coating of MEA in PEMFC - Google Patents

Abstract

The present invention relates to an internal design method of a slot coating die for continuous homogeneous coating of an electrode coating catalyst slurry used in an electrode-membrane assembly (MEA) for polymer electrolyte membrane fuel cells (PEMFC). And its device.
Therefore, in the present invention, as an internal design method of a slot coating die for continuous uniform coating of an electrode coating catalyst slurry used in an electrode-membrane assembly for a polymer electrolyte membrane fuel cell, flow characteristics within the die of the fluid from the rheological information of the catalyst slurry fluid Selecting a fluid model to analyze the fluid, determining the shape of the chamber inside the catalyst slurry slot coating die of the electrode-membrane assembly in consideration of the rheological properties of the catalyst slurry fluid, and minimizing the shear thinning and uniformity. Deriving the process conditions under which the coating is formed in one thickness is provided.
In addition, by the design method for continuous uniform coating of the electrode coating catalyst slurry, one of the chamber and the curved semi-cylindrical chamber for receiving the catalyst slurry from the feed pipe and the feed pipe into which the catalyst slurry flows in and outflowing the catalyst slurry into the slit Provided is a slot coating die apparatus of an electrode-membrane assembly for a polymer electrolyte membrane fuel cell, comprising a slit composed of upper and lower flat plates on a side surface and a die lip which is a catalyst slurry outlet.

Description

Design method of internal die structure and slit coating die apparatus for uniform coating of MEA in PEMFC for uniform coating of electrode-membrane assembly for polymer electrolyte membrane fuel cell

Method for designing the inside of a slot coating die which can maximize productivity by coating and manufacturing an electrode-membrane assembly (MEA), which is the core of a polymer electrolyte membrane fuel cell (PEMFC) performance, through a slot die coating in a uniform thickness. And to the apparatus.

A battery is an electrochemical cell and is a power generation system that directly converts chemical energy generated by electrochemical reaction between fuel (hydrogen or methanol) and oxidant (oxygen or air) to electrical energy. The fuel cell is characterized in that it can simultaneously use electricity generated by electrochemical reaction of hydrogen and oxygen and heat as a byproduct thereof without a combustion process.

The fuel cell is a phosphate fuel cell operating at a temperature of about 150 to 200 ° C., a molten carbonate fuel cell operating at a high temperature of 600 to 700 ° C., and a solid oxide type operating at a high temperature of 1000 ° C. or more, depending on the type of electrolyte used. It is classified into a fuel cell and a polymer electrolyte type and an alkaline type fuel cell operating at room temperature to 100 ° C. or lower. Each of these fuel cells operates on essentially the same principle, but differs in the type of fuel used, operating temperature, catalyst, and electrolyte. Among these, polymer electrolyte membrane fuel cells (PEMFCs), which are being developed recently, have excellent output characteristics, low operating temperatures, fast start-up and response characteristics compared to other fuel cells, methanol, ethanol, natural Hydrogen produced by reforming gas is used as fuel and has a wide range of applications such as mobile power sources such as automobiles, as well as distributed power sources such as homes and public buildings, and small power sources such as electronic devices.

A unit cell structure of a polymer electrolyte membrane fuel cell (PEMFC) composed of a fuel electrode (anode), a cathode (Cathode), a gas diffusion layer (GDL), and an electrode-membrane assembly (MEA) is shown in FIG. The polymer electrolyte membrane fuel cell (PEMFC) is a fuel cell that operates at a low temperature, and thus receives a lot of attention in the industry, such as a fuel cell for automobiles. The principle of the polymer electrolyte membrane fuel cell (PEMFC) is to produce electricity through a reaction in which hydrogen ions produced by oxidizing hydrogen in an anode are transferred to a cathode where oxygen is reduced through the polymer membrane. will be. The polymer membrane through which hydrogen ions pass is an electrode-membrane assembly (MEA) and how the positive and negative electrode slurry materials are coated on the electrode-membrane assembly (MEA) determines the performance and productivity of the polymer electrolyte membrane fuel cell (PEMFC).

An example of a method of manufacturing a membrane-electrode assembly (MEA) is a method of coating a catalyst material on a gas diffusion layer to form a catalyst layer (electrode layer), and bonding the electrolyte membrane and a high temperature press process at an appropriate pressure and temperature. The gas diffusion layer has pores and pores, and a material suitable for smooth access of the fuel and the reactor gas to the catalyst layer is suitable. The gas diffusion layer transmits electric current generated by an electrochemical reaction through a bipolar plate or a monopolar plate. It is connected to the circuit. In general, carbon paper and carbon fiber fabric are used as substrates for the gas diffusion layer, and they inject carbon produced by carbonizing polymer materials such as pitch and PAN at a high temperature of 2000 ° C. or higher to form a fiber. Compressed again to produce thin sheets of paper or the fibers are rewoven into fabrics through complex weaving processes.

In addition, the catalyst layer uses a form in which homogeneous or heterogeneous platinum group catalysts are evenly distributed on the surface of the conductive carbon, each of which may cause a decomposition reaction of a fuel and a reduction reaction of oxygen, respectively, and improves the reaction efficiency by increasing the specific surface area of the catalyst. In order to achieve this, studies are being actively conducted on a method of supporting a catalyst on a very finely divided carbon surface such as active carbon powder, carbon nanotube, or carbon nanohorn.

The most common method of coating the membrane-electrode assembly is a method of applying a small amount of a highly dispersed catalyst slurry having a very low viscosity on a gas diffusion layer or a polymer electrolyte membrane over a long time by a spray method. This method has the advantage that the highly dispersed catalyst is evenly applied on the gas diffusion layer or the polymer electrolyte membrane, but it is impossible to produce a large amount of electrodes because the application time is very long.

In addition, electrode manufacturing by roll coating method further deforms the catalyst slurry to make gum-like, forms a thin sheet type catalyst layer using a roll, and then dries it using a press machine. By adhering the catalyst layer and the gas diffusion layer prepared in advance, the electrode production is completed.

In the case of the roll coating method, it is difficult to produce a wide and uniform catalyst layer because the gum-like catalyst layer has to be formed in a plate shape in advance, and also has a large area to bond the catalyst layer and the gas diffusion layer with a large area. There is a problem of requiring a compactor. In particular, when compressing the catalyst layer and the gas diffusion layer, a uniform stress must be applied over the entire surface of the catalyst layer. Otherwise, if the uniform stress is not applied, partial separation of the catalyst layer occurs. However, in reality, there are many economic and technical difficulties in manufacturing a compactor that can apply a wide and uniform stress. In addition, the roll coating method and the D / B (doctor blade) coating method allow a significant amount of catalyst to penetrate into the porous gas diffusion layer, thereby lowering the efficiency of the catalyst and increasing the amount of applied catalyst, as well as forming a thick catalyst layer. And there is a problem that can bring about deformation of the substrate.

On the other hand, as another method for coating the membrane-electrode assembly of a high efficiency polymer fuel cell, in order to localize the catalyst at the interface between the catalyst, the electrolyte membrane, and the electrode, platinum is sputtered on the gas diffusion layer to a thickness of 500 kPa on the electrode surface. Although a method of sputtering is known, it is impossible to produce an electrode coated with a uniform thickness by the above method.

In addition, although the spray or bar coating method is widely used for research as a method of manufacturing a membrane-electrode assembly (MEA), these methods cannot be actually mass-produced by batch or intermittent coating method, rather than continuous production. It is very unlikely to be a coating process for industrialization.

In recent years, the slot die coating method, which is utilized in display processes, as an electrode coating method, has been actively studied. A schematic of a typical slot coating process is shown in FIG. The die internal structure is shown in (a) and the die external structure (called the coating bead area) is shown in (b). First, the fluid enters the chamber through a feed, fills the chamber, and then exits through a slit. The coating liquid exiting the slit is coated onto a moving web or substrate. Inside the die, it is very important to ensure that the velocity of the coating liquid exiting the die exit through the slit is even in the width direction. Outside the die, the coating thickness may become unstable depending on the operating conditions such as the speed of the substrate or the coating spacing. In particular, Figure 3 is a result of considering the fluidity of the catalyst slurry for membrane-electrode assembly using a conventional slot coating equipment (a) is a phenomenon that the solution leaking as the speed is increased at a low speed, (b) is uniform And stable flow, (c) unstable ribbing, and (d) unstable rivulet. That is, it is very important for the fuel electric industrialization to establish a principle and methodology for the die design suitable for a given slurry rheological properties.

The present invention was devised in view of the problems of the prior art as described above, and its object is to continuously coat the electrolyte membrane or the gas diffusion layer with a uniform thickness to increase the productivity and maintain the uniformity of the continuous membrane-electrode assembly. It is to provide a slot die coating method that is utilized in the display process as an electrode coating method of the. In particular, the present invention proposes a slot coating method capable of continuous coating and based on the rheological properties of the catalyst slurry used to design the optimum internal coating design method of the slot coating die through computer simulation Presenting and providing the coating die apparatus.

Most of the catalyst slurries used in the membrane-electrode assembly are non-Newtonian fluids whose viscosity changes with shear rate. It is almost impossible to coat with a uniform thickness. Since most catalyst slurries have non-Newtonian rheological properties, when using a die that does not reflect the physical properties of the coating solution, that is, not designed optimally, the center point in the die width direction has a flow velocity. Fast and slow flow rates are common at both ends. In other words, a difference in coating thickness occurs in the width direction. In order to overcome this problem, it is possible to obtain a uniform velocity distribution of the coating liquid in the width direction by designing a die-in-chamber structure in the form of a coat-hanger by examining the flow rate relationship due to physical properties. There is a limit to conducting this optimal design on an experimental basis, so it is performed by computer simulation. In order to secure such a uniform coating, it is necessary to secure the rheological information of the coating liquid and to identify the correlation of the structural change of the optimal die according to the physical property change.

The present invention provides a die internal design method required for producing a slot die coating for continuously coating a catalyst slurry with a uniform thickness for the production of electrodes of a membrane-electrode assembly used in a polymer electrolyte membrane fuel cell. Utilizing the die internal design method proposed in the present invention and the die apparatus thereof, the catalyst slurry ensures that the coating liquid flows out at the die outlet with a uniform thickness and speed. That is, the membrane-electrode assembly slot coating die device of the present invention enables industrial mass production of the membrane-electrode assembly, thereby maximizing the productivity of the fuel cell field as well as the polymer electrolyte membrane fuel cell.

1 is a schematic diagram of a single cell of a polymer electrolyte membrane fuel cell (PEMFC).
2 is a schematic diagram of a slot coated die internal structure.
Figure 3 is a photograph of each phenomenon during the slot coating experiment (a) is unstable leaking phenomenon, (b) is a stable phenomenon, (c) is an unstable ribbing phenomenon, (d) is an unstable rivulet phenomenon
Figure 4 compares the results obtained by measuring the viscosity of the shear strain rate of the catalyst slurry used in the electrode-membrane by using a rheometry and the results of deriving the material variables according to the Power-law fluid model One graph.
5 is an initial basic structure of a typical slot coated die for optimal die optimal design. (a) die internal side view, (b) top view of die internal design
FIG. 6 is a graph comparing flow rates of catalyst slurry in a die exit width direction in the basic die of FIG. 5 and an optimally designed die for uniform coating. FIG.
FIG. 7 is a graph showing the convexity (coat-hanger shape width) for uniform coating of catalyst slurry in a chamber having a semi-cylindrical shape in which a central portion is convexly curved laterally.
FIG. 8 is a graph showing a width of a chamber (coat-hanger shape) having an optimal hanger-shaped semi-cylindrical shape for various catalyst slurry fluids having different power series indexes.
9 is a plan view of the inside of an optimal slot coating die representing the width of a coat-hanger shape in the die interior design plan.

The present invention selects a fluid model for analyzing the characteristics of fluid flow in the die from the rheological properties of the catalyst slurry fluid, and considers the shape of the chamber of the membrane slurry slot coating die in the membrane-electrode assembly considering the rheological properties of the catalyst slurry fluid. Optimal inside slot coating dies for uniform coating of membrane-electrode assemblies for polymer electrolyte membrane fuel cells, including determining and deriving optimal process conditions with minimum shear thinning and coating with uniform thickness. The design method and the coating die device by this design is composed.

Selection of catalyst slurry fluid model,

In order to analyze the flow in the die of the catalyst slurry from the rheological properties of the catalyst slurry, the viscosity is measured according to the shear strain rate of the catalyst slurry using a viscosity meter to select a fluid model for optimal design of the slot coating die. Figure 4 shows the viscosity results for one type of catalyst slurry for membrane-electrode assembly measured using the TA 2000 AR2000 viscometer. In general, most catalyst slurries exhibit shear thinning behavior in which viscosity decreases with shear strain rate as shown in FIG. 4. A power-law model was chosen here as a fluid model based on viscosity behavior for numerical simulation of the flow inside the die.

power law model:

: 점도,

: 전단변형률속도Where K is a constant, n is a power exponent,

: Viscosity,

: Shear strain rate

The catalyst slurry of FIG. 4 has a value of K = 2.58, n = 0.58 in the shear strain rate range inside the slot coater.

Determining step in the form of a chamber inside a slot coating die,

Slot coating for homogeneous coating of membrane-electrode assembly for polymer electrolyte membrane fuel cell The determination of the shape of the chamber inside the die for optimal design inside the die is determined to be made in the form that the velocity of the coating liquid is uniform in the width direction at the exit of the die. . Since the catalyst slurry for the membrane-electrode assembly used in the present invention is a non-Newtonian fluid, it is difficult to guarantee a uniform coating by using a conventional die internal design without rheological considerations. The internal design of the slot coated die device used Gambit of Ansys and the general basic die structure is as shown in FIG. Basic dimensions The dimensions of each part of the die are as follows.

Name Dimensions (mm) Chamber diameter 13 Slit length 150 Slit width 180 Slit gap 0.5 Supply pipe diameter 5 Supply pipe length 30

Using the same program for the flow analysis in the die structure as above, the computational area was composed of about 300,000 cubes in detail and three-dimensional numerical simulation was performed with Fluent Ansys. The boundary conditions for the flow calculation were fixed at 0.08 m / s for the slurry to enter the feed line, considering the conditions for practical industrial applications, and the temperature was kept constant at room temperature (300 K). The catalyst slurry obtained from the initial dimensional information as in FIG. 5 shows the velocity distribution of parabolic opening at the die outlet. This means that the coating thickness is large in the center portion and the coating thickness decreases toward both ends. Therefore, in order to increase the fluid velocity at both ends of the die, both chambers are designed to be more forward than the central part, so that the central part of the left and right sides of the semi-cylindrical chamber is convexly curved in the opposite direction to the slit outflow from both ends in the semi-cylindrical chamber. It is effective to reduce the residence time of fluid by becoming coat-hanger shape and hanger shape chamber).

Sizing of the chamber to form a catalyst layer of uniform thickness,

By changing the width of the coat-hanger shape of the chamber to 1.02mm from the initial set basic dimension, the thickness variation of the catalyst slurry is minimized, and the optimum slot coating die device can be realized. Therefore, by adjusting the width of the coat-hanger (hanger shape) from 0.3 mm to 2.1 mm according to the catalyst slurry having various kneading index, it is possible to implement the slot coating die device that is optimal for each catalyst slurry. In FIG. 8, the optimum coat-hanger shape widths of various catalyst slurry fluids having different power series indexes are calculated.

The slot coating die device for uniform coating of the membrane-electrode assembly for a polymer electrolyte membrane fuel cell has a feed pipe into which the catalyst slurry is introduced is coupled to the lower side of the chamber, and the catalyst slurry is introduced into the chamber through the feed pipe in a vacuum inlet manner. The introduced catalyst slurry flows out from the top of the semi-cylindrical chamber into a slit consisting of upper and lower balance plates, and flows out to the die lip outlet to be coated on the web and the substrate surface.

Furthermore, in order to correlate the optimum die design according to the change of the dedicated charge behavior of the catalyst slurry, the coat-hanger width was investigated to minimize the thickness variation by varying the power series index under the same constant (K) condition. . As shown in FIG. 7, the coat-hanger width became shorter as the water-water index increased. This is because the closer the power series index is to 1, the more the Newtonian fluid characteristic is, and therefore, it is not affected by the shear strain rate in the flow. The correlation between the optimal coat-hanger shape width and the power series index is

: coat-hanger(옷걸이 모양)의 너비, n : 멱급수 지수here,

= width of coat-hanger, n: power index

9 is a schematic diagram of a slot coating die apparatus for uniform coating of a membrane-electrode assembly for a polymer electrolyte membrane fuel cell, the width of the coat-hanger and the chamber diameter optimal for a catalyst slurry having an arbitrary water-supply index. The die device can be implemented by determining the ratio.

The correlation between the properties of the non-Newtonian fluid and the die structure according to the shear thinning behavior enables stable and uniform continuous coating of the membrane-electrode assembly used in the polymer electrolyte membrane fuel cell.

Claims (10)

A feed pipe into which the catalyst slurry is introduced, a chamber for receiving the catalyst slurry from the feed pipe and flowing the catalyst slurry into the slit, a slit consisting of upper and lower flat plates on one side of the upper chamber, and a die lip as the catalyst slurry outlet As an internal design method of a catalyst slurry slot coating die of an electrode-membrane assembly for a polymer electrolyte membrane fuel cell comprising a
(a) characterizing the catalyst slurry fluid to select a fluid model;
(b) determining the chamber shape inside the catalyst slurry slot coating die; and
(c) determining process conditions for forming a catalyst layer of uniform thickness;
Step (a) is a polymer electrolyte membrane fuel cell electrode, characterized in that for selecting the catalyst slurry having an arbitrary kneading index by analyzing the fluid properties of the catalyst slurry in relation (1) below the viscosity and shear strain rate of the fluid A method for designing a catalyst slurry slot coating die inside a membrane assembly.
<Relationship (1)>
power law model: η = K | γ | ^n-1
K: constant, n: power series index, η: viscosity, γ: shear strain rate delete The method according to claim 1, wherein step (b) comprises the steps of (b1) calculating the outflow rate of the catalyst slurry in the width direction at the coating die lip outlet; and (b2) the flow rate deviation of the center portion and both ends of the die lip outlet is the minimum The method of designing the inside of the slot coating die of the electrode-membrane assembly for a polymer electrolyte membrane fuel cell comprising the step of determining the chamber shape inside the slot coating die.
The method of claim 3, wherein the step (b1) is a slot coating of the electrode-membrane assembly for a polymer electrolyte membrane fuel cell, characterized in that for calculating the flow rate distribution in the width direction at the exit of the die lip at a constant inlet speed and temperature of the catalyst slurry How to design inside the die. The method of claim 3, wherein in the step (b2), the shape of the chamber for minimizing the outflow rate deviation calculated in the step (b1) is opposite to the slit outflow of the semi-cylindrical chambers from the left and right sides of the semi-cylinder. A slot coating die internal design method of an electrode-membrane assembly for a polymer electrolyte membrane fuel cell, characterized in that it is determined to have a hanger shape convexly curved in a direction.
The method of claim 1, wherein the step (c) is a slot in the chamber having a hanger-shaped semi-cylindrical shape in which the central portion for any catalyst slurry is convexly laterally convex in the following relation (2) to form a catalyst layer having a uniform thickness. The internal design method of the slot coating die of the electrode-membrane assembly for a polymer electrolyte membrane fuel cell, characterized in that the width is determined to the side of the convexly curved center portion.
<Relationship (2)>

Is the width from the slit to the side of the convexly curved center, n is the power index A feed pipe into which the catalyst slurry is introduced, a semi-cylindrical chamber receiving the catalyst slurry from the feed pipe and flowing the catalyst slurry into the slit, a slit consisting of upper and lower flat plates on one side of the chamber, and a catalyst It comprises a die lip which is a slurry outlet,
The chamber has a semi-cylindrical shape in which a central portion of the left and right sides is convexly curved in a direction opposite to the slit outflow from both ends,
The ratio of the width and the chamber diameter of the convex center portion of the chamber having a semi-cylindrical shape in which the center portion is convexly curved is 0.3 to 2.1 with respect to the catalyst slurry selected to have an arbitrary water index according to <Equation (1)>. : 13 is a slot coating die apparatus of the electrode-membrane assembly for polymer electrolyte membrane fuel cells.
<Relationship (1)>
power law model: η = K | γ | ^n-1
K: constant, n: power series index, η: viscosity, γ: shear strain rate delete delete The method according to claim 7, wherein the ratio of the width and the chamber diameter of the convex central portion of the chamber having a semi-cylindrical shape of a hanger shape in which the central portion is convexly curved is about 1.03: 13 for the catalyst slurry having a value of 0.58. The slot coating die apparatus of the electrode-membrane assembly for polymer electrolyte membrane fuel cells.

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