Reversible clamp for spraying membrane electrode

Abstract

The utility model relates to the technical field of hydrogen fuel cells, and discloses a turnover clamp for spraying a membrane electrode, which is characterized by comprising a vacuum heating boss (2), a first layer of hollow frame (3), a second layer of hollow frame (4) and a top frame (5) which are sequentially stacked from bottom to top, wherein the size of an inner hole of the top frame (5) is consistent with the size of a target membrane electrode and is smaller than the size of the periphery of the vacuum heating boss (2). According to the membrane electrode, damage and wrinkles at the edge of the proton membrane catalyst layer can be remarkably reduced, so that the yield of the membrane electrode in the spraying process is improved, the hydrogen permeation rate of the membrane electrode is reduced, the performance of the membrane electrode is improved, and the cost of the membrane electrode is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of hydrogen fuel cells, in particular to a membrane electrode spraying reversible clamp. Background Art

[0002] At present, proton exchange membrane fuel cell technology has made great progress. Fuel cell stacks are widely used in transportation, drones, nuclear submarines, satellites and other fields. Its main working principle is to use the catalytic action of electrocatalysts to make the following reactions occur at the positive and negative electrodes respectively:

[0003] Cathode oxygen reduction reaction: O2+4H3O + +4e - →6H2O;

[0004] Anodic hydrogen oxidation reaction: H2+2H2O-2e - →2H3O + ;

[0005] The membrane electrode is the heart of the fuel cell and determines the power output of the fuel cell stack. At present, the production processes of commercial membrane electrodes mainly include spraying process, coating process and other production processes. Among them, the spraying process has become an excellent process for commercial membrane electrode production because of its wide slurry formula conditions and stable membrane electrode thickness control.

[0006] In the membrane electrode spraying process, in order to accurately control the size of the catalyst layer, it is often necessary to achieve the size of the catalyst layer by laying a fixture of a certain size flat on the proton membrane.

[0007] CN103811770A discloses a fuel cell membrane electrode preparation fixture and a processing technology thereof. The fixture avoids repeated disassembly and assembly of a proton exchange membrane through upper and lower metal frames and a long tail clip, and realizes simultaneous spraying of multiple membrane electrodes through a spray mask.

[0008] CN210815860U discloses a CCM membrane electrode spraying fixture and its lower fixture. The design of the upper and lower fixtures solves the problem of peeling and laying out the proton exchange membrane and ensuring that the spraying areas on both sides are accurately aligned. However, the proton exchange membrane is clamped only by the gravity of the fixture and there is no handle design. The proton membrane is easily curled due to loose clamping, and it is difficult to remove the fixture and turn it over.

[0009] CN213670036U discloses a spraying fixture for producing hydrogen-oxygen membrane electrodes for vehicles. Compared with the above patents, the stability of clamping the proton exchange membrane is increased by adding handles and magnets, and the operation is facilitated.

[0010] However, in the existing patents for the membrane electrode reversible spraying fixture, the proton exchange membrane is clamped in two open fixtures, and one of the fixture openings is placed on the vacuum adsorption heating table to achieve double-sided spraying of the proton membrane in a clamped state. However, in order to achieve the flipping operation in the actual operation process, it is impossible for the contact position between the fixture opening and the vacuum adsorption platform to be perfectly matched, and there must be a gap. Under high temperature and vacuum adsorption conditions, it is very easy to damage the very thin, deformable and curled proton exchange membrane at this position. This position is the spraying edge area, located at the edge of the catalyst layer. If this position is damaged in the fuel cell, it is easy to cause increased hydrogen permeation, hydrogen-oxygen cross-gassing, and other situations that seriously affect the operation of the battery, resulting in a decrease in the yield rate of the membrane electrode preparation process. Utility Model Content

[0011] The purpose of the utility model is to overcome the problem that the clamps in the prior art often cause wrinkles and damage at the edges of the proton membrane catalyst layer during the spraying process, and to provide a flip clamp for membrane electrode spraying. The utility model controls the inner hole size of the clamp top frame to be consistent with the target membrane electrode size, separates the clamping and adsorption area of ​​the clamp edge from the active area of ​​the sprayed catalyst layer, significantly reduces the damage and wrinkles at the edge of the proton membrane catalyst layer, thereby improving the yield rate of the membrane electrode in the spraying process, reducing the hydrogen permeation rate of the membrane electrode, improving the performance of the membrane electrode, and reducing the cost of the membrane electrode.

[0012] In order to achieve the above-mentioned purpose, the utility model provides a membrane electrode spraying reversible fixture, which comprises a vacuum heating boss 2, a first layer inner hollow frame 3, a second layer inner hollow frame 4, and a top frame 5 stacked in sequence from bottom to top;

[0013] The inner hole size of the top frame 5 is consistent with the target membrane electrode size and is smaller than the outer peripheral size of the vacuum heating boss 2 .

[0014] Through the above technical solution, the utility model has the following beneficial effects:

[0015] The utility model provides a reversible fixture for membrane electrode spraying, comprising a vacuum heating boss, a first layer of inner hollow frame, a second layer of inner hollow frame, and a top frame stacked in sequence from bottom to top, wherein a proton exchange membrane is adsorbed on the upper surface of the vacuum heating boss to stabilize the proton membrane, and the proton membrane is pressed onto the vacuum heating boss through the second layer of inner hollow frame, so that the catalyst layer structure is stably formed during spraying, and damage and wrinkles at the edge of the catalyst layer of the membrane electrode are significantly reduced, thereby improving the yield rate of the membrane electrode in the spraying process, reducing the occurrence of hydrogen permeation or cross-gassing of the membrane electrode during actual use, reducing the hydrogen permeation rate of the membrane electrode, improving the safety and stability of the membrane electrode, and reducing the cost of the membrane electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1It is a schematic diagram of the membrane electrode spraying fixture provided by the utility model;

[0017] Figure 2 It is a schematic diagram of the top frame protrusion of the membrane electrode spraying fixture provided by the utility model;

[0018] Figure 3 It is a schematic diagram of the membrane electrode spraying fixture provided by the utility model after being overlapped;

[0019] Figure 4 It is the hydrogen permeation current test curve of the membrane electrode prepared by the utility model;

[0020] Figure 5 It is the fitting result of the hydrogen permeation current test curve of the membrane electrode prepared by the utility model.

[0021] Description of Reference Numerals

[0022] 1- Vacuum heating boss base 2- Vacuum heating boss 3- First layer inner empty frame

[0023] 4-Second layer inner empty frame 5-Top frame 6-Second double handle

[0024] 7- first double-ear handle 8- third double-ear handle 9- top frame protrusion DETAILED DESCRIPTION

[0025] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0026] The utility model provides a membrane electrode spraying reversible fixture, such as Figure 1 As shown, the fixture includes a vacuum heating boss 2, a first layer inner hollow frame 3, a second layer inner hollow frame 4, and a top frame 5 which are stacked in sequence from bottom to top;

[0027] The inner hole size of the top frame 5 is consistent with the target membrane electrode size and is smaller than the outer peripheral size of the vacuum heating boss 2 .

[0028] In the utility model, Figure 1As shown, preferably, the vacuum heating boss base 1 and the vacuum heating boss 2 of the fixture are placed on the surface of the sprayer base, and the first layer of inner hollow frame 3, the proton membrane, the second layer of inner hollow frame 4 and the top frame 5 are stacked in sequence from bottom to top, the first layer of inner hollow frame 3 and the second layer of inner hollow frame 4 are positioned and fitted, and after the top frame 5 and the second layer of inner hollow frame 4 are positioned and fitted by the top frame protrusion 9, the slurry containing the catalytic layer is sprayed on one side of the proton membrane by the sprayer.

[0029] In the prior art, during the spraying process of the catalyst coating membrane (CCM), the proton membrane is easily deformed and damaged due to the gap between the fixture opening and the vacuum adsorption platform, which in turn increases the hydrogen permeation rate of the fuel cell and affects the safe operation of the fuel cell.

[0030] In the utility model, the spraying area of ​​the catalyst layer is regulated by adjusting the inner hole size of the top frame 5 so that it is smaller than the outer peripheral size of the vacuum heating boss 2. The clamp edge clamps the adsorption area and separates it from the active area of ​​the sprayed catalyst layer, thereby reducing the damage and wrinkles at the edge of the proton membrane catalyst layer, reducing the hydrogen permeation rate of the membrane electrode, and reducing the occurrence of hydrogen permeation or cross-talk of the membrane electrode during actual use, thereby improving the performance of the membrane electrode, and at the same time improving the yield rate of the membrane electrode in the spraying process and reducing costs.

[0031] In the present invention, the type of proton membrane used for spraying is not particularly limited, and it is a conventional polymer membrane for preparing membrane electrodes in the art. It is preferably a perfluorosulfonic acid diaphragm and / or a polytetrafluoroethylene proton exchange membrane, such as at least one of NafionN211, Nafion N212, Gore MX765.08, Gore MX20.10, Gore M740.18, Gore M735.18, GoreM820.15 and Gore M815.15. In the present invention, the type of material of the catalytic layer is not particularly limited, and it is a conventional Pt-containing catalyst in the art, preferably selected from at least one of a Pt / C catalyst, a PtNi / C catalyst, a PtCo / C catalyst and a PtCoCe / C catalyst.

[0032] In the utility model, the outer peripheral size of the boss of the vacuum heating boss 2 and the inner hole size of the first layer inner hollow frame 3 and the second layer inner hollow frame 4 are not particularly limited, and are conventional fixture sizes in the field, which can be used for spraying of the proton membrane catalyst layer. When spraying is performed using a spray coater, the size of the fixture can be adjusted according to the adaptability of the spray coater size. Preferably, the outer peripheral size of the boss of the vacuum heating boss 2 is consistent with the inner hole size of the first layer inner hollow frame 3 and the second layer inner hollow frame 4. Preferably, the outer peripheral size of the boss of the vacuum heating boss 2 is 1.5-15cm×1.5-30cm.

[0033] In the utility model, the vacuum heating boss 2 has a porous surface, and the proton membrane is adsorbed on the vacuum heating boss 2 by vacuuming to prevent the proton membrane from swelling and deforming during spraying; an electric heating device is provided in the boss to heat the proton membrane to a target temperature, so that the slurry can be quickly evaporated and dried after being sprayed onto the membrane surface to obtain a catalytic layer.

[0034] In the present invention, the height of the boss of the vacuum heating boss 2 and the thickness of the first layer inner hollow frame 3 and the thickness of the second layer inner hollow frame 4 are not particularly limited. Preferably, the height of the boss of the vacuum heating boss 2 is consistent with the thickness of the first layer inner hollow frame 3 and the thickness of the second layer inner hollow frame 4. Preferably, the height of the boss of the vacuum heating boss 2, the thickness of the first layer inner hollow frame 3 and the thickness of the second layer inner hollow frame 4 are 0.2-5 cm respectively.

[0035] In the utility model, the unsprayed proton membrane is adsorbed on the surface of the vacuum heating boss 2 by the vacuum heating boss 2 and the first layer of inner hollow frame 3 to stabilize the proton membrane, and the proton membrane is pressed on the vacuum heating boss by the second layer of inner hollow frame 4, so that the catalyst layer structure can be stably formed during spraying. The proton membrane is further stably placed by the top frame 5, and the inner hole size of the top frame determines the specific size and area of ​​the catalyst layer.

[0036] In the present invention, preferably, the inner hole size of the top frame 5 is smaller than the outer periphery size of the vacuum heating boss 2. Preferably, the inner hole size of the top frame 5 is 1-14 cm×1-29 cm.

[0037] In the present utility model, unless otherwise specified, "first", "second" and "third" do not indicate a sequence of precedence or a limitation on each component or step, but are only used to distinguish that they are not the same component or step.

[0038] In the present invention, preferably, the side of the first layer inner hollow frame 3 is provided with a first double-ear handle 7, the side of the second layer inner hollow frame 4 is provided with a second double-ear handle 6, and the side of the top frame 5 is provided with a third double-ear handle 8. The clamp can be disassembled by a manipulator to take and place the proton membrane and flip the proton membrane to achieve double-sided spraying. In the present invention, there is no special limitation on the arrangement of the first double-ear handle 7, the second double-ear handle 6 and the third double-ear handle 8. Preferably, the first double-ear handle 7 and the second double-ear handle 6 are arranged in the same direction.

[0039] In the utility model, Figure 2 and Figure 3As shown, preferably, the first double-ear handle 7 and the second double-ear handle 6 do not completely overlap along the stacking direction. The incomplete overlap along the stacking direction means that after the first layer of inner hollow frame 3 and the second layer of inner hollow frame 4 are positioned and fitted, the first double-ear handle 7 and the second double-ear handle 6 do not completely overlap.

[0040] In the present invention, preferably, the third double-ear handle 8 does not completely overlap with the first double-ear handle 7 and the second double-ear handle 6, and can be vertically arranged or incompletely overlapped in parallel directions. Preferably, the third double-ear handle 8 is vertically arranged with the first double-ear handle 7 and the second double-ear handle 6.

[0041] In the present invention, the sizes of the first double-ear handle 7, the second double-ear handle 6 and the third double-ear handle 8 are not particularly limited. Those skilled in the art can adjust the sizes of the first double-ear handle 7, the second double-ear handle 6 and the third double-ear handle 8 according to the size of the membrane electrode preparation equipment, so that the robot can realize the disassembly of the clamp and the flipping of the proton membrane.

[0042] In the utility model, when the spraying equipment is used to spray the proton membrane, the third double-ear handle 8 is moved, the first double-ear handle 7 and the second double-ear handle 6 are turned over, and the fixture is reassembled to continue spraying the other side of the proton membrane, so as to obtain a proton membrane with catalytic layers sprayed on both sides, which can improve the spraying efficiency and product yield.

[0043] In the present invention, the method for preparing a membrane electrode by spraying a catalyst layer on the surface of a proton membrane is not particularly limited, and those skilled in the art can use conventional spraying equipment and spraying methods to spray the catalyst layer.

[0044] In the present utility model, preferably, the fixture further comprises a vacuum heating boss base 1 for fixing the vacuum heating boss 2. The outer circumference of the vacuum heating boss base 1 is larger than the outer circumference of the vacuum heating boss 2. Preferably, the size of the vacuum heating boss base 1 is 4-18cm×4-33cm, and the thickness of the vacuum heating boss base is 2-5cm. The vacuum heating boss base 1 is used to support and fix the vacuum heating boss 2 and the first layer inner empty frame 3, the second layer inner empty frame 4 and the top frame 5 stacked from bottom to top.

[0045] In the present invention, preferably, the outer side of the frame of the first layer inner empty frame 3 has two to four protrusions for positioning and fitting. The outer side of the frame refers to the outer side of the first layer inner empty frame 3 along the stacking plane direction, and the protrusions are positioned and fitted with the second layer inner empty frame 4.

[0046] In the present invention, the height of the protrusion of the first layer inner hollow frame 3 is not particularly limited. Preferably, the height of the protrusion is less than or equal to the thickness of the second layer inner hollow frame 4, and preferably the height of the protrusion is equal to the thickness of the second layer inner hollow frame 4, so that the first layer inner hollow frame 3 and the second layer inner hollow frame 4 can be better fitted.

[0047] In the present invention, preferably, two to four hollowings are provided at positions of the second layer inner hollow frame 4 corresponding to the protrusions of the first layer inner hollow frame 3 , and the shape and size of the hollowings are consistent with the protrusions of the first layer inner hollow frame 3 .

[0048] In the present invention, the shapes of the hollowing and protrusions are not particularly limited. Preferably, the shapes of the hollowing and protrusions are selected from at least one of a circle, an ellipse and a polygon, preferably a circle. The shapes and sizes of the hollowing and protrusions are the same, and can achieve the effect of positioning and fitting.

[0049] In the present invention, the outer perimeter dimensions of the first layer inner hollow frame 3, the second layer inner hollow frame 4, and the top frame 5 are not particularly limited, and the assembled fixture can be placed in the proton membrane spraying equipment. Preferably, the outer perimeter dimensions of the first layer inner hollow frame 3, the second layer inner hollow frame 4, and the top frame 5 are independently 4-18 cm × 4-33 cm.

[0050] In the utility model, Figure 2 As shown, the outer edge of the inner hole of the top frame 5 is provided with a circle of top frame protrusions 9, which are used for positioning and fitting with the second layer inner hollow frame 4. The protrusion height of the top frame protrusions 9 is consistent with the thickness of the second layer inner hollow frame 4. The top frame protrusions 9 are used to position and fit the top frame 5 and the second layer inner hollow frame 4, which can avoid the problem of proton membrane damage and uneven spraying caused by the movement of the top frame during the proton membrane spraying process.

[0051] In the present invention, the materials of the top frame 5, the first layer inner hollow frame 3 and the second layer inner hollow frame 4 are not particularly limited. Preferably, the materials of the top frame 5, the first layer inner hollow frame 3 and the second layer inner hollow frame 4 are selected from at least one of stainless steel 314, stainless steel 316L and polytetrafluoroethylene.

[0052] In the present invention, preferably, the cathode diffusion layer and the anode diffusion layer are covered on the outer surface of the proton membrane sprayed with the catalytic layer on both sides, and hot pressing is performed to obtain a membrane electrode. The types and hot pressing conditions of the cathode diffusion layer and the anode diffusion layer are not particularly limited. Those skilled in the art can select conventional cathode diffusion layers and anode diffusion layers for membrane electrodes. Preferably, the hot pressing temperature is 100-150°C and the pressure is 1-10kg / cm 2 , time is 60-120s.

[0053] In the utility model, the membrane electrode is assembled into a fuel cell single cell, and the hydrogen permeation current of the membrane electrode is tested.

[0054] The present invention will be described in detail below through examples and comparative examples. In the following examples and comparative examples, unless otherwise specified, the reagents used in the present invention are all commercially available.

[0055] The proton membrane is a Gore proton membrane with the brand number of MX765.08.

[0056] Example 1

[0057] Place the vacuum base of this fixture on the surface of the sprayer base. The size of the vacuum heating boss base 1 is 4cm×4cm, the thickness is 2cm, and the material is 316L; the outer peripheral size of the vacuum heating boss 2 is 3cm×3cm; the outer peripheral size of the first layer inner empty frame 3, the second layer inner empty frame 4 and the top frame 5 is 4cm×4cm, the boss protrusion height of the vacuum heating boss 2, the thickness of the first layer inner empty frame 3, the second layer inner empty frame 4 and the top frame 5 is 1cm, and the inner hole size of the top frame 5 is 2cm×2cm.

[0058] 8 mg of Pt / C (Pt mass percentage is 40 wt%) catalyst is taken and placed in a glass bottle, then 400 μL of water is added, ultrasonic vibration is performed several times, then 106 μL of perfluorosulfonic acid type polymer solution (Nafion solution, mass fraction is 5 wt%) is added, then vibration is performed several times, and finally 800 μL of isopropanol is added, ultrasonic vibration is performed for 30 min, and the slurry is numbered as slurry A. The above-mentioned fixture is placed inside the spraying apparatus, and the vacuum heating boss 2, the first layer inner hollow frame 3, the proton membrane (3.5 cm×3.5 cm), the second layer inner hollow frame 4 and the top frame 5 are placed from bottom to top in sequence, and the surface temperature of the vacuum heating boss 2 is controlled to be 70° C. After the slurry A is sprayed on one side of the proton membrane by the spraying apparatus, the first layer inner hollow frame 3 and the second layer inner hollow frame 4 are turned over to spray the other side to form a complete catalyst coating proton membrane (CCM).

[0059] Comparative Example 1

[0060] The proton membrane was sprayed using the fixture of Example 1 of patent CN210815860U. The spraying method was the same as that of the present utility model. The proton membrane area and catalyst content obtained by spraying were the same as those in Example 1. The catalyst coated proton membrane (CCM) obtained was recorded as Comparative Example 1.

[0061] Application Examples

[0062] The cathode diffusion layer (SGL gas diffusion layer SGL28BC) and the anode diffusion layer (SGL gas diffusion layer SGL28BC) were covered on the outer surface of the catalyst coated proton membrane (CCM) of the above Example 1 and Comparative Example 1, and hot pressed at a temperature of 130°C and a pressure of 5 kg / cm 2 , time is 100s, and a membrane electrode is obtained.

[0063] Two bipolar plates (Qun Yi Company, graphite material, serpentine channel, channel size of 5cm×5cm) were aligned on a flat table with their channel sides, and then two polytetrafluoroethylene membranes with square holes in the middle were placed in the middle of the bipolar plates for sealing. Two copper sheets were placed on both sides of the two bipolar plates for collecting current. At the same time, heating pads were placed on both sides of the clamp. The membrane electrode was placed in the middle of the polytetrafluoroethylene membrane and fixed to obtain a fuel cell cell.

[0064] Test Case

[0065] The method for testing the hydrogen permeability of the membrane electrode is as follows: the single cell test instrument is the 850e test system developed by Scibner, and the maximum test current is 50A.

[0066] The temperature of the single cell was set to 80°C, the gases at the anode and cathode were nitrogen and hydrogen, with flow rates of 500 mL / min and 200 mL / min, respectively, the back pressure was normal pressure, the temperature was 80°C, and the relative humidity RH was 100%.

[0067] The single cell was scanned in the potential range of 0.2-0.5V, with a scan rate of 0.5mV / s, to obtain a current density-potential curve. The data of the approximate straight line in the range of 0.4-0.5V of the obtained curve were subjected to regression analysis to obtain a regression curve, whose intersection on the y-axis is the membrane electrode hydrogen permeation current obtained by the test.

[0068] Figure 4 The hydrogen permeation current test curves of the membrane electrode prepared in the comparative example and the embodiment are shown in the figure after linear fitting of the curves in the 0.4-0.5V region. Figure 5 As shown. Figure 4 and Figure 5 It can be seen that:

[0069] Example 1 curve is

[0070] CurrentDensity=1.78+0.88×E

[0071] The curve of comparative example 1 is

[0072] CurrentDensity=9.89+0.88×E

[0073] The hydrogen permeation current of the membrane electrode of Example 1 is 1.78 mA / cm2 The hydrogen permeation current of the membrane electrode of comparative example 1 is 9.89 mA / cm 2 The hydrogen permeation of the membrane electrode in Example 1 is significantly lower than that in the comparative example. It can be concluded that by using this utility model fixture, the damage and wrinkles at the edge of the membrane electrode catalyst layer are reduced, the hydrogen permeation rate of the membrane electrode is reduced, and the safety and stability of the membrane electrode are improved.

[0074] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including combining various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A membrane electrode spraying reversible fixture, characterized in that: The fixture comprises a vacuum heating boss (2), a first layer inner hollow frame (3), a second layer inner hollow frame (4), and a top frame (5) which are stacked in sequence from bottom to top; The inner hole size of the top frame (5) is consistent with the target membrane electrode size and is smaller than the outer peripheral size of the vacuum heating boss (2).

2. The clamp according to claim 1, characterized in that: The outer perimeter size of the vacuum heating boss (2) is consistent with the inner hole size of the first layer inner hollow frame (3) and the second layer inner hollow frame (4); The protruding height of the vacuum heating protrusion (2) is consistent with the thickness of the first layer inner hollow frame (3) and the thickness of the second layer inner hollow frame (4).

3. The clamp according to claim 2, characterized in that: The outer perimeter size of the vacuum heating boss (2) is 1.5-15 cm×1.5-30 cm; The protrusion height of the vacuum heating protrusion (2) is 0.2-5 cm.

4. The clamp according to claim 1, characterized in that: The inner hole size of the top frame (5) is 1-14cm×1-29cm.

5. The clamp according to claim 1, characterized in that: The fixture further comprises a vacuum heating boss base (1) for fixing the vacuum heating boss (2); The outer circumference size of the vacuum heating boss base (1) is greater than the outer circumference size of the vacuum heating boss (2).

6. The clamp according to claim 1, characterized in that: The first layer inner hollow frame (3) has two to four protrusions on the outer side of the frame, which are used for positioning and fitting with the second layer inner hollow frame (4).

7. The clamp according to claim 6, characterized in that Two to four hollowings are arranged at positions of the second layer inner hollow frame (4) corresponding to the protrusions of the first layer inner hollow frame (3), and the shape and size of the hollowings are consistent with the protrusions of the first layer inner hollow frame (3).

8. The clamp according to claim 1, characterized in that: The outer peripheral dimensions of the first layer inner hollow frame (3), the second layer inner hollow frame (4) and the top frame (5) are independently 4-18cm×4-33cm.

9. The clamp according to claim 1, characterized in that: The outer edge of the inner hole of the top frame (5) is provided with a circle of top frame protrusions (9) for positioning and fitting with the second layer inner hollow frame (4); The protrusion height of the top frame protrusion (9) is consistent with the thickness of the second layer inner hollow frame (4).

10. The clamp according to claim 1, characterized in that A first double-ear handle (7) is provided on the side of the first-layer inner hollow frame (3), a second double-ear handle (6) is provided on the side of the second-layer inner hollow frame (4), and a third double-ear handle (8) is provided on the side of the top frame (5); The first double-ear handle (7) and the second double-ear handle (6) do not completely overlap along the stacking direction.

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