KR20070025569A - A manifold structure for fuel cell stack - Google Patents

Abstract

Provided is a manifold structure for a fuel cell stack, which is able to distribute gas between the manifold and inlet of each channel uniformly, and thus cause no difference in voltage between cells, and ensures high quality of a fuel cell. The manifold structure for a fuel cell comprises a distribution port(P) for a uniform distribution of gas between the manifold(M) of a fuel cell stack and the inlet of each channel(C1-C5). The distribution port is formed in such a manner that the distance between the manifold and the inlet of each channel is the same or different. The distribution port is symmetrically formed based on the central axis of the manifold. Otherwise, the distribution port is formed only at one side of both sides of the central axis of the manifold.

Description

Manifold structure for fuel cell stack

1 is a structural diagram of a manifold for introducing fuel gas of a conventional fuel cell stack;

2 is a structural diagram of a manifold having a distribution port according to a first embodiment of the present invention;

3 is a structural diagram of a manifold having a distribution port according to a second embodiment of the present invention;

4 is a structural diagram of a manifold having a distribution port according to a third embodiment of the present invention;

5 is a gas flow rate distribution diagram in the manifold according to the present invention;

6 is a shape and gas distribution diagram of a conventional manifold and a channel,

7 is a gas distribution diagram in the manifold of the present invention shown in FIG.

8 is a gas distribution diagram in the manifold of the present invention shown in FIG.

9 is a graph showing a gas distribution between cells of a 60 cell stack according to a distributed port structure;

FIG. 10 is a distribution diagram of gas inflows for each type in a manifold having an extended dispersion port;

11 is a cell voltage comparison graph of a sub-stack (prior art and the present invention).

12 is a graph comparing cell voltages during operation of a 1-2 kW fuel cell stack (invention and prior art)

FIG. 13 is a manifold having a dispersion port including a primary dispersion portion and a secondary dispersion portion as another embodiment of the manifold structure according to the present invention;

14 is a manifold having an asymmetric distribution port as another embodiment of the manifold structure according to the present invention;

Figure 15 is another embodiment of the manifold structure according to the present invention is a manifold having a dispersion port consisting of asymmetric and primary and secondary dispersion,

16 is a manifold structure according to another modified example of the present invention.

* Explanation of symbols for main parts of the drawings

M: Manifold C: Channel

C1, C, C3, C4, C5: Channel Inlet P: Distributed Port

P1: primary dispersion P2: secondary dispersion

W: side wall

The present invention relates to a manifold structure of a fuel cell stack for evenly dispersing fuel and reducing gas in order to reduce the voltage difference between cells of a fuel cell and to ensure the stability of fuel cell performance.

A fuel cell is a device that generates electricity and heat through an electrochemical reaction between hydrogen and oxygen. The fuel cell generates water by reacting with a fuel electrode that reacts with hydrogen as a fuel to decompose into cations and electrons, and with cations and oxygen that have moved through an electrolyte. It has a basic structure of an electrolyte in which cations generated in the oxygen electrode and the fuel electrode move.

The fuel electrode and the oxygen electrode include a catalyst layer for causing an electrochemical reaction, a gas diffusion layer (GDL) for dispersing the reaction gas in the catalyst, and a gas channel through which the gas moves. In addition, a bipolar plate (BP), which serves as a current collector plate through which generated electrons may move, serves as an electrode, and gas channels are formed in the separator. The gas channel formed in the separator has a unique structure in order to maximize gas diffusion and gas contact. Among them, a parallel type, a meandering structure, and the like are used.

In this structure, a plurality of channels exist in one separator plate, and the gas supplied through the manifold is dispersed in each cell and channel. The inlet through which the gas supplied to the manifold can be supplied to each cell increases in proportion to the number of channels, so that the amount of gas introduced into each channel becomes nonuniform.

The non-uniform amount of gas flowing into the gas channel creates a non-uniform distribution of reactants in the unit cell, thereby degrading the current distribution in the cell, causing an overall cell-specific performance difference.

In order to solve this phenomenon, efforts have been made to improve the flow distribution inside the manifold, such as WO 09317465A1, WO 09670721A1, US 4873155, US 6517962 and the like. These efforts have attempted to increase the gas distribution, primarily by changing the size of the location-specific manifolds or by changing the dimensions of the location-specific gas channel inlets. However, this change requires the introduction of a different type of separator for each location, which increases fuel cell production costs and reduces productivity due to cumbersome manufacturing methods.

The conventional fuel cell stack has a direct gas inflow (direct dispersion) method from the manifold M to the gas channel C, as shown in FIG. In this method, the gas inflow rate for each channel is increased due to the gas inlet of the multi-channel, and the distribution of the inflow gas is inevitably lowered as the number of channels increases.

The following Table 1 shows the computational fluid dynamics (CFD) of the distribution of the amount of gas flowing in each channel in the type of separation plate having only the number of channels with the same amount of gas flowing in and the size of the gas channel being constant. It is an example of the value calculated using.

[Table 1] Gas flow rate distribution table by gas channel according to the number of channels

In Table 1, the standard deviation ratio of each channel increases as the number of channels increases. The problem of the multi-channel structure may be, first, a problem in gas inflow distribution for each channel in one cell, and second, a problem in gas inflow distribution for each cell in the entire stack.

The way to overcome this phenomenon is to make one gas inlet channel for each cell. However, the flow path of the separator having a single channel requires a higher gas inflow pressure than the multi-channel separator flow passage, which increases the parasitic power of the fuel cell system and lowers the efficiency of the entire system. In addition, due to the high gas inlet pressure, it is necessary to select a structure and a material capable of sealing the stack at a high pressure, thereby making it difficult to manufacture the stack.

In addition, it is necessary to maintain a constant cell-to-cell voltage for stable operation of the fuel cell stack. The difference in cell-specific voltages degrades stack performance. In particular, voltage drops in certain cells have a critical impact on stack life. The voltage drop of a specific cell is caused by the supply shortage of the reaction gas required for the reaction, and stack operation in a state in which the reaction gas is insufficient causes deformation or destruction of the catalyst and membrane of the MEA. In other words, stable and even supply of reaction gas is important for securing the stability and life of the fuel cell.

According to the present invention, the distribution of inflow gas is not uniform due to the direct inflow of fuel and reducing gas from the manifold to the gas channel in the conventional fuel cell stack. In order to solve the problem that cannot be secured, an object of the present invention is to introduce a new gas dispersing port into the cell structure to achieve even distribution of fuel and reducing gas to each channel, thereby eliminating voltage variations between cells and providing stable fuel. It is to enable battery performance.

In order to achieve the above object, the present invention provides a manifold structure in which a distribution port for uniform distribution of gas is provided between the manifold of the fuel cell stack and the inlet of each channel. The same distance between the channel inlets is formed, or the distance between each channel inlet in the manifold is different, but a constant tilt value from the sidewall of the distribution port to each channel inlet from the channel inlet closest to the manifold to the channel inlet farther away. Is formed on a slanted surface to provide a manifold structure of a fuel cell stack in which fuel or reducing gas supplied from the manifold is uniformly dispersed and introduced into each channel at the distribution port.

2 to 4, the gas inlet distribution port P is applied to improve the gas inflow distribution in the fuel cell stack, as shown in FIGS. After the gas is introduced into the dispersion port having the inlet, the gas is distributed to each channel C so that the gas inflow distribution between the cells can be made more uniform.

In the embodiment shown in FIG. 2, the dispersion ports P have the same distance between the channel inlets C1 to C5 in the manifold M. FIG.

In the embodiments shown in FIGS. 3 and 4, the distance between the channel inlets C1 to C5 in the manifold M is different, but the channel inlet far from the channel inlet C1 close to the manifold M. The distances from the sidewalls (W) of the manifold (M) and the distribution port (P) to each channel inlet (C1, C2, C3, C4, C5) to (C2, C3, C4, C5) are equal. The side wall W is formed in the inclined surface.

The distributed port P of the embodiment shown in FIG. 3 is formed symmetrically from left to right (up and down in the drawing) at the virtual center of the manifold M, and the distributed port P of the embodiment shown in FIG. Is formed to be inclined to only one side from the virtual center of the manifold (M), it shows that the shape of the distribution port can be variously changed depending on the position of the manifold formed on the outside of the cell.

2 to 4 are hypothetical examples for explaining the concept of the present invention, and in the actual cells constituting the fuel cell stack, the number of channels is greater than that shown in FIGS. 2 to 4. It will be apparent to those skilled in the art that the number and width of the channels may also differ from those shown in the drawings.

In addition, the manifold structure of the present invention is not limited to the form shown in FIGS. 2 to 4 described above, and may take the form shown in FIGS. 13 to 16 to be described later.

Table 2 below shows the gas inflow distribution according to the position of the cells in the structure of the 60-cell stack having the dispersion port under the same conditions and the gas flowing into the channel without the dispersion port (direct dispersion method) (front end, center, An example of the difference) is shown.

[Table 2] Gas flow rate distribution table for each cell according to the structure having the dispersion port and the position of the conventional direct dispersion method

As can be seen in Table 2, when the distribution port (P) is introduced between the manifold (M) and the channel (C), it can be seen that the distribution of gas flow rate per cell is improved.

As confirmed above, the present invention can be seen that by introducing a distribution port between the manifold and the channel, compared to the direct distribution from the manifold to the gas channel, it is possible to improve the gas inflow distribution between cells uniformly, It can be predicted that the stability of the overall performance can be secured by reducing the voltage distribution difference per cell generated in the stack using the multi-channel separator.

In addition, the distribution port of the present invention serves to evenly distribute the gas uniformly introduced into each channel to each channel. In general, the direct dispersion method as shown in FIG. 1 has a large ratio between the size of the manifold and the size of the gas inlet, which increases the fluidity of the inlet gas, which is disadvantageous for dispersion between channels. Unlike this, in the present invention, the gas uniformly introduced for each dispersion port may improve the inflow amount of gas for each channel by designing a dispersion port that is advantageous for gas dispersion.

2 to 4 illustrate various types of distribution ports P for improving the distribution of inflow gas amount per channel, and the distribution ports P shown in FIGS. 2 to 4 are the same as described above. As described above, by controlling the flow of fuel or reducing gas in the dispersion port P, the gas inflow amount distribution to each channel C may be adjusted to be uniform.

FIG. 5 shows three types of distribution ports subdividing the shape of the manifold shown in FIG. 4 and the gas inflow distribution for each channel according to each type thereof. The gas inflow distribution table by channel.

The three types of distributed ports shown in FIG. 5 basically follow the form shown in FIG. 4, but the channel inlet positions of the respective channels are different from each other. Arranged so that they are all placed in the same position regardless of the distance from the side wall (Parallel type), and the central distributed port type has the opposite slope of the channel side and the slope of the channel inlet as the channel inlet is moved away from the manifold. The distributed port shape on the right side is formed to be inclined so that the inclined value of the side wall of the distributed port and the channel inlet can be maintained similarly even when the channel inlet is moved away from the manifold. (Inclined type).

In the present invention, the inclination of the side wall surface and the channel inlet may be applied differently according to the area and the flow rate of the cell.

As can be seen in Figure 5 and Table 3 inclined type has the best dispersion effect.

[Table 3] Distribution table of gas inflows by channel according to distributed distributed port structure

By introducing a distribution port P between the manifold (M) and the gas channel (C) as described above, it is possible to improve the distribution of inflow gas amount between cells, and to ensure the stability of the fuel cell stack performance by adjusting the gas flow rate for each channel. . This distribution port is to control the flow between the cells by adjusting the inlet of the gas flowing from the manifold to a single inlet, it is to help uniformly supply gas to each channel from the distribution port.

In the present invention, a dispersion port is introduced to assist gas dispersion between the manifold and the gas channel. After designing it through CFD, the actual stack is manufactured / evaluated to verify its effectiveness. The fuel cell stack applicable to the above study is as follows.

Iii) fuel cell stack using polymer electrolyte membrane (PEMFC)

The polymer electrolyte membrane is a polymer electrolyte fuel cell stack using a fluorine-based Nafion, or other electrolyte membrane, or a hydrocarbon-based electrolyte membrane.

Ii) a fuel cell stack using hydrogen and reformulated gas as fuel.

Fuels of reformed gas include mixed gas containing natural gas, gas generated from regeneration gas or fossil fuel, and gas generated from refining petroleum or hydrogen, and hydrogen content by reforming reaction of such fuel. A fuel cell stack that uses high gas as fuel.

Iii) fuel cell stack using oxygen and air as reducing gas

Iii) fuel cell stacks with operating pressure between normal and 5 atm;

It can be applied to all polyelectrolyte fuel cells used in home power supply that meets the above specifications, or used as portable power source or vehicle power source.

(Example)

In order to confirm the performance of the present invention, the present inventors fabricated an actual fuel cell stack as an example to evaluate / compare the performance.

(Design of the stack)

Two stacks with the same active area were designed and fabricated in a structure with distributed ports and a direct distributed structure. In the distributed port design of the distributed port structure, the CFD was performed using the flow conditions under constant operating conditions to obtain a design having an optimal value. Operation conditions and the structure of the distributed port are as follows.

Operating conditions

 Fuel utilization rate: 50-100%

 -Reduction gas utilization: 30 ~ 80%

 Operating temperature: 10 ~ 80 ℃

 -Composition of fuel: pure hydrogen / reforming gas (containing hydrogen, carbon dioxide, nitrogen, methane, etc., 10 ppm carbon monoxide)

Distributed Port Structure

 Distributed Port Structure: Expandable / Matched

 -Structure of scalable distributed port: inclined type

Slope value: side wall = 58.34 ° skew

Channel inlet = 59.3 ° tilt relative to horizontal plane

Structure of Separator Channel

 -Number of channels: 5 channels

 Channel type: meander structure

 -Channel size: width: 1.6 ~ 2.0mm, depth: 0.6 ~ 1mm

The stack was designed based on the above conditions. The stack is designed with a no-port, scalable distributed port structure, and distributed distributed port structure, respectively, and performs CFD to distribute the gas from the manifold to the distributed port (or channel), and the channel at the distributed port. The gas dispersion in the furnace was checked.

The structure of the manifold and the dispersion port that performed the CFD and the flow in the CFD result manifold are shown in FIGS. 6, 7, and 8.

As can be seen in FIG. 6, the problem with the conventional structure having the direct dispersion method is that the number of inlets through which gas can be introduced to be distributed from the manifold to the channel is large, making it difficult to evenly distribute the gas inflow amount for each channel. However, according to the present invention, as the gas is introduced into a single inlet for each cell as shown in FIGS. 7 and 8 due to the introduction of the dispersion port, the gas inflow distribution for each cell is improved. The gas dispersion according to each structure is as follows.

CFD Results

① Gas distribution from manifold to cell

As shown in FIG. 7 and FIG. 8, the gas distribution between the cells was improved due to the introduction of the dispersion port. In particular, it can be seen that the gas distribution at the gas inlet side is significantly improved, which has the effect of suppressing the voltage drop of the cell occurring during the operation of the actual stack.

This effect can be confirmed in the comparison graph of FIG. 9, but it can be seen that the gas distribution between cells is relatively uniform when the dispersion port (dispersion type, expansion type) according to the present invention is applied as compared with the conventional direct dispersion type.

② Gas distribution from distribution port to channel

Based on the improved cell-to-cell distribution, the design and CFD for gas distribution were performed. CFD results of the distributed distributed port structure are shown in FIGS. 5 and 3, and CFD results of the extended distributed port structure are shown in FIGS. 10 and 4.

As described above, through the inclined structure of the distributed and expandable distributed ports, the distributed ports could improve the gas dispersion per channel.

③ Stack Performance Evaluation

Based on the above CFD results, five stacks of inclined distributed distributed port structure and direct distributed structure were stacked for each sub-stack, and the performance was evaluated under the same conditions. .

11 is a graph illustrating comparison of cell voltages under the same operating conditions. The fuel used a reforming gas and the reducing gas used air. Fuel utilization was 80%, air utilization was 50%, and operating temperature was 65 ℃.

The graph (a) of the upper part in FIG. 11 shows a cell voltage graph of the direct dispersion type stack according to the conventional structure in which gas is directly introduced into the channel from the manifold. As shown in the graph, a stable cell voltage up to 30A of current in the stack shows an average cell voltage of 0.73V. However, as the current of the stack increases, the voltage of the cell can be seen to swing after the current of 35A. As the load increases, the performance of the cell that lacks the amount of fuel flowing in decreases and the cell voltage decreases. In addition, as the voltage drops and the amount of water generated in the stack increases due to the high load, water droplets form in each channel of the separator. The generated water droplets disturb the flow of gas from channel to channel, causing the channel and cell voltages to swing.

Meanwhile, the lower graph (b) of FIG. 11 shows the performance of a 5-cell sub-stack in which a distribution port is introduced. The performance is similar to the direct inflow method (approximately 0.73V on average) at a current of 30A and a stable cell voltage. Since the current increases, the cell voltage remains stable even at a current of 60A. This makes it possible to know that the amount of gas flowing from cell to cell in the manifold remains uninterrupted and constant due to the introduction of a dispersion port.

These results are in agreement even when the stack is evaluated in terms of performance. 12 is a graph showing the performance of the 1 ~ 2 kW class fuel cell stack stacked with 60 ~ 70 cells. Similar to the sub-stack result of FIG. 11, the channel direct dispersion stack (b graph) shows a sudden fluctuation of the cell voltage in the cell of the gas inlet during operation, and shows the result of the voltage of the specific cell falling to (−). This reverse voltage can damage the MEA of the cell, reducing the lifespan of the stack, and seriously risking operation.

As shown in the above embodiment, the introduction of a dispersion port to help gas dispersion from the manifold to the cell and from the cell to the channel has been shown to improve the performance and stability of the fuel cell stack. The structure of the distribution port comprises a gas inlet through a single inlet for each cell in the manifold, and then includes a structure for maintaining a constant amount of gas flowing into the channel from the distribution port through a specific structure. These gas dispersion structures into channels are said to have parallel, declined, inclined and similar gas dispersion structures, which vary in scope depending on the number of channels and the size of the manifolds and distribution ports.

FIG. 13 is a variation of FIG. 3, in which the dispersion port P starts at the manifold M and gradually spreads at an angle, and each channel at the end of the primary diffuser P1. It consists of a secondary diffusion portion (P2) that is diffused at a wider angle toward the inlet (C1 ~ C9).

14 and 15 are modified examples of FIG. 4, in which the dispersion port P is formed to be inclined to one side only from the virtual center of the manifold M, and the channel inlets C1 to C5 are proved to be excellent experimentally. It is in Inclined form.

The side wall W of the dispersion port P shown in FIG. 14 is inclined in a straight line from the manifold M to the terminal channel C5, and the side wall of the dispersion port P shown in FIG. (W) is generally such that its middle portion is further extended at a predetermined angle, and the distal end portion of the side wall is curved.

FIG. 16 is a compromise between the embodiments illustrated in FIGS. 3 and 4, in which the dispersion ports P are asymmetric in left and right (up and down in the drawings).

The manifold structure of the present invention is not limited to the drawings attached to the present invention, but a port for dispersing gas between the manifold and each channel (in the present invention, the term 'port' is used for convenience. It is obvious that any form of manifold having a 'space' or 'path' or 'chamber' term is included in the claims of the present invention described below.

As described above, the present invention forms a distribution port for uniform distribution of gas between the manifold and each channel inlet of the fuel cell stack, and the distribution port uniformly distributes the inlet gas to each cell and channel. Induction can have a useful effect of minimizing voltage variations between cells and ensuring stability of fuel cell performance.

Claims (6)

A manifold structure of a fuel cell stack, comprising a distribution port for uniform distribution of gas between the manifold of the fuel cell stack and each channel inlet. The method according to claim 1, The distribution port is a manifold structure of a fuel cell stack, characterized in that the same distance between each channel inlet in the manifold is formed. The method according to claim 1, The distribution port is formed with a different distance between each channel inlet in the manifold, the slope of the side wall of the distribution port and the channel inlet from the channel inlet close to the channel in the manifold to maintain a constant value Manifold structure of the fuel cell stack. The method according to claim 3, The distribution port is a manifold structure of a fuel cell stack, characterized in that formed in the left and right symmetry in the center line of the manifold. The method according to claim 3, The distribution port is formed only on one side of the left and right of the center line of the manifold manifold structure of the fuel cell stack The method according to claim 1, The dispersion port comprises a primary diffusion portion starting from the manifold and gradually spreading at an angle, and a secondary diffusion portion diffused at a wider angle from the end of the primary diffusion portion to each channel inlet side. Fold structure.

Images