Iron-selenium double-site full-pH oxygen reduction catalyst as well as preparation method and application thereof

Abstract

The invention discloses an iron-selenium double-site full-pH oxygen reduction catalyst as well as a preparation method and application thereof, and belongs to the technical field of electrochemical energy conversion and catalytic materials. The oxygen reduction catalyst is an iron-selenium double-site full-pH oxygen reduction catalyst FeSe-NC obtained by anchoring iron and selenium on a nitrogen-doped carbon matrix through secondary pyrolysis respectively. The prepared double-site catalyst FeSe-NC has excellent oxygen reduction activity and stability in different media, and a non-noble metal catalyst is promoted to evolve towards full pH and high stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrochemical energy conversion and catalytic materials, and particularly relates to a full-pH range oxygen reduction reaction catalyst based on iron-selenium (Fe-Se) double active sites, a preparation method thereof and application thereof in metal-air batteries. BACKGROUND

[0002] Oxygen reduction (ORR) is a core chemical process in electrochemical energy storage and conversion technology, and the level of its reaction activity directly determines the efficiency and service life of new energy devices such as fuel cells and metal-air batteries. To achieve efficient and stable operation of the oxygen reduction reaction in various energy devices, the key is to find catalysts that can precisely control the reaction process and significantly improve the reaction efficiency. For a long time, improving the efficiency and stability of catalysts in alkaline or acidic media has been the focus of ORR research, which to some extent limits the application expansion of ORR in diversified environments such as neutral medium and seawater. In view of the increasingly urgent demand for efficient and stable energy conversion technology, exploring and constructing a catalyst system that can efficiently drive the oxygen reduction reaction under various environmental conditions has become a key scientific problem to be solved at present.

[0003] Although platinum group metal catalysts have high catalytic activity, their scarcity and insufficient stability have prompted researchers to focus on transition metal catalysts and expect them to be an economic alternative to noble metals. Among the many transition metal catalysts, Fe-NC has become the most promising alternative due to its high electrical conductivity and intrinsic activity. The catalytic dynamics of Fe-NC mainly come from the interaction between the adsorbed species and the orbital of the active site, but it also faces many challenges in different environmental conditions. In neutral electrolyte, the lower ionic conductivity will limit the adsorption and conversion of oxygen intermediates (such as ·OH), resulting in a slow ORR reaction kinetics process; in acidic electrolyte, the Fenton effect of Fe-NC will cause significant activity decay. Therefore, a single structure form is difficult to meet the requirements of the catalyst to continuously maintain high efficiency in a complex and variable environment. To solve the above problems, introducing other atoms to construct a heteronuclear dual-site strategy provides a new idea to improve the conversion efficiency of the catalyst. Previous studies have mainly focused on the construction of double-d-region metal catalysts, but the problems brought by multi-metal sites still need to be solved, as follows: The synthesis process usually involves complex precursors and high-temperature treatment processes, which makes the synthesis process difficult to control, resulting in uneven distribution of active sites; in addition, d-region elements are easy to interact with other substances, generating structures that are not conducive to catalytic reactions, such as metal carbide-like structures or metal-metal bond combination forms. This structural change will significantly reduce the atomic dispersion, making it difficult for the catalyst activity to reach the ideal level. At the same time, multi-metal sites also face the challenge of the contradiction of synergistic effect, that is, the double-metal site may weaken the adsorption / desorption ability of the key intermediate due to electronic competition (such as d-d orbital hybridization). SUMMARY

[0004] The present application mainly aims at the problems of insufficient activity and poor stability of the oxygen reduction catalyst in the prior art under neutral, alkaline and acidic conditions, and the high dependence on noble metals, and provides an iron-selenium dual-site full-pH oxygen reduction catalyst, a preparation method and application thereof. The present application realizes the efficient oxygen reduction performance of the non-noble metal catalyst in a wide pH range through the synergistic effect of iron-selenium dual sites. The present application combines the performance regulation advantage of p-region element selenium doping and the dual-site synergistic catalysis design concept, and provides a key solution for developing a low-cost and high-adaptability generation of clean energy devices.

[0005] To achieve the above application purposes, the technical scheme adopted by the present application is as follows: an iron-selenium dual-site full-pH oxygen reduction catalyst is an iron-selenium dual-site full-pH oxygen reduction catalyst FeSe-NC obtained by anchoring iron and selenium on a nitrogen-doped carbon matrix through secondary pyrolysis.

[0006] A preparation method of an iron-selenium dual-site full-pH oxygen reduction catalyst, comprising the following steps:

[0007] 1) dissolving a precursor zinc salt in anhydrous methanol to obtain solution A; dissolving a precursor ferric salt and 2-methylimidazole in anhydrous methanol to obtain solution B; slowly injecting solution A into solution B at room temperature, continuously stirring for 10-24 hours, centrifugally separating the obtained mixture, washing with methanol, and vacuum drying to obtain Fe@ZIF-8;

[0008] 2) pyrolyzing Fe@ZIF-8 in a tube furnace under inert gas protection, and naturally cooling to room temperature to obtain Fe-NC;

[0009] 3) mixing Fe-NC and SeO2 powder, grinding and uniformly mixing, transferring to a quartz boat, and pyrolyzing in inert gas to obtain iron-selenium dual-site full-pH oxygen reduction catalyst FeSe-NC.

[0010] Further, in step 1), the zinc salt is selected from zinc nitrate, zinc chloride, zinc acetate or zinc acetylacetonate.

[0011] Further, in step 1), the ferric salt is selected from ferric acetylacetonate, ferric nitrate, ferric chloride or ferric acetate.

[0012] Further, in step 1), the molar ratio of zinc salt to ferric salt is 1:(0.05-0.5).

[0013] Further, in step 2), the inert gas is nitrogen or argon; the pyrolysis is performed at a heating rate of 3-5℃·min -1 -5℃·min -1 , a pyrolysis temperature of 800-1000℃, and a pyrolysis time of 1.5-3 hours.

[0014] Further, in step 3), the mass ratio of Fe-NC to SeO2 is 1:(1-2).

[0015] Further, in step 3), the inert gas is nitrogen or argon; the pyrolysis is performed at a heating rate of 3-5℃·min -1 -5℃·min -1 , a pyrolysis temperature of 800-1000℃, and a pyrolysis time of 1-2 hours.

[0016] The application provides a use of the iron-selenium dual-site full-pH oxygen reduction catalyst FeSe-NC in a metal-air battery.

[0017] Further, the method is as follows: loading FeSe-NC composite carbon paper as a cathode, zinc foil as an anode to assemble a zinc-air battery device, and an electrolyte being a 6mol·L -1 KOH solution containing 0.2mol·L -1 KOH or a 6mol·L -14 mol·L -1 NH4Cl and 2 mol·L -1 KCl mixed solution.

[0018] The beneficial effects of the present application are:

[0019] 1. The present application solves the problems of stability and activity of Fe-NC catalyst under neutral / acidic conditions by p-region non-metallic element doping and heteronuclear double site structure, aiming at the insufficient activity of Fe-NC catalyst under neutral / acidic conditions and the complexity of multi-metal site design. The FeSe double site oxygen reduction catalyst constructed by non-metallic selenium doping exhibits high efficiency and stable operation performance in the full pH range, providing direction and strong reference for the development of high-performance full-pH range oxygen reduction catalysts in the future.

[0020] 2. The present application successfully prepares FeSe-NC double site oxygen reduction catalyst by adopting a two-step pyrolysis strategy to anchor Fe and Se on a nitrogen-doped carbon matrix. The two-step pyrolysis strategy effectively improves the graphitization degree of the catalyst, promotes the uniform dispersion of FeSe sites in the catalyst, and ensures the appropriate loading amount of FeSe sites.

[0021] 3. The iron-selenium double site full-pH oxygen reduction catalyst prepared by the present application utilizes the interaction between iron and selenium to optimize the catalyst, which exhibits excellent electrocatalytic oxygen reduction activity in the full pH range. Among them, the E 1.2 of FeSe1-NC in 0.1M PBS, 0.1M KOH solution and 0.5M H2SO4 solution is 0.788V, 0.872V and 0.747V, respectively. 1 / 2 The open-circuit voltage of the assembled alkaline liquid zinc-air battery and neutral liquid zinc-air battery is as high as 1.51V and 1.39V, and the peak power density can reach 143.8Mw·cm -2 and 47.4mW·cm -2 , respectively. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The SEM image (a) of Fe 1.2 @ZIF-8, the TEM image (b) of Fe 1.2 -NC, the TEM image (c) of Fe 1.2 Se1-NC and the EDS spectrum (d) prepared in Example 1.

[0023] Figure 2 The XRD spectrum of Fe x Se1-NC prepared in Example 1.

[0024] Figure 3 The XRD spectrum of Fe1.2 Nitrogen adsorption / desorption plot of Se1-NC.

[0025] Figure 4 Fe prepared for Example 1 1.2 LSV plot (a) and H2O2 yield / number of transferred electrons (b) of Se1-NC in neutral medium.

[0026] Figure 5 Fe prepared for Example 1 1.2 LSV plot (a, c) and H2O2 yield / number of transferred electrons (b, d) of Se1-NC in alkaline and acidic medium.

[0027] Figure 6 Fe prepared for Example 1 1.2 LSV plot (a), (b), (c) and I-t chronoresponse (d), (e), (f) of Se1-NC in 0.1 M PBS, 0.1 M KOH and 0.5 M H2SO4 medium respectively before and after 3k consecutive cycles.

[0028] Figure 7 Fe prepared for Example 1 1.2 Discharge power density plot (a), open circuit voltage (b) and cycling stability (c) of Se1-NC in alkaline and neutral liquid zinc-air batteries.

[0029] Figure 8 Fe prepared for Example 1, 3 and 4 respectively x Se1-NC, Fe 1.2 Se1-NC / 800 and Fe 1.2 LSV plot of Se1-NC / 900 in 0.1 M PBS medium. DETAILED DESCRIPTION

[0030] Example 1 Iron-selenium dual site all-pH oxygen reduction catalyst (Fe x Se1-NC)

[0031] (i) Preparation of Fe x Se1-NC was prepared as follows:

[0032] 1. Synthesis of Fe x @ZIF-8

[0033] Dissolve zinc nitrate hexahydrate (1.6659 g, 5.6 mmol) in 20 mL of methanol to obtain solution A. Dissolve iron trisacetylacetonate (0.4 mmol, 0.8 mmol, 1.2 mmol, 1.6 mmol, 2 mmol, 2.8 mmol, 3.6 mmol) and 2-methylimidazole (1.8390 g) in 45 mL of methanol, respectively, to obtain solution B. Slowly inject solution A into solution B and stir at room temperature for 12 h. After the reaction is completed, a brick red suspension is obtained, and the solid is collected by centrifugation. The collected solid is washed with methanol until the solution is colorless, and finally placed in a vacuum oven at 60°C for 12 h to obtain Fe x @ZIF-8, Fe 0.4 @ZIF-8, Fe 0.8 @ZIF-8, Fe 1.2 @ZIF-8, Fe 1.6 @ZIF-8, Fe2@ZIF-8, Fe 2.8 @ZIF-8, Fe 3.6 @ZIF-8.

[0034] 2, Fe x Synthesis of Fe

[0035] Dissolve Fe x @ZIF-8 obtained in step 1 in methanol to obtain solution A. Dissolve iron trisacetylacetonate (0.4 mmol, 0.8 mmol, 1.2 mmol, 1.6 mmol, 2 mmol, 2.8 mmol, 3.6 mmol) in 45 mL of methanol to obtain solution B. Slowly inject solution A into solution B and stir at room temperature for 12 h. After the reaction is completed, a brick red suspension is obtained, and the solid is collected by centrifugation. The collected solid is washed with methanol until the solution is colorless, and finally placed in a vacuum oven at 60°C for 12 h to obtain Fe -1 @ZIF-8, Fe x @ZIF-8, Fe 0.4 @ZIF-8, Fe 0.8 @ZIF-8, Fe 1.2 @ZIF-8, Fe 1.6 @ZIF-8, Fe2@ZIF-8, Fe 2.8 @ZIF-8, Fe 3.6 @ZIF-8.

[0036] 3, Fe x Synthesis of Fe

[0037] Mix Fe x @ZIF-8 powder obtained in step 2 and SeO2 in a mass ratio of 1:1, grind uniformly, and then transfer and lay flat in a quartz boat. Place the quartz boat in a tube furnace, heat to 1000°C at a heating rate of 5°C·min -1 -1 in argon, and keep for 1 h. After cooling to room temperature, take out the black powder, which is Fe x Se1-NC, sequentially named Fe 0.4 Se1-NC, Fe 0.8 Se1-NC, Fe 1.2Se1-NC, Fe 1.6 Se1-NC, Fe2Se1-NC, Fe 2.8 Se1-NC, Fe 3.6 Se1-NC.

[0038] (II) Comparative Example 1 - Iron site catalyst Fe-NC

[0039] The preparation method is as follows: Fe 1.2 -NC was prepared by mixing the obtained ZIF-8 and SeO2 powders in a mass ratio of 1:1, grinding and uniformly mixing, and then transferring and laying flat in a quartz boat. The quartz boat was placed in a tube furnace and heated to 1000°C at a heating rate of 5°C·min -1 -1 under argon for 1 h, and the black powder was removed after cooling to room temperature to obtain the catalyst Fe-NC.

[0040] (III) Comparative Example 2 - Selenium site catalyst Se-NC

[0041] The preparation method is as follows:

[0042] 1. Synthesis of ZIF-8

[0043] Dissolve zinc nitrate hexahydrate (1.6659 g) in 20 mL of methanol to obtain solution A. Dissolve 2-methylimidazole (1.8390 g) in 45 mL of methanol to obtain solution B. Slowly inject solution A into solution B and stir at room temperature for 12 h. After the reaction is completed, a white suspension is obtained, and the solid is collected by centrifugation. The collected solid is washed with methanol several times, and finally placed in a vacuum oven at 60°C for 12 h to obtain ZIF-8.

[0044] 2. Synthesis of NC

[0045] The obtained ZIF-8 was laid flat in a quartz boat and placed in a tube furnace under argon protection, heated to 900°C at a heating rate of 5°C·min -1 -1, and pyrolyzed for 2 h to obtain black powder NC.

[0046] 3. Synthesis of Se-NC

[0047] The NC powder and SeO2 powder were mixed in a mass ratio of 1:1, ground and uniformly mixed, and then transferred and laid flat in a quartz boat. The quartz boat was placed in a tube furnace and heated to 1000°C at a heating rate of 5°C·min -1 -1 under argon for 1 h, and the black powder was removed after cooling to room temperature to obtain the catalyst Se-NC.

[0048] (IV) Characterization

[0049] The prepared catalyst Fe xSe1-NC was subjected to scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, nitrogen adsorption / desorption, and inductively coupled plasma atomic emission spectroscopy.

[0050] Figure 1 For the preparation of Fe 1.2 SEM image of ZIF-8 (a), Fe 1.2 TEM image of -NC (b), Fe 1.2 TEM image (c) and EDS spectrum (d) of Se1-NC. Figure 1 It can be seen that the precursor Fe 1.2 @ZIF-8 exhibits a uniformly sized rhombic dodecahedral structure. After two pyrolysis treatments, the catalyst still maintains its initial dodecahedral morphology with only slight size shrinkage. Figure 1 The energy dispersive spectrum (EDS) plot presented by d indicates that Fe 1.2 The Fe, Se, C, N and O elements are evenly distributed in Se1-NC.

[0051] Figure 2 For the preparation of Fe x XRD pattern of Se1-NC. (From...) Figure 2 It can be seen that the broadened diffraction peaks at 26° and 44° correspond to the (002) and (101) crystal planes of graphite carbon, respectively.

[0052] Figure 3 For the preparation of Fe 1.2 Nitrogen adsorption / desorption diagram for Se1-NC. (From...) Figure 3 It can be seen that Fe 1.2 The Se1-NC catalyst exhibits a typical type IV curve and an H4 type hysteresis loop, confirming its rich microporous-mesoporous hierarchical porous structure, with a BET specific surface area as high as 1250 m². 2 ·g -1 .

[0053] Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis showed that Fe 1.2 Se 1- The atomic loadings of iron and selenium in NC were 2.45 wt.% and 3.45 wt.%, respectively.

[0054] Example 2: Iron-selenium dual-site full-pH oxygen reduction catalyst (Fe x Se2-NC)

[0055] The preparation method is as follows:

[0056] 1. Fe x Synthesis of @ZIF-8

[0057] Same as in Example 1, Fe was obtained respectively. 0.4ZIF-8, Fe 0.8 ZIF-8, Fe 1.2 ZIF-8, Fe 1.6 ZIF-8, Fe2ZIF-8, Fe 2.8 ZIF-8, Fe 3.6 ZIF-8.

[0058] 2, Fe x Synthesis of Fe

[0059] The same as Example 1, respectively obtained Fe 0.4 -NC, Fe 0.8 -NC, Fe 1.2 -NC, Fe 1.6 -NC, Fe2-NC, Fe 2.8 -NC, Fe 3.6 -NC.

[0060] 3, Fe x Synthesis of Fe

[0061] According to the mass ratio of 1:2, respectively Fe x -NC powder obtained in step 2 and SeO2 were mixed, grinded and mixed uniformly, then transferred and laid flat in a quartz boat. The quartz boat was placed in a tube furnace, heated to 1000℃ at a rate of 5℃·min -1 -1 in argon, and kept for 1h, and the black powder was taken out after cooling to room temperature, which was Fe x Se2-NC, named as Fe 0.4 Se2-NC, Fe 0.8 Se2-NC, Fe 1.2 Se2-NC, Fe 1.6 Se2-NC, Fe2Se2-NC, Fe 2.8 Se2-NC, Fe 3.6 Se2-NC.

[0062] Example 3 Iron-selenium dual-site all-pH oxygen reduction catalyst (Fe x Se1-NC / 800)

[0063] The preparation method is as follows:

[0064] 1, Fe x Synthesis of Fe

[0065] The same as Example 1, respectively obtained Fe 0.4 @ZIF-8, Fe 0.8 @ZIF-8, Fe 1.2 @ZIF-8, Fe 1.6@ZIF-8、Fe2@ZIF-8、Fe 2.8 @ZIF-8、Fe 3.6 @ZIF-8.

[0066] 2. Fe x -NC Synthesis

[0067] Same as in Example 1, Fe was obtained respectively. 0.4 -NC、Fe 0.8 -NC、Fe 1.2 -NC、Fe 1.6 -NC, Fe2-NC, Fe 2.8 -NC、Fe 3.6 -NC.

[0068] 3. Fe x Synthesis of Se1-NC / 800

[0069] The Fe obtained in step 2 were mixed at a mass ratio of 1:1. x - NC powder and SeO2 are mixed, ground until homogeneous, and then transferred and spread evenly in a quartz boat. The quartz boat is placed in a tube furnace and heated at 5°C / min in argon atmosphere. -1 The temperature was increased to 800℃ at a certain rate and held for 1 hour. After cooling to room temperature, the black powder was removed, which is Fe. x Se1-NC / 800, named sequentially as Fe 0.4 Se1-NC / 800, Fe 0.8 Se1-NC / 800, Fe 1.2 Se1-NC / 800, Fe 1.6 Se1-NC / 800, Fe2Se1-NC / 800, Fe 2.8 Se1-NC / 800, Fe 3.6 Se1-NC / 800.

[0070] Example 4: Iron-selenium dual-site full-pH oxygen reduction catalyst (Fe x Se1-NC / 900)

[0071] The preparation method is as follows:

[0072] 1. Fe x Synthesis of @ZIF-8

[0073] Same as in Example 1, Fe was obtained respectively. 0.4 @ZIF-8、Fe 0.8 @ZIF-8、Fe 1.2 @ZIF-8、Fe 1.6 @ZIF-8、Fe2@ZIF-8、Fe 2.8 @ZIF-8、Fe3.6 @ZIF-8.

[0074] 2. Fe x -NC Synthesis

[0075] Same as in Example 1, Fe was obtained respectively. 0.4 -NC、Fe 0.8 -NC、Fe 1.2 -NC、Fe 1.6 -NC, Fe2-NC, Fe 2.8 -NC、Fe 3.6 -NC.

[0076] 3. Fe x Synthesis of Se1-NC / 900

[0077] The Fe obtained in step 2 were mixed at a mass ratio of 1:1. x - NC powder and SeO2 are mixed, ground until homogeneous, and then transferred and spread evenly in a quartz boat. The quartz boat is placed in a tube furnace and heated at 5°C / min in argon atmosphere. -1 The temperature was increased to 900℃ at a certain rate and held for 1 hour. After cooling to room temperature, the black powder was removed, which is Fe. x Se1-NC / 900, named sequentially as Fe 0.4 Se1-NC / 900, Fe 0.8 Se1-NC / 900, Fe 1.2 Se1-NC / 900, Fe 1.6 Se1-NC / 900, Fe2Se1-NC / 900, Fe 2.8 Se1-NC / 900, Fe 3.6 Se1-NC / 900.

[0078] Example 5: Iron-Selenium Dual-Site Full-pH Oxygen Reduction Catalyst Fe 1.2 Electrochemical performance of Se1-NC (I) Fe 1.2 Oxygen reduction activity test of Se1-NC catalyst in neutral medium

[0079] Test method: 5 mg of Fe prepared in Example 1 was used. 1.2 Se1-NC catalyst was dispersed in 950 μL of ethanol and 50 μL of 5% Nafion solution, and homogeneous Fe was obtained by sonication. 1.2 Se1-NC catalyst ink. 20 μL Fe... 1.2Se1-NC catalyst ink was drop-casted on the surface of a rotating ring-disk electrode and air-dried. The oxygen reduction activity of the catalyst was tested in 0.1 M PBS (pH 7.0) solution saturated with O2. Electrochemical measurements were performed on a CHI 760E electrochemical workstation using a three-electrode system: the working electrode was a rotating ring-disk electrode (RRDE), the counter electrode was a carbon rod, and the reference electrode was an Ag / AgCl electrode. Catalysts Fe-NC, Se-NC, and Pt / C were used as controls.

[0080] The oxygen reduction activity of Fe 1.2 Se1-NC, Fe-NC, Se-NC, and Pt / C in oxygen-saturated PBS solution was measured and evaluated by RRDE. Figure 4 LSV curves (a) show that Fe 1.2 The half-wave potential (E 1 / 2 ) of Se1-NC catalyst in 0.1 M PBS solution was 0.788 V, and the limiting current density (j L ) was 5.14 mA·cm -2 , which was significantly better than the controls Fe-NC, Se-NC, and commercial Pt / C. Figure 4 H2O2 yield / electron number transferred (b) shows that the H2O2 yield of Fe 1.2 Se1-NC was less than 1%, and the electron number transferred (n) ranged from 3.94 to 3.97 between 0.1 V and 0.6 V, indicating that the oxygen reduction process catalyzed by Fe 1.2 Se1-NC was more inclined to 4-electron transfer.

[0081] (II) Oxygen reduction activity test of Fe 1.2 Se1-NC catalyst in alkaline and acidic media

[0082] Test method: 5 mg of Fe 1.2 Se1-NC catalyst prepared in Example 1 was dispersed in 950 μL of ethanol and 50 μL of 5% Nafion solution, and ultrasonic treatment was used to obtain a uniform Fe 1.2 Se1-NC catalyst ink. 20 μL of Fe 1.2 Se1-NC catalyst ink was drop-casted on the surface of a rotating ring-disk electrode and air-dried. The oxygen reduction activity of the catalyst was tested in 0.1 M KOH solution and 0.5 M H2SO4 solution saturated with O2. Electrochemical measurements were performed on a CHI 760E electrochemical workstation using a three-electrode system: the working electrode was a rotating ring-disk electrode (RRDE), the counter electrode was a carbon rod, and the reference electrode was an Ag / AgCl electrode. Catalyst Pt / C was used as a control.

[0083] Figure 5 LSV curves (a, c) show that Fe1.2 H2O2 yield / number of transferred electrons (b, d) in 0.1 M KOH and 0.5 M H2SO4 solutions, respectively, demonstrate that Fe 1 / 2 are 0.872 V and 0.747 V, respectively, j L are 6.79 mA·cm -2 and 6.85 mA·cm -2 . Figure 5 H2O2 yield / number of transferred electrons (b, d) in 0.1 M KOH and 0.5 M H2SO4 solutions, respectively, demonstrate that Fe 1.2 The H2O2 yield of Se1-NC catalyst in 0.1 M KOH and 0.5 M H2SO4 solutions at 0.4 V potential is 1.62% and 2.13%, respectively, and n is 3.97 and 3.93, respectively, which is still superior to commercial Pt / C.

[0084] (Three) Fe 1.2 Stability test of Se1-NC catalyst in different media

[0085] Test method: Fe 1.2 The evaluation methods of the stability of Se1-NC catalyst are as follows: one is accelerated durability test (ADT), and the other is chronoamperometry (I-t). Specifically, ADT evaluates the performance of the catalyst by comparing the linear sweep voltammetry (LSV) curves before and after 3000 cycles of cyclic voltammetry (CV) scanning in oxygen-saturated electrolyte. The chronoamperometry test evaluates the current retention ability of the catalyst by real-time monitoring of the current change during the continuous operation of the catalyst for 24 h, thereby reflecting the stability of the catalyst.

[0086] Figure 6 Fe 1.2 Se1-NC prepared in Example 1, LSV curves (a), (b), (c) and I-t chronoamperometric responses (d), (e), (f) before and after 3k continuous cycles in 0.1 M PBS, 0.1 M KOH and 0.5 M H2SO4 media, respectively. The stability test results show that Fe 1.2 Se1-NC catalyst exhibits applicability in the full pH range and is an oxygen reduction catalyst with good stability. In acidic (pH 0.3), neutral (pH 7.0) and alkaline (pH 13) electrolytes with different pH values, Fe 1.2 Se1-NC catalyst, after 3000 cycles of CV, the E 1 / 2 all do not decrease significantly, indicating that the active sites of the catalyst remain relatively stable during the CV cycle. At the same time, the chronoamperometry test shows that the current remains basically stable within 15 h of continuous operation, and the current does not decrease significantly after 24 h of operation (the current retention rate is higher than 93%), which fully proves that Fe 1.2Se1-NC catalyst has excellent stability in the full pH range.

[0087] (Four) Fe 1.2 Se1-NC catalyst assembled alkaline or neutral liquid zinc-air battery test

[0088] Assembly method of liquid zinc-air battery: zinc foil as anode, Fe 1.2 Se1-NC catalyst loaded composite carbon paper as air cathode, 6M KOH (containing 0.2M Zn(OAc)2) as alkaline electrolyte, 4M NH4Cl and 2M KCl (containing 0.2M Zn(OAc)2) as neutral electrolyte. The preparation method of air electrode is to uniformly drop the prepared catalyst ink on the carbon paper, and then dry at 80℃ for 1h, the loading amount is 1mg·cm -2 The open circuit voltage of the battery was tested by electrochemical workstation OCPT, and the maximum power density of zinc-air battery was tested by LSV curve.

[0089] Figure 7 Fe 1.2 Se1-NC in alkaline and neutral liquid zinc-air battery discharge power density curve (a), open circuit voltage (b) and cycle stability (c). Figure 7 It is shown that the alkaline liquid zinc-air battery exhibits excellent performance, with an open circuit voltage of up to 1.51V and a peak power density of 143.8mW·cm -2 It is worth mentioning that the Fe 1.2 Se1-NC based neutral liquid zinc-air battery also exhibits excellent battery performance, with an open circuit voltage of 1.39V and a peak power density of 47.4mW·cm -2 In the long-term charge-discharge cycle test of up to 140h, the Fe 1.2 Se1-NC based alkaline and neutral liquid zinc-air battery both exhibit excellent stability, that is, the charge-discharge voltage remains stable throughout the whole charge-discharge process without obvious fluctuation or attenuation.

[0090] Example 6 Iron selenium dual site full pH oxygen reduction catalyst Fe x Se1-NC, Fe 1.2 Se1-NC / 800 and Fe 1.2 Se1-NC / 900 in neutral medium

[0091] As in Example 5, Fe x Se1-NC, Fe 1.2 Se1-NC / 800 and Fe 1.2The oxygen reduction performance of Se1-NC / 900 in O2-saturated 0.1 M PBS (pH 7.0) solution. Figure 8 The LSV curves in Figure 6 prove that the iron-selenium dual-site all-pH oxygen reduction catalysts prepared in Examples 1, 3 and 4 all exhibit oxygen reduction performance similar to, or even better than, the Pt / C catalyst in neutral medium. The iron-selenium dual-site catalysts have a clear onset potential, ranging from 0.90 V to 0.94 V; their j L ranging from 4.39 mA·cm -2 -5.14 mA·cm -2 .

Claims

1. An iron-selenium bi-site all-pH oxygen reduction catalyst, characterized in that, FeSe-NC is a full-pH oxygen reduction catalyst with iron-selenium dual sites, which is obtained by anchoring iron and selenium on nitrogen-doped carbon matrix through secondary pyrolysis.

2. The method for preparing a full-pH oxygen reduction catalyst with iron and selenium dual sites according to claim 1, characterized in that, The preparation method comprises the following steps: 1) dissolving a precursor zinc salt in anhydrous methanol to obtain solution A; dissolving a precursor ferric salt and 2-methyl imidazole in anhydrous methanol to obtain solution B; slowly injecting solution A into solution B at room temperature, continuously stirring for 10-24 hours, centrifuging the obtained mixture, washing with methanol, vacuum drying, and obtaining Fe@ZIF-8; 2) pyrolyzing Fe@ZIF-8 in a tube furnace under inert gas protection, and naturally cooling to room temperature to obtain Fe-NC; 3) mixing Fe-NC with SeO2 powder, grinding and mixing uniformly, transferring to a quartz boat, and pyrolyzing in inert gas to obtain the full-pH oxygen reduction catalyst with iron-selenium dual sites FeSe-NC.

3. The preparation method of the iron-selenium bi-site all-pH oxygen reduction catalyst according to claim 2, characterized in that, In step 1), the zinc salt is selected from zinc nitrate, zinc chloride, zinc acetate or zinc acetylacetonate.

4. The preparation method of the iron-selenium bi-site all-pH oxygen reduction catalyst according to claim 2, characterized in that, In step 1), the ferric salt is selected from iron trisacetylacetonate, iron nitrate, iron chloride or iron acetate.

5. The preparation method of the iron-selenium bi-site all-pH oxygen reduction catalyst according to claim 2, characterized in that, In step 1), the molar ratio of zinc salt to ferric salt is 1:(0.05-0.5).

6. The preparation method of the iron-selenium bi-site all-pH oxygen reduction catalyst according to claim 2, characterized in that, In step 2), the inert gas is nitrogen or argon; the pyrolysis is: the heating rate is 3℃·min -1 -5℃·min -1 , the pyrolysis temperature is 800℃-1000℃, and the pyrolysis time is 1.5h-3h.

7. The method for preparing an iron-selenium dual-site full-pH oxygen reduction catalyst according to claim 2, characterized in that, In step 3), the mass ratio of Fe-NC to SeO2 is 1:(1-2).

8. The preparation method of the iron-selenium bi-site all-pH oxygen reduction catalyst according to claim 2, characterized in that, In step 3), the inert gas is nitrogen or argon; the pyrolysis is: the heating rate is 3℃·min -1 -5℃·min -1 , the pyrolysis temperature is 800℃-1000℃, and the pyrolysis time is 1h-2h.

9. Use of the full-pH oxygen reduction catalyst with iron-selenium dual sites FeSe-NC in a metal-air battery.

10. Use according to claim 9, characterized in that, The method is as follows: A zinc-air battery device is assembled using FeSe-NC-loaded composite carbon paper as the cathode and zinc foil as the anode. The electrolyte contains 0.2 mol·L⁻¹ -1 6 mol·L of zinc acetate -1 KOH solution or containing 0.2 mol·L -1 4 mol·L of zinc acetate -1 NH4Cl and 2 mol·L -1 KCl mixed solution.

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