Iron-based self-supporting electrocatalyst as well as preparation method and application thereof

Abstract

The invention discloses an iron-based self-supporting electrocatalyst as well as a preparation method and application thereof, and belongs to the technical field of small molecule oxidation. The preparation method comprises the following steps: firstly, preparing a FeOOH / NF cross-linked nanosheet array by taking foamed nickel as a substrate, then preparing a Fe4N / NF nanoparticle array by virtue of a calcination method, and finally, preparing the Act-Fe4N / NF self-supporting electrocatalyst with catalytic activity by virtue of electrochemical activation. It is guaranteed that the electrocatalyst still has excellent oxygen evolution performance and micromolecule oxidation performance even under the condition of high current density (500 mA cm <-2 >), and improvement of oxygen evolution reaction and micromolecule oxidation performance is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of small molecule oxidation, and in particular to an iron-based self-supporting electrocatalyst, a preparation method thereof and an application thereof. Background Art

[0002] Small molecule oxidation reactions (such as ethanol, urea and water molecule oxidation) are core technologies for clean energy conversion, high-value chemical synthesis and environmental pollutant degradation. However, the oxidation paths and catalytic mechanisms of different small molecule systems are significantly different, and it is difficult for existing technologies to simultaneously meet the industrialization requirements of high efficiency, stability, low cost and environmental friendliness.

[0003] Energy, as the basis for human survival and development, is of crucial significance for promoting the economic and social development. In recent years, the world's energy use structure has been mainly based on three traditional energy sources: petroleum, coal and natural gas. The excessive consumption of traditional fossil fuels has caused a sharp decline in the reserves of traditional energy sources. The development of new energy and the promotion of clean and low-carbon energy development are imminent. New renewable energy sources are rich in resources and can be continuously utilized by people. Solar energy, wind energy, tidal energy and geothermal energy are considered to be very potential green energy sources. However, due to their low conversion efficiency, there is still a large room for open utilization. Hydrogen energy is an ideal renewable clean energy, with advantages such as high energy, rich resources and zero pollution, and is considered to be an ideal green energy carrier.

[0004] Developing efficient electrocatalysts for oxygen evolution reaction (OER) and urea oxidation reaction (UOR) is of great significance for hydrogen production. The thermodynamic potential required for UOR is only 0.37V lower than the thermodynamic potential (1.23V) required for OER, thus reducing the energy consumption by 70%. In addition to the minimum energy consumption in the hydrogen production process, UOR electrolysis also provides an opportunity for the purification of urea-rich wastewater, demonstrating great potential for practical applications. In order to further improve the efficiency of water splitting, replacing the OER reaction on the anode with ethanol oxidation reaction (EOR) is an effective strategy, because it reduces the oxidation potential of hydrogen production and accelerates the reaction kinetics. In addition, ethanol is a biomass fuel with high energy density, low cost and low toxicity, and has the potential for sustainable large-scale application. However, the oxygen evolution reaction (OER) at the anode of electrolyzed water involves a multi-electron transfer and multi-step reaction process, resulting in slow reaction kinetics. Although noble metal Ru / Ir oxides can reduce the OER overpotential, considering their reserves and costs, finding low-cost and high-catalytic-activity OER catalytic materials is of great research significance for promoting the sustainable development of electrolyzed water hydrogen production. Summary of the Invention

[0005] The object of the present invention is to provide an iron-based self-supported electrocatalyst, a preparation method and an application thereof. The iron-based self-supported electrocatalyst is prepared by a hydrothermal method and a calcination method. The preparation process is simple, fast and low in cost; and the prepared catalyst has a large number of active sites and high catalytic activity and good stability for water / ethanol / urea oxidation under alkaline conditions.

[0006] To achieve the above object, the present invention provides a preparation method of an iron-based self-supported electrocatalyst, comprising the following steps:

[0007] (1) Ultrasonically clean nickel foam, and obtain pretreated nickel foam after drying;

[0008] (2) Put the pretreated nickel foam into deionized water containing an iron source and a reducing agent, transfer it to a polytetrafluoroethylene autoclave for a water bath heating reaction, and obtain iron oxyhydroxide supported on nickel foam;

[0009] (3) Place the precursor iron oxyhydroxide in the middle of a tubular furnace, evacuate and then introduce a nitrogen source atmosphere, and calcine to obtain iron nitride supported on nickel foam;

[0010] (4) Electrochemically activate the iron nitride for 4-6 h to obtain the target product supported on nickel foam.

[0011] Preferably, in step (1), nickel foam is ultrasonically treated and cleaned successively with 1 M dilute hydrochloric acid, absolute ethanol and deionized water, and the drying time is 12 hours.

[0012] Preferably, in step (2), the molar ratio of the iron source to the reducing agent is 1:18; wherein, the iron source is a ferric salt, and the reducing agent is one or more of urea, ammonium fluoride, and ammonium chloride.

[0013] Preferably, in step (2), the temperature of the water bath heating is 100-140 °C, and the time of the water bath heating is 10-14 h.

[0014] Preferably, in step (3), the nitrogen source is one of a mixture of ammonia and argon, a mixture of ammonia and nitrogen, ammonia water, and diethylenediamine.

[0015] Preferably, in step (3), the calcination temperature is 300-500 °C; the calcination time is 30 min-1 h.

[0016] The present invention also provides an iron-based self-supported electrocatalyst prepared by the above preparation method.

[0017] The present invention also provides an application of the above iron-based self-supported electrocatalyst in a small molecule oxidation reaction.

[0018] Preferably, the small molecule oxidation reaction is one of electrolysis of water, ethanol oxidation, and urea oxidation.

[0019] Preferably, when the iron-based self-supported electrocatalyst is used as the anode for water electrolysis, ethanol oxidation, and urea oxidation, it has overpotentials of 288 mV, 185 mV, and 296 mV at a current density of 500 mA cm -2 .

[0020] The catalyst provided by the present invention is an iron-based self-supported electrocatalyst loaded on the conductive substrate nickel foam. The synthesis method is novel, the raw materials are cheap and easy to obtain, the conditions are simple and easy to operate, and it is fast and efficient.

[0021] In the present invention, nickel foam is used as the substrate, enabling the electrocatalyst to have the inherent structural advantages of a self-supported electrocatalyst (the self-supported structure avoids the use of polymer binders, reduces the contact internal resistance between the active material and the conductive substrate, and realizes the rapid desorption of gas). Moreover, the meso-nano filamentous structure endows the catalyst with a larger specific surface area, which can increase the contact area between the electrode and the electrolyte, expose more active sites, improve electron conductivity, and significantly enhance the catalytic activity and stability of the catalyst, facilitating rapid charge and mass transfer and excellent reaction kinetics; the metal nitride formed by nitridation can achieve the synergistic effect between metal ions and non-metal oxygen anions, enhancing the intrinsic activity of the catalyst, thus ensuring that the electrocatalyst still has excellent oxidation performance even under high current density conditions (500 mA cm -2 ), which is beneficial to the improvement of the oxidation performance of small molecules.

[0022] The technical solution of the present invention will be further described in detail below through the drawings and examples. Description of the Drawings

[0023] Figure 1 SEM image of the FeOOH / NF electrocatalyst prepared in Example 1

[0024] Figure 2 SEM image of the Fe4N / NF electrocatalyst formed after calcination in Example 1

[0025] Figure 3 SEM image of the Act-Fe4N / NF electrocatalyst formed after activation in Example 1

[0026] Figure 4 TEM image of the Act-Fe4N / NF electrocatalyst prepared in Example 1

[0027] Figure 5 Element mapping image of the Act-Fe4N / NF electrocatalyst prepared in Example 1

[0028] Figure 6Polarization curves of the materials obtained in Example 1 of the present invention (FeOOH / NF, Fe4N / NF, and Act-Fe4N / NF) for oxygen evolution reaction (OER) in 1.0 M KOH solution.

[0029] Figure 7 Polarization curves of the materials obtained in Example 1 of the present invention (FeOOH / NF, Fe4N / NF, and Act-Fe4N / NF) for ethanol oxidation reaction (EOR) in 1.0 M KOH + 1.0 M ethanol solution.

[0030] Figure 8 Polarization curves of the materials obtained in Example 1 of the present invention (FeOOH / NF, Fe4N / NF, and Act-Fe4N / NF) for urea oxidation reaction (UOR) of ethanol in 1.0 M KOH + 0.33 M urea solution. Detailed implementation manners

[0031] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and examples. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent substitution methods and shall be included in the protection scope of the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application and belong to the protection scope of the present invention.

[0032] Referring to "embodiment" herein means that the specific features, structures, or characteristics described in connection with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various positions in the specification does not necessarily refer to the same embodiment, nor is it particularly limited to the independence or relevance with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0033] Unless otherwise defined, the meanings of the technical terms used herein are the same as those commonly understood by those skilled in the technical field to which the present application belongs; the use of the relevant terms herein is only for describing specific embodiments and is not intended to limit the present application.

[0034] Unless otherwise specified in the present invention, the materials, reagents, instruments, equipment, and performance testing methods used are all the materials, reagents, instruments, equipment, and methods commonly used by those skilled in the art.

[0035] Example 1

[0036] This embodiment provides a preparation method of an iron-based self-supporting electrocatalyst, comprising the following steps:

[0037] (1) Place nickel foam (NF) (1 cm × 2 cm) in 1 M HCl, anhydrous ethanol, and deionized water in sequence, and ultrasonically clean each for 15 min, then dry at 60 °C for 12 h for standby.

[0038] (2) Weigh 1.0 mmol of Fe(NO3)3·9H2O, 10.0 mmol of urea, and 8.0 mmol of ammonium fluoride, dissolve them in 40 mL of deionized water, stir well for 30 min to form a homogeneous solution. Put the treated NF into this solution, transfer it to a 100 mL polytetrafluoroethylene autoclave, and keep the reaction at 120 °C for 12 h. After the autoclave cools down, rinse the nickel foam with deionized water and ethanol several times, and then vacuum dry at 60 °C for 12 h to obtain a pure precursor FeOOH / NF.

[0039] (3) Place the above precursor FeOOH / NF in a tubular furnace. After assembly, purge with argon for 30 min to exhaust the air in the tubular furnace, and then calcine at 500 °C for 1 h under a mixed atmosphere of ammonia and argon to prepare the Fe4N / NF material.

[0040] (4) Electrochemically activate the calcined material Fe4N / NF for 4 h to obtain the final product Act-Fe4N / NF electrocatalyst.

[0041] Example 2

[0042] The difference between this example and Example 1 is only that: in step (2), ammonium fluoride as the reducing agent is replaced by ammonium chloride, and the rest are the same as in Example 1, so they will not be repeated here.

[0043] Example 3

[0044] The difference between this example and Example 1 is only that: in step (3), the nitrogen source is ammonia water, and the rest are the same as in Example 1, so they will not be repeated here.

[0045] Example 4

[0046] The difference between this example and Example 1 is only that: in step (3), the nitrogen source is diethylenediamine, and the rest are the same as in Example 1, so they will not be repeated here.

[0047] Example 5

[0048] The difference between this example and Example 1 is only that: in step (4), the activation time is 6 h, and the rest are the same as in Example 1, so they will not be repeated here.

[0049] Characterization and testing

[0050] The intermediate product electrocatalyst and the target product iron-based self-supported electrocatalyst prepared in Example 1 were respectively subjected to scanning electron microscopy, transmission electron microscopy and elemental mapping tests, and the results are as Figures 1 to 5 shown.

[0051] It can be seen from Figure 1 that the FeOOH / NF electrocatalyst prepared by the hydrothermal method is composed of cross-linked nanosheets; it can be seen from Figure 2 that after calcination, the FeOOH / NF electrocatalyst is successfully transformed into the Fe4N / NF electrocatalyst, and the morphology is changed from cross-linked nanosheets to nanometer particles; it can be seen from Figure 3 that the morphology of the prepared Act-Fe4N / NF electrocatalyst is significantly different from that of the Fe4N / NF electrocatalyst, mainly composed of nanosheets and nanowires. The internal nanosheets provide a growth site for the outer nanowires, and many nanowire arrays grow on the nanosheets. The nanowire array structure not only endows the electrode material with a larger specific surface area, which is beneficial to exposing more active sites, but also the rich open space in the array can ensure that the electrolyte easily penetrates onto the electrode, shortening the ion diffusion length and accelerating the reaction process. Figure 4 Figure 12 is a TEM image of the Act-Fe4N / NF electrocatalyst. The microstructure of the Act-Fe4N / NF electrocatalyst was analyzed, further confirming that the Act-Fe4N / NF electrocatalyst is composed of a structure of nanosheets and nanowires.

[0052] Figure 5 Figure 17 is an EDS spectrum of the corresponding elements in the target product electrocatalyst prepared in Example 1. The elemental distribution in the electrocatalyst can be clearly observed from Figure 5 . The Fe element is evenly distributed in the prepared electrocatalyst. It can be seen that the introduction of the nitrogen element not only inhibits the segregation of the iron element, but also the synergistic effect between the two is beneficial to improving the intrinsic activity of the catalyst, thereby improving its catalytic reaction. The above tests show that the iron-based self-supported Act-Fe4N / NF electrocatalyst was successfully prepared in the present invention.

[0053] Test Example 1

[0054] The electrocatalytic performance test was carried out using a CHI 760E electrochemical workstation produced by Shanghai Chenhua Co., Ltd. The oxygen evolution performance of the catalyst was tested using a three-electrode system. The working electrode was the Act-Fe4N / NF electrode prepared in Example 1, the counter electrode was a graphite electrode, and the reference electrode was a Hg / HgO electrode. The electrolyte was 1 M KOH.

[0055] The target product Act-Fe4N / NF electrocatalyst, the intermediate product FeOOH / NF electrocatalyst, and the Fe4N / NF electrocatalyst prepared in Example 1 were subjected to linear sweep voltammetry for OER under alkaline conditions in a voltage range of 0.2 - 0.8 V at a scan rate of 2 - 5 mV s -1 , with a standing time of 1 - 10 s. The linear sweep voltammograms obtained are as shown in Figure 6 . It can be seen from Figure 6 that the target product iron-based self-supported electrocatalyst of the present invention exhibits excellent OER catalytic activity under alkaline conditions. At a current density of 500 mA cm -2 , the overpotential is 288 mV, which is better than that of FeOOH / NF and Fe4N / NF.

[0056] Test Example 2

[0057] The electrocatalytic performance was tested using a CHI 760E electrochemical workstation produced by Shanghai Chenhua Co., Ltd. The electrocatalytic ethanol oxidation performance of the catalyst was tested using a three-electrode system. The working electrode was the Act-Fe4N / NF electrode prepared in Example 1, the counter electrode was a graphite electrode, and the reference electrode was a Hg / HgO electrode. The electrolyte was 1 M KOH + 1 M ethanol.

[0058] The target product Act-Fe4N / NF electrocatalyst, the intermediate product FeOOH / NF electrocatalyst, and the Fe4N / NF electrocatalyst prepared in Example 1 were subjected to linear sweep voltammetry for EOR under alkaline conditions in a voltage range of 0.2 - 0.8 V at a scan rate of 2 - 5 mV s -1 , with a standing time of 1 - 10 s. The linear sweep voltammograms obtained are as shown in Figure 7 . It can be seen from Figure 7 that the target product iron-based self-supported electrocatalyst of the present invention exhibits excellent EOR catalytic activity under alkaline conditions. At a current density of 500 mA cm -2 , the overpotential is 185 mV, which is better than that of FeOOH / NF and Fe4N / NF.

[0059] Test Example 3

[0060] The electrocatalytic performance was tested using a CHI 760E electrochemical workstation produced by Shanghai Chenhua Co., Ltd. The electrocatalytic ethanol oxidation performance of the catalyst was tested using a three-electrode system. The working electrode was the Act-Fe4N / NF electrode prepared in Example 1, the counter electrode was a graphite electrode, and the reference electrode was a Hg / HgO electrode. The electrolyte was 1 M KOH + 0.33 M urea.

[0061] The target product Act-Fe4N / NF electrocatalyst prepared in Example 1, the intermediate product FeOOH / NF electrocatalyst, and the Fe4N / NF electrocatalyst were subjected to linear sweep voltammetry for UOR under alkaline conditions. The voltage range was 0.2 - 0.8 V, and the scan rate was 2 - 5 mV s -1 , with a standing time of 1 - 10 s. The measured linear sweep voltammetry curves are as Figure 8 shown. As Figure 8 can be seen, the target product iron-based self-supporting electrocatalyst of the present invention exhibits excellent EOR catalytic activity under alkaline conditions. At a current density of 500 mA cm -2 , the overpotential was 296 mV, which was superior to FeOOH / NF and Fe4N / NF.

[0062] From the above examples and test examples, it can be seen that the target product iron-based self-supporting electrocatalyst Act-Fe4N / NF prepared by the present invention shows excellent catalytic activity for small molecule oxidation, mainly due to the following points: (1) Growing the active material on the nickel foam substrate not only avoids the use of polymer binders, reduces the contact internal resistance between the active material and the conductive substrate, and realizes the rapid desorption of gas; but also increases the contact area between the electrode and the electrolyte and improves the electron conductivity; (2) Growing the nanowire-like structure on the nanosheets not only gives the electrocatalyst a larger specific surface area, which is beneficial to exposing more active sites, but also the rich open space in the array can ensure that the electrolyte easily penetrates onto the electrode, shortening the ion diffusion length and accelerating the reaction process; (3) The synergistic effect between Fe and N elements can enhance the intrinsic activity of the catalyst, inhibit the segregation of Fe elements, and further improve the reaction efficiency of small molecule oxidation.

[0063] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of an iron-based self-supported electrocatalyst, characterized in that, It includes the following steps: (1) Ultrasonically clean nickel foam, and obtain pretreated nickel foam after drying; (2) Put the pretreated nickel foam into deionized water containing an iron source and a reducing agent, transfer it to a polytetrafluoroethylene autoclave for water bath heating reaction, and obtain iron oxyhydroxide loaded on the nickel foam; (3) Place the precursor iron oxyhydroxide in the middle of a tubular furnace, evacuate and then introduce a nitrogen source atmosphere, and calcine to obtain iron nitride loaded on the nickel foam; (4) Electrochemically activate the iron nitride for 4 - 6 h to obtain the target product loaded on the nickel foam.

2. The preparation method of an iron-based self-supporting electrocatalyst according to claim 1, wherein: In step (1), nickel foam is ultrasonically treated and cleaned successively with 1 M dilute hydrochloric acid, absolute ethanol and deionized water, and the drying time is 12 hours.

3. The preparation method of an iron-based self-supported electrocatalyst according to claim 1, wherein: In step (2), the molar ratio of the iron source to the reducing agent is 1:18; wherein, the iron source is a ferric salt, and the reducing agent is one or more of urea, ammonium fluoride, and ammonium chloride.

4. The preparation method of an iron-based self-supported electrocatalyst according to claim 1, wherein: In step (2), the temperature of the water bath heating is 100 - 140 °C, and the time of the water bath heating is 10 - 14 h.

5. The preparation method of an iron-based self-supported electrocatalyst according to claim 1, wherein: In step (3), the nitrogen source is one of a mixture of ammonia and argon, a mixture of ammonia and nitrogen, ammonia water, and diethylenediamine.

6. The preparation method of an iron-based self-supported electrocatalyst according to claim 1, characterized in that: In step (3), the calcination temperature is 300 - 500 °C; the calcination time is 30 min - 1 h.

7. An iron-based self-supported electrocatalyst, characterized in that: The iron-based self-supporting electrocatalyst is prepared by the preparation method described in any one of claims 1 - 6.

8. The application of an iron-based self-supported electrocatalyst according to claim 7, characterized in that: The iron-based self-supporting electrocatalyst is applied to small molecule oxidation reactions.

9. Use of an iron-based self-supported electrocatalyst according to claim 8, characterized in that: The small molecule oxidation reaction is one of electrolysis of water, ethanol oxidation, and urea oxidation.

10. The application of an iron-based self-supporting electrocatalyst according to claim 9, wherein: When the iron-based self-supported electrocatalyst is used as the anode for water electrolysis, ethanol oxidation, and urea oxidation, it has overpotentials of 288 mV, 185 mV, and 296 mV at a current density of 500 mA cm -2 .

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