Solid oxide fuel cell system and manufacturing method of the same

Abstract

One embodiment of the present invention provides a solid oxide fuel cell system comprising: a solid oxide fuel cell member made of a stainless steel material containing chromium; and a nickel plating layer coated on the surface of the solid oxide fuel cell member to suppress the volatilization of the chromium, wherein at least a portion of the nickel plating layer melts when the solid oxide fuel cell member is brazed.

Description

Technology Field

[0001] The present invention relates to a solid oxide fuel cell system and a method for manufacturing the same, and more specifically, to a solid oxide fuel cell system and a method for manufacturing the same in which a nickel plating layer capable of acting as a filler material is provided on a solid oxide fuel cell member, thereby suppressing the volatilization of chromium from the solid oxide fuel cell member while reducing the use of filler material during brazing. Background Technology

[0002] A fuel cell is a device that converts the chemical energy contained in fuel into electrical energy. Generally, it refers to a power generation system that produces electricity by electrochemically reacting hydrogen from reformed gas—obtained by reforming fuels such as natural gas, methanol, or gasoline—with oxygen from the air at the anode and cathode of a stack. Fuel cells have the advantage of being highly environmentally friendly because they use hydrogen as fuel and produce no byproducts other than water. Furthermore, fuel cells possess the advantage of being a highly efficient method of power generation because they can obtain electrical energy from chemical energy through a relatively simple energy conversion process.

[0003] Fuel cells include polymer electrolyte fuel cells (PEMFC), direct methanol fuel cells (DMFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), and alkaline fuel cells (AFC), depending on the type of electrolyte and electrode.

[0004] Recently, Solid Oxide Fuel Cells (SOFCs) have been attracting significant attention as an eco-friendly and highly efficient method of energy production. An SOFC system is broadly composed of two main components: the components and the stack. Since SOFCs operate at high temperatures, the components consist of parts exposed to high temperatures and those that are not. However, commercialization faces significant challenges due to the degradation of stack performance caused by byproducts generated from gas piping components exposed to high-temperature environments, specifically the Hot Balance of Plant (Hot BOP).

[0005] BOPs primarily utilize SUS components containing chromium and iron. When chromium is present, it volatilizes from the BOP and adsorbs onto the SOFC cell surface when high-pressure gas is introduced in a high-temperature environment. This leads to chromium poisoning at the air electrode, which can block catalytic reaction sites on the electrode surface or react with perovskite electrodes to form non-conductive secondary phases, thereby accelerating electrode performance degradation. Consequently, stacks contaminated with chromium oxide suffer from reduced output performance and durability. The problem to be solved

[0006] The purpose of the present invention is to provide a solid oxide fuel cell system and a method for manufacturing the same, which can reduce the use of filler material during brazing while suppressing the volatilization of chromium from a solid oxide fuel cell member by providing a nickel plating layer capable of acting as a filler material on the solid oxide fuel cell member.

[0007] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0008] One embodiment of the present invention for solving the above problem provides a solid oxide fuel cell system comprising: a solid oxide fuel cell member made of a stainless steel material containing chromium; and a nickel plating layer coated on the surface of the solid oxide fuel cell member to suppress the volatilization of the chromium, wherein at least a portion of the nickel plating layer melts when the solid oxide fuel cell member is brazed.

[0009] According to an embodiment, the nickel plating layer is formed by an electroless plating method using a nickel plating solution containing an additive, and the additive may be precipitated on the nickel plating layer.

[0010] According to an example, the thickness of the nickel plating layer may be 1 μm to 10 μm.

[0011] According to an example, the grain size of the nickel plating layer may be 1 μm to 10 μm.

[0012] According to an embodiment, the method further comprises a filler material applied to at least a portion of the solid oxide fuel cell member for brazing the solid oxide fuel cell member, wherein the melting point of the nickel plating layer may be within a range of ±100℃ of the melting point of the filler material.

[0013] According to an embodiment, the additive is phosphorus, and the content of the additive in the nickel plating layer is determined by Formula 1, where Formula 1 is A=-X1*(B²+X2*B-X3), where A is the melting point of the nickel plating layer, B is the weight% of the additive relative to nickel, X1 is a constant determined in the range of 1 to 10, X2 is a constant determined in the range of 20 to 30, and X3 is a constant determined in the range of 100 to 500.

[0014] According to an example, the arithmetic mean roughness (Ra) of the surface of the solid oxide fuel cell member may be 0 μm to 3 μm.

[0015] According to an embodiment, the solid oxide fuel cell member may further include a stack comprising a fuel electrode and an air electrode, wherein the solid oxide fuel cell member may be a heat exchanger for heating air supplied to the air electrode.

[0016] Another embodiment of the present invention for solving the above problem provides a method for manufacturing a solid oxide fuel cell system comprising: a step of coating a nickel plating layer on the surface of a solid oxide fuel cell member made of a stainless steel material containing chromium; and a step of brazing the solid oxide fuel cell member; wherein at least a portion of the nickel plating layer is melted during the brazing step.

[0017] According to an embodiment, the coating step is performed by an electroless plating method using a nickel plating solution containing an additive, and the additive may be precipitated on the nickel plating layer during the coating step.

[0018] According to an embodiment, in the brazing step, the filler material applied to at least a portion of the solid oxide fuel cell member and at least a portion of the nickel plating layer may be melted simultaneously.

[0019] According to an embodiment, the step of heat-treating the solid oxide fuel cell member coated with the nickel plating layer after the coating step may be further included.

[0020] According to an embodiment, the heat treatment step may include a first heat treatment step of heat-treating the solid oxide fuel cell member at 300°C to 400°C and a second heat treatment step of heat-treating the solid oxide fuel cell member at 500°C to 700°C.

[0021] According to an embodiment, the heating and cooling rates of the solid oxide fuel cell member in the first heat treatment step and the second heat treatment step can be controlled to 1℃ / min to 20℃ / min. Effects of the invention

[0022] According to the present invention, by providing a nickel plating layer on a solid oxide fuel cell member made of stainless steel containing chromium, the volatilization of chromium from the solid oxide fuel cell member can be suppressed. That is, the generation of chromium oxide can be minimized. Ultimately, contamination of the stack by chromium oxide is prevented, and the output performance and durability of the stack can be maintained for a long time.

[0023] In addition, by forming a nickel plating layer using an electroless plating method, the amount of additive precipitation can be controlled, allowing the thickness of the nickel plating layer to be uniformly formed within a target range.

[0024] In addition, by controlling the melting point of the nickel plating layer to a range similar to that of the filler material, preferably within ±100°C of the filler material's melting point, the nickel plating layer is allowed to perform the role of a filler material by melting at least partially during the brazing of the solid oxide fuel cell component. Accordingly, since the use of filler material during brazing can be reduced, cost reduction is possible.

[0025] In particular, the melting point of the nickel plating layer can be easily controlled by adjusting the weight percentage of phosphorus relative to nickel in the nickel plating layer.

[0026] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims. Brief explanation of the drawing

[0027] FIG. 1 is a schematic diagram illustrating the interior of a high-temperature box of a solid oxide fuel cell system according to one embodiment of the present invention. FIG. 2a is a schematic diagram illustrating the surface of a conventional solid oxide fuel cell component. FIG. 2b is a schematic diagram showing the surface of a solid oxide fuel cell component of FIG. 1. Figure 3 is a drawing showing the state in which a filler material is applied to the surface of a solid oxide fuel cell component of Figure 2b. Figure 4 is a graph showing the melting point of a nickel plating layer according to the weight percentage of phosphorus relative to nickel. FIG. 5 is a diagram showing a method for manufacturing a solid oxide fuel cell system according to one embodiment of the present invention. Specific details for implementing the invention

[0028] Hereinafter, preferred embodiments of the solid oxide fuel cell system and the method for manufacturing the same according to the present invention will be described with reference to the attached drawings.

[0029] Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intention or practice of the user or operator; additionally, the following embodiments are not intended to limit the scope of the present invention but are merely exemplary details of the components presented in the claims of the present invention.

[0030] To clearly explain the present invention, parts unrelated to the description have been omitted, and the same reference numerals are used for identical or similar components throughout the specification. Throughout the specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may additionally include other components.

[0031] In addition, components referred to as '~parts' throughout the specification may consist of two or more components combined into a single component, or a single component may be divided into two or more components based on more detailed functions. Furthermore, each component described below may additionally perform some or all of the functions performed by other components in addition to its primary function, and it goes without saying that some of the primary functions performed by each component may be exclusively performed by other components.

[0033] As illustrated in FIG. 2b, the solid oxide fuel cell system of the present invention comprises a solid oxide fuel cell member made of a stainless steel material containing chromium, and a nickel plating layer (100) coated on the surface of the solid oxide fuel cell member to suppress the volatilization of chromium.

[0034] FIG. 1 schematically illustrates the interior of a high-temperature box (1) of a solid oxide fuel cell system according to one embodiment of the present invention. In this embodiment, a stack (10) including an air electrode (cathode, 11) and a fuel electrode (anode, 12), a heat exchanger (20) for heating air supplied to the air electrode (11), and a burner (30) for supplying heat to the heat exchanger (20) are arranged inside the high-temperature box (1). Accordingly, air is heated in the heat exchanger (20) and then supplied to the air electrode (11), and fuel is supplied to the fuel electrode (12), and the fuel and air undergo an electrochemical reaction in the stack (10) to produce electricity. Subsequently, all exhausts from the air electrode (11) and the fuel electrode (12), respectively, are supplied to the burner (30) and combusted, and the combustion gas supplies heat to the heat exchanger (20). However, this is not limited thereto, and various embodiments of solid oxide fuel cell systems may be applied.

[0035] Here, the gas pipe, etc., which is placed inside the heat exchanger (20), burner (30), and high-temperature box (1) and serves as a passage for movement between the stack (10), heat exchanger (20), and burner (30), may correspond to a solid oxide fuel cell component made of stainless steel containing chromium.

[0036] Since the operating temperature of a solid oxide fuel cell system is generally between 500°C and 800°C, the solid oxide fuel cell components placed inside the high-temperature box (1) are exposed to a high-temperature environment, causing chromium to oxidize and volatilize in the form of vapor (see FIG. 2a). Accordingly, in the present invention, by providing a nickel plating layer (100) on the solid oxide fuel cell components, the volatilization of chromium from the solid oxide fuel cell components can be suppressed (see FIG. 2b). That is, the generation of chromium oxide can be minimized. Ultimately, contamination of the stack (10) by chromium oxide is prevented, and the output performance and durability of the stack (10) can be maintained for a long time.

[0037] Below, the description is based on the assumption that a nickel plating layer (100) is provided in a heat exchanger (20) for heating the air supplied to the air electrode (11) of the stack (10). However, it is not limited to this, and a nickel plating layer (100) may also be provided in a gas pipe (especially a gas pipe through which air travels) placed inside a burner (30) or a high-temperature box (1).

[0038] Specifically, the nickel plating layer (100) can be formed by an electroless plating method using a nickel plating solution containing an additive. This allows a uniform crystalline coating layer to be formed on the surface of the heat exchanger (20). As an example, the additive may be phosphorus (P) or boron (B).

[0039] When sodium hypophosphite (NaH2PO2·H2O) is used as a reducing agent, as in general electroless Ni-P plating, a nickel plating layer (100) is formed by the following reduction reaction (reaction equations (1) to (3)).

[0040] Reaction Equation (1) -----

[0041] Reaction Equation (2) -----

[0042] Reaction Equation (3) -----

[0043] In this way, additives are deposited in the nickel plating layer (100). That is, during the process of nickel being deposited on the surface of the heat exchanger (20), phosphorus (P) is also deposited between the plating layers. When forming the nickel plating layer (100) using an electroless plating method in this manner, the thickness of the nickel plating layer (100) can be uniformly formed within a target range by controlling the amount of additives deposited.

[0044] The thickness and grain size of the nickel plating layer (100) are closely related to the amount of chromium vapor generated, and the two ratios enable control of the amount of chromium vapor generated. Therefore, it is preferable that the thickness of the nickel plating layer (100) be 1 μm to 10 μm, and it is also preferable that the grain size of the nickel plating layer (100) be 1 μm to 10 μm.

[0045] Since the heat exchanger (20) and the nickel plating layer (100) have different thermal expansion rates, delamination may occur when they expand laterally in a high-temperature environment. Therefore, to prevent delamination between the heat exchanger (20) and the nickel plating layer (100), the adhesion between the heat exchanger (20) and the nickel plating layer (100) can be improved by applying an appropriate roughness to the surface of the heat exchanger (20).

[0046] At this time, it is preferable that the arithmetic mean roughness (Ra) of the surface of the heat exchanger (20) be 0㎛ to 3㎛. This value was selected so as not to cause peeling between the heat exchanger (20) and the nickel plating layer (100) and not to affect the thickness of the heat exchanger (20).

[0047] As a method for controlling roughness, a process (Sand blasting) that imparts a target level of roughness to the surface of the heat exchanger (20) through a physical method, a process (Sand blasting) that imparts roughness by removing scale, oxide film, etc. through an acid treatment as a chemical method, or a process (Ni strike) that imparts roughness by precipitating metals with a high ionization tendency other than Ni on the surface of the heat exchanger (20).

[0048] Furthermore, to increase the bonding strength between the heat exchanger (20) and the nickel plating layer (100), the heat exchanger (20) equipped with the nickel plating layer (100) may be further heat-treated. The heat treatment temperature is a factor determining the bonding strength of the nickel plating layer (100), and an appropriate heat treatment process is required to prevent peeling of the nickel plating layer (100) at high temperatures. However, since heat treatment exceeding the necessary level causes thermal stress in the heat exchanger (20) and heat treatment below the appropriate level causes peeling of the nickel plating layer (100), heat treatment at an appropriate temperature is required.

[0049] After heat treatment, the heat exchanger (20) and the nickel plating layer (100) form a high bonding strength through mutual diffusion. Specifically, after heat treatment, the nickel plating layer (100) can be divided into a Ni / Fe / Cr mixed layer, a Ni layer, and a NiO layer. That is, through heat treatment, a mixed layer is formed at the interface between the nickel plating layer (100) and the surface of the heat exchanger (20).

[0050] Specifically, the heat treatment can be performed in two stages. First, the heat exchanger (20) equipped with a nickel plating layer (100) can be heat-treated at 300°C to 400°C in the first stage, and then heat-treated at 500°C to 700°C in the second stage. Here, the first stage heat treatment is a stage for hydrogen embrittlement and bonding strength enhancement, and the second stage heat treatment is a stage for oxide film formation and bonding strength enhancement. At this time, the heating and cooling rates of the heat exchanger (20) during the first and second stages of heat treatment are controlled to 1°C / min to 20°C / min.

[0051] The heat-treated heat exchanger (20) can be joined by brazing. To do this, a filler material (200) is applied to at least a portion of the surface of the heat exchanger (20) as shown in FIG. 3. The filler material (200) changes into a liquid state when it reaches its melting point and serves to perform face-to-face joining.

[0052] In particular, in the present invention, at least a portion of the nickel plating layer (100) is melted during brazing of the heat exchanger (20). That is, by controlling the melting point of the nickel plating layer (100) to a range similar to the melting point of the filler material (200), the nickel plating layer (100) is made to serve the role of the filler material (200). Accordingly, the use of the filler material (200) during brazing can be reduced, thereby enabling cost reduction. In addition, pressure resistance can be secured when manufacturing the heat exchanger (20) through brazing under appropriate vacuum conditions.

[0053] Preferably, the melting point of the nickel plating layer (100) is controlled to a range within ±100°C of the melting point of the filler material (200). This is because if the melting point of the nickel plating layer (100) is too low compared to the melting point of the filler material (200), the flowability becomes too high, causing the nickel plating layer to flow and accumulate in the direction of gravity, making it impossible to control the thickness of the nickel plating layer and resulting in the loss of the original purpose of plating. On the other hand, if the melting point of the nickel plating layer (100) is too high compared to the melting point of the filler material (200), there is no flowability, so it cannot spread evenly on the brazing surface, and thus brazing is not performed smoothly.

[0054] FIG. 4 is a graph showing the melting point of the nickel plating layer (100) according to the weight percentage of phosphorus relative to nickel in the nickel plating layer (100). Referring to FIG. 4, it can be seen that when the weight percentage of phosphorus relative to nickel in the nickel plating layer (100) is within 10%, the melting point of the nickel plating layer (100) decreases as the concentration of the additive increases. Therefore, it is important to ensure that the nickel plating layer (100) acts as a filler material (200) by controlling the appropriate concentration of the additive.

[0055] Specifically, when the additive is phosphorus (P), the content of the additive in the nickel plating layer (100) can be determined by Equation 1. Equation 1 is A = -X1 * (B² + X2 * B - X3), where A is the melting point of the nickel plating layer (100), B is the weight percentage of the additive relative to nickel, X1 is a constant determined in the range of 1 to 10, X2 is a constant determined in the range of 20 to 30, and X3 is a constant determined in the range of 100 to 500. For example, in the case of the most commonly used BNi₂ filler material, it melts at approximately 1080°C and has flowability, so in this case, A can be determined as 1080. Additionally, when X1, X2, and X3 are determined as constants within their respective ranges, the weight percentage (B) of the additive relative to nickel in the nickel plating layer (100) can finally be determined. In this way, the melting point of the nickel plating layer (100) can be easily controlled by adjusting the weight percentage of phosphorus relative to nickel in the nickel plating layer (100).

[0056] Conventionally, when stainless steel is used as the base material, the BNi₂ filler material must be applied with a thickness of 10 to 100 μm to ensure the necessary bonding strength during brazing. However, in the present invention, since the nickel plating layer (100) also serves as the filler material, the amount of filler material used can be reduced by about 50% when manufacturing a heat exchanger through brazing.

[0058] Next, we will look at a method for manufacturing a solid oxide fuel cell system with reference to Fig. 5.

[0059] A method for manufacturing a solid oxide fuel cell system comprises a step (S1) of coating a nickel plating layer (100) on the surface of a solid oxide fuel cell member made of a stainless steel material containing chromium, and a step (S2) of brazing the solid oxide fuel cell member. Specifically, the coating step (S1) is performed by an electroless plating method using a nickel plating solution containing an additive, and as described above, the additive is precipitated on the nickel plating layer (100) during the coating step (S1).

[0060] In the brazing step (S2), at least a portion of the nickel plating layer (100) is melted. In the brazing step (S2), at least a portion of the nickel plating layer (100) and the filler material (200) applied to at least a portion of the solid oxide fuel cell member are melted simultaneously. That is, by controlling the melting point of the nickel plating layer (100) to a range similar to the melting point of the filler material (200), the nickel plating layer (100) is made to serve the role of the filler material (200). Accordingly, the use of the filler material (200) during brazing can be reduced, thereby enabling cost reduction.

[0061] Additionally, after the coating step (S1), the method may further include a step (S3) of heat-treating the solid oxide fuel cell member coated with a nickel plating layer (100). Specifically, the heat-treating step (S3) includes a first heat treatment step (S3-1) of heat-treating the solid oxide fuel cell member at 300°C to 400°C and a second heat treatment step (S3-2) of heat-treating the solid oxide fuel cell member at 500°C to 700°C. Here, the first heat treatment step (S3-1) is a step for improving hydrogen embrittlement and bonding strength, and the second heat treatment step (S3-2) is a step for forming an oxide film and improving bonding strength. At this time, the heating and cooling rates of the solid oxide fuel cell member during the first heat treatment step (S3-1) and the second heat treatment step (S3-2) are controlled to 1°C / min to 20°C / min. Accordingly, the bonding strength between the solid oxide fuel cell component and the nickel plating layer (100) can be improved.

[0062] The present invention is not limited to the specific embodiments and descriptions described above, and various modifications can be made by anyone with ordinary knowledge in the technical field to which the present invention pertains without departing from the essence of the invention as claimed in the claims, and such modifications fall within the scope of protection of the present invention. Explanation of the symbols

[0063] 1: High-temperature box 10: Stack 11: Air electrode 12: Fuel electrode 20: Heat exchanger 30: Burner 100: Nickel plating layer 200: Filler material

Claims

Claim 1 A solid oxide fuel cell system comprising: a solid oxide fuel cell member made of a stainless steel material containing chromium; and a nickel plating layer coated on the surface of the solid oxide fuel cell member to suppress the volatilization of the chromium; wherein, when the solid oxide fuel cell member is brazed, at least a portion of the nickel plating layer melts, and further comprising a filler material applied to at least a portion of the solid oxide fuel cell member for brazing the solid oxide fuel cell member, wherein the melting point of the nickel plating layer is within a range of ±100℃ of the melting point of the filler material. Claim 2 A solid oxide fuel cell system according to claim 1, wherein the nickel plating layer is formed by an electroless plating method using a nickel plating solution containing an additive, and the additive is precipitated in the nickel plating layer. Claim 3 A solid oxide fuel cell system according to claim 2, characterized in that the thickness of the nickel plating layer is 1 μm to 10 μm. Claim 4 A solid oxide fuel cell system according to claim 2, characterized in that the grain size of the nickel plating layer is 1 μm to 10 μm. Claim 5 delete Claim 6 A solid oxide fuel cell system according to claim 2, wherein the additive is phosphorus, and the content of the additive in the nickel plating layer is determined by Formula 1, wherein Formula 1 is A=-X1*(B²+X2*B-X3), where A is the melting point of the nickel plating layer, B is the weight% of the additive relative to nickel, X1 is a constant determined in the range of 1 to 10, X2 is a constant determined in the range of 20 to 30, and X3 is a constant determined in the range of 100 to 500. Claim 7 A solid oxide fuel cell system according to claim 2, characterized in that the arithmetic mean roughness (Ra) of the surface of the solid oxide fuel cell member is 0㎛ to 3㎛. Claim 8 A solid oxide fuel cell system according to claim 2, further comprising a stack including a fuel electrode and an air electrode, wherein the solid oxide fuel cell member is a heat exchanger for heating air supplied to the air electrode. Claim 9 A method for manufacturing a solid oxide fuel cell system comprising: a step of coating a nickel plating layer on the surface of a solid oxide fuel cell member made of a chromium-containing stainless steel material; and a step of brazing the solid oxide fuel cell member; wherein, in the brazing step, a filler material applied to at least a portion of the solid oxide fuel cell member and at least a portion of the nickel plating layer are simultaneously melted, and the melting point of the nickel plating layer is within a range of ±100℃ of the melting point of the filler material. Claim 10 A method for manufacturing a solid oxide fuel cell system according to claim 9, wherein the coating step is performed by an electroless plating method using a nickel plating solution containing an additive, and wherein the additive is precipitated on the nickel plating layer during the coating step. Claim 11 delete Claim 12 A method for manufacturing a solid oxide fuel cell system, further comprising, in claim 10, a step of heat-treating the solid oxide fuel cell member coated with the nickel plating layer after the coating step. Claim 13 A method for manufacturing a solid oxide fuel cell system according to claim 12, wherein the heat treatment step comprises a first heat treatment step of heat-treating the solid oxide fuel cell member at 300°C to 400°C and a second heat treatment step of heat-treating the solid oxide fuel cell member at 500°C to 700°C. Claim 14 A method for manufacturing a solid oxide fuel cell system according to claim 13, characterized in that the heating and cooling rates of the solid oxide fuel cell member in the first heat treatment step and the second heat treatment step are controlled to 1℃ / min to 20℃ / min.

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