A method for infrasonic vibration pretreatment of molybdenum carbide catalyst for hydrogen production by water electrolysis

Abstract

This invention belongs to the field of water electrolysis for hydrogen production technology, and proposes an infrasonic vibration pretreatment method for molybdenum carbide catalysts used in water electrolysis for hydrogen production. Micron-sized molybdenum carbide powder is fixed in a clamping device, and infrasonic energy is transferred to the particles through a probe to achieve nano-sizing and the formation of a crystalline-amorphous core / shell structure. By controlling the vibration power, frequency, and time, the surface active sites and specific surface area can be significantly increased, thereby improving the electrocatalytic hydrogen evolution performance. This method is mild, simple, requires no high temperature or complex precursors, avoids pollution and high energy consumption, has low raw material costs, and is controllable. The treated molybdenum carbide exhibits high performance at 10 mA·cm⁻¹. ‑2 The hydrogen evolution overpotential is significantly reduced at lower current densities, exhibiting high activity and stability, providing a scalable preparation method for hydrogen production via water electrolysis and methane reforming. This invention was supported by the Liaoning Binhai Laboratory Science and Technology Project (Project No.: LBLF-202306).

Description

Technical Field

[0001] This invention belongs to the field of water electrolysis for hydrogen production technology, and relates to a method for preparing molybdenum carbide catalysts for industrial water electrolysis for hydrogen production through infrasonic vibration pretreatment. The infrasonic vibration pretreatment method can significantly improve the catalytic performance of the catalyst. Background Technology

[0002] Hydrogen energy, as a green, clean, and efficient energy carrier, is a core force in replacing traditional fossil fuels and achieving the "dual carbon" goal. Electrolysis of water to produce hydrogen is a widely recognized green hydrogen production method, mainly consisting of two half-reactions: the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Commonly used catalytically active electrode materials for water electrolysis are precious metals such as Pt, Pd, and Ru, and their alloys. For example, patent CN120006335B discloses a water electrolysis catalyst that effectively improves the catalytic activity of hydrogen evolution through the synergistic effect of Ru, Co, and Ni. However, the scarcity and high price of precious metals such as Pt and Ru limit their large-scale application. Currently, the field of water electrolysis for hydrogen production urgently needs to develop low-cost hydrogen evolution catalysts that maintain stability and high efficiency under high current densities.

[0003] Molybdenum carbide (MoC) has become a hot topic in the research of novel inorganic catalytic materials due to its unique electronic structure and excellent catalytic performance. In fields such as methane reforming and water electrolysis for hydrogen production, MoC is comparable to precious metals such as platinum and iridium, and is known as a "platinum-like catalyst," attracting widespread attention from scholars both domestically and internationally. However, MoC is generally produced from molybdenum oxide, and traditional processes result in high-priced MoC with low catalytic activity, failing to meet market demand. Currently, in the field of water electrolysis for hydrogen production, MoC is being extensively studied as a potential electrocatalytic hydrogen evolution catalyst. However, MoC electrocatalytic hydrogen evolution catalysts have a low specific surface area; excessive carbon material covers the active sites of molybdenum atoms on the surface of MoC during synthesis, reducing the number of exposed active sites.

[0004] To address the shortcomings of molybdenum carbide as a hydrogen production catalyst, patent CN103240108B discloses a formic acid hydrogen production catalyst supported on cordierite, activated carbon, or carbon nanotubes. Patent CN111905783A discloses a molybdenum carbide / carbon nanotube hydrogen production catalyst synthesized using ink. However, both patents involve cumbersome processes, high costs, complex synthesis routes, and are prone to introducing impurities.

[0005] Therefore, given the shortcomings of existing technologies, it is necessary to improve existing molybdenum carbide-based catalysts. Summary of the Invention

[0006] This invention proposes a method for preparing molybdenum carbide electrocatalytic hydrogen evolution catalysts using infrasound vibration physical pretreatment. By using a probe to directly apply infrasound mechanical vibration energy to fixed molybdenum carbide particles, the particle size is reduced, the specific surface area is increased, and a core-shell structure is formed, thereby significantly improving the electrochemical activity of the catalyst.

[0007] Raw material preparation and fixing

[0008] Commercially available micron-sized molybdenum carbide (MoC) powder was selected as the precursor, with an initial particle size distribution in the range of 10–80 μm.

[0009] Infrasound vibration treatment process

[0010] The clamped sample is placed in the infrasonic vibration device, and the probe, through contact clips, directly applies infrasonic vibration energy to the particles. Key parameters are set as follows: vibration power 0.5–2.0 kW, frequency 5–20 Hz, and processing time 20–32 hours.

[0011] During infrasound vibration, the mechanical vibration and cavitation effect generated by the probe work synergistically to: break up particle agglomeration and improve dispersion; induce micro-stress concentration and local structural rearrangement inside the particles; and form a crystalline-amorphous core / shell structure, in which the core maintains the crystalline structure to ensure conductivity and structural stability, while the outer shell is an amorphous molybdenum carbide layer rich in defects and dangling bonds, which significantly increases the number of active sites.

[0012] Post-processing and collection

[0013] After processing, the particles were gently brushed off the surface of the device with a clean brush and collected into a sample container to obtain uniformly dispersed and uncontaminated molybdenum carbide nanoparticles.

[0014] Preparation of working electrode

[0015] To evaluate the electrochemical hydrogen evolution performance of the catalyst, the molybdenum carbide nanocatalyst obtained above needs to be prepared into a working electrode. The specific steps are as follows:

[0016] Weigh 5 mg of molybdenum carbide (MoC) catalyst and mix it with 500 μL of deionized water, 500 μL of isopropanol and 20 μL of Nafion dispersant. Disperse the mixture by ultrasonication in an ice bath for 30 minutes to form a uniform catalyst slurry. Then, measure 100 μL of the slurry and uniformly drop it onto a 1 cm × 1 cm carbon paper. After drying at room temperature, the working electrode is obtained.

[0017] Explanation of the mechanism for improving catalytic performance

[0018] During the treatment process, infrasonic vibration, under the influence of the solid-gas interface, breaks up particle agglomeration and increases specific surface area through infrasonic vibration and cavitation effects. These effects also induce microscopic stress concentration and local structural rearrangement, forming numerous highly active sites. Controlling the treatment time within the optimal window maximizes the formation of the crystalline-amorphous core / shell structure while avoiding damage to the outer shell or disruption of the inner core due to excessive vibration. This ensures a stable catalyst microstructure, high specific surface area, and excellent electrochemical activity.

[0019] This method is simple, mild, and does not require high-temperature chemical reactions or complex precursors. It is suitable for the industrial-scale preparation of molybdenum carbide electrocatalytic hydrogen evolution catalysts and has the advantages of high operational controllability, low raw material cost, and significantly improved catalytic performance.

[0020] Beneficial effects

[0021] Compared with existing technologies that improve the catalytic performance of molybdenum carbide through chemical synthesis or composite modification, the infrasonic vibration physical pretreatment method provided by this invention brings the following substantial features and significant progress.

[0022] This invention breaks through the limitations of traditional chemical methods and provides a completely new process route. Existing technologies, such as the invention patent with patent number CN111905783A, disclose a molybdenum carbide / carbon nanoparticle hydrogen production catalyst synthesized using ink. These generally rely on high-temperature chemical reactions, the use of specific supports or precursors, and are complex processes that may introduce impurities. This invention takes a different approach, using a purely physical infrasound vibration energy field to directly process commercial molybdenum carbide. This method is carried out at room temperature and does not involve any chemical reactions. Therefore, the process is simple and easy to control, fundamentally avoiding the pollution, high energy consumption, and uncertain product composition problems that may arise from chemical methods.

[0023] This invention achieves highly efficient value-added processing of inexpensive commercial raw materials, significantly reducing application costs. It directly uses commercially available, low-cost micron-sized molybdenum carbide particles as the sole raw material, and activates and enhances their catalytic activity through physical pretreatment. This eliminates a series of complex steps involved in synthesizing catalysts from molybdenum and carbon sources, significantly reducing raw material costs and greatly simplifying the process.

[0024] The catalytic performance enhancement is direct and significant, stemming from a unique physical cavitation effect. The core effect of this invention lies in the efficient reduction of 10-80 μm commercial molybdenum carbide particles to 50-300 nm using optimized infrasonic vibration parameters (power 0.5-2.0 KW, frequency 5-20 Hz, duration 20-32 hours) through cavitation and infrasonic resonance in a solid-gas medium. This nano-sizing process, dominated by cavitation, directly leads to an increase in the catalyst's specific surface area and electrochemically active area. Combined with TEM analysis (e.g., ...), the catalytic performance is significantly improved.Figure 4 (c) and Figure 5 (g) reveals the microscopic relationship: the untreated sample exhibits fuzzy lattice fringes, low crystallinity, discontinuous electron transport paths, and irregular distribution of active sites; while the sample treated with 24 hours of infrasonic vibration shows clear, continuous, and regularly arranged lattice fringes, indicating the formation of high-crystallinity crystalline regions within the material, providing rapid electron conduction channels. Its surface atoms are regularly arranged, which is beneficial for stable and efficient catalytic active sites. The amorphous shell is rich in defects and dangling bonds, providing a large number of active sites for the hydrogen evolution reaction; the crystal structure retained in the core ensures conductivity and stability, and the two synergistically significantly improve the overall performance of the catalyst. Experimental data (see Example 2) show that the hydrogen evolution overpotential (10 mA·cm) of the sample treated for 24 hours is significantly lower. -2 The voltage decreased from 252 mV before treatment to 169 mV, a reduction of 83 mV; simultaneously, the electrochemical active area also increased. This demonstrates the effectiveness of this physical method in enhancing intrinsic catalytic activity.

[0025] The key process window for initiating effective cavitation and achieving optimal nano-sizing is defined. This parameter window ensures that the vibrational energy effectively breaks up the particles while preventing insufficient energy or overtreatment (as shown in Example 4, where performance declined after 32 hours of treatment). This makes the method highly processable and reproducible, facilitating the acquisition of catalyst products with stable and consistent performance. Attached Figure Description

[0026] Figure 1 Schematic diagram of catalyst pretreated by infrasound vibration;

[0027] Figure 2 LSV polarization curves of MoC catalysts subjected to infrasonic vibration at different times;

[0028] Figure 3 A bar chart showing the overpotential of MoC catalysts subjected to infrasonic vibration at different times;

[0029] Figure 4 Transmission electron microscopy (TEM) image of the original MoC catalyst sample;

[0030] Figure 5 The image shows a transmission electron microscope (TEM) image of the MoC core-shell structure after 24 hours of infrasonic vibration treatment.

[0031] Figure 6 This is a transmission electron microscope (TEM) image of the MoC catalyst after 32 hours of infrasonic vibration treatment. Detailed Implementation

[0032] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the protection scope of this invention.

[0033] Example 1: Infrasonic vibration pretreatment of molybdenum carbide (MoC) catalyst for 20 hours

[0034] Commercial molybdenum carbide (MoC) powder with a particle diameter of 70 μm was clamped and fixed using two clean stainless steel spacers to form a "sandwich" structure. The probe was placed in contact with the spacers, and the vibration power was set to 1.5 kW and the vibration frequency to 10 Hz, with continuous vibration treatment for 20 hours. After treatment, sheet-like / granular molybdenum carbide nanoparticles with a thickness of approximately 300 nm were obtained.

[0035] Electrode preparation: Weigh 5 mg of treated molybdenum carbide nanoparticles, add 500 μL of deionized water, 500 μL of isopropanol and 20 μL of Nafion dispersant, and sonicate for 30 minutes to obtain a uniform slurry; take 100 μL and drop it onto 1 cm × 1 cm carbon paper, and air dry at room temperature to prepare the working electrode.

[0036] Hydrogen evolution electrochemical performance test: Using the Chenhua CHI760E electrochemical workstation, in 1 M KOH electrolyte, with the prepared electrode as the working electrode, platinum mesh as the counter electrode, and Hg / HgO as the reference electrode (all test potentials have been converted to relative to the reversible hydrogen electrode, RHE, according to standard methods), linear sweep voltammetry (LSV) was performed.

[0037] Example 2: Infrasonic vibration pretreatment of molybdenum carbide (MoC) catalyst for 24 hours

[0038] The sample fixation and treatment method of Example 1 was repeated, but the vibration duration was extended to 24 hours. Nanoscaled molybdenum carbide particles with an average thickness of approximately 150 nm were obtained after treatment.

[0039] The working electrode was fabricated using the same electrode fabrication process as in Example 1.

[0040] Electrochemical test results showed: 10 mA·cm -2 At current density, the hydrogen evolution overpotential drops to 169 mV, which is 83 mV lower than that of untreated commercial molybdenum carbide.

[0041] TEM comparative analysis:

[0042] Compared with original commercial molybdenum carbide particles ( Figure 4 Compared to (a–d), the treated particles exhibit a nanostructure (50–300 nm) and simultaneously form a core-shell structure;

[0043] In the core-shell structure, the core maintains a crystalline structure, giving the catalyst good electrical conductivity and structural stability; the outer shell is an amorphous molybdenum carbide layer induced by infrasound vibration, which is rich in defects and dangling bonds, significantly increasing the number of active sites on the catalyst surface.

[0044] The particles are uniformly distributed and have a significantly increased specific surface area, providing more interfaces for electrocatalysis;

[0045] TEM images show that the amorphous outer shell and the crystalline core work together to form a large number of highly active sites. This improvement in microstructure directly corresponds to the improvement in hydrogen evolution performance, verifying the unique mechanism by which infrasonic vibration treatment optimizes catalytic performance through micro-stress concentration, local structural rearrangement and defect formation.

[0046] Example 3: Infrasonic vibration pretreatment of molybdenum carbide (MoC) catalyst for 28 hours

[0047] Commercial molybdenum carbide powder with a particle diameter of 70 μm was clamped and fixed as described in Example 1. The probe was brought into contact with the clamp, and the vibration power was set to 1.5 kW and the vibration frequency to 10 Hz for 28 hours.

[0048] The working electrode was fabricated using the same electrode fabrication process as in Example 1.

[0049] Electrochemical performance tests showed that at 10 mA·cm -2 The hydrogen evolution overpotential at current density is approximately 221 mV, which is 31 mV lower than that of the original commercial particles (252 mV), but higher than that of the 24-hour treated sample (169 mV).

[0050] Example 4: Infrasonic vibration pretreatment of molybdenum carbide (MoC) catalyst for 32 hours

[0051] Commercial molybdenum carbide powder material with a particle diameter of 70 μm was clamped and fixed as described in Example 1. The probe was brought into contact with the clamp, and the vibration power was set to 1.5 kW and the vibration frequency to 10 Hz, and the treatment was carried out continuously for 32 hours.

[0052] The working electrode was fabricated using the same electrode fabrication process as in Example 1.

[0053] HER performance was tested in 1 M KOH electrolyte. Results showed that the catalyst achieved a driving effect of 10 mA·cm⁻¹. -2The hydrogen evolution overpotential at the current density increased compared to Example 2 (24-hour treatment), indicating a decrease in catalytic performance.

[0054] TEM analysis showed that prolonged infrasound vibration treatment caused partial damage to the original core-shell structure: the amorphous outer shell layer showed local breakage and peeling, the crystal core also showed structural disorder, decreased particle uniformity, and reduced specific surface area compared to 24-hour treatment.

[0055] The fundamental reason for the performance degradation is excessive mechanical vibration. Continuous infrasound vibration damages the already formed nano-amorphous-crystalline-amorphous core-shell structure, resulting in a decrease in the number and uniformity of active sites, thereby reducing the electrochemical activity of the catalyst.

[0056] Therefore, it can be seen that there is an optimal range for the infrasound vibration treatment time in this invention (approximately 20–32 hours). By controlling the treatment time to around 24 hours, the formation of the core-shell structure and the exposure of active sites can be maximized, while avoiding structural damage caused by excessive infrasound vibration, thereby obtaining the best electrocatalytic performance.

Claims

1. A method for infrasonic vibration pretreatment of a molybdenum carbide catalyst for hydrogen production via water electrolysis, characterized in that: The catalyst precursor is molybdenum carbide particles with a diameter of 10–80 μm. The precursor is pretreated by infrasonic vibration, whereby the infrasonic vibration is applied to the clamped molybdenum carbide particles via a probe at a frequency of 5–20 Hz and a power of 0.5–2.0 kW for 20–32 hours. The probe forms mechanical contact with the precursor, generating periodic micro-stress and cavitation effects within the particles through infrasonic vibration, promoting particle refinement and exposure of surface active sites. The molybdenum carbide particles prepared by this method exhibit a nanostructure with an average size of 50–300 μm. The surface area increases, and the active sites on the particle surface are evenly distributed. Infrasonic vibration treatment induces the formation of a crystalline-amorphous core / shell structure on the surface of molybdenum carbide particles, where the core is crystalline molybdenum carbide and the shell is an infrasonic vibration-induced amorphous molybdenum carbide layer, rich in defects and dangling bonds, to increase the number of active sites and improve the specific surface area of ​​the catalyst. The infrasonic vibration treatment can inhibit particle agglomeration, form highly dispersed nanoparticles, and maintain the conductivity and structural stability of the particles to improve the long-term performance of the catalyst. The infrasonic vibration treatment time is controlled at 20~32 hours to ensure particle nano-sizing and core-shell structure formation while avoiding excessive infrasonic vibration that could lead to particle breakage, structural disorder, or performance degradation.

2. The method according to claim 1, characterized in that, The precursor is clamped and fixed between two stainless steel clips. The probe transmits the infrasonic vibration energy evenly to the particles through the contact clips, and induces micro-stress concentration and local structural rearrangement inside the particles.

3. The method according to claim 1, characterized in that, The method described herein is applicable to the industrial-scale preparation of molybdenum carbide electrocatalytic hydrogen evolution catalysts. The resulting catalysts possess high specific surface area, uniform active site distribution, excellent catalytic activity, and structural stability, and can be widely applied in electrochemical reaction systems.

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