High-entropy spinel oxide oxygen evolution electrocatalyst based on chromium-zinc synergistic dynamic mechanism conversion and preparation method and application thereof

Abstract

This invention relates to high-entropy spinel oxide electrocatalysts for the oxygen evolution reaction (OER), their preparation methods, and applications. It aims to solve the technical problem of the difficulty in simultaneously achieving activity and stability in existing spinel oxide OER electrocatalysts. This catalyst is a high-entropy spinel oxide supported on nickel foam, composed of Cr, Fe, Co, Ni, Zn, and O elements. The oxide has a single-phase face-centered cubic spinel structure, which is formed by assembling nanosheets into a nanoflower structure. It is obtained by immersing nickel foam in a mixed solution containing Cr, Fe, Co, Ni, and Zn ions for hydrothermal treatment followed by calcination. During the OER reaction in an alkaline electrolyte, this catalyst undergoes Zn oxidation. 2+ Selective leaching occurs and surface reconstruction is induced to form a MOOH shell. This catalyst achieves 10 mA cm⁻¹ in 1.0 M KOH. ‑2 The required overpotential is as low as 229 mV, at 100 mA cm⁻¹ ‑2 It can operate stably for more than 250 hours and can be used in the field of oxygen evolution electrocatalysis.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials and alkaline water electrolysis technology, specifically relating to a high-entropy spinel oxide electrocatalyst for the oxygen evolution reaction and its preparation method. Background Technology

[0002] Hydrogen production by water electrolysis is considered a key technology for building a green hydrogen energy system due to its advantages such as clean products, controllable process, and the ability to be coupled with renewable electricity. However, in the water electrolysis reaction, the oxygen evolution reaction (OER) at the anolyte involves four electron transfers and multi-step intermediate evolution, which is kineticly slow and is a key bottleneck limiting the overall water splitting efficiency.

[0003] Currently, noble metal oxides such as RuO2 and IrO2 are commonly used as reference catalysts for OER, but their limited reserves and high prices make it difficult to meet the needs of large-scale applications. Transition metal oxides, especially spinel-type oxides, have attracted widespread attention in OER electrocatalysis due to their abundant elements, tunable structure, and high redox activity. However, traditional low-entropy or single spinel oxides usually mainly follow the adsorbate evolution mechanism (AEM), which is limited by the scaling relationship between the adsorption energies of *OH and *OOH, making it difficult to further reduce the theoretical overpotential.

[0004] The lattice oxygen mechanism (LOM) can, to some extent, bypass the AEM scaling relation limitation through the direct participation of lattice oxygen in OO coupling, thereby improving reaction kinetics. However, uncontrolled lattice oxygen participation often leads to lattice oxygen loss, metal cation dissolution, and structural degradation, resulting in decreased catalyst stability. Therefore, for OER catalysts, the challenge lies not in simply enhancing lattice oxygen activity, but in achieving high activity while avoiding structural instability caused by excessive LOM.

[0005] High-entropy oxides, through the high mixing of multiple metal elements in the same lattice, can exhibit characteristics such as entropy stability, local lattice distortion, slow diffusion effects, and multi-cation electronic coupling. High-entropy spinel oxides, with their AB₂O₄ structure, can accommodate multiple metal cations at tetrahedral and octahedral sites, providing a structural basis for regulating adsorption energy, metal-oxygen covalent properties, oxygen vacancies, and surface reconstruction. However, existing high-entropy oxide OER catalysts often emphasize static composition control or single reaction pathway selection, failing to adequately utilize the dynamic transition between the initial high-activity LOM and the later stable AEM, making it difficult to simultaneously achieve both activity and stability. Therefore, there is an urgent need to develop a high-entropy spinel OER electrocatalyst capable of achieving dynamic mechanism transformation during the reaction process, balancing high activity and long-lifetime stability. Summary of the Invention

[0006] This invention aims to address the technical problem of balancing activity and stability in existing spinel oxide oxygen evolution electrocatalysts, and provides a high-entropy spinel oxide oxygen evolution electrocatalyst based on a chromium-zinc synergistic dynamic mechanism, along with its preparation method and applications. This invention achieves dynamic conversion of the OER reaction pathway by obtaining a high-entropy spinel oxide electrocatalyst through Cr-controlled metal-oxygen covalent and Zn-selective leaching-induced surface reconstruction.

[0007] The high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism conversion of the present invention is a high-entropy spinel oxide supported on nickel foam. The high-entropy spinel oxide is composed of Cr, Fe, Co, Ni, Zn and O elements, has a single-phase face-centered cubic spinel structure, and exhibits a nanoflower-like structure formed by the assembly of nanosheets.

[0008] The high-entropy spinel oxide oxygen evolution electrocatalyst of the present invention, under alkaline OER conditions, Zn 2+ Selective leaching and electrochemical reconstruction form a MOOH shell rich in high-valence metal sites. The MOOH shell is an amorphous or low-crystallinity layer with a thickness of 2-4 nm, denoted as (CrFeCoNiZn)3O4@MOOH. This invention introduces multiple metal elements, Cr, Fe, Co, Ni, and Zn, into spinel oxide to form a single-phase high-entropy spinel structure. Cr enhances metal-oxygen covalent properties, reduces the energy difference between the metal 3d state and the O2p state, and promotes the participation of initial lattice oxygen in the reaction. Zn undergoes preferential but limited leaching during OER, inducing in-situ surface reconstruction to form a metal (oxygen) hydroxide shell rich in high-valence Fe, Co, and Ni sites. This gradually shifts the dominant reaction pathway from initial LOM participation to a more stable AEM-dominated pathway. This Cr / Zn synergistic effect enables the catalyst to achieve rapid reaction kinetics in the initial stage, while the in-situ formed core-shell structure suppresses continuous cation loss and bulk structure collapse during long-term operation, achieving simultaneous improvement in activity and stability.

[0009] The preparation method of the high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism of the present invention is carried out according to the following steps:

[0010] I. Pretreatment of nickel foam: The nickel foam is ultrasonically cleaned in acetone and hydrochloric acid solutions in sequence to remove organic matter, metal oxides and impurities from the surface; then it is washed with deionized water and ethanol and dried for later use.

[0011] II. Preparation of High-Entropy Hydroxide Precursor / NF: Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, NH4F, and urea were added to a solvent and stirred to form a homogeneous mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined autoclave, and the pretreated nickel foam was immersed in the mixed solution inside the autoclave. After sealing, a hydrothermal reaction was carried out. After the reaction was completed, the solution was cooled, washed, and dried to obtain the high-entropy hydroxide precursor loaded on the nickel foam, denoted as high-entropy hydroxide precursor / NF.

[0012] III. Preparation of high-entropy spinel oxide / NF: The high-entropy hydroxide precursor / NF obtained in step II was placed in a high-temperature furnace and calcined in air atmosphere to obtain a high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism conversion, denoted as (CrFeCoNiZn)3O4 / NF.

[0013] Furthermore, the pretreatment of the nickel foam described in step one is as follows: the nickel foam is ultrasonically treated in acetone and 2.0MHCl for 30 min respectively, then rinsed with deionized water and ethanol in sequence, and then dried at 60 °C to complete the pretreatment of the nickel foam.

[0014] Furthermore, the solvent mentioned in step two is water;

[0015] Furthermore, in the mixed solution described in step two, the concentrations of Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, and Ni(NO3)2·6H2O are all 20~25 mM, the concentration of Zn(NO3)2·6H2O is 10~15 mM, the concentration of NH4F is 100~150 mM, and the concentration of urea is 300~350 mM.

[0016] Furthermore, the temperature of the hydrothermal reaction in step two is 110~130 °C, and the reaction time is 10~15 h;

[0017] Furthermore, the washing described in step two is done with ethanol.

[0018] Furthermore, the drying process described in step two involves drying at a temperature of 50-70 °C for 8-12 hours.

[0019] Furthermore, the calcination described in step three is carried out at 2~5 °C for 1 minute. -1 The temperature was increased to 350-400°C at a heating rate and held for 2-3 hours.

[0020] The aforementioned application of the high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism involves using this electrocatalyst in the anodic oxygen evolution reaction (OER) in an alkaline electrolyte. During the OER reaction in the alkaline electrolyte, the Zn in (CrFeCoNiZn)3O4 / NF... 2+ Selective leaching and surface reconstruction occur, forming a MOOH shell rich in high-valence metal sites on the (CrFeCoNiZn)3O4 / NF surface. The thickness of the MOOH shell is 2~4 nm, and it is an amorphous or low-crystallinity shell. The core-shell electrocatalyst in this working state is denoted as (CrFeCoNiZn)3O4@MOOH / NF.

[0021] In the high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism of this invention, the introduction of Cr shifts the O 2p band center from approximately -1.74 eV to approximately -1.70 eV, shifts the overall metal 3d band center from approximately -2.60 eV to approximately -1.87 eV, and reduces the energy difference ΔU between the M 3d and O 2p band centers from approximately 0.86 eV to approximately 0.17 eV; simultaneously, the Co 3d-O 2p energy difference decreases from approximately 0.28 eV to approximately 0.06 eV. This electronic structure modulation enhances metal-oxygen hybridization and metal-oxygen covalent properties, which is beneficial for the initial participation of lattice oxygen in the reaction, thus improving OER kinetics.

[0022] In the high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism conversion of the present invention, Zn 2+ The leaching process exhibits selective leaching behavior, with the Zn concentration in the electrolyte reaching approximately 0.65 ppm in the first 2 hours, followed by a significant decrease in the leaching rate. The dissolution amounts of Fe, Co, and Ni are relatively low. The preferential but limited leaching of Zn induces the formation of a MOOH shell rich in high-valence Fe, Co, and Ni sites on the surface. This shell promotes the AEM pathway and inhibits the continuous loss of subsequent cations, thereby improving long-term structural stability.

[0023] The (CrFeCoNiZn)3O4 / NF electrocatalyst prepared in this invention achieves a viscosity of 10 mA cm⁻¹ in 1.0 M KOH. -2 The required overpotential for current density is as low as 229 mV, which is superior to (CrFeCoNi)3O4 / NF (257 mV), (FeCoNiZn)3O4 / NF (311 mV), (FeCoNi)3O4 / NF (285 mV), and commercial RuO2 / NF (242 mV). Its Tafel slope is 63.42 mV dec. -1 The concentration of the catalyst at 100 mA cm⁻¹ is lower than that of the corresponding reference sample, indicating faster reaction kinetics. -2It can operate stably for more than 250 hours and forms a stable working state after initial activation, exhibiting excellent OER activity and long-term durability.

[0024] This invention does not simply select either AEM or LOM pathways, but rather achieves dynamic conversion of the OER reaction pathway through the synergistic design of Cr and Zn; Cr enhances metal-oxygen covalent bonding and promotes initial LOM participation, thereby breaking through the limitations of traditional AEM scaling relationships and improving initial activity; Zn 2+ Selective leaching induces in-situ surface reconstruction to form a MOOH shell, gradually shifting the reaction to a stable AEM-dominated pathway and inhibiting continuous lattice oxygen loss and structural degradation. The high-entropy spinel framework provides multi-cation coupling, local lattice distortion, and structural buffering, which is beneficial to improving the mechanical robustness and long-life stability of the catalyst. The preparation method of this invention adopts a hydrothermal and air calcination process, which is simple, mild, and suitable for the large-scale preparation of nickel foam self-supporting electrodes. Attached Figure Description

[0025] Figure 1 This is a flowchart of the preparation process of (CrFeCoNiZn)3O4 / NF prepared in step three of Example 1;

[0026] Figure 2 Here is a SEM image of (CrFeCoNiZn)3O4 / NF prepared in step three of Example 1:

[0027] Figure 3 These are TEM images, HRTEM images, SAED images, and EDS elemental distribution maps of (CrFeCoNiZn)3O4 / NF prepared in step three of Example 1.

[0028] Figure 4 These are the XRD patterns of (CrFeCoNiZn)3O4 / NF prepared in Example 1 and the control sample;

[0029] Figure 5 The images show the SEM, TEM, and elemental distribution of the control sample (CrFeCoNi)3O4 / NF.

[0030] Figure 6 The images show the SEM, TEM, and elemental distribution of the control sample (FeCoNiZn)3O4 / NF.

[0031] Figure 7 This is a SEM, TEM, and elemental distribution diagram of the control sample (FeCoNi)3O4 / NF.

[0032] Figure 8The high-resolution XPS spectra of (CrFeCoNiZn)3O4 / NF prepared in Example 1 are shown, where (a) Cr 2p, (b) Fe 2p, (c) Co 2p, (d) Ni 2p, (e) Zn 2p and (f) O 1s;

[0033] Figure 9 This is a comparison chart of the OER performance of (CrFeCoNiZn)3O4 / NF prepared in Example 1, the control sample, and commercial RuO2 / NF, including LSV curves, Tafel slopes, EIS plots, and C. dl / ECSA analysis;

[0034] Figure 10 The cycling stability of (CrFeCoNiZn)3O4 / NF prepared in Example 1;

[0035] Figure 11 This is a chronopotential stability test chart of (CrFeCoNiZn)3O4 / NF prepared in Example 1;

[0036] Figure 12 The images show the CV curves of (CrFeCoNiZn)3O4 / NF prepared in Example 1 and the control sample after 100 and 500 cycles, as well as the LSV curves before and after activation.

[0037] Figure 13 These are TEM images and EDS elemental distribution maps of (CrFeCoNiZn)3O4 / NF prepared in Example 1 before and after OER testing;

[0038] Figure 14 This is a graph showing the concentrations of Cr, Fe, Co, and Zn ions dissolved in 1.0 M KOH electrolyte after different stability test times for (CrFeCoNiZn)3O4 / NF prepared in Example 1.

[0039] Figure 15 The high-resolution XPS spectra of (CrFeCoNiZn)3O4 / NF prepared in Example 1 after OER testing are shown, where (a) Cr 2p, (b) Fe 2p, (c) Co 2p, (d) Ni 2p, (e) Zn 2p and (f) O 1s;

[0040] Figure 16 The pH dependence test and corresponding proton series diagram of (CrFeCoNiZn)3O4 / NF prepared in Example 1 and the control sample are shown.

[0041] Figure 17 These are TMAOH probe test images of (CrFeCoNiZn)3O4 / NF prepared in Example 1 and the control sample;

[0042] Figure 18 These are the PDOS plots calculated by DFT for (CrFeCoNiZn)3O4 prepared in Example 1 and the control sample (FeCoNiZn)3O4;

[0043] Figure 19 The (CrFeCoNiZn)3O4 / NF and (CrFeCoNiZn)3O4 / NF-AR prepared in Example 1 18 O isotope DEMS testing;

[0044] Figure 20 This is the in-situ ATR-FTIR image of (CrFeCoNiZn)3O4 / NF-AR prepared in Example 1. Detailed Implementation

[0045] The technical solution of the present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Without departing from the core idea of ​​the present invention, those skilled in the art can make appropriate adjustments to the metal salt concentration, hydrothermal conditions, calcination conditions, electrochemical activation method and electrode size, and all such adjustments should fall within the scope of protection of the present invention.

[0046] Example 1: The preparation method of the high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism conversion in this example is carried out according to the following steps:

[0047] I. Pretreatment of nickel foam: Prepare nickel foam with dimensions of 2×3 cm. 2 The nickel foam was subjected to ultrasonic treatment in acetone and 2.0 M HCl for 30 min each to remove surface oil, metal oxides and impurities; then it was rinsed three times with distilled water and ethanol in sequence, and finally dried in a constant temperature oven at 60 °C for 8 hours to complete the pretreatment of the nickel foam.

[0048] II. Preparation of high-entropy hydroxide precursor / NF: The following concentrations were added to water: Cr(NO3)3·9H2O (20 mM), Fe(NO3)3·9H2O (20 mM), Co(NO3)2·6H2O (20 mM), Ni(NO3)2·6H2O (20 mM), Zn(NO3)2·6H2O (10 mM), NH4F (100 mM), and urea (300 mM). The mixture was magnetically stirred for 30 min to form a homogeneous pink mixed solution.

[0049] The mixed solution was transferred to a polytetrafluoroethylene-lined autoclave, and the pretreated nickel foam was immersed in the mixed solution inside the autoclave. After sealing, it was placed in an oven at 130 °C for 12 h for hydrothermal reaction. After the reaction was completed, it was cooled to room temperature, washed three times with ethanol, and dried in an oven at 60 °C for 12 h to obtain the high-entropy hydroxide precursor loaded on the nickel foam, denoted as high-entropy hydroxide precursor / NF.

[0050] III. Preparation of High-Entropy Spinel Oxide / NF: The high-entropy hydroxide precursor / NF obtained in step II was placed in a high-temperature furnace and calcined in air to obtain high-entropy spinel oxide (CrFeCoNiZn)3O4 / NF supported on nickel foam; the high-entropy hydroxide precursor / NF obtained in step II was placed in a muffle furnace and calcined in air at 2 °C for min. -1 The temperature was increased to 400 °C at a heating rate and held for 2 h. After cooling, a high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism was obtained, denoted as (CrFeCoNiZn)3O4 / NF.

[0051] The preparation flow chart of (CrFeCoNiZn)3O4 / NF prepared in step three of Example 1 is shown below. Figure 1 As shown.

[0052] The SEM image of (CrFeCoNiZn)3O4 / NF prepared in step three of Example 1 is shown below. Figure 2 As shown, from Figure 2 As can be seen, (CrFeCoNiZn)3O4 / NF is blackish-gray in color, and is composed of nanosheets assembled to form a nanoflower-like structure, which is uniformly covered on the surface of the nickel foam substrate.

[0053] TEM, HRTEM, SAED, and EDS elemental distribution maps of (CrFeCoNiZn)3O4 / NF prepared in step three of Example 1 are as follows: Figure 3 As shown, TEM images reveal that the nanosheets assemble to form a nanoflower-like structure, uniformly covering a nickel foam substrate. HRTEM shows interplanar spacings of 0.295 and 0.252 nm, corresponding to the (220) and (311) crystal planes of the spinel phase, respectively; SAED shows polycrystalline spinel diffraction rings; EDS elemental distribution confirms uniform distribution of Cr, Fe, Co, Ni, Zn, and O.

[0054] Comparative Example 1: This comparative example is for the preparation of (CrFeCoNi)3O4 / NF. The difference between this comparative example and Example 1 is that Zn(NO3)2·6H2O is omitted in step two. Other steps and parameters are the same as in Example 1, and the catalyst (CrFeCoNi)3O4 / NF is obtained.

[0055] Comparative Example 2: This comparative example is for the preparation of (FeCoNiZn)3O4 / NF. The difference between this comparative example and Example 1 is that Cr(NO3)3·9H2O is omitted in step two. Other steps and parameters are the same as in Example 1, and the catalyst (FeCoNiZn)3O4 / NF is obtained.

[0056] Comparative Example 3: This comparative example is for the preparation of (FeCoNi)3O4 / NF. The difference between this comparative example and Example 1 is that Cr(NO3)3·9H2O and Zn(NO3)2·6H2O are omitted in step two. Other steps and parameters are the same as in Example 1, and the catalyst (FeCoNiZn)3O4 / NF is obtained.

[0057] The XRD patterns of (CrFeCoNiZn)3O4 / NF prepared in Example 1, (CrFeCoNi)3O4 / NF prepared in Comparative Example 1, (FeCoNiZn)3O4 / NF prepared in Comparative Example 2, and (FeCoNi)3O4 / NF prepared in Comparative Example 3 are shown below. Figure 4 As shown, from Figure 4 It can be seen that all of the above samples belong to the spinel phase, indicating that the preparation method described above can be used to obtain spinel oxide reference electrodes with different compositions.

[0058] Figure 5 The images show the SEM, TEM, and elemental distribution of the control sample (CrFeCoNi)3O4 / NF prepared in Comparative Example 1. SEM and TEM images show that (CrFeCoNi)3O4 / NF has a similar microstructure to (CrFeCoNiZn)3O4 / NF, also consisting of nanosheets assembled into a nanoflower-like structure uniformly covering the surface of the nickel foam substrate. HRTEM shows a crystal plane spacing of 0.291 nm, corresponding to the spinel phase (220) crystal plane; EDS elemental distribution confirms the uniform distribution of Cr, Fe, Co, Ni, and O.

[0059] Figure 6 The images show the SEM, TEM, and elemental distribution of the control sample (FeCoNiZn)3O4 / NF prepared in Comparative Example 2. SEM and TEM images reveal that the microstructure of (FeCoNiZn)3O4 / NF differs slightly from that of (CrFeCoNiZn)3O4 / NF; the nanosheets are narrower and more irregular, but the overall structure is still composed of nanosheets assembled into a nanoflower-like structure, uniformly covering the surface of the nickel foam substrate. HRTEM shows a crystal plane spacing of 0.297 nm, corresponding to the spinel phase (220) crystal plane; EDS elemental distribution confirms the uniform distribution of Fe, Co, Ni, Zn, and O.

[0060] Figure 7This is a SEM, TEM, and elemental distribution image of the control sample (FeCoNi)3O4 / NF prepared in Comparative Example 3. SEM and TEM images show that the microstructure of (FeCoNi)3O4 / NF is significantly different from that of (CrFeCoNiZn)3O4 / NF, changing from nanosheets to nanowires, uniformly covering the surface of the nickel foam substrate. HRTEM shows a crystal plane spacing of 0.292 nm, corresponding to the spinel phase (220) crystal plane; EDS elemental distribution confirms the uniform distribution of Fe, Co, Ni, and O.

[0061] Figure 8 The high-resolution XPS spectra of (CrFeCoNiZn)3O4 / NF prepared in Example 1 are shown, where (a) Cr 2p, (b) Fe 2p, (c) Co 2p, (d) Ni 2p, (e) Zn 2p and (f) O 1s. As can be seen from the figure, in the Cr 2p spectrum of (CrFeCoNiZn)3O4, Cr 2p... 3 / 2 The peak is mainly composed of Cr 3+ (2p) 3 / 2 Composed of 577.2 eV, along with a small amount of high-valent Cr 6+ (2p) 3 / 2 (579.4 eV) Surface species, no distinguishable low-valent Cr was observed. 2+ Or the signal of metallic Cr. High-resolution Fe 2p, Co 2p, and Ni 2p spectra all exhibit typical mixed valence state characteristics, indicating that Fe... 2+ / Fe 3+ Co 2+ / Co 3+ and Ni 2+ / Ni 3+ Coexistence. Zn mainly exists as Zn 2+ The O 1s spectrum contains peaks that are attributed to lattice oxygen (O 1s). L 529.56 eV), oxygen vacancies (O V , 531.06 eV) and adsorbed water (H2O, 532.46 eV).

[0062] Comparative Example 4: This comparative example describes the preparation of a commercial RuO2 / NF electrode. The specific preparation method is as follows:

[0063] 4.7 mg RuO2 was dispersed in a mixture of 650 μL deionized water, 350 μL isopropanol, and 30 μL of 5% Nafion solution, and sonicated for 20 min to obtain a homogeneous dispersion. Then, 1.03 mL of the dispersion was drop-spread onto a clean 1×1 cm² plate. 2 On a nickel foam substrate, the RuO2 loading was 4.7 mg cm⁻¹. -2Commercial RuO2 / NF electrodes were obtained.

[0064] The (CrFeCoNiZn)3O4 / NF prepared in Example 1, the (CrFeCoNi)3O4 / NF prepared in Comparative Example 1, the (FeCoNiZn)3O4 / NF prepared in Comparative Example 2, the (FeCoNi)3O4 / NF prepared in Comparative Example 3, and the commercial RuO2 / NF electrode in Comparative Example 4 were used as working electrodes, respectively. A graphite electrode was used as the counter electrode, and a Hg / HgO electrode was used as the reference electrode. Electrochemical linear voltammetry (LSV) tests were performed using a standard three-electrode system at a scan rate of 1 mV / s. -1 The potential range was set to 0–1 V vs. Hg / HgO, and the polarization curves were corrected for 95% iR. Electrochemical activation in 1.0 M KOH electrolyte was performed using 100 and 500 cyclic voltammetric scans, respectively, with a potential range of 0–1 V vs. Hg / HgO, at 100 mA cm⁻¹. -2 At current density, chronopotential stability was tested under a constant current time. Figure 9 This is a comparison chart of the OER performance of the (CrFeCoNiZn)3O4 / NF prepared in Example 1, the (CrFeCoNi)3O4 / NF prepared in Comparative Example 1, the (FeCoNiZn)3O4 / NF prepared in Comparative Example 2, the (FeCoNi)3O4 / NF prepared in Comparative Example 3, and the commercial RuO2 / NF electrode in Comparative Example 4. In the chart, a is the LSV curve, b is the Tafel slope, c is the EIS plot, and d is the C... dl / ECSA analysis. The data are listed in Table 1.

[0065] Table 1. Comparison of OER performance of each electrode in Example 1 and Comparative Examples 1-4

[0066] Example number electrode <![CDATA[Reaching 10 mA cm -2 Required overpotential (mV)]]> <![CDATA[Tafel slope (mV dec -1 ).]]> Example 1 <![CDATA[(CrFeCoNiZn)3O4 / NF]]> 229 63.42 Comparative Example 1 <![CDATA[(CrFeCoNi)3O4 / NF]]> 257 76.81 Comparative Example 2 <![CDATA[(FeCoNiZn)3O4 / NF]]> 311 113.16 Comparative Example 3 <![CDATA[(FeCoNi)3O4 / NF]]> 285 220.70 Comparative Example 4 <![CDATA[Commercial RuO2 / NF]]> 242 -

[0067] Table 1 and Figure 9 Test results show that (CrFeCoNiZn)3O4 / NF reaches 10 mA cm⁻¹. -2 The required overpotential is only 229 mV, lower than (CrFeCoNi)3O4 / NF, (FeCoNiZn)3O4 / NF, (FeCoNi)3O4 / NF, and commercial RuO2 / NF. The Tafel slope of (CrFeCoNiZn)3O4 / NF is 63.42 mV dec. -1The values ​​were lower than those of (CrFeCoNi)3O4 / NF, (FeCoNiZn)3O4 / NF, and (FeCoNi)3O4 / NF, indicating that the catalyst (CrFeCoNiZn)3O4 / NF prepared in Example 1 has faster OER kinetics. EIS testing results showed that the semi-circular diameter of (CrFeCoNiZn)3O4 / NF was smaller than that of the control sample, indicating a lower charge transfer resistance. C was calculated using CV curves at different scan rates. dl C of (CrFeCoNiZn)3O4 / NF dl 42.96 mF cm -2 This indicates that the material has a large number of exposed active sites. Even after ECSA normalization, the material still exhibits the highest intrinsic activity, demonstrating that the high-entropy composition and Cr / Zn synergistic regulation play a crucial role in improving intrinsic catalytic performance.

[0068] The (CrFeCoNiZn)3O4 / NF prepared in Example 1 was subjected to 2500 cyclic voltammetry (CV) tests. The specific cyclic voltammetry (CV) test method was as follows: (CrFeCoNiZn)3O4 / NF was used as the working electrode, a graphite electrode as the counter electrode, and a Hg / HgO electrode as the reference electrode. The standard three-electrode system was used in a 1.0 M KOH electrolyte, with a voltage range of 0–1 V vs. Hg / HgO and a scan rate of 50 mV / s. -1 The number of scans is set to 2500. Figure 10 The LSV curves before and after 2500 CV cycle stability tests are shown in the inset. The results show that the OER activity of the catalyst (CrFeCoNiZn)3O4 / NF did not decrease after cycling, but instead increased, indicating that surface activation and reconstruction beneficial to OER occurred during the electrochemical process.

[0069] Further at 100 mA cm -2 Long-term chronopotential testing was performed on the (CrFeCoNiZn)3O4 / NF prepared in Example 1 at a specific current density. The specific testing method was as follows: using (CrFeCoNiZn)3O4 / NF as the working electrode, a graphite electrode as the counter electrode, and a Hg / HgO electrode as the reference electrode, a standard three-electrode system was used in a 1.0 M KOH electrolyte, with the current set at 100 mA cm⁻¹. -2 The time is 250 hours. Figure 11 The results of the chronoelectric chronoelectric stability test showed that the catalyst underwent significant electrochemical activation within the first 6 hours of the test, with the overpotential decreasing by about 37 mV; subsequently, the potential remained stable during 250 hours of continuous operation.

[0070] The (CrFeCoNiZn)3O4 / NF prepared in Example 1, (CrFeCoNi)3O4 / NF prepared in Comparative Example 1, (FeCoNiZn)3O4 / NF prepared in Comparative Example 2, and (FeCoNi)3O4 / NF prepared in Comparative Example 3 were subjected to CV activation. (CrFeCoNiZn)3O4 / NF was used as the working electrode, a graphite electrode as the counter electrode, and a Hg / HgO electrode as the reference electrode. The tests were conducted in a standard three-electrode system in 1.0 M KOH electrolyte, with a voltage range of 0–1 V vs. Hg / HgO and a scan rate of 50 mV / s. -1 The number of scan cycles was set to 100 and 500 respectively. The LSV curves before and after CV activation are shown below. Figure 12 As shown, Figure 12 The study demonstrated the CV activation process of (CrFeCoNiZn)3O4 / NF during the OER process. (CrFeCoNiZn)3O4 exhibited a significantly lower overpotential after activation, while zinc-free (CrFeCoNi)3O4 showed only limited activity improvement after 500 CV cycles. Similarly, a comparison between (FeCoNiZn)3O4 and (FeCoNi)3O4 yielded the same conclusion, indicating that zinc incorporation contributes to surface reconstruction and activation.

[0071] The (CrFeCoNiZn)3O4 / NF prepared in Example 1 was subjected to OER testing. Specifically, (CrFeCoNiZn)3O4 / NF was used as the working electrode, a graphite electrode as the counter electrode, and a Hg / HgO electrode as the reference electrode. The standard three-electrode system was used in a 1.0 M KOH electrolyte, and the current was set to 100 mA cm⁻¹. -2 The time was 250 hours; the TEM image and EDS elemental distribution map after OER testing are as follows: Figure 13 As shown, Figure 13 This indicates that an amorphous MOOH shell of approximately 3 nm was formed in situ on the catalyst surface after OER testing, resulting in a (CrFeCoNiZn)3O4@MOOH / NF working core-shell electrocatalyst.

[0072] The stability of (CrFeCoNiZn)3O4 / NF prepared in Example 1 was tested. The test procedure was as follows: using (CrFeCoNiZn)3O4 / NF as the working electrode, a graphite electrode as the counter electrode, and a Hg / HgO electrode as the reference electrode, a standard three-electrode system was used in 1.0 M KOH electrolyte, and the current was set to 100 mA cm⁻¹. -2 The stability tests were conducted at times of 2, 4, 6, and 8 hours. After each stability test, the concentrations of dissolved Cr, Fe, Co, and Zn ions in the 1.0 M KOH electrolyte were measured using ICP-OES. The results are as follows: Figure 14 As shown; Figure 14 The results show that Zn leaching was the most significant, reaching a concentration of approximately 0.65 ppm within the first 2 hours, after which the leaching rate slowed considerably after 6 hours; the leaching amounts of Fe, Co, and Ni were relatively small. These results indicate that Zn... 2+ Preferred but limited leaching occurs during the OER process.

[0073] XPS analysis was performed on the (CrFeCoNiZn)3O4 / NF (abbreviated as (CrFeCoNiZn)3O4-AR) prepared in Example 1 after OER testing to analyze its surface electronic valence states. The results are as follows: Figure 15 As shown, Fe after OER 3+ / Fe 2+ Co 3+ / Co 2+ and Ni 3+ / Ni 2+ Area ratio compared to before reaction ( Figure 8 The O 1s spectrum showed a significant increase in Cr, Fe, Co, and Ni, indicating the formation of MOOH species rich in high-valence Cr, Fe, Co, and Ni on the surface.

[0074] pH dependence tests were performed on the (CrFeCoNiZn)3O4 / NF prepared in Example 1 and the control sample. Specifically, the pH of the electrolyte was adjusted by replacing the 1.0 M KOH electrolyte with KOH electrolytes at pH = 13.7, 13.4, 13.1, and 12.8, respectively. The (CrFeCoNiZn)3O4 / NF prepared in Example 1 and the control sample were used as the working electrode, with a graphite electrode as the counter electrode and a Hg / HgO electrode as the reference electrode. Linear voltammetry (LSV) tests were performed using a standard three-electrode system. The results are shown below. Figure 16 As shown, Figure 16 The results show that the OER activity of (CrFeCoNiZn)3O4 increases significantly with increasing pH, and the proton reaction order is 0.97, which is significantly higher than that of (CrFeCoNi)3O4 (0.70), (FeCoNiZn)3O4 (0.41), and (FeCoNi)3O4 (0.37). This indicates that the catalyst (CrFeCoNiZn)3O4 / NF prepared in Example 1 has a more obvious lattice oxygen participation characteristic in the initial stage.

[0075] The (CrFeCoNiZn)3O4 / NF prepared in Example 1 and the control sample were subjected to TMAOH chemical probe testing. Specifically, the (CrFeCoNiZn)3O4 / NF prepared in Example 1 and the control sample were used as the working electrode, a graphite electrode as the counter electrode, and an Hg / HgO electrode as the reference electrode. A standard three-electrode system was used, and linear voltammetry (LSV) was performed in a 1.0 M tetramethylammonium hydroxide (TMAOH) electrolyte. The results are shown below. Figure 17 As shown, the OER current of (CrFeCoNiZn)3O4 / NF is most significantly suppressed in TMAOH, indicating that there is a lattice oxygen-related intermediate that can be disturbed by TMAOH in its initial OER process.

[0076] DFT calculations were performed on the (CrFeCoNiZn)3O4 / NF prepared in Example 1 and the control sample (FeCoNiZn)3O4 / NF. Figure 18 The PDOS plots for both methods show that, compared to (FeCoNiZn)3O4 / NF, the O 2p band center in (CrFeCoNiZn)3O4 / NF shifts from -1.74 eV to -1.70 eV, the overall metal 3d band center shifts from -2.60 eV to -1.87 eV, and the energy difference between the M 3d and O 2p band centers decreases from 0.86 eV to 0.17 eV. Simultaneously, the Co 3d-O 2p energy difference decreases from 0.28 eV to 0.06 eV, and the Cr 3d center remains at a high energy position of 0.84 eV. These results indicate that Cr introduces a higher-position 3d state and enhances MO hybridization, which is beneficial for lattice oxygen activation.

[0077] Online differential electrochemical mass spectrometry (DEMS) was performed on the (CrFeCoNiZn)3O4 / NF prepared in Example 1 to evaluate the participation of lattice oxygen in the OER process using a PM-DEMS instrument (Shanghai Jingpu Ruo Technology Co., Ltd). The tests were conducted using a three-electrode system in an electrolytic cell. 18 O-labeled (CrFeCoNiZn)3O4 / NF was used as the working electrode. First, (CrFeCoNiZn)3O4 / NF was subjected to 1.0 M KOH H2... 18 O aqueous solution (denoted as 18 In O-KOH, the electrolyte was labeled for 30 min at 0.8 V vs. Hg / HgO, followed by rinsing with deionized water. After rinsing, the electrolyte was replaced with 1.0 MkOH H2. 16 O aqueous solution (denoted as 16O-KOH). Subsequently, as the potential was scanned from 0 V to 1.0 V vs. Hg / HgO, the mass spectrometry signal of the generated oxygen species was monitored in real time, providing direct evidence for the lattice oxygen-mediated reaction mechanism. Figure 19 The (CrFeCoNiZn)3O4 / NF and (CrFeCoNiZn)3O4 / NF-AR prepared in Example 1 18 O isotope DEMS test image. Figure 19 The 'a' indicates that the result detected 34 O2 and 36 The O2 signal indicates that oxygen in the catalyst lattice participates in the oxygen evolution process, proving the existence of a LOM pathway in the initial stage. After long-term OER testing, DEMS analysis was performed on (CrFeCoNiZn)3O4-AR. Figure 19 b shows that in the DEMS spectrum of (CrFeCoNiZn)3O4-AR 34 The weak O2 signal indicates that the contribution of lattice oxygen to the oxygen evolution process has been significantly reduced. Figure 19 As can be seen from c, compared with the original (CrFeCoNiZn)3O4, (CrFeCoNiZn)3O4-AR 34 O2 / 32 The O2 peak area ratio decreased significantly to about 0.004, close to the abundance of natural isotopes in water, further indicating that the LOM pathway was suppressed and confirming that the AEM pathway is dominant.

[0078] In-situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR, Nicolet iS 50) was used to test the in-situ ATR-FTIR spectrum of (CrFeCoNiZn)3O4 / NF-AR formed after activation of (CrFeCoNiZn)3O4 / NF prepared in Example 1. The specific tests were performed in a 1.0 M KOH electrolyte using a three-electrode system. (CrFeCoNiZn)3O4 was scraped from the nickel foam surface of (CrFeCoNiZn)3O4 / NF and prepared into a catalyst ink, which was then drop-coated onto the surface of a glassy carbon electrode (GCE) as the working electrode; a platinum wire was used as the counter electrode, and a Hg / HgO electrode was used as the reference electrode. FT-IR spectra were recorded within the applied potential range of 0.21–0.81 V vs. Hg / HgO. The resulting in-situ ATR-FTIR spectrum of (CrFeCoNiZn)3O4 / NF-AR is shown below. Figure 20 As shown. From Figure 20 It can be seen that at the OER operating potential, (CrFeCoNiZn)3O4-AR at 1099 cm⁻¹ -1 A distinct vibrational band is observed at this point, corresponding to *OOH generated through the AEM pathway, accompanied by a peak value of 1126 cm⁻¹.-1 The activity originates from nearby hydrogen bond interactions. No characteristic signals attributable to peroxide or superoxide-like lattice oxygen were observed. These results indicate that activated (CrFeCoNiZn)3O4-AR is primarily advanced via the AEM pathway, with significantly reduced involvement of lattice oxygen.

Claims

1. A high-entropy spinel oxide oxygen evolution electrocatalyst based on a chromium-zinc synergistic dynamic mechanism, characterized in that, The electrocatalyst is a high-entropy spinel oxide supported on nickel foam. The high-entropy spinel oxide is composed of Cr, Fe, Co, Ni, Zn and O elements, has a single-phase face-centered cubic spinel structure, and exhibits a nanoflower-like structure formed by the assembly of nanosheets.

2. The method for preparing the high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism of conversion as described in claim 1, characterized in that, This method is performed in the following steps: I. Pretreatment of nickel foam: The nickel foam is ultrasonically cleaned in acetone and hydrochloric acid solutions in sequence to remove organic matter, metal oxides and impurities from the surface; then it is washed with deionized water and ethanol and dried for later use. II. Preparation of high-entropy hydroxide precursor / NF: Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, NH4F and urea were added to the solvent and stirred to form a homogeneous mixed solution; The mixed solution was transferred to a polytetrafluoroethylene-lined autoclave, and the pretreated nickel foam was immersed in the mixed solution inside the autoclave. After sealing, a hydrothermal reaction was carried out. After the reaction was completed, the sample was cooled, washed, and dried to obtain a high-entropy hydroxide precursor loaded on nickel foam, denoted as high-entropy hydroxide precursor / NF. III. Preparation of high-entropy spinel oxide / NF: The high-entropy hydroxide precursor / NF obtained in step II was placed in a high-temperature furnace and calcined in air atmosphere to obtain a high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism conversion, denoted as (CrFeCoNiZn)3O4 / NF.

3. The method for high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism conversion according to claim 2, characterized in that, The pretreatment of nickel foam described in step one is as follows: the nickel foam is ultrasonically treated in acetone and 2.0 MHCl for 30 min respectively, then rinsed with deionized water and ethanol in sequence, and then dried at 60 °C to complete the pretreatment of nickel foam.

4. The method for high-entropy spinel oxide oxygen evolution electrocatalyst based on the synergistic dynamic mechanism of chromium and zinc conversion according to claim 2 or 3, characterized in that, The solvent mentioned in step two is water.

5. The method for high-entropy spinel oxide oxygen evolution electrocatalyst based on the synergistic dynamic mechanism of chromium and zinc conversion according to claim 2 or 3, characterized in that, In the mixed solution described in step two, the concentrations of Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, and Ni(NO3)2·6H2O are all 20~25 mM, the concentration of Zn(NO3)2·6H2O is 10~15 mM, the concentration of NH4F is 100~150 mM, and the concentration of urea is 300~350 mM.

6. The method for high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism conversion according to claim 2 or 3, characterized in that, The hydrothermal reaction in step two is carried out at a temperature of 110-130 °C for 10-15 h.

7. The method for a high-entropy spinel oxide oxygen evolution electrocatalyst based on a chromium-zinc synergistic dynamic mechanism conversion according to claim 2 or 3, characterized in that, The washing described in step two is done with ethanol.

8. The method for high-entropy spinel oxide oxygen evolution electrocatalyst based on chromium-zinc synergistic dynamic mechanism conversion according to claim 2 or 3, characterized in that, The drying process described in step two involves drying at a temperature of 50-70 °C for 8-12 hours.

9. The method for a high-entropy spinel oxide oxygen evolution electrocatalyst based on a chromium-zinc synergistic dynamic mechanism conversion according to claim 2 or 3, characterized in that, The calcination described in step three is carried out at 2~5 °C for 1 minute. -1 The temperature was increased to 350-400 °C at a heating rate and held for 2-3 hours.

10. The application of the high-entropy spinel oxide oxygen evolution electrocatalyst based on the chromium-zinc synergistic dynamic mechanism conversion as described in claim 1, characterized in that, This application utilizes a high-entropy spinel oxide oxygen evolution electrocatalyst based on a chromium-zinc synergistic dynamic mechanism for the anodic oxygen evolution reaction in an alkaline electrolyte.

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