A proton fuel cell air electrode having a gradient porosity structure and a method of making the same

Abstract

This invention provides an air electrode for a proton fuel cell with a gradient pore structure and its preparation method. The air electrode includes an inner functional layer in contact with the electrolyte layer and an outer diffusion layer disposed outside the inner functional layer. The inner functional layer is prepared using a composite air electrode material without added pore-forming agent. The outer diffusion layer is prepared using a composite air electrode material with added pore-forming agent. The porosity of the outer diffusion layer is higher than that of the inner functional layer, thus forming a gradient pore structure that gradually increases from the electrolyte layer side to the air side. The air electrode material contains PNC and BZCYYb in a mass ratio of 7:3. Based on the total mass of PNC and BZCYYb, the mass fraction of the pore-forming agent is 5wt.%~20wt.%, preferably 10wt.%. Electrochemical tests show that the polarization resistance of the cathode with 10% pore-forming agent is only 0.162Ω·cm at 650℃. 2 Compared to the method without pore-forming agents, the activation energy is reduced by 54%, reaching as low as 1.269 eV. This invention significantly improves oxygen reduction reaction performance by synergistically optimizing gas diffusion and charge transfer through a gradient pore structure.

Description

Technical Field

[0001] This invention relates to the field of proton ceramic fuel cell technology, specifically to an air electrode for a proton ceramic fuel cell with a gradient porosity bilayer structure, its preparation method, and a proton ceramic fuel cell containing the air electrode. Background Technology

[0002] Proton ceramic fuel cells (PCFCs) represent an important development direction for solid oxide fuel cells, utilizing protons (H+) as the primary energy source. + Using protons as the primary charge carriers, and leveraging the low activation energy of proton migration in ceramic electrolytes, PCFCs can achieve high-efficiency operation in the low-temperature range of 400-600℃. Compared to traditional oxygen-ion conductor solid oxide fuel cells, PCFCs not only effectively reduce the risks of thermal stress and material degradation, but also offer advantages such as water generation on the air electrode side, no anode fuel dilution, high fuel utilization, and simplified system structure. Therefore, they are considered an important candidate technology for next-generation low-temperature high-efficiency fuel cells.

[0003] In PCFCs, the air electrode is responsible for the oxygen reduction reaction (ORR) process, and its reaction kinetics directly affect the overall battery performance. Under medium and low temperature operating conditions, the rates of processes such as oxygen adsorption, oxygen molecule dissociation, surface diffusion, and interfacial charge transfer decrease, leading to an increase in the polarization resistance of the air electrode. Therefore, the air electrode is often a significant factor limiting the improvement of PCFC performance.

[0004] Currently, perovskite oxides are widely used in PCFC air electrodes due to their high electronic conductivity and good oxygen surface exchange capacity. Among them, PrNi... 0.7 Co 0.3 O3 (PNC) materials possess both high electronic conductivity and good oxygen reduction catalytic activity, making them suitable as air electrode materials for PCFCs. However, traditional uniform porous air electrodes struggle to simultaneously meet the requirements of gas diffusion and charge transport. While lower porosity structures are beneficial for forming a continuous conductive network and enhancing interfacial bonding, they tend to restrict oxygen diffusion; higher porosity structures, while promoting gas transport, may lead to weakened particle contact, reduced mechanical strength, and decreased interfacial charge transfer capacity.

[0005] To address these issues, some studies in recent years have employed functional stratification or porous structure designs to improve the performance of air electrodes. However, systematic research on the construction of porosity gradients between different layers and their synergistic regulation mechanisms remains lacking. Therefore, developing a gradient porosity air electrode that balances oxygen diffusion capacity, interfacial bonding capacity, and charge transport capacity is of great significance for improving the electrochemical performance and long-term operational stability of PCFCs. Summary of the Invention

[0006] The present invention aims to provide a proton fuel cell air electrode with a gradient pore structure and its preparation method, so as to solve the problem that existing air electrodes with uniform pore structure are difficult to balance oxygen diffusion and interfacial charge transport.

[0007] To achieve the above objectives, the specific solution adopted by the present invention is as follows: In a first aspect, the present invention provides an air electrode for a proton fuel cell with a gradient pore structure, the air electrode comprising an inner functional layer in contact with an electrolyte layer and an outer diffusion layer disposed outside the inner functional layer; The inner functional layer is prepared using a composite air electrode material without added pore-forming agent to form a low porosity structure; the outer diffusion layer is prepared using a composite air electrode material with added pore-forming agent to form a high porosity structure; wherein, the porosity of the outer diffusion layer is higher than that of the inner functional layer, thereby forming a gradient pore structure that gradually increases from the electrolyte layer side to the air side. The inner functional layer and the outer diffusion layer are both made of air electrode material, which contains PNC and BZCYYb, and the mass ratio of PNC to BZCYYb is 7:3.

[0008] Furthermore, based on the total mass of PNC and BZCYYb in the outer diffusion layer, the mass fraction of the pore-forming agent is 5 wt.% to 20 wt.%.

[0009] Furthermore, the amount of the pore-forming agent added is 10 wt.%.

[0010] Furthermore, the pore-forming agent is corn starch.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned air electrode with gradient porosity, comprising the following steps: S1. Mix PNC powder and BZCYYb powder at a mass ratio of 7:3, add binder, grind evenly to obtain inner functional layer slurry; S2. Mix PNC powder and BZCYYb powder at a mass ratio of 7:3, add pore-forming agent and binder, and grind evenly to obtain the outer diffusion layer slurry; wherein, based on the total mass of PNC and BZCYYb, the amount of pore-forming agent added is 5wt.% to 20wt.%. S3. The inner functional layer slurry is coated onto the surface of the electrolyte sheet and dried to form the inner functional layer precursor. S4. Coat the outer diffusion layer slurry onto the inner functional layer precursor and dry it to form the outer diffusion layer precursor. S5. The coated electrolyte sheet is calcined to allow the pore-forming agent to volatilize and form pores in the outer diffusion layer, while the inner functional layer and the outer diffusion layer are sintered and solidified to obtain the air electrode.

[0012] Furthermore, the preparation method of the PNC powder used in steps S1 and S2 is as follows: Weigh out Pr(NO3)3·6H2O, Ni(NO3)2, and Co(NO3)2·6H2O according to the stoichiometric ratio, and dissolve them in deionized water; Add citric acid and EDTA in a molar ratio of metal cation:citric acid:EDTA = 1:1.5:1 and stir to mix; Add ammonia to adjust the pH to 7-8; Stir at 80°C until gelation occurs, and dry at 200°C for 10 hours to obtain a dry gel. The dry gel was ground and then calcined at 1000℃ for 5 hours to obtain PNC powder.

[0013] Furthermore, the adhesive used in steps S1 and S2 is prepared by mixing terpineol and ethyl cellulose at a mass ratio of 95:5 and stirring magnetically until fully dissolved.

[0014] Furthermore, in step S5, the calcination process is as follows: the temperature is increased to 500°C at a rate of 2°C / min, held for 1 hour, then increased to 1000°C and held for 5 hours.

[0015] Furthermore, the electrolyte sheet used in step S3 is prepared by the following method: BZCYYb powder and NiO were mixed at a mass ratio of 99:1, PVB ethanol solution was added as a binder, and the mixture was ground evenly. The ground powder is placed into a circular tableting mold and dry-pressed at 18MPa for 2 minutes. After demolding, the blank is obtained. The blank was placed in a ceramic boat covered with BZCYYb powder, and a layer of BZCYYb powder was covered on the surface of the blank to reduce the volatilization of Ba element during high-temperature sintering; then the temperature was increased to 450℃ at 2℃ / min and held for 2h to remove organic matter; then the temperature was increased to 1450℃ and held for 6h to obtain a dense electrolyte sheet.

[0016] The core of this invention lies in constructing a gradient structure with porosity gradually increasing from the electrolyte side outwards, thereby synergistically optimizing gas diffusion, surface oxygen exchange, and charge transport behavior within the air electrode. Specifically, the inner functional layer near the electrolyte is free of pore-forming agents and, after calcination, forms a structure with low porosity. This structure has two important functions: first, lower porosity means tighter contact between particles, which is beneficial for forming a continuous electronic and ionic conductive network, thereby reducing interfacial charge transfer resistance; second, the inner functional layer is in direct contact with the electrolyte sheet, and the low porosity ensures a large contact area and good interfacial bonding strength, avoiding interfacial delamination or cracking, and providing stable interfacial conditions for charge transport. The outer diffusion layer, after adding pore-forming agents and calcination, volatilizes to form abundant pores, resulting in higher porosity. The high porosity structure facilitates the diffusion of oxygen molecules from the gas phase into the electrode interior, shortening the diffusion path and improving gas transport efficiency. By combining the low-porosity inner functional layer and the high-porosity outer diffusion layer, a gradient structure with gradually increasing porosity from the electrolyte side outwards is formed. This gradient structure gradually reduces the resistance encountered by oxygen during diffusion, while also optimizing the resistance encountered by charge during transport. Specifically, in each elementary step of ORR: oxygen molecules first rapidly diffuse and adsorb in the highly porous region of the outer diffusion layer, then dissociate into oxygen atoms on the particle surface. These oxygen atoms then reach the three-phase interface through surface diffusion or bulk diffusion, finally combining with electrons and protons at the interface to form water. The gradient porosity structure allows each step to occur in an optimal microenvironment, thereby reducing the overall polarization resistance. Furthermore, this invention introduces both PNC and BZCYYb into the air electrode material. PNC, as a perovskite oxide, possesses excellent electronic conductivity and a high surface oxygen exchange rate, making it the main catalytically active phase in ORR. BZCYYb is a proton conductor; combining it with PNC expands the three-phase reaction interface, allowing protons to react with oxygen within the air electrode without needing to be transported remotely to the PNC surface via the electrolyte, thus further improving reaction efficiency. The mass ratio of PNC to BZCYYb is 7:3, which has been experimentally verified as the optimal ratio, ensuring both sufficient electronic conduction pathways and providing ample proton conduction phase. The choice of pore-forming agent is also crucial. This invention uses corn starch as the pore-forming agent, which has the following advantages: corn starch particles are relatively uniform in size, can completely decompose and volatilize during calcination without leaving residue; its volatilization temperature range matches the sintering temperature of the air electrode, enabling the formation of pores while sintering to form the framework; and corn starch is widely available and inexpensive, making it suitable for large-scale applications.In the calcination process, the temperature is first raised to 500℃ at a slow rate of 2℃ / min and held for 1 hour. This allows the binder and pore-forming agent to fully decompose and volatilize, preventing cracking caused by rapid decomposition of organic matter due to excessive heating. Then, the temperature is raised to 1000℃ and held for 5 hours to allow appropriate sintering between the air electrode material particles, forming a porous framework with sufficient mechanical strength while ensuring good electrical contact between particles. In summary, this invention, through material selection, bilayer structure design, pore-forming agent content control, and calcination process optimization, successfully constructs a PNC-based air electrode with gradient porosity, significantly improving the oxygen reduction reaction performance of proton ceramic fuel cells.

[0017] This invention selects a composite of PNC and BZCYYb as the air electrode material, which has the following special effects: PNC, as a perovskite oxide, has excellent electronic conductivity and a high surface oxygen exchange rate, making it the main catalytic active phase for the oxygen reduction reaction (ORR); BZCYYb is a proton conductor, and its combination with PNC can form a continuous proton conduction network inside the air electrode. In proton ceramic fuel cells (PCFCs), the oxygen reduction reaction requires the participation of electrons, protons, and oxygen. Traditional single-phase electronically conductive air electrodes can only achieve ORR at the air electrode / electrolyte / gas three-phase interface. However, the introduction of BZCYYb in this invention allows protons to be directly transported inside the air electrode, extending the three-phase reaction interface from a two-dimensional interface to a three-dimensional bulk phase, significantly increasing the number of reactive sites, and thus greatly improving ORR efficiency.

[0018] The design principle of this invention, which eliminates the addition of a pore-forming agent to the inner functional layer, is as follows: The inner functional layer, located near the electrolyte, plays a crucial role in interfacial charge transport. The absence of a pore-forming agent results in a lower porosity in the inner functional layer, allowing for thorough sintering between particles and forming a continuous and dense electronic and ionic conductive network, thus ensuring low-resistance interfacial contact with the electrolyte. If a pore-forming agent were added to the inner functional layer, the resulting pores after calcination would disrupt the continuity of the conductive network, increasing interfacial contact resistance and charge transfer impedance, ultimately reducing the performance of the air electrode. Therefore, this invention employs a differentiated design with no pore-forming agent in the inner functional layer and an added pore-forming agent in the outer diffusion layer, achieving synergistic optimization of "the inner functional layer preserving charge transport and the outer diffusion layer promoting gas diffusion." This is the core innovation of the gradient pore structure in this invention.

[0019] Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: (1) This invention achieves a low porosity structure by not adding a pore-forming agent to the inner functional layer (near the electrolyte layer), ensuring sufficient interfacial contact and continuous ion / electron transport channels with the electrolyte; and by adding a pore-forming agent to the outer diffusion layer and calcining it to form a high-porosity porous structure, effectively enhancing oxygen diffusion and reactant transport capabilities. This gradient structure with gradually increasing porosity from the electrolyte side to the outside solves the contradiction that traditional single-layer air electrodes cannot simultaneously achieve oxygen diffusion, interfacial reaction, and charge transport, thus significantly improving ORR kinetic performance. Experiments show that, in an air atmosphere at 650℃, the polarization resistance of the double-layer air electrode with 10wt.% pore-forming agent is only 0.162Ω·cm. 2 The pore size was reduced by approximately 54% compared to the sample without added pore-forming agent.

[0020] (2) This invention found that the content of pore-forming agent has a significant impact on the performance of air electrode. When the content of pore-forming agent is too low, the pore development is insufficient and oxygen diffusion is restricted; when the content of pore-forming agent is too high, the air electrode skeleton is loose, the particle contact is weakened and the density of active sites decreases, resulting in a significant increase in polarization impedance. Through systematic research, it was determined that, based on the total mass of PNC and BZCYYb, a gradient pore structure can be achieved with a pore-forming agent mass fraction of 5wt.% to 20wt.%, with 10wt.% being the optimal addition amount. At this amount, the air electrode exhibits the lowest impedance contribution in key reaction steps such as oxygen surface diffusion, oxygen adsorption and dissociation, and charge transfer at the three-phase interface, and has the lowest ORR activation energy (1.269eV), indicating that it has the lowest intrinsic reaction energy barrier and the best catalytic kinetic characteristics.

[0021] (3) The gradient pore air electrode of the present invention exhibits excellent performance response under different oxygen partial pressure conditions. As the oxygen partial pressure increases from 1% to 100%, the total polarization resistance decreases by 70.32%, indicating that the gradient pore structure can effectively promote oxygen diffusion and surface exchange processes. Attached Figure Description

[0022] Figure 1 The XRD pattern of PNC powder.

[0023] Figure 2 The images show the microstructure of the air electrodes, where (a) is an image of the interface between the double-layer PNC electrode and the electrolyte, (b) is a magnified image of a portion of the GPE-0 air electrode, (c) is a magnified image of a portion of the GPE-10 air electrode, and (d) is a magnified image of a portion of the GPE-20 air electrode.

[0024] Figure 3The figures show the electrochemical performance characterization of symmetric batteries with different pore-forming agent contents. (a) shows the EIS experimental measurement values ​​and equivalent circuit fitting results of each sample at 650℃ and 3% H2O atmosphere. (b) shows the corresponding DRT analysis curves. (c) shows the comparison of polarization resistance of each sample at 650℃ in different frequency bands. (d) shows the Arrhenius curve of polarization conductivity of GPE-n (n=5-20) symmetric batteries.

[0025] Figure 4 The figures show the electrochemical impedance spectroscopy and relaxation time distribution of the GPE-10 symmetric cell at 650℃ under different partial pressures. (a,b) are the Nyquist impedance spectra and corresponding DRT spectra under different oxygen partial pressures, and (c,d) are the Nyquist impedance spectra and corresponding DRT spectra under different water vapor pressures.

[0026] Figure 5 A schematic diagram of fuel cells with different addition rates. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0028] First, the structure of the air electrode with gradient porosity, the structure of the proton ceramic fuel cell containing the air electrode, and the preparation method of the present invention are described in detail.

[0029] (a) Structure of the air electrode The air electrode with gradient porosity provided by this invention has a double-layer structure, including an inner functional layer and an outer diffusion layer. The inner functional layer is used for direct contact with one side of the electrolyte sheet, while the outer diffusion layer is stacked on the side of the inner functional layer away from the electrolyte sheet. The inner functional layer is made of air electrode material without added pore-forming agents, thus its porosity is low, ensuring sufficient interfacial contact and continuous ion / electron transport channels with the electrolyte. The outer diffusion layer is made of porous air electrode material with added pore-forming agents, formed by calcination. Due to the volatilization of the pore-forming agents during calcination, the outer diffusion layer forms abundant pores, with a porosity greater than that of the inner functional layer. Therefore, the entire air electrode forms a gradient structure with gradually increasing porosity from the electrolyte sheet outwards.

[0030] Both the inner functional layer and the outer diffusion layer are made from air electrode material, which contains PNC (PrNi) 0.7 Co 0.3O3 and BZCYYb (BaZr) 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ The PNC to BZCYYb composition has a mass ratio of 7:3. PNC, as the primary electrochemical active material, provides electronic conductivity and ORR catalytic activity; BZCYYb, as the proton conductor phase, expands the three-phase reaction interface and enhances proton transport capability. The combination of these two components synergistically improves the overall performance of the air electrode.

[0031] It is worth further explaining that this invention chooses a composite of PNC and BZCYYb, rather than using PNC alone, based on a comprehensive consideration of the unique reaction mechanism of proton ceramic fuel cells and the stability of the air electrode interface. In PCFCs, the oxygen reduction reaction (ORR) of the air electrode involves not only the adsorption, dissociation, and electron transport of oxygen, but also the participation of protons. PNC is a typical mixed oxygen ion-electron conductor (MIEC) air electrode material, possessing high electronic conductivity, good oxygen ion transport capability, and excellent oxygen surface exchange activity, which can effectively promote the oxygen adsorption and oxygen reduction reaction processes. However, single PNC lacks effective proton conduction capability; protons must be transported from the electrolyte to the air electrode / electrolyte interface before participating in the reaction, thus the reaction region is mainly limited to the vicinity of the interface. The introduction of BZCYYb endows the air electrode with a certain proton conduction capability, enabling the oxygen reduction reaction to occur over a larger area within the air electrode, thereby effectively expanding the three-phase reaction interface area and improving the reaction kinetics performance of the air electrode. Furthermore, since the electrolyte material used in this invention is also BZCYYb, introducing BZCYYb into the air electrode can effectively reduce the thermal expansion coefficient mismatch between the air electrode and the electrolyte, improve their thermomechanical compatibility, reduce interfacial stress accumulation during high-temperature sintering and long-term operation, thereby enhancing the stability of the air electrode / electrolyte interface and improving the long-term reliability of the battery. Experiments have shown that the polarization resistance of this air electrode is as low as 0.162 Ω·cm at 650℃. 2 The performance is significantly better than that of a single air electrode.

[0032] Furthermore, the absence of pore-forming agents in the inner functional layer is a crucial structural design feature determined through systematic optimization in this invention. Pore-forming agents volatilize during high-temperature calcination, forming porous structures. For the outer diffusion layer, appropriate porosity is beneficial for improving oxygen diffusion capacity and gas transport efficiency. For the inner functional layer, located near the electrolyte, its main function is to construct continuous charge transport pathways and enhance the interfacial bonding between the air electrode and the electrolyte. Introducing excessive porosity into the inner layer weakens the connection between particles, reduces the density of interfacial contact, thereby increasing interfacial resistance and affecting charge transport efficiency. Comparative experiments revealed that adding pore-forming agents to the inner functional layer resulted in varying degrees of increase in the polarization impedance of the air electrode, indicating that the low-porosity structure of the inner layer is more conducive to interfacial charge transfer and improving the overall reaction kinetics performance of the air electrode. Therefore, this invention explicitly limits the inner functional layer to be prepared using a composite air electrode material without added pore-forming agents to ensure that the air electrode has low interfacial impedance and good structural stability.

[0033] The content of the pore-forming agent in the outer diffusion layer of this invention is adjustable. Based on the total mass of PNC and BZCYYb, the mass fraction of the pore-forming agent is from 5 wt.% to 20 wt.%. The pore-forming agent is preferably corn starch, which completely volatilizes during calcination, leaving no residue and preventing electrode contamination. The overall performance of the air electrode is optimal when the mass fraction of the pore-forming agent is 10 wt.%.

[0034] (II) Preparation method of air electrode The air electrode preparation method provided by this invention includes the following steps: S1. Preparation of PNC powder: The sol-gel method was used. Pr(NO3)3·6H2O, Ni(NO3)2, and Co(NO3)2·6H2O were accurately weighed according to the stoichiometric ratio and dissolved in deionized water. Citric acid and EDTA were weighed according to the molar ratio of metal cation:citric acid:EDTA = 1:1.5:1. "Metal cation" refers to the Pr(NO3)3·6H2O, Ni(NO3)2, and Co(NO3)2·6H2O contained in the raw materials. 3+ Ni 2+ Co 2+The sum of the three metal cations was mixed with citric acid in an appropriate amount of deionized water and then with the above nitrate solution. The mixture was thoroughly stirred in a magnetically heated stirrer, and then EDTA was added. Ammonia was then added in small amounts several times to adjust the pH of the solution to 7-8. The pH-adjusted solution was stirred at 80°C until it reached a gel state, allowing the water to evaporate completely and the solution to become viscous. The solution was then transferred to a drying oven and dried at 200°C for 10 hours to obtain a brittle dry gel. The dry gel was simply ground and placed in a crucible, then calcined in a muffle furnace at 1000°C for 5 hours to obtain black PNC electrode powder. This preparation method can obtain pure-phase perovskite structure, well-crystallized PNC powder, providing high-quality raw materials for subsequent electrode preparation. S2. Preparation of the inner functional layer slurry: PNC powder and BZCYYb powder are mixed at a mass ratio of 7:3, a binder is added, and the mixture is ground evenly to obtain the inner functional layer slurry. The binder serves to ensure uniform dispersion of the powder particles and to provide a certain viscosity for subsequent coating. The binder is prepared by mixing terpineol and ethyl cellulose at a mass ratio of 95:5 and then dissolving them thoroughly by magnetic stirring. Terpineol acts as a solvent, and ethyl cellulose acts as a thickener and binder; their combination yields suitable slurry rheological properties. S3. Preparation of the outer diffusion layer slurry: PNC powder and BZCYYb powder are mixed at a mass ratio of 7:3, a pore-forming agent and a binder are added, and the mixture is ground uniformly to obtain the outer diffusion layer slurry. The amount of pore-forming agent added is 5 wt.% to 20 wt.% based on the total mass of PNC and BZCYYb. The role of the pore-forming agent is to volatilize during subsequent calcination, leaving pores in the outer diffusion layer, thereby forming a porous structure. Corn starch is preferably used as the pore-forming agent because it has uniform particle size and a volatilization temperature that matches well with the sintering temperature of the air electrode. S4. Forming the inner functional layer precursor: The inner functional layer slurry is coated onto the surface of the electrolyte sheet and then dried (e.g., at 100°C) to form the inner functional layer precursor. Coating can be done manually. The purpose of drying is to remove the solvent from the slurry and allow the coating to set. S5. Forming the outer diffusion layer precursor: The outer diffusion layer slurry is coated onto the inner functional layer precursor and dried (e.g., at 100°C) to form the outer diffusion layer precursor. Using a layer-by-layer coating method ensures good bonding between the two layers while preventing them from mixing. S6. Calcination: The coated electrolyte sheet is calcined. The calcination process is as follows: the temperature is increased to 500℃ at a rate of 2℃ / min and held for 1 hour to remove organic matter (including binders and pore-forming agents); then the temperature is further increased to 1000℃ and held for 5 hours to sinter and solidify the inner functional layer and the outer diffusion layer. During calcination, the pore-forming agent volatilizes, forming pores in the outer diffusion layer; simultaneously, sintering bonds occur between the air electrode material particles of the inner functional layer and the outer diffusion layer, forming a porous framework with sufficient mechanical strength. After calcination, the sheet is cooled in the furnace to obtain an air electrode with gradient porosity.

[0035] (III) Preparation method of electrolyte tablets The BZCYYb electrolyte tablets used in this invention can be prepared by the following method: BZCYYb powder and NiO were mixed at a mass ratio of 99:1, and PVB ethanol solution was added as a binder. The mixture was then ground until homogeneous. NiO, acting as a sintering aid, lowered the sintering temperature of BZCYYb while increasing its density. The ground powder was placed in a circular pressing mold (e.g., 13 mm in diameter) and dry-pressed at 18 MPa for 2 minutes. After demolding, a green body was obtained. The green body was placed in a ceramic boat filled with BZCYYb powder, and a layer of BZCYYb powder was placed on top of the green body to prevent the Ba element in the electrolyte material from evaporating at high temperatures. The temperature was then increased to 450°C at a rate of 2°C / min and held for 2 hours to remove the binder. The temperature was then increased to 1450°C and calcined for 6 hours to obtain a dense BZCYYb electrolyte sheet.

[0036] The proton ceramic fuel cell provided by this invention includes an electrolyte layer and the aforementioned air electrode disposed on at least one side of the electrolyte layer. The electrolyte layer is composed of BZCYYb electrolyte sheets, and the inner functional layer of the air electrode is in direct contact with the electrolyte layer. The anode of the fuel cell can be made of conventional materials in the art; however, the focus of this invention is on the air electrode structure, therefore the anode portion is not limited in detail. Figure 5 Schematic diagrams of proton ceramic fuel cells with different pore-forming agent gradients clearly illustrate the layered structure of the electrolyte layer, inner functional layer, and outer diffusion layer, as well as the correspondence between the amount of pore-forming agent added (5wt.%, 10wt.%, 15wt.%, 20wt.%) in the outer diffusion layer and the porosity gradient. Figure 5 It can be clearly seen that as the amount of pore-forming agent added to the outer diffusion layer gradually increases from 5 wt.% to 20 wt.%, the porosity of the outer electrode layer increases in a gradient.

[0037] It should be noted that, in order to reduce the influence of the fuel electrode, the overall battery structure, and interfacial coupling factors on the test results, and to more accurately characterize the oxygen reduction reaction (ORR) kinetics and electrochemical performance of the air electrode, this invention employs a symmetrical battery structure for electrochemical testing. The symmetrical battery structure is: PNC-BZCYYb (outer diffusion layer) / PNC-BZCYYb (inner functional layer) / / BZCYYb / / PNC-BZCYYb (inner functional layer) / PNC-BZCYYb (outer diffusion layer), that is, two-layer air electrodes with identical structure and composition are fabricated on both sides of the BZCYYb electrolyte sheet. When using this symmetrical battery structure, the measured impedance mainly originates from the oxygen reduction reaction process on the air electrode side, including microscopic reaction steps such as oxygen adsorption and dissociation, surface diffusion, and interfacial charge transfer. This allows for a more accurate evaluation of the influence of air electrodes with different gradient pore structures on ORR kinetic performance. Examples 1-4 and the comparative examples below all use the above-described symmetrical battery structure for preparation and testing.

[0038] Example 1 (GPE-10) This embodiment provides a method for preparing a symmetrical battery (including the preparation of an air electrode), which mainly includes the following steps: S1. Preparation of PNC Powder: PNC powder was prepared using the sol-gel method. 4.350 g of Pr(NO3)3·6H2O, 2.036 g of Ni(NO3)2, and 0.873 g of Co(NO3)2·6H2O were accurately weighed according to the stoichiometric ratio and dissolved in deionized water. 5.764 g of citric acid and 5.845 g of EDTA were weighed according to the molar ratio of metal cation:citric acid:EDTA = 1:1.5:1. The citric acid was dissolved in an appropriate amount of deionized water and then mixed with the above nitrate solution. The mixture was thoroughly mixed in a magnetically heated stirrer, and then EDTA was added. Ammonia was added in small amounts several times to adjust the pH of the solution to 7-8. The pH-adjusted solution was stirred at 80°C until it reached a gel state, allowing the water to evaporate completely and the solution to become viscous. The solution was then transferred to a drying oven and dried at 200°C for 10 hours to obtain a brittle dry gel. The dry gel was simply ground and placed in a crucible, and calcined in a muffle furnace at 1000℃ for 5 hours to obtain black PNC electrode powder. S2. Preparation of BZCYYb Electrolyte Tablets: Prepare 3g of tableting raw material: Weigh 2.97g of BZCYYb powder and 0.03g of NiO at a mass ratio of 99:1, mix them, pour into a mortar, add an equal amount of PVB ethanol solution, and hand-grind for 1 hour. Weigh 0.3g of the ground powder and place it in a 13mm diameter circular tableting mold. Dry-press under 18MPa pressure for 2 minutes. After demolding, a white electrolyte sheet blank is obtained. Place the blank in a ceramic boat filled with BZCYYb powder and evenly cover it with a layer of BZCYYb powder to prevent Ba evaporation. Place the ceramic boat in a high-temperature muffle furnace and heat at a rate of 2℃ / min. Calcinate at 450℃ for 2 hours, then heat to 1450℃ for 6 hours to obtain a black, dense electrolyte sheet. S3. Preparation of binder: Terpineol and ethyl cellulose are mixed at a mass ratio of 95:5 and fully dissolved under magnetic stirring to obtain the binder; S4. Preparation of inner functional layer slurry and outer diffusion layer slurry: PNC and BZCYYb are mixed at a mass ratio of 7:3 and used as air electrode functional materials. For the inner functional layer slurry, take the above mixed powder, add binder (each 0.5g binder corresponds to the total mass of the mixed powder), and grind thoroughly to obtain a uniform slurry without adding pore-forming agent. For the outer diffusion layer slurry, take the mixed powder, add 10wt.% (based on the total mass of PNC and BZCYYb) of corn starch as a pore-forming agent, then add the same proportion of binder, and grind thoroughly to obtain a uniform slurry. S5. Coating and Calcination: A layer-by-layer coating method was used to coat the surface of the BZCYYb electrolyte sheet: first, an inner functional layer slurry without pore-forming agent was coated and dried at 100℃; then, an outer diffusion layer slurry containing pore-forming agent was coated on the inner functional layer and dried at 100℃. This process was repeated on both sides of the electrolyte to prepare a symmetrical cell structure (a symmetrical cell is required to evaluate the electrochemical performance of the air electrode). The coated cell was heated to 500℃ in air at a rate of 2℃ / min and held for 1 hour to remove organic matter, followed by calcination at 1000℃ for 5 hours to obtain a symmetrical cell. Silver paste was then coated onto the electrode surface as a current collector and dried at 100℃ for 30 minutes. S6. Preparation of the symmetrical cell: A manual coating method was used. First, an inner functional layer slurry was coated onto one side of the BZCYYb electrolyte sheet and dried at 100℃ to form the inner functional layer precursor. Then, an outer diffusion layer slurry was coated onto the inner functional layer precursor and dried at 100℃ to form the outer diffusion layer precursor. The same layer-by-layer coating operation was repeated on the other side of the electrolyte sheet. The coated electrolyte sheet was heated to 500℃ in air at a rate of 2℃ / min and held for 1 hour to remove organic matter. Then, the temperature was increased to 1000℃ and held for 5 hours, followed by furnace cooling. Finally, silver paste was coated onto the surfaces of both electrodes as current collectors and dried at 100℃ for 30 minutes to obtain the symmetrical cell, denoted as GPE-10.

[0039] Example 2: GPE-5 (5wt.% pore-forming agent addition) The only difference from Example 1 is that the amount of corn starch added to the outer diffusion layer slurry is 5 wt.% (based on the total mass of PNC and BZCYYb), and the rest is exactly the same. The resulting symmetric cell is denoted as GPE-5.

[0040] Example 3: GPE-15 (pore-forming agent addition amount 15wt.%) The only difference from Example 1 is that the amount of corn starch added to the outer diffusion layer slurry is 15 wt.%, and the rest is exactly the same. The resulting symmetrical cell is denoted as GPE-15.

[0041] Example 4: GPE-20 (pore-forming agent addition amount 20wt.%) The only difference from Example 1 is that the amount of corn starch added to the outer diffusion layer slurry is 20 wt.%, and the rest is exactly the same. The resulting symmetrical cell is denoted as GPE-20.

[0042] Comparative example: GPE-0 (without pore-forming agent) No corn starch was added to the outer diffusion layer slurry, and the rest was the same as in Example 1. The resulting symmetrical cell was designated as GPE-0 and used as a comparison.

[0043] III. Performance Testing Methods and Results (I) Crystal structure characterization The crystal structure of the PNC powder prepared in Example 1 was analyzed by X-ray diffraction (XRD), with a test range of 2θ = 20° to 80°. The results are as follows: Figure 1As shown, the sample exhibits a series of sharp and high-intensity characteristic diffraction peaks near 32°, 40°, 47°, 58°, 68°, and 78°, with no obvious impurity peaks present. This indicates that the prepared PNC material has a pure-phase perovskite structure, good crystallinity, and no impurity phase formation, resulting in high crystal phase purity. The positions of each diffraction peak highly match the standard characteristic peaks of the perovskite structure, indicating the absence of phase transformation or impurity phase precipitation. The material demonstrates excellent crystal structure stability, providing a structural basis for the stable performance of subsequent electrochemical applications.

[0044] (II) Microscopic morphological characterization The microstructure of the air electrodes in the examples and comparative examples was observed using a scanning electron microscope (SEM). Figure 2 (a) shows that the air electrode and the BZCYYb electrolyte interface are in close contact with each other, without obvious cracks, delamination or pore defects. This indicates that the air electrode material and the electrolyte have good chemical compatibility and thermomechanical compatibility, excellent interfacial bonding force, and can effectively reduce interfacial contact resistance, providing stable interfacial conditions for charge transport.

[0045] Surface morphology comparison results show that the amount of pore-forming agent added has a significant regulatory effect on the pore structure of the air electrode. As the amount of pore-forming agent added gradually increases, the number of pores in the air electrode gradually increases, and the porosity continuously improves. The GPE-0 air electrode without added pore-forming agent has fewer pores. Figure 2 b); As the content of the pore-forming agent gradually increased to 10 wt.% and 20 wt.%, the internal pore structure of the air electrode gradually strengthened, indicating that the pore-forming agent can effectively regulate the formation of the porous structure of the air electrode. Figure 2 cd).

[0046] (III) Electrochemical performance testing Electrochemical performance testing was conducted using an Interface 1000 electrochemical workstation manufactured by Gamry Instruments. During testing, the symmetrical cells prepared in Examples 1-4 and the comparative examples were connected to the test fixtures in the tube furnace via silver wires. Testing was carried out under conditions of ensuring the airtightness of the device, with different atmospheres introduced through the inlet and discharged through the outlet.

[0047] Electrochemical impedance spectroscopy (EIS) testing at 10 -2 -10 6 The test was conducted within the Hz frequency range, with an AC disturbance voltage of 15mV. EIS primarily presents data using a Nyquist plot, with the real part of the impedance on the horizontal axis and the imaginary part on the vertical axis. The horizontal intercept represents the battery's ohmic resistance Ro, while the distance between the two intersection points represents the battery's polarization resistance Rp.

[0048] The electrochemical performance testing temperature range of this invention is 500℃-650℃. The heating rate is set to 2℃ / min, and a cooling test is used to ensure the activation performance of the electrode. After the temperature rises to 650℃, it is held for 30 minutes before measurement begins. Tests are performed every 50℃, with a 10-minute holding period before each test. Simultaneously, the oxygen partial pressure can be tested by changing the oxygen content of the synthetic air, with oxygen partial pressures of 1%, 10%, 20%, 50%, and 100% oxygen content. Water pressure can be tested by controlling the water temperature, with water pressures of 3 kPa at 25℃, 5 kPa at 33℃, and 10 kPa at 46℃.

[0049] All impedance data were analyzed using an equivalent circuit model R0-(R1Q1)-(R2Q2)-(R3Q3), where R0 represents the total ohmic resistance composed of the electrolyte, leads, and contact resistance, and R... i With Q i Polarization resistors and constant phase angle elements, respectively corresponding to different polarization processes, can accurately separate the polarization contribution in the electrode micro-process.

[0050] (1) Electrochemical performance at different pore-forming agent contents (see...) Figure 3 ) EIS tests were performed on symmetrical cells with pore-forming agent additions of 0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.% at 650℃ in air atmosphere. The polarization resistances (Rp) obtained by equivalent circuit fitting were 0.351, 0.347, 0.162, 0.372, and 0.648 Ω·cm, respectively. 2 Comparison of the electrochemical performance of various samples within the temperature range of 500-650℃ revealed that the GPE-10 air electrode exhibited the lowest Rp value at all test temperatures. Furthermore, its polarization resistance increased significantly less with decreasing temperature compared to other samples, indicating that the pore structure corresponding to a 10wt.% pore-forming agent addition was most favorable for the ORR kinetics. The introduction of an appropriate amount of pore-forming agent can form a well-connected hierarchical pore structure within the air electrode, effectively shortening the oxygen diffusion path, increasing gas transport channels, and enhancing the three-phase interface reaction activity, which is beneficial for the synergistic processes of oxygen adsorption, dissociation, and charge transport. However, when the pore-forming agent content is low, pore development is insufficient, and oxygen diffusion is restricted; while excessive pore-forming agent leads to a loose air electrode framework, weakened particle contact, and a decrease in active site density, resulting in a significant increase in polarization resistance.

[0051] To further elucidate the regulatory mechanism of different pore-forming agent addition amounts on the ORR kinetic process, relaxation time distribution (DRT) analysis was performed on the EIS results of each sample at 650℃. The results are as follows: Figure 3As shown in (b), the DRT spectrum clearly decomposes into three characteristic relaxation peaks, corresponding to the ORR elementary reaction steps in different frequency ranges: the high-frequency region (HF) corresponds to the charge transfer step of oxygen species at the electrode-electrolyte three-phase interface, the mid-frequency region (IF) corresponds to the adsorption and dissociation steps of adsorbed oxygen species, and the low-frequency region (LF) corresponds to the surface diffusion and transport process of gaseous oxygen molecules. Comparing the DRT peak intensities of different samples, it can be found that the areas of the three relaxation peaks of GPE-10 are significantly lower than those of other samples, with the most significant decreases in the low-frequency region (oxygen adsorption and dissociation) and the mid-frequency region (oxygen species diffusion). This indicates that the addition of 10 wt.% pore-forming agent can simultaneously optimize the mass transfer and reaction kinetics of ORR, comprehensively reducing the resistance of each elementary step. In contrast, the DRT peak intensity of GPE-20 is significantly increased, consistent with the test results of high polarization resistance, indicating that excessive pore-forming agent will lead to the deterioration of reaction sites and mass transfer pathways.

[0052] To quantitatively analyze the contribution of each elementary reaction step to the total polarization impedance, the total polarization resistance is further decomposed into low-frequency resistance (Ri) by DRT deconvolution. L (corresponding to oxygen surface diffusion process), intermediate frequency resistance (R) M (corresponding to oxygen adsorption and dissociation processes) and high-frequency resistance (R) H (corresponding to the charge transfer process at the three-phase interface), the results are as follows: Figure 3 (c) shows that the total polarization resistance of the GPE-0 sample without added pore-forming agent is 0.351 Ω·cm. 2 , where R M and R H The presence of a dominant pore-forming agent indicates that oxygen adsorption dissociation and interfacial charge transfer are key steps limiting its performance. With increasing pore-forming agent content, the R of GPE-10 decreases. M and R H All decreased significantly, with the total polarization resistance dropping to 0.162 Ω·cm. 2 The total polarization resistance of GPE-20 decreased by approximately 54% compared to GPE-0; while GPE-5 showed some improvement, its optimization effect was still weaker than that of GPE-10. Further increasing the pore-forming agent content caused the total polarization resistance of GPE-20 to rapidly increase to 0.648 Ω·cm. 2 , where R L The significant increase indicates that excessively high porosity leads to a deterioration of the oxygen diffusion path and becomes the main cause of performance degradation. Further comparison of the impedance across different segments reveals that GPE-10 achieved significant optimization across all three response frequency bands. Specifically, R... L From GPE-0 0.053Ω·cm 2 Reduced to 0.029 Ω·cm 2 The decrease was approximately 45%; R M From 0.123Ω·cm 2 Reduced to 0.084 Ω·cm 2The decrease was approximately 31%; R H Then from 0.175Ω·cm 2 Significantly reduced to 0.049 Ω·cm 2 The reduction rate reached 72%. The results show that the gradient pore structure constructed by an appropriate amount of pore-forming agent not only effectively promotes oxygen diffusion and surface exchange processes but also significantly enhances charge transfer kinetics at the three-phase interface, thereby achieving a synergistic improvement in the overall ORR performance. Combined with activation energy analysis results, GPE-10 exhibits a lower reaction energy barrier and superior interfacial reactivity, further verifying the effectiveness and rationality of the 10 wt.% pore-forming agent addition in regulating the pore structure of the air electrode.

[0053] The activation energy (Ea) of the oxygen reduction reaction (ORR) for each symmetrical cell was obtained by fitting the Arrhenius curve, as shown in the following results. Figure 3 As shown in (d), the ORR activation energies of GPE-5, GPE-10, GPE-15, and GPE-20 are 1.398, 1.269, 1.332, and 1.269 eV, respectively. Among them, GPE-10 has the lowest activation energy (1.269 eV), indicating that it has the lowest intrinsic energy barrier for the ORR reaction and the most significant reaction kinetic advantage. The activation energies of GPE-20 (1.309 eV) and GPE-15 (1.332 eV) are slightly higher than those of GPE-10, while GPE-5 has the highest activation energy (1.398 eV), indicating that insufficient or excessive addition of pore-forming agent will lead to an increase in the reaction energy barrier and inhibit the ORR kinetic process. It is worth noting that although the activation energies of some samples are relatively similar, the absolute value of the polarization resistance of GPE-10 is still significantly lower than that of other samples across the entire temperature range. This is because the hierarchical porous structure introduced by the 10 wt.% pore-forming agent not only lowers the intrinsic reaction energy barrier but also significantly optimizes the gas mass transfer process, shortens the oxygen diffusion path, and achieves a synergistic improvement in reaction kinetics and mass transfer efficiency.

[0054] (2) Effect of oxygen partial pressure on the performance of GPE-10 air electrode (see Figure 4 a, 4b) EIS tests were performed on the GPE-10 symmetric cell under oxygen partial pressure gradient conditions of 1% to 100% at 650℃, and the impedance spectrum was deconvolved using DRT. The results show that the total polarization resistance of the GPE-10 symmetric cell decreases significantly and continuously as pO2 increases from 1% to 100%: the electrode Rp is 0.458, 0.218, 0.162, 0.152, and 0.136 Ω·cm for pO2 values ​​of 1%, 10%, 20%, 50%, and 100%, respectively. 2Compared to a 1% low-oxygen atmosphere, the Rp decrease was as high as 70.32% under 100% pure oxygen conditions, proving that increasing the oxygen partial pressure can directly enhance the entire process of oxygen adsorption, dissociation, and charge transfer, significantly improving the ORR kinetic rate. With increasing oxygen partial pressure, the polarization resistance corresponding to all three frequency ranges decreased significantly, with the most significant decreases in the low-frequency and mid-frequency regions. This indicates that increasing oxygen concentration has the most prominent promoting effect on oxygen adsorption, dissociation, and surface diffusion processes, comprehensively optimizing the entire ORR reaction pathway.

[0055] (3) Effect of water vapor pressure on the performance of GPE-10 air electrode (see Figure 4 c, 4d) EIS tests were performed on the GPE-10 symmetric cell at 650℃ under a water vapor pressure gradient of 3%–10%. The results showed that the total polarization resistance of the GPE-10 symmetric cell continuously increased with increasing pH2O from 3% to 10%: the electrode Rp values ​​were 0.162, 0.186, and 0.193 Ω·cm at pH2O of 3%, 5%, and 10%, respectively. 2 Compared to a low humidity of 3%, the Rp increase was approximately 19% under a high humidity of 10%, indicating that excessively high moisture pressure inhibits ORR kinetics. DRT analysis showed that the polarization resistance in each frequency range exhibited differentiated evolution with increasing moisture pressure: the peak area in the low-frequency region decreased significantly with increasing moisture pressure, indicating that moderate humidification can improve the wettability of the air electrode surface and promote surface diffusion and transport of oxygen species; however, the polarization resistance in the mid-frequency region corresponding to oxygen adsorption-dissociation processes and the high-frequency region corresponding to interfacial charge transfer processes both showed significant increases, with increases far exceeding the optimization effect in the low-frequency region, ultimately leading to an increase in total polarization resistance. These results confirm that the inhibitory effect of increased moisture pressure on oxygen charge transfer and adsorption-dissociation is dominant. This is because excessive water molecules competitively occupy active sites on the air electrode surface, hindering oxygen adsorption and activation, and interfering with the proton-oxygen coupling reaction pathway, ultimately leading to a decrease in ORR catalytic activity.

[0056] In summary, this invention constructs a bilayer air electrode structure with a porosity gradient. By not adding a pore-forming agent to the inner functional layer and quantitatively introducing a pore-forming agent into the outer diffusion layer, the microstructure of the air electrode can be controllably adjusted. Electrochemical test results show that the pore-forming agent content has a significant impact on the ORR performance of the air electrode. Among them, the GPE-10 air electrode with 10 wt.% pore-forming agent exhibits the best electrochemical performance, with a polarization resistance as low as 0.162 Ω·cm at 650℃ in an air atmosphere. 2Compared to GPE-0 without pore-forming agents, the impedance of GPE-10 decreased by approximately 54%. DRT analysis further showed that GPE-10 exhibited lower impedance contributions in key reaction steps such as oxygen surface diffusion, oxygen adsorption dissociation, and three-phase interfacial charge transfer, indicating that the appropriate construction of a hierarchical porous structure can simultaneously optimize gas transport and interfacial reaction kinetics. Furthermore, Arrhenius fitting results showed that GPE-10 had the lowest ORR activation energy (1.269 eV), indicating a lower intrinsic reaction energy barrier and superior catalytic kinetics. Oxygen partial pressure dependence studies showed that as the oxygen partial pressure increased, the polarization impedance of the GPE-10 air electrode continuously decreased, with a total polarization resistance reduction of 70.32% in the 1%-100% O2 range, indicating that the gradient pore structure can effectively promote oxygen diffusion and surface exchange processes. However, under high water vapor partial pressure conditions, competitive adsorption of water molecules somewhat inhibited oxygen adsorption and charge transfer processes, leading to a slight increase in polarization impedance.

[0057] The bilayer gradient porosity air electrode structure of this invention effectively coordinates the relationship between oxygen diffusion, interfacial reactions, and charge transport, achieving a synergistic improvement in ORR kinetic performance and long-term stability. The pore structure corresponding to 10 wt.% pore-forming agent is most beneficial for optimizing air electrode performance. This study not only reveals the mechanism by which porosity gradient regulation affects the ORR behavior of PCFC air electrodes but also provides important theoretical basis and experimental reference for the structural design and engineering application of high-performance air electrodes in low- and medium-temperature proton ceramic fuel cells.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. An air electrode for a proton fuel cell with a gradient pore structure, characterized in that, The air electrode includes an inner functional layer in contact with the electrolyte layer and an outer diffusion layer disposed outside the inner functional layer. The inner functional layer is prepared using a composite air electrode material without added pore-forming agent to form a low porosity structure; the outer diffusion layer is prepared using a composite air electrode material with added pore-forming agent to form a high porosity structure; wherein, the porosity of the outer diffusion layer is higher than that of the inner functional layer, thereby forming a gradient pore structure that gradually increases from the electrolyte layer side to the air side. The inner functional layer and the outer diffusion layer are both made of air electrode material, which contains PNC and BZCYYb, and the mass ratio of PNC to BZCYYb is 7:

3.

2. The air electrode according to claim 1, characterized in that, Based on the total mass of PNC and BZCYYb in the outer diffusion layer, the mass fraction of the pore-forming agent is 5 wt.% to 20 wt.%.

3. The air electrode according to claim 2, characterized in that, The amount of pore-forming agent added is 10%.

4. The air electrode according to claim 1, characterized in that, The pore-forming agent is corn starch.

5. A proton fuel cell air electrode with a gradient pore structure according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Mix PNC powder and BZCYYb powder at a mass ratio of 7:3, add binder, grind evenly to obtain inner functional layer slurry; S2. Mix PNC powder and BZCYYb powder at a mass ratio of 7:3, add pore-forming agent and binder, and grind evenly to obtain the outer diffusion layer slurry; wherein, based on the total mass of PNC and BZCYYb, the amount of pore-forming agent added is 5wt.% to 20wt.%. S3. The inner functional layer slurry is coated onto the surface of the electrolyte sheet and dried to form the inner functional layer precursor. S4. Coat the outer diffusion layer slurry onto the inner functional layer precursor and dry it to form the outer diffusion layer precursor. S5. The coated electrolyte sheet is calcined to allow the pore-forming agent to evaporate and form pores in the outer diffusion layer, while the inner functional layer and the outer diffusion layer are sintered and solidified to obtain the air electrode.

6. The preparation method according to claim 5, characterized in that, The preparation method of the PNC powder used in steps S1 and S2 is as follows: Weigh out Pr(NO3)3·6H2O, Ni(NO3)2, and Co(NO3)2·6H2O according to the stoichiometric ratio, and dissolve them in deionized water; Add citric acid and EDTA in a molar ratio of metal cation:citric acid:EDTA = 1:1.5:1, and stir to mix. Add ammonia to adjust the pH to 7-8; Stir at 80°C until gelation occurs, and dry at 200°C for 10 hours to obtain a dry gel. The dry gel was ground and then calcined at 1000℃ for 5 hours to obtain PNC powder.

7. The preparation method according to claim 5, characterized in that, The adhesive used in steps S1 and S2 is prepared by mixing terpineol and ethyl cellulose at a mass ratio of 95:5 and stirring magnetically until fully dissolved.

8. The preparation method according to claim 5, characterized in that, In step S5, the calcination process is as follows: the temperature is increased to 500℃ at a rate of 2℃ / min, held for 1 hour, then increased to 1000℃ and held for 5 hours.

9. The preparation method according to claim 5, characterized in that, The electrolyte sheet used in step S3 is prepared by the following method: BZCYYb powder and NiO were mixed at a mass ratio of 99:1, PVB ethanol solution was added as a binder, and the mixture was ground evenly. The ground powder is placed into a circular tableting mold and dry-pressed at 18MPa for 2 minutes. After demolding, the blank is obtained. The blank is placed in a porcelain boat covered with BZCYYb powder, and a layer of BZCYYb powder is covered on top of the blank; The electrolyte tablets are obtained by heating to 450°C at a rate of 2°C / min, holding at that temperature for 2 hours, then heating to 1450°C and calcining for 6 hours.

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