A method of predicting transition metal catalytic strength for borohydride

Abstract

The application discloses a method for predicting catalytic strength of transition metal on borohydride, comprising: constructing a model of metal and a model of BH4 group, setting parameters related to the model, performing structure optimization calculation on the constructed model, obtaining work functions (W f ) of surfaces of nine transition metals as indexes of inherent properties of the transition metals, marking catalytic strength of different 4d transition metals on BH4, and obtaining predicted catalytic strength by using a data analysis method. The method can realize efficient prediction and selection of a suitable borohydride metal catalyst, reduce prediction cost, has good practicability, and provides a new insight into catalytic performance of transition metal on borohydride.

Description

Technical Field

[0001] This invention relates to the field of catalytic hydrogen evolution technology, specifically a method for predicting the catalytic strength of transition metals for borohydrides. Background Technology

[0002] In recent years, the non-renewable nature of traditional energy sources, the increasing pollution levels, and the massive global energy consumption have made the search for a new, sustainable energy source urgent. Hydrogen, with its excellent energy density, cleanliness, and renewability, has become a subject of intense research among scientists. However, the storage and transportation of hydrogen has always been a major challenge for many researchers. Hydrogen storage generally involves high-pressure gas storage, cryogenic liquid storage, or solid-state hydrogen storage. Currently, storing hydrogen in metal hydrides through chemical or physical adsorption is a relatively safe and efficient method. Among these, metal borohydrides are favored by researchers due to their extremely high volumetric hydrogen density and hydrogen storage capacity. However, the excellent thermal stability of metal borosilicates results in high requirements for the temperature and other conditions necessary for hydrogen release. Therefore, finding a feasible method to reduce the conditions and difficulties for releasing hydrogen from metal borohydrides is essential.

[0003] Currently known methods for improving the hydrogen evolution efficiency of metal borohydrides include adding metals, metal halides or oxides, and metal hydrides to disrupt their thermodynamic stability; catalyst introduction and nanoengineering are also common methods to improve their hydrogen storage performance, with the addition of transition metals often being one of the most frequently used techniques to enhance the performance of metal borohydrides. Although the catalytic ability of transition metals for borohydrides has been extensively demonstrated, a straightforward method for predicting specific catalytic intensities is lacking. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for predicting the catalytic intensity of transition metals on borohydrides, based on first-principles calculations. This method enables efficient prediction and selection of suitable borohydride metal catalysts, reduces prediction costs, and offers good practicality, providing new insights into the catalytic performance of transition metals on borohydrides.

[0005] The technical solution to achieve the objective of this invention is:

[0006] A method for predicting the catalytic strength of transition metals for borohydrides includes the following steps:

[0007] 1) Select the most stable structure of the most stable surface corresponding to the nine 4d transition metals Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd and Ag, and construct the metal model to be calculated and the model of the BH4 group. According to the physical chemistry handbook, the most stable structure of Nb and Mo is the BCC structure, the most stable structure corresponding to Rh, Pd and Ag is the FCC structure, and the most stable structure of the last four Y, Zr, Tc and Ru is the HCP structure. For the three metals with different structures BCC, FCC and HCP, the 110 facet, 111 facet and 0001 facet are selected as the most stable surfaces corresponding to the three structures respectively.

[0008] 2) Set the relevant parameters for the model and perform structural optimization calculations on the constructed model: When optimizing the 4d transition metal surface, the preferred optimization parameters are: the k-space mesh is preferably 6×6×1, and the plane wave energy accuracy is 1×10⁻⁶. -5 eV / atom, plane wave cutoff energy Ecut is 450eV, self-consistent convergence error is 1×10 -4 When optimizing the BH4 group model, the k-space grid is 5×5×5; the cutoff energy and self-consistent convergence error are preferably set the same as those when optimizing the 4d transition metal, resulting in 9 stable 4d transition metal surface structures.

[0009] 3) The work function (W) of nine transition metal surfaces was calculated using VASP. f As an intrinsic property index of transition metals, the work function is the minimum energy required to transfer an electron from the Fermi level to a field-free region. It is an important fundamental electronic property of metal surfaces, as shown in formula (1):

[0010] W f =φ0-E f (1),

[0011] Where φ0 is the electrostatic potential energy under the vacuum level corresponding to the current transition metal structure model, E f This is represented as the Fermi energy of the current structural model;

[0012] 4) After obtaining the stable surface structures of nine 4d transition metals and the stable BH4 group structure, the adsorption sites of the three 4d transition metals were tested. In the optimized adsorption model, the BH4 group tended to adsorb at the HCP site. The HCP site was selected to complete the adsorption of the transition metal on the BH4 group.

[0013] 5) After obtaining the stable state structural models of 9 TM@BH4, the BH bond length in BH4 was measured using the first-principles simulation software MaterialsStudio. This was used to mark the catalytic strength of different 4d transition metals for BH4. The longer the BH bond length, the higher the catalytic strength of the corresponding 4d transition metal.

[0014] 6) The number of valence electrons in TM@BH4 was calculated and analyzed using Bader charge analysis to study the electron exchange between the transition metal and the BH4 group in TM@BH4. The catalytic intensity was predicted by the properties of the transition metal through data analysis.

[0015] This method enables efficient prediction and selection of suitable borohydride metal catalysts, reduces prediction costs, and is highly practical, providing new insights into the catalytic performance of transition metals on borohydrides. Attached Figure Description

[0016] Figure 1 These are schematic diagrams of the three metal structures selected in the embodiments;

[0017] Figure 2 This is a graph showing the trend of work function changes for the nine 4d transition metals obtained in the examples.

[0018] Figure 3 This is a schematic diagram of the TM@BH4 structure after BH4 adsorption obtained in the example;

[0019] Figure 4 The graph shows the variation trend of BH bond lengths corresponding to BH4 adsorbed on the surfaces of the nine 4d transition metals obtained in the examples.

[0020] Figure 5 The charge transfer amount corresponds to the three H atoms adsorbed on the metal surface by TM@BH4 in the example. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this is not intended to limit the scope of the invention.

[0022] Example:

[0023] A method for predicting the catalytic strength of transition metals for borohydrides includes the following steps:

[0024] 1) Select the most stable structures of the most stable surfaces corresponding to the nine 4d transition metals: Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag. Using the first-principles simulation software Materials Studio, construct the metal models to be calculated and the BH4 group model. According to the physical chemistry handbook, the most stable structure for Nb and Mo is the BCC structure, for Rh, Pd, and Ag it is the FCC structure, and for the last four (Y, Zr, Tc, and Ru) it is the HCP structure. For the three metals with different structures (BCC, FCC, and HCP), the 110, 111, and 0001 planes are selected as the most stable surfaces corresponding to the three structures, respectively. Figure 1 As shown;

[0025] 2) Set the relevant parameters for the model and perform structural optimization calculations on the constructed model: When optimizing the 4d transition metal surface, the preferred optimization parameters are: the k-space mesh is preferably 6×6×1, and the plane wave energy accuracy is 1×10⁻⁶. -5 eV / atom, plane wave cutoff energy Ecut is 450eV, self-consistent convergence error is 1×10 -4 eV / atom, when optimizing the BH4 group model, the k-space grid is 5×5×5; the cutoff energy and self-consistent convergence error are preferably set the same as when optimizing the 4d transition metal, resulting in 9 stable 4d transition metal surface structures and BH4 group structures.

[0026] 3) The work function (W) of nine transition metal surfaces was calculated using VASP. f As an intrinsic property index of transition metals, the work function is the minimum energy required to transfer an electron from the Fermi level to a field-free region. It is an important fundamental electronic property of metal surfaces, as shown in formula (1):

[0027] W f =φ0-E f (1),

[0028] Where φ0 is the electrostatic potential energy under the vacuum level corresponding to the current transition metal structure model, E f This is represented as the Fermi energy of the current structural model;

[0029] The final calculations yielded the following trends in the work functions of the nine 4d transition metals: Figure 2As shown, the calculated values ​​in this example are compared with the calculated data included in the Materials Project data database to ensure the accuracy of the data. The errors in the data obtained in this example are all within an acceptable range. The work function means the strength of the binding force on electrons. Obviously, as the atomic number increases, the binding force on electrons of each transition metal in the same period gradually increases. In the case of Ag metal, its work function will return to an average value.

[0030] 4) After obtaining the stable state of nine 4d transition metal surface structures and the stable state of the BH4 group structure, this invention tested the adsorption sites of the 4d transition metals in the three structures. In this example, for the 110 facet of the BCC structure, there are three adsorption sites: the Top site, the Bridge site, and the Hcp site. For the 111 facet of the FCC structure and the 0001 facet of the HCP structure, in addition to the above three sites, there is an additional Fcc site. After multiple tests, it was found that for different faces of the three different structures, the BH4 group tends to adsorb at the Hcp site in the optimized adsorption model. Therefore, the Hcp site was selected to complete the adsorption of the transition metal on the BH4 group. The adsorption results are as follows: Figure 3 As shown, for most of the selected transition metals, the entire group is adsorbed at the Hcp site. Except for the H atom at the top of the BH4 group, the other H atoms are all located at the Top site. However, for the Y transition metal structure, the three H atoms are adsorbed at the bridge site between the metals. The more obvious difference is reflected in the adsorption state on the Nb metal surface. Of the three H atoms, two H atoms are adsorbed on the metal-metal bond, while the other H atom is in a suspended state. All adsorption energies are negative, that is, the BH4 group tends to spontaneously adsorb onto the TM surface.

[0031] 5) After obtaining the stable-state structural models of 9 TM@BH4, the BH bond lengths in BH4 were measured using the first-principles simulation software MaterialsStudio. This was used to indicate the catalytic strength of different 4d transition metals for BH4, and the trends are shown below. Figure 4 As shown, the longer the BH bond length, the higher the catalytic strength of the corresponding 4d transition metal. The bond length of a single BH4 group after optimization is approximately... from Figure 4It is not difficult to observe that for all transition metals, the bond length changes of the BH4 group show a similar trend: the H atom at the top of the group is compressed, and the bond length becomes shorter; while the boron-hydrogen bond lengths corresponding to the other three H atoms adsorbed on the surface are stretched to varying degrees. Therefore, it can be preliminarily determined that under the catalytic effect of transition metals, the bond energy of the BH bond in the BH4 group is weakened to varying degrees. The trend shows that it first gradually increases, reaches a peak at Rh, and then decreases. Among them, Rh has the strongest catalytic ability for the BH4 group. Except for Y and Nb, which have different bond lengths due to different adsorption states, this trend has a certain positive correlation with the previously measured work function of transition metals.

[0032] 6) This example uses Bader charge analysis to calculate and analyze the number of valence electrons in TM@BH4, and studies the changing trend of electron exchange between the transition metal and the BH4 group in TM@BH4. Figure 5 As shown, all H atoms adsorbed on the surface exhibit weak negative charge. For each transition metal, the higher the corresponding work function, the stronger the ability to gain electrons and the weaker the ability to lose electrons. Since Rh and Pd metals have high work functions, fewer electrons can be provided to the BH4 group on the metal surface. This leads to a decrease in the number of electrons that H atoms adsorbed on their surfaces can gain. Y metal, which has the highest H atom charge transfer, also corresponds to the lowest work function of its structure. Except for Y and Nb, which have different bond lengths due to different adsorption states, the charge transfer trend of other H atoms is basically negatively correlated with the BH bond length. That is, Rh@BH4, which has the longest BH bond, has the lowest number of electrons gained by H atoms.

[0033] In summary, there is a strong correlation between the intrinsic work function of 4d transition metals and the BH bond length and H charge transfer in TM@BH4, which means that the weakening ability of the BH bond in the BH4 group can be roughly predicted by the work function of different structures and surfaces of the transition metal.

Claims

1. A method for predicting the catalytic strength of transition metals for borohydrides, characterized in that, Includes the following steps: 1) Select the most stable structure of the most stable surface corresponding to the nine 4d transition metals Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd and Ag, and construct the metal model to be calculated and the model of the BH4 group. According to the physical chemistry handbook, the most stable structure of Nb and Mo is the BCC structure, the most stable structure corresponding to Rh, Pd and Ag is the FCC structure, and the most stable structure of the last four Y, Zr, Tc and Ru is the HCP structure. For the three metals with different structures BCC, FCC and HCP, the 110 facet, 111 facet and 0001 facet are selected as the most stable surfaces corresponding to the three structures respectively. 2) Set the relevant parameters for the model and perform structural optimization calculations on the constructed model: When optimizing the 4D transition metal surface, the optimization parameters are: k-space mesh is 6×6×1, and plane wave energy accuracy is 1×10. -5 eV / atom, plane wave cutoff energy Ecut is 450eV, self-consistent convergence error is 1×10 -4 When optimizing the BH4 group model, the k-space grid is 5×5×5; the cutoff energy and self-consistent convergence error are consistent with the settings when optimizing the 4d transition metal, resulting in 9 stable 4d transition metal surface structures. 3) The work function (W) of nine transition metal surfaces was calculated using VASP. f As an intrinsic property index of transition metals, the work function is the minimum energy required to transfer an electron from the Fermi level to a field-free region, as shown in equation (1): W f =φ0-E f (1), Where φ0 is the electrostatic potential energy under the vacuum level corresponding to the current transition metal structure model, E f This is represented as the Fermi energy of the current structural model; 4) After obtaining the stable surface structures of nine 4d transition metals and the stable BH4 group structure, the adsorption sites of the three 4d transition metals were tested. In the optimized adsorption model, the BH4 group tended to adsorb at the HCP site. The HCP site was selected to complete the adsorption of the transition metal on the BH4 group. 5) After obtaining the stable state structural models of 9 TM@BH4, the BH bond length in BH4 was measured using the first-principles simulation software Materials Studio. This was used to mark the catalytic strength of different 4d transition metals for BH4. The longer the BH bond length, the higher the catalytic strength of the corresponding 4d transition metal. 6) The number of valence electrons in TM@BH4 was calculated and analyzed using Bader charge analysis to study the electron exchange between the transition metal and the BH4 group in TM@BH4. The catalytic intensity was predicted by the properties of the transition metal through data analysis.

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