CN111482185A

CN111482185A - Self-supporting FeSxElectrocatalyst and preparation method and application thereof

Info

Publication number: CN111482185A
Application number: CN201910084511.9A
Authority: CN
Inventors: 王新炜; 熊威
Original assignee: Peking University Shenzhen Graduate School
Current assignee: Peking University Shenzhen Graduate School
Priority date: 2019-01-29
Filing date: 2019-01-29
Publication date: 2020-08-04
Anticipated expiration: 2039-01-29
Also published as: CN111482185B

Abstract

The invention discloses a self-supporting FeS_xAn electrocatalyst, a method of making and use thereof, the method comprising: providing an iron substrate; subjecting the iron substrate to a plasma treatment, the plasma comprising H₂S, forming FeS on the surface of the iron base material_xObtaining the self-supporting FeS_xAn electrocatalyst, wherein x is 0.5-2. The invention provides a simple, economic and effective plasma vulcanization method for preparing a novel self-supporting materialProp FeS_xElectrocatalyst, such FeS when applied to electrocatalytic reduction of nitrogen at ambient conditions_xthe/Fe electrode demonstrated excellent ammonia production, 4.25 × 10^‑10mol·s^‑1·cm^‑2And the Faraday efficiency is high and 18.1 percent, which is obviously better than other non-noble metal catalysts. FeS synthesized in view of plasma sulfurization method_xThe Fe has good performance and lower cost, and has wide application prospect in electrochemical ammonia synthesis.

Description

Self-supporting FeSxElectrocatalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of electrocatalysts, in particular to a self-supporting FeS_xAn electrocatalyst, a preparation method and an application thereof.

Background

Ammonia (NH)₃) Is the largest chemical product in the world, and the annual output of the whole world is up to 1.5 hundred million tons. Currently, more than 90% of the synthetic ammonia is produced by the industrial Haber-Bosch process, i.e. using N₂And H₂The gas is used for synthesizing ammonia on the surface of the iron-based catalyst under the conditions of high temperature (400-500 ℃) and high pressure (150-200 atm). This process consumes 1% of the energy supplied globally and produces large quantities of CO₂. In sharp contrast, many natural plants and bacteria carry metal-nitrogen-fixing enzymes that activate the strong N ≡ N triple bond (941kj/mol) at ambient conditions, reducing the nitrogen in the air to ammonia. Inspired by this biological process, much work began to investigate how nitrogen can be reduced to ammonia under mild conditions. Recently, the electrochemical nitrogen reduction of aqueous phase at room temperature for ammonia synthesis has attracted extensive research interest. This electrochemical process, which directly utilizes abundant water resources as a hydrogen source, can be easily combined with intermittent renewable energy sources (such as wind, solar or ocean) to provide the required electricity, and is therefore well suited for use in areas where transportation is inconvenient and where it is not suitable for building large chemical plants. However, activation of the N ≡ N bond under mild conditions is a major challenge, not only because of its very high bond energy but also due to the lack of dipole moment, and thus this electrochemical process requires the help of an electrocatalyst. In addition, the electrochemical reduction of Nitrogen (NRR) in the aqueous phase also faces the challenge of competing with electrochemical Hydrogen Evolution (HER). Because the reduction potentials of these two reactions are very close, this places more stringent requirements on the selectivity of the nitrogen reduction catalyst.

Recently reported monogenicRuthenium (Ru) -based and gold (Au) nanoparticle catalysts exhibit high ammonia yields and faraday efficiencies. However, the use of monoatomic Ru and nanoparticle Au, which are complicated and expensive in synthesis, severely limits their large-scale use. And other non-noble metal catalyst materials (e.g., Fe)₂O₃，Bi₄V₂O₁₁，MoS₂) And carbon materials, although widely studied, the reported ammonia yields and faraday efficiencies remain quite low. Therefore, there is a strong need to develop a non-noble metal nitrogen reduction catalyst that is simple to synthesize, economical and effective.

Accordingly, the prior art is yet to be improved and developed.

Disclosure of Invention

In view of the above-mentioned deficiencies of the prior art, it is an object of the present invention to provide a self-supporting FeS_xAn electrocatalyst, a preparation method and application thereof, aiming at solving the problems that the existing metal catalyst material synthesis method is complex and expensive, and the ammonia yield and Faraday efficiency of non-noble metal catalyst materials are very low.

The technical scheme of the invention is as follows:

self-supporting FeS_xA method of preparing an electrocatalyst, comprising:

providing an iron substrate;

subjecting the iron substrate to a plasma treatment, the plasma comprising H₂S, forming FeS on the surface of the iron base material_xObtaining the self-supporting FeS_xAn electrocatalyst, wherein x is 0.5-2.

The self-supporting FeS_xThe preparation method of the electrocatalyst is characterized in that the iron substrate is foamed iron, an iron sheet or a stainless steel sheet.

The self-supporting FeS_xA method for preparing an electrocatalyst, wherein the plasma is H₂S or H₂S and inert gas.

The self-supporting FeS_xThe preparation method of the electrocatalyst, wherein the treatment temperature is 25-300 ℃.

The self-supporting FeS_xThe preparation method of the electrocatalyst, wherein the treatment time is 5-180 min.

The self-supporting FeS_xThe preparation method of the electrocatalyst is characterized in that the plasma treatment of the foamed iron is carried out in a quartz tube in a tube furnace system, and the plasma is H₂S, the treatment process comprises cutting the foamed iron into pieces of 1cm × 2cm, and placing in the central region of a quartz tube H₂Heating to 160 ℃ during the S plasma treatment; h of 50sccm is continuously introduced₂S, entering a quartz tube, and maintaining the pressure in the quartz tube at 600mtorr by a vacuum pump; the upstream part of the quartz tube was wrapped with a copper coil, and 60W of RF power was supplied through the copper coil to generate H in the upstream region of the tube₂S, plasma; the plasma power supply is in pulse mode, each plasma pulse length is 15s, and the whole H₂S plasma treatment process is composed of 200H₂And (4) forming a plasma pulse cycle.

Self-supporting FeS_xElectrocatalyst, wherein the self-supporting FeS_xThe electrocatalyst comprises an iron substrate and FeS on the surface of the iron substrate_xSaid self-supporting FeS_xThe electrocatalyst adopts the self-supporting FeS_xThe preparation method of the electrocatalyst is provided.

The self-supporting FeS_xElectrocatalyst, wherein the self-supporting FeS_xThe electrocatalyst is self-supporting FeS₂An electrocatalyst.

The invention relates to a self-supporting FeS_xApplication of an electrocatalyst in preparing ammonia by electrochemically reducing nitrogen.

Has the advantages that: the invention provides a new method for simply carrying out H on the surface of an iron base material₂S plasma treatment to form FeS_xA nitrogen reduction catalytic material. Through H₂S plasma sulfurizing to form one FeS layer on the surface of foamed iron_xAnd exhibits excellent ammonia-producing performance by nitrogen reduction. With this FeS_xFe directly as the working electrode, which exhibits a potential of-0.30V versus the Reversible Hydrogen Electrode (RHE)Has excellent ammonia yield of 4.25 × 10^-10mol·s^-1·cm^-2And a very high faradaic efficiency of 18.1%, which is significantly higher than that of the reported non-noble metal catalysts. Notably, the site of nitrogen activation of biological nitrogen fixation enzymes is located on the cluster of Fe-S molecules. They are used in combination with the pure inorganic FeS of the invention_xThe similarity of catalysts makes this work even more interesting, as it can provide an important aid in simulating the natural nitrogen fixation process.

Drawings

FIG. 1 (a) shows an example FeS_xSEM picture of/Fe, (b) corresponding EDS, (c) STEM HADDF picture of cross section, (d-g) corresponding EDS elemental distribution map, (h) XPS measurement spectrum, (i) corresponding high resolution spectrum Fe 2p, and (j) corresponding high resolution spectrum S2 p.

FIG. 2 is a characterization of the electrocatalytic nitrogen reduction performance in the examples: (a) is FeS_xElectrochemical polarization curves of the/Fe electrode in a saturated solution of nitrogen and argon, the inset schematically illustrates the measuring device; (b) a time ampere curve for potentiostatic measurements; (c) the photograph and the absorption spectrum of the nitrogen reduction product are measured by an indophenol blue method; (b) the yields of ammonia at different potentials adopt the same line color; (e) the Faraday efficiency of ammonia and the potential corresponding to delta j/j nitrogen; (f) is Fe, Fe₂O₃、FeS_xAmmonia production and faraday efficiency.

FIG. 3 is a graph of (a) Nyquist and (b) baud for-0.30V (vs. RHE) in the example, tested in saturated solutions of nitrogen and argon, respectively; (c) for RNRR at each potential^-1/(RNRR^-1+RHER^-1) And the curve and the inset are equivalent circuits obtained by fitting.

FIG. 4 shows steady-state currents measured in the examples using chronoamperometry under saturated solutions of nitrogen and argon, respectively, each potential being maintained for 120 s.

FIG. 5 shows absolute standard curves (a, b) in the examples, the Nyquist method (c, d) for analyzing ammonia production (e, f), and the Watt-Chrisp method for analyzing hydrazine production, respectively.

FIG. 6 is a photograph showing the yield of ammonia analyzed by the Neisseria reagent method in example and an absorption spectrum measured.

FIG. 7 is a photograph and an absorption spectrum curve of the Watt-Chrisp method for measuring hydrazine production in the example.

FIG. 8 shows Nyquist (a, c, e, g) and Bode plots (b, d, f, h) for the examples under nitrogen and argon saturation conditions.

FIG. 9 is a comparison of SEM and EDS before and after the reaction in the examples.

FIG. 10 shows FeS before and after the reaction in example_xAnd raman contrast for synthesis of pure FeS.

FIG. 11 is XPS analysis after nitrogen reduction in examples.

FIG. 12 shows the FeS test by cyclic voltammetry in the examples_x(a) And Fe₂O₃(b) The obtained magnitude of the electric double layer capacitance (c) is calculated.

Detailed Description

The invention provides a self-supporting FeS_xThe present invention is further described in detail below in order to make the objects, technical solutions, and effects of the present invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The invention provides a self-supporting FeS_xA method of preparing an electrocatalyst, comprising:

providing an iron substrate;

The invention provides a new method for simply carrying out H on the surface of an iron base material₂S plasma treatment to form FeS_xA nitrogen reduction catalytic material. Through H₂S plasma sulfurizing to form one FeS layer on the surface of iron base material_xAnd exhibits excellent ammonia-producing performance by nitrogen reduction. With this FeS_xThe Fe is directly used as a working electrode and is at the potential of-0.30VIt exhibits excellent ammonia yield, up to 4.25 × 10, relative to Reversible Hydrogen Electrode (RHE)^-10mol·s^-1·cm^-2And a very high faradaic efficiency of 18.1%, which is significantly higher than that of the reported non-noble metal catalysts. Notably, the site of nitrogen activation of biological nitrogen fixation enzymes is located on the cluster of Fe-S molecules. They are used in combination with the pure inorganic FeS of the invention_xThe similarity of catalysts makes this work even more interesting, as it can provide an important aid in simulating the natural nitrogen fixation process.

Preferably, the iron substrate is foamed iron, an iron sheet or a stainless steel sheet. More preferably, the iron substrate is foamed iron. Excellent porosity is advantageous for electrocatalysis because they allow rapid diffusion of active species, promote efficient permeation of electrolyte, and significantly enlarge the surface area of the electrochemical reaction.

Preferably, the plasma is H₂S or H₂S and an inert gas (e.g., argon, etc.).

Preferably, the temperature of the treatment is 25-300 ℃. More preferably, the temperature of the treatment is 150 ℃ and 170 ℃ (e.g., 160 ℃). The present invention selects this temperature for plasma treatment in order to limit the diffusion of sulfur in the iron and thus its depth of sulfidation.

Preferably, the time of the treatment is 5-180 min. More preferably, the treatment time is 40-60min (e.g., 50 min). According to the invention, the FeS with uniform thickness can be formed on the surface of the iron base material by plasma treatment for the time_x。

Specifically, the plasma treatment of the foamed iron is carried out in a quartz tube in a tube furnace system, and the plasma is H₂S, the treatment process comprises cutting the foamed iron into pieces of 1cm × 2cm, and placing in the central region of a quartz tube H₂Heating to 160 ℃ during the S plasma treatment; h of 50sccm is continuously introduced₂S, entering a quartz tube, and maintaining the pressure in the quartz tube at 600mtorr by a vacuum pump; the upstream part of the quartz tube was wrapped with a copper coil, and 60W of RF power was supplied through the copper coil to generate H in the upstream region of the tube₂S, plasma; the plasma power supply is in pulse mode, each plasma pulse length is 15s, and the whole H₂S plasma treatment process is composed of 200H₂And (4) forming a plasma pulse cycle.

The invention also provides self-supporting FeS_xElectrocatalyst, wherein the self-supporting FeS_xThe electrocatalyst comprises an iron substrate and FeS on the surface of the iron substrate_xThe self-supporting FeS provided by the invention is adopted_xThe preparation method of the electrocatalyst is provided.

In the present invention, the self-supporting FeS_xThe electrocatalyst may be self-supporting FeS₂An electrocatalyst.

The invention also provides the self-supporting FeS_xApplication of an electrocatalyst in preparing ammonia by electrochemically reducing nitrogen.

The present invention will be described in detail below with reference to examples.

1、H₂S plasma treatment of foam iron (preparation of FeS)_xFe electrode) H in a quartz tube in a self-made tube furnace System₂Plasma treatment commercial foam iron was first cut into 1cm × 2cm pieces and then the sample was placed in the center region of a quartz tube, which was heated to 160 ℃ during plasma treatment and was continuously charged with 50sccm of H₂S (3% Ar dilution) was passed into a quartz tube, and the pressure inside the tube was maintained at 600mtorr by a vacuum pump. The upstream portion of the quartz tube was wrapped with a copper coil through which 60W of RF power (13.56MHz) was supplied to generate H in the upstream region of the tube₂And (5) S plasma. The plasma power supply is pulsed to avoid overheating of the tube. Each plasma pulse length is 15s, and the whole vulcanization process is carried out by 200H₂And (4) forming a plasma pulse cycle.

2. Electrochemical nitrogen reduction test: as shown in fig. 2a, the entire test was carried out in a two-compartment cell, the middle of which was blocked with Nafion 211 exchange membrane. Before the experiment, the Nafion film was pretreated, and immersed continuously in a 5% hydrogen peroxide solution and ultrapure water at 80 ℃ for 1 hour. Electrochemical data were tested with the CHI604E workstation under a three-electrode system. Pt as a counter electrode, Hg/HgO as a reference electrode, and 0.1M KOH in water. All displayed potentials are corrected by iR and correspond to a Reversible Hydrogen Electrode (RHE), an electrochemical polarization curve is obtained by a constant potential chronoamperometry, and each potential is maintained for 120s so as to achieve a steady-state current. To characterize the nitrogen reduction, pure nitrogen (99.999%, 1atm) was continuously passed to the working electrode in aqueous solution, with 30 minutes of nitrogen being passed before data collection. For comparison, argon (99.999%, 1 atm.) was substituted for nitrogen, and all other tests were the same as in nitrogen.

3. Electrochemical impedance test (EIS): the frequencies tested were 0.1Hz to 10kHz, the bias voltages were set to-0.14, -0.22, -0.30, -0.38 and-0.42V vs. RHE, respectively, the AC amplitude was 5mV, and the impedance fitting was done with ZView software.

4. Preparation of Fe₂O₃The electrode of/Fe: heating the foam iron in the air at 600 ℃ for 1h to obtain Fe on the surface of the foam iron₂O₃。

The experimental results are as follows:

through H₂After S plasma treatment, the color of the whole foam iron is changed uniformly, which indicates that FeS_xThe coverage on Fe is completely uniform, indicating that this plasma sulfidation process is easily scaled up. Then to FeS_xThe microstructure of/Fe was tested by Scanning Electron Microscopy (SEM). Fig. 1a, b show typical SEM images and corresponding energy dispersive x-ray spectroscopy (EDS). H₂After S plasma treatment, the porous foam structure is complete, and the surface is FeS_xThe layer was uniform and smooth. Excellent porosity and surface uniformity conversion to FeS_xAre important for electrocatalysis because they allow rapid diffusion of the active species, promote efficient permeation of the electrolyte, and significantly enlarge the surface area of the electrochemical reaction.

To the surface of FeS_xThe layers were further subjected to cross-sectional Scanning Transmission Electron Microscopy (STEM) testing. To prepare STEM samples, first FeS was used_xDepositing a Pt protective layer on the surface of the Fe. FIG. 1c shows FeS_xHigh Angle Annular Dark Field (HAADF) STEM pictures of layers. FIGS. 1d-g show the corresponding element distributions obtained by EDS. These knotsAs clearly shown, a layer of FeS with a thickness of about 70nm was uniformly formed on the surface of the foam iron_x. Further investigating FeS by X-ray photoelectron spectroscopy (XPS)_xComposition of the layer. FIG. 1h shows the full spectrum of XPS, and FIGS. 1i, j show the high resolution lines of Fe 2p and S2 p. The spectra of Fe at 707.3(2p3/2) and 720.0eV (2p1/2) show peaks for a pair of spin orbitals, the spectra of S at 162.5(2p3/2) and 163.7eV (2p1/2) show peaks for a pair of spin orbitals, and these binding energies have the same values as those of FeS₂Corresponds to (D) in (D), indicating surface-formed FeS_xPossibly FeS₂. Meanwhile, the integration of the peak areas of the Fe and S2 p spectral lines can obtain that the atomic ratio of S/Fe is 2.03 +/-0.03, which indicates that FeS is formed₂. Raman spectroscopy (FIG. 11) further shows that FeS is formed₂Is mixed FeS of pyrite and white iron ore₂Analogous to the use of H₂S plasma atomic layer deposition FeS₂But no raman signal of element S was observed.

FeS pair with a two-chamber cell at room temperature of 21 ℃ in 0.1M KOH solution_xThe three-electrode test was performed with electrocatalytic nitrogen reduction. FeS_xthe/Fe was used directly as the working electrode and pure nitrogen was continuously passed to the electrolyte. To investigate its competition with electrochemical hydrogen evolution, pure argon was used as a control instead of nitrogen. The electrochemical polarization curve reached steady state current by a step-growth potential (-0.14 to-0.42 vvs. rhe), each potential held for 120s (fig. 4). The steady state current values were then used to generate polarization curves for measurements under nitrogen or argon bubbling as shown in figure 2 a. The current density generated under nitrogen (j nitrogen) was found to be greater than that generated under argon (j argon), particularly in the interval of potentials from-0.22 to-0.38V (vs. rhe). Assuming that the current under argon bubbling should correspond to electrochemical hydrogen evolution, assuming electrochemical hydrogen evolution and nitrogen reduction are two independent competing processes, the difference between the two upper curves (Δ j ═ j nitrogen-j argon) should correspond to nitrogen reduction. The results showed that the difference in current density reached a maximum of-138. mu.A/cm when the potential was-0.30V (vs. RHE)²This value is up to 19.1% of the total current density under nitrogen bubbling conditions. Δ j of the high ratio columnj nitrogen means that there is a significant portion of the cathodic current used to reduce the nitrogen.

Products of nitrogen reduction (e.g. NH)₃And N₂H₄) The quantization was performed in the following manner. First, FeS is subjected to quantitative analysis in order to obtain a sufficient amount of product_xThe Fe electrode is biased for 20h under a certain constant potential, and then FeS is collected_xElectrolyte at the electrode side, the accumulated product amount was analyzed. This process was repeated at respective potentiostats-0.14, -0.22, -0.30, -0.38 and-0.42V (vs. rhe), while recording the change in current density with potential over the 20 h. As shown in FIG. 2b, the current density remained fairly constant over time, indicating FeS_xthe/Fe electrode has good electrocatalytic stability. Meanwhile, a negligible slight change in current density also indicates that the production rate of the reaction product is constant, and therefore the production rate of the product can be calculated by dividing the total production amount by the total reaction time. Ammonia as a main product of nitrogen reduction was quantitatively analyzed by indophenol blue method and nesian reagent method, respectively. FIG. 2c shows a photograph and an absorption spectrum curve measured by indophenol blue method, and the corresponding absolute calibration curve is shown in FIG. 5, which can obtain the ammonia concentration in the reaction product solution. Also, the photograph and the absorption spectrum measured by the Neisseria reagent method are shown in FIG. 9, and the absolute calibration curve is shown in FIG. 5. The ammonia concentration obtained from the absolute calibration curve can be used to calculate FeS_xThe yields of ammonia at different potentials for the electrocatalysts are very similar (within 4%) as shown in Table 1, and therefore the average of the two methods is simply used as the yield of ammonia FIG. 2d plots the ammonia yield against the corresponding potential (see Table 2) and it can be seen that at a potential of-0.30V (vs. RHE) the ammonia yield reaches a maximum of 4.25 × 10^-10mol·s^-1·cm^-2. The yield of this ammonia was rather high, essentially one of the most recently reported optimal values (table 3). The Faraday efficiency of ammonia was also calculated in this example, as shown in FIG. 2e, at a potential of-0.30V (vs. RHE), as high as 18.1%, which is also one of the best values reported so far. (Table 3). In addition, FIG. 2e also shows the comparison between Faraday efficiency and Δ j/j nitrogen,by comparison, the Delta j/j nitrogen is only higher than that of the ammonia production method (0.3-2.7%), which shows that the catalyst has high selectivity to ammonia in electrochemical reduction compared with other reduction products. In fact, the Watt-Chrisp spectrophotometry method was also used to quantify N₂H₄Yield of (2) (FIGS. 5 and 7), found N₂H₄Is the major by-product, thus explaining the source of the small error between faradaic efficiency and Δ j/j nitrogen (see table 2). In summary, FeS prepared by plasma treatment_xThe method has good performance of preparing ammonia by electrocatalytic reduction of nitrogen under the environmental condition, high ammonia yield, high Faraday efficiency and good stability.

To gain an insight into the electrocatalytic mechanism, FeS was treated separately in saturated solutions of argon and nitrogen_xthe/Fe electrode was subjected to Electrochemical Impedance Spectroscopy (EIS) measurements. Fig. 3a, b show nyquist and baud curves at-0.30V (vs. rhe). The nyquist plot shows that in both cases, the half circle is a single half circle, but the half circle diameter is smaller in the case of nitrogen saturation than in the case of argon saturation; the bode plot shows a single peak in the frequency range of 0.1Hz to 10khz, while the peak frequency for nitrogen saturation is greater than the peak frequency for argon saturation. Similar results were observed for the other potentials (fig. 8), with a single nyquist semicircle and baud peak representing a single equivalent charge transfer process in the frequency range 0.1Hz-10khz, indicating that electrochemical nitrogen reduction does compete with hydrogen evolution for reaction rate, perhaps considering them as two parallel processes. Thus, a slightly modified equivalent circuit was used to fit the EIS data in a nitrogen saturated solution, as shown in the inset of fig. 3c, where the charge transfer resistance (Rct) was divided into two reaction channels, RHER and RNRR, connected in parallel, and the RHER value was taken only for EIS data where no nitrogen reduction occurred in the argon saturated solution. The fitting results are detailed in table 4. Further calculation of RNRR at each potential^-1/(RNRR^-1+RHER^-1) And corresponds to a percentage of nitrogen reduction current. As shown in FIG. 3c, RNRR^-1/(RNRR^-1+RHER^-1) Shows the same trend as Δ j/j nitrogen (FIG. 2e), indicating good agreement between DC and AC tests.

Further reducing FeS after nitrogen_xThe surface composition of (a) was subjected to material characterization. As shown in FIG. 9, FeS was reduced with nitrogen_xThe surface appearance of the/Fe electrode is basically kept unchanged. However, Raman spectroscopy indicates FeS_xThis conclusion was also verified by XPS after nitrogen reduction of the mackinoi FeS with the crystal structure of the surface changed (fig. 10), and the peak positions of Fe 2p and S2 p were found to shift to the mackinoi FeS (fig. 11). Thus, the mackenoite FeS is likely to be a practical electrocatalyst. Furthermore, XPS spectra also showed the presence of nitrogen-containing species on the catalyst surface after nitrogen reduction (fig. 11): the observed binding energy of N1 s is 399.6eV, which may correspond to the formation of nitrogen-hydrogen compounds (e.g., NH) on the surface of the catalyst_xOr N_xH_y)。

Finally, FeS was also compared_xWith Fe₂O₃Nitrogen reducing property of, Fe₂O₃Is a good nitrogen reduction electrocatalyst which is reported recently. Fe is obtained on the surface of the same foamed iron in an oxidation mode₂O₃Catalyst, FeS can be obtained by testing_xFe electrode and Fe₂O₃The surface area of the/Fe electrodes was essentially the same (FIG. 12). Fe was obtained by the same measurement procedure₂O₃Maximum nitrogen yield and farada efficiency of the electrocatalyst are shown in figure 2 f. Note that pure iron foam did not show any measurable ammonia production. In fact, Fe₂O₃The catalyst showed a good ammonia yield of 4.25 × 10^-10mol·s^-1·cm^-2-0.3vvs. rhe), and a faraday efficiency of 2.2%, these values being in accordance with previous reports. These values are then significantly lower than the FeS in the present example_xA catalyst.

TABLE 1 comparison of ammonia production by indophenol blue and Neisseria reagent methods and average values, unit scale 10^-10mol·s^-1·cm^-2

TABLE 2 yield of ammonia and hydrazine, Faraday efficiency

TABLE 3 FeS_xComparison of Fe Performance with other catalysts

Table 4, results of EIS fitting, electric double layer capacitance (C)_dl) By passing

And (4) calculating. T and

parameters corresponding to CPE

In conclusion, the invention provides a simple, economical and effective plasma vulcanization method for preparing novel self-supporting FeS_xElectrocatalyst, such FeS when applied to electrocatalytic reduction of nitrogen at ambient conditions_xthe/Fe electrode demonstrated excellent ammonia production, 4.25 × 10^-10mol·s^-1·cm^-2And the Faraday efficiency is high and 18.1 percent, which is obviously better than other non-noble metal catalysts. FeS synthesized in view of plasma sulfurization method_xFe has good performance and lower cost, and is used in electrochemical ammonia synthesisHas wide application prospect. Furthermore, FeS_xThe catalyst is similar to Fe-S cluster in biological nitrogen fixation enzyme in a certain degree, which may provide important insight for simulating natural nitrogen fixation process.

It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.

Claims

1. Self-supporting FeS_xA method of preparing an electrocatalyst, comprising:

providing an iron substrate;

2. Self-supporting FeS according to claim 1_xThe preparation method of the electrocatalyst is characterized in that the iron substrate is foamed iron, an iron sheet or a stainless steel sheet.

3. Self-supporting FeS according to claim 1_xThe preparation method of the electrocatalyst is characterized in that the plasma is H₂S or H₂S and inert gas.

4. Self-supporting FeS according to claim 1_xThe preparation method of the electrocatalyst is characterized in that the treatment temperature is 25-300 ℃.

5. Self-supporting FeS according to claim 1_xThe preparation method of the electrocatalyst is characterized in that the treatment time is 5-180 min.

6. Self-supporting FeS according to claim 2_xOf electrocatalystsThe preparation method is characterized in that the plasma treatment of the foamed iron is carried out in a quartz tube in a tube furnace system, and the plasma is H₂S, the treatment process comprises cutting the foamed iron into pieces of 1cm × 2cm, and placing in the central region of a quartz tube H₂Heating to 160 ℃ during the S plasma treatment; h of 50sccm is continuously introduced₂S, entering a quartz tube, and maintaining the pressure in the quartz tube at 600mtorr by a vacuum pump; the upstream part of the quartz tube was wrapped with a copper coil, and 60W of RF power was supplied through the copper coil to generate H in the upstream region of the tube₂S, plasma; the plasma power supply is in pulse mode, each plasma pulse length is 15s, and the whole H₂S plasma treatment process is composed of 200H₂And (4) forming a plasma pulse cycle.

7. Self-supporting FeS_xElectrocatalyst, characterized in that the self-supporting FeS_xThe electrocatalyst comprises an iron substrate and FeS on the surface of the iron substrate_xSaid self-supporting FeS_xThe electrocatalyst adopts the self-supporting FeS of any one of claims 1 to 6_xThe preparation method of the electrocatalyst is provided.

8. Self-supporting FeS according to claim 7_xElectrocatalyst, characterized in that the self-supporting FeS_xThe electrocatalyst is self-supporting FeS₂An electrocatalyst.

9. Self-supporting FeS according to any one of claims 7 to 8_xApplication of an electrocatalyst in preparing ammonia by electrochemically reducing nitrogen.