A garnet-type proton conductor based on proton substitution and its preparation method

Abstract

The present invention discloses a garnet-type proton conductor based on proton substitution and a preparation method thereof, belonging to the technical field of proton conductors. The garnet-type proton conductor and its derivative system of the present invention have the chemical formula Li 28(1‑x) H 28x La 12 Zr8O 48 Since the present invention is based on garnet-type solid electrolyte Li7La3Zr2O 12 The proton substitution of Li7La3Zr2O introduces hydrogen ions into it to form a proton conductor, and its proton conductivity is at an excellent level compared to traditional perovskite proton conductors. 12 The protonated garnet-type proton conductors exhibit high proton and oxygen ion conductivity at medium and high temperatures, ensuring their effectiveness as solid electrolytes linking hydrogen and electricity. Substituting Al or similar elements for the hydrogen element in these materials can further enhance their stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of proton conductors, and in particular relates to a garnet-type proton conductor based on proton substitution and a preparation method thereof. Background Art

[0002] Since the advent of the industrial age, human society has been consuming large amounts of non-renewable fossil energy. The combustion and utilization of these fuels produces large amounts of carbon dioxide and other harmful gases, leading to environmental pollution, the greenhouse effect, and energy crises. The development and utilization of renewable, clean energy can help address the environmental impacts and energy crises associated with fossil fuels, becoming a key development strategy for countries around the world. Currently, hydrogen energy is the most promising renewable, clean energy source. Its primary energy carrier is hydrogen, which offers advantages such as being pollution-free, storable, and highly efficient. Electrochemical devices for energy generation and storage, such as electrolyzers and fuel cells, are crucial for developing ecologically and sustainable lifestyles that utilize hydrogen as a pollution-free energy carrier.

[0003] A proton conductor is a solid electrolyte that conducts hydrogen ions. These materials are broadly classified into inorganic proton conductors, organic polymer proton conductors, carbon-based proton conductors, periodic porous proton conductors, and oxide proton conductors. They are widely used in the aforementioned electrochemical energy storage and conversion devices, serving as a technological "bridge" between hydrogen and electrical energy. Fuel cells are highly efficient power generation devices that directly use hydrogen as fuel to convert chemical energy into electrical energy. One of their core components is a proton conductor that conducts hydrogen ions. Solid oxide fuel cells (SOFCs) have the highest energy density among fuel cells and are considered to have broad application prospects due to their high energy conversion efficiency, low carbon emissions, and wide fuel compatibility. However, they face the challenge of operating at high temperatures, making the development of high-temperature-resistant proton conductors a significant task. Solid oxide electrolytes are used as electrolyte materials in SOFCs due to their excellent electrochemical stability, corrosion resistance, lack of electrolyte leakage, and wide fuel compatibility. Partially oxidized proton conductors exhibit excellent proton conductivity at high temperatures (600-1200°C). Due to their high-temperature resistance, they are also suitable for applications in hydrogen sensors, steam electrolysis, and other fields. Most high-temperature proton conductors have a perovskite structure, in which proton conduction is closely related to the crystal structure and is influenced by proton concentration and mobility. Currently, the most common perovskites are Sr-based and Ba-based. While these materials exhibit high proton conductivity, they readily react with CO₂ and H₂O to form other species, limiting their application in fuel cells. In addition to perovskite proton conductors, oxide materials containing MO₄ tetrahedral structures have also been found to exhibit proton conductivity at high temperatures and are less reactive to CO₂ and H₂O, but their proton conductivity performance is less than ideal. Finding materials that combine high proton conductivity with stability remains a key research focus for proton conductors. Garnet-type solid electrolytes (LLZO) have attracted widespread attention due to their excellent lithium ion conductivity, good electrochemical stability, low cost and easy preparation. Studies have shown that there is a reversible ion exchange reaction between lithium ions and hydrogen ions in garnet-type solid electrolytes. 12 The introduction of hydrogen ions to replace the lithium ions in the electrolyte promotes its protonation, thereby obtaining a proton conductor Li with high proton conductivity and good electrochemical stability. 7-x H x La3Zr2O 12 .

[0004] Through the above analysis, the problems and defects of the existing technology are as follows:

[0005] (1) Existing perovskite-based proton conductors have strong proton conductivity properties but are easily reacted with H2O and CO2 produced during hydrogen energy utilization to produce other by-products, affecting the performance of electrochemical devices.

[0006] (2) Although the existing MO4 tetrahedral oxide material has proton conductivity at high temperature and is insensitive to CO2 and H2O, its proton conductivity performance is not ideal.

[0007] (3) The design of proton conductors with good proton conductivity and stable structure during hydrogen energy utilization is an important issue that needs to be solved urgently. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides a garnet-type proton conductor based on proton substitution and a preparation method thereof.

[0009] The present invention is achieved by a garnet-type proton conductor based on proton substitution, wherein the garnet-type proton conductor is composed of a garnet-type solid electrolyte (Li7La3Zr2O 12 )4 is protonated, and the chemical formula is: Li 28(1-x) H 28x La 12 Zr8O 48 ; Wherein, the value range of x is 0 to 1 and x≠0.

[0010] Furthermore, if x is 0.25, the garnet-type proton conductor is Li 21 H7L 12 Zr8O 48 .

[0011] Furthermore, if x is 0.5, the garnet-type proton conductor is Li 14 H 14 La 12 Zr8O 48 .

[0012] Furthermore, if x is 0.75, the garnet-type proton conductor is Li7H 21 La 12 Zr8O 48 .

[0013] Furthermore, if x is 1.0, the garnet proton conductor is H 28 La 12 Zr8O 48 .

[0014] Furthermore, by replacing part of H with Al or its homologous elements, the proton conductor Li can be obtained. 28(1-x) H 16x A 4x La 12 Zr8O 48 , A=B,Al,Ga,In,Ta.

[0015] Another object of the present invention is to provide a garnet-type proton conductor based on proton substitution, wherein the garnet-type proton conductor is made by protonating the garnet-type solid electrolyte.

[0016] Another object of the present invention is to provide a method for preparing a garnet-type proton conductor based on proton substitution, comprising the following steps: 12 The Li in the garnet is replaced by H, and the ratio of Li and H is determined. The obtained garnet-type proton conductor is Li 28(1-x) H 28x La 12 Zr8O 48 , x = 0.25, 0.5, 0.75, or 1.0.

[0017] In combination with the above technical solutions and the technical problems solved, the present invention analyzes the advantages and positive effects of the technical solutions to be protected by the present invention from the following aspects:

[0018] First, in view of the technical problems existing in the above-mentioned prior art and the difficulty of solving these problems, this paper closely combines the technical solutions to be protected by the present invention and the results and data during the research and development process, and analyzes in detail and in depth how the technical solutions of the present invention solve the technical problems and some creative technical effects brought about by solving the problems. The specific description is as follows:

[0019] Based on first principles and ab initio molecular dynamics, the present invention studies the Li7La3Zr2O 12 The garnet electrolyte is protonated, replacing the lithium with hydrogen. The effects of varying ratios of Al to H on its proton conductivity are analyzed. In the energy sector, this invention can be used as a proton conductor in electrochemical devices such as fuel cells and hydrogen sensors.

[0020] The purpose of the present invention is to protonate Li7La3Zr2O 12 The introduction of hydrogen ions into the electrolyte material can achieve the effect of higher hydrogen ion conductivity due to the high lithium ion conductivity of the material and the smaller radius of hydrogen ions than lithium ions. And by adjusting the H / Li element content ratio, the hydrogen ion conductivity of the material, that is, the proton conductivity, is improved. In order to analyze the optimal ratio of H / Li element content, the present invention is to analyze the original Li7La3Zr2O 12 Protonation is carried out to introduce hydrogen ions to replace the lithium ions, thereby constructing a material system, namely Li 28(1-x) H 28x La 12 Zr8O 48(x=0.25, 0.5, 0.75, 1.0). The present invention uses ab initio molecular dynamics simulation method based on density functional theory to analyze Li 28(1-x) H 28x La 12 Zr8O 48 Dependence of proton conductivity on doping.

[0021] It can be seen from the experimental results that the Li 28(1-x) H 28x La 12 Zr8O 48 The mean square displacement (MSD) of hydrogen ions in the unit cell (x = 0.25, 0.5, 0.75, 1.0) increases significantly with the increase of hydrogen ion content, indicating that the hydrogen ion concentration affects its diffusion in the unit cell. A higher hydrogen ion concentration can effectively increase the diffusion coefficient of hydrogen ions, reduce the diffusion barrier of hydrogen ions, and enhance its proton conductivity. 28(1-x) H 28x La 12 Zr8O 48 During the ab initio molecular dynamics simulation of the material system at high temperature, the crystal structure skeleton remains intact, indicating that it has good thermal stability. 28 La 12 Zr8O 48 The highest hydrogen ion mobility coefficient and the most excellent proton conductivity performance. By doping the derivative material with high proton conductivity with Al or Ta elements, its thermal stability can be further improved.

[0022] Second, considering the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by the present invention are described in detail as follows:

[0023] (1) Due to the high lithium ion conductivity of garnet-type solid electrolyte (Li7La3Zr2O 12 ) was protonated, hydrogen ions were introduced and Li7La3Zr2O was regulated. 12 The ratio of Li to H in the 28(1-x) H 28x La 12 Zr8O 48 (x=0.25, 0.5, 0.75, 1.0) material system, the present invention is compared with the original Li7La3Zr2O 12 In particular, a garnet-type proton conductor Li was designed based on the lithium ion conductor. 28(1-x) H 28x La 12 The Zr8O4 system has excellent high-temperature proton conductivity and stability.

[0024] (2) Adjust Li 28(1-x) H 28x La 12 A series of conductor materials obtained by adjusting the ratio of H to Li in Zr8O4 still maintain a good level of electrochemical stability, and their safety performance and working efficiency as proton conductors are guaranteed.

[0025] (3) Compared with the original lithium ion conductor Li7La3Zr2O 12 In contrast, if it is protonated and the proportion of hydrogen ions is increased, the diffusion coefficient of hydrogen ions will be significantly improved. 28 La 12 Zr8O 48 The hydrogen ion diffusion coefficient is improved to that of the original Li7La3Zr2O 12 The lithium ion diffusion coefficient is one order of magnitude larger, and it is a material with excellent proton conductivity.

[0026] Third, as auxiliary evidence of the inventiveness of the claims of the present invention, it is also reflected in the expected benefits and commercial value after the technical solution of the present invention is transformed into:

[0027] A design method for a garnet-type proton conductor is provided. The proton conductor has high proton conductivity and stability, and is made based on an existing garnet-type solid electrolyte, which can greatly reduce the manufacturing cost of the proton conductor. The proton conductor can be applied to electrochemical devices such as solid oxide fuel cells, hydrogen sensors and electrolyzers, and has broad market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0029] Figure 1 is the Li provided in Example 1 of the present invention 28(1-x) H 28x La 12 Zr8O 48 (x=0.25,0.5,0.75,1.0) Crystal structure diagram of the material system;

[0030] Figure 2 is the Li provided in Example 1 of the present invention 28(1-x) H 28x La 12 Zr8O 48 The trend diagram of the unit cell volume changing with the x value;

[0031] Figure 3 It is Li7La3Zr2O provided in Example 1 of the present invention 12 The trend of the average mean square displacement (MSD) of each atom of the material at 1273K over time;

[0032] Figure 4 is the Li provided in Example 1 of the present invention 28(1-x) H 28x La 12 Zr8O 48 When x is 1.0 (i.e. H 28 La 12 Zr8O 48 ) The trend of the average mean square displacement (MSD) of each atom at 1273K over time;

[0033] Figure 5 is H provided in Example 1 of the present invention 28 La 12 Zr8O 48 The trend of the average mean square displacement (MSD) of each atom of the material at different temperatures over time;

[0034] Figure 6 is H provided in Example 1 of the present invention 28 La 12 Zr8O 48 The trend diagram of the diffusion coefficient of each ion of the material changing with temperature;

[0035] Figure 7 is H provided in Example 1 of the present invention 28 La 12 Zr8O 48 Diffusion coefficients of hydrogen and oxygen ions and corresponding diffusion barrier diagrams of materials at different temperatures;

[0036] Figure 8 is H provided in Example 1 of the present invention 28 La 12 Zr8O 48 A graph of the hydrogen ion (proton) conductivity of a material at different temperatures;

[0037] Figure 9 They are respectively Li provided in Example 1 of the present invention 28(1-x) H 28x La 12 Zr8O 48 The Li, H, and O ion diffusion coefficients at 1273K and the Li and H ion conductivity at 1273K are plotted as a function of x.

[0038] Figure 10They are respectively Li provided in the embodiments of the present invention 28(1-x) H 16x A 4x La 12 Zr8O 48 Temperature variation trend of the hydrogen and oxygen ion diffusion coefficients of the material when x is 1 and A = Ta, Al; Temperature variation trend of the ratio of the hydrogen ion diffusion coefficient to the diffusion constant; Temperature variation trend of the lithium ion migration barrier and room temperature conductivity of the system as a function of x value; Temperature variation trend of the hydrogen and oxygen ion diffusion barriers. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] In view of the problems existing in the prior art, the present invention provides an aluminosilicate lithium ion solid electrolyte and a design method thereof. The present invention is described in detail below with reference to the accompanying drawings.

[0041] In order to enable those skilled in the art to fully understand how to implement the present invention, this section provides an illustrative embodiment that expands upon the technical solutions of the claims.

[0042] The garnet-type proton conductor provided in the embodiment of the present invention is a protonated derivative system of LLZO, and its chemical formula is: Li 28(1-x) H 28x La 12 Zr8O 48 ; Wherein, the value range of x is 0 to 1 and x≠0.

[0043] The optimal ratio of the solid electrolyte provided by the embodiment of the present invention includes the following components:

[0044] Li 21 H7L 12 Zr8O 48 ;

[0045] Li 14 H 14 La 12 Zr8O 48 ;

[0046] 7H 21 La 12 Zr8O 48 ;

[0047] H 28 La 12 Zr8O 48 ;

[0048] The embodiment of the present invention also provides a method for preparing a garnet-type proton conductor, comprising: preparing a garnet-type solid electrolyte (Li7La3Zr2O 12 )4 Protonation construction material system uses ab initio molecular dynamics simulation method based on density functional theory to analyze and calculate Li 28(1-x) H 28x La 12 Zr8O 48 The conductivity of lithium ions and hydrogen ions in the electrolyte. Determine the optimal ratio of H / Li element content: H 28 La 12 Zr8O 48 On this basis, the proton conductor Li was prepared by doping 28(1-x) H 16x A 4x La 12 Zr8O 48 , A=B,Al,Ga,In,Ta.

[0049] Example 1

[0050] In the embodiment of the present invention, the garnet-type solid electrolyte material Li7La3Zr2O 12 Protonation was performed, hydrogen ions were introduced and Li7La3Zr2O was regulated. 12 The ratio of Li to H elements in the proton conductor Li is designed 28(1-x) H 28x La 12 Zr8O 48 (x=0.25, 0.5, 0.75, 1.0) material system, in order to analyze the optimal ratio of H / Li element content, the present invention adopts the ab initio molecular dynamics simulation method based on density functional theory to analyze the Li 28(1-x) H 28x La 12 Zr8O 48 Diffusion coefficients of lithium ions and hydrogen ions and their electrical conductivity.

[0051] (1) The purpose of the present invention provided by the embodiment of the present invention is to provide Li 28(1-x) H 28x La 12 Zr8O 48 The design method for the optimal ratio of elements includes the following steps:

[0052] Establish Li with different H / Li content 28(1-x) H 28x La 12 Zr8O 48The constructed models were structurally optimized, and the lattice parameters and ion positions were completely relaxed until the total energy and ion force were less than 10 -5 eV and Optimized Li 28(1-x) H 28x La 12 Zr8O 48 Crystal structure such as Figure 1 shown.

[0053] (2) Li provided by the embodiment of the present invention 28(1-x) H 28x La 12 Zr8O 48 The volume of the crystal structure after proton conductor optimization gradually increases with the increase of H content, indicating that with the increase of H content, the size of the hydrogen ion migration channel in the structure also increases, which is beneficial to improve the proton conductivity, such as Figure 2 shown.

[0054] (3) The electrical conductivity properties of lithium ions and hydrogen ions in the materials provided by the embodiments of the present invention can be calculated according to the following Nernst-Einstein equation:

[0055]

[0056] Where σ is the conductivity, n is the number density of lithium ions or hydrogen ions, e is the charge of the elementary charge, Z is the valence of a single lithium ion, and k B is the Boltzmann constant, T is the temperature, and D is the diffusion coefficient of lithium ions. All physical quantities except the diffusion coefficient D can be obtained from the unit cell parameters and the calculation simulation parameters. Where MSD is the average mean square displacement of lithium ion or hydrogen ion diffusion, which can be calculated by ab initio molecular dynamics simulation. The larger the ratio of the average mean square displacement value to time, the larger the diffusion coefficient of lithium ions and the corresponding greater the conductivity of lithium ions or hydrogen ions.

[0057] (4) Figure 3 Demonstrated pristine Li7La3Zr2O 12 The change of the average mean square displacement of each ion with time at a temperature of 1273K shows that only lithium ions migrate in the material, and other ions only oscillate at their equilibrium positions, indicating that the structural framework of the material remains stable during the simulation calculation process.

[0058] (5) Figure 4 Shows Li 28(1-x) H 28x La 12 Zr8O 48 The structure in which Li is completely replaced by H in the material, i.e. H 28La 12 Zr8O 48 The change in the average mean square displacement of each ion over time at a temperature of 1273K shows that when only Li is replaced, the hydrogen ion diffusion capacity of the replaced proton conductor is obviously much higher than the lithium ion diffusion capacity in the original material, indicating that the proton conductor has a good ability to conduct hydrogen ions. However, other ions also moved slightly during the simulation process, and the structural stability needs further research and improvement.

[0059] (6) Figure 5 Shows H 28 La 12 Zr8O 48 The average mean square displacement of H, La, Zr, and O ions at various temperatures changes with time. The results show that the material's ability to conduct hydrogen ions increases with increasing temperature, and when the temperature is higher than 873K, other ions besides H also migrate. This shows that the material can maintain good stability under conditions below 873K.

[0060] (7) Figure 6 Shows H 28 La 12 Zr8O 48 The relationship between the diffusion coefficients of H, La, Zr, and O ions and temperature. The diffusion coefficient of hydrogen ions increases with temperature, which is obviously greater than that of other ions. The diffusion coefficient of oxygen ions is second only to that of hydrogen ions. The reason is that part of the proton migration in the material is in the form of H3O + achieved by ion diffusion.

[0061] (8) Figure 7 The changes in the diffusion coefficients of hydrogen and oxygen ions with temperature and the corresponding diffusion barriers are demonstrated. The results show that at high temperatures, oxygen ions also have obvious migration phenomena in proton conductors, which is conducive to the protonation reaction of the material with water vapor. In addition, the high mobility of oxygen ions can also increase their migration speed to the anode in the fuel cell, accelerate their reaction with hydrogen, and increase the power of converting hydrogen energy into electrical energy.

[0062] (9) Figure 8 Shows H 28 La 12 Zr8O 48 The proton conductivity of the material changes with temperature. The proton conductivity is calculated using the Nernst-Einstein equation shown in the figure. Its proton conductivity at 900K is excellent, reaching 0.02S / cm, comparable to or even exceeding some common perovskite-type proton conductors.

[0063] (10) Figure 9 Shows Li 28(1-x) H28x La 12 Zr8O 48 The trend of the Li, H, and O ion diffusion coefficients as a function of x at 1273K, as well as the trend of the Li and H ion conductivity as a function of x, show that at the same temperature, an increase in the hydrogen ion concentration significantly increases the hydrogen ion diffusion coefficient. When the x value is greater than 0.75, the oxygen ion diffusion coefficient is also significantly improved, and the proton conductivity reaches 10 at high temperature. -2 Order of magnitude.

[0064] The embodiment of the present invention makes the garnet-type solid electrolyte Li7La3Zr2O 12 Protonation occurs to replace the lithium ions with hydrogen ions, forming a series of proton conductors Li according to the degree of replacement. 28(1-x) H 28x La 12 Zr8O 48 , with the increase of H content, the proton conductivity of the material will also be enhanced, among which H 28 La 12 Zr8O 48 The proton conductivity of the material is excellent. Moreover, the proton material system has obvious migration of H and O at high temperatures, making it suitable for electrochemical devices where hydrogen energy participates in reactions as chemical energy.

[0065] Example 2

[0066] The implementation is similar to Example 1, except that Li 28(1-x) H 28x La 12 Zr8O 48 The H element in the molten pool is partially or completely replaced by its Al homologous element to obtain Li 28(1-x) H 16x A 4x La 12 Zr8O 48 , A=B,Al, Ga,In,Ta. (x=0.25, 0.5, 0.75, 1.0). like Figure 10 As shown in Figure 2, since O atoms are fixed by Ta or Al, the stability is improved after doping, but the diffusion rate decreases. The stability of the Al-doped structure is better than that of the Ta-doped structure, but the proton diffusion rate is lower.

[0067] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a garnet-type proton conductor based on proton substitution, characterized in that: The following steps are involved: For the original Li7La3Zr2O 12 The Li in the garnet is replaced by H, and the ratio of Li to H is determined to obtain a garnet-type proton conductor. The garnet-type proton conductor is composed of a garnet-type solid electrolyte (Li7La3Zr2O 12 )4 is protonated, and the chemical formula is: Li 28(1-x) H 28x La 12 Zr8O 48 ; in, x The value range is 0~1 and x ≠0; Substituting Al or its homologous elements for part of H can produce proton conductor Li 28(1-x) H 16x A 4x La 12 Zr8O 48 , A = B,Al, Ga, In, Ta.

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