Spinel type urea oxidation catalyst as well as preparation method and application thereof

Abstract

The invention relates to a spinel type urea oxidation catalyst as well as a preparation method and application thereof. The spinel type urea oxidation catalyst comprises a substrate material and an active component loaded on the substrate material, the active component comprises NiCo2O4 doped with Ce or a mixture of the NiCo2O4 doped with Ce and CeO2; in the mixture of the Ce-doped NiCo < 2 > O < 4 > and the CeO < 2 >, a heterostructure is formed between the Ce-doped NiCo < 2 > O < 4 > and the CeO < 2 >. By introducing the rare earth element Ce, the performance of NiCo2O4 in the urea oxidation (UOR) catalysis process is remarkably improved, the adsorption process of a urea oxidation reaction intermediate can be optimized, and more active sites can be generated at an interface, so that the reaction is accelerated, the overpotential in the UOR reaction process is reduced, and the catalyst shows a better urea oxidation effect; meanwhile, the stability of the catalyst is more excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of energy conversion, and in particular to a spinel-type urea oxidation catalyst, a preparation method thereof, and uses thereof. Background Art

[0002] With economic growth and improved living standards, people's demand for energy is increasing. However, the excessive use of fossil energy has led to the increasing depletion of energy and the gradual escalation of the global environmental crisis. Among various energy sources, hydrogen energy has gradually been regarded as one of the important energy sources that can effectively replace fossil fuels in the 21st century due to its advantages such as high energy density and low environmental pollution. Among the various hydrogen production methods, water electrolysis hydrogen production technology has become a hot topic of research today due to its high efficiency, low pollution, simplicity and convenience. However, the high cost and resource scarcity of precious metal catalysts (Ru, Ir, etc.) have limited their large-scale application. Therefore, regulating the electronic structure of non-precious metal catalysts and improving the catalyst activity and stability have become the key to reducing the cost of water electrolysis hydrogen production technology.

[0003] The hydrogen production reaction via water electrolysis consists of two half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). While the HER is highly efficient, the OER has relatively slow kinetics and requires a high overpotential, significantly limiting the overall hydrogen production efficiency. Therefore, exploring advanced reaction pathways that can effectively replace the OER is crucial for advancing the advancement and application of hydrogen production technologies.

[0004] In recent years, the urea oxidation reaction (UOR) has attracted widespread attention in the scientific community. This reaction has a significant advantage, namely, its theoretical thermodynamic potential is only 0.37V. Compared with the high overpotential of OER, UOR shows lower energy consumption requirements. If UOR is used instead of OER in the hydrogen production process, energy consumption will be significantly reduced, while the energy conversion efficiency will be improved. This means that by replacing OER with UOR, hydrogen can be effectively produced at a lower energy input, thereby improving the overall economic efficiency of hydrogen production.

[0005] Furthermore, urea, a compound widely present in industrial wastewater, can be effectively treated through the application of UOR. Urea can also be converted into useful energy. This conversion process is not only of great significance to environmental protection, reducing the pollution burden associated with wastewater treatment, but also transforms urea into a renewable energy source, achieving the dual benefits of wastewater treatment and energy production, providing strong support for sustainable development.

[0006] Current technologies are complex and costly in catalyst preparation, making large-scale production a significant challenge. Therefore, developing non-precious metal catalysts with superior performance, ease of preparation, and low cost is crucial for achieving widespread adoption of alkaline water electrolysis for hydrogen production, and represents a critical issue that needs to be addressed urgently. Summary of the Invention

[0007] In order to solve the above technical problems, the purpose of the present invention is to provide a spinel-type urea oxidation catalyst and its preparation method and use. The spinel-type urea oxidation catalyst of the present invention has high activity and good stability, a simple and efficient preparation method, low cost, and is suitable for large-scale preparation, providing a new solution for urea wastewater treatment and efficient hydrogen production.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a spinel-type urea oxidation catalyst, which includes a base material and an active component loaded on the base material; the active component includes Ce-doped NiCo2O4 or a mixture of Ce-doped NiCo2O4 and CeO2; in the mixture of Ce-doped NiCo2O4 and CeO2, a heterogeneous structure is formed between the Ce-doped NiCo2O4 and CeO2.

[0010] The spinel-type urea oxidation catalyst provided by the present invention is prepared by doping the rare earth element Ce into NiCo2O4, a metal oxide having a spinel crystal structure. Some of the octahedral sites in the spinel crystal structure are occupied by Ce single atoms. The introduction of Ce single atoms enables the metal oxide to generate more oxygen vacancies during the catalytic process. The electron transfer between the oxygen vacancies and the Ce-OA (A=Co / Ni) configuration enhances the electron localization at the A site, optimizes the adsorption process of urea oxidation intermediates, and thus accelerates the reaction. Furthermore, the catalyst maintains good stability during the urea oxidation process.

[0011] In addition, when Ce single atoms and CeO2 exist simultaneously in the spinel-type urea oxidation catalyst, CeO2 will form a heterojunction with the spinel crystal structure doped with Ce single atoms. The construction of the CeO2 heterojunction interface can not only form a built-in electric field, promote the surface reconstruction of the Ce single atom-doped spinel crystal structure, and optimize the electronic distribution state of the surface Co atoms, but also generate more active sites at the interface, thereby accelerating the reaction, reducing the overpotential during the UOR reaction, and making the catalyst exhibit better urea oxidation effect.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0013] Preferably, the total molar amount of Ce element accounts for X of the total molar amount of metal elements in the active component, wherein 1%≤X≤15%. For example, X can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0014] Preferably, the base material comprises any one of carbon cloth, nickel foam, copper foam or nickel-molybdenum foam, or a combination of at least two thereof, preferably carbon cloth.

[0015] Preferably, when the total molar amount of the Ce element accounts for 1%≤X<10% of the total molar amount of the metal elements in the active component, for example, it can be 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or 1%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. The spinel-type urea oxidation catalyst is NiCo2O4 doped with Ce;

[0016] Preferably, when the total molar amount of the Ce element accounts for 10%≤X≤15% of the total molar amount of the metal elements in the active component, for example, it can be 10%, 11%, 12%, 13%, 14% or 15%, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable. The spinel-type urea oxidation catalyst is a mixture of Ce-doped NiCo2O4 and CeO2.

[0017] In the present invention, by regulating the total molar amount of the Ce element in the catalyst to the total molar amount of the metal elements in the active component, the electronic structure of the catalyst's urea oxidation activity can be regulated to varying degrees. In practical applications, the molar ratio can be selected as needed. By controlling the molar ratio within a range of 1% to 15%, the catalytic effect of the catalyst in the alkaline urea oxidation process can be further improved. If the total molar amount of the Ce element to the total molar amount of the metal elements in the active component is too large, the performance is improved but the optimal activity is not achieved.

[0018] In a second aspect, the present invention provides a method for preparing the spinel-type urea oxidation catalyst according to the first aspect, the preparation method comprising the following steps:

[0019] A nickel source, a cobalt source and a cerium source are mixed to obtain a pre-deposition aqueous solution; an active component is electrodeposited on a base material using the pre-deposition aqueous solution as an electrodeposition solution; and the base material with the deposited active component is calcined to obtain a spinel-type urea oxidation catalyst.

[0020] The present invention adopts a one-step electrodeposition method combined with a calcination method to prepare the spinel-type urea oxidation catalyst. The preparation method is simple and efficient, and the drugs used are relatively common and low in cost, and is suitable for large-scale preparation.

[0021] Preferably, the molar ratio of the metal elements in the nickel source and the cobalt source is Ni:Co 1:(2-3), for example, 1:2, 1:2.5 or 1:3, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the cerium source includes any one of cerium nitrate, cerium nitrate hydrate, cerium chloride, cerium chloride hydrate, cerium sulfate or cerium sulfate hydrate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of cerium nitrate and cerium nitrate hydrate, a combination of cerium chloride and cerium chloride hydrate, a combination of cerium sulfate and cerium sulfate hydrate, a combination of cerium nitrate, cerium chloride and cerium sulfate, a combination of cerium nitrate hydrate, cerium chloride hydrate and cerium sulfate hydrate, preferably cerium nitrate and / or cerium nitrate hydrate.

[0023] Preferably, the cobalt source includes any one of cobalt nitrate, cobalt nitrate hydrate, cobalt chloride, cobalt chloride hydrate, cobalt sulfate or cobalt sulfate hydrate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of cobalt nitrate and cobalt nitrate hydrate, a combination of cobalt chloride and cobalt chloride hydrate, a combination of cobalt sulfate and cobalt sulfate hydrate, a combination of cobalt nitrate, cobalt chloride and cobalt sulfate, a combination of cobalt nitrate hydrate, cobalt chloride hydrate and cobalt sulfate hydrate, preferably cobalt nitrate and / or cobalt nitrate hydrate.

[0024] Preferably, the nickel source includes any one of nickel nitrate, nickel nitrate hydrate, nickel chloride, nickel chloride hydrate, nickel sulfate or nickel sulfate hydrate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of nickel nitrate and nickel nitrate hydrate, a combination of nickel chloride and nickel chloride hydrate, a combination of nickel sulfate and nickel sulfate hydrate, a combination of nickel nitrate, nickel chloride and nickel sulfate, a combination of nickel nitrate hydrate, nickel chloride hydrate and nickel sulfate hydrate, preferably nickel nitrate and / or nickel nitrate hydrate.

[0025] Preferably, the total concentration of metal ions in the pre-deposition aqueous solution is 0.1 mol / L-1.0 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L or 1.0 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the electrodeposition voltage is -1.5V to -0.1V relative to the Ag / AgCl electrode, for example, -1.5V, -1.2V, -1.0V, -0.8V, -0.5V, -0.2V or -0.1V, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, the electrodeposition time is 5 min-20 min, for example, 5 min, 8 min, 10 min, 12 min, 15 min, 18 min or 20 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] The present invention further regulates the voltage and time of electrodeposition, which is more conducive to the uniform deposition of Ce and A elements, thereby obtaining a catalyst with a more uniform element distribution and further optimizing the performance of the catalyst; if the electrodeposition voltage is too low or the electrodeposition time is too short, the active material is less and the performance improvement is not obvious; if the electrodeposition voltage is too high or the electrodeposition time is too long, the active material reaches saturation and the surface covering layer is thick, which affects the exposure of the active sites.

[0029] Preferably, after the electrodeposition is completed and before calcination, the electrodeposited base material is further cleaned and dried.

[0030] Preferably, the drying temperature is 60°C-120°C, for example, it can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 70°C-100°C.

[0031] Preferably, the drying time is 6 hours to 8 hours, for example, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] Preferably, the calcination temperature is 200°C-500°C, for example, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C or 500°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] Preferably, the calcination time is 2 h to 4 h, for example, 2 h, 2.5 h, 3 h, 3.5 h or 4 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] The present invention further controls the calcination temperature to 200° C.-500° C. and the calcination time to 2 h-4 h, which is more conducive to promoting the substitution of Ce single atoms for some octahedral sites of the spinel crystal structure and promoting the formation of a heterojunction between CeO2 particles and the spinel crystal structure doped with Ce single atoms, thereby further improving the urea oxidation performance of the catalyst. If the calcination temperature is too high or the calcination time is too long, excessive oxidation will occur, structural strain will occur, the spinel structure will be destroyed, and the catalytic activity will be affected; if the calcination temperature is too low or the calcination time is too short, the catalyst will not be completely oxidized, will contain hydroxide, and the active sites will not be fully exposed.

[0035] Preferably, the substrate material is pretreated before electrodeposition.

[0036] Preferably, the pretreatment comprises: ultrasonically cleaning the substrate material with acetone, hydrochloric acid and ethanol respectively, and then cleaning with water until the cleaning solution is neutral.

[0037] Preferably, the ultrasonic time is 10 min-40 min, for example, 10 min, 20 min, 30 min or 40 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0039] (1) ultrasonically cleaning the substrate material with acetone, hydrochloric acid, and ethanol for 10 to 40 minutes, respectively, and then washing with water until the cleaning solution is neutral to obtain a pretreated substrate material;

[0040] (2) mixing a nickel source, a cobalt source, and a cerium source to obtain a pre-deposition aqueous solution with a concentration of 0.1 mol / L to 1.0 mol / L, with a Ni:Co molar ratio of 1:(2-3) and a total molar amount of Ce element accounting for 1% to 15% of the total molar amount of metal elements in the active component;

[0041] (3) Using the pre-deposited aqueous solution as the electrodeposition solution, applying a voltage of -1.5V to -0.1V, depositing the active component on the substrate material, and electrodepositing for 5min-20min, cleaning the substrate material with the active component electrodeposited, drying at 60°C-120°C for 6h-8h, and calcining at 200°C-500°C for 2h-4h to obtain the spinel-type urea oxidation catalyst.

[0042] In a third aspect, the present invention provides a use of the spinel-type urea oxidation catalyst as described in the first aspect, wherein the spinel-type urea oxidation catalyst is used for producing hydrogen by electrolysis of water.

[0043] The spinel urea oxidation catalyst provided by the present invention has high activity and excellent stability for producing hydrogen by electrolysis of water and has broad application prospects.

[0044] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0045] Compared with the prior art, the present invention has at least the following beneficial effects:

[0046] (1) The present invention successfully incorporates Ce single atoms or Ce single atoms and CeO2 particle heterogeneous structures into the NiCo2O4 spinel crystal structure, which prompts the spinel crystal structure to produce more oxygen vacancies in the catalyst during the catalytic process. The oxygen vacancies and electron transfer in the Ce-OA (Co / Ni) configuration can enhance the degree of electron localization at the A site, optimize the adsorption process of the reaction intermediates, and thus accelerate the reaction. At the same time, the catalyst can maintain good stability during the urea oxidation process and can operate stably for more than 180 hours.

[0047] (2) The present invention adopts a one-step electrodeposition method and a calcination method to prepare a NiCo2O4 spinel crystal structure doped with Ce single atoms and CeO2 particles. This method is simple and efficient, and the chemicals used are relatively common and low in cost, making it suitable for large-scale preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 1 is an XRD pattern of the spinel urea oxidation catalysts provided in Example 1, Example 2, Example 6 and Comparative Example 1 of the present invention;

[0049] Figure 2 1 is an SEM image of the spinel urea oxidation catalyst provided in Example 1, Example 2, Example 6 and Comparative Example 1 of the present invention;

[0050] Figure 3 is a TEM image of the spinel-type urea oxidation catalyst provided in Example 1 of the present invention;

[0051] Figure 4 is a HRTEM image of the spinel-type urea oxidation catalyst provided in Example 1 of the present invention;

[0052] Figure 5 This is a mapping diagram of the spinel urea oxidation catalyst provided in Example 1 of the present invention;

[0053] Figure 6 1 is a linear voltammogram of the spinel urea oxidation catalysts provided in Example 1, Example 2, Example 6 and Comparative Example 1 of the present invention;

[0054] Figure 7 1 is a comparison of the linear voltammetric curves of Example 1 of the present invention during urea oxidation and alkaline oxygen evolution;

[0055] Figure 8 1 is a comparison of the linear voltammetric curves of Example 2 of the present invention during urea oxidation and alkaline oxygen evolution;

[0056] Figure 9 1 is a comparison of the linear voltammetric curves of Example 6 of the present invention during urea oxidation and alkaline oxygen evolution;

[0057] Figure 10 The figure is a comparison of the linear voltammetric curves of Comparative Example 1 of the present invention during urea oxidation and alkaline oxygen evolution;

[0058] Figure 11 This is a stability test chart of the spinel-type urea oxidation catalyst provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0059] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0060] In the following examples and comparative examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the field; unless otherwise specified, the experimental methods and technical means used were conventional methods and means in the field.

[0061] Example 1

[0062] This embodiment provides a spinel-type urea oxidation catalyst, comprising a carbon cloth substrate and an active component supported on the substrate, wherein the active component comprises a mixture of Ce-doped NiCo2O4 and CeO2; the total molar amount of the Ce element accounts for 10% of the total molar amount of the metal elements in the active component;

[0063] The preparation method of the spinel urea oxidation catalyst provided in this embodiment comprises the following steps:

[0064] (1) Cut the carbon cloth base material into 2*1cm 2 The carbon cloth is soaked in ethanol and ultrasonicated for 10 minutes, and then the ultrasonicated carbon cloth is respectively placed in acetone and a 2 mol / L hydrochloric acid aqueous solution and ultrasonicated for 20 minutes, and then the ultrasonicated carbon cloth is washed with deionized water 2 to 3 times until the solution is neutral to obtain a flexible hydrophilic carbon cloth, and the treated carbon cloth is placed in a solution with a volume ratio of ethanol to water of 1:1 for standby use;

[0065] (2) Ni(NO3)2·6H2O, Co(NO3)3·6H2O and Ce(NO3)3·6H2O were mixed to obtain a pre-deposition aqueous solution with a concentration of 0.1 mol / L, according to a Ni:Co molar ratio of 1:3 and a total molar amount of Ce element accounting for 10% of the total molar amount of metal elements in the active component;

[0066] (3) Using the pre-deposited aqueous solution as the electrodeposition solution, using carbon cloth as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode, the deposition voltage is -1 V, and the active component is deposited on the substrate material for 10 minutes. The substrate material with the active component electrodeposited is cleaned with ethanol, dried at 80°C for 6 hours, and after the ethanol evaporates, calcined at 400°C in an air atmosphere for 2 hours to obtain the spinel urea oxidation catalyst.

[0067] The XRD pattern of the prepared spinel urea oxidation catalyst is shown in Figure 1 As shown, from Figure 1 It can be seen that the XRD peak position is consistent with the standard XRD card of NiCo2O4, indicating that Ce doping does not cause the formation of a new phase in the catalyst material prepared by the preparation method of the present invention. However, the CeO2 peak is not shown in the catalysts prepared in Example 1 and Example 8, which is presumably due to the low CeO2 content.

[0068] The SEM image of the prepared spinel urea oxidation catalyst is shown in Figure 2 As shown, from Figure 2 It can be seen that the spinel urea oxidation catalyst exists in the morphology of nanosheets.

[0069] The TEM image of the prepared spinel urea oxidation catalyst is shown in Figure 3 As shown, from Figure 3 Nanoparticles of NiCo2O4 and CeO2 can be seen in the image.

[0070] The HRTEM image of the prepared spinel urea oxidation catalyst is shown in Figure 4 As shown, from Figure 4 It can be seen that Ce single atoms are successfully incorporated into the lattice of metal oxides, and the lattice fringes of NiCo2O4 and CeO2 can be clearly seen. The lattice spacings are measured to be 0.469nm and 0.314nm, corresponding to the (111) crystal plane of NiCo2O4 and the (111) crystal plane of CeO2.

[0071] The mapping diagram of the prepared spinel urea oxidation catalyst is as follows: Figure 5 As shown, from Figure 5It can be seen that Ce atoms, Co atoms, Ni atoms and O atoms are evenly distributed in the crystal structure.

[0072] Example 2

[0073] This embodiment provides a spinel-type urea oxidation catalyst, comprising a base material and an active component supported on the base material, wherein the active component comprises NiCo2O4 doped with Ce; the total molar amount of the Ce element accounts for 5% of the total molar amount of the metal elements in the active component;

[0074] The preparation method of the spinel urea oxidation catalyst provided in this embodiment comprises the following steps:

[0075] (1) Cut the carbon cloth base material into 2*1cm 2 The carbon cloth is soaked in ethanol and ultrasonicated for 10 minutes, and then the ultrasonicated carbon cloth is respectively placed in acetone and a 2 mol / L hydrochloric acid aqueous solution and ultrasonicated for 20 minutes, and then the ultrasonicated carbon cloth is washed with deionized water 2 to 3 times until the solution is neutral to obtain a flexible hydrophilic carbon cloth, and the treated carbon cloth is placed in a solution with a volume ratio of ethanol to water of 1:1 for standby use;

[0076] (2) Ni(NO3)2·6H2O, Co(NO3)3·6H2O and Ce(NO3)3·6H2O were prepared into a pre-deposition aqueous solution with a concentration of 0.1 mol / L, according to the Ni:Co molar ratio of 1:3 and the total molar amount of Ce element accounting for 5% of the total molar amount of metal elements in the active component;

[0077] (3) Using the pre-deposited aqueous solution as the electrodeposition solution, using carbon cloth as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode, the electrodeposition voltage is -1 V, and the electrodeposition is carried out for 10 minutes. The substrate material with the active component electrodeposited is cleaned with ethanol, dried at 80°C for 6 hours, and after the ethanol evaporates, calcined at 400°C in an air atmosphere for 2 hours to obtain the spinel-type urea oxidation catalyst.

[0078] The XRD pattern of the prepared spinel urea oxidation catalyst is shown in Figure 1 As shown, from Figure 1 It can be seen that the prepared catalyst corresponds one to one with the standard card of NiCo2O4, and no peak related to CeO2 is shown. This is because Ce exists in the form of a single atom.

[0079] The SEM image of the prepared spinel urea oxidation catalyst is shown in Figure 2 As shown, from Figure 2 It can be seen that the catalyst exists in a sheet-like structure, which can expose more active sites during the reaction and accelerate the reaction.

[0080] Example 3

[0081] This embodiment provides a spinel-type urea oxidation catalyst, which includes a base material of nickel foam and an active component supported on the base material, wherein the active component includes NiCo2O4 doped with Ce; the total molar amount of the Ce element accounts for 5% of the total molar amount of the metal elements in the active component;

[0082] The preparation method of the spinel urea oxidation catalyst provided in this embodiment comprises the following steps:

[0083] (1) Cut the base material nickel foam into pieces with an area of ​​2*1cm 2 The nickel foam substrate is immersed in ethanol and ultrasonicated for 10 minutes, and then the nickel foam after ultrasonication is respectively placed in acetone and a 2 mol / L hydrochloric acid aqueous solution and ultrasonicated for 20 minutes, and then the nickel foam after ultrasonication is washed 2 to 3 times with deionized water until the solution is neutral to obtain a flexible hydrophilic nickel foam, and the treated nickel foam is placed in a solution with a volume ratio of ethanol to water of 1:1 for standby use;

[0084] (2) Ni(NO3)2·6H2O, Co(NO3)3·6H2O and Ce(NO3)3·6H2O were mixed to obtain a pre-deposition aqueous solution with a concentration of 0.1 mol / L, according to a Ni:Co molar ratio of 1:3 and a total molar amount of Ce element accounting for 5% of the total molar amount of metal elements in the active component;

[0085] (3) Using the pre-deposited aqueous solution as the electrodeposition solution, using nickel foam as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode, the electrodeposition voltage is -1 V, and the electrodeposition is performed for 10 minutes. The substrate material having the active component electrodeposited is cleaned with ethanol, dried at 80°C for 6 hours, and after the ethanol evaporates, calcined at 400°C in an air atmosphere for 2 hours to obtain the spinel-type urea oxidation catalyst.

[0086] Example 4

[0087] This embodiment provides a spinel-type urea oxidation catalyst, which differs from Example 1 only in that, when preparing the spinel-type urea oxidation catalyst, the voltage of the electrodeposition in step (3) is -0.1 V (Vs.Ag / AgCl), the time is 20 min, and the calcination temperature is 200° C., and the time is 4 h.

[0088] Example 5

[0089] This embodiment provides a spinel-type urea oxidation catalyst, which differs from Example 1 only in that, when preparing the spinel-type urea oxidation catalyst, the voltage of the electrodeposition in step (3) is -1.5 V (Vs.Ag / AgCl), the time is 5 min, and the calcination temperature is 500° C., and the time is 3 h.

[0090] Example 6

[0091] This embodiment provides a spinel-type urea oxidation catalyst, which differs from Example 1 only in that the total molar amount of Ce element in the active component of the spinel-type urea oxidation catalyst accounts for 15% of the total molar amount of metal elements in the active component;

[0092] The preparation of the spinel urea oxidation catalyst differs from Example 1 only in that the total molar amount of the Ce element added in step (2) accounts for 15% of the total molar amount of the metal elements in the active component.

[0093] The XRD pattern of the prepared spinel urea oxidation catalyst is shown in Figure 1 As shown, from Figure 1 It can be seen that the prepared catalyst corresponds one to one with the standard card of NiCo2O4, and no peak related to CeO2 is shown, which is due to the low content of CeO2.

[0094] The SEM image of the prepared spinel urea oxidation catalyst is shown in Figure 2 As shown, from Figure 2 It can be seen that the prepared catalyst exists in a sheet-like structure, which can expose more active sites and thus accelerate the reaction.

[0095] Example 7

[0096] This embodiment provides a spinel-type urea oxidation catalyst, which differs from embodiment 1 only in that the spinel-type urea oxidation catalyst comprises a carbon cloth substrate and an active component supported on the substrate, wherein the active component comprises NiCo2O4 doped with Ce; the total molar amount of the Ce element accounts for 1% of the total molar amount of the metal elements in the active component;

[0097] The preparation of the spinel urea oxidation catalyst differs from Example 1 only in that the total molar amount of the Ce element added in step (2) accounts for 1% of the total molar amount of the metal elements in the active component.

[0098] Example 8

[0099] This embodiment provides a spinel-type urea oxidation catalyst, which differs from Example 1 only in that, when preparing the spinel-type urea oxidation catalyst, the voltage of the electrodeposition in step (3) is -2 V (Vs.Ag / AgCl) and the time is 3 min.

[0100] Example 9

[0101] This embodiment provides a spinel-type urea oxidation catalyst, which differs from Example 1 only in that, when preparing the spinel-type urea oxidation catalyst, the voltage of the electrodeposition in step (3) is -0.05 V (Vs.Ag / AgCl) and the time is 30 min.

[0102] Example 10

[0103] This embodiment provides a spinel-type urea oxidation catalyst, which differs from Example 1 only in that, when preparing the spinel-type urea oxidation catalyst, the calcination temperature in step (3) is 100° C. and the calcination time is 5 h.

[0104] Example 11

[0105] This embodiment provides a spinel-type urea oxidation catalyst, which differs from embodiment 1 only in that, when preparing the spinel-type urea oxidation catalyst, the calcination temperature in step (3) is 700° C. and the calcination time is 1 h.

[0106] Comparative Example 1

[0107] This comparative example provides a spinel-type urea oxidation catalyst, which differs from Example 1 only in that the spinel-type urea oxidation catalyst comprises a base material carbon cloth and an active component supported on the base material, wherein the active component comprises NiCo2O4 and does not contain Ce element;

[0108] When preparing the spinel-type urea oxidation catalyst, Ce(NO3)3·6H2O is not added in step (2).

[0109] The materials prepared in Examples 1-11 and Comparative Example 1 were used as catalysts to perform urea oxidation (UOR) performance tests. The test results are shown in Table 1.

[0110] The catalysts obtained in Example 1, Example 2, Example 6 and Comparative Example 1 were tested for alkaline OER performance, and the test method was as follows:

[0111] (1) Prepare 1 mol / L KOH solution and 1 mol / L KOH + 0.33 mol / L urea solution and set aside.

[0112] (2) An electrochemical workstation was used to conduct the test using a three-electrode system. The counter electrode was a platinum electrode, the reference electrode was an Ag / AgCl electrode, and the electrolyte was 1 mol / L KOH + 0.33 mol / L urea (UOR) or 1 mol / L KOH solution (OER). The test voltage range was 1–2 V (vs. RHE). A linear voltammetric curve was obtained and the current density was recorded up to 10 mA cm. -2The overpotential of the catalyst was used to test its stability. The test results are shown in Table 1 and Figure 6-10 As shown:

[0113] The linear voltammetric curves of the spinel urea oxidation catalysts provided in Example 1, Example 2, Example 6 and Comparative Example 1 are shown in FIG. Figure 6 As shown in the figure, it can be seen that the introduction of Ce element improves the reaction activity of the catalyst in the urea oxidation process, and the best result is when the Ce content is 10%;

[0114] The linear voltammetric curve of the spinel urea oxidation catalyst provided in Example 1 during urea oxidation and alkaline oxygen evolution is shown in FIG. Figure 7 As shown in the figure, compared with the oxygen evolution reaction, the urea oxidation reaction requires a lower voltage to achieve the same current density, revealing the huge potential of the urea oxidation reaction in hydrogen production;

[0115] The linear voltammetric curve of the spinel urea oxidation catalyst provided in Example 2 during urea oxidation and alkaline oxygen evolution is shown in FIG. Figure 8 As shown in the figure, it can be seen that the potential is lower at the same current, which can reduce energy consumption;

[0116] The linear voltammetric curve of the spinel urea oxidation catalyst provided in Example 6 during urea oxidation and alkaline oxygen evolution is shown in FIG. Figure 9 As shown in the figure, it can be seen that the potential is lower at the same current, which can reduce energy consumption;

[0117] The linear voltammetric curve comparison diagram of the spinel urea oxidation catalyst provided in Comparative Example 1 during urea oxidation and alkaline oxygen evolution is shown in FIG. Figure 10 As shown in the figure, it can be seen that the potential is lower at the same current, which can reduce energy consumption;

[0118] The stability test diagram of the spinel urea oxidation catalyst provided in Example 1 is as follows: Figure 11 As shown in the figure, it can be seen that this catalyst can maintain good stability during the urea oxidation process and can operate stably for more than 180 hours.

[0119] Table 1

[0120]

[0121]

[0122] The test results show that:

[0123] (1) It can be seen from Examples 1 to 7 that the present invention can optimize the adsorption process of urea oxidation reaction intermediates by doping the rare earth element Ce into the metal oxide NiCo2O4 having a spinel crystal structure, or when Ce single atoms and CeO2 are simultaneously present in the spinel-type urea oxidation catalyst, and more active sites will be generated at the interface, thereby accelerating the reaction and reducing the overpotential during the UOR reaction. The catalyst exhibits better urea oxidation effect and can maintain good stability during the urea oxidation process.

[0124] (2) By comparing Example 1 with Examples 8-9, it can be seen that the present invention is more conducive to the uniform deposition of Ce and A elements by further regulating the voltage and time of electrodeposition, thereby obtaining a catalyst with a more uniform element distribution and further optimizing the performance of the catalyst; if the electrodeposition voltage is too small or the electrodeposition time is too short, the catalyst has fewer active sites and the performance is not outstanding; if the electrodeposition voltage is too large or the electrodeposition time is too long, the catalyst has reached saturation and the catalytic effect is not significantly improved.

[0125] (3) By comparing Example 1 with Example 10-Example 11, it can be seen that the present invention is more conducive to promoting the substitution of Ce single atoms for some octahedral sites of the spinel crystal structure by Ce single atoms, and promoting the formation of a heterojunction between CeO2 particles and the spinel crystal structure doped with Ce single atoms, thereby further improving the urea oxidation performance of the catalyst. If the calcination temperature is too high or the calcination time is too long, excessive oxidation will occur and structural strain will occur; if the calcination temperature is too low or the calcination time is too short, the catalyst is not completely oxidized, contains hydroxide, and the active sites are not completely exposed.

[0126] (4) It can be seen from Example 1 and Comparative Example 1 that the introduction of the rare earth element Ce in the present invention significantly improves the performance of NiCo2O4 in the urea oxidation (UOR) catalytic process, can optimize the adsorption process of urea oxidation reaction intermediates, and will produce more active sites at the interface, thereby accelerating the reaction and reducing the overpotential in the UOR reaction process. The catalyst exhibits better urea oxidation effect and the stability of the catalyst is more excellent.

[0127] In summary, the present invention dopes the rare earth element Ce into the metal oxide NiCo2O4 having a spinel crystal structure. The introduction of Ce single atoms can enable the metal oxide to generate more oxygen vacancies during the catalytic process. The electron transfer between oxygen vacancies and the Ce-OA (A=Co / Ni) configuration can enhance the degree of electron localization at the A site, optimize the adsorption process of the urea oxidation reaction intermediate, and thus accelerate the reaction. At the same time, the catalyst can maintain good stability during the urea oxidation process. At the same time, when Ce single atoms and CeO2 are present in the spinel-type urea oxidation catalyst at the same time, CeO2 will form a heterojunction with the spinel crystal structure doped with Ce single atoms. The construction of the CeO2 heterojunction interface can not only form a built-in electric field, promote the reconstruction of the surface of the Ce single atom-doped spinel crystal structure, and optimize the electronic distribution state of the surface Co atoms, but also generate more active sites at the interface, thereby accelerating the reaction, reducing the overpotential during the UOR reaction, and making the catalyst exhibit better urea oxidation effect.

[0128] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A spinel-type urea oxidation catalyst, characterized in that: The spinel urea oxidation catalyst comprises a base material and an active component supported on the base material; the active component comprises Ce-doped NiCo2O4 or a mixture of Ce-doped NiCo2O4 and CeO2; In the mixture of Ce-doped NiCo2O4 and CeO2, a heterogeneous structure is formed between the Ce-doped NiCo2O4 and CeO2.

2. The spinel-type urea oxidation catalyst according to claim 1, characterized in that: The total molar amount of Ce element accounts for X of the total molar amount of metal elements in the active component, where 1%≤X≤15%; Preferably, the base material comprises any one of carbon cloth, nickel foam, copper foam or nickel-molybdenum foam, or a combination of at least two thereof, preferably carbon cloth.

3. The spinel-type urea oxidation catalyst according to claim 1 or 2, characterized in that: When the total molar amount of the Ce element accounts for 1%≤X<10% of the total molar amount of the metal elements in the active component, the spinel-type urea oxidation catalyst is NiCo2O4 doped with Ce; Preferably, when the total molar amount of the Ce element accounts for 10%≤X≤15% of the total molar amount of the metal elements in the active component, the spinel-type urea oxidation catalyst is a mixture of Ce-doped NiCo2O4 and CeO2.

4. A method for preparing the spinel-type urea oxidation catalyst according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: A nickel source, a cobalt source and a cerium source are mixed to obtain a pre-deposition aqueous solution; an active component is electrodeposited on a base material using the pre-deposition aqueous solution as an electrodeposition solution; and the base material with the deposited active component is calcined to obtain a spinel-type urea oxidation catalyst.

5. The preparation method according to claim 4, characterized in that The molar ratio of the metal elements in the nickel source and the cobalt source is Ni:Co 1:(2-3); Preferably, the cerium source comprises any one of cerium nitrate, cerium nitrate hydrate, cerium chloride, cerium chloride hydrate, cerium sulfate or cerium sulfate hydrate, or a combination of at least two thereof; Preferably, the cobalt source comprises any one of cobalt nitrate, cobalt nitrate hydrate, cobalt chloride, cobalt chloride hydrate, cobalt sulfate or cobalt sulfate hydrate, or a combination of at least two thereof; Preferably, the nickel source includes any one of nickel nitrate, nickel nitrate hydrate, nickel chloride, nickel chloride hydrate, nickel sulfate or nickel sulfate hydrate, or a combination of at least two thereof.

6. The preparation method according to claim 4 or 5, characterized in that The total concentration of metal ions in the pre-deposition aqueous solution is 0.1 mol / L-1.0 mol / L; Preferably, the electrodeposition voltage is -1.5V to -0.1V relative to the Ag / AgCl electrode; Preferably, the electrodeposition time is 5 min-20 min.

7. The preparation method according to any one of claims 4 to 6, characterized in that After the electrodeposition is completed, the electrodeposited substrate material is cleaned and dried before calcination; Preferably, the drying temperature is 60°C-120°C, preferably 70°C-100°C; Preferably, the drying time is 6h-8h.

8. The preparation method according to any one of claims 4 to 7, characterized in that The calcination temperature is 200°C-500°C; Preferably, the calcination time is 2h-4h; Preferably, the substrate material is further pretreated before electrodeposition; Preferably, the pretreatment comprises: ultrasonically cleaning the substrate material with acetone, hydrochloric acid and ethanol respectively, and then cleaning with water until the cleaning solution is neutral.

9. The preparation method according to any one of claims 4 to 8, characterized in that The preparation method comprises the following steps: (1) ultrasonically cleaning the substrate material with acetone, hydrochloric acid, and ethanol for 10 to 40 minutes, respectively, and then washing with water until the cleaning solution is neutral to obtain a pretreated substrate material; (2) mixing a nickel source, a cobalt source, and a cerium source to obtain a pre-deposition aqueous solution with a concentration of 0.1 mol / L to 1.0 mol / L, with a Ni:Co molar ratio of 1:(2-3) and a total molar amount of Ce element accounting for 1% to 15% of the total molar amount of metal elements in the active component; (3) Using the pre-deposited aqueous solution as the electrodeposition solution, applying a voltage of -1.5V to -0.1V, depositing the active component on the substrate material, and electrodepositing for 5min-20min, cleaning the substrate material with the active component electrodeposited, drying at 60°C-120°C for 6h-8h, and calcining at 200°C-500°C for 2h-4h to obtain the spinel-type urea oxidation catalyst.

10. Use of the spinel-type urea oxidation catalyst according to any one of claims 1 to 3, characterized in that: The spinel urea oxidation catalyst is used for producing hydrogen by electrolyzing water.

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