Preparation method of high-entropy feconicu s homojunction electrocatalyst, and preparation method and application thereof

Abstract

The application relates to the technical field of electrocatalysts, in particular to a preparation method of a high-entropy FeCoNiCuS homojunction electrocatalyst, a preparation method thereof and application, which comprises the following steps: through a simple one-step hydrothermal method, a mixed solution containing nickel nitrate, iron nitrate, cobalt nitrate, copper nitrate and sodium thiosulfate is placed in a reaction kettle together with foamed nickel, and a high-entropy FeCoNiCuS homojunction electrocatalyst is obtained through co-heating. The electrochemical performance measurement shows that the prepared catalyst has good catalytic activity and stability in terms of oxygen evolution and overall water splitting under high current density. The method has the advantages of simple preparation process, environmental friendliness, convenient operation, low cost and certain actual production prospect.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrocatalysts, in particular to a preparation method of a high-entropy FeCoNiCuS homojunction electrocatalyst and the preparation method and application thereof. BACKGROUND

[0002] Hydrogen (H2) is one of the ideal substitutes for future fossil fuels, which has attracted extensive attention of researchers due to its high heat value and environmental friendliness. Compared with other hydrogen production technologies, water electrolysis is considered as one of the promising methods due to its clean and efficient advantages. However, due to its high overpotential and slow reaction kinetics, a catalyst is needed to improve the situation. At present, Pt / C catalyst for hydrogen evolution reaction (HER) and IrO2 or RuO2 for oxygen evolution reaction (OER) are considered as the best catalysts. However, due to its scarcity and high cost, its large-scale practical production application is limited. Therefore, it is of great significance to develop an electrocatalyst with low raw material price and wide source.

[0003] Transition metal sulfides (TMS) have attracted extensive attention of researchers due to their moderate electronic band gap, band position and highly exposed active sites. More importantly, the larger specific surface area and H adsorption active sites of TMS and strong stability help to achieve significant overall water splitting (OWS) performance. Although TMS M x S y is considered as a good electrocatalyst, it has poor thermodynamic stability and is easy to separate from the substrate under highly oxidizing electrochemical conditions. At the same time, M x S y composed of single or binary metals lacks wide composition controllability. Therefore, it is necessary to improve the traditional TMS and improve its catalytic ability. In recent years, high-entropy materials (HEM) have attracted extensive attention in the field of electrocatalysis due to their slow diffusion effect, high-entropy effect and other characteristics. Due to the random distribution of multiple components of its elements, it tends to induce more defects and vacancies on the catalyst, so compared with single-unit catalysts, HEM catalysts expose more catalytically active centers, which promote more efficient water splitting. Specifically, due to the stabilizing effect of multiple elements, high-entropy sulfides usually exhibit enhanced structural stability due to the high-entropy effect. Benefiting from the above characteristics, high-entropy materials show wide potential in hydrogen evolution reaction, oxygen evolution reaction and overall water splitting.

[0004] Based on the above reasons, how to find a non-precious metal-based and simple preparation process, raw material source easy to get high stability, high conductivity, rich electric catalytic activity site of sulfur element doped high entropy compound electric catalytic agent, is the main problem to be solved by the present application. SUMMARY

[0005] The purpose of the present application is to solve the problems existing in the prior art, and a preparation method of high-entropy FeCoNiCuS homojunction electrocatalyst and its preparation method and application are proposed. The method is prepared by a simple one-step hydrothermal method. The high-entropy FeCoNiCuS homojunction electrocatalyst prepared by the present application shows good catalytic activity and stability in oxygen evolution and overall water splitting, and has potential commercial application value.

[0006] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0007] A high-entropy FeCoNiCuS homojunction electrocatalyst, wherein the FeCoNiCuS is loaded on a nickel foam in the form of a homojunction high-entropy compound to form a high-entropy FeCoNiCuS homojunction electrocatalyst.

[0008] A preparation method of a high-entropy FeCoNiCuS homojunction electrocatalyst, comprising the following steps:

[0009] Step 1, cutting a nickel foam substrate, soaking the cut nickel foam in an HCl solution for a certain time to remove the surface oxides of the nickel foam, and then rinsing the soaked nickel foam clean; finally, drying the nickel foam to obtain a pretreated nickel foam;

[0010] Step 2, mixing Na2S2O3, Ni(NO3)2, Fe(NO3)3, Co(NO3)2, Cu(NO3)2 and H2O, continuously stirring to completely dissolve them, obtaining a mixed liquid, transferring the mixed liquid and the pretreated nickel foam into a Teflon-lined stainless steel autoclave, and hydrothermally reacting, washing and drying the final product to obtain a high-entropy FeCoNiCuS homojunction electrocatalyst loaded on the nickel foam.

[0011] Preferably, in step 1, the size of the cut nickel foam is 2.5-3.5 cm*1.5-2.5 cm, the concentration of the HCl solution for soaking is 2-6 M, the soaking time is 10-25 min, and the washing is alternating washing with anhydrous ethanol, acetone and ultrapure water for 6-8 times; the drying is vacuum drying, the drying temperature is 40-60 DEG C, and the drying time is 6-12 h.

[0012] Preferably, in step 2, the concentration of the solution is: 3-12 mmol Na2S2O3, 0.5-2 mmol Ni(NO3)2, 0.125-0.5 mmol Fe(NO3)3, 0.125-0.5 mmol Co(NO3)2, 0.125-0.5 mmol Cu(NO3)2; the prepared solution is continuously stirred at 500-1000 r / min for 30 min to make it fully dissolved.

[0013] Preferably, in step 2, the hydrothermal reaction is carried out at a temperature of 110-140 DEG C, and the reaction time is 4-6 hours; the washing is alternating washing with anhydrous ethanol, acetone and ultrapure water for 6-8 times; and the drying is vacuum drying at a drying temperature of 40-60 DEG C for 6-12 h.

[0014] The application further provides application of the high-entropy FeCoNiCuS homojunction electrocatalyst prepared by the preparation method to oxygen evolution reaction (OER) and electrocatalytic overall water splitting (OWS).

[0015] By adopting the technical scheme, the high-entropy FeCoNiCuS homojunction electrocatalyst in the application is in the form of irregular nanoparticles attached to the surface of the nickel foam, has a large specific surface area, and can provide more active sites; thanks to the slow diffusion effect of the high-entropy material and the more H adsorption active sites of the transition metal sulfide, the prepared material has good catalytic performance and catalytic stability in oxygen evolution and overall water splitting.

[0016] Compared with the prior art, the application has the following beneficial effects:

[0017] 1. The preparation process of the application is simple, safe and non-toxic, the raw materials are commercial materials, compatible with industrial alkaline electrolytic cell hydrogen production technology, and is expected to realize large-scale and practical application.

[0018] 2. The application avoids using poor-conductivity polymer adhesives such as Naflon and other mask active sites through a simple synthesis process, promotes charge transfer in the reaction process, and at the same time, the low crystallinity structure promotes the generation of coordination unsaturated sites and surface defects, generates more catalytically active centers, and improves water splitting performance.

[0019] 3. The application obtains, through experiments, that in a 1M KOH medium, for OER, only a low overpotential of 267 / 615 mV is required to achieve a current density of 100 / 500 mAcm -2 , and at about 50 mAcm -2 and 1750 mAcm -2showed long-term catalytic stability of about 200h / 190h at current density, which was comparable to the performance of commercial noble metal RuO2electrocatalyst. The assembled electrolytic cell of Pt / C||FeCoNiCuS only required a low battery voltage of 2.202V to drive 1Acm -2 to perform water splitting, and maintained long-term stability of about 210 hours at 2Acm -2 current density. Its better catalytic activity and stability not only are compatible with commercial alkaline electrolytic cells, but also are expected to realize industrialization and large-scale application of water electrolysis to produce hydrogen. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a transmission electron microscope image of the catalyst prepared in Example 1 of the present application;

[0021] Figure 2 is a powder X-ray diffraction pattern of the catalyst prepared in Example 1 of the present application;

[0022] Figure 3 is a high-resolution transmission electron microscope image of the catalyst prepared in Example 1 of the present application;

[0023] Figure 4 is a selected area electron diffraction pattern of the catalyst prepared in Example 1 of the present application;

[0024] Figure 5 is an energy dispersive spectroscopy pattern of the catalyst prepared in Example 1 of the present application;

[0025] Figure 6 is an LSV polarization curve of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 2 of the present application for electrocatalytic oxygen evolution in alkaline 1M KOH electrolyte;

[0026] Figure 7 is a Nyquist curve of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 2 of the present application for oxygen evolution;

[0027] Figure 8 is a graph of the stability test of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 2 of the present application for oxygen evolution at different constant voltages;

[0028] Figure 9 is a comparison graph of the LSV polarization curves of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 2 of the present application for electrocatalytic oxygen evolution in alkaline 1M KOH electrolyte before and after continuous 1000-cycle CV test;

[0029] Figure 10 is an activity curve of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 3 of the present application for electrocatalytic overall water splitting in alkaline 1M KOH electrolyte;

[0030] Figure 11 Figure 3 is a stability test diagram of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 3 of the present application for full water splitting at a constant voltage;

[0031] Figure 12 Figure 4 is a schematic diagram of the electrochemical full water splitting performance test of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 4 of the present application in an AEM;

[0032] Figure 13 Figure 5 is an activity curve diagram of the electrochemical full water splitting of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 4 of the present application in an AEM. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings, so that those skilled in the art can better understand the advantages and features of the present application, and the protection scope of the present application can be defined more clearly. The described embodiments of the present application are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0034] Reagents:

[0035] Ethanol, acetone, ferric nitrate, nickel nitrate hexahydrate, copper nitrate, cobalt nitrate hexahydrate and sodium thiosulfate pentahydrate were all purchased from Shanghai Mayrl Chemical Technology Co., Ltd.

[0036] The water used in the experimental process was deionized water.

[0037] Unless otherwise specified, other chemical reagents are analytical pure, do not need further purification and treatment, and can be used directly.

[0038] Example 1: Preparation of high-entropy FeCoNiCuS homojunction electrocatalyst

[0039] Cutting the foam nickel substrate with an area of about 30 mm long * 20 mm wide, soaking the cut foam nickel in 3M HCl solution for 20 minutes to remove oxides, and then washing it with anhydrous ethanol, acetone and ultrapure water alternately for 8 times. Finally, the foam nickel is dried in a 60-degree Celsius oven for 12 hours. A solution consisting of 6 mmol Na2S2O3, 1 mmol Ni(NO3)2, 0.25 mmol Fe(NO3)3, 0.25 mmol Co(NO3)2 and 0.25 mmol Cu(NO3)2 is prepared, and is completely dissolved by continuous stirring for 30 minutes to obtain a mixed liquid. The mixed liquid and the pretreated foam nickel are transferred to a Teflon-lined stainless steel autoclave, and reacted at 120°C for 4 hours. The final product is washed with anhydrous ethanol, acetone and ultrapure water alternately for 8 times, and then vacuum dried at 60°C for 12 hours to obtain a high-entropy FeCoNiCuS heterojunction electrocatalyst loaded on the foam nickel.

[0040] Example 2: Study on the electrochemical oxygen evolution performance of the high-entropy FeCoNiCuS heterojunction electrocatalyst

[0041] In order to accurately test the water electrolysis oxygen evolution activity of the high-entropy FeCoNiCuS heterojunction electrocatalyst, the present application adopts a Chenhua CHI 660E electrochemical workstation as an electrocatalytic performance testing instrument, and uses a standard three-electrode system to perform performance testing. In the three-electrode system, the high-entropy FeCoNiCuS heterojunction electrocatalyst loaded on the foam nickel prepared in Example 1 is used as a working electrode, a silver / silver chloride electrode is used as a reference electrode, a carbon rod is used as a counter electrode, and a 1M KOH solution is used as an electrolyte solution to study the electrochemical oxygen evolution performance of the material.

[0042] Example 3: Study on the electrochemical overall water splitting performance of the high-entropy FeCoNiCuS heterojunction electrocatalyst

[0043] The Chenhua CHI 660E electrochemical workstation is used as an electrocatalytic performance testing instrument, a 1M KOH solution is used as an electrolyte solution, the high-entropy FeCoNiCuS heterojunction electrocatalyst loaded on the foam nickel prepared in Example 1 is used as a positive electrode, and a foam nickel loaded with 20% Pt / C is used as a negative electrode to study the electrochemical overall water splitting performance of the material.

[0044] Example 4: Study on the electrochemical overall water splitting performance of the high-entropy FeCoNiCuS heterojunction electrocatalyst in MEA

[0045] The anion exchange membrane (MEA) assembly and testing schematic is as shown in Figure 12 The rest of the conditions are the same as those in Example 3 to study the electrochemical overall water splitting performance of the material.

[0046] Figure 1Transmission electron microscopy image of the catalyst prepared in Example 1 of the present invention. As shown in Figure 1 , the image shows the successful synthesis of high-entropy FeCoNiCuS homojunction electrocatalyst and has an irregular nanoparticle structure.

[0047] Figure 2 X-ray powder diffraction pattern of the catalyst prepared in Example 1 of the present invention. As shown in Figure 2 , the crystalline phase composition of the high-entropy FeCoNiCuS homojunction electrocatalyst is obtained according to the powder X-ray diffraction pattern, and the diffraction peak is consistent with COD ID:9007695, indicating the successful synthesis of the high-entropy FeCoNiCuS homojunction electrocatalyst.

[0048] Figure 3 High-resolution transmission electron microscopy image of the catalyst prepared in Example 1 of the present invention. As shown in Figure 3 , the HRTEM image further proves the existence of these phases, in which the 0.290 nm lattice fringes correspond to the (1-13) plane of FeCoNiCuS (COD ID:9007695).

[0049] Figure 4 Selected area electron diffraction pattern of the catalyst prepared in Example 1 of the present invention. As shown in Figure 4 , the diffraction rings in the SAED image correspond to the (0-12), (202), (1-13) and (004) planes of FeCoNiCuS (COD ID:9007695), respectively. Further proving the successful synthesis of the high-entropy FeCoNiCuS homojunction electrocatalyst.

[0050] Figure 5 Elemental energy dispersive spectroscopy image of the catalyst prepared in Example 1 of the present invention. As shown in Figure 5 , the EDS image shows that the elements of Ni, Fe, Co, Cu and S are uniformly distributed on the surface of the material.

[0051] Figure 6 Electrocatalytic oxygen evolution LSV polarization curve of the high-entropy FeCoNiCuS homojunction electrocatalyst prepared in Example 2 of the present invention in alkaline 1M KOH electrolyte. As shown in Figure 6 , the oxygen evolution LSV polarization curve shows that the prepared electrocatalyst only needs an overpotential of 615 mV to reach a current density of 1000 mAcm -2 .

[0052] Figure 7 Nyquist curve diagram of the high-entropy FeCoNiCuS homojunction electrocatalyst prepared in Example 2 of the present invention for oxygen evolution. As shown in Figure 7 , it shows that it has a small charge transfer resistance (1.20 ohm).

[0053] Figure 8 The figure is the oxygen evolution stability test diagram of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 2 of the present application under different constant voltages. As shown in the figure, the present application uses a constant potential test method to explore the long-term stability of the high-entropy FeCoNiCuS homojunction electrocatalyst under a fixed overpotential. The electrocatalyst shows almost no decay in the electrode for about 200 / 190 hours under low current density (50 mA cm -2 ) and high current density (1750 mA cm -2 ), which indicates that the prepared material still has excellent stability under long-term test conditions. Figure 8

[0054] Figure 9 The figure is the electrocatalytic oxygen evolution LSV polarization curve comparison diagram of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 2 of the present application before and after 1000 cycles of CV test in alkaline 1M KOH electrolyte. As shown in the figure, the LSV polarization curves before and after 1000 cycles of CV are almost coincident, indicating that the prepared electrocatalyst has good catalytic activity and stability. Figure 9

[0055] Figure 10 The figure is the electrocatalytic overall water splitting activity curve diagram of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 3 of the present application in alkaline 1M KOH electrolyte. As shown in the figure, the Pt / C||FeCoNiCuS system only needs a battery voltage of 2.022 V to drive a current density of 1000 mA cm -2 , which is superior to the commercial noble metal Pt / C||RuO2 system. Figure 10

[0056] Figure 11 The figure is the overall water splitting stability test diagram of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 3 of the present application under constant voltage. As shown in the figure, the Pt / C||FeCoNiCuS system has no obvious decay in current density within about 210 hours under a constant voltage of 2.1 V. This indicates that the prepared catalyst has excellent stability. Figure 11

[0057] Figure 12 The figure is the electrochemical overall water splitting performance test schematic diagram of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 4 of the present application in AEM. As shown in the figure, the test is carried out in the MEA device shown. Figure 12

[0058] Figure 13 The figure is the electrochemical overall water splitting activity curve diagram of the high-entropy FeCoNiCuS homojunction electrocatalyst in Example 4 of the present application in AEM. As shown in the figure, the test is carried out in the MEA device shown. Figure 13 ​​​​​As shown, only 1.501, 1.6 and 1.686 V battery voltage is required to achieve 100, 200 and 300 mAcm -2 Current density, respectively.

[0059] In summary, the high-entropy FeCoNiCuS homojunction electrocatalyst prepared by the simple one-step hydrothermal method has good catalytic activity and stability in oxygen evolution and overall water splitting, and has potential commercial application value.

[0060] The description and practice disclosed in the present application are easy to think and understand for ordinary skilled in the art, and some improvements and refinements can be made without departing from the principles of the present application. Therefore, the modifications or improvements made without departing from the spirit of the present application should be considered as the protection scope of the present application.

Claims

1. A method for preparing a high-entropy FeCoNiCuS homologous junction electrocatalyst, characterized in that, The FeCoNiCuS is loaded on the nickel foam in the form of a homologous high-entropy compound to form a high-entropy FeCoNiCuS homologous electrocatalyst; The preparation method comprises the following steps: Step 1, cutting a nickel foam substrate, soaking the cut nickel foam in an HCl solution for a certain period of time to remove the surface oxides of the nickel foam, and then rinsing the soaked nickel foam; finally, drying the nickel foam to obtain a pretreated nickel foam; Step 2, mixing Na2S2O3, Ni(NO3)2, Fe(NO3)3, Co(NO3)2 and Cu(NO3)2 with H2O, continuously stirring to completely dissolve them, obtaining a mixed liquid, and then transferring the mixed liquid and the pretreated nickel foam into a Teflon-lined stainless steel autoclave to perform a hydrothermal reaction, washing the final product and drying it to obtain a high-entropy FeCoNiCuS homologous electrocatalyst loaded on the nickel foam; In step 1, the size of the cut nickel foam is 2.5-3.5 cm*1.5-2.5 cm, the concentration of the HCl solution for soaking is 2-6 M, the soaking time is 10-25 min, and the washing is performed by alternately washing with anhydrous ethanol, acetone and ultrapure water for 6-8 times; the drying is vacuum drying, the drying temperature is 40-60 DEG C, and the drying time is 6-12 h; In step 2, the solution concentration is: 3-12 mmol Na2S2O3, 0.5-2 mmol Ni(NO3)2, 0.125-0.5 mmol Fe(NO3)3, 0.125-0.5 mmol Co(NO3)2, and 0.125-0.5 mmol Cu(NO3)2; the prepared solution is continuously stirred at 500-1000 r / min for 30 min to completely dissolve it; In step 2, the hydrothermal reaction is performed at a temperature of 110-140 DEG C for 4-6 hours, the washing is performed by alternately washing with anhydrous ethanol, acetone and ultrapure water for 6-8 times, and the drying is vacuum drying, the drying temperature is 40-60 DEG C, and the drying time is 6-12 h.

2. Application of a high-entropy FeCoNiCuS homologous electrocatalyst obtained by the preparation method of claim 1 in an oxygen evolution reaction and an electrocatalytic overall water splitting.

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