Bipolar plate three-dimensional topological flow field structure of proton exchange membrane electrolytic tank

Abstract

The invention discloses a three-dimensional topological flow field structure of a bipolar plate of a proton exchange membrane electrolytic tank, which is specifically characterized in that the surface of a rectangular bipolar plate is provided with a sinking groove, the periphery of the sinking groove is provided with groove walls, and the opposite groove walls are respectively provided with a rectangular air inlet hole and an air outlet hole. And m * n array ridge unit bodies are arranged at the bottom of the sinking groove. The ridge unit body is of a cuboid door-shaped outline structure, and the bottom of the ridge unit body is connected with a cuboid with the same thickness as the upper wall of the ridge. Square areas on the two sides of the ridge unit are flow channels except for the position, close to the groove wall, of the ridge unit. Under the condition that the contact area of the spatially topological ridge and the porous transmission layer and the contact area of the spatially topological ridge and the polar plate respectively account for 50%, the arrangement of the ridge units enables the current transmission uniformity to be improved, so that the uniformity of electrochemical reaction can be effectively improved. According to the structural design, the space proportion of the ridge in the counter tank of the polar plate is reduced, so that a fluid flowing area is enlarged, the fluid flowing resistance is obviously reduced, gas generated in the electrolysis process is promoted to be exhausted, and the mass transfer loss is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogen production by electrolysis cell, and in particular to a three-dimensional topological flow field structure design of a bipolar plate of a proton exchange membrane electrolysis cell. Background Art

[0002] As a secondary energy source for green production, hydrogen energy has the advantages of high efficiency, greenness and cleanliness. By using renewable energy to electrolyze water to produce hydrogen, on the one hand, it can provide green hydrogen for industries such as transportation and chemical industry, and achieve deep decarbonization. On the other hand, producing hydrogen during off-peak electricity (where electricity prices are the lowest) can also significantly reduce the production cost of hydrogen energy.

[0003] The proton exchange membrane electrolyzer (PEMEC) is an indispensable equipment in the process of hydrogen electrolysis, which is mainly composed of bipolar plates (including flow channels and ridges), porous transport layers, membrane electrodes and other fixed components. The flow field is embedded in the bipolar plate, and the design and optimization of the flow field is one of the most critical issues in PEMEC research. By designing and optimizing the flow field structure, the performance and service life of PEMEC can be effectively improved. However, since the currently disclosed flow field structure technology mainly focuses on the groove and ridge structure, such as parallel flow field and single serpentine flow field, the flow field design of this type of structure is simple, that is, the plane design is stretched. Therefore, its groove and ridge ratio does not have spatial variability, which easily causes the end of the flow channel to be filled with the generated gas products, resulting in the flow of the reactant liquid water in the flow channel being obstructed, thereby reducing the proportion of reactant content on the surface of the terminal initial catalytic layer. Summary of the invention

[0004] In view of the defects in the current flow field design of proton exchange membrane electrolyzers, the purpose of the present invention is to provide a flow field structure design, which can significantly expand the fluid domain in the flow channel and strengthen the gas-water two-phase flow without excessively losing the conductivity of the ridge plate, while promoting the discharge of gas in the bipolar plate and the uniformity of the electrochemical reaction.

[0005] The technical solution of the three-dimensional topological flow field structure of the bipolar plate of the proton exchange membrane electrolyzer is as follows: a trough is provided on the surface of the rectangular bipolar plate, a trough wall is provided around the trough, a rectangular air inlet and a rectangular air outlet are provided on the opposite side trough walls respectively, and m rows × n rows of ridge units with gas-water diversion function are distributed at the bottom of the trough.

[0006] Furthermore, the ridge unit body is a rectangular gate-shaped outline structure, and the bottom of the ridge unit body is connected to a rectangular block with the same thickness as the ridge upper wall. Except for the position where the ridge unit is close to the groove wall, the square areas on both sides of the ridge unit are flow channels.

[0007] The bipolar plate trough is divided into a flow field area and a ridge area. The flow field area is separated by ridge units. Therefore, the ridge unit plays a role in structural segmentation. Its structural form, size, arrangement and size parameters all determine the geometric configuration of the flow field area.

[0008] The flow field structure can be considered to be composed of a sufficient number of ridge units, the outer contours of which are all millimeter-level, arranged and connected along the horizontal array to form a single row of flow fields. The second row of the array is formed by folding the previous row along the z (vertical) direction, and is connected end to end with the ridge units of the previous row, and so on, and finally spliced ​​to form a flow field structure of the designed length.

[0009] Compared with the current electrolytic cell flow channel structure, the characteristics and beneficial effects of the present invention are as follows:

[0010] (1) When the contact area between the spatial topological ridge and the porous transport layer and the electrode plate accounts for 50%, the staggered arrangement of the contacts between the conductors improves the uniformity of current transmission, thereby effectively improving the uniformity of the electrochemical reaction; the extremely high contact area ratio means that the use of the ridge plate will not cause excessive ohmic losses.

[0011] (2) The spatial topological ridge structure design of the present invention reduces the space occupied by the ridge in the electrode plate trough, thereby expanding the area for fluid flow, thereby greatly reducing fluid flow resistance, promoting the removal of gas generated during the electrolysis process, and reducing mass transfer losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a three-dimensional principle structure diagram of the bipolar plate of the present invention.

[0013] Figure 2a This is a schematic diagram of the current three-dimensional structure of a single-row groove-ridge flow field.

[0014] Figure 2b It is a schematic diagram of the three-dimensional structure of the three-dimensional topological single-row flow field of the present invention.

[0015] In both figures, the solid arrows indicate the flow direction of liquid water; the dotted arrows indicate the flow direction of generated oxygen, and component 3 indicates a porous transmission layer.

[0016] Figure 3 The three-dimensional topological flow field ridge unit structure and principle diagram of the bipolar plate of the electrolytic cell of the present invention.

[0017] Figure 4a The current density is 3A / cm 2 Distribution cloud diagram of current density on the membrane surface in parallel flow field under working conditions.

[0018] Figure 4b The current density is 3A / cm 2Cloud diagram of current density distribution on the membrane surface of the three-dimensional topological flow field under working conditions.

[0019] Figure 5 Comparison of polarization curves of single cell in simulated parallel flow field and three-dimensional topological flow field;

[0020] Figure 6a The current density is 3A / cm 2 Cloud diagram of oxygen volume fraction in the porous transport layer of parallel flow field under working conditions.

[0021] Figure 6b The current density is 3A / cm 2 Cloud diagram of oxygen volume fraction in the porous transport layer of the three-dimensional topological flow field under working conditions. DETAILED DESCRIPTION

[0022] The structural principle of the present invention is further explained and illustrated below in conjunction with the accompanying drawings and specific embodiments. The embodiments are only used to explain the present invention, but are not intended to limit the present invention.

[0023] The three-dimensional topological flow field structure of the bipolar plate of the proton exchange membrane electrolyzer has the following specific structure: a trough 1-1 is provided on the surface of the rectangular bipolar plate, a trough wall 1-2 is provided around the trough, and a rectangular air inlet 1-3 and a rectangular air outlet 1-4 are provided on the opposite side trough walls. The bottom of the trough is distributed with m rows×n rows of ridge units 1-5 with gas-water diversion function.

[0024] The ridge unit body is a rectangular gate-shaped outline structure, and the bottom of the ridge unit body is connected to a rectangular block with the same thickness as the ridge upper wall. Except for the position where the ridge unit is close to the groove wall, the square areas on both sides of the ridge unit are flow channels.

[0025] By changing the geometric parameters inside the ridge unit body, bipolar plates with different porosities and equivalent conductivity can be obtained. The geometric parameters include: the ridge side wall thickness b, the ridge wall thickness d, the flow channel width w and the flow channel height h of the unit body; the unit body length L and the number of ridge unit bodies arranged m×n. The ridge unit body has the function of guiding air and water, and the m columns and n rows of ridge unit bodies are evenly distributed at the bottom of the bipolar plate sink. In the embodiment, the positional relationship between the m columns and n rows is only for simplifying the description, and does not stipulate the specific position that the ridge unit body must have.

[0026] The rectangular air inlet and the rectangular air outlet are located at diagonal positions of the groove wall, and the two air holes have the same shape and size. The rectangular air inlet and the rectangular air outlet are rectangular; or square.

[0027] like Figure 3 As shown, a bipolar plate flow field structure provided in this embodiment can be regarded as being composed of a sufficient number of ridge units, and the outer contours of the ridge unit structure are all in the millimeter level, along the horizontal direction ( Figure 3The second row is connected along the x direction of the previous row. Figure 3 As shown, it is folded in the z direction and connected end to end with the previous row, and each subsequent row of ridges repeats the above operation to form a flow field structure of sufficient length.

[0028] When the ridge side wall thickness b and the ridge top wall thickness d are increased, the plate conductivity can be slightly improved, but the overall porosity and permeability will be reduced, thereby increasing the fluid flow resistance and reducing the water penetration uniformity to a certain extent. Therefore, it is necessary to test the geometric parameters before use to ensure the performance improvement. The flow field structure provided in this embodiment can be completed on a five-axis machining center, and the plate material is titanium metal.

[0029] refer to Figure 2a and Figure 2b , a flow channel composed of a row of ridge units was selected for comparison with a flow channel composed of a single row (traditional groove and ridge flow field) of the same size. Since the present invention uses space for topological ridge plate design, the ridges not only play a supporting role, but also reasonably divide the space, significantly expanding the fluid domain. Compared with the traditional groove and ridge flow channel design, this structure expands the fluid domain by at least 60%, which significantly increases the volume flow and reduces the air-water flow resistance.

[0030] Compared with the traditional groove-ridge flow field, because the boundaries between the traditional grooves and ridges are clear, the concentration of reactants under the ridges is low, and the generated gas accumulates inside the porous transport layer (component 3 in Figure 2) and is difficult to eliminate. The scientific ridge (channel) arrangement of the three-dimensional topological flow field structure of the bipolar plate can solve this problem well. Although the ridges based on spatial topology reduce the volume share of the conductor, due to the high electrical conductivity of titanium metal and the uniform electrochemical reaction, the increase of ohmic loss can be well avoided and the activation loss can be effectively reduced. In addition, the contact surface between the flow channel in the flow plate and the porous transport layer is regarded as the outlet of the transport layer. This dislocated (transport layer outlet) setting allows the generated gas to flow into the flow channel more evenly, and thanks to the smaller flow resistance in the flow channel, the large volume flow of liquid water can take away and discharge the bubbles in time, avoiding the phenomenon of excessive bubble accumulation in the flow channel, thereby improving the exhaust capacity of the bipolar plate and effectively reducing mass transfer losses.

[0031] Example:

[0032] As a preferred embodiment of the present invention, the side wall thickness b of the ridge unit is 0.5 mm, the wall thickness d on the ridge is 0.5 mm, the flow channel width w is 1.5 mm, the flow channel height h is 1.5 mm, and the flow channel length L is 5 mm. The total width of the reaction area of ​​a single electrolytic cell is 50 mm, and the length is 50 mm. The number of ridge unit columns m is 13 according to the total width of the reaction area, and the number of ridge unit rows n is 10 according to the total length of the reaction area.

[0033] The length of the bipolar plate inner groove is 50mm, the width is 50mm and the depth is 2mm.

[0034] The rectangular air inlet and outlet holes are located at diagonal positions, and both have a width of 2 mm.

[0035] In order to verify the influence of the three-dimensional topological structure design on the uniformity of electrochemical reaction and three overpotentials during electrolysis, a three-dimensional numerical model was used for simulation analysis. The embodiment uses two proton exchange membrane electrolyzer bipolar plates, one of which adopts the structure of the present invention; the other adopts a traditional flat flow field that has not been optimized. Except for the different flow field structures, the other technical parameters and materials of the two bipolar plates are exactly the same.

[0036] Both batteries (plates) were simulated and tested under the same working conditions. The electrolytic cell was operated in constant current mode and the measuring current range was 0A / cm 2 Up to 3A / cm 2 , the operating temperature is 70℃, saturated liquid water is introduced into the anode, the gas volume fraction content is 0%, and the back pressure is 1atm. There is no inlet at the cathode, and the back pressure is 1atm.

[0037] The current density distribution on the membrane surface of the three-dimensional topological flow field is as follows Figure 4b As shown, the current density distribution on the surface of the conventional parallel flow field membrane is as follows Figure 4a According to the current density distribution, it can be found that the uniformity of the topological flow field is much higher than that of the traditional flow field. The maximum current density of the traditional flow field in the reaction zone is as high as 3.2A / cm 2 , while the three-dimensional topological flow field is slightly higher than 3.1A / cm 2 , a smaller current density difference along the flow direction means a better uniformity of the electrochemical reaction.

[0038] Use a three-dimensional numerical model to simulate and analyze this structure (such as Figure 5 The comparison of the polarization curve of the electrolytic cell using the three-dimensional topological flow field (shown in Figure 1) and the one using the traditional parallel flow field shows that the overall performance of the electrolytic cell using the three-dimensional topological flow field of the present invention is significantly better than that of the traditional parallel flow field; as the current density increases, the difference in activation overpotential will become more significant due to the uneven distribution of current density. Compared with the parallel flow field, when the working condition is 3A / cm 2 The total overpotential is reduced by 13%. Not only is this performance improvement limited, but when under higher current density conditions, the optimization of mass transfer loss brought about by the present invention will also be more prominent.

[0039] like Figure 6a and Figure 6bAs shown, in the three-dimensional numerical model simulation analysis, by comparing the flow field outlet, it can be found that the gas volume in the transmission layer of the flow field outlet section of the present invention is about 37%, while the gas volume in the parallel flow field is about 42%. The use of the three-dimensional topological flow field of the present invention can effectively reduce the retention of generated oxygen inside the transmission layer, and significantly improve the exhaust capacity of the bipolar plate. Secondly, thanks to the regular staggered distribution of the outlet of the transmission layer, the material exchange between each flow channel is carried out inside the transmission layer, which significantly improves the uniformity of the distribution of the reactants and thus improves the electrochemical reaction rate. The inlet and outlet pressure difference of the traditional flow field is 1257Pa, while the inlet and outlet pressure difference of the three-dimensional topological flow field is 820Pa, so the use of the present invention effectively reduces the inlet and outlet pressure difference, and can effectively reduce the pumping work required for water supply. Therefore, the use of the present invention can effectively save the cost of hydrogen production, so that more electrical energy can be used to participate in the electrochemical reaction, thereby improving the electrolysis efficiency.

Claims

1. A three-dimensional topological flow field structure of a bipolar plate of a proton exchange membrane electrolyzer, characterized in that: A trough (1-1) is provided on the surface of a rectangular bipolar plate, a trough wall (1-2) is provided around the trough, a rectangular air inlet (1-3) and a rectangular air outlet (1-4) are respectively provided on the opposite side trough walls, and m rows×n rows of ridge units (1-5) having an air-water diversion function are distributed at the bottom of the trough.

2. The three-dimensional topological flow field structure of the bipolar plate of the proton exchange membrane electrolyzer according to claim 1, characterized in that: The ridge unit body is a rectangular gate-shaped outline structure, and the bottom of the ridge unit body is connected to a rectangular block with the same thickness as the ridge upper wall. Except for the position where the ridge unit is close to the groove wall, the square areas on both sides of the ridge unit are flow channels.

3. The three-dimensional topological flow field structure of the bipolar plate of the proton exchange membrane electrolyzer according to claim 1, characterized in that: By changing the geometric parameters inside the ridge unit body, bipolar plates with different porosities and equivalent conductivities can be obtained. The geometric parameters include: the ridge side wall thickness, ridge wall thickness, flow channel width and flow channel height of the unit body; the unit body length and the number of ridge unit body arrangements m×n.

4. The three-dimensional topological flow field structure of the bipolar plate of the proton exchange membrane electrolyzer according to claim 1, characterized in that: The ridge unit body has an air-water guiding function, and the m columns and n rows of ridge unit bodies are evenly distributed at the bottom of the bipolar plate sink.

5. The three-dimensional topological flow field structure of the bipolar plate of the proton exchange membrane electrolyzer according to claim 1, characterized in that: The rectangular air inlet and the rectangular air outlet are located at diagonal positions of the groove wall, and the two air holes have the same shape and size.

6. The three-dimensional topological flow field structure of the bipolar plate of the proton exchange membrane electrolyzer according to claim 1, characterized in that: The rectangular air inlet and the rectangular air outlet are rectangular; or square.

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