Membrane electrode for high-temperature proton exchange membrane fuel cell and preparation method and equipment thereof

Abstract

This invention discloses a membrane electrode assembly (MEA) for a high-temperature proton exchange membrane fuel cell and its preparation method and equipment. The MEA includes a configuration box with a sealing plate fixedly connected inside. A motor is fixedly mounted on the lower inner wall of the configuration box, and a rotating rod is fixedly connected to the output end of the motor. The rotating rod passes through the sealing plate, and multiple fixed shafts are arranged on the outer side of the rotating rod, each shaft connected to the rotating rod. Multiple shearing blades are fixedly connected to the side wall of each fixed shaft, and an ultrasonic vibrator is fixedly mounted on the side wall of each fixed shaft. This invention uses a catalyst with a high precious metal content, which is beneficial for reducing the coating thickness while maintaining the same precious metal content, thereby improving coating quality and contributing to improved battery performance. While reducing the total number of catalytic active sites, it also reduces the coating thickness. Combined with adjustments to subsequent processes, this ensures good battery performance.

Description

[0001] This application is a divisional application of the patent filed on July 18, 2023, with application number 2023108818578, entitled "Membrane Electrode for High-Temperature Proton Exchange Membrane Fuel Cell and its Preparation Method and Equipment". Technical Field

[0002] This invention relates to the field of membrane electrodes for fuel cells, and more particularly to membrane electrodes for high-temperature proton exchange membrane fuel cells, as well as their preparation methods and equipment. Background Art

[0003] Fuel cells, as a crucial application of hydrogen energy, have attracted significant attention. The membrane electrode assembly (MEA), a core component of fuel cells, directly impacts the performance, cost, and lifespan of the entire fuel cell stack due to its fabrication process. Currently, there is considerable research on MEAs for low-temperature proton exchange membrane fuel cells, but very little attention has been paid to MEAs for high-temperature proton exchange membrane fuel cells.

[0004] Unlike the membrane electrode structure of low-temperature proton exchange membrane fuel cells (PEMFCs), the catalyst layer of the membrane electrode in high-temperature PEMFCs is generally designed on the gas diffusion layer, rather than on both sides of the proton exchange membrane. Therefore, the fabrication of the membrane electrode for high-temperature PEMFCs often employs the gas diffusion electrode (GDE) process, rather than the catalyst coated membrane (CCM) process.

[0005] However, the traditional GDE process suffers from high resistance and low power density, which severely restricts the application of high-temperature proton exchange membrane fuel cells. Furthermore, in order to ensure the catalytic activity of the membrane electrode, the catalyst dosage of previous high-temperature proton exchange membrane fuel cells was very high (approximately 2-5 mg / cm2), resulting in high battery manufacturing costs. Therefore, there is an urgent need for a new preparation process that can achieve better battery performance with lower catalyst dosage. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies, such as high resistance, low power density, which severely restrict the application of high-temperature proton exchange membrane fuel cells, and high catalyst consumption, which keeps the battery manufacturing cost high. The invention proposes a membrane electrode for high-temperature proton exchange membrane fuel cells, as well as its preparation method and equipment.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An apparatus for preparing membrane electrode assemblies (MEAs) for high-temperature proton exchange membrane fuel cells includes a configuration box. A sealing plate is fixedly connected inside the configuration box. A motor is fixedly mounted on the lower inner wall of the configuration box. A rotating rod is fixedly connected to the output end of the motor and passes through the sealing plate. Multiple fixed shafts are arranged on the outer side of the rotating rod and are connected to the rotating rod. Multiple shearing blades are fixedly connected to the side wall of each fixed shaft. An ultrasonic vibrator is fixedly mounted on the side wall of each fixed shaft. A connecting shaft is located at the top of each fixed shaft, and a fixed gear is fixedly connected to the top of each connecting shaft. A fixed gear ring is fixedly connected to the upper inner wall of the configuration box, and the fixed gear ring meshes with each fixed gear.

[0009] Preferably, a connecting cavity is provided at the bottom of each fixed shaft, a movable plate is slidably connected inside each connecting cavity, a connecting rod is fixedly connected to the bottom of each movable plate, each connecting rod extends through the lower inner wall of the connecting cavity to the outside of the fixed shaft, a connecting pad is fixedly connected to the bottom of each connecting rod, the bottom of each connecting pad is in contact with the top of the sealing plate, a connecting spring is fixedly connected to the top of each movable plate, and the end of each connecting spring away from the corresponding movable plate is fixedly connected to the upper inner wall of the connecting cavity, the surface of the connecting pad is smooth, and the connecting pad is made of hard rubber.

[0010] Preferably, a sliding groove is provided at the top end of the fixed shaft, the connecting shaft extends through the upper inner wall of the sliding groove and into the interior of the sliding groove, and the connecting shaft is slidably connected to the inner wall of the sliding groove. An elastic rod is fixedly connected to the bottom end of the connecting shaft, and the end of the elastic rod away from the connecting shaft is fixedly connected to the lower inner wall of the sliding groove.

[0011] Preferably, multiple mounting rods are fixedly connected to the side wall of the rotating rod, each mounting rod corresponds to a fixed shaft, and a mounting sleeve is fixedly connected to the end of each mounting rod. Each mounting sleeve is rotatably sleeved on the outside of a fixed shaft.

[0012] A method for preparing a membrane electrode for a high-temperature proton exchange membrane fuel cell includes the following steps:

[0013] S1, a membrane electrode slurry is prepared by mixing and stirring a catalyst, ultrapure water, solvent and resin. The catalyst is a Pt-based noble metal carbon supported catalyst with a noble metal content of more than 40%. The ratio of solvent to ultrapure water is (1-4):(6-9). The solid content of the membrane electrode slurry is 5-20%.

[0014] S2, the membrane electrode slurry is dispersed and the temperature is controlled at 5-15℃ so that the D50 particle size of the membrane electrode slurry is 0.5-1.5 micrometers. Then the membrane electrode slurry is coated on the gas diffusion layer by slit coating to obtain a gas diffusion coating. After drying, a gas diffusion electrode with a noble metal content of 0.5-2 mg / cm2 is obtained.

[0015] S3, the two gas diffusion electrodes are placed on both sides of the high-temperature proton exchange membrane, and together with the sealing element, they are combined by hot pressing, bonding or pasting to obtain the high-temperature proton exchange membrane electrode.

[0016] Preferably, the thickness of the gas diffusion coating is 0.05-0.75 mm, the drying temperature is 50-100℃, and the time is 1-15 min.

[0017] Preferably, the solvent is at least one of methanol, ethanol, diethyl ether, n-propanol, and isopropanol, the resin is at least one of PTFE, PVDF, PBI, Nafion, and PVA, and the dispersion treatment is at least one of ultrasonication, high-speed shearing, high-pressure shearing, and high-pressure microfluidics.

[0018] Preferably, the anode and cathode end plates are placed on both sides of the high-temperature proton exchange membrane electrode, and together with the sealing components, they are mechanically pressed together to assemble a high-temperature proton exchange membrane fuel cell.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. Using catalysts with higher precious metal content is beneficial for reducing coating thickness under the same precious metal content, thereby improving coating quality and helping to improve battery performance. Although reducing the amount of catalyst reduces the total number of catalytic active sites, it also reduces coating thickness. With the adjustment of other processes, good battery performance can be guaranteed.

[0021] 2. Using a formulation with a low solvent-to-ultrapure water ratio is beneficial for mixing and stirring the membrane electrode slurry, and it is safer to prepare the slurry than a formulation with a high solvent-to-ultrapure water ratio.

[0022] 3. The use of a low solvent and ultrapure water ratio formulation is beneficial to the uniformity of drying when the coating thickness is moderate.

[0023] 4. An ultrasonic shearing dispersion process is used to control the D50 particle size to approximately 0.5-1.5 micrometers, which is beneficial to improving battery performance.

[0024] 5. This device uses ultrasound to rotate the shear blade, which stirs and shears the particles in the solvent. Moreover, the shear blade also rotates on its own axis while rotating, which greatly improves the shearing effect. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the fabrication equipment for the membrane electrode of a high-temperature proton exchange membrane fuel cell proposed in this invention;

[0026] Figure 2 for Figure 1 Enlarged view of point A in the middle;

[0027] Figure 3 This is a three-dimensional structural diagram of the shear blade in the fabrication equipment for the membrane electrode of a high-temperature proton exchange membrane fuel cell proposed in this invention;

[0028] In the diagram: 1. Configuration box, 2. Sealing plate, 3. Motor, 4. Rotating rod, 5. Fixed shaft, 6. Shearing blade, 7. Connecting shaft, 8. Sliding groove, 9. Fixed gear, 10. Fixed gear ring, 11. Ultrasonic vibrator, 12. Connecting rod, 13. Connecting cavity, 14. Moving plate, 15. Connecting spring, 16. Connecting pad, 17. Mounting rod, 18. Mounting sleeve. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0030] Reference Figures 1-3A fabrication apparatus for membrane electrode assemblies (MEAs) in high-temperature proton exchange membrane fuel cells includes a configuration box 1. A sealing plate 2 is fixedly connected inside the configuration box 1. A motor 3 is fixedly mounted on the lower inner wall of the configuration box 1. A rotating rod 4 is fixedly connected to the output end of the motor 3. The rotating rod 4 passes through the sealing plate 2. Multiple fixed shafts 5 are arranged on the outer side of the rotating rod 4, and each fixed shaft 5 is connected to the rotating rod 4. Multiple shearing blades 6 are fixedly connected to the side wall of each fixed shaft 5. An ultrasonic vibrator 11 is fixedly mounted on the side wall of each fixed shaft 5. A connecting shaft 7 is located at the top of each fixed shaft 5, and a fixed gear 9 is fixedly connected to the top of each connecting shaft 7. A fixed gear 9 is fixedly mounted on the upper inner wall of the configuration box 1. A fixed gear ring 10 is connected, and the fixed gear ring 10 meshes with each fixed gear 9. The membrane electrode slurry is fed into the preparation box 1. The motor 3 is started, and the output end of the motor 3 drives the rotating rod 4 to rotate, thereby causing multiple fixed rods 5 to rotate around the rotating rod 4, which in turn drives multiple shear blades 6 to rotate. At the same time, when the shear blades 6 rotate, the connecting shaft 7 also rotates, which drives the fixed gears 9 to rotate around the rotating rod 4. Under the action of the fixed gear ring 10, the fixed gears 9 will also rotate on their own axis while revolving, thereby causing the shear blades 6 to rotate on their own axis. Moreover, after the ultrasonic vibrator 11 is started, it will cause the shear blades 6 to vibrate violently, stirring and shearing the solvent, so that the various components in the membrane electrode slurry are evenly mixed.

[0031] Each fixed shaft 5 has a connecting cavity 13 at its bottom. A movable plate 14 is slidably connected inside each connecting cavity 13. A connecting rod 12 is fixedly connected to the bottom of each movable plate 14. Each connecting rod 12 extends through the lower inner wall of the connecting cavity 13 and out to the outside of the fixed shaft 5. A connecting pad 16 is fixedly connected to the bottom of each connecting rod 12. The bottom of each connecting pad 16 is in contact with the top of the sealing plate 2. A connecting spring 15 is fixedly connected to the top of each movable plate 14. The end of each connecting spring 15 away from the corresponding movable plate 14 is fixedly connected to the upper inner wall of the connecting cavity 13. The surface of the connecting pad 16 is smooth and made of hard rubber. The connecting rod 12 and the movable plate 14 cooperate to enable the fixed shaft 5 to vibrate, while the connecting spring 15 amplifies the vibration and further enhances the vibration. The connecting pad 16 protects the connecting rod 12 from damage.

[0032] A sliding groove 8 is provided at the top of the fixed shaft 5. The connecting shaft 7 extends through the upper inner wall of the sliding groove 8 and is slidably connected to the inner wall of the sliding groove 8. An elastic rod is fixedly connected to the bottom of the connecting shaft 7. The end of the elastic rod away from the connecting shaft 7 is fixedly connected to the lower inner wall of the sliding groove 8, so that the vibration of the fixed shaft 5 will not affect the connecting shaft 7.

[0033] Multiple mounting rods 17 are fixedly connected to the side wall of the rotating rod 4. Each mounting rod 17 corresponds to a fixed shaft 5. Each mounting rod 17 has a mounting sleeve 18 fixedly connected to its end. Each mounting sleeve 18 is rotatably sleeved on the outside of a fixed shaft 5, connecting the rotating rod 4 to the fixed shaft 5.

[0034] A membrane electrode assembly for a high-temperature proton exchange membrane fuel cell and its preparation method, comprising the following steps:

[0035] S1, a membrane electrode slurry is prepared by mixing and stirring the catalyst, ultrapure water, solvent and resin. The catalyst is a Pt-based noble metal carbon supported catalyst with a noble metal content greater than 40%. The ratio of solvent to ultrapure water is (1-4):(6-9). The solid content of the membrane electrode slurry is 5-20%. Methanol, ethanol, diethyl ether, n-propanol and isopropanol can be used as solvents. PTFE, PVDF, PBI, Nafion and PVA can be used as resins.

[0036] S2, the membrane electrode slurry is dispersed and the temperature is controlled at 5-15℃ so that the D50 particle size of the membrane electrode slurry is 0.5-1.5 micrometers. Then the membrane electrode slurry is coated on the gas diffusion layer by slit coating to obtain a gas diffusion coating. After drying, a gas diffusion electrode with a noble metal content of 0.5-2 mg / cm2 is obtained.

[0037] S3, the two gas diffusion electrodes are placed on both sides of the high-temperature proton exchange membrane, and together with the sealing element, they are combined by hot pressing, bonding or pasting to obtain the high-temperature proton exchange membrane electrode.

[0038] The thickness of the gas diffusion coating is 0.05-0.75 mm; the drying temperature is 50-100℃ and the time is 1-15 min; the dispersion treatment is ultrasonic shearing.

[0039] Example 1: Refer to Figures 1-3 ,

[0040] Preparation of low loading, low solvent and ultrapure water ratio, high noble metal content catalyst, and ultra-small particle size: (1) Mix 46% Pt / C catalyst, ultrapure water, isopropanol and PTFE resin in a ratio of 2:21:9:1 to prepare membrane electrode slurry.

[0041] (2) The membrane electrode slurry is subjected to ultrasonic crushing and dispersion treatment for 30 minutes, with the temperature controlled at 10°C;

[0042] (3) The dispersed membrane electrode slurry is coated onto the gas diffusion layer using a slit coater and the coating thickness is controlled to be 0.2-0.4 mm. Then, it is dried at 80°C for 10 minutes. After drying, a gas diffusion electrode with a noble metal content of about 1 mg / cm2 is obtained.

[0043] Example 2: Refer to Figures 1-3 ,

[0044] Preparation of low loading, low solvent and ultrapure water ratio, high noble metal content catalyst, and small particle size: (1) Mix 46% Pt / C catalyst, ultrapure water, isopropanol and PTFE resin in a ratio of 2:21:9:1 to prepare membrane electrode slurry.

[0045] (2) The membrane electrode slurry is ultrasonically dispersed for 30 minutes, and the temperature is controlled at 10℃; (3) The dispersed membrane electrode slurry is coated onto the gas diffusion layer using a slit coater and the coating thickness is controlled at 0.2-0.4 mm. Then, it is dried at 80℃ for 10 minutes. After drying, a gas diffusion electrode with a noble metal content of about 1 mg / cm2 is obtained.

[0046] Example 3: Refer to Figures 1-3 ,

[0047] Preparation of low loading, low solvent and ultrapure water ratio, low precious metal content catalyst, and ultra-small particle size: (1) 20% Pt / C catalyst, ultrapure water, isopropanol and PTFE resin were mixed and stirred in a ratio of 1.2:15.9:6.8:1 to prepare membrane electrode slurry;

[0048] (2) The membrane electrode slurry is subjected to ultrasonic crushing and dispersion treatment for 30 minutes, with the temperature controlled at 10°C;

[0049] (3) The dispersed membrane electrode slurry was coated onto the gas diffusion layer using a slit coater and the coating thickness was controlled to be 0.8-1.0 mm. Then, it was dried at 80°C for 15 minutes. After drying, a gas diffusion electrode with a Pt loading of about 1 mg / cm2 was obtained.

[0050] Clearly, for the same platinum loading requirement, the coating thickness is much thicker when using 20% ​​catalyst than when using 46% Pt / C catalyst.

[0051] Example 4: Refer to Figures 1-3 ,

[0052] Low loading, typical solvent to ultrapure water ratio, high noble metal content catalyst, and ultra-small particle size preparation:

[0053] (1) A membrane electrode slurry was prepared by mixing and stirring 46% Pt / C catalyst, ultrapure water, isopropanol and PTFE resin in a ratio of 2:9:21:1.

[0054] (2) The membrane electrode slurry is subjected to ultrasonic crushing and dispersion treatment for 30 minutes, with the temperature controlled at 10°C;

[0055] (3) The dispersed membrane electrode slurry is coated onto the gas diffusion layer using a slit coater and the coating thickness is controlled to be 0.2-0.4 mm. Then, it is dried at 80°C for 10 minutes. After drying, a gas diffusion electrode with a noble metal content of about 1 mg / cm2 is obtained.

[0056] Example 5: Refer to Figures 1-3 ,

[0057] High loading, general solvent to ultrapure water ratio, low precious metal content catalyst, small particle size preparation: (1) Mix 20% Pt / C catalyst, ultrapure water, isopropanol and PTFE resin in a ratio of 1.2:14:9:1 to prepare membrane electrode slurry;

[0058] (2) The membrane electrode slurry is ultrasonically dispersed for 30 minutes, and the temperature is controlled at 10℃; (3) The dispersed membrane electrode slurry is coated onto the gas diffusion layer using a slit coater and the coating thickness is controlled at 1.2-1.5 mm. Then, it is dried at 80℃ for 10 minutes. After drying, a gas diffusion electrode with a noble metal content of about 1.5 mg / cm2 is obtained.

[0059] In this invention, a membrane electrode slurry is prepared by mixing and stirring a catalyst, ultrapure water, a solvent, and a resin. The catalyst is a Pt-based noble metal carbon-supported catalyst with a noble metal content greater than 40%. The ratio of the solvent to ultrapure water is (1-4):(6-9). The solid content of the membrane electrode slurry is 5-20%. The membrane electrode slurry is dispersed and then introduced into a preparation tank 1. The motor 3 is started, and the output end of the motor 3 drives the rotating rod 4 to rotate, thereby causing multiple fixed rods 5 to rotate around the rotating rod 4. This causes multiple shear blades 6 to rotate accordingly. Simultaneously, when the shear blades 6 rotate, the connecting shaft 7 rotates, causing the fixed gear 9 to rotate around the rotating rod 4. Under the action of the fixed gear ring 10, the fixed gear 9 also rotates on its own axis while revolving, thereby causing the shear blades 6 to rotate. Moreover, after the ultrasonic vibrator 11 is started, the shearing blade 6 vibrates violently with the cooperation of the connecting rod 12 and the moving plate 14. The connecting spring 15 can amplify the vibration and further enhance the vibration, stirring and shearing the solvent, so that the various components in the solvent are evenly mixed. The temperature is controlled at 5-15℃, so that the particle size of the membrane electrode slurry D50 is 0.5-1.5 micrometers. Then, the membrane electrode slurry is coated on the gas diffusion layer by slit coating to obtain a gas diffusion coating. After drying, a gas diffusion electrode with a precious metal content of 0.5-2 mg / cm2 is obtained. The two gas diffusion electrodes are placed on both sides of the high-temperature proton exchange membrane and combined with the sealing element by hot pressing, bonding or pasting to obtain the high-temperature proton exchange membrane electrode.

[0060] Two gas diffusion electrodes prepared in Example 1, each 5*5cm2, were placed on both sides of the high-temperature proton exchange membrane and assembled together with the sealing element by hot pressing to form a membrane electrode. Then, the membrane electrode was assembled together with the electrode plate, end plate and sealing element and other accessories to form a high-temperature proton exchange membrane fuel cell, which was designated as battery 1, and its performance was tested.

[0061] Using the same method, the gas diffusion electrodes prepared in Example 2 to the comparative example were assembled into high-temperature proton exchange membrane fuel cells, and labeled as cells 2, 3, 4 and 5 respectively, and their performance was tested.

[0062] The test results are shown below:

[0063] Voltage (V) at 0.2 electrical density Maximum power density (W / cm2) Battery 1 0.65 0.45 Battery 2 0.63 0.38 Battery 3 0.62 0.36 Battery 4 0.63 0.4 Battery 5 0.64 0.38

[0064] Clearly, the battery 1 prepared by Example 1 exhibits a significantly higher power density than a typical battery (less than 0.4 W / cm2).

[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a membrane electrode for a high-temperature proton exchange membrane fuel cell, characterized in that, It consists of the following steps: S1, a membrane electrode slurry is prepared by mixing and stirring a catalyst, ultrapure water, solvent and resin. The catalyst is a Pt-based noble metal carbon supported catalyst with a noble metal content of more than 40%. The ratio of solvent to ultrapure water is (1-4):(6-9). The solid content of the membrane electrode slurry is 5-20%. S2, the membrane electrode slurry is dispersed and the temperature is controlled at 5-15℃ so that the D50 particle size of the membrane electrode slurry is 0.5-1.5 micrometers. Then the membrane electrode slurry is coated on the gas diffusion layer by slit coating to obtain a gas diffusion coating. After drying, a gas diffusion electrode with a noble metal content of 0.5-2 mg / cm2 is obtained. S3, the two gas diffusion electrodes are placed on both sides of the high-temperature proton exchange membrane, and together with the sealing element, they are combined by hot pressing, bonding or pasting to obtain the high-temperature proton exchange membrane electrode. Its further characteristic lies in that the preparation method employs the following equipment: including a configuration box, a sealing plate fixedly connected inside the configuration box, a motor fixedly mounted on the lower inner wall, a rotating rod fixedly connected to the output end of the motor, the rotating rod penetrating the sealing plate, multiple fixed shafts arranged on the outer side of the rotating rod, each fixed shaft being connected to the rotating rod, multiple shearing blades fixedly connected to the side wall of each fixed shaft, an ultrasonic vibrator fixedly mounted on the side wall of each fixed shaft, a connecting shaft at the top of each fixed shaft, a fixed gear fixedly connected to the top of each connecting shaft, and a fixed gear ring fixedly connected to the upper inner wall of the configuration box. It meshes with each fixed gear; a connecting cavity is provided at the bottom of the interior of each fixed shaft, a movable plate is slidably connected inside each connecting cavity, a connecting rod is fixedly connected to the bottom of each movable plate, each connecting rod extends through the lower inner wall of the connecting cavity to the outside of the fixed shaft, a connecting pad is fixedly connected to the bottom of each connecting rod, the bottom of each connecting pad is in contact with the top of the sealing plate, a connecting spring is fixedly connected to the top of each movable plate, and the end of each connecting spring away from the corresponding movable plate is fixedly connected to the upper inner wall of the connecting cavity, the surface of the connecting pad is smooth, and the connecting pad is made of hard rubber.

2. The method for preparing the membrane electrode for a high-temperature proton exchange membrane fuel cell according to claim 1, characterized in that, The thickness of the gas diffusion coating is 0.05-0.75 mm, and the drying treatment temperature is 50-100℃ for 1-15 min.

3. The method for preparing the membrane electrode for a high-temperature proton exchange membrane fuel cell according to claim 1, characterized in that, The solvent is at least one of methanol, ethanol, diethyl ether, n-propanol, and isopropanol; the resin is at least one of PTFE, PVDF, PBI, Nafion, and PVA; and the dispersion treatment is at least one of ultrasonication, high-speed shearing, high-pressure shearing, and high-pressure microfluidics.

4. A high-temperature proton exchange membrane fuel cell, characterized in that, Using the method for preparing the membrane electrode for a high-temperature proton exchange membrane fuel cell as described in claim 1, the anode and cathode end plates are respectively placed on both sides of the high-temperature proton exchange membrane electrode, and together with the sealing component, they are mechanically pressed together to assemble a high-temperature proton exchange membrane fuel cell.

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