Solid oxide electrolytic cell

Abstract

The invention discloses a solid oxide electrolytic cell, which belongs to the technical field of electrolytic cells, and comprises a bottom plate, a metal connecting piece, a sealing piece, a single electrolytic cell, a top plate and a fastening piece, the electrolytic cell is formed by alternately stacking a bottom plate, a plurality of metal connecting pieces, a plurality of sealing pieces, a plurality of single electrolytic cells and a top plate and is fixed by a fastening piece penetrating through the electrolytic cell and the bottom plate and the top plate, and a cathode gas inlet total channel, a cathode gas outlet total channel, a plurality of cathode gas grooves and a plurality of anode gas grooves are integrated in the metal connecting pieces. And the cathode gas tank is communicated with the cathode layer of the adjacent single electrolytic tank through the channel of the sealing element and is used for distributing water vapor to each single electrolytic tank and collecting hydrogen generated by electrolysis, so that pipelines and control parts are reduced, the system structure is remarkably simplified, the manufacturing cost and the maintenance complexity are reduced, and meanwhile, the overall reliability is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytic cells, and more particularly, to a solid oxide electrolytic cell. Background Art

[0002] A solid oxide electrolysis cell (SOEC) is an all-solid device that electrolyzes water into hydrogen and oxygen at a high temperature of 500 - 850 °C. Due to operating at high temperatures, it can rely on electrical energy and heat energy to break the hydrogen-oxygen bond, and part of the energy for water electrolysis can be obtained through heat energy, thereby reducing power consumption. Therefore, compared with alkaline and PEM electrolytic cells, it has higher electrochemical performance and electrolysis efficiency. Classified from the technical principle, SOEC can be divided into oxygen ion-conducting SOEC and proton-conducting SOEC, mainly focusing on oxygen ion-conducting SOEC. The electrolytic cell is the core component of the SOEC system, and its performance determines the efficiency, reliability, and lifespan of the system.

[0003] In the prior art, the publication number is CN113718277A, which discloses a self-heating electrolytic cell hydrogen production system, including an oxygen supply line that provides compressed air for the solid oxide electrolytic cell, a water supply line that provides water vapor for the solid oxide electrolytic cell, a hydrogen outlet line that exports hydrogen from the solid oxide electrolytic cell, and a water-gas separation device is provided at the end of the hydrogen outlet line. The gas outlet end of the water-gas separation device is connected to a gas storage tank, and the gas storage tank is connected to the water supply line through a water-gas mixing device. A first heat exchanger for heating water vapor is provided on the water supply line, and a second heat exchanger for heating air is provided on the oxygen supply line, and a heating device supplies heat to the first heat exchanger and the second heat exchanger respectively. By replacing the electric heating device with the first heat exchanger and the second heat exchanger, the potential safety hazards caused by using an electric heater can be eliminated, resource waste can be reduced, the hydrogen production efficiency can be improved, and the external power consumption can be reduced.

[0004] Although this device has many beneficial effects, there are still the following problems: Although this electrolytic cell hydrogen production system reduces resource waste, improves hydrogen production efficiency, and reduces external power consumption, traditional electrolytic cell designs usually include a total anode inlet channel and a total anode outlet channel. These channels not only increase the structural complexity of the electrolytic cell but may also lead to an increase in maintenance and repair costs. Summary of the Invention

[0005] (1) Technical Problems to be Solved

[0006] Aiming at the deficiencies of the prior art, the present invention provides a solid oxide electrolytic cell, which solves the above problems.

[0007] (2) Technical Solutions

[0008] To achieve the above object, the present invention provides the following technical solution: A solid oxide electrolyzer, including an electrolyzer composed of a bottom plate, a metal connector, a seal, a single electrolytic cell, a top plate, and a fastener. The electrolyzer is a flat multi-layer stacked structure, which is alternately laminated by the bottom plate, several metal connectors, several seals, several single electrolytic cells, and the top plate, and is fixed by a fastener passing through the bottom plate and the top plate of the electrolyzer. The metal connector integrates a cathode inlet main channel, a cathode outlet main channel, several cathode gas channels, and several anode gas channels. The cathode gas channels are connected to the cathode layer of the adjacent single electrolytic cell through the channels of the seal, for distributing water vapor to each single electrolytic cell and collecting the hydrogen generated by electrolysis. The anode gas channels are directly connected to the external environment, for discharging the oxygen generated by electrolysis. The electrolyzer has no independent anode inlet main channel and anode outlet main channel, and the oxygen on the anode side is directly discharged through the anode gas channels.

[0009] Preferably, the metal connector is a high-temperature conductive metal plate, and its surface is provided with a groove structure matching the single electrolytic cell. The cathode gas channels and the anode gas channels are radially or parallel-array distributed on the same plane of the metal connector. Among them, the cross-sectional area of the cathode gas channels is larger than that of the anode gas channels, and the depth of the anode gas channels is 1 / 3 to 1 / 2 of that of the cathode gas channels, so as to reduce the oxygen discharge resistance and optimize the hydrogen collection efficiency.

[0010] Preferably, the cathode inlet main channel and the cathode outlet main channel of the metal connector are respectively located at its two side edges, and are connected to each layer of cathode gas channels through vertical channels extending along the stacking direction. The anode gas channels are evenly distributed in the central area of the metal connector, and each anode gas channel is provided with a flared structure at its end, so as to enhance the oxygen diffusion rate and prevent local pressure accumulation.

[0011] Preferably, the seal is made of a ceramic matrix composite material, and its interior is embedded with through holes that perfectly match the cathode inlet main channel and the cathode outlet main channel of the metal connector. The thickness of the seal is 0.5 - 2 mm, and its surface is coated with a high-temperature oxidation-resistant coating to ensure airtightness and long-term stability at a working temperature of 500 - 850 °C.

[0012] Preferably, the single electrolytic cell is an oxygen ion-conducting solid oxide electrolytic cell, including a porous cathode layer, a dense electrolyte layer, and a porous anode layer. The cathode layer faces the cathode gas channels of the metal connector, and its surface is loaded with nickel-based. The anode layer faces the anode gas channels, and its surface is loaded with a perovskite-type oxide catalyst. The thickness of the electrolyte layer is 10 - 50 μm, and it is made of yttria-stabilized zirconia material.

[0013] Preferably, the fastener is a high-strength alloy bolt or a high-temperature resistant ceramic fixture, which passes through the positioning holes preset by the bottom plate and the top plate of the electrolytic cell, and applies uniform axial pressure through torque control, so that each layer of metal connectors, seals and single electrolytic cells are closely attached, and the contact resistance is less than 10 mΩ·cm 2 。

[0014] Preferably, the electrolytic cell is made of a nickel-based superalloy for the bottom plate and the top plate, and its surface is provided with positioning protrusions and grooves matching the shape of the metal connectors. The bottom of the bottom plate of the electrolytic cell is integrated with an insulating and heat-insulating layer, and the top of the top plate is provided with conductive terminals connected to an external power source to achieve a series or parallel circuit configuration of the electrolytic cells.

[0015] Preferably, the operating temperature of the electrolytic cell is 600 - 800 °C, the water vapor pressure introduced into the cathode inlet total channel is 0.1 - 0.5 MPa, the oxygen discharge pressure of the anode gas tank is at atmospheric pressure, the electrolysis efficiency of the electrolytic cell is ≥ 85%, and the voltage decay rate of a single electrolytic cell under the rated current density is less than 2% / 1000 hours.

[0016] Preferably, the number of stacked layers of the electrolytic cell is 10 - 40 layers, and each layer of single electrolytic cells is connected in series through the conductive characteristics of the metal connectors. The total output voltage is 20 - 200 V, the total height of the stacked structure is 50 - 300 mm, and the effective reaction area of each layer of single electrolytic cells is 100 - 1000 cm 2 。

[0017] Preferably, a one-way valve or a labyrinth type anti-backflow structure is provided at the outlet of the anode gas tank, and its material is a high-temperature resistant ceramic or a metal-ceramic composite material. The opening and closing pressure threshold of the anti-backflow structure is 0.05 - 0.1 MPa to prevent external gas from flowing back or impurities from entering the inside of the electrolytic cell, while allowing oxygen to freely discharge after the electrolysis reaction.

[0018] (III) Beneficial effects

[0019] Compared with the prior art, the present invention provides a solid oxide electrolytic cell, which has the following beneficial effects:

[0020] 1. For this solid oxide electrolytic cell, the electrolytic cell has no independent anode inlet / outlet total channels, and oxygen is directly discharged through the anode gas tank of the metal connectors, reducing pipelines and control components, significantly simplifying the system structure, reducing the manufacturing cost and maintenance complexity, and at the same time improving the overall reliability.

[0021] 2. For this solid oxide electrolyzer, the cross-sectional area of the cathode gas channel of the metal connector is larger than that of the anode gas channel, and it adopts a radial / parallel array distribution to optimize the flow paths of water vapor and hydrogen, reduce the pressure drop, and improve the electrolysis efficiency; the flared structure at the end of the anode gas channel enhances the oxygen diffusion rate and avoids local pressure accumulation.

[0022] 3. For this solid oxide electrolyzer, the seal is made of a ceramic matrix composite material with a thickness of 0.5 - 2 mm, and the surface is coated with a high-temperature oxidation-resistant coating to ensure long-term airtightness at 500 - 850 °C; the metal connectors and fasteners use high-temperature-resistant conductive alloys or ceramic clamps to withstand extreme working environments and reduce the risk of material aging.

[0023] 4. For this solid oxide electrolyzer, the cathode layer of a single electrolytic cell is loaded with a nickel-based catalyst, and the anode layer is loaded with a perovskite-type oxide catalyst. Combining with an oxygen ion-conducting electrolyte, it accelerates the dissociation of water vapor and the conduction of oxygen ions, achieving an electrolysis efficiency of ≥ 85% and reducing the power demand.

[0024] 5. For this solid oxide electrolyzer, a one-way valve or a labyrinth-type anti-backflow structure is set at the anode gas channel outlet, with an opening and closing threshold of 0.05 - 0.1 MPa, to prevent external gas backflow or impurity intrusion and ensure the safety and purity of the system.

[0025] 6. For this solid oxide electrolyzer, the number of stacked layers is 10 - 40 layers, the total output voltage is 20 - 200 V, the effective reaction area is 100 - 1000 cm 2 / layer, and the total height is 50 - 300 mm. The output power and reaction scale can be flexibly adjusted according to requirements to adapt to different application scenarios. Description of the Drawings

[0026] Figure 1 It is an assembly drawing of a solid oxide electrolyzer.

[0027] Figure 2 It is an exploded view of the battery unit of a solid oxide electrolyzer.

[0028] Figure 3 It is a rear view of the metal connector of a solid oxide electrolyzer.

[0029] In the figure: 1. The electrolyzer consists of a bottom plate; 2. Metal connector; 3. Seal; 4. Single electrolytic cell; 5. Top plate; 6. Fastener. Detailed Embodiments

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] Please refer to Figures 1-3 , the present invention provides a technical solution:

[0032] Embodiment 1:

[0033] A solid oxide electrolyzer includes an electrolyzer composed of a bottom plate 1, a metal connector 2, a seal 3, a single electrolytic cell 4, a top plate 5, and a fastener 6. The electrolyzer is a flat multi-layer stacked structure, which is alternately laminated by a bottom plate 1, a plurality of metal connectors 2, a plurality of seals 3, a plurality of single electrolytic cells 4, and a top plate 5, and is fixed by a fastener 6 passing through the bottom plate 1 and the top plate 5 of the electrolyzer. The metal connector 2 internally integrates a cathode inlet main channel, a cathode outlet main channel, a plurality of cathode gas channels, and a plurality of anode gas channels. The cathode gas channels are connected to the cathode layer of the adjacent single electrolytic cell 4 through the channels of the seal 3, and are used to distribute water vapor to each single electrolytic cell 4 and collect the hydrogen generated by electrolysis. The anode gas channels are directly connected to the external environment and are used to discharge the oxygen generated by electrolysis. The electrolyzer has no independent anode inlet main channel and anode outlet main channel, and the oxygen on the anode side is directly discharged through the anode gas channels.

[0034] Water vapor enters through the cathode inlet main channel at the bottom of the electrolyzer. This channel is located at one side edge of the metal connector 2. Subsequently, the water vapor is distributed to the cathode gas channels of each layer through the vertical channels. The cross-sectional area of the cathode gas channels is designed to be relatively large to optimize the distribution of water vapor and the electrolysis efficiency. In the cathode layer, the water vapor reacts with the nickel-based catalyst to undergo the electrolysis process, generating hydrogen and oxygen ions. The nickel-based catalyst promotes the dissociation of water vapor and the generation of hydrogen. The generated hydrogen is collected in the cathode gas channels and discharged from the electrolyzer through the cathode outlet main channel (located on the other side edge of the metal connector 2) for subsequent use or storage.

[0035] Embodiment 2:

[0036] Furthermore, the metal connector 2 is a high-temperature resistant conductive metal plate, and its surface is provided with a groove structure matching the single electrolytic cell 4. The cathode gas channels and the anode gas channels are radially or parallelly arrayed on the same plane of the metal connector 2. Among them, the cross-sectional area of the cathode gas channels is larger than that of the anode gas channels, and the depth of the anode gas channels is 1 / 3 to 1 / 2 of that of the cathode gas channels to reduce the oxygen emission resistance and optimize the hydrogen collection efficiency.

[0037] Furthermore, the cathode inlet main channel and the cathode outlet main channel of the metal connector 2 are respectively located at its two side edges, and are communicated with each layer of cathode gas grooves through vertical channels extending along the stacking direction. The anode gas grooves are evenly distributed in the central area of the metal connector 2, and each anode gas groove is provided with a flared structure at its end to enhance the oxygen diffusion rate and prevent local pressure accumulation.

[0038] Furthermore, the seal 3 is made of a ceramic matrix composite material, and through holes completely matching the cathode inlet main channel and the cathode outlet main channel of the metal connector 2 are embedded therein. The thickness of the seal 3 is 0.5 - 2 mm, and its surface is coated with a high-temperature oxidation-resistant coating to ensure airtightness and long-term stability at a working temperature of 500 - 850 °C.

[0039] Furthermore, the single electrolytic cell 4 is an oxygen ion-conducting solid oxide electrolytic cell, including a porous cathode layer, a dense electrolyte layer, and a porous anode layer. The cathode layer faces the cathode gas groove of the metal connector 2, and nickel-based material is loaded on its surface. The anode layer faces the anode gas groove, and a perovskite-type oxide catalyst is loaded on its surface. The thickness of the electrolyte layer is 10 - 50 μm and is made of yttria-stabilized zirconia material.

[0040] Furthermore, the fastener 6 is a high-strength alloy bolt or a high-temperature-resistant ceramic fixture. It passes through the positioning holes preset by the bottom plate 1 and the top plate 5 of the electrolytic cell, and uniform axial pressure is applied through torque control to make each layer of the metal connector 2, the seal 3, and the single electrolytic cell 4 fit tightly, with a contact resistance less than 10 mΩ·cm 2 。

[0041] During the electrolysis process, the generated oxygen ions are conducted through the dense electrolyte layer (made of yttria-stabilized zirconia material) to the anode layer. The anode layer is loaded with a perovskite-type oxide catalyst to promote the reduction reaction of oxygen ions to generate oxygen. The generated oxygen is directly discharged to the external environment through the anode gas groove in the metal connector 2. The design of the anode gas groove takes into account reducing the discharge resistance and preventing local pressure accumulation, and enhances the oxygen diffusion rate through the flared structure. The seal 3 is made of a ceramic matrix composite material to ensure airtightness and long-term stability in a high-temperature working environment. Through holes completely matching the cathode inlet main channel and the cathode outlet main channel of the metal connector 2 are embedded therein to ensure gas flow. The metal connector 2 not only serves as a gas channel but also as an electrical conduction channel to realize the series connection of each layer of the single electrolytic cell 4. Uniform axial pressure is applied through the fastener 6 to ensure tight fitting of each layer and reduce the contact resistance.

[0042] Example 3:

[0043] Furthermore, the electrolytic cell is made of a nickel-based superalloy for the bottom plate 1 and the top plate 5, and the surfaces thereof are provided with positioning protrusions and grooves that match the shape of the metal connector 2. The bottom of the bottom plate 1 of the electrolytic cell is integrated with an insulating and heat-insulating layer, and the top of the top plate 5 is provided with a conductive terminal connected to an external power source to achieve a series or parallel circuit configuration of the electrolytic cells.

[0044] Furthermore, the operating temperature of the electrolytic cell is 600 - 800 °C, the water vapor pressure introduced into the total cathode gas inlet channel is 0.1 - 0.5 MPa, the oxygen discharge pressure of the anode gas tank is at atmospheric pressure, the electrolysis efficiency of the electrolytic cell is ≥ 85%, and the voltage decay rate of the single electrolytic cell 4 at the rated current density is less than 2% / 1000 hours.

[0045] Furthermore, the stacking layer number of the electrolytic cells is 10 - 40 layers, each layer of single electrolytic cell 4 is connected in series through the conductive property of the metal connector 2, the total output voltage is 20 - 200 V, the total height of the stacking structure is 50 - 300 mm, and the effective reaction area of each layer of single electrolytic cell 4 is 100 - 1000 cm 2 。

[0046] Furthermore, a one-way valve or a labyrinth anti-backflow structure is provided at the outlet of the anode gas tank, and the material thereof is a high-temperature resistant ceramic or a metal-ceramic composite material. The opening and closing pressure threshold of the anti-backflow structure is 0.05 - 0.1 MPa to prevent external gas from flowing back or impurities from entering the interior of the electrolytic cell, while allowing oxygen to freely discharge after the electrolysis reaction.

[0047] The operating temperature of the electrolytic cell is controlled at 600 - 800 °C, which is the high-efficiency operating temperature range of the solid oxide electrolysis technology. The water vapor pressure introduced into the total cathode gas inlet channel is controlled at 0.1 - 0.5 MPa to optimize the electrolysis efficiency. The oxygen discharge pressure of the anode gas tank is at atmospheric pressure. The electrolytic cell adopts a multi-layer stacking structure, with the stacking layer number being 10 - 40 layers, the total output voltage being 20 - 200 V, the total height of the stacking structure being 50 - 300 mm, and the effective reaction area of each layer of single electrolytic cell 4 being 100 - 1000 cm 2 to ensure efficient electrolysis reaction. The electrolysis efficiency of the electrolytic cell is ≥ 85%, and the voltage decay rate of the single electrolytic cell 4 at the rated current density is less than 2% / 1000 hours, indicating its good stability and durability. A one-way valve or a labyrinth anti-backflow structure is provided at the outlet of the anode gas tank to prevent external gas from flowing back or impurities from entering the interior of the electrolytic cell, while allowing oxygen to freely discharge. These anti-backflow structures are made of high-temperature resistant ceramics or metal-ceramic composite materials to ensure reliability and durability in a high-temperature environment.

[0048] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and the descriptions in the specification are only preferred examples of the present invention, which are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A solid oxide electrolyzer, comprising an electrolyzer consisting of a bottom plate (1), a metal connector (2), a seal (3), a single electrolytic cell (4), a top plate (5), and a fastener (6), characterized in that: The electrolytic cell is a flat multi-layer stacked structure, which is alternately laminated by a bottom plate (1), a plurality of metal connectors (2), a plurality of seals (3), a plurality of single electrolytic cells (4) and a top plate (5), and is fixed by a fastener (6) passing through the bottom plate (1) and the top plate (5) of the electrolytic cell. The metal connector (2) internally integrates a cathode inlet main channel, a cathode outlet main channel, a plurality of cathode gas channels and a plurality of anode gas channels. The cathode gas channels are connected to the cathode layers of adjacent single electrolytic cells (4) through the channels of the seals (3), and are used to distribute water vapor to each single electrolytic cell (4) and collect the hydrogen generated by electrolysis. The anode gas channels are directly connected to the external environment and are used to discharge the oxygen generated by electrolysis. The electrolytic cell has no independent anode inlet main channel and anode outlet main channel, and the oxygen on the anode side is directly discharged through the anode gas channels.

2. The solid oxide electrolyzer according to claim 1, wherein: The metal connector (2) is a high-temperature resistant conductive metal plate, and its surface is provided with a groove structure matching the single electrolytic cell (4). The cathode gas channels and the anode gas channels are radially or parallelly arrayed on the same plane of the metal connector (2). Among them, the cross-sectional area of the cathode gas channels is larger than that of the anode gas channels, and the depth of the anode gas channels is 1 / 3 to 1 / 2 of that of the cathode gas channels, so as to reduce the oxygen discharge resistance and optimize the hydrogen collection efficiency.

3. The solid oxide electrolyzer according to claim 2, characterized in that: The cathode inlet main channel and the cathode outlet main channel of the metal connector (2) are respectively located on its two side edges, and are connected to each layer of cathode gas channels through vertical channels extending along the stacking direction. The anode gas channels are evenly distributed in the central area of the metal connector (2), and each anode gas channel is provided with a flared structure at its end to enhance the oxygen diffusion rate and prevent local pressure accumulation.

4. A solid oxide electrolyzer according to claim 3, characterized in that: The seal (3) is made of a ceramic matrix composite material, and its interior is embedded with through holes that perfectly match the cathode inlet main channel and the cathode outlet main channel of the metal connector (2). The thickness of the seal (3) is 0.5 - 2 mm, and its surface is coated with a high-temperature oxidation-resistant coating to ensure airtightness and long-term stability at a working temperature of 500 - 850 °C.

5. A solid oxide electrolyzer according to claim 4, characterized in that: The single electrolytic cell (4) is an oxygen ion-conducting solid oxide electrolytic cell, which includes a porous cathode layer, a dense electrolyte layer and a porous anode layer. The cathode layer faces the cathode gas channels of the metal connector (2), and its surface is loaded with nickel-based materials. The anode layer faces the anode gas channels, and its surface is loaded with a perovskite-type oxide catalyst. The thickness of the electrolyte layer is 10 - 50 μm and is made of yttria-stabilized zirconia material.

6. The solid oxide electrolyzer according to claim 5, characterized in that: The fastener (6) is a high-strength alloy bolt or a high-temperature resistant ceramic fixture, which passes through the positioning holes preset by the bottom plate (1) and the top plate (5) of the electrolytic cell, and applies uniform axial pressure through torque control, so that each layer of metal connectors (2), seals (3) and single electrolytic cells (4) are closely attached, and the contact resistance is less than 10 mΩ·cm 2 .

7. A solid oxide electrolyzer according to claim 6, characterized in that: The bottom plate (1) and the top plate (5) of the electrolytic cell are made of nickel-based superalloy, and their surfaces are provided with positioning protrusions and grooves matching the shape of the metal connector (2). The bottom of the bottom plate (1) of the electrolytic cell is integrated with an insulating and heat-insulating layer, and the top of the top plate (5) is provided with conductive terminals connected to an external power source to realize the series or parallel circuit configuration of the electrolytic cells.

8. A solid oxide electrolyzer according to claim 7, characterized in that: The operating temperature of the electrolytic cell is 600 - 800 °C, the steam pressure introduced into the total cathode inlet channel is 0.1 - 0.5 MPa, the oxygen discharge pressure of the anode gas tank is at atmospheric pressure, the electrolysis efficiency of the electrolytic cell is ≥ 85%, and the voltage decay rate of the single electrolytic cell (4) at the rated current density is less than 2% / 1000 hours.

9. The solid oxide electrolyzer according to claim 8, wherein: The number of stacked layers of the electrolytic cell is 10 - 40 layers. Each single electrolytic cell (4) is connected in series through the conductive characteristics of the metal connector (2). The total output voltage is 20 - 200V. The total height of the stacked structure is 50 - 300mm, and the effective reaction area of each single electrolytic cell (4) is 100 - 1000 cm 2 .

10. A solid oxide electrolyzer according to claim 9, characterized in that: A one-way valve or a labyrinth anti-backflow structure is provided at the outlet of the anode gas tank, and its material is a high-temperature resistant ceramic or a metal-ceramic composite material. The opening and closing pressure threshold of the anti-backflow structure is 0.05 - 0.1 MPa to prevent external gas from flowing back or impurities from entering the interior of the electrolytic cell, while allowing oxygen to freely discharge after the electrolysis reaction.

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