CN114665131B - H for representing oxygen electrode material 3 O + Method of transmissibility - Google Patents

Abstract

The invention relates to a method for characterizing H₃O⁺ transmission of an oxygen electrode material. The method comprises the following steps: step 1, spraying the oxygen electrode material on one side of a Nafion film, and then performing hot pressing on the Nafion film on one side of the oxygen electrode material; spraying Pt/C electrodes on the outer side of the Nafion film to form a Pt/C | Nafion | cathode material | Nafion | Pt/C structure; and assembling carbon paper on two sides of the structure to form a proton exchange membrane fuel cell; and step 2, introducing hydrogen and air on two sides of the proton exchange membrane fuel cell to perform single cell testing, performing impedance testing under an open-circuit voltage, and calculating the H₃O⁺ conductivity through the impedance. According to the method, the electronic insulation characteristic of the Nafion film is utilized, the electron transmission on two sides of an oxide layer is isolated, the interlayer transmission of H₃O⁺ is realized, and the result is evaluated.

Description

A method to characterize the H3O+ transportability of oxygen electrode materials

Technical field

The invention relates to a new four-phase conductor proton conductor oxygen electrode material preparation and high-temperature in-situ characterization method, and more specifically to the optimization of proton conductor solid oxide fuel cell cathode materials and proton conductor solid oxide electrolytic cell oxygen electrode materials.

Background technique

Due to the urgent need to protect the ecological environment and obtain clean energy, solid oxide fuel cells have attracted worldwide attention. On the one hand, they operate cleanly and without pollution, and have extremely high energy conversion efficiency and diverse fuel selectivity. Advantages, on the other hand, are its ability to operate reversibly as a solid oxide electrolytic cell, which can produce hydrogen by electrolyzing water. The development of large-scale industrialization of traditional solid oxide fuel cells/electrolyzers is seriously hampered by extremely high operating temperatures (800-1000°C). Therefore, in order to improve the stability of fuel cells/electrolytic cells, reduce material costs and promote the large-scale industrial application of fuel cells/electrolytic cells, the operating temperature of medium and low temperatures (400-700°C) is its development trend. As the operating temperature decreases, the superiority of proton conductors becomes apparent. Compared with oxygen ion conductors, the advantage of proton conductor solid oxide fuel cells/electrolytic cells is that protons have a smaller ionic radius, so there is less energy during transmission. The activation energy; as the temperature decreases, the proton migration number increases; for proton conductor solid oxide fuel cells, water is generated at the cathode, which does not dilute the fuel gas and increases the recyclability of the fuel; for proton conductor solid oxide fuel cells For solid oxide electrolysis cells, the hydrogen electrode can produce dry pure hydrogen without the need for subsequent processes to remove water vapor. Therefore, the development of proton conductor fuel cell (electrolytic cell) cathode (oxygen electrode) materials is a breakthrough direction in fuel cell research.

However, existing proton conductor oxygen electrode materials still have problems such as low oxygen reduction ability, proton conductivity, and electronic conductivity.

Contents of the invention

The invention provides a high-performance material Na _0.3 Sr _0.7 Ti _0.1 Fe _0.9 O _3-δ (NSTF0.3) that can be used as both a proton conductor solid oxide fuel cell cathode and a proton conductor solid oxide electrolytic cell oxygen electrode. Preparation methods and applications.

The invention also provides a method for testing the diffusion of H ₃ O ⁺ in solid oxide materials. This method utilizes the electronic insulation properties of the Nafion film to isolate electron transmission on both sides of the oxide layer and realize the diffusion of H ₃ O ⁺ Transfer between layers and evaluate the results.

The invention also provides a method for detecting whether water vapor enters the bulk phase of the proton conductor solid oxide fuel cell cathode material during the working process. The target material of this method is the cathode, and Ag is the anode. Through directional current output and input, the cathode electrons are realized The outflow of electrons from the anode is the same as the electron transmission state in the actual working state, realizing the replication of the cathode reaction. Through synchrotron radiation testing, the electronic structure changes of the material and the metal valence state changes when the electrode reaction occurs are observed, and the water vapor affinity is finally detected.

An oxide material whose molecular structural formula is: Na _x Sr _1-x Ti _0.1 Fe _0.9 O _3-δ , x=0.05<x<0.5, δ represents the oxygen vacancy content, and the main phase in the oxide is perovskite phase, and also contains the additional phase β-NaFeO ₂ (NF).

0≤δ≤1.

The preparation method of the oxide material is through a sol-gel method.

The preparation process of the sol-gel method includes: adding tetrabutyl titanate and citric acid monohydrate into deionized water, heating and dissolving, then mixing the two with sodium nitrate and ferric nitrate, dissolving and heating and stirring; adding acetate. diamine tetraacetic acid, and then dropwise add ammonia water until the pH of the solution is between 7 and 8, evaporate the water under heating and stirring conditions to obtain a gel-like substance; place the gel-like substance in an oven to dry to obtain the cathode material precursor The precursor is then roasted in a muffle furnace to obtain the oxide material.

The total molar ratio of ethylenediaminetetraacetic acid and citric acid to metal ions (sodium, strontium, titanium and iron) is 2:0.5-1.5:0.5-1.5.

The roasting parameters are 950-1050℃ for 1-10h.

Application of the above-mentioned oxide materials in solid oxide fuel cells and/or solid oxide electrolytic cells.

In solid oxide fuel cells, BaZr _0.1 Ce _0.7 Y _0.1 Yb _0.1 O ₃ is used as the electrolyte.

In the solid oxide electrolytic cell, the hydrogen electrode material uses a composite electrode composed of NiO and BaZr _0.1 Ce _0.7 Y _0.1 Yb _0.1 O ₃ (BZCYYb). The mass ratio of NiO and BZCYYb in the composite hydrogen electrode is (3-5):( 5-7).

A method for characterizing the H ₃ O ⁺ transportability of oxygen electrode materials, including the following steps:

Step 1: Spray oxygen electrode material on one side of the Nafion film, and then hot-press the Nafion film on one side of the oxygen electrode material; spray Pt/C electrode on the outside of the Nafion film to form Pt/C | Nafion | cathode material | Nafion|Pt/C structure; carbon paper is assembled on both sides of the structure to form a proton exchange membrane fuel cell;

Step 2: Pass hydrogen and air on both sides of the proton exchange membrane fuel cell to conduct a single cell test, conduct an impedance test under open circuit voltage, and calculate the H ₃ O ⁺ conductivity through the impedance.

The oxygen electrode material loading is 0.025gcm ^-2 , and the Pt loading in the Pt/C catalyst is 0.1mgcm ^-2 .

The test temperature of the proton exchange membrane fuel cell is 60-80°C, and 1-5vol.% water vapor is added to both sides of the cathode and anode at the same time.

When spraying Pt/C electrodes, the mass ratio of Pt/C to solvent in the slurry is 0.1-5:100, and the solvent is an alcohol solvent.

When spraying oxygen electrode material, the ratio of oxygen electrode material and solvent in the slurry is 0.5g oxygen electrode material: 5-20mL solvent; the solvent is an alcohol solvent.

A method for detecting the proton absorption capacity of a proton conductor solid oxide fuel cell cathode material under working conditions, including the following steps:

Step 1: Spray oxygen electrode material on one side of the electrolyte, and then apply silver on the other side of the electrolyte after calcination;

Step 2: Connect both sides of the electrolyte to a closed loop, apply current under low and high temperature conditions respectively, and measure the K-edge characteristics of the Fe element in fluorescence mode;

Step 3. Repeat the test in Step 2 in a water vapor environment;

If the valence state of Fe rebounds under water vapor conditions, it is determined that the bulk phase of the material can absorb protons.

In step 1, the step of spraying the oxygen electrode material is: after preparing a slurry containing oxygen electrode powder, spray it on the electrolyte side; the concentration of the oxygen electrode powder in the slurry is 5-20wt%.

Alcohol solvents, ether solvents, benzene solvents or ester solvents are used in the slurry.

In the described step 1, the calcining conditions are 800-1200°C for 1-5 hours; the electrolyte is BZCYYb.

In the step 2, the low temperature is room temperature and the high temperature is 400-500°C.

In the step 2, the water vapor environment refers to the 1-5vol.% water vapor environment.

beneficial effects

(1) Through proton exchange membrane fuel cell testing, the one with NSTF0.3 oxide as the intermediate layer has achieved relatively excellent performance, reaching 126mW/cm ² at 70°C, and has a H ₃ O ⁺ conductivity of 0.022S/cm.

(2) Solid oxide fuel cell cathode/solid oxide electrolytic cell oxygen electrode material NSTF0.3 prepared by sol-gel method. With high battery output performance, the output power of single cells prepared with Ni-BZCYYb as anode support reached 1118mW cm ^-2 under the optimal water vapor conditions of 650℃, 600℃, 550℃, 500℃, 450℃ and 400℃ respectively. , 807mW cm ^-2 , 605mW cm ^-2 , 427mW cm ^-2 , 268mW cm ^-2 , 143mW cm ^-2 .

(3) Through the proton exchange membrane fuel cell testing method, we found that there is H3O+ transport between the two phases of NSTFx, which improved the cathode proton transport capability.

(4) For proton conductor solid oxide fuel cells, the generation of cathode water vapor will dilute the air and reduce the oxygen partial pressure, which is not conducive to the surface diffusion of oxygen. The highest value of cathode performance can be sought by controlling the surface water vapor concentration.

(5) Through the impregnation of surface oxygen active material SrCoO _3-δ , the surface oxygen activity ability was strengthened, and a proton conductor material with both proton transport and high oxygen activation ability was obtained;

(6) In the electrolysis mode, it was found that the solid oxide electrolytic cell using NSTFx as the oxygen electrode also achieved excellent performance, indicating that its excellent proton transport capability also enables it to be used as an oxygen electrode material for the solid oxide electrolytic cell.

Description of the drawings

Figure 1 is the refined XRD pattern of NSTFx at room temperature;

Figure 2 is the SEM and FIB-TEM images of NSTF0.3;

Figure 3 shows the performance of a proton exchange membrane fuel cell with oxide as the intermediate layer and the H ₃ O ⁺ conductivity of each material;

Figure 4 is a SEM image of the oxide layer of a proton exchange membrane fuel cell;

Figure 5 is the desorption diagram of heated water after NSTF0.3 and comparative materials were treated with water at 250°C and 500°C respectively;

Figure 6 is the high-temperature in-situ synchrotron radiation data diagram and on-site device diagram of NSTF0.3 and NSTF0 cathode materials;

Figure 7 shows the active site distribution of the cathode material at 600°C;

Figure 8 is the impedance diagram of the cathode material at various temperatures under 5% water vapor conditions;

Figure 9 shows the performance diagram of cathode NSTF0.3 under different cathode atmospheres;

Figure 10 shows the impedance and optimal battery performance of the cathode NSTF0.3 after SC impregnation, the cross-sectional view of the single cell, and the cathode pore channel morphology after SC impregnation.

Figure 11 is the I-V curve of the solid oxide electrolytic cell at 600 degrees under different water pressures on the oxygen electrode side.

Figure 12 shows the change of Faradaic efficiency with current density at 500 and 550°C when the water pressure on the oxygen electrode side of the solid oxide electrolytic cell is 80%.

Figure 13 is a schematic diagram of the technical concept of this patent.

Detailed ways

The invention involves a series of design optimization strategies for proton conductor oxygen electrode materials. The iron-based perovskite SrTi _0.1 Fe _0.9 O _3-δ is doped with A-site Na to prepare a product with the molecular formula of Na _x Sr _1-x Ti _0.1 Fe _0.9 O _3-δ (NSTFx,x=0,0.1,0.2,0.3 and 0.4) oxygen electrode materials, where δ represents the oxygen vacancy content, belongs to the field of solid oxide fuel cell cathodes and solid oxide electrolytic cell oxygen electrode materials. The single cell performance is improved through three optimization strategies: ion doping, surface water vapor partial pressure control and oxygen active material impregnation. Through preparation, NSTF0.3 achieved the best performance, a composite oxygen electrode material composed of the main phase perovskite phase and the additional phase β-NaFeO ₂ (NF). And we discovered a new form of proton transport, interlayer transport of H ₃ O ⁺ . Such a four-phase conductivity (H ₃ O ⁺ /H ⁺ /O ^2- /e ^- ) will greatly improve oxygen Electrode performance, and provide optimization ideas for the design of proton conductor solid oxide fuel cell cathodes and solid oxide electrolytic cell oxygen electrode materials. At the same time, high-temperature in-situ synchrotron radiation was used to characterize the material, and its material electrode structure changes in the working environment were analyzed.

The design concept of the above materials is: NSTFx uses the parent material Sr _0.9 Ti _0.1 Fe _0.9 O _3-δ , which has a certain oxygen activation ability and is used in oxygen ion solid oxide fuel cells. However, in the proton conductor solid oxidation The fields of fuel cells and proton conductor solid oxide electrolytic cells have not been optimized and applied. The present invention found that by doping the A-site of the cheap Na element, the function is enhanced in proton absorption and transmission; and by stripping out the second phase β-NaFeO ₂ (NF) during phase formation at high temperature, the proton absorption capacity is enhanced, and it is expected that Provides ion transport between two-phase layers; at the same time, the emergence of the second phase will provide dispersed oxygen and water vapor active sites under specific water vapor, maximizing the utilization of active sites. Through multi-phase material modification, we continuously make up for the lack of characteristics of proton conductor electrodes and obtain excellent proton conductor electrode materials.

Preparation of low-temperature proton conductor oxygen electrode material Na _x Sr _1-x Ti _0.1 Fe _0.9 O _3-δ (x=0, 0.1, 0.2, 0.3 and 0.4) in Example 1

(1) Weigh 1.7015g of tetrabutyl titanate and 42g of citric acid monohydrate, add 50mL of deionized water, heat and stir to dissolve until a clear solution;

(2) Weigh 0.4250g, 0.8499g, 1.2749g, and 1.6999g of sodium nitrate (no sodium nitrate is added when until dissolved;

(3) Weigh 29g of ethylenediaminetetraacetic acid as a complexing agent and add it to the solution containing dissolved metal ions. Add an appropriate amount of ammonia dropwise to bring the pH of the solution to between 7 and 8, and then stir it under magnetic stirring until the water is complete. Evaporation gives a gel-like substance;

(4) Place the gel-like material in an oven and calcine at 180°C for 5 hours to obtain the required foam precursor;

(5) Place the precursor in a high-temperature muffle furnace and calcine at 1000°C for 5 hours to obtain the required oxygen electrode powder.

Example 2 Preparation of comparative material β-NaFeO ₂

(1) Weigh 4.2495g of sodium nitrate and 20.2g of iron nitrate respectively and put them into deionized water and stir until dissolved;

(2) Weigh 29g of ethylenediaminetetraacetic acid and 42g of citric acid monohydrate as complexing agents and add them to the solution containing dissolved metal ions. Add an appropriate amount of ammonia dropwise to bring the pH of the solution to between 7 and 8, and then stir with magnetic force. Stir the water under the conditions to completely evaporate and obtain a gel-like substance;

(3) Place the gel-like material in an oven and calcine at 180°C for 5 hours to obtain the required foam precursor;

(4) Place the precursor in a high-temperature muffle furnace and calcine at 1000°C for 5 hours to obtain the required oxygen electrode powder.

Material characterization

1.XRD characterization

Area a in Figure 1 is the XRD pattern of NSTFx series cathode materials at room temperature. It can be seen from the figure that when not doped with Na element, NSTF0 presents a cubic perovskite single-phase material. With a little Na doping, NSTF0. 1 can still maintain the pure cubic perovskite phase, but when the Na ratio exceeds 0.2, a second phase is desolvated from the matrix. After XRD verification, it is the NF phase, and as the doping ratio of Na increases, the second phase The relative peak intensity of the two phases is improved.

Areas b, c, d, e, and f in Figure 1 are the XRD refinement results of NSTF0-NSTF0.4 respectively. By increasing the doping ratio of Na, the proportion of NF phase also increases accordingly.

Through Na doping, the parent single-phase cubic perovskite strips out the second phase and becomes a composite oxygen electrode material. The addition of the second phase will enhance the proton absorption capacity of the oxygen electrode material and form interlayer proton species transmission.

2. Powder morphology characterization analysis

Picture a in Figure 2 is the SEM picture of NSTF0.3. The second phase NF is in the form of nanosheets covering the large perovskite particles.

b, c, and d of Figure 2 are FIB-TEM images. It is found that not only is there an NF phase on the surface, but there is also a nanoscale NF phase embedded in the perovskite phase on the near inner surface of the perovskite.

The e picture in Figure 2 shows the element mapping analysis of FIB-SEM, which verifies that the NF phase is formed on the surface and bulk surface.

Proton exchange membrane battery testing using oxide as ion transport layer

(1) Pour 0.5g of oxygen electrode powder and 10mL of isopropyl alcohol into a high-energy ball mill. After ball milling at 400r/min for 30 minutes, use a straw to transfer to the strain bottle to obtain the required oxygen electrode slurry;

(2) Add commercial Pt/C and isopropyl alcohol into the strain bottle at a mass ratio of 1:99 and use ultrasound to disperse evenly;

(3) Spray the oxygen electrode material using a thermal spray machine (Siansonic UC 320). At 75°C, take 2 mL of slurry and spray it on the commercial Nafion membrane (Dupont, USA), with an effective area of 4 cm ² ;

(4) Cover the oxide layer with another Nafion film and press it with a hot press to form a (Nafion | oxide layer | Nafion) sandwich structure;

(5) Use a thermal spray machine to spray Pt/C slurry (6 mg 20% Pt/C, 40 mg Nafion and 2 mL isopropyl alcohol ultrasonically mixed) on both sides of the three-layer film, so that the Pt loading on both sides is 0.1 mg cm ^-2 ;

(6) Finally, the edges are sealed with polytetrafluoroethylene, and carbon paper is used as the electron current collector and gas diffusion layer on both sides, and assembled into a proton exchange membrane fuel cell with a solid oxide as the middle spacer layer;

(7) Conduct a single cell test by passing high-purity hydrogen and high-purity air on both sides, and conduct an impedance test under open circuit voltage.

Diagram a of Figure 3 is a schematic structural diagram of a proton exchange membrane. A proton exchange membrane battery using oxide as the proton species diffusion layer was designed to isolate the electronic conductivity of the oxide while studying whether there is H between the oxide layers. ₃ Diffusion of O ⁺ . Due to the electronic insulation properties of the Nafion film, it isolates electron transmission on both sides of the oxide layer and meets the electronic insulation requirements of the electrolyte in the proton exchange membrane battery. At the same time, protons exist in the form of H ₃ O ⁺ in the Nafion film. At low temperatures, proton transport in the oxide bulk phase is almost impossible to achieve. Proton diffusion on the surface is the best choice, and interlayer transport of H ₃ O ⁺ is the best choice. Maximum possible proton transport. Due to the water absorption capacity of the oxide, protons will use water as the transmission medium on the surface to realize interlayer transport of H ₃ O ⁺ , and due to the difference in their water adsorption capacity, the proton transmission capacity is different.

Figure 3 b, c, d, and e are performance diagrams of proton exchange membrane single cells with various oxides as intermediate layers. Through single cell testing, it was found that the performance of proton exchange membrane batteries without oxide intermediate layers is much greater than that of other proton exchange membrane batteries with oxides as the intermediate layer. The performance of the proton exchange membrane single cell with NSTF0.3, NSTF0 and β-NaFeO ² as the middle layer is 126mW/ ^cm2 , 5mW/ ^cm2 and 13.5 respectively _. mW/cm ² , it can be seen from the results that there is almost no H ₃ O ⁺ conduction in the single-phase perovskite bulk phase and grain boundaries. Similarly, H ₃ O ⁺ conduction in the β-NaFeO ₂ bulk phase and grain boundaries is also very weak. However, when the two phases are combined, there is excellent H ₃ O ⁺ conduction between the two phase layers.

The f diagram in Figure 3 is the ohmic impedance of each proton exchange membrane single cell tested at the open circuit voltage. It can be seen from the figure that NSTF0.3 has the best H ₃ O ⁺ conduction.

The g diagram in Figure 3 is the H ₃ O ⁺ conductivity calculated from the impedance. The H ₃ O ⁺ conductivity between the NSTF0.3 two-phase layers is much higher than that of the other two single-phase materials.

Figure 4 is a cross-sectional view of the oxide layer of each proton exchange membrane single cell in which the oxide is the intermediate layer. By placing it in liquid nitrogen for 30 seconds and then cutting the section with a blade, we can obtain a cross-section with a relatively good morphology. Through SEM As can be seen from the figure, the thicknesses of the NF, NSTF0, and NSTF0.3 oxide layers are 23.8 microns, 48 microns, and 65.2 microns respectively. By measuring the thickness, we can calculate the ionic conductivity.

Effect of the presence of water vapor on oxygen transport properties

The influence of materials on oxygen transport in the presence of water vapor was investigated through programmed temperature desorption experiments of water and oxygen.

Picture a in Figure 5 shows a powder sample that was treated with 20vol.% H ₂ O-80vol.% air at 250°C for 3 hours, and then quenched to room temperature. The sample was then subjected to a temperature-programmed desorption experiment of H ₂ O. We found that NSTF0.3 has the largest and sharpest desorption peak, proving that a large amount of water vapor is stored at the two-phase interface and has rapid interlayer water vapor transport capabilities.

Picture b in Figure 5 shows that the powder sample was treated at 500°C with 20vol% H ₂ O-80vol% air for 3 hours, then quenched to room temperature, and then the sample was subjected to a temperature-programmed desorption experiment of H ₂ O. With the increase of the second phase NF phase, the material's ability to store water vapor becomes stronger and stronger, proving that at 500°C, water vapor still exists at the two-phase interface, which is consistent with the water vapor absorption that can occur within the battery operating temperature range.

Picture c in Figure 5 shows a powder sample that was treated at 250°C with 20vol% H ₂ O-80vol% air for 3 hours, then quenched to room temperature, and then the sample was subjected to a temperature-programmed O ₂ desorption experiment. We found that NSTF0.3 also has a desorption peak of O ₂ at 271°C, indicating that water vapor and oxygen are desorbed at the same time, and the two species have different adsorption sites.

Picture d in Figure 5 shows that the powder sample was treated at 250°C, 20vol% H ₂ O-80vol% air for 3 hours, and then quenched to room temperature. The sample was then subjected to a programmed temperature rise desorption experiment of O ₂ and a direct O desorption experiment without water vapor treatment. Comparison of programmed temperature desorption experiments of ₂ . We found that the desorption temperature of NSTF0 moved backward after water vapor treatment, indicating that water vapor absorption affected the desorption of oxygen, and the two species competed for adsorption.

It can be seen that the NSTF0.3 material can effectively avoid the impact on the oxygen transport performance of the material in the presence of H ₂ O. Testing of changes in electronic structure of proton conductor solid oxide fuel cell cathode materials under operating conditions

In-situ synchrotron radiation testing using high-temperature proton conductor oxygen electrode:

(1) Weigh 1g of the oxygen electrode powder NSTF0.3 prepared in Example 1, 10ml of isopropyl alcohol, 2ml of ethylene glycol, and 0.8ml of glycerin, pour them into a high-energy ball mill, and grind at 400r/min. After ball milling for 30 minutes, use a straw to transfer to the strain bottle to obtain the required oxygen electrode slurry.

(2) Grind the edge of the BZCYYb electrolyte sheet into a disc with a diameter of 1cm, place it on the heating table and preheat it at 200°C, and use a spray gun to evenly spray the prepared oxygen electrode slurry on the electrolyte under the push of inert gas. On one side of the surface, after the liquid has completely evaporated, place the sprayed half-cell in a high-temperature muffle furnace and calcine at 1000°C for 2 hours;

(3) Apply silver paste to the other side of the BZCYYb battery, and connect silver wires on both sides to form a (NSTF0.3|BZCYYb|Ag) battery structure;

(4) Place the battery in a high-temperature in-situ synchrotron radiation device, and connect the oxygen electrode side and Ag electrode side wires to the electrochemical workstation for testing;

(5) At room temperature and high temperature of 450°C, current is applied on both sides. Dry air and humid air (3vol.% H ₂ O) are passed through the high-temperature device cavity. Oxygen reduction reaction occurs on the oxygen electrode material side, and the oxygen electrode surface is synchronized. Radiation test, test conditions fluorescence mode test Fe element K-edge; here, the target material is used as the cathode and Ag is the anode. Through directional current output and input, the outflow of cathode electrons and the outflow of anode electrons are realized, which is consistent with the actual working state of electron transmission. The same, achieving replication of the cathode reaction. Through synchrotron radiation testing, the electronic structure changes of the material and the metal valence state changes are observed when the electrode reaction occurs. The K-edge test of Fe is often used to observe the valence state and electronic structure of Fe ions. The high-energy shift of the peak position is the valence state. The rise and fall of the diffraction peak in R space represents the change in the coordination number of anions/cations bonded to Fe ions. Here is the change in the coordination number of Fe-O. The upward shift of the peak indicates the increase in the coordination number of Fe-O.

Pictures a and b in Figure 6 are the synchrotron radiation patterns of the NSTF0 material at room temperature and high temperature in situ. After heating, the valence state of Fe decreased. This was due to the generation of oxygen vacancies. After passing water, it was found that the valence state of Fe increased, but it was not obvious enough. As shown in Figure b, the Fe-O coordination peak increases with the The increase in temperature has weakened, and the loss of coordination bonds caused by the temperature rise and desorption of lattice oxygen has not rebounded significantly with the increase of water vapor. This shows that during the actual process of NSTF0 cathode, water vapor has not entered the bulk phase, and will It is very likely to compete with oxygen for adsorption.

Pictures c and d in Figure 6 are synchrotron radiation patterns of NSTF0.3 material at room temperature and high temperature in situ. After the temperature rises, the valence state of Fe decreases. This is due to the generation of oxygen vacancies. After passing water, it is found that the valence state of Fe rebounds significantly. From the d figure, it can be seen that the Fe-O coordination peak weakens as the temperature rises. , the loss of coordination bonds caused by the temperature rise and desorption of lattice oxygen has rebounded significantly with the increase of water vapor. This shows that during the actual process of NSTF0.3 cathode, water vapor undergoes a violent hydration reaction on the surface, and the oxygen vacancies are filled. , causing the valence state of surrounding Fe to recover. It is proved that NSTF0.3 is extremely attached to water vapor, which is conducive to the surface formation and adsorption of H ₃ O ⁺ .

ASR test under water vapor conditions

(1) Weigh 1g of the oxygen electrode powder NSTF0.3 prepared in Example 1, 10ml of isopropyl alcohol, 2ml of ethylene glycol, and 0.8ml of glycerin, pour them into a high-energy ball mill, and grind at 400r/min. After ball milling for 30 minutes, use a straw to transfer to the strain bottle to obtain the required oxygen electrode slurry.

(2) Place the prepared BZCYYb and SDC electrolytes on the heating table to preheat at 200°C. Use a spray gun to evenly spray the prepared oxygen electrode slurry on both sides of the electrolyte under the push of inert gas, and wait until the liquid evaporates. After completion, the sprayed electrolyte is placed in a high-temperature muffle furnace and calcined at 1000°C for 2 hours to obtain the required symmetrical battery, which can be used to test the polarization impedance of oxygen electrode materials in the temperature range of 500 to 700°C.

(3) Weigh 6.3489g strontium nitrate, 8.7309g cobalt nitrate and 6.7563g glycine, dissolve them into a clear solution with 100mL of deionized water, measure 20mL of the solution and 5mL of absolute ethanol to form an impregnation solution;

(4) Use a dropper to take the impregnation solution and drop it into the cathode skeleton three times. The first two times are at 400°C for 30 minutes, and the last time is at 700°C for 2 hours. Prepare the required symmetrical battery for testing the polarization impedance of oxygen electrode materials in the temperature range of 500 to 700°C.

Panel a of Figure 7 shows the electrode polarization ASR diagram of each electrode material of the SDC-supported symmetrical battery under dry air, and evaluates the ORR activity of each material in the absence of proton carriers. Under these conditions, the single-phase STF electrode produced the lowest ASR, and the ASR increased with increasing Na content in the NSTFx nanocomposite electrode until the ASR began to decrease after x reached 0.2. Panel b of Figure 7 shows the DRT analysis of dry air at 600°C. The DRT spectrum shows three different peaks, corresponding to three different electrocatalytic processes. The small peak in the high frequency band near 1000Hz may be related to the charge transfer process at the electrode/electrolyte interface. The peaks appearing in the frequency range of 100-300Hz are likely related to the ion diffusion within the bulk phase of the porous oxygen electrode. Finally, we attribute the large peaks in the frequency range from 1-100 Hz to the combined effects of _O2 adsorption/desorption, dissociation, surface O2 ^- diffusion, and ^O2 gas diffusion. The size and shape of the high-frequency and mid-frequency peaks are similar for all samples. However, the size and position of the low-frequency band peaks shift significantly with changes in Na content, indicating that the incorporation of Na (and/or the formation of ORR inactive NF second phase) may have adverse effects on oxygen ion surface transport and the reaction of surface active oxygen species. As the amount of Na doping increases, the low-frequency peak first increases (until x=0.2) and then decreases, while its position continues to move toward low frequency. In the ch diagram of Figure 7, the low-frequency peak in the DRT spectrum is most affected. It can be concluded that the adsorbed water will negatively affect the adsorption of oxygen and the surface reaction process. As shown in the i diagram of Figure 7, the comparison of ASR under different water vapor and ASR under dry air for SDC symmetrical cells. ASR increases with the increase of water vapor content, and for most electrode compounds, the relative ASR increase is usually Between 1.5-2.5 times. However, the ASR increase of the NSTF0.3 electrode at low water vapor content was significantly smaller, with a relative increase of 1.17 times in 2.5 vol.% H ₂ O and a relative increase of 1.23 times in 5 vol. % H ₂ O. This shows that the NSTF0.3 electrode can achieve an optimal balance between the ORR activity provided by the NSTF phase and the water absorption capacity provided by the NF phase, thereby minimizing the competition between oxygen and water adsorbates under low water vapor partial pressure conditions. , this finding is also consistent with the results of H ₂ O-TPD.

Proton Conductor Performance Test

Preparation of single cells and electrolytic cells

(1) Weigh 1g of the powder NSTF0.3 prepared in Example 1, 10ml of isopropyl alcohol, 2ml of ethylene glycol, and 0.8ml of glycerin, pour them into a high-energy ball mill, and grind at 400r/min. After 30 minutes, use a pipette to transfer to the strain bottle to obtain the required oxygen electrode slurry.

(2) Place the prepared dry-pressed battery sheet on a heating table and preheat it at 200°C. Use a spray gun to evenly spray the prepared oxygen electrode slurry on the electrolyte surface of the dry-pressed sheet under the push of inert gas. After the liquid has completely evaporated, the sprayed dry-pressure battery is placed in a high-temperature muffle furnace and calcined at 1000°C for 2 hours to obtain the required single cell, which is used for oxygen electrode materials in the temperature range of 400 to 650°C. and electrolytic cell performance testing.

(3) Use a dropper to take the impregnation solution and drop it into the cathode skeleton three times. The first two times are 400°C for 30 minutes, and the last time is 700°C for 2 hours. Prepare the required symmetrical battery for single cell performance testing of oxygen electrode materials in the temperature range of 400 to 600°C. To prepare the impregnation solution, dissolve strontium nitrate, cobalt nitrate and glycine in 100mL of deionized water at the concentrations of 0.3mol L ^-1 , 0.3mol L ^-1 and 0.9mol L ^-1 respectively. Take 20mL of the ionic solution and 5mL of anhydrous water. Ethanol mix.

Figure 8 shows the impedance diagram of the oxygen electrode material at various temperatures under 5% water vapor. In this case, the ORR and hydration reactions occur simultaneously, and the proton carrier plays a role in electrochemistry. Under these conditions, the single-phase STF electrode produced the maximum ASR, which decreased significantly for a range of NSTFx cathodes, reaching the minimum for NSTF0.3.

Figure 9 shows the performance diagram of the oxygen electrode material NSTF0.3 under different oxygen electrode atmospheres. Under static air, NSTF0.3 obtained power outputs of 97mW cm ^-2 to 770mW cm ^-2 in the temperature range of 400-650℃. . After flowing air was introduced, a power output of 143mW cm ^-2 to 1116mW cm ^-2 was obtained in the temperature range of 400-650°C. It can be seen that when the water vapor content in the cathode cavity is controlled to a certain extent, the maximum power output can be obtained. Optimized performance.

Figure 10 a shows the impedance of the oxygen electrode material NSTF0.3 after SC impregnation and the optimal battery performance diagram. The PPD of the NSTF0.3@SC single cell at 600°C is 966mW cm ^-2 and the optimal air flow rate is 550mL. min ^-1 , while the standard NSTF0.3 battery has a PPD of 807mW cm ^-2 at an optimal air flow rate of 400mL min ^-1 . Picture b shows the morphology of the oxygen electrode pore channel. The higher optimal air flow rate that the SC-impregnated single cell can withstand also indicates that the three-phase oxygen electrode has better water absorption capacity than the two-phase NSTF0.3. ASR of NSTF0.3@SC in humid air (5 vol.% H ₂ O) on BZCYYb electrolyte and symmetric cells in dry air on SDC electrolyte both showed that SC catalyst impregnation significantly enhanced the ORR activity.

Figure 11 is a graph showing the electrolysis performance of oxygen electrode material NSTF0.3 under different oxygen electrode atmospheres. At 600°C, when the air moisture pressure on the oxygen electrode side increases from 10vol.% to 80vol.%, the power density of the electrolytic cell at 1.28V rises from -1.22Acm ^-2 to -1.42A cm ^-2 . This is due to the As the humidity on the oxygenated electrode side increases, the ohmic impedance and polarization impedance of the electrolytic cell decrease.

Figure 12 shows the Faradaic efficiency of a solid oxide electrolytic cell using NSTF0.3 as the oxygen electrode, BZCYYb as the electrolyte, and NiO+BZCYYb as the hydrogen electrode at different temperatures and different current densities. As the current density increases, the Faradaic efficiency increases rapidly at first and then gradually decreases. When the current density is -0.5A cm ^-2 , the Faradaic efficiency is as high as 98%, and the hydrogen production rate at this time is greater than 3.3mL min ^-1 cm ^-2 , demonstrating the great potential of NSTF0.3 as an oxygen electrode in solid oxide electrolytic cells. Advantage.

Claims (8)

1. H for representing oxygen electrode material ₃ O ⁺ A method of transmissibility comprising the steps of:

step 1, spraying an oxygen electrode material on one side of a Nafion film, and hot-pressing the Nafion film on one side of the oxygen electrode material; spraying Pt/C electrodes on the outer sides of the Nafion films respectively to form a Pt/C|Nafion|oxygen electrode material|Nafion|Pt/C structure; respectively assembling carbon paper on two sides of the structure to form a proton exchange membrane fuel cell;

step 2, hydrogen and air are respectively introduced into two sides of the proton exchange membrane fuel cell to test single cellsImpedance test under open circuit voltage and calculation of H by impedance ₃ O ⁺ Conductivity of the material;

the molecular structural formula of the oxygen electrode material is as follows: na (Na) _x Sr _1-x Ti _0.1 Fe _0.9 O _3-δ ，0.2<x<0.4, delta is more than or equal to 0 and less than or equal to 1; delta represents the oxygen vacancy content and the oxide is composed of a main phase perovskite phase and an additional phase beta-NaFeO ₂ Composition is prepared.

2. The method for characterizing H of an oxygen electrode material according to claim 1 ₃ O ⁺ A method for transporting an oxygen electrode material, characterized in that the oxygen electrode material is supported in an amount of 0.025 g/cm ^-2 。

3. The method for characterizing H of an oxygen electrode material according to claim 1 ₃ O ⁺ The transmissibility method is characterized in that the testing temperature of the proton exchange membrane fuel cell is 60-80 ℃.

4. The method for characterizing H of an oxygen electrode material according to claim 1 ₃ O ⁺ The transmission method is characterized in that 1-5vol.% of water vapor is simultaneously added to both sides of the anode and cathode of the proton exchange membrane fuel cell.

5. The method for characterizing H of an oxygen electrode material according to claim 1 ₃ O ⁺ The transmissibility method is characterized in that when the Pt/C electrode is sprayed, the mass ratio of Pt/C to solvent in the slurry is 0.1-5:100.

6. the method of characterizing H of an oxygen electrode material according to claim 5 ₃ O ⁺ A method of transmissibility, characterized in that said solvent is an alcoholic solvent.

7. The method for characterizing H of an oxygen electrode material according to claim 1 ₃ O ⁺ The transmissibility method is characterized in that when the oxygen electrode material is sprayed, the ratio of the oxygen electrode material to the solvent in the slurry is 0.5g of the oxygen electrode material: 5-20mL of solvent.

8. The method for characterizing H of an oxygen electrode material according to claim 7 ₃ O ⁺ A method of transmissibility, characterized in that said solvent is an alcoholic solvent.