Bifunctional electrocatalytic water-splitting materials, preparation and use thereof

Abstract

This invention belongs to the field of electrocatalytic materials, specifically relating to bifunctional electrocatalytic water splitting materials and their preparation and application. The preparation steps include: performing a first coordination reaction on a first MOF precursor material in a solution containing promoter a and promoter b to obtain a first MOF; using the first MOF as a substrate, performing a second coordination reaction on a second MOF precursor material in a solution containing promoter c to deposit the second MOF onto the first MOF, thus obtaining a core-shell bifunctional MOF material; subjecting the core-shell bifunctional MOF material to heat treatment to obtain a heat-treated material; then mixing the heat-treated material with a phosphorus source for phosphating and calcination, and rapidly cooling the phosphating product while hot in a liquid-phase cooling medium to obtain the bifunctional electrocatalytic water splitting material. The bifunctional electrocatalytic water splitting material prepared by the method of this invention exhibits excellent dual catalytic activity for both HER and OER.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials, specifically relating to the technical field of catalytic materials for water electrolysis. Background Technology

[0002] Water electrolysis is a method of converting electrical energy into chemical energy, specifically involving the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Catalysts for water electrolysis typically include an anode catalyst and a cathode catalyst. The anode catalyst primarily participates in the oxidation reaction to produce oxygen, while the cathode catalyst primarily participates in the reduction reaction of hydrogen ions to produce hydrogen gas.

[0003] OER and HER are different reaction types, and therefore require different catalytic materials. However, this increases the cost of water electrolysis. To address this, existing technologies are also attempting to develop bifunctional catalytic materials that can perform both OER and HER reactions.

[0004] For example, patent document CN109453811A discloses a bifunctional composite water electrolysis catalyst, which first prepares RuCo-MOF through a hydrothermal reaction, and then carbonizes it to obtain RuCo@NC. Patent document CN113755882A discloses a bimetallic nanoparticle for water electrolysis and its preparation method, specifically describing a method of preparing MOF / PDA by carbon coating of FeCo bimetallic organic framework compounds, followed by ammonia annealing and carbonization. Patent document CN114574899A discloses a bifunctional electrocatalyst for water electrolysis, specifically describing a FeCoMOF / BP composite bifunctional water electrolysis catalyst. Patent document CN114921796A discloses a bifunctional self-supporting water electrolysis catalyst material, which synthesizes a low-content ruthenium-loaded chromium-doped iron-based MOF self-supporting catalyst material (Ru@CrFe-NF) by introducing trace amounts of chromium into an iron-based MOF via a stepwise hydrothermal method.

[0005] In summary, existing technologies have disclosed some ideas for preparing electrocatalytic materials based on MOF materials, but the active components and active sites of bifunctional materials prepared by existing processes are not evenly distributed, and the electrocatalytic activity and stability still need to be further improved. Summary of the Invention

[0006] To address the problems existing in current HER and OER bifunctional materials, the primary objective of this invention is to provide a method for preparing bifunctional electrocatalytic water splitting materials, aiming to prepare materials that combine excellent HER and OER properties.

[0007] The second objective of this invention is to provide a bifunctional electrocatalytic water splitting material prepared by the aforementioned method.

[0008] The third objective of this invention is to provide the aforementioned bifunctional electrocatalytic water splitting material for use in water electrocatalysis.

[0009] A method for preparing bifunctional electrocatalytic water splitting materials involves carrying out a first coordination reaction of a first MOF precursor material in a solution containing auxiliaries a and b to obtain the first MOF.

[0010] Using the first MOF as a substrate, the second MOF precursor material undergoes a second-stage coordination reaction in a solution of auxiliary agent c, and the second MOF is deposited on the first MOF to obtain a core-shell dual MOF material; the core-shell dual MOF material is heat-treated to obtain a heat-treated material; the heat-treated material is then mixed with a phosphorus source and subjected to phosphating and calcination treatment, and the phosphating product is placed in a liquid phase cooling medium for rapid cooling treatment while hot to obtain the bifunctional electrocatalytic water splitting material;

[0011] The first MOF precursor material and the second MOF precursor material are raw materials capable of forming MOFs, which include a transition metal source and a ligand capable of coordinating with the transition metal source.

[0012] The aforementioned auxiliary agent a is a surfactant;

[0013] Additive b is a water-soluble compound that can provide at least one of molybdenum, tungsten, niobium, and chromium;

[0014] The auxiliary agent c is a compound of formula 1;

[0015] Formula 1;

[0016] In Formula 1, R1 is a mercapto group, a sulfonic acid group, or a sulfate group; X is a C1~C1 group. 10 saturated carbon chain, C4~C 10 The saturated carbon ring; wherein R2 is H, hydroxyl, amino, carboxyl or ester group;

[0017] The liquid cooling medium is a solution containing additive d, which includes at least one of water-soluble phosphorus source, ammonium salt, organic amine, and persulfate.

[0018] This invention innovatively prepares a first MOF material by first performing a coordination reaction on a first MOF precursor material under the synergistic effect of additives a and b. Then, using the first MOF material as a substrate, a second coordination reaction is performed with the assistance of additive c, coating the first MOF with a second MOF to obtain a core-shell double-coated MOF material. Further, the core-shell double MOF undergoes heat treatment, phosphating, and rapid quenching in a system containing additive d. This process constructs abundant defects and dual electrocatalytic active sites within the material, altering the distribution of active sites and improving the interfacial structural stability. The bifunctional electrocatalytic water splitting material prepared by the method described in this invention exhibits excellent dual catalytic activity for both HER and OER.

[0019] In this invention, the transition metal source is a water-soluble salt of a transition metal, wherein the transition metal comprises at least one element selected from iron, zinc, manganese, cobalt, nickel, titanium, and vanadium; preferably, it comprises two or more elements selected from these elements. More preferably, the transition metal element contains at least Zn, and selectively contains at least one element selected from titanium, nickel, iron, and cobalt. Studies have shown that using a composite transition metal source containing zinc can further optimize the uniformity of the distribution of active centers based on the process of this invention, thereby further optimizing the HER and OER performance of the prepared material under alkaline conditions.

[0020] The ligands include at least one of dimethylimidazole, 2-aminoimidazole, terephthalic acid, 2,5-pyridinedicarboxylic acid, 2-(diphenylphosphine)terephthalic acid, and N-oxypyridinecarboxylic acid.

[0021] In this invention, the ratio between the transition metal source and the ligand can be reasonably controlled according to the conventional MOF assembly principle. For example, the molar ratio of the ligand to the transition metal source in the first MOF precursor material can be 1~50:1; further, it can be 5~20:1; further, it can be 10~15:1.

[0022] In this invention, a transition metal source, ligand, auxiliary agent a, and auxiliary agent b are dispersed in a solvent and subjected to a first-stage coordination reaction. The solvent can be, for example, water or a water-organic solvent mixture. The organic solvent can be, for example, a water-soluble organic component such as a C1-C4 alcohol or acetone. Alternatively, the solvent can be an alcohol-water mixture with a volume ratio of 1:0.5-2.

[0023] This invention innovatively utilizes additives a and b to perform the first stage of MOF synthesis reaction. This optimizes the physicochemical structure and surface of the first MOF, which serves as the base for the second stage coordination reaction. This facilitates the induction of a highly stable interfacial composite between the second MOF and the first MOF, and works synergistically with subsequent processes to construct and homogenize the distribution of active centers, thereby optimizing the OER and HER performance of the prepared material under alkaline conditions.

[0024] In this invention, the auxiliary agent a includes at least one of cationic surfactants, anionic surfactants, and neutral surfactants. The cationic surfactant is, for example, a quaternary ammonium salt having 1 to 2 long chains of 6 to 14 carbons. Further, the other carbon chains in the quaternary ammonium salt are short-chain alkyl groups of C1 to C3. The anionic surfactant is, for example, at least one of sulfate esters having 6 to 14 carbon chains (e.g., straight chains), sulfonates having 6 to 14 carbon chains (e.g., straight chains), benzene sulfonates, and alkylbenzene sulfonates having 1 to 6 carbon chains.

[0025] Preferably, the auxiliary agent a is an anionic surfactant. Research in this invention shows that using anionic surfactants in conjunction with the process described in this invention can achieve better synergistic effects and superior HER and OER bifunctional performance.

[0026] In this invention, the auxiliary agent b includes one or more of the following: molybdenum pentachloride, phosphomolybdic acid, tungsten hexachloride, sodium tungstate, niobium pentachloride, niobium oxalate, chromium chloride, and zirconium chloride.

[0027] The weight ratio of the transition metal source, additive a, and additive b in the first MOF precursor material is 1:0.001~0.005:0.002~0.01.

[0028] In this invention, the temperature and time of the first coordination reaction can be adjusted as needed. For example, the temperature can be 15~100℃, or more specifically 20~40℃, and the time can be 1~15h, or more specifically 6~10h.

[0029] In this invention, a first MOF is used as a matrix, and a second coordination stage is performed with the assistance of additive c. This allows for the induction and deposition of a second MOF on the first MOF material, improving the material interface and thereby enhancing the dual functions of HER and OER in the final material.

[0030] In this invention, the selection range of the second MOF precursor material and the first MOF precursor material is the same, but the specific types can be the same or different.

[0031] In this invention, the auxiliary agent c assists in the synthesis of the second-stage MOF, which can further facilitate the high interfacial stability of the second-stage MOF on the first MOF, and is conducive to the synergy with the process to construct and homogenize the active sites of water electrolysis, thereby improving its HER and OER performance under alkaline conditions.

[0032] Preferably, the auxiliary agent c includes at least one of Formula 1A and Formula 1B;

[0033] Formula 1A;

[0034] Formula 1B;

[0035] Further preferably, the additive c is of formula 1A and formula 1B with a molar ratio of 1:0.5~2. Research in this invention shows that, with the preferred additive c, it can be further combined and synergistically integrated with the process, helping to further enhance the HER and OER performance of the prepared material under alkaline conditions.

[0036] The weight ratio of transition metal source and additive C in the second MOF precursor is 1:0.005~0.05; it can be further 1:0.005~0.01.

[0037] The weight ratio of the transition metal source in the second MOF precursor to the transition metal source in the first MOF precursor is 0.1 to 2:1; it can further be 0.5 to 1:1.

[0038] In this invention, the molar ratio of ligand to transition metal source in the second MOF precursor can also be adjusted as needed, for example, it can be 1~50:1; further, it can be 5~20:1; further, it can be 10~15:1.

[0039] In this invention, the temperature and time of the second coordination reaction can be adjusted as needed. For example, the temperature can be 15~100℃, or more specifically 50~70℃, and the time can be 1~15h, or more specifically 4~8h.

[0040] In this invention, the core-shell dual MOF material is innovatively pre-heat-treated, followed by phosphating and rapid cooling assisted by additive d. This facilitates the construction of defective structures and active sites suitable for water electrolysis, and improves its dual HER and OER properties.

[0041] In this invention, the heat treatment temperature is 200~600℃, and can be further 300~550℃.

[0042] In this invention, the heat treatment process is carried out under normal pressure or negative pressure, preferably under negative pressure. Research in this invention shows that performing the heat treatment under negative pressure can further enhance the synergy between components, facilitate the construction of active sites and beneficial defects, and help to further enhance the dual properties of HER and OER.

[0043] In this invention, the heat treatment time is 1 to 6 hours, and can be further 2 to 4 hours.

[0044] In this invention, the phosphorus source includes at least one of organic phosphorus and inorganic phosphorus.

[0045] The organophosphates mentioned above can be, for example, C2~C3. 20Phosphate esters, organophosphonic acids, etc.; further, it can be at least one of dimethyl methyl phosphate, vinylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, adenosine triphosphate, hexafluorocyclotriphosphazene, and phytic acid.

[0046] The inorganic phosphorus is, for example, at least one of ammonium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, etc.

[0047] Preferably, the phosphorus source is an organophosphorus compound. Studies have shown that phosphating treatment involving preferred organophosphorus compounds can further enhance both HER and OER properties.

[0048] In this invention, the weight ratio of the heat-treated product to the phosphorus source is 1:0.2~2, and can be further 1:0.5~1.

[0049] The phosphating roasting temperature is 300~600℃, and can be further 350~550℃;

[0050] The phosphating roasting time is 0.5~4h, and can be further extended to 2~4h.

[0051] In this invention, there are no special requirements for the atmosphere during the phosphating roasting stage; for example, it can be at least one of nitrogen or rare gases.

[0052] In this invention, the solvent in the liquid cooling medium is water or a mixture of water and an organic solvent; the organic solvent is an organic solvent that is miscible with water.

[0053] Additive d includes at least one of water-soluble hypophosphite, phytic acid, cyanamide, thiourea, and ammonium persulfate.

[0054] The concentration of additive d in the liquid cooling medium can be 0.005~2M; further, it can be 0.01~1M.

[0055] During the rapid cooling process, the initial temperature difference between the phosphating product and the liquid cooling medium is above 200℃, and can further be 200~500℃.

[0056] The liquid-to-solid ratio during the rapid cooling process can be above 1 mL / g, and can further be 10~50 mL / g.

[0057] The present invention also provides a bifunctional electrocatalytic water splitting material prepared by the above preparation method.

[0058] The preparation method described in this invention can endow the prepared material with special physicochemical characteristics, and the material prepared by the method can also have excellent dual catalytic activity of HER and OER.

[0059] The present invention also provides an application of the aforementioned bifunctional electrocatalytic water splitting material, using it as a HER catalyst and / or an OER catalyst for electrocatalytic water splitting.

[0060] A further application of this invention is to use the bifunctional electrocatalytic water splitting material described herein as a HER catalyst and / or an OER catalyst for the electrolysis of water from an alkaline aqueous solution. The alkaline aqueous solution is, for example, a sodium hydroxide solution with a concentration of 0.5–5 M.

[0061] In this invention, the bifunctional electrocatalytic water splitting material described herein can be used as a catalytic active ingredient for electrocatalytic water splitting based on known processes.

[0062] A further application of this invention is its use in the preparation of fuel cells from bifunctional electrocatalytic water splitting materials.

[0063] Beneficial effects

[0064] This invention innovatively utilizes the assistance of additives a to c to perform the aforementioned two-stage coordination reaction, yielding a core-shell dual-coated MOF material. Furthermore, the core-shell dual MOF material undergoes heat treatment, phosphating, and rapid quenching in a system containing additive d, thereby constructing abundant defects and dual electrocatalytic active sites within the material, optimizing the distribution of active sites, and improving the stability of the material's interfacial structure. The bifunctional electrocatalytic water splitting material prepared by the method described in this invention exhibits excellent dual catalytic activity for both HER and OER reactions.

[0065] This invention also shows that using a Zn-containing composite transition metal for the aforementioned treatment helps to further improve the HER and OER performance of the prepared catalytic material.

[0066] The study also showed that using anionic surfactants as auxiliaries a in the first coordination reaction helps improve the HER and OER performance of the prepared catalytic materials.

[0067] Using Formula 1A and Formula 1B together as promoter c in the second coordination reaction helps to improve the HER and OER performance of the prepared catalytic material.

[0068] Furthermore, using negative pressure for the heat treatment helps to further optimize the overall physicochemical structure of the material and improve the HER and OER performance of the prepared catalytic material. Attached Figure Description

[0069] Figure 1 This is a SEM image of the electrocatalyst material prepared in step 4 of Example 1.

[0070] Figure 2The XRD patterns are those of the composite MOF precursor prepared in step 2 of Example 1 and the electrocatalyst material prepared in step 4.

[0071] Figure 3 This is a TEM image of the electrocatalyst material prepared in step 4 of Example 1.

[0072] Figure 4 The LSV curves of OER and HER of the electrocatalyst material prepared in step 4 of Example 1 are shown, where (a) is the OER performance graph and (b) is the HER performance graph. Detailed Implementation

[0073] Example 1

[0074] Step 1: Dissolve the ligand (2-methylimidazole) and transition metal salt (in this case, the transition metal salt includes Zn and iron sulfate in a molar ratio of 1:1) in a methanol-water mixture with a volume ratio of 1:1 (the molar ratio of 2-methylimidazole to the transition metal element in the transition metal salt is 10:1, and the concentration of 2-methylimidazole in the solution is 2M). Add structural aid a (SDS, 0.2% of the weight of the transition metal salt) and functional aid b (phosphomolybdic acid, 0.5% of the weight of the transition metal salt). Stir at 30°C for 8 hours to carry out the first coordination reaction. After the reaction is completed, separate the solid and liquid and dry the filter cake for later use.

[0075] Step 2: Disperse the dried material obtained in the previous step in a methanol-water mixed solution containing the ligand (2-methylimidazole) (methanol-water volume ratio of 1:1), and add regulating agent c (Formula 1A, amount of which is 0.8% of the weight of the transition metal salt in this step), and then add the transition metal salt (Zn and nickel sulfate with a molar ratio of 1:1; the molar ratio of the ligand and the transition metal sulfate in Step 2 is 10:1; the amount of transition metal is 50% of the weight of the transition metal in Step 1). Then stir at 60℃ to carry out the second coordination reaction for 6 hours. After the reaction is completed, the solid and liquid are separated and the filter cake is dried to obtain the composite MOF precursor.

[0076] Step 3: Place the product obtained in Step 2 in an atmosphere furnace and heat treat it at 350°C under vacuum for 4 hours.

[0077] Step 4: The product from Step 3 and the phosphorus source (dimethyl methyl phosphate, the weight ratio of the product from Step 3 to the phosphorus source is 1:1) are then phosphated at 550°C for 2 hours under an Ar atmosphere; then, while still hot, they are immersed in a cooling liquid for rapid cooling.

[0078] The coolant is an aqueous solution containing 0.01M phytic acid (liquid-to-solid ratio can be 10~20mL / g) at a temperature of 10℃.

[0079] After solid-liquid separation, alternating washing with water and ethanol, and drying, the electrocatalyst was obtained. SEM images of the product are shown below. Figure 1 XRD Figure 2 TEM Figure 3 .

[0080] Preparation of working electrode: Weigh the prepared electrocatalyst powder and mix it with isopropanol and Nafion (the weight ratio of electrocatalyst powder to Nafion is 9:1) to prepare a mixed slurry. Drop the slurry onto the glassy carbon electrode and dry it at room temperature to obtain the working electrode.

[0081] OER test: LSV test was performed in 1M KOH under the following conditions: 0 ~ 0.7 V vs. Ag / AgCl, scan rate of 5 mV s. -1 The rotational speed was 1600 rpm; stability testing was performed using the chronovoltammetry method with a current density of 10 mA cm⁻¹. -2 .

[0082] HER testing: LSV testing was performed in 1M KOH under the following conditions: -0.9 ~ -1.3 V vs. Hg / HgO, with a scan rate of 5 mV s. -1 The rotational speed was 1600 rpm; stability testing was performed using the chronovoltammetry method with a current density of 10 mA cm⁻¹. -2 .

[0083] The LSVs of OER and HER of the catalyst material in Example 1 are shown below. Figure 4 .

[0084] Example 2

[0085] Compared to Example 1, the only difference is the change in the types of ligands and transition metals. The experimental groups are as follows:

[0086] A: The transition metal salts in steps 1 and 2 are both single ferric sulfate salts, and the total amount of transition metal elements in the transition metal salts and other operations are the same as in Example 1.

[0087] B: The transition metal salt in step 2 is the same as the transition salt in step 1, which is a sulfate of Zn and iron in a molar ratio of 1:1; wherein, the composition ratio, amount and other operations of the transition metal salt in step 2 are the same as in Example 1.

[0088] C: The ligands in both steps 1 and 2 are terephthalic acid, and the molar ratio of the ligands to the transition metals in the transition metal salts is 15:1.

[0089] The results of Examples 1 and 2 are shown in Table 1:

[0090]

[0091] As can be seen from Examples 1 and 2, the use of composite transition metals, especially composite transition metals containing Zn, can further enhance the OER and HER properties of the prepared materials.

[0092] Example 3

[0093] Compared with Example 1, the only difference is that the type of adjuvant a in step 1 is changed, and the experimental groups are as follows:

[0094] Group A: Additive a is the cationic surfactant CTAB;

[0095] Group B: Additive a is a nonionic (neutral) surfactant, lauryl ether-7.

[0096] Group C: Additive a is 0.5% of the weight of the transition metal salt.

[0097] All other operations and parameters are the same as in Example 1.

[0098] The test results are shown in Table 2:

[0099]

[0100] As can be seen from Examples 1 and 3, using anionic surfactants as additive a helps to further enhance the physicochemical structure of the prepared material and further enhance the OER and HER properties of the prepared material.

[0101] Example 4

[0102] Compared with Example 1, the only difference is that the type of adjuvant b in step 1 is changed, and the experimental groups are as follows:

[0103] Group A: Additive b is sodium tungstate;

[0104] Group B: Additive b is niobium oxalate;

[0105] Group C: Additive b is 1% of the weight of the transition metal salt.

[0106] All other operations and parameters are the same as in Example 1.

[0107] The test results are shown in Table 3:

[0108]

[0109] As can be seen from Examples 1 and 4, the use of the aforementioned additive b is beneficial to enhancing the OER and HER properties of the prepared materials.

[0110] Example 5

[0111] Compared with Example 1, the only difference is that the type of adjuvant c in step 2 is changed, and the experimental groups are as follows:

[0112] Group A: Additive c is Formula 1B;

[0113] Group B: Additive c is a mixture of Formula 1A and Formula 1B (the weight ratio of the two is 1:1).

[0114] Group C: Additive c is 4% of the transition metal salt in step 2.

[0115] All other operations and parameters are the same as in Example 1.

[0116] The test results are shown in Table 4:

[0117]

[0118] As can be seen from Examples 1 and 5, the use of the aforementioned additive c, especially the additive c combining Formula 1A and Formula 1B, can further enhance the OER and HER properties of the prepared material.

[0119] Example 6

[0120] Compared to Example 1, the only difference is that the conditions in step 3 are changed, and the experimental groups are as follows:

[0121] Group A: The heat treatment temperature is 550℃; the time is 2 hours.

[0122] Group B: The heat treatment process is carried out at atmospheric pressure, and the atmosphere is Ar.

[0123] All other operations and parameters are the same as in Example 1.

[0124] The test results are shown in Table 5:

[0125]

[0126] As can be seen from Examples 1 and 6, the negative pressure heat treatment process can further enhance the OER and HER properties of the prepared material.

[0127] Example 7

[0128] Compared to Example 1, the only difference is that the type and amount of phosphorus source in step 4 are changed. The experimental groups are as follows:

[0129] Group A: The phosphorus source is adenosine triphosphate;

[0130] Group B: The phosphorus source is ammonium phosphate;

[0131] Group C: The weight ratio of the product from step 3 to the phosphorus source is 1:0.5;

[0132] Group D: Phosphating temperature was 350℃, and time was 4 hours;

[0133] All other operations and parameters are the same as in Example 1.

[0134] The test results are shown in Table 6:

[0135]

[0136] As can be seen from Examples 1 and 7, the phosphating process described in this invention, especially the use of organic phosphorus as a phosphorus source, can effectively enhance the OER and HER properties of the prepared materials.

[0137] Example 8

[0138] Compared to Example 1, the only difference is that the type of coolant in step 4 is changed. The experimental groups are as follows:

[0139] Group A: The coolant is 1M thiourea, and the solvent is water;

[0140] Group B: The coolant is 0.5M sodium hypophosphite, and the solvent is water;

[0141] All other operations and parameters are the same as in Example 1.

[0142] The test results are shown in Table 7:

[0143]

[0144] As can be seen from Examples 1 and 8, the functionalized rapid cooling process described in this invention can effectively enhance the OER and HER properties of the prepared material.

[0145] Comparative Example 1

[0146] Compared with Example 1, the only difference is that in step 1, no additives a and b were added; all other operations and parameters are the same as in Example 1.

[0147] Comparative Example 2

[0148] Compared with Example 1, the only difference is that in step 1, no additive a was added; all other operations and parameters are the same as in Example 1.

[0149] Comparative Example 3

[0150] Compared with Example 1, the only difference is that in step 1, no additive b was added; all other operations and parameters are the same as in Example 1.

[0151] Comparative Example 4

[0152] Compared with Example 1, the only difference is that in step 2, no additive c is added; all other operations and parameters are the same as in Example 1.

[0153] Comparative Example 5

[0154] Compared with Example 1, the only difference is that step 2 is not performed. Instead, the raw materials such as ligands, additives c and transition metal sources in step 2 are added together in step 1. All other operations and parameters are the same as in Example 1.

[0155] Comparative Example 6

[0156] Compared with Example 1, the only difference is that step 3 is omitted, and the product of step 2 is directly processed in step 4. All other operations and parameters are the same as in Example 1.

[0157] Comparative Example 7

[0158] Compared with Example 1, the only difference is that in step 4, the phosphating is cooled with the furnace, while other operations and parameters are the same as in Example 1.

[0159] Comparative Example 8

[0160] Compared with Example 1, the only difference is that in step 4, no additive d is added to the coolant; all other operations and parameters are the same as in Example 1.

[0161] Comparative Example 9

[0162] Compared with Example 1, the only difference is that no additive b is added in step 1 and no additive c is added in step 2. Instead, additive b and additive c are mixed with the phosphorus source and phosphated together in step 3. All other operations and parameters are the same as in Example 1.

[0163] The test results for each comparative example are shown in Table 8:

[0164]

[0165] As demonstrated in Example 1 and Comparative Examples 1, the innovative two-stage coordination reaction, assisted by additives a to c, yields a core-shell dual-coated MOF material. Further heat treatment, phosphating, and rapid quenching in a system containing additive d of the core-shell dual MOF material create abundant defects and dual electrocatalytic active sites within the material, improving the interfacial structural stability. The bifunctional electrocatalytic water splitting material prepared by the method described in this invention exhibits excellent dual catalytic activity for both HER and OER.

Claims

1. A method for preparing a bifunctional electrocatalytic water splitting material, characterized in that, The first MOF precursor material is subjected to a first coordination reaction in a solution containing additive a and additive b to obtain the first MOF; Using the first MOF as a substrate, the second MOF precursor material undergoes a second-stage coordination reaction in a solution of auxiliary agent c, and the second MOF is deposited on the first MOF to obtain a core-shell dual MOF material; the core-shell dual MOF material is heat-treated to obtain a heat-treated material; the heat-treated material is then mixed with a phosphorus source and subjected to phosphating and calcination treatment, and the phosphating product is placed in a liquid phase cooling medium for rapid cooling treatment while hot to obtain the bifunctional electrocatalytic water splitting material; The first MOF precursor material and the second MOF precursor material are raw materials capable of forming MOFs, which include a transition metal source and a ligand capable of coordinating with the transition metal source. Additive a includes at least one of cationic surfactants, anionic surfactants, and neutral surfactants; Additive b includes one or more of molybdenum pentachloride, phosphomolybdic acid, tungsten hexachloride, sodium tungstate, niobium pentachloride, and niobium oxalate; The weight ratio of the transition metal source, additive a, and additive b in the first MOF precursor material is 1:0.001~0.005:0.002~0.01; Additive c includes at least one of Formula 1A and Formula 1B; Formula 1A; Formula 1B; The weight ratio of transition metal source and additive C in the second MOF precursor is 1:0.005~0.05; The liquid cooling medium is a solution containing additive d, wherein additive d includes at least one of water-soluble hypophosphite, phytic acid, and thiourea.

2. The preparation method of the bifunctional electrocatalytic water splitting material as described in claim 1, characterized in that, The transition metal source is a water-soluble salt of a transition metal, wherein the transition metal includes at least one element selected from iron, zinc, manganese, cobalt, nickel, titanium, and vanadium. The ligands include at least one of dimethylimidazole, 2-aminoimidazole, terephthalic acid, 2,5-pyridinedicarboxylic acid, 2-(diphenylphosphine)terephthalic acid, and N-oxypyridinecarboxylic acid; The molar ratio of ligand to transition metal source is 1 to 50:

1.

3. The preparation method of the bifunctional electrocatalytic water splitting material as described in claim 1, characterized in that, The weight ratio of the transition metal source in the second MOF precursor to the transition metal source in the first MOF precursor is 0.1~2:

1.

4. The preparation method of the bifunctional electrocatalytic water splitting material as described in claim 1, characterized in that, The heat treatment temperature is 200~600℃; The heat treatment is carried out under negative pressure; The heat treatment time is 1 to 6 hours.

5. The preparation method of the bifunctional electrocatalytic water splitting material as described in claim 1, characterized in that, Phosphorus sources include at least one of organic phosphorus and inorganic phosphorus; The weight ratio of heat-treated product to phosphorus source is 1:0.2~2; The phosphating roasting temperature is 300~600℃; The phosphating roasting time is 0.5~4h.

6. The preparation method of the bifunctional electrocatalytic water splitting material as described in claim 1, characterized in that, The solvent in the liquid cooling medium is water or a mixture of water and an organic solvent; the organic solvent is an organic solvent that is miscible with water. During the rapid cooling process, the initial temperature difference between the phosphating product and the liquid cooling medium is above 200℃.

7. A bifunctional electrocatalytic water splitting material prepared by the preparation method according to any one of claims 1 to 6.

8. The application of a bifunctional electrocatalytic water splitting material prepared by the preparation method according to any one of claims 1 to 6, characterized in that, It can be used as a HER catalyst and / or an OER catalyst for the electrocatalytic splitting of water.

9. The application as described in claim 8, characterized in that, It is used to prepare fuel cells.

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