Electrolytic bath and electrolytic cell active area height design method

Abstract

The invention discloses an electrolytic cell and an electrolytic cell active area height design method. The electrolytic cell comprises a first end plate; the first end plate and the second end plate are horizontally arranged; the electrolytic cell core is arranged between the first end plate and the second end plate, and the electrolytic cell core comprises a cathode side polar plate, a membrane electrode and an anode side polar plate which are arranged in the horizontal direction. The invention discloses a method for designing the height of an active region of an electrolysis cell. The method comprises the following steps: according to an oxygen production volume equation # imgabs0 # of the electrolysis cell and a relational expression V (t) < pi * a * R2 + d * N according to the minimum volume of the cell filled with bubbles and the oxygen production of a cross section, wherein the relational expression is as follows: V (t) < pi * a * R2 + d * N; according to the method, bubbles can be effectively discharged, the mass transfer resistance is reduced, the energy consumption is greatly reduced, and the relation between the height of the active region and different current densities and the height of the header pipe is given, so that the height of the active region of the small chamber is quantitatively designed.

Description

Technical Field

[0001] The invention relates to the technical field of electrolytic devices, in particular to a method for designing the height of active areas of electrolytic cells and electrolytic chambers. Background Art

[0002] Hydrogen production using proton exchange membrane electrolysis (PEMWE) technology has the lowest carbon emissions among the many hydrogen source options currently available, and is therefore widely recognized in green hydrogen production technologies.

[0003] The current rated current density of current-producing PEM electrolyzers is generally low, ranging from 1 to 1.5 A / cm2. The low rated current density will lead to an increase in the number and area of ​​small chambers in the large-sized electrolyzer hydrogen production equipment, making the entire electrolyzer too bulky and increasing the material cost.

[0004] The low rated point operation of PEM electrolyzers is also an important reason for the current high cost. The high current density operation of future PEM electrolyzer designs is a trend.

[0005] However, when the electrolyzer is operated at a high current density, a series of problems will arise, the most prominent of which is the problem of bubble discharge. The increase in current density causes a sharp increase in the gas production per unit time in the small chamber.

[0006] The electrolytic cell in the prior art is generally placed vertically, which causes the two pole sides of the membrane electrode to be arranged up and down. The bubbles generated by electrolysis are easy to accumulate near the membrane electrode. At this time, the bubbles cannot be discharged in time, resulting in increased mass transfer resistance, which is not conducive to the normal electrolysis and is prone to component failure.

[0007] Although there is a method in the prior art to set the electrolytic cell in a horizontal position so that the two polar sides of the membrane electrode are arranged left and right, so that the bubbles generated by electrolysis can float up due to the effect of gravity to avoid the bubbles accumulating near the membrane electrode, thereby ensuring the normal operation of the electrolytic cell. However, the height of the active area of ​​the general electrolytic chamber and the height of the total pipe are generally fixed values. For high current density, the problem of bubble accumulation still occurs. The height of the active area of ​​the electrolytic chamber is closely related to the bubble discharge of the electrolytic cell. At present, there is no method for quantitatively designing the active area of ​​the electrolytic chamber. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a method for designing the height of the active area of ​​an electrolytic cell and an electrolytic chamber to solve one or more technical problems existing in the prior art and at least provide a beneficial choice or create conditions.

[0009] The solution of the present invention to solve its technical problem is:

[0010] Electrolyzer, comprising:

[0011] An electrolytic cell core, the electrolytic cell core comprising a plurality of vertically arranged electrode plates and a plurality of membrane electrodes, the plurality of electrode plates and the plurality of membrane electrodes being arranged in a staggered and overlapping manner in a transverse direction, two adjacent electrode plates forming an electrolytic chamber, the electrolytic chamber being provided with an active area, the membrane electrode being arranged in the active area, the top of the electrolytic cell core being provided with a plurality of main pipes extending up and down, the main pipes being connected with the top of the electrolytic chamber;

[0012] The clamping and fixing device comprises a connecting assembly and two end plates, wherein the two end plates are respectively located at two lateral ends of the electrolytic cell core, and the connecting assembly connects the two end plates and fixes the two end plates relatively.

[0013] Through the above technical solution, the bubbles generated by electrolysis can automatically float up due to the action of gravity, and the main pipe can provide a space for the bubbles to accumulate, which can avoid excessive bubble production under high current density and cause the bubbles to accumulate near the membrane electrode, thereby ensuring that the electrolyzer can operate normally under high current density.

[0014] As a further improvement of the above scheme, the connecting assembly includes a plurality of screws and a plurality of nuts, the plurality of screws are evenly arranged, the ends of the screws pass through the two end plates, the ends of the screws are threadedly connected to the nuts, the nuts are located on the outside of the end plates, and the nuts are used to resist the end plates to limit the end plates.

[0015] As a further improvement of the above solution, the connection assembly further includes an elastic member, and the elastic member is arranged between the nut and the end plate.

[0016] As a further improvement of the above solution, the elastic component is a disc spring.

[0017] As a further improvement of the above solution, the membrane electrode comprises a proton exchange membrane, a catalyst layer and a gas diffusion layer, and the catalyst layer and the gas diffusion layer are sequentially stacked on one side of the proton exchange membrane.

[0018] The method for designing the height of the active area of ​​the electrolytic chamber is applicable to the electrolytic cell described above, and the method for designing the height of the active area of ​​the electrolytic chamber comprises the following steps:

[0019] Based on the oxygen production volume formula of the electrolysis chamber:

[0020]

[0021] Where V(t) is the volume of oxygen produced per unit time section; W is the current density; H is the height of the active area of ​​the electrolysis chamber; V m is the molar volume; F is the Faraday constant;

[0022] And the relationship between the minimum volume of bubbles required to fill the chamber and the oxygen production in the cross section is:

[0023] V(t)<π×a×R 2 +d×N;

[0024] Where R is half of the distance between the membrane electrode and the electrode plate, that is, half of the flow field depth; a is the porosity of the active area; d is the thickness of the cell; N is the total tube section height;

[0025] Get the formula

[0026] Thus, it can be concluded that

[0027] The beneficial effects of the present invention are as follows: the present invention starts from improving the bubble discharge problem caused by high current density conditions, and provides an electrolytic cell placement method that improves mass transfer, which can effectively realize the effective discharge of bubbles under high current density and low water flow conditions, reduce mass transfer resistance, and greatly reduce energy consumption.

[0028] In addition, the present invention also provides the relationship between the chamber size parameters and different current densities to quantitatively design the chamber size to prevent the bubble aggregation in the chamber under high current density, so as to prevent the occurrence of "cavities" that lead to water shortage and failure of the active area. This patent provides an electrolyzer structure that improves mass transfer, which is suitable for the design of highly integrated and lightweight hydrogen production devices with high current density, small size and high hydrogen production in the future.

[0029] The invention is used in the technical field of electrolysis devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly describes the drawings required for use in the description of the embodiments. Obviously, the drawings described are only part of the embodiments of the present invention, not all of the embodiments, and those skilled in the art can also obtain other design solutions and drawings based on these drawings without creative work.

[0031] Figure 1 This is a diagram of the placement of the electrolytic cell when it is in operation;

[0032] Figure 2 Schematic diagram of bubble generation inside the chamber under high current density;

[0033] Figure 3 This is a comparison chart of cell voltages in different electrolytic cell operation modes;

[0034] Figure 4 This is a graph showing the change in water flow and internal resistance under different operating modes at high electrical density.

[0035] In the figure, 100, the first end plate; 101, the second end plate; 102, the screw and the disc spring; 103, the electrolytic cell core; 200, the cathode side plate; 201, the flow channel in the cathode plate; 202, the flow channel in the anode plate; 203, the diffusion layer; 204, the proton exchange membrane; 205, the air bubble; 206, the anode side plate; 207, the main pipe opening. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in combination with the embodiments and drawings, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by technicians in this field without creative work are all within the scope of protection of the present invention. In addition, all the connection / connection relationships mentioned in the text do not refer to the direct connection of components, but refer to the formation of a better connection structure by adding or reducing connection accessories according to the specific implementation situation. The various technical features in the invention can be combined interchangeably without conflicting with each other.

[0037] Reference Figures 1 to 4 ,exist Figure 1 In FIG. 1 , 100 represents the first end plate, 101 represents the second end plate, 102 represents the screw and the disc spring, and 103 represents the electrolytic cell core; Figure 2 200 represents the cathode side plate, 201 represents the flow channel in the cathode plate, 202 represents the flow channel in the anode plate, 203 represents the diffusion layer, 204 represents the membrane electrode, 205 represents the bubble, 206 represents the anode side plate, and 207 represents the main pipe port.

[0038] The present invention aims to improve the problem of gas bubble 205 discharge caused by high current density conditions, and provides an electrolytic cell placement method for improving mass transfer, which can effectively realize the effective discharge of gas bubbles 205 under high current density, reduce mass transfer resistance, and greatly reduce energy consumption.

[0039] The increase in mass transfer resistance is caused by the accumulation of bubbles 205 inside the reaction zone of the chamber. The increase in mass transfer resistance increases the voltage of the electrolysis chamber, leading to component oxidation and high-potential corrosion that affects durability.

[0040] The improvement of the problem of the discharge of the bubbles 205 in the present solution is achieved by adjusting the placement direction of the electrolytic cell, and utilizing gravity to promote the effective discharge of the bubbles 205.

[0041] Specifically, the electrolytic cell includes a clamping and fixing device and an electrolytic cell core. The clamping and fixing device includes two end plates and a connecting assembly, the two end plates are respectively provided as a first end plate and a second end plate, the first end plate and the second end plate are respectively provided at two ends of the electrolytic cell core, and the connecting assembly is used to connect the first end plate and the second end plate, and to fix the first end plate and the second end plate relatively.

[0042] The electrolytic cell core comprises a plurality of membrane electrodes and a plurality of electrode plates, which are arranged in an alternating and overlapping manner, and two adjacent electrode plates form an electrolytic chamber, and the electrolytic chamber is provided with an active area, and the membrane electrode is arranged in the active area. The top of the electrolytic cell core is provided with a plurality of main pipes extending up and down, and the main pipes are connected with the top of the electrolytic chamber so that bubbles can enter the main pipes from the active area of ​​the electrolytic chamber.

[0043] The membrane electrode comprises a gas diffusion layer, a catalyst layer and a proton exchange membrane. The number of the gas diffusion layer and the catalyst layer is set to two, and the two gas diffusion layers and the two catalyst layers are respectively arranged on both sides of the proton exchange membrane, and the two sides of the proton exchange membrane are respectively set as the anode side and the cathode side. The catalyst layer and the gas diffusion layer are stacked in sequence on one side of the proton exchange membrane.

[0044] Here, several electrolytic cell placement methods are listed, and the electrolytic cell placement directions include three types: electrolytic cell vertical type 1, electrolytic cell vertical type 2, and electrolytic cell side type. The polarity orientation of the membrane electrode 204 of the electrolytic cell vertical type 1 is that the anode faces downward and the cathode faces upward; the polarity orientation of the membrane electrode 204 of the electrolytic cell vertical type 2 is that the anode faces upward and the cathode faces downward; the polarity orientation of the membrane electrode 204 of the electrolytic cell side type is that the anode and the cathode face left and right respectively.

[0045] The polarity of the membrane electrode 204 of the vertical electrolyzer 1 is that the anode faces downward and the cathode faces upward. The density of the bubbles 205 generated at this time is less than the density of water. The bubbles 205 will float due to gravity and accumulate on the surface of the anode side catalyst layer of the membrane electrode 204. If the current density during operation is increased, the oxygen production per unit time of the small chamber will increase. Under the condition that the water flow rate remains unchanged, a large number of bubbles 205 will accumulate on the surface of the anode side catalyst layer of the membrane electrode 204, "cutting off" the effective replenishment of the reaction water, so that the mass transfer resistance and the small chamber voltage increase.

[0046] The polarity of the membrane electrode 204 of the vertical electrolyzer 2 is that the anode faces upward and the cathode faces downward; the bubbles 205 generated at this time float up due to gravity and accumulate on the surface of the plate above the membrane electrode 204; the position of the bubbles 205 changes, and the anode side surface of the membrane electrode 204 is less likely to retain bubbles 205 than the vertical electrolyzer 1, which can promote the bubbles 205 to a certain extent to be discharged from the anode catalyst layer, which is beneficial to mass transfer. If the current density during operation is increased, the oxygen production per unit time of the small chamber increases, and a large number of bubbles 205 accumulate on the plate above the membrane electrode 204 when the water flow rate remains unchanged, causing the bubbles 205 to "isolate" the reaction water. At this time, the contact resistance between the plate and the membrane electrode increases, resulting in an increase in the voltage of the electrolyzer small chamber.

[0047] The schematic diagram of the placement of the vertical electrolytic cell 1 and the vertical electrolytic cell 2 is as follows: Figure 1 The left part is shown.

[0048] The polarity of the membrane electrode 204 of the electrolytic cell side type is that the anode and the cathode are facing the left and right directions respectively. When the electrolytic cell is placed on its side, the bubbles 205 generated float up due to gravity. Since the membrane electrode is placed vertically, the bubbles 205 will eventually float up to the main pipe and accumulate. At this time, the accumulation position of the bubbles 205 is not in the active area, which will not hinder the entry of the reaction water of the catalyst layer, nor will it cause the contact resistance between the membrane electrode 204 and the anode side plate 206 or the cathode side plate 200 to increase.

[0049] The schematic diagram of the side placement of the electrolytic cell is as follows Figure 1 The right part is shown.

[0050] Under the same electrolytic cell placement, the improvement of the gas bubble 205 discharge is achieved by increasing the water flow rate. The increase in the amount of water flowing between the membrane electrode and the electrode plate will reduce the volume of a single gas bubble 205 to promote the timely discharge of the gas bubble 205.

[0051] The polarity of the membrane electrode 204 of the vertical electrolyzer 1 is that the anode faces downward and the cathode faces upward; it operates normally for a long time at the rated current density of W1. When the current density increases to W2, more bubbles 205 are generated inside the chamber. If the monitoring chamber voltage increases at this time, there may be a problem that bubbles 205 accumulate on the surface of the anode side catalyst layer of the membrane electrode 204 inside the electrolysis chamber, "cutting off" the effective replenishment of reaction water. At this time, increasing the water flow rate L1 increases the water flow rate and internal water pressure inside the electrolysis chamber, so that the volume of the bubbles 205 is reduced and quickly discharged at a high water flow rate.

[0052] The polarity of the membrane electrode 204 of the vertical electrolytic cell 2 is that the anode faces upward and the cathode faces downward; it operates normally for a long time at the rated current density of W1. When the current density increases to W2, more bubbles 205 are generated inside the chamber. If the monitored chamber voltage increases at this time, a large number of bubbles 205 may accumulate on the plate above the membrane electrode 204 inside the chamber, and the bubbles 205 appear to "isolate" the reaction water. At this time, the contact resistance between the plate above the membrane electrode 204 and the membrane electrode increases, resulting in an increase in the voltage of the electrolytic chamber. At this time, increasing the water flow rate L2 increases the water flow rate and the internal water pressure inside the electrolytic chamber, so that the volume of the bubbles 205 is reduced and they are quickly discharged at a high water flow rate.

[0053] The membrane electrode of the electrolyzer side is placed vertically; it operates normally for a long time at the rated current density of W1. When the current density increases to W2, more bubbles 205 are generated inside the electrolysis chamber. At this time, since the membrane electrode is placed vertically, a large number of bubbles 205 will eventually float to the side of the main pipe mouth and accumulate. At this time, the accumulation position of the bubbles 205 is not in the active area, which will not hinder the reaction water from entering the catalyst layer, nor will it cause the contact resistance between the membrane electrode 204 and the electrode plate to increase. Increasing the water volume L3 will prompt the bubbles 205 in the main pipe to be discharged in time.

[0054] Under the three electrolytic cell placement methods, the comparison of the minimum water flow rate (unit: L / min) to ensure that the voltage and mass transfer resistance are within the normal range is: vertical electrolytic cell 1> vertical electrolytic cell 2> side electrolytic cell.

[0055] The reduction of water flow can reduce the power consumption of the electrolyzer hydrogen production system to a certain extent and improve the hydrogen production efficiency.

[0056] When the electrolyzers are placed in different ways and under high current density (large gas production per unit time), the gas cannot be discharged to the main pipe in time, so that the active area of ​​the electrolytic chamber is occupied by gas and appears "half full". As a result, the "half full" part of the active area of ​​the electrolyzer is not replenished with reactive water in time and appears "dry burning", which leads to a sharp increase in voltage and eventually component failure.

[0057] In order to match the mass transfer problem caused by the bubbles 205 under high current density, the present invention uses gravity to reduce the time that the bubbles 205 stay in the active zone, thereby avoiding the local "dry burning" state in the active zone caused by the untimely discharge of the bubbles 205.

[0058] However, as the size of the electrolytic cell increases in the future and the current density at the working point increases, the total amount of gas produced per unit time will also increase exponentially. At this time, although the gas can rely on gravity to quickly flow from the active area into the main pipe, when the volume of the main pipe is not enough to accommodate so much reaction gas, excess gas will continue to occupy the active area, and the "half-full state" will appear again.

[0059] To this end, in addition to providing a placement method for removing bubbles 205 by gravity, the present invention also provides quantitative suggestions for the limit dimensions of the electrolytic cell active area height H and the total pipe height N at different working points.

[0060] When quantitative suggestions are given for the limit dimensions of the electrolyzer active zone height H and the total tube height N at different operating points, the effect of water flow rate on gas mass transfer is not considered.

[0061] When giving quantitative suggestions for the limit dimensions of the electrolytic cell active zone height H and the total tube height N at different working points, only the sideways state of the electrolytic cell is considered.

[0062] When the height of the electrolytic cell chamber is H, the relationship between the oxygen production (cross section) and the current density W is as follows:

[0063]

[0064] Where V(t) is the volume of oxygen produced per unit time section, in L / (cm*s); W is the current density, in A / cm2; H is the height of the chamber, in cm; Vm is the molar volume, in L / mol; F is the Faraday constant. Since V(t) is the volume of oxygen produced per unit time section, the time here can be ignored.

[0065] The relationship between the minimum volume of the bubble 205 required to fill the chamber and the oxygen production of the cross section is as follows:

[0066] V(t)<π×a×R 2 +d×N

[0067]

[0068] Where R is half of the distance between the membrane electrode and the electrode plate (flow field depth), in cm; a is the active area opening rate; d is the chamber thickness, in cm; N is the total pipe section height, in cm; P is the electrolyzer chamber design parameter, K is a linear constant

[0069]

[0070] Available This formula can be used to derive the relationship between the height of the active area of ​​the electrolytic cell and the current density and the total tube cross-sectional height, thereby quantitatively calculating the height of the electrolytic chamber.

[0071] When the opening ratio and the channel depth remain unchanged, the smaller the chamber height H is, the greater the upper limit of the applicable current density is.

[0072] When the opening rate is 50%, the flow channel depth is 0.2 cm, and the chamber thickness is 0.45 cm, the active zone height H at different working points and different total pipe heights is shown in Table 1.

[0073]

[0074] Table 1

[0075] The preferred embodiments of the present invention are specifically described above, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. An electrolytic cell, characterized in that: include: An electrolytic cell core, the electrolytic cell core comprising a plurality of vertically arranged electrode plates and a plurality of membrane electrodes, the plurality of electrode plates and the plurality of membrane electrodes being arranged in a staggered and overlapping manner in a transverse direction, two adjacent electrode plates forming an electrolytic chamber, the electrolytic chamber being provided with an active area, the membrane electrode being arranged in the active area, the top of the electrolytic cell core being provided with a plurality of main pipes extending up and down, the main pipes being connected with the top of the electrolytic chamber; The clamping and fixing device comprises a connecting assembly and two end plates, wherein the two end plates are respectively located at two lateral ends of the electrolytic cell core, and the connecting assembly connects the two end plates and fixes the two end plates relatively.

2. The electrolytic cell according to claim 1, characterized in that: The connecting assembly includes a plurality of screw rods and a plurality of nuts. The plurality of screw rods are evenly arranged. The ends of the screw rods pass through the two end plates. The ends of the screw rods are threadedly connected to the nuts. The nuts are located on the outside of the end plates. The nuts are used to resist the end plates to limit the end plates.

3. The electrolytic cell according to claim 2, characterized in that: The connection assembly further includes an elastic member disposed between the nut and the end plate.

4. The electrolytic cell according to claim 3, characterized in that: The elastic component is a disc spring.

5. The electrolytic cell according to claim 1, characterized in that: The membrane electrode comprises a proton exchange membrane, a catalyst layer and a gas diffusion layer, wherein the catalyst layer and the gas diffusion layer are sequentially stacked on one side of the proton exchange membrane.

6. A method for designing the height of an active area of ​​an electrolytic chamber, characterized in that: Applicable to the electrolytic cell according to any one of claims 1 to 5, the method for designing the height of the active area of ​​the electrolytic chamber comprises the following steps: Based on the oxygen production volume formula of the electrolysis chamber: Where V(t) is the volume of oxygen produced per unit time section; W is the current density; H is the height of the active area of ​​the electrolysis chamber; V m is the molar volume; F is the Faraday constant; And the relationship between the minimum volume of bubbles required to fill the electrolysis chamber and the oxygen production in the cross section is: V(t)<π×a×R 2 +d×N; Where R is half of the distance between the membrane electrode and the electrode plate; a is the porosity of the active area; d is the thickness of the electrolysis chamber; N is the total tube section height; Get the formula Thus, it can be concluded that

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