CN116581314B - High-entropy oxide catalyst for fuel cell and preparation method thereof - Google Patents

Abstract

The invention discloses a high-entropy oxide catalyst for fuel cells and a preparation method. The chemical formula of the high-entropy oxide catalyst is: , where A is at least one of Ca, Sr, and Ba elements, B is at least five of Ni, Cu, Fe, Co, Mn, Zn, Cr, Ti, Al, and Ga elements, and each element in B The molar ratio between each other is 0.6~1.7, the value of The value of satisfies the following relationship: , . The high-entropy oxide catalyst provided by the invention has good catalytic performance in low-temperature and room-temperature environments, has a simple preparation process, low cost, good repeatability tests, and broad application prospects, and can be applied to ammonia fuel cells.

Description

A high-entropy oxide catalyst for fuel cells and preparation method

Technical field

The invention belongs to the technical field of fuel cells, and specifically relates to a high-entropy oxide catalyst for fuel cells and a preparation method.

Background technique

Ammonia energy (NH ₃ ), as a hydrogen-rich, carbon-free clean energy, is a hydrogen storage medium with great potential. Its mature industrial system has laid a solid foundation for the long-term, large-scale storage and transportation of hydrogen energy. The promotion of ammonia energy It is of great significance to shape the new pattern of global energy development. Based on the zero-carbon energy system, the sources of ammonia are also very wide. Whether it is green ammonia synthesized through electrolysis of hydrogen produced from renewable energy, or ammonia-containing wastewater discharged in daily production and life, it can be directly used for ammonia fuel cell power generation without any Produce greenhouse gases and provide strong support for achieving the "double carbon" goal.

For example, patent CN114709433A provides a metal catalyst with nitrogen-doped carbon supporting Pt for electrocatalytic oxidation of ammonia and its preparation method and application. The catalyst includes an active component and a carrier, the active component is Pt, and the carrier is nitrogen-doped carbon; Silica is used as the template, formaldehyde and melamine are used as the carbon and nitrogen sources respectively. After high-temperature pyrolysis, nitrogen-doped hollow porous carbon spheres are obtained by etching with hydrogen fluoride. The impregnation reduction method is used, and sodium borohydride is used as the reducing agent. Under vigorous stirring at room temperature The Pt precursor is reduced to synthesize the Pt/N-C catalyst. This solution provides a catalyst preparation method for nitrogen-doped carbon supported Pt, which has good application prospects in alkaline membrane direct ammonia fuel cells.

However, the ammonia oxidation reaction catalyst involved in ammonia fuel cell power generation has problems such as complex preparation process, high cost, and slow reaction kinetics.

Since the concept of higher building entropy was introduced into the field of oxide ceramics, there have been studies on applying Ruddlesden-Popper type layered perovskite structural materials to the cathode of solid oxide fuel cells. For example, patent CN114824303A provides an RP-type layered medium-entropy perovskite structure cathode material and its preparation method. The molecular formula is La _1.4 Sr _0.6 (Co, Fe, Ni, Mn) _1/4 O _4+δ , where δ represents Oxygen vacancy content. Its preparation method: using compounds containing La ³⁺ , Sr ²⁺ , Co ²⁺ , Fe ³⁺ , Ni ²⁺ and Mn ²⁺ respectively as raw materials, weigh each raw material according to the stoichiometric ratio of the corresponding elements in the molecular formula, and Add each raw material to deionized water, stir, dissolve, and mix uniformly to obtain solution A; add citric acid and ethylene glycol to solution A, heat, stir, and dissolve, then transfer to an electric furnace and heat until spontaneous combustion, and continue to heat until burning to form ash. Precursor; the cathode powder obtained by grinding the precursor and transferring it to a Mabo furnace for heating is the RP-type layered medium-entropy perovskite structure cathode material. The medium-entropy perovskite structural material proposed in the patent can only improve the stability and conductivity of the cathode and reduce the thermal expansion coefficient of the cathode material.

Therefore, how to combine the Ruddlesden-Popper type layered perovskite structure to develop an efficient, economical and industrialized catalyst for ammonia fuel cells has become an urgent problem for those skilled in the art.

Contents of the invention

In view of the defects existing in the above-mentioned prior art, the present invention provides a high-entropy oxide catalyst for fuel cells and a preparation method. The chemical formula of the high-entropy oxide catalyst is: , where A is at least one of Ca, Sr, and Ba elements, B is at least five of Ni, Cu, Fe, Co, Mn, Zn, Cr, Ti, Al, and Ga elements, and each element in B The molar ratio between each other is 0.6~1.7, the value of The value of satisfies the following relationship: ,/> . The high-entropy oxide catalyst provided by the invention has good catalytic performance in low-temperature and room-temperature environments, has a simple preparation process, low cost, good repeatability tests, and broad application prospects, and can be used in ammonia fuel cells and electrolytic production. hydrogen field.

In a first aspect, the present invention provides a high-entropy oxide catalyst for fuel cells, including:

The chemical formula of high-entropy oxide catalyst is: , where A is at least one of Ca, Sr, and Ba elements, B is at least five of Ni, Cu, Fe, Co, Mn, Zn, Cr, Ti, Al, and Ga elements, and each element in B The molar ratio between each other is 0.6~1.7, the value of x is 0.075~0.925, and the value of n is 2 or 3;

The crystal structure of the high-entropy oxide catalyst is Ruddlesden-Popper type, δ is the oxygen vacancy content, and the value of δ satisfies the following relationship: ,/> .

Further, the value of x is 0.25~0.75.

Furthermore, B contains Ni and Cu elements.

In a second aspect, the present invention also provides a method for preparing the high-entropy oxide catalyst for the above-mentioned fuel cell, including the following steps:

Weigh the metal nitrate or acetate containing elements A and B according to the stoichiometric ratio, dissolve it in deionized water, and stir magnetically at room temperature to obtain a mixed solution;

Add citric acid and ethylenediaminetetraacetic acid to the mixed solution until the pH value of the mixed solution is 0.5~2, and then adjust the pH value of the mixed solution to 6~8 with ammonia water to obtain a clear solution;

The clear solution is heated to form a gel with a skeleton structure or a grid structure, and the gel is sintered at high temperature to prepare a solid powder;

The solid powder is subjected to at least two alternating grinding and high-temperature calcinations, and then is annealed in an inert atmosphere or a reducing atmosphere, where the annealing temperature is 100~600°C, the annealing time is 0.5~2h, and the annealing heating temperature and/or The cooling rate is 1~10 ℃/min.

Further, the ratio of the total molar amount of the metal elements A and B to the molar amount of citric acid is 1:1~1:4, and the ratio of the total molar amount of the metal elements A and B to the molar amount of ethylenediaminetetraacetic acid is 1:1~1:5.

Further, the clarified solution is heated to form a gel with a skeleton structure or a grid structure, specifically:

The heating temperature for heating the clear solution is 80~160℃, and the heating time is 2~24h.

Further, the clarified solution is heated to form a gel with a skeleton structure or a grid structure, specifically:

The heating temperature for heating the clear solution is 90~110℃, and the heating time is 12~20h.

Further, the gel is sintered at high temperature, specifically as follows:

The high-temperature sintering temperature for high-temperature sintering of gel is 320~450℃, and the high-temperature sintering time is 3~6h.

Further, the solid powder is subjected to at least two alternate grinding and high-temperature calcinations, specifically:

When performing high-temperature calcination of solid powder, the high-temperature calcination temperature is 500~1200℃, the high-temperature calcination time is 2~6h, and the heating and/or cooling rate of high-temperature calcination is 1~10℃/min.

Further, the annealing treatment is performed in an inert atmosphere or a reducing atmosphere, specifically: the inert atmosphere or the reducing atmosphere is at least one of nitrogen, argon, and hydrogen, the annealing temperature is 300~500°C, and the annealing time is 0.5~ 1h, the heating and/or cooling rate of annealing is 5~10 ℃/min.

The invention provides a high-entropy oxide catalyst for fuel cells and a preparation method, which at least include the following beneficial effects:

(1) The high-entropy oxide catalyst provided by the present invention combines high-entropy materials with perovskite layered structures, allowing rich and flexible component design to reduce dependence on a single element. At the same time, the electronic structure can also be controlled by changing the stoichiometric ratio, further improving the catalytic activity.

(2) The high-entropy effect of thermodynamics and the hysteretic diffusion effect of dynamics enable high-entropy oxides to maintain structural stability under extreme conditions. Combined with the Ruddlesden-Popper type layered structure, the stability is further enhanced.

(3) The multi-metallic synergy of high-entropy materials and the highly disordered and twisted lattice are beneficial to the migration of electrons and ions, and in the Ruddlesden-Popper type structure, the increase of the perovskite layer (i.e. n) can further Expanding three-dimensional properties is beneficial to improving catalytic activity.

(4) Using ammonia water to adjust the pH of the mixed solution can change the original acidic system of the mixed solution, avoiding the inhibition of the ionization of citric acid and poor complexation of citrate ions and metal ions, causing the metal nitrate to re-precipitate and precipitate in the form of crystals. At the bottom of the container, it is almost impossible to initiate high-temperature sintering, and the reaction is incomplete. Precise control of the pH value range can ensure that the reaction proceeds according to the route designed by the components, achieving full complexation and complete high-temperature sintering.

(5) The high-entropy oxide catalyst provided by the present invention has good catalytic activity at low temperatures and even room temperature, has a simple preparation process, low cost, good repeatability tests, and broad application prospects. It can be used in ammonia fuel cells and can also be used. In the field of electrolytic hydrogen production.

Description of the drawings

Figure 1 is an XRD data diagram of the high-entropy oxide catalyst prepared in Example 1 provided by the present invention;

Figure 2 is an SEM image at a scale of 100 μm of the high-entropy oxide catalyst prepared in Example 1 provided by the present invention;

Figure 3 is a test curve diagram of the ammoxidation reaction of the catalysts prepared in Example 1 and Comparative Example 7 respectively in 0.5 M KOH + 55 mM NH ₄ Cl solution provided by the present invention.

Detailed ways

In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation modes. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

The terminology used in the embodiments of the present invention is only for the purpose of describing specific embodiments and is not intended to limit the present invention. As used in this embodiment and the appended claims, the singular forms "a," "the" and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. Usually contains at least two kinds.

It should also be noted that the terms "comprises", "comprises" or any other variation thereof are intended to cover a non-exclusive inclusion, such that a good or apparatus including a list of elements includes not only those elements but also those not expressly listed other elements, or elements inherent to such goods or devices. Without further limitation, an element defined by the statement "comprises a..." does not exclude the presence of other identical elements in the goods or devices including the stated element.

Ruddlesden-Popper type layered perovskite structure dielectric materials have attracted widespread attention due to their excellent stability, rich crystal structure, diverse components, controllable physical and chemical properties and other advantages. Utilizing the rules of structural evolution, Ruddlesden-Popper type layered perovskite structural compounds with different sizes are designed and synthesized in order to obtain materials with different functions.

The current medium-entropy oxides are synergistic with the Ruddlesden-Popper type layered perovskite structure, are easier to synthesize, can improve the stability and conductivity of the cathode, and reduce the thermal expansion coefficient of the cathode material, but have limited improvement in catalytic activity.

High-entropy oxides refer to materials mainly composed of five or more metal elements in equal or near molar ratios. They are widely used in fields such as energy conversion and energy storage, thanks to their rich activity. Characteristics such as site, adjustable specific surface area, stable crystal structure, and customizable ingredients show broad application prospects in the field of catalysis.

In order to improve the comprehensive performance of ammonia fuel cell anode catalysts and achieve stable application, and reduce the requirements for the use environment, high-entropy materials are combined with Ruddlesden-Popper type layered perovskite structures to develop and design anode catalysts with excellent catalytic activity and stability. catalyst. Therefore, the present invention proposes a high-entropy oxide catalyst for fuel cells, including: the chemical formula of the high-entropy oxide catalyst is: , where A is at least one of Ca, Sr, and Ba elements, B is at least five of Ni, Cu, Fe, Co, Mn, Zn, Cr, Ti, Al, and Ga elements, and each element in B The molar ratio between each other is 0.6~1.7, the value of x is 0.075~0.925, and the value of n is 2 or 3;

The crystal structure of the high-entropy oxide catalyst is Ruddlesden-Popper type, δ is the oxygen vacancy content, and the value of δ satisfies the following relationship: ,/> . -δ indicates that there are oxygen defects in the crystal structure, that is, oxygen defects caused by oxygen overflow. For example, when n=2, there should be 7 oxygen atoms according to the chemical formula, but after the A element doping and calcination and annealing in the preparation process, After the other steps, oxygen will overflow, making the number of oxygen atoms less than 7. When the value of δ is in the range of 0.35 to 1.4, the prepared high-entropy oxide catalyst has the best catalytic performance. If the value of -δ exceeds 20% of the number of oxygen atoms, the Ruddlesden-Popper type crystal structure is unstable and there is a possibility of structural collapse.

Preferably, the value of x is 0.25~0.75.

Preferably, B contains Ni and Cu elements.

The Ruddlesden-Popper high-entropy oxide catalyst prepared by the invention can be coupled or used alone for ammonia oxidation reaction (Ammonia Oxidation Reaction, AOR), hydrogen evolution reaction (Hydrogen Evolution Reaction, HER) or oxygen evolution reaction (Oxygen Evolution Reaction, OER). ), has good catalytic activity and stability.

The high-entropy oxide catalyst provided by the present invention combines the concept of high entropy with the perovskite layered structure, allowing rich and flexible component design, thereby reducing dependence on a single element, and regulating its electrons by changing the stoichiometric ratio. structure to further improve catalytic activity; the thermodynamic high-entropy effect and the kinetic hysteresis-diffusion effect allow high-entropy oxides to maintain structural stability under extreme conditions, and combined with the Ruddlesden-Popper type layered structure, further enhances its stability ; The highly disordered and twisted lattice of high-entropy materials is conducive to the migration of electrons and ions, and in the Ruddlesden-Popper structure, the increase of the perovskite layer (i.e. n) further improves the conductivity of the material.

The high-entropy oxide catalyst provided by the present invention has good catalytic activity at low temperatures and even room temperature, has a simple preparation process, low cost, good repeatability tests, and broad application prospects. It can be applied to ammonia fuel cells and can also be used in electrolytic production. hydrogen field.

The high-entropy oxide catalyst of the present invention and the specific preparation process are described below through examples and comparative examples:

Example 1:

The chemical formula of the Ruddlesden-Popper type high-entropy oxide catalyst given in this example is: (La _0.75 Sr _0.25 ) ₃ (Ni _0.2 Cu _0.2 Fe _0.2 Co _0.2 Mn _0.2 ) ₂ O _7-δ , at this time, A is Sr , B is Ni, Cu, Fe, Co and Mn, the molar amounts of each element of B are the same, the value of x is 0.25, the value of n is 2, and the value of δ is between 0.35 and 1.4.

The preparation method of the Ruddlesden-Popper type high-entropy oxide catalyst specifically includes the following steps:

According to the stoichiometric ratio of La, A, and B in the chemical formula (La _0.75 Sr _0.25 ) ₃ (Ni _0.2 Cu _0.2 Fe _0.2 Co _0.2 Mn _0.2 ) ₂ O _7-δ, the stoichiometric ratios of La, A, and B are accurately weighed to contain lanthanum (La) and strontium (Sr) respectively. , Nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn) nitrates, specifically:

0.0197 mol of La(NO ₃ ) ₃ ·6H ₂ O, 0.0066 mol of Sr(NO ₃ ) ₂ ·4H ₂ O, 0.0035 mol of Ni(NO ₃ ) ₂ ·6H ₂ O, 0.0035 mol of Cu(NO ₃ ) ₂ ·3H ₂ O, 0.0035 mol of Fe(NO ₃ ) ₃ ·9H ₂ O, 0.0035 mol of Co(NO ₃ ) ₂ ·6H ₂ O, and 0.0035 mol of Mn(NO ₃ ) ₂ ·4H ₂ O.

Dissolve the above nitrate in deionized water and stir magnetically at room temperature to obtain a uniform mixed solution.

Then, add anhydrous citric acid and ethylenediaminetetraacetic acid to the mixed solution. The ratio of the total molar amount of metal elements (La, A, B) to the molar amount of citric acid is 1:1.5, and the ratio of the total molar amount of metal elements (La, A, B) to the molar amount of citric acid is 1:1.5. The ratio of the total molar amount of A, B) to the molar amount of ethylenediaminetetraacetic acid is 1:2, that is, 0.0525 mol of anhydrous citric acid and 0.0875 mol of ethylenediaminetetraacetic acid are added in sequence, and the mixed solution is measured after stirring for 1 hour. The pH value was 1.15, and then the pH value of the mixed solution was adjusted to 6 with ammonia water to obtain a clear solution. Subsequently, the clear solution was heated at 90°C for 12 hours to form a gel with a skeleton structure.

The formed gel with a skeleton structure is sintered at a high temperature, where the temperature of the high-temperature sintering is 400°C. After the gel is sintered at a high temperature, a dry solid powder can be obtained.

After the obtained solid powder is cooled to room temperature, fully grind it with a mortar, then pour the powder into a crucible, place it in a tube furnace, and calcine in an air atmosphere, raising the temperature to 350°C at a heating rate of 5°C/min. ℃, and keep it warm for 2 hours. After the temperature drops to room temperature, take it out and grind it thoroughly with a mortar to obtain the high-entropy oxide catalyst precursor.

Then take an appropriate amount of high-entropy oxide catalyst precursor and pour it into the crucible, place it in a tube furnace, calcine in an air atmosphere, raise it to 1000°C at a heating rate of 5°C/min, and keep it warm for 3 hours, and then heat it at 5°C/min. min cooling rate to room temperature and take out.

Pour an appropriate amount of the powder that has been fully ground in the above steps into a crucible, place it in a tube furnace, perform annealing treatment in a nitrogen atmosphere, raise it to 500°C at a heating rate of 5°C/min, and keep it warm for 1 hour, and then anneal at 5°C/min. The cooling rate of ℃/min is reduced to room temperature and then taken out to obtain a Ruddlesden-Popper type high-entropy oxide catalyst.

The prepared Ruddlesden-Popper type high-entropy oxide catalyst was tested by XRD, and the SEM image at the 100 μm scale was observed.

As shown in Figure 1-2, the high-entropy oxide catalyst has a Ruddlesden-Popper type orthorhombic phase structure. Microscopic observation shows that the particle size of the high-entropy oxide catalyst is on the order of microns.

Example 2:

Based on Example 1, Example 2 adjusts the following parameters.

The chemical formula of the Ruddlesden-Popper type high-entropy oxide catalyst given in this example is: (La _0.75 Ca _0.25 ) ₃ (Ni _0.25 Cu _0.15 Fe _0.15 Co _0.15 Mn _0.15 Ti _0.15 ) ₂ O _7-δ , at this time, A is Ca, B is Ni, Cu, Fe, Co, Mn and Ti, the molar ratio between the elements of B is 5:3:3:3:3:3, the value of x is 0.25, and the value of n is 2, and the value of δ is between 0.35 and 1.4.

According to the chemical formula (La _0.75 Ca _0.25 ) ₃ (Ni _0.25 Cu _0.15 Fe _0.15 Co _0.15 Mn _0.15 Ti _0.15 ) ₂ O _7-δ , accurately weigh the stoichiometric ratios of La, A, and B to contain lanthanum (La) and calcium ( Acetates of Ca), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn) and titanium (Ti).

Example 3:

Based on Example 1, Example 3 adjusts the following parameters.

The chemical formula of the Ruddlesden-Popper type high-entropy oxide catalyst given in this example is: (La _0.75 Sr _0.2 Ba _0.05 ) ₃ (Ni _0.2 Cu 0.2 Fe _0.2 Cr _{0.2 Zn 0.2 ) 2} O _7-δ , at this time, A are Sr and Ba, the molar ratio of Sr to Ba is 4:1, B is Ni, Cu, Fe, Cr and Zn, the molar amounts of each element of B are the same, the value of x is 0.25, and the value of n is 2, and the value of δ is between 0.35 and 1.4.

According to the chemical formula (La _0.75 Sr _0.2 Ba _0.05 ) ₃ (Ni _0.2 Cu _0.2 Fe _0.2 Cr _0.2 Zn _0.2 ) ₂ O _7-δ, accurately weigh the stoichiometric ratio of La, A, and B to contain lanthanum (La) and strontium ( Nitrates of Sr), barium (Ba), nickel (Ni), copper (Cu), iron (Fe), chromium (Cr) and zinc (Zn).

Example 4:

Based on Example 1, Example 4 adjusts the following parameters.

The chemical formula of the Ruddlesden-Popper type high-entropy oxide catalyst given in this example is: (La _0.25 Sr _0.75 ) ₃ (Ni _0.1 Cu _0.1 Fe _0.1 Co _0.1 Mn _0.1 Ti _0.1 Ga _0.1 Al _0.1 Cr _0.1 Zn _0.1 ) ₂ O _7-δ , at this time, A is Sr, B is Ni, Cu, Fe, Co, Mn, Ti, Ca, Al, Cr and Zn, the molar amounts of each element of B are the same, and the value of x is 0.75 , the value of n is 2, and the value of δ is between 0.35 and 1.4.

(La _0.25 Sr _0.75 ) ₃ (Ni _0.1 Cu _0.1 Fe _0.1 Co _0.1 Mn _0.1 Ti _0.1 Ga _0.1 Al _0.1 Cr _0.1 Zn _0.1 ) ₂ O _7-δ The stoichiometric ratio of La, A, and B in δ is accurately weighed and contains lanthanum respectively. (La), strontium (Sr), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), titanium (Ti), gallium (Ga), aluminum (Al), chromium (Cr) and zinc (Zn) acetates.

Example 5:

Based on Example 1, Example 5 adjusts the following parameters.

The chemical formula of the Ruddlesden-Popper type high-entropy oxide catalyst given in this example is: (La _0.25 Sr _0.75 ) ₃ (Ni _0.2 Cu _0.2 Fe _0.2 Co _0.2 Mn _0.2 ) ₂ O _7-δ , at this time, A is Sr , B is Ni, Cu, Fe, Co, Mn, the molar amounts of each element of B are the same, the value of x is 0.75, the value of n is 2, and the value of δ is between 0.35 and 1.4.

According to the stoichiometric ratio of La, A, and B in (La _0.25 Sr _0.75 ) ₃ (Ni _0.2 Cu _0.2 Fe _0.2 Co _0.2 Mn _0.2 ) ₂ O _7-δ, the stoichiometric ratios of La, A, and B are accurately weighed to contain lanthanum (La), strontium (Sr), and Nitrates of nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), and manganese (Mn).

Example 6:

Based on Example 1, Example 6 adjusts the following parameters.

This example gives the chemical formula of the Ruddlesden-Popper type high-entropy oxide catalyst: (La _0.5 Sr _0.25 Ca _0.25 ) ₄ (Ni _0.1 Cu _0.1 Fe _0.1 Co _0.1 Mn _0.1 Ti _0.1 Ga _0.1 Al _0.1 Cr _0.1 Zn _0.1 ) ₃ O _10-δ , at this time, A is Sr and Ca, the molar ratio of Sr and Ca is 1:1, B is Ni, Cu, Fe, Co, Mn, Ti, Ca, Al, Cr and Zn, each element of B The molar amounts between them are the same, the value of x is 0.5, the value of n is 3, and the value of δ is between 0.5 and 2.

(La _0.5 Sr _0.25 Ca _0.25 ) ₄ (Ni _0.1 Cu _0.1 Fe _0.1 Co _0.1 Mn _0.1 Ti _0.1 Ga _0.1 Al _0.1 Cr _0.1 Zn _0.1 ) ₃ O _10-δ The stoichiometric ratios of La, A and B are accurately weighed respectively. Contains lanthanum (La), strontium (Sr), calcium (Ca), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), titanium (Ti), gallium (Ga) , aluminum (Al), chromium (Cr) and zinc (Zn) acetate.

Example 7:

Based on Example 1, Example 7 adjusts the following parameters.

Regarding the preparation process of Example 1, in Example 7, citric acid and ethylenediaminetetraacetic acid were added to the mixed solution until the pH value of the mixed solution was 0.5~2, and then ammonia was used to adjust the pH value of the mixed solution to 8. , the remaining operating steps and conditions remain unchanged.

Example 8:

Based on Example 1, Example 8 adjusts the following parameters.

Compared with the preparation process of Example 1, in Example 8, an appropriate amount of high-entropy oxide catalyst precursor was poured into a crucible, placed in a tube furnace, and calcined in an air atmosphere at a heating rate of 5°C/min. to 1200°C and kept for 5 hours, then lowered to room temperature at a cooling rate of 5°C/min and taken out. The remaining operating steps and conditions remain unchanged.

Example 9:

Based on Example 1, Example 9 adjusts the following parameters.

Compared with the preparation process of Example 1, in Example 9, an appropriate amount of the powder that has been fully ground in the above steps is poured into a crucible, placed in a tube furnace, and annealed in a hydrogen-argon mixed atmosphere, where the hydrogen-argon mixed gas It was 5%H ₂ /95% Ar, raised to 500°C at a heating rate of 5°C/min, and kept for 1 hour, then lowered to room temperature at a cooling rate of 5°C/min and taken out. The remaining operating steps and conditions remain unchanged.

Example 10:

Based on Example 1, Example 10 adjusts the following parameters.

Compared with the preparation process of Example 1, in Example 10, an appropriate amount of the powder that has been fully ground in the above steps is poured into a crucible, placed in a tube furnace, and annealed in a nitrogen atmosphere, with a temperature rise of 5°C/min. The temperature was increased to 300°C and kept at the temperature for 0.5 h. Then, the temperature was lowered to room temperature at a cooling rate of 5°C/min and then taken out. The remaining operating steps and conditions remain unchanged.

Comparative example 1:

On the basis of Example 1, the following parameters were adjusted in Comparative Example 1.

The chemical formula of the Ruddlesden-Popper type high-entropy oxide catalyst given in this comparative example is: Sr ₃ (Ni _0.2 Cu _0.2 Fe _0.2 Co _0.2 Mn _0.2 ) ₂ O _7-δ , at this time, A is Sr, B is Ni, The molar amounts of Cu, Fe, Co, Mn, and B among the elements are the same, the value of x is 1, and the value of n is 2.

_{Accurately weigh strontium} ( _Sr ), nickel ₍ Ni), _copper ( _Cu ), iron ( _Fe ), and cobalt ( Co) and manganese (Mn) nitrates.

In Comparative Example 1, the element lanthanum (La) is not included, and the target sample for performance testing was not prepared in Comparative Example 1.

Comparative example 2:

On the basis of Example 1, the following parameters were adjusted in Comparative Example 2.

The chemical formula of the Ruddlesden-Popper type high-entropy oxide catalyst given in this comparative example is: La ₃ (Ni _0.2 Cu _0.2 Fe _0.2 Co _0.2 Mn _0.2 ) ₂ O _7-δ , at this time, there is no A element, and B is Ni, The molar amounts of Cu, Fe, Co, Mn, and B among the elements are the same, the value of x is 0, the value of n is 2, and the value of δ is less than 0.2.

_{Accurately weigh} lanthanum (La), nickel ( _{Ni ) ,} copper (Cu) _, iron _{( Fe} ), and cobalt ( Co) and manganese (Mn) nitrates.

Comparative example 3:

On the basis of Example 1, the following parameters were adjusted in Comparative Example 3.

The chemical formula of the Ruddlesden-Popper type high-entropy oxide catalyst given in this comparative example is: (La _0.75 Sr _0.25 ) ₂ (Ni _0.2 Cu _0.2 Fe _0.2 Co _0.2 Mn _0.2 )O _4-δ , at this time, A is Sr, B is Ni, Cu, Fe, Co and Mn. The molar amounts of each element of B are the same. The value of x is 0.25 and the value of n is 1.

Accurately weigh lanthanum (La), strontium (Sr), nickel (Ni) _, and copper (Cu) according to the stoichiometric ratio of the chemical formula (La _0.75 Sr _0.25 ) ₂ (Ni _0.2 Cu _0.2 Fe _0.2 Co 0.2 Mn _0.2 )O _4-δ ), iron (Fe), cobalt (Co) and manganese (Mn) nitrates.

Comparative example 4:

On the basis of Example 1, the following parameters were adjusted in Comparative Example 4.

Compared with the preparation process of Example 1, in this comparative example, citric acid and ethylenediaminetetraacetic acid are added to the mixed solution until the pH value of the mixed solution is 0.5~2, and then ammonia is not used to adjust the pH value of the mixed solution to obtain a clear solution. , and the clarified solution is heated to form a gel process of a skeleton structure or a grid structure, but the mixed solution with a pH value of 0.5~2 is directly sintered at high temperature, and the remaining operating steps and conditions remain unchanged.

In Comparative Example 4, the mixed solution was almost unable to induce high-temperature sintering. At the same time, it was detected that the reaction in the mixed solution was incomplete, and a target sample for performance testing could not be prepared.

Comparative example 5:

On the basis of Example 1, the following parameters were adjusted in Comparative Example 5.

Compared with the preparation process of Example 1, this comparative example does not perform subsequent annealing treatment after at least two alternating grinding and high-temperature sintering of the solid powder, that is, it does not include the "taking an appropriate amount of sufficient amount of the above steps in Example 1 The ground powder was poured into a crucible, placed in a tube furnace, annealed in a nitrogen atmosphere, raised to 500°C at a heating rate of 5°C/min, and kept for 1 h, and then cooled down at a rate of 5°C/min. Remove after cooling to room temperature."

In Comparative Example 5, the chemical formula of the prepared high-entropy oxide catalyst is the same as that of Example 1, that is, (La _0.75 Sr _0.25 ) ₃ (Ni _0.2 Cu _0.2 Fe _0.2 Co _0.2 Mn _0.2 ) ₂ O _7-δ , but δ The value is less than 0.2.

Comparative example 6:

On the basis of Example 1, the following parameters were adjusted in Comparative Example 6.

Compared with the preparation process of Example 1, in this comparative example, after the gel is sintered at high temperature to obtain dry solid powder, grinding is not performed in the subsequent high-temperature calcination and annealing steps.

Comparative Example 7:

On the basis of Example 1, the following parameters were adjusted in Comparative Example 7.

The chemical formula of the Ruddlesden-Popper type medium-entropy oxide catalyst given in this comparative example is: (La _0.75 Sr _0.25 ) ₃ (Ni _0.25 Cu _0.25 Fe _0.25 Co _0.25 ) ₂ O _7-δ , at this time, A is Sr, B are Ni, Cu, Fe and Co, the molar amounts of each element of B are the same, the value of x is 0.25, and the value of n is 2.

According to the chemical formula (La _0.75 Sr _0.25 ) ₃ (Ni _0.25 Cu _0.25 Fe _0.25 Co _0.25 ) ₂ O _7-δ, accurately weigh the stoichiometric ratios of La, A, and B to contain lanthanum (La), strontium (Sr), and nickel respectively. Nitrates of (Ni), copper (Cu), iron (Fe), and cobalt (Co).

Performance Testing:

The samples obtained in the above examples and comparative examples were used for performance testing in catalytic ammonia oxidation reactions. The specific test conditions and steps are as follows:

Prepare a mixed electrolyte solution of 0.5 M KOH and 55 mM NH ₄ Cl to simulate an ammonia-containing environment;

Under the same conditions, a three-electrode system is used for electrochemical testing. The relevant process parameters in the electrochemical testing method are as follows:

Use the samples obtained from each example and comparative example as catalysts. Mix the catalyst with carbon black, Nafion, anhydrous ethanol and deionized water to obtain a slurry. Apply the above slurry on a 2'2cm clean carbon cloth. After natural drying, an electrode sheet was prepared. As the working electrode, Ag/AgCl was used as the reference electrode and a platinum mesh electrode was used as the counter electrode.

In the cyclic voltammetry curve obtained through the above electrochemical tests, the scan rate used is 50 mV/s, the scan potential range is 0~0.6 V, and the number of cycles is 100.

Table 1 Test results of Examples and Comparative Examples

The data in Table 1 includes the test results of the catalysts prepared in various embodiments of the present invention for the ammonia oxidation electrocatalytic reaction. When the relative potential is 0.5 V, the current density is higher than 9.5 mA/cm ² , and Example 1 When the prepared catalyst was used in the electrocatalytic reaction of ammonia oxidation, when the relative potential was 0.5 V, the current density was the highest at 12.6 mA/cm ² .

Including the test results of catalysts prepared in various comparative examples of the present invention for ammonia oxidation electrocatalytic reactions, when the relative potential is 0.5 V, the current density is lower than 7 mA/cm ² , among which, the medium-entropy oxidation obtained in Comparative Example 7 The sample was used for the electrocatalytic reaction of ammonia oxidation. When the relative potential was 0.5 V, the current density was the lowest at 3.9 mA/cm ² . In addition, the target sample cannot be prepared due to the absence of La element in Comparative Example 1 and the lack of pH adjustment of the mixed solution with ammonia water in Comparative Example 4.

As shown in Figure 3, the cyclic voltammogram curves of the catalysts prepared in Example 1 and Comparative Example 7 for the ammonia oxidation electrocatalytic reaction are shown. When the catalyst obtained in Example 1 is used for the ammonia oxidation electrocatalytic reaction, during the entire scan It shows higher current density in the potential range.

The above test results show that the Ruddlesden-Popper type high-entropy oxide catalyst prepared in each embodiment has significant ammonia oxidation activity.

The excellent ammonia oxidation activity of the high-entropy oxide catalyst provided by the present invention comes from:

(1) The micron-level particle size of high-entropy oxide catalysts leads to an increase in active sites and improves catalytic activity;

(2) The highly disordered and twisted lattice of Ruddlesden-Popper type high-entropy oxide is conducive to the migration of electrons and ions. The perovskite layer further expands the three-dimensional properties and can accommodate high concentrations of heterovalent ions, which not only improves the conductivity The catalytic activity is also enhanced;

The combination of elements A and B in the chemical formula, the high entropy effect and the annealing process introduced in the catalyst preparation process cause the obtained high entropy oxide catalyst to have oxygen defects caused by oxygen overflow. The increase in oxygen defect content further enhances the The migration of electrons and ions improves catalytic activity;

(3) The synergistic effect between B elements promotes charge transfer and improves the interface between the electrode and the electrolyte, thus enhancing the catalytic activity.

Although the preferred embodiments of the present invention have been described, those skilled in the art will be able to make additional changes and modifications to these embodiments once the basic inventive concepts are apparent. Therefore, it is intended that the appended claims be construed to include the preferred embodiments and all changes and modifications that fall within the scope of the invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the invention. In this way, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims (9)

1. A method for preparing a high entropy oxide catalyst for a fuel cell, comprising:

the chemical formula of the high entropy oxide catalyst is: (La) _1−x A _x ) _n+1 B _n O _3n+1-δ Wherein, A is at least one of Ca, sr and Ba,b is at least five of Ni, cu, fe, co, mn, zn, cr, ti, al, ga elements, the molar ratio of the elements in B is 0.6-1.7, the value of x is 0.075-0.925, and the value of n is 2 or 3;

the crystal structure of the high-entropy oxide catalyst is Ruddlesden-Popper type, delta is oxygen vacancy content, and the value of delta satisfies the following relationship:the high entropy oxide catalyst is used for ammoxidation;

the preparation method comprises the following steps:

weighing metal nitrate or acetate containing elements A and B according to stoichiometric ratio, dissolving in deionized water, and magnetically stirring at room temperature to obtain mixed solution;

adding citric acid and ethylenediamine tetraacetic acid into the mixed solution until the pH value of the mixed solution is 0.5-2, and then regulating the pH value of the mixed solution to 6-8 by using ammonia water to obtain a clear solution;

heating the clarified solution to form gel with a skeleton structure or a grid structure, and sintering the gel at high temperature to prepare solid powder;

and (3) carrying out at least two times of alternate grinding and high-temperature calcination on the solid powder, and then carrying out annealing treatment in an inert atmosphere or a reducing atmosphere, wherein the annealing temperature is 100-600 ℃, the annealing time is 0.5-2 h, and the heating and/or cooling rate of annealing is 1-10 ℃/min.

2. The method for preparing a high entropy oxide catalyst for a fuel cell according to claim 1, wherein x has a value of 0.25 to 0.75.

3. The method for producing a high entropy oxide catalyst for a fuel cell according to claim 1, wherein B contains Ni and Cu.

4. The method for producing a high entropy oxide catalyst for a fuel cell according to claim 1, wherein the ratio of the total molar amount of the metal elements of a and B to the molar amount of citric acid is 1: 1-1: the ratio of the total molar amount of the metal elements of 4, A and B to the molar amount of ethylenediamine tetraacetic acid is 1: 1-1: 5.

5. the method for preparing a high entropy oxide catalyst for a fuel cell according to claim 1, wherein the clarified solution is heated to form a gel of a skeletal structure or a network structure, specifically:

and heating the clear solution at the heating temperature of 80-160 ℃ for 2-24 hours.

6. The method for preparing a high entropy oxide catalyst for a fuel cell according to claim 5, wherein the clarified solution is heated to form a gel of a skeletal structure or a network structure, specifically:

and heating the clear solution at a heating temperature of 90-110 ℃ for 12-20 hours.

7. The method for preparing a high entropy oxide catalyst for a fuel cell according to claim 1, wherein the gel is sintered at a high temperature, specifically:

and (3) performing high-temperature sintering on the gel at a high-temperature sintering temperature of 320-450 ℃ for 3-6 hours.

8. The method for preparing a high entropy oxide catalyst for a fuel cell according to claim 1, wherein the solid powder is subjected to at least two alternating grinding and high temperature calcination, specifically:

the high-temperature calcination temperature of the solid powder is 500-1200 ℃, the high-temperature calcination time is 2-6 h, and the heating and/or cooling rate of the high-temperature calcination is 1-10 ℃/min.

9. The method for producing a high entropy oxide catalyst for fuel cells according to claim 1, wherein the annealing treatment is performed in an inert atmosphere or a reducing atmosphere, specifically:

the inert atmosphere or the reducing atmosphere is at least one of nitrogen, argon and hydrogen, the annealing temperature is 300-500 ℃, the annealing time is 0.5-1 h, and the heating and/or cooling rate of annealing is 5-10 ℃/min.