Molybdenum carbide catalyst based on vacuum interconnection and preparation method and application thereof

Abstract

The invention discloses a molybdenum carbide catalyst based on vacuum interconnection and a preparation method and application thereof, the catalyst comprises a molybdenum carbide thin layer and an oxide MoxCyOz which is at least formed on the surface layer of the molybdenum carbide thin layer and is formed by an oxidation process, x = 1, y = 0-0.5, z = 0-3, and the oxide is at least selected from molybdenum carbon oxygen species and / or molybdenum oxygen species and / or carbon deposition species. On the premise of vacuum interconnection, the intrinsic performance of the molybdenum carbide alkaline HER pre-catalyst is realized, and the HER performance of the molybdenum carbide catalytic material is effectively improved through a controllable oxidation process.

Description

Technical Field

[0001] The present invention relates to water electrolysis catalyst technology, and in particular to a molybdenum carbide catalyst based on vacuum interconnection and a preparation method and application thereof. Background Art

[0002] In recent years, global energy and environmental problems have become increasingly serious while demand has continued to grow. my country's energy structure of more coal, less oil and less gas has made the design and development of new energy catalytic materials attract much attention. Hydrogen energy, as a new energy source, has the characteristics of high energy density, abundant reserves and no pollution to the environment, which has attracted great attention. The hydrogen evolution reaction (HER) by water electrolysis has attracted much attention as a clean and sustainable way to produce hydrogen on a large scale using the abundant water resources on the earth. The development of low-cost, low open circuit voltage, low Tafel slope, high-efficiency and high-stability electrocatalysts based on transition metals (non-precious metals) is the first and most urgent problem to be solved in the current research and application of electrocatalytic water splitting.

[0003] Transition metal carbides are a class of materials with special properties. Their components can be abbreviated as MCx, where x can be an integer or a fraction. As an intermetallic filling compound, C atoms are formed by interstitially melting into the lattice of transition metals. Their electronic properties and catalytic activity are similar to those of precious metals such as Pt, and they are called "quasi-platinum catalysts." Taking molybdenum carbide as an example, common molybdenum carbide materials include α-MoC, β-Mo 2 C and other phases, thermodynamically β-Mo 2 C is more stable than α-MoC. Due to its platinum-like precious metal properties, molybdenum carbide has special properties and applications in related water-activated reactions and has attracted widespread attention. However, due to the high activity of molybdenum carbide materials, when used as a pre-catalyst material for HER, there is mostly an uncontrollable reconstruction process under reaction conditions, which seriously limits the electrochemical application research of this type of catalyst.

[0004] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0005] The purpose of the present invention is to provide a molybdenum carbide catalyst based on vacuum interconnection, a preparation method and an application. Under the premise of vacuum interconnection, the intrinsic performance of the molybdenum carbide alkaline HER pre-catalyst is achieved, and the HER performance of the molybdenum carbide catalytic material is effectively improved through a controllable oxidation process.

[0006] To achieve the above object, an embodiment of the present invention provides a vacuum interconnected molybdenum carbide catalyst, comprising a molybdenum carbide thin layer, and an oxide Mo formed by an oxidation process at least on the surface of the molybdenum carbide thin layer. x C y O z , wherein x=1, y=0-0.5, z=0-3, and the oxide is at least selected from molybdenum carbon oxygen species and / or molybdenum oxygen species and / or carbon deposit species. Specifically, the oxidation process is Mo 2 Some Mo species in C are oxidized and finally transformed into MoO in a fully oxidized state. 3 The process is that the theoretical change is from x=1, y=0.5, z=0 to x=1, y=0, z=3.

[0007] In one or more embodiments of the present invention, the molybdenum in the carbon-molybdenum-oxygen species is present in the +4 and / or +6 valence states.

[0008] In one or more embodiments of the present invention, the molybdenum in the molybdenum oxy species is present in the +4 and / or +6 valence states.

[0009] In one or more embodiments of the present invention, the oxidation process is carried out at an oxygen partial pressure of 10 -6 The oxidation is carried out at mbar-1mbar. Preferably 0.1mbar

[0010] In one or more embodiments of the present invention, the oxidation temperature ranges from 600-700K.

[0011] In one or more embodiments of the present invention, the oxidation is carried out at a constant temperature after reaching the oxidation temperature. For example, the oxidation is carried out at a constant temperature for 10 minutes after reaching the preset oxidation temperature under 0.1 mbar oxygen.

[0012] In one or more embodiments of the present invention, the oxidation time of the oxidation process is 1 min to 60 min.

[0013] In one or more embodiments of the present invention, the thickness of the molybdenum carbide thin layer is in the order of hundreds of nanometers, that is, the thickness range is selected from not more than 1 micrometer.

[0014] In one or more embodiments of the present invention, a method for preparing a vacuum interconnected molybdenum carbide catalyst comprises the following steps: preparing a pure molybdenum carbide film; and gradually heating the atmosphere from room temperature to oxidation temperature under an oxygen partial pressure of 0.1 mbar.

[0015] In one or more embodiments of the present invention, a vacuum interconnected molybdenum carbide catalyst or a supported material thereof is used in water electrolysis.

[0016] Compared with the prior art, the vacuum interconnected molybdenum carbide catalyst, preparation method, and application according to the embodiment of the present invention are based on the material preparation and electrochemical experiments in the existing electrocatalytic field, which are all carried out under atmospheric conditions. The related transition metal carbides, transition metal nitrides, etc. are highly active and are easily disturbed by impurities such as water and oxygen in the air. Uncontrollable oxidation has occurred on the surface of the material before application or detection. Therefore, in order to obtain the intrinsic electrocatalytic performance of pure transition metal carbides and transition metal nitrides, the influence of interference conditions such as the atmosphere is taken into account. The present invention realizes the intrinsic performance of the molybdenum carbide alkaline HER precatalyst under the premise of vacuum interconnection, and effectively improves the HER performance of the molybdenum carbide catalytic material through a controllable oxidation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is an in-situ XPS spectrum of a molybdenum carbide film oxidized in 0.1 mbar oxygen according to an embodiment of the present invention, wherein the conditions corresponding to the curves shown in Figures a, b, and c from top to bottom correspond to each other one by one;

[0018] Figure 2 A pure molybdenum carbide film (bare MoC x ) and the HER performance of MoC thin film samples with oxidation degree varying from low to high. DETAILED DESCRIPTION

[0019] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0020] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising”, etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0021] The present invention uses ultra-high vacuum interconnection technology, and uses a near ambient pressure X-ray photoelectron spectroscopy system (NAP-XPS) and other equipment in combination. Under the condition of being completely not exposed to interference factors such as air, a flat Mo metal multi-crystalline wafer or a polished Mo metal block is used as a substrate. First, a carbonization process with controllable variables such as atmosphere and temperature is carried out. On this basis, the material is further subjected to controllable oxidation treatment at different oxygen partial pressures or different oxidation temperatures to prepare a series of molybdenum carbide electrocatalytic materials with different oxidation degrees. Using a vacuum interconnection pipeline, the prepared electrocatalyst is transferred to a glove box for HER reaction without being exposed to air, thereby realizing the performance study of molybdenum carbide and molybdenum carbide with different oxidation degrees as catalysts in the HER reaction.

[0022] Including but not limited to the following embodiments, the molybdenum carbide film is obtained by in-situ carbonization of a metal molybdenum sheet in a NAP-XPS system, followed by ultra-high vacuum annealing to obtain a pure, micron-level thick, uniform and flat molybdenum carbide film.

[0023] A pre-prepared 200nm thick 10*10mm MoC film was heated in an oxygen atmosphere and in-situ tracked using NAP-XPS, such as Figure 1 For example, after 0.1 mbar of oxygen is introduced at room temperature, there is no obvious change on the surface; then the temperature is gradually increased (rapid heating is used, such as rapid heating from room temperature to oxidation temperature within 1 minute by laser addition). Before 600K, the main changes on the surface are the generation of surface molybdenum carbon oxygen species (O 1s 530.5 eV) and the elimination of carbon deposits; when the temperature reaches 650K or higher, the surface changes begin to intensify, the C1s peak (283 eV) of the carbide is significantly weakened, the O1s peak (530.5 eV) of the molybdenum carbon oxygen species and (or) molybdenum oxygen species is significantly enhanced, the Mo 3d peak (228 eV) attributed to molybdenum carbide begins to weaken, and the peak attributed to MoO 2 and MoO 3 The Mo 3d peaks (229eV and 233eV) begin to appear; when the temperature rises above 770K, the surface carbon species have almost no detectable signal and are completely converted into molybdenum oxide species with a valence of MoO 2 This shows that the scheme of the present invention can realize the controllable oxidation of molybdenum carbide film, and the oxidation depth can be regulated by 1-100nm.

[0024] Embodiment Group 1

[0025] In this group of embodiments, the catalyst is:

[0026] Four pure molybdenum carbide films with a thickness of 200nm and a size of 10*10mm were prepared. Three of them were further oxidized to become molybdenum carbide films with a gradient of oxidation degree from low to high. The oxidation conditions were: 0.1mbar oxygen, oxidation temperature was 400K, 600K and 700K respectively. At each oxidation temperature, the oxidation time of the sample was 10min. The samples were respectively recorded as Mo x C y O z -11 (the sample oxidation depth is about 5nm), Mo x C y O z -12 (the sample oxidation depth is about 20nm), Mo x C y O z -13 (the oxidation depth of the sample is about 50nm). The above four pre-catalyst samples (MoC film 10, Mo x C y O z -11. Mo x C y O z -12, Mo x C y O z -13), to evaluate the HER reaction performance, such as Figure 2 As shown in the figure, it can be seen that the alkaline HER activity of the MoC films with different oxidation degrees is better than that of the pure MoC film itself. Among the three MoC film samples with different oxidation degrees, the MoC film with the weakest oxidation degree has the highest HER activity. x C y O z The alkaline HER activity of -11 catalyst is the highest. The above results show that the controllable weak oxidation process of molybdenum carbide material can effectively improve the HER performance of the material.

[0027] Embodiment Group 2

[0028] The difference between this group of embodiments and the first group of embodiments is that the oxidation process is carried out at an oxygen partial pressure of 10 -6 The above four pre-catalyst samples (MoC film 20, Mo x C y O z -21 (the sample oxidation depth is about 1nm), Mo x C y O z -22 (the sample oxidation depth is about 2nm), Mox C y O z -23 (the oxidation depth of the sample is about 4nm)), and the HER reaction performance is evaluated. It can be seen that the alkaline HER activity of the molybdenum carbide films with different oxidation degrees is better than that of the pure molybdenum carbide film itself. Among the three molybdenum carbide film samples with different oxidation degrees, the Mo x C y O z -23 catalyst has the highest alkaline HER activity, but is still far inferior to Mo x C y O z The above results show that the controllable weak oxidation process of molybdenum carbide materials can effectively optimize the HER performance of the material.

[0029] Embodiment Group 3

[0030] The difference between this group of examples and Example 1 is that the oxidation process is tested under an oxygen partial pressure of 1 mbar. The above four pre-catalyst samples (molybdenum carbide film 30, Mo x C y O z -31 (the sample oxidation depth is about 15nm), Mo x C y O z -32 (the sample oxidation depth is about 50nm), Mo x C y O z -33 (the oxidation depth of the sample is about 90nm)), and the HER reaction performance is evaluated. It can be seen that the alkaline HER activity of the MoC films with different oxidation degrees is better than that of the pure MoC films themselves. Among the three MoC film samples with different oxidation degrees, the MoC film with the weakest oxidation degree has the highest HER activity. x C y O z The alkaline HER activity of -31 catalyst is the highest, but still far inferior to that of Mo x C y O z The above results show that the controllable weak oxidation process of molybdenum carbide materials can effectively optimize the HER performance of the material.

[0031] Embodiment Group 4

[0032] The difference between this group of examples and Example 1 is that the constant temperature oxidation time during the oxidation process is 1 min. The above four pre-catalyst samples (molybdenum carbide film 40, Mo x C y O z -41 (the sample oxidation depth is about 1nm), Mo x C y O z -42 (the sample oxidation depth is about 3nm), Mo x C y O z -43 (the sample oxidation depth is about 3.5nm)), and the HER reaction performance is evaluated. It can be seen that the alkaline HER activity of the MoC films with different oxidation degrees is better than that of the pure MoC films themselves. Among the three MoC film samples with different oxidation degrees, the MoC film with the highest oxidation degree has a x C y O z -43 catalyst has the highest alkaline HER activity, but is still far inferior to Mo x C y O z The above results show that the controllable weak oxidation process of molybdenum carbide materials can effectively optimize the HER performance of the material.

[0033] Embodiment Group 5

[0034] The difference between this group of examples and Example 1 is that the constant temperature oxidation time during the oxidation process is 60 minutes. The above four pre-catalyst samples (MoC film 50, Mo x C y O z -51 (the oxidation depth of the sample is about 18nm), Mo x C y O z -52 (the oxidation depth of the sample is about 65nm), Mo x C y O z -53 (the oxidation depth of the sample is about 100nm)) to evaluate the HER reaction performance. It can be seen that the alkaline HER activity of the MoC films with different oxidation degrees is better than that of the pure MoC films themselves. Among the three MoC film samples with different oxidation degrees, the MoC film with the weakest oxidation degree has the highest HER activity. x C y O z -51 catalyst has the highest alkaline HER activity, but is still far inferior to Mo x Cy O z The above results show that the controllable weak oxidation process of molybdenum carbide materials can effectively optimize the HER performance of the material.

[0035] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A molybdenum carbide catalyst based on vacuum interconnection, comprising Molybdenum carbide thin layer, and an oxide Mo formed by oxidation at least on the surface of the molybdenum carbide thin layer. x C y O z , wherein x=1, y=0-0.5, z=0-3, and the oxide is at least selected from molybdenum carbon oxygen species and / or molybdenum oxygen species and / or carbon deposition species.

2. The molybdenum carbide catalyst based on vacuum interconnection as claimed in claim 1, It is characterized in that The molybdenum in the carbon-molybdenum-oxygen species exists in a valence state of +4 and / or +6.

3. The molybdenum carbide catalyst based on vacuum interconnection as claimed in claim 1, It is characterized in that The molybdenum in the molybdenum oxy species is present in a +4 and / or +6 valence state.

4. The molybdenum carbide catalyst based on vacuum interconnection as claimed in claim 1, It is characterized in that The oxidation process is carried out at an oxygen partial pressure of 10 -6 mbar-1mbar.

5. The molybdenum carbide catalyst based on vacuum interconnection as claimed in claim 4, It is characterized in that The oxidation time of the oxidation process is 1 min to 60 min.

6. The molybdenum carbide catalyst based on vacuum interconnection as claimed in claim 1, It is characterized in that The thickness of the molybdenum carbide thin layer is on the order of hundreds of nanometers.

7. The method for preparing a molybdenum carbide catalyst based on vacuum interconnection according to any one of claims 1 to 5, comprising the following steps: Prepare pure MoC thin film; Under an oxygen partial pressure of 0.1 mbar, the temperature is gradually increased from room temperature to the oxidation temperature.

8. The method for preparing a molybdenum carbide catalyst based on vacuum interconnection according to claim 7, It is characterized in that The oxidation temperature ranges from 600-700K.

9. The method for preparing a molybdenum carbide catalyst based on vacuum interconnection according to claim 8, It is characterized in that During oxidation, the oxidation is carried out at a constant temperature after the oxidation temperature is reached.

10. Use of the vacuum interconnected molybdenum carbide catalyst or its support in water electrolysis as described in any one of claims 1 to 5.

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