A tungsten diboride self-supporting electrode with a porous network structure and its preparation method and application
The porous network structure of tungsten diboride self-supporting electrode is prepared by low-temperature rapid sintering, which solves the problem of insufficient catalytic activity of tungsten diboride powder in the existing technology and realizes efficient water electrolysis to produce hydrogen and fuel cell applications.
Patent Information
- Application Number
- CN202410915190.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-09
- Publication Date
- 2025-09-23
- Estimated Expiration
- 2044-07-09
AI Technical Summary
Existing technologies make it difficult to mass-produce high-purity nanoscale tungsten diboride powder. Existing preparation methods also result in larger particles, uneven catalyst dispersion, and buried active sites, making it impossible to fully exert its catalytic activity in water electrolysis.
Using a low-temperature rapid sintering method, the lamellar tungsten diboride powder is sintered at 700°C to 850°C into a tungsten diboride block material with a porous network structure, and a self-supporting electrode is made to expose more catalytic active sites.
The electrochemical specific surface area and mechanical stability are improved, the catalytic activity of water electrolysis to hydrogen production is enhanced, and larger electrochemical active sites are provided, making it suitable for the fields of water electrolysis to hydrogen production and fuel cells.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of energy materials, and in particular relates to a tungsten diboride self-supporting electrode with a porous network structure, a preparation method thereof, and an application thereof. Background Art
[0002] As a highly efficient, low-carbon secondary energy source, the cleanest energy carrier with the highest energy density, and a green and clean industrial raw material, hydrogen is considered the best alternative to fossil fuels. Currently, hydrogen is primarily produced through the reforming of fossil fuels such as coal and natural gas. However, this process produces significant amounts of CO2, resulting in the production of "gray hydrogen." Water electrolysis technology is crucial for transitioning from "gray hydrogen" to "green hydrogen." However, the limited reserves and high costs of precious metals, currently the most advanced water electrolysis catalysts, preclude large-scale production.
[0003] In recent years, the boron element in transition metal borides has a large electronegativity and a unique outer electron configuration. This modified electronic structure can reduce the kinetic energy barrier in electrochemical processes, alleviate metal oxidation, and exhibit excellent catalytic performance with extremely high stability. Among them, the transition metal tungsten is second only to the precious metals in the volcano diagram of water electrolysis activity calculated by first-principles (DFT) theory. It can promote bonding between hydrogen atoms and accelerate hydrogen generation. Synthesized tungsten diboride has good chemical stability and conductivity. The existing structural defects can expose more active sites, making it a candidate material with high intrinsic activity in water electrolysis, making it a candidate material for replacing precious metals. However, like most boride compounds, they are prepared under extreme conditions (high temperature and high pressure), resulting in large particles that are difficult to use in the field of catalysis; and for some nanoscale (1-100 nm) WB2 powders prepared by hydrothermal method, molten salt method and solid-phase decomposition, good catalytic activity can be detected by drop casting method (Chemical Communications 56(90)(2020)13983-13986), but the synthesis process of nanoscale powders is complex and the yield is low, and most of them are irregular particles with low purity, which cannot be produced on a large scale.
[0004] This is mainly because the preparation method of the electrode will affect the electrochemical properties of the material and play a key role in accurately evaluating the activity of the material. For larger particle powders, the drop casting method is difficult to test its intrinsic activity, mainly because the uneven dispersion of the catalyst buries a large number of active sites, which reduces the activity, and due to insufficient binding force, there is partial shedding during the long-term test process, which cannot reflect the excellent stability of the boride. There is also a method of sintering a dense WB2 block to make a self-supporting electrode test to obtain higher electrochemical performance, but after high-temperature sintering, the crystal grains grow and the surface pores decrease, resulting in a decrease in the active sites exposed on the electrode surface (ChemSusChem 12(16)(2019)3726-3731). Porous self-supporting electrodes can effectively circumvent this disadvantage. The catalyst is directly grown on the porous nickel foam skeleton through the hydrothermal / solvothermal method, but the composition adjustment is very difficult and it is difficult to synthesize high-purity catalysts. Therefore, if a high-purity porous WB2 self-supporting electrode can be directly prepared, the highest water electrolysis catalytic activity will be obtained.
[0005] In order to avoid the underestimation of the electrolytic water activity of submicron-sized, high-purity lamellar tungsten diboride synthesized by boron / carbon thermal reduction method, it is urgent to prepare a porous WB2 self-supporting electrode material with high catalytic activity. Summary of the Invention
[0006] In order to solve the shortcomings and deficiencies of the above-mentioned prior art in the electrolysis water preparation technology that it is difficult to test the intrinsic activity of larger particles of tungsten diboride, the primary purpose of the present invention is to provide a method for preparing a tungsten diboride self-supporting electrode with a porous network structure; the method first synthesizes WB2 (~300nm) with a lamellar structure, uses the WB2 as a raw material, and quickly sinters it at a low temperature to make the lamellar grains bonded to each other to obtain a porous network tungsten diboride block material, and then makes the tungsten diboride block material into a self-supporting electrode.
[0007] Another object of the present invention is to provide a tungsten diboride bulk material having a porous network structure prepared by the above preparation method.
[0008] Another object of the present invention is to provide a tungsten diboride self-supporting electrode having a porous network structure prepared by the above preparation method.
[0009] Another object of the present invention is to provide an application of the above-mentioned tungsten diboride self-supporting electrode with a porous network structure.
[0010] The purpose of the present invention is achieved through the following technical solutions:
[0011] A method for preparing a tungsten diboride self-supporting electrode having a porous network structure comprises the following steps:
[0012] (1) Weigh tungsten trioxide (WO3) powder, boron carbide (B4C) powder, and carbon source powder into a container, add grinding balls, and ball mill under argon atmosphere to obtain a uniformly mixed powder;
[0013] (2) using a dry press to press the uniformly mixed powder obtained in step (1) into a green compact, and sintering and holding the green compact at 1300° C. to 1500° C. under vacuum for 0.5 to 2 hours, grinding and sieving the green compact after furnace cooling to obtain a lamellar tungsten diboride powder;
[0014] (3) placing the tungsten diboride powder obtained in step (2) into a graphite mold for pre-pressing, and performing low-temperature rapid sintering, i.e., keeping the temperature at 700° C. to 850° C. and a pressure of 10 to 30 MPa for 10 minutes, to obtain a tungsten diboride block material having a porous network structure;
[0015] (4) The tungsten diboride block material obtained in step (3) is adhered to a copper sheet through a conductive silver paste and the surface that does not participate in the reaction is wrapped with a resin to prepare a tungsten diboride self-supporting electrode with a porous network structure.
[0016] The material of the grinding balls in step (1) is tungsten carbide; the ball milling time is 0.5 to 2 hours; the molar ratio of the tungsten trioxide (WO3) powder, boron carbide (B4C) powder and carbon source powder is in the range of 2: (1 to 1.5): (4.7 to 5).
[0017] The mass ratio of the total mass of the tungsten trioxide (WO3) powder, boron carbide (B4C) powder and carbon source powder in step (1) to the mass of the grinding balls is 1: (3 to 5).
[0018] In step (2), the briquetting pressure of the dry press is between 3 and 30 MPa; the grinding is carried out in an agate mortar, and the screening is carried out through a 200-mesh sieve.
[0019] The sintering and heat preservation time in step (2) is 1 to 2 hours.
[0020] The pre-pressing pressure in step (3) is 3-30 MPa; the low-temperature rapid sintering is carried out in an argon or vacuum atmosphere, preferably using spark plasma sintering.
[0021] The low-temperature rapid sintering can also be performed by flash sintering, microwave sintering, oscillating pressure sintering, or other sintering methods.
[0022] A tungsten diboride bulk material with a porous network structure prepared by the above preparation method.
[0023] A tungsten diboride self-supporting electrode with a porous network structure prepared by the above preparation method.
[0024] The above-mentioned tungsten diboride bulk material with a porous network structure is used in the fields of water electrolysis to produce hydrogen and fuel cells.
[0025] The present invention has the following advantages and effects compared to the prior art:
[0026] (1) The present invention first synthesizes WB2 (~300nm) with a lamellar structure. Using WB2 as raw material, the lamellar grains are bonded to each other into a network structure by rapid sintering to obtain a tungsten diboride bulk material with a porous network structure. The material has high conductivity, can provide a larger electrochemical specific surface area, and expose more catalytic active sites.
[0027] (2) The tungsten diboride bulk material with a porous network structure obtained by the present invention has a large electrochemical specific surface area and high mechanical stability.
[0028] (3) The present invention designs a porous mesh self-supporting electrode which has high catalytic activity.
[0029] (4) The tungsten diboride bulk material with a porous network structure prepared by the present invention can be effectively used in related industrial fields such as water electrolysis hydrogen production catalysis and fuel cells.
[0030] (5) Chinese patent application No. 2021103594798 discloses a bulk sample with nano-grain size prepared by low-temperature rapid sintering, but there is a substantial difference between this invention and the present invention, because in the present invention, after the initial sintering, the lamellar powder is bonded and connected to each other to form a porous network structure, which has better mechanical stability and provides a larger electrochemically active specific surface area.
[0031] (6) In the paper "High-Current-Density HER Electrocatalysts: Graphene-like Boron Layer and Tungsten as Key Ingredients in Metal Diborides", the WB2 dense block sintered to improve the electrode surface coverage was tested, and the overpotential was 271mV (at 10mA / cm 2 ), the Tafel slope is 79.6mV / dec. The difference is that the present invention uses WB2 block material with porous network structure sintered at low temperature, which can expose more active sites and improve its catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Figure 1 These are the XRD patterns of tungsten diboride powder after pressureless heat treatment and WB2 bulk material after SPS sintering.
[0033] Figure 2 SEM images of tungsten diboride powder after pressureless heat treatment and WB2 bulk material after SPS sintering.
[0034] Figure 3 LSV curve of porous WB2 self-supporting electrode material and the corresponding Tafel slope diagram.
[0035] Figure 4 The electronic transfer impedance diagram and double-layer capacitance of the porous WB2 self-supporting electrode material.
[0036] Figure 5 This is the current-time diagram of the porous WB2 self-supporting electrode material for 20 hours. DETAILED DESCRIPTION
[0037] The present invention is further described below with reference to specific examples, but these examples should not be construed as limiting the present invention.
[0038] Example 1:
[0039] (1) In an argon atmosphere glove box, tungsten trioxide powder, boron carbide powder, and carbon black were weighed and mixed in a molar ratio of 2:1.075:4.9 and placed in a high-energy ball mill. Six tungsten carbide grinding balls were added, and the mass ratio of grinding balls to mixed powder was 4:1. The mixture was ball milled for 1 hour to obtain a uniformly mixed powder.
[0040] (2) The uniformly mixed powder obtained in step (1) is pre-pressed into a briquetting pressure of 3 to 30 MPa using a dry press, and is vacuum-insulated at a temperature of 1400° C. for 1 hour. After cooling, it is ground in an agate mortar and sieved through a 200-mesh sieve to obtain tungsten diboride powder.
[0041] (3) 2 g of the tungsten diboride powder obtained in step (1) was placed in a graphite mold for pre-compression, and the mixture was sintered in an argon atmosphere at 750° C. and a sintering pressure of 30 MPa for 10 minutes to obtain a tungsten diboride bulk material.
[0042] (4) The tungsten diboride block material was polished into a 0.1 g square sample of 3 × 3 × 2 mm, bonded to a copper sheet with conductive silver paste, and the copper sheet and other surfaces except the top were wrapped with resin. The porous WB2 self-supporting electrode was obtained by standing at room temperature for 24 h.
[0043] Characterization of material phase, morphology and electrochemical properties:
[0044] The phase analysis of the tungsten diboride powder synthesized in step (2) and the tungsten diboride bulk material after sintering in step (3) was performed by X-ray diffractometer (XRD). Figure 1The results show that the samples after SPS low temperature sintering are consistent with the powder after heat treatment, and both are high-purity WB2 (P63 / mmc, PDF#04-004-1673). Figure 2 The following are SEM images of the surface morphology of the tungsten diboride powder synthesized in step (2) of this example and the tungsten diboride bulk material after sintering in step (3). The synthesized WB2 powder is mostly lamellar, with a grain size of approximately 200-300nm. After sintering at 750°C, the grains are also mainly lamellar, maintaining the characteristics of the raw material powder. At the same time, it is also observed that the grains are bonded and consolidated with each other, and most of them exhibit a network structure. This structure can significantly increase the specific surface area of the sample and expose more active sites. Figure 3 The LSV curve and Tafel slope of the porous WB2 self-supporting electrode prepared in this example were tested in 0.5M H2SO4. 10mA / cm 2 The lower overpotential is as low as 141mV, and the Tafel slope under the corresponding overpotential is only 63.1mV / dec. Figure 4 The porous WB2 self-supporting electrode sample prepared in this embodiment is 2 Electron transfer impedance diagram and double layer capacitance C at corresponding voltages dl The electron transfer impedance is only 1.76Ω, indicating that the grains are bonded to each other and the high crystallinity sample has high conductivity, as well as extremely high C dl Value (416.2mF / cm 2 ) shows that the network structure formed by the mutual bonding between the grains provides a large electrochemically active specific surface area. Figure 5 The 20-hour stability test of the porous WB2 self-supporting electrode prepared in this example shows that the current density does not change significantly and shows an upward trend, indicating good stability. In summary, the prepared porous WB2 self-supporting electrode material has a much higher HER activity, electrochemical specific surface area, and stability in acidic electrolytes than existing WB2 catalysts.
[0045] Example 2:
[0046] The tungsten diboride powder obtained in step (2) of Example 1 was taken and pre-pressed in a graphite grinder. It was sintered at 800°C for 10 minutes in a spark plasma sintering furnace. The protective atmosphere was argon and the sintering pressure was 30 MPa to obtain a porous tungsten diboride bulk material. The tungsten diboride bulk material was polished to a 0.1g square sample of 3×3×2mm, bonded to a copper sheet with conductive silver paste, and the copper sheet and other surfaces except the top were wrapped with resin. The self-supporting electrode was left to stand at room temperature for 24 hours. The overpotential was 166mV (at 10mA / cm2) in a 0.5M H2SO4 electrolyte using an electrochemical workstation. 2), the Tafel slope is 59.6mV / dec.
[0047] Comparative Example 1:
[0048] The tungsten diboride powder obtained in step (2) of Example 1 was taken and pre-pressed in a graphite grinder. It was sintered at 1600°C for 10 minutes using a spark plasma sintering furnace. The protective atmosphere was argon and the sintering pressure was 30 MPa to obtain a dense (density 93.1%) tungsten diboride block. The tungsten diboride block material was polished to a 0.1g square sample of 3×3×2mm, bonded to a copper sheet with conductive silver paste, and the copper sheet and other surfaces except the top were wrapped with resin. The self-supporting electrode was obtained by standing at room temperature for 24 hours. The overpotential was 281.2mV (at 10mA / cm2) in 0.5M H2SO4 electrolyte using an electrochemical workstation. 2 ), and the Tafel slope was 82.2 mV / dec. Compared with the above examples, the catalytic activity of the sample in this comparative example was significantly reduced. This is mainly because the grain size grew to ~1 μm after high-temperature sintering, the porosity decreased, the sample became dense, and the specific surface area was reduced, burying a large number of active sites.
[0049] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.
Claims
1. A method for preparing a tungsten diboride self-supporting electrode with a porous network structure, characterized in that The following steps are included: (1) Weigh tungsten trioxide powder, boron carbide powder, and carbon source powder into a can, add grinding balls, and ball mill under argon atmosphere to obtain a uniformly mixed powder; (2) using a dry press to press the uniformly mixed powder obtained in step (1) into a green compact, and sintering and holding the green compact at 1300°C to 1500°C under vacuum for 0.5 to 2 hours, grinding and sieving the green compact after furnace cooling to obtain a lamellar tungsten diboride powder; (3) The tungsten diboride powder obtained in step (2) is placed in a graphite mold for pre-pressing, and is subjected to low-temperature rapid sintering, that is, keeping the temperature at 700°C to 850°C and a pressure of 10 to 30 MPa for 10 minutes to obtain a tungsten diboride block material with a porous network structure; the low-temperature rapid sintering is carried out in an argon or vacuum atmosphere using a spark plasma sintering method; (4) The tungsten diboride bulk material with a porous network structure obtained in step (3) is adhered to a copper sheet through a conductive silver paste and the surface that does not participate in the reaction is wrapped with a resin to prepare a tungsten diboride self-supporting electrode with a porous network structure.
2. The method for preparing a tungsten diboride self-supporting electrode having a porous network structure according to claim 1, characterized in that: The material of the grinding balls in step (1) is tungsten carbide; the ball milling time is 0.5 to 2 hours; and the molar ratio of the tungsten trioxide powder, boron carbide powder, and carbon source powder is in the range of 2: (1 to 1.5): (4.7 to 5).
3. The method for preparing a tungsten diboride self-supporting electrode having a porous network structure according to claim 1, characterized in that: The mass ratio of the total mass of the tungsten trioxide powder, boron carbide powder and carbon source powder in step (1) to the mass of the grinding balls is 1: (3-5).
4. The method for preparing a tungsten diboride self-supporting electrode having a porous network structure according to claim 1, characterized in that: In step (2), the briquetting pressure of the dry press is between 3 and 30 MPa; the grinding is performed in an agate mortar, and the screening is performed through a 200-mesh sieve.
5. The method for preparing a tungsten diboride self-supporting electrode having a porous network structure according to claim 1, characterized in that: The sintering and heat preservation time in step (2) is 1 to 2 hours.
6. The method for preparing a tungsten diboride self-supporting electrode having a porous network structure according to claim 1, characterized in that: The pre-pressing pressure in step (3) is 3 to 30 MPa.
7. A tungsten diboride self-supporting electrode having a porous network structure prepared by the preparation method according to any one of claims 1 to 6.
8. Use of the tungsten diboride self-supporting electrode with a porous network structure according to claim 7 in electrocatalytic hydrogen production and fuel cells.