Ammonia fuel cell system and ammonia fuel cell pretreatment method

Abstract

The present invention relates to an ammonia fuel cell system comprising a fuel cell that comprises: a fuel electrode containing a nitride of an active metal; an air electrode; and an electrolyte interposed between the fuel electrode and the air electrode, wherein, by appropriately controlling distribution of active metal and nitrogen contents in a surface region of the fuel electrode, stress generation due to formation of a metal nitride in the surface region of the fuel electrode is minimized, and surface defects and cracks caused by excessive nitridation in an outermost surface portion of the fuel electrode are minimized or prevented, thereby improving durability of the fuel cell.

Description

Ammonia fuel cell system and ammonia fuel cell pretreatment method

[0001] The present invention relates to an ammonia fuel cell system.

[0002] In addition, the present invention relates to a method for pre-treating an ammonia fuel cell.

[0003] As ammonia emerges as an alternative for green hydrogen transportation, fuel cell technology that generates electricity using ammonia as fuel is garnering attention. In particular, ammonia-fueled high-temperature solid oxide fuel cell (SOFC) technology is receiving particular interest for simultaneously possessing the convenience of ammonia storage and transportation with the high efficiency characteristics of SOFCs. However, since these fuel cells are exposed to various reaction gases in high-temperature environments, repeated use can lead to the degradation of internal components and a decline in performance. Therefore, there is a need for technological development to improve the durability of fuel cells.

[0004] (Patent Document 1) Republic of Korea Registered Patent Publication No. 10-2254196

[0005] The problem that the technical concept of the present invention aims to solve is to provide an ammonia fuel cell system with improved durability.

[0006] In addition, the problem that the technical concept of the present invention aims to solve is to provide a method for manufacturing an ammonia fuel cell with improved durability.

[0007] The problems of the present invention are not limited to those described above. A person skilled in the art to which the present invention pertains will have no difficulty understanding additional problems of the present invention from the overall details of the specification.

[0008] According to exemplary embodiments for solving the problem of the present invention, an ammonia fuel cell system is provided. The ammonia fuel cell system comprises a fuel electrode comprising a nitride of an active metal; an air electrode; and an electrolyte interposed between the fuel electrode and the air electrode, wherein the fuel electrode satisfies the following equation 1.

[0009] [Relationship 1]

[0010] 0.20 ≤ [N1] / ([N1]+[M1]) ≤ 0.40

[0011] In the above equation 1, [N1] is the average nitrogen content (at%) in the electrode surface layer up to a depth of 15 μm in the thickness direction from the surface of the fuel electrode, and [M1] is the average active metal content (at%) in the electrode surface layer of the fuel electrode.

[0012] The above fuel electrode can satisfy the following relationship 2.

[0013] [Relationship 2]

[0014] 0.01 ≤ [N2] / ([N2]+[M2]) ≤ 0.20

[0015] In the above equation 2, [N2] is the average nitrogen content (at%) in the surface layer from the electrode surface layer of the fuel electrode to a depth of 50 μm in the thickness direction, and [M2] is the average active metal content (at%) in the surface layer of the fuel electrode.

[0016] The operating temperature of the above fuel cell may be less than 700℃.

[0017] The above fuel cell may be a solid oxide type fuel cell in which the electrolyte comprises a solid oxide.

[0018] The above active metal may be any one of nickel (Ni), cobalt (Co), ruthenium (Ru), palladium (Pd), platinum (Pt), iron (Fe), molybdenum (Mo), and alloy elements thereof.

[0019]

[0020] According to other exemplary embodiments, an ammonia fuel cell pretreatment method is provided. The ammonia fuel cell pretreatment method comprises the step of nitrating an active metal of the fuel electrode by providing a first gas containing ammonia to the fuel electrode of a fuel cell comprising a fuel electrode; an air electrode; and an electrolyte interposed between the fuel electrode and the air electrode, wherein the nitrating step may be performed under open circuit voltage (OCV) conditions.

[0021] The temperature of the first gas above may be 850℃ or lower.

[0022] The ammonia content of the first gas above may be 10 to 100% in volume%.

[0023] The supply flow rate of the first gas is 100 cm² of the active area of ​​the fuel electrode. 2 It can be controlled at 0.5~2 l / min per day.

[0024] The supply flow rate of the first gas above may be 0.075 l / min or more.

[0025] The above nitriding step can be performed for 5 to 120 minutes.

[0026] The above-mentioned fuel electrode may further include a preliminary reduction step of providing a second gas containing hydrogen and nitrogen.

[0027] The second gas may contain 10 to 50 percent hydrogen and the remainder nitrogen in volume percent.

[0028] The temperature of the second gas above may be 850℃ or lower.

[0029] The supply flow rate of the second gas above is for an active area of ​​100 cm² of the fuel electrode 2 It can be controlled at 0.5~2 l / min per day.

[0030] The above preliminary reduction step may further include a preliminary pretreatment step of providing a third gas containing hydrogen to the fuel electrode.

[0031] The temperature of the third gas may be 750 to 850°C.

[0032] The supply flow rate of the third gas above is for an active area of ​​100 cm² of the fuel electrode 2 It can be controlled at 0.5~2 l / min per day.

[0033] The above nitriding step may include a first nitriding step of maintaining at 750 to 850°C for 5 to 20 minutes; and a second nitriding step of cooling from the temperature of the first nitriding step to a temperature of 700°C or higher and below the temperature of the first nitriding step.

[0034] The cooling rate of the second nitriding step above may be 1.0 to 3.0℃ / min.

[0035] According to exemplary embodiments of the present invention, an ammonia fuel cell system with improved durability can be provided.

[0036] According to other exemplary embodiments of the present invention, a pretreatment method for an ammonia fuel cell with improved durability can be provided.

[0037] The various and beneficial advantages and effects of the present invention are not limited to those described above and will be more easily understood in the process of explaining specific embodiments of the present invention.

[0038] FIG. 1 is a drawing for illustrating an ammonia fuel cell system according to exemplary embodiments.

[0039] FIG. 2 is a drawing for illustrating a fuel cell according to exemplary embodiments.

[0040] FIG. 3 is a drawing for illustrating a fuel cell according to other exemplary embodiments.

[0041] Figure 4 is a graph showing the voltage change according to the constant current application time.

[0042] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor can appropriately define the concepts of terms to best describe his invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0043] In the following descriptions with reference to the drawings, identical or corresponding components are assigned the same reference numerals, and redundant descriptions thereof will be omitted.

[0044] In the following embodiments, the terms first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component.

[0045] In the following embodiments, the singular expression includes the plural expression unless the context clearly indicates otherwise.

[0046] In the following embodiments, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added.

[0047] In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, so the present invention is not necessarily limited to what is illustrated.

[0048] Where an embodiment can be implemented differently, a specific process sequence may be performed differently from the order described. For example, two processes described consecutively may be performed substantially simultaneously or proceed in the reverse order of the description.

[0049] In addition, in describing the present invention, if it is determined that a detailed description of related known components or functions may obscure the essence of the invention, such detailed description is omitted.

[0050] The present invention will be described in detail below through each embodiment. It should be noted that each embodiment described in this specification is not limited to a single embodiment but may also be combined with other embodiments. Accordingly, the citation of claims in the patent claims is merely an example of an embodiment, and the technical concept of the present invention should not be interpreted as being limited only to a combination with the cited claims; rather, combinations with various claims are also included within the scope of the technical concept of the present invention.

[0051] The present invention will be described in detail below through examples. However, it should be noted that the following examples are intended merely to illustrate and embody the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0052] [Ammonia Fuel Cell System]

[0053] FIG. 1 is a drawing for illustrating an ammonia fuel cell system (10) according to exemplary embodiments.

[0054] FIG. 2 is a drawing for illustrating a fuel cell (100_1) according to exemplary embodiments. FIG. 3 is a drawing for illustrating a fuel cell (100_2) according to other exemplary embodiments.

[0055] Referring to FIGS. 1 to 3, an ammonia fuel cell system (10) includes a fuel cell (100). The fuel cell (100) includes a fuel electrode (110), an air electrode (120), and an electrolyte (130).

[0056] A fuel cell (100) is a cell configured to produce electric and thermal energy through an electrochemical reaction and can produce hydrogen depending on the fuel gas. According to exemplary embodiments, the fuel cell (100) may be a direct ammonia fuel cell (100) that uses ammonia as a direct raw material. In this case, ammonia gas may be supplied to the fuel electrode (110) of the fuel cell (100). In the present invention, the fuel cell (100) may be selected without limitation within the scope of the technical concept of the present invention, but as a non-limiting example, the fuel cell (100) may be a solid oxide fuel cell (SOFC). That is, the fuel cell (100) may be a solid oxide fuel cell in which the electrolyte (130) includes a solid oxide.

[0057] A fuel cell (100) may include a fuel electrode (110), an air electrode (120), and an electrolyte (130). The electrolyte (130) may be interposed between the fuel electrode (110) and the air electrode (120). That is, the fuel electrode (110), the electrolyte (130), and the air electrode (120) may be stacked sequentially.

[0058] According to exemplary embodiments, the fuel cell (100) may be provided in the form of a single unit cell in which a fuel electrode (110), an electrolyte (130), and an air electrode (120) are stacked. According to other exemplary embodiments, the fuel cell (100) may be provided in the form of a stack in which a plurality of unit cells are stacked together with a separator.

[0059] The fuel electrode (110) is an electrode in which an electrochemical reaction occurs using fuel gas, and may include a catalyst capable of catalyzing the electrochemical reaction of the fuel gas. More specifically, an ammonia decomposition reaction may be performed at the fuel electrode (110), and the catalyst may catalyze the ammonia decomposition reaction. The ammonia decomposition reaction may follow the following reaction equation 1.

[0060] [Reaction Equation 1]

[0061] 2 / 3NH3→ 1 / 3N2+ H2 (ΔH1= 30.81kJ / mol)

[0062] The catalyst contains an active metal, and a nitration reaction of the active metal may occur during the ammonia decomposition process. Conventionally, this nitration reaction was not properly controlled, causing cracks in the fuel electrode (110) and reducing the durability of the fuel electrode (110). However, according to exemplary embodiments, the durability of the fuel electrode (110) can be improved by properly controlling the distribution of the content of the active metal and nitrogen in the surface region (electrode surface and surface) of the fuel electrode (110). That is, the fuel electrode (110) may contain a nitride of the active metal.

[0063] According to exemplary embodiments, the fuel electrode (110) can satisfy the following relationship 1.

[0064] [Relationship 1]

[0065] 0.20 ≤ [N1] / ([N1]+[M1]) ≤ 0.40

[0066] In the above equation 1, [N1] is the average nitrogen content (at%) in the electrode surface layer up to a depth of 15 μm in the thickness direction from the surface of the fuel electrode, and [M1] is the average active metal content (at%) in the electrode surface layer of the fuel electrode.

[0067] The formed metal nitride can function as an ammonia decomposition catalyst and contribute to improving the ammonia conversion rate. Additionally, by controlling the content distribution of active metal and nitrogen in the electrode surface layer of the fuel electrode (110), surface defects and cracks in the fuel electrode (110) caused by excessive nitridation reactions in the electrode surface layer can be minimized or prevented. Accordingly, by forming a relatively stable active metal nitride, it can contribute to improving the durability of the fuel electrode (110).

[0068] Furthermore, according to exemplary embodiments, the fuel electrode (110) can satisfy the following relationship 2.

[0069] [Relationship 2]

[0070] 0.01 ≤ [N2] / ([N2]+[M2]) ≤ 0.20

[0071] In the above equation 2, [N2] is the average nitrogen content (at%) in the surface layer from the electrode surface layer of the fuel electrode to a depth of 50 μm in the thickness direction, and [M2] is the average active metal content (at%) in the surface layer of the fuel electrode.

[0072] In this way, by controlling the content distribution of active metal and nitrogen in the surface region below the surface layer, stress generation caused by the formation of metal nitrides inside the surface region of the fuel electrode (110) can be minimized. As a result, the occurrence of cracks or defects inside the fuel electrode (110) can be minimized.

[0073] According to exemplary embodiments, the active metal may be any one of nickel (Ni), cobalt (Co), ruthenium (Ru), palladium (Pd), platinum (Pt), iron (Fe), molybdenum (Mo), and alloy elements thereof.

[0074] Meanwhile, the generated active metal nitride can be reduced back to the active metal by the reducing atmosphere formed during the ammonia decomposition process. Additionally, the reduced active metal can be nitrated again to form an active metal nitride. In this way, if the reduction reaction and the nitration reaction are performed repeatedly, irreversible damage may be caused to the fuel electrode (110). As a result, the durability of the fuel cell (100) may be reduced. To prevent this, according to exemplary embodiments, the operating temperature of the fuel cell (100) may be less than 700°C. If the operating temperature of the fuel cell (100) is 700°C or higher, the reduction reaction is accelerated, and subsequent continuous nitration reactions may occur, thereby reducing the durability of the fuel electrode (110). Therefore, in terms of durability, a lower operating temperature of the fuel cell (100) is advantageous. However, if the operating temperature of the fuel cell (100) is excessively low, the ammonia decomposition efficiency may be reduced. Accordingly, as a non-limiting example, the operating temperature of the fuel cell (100) may be 480°C or higher.

[0075] The air electrode (120) may be an electrode that comes into contact with an air gas containing oxygen.

[0076] According to exemplary embodiments, the air electrode (120) may include any one of LSC (Lanthanum Strontium Cobalt Oxide), LSCF (Lanthanum Strontium Cobalt Iron Oxide), LSM (Lanthanum Strontium Manganite), and combinations thereof.

[0077] The electrolyte (130) may be interposed between the fuel electrode (110) and the air electrode (120). The electrolyte (130) may provide a path for the movement of ions necessary for the reaction occurring within the fuel cell.

[0078] According to exemplary embodiments, the electrolyte (130_1) contained in the fuel cell (100_1) contains oxygen ions (O 2-) It may be a conductive electrolyte. In this case, at the air electrode (120), oxygen is reduced to oxygen ions (O 2- ) can be provided. Oxygen ions (O 2- ) can diffuse and move toward the fuel electrode (110) through the electrolyte (130_1). Oxygen ions (O) diffused toward the fuel electrode (110) 2- ) can generate water vapor and electrons by causing an electrochemical reaction with hydrogen at the triple phase boundary between the fuel electrode (110) and the electrolyte (130_1). The generated electrons can move to the air electrode (120) through an external circuit configured to electrically connect the fuel electrode (110) and the air electrode (120).

[0079] The oxygen reduction reaction described above can follow the following reaction equation.

[0080] [Reaction Equation 2]

[0081] 0.5O2 + 2e- → O 2-

[0082] The above-described reaction for the generation of water vapor and electrons can follow the following reaction equation.

[0083] [Reaction Equation 3]

[0084] H2+ O 2- → H2O + 2e -

[0085] According to exemplary embodiments, the electrolyte (130_1) may be any one of YSZ (Y2O3-stabilized ZrO2), SDC (Sm2O3-doped CeO2), GDC (Gd2O3-doped CeO2), ScCeSZ (Sc2O3 & CeO2-stabilized ZrO2), ESB (Er2O3-stabilized Bi2O3), LSGM (Sr and Mg-doped LaGaO3), and combinations thereof.

[0086] According to other exemplary embodiments, the electrolyte (130_2) contained in the fuel cell (100_2) is hydrogen ions (H +) It may be a conductive electrolyte. In this case, at the fuel electrode (110), hydrogen generated from ammonia is oxidized to form hydrogen ions (H + ) and electrons can be provided. The generated electrons can move to the air electrode (120) through an external circuit configured to electrically connect the fuel electrode (110) and the air electrode (120). Hydrogen ions (H + ) can diffuse and move through the electrolyte (130_2) to the air electrode (120). Hydrogen ions (H) diffused toward the air electrode (120) + ) can react with oxygen at the three-phase interface between the air electrode (120) and the electrolyte (130_2) to generate water vapor.

[0087] The hydrogen oxidation reaction described above can follow the following reaction equation.

[0088] [Reaction Equation 4]

[0089] H2→ 2H + + 2e -

[0090] The above-described water vapor generation reaction may follow the following reaction equation.

[0091] [Reaction Equation 5]

[0092] 0.5O2+ 2H + + 2e - → H2O

[0093] According to exemplary embodiments, the electrolyte (130_2) is BCY (BaCe 1-x Y x O 3-δ ), BZY(BaZr 1-x Y x O 3-δ ), BCZY(BaCe 1-x-y Zr x Y y O 3-δ ), BCG(BaCe 1-x Gd x O 3-δIt may include any one of ), and combinations thereof. In this case, x is 0 < x ≤ 0.2, y is 0 < y ≤ 0.8, and δ is 0 < δ < 0.3.

[0094]

[0095] [Ammonia Fuel Cell Pretreatment Method]

[0096] According to exemplary embodiments, an ammonia fuel cell pretreatment method comprises the step of nitrating an active metal of a fuel electrode by providing a first gas containing ammonia to the fuel electrode of a fuel cell comprising a fuel electrode; an air electrode; and an electrolyte interposed between the fuel electrode and the air electrode.

[0097] A fuel electrode that has not undergone pretreatment may contain active metals and oxides of active metals. If voltage and fuel gas are supplied directly to a fuel electrode in this state to operate a fuel cell, the nitrification reaction of the fuel electrode may not be properly controlled. Therefore, according to exemplary embodiments, by pretreating the fuel electrode, nitrogen can be controlled to be properly distributed on the surface layer of the fuel electrode. As a result, the durability of the fuel cell can be improved.

[0098] Except as specifically mentioned in this embodiment, any details overlapping with the fuel cell described in the ammonia fuel cell system described above may be equally applied to this ammonia fuel cell pretreatment method. Therefore, a detailed description of such overlapping details is omitted.

[0099] The first gas is a gas containing ammonia for nitriding the active metals of the fuel electrode. The ammonia content of the first gas may be 10 to 100% in volume percent. If the ammonia content in the first gas is excessively low, sufficient nitride may not be formed. Therefore, it is desirable for the ammonia content in the first gas to be higher. Additionally, as a remainder component, the first gas may further contain nitrogen, but the present invention is not necessarily limited thereto.

[0100] The temperature of the first gas may be 850°C or lower. If the temperature of the first gas is excessively high, the formed nitride may cause a reduction reaction, and the nitride of the active metal may not be properly formed. If a nitridation reaction of the active metal occurs, the temperature of the first gas is not particularly limited, but as a non-limiting example, the temperature of the first gas may be 0°C or higher. For more active nitride formation, the temperature of the first gas may be 300°C or higher.

[0101] The supply flow rate of the first gas is for an active area of ​​100 cm² of the fuel electrode 2 It can be controlled to 0.5 to 2 l / min. If the supply flow rate of the first gas is excessively high compared to the active area of ​​the fuel electrode, ammonia slip may occur where ammonia does not react sufficiently and leaks out. If the supply flow rate of the first gas is excessively low compared to the active area of ​​the fuel electrode, the nitriding reaction efficiency may decrease. In this regard, according to exemplary embodiments, the supply flow rate of the first gas can be controlled to 0.075 l / min or higher.

[0102] According to exemplary embodiments, the nitriding step may be performed for 5 to 120 minutes. If the time of the nitriding step falls outside the range described above, the nitride of the active metal may not be properly formed.

[0103] According to exemplary embodiments, the nitriding step can be performed under open circuit voltage (OCV) conditions. This allows for the stable formation of nitrides of active metals. Under open circuit voltage conditions, electrical connections are maintained within the fuel cell, but no current flows, so the potential difference between the electrodes can be maintained. As a result, the nitriding reaction occurs evenly on the surface of the fuel electrode, and an appropriate nitrogen distribution can be secured in the surface region of the fuel electrode. However, if the conditions are not open circuit voltage, the nitriding reaction may not be properly controlled.

[0104] According to exemplary embodiments, the nitriding step may include a first nitriding step of maintaining at 750 to 850°C for 5 to 20 minutes; and a second nitriding step of cooling from the temperature of the first nitriding step to a temperature of 700°C or higher and below the temperature of the first nitriding step. In this way, after nitriding an active metal under relatively high temperature conditions, the temperature atmosphere can be cooled before the nitride of the active metal is reduced again, thereby stably maintaining the nitride of the active metal. The temperature of the first nitriding step can be maintained by heating a first gas. The temperature of the second nitriding step can be maintained by supplying a first gas at a temperature lower than the temperature of the first gas supplied to the first nitriding step.

[0105] According to exemplary embodiments, the cooling rate of the second nitriding step may be 1.0 to 3.0 °C / min. If the cooling rate of the second nitriding step is excessively slow, the nitride may be partially reduced, causing damage to the fuel electrode. If the cooling rate of the second nitriding step is excessively fast, partial cracks may occur due to rapid shrinkage of the components contained in the fuel electrode, air electrode, or electrolyte, which may affect the performance of the fuel cell.

[0106] According to exemplary embodiments, the ammonia fuel cell pretreatment method may further include a preliminary reduction step of providing a second gas containing hydrogen and nitrogen to the fuel electrode. After manufacturing the fuel cell, the active metal may react with oxygen in the atmosphere during the transfer process to form an oxide. Additionally, a fuel cell that has been shut down for reasons such as maintenance after operation may also form an oxide as the active metal of the fuel electrode oxidizes. According to exemplary embodiments, the formation of nitrides can be controlled more precisely by pre-reducing the oxide formed during the transfer process or the atmospheric process after operation. The preliminary reduction step may be performed before the nitriding step.

[0107] The second gas may contain 10 to 50 percent hydrogen by volume and the remainder nitrogen. In this way, by using a mixed gas of hydrogen, which is a reducing gas, and relatively stable nitrogen, the active metal can be stably reduced. If the hydrogen content is excessively low, the reduction reaction of the active metal oxide may not proceed sufficiently. If the hydrogen content is excessively high, it may be difficult to control the reduction reaction.

[0108] The temperature of the second gas may be 850°C or lower. If the temperature of the second gas is excessively high, excessive energy may be consumed to reach the target temperature. If the oxide of the active metal is reduced, the temperature of the second gas is not particularly limited, but as a non-limiting example, the temperature of the second gas may be 0°C or higher. In terms of reduction reactivity, the temperature of the second gas may be 300°C or higher.

[0109] The supply flow rate of the second gas is the active area of ​​the fuel electrode 100 cm² 2It can be controlled to 0.5 to 2 l / min. If the supply flow rate of the second gas is excessively high compared to the active area of ​​the fuel electrode, hydrogen that does not participate in the reaction is generated, and resource efficiency may be lowered. If the supply flow rate of the second gas is excessively low compared to the active area of ​​the fuel electrode, the reduction reaction efficiency may be reduced. In this regard, according to exemplary embodiments, the supply flow rate of the second gas can be controlled to 0.075 l / min or higher.

[0110] Optionally, the preliminary reduction step may further include a preliminary pretreatment step of providing a third gas containing hydrogen to the fuel electrode. The preliminary pretreatment step may be performed after the second gas supply and before the nitriding step. This allows for the effective formation of nitrides in the subsequent nitriding step by further reducing oxides of the active metal that may remain after the preliminary reduction step. The third gas may consist of hydrogen.

[0111] The temperature of the third gas can be 750 to 850°C. In this way, by creating a high-temperature reducing atmosphere, oxides of active metals can be effectively reduced.

[0112] The supply flow rate of the third gas can be controlled to 0.5 to 2 l / min per 100 cm² of active surface area of ​​the fuel electrode. As a result, any remaining oxides of the active metal can be reduced to properly form nitrides of the active metal thereafter.

[0113] [Test Example]

[0114] A test was conducted to verify whether the durability of the fuel cell can be improved by forming an active metal nitride.

[0115] (Example 1)

[0116] A fuel electrode containing nickel as the active metal of the catalyst was prepared. Pure ammonia gas (first gas) was supplied to this fuel electrode under open-circuit voltage conditions. At this time, a nitriding atmosphere was maintained at approximately 800°C for approximately 10 minutes, and then cooled to 750°C at a cooling rate of approximately 2.5°C / min to prepare a fuel cell containing a fuel electrode in which nickel nitride was formed.

[0117] (Comparative Example 1)

[0118] A fuel cell was prepared in the same manner as in Example 1, except that pure hydrogen gas was used as the first gas.

[0119] Afterwards, each fuel cell was driven by applying a constant current of 0.3 A / cm2 in an environment supplying pure ammonia at approximately 680°C.

[0120] Figure 4 is a graph showing the voltage change according to the constant current application time.

[0121] Referring to FIG. 4, it was confirmed that the performance of Example 1 remained constant. However, in the case of Comparative Example 1, it was confirmed that although the initial performance was excellent, the performance deteriorated over time.

[0122] Although the invention has been described with reference to the above embodiments, those skilled in the art will understand that various modifications and changes can be made to the invention without departing from the spirit and scope of the invention as described in the following claims.

[0123] (Explanation of symbols)

[0124] 10: Ammonia fuel cell system

[0125] 100: Fuel cell

[0126] 110: Fuel electrode

[0127] 120: Air electrode

[0128] 130: Electrolyte

Claims

1. A fuel cell comprising a fuel electrode comprising a nitride of an active metal; an air electrode; and an electrolyte interposed between the fuel electrode and the air electrode, and The above fuel electrode is an ammonia fuel cell system satisfying the following relationship 1. [Relationship 1] 0.20 ≤ [N1] / ([N1]+[M1]) ≤ 0.40 (In the above Equation 1, [N1] is the average nitrogen content (at%) in the electrode surface layer up to a depth of 15 μm in the thickness direction from the surface of the fuel electrode, and [M1] is the average active metal content (at%) in the electrode surface layer of the fuel electrode.) 2. In Paragraph 1, The above fuel electrode is an ammonia fuel cell system satisfying the following relationship 2. [Relationship 2] 0.01 ≤ [N2] / ([N2]+[M2]) ≤ 0.20 (In the above Equation 2, [N2] is the average nitrogen content (at%) in the surface layer up to a depth of 50 μm in the thickness direction from the electrode surface layer of the fuel electrode, and [M2] is the average active metal content (at%) in the surface layer of the fuel electrode.) 3. In Paragraph 1, An ammonia fuel cell system in which the operating temperature of the above fuel cell is less than 700℃.

4. In Paragraph 1, The above fuel cell is an ammonia fuel cell system in which the electrolyte is a solid oxide type fuel cell comprising a solid oxide.

5. In Paragraph 1, The above active metal is an ammonia fuel cell system in which any one of nickel (Ni), cobalt (Co), ruthenium (Ru), palladium (Pd), platinum (Pt), iron (Fe), molybdenum (Mo) and alloy elements thereof.

6. A fuel cell comprising a fuel electrode; an air electrode; and an electrolyte interposed between the fuel electrode and the air electrode, comprising the step of providing a first gas containing ammonia to the fuel electrode to nitrate the active metal of the fuel electrode. The above nitrifying step is an ammonia fuel cell pretreatment method performed under open circuit voltage (OCV) conditions.

7. In Paragraph 6, A method for pre-treating an ammonia fuel cell in which the temperature of the first gas is 850℃ or lower.

8. In Paragraph 6, A method for pre-treating an ammonia fuel cell in which the ammonia content of the first gas is 10 to 100% in volume%.

9. In Paragraph 6, The supply flow rate of the first gas is 100 cm² of the active area of ​​the fuel electrode. 2 Ammonia fuel cell pretreatment method controlled at 0.5~2 l / min per gram.

10. In Paragraph 9, A method for pre-treating an ammonia fuel cell in which the supply flow rate of the first gas is 0.075 l / min or more.

11. In Paragraph 6, The above nitriding step is an ammonia fuel cell pretreatment method performed for 5 to 120 minutes.

12. In Paragraph 6, Ammonia fuel cell pretreatment method further comprising a preliminary reduction step of providing a second gas containing hydrogen and nitrogen to the above fuel electrode.

13. In Paragraph 12, The above second gas is an ammonia fuel cell pretreatment method comprising, in volume %, 10 to 50 percent hydrogen and the remainder nitrogen.

14. In Paragraph 12, A method for pre-treating an ammonia fuel cell in which the temperature of the second gas is 850℃ or lower.

15. In Paragraph 12, A method for pre-treating an ammonia fuel cell in which the supply flow rate of the second gas is controlled to 0.5 to 2 l / min per 100 cm² of active area of ​​the fuel electrode.

16. In Paragraph 12, The above preliminary reduction step Ammonia fuel cell pretreatment method further comprising a preliminary pretreatment step of providing a third gas containing hydrogen to the above fuel electrode.

17. In Paragraph 16, Ammonia fuel cell pretreatment method in which the temperature of the third gas is 750~850℃.

18. In Paragraph 16, The supply flow rate of the third gas above is for an active area of ​​100 cm² of the fuel electrode 2 Ammonia fuel cell pretreatment method controlled at 0.5~2 l / min per gram.

19. In Paragraph 6, The above nitriding step is, A first nitriding step of maintaining at 750~850℃ for 5~20 minutes; and Ammonia fuel cell pretreatment method comprising a second nitriding step of cooling from the temperature of the first nitriding step to a temperature of 700°C or higher and below the first nitriding step maintenance temperature.

20. In Paragraph 19, Ammonia fuel cell pretreatment method in which the cooling rate of the second nitriding step is 1.0 to 3.0℃ / min.

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