A cathode material for high-density fuel cells

Abstract

The present invention discloses a cathode material for a high-density fuel cell. The chemical formula of this cathode material is La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ , and when it is prepared, Ruddlesden-Popper type oxide La2NiO 4+δ is used as the matrix and an oxide or carbonate of Sr is used as the raw material for solid-phase heat treatment to obtain a bulk calcined product of A-site doped La 2‑x Sr x NiO 4+δ . Then, the A-site doped La 2‑x Sr x NiO 4+δ bulk calcined product obtained by the above method is used as an intermediate product, and after being melt-sprayed by an ultrasonic metal atomization process, it is formed on the surface of the La 2‑x Sr x NiO 4+δ bulk calcined product in the form of atomized powder, and after one reduction heat treatment, it is then subjected to solid-phase calcination to obtain the cathode material with B-site doping. The cathode material of the present invention can be used to prepare the cathode material of a high-density fuel cell, and it has better structural stability, oxygen transport performance and oxygen reduction activity.

Description

Technical Field

[0001] The invention relates to the technical field of fuel cells in energy conversion devices, and in particular to a cathode material of a high-density fuel cell. Background Art

[0002] Solid Oxide Fuel Cell (SOFC) is an energy conversion device that directly converts chemical energy in fuel into electrical energy. It is the fourth power generation technology after hydropower, thermal power generation and atomic power generation. Due to the electrochemical reaction characteristics of the fuel cell energy conversion process, it converts the Gibbs free energy in the chemical energy of the fuel into electrical energy. There is no high-temperature combustion process in this energy conversion process, so it is not limited by the Carnot cycle effect and has an extremely high energy conversion ratio (usually above 50%, and the highest can reach 70-75%). At the same time, the battery's all-solid structure does not have the problem of electrolyte loss and corrosion, and no toxic or harmful substances are produced during operation. Therefore, it also has the advantages of environmental protection and long service life. It is a truly green, environmentally friendly and efficient energy conversion device.

[0003] At present, the cost and life issues limit the commercial development of solid oxide fuel cells. When the battery is running, the operating temperature in the device is high (up to 800-1000°C), which makes the various components of the solid oxide fuel cell, such as the anode, cathode, electrolyte membrane and bipolar connection materials, prone to high-temperature chemical reactions under the working conditions of the solid oxide fuel cell, resulting in a significant increase in the internal resistance of the solid oxide fuel cell and a reduced life. Based on the above reasons, reducing the operating temperature of the solid oxide fuel cell is an optional technical path. By reducing the operating temperature of the solid oxide fuel cell from the high temperature section (800-1000°C) to the medium and low temperature section (600-700°C), the electrochemical reaction between the battery components can be slowed down and the microstructure of the electrode can be stabilized, thereby reducing the technical requirements of the anode, electrolyte and cathode, expanding the scope of use of the material, and extending the life of the solid oxide fuel cell. Therefore, the development of medium and low temperature solid oxide fuel cells is the only way for solid oxide fuel cells to achieve commercialization as soon as possible, which is conducive to reducing the manufacturing and operation costs of solid oxide fuel cells.

[0004] The performance of the cathode is one of the key materials that determines the life of the solid oxide fuel cell. 2 Reduction to O 2-ions and transport them to the interface between the cathode and the electrolyte, which results in the performance of the solid oxide fuel cell being mainly restricted by the rate of the oxygen reduction reaction (cathode ORR process) at the cathode. The technical path of reducing the operating temperature of the solid oxide fuel cell will not only lead to a significant increase in the electrolyte resistance but also a decrease in the electrode activity, especially the oxygen reduction reaction (ORR) activity of the cathode material, which will cause a significant decrease in the output power and energy density of the solid oxide fuel cell.

[0005] For the above reasons, when designing medium and low temperature solid oxide fuel cells, a cathode material with excellent performance is needed. Traditional high-performance cathode materials are mainly cobalt-based materials. Although they have the advantages of high energy density and good adaptability, and can ensure the rate of oxygen reduction reaction in the cathode of solid oxide fuel cells, they are expensive, have a large thermal expansion coefficient, and have poor thermal stability, which restricts their application in the medium temperature range. At present, the main single perovskite (ABO) cathode materials on the market are 3 ), double perovskite type (A 2 B 2 O 5 ), spinel type (AB 2 O 4 ) and fluorite type (AB 2 ) (in the above chemical formula, A represents a rare earth or alkali metal element, and B represents a transition metal element). The cathode used in solid oxide fuel cells is mostly perovskite (including single perovskite and double perovskite) and spinel metal oxide materials, while Ruddlesden-Popper oxide (A n+1 B n O 3n+1 ; n is a positive integer) is a good ion-electron mixed conductor oxide, a layered derivative of a single perovskite type, with a suitable thermal expansion coefficient, excellent oxygen surface exchange performance, high oxygen ion migration ability and good medium and low temperature stability, and has great potential to replace cobalt-based materials. However, Ruddlesden-Popper oxide (A n+1 B n O 3n+1 ) conductivity is not ideal, which is the biggest drawback restricting its application. n+1 B n O 3n+1 ) can affect the material properties by doping elements at the A, B and A / B positions, directly affecting the thermal expansion coefficient, electrical conductivity, oxygen transport and electrochemical properties of the material.

[0006] Based on the above reasons, Ruddlesden-Popper type oxides can be modified by element doping to obtain solid oxide fuel cell cathode materials with excellent performance. Summary of the invention

[0007] The technical problem solved by the present invention is to provide a cathode material for a high-density fuel cell, which has better oxygen reduction (ORR) activity and a stable structural phase, can meet the needs of industrial production of solid oxide fuel cells, and solve the defects in the above technical background.

[0008] A high-density fuel cell cathode material with the chemical formula La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ , the cathode material is specifically prepared by the following method:

[0009] S1, take Ruddlesden-Popper type oxide La 2 NiO 4+δ and Sr oxide or carbonate as raw materials, weighed according to the stoichiometric ratio and mixed, and after mixing, crushed and ground to obtain a mixture powder passing through a 300-mesh sieve;

[0010] S2, dry-press the mixture powder into strips and blocks, and calcine the mixture at a temperature of 1200-1250°C for 8-12 hours. After calcination, take out the mixture to obtain La doped at the A position. 1.75 Sr 0.25 NiO 4+δ Block roasted products;

[0011] S3, according to the stoichiometric ratio, the copper element is sprayed on the La in the form of atomized powder by ultrasonic metal atomization process. 1.75 Sr 0.25 NiO 4+δ The surface of the block roasted material is then subjected to a reduction heat treatment, during which the temperature is maintained at 450-500°C in a reducing gas environment for 45-70 minutes; the block material is then taken out, crushed and ground, and then dry-pressed into strips and blocks for roasting again, the roasting temperature is 900-950°C, the roasting time is 5-8 hours, and after secondary crushing and grinding, the cathode material doped at the B position is obtained.

[0012] As a further limitation, the Ruddlesden-Popper type oxide La 2 NiO 4+δ The aminopolycarboxylic acid complex method is used for synthesis in the preparation method:

[0013] Using La(OH) 3 、NiCO 3 ·2Ni(OH) 2 ·4H 2 O as a raw material, after weighing according to the stoichiometric ratio, DTPA is added as an organic ligand, and the precipitate is completely dissolved by heating and stirring to form a transparent precursor solution; after filtering the precursor solution, it is placed in a constant temperature drying oven for constant temperature drying to form a solid, and the solid is heat-treated to obtain a formed La after cooling. 2 NiO 4+δ ;

[0014] During the heat treatment process, the solid matter is first put into the furnace body, a nitrogen environment is set, the furnace temperature is raised to 500-550°C at a rate of 30-40°C / min, and after heat preservation treatment for 90-120 minutes, oxygen is slowly introduced at a rate of 10-15%N / min, N is the volume of the furnace body, and maintained for 10-15 minutes, and then the furnace temperature is quickly raised to 1050-1200°C at a rate of 60-90°C / min, and maintained for 30-45 minutes to complete the heat treatment step.

[0015] As a further limitation, when the powder material is dry-pressed into strips and blocks in step S2 and step S3, the dry-pressing pressure of the dry-pressing equipment is 250-300 MPa.

[0016] As a further limitation, when the copper element is treated by ultrasonic metal atomization process, the control technical parameters are: ultrasonic frequency 35-42kHz; ultrasonic power 150-180W; atomization particle size D90≤200μm; atomization volume 5-8L / h.

[0017] Beneficial effects: The cathode material of the high-density fuel cell of the present invention has a stable cubic structure at room temperature, good chemical stability and structural stability, and exhibits excellent oxygen non-stoichiometric ratio and oxygen ion vacancy concentration on the outer surface. It has excellent chemical compatibility and low polarization impedance with solid oxide fuel cell electrolyte material systems such as SDC, GDC, and LSGM at medium temperature (650-750°C), and has excellent oxygen transmission performance, oxygen volume diffusion coefficient and surface exchange coefficient. The oxygen reduction kinetics study shows that it has good oxygen reduction (ORR) activity, and when used in a fuel cell, the maximum output power density of a single cell is greater than 650mW / cm 2 , and is therefore a medium-temperature solid oxide fuel cell cathode material with practical prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The chemical formula is La 1.75 Sr 0.25 Ni0.7 Cu 0.3 O 4+δ XRD spectrum of cathode material.

[0019] Figure 2 The chemical formula is La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ The cathode material is Ce 0.9 G 0.1 O 1.9 (GDC) XRD spectrum measured after mixing and calcination. DETAILED DESCRIPTION

[0020] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments.

[0021] Unless otherwise defined, the terms used herein have the same meanings as those generally understood by technicians in the technical field to which the present invention belongs. The terms used in the specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0022] This embodiment first provides a cathode material for a high-density fuel cell. The chemical formula of the cathode material for the high-density fuel cell is La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ .

[0023] When preparing the above cathode material, first prepare the Ruddlesden-Popper type oxide La as the matrix 2 NiO 4+δ , prepared according to La 2 NiO 4+δ The stoichiometric ratio of the metal elements is La(OH) 3 and basic nickel carbonate (NiCO 3 ·2Ni(OH) 2 ·4H 2 O), deionized water is added and mixed, and then DTPA is added as an organic ligand, and the organic ligand is heated to 75° C. and stirred to completely dissolve the precipitate, thereby forming a transparent precursor solution.

[0024] After filtering the precursor solution, put it into a constant temperature drying oven, heat and dry it at a set temperature of 100°C to obtain a solid glassy substance. The obtained solid glassy substance is broken into small pieces and added to a roasting furnace for roasting. A nitrogen protection environment is set before roasting. In a nitrogen environment, the furnace temperature is first raised to 500°C at a heating rate of 35°C / min. After heat preservation for 100 minutes, oxygen is slowly introduced at a rate of 12%N / min, where N is the volume of the furnace, and maintained for 10 minutes. Then, the furnace temperature is quickly raised to 1100°C at a rate of 70°C / min, maintained for 40 minutes, and ground into a suitable particle size after cooling to obtain La as a matrix. 2 NiO 4+δ .

[0025] In this embodiment, block calcination combined with nitrogen environment can make the organic groups in the glass material in the first stage of pyrolysis process in a high proportion of the activated state. In this case, the introduction of oxygen can make the organic groups of the glass material as a precursor fully decomposed during the calcination process, and make the carbon element therein discharged after combustion. Compared with the traditional technical solution of grinding the solid glass material and then calcining it, the obtained matrix La 2 NiO 4+δ The present embodiment has a lower carbon content, and considering the process difficulty of the special crucible grinding operation, the process complexity and process controllability of the present embodiment are more excellent; wherein the La obtained by grinding the glass material to 200 mesh and then calcining 2 NiO 4+δ The carbon content is about 0.32%; the La obtained by grinding the glass material to 300 mesh and then calcining it 2 NiO 4+δ The carbon content is about 0.17%; and the La 2 NiO 4+δ The carbon content is about 0.04-0.06%.

[0026] When preparing the cathode material, the La obtained in the above technical solution is 2 NiO 4+δ and SrO as raw materials. During preparation, the two are quantitatively weighed according to the stoichiometric ratio and then mixed. After mixing, they are crushed and ground to obtain a mixture powder that passes through a 300-mesh sieve. The mixture powder is pressed into a long strip material block with a length, width and height of 350 mm, 170 mm and 20 mm by a high-pressure dry pressing device under a pressure of 300 MPa. The above-mentioned material block is then added to a roasting furnace and roasted at a set furnace temperature of 1200°C for 10 hours. After the roasting is completed, it is taken out to obtain La doped at the A position. 1.75 Sr 0.25 NiO 4+δBlock roasted material.

[0027] The obtained La 1.75 Sr 0.25 NiO 4+δ After the block is cooled, it is laid flat, and the copper element is sprayed on the surface of the La in the form of atomized powder using an ultrasonic metal atomization process. 1.75 Sr 0.25 NiO 4+δ The surface of the block roasted material, the amount of copper element used is based on La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ The stoichiometric ratio is controlled at 40kHz and 160W for atomization spraying; when atomizing the molten copper, the atomization particle size is controlled to be D90≤200μm and the atomization volume is 7L / h.

[0028] The obtained block was heated in CH 4 The reduction heat treatment is carried out under the reducing gas condition. The temperature of the reduction heat treatment is controlled to 450°C and the treatment time is 60 minutes. Through the reduction heat treatment, most of the atomized copper can be attached to La in the form of active copper element. 1.75 Sr 0.25 NiO 4+δ The surface of the block has a low bulk density, and a small part is attached to La in the form of copper oxide. 1.75 Sr 0.25 NiO 4+δ The block material is then quickly crushed and ground, and after passing through a 300-mesh sieve, it is pressed again by high-pressure dry pressing equipment under a pressure of 300 MPa into a long strip of material with a length, width and height of 350 mm*170 mm*20 mm, and then calcined for the second time. The calcination temperature of the calcination furnace is controlled to be 900 ° C, and the calcination time is 6 hours. After the calcination is completed, it is taken out, and after the secondary crushing and grinding process particle size, the B-position doping is completed, and the chemical formula is La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ of cathode material.

[0029] The XRD spectrum of the cathode material is shown in Figure 1 shown.

[0030] The obtained La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ Cathode materials and Ce as a common solid oxide fuel cell electrolyte material0.9 G 0.1 O 1.9 The chemical compatibility test of GDC was carried out by mixing the two uniformly and then calcining them at 700°C for 6 hours. The measured XRD spectrum is shown in Figure 2 shown.

[0031] It can be found from the drawings in the specification that the diffraction peaks of the XRD spectrum of the cathode material correspond one to one with the diffraction peaks of the cathode material and GDC, and no new diffraction peaks appear or the positions of the diffraction peaks shift, indicating that the cathode material of this embodiment has good chemical compatibility under the temperature condition of 700°C (the medium representative temperature of the solid oxide fuel cell).

[0032] The cathode material La in this example 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ The impedance performance was tested using a commercial impedance test symmetrical cell and the cathode material La without A / B doping was used. 2 NiO 4+δ As a comparison group, the measured Rp values ​​of the cathode materials are as follows:

[0033]

[0034] From the above table, we can conclude that La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ The cathode material is better than the Ruddlesden-Popper oxide La as the parent material in the medium temperature region. 2 NiO 4+δ Its performance is significantly improved, and the polarization resistance can be as low as 0.032Ω.cm 2 It has excellent chemical compatibility with GDC electrolyte materials at high temperatures, and when the temperature is reduced to 700 °C, La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ The cathode material still has good polarization resistance performance.

[0035] In addition, the cathode material La of this embodiment 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δThe electrochemical test using a commercial anode-supported half-cell as a carrier obtained a single cell with a peak power density of 542 mW / cm at 650°C, 700°C, and 750°C, respectively. 2 、712mW / cm 2 and 992W / cm 2 , because the cathode material La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ In the medium temperature working range of 650~750℃, it has better energy density.

[0036] In order to obtain the above-mentioned performance enhancement, the cathode material of this embodiment is Ruddlesden-Popper type oxide La 2 NiO 4+δ As a matrix, the performance of the matrix material is improved by doping elements at A / B positions. Doping Sr elements at the A position by a solid phase method can effectively increase the grain boundary size of the corresponding cathode material, thereby increasing the active sites for the oxygen reduction reaction; and by doping Cu elements at the B position, the unit cell volume can be shrunk and the oxygen vacancy concentration of the material can be increased, thereby promoting the formation of oxygen vacancies in the cathode material and increasing the oxygen mobility in the crystal lattice, thereby effectively improving the oxygen reduction electrocatalytic activity and electrocatalytic performance of the cathode material; and the grain boundary size of the cathode material increased by doping Sr elements at the A position will effectively improve the unit energy density of the cathode material after the unit cell volume shrinks.

[0037] In the technical solution of this embodiment, ultrasonic metal atomization is also used when performing B-site doping treatment. This ultrasonic metal atomization process is a type of process used for nano-metal powder processing. It uses high-frequency vibrations generated by ultrasonic waves to form tiny droplets of molten metal with medium and low melting points in the gas phase. The metal droplets are sprayed out after being pressurized, and solidified into nano-state metal powder with high activity after being cooled on the medium. In this embodiment, ultrasonic treatment is used to obtain atomized copper element, and then the atomized copper element is directly sprayed on La 1.75 Sr 0.25 NiO 4+δ Surface, this treatment method can make La 1.75 Sr 0.25 NiO 4+δ The surface is attached with nano-scale copper in a molten state. 1.75 Sr 0.25 NiO 4+δ It has a high conversion activity at the interface, which can further stimulate the electrocatalytic effect of the material after B-site doping. The electrocatalytic performance of the solid oxide fuel cell cathode material mainly directly affects the oxygen reduction (ORR) activity of the material.

[0038] In addition, doping Cu at the B site can effectively stabilize La 1.75 Sr 0.25 Ni 0.7 Cu 0.3 O 4+δ The tetragonal phase structure of the cathode material significantly improves the electrocatalytic performance of the doped and modified cathode material and the long-term stability of the battery.

[0039] In addition, the cathode material in this embodiment can also be enhanced in performance by treating the cathode material surface with nano-oxide particles. The nano-oxide particles that can be used for surface treatment are nano-CuO, nano-Fe 2 O 3 、Nano-Fe 2 O 3 During the treatment, a saturated solution of nano-oxide is prepared using deionized water, and then the cathode material is added to the above saturated solution using a vacuum impregnation device and treated according to the vacuum impregnation process. After being treated by the vacuum impregnation device, the nano-oxide particles can attach the corresponding nano-oxide particles to the surface of the cathode material in the form of clusters, thereby forming an oxide composite interface on the material surface of the cathode material. This oxide composite interface can effectively improve the thermal stability of the cathode material and can improve the CO conversion rate under the working conditions of the fuel cell, from about 85% in the working state of the cathode material without nano-oxide particles to 93%, thereby reducing the CO poisoning time of the cathode material and extending the service life of the cathode material.

[0040] In the above embodiment, considering that the corresponding nano-oxides in the saturated solution of nano-oxides are easily agglomerated due to the Van der Waals force and easily settle to the bottom of the impregnation solution, thereby affecting the vacuum impregnation effect, a magnetic stirrer can be used to assist in the vacuum impregnation treatment to optimize the impregnation treatment effect.

[0041] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A cathode material for a fuel cell, It is characterized in that The material chemical formula of the cathode material is , the cathode material is specifically prepared by the following method: S1, take Ruddlesden-Popper type oxide and Sr oxide or carbonate as raw materials, weighed according to a stoichiometric ratio and mixed, and after mixing, crushed and ground to obtain a mixture powder passing through a 300-mesh sieve; S2, dry-press the mixture powder into strips and blocks, and calcine it at a temperature of 1200-1250°C for 8-12 hours. After calcination, take it out to obtain A-doped Block roasted products; S3, referring to the stoichiometric ratio, using ultrasonic metal atomization process to spray copper in the form of atomized powder The surface of the block roasted material is then subjected to a reduction heat treatment, during which the temperature is maintained at 450-500°C in a reducing gas environment for 45-70 minutes; the block material is then taken out, crushed, ground, and dry-pressed into strips and blocks for roasting, the roasting temperature is 900-950°C, the roasting time is 5-8 hours, and the cathode material doped at the B position is obtained after secondary crushing and grinding; When using ultrasonic metal atomization process to treat copper, the control technical parameters are: ultrasonic frequency 35~42kHz; ultrasonic power 150~180W; atomization particle size D90≤200μm; atomization volume 5~8L / h.

2. The cathode material of the fuel cell according to claim 1, It is characterized in that The Ruddlesden-Popper type oxide The aminopolycarboxylic acid complex method is used for synthesis during the preparation: use , As a raw material, DTPA is added as an organic ligand after being weighed in a stoichiometric ratio, and the precipitate is completely dissolved by heating and stirring to form a transparent precursor solution; after filtering the precursor solution, it is placed in a constant temperature drying oven for constant temperature drying to form a solid, and the solid is heat treated to obtain a molding ; During the heat treatment process, the solid material is first put into the furnace body, a nitrogen environment is set, the furnace temperature is raised to 500-550°C at a rate of 30-40°C / min, and after heat preservation for 90-120 minutes, oxygen is slowly introduced at a rate of 10-15%N / min, N is the volume of the furnace body, and maintained for 10-15 minutes, and then the furnace temperature is rapidly raised to 1050-1200°C at a rate of 60-90°C / min, and maintained for 30-45 minutes to complete the heat treatment process.

3. The cathode material of the fuel cell according to claim 1, It is characterized in that When the powder material is dry-pressed into strips and blocks in step S2, the dry-pressing pressure of the dry-pressing equipment is 250-300 MPa.

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