A cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology and a preparation method and application thereof

Abstract

The application provides a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology and a preparation method and application thereof. The preparation method comprises the following steps: dissolving cobalt nitrate and iron nitrate in a mixed solution of ethanol and N,N-dimethylformamide, adding polyvinylpyrrolidone, and fully mixing to obtain a mixed sol; then, electrospinning, drying and calcining are performed to obtain cobalt ferrite nanofibers; the cobalt ferrite nanofibers and sodium hypophosphite are respectively placed in a tube furnace, the cobalt ferrite nanofibers are placed on one side of the gas outlet of the protective gas in the tube furnace, and the sodium hypophosphite is placed on one side of the gas inlet of the protective gas in the tube furnace; and the cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology is obtained through calcining under the protective gas atmosphere. The preparation method is simple and low in price; the obtained catalyst material has high activity, fast electron transmission and small overpotential in an electrocatalytic oxygen evolution reaction, and has excellent electrocatalytic oxygen evolution performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology and a preparation method and application thereof, and belongs to the field of new energy materials and electrocatalytic oxygen evolution. BACKGROUND

[0002] Since the first industrial revolution in the 1660s, the consumption of coal, oil and natural gas has become increasingly serious, and is close to exhaustion. The use of fossil fuels has brought major changes to today's society, but at the same time has caused serious pollution of the earth's ecological environment. Therefore, the concept of sustainable development is now vigorously advocated, and the development of clean energy and the search for alternatives to traditional energy have become the urgent task and challenge for current researchers. Hydrogen energy has the characteristics of high energy density, cleanliness and high efficiency, and is considered as one of the potential alternatives to fossil fuels in the future.

[0003] Water electrolysis is currently the most ideal hydrogen production technology, because the raw material for water electrolysis is water, which is abundant, and only consumes electricity during the hydrogen production process without generating polluting gases, and the resulting hydrogen gas is of high purity and does not need further purification. Water electrolysis is composed of two half-reactions, cathode hydrogen evolution (HER) and anode oxygen evolution (OER). Under standard reaction conditions, theoretically only 1.23V of voltage is required for water electrolysis. However, due to the existence of certain contact resistance and intrinsic potential barrier during the reaction, and the solution resistance of the electrolyte, the actual voltage required for water electrolysis is often higher than the theoretical voltage. In order to reduce this part of the voltage higher than the theoretical voltage and achieve the purpose of energy saving, hydrogen and oxygen evolution catalysts need to be loaded on the cathode and anode respectively to accelerate the water electrolysis reaction. Compared with the two-electron process of HER, OER is a four-electron transfer process with a higher energy barrier and requires a higher overpotential to proceed. OER is the rate-limiting step of water electrolysis and seriously affects its development. Therefore, in order to vigorously develop electrocatalytic hydrogen production technology and reduce costs, high-efficiency and stable OER catalysts need to be developed first to improve the performance and efficiency of the anode OER of water electrolysis.

[0004] The efficiency of electrocatalytic water splitting is mainly affected by the electrocatalyst, so developing high-efficiency electrocatalysts is an effective measure to improve the efficiency of water electrolysis. Currently, noble metals, including their alloys, oxides, etc., have excellent OER performance and are the most popular research object among scientists. Among them, ruthenium (Ru) and iridium (Ir) based materials are considered to be the best OER catalysts. However, due to the problems of high cost and low reserves, they cannot be used on a large scale. Therefore, developing non-noble metal-based oxygen evolution electrocatalysts with low price, abundant reserves, high efficiency and stability is the main direction of current research.

[0005] Transition metal phosphides have attracted much attention due to their abundant active sites, adjustable component structures and excellent electrical conductivity, and are considered as a promising anode oxygen evolution catalyst to replace RuO2 and IrO2. At present, transition metal phosphides show excellent electrocatalytic performance among a large number of transition metal-based catalysts. Moreover, the synergistic effect of bimetallic or multi-metallic materials has been proved to be an effective means to improve the electrocatalytic activity of materials in many studies. For example, Chinese patent document CN111533106A discloses a cobalt-iron bimetallic olivine phase electrocatalyst and a preparation method and application thereof. The electrocatalyst comprises a lithium cobalt iron phosphate material; in the lithium cobalt iron phosphate material, the molar ratio of cobalt to iron is (3-4): 1. The electrocatalyst prepared by the invention is an olivine type material containing Co-Fe bimetallic; but the overpotential of the catalyst is 363 mV at a current density of 10 mA·cm -2 The lower overpotential is 363 mV, which is relatively large, and the electrocatalytic oxygen evolution performance is poor.

[0006] In summary, there is an urgent need to develop an electrocatalyst with simple preparation, low price, low overpotential, fast electron transport and excellent oxygen evolution performance for the field of electrocatalytic oxygen evolution. SUMMARY

[0007] In order to solve the defects of the prior art, the purpose of the present application is to provide a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology and a preparation method and application thereof, to solve the problems of low activity, large overpotential, poor electrocatalytic oxygen evolution performance and high cost of electrocatalyst materials in the prior art. The preparation method is simple, the price is low, and the obtained catalyst material has high activity, fast electron transport, small overpotential and excellent electrocatalytic oxygen evolution performance in the electrocatalytic oxygen evolution reaction.

[0008] The technical scheme of the present application is as follows:

[0009] A cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology, the micro-morphology of the electrocatalytic material is that the surface is loaded with nanoparticles of nanofibers.

[0010] According to the present application, the diameter of the nanofiber is preferably 150-200 nm, and the length is 4-10 pm.

[0011] The preparation method of the above-mentioned cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology comprises the following steps:

[0012] (1) Dissolve cobalt nitrate and iron nitrate in a mixed solution of ethanol and N,N-dimethylformamide, add polyvinylpyrrolidone (PVP), mix thoroughly, and obtain a mixed sol; then perform electrospinning, drying and calcination to obtain cobalt ferrite nanofibers;

[0013] (2) placing the cobalt ferrite nanofiber and sodium hypophosphite into a tube furnace respectively, placing the cobalt ferrite nanofiber on one side of the outlet of the protective gas in the tube furnace, and placing the sodium hypophosphite on one side of the inlet of the protective gas in the tube furnace; and obtaining the cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology through calcination under the protective gas atmosphere.

[0014] According to the application, preferably, in step (1), the molar ratio of the cobalt nitrate and the ferric nitrate is 1:2.

[0015] According to the application, preferably, in step (1), the volume ratio of the ethanol to the N,N-dimethylformamide in the mixed solution of the ethanol and the N,N-dimethylformamide is (3-5):1, preferably 4:1.

[0016] According to the application, preferably, in step (1), the volume ratio of the molar amount of the cobalt nitrate to the mixed solution is 0.01-0.1 mmol / L. -1 .

[0017] According to the application, preferably, in step (1), the mass ratio of the polyvinylpyrrolidone (PVP) to the cobalt nitrate is 1:(0.05-0.2).

[0018] According to the application, preferably, in step (1), the weight average molecular weight of the polyvinylpyrrolidone (PVP) is 1-1.5 million; most preferably, the weight average molecular weight of the polyvinylpyrrolidone is 1.3 million.

[0019] According to the application, preferably, in step (1), the electrospinning condition is that the temperature is room temperature, the voltage is 15-25 kV, the humidity is 20-30%, the receiving distance is 10-30 cm, and the advancing speed is 0.5-1.5 mL / h. -1 The receiving distance refers to the vertical distance from the electrospinning needle to the receiving device.

[0020] According to the application, preferably, in step (1), the drying temperature is 60-80℃, and the drying time is 8-12 h.

[0021] According to the application, preferably, in step (1), the calcination temperature is 400-600℃, the calcination time is 60-180 min, the temperature rising rate is 2-5℃ / min, and the calcination atmosphere is air. -1

[0022] According to the application, preferably, in step (2), the mass ratio of the cobalt ferrite nanofiber to the sodium hypophosphite is 1:(10-20).

[0023] According to the application, preferably, in step (2), the cobalt ferrite nanofiber and the sodium hypophosphite are respectively placed in a porcelain boat, and then the two porcelain boats are placed in the tube furnace. ​

[0024] According to the application, preferably, in step (2), the protective gas is argon or nitrogen.

[0025] According to the application, preferably, in step (2), after the cobalt ferrite nanofiber is placed in the tube furnace with sodium hypophosphite, the tube furnace is vacuumized, and then the protective gas is introduced.

[0026] According to the application, preferably, in step (2), during the calcination process, the protective gas is continuously introduced into the tube furnace; the outlet end of the tube furnace is connected to the tail gas absorption liquid through a pipeline, and the gas discharged from the pipeline to the tail gas absorption liquid generates a bubble rate of (1-3) bubbles / s in the tail gas absorption liquid.

[0027] According to the application, preferably, in step (2), the calcination conditions are as follows: the heating rate is 2-5℃ / min -1 , the calcination temperature is 350-500℃, and the holding time is 2-5h.

[0028] According to the application, in step (2), during the calcination process, sodium hypophosphite is decomposed, and the generated gas substance performs an in-situ reduction reaction on the cobalt ferrite nanofiber to prepare a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology.

[0029] The cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology is applied as a catalyst for electrocatalytic oxygen evolution.

[0030] Technical features and beneficial effects of the application:

[0031] 1. The preparation method of the application is simple, and the raw materials are cheap and easy to obtain. The cobalt-iron bimetallic phosphide electrocatalytic material obtained by the method has a nanofiber surface loaded with nanoparticles. The catalyst material obtained by the application has high activity, fast electron transfer, small overpotential, and excellent electrocatalytic oxygen evolution performance in the electrocatalytic oxygen evolution reaction; when the current density reaches 10mAcm -2 , the overpotential of OER is only 268.8mV, and the Tafel slope is only 33.6mV dec -1 ; the performance is comparable to that of noble metal catalysts, and has good application prospect.

[0032] 2. In the preparation method of the cobalt ferrite nanofiber of the application, the preparation of the nanofiber is affected by the raw material ratio, the type of solvent, the high molecular binder, the electrospinning conditions, the calcination temperature and time, etc. The preparation of the cobalt ferrite nanofiber is optimized by integrating the influences of various aspects to find the optimal proportion, and finally exhibits the best properties.

[0033] 3、The application obtains a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology by in-situ phosphorization reduction of cobalt ferrite nanofiber using the gas of sodium hypophosphite decomposition at high temperature in an inert gas atmosphere. The reaction of in-situ phosphorization is more sufficient by suitable reaction temperature and time, and the crystallinity of the obtained cobalt-iron bimetallic phosphide is better, and the electrocatalytic performance is also better.

[0034] 4、The application prepares a cobalt-iron bimetallic phosphide electrocatalyst with one-dimensional morphology by the method of combination of electrospinning and calcination, which has uniform and continuous one-dimensional morphology, and the one-dimensional nanofiber can provide more active sites, and the unique electronic configuration of the phosphide and the synergistic effect of the bimetallic make the cobalt-iron bimetallic phosphide with one-dimensional morphology prepared by the application have good electrocatalytic activity. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 X-ray diffraction pattern (XRD) of the electrocatalytic material prepared for the application example 1 and the comparative example 1.

[0036] Figure 2 Scanning electron microscope (SEM) of the cobalt-iron bimetallic phosphide electrocatalytic material prepared for the application example 1.

[0037] Figure 3 Transmission electron microscope (TEM) of the cobalt-iron bimetallic phosphide electrocatalytic material prepared for the application example 1.

[0038] Figure 4 Scanning electron microscope (SEM) of the electrocatalytic material prepared for the application comparative example 1.

[0039] Figure 5 OER linear sweep voltammetry (LSV) polarization curve of the electrocatalytic material prepared for the application examples 1-4 and the comparative example 1.

[0040] Figure 6 Tafel slope diagram of the electrocatalytic material prepared for the application examples 1-4 and the comparative example 1.

[0041] Figure 7 OER Nyquist diagram (EIS) of the electrocatalytic material prepared for the application examples 1-4 and the comparative example 1. DETAILED DESCRIPTION

[0042] The application will be further described below in combination with specific examples. But it is not limited to this.

[0043] The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents, materials and devices, unless otherwise specified, can be obtained commercially. Among them: polyvinylpyrrolidone is polyvinylpyrrolidone K90, the weight average molecular weight is 1.3 million.

[0044] Example 1

[0045] A preparation method of a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology, comprising the following steps:

[0046] (1) 0.5 mmol of cobalt nitrate hexahydrate and 1 mmol of iron nitrate nonahydrate were dissolved in a mixture of 8 mL of anhydrous ethanol and 2 mL of N,N-dimethylformamide, stirred for 30 min, and completely dissolved to obtain a red clear solution.

[0047] (2) 0.8 g of polyvinylpyrrolidone (PVP) was added to the cobalt nitrate / iron nitrate mixed solution obtained in step (1), and stirred until the solution was fully mixed and uniform to obtain a cobalt nitrate / iron nitrate mixed sol.

[0048] (3) The cobalt nitrate / iron nitrate mixed sol prepared in step (2) was electrospun at room temperature, and the spinning conditions were: 20 kV voltage, humidity 25%, receiving distance 20 cm, and pushing speed 0.5 mL h -1 , to obtain a precursor fiber.

[0049] (4) The obtained precursor fiber was dried in a 60°C drying box for 12 h.

[0050] (5) The precursor fiber prepared in step (4) was placed in a muffle furnace, and heated to 500°C at a rate of 2°C / min -1 in an air atmosphere, and kept for 120 min to prepare cobalt ferrite nanofibers.

[0051] (6) 0.05 g of the cobalt ferrite nanofiber prepared in step (5) was taken in a porcelain boat, and additionally 1 g of NaH2PO2·H2O was taken in another porcelain boat of the same size.

[0052] (7) The porcelain boat containing NaH2PO2·H2O was placed on the side of the gas inlet of the protective gas in the tube furnace, and the porcelain boat containing the cobalt ferrite nanofiber was placed on the side of the gas outlet of the protective gas in the tube furnace.

[0053] (8) The tube furnace was vacuumed three times in succession to remove the air in the tube furnace, and then N2 was introduced.

[0054] (9) The temperature rising program of the tube furnace was set to 2°C / min -1The temperature rising rate is increased to 500℃, and the temperature is kept for 3 hours. During the calcination process, N2 is continuously introduced into the tube furnace. The outlet end of the tube furnace is connected to the tail gas absorption liquid through a pipeline. The gas discharged from the pipeline to the tail gas absorption liquid generates bubbles at a rate of 1 bubble / s in the tail gas absorption liquid.

[0055] (10) After being reduced to room temperature, the porcelain boat is taken out, and the cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology is obtained by in-situ phosphorization of the cobalt-iron bimetallic nanofiber in the magnetic boat.

[0056] Figure 1 The X-ray diffraction (XRD) of the cobalt-iron bimetallic phosphide electrocatalytic material prepared in this example is shown in the figure. The diffraction peaks are basically consistent with the standard PDF cards CoP (89-2747) and FeP (71-2262), and there is no diffraction peak of CoFe2O4, indicating that the cobalt-iron bimetallic phosphide composite material is synthesized.

[0057] Figure 2 The scanning electron microscope (SEM) of the cobalt-iron bimetallic phosphide electrocatalytic material prepared in this example is shown in the figure. The prepared cobalt-iron bimetallic phosphide electrocatalytic material has one-dimensional fiber morphology, the nanofiber diameter is about 200 nm, and the length is about 5 μm. Through in-situ phosphorization, the originally rough nanofiber surface grows nanometer particles.

[0058] Figure 3 The transmission electron microscope (TEM) of the cobalt-iron bimetallic phosphide electrocatalytic material prepared in this example is shown in the figure. The prepared cobalt-iron bimetallic phosphide electrocatalytic material has one-dimensional nanomaterial morphology, which is uniform and continuous, proving the formation of the composite material.

[0059] Example 2

[0060] A preparation method of a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology, comprising the following steps:

[0061] (1) 0.5 mmol of cobalt nitrate hexahydrate and 1 mmol of iron nitrate nonahydrate are dissolved in 8 mL of a mixed solution of anhydrous ethanol and 2 mL of N,N-dimethylformamide, stirred for 30 min, and completely dissolved to obtain a red clear solution.

[0062] (2) 0.8 g of polyvinylpyrrolidone (PVP) is added to the cobalt nitrate / iron nitrate mixed solution obtained in step (1), and stirred until the solution is fully mixed and uniform to obtain a cobalt nitrate / iron nitrate mixed sol.

[0063] (3) The cobalt nitrate / iron nitrate mixed sol prepared in step (2) is electrospun at room temperature, with a voltage of 20 kV, a humidity of 25%, a receiving distance of 20 cm, and a pushing speed of 0.5 mL h -1 , to obtain a precursor fiber.

[0064] (4) The obtained precursor fiber is dried in a 60°C drying box for 12 h.

[0065] (5) The precursor fiber prepared in step (4) is placed in a muffle furnace, and heated to 500°C at a rate of 2°C min -1 per minute in an air atmosphere, and kept at 500°C for 120 min, to obtain a cobalt ferrite nanofiber.

[0066] (6) 0.05 g of the cobalt ferrite nanofiber prepared in step (5) is weighed into a porcelain boat, and 1 g of NaH2PO2·H2O is weighed into another porcelain boat of the same size.

[0067] (7) The porcelain boat containing NaH2PO2·H2O is placed on the side of the gas inlet of the protective gas in the tube furnace, and the porcelain boat containing the cobalt ferrite nanofiber is placed on the side of the gas outlet of the protective gas in the tube furnace.

[0068] (8) The tube furnace is vacuumed three times in succession, so as to remove the air in the tube furnace, and then N2is introduced.

[0069] (9) The temperature rising program of the tube furnace is set to rise to 500°C at a rate of 2°C min -1 per minute, and kept at 500°C for 2 h; during the calcination process, N2is continuously introduced into the tube furnace; the gas outlet end of the tube furnace is connected to the tail gas absorption liquid by a pipeline, and the gas discharged from the pipeline to the tail gas absorption liquid generates a bubble rate of 1 bubble / s in the tail gas absorption liquid.

[0070] (10) After being cooled to room temperature, the porcelain boat is taken out, and the cobalt ferrite nanofiber in the magnetic boat is in-situ phosphorized to obtain a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology.

[0071] Example 3

[0072] A preparation method of a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology, comprising the following steps:

[0073] (1) 0.5 mmol of cobalt nitrate hexahydrate and 1 mmol of iron nitrate nonahydrate are weighed into a mixed solution of 8 mL of anhydrous ethanol and 2 mL of N,N-dimethylformamide, stirred for 30 min, and completely dissolved to obtain a red clear solution.

[0074] (2) To the mixed solution of cobalt nitrate / iron nitrate obtained in step (1), 0.8 g of polyvinylpyrrolidone (PVP) was added, and stirred until the solution was fully mixed and uniform, to obtain a mixed sol of cobalt nitrate / iron nitrate.

[0075] (3) The mixed sol of cobalt nitrate / iron nitrate prepared in step (2) was electrospun at room temperature, with a voltage of 20 kV, a humidity of 25%, a receiving distance of 20 cm, and a pushing speed of 0.5 mL h -1 , to obtain precursor fibers.

[0076] (4) The obtained precursor fibers were dried in a drying oven at 60°C for 12 h.

[0077] (5) The precursor fibers prepared in step (4) were placed in a muffle furnace, and heated to 500°C at a rate of 2°C min -1 , and kept at 500°C for 120 min, to obtain cobalt ferrite nanofibers.

[0078] (6) 0.05 g of the cobalt ferrite nanofibers prepared in step (5) were weighed into a porcelain boat, and 1 g of NaH2PO2·H2O was weighed into another porcelain boat of the same size.

[0079] (7) The porcelain boat containing NaH2PO2·H2O was placed on the side of the gas inlet of the protective gas in the tube furnace, and the porcelain boat containing the cobalt ferrite nanofibers was placed on the side of the gas outlet of the protective gas in the tube furnace.

[0080] (8) The tube furnace was vacuumed three times in succession, to remove the air in the tube furnace, and then N2was introduced.

[0081] (9) The temperature rising program of the tube furnace was set to rise to 400°C at a rate of 2°C min -1 , and kept at 400°C for 3 h; during the calcination process, N2was continuously introduced into the tube furnace; the end of the gas outlet of the tube furnace was connected to a tail gas absorption liquid by a pipeline, and the gas discharged from the pipeline to the tail gas absorption liquid generated a bubble rate of 1 bubble / s in the tail gas absorption liquid.

[0082] (10) After cooling to room temperature, the porcelain boat was taken out, and the cobalt ferrite nanofibers in the magnetic boat were in-situ phosphorized to obtain a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology.

[0083] Example 4

[0084] A preparation method of a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology, comprising the following steps:

[0085] (1) 0.5 mmol of cobalt nitrate hexahydrate and 1 mmol of iron nitrate nonahydrate were dissolved in a mixture of 8 mL of anhydrous ethanol and 2 mL of N,N-dimethylformamide, and stirred for 30 min to completely dissolve, to obtain a red clear solution.

[0086] (2) 0.8 g of polyvinylpyrrolidone (PVP) was added to the cobalt nitrate / iron nitrate mixed solution obtained in step (1), and stirred until the solution was fully mixed and uniform, to obtain a cobalt nitrate / iron nitrate mixed sol.

[0087] (3) The cobalt nitrate / iron nitrate mixed sol prepared in step (2) was electrospun at room temperature, and the spinning conditions were: a voltage of 20 kV, a humidity of 25%, a receiving distance of 20 cm, and a pushing speed of 0.5 mL h -1 , to obtain a precursor fiber.

[0088] (4) The obtained precursor fiber was dried in a drying oven at 60°C for 12 h.

[0089] (5) The precursor fiber prepared in step (4) was placed in a muffle furnace, and heated to 500°C at a rate of 2°C min -1 , and kept for 120 min, to obtain a cobalt ferrite nanofiber.

[0090] (6) 0.05 g of the cobalt ferrite nanofiber prepared in step (5) was taken in a porcelain boat, and 1 g of NaH2PO2·H2O was taken in another porcelain boat of the same size.

[0091] (7) The porcelain boat containing NaH2PO2·H2O was placed at the gas inlet side of the protective gas in the tube furnace, and the porcelain boat containing the cobalt ferrite nanofiber was placed at the gas outlet side of the protective gas in the tube furnace.

[0092] (8) The tube furnace was vacuumed three times in succession, to remove the air in the tube furnace, and then N2was introduced.

[0093] (9) The temperature rising program of the tube furnace was set to rise to 400°C at a rate of 2°C min -1 , and kept for 2 h; during the calcination process, N2was continuously introduced into the tube furnace; the gas outlet end of the tube furnace was connected to a tail gas absorption liquid by a pipeline, and the gas discharged from the pipeline to the tail gas absorption liquid generated a bubble rate of 1 bubble / s in the tail gas absorption liquid.

[0094] (10) After cooling to room temperature, the porcelain boat was taken out, and the cobalt ferrite nanofiber in the magnetic boat was in-situ phosphorized to obtain a cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology.

[0095] Comparative Example 1

[0096] A preparation method of a cobalt ferrite electrocatalytic material, steps are as follows:

[0097] (1) 0.5 mmol of cobalt nitrate hexahydrate and 1 mmol of iron nitrate nonahydrate are weighed and dissolved in a mixed solution of 8 mL of anhydrous ethanol and 2 mL of N,N-dimethylformamide, stirred for 30 min, and completely dissolved to obtain a red clear solution.

[0098] (2) 0.8 g of polyvinylpyrrolidone (PVP) is added to the cobalt nitrate / iron nitrate mixed solution obtained in step (1), and stirred until the solution is fully mixed and uniform, to obtain a cobalt nitrate / iron nitrate mixed sol.

[0099] (3) The cobalt nitrate / iron nitrate mixed sol prepared in step (2) is electrospun at room temperature, and the spinning conditions are: 20 kV voltage, humidity of 25%, receiving distance of 20 cm, and pushing speed of 0.5 mL h -1 , to obtain precursor fibers.

[0100] (4) The obtained precursor fibers are dried in a 60°C drying box for 12 h.

[0101] (5) The precursor fibers prepared in step (3) are placed in a muffle furnace, heated to 500°C at a rate of 2°C / min -1 in an air atmosphere, and kept for 120 min to obtain cobalt ferrite nanofibers.

[0102] The XRD of the cobalt ferrite nanofibers (CoFe2O4) is shown in Figure 1 , which is consistent with the standard PDF card CoFe2O4 (79-1744), indicating that CoFe2O4 nanofibers are synthesized.

[0103] The SEM image of the cobalt ferrite nanofibers (CoFe2O4) is shown in Figure 4 a, b, which is a one-dimensional nanofiber morphology, and the surface is not loaded with nanoparticles.

[0104] Application example

[0105] The electrocatalytic materials prepared in Examples 1-4 and Comparative Example 1 are tested for electrocatalytic oxygen evolution performance, and the specific test method is as follows: a three-electrode system controlled by an electrochemical workstation is used for determination. The working electrode is controlled by a commercial rotating disk electrode system, and the electrode is kept rotating at 1600 rpm during the test to remove the gas bubbles generated on the surface of the electrocatalytic material. In the test, the glassy carbon rotating disk electrode (RDE) is loaded with the electrocatalytic material (the loading amount of the electrocatalytic material is about 0.3 mg cm -2) As the working electrode, graphite rod is the counter electrode, and Hg / HgO electrode is the reference electrode. The polarization curve (linear voltammetry scan, LSV) test is carried out in 1M KOH aqueous solution saturated with N2, and the polarization curve is compensated by 90% IR, and the scanning speed is 5mV s -1 . The electrochemical impedance spectrum (EIS) measurement is carried out from 100000 to 0.1Hz, and the amplitude is 5mV at 1.47V relative to RHE.

[0106] It can be seen from Figure 5 that the overpotential of the electrocatalytic material prepared in Examples 1, 2, 3, 4 and Comparative Example 1 is 266.8mV, 274.8mV, 278.8mV, 285.8mV and 464.8mV respectively. Examples 1-4 have larger limiting current density compared with Comparative Example 1, and can reach larger current density at smaller overpotential. At the same time, the cobalt-iron bimetallic phosphide prepared in Examples 1, 2 has smaller overpotential compared with Examples 3, 4, and has superior electrocatalytic performance.

[0107] The Tafel slope of the electrocatalytic material prepared in Examples 1, 2, 3, 4 and Comparative Example 1 is shown in Figure 6 From the figure, it can be seen that the electrocatalytic material prepared in the examples has a lower Tafel slope compared with the comparative example, and the Tafel slope of Example 1 is the lowest, and the electrocatalytic oxygen evolution performance is the best.

[0108] The electrochemical impedance diagram of the electrocatalytic material prepared in Examples 1, 2, 3, 4 and Comparative Example 1 is shown in Figure 7 It can be seen that the charge transfer resistance of the electrocatalytic material prepared in Examples 1-4 is greatly reduced compared with Comparative Example 1, and the electron transmission is fast; and the cobalt-iron bimetallic phosphide prepared in Examples 1, 2 has the smallest electrochemical impedance compared with Examples 3, 4.

[0109] In summary, the cobalt-iron bimetallic phosphide electrocatalytic material prepared in the present application has good electrocatalytic activity, and the electrocatalytic performance is greatly improved compared with cobalt ferrite nanofibers.

Claims

1. A cobalt-iron bimetallic phosphide electrocatalytic material having a one-dimensional morphology, characterized in that, The micro-morphology of the electro-catalytic material is: nanofibers with nanoparticles loaded on the surface; The preparation method of the cobalt-iron bimetallic phosphide electro-catalytic material with one-dimensional morphology comprises the following steps: (1) dissolving cobalt nitrate and iron nitrate in a mixture of ethanol and N,N-dimethylformamide, adding polyvinylpyrrolidone (PVP), mixing uniformly, obtaining a mixed sol; then electrospinning, drying, calcining, obtaining cobalt ferrite nanofiber; the molar ratio of cobalt nitrate and iron nitrate is 1:2; the mass ratio of polyvinylpyrrolidone (PVP) and cobalt nitrate is 1:(0.05-0.2); the electrospinning conditions are: temperature is room temperature, voltage is 15-25 kV, humidity is 20-30 %, receiving distance is 10-30 cm, advancing speed is 0.5-1.5 mL h -1 ; the calcining temperature is 400-600 °C, the calcining time is 60-180 min, the temperature rising rate is 2-5 °C min -1 , the calcining atmosphere is air; (2) placing the cobalt ferrite nanofiber and sodium hypophosphite separately in a tube furnace, placing the cobalt ferrite nanofiber at one side of the outlet of the protective gas in the tube furnace, and placing the sodium hypophosphite at one side of the inlet of the protective gas in the tube furnace; obtaining the cobalt-iron bimetallic phosphide electrocatalytic material with one-dimensional morphology through calcination under a protective gas atmosphere; the mass ratio of the cobalt ferrite nanofiber to the sodium hypophosphite is 1:(10-20); the calcination condition is that the heating rate is 2-5 °C / min, the calcination temperature is 500 °C, and the holding time is 2-3 h. -1 ​ 2. The cobalt-iron bimetallic phosphide electrocatalytic material having one-dimensional morphology according to claim 1, wherein, The diameter of the nanofiber is 150-200 nm, and the length is 4-10 μm.

3. The cobalt-iron bimetallic phosphide electrocatalytic material having one-dimensional morphology according to claim 1, wherein, In step (1), one or more of the following conditions are included: i. In the mixed solution of ethanol and N,N-dimethylformamide, the volume ratio of ethanol to N,N-dimethylformamide is (3-5):1; ii. The molar amount of cobalt nitrate and the volume ratio of the mixed solution is 0.01-0.1 mmol / L -1 ; iii. The weight average molecular weight of the polyvinylpyrrolidone (PVP) is 1-1.5 million; iv. The drying temperature is 60-80°C, and the drying time is 8-12 h.

4. The cobalt-iron bimetallic phosphide electrocatalytic material having one-dimensional morphology according to claim 1, wherein, In step (2), one or more of the following conditions are included: i. The cobalt ferrite nanofiber and sodium hypophosphite are respectively placed in a porcelain boat, and then the two porcelain boats are placed in a tube furnace; ii. After placing the cobalt ferrite nanofiber and sodium hypophosphite in the tube furnace, the tube furnace is vacuumized, and then a protective gas is introduced.

5. The cobalt-iron bimetallic phosphide electrocatalytic material having one-dimensional morphology according to claim 1, wherein, In step (2), the protective gas is argon or nitrogen.

6. The cobalt-iron bimetallic phosphide electrocatalytic material having one-dimensional morphology according to claim 1, wherein, In step (2), during the calcination process, the protective gas is continuously introduced into the tube furnace; the outlet end of the tube furnace is connected to the tail gas absorption liquid by a pipeline, and the gas discharged from the pipeline to the tail gas absorption liquid produces a bubble rate of (1-3) bubbles / s in the tail gas absorption liquid.

7. Use of a cobalt-iron bimetallic phosphide electrocatalytic material having a one-dimensional morphology according to any one of claims 1 to 6, characterized in that, As a catalyst for electro-catalytic oxygen evolution.

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