Preparation Method of a Heterostructure Self-Supported Electrode and Its Application in Hydrogen Production by Electrolytic Water

Abstract

The present invention discloses a preparation method of a heterostructure self-supporting electrode and its application in electrolytic water hydrogen production. The method includes: performing low-temperature phosphating treatment on a foam metal to obtain a precursor, where the foam metal is a transition metal; immersing the precursor in an organic solvent dissolved with a metal nitrate, and obtaining a composite of a metal oxide and the precursor after standing; the metal oxide is formed in-situ on the precursor, and the metal in the metal nitrate is a transition metal; performing nitriding treatment on the composite to obtain a heterostructure self-supporting electrode of a metal nitride and a phosphide. The preparation method provided by the present invention has the advantages of simple operation, high cost performance, etc. When the self-supporting electrode prepared by the present invention is used as an anode for electrolytic water oxygen evolution reaction, it has excellent catalytic activity and stability at a high current density, and can solve the problem of high energy consumption in industrial electrolytic water hydrogen production.

Description

Technical Field

[0001] The present invention belongs to the field of hydrogen production by electrolyzing water, and more specifically, relates to a preparation method of a heterostructure self-supporting electrode and an application in hydrogen production by electrolyzing water. Background Art

[0002] Hydrogen energy is considered to be a clean energy source with the most promising application prospects because of its advantages such as clean and pollution-free, high calorific value of combustion, and rich raw material sources. The main methods for hydrogen production include biological hydrogen production, water photolysis hydrogen production, and electrolytic water hydrogen production, etc. Among them, electrolytic water hydrogen production is widely regarded as an ideal hydrogen production method because of its high hydrogen production purity, high conversion efficiency, and environmental friendliness. The process of electrolyzing water mainly consists of two half-reactions: hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode. Because of problems such as high overpotential and poor stability of the electrocatalyst at high current density during the OER reaction process, it is difficult to make effective progress in the field of industrial electrolytic water hydrogen production. Therefore, developing an oxygen evolution electrode material with high activity and stable operation at high current density (>500 mA cm -2 ) applicable to the industrial electrolytic water field is still a huge challenge.

[0003] Currently, the materials with the best electrolytic water performance are platinum, rhodium, ruthenium-based noble metal catalysts, but the noble metal catalysts are expensive and cannot meet industrial demands. In contrast, non-noble metal self-supporting electrocatalysts such as transition metal nitrides, phosphides, carbides, and sulfides, etc., are expected to replace traditional noble metal catalysts as more ideal electrolytic water catalysts because of their low cost and excellent performance. Compared with powder catalysts, self-supporting catalysts are more suitable for practical applications because they do not require the use of conductive binders. Self-supporting heterojunction electrodes often exhibit excellent electrochemical activity and stability because they have rich heterointerfaces, which can provide more active sites and material transport. Therefore, forming a lattice-matched heterojunction can give play to the common advantages of transition metal nitrides and phosphides, and improve their catalytic activity and stability through the synergistic effect between the heterointerfaces and the self-supporting catalysts. This measure has great application prospects in the field of industrial electrolytic water.

[0004] Currently, the OER electrodes in the field of electrolytic water hydrogen production still have problems such as low activity and poor high-current stability. Most OER electrodes can only operate stably at a current density of 10 mA cm -2 or 100 mA cm -2 .

[0005] It can be seen that the catalytic activity and high-current stability of the self-supporting heterojunction electrodes prepared by the current existing technologies need to be further improved. Summary of the Invention

[0006] In view of the above deficiencies or improvement requirements of the prior art, the present invention provides a preparation method of a heterostructure self-supporting electrode and its application in electrolytic water hydrogen production. The purpose is to prepare a self-supporting heterostructure electrode through low-temperature phosphidation, ion exchange method and nitridation treatment, so as to increase the specific surface area of the self-supporting heterostructure electrode, promote the exposure of active sites, and further enhance the electrochemical activity and stability of the catalyst. Thus, the technical problems of poor OER electrode activity and poor large-current stability in the current field of electrolytic water hydrogen production are solved.

[0007] To achieve the above object, according to one aspect of the present invention, a preparation method of a heterostructure self-supporting electrode is provided, including the following steps:

[0008] (1) Perform low-temperature phosphidation treatment on the foam metal to obtain a precursor. The foam metal is a transition metal, and the temperature of the low-temperature phosphidation treatment is 300-400 °C;

[0009] (2) Immerse the precursor in an organic solvent dissolved with metal nitrate, and after standing, obtain a composite of metal oxide and precursor; the metal oxide is formed in-situ on the precursor, and the metal in the metal nitrate is a transition metal;

[0010] (3) Perform nitridation treatment on the composite to obtain a heterostructure self-supporting electrode of metal nitride and phosphide.

[0011] Preferably, the metal nitrate is cobalt nitrate, nickel nitrate or iron nitrate; the concentration of the metal nitrate solution is 0.6-1 g / mL; the organic solvent is N,N-dimethylformamide.

[0012] Preferably, the low-temperature phosphidation treatment is to place the phosphorus source material and the foam metal at the upstream and downstream of the quartz boat respectively, and perform low-temperature phosphidation in a tube furnace. The tube furnace is heated to 300-400 °C at a heating rate of 1-5 °C / min.

[0013] Preferably, the atmosphere of the nitridation treatment is a mixed atmosphere of ammonia and argon, and it is heated to 400-500 °C at a heating rate of 1-5 °C / min; the nitridation treatment time is 1-2 h.

[0014] Preferably, the phosphidation time of the low-temperature phosphidation treatment is 1-3 h; the phosphorus source material is sodium hypophosphite; for foam iron, for every 1.5 g / cm 3 of foam iron, the mass of sodium hypophosphite is 0.3-1.5 g.

[0015] Preferably, the standing time in step (2) is 5-8 h.

[0016] Preferably, the metallic foam is iron foam or copper foam. Before the low-temperature phosphating treatment, the metallic foam is pretreated by successively immersing it in hydrochloric acid solution, absolute ethanol, and deionized water for ultrasonic cleaning, followed by drying.

[0017] According to another aspect of the present invention, a heterostructured self-supporting electrode is provided.

[0018] Preferably, the heterostructured self-supporting electrode comprises a metallic foam, dendritic metal phosphide grown in-situ on the metallic foam, and granular metal nitride grown in-situ on the metal phosphide.

[0019] According to yet another aspect of the present invention, an application of the heterostructured self-supporting electrode is provided, where the heterostructured self-supporting electrode is used as an oxygen evolution electrode for hydrogen production by electrolyzing water.

[0020] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, at least the following beneficial effects can be achieved.

[0021] (1) Using metal nitrates and metallic foam as raw materials, the present invention prepares a self-supporting heterostructured electrode through low-temperature phosphating, ion exchange, and nitriding treatments. Compared with ordinary self-supporting catalysts, it has a heterointerface of metal nitride and phosphide, thus having a special interfacial effect. This measure increases the specific surface area of the self-supporting heterostructured electrode and promotes the exposure of active sites. When used as an electrocatalytic oxygen evolution catalyst under industrial alkaline electrolyzed water conditions (30 wt% KOH), the self-supporting electrode exhibits excellent oxygen evolution activity and high-current stability (800 mA cm -2 It can operate stably for 120 h).

[0022] (2) The catalyst grown in-situ based on the metallic foam of the present invention can be directly used as a working electrode. This improvement not only avoids the use of binders but also greatly enhances the electrochemical activity and stability of the catalyst. Description of the Drawings

[0023] Figure 1 Figures (a) and (b) are respectively scanning electron microscope (SEM) images of the phosphide precursor (Fe x P / FF) prepared in Example 1 at different magnifications;

[0024] Figure 2 Figures (a) and (b) are respectively scanning electron microscope (SEM) images of the metal nitride / phosphide heterojunction self-supporting high-performance oxygen evolution electrode (Ni 3 N|NiFeP / FF) prepared in Example 1 at different magnifications;

[0025] Figure 3 Transmission electron microscope (TEM) image of the self-supported high-performance oxygen evolution electrode (Ni 3 N|NiFeP / FF) prepared in Example 1;

[0026] Figure 4 Among them, (a) and (b) are the scanning electron microscope (SEM) images of the heterostructure self-supported oxygen evolution electrode (Ni 3 N|NiFeP / FF-4) prepared in Comparative Example 2;

[0027] Figure 5 Linear sweep voltammetry curves of electrocatalytic oxygen evolution of two different electrodes, namely the heterostructure self-supported oxygen evolution electrode (Ni 3 N|NiFeP / FF) prepared in Example 1 and Comparative Example 1 in 1 M KOH;

[0028] Figure 6 Linear sweep voltammetry curves of electrocatalytic oxygen evolution of two different electrodes, namely the heterostructure self-supported oxygen evolution electrode (Ni 3 N|NiFeP / NF) prepared in Example 1 and Comparative Example 2 in 1 M KOH;

[0029] Figure 7 Linear sweep voltammetry curves of electrocatalytic oxygen evolution of two different electrodes, namely the heterostructure self-supported oxygen evolution electrode (Ni 3 N|NiFeP / NF) prepared in Example 1 and Comparative Example 1 in 30 wt% KOH;

[0030] Figure 8 Chronopotentiometry curve of the heterostructure self-supported oxygen evolution electrode prepared in Example 1 in 30 wt% KOH. Detailed implementation manners

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Example 1

[0033] This example provides a preparation method of a self-supported electrode with a heterostructure, and the method includes:

[0034] (1) Cut a certain size of iron foam (2*2 cm 2, 95 PPI, 1 mm), it was successively placed in hydrochloric acid (0.1 M), absolute ethanol and deionized water for ultrasonic impurity removal. The ultrasonic time was 20 min each time, and then it was placed in a vacuum oven at 60 °C for drying for 12 h;

[0035] (2) Sodium hypophosphite and the iron foam obtained in step (1) were respectively placed at the upstream and downstream of a quartz boat. The mass of sodium hypophosphite was 1 g. Subsequently, it was transferred to a tubular furnace, and under an argon atmosphere, it was heated to 350 °C at a heating rate of 5 °C / min, the argon gas flow rate was controlled to be 50 sccm, and it was kept at 350 °C for 2 h. After the reaction was cooled to room temperature, it was taken out to obtain Fe x P / FF precursor.

[0036] (3) Weigh 6 g of nickel nitrate and dissolve it in 10 ml of DMF solution, stir evenly to form solution A;

[0037] (4) Take the Fe x P / FF prepared in step (2) and immerse it in solution A obtained in step (3), and let it stand at room temperature for 5 h. After the reaction was completed, the electrocatalyst was taken out and naturally air-dried for 12 h to obtain NiO x |Fe x P / FF precursor catalyst;

[0038] (5) Place the NiO x |Fe x P / FF precursor catalyst in a tubular furnace, under a mixed atmosphere of NH 3 and Ar, where the NH 3 gas flow rate is 120 sccm, the gas flow ratio of NH 3 to Ar is 3:1, heat it to 450 °C at a heating rate of 5 °C / min, and keep it at 450 °C for 1 h. After the reaction was cooled to room temperature, it was taken out to obtain the target product Ni 3 N|NiFeP / FF self-supporting electrode.

[0039] Example 2

[0040] This example provides a preparation method of a self-supporting electrode with a heterostructure, and the method includes:

[0041] (1) Cut a certain size of iron foam (2*2 cm 2 , 95 PPI, 1 mm), successively place it in hydrochloric acid (0.1 M), absolute ethanol and deionized water for ultrasonic impurity removal. The ultrasonic time is 20 min each time, and then place it in a vacuum oven at 60 °C for drying for 12 h;

[0042] (2) Place sodium hypophosphite and the iron foam obtained in step (1) at the upstream and downstream of a quartz boat respectively. The mass of sodium hypophosphite is 1 g. Subsequently, transfer it to a tube furnace, and under an argon atmosphere, heat it to 350 °C at a heating rate of 5 °C / min, control the argon gas flow rate to be 50 sccm, and keep it at 350 °C for 2 h. After the reaction cools down to room temperature, take it out to obtain the target product Fe x P / FF precursor;

[0043] (3) Weigh 10 g of nickel nitrate and dissolve it in 10 ml of DMF solution, stir evenly to form solution A;

[0044] (4) Take the Fe x P / FF prepared in step (2) and immerse it in solution A obtained in step (3), and let it stand at room temperature for 5 h. After the reaction is completed, take out the electrocatalyst and air-dry it for 12 h to obtain NiO x |Fe x P / FF precursor catalyst;

[0045] (5) Place the NiO x |NiFeP / FF precursor catalyst in a tube furnace, under a mixed atmosphere of NH 3 and Ar, where the NH 3 gas flow rate is 120 sccm, the gas flow ratio of NH 3 to Ar is 3:1, heat it to 450 °C at a heating rate of 5 °C / min, and keep it at 450 °C for 1 h. After the reaction cools down to room temperature, take it out to obtain the target product Ni 3 N|NiFeP / FF self-supporting electrode.

[0046] Example 3

[0047] This example provides a preparation method of a self-supporting electrode with a heterostructure, and the method includes:

[0048] (1) Cut a certain size of iron foam (2*2 cm 2 , 95 PPI, 1 mm), place it in hydrochloric acid (0.1 M), absolute ethanol and deionized water in sequence for ultrasonic impurity removal, each ultrasonic time is 20 min, and then place it in a vacuum oven at 60 °C for drying for 12 h;

[0049] (2) Place sodium hypophosphite and the iron foam obtained in step (1) at the upstream and downstream of a quartz boat respectively. The mass of sodium hypophosphite is 0.3 g. Subsequently, transfer it to a tube furnace, and under an argon atmosphere, heat it to 400 °C at a heating rate of 5 °C / min, control the argon gas flow rate to be 50 sccm, and keep it at 400 °C for 2 h. After the reaction cools down to room temperature, take it out to obtain the target product Fe x P / FF precursor.

[0050] (3) Weigh 6 g of nickel nitrate and dissolve it in 10 ml of DMF solution, stir evenly to form solution A;

[0051] (4) Take the Fe x P / FF prepared in step (2) and immerse it in solution A obtained in step (3), and let it stand for 5 h at room temperature. After the reaction is completed, take out the electrocatalyst and air-dry it naturally for 12 h to obtain NiO x |Fe x P / FF precursor catalyst;

[0052] (5) Place the NiO x |Fe x P / FF precursor catalyst in a tubular furnace, under the mixed atmosphere of NH 3 and Ar, where the gas flow rate of NH 3 is 120 sccm, and the gas flow ratio of NH 3 to Ar is 3:1. Heat it up to 450 °C at a heating rate of 5 °C / min and keep it at 450 °C for 1 h. After the reaction is cooled to room temperature, take it out to obtain the target product Ni 3 N|NiFeP / FF self-supporting electrode.

[0053] Example 4

[0054] This example provides a preparation method of a self-supporting electrode with a heterostructure, and the method includes:

[0055] (1) Cut a certain size of iron foam (3*3 cm 2 , 95 PPI, 1 mm), place it in hydrochloric acid (1 M), absolute ethanol and deionized water in sequence for ultrasonic impurity removal, with the ultrasonic time of 20 min each time, and then place it in a vacuum oven at 60 °C for drying for 12 h;

[0056] (2) Place sodium hypophosphite and the iron foam obtained in step (1) at the upstream and downstream of the quartz boat respectively. The mass of sodium hypophosphite is 1 g. Then transfer it to a tubular furnace, under the argon atmosphere, heat it up to 400 °C at a heating rate of 5 °C / min, control the argon gas flow rate to be 50 sccm, and keep it at 400 °C for 2 h. After the reaction is cooled to room temperature, take it out to obtain the target product Fe x P / FF precursor.

[0057] (3) Weigh 4 g of cobalt nitrate and dissolve it in 20 ml of DMF solution, stir evenly to form solution A;

[0058] (4) Take the Fe xImmerse it in the solution A obtained in step (3) of P / FF immersion, and let it stand at room temperature for 5 h. After the reaction is completed, take out the electrocatalyst and air-dry it naturally for 12 h to obtain CoO x |Fe x P / FF precursor catalyst;

[0059] (5) Place CoO x |Fe x P / FF precursor catalyst in a tubular furnace, and under the mixed atmosphere of NH 3 and Ar, where the gas flow rate of NH 3 is 120 sccm, the gas flow ratio of NH 3 to Ar is 3:1, heat it up to 450 °C at a heating rate of 5 °C / min, and keep it at 450 °C for 1 h. After the reaction is cooled to room temperature, take it out to obtain the target product Co 2 N|FeCoP / FF self-supporting electrode.

[0060] Example 5

[0061] This example provides a preparation method of a self-supporting electrode with a heterostructure, and the method includes:

[0062] (1) Cut a certain size of copper foam (3*3 cm 2 , 95 PPI, 1 mm), place it in hydrochloric acid (1 M), absolute ethanol and deionized water in sequence for ultrasonic impurity removal, the ultrasonic time is 20 min each time, and then place it in a vacuum oven at 60 °C for drying for 12 h;

[0063] (2) Place sodium hypophosphite and the copper foam obtained in step (1) at the upstream and downstream of the quartz boat respectively. The mass of sodium hypophosphite is 1 g. Then transfer it to a tubular furnace, and under the argon atmosphere, heat it up to 350 °C at a heating rate of 5 °C / min, control the argon gas flow rate to be 50 sccm, and keep it at 350 °C for 2 h. After the reaction is cooled to room temperature, take it out to obtain the target product Cu x P / FF precursor.

[0064] (3) Weigh 4 g of nickel nitrate and dissolve it in 20 ml of DMF solution, stir evenly to form solution A;

[0065] (4) Take the Cu x P / FF prepared in step (2) and immerse it in the solution A obtained in step (3), and let it stand at room temperature for 5 h. After the reaction is completed, take out the electrocatalyst and air-dry it naturally for 12 h to obtain NiO x |Cu x P / CF precursor catalyst;

[0066] (5) Place NiO x |Cux The P / CF precursor catalyst was placed in a tubular furnace and, under the mixed atmosphere of NH 3 and Ar, where the gas flow rate of NH 3 was 120 sccm, the gas flow ratio of NH 3 to Ar was 3:1, and it was heated to 450 °C at a heating rate of 5 °C / min and held at 450 °C for 1 h. After the reaction was cooled to room temperature, it was taken out to obtain the target product Ni 3 N|CoCuP / CF self-supporting electrode.

[0067] Comparative Example 1

[0068] First, a certain size of iron foam (2*2 cm 2 , 95 PPI, 1 mm) was cut, and then it was successively placed in hydrochloric acid (1 M), absolute ethanol, and deionized water for ultrasonic treatment. The ultrasonic treatment time was 20 min each time, and then it was placed in a vacuum oven at 60 °C for drying for 12 h. Finally, the iron foam comparative sample was obtained.

[0069] Comparative Example 2

[0070] The present invention provides a preparation method the same as that in Example 1 but with too low a concentration of nickel nitrate. The preparation method is as follows:

[0071] (1) A certain size of iron foam (2*2 cm 2 , 95 PPI, 1 mm) was cut and successively placed in hydrochloric acid (0.1 M), absolute ethanol, and deionized water for ultrasonic impurity removal. The ultrasonic treatment time was 20 min each time, and then it was placed in a vacuum oven at 60 °C for drying for 12 h;

[0072] (2) Sodium hypophosphite and the iron foam obtained in step (1) were respectively placed upstream and downstream of a quartz boat. The mass of sodium hypophosphite was 1 g. Subsequently, it was transferred to a tubular furnace and heated to 350 °C at a heating rate of 5 °C / min under an argon atmosphere, controlling the argon gas flow rate to be 50 sccm, and held at 350 °C for 2 h. After the reaction was cooled to room temperature, it was taken out to obtain the target product Fe x P / FF precursor;

[0073] (3) Weighed 4 g of nickel nitrate and dissolved it in 10 ml of DMF solution and stirred evenly to form solution A;

[0074] (4) The Fe x P / FF prepared in step (2) was immersed in solution A obtained in step (3) and left standing at room temperature for 5 h. After the reaction was completed, the electrocatalyst was taken out and air-dried for 12 h to obtain the NiO x |Fe x P / FF-4 precursor catalyst;

[0075] (5) Place NiO x | The NiFeP / FF-4 precursor catalyst is placed in a tubular furnace and, under a mixed atmosphere of NH 3 and Ar, where the flow rate of the NH 3 gas is 120 sccm, the gas flow ratio of NH 3 to Ar is 3:1, and it is heated to 450 °C at a heating rate of 5 °C / min and held at 450 °C for 1 h. After the reaction is cooled to room temperature, it is taken out to obtain the target product Ni 3 N|NiFeP / FF-4 self-supporting electrode.

[0076] Application Example 1

[0077] The self-supporting electrodes obtained in Example 1 and Comparative Example 1 are used as catalysts for the industrial electrolytic water oxygen evolution reaction (OER), and the activity of the catalysts is evaluated.

[0078] Electrochemical performance tests are carried out under room temperature conditions using a three-electrode system. The specific implementation steps are as follows: Cut the self-supporting oxygen evolution electrode (Ni 3 N|NiFeP / FF 0.5*0.5 cm 2 ) obtained in Example 1. This is used as the working electrode, a carbon rod as the counter electrode, and a self-made reversible hydrogen electrode as the reference electrode. First, the electrocatalyst is scanned 50 cycles from an initial potential of 1 V to 2 V (relative to the reversible hydrogen electrode) at a scan rate of 50 mV / s in an oxygen-saturated 1 M KOH solution to activate the catalyst. Subsequently, in an oxygen-saturated 1 M KOH solution, it is scanned from 1 - 1.9 V at a speed of 10 mV / s to obtain the linear sweep voltammogram of the self-supporting heterojunction electrode (Ni 3 N|NiFeP / FF). The linear voltammogram of the catalyst obtained in Example 1 corresponds to Figure 4 the dashed line in the figure.

[0079] Application Example 2

[0080] The self-supporting electrodes obtained in Example 1 and Comparative Example 2 are used as catalysts for the industrial electrolytic water oxygen evolution reaction (OER), and the activity of the catalysts is evaluated.

[0081] Electrochemical performance tests are carried out under room temperature conditions using a three-electrode system. The specific implementation steps are as follows: Cut the self-supporting oxygen evolution electrode (Ni 3 N|NiFeP / FF 0.5*0.5 cm 2)。Using this as the working electrode, a carbon rod as the counter electrode, and a self-made reversible hydrogen electrode as the reference electrode. First, the electrocatalyst was scanned 50 cycles from an initial potential of 1 V to 2 V (relative to the reversible hydrogen electrode) at a scan rate of 50 mV / s in an oxygen-saturated 1 M KOH solution to activate the catalyst. Subsequently, in an oxygen-saturated 1 M KOH solution, it was scanned from 1 - 1.9 V at a rate of 10 mV / s to obtain the linear sweep voltammetry curve of the self-supported heterojunction electrode (Ni 3 N|NiFeP / FF). The linear voltammetry curve of the catalyst obtained in Example 1 corresponds to Figure 5 the dashed line in

[0082] Application Example 3

[0083] The self-supported electrodes obtained in Example 1 and Comparative Example 1 were used as catalysts for the industrial alkaline water electrolysis oxygen evolution reaction (OER), and the activity of the catalysts was evaluated.

[0084] The three-electrode system was used to conduct electrochemical performance tests at room temperature. The specific implementation steps were as follows: Cut the self-supported oxygen evolution electrode (Ni 3 N|NiFeP / FF 0.5*0.5 cm 2 ) obtained in Example 1. Using this as the working electrode, a carbon rod as the counter electrode, and a self-made reversible hydrogen electrode as the reference electrode. First, the electrocatalyst was scanned 50 cycles from an initial potential of 1 V to 2 V (relative to the reversible hydrogen electrode) at a scan rate of 50 mV / s in an oxygen-saturated 30 wt% KOH solution to activate the catalyst. Subsequently, in an oxygen-saturated 30 wt% KOH solution, it was scanned from 1 - 1.9 V at a rate of 10 mV / s to obtain the linear sweep voltammetry curve of the self-supported heterojunction electrode (Ni 3 N|NiFeP / FF). The linear voltammetry curve of the catalyst obtained in Example 1 corresponds to Figure 6 the dashed line in. And it stably worked for 120 h at a current density of 800 mA cm -2 . The chronoamperometry curve of the catalyst obtained in Example 1 is as shown in Figure 7 .

[0085] Result Analysis

[0086] For the self-supported heterojunction electrodes prepared in the above examples, their morphologies and electrochemical properties were mainly characterized by scanning electron microscopy and electrochemical tests under a three-electrode system respectively.

[0087] From Figure 1 (a) and (b) in, it can be seen that in the precursor (Fe x P / FF) prepared in Example 1 of the present invention, dendritic Fe x P fills the pores of the iron foam, providing a growth platform for the growth of subsequent nickel-based particles.

[0088] From Figure 2 (a) and (b), it can be seen that in the heterostructure self-supporting oxygen evolution electrode (Ni 3 N|NiFeP / FF) prepared in Example 1 of the present invention, the nickel-based particles are closely connected to the Fe x P flakes and uniformly grow on the surface of the iron foam.

[0089] From Figure 3 it can be seen that the heterostructure self-supporting oxygen evolution electrode (Ni 3 N|NiFeP / FF) prepared in Example 1 of the present invention has two microscopic morphologies: the flaky structure of the bimetallic phosphide and the nickel-based granular shape. This hybrid heterostructure provides a rich heterointerface for excellent electrochemical performance and ultimately effectively improves the electrochemical activity of the electrode.

[0090] From Figure 4 (a) and (b), it can be seen that in the Ni 3 N|NiFeP / FF-4 prepared in Comparative Example 2 of the present invention, the nickel-based particles are sparser and more dispersed compared to Figure 2 those, so the electrochemical performance shown is slightly weaker.

[0091] From Figure 5 it can be seen that in the alkaline electrolyte (1M KOH), the heterostructure self-supporting oxygen evolution electrode (Ni 3 N|NiFeP / FF) prepared in Example 1 of the present invention can reach 500 mA / cm 2 at a lower potential, indicating that the prepared self-supporting heterojunction electrode has high electrochemical oxygen evolution activity in the industrial electrolyzed water system.

[0092] From Figure 6 it can be seen that in the alkaline electrolyte (1M KOH), when the heterostructure self-supporting oxygen evolution electrode (Ni 3 N|NiFeP / FF) prepared in Example 1 of the present invention is at 100 mA / cm 2 , the corresponding reversible hydrogen electrode potential is less than that of Comparative Example 2, indicating that the concentration of metal nitrate should not be too low during the preparation process.

[0093] From Figure 7 it can be seen that in the industrial alkaline electrolyte (30 wt% KOH), when the heterostructure self-supporting oxygen evolution electrode (Ni 3 N|NiFeP / FF) prepared in Example 1 of the present invention is at 500 mA / cm 2 , the corresponding reversible hydrogen electrode potential is less than that of Comparative Example 1, indicating that the prepared self-supporting heterojunction electrode has high electrochemical oxygen evolution activity in the industrial electrolyzed water system.

[0094] From Figure 8 It can be seen that in an industrial alkaline electrolyte (30 wt% KOH), the heterostructure self-supporting oxygen evolution electrode (Ni 3 N|NiFeP / FF) prepared in Example 1 of the present invention can stably operate for 120 h at 800 mA / cm 2 and has high electrochemical stability at high current densities.

[0095] It is easy for those skilled in the art to understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a heterostructure self-supporting electrode, characterized in that, it comprises the following steps: (1) Perform low-temperature phosphating treatment on the foam metal to obtain a precursor. The foam metal is a transition metal, and the temperature of the low-temperature phosphating treatment is 300 - 400 °C; the phosphorus source material is sodium hypophosphite; the foam metal is foam iron; (2) Immerse the precursor in an organic solvent dissolved with metal nitrate, and after standing, obtain a composite of metal oxide and precursor; the metal oxide is formed in-situ on the precursor, and the metal in the metal nitrate is a transition metal; the concentration of the metal nitrate solution is 0.6 - 1 g / mL; (3) Perform nitridation treatment on the composite to obtain a heterostructure self-supporting electrode of metal nitride and phosphide.

2. The preparation method according to claim 1, characterized in that, the metal nitrate is cobalt nitrate, nickel nitrate or iron nitrate; the organic solvent is N,N-dimethylformamide.

3. The preparation method according to claim 1, characterized in that, the low-temperature phosphating treatment is to place the phosphorus source material and the foam metal at the upstream and downstream of a quartz boat respectively, and perform low-temperature phosphating in a tube furnace. The tube furnace is heated to 300 - 400 °C at a heating rate of 1 - 5 °C / min.

4. The preparation method according to claim 1, characterized in that, the atmosphere of the nitridation treatment is a mixed atmosphere of ammonia and argon, and it is heated to 400 - 500 °C at a heating rate of 1 - 5 °C / min; the nitridation treatment time is 1 - 2 h.

5. The preparation method according to claim 3, characterized in that, the phosphating time of the low-temperature phosphating treatment is 1 - 3 h.

6. The preparation method according to claim 1, characterized in that, the standing time in step (2) is 5 - 8 h.

7. The preparation method according to claim 1 or 2, characterized in that, before performing the low-temperature phosphating treatment, perform pretreatment on the foam metal. The pretreatment is to sequentially immerse the foam metal in hydrochloric acid solution, absolute ethanol and deionized water for ultrasonic cleaning, and then perform drying treatment.

8. A heterostructure self-supporting electrode prepared by the preparation method according to any one of claims 1 - 7.

9. The heterostructure self-supporting electrode according to claim 8, characterized in that, it comprises a foam metal, dendritic metal phosphide grown in-situ on the foam metal, and granular metal nitride grown in-situ on the metal phosphide.

10. An application of the heterostructure self-supporting electrode according to claim 8 or 9, characterized in that, it is used as an oxygen evolution electrode for water electrolysis to produce hydrogen.

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