CN117865242A

CN117865242A - OER electrocatalyst and preparation method and application thereof

Info

Publication number: CN117865242A
Application number: CN202410277963.XA
Authority: CN
Inventors: 李爽; 吴慧娟; 程冲; 孔玉璇; 汪茂; 汪映寒
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2024-03-12
Filing date: 2024-03-12
Publication date: 2024-04-12
Anticipated expiration: 2044-03-12
Also published as: CN117865242B

Abstract

The invention relates to an OER electrocatalyst, a preparation method and application thereof, and belongs to the field of electrocatalysts. The invention provides a preparation method of an OER electrocatalyst, which comprises the following steps: the preparation method comprises the steps of preparing NiFeMn hydroxide, namely the OER electrocatalyst, from iron salt, nickel salt and Mn-terephthalic acid coordination polymer serving as raw materials through interfacial atom replacement. The obtained electrocatalyst can reach 100mA cm in electrolyte of 1M KOH and alkaline seawater by only needing over-potential of 213mV and 251mV of NiFeMn ^‑2 Is used for the current density of the battery.

Description

OER electrocatalyst and preparation method and application thereof

Technical Field

The invention relates to an OER electrocatalyst, a preparation method and application thereof, and belongs to the field of electrocatalysts.

Background

Electrochemical water electrolysis hydrogen production can be used as a low-carbon green sustainable strategyThe problems of the exploitation of the fossil fuel and the global atmosphere pollution which are not enough heavy are solved. The two-pole reactions of electrochemical water decomposition consist of an Oxygen Evolution Reaction (OER) at the anode and a Hydrogen Evolution Reaction (HER) at the cathode, respectively. In principle, OER kinetics involve multiple proton-coupled electron transfer steps, with slower kinetics, which limits the overall water splitting efficiency to a large extent. Electrochemical water splitting systems often require pure water as a feedstock. The fresh water resources required for large-scale industrialization are incompatible with pure water reserves on earth, which makes seawater electrolysis more attractive. However, the use of seawater places a number of challenging demands on the catalyst due to the complexity of the seawater composition. The sea water contains a large amount of chloride ions (Cl) ^- ），Cl ^- The oxidation reaction involved in the electrolysis of seawater is the chlorine evolution reaction (CIER). The competition of OER and CIER at the anode has hindered its large scale development in seawater electrolysis. In addition, hypochlorite and Cl-corrosion effects generated by CIER reactions can also impair the long-term operation of seawater electrolysis, thereby inhibiting continuous hydrogen production by seawater electrolysis. Studies have shown that the theoretical potential of CIER is about 490mV higher than OER at ph=14, which suggests that alkaline seawater electrolysis can inhibit CIER. For practical seawater electrolysis, the development of anode electrocatalysts that are capable of efficiently and permanently evolving oxygen at high current densities and avoiding the evolution of chlorine in alkaline seawater remains a current challenge.

Transition metal hydroxides, especially NiFe-based hydroxides, are the most effective OER catalysts among all the above candidates reported so far, and have also been demonstrated to be the true catalytically active species generated from the surface reconstruction of many types of oxygen evolving materials. However, the OER performance of hydroxides in seawater is still unsatisfactory due to insufficient long-term stability in Cl-containing media. Although some hydroxide electrocatalysts exhibit considerable stability, they do not exhibit sufficient catalytic capacity to conduct rapid electrolysis at low overpotential.

To date, the search for high performance catalysts with rich active centers and resistance to corrosion by salt electrolytes has been at the beginning of the study with great potential. To promote the O of NiFe hydroxide catalystER activity, researchers coupled Ni/Fe hydroxides with other transition metal compounds, such as NiOOH/Ni, by interfacial engineering ₅ P ₄ 、Ni ₂ P/FeOOH、NiFe(OH) _x FeS, niFeOOH@FeNi and Ni ₃ S ₂ And (3) at NiFeOOH, so as to achieve the purposes of optimizing the adsorption of the oxygen intermediate and improving the OER activity.

However, there is no new OER electrocatalyst prepared by growing NiFe hydroxide on the surface of Mn-terephthalic acid coordination polymer (Mn TPA) as template and Mn source.

Disclosure of Invention

According to the invention, mn TPA is used as a template and a Mn source, niFe hydroxide grows on the surface of the Mn TPA, mn ions are leached out in the synthesis process and doped into the hydroxide on the surface layer, so that the electrocatalyst with a NiFeMn hydroxide-Mn TPA heterostructure (i.e. heterojunction electrocatalyst NiFeMn) is formed. The synergistic effect of the NiFeMn hydroxide on the surface layer and the Mn TPA substrate makes the NiFeMn show excellent OER activity and selectivity in the seawater electrolyte. The obtained electrocatalyst can reach 100mA cm in electrolyte of 1M KOH and alkaline seawater by only needing over-potential of 213mV and 251mV of NiFeMn ^-2 Is used for the current density of the battery. In addition, mn element has a certain electronic regulation and control effect on Ni/Fe active sites, so that the selectivity and activity of OER are promoted to a certain extent, and the Faraday efficiency of OER is up to 91.89%. And NiFeMn has high stability in the process of electrolyzing seawater, and the potential hardly decays after 88 hours of operation. Therefore, the invention not only has great practical value in the application of hydrogen evolution of the electrolytic seawater, but also provides an effective new strategy for researching the corrosion-resistant high-activity electrolytic seawater catalyst.

The technical scheme of the invention is as follows:

the first technical problem to be solved by the invention is to provide a preparation method of an OER electrocatalyst, which comprises the following steps: the method takes ferric salt, nickel salt and Mn-terephthalic acid coordination polymer (Mn TPA) as raw materials, and prepares NiFeMn hydroxide with a heterostructure through interfacial atom replacement, namely the OER electrocatalyst.

Further, the mass ratio of the raw materials is as follows: iron salt: nickel salt: mn-terephthalic acid coordination polymer=5-20:5-20:1-5.

Further, the iron salt is selected from: feSO ₄ ·7H ₂ O or FeCl ₂ ·4H ₂ O。

Further, the nickel salt is selected from: ni (NO) ₃ ） ₂ ·6H ₂ O、NiSO ₄ ·6H ₂ O or NiCl ₂ ·6H ₂ O。

Further, the Mn TPA is prepared by the following method: dissolving manganese salt and terephthalic acid (TPA) in a solvent to obtain a mixed solution, and then reacting the obtained mixed solution in corrosion-resistant reaction equipment at 100-150 ℃ for 20-30 h; naturally cooling to the ambient temperature after the reaction is finished; collecting the precipitate, and washing with alcohol and deionized water for at least 3 times; finally, vacuum drying is carried out to obtain Mn TPA (Mn-terephthalic acid coordination polymer).

Further, the manganese salt is selected from: mnCl ₂ ·4H ₂ O、MnSO ₄ ·xH ₂ O or Mn (NO) ₃ ) ₂ ·xH ₂ O。

Further, in the above method for producing Mn TPA, the solvent is selected from the group consisting of: deionized water, laboratory grade II pure water or ultrapure water; the alcohol substance is ethanol.

Further, the preparation method of the OER electrocatalyst comprises the following steps: mixing Mn-terephthalic acid coordination polymer and alcohol substances (ethanol), and performing ultrasonic treatment to form a uniformly dispersed suspension A; dissolving ferric salt and nickel salt in ultrapure water, and then adding urea for dissolving to obtain a solution B;

at normal temperature, the suspension A and the solution B are rapidly mixed and sealed, and are placed in 20-30 ℃ for reaction for 5-25 hours; and after the reaction is finished, washing with water and alcohol substances (ethanol) for 3-5 times respectively, and drying to obtain the NiFeMn hydroxide with the heterostructure, namely the OER electrocatalyst.

Further, in the preparation method of the OER electrocatalyst, the mass ratio of the ferric salt to the nickel salt to the urea is: 5-20: 5-20: 10-40.

The second technical problem to be solved by the invention is to provide an OER electrocatalyst which is prepared by the preparation method.

Further, the obtained electrocatalyst can reach 100mA cm in electrolyte of 1M KOH and alkaline seawater by only using overpotential of 213mV and 251mV ^-2 Is used for the current density of the battery.

The third technical problem to be solved by the present invention is to indicate the use of the OER electrocatalyst described above for the electrolysis of water or seawater.

The invention has the beneficial effects that:

the invention synthesizes a NiFeMn hydroxide catalyst of a heterostructure for electrocatalytic oxygen evolution by utilizing an interfacial atom replacement strategy, takes Mn TPA as a template and an Mn source, grows NiFe hydroxide on the surface of the catalyst, thereby realizing controllable Mn replacement in NiFeMn, and constructing a heterojunction structure to obtain the OER electrocatalyst. As a result, it was found that the Ni and Fe electronic structures were controlled after Mn substitution incorporation, and Ni and Fe exhibited rich high valence states. Electrochemical tests show that NiFeMn loaded on carbon cloth in alkaline seawater medium can reach 100mA cm under the overpotential of 251mV ^-2 And at 50 and 100mA cm ^-2 Can work stably>80h) A. The invention relates to a method for producing a fibre-reinforced plastic composite The OER Faraday efficiency is as high as 91.89%, and the selectivity is high; it can be seen that the addition of a specific Mn source can promote high activity and high selectivity of NiFe hydroxide in alkaline seawater. Therefore, the NiFeMn catalyst with the atomic interface substitution has great practical value, which provides an effective strategy for realizing the high-activity and corrosion-resistant electrolytic alkaline seawater catalyst.

Drawings

FIG. 1 is a schematic diagram of the application of the NiFeMn heterojunction electrocatalyst OER according to the invention.

FIG. 2 (a) NiFe, (b) Mn TPA and (c) NiFeMn heterojunction electrocatalyst SEM images.

Fig. 3 a-e: transmission Electron Microscope (TEM) images of NiFeMn heterojunction electrocatalyst at different multiplying powers; and f, selecting an electron diffraction pattern of the region.

FIG. 4 a is a HAADF diagram of a NiFeMn heterojunction electrocatalyst; b element map; element map of c-f Ni, fe, mn and O elements.

Figure 5 XRD patterns of NiFeMn electrocatalyst and NiFe, mnTPA.

FIG. 6 Fourier infrared spectra of NiFeMn heterojunction electrocatalyst and NiFe, mn TPA.

FIG. 7a is an XPS overview of NiFeMn, niFe and Mn TPA; b-c high resolution XPS spectra of Ni 2p and Fe2p of NiFeMn.

FIG. 8 a LSV plot of OER for NiFeMn-CC electrocatalyst, niFe-CC and Mn TPA-CC at 1M KOH; b, an overpotential statistical graph of NiFeMn electrocatalyst and NiFe under different current densities; c. tafel plot of NiFeMn electrocatalyst, niFe and MnTPA; in the figures, (1), (2) and (3) represent Mn TPA, niFe and NiFeMn, respectively.

FIG. 9 different substrates (MnO) ₂ 、Mn ₃ O ₄ And Mn TPA) LSV profile of NiFeMn electrocatalyst in 1M KOH.

FIG. 10 is a graph of the stability results of NiFeMn electrocatalyst under alkaline conditions.

FIG. 11 a-b LSV graph and Tafel graph of NiFeMn electrocatalyst in alkaline seawater, wherein (1), (2) and (3) represent Mn TPA, niFe and NiFeMn, respectively; c a overvoltage map at different current densities; d NiFeMn electrocatalyst and advanced electrolytic seawater OER catalyst activity statistics.

FIG. 12 is a graph of the stability results of NiFeMn electrocatalyst in alkaline seawater.

FIG. 13 Faraday efficiency and yield plot of OER of NiFeMn electrocatalyst in alkaline seawater; wherein the bar graph represents the yield and the wire graph represents the faraday efficiency.

Detailed Description

The invention takes Mn TPA as a template and Mn source, and grows NiFe hydroxide on the surface of the Mn TPA to form the electrocatalyst with a NiFeMn hydroxide-Mn TPA heterostructure. The synergistic effect of the NiFeMn hydroxide on the surface layer and the Mn TPA substrate makes the NiFeMn show excellent OER activity and selectivity in the seawater electrolyte. The obtained electrocatalyst can reach 100mA cm in electrolyte of 1M KOH and alkaline seawater by only needing over-potential of 213mV and 251mV of NiFeMn ^-2 Is used for the current density of the battery.

The following describes the invention in further detail with reference to examples, which are not intended to limit the invention thereto.

EXAMPLE 1 Synthesis of Mn TPA

1.0mmol MnCl ₂ ·4H ₂ O and 1.0mmol of terephthalic acid (PTA) were dissolved in 20ml of DMF (N, N-dimethylformamide) to obtain a mixed solution, and the above solution was put into a 50ml polytetrafluoroethylene liner, heated, and kept at 120℃for reaction 24 h. After the reaction is completed, naturally cooling to the ambient temperature. The resulting precipitate was collected by centrifugation and washed 3-5 times with ethanol and deionized water. Finally, vacuum drying is carried out for 6 hours at 70 ℃ to obtain the product of Mn TPA.

Synthesis of heterostructured NiFeMn hydroxides

Mn TPA of 20 mg and ethanol of 6mL were mixed and sonicated for 30min to form a uniformly dispersed suspension A. At the same time, 50 mg FeSO is weighed ₄ ·7H ₂ O and 150 mg Ni (NO) ₃ ） ₂ ·6H ₂ O was dissolved in 4 mL ultrapure water, and then 200 mg urea was weighed and dissolved in the above salt solution to obtain a solution B.

At normal temperature, rapidly mixing the suspension A and the solution B, and sealing the glass vial for reaction; placing the mixture in an oil bath at 80 ℃ for reaction for 20 hours; after the reaction is finished, washing the mixture with water and ethanol for 3-5 times respectively, and drying the mixture at 70 ℃ overnight to obtain NiFeMn hydroxide (abbreviated as NiFeMn) with a heterostructure.

Example 2

The preparation was identical to example 1, except that the amount of Mn TPA added was 10mg.

Example 3

The preparation was identical to example 1, except that the amount of Mn TPA added was 15mg.

Comparative example 1

The preparation was the same as in example 1, except that Mn TPA was replaced with MnO ₂ 。

Comparative example 2

The preparation process was the same as in example 1, except that Mn TPA was replaced with Mn ₃ O ₄ 。

Comparative example 3

Synthesis of NiFe (NiFe hydroxide): weighing 50 mg FeSO ₄ ·7H ₂ O and 150 mg Ni (NO) ₃ ） ₂ ·6H ₂ O was dissolved in 4. 4 mL ultrapure water and 6ml of ethanol, and then 200. 200 mg urea was weighed and dissolved in the above-mentioned salt solution. The reaction was carried out in an oil bath at 80℃for 20 hours. After the reaction is finished, washing the mixture with water and ethanol for 3-5 times respectively, and then drying the mixture at 70 ℃ overnight.

Microstructure and performance results

1. Structural characterization

SEM was used to characterize the basic morphology of NiFeMn hydroxide. FIG. 2 is an SEM topography of NiFe (FIG. 2 a), mn-TPA (FIG. 2 b) and NiFeMn (FIG. 2 c), respectively. From fig. 2, c, it can be observed that layered NiFe hydroxide uniformly grows vertically on the surface of Mn TPA, resulting in NiFeMn resembling petal-like spheres. The ultrathin petal-shaped morphology ensures that the material has large specific surface area and provides rich active sites for electrochemical reaction. In addition, the resulting high density of the spatial gap between the laminar sheet and the substrate may promote sufficient contact with the electrolyte, electron transfer and release of the generated gas. Therefore, mn TPA is used as a Mn source, mn ions are leached out in the growth process and slowly doped into hydroxide, so that controllable doping of Mn ions is realized.

The microstructure and its constituent components of nifenn were further studied using TEM and HRTEM. As can be seen from the graph of FIG. 3 and a, the NiFeMn has a layered petal sphere with a diameter of about 1.54. Mu.m. And the flakes uniformly grown on the outer layer of the sphere are NiFeMn hydroxide (as shown in FIG. 3 b-d). Obvious lattice fringes of NiFe hydroxide with lattice spacing of 0.197 nm and 0.230 nm, respectively due to the (018) and (015) crystal planes of NiFe hydroxide, can be observed in the HRTEM image (fig. 3 e). Selected Area Electron Diffraction (SAED) results showed distinct (110) and (012) diffraction rings, further demonstrating the NiFe hydroxide grown on the surface. Furthermore, the present invention speculates that the Mn ions do not disrupt the crystal structure of the NiFe hydroxide during substitutional doping (FIG. 3 f).

Fig. 4 is an energy dispersive X-ray spectroscopy (EDX) elemental profile of NiFeMn, which reflects mainly the spatial distribution of the different elements in NiFeMn materials. FIG. 4 a-b is a HAADF image of a NiFeMn heterojunction catalyst and FIG. 4 c-f is a map of the elements Ni, fe, mn, O, respectively. The results show that Ni and Fe elements are uniformly distributed in the whole petal sphere, and Mn elements are distributed in the petal sphere in a way of becoming thinner from the center to the outermost layer. It is inferred that the Mn element in the layered hydroxide is elution-doped in the Mn TPA substrate having the center, so that the Mn content of the outer layer is small. In combination with SEM and TEM results, the present invention considers that NiFe hydroxide grows uniformly on Mn TPA, and Mn ions slowly dissolve out during solvothermal reaction, thereby replacing NiFe hydroxide doped to the surface layer to form NiFeMn.

Characterization of the phase composition of the material by XRD technique, results are shown in fig. 5, where the diffraction peak is at 2θ=9.56 ^o ，14.27 ^o ，18.20 ^o Corresponds to the (200), (110), (111) planes of MnTPA, respectively. Characteristic peaks of both MnTPA and NiFe hydroxide exist on the XRD spectrum of NiFeMn synthesized on Mn TPA substrate. Wherein 2θ=11.39 ^o ，23.06 ^o ，34.55 ^o ，38.81 ^o ，45.83 ^o ，60.08 ^o The diffraction peaks of (3) correspond to the (003), (006), (012), (015), (018), (110), (019) crystal planes of NiFe hydroxide, respectively. But also has better crystallinity. This fully demonstrates that NiFe hydroxide and MnTPA are present in the NiFeMn system at the same time. Compared with NiFe hydroxide and MnTPA, the characteristic peak of NiFeMn is not significantly shifted, and the crystallization performance is not changed, which indicates that in-situ doping of Mn does not have a significant effect on the structure of the material.

The structure of NiFeMn was further confirmed by fourier infrared spectroscopy (FTIR). FIG. 6 shows the infrared curves for Mn TPA, niFe and NiFeMn. In the infrared spectrum of NiFeMn, 1574cm ^-1 And 1385cm ^-1 The nearby absorption peaks are only to be attributed to the asymmetric and symmetric tensile vibration peaks of the carboxylic acid groups in MnTPA; 819cm ^-1 And 747cm ^-1 Out-of-plane ring C-H flexural vibration of nearby absorption peaks and TPA ligandsRelated to the following. In addition, the characteristic peaks of NiFeMn correspond to the characteristic peaks of NiFe hydroxide one by one. Therefore, the infrared results further demonstrate the presence of MnTPA substrate and NiFe hydroxide in nifenn.

In order to study the elemental composition and valence structure of NiFeMn, XPS test was performed on the material, and the results are shown in fig. 7. From XPS spectrum, it is known that NiFeMn and NiFe hydroxide materials contain Ni, fe, O, C and other elements (FIG. 7 a). In combination with EDX test results, the invention deduces that the Mn 2p is covered by Ni LMM probably because the content of Mn element in a NiFeMn system is relatively small, so that no obvious characteristic peak of Mn 2p exists in XPS full spectrum. In the XPS spectrum of high resolution Ni 2p (as in FIG. 7 b), the positions of the peaks at 855.28 and 860.78 eV correspond to Ni 2p, respectively _3/2 And Ni 2p _1/2 This is a characteristic peak of divalent Ni; ni 2p relative to NiFe hydroxide _3/2 Ni 2p of NiFeMn _3/2 Offset 0.25eV to the high energy direction, indicating that Mn incorporation promotes Ni ²⁺ Conversion of the species to higher valence Ni produces NiOOH active species that enhance OER reactions. Cl may occur during the electrolysis of seawater ^- And OH (OH) ^- Is a competitive adsorption of (a) by (b). The theory of absolute soft acid and hard base shows that Ni with higher valence belongs to harder Lewis acid, and is preferentially matched with hard base OH ^- Binding, so the selectivity of OER is enhanced. In the XPS spectrum of high resolution Fe2p (as in FIG. 7 c), fe2p at 711.68 and 724.65eV _3/2 And Fe2p _1/2 The characteristic peak of (2) is a trivalent oxidation peak of Fe, and Fe is 2p _3/2 An offset of 0.1eV occurs in the high energy direction, i.e. Fe is in a higher valence state. Overall, the shift of these peaks suggests that in situ doping of Mn causes electron transfer of Ni and Fe with it, thus changing the local electron state of the active center, promoting OER activity optimization in the material.

The elemental content of the nifenn electrocatalyst was quantitatively analyzed by XPS surface composition analysis and plasma spectrometer (ICP-OES) test results. As can be seen from the results of XPS elemental analysis in FIG. 7, the NiFeMn and NiFe hydroxides have similar NiFe atomic ratios, and the Ni/Fe ratio is approximately 3/1. In the result of XPS analysis, since the content of Mn in NiFeMn is small, the characteristic peak thereof is covered with the peak of Ni LM2, and the content of Mn element cannot be estimated. Therefore, the ICP-OES test is adopted to further accurately quantify Mn element. From the ICP-OES results, it was found that the Ni and Fe contents were consistent with the XPS results, and the Mn element content was about 1.97%.

2. Characterization of oxygen evolution catalytic performance in alkaline environments

To evaluate the catalytic activity of the nifenn electrocatalyst (nifenn in the present invention, not specifically described, refers to the electrocatalyst obtained in example 1) in 1M KOH electrolyte, a three electrode system was used to study the OER performance of the catalyst. 100 μl of ink of NiFeMn was uniformly dispersed in 1cm of good conductivity ^-2 On Carbon Cloth (CC) (load amount of 1mg cm) ^-2 ) So as to achieve the purpose of improving OER activity. As can be seen from fig. 8, niFeMn exhibits very excellent activity on carbon cloth. To 100, 500 and 1000mAcm ^-2 The NiFeMn-CC only requires overpotentials of 213, 283 and 343 mV. Compared with NiFeMn-KB, niFeMn-CC can reach 1A cm at lower potential ^-2 To achieve a highly efficient OER reaction (e.g. fig. 8 a, b); its Tafel slope (33.43 mV dec ^-1 ) Is also significantly smaller than NiFe (59.30 mV dec ^-1 ) And MnTPA (306.85 mV dec ^-1 ) Tafe slope of (e.g., FIG. 8 c).

To further demonstrate that the heterostructure of NiFeMn hydroxide-Mn TPA of NiFeMn electrocatalyst can promote OER activity of the material, the present invention uses MnO ₂ And Mn of ₃ O ₄ NiFeMn hydroxide (respectively designated as NiFeMn-MnO) was synthesized for the substrate ₂ And NiFeMn-Mn ₃ O ₄ ) As a control sample, and its OER activity was tested in 1M KOH electrolyte. As shown in FIG. 9, the overpotential of NiFeMn is much lower than that of NiFeMn-MnO ₂ And NiFeMn-Mn ₃ O ₄ This illustrates that Mn TPA-based NiFeMn heterojunction plays an important role in the electrocatalytic process.

To evaluate the stability of the NiFeMn-CC electrocatalyst, two current steps were used for chronopotentiometric measurements. Stability results As shown in FIG. 10, the NiFeMn electrocatalyst can be used at 20 and 50mA cm ^-2 And stably operates at current density. At 20mA cm ^-2 Lower work 22After h, only 20mV was attenuated. After this stage, again at 50mA cm ^-2 The lower stable is carried out for 22h, and the potential hardly decays during the period. Since CC has no OER activity, the activities of NiFeMn-CC are all contributed by NiFeMn. It can be seen that the NiFeMn catalyst has stable OER performance at 1M KOH.

3. Characterization of oxygen evolution catalytic performance in alkaline seawater environment

To investigate the OER performance of NiFeMn in alkaline seawater, the invention tested the OER activity of NiFeMn-CC with a three electrode system in alkaline seawater electrolytes. CC is known to be hardly active in alkaline seawater. It is therefore evident from FIG. 11a that NiFeMn-CC shows significantly better OER performance in the electrolyte than NiFe-CC and MnTPA-CC, allowing higher current densities to be achieved at lower potentials. The Tafel slope of NiFeMn-CC is only 24.66mV dec ^-1 Kinetics superior to that of NiFe-CC (35.88 mV dec) ^-1 ). (FIG. 11 b) and MnTPA-CC have little activity, which suggests that Mn is not an active site of OER, but rather acts to regulate the electronic structure and optimize OER activity in NiFeMn. In alkaline seawater, niFeMn-CC can reach 500mA cm with only 403mV overpotential ^-2 While NiFe-CC requires 523mV. (FIG. 11 c) even in seawater containing a large amount of salt, the OER activity of NiFeMn is not significantly attenuated, but rather is superior to that of NiFe, and it is presumed that Mn doping is advantageous to some extent for OER selectivity in seawater. In summary, in situ doping of Mn promotes efficient OER of NiFeMn electrocatalysts in alkaline seawater (see fig. 11 d).

NiFeMn also has better stability in alkaline seawater. The invention tests that the current density is 50 and 100mA cm ^-2 The potential of the lower run 88h was varied. At 50mA cm ^-2 At this time, the potential decayed from 1.647V to 1.663V by 16mV. And at 100mA cm ^-2 The potential was changed from 1.818V to 1.790V with little decay. Laterally reflect Cl generated by CIER competition reaction ₂ Less poisoning of the catalyst (see fig. 12). The potential decay causes and the decay in alkaline medium always cause unstable dissolution of Ni and Fe atoms, resulting in reduction of active sites. After the unstable atoms are dissolved out, the catalyst is catalyzedThe stability of the chemical agent is almost unchanged.

To further verify that NiFeMn can inhibit CIER reaction and enhance OER selectivity, the invention collects catalyst at 50mA cm by water displacement method ^-2 The faraday efficiency is calculated based on the gas product produced at the current density. As is well known, cl ₂ Is a yellow-green gas and is easily dissolved in water. The gas production and faraday efficiency over the cumulative time are shown in figure 13. The calculation conclusion shows that the FE% of NiFeMn in alkaline seawater is as high as 91.89%. This fully demonstrates that NiFeMn has good OER catalytic activity and can effectively inhibit the CIER reaction in alkaline seawater solutions.

In conclusion, the NiFeMn synthesized by the strategy of in-situ interface atom replacement can obviously optimize the electrolytic seawater OER performance of the NiFe catalyst. Compared to NiFe catalysts, niFeMn catalysts exhibit higher OER activity and stability. Electron structural analysis shows that the Mn interface doped NiFe catalyst can enhance electron transfer of Ni and Fe to Mn species, so that high-valence Ni and Fe atoms exist in the catalyst. The test of the electrocatalyst further proves that the NiFeMn catalyst reaches 100mA cm after being doped in alkaline fresh water and seawater ^-2 Only 213 and 251mV overpotential is required. And NiFeMn can resist Cl in alkaline seawater medium ^- Exhibits high OER selectivity (FE% = 91.56%) and long-term stability [ ]>80h）。

Claims

1. The preparation method of the OER electrocatalyst is characterized by comprising the following steps: the preparation method comprises the steps of preparing NiFeMn hydroxide, namely the OER electrocatalyst, from iron salt, nickel salt and Mn-terephthalic acid coordination polymer serving as raw materials through interfacial atom replacement.

2. The preparation method of the OER electrocatalyst according to claim 1, wherein the mass ratio of each raw material is: iron salt: nickel salt: mn-terephthalic acid coordination polymer=5 to 20: 5-20: 1-5.

3. A method according to claim 1 or 2A process for the preparation of OER electrocatalyst, characterised in that the iron salt is selected from: feSO ₄ ·7H ₂ O or FeCl ₂ ·4H ₂ O；

The nickel salt is selected from: ni (NO) ₃ ） ₂ ·6H ₂ O、NiSO ₄ ·6H ₂ O or NiCl ₂ ·6H ₂ O。

4. The method for preparing the OER electrocatalyst according to claim 1 or 2, wherein the Mn-terephthalic acid coordination polymer is prepared by: dissolving manganese salt and terephthalic acid in a solvent to obtain a mixed solution, and then reacting the obtained mixed solution in corrosion-resistant reaction equipment at 100-150 ℃ for 20-30 h; naturally cooling to the ambient temperature after the reaction is finished; collecting the precipitate, and washing with alcohol and deionized water for at least 3 times; finally, vacuum drying is carried out to obtain the Mn-terephthalic acid coordination polymer.

5. The method for preparing an OER electrocatalyst according to claim 4 wherein the manganese salt is selected from the group consisting of: mnCl ₂ ·4H ₂ O、MnSO ₄ ·xH ₂ O or Mn (NO) ₃ ) ₂ ·xH ₂ O；

The solvent is selected from: deionized water, laboratory grade II pure water or ultrapure water;

the alcohol substance is ethanol.

6. The method for preparing the OER electrocatalyst according to claim 1 or 2, wherein the method for preparing the OER electrocatalyst comprises: mixing Mn-terephthalic acid coordination polymer and alcohol substances, and performing ultrasonic treatment to form a uniformly dispersed suspension A; dissolving ferric salt and nickel salt in ultrapure water, and then adding urea for dissolving to obtain a solution B;

mixing the suspension A and the solution B at normal temperature, sealing, and reacting for 5-25 hours at 20-30 ℃; and after the reaction is finished, washing with water and alcohol substances for 3-5 times respectively, and drying to obtain the NiFeMn hydroxide.

7. The preparation method of the OER electrocatalyst according to claim 6, wherein the mass ratio of the iron salt to the nickel salt to the urea is: 5-20: 5-20: 10-40.

8. An OER electrocatalyst, characterised in that it is obtainable by a process according to any one of claims 1 to 7.

9. An OER electrocatalyst according to claim 8 wherein the electrocatalyst requires an overpotential of 213mV and 251mV up to 100mA cm in an electrolyte of 1M KOH and alkaline seawater ^-2 Is used for the current density of the battery.

10. Use of the OER electrocatalyst produced by the production process of any one of claims 1 to 7 for the electrolysis of water or seawater.