High-valence 5d metal doped ferrocobalt oxide catalyst and preparation and non-crystallization method thereof

Abstract

The invention relates to the technical field of electro-catalysis water decomposition, in particular to a high-valence 5d metal doped ferrocobalt oxide catalyst and a preparation and non-crystallization method thereof, and the chemical formula of the catalyst is CoaFebMcOx, wherein 1 < = a < = 5, 1 < = b < = 2, and 0 < = c < = 5; m is any one or a combination of at least two of Hf < 4 + >, Ta < 5 + > or W < 6 + >; the catalyst comprises a crystalline oxide, a crystalline-amorphous composite oxide or an amorphous oxide, and the particle size of the catalyst is smaller than 500nm. According to the high-valence 5d metal doped ferrocobalt oxide catalyst and the preparation and amorphization method, cobalt salt, ferric salt and high-oxidation-state metal salt are used as raw materials, and the cobalt salt, the ferric salt and the high-oxidation-state metal salt are used as raw materials to prepare the high-valence 5d metal doped ferrocobalt oxide catalyst. The electrocatalyst material is synthesized through a sol-gel method, the cost advantage is remarkable, amorphization of the ferrocobalt-based oxide electrocatalyst can be achieved, the number of active sites is remarkably increased, and the regulation and control process is simple, convenient and easy to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic water splitting, and specifically to a high-valence 5d metal-doped cobalt iron oxide catalyst and its preparation and amorphization method. Background Art

[0002] With the growth of the population and the development of society, non-renewable fossil energy is becoming increasingly depleted. The importance of developing renewable clean energy to address environmental and energy crises has become even more prominent. Among them, electrocatalytic water splitting to produce hydrogen plays a key role in promoting energy transformation. In various electrolytic water hydrogen production technologies, anion exchange membrane water electrolyzers have a small stack size and can use non-precious metals as electrocatalysts, showing great cost advantages and becoming a viable option for large-scale sustainable hydrogen production. However, the slow kinetics of the oxygen evolution reaction (OER) on the anode side significantly hinders the hydrogen production efficiency. Although noble metal catalysts (IrO2 and RuO2) exhibit excellent OER activity, their stability and cost severely limit large-scale applications. Recently, cobalt iron oxides with abundant reserves on Earth have attracted much attention due to their good performance in OER.

[0003] Due to the fact that the crystal structure of cobalt iron oxides (such as CoFe2O4, spinel structure) is more stable thermodynamically, the reported cobalt iron oxide electrocatalysts are mainly crystalline materials. Compared with crystalline electrocatalysts, amorphous electrocatalysts can greatly optimize the activity and stability of OER due to their good dynamic structure adaptability, high active site density, and strong charge transport ability. Therefore, breaking through the thermodynamic limit to prepare cobalt iron amorphous oxides has become a research hotspot. Currently, the methods for preparing cobalt iron amorphous oxide electrocatalysts mainly include chemical etching method, template method, and electrochemical deposition method. However, these methods all have certain limitations. The chemical etching method can only make the near-surface of the material amorphous and will damage the structural stability of the catalyst. The template method has a low yield and causes a large amount of raw material waste. The electrochemical deposition method is prone to uneven element distribution, causing heterogeneous nucleation. Therefore, it is still a huge problem in the industrialization of electrocatalytic water splitting to batch synthesize bulk amorphous and elementally uniform cobalt iron-based oxide electrocatalysts through a simple method and at the same time exhibit outstanding activity and stability during the OER process. Doping, as a simple and effective regulation means, can achieve structural modification of the matrix material. Uniformly doping high-valence 5d metals into the cobalt iron oxide structure is expected to achieve amorphization and optimize the electronic structure of the catalyst. However, due to the significant differences in ionic charge, coordination environment, and water solubility between high-valence 5d metals and 3d cobalt iron elements, synthesizing cobalt iron-based oxide catalysts with a high doping amount and uniform element distribution is still a challenge. Therefore, in view of the above current situation, there is an urgent need to develop high-valence 5d metal-doped cobalt iron oxide catalysts and their preparation methods and applications to overcome the deficiencies in current practical applications. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-valence 5d metal-doped cobalt iron oxide catalyst and its preparation and amorphization methods to solve the problems raised in the above background technology.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A high-valence 5d metal-doped cobalt iron oxide catalyst, and the chemical formula of the catalyst is Co a Fe b M c O x ;

[0007] wherein, 1 ≤ a ≤ 5, 1 ≤ b ≤ 2, 0 ≤ c ≤ 5;

[0008] M is any one or a combination of at least two of Hf 4+ , Ta 5+ or W 6+ ;

[0009] The catalyst includes crystalline oxides, crystalline-amorphous composite oxides or amorphous oxides, and the particle size of the catalyst is less than 500 nm.

[0010] As a further aspect of the present invention: M is W 6+ , and c is 0.5 or 1.6;

[0011] wherein, when c is 0.5 or 1.6, the overpotentials of the catalyst at a current density of 10 mA cm -2 are not higher than 340 mV, 299 mV or 274 mV respectively.

[0012] As a further aspect of the present invention: M is Hf 4+ or Ta 5+ , and c is 1.6;

[0013] wherein, when M is Ta 5+ and c is 1.6, the overpotential of the catalyst at a current density of 10 mA cm -2 is not higher than 315 mV;

[0014] when M is Hf 4+ and c is 1.6, the overpotential of the catalyst at a current density of 10 mA cm -2 is not higher than 298 mV.

[0015] A preparation and amorphization method of the high-valence 5d metal-doped cobalt iron oxide catalyst according to the above, comprising the following steps:

[0016] S1. Ultrasonically dissolve cobalt salts, iron salts and high-valence 5d metal salts in an ice-water bath to prepare a precursor solution;

[0017] S2. Add a gelation initiator to the solution in step S1 and age it to obtain a wet gel;

[0018] S3. Centrifuge and wash the wet gel obtained in step S2, freeze-dry it to obtain a dry gel, and calcine it to obtain the oxide catalyst.

[0019] As a further scheme of the present invention: in step S1, the cobalt salt is any one or a combination of at least two of CoCl2, Co(NO3)2·6H2O and CoSO4·7H2O;

[0020] The iron salt is any one or a combination of at least two of FeCl3, Fe(NO3)3·9H2O and FeSO4·7H2O;

[0021] The high-valence 5d metal salt is any one or a combination of at least two of HfCl4, TaCl5 and WCl6;

[0022] The solvent of the solution is any one or a combination of at least two of anhydrous methanol, anhydrous ethanol and anhydrous dimethylformamide.

[0023] As a further scheme of the present invention: the molar ratio of cobalt to iron is (1.5 - 2.5):1, the molar ratio of the high-valence 5d metal to the total metal elements is (0 - 0.65):1, the ratio of the volume of the solvent to the molar amount of the total metal elements is (1 - 2) L:1 mol, and the ultrasonic dissolution time is 60 - 90 min.

[0024] As a further scheme of the present invention: in step S2, the gelation initiator is any one or a combination of at least two of deionized water, ethanol or propylene oxide, and the ratio of the initiator to the molar amount of the total metal elements is (0.5 - 1.5) L:1 mol;

[0025] The aging temperature is 30 - 60 °C and the aging time is 6 - 24 h.

[0026] As a further scheme of the present invention: in step S3, the freeze-drying time is 20 - 30 h, the calcination temperature is 300 - 400 °C, the calcination time is 8 - 12 h, and the heating rate is 2 - 10 °C / min.

[0027] An application of the high-valence 5d metal-doped cobalt-iron oxide catalyst according to the above in electrocatalytic water splitting, and the catalyst is used for alkaline electrocatalytic oxygen evolution reaction.

[0028] As a further solution of the present invention: the catalyst can be used as an anode in an anion exchange water electrolyzer, and at a current density of 1000 mA cm -2 , the cell voltage can be no higher than 1.69 V and stably operate for no less than 600 h.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. The present invention prepares a high-valence 5d metal element-doped cobalt iron oxide nanocatalyst by a mild sol-gel method. By changing the content of the dopant, the crystal structure of the catalyst can be easily controlled, realizing the adjustability of crystalline, crystalline-amorphous and amorphous states. Its preparation process is simple, with low energy consumption and wide raw material sources, suitable for large-scale synthesis;

[0031] 2. The cobalt iron-based amorphous oxide electrocatalyst of the present invention is bulk amorphous, different from the surface amorphous reported in the past. This structural characteristic enables the catalyst to have good dynamic structural adaptability, significantly increases the electrochemically active surface area of the catalyst, maximizes the utilization of active sites, and at the same time greatly improves the charge transfer rate;

[0032] 3. The electrocatalyst of the present invention is applied to the OER process. Compared with other non-precious metal-based oxide electrocatalysts, its activity and stability in an anion exchange membrane water electrolyzer have been greatly improved. At 80 °C, a cell voltage of only 1.69 V can achieve a current density of 1000 mA cm -2 , and stably operate for at least 600 h, having good industrial application prospects. Description of the Drawings

[0033] Figure 1 It is the X-ray diffraction pattern of the samples prepared in Examples 1-5 in the examples of the present invention.

[0034] Figure 2 It is the transmission electron microscope image and scanning transmission electron microscope X-ray energy spectrum surface scan map of the electrocatalyst prepared in Example 3 in the examples of the present invention.

[0035] Figure 3 It is a schematic diagram of the linear sweep voltammetry curve of the samples prepared in Examples 1-5 in the examples of the present invention in a three-electrode system.

[0036] Figure 4 It is a schematic diagram of the double-layer capacitance value of the samples prepared in Examples 1, 2 and 3 in the examples of the present invention in a three-electrode system.

[0037] Figure 5 It is the electrochemical impedance spectrum of the samples prepared in Examples 1, 2 and 3 in the examples of the present invention in a three-electrode system.

[0038] Figure 6 Schematic diagram of the linear sweep voltammetry curve of the sample prepared in Example 3 of the embodiments of the present invention at 80 °C in an anion exchange membrane water electrolyzer.

[0039] Figure 7 Schematic diagram of the chronopotentiometry curve of the sample prepared in Example 3 of the embodiments of the present invention at 80 °C in an anion exchange membrane water electrolyzer. Detailed implementation manners

[0040] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described 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 embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] The following describes the specific implementation of the present invention in detail with specific embodiments.

[0042] Please refer to Figures 1 - 7 , in the first aspect, the present invention provides a high-valence 5d metal-doped cobalt iron oxide catalyst, and the catalyst includes a crystalline oxide, a crystalline-amorphous composite oxide, and an amorphous oxide;

[0043] The chemical formula of the catalyst is Co a Fe b M c O x , where 1 ≤ a ≤ 5, 1 ≤ b ≤ 2, 0 ≤ c ≤ 5, and M includes Hf 4+ , Ta 5+ or W 6+ or any combination of at least two of them;

[0044] The high-valence 5d metal-doped cobalt iron oxide catalyst provided by the present invention has a particle size of less than 500 nm. The catalyst includes a crystalline oxide, a crystalline-amorphous composite oxide, and an amorphous oxide. The amorphous oxide has good dynamic structure adaptability, a high density of active sites, and strong charge transport ability, can optimize the activity and stability of OER, and at the same time solves the problem of mutual restriction between the activity and stability of existing electrocatalysts.

[0045] The high-valence 5d metal-doped cobalt iron oxide catalyst provided by the present invention, wherein the introduced high-valence 5d metal element can disrupt the charge balance and lattice symmetry to stabilize the low-valence cobalt and promote the generation of an amorphous structure. By changing the content of the high-valence 5d metal element in the catalyst, the electronic structure and crystal structure of the catalyst can be regulated. Among them, the more the content of the low-valence cobalt in the oxide electrocatalyst, the higher the degree of disorder of the structure, which is more conducive to the pre-oxidation of cobalt sites to generate more active sites and improve the OER performance.

[0046] In a second aspect, the present invention provides a preparation and amorphization method of the high-valence 5d metal-doped cobalt iron oxide catalyst as described in the first aspect, including the following steps:

[0047] S1. Ultrasonically dissolve a certain proportion of cobalt salt, iron salt and high-valence 5d metal salt in an ice-water bath for a certain time to prepare a precursor solution;

[0048] S2. Add a gelation initiator to the solution in step S1, and age for a certain period of time at a certain temperature to obtain a wet gel;

[0049] S3. Centrifuge and wash the wet gel obtained in step S2, freeze-dry to obtain a dry gel, and then calcine the dry gel in an air atmosphere to obtain a high-valence 5d metal element-doped cobalt iron oxide catalyst.

[0050] The preparation and amorphization method provided by the present invention dissolves various metal salts and uniformly disperses them into a precursor solution. The initiator plays a role in initiating metal hydrolysis, thereby forming a wet gel with uniform element distribution. After high-temperature calcination, the catalyst is dehydrated to form a more stable oxide form.

[0051] The cobalt salt in S1 is any one or a combination of at least two of CoCl2, Co(NO3)2·6H2O and CoSO4·7H2O; the iron salt is any one or a combination of at least two of FeCl3, Fe(NO3)3·9H2O and FeSO4·7H2O; the high-valence 5d metal salt is any one or a combination of at least two of HfCl4, TaCl5 and WCl6; the solvent of the solution is any one or a combination of at least two of anhydrous methanol, anhydrous ethanol and anhydrous dimethylformamide.

[0052] In step S1, the molar ratio of cobalt to iron is (1.5 - 2.5):1; the molar ratio of the high-valence 5d metal to the total metal element is (0 - 0.65):1; the ratio of the volume of the solvent to the molar amount of the total metal element is (1 - 2) L:1 mol; the ultrasonic dissolution time is 60 - 90 min.

[0053] In step S2, the initiator is any one or a combination of at least two of deionized water, ethanol, and propylene oxide. The molar ratio of the initiator to the total metal element is (0.5 - 1.5) L: 1 mol. The aging temperature is 30 - 60 °C, and the aging time is 6 - 24 h.

[0054] In step S3, the freeze-drying time of the xerogel is 20 - 30 h, the calcination temperature is 300 - 400 °C, the time is 8 - 12 h, and the heating rate is 2 - 10 °C / min.

[0055] Thirdly, the present invention provides a catalyst for OER prepared by a synthesis and amorphization method of a high-valence 5d metal-doped cobalt iron oxide catalyst, which is applied to a traditional three-electrode system and an anion exchange membrane water electrolyzer in the field of electrocatalytic water splitting technology.

[0056] The high-valence 5d metal-doped cobalt iron oxide catalyst provided by the present invention exhibits excellent water electrolysis activity in a three-electrode system.

[0057] When tested in a three-electrode system, the electrolyte is a potassium hydroxide solution with pH = 14.

[0058] In the three-electrode system, a carbon paper coated with the catalyst is used as the working electrode, and the area of the carbon paper is 0.25 cm 2 , and the catalyst loading is 0.9 mg cm -2 . The counter electrode is a carbon rod, and the reference electrode is a mercury / mercuric oxide electrode.

[0059] In the three-electrode system Co2FeO x The overpotential of the nanocatalyst is not higher than 340 mV at a current density of 10 mA cm -2 .

[0060] In the three-electrode system Co2FeW 0.5 O x The overpotential of the nanocatalyst is not higher than 299 mV at a current density of 10 mA cm -2 .

[0061] In the three-electrode system Co2FeW 1.6 O x The overpotential of the nanocatalyst is not higher than 274 mV at a current density of 10 mA cm -2 .

[0062] In the three-electrode system Co2FeTa 1.6 O x The overpotential of the nanocatalyst is not higher than 315 mV at a current density of 10 mA cm -2 .

[0063] In the three-electrode system Co2FeHf1.6 O x The overpotential of the nano-catalyst is no higher than 298 mV at a current density of 10 mA cm -2 .

[0064] The high-valence 5d metal-doped cobalt-iron amorphous oxide catalyst provided by the present invention exhibits industrial-level catalytic performance in an anion exchange membrane water electrolyzer, with excellent activity and stability.

[0065] In the anion exchange membrane water electrolyzer, the electrolyte is potassium hydroxide solution with pH = 14, and the test temperature is 80 °C.

[0066] In the anion exchange membrane water electrolyzer, a catalyst-coated nickel foam is used as the anode, and the area of the nickel foam is 1 = cm 2 , and the catalyst loading is 5 mg cm -2 . The cathode is a carbon paper coated with Pt / C (Pt mass fraction is 60%), the area of the carbon paper is 1 cm 2 , and the catalyst loading is 2.5 mg cm -2 .

[0067] In the anion exchange membrane water electrolyzer, Co2FeW 1.6 O x The overpotential of the nano-catalyst is no higher than 1.69 mV at a current density of 1000 mA cm -2 .

[0068] In the anion exchange membrane water electrolyzer, Co2FeW 1.6 O x The nano-catalyst can stably operate for no less than 600 h at a current density of 1000 mA cm -2 , and the voltage decay per hour is no higher than 0.07%.

[0069] Example 1:

[0070] Prepare a cobalt-iron oxide electrocatalyst (Co2FeO x ) with a high oxidation state metal doping amount of 0%;

[0071] Weigh 2 mmol of CoCl2 and 1 mmol of FeCl3 according to a cobalt / iron molar ratio of 2:1 and add them to 5 mL of anhydrous ethanol. Ultrasonically dissolve them in an ice-water bath for 60 min. Subsequently, add 1 mL of a mixed solution of deionized water / ethanol (volume ratio 1:4) and mix well, then add 2 mL of propylene oxide and mix well. Place the precursor solution at 50 °C for aging for 12 h to obtain a wet gel. After centrifugally washing with deionized water and freeze-drying for 24 h, a dry gel is obtained. The dry gel is calcined in a muffle furnace at 350 °C for 10 h, with a heating rate of 5 °C / min. The calcination atmosphere is air. After naturally cooling to room temperature, it is ground to obtain a sample. The XRD pattern of the crystalline cobalt-iron oxide electrocatalyst prepared in this example is as shown in Figure 1 shown.

[0072] Example 2:

[0073] Prepare a cobalt-iron oxide electrocatalyst with a W doping amount of 15% (Co2FeW 0.5 O x );

[0074] Weigh 1.7 mmol of CoCl2, 0.85 mmol of FeCl3 and 0.45 mmol of WCl6 according to a cobalt / iron / tungsten molar ratio of 2:1:0.5 and add them to 5 mL of anhydrous ethanol. Ultrasonically dissolve them in an ice-water bath for 60 min. Subsequently, add 1 mL of a mixed solution of deionized water / ethanol (volume ratio 1:4) and mix well, then add 2 mL of propylene oxide and mix well. Place the precursor solution at 50 °C for aging for 12 h to obtain a wet gel. After centrifugally washing with deionized water and freeze-drying for 24 h, a dry gel is obtained. The dry gel is calcined in a muffle furnace at 350 °C for 10 h, with a heating rate of 5 °C / min. The calcination atmosphere is air. After naturally cooling to room temperature, it is ground to obtain a sample. The XRD pattern of the W-doped crystalline-amorphous cobalt-iron oxide electrocatalyst prepared in this example is as shown in Figure 1 shown.

[0075] Example 3:

[0076] Prepare a cobalt-iron oxide electrocatalyst with a W doping amount of 35% (Co2FeW 1.6 O x );

[0077] Weigh 1.3 mmol CoCl2, 0.65 mmol FeCl3, and 1.05 mmol WCl6 according to a cobalt / iron / tungsten molar ratio of 2:1:1.6, add them to 5 mL of absolute ethanol, and ultrasonically dissolve them in an ice-water bath for 60 min. Subsequently, add 1 mL of a mixed solution of deionized water / ethanol (volume ratio 1:4) and mix well, then add 2 mL of propylene oxide and mix well. Place the precursor solution at 50 °C for aging for 12 h to obtain a wet gel. After centrifugally washing with deionized water and freeze-drying for 24 h, a dry gel is obtained. The dry gel is calcined in a muffle furnace at 350 °C for 10 h, with a heating rate of 5 °C / min, a calcination atmosphere of air, and ground to obtain a sample after natural cooling to room temperature. The XRD pattern of the W-doped amorphous cobalt-iron oxide electrocatalyst prepared in this example is as shown in Figure 1 shown.

[0078] Example 4:

[0079] Prepare a cobalt-iron oxide electrocatalyst with a Ta doping amount of 35% (Co2FeTa 1.6 O x );

[0080] Weigh 1.3 mmol CoCl2, 0.65 mmol FeCl3, and 1.05 mmol TaCl5 according to a cobalt / iron / tungsten molar ratio of 2:1:1.6, add them to 5 mL of absolute ethanol, and ultrasonically dissolve them in an ice-water bath for 60 min. Subsequently, add 1 mL of a mixed solution of deionized water / ethanol (volume ratio 1:4) and mix well, then add 2 mL of propylene oxide and mix well. Place the precursor solution at 50 °C for aging for 12 h to obtain a wet gel. After centrifugally washing with deionized water and freeze-drying for 24 h, a dry gel is obtained. The dry gel is calcined in a muffle furnace at 350 °C for 10 h, with a heating rate of 5 °C / min, a calcination atmosphere of air, and ground to obtain a sample after natural cooling to room temperature. The XRD pattern of the Ta-doped amorphous cobalt-iron oxide electrocatalyst prepared in this example is as shown in Figure 1 shown.

[0081] Example 5:

[0082] Prepare a cobalt-iron oxide electrocatalyst with an Hf doping amount of 35% (Co2FeHf 1.6 O x );

[0083] Weigh 1.3 mmol of CoCl2, 0.65 mmol of FeCl3 and 1.05 mmol of HfCl4 according to the molar ratio of cobalt / iron / tungsten of 2:1:1.6, add them to 5 mL of absolute ethanol, and ultrasonically dissolve them in an ice-water bath for 60 min. Subsequently, add 1 mL of a mixed solution of deionized water / ethanol (volume ratio of 1:4) and mix well, then add 2 mL of propylene oxide and mix well. Place the precursor solution at 50 °C for aging for 12 h to obtain a wet gel. After centrifugally washing with deionized water and freeze-drying for 24 h, a dry gel is obtained. The dry gel is calcined in a muffle furnace at 350 °C for 10 h, with a heating rate of 5 °C / min, and the calcination atmosphere is air. After natural cooling to room temperature, it is ground to obtain a sample. The XRD pattern of the Hf-doped amorphous cobalt iron oxide electrocatalyst prepared in this example is as Figure 1 shown.

[0084] Example 6:

[0085] Characterization of the crystal structure and element distribution of the sample;

[0086] Figure 1 is the X-ray diffraction pattern of the samples prepared in Examples 1-5. The diffraction peaks of the sample with a high oxidation state metal doping amount of 0% can be well indexed to the cubic spinel structure. As the W doping amount increases, the diffraction peak intensity of the electrocatalyst gradually decreases and broadens. When the doping amount is 35%, the diffraction peak disappears, achieving complete amorphization. When the Ta and Hf doping amounts are 35%, an amorphous structure is also exhibited, indicating that doping with high-valence 5d metal elements can achieve the amorphization of cobalt iron oxides.

[0087] Figure 2 is the transmission electron microscope image and scanning transmission electron microscope X-ray energy spectrum surface scan map of the sample prepared in Example 3. Among them, the three elements of cobalt, iron, and tungsten are evenly distributed in the sample, and there is no phase separation phenomenon of element aggregation, indicating that the sample prepared by this synthesis method has very good homogeneity.

[0088] Example 7:

[0089] Electrochemical characterization of the sample in a three-electrode system and an anion exchange membrane water electrolyzer;

[0090] Test method for testing the electrochemical performance of the three-electrode system: The sample is loaded onto a 0.25 cm -2 conductive carbon paper with a loading amount of 0.9 mg cm 2 as the working electrode, a carbon rod as the counter electrode, and a Hg / HgO electrode as the reference electrode. In a 1 M KOH electrolyte, the electrochemical performance of the three-electrode system is characterized using an electrochemical workstation. Using the formula E (RHE) = E (Hg / HgO)+0.098 + 0.059×pH calibrates the measured potential to the reversible hydrogen electrode (RHE).

[0091] Figure 3 Linear sweep voltammetry curves of the samples prepared for Examples 1 - 5. It can be seen that with the gradual amorphization caused by the increase in W doping amount, the OER performance of the samples is also gradually improving. The overpotential of the completely amorphous cobalt-iron oxide electrocatalyst to reach 10 mA cm -2 is reduced by 66 mV compared to the crystalline state. The OER activity of the Ta- and Hf-doped amorphous samples is also significantly improved compared to the undoped crystalline samples, indicating that the amorphization of the cobalt-iron oxide electrocatalyst significantly improves the OER performance.

[0092] Figure 4 Double-layer capacitance values of the samples prepared for Examples 1 - 3 in a three-electrode system. Among them, with the increase in W doping amount, the double-layer capacitance gradually increases. The double-layer capacitance value of the cobalt-iron amorphous oxide electrocatalyst with a W doping amount of 35% is about 27 times that of the cobalt-iron crystalline compound electrocatalyst with a doping amount of 0%. Thus, it can be seen that amorphization increases the density of available active sites in the catalyst.

[0093] Figure 5 Electrochemical impedance spectroscopy diagrams of the samples prepared for Examples 1 - 3 in a three-electrode system. With the increase in W doping amount, the charge transfer resistance decreases significantly, which proves that amorphization improves the charge transfer rate during the reaction.

[0094] Test method for the electrochemical performance of an anion exchange membrane water electrolyzer: 5 mg of the sample is loaded onto 1 cm 2 of nickel foam as the anode, 2.5 mg of Pt / C catalyst (Pt mass fraction is 60%) is loaded onto 1 cm 2 of nickel foam as the cathode, and a Grade T anion exchange membrane is used as the diaphragm. The electrochemical performance of the anion exchange membrane water electrolyzer is characterized in a flowing 1 M KOH electrolyte at 80 °C. Figure 6 Linear sweep voltammetry curve of the sample prepared for Example 3. It can be seen that the prepared Co2FeW 1.6 O x sample only requires a cell voltage of 1.69 V to achieve a large current density of 1000 mA cm -2 .

[0095] Figure 7 Chronopotentiometry curve of the sample prepared for Example 3. Under the conditions of 80 °C and 1000 mA cm -2 , the Co2FeW 1.6 O x amorphous oxide electrocatalyst can operate stably for 600 h, and the voltage decay rate is only 1.2 mV h -1In summary, the electrocatalyst prepared by inducing the amorphization of cobalt iron oxide through high-valence metal doping has very good activity and stability at industrial-level current densities.

[0096] In summary, the amorphous electrocatalyst prepared in the present invention is synthesized by a low-energy-consuming sol-gel method using raw materials such as cobalt salts, iron salts, and high-oxidation-state metal salts. The synthesis method is simple and the cost is controllable; samples with different degrees of crystallinity can be obtained by adjusting the doping amount of the high-oxidation-state metal. The method is simple, easy to operate, and has high repeatability; the prepared amorphous electrocatalyst has excellent dynamic structure adaptability, which enables it to exhibit good stability, and has a large electrochemically active surface area, which can maximize the utilization of the active sites therein, and at the same time can improve the charge transfer rate during the reaction. Applying it to the electrocatalytic water splitting reaction shows excellent catalytic activity and stability, which is of great significance for the industrialization of electrocatalytic water splitting technology.

[0097] It should be noted that in the present invention, it should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A high-valence state 5d metal-doped cobalt iron oxide catalyst, characterized in that, The chemical formula of the catalyst is Co a Fe b M c O x ; Among them, 1 ≤ a ≤ 5, 1 ≤ b ≤ 2, 0 ≤ c ≤ 5; M is Hf 4+ , Ta 5+ or W 6+ or a combination of any one or at least two of them; The catalyst includes a crystalline oxide, a crystalline-amorphous composite oxide or an amorphous oxide, and the particle size of the catalyst is less than 500 nm.

2. The high-valence 5d metal-doped cobalt iron oxide catalyst according to claim 1, characterized in that, The M is W 6 + , and c is 0.5 or 1.6; Among them, when c is 0.5 or 1.6, the overpotential of the catalyst at a current density of 10 mA cm -2 is not higher than 340 mV, 299 mV or 274 mV, respectively.

3. The high-valence 5d metal-doped cobalt iron oxide catalyst according to claim 1, characterized in that, where M is Hf 4+ or Ta 5+ , and c is 1.6; Among them, when M is Ta 5+ and c is 1.6, the overpotential of the catalyst at a current density of 10 mA cm -2 is not higher than 315 mV; When M is Hf 4+ and c is 1.6, the overpotential of the catalyst at a current density of 10 mA cm -2 is not higher than 298 mV.

4. A preparation and amorphization method of a high-valence state 5d metal-doped cobalt iron oxide catalyst according to any one of claims 1-3, characterized in that, It includes the following steps: S1. Ultrasonically dissolve cobalt salt, iron salt and high-valence 5d metal salt in an ice-water bath to prepare a precursor solution; S2. Add a gelation initiator to the solution in step S1 and age to obtain a wet gel; S3. Centrifuge and wash the wet gel obtained in step S2, freeze-dry to obtain a dry gel, and calcine to obtain the oxide catalyst.

5. The preparation and amorphization method of the high-valence 5d metal-doped cobalt iron oxide catalyst according to claim 4, characterized in that In step S1, the cobalt salt is any one or a combination of at least two of CoCl2, Co(NO3)2·6H2O and CoSO4·7H2O; The iron salt is any one or a combination of at least two of FeCl3, Fe(NO3)3·9H2O and FeSO4·7H2O; The high-valence 5d metal salt is any one or a combination of at least two of HfCl4, TaCl5 and WCl6; The solvent of the solution is any one or a combination of at least two of anhydrous methanol, anhydrous ethanol and anhydrous dimethylformamide.

6. The preparation and amorphization method of the high-valence 5d metal-doped cobalt iron oxide catalyst according to claim 5, characterized in that, The molar ratio of cobalt to iron is (1.5 - 2.5):1, the molar ratio of high-valence 5d metal to total metal elements is (0 - 0.65):1, the ratio of the volume of the solvent to the molar amount of total metal elements is (1 - 2) L:1 mol, and the ultrasonic dissolution time is 60 - 90 min.

7. The preparation and amorphization method of the high-valence state 5d metal-doped cobalt iron oxide catalyst according to claim 4, characterized in that, In step S2, the gelation initiator is any one or a combination of at least two of deionized water, ethanol or propylene oxide, and the molar ratio of the initiator to the molar amount of total metal elements is (0.5 - 1.5) L:1 mol; The aging temperature is 30 - 60 °C, and the aging time is 6 - 24 h.

8. The preparation and amorphization method of the high-valence 5d metal-doped cobalt iron oxide catalyst according to claim 4, characterized in that In step S3, the freeze-drying time is 20 - 30 h, the calcination temperature is 300 - 400 °C, the calcination time is 8 - 12 h, and the heating rate is 2 - 10 °C / min.

9. Use of the high-valence state 5d metal-doped cobalt iron oxide catalyst according to any one of claims 1-3 in electrocatalytic water splitting, characterized in that, The catalyst is used for the alkaline electrocatalytic oxygen evolution reaction.

10. Use of the high-valence 5d metal-doped cobalt iron oxide catalyst according to claim 9, characterized in that, The catalyst can be used as an anode in an anion exchange water electrolyzer, and at a current density of 1000 mA cm -2 , the cell voltage can be no higher than 1.69 V and stably operate for no less than 600 h.

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