Passive direct methanol fuel cell with enhanced cathode water back-diffusion to anode

Abstract

The application discloses a passive direct methanol fuel cell with enhanced cathode water back-diffusion anode capability, and belongs to the field of proton exchange membrane fuel cells. The structure comprises a methanol solution storage cavity, a perforated plate, a vapor cavity, an insulating gasket, an anode current collecting plate, a composite membrane electrode, a cathode current collecting plate and a cathode air self-breathing cavity, and the components are connected and fixed by means of holes, insulating bolts and nuts. The cell uses a polyvinyl alcohol film to transport water generated by the cathode back to the anode, thereby relieving the problem of cathode water flooding, relieving the problem of anode methanol penetration, slowing down the speed of anode catalyst poisoning and ensuring the water content of the proton exchange membrane. The output power, energy conversion rate and service life of the fuel cell are improved. The direct methanol fuel cell can use a higher concentration methanol solution or pure methanol as fuel to normally work, and the total power generation of the cell is improved.

Description

Technical Field

[0001] This invention belongs to the field of proton exchange membrane fuel cells and relates to a passive direct methanol fuel cell that enhances the ability of cathode water to replenish anode. Background Technology

[0002] Fuel cells directly convert chemical energy into electrical energy through electrochemical processes. They boast high energy conversion efficiency, are environmentally friendly, and emit virtually no nitrogen oxides or sulfur oxides, making them promising candidates for portable and mobile power sources. Due to these significant advantages, the research and development of fuel cell technology has received considerable attention from governments worldwide.

[0003] Passive direct methanol fuel cells rely on concentration gradient diffusion and natural convection to provide fuel and oxidant, eliminating the need for auxiliary equipment and simplifying the cell structure. However, due to the limited total methanol storage capacity within the cell, the theoretical power output is significantly affected by the methanol concentration; therefore, higher concentrations of methanol are often used as fuel to achieve higher power generation. The liquid water generated at the cathode reaction slowly accumulates over time, leading to flooding and ultimately hindering oxygen mass transfer. The anode requires a certain amount of water to participate in the electrode reaction, reduce the local methanol concentration, and prevent large amounts of unreacted methanol from crossing the proton exchange membrane to the cathode or poisoning the anode catalyst.

[0004] Polyvinyl alcohol (PVA) film is a water-soluble, hydrophilic organic polymer film. Its water solubility can be reduced by cross-linking with chemical reagents or physical means. PVA film exhibits preferential water permeability, allowing water vapor to pass through, but has poor permeability to alcohol vapor, oxygen, and carbon dioxide. It can be used for applications such as alcohol-water separation. Summary of the Invention

[0005] A passive direct methanol fuel cell with enhanced cathode water backfilling capability is characterized in that the cell is a proton exchange membrane fuel cell single cell, and its structure includes a methanol solution storage chamber 1, a perforated plate 3, a vapor chamber 4, an insulating gasket 7, an anode current collector 6, a composite membrane electrode 8, a cathode current collector 9, and a cathode air self-breathing chamber 10. The centers of each component are coaxial, and each component is connected and fixed by insulating bolts and nuts through holes 12 at the four corners and sides.

[0006] A groove 1-3 is located on the surface of the methanol solution storage chamber 1 adjacent to the perforated plate 3. A pervaporation membrane 2 is placed in the groove 1-3, and the size and depth of the groove 1-3 are equal to the size of the pervaporation membrane 2. Changing the porosity of the perforated plate 3 can change the flow rate of the anode reactant.

[0007] The composite membrane electrode 8 comprises six parts: an anode diffusion layer 8-1, an anode catalyst layer 8-2, a proton exchange membrane 8-3, a cathode catalyst layer 8-4, a cathode diffusion layer 8-5, and a polyvinyl alcohol membrane 8-6. The anode diffusion layer 8-1, anode catalyst layer 8-2, proton exchange membrane 8-3, cathode catalyst layer 8-4, and cathode diffusion layer 8-5 are of equal length and width, and are sequentially pressed together. The polyvinyl alcohol membrane 8-6 is located around the perimeter, while the entire structure formed by the anode diffusion layer 8-1, anode catalyst layer 8-2, proton exchange membrane 8-3, cathode catalyst layer 8-4, and cathode diffusion layer 8-5 is located in the center. The inner side boundaries of the polyvinyl alcohol membrane 8-6 are bonded to the outer side boundaries of each layer in the center using Nafion emulsion, ensuring a tight connection without gaps. The thickness of the polyvinyl alcohol membrane 8-6 is equal to the thickness of the entire structure formed by the anode diffusion layer 8-1, anode catalyst layer 8-2, proton exchange membrane 8-3, cathode catalyst layer 8-4, and cathode diffusion layer 8-5.

[0008] The cathode current collector 9 includes an oxygen channel 9-1, a ridge 9-2, and a current collection hole 9-3. The oxygen channel 9-1 and the ridge 9-2 are parallel to each other and arranged alternately to form the cathode flow field. The oxygen channel 9-1 is open on both sides, and its length is greater than the length of the cathode diffusion layer 8-5. The total width of the cathode flow field is greater than the width of the cathode diffusion layer 8-5.

[0009] The anode current collector 6 includes methanol channels 6-1, ridges 6-2, water channels 6-3, and current collection holes 6-4. The side closest to the composite membrane electrode 8 (referred to as the front side) has methanol channels 6-1, ridges 6-2, and water channels 6-3, while the opposite side (referred to as the back side) has methanol channels 6-1. The depth of the water channels 6-3 formed by slotting on the front side is half the thickness of the anode current collector 6. The unslotted portions within all channels are called ridges 6-2. The water channels 6-3 and ridges 6-2 are parallel to each other and staggered. The two ends of each parallel water channel 6-3 are connected by a vertical channel. The length of the water channel 6-3 is greater than the length of the anode diffusion layer 8-1. Two through slots are cut in the center of a portion of the ridges 6-2 to form methanol channels 6-1. The length of the methanol channels 6-1 is equal to the length of the anode diffusion layer 8-1, and the width of the area containing all methanol channels 6-1 is equal to the width of the anode diffusion layer 8-1. Methanol channel 6-1, ridge 6-2, and water channel 6-3 together form the anode flow field.

[0010] The cathode air breathing chamber 10 has a self-breathing through-hole 10-1 and a groove 10-2. The cathode water management layer 11 is placed inside the groove 10-2. The area of ​​the self-breathing through-hole 10-1 is smaller than the area of ​​the cathode water management layer 11. The size and depth of the groove 10-2 are equal to those of the cathode water management layer 11. The cathode water management layer 11 is hydrophobic.

[0011] Furthermore, the vapor chamber 4 uses transparent plexiglass as the material, and has a hole 5 at the top for venting carbon dioxide produced by the anode reaction.

[0012] Furthermore, the anode diffusion layer 8-1 is hydrophilically treated, and the polyvinyl alcohol film 8-6 is insoluble in water and / or methanol at the operating temperature.

[0013] Furthermore, the dimensions of the cathode and anode flow fields are equal. Changing the width of oxygen channel 9-1 and ridge 9-2 can alter the reactant flow rate at the cathode. Changing the width of methanol channel 6-1 and ridge 6-2 can alter the reactant flow rate at the anode.

[0014] A method for adding fuel to the fuel storage chamber of a passive direct methanol fuel cell, characterized by comprising the following steps:

[0015] Step 1: Remove the methanol solution storage chamber 1 and the perforated plate 3 together;

[0016] Step 2: Remove the perforated plate 3 and replace it with a solid plate that is not permeable to methanol;

[0017] Step 3: Remove the bottom plate 1-1 of the methanol solution storage chamber, and then directly inject methanol;

[0018] Step 4: Reassemble the bottom plate 1-1 of the methanol solution storage chamber;

[0019] Step 5: Remove the replacement board and replace it with perforated board 3;

[0020] Step 6: Reassemble the battery.

[0021] Throughout all the above steps, the opening should be kept facing upwards to prevent fuel leakage or outflow.

[0022] This invention proposes a passive direct methanol fuel cell structure that enhances the cathode water-to-anode capability. This structure improves the cathode water-to-anode capability by returning water generated at the cathode to the anode, solving the cathode flooding problem and alleviating anode water shortage; it also reduces the anode methanol concentration, mitigating anode methanol permeation and slowing anode catalyst poisoning; it ensures the water content of the proton exchange membrane; and it increases the fuel cell's output power, energy conversion efficiency, and lifespan. This allows the direct methanol fuel cell to operate normally using higher concentration methanol solutions or pure methanol as fuel, increasing the battery's total power generation. The use of a fully sealed fuel storage chamber avoids fuel leakage problems. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the passive direct methanol fuel cell structure of the present invention, which enhances the ability of cathode water to replenish anode.

[0024] In the diagram: 1. Methanol solution storage chamber; 2. Pervaporation membrane; 3. Perforated plate; 4. Vapor chamber; 5. Carbon dioxide emission port; 7. Insulating gasket; 6. Anode current collector; 8. Composite membrane electrode; 9. Cathode current collector; 10. Cathode air self-breathing chamber; 11. Cathode water management layer; 12. Connection hole.

[0025] Figure 2 This is a schematic diagram of the structure of the methanol solution storage chamber 1 in the passive direct methanol fuel cell of the present invention, which enhances the ability of cathode water to replenish anode.

[0026] In the diagram: 1-1 bottom plate of methanol solution storage chamber; 1-2 side wall of methanol solution storage chamber; 1-3 tank.

[0027] Figure 3 This is a schematic diagram of the front structure of the passive direct methanol fuel cell anode current collector plate for enhancing the cathode water backfilling anode capability according to the present invention.

[0028] In the diagram: 6-1 Methanol channel; 6-2 Ridge; 6-3 Water flow channel; 6-4 Orifice for collecting current.

[0029] Figure 4 This is a schematic diagram of the back structure of the anode current collector of a passive direct methanol fuel cell, which enhances the cathode water backfilling capability of the present invention.

[0030] Figure 5 This is a front view schematic diagram of the passive direct methanol fuel cell composite membrane electrode structure for enhancing the cathode water backfilling anode capability according to the present invention.

[0031] Figure 6 These are cross-sectional and partially enlarged views of the passive direct methanol fuel cell composite membrane electrode assembly with enhanced cathode water backfilling capability according to the present invention.

[0032] In the figure: 8-1 Anode diffusion layer; 8-2 Anode catalyst layer; 8-3 Proton exchange membrane; 8-4 Cathode catalyst layer; 8-5 Cathode diffusion layer; 8-6 Polyvinyl alcohol membrane.

[0033] Figure 7 This is a schematic diagram of the cathode current collector structure of the passive direct methanol fuel cell that enhances the cathode water backfilling anode capability according to the present invention.

[0034] In the diagram: 9-1 Oxygen channel; 9-2 Ridge; 9-3 Orifice for collecting current.

[0035] Figure 8 This is a schematic diagram of the cathode air self-breathing chamber structure of the passive direct methanol fuel cell that enhances the cathode water backfilling anode capability according to the present invention.

[0036] In the diagram: 10-1 self-breathing through hole; 10-2 groove. Detailed Implementation

[0037] like Figure 1 The passive direct methanol fuel cell shown is an enhanced cathode water-to-anode anode anode anode. It includes a methanol solution storage chamber 1, a perforated plate 3, a vapor chamber 4, an insulating gasket 7, an anode current collector 6, a composite membrane electrode 8, a cathode current collector 9, and a cathode air self-breathing chamber 10. The components are connected and fixed to each other by means of insulating bolts and nuts through holes 12.

[0038] like Figure 5 , Figure 6 The composite membrane electrode 8 shown comprises six parts: an anode diffusion layer 8-1, an anode catalyst layer 8-2, a proton exchange membrane 8-3, a cathode catalyst layer 8-4, a cathode diffusion layer 8-5, and a polyvinyl alcohol membrane 8-6. The anode diffusion layer 8-1, anode catalyst layer 8-2, proton exchange membrane 8-3, cathode catalyst layer 8-4, and cathode diffusion layer 8-5 are of equal length and width, and are sequentially pressed together. The polyvinyl alcohol membrane 8-6 is entirely on the same plane as the anode diffusion layer 8-1, anode catalyst layer 8-2, proton exchange membrane 8-3, cathode catalyst layer 8-4, and cathode diffusion layer 8-5, with the polyvinyl alcohol membrane 8-6 on the periphery and the anode diffusion layer 8-1, anode catalyst layer 8-2, proton exchange membrane 8-3, cathode catalyst layer 8-4, and cathode diffusion layer 8-5 in the center. The inner side boundary of the polyvinyl alcohol membrane 8-6 is bonded to the outer side boundary of each layer in the center using Nafion emulsion, ensuring a tight connection without gaps. The thickness of the polyvinyl alcohol membrane 8-6 is equal to the overall thickness of the other five parts, preventing reactants from leaking from the side. Changing the cathode flow field area and the area of ​​the cathode diffusion layer 8-5 can change the effective area of ​​the polyvinyl alcohol membrane 8-6 by the difference between the two, thereby changing the water flow rate from the cathode through the composite membrane electrode 8 to the anode under the influence of the concentration gradient.

[0039] like Figure 7 The cathode current collector 9 shown includes an oxygen channel 9-1, a ridge 9-2, and a current collection hole 9-3. The oxygen channel 9-1 and the ridge 9-2 are parallel to each other and arranged alternately to form the cathode flow field. The oxygen channel 9-1 is bi-directional, with a channel length greater than the length of the cathode diffusion layer 8-5, and the total width of the cathode flow field greater than the width of the cathode diffusion layer 8-5. An insulating gasket 7 is located on the side of the cathode current collector 9 near the cathode air intake chamber 10 to prevent current from passing through.

[0040] like Figure 3 , Figure 4The anode current collector 6 shown includes a methanol channel 6-1, a ridge 6-2, a water channel 6-3, and a current collection hole 6-4. The side closest to the composite membrane electrode 8 (referred to as the front side) has the methanol channel 6-1, ridge 6-2, and water channel 6-3, while the opposite side (referred to as the back side) has the methanol channel 6-1. The depth of the water channel 6-3 formed by slotting on the front side is half the thickness of the anode current collector 6. The unslotted portion within all channels is called the ridge 6-2. The water channels 6-3 and ridges 6-2 are parallel to each other and staggered. The two ends of each parallel water channel 6-3 are connected by a vertical channel. Two through slots are cut in the center of a portion of the ridges 6-2 to form the methanol channel 6-1. The length of the methanol channel 6-1 is equal to the length of the anode diffusion layer 8-1, and the width of the region containing all methanol channels 6-1 is equal to the width of the anode diffusion layer 8-1. The methanol channel 6-1, ridge 6-2, and water channel 6-3 together form the anode flow field. An insulating gasket 7 is placed between the anode current collector 6 and the vapor chamber 4 to prevent current from passing through.

[0041] When water generated in the cathode catalyst layer 8-4 leaves the cathode diffusion layer 8-5, it first enters the central part of the oxygen channel 9-1, then flows towards both ends along the flow channel. Under the control of the water concentration and pressure differences on both sides of the polyvinyl alcohol membrane 8-6, it diffuses through the polyvinyl alcohol membrane 8-6. Water passing through the polyvinyl alcohol membrane 8-6 first reaches the two ends of the water flow channel 6-3, and flows towards the center along the flow channel. After passing through the hydrophilic anode diffusion layer 8-1, it reaches the anode catalyst layer 8-2 to participate in the electrode reaction and is continuously consumed. In this process, since water is continuously consumed as a reactant in the anode catalyst layer 8-2, a stable water concentration gradient can be maintained between the components, providing the driving force for water in the central part of the oxygen channel 9-1 to pass through the polyvinyl alcohol membrane 8-6. The hydrophobic cathode water management layer 11 completely covers the cathode flow field and has a porous structure. Without affecting the air entering the cathode, it prevents water from passing through the cathode, reduces the ability of cathode water to be discharged from the battery, and ensures water circulation within the battery.

[0042] like Figure 1 The vapor chamber 4 shown has a hole 5 at the top for venting carbon dioxide produced by the anodic reaction. The vapor chamber 4 can be made of transparent plexiglass to allow observation of the vaporization and flow of methanol through the pervaporation membrane 2, as well as the emission of carbon dioxide.

[0043] like Figure 2The methanol solution storage chamber 1 shown includes a bottom plate 1-1 and a side wall 1-2. An insulating gasket 7 is placed between the bottom plate 1-1 and the side wall 1-2 to prevent leakage between the hard contact surfaces. On the surface of the methanol solution storage chamber opposite to the bottom plate 1-1, there is a groove 1-3 of the same size as the pervaporation membrane, used to place and fix the position of the pervaporation membrane 2. On the other side of the pervaporation membrane 2 is a perforated plate 3, which presses the pervaporation membrane 2 tightly within the groove 1-3. Changing the diameter of the holes on the perforated plate 3 changes the porosity of the perforated plate, thereby adjusting the methanol vapor flow rate through the perforated plate 3. When injecting methanol into the methanol solution storage chamber 1, the methanol solution storage chamber 1 and the perforated plate 3 can be removed. The perforated plate 3 can be replaced with a metal plate that does not allow methanol to pass through. The bottom plate 1-1 of the methanol solution storage chamber can then be removed, and methanol can be injected directly. Afterwards, the bottom plate 1-1 of the methanol solution storage chamber can be reassembled, the replaced metal plate can be removed and replaced with the perforated plate 3 again, and the battery can be reassembled. The purpose of this is to avoid creating a hole in the methanol solution storage chamber for injecting methanol solution and the resulting sealing problems.

Claims

1. A passive direct methanol fuel cell with enhanced cathode water-to-anode recharge capability, characterized in that, The battery is a single cell of a proton exchange membrane fuel cell. Its structure includes a methanol solution storage chamber (1), a perforated plate (3), a vapor chamber (4), an insulating gasket (7), an anode current collector (6), a composite membrane electrode (8), a cathode current collector (9), and a cathode air self-breathing chamber (10). The centers of each component are coaxial, and each component is connected and fixed by insulating bolts and nuts through holes (12) at the four corners and sides. There is a groove (1-3) on the surface of the methanol solution storage chamber (1) adjacent to the perforated plate (3). A pervaporation membrane (2) is placed in the groove (1-3). The size and depth of the groove (1-3) are equal to the size of the pervaporation membrane (2). Changing the porosity of the perforated plate (3) can change the flow rate of the anode reactant. The composite membrane electrode (8) comprises six parts: an anode diffusion layer (8-1), an anode catalyst layer (8-2), a proton exchange membrane (8-3), a cathode catalyst layer (8-4), a cathode diffusion layer (8-5), and a polyvinyl alcohol membrane (8-6). The anode diffusion layer (8-1), anode catalyst layer (8-2), proton exchange membrane (8-3), cathode catalyst layer (8-4), and cathode diffusion layer (8-5) are of equal length and width, and are sequentially pressed together. The polyvinyl alcohol membrane (8-6) is located around the perimeter, while the anode diffusion layer (8-1), anode… The catalyst layer (8-2), proton exchange membrane (8-3), cathode catalyst layer (8-4), and cathode diffusion layer (8-5) form a whole at the center. The inner side boundary of the polyvinyl alcohol membrane (8-6) is bonded to the outer side boundary of each layer at the center with Nafion emulsion, forming a tight connection without gaps. The thickness of the polyvinyl alcohol membrane (8-6) is equal to the thickness of the whole formed by the anode diffusion layer (8-1), anode catalyst layer (8-2), proton exchange membrane (8-3), cathode catalyst layer (8-4), and cathode diffusion layer (8-5). The cathode current collector (9) includes an oxygen channel (9-1), a ridge (9-2), and a hole (9-3) for collecting current; the oxygen channel (9-1) and the ridge (9-2) are parallel to each other and staggered to form a cathode flow field; the oxygen channel (9-1) is open on both sides, and the channel length is greater than the length of the cathode diffusion layer (8-5), and the total width of the cathode flow field is greater than the width of the cathode diffusion layer (8-5); The anode current collector (6) includes a methanol channel (6-1), a ridge (6-2), a water channel (6-3), and a current collection hole (6-4). The side closest to the composite membrane electrode (8) is called the front side, which has the methanol channel (6-1), ridge (6-2), and water channel (6-3). The side opposite the front side is called the back side, which has the methanol channel (6-1). The depth of the water channel (6-3) formed by the groove on the front side is half the thickness of the anode current collector (6). The ungrooved part within all channels is called the ridge (6-2). The water channel (6-3) and the ridge (6-2) are mutually... The parallel water channels (6-3) are arranged in an alternating pattern. Each parallel water channel (6-3) is connected at both ends by a vertical channel. The length of the water channel (6-3) is greater than the length of the anode diffusion layer (8-1). Two through slots are opened in the center of a portion of the ridge (6-2) to serve as methanol channels (6-1). The length of the methanol channel (6-1) is equal to the length of the anode diffusion layer (8-1), and the width of the region containing all methanol channels (6-1) is equal to the width of the anode diffusion layer (8-1). The methanol channels (6-1), ridges (6-2), and water channels (6-3) together form the anode flow field. The cathode air breathing chamber (10) has a breathing hole (10-1) and a groove (10-2); the cathode water management layer (11) is placed in the groove (10-2); the area of ​​the breathing hole (10-1) is smaller than the area of ​​the cathode water management layer (11); the size and depth of the groove (10-2) are equal to those of the cathode water management layer (11).

2. A passive direct methanol fuel cell with enhanced cathode water-to-anode capability according to claim 1, characterized in that, The vapor chamber (4) is made of transparent plexiglass and has a hole (5) at the top for venting carbon dioxide produced by the anode reaction.

3. A passive direct methanol fuel cell with enhanced cathode water-to-anode capability according to claim 1, characterized in that, The anode diffusion layer (8-1) is hydrophilically treated, and the polyvinyl alcohol film (8-6) is insoluble in water and / or methanol at the operating temperature.

4. A passive direct methanol fuel cell with enhanced cathode water-to-anode capability according to claim 1, characterized in that, The cathode flow field and the anode flow field are of equal size; changing the width of the oxygen channel (9-1) and the ridge (9-2) can change the reactant flow rate at the cathode; changing the width of the methanol channel (6-1) and the ridge (6-2) can change the reactant flow rate at the anode.

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