Method for operating high-temperature water electrolysis stack

Abstract

A method for operating a high-temperature water electrolysis stack. The disclosed method for operating a high-temperature water electrolysis stack comprises the steps of: (S210) injecting a reducing gas into a hydrogen electrode of a high-temperature water electrolysis stack; (S220) initially increasing the temperature of the hydrogen electrode of the high-temperature water electrolysis stack; (S230) blocking the reducing gas injected into the hydrogen electrode of the high-temperature water electrolysis stack; (S240) primarily oxidizing the hydrogen electrode of the high-temperature water electrolysis stack; (S250) reinjecting the reducing gas into the hydrogen electrode of the high-temperature water electrolysis stack; (S260) blocking, again, the reducing gas injected into the hydrogen electrode of the high-temperature water electrolysis; (S270) secondarily oxidizing the hydrogen electrode of the high-temperature water electrolysis stack; and (S280) reinjecting the reducing gas into the hydrogen electrode of the high-temperature water electrolysis stack and performing normal operation.

Description

Operating method of high-temperature electrolysis stack

[0001] A method for operating a high-temperature electrolysis stack is disclosed. More specifically, a method for operating a high-temperature electrolysis stack capable of improving the efficiency of the high-temperature electrolysis stack is disclosed.

[0002] As interest in clean energy has increased recently, research on hydrogen energy is actively underway.

[0003] The use of hydrogen energy is preferred due to its high efficiency and its advantages in terms of economic and environmental aspects, and it is clear that it will become an ideal energy circulation system.

[0004] In order to utilize hydrogen energy, a hydrogen production process is required to supply hydrogen, and an energy conversion device to consume the produced hydrogen is also required.

[0005] Several methods for producing and using hydrogen energy are currently being developed.

[0006] Hydrogen production can be divided into a method using existing hydrocarbons as raw materials (hydrocarbon reforming) and a method using water to produce hydrogen based on the raw materials used to produce hydrogen.

[0007] Hydrocarbon reforming is a method of converting existing hydrocarbon fuels such as diesel, gasoline, and natural gas into hydrogen using heat and catalysts.

[0008] The most common method of utilizing existing hydrocarbons is to burn them using an internal combustion engine, but converting hydrocarbons into hydrogen and utilizing them has advantages in terms of efficiency.

[0009] If stored hydrogen is supplied in the form of hydrocarbons and then reformed and used, it can be directly applied to the current fossil fuel-based energy supply system, and has the advantage of eliminating the need to store hydrogen separately.

[0010] However, because it uses fuel that is a mixture of various substances, there is a high possibility that impurities will be added to the product, and in the case of high hydrocarbon fuels such as diesel, problems such as carbon deposition may occur, which is a disadvantage.

[0011] On the other hand, hydrogen production using water as fuel involves decomposing water into hydrogen and oxygen using heat and electrical energy. This method has the advantage of virtually limitless access to water, making it virtually infinitely accessible, and thus significantly reducing fuel usage.

[0012] However, the process of decomposing water into hydrogen and oxygen requires more energy than the energy obtained by combining hydrogen and oxygen, and all of the energy required must be supplied externally.

[0013] Methods for producing hydrogen from water can be broadly classified into thermochemical production and water electrolysis.

[0014] The thermochemical process is a method of producing pure hydrogen by adding various substances to water and going through a chemical process.

[0015] Electrolysis is a method of decomposing water (water vapor) into hydrogen and oxygen using electrical energy.

[0016] Electrolysis methods such as the above can be categorized into alkaline water electrolysis, polymer electrolyte membrane electrolysis, and high-temperature electrolysis (HTE). Among these, HTE has the advantages of high-temperature electrolysis, which enables high-efficiency water decomposition, ease of maintenance, and suitability for large-scale production.

[0017] In addition, high-temperature electrolysis can produce hydrogen at high temperatures (550-900℃) and is operated by a solid oxide electrolysis cell (SOEC).

[0018] A solid oxide electrolytic cell (SOEC) is an electrolytic device that uses a solid oxide as an electrolyte. It consists of a hydrogen electrode, an electrolyte, and an oxygen electrode. In a SOEC, when water vapor is supplied to the hydrogen electrode and electricity is applied, the water vapor is electrolyzed, causing oxygen ions to migrate through the electrolyte. These oxygen ions combine with oxygen at the oxygen electrode to form a gaseous state, leaving only hydrogen at the hydrogen electrode. Therefore, water can be decomposed to produce gaseous hydrogen and oxygen, respectively. This is the opposite reaction (reverse reaction) to that of a solid oxide fuel cell (SOFC), and its structure is also very similar to that of an SOFC.

[0019] In addition, solid oxide electrolytic cells operate at high temperatures of approximately 550–900°C, and their thermodynamic efficiency is high at high temperatures. From a thermodynamic perspective, the process of decomposing water into hydrogen and oxygen is a non-spontaneous reaction that requires energy, and the energy required for the reaction (△H: Enthalpy) must be supplied to induce the reaction. Since the hydrogen electrode plays a role in decomposing water vapor, it is inevitably exposed to high-temperature water vapor during operation. However, the high-temperature water vapor environment easily corrodes metal materials and induces oxidation, so the water vapor causes problems with the performance of the hydrogen electrode. For the above reasons, nickel (Ni) and yttria-stabilized zirconia (YSZ) are used as the hydrogen electrode in solid oxide electrolytic cells, and a method has been proposed to prevent oxidation of the hydrogen electrode by supplying hydrogen gas (concentration of approximately 10%) together with high-temperature water vapor to the space where the hydrogen electrode is located. Specifically, in the past, to prevent oxidation of hydrogen electrode materials (such as Ni-YSZ), the temperature was raised (550°C to 900°C) while injecting reducing gas, and then the process was switched to normal operation mode.

[0020] One embodiment of the present invention provides a method for operating a high-temperature electrolysis stack capable of improving the efficiency of the high-temperature electrolysis stack.

[0021] One aspect of the present invention is:

[0022] Step of injecting reducing gas into the hydrogen electrode of a high-temperature electrolysis stack (S210);

[0023] A step of initially heating the hydrogen electrode of the high-temperature electrolysis stack (S220);

[0024] Step (S230) of blocking the reducing gas injected into the hydrogen electrode of the high-temperature electrolysis stack;

[0025] Step (S240) of first oxidizing the hydrogen electrode of the high-temperature electrolysis stack;

[0026] A step of reinjecting reducing gas into the hydrogen electrode of the high-temperature electrolysis stack (S250);

[0027] Step (S260) of again blocking the reducing gas injected into the hydrogen electrode of the high-temperature electrolysis stack;

[0028] A step of secondary oxidation of the hydrogen electrode of the high-temperature electrolysis stack (S270); and

[0029] A method for operating a high-temperature electrolysis stack is provided, including a step (S280) of reinjecting reducing gas into the hydrogen electrode of the high-temperature electrolysis stack to perform normal operation.

[0030] In the above step (S210), the hydrogen electrode of the high-temperature electrolysis stack may include Ni / YSZ, Ni / LSM, Ni / GDC, or a combination thereof.

[0031] In the above step (S210), the above step (S250) and the above step (S280), the reducing gas may be hydrogen or a hydrogen-containing gas.

[0032] The above step (S220) may be a step of raising the temperature of the hydrogen electrode of the high-temperature electrolysis stack from room temperature to 550 to 900°C.

[0033] In the above steps (S230) to (S280), the temperature of the hydrogen electrode of the high-temperature electrolysis stack can be maintained at 550 to 900°C.

[0034] The total duration of the above steps (S240) and (S270) may be 10 to 20 minutes.

[0035] The duration of the above step (S250) may be 10 to 200 milliseconds.

[0036] The method for operating the high-temperature electrolysis stack may further include, between the steps (S270) and (S280), a step of repeating the steps (S250) to (S270) one or more times in this order.

[0037] The total duration of the above step (S240) and two or more of the above steps (S270) may be 10 to 20 minutes.

[0038] The total duration of two or more of the above steps (S250) may be 10 to 200 milliseconds.

[0039] The above high temperature electrolysis stack may be a solid oxide electrolysis cell stack as a system for producing hydrogen.

[0040] A method for operating a high-temperature electrolysis stack according to one embodiment of the present invention can improve the efficiency of the high-temperature electrolysis stack.

[0041] Figure 1 is a flow chart showing the operation method of a conventional high-temperature water electrolysis stack.

[0042] Figure 2 is a flow chart showing an operation method of a high-temperature electrolysis stack according to a reference example.

[0043] Figure 3 is a flowchart showing a method for operating a high-temperature electrolysis stack according to one embodiment of the present invention.

[0044] Hereinafter, a method of operating a high-temperature electrolysis stack according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0045] In this specification, “relative efficiency” means a value obtained by dividing the efficiency (xkW / H2kg) of a high-temperature electrolysis stack obtained according to the operating method of a high-temperature electrolysis stack illustrated in FIG. 1 by the efficiency (ykW / H2kg) of a high-temperature electrolysis stack obtained according to a specific operating method of a high-temperature electrolysis stack, and expressing the result as a percentage (y / x × 100).

[0046] Figure 1 is a flow chart showing the operation method of a conventional high-temperature water electrolysis stack.

[0047] Referring to FIG. 1, a conventional method for operating a high-temperature electrolysis stack includes a step of injecting reducing gas into a hydrogen electrode of a high-temperature electrolysis stack (S10), a step of initially heating the hydrogen electrode of the high-temperature electrolysis stack (S20), and a step of continuously injecting reducing gas into the hydrogen electrode of the high-temperature electrolysis stack while performing normal operation (S30).

[0048] The relative efficiency of a high-temperature electrolysis stack obtained according to the operating method of a conventional high-temperature electrolysis stack illustrated in Fig. 1 is defined as 100%.

[0049] Figure 2 is a flow chart showing an operation method of a high-temperature electrolysis stack according to a reference example.

[0050] Referring to FIG. 2, the operating method of a high-temperature electrolysis stack according to a reference example includes a step of injecting reducing gas into a hydrogen electrode of a high-temperature electrolysis stack (S110), a step of initially heating the hydrogen electrode of the high-temperature electrolysis stack (S120), a step of blocking reducing gas injected into the hydrogen electrode of the high-temperature electrolysis stack (S130), a step of primarily oxidizing the hydrogen electrode of the high-temperature electrolysis stack (S140), and a step of reinjecting reducing gas into the hydrogen electrode of the high-temperature electrolysis stack to perform normal operation (S150).

[0051] The relative efficiency of the high-temperature electrolysis stack obtained according to the operating method of the high-temperature electrolysis stack according to the reference example illustrated in Fig. 2 can exceed 100%.

[0052] Figure 3 is a flowchart showing a method for operating a high-temperature electrolysis stack according to one embodiment of the present invention.

[0053] Referring to FIG. 3, a method for operating a high-temperature water electrolysis stack according to an embodiment of the present invention includes a step of injecting reducing gas into a hydrogen electrode of a high-temperature water electrolysis stack (S210), a step of initially heating the hydrogen electrode of the high-temperature water electrolysis stack (S220), a step of blocking reducing gas injected into the hydrogen electrode of the high-temperature water electrolysis stack (S230), a step of primarily oxidizing the hydrogen electrode of the high-temperature water electrolysis stack (S240), a step of reinjecting reducing gas into the hydrogen electrode of the high-temperature water electrolysis stack (S250), a step of again blocking reducing gas injected into the hydrogen electrode of the high-temperature water electrolysis stack (S260), a step of secondary oxidizing the hydrogen electrode of the high-temperature water electrolysis stack (S270), and a step of reinjecting reducing gas into the hydrogen electrode of the high-temperature water electrolysis stack to perform normal operation (S280).

[0054] In the above step (S210), the hydrogen electrode of the high-temperature electrolysis stack is Ni / YSZ (yttria stabilised zirconia), Ni / LSM (La 1-x Sr x MnO3(0≤x≤0.5)), Ni / GDC(gadolinia doped ceria), or a combination thereof.

[0055] In the above step (S210), the above step (S250) and the above step (S280), the reducing gas may be hydrogen or a hydrogen-containing gas.

[0056] The above hydrogen-containing gas may include hydrogen and nitrogen.

[0057] The above step (S220) may be a step of raising the temperature of the hydrogen electrode of the high-temperature electrolysis stack from room temperature (10 to 40°C) to 550 to 900°C.

[0058] In the above steps (S230) to (S280), the temperature of the hydrogen electrode of the high-temperature water electrolysis stack can be maintained at 550 to 900°C. Specifically, in the steps (S230) to (S280), the temperature of the hydrogen electrode of the high-temperature water electrolysis stack can be maintained at an equal level. More specifically, in the steps (S230) to (S280), the temperature of the hydrogen electrode of the high-temperature water electrolysis stack can be maintained at 550 to 600°C, 600 to 650°C, 650 to 700°C, 700 to 750°C, 750 to 800°C, 800 to 850°C, or 850 to 900°C.

[0059] In the above step (S240) and the above step (S270) (which may be collectively referred to as the “oxidation step”), the hydrogen electrode of the high-temperature water electrolysis stack may be oxidized and its volume may expand.

[0060] The total duration of the above steps (S240) and (S270) may be the same as the total time for blocking the reducing gas injected into the hydrogen electrode of the high-temperature electrolysis stack between the above steps (S210) and (S280). Specifically, the total duration of the above steps (S240) and (S270) may be 10 to 20 minutes.

[0061] In the above steps (S250) and (S280), the hydrogen electrode of the high-temperature electrolysis stack may be re-reduced to form micropores. Due to the increase in the triple phase boundary (TPB) caused by these micropores, the active area increases, thereby increasing the efficiency of the high-temperature electrolysis stack.

[0062] The duration of the above step (S250) (which may be referred to as the “reducing gas reinjection step”) may be 10 to 200 milliseconds.

[0063] If the total duration of the above step (S240) and the above step (S270), and the duration of the above step (S250) are each within the above range, the relative efficiency of the high-temperature water electrolysis stack can be improved.

[0064] The method for operating the high-temperature electrolysis stack may further include, between the steps (S270) and (S280), a step of repeating the steps (S250) to (S270) in this order one or more times. In this case, the total duration of the steps (S240) and the two or more steps (S270) may be the same as the total time for blocking the reducing gas injected into the hydrogen electrode of the high-temperature electrolysis stack between the steps (S210) and (S280). In addition, in this case, the total duration of the steps (S240) and the two or more steps (S270) may be 10 to 20 minutes. In addition, in this case, the total duration of the two or more steps (S250) may be 10 to 200 milliseconds. If the total duration of the above step (S240) and two or more of the above steps (S270), and the duration of two or more of the above steps (S250) are each within the above range, the relative efficiency of the high-temperature water electrolysis stack can be improved.

[0065] Additionally, the high-temperature electrolysis stack may be a solid oxide electrolysis cell stack as a system for producing hydrogen (e.g., green hydrogen).

[0066] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0067] Manufacturing Example 1: Fabrication of a high-temperature water electrolysis stack

[0068] A laboratory-scale SOEC unit cell (effective area of ​​the cathode: 10 cm × 10 cm) was fabricated and efficiency experiments were conducted according to the operating method. The fuel electrode was manufactured by stacking seven NiO-YSZ sheets and then stacking a CFL (cathode functional layer) on the top layer. Here, the NiO-YSZ sheet was used as the CFL. The manufactured fuel electrode was pre-sintered at 1100°C for 1 hour. Then, a YSZ sheet with a thickness of 30 μm was stacked as an electrolyte on the pre-sintered fuel electrode, and then co-sintered at 1400°C for 2 hours. The air electrode was coated with LSM-YSZ (LaSrMnO3 / 8 wt% Y2O3+92 wt% ZrO2) by screen printing to the effective area and sintered at 1400°C for 2 hours to complete the final unit cell. As a result, 1.4 V, 500 mA / cm 2 (50A) A SOEC unit cell with a standard rating of 70W was obtained.

[0069] Comparative Example 1: Operation of a high-temperature water electrolysis stack

[0070] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in Fig. 1. Specifically, the gas used in step (S10) was hydrogen, the initial temperature increase in step (S20) was from room temperature (25°C) to 725°C, and in step (S30), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0071] Reference Example 1: Operation of a high-temperature electrolysis stack

[0072] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in Fig. 2. Specifically, the gas used in step (S110) was hydrogen, the initial temperature increase in step (S120) was from room temperature (25°C) to 725°C, the holding time in step (S140) (i.e., the oxidation step) was 15 minutes, and in steps (S130), (S140), and (S150), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0073] Reference Example 2: Operation of a high-temperature electrolysis stack

[0074] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in FIG. 3. Specifically, the gas used in step (S210) was hydrogen, the initial temperature increase in step (S220) was from room temperature (25°C) to 725°C, the holding times of steps (S240) and (S270) (i.e., oxidation step) were each 2.5 minutes, the holding time of step (S250) (i.e., reducing gas reinjection step) was 100 milliseconds, and in steps (S230), (S240), (S250), (S260), (S270), and (S280), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0075] Reference Example 3: Operation of a high-temperature electrolysis stack

[0076] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in FIG. 3. Specifically, the gas used in step (S210) was hydrogen, the initial temperature increase in step (S220) was from room temperature (25°C) to 725°C, the holding times of steps (S240) and (S270) (i.e., oxidation step) were each 12.5 minutes, the holding time of step (S250) (i.e., reducing gas reinjection step) was 100 milliseconds, and in steps (S230), (S240), (S250), (S260), (S270), and (S280), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0077] Reference Example 4: Operation of a high-temperature water electrolysis stack

[0078] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in FIG. 3. Specifically, the gas used in step (S210) was hydrogen, the initial temperature increase in step (S220) was from room temperature (25°C) to 725°C, the holding times of steps (S240) and (S270) (i.e., oxidation step) were each 7.5 minutes, the holding time of step (S250) (i.e., reducing gas reinjection step) was 5 milliseconds, and in steps (S230), (S240), (S250), (S260), (S270), and (S280), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0079] Reference Example 5: Operation of a high-temperature electrolysis stack

[0080] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in FIG. 3. Specifically, the gas used in step (S210) was hydrogen, the initial temperature increase in step (S220) was from room temperature (25°C) to 725°C, the holding times of steps (S240) and (S270) (i.e., oxidation step) were each 7.5 minutes, the holding time of step (S250) (i.e., reducing gas reinjection step) was 250 milliseconds, and in steps (S230), (S240), (S250), (S260), (S270), and (S280), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0081] Example 1: Operation of a high-temperature water electrolysis stack

[0082] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in FIG. 3. Specifically, the gas used in step (S210) was hydrogen, the initial temperature increase in step (S220) was from room temperature (25°C) to 725°C, the holding times of steps (S240) and (S270) (i.e., oxidation step) were each 7.5 minutes, the holding time of step (S250) (i.e., reducing gas reinjection step) was 100 milliseconds, and in steps (S230), (S240), (S250), (S260), (S270), and (S280), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0083] Example 2: Operation of a high-temperature electrolysis stack

[0084] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in FIG. 3. Specifically, the gas used in step (S210) was hydrogen, the initial temperature increase in step (S220) was from room temperature (25°C) to 725°C, the holding times of steps (S240) and (S270) (i.e., oxidation step) were each 5 minutes, the holding time of step (S250) (i.e., reducing gas reinjection step) was 100 milliseconds, and in steps (S230), (S240), (S250), (S260), (S270), and (S280), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0085] Example 3: Operation of a high-temperature electrolysis stack

[0086] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in FIG. 3. Specifically, the gas used in step (S210) was hydrogen, the initial temperature increase in step (S220) was from room temperature (25°C) to 725°C, the holding times of steps (S240) and (S270) (i.e., oxidation step) were each 10 minutes, the holding time of step (S250) (i.e., reducing gas reinjection step) was 100 milliseconds, and in steps (S230), (S240), (S250), (S260), (S270), and (S280), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0087] Example 4: Operation of a high-temperature electrolysis stack

[0088] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in FIG. 3. Specifically, the gas used in step (S210) was hydrogen, the initial temperature increase in step (S220) was from room temperature (25°C) to 725°C, the holding times of steps (S240) and (S270) (i.e., oxidation step) were each 7.5 minutes, the holding time of step (S250) (i.e., reducing gas reinjection step) was 10 milliseconds, and in steps (S230), (S240), (S250), (S260), (S270), and (S280), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0089] Example 5: Operation of a high-temperature electrolysis stack

[0090] The high-temperature electrolysis stack manufactured in the above Manufacturing Example 1 was operated according to the operation method of the high-temperature electrolysis stack illustrated in FIG. 3. Specifically, the gas used in step (S210) was hydrogen, the initial temperature increase in step (S220) was from room temperature (25°C) to 725°C, the holding times of steps (S240) and (S270) (i.e., oxidation step) were each 7.5 minutes, the holding time of step (S250) (i.e., reducing gas reinjection step) was 200 milliseconds, and in steps (S230), (S240), (S250), (S260), (S270), and (S280), the temperature of the hydrogen electrode was maintained at 725°C while reducing gas was continuously injected into the hydrogen electrode.

[0091] Example 6: Operation of a high-temperature water electrolysis stack

[0092] The high-temperature electrolysis stack manufactured in the above manufacturing example 1 was operated according to the operation method of the high-temperature electrolysis stack shown in FIG. 3, but between the step (S270) and the step (S280), the steps (S250) to (S270) were repeated once in this order. Specifically, the gas used in step (S210) is hydrogen, the initial temperature increase in step (S220) is from room temperature (25°C) to 725°C, the holding time (i.e., oxidation step) of step (S240), the first step (S270), and the second step (S270) is 5 minutes for each step, the holding time of the first step (S250) and the second step (S250) (i.e., reducing gas reinjection step) is 50 milliseconds for each step, and in step (S230), step (S240), the first and second steps (S250), the first and second steps (S260), the first and second steps (S270), and step (S280), the temperature of the hydrogen electrode was maintained at 725°C while the reducing gas was continuously injected into the hydrogen electrode.

[0093] Example 7: Operation of a high-temperature electrolysis stack

[0094] The high-temperature electrolysis stack manufactured in the above manufacturing example 1 was operated according to the operation method of the high-temperature electrolysis stack shown in FIG. 3, but between the step (S270) and the step (S280), the steps (S250) to (S270) were repeated four times in this order. Specifically, the gas used in step (S210) is hydrogen, the initial temperature increase in step (S220) is from room temperature (25°C) to 725°C, the holding time in step (S240) and the 1st to 4th steps (S270) (i.e., the oxidation step) is 3 minutes for each step, the holding time in step (S250) (i.e., the reducing gas reinjection step) is 25 milliseconds for each step, and in step (S230), step (S240), the 1st to 4th steps (S250), the 1st to 4th steps (S260), the 1st to 4th steps (S270) and step (S280), the temperature of the hydrogen electrode was maintained at 725°C while the reducing gas was continuously injected into the hydrogen electrode.

[0095] Example 8: Operation of a high-temperature water electrolysis stack

[0096] The high-temperature electrolysis stack manufactured in the above manufacturing example 1 was operated according to the operation method of the high-temperature electrolysis stack shown in FIG. 3, but between the step (S270) and the step (S280), the steps (S250) to (S270) were repeated 10 times in this order. Specifically, the gas used in step (S210) is hydrogen, the initial temperature increase in step (S220) is from room temperature (25°C) to 725°C, the total holding time of step (S240) and the 1st to 10th steps (S270) (i.e., the oxidation step) is 15 minutes, the total holding time of the 1st to 10th steps (S250) (i.e., the reducing gas reinjection step) is 100 milliseconds, and in steps (S230), (S240), the 1st to 10th steps (S250), the 1st to 10th steps (S260), the 1st to 10th steps (S270) and (S280), the temperature of the hydrogen electrode was maintained at 725°C while the reducing gas was continuously injected into the hydrogen electrode.

[0097] In the operation methods of the high-temperature electrolysis stacks of Comparative Example 1, Reference Examples 1 to 5, and Examples 1 to 8, the total maintenance time of the oxidation step and the total maintenance time of the reduction gas reinjection step (excluding step (S150) of FIG. 2 and step (S280) of FIG. 3) are summarized and shown in Table 1 below.

[0098] Operating method of high temperature electrolysis stack Total holding time of oxidation step (minutes) Total holding time of reduction gas reinjection step (milliseconds) Comparative example 1 degree 1--Reference example 1 degree 215-Reference example 2 degree 35100Reference example 3 degree 325100Reference example 4 degree 3155Reference example 5 degree 315250Example 1 degree 315100Example 2 degree 310100Example 3 degree 320100Example 4 degree 31510Example 5 degree 315200Example 6 degree 315100Example 7 degree 315100Example 8 degree 315100

[0099]

[0100] Evaluation Example 1: Evaluation of the relative efficiency of a high-temperature electrolysis stack according to its operating method.

[0101] The efficiency (xkW / H2kg) of the high-temperature electrolysis stack obtained in Comparative Example 1 was divided by the efficiency (ykW / H2kg) of the high-temperature electrolysis stack obtained in Comparative Example 1, Reference Examples 1 to 5, and Examples 1 to 8, and the obtained value was expressed as a percentage (y / x × 100) to obtain the relative efficiency, and the results are shown in Table 2 below.

[0102] Comparative Example 1 Reference Example Example 1 12345 Relative Efficiency (%) 100 103 103 104 105 105 113 Example 2 345 678 Relative Efficiency (%) 114 114 113 114 116 117 118

[0103]

[0104] Referring to Table 2 above, the relative efficiency of the high-temperature water electrolysis stacks obtained in Examples 1 to 8 was found to be higher than the relative efficiency of the high-temperature water electrolysis stacks obtained in Reference Examples 1 to 5 and Comparative Example 1.

[0105] While the present invention has been described with reference to the drawings and examples, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent implementations are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. Step of injecting reducing gas into the hydrogen electrode of a high-temperature water electrolysis stack (S210); A step of initially heating the hydrogen electrode of the high-temperature electrolysis stack (S220); Step (S230) of blocking the reducing gas injected into the hydrogen electrode of the high-temperature electrolysis stack; Step (S240) of first oxidizing the hydrogen electrode of the high-temperature electrolysis stack; A step of reinjecting reducing gas into the hydrogen electrode of the high-temperature electrolysis stack (S250); Step (S260) of again blocking the reducing gas injected into the hydrogen electrode of the high-temperature electrolysis stack; A step of secondary oxidation of the hydrogen electrode of the high-temperature electrolysis stack (S270); and A method for operating a high-temperature electrolysis stack, comprising a step (S280) of reinjecting reducing gas into the hydrogen electrode of the high-temperature electrolysis stack to perform normal operation.

2. In paragraph 1, In the above step (S210), the hydrogen electrode of the high-temperature electrolysis stack is a method for operating a high-temperature electrolysis stack including Ni / YSZ, Ni / LSM, Ni / GDC or a combination thereof.

3. In paragraph 1, A method for operating a high-temperature water electrolysis stack in the above step (S210), the above step (S250) and the above step (S280), wherein the reducing gas is hydrogen or a hydrogen-containing gas.

4. In paragraph 1, The above step (S220) is a method for operating a high-temperature electrolysis stack, which is a step for raising the temperature of the hydrogen electrode of the high-temperature electrolysis stack from room temperature to 550 to 900°C.

5. In paragraph 1, A method for operating a high-temperature electrolysis stack, wherein in the above steps (S230) to (S280), the temperature of the hydrogen electrode of the high-temperature electrolysis stack is maintained at 550 to 900°C.

6. In paragraph 1, A method for operating a high-temperature electrolysis stack, wherein the total duration of the above steps (S240) and (S270) is 10 to 20 minutes.

7. In paragraph 1, A method for operating a high-temperature electrolysis stack in which the duration of the above step (S250) is 10 to 200 milliseconds.

8. In paragraph 1, A method for operating a high-temperature electrolysis stack, further comprising a step of repeating steps (S250) to (S270) in this order at least once between the above steps (S270) and (S280).

9. In paragraph 8, A method for operating a high-temperature electrolysis stack, wherein the total duration of the above step (S240) and two or more of the above steps (S270) is 10 to 20 minutes.

10. In paragraph 8, A method for operating a high-temperature electrolysis stack, wherein the total duration of two or more of the above steps (S250) is 10 to 200 milliseconds.

11. In paragraph 1, The above high temperature electrolysis stack is a solid oxide electrolysis cell stack as a system for producing hydrogen, and is a method for operating a high temperature electrolysis stack.

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