Fuel cell stack

Abstract

The invention relates to a fuel cell stack (1). The fuel cell stack (1) comprises a first end plate (2) with a coolant inlet (11) and a coolant outlet (12), a second end plate (3) through which a coolant channel (15) extends, and a plurality of fuel cells (4) arranged between the end plates (2, 3). Furthermore, the fuel cell stack (1) comprises at least one positioning pin (5) extending through positioning openings (6) in the fuel cells (4) between the first end plate (2) and the second end plate (3), and having a coolant-permeable hollow profile (26) that fluidically connects the first end plate (2) and the second end plate (3).

Description

[0001] The invention relates to a fuel cell stack.

[0002] From WO 2016 11 03 44 A1 a device for supplying fuel cells of a fuel cell stack with a medium is known.

[0003] The fuel cell stack according to the invention comprises a first end plate with a coolant inlet and a coolant outlet, a second end plate through which a coolant channel extends, and a plurality of fuel cells arranged between the end plates. Furthermore, the fuel cell stack according to the invention comprises at least one positioning pin extending through positioning openings in the fuel cells between the first end plate and the second end plate, and having a hollow profile through which coolant can flow, fluidly connecting the first end plate and the second end plate.

[0004] Because the first end plate incorporates both the coolant inlet and outlet, the fuel cell stack can be easily integrated into higher-level systems and connected to auxiliary components such as cooling devices. Starting at the coolant inlet, the coolant flows through the fuel cell stack in a U-shape, absorbing heat from the fuel cells. Some of this heat can then be transferred to the second end plate via its coolant channel, resulting in a homogeneous temperature distribution across the entire fuel cell stack. The coolant can then be returned to the first end plate via the at least one positioning pin with its flow-through hollow profile, without requiring any additional openings beyond those already present in the fuel cells. This results in a very compact design for the fuel cell stack according to the invention.

[0005] In a preferred embodiment, the positioning pin is fluidically connected to the coolant outlet of the first end plate via a channel running through the first end plate. The returning coolant can transfer heat to the first end plate through this channel. This equalizes the temperatures of the first and second end plates and achieves an even more uniform temperature distribution across the entire fuel cell stack.

[0006] One aspect stipulates that the first end plate includes a first receiving opening in which the first end face of the positioning pin is received, and that the second end plate includes a second receiving opening in which the second end face of the positioning pin is received. During assembly of the fuel cell stack, the positioning pin can be inserted into the respective receiving openings, thus enabling precise positioning of the end plates and the intervening fuel cells relative to each other in a technically simple manner.

[0007] Another aspect is that the fuel cell stack includes sealing rings that are inserted into the respective receiving openings for the positioning pin. For example, a first sealing ring is provided, which is inserted into the first receiving opening and seals the first end face of the positioning pin against the first end plate, and a second sealing ring, which is inserted into the second receiving opening and seals the second end face of the positioning pin against the second end plate. The sealing rings ensure that no coolant can escape at the transitions between the positioning pin and the respective end plates.

[0008] To improve heat transfer between the coolant and the second endplate, the coolant channel through the second endplate can be designed to run in a spiral or meandering pattern. The channel through the first endplate can also be spiral or meandering. This reduces temperature differences or gradients within the fuel cell stack and helps to equalize the temperatures of the fuel cells and endplates. This, in turn, has a positive effect on the overall operating efficiency and the lifespan of the fuel cells.

[0009] In one variant, the fuel cells of the fuel cell stack are each formed by stacked half-shells. For example, anode and cathode half-shells are provided, which, when assembled, form bipolar plates through which coolant flows. The half-shells or bipolar plates each have a coolant distribution opening and a coolant collection opening. The coolant distribution openings together form a coolant distribution channel running through the fuel cell stack. The coolant collection openings together form a coolant collection channel running through the fuel cell stack. This design is technically simple to implement and ensures efficient and uniform heat dissipation across all fuel cells.

[0010] The coolant distribution channel is fluidically connected to the coolant inlet of the first end plate, and the coolant collection channel is fluidically connected to an inlet of the coolant channel of the second end plate. This makes it possible to distribute fresh coolant from the coolant inlet to the individual fuel cells via the coolant distribution channel, thus cooling them evenly. The coolant is then collected in the coolant collection channel and fed to the inlet of the coolant channel of the second end plate, where it transfers some of the previously absorbed heat to the second end plate, thus equalizing its temperature with that of the fuel cells.

[0011] Another aspect stipulates that, in addition to the coolant distribution opening and coolant collection opening, each half-shell has a fuel distribution opening, a fuel collection opening, an oxidizer distribution opening, an oxidizer collection opening, and two spaced-apart positioning openings. Further openings in the half-shells or external hose arrangements for returning the coolant from the second end plate to the first end plate can generally be omitted, thus saving installation space and reducing assembly effort as well as the overall risk of leakage.

[0012] The hollow profile of the positioning pin is preferably fluidically connected to an outlet of the coolant channel of the second end plate, so that the coolant from the second end plate can be guided back to the first end plate via the positioning pin. This results in a particularly homogeneous temperature distribution across the entire fuel cell stack, including both end plates.

[0013] In one embodiment, the fuel cell stack includes at least one second positioning pin that extends through positioning openings in the fuel cells between the first and second end plates and features a hollow profile through which coolant flows, fluidly connecting the first and second end plates. The two positioning pins can be of identical design and, for example, positioned at diagonally opposite corners of the fuel cell stack. Using two positioning pins improves the positional accuracy of the individual half-shells and the end plates relative to each other, while simultaneously achieving a more homogeneous temperature distribution across the entire fuel cell stack.

[0014] Preferred embodiments are explained in more detail with reference to the following figures. These show - Fig. 1 a schematic representation of an embodiment of a fuel cell stack according to the invention; and - Fig. 2 a schematic representation of one half of the fuel cell stack made of Fig. 1.

[0015] The in Fig. The fuel cell stack shown comprises a first end plate 2, a second end plate 3 and a plurality of fuel cells 4 arranged between the end plates 2, 3.

[0016] The end plates 2, 3 are made of steel or aluminum, for example, and therefore have high stability and thermal conductivity.

[0017] Furthermore, the fuel cell stack 1 comprises two positioning pins 5 spaced apart from each other, which extend through positioning openings 6 in the fuel cells 4 between the first end plate 2 and the second end plate 3 and fix the fuel cells 4 and end plates 2, 3 in their position and orientation relative to each other.

[0018] At the in Fig. In the variant shown in Figure 1, the first end plate has two receiving openings 7, and the second end plate has three receiving openings 8. The positioning pins 5 each have a first end face 9 that is inserted into one of the first receiving openings 7 of the first end plate 2.

[0019] Furthermore, the positioning pins 5 each have a second end face 10 which is inserted into one of the second receiving openings 8 of the second end plate 3.

[0020] The first end plate 2 is designed as a media connection plate and includes a coolant inlet 11, a coolant outlet 12 and a channel 13 through which coolant can flow. The coolant inlet 11 and the coolant outlet 12 are connected to a cooling system 14, which is designed to circulate coolant through the fuel cell stack 1 in order to dissipate process heat released during the operation of the fuel cells 4.

[0021] The second end plate 3 has a coolant channel 15 which is fluidically connected to the coolant inlet 11 and the coolant outlet 12, so that the second end plate 3 can also be permeated by coolant.

[0022] Both the channel 13 of the first end plate 2 and the coolant channel 15 of the second end plate 3 have a meandering shape. This ensures good heat transfer between the respective end plates 2, 3 and the coolant. Fig. Figure 1 shows the fluid flow through the end plates 2 and 3 only schematically. For simplification, the channel 13 through the first end plate 2 and the coolant channel 15 through the second end plate 3 are shown as straight lines, i.e., without meandering.

[0023] The fuel cells 4 between the two end plates 2, 3 are each formed from stacked half-shells 16.

[0024] In Fig. 2 is one of the hemispheres 16 shown schematically.

[0025] The half-shells 16 each have a coolant distribution opening 17, a coolant collection opening 18, a fuel distribution opening 19, a fuel collection opening 20, an oxidizer distribution opening 21, an oxidizer collection opening 22 and two positioning openings 6 spaced apart from each other for the positioning pins 5.

[0026] As in Fig. As shown in Figure 1, the coolant distribution openings 17 of the half-shells 16, when stacked, together form a coolant distribution channel 23 running through the fuel cell stack 1. In the Fig. In the variant shown in Figure 1, the coolant distribution channel 23 is fluidically connected to the coolant inlet 11 of the first end plate 2.

[0027] In their stacked state, the coolant collection openings 18 together form a coolant collection channel 24 running through the fuel cell stack 1, which is fluidically connected to an inlet 25 of the coolant channel 15 of the second end plate 3.

[0028] During operation, coolant introduced via the coolant inlet 11 of the first end plate 2 is distributed to the individual fuel cells 4 via the coolant distribution channel 23 to ensure uniform cooling. It is then collected in the coolant collection channel 24 and flows from there into the coolant channel 15 of the second end plate 3, where it can transfer some of the previously absorbed heat to the second end plate.

[0029] To guide the coolant from the second end plate 3 back to the first end plate 2, the positioning pins 5 are designed as tubes. More precisely, each positioning pin 5 has a hollow profile 26 through which coolant can flow, fluidically connecting the first end plate 2 and the second end plate 3.

[0030] At the in Fig. In the variant shown in Figure 1, the coolant channel 15 of the second end plate 3 and the channel 13 running through the first end plate 2 are fluidically coupled to each other via the hollow profiles 26 of the positioning pins 5. During operation, the coolant can flow through outlets 27 of the coolant channel 15 of the second end plate 3, through the hollow profiles 26 of the positioning pins 5, into the channel 13 of the first end plate 2 and from there to the coolant outlet 12.

[0031] To ensure that no coolant can escape at the transition between the positioning pins 5 and the end plates 2, 3, the fuel cell stack 1 includes first sealing rings 28, which are inserted into the first receiving openings 7 of the first end plate 2 and seal the first end faces 9 of the positioning pins 5 against the first end plate 2. Furthermore, the fuel cell stack 1 includes second sealing rings 29, which are inserted into the second receiving openings 8 of the second end plate 3 and seal the second end faces 10 of the positioning pins 5 against the second end plate 3.

[0032] At the in Fig. In the fuel cell stack 1 shown, coolant is circulated through both the first end plate 2 and the second end plate 3 during operation. This ensures a more homogeneous temperature distribution across the entire fuel cell stack 1.

[0033] This is particularly advantageous during startup processes.

[0034] In many known fuel cell cooling concepts, heat conduction between the fuel cells 4 near the edges and the end plates 2, 3 can lead to very high temperature differences of up to 50 °C between the fuel cells 4 in the center of the stack and those located at the edges, depending on the ambient temperature, power output, and stack size. Due to the lower temperatures in the fuel cells 4 near the edges, the electrochemical processes there proceed more slowly, resulting in lower power output and a correspondingly negative impact on overall efficiency.

[0035] In contrast, the fluid flow through the end plates 2, 3 of the in Fig.In the fuel cell stack shown in Figure 1, temperature differences between the fuel cells 4 in the center of the stack and those at the edge near the end plates 2, 3 are prevented or at least reduced. During start-up, the coolant can transport heat from the center of the stack to the end plates 2, 3, causing the end plates 2, 3 to heat up faster and drawing less heat from the fuel cells 4 near the edge. This temperature equalization results in more uniform operation of the fuel cells 4, which improves start-up reliability and also has a positive effect on the service life of the fuel cells 4.

[0036] At the same time, the coolant return via the positioning pins 5 creates a U-shaped flow through the fuel cell stack 1, which makes it very easy to integrate the fuel cell stack 1 into higher-level systems without having to provide additional openings in the half-shells 16 or external hoses. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2016 11 03 44 A1

[0002]

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