CN114843534A - Method for efficiently designing potential ORR and NRR catalysts based on air as reaction gas source - Google Patents

Abstract

The invention provides a method for efficiently designing potential ORR and NRR catalysts based on air as a reaction air source, which is characterized in that a single-atom catalyst model is constructed based on different N-C coordination environments and different active site Tm atoms, and a potential ORR or NRR catalyst which is suitable for air as a reaction air source is rapidly positioned by carrying out layer-by-layer progressive screening of stability analysis, competitive adsorption of air main components and desorption of substances based on a first principle density functional theory. The invention can quickly realize the ORR and NRR catalyst design by taking the air source as the reaction gas source, and improves the catalyst design efficiency and the air source adaptability. The large-scale use of the related catalyst can promote the popularization of new energy, reduce environmental pollution and protect ecological environment.

Description

A method for efficient design of potential ORR and NRR catalysts based on air as the reactive gas source

technical field

The invention provides a method for efficiently designing potential ORR and NRR catalysts based on air as a reaction gas source, belonging to the technical field of air purification catalysts.

Background technique

Energy crisis and environmental pollution are serious global problems, and in the field of electrocatalytic materials science research, there is an urgent need to discover efficient and robust electrochemical energy conversion and storage systems/devices for a sustainable future. Oxygen reduction reaction (ORR) and nitrogen reduction reaction (NRR) play a pivotal role in oxygen electrocatalysis.

ORR Background Implications: Proton membrane fuel cells have the advantages of high efficiency and low emissions compared to petroleum combustion, but the main obstacle to commercialization of fuel cells is the slow kinetics of ORR at the fuel cell cathode, which may lead to reduced PMT efficiency30 %, so in order to solve this problem of the proton membrane fuel cell, it is necessary to select a suitable catalyst for use in the fuel cell to improve its efficiency, so that it can be widely used in social life. While improving social and economic benefits, it can also protect the ecological environment. The precious metal platinum is commonly used as an ORR catalyst. If the rare and expensive noble metal-based electrocatalysts cannot be replaced by other low-cost, noble metal-free but highly efficient and durable electrodes, the large-scale practical application of these renewable energy devices will be greatly hindered. The exploration of cheap, efficient, and stable bifunctional non-precious metal (NPM) alternatives is of particular importance today.

NRR Background Implications: Ammonia is one of the world's most produced chemical products and plays an important role in the global economy. At present, global ammonia production mainly comes from the traditional Haber ammonia synthesis process: that is, using iron-based catalysts to convert high-purity nitrogen and hydrogen into ammonia under high temperature and high pressure conditions. Since the N≡N bond in nitrogen has strong bond energy (945kJmol ^-1 ), the process must be activated at high temperature (300-500℃) and high pressure (150-300atm), resulting in energy consumption and CO ₂ Emissions account for 1-3% and 1.6-3% of the global total, respectively. The Haber process for ammonia synthesis has high energy consumption and serious pollution. Therefore, it is of great significance for the sustainable development of the national economy to find a green, environmentally friendly and low-energy-consumption ammonia synthesis method. The electrochemical ammonia synthesis method can make the thermodynamic non-spontaneous ammonia synthesis reaction not limited by the thermodynamic equilibrium under the promotion of electric energy, and realize the synthesis of ammonia at room temperature and pressure, so it has become a research field that has attracted much attention.

For example, to synthesize a single-atom catalyst: 2-methylimidazole 2-MeIm and zinc nitrate Zn(NO ₃ ) ₂ are mixed in an appropriate amount of methanol CH ₃ OH solvent at a mass of 1:2 to prepare a ZIF8 solution. Then add transition metal-acetylacetonate Tm-(acac) _X with zinc nitrate and other substances, stir for 0.5 hours, then transfer to a polytetrafluoroethylene hydrothermal synthesis reactor, heat to 120°C and keep for 4 hours. The precipitate was obtained by high-speed centrifugation in a centrifuge, washed with methanol CH ₃ OH, and then vacuum-dried at a constant temperature of 60 °C for 12 hours to obtain the precursor Tm@ZIF8 encapsulating Tm-(acac) _X. The prepared precursor Tm@ZIF8 was put into a tube furnace and heated to 920 °C (slightly higher than the boiling point of Zn at 907 °C) at a heating rate of ₅ °C/min under flowing N conditions, evaporating Zn while leaving High boiling point transition metal Tm) and kept for 2 hours, annealed to room temperature with the furnace. Then, the powder was acid-washed with an appropriate amount of H ₂ SO ₄ at room temperature for 2 hours to remove potential large-sized metal substances. Finally, it was washed with ultrapure water by centrifugation, and was vacuum-dried at a constant temperature of 60 °C for 24 hours to obtain the transition metal-doped porous carbon. based single-atom catalysts.

Characterization phase information: BET specific surface area and pore size distribution were determined by nitrogen adsorption instrument. The structure and phase of the synthesized catalyst samples were determined by X-ray diffractometer. The microstructure and morphology were observed by transmission electron microscope TEM and scanning electron microscope SEM; the content and distribution of different elements in the synthesis catalyst were detected by X-ray energy dispersive analyzer EDS; and the inductively coupled plasma mass spectrometer ICP-MS was used to accurately The elemental content of transition metals was determined. The overall phase information of the catalyst at the microscopic level is obtained through relevant test analysis. At the same time, the relevant information of the active center configuration of the synthesized catalyst can be further obtained by high-angle annular dark-field scanning electron microscope HAADF-STEM and selected area electron diffraction SAED; X-ray photoelectron spectroscopy was used to study the active center configuration of the catalyst samples by XPS spectrometer system. Elements and their valence states; based on X-ray absorption near-edge spectroscopy XANES and extended X-ray absorption fine structure EXAFS to characterize the coordination relationship of the active center configuration. The above-mentioned test characterization comprehensively provides specific information on the Tm active site and the N-C coordination environment.

Electrochemical test: 5 mg of catalyst sample dispersed in a mixture of 480 μL of ethanol, 480 μL of H ₂ O and 40 μL of 5% perfluorosulfonic acid in ethanol was degraded by sonication for 0.5 h. Then, the catalyst juice was dropped on a polished glassy carbon rotating disk electrode RDE or rotating disk ring electrode RRDE with a diameter of d=5 mm and dried at room temperature. The catalyst loading was -0.5 mg/cm ² .

ORR: A three-electrode system was used for the test at room temperature, in an acidic environment: the electrolyte was a saturated _N2 / _O2 aqueous solution of 0.1 M _HClO4 , respectively, the reference electrode was a saturated calomel electrode SCE, and the counter electrode was a carbon electrode. All measured potentials were converted to the reversible hydrogen electrode potential RHE. First, perform CV scan by cyclic voltammetry to calculate electric double layer capacitance C _dl and electrochemical specific surface area ECSA; then perform linear scan voltammetry LSV scan to obtain ORR onset potential E _onset , half-wave potential E _1/2 and limit Diffusion current density DLCD, and then the electrocatalytic ORR overpotential η was obtained, the Tafel slope was obtained by fitting the LSV curve, the reaction rate-limiting step RDS was determined, and the Nyquist diagram was obtained based on the electrochemical impedance spectroscopy EIS test, and the charge transfer resistance Rct was obtained; Finally, by testing the CV curve in neutral phosphate buffered saline (PBS), the TOF of the switching frequency of the catalyst was explored. The stable durability of the catalyst was analyzed by cycle durability test and potentiostatic durability test. The electron transfer number n during ORR was calculated from the slope of the _{Koutecky -} Levich (KL) curve, and the yield of the side reaction H2O2 was calculated based on the electron transfer number n.

NRR: Using Nafion 117 as the anion exchange membrane, the NRR electrochemical performance of various catalysts was investigated on a typical H-type cell of the CHI660 electrochemical workstation in Shanghai Chenhua. Electrochemical measurements were performed at room temperature using a three-electrode system, in which ammonia was measured by colorimetry, hydrogen was detected by gas chromatography (GC Agilent 7890B), and by-product hydrazine was characterized by Watt and Chrisp methods. Obtain the catalytic performance parameters such as Faradaic efficiency FE and ammonia yield in NRR process.

The above method cannot directly utilize air, and requires pure oxygen and nitrogen to study and participate in the reaction respectively. Pure oxygen and nitrogen need to be industrially separated by using air as raw material (the air is liquefied at high pressure and low temperature, the boiling point of nitrogen is -195.8°C, and the boiling point of oxygen is -183°C. Gas and liquid can be separated). The separation process consumes high energy, and the pure gas needs to be stored and transported through high-pressure gas cylinders. The process is complicated, the cycle is long, the cost is high, and there is a certain safety. In addition, with pure gas as the gas source, the related equipment needs to be connected to the high-pressure gas cylinder device, which leads to the complex structure of the equipment.

The catalyst research and development process based on experimental synthesis of catalysts, analysis and characterization of phase information, and electrochemical testing of catalytic performance faces challenges such as long research and development cycles, large consumption of manpower and material resources, resulting in three wastes and time-consuming and laborious processing. In addition, the sensitivity of catalysts to other gases is unknown, Unknown catalytic mechanism and other deficiencies can easily lead to blindly prepared catalysts that cannot be truly practical.

SUMMARY OF THE INVENTION

In the whole electrochemical catalysis process of ORR and NRR, involving rather complex reaction pathways and slow kinetics, the selection of suitable electrocatalysts plays a decisive role in catalytic activity, durability, product selectivity, and practical cost. Because the main components in the air are N ₂ and O ₂ , it also contains a small amount of H ₂ O and CO ₂ and other gases, and a small amount of H ₂ O and CO ₂ and other gases are dissolved in water when they are passed into the solution, because of their content The acid-prone environmental impact on proton membrane fuel cells and NRR catalysts is almost zero. The reactant of ORR is O ₂ , and the reactant of NRR is N ₂ , so the most economical, convenient and safe reactant of ORR and NRR comes from air, in which a small amount of H ₂ O and CO ₂ in the air can dissolve Therefore, based _on the Tm _- NC coordination relationship to regulate the selective adsorption of N and O, it can provide guidance for the screening of potential ORR and NRR catalysts.

Building a model for analysis and calculation based on theory is an important method and means for scientific research, and has important data support for further experimental analysis. How to quickly determine the efficient selection of potential ORR/NRR catalysts based on theoretical research is a very important technology. The present invention provides a simple and feasible advanced screening process for efficiently selecting potential ORR/NRR catalyst models, which can directly pass air into the catalyst.

The present invention avoids the complicated and energy-consuming process of preparing pure O ₂ /N ₂ , and now directly passes air into the catalyst, which can be more convenient and energy-saving. The invention constructs a single-atom catalyst model based on different NC coordination environments and different active site Tm atoms, and relies on first-principles to carry out stability analysis → competitive adsorption of air main components → product desorption layer-by-layer progressive screening, and rapid positioning A catalyst for ORR or NRR that can potentially adapt to air as the reactive gas source.

The specific method is:

A method for the efficient design of potential ORR and NRR catalysts based on air as the reactive gas source, including the following steps:

S1. Based on the first-principles density functional theory, construct a base catalyst model including all transition metals in single and double vacancies and N-doped graphene with different concentrations, which are denoted as Tm-N _X -C _3-X -Gra and Tm-N _X -C _4-X -Gra; according to the nitrogen-carbon combination configuration, the Tm-N ₂ -C ₂ -Gra configuration is divided into five-membered ring pen, para-type opp and six-membered ring type hex;

S2. For the double vacancy catalyst model formed by N-coordinate single transition metal doped graphene, the formation energy ΔE _f of all pre-screened models is calculated according to the formation energy ΔE _f calculation formula (1) and the binding energy ΔE _b calculation formula (2). and binding energy ΔE _b ; screen stable catalyst configurations according to ΔE _f <0eV and ΔE _b <E _coh ; E _coh is the metal cohesion energy;

和E_Gra分别代表双空位型单原子催化剂Tm-N_X-C_4-X-Gra、缺过渡金属的催化剂模型N_X-C_4-X-Gra和石墨烯Gra的体系能量，E_C、E_Tm、E_N分别代表单原子C、N、Tm的能量；in

and E _Gra represent the system energies of the double-vacancy single-atom catalyst Tm-N _X -C _4-X- Gra, the transition metal-deficient catalyst model N _X -C _4-X -Gra and graphene Gra, respectively, E _C , E _Tm and EN represent the energy of single atoms C, _N and Tm, respectively;

和

分别代表单空位型单原子催化剂Tm-N_X-C_3-X-Gra和缺过渡金属的催化剂模型N_X-C_3-X-Gra体系能量；For the single-vacancy catalyst model, its formation energy ΔE _f and binding energy ΔE _b are calculated as formulas (3) and (4), respectively; where

and

represent the energies of the single-vacancy single-atom catalyst Tm-N _X -C _3-X- Gra and the transition metal-deficient catalyst model N _X -C _3-X- Gra system, respectively;

S3, construct the adsorption model of O ₂ under different adsorption modes and optimize the structure, select the adsorption model with the lowest energy, and calculate the adsorption energy of the catalyst for O ₂ according to formula (5);

是指催化剂吸附O₂的体系总能量，

是指单个O₂分子的能量，sub为催化剂基底模型，单空位和双空位模型，分别记为Tm-N_X-C_3-X-Gra和Tm-N_X-C_4-X-Gra；in

is the total energy of the system for adsorbing _O2 by the catalyst,

refers to the energy of a single O ₂ molecule, sub is the catalyst substrate model, single-vacancy and double-vacancy models, respectively denoted as Tm-N _X -C _3-X- Gra and Tm-N _X -C _4-X- Gra;

S4, construct the adsorption model of N ₂ under different adsorption modes and optimize the structure, select the adsorption model with the lowest energy, and calculate the adsorption energy of the catalyst for N ₂ according to formula (6);

是指催化剂吸附N₂的体系总能量，

是指单个N₂分子的能量；in

is the total energy of the system for the adsorption of _N2 by the catalyst,

refers to the energy of a single _N2 molecule;

S5. Comparing the adsorption energy of O ₂ and N ₂ on the same substrate, when the O ₂ adsorption energy is equal to or approximately equal to the N ₂ adsorption energy, it means that there will be co-adsorption of oxygen and nitrogen when air is used as the gas source. There is mixed coexistence of ORR and NRR; this situation is neither suitable for NRR nor ORR, discarded;

也即O₂吸附能力>N₂吸附能力时，说明催化剂会优先吸附氧气；

越小于

则选择性吸附O₂的能力越强；因考虑催化剂循环性，产物须较容易脱附或者不吸附；ORR反应产物为H₂O，所以进一步探究H₂O的吸附能，根据公式(7)；若

也即H₂O的吸附能力<O₂吸附能力，若当

则产物不会自发脱附，但易于强吸附的反应物挤占吸附位点导致脱附；若当

则产物有自发脱附的趋势；两种情况都表明满足

该催化剂适合用于ORR；反之不满足

则不适合做ORR，应舍去；S6, when

That is, when O ₂ adsorption capacity>N ₂ adsorption capacity, it means that the catalyst will preferentially adsorb oxygen;

less than

The ability to selectively adsorb O ₂ is stronger; due to the consideration of the catalyst cycle, the product must be easily desorbed or not adsorbed; the ORR reaction product is H ₂ O, so the adsorption energy of H ₂ O is further explored, according to formula (7) ;like

That is, the adsorption capacity of H ₂ O < the adsorption capacity of O ₂ , if when

The product will not desorb spontaneously, but the reactants that are easy to strongly adsorb will crowd the adsorption site and cause desorption;

then the product has a tendency to spontaneously desorb; both cases indicate that the

The catalyst is suitable for ORR; otherwise it is not satisfied

It is not suitable for ORR and should be discarded;

指催化剂吸附H₂O的体系总能量，

指单个H₂O分子的能量；in

refers to the total energy of the system for the adsorption of H ₂ O by the catalyst,

refers to the energy of a single H ₂ O molecule;

也即O₂吸附能力<N₂吸附能力时，因NRR反应产物为NH₃，所以进一步探究NH₃的吸附能，根据公式(8)；若

也即NH₃的吸附能力<N₂吸附能力，则该催化剂能循环NRR反应，也即能适合用于NRR；反之

表明活性位点吸附产物NH₃能力太强，即催化剂活性位点被产物NH₃钝化，无法循环应舍去；S7, when

That is, when O ₂ adsorption capacity<N ₂ adsorption capacity, since the NRR reaction product is NH ₃ , the adsorption energy of NH ₃ is further explored, according to formula (8); if

That is, the adsorption capacity of NH ₃ <N ₂ adsorption capacity, then the catalyst can cycle NRR reaction, that is, it can be suitable for NRR;

It shows that the ability of the active site to adsorb the product _NH3 is too strong, that is, the active site of the catalyst is passivated by the product _NH3 , which cannot be recycled and should be discarded;

指催化剂吸附NH₃的体系总能量，

指单个NH₃分子的能量；in

refers to the total system energy of the catalyst adsorbing _NH3 ,

Refers to the energy of a single _NH3 molecule;

Based on the progressive screening of the above S2-S7 steps, the scope of the research model is narrowed, the required model is quickly and accurately located, and the catalyst model of potential ORR/NRR is obtained, which provides design guidance for the experimental development of NRR and ORR catalysts with air as the reaction gas source .

The beneficial effects brought by the technical solution of the present invention:

In the industrial separation method, the air is first liquefied at high pressure and low temperature. The boiling point of nitrogen is -195.8°C, and the boiling point of oxygen is -183°C. As long as the temperature is controlled at -195.8°C to -183°C, gas and liquid can be separated. _In the present invention, air is directly used as the gas source of the reaction gas, and it is no longer _necessary to separate the N and O in the air first through the strategy of separating the gases according to the different boiling points of nitrogen and oxygen. participate in the reaction in the liquid. Avoid the use of high-pressure gas cylinders, reduce high-pressure gas docking equipment, simplify the process, and improve safety at the same time. In addition, it also has many advantages such as saving gas production costs, transportation costs, and avoiding unnecessary energy waste.

Based on the design method provided by the present invention, the design of the ORR and NRR catalysts using the air source as the source of the reaction gas can be quickly realized, and the catalyst design efficiency and the adaptability of the gas source are improved. The large-scale use of relevant catalysts can promote the popularization of new energy, reduce environmental pollution, protect the ecological environment, help my country achieve the task of double-carbon emission reduction, and improve the technological competitiveness of the catalytic industry.

Description of drawings

Figure 1 is a flow chart of the present invention.

Detailed ways

The specific technical solutions of the present invention are described with reference to the embodiments.

As shown in the process shown in Figure 1, the present invention is realized by progressive screening in order to achieve efficient selection of ORR and NRR catalysts; the selective adsorption of O ₂ /N ₂ is regulated based on the Tm-NC coordination relationship; the specific technical description scheme is as follows:

A method for the efficient design of potential ORR and NRR catalysts based on air as the reactive gas source, including the following steps:

S1. Based on the first-principles density functional theory, construct a base catalyst model including all transition metals in single and double vacancies and N-doped graphene with different concentrations, which are denoted as Tm-N _X -C _3-X -Gra and Tm-N _X -C _4-X -Gra; according to the nitrogen-carbon combination configuration, the Tm-N ₂ -C ₂ -Gra configuration is divided into five-membered ring pen, para-type opp and six-membered ring type hex;

S2. For the double-vacancy catalyst model formed by N-coordinated single transition metal doped graphene, the formation energies _{ΔE f and} Binding energy ΔE _b ; screen stable catalyst configurations according to ΔE _f <0 eV and ΔE _b <E _coh ; E _coh is the metal cohesion energy;

和E_Gra分别代表双空位型单原子催化剂Tm-N_X-C_4-X-Gra、缺过渡金属的催化剂模型N_X-C_4-X-Gra和石墨烯Gra的体系能量，E_C、E_Tm、E_N分别代表单原子C、N、Tm的能量；in

and E _Gra represent the system energies of the double-vacancy single-atom catalyst Tm-N _X -C _4-X- Gra, the transition metal-deficient catalyst model N _X -C _4-X -Gra and graphene Gra, respectively, E _C , E _Tm and EN represent the energy of single atoms C, _N and Tm, respectively;

和

分别代表单空位型单原子催化剂Tm-N_X-C_3-X-Gra和缺过渡金属的催化剂模型N_X-C_3-X-Gra体系能量；For the single-vacancy catalyst model, its formation energy ΔE _f and binding energy ΔE _b are calculated as formulas (3) and (4), respectively; where

and

represent the energies of the single-vacancy single-atom catalyst Tm-N _X -C _3-X- Gra and the transition metal-deficient catalyst model N _X -C _3-X- Gra system, respectively;

S3, construct the adsorption model of O ₂ under different adsorption modes and optimize the structure, select the adsorption model with the lowest energy, and calculate the adsorption energy of the catalyst for O ₂ according to formula (5);

是指催化剂吸附O₂的体系总能量，

是指单个O₂分子的能量，sub为催化剂基底模型，单空位和双空位模型，分别记为Tm-N_X-C_3-X-Gra和Tm-N_X-C_4-X-Gra；in

is the total energy of the system for adsorbing _O2 by the catalyst,

refers to the energy of a single O ₂ molecule, sub is the catalyst substrate model, single-vacancy and double-vacancy models, respectively denoted as Tm-N _X -C _3-X- Gra and Tm-N _X -C _4-X- Gra;

S4, construct the adsorption model of N ₂ under different adsorption modes and optimize the structure, select the adsorption model with the lowest energy, and calculate the adsorption energy of the catalyst for N ₂ according to formula (6);

是指催化剂吸附N₂的体系总能量，

是指单个N₂分子的能量；in

is the total energy of the system for the adsorption of _N2 by the catalyst,

refers to the energy of a single _N2 molecule;

S5. Comparing the adsorption energy of O ₂ and N ₂ on the same substrate, when the O ₂ adsorption energy is equal to or approximately equal to the N ₂ adsorption energy, it means that there will be co-adsorption of oxygen and nitrogen when air is used as the gas source. There is mixed coexistence of ORR and NRR; this situation is neither suitable for NRR nor ORR, discarded;

也即O₂吸附能力>N₂吸附能力时，说明催化剂会优先吸附氧气；

越小于

则选择性吸附O₂的能力越强；因考虑催化剂循环性，产物须较容易脱附或者不吸附；ORR反应产物为H₂O，所以进一步探究H₂O的吸附能，根据公式(7)；若

也即H₂O的吸附能力<O₂吸附能力，若当

则产物不会自发脱附，但易于强吸附的反应物挤占吸附位点导致脱附；若当

则产物有自发脱附的趋势；两种情况都表明满足

该催化剂适合用于ORR；反之不满足

则不适合做ORR，应舍去；S6, when

That is, when O ₂ adsorption capacity>N ₂ adsorption capacity, it means that the catalyst will preferentially adsorb oxygen;

less than

The ability to selectively adsorb O ₂ is stronger; due to the consideration of the catalyst cycle, the product must be easily desorbed or not adsorbed; the ORR reaction product is H ₂ O, so the adsorption energy of H ₂ O is further explored, according to formula (7) ;like

That is, the adsorption capacity of H ₂ O < the adsorption capacity of O ₂ , if when

The product will not desorb spontaneously, but the reactants that are easy to strongly adsorb will crowd the adsorption site and cause desorption;

then the product has a tendency to spontaneously desorb; both cases indicate that the

The catalyst is suitable for ORR; otherwise it is not satisfied

It is not suitable for ORR and should be discarded;

指催化剂吸附H₂O的体系总能量，

指单个H₂O分子的能量；in

refers to the total energy of the system for the adsorption of H ₂ O by the catalyst,

refers to the energy of a single H ₂ O molecule;

也即O₂吸附能力<N₂吸附能力时，因NRR反应产物为NH₃，所以进一步探究NH₃的吸附能，根据公式(8)；若

也即NH₃的吸附能力<N₂吸附能力，则该催化剂能循环NRR反应，也即能适合用于NRR；反之

表明活性位点吸附产物NH₃能力太强，即催化剂活性位点被产物NH₃钝化，无法循环应舍去；S7, when

That is, when O ₂ adsorption capacity<N ₂ adsorption capacity, since the NRR reaction product is NH ₃ , the adsorption energy of NH ₃ is further explored, according to formula (8); if

That is, the adsorption capacity of NH ₃ <N ₂ adsorption capacity, then the catalyst can cycle NRR reaction, that is, it can be suitable for NRR;

It shows that the ability of the active site to adsorb the product _NH3 is too strong, that is, the active site of the catalyst is passivated by the product _NH3 , which cannot be recycled and should be discarded;

指催化剂吸附NH₃的体系总能量，

指单个NH₃分子的能量；in

refers to the total system energy of the catalyst adsorbing _NH3 ,

Refers to the energy of a single _NH3 molecule;

Based on the progressive screening of the above S2-S7 steps, the scope of the research model is narrowed, the required model is quickly and accurately located, and the catalyst model of potential ORR/NRR is obtained, which provides design guidance for the experimental development of NRR and ORR catalysts with air as the reaction gas source .

Claims (2)

1. The method for efficiently designing the potential ORR and NRR catalysts based on air as a reaction air source is characterized in that a single-atom catalyst model is constructed based on different N-C coordination environments and different active site Tm atoms, and the potential ORR or NRR catalysts which adapt to air as a reaction air source are rapidly positioned by carrying out layer-by-layer progressive screening of stability analysis, competitive adsorption of air main components and desorption of substances according to a first principle density functional theory.

2. The method for efficient design of potential ORR and NRR catalysts based on air as a reactive gas source as claimed in claim 1, comprising the following steps:

s1, constructing substrate catalyst models of all transition metals including single-vacancy and double-vacancy and N-doped graphene with different concentrations based on first principle density functional theory, and respectively recording the models as Tm-N _X -C _3-X -Gra and Tm-N _X -C _4-X -Gra; wherein Tm-N is converted according to a nitrogen-carbon combination configuration ₂ -C ₂ the-Gra configuration is divided into five-membered ring type pen, para type opp and six-membered ring type hex;

s2, regarding a double-vacancy catalyst model formed by doping N-coordinated single transition metal with graphene, according to the formation energy delta E _f Calculating the formation energy delta E of all the pre-screened models by the calculation formula (1) and the combination energy delta Eb calculation formula (2) _f And binding energy Δ E _b (ii) a According to Δ E _f <0eV and Δ E _b <E _coh Screening a stable catalyst configuration; e _coh The energy is the metal cohesive energy;

wherein

And E _Gra Respectively represent a double-vacancy type single-atom catalyst Tm-N _X -C _4-X Catalyst model N of Gra, deficient in transition Metal _X -C _4-X System energy of Gra and graphene Gra, E _C 、E _Tm 、E _N Respectively representing the energy of single atoms C, Tm and N;

for a single-vacancy catalyst model, its energy of formation Δ E _f And binding energy Δ E _b Respectively as calculation formulas (3) and (4); wherein

And

respectively represent a single-vacancy type monatomic catalyst Tm-N _X -C _3-X Catalyst model N for Gra and deficient transition metals _X -C _3-X -Gra system energy;

s3 construction of O under different adsorption modes ₂ The adsorption model and the optimized structure are adopted, the adsorption model with the lowest energy is selected, and the O of the catalyst is calculated according to the formula (5) ₂ The adsorption energy of (c);

wherein

Means that the catalyst adsorbs O ₂ The total energy of the system (2) is,

refers to a single O ₂ The energy of the molecule, sub, is the catalyst substrate model, the single-vacancy and double-vacancy models, respectively denoted as Tm-N _X -C _3-X -Gra and Tm-N _X -C _4-X -Gra；

S4 construction of N under different adsorption modes ₂ The adsorption model and the optimized structure are adopted, the adsorption model with the lowest energy is selected, and the N of the catalyst is calculated according to the formula (6) ₂ The adsorption energy of (c);

wherein

Means that the catalyst adsorbs N ₂ The total energy of the system (2) is,

refers to a single N ₂ The energy of the molecule;

s5, comparing the same substrates, to O ₂ And to N ₂ When adsorption energy of (1) is in the range of O ₂ Adsorption energy equal or approximately equal to N ₂ Adsorption energy means that the co-adsorption of oxygen and nitrogen exists by taking air as a gas source, and ORR and NRR coexist in the follow-up process; this case is neither suitable for NRR nor ORR, left off;

s6, when

I.e. O ₂ Adsorption capacity>N ₂ When the adsorption capacity is high, the catalyst can preferentially adsorb oxygen;

the smaller the size

Then O is selectively adsorbed ₂ The stronger the ability of (c); because of the consideration of catalyst cyclicity, the product must be easily desorbed or not adsorbed; the ORR reaction product is H ₂ O, therefore, further study of H ₂ Adsorption energy of O according to formula (7); if it is

That is to say H ₂ Adsorption capacity of O<O ₂ Adsorption capacity if

The product can not be desorbed spontaneously, but the reactant which is easy to be adsorbed strongly occupies the adsorption site to cause desorption; if when it is used

The product has a tendency to desorb spontaneously; both cases show satisfaction

The catalyst is suitable for use in ORR; otherwise, it is not satisfied

The ORR is not suitable and should be omitted;

wherein

Means that the catalyst adsorbs H ₂ The total energy of the system of O,

means single H ₂ The energy of the O molecule;

s7, when

I.e. O ₂ Adsorption capacity<N ₂ In case of adsorption capacity, the reaction product is NH due to NRR ₃ Therefore, further exploration of NH ₃ According to formula (8); if it is

Namely NH ₃ Adsorption capacity of<N ₂ Adsorption capacity, the catalyst can be recycled for NRR reaction, i.e., can be suitably used for NRR; otherwise, the reverse is carried out

Indicating the active site adsorption product NH ₃ Too strong a capacity, i.e. catalyst active sites are covered by product NH ₃ Passivation, which cannot be circularly eliminated;

wherein

Means that the catalyst adsorbs NH ₃ The total energy of the system (2) is,

refers to a single NH ₃ The energy of the molecule.

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