FUEL ELECTRODE FOR SOLID OXIDE ELECTROLYSIS CELL WITH IMPROVED HIGH-TEMPERATURE ELECTROLYSIS EFFICIENCY AND STABILITY AND METHOD OF MANUFACTURING SAME

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims, under 35 U.S.C. § 119(a), the benefit of priority from Korean Patent Application No. 10-2024-0186289, filed on Dec. 13, 2024, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a fuel electrode for a solid oxide electrolysis cell with improved high-temperature electrolysis efficiency and stability and a method of manufacturing the same, in which high cell performance and durability may be achieved using a novel material for a solid oxide electrolysis cell.

BACKGROUND

Among green hydrogen production methods, a solid oxide electrolysis cell (SOEC) has the advantages of high efficiency and low operating voltage compared to polymer electrolyte membrane electrolysis (PEM electrolysis) and alkaline electrolysis. However, currently developed solid oxide electrolysis cells utilize elements of existing solid oxide fuel cells and have problems of insufficient performance and reduced durability due to the absence of dedicated materials. In particular, a conventional nickel-YSZ (yttria-stabilized zirconia)-based fuel electrode is problematic in that its stability is greatly reduced due to nickel deterioration. Accordingly, there is a need for new materials that can be used in fuel electrodes that provide improved performance characteristics such as, for example, increased stability and/or efficiency.

SUMMARY

The present disclosure provides, among other advancements in the art, a fuel electrode for a solid oxide electrolysis cell with improved high-temperature electrolysis efficiency and stability, and a method of manufacturing the same.

The advantages, objects, aspects, and embodiments of the present disclosure are not limited to the foregoing or those explicitly described herein. One of skill in the art will be able to clearly understand the full scope of the advantages and features of the disclosure through the following description, illustrative examples, and the claims.

An aspect of the present disclosure provides a fuel electrode for a solid oxide electrolysis cell, including a support comprising a first alloy derived from first particles including nickel (Ni) and second particles including yttria-stabilized zirconia (YSZ), and a catalyst comprising a second alloy derived from a first element including any one of, or selected from the group consisting of, iron (Fe), cobalt (Co), palladium (Pd), copper (Cu), molybdenum (Mo), manganese (Mn), and combinations thereof, and a second element including samarium-doped ceria (SDC), wherein the catalyst is supported on the support, and the first alloy has catalytic activity.

In one embodiment, a size (D50) of the first alloy may be 1 μm or less (e.g., no greater than about 1 μm).

In one embodiment, a size (D50) of the second particles may be 350 nm to 500 nm.

In one embodiment, a size (D50) of the second element may be 20 nm to 60 nm.

In one embodiment, SDC may be represented by the Chemical Formula below:

• • wherein x is 0.1 to 0.4.

Another aspect of the present disclosure provides a method of manufacturing a fuel electrode for a solid oxide electrolysis cell, comprising preparing an intermediate support including first particles including nickel (Ni) and second particles including yttria-stabilized zirconia (YSZ), obtaining a first intermediate by injecting a precursor of a first element including any one of, or selected from the group consisting of, iron (Fe), cobalt (Co), palladium (Pd), copper (Cu), molybdenum (Mo), manganese (Mn), and combinations thereof into the intermediate support and performing a first heat treatment to form the first intermediate, obtaining a second intermediate by injecting a precursor of a second element including samarium-doped ceria (SDC) into the first intermediate and performing a second heat treatment to form the second intermediate, and obtaining a fuel electrode by reducing the second intermediate in a hydrogen atmosphere, wherein the fuel electrode includes a support comprising a first alloy derived from the first particles and the second particles; and a catalyst comprising a second alloy derived from the first element and the second element, wherein the catalyst is supported on the support, and wherein the first alloy has catalytic activity.

In one embodiment, the method may further include heat treating the intermediate support before injecting the precursor of the first element into the intermediate support.

In one embodiment, a first solution comprising the precursor of the first element, a complexing agent, and a mixed solvent including an aqueous solvent and an alcohol solvent may be injected into the intermediate support.

In one embodiment, the precursor of the first element and the complexing agent may be in a molar ratio of 1:1-10, with respect to the amount of cations of the first element complexing agent.

In one embodiment, the complexing agent may include any one of, or may be selected from the group consisting of, urea, glycine, Triton X (C₁₄H₂₂O(C₂H₄O)_n, n=9-10)), citric acid, and combinations thereof.

In one embodiment, the alcohol solvent and the aqueous solvent in the mixed solvent may be in a volume ratio of 1:0.25-4.

In one embodiment, the first heat treatment may be performed at a temperature of 500° C. or less (e.g., no more than about 500° C.).

In one embodiment, the first heat treatment may include subjecting the intermediate support and the precursor of the first element to heating at 50° C. to 100° C. for 1 to 3 hours, heating at 120° C. to 200° C. for 1 to 2 hours, and heating at 300° C. to 500° C. for 1 to 3 hours.

In one embodiment, a second solution including the precursor of the second element, a complexing agent, and a mixed solvent of an aqueous solvent and an alcohol solvent may be injected into the first intermediate.

In one embodiment, the precursor of the second element may include a hydrate of cerium (III) nitrate and a hydrate of samarium (III) nitrate.

In one embodiment, the precursor of the second element may include the hydrate of cerium (III) nitrate and the hydrate of samarium (III) nitrate in a molar ratio of 9:1 to 6:4, respectively.

In one embodiment, the precursor of the second element and the complexing agent may be in a molar ratio of 1:1-10, with respect to the amount of cations of the second element:complexing agent.

In one embodiment, the complexing agent may include any one of, or may be selected from the group consisting of, urea, glycine, Triton X (C₁₄H₂₂O(C₂H₄O)_n, n=9-10)), citric acid, and combinations thereof.

In one embodiment, the alcohol solvent and the aqueous solvent in the mixed solvent may be in a volume ration of 1:0.25-4.

In one embodiment, the second heat treatment may be performed at a temperature of 500° C. or less (e.g., no more than about 500° C.).

In one embodiment, the second heat treatment may include subjecting the first intermediate and the precursor of the second element to heating at 50° C. to 100° C. for 1 to 3 hours, heating at 120° C. to 200° C. for 1 to 2 hours, and heating at 300° C. to 500° C. for 1 to 3 hours, and the second heat treatment may be performed at least once.

In one embodiment, the fuel electrode may be obtained by reducing the second intermediate in a hydrogen atmosphere at a temperature of 700° C. to 800° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof, illustrated in the accompanying examples and drawings which are given hereinbelow by way of illustration only, and thus are not limiting to the present disclosure or appended claims.

FIG. 1 shows the configuration of an intermediate support according to one embodiment of the present disclosure;

FIG. 2 shows the configuration of a fuel electrode according to one embodiment of the present disclosure;

FIG. 3 shows results of comparing polarization resistance values of half-cells to which a fuel electrode using only the support of the present disclosure and a fuel electrode manufactured by supporting an SDC catalyst on the support while controlling the content of samarium (Sm) are applied;

FIG. 4 shows results of comparing temperature-dependent resistance values of half-cells to which a fuel electrode using only the support of the present disclosure and a fuel electrode manufactured by supporting an SDC catalyst on the support while controlling the content of samarium (Sm) are applied;

FIG. 5 shows results of comparing resistance values of a fuel electrode using only the support of the present disclosure and a fuel electrode manufactured by supporting an SDC catalyst on the support while controlling the content of samarium (Sm);

FIG. 6 shows results of electrochemical performance of unit cells to which fuel electrodes according to an Example and Comparative Examples 1 to 3 are applied;

FIG. 7 shows results of analyzing the cross-section and the elemental distribution of nickel (Ni), iron (Fe), and cerium (Ce) included in the cross-section using TEM-EDS (transmission electron microscopy-energy dispersive X-ray spectroscopy) after electrochemical evaluation of a unit cell to which the fuel electrode according to an Example is applied;

FIG. 8 shows results of analyzing the cross-section of the fuel electrode according to Comparative Example 1 using SEM (scanning electron microscopy);

FIG. 9 shows results of analyzing the cross-section of the fuel electrode according to an Example using SEM, with some SDC nanocatalysts and particle sizes thereof,

FIG. 10 shows results of durability and stability evaluation for unit cells to which the fuel electrodes according to an Example and Comparative Examples 1 and 3 are applied, in terms of voltage and normalized voltage;

FIG. 11(a) shows electrochemical performance before and after durability evaluation of a unit cell to which the fuel electrode according to Comparative Example 1 is applied, and FIG. 11(b) shows polarization resistance of the same unit cell before and after durability evaluation; and

FIG. 12(a) shows electrochemical performance before and after durability evaluation of a unit cell to which the fuel electrode according to an Example is applied, and FIG. 12(b) shows polarization resistance of the same unit cell before and after durability evaluation.

DETAILED DESCRIPTION

The above and other objects, features and advantages of the present disclosure will be more clearly understood from the following aspects and embodiments, including preferred embodiments, taken in conjunction with the accompanying drawings. However, the present disclosure is not limited to the illustrative embodiments disclosed herein and may be modified into different forms and/or with different features. These illustrative descriptions and embodiments are provided to thoroughly explain the disclosure and to sufficiently transfer the spirit of the present disclosure to those skilled in the art.

Throughout the drawings, the same reference numerals will refer to the same or like elements. For the sake of clarity of the present disclosure, the dimensions of structures are depicted as being larger than the actual sizes thereof. It will be understood that, although terms such as “first”, “second”, etc. may be used herein to describe various elements, these elements are not to be limited by these terms. These terms are only used to distinguish one element from another element. For instance, a “first” element discussed below could be termed a “second” element without departing from the scope of the present disclosure. Similarly, the “second” element could also be termed a “first” element. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It will be further understood that the terms “comprise”, “include”, “have”, etc., when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Also, it will be understood that when an element such as a layer, film, area, or sheet is referred to as being “on” another element, it may be directly on the other element, or intervening elements may be present therebetween. Similarly, when an element such as a layer, film, area, or sheet is referred to as being “under” another element, it may be directly under the other element, or intervening elements may be present therebetween.

Unless specified otherwise, all numbers, values, and/or representations that express the amounts of components, reaction conditions, polymer compositions, and mixtures used herein are to be taken as approximations including various uncertainties affecting measurement that inherently occur in obtaining these values, among others, and thus should be understood to be modified by the term “about” in all cases. Furthermore, when a numerical range is disclosed in this specification, the range is continuous, and includes all values from the minimum value of said range to the maximum value thereof, unless otherwise indicated. Moreover, when such a range pertains to integer values, all integers including the minimum value to the maximum value are included, unless otherwise indicated.

In the present specification, when a range is described for a variable, it will be understood that the variable includes all values including the end points described within the stated range. For example, the range of “5 to 10” will be understood to include any subranges, such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, and the like, as well as individual values of 5, 6, 7, 8, 9 and 10, and will also be understood to include any value between valid integers within the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, and the like. Also, for example, the range of “10% to 30%” will be understood to include subranges, such as 10% to 15%, 12% to 18%, 20% to 30%, etc., as well as all integers including values of 10%, 11%, 12%, 13% and the like up to 30%, and will also be understood to include any value between valid integers within the stated range, such as 10.5%, 15.5%, 25.5%, and the like.

Furthermore, unless specifically stated otherwise, the term “about” as noted above, and as used herein may be understood within a range of error that is typical in the art (e.g., within 2 standard deviations of the mean). “About” may be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value.

In addition, “vehicle” or “automobile” or other similar terms used herein are understood to include general automobiles such as sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, etc., and transportation means such as trains, ships, and aircraft, and also include hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuel derived from resources other than petroleum). “Hybrid vehicle” as used herein means a vehicle that has two or more power sources (e.g., a gasoline-powered vehicle and an electric-powered vehicle).

When a certain computational ability is required to perform any method or program herein, it may be understood that it is driven by a hardware device that includes a memory and a processor and is specifically programmed to execute the method or program described herein. The memory is configured to store a module, and the processor is specifically configured to execute the module to perform one or more processes as further described below.

Also, it may be implemented as a non-transitory computer readable medium on a computer readable medium including executable program instructions executed by a processor, controller, etc. Examples of the computer readable medium include, but are not limited to, ROM, RAM, compact disc (CD)-ROM, magnetic tape, floppy disks, flash drives, smart cards, and optical data storage devices. The computer readable medium may also be distributed to networked computer systems for storage and execution in a distributed manner, such as a telematics server or a CAN (controller area network).

A solid oxide electrolysis cell according to one embodiment of the present disclosure may include a porous fuel electrode, a dense electrolyte, and a porous air electrode. As a reactant, water vapor flows into a fuel channel, and when voltage is applied to the fuel electrode, decomposition reaction of water vapor occurs. Respective half-reactions at the fuel electrode and the air electrode and overall reaction are as follows.

A method of manufacturing a fuel electrode for a solid oxide electrolysis cell according to an embodiment of the present disclosure may comprise preparing an intermediate support including first particles including nickel (Ni) and second particles including YSZ (yttria-stabilized zirconia), obtaining a first intermediate by injecting a precursor of a first element including any one of, or selected from the group consisting of, iron (Fe), cobalt (Co), palladium (Pd), copper (Cu), molybdenum (Mo), manganese (Mn), and combinations thereof into the intermediate support and performing a first heat treatment, obtaining a second intermediate by injecting a precursor of a second element including SDC (samarium-doped ceria) into the first intermediate and performing a second heat treatment, and obtaining a fuel electrode by reducing the second intermediate in a hydrogen atmosphere.

The first particles and the second particles herein may be understood to refer to a plurality of particles

The method of preparing the intermediate support is not particularly limited, and the intermediate support may be prepared by any conventionally known method. For example, an intermediate support may be prepared by spray drying a mixed solution obtained by mixing nickel oxide (NiO), YSZ, and a solvent to afford a powder and then pressurizing or slurrying the powder followed by tape casting.

In addition, the term “intermediate support” in the present specification may be understood to refer to a support that corresponds to any stage prior to the completion of the fuel electrode, after the prepared support has undergone multiple heat treatment processes.

In addition, a solid oxide electrolysis cell may be prepared by stacking an electrolyte, an air electrode, etc. on the intermediate support.

FIG. 1 shows the configuration of an intermediate support according to example embodiments of the present disclosure.

The first particles including nickel (Ni) may be electronically conductive. The size of the first particles may be 1 μm or less. The size may refer to D50 average diameter. The lower limit of the size of the first particles is not particularly limited and may be 100 nm or more, 300 nm or more, 500 nm or more, or 700 nm or more. Herein, the statement that the size of the first particles satisfies a specific numerical range does not mean that all of the first particles must have a particle size within the range. Rather, it is to be understood that, when the particle size of the first particles located within a certain region is measured using known means such as SEM or TEM, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 99% or more of the first particles may have a size within the numerical range. Unless otherwise specified herein, the size of any component should be understood in the same manner.

The second particles including YSZ may be oxygen ion conductive. The size of the second particles may be 350 nm to 500 nm.

The intermediate support may be a mixture of the first particles and the second particles.

The manufacturing method according to the present disclosure may further include heat treating the intermediate support, before injecting the precursor of the first element into the intermediate support. For example, the intermediate support may be heat treated at about 300° C. to 500° C.

In one embodiment, injecting the precursor of the first element into the intermediate support may be performed by injecting a first solution including the precursor of the first element, a complexing agent, and a mixed solvent of an aqueous solvent and an alcohol solvent into the intermediate support. Accordingly, the precursor of the first element may infiltrate the pores of the support. That is, “injecting the precursor of the first element into the intermediate support” may be understood as bringing the first solution into contact with the intermediate support by any methods or means (for example, a micropipette) in order to infiltrate the first solution into the intermediate support.

In embodiments, the first element may include any one of iron (Fe), cobalt (Co), palladium (Pd), copper (Cu), molybdenum (Mo), manganese (Mn), and combinations thereof, as a component of the catalyst. In some embodiments, the first element may be selected from the group consisting of iron (Fe), cobalt (Co), palladium (Pd), copper (Cu), molybdenum (Mo), manganese (Mn), and combinations thereof, as a component of the catalyst.

In embodiments, the precursor of the first element may include a nitrate, acetate, or chloride compound of the first element.

In one embodiment, the complexing agent may include any of urea, glycine, Triton X (C₁₄H₂₂O(C₂H₄O)_n, n=9-10)), citric acid, and combinations thereof. In some embodiments, the complexing agent may be selected from the group consisting of urea, glycine, Triton X (C₁₄H₂₂O(C₂H₄O)_n, n=9-10)), citric acid, and combinations thereof.

The amount of the complexing agent that is added is not particularly limited, and in some example embodiments, the molar ratio of the cation of the precursor of the first element to the complexing agent may be in a range of 1:1-10.

In one embodiment, the volume ratio of the alcohol solvent to the aqueous solvent in the mixed solvent may be 1:0.25-4. In such embodiments, the alcohol solvent may include at least one of methanol, ethanol, propanol, and butanol.

In embodiments, the first solution may be prepared by dissolving the precursor of the first element in an aqueous solvent, adding a complexing agent, and adding an alcohol solvent.

In embodiments, after the first solution is injected into the intermediate support, the result is subjected to a first heat treatment, obtaining a first intermediate in which an oxide of the first element is supported on the intermediate support.

In such embodiments, the first heat treatment may be performed at a temperature of 500° C. or less, and in some preferred embodiments, the first heat treatment includes a process of subjecting an object (e.g., intermediate support) to heating at 50° C. to 100° C. for 1 to 3 hours, heating at 120° C. to 200° C. for 1 to 2 hours, and heating at 300° C. to 500° C. for 1 to 3 hours. This first heat treatment may be repeated one or more times as necessary.

In embodiments, the object may be understood as a substance in which the precursor of the first element is injected onto the intermediate support.

In embodiments wherein the first solution is injected into the intermediate support to allow the precursor of the first element to infiltrate the pores of the intermediate support and the result is heated to 50° C. to 100° C., the complexing agent decomposes and the precursor of the first element precipitates on the intermediate support. Thereafter, when the temperature is increased to 300-500° C. via 120-200° C., the precursor of the first element is supported in the form of an oxide on the intermediate support.

In embodiments, a second solution including the precursor of the second element, a complexing agent, and a mixed solvent of an aqueous solvent and an alcohol solvent may be injected into the first intermediate thus obtained to allow the precursor of the second element to infiltrate the pores of the intermediate support.

In embodiments, the second element may include SDC (samarium-doped ceria) as a component of the catalyst.

In embodiments, the precursor of the second element may include a nitrate, acetate, or chloride compound of cerium (Ce) and samarium (Sm), and/or hydrates thereof. For example, in some embodiments the precursor of the second element may include a hydrate of cerium (III) nitrate and a hydrate of samarium (III) nitrate, and some further embodiments, may include cerium nitrate hexahydrate (Ce(NO₃)₃6H₂O) and/or samarium nitrate hexahydrate (Sm(NO₃)₃6H₂O).

In some embodiments, the precursor of the second element may include the hydrate of cerium (III) nitrate and the hydrate of samarium (III) nitrate in a molar ratio of 9:1 to 6:4. When the precursor of the second element includes the hydrate of cerium nitrate and the hydrate of samarium nitrate satisfying the molar ratio described above, the second element including SDC may be represented by the following chemical formula:

• • wherein x is 0.1 to 0.4.

In conventional cerium-based catalysts, it is known that conductivity is high when the proportion of a dopant (Sm) is less than or equal to 20 atomic % (at %), so in that context, the content of samarium in SDC is limited to 10 at % to 20 at %. In contrast, the fuel electrode manufactured according to the present disclosure, the first element and the second element are applied to the intermediate support using the first solution and the second solution by a continuous impregnation technique, and as described below, the first heat treatment and the second heat treatment are performed at relatively low temperatures (e.g., 500° C. or less), whereby the best electronic conductivity is exhibited in a higher dopant proportion, for example, about 30 at %, and the dopant may be used in a wider range.

In some embodiments, the complexing agent included in the second solution may include any one of urea, glycine, Triton X (C₁₄H₂₂O(C₂H₄O)_n, n=9-10)), citric acid, and combinations thereof. In some embodiments, the complexing agent included in the second solution is selected from the group consisting of urea, glycine, Triton X (C₁₄H₂₂O(C₂H₄O)_n, n=9-10)), citric acid, and combinations thereof.

The amount of the complexing agent that is added is not particularly limited, and in some example embodiments, the molar ratio of the cation of the precursor of the second element to the complexing agent may be in the range of 1:1-10.

In embodiments, the volume ratio of the alcohol solvent to the aqueous solvent in the mixed solvent included in the second solution may be 1:0.25-4. In such embodiments, the alcohol solvent may include at least one of methanol, ethanol, propanol, and butanol.

In embodiments, the second solution may be prepared by dissolving the precursor of the second element in an aqueous solvent, adding a complexing agent, and adding an alcohol solvent.

In some embodiments, after the second solution is injected into the first intermediate, the result is subjected to second heat treatment, obtaining a second intermediate in which the oxide of the first element and the second element are supported on the intermediate support.

In such embodiments, the second heat treatment may be performed at a temperature of 500° C. or less, and in some preferred embodiments, the second heat treatment includes a process of subjecting an object to heating at 50° C. to 100° C. for 1 to 3 hours, heating at 120° C. to 200° C. for 1 to 2 hours, and heating at 300° C. to 500° C. for 1 to 3 hours. Also, the second heat treatment may be performed one or more times.

In some embodiments, when the second solution is injected into the intermediate support to allow the precursor of the second element to infiltrate the pores of the intermediate support and the result is heated to 50° C. to 100° C., the complexing agent decomposes and the precursor of the second element precipitates on the intermediate support. Thereafter, when the temperature is increased to 300-500° C. via 120-200° C., the second element is supported on the support.

Thereafter, the second intermediate may be reduced in a hydrogen atmosphere at a temperature of 700° C. to 800° C., thereby obtaining a fuel electrode.

The method of forming the hydrogen atmosphere is not particularly limited, and, in some embodiments, the hydrogen atmosphere may include about 3 vol % of water vapor and about 97 vol % of hydrogen gas, or may be formed using a mixed gas of nitrogen gas and hydrogen gas.

FIG. 2 shows the configuration of a fuel electrode according to one embodiment of the present disclosure.

In embodiments, the fuel electrode may include a support and a catalyst supported on the support.

In embodiments, the support may include a first alloy derived from first particles including nickel (Ni) and second particles including YSZ (yttria-stabilized zirconia). Herein, the statement that “the first alloy is derived from the first particles” may mean that the first element diffuses into the surface and interior of the prepared first particles, causing an alloying reaction, and thereby forming an alloy between the first particles and the first element. Accordingly, the particle size of the formed first alloy may be similar to that of the original first particles.

In embodiments, the first alloy may serve as a support for the catalyst while simultaneously functioning as a catalyst for the electrolysis cell reaction itself, thereby exhibiting bifunctionality.

In embodiments, the catalyst may include a second alloy derived from a first element including any one of iron (Fe), cobalt (Co), palladium (Pd), copper (Cu), molybdenum (Mo), manganese (Mn), and combinations thereof, and a second element including SDC (samarium-doped ceria). In some embodiments, the catalyst comprises a first element selected from the group consisting of iron (Fe), cobalt (Co), palladium (Pd), copper (Cu), molybdenum (Mo), manganese (Mn), and combinations thereof, and a second element including SDC (samarium-doped ceria). Herein, the statement that “the second alloy is derived from the first element” may mean that a portion of the first particles diffuses into the surface and interior of the first element attached to the surface of the intermediate support, thereby causing an alloying reaction, and thus forming an alloy between the first element and the first particles. Accordingly, the particle size of the formed second alloy may be similar to that of the original first element.

That is, in one embodiment, the first alloy and the second alloy may both comprise alloys of the same metallic elements, but may differ in their average particle size.

In embodiments, the size of the catalyst according to the present disclosure, and in some particular embodiments, the second element and second element, may be 20 nm to 60 nm, respectively.

Both the first heat treatment and the second heat treatment in the process of manufacturing the fuel electrode according to embodiments of the present disclosure are performed at a temperature of 500° C. or less. In contrast, the conventional method of manufacturing a fuel electrode for a solid oxide electrolysis cell involves a heat treatment process at a high temperature of 1000° C. or more, particularly at a high temperature of 1300° C. or more. During this process, catalyst agglomeration occurs, which increases the size of the catalyst particles and decreases the surface area, resulting in various problems, for example deteriorated catalytic performance.

In the process of manufacturing the fuel electrode according to embodiments of the present disclosure, since the first heat treatment and the second heat treatment are performed at relatively low temperatures of 500° C. or less, catalyst agglomeration is suppressed, and thus, the particle size of the catalyst may be controlled with nanometer precision.

In one embodiment, the fuel electrode may comprise: a support including a first alloy derived from the first particles and the second particles; and a catalyst including a second alloy derived from the first element and the second element. The catalyst may be supported on the support. Specifically, the particles of the second alloy and the particles of the second element may each be uniformly dispersed and supported on the surfaces of the first alloy and the second particles, respectively.

In some specific embodiments, when the second intermediate is heat treated in a hydrogen atmosphere, nickel oxide (NiO) is reduced into nickel (Ni), and the oxide of the first element is reduced into the first element, so that an alloy of nickel (Ni) and the first element may be formed. Herein, it can be understood that when the alloying reaction occurs on the surface and inside of the first particles, the first alloy is formed, and when the alloying reaction occurs on the surface and inside of the first element, the second alloy is formed.

The fuel electrode according to embodiments the present disclosure is capable of further lowering the activation energy of hydrogen production reaction by forming an alloy between the first particles and the first element compared to when the first element is provided alone. Accordingly, hydrogen production may be facilitated.

In embodiments, the present disclosure is characterized in that the precursor of the first element first infiltrates the intermediate support and is supported thereon, and subsequently, the precursor of the second element is introduced. If the precursor of the second element is introduced first, alloying of the first element and the first particles may not occur efficiently. The fuel electrode according to embodiments of the present disclosure includes the first particles and the first element alloyed together, and the second element supported on the surface of the support in a non-alloyed state with the first particles.

In such embodiments, the support including the first alloy and second particles has a limited number of reaction sites because hydrogen production reaction occurs only at an interface therebetween. In contrast, when the second element is doped into the first particles or is alloyed, the catalytic reaction site of the second element may be limited to the interface of the support, resulting in deteriorated catalytic effect. According to the present disclosure, since the second element is supported in a non-alloyed state with the first particles of the support, hydrogen production reaction may occur at the surface or interface of Ni-SDC, SDC-SDC, or SDC-YSZ, so that electrode resistance may be lowered and electrolysis efficiency may be increased.

A better understanding of the present disclosure may be obtained through the following illustrative examples and comparative examples. However, these examples are only exemplary and are not to be construed as limiting the technical spirit of the present disclosure.

Test Example 1

In order to verify the catalytic effect of a second element (SDC) supported on a support including first alloy derived from the first particles (Ni) and second particles (YSZ) and performance depending on the doping proportion of samarium in SDC, a half-cell was manufactured as follows.

Specifically, an intermediate support slurry was prepared by ball milling nickel powder, YSZ powder, and a solvent, after which the intermediate support slurry was applied onto both sides of a YSZ electrolyte layer with a thickness of about 3 μm, followed by heat treatment to manufacture an intermediate cell. Here, the type of solvent used is not particularly limited, and may include, for example, water (DI water), ethanol, α-terpineol, etc. In addition, a PVB (polyvinyl butyral resin) binder and a DBP (dibutyl phthalate) plasticizer may also be included as needed.

Thereafter, cerium nitrate hexahydrate and samarium nitrate hexahydrate were added to distilled water in molar ratios of 9:1, 8:2, 7:3, and 6:4, and urea was added so that the molar ratio of the cations (i.e., cerium and samarium) to urea was 1:10. Also, a second solution was obtained by adding ethanol so that the volume ratio of distilled water to ethanol was 1:3.

The second solution was added dropwise onto the intermediate cell using a micropipette and infiltrated the same, followed by second heat treatment at 80° C. for 2 hours, 150° C. for 1 hour, and 400° C. for 2 hours. The second heat treatment was performed three times. An intermediate obtained by the second heat treatment was reduced in a hydrogen atmosphere at 800° C., thereby manufacturing a half-cell including a fuel electrode.

The completed half-cell was prepared by joining a Ni or Pt metal current collector and a Pt current collector wire to a metal and ceramic jig, and EIS electrochemical characterization was performed by injecting fuel gas (H₂O+H₂). For EIS electrochemical characterization, devices such as IviumStat (HS Technologies), or the like, were used.

FIG. 3 shows results of comparing the polarization resistance values of a half-cell using the intermediate cell as is, without applying the second solution and a half-cell to which a fuel electrode manufactured by supporting the SDC catalyst on the support while controlling the content of samarium (Sm) was applied. FIG. 4 shows results of comparing the temperature-dependent resistance values thereof, and FIG. 5 shows results of comparing the catalyst-dependent resistance values thereof.

For reference, a half-cell using the intermediate cell as is, without applying the second solution is represented as Ni/YSZ, a half-cell using cerium nitrate hexahydrate and samarium nitrate hexahydrate in a molar ratio of 9:1 is represented as Ni/YSZ+SDC 10 (or SDC 10), a half-cell in a molar ratio of 8:2 is represented as Ni/YSZ+SDC 20 (or SDC 20), a half-cell in a molar ratio of 7:3 is represented as Ni/YSZ+SDC 30 (or SDC 30), a half-cell in a molar ratio of 6:4 is represented as Ni/YSZ+SDC 40 (or SDC 40), and a half-cell in a molar ratio of 5:5 is represented as Ni/YSZ+SDC 50 (or SDC 50).

Referring to FIG. 3, when the SDC catalyst was introduced onto the Ni/YSZ support according to the present disclosure through the second solution, it was confirmed that electrochemical performance increased (polarization resistance decreased) under the condition that the content of doped samarium (Sm) in SDC was 10 at % to 40 at %. In addition, it was confirmed that the temperature-dependent resistance values and the catalyst-dependent resistance values decreased compared to when the SDC catalyst was not introduced.

However, when the proportion of doped Sm in SDC was 50 at %, the polarization resistance, temperature-dependent resistance, and catalyst-dependent resistance values actually increased. Without being limited by mechanism or theory, this may be because the ionic conductivity due to oxygen vacancies increases with an increase in the proportion of doped samarium in SDC, but oxygen clusters that increase in oxygen vacancies beyond a certain critical point are formed, and the formed clusters are not utilized as ion passages, which actually decreases conductivity.

In addition, when the proportion of doped Sm in SDC was 30 at %, all types of resistance values were low, confirming that the use of SDC according to the formula Sm_0.3Ce_0.7O_2-δ exhibited the highest fuel electrode performance.

EXAMPLE

An air electrode and an electrolyte were prepared using a known method. In various examples, the air electrode may include La, Sr, and Co, and the electrolyte may include YSZ.

An intermediate support with evenly dispersed nickel oxide and YSZ was prepared using the same method as above.

A first solution was prepared as follows. After diluting Fe(NO₃)₃·9H₂O in distilled water, urea was added so that the molar ratio of the cation thereof to urea was 1:10. The first solution was obtained by adding ethanol so that the volume ratio of distilled water to ethanol was 4:1.

A second solution was prepared as follows. Cerium nitrate hexahydrate (Ce(NO₃)₃·6H₂O) and samarium nitrate hexahydrate (Sm(NO₃)₃·6H₂O) were diluted in distilled water so that the molar ratio of cerium (Ce) to samarium (Sm) was 7:3, after which urea was added so that the molar ratio of the cations thereof to urea was 1:10. The second solution was obtained by adding ethanol so that the volume ratio of distilled water to ethanol was 1:3.

The intermediate support was heat pretreated at about 400° C.

After heat pretreatment, the intermediate support was sufficiently cooled, and the first solution was dropped onto the intermediate support using a micropipette and infiltrated the support, and was followed by a first heat treatment at 80° C. for 2 hours, 150° C. for 1 hour, and 400° C. for 2 hours. The first heat treatment was performed once and was sufficient to prepare the first intermediate.

The first intermediate obtained by the first heat treatment was sufficiently cooled, and the second solution was dropped onto the intermediate support using a micropipette and infiltrated the first intermediate, followed by second heat treatment at 80° C. for 2 hours, 150° C. for 1 hour, and 400° C. for 2 hours. The second heat treatment was performed two times and was sufficient to prepare the second intermediate.

The second intermediate obtained by the second heat treatment was reduced in a hydrogen atmosphere at 800° C., thereby obtaining a fuel electrode according to this Example.

Thereafter, a unit cell was manufactured by attaching the fuel electrode to the prepared electrolyte.

Comparative Example 1

A fuel electrode and a unit cell including the same according to Comparative Example 1 were manufactured through the same process as in Example, with the exception that the intermediate support alone, which was not permeated with the first solution and the second solution, was used as the fuel electrode.

Comparative Example 2

A fuel electrode and a unit cell including the same according to Comparative Example 2 were manufactured through the same process as in Example, with the exception that praseodymium nitrate hexahydrate (Pr(NO₃)₃·6H₂O) was used instead of samarium nitrate hexahydrate in the process of preparing the second solution.

Comparative Example 3

A fuel electrode and a unit cell including the same according to Comparative Example 3 were manufactured through the same process as in Example, with the exception that gadolinium nitrate hexahydrate (Gd(NO₃)₃·6H₂O) was used instead of samarium nitrate hexahydrate in the process of preparing the second solution.

Test Example 2

In order to evaluate the performance of unit cells to which the fuel electrodes according to Example and Comparative Examples 1 to 3 were applied, the completed unit cell was prepared by joining a Ni metal current collector, a CuMn metal current collector on the fuel electrode, and a sealant to an Inconel metal jig, and EIS electrochemical characterization was conducted by injecting fuel gas (H₂O+H₂). For EIS electrochemical characterization, devices such as IviumStat (HS Technologies), etc. were used.

The results thereof are shown in FIG. 6 and Table 1 below.

	TABLE 1
	1.3 V, 700° C.	Current density (A/cm2)
	Comparative Example 1	1.215
	Comparative Example 2	1.420
	(Pr: 30 at %)	(16.9%, 2% lower than GDC)
	Comparative Example 3	1.450
	(Gd: 30 at %)	(19.3%)
	Example (Sm: 30 at %)	1.500
		(23.5%, 3.4% higher than GDC)

Referring to FIG. 6 and Table 1, SDC with Sm, among the elements Gd, Sm, and Pr doped into cerium, exhibited the highest IV performance. In particular, IV performance of the solid oxide electrolysis cell (SOEC) to which 30 at % of SDC was applied increased by about 23.5% compared to Comparative Example 1 to which SDC was not applied. In addition, since the amount of hydrogen produced increased with an increase in the current density at the same voltage, hydrogen production efficiency of the fuel electrode according to the present disclosure was the greatest.

Test Example 3

After evaluation according to Test Example 2, a unit cell to which the fuel electrode according to Example was applied was subjected to FIB milling to prepare a specimen for TEM. The surface of the fuel electrode was confirmed in the prepared specimen using TEM, and Fe diffused into Ni and Ce on the support surface were observed using energy-dispersive X-ray spectroscopy (EDS). The results thereof are shown in FIG. 7.

Referring to FIG. 7, Fe was evenly distributed on the Ni lattice, confirming that Fe and Ni were in the form of an alloy. Also, it was confirmed that Ce was evenly covered on the surface rather than diffusing into Ni to form an alloy.

Test Example 4

After evaluation according to Test Example 2, a unit cell to which the fuel electrode according to Example was applied and a unit cell to which the fuel electrode according to Comparative Example 1 was applied were subjected to FIB milling to prepare specimens for SEM. FIG. 8 shows results of analyzing the cross-section of the fuel electrode according to Comparative Example 1 using SEM (scanning electron microscopy), and FIG. 9 shows results of analyzing the cross-section of the fuel electrode according to Example using SEM, with some SDC nanocatalysts and particle sizes thereof.

Referring to FIG. 8, in Comparative Example 1 in which the catalyst according to the present disclosure was not applied, no catalyst supported on the surface of the support was observed, and referring to FIG. 9, in Example, the SDC catalyst supported on the surface of the support was confirmed, and the SDC catalyst had a size of about 20 nm to 60 nm and was evenly distributed.

Test Example 5

Durability stability evaluation of unit cells with the fuel electrodes applied according to Example and Comparative Examples 1 and 3 were performed for 500 hours under conditions of 700° C., 50% H₂O, and 1.0 A/cm². FIG. 10 shows results of evaluation of durability stability of the unit cells to which the fuel electrodes according to Example and Comparative Examples 1 and 3 are applied, in terms of voltage and normalized voltage.

FIG. 11(a) shows electrochemical performance before and after durability evaluation of a unit cell to which the fuel electrode according to Comparative Example 1 is applied, and FIG. 11(b) shows polarization resistance of the same unit cell before and after durability evaluation.

FIG. 12(a) shows electrochemical performance before and after durability evaluation of a unit cell to which the fuel electrode according to Example is applied, and FIG. 12(b) shows polarization resistance of the same unit cell before and after durability evaluation.

Based on results of calculation of the degradation rate through the initial voltage and final voltage determined as shown in FIGS. 10, 11(a) and 11(b), and 12(a) and 12(b), the degradation rate was calculated to be about 9.0% in Comparative Example 1, about 7.3% in Comparative Example 3, and about 6.6% in Example. Thereby, durability of the fuel electrode with the Fe/SDC catalyst applied onto the Ni/YSZ support according to the present disclosure was confirmed to be superior to Comparative Example 1 in which the Fe/SDC catalyst was not applied and also superior to Comparative Example 3 in which the Fe/GDC catalyst was applied.

As is apparent from the foregoing, a fuel electrode for a solid oxide electrolysis cell according to the present disclosure is configured such that a catalyst including a first element that is a metal capable of alloying with nickel and a second element including SDC (samarium-doped ceria) is supported on a support including nickel (Ni) and YSZ (yttria-stabilized zirconia), thereby improving performance and durability of the cell.

The effects of the present disclosure are not limited to the foregoing. It should be understood that the effects of the present disclosure include all effects that can be inferred from the description of the present disclosure.

As the embodiments of the present disclosure have been described above, those skilled in the art will appreciate that various modifications and alterations are possible through change, deletion or addition of components without departing from the scope and spirit of the present disclosure as described in the accompanying claims, which will also be said to be included within the scope of rights of the present disclosure.