JP7809744B2 - Electrolysis cell stack, electrolysis cell cartridge, electrolysis cell module, and method for manufacturing an electrolysis cell stack - Google Patents

Description

The present disclosure relates to electrolysis cell stacks, electrolysis cell cartridges, electrolysis cell modules, and methods for manufacturing electrolysis cell stacks.

Water electrolysis, which produces hydrogen and oxygen by electrochemically decomposing water, is a hydrogen production method that does not emit carbon dioxide and has excellent environmental properties. There are various methods, such as alkaline electrolysis, which electrolyzes liquid water, solid polymer electrolysis, and steam electrolysis, which electrolyzes water vapor.

Among these, solid oxide electrolysis cells (SOECs, hereafter referred to as "electrolysis cells"), which electrolyze high-temperature water vapor, use ceramics with oxygen ion conductivity, such as yttria-stabilized zirconia, as the electrolyte, and can utilize the thermal energy of the high-temperature water vapor as part of the energy required for the electrolysis reaction, making it possible to produce hydrogen more efficiently than other electrolysis methods.

Patent Document 1 discloses a hydrogen generation system equipped with a cell stack in which multiple electrolytic cells, each having a hydrogen electrode, a solid electrolyte membrane, and an oxygen electrode, are arranged on a substrate tube. In this hydrogen generation system, the SOEC described in Patent Document 1 has a hydrogen electrode made of a composite oxide of Ni and a zirconia-based electrolyte material.

Patent No. 7282968

In SOECs, it is desirable to increase the amount of hydrogen produced per unit cell.
Increasing the current flowing through the SOEC promotes the electrochemical decomposition (electrolysis) of water, thereby increasing the amount of hydrogen produced. However, for the following reasons, when increasing the electrolysis current so that the electrolysis voltage exceeds the thermoneutral potential, consideration must be given to the durability of the cell and the allowable temperature of the metal material.

When a current is passed through an SOEC, Joule heat is generated due to the internal resistance of the cell, but water electrolysis is an endothermic reaction, and at low currents, the endothermic reaction is dominant, so there is no problem with temperature rise. However, when attempting to operate at a high current above the thermoneutral potential, the cell temperature rises due to heat generated by Joule heat associated with the electrolysis reaction. When an SOEC is exposed to high temperatures, the nickel in the hydrogen electrode sinters, gradually increasing the internal resistance of the SOEC and making stable electrolysis over long periods of time difficult, so it is necessary to keep the maximum cell temperature below the allowable value.

In SOEC steam electrolysis, it is necessary to make the temperature of the reaction section as uniform as possible and keep the maximum temperature below the allowable temperature in order to reduce the internal resistance of the cell. SOECs are typically operated at a high current above the thermal neutral point to ensure thermal self-sustainability of the cell stack. This is higher than the operating current of a fuel cell, which is the reverse reaction. As a result, the supply gas flow rate also increases, and the gas temperature at the outlet of the raw gas (steam) flow tends to rise. For this reason, it is necessary to install appropriate heat exchange units on the inlet and outlet sides in order to make the operating temperature of the electrolytic cell (reaction section) as uniform as possible, maintain the maximum temperature below the set temperature, and keep the exhaust gas temperature from the cell stack below the allowable temperature of the components installed downstream of the cell stack.

On the other hand, because the heat exchanger needs to seal the gas being supplied to or discharged from the cell stack, it is desirable that it be made of a metal material that can withstand high temperatures and have a structure that is integrated with the electrolysis cell. For example, in a flat-plate cell stack, the temperature of the gas discharged from the SOEC cell stack can be reduced by using a stack structure in which flat-plate heat exchangers consisting of heat transfer sections and gas header sections are integrated above and below the stacked electrolysis cells (reaction sections).

In addition, in a cylindrical SOEC stack, it is possible to have a stack structure with heat exchange sections on both sides of the electrolytic cell reaction section constructed on the same substrate tube, but both ends of the cell stack require metal retaining members (sealing members) to seal between the raw material gas and the oxidizing gas. If these retaining members are exposed to high temperatures for long periods of time, their durability will decrease due to oxidation corrosion, so the electrolytic current flowing through the SOEC is limited to a range that does not exceed the allowable temperature of these retaining members.

The present disclosure has been made in light of these circumstances, and aims to provide an electrolysis cell stack, electrolysis cell cartridge, electrolysis cell module, and method for manufacturing an electrolysis cell stack that can increase the amount of hydrogen produced by electrolysis while keeping the temperature rise of the exhaust gas and gas-sealing retaining members from the heat exchange units provided on the inlet and outlet sides of the SOEC cell stack within an acceptable range.

To solve the above problems, the manufacturing methods of the electrolysis cell stack, electrolysis cell cartridge, electrolysis cell module, and electrolysis cell stack disclosed herein employ the following measures.

The present disclosure provides a hydrogen generation unit including an electrolysis cell having a nickel-containing hydrogen electrode, an oxygen electrode, and a solid electrolyte membrane sandwiched between the hydrogen electrode and the oxygen electrode; a raw material gas supply port for supplying a raw material gas to the hydrogen electrode of the hydrogen generation unit; a hydrogen gas outlet port for discharging hydrogen gas generated in the hydrogen generation unit; a raw material gas supply-side heat exchange unit located on the raw material gas supply port side of the hydrogen generation unit and performing heat exchange between the raw material gas and an oxidizing gas discharged from the oxygen electrode side; and a front heat exchange unit located on the hydrogen gas outlet side of the hydrogen generation unit. and a hydrogen gas discharge side heat exchanger that exchanges heat between the hydrogen gas and an oxidizing gas supplied to the oxygen electrode side, wherein the raw material gas supply side heat exchanger has a heat transfer section where the flow rate of the oxidizing gas is faster than when the oxidizing gas flows through the hydrogen generation section, and the hydrogen gas discharge side heat exchanger has a heat transfer section where the flow rate of the oxidizing gas is faster than when the oxidizing gas flows through the hydrogen generation section, and the area of the heat transfer section of the hydrogen gas discharge side heat exchanger is larger than the area of the heat transfer section of the raw material gas supply side heat exchanger.

The present disclosure provides an electrolysis cell cartridge including the electrolysis cell stack described above.

The present disclosure provides an electrolysis cell module including the electrolysis cell cartridge described above.

The present disclosure provides a hydrogen generation unit including an electrolysis cell having a nickel-containing hydrogen electrode, an oxygen electrode, and a solid electrolyte membrane sandwiched between the hydrogen electrode and the oxygen electrode; a raw material gas supply port for supplying a raw material gas to the hydrogen electrode of the hydrogen generation unit; a hydrogen gas outlet port for discharging hydrogen gas generated in the hydrogen generation unit; a raw material gas supply-side heat exchange unit, located on the raw material gas supply port side of the hydrogen generation unit, for heat exchange between the raw material gas and an oxidizing gas discharged from the oxygen electrode side; and a raw material gas supply-side heat exchange unit, located on the hydrogen gas outlet side of the hydrogen generation unit, for heat exchange between the hydrogen gas and the oxygen electrode. and a hydrogen gas discharge-side heat exchanger that exchanges heat with an oxidizing gas supplied to a feed gas supply side, wherein the feed gas supply-side heat exchanger has a heat transfer section that makes the flow rate of the oxidizing gas faster than when the oxidizing gas flows through the hydrogen generation section, and the hydrogen gas discharge-side heat exchanger has a heat transfer section that makes the flow rate of the oxidizing gas faster than when the oxidizing gas flows through the hydrogen generation section, and the area of the heat transfer section of the hydrogen gas discharge-side heat exchanger is made larger than the area of the heat transfer section of the feed gas supply-side heat exchanger.

According to the present disclosure, by making the heat transfer area of the hydrogen gas discharge side heat exchanger larger than the heat transfer area of the feed gas supply side heat exchanger, it is possible to increase the amount of heat required to cool the hydrogen gas generated in the hydrogen generation unit. This makes it possible to keep the temperature of the hydrogen gas discharged from the hydrogen gas outlet lower than conventional methods.

The high-temperature steam used as the feedstock for SOEC does not undergo an endothermic chemical reaction in the feedstock gas supply-side heat exchanger. Therefore, even if the heat transfer area of the feedstock gas supply-side heat exchanger is reduced, there is no temperature drop due to an endothermic reaction, and the temperature of the feedstock gas rises due to heat exchange with the oxidizing gas, making it possible to increase the operating temperature of the electrolytic cell stack. A higher operating temperature reduces the internal resistance of the cell, thereby reducing the power required to generate hydrogen per unit flow rate.

Such an electrolysis cell stack can keep the maximum temperature of the cell stack within an acceptable range even if the current density flowing through the hydrogen generation section increases, and can control the temperature of the hydrogen gas discharged from the electrolysis cell stack and the stack's holding members so that they do not exceed the acceptable temperature.

FIG. 1 illustrates an embodiment of a cylindrical electrolysis cell stack according to an embodiment of the present disclosure. FIG. 2 is an enlarged schematic cross-sectional view of the end of a fuel supply side heat exchanger of the cell stack. FIG. 1 illustrates one embodiment of a cross-section of an electrolysis cell cartridge according to an embodiment of the present disclosure. FIG. 1 illustrates an embodiment of an electrolysis cell module according to an embodiment of the present disclosure. FIG. 10 is a diagram showing the relationship between the operating temperature and the IV characteristics of the cell stack. 1 is a graph showing predicted temperature distributions of the cell stack, supplied steam, and oxidizing gas in Example 1 and Comparative Example 1. FIG. FIG. 10 is a diagram showing test conditions and simulation results for Examples 2 to 4 and Comparative Examples 2 and 3. FIG. 10 is a diagram showing test conditions and simulation results for Examples 5 to 7 and Comparative Examples 4 and 5. FIG. 10 is a diagram showing test conditions and simulation results for Examples 8 to 10 and Comparative Examples 6 and 7. FIG. 10 is a diagram showing test conditions and simulation results for Examples 11 to 13 and Comparative Examples 8 and 9. FIG. 10 is a diagram showing test conditions and simulation results for Examples 14 to 16 and Comparative Examples 10 and 11. 1 is a graph plotting the amount of hydrogen produced with the ratio (L ₃ /L ₁ ) of the length of the lower heat exchange section (L ₃ ) to the heat transfer section length (L ₁ ) of the upper heat exchange section as the horizontal axis.

Below, one embodiment of the electrolysis cell stack, electrolysis cell cartridge, electrolysis cell module, and electrolysis cell stack manufacturing method according to the present disclosure will be described with reference to the drawings.

In this embodiment, "electrolysis" means "steam electrolysis."

In the following, for the sake of convenience, the positional relationships of each component described using the terms "above" and "below" with respect to the plane of the paper indicate the vertically upper and lower sides, respectively. Furthermore, in this embodiment, for components that can achieve similar effects in both the vertical and horizontal directions, the vertical direction on the plane of the paper is not necessarily limited to the vertical direction, but may also correspond to, for example, a horizontal direction perpendicular to the vertical direction.

(cell stack)
First, a cylindrical electrolysis cell stack using a substrate tube will be described as an example according to this embodiment with reference to Figures 1 and 2. When a substrate tube is not used, for example, the hydrogen electrode may be formed thick and serve as the substrate tube, and the use of a substrate tube is not limited. Furthermore, although the substrate tube in this embodiment is described as having a cylindrical shape, the substrate tube may be cylindrical and does not necessarily have to have a circular cross section, and may have, for example, an elliptical cross section. A cell stack such as a flat tubular cylinder in which the peripheral side surface of a cylinder is crushed vertically may also be used. Furthermore, a stack structure in which a plurality of flat-plate electrochemical unit cells, separators, and flat-plate heat exchangers are stacked may also be used.

Figure 1 is a schematic diagram showing one embodiment of a cell stack (cylindrical electrolysis cell stack) according to this embodiment. The cell stack 101 has a hydrogen generation unit 10 in the center in the longitudinal direction. The cell stack 101 has a raw material gas supply port 11 and a hydrogen gas discharge port 12. The cell stack 101 also has a raw material gas supply-side heat exchange unit (hereinafter referred to as the upper heat exchange unit) 13 and a discharge-side heat exchange unit (hereinafter referred to as the lower heat exchange unit) 14, sandwiching the hydrogen generation unit 10 from both sides in the longitudinal direction.

The raw material gas that can be supplied to the hydrogen electrode of the cell stack 101 and used is a gas that serves as a hydrogen generation source in the hydrogen generation unit 10 and does not cause an endothermic reaction in the upper heat exchange unit 13 or the lower heat exchange unit 14. In this embodiment, the raw material gas is water vapor. The gas supplied to the raw material gas supply port 11 often contains hydrogen in addition to the water vapor used for electrolysis. Furthermore, the gas discharged from the hydrogen gas discharge port 12 may contain water vapor, which is the remainder of the raw material gas, in addition to the hydrogen gas generated in the hydrogen generation unit 10. However, to avoid confusion in the following explanation, the supply gas containing hydrogen will be referred to as "supplied water vapor" and the hydrogen gas containing this remaining water vapor will be referred to as "produced hydrogen."

The upper heat exchanger 13 is located on the source gas supply port (steam supply port) 11 side of the hydrogen generation unit 10. The upper heat exchanger 13 is a region where the supply steam supplied from the steam supply port 11 into the cell stack 101 exchanges heat with the oxidizing gas flowing outside the cell stack 101 before entering the hydrogen generation unit 10. The upper heat exchanger 13 may include a lead portion (the lead film 115 described below) electrically connected to the hydrogen generation unit 10. Specifically, the upper heat exchanger 13 is the region from the end (outer end) of the electrolysis cell 105 on the source gas supply port (steam supply port) 11 side formed in the cell stack 101 to the upper tube plate 225a described below. Note that the upper heat exchanger 13 does not include the area from the upper tube plate 225a to the top end of the cell stack 101. Furthermore, the upper heat exchanger 13 does not necessarily have to be molded integrally with the hydrogen generation unit 10, but may be a structure or heat exchanger capable of exchanging heat between the oxidizing gas and the supply steam.

Of the upper heat exchange section 13, the oxidizing gas upper penetration 235b (described later) that exchanges heat between the raw material gas and the oxidizing gas is defined as the heat transfer section (L ₁ ). The oxidizing gas upper penetration 235b is a passage for the oxidizing gas formed between the outer surface of the cell stack 101 and the upper heat insulator 227a (described later), and is the region where heat exchange between the raw material gas and the oxidizing gas occurs. In other words, the upper heat exchange section 13 is the combined region of the region from the end (outer end) of the electrolysis cell 105 on the raw material gas supply port (steam supply port) 11 side formed in the cell stack 101 to the oxidizing gas upper penetration 235b (heat transfer section L ₁ ), the heat transfer section (L ₁ ), and the portion that penetrates the oxidizing gas discharge header 223.

The lower heat exchanger 14 is located on the hydrogen gas outlet (produced hydrogen outlet) 12 side of the hydrogen generation unit 10. The lower heat exchanger 14 is the region where heat exchange occurs between the hydrogen gas (produced hydrogen) generated in the hydrogen generation unit 10 and the oxidizing gas flowing outside the cell stack 101. The lower heat exchanger 14 may include a lead portion (lead film 115 described below) electrically connected to the hydrogen generation unit 10. Specifically, the lower heat exchanger 14 is the region from the end (outer end) of the electrolysis cell 105 on the hydrogen gas outlet (produced hydrogen outlet) 12 side formed in the cell stack 101 to the lower tube plate 225b described below. Note that the lower heat exchanger 14 does not include the area from the lower tube plate 225b to the lower end of the cell stack 101. Furthermore, the lower heat exchanger 14 does not necessarily have to be molded integrally with the hydrogen generation unit 10, but may be a structure or heat exchanger capable of exchanging heat between the oxidizing gas and hydrogen gas (produced hydrogen).

Of the lower heat exchange section 14, the oxidizing gas lower penetration 235a, which exchanges heat between hydrogen gas (produced hydrogen) and oxidizing gas, is defined as the heat transfer section ( _L3 ). The oxidizing gas lower penetration 235a is a passage for oxidizing gas formed between the outer surface of the cell stack 101 and the lower heat insulator 227b described later, and is the region where heat exchange between hydrogen gas (produced hydrogen) and oxidizing gas occurs. In other words, the lower heat exchange section 14 is the combined region of the region from the end (outer end) of the electrolysis cell 105 on the hydrogen gas outlet (produced hydrogen outlet) 12 side formed in the cell stack 101 to the inlet of the oxidizing gas lower penetration 235a, the heat transfer section ( _L3 ) in the oxidizing gas lower penetration, and the portion penetrating the oxidizing gas supply header 221.

The heat transfer area ( _S3 ) of the heat transfer section ( _L3 ) of the lower heat exchange section 14 is larger than the heat transfer area ( _S1 ) of the heat transfer section ( _L1 ) of the upper heat exchange section 13. As shown in Fig. 12 described later, the ratio ( _S3/S1 ) of the heat transfer area ( _S3 ) of the heat transfer section ( _L3 ) of the lower heat exchange section 14 to the heat transfer area ( _S1 ) of the heat transfer section ( _L1 ) of the upper heat exchange section ₁₃ is 2 or more, preferably 3 or more and 9 or less, and more preferably 3 or more and 7 or less.

Here, the effective area (S) of the cell stack 101 is defined as the sum of the heat transfer area (S ₁ ) of the upper heat exchange section 13 , the reaction area (S ₂ ) of the hydrogen generation section 10 , and the heat transfer area (S ₃ ) of the lower heat exchange section 14 .
Effective area of electrolysis cell stack (S) = Heat transfer area of upper heat exchange section (S ₁ )
+ reaction area of the hydrogen generation section (S ₂ ) + heat transfer area of the lower heat exchange section (S ₃ )

When the diameter of the substrate tube 103 is uniform, the heat transfer area may be considered as the length.
The length (L) of the effective portion of the cell stack 101 is the sum of the length (L ₁ ) of the heat transfer portion of the upper heat exchange portion 13, the length (L ₂ ) of the hydrogen generation portion 10, and the length (L ₃ ) of the heat transfer portion of the lower heat exchange portion 14.
Effective length of electrolysis cell stack (L) = heat transfer length of upper heat exchange section (L ₁ )
+ length of the hydrogen generating section (L ₂ ) + length of the heat transfer section of the lower heat exchange section (L ₃ )

If the diameter of the base tube 103 is uniform, the heat transfer section length ( _L3 ) of the lower heat exchange section 14 is longer than the heat transfer section length ( _L1 ) of the upper heat exchange section 13. The ratio (L3 _/L1 ) of the heat transfer section length (L3) of the lower heat exchange section 14 to the heat transfer section length ( _L1 ) of the upper heat exchange section ₁₃ is 2 or more, preferably 3 or more and 9 or less, and more preferably 3 or more _and 7 or less.

Figure 2 is an enlarged schematic cross-sectional view of the end of the hydrogen generation unit of the cell stack. The hydrogen generation unit 10 is formed on the outer peripheral surface of a cylindrical substrate tube 103. The diameter (outer diameter and inner diameter) of the substrate tube 103 may be uniform along its length. The outer diameter of the substrate tube 103 is, for example, 10 to 50 mm. The overall length of the substrate tube 103 is, for example, 500 to 3000 mm.

The hydrogen generation unit 10 comprises multiple electrolytic cells 105 arranged in the axial direction of the substrate tube 103 and interconnectors 107 formed between adjacent electrolytic cells 105.

The electrolysis cell 105 is composed of a stack of a hydrogen electrode 109, a solid electrolyte membrane 111, and an oxygen electrode 113. The solid electrolyte membrane 111 is sandwiched between the hydrogen electrode 109 and the oxygen electrode 113.

The cell stack 101 has a plurality of electrolytic cells 105 formed on the outer peripheral surface of the base tube 103. The cell stack 101 has a lead film 115 electrically connected via an interconnector 107 to the oxygen electrode 113 of the electrolytic cell 105 formed at one end of the base tube 103 in the axial direction, and a lead film 115 electrically connected to the hydrogen electrode 109 of the electrolytic cell 105 formed at the other end. The outer end of the oxygen electrode 113 of the electrolytic cell 105 located at the end serves as the end of the hydrogen generation section 10.

The base tube 103 is made of a porous material and has as its main component, for example, CaO-stabilized _ZrO2 (CSZ), a mixture of CSZ and nickel oxide (NiO) (CSZ+NiO), _{Y2O3 -} stabilized _ZrO2 ( _YSZ ), or _MgAl2O4 . The base tube 103 supports the electrolytic cell 105, the interconnector 107, and the lead film 115, and also diffuses the supplied water vapor supplied to the inner circumferential surface of the base tube 103 through the pores of the base tube 103 to the hydrogen electrode 109 formed on the outer circumferential surface of the base tube 103. Openings at both ends of the base tube 103 can serve as a water vapor supply port and a produced hydrogen discharge port.

The hydrogen electrode 109 is made of a composite oxide of nickel and a zirconia-based electrolyte material, such as Ni/YSZ. The thickness of the hydrogen electrode 109 is 50 μm to 250 μm, and the hydrogen electrode 109 may be formed by screen printing a slurry.

YSZ, which has gas-tightness that makes it difficult for gas to pass through and high oxygen ion conductivity at high temperatures, is mainly used for the solid electrolyte membrane 111. The solid electrolyte membrane 111 transfers oxygen ions (O ²⁻ ) generated at the hydrogen electrode 109 to the oxygen electrode 113. The thickness of the solid electrolyte membrane 111 located on the surface of the hydrogen electrode 109 is 5 μm to 100 μm, and the solid electrolyte membrane 111 may be formed by screen-printing a slurry.

The oxygen electrode 113 is made of, for example, an LaSrMnO3 _- based oxide or an _LaCoO3 -based oxide. The oxygen electrode 113 is coated with a slurry by screen printing or using a dispenser.

The oxygen electrode 113 can also have a two-layer structure. In this case, the oxygen electrode layer (oxygen electrode intermediate layer) on the solid electrolyte membrane 111 side is made of a material that exhibits high ionic conductivity and excellent catalytic activity. The oxygen electrode intermediate layer may be made of Sm-doped ceria, which exhibits high ionic conductivity, and the oxygen electrode layer (oxygen electrode conductive layer) on the oxygen electrode intermediate layer may be made of a perovskite-type oxide such as Sr- and Ca-doped _LaMnO3 .

By applying a negative voltage to the hydrogen electrode 109 and a positive voltage to the oxygen electrode 113, the water vapor contained in the supplied water vapor receives electrons at the hydrogen electrode 109 and is electrolyzed to generate hydrogen molecules and oxygen ions (O ^2- ) (see reaction formula (1) below). The generated hydrogen is extracted to the outside together with the supplied water vapor.

Meanwhile, oxygen ions pass through the solid electrolyte membrane 111 due to the potential difference, move to the oxygen electrode 113, release electrons, and become oxygen molecules (see reaction formula (2) below). The generated oxygen is discharged to the outside together with the oxidizing gas supplied to the oxygen electrode 113.

H ₂ O + 2e ^- → H ₂ + O ² - (1)
2O ^2- →O ₂ +4e ^-... (2)

The oxidizing gas is not directly involved in the electrolytic reaction, but it supplies the heat necessary for the electrolytic reaction (endothermic) and expels excess heat generated by the electrolytic reaction. The oxidizing gas typically contains approximately 15% to 30% oxygen, with air being a typical example. However, other gases that can be used include a mixture of combustion exhaust gas and air, a mixture of oxygen and air, and inert gases such as nitrogen.

The interconnector 107 is made of a conductive perovskite oxide represented by M1 _{-xLxTiO3 (} M is an alkaline earth metal element, L is a lanthanoid element), such as _SrTiO3 , and is formed by screen-printing a slurry. The interconnector 107 is _a dense film that prevents the water vapor supplied to the hydrogen electrode 109 from mixing with the oxidizing gas supplied to the oxygen electrode 113. The interconnector 107 also has stable durability and electrical conductivity in both oxidizing and reducing atmospheres. This interconnector 107 electrically connects the oxygen electrode 113 of one electrolytic cell 105 to the hydrogen electrode 109 of the other electrolytic cell 105, thereby connecting the adjacent electrolytic cells 105 in series.

The lead film 115 is required to have electronic conductivity and a thermal expansion coefficient close to that of the other materials constituting the cell stack 101, and is therefore made of a composite material of nickel and zirconia-based electrolyte material, such as Ni/ _YSZ , or M1 _{- xLxTiO3} (M is an alkaline earth metal element, L is a lanthanoid element) such as _SrTiO3 . The lead film 115 supplies DC power to the multiple electrolysis cells 105 connected in series by the interconnectors 107. Furthermore, the surface on the oxidizing gas side may be protected with an airtight oxidation-resistant material to prevent oxidation of metal materials such as Ni.

A portion of the lead film 115 may be located on the upper heat exchange section 13 (or the lower heat exchange section 14). In this case, the upper heat exchange section 13 (or the lower heat exchange section 14) will have the function of allowing current to flow.

Next, a method for manufacturing the cell stack will be described.
The substrate tube 103 is formed by, for example, an extrusion molding method.
The outer peripheral surface of the substrate tube 103 is divided into an upper heat exchange region, a hydrogen generation region, and a lower heat exchange region along the axial direction (longitudinal direction). The hydrogen generation region is located in the axial center of the substrate tube 103, the upper heat exchange region is located on the raw material gas supply port side of the hydrogen generation region, and the lower heat exchange region is located on the produced hydrogen outlet side of the hydrogen generation region.

The upper heat exchange section region and the lower heat exchange section region are set so that the heat transfer section area ( _S3 ) of the lower heat exchange section is larger than the heat transfer section area ( _S1 ) of the upper heat exchange section. The ratio ( _S3 / _S1 ) of the heat transfer section area ( _S3 ) of the lower heat exchange section to the heat transfer section area ( _S1 ) of the upper heat exchange section is 2 or more, preferably 3 or more and 9 or less, and more preferably 3 or more and 7 or less.

If the diameter of the substrate tube 103 is uniform in the longitudinal direction, the "heat transfer area" may be converted to "length" to set the heat transfer section length of the upper heat exchange section, the hydrogen generation section length, and the heat transfer section length of the lower heat exchange section.

A slurry for the hydrogen electrode is applied to the outer surface of the substrate tube 103 in the hydrogen generation region. Next to the slurry for the hydrogen electrode applied at the very edge, a slurry for the lead film is applied. The slurry for the lead film may straddle the upper heat exchange region (or lower heat exchange region) and the hydrogen generation region.

After applying the slurry for the hydrogen electrode, the slurry for the solid electrolyte membrane and the slurry for the interconnector are applied in that order.

The substrate tube 103, on which the slurry films of the hydrogen electrode 109, solid electrolyte membrane 111, interconnector 107, and lead membrane 115 are formed, is co-sintered in air. The sintering temperature is, for example, 1350°C to 1450°C.

Next, the oxygen electrode slurry is applied to the co-sintered substrate tube 103. The outermost edge of the oxygen electrode slurry applied to the outermost edge becomes the edge of the hydrogen generation region.

The substrate tube 103 on which the slurry film of the oxygen electrode 113 has been formed is sintered in the atmosphere. The sintering temperature is, for example, 1100°C to 1250°C. This sintering temperature is lower than the co-sintering temperature after the substrate tube 103 to interconnector 107 are formed.

This provides a cell stack 101 in which the heat transfer area (S ₃ ) of the lower heat exchange section 14 is larger than the heat transfer area (S ₁ ) of the upper heat exchange section 13 .

Next, the cartridge (electrolysis cell cartridge) and module (electrolysis cell module) according to this embodiment will be described with reference to Figures 3 and 4. Here, Figure 3 shows one embodiment of the cartridge according to this embodiment. Also, Figure 4 shows a cross-sectional view of one embodiment of the module according to this embodiment.

(SOEC cartridge)
As shown in Figure 3, the cartridge 203 includes a plurality of cell stacks 101, steam electrolysis chambers 215, a steam supply header 217, a product hydrogen discharge header 219, an oxidizing gas (air) supply header 221, and an oxidizing gas discharge header 223. The cartridge 203 also includes an upper tube plate 225a, a lower tube plate 225b, an upper heat insulator 227a, and a lower heat insulator 227b. In this embodiment, the cartridge 203 has the steam supply header 217, the product hydrogen discharge header 219, the oxidizing gas supply header 221, and the oxidizing gas discharge header 223 arranged as shown in Figure 2, thereby providing a structure in which the supply steam and the oxidizing gas flow in opposite directions inside and outside the cell stack 101. However, this is not necessarily required. For example, the flow may be parallel inside and outside the cell stack 101, or the oxidizing gas may flow in a direction perpendicular to the longitudinal direction of the cell stack 101.

3, the upper heat exchange section 13 of the cell stack 101 is located between the lower surface of the upper tube plate 225a and the upper end (outer end) of the electrolysis cell 105 located at the uppermost position among the plurality of electrolysis cells 105.
In Figure 3, the lower heat exchange section 14 of the cell stack 101 extends from the lower end (outer end) of the electrolytic cell 105 located at the lowest position among the multiple electrolytic cells 105 to the upper surface of the lower tube sheet 225b.

The steam electrolysis chamber 215 is an area formed between the upper insulator 227a and the lower insulator 227b. This steam electrolysis chamber 215 is an area where the electrolysis cells 105 of the cell stack 101 are located, and is an area where water vapor is electrolyzed to produce hydrogen. The temperature near the center of the longitudinal direction of the cell stack 101 in this steam electrolysis chamber 215 may be monitored by a temperature measurement unit 620 (such as a temperature sensor or thermocouple); during steady-state operation of the electrolysis cell module 201, the high-temperature atmosphere is approximately 700°C to 1000°C.

The water vapor supply header 217 is an area surrounded by the upper casing 229a and upper tube plate 225a of the cartridge 203, and is connected to the water vapor supply branch pipe 207a by a water vapor supply pipe 231a provided at the top of the upper casing 229a. The multiple cell stacks 101 are joined to the upper tube plate 225a by an upper seal member 237a, and the water vapor supply header 217 guides the water vapor supplied from the water vapor supply branch pipe 207a via the water vapor supply pipe 231a into the interior of the base tubes 103 of the multiple cell stacks 101 at a substantially uniform flow rate, thereby substantially uniforming the hydrogen generation performance of the multiple cell stacks 101.

The produced hydrogen discharge header 219 is an area surrounded by the lower casing 229b and lower tube plate 225b of the cartridge 203, and is connected to the produced hydrogen discharge branch pipe 209a by a produced hydrogen discharge pipe 231b provided in the lower casing 229b. Furthermore, the multiple cell stacks 101 are joined by the lower tube plate 225b and lower seal member 237b, and the produced hydrogen discharge header 219 collects the produced hydrogen that passes through the inside of the base tubes 103 of the multiple cell stacks 101 and is supplied to the produced hydrogen discharge header 219, and directs it to the produced hydrogen discharge branch pipe 209a via the produced hydrogen discharge pipe 231b.

The oxidizing gas supply main pipe (not shown) branches into oxidizing gas supply branch pipes (not shown) at a predetermined flow rate corresponding to the operating temperature of the module 201, and supplies the oxidizing gas to multiple cartridges 203. The oxidizing gas supply header 221 is an area surrounded by the lower casing 229b, lower tube plate 225b, and lower insulator 227b of the cartridge 203, and is connected to an oxidizing gas supply branch pipe (not shown) by an oxidizing gas supply pipe 233a provided on the side of the lower casing 229b. This oxidizing gas supply header 221 guides a predetermined flow rate of oxidizing gas supplied from the oxidizing gas supply branch pipe (not shown) via the oxidizing gas supply pipe 233a to the steam electrolysis chamber 215 via the oxidizing gas lower penetration 235a (described below).

The oxidizing gas discharge header 223 is an area surrounded by the upper casing 229a, upper tube plate 225a, and upper insulation 227a of the cartridge 203, and is connected to an oxidizing gas discharge branch pipe (not shown) via an oxidizing gas discharge pipe 233b provided on the side of the upper casing 229a. This oxidizing gas discharge header 223 guides the exhaust oxidizing gas supplied to the oxidizing gas discharge header 223 from the steam electrolysis chamber 215 via the upper oxidizing gas penetration 235b (described below) to the oxidizing gas discharge branch pipe (not shown) via the oxidizing gas discharge pipe 233b.

The upper tube plate 225a is fixed to the side plate of the upper casing 229a, between the top plate of the upper casing 229a and the upper insulator 227a, so that the upper tube plate 225a, the top plate of the upper casing 229a, and the upper insulator 227a are approximately parallel. The upper tube plate 225a also has multiple holes corresponding to the number of cell stacks 101 provided in the cartridge 203, and a cell stack 101 is inserted into each of the holes. The upper tube plate 225a airtightly supports one end of the multiple cell stacks 101 via either or both of the upper seal member 237a and adhesive member, and also isolates the steam supply header 217 from the oxidizing gas discharge header 223.

The upper heat insulator 227a is disposed at the lower end of the upper casing 229a so that the upper heat insulator 227a, the top plate of the upper casing 229a, and the upper tube plate 225a are substantially parallel, and is fixed to the side plate of the upper casing 229a. The upper heat insulator 227a has a plurality of holes formed therein corresponding to the number of cell stacks 101 provided in the cartridge 203. The diameters of the holes are set larger than the outer diameters of the cell stacks 101. The upper heat insulator 227a has upper oxidizing gas penetrations 235b formed between the inner surfaces of the holes and the outer surfaces of the cell stacks 101 inserted through the upper heat insulator 227a. The upper oxidizing gas penetrations 235b are regions (heat transfer sections _L1 ) where heat exchange between the supply steam (raw material gas) and the oxidizing gas takes place.

This upper insulator 227a separates the steam electrolysis chamber 215 from the oxidizing gas discharge header 223, and prevents the atmosphere surrounding the upper tube sheet 225a from becoming too hot, which could result in a decrease in strength and increased corrosion due to the oxidizing agents contained in the oxidizing gas. Furthermore, to prevent thermal deformation of the upper tube sheet 225a and other components due to temperature differences when exposed to the high temperatures within the steam electrolysis chamber 215, a metal material with high temperature resistance, such as a Ni-based alloy, may be used. The upper insulator 227a guides the exhaust oxidizing gas, which has been exposed to high temperatures after passing through the steam electrolysis chamber 215, through the upper oxidizing gas penetration 235b and into the oxidizing gas discharge header 223.

Heat exchange between the supply steam and the oxidizing gas in the upper heat exchange section 13 occurs when the oxidizing gas passes through the oxidizing gas upper penetration 235b (heat transfer section _L1 of the upper heat exchange section). Note that heat exchange in the region of the upper heat exchange section 13 other than the heat transfer section _L1 (the region from the end (outer end) of the electrolysis cell 105 on the raw material gas supply port (steam supply port) 11 side formed in the cell stack 101 to the oxidizing gas upper penetration 235b and the portion penetrating the oxidizing gas discharge header 223) is slight and can be ignored.

The thickness of the upper insulation 227a can be adjusted appropriately so that the temperature of the upper tube plate 225a is below the allowable temperature. Increasing the thickness of the upper insulation 227a can increase the amount of heat exchanged. The volume of the oxidizing gas discharge header 223 can be constant, regardless of the heat transfer area (length) of the upper heat exchange section 13.

In this embodiment, the structure of the cartridge 203 described above allows the supply steam and oxidizing gas to flow in opposite directions inside and outside the cell stack 101. As a result, heat exchange occurs between the exhaust oxidizing gas and the steam supplied to the steam electrolysis chamber 215 through the interior of the base tube 103, and the exhaust oxidizing gas is cooled to a temperature that prevents damage due to stress to the upper tube plate 225a, which is made of a metallic material, and is then supplied to the oxidizing gas discharge header 223. Furthermore, the supply steam is heated by heat exchange with the exhaust oxidizing gas discharged from the steam electrolysis chamber 215, and is then supplied to the steam electrolysis chamber 215. As a result, steam preheated to the temperature required for the electrolysis reaction can be supplied to the steam electrolysis chamber 215 without using a heater or the like.

The lower tube plate 225b is fixed to the side plate of the lower casing 229b between the bottom plate of the lower casing 229b and the lower insulator 227b so that the lower tube plate 225b, the bottom plate of the lower casing 229b, and the lower insulator 227b are approximately parallel. The lower tube plate 225b also has multiple holes corresponding to the number of cell stacks 101 provided in the cartridge 203, and a cell stack 101 is inserted into each of the holes. The lower tube plate 225b airtightly supports the other ends of the multiple cell stacks 101 via either or both of the lower seal member 237b and adhesive member, and also isolates the produced hydrogen discharge header 219 from the oxidizing gas supply header 221.

The lower heat insulator 227b is disposed at the upper end of the lower casing 229b so that the lower heat insulator 227b, the bottom plate of the lower casing 229b, and the lower tube plate 225b are substantially parallel, and is fixed to the side plate of the lower casing 229b. The lower heat insulator 227b has a plurality of holes formed therein corresponding to the number of cell stacks 101 provided in the cartridge 203. The diameters of the holes are set larger than the outer diameters of the cell stacks 101. The lower heat insulator 227b has lower oxidizing gas penetrations 235a (heat transfer section _L3 ) formed between the inner surfaces of the holes and the outer surfaces of the cell stacks 101 inserted through the lower heat insulator 227b. The lower oxidizing gas penetrations 235a are regions (heat transfer sections _L3 ) where heat exchange between hydrogen gas (produced hydrogen) and the oxidizing gas takes place.

This lower insulator 227b separates the steam electrolysis chamber 215 from the oxidizing gas supply header 221, and prevents the atmosphere surrounding the lower tube sheet 225b from becoming too hot, which could result in a decrease in strength or increased corrosion due to the oxidizing agent contained in the oxidizing gas. Furthermore, to prevent the lower tube sheet 225b and other components from being thermally deformed due to temperature differences when exposed to the high temperatures within the steam electrolysis chamber 215, a metal material with high temperature resistance, such as a Ni-based alloy, may be used. The lower insulator 227b guides the oxidizing gas supplied to the oxidizing gas supply header 221 through the lower oxidizing gas penetration 235a and into the steam electrolysis chamber 215.

Heat exchange between the produced hydrogen and the oxidizing gas in the lower heat exchange section 14 occurs when the oxidizing gas passes through the oxidizing gas lower penetration 235a (heat transfer section _L3 of the lower heat exchange section). Note that heat exchange in areas of the lower heat exchange section 14 other than the heat transfer section _L3 (the area from the end (outer end) of the electrolysis cell 105 on the produced hydrogen discharge port (hydrogen gas discharge port) 12 side formed in the cell stack 101 to the oxidizing gas lower penetration 235a and the portion penetrating the oxidizing gas supply header 221) is slight and can be ignored.

The thickness of the lower insulator 227b can be adjusted appropriately so that the temperature of the lower tube plate is below the allowable temperature. Increasing the thickness of the lower insulator 227b increases the amount of heat exchanged. The volume of the oxidizing gas supply header 221 can be constant, regardless of the heat transfer area (length) of the lower heat exchange section 14.

In this embodiment, the structure of the cartridge 203 described above allows the produced hydrogen and oxidizing gas to flow in opposite directions inside and outside the cell stack 101. As a result, the produced hydrogen that passes through the interior of the base tube 103 and passes through the steam electrolysis chamber 215 exchanges heat with the oxidizing gas supplied to the steam electrolysis chamber 215, and is cooled to a temperature that prevents damage due to stress to the lower tube plate 225b, which is made of a metal material, before being supplied to the produced hydrogen discharge header 219. In addition, the oxidizing gas is heated by heat exchange with the produced hydrogen and supplied to the steam electrolysis chamber 215. As a result, oxidizing gas heated to the temperature required for the electrolysis reaction can be supplied to the steam electrolysis chamber 215 without using a heater or the like.

(SOEC module)
4, the module (electrolysis cell module) 201 includes, for example, a plurality of cartridges (electrolysis cell cartridges) 203 and a module container 205 that houses the plurality of cartridges 203. The module 201 includes a water vapor supply header 207, a plurality of water vapor supply branch pipes 207a, a produced hydrogen discharge header 209, and a plurality of produced hydrogen discharge branch pipes 209a. The module 201 also includes an oxidizing gas supply header (not shown) and a plurality of oxidizing gas supply branch pipes (not shown).

The steam supply main pipe 207 is provided inside the module container 205 and is connected to a steam supply unit that supplies steam at a predetermined gas composition and flow rate corresponding to the amount of hydrogen generated by the module 201, and is also connected to multiple steam supply branch pipes 207a. This steam supply main pipe 207 branches and directs the predetermined flow rate of steam supplied from the steam supply unit to multiple steam supply branch pipes 207a. The steam supply branch pipe 207a is also connected to the steam supply main pipe 207 and to steam supply pipes 231a of multiple cartridges 203. This steam supply branch pipe 207a directs the steam supplied from the steam supply main pipe 207 to the multiple cartridges 203 at a substantially uniform flow rate, thereby substantially equalizing the electrolysis voltage of the multiple cartridges 203.

The produced hydrogen discharge branch pipe 209a is connected to the produced hydrogen discharge pipes 231b of the multiple cartridges 203 and is also connected to the produced hydrogen discharge main pipe 209. This produced hydrogen discharge branch pipe 209a guides the produced hydrogen discharged from the cartridges 203 to the produced hydrogen discharge main pipe 209. The produced hydrogen discharge main pipe 209 is also connected to multiple produced hydrogen discharge branch pipes 209a, and a portion of the produced hydrogen discharge main pipe 209 is located outside the module container 205. This produced hydrogen discharge main pipe 209 guides the produced hydrogen, which is discharged at a substantially uniform flow rate from the produced hydrogen discharge branch pipe 209a, to the outside of the module container 205.

The module container 205 is operated with an internal pressure of atmospheric pressure to several MPa and a surface temperature of atmospheric temperature to approximately 300°C, and is preferably made of materials such as carbon steel from the perspective of low cost.

In this embodiment, a configuration in which multiple cartridges 203 are grouped together and stored in a modular container 205 is described, but this is not limited to this. For example, the cartridges 203 may also be stored in the modular container 205 without being grouped together.

The DC power required for the electrolysis reaction is converted to a predetermined voltage by a power converter such as a power conditioner and then supplied to the module. The power supplied to the module is distributed according to the number of cartridges connected in series and in parallel. In each cartridge 203, power is supplied to a power supply member (not shown) via a power supply plate (not shown), and is then passed to the electrolysis cells near the ends of the cell stack 101 via lead films 115 made of Ni/YSZ or the like provided on the multiple electrolysis cells 105.

Next, we will explain the basis for setting the heat transfer area (length) of the upper heat exchange section, lower heat exchange section, and hydrogen generation section.

(Relationship between cell stack temperature and resistance)
Figure 5 shows the relationship between the operating temperature of the cell stack and the IV characteristics. In this figure, the horizontal axis represents the electrolysis current (A) flowing through the cell stack, and the vertical axis represents the electrolysis voltage (V). The slope of each line represents the resistance. The greater the slope, the greater the resistance. The "thermonutral potential" is the potential at which the amount of heat absorbed by the electrolysis reaction balances the amount of heat generated by the internal resistance of the electrolysis cell during the electrolysis reaction. To maintain high energy efficiency in hydrogen conversion, a low electrolysis voltage (close to the thermoneutral voltage) is generally preferable.

As the electrolysis current in the cell stack increases, the electrolysis voltage also increases. For the same electrolysis current, the lower the cell stack temperature, the higher the electrolysis voltage. In other words, when the cell stack temperature is low, the internal resistance of the electrolytic cell increases, and the cell voltage required to generate the same amount of hydrogen increases, resulting in increased internal heat generation and a decrease in the energy efficiency of hydrogen conversion. Therefore, in order to increase the amount of hydrogen produced and improve the energy efficiency of hydrogen conversion, it is effective to increase the operating temperature of the cell stack and increase the electrolysis current while maintaining the electrolysis voltage near the thermal neutral voltage.

(Test 1)
Using the cell stack (Example 1) described in the above embodiment and a comparative cell stack (Comparative Example 1), the temperature distributions of the cell stack, supplied steam, and oxidizing gas when the same current was passed were predicted.

Here, the total length of the heat transfer section of the upper heat exchange section (L ₁ ), the length of the hydrogen generation section (L ₂ ), and the length of the heat transfer section of the lower heat exchange section (L ₃ ) was set to 1, and the length of the hydrogen generation section (L ₂ ) was set to 0.9 in both Example 1 and Comparative Example 1. Furthermore, the heat transfer section length of the lower heat exchange section (L ₃ ) in Example 1 was set to 9 times the heat transfer section length of the upper heat exchange section (L ₁ ), and the heat transfer section length of the lower heat exchange section (L ₃ ) and the heat transfer section length of the upper heat exchange section (L ₁ ) in Comparative Example 1 were set to be the same.

In addition, in all calculations, the allowable lower tube sheet temperature was assumed to be 600°C, the upper limit of the current value below the allowable value was determined, and the amount of hydrogen produced was calculated from this.

The results are shown in Figure 6. In the figure, the solid line represents the predicted temperature distribution of the raw material gas/produced gas in Example 1, and the dashed line represents the predicted temperature distribution of the raw material gas/produced gas in Comparative Example 1. In Example 1, the temperature of the produced hydrogen was highest at the end of the hydrogen generation section on the side of the produced hydrogen outlet. This tendency was also confirmed in Comparative Example 1.

On the other hand, when the steam supply temperature was the same in Example 1 and Comparative Example 1, the lower tube sheet temperature in Example 1 ( _L3 lower end temperature) was lower than the lower tube sheet temperature in Comparative Example 1 (L3 _' lower end temperature). These results confirmed that by making the heat transfer section length of the lower heat exchange section longer than the heat transfer section length of the upper heat exchange section, the temperature rise of the lower tube sheet temperature can be suppressed even if the hydrogen generation section length ( _L2 , L2 _' ) and the total heat transfer section length of the upper and lower heat exchange sections are the same. Note that both ends of the cell stack are held by holding members (upper and lower tube sheets) made of a metal material that is resistant to high temperatures. However, because exposure of these holding members to high temperatures reduces their durability due to oxidation, it is necessary to design the length of the heat transfer section of the lower heat exchange section so that the lower tube sheet temperature is below the allowable temperature so that the holding members do not exceed the allowable temperature.

(Test 2)
Next, for each case in which the length (L ₂ ) of the hydrogen generation section relative to the effective length (L) of the electrolysis cell stack was changed to 0.9, 0.8, 0.7, 0.6, and 0.5, the effect of the ratio of the heat transfer section length (L ₁ ) of the upper heat exchange section to the heat transfer section length (L ₃ ) of the lower heat exchange section on the performance (amount of hydrogen produced) of the electrolysis cell was evaluated.

The diameter of the substrate tube used in the cell stack was uniform in the longitudinal direction, and the width of the multiple electrolytic cells in the hydrogen generation section was all the same. The number of elements was assumed to be proportional to the length ( _L2 ) of the hydrogen generation section of the cell stack, and the amount of hydrogen generated was calculated from the electrolytic current of the elements and the number of elements.

The temperature distribution of the lower tube sheet was predicted based on a heat balance calculation of the element resistance value of the hydrogen generation section at each temperature in the gas flow direction, the amount of heat generated by the current, and the amount of heat exchanged in the heat transfer section of the upper and lower heat exchange sections. As with Test 1, the current value at which the lower tube sheet temperature reached the allowable value (600°C) was determined. The calculation conditions were as follows:

Average electrolysis voltage: 1.5V
Cell stack maximum allowable temperature: 950°C
Lower tube sheet maximum allowable temperature: 600°C
Supply steam composition: 90% _H2O ; 10% _H2
Steam utilization rate: 70%
Oxidizing gas utilization rate: 30%
Cell stack effective length (L = sum of _L1 , _L2 and _L3 ): 1 (= constant)

For each case where the length (L ₂ ) of the hydrogen generation section was 0.9, 0.8, 0.7, 0.6, and 0.5, the ratio of the heat transfer section length (L ₁ ) of the upper heat exchange section to the heat transfer section length (L ₃ ) of the lower heat exchange section was changed, and the calculation results for performance prediction were shown in Figures 7 to 11. In addition, the amount of hydrogen generated in each case was shown as a relative ratio, with the amount of hydrogen generated when L ₃ /L ₁ = 1 as the reference.

In Examples 2 to 16, the heat transfer section length (L ₃ ) of the lower heat exchange section is longer than the heat transfer section length (L ₁ ) of the upper heat exchange section. In Comparative Examples 2, 4, 6, 8, and 10, the heat transfer section length (L ₃ ) of the lower heat exchange section is equal to the heat transfer section length (L ₁ ) of the upper heat exchange section. In Comparative Examples 3, 5, 7, 9, and 11, the heat transfer section length (L ₃ ) of the lower heat exchange section is shorter than the heat transfer section length (L ₁ ) of the upper heat exchange section.

7, the amount of hydrogen generated in Examples 2 to 4 ( _L1 < _L3 ), in which the heat transfer section length of the lower heat exchange section was longer than that of the upper heat exchange section, was higher than that in Comparative Examples 2 and ₃ , in which _L1 = L3. The amount of hydrogen generated increased as the ratio of the heat transfer section length of the lower heat exchange section to that of the upper heat exchange section ( _L3 / _L1 ) increased. The amount of hydrogen generated in Comparative Example 3 ( _L1 > _L3 ), in which the heat transfer section length of the upper heat exchange section was longer than that of the lower heat exchange section, was lower than that in Comparative Example 2, in which _L1 = _L3 .

A similar trend was observed in Figures 8 to 11.

7 to 11, an increase in the amount of hydrogen generated per cell stack was confirmed in examples where the ratio of the heat transfer section length (L ₃ ) of the lower heat exchange section to the effective section length (L) of the cell stack was 0.07 or more and 0.45 or less.

7 to 11, an increase in the amount of hydrogen generated per cell stack was confirmed in examples in which the ratio (L ₃ /L ₁ ) of the length of the lower heat exchange section (L ₃ ) to the length of the upper heat exchange section (L 1 ) was greater than 1 _and not greater than 9.

7 to 11, the current density increases as the length ( _L2 ) of the hydrogen generation unit decreases. However, when the length of the hydrogen generation unit decreases, the number of cells included in the hydrogen generation unit decreases. Therefore, when the change in the number of cells is taken into account, shortening _L2 reduces the amount of hydrogen generated per cell stack.

Figure 12 shows the hydrogen production amounts obtained in Figures 7 to 11, organized by the ratio (L _{3 /} L ₁ ) of the length of the heat transfer section of the lower heat exchange section to the length of the heat transfer section of the upper heat exchange section, with the hydrogen production amount in Comparison Example 2 set to 1 when the length (L ₂ ) of the hydrogen generation section is 0.9 and the ratio (L ₃ /L ₁ ) of the length of the heat transfer section of the lower heat exchange section to the length of the heat transfer section of _the upper heat exchange section is _1.0 .

12, it was confirmed that by making the overall length of the lower heat exchange section ( _L3 ) longer than the length of the upper heat exchange section ( _L1 ), the amount of hydrogen generated per cell stack increased compared to the reference comparative example 2. When the ratio ( _L3/L1 ) of the heat transfer section length ( _L3 ) of the lower heat exchange section to the heat transfer section length (L1) of the upper heat exchange section is ₂ or _more , the increase in the amount of hydrogen generated is large, more preferably 3 or more and 9 or less, and even more preferably 3 or more and 7 or less.

The manufacturing methods of the electrolytic cell stack, electrolytic cell cartridge, electrolytic cell module, and electrolytic cell stack described in the above-described embodiments can be understood, for example, as follows:

The electrolysis cell stack (101) according to the first aspect of the present disclosure comprises a hydrogen generation unit (10) including an electrolysis cell (105) having a Ni-containing hydrogen electrode (109), an oxygen electrode (113), and a solid electrolyte membrane (111) sandwiched between the hydrogen electrode and the oxygen electrode; a raw material gas supply port (11) for supplying raw material gas to the hydrogen electrode of the hydrogen generation unit; a hydrogen gas outlet (12) for discharging hydrogen gas generated in the hydrogen generation unit; and a hydrogen gas supply port (13) for discharging the raw material gas and the hydrogen gas generated in the hydrogen generation unit, located closer to the raw material gas supply port than the hydrogen generation unit. The system comprises a raw gas supply-side heat exchanger (13) that exchanges heat with the oxidizing gas supplied to the oxygen electrode side, and a hydrogen gas discharge-side heat exchanger (14) that is located closer to the hydrogen gas outlet than the hydrogen generation section and exchanges heat with the oxidizing gas supplied to the oxygen electrode side, the raw gas supply-side heat exchanger and the hydrogen gas discharge-side heat exchanger each consisting of a heat transfer section and a header section, and the heat transfer section area of the hydrogen gas discharge-side heat exchanger is larger than the heat transfer section area of the raw gas supply-side heat exchanger.

By making the heat transfer area of the hydrogen gas discharge side heat exchanger larger than that of the raw gas supply side heat exchanger, heat exchange between the hydrogen gas generated in the hydrogen generation unit and the supplied oxidizing gas can be promoted. This makes it possible to keep the temperature of the hydrogen gas discharged from the hydrogen gas outlet lower than when the heat transfer area of the raw gas supply side heat exchanger and the heat transfer area of the hydrogen gas discharge side heat exchanger are the same.

The feed gas used for steam electrolysis is water vapor, which does not undergo an endothermic chemical reaction in the feed gas supply heat exchanger. Therefore, unlike when a feed gas containing methane or other gases is supplied, there is no temperature drop due to an endothermic reaction, and even if the heat transfer area of the feed gas supply heat exchanger is smaller than the heat transfer area of the hydrogen gas discharge heat exchanger, the temperature of the feed gas rises, making it possible to maintain the inlet temperature of the electrolysis section of the electrolysis cell stack. A high operating temperature reduces the internal resistance of the cell, lowering the electrolysis voltage and improving hydrogen generation efficiency.

The electrolysis cell stack according to a second aspect of the present disclosure is the first aspect described above, wherein the ratio of the heat transfer area of the hydrogen gas discharge side heat exchanger to the heat transfer area of the raw material gas supply side heat exchanger is 2 or greater.

In an electrolytic cell stack where the ratio of the heat transfer area of the hydrogen gas discharge side heat exchanger to the heat transfer area of the raw gas supply side heat exchanger is within the above range, the amount of hydrogen produced is greater than in conventional electrolytic cell stacks where the heat transfer area of the hydrogen gas discharge side heat exchanger is equal to the heat transfer area of the raw gas supply side heat exchanger.

The electrolysis cell stack according to a third aspect of the present disclosure is the first or second aspect described above, wherein the ratio of the heat transfer area of the hydrogen gas discharge side heat exchanger to the heat transfer area of the raw material gas supply side heat exchanger is 3 or more and 9 or less.

In electrolysis cell stacks where the ratio of the heat transfer area of the heat exchanger on the hydrogen gas discharge side to the heat transfer area of the heat exchanger on the raw material gas supply side is within the above range, the increase in hydrogen production is particularly large.

The electrolysis cell stack according to a fourth aspect of the present disclosure is any one of the first to third aspects described above, wherein the ratio of the heat transfer section length of the hydrogen gas discharge side heat exchange section to the heat transfer section length of the raw material gas supply side heat exchange section is 2 or greater.

The electrolytic cell cartridge (203) according to the fifth aspect of the present disclosure includes an electrolytic cell stack described in any one of the first to fourth aspects above.

The electrolysis cell module (201) according to the sixth aspect of the present disclosure includes the electrolysis cell cartridge described in the fifth aspect above.

A seventh aspect of the present disclosure provides a method for manufacturing an electrolytic cell stack comprising: a hydrogen generation unit including an electrolytic cell having a Ni-containing hydrogen electrode, an oxygen electrode, and a solid electrolyte membrane sandwiched between the hydrogen electrode and the oxygen electrode; a raw material gas supply port for supplying raw material gas to the hydrogen electrode of the hydrogen generation unit; a hydrogen gas outlet port for discharging hydrogen gas generated in the hydrogen generation unit; a raw material gas supply-side heat exchanger located closer to the raw material gas supply port than the hydrogen generation unit and performing heat exchange between the raw material gas and an oxidizing gas supplied to the oxygen electrode; and a hydrogen gas outlet-side heat exchanger located closer to the hydrogen gas outlet port than the hydrogen generation unit and performing heat exchange between the hydrogen gas and the oxidizing gas supplied to the oxygen electrode, wherein the raw material gas supply-side heat exchanger and the hydrogen gas outlet-side heat exchanger each comprise a heat transfer section and a header section, and the heat transfer section area of the hydrogen gas outlet-side heat exchanger is larger than the heat transfer section area of the raw material gas supply-side heat exchanger.

10 Hydrogen generating section 11 Steam supply port (raw material gas supply port)
12. Produced hydrogen outlet (hydrogen gas outlet)
13 Upper heat exchange section (raw material gas supply side heat exchange section)
14 Lower heat exchange section (hydrogen gas discharge side heat exchange section)
101 Cell stack (electrolysis cell stack)
103 Substrate tube 105 Electrolytic cell 107 Interconnector 109 Hydrogen electrode (fuel electrode)
111 Solid electrolyte membrane 113 Oxygen electrode 115 Lead membrane 201 Module (electrolysis cell module)
203 Cartridge (electrolytic cell cartridge)
205 Module container 207 Steam supply header 207a Steam supply branch pipe 209 Produced hydrogen discharge header 209a Produced hydrogen discharge branch pipe 215 Steam electrolysis chamber 217 Steam supply header 219 Produced hydrogen discharge header 221 Oxidizing gas supply header 223 Oxidizing gas discharge header 225a Upper tube plate 225b Lower tube plate 227a Upper heat insulator 227b Lower heat insulator 229a Upper casing 229b Lower casing 231a Steam supply pipe 231b Produced hydrogen discharge pipe 233a Oxidizing gas supply pipe 233b Oxidizing gas discharge pipe 235a Oxidizing gas lower penetration 235b Oxidizing gas upper penetration 237a Upper seal member 237b Lower seal member 620 Temperature measurement section L ₁ (S ₁ ) Heat transfer section of upper heat exchange section (heat transfer section area)
L ₂ (S ₂ ) Hydrogen generating section (reaction area of hydrogen generating section)
_L3 ( _S3 ) Heat transfer area of the lower heat exchange section (heat transfer area)

Claims (7)

a hydrogen generating unit including an electrolytic cell having a nickel-containing hydrogen electrode, an oxygen electrode, and a solid electrolyte membrane sandwiched between the hydrogen electrode and the oxygen electrode;
a raw material gas supply port for supplying a raw material gas to the hydrogen electrode of the hydrogen generating unit;
a hydrogen gas outlet for discharging the hydrogen gas generated in the hydrogen generation unit;
a raw material gas supply-side heat exchange unit, which is located closer to the raw material gas supply port than the hydrogen generation unit and which exchanges heat between the raw material gas and an oxidizing gas discharged from the oxygen electrode side;
a hydrogen gas discharge side heat exchanger located closer to the hydrogen gas discharge port than the hydrogen generation unit and performing heat exchange between the hydrogen gas and an oxidizing gas supplied to the oxygen electrode side;
Equipped with
the raw material gas supply-side heat exchange unit has a heat transfer unit through which the flow rate of the oxidizing gas is increased compared to when the oxidizing gas flows through the hydrogen generation unit, and the hydrogen gas discharge-side heat exchange unit has a heat transfer unit through which the flow rate of the oxidizing gas is increased compared to when the oxidizing gas flows through the hydrogen generation unit,
an electrolysis cell stack in which the area of the heat transfer portion of the hydrogen gas discharge side heat exchanger is larger than the area of the heat transfer portion of the raw material gas supply side heat exchanger; The electrolysis cell stack of claim 1, wherein the ratio of the heat transfer area of the hydrogen gas discharge side heat exchanger to the heat transfer area of the raw material gas supply side heat exchanger is 2 or greater. The electrolysis cell stack of claim 1, wherein the ratio of the heat transfer area of the hydrogen gas discharge side heat exchanger to the heat transfer area of the raw material gas supply side heat exchanger is 3 or more and 9 or less. The electrolysis cell stack of claim 1, wherein the ratio of the heat transfer section length of the hydrogen gas discharge side heat exchange section to the heat transfer section length of the raw material gas supply side heat exchange section is 2 or greater. An electrolytic cell cartridge equipped with the electrolytic cell stack described in any one of claims 1 to 4. An electrolytic cell module equipped with the electrolytic cell cartridge described in claim 5. a hydrogen generating unit including an electrolytic cell having a nickel-containing hydrogen electrode, an oxygen electrode, and a solid electrolyte membrane sandwiched between the hydrogen electrode and the oxygen electrode;
a raw material gas supply port for supplying a raw material gas to the hydrogen electrode of the hydrogen generating unit;
a hydrogen gas outlet for discharging the hydrogen gas generated in the hydrogen generation unit;
a raw material gas supply-side heat exchange unit, which is located closer to the raw material gas supply port than the hydrogen generation unit and which exchanges heat between the raw material gas and an oxidizing gas discharged from the oxygen electrode side;
a hydrogen gas discharge side heat exchanger located closer to the hydrogen gas discharge port than the hydrogen generation unit and performing heat exchange between the hydrogen gas and an oxidizing gas supplied to the oxygen electrode side;
A method for manufacturing an electrolysis cell stack comprising:
the raw material gas supply-side heat exchange unit has a heat transfer unit through which the flow rate of the oxidizing gas is increased compared to when the oxidizing gas flows through the hydrogen generation unit,
the hydrogen gas discharge side heat exchange unit has a heat transfer unit through which the flow rate of the oxidizing gas is faster than when the oxidizing gas flows through the hydrogen generation unit,
a heat transfer section area of the hydrogen gas discharge side heat exchange section being larger than a heat transfer section area of the raw material gas supply side heat exchange section;