Method for operating electrochemical stack, electrochemical cell and electrochemical stack

Abstract

The invention relates to a method for operating an electrochemical stack (1), in particular an electrolysis stack, comprising a plurality of electrochemical cells (2), in particular electrolysis cells, comprising the following steps: supplying a fluid to the cells (2) via inlet channels (3) extending through the stack (1) in a stacking direction and arranged on opposite sides (S1, S2) of the stack (1), and-discharging the fluid via an outlet channel (4) extending through the stack (1) in the stacking direction and arranged opposite the inlet channel (3) such that the fluid flows through each cell (2) in two substantially opposite directions (D1, D2). The invention also relates to an electrochemical cell (2) and an electrochemical stack (1).

Description

Technical Field

[0001] This invention relates to a method for operating an electrochemical stack (e.g., an electrolytic stack or a fuel cell stack). Furthermore, this invention also relates to electrochemical cells and electrochemical stacks, such as electrolytic stacks or fuel cell stacks. Background Technology

[0002] Electrochemical cell stacks, such as fuel cell stacks or electrolyzer stacks, are well known in the art. Each cell in such a stack has a layered structure and typically includes: - An electrically insulating and chemically separated but ionicly conductive (composite polymer) membrane, with corresponding electrode / catalyst layers disposed on each side to form an anode and a cathode. The anode and cathode catalyst layers comprise catalyst particles mixed with a binder and a support material (typically an ionomer). This layered assembly of membrane and electrode is commonly referred to as a membrane electrode assembly (MEA) or catalyst-coated membrane (CCM), where the catalyst-coated membrane refers to a conventional MEA manufacturing process that coats the membrane using an electrode-catalyst mixture dissolved in a volatile solvent.

[0003] A porous transport layer or gas diffusion layer (PTL / GDL) located on either side of the MEA / CCM is used to transport current to or from the electrode, while allowing electrolytes and / or electrochemical reactants and products to or from the corresponding electrode of the CCM. In some publications on electrochemical stacks, the MEA is defined as including the PTL / GDL. In fact, the catalyst can be applied to the PTL / GDL instead of the membrane; in this case, the PTL / GDL thus coated is often referred to as a porous transport electrode (PTE). The PTL / GDL can be provided as metal foam, (sintered) metal powder, metal fiber / whisker felt or mesh, (woven or nonwoven) carbon fiber, etc. Effective porosity, average pore size, tortuosity, and conductivity are all relevant characteristics of the PTL / GDL.

[0004] - Metal bipolar plates (BPPs) shared between adjacent cells and chemically separating adjacent cells for correspondingly coupling current from or into these cells. The BPPs may be corrugated, thus defining a fluid flow field for delivering electrolytes, reactants, products, and / or cooling media throughout the active region of the cell.

[0005] Within the electrochemical stack, multiple channels are provided along the stack height (i.e., along the cell stacking direction). These channels include inlet and outlet channels for supplying and discharging reactants and / or products. The channels are formed by overlapping pores in the BBP and layers present between the BBPs. Cross channels formed by the corrugations of the BBP connect these channels to the PTL / GDL on the anode or cathode side of each cell.

[0006] During operation of the water electrolysis reactor, water, as a reactant, is supplied to the corresponding anode side of each cell via an inlet channel, transported through the corresponding PTL / GDL of each cell, and allowed to exit the cell via an outlet channel. Typically, the H2O inlet and outlet channels are located on opposite sides of the reactor to ensure that the reactants are uniformly distributed throughout the so-called "active region" where the electrochemical reaction occurs. The active region more or less corresponds to the surface area of ​​the corresponding PTL / GDL. As the water flows through the active region, oxygen, as an electrolysis product, accumulates within it. The oxygen content of the gas-liquid mixture increases with increasing proximity to the outlet channel.

[0007] The water flow on the anode side serves not only to supply water as an electrolysis reactant and remove oxygen as an electrolysis product, but also to remove waste heat from the active areas of the cell. Therefore, water also functions as a coolant. During steady-state operation of the stack, the water temperature increases along the flow direction as it flows through the cell. With increasing temperature, the reaction rate of water electrolysis increases, causing the reaction rate to vary between cells. Furthermore, the increased water temperature exacerbates cell degradation due to membrane / ionomer degradation, catalyst dissolution, and the formation of oxide layers at the interfaces of different layered components, all of which are temperature-dependent. Therefore, the cells degrade unevenly. Summary of the Invention

[0008] The purpose of this invention is to homogenize the reaction rate and cell degradation among the cells in an electrochemical stack (especially an electrolytic stack).

[0009] This objective is achieved by the method according to the invention, the electrochemical cell according to the invention, and the electrochemical stack according to the invention.

[0010] The proposed operation includes multiple electrochemical cells, particularly electrolytic cells, and especially electrolytic cells, in a method comprising the following steps: - Fluid is supplied to the battery via an inlet channel that extends through the stack along the stacking direction and is positioned on opposite sides of the stack. - The fluid is discharged via an outlet channel that extends through the stack in the stacking direction and is positioned opposite the inlet channel, such that the fluid flows through each cell in two substantially opposite directions.

[0011] The fluid flowing through the battery is used to remove waste heat. Therefore, the fluid temperature rises as it passes through the battery. Since the fluid flowing through each battery travels in two substantially opposite directions, the fluid temperature on either side of each battery, and consequently the thermal stress, is substantially equal. Therefore, battery degradation caused by thermal stress is substantially uniform across the individual cells.

[0012] Preferably, the fluid supplied to the battery is water. In this case, the fluid acts as a reactant during the electrochemical reaction within the battery, thereby producing hydrogen and oxygen. The oxygen is discharged from the battery along with the fluid, i.e., the water. Therefore, the term "fluid" can refer to liquids, gases, and / or gas-liquid mixtures.

[0013] If the fluid is a reactant, such as water, then the fluid temperature affects the reaction rate during the electrochemical reaction within the cell. By operating the stack according to the proposed method, the fluid temperature, and therefore the reaction rate, remains substantially uniform across the individual cells.

[0014] In a preferred embodiment of the invention, the fluid flowing through the battery is guided by guiding elements and / or battery separators (e.g., by walls). Guiding the fluid flow prevents cross-current between inlet and outlet channels located on the same side of the stack. Thus, by guiding the fluid, a fluid flow path is defined, extending from an inlet channel on one side of the stack to an outlet channel on the corresponding opposite side. Consequently, the fluid is uniformly distributed among the batteries, particularly in the active regions of each battery.

[0015] Preferably, fluid supplied via a single inlet channel is discharged via two or more outlet channels disposed opposite to the corresponding inlet channel. Thus, the fluid flow is diverted and distributed between the two or more outlet channels. This provides an enlarged flow cross-sectional area for discharging the fluid. This is particularly advantageous if the supplied fluid is water and the discharged fluid is oxygenated water. More preferably, the single inlet channel is centered relative to the two or more outlet channels to ensure a uniform distribution of the fluid flow between the two or more outlet channels.

[0016] To achieve the objectives of this invention, an electrochemical cell, particularly an electrolytic cell, for use in an electrochemical reactor, is proposed. The cell has a plurality of inlet ports disposed on opposite sides of the cell and a plurality of outlet ports disposed opposite to the inlet ports, such that each side of the cell has at least one inlet port and at least one outlet port.

[0017] The inlet port is used to supply fluid, such as water, to the battery. The fluid flows from the inlet port to an outlet port located on the opposite side of the battery. The fluid then exits through the outlet port. By positioning the inlet ports on opposite sides of the battery, the fluid flows through the battery in two substantially opposite directions. The effect is that the fluid temperature throughout the battery, and therefore the battery degradation caused by thermal stress, is more uniform. Furthermore, assuming the fluid is a reactant, the reaction rate throughout the battery is homogenized.

[0018] In a preferred embodiment of the invention, inlet ports and outlet ports are arranged alternately on at least one or either side of the battery. In the latter case, each outlet port is assigned to one inlet port, such that the number of outlet ports corresponds to the number of inlet ports. Alternatively, the number of outlet ports may differ from the number of inlet ports.

[0019] In another preferred embodiment of the invention, the number of outlet ports is at least twice the number of inlet ports. Therefore, two or more outlet ports are arranged opposite and assigned to a single inlet port. The effect is that the flow cross-sectional area for the discharged fluid is increased. This is particularly advantageous for electrolytic cells, which are supplied with water as a reactant via an inlet channel. The water serves not only as a reactant but also to remove oxygen generated during the electrochemical process in the cell. Therefore, more fluid is discharged than supplied.

[0020] Therefore, preferably, the total flow cross-sectional area of ​​the inlet port is smaller than the total flow cross-sectional area of ​​the outlet port, especially if the electrochemical cell is an electrolytic cell. This can be achieved by increasing the number of outlet ports relative to the number of inlet ports. Alternatively or additionally, the flow cross-sectional area of ​​each inlet port may be smaller than the flow cross-sectional area of ​​each outlet port.

[0021] More preferably, guiding elements and / or battery separators (e.g., walls) are provided to separate flow paths with opposite flow directions. Guiding the fluid flow prevents cross-current between inlet and outlet ports located on the same side of the battery. Therefore, the fluid is forced to flow from the inlet port to a single or multiple outlet ports located on the corresponding opposite side of the battery. This results in uniform fluid distribution throughout the battery.

[0022] Advantageously, multiple electrochemical cells according to the invention are stacked. In this arrangement, the multiple cells form an electrochemical stack.

[0023] Therefore, an electrochemical stack, particularly an electrolytic stack, according to the invention is further proposed, comprising a plurality of electrochemical cells, particularly electrolytic cells. The proposed electrochemical stack is suitable for performing the method according to the invention. Thus, when operating according to the method of the invention, the same advantages can be achieved using the electrochemical stack. In particular, uniform fluid temperature during operation and therefore uniform cell degradation over the lifetime can be achieved. Assuming the electrochemical stack is an electrolytic stack, temperature-sensitive reaction rates throughout the cell can be homogenized.

[0024] Preferably, the inlet ports of the stacked batteries overlap and define an inlet channel extending through the stack in the stacking direction. Furthermore, the outlet ports of the batteries overlap and define an outlet channel extending through the stack in the stacking direction. Attached Figure Description

[0025] Preferred embodiments of the present invention will be described in conjunction with the accompanying drawings. The drawings show: Figure 1 This is a top view of an electrochemical cell according to a first preferred embodiment of the present invention. Figure 2 This is a top view of an electrochemical cell according to a second preferred embodiment of the present invention. Figure 3 This is a top view of an electrochemical cell according to a third preferred embodiment of the present invention. Figure 4 This is a top view of an electrochemical cell according to a fourth preferred embodiment of the present invention. Figure 5 This is a top view of an electrochemical cell according to a fifth preferred embodiment of the present invention. Figure 6 This is a top view of an electrochemical cell according to a sixth preferred embodiment of the present invention. Figure 7 It is a cross-sectional view through an electrochemical stack according to a first preferred embodiment of the invention; and Figure 8 This is a cross-sectional view through an electrochemical stack according to a second preferred embodiment of the present invention. Detailed Implementation

[0026] Figure 1 A first preferred embodiment of the electrochemical cell 1 is shown. The cell 2 is provided with an inlet port 7 and an outlet port 8 for fluids (e.g., reactants, products, and / or combinations thereof). In a stack 1 comprising multiple identical cells 2, overlapping inlet ports 7 form an inlet channel 3, and overlapping outlet ports 8 form an outlet channel 4 (e.g., ...). Figure 7 and Figure 8 (As shown). In Figure 1In this configuration, inlet port 7 and outlet port 8 are located on two opposite sides S1 and S2 of battery 2, such that inlet ports 7 and outlet ports 8 on each side S1 and S2 are alternately arranged. The number of inlet ports 7 is equal to the number of outlet ports 8. Each inlet port 7 is assigned an outlet port 8 opposite to it. Therefore, the fluid supplied to battery 2 flows through battery 2 in two opposite directions D1 and D2.

[0027] Assumption Figure 1 The electrochemical cell 2 in the battery is an electrolytic cell, and the fluid supplied to cell 2 is water. During the electrolysis process within cell 2, water serves as a reactant. Hydrogen and oxygen are produced during this process. The treated oxygen is removed along with the water via outlet port 8. Another function of water is to remove the waste heat also generated during the electrolysis process. Therefore, the temperature of the water increases with distance from inlet port 7, through which water is supplied. A uniform fluid temperature throughout cell 2 is advantageous because cell degradation and reaction rates are affected by fluid temperature. According to the invention, this is achieved by supplying fluid to cell 2 from two opposite sides S1, S2.

[0028] Figure 2 Another preferred embodiment of the electrochemical cell 2, particularly the electrolytic cell, according to the present invention is shown. In this embodiment, two outlet ports 8 are assigned to a single inlet port 7, such that the number of outlet ports 8 is twice the number of inlet ports 7. Therefore, the total flow cross-sectional area of ​​the outlet ports 8 is larger than the total flow cross-sectional area of ​​the inlet ports 7. This arrangement facilitates the removal of oxygen via the outlet ports 8. The fluid flow from the inlet port 7 to the outlet port 8 is diverted and distributed between the two outlet ports 8. Since the number of inlet ports 7 or outlet ports 8 is the same on either side S1, S2 of the cell 2, the fluid is uniformly distributed on the cell 2.

[0029] To further enhance uniform fluid distribution, the inlet port 7 can be precisely positioned at the midpoint between the two outlet ports 8 on the corresponding opposite sides of the battery 2, such as... Figure 3 As shown.

[0030] Figures 4 to 6 The preferred embodiments are similar to Figures 1 to 3 The embodiment shown differs only in that the flow path is defined by the guide element 5 and / or the battery separator 6. The guide element 5 or the battery separator 6 can be implemented by a wall separating flow paths having opposite flow directions D1, D2. This wall prevents cross-current between the inlet port 7 and the outlet port 8 on the same side of the battery 2.

[0031] Figure 7 and Figure 8Both diagrams show an electrochemical stack 1 comprising multiple electrochemical cells 2. The stack 1 is provided with an inlet channel 3 for supplying fluid and an outlet channel 4 for discharging fluid. The inlet channel 3 and outlet channel 4 extend along the height of the stack 1 and are open at one end of their respective ends. Figure 7 In the middle, inlet passage 3 and outlet passage 4 are open at opposite ends of pile 1. Figure 8 In this configuration, the inlet channel 3 and the outlet channel 4 are open at the same end of the stack 1. The stack 1 according to the invention can have two designs.

Claims

1. A method for operating an electrochemical stack (1), particularly an electrolytic stack, said electrochemical stack comprising a plurality of electrochemical cells (2), particularly electrolytic cells, said method comprising the following steps: - Fluid is supplied to the battery (2) via an inlet channel (3) that extends through the stack (1) in the stacking direction and is disposed on opposite sides (S1, S2) of the stack (1), and - The fluid is discharged via an outlet channel (4) that extends through the stack (1) in the stacking direction and is positioned opposite the inlet channel (3) such that the fluid flows through each cell (2) in two substantially opposite directions (D1, D2).

2. The method according to claim 1, Its features are, The fluid flowing through the battery (2) is guided by the guiding element (5) and / or the battery separator (6), for example by the wall.

3. The method according to claim 1 or 2, Its features are, Fluid supplied via a single inlet channel (3) is discharged via two or more outlet channels (4) arranged opposite to the corresponding inlet channel (3).

4. An electrochemical cell (2), particularly an electrolytic cell, for use in an electrochemical stack (1), particularly an electrolytic stack, the electrochemical cell having a plurality of inlet ports (7) disposed on opposite sides (S1, S2) of the cell (2) and a plurality of outlet ports (8) disposed opposite to the inlet ports (7), such that each side (S1, S2) of the cell (2) is provided with at least one inlet port (7) and at least one outlet port (8).

5. The battery (2) according to claim 4. Its features are, The number of exit ports (8) is at least twice the number of inlet ports (7).

6. The battery (2) according to claim 4 or 5. Its features are, The total flow cross-sectional area of ​​the inlet port (7) is smaller than the total flow cross-sectional area of ​​the outlet port (8).

7. The battery (2) according to any one of claims 4 to 6. Its features are, Provide guiding elements (5) and / or battery separators (6), such as walls, to separate flow paths with opposite flow directions (D1, D2).

8. An electrochemical stack (1), particularly an electrolytic stack, said electrochemical stack comprising a plurality of electrochemical cells (2), particularly electrolytic cells, according to any one of claims 4 to 7.

9. The heap (1) according to claim 8. Its features are, The inlet port (7) of the battery (2) overlaps and defines an inlet channel (3) extending through the stack (1) in the stacking direction, and the outlet port (8) of the battery (2) overlaps and defines an outlet channel (4) extending through the stack (2) in the stacking direction.

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