P-doped Fe-Co-Se electrocatalytic oxygen evolution material and preparation method and application thereof

Abstract

The application discloses a P-doped Fe-Co-Se electrocatalytic oxygen evolution material and a preparation method and application thereof. The Fe-Co-Se is prepared on carbon cloth through a hydrothermal method and a hot selenization method, and then P-doping is carried out through a hot phosphorization method. By introducing a proper content of P, the activity sites of the electrocatalytic oxygen evolution material are increased, the energy barrier of the water decomposition reaction is successfully reduced, and the water decomposition is accelerated in kinetics. The activity sites and surface roughness of the electrocatalytic oxygen evolution material are increased, the hydrophilicity of the electrocatalytic oxygen evolution material is improved, the release of bubbles is promoted, the effective adjustment of the basal surface of the electrocatalytic oxygen evolution material is realized, and the OER performance of the electrocatalytic oxygen evolution material is improved. A new idea is provided for the development, design and utilization of new energy materials.

Description

TECHNICAL FIELD

[0001] The present application relates to a P-doped Fe-Co-Se electrocatalytic oxygen evolution material and a preparation method and application thereof, and belongs to the technical field of electrocatalytic materials. BACKGROUND

[0002] In recent years, the overuse of fossil fuels has triggered global problems such as environmental pollution and climate warming, and the development of alternative energy or more efficient use of fossil energy has gradually become the consensus of people. Among the many alternative energies developed, green hydrogen energy is the most outstanding. Water electrolysis to produce hydrogen is a quite old reaction, which can be traced back to the 19th century, but electrocatalytic water decomposition as the core technology of future hydrogen energy has only attracted the attention of the industry and academia in the past decade. The oxygen evolution reaction (OER, 4OH - +4e - =O2+2H2O) is the anode reaction in the hydrogen production reaction of water electrolysis. However, the process of four-electron transfer plus the high thermodynamic potential barrier greatly slows down the OER kinetics, making it a major obstacle to higher energy conversion systems. Therefore, it is urgent to use a reasonable electrocatalyst to reduce the overpotential of the oxygen evolution reaction. At present, noble metal catalysts such as RuO2 and IrO2 perform the most outstanding in reducing the energy barrier of water oxidation reaction. However, due to its high cost and low stability, the demand for more efficient and more economical non-noble metal electrocatalyst substitutes is still huge.

[0003] In recent years, people have explored a variety of transition metal oxides, hydroxides, nitrides, phosphides, sulfides and selenides to obtain efficient and economical OER electrocatalysts. Compared with other compounds, transition metal selenides, especially bimetallic selenides, have been widely concerned in electrocatalytic water oxidation due to their metalloid properties and high intrinsic electrical conductivity. It has been proven that bimetallic selenides have more advantages in electrocatalytic activity than monometallic selenides. In particular, Fe-Co-based selenides, the existence of synergistic effect between Fe and Co makes the catalyst have a more optimized electronic structure, superior electrical conductivity and enhanced stability, which are all conducive to obtaining more excellent electrocatalytic oxygen evolution activity.

[0004] However, despite these advantages, the OER electrocatalytic activity of Fe-Co-based selenides still needs to be improved due to low active site exposure and poor stability. SUMMARY

[0005] Invention purposes: The first purpose of the present application is to provide a super-hydrophilic and super-gas-repellent dandelion flower-shaped P-doped Fe-Co-Se electrocatalytic oxygen evolution material, the second purpose of the present application is to provide a preparation method of the P-doped Fe-Co-Se electrocatalytic oxygen evolution material, and the third purpose of the present application is to provide an application of the P-doped Fe-Co-Se electrocatalytic oxygen evolution material in electrocatalytic oxygen evolution.

[0006] Technical scheme: The preparation method of the P-doped Fe-Co-Se electrocatalytic oxygen evolution material provided by the present application comprises the following steps: Fe(NO3)3·9H2O and Co(NO3)2·6H2O are used as raw materials, a precursor Fe-Co-Precursor / CC is prepared on carbon cloth (CC) by a hydrothermal method, then a Fe-Co-Se / CC is obtained by a hot selenization method, and finally a polar anion P is doped on the surface of the Fe-Co-Se / CC.

[0007] Further, the preparation method of the P-doped Fe-Co-Se electrocatalytic oxygen evolution material comprises the following steps:

[0008] (1) Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Co(NH2)2 and NH4F are dissolved in deionized water, ultrasonic treatment is performed, a mixed solution is obtained, carbon cloth is placed in the mixed solution, a hydrothermal reaction is performed, washing is performed, vacuum drying is performed, and a precursor Fe-Co-Precursor / CC is obtained;

[0009] (2) The precursor Fe-Co-Precursor / CC is placed in the downstream of a tube furnace, Se powder is placed in the upstream of the tube furnace, a selenization reaction is performed, water washing is performed, vacuum drying is performed, and a Fe-Co-Se / CC is obtained;

[0010] (3) The Fe-Co-Se / CC is placed in the downstream of a tube furnace, a phosphorus source is placed in the upstream of the tube furnace, a phosphorization reaction is performed, cooling is performed, washing is performed, vacuum drying is performed, and a Fe-Co-Se-P / CC is obtained.

[0011] Further, in step (1), the molar ratio of Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Co(NH2)2 and NH4F is (0.2-0.4):(0.2-0.4):1:1.

[0012] Further, in step (1), the temperature of the hydrothermal reaction is 110-130 DEG C, and the time of the hydrothermal reaction is 11-13 h.

[0013] Further, in step (1), the washing is repeatedly performed on the carbon cloth on which the precursor Fe-Co-Precursor is grown by using deionized water and anhydrous ethanol.

[0014] Further, in step (1), the carbon cloth is pretreated by using a mixed solution of HNO3 and H2SO4 with a volume ratio of 2-4:1 to ultrasonically treat the carbon cloth for 0.5-1.5 h, repeatedly rinsing with deionized water and anhydrous ethanol, and vacuum drying.

[0015] Further, in step (2), the added amount of the Se powder is 0.5-1 g.

[0016] Further, in step (2), the calcination heating rate of the selenization reaction is 1-3℃ / min. -1 Further, in step (2), the selenization is performed at 300-400℃ for 1-3 h under a nitrogen atmosphere.

[0017] Further, in step (3), the phosphorus source is NaH2PO2·H2O.

[0018] Further, in step (3), the added amount of the phosphorus source is 0.15-0.45 g.

[0019] Further, in step (3), the phosphorization reaction is heating at 300-400℃ for 1-3 h under a nitrogen atmosphere.

[0020] Further, in steps (1), (2) and (3), the temperature of the vacuum drying is 55-65℃.

[0021] The P-doped Fe-Co-Se electrocatalytic oxygen evolution material prepared by the preparation method has a dandelion flower shape.

[0022] The application further includes the application of the P-doped Fe-Co-Se electrocatalytic oxygen evolution material in electrocatalytic oxygen evolution.

[0023] The application can obtain Fe-Co-Se-P / CC with different doping ratios by controlling the amount of phosphorization. When the P content is 0.1, the Fe-Co-Se-P / CC has the best electrocatalytic oxygen evolution performance. The introduction of P not only reduces the energy barrier of water decomposition and intermediate adsorption, but also accelerates the decomposition of water in kinetics, increases the active sites and roughness of the electrocatalytic oxygen evolution material, improves the hydrophilicity of the electrocatalytic oxygen evolution material, and promotes the release of gas bubbles.

[0024] Advantages: Compared with the prior art, the application has the following obvious advantages:

[0025] The present application obtains Fe-Co-Se-P / CC electrocatalytic oxygen evolution material with optimal electrocatalytic oxygen evolution performance by effectively controlling the phosphorization amount of Fe-Co-Se / CC. It is proved by a series of means such as scanning electron microscopy, XPS, electrochemical characterization and the like that the introduction of appropriate content of P can increase the active sites of the electrocatalytic oxygen evolution material, successfully reduce the energy barrier of water decomposition reaction, and accelerate the decomposition of water in kinetics. Through the contact angle test, it is clear that the introduction of P element can increase the roughness of the material surface, improve the hydrophilicity of the electrocatalytic oxygen evolution material, promote the release of bubbles, realize the effective adjustment of the surface of the electrocatalytic oxygen evolution material, and finally improve the OER performance of the electrocatalytic oxygen evolution material. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Flow chart of Fe-Co-Precursor / CC prepared for Example 1;

[0027] Figure 2 XRD patterns of Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1, Fe-Co-Se-P / CC synthesized for Example 2 and Fe-Co-Se-P / CC synthesized for Example 3; 0.5 1.5

[0028] Figure 3 SEM patterns of Fe-Co-Precursor / CC, Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1;

[0029] Figure 4 TEM and HRTEM patterns of Fe-Co-Se-P / CC synthesized for Example 1;

[0030] Figure 5 XPS patterns of Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1;

[0031] Figure 6 Electrocatalytic performance patterns of Fe-Co-Precursor / CC, Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1;

[0032] Figure 7 Electrocatalytic performance patterns of Fe-Co-Se-P / CC synthesized for Example 1, Fe-Co-Se-P / CC synthesized for Example 2 and Fe-Co-Se-P / CC synthesized for Example 3; 0.5 1.5

[0033] Figure 8 ​​​​Fe-Co-Precursor / CC, Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1, Fe-Co-Se-P synthesized for Example 2 0.5 Fe-Co-Se-P synthesized for Example 3 1.5 overpotential plots at 10 mA cm-2current density for Fe-Co-Precursor / CC, Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1, Fe-Co-Se-P synthesized for Example 2 -2 overpotential plots at 10 mA cm-2current density for Fe-Co-Precursor / CC, Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1, Fe-Co-Se-P synthesized for Example 2

[0034] Figure 9 CV plots for Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1, Fe-Co-Se-P synthesized for Example 2 0.5 CV plots for Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1, Fe-Co-Se-P synthesized for Example 2 1.5 CV plots for Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1, Fe-Co-Se-P synthesized for Example 2

[0035] Figure 10 Hydrophilic contact angle plots for Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized for Example 1

[0036] Figure 11 Chronoamperometry plots for Fe-Co-Se-P / CC synthesized for Example 1 at 1.65 V vs. RHE

[0037] Figure 12 LSV plots for Fe-Co-Se-P / CC synthesized for Example 1 before and after 1000 CV cycles

[0038] Figure 13 XRD, SEM, TEM and HRTEM plots for Fe-Co-Se-P / CC synthesized for Example 1 after stability test

[0039] Figure 14 XPS plots for Fe-Co-Se-P / CC synthesized for Example 1 after stability test DETAILED DESCRIPTION

[0040] The technical solutions of the present application will be further described below with reference to the accompanying drawings.

[0041] Example 1

[0042] (1) Pretreatment of carbon cloth

[0043] A rectangular carbon cloth of 2 cm x 3 cm size was placed in a mixed solution of HNO3 and H2SO4 (volume ratio = 3:1) under ultrasonication for 1 h, after which the carbon cloth was repeatedly rinsed with deionized water and anhydrous ethanol to ensure no residual acid. It was then vacuum dried at 60 °C for subsequent use.

[0044] (2) Preparation of Fe-Co-Precursor / CC

[0045] Fe(NO3)3·9H2O (0.6 mmol), Co(NO3)2·6H2O (0.6 mmol), Co(NH2)2 (2 mmol), NH4F (2 mmol) were dissolved in 30 mL of deionized water, and ultrasonic treatment was performed until the solution became transparent and uniform to obtain a mixed solution. The mixed solution was placed in a 100 mL polytetrafluoroethylene (PTFE) liner together with the clean carbon cloth pretreated in step (1), and then the liner was placed in an autoclave for a hydrothermal reaction at 120 °C for 12 h. After the reaction was completed, the autoclave was cooled to 25 °C, and the carbon cloth on which the Fe-Co-Precursor grew was taken out of the solution in the autoclave. In order to remove excess ions and facilitate subsequent calcination, the carbon cloth on which the Fe-Co-Precursor grew was repeatedly washed with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 60 °C to obtain Fe-Co-Precursor / CC.

[0046] (3) Preparation of Fe-Co-Se / CC

[0047] The Fe-Co-Precursor / CC was placed in a quartz boat and placed downstream of a tube furnace, and 0.63 g of Se powder was placed upstream of the tube furnace for selenization at 350 °C for 2 h. After the selenization reaction was completed and the reaction was cooled, the prepared Fe-Co-Se / CC was washed with deionized water and anhydrous ethanol. Next, the Fe-Co-Se / CC was dried in a vacuum drying oven at 60 °C for 8 h to obtain Fe-Co-Se / CC.

[0048] (4) Preparation of Fe-Co-Se-P / CC

[0049] The Fe-Co-Se / CC was placed in a porcelain boat and placed downstream of a tube furnace, and 0.30 g of NaH2PO2·H2O was used as a phosphorus source and placed upstream of the tube furnace for phosphorization at 350 °C for 2 h. After the phosphorization reaction was completed and the reaction was cooled, the prepared Fe-Co-Se-P / CC was washed with deionized water and anhydrous ethanol. Next, the Fe-Co-Se-P / CC was dried in a vacuum drying oven at 60 °C for 8 h to obtain Fe-Co-Se-P / CC. The entire preparation process is shown in Figure 1

[0050] Example 2 Preparation of Fe-Co-Se-P / CC 0.5

[0051] Steps (1), (2), and (3) are the same as in Example 1, except that step (4) is different, and Fe-Co-Se-P / CC is prepared 0.5 ​​When the concentration is / CC, 0.15g of NaH2PO2·H2O is used to replace the 0.30g of NaH2PO2·H2O in Example 1, and the resulting electrocatalytic oxygen evolution material is Fe-Co-Se-P. 0.5 / CC.

[0052] Example 3 Fe-Co-Se-P 1.5 / CC preparation

[0053] Steps (1), (2), and (3) are the same as in Example 1, except that in step (4), Fe-Co-Se-P is prepared. 1.5 When the concentration is / CC, 0.45g of NaH2PO2·H2O is used to replace the 0.30g of NaH2PO2·H2O in Example 1, and the resulting electrocatalytic oxygen evolution material is Fe-Co-Se-P. 1.5 / CC.

[0054] X-ray powder diffraction (XRD) was used to analyze the electrocatalytic oxygen evolution materials Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1, and Fe-Co-Se-P synthesized in Example 2. 0.5 / CC and Fe-Co-Se-P synthesized in Example 3 1.5 The crystal phase of / CC was characterized, and the results are as follows: Figure 2 As shown. Figure 2 The Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1, and the Fe-Co-Se-P synthesized in Example 2. 0.5 / CC and Fe-Co-Se-P synthesized in Example 3 1.5 XRD patterns of Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1, where (a) is the XRD pattern of Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1, (b) is the XRD pattern of (a) magnified between 27° and 40°, and (c) is the XRD pattern of Fe-Co-Se-P / CC synthesized in Example 1 and Fe-Co-Se-P / CC synthesized in Example 2. 0.5 / CC and Fe-Co-Se-P synthesized in Example 3 1.5 XRD pattern of / CC. Figure 2(a) shows that the diffraction peaks of Fe-Co-Se / CC at 31.19°, 34.72°, 38.01° and 51.78° can be well indexed to the (200), (210), (211) and (311) planes of FeSe2(PDF #48-1881). Among them, the diffraction peaks marked with "*" near 26.14° and 44.024° belong to carbon cloth (PDF #26-1077) obviously. In addition, the diffraction peaks at 29.77°, 34.72°, 37.29° and 43.09° can be attributed to the (101), (111), (200) and (121) planes of CoSe2(PDF #53-0449), respectively. The above results show that the prepared Fe-Co-Se / CC is a composite electrocatalytic oxygen evolution material composed of FeSe2and CoSe2. Figure 2 (b) shows that after the introduction of P, the diffraction peaks of Fe-Co-Se / CC are almost all retained, but the integral diffraction peaks show an increase in intensity and an increase in angle. This is because the smaller P atoms replace the Se atoms, causing lattice distortion. The changes in the XRD pattern of Fe-Co-Se-P / CC indicate the successful doping of P element and the successful synthesis of Fe-Co-Se-P. Figure 2 (c) shows that the crystallinity of the electrocatalytic oxygen evolution material is affected by the amount of NaH2PO2·H2O. When the amount of NaH2PO2·H2O increases, the crystallinity of the electrocatalytic oxygen evolution material also increases. In the Fe-Co-Se-P 0.5 , Fe-Co-Se-P, Fe-Co-Se-P 1.5 samples, as the dosage of NaH2PO2·H2O increases from 0.15 mg to 0.45 mg, the diffraction peaks at 34.72°, 38.01°, 52.1°, 56.2° and 58.09° are stronger.

[0055] The micro-morphology of Fe-Co-Precursor / CC, Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1 was analyzed by scanning electron microscopy. The results are shown in Figure 3 . Figure 3 SEM images of Fe-Co-Precursor / CC, Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1, wherein (a) and (b) are SEM images of Fe-Co-Precursor / CC synthesized in Example 1 at different magnifications, (c) and (d) are SEM images of Fe-Co-Se / CC synthesized in Example 1 at different magnifications, and (e) and (f) are SEM images of Fe-Co-Se-P / CC synthesized in Example 1 at different magnifications. Figure 3(a) (b) It can be seen that the Fe-Co-Precursor grown on the carbon cloth skeleton is composed of dense nanosheet structures and nanoneedle structures, and the nanoneedles pass through the nanosheets to form an interconnected structure. By Figure 3 (c) (d) It can be seen that after the selenization treatment, the precursor Fe-Co-Precursor / CC is converted into the dandelion flower-like structure Fe-Co-Se / CC composed of smooth, conical nanorods. By Figure 3 (e) (f) It can be seen that the Fe-Co-Se / CC after phosphating Fe-Co-Se-P / CC still maintains the dandelion flower-like structure, but the surface is rougher. This change is conducive to exposing more active sites, increasing the contact between the electrocatalytic oxygen evolution material and the electrolyte solution, and accelerating the mass transfer.

[0056] The fine structure of the Fe-Co-Se-P / CC synthesized in Example 1 was analyzed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), and the results are shown in Figure 4 Figure 4 TEM and HRTEM images of the Fe-Co-Se-P / CC synthesized in Example 1, wherein (a) is a TEM image of the Fe-Co-Se-P / CC synthesized in Example 1 at 500 nm, (b) is an HRTEM image of the Fe-Co-Se-P / CC synthesized in Example 1, (c) is a SAED image of the Fe-Co-Se-P / CC synthesized in Example 1, (d) is a TEM image of the Fe-Co-Se-P / CC synthesized in Example 1 at 100 nm, (e) is a Fe element mapping image of the Fe-Co-Se-P / CC, (f) is a Co element mapping image of the Fe-Co-Se-P / CC, (g) is a Se element mapping image of the Fe-Co-Se-P / CC, (h) is a P element mapping image of the Fe-Co-Se-P / CC, (b1) is an enlarged view of the No. 1 yellow area in (b), and (b2) is an enlarged view of the No. 2 yellow area in (b). By Figure 4 (a) It can be seen that the Fe-Co-Se nanorods are uniformly distributed with P-doped nanoparticles, By Figure 4 (b1) and (b2) It can be seen that two clear crystal lattice fringes of 0.238 nm and 0.358 nm correspond to the (211) crystal plane of FeSe2 and the (110) crystal plane of CoSe2, respectively. In selected area electron diffraction (SAED) Figure 4 (c), diffraction points corresponding to the (211), (200) crystal planes of FeSe2 and the (310), (110), (131) crystal planes of CoSe2 were also found. The above characterization proves that the Fe-Co-Se-P / CC is a solid solution composed of FeSe2 and CoSe2, rather than a simple mechanical mixture. In addition, By Figure 4 ​(e)-(h) The element mapping of Fe-Co-Se-P / CC can clearly see that the Fe, Co, Se, P elements are uniformly distributed, which further proves the successful doping of P element.

[0057] The chemical composition and surface state of the electrocatalytic oxygen evolution material Fe-Co-Se / CC and Fe-Co-Se-P / CC prepared in Example 1 were characterized by X-ray photoelectron spectroscopy (XPS). The results are shown in Figure 5 . Figure 5 The XPS graphs of Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1, (a) is the full spectrum graph of Fe-Co-Se / CC and Fe-Co-Se-P / CC, (b) is the Fe 2p high resolution spectrum graph of Fe-Co-Se / CC and Fe-Co-Se-P / CC, (c) is the Co 2p high resolution spectrum graph of Fe-Co-Se / CC and Fe-Co-Se-P / CC, (d) is the Se 3d high resolution spectrum graph of Fe-Co-Se / CC and Fe-Co-Se-P / CC, (e) is the P 2p high resolution spectrum graph of Fe-Co-Se / CC and Fe-Co-Se-P / CC. First, the existence of iron, cobalt, selenium and phosphorus elements can be seen from Figure 5 (a). Figure 5 From (b), it can be seen that the Fe 2p 3 / 2 and Fe 2p 1 / 2 of Fe-Co-Se / CC and Fe-Co-Se-P / CC are composed of two peaks, respectively, and the peaks at 718.38 eV and 732.08 eV are two shoulder peaks. 2+ However, after the introduction of P, the 2p 3 / 2 peaks of Fe 3+ and Fe 2+ move to 710.38 eV and 711.78 eV in the direction of lower binding energy, respectively, which is 0.32 eV and 1.2 eV lower than the corresponding peaks in Fe-Co-Se / CC (710.70 eV and 712.98 eV), respectively. This proves that the introduction of P effectively adjusts the electron density of Fe 3+ and Fe 2+ . Figure 5 From (c), it can be seen that Co 2p is divided into two spin-orbit peaks under the action of two satellite peaks: Co 2p 1 / 2 (-797.0 eV) and Co 2p 3 / 2 (-781.0 eV). The Co 3+ and Co 2 at high binding energy of Fe-Co-Se-P / CC are 785.48 eV and 780.48 eV, respectively, which are 12.52 eV and 11.52 eV lower than the corresponding peaks in Fe-Co-Se / CC (798.0 eV and 791.0 eV), respectively. +at 780.48 eV and 782.28 eV, which are 0.19 eV and 0.42 eV higher than 780.29 eV and 781.86 eV of Fe-Co-Se / CC, respectively. It is well known that the presence of Co 2+ is beneficial to the formation of CoOOH intermediate, which is crucial for improving OER activity. Therefore, the higher the atomic ratio of Co 2+ / Co 3+ , the better the electrocatalytic OER performance of the material. The relative ratio of Co 2+ / Co 3+ can be calculated by the peak area of Co 3+ and Co 2+ , see Table 1, which is the peak area corresponding to Co 2+ and Co 3+ in XPS.

[0058] Table 1

[0059]

[0060] As can be seen from Table 1, the atomic ratio of Co 2+ / Co 3+ after P doping is 0.97, while before doping, the atomic ratio of Co 2+ / Co 3+ in Fe-Co-Se / CC is 0.55. It can be seen that the introduction of P increases the concentration of Co 2+ , thereby promoting the formation of active intermediate CoOOH and obtaining optimal OER activity. In addition, it can be seen from Figure 5 (d) that there are three peaks in the Se 3d fine spectrum, which are Se-O (-58.65 eV), Se 3d 3 / 2 (-56 eV) and Se 3d 5 / 2 (-54.9 eV), respectively. After introducing P, the Se 3d 3 / 2 (56 eV) peak and Se 3d 5 / 2 (55 eV) peak of Fe-Co-Se / CC move to lower binding energy (55.9 eV, 54.8 eV). Therefore, the introduction of P also affects the electronic environment of Se. However, Figure 5 (d), the relative intensity of Se-Fe(Co) peak (-55.5 eV) increases sharply after introducing P, which indicates that the doping of P enhances the interaction between Se and metal atoms. The enhancement of metal bond not only can improve the conductivity of the material, but also is beneficial to the state density across the Fermi level, and enhances the characteristics of metalloid. As can be seen from Figure 5 (e), Figure 5The high-resolution P2p spectrum of (e) further confirms the successful doping of P. The peaks centered at 132.0 eV and 133.1 eV are related to P-Fe(Co) bonds of P2p 3 / 2 , and the peaks at 132.6 eV and 133.7 eV correspond to P-O bonds. Since the electronic interaction is affected by the electron distribution, which in turn is affected by the difference in electronegativity between two atoms. Therefore, after doping P, the difference in electronegativity between Se (2.48) and P (2.19) promotes the electronic polarization distribution, thereby enhancing the electronic interaction. Therefore, it can be reasonably speculated that the modulation of P in Fe-Co-Se-P / CC successfully improves the electronic structure of Co, Fe and Se, which is beneficial to improve its oxygen evolution activity. In particular, the XPS analysis calculated that the surface Se and P content of Fe-Co-Se-P / CC is P:Se = 0.2. Since the XPS analysis is for the surface of the electrocatalytic oxygen evolution material Fe-Co-Se-P / CC, and the inductively coupled plasma emission spectroscopy (ICP-OES) can analyze the composition of the whole electrocatalytic oxygen evolution material Fe-Co-Se-P / CC, the results are shown in Table 2.

[0061] Table 2

[0062]

[0063] The results of ICP-OES in Table 2 reflect that the percentage of P doping is 0.4 / (0.4+3.6) = 0.1 (the doping ratio is calculated by the content of phosphorus divided by the total amount of selenium and phosphorus). The comparison of the two results shows that the P content on the surface of the electrocatalytic oxygen evolution material Fe-Co-Se-P / CC is higher than that in the bulk phase, which directly indicates that the dopant is mainly distributed on the surface of the electrocatalytic oxygen evolution material Fe-Co-Se-P / CC. This structure is very conducive to the surface reconstruction that occurs during the OER process, forming a real active substance (oxyhydroxide), plus the internal selenide can always maintain high conductivity, accelerating the transfer of electrons, so the material has very high electrocatalytic oxygen evolution activity.

[0064] Example 4

[0065] The electrochemical performance of Fe-Co-Se-P / CC synthesized in Example 1 in 1 M KOH solution at room temperature was studied using a standard three-electrode system. In order to compare, Fe-Co-Precursor / CC, Fe-Co-Se / CC and commercial RuO2 / CC with the same loading were also tested under the same conditions. In addition to the above three samples, Fe-Co-Se-P 0.5 / CC, Fe-Co-Se-P 1.5 / CC with different phosphorus doping amounts of Example 2 and Example 3 and bare carbon cloth (CC) were also detected as control samples.

[0066] To eliminate the solution resistance in the reaction process, the data of linear scan voltammetry (LSV) were compensated by 90% iR. The results are shown in Figures 6-8 . Figure 6 The electrocatalytic performance graphs of Fe-Co-Precursor / CC, Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1, wherein (a) is the LSV graph, (b) is the Tafel graph, (c) is the EIS graph, and (d) is the C dl graph. Figure 7 The electrocatalytic performance graphs of Fe-Co-Se-P / CC synthesized in Example 1, Fe-Co-Se-P 0.5 / CC synthesized in Example 2 and Fe-Co-Se-P 1.5 / CC synthesized in Example 3, wherein (a) is the LSV graph, (b) is the Tafel graph, (c) is the EIS graph, and (d) is the C dl graph. Figure 8 The overpotential graphs of Fe-Co-Precursor / CC, Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1, Fe-Co-Se-P 0.5 / CC synthesized in Example 2 and Fe-Co-Se-P 1.5 / CC synthesized in Example 3 at 10 mA cm -2 current density.

[0067] It can be seen from Figure 6 (a) and Figure 8 together that the overpotential of Fe-Co-Se-P / CC is the lowest, which is 210 mV at 10 mA cm -2 current density. The other comparative samples cannot realize the oxygen evolution reaction at the same small overpotential at the same current density, especially Figure 7 (a) reflects that in the process of gradually increasing the amount of phosphorus doping, the OER performance of Fe-Co-Se-P 0.5 / CC, Fe-Co-Se-P / CC and Fe-Co-Se-P 1.5 / CC does not increase in direct proportion, but the Fe-Co-Se-P / CC containing 0.1 doping amount has the best catalytic ability. It is well known that the kinetics is very high for the complex four-electron reaction process of OER. The Tafel slope is often used as an index to test the kinetics of OER, and the smaller the Tafel slope is, the faster the chemical reaction kinetics is. From Figure 6 (b) and Figure 7 (b), it can be seen that the Tafel slope of Fe-Co-Se-P / CC is 45.3 mV dec -1 , while the Tafel slope of Fe-Co-Se-P0.5 / CC, Fe-Co-Se-P 1.5 The slope values of / CC, Fe-Co-Se / CC, Fe-Co Precursor / CC, RuO2 / CC and / CC are all larger. This result shows that after the P element is doped with 0.1, the rate determining step (RDS) of Fe-Co-Se-P / CC in the catalytic reaction has been changed to the third electron transfer reaction, which is beneficial to generate a large number of active intermediates (Fe(Co)OOH). It can be concluded that the introduction of P greatly affects the binding energy of the electrocatalytic oxygen evolution material for OH - , promotes the formation of active intermediates, thereby changing the OER reaction process, and obtaining faster reaction kinetics.

[0068] In addition, in the charge transfer kinetics study, electrochemical impedance spectroscopy (EIS) is mainly used to study the mass transfer effect between the electrode and the electrolyte. From Figure 6 (c), Figure 7 (c) and Table 3 (Table 3 is the fitting data of EIS diagram to equivalent circuit, including solution diffusion resistance (Rs) and charge transfer resistance (Rct) with parallel constant phase element (CPE)) can be directly seen that in all the comparative examples, Fe-Co-Se-P / CC has the smallest Rct (12.5 Ω). This shows that after P doping, the electron transfer of Fe-Co-Se / CC is greatly improved. Fe-Co-Se-P / CC has the most favorable interface charge transfer kinetics for water oxidation.

[0069] Table 3

[0070]

[0071] The electrochemical specific surface area (ECSA) is another important basis for testing whether the electrocatalytic oxygen evolution material has excellent OER electrocatalytic performance. Therefore, the cyclic voltammetry (CV) curve of the electrocatalytic oxygen evolution material in the potential range of 0.05-0.5 V vs RHE was tested, and the results are shown in Figure 9 , Figure 9 CV curves of Fe-Co-Precursor / CC, Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1, Fe-Co-Se-P / CC synthesized in Example 2 and Fe-Co-Se-P / CC synthesized in Example 3, wherein (a) is the CV curve of Fe-Co-Se-P / CC, (b) is the CV curve of Fe-Co-Se-P / CC, (c) is the CV curve of Fe-Co-Se-P / CC. 0.5 1.5 0.5 1.5 ​​​(d) is the Fe-Co-Se / CC plot, and (e) is the Fe-Co-Precursor / CC plot. Then, the bilayer capacitance (C0) of each electrocatalytic oxygen evolution material was calculated using its CV curves. dl ),See Figure 6 (d) and Figure 7 (d). C of Fe-Co-Se-P / CC dl (89.07mF cm -2 The phosphorus content was the highest among all prepared samples. This result indicates that Fe-Co-Se-P / CC exhibits unparalleled advantages in terms of active sites and oxygen evolution surface area after appropriate phosphorus doping.

[0072] Contact angles of the Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1 were measured under the same conditions, and the results are as follows: Figure 10 As shown, Figure 10 The figures show the hydrophilic contact angles of Fe-Co-Se / CC and Fe-Co-Se-P / CC synthesized in Example 1. (a) shows the hydrophilic contact angle of Fe-Co-Se / CC synthesized in Example 1, and (b) shows the hydrophilic contact angle of Fe-Co-Se-P / CC synthesized in Example 1. Since the hydrophilicity of the material greatly affects the electrolyte penetration during the catalytic process, a smaller contact angle between the electrocatalytic oxygen evolution material and water indicates higher hydrophilicity. Figure 10 As shown in (a) and (b), the contact angle between the Fe-Co-Se-P film and water (θ = 26°) is smaller than that of the Fe-Co-Se film (θ = 54°), indicating that P doping is beneficial for increasing the contact area between the electrocatalytic oxygen evolution material and water. The excellent wetting properties of Fe-Co-Se-P and water reflect its good hydrophilicity, which is very beneficial for the OER reaction. Therefore, Fe-Co-Se-P / CC is a very promising electrocatalytic oxygen evolution material for catalytic water splitting to produce oxygen.

[0073] Besides the above characteristics, stability and durability are also important indicators for evaluating whether electrocatalytic oxygen evolution materials are suitable for practical applications. Stability was assessed using normalized current-time (it) curves. The results are as follows... Figure 11 As shown, Figure 11 The figure shows the chronovoltametry of Fe-Co-Se-P / CC synthesized in Example 1 at 1.65V vs. RHE. Figure 11 It can be seen that at a current density of 50 mA cm⁻¹ -2 Under these conditions, the current density loss rate was less than 5% within 30 hours. Next, to verify durability, the Fe-Co-Se-P / CC synthesized in Example 1 was subjected to 1000 cycles of continuous CV scan testing. The results are as follows... Figure 12 As shown,Figure 12 LSV plots of Fe-Co-Se-P / CC synthesized in Example 1 before and after 1000 CV cycles. As can be seen from Figure 12, the loss of current density and overpotential can be negligible.

[0074] In addition, the XRD, SEM, TEM and XPS spectra of Fe-Co-Se-P / CC synthesized in Example 1 after OER cycling were also tested, as shown in Figure 13 and Figure 14 for further study on the structure and composition of the tested Fe-Co-Se-P / CC.

[0075] Figure 13 XRD, SEM, TEM and HRTEM of Fe-Co-Se-P / CC synthesized in Example 1 after stability test, wherein (a) is the XRD pattern, (b) is the SEM pattern, (c) is the TEM pattern, (d) is the HRTEM pattern, (e) is the SAED pattern, (d1) is the magnified view of No. 1 yellow area in (d) (d2) is the magnified view of No. 2 yellow area in (d) (d3) is the magnified view of No. 3 yellow area in (d). As can be seen from Figure 13 It can be found that after OER test, Figure 13 (a), (b), (c), (d) and (e) show that the structure and composition of the electrocatalytic oxygen evolution material have no obvious change.

[0076] Figure 14 XPS of Fe-Co-Se-P / CC synthesized in Example 1 after stability test, wherein (a) is the full spectrum of Fe-Co-Se-P / CC after stability test, (b) is the Fe 2p high resolution spectrum of Fe-Co-Se-P / CC after stability test, (c) is the Co 2p high resolution spectrum of Fe-Co-Se-P / CC after stability test, (d) is the Se 3d high resolution spectrum of Fe-Co-Se-P / CC after stability test, (e) is the P 2p high resolution spectrum of Fe-Co-Se-P / CC after stability test, (f) is the O 1s high resolution spectrum of Fe-Co-Se-P / CC after stability test. In Figure 14 In (c), in the Co 2p spectrum after OER test, Co 3+ The peak at 780.02 eV is stronger than Co 2+ The peak at 783.08 eV is stronger, and the shoulder peak is weakened, which proves that the original Co 2+ state is oxidized, and active intermediate CoOOH is formed in the catalytic process. In Figure 14(b) In the Fe 2p spectrum, the peak at 713.98 eV can be attributed to the binding energy of iron in FeOOH. In addition, the peaks at 711.48 eV and 710.48 eV in the Fe 2p spectrum can be attributed to the binding energy of iron in Fe2O3 and Fe3O4, respectively. Figure 14 (f) In the O 1s spectrum, the peaks at 529.48 eV and 529.48 eV correspond to oxygen in oxides / hydroxides.

[0077] Based on the above characterization, the real active substance Fe(Co)OOH indeed appeared in the OER test, which is conducive to the progress of water electrolysis. All these findings show that Fe-Co-Se-P / CC has significant OER stability and durability, which makes it promising for use in commercial applications.

[0078] In summary, it can be concluded that Fe-Co-Se / CC obtained by hydrothermal and hot selenization method, when the surface of which is doped with 0.1 P element, can obtain Fe-Co-Se-P / CC electrocatalytic oxygen evolution material with the best electrocatalytic oxygen evolution performance. Due to the introduction of appropriate content of P, the electrocatalytic oxygen evolution material has high density of active sites, reduced water decomposition reaction energy barrier and accelerated reaction kinetics. It is also clear through the contact angle test that the introduction of P element effectively increases the roughness of the material surface, improves the hydrophilicity of the electrocatalytic oxygen evolution material, promotes the release of gas bubbles, realizes the effective regulation of the surface of the electrocatalytic oxygen evolution material, and finally improves the OER performance of the electrocatalytic oxygen evolution material. Overall, the present application provides more abundant choices for the design of transition metal OER electrocatalytic oxygen evolution materials, and promotes the development of electrocatalytic oxygen production towards high efficiency and low cost.

Claims

1. A method for preparing a P-doped Fe-Co-Se electrocatalytic oxygen evolution material, characterized in that, The preparation method comprises the following steps: (1) dissolving Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Co(NH2)2 and NH4F in deionized water, and then performing ultrasonic treatment to obtain a mixed solution; placing carbon cloth subjected to ultrasonic treatment for 0.5-1.5 h by using a mixed solution of HNO3 and H2SO4 at a volume ratio of 2-4:1 into the mixed solution, and then performing hydrothermal reaction; cleaning; and vacuum drying to obtain a precursor Fe-Co-Precursor / CC, wherein the molar ratio of Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Co(NH2)2 and NH4F is 0.2-0.4:0.2-0.4:1:1; (2) placing the precursor Fe-Co-Precursor / CC into the downstream of a tube furnace, placing Se powder into the upstream of the tube furnace, and then performing selenization reaction; water washing; and vacuum drying to obtain Fe-Co-Se / CC, wherein the addition amount of the Se powder is 0.5-1 g; (3) placing Fe-Co-Se / CC into the downstream of a tube furnace, placing a phosphorus source into the upstream of the tube furnace, and then performing phosphorization reaction; cooling; cleaning; and vacuum drying to obtain Fe-Co-Se-P / CC, wherein the addition amount of the phosphorus source is 0.15-0.45 g. In step (1), the temperature of the hydrothermal reaction is 110-130 °C, and the time of the hydrothermal reaction is 11-13 h.

2. The production method according to claim 1, characterized by, In step (1), the ultrasonic treatment is performed until the solution is transparent and uniform, and the cleaning is repeatedly performed by using deionized water and anhydrous ethanol to clean the carbon cloth on which the precursor Fe-Co-Precursor is grown.

3. The preparation method according to claim 1, characterized in that, In step (3), the phosphorus source is NaH2PO2·H2O, and the phosphorization reaction is heating at 300-400 °C for 1-3 h under a nitrogen atmosphere.

4. The method of claim 1, wherein, In step (2), the calcination heating rate of the selenylation reaction is 1-3 °C min -1 selenylation at 300-400 °C for 1-3 h under a nitrogen atmosphere.

5. The preparation method according to claim 1, characterized in that, In steps (1), (2) and (3), the temperature of the vacuum drying is 55-65 °C.

6. The production method according to claim 1, characterized by, 7. A P-doped Fe-Co-Se electrocatalytic oxygen evolution material obtained by the preparation method according to any one of claims 1-6.

8. Application of the P-doped Fe-Co-Se electrocatalytic oxygen evolution material according to claim 7 in electrocatalytic oxygen evolution. ​

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