Vanadium-based solid solution hydrogen storage alloy with high activation performance

Abstract

The invention discloses a high-activation-performance vanadium-based solid solution hydrogen storage alloy, and relates to the field of hydrogen storage alloys, the hydrogen storage alloy has a gradient nanostructure, and comprises a core area: an isometric crystal structure with a grain size of 50-200 nm; the transition area is of a nanocrystalline structure with the grain size of 20-50 nm; and the surface layer area is an amorphous / nanocrystalline composite layer with the thickness of 2-8nm, by designing a gradient nanostructure and through the synergistic effect of the core area, the transition area and the surface layer area, the mechanical strength of the alloy is guaranteed, the surface activation performance is improved, and by means of the novel preparation technology combining ball milling with gradient sintering and accurately controlling technological parameters of all stages, the mechanical strength of the alloy is improved. And the optimized distribution of the additive and the controllable formation of the nano structure are realized.

Description

Technical Field

[0001] The present invention relates to the field of hydrogen storage alloys, in particular to a vanadium-based solid solution hydrogen storage alloy with high activation performance. Background Art

[0002] With the rapid development of hydrogen energy technology, hydrogen storage materials, as a key link in hydrogen energy utilization, have a direct impact on the efficiency and reliability of fuel cell systems. Traditional hydrogen storage alloys mainly include AB5 type (such as LaNi5) and AB2 type (such as TiMn2) alloys. Although they have certain hydrogen storage capacity, they generally have the following technical bottlenecks:

[0003] Traditional alloys require high temperature and high pressure activation for the first hydrogen absorption, and many activation cycles, which seriously restricts their practical application efficiency.

[0004] Therefore, it is necessary to propose a vanadium-based solid solution hydrogen storage alloy with high activation performance to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a vanadium-based solid solution hydrogen storage alloy with high activation performance to solve the problem that traditional alloys require high temperature and high pressure activation for the first hydrogen absorption and the number of activation cycles is large, which seriously restricts their practical application efficiency.

[0006] To achieve the above object, the present invention provides the following technical solution: a vanadium-based solid solution hydrogen storage alloy with high activation performance, composed of the following elements in percentage by mass: vanadium: 35%-48%, titanium: 12%-18%, chromium: 8%-12%, iron: 12%-18%;

[0007] The hydrogen storage alloy has a gradient nanostructure, comprising:

[0008] Core area: equiaxed crystal structure with a grain size of 50-200nm, Cr-Fe phase enriched at the grain boundaries, forming hydrogen diffusion channels, where the lattice distortion is ≤5% and the BCC phase purity is ≥95%;

[0009] Transition zone: nanocrystalline structure with grain size of 20-50nm and gradient dislocation density;

[0010] Surface layer: an amorphous / nanocrystalline composite layer with a thickness of 2-8 nm, and an amorphous phase accounting for 30%-50%;

[0011] The surface layer generates a compound phase containing additive elements through in-situ reaction. The additive is selected from at least one of carbon nanotubes, graphene, and boron nitride, and the addition amount is 0.2%-0.8% of the total mass of the raw materials.

[0012] The surface region comprises the following features:

[0013] Carbon nanotube or graphene-derived carbide phase, uniformly distributed in the form of nano-islands

[0014] The BN phase derived from boron nitride is distributed in the form of a continuous network;

[0015] The oxygen content is ≤1.5at.%, and oxygen is mainly stored in compounds.

[0016] Preferably, at 25°C and 1.5 MPa hydrogen pressure:

[0017] Initial hydrogen absorption rate ≥ 2.5wt.% / min;

[0018] More than 90% of the maximum hydrogen absorption capacity can be achieved within 10 minutes;

[0019] Capacity retention rate after 100 cycles ≥95%

[0020] Preferably, the hydrogen storage alloy maintains stable hydrogen storage performance within a temperature range of -30°C to 80°C, and the capacity fluctuation caused by temperature difference is ≤5%.

[0021] The present invention also discloses a method for preparing a vanadium-based solid solution hydrogen storage alloy with high activation performance, comprising the following steps:

[0022] Raw material pretreatment: anneal vanadium powder, titanium powder, chromium powder and iron powder in vacuum at 200-300℃ for 1-2 hours respectively;

[0023] Graded ball milling;

[0024] Gradient sintering;

[0025] Controllable cooling;

[0026] Wherein, the graded ball milling comprises:

[0027] Primary ball milling: ball-to-material ratio 5:1, speed 200-300 rpm, time 1-2 hours;

[0028] Fine ball milling: ball-to-material ratio 15:1, speed 450-550rpm, time 3-4 hours, while adding additives;

[0029] Preferably, the gradient sintering includes:

[0030] The first stage: 800-900℃, 1 hour, argon atmosphere;

[0031] The second stage: 1100-1150℃, 2-3 hours, vacuum degree ≤10^-3Pa.

[0032] Preferably, in the controlled cooling, the first cooling is performed at a rate of 50-100°C / min to 600°C, and the second cooling is performed at a rate of 10-20°C / min to room temperature.

[0033] Preferably, during the graded ball milling process:

[0034] Zirconia balls with a diameter of 10 mm were used for primary ball milling;

[0035] Fine ball milling uses tungsten carbide balls with a diameter of 5 mm;

[0036] During the ball milling process, argon gas was introduced for protection and the oxygen content was ≤50ppm.

[0037] Preferably, intermittent ultrasonic treatment is applied in the range of 600-400° C. during the controlled cooling, with a frequency of 20-40 kHz and a power of 500-800 W.

[0038] Preferably, during the controllable cooling, when the cooling temperature reaches below 300° C., a surface passivation treatment is performed, and an argon mixture containing 1% to 3% hydrogen is introduced.

[0039] Preferably, the graded ball milling uses a planetary ball mill and a vibrating ball mill.

[0040] Technical effects and advantages of the present invention:

[0041] 1. A gradient nanostructure is designed, which ensures the mechanical strength of the alloy and improves the surface activation performance through the synergistic effect of the core area, transition area and surface area.

[0042] 2. Through a new preparation process combining graded ball milling with gradient sintering, the optimized distribution of additives and the controllable formation of nanostructures are achieved by precisely controlling the process parameters at each stage.

[0043] 3. Innovative methods such as pulsed magnetic field and ultrasonic treatment were introduced during the cooling process to effectively control the microstructure and surface state of the alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of the preparation method of the present invention. DETAILED DESCRIPTION

[0045] The present invention provides Figure 1 The high activation performance vanadium-based solid solution hydrogen storage alloy shown is composed of the following elements in percentage by mass: vanadium: 35%-48%, titanium: 12%-18%, chromium: 8%-12%, iron: 12%-18%;

[0046] Vanadium constitutes the BCC solid solution matrix, and the lattice gap size (0.21-0.23nm) is adapted to the diffusion of hydrogen atoms. Titanium is used to expand the lattice constant (a=0.302→0.315nm) and reduce the hydrogen desorption enthalpy. Chromium forms a passivation film (Cr2O3) to inhibit oxygen penetration. Iron catalyzes the dissociation of hydrogen molecules and reduces the activation energy barrier to 0.3eV.

[0047] Specifically, vanadium, as the main element, constitutes a body-centered cubic (BCC) solid solution matrix with a lattice gap size between 0.21-0.23 nm. This size range is highly compatible with the size of hydrogen atoms, providing a good channel for the diffusion of hydrogen atoms, allowing hydrogen atoms to move smoothly inside the alloy, thus creating favorable conditions for the hydrogen storage process.

[0048] The addition of titanium plays a key role, effectively expanding the lattice constant from 0.302nm to 0.315nm.

[0049] This increase in the lattice constant not only helps to further optimize the diffusion path of hydrogen atoms in the alloy, but also reduces the hydrogen desorption enthalpy, making it easier for hydrogen atoms to be released from the alloy, thereby improving the hydrogen storage efficiency and reversibility of the hydrogen storage alloy. Chromium plays a major protective role in the alloy, forming a dense passivation film (Cr2O3) on the surface of the alloy. This passivation film can effectively inhibit the penetration of oxygen and prevent the alloy from being oxidized in the air, thereby extending the service life of the alloy and ensuring the stability of its hydrogen storage performance. Iron, as a catalyst, can catalyze the dissociation of hydrogen molecules and reduce the activation energy barrier to 0.3 eV.

[0050] This lower activation energy barrier means that hydrogen molecules are more easily decomposed into hydrogen atoms on the alloy surface, and then enter the alloy interior for storage, greatly improving the alloy's hydrogen storage reaction rate.

[0051] The hydrogen storage alloy has a gradient nanostructure, including:

[0052] Core area: Equiaxed crystal structure with grain size of 50-200nm, providing mechanical support and anti-powdering (volume expansion rate <8%).

[0053] Transition zone: nanocrystalline structure with grain size of 20-50nm, fast hydrogen diffusion channel.

[0054] Surface region: Amorphous / nanocrystalline composite layer with a thickness of 2-8 nm (containing VC nano-islands (5-15 nm) and h-BN network structure (interlayer spacing 0.33 nm)), providing high-density active sites and blocking oxygen diffusion.

[0055] The surface layer generates a compound phase containing additive elements through in-situ reaction. The additive is selected from at least one of carbon nanotubes, graphene, and boron nitride, and the addition amount is 0.2%-0.8% of the total mass of the raw materials.

[0056] The surface area contains the following features:

[0057] Carbon nanotube or graphene-derived carbide phase, uniformly distributed in the form of nano-islands

[0058] The BN phase derived from boron nitride is distributed in the form of a continuous network;

[0059] The oxygen content is ≤1.5at.%, and oxygen is mainly stored in compounds.

[0060] The nano-island structure not only increases the density of active sites on the surface, but also improves the electrical conductivity and thermal stability of the alloy. The boron nitride-derived BN phase is distributed in the surface region in a continuous network. This network structure effectively blocks oxygen diffusion and improves the thermal conductivity and chemical stability of the alloy.

[0061] At 25°C and 1.5MPa hydrogen pressure:

[0062] The initial hydrogen absorption rate is ≥2.5wt.% / min (traditional alloys ≤1.0wt.% / min), the hydrogen absorption capacity reaches more than 90% in 10 minutes, and the number of activation cycles is ≤3 times (traditional alloys require 10-20 times), with ultra-high activation performance.

[0063] More than 90% of the maximum hydrogen absorption capacity can be achieved within 10 minutes;

[0064] Capacity retention rate after 100 cycles ≥95%

[0065] The hydrogen storage alloy maintains stable hydrogen storage performance in the temperature range of -30°C to 80°C, and the capacity fluctuation caused by temperature difference is ≤5%.

[0066] This enables the alloy to work stably under various ambient temperature conditions, ensuring that its hydrogen storage performance is not affected, whether it is cold winter or hot summer, thereby greatly expanding the application range of the alloy and enabling it to meet the needs of more practical applications.

[0067] The present invention also discloses a method for preparing a vanadium-based solid solution hydrogen storage alloy with high activation performance, comprising the vanadium-based solid solution hydrogen storage alloy with high activation performance according to any one of claims 1 to 3, further comprising the following steps:

[0068] Raw material pretreatment: anneal vanadium powder, titanium powder, chromium powder and iron powder in vacuum at 200-300℃ for 1-2 hours to remove surface adsorbed water (H2O content <100ppm) and improve powder fluidity.

[0069] Removing surface adsorbed water prevents the adverse effects of moisture on alloy properties during subsequent preparation processes. For example, it prevents hydrogen and oxygen generated by water decomposition at high temperatures from reacting with alloying elements, thereby ensuring the purity and stability of the alloy. Improving the flowability of the powder facilitates uniform mixing during subsequent mixing processes such as ball milling, ensuring uniform distribution of the elements in the alloy.

[0070] Graded ball milling;

[0071] Gradient sintering;

[0072] Controllable cooling;

[0073] Among them, graded ball milling includes primary ball milling and fine ball milling;

[0074] Graded ball milling includes: primary ball milling uses zirconia balls with a diameter of 10mm; fine ball milling uses tungsten carbide balls with a diameter of 5mm;

[0075] During the ball milling process, argon gas was introduced for protection and the oxygen content was ≤50ppm.

[0076] Primary ball milling: ball-to-material ratio 5:1, speed 200-300rpm, time 1-2 hours, coarse crushing, mixing uniformity >99%

[0077] Fine ball milling: ball-to-material ratio 15:1, rotation speed 450-550rpm, time 3-4 hours, while adding additives to introduce high-density dislocations to form nanocrystalline precursors.

[0078] The presence of high-density dislocations provides more nucleation sites for grain growth during the subsequent sintering process, which is conducive to the formation of fine nanocrystalline structures, thereby improving the hydrogen storage performance of the alloy. At the same time, the addition of additives also makes it possible to optimize the surface properties and microstructure of the alloy.

[0079] The classifying ball milling uses a planetary ball mill and a vibration ball mill.

[0080] Gradient sintering includes the first stage and the second stage;

[0081] The first stage involves 800-900°C for one hour in an argon atmosphere to eliminate internal stress and perform pre-alloying. The argon atmosphere effectively prevents powder oxidation during ball milling, ensuring powder purity and alloy stability. Keeping the oxygen content extremely low prevents the formation of excessive oxide impurities in the alloy, thereby maintaining the alloy's hydrogen storage properties.

[0082] The second stage: 1100-1150℃, 2-3 hours.

[0083] During the gradient sintering process, the heating rate in the first stage is 10-15°C / min, and the heating rate in the second stage is 5-8°C / min. During the second stage of heat preservation, a pulsed magnetic field of 0.5-1T is applied. The pulsed magnetic field (0.5-1T) induces oriented growth of grains <100nm.

[0084] In the controlled cooling, the first cooling is performed at a rate of 50-100°C / min to 600°C, and the second cooling is performed at a rate of 10-20°C / min to room temperature.

[0085] During controlled cooling, intermittent ultrasonic treatment is applied in the range of 600-400℃, with a frequency of 20-40kHz and a power of 500-800W. The cavitation effect eliminates residual stress (reduced by 85%) and reduces microcracks.

[0086] During controlled cooling, when the cooling temperature reaches below 300℃, surface passivation treatment is performed and a mixture of argon and hydrogen (1%-3%) is introduced to form VH 0.5 A protective layer (thickness ≈ 3 nm) inhibits further oxidation.

[0087] A gradient nanostructure was designed, which ensured the mechanical strength of the alloy and improved the surface activation performance through the synergistic effect of the core zone, transition zone and surface zone.

[0088] Through a new preparation process combining graded ball milling with gradient sintering, the optimized distribution of additives and the controllable formation of nanostructures are achieved by precisely controlling the process parameters at each stage.

[0089] Innovative methods such as pulsed magnetic field and ultrasonic treatment were introduced during the cooling process to effectively regulate the microstructure and surface state of the alloy.

[0090] The gradient nanostructure of the hydrogen storage alloy (core region → transition region → surface region) is mainly achieved through the collaborative process of graded ball milling + gradient sintering + controlled cooling. The specific formation process is as follows:

[0091] Graded ball milling: preliminary construction of nanocrystalline and amorphous phases.

[0092] Primary ball milling (coarse crushing) is used to initially alloy metal powders such as vanadium, titanium, chromium, and iron to form micron-sized composite particles (1-10 μm). The ball-to-material ratio is 5:1, the rotation speed is 200-300 rpm, and the time is 1-2 hours. 10 mm zirconia balls are used to produce plastic deformation through high-energy collisions, introducing dislocations and subgrain boundaries.

[0093] Fine ball milling (nano- and amorphization) further refines the grains and introduces an amorphous phase on the surface. 5mm tungsten carbide balls (higher hardness) are used to generate more intense shear forces, reducing the grain size to 20-50nm. The ball-to-material ratio is 15:1, the rotation speed is 450-550rpm, and the time is 3-4 hours.

[0094] Additives (carbon nanotubes / graphene / boron nitride) are embedded in the particle surface during ball milling, and compound phases (such as VCx and BN) are generated in situ during subsequent sintering. Severe mechanical deformation leads to lattice distortion, increased grain boundary energy, and amorphous transformation in some areas (especially the surface). The additives are evenly dispersed during ball milling, providing a template for the subsequent gradient structure.

[0095] Gradient sintering: grain control in the core and transition zones.

[0096] Among them, the first stage (800-900℃, 1h, argon protection) is used to promote the formation of solid solution but inhibit excessive grain growth. The formation mechanism is:

[0097] Low-temperature sintering allows the alloying elements (V, Ti, Cr, Fe) to fully diffuse into each other and form a BCC solid solution. Since the initial powder has been nanosized, 50-200nm equiaxed grains are retained in the core area after sintering (Ti-Cr enriched grain boundaries inhibit grain growth).

[0098] In the second stage (1100-1150℃, 2-3h, high vacuum), the temperature gradient is used to drive the segregation of elements to form transition zone nanocrystals. The formation mechanism is as follows:

[0099] At high temperatures, Cr and Fe migrate to the grain boundaries to form nanoscale Cr-Fe precipitates (size 10-30 nm);

[0100] Ti-V undergoes spinodal decomposition, forming a 5-15nm Ti-rich / V-rich domain structure (transition zone characteristics);

[0101] Because the surface layer is exposed to the vacuum environment, some elements (such as Ti) evaporate preferentially, forming a defect-rich area.

[0102] Controlled cooling: the final formation of the surface amorphous / nanocrystalline composite layer.

[0103] The first stage is rapid cooling (50-100℃ / min→600℃), which is used to lock the high-temperature phase and avoid grain coarsening. The specific formation mechanism is: rapid cooling keeps the core area equiaxed, while the transition area forms 20-50nm nanocrystals due to the high defect density.

[0104] The second stage is slow cooling (10-20°C / min to room temperature) to promote surface amorphization and compound phase formation. The formation mechanism is as follows: ultrasonic waves (20-40kHz) are applied in the range of 600-400°C. The cavitation effect promotes the rearrangement of surface atoms and forms an amorphous phase (30% to 50% amorphous).

[0105] Additives (such as carbon nanotubes) react with V / Ti to form VCx nanoislands (3-8nm).

[0106] Surface passivation below 300°C (1% to 3% H2 / Ar mixed gas) allows hydrogen atoms to penetrate into the surface amorphous area, stabilizing the structure and inhibiting oxidation. Boron nitride (BN) forms a continuous network structure covering the surface of the amorphous layer.

Claims

1. High activation performance vanadium-based solid solution hydrogen storage alloy, characterized by: The following elements are present in percentage by mass composition: Vanadium: 35%-48%, Titanium: 12%-18%, Chromium: 8%-12%, Iron: 12%-18%; The hydrogen storage alloy has a gradient nanostructure, comprising: Core area: equiaxed crystal structure with a grain size of 50-200nm, Cr-Fe phase enriched at the grain boundaries, forming hydrogen diffusion channels, where the lattice distortion is ≤5% and the BCC phase purity is ≥95%; Transition zone: nanocrystalline structure with grain size of 20-50nm and gradient dislocation density; Surface layer: an amorphous / nanocrystalline composite layer with a thickness of 2-8 nm, and an amorphous phase accounting for 30%-50%; The surface layer generates a compound phase containing additive elements through an in-situ reaction, wherein the additive is selected from at least one of carbon nanotubes, graphene, and boron nitride, and the addition amount is 0.2%-0.8% of the total mass of the raw materials; Carbon nanotube or graphene-derived carbide phase, uniformly distributed in the form of nano-islands; The BN phase derived from boron nitride is distributed in the form of a continuous network; The oxygen content is ≤1.5at.%, and oxygen is mainly stored in compounds.

2. The vanadium-based solid solution hydrogen storage alloy with high activation performance according to claim 1, characterized in that: At 25°C and 1.5MPa hydrogen pressure: Initial hydrogen absorption rate ≥ 2.5wt.% / min; More than 90% of the maximum hydrogen absorption capacity can be achieved within 10 minutes; The capacity retention rate after 100 cycles is ≥95%.

3. The vanadium-based solid solution hydrogen storage alloy with high activation performance according to claim 3, characterized in that: The hydrogen storage alloy maintains stable hydrogen storage performance within a temperature range of -30°C to 80°C, and the capacity fluctuation caused by temperature difference is ≤5%.

4. A method for preparing a vanadium-based solid solution hydrogen storage alloy with high activation performance, characterized in that: The method comprises the vanadium-based solid solution hydrogen storage alloy with high activation performance according to any one of claims 1 to 3, further comprising the following steps: Raw material pretreatment: anneal vanadium powder, titanium powder, chromium powder and iron powder in vacuum at 200-300℃ for 1-2 hours respectively; Graded ball milling; Gradient sintering; Controllable cooling; Wherein, the graded ball milling includes primary ball milling and fine ball milling; Primary ball milling: ball-to-material ratio 5:1, speed 200-300 rpm, time 1-2 hours; Fine ball milling: ball-to-material ratio 15:1, speed 450-550rpm, time 3-4 hours, while adding additives.

5. The method for preparing a vanadium-based solid solution hydrogen storage alloy with high activation performance according to claim 4, characterized in that: The gradient sintering comprises: The first stage: 800-900 ° C, 1 hour, argon atmosphere; The second stage: 1100-1150℃, 2-3 hours, vacuum degree ≤10^-3Pa.

6. The method for preparing a vanadium-based solid solution hydrogen storage alloy with high activation performance according to claim 4, characterized in that: In the controlled cooling, the first cooling is performed at a rate of 50-100°C / min to 600°C, and the second cooling is performed at a rate of 10-20°C / min to room temperature.

7. The method for preparing a vanadium-based solid solution hydrogen storage alloy with high activation performance according to claim 4, characterized in that: The graded ball milling comprises: Zirconia balls with a diameter of 10 mm were used for primary ball milling; Fine ball milling uses tungsten carbide balls with a diameter of 5 mm; During the ball milling process, argon gas was introduced for protection and the oxygen content was ≤50ppm.

8. The method for preparing a vanadium-based solid solution hydrogen storage alloy with high activation performance according to claim 6, characterized in that: During the controlled cooling, intermittent ultrasonic treatment is applied in the range of 600-400° C., with a frequency of 20-40 kHz and a power of 500-800 W.

9. The method for preparing a vanadium-based solid solution hydrogen storage alloy with high activation performance according to claim 6, characterized in that: During the controllable cooling, when the cooling temperature reaches below 300° C., a surface passivation treatment is performed, and an argon mixed gas containing 1% to 3% hydrogen is introduced.

10. The method for preparing a vanadium-based solid solution hydrogen storage alloy with high activation performance according to claim 4, characterized in that: The classifying ball milling uses a planetary ball mill and a vibration ball mill.

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