Method for judging hydrogen desorption thermodynamics of BCC high-entropy hydrogen storage alloy

Abstract

The invention discloses a criterion method for hydrogen desorption thermodynamics of a BCC high-entropy hydrogen storage alloy, which comprises the following steps: step 1, in a given high-entropy hydrogen storage alloy system, obtaining phase components of the alloy at different temperatures through phase diagram thermodynamics calculation; 2, according to alloy phase components at different temperatures, high-temperature water quenching heat treatment is conducted on a given initial alloy within a single-phase BCC temperature interval, and then it is determined that all alloy systems are of a single-phase BCC structure in a characterization mode through a phase structure characterization means; 3, the average valence electron concentration and the modified modulus-volume ratio of the alloy are calculated respectively; and 4, based on the average valence electron concentration and the modified modulus-volume ratio, a high-entropy alloy hydrogen desorption thermodynamic criterion function is defined, and the hydrogen desorption thermodynamics of the alloy is judged through the criterion function. According to the method, effective correlation between alloy components and hydrogen desorption temperature or hydrogen absorption and desorption balance pressure of hydrogen desorption thermodynamics can be rapidly established, and the modification design of the BCC high-entropy hydrogen storage alloy is effectively guided.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogen energy, and in particular to a criterion method for hydrogen desorption thermodynamics of a BCC high entropy hydrogen storage alloy. Background Art

[0002] Hydrogen energy is a secondary energy source with a wide range of sources, green and low-carbon, flexible and efficient, and rich application scenarios. It is an ideal interconnected medium to promote the clean and efficient use of traditional fossil energy and support the large-scale development of renewable energy. In the entire hydrogen energy industry chain, midstream hydrogen storage and transportation is a key bridge connecting the hydrogen production end and the application end. The development of efficient, safe and low-cost hydrogen storage and transportation technology has become a key bottleneck restricting the hydrogen energy industry.

[0003] Compared with the high-pressure hydrogen storage technology of traditional 35 or 70MPa hydrogen storage bottles, hydrogen storage alloys can store hydrogen at low temperature and low pressure by utilizing the reversible chemical reaction of hydrogen and metals. They have intrinsic safety characteristics and provide a key premise for solving the problem of safe hydrogen storage and transportation. The application-oriented design of hydrogen storage alloys usually requires full coordination of hydrogen absorbing elements and hydrogen releasing elements in the alloy system to ensure that the alloy material can release a large amount of hydrogen at a certain temperature while having a high hydrogen absorption capacity. Traditional hydrogen storage alloys are mainly composed of one or two metal elements. Due to the phase structure of the alloy, the space for selecting components is narrow, and therefore the space and effect of regulating and modifying hydrogen absorption and release are limited.

[0004] High entropy alloys are a new type of high-performance hydrogen storage alloy reported in recent years. They have attracted extensive attention from scientific researchers for their high hydrogen storage capacity, long cycle performance, and rapid hydrogen absorption and desorption kinetics. Because they break the traditional design concept of alloys based on one element and highlight the large number of undeveloped components in the central area of ​​the phase diagram, while bringing a wide range of component selection space and more performance adjustment possibilities to the design of hydrogen storage alloys, they also lead to the problem of difficulty in accurately controlling the performance of alloys in a massive component space.

[0005] For the thermodynamic regulation of hydrogen release of high entropy hydrogen storage alloys with body-centered cubic (BCC) crystal structure, relevant research has reported certain design methods. et al. proposed that valence electron concentration (VEC) can be used as a thermodynamic criterion for BCC high entropy hydrogen storage alloys. They found that in some BCC structure high entropy hydrogen storage alloy systems, the dehydrogenation temperature of the alloy decreases with the increase of VEC, and predicted that when VEC increases to a certain value, the alloy will be able to dehydrogenate at room temperature. Although this design method can guide the design of some hydrogen storage alloys, it is not applicable to some alloy systems with the same valence electron concentration; it is also found that the correlation between VEC and dehydrogenation temperature in TiVZrNbM (M=Mg, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ta) high entropy alloys is completely opposite to the above rule.

[0006] Through the above analysis, the defect of the prior art is the lack of a simple and effective alloy design method to guide the thermodynamic design of hydrogen desorption of BCC high entropy hydrogen storage alloys. This is mainly because: on the one hand, high entropy alloys are usually alloyed with multiple elements as the main element at the same time, and the same period / sub-group elements often appear in the alloy composition, resulting in alloys of different components having the same valence electron concentration or the same lattice constant. Therefore, the simple valence electron concentration is difficult to reflect the thermodynamic changes of hydrogen desorption caused by the change of alloy composition; on the other hand, in BCC high entropy hydrogen storage alloys, although the simple change of valence electron concentration can partially reflect the situation of hydrogen-metal bonds, it is difficult to reflect the volume expansion and contraction of the alloy hydride lattice during the process of alloy absorption and desorption of hydrogen.

[0007] Therefore, inventing a criterion method that can effectively and reliably guide the thermodynamic design of alloy dehydrogenation is a top priority in the current design of BCC high entropy hydrogen storage alloys. Summary of the invention

[0008] In order to solve the above technical problems existing in the prior art, the present invention proposes a criterion method for the dehydrogenation thermodynamics of BCC high entropy hydrogen storage alloys, which can quickly establish an effective correlation between the alloy composition and the dehydrogenation temperature or the hydrogen absorption and dehydrogenation equilibrium pressure of the dehydrogenation thermodynamics, and effectively guide the modification design of BCC high entropy hydrogen storage alloys. The specific technical scheme is as follows:

[0009] A method for determining the thermodynamics of hydrogen release of a BCC high entropy hydrogen storage alloy comprises the following steps:

[0010] Step 1: In a given high entropy hydrogen storage alloy system, obtain the phase composition of the alloy at different temperatures through phase diagram thermodynamic calculation;

[0011] Step 2: According to the alloy phase composition at different temperatures, the given initial alloy is subjected to high-temperature water quenching heat treatment in the single-phase BCC temperature range, and then the alloy system is characterized and determined to be a single-phase BCC structure by means of phase structure characterization;

[0012] Step 3: Calculate the average valence electron concentration and modified modulus-volume ratio of the alloy respectively;

[0013] Step 4: Based on the average valence electron concentration and the modified modulus-to-volume ratio, define a criterion function for the dehydrogenation thermodynamics of the high entropy alloy, and determine the dehydrogenation thermodynamics of the alloy using the criterion function.

[0014] Furthermore, in step 3, the average valence electron concentration of the alloy is calculated by the theoretical composition of the alloy, and a linear weighted formula is used for calculation: Among them, C i is the atomic ratio of metal elements in the alloy, VEC iis the valence electron concentration of the metal element, and n is the type of metal element in the alloy.

[0015] Furthermore, in step 3, the molar volume of the alloy is corrected using the stacking density and the linear expansion coefficient, and the corrected modulus-volume ratio of the alloy is calculated. The specific expression is as follows:

[0016]

[0017] V i =V oi (1+α i (TT o )) 3 ,

[0018] V oi =V o ×k,

[0019]

[0020] Among them, V i is the modified molar volume of a single element in the alloy, α i is the linear expansion coefficient of a single element in the alloy, T o is room temperature, T is the melting point of the alloy, V o is the molar volume of a single element in the alloy, k is the atomic stacking density corresponding to a single element, It is the melting point of a single metallic element in an alloy.

[0021] Further, in step 4, the thermodynamic criterion function expression of the high entropy alloy dehydrogenation is: The average valence electron concentration VEC and the modified modulus-volume ratio of the alloy At the same time as an independent variable, and satisfy:

[0022] 1. The larger the VEC, The larger the value, the greater the criterion function The bigger;

[0023] 2. VEC remains unchanged. The larger the value, the greater the criterion function The bigger;

[0024] 3. The larger the VEC, When unchanged, the criterion function The bigger.

[0025] Furthermore, when the criterion function The larger the value, the higher the dehydrogenation equilibrium pressure or dehydrogenation temperature of the alloy, or the lower the absolute value of the dehydrogenation enthalpy change.

[0026] Furthermore, the physical structure characterization method adopts X-ray diffraction technology.

[0027] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0028] (1) The thermodynamic criterion function for dehydrogenation of the BCC high entropy hydrogen storage alloy proposed in the present invention includes both the valence electron concentration and the modified modulus-to-volume ratio, which can simultaneously reflect the chemical interaction and volume elastic effect in the hydrogen absorption and dehydrogenation process of the BCC high entropy hydrogen storage alloy, and is helpful to accurately establish the thermodynamic relationship between alloy composition and dehydrogenation, so as to guide the design of hydrogen storage alloys with excellent dehydrogenation performance.

[0029] (2) The present invention considers using stacking density, linear expansion coefficient, etc. to make certain corrections to the molar volume of the alloy, which reflects the lattice distortion characteristics of high entropy alloys. At the same time, since the electron concentration and the modified modulus-to-volume ratio are considered in the definition of the criterion function, the situation in which only the valence electron concentration or the modified modulus-to-volume ratio is used and the criterion is difficult to guide is effectively avoided, and the multi-principal component substitution effect in the design process of BCC high entropy hydrogen storage alloys is fully considered.

[0030] (3) The present invention is an empirical criterion function designed for the modification of the thermodynamic composition of hydrogen desorption of BCC high entropy hydrogen storage alloys. Through this empirical criterion function obtained by simple calculation directly from the alloy composition, the variation law of the thermodynamics of hydrogen desorption of the alloy with the alloy composition can be quickly known, which is simpler and more convenient than the complex and tedious first-principles calculation. Traditional experimental methods usually require a lot of time and resources to characterize and test the thermodynamics of hydrogen desorption of alloys in order to achieve alloy composition modification. The present method can predict the changes in the thermodynamics of hydrogen desorption of alloys through empirical criteria, thereby greatly saving time and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 : is a thermodynamic phase diagram of TiVNbCr high entropy alloys with different Ti contents in this embodiment, wherein (a) corresponds to Ti40V30Nb10Cr20, (b) corresponds to Ti35V30Nb10Cr25, (c) corresponds to Ti30V30Nb10Cr30, and (d) corresponds to Ti25V30Nb10Cr35;

[0032] Figure 2 is a phase structure characterization diagram of TiVNbCr high entropy alloys with different Ti contents in this embodiment;

[0033] Figure 3 TG-DSC synchronous thermal analysis diagram of the TiVNbCrMo series high entropy alloy hydride of the present embodiment;

[0034] Figure 41 is a schematic diagram of the PCT curves of the TiVNbCrFe alloys with different Fe contents in this embodiment and the corresponding Van't Hoff fitting. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and technical effect of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0036] A criterion method for the thermodynamics of hydrogen release of a BCC high entropy hydrogen storage alloy of the present invention comprises the following steps:

[0037] Step 1: In a given high entropy hydrogen storage alloy system, obtain the phase composition of the alloy at different temperatures through phase diagram thermodynamic calculation.

[0038] Step 2: According to the alloy phase composition at different temperatures, the given initial alloy is subjected to high-temperature water quenching heat treatment in the single-phase BCC temperature range, and then the alloy system is determined to be a single-phase BCC structure through phase structure characterization means.

[0039] Step 3: Calculate the average valence electron concentration and modified modulus-to-volume ratio of the alloy, respectively.

[0040] Specifically, the valence electron concentration of the alloy reflects the electronic structure of the metal itself, and to a certain extent can reflect the hydrogen-metal chemical interaction during the absorption and desorption of hydrogen by the BCC high entropy hydrogen storage alloy. Therefore, the embodiment of the present invention calculates the average valence electron concentration of the alloy by the theoretical composition of the alloy, and adopts a linear weighted formula for calculation: Among them, C i is the atomic ratio of metal elements in the alloy, VEC i is the valence electron concentration of the metal element, and n is the type of metal element in the alloy.

[0041] For the modified modulus-volume ratio, the larger the radius of the metal atom, the larger the interstitial position, so the thermodynamics of hydrogen desorption of the alloy is closely related to the volume of the alloy; at the same time, the bulk modulus is related to the expansion and contraction ability of its constituent chemical bonds, which is determined by the strength and compressibility of the chemical bonds at the microscopic level. Therefore, in theory, the volume elastic effect caused by the hydrogen absorption process of the alloy can be expressed to a certain extent by the ratio of bulk modulus to molar volume.

[0042] Another major feature of high entropy alloys is the severe lattice distortion in their structure. Due to the random arrangement of multiple principal elements, the alloy crystal structure is severely distorted, and the bond length of hydrogen-alloy interaction changes irregularly. For the complex interaction caused by this lattice distortion, it must be corrected when calculating the molar volume of BCC high entropy hydrogen storage alloys.

[0043] The present invention uses stacking density, linear expansion coefficient, etc. to correct the alloy molar volume and calculates the modified modulus-volume ratio of the alloy. Right now:

[0044]

[0045] V i =V oi (1+α i (TT o )) 3 ,

[0046] V oi =V o ×k,

[0047]

[0048] Among them, V i is the modified molar volume of a single element in the alloy, α i is the linear expansion coefficient of a single element in the alloy, T o is room temperature, T o Take 300K, T is the melting point of the alloy, V o is the molar volume of a single element in the alloy, k is the atomic stacking density corresponding to a single element, It is the melting point of a single metallic element in an alloy.

[0049] Step 4: Define the thermodynamic criterion function for hydrogen desorption of high entropy alloys based on the average valence electron concentration and the modified modulus-volume ratio The dehydrogenation thermodynamics of the alloy is determined by the criterion function, where VEC and At the same time, as an independent variable, is the dependent variable.

[0050] The criterion function satisfies the following mapping requirements:

[0051] 1. The larger the VEC, The larger the value, the greater the criterion function The bigger;

[0052] 2. VEC remains unchanged. The larger the value, the greater the criterion function The bigger;

[0053] 3. The larger the VEC, When unchanged, the criterion function The bigger.

[0054] According to the above mapping requirements, as long as VEC or If the value of any parameter increases, The value increases, the larger The value corresponds to a lower dehydrogenation temperature or a higher hydrogen absorption and dehydrogenation equilibrium pressure parameter, that is, the criterion function The larger it is, the more unstable the alloy's dehydrogenation thermodynamics is, which means that the alloy's dehydrogenation equilibrium pressure or dehydrogenation temperature increases or the absolute value of the dehydrogenation enthalpy change decreases.

[0055] Embodiment 1:

[0056] This embodiment provides a criterion method for the dehydrogenation thermodynamics of a BCC high entropy hydrogen storage alloy in a TiVNbCr system, as follows:

[0057] ① Four TiVNbCr-based high entropy hydrogen storage alloys with different Cr contents were designed, and their compositions are Ti40V30Nb10Cr20, Ti35V30Nb10Cr25, Ti30V30Nb10Cr30 and Ti25V30Nb10Cr35 respectively.

[0058] ② Calculate the thermodynamic equilibrium phase diagrams of the four alloys in ① above respectively, and obtain the phase structure of the alloys at different temperatures, such as Figure 1 As shown. It can be seen that the four alloys have a single-phase BCC phase region in the high temperature range. For example, the single-phase BCC temperature range of Ti25V30Nb10Cr35 is 1070~1826K. In order to ensure that the designed alloy is a single-phase BCC structure, all alloys are subjected to high-temperature quenching treatment at 1473K. The phase structure of the alloy obtained after quenching is determined to be a single-phase BCC structure by X-ray diffraction technology XRD characterization, as shown in Figure 2 shown.

[0059] ③ The average valence electron concentration and modified modulus-volume ratio of the four alloys were calculated respectively, and the relevant parameters were obtained as shown in Table 1:

[0060] Table 1: Composition parameters of TiVNbCr high entropy alloys with different Ti contents

[0061]

[0062] From the obtained parameters, it can be seen that as the Ti content decreases, the average valence electron concentration VEC of the alloy increases, and the modified modulus-volume ratio Increase, according to the criterion function, it is expected that with the decrease of Ti content, the thermodynamic stability of alloy hydride decreases and the hydrogen desorption performance improves.

[0063] ④Verify the validity of the criterion function. PCT tests were performed on the four alloys at different temperatures. The dehydrogenation enthalpy changes of the alloys were calculated by combining the actual experimental data with the Van't Hoff equation. The calculations show that the dehydrogenation enthalpy changes of Ti40, Ti35, Ti30 and Ti25 alloys are -61.19, -57.94, -51.38 and -49.30 kJ / mol, respectively. The decrease in the absolute value of the dehydrogenation enthalpy change of the alloys indicates that the stability of the alloy hydride decreases, that is, the dehydrogenation performance improves. The relevant results are completely consistent with the prediction results of the criterion function, indicating the validity of the criterion function.

[0064] Embodiment 2:

[0065] The dehydrogenation thermodynamic modification design of TiVNbCrMo system high entropy hydrogen storage alloy is as follows:

[0066] ① Four TiVNbCrMo high entropy hydrogen storage alloys with different Mo contents were designed, and their compositions are Ti25V30Nb10Cr35, Ti25V30Nb10Cr33Mo2, Ti25V30Nb10Cr31Mo4, and Ti25V30Nb10Cr29Mo6 alloys respectively.

[0067] ② The thermodynamic equilibrium phase diagrams of the above four alloys were calculated respectively to obtain the phase structures of the alloys at different temperatures. It can be seen that the four alloys have a single-phase BCC phase region in the high temperature range. In order to ensure that the designed alloys are single-phase BCC structures, all alloys were subjected to high-temperature quenching treatment at 1473K. The phase structure of the alloy obtained after quenching was determined to be a single-phase BCC structure by XRD characterization.

[0068] ③ The average valence electron concentration and modified modulus-volume ratio of the four alloys were calculated respectively, and the relevant parameters were obtained as shown in Table 2:

[0069] Table 2: Composition parameters of TiVNbCrMo high entropy alloys with different Mo contents

[0070]

[0071] From the obtained parameters, it can be seen that with the addition of Mo content, the average valence electron concentration VEC of the alloy remains unchanged, and the modified modulus-volume ratio Increase, according to the criterion function, it is expected that with the increase of Mo content, the thermodynamic stability of alloy hydride decreases and the hydrogen desorption performance improves.

[0072] ④ Verify the validity of the criterion function. DSC tests were performed on the hydrides formed by the four alloys to determine the thermodynamic stability of the hydrides. The DSC heating curves obtained by the tests are shown in Figure 4. Figure 3As shown in the figure, it can be seen that the first endothermic peak positions of Ti25, Mo2, Mo4, and Mo6 hydrides are 623, 577, 493, and 436 K, respectively. As the Mo content increases, the decomposition endothermic peak temperature of the alloy hydride decreases, which indicates that the stability of the alloy hydride decreases, that is, the hydrogen release performance improves. The relevant results are completely consistent with the prediction results of the criterion function, indicating the effectiveness of the criterion function.

[0073] Embodiment 3:

[0074] The dehydrogenation thermodynamic modification design of TiVNbCrFe system high entropy hydrogen storage alloy is as follows:

[0075] ① Four TiVNbCrFe-based high entropy hydrogen storage alloys with different Fe contents were designed, and their compositions are Ti25V30Nb10Cr35, Ti25V30Nb10Cr33Fe2, Ti25V30Nb10Cr31Fe4, and Ti25V30Nb10Cr29Fe6 alloys respectively.

[0076] ② The thermodynamic equilibrium phase diagrams of the above four alloys were calculated respectively to obtain the phase structures of the alloys at different temperatures. It can be seen that the four alloys have a single-phase BCC phase region in the high temperature range. In order to ensure that the designed alloys are single-phase BCC structures, all alloys were subjected to high-temperature quenching treatment at 1473K. The phase structure of the alloy obtained after quenching was determined to be a single-phase BCC structure by XRD characterization.

[0077] ③ The average valence electron concentration and modified modulus-volume ratio of the four alloys were calculated respectively, and the relevant parameters were obtained as shown in Table 3:

[0078] Table 3: Composition parameters of TiVNbCrFe high entropy alloys with different Fe contents

[0079]

[0080] From the obtained parameters, it can be seen that with the addition of Fe content, the average valence electron concentration VEC of the alloy increases, and the modified modulus-volume ratio According to the criterion function, it is expected that with the increase of Fe content, the thermodynamic stability of alloy hydrides will decrease and the hydrogen desorption performance will improve.

[0081] ④ Verify the validity of the criterion function. The four alloys were subjected to PCT tests of hydrogen absorption and desorption at 303K, 313K, and 323K, respectively. The PCT curves obtained are shown in Figure 4. Figure 4As shown in the figure, it can be seen that the dehydrogenation pressures of Ti25, Fe2, Fe4, and Fe6 at 323K are 0.12MPa, 0.21MPa, and 0.28MPa, respectively. With the increase of Fe content, the dehydrogenation equilibrium pressure of the alloy increases, which indicates that the stability of the alloy hydride decreases, that is, the dehydrogenation performance improves. The relevant results are completely consistent with the prediction results of the criterion function, indicating the effectiveness of the criterion function.

[0082] The above is only a preferred implementation case of the present invention and does not limit the present invention in any form. Although the implementation process of the present invention is described in detail above, for those familiar with the art, they can still modify the technical solutions recorded in the above examples, or replace some of the technical features therein with equivalents. All modifications, equivalent replacements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining the thermodynamics of hydrogen release of a BCC high entropy hydrogen storage alloy, characterized in that: The following steps are involved: Step 1: In a given high entropy hydrogen storage alloy system, obtain the phase composition of the alloy at different temperatures through phase diagram thermodynamic calculation; Step 2: According to the alloy phase composition at different temperatures, the given initial alloy is subjected to high-temperature water quenching heat treatment in the single-phase BCC temperature range, and then the alloy system is characterized and determined to be a single-phase BCC structure by means of phase structure characterization; Step 3: Calculate the average valence electron concentration and modified modulus-volume ratio of the alloy respectively; Step 4: Based on the average valence electron concentration and the modified modulus-to-volume ratio, define a criterion function for the dehydrogenation thermodynamics of the high entropy alloy, and determine the dehydrogenation thermodynamics of the alloy using the criterion function.

2. The judgment method according to claim 1, characterized in that: In step 3, the average valence electron concentration of the alloy is calculated by the theoretical composition of the alloy, and the linear weighted formula is used for calculation: Among them, C i is the atomic ratio of metal elements in the alloy, VEC i is the valence electron concentration of the metal element, and n is the type of metal element in the alloy.

3. The judgment method according to claim 2, characterized in that: In step 3, the molar volume of the alloy is corrected using the stacking density and the linear expansion coefficient, and the corrected modulus-volume ratio of the alloy is calculated. The specific expression is as follows: V i =V oi (1+α i (T-T o )) 3 , V oi =V o ×k, Among them, V i is the modified molar volume of a single element in the alloy, α i is the linear expansion coefficient of a single element in the alloy, T o is room temperature, T is the melting point of the alloy, V o is the molar volume of a single element in the alloy, k is the atomic stacking density corresponding to a single element, It is the melting point of a single metallic element in an alloy.

4. The judgment method according to claim 3, characterized in that: In step 4, the thermodynamic criterion function expression of the high entropy alloy dehydrogenation is: The average valence electron concentration VEC and the modified modulus-volume ratio of the alloy At the same time as an independent variable, and satisfy:

1. The larger the VEC, The larger the value, the greater the criterion function The bigger; 2. VEC remains unchanged. The larger the value, the greater the criterion function The bigger; 3. The larger the VEC, When unchanged, the criterion function The bigger.

5. The judgment method according to claim 4, characterized in that: When the criterion function The larger the value, the higher the dehydrogenation equilibrium pressure or dehydrogenation temperature of the alloy, or the lower the absolute value of the dehydrogenation enthalpy change.

6. The judgment method according to claim 1, characterized in that: The physical phase structure characterization method adopts X-ray diffraction technology.

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