Nano nickel oxide and preparation method thereof

Abstract

The invention provides nano nickel oxide and a preparation method thereof. Wherein the ratio of trivalent nickel to divalent nickel on the surface of the nano nickel oxide is 1.5-4.0. The ratio of trivalent nickel to divalent nickel on the surface of the nano nickel oxide is controlled to be 1.5-4.0, so that the activity of the nano nickel oxide in oxygen evolution reaction (OER) can be improved. Therefore, the nano nickel oxide can become a potential substitute material, can replace a traditional noble metal electrode, and is applied to a water electrolysis hydrogen production reaction. And nano nickel oxide is used as an electrode material, so that the cost of hydrogen production by electrolyzing water is effectively reduced, and a new possibility is provided for realizing more economical and sustainable hydrogen production.

Description

Technical Field

[0001] This application relates to the fields of electrochemistry and new energy materials, specifically to a nano-nickel oxide and its preparation method. Background Technology

[0002] Nano-nickel oxide is a typical semiconductor with excellent thermosensitive and gas-sensitive properties, making it a promising functional material. With the ultrafine reduction of nano-nickel oxide, its surface and crystal structures undergo unique changes, leading to surface effects, small size effects, quantum size effects, and macroscopic quantum tunneling effects. This results in nano-nickel oxide exhibiting superior catalytic and electrochemical properties. Based on these excellent properties, nano-nickel oxide is also commonly used as a catalyst, sensor, and battery electrode material.

[0003] Because nickel has an electron configuration of 1s 2 2s 2 2p 6 3s 2 3p 6 3D 8 4s 2 This means it has an unfilled 3d shell and a partially filled 4s shell, allowing nickel to lose different numbers of electrons during chemical reactions, thus forming different oxidation states. The diverse stoichiometric ratios between atoms give it a rich array of physicochemical properties. Therefore, nano-nickel oxide used in functional materials generally also possesses trivalent nickel (Ni) oxidation states. 3+ ) and divalent nickel (Ni 2+ This makes it a promising anodic oxygen evolution electrocatalyst material for commercial applications under alkaline conditions. However, in practical applications, there are still many obstacles to using nano-nickel oxide for anodic oxygen evolution. Summary of the Invention

[0004] This application aims to address at least one of the technical problems existing in the prior art, to at least some extent.

[0005] In a first aspect, this application proposes a nano-nickel oxide. According to embodiments of this application, the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide is between 1.5 and 4.0. By controlling the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide to 1.5-4.0, the activity of the nano-nickel oxide in the oxygen evolution reaction (OER) can be improved. Therefore, the nano-nickel oxide of this application can be a promising alternative material that can replace traditional precious metal electrodes in the electrolysis of water to produce hydrogen. Using nano-nickel oxide as an electrode material not only effectively reduces the cost of hydrogen production through water electrolysis but also enables more economical and sustainable hydrogen production.

[0006] In a second aspect of this application, a method for preparing the nano-nickel oxide described in the first aspect is proposed. According to an embodiment of this application, the method includes: obtaining nano-nickel oxide to be treated; determining the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide to be treated, denoted as the measured value I0; obtaining a comparison result between the measured value I0 and a target value I; and selecting oxidation or reduction treatment based on the comparison result to control the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide to be treated within the range of the target value I, thereby obtaining the nano-nickel oxide, wherein the target value I is 1.5-4.0. Therefore, the method described in this application has several advantages. First, it is simple to operate, involves few steps, and is easy to implement for industrial production, making it suitable for large-scale applications. Second, this method does not introduce additional impurities, ensuring the purity and performance of the product while reducing production costs. Furthermore, compared with other methods, this process has low energy consumption, contributing to improved economic efficiency. In addition, by adjusting the processing conditions, the ratio of nickel ions can be precisely controlled, thereby optimizing the performance of the nano-nickel oxide.

[0007] According to embodiments of this application, the method for controlling the nickel valence state on the surface of nano-nickel oxide may further include at least one of the following additional technical features:

[0008] According to an embodiment of this application, when the measured value I0 is less than the minimum value of the target value I, the nano-nickel oxide to be treated is subjected to oxidation treatment; when the measured value I0 is greater than the maximum value of the target value I, the nano-nickel oxide to be treated is subjected to reduction treatment. Thus, the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide to be treated can be precisely controlled, keeping it within the range of 1.5-4.0.

[0009] According to an embodiment of this application, the oxidation treatment includes: subjecting the nano-nickel oxide to be treated to an oxidative calcination treatment under a first oxygen content condition. Thus, the oxidation treatment can oxidize a portion of the divalent nickel on the surface of the nano-nickel oxide to be treated to trivalent nickel, thereby facilitating the removal of Ni from the surface of the nano-nickel oxide. 3+ with Ni 2+ The ratio is controlled within the range of 1.5-4.0.

[0010] According to an embodiment of this application, the first oxygen content is 0.1%-20%. Therefore, by keeping the first oxygen content within the above range, the nano-nickel oxide to be treated can undergo weak oxidation, allowing some of the Ni to... 2+ Oxidation to Ni 3+ Reduce Ni 2+ Excessive conversion to Ni 3+ The probability of.

[0011] According to an embodiment of this application, the oxidation calcination treatment includes: sequentially heating the nano-nickel oxide to be treated to undergo a first oxidation calcination and a second oxidation calcination. The first oxidation calcination temperature is 120℃-140℃, and the time is 20min-40min; the second oxidation calcination temperature is 200℃-400℃, and the time is 0.5h-5h. Thus, by performing calcination through a stepped heating method, adsorbed water on the surface of the nano-nickel oxide is removed without altering its structure, reducing the attraction between nano-nickel oxide particles and preventing agglomeration of the nano-nickel oxide particles caused by direct high-temperature calcination.

[0012] According to an embodiment of this application, the reduction treatment includes: subjecting the mixture of the nano-nickel oxide to be treated and the carbon-containing material to a reduction calcination treatment under a second oxygen content condition. Thus, the reduction treatment can reduce a portion of the trivalent nickel on the surface of the nano-nickel oxide to be treated to divalent nickel, thereby facilitating the reduction of Ni on the surface of the nano-nickel oxide. 3+ with Ni 2+ The ratio is controlled within the range of 1.5-4.0.

[0013] According to embodiments of this application, the second oxygen content is 0.1%-20%. Therefore, by keeping the second oxygen content within the above range, carbonaceous materials can undergo an incomplete reaction to generate carbon monoxide gas, thereby causing a weak reduction of the nano-nickel oxide to be treated, and partially reducing the Ni content. 3+ Reduced to Ni 2+ Reduce Ni 3+ Excessive conversion to Ni 2+ The probability of.

[0014] According to an embodiment of this application, the reduction calcination treatment includes: firstly, heating the mixture sequentially to perform a first reduction calcination and a second reduction calcination. The first reduction calcination temperature is 120℃-140℃, and the time is 20min-40min; the second reduction calcination temperature is 250℃-450℃, and the time is 0.5h-5h. Thus, by performing calcination through a stepped heating method, adsorbed water on the surface of the nickel nano-oxide is removed without altering the structure of the nickel nano-oxide itself, reducing the attraction between the nickel nano-oxide particles and thereby promoting Ni… 3+ Converted into Ni 2+ .

[0015] According to an embodiment of this application, the mass ratio of the nickel nano-oxide to be treated to the carbon-containing material is 1:(1-3). Therefore, by keeping the mass ratio of the nickel nano-oxide to the carbon-containing material within the above range, the nickel nano-oxide to be treated can undergo weak reduction, allowing some of the Ni to be removed. 3+ Reduced to Ni 2+ Thus, the Ni on the surface of the nano-nickel oxide to be treated3+ with Ni 2+ The ratio is controlled within the range of 1.5-4.0.

[0016] According to embodiments of this application, the carbon-containing material includes at least one of carbon black and graphite. Therefore, by employing the aforementioned type of carbon-containing material, the nano-nickel oxide to be treated can undergo weak reduction, allowing some of the Ni to be removed. 3+ Reduced to Ni 2+ Thus, the Ni on the surface of the nano-nickel oxide to be treated 3+ with Ni 2+ The ratio is controlled within the range of 1.5-4.0.

[0017] According to embodiments of this application, the oxidation treatment or the reduction treatment is carried out in a tubular furnace. This allows for control of the oxygen content within the furnace and the content of reducing gases generated during the reduction treatment, thereby controlling the occurrence of the oxidation and reduction reactions.

[0018] According to an embodiment of this application, prior to the oxidation treatment or the reduction treatment, a further step is to perform a vacuum treatment inside the tubular furnace, wherein the gas pressure inside the tubular furnace is 10. -3 Pa to 10 -5 Pa. This allows for the removal of impurity atmospheres within the tubular furnace.

[0019] In a third aspect of this application, the application proposes the use of the nano-nickel oxide described in the first aspect or the nano-nickel oxide prepared by the method described in the second aspect as an anode electrode for the electrolysis of water to produce hydrogen.

[0020] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0021] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0022] Figure 1 This is an experimental flowchart of the oxidation treatment according to an embodiment of this application;

[0023] Figure 2 This is an experimental flowchart of the restoration process according to an embodiment of this application. Detailed Implementation

[0024] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0025] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0027] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this application but do not exclude other contents.

[0028] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0029] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0030] Studies have shown that nickel oxide-based materials have promising applications in the oxygen evolution reaction (OER) and are considered potential alternatives to noble metals such as platinum (Pt). However, nickel oxide with a stoichiometric ratio of 1 typically exhibits low activity, meaning that pure divalent nickel oxide has insufficient electrochemical oxygen evolution activity. This is mainly because, during water oxidation, the exposed Ni... 2+ The reaction site will first be oxidized to Ni 3+This leads to the generation of high overpotentials. Furthermore, many studies have shown that Ni in nickel oxide... 2+ With t2g 6 e g 2 The electronic configuration of Ni, and 3+ Then it has t 2g 6 e g 1 The electronic configuration of Ni, due to the suitable metal-oxygen bond, 3+ (t 2g 6 e g 1 The ) site is an ideal candidate site for the anodic oxygen evolution reaction, t 2g 6 e g 1 This configuration is considered an ideal structure for promoting the OER process, and therefore has high Ni content. 3+ Ni content is key to improving the OER activity of nickel oxide materials, but Ni 3+ (t 2g 6 e g 1 The sites are not stable, so regulating the trivalent nickel (Ni) in nano-nickel oxide materials is crucial. 3+ ) and divalent nickel (Ni 2+ The ratio of ) to effectively improve its activity in the oxygen evolution reaction is crucial to its performance.

[0031] Currently, conventional methods for preparing nano-nickel oxide typically involve first synthesizing nano-nickel hydroxide, followed by thermal decomposition in a sufficient oxygen atmosphere to obtain nano-nickel oxide. However, due to the small size and high surface energy of nano-nickel hydroxide particles, they are prone to spontaneous combustion during calcination. This combustion reaction is extremely vigorous, making it difficult to control the degree of oxidation. Therefore, the final nano-nickel oxide has a Ni content on its surface. 3+ and Ni 2+ The ratio is also uncontrollable. This makes it impossible to directly control the Ni content on the surface of nano-nickel oxide during the synthesis process. 3+ with Ni 2+ The proportion becomes very difficult to determine.

[0032] Furthermore, in the post-processing stage, the Ni content can be increased by oxidizing the nickel oxide. 3+The content of nickel oxide is increased to enhance its activity in the oxygen evolution reaction (OER). However, due to the small size of nanomaterials, they exhibit a certain size effect (nanoscale materials possess properties such as high specific surface area). Over-processing of this material may lead to the agglomeration of nano-nickel oxide into large particles, which is detrimental to applications. Furthermore, while reduction reactions under a hydrogen atmosphere can reduce some of the Ni content... 3+ The content of Ni is important, but the degree of hydrogen reduction is difficult to control precisely; excessive reduction may damage Ni. 3+ Reduced to Ni 0 This further affects the material's properties.

[0033] Therefore, Ni 3+ with Ni 2+ Within what range should the Ni ratio be controlled, and how can precise control of the Ni content on the nano-nickel oxide surface be achieved? 3+ and Ni 2+ The ratio remains a challenge and is crucial for improving the performance of nickel oxide materials in various fields.

[0034] Nano nickel oxide

[0035] In view of this, this application proposes a nano-nickel oxide. According to embodiments of this application, the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide is between 1.5 and 4.0. Through extensive experimentation, the inventors have discovered that by controlling the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide to 1.5-4.0, the activity of the nano-nickel oxide in the oxygen evolution reaction (OER) can be effectively improved, while simultaneously preventing the nano-nickel oxide from agglomerating into large particles that would affect its application. Therefore, the nano-nickel oxide of this application can be a promising alternative material, capable of replacing traditional precious metal electrodes in the electrolysis of water to produce hydrogen. Using nano-nickel oxide as an electrode material not only effectively reduces the cost of hydrogen production through water electrolysis but also enables more economical and sustainable hydrogen production.

[0036] Methods for preparing nano-nickel oxide

[0037] This application proposes a method for preparing the aforementioned nano-nickel oxide. According to an embodiment of this application, the method includes: obtaining nano-nickel oxide to be treated; determining the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide to be treated, denoted as the measured value I0; obtaining a comparison result between the measured value I0 and a target value I; and selecting oxidation or reduction treatment based on the comparison result to control the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide to be treated within the range of the target value I, thereby obtaining the nano-nickel oxide, wherein the target value I is 1.5-4.0. Therefore, the method described in this application has several advantages. First, it is simple to operate, involves few steps, and is easy to implement for industrial production, making it suitable for large-scale applications. Second, this method does not introduce additional impurities, ensuring the purity and performance of the product while reducing production costs. Furthermore, compared with other methods, this process has low energy consumption, contributing to improved economic efficiency. In addition, by adjusting the processing conditions, the ratio of nickel ions can be precisely controlled, thereby optimizing the performance of the nano-nickel oxide.

[0038] It should be noted that this application does not impose any limitation on the "nano nickel oxide to be treated," which can be obtained by purchase or preparation, and the ratio of trivalent nickel to divalent nickel on the surface of the nano nickel oxide to be treated is uncertain. By employing the method of this application, it is possible to treat the Ni content on the surface of nano nickel oxide obtained from different manufacturers, different preparation methods, and different batches. 3+ and Ni 2+ The ratio is adjusted to the range of 1.5-4 to ensure the uniformity of nano-nickel oxide.

[0039] In some embodiments of this application, when the measured value I0 is less than the minimum value of the target value I, the nano-nickel oxide to be treated is subjected to oxidation treatment, referring to... Figure 1 The oxidation process includes:

[0040] S100: Oxidation calcination treatment

[0041] In this step, the nano-nickel oxide to be treated is subjected to an oxidation-calcination treatment under a first oxygen content condition. The oxidation-calcination treatment includes a first oxidation-calcination S101 and a second oxidation-calcination S102. Through this oxidation-calcination treatment, a portion of the divalent nickel on the surface of the nano-nickel oxide to be treated can be oxidized to trivalent nickel, thereby facilitating the removal of Ni from the nano-nickel oxide. 3+ with Ni 2+ The ratio is controlled within the range of 1.5-4.0.

[0042] In some embodiments of this application, the first oxygen content is 0.1%-20%. For example, it can be 0.1%, 1%, 5%, 10%, 15%, 20%, etc., or a range of any of the above values. Therefore, by keeping the first oxygen content within the above range, the nano-nickel oxide to be treated can undergo weak oxidation, further oxidizing some of the divalent nickel to trivalent nickel, thus reducing the Ni content. 2+ Excessive conversion to Ni 3+ The probability of this helps to improve the Ni content on the surface of the nano-nickel oxide to be treated. 3+ with Ni 2+ The ratio is controlled within the range of 1.5-4.0.

[0043] In some embodiments of this application, the oxygen purity in the first oxygen is greater than or equal to 99.9%. Therefore, high-purity oxygen is beneficial for obtaining more high-valence nickel from the nano-nickel oxide to be treated, reduces the presence of other impurity gases, thereby reducing the probability of side reactions and facilitating the acquisition of the target valence state.

[0044] S101: First oxidation calcination

[0045] In this step, the nickel nanoparticles to be treated are heated to undergo a first oxidation calcination. This first oxidation calcination removes adsorbed water from the surface of the nickel nanoparticles, reducing the attraction between the nanoparticles caused by the adsorbed water. The adsorbed water is mechanically adsorbed on the surface or between the nanoparticles and does not participate in the formation of the crystal lattice. Therefore, when a fixed temperature is reached, all the adsorbed water will escape, and this escape does not cause any change in the structure of the nickel nanoparticles themselves.

[0046] In some embodiments of this application, the temperature of the first oxidation calcination is 120℃-140℃. For example, it can be 120℃, 122℃, 125℃, 128℃, 130℃, 132℃, 135℃, 138℃, 140℃, or any range of the above values. Therefore, by keeping the temperature of the first oxidation calcination within the above range, adsorbed water on the surface of the nickel nanoparticles to be treated can be removed, reducing the attraction between the nickel nanoparticles.

[0047] In some embodiments of this application, the first oxidation calcination time is 20-40 minutes. For example, it can be 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, or any range of the above values. Therefore, by keeping the first oxidation calcination time within the above range, the adsorbed water on the surface of the nickel nanoparticles to be treated can be removed more completely, and the attraction between the nickel nanoparticles can be reduced.

[0048] S102: Second oxidation calcination

[0049] In this step, the nano-nickel oxide to be treated after the first oxidation calcination treatment is further heated for a second oxidation calcination. This second oxidation calcination promotes the oxidation process. In this process, oxygen acts as an oxidant, its main role being to accept electrons and provide oxygen atoms. Specifically, oxygen molecules (O2) gain electrons in the reaction, becoming oxygen atoms (O). These oxygen atoms then react with divalent nickel (Ni) on the surface of the nano-nickel oxide to be treated. 2+ ) combine to form trivalent nickel (Ni) 3+ ).

[0050] In some embodiments of this application, the temperature of the second oxidation calcination is 200℃-400℃. For example, it can be 200℃, 220℃, 250℃, 280℃, 300℃, 320℃, 350℃, 380℃, 400℃, etc., or any range of the above values. Therefore, by keeping the temperature of the second oxidation calcination within the above range, the oxidation reaction can be promoted, thereby promoting the conversion of divalent nickel to trivalent nickel on the surface of the nano-nickel oxide to be treated.

[0051] In some embodiments of this application, the second oxidation calcination time is 0.5h-5h. For example, it can be 0.5h, 1h, 2h, 3h, 4h, 5h, or any range of the above values. Thus, by keeping the second oxidation calcination time within the above range, the divalent nickel on the surface of the nano-nickel oxide to be treated can be converted into trivalent nickel, thereby controlling the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide to be treated to be 1.5-4.0.

[0052] In some embodiments of this application, the oxidation process is carried out in a tubular furnace. This allows for control of the oxygen content within the furnace, thereby controlling the oxidation reaction and promoting the conversion of divalent nickel to trivalent nickel.

[0053] In some embodiments of this application, prior to the oxidation treatment, a vacuum process is further performed inside the tubular furnace, with the pressure inside the furnace being 10... -3 Pa to 10 -5 Pa. For example, it can be 10. -3 Pa, 10 -3.5 Pa, 10 -4 Pa, 10 -4.5 Pa, 10 -5 Pa, etc., or any range of the above values. This allows for the removal of impurities from the tubular furnace atmosphere, resulting in an atmosphere containing oxygen and nitrogen.

[0054] In some embodiments of this application, when the measured value I0 is greater than the maximum value of the target value I, the nano-nickel oxide to be treated is subjected to a reduction treatment. Figure 2 The reduction process includes:

[0055] S200: Reduction calcination treatment

[0056] In this step, the mixture of the nano-nickel oxide to be treated and the carbon-containing material is subjected to reduction calcination under a second oxygen content condition. The reduction calcination treatment includes a first reduction calcination S201 and a second reduction calcination S202. Through this reduction calcination treatment, a portion of the trivalent nickel on the surface of the nano-nickel oxide to be treated can be reduced to divalent nickel, thereby facilitating the removal of Ni from the nano-nickel oxide. 3+ with Ni 2+ The ratio is controlled within the range of 1.5-4.0.

[0057] In some embodiments of this application, the second oxygen content is 0.1%-20%. For example, it can be 0.1%, 1%, 5%, 10%, 15%, 20%, etc., or a range of any of the above values. Therefore, by keeping the second oxygen content within the above range, the carbon-containing material can undergo incomplete reaction to generate carbon monoxide gas, thereby causing a weak reduction of the nano-nickel oxide to be treated, further reducing some of the trivalent nickel to divalent nickel, and lowering the Ni content. 3+ Excessive conversion to Ni 2+ The probability of this helps to improve the Ni content on the surface of the nano-nickel oxide to be treated. 3+ with Ni 2+ The ratio is controlled within the range of 1.5-4.0.

[0058] In some embodiments of this application, the carbon-containing material includes at least one of carbon black and graphite. Therefore, by employing the aforementioned type of carbon-containing material, under oxygen-deficient conditions, it can undergo an incomplete reaction with oxygen at high temperatures to generate carbon monoxide (reducing agent) gas in situ. The specific reaction formula is 2C + O₂ → 2CO. CO will undergo a redox reaction with the nickel nano-oxide to be treated, causing some Ni on the surface of the nickel nano-oxide to... 3+ Reduced to Ni 2+ By controlling the content of the second oxygen, the amount of carbon monoxide generated can be further controlled, thus achieving precise regulation of the Ni content on the nano-nickel oxide surface. 3+ and Ni 2+ The proportion.

[0059] In some embodiments of this application, the mass ratio of the nickel nano-oxide to be treated to the carbon-containing material is 1:(1-3). For example, it can be 1:1, 1:2, 1:3, or any range of the above values. Therefore, by keeping the mass ratio of the nickel nano-oxide to the carbon-containing material within the above range, oxygen can be more completely converted into carbon monoxide, thereby promoting the formation of Ni on the surface of the nickel nano-oxide. 3+ Reduced to Ni 2+ The reaction proceeds.

[0060] In some embodiments of this application, the oxygen purity in the second oxygen is greater than or equal to 99.9%. This reduces the presence of other impurity gases, thereby lowering the probability of side reactions and facilitating the attainment of the target valence state.

[0061] S201: First reduction calcination

[0062] In this step, the nickel nanoparticles to be treated are heated to undergo a first reduction calcination. This first reduction calcination removes adsorbed water from the surface of the nickel nanoparticles, reducing the attraction between the nanoparticles caused by the adsorbed water. The adsorbed water is mechanically adsorbed on the surface or between the nanoparticles and does not participate in the formation of the crystal lattice. Therefore, when a fixed temperature is reached, all the adsorbed water will escape, and this escape does not cause any change in the structure of the nickel nanoparticles themselves.

[0063] In some embodiments of this application, the temperature of the first reduction calcination is 120℃-140℃. For example, it can be 120℃, 122℃, 125℃, 128℃, 130℃, 132℃, 135℃, 138℃, 140℃, or any range of the above values. Therefore, by keeping the temperature of the first reduction calcination within the above range, adsorbed water on the surface of the nickel oxide nanoparticles to be treated can be removed, reducing the attraction between the nickel oxide nanoparticles.

[0064] In some embodiments of this application, the first reduction calcination time is 0.5h-5h. For example, it can be 0.5h, 1h, 2h, 3h, 4h, 5h, or any range of the above values. Therefore, by keeping the first reduction calcination time within the above range, the adsorbed water on the surface of the nickel nano-oxide to be treated can be removed more completely, and the attraction between the nickel nano-oxide particles can be reduced.

[0065] S202: Second reduction calcination

[0066] In this step, the nano-nickel oxide to be treated, after the first reduction calcination treatment, is further heated for a second reduction calcination. This second reduction calcination promotes the reduction process. During this process, carbon-containing substances react with oxygen at high temperatures to generate carbon monoxide gas in situ (2C + O2 → 2CO). This carbon monoxide gas acts as a reducing agent, reacting with the nano-nickel oxide to promote the reduction of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide.

[0067] In some embodiments of this application, the temperature of the second reduction calcination is 250℃-450℃. For example, it can be 250℃, 280℃, 300℃, 320℃, 350℃, 380℃, 400℃, 450℃, etc., or any range of the above values. Therefore, by keeping the temperature of the second reduction calcination within the above range, carbon-containing materials can generate carbon monoxide gas, thereby promoting the reaction between carbon monoxide and the nano-nickel oxide to be treated, and promoting the reduction of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide.

[0068] In some embodiments of this application, the second reduction calcination time is 0.5h-5h. For example, it can be 0.5h, 1h, 2h, 3h, 4h, 5h, or any range of the above values. Thus, by keeping the second reduction calcination time within the above range, the trivalent nickel on the surface of the nano-nickel oxide to be treated can be converted into divalent nickel, thereby controlling the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide to be treated to be 1.5-4.0.

[0069] In some embodiments of this application, the reduction process is carried out in a tubular furnace. This allows for control of the oxygen content within the furnace, thereby controlling the reduction reaction and promoting the conversion of trivalent nickel to divalent nickel.

[0070] In some embodiments of this application, prior to the reduction process, a vacuum process is further performed inside the tubular furnace, wherein the gas pressure inside the tubular furnace is 10. -3 Pa to 10 -5 Pa. For example, it can be 10. -3 Pa, 10 -3.5 Pa, 10 -4 Pa, 10 -4.5 Pa, 10 -5 Pa, etc., or any range of the above values. This allows for the removal of impurities from the tubular furnace atmosphere, resulting in an atmosphere containing oxygen and nitrogen.

[0071] use

[0072] This application proposes the use of the aforementioned nano-nickel oxide, or nano-nickel oxide prepared by the aforementioned method, as an anode electrode in the electrolysis of water to produce hydrogen. As mentioned above, by controlling the ratio of trivalent nickel to divalent nickel on the surface of nano-nickel oxide to 1.5-4.0, the oxygen evolution reaction activity of nano-nickel oxide can be improved. Therefore, nano-nickel oxide can replace traditional noble metal electrodes for the electrolysis of water to produce hydrogen.

[0073] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0074] Example 1

[0075] After cleaning the crucible, place it in an oven and dry at 80°C. Weigh out nano-nickel oxide (commercially purchased, the initial Ni content of which is...). 3+ with Ni 2+ The proportion of the sample (measured to be 1.45) was placed in a crucible, then placed in a tube furnace, sealed, and vacuumed seven times. Oxygen and nitrogen were introduced separately, and the initial oxygen concentration in the tube furnace was controlled to be 5%. Calcination was then carried out, with the first oxidation calcination temperature maintained at 130℃ for 0.5 hours. The temperature was then raised to 250℃ for the second oxidation calcination for 1 hour, resulting in surface-modified nano-nickel oxide particles.

[0076] Example 2

[0077] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the initial oxygen concentration in the tube furnace was controlled to be 10%.

[0078] Example 3

[0079] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the initial oxygen concentration in the tube furnace was controlled to be 15%.

[0080] Example 4

[0081] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the initial oxygen concentration in the tube furnace was controlled to be 20%.

[0082] Example 5

[0083] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the initial oxygen concentration in the tube furnace was controlled to be 30%.

[0084] Example 6

[0085] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the initial oxygen concentration in the tube furnace was controlled to be 0.1%.

[0086] Example 7

[0087] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the first oxidation calcination temperature was maintained at 120°C and the calcination time was 0.5 h.

[0088] Example 8

[0089] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the first oxidation calcination temperature was maintained at 140°C and the calcination time was 0.5 h.

[0090] Example 9

[0091] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the second oxidation calcination temperature was maintained at 200°C and the calcination time was 1 hour.

[0092] Example 10

[0093] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the second oxidation calcination temperature was maintained at 400°C and the calcination time was 1 hour.

[0094] Example 11

[0095] Surface-modified nickel oxide nanoparticles were prepared according to the method described in Example 1, except that the second oxidation calcination temperature was maintained at 500°C and the calcination time was 1 hour.

[0096] Example 12

[0097] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the second oxidation calcination temperature was maintained at 250°C and the calcination time was 0.5 h.

[0098] Example 13

[0099] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the second oxidation calcination temperature was maintained at 250°C and the calcination time was 5 hours.

[0100] Example 14

[0101] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 1, except that the initial oxygen concentration in the tube furnace was 20%, the second oxidation calcination temperature was maintained at 400°C, and the calcination time was 5 hours.

[0102] Example 15

[0103] After cleaning the crucible, place it in an oven and dry at 80°C. Weigh out nano-nickel oxide and carbon black (both commercially available, with the initial Ni content of the purchased nano-nickel oxide being...). 3+ with Ni 2+ The proportions of nickel oxide and carbon black were approximately 2.8. They were placed in crucibles to make the mass ratio of nano-nickel oxide to carbon black 1:2. The crucibles were then placed in a tube furnace, sealed, and vacuumed seven times. Oxygen and nitrogen were introduced at the same time, and the initial oxygen concentration in the tube furnace was controlled at 5%. The furnace was then calcined. The temperature of the first reduction calcination was maintained at 130°C for 0.5 hours. The temperature was then raised to 250°C for the second reduction calcination for 1 hour, resulting in surface-modified nano-nickel oxide particles.

[0104] Among them, due to the Ni on the surface of the purchased nano nickel oxide 3+ with Ni 2+ The proportion of nickel oxide is not uniform, resulting in poor oxygen evolution performance. The method described in this application allows for the control of nano-nickel oxide to obtain Ni... 3+ with Ni 2+ The proportion of uniform nano-nickel oxide is used to improve the oxygen evolution performance of nano-nickel oxide.

[0105] Example 16

[0106] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 15, except that the oxygen partial pressure inside the tube furnace was controlled at 10%.

[0107] Example 17

[0108] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 15, except that the oxygen partial pressure inside the tube furnace was controlled at 15%.

[0109] Example 18

[0110] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 15, except that the oxygen partial pressure inside the tube furnace was controlled at 20%.

[0111] Example 19

[0112] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 15, except that the oxygen partial pressure inside the tube furnace was controlled at 30%.

[0113] Example 20

[0114] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 15, except that the oxygen partial pressure inside the tube furnace was controlled at 0.1%.

[0115] Example 21

[0116] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 15, except that the initial oxygen concentration in the tube furnace was 20%, the second reduction calcination temperature was maintained at 450°C, and the calcination time was 2 hours.

[0117] Example 22

[0118] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 15, except that the temperature of the second reduction calcination was maintained at 300°C and the calcination time was 1 hour.

[0119] Example 23

[0120] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 15, except that the temperature of the second reduction calcination was maintained at 450°C and the calcination time was 1 hour.

[0121] Example 24

[0122] Surface-modified nano-nickel oxide particles were prepared according to the method described in Example 15, except that the temperature of the second reduction calcination was maintained at 550°C and the calcination time was 1 hour.

[0123] Comparative Example 1

[0124] After cleaning the crucible, place it in an oven and dry at 80°C. Weigh out nano-nickel oxide (commercially purchased, the initial Ni content of which is...). 3+ with Ni 2+ The ratio of approximately 2.8% was placed in a crucible, then placed in a tube furnace, sealed, and vacuumed seven times. High-purity oxygen was directly introduced, and the initial pressure inside the tube furnace was controlled at 0.2 MPa (greater than atmospheric pressure). Calcination was then carried out, with the first oxidation calcination temperature maintained at 130℃ for 0.5 hours. The temperature was then raised to 400℃ for the second oxidation calcination for 5 hours, resulting in surface-modified nano-nickel oxide particles.

[0125] Comparative Example 2

[0126] After cleaning the crucible, place it in an oven and dry at 80°C. Weigh out nano-nickel oxide (obtained commercially, with the initial Ni content of the purchased nano-nickel oxide). 3+ with Ni 2+ The ratio of approximately 2.8 is placed in a crucible, then placed in a tube furnace, sealed, and vacuumed 7 times. An argon-hydrogen mixture is then introduced, and the initial hydrogen concentration in the tube furnace is controlled at 10%. Calcination is then carried out at 500℃ for 2 hours to obtain surface-modified nano-nickel oxide particles.

[0127] The differences between Examples 1-20 and Comparative Examples 1-2 are shown in Table 1. The method for determining the ratio of divalent to trivalent nickel in the surface-modified nano-nickel oxide particles in Examples 1-20 and Comparative Examples 1-2 is as follows:

[0128] Surface analysis of surface-modified nickel oxide nanoparticles was performed using X-ray photoelectron spectroscopy (XPS). The collected data was processed using XPS spectral analysis software, including peak fitting, background correction, and elemental content calculation, to obtain the valence state information of the elements.

[0129] Table 1

[0130]

[0131] Note: "-" indicates that it cannot be measured.

[0132] Performance testing

[0133] 1. The oxygen evolution performance of the nano-nickel oxide-platinum electrodes prepared with surface-modified nickel oxide obtained in Examples 1-24 and Comparative Examples 1-2 was tested. The specific process is as follows:

[0134] A three-electrode system was used, with the working electrode being the prepared nano-nickel oxide-platinum electrode (5 mg of nano-nickel oxide was accurately weighed and dispersed in 400 μl of dispersant (dispersant composition: 395 μl isopropanol + 5 μl Nafion proton solution), and the mixture was then thinly coated onto the surface of the platinum electrode). The counter electrode was a platinum sheet electrode, and the reference electrode was a saturated Hg / HgO electrode. Electrochemical tests were performed on an electrochemical workstation. Oxygen evolution reaction (OER) test: The electrolyte was a 1 mol / L potassium hydroxide solution. The test was conducted at 100 mA / cm². 2 Overpotential values ​​of Pt electrode surface loaded with nano-nickel oxide at current density.

[0135] Generally, a lower overpotential indicates a smaller energy barrier for electron transfer and a faster reaction rate, thus suggesting higher activity and a greater likelihood of reaction. The test results are shown in Table 2. The overpotential values ​​of Examples 1-24 are lower than those of Comparative Examples 1 and 2, therefore, only samples with suitable Ni... 3 with Ni 2+ The proportion of nano-nickel oxide, that is, the Ni on the surface of nano-nickel oxide 3+ / Ni 2+ When the ratio is in the range of 1.5-4.0, it can exhibit high activity in the oxygen evolution reaction.

[0136] In addition, Comparative Example 1 controlled the valence state of the nano-nickel oxide surface under oxygen-rich conditions. However, this condition leads to the "Oswald ripening" effect during the processing of nano-nickel oxide. At high temperatures, active nanoparticles, induced by oxygen molecules, tend to aggregate towards larger particles, resulting in larger particles becoming larger and smaller particles becoming smaller until they dissolve. Comparative Example 2 used hydrogen to reduce the valence state of the nano-nickel oxide surface, but hydrogen reduction is very strong and extremely difficult to control stably. It easily reduces divalent and trivalent nickel to zero-valent nickel, and Ni cannot be measured on the particle surface using the same method. 3 with Ni 2+ The product characteristics have changed significantly. Therefore, compared with Comparative Examples 1 and 2, the method of this application can control the degree of oxidation and reduction by controlling the reaction conditions, and can precisely regulate the valence state of the nano nickel oxide surface.

[0137] Furthermore, comparing Examples 5, 11, 1-4, 6-10, and 12-14, the inventors found that excessively high oxygen concentration or excessively high second oxidation calcination temperature during the oxidation process leads to agglomeration of nano-nickel oxide, resulting in non-uniform nano-nickel oxide particle size. Comparing Examples 19, 24, 15-18, and 20-23, it was found that excessively high oxygen concentration or excessively high second reduction calcination temperature during the reduction process also leads to agglomeration of nano-nickel oxide, resulting in non-uniform nano-nickel oxide particle size.

[0138] Meanwhile, excessive treatment (oxygen-rich conditions, argon-hydrogen mixed atmosphere, excessively high oxygen concentration during treatment, or excessively high calcination temperature) will affect the properties of nano-nickel oxide itself (severe particle agglomeration), leading to a reduction in exposed active sites, which in turn leads to an increase in overpotential value and affects its activity during the oxygen evolution reaction.

[0139] Table 2

[0140] Overpotential value (mV) Example 1 535 Example 2 480 Example 3 397 Example 4 337 Example 5 410 Example 6 574 Example 7 537 Example 8 536 Example 9 570 Example 10 501 Example 11 547 Example 12 559 Example 13 506 Example 14 242 Example 15 450 Example 16 471 Example 17 498 Example 18 512 Example 19 525 Example 20 435 Example 21 564 Example 22 457 Example 23 466 Example 24 513 Comparative Example 1 587 Comparative Example 2 624

[0141] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0142] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A nano-nickel oxide, characterized in that, The ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide is between 1.5 and 4.

0.

2. A method for preparing the nano-nickel oxide according to claim 1, characterized in that, include: The nano-nickel oxide to be treated was obtained, and the ratio of trivalent nickel to divalent nickel on the surface of the nano-nickel oxide to be treated was determined and recorded as the measured value I0. The measured value I0 is compared with the target value I. Based on the comparison result, oxidation treatment or reduction treatment is selected to control the ratio of trivalent nickel to divalent nickel on the surface of the nano nickel oxide to be treated within the range of the target value I, thereby obtaining the nano nickel oxide, wherein the target value I is 1.5-4.

0.

3. The method according to claim 2, characterized in that: When the measured value I0 is less than the minimum value of the target value I, the nano-nickel oxide to be treated is subjected to oxidation treatment; When the measured value I0 is greater than the maximum value of the target value I, the nano-nickel oxide to be treated is subjected to reduction treatment.

4. The method according to claim 3, characterized in that, The oxidation treatment includes: The nano-nickel oxide to be treated is subjected to oxidation and calcination treatment under a first oxygen content condition; preferably, the first oxygen content is 0.1%-20%.

5. The method according to claim 4, characterized in that, The oxidation and calcination treatment includes: The nano-nickel oxide to be treated is sequentially heated to undergo a first oxidation calcination and a second oxidation calcination. The temperature of the first oxidation calcination is 120℃-140℃, and the time is 20min-40min. The temperature of the second oxidation calcination is 200℃-400℃, and the time is 0.5h-5h.

6. The method according to claim 3, characterized in that, The reduction process includes: The mixture of the nano-nickel oxide to be treated and the carbon-containing material is subjected to reduction calcination under a second oxygen content condition; preferably, the second oxygen content is 0.1%-20%.

7. The method according to claim 6, characterized in that, The reduction calcination treatment includes: The mixture is heated sequentially to undergo a first reduction calcination and a second reduction calcination. The temperature of the first reduction calcination is 120℃-140℃, and the time is 20min-40min. The temperature of the second reduction calcination is 250℃-450℃, and the time is 0.5h-5h.

8. The method according to claim 7, characterized in that, The mass ratio of the nano-nickel oxide to be treated to the carbon-containing material is 1:(1-3); And / or, the carbon-containing material includes at least one of carbon black and graphite.

9. The method according to any one of claims 1-8, characterized in that, The oxidation treatment or the reduction treatment is carried out in a tube furnace.

10. The method according to claim 9, characterized in that, Prior to the oxidation or reduction treatment, a further step includes evacuating the tubular furnace to a pressure of 10. -3 Pa to 10 -5 Pa.

11. The use of the nano-nickel oxide according to claim 1 or the nano-nickel oxide prepared by the method according to any one of claims 2-10 as an anode electrode for hydrogen production by water electrolysis.

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