阅读说明：本技术 一种利用废弃钴酸锂制备双功能三元金属羟基氮化物电催化剂的方法 (Method for preparing bifunctional ternary metal hydroxyl nitride electrocatalyst by using waste lithium cobaltate ) 是由 李虎林 李毅 蔡建荣 杜佳 郑成 王宇 魏海滨 杨霄 于 2020-12-29 设计创作，主要内容包括：本发明公开一种利用废弃钴酸锂制备双功能三元金属羟基氮化物电催化剂的方法,(1)将废弃钴酸锂正极材料经过粉碎后过筛,将筛下物磨成粉,放入稀盐酸中浸泡,取上清液记为A；(2)向A加入氢氧化钠溶液,至溶液PH值为7为止,得B；(3)分别向B中加入硝酸铁溶液和乙醇,得C；(4)向C放入直径为1cm×1cm的泡沫铝,以泡沫铝为工作电极,以C为反应溶液,将泡沫铝侵泡在C溶液表面,同时在氮气气氛下对泡沫铝等离子体放电,使其在表面发生化学反应；(5)将上述自支撑电极洗涤后真空干燥,即获得了双功能三元金属羟基氮化物电催化剂。本发明方法简单,整个生产过程简单,条件温和,过程易于控制,成本低,适用于大规模生产。(The invention discloses a method for preparing a bifunctional ternary metal hydroxy nitride electrocatalyst by using waste lithium cobaltate, which comprises the following steps of (1) crushing and sieving a waste lithium cobaltate positive electrode material, grinding undersize into powder, soaking the powder in dilute hydrochloric acid, and taking supernatant liquid as A; (2) adding sodium hydroxide solution into the solution A until the pH value of the solution is 7 to obtain B; (3) respectively adding ferric nitrate solution and ethanol into B to obtain C; (4) placing foamed aluminum with the diameter of 1cm multiplied by 1cm into the C, soaking the foamed aluminum on the surface of the C solution by taking the foamed aluminum as a working electrode and the C as a reaction solution, and simultaneously discharging plasma of the foamed aluminum in a nitrogen atmosphere to enable the foamed aluminum to generate chemical reaction on the surface; (5) and washing the self-supporting electrode, and then drying in vacuum to obtain the bifunctional ternary metal hydroxyl nitride electrocatalyst. The method is simple, the whole production process is simple, the conditions are mild, the process is easy to control, the cost is low, and the method is suitable for large-scale production.)

1. A method for preparing a bifunctional ternary metal hydroxyl nitride electrocatalyst by using waste lithium cobaltate is characterized by sequentially carrying out the following steps:

(1) crushing and sieving the waste lithium cobalt oxide positive electrode material, taking undersize, grinding the undersize into powder, soaking the powder in dilute hydrochloric acid, and taking supernatant liquid A;

(2) adding sodium hydroxide solution into the solution A until the pH value of the solution is 7 to obtain B;

(3) respectively adding 5-10mL of ferric nitrate solution and ethanol into the B in sequence, and uniformly stirring to obtain C;

(4) placing foamed aluminum with the diameter of 1cm multiplied by 1cm into the C, soaking the foamed aluminum on the surface of the C solution by taking the foamed aluminum as a working electrode and the C as a reaction solution, and simultaneously carrying out plasma discharge on the foamed aluminum in a nitrogen atmosphere to enable the foamed aluminum to quickly and efficiently carry out chemical reaction on the surface;

(5) and (3) washing the self-supporting electrode for 3-6 times by using absolute ethyl alcohol and deionized water in sequence, and drying in vacuum to obtain the bifunctional ternary metal hydroxyl nitride electrocatalyst.

2. The method for preparing a bifunctional ternary metal hydroxy nitride electrocatalyst using lithium cobaltate disused according to claim 1, wherein in step (1), the undersize is pulverized to have a particle size of 400 mesh.

3. The method for preparing the bifunctional ternary metal hydroxy nitride electrocatalyst according to claim 1, wherein in step (1), the concentration of the dilute hydrochloric acid is 3-6M, and the soaking time is 3-8 h.

4. The method for preparing a bifunctional ternary metal hydroxy nitride electrocatalyst using discarded lithium cobaltate as claimed in claim 1, wherein the concentration of ferric nitrate in step (3) is 100-150 mM.

5. The method for preparing the bifunctional ternary metal hydroxy nitride electrocatalyst according to claim 1, wherein in step (4), the voltage of the plasma discharge is 50V, and the reaction time is 10-120 s.

6. The method for preparing the bifunctional ternary metal hydroxy nitride electrocatalyst according to claim 1, wherein in step (5), the drying temperature is 60-100 ℃ and the drying time is 6-12 h.

7. The method for preparing the bifunctional ternary metal hydroxy nitride electrocatalyst according to claim 1, wherein in step (4), the foamed aluminum has a thickness of 0.01 cm.

8. The method for preparing the bifunctional ternary metal hydroxy-nitride electrocatalyst according to any one of claims 1 to 7, wherein the bifunctional ternary metal hydroxy-nitride electrocatalyst is nanotopography composed of nanoparticle cross-linking, with particle size 50-100 nm.

Technical Field

The invention belongs to the field of waste resource utilization and catalytic chemistry, relates to a preparation method of a bifunctional electrocatalyst, and particularly relates to a method for preparing a bifunctional ternary metal hydroxyl nitride electrocatalyst by using waste lithium cobalt oxide.

Background

The drive of electrocatalytic decomposition of water by renewable electrical energy has been considered the most promising way to produce clean hydrogen fuel from abundant water resources, support energy safety and reduce emissions. The key of the large-scale application of the electrolyzed water is how to reduce the overpotential of the anodic Oxygen Evolution Reaction (OER) and the cathodic Hydrogen Evolution Reaction (HER), realize the large-current hydrogen production under the low potential, and further reduce the electric energy consumption and the hydrogen production cost. Researches show that noble metals such as Ru, Ir, Pt and the like and oxides thereof have the most excellent hydrogen evolution catalytic performance, but the materials are limited to be widely applied due to high price and resource shortage. Therefore, the development of the cheap and efficient non-noble metal water electrolysis catalyst has very important scientific significance and practical value.

The existing catalyst usually has higher catalytic activity only for one reaction (OER or HER), and the catalyst has higher catalytic activity for both reactions at the same time. However, in the water electrolysis reaction process, two different types of catalysts are required to catalyze the oxygen evolution reaction and the hydrogen evolution reaction together so as to improve the overall reaction rate. This makes the water electrolysis apparatus more complicated and increases the running cost. Current research on electrocatalysts has mainly focused on the development of monofunctional electrocatalysts with a single Hydrogen Evolution Reaction (HER) or Oxygen Evolution Reaction (OER), but achieving simultaneous bifunctional (hydrogen and oxygen evolution catalysis) on a single catalyst basis has presented enormous challenges.

Lithium ion batteries using lithium cobaltate as the positive electrode have been widely used commercially due to a series of unique advantages such as low cost and long cycle life. However, due to the limited lifetime of battery materials, the retirement period is gradually coming, and a large amount of waste lithium ion batteries face the disposal problem after retirement. Because the waste electrode material contains recoverable metal (such as cobalt and the like), if the waste electrode material is directly discarded, the waste electrode material is treated as dangerous waste, on one hand, the treatment cost is increased, on the other hand, the waste of useful resources is directly caused, and the effects of recycling and increasing the value of the waste material cannot be realized. Therefore, the research and development of the recycling of the lithium ion battery material have very important significance. If the cobalt element in the lithium cobaltate cathode material is recycled and prepared into a heterogeneous nano material with a hierarchical structure, a bifunctional full-hydrolysis catalyst is synthesized, so that the problems can be effectively solved, the catalyst can be used as a catalyst to be applied to the field of electrolytic water, the cost of the electrolytic water can be reduced, the environmental pressure can be relieved, and the efficient recycling of waste resources can be realized.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a method for preparing a bifunctional ternary metal hydroxyl nitride electrocatalyst by using waste lithium cobaltate, iron ions, cobalt ions and foamed aluminum can rapidly react with nitrogen atoms in situ under a reaction solution system in a plasma discharge nitrogen atmosphere, the element distribution is effectively adjusted under the plasma discharge effect, and the ternary metal hydroxyl nitride with a large number of active sites is finally formed.

The technical scheme provided by the invention is as follows:

a method for preparing a bifunctional ternary metal hydroxyl nitride electrocatalyst by using waste lithium cobaltate sequentially comprises the following steps:

(1) crushing and sieving the waste lithium cobalt oxide positive electrode material, taking undersize, grinding the undersize into powder, soaking the powder in dilute hydrochloric acid, and taking supernatant liquid A;

(2) adding sodium hydroxide solution into the solution A until the pH value of the solution is 7 to obtain B;

in the step, the pH of the solution B needs to be controlled to 7, that is, the solution is neutral, the pH value of the solution is closely related to the concentration of cobalt ions in the solution, and the concentration of cobalt ions affects the in-situ reaction in the subsequent plasma discharge process, during the plasma discharge reaction, each element has a competitive reaction, the amount of cobalt atoms contained in the catalyst material and the active sites thereof are related to the final catalytic performance, the cobalt elements need to cooperate with other elements to improve the catalytic performance of the catalyst, and therefore, the content thereof needs to be controlled within a certain range, and the catalyst of the present invention cannot be prepared when the pH of the solution is less than 7 or more than 7;

(3) respectively adding 5-10mL of ferric nitrate solution and ethanol into the B in sequence, and uniformly stirring to obtain C;

in the step, ferric nitrate is added, so that the overall reaction rate is accelerated through the redox reaction of ferric iron and foamed aluminum in the subsequent plasma discharge treatment process, the specific expression is that ferric iron can show extremely strong oxidability in the current solution environment, foamed aluminum has extremely strong reducibility, the ferric iron and the foamed aluminum can carry out the redox reaction, and then nanoparticles with regular shapes can be rapidly and efficiently prepared, and the hydroxyl metal compound can be generated in the subsequent chemical reaction process after ethanol is introduced into a reaction system;

(4) placing foamed aluminum with the diameter of 1cm multiplied by 1cm into the C, soaking the foamed aluminum on the surface of the C solution by taking the foamed aluminum as a working electrode and the C as a reaction solution, and simultaneously carrying out plasma discharge on the foamed aluminum in a nitrogen atmosphere to enable the foamed aluminum to quickly and efficiently carry out chemical reaction on the surface;

in the step, the nitrogen generates a large amount of electron energy in the plasma discharging process, metal ions around the foamed aluminum can be activated to react with the nitrogen, and a hydroxyl metal compound can be generated in the discharging process under a large amount of ferric ethanol solution systems, and the hydroxyl metal compound and the metal nitride which have controllable content and specific distribution have a bifunctional catalytic effect;

(5) and (3) washing the self-supporting electrode for 3-6 times by using absolute ethyl alcohol and deionized water in sequence, and drying in vacuum to obtain the bifunctional ternary metal hydroxyl nitride electrocatalyst.

As a limitation of the present invention:

in the step (1), the undersize is ground into powder with the particle size of 400 meshes.

In the step (1), the concentration of the dilute hydrochloric acid is 3-6M, and the soaking time is 3-8 h.

(III) in the step (3), the concentration of the ferric nitrate is 100-150 mM.

In the step (4), the voltage of the plasma discharge is 50V, and the reaction lasts for 10-120 s;

in the step, the plasma discharge voltage and the discharge time have important influence on the appearance and the particle size of a final product, and when the discharge voltage is less than 50V, metal ions do not react sufficiently on the foamed aluminum, so that the self-supporting electrode has poor cohesiveness, the electrocatalyst is easy to fall off in the electrocatalysis process, and the catalytic effect is influenced; when the discharge voltage is more than 50V, more nano particles are quickly generated in the discharge process, and the nano particles are easy to agglomerate, so that the transmission of electrolyte ions and electrons among the nano particles is weakened, and the electro-catalysis performance is reduced;

when the plasma discharge time is less than 10s, the nitridation reaction is insufficient in the discharge process, so that the synthesis of the metal nitride in the dual-function electrocatalyst is influenced, and the performance of the nano composite electrocatalyst is reduced; when the plasma discharge time is more than 120s, although nitridation completely reacts in the discharge process, the synthesis of the hydroxyl metal compound is affected, the distribution of the hydroxyl metal compound is uneven, and the bifunctional electrocatalytic performance is reduced.

And (V) in the step (5), the drying temperature is 60-100 ℃, and the drying time is 6-12 h.

And (sixthly), in the step (4), the thickness of the foamed aluminum is 0.01 cm.

The invention also has a limitation that the bifunctional ternary metal hydroxy nitride electrocatalyst is in a nano shape formed by crosslinking nano particles, and the particle size is 50-100 nm; as is well known, the morphology and the structure influence the catalytic performance of the catalyst, and the morphology structure is beneficial to the transmission of ions and electrons, thereby laying a foundation for the good catalytic performance of the catalyst.

In the plasma discharge treatment process, cobalt ions, iron ions and foamed aluminum can rapidly react with activated nitrogen in situ under the action of ethanol, the introduction of the ethanol and the parameters of plasma discharge are crucial to the preparation of the bifunctional metal hydroxyl nitride electrocatalyst, and the ethanol and the plasma discharge can control the formation and content distribution of the metal hydroxyl nitride and further influence the morphology and catalytic activity of the product. The preparation is carried out by adopting the process parameters disclosed by the invention, so that the nano-catalyst with excellent bifunctional catalytic activity is finally formed, and the existence of ethanol and the in-situ introduction of nitrogen are closely related to the catalytic activity of the catalyst in the process.

The above-described preparation process as a whole for preparing the catalyst of the invention is associated with the fact that the individual steps are not readily cleavable.

Compared with the prior art, the invention has the following advantages:

1. the waste lithium cobaltate material is efficiently recycled by using an oxidation-reduction and plasma discharge method in the preparation process to prepare the bifunctional ternary metal hydroxyl nitride electrocatalyst, the reaction condition is mild, the production process is simple and controllable, and the method is suitable for large-scale industrial production.

2. Nitrogen atoms are introduced in situ in the plasma discharge process, and the element distribution of the electrocatalyst can be controlled by the plasma discharge method, so that the ternary metal hydroxyl nitride with the bifunctional electrocatalytic activity is prepared, and the hydrogen evolution and oxygen evolution catalytic performances of the ternary metal hydroxyl nitride are greatly improved.

3. In the catalytic process, the three-element metal and the hydroxyl nitride are cooperatively catalyzed, so that the catalyst has excellent difunctional electrocatalytic activity, excellent hydrogen evolution and oxygen evolution electrocatalytic activity and high catalytic stability.

4. Realizes the recycling of waste, can realize large-scale production and realizes industrialization.

The method is suitable for recycling and resource utilization of the lithium cobaltate cathode material recycled from the waste lithium ion battery, and is further used for preparing the ternary metal hydroxyl nitride with the bifunctional electrocatalytic activity.

The following description of the embodiments of the present invention will be described in further detail with reference to the accompanying drawings.

Drawings

FIG. 1 is a graph of oxygen evolution LSV performance of samples made in example 1 of the present invention;

FIG. 2 is a graph of the hydrogen evolution LSV performance of samples made in example 2 of the present invention;

FIG. 3 is a scanning electron microscope image of a sample prepared in example 3 of the present invention;

FIG. 4 is a diagram of elemental analysis of a sample prepared in example 4 of the present invention;

FIG. 5 is a graph comparing hydrogen evolution LSV curves for samples prepared according to examples 4, 5 and 6 of the present invention, respectively;

FIG. 6 is a graph comparing oxygen evolution LSV curves for samples prepared in example 4, example 5 and example 6 of the present invention, respectively;

FIG. 7 is a graph comparing bifunctional perhydrolysis LSV curves for samples prepared according to the present invention, example 4, example 5, and example 6, respectively.

Detailed Description

The reagents used in the following examples are commercially available reagents unless otherwise specified, and the preparation methods and detection methods used therefor are well known in the art.

Example 1

A method for preparing a bifunctional ternary metal hydroxyl nitride electrocatalyst by using waste lithium cobaltate sequentially comprises the following steps:

(11) crushing and sieving a lithium cobaltate positive electrode material recovered from a waste lithium ion battery, taking undersize, grinding the undersize into powder, sieving with a 400-mesh sieve, soaking in 3M dilute hydrochloric acid for 5 hours, and taking a supernatant A;

(12) adding a certain amount of sodium hydroxide solution into the solution A until the pH value of the solution is 7 to obtain a solution B;

(13) respectively and sequentially adding 5mL of 100mM ferric nitrate solution and 5 mM ethanol into the B to obtain C;

(14) placing foamed aluminum (the thickness is 0.01 cm) with the diameter of 1cm multiplied by 1cm into the C, using the foamed aluminum as a working electrode and the C as a reaction solution, soaking the foamed aluminum on the surface of the C solution, and simultaneously carrying out plasma discharge on the foamed aluminum under the voltage of 50V for 10s in the nitrogen atmosphere so as to enable the foamed aluminum to rapidly and efficiently generate electrochemical reaction on the surface;

(15) and (3) washing the self-supporting electrode for 3 times by using absolute ethyl alcohol and deionized water in sequence, and drying the washed self-supporting electrode for 8 hours in vacuum at the temperature of 60 ℃ to obtain the bifunctional ternary metal hydroxyl nitride electrocatalyst.

FIG. 1 is a graph of oxygen evolution LSV of a sample prepared in example 1 of the present invention at a current density of 10mA^-2The overpotential for oxygen evolution of the material prepared in example 1 was 196mV, indicating that the ternary metal hydroxy nitride has excellent catalytic activity for oxygen evolution.

Example 2

A method for preparing a bifunctional ternary metal hydroxyl nitride electrocatalyst by using waste lithium cobaltate sequentially comprises the following steps:

(21) crushing and sieving the waste lithium cobalt oxide positive electrode material, taking undersize, grinding the undersize into powder, sieving the powder with a 400-mesh sieve, soaking the powder in 6M dilute hydrochloric acid for 3 hours, and taking supernatant liquid as A;

(22) adding a certain amount of sodium hydroxide solution into the solution A until the pH value of the solution is 7 to obtain a solution B;

(23) respectively and sequentially adding 150mM ferric nitrate solution and 8mL of ethanol into the solution B to obtain a solution C;

(24) placing foamed aluminum (the thickness is 0.01 cm) with the diameter of 1cm multiplied by 1cm into the C, using the foamed aluminum as a working electrode and the C as a reaction solution, soaking the foamed aluminum on the surface of the C solution, and simultaneously carrying out plasma discharge on the foamed aluminum for 120s under the voltage of 50V in the nitrogen atmosphere so as to enable the foamed aluminum to rapidly and efficiently generate electrochemical reaction on the surface;

(25) and (3) washing the self-supporting electrode for 6 times by using absolute ethyl alcohol and deionized water in sequence, and drying the washed self-supporting electrode for 12 hours in vacuum at the temperature of 100 ℃ to obtain the bifunctional ternary metal hydroxyl nitride electrocatalyst.

FIG. 2 is a graph of hydrogen evolution LSV of a sample prepared in example 2 of the present invention at a current density of 10mA^-2Meanwhile, the overpotential for hydrogen evolution of the material prepared in example 2 is 177mV, which shows that the ternary metal hydroxy nitride has excellent hydrogen evolution catalytic activity.

Example 3

A method for preparing a bifunctional ternary metal hydroxyl nitride electrocatalyst by using waste lithium cobaltate sequentially comprises the following steps:

(31) crushing and sieving the waste lithium cobalt oxide positive electrode material, taking undersize, grinding the undersize into powder, sieving the powder with a 400-mesh sieve, soaking the powder in 5M dilute hydrochloric acid for 8 hours, and taking supernatant liquid as A;

(32) adding a certain amount of sodium hydroxide solution into the solution A until the pH value of the solution is 7 to obtain a solution B;

(33) respectively and sequentially adding 110mM ferric nitrate solution and 10mL of ethanol into the B to obtain C;

(34) placing foamed aluminum (the thickness is 0.01 cm) with the diameter of 1cm multiplied by 1cm into the C, soaking the foamed aluminum on the surface of the C solution by taking the foamed aluminum as a working electrode and the C as a reaction solution, and simultaneously carrying out plasma discharge on the foamed aluminum under the voltage of 50V for 60s in the nitrogen atmosphere so as to enable the foamed aluminum to rapidly and efficiently generate electrochemical reaction on the surface;

(35) and (3) washing the self-supporting electrode for 5 times by using absolute ethyl alcohol and deionized water in sequence, and drying for 6 hours in vacuum at the temperature of 80 ℃ to obtain the bifunctional ternary metal hydroxyl nitride electrocatalyst.

FIG. 3 is a scanning electron microscope image of the sample prepared in example 3 of the present invention under high magnification, from which it can be seen that the sample is composed of nanoparticles with a particle size of 50-100 nm.

Example 4

A method for preparing a bifunctional ternary metal hydroxyl nitride electrocatalyst by using waste lithium cobaltate sequentially comprises the following steps:

(41) crushing and sieving the waste lithium cobalt oxide positive electrode material, taking undersize, grinding the undersize into powder, sieving the powder with a 400-mesh sieve, soaking the powder in 5M dilute hydrochloric acid for 5 hours, and taking supernatant liquid as A;

(42) adding a certain amount of sodium hydroxide solution into the solution A until the pH value of the solution is 7 to obtain a solution B;

(43) respectively and sequentially adding 8mL of 120mM ferric nitrate solution and 8 mM ethanol into the solution B to obtain a solution C;

(44) placing foamed aluminum (the thickness is 0.01 cm) with the diameter of 1cm multiplied by 1cm into the C, using the foamed aluminum as a working electrode and the C as a reaction solution, soaking the foamed aluminum on the surface of the C solution, and simultaneously carrying out plasma discharge on the foamed aluminum under the voltage of 50V for 60s in the nitrogen atmosphere so as to enable the foamed aluminum to rapidly and efficiently generate electrochemical reaction on the surface;

(45) washing the self-supporting electrode for 3 times by absolute ethyl alcohol and deionized water in sequence, and drying for 6 hours in vacuum at 60 ℃ to obtain the bifunctional ternary metal hydroxyl nitride electrocatalyst;

fig. 4 is an elemental analysis diagram of a sample prepared in example 4 of the present invention, from which it can be seen that the material is a ternary metal hydroxy nitride of Fe-Co-Al, and it is proved that cobalt ions, iron ions and aluminum ions in the waste lithium anode material undergo hydroxylation and nitridation reactions simultaneously under the action of plasma discharge in an ethanol and nitrogen environment, and the content of cobalt accounts for 9.12 percent.

Example 5 comparative example

This example is a method for preparing a ternary metal hydroxy electrocatalyst using waste lithium cobaltate, which is similar to the preparation method of example 4, except that: plasma discharge is not adopted in the preparation process.

The specific steps are carried out in sequence as follows:

(51) crushing and sieving the waste lithium cobalt oxide positive electrode material, taking undersize, grinding the undersize into powder, sieving the powder with a 400-mesh sieve, soaking the powder in 5M dilute hydrochloric acid for 5 hours, and taking supernatant liquid as A;

(52) adding a certain amount of sodium hydroxide solution into the solution A until the pH value of the solution is 7 to obtain a solution B;

(53) respectively and sequentially adding 8mL of 120mM ferric nitrate solution and 8 mM ethanol into the solution B to obtain a solution C;

(54) placing foamed aluminum (the thickness is 0.01 cm) with the diameter of 1cm multiplied by 1cm into the C, taking the foamed aluminum as a working electrode and the C as a reaction solution, and soaking the foamed aluminum on the surface of the C solution to enable the foamed aluminum to generate chemical reaction on the surface;

(55) and (3) washing the self-supporting electrode for 3 times by using absolute ethyl alcohol and deionized water in sequence, and drying for 6 hours in vacuum at the temperature of 60 ℃ to obtain the ternary metal hydroxy electrocatalyst.

FIG. 5 is a graph comparing the oxygen evolution electrocatalytic performance of samples prepared in example 4, example 5 and example 6 of the present invention (examples described below). As can be seen from the figure, under the combined action of plasma discharge in a nitrogen atmosphere and ethanol, the ternary metal hydroxyl nitride of Fe-Co-Al prepared in the embodiment 4 has the highest hydrogen evolution catalytic activity, which shows that the introduction of ethanol in a plasma discharge method and a reaction system has an important role in preparing a high-activity bifunctional electrocatalytic material, in the preparation process, metal ions in a solution react with ethanol in a hydroxylation reaction manner, and nitrogen atoms can participate in hydroxylation and nitridation reactions in situ in the plasma discharge process in the nitrogen atmosphere, so that the ternary metal hydroxyl nitride with the bifunctional electrocatalytic activity can be formed, and the mutually crosslinked nano-particle morphology is formed, in the catalytic hydrogen evolution process, it can be seen that the plasma method is not adopted in the embodiment 5, and the prepared sample has very poor hydrogen evolution catalytic activity, the nitridation of the plasma under the nitrogen atmosphere plays an important role in improving the catalytic activity of hydrogen evolution. In the catalytic reaction process of the catalyst, three metals of Fe, Co and Al and nitrogen atoms are subjected to synergistic catalysis, and a composite active center beneficial to hydrogen evolution catalytic reaction is formed, so that the synergistic catalytic effect is achieved.

Example 6 comparative example

This example is a method of preparing a ternary metal nitride electrocatalyst using waste lithium cobaltate, similar to the preparation procedure of example 4, except that: no ethanol is added in the preparation process.

The specific preparation process comprises the following preparation steps in sequence:

(61) crushing and sieving the waste lithium cobalt oxide positive electrode material, taking undersize, grinding the undersize into powder, sieving the powder with a 400-mesh sieve, soaking the powder in 5M dilute hydrochloric acid for 5 hours, and taking supernatant liquid as A;

(62) adding a certain amount of sodium hydroxide solution into the solution A until the pH value of the solution is 7 to obtain a solution B;

(63) adding 8mL of 120mM ferric nitrate solution into the B to obtain C;

(64) placing foamed aluminum (the thickness is 0.01 cm) with the diameter of 1cm multiplied by 1cm into the C, taking the foamed aluminum as a working electrode and the C as a reaction solution, soaking the foamed aluminum on the surface of the C solution, and simultaneously carrying out plasma discharge on the foamed aluminum under the nitrogen atmosphere at the voltage of 50V for 60s to enable the foamed aluminum to generate electrochemical reaction on the surface;

(65) washing the self-supporting electrode with absolute ethyl alcohol and deionized water for 3 times in sequence, and drying the electrode in vacuum at 60 ℃ for 6 hours to obtain the electrocatalyst;

FIG. 6 is a graph comparing the oxygen evolution electrocatalytic performance of samples prepared in example 4, example 5 and example 6 of the present invention. As can be seen from the figure, under the combined action of plasma discharge in a nitrogen atmosphere and ethanol, the oxygen evolution catalytic activity of the Fe-Co-Al ternary metal hydroxy nitride prepared in example 4 is the highest, which shows that the plasma discharge method and the addition of ethanol have an important role in preparing a high-activity bifunctional electrocatalytic material, and in the preparation process, metal ions in the solution can undergo hydroxylation reaction with ethanol, and nitrogen atoms can participate in hydroxylation and nitridation reactions in situ in the plasma discharge process in the nitrogen atmosphere, so that the ternary metal hydroxy nitride with bifunctional electrocatalytic activity can be formed, and the appearance of the cross-linked nanoparticles described in the present application is formed. In the process of catalytic oxygen evolution, it can be seen that no ethanol is added in example 6, and the oxygen evolution catalytic activity of the sample is very poor, so that the addition of ethanol has an important effect on the promotion of the oxygen evolution catalytic activity. In the catalytic reaction process of the catalyst, three metals of Fe, Co and Al and nitrogen atoms are subjected to synergistic catalysis, and a composite active center beneficial to oxygen evolution catalytic reaction is formed, so that the synergistic catalytic effect is achieved.

FIG. 7 is a graph comparing the catalytic performance of bifunctional electrolyzed water for samples prepared in example 4, example 5 and example 6 of the present invention. As can be seen from the figure, under the combined action of plasma discharge in a nitrogen atmosphere and ethanol, the Fe-Co-Al ternary metal hydroxy nitride prepared in example 4 has the highest bifunctional catalytic activity, which shows that the plasma technology and the addition of ethanol play an important role in preparing a high-activity bifunctional electrocatalytic material. In the process of catalytic hydrogen evolution, it can be seen that the plasma discharge method is not adopted in the example 5, and the sample has very poor hydrogen evolution catalytic activity, resulting in poor bifunctional electrocatalytic activity; in the process of catalytic oxygen evolution, the fact that no ethanol is added in the example 6 can be seen, the catalytic activity of oxygen evolution of the sample is very poor, and the dual-function electrocatalytic activity of the sample is poor.

Finally, it should be noted that: the above-mentioned embodiments are only used for illustrating the technical solution of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.