Low-temperature high-activity layered M0. 15Sr2. 85Co4O9-delta material as well as preparation method and application thereof

Abstract

The invention discloses a low-temperature and high-activity layered M < 0.15 > Sr < 2.85 > Co < 4 > O < 9-delta > material as well as a preparation method and application thereof. According to the method, the layered M < 0.15 > Sr < 2.85 > Co < 4 > O < 9-delta > material is synthesized by using a combustion method. The layered M0. 15Sr2. 85Co4O9-delta material prepared by the preparation method disclosed by the invention is relatively good in phase structure, relatively good in catalytic activity at medium and low temperatures as an oxygen electrode material of a solid oxide fuel cell, stable in structure in an air atmosphere, and good in thermal matching and chemical compatibility with electrolyte BZCYYb, and has a wide application prospect in the field of proton conduction type solid oxide fuel cells.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fuel cell electrode materials, and particularly relates to a low-temperature high-activity layered M 0.15 Sr 2.85 Co4O 9-δ material, a preparation method and application thereof. BACKGROUND

[0002] Under the driving of global energy transformation and the "double carbon" target, it is essential to develop efficient and clean energy conversion technology. Proton-conducting solid oxide fuel cells (H-SOFCs) are considered as a promising technology in distributed power generation and transportation due to their high efficiency in the medium-low temperature range (400-600℃) by utilizing proton conduction. However, the sluggish oxygen reduction reaction (ORR) kinetics at low temperatures severely restricts the power density and efficiency of H-SOFCs, which is one of the main bottlenecks for their commercialization. Therefore, developing oxygen electrode materials with high ORR catalytic activity at medium-low temperatures is the key to improving the performance of H-SOFCs.

[0003] Currently, the commonly used oxygen electrode materials for H-SOFCs are mainly perovskites (such as La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ , LSCF) and their derivative materials. These materials exhibit good catalytic activity at relatively high temperatures (>700℃). However, when the operating temperature is reduced to the typical medium-low temperature range of H-SOFCs (400-600℃), their ORR catalytic activity decreases significantly, leading to a sharp decline in cell performance. In addition, these perovskite materials generally have a high thermal expansion coefficient (TEC) (usually >14×10 -6 K -1 ), which is significantly mismatched with the commonly used proton conductor electrolyte materials (such as BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ , BZCYYb, TEC≈10-12×10 -6 K -1 ). This mismatch generates a huge thermal stress during cell preparation and thermal cycling, which easily leads to delamination or cracking of the electrode / electrolyte interface, seriously affecting the service life of the cell.

[0004] Misfit layered oxides have been studied in the field of solid oxides, for example, Nagasawa et al. synthesized Ca3Co4O 9-δThe material is used as an oxygen electrode made of solid oxide, but due to its solid-state synthesis, the powder particles are relatively large, resulting in insufficient performance; the polarization impedance at 700℃ is 3.0 Ωcm. 2 (NAGASAWAK, MENTRE O, DAVIERO-MINAUD S, et al. The Electrochemical and Thermal Performances ofCa3Co4O 9-δ As a Cathode Material for IT-SOFCs; procedures of the 11th International Symposium on Solid Oxide Fuel Cells (SOFC), Vienna, AUSTRIA, F Oct 04-09, 2009 [C]. 2009.); Arus et al. prepared Ca3Co4O as a Cathode Material for IT-SOFCs using the sol-gel method. 9-δ The oxygen electrode has a peak power density of 227 mW / cm³ at 700 °C. -2 (Arus. Layered cobalt-based cathode material for solid oxide fuel cells Ca3Co4O) 9-δ Preparation and performance characterization of Sr3Co4O [D], 2015. Currently, there is no known method for preparing and characterizing Sr3Co4O. 9-δ Literature reports on the application of materials in H-SOFCs. In addition, traditional Sr3Co4O... 9-δ The materials are mostly synthesized by solid-state reaction method. This method has disadvantages such as high reaction temperature, long reaction time, high energy consumption, and large and uneven product particles, which are not conducive to obtaining high specific surface area and uniform microstructure, thus affecting the electrochemical activity of the electrode. Summary of the Invention

[0005] To address the problems of poor activity and high coefficient of thermal expansion of traditional oxygen electrodes in solid oxide fuel cells at low temperatures, this invention provides a low-temperature, high-activity layered M... 0.15 Sr 2.85 Co4O 9-δ Materials, their preparation methods, and applications. This invention involves selecting alkali metals or lanthanides to dope Sr sites in a specific ratio, forming materials with the general chemical formula M0. 0.15 Sr 2.85 Co4O 9-δ By effectively controlling the crystal structure, electronic structure and oxygen defect concentration of the material, the oxygen ion diffusion and surface exchange kinetics at medium and low temperatures are optimized, thereby improving the ORR catalytic activity.

[0006] The technical solution of the present invention is as follows:

[0007] Low-temperature, highly active layered M0.15 Sr 2.85 Co4O 9-δ The material is a mismatched layered oxide, consisting of rock salt phase M. 0.15 Sr2CoO 3-δ Layers and pseudo-hexagonal CoO 2-δ The layers are stacked in an alternating mismatched ratio of 1:1.6, where M is at least one of Na, Pr, and K, and δ is the stoichiometric ratio of oxygen vacancies determined by the doping element and the atmosphere in which the material is located.

[0008] The above-mentioned low-temperature, highly active layered M 0.15 Sr 2.85 Co4O 9-δ The method for preparing the material includes the following steps:

[0009] (1) Dissolve the soluble salt containing M, the soluble salt containing Sr, and the soluble salt containing Co in water at a stoichiometric ratio of 0.15:3:4 and stir to form a homogeneous mixed solution.

[0010] (2) Add the combustion agent to the mixed solution, stir to dissolve and adjust its pH value;

[0011] (3) The solution obtained in step (2) is heated and evaporated to a viscous state to trigger a self-propagating combustion reaction and obtain precursor powder;

[0012] (4) After grinding the precursor powder, calcining it in air at 700-900℃ for 2-4 hours to obtain layered M 0.15 Sr 2.85 Co4O 9-δ Material.

[0013] Further, in step (1), the soluble salt containing element M is a nitrate, chloride, or sulfate; the soluble salt containing element Sr is a nitrate, chloride, or sulfate; and the soluble salt containing element Co is a nitrate, chloride, or sulfate. Preferably, the soluble salt containing element M is NaNO3, KNO3, or PrNO3; the soluble salt containing element Sr is Sr(NO3)2; and the soluble salt containing element Co is Co(NO3)3·6H2O.

[0014] Furthermore, in step (2), the final obtained layered M can be controlled by adjusting the pH. 0.15 Sr 2.85 Co4O 9-δ The particle size of the material is smaller as the pH increases, but excessively high pH values ​​can cause precipitation in the solution and thus affect the elemental uniformity. The preferred pH is 6 to 8, and the more preferred pH is 6.8.

[0015] Further, in step (2), the molar ratio of the burning agent to the total metal ions in the mixed solution is 1:2.

[0016] Further, in step (2), the heating evaporation temperature is 350±50℃.

[0017] Further, in step (2), the burning agent is glycine, alanine, urea, citric acid or oxalic acid, etc. Preferably, the burning agent is glycine.

[0018] The application also provides the layered M 0.15 Sr 2.85 Co4O 9-δ The application also provides the use of the material as an oxygen electrode material in a proton-conducting solid oxide fuel cell.

[0019] Further, the electrolyte of the proton-conducting solid oxide fuel cell is a common proton-conducting electrolyte in the art, including but not limited to BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ , BaZr 0.4 Ce 0.4 Y 0.1 Yb 0.1 O 3-δ , BaCe 0.8 Y 0.2 O 3-δ (BCY), BaCe 0.7 Zr 0.2 Y 0.1 O 3-δ (BCZY), etc. In the detailed description of the application, BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ is taken as an example.

[0020] Further, the structure of the proton-conducting solid oxide fuel cell is a common cell structure in the art, including but not limited to a hydrogen electrode support type and an electrolyte support type, etc.

[0021] Further, the proton-conducting solid oxide fuel cell is of the hydrogen electrode support type, the hydrogen electrode material is Ni-BZCYYb, and the layered M 0.15 Sr 2.85 Co4O 9-δ The material is an oxygen electrode material.

[0022] Compared with the prior art, the application has the following advantages:

[0023] (1) This invention uses a combustion method to prepare M 0.15 Sr 2.85 Co4O 9-δ The material utilizes the high energy released from the combustion of the propellant to achieve molecular-level mixing and rapid reaction of the reactants, significantly reducing the synthesis temperature and shortening the reaction time. Furthermore, compared to traditional solid-phase reaction synthesis methods, the material prepared by this method exhibits finer and more uniform particle size, higher specific surface area, and lower agglomeration tendency, which is beneficial for exposing more active sites.

[0024] (2) The layered M of the present invention 0.15 Sr 2.85 Co4O 9-δ The material exhibits a low coefficient of thermal expansion that matches that of the proton-conducting electrolyte, effectively improving the thermomechanical compatibility of the electrode / electrolyte interface and reducing the risk of interface failure.

[0025] (3) The layered M of the present invention 0.15 Sr 2.85 Co4O 9-δ The material exhibits excellent ORR catalytic activity and relatively small polarization resistance temperature dependence in the H-SOFC operating temperature range (400-600℃), providing a new material option for improving the performance and stability of H-SOFC at medium and low temperatures. Attached Figure Description

[0026] Figure 1 The AC impedance spectrum of the NSC|BZCYYb|NSC symmetric cell prepared in Example 1.

[0027] Figure 2 M prepared in Examples 1, 2 and 3 0.15 Sr 2.85 Co4O 9-δ |BZCYYb|M 0.15 Sr 2.85 Co4O 9-δ AC impedance spectrum of a symmetrical cell (M = Na, K, and Pr).

[0028] Figure 3 The NSC|BZCYYb|NSC and Sr3Co4O prepared for Example 1 and Comparative Example 1 9-δ |BZCYYb|Sr3Co4O 9-δ AC impedance diagram of a symmetrical cell.

[0029] Figure 4 The AC impedance spectra of the NSC|BZCYYb|NSC symmetric cells prepared in Examples 1, 4, and 5 are shown.

[0030] Figure 5AC impedance plot of NSC|BZCYYb|NSC symmetric cell prepared for Example 1 combustion method and Comparative Example 2 sol-gel method.

[0031] Figure 6 Na 0.15 Sr 2.85 Co4O 9-δ Material X-ray diffraction (XRD) pattern.

[0032] Figure 7 Na 0.15 Sr 2.85 Co4O 9-δ Material SEM pattern.

[0033] Figure 8 Na 0.15 Sr 2.85 Co4O 9-δ Material and BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ Thermal expansion coefficient plot of (BZCYYb) material.

[0034] Figure 9 I-V plot of NSC|BZCYYb|Ni-BZCYYb single cell prepared for Example 6.

[0035] Figure 10 AC impedance plot of NSC|BZCYYb|Ni-BZCYYb single cell prepared for Example 6. DETAILED DESCRIPTION

[0036] The application will be further described below in connection with specific embodiments and drawings.

[0037] Example 1

[0038] 1. Layered Na 0.15 Sr 2.85 Co4O 9-δ Material Preparation, comprising the following steps:

[0039] (1) Weigh raw materials according to stoichiometric ratio of NaNO3, Sr(NO3)2 and Co(NO3)3·6H2O as 0.15:2.85:4, and mix them in deionized water, and stir until a homogeneous mixed solution is formed;

[0040] (2) Add glycine to the mixed solution according to the ratio of total metal ion molar amount in the mixed solution to glycine molar amount as 1:2, continue stirring until complete dissolution, and add ammonia water dropwise to adjust pH to 6.8;

[0041] (3) The solution formed in step (2) is transferred to an evaporation dish and placed in a constant temperature heating device to evaporate at 350°C to a viscous state, triggering a self-propagating combustion reaction, and collecting the loose precursor powder generated by the combustion;

[0042] (4) The collected precursor powder is finely ground with a agate mortar and placed in a crucible for calcination in a muffle furnace at 800°C for 2h to obtain layered Na 0.15 Sr 2.85 Co4O 9-δ (NSC) material.

[0043] The X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and thermal expansion coefficient (TEC) of the NSC are shown in Figure 6 , Figure 7 and Figure 8 respectively. From the XRD results, it can be seen that the NSC phase is relatively pure. From the SEM results, although the NSC retains the characteristics of the flaky structure, the original large flaky layers are significantly decomposed into pieces of different sizes, and some areas show interlayer dislocation or local curling, which is caused by the uneven distribution of interlayer stress triggered by the larger ionic radius of Sr 2+ .

[0044] 2. Construction and performance detection of NSC|BZCYYb|NSC symmetrical battery, the NSC|BZCYYb|NSC symmetrical battery is prepared by the tabletting method, and the specific steps are as follows:

[0045] (1) The proton conductor electrolyte is BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ (BZCYYb) as a conventional material, 1g of BZCYYb powder is weighed in a mortar, and an appropriate amount of polyvinyl butyral (PVB) solution is added as a binder, and the powder is ground until it is dry and fine enough to have sufficient fluidity. Then the powder is added to the mold, and the pressure is maintained at 10MPa for 2min to obtain a circular electrolyte embryo, and the embryo is calcined at 1450°C for 4h to make it dense, and the BZCYYb electrolyte support is obtained.

[0046] (2) 1g of layered Na 0.15 Sr 2.85 Co4O 9-δ material is weighed and placed in a mortar, and an appropriate amount of terpineol and cellulose is added, and the powder is ground into a uniform viscous slurry, and is brushed onto the BZCYYb electrolyte support using a screen printing method, and is placed in a constant temperature oven at 80°C for 20min to dry, and the effective area of the screen printing is 0.5cm 2, and calcined in a muffle furnace at a temperature of 900℃ with a heating and cooling rate of 1℃ / min -1 , and a holding time of 2h to obtain a NSC|BZCYYb|NSC symmetric cell.

[0047] (3) The electrochemical performance of the NSC|BZCYYb|NSC symmetric cell was tested by AC impedance method. The frequency range was 0.1Hz-100000Hz, and the AC amplitude was 20mV. The symmetric cell to be tested was placed in a tube furnace and heated to 650℃. The AC impedance was measured under a 5%H2O+95%Air atmosphere in the range of 650℃-500℃.

[0048] The impedance of the constructed NSC|BZCYYb|NSC symmetric cell under a 5%H2O+95%Air atmosphere at 600℃ was only 0.36Ωcm 2 , as shown in Figure 1 . The polarization impedance of NSC gradually increased from 0.190Ωcm 2 at 650℃ to 0.911Ωcm 2 at 500℃, with an overall increase of about 4.8 times. The introduction of Na effectively alleviated the deterioration trend of the oxygen electrode reaction kinetics at low temperatures, which may be related to the synergistic optimization of the electronic and ionic conductivity of the material and the interface reaction activity.

[0049] Example 2

[0050] This example is basically the same as Example 1, except that NaNO3 is replaced by KNO3 to obtain layered K 0.15 Sr 2.85 Co4O 9-δ material. The constructed K 0.15 Sr 2.85 Co4O 9-δ |BZCYYb|K 0.15 Sr 2.85 Co4O 9-δ symmetric cell has an impedance of only 0.41Ωcm 2 under a 5%H2O+95%Air atmosphere at 600℃, as shown in Figure 2 .

[0051] Example 3

[0052] This example is basically the same as Example 1, except that NaNO3 is replaced by PrNO3 to obtain layered Pr 0.15 Sr 2.85 Co4O 9-δ material. The constructed Pr 0.15 Sr 2.85 Co4O 9-δ| BZCYYb | Pr 0.15 Sr 2.85 Co4O 9-δ The symmetric cell has an impedance of only 0.44 Ωcm at 600°C, 5% H2O + 95% Air atmosphere 2 As shown in Figure 2

[0053] Comparative Example 1

[0054] This comparative example is basically the same as Example 1, except that the metal nitrate raw materials are only Sr(NO3)2 and Co(NO3)3·6H2O, with a stoichiometric ratio of 3:4, to obtain Sr3Co4O 9-δ material. The constructed Sr3Co4O 9-δ | BZCYYb | Sr3Co4O 9-δ The symmetric cell has an impedance of 0.65 Ωcm at 600°C, 5% H2O + 95% Air atmosphere 2 As shown in Figure 3

[0055] Example 4

[0056] This example is basically the same as Example 1, except that the muffle calcination temperature is 700°C, to obtain layered Na 0.15 Sr 2.85 Co4O 9-δ material. The constructed NSC | BZCYYb | NSC symmetric cell has an impedance of only 0.37 Ωcm at 600°C, 5% H2O + 95% Air atmosphere 2 As shown in Figure 4

[0057] Example 5

[0058] This example is basically the same as Example 1, except that the muffle calcination temperature is 900°C, to obtain layered Na 0.15 Sr 2.85 Co4O 9-δ material. The NSC | BZCYYb | NSC symmetric cell has an impedance of only 0.38 Ωcm at 600°C, 5% H2O + 95% Air atmosphere 2 As shown in Figure 4

[0059] Comparative Example 2

[0060] This comparative example uses a sol-gel method to prepare Na 0.15 Sr 2.85 Co4O 9-δ material, and the specific steps are as follows:

[0061] ​​​​(1) Precisely weigh high-purity NaNO3, Sr(NO3)2 and Co(NO3)3·6H2O in a stoichiometric ratio of 0.15:2.85:4, dissolve in deionized water, and stir until a mixed solution is formed;

[0062] (2) According to the molar ratio of total metal ions in the mixed solution: citric acid: ethylene glycol = 1:1.5:2, first add citric acid to the mixed solution, stir until dissolved, then add ethylene glycol, continue to stir for 30 minutes until fully complexed, and add ammonia water dropwise to adjust the pH to 6.8, stir for 20 minutes to obtain a transparent precursor sol;

[0063] (3) Place the transparent precursor sol in a constant temperature stirring evaporator at 80°C until a viscous gel without obvious liquid is formed, then move it to an oven and heat at 150°C for 12 hours to obtain a loose precursor powder;

[0064] (4) Finely grind the collected precursor powder with a marquis mortar, place it in a crucible and calcine it in a muffle furnace at 800°C for 2 hours to obtain Na 0.15 Sr 2.85 Co4O 9-δ material.

[0065] The Na 0.15 Sr 2.85 Co4O 9-δ material prepared by calcining based on the sol-gel method constructs an NSC|BZCYYb|NSC symmetric battery with an impedance of only 0.55 Ωcm 2 , as shown in Figure 5 .

[0066] Example 6

[0067] The preparation method of the hydrogen electrode support single cell, taking Ni-BZCYYb as the hydrogen electrode active layer material, Ni-BZCYYb as the hydrogen electrode support layer material, and BZCYYb as the electrolyte layer material, and the layered Na 0.15 Sr 2.85 Co4O 9-δ material prepared in Example 1 as the oxygen electrode material, the specific steps are as follows:

[0068] (1) Mix the ceramic powder mixture, deionized water, pore-forming agent, dispersant, dilute ammonia water, binder, plasticizer, defoaming agent, and surfactant in a ball mill jar according to the proportion, and mix uniformly by ball milling to obtain a hydrogen electrode slurry; mix the proton conductor ceramic powder, deionized water, dispersant, dilute ammonia water, binder, plasticizer, defoaming agent, and surfactant in a ball mill jar according to the proportion, and mix uniformly by ball milling to obtain an electrolyte slurry;

[0069] (2) separately mix the hydrogen electrode slurry and electrolyte slurry to be uniform, after vacuum degassing treatment, adjust the desired knife height on the casting machine for composite casting to obtain electrolyte / hydrogen electrode composite membrane green body, and dry;

[0070] (3) after the electrolyte / hydrogen electrode composite membrane green body is dried, it is taken out and cut into green body pieces of desired size and placed under static pressure, after drying and debinding, the green body pieces are co-fired to obtain Ni-BZCYYb (support layer) | Ni-BZCYYb (active layer) | BZCYYb half-cell;

[0071] (4) the NSC slurry is printed onto the surface of the half-cell electrolyte as the battery oxygen electrode by using silk screen printing, and is placed in an 80°C constant temperature oven for 20 min for drying, the effective area of silk screen printing is 0.5 cm 2 , the silk screen specification is 150 mesh, then it is placed in a muffle furnace for calcination, the calcination temperature is 900°C, the heating and cooling rate is 1°C / min -1 , the holding time is 2h, and a hydrogen electrode support NSC|BZCYYb|Ni-BZCYYb single cell is obtained.

[0072] The prepared single cell is sealed on a corundum tube with ceramic glue, and then is placed in an experimental furnace, the cathode side of the cell is connected to 5% H2O+95% Air with a flow rate of 80 ml / min -1 , and the hydrogen electrode side is connected to H2 with a flow rate of 20 ml / min -1 , and the electrochemical performance of the cell at 650-500°C is tested, as shown in Figure 9 and Figure 10 . The power density of the NSC|BZCYYb|Ni-BZCYYb single cell at 650-500°C is 1273, 1095, 704 and 362 mW / cm -2 , which is due to its high catalytic activity reducing the polarization impedance and low thermal expansion coefficient reducing the ohmic impedance, so that it has excellent electrochemical performance.

Claims

1. Layered M 0.15 Sr 2.85 Co4O 9-δ material, characterized in that, It is a mismatched layered oxide, consisting of rock salt phase M 0.15 Sr2CoO 3-δ Layers and pseudo-hexagonal CoO 2-δ The layers are stacked in an alternating mismatched ratio of 1:1.6, where M is at least one of Na, Pr, and K, and δ is the stoichiometric ratio of oxygen vacancies determined by the doping element and the atmosphere in which the material is located.

2. The low-temperature highly active layered M 0.15 Sr 2.85 Co4O 9-δ Method for producing a material, characterized in that, The method comprises the following steps: (1) dissolving soluble salt containing M element, soluble salt containing Sr element and soluble salt containing Co element in water according to stoichiometric ratio of 0.15:3:4, and stirring to form a homogeneous mixed solution; (2) adding a combustion agent into the mixed solution, stirring to dissolve and adjusting the pH value; (3) heating and evaporating the solution obtained in step (2) to a viscous state, triggering a self-propagating combustion reaction, and obtaining a precursor powder; (4) The precursor powder is ground and calcined at 700-900 °C in air for 2-4 hours to obtain layered M 0.15 Sr 2.85 Co4O 9-δ material.

3. The preparation method according to claim 2, characterized in that, In step (1), the soluble salt containing M element is nitrate, chloride or sulfate, the soluble salt containing Sr element is nitrate, chloride or sulfate, and the soluble salt containing Co element is nitrate, chloride or sulfate; in step (2), the pH value is 6-8.

4. The preparation method according to claim 2, characterized in that, In step (1), the soluble salt containing M element is NaNO3, KNO3 or PrNO3, the soluble salt containing Sr element is Sr(NO3)2, and the soluble salt containing Co element is Co(NO3)3·6H2O; in step (2), the pH value is 6.

8.

5. The preparation method according to claim 2, characterized in that, In step (2), the molar ratio of the combustion agent to the total metal ions in the mixed solution is 1:

2.

6. The preparation method according to claim 2, characterized in that, In step (2), the heating and evaporating temperature is 350±50℃, and the combustion agent is glycine, alanine, urea, citric acid or oxalic acid.

7. The layered M 0.15 Sr 2.85 Co4O 9-δ application of the material as an oxygen electrode material in a proton-conducting solid oxide fuel cell.

8. Use according to claim 7, characterized in that, The electrolyte of the proton-conducting solid oxide fuel cell is BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ , BaZr 0.4 Ce 0.4 Y 0.1 Yb 0.1 O 3-δ , BaCe 0.8 Y 0.2 O 3-δ or BaCe 0.7 Zr 0.2 Y 0.1 O 3-δ .

9. Use according to claim 7, characterized in that, The structure of the proton-conducting solid oxide fuel cell is hydrogen electrode support type or electrolyte support type.

10. Use according to claim 7, characterized in that, The proton-conducting solid oxide fuel cell is of hydrogen electrode support type, and Ni-BZCYYb is used as hydrogen electrode material, and layered M 0.15 Sr 2.85 Co4O 9-δ material is used as oxygen electrode material.

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