Lithium-doped perovskite oxygen reduction electrocatalyst and preparation method thereof

Abstract

The invention provides a lithium-doped perovskite oxygen reduction electrocatalyst and a preparation method thereof, the prepared catalyst is based on a perovskite structure, and the electrocatalytic performance of the catalyst is optimized through lithium doping. The preparation method comprises the following specific steps: dissolving lanthanum salt, lithium salt and manganese salt in ultrapure water, adding citric acid and ethylene glycol, adjusting the pH to be alkaline, then evaporating to dryness at high temperature to form sol, and continuously heating to convert into gel; and drying the obtained gel to generate a precursor, grinding, and calcining at high temperature to finally prepare catalyst powder. According to the invention, LaxLi1-xMnO3 is prepared through lithium doping, so that the activity of perovskite in electrocatalytic oxygen reduction reaction is improved, and thinking and direction are provided for application of perovskite in oxygen reduction reaction (ORR) and fuel cells.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly to a lithium-doped perovskite oxygen reduction electrocatalyst and a preparation method thereof. Background Art

[0002] The rapid development of electrochemical energy conversion and storage technologies is crucial for achieving carbon neutrality. Among them, the development of fuel cell (FCs) technologies, including low-temperature proton exchange membrane fuel cells (LT-PEMFCs) and high-temperature proton exchange membrane fuel cells (HT-PEMFCs) technologies, has attracted the attention of many researchers due to their advantages such as environmental friendliness, high power energy density, and diverse application scenarios.

[0003] However, FCs still face certain challenges and problems in the actual application process. In particular, the oxygen reduction reaction with slow reaction kinetics seriously affects the overall reaction rate of FCs. Therefore, the improvement of the kinetics of ORR is particularly important. Although the traditional platinum-carbon (Pt / C) catalyst has good ORR activity, its high cost and scarce raw materials limit its large-scale application. In this regard, it is still very necessary to develop low-cost and high-activity ORR catalysts.

[0004] Perovskite-type oxide materials ABO3 (such as LaMnO3) are potential electrocatalytic material candidates due to their advantages such as a wide range of constituent elements, flexible structures, and low prices. However, their poor intrinsic activity still cannot meet the actual application of ORR. Therefore, the activity of improving the catalytic activity of perovskite-type oxide materials ABO3 is still worthy of in-depth study.

[0005] Currently, there are few studies on perovskite oxide materials ABO3 in the electrocatalytic oxygen reduction reaction, and most of the research directions focus on doping (A, B, AB sites), oxygen vacancy regulation, structure optimization, and material modification, which have certain limitations for improving their electrocatalytic oxygen reduction activity. Based on this, the present invention proposes a method for optimizing the ORR activity of perovskite oxide materials (ABO3) by lithium doping. Summary of the Invention

[0006] The purpose of the present invention is to provide a lithium-doped perovskite oxygen reduction electrocatalyst and a preparation method thereof. By doping lithium in LaMnO3 (LMO) to form La x Li 1-x MnO3, the crystal plane spacing of LMO is changed, thereby achieving an improvement in the ORR activity of LMO.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A lithium-doped perovskite oxygen reduction electrocatalyst with the chemical formula La x Li 1-x MnO3, where 0.1 ≤ x ≤ 0.9. Preferably, 0.4 ≤ x ≤ 0.9.

[0009] A preparation method of a lithium-doped perovskite-type oxygen reduction electrocatalyst, comprising the following preparation steps:

[0010] (1) Dissolve lanthanum salt and lithium salt in water, and then add manganese salt with the sum of the molar amounts of lanthanum salt and lithium salt to form a mixed salt solution;

[0011] (2) Add citric acid and ethylene glycol to the mixed salt solution, stir and mix evenly, then add ammonia water to adjust the pH of the solution to 8 - 12, heat and stir until the solution evaporates to dryness to form a gel state, and continue to dry to obtain a solid precursor;

[0012] (3) Grind the solid precursor into powder, heat it at 350 - 500 °C and then raise the temperature to 700 - 1000 °C for calcination, and cool to obtain the target product La x Li 1-x MnO3.

[0013] Specifically, the lithium salt in step (1) includes but is not limited to lithium acetate, lithium chloride, lithium carbonate, lithium bromide, lithium iodide, lithium nitrate, preferably lithium acetate; the lanthanum salt includes but is not limited to lanthanum nitrate, lanthanum acetate, lanthanum sulfate, preferably lanthanum nitrate; the manganese salt includes but is not limited to manganese nitrate, manganese acetate, manganese sulfate, preferably manganese nitrate.

[0014] Specifically, in step (2), add ammonia water to adjust the pH of the solution to 8 - 12, place the mixed solution on a stirrer at 80 - 90 °C, stir at 200 - 500 rpm until the solution evaporates to dryness to form a gel state, and then place it in an oven at 110 - 150 °C for drying for 6 - 24 hours to obtain a solid precursor.

[0015] Specifically, in step (2), the molar ratio of citric acid and ethylene glycol to the total metal ions in the mixed salt solution is 1.5 - 2.5:0.5 - 1.5:2, preferably 2:1:2.

[0016] Specifically, in step (3), grind the solid precursor into powder, heat it at 350 - 500 °C and then raise the temperature to 700 - 1000 °C at a rate of 5 - 15 °C / min, and the calcination time is 1 - 4 hours. The calcination temperature is 700 - 750 °C, 750 - 800 °C, 800 - 850 °C, 850 - 900 °C, 900 - 950 °C, 950 - 1000 °C.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention adjusts and optimizes the structure of perovskite oxide materials (ABO3) through a simple and easy-to-operate doping strategy, explores the improvement of the ORR performance of perovskite oxide materials (ABO3) with different lithium doping ratios, successfully introduces lithium into the crystal structure of perovskite oxide materials (ABO3), optimizes the ion diffusion channels and electronic density of states, and thus improves the ORR activity. On the premise of ensuring the catalyst performance, the raw material cost is effectively reduced, thereby providing a more economical solution for the large-scale application of La x Li 1- x MnO3 catalyst.

[0019] (2) The La x Li 1-x MnO3 catalyst prepared by the present invention exhibits relatively excellent catalytic activity and has the potential for application in fuel cells.

[0020] (3) The La x Li 1-x MnO3 catalyst prepared by the present invention has a certain stability and can avoid the performance degradation problem faced during long-term operation. Brief Description of the Drawings

[0021] Figure 1 It is the X-ray diffraction test pattern (XRD) of the lithium-doped perovskite-type oxygen reduction catalyst prepared in Examples 1-3.

[0022] Figure 2 It is the linear voltammetry scan pattern (LSV) of the lithium-doped perovskite-type oxygen reduction catalyst prepared in Examples 1-3.

[0023] Figure 3 It is the scanning electron microscope image (SEM) of the lithium-doped perovskite-type oxygen reduction catalyst prepared in Example 1.

[0024] Figure 4 It is the transmission electron microscope image (TEM) of the catalysts prepared in Example 1 and Comparative Example 1. Detailed Description of the Embodiments

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0026] Example 1

[0027] This example provides a preparation method for a lithium-doped perovskite-type oxygen reduction catalyst, including the following steps:

[0028] (1) Preparation of LLMO precursor: First, lanthanum nitrate hexahydrate and lithium acetate were added to ultrapure water at a molar ratio of 0.4:0.6. Then, manganese nitrate with a molar amount equal to the sum of the lanthanum salt and lithium salt was added. The mixture was stirred at room temperature for 0.5 hours to completely dissolve, obtaining a mixed salt solution. Next, citric acid and ethylene glycol were added, and stirring was continued for 0.5 hours to fully dissolve them. The molar ratio of citric acid, ethylene glycol to the total metal ions in the mixed salt solution was 2:1:2. Then, after adjusting the pH of the solution to 10 with ammonia water, the beaker was placed on a stirrer preheated to 90 °C and evaporated to a gel at a stirring speed of 300 rpm. Finally, the gel was transferred to an oven at 130 °C and dried for 12 hours to obtain the LLMO precursor.

[0029] (2) Preparation of LLMO catalyst: After grinding the LLMO precursor into powder, it was placed in a crucible and heated to 350 °C at a heating rate of 5 °C / min and held for 1 hour. Subsequently, it was continuously heated to 850 °C at the same rate and held for 2 hours. After natural cooling to room temperature, the target product LLMO (La 0.4 Li 0.6 MnO3) was obtained.

[0030] Example 2

[0031] In this example, except that the molar ratio of lanthanum nitrate hexahydrate to lithium acetate in step (1) was 0.6:0.4, the others were the same as in Example 1. Finally, the catalyst LLMO (La 0.6 Li 0.4 MnO3) was prepared.

[0032] Example 3

[0033] In this example, except that the molar ratio of lanthanum nitrate hexahydrate to lithium acetate in step (1) was 0.9:0.1, the others were the same as in Example 1. Finally, the catalyst LLMO (La 0.9 Li 0.1 MnO3) was prepared.

[0034] Example 4

[0035] In this example, except that the molar ratio of lanthanum nitrate hexahydrate to lithium acetate in step (1) was 0.1:0.9, the others were the same as in Example 1. Finally, the catalyst LLMO (La 0.1 Li 0.9 MnO3) was prepared.

[0036] Comparative Example 1

[0037] This example provides a preparation method of an LMO perovskite-type oxygen reduction catalyst, including the following steps:

[0038] (1) Preparation of LMO precursor: First, lanthanum nitrate hexahydrate was added to ultrapure water, and then manganese nitrate was added. It was stirred at room temperature for 0.5 hours to completely dissolve, obtaining a mixed salt solution. Then, citric acid and ethylene glycol were added, and stirring was continued for 0.5 hours to fully dissolve. The molar ratio of citric acid and ethylene glycol to the total metal ions in the mixed salt solution was 2:1:2. Then, the pH of the solution was adjusted to 10 with ammonia water. After that, the beaker was placed on a stirrer heated to 90 °C and evaporated to a gel at a stirring speed of 300 rpm. Finally, the gel was transferred to an oven at 120 °C and dried for 12 hours to obtain the LMO precursor.

[0039] (2) Preparation of LMO catalyst: After grinding the LMO precursor into powder, it was placed in a crucible and heated to 350 °C at a heating rate of 5 °C / min and held for 1 hour. Subsequently, it was continuously heated to 850 °C at the same rate and held for 2 hours. After natural cooling to room temperature, the target product LMO was obtained.

[0040] Figure 1 XRD pattern of the LLMO catalyst prepared in Examples 1 - 3 of the present invention. As can be seen from the figure, it basically corresponds to LaMnO3 of the standard card 50 - 0298, indicating that the prepared LLMO catalyst has the same structure as LaMnO3.

[0041] Figure 2 Linear voltammetry scanning curves of the LLMO catalyst prepared in Examples 1 - 3 of the present invention and the LMO catalyst prepared in Comparative Example 1. As shown in the figure, at 1600 rpm, in an alkaline condition (0.1 M KOH solution), the ORR half-wave potential of the La 0.4 Li 0.6 MnO3 catalyst is the best, being 0.77 V (the scanning range is -0.90 to 0.30 V).

[0042] Figure 3 Scanning electron microscope image of the catalyst prepared in Example 1 of the present invention, with a honeycomb-like small hole structure evenly distributed on the surface, and there are slight differences in the hole sizes.

[0043] Figure 4 Transmission electron microscope images of the catalysts prepared in Example 1 and Comparative Example 1 of the present invention. As can be seen from the figure, the neat lattice fringes represent their high crystallinity. The interplanar spacing of the (110) crystal plane decreases from 0.280 nm in Comparative Example 1 to 0.275 nm in Example 1, indicating that the atomic arrangement inside the crystal is more compact and the stability of the LLMO catalyst is improved.

Claims

1. A lithium-doped perovskite oxygen reduction electrocatalyst, characterized in that, The chemical formula is La x Li 1-x MnO3, where 0.1 ≤ x ≤ 0.

9.

2. The preparation method of the lithium-doped perovskite-type oxygen reduction electrocatalyst according to claim 1, characterized in that, It includes the following preparation steps: (1) Dissolve lanthanum salt and lithium salt in water, and then add manganese salt with the sum of the molar amounts of lanthanum salt and lithium salt to form a mixed salt solution; (2) Add citric acid and ethylene glycol to the mixed salt solution, stir and mix evenly, then add ammonia water to adjust the pH of the solution to 8 - 12, heat and stir until the solution evaporates to dryness to form a gel state, and continue drying to obtain a solid precursor; (3) Grind the solid precursor into powder, heat it at 350 - 500 °C and then increase the temperature to 700 - 1000 °C for calcination, and obtain the target product La x Li 1-x MnO3.

3. The preparation method of the lithium-doped perovskite-type oxygen reduction electrocatalyst according to claim 2, characterized in that, In step (1), the lithium salt is lithium acetate, lithium chloride, lithium carbonate, lithium bromide, lithium iodide or lithium nitrate; the lanthanum salt is lanthanum nitrate, lanthanum acetate or lanthanum sulfate; the manganese salt is manganese nitrate, manganese acetate or manganese sulfate.

4. The preparation method of the lithium-doped perovskite-type oxygen reduction electrocatalyst according to claim 2, wherein In step (2), add ammonia water to adjust the pH of the solution to 8 - 12, place the mixed solution on a stirrer at 80 - 90 °C, stir at 200 - 500 rpm until the solution evaporates to dryness to form a gel state, and then place it in an oven at 110 - 150 °C for 6 - 24 hours to obtain a solid precursor.

5. The preparation method of the lithium-doped perovskite-type oxygen reduction electrocatalyst according to claim 2, characterized in that, In step (2), the molar ratio of citric acid and ethylene glycol to the total metal ions in the mixed salt solution is 1.5 - 2.5:0.5 - 1.5:

2.

6. The preparation method of the lithium-doped perovskite-type oxygen reduction electrocatalyst according to claim 2, characterized in that, In step (2), the molar ratio of citric acid and ethylene glycol to the total metal ions in the mixed salt solution is 2:1:

2.

7. The preparation method of the lithium-doped perovskite-type oxygen reduction electrocatalyst according to claim 2, wherein In step (3), grind the solid precursor into powder, heat it at 350 - 500 °C and then increase the temperature to 700 - 1000 °C at a rate of 5 - 15 °C / min, and the calcination time is 1 - 4 hours.

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