Method for manufacturing solid oxide electrolytic cells using a continuous furnace

Abstract

To provide a production method of a solid oxide electrolysis cell (SOEC) using a continuous furnace, which can suppress costs compared to a batch processing.SOLUTION: A production method of a solid oxide electrolysis cell (SOEC) 20 includes: removing a binder from the SOEC by using microwave radiation while the SOEC is arranged in a first zone 160 of a furnace; and sintering the SOEC while the SOEC is arranged in a second zone 170 of the furnace.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This application is a non-provisional application claiming the benefits of U.S. Provisional Application No. 63 / 137,941, filed on 15 January 2021, the contents of which said Provisional Application are incorporated herein by reference in their entirety.

[0002] Embodiments of this disclosure relate to a method for manufacturing electrolytic cells using a continuous furnace. [Background technology]

[0003] Hydrogen can be produced using solid oxide electrolytic cells (SOECs). However, manufacturing SOECs is relatively expensive. [Overview of the Initiative]

[0004] In various embodiments, a method for manufacturing SOEC includes removing a binder from SOEC using microwave radiation while SOEC is placed in a first zone of a furnace, and sintering SOEC while SOEC is placed in a second zone of a furnace. [Brief explanation of the drawing]

[0005] [Figure 1] Figure 1 shows the operation of a solid oxide electrolytic cell according to various embodiments of this disclosure. [Figure 2A] Figure 2A is a perspective view of a solid oxide electrolytic cell stack. [Figure 2B] Figure 2B is a partial longitudinal cross-sectional view of the stack shown in Figure 2A. [Figure 3] Figure 3 shows a method for forming an SOEC according to various embodiments of this disclosure. [Modes for carrying out the invention]

[0006] Solid oxide fuel cells (SOFCs) can operate as SOECs to produce hydrogen and oxygen from water using electrolysis. In SOFC mode, oxide ions are transported from the cathode side (air) to the anode side (fuel), driven by the chemical gradient of the oxygen partial pressure within the electrolyte. In SOEC mode, a positive potential (e.g., 1-1.5V) is applied to the air side of the cell, and oxide ions are transported from the "fuel" (e.g., water) side to the air side. Since the cathode and anode are reversed between SOFC and SOEC (i.e., the SOFC cathode is the SOEC anode, and the SOFC anode is the SOEC cathode), the SOFC cathode (SOEC anode) will be referred to as the air electrode, and the SOFC anode (SOEC cathode) will be referred to as the fuel electrode.

[0007] Figure 1 shows the operation of SOEC20 according to various embodiments of the present disclosure. Referring to Figure 1, an airflow is supplied to the air electrode 23, and a fuel flow containing water (e.g., a water flow, a water-hydrogen mixture, etc.) is supplied to the fuel electrode 27. At the fuel electrode 27, the water is reduced by the reaction equation: H2O + 2e → O 2- +H2 produces H2 gas and O 2- It becomes an ion. 2- The ions are transported through the solid oxide electrolyte 25 and then oxidized at the air electrode 23 (O 2- It is converted from O2 to produce oxygen molecules.

[0008] Figure 2A is a perspective view of a solid oxide electrolytic cell stack 100, and Figure 2B is a partial longitudinal section of the stack 100 in Figure 2A. As used herein, the term “electrolytic cell stack” means a plurality of stacked electrolytic cells that may optionally share a common water inlet and exhaust passage or riser. As used herein, “electrolytic cell stack” includes separate electrical components that constitute part of an electrolytic cell column, including two end plates that are directly connected to a power regulator and the power (i.e., electrical) input section of the stack, or terminal plates that provide electrical inputs.

[0009] For example, stack 100 can include a plurality of SOECs 20 separated by an interconnect 10, also referred to as a gas flow separator plate or a bipolar plate. Each SOEC 20 includes an air electrode 23, a solid oxide electrolyte 25, and a fuel electrode 27. Stack 100 can optionally include an internal fuel riser channel 22 (the fuel can be, for example, water).

[0010] The air electrode 23 can include a conductive material such as a conductive perovskite material such as lanthanum strontium manganite (LSM). Other conductive perovskites such as lanthanum strontium cobaltite (LSC), lanthanum strontium cobalt manganite (LSCM), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium ferrite (LSF), La 0.85 Sr 0.15 Cr 0.9 Ni 0.1 O3 (LSCN), or a metal such as Pt can also be used. In some embodiments, the air electrode 23 can include a mixture of a conductive material and an ion-conductive ceramic material. For example, the air electrode 23 can include from about 10 wt% to about 90 wt% of the above conductive material (e.g., LSM, etc.) and from about 10 wt% to about 90 wt% of an ion-conductive material. Suitable ion-conductive materials include zirconia-based and / or ceria-based materials. For example, the ion-conductive material can include scandia-stabilized zirconia (SSZ), ceria, and at least one of yttria and ytterbia. In some embodiments, the ion-conductive material can be represented by the following formula. (ZrO2) 1-W-X-Z (Sc2O3) W (CeO2) X (Y2O3) a (Yb2O3) b , where 0.09 ≦ W ≦ 0.11, 0 < X ≦ 0.0125, a + b = Z, and 0.0025 ≦ Z ≦ 0.0125. In some embodiments, 0.009 < X ≦ 0.011, and 0.009 ≦ Z ≦ 0.011, and optionally, if one of a or b is non-zero, the other of a or b may be zero.

[0011] Electrolyte 25 can include stabilized zirconia such as scandia-stabilized zirconia (SSZ), yttria-stabilized zirconia (YSZ), scandia-ceria-stabilized zirconia (SCSZ), scandia-ceria-yttria-stabilized zirconia (SCYSZ), and scandia-ceria-ytterbia-stabilized zirconia (SCYbSZ). For example, electrolyte 25 can include scandia and ceria-stabilized zirconia containing 5-12 mol% scandia, 1-7 mol% ceria, and 80-94% zirconia, and optionally 0.5-3 mol% ytterbia. Alternatively, electrolyte 25 can include yttria and ceria-stabilized zirconia containing 3-10 mol% yttria, 1-6 mol% ceria, and 84-96 mol% zirconia. Alternatively, the electrolyte 25 may include other ion-conducting materials such as doped ceria, for example, Samaria doped ceria (SDC), Gadolinia doped ceria (GDC), or Yttria doped ceria (YDC).

[0012] The fuel electrode 27 may include a cermet layer comprising a metal-containing phase and a ceramic phase. The metal-containing phase may include a metal catalyst that acts as an electron conductor, such as nickel (Ni), cobalt (Co), copper (Cu), or alloys thereof. The metal catalyst may be in a metallic state or an oxide state. For example, if the metal catalyst is in an oxide state, it forms a metal oxide. Thus, prior to the operation of the SOEC, the fuel electrode 27 can be annealed in a reducing atmosphere to reduce the oxidized metal catalyst back to a metallic state. The ceramic phase of the fuel electrode 37 may include, but is not limited to, gadolinia-doped ceria (GDC), samaria-doped ceria (SDC), ytterbia-doped ceria (YDC), scandia-stabilized zirconia (SSZ), ytterbia-scandia-stabilized zirconia (YbCSSZ), and the like. As disclosed in U.S. Patent No. 8,580,456, incorporated herein by reference, YbCSSZ may contain scandia in an amount equal to 9–11 mol%, e.g., 10 mol%, ceria in an amount greater than 0 (e.g., at least 0.5 mol%) and 2.5 mol% or less, e.g., 1 mol%, and at least one of yttria and ytterbia in an amount greater than 0 and 2.5 mol% or less, e.g., 1 mol%.

[0013] Each interconnect 10 electrically connects adjacent SOECs 20 within the stack 100. In particular, an interconnect 10 can electrically connect the air electrode 23 of one SOEC 20 to the fuel electrode 27 of an adjacent SOEC 20. Figure 2B shows that the lower SOEC 20 is positioned between two interconnects 10. Each interconnect 10 includes ribs 12 that at least partially define the fuel channel 18A and the air channel 18B. The interconnect 10 can act as a reactant separator, separating a first reactant, such as water containing the fuel flow, from a second reactant, such as air supplied to the adjacent SOEC 20. The ends of the stack 100 may have air end plates or fuel end plates (not shown) for supplying air or fuel to the end electrodes, respectively. Each interconnect 10 may consist of, or include, a conductive material such as a metal alloy (e.g., chromium-iron alloy) having a coefficient of thermal expansion equivalent to that of the solid oxide electrolyte 25 (e.g., a difference of 0-10%). For example, the interconnect 10 may include a metal (e.g., a chromium-iron alloy such as an alloy of 4-6% by weight of iron (e.g., 5% by weight of iron), optionally 1% by weight or less of yttrium and the remainder chromium).

[0014] Figure 3 is a process diagram illustrating an exemplary method for producing an SOEC by screen printing fuel electrodes and air electrodes onto an electrolyte, followed by drying and firing. Referring to Figure 3, a bare, plate-shaped solid oxide electrolyte 25, such as a stabilized zirconia electrolyte, is unpacked and loaded into a slotted cassette 101. Each cassette 101 is placed on an elevator 103 that aligns the individual electrolytes 25 onto a walking beam conveyor 105. The walking beam conveyor 105 transports the electrolytes 25 to a printing tool plate 107 while minimizing wear on the electrolytes 25 during the process. A pickup head 109 can be used to position the electrolytes 25 onto the tool plate 107 from the end of the walking beam conveyor 105. The pickup head 109 can be configured to pick up the electrolytes 25 using a Bernoulli pad or a vacuum pogo pin array.

[0015] The screen printing cycle begins when the pickup head 109 lowers the electrolyte 25 onto the tool plate 107. First, several snugger alignment pins 111 close inward toward the electrolyte 25. The pins 111 may be fixed and / or pressure applied. The inward movement combines to position the electrolyte 25 at a predetermined alignment position. A weak suction of the tool plate 107 is used to prevent the electrolyte 25 from vibrating between the alignment pins 111. Once the electrolyte 25 is positioned, hold-down suction acts, and the alignment pins 111 retract away from the work area. Subsequently, the carriage 113 of the tool plate 107 reciprocates beneath the mesh screen 115 (e.g., a high-wire-density calender mesh), and the printing cycle begins. The printing cycle includes a screen printing process using an ink suitable for screen printing, for example, an ink with a relatively high solids content of 80-93% by weight, and screen tooling that defines the formed ink image and the film formation characteristics of the ink. The ink contains an organic binder and powder particles of electrode active material in a solvent.

[0016] After the electrode screen printing is complete, the printed electrolyte 25 is lifted from the tool plate 107 manually or by a suitable machine or device such as a pickup head 109. The tool plate 107 returns to its home position to receive the next electrolyte 25. The printed electrolyte 25 is transported on the conveyor 117 to a predetermined pickup position. Another pickup head 119, such as a robotic pickup head, descends and surrounds the electrolyte 25 with two or more cleats. The cleats do not apply pressure to the printed material in order to minimize chipping or damage to the ink-printed electrolyte 25. The pickup head 119 lifts and holds the electrolyte 25 against gravity. The pickup head 119 then transports the electrolyte 25 to the drying belt 121 and releases the electrolyte 25 onto the drying belt 212.

[0017] Any suitable drying device is used. For example, the drying device 120 can include a drying conveyor belt 121, such as a woven stainless steel belt or other suitable conveyor belt, that moves through an infrared heating zone 123 heated by one or more infrared heating lamps 125. The electrolyte 25 is conveyed by the belt 121 to the heating zone 123 and heated by the heating lamp 125 in the heating zone. During the heating process of preparing the printed material for further processing, a certain proportion of the ink organic matter is released from the electrode.

[0018] The belt 121 may continue to move continuously while conveying the electrolyte 25 through the heating zone. Alternatively, the belt 121 may convey the electrolyte 25 to the heating zone, then stop while the printed material is being heated, and subsequently move the electrolyte 25 out of the heating zone after heating is completed.

[0019] If necessary, the drying device can include two or more belts and / or two or more heating zones. When there are two or more belts 121, the pick-up head 119 may be pre-programmed or controlled by an operator or a control system to sequentially place the printed material on different belts in order to dry the printed material in parallel rather than in series. The drying process can be carried out at a temperature below 150°C, for example, 50 - 100°C, for example, 70 - 80°C.

[0020] Next, the dried printed electrolyte 25 is moved from the drying device 120 manually or by a machine. Any suitable machine is used. For example, a suction pick-up head 127 consisting of a robotic Bernoulli pad or a pogo pin can be arranged near the outlet of the drying device. The pad or head moves the electrolyte 25 from the drying belt and places the electrolyte 25 on the walking beam conveyor 129. The walking beam conveyor 129 conveys the printed material to the outlet elevator 131 and then loads the electrolyte 25 into a cassette for subsequent processing.

[0021] In particular, the above process can be repeated to apply an additional electrode ink layer on the same side of the electrolyte 25 and / or print one or more electrode ink layers on the opposite side of the electrolyte 25 to form the SOEC20. In various embodiments, various electrode inks can be applied on both sides and / or the same side of the electrolyte 25 to form the SOEC.

[0022] Conventionally, an electrolyte printed with one or more electrode inks is heat-treated in a batch furnace to remove the ink binder (e.g., burnout) and sinter the ink printed on the electrolyte to form an electrode. However, the conventional binder burnout process requires a long heat treatment time to avoid delamination between electrode layers and may require mechanical restraint of the electrolyte to prevent excessive distortion of the electrolyte. The equipment required to restrain the electrolyte also increases the thermal mass of the process, which increases the processing time and reduces the processing capacity.

[0023] Conventional batch furnaces cannot process a new batch of electrolyte until they are cooled after sintering is complete, which extends the processing time and increases energy loss. Furthermore, conventional electric batch furnaces are also vulnerable to failures of the heating elements, resulting in a reduction of the overall furnace load of the electrolyte and a significant increase in costs.

[0024] In view of the above and / or other drawbacks of the conventional methods, various embodiments provide an improved method for binder removal and electrode sintering that utilizes microwave heating. The electrolyte 25 can be subjected to microwave heating for a layer of one dried electrode ink (e.g., fuel or air electrode ink) printed on one side of the electrolyte 25 or two dried electrode inks (e.g., both fuel and air electrode inks) printed on each of the opposing sides of the electrolyte 25.

[0025] In particular, after the electrode ink has been printed onto one or both sides of the electrolyte 25, the SOEC 20 can be loaded onto a ceramic frame or support 140. Specifically, the support 140 may include one or more rails or rings that support each SOEC 20 so that the dried electrode ink is exposed (for example, without contact with adjacent SOEC 20s).

[0026] The support 140 can be loaded into a continuous furnace 150, for example, a continuous pusher or a roller hearth kiln. The furnace 150 may include ceramic rollers 152 that are driven continuously or at a variable speed to move the support 140 through the furnace 150. The furnace 150 may include at least one microwave generator 162 and at least one additional heating element 172. The furnace 150 can be divided into a first zone 160 and a second zone 170. The furnace 150 can be configured to maintain a selected atmosphere and / or temperature inside the first zone 160 and / or the second zone 170. For example, the furnace 150 can be configured to maintain an internal atmosphere with a selected oxygen partial pressure.

[0027] During operation, the support 140 loaded with SOEC 20 (e.g., printed electrolyte 25) can be supplied to a first zone 160 for binder removal (e.g., burnout). In particular, the microwave oscillator 162 may include one or more microwave sources configured to radiate microwaves onto the SOEC 20 as the support 140 moves through the first zone 160. The microwave oscillator 162 may be configured to heat the SOEC 20 to a sufficient temperature to remove (e.g., volatilize) the binder from the electrode ink printed thereon. For example, the SOEC 20 can be debindered at temperatures above 300°C, e.g., in the range of about 400°C to about 800°C. In some embodiments, the first zone 160 can be heated by the heat generated in the second zone 170 to accelerate the rate at which the binder burns out. Thus, the binder removal process can be referred to as a microwave-assisted binder burnout process.

[0028] After the binder is removed, the support 140 can be moved into a second zone 170. The second zone 170 can be heated by a heating element 172. In some embodiments, the heating element 172 may include one or more gas heating elements (e.g., gas combustion burners). However, in other embodiments, the heating element 172 may optionally include one or more resistance heating elements. The gas heating element may be placed in a separate chamber of the furnace so that the combustion gas does not affect the internal atmosphere of the furnace 150. For example, high-temperature combustion gas may be routed around the second zone 170 to heat the side walls of the furnace 150, thereby indirectly heating the electrolyte 25.

[0029] The second zone 170 can be maintained at a temperature sufficient to sinter the SOEC 20 as it passes through the second zone 170. In other words, the ceramic or cermet electrodes (23 and / or 27) are sintered on the electrolyte 25. For example, the SOEC 20 can be sintered at temperatures above 1000°C, for example, in the range of about 1100°C to about 1400°C.

[0030] After sintering, the support 140 is removed from the furnace 150 and cooled. After cooling, the sintered SOEC 20 is removed from the support 140.

[0031] According to various embodiments, the disclosed continuous binder burnout and sintering process can result in unexpected cost reductions compared to conventional batch processing. For example, SOEC output can be increased by more than four times with the same or similar operating costs as conventional batch processing. For instance, the continuous furnace used in this embodiment can have a smaller cross-section compared to conventional batch furnaces, which reduces thermal mass and associated energy consumption costs. Furthermore, the continuous furnace of this embodiment does not require resistance heating elements and can withstand thermal cycling, thus significantly reducing the failure rate. As a result, the use of a continuous furnace can also keep overall maintenance costs low.

[0032] The foregoing description of the disclosed embodiments is provided to enable those skilled in the art to practice or utilize the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the scope of the invention. Accordingly, the invention is not intended to be limited to the embodiments shown herein, but rather should be given the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for manufacturing a solid oxide electrolytic cell (SOEC), To supply the SOEC to the first zone of the reactor, While the SOEC is being continuously moved through the first zone of the furnace to the second zone of the furnace, the binder is removed from the SOEC using microwave radiation, and during this process, the first zone is maintained at a first temperature while the SOEC is moving through the first zone to the second zone, and The process includes sintering the SOEC using a heating element while the SOEC is continuously moved through the second zone of the furnace, and maintaining the second zone at a second temperature during this process. A method comprising a microwave source located in the first zone and a heating element located in the second zone.

2. The method according to claim 1, wherein the furnace is a continuous pusher or a roller hearth kiln.

3. The supply includes loading a plurality of SOECs onto a ceramic support and supplying the ceramic support to the first zone, The method according to claim 1, wherein removing the binder includes removing the binder from the plurality of SOECs loaded onto the ceramic support while the ceramic support moves through the first zone of the furnace using microwave radiation.

4. The method according to claim 3, wherein the sintering includes sintering the plurality of SOECs loaded onto the ceramic support while the ceramic support moves through the second zone of the furnace.

5. The method according to claim 1, wherein removing the binder includes removing the binder from the electrode ink coated on one side of the solid oxide electrolyte of the SOEC.

6. The method according to claim 1, wherein removing the binder includes removing the binder from each of the first and second electrode inks coated on the opposing first and second surfaces of the solid oxide electrolyte of the SOEC.

7. Printing the first electrode ink onto the first surface of the solid oxide electrolyte, To dry the first electrode ink, Printing the second electrode ink onto the second surface of the electrolyte, The second electrode ink is dried to form the SOEC. After drying the first and second electrode inks, supply the SOEC to the first zone of the furnace, and The method according to claim 6, further comprising cooling the SOEC outside the furnace.

8. The method according to claim 1, wherein the first zone includes a plurality of microwave sources configured to generate the microwave radiation.

9. The method according to claim 1, wherein the heating element includes a gas heating element.

10. The method according to claim 1, wherein the SOEC moves continuously through the first zone and the second zone at a constant speed.

11. The method according to claim 1, wherein the SOEC passes through the first and second zones without leaving the furnace.

12. The method according to claim 1, wherein the first temperature includes a constant temperature of 400°C to 800°C.

13. The method according to claim 12, wherein the second temperature includes a constant temperature of 1100°C to 1400°C.

14. The method according to claim 1, wherein the sintering is performed by sintering at least one electrode of the SOEC onto the solid oxide electrolyte of the SOEC.

15. The method according to claim 14, wherein the solid oxide electrolyte comprises stabilized zirconia or a doped ceria material.

16. The method according to claim 15, wherein the at least one electrode includes an air electrode containing a conductive perovskite material.

17. The method according to claim 16, wherein the air electrode comprises a mixture of the conductive perovskite material and the ion-conductive ceramic material.

18. The method according to claim 15, wherein the at least one electrode includes a fuel electrode made of a cermet material.

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