Core-shell built-in electric field catalyst and preparation method and application thereof

Abstract

The invention discloses a core-shell built-in electric field catalyst as well as a preparation method and application thereof. The catalyst is prepared from Co3O4 and RuO2, wherein the catalyst is of a spherical structure coated with nanosheets. The catalyst is a Co3O4 composite RuO2 catalyst obtained by coupling an electro-deposition process and a low-temperature oxidation process. Wherein the RuO2 nanosheets are uniformly coated on the surface of the spherical Co3O4 structure to form the core-shell heterostructure catalyst. The catalyst is applied to a hydrogen evolution reaction and an oxygen evolution reaction in proton exchange membrane electrolyzed water, and has extremely high catalytic activity and stability at industrial high temperature and large current density.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen production by electrolyzing water, and particularly relates to a core-shell built-in electric field catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] As the most potential clean energy, in the green hydrogen production technology, proton exchange membrane water electrolysis (PEMWE) stands out due to its high efficiency, rapid response, and high hydrogen purity (>99.99%) without alkali pollution, making it an ideal choice for integration with intermittent solar and wind energy. However, its core production technology still faces key material bottlenecks.

[0003] Currently, the prior art mainly uses iridium oxide (IrO2) as a catalyst. Although it can achieve efficient oxygen evolution reaction (OER), its production capacity is insufficient and the price is high, making it difficult to support the large-scale development of the hydrogen energy industry. Based on this, the prior art uses ruthenium oxide (RuO2) as a substitute for IrO2. RuO2 has excellent OER activity, lower cost, and higher natural abundance than IrO2, and has a cost advantage and better intrinsic activity compared to Ir. However, this alternative material has a fatal structural stability defect: under strong acidic and high-potential conditions, the dissolution mechanism involving lattice oxygen will cause crystal collapse, and at the same time, Ru atoms will be peroxidized to form soluble high-valent substances, leading to rapid decay of the catalyst. In addition, the existing ruthenium-based catalysts generally lack bifunctional catalytic ability and cannot simultaneously meet the differential adsorption energy requirements of the anodic OER and cathodic hydrogen evolution reaction (HER), which severely restricts the improvement of the overall electrolysis efficiency. Summary of the Invention

[0004] Aiming at the above deficiencies of the prior art, the purpose of the present invention is to provide a core-shell built-in electric field catalyst, a preparation method thereof, and an application thereof, so as to solve the problems of low catalyst activity, high overpotential, and poor corrosion resistance in the prior art.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A core-shell built-in electric field catalyst, the catalyst is composed of Co3O4 and RuO2; wherein, the catalyst is a spherical structure coated with nanosheets.

[0007] Preferably, in the catalyst, the diameter of the spherical structure is 200nm - 300nm, and the thickness of the nanosheets is 10nm - 20nm.

[0008] The present invention provides a preparation method of a core-shell built-in electric field catalyst for preparing the above catalyst, and the specific steps are as follows:

[0009] Step 1: Clean the carbon substrate.

[0010] Step 2: Dissolve the cobalt source in water to prepare solution A, and dissolve the ruthenium source in water to prepare solution B; Place the substrate treated in Step 1 in an electrolytic cell, use solution A as the electrolyte, an Ag / AgCl electrode as the reference electrode, a platinum sheet as the counter electrode, and nickel as the working electrode; Apply a negative voltage to the working electrode to deposit cobalt ions on the substrate to obtain precursor A; wherein, the molar ratio of the two metal ions in the cobalt source and the ruthenium source is (1-3):(1-3);

[0011] Step 3: Use precursor A as the working electrode, place it in solution B, use an Ag / AgCl electrode as the reference electrode, and a platinum sheet electrode as the counter electrode; Apply a negative voltage to the working electrode to deposit ruthenium ions in solution B on precursor A to obtain precursor B;

[0012] Step 4: Perform an oxidation reaction treatment on the precursor obtained in Step 3 in an air atmosphere to obtain the catalyst; wherein, the temperature of the oxidation reaction is 300°C to 500°C, and the oxidation time is 1h to 3h.

[0013] Preferably, in Step 1, the carbon substrate is carbon fiber paper.

[0014] Preferably, the ruthenium source includes one of nitrates, sulfates, or chlorides; the cobalt source includes one of nitrates or chlorides.

[0015] Preferably, in Step 2 and Step 3, the electrodeposition voltage is -0.5 to -1.5V, and the electrodeposition time is 5min to 15min.

[0016] Preferably, the concentration of cobalt element in solution A is 0.04 to 0.05mol / L; the concentration of ruthenium element in solution B is 0.04 to 0.05mol / L.

[0017] Preferably, NH4Cl is also added to solution A and solution B; in solution A and solution B, the concentration of NH4Cl is 0.04 to 0.05mol / L respectively.

[0018] The present invention provides an application of a core-shell internal electric field catalyst. The above catalyst or the catalyst prepared by the above preparation method is used for acidic electrolytic water hydrogen production under high temperature and high current density conditions. In the present invention, the high temperature means that the temperature is at least higher than 50°C, the high current density means that the current density is at least higher than 100mAcm -2 , and the acidic condition means that the pH value is at least less than 4.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The catalyst of the present invention adopts a spherical core-shell structure coated with nanosheets. The number of active sites is significantly increased through the synergistic effect of the high specific surface area of ​​the nanosheets and the spherical inner core. The nanosheet structure not only provides more surface exposed sites, but its two-dimensional characteristics also accelerate the transfer rate of electrons at the catalyst interface. At the same time, the spherical inner core serves as a supporting skeleton, which can effectively prevent the stacking and agglomeration of the nanosheets, further optimizing the mass transfer kinetics. This structural design combines the high activity of nanomaterials with the stability of the macroscopic structure. The lattice stress field between the spherical inner core and the nanosheet outer shell can adjust the d-band center position of the active site and optimize the intermediate adsorption energy, thereby synergistically improving the intrinsic activity and mass transfer kinetics, and solving the problem of active site loss caused by structural collapse of traditional catalysts.

[0021] 2. The heterogeneous interface formed by Co3O4 and RuO2 in the catalyst of the present invention triggers directional electron transfer through the difference in work function, thereby constructing a built-in electric field (BIEF); the electric field drives the RuO2 shell to inject electrons into the Co3O4 core, so that the Ru site is electron-deficient and the Co site is electron-rich; this asymmetric charge distribution can simultaneously reduce the energy barrier for OOH formation in the OER process and the energy barrier for H desorption in the HER process, thereby achieving a synergistic improvement in the bifunctional catalytic activity, and avoiding the "polarization deactivation" phenomenon of active sites caused by uneven charge distribution on the surface of traditional catalysts, so that the catalyst has bifunctional activity, thus breaking through the limitation that a single material is difficult to take into account both hydrogen evolution and oxygen evolution.

[0022] 3. The catalyst of the present invention can reach 10 mA cm in the hydrogen evolution reaction (HER) with an overpotential of only 55 mV. -2 Current density, Tafel slope as low as 23mV dec -1 , indicating that it follows an efficient Volmer-Heyrovsky reaction pathway; the oxygen evolution reaction (OER) overpotential is 189 mV (10 mA cm -2 ) is significantly better than commercial RuO2 (206mV); more importantly, the PEM electrolyzer assembled based on this catalyst can output 1000mAcm at a voltage of 1.68V. -2 Industrial-grade current density; the core-shell structure anchors Ru atoms through interfacial chemical bonds (Co-O-Ru) to suppress high-priced Ru 4+ →Ru 5+ The irreversible oxidation of the battery enables it to operate continuously for 400 hours at industrial high temperature (50°C) with a voltage loss rate of only 14.5μVh -1 , which is superior to the lifespan of Ru-based catalysts in the prior art. This excellent performance is due to the protection of the core-shell structure on the active components and the optimization of the reaction path by BIEF, which effectively inhibits the dissolution and structural degradation of Ru. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Morphology photograph of Example 1 of the present invention; wherein: Figure 1 a is a scanning electron microscope image of Example 1 (Co3O4@RuO2); Figure 1 b is a transmission electron microscope image of Example 1; Figure 1 c~ Figure 1 d is a high-resolution transmission electron microscope image of the nanosheets of Example 1; Figure 1 e is a HAADF-STEM image of Example 1 and elemental mapping images of Co, Ru, and O.

[0024] Figure 2 Oxygen evolution performance diagram of the examples of the present invention and commercial catalyst RuO2; wherein, Figure 2 a is an oxygen evolution LSV curve diagram of the examples and commercial catalyst RuO2 in 1M H2SO4; Figure 2 b is a Tafel diagram of the polarization curve of Example 1; Figure 2 c is a Nyquist diagram of the example; Figure 2 d is the Cdl value of the example; Figure 2 e is the mass activity and TOF value of the example; Figure 2 f is the overpotential comparison of Example 1 with other catalysts; Figure 2 g is a diagram of the oxygen evolution reaction stability test of the example; Figure 2 h is the concentration curve of ruthenium ions in the electrolyte.

[0025] Figure 3 Hydrogen evolution performance diagram of the examples of the present invention and commercial catalyst RuO2; wherein, a is an LSV curve diagram of the examples and commercial catalyst RuO2 in 1M H2SO4; b is the current density diagram of the example; c is the Tafel diagram of the example; d is a diagram of the hydrogen evolution reaction stability test of the example; e is the overpotential comparison of Example 1 with other catalysts; f is a schematic diagram of a proton exchange membrane electrolyzer; g is a voltage-current density curve diagram of the example; h is a stability test diagram of the proton exchange membrane electrolyzer. Detailed implementation manners

[0026] The present invention will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the present invention belong to the scope of protection of the present invention.

[0027] Unless otherwise specified in specific circumstances in the present invention, the numerical ranges listed herein include the upper and lower limit values, as well as all integers and fractions within that range, rather than the specific values listed when defining the range.

[0028] I. A core-shell internal electric field catalyst

[0029] The catalyst of the present invention is composed of Co3O4 and RuO2; wherein, the catalyst is a spherical structure coated with nanosheets.

[0030] In the in-depth study of the existing RuO2 catalyst in the present invention, it is found that under strong acidic and high potential conditions, the dissolution mechanism involving lattice oxygen in RuO2 will cause crystal collapse, and at the same time, Ru atoms are peroxidized to form soluble high-valent substances, leading to rapid decay of the catalyst. In addition, the existing ruthenium-based catalysts generally lack bifunctional catalytic ability and cannot simultaneously meet the different adsorption energy requirements of the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER), which severely restricts the improvement of the overall electrolysis efficiency.

[0031] Based on this, the present invention attempts to improve the stability of RuO2 through modification means. However, simply improving the stability of the catalyst is not enough, and achieving a balance between the catalyst stability and performance is also the goal to be achieved in the present invention. At the same time, the present invention also expects to provide the catalyst with special bifunctional catalytic activity so that it can be used as both the anode and the cathode of PEMWE, which is difficult to achieve for most acidic ruthenium-based OER catalysts in the prior art; and, the present invention also needs to consider simultaneously enhancing the catalytic activities of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), which requires considering optimizing the adsorption and desorption kinetics of their respective intermediates; generally, the electron-deficient region on the catalyst surface is beneficial to the adsorption of oxygen intermediates, while the electron-rich region is beneficial to the adsorption of hydrogen intermediates. Based on the above design ideas, the present invention considers coupling RuO2 with another material having a different crystal structure and energy to establish a BIEF, thereby regulating the charge distribution and finally achieving a two-way optimization of the adsorption behavior of hydrogen and oxygen intermediates.

[0032] After studying the preparation method of the catalyst, the present invention unexpectedly prepared a catalyst with a nanosheet-coated spherical composite structure. This structure utilizes the lattice stress of the spherical core to induce the epitaxial growth of RuO2 nanosheets, achieving a synergistic improvement in specific surface area and electrochemically active area. This spatial configuration brings unexpected technical effects to the catalyst: by constructing a nanosheet-coated spherical core-shell structure (Co3O4@RuO2), a synergistic improvement in the number of active sites and electron transfer efficiency is realized. The nanosheets provide a high specific surface area to expose more catalytic sites, while the spherical core suppresses structural collapse through three-dimensional support. This design transcends the limitations of traditional single morphology regulation; by driving electron transfer using the work function difference (BIEF), the surface charge distribution is reconstructed to eliminate the polarization phenomenon in the electron-rich / electron-poor regions of traditional catalysts; this strategy is different from existing doping or coating methods. By dynamically balancing charges, the adsorption energies of HER and OER intermediates are simultaneously optimized, solving the problem that it is difficult to dual-functionalize acidic ruthenium-based catalysts; at the same time, through the energy band structures of Co3O4 and RuO2, directional electron transfer is formed at the interface, constructing a continuous gradient charge distribution, which solves the problem of mutual inhibition of HER / OER activities caused by local charge polarization in traditional heterojunction catalysts, reducing the *OOH adsorption energy and the H desorption energy. Through Co-O-Ru covalent bonds, atomic-level interface interlocking is achieved. Combining the rapid consumption of surface protons on RuO2 under working conditions to avoid Ru peroxidation can effectively inhibit the Ru dissolution rate. This "static bonding + dynamic repair" strategy enables PEMWE to stably operate at 1.68V@1000mA / cm 2 for 400 hours (voltage loss rate 14.5 μV / h) under the conditions, filling the technical gap of highly efficient and stable bifunctional catalysts in acidic media.

[0033] In some embodiments of the present invention, in the catalyst, the diameter of the spherical structure is 200 nm to 300 nm, and the thickness of the nanosheets is 10 nm to 20 nm.

[0034] II. A preparation method of a core-shell built-in electric field catalyst

[0035] Step 1: Clean the carbon substrate.

[0036] Step 2: Dissolve the cobalt source in water to prepare solution A, and dissolve the ruthenium source in water to prepare solution B; place the substrate treated in Step 1 in an electrolytic cell, use solution A as the electrolyte, an Ag / AgCl electrode as the reference electrode, a platinum sheet as the counter electrode, and nickel as the working electrode; apply a negative voltage to the working electrode to deposit cobalt ions on the substrate to obtain precursor A; wherein, the molar ratio of the two metal ions in the cobalt source and the ruthenium source is (1 to 3):(1 to 3).

[0037] Step 3: Use the precursor A as the working electrode, place it in solution B, use the Ag / AgCl electrode as the reference electrode, and the platinum sheet electrode as the counter electrode; apply a negative voltage to the working electrode to deposit ruthenium ions in solution B on the precursor A to obtain precursor B;

[0038] Step 4: Perform an oxidation reaction treatment on the precursor obtained in Step 3 in an air atmosphere to obtain the catalyst; wherein, the temperature of the oxidation reaction is 300°C to 500°C, and the oxidation time is 1h to 3h.

[0039] In some embodiments of the present invention, in Step 1, the carbon substrate is carbon fiber paper, carbon cloth or carbon felt. The present invention does not limit the material of the carbon substrate, and an appropriate carbon substrate can be selected according to actual applications for preparation.

[0040] In some embodiments of the present invention, the ruthenium source includes one of nitrates, sulfates or chlorides, for example, ruthenium nitrate, ruthenium sulfate or ruthenium chloride. The cobalt source includes one of nitrates or chlorides, for example, cobalt nitrate or cobalt chloride.

[0041] In some embodiments of the present invention, the deposition sequence of cobalt and ruthenium has no effect on the performance of the catalyst. Cobalt can be deposited first and then ruthenium; or ruthenium can be deposited first and then cobalt. The molar ratio of the two metal ions in the cobalt source and ruthenium source can be 1:3, 1:2, 1:1, 2:1, 3:1, etc., as well as all ranges and sub-ranges between the above values. It should be understood that in the implementation scheme, any of the above ranges can be combined with any other range in other implementation schemes.

[0042] In some embodiments of the present invention, in Steps 2 and 3, the electrodeposition voltage is -0.5 to -1.5V, and the electrodeposition time is 5min to 15min. When the deposition voltage is too small (or the deposition time is too short), it is easy to cause the metal element not to deposit, and it cannot play a catalytic role; but when the deposition voltage is too high (or the deposition time is too long), it will cause the metal element to deposit too thickly, and then it is easier to fall off in the electrolytic water reaction. Therefore, the electrodeposition voltage can be -1.5V, -1.0V, -0.5V, etc., as well as all ranges and sub-ranges between the above values; the electrodeposition time can be 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min, 15min, etc., as well as all ranges and sub-ranges between the above values. It should be understood that in the implementation scheme, any of the above ranges can be combined with any other range in other implementation schemes.

[0043] In some embodiments of the present invention, the concentration of cobalt element in solution A is 0.04 to 0.05mol / L; the concentration of ruthenium element in solution B is 0.04 to 0.05mol / L.

[0044] In some embodiments of the present invention, NH4Cl is further added to solution A and solution B; in solution A and solution B, the concentration of NH4Cl is 0.04 - 0.05 mol / L respectively. The addition of NH4Cl is beneficial to the deposition process and can make the deposition effect of metal elements better.

[0045] In some embodiments of the present invention, in step 3, the temperature of the oxidation reaction can be 300°C, 350°C, 400°C, 450°C, 500°C, etc., and all ranges and sub - ranges between the above values; the oxidation time can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, etc., and all ranges and sub - ranges between the above values. It should be understood that in the embodiments, any of the above ranges can be combined with any other range in other embodiments.

[0046] III. Application of a core - shell built - in electric field catalyst

[0047] The above catalyst or the catalyst prepared by the above preparation method is used for hydrogen production by acidic electrolyzed water under high - temperature and high - current - density conditions. In the present invention, the high temperature means that the temperature is at least higher than 50°C, the high current density means that the current density is at least higher than 100 mA / cm -2 , and the acidic condition means that the pH value is at least less than 4.

[0048] IV. Examples and comparative examples

[0049] Example 1

[0050] Step 1: Pretreatment of the carbon substrate

[0051] The carbon fiber paper substrate is pretreated with dilute sulfuric acid solution to remove surface impurities and increase the hydrophilicity of the substrate, and then washed repeatedly with deionized water and ethanol;

[0052] Step 2: Preparation of Co3O4@RuO2 precursor

[0053] The clean carbon fiber paper (CP), Pt sheet and Ag / AgCl are used as the working electrode, counter electrode and reference electrode respectively. A CoCl2 aqueous solution with a concentration of 0.05 mol / L is prepared and marked as solution A, and NH4Cl is added to solution A with a concentration of 0.05 mol / L. A RuCl3 aqueous solution with a concentration of 0.01 mol / L is prepared and marked as solution B, and NH4Cl is added to solution B with a concentration of 0.05 mol / L.

[0054] First, cobalt was deposited on the CP. The carbon fiber paper was placed in Solution A and electro-deposited for 5 minutes at a constant voltage of -1V vs. Ag / AgCl. Then, the carbon fiber paper with deposited cobalt was placed in Solution B and continued to be deposited for 5 min at a constant voltage of -1V vs. Ag / AgCl. Finally, the deposited carbon fiber paper was slowly rinsed several times with alcohol and deionized water.

[0055] Step 3: Preparation of Co3O4@RuO2

[0056] Subsequently, the carbon fiber paper treated in Step 2 was placed in a tube furnace at 350 °C and calcined for 5 h in an air atmosphere. After cooling, the Co3O4@RuO2 sample was prepared.

[0057] Example 2

[0058] Based on Example 1 with improvements, the difference lies in: in Step 2, the deposition sequence is to deposit ruthenium first and then cobalt, and the molar ratio of cobalt element to ruthenium element is 1:1. Other steps are exactly the same as those in Example 1.

[0059] Example 3

[0060] Based on Example 1 with improvements, the difference lies in: in Step 2, the deposition sequence is to deposit cobalt first and then ruthenium, and the molar ratio of cobalt element to ruthenium element is 1:2. Other steps are exactly the same as those in Example 1.

[0061] Example 4

[0062] Based on Example 1 with improvements, the difference lies in: in Step 2, the deposition sequence is to deposit ruthenium first and then cobalt, and the molar ratio of cobalt element to ruthenium element is 1:2. Other steps are exactly the same as those in Example 1.

[0063] Example 5

[0064] Based on Example 1 with improvements, the difference lies in: in Step 2, the deposition sequence is to deposit cobalt first and then ruthenium, and the molar ratio of cobalt element to ruthenium element is 1:3. Other steps are exactly the same as those in Example 1.

[0065] Example 6

[0066] Based on Example 1 with improvements, the difference lies in: in Step 2, the deposition sequence is to deposit ruthenium first and then cobalt, and the molar ratio of cobalt element to ruthenium element is 1:3. Other steps are exactly the same as those in Example 1.

[0067] Comparative Example 1

[0068] The commercially available RuO2 catalyst was used as Comparative Example 1.

[0069] Comparative Example 2

[0070] The Co3O4 catalyst purchased on the current market was used as Comparative Example 2.

[0071] III. Performance Analysis

[0072] 1. Microscopic Morphology

[0073] Taking Examples 1 - 3 as representatives, their performances were analyzed and compared. The morphology of the catalyst of Example 1 (Co3O4@RuO2) was detected. As Figure 1 shown in a, the scanning electron microscope (SEM) image shows that Co3O4@RuO2 exhibits a unique nanosheet - coupled spherical morphology. The hierarchical structure of Co3O4@RuO2 provides a large specific surface area and rich porosity, which helps the efficient transport of the electrolyte through the catalytic system. TEM analysis proves a well - defined core - shell heterostructure, with the spherical core evenly wrapped by the nanosheet shell structure ( Figure 1 b). The high - resolution TEM (HRTEM) image reveals lattice fringes with spacings of 0.280 nm and 0.285 nm, corresponding to the (111) crystal plane of RuO2 and the (220) plane of Co3O4 respectively ( Figure 1 c). In addition, the lattice spacings of 0.242 nm and 0.233 nm observed in Figure 1 d correspond to the (200) plane of RuO2 and the (222) plane of Co3O4 respectively. The high - angle annular dark - field scanning TEM (HAADF - STEM) image reveals an obvious contrast change, with a characteristic dark band around the spherical core structure ( Figure 1 e). The energy - dispersive spectroscopy (EDS) image confirms the seamless encapsulation of the Co3O4 core by the RuO2 shell, clearly verifying the formation of the Co3O4@RuO2 core - shell heterostructure. Other examples also have the same above - mentioned structure.

[0074] 2. Catalytic Performance in Acidic Environment

[0075] In a 0.5 mol / L H2SO4 electrolyte solution, using a three - electrode system, the OER electro - chemical performances of the Co3O4@RuO2 prepared in Example 1 and the catalysts of Comparative Examples 1 - 2 were evaluated respectively. Figure 2 a shows the linear sweep voltammetry (LSV) curves of various catalysts. Compared with Co3O4 and RuO2, Co3O4@RuO2 exhibits enhanced OER activity. Specifically, Co3O4@RuO2 at 10 and 100 mAcm -2At current densities of, overpotentials of 189 and 254 mV were achieved respectively, significantly lower than those of Co3O4 (279 and 489 mV) and RuO2 (206 and 307 mV). To systematically and comprehensively evaluate the OER catalytic activities of these materials, several representative metrics were measured and calculated. As Figure 2 shown in Fig. b, the Tafel slope of Co3O4@RuO2 was only 41 mV dec -1 , much lower than that of RuO2 (59 mV dec -1 ) and Co3O4 (119 mV dec -1 ), indicating that the OER kinetics of the catalyst prepared in Example 1 was accelerated. In addition, Figure 2 as shown in Fig. c, the charge transfer resistance (Rct) of Co3O4@RuO2 was the lowest among the three catalysts, confirming its excellent electron transfer rate and thus obtaining the best catalytic activity. In cyclic voltammetry (CV) measurements, Figure 2 the electrochemical double-layer capacitance (Cdl) values of the catalysts shown in Fig. d followed the order: Co3O4@RuO2 (14.95 mF cm -2 ) > RuO2 (8.82 mF cm- 2 ) > Co3O4 (6.32 mF cm -2 ), indicating that Co3O4@RuO2 had the largest electrochemically active surface area (ECSA).

[0076] 3. Intrinsic Activity of the Catalyst

[0077] Figure 2 The normalized mass activity shown on the left side of Fig. e indicated that the mass activity of Co3O4@RuO2 was 210 AgRu -1 , approximately 5.7 times that of RuO2 (37 AgRu -1 ). Figure 3 The comparison of the turnover frequency (TOF) on the right side of Fig. e showed that Co3O4@RuO2 achieved a TOF of 0.117 s -1 at 1.52 V vs. RHE, which was 7.8 times higher than that of RuO2. These results confirmed that the combination of Co3O4@RuO2 significantly enhanced the intrinsic activity of the catalyst. It should be noted that even compared with some recently reported noble metal catalysts, this performance was still highly competitive, as Figure 3 shown in Fig. f.

[0078] 4. Durability of the Catalyst in Acidic Electrolyte

[0079] Durability in acidic electrolyte is another key parameter for practical applications. Using carbon paper as the current collector, at 100 mA cm -2Chronopotentiometry tests (CP) were carried out at a high current density to evaluate the stability of the catalyst ( Figure 3 g). Pure RuO2 has poor stability, and the overpotential increases significantly within 20 hours, which may be due to the formation of highly soluble Ru species with an oxidation valence greater than 4 under an external voltage. In contrast, the voltage change of Co3O4@RuO2 can be ignored within 100 hours, showing very excellent stability. This result strongly supports the role of BIEF in suppressing the overoxidation of Ru sites. In addition, inductively coupled plasma mass spectrometry (ICP-MS) was used to monitor the change of Ru ion concentration in the electrolyte over time, as shown in Figure 3 h. A small amount of Ru leaching was observed in the first few hours of the operation of Co3O4@RuO2, which may be due to the dissolution of surface-unstable metals. Subsequently, the Ru concentration in the solution increased very slowly during the monitoring period. In contrast, RuO2 not restricted by BIEF showed continuous dissolution.

[0080] The core-shell BIEF strategy not only significantly enhances the OER activity but also shows an obvious effect on the HER performance. When used as a HER catalyst in an acidic electrolyte ( Figure 3 a), the Co3O4@RuO2 composite material only needs 95 mV to reach a current density of 100 mA cm -2 , which is significantly better than pure RuO2 (135 mV) and Co3O4 (277 mV). It is worth noting that at an overpotential of 100 mV, the current density provided by the composite material Co3O4@RuO2 is about 100 times and 3.7 times higher than that of Co3O4 and RuO2, respectively ( Figure 3 b). Tafel analysis further confirmed the excellent catalytic efficiency ( Figure 3 c), and Co3O4@RuO2 showed the smallest Tafel slope (23 mV dec -1 ) among all the tested samples, strongly verifying the effectiveness of the core-shell BIEF strategy. In addition, the composite material Co3O4@RuO2 showed excellent operating stability during continuous operation at -100 mA cm -2 for 100 hours, and the performance degradation was negligible ( Figure 3 d). It is worth noting that compared with most reported noble metal catalysts, Co3O4@RuO2 shows a lower HER overpotential and faster reaction kinetics ( Figure 3 e).

[0081] 5. Practical applications

[0082] To evaluate the practical applicability in PEMWE, the present invention constructed a membrane electrode assembly using Nafion 115, and Co3O4@RuO2 was used as the anode and cathode catalysts (Figure 3 f). Among them, the test temperature of the PEMWE component and the temperature of the stability test are 50 °C. The current density-voltage curve ( Figure 3 g) shows that the PEMWE system based on Co3O4@RuO2 can achieve a current density of 1 A cm -2 at only 1.68 V, which is much lower than the 1.92 V required for the PEMWE system based on RuO2. It is worth noting that this voltage is even lower than that of many PEMWEs using Pt / C as the cathode. More importantly, the PEM electrolyzer using the Co3O4@RuO2 catalyst has been stably operating at a current density of 1 A cm -2 for 400 h, and the degradation rate is only 14.5 μV h -1 ( Figure 3 h), indicating that Co3O4@RuO2 not only has excellent stability in acidic water electrolysis for hydrogen production, but also has the same excellent stability in a high-temperature working environment, thus enabling the catalyst to adapt to more and more demanding working environments and having good application prospects.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and do not limit the technical solutions. Those of ordinary skill in the art should understand that any modifications or equivalent replacements of the technical solutions of the present invention without departing from the purpose and scope of the present technical solution should be covered by the scope of the claims of the present invention.

Claims

1. A core-shell internal electric field catalyst, characterized in that, The catalyst is composed of Co3O4 and RuO2; wherein, the catalyst is a spherical structure coated with nanosheets.

2. The catalyst according to claim 1, characterized in that, In the catalyst, the diameter of the spherical structure is 200 nm to 300 nm, and the thickness of the nanosheets is 10 nm to 20 nm.

3. A preparation method of a core-shell built-in electric field catalyst, characterized in that To prepare the catalyst according to any one of claims 1 to 2, the specific steps are as follows: Step 1: Clean the carbon substrate. Step 2: Dissolve the cobalt source in water to prepare solution A, and dissolve the ruthenium source in water to prepare solution B; place the substrate treated in Step 1 in an electrolytic cell, use solution A as the electrolyte, an Ag / AgCl electrode as the reference electrode, a platinum sheet as the counter electrode, and nickel as the working electrode; apply a negative voltage to the working electrode to deposit cobalt ions on the substrate to obtain precursor A; wherein, the molar ratio of the two metal ions in the cobalt source and the ruthenium source is (1 to 3):(1 to 3). Step 3: Use precursor A as the working electrode, place it in solution B, use an Ag / AgCl electrode as the reference electrode, and a platinum sheet electrode as the counter electrode; apply a negative voltage to the working electrode to deposit ruthenium ions in solution B on precursor A to obtain precursor B. Step 4: Perform an oxidation reaction treatment on the precursor obtained in Step 3 in an air atmosphere to obtain the catalyst; wherein, the temperature of the oxidation reaction is 300 °C to 500 °C, and the oxidation time is 1 h to 3 h.

4. The preparation method according to claim 3, wherein In Step 1, the carbon substrate is carbon fiber paper.

5. The preparation method according to claim 3, characterized in that, The ruthenium source includes one of nitrate, sulfate, or chloride; the cobalt source includes one of nitrate or chloride.

6. The preparation method according to claim 3, characterized in that, In Steps 2 and 3, the electrodeposition voltage is -0.5 to -1.5 V, and the electrodeposition time is 5 min to 15 min.

7. The preparation method according to claim 3, characterized in that, The concentration of cobalt element in solution A is 0.04 to 0.05 mol / L; the concentration of ruthenium element in solution B is 0.04 to 0.05 mol / L.

8. The preparation method according to claim 3, characterized in that, NH4Cl is also added to solution A and solution B; in solution A and solution B, the concentration of NH4Cl is 0.04 to 0.05 mol / L.

9. Application of a core-shell internal electric field catalyst, characterized in that, The catalyst according to any one of claims 1 to 2 or the catalyst prepared by the preparation method according to any one of claims 3 to 8 is used for acidic electrolytic water hydrogen production under high temperature and high current density conditions.

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