A seawater corrosion resistant high-entropy alloy hydrogen catalyst, a preparation method and application thereof

Abstract

The application relates to the technical field of catalysts, and discloses a seawater corrosion-resistant high-entropy alloy hydrogen catalyst as well as a preparation method and application thereof, wherein the catalyst has a core-shell structure, the core structure is composed of a solid solution made of Fe, Co, Ni, Cr and Mo, the shell structure is a Cr2O3 / MoO2 composite passivation layer, and a chemical bonding interface is formed between the core structure and the shell structure. The catalyst obtained by the application not only has high corrosion resistance, but also has high activity, and can well catalyze seawater or industrial wastewater to obtain hydrogen.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a seawater corrosion resistant high-entropy alloy hydrogen catalyst and a preparation method and application thereof. BACKGROUND

[0002] In the prior art, hydrogen energy is one of the cleanest renewable energies. Among numerous clean energies, hydrogen energy is undoubtedly the most promising to replace fossil fuels in the future and then build a new green energy system with hydrogen as the carrier.

[0003] There are many ways to obtain hydrogen energy, among which water electrolysis technology can be driven by renewable energy and is an environmentally friendly technology for producing high-purity hydrogen. However, due to the large overpotential required by the hydrogen evolution reaction, a catalyst needs to be used on the electrode material. Traditional electrocatalytic hydrogen production technology mainly relies on noble metal catalysts (Pt / C) or transition metal sulfides (MoS2), but such catalysts limit the traditional electrocatalytic hydrogen production technology to only work in fresh water. For seawater electrolysis, industrial wastewater hydrogen production and other extreme water conditions, the existing catalysts face severe challenges. Pt-containing catalysts are prone to anodic dissolution in Cl⁻-containing media. For example, in a 3.5% NaCl solution, the Pt surface will lose active sites due to the formation of soluble PtCl4 2- complexes, and the overpotential will increase by more than 40% after 500 hours of operation. MoS2 is easily oxidized to MoO4 2- in alkaline conditions (pH>9), and the sulfur vacancies are easily poisoned by S 2- .

[0004] Therefore, it is still a technical bottleneck to be broken through to develop a hydrogen production catalyst with high activity, strong corrosion resistance and low cost. SUMMARY

[0005] To solve the above technical problems, the present application provides a seawater corrosion resistant high-entropy alloy hydrogen catalyst and a preparation method and application thereof. The catalyst obtained by the present application not only has high corrosion resistance, but also has high activity and can well catalyze seawater or industrial wastewater to obtain hydrogen.

[0006] The present application provides a seawater corrosion resistant high-entropy alloy hydrogen catalyst, which has a core-shell structure. The core structure is composed of a solid solution made of Fe, Co, Ni, Cr and Mo. The shell structure is a Cr2O3 / MoO2 composite passivation layer. A chemical bonding interface is formed between the core structure and the shell structure.

[0007] Further, the percentage of Fe atoms in the catalyst is 25%-35%, the percentage of Co atoms is 15%-25%, the percentage of Ni atoms is 15%-25%, the percentage of Cr atoms is 10%-20%, and the percentage of Mo atoms is 5%-15%.

[0008] Further, the thickness of the composite passivation layer is 2-5 nm.

[0009] Further, the catalyst is a porous structure, and the pore size is 50-200 nm or 1-5 μm.

[0010] Further, the specific surface area of the catalyst is 120-250 m 2 2 / g.

[0011] The application also provides a preparation method of the catalyst, and the preparation method comprises the following steps:

[0012] S1: according to the atomic percentage of the catalyst, iron, cobalt, nickel, chromium and molybdenum are weighed respectively, and the mixture of iron, cobalt, nickel, chromium and molybdenum is ball milled under the assistance of a plasma generator;

[0013] S2: the powder after ball milling is sieved, and the sieved powder is subjected to stage annealing; and

[0014] Further, the atomic percentage of Fe in the catalyst is 25-35%, the atomic percentage of Co is 15-25%, the atomic percentage of Ni is 15-25%, the atomic percentage of Cr is 10-20%, and the atomic percentage of Mo is 5-15%.

[0015] Further, during the ball milling, the ball-to-material ratio is 8-10:1.

[0016] Further, during the ball milling, the assistance of the plasma generator is adopted, the pressure is 0.1-0.3 MPa, the power is 600-1000 W, argon and hydrogen are introduced, and the volume ratio of argon to hydrogen is 95:5.

[0017] Further, the ball milling time is 6-12 h.

[0018] Further, the ball milling time is 8-10 h.

[0019] During the ball milling process, stable temperature can avoid oxidation, agglomeration or lattice defects caused by local overheating of the powder, and improve the uniformity of the alloy composition. Therefore, the rotation direction can be switched every 30 minutes during the ball milling process, and the powder temperature is monitored in real time and controlled in the range of 300-350 K, so as to ensure that the alloy powder is fully mechanically alloyed and a uniform solid solution precursor is formed.

[0020] Further, the D50 of the sieved powder is 50±5 nm.

[0021] ​Further, the process of the stage annealing comprises: a first stage, 250-350 DEG C for 0.5-2h; a second stage, 550-650 DEG C for 1-3h.

[0022] Further, the heating rate of the first stage is 3-8 DEG C / min, and the heating rate of the second stage is 1-3 DEG C / min.

[0023] Further, the first stage needs to pass mixed gas of ammonia and hydrogen, the volume ratio of ammonia and hydrogen is 1:3, and the flow rate is 30-100sccm; the second stage needs to pass argon.

[0024] Further, the cooling rate of the cooling is not less than 200 DEG C / s.

[0025] Further, the cooling rate of the cooling is 200-500 DEG C / s.

[0026] The application further provides application of the catalyst in electrocatalytic hydrogen production in seawater or waste water.

[0027] The application has the following technical effects:

[0028] 1. The application obtains a catalyst with core-shell structure, the shell structure is a Cr2O3 / MoO2 composite passivation layer, the composite passivation layer not only has corrosion resistance, but also has self-repairing ability. In addition, the atomic radii of Fe, Co and Ni in the core structure are similar, and the lattice distortion energy can be reduced after mixing with Cr and Mo, a stable solid solution can be formed, and segregation can be reduced.

[0029] 2. The application obtains a catalyst which can be applied in seawater or waste water, and is used for catalyzing seawater or waste water to form hydrogen. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0031] Figure 1 is a micrograph provided by the application, wherein Figure 1 a is a layered structure diagram in the above, Figure 1 b is a pore photograph of the catalyst, Figure 1 c is a Fe element distribution diagram in the catalyst,Figure 1 d is the Co element distribution map in the catalyst, Figure 1 e is the Ni element distribution map in the catalyst, Figure 1 f is the Cr element distribution map in the catalyst, Figure 1 g is the Mo element distribution map in the catalyst.

[0032] Figure 2 is the XRD pattern in the preparation process of Example 1 of the application.

[0033] Figure 3 is the test data of the application examples and comparative examples, wherein Figure 3 a is the overpotential data, Figure 3 b is the resistance data.

[0034] Figure 4 is the charge density of the application examples.

[0035] Figure 5 is the test data of the application examples applied to seawater electrolysis for hydrogen production.

[0036] Figure 6 is the hydrogen evolution overpotential comparison of the examples and comparative examples.

[0037] Figure 7 is the corrosion current density of the examples and comparative examples.

[0038] Figure 8 is the overpotential increase test data of the examples and comparative examples. DETAILED DESCRIPTION

[0039] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0040] In some embodiments of the first aspect, the application provides a seawater corrosion resistant high-entropy alloy hydrogen catalyst, which has a core-shell structure, the core structure is composed of a solid solution of Fe, Co, Ni, Cr and Mo, the shell structure is a Cr2O3 / MoO2 composite passivation layer, and a chemical bonding interface is formed between the core structure and the shell structure.

[0041] In the present application, the composite passivation layer (Cr2O3 / MoO2) blocks Cl - and S 2-The corrosion of the catalyst can be significantly improved; meanwhile, the chemical bonding interface (such as Cr-O-Mo bond) between the core-shell structures enhances the interface bonding force. In the long-term operation, the composite passivation layer may be locally corroded to cause a small amount of Cr / Mo to be dissolved out; based on the chemical bonding interface formed between the shell structures, the Cr and Mo in the core structure migrate to the passivation layer defects through surface diffusion or oxidation reaction to form a new Cr2O3 / MoO2 cover layer, thereby achieving dynamic self-repairing.

[0042] In the annealing process of the present application, Cr and Mo preferentially migrate to the alloy surface due to the difference in surface energy, and combine with oxygen to form a Cr2O3 / MoO2 composite passivation layer. By adjusting the atomic ratio of the catalyst (Fe: 25-35%, Co: 15-25%, Ni: 15-25%, Cr: 10-20%, Mo: 5-15%), on the one hand, the segregation of chromium and molybdenum is further hindered; on the other hand, the atomic radii of Fe, Co and Ni are similar, and the 3d electrons (unfilled orbitals) of Fe are strongly bonded with Co and Ni to form a uniform electron cloud distribution, thereby reducing the surface energy. Therefore, the lattice distortion energy of the mixture of Fe, Co and Ni is reduced, which not only forms a stable solid solution structure with Cr and Mo, but also avoids further segregation of Cr and Mo. It can be seen that by adjusting the atomic ratio of the catalyst as described above, the catalyst of the present application not only forms a passivation layer, which is beneficial to improve the corrosion resistance of the catalyst, but also forms a high-configuration-entropy core structure, which ensures the catalytic activity of the catalyst.

[0043] In the present application, a strong chemical bonding interface is formed between the core-shell structures through Cr-O-Mo bond. This interface not only enhances the strength of the core-shell combination through chemical bond, but also provides a channel for the migration of Cr / Mo. When the passivation layer is damaged, the Cr / Mo in the core structure diffuses to the defect site through the interface, and reacts with O 2- to generate a new passivation layer.

[0044] In some embodiments, the percentage of Fe atoms in the catalyst is 25%-35%, the percentage of Co atoms is 15%-25%, the percentage of Ni atoms is 15%-25%, the percentage of Cr atoms is 10%-20%, and the percentage of Mo atoms is 5%-15%.

[0045] In the present application, the percentage of Cr atoms and Mo atoms not only needs to form a stable solid solution with Fe, Co and Ni, but also needs to form a passivation layer with a certain thickness. The control of the proportion of Fe, Co and Ni not only realizes a uniform solid solution, but also avoids further segregation of Cr atoms and Mo atoms. In addition, the entropy of the catalyst is also improved. The high-configuration-entropy catalyst obtained by the present application not only has a longer service life, but also has good catalytic activity.

[0046] In some embodiments, the thickness of the composite passivation layer is 2-5 nm.

[0047] In the present application, the thickness of the composite passivation layer not only ensures the catalytic activity of the catalyst, but also improves the corrosion resistance of the catalyst.

[0048] In some embodiments, the catalyst has a porous structure with a pore size of 50-200 nm or 1-5 microns.

[0049] In the present application, the porous structure of the catalyst improves the specific surface area of the catalyst, thereby improving the catalytic efficiency.

[0050] In some embodiments, the specific surface area of the catalyst is 120-250 m 2 2 / g.

[0051] In a second aspect, the present application provides a preparation method of the catalyst, which comprises:

[0052] Step S1: according to the atomic percentage of the catalyst, iron, cobalt, nickel, chromium and molybdenum are weighed, and the iron, cobalt, nickel, chromium and molybdenum are ball milled under the assistance of a plasma generator;

[0053] Step S2: the ball milled powder is sieved, and the sieved powder is annealed in stages; and the catalyst is obtained after cooling.

[0054] In the present application, the plasma generator is used for assistance. First, the plasma generator provides additional energy, which can accelerate the mixing of metal powder; second, the high temperature generated can promote atomic diffusion and promote alloying; third, it improves efficiency and saves cost; finally, the impact of plasma on the surface of material particles can increase the number of defect sites and improve the catalytic activity.

[0055] In the method of the present application, by stage calcination and ball milling, not only the formation of the composite passivation layer is realized, but also the formation of the porous structure in the catalyst is realized. In the ball milling process, the atoms are uniformly dispersed, which is beneficial to the formation of solid solution in the stage annealing process.

[0056] In some embodiments, the atomic percentage of Fe in the catalyst is 25-35%, the atomic percentage of Co is 15-25%, the atomic percentage of Ni is 15-25%, the atomic percentage of Cr is 10-20%, and the atomic percentage of Mo is 5-15%.

[0057] In some embodiments, the ball-to-material ratio during ball milling is 8-10:1.

[0058] ​In some embodiments, the ball milling is assisted by a plasma generator, the pressure is 0.1-0.3 MPa, the power is 600-1000 W, argon and hydrogen are introduced, and the volume ratio of argon to hydrogen is 95:5.

[0059] In some embodiments, the ball milling time is 6-12 h.

[0060] In the present application, the ball milling can achieve the target particle size (D50=50±5 nm) and component uniformity; when the ball milling time is less than 6 h, the powder mixing is insufficient, resulting in uneven core-shell structure; when the ball milling time is more than 12 h, excessive oxidation or lattice defects may be caused. Therefore, in the present application, the ball milling time is controlled to be 6-12 h.

[0061] In some embodiments, the ball milling time is 8-10 h.

[0062] In the present application, when the ball milling time is controlled to be 8-10 h, the element distribution in the catalyst after ball milling is more uniform, and the performance of the catalyst is better.

[0063] In some embodiments, the D50 of the sieved powder is 50±5 nm.

[0064] In some embodiments, the process of the stage annealing includes: a first stage, 250-350℃ for 0.5-2 h; a second stage, 550-650℃ for 1-3 h.

[0065] In some embodiments, the heating rate to reach 250-350℃ in the first stage is 3-8℃ / min, and the heating rate to reach 550-650℃ in the second stage is 1-3℃ / min.

[0066] In the stage annealing process, the catalyst is induced to transform from body-centered cubic phase (BCC) to face-centered cubic phase (FCC), and the open lattice of the FCC structure is beneficial to the exposure of active sites and the diffusion of reactants, thereby improving the catalytic activity. In addition, the high symmetry of the FCC phase helps to reduce the surface energy, reduce element segregation, and enhance the uniformity of the core-shell structure.

[0067] In some embodiments, in the first stage, a mixed gas of ammonia and hydrogen is also introduced, the volume ratio of ammonia to hydrogen is 1:3, and the flow rate is 30-100 sccm; in the second stage, argon is also introduced.

[0068] In the present application, by controlling the kinetics in the stage annealing process (300-600℃), the active N atoms in NH3 / H2 atmosphere fill the grain boundaries, limiting the further excessive segregation of Cr / Mo, so as to not excessively affect the formation of solid solution.

[0069] In the present application, by controlling the flow of ammonia, the formation of vacancies in the catalyst and the number of formed vacancies are controlled, so as to ensure the stability of the catalyst structure and improve the catalytic activity of the catalyst.

[0070] In some embodiments, the cooling rate of the cooling is not less than 200℃ / s.

[0071] In the present application, by controlling the cooling rate to be not less than 200℃ / s, the formation of adverse phases can be inhibited, which is beneficial to maintaining the face-centered cubic phase structure formed at high temperature, which is beneficial to the exposure of active sites and the diffusion of reactants (protons (H + ) in water or intermediates ), avoiding the occupation of active sites by reactants, thereby improving the catalytic activity. At the same time, the rapid cooling can reduce the aggregation of elements to the grain boundaries or crystal faces through diffusion, thereby forming uneven segregation, and the cooling rate is beneficial to maintaining the uniform distribution of elements, thereby forming a stable solid solution structure. Rapid cooling helps to refine the grain size, increase the number of grain boundaries, and thus improve the strength and toughness of the material, so that the hardness and strength of the catalyst are improved. When the catalyst is applied to the catalytic environment of seawater or industrial wastewater, the improvement of the hardness and strength of the catalyst is beneficial to improving the corrosion resistance, chemical stability and mechanical wear resistance of the catalyst.

[0072] In some embodiments, the cooling rate of the cooling is 200℃ / s-500℃ / s.

[0073] In a third aspect, some embodiments of the present application also provide the use of the catalyst in the electrocatalytic hydrogen production in seawater or wastewater.

[0074] The following will be described in conjunction with specific examples and comparative examples:

[0075] Example 1:

[0076] Step S1: According to the atomic percentage of the catalyst, the metal powders of iron, cobalt, nickel, chromium and molybdenum (purity > 99.9%, particle size < 45 μm) were weighed, respectively, wherein the iron was weighed 26.8 g, the cobalt was weighed 18.9 g, the nickel was weighed 18.8 g, the chromium was weighed 12.5 g and the molybdenum was weighed 23.0 g, and the total mass was 100 g. After mixing uniformly in the argon glove box, it was loaded into a hard alloy ball mill pot, and the mixture of iron, cobalt, nickel, chromium and molybdenum balls was ball milled under a mixed atmosphere of argon and hydrogen. Plasma assisted ball milling: Ar / H2 mixed gas (volume ratio 95:5, pressure 0.2 MPa) was introduced; a 20 kHz plasma generator (power 800 W) was started, and the ball milling was carried out for 8 hours, with the rotation direction being switched every 30 minutes. The powder temperature was monitored in real time (dynamic fluctuation of 300 K-350 K), and the ball milling power fluctuation was controlled by PID to be ≤±5%, so as to ensure that the powder temperature was stable in the target interval.

[0077] Step S2: The ball milled powder was sieved, and the ball milled powder was filtered through a 200 mesh sieve to obtain an alloy powder with D50=50±5 nm. The sieved powder was subjected to stage annealing;

[0078] First stage: The powder was placed in a tube furnace, NH3 / H2 mixed gas (volume ratio 1:3, flow rate 50 sccm) was introduced, and the temperature was raised to 300℃ at a rate of 5℃ / min, and kept for 1 hour; a composite passivation layer was formed;

[0079] Second stage: Switch to Ar protective atmosphere, heat to 600℃ at a rate of 2℃ / min, keep for 2 hours; liquid nitrogen atomization rapid cooling (cooling rate > 200℃ / s), obtain catalyst Fe 30 Co 20 Ni 20 Cr 15 Mo 15 The microstructure of the obtained catalyst is shown in Figure 1 , wherein, Figure 1 a is the catalyst layer structure diagram in Figure 1 b is the catalyst pore actual diagram in Figure 1 c is the Fe element distribution diagram in the catalyst in Figure 1 d is the Co element distribution diagram in the catalyst in Figure 1 e is the Ni element distribution diagram in the catalyst in Figure 1 f is the Cr element distribution diagram in the catalyst in Figure 1 g is the Mo element distribution diagram in the catalyst in

[0080] Comparative Example 1:

[0081] Step S1: According to the target atomic percentage of the catalyst (Fe: 20%, Co: 25%, Ni: 25%, Cr: 20%, Mo: 10%), iron powder 21.4g, cobalt powder 24.6g, nickel powder 24.5g, chromium powder 16.4g, and molybdenum powder 13.1g (total mass 100g) were weighed. After mixing uniformly in an argon glove box, they were loaded into a hard alloy ball mill jar and ball milled under a mixed atmosphere of argon and hydrogen. Plasma-assisted ball milling was performed by introducing Ar / H2 mixed gas (volume ratio 95:5, pressure 0.2 MPa) and turning on a 20 kHz plasma generator (power 800 W) for 8 hours, with the rotation direction switched every 30 minutes. The powder temperature (dynamic fluctuation between 300 K and 350 K) was monitored in real time, and the ball milling power fluctuation was controlled by PID to be ≤±5%, ensuring that the powder temperature was stable in the target interval.

[0082] Step S2: The ball-milled powder was sieved. The ball-milled powder was filtered through a 200-mesh sieve to obtain an alloy powder with D50=50±5nm. The sieved powder was subjected to stage annealing.

[0083] First stage: The powder was placed in a tube furnace and introduced into NH3 / H2 mixed gas (volume ratio 1:3, flow rate 50 sccm). The temperature was raised to 300°C at a rate of 5°C / min and held for 1 hour.

[0084] Second stage: The atmosphere was switched to Ar protection. The temperature was raised to 600°C at a rate of 2°C / min and held for 2 hours. Rapid cooling was performed by liquid nitrogen atomization (cooling rate >200°C / s), and a Cr2O3 / MoO2 passivation layer-free catalyst Fe 20 Co 25 Ni 25 Cr 20 Mo 10 .

[0085] Comparative Example 2:

[0086] Step S1: According to the atomic percentage of the catalyst, iron, cobalt, nickel, chromium, and molybdenum metal powders (purity >99.9%, particle size <45μm) were weighed, wherein iron was weighed as 26.8g, cobalt as 18.9g, nickel as 18.8g, chromium as 12.5g, and molybdenum as 23g, with a total mass of 100g. After mixing uniformly in an argon glove box, they were loaded into a hard alloy ball mill jar and ball milled under a mixed atmosphere of argon and hydrogen. Plasma-assisted ball milling was performed by introducing Ar / H2 mixed gas (volume ratio 95:5, pressure 0.2 MPa) and turning on a 20 kHz plasma generator (power 800 W) for 8 hours, with the rotation direction switched every 30 minutes. The powder temperature (dynamic fluctuation between 300 K and 350 K) was monitored in real time, and the ball milling power fluctuation was controlled by PID to be ≤±5%, ensuring that the powder temperature was stable in the target interval.

[0087] Step S2: Sieving the ball-milled powder, the ball-milled powder is filtered through a 200-mesh sieve to obtain an alloy powder with a D50 = 50 ± 5 nm, and the sieved powder is single-annealed;

[0088] Step S3: Directly single-annealing the sieved powder: heating to 600°C at 5°C / min, introducing NH3 / H2 mixed gas (volume ratio 1:3, flow rate 50 sccm), and after 3 h of heat preservation, liquid nitrogen atomization cooling (cooling rate > 200°C / s) to obtain the catalyst Fe 30 Co 20 Ni 20 Cr 15 Mo 15 .

[0089] Comparative Example 3:

[0090] Pt / C.

[0091] Comparative Example 4:

[0092] Step S1: According to the atomic percentage of the catalyst, metal powders of iron, cobalt and nickel (purity > 99.9%, particle size < 45 μm) are weighed, wherein 40 g of iron, 30 g of cobalt and 30 g of nickel are weighed. After mixing uniformly in an argon glove box, they are loaded into a hard alloy ball mill jar, and the iron, cobalt and nickel are ball milled under a mixed atmosphere of argon and hydrogen. Plasma-assisted ball milling: introducing Ar / H2 mixed gas (volume ratio 95:5, pressure 0.2 MPa); turning on a 20 kHz plasma generator (power 800 W), ball milling for 8 hours, and switching the rotation direction every 30 minutes. The powder temperature is monitored in real time (dynamic fluctuation of 300 K-350 K), and the ball milling power fluctuation is controlled by PID to be ≤±5% to ensure that the powder temperature is stable in the target interval.

[0093] Step S2: Sieving the ball-milled powder, the ball-milled powder is filtered through a 200-mesh sieve to obtain an alloy powder with a D50 = 50 ± 5 nm, and the sieved powder is single-annealed;

[0094] First stage: placing the powder in a tube furnace, introducing NH3 / H2 mixed gas (volume ratio 1:3, flow rate 50 sccm), heating to 300°C at 5°C / min, and heat preserving for 1 hour;

[0095] Second stage: switching to Ar protective atmosphere, heating to 600°C at 2°C / min, heat preserving for 2 hours; liquid nitrogen atomization rapid cooling (cooling rate > 200°C / s) to obtain the catalyst Fe 40 Co 30 Ni 30 .

[0096] Comparative Example 5:

[0097] Conventional ternary alloy catalyst in the prior art: Fe 50 Co 30 Ni 20 .

[0098] Comparative Example 6: Physical deposition is used:

[0099] Step S1: According to the atomic percentage of the catalyst, metal powders (purity > 99.9%, particle size < 45 μm) of iron, cobalt, nickel, chromium and molybdenum are weighed, respectively, wherein iron is weighed 26.8g, cobalt is weighed 18.9g, nickel is weighed 18.8g, chromium is weighed 12.5g and molybdenum is weighed 23.0g, and the total mass is 100g. After mixing uniformly in the argon glove box, it is loaded into a hard alloy ball mill jar, and iron, cobalt, nickel, chromium and molybdenum are ball milled under a mixed atmosphere of argon and hydrogen. Plasma assisted ball milling: Ar / H2 mixed gas (volume ratio 95:5, pressure 0.2 MPa) is introduced; a 20 kHz plasma generator (power 800 W) is turned on, and the ball milling is carried out for 8 hours, and the rotation direction is switched every 30 minutes. The powder temperature (300K-350K dynamic fluctuation) is monitored in real time, and the ball milling power fluctuation is controlled by PID to be ≤±5%, so as to ensure that the powder temperature is stable in the target interval.

[0100] Step S2: The ball milled powder is sieved, and the ball milled powder is filtered through a 200 mesh sieve to obtain an alloy powder with D50=50±5nm. The sieved powder is deposited on the alloy surface by magnetron sputtering method (physical vapor deposition) to deposit Cr2O3 (thickness 2nm) and MoO2 (thickness 3nm) in sequence.

[0101] Deposition parameters: substrate temperature 200℃, sputtering power 150W, Ar / O2 mixed gas (volume ratio 4:1), vacuum degree 5×10 -3 Pa.

[0102] The catalysts obtained in the examples and comparative examples are tested and applied:

[0103] (1) The specific surface area of the obtained catalyst is tested, and the pore size of the porous structure thereof is tested.

[0104] (2) XPS detection: X-ray photoelectron spectrometer was used, monochromatic Al Kα ray (1486.6 eV) was used as excitation source, and the analysis depth was about 5-10 nm. After removing the surface contaminants by argon ion sputtering (1 keV, 60 s), the C 1s peak (284.8 eV) was used for charge correction. The high-resolution spectrum was peak-fitted by Avantage software, and the element chemical state was analyzed by combining NIST XPS database, focusing on the changes of Cr 2p, Mo 3d, Fe 2p, Co 2p and Ni 2p orbital binding energy, and the ratio of Cr2O3 and MoO2 in the passivation layer and the interface chemical bonding state were quantitatively analyzed.

[0105] (3) XRD detection: X-ray diffractometer was used, Cu Kα radiation, scanning range 10°-90°, step 0.02°, scanning rate 2° / min. The phase composition and crystal structure were analyzed by comparing the PDF card by Jade 6.0 software, and the lattice constant and grain size were calculated.

[0106] (4) TEM: Transmission electron microscope was used, acceleration voltage 200 kV. The sample was dropped onto the ultrathin carbon film copper net after ultrasonic dispersion by ethanol. The atomic arrangement and chemical bonding characteristics of the core-shell interface were observed by high-resolution TEM (HRTEM), and the lattice orientation was analyzed by selected area electron diffraction (SAED); the element spatial distribution was verified by energy spectrum area scanning (STEM-EDS).

[0107] (5) EDS: Energy spectrum area scanning was carried out under scanning electron microscope, acceleration voltage 15 kV, beam spot size 5 nm. The atomic percentage gradient of Fe, Co, Ni, Cr, Mo in the core-shell area was quantitatively analyzed by line scanning analysis of the cross section of the catalyst, and the element segregation degree and the uniformity of the passivation layer thickness were verified.

[0108] (6) The pore distribution of the catalyst was determined by nitrogen adsorption-desorption isotherm.

[0109] (7) The obtained catalyst was tested for electrochemical performance:

[0110] An electrochemical workstation was used, and a three-electrode system was used (working electrode: catalyst / foam nickel; reference electrode: Hg / HgO (1M KOH); counter electrode: platinum plate). Test conditions:

[0111] Linear sweep voltammetry: scan rate 2 mV / s, electrolyte 3.5% NaCl solution (pH=8.5), 25°C. The hydrogen evolution overpotential and Tafel slope were calculated by Tafel equation.

[0112] Electrochemical impedance spectroscopy: frequency range 0.1 Hz-100 kHz, amplitude 10 mV, equivalent circuit fitting to obtain charge transfer resistance and double-layer capacitance.

[0113] Cycling stability: constant current density 50mA / cm 2 Run continuously for 1000 h, and record the voltage change and activity decay rate.

[0114] (8) The catalyst obtained in the example is applied to the electrode:

[0115] Electrode preparation: Catalyst powder was mixed with Nafion solution (5 wt%) at a ratio of 9:1; after ultrasonic dispersion, it was coated on nickel foam (loading capacity 1 mg / cm 2 ); vacuum drying at 80° C. for 12 hours to form a porous electrode.

[0116] Electrolyzer integration: paired with IrO2 / Ti anode (electrode spacing 8mm); using Nafion 117 proton exchange membrane, electrolyte circulation flow rate 50mL / min.

[0117] Working condition verification: In industrial wastewater (COD=4200mg / L, Cl - =3.2mol / L): current density 500mA / cm 2 The voltage is 2.1V; the hydrogen purity is greater than 99.95%, the Faraday efficiency is 97.3%; the activity decay rate is less than 3% after 30 days of continuous operation.

[0118] Results and Analysis:

[0119] Table 1 Catalyst performance test

[0120]

[0121] The catalyst of Example 1 was successfully obtained by the method of the present invention. Figure 1 shown. Figure 1 In (a), it can be found that the catalyst of the present invention has obvious stratification, which shows that the catalyst of the present invention has a core-shell structure. Figure 1 In (b), it can be found that the surface of the catalyst has pores, and the pore size distribution is 50nm-200nm. Figure 1 In (c)-(g), it can be seen that the Fe, Co, Ni, Cr and Mo elements in the catalyst are evenly distributed in the catalyst. It can be seen that the method of the present invention achieves a uniform distribution of atoms in the catalyst, which is conducive to the formation of a solid solution.

[0122] The mixture prepared in Example 1 was tested using XRD, and the test results are as follows: Figure 2 It can be seen that a solid solution is successfully formed in Example 1 after annealing.

[0123] Figure 3 The catalytic activity of the catalysts obtained in Example 1, Comparative Example 5 and Comparative Example 3 was tested.Figure 3 As shown. It can be found that the polarization curve of Example 1 shows the smallest overpotential and the smallest Tafel slope, indicating that Example 1 has the highest catalytic activity. At the same time, the radius of the electrochemical impedance curve of Example 1 is the smallest, indicating that the conductivity of the catalyst of Example 1 is better than that of the comparative example. It is speculated that the reason why Example 1 of the present invention is better is that the method of the present invention successfully forms a high configurational entropy solid solution with Fe, Co, Ni and Cr and Mo in the core structure, and the solid solution forms a face-centered cubic phase structure (such as Figure 2 As shown, this structure facilitates the exposure of active sites and the diffusion of reactants, and the active sites are evenly dispersed, preventing reactants from occupying the active sites, thereby improving catalytic activity. Furthermore, by regulating the atomic ratios in the catalyst, further segregation of chromium and molybdenum is hindered. Furthermore, Fe, Co, and Ni not only have similar atomic radii, but the 3d electrons of Fe (unfilled orbitals) also form strong metallic bonds with Co and Ni, forming a uniform electron cloud distribution and reducing surface energy. Therefore, the lattice distortion energy of Fe, Co, and Ni is reduced after mixing, allowing them to form a stable solid solution structure with Cr and Mo while also preventing further segregation of Cr and Mo. In contrast, the BCC / FCC mixed phase of Comparative Example 5 and the non-alloy structure of Comparative Example 3 exhibit reduced active site density due to lattice distortion, which is directly reflected in the lowest Tafel slope (32 mV / dec) in Example 1. In addition, the core-shell interface in Example 1 of the present invention forms a strong chemical bond through the Cr-O-Mo bond, which optimizes the electron transfer path from the core to the shell, making the charge transfer resistance (Rct=2.5Ω) significantly lower than that of Comparative Example 5 (12.3Ω). Figure 3 As shown in (b), the multi-level pore structure and high specific surface area provide a fast channel for the diffusion of reactants, reducing concentration polarization, while the comparative example 5 (45m 2 / g) and Pt / C (25m 2 / g) limits the mass transfer efficiency, resulting in its overpotential (η 10 =72mV and 72mV) are much higher than that of Example 1 (38mV). In addition, the Cr2O3 / MoO2 composite passivation layer blocks Cl through a dense oxide network. - and S 2- Corrosion, Cr / Mo in the core dynamically repairs the passivation layer defects through interface diffusion, thereby reducing the loss of catalyst active sites. Therefore, the corrosion current density in Example 1 is as low as 1.2×10 -7 A / cm 2 , whereas Comparative Example 5 lacks a passivation layer, and Comparative Example 3 suffers from continuous loss of active sites due to Pt dissolution, resulting in significantly higher corrosion current densities than Example 1. This indicates that the design of the catalyst in Example 1 of the present invention facilitates the structural advantages of Example 1, enabling Example 1 to achieve high activity, strong corrosion resistance, and a long life under extreme operating conditions.

[0124] On this basis, the charge density of the catalyst obtained in Example 1 was theoretically calculated, and the results are shown in Figure 4 It can be found that the charge density of the catalyst obtained in the present application is 0.27 e / Å 3 , which is significantly improved compared with the traditional ternary alloy (Comparative Example 5, 0.12 e / Å 3 ) and Pt / C (Comparative Example 3, 0.18 e / Å 3 ). This value indicates that the synergistic effect of Fe, Co, Ni, Cr and Mo elements restructures the electron cloud distribution through high-entropy solid solution effect, forming a local high charge density area (peak value of 0.35 e / Å 3 ) at the core-shell interface, and the solid solution effectively enhances the adsorption capacity of H + and reduces the hydrogen desorption energy barrier (calculated value ), thereby greatly improving the hydrogen evolution reaction kinetics. In addition, the spatial uniformity of the charge density (coefficient of variation <5%) further verifies the uniformity of the solid solution structure, avoiding the passivation of active sites caused by element segregation, and the charge gradient (change from the core to the shell is 0.27 e / Å 3 -0.15 e / Å 3 ) at the Cr-O-Mo bonding interface provides a directional channel for electron transfer, reducing the charge transfer resistance. The charge gradient and directional transfer at the core-shell interface, as well as the local high charge density area, can significantly reduce the charge transfer resistance and accelerate the migration of protons (H + ) to the active site. This electronic structure characteristic is highly consistent with the test results of catalytic activity (η 10 = 38 mV), which theoretically reveals the essential mechanism of the synergistic optimization of active sites by multiple elements. It can be seen that the catalyst of the present application selects several elements to jointly change the electron cloud distribution. When the electron cloud distribution changes, the atoms of different elements re-adjust the aggregation state of electrons through interaction. This adjustment forms some "dense areas" or "sparse areas" of electrons on the surface of the material. The dense areas of electrons are more likely to attract positively charged reactants, achieving rapid adsorption of reactants to the surface of the catalyst; and the sparse areas of electrons are conducive to the stability and conversion of reaction intermediates, so the catalytic activity of the catalyst obtained in Example 1 is significantly improved.

[0125] The catalyst obtained in Example 1 was applied to a seawater electrolysis hydrogen production system, and the results are shown in Figure 5 It can be found that the working voltage curve of the catalyst obtained in Example 1 presents a smooth trend after working for 1200 hours, proving that the catalyst obtained in the present application has excellent stability and the ability to maintain high efficiency and corrosion resistance for a long time in harsh environments.

[0126] In Table 1, the corrosion resistance of the catalysts obtained in Example 1 and Comparative Example 1 was tested in a 3.5% NaCl solution, and the corrosion current density of Comparative Example 1 reached 5.8 x 10 -5 A / cm², while the corrosion current density of Example 1 was 1.2 x 10 -7 A / cm². On this basis, the activity decay of the catalysts was further tested. The catalysts obtained in Example 1 and Comparative Example 1 were placed in a simulated seawater electrolysis environment (3.5% NaCl solution, pH = 8.5, 25°C) to continuously operate at a constant current density of 50 mA / cm 2 for 500 hours, and the activity decay was tested. Specifically, the catalysts were loaded on a nickel foam electrode (loading amount 1 mg / cm 2 ), paired with an IrO2 / Ti anode, and a Nafion 117 proton exchange membrane was used, and the electrolyte circulation flow rate was 50 mL / min. The operating voltage was recorded every 24 hours, and the hydrogen evolution overpotential (η 10 ) change was determined by linear sweep voltammetry (LSV, scan rate 2 mV / s), and the metal ion concentration (ICP-MS) in the electrolyte was monitored to evaluate the degree of corrosion. After the operation was completed, the catalyst surface morphology was observed by SEM, and the passivation layer composition stability was analyzed by XPS. The test results showed that after 20 hours of operation, the overpotential of Example 1 increased by <3%, while the overpotential of Comparative Example 1 increased by >30% due to the lack of Cr / Mo passivation layer protection, and the Fe, Co, and Ni ion concentrations in the electrolyte increased significantly, confirming that the activity decay was caused by severe corrosion. In summary, the catalyst obtained in the present application has good corrosion resistance and stability because the composite passivation layer is derived from Cr and Mo. In addition, the composite passivation layer of the catalyst obtained in the present application has corrosion resistance, and its dynamic self-repairing ability improves the stability of the catalyst. This can also be verified by Comparative Example 6. In Table 1, the corrosion potential of Comparative Example 6 was significantly higher than that of Example 1. It can be seen that the physically deposited Cr2O3 / MoO2 layer is only combined with the core structure through physical adsorption, lacks Cr-O-Mo chemical bonding, has weak interfacial bonding force, and is easy to peel off in the electrolyte. After the passivation layer is damaged, the Cr / Mo in the core structure cannot repair the defects through interfacial diffusion, resulting in an increase in the corrosion current density and a continuous loss of active sites. The physical deposition method can only form a mechanically combined passivation layer and cannot realize element migration and dynamic protection driven by the interface, which confirms the necessity of the stage annealing process in the present application.

[0127] The hydrogen evolution overpotentials of the catalysts obtained in Example 1, Comparative Examples 1-3, and Comparative Example 5 were compared, and the results are shown in Table 1. Figure 6The hydrogen evolution overpotential of Example 1 is the lowest (38 mV), which is significantly better than all the comparative examples (58 mV-85 mV), indicating that the catalytic activity of Example 1 is the highest. The comparison between Example 1 and Comparative Example 1 shows that during the ball milling and step annealing process of Example 1, an interface bonding is formed on the surface of Example 1, while no interface bonding is formed on Comparative Example 1, and the overpotential thereof is 38 mV and 85 mV respectively, indicating that the Cr / Mo composite passivation layer and the chemical bonding interface are the key to improve the activity.

[0128] The comparison between Example 1 and Comparative Example 2 shows that Example 1 adopts step annealing, and during the step annealing process, the catalyst is induced to transform from a body-centered cubic phase (BCC) to a face-centered cubic phase (FCC), and the open lattice of the FCC structure is conducive to the exposure of active sites and the diffusion of reactants, thereby improving the catalytic activity. In addition, the high symmetry of the FCC phase helps to reduce the surface energy, reduce element segregation, and enhance the uniformity of the core-shell structure. It can be seen that in the method of the present application, the first stage of the step annealing process stabilizes the passivation layer, and the high-temperature phase transformation (second stage) optimizes the crystal structure, and the step annealing process is conducive to improving the activity of the catalyst. This can be verified by comparing Example 1 and Comparative Example 2. The catalytic activity of the catalyst obtained by Example 1 and Comparative Example 2 is tested. The results show that the hydrogen evolution overpotential η 10 =58 mV (38 mV for Example 1), and the charge transfer resistance Rct=5.2 Ω (2.5 Ω for Example 1). It can be seen that the step annealing process obtained by the present application is conducive to the transformation of the structure of the catalyst to the face-centered cubic phase structure, and this structure is conducive to improving the catalytic activity of the catalyst.

[0129] In Figure 7 , the corrosion current density of Example 1 is always stable at 1.2×10 -7 A / cm 2 , and hardly changes with time, indicating that the passivation layer thereof has long-term protection capability. The corrosion current density of Comparative Example 1 (without Cr / Mo) rapidly rises from 5.8×10 -5 A / cm 2 to 8×10 -4 A / cm 2 (1000 hours), and it can be seen that the corrosion is out of control when there is no Cr2O3 / MoO2 passivation layer. The corrosion current density (5.1×10 -6 A / cm 2 ) of Comparative Example 3 (Pt / C) is lower than that of Comparative Example 1, but is still 2 orders of magnitude higher than that of Example 1, further verifying the corrosion resistance advantage of the high-entropy alloy core-shell structure.

[0130] In Figure 8In the middle, the overpotential increment of Example 1 is only 3%, far below the threshold value (10%), indicating that its long-term operation stability is excellent. The increments of Comparative Example 1 and Comparative Example 5 are 30% and 25% respectively, indicating that the loss of passivation layer and self-repairing mechanism leads to rapid performance decay. The increment of Comparative Example 3 (Pt / C) is as high as 40%, further proving the unsuitability of traditional noble metal catalysts under extreme working conditions.

[0131] In summary, the catalyst obtained by the application can be applied in seawater or wastewater, and has good catalytic activity and corrosion resistance.

[0132] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the technical solutions of the embodiments of the present application.

Claims

1. A seawater corrosion-resistant high-entropy alloy hydrogen catalyst, characterized in that: The catalyst has a core-shell structure, wherein the core structure is composed of a solid solution of Fe, Co, Ni, Cr and Mo, and the shell structure is a Cr2O3 / MoO2 composite passivation layer, and a chemical bonding interface is formed between the core structure and the shell structure.

2. The catalyst according to claim 1, characterized in that The catalyst contains 25%-35% Fe atomic percentage, 15%-25% Co atomic percentage, 15%-25% Ni atomic percentage, 10%-20% Cr atomic percentage, and 5%-15% Mo atomic percentage.

3. The catalyst according to claim 1, characterized in that The thickness of the composite passivation layer is 2nm-5nm.

4. The catalyst according to claim 1, characterized in that The catalyst has a porous structure with a pore size of 50nm-200nm or 1μm-5μm; the specific surface area of ​​the catalyst is 120m 2 / g-250m 2 / g.

5. The method for preparing the catalyst according to any one of claims 1 to 4, characterized in that: The preparation method comprises: Step S1: Weighing iron, cobalt, nickel, chromium, and molybdenum according to the atomic percentage of the catalyst, and ball-milling the mixture of iron, cobalt, nickel, chromium, and molybdenum in a mixed atmosphere of argon and hydrogen; Step S2: sieving the ball-milled powder, annealing the sieved powder in stages, and cooling the powder to obtain a catalyst; The staged annealing process includes: a first stage, keeping the temperature at 250° C.-350° C. for 0.5 h-2 h; and a second stage, keeping the temperature at 550° C.-650° C. for 1 h-3 h.

6. The preparation method according to claim 5, characterized in that The catalyst contains 25%-35% Fe atomic percentage, 15%-25% Co atomic percentage, 15%-25% Ni atomic percentage, 10%-20% Cr atomic percentage, and 5%-15% Mo atomic percentage.

7. The preparation method according to claim 5, characterized in that During the ball milling, the ball-to-material ratio is 8-10:1; the volume ratio of argon gas to hydrogen gas is 95:5; During the ball milling, plasma is used for assistance, with a pressure of 0.1-0.3 MPa and a power of 600-1000W.

8. The preparation method according to claim 5, characterized in that In the first stage, the heating rate to 250°C-350°C is 3-8°C / min, and in the second stage, the heating rate to 550°C-650°C is 1-3°C / min; During the first stage, a mixed gas of ammonia and hydrogen needs to be introduced, with a volume ratio of ammonia to hydrogen of 1:3 and a flow rate of 30-100 sccm; during the second stage, argon needs to be introduced.

9. Use of the catalyst according to any one of claims 1 to 4 in electrocatalytic hydrogen production from seawater or wastewater.

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