Metal fluoride-phosphide self-supporting electrode, preparation thereof and application of metal fluoride-phosphide self-supporting electrode in electrolyzed water

Abstract

The invention belongs to the field of water electrolysis, and particularly relates to a metal fluoride-phosphide self-supporting electrode which comprises a foam substrate and a metal fluoride-phosphide active layer compounded on the surface of the foam substrate, the active layer comprises a transition metal phosphide layer and a fluoride layer of the transition metal phosphide layer, the phosphide layer is compounded on the side of the foam substrate, and the fluoride layer is compounded on the side of the foam substrate. And the fluoride layer is arranged on the surface layer. The invention also comprises preparation and application of the electrode. Transition metal is innovatively modified on a foam substrate in a solvothermal mode assisted by the aid of the aid A and the aid B in advance, and then subsequent gas-phase phosphating and gas-phase fluorination treatment is sequentially performed by taking the transition metal as a nucleation target spot, so that the hierarchical structure of the material can be optimized, the interface stability of the material is improved, and the performance of the material is improved. Furthermore, the alkali resistance of the prepared material can be remarkably improved, the HER / OER performance of the material is improved, and the water full electrolysis performance is improved.

Description

Technical Field

[0001] The invention belongs to the field of electrocatalytic water electrolysis, and in particular relates to a self-supporting metal phosphide electrocatalyst material. Background Art

[0002] Water electrolysis is an electrochemical process that decomposes water into hydrogen (H2) and oxygen (O2) through electrical energy. It is an effective way to achieve renewable energy storage and utilization. This process includes hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), both of which require efficient electrocatalysts to reduce the reaction overpotential, improve energy conversion efficiency and reaction rate, and thus achieve economical and efficient hydrogen production. Although traditional precious metal catalysts (such as platinum and iridium) show excellent catalytic performance, their high cost and rarity limit their large-scale application. Therefore, the development of efficient, low-cost and stable electrocatalysts has become the focus of current research.

[0003] Transition metal-based catalysts, especially transition metal phosphides (such as cobalt phosphide, nickel phosphide and iron phosphide), have attracted much attention due to their low cost, abundant reserves and excellent electrocatalytic performance; these materials not only have high catalytic activity but also exhibit good chemical stability and mechanical durability, making them ideal candidates for HER and OER.

[0004] Existing electrocatalytic electrolysis mainly includes coated electrodes and self-supporting electrodes. Coated electrodes are prone to problems such as polymer embedding, and their activity is difficult to effectively exert. The active material is easy to peel off, and the stability needs to be improved. In response to the problems faced by coated electrodes, self-supporting materials can effectively solve the problems of active material embedding, but they are also prone to problems such as corrosion during the electrolysis stage, which makes it difficult to maintain stability.

[0005] In view of the problems existing in self-supporting electrolysis, the prior art also provides some improvement methods. For example, the Chinese patent document with publication number CN118888933A discloses a metal-gas battery based on a flexible self-supporting carbon fiber catalyst, wherein the flexible self-supporting carbon fiber catalyst is a carbon fiber material rich in surface defects; the flexible self-supporting carbon fiber catalyst is prepared by electrostatic spinning technology. The Chinese patent document CN118497815A discloses a preparation method and application of a self-supporting ternary metal phosphide heterojunction bifunctional catalyst for the complete decomposition of seawater, wherein the preparation steps of the catalytic material are as follows: placing a foamed nickel substrate in a mixed solution containing cobalt salt, iron salt, urea and ammonium fluoride for homogeneous hydrothermal treatment, synthesizing a CoFeNi intermediate in situ on the substrate, and then phosphating to obtain a catalyst. For another example, the Chinese patent document with the publication number CN112774704A discloses a self-supporting FeCo phosphide electrocatalyst using foamed nickel and a preparation method thereof, wherein the foamed nickel, a soluble cobalt salt and a soluble iron salt are subjected to hydrothermal reaction to obtain FeCo hydroxide; then the FeCo hydroxide and a salt providing elemental phosphorus are placed in a quartz boat, and the quartz boat is placed in a tubular furnace for phosphating treatment to obtain a foamed nickel self-supporting FeCo phosphide catalytic material.

[0006] In summary, although the prior art discloses some self-supporting metal phosphide electrocatalytic materials, the existing self-supporting materials have unsatisfactory alkali resistance, and it is difficult to simultaneously take into account excellent HER and OER performances, and it is difficult to adapt to the requirements of full hydrolysis applications. At the same time, during the catalytic process, the coating material on the self-supporting substrate is easy to fall off. Summary of the invention

[0007] In view of the insufficient performance of existing water electrolysis reaction catalysts, the first purpose of the present invention is to provide a method for preparing a metal fluoride@phosphide self-supporting electrode, aiming to prepare an electrode with good water electrolysis performance.

[0008] The second object of the present invention is to provide a metal fluoride@phosphide self-supporting electrode prepared by the preparation method and its application in water electrolysis.

[0009] The third object of the present invention is to provide a water electrolysis device comprising the metal fluoride@phosphide self-supporting electrode.

[0010] A metal fluoride@phosphide self-supporting electrode comprises a foam substrate and a metal fluoride@phosphide active layer composited on the surface thereof, wherein the active layer comprises a transition metal phosphide layer and a fluoride layer thereof, wherein the phosphide layer is composited on the foam substrate side and the fluoride layer is arranged on the surface.

[0011] The present invention innovatively deposits a transition metal phosphide layer on a foam substrate in advance, and then in situ composites the transition metal fluoride layer. Based on the combination of the components and the hierarchical structure, the alkali resistance of the material can be improved, and excellent HER and OER performance can be simultaneously taken into account, thereby improving its performance in full water electrolysis.

[0012] In the present invention, the foam substrate includes at least one of a foam metal substrate, a foam carbon-based substrate, and a foam polymer substrate. The foam metal substrate may be foam nickel, foam copper, or the like.

[0013] In the present invention, the transition metal includes at least one of iron, cobalt, nickel, manganese, copper and zinc; more preferably, two or more, and more preferably, a ternary metal of Fe, Ni and Co (the weight ratio of Fe, Ni and Co in the ternary metal is not particularly required, for example, it can be 1:0.1~0.5:0.5~1). The present invention has shown that the use of the elemental composition, combined with the composition and structure of the present invention, can further optimize the electrolytic water performance of the material based on the medium entropy physicochemical characteristics.

[0014] The present invention also provides a method for preparing the metal fluoride@phosphide self-supporting electrode, wherein a raw material solution including a foam substrate, a transition metal source, an auxiliary agent A and an auxiliary agent B is pre-solvent-heat-treated to obtain a precursor electrode modified with a transition metal; the auxiliary agent A is an organic carboxylic acid; the auxiliary agent B is at least one of a free organic amine and a salt thereof; The precursor electrode is subjected to a gas phase phosphating treatment in an atmosphere containing a P source, and then subjected to a gas phase fluorination treatment in an atmosphere containing a fluorine source, so as to obtain the metal fluoride@phosphide self-supporting electrode.

[0015] The present invention innovatively pre-modifies the transition metal on the foam substrate by a solvent thermal method assisted by additives A and additives B, and then uses it as a nucleation target for subsequent gas phase phosphating and gas phase fluorination treatments. This can optimize the hierarchical structure of the material, improve the interface stability of the material, and further significantly improve the alkali resistance of the prepared material, improve its HER / OER performance, and improve the performance of water full electrolysis.

[0016] In the present invention, the transition metal source is one or more of chlorides, sulfates, sulfites, nitrates and nitrites of transition metals.

[0017] Preferably, the auxiliary agent A comprises at least one of citric acid and alginic acid; preferably, it is a composite of citric acid and alginic acid in a weight ratio of 0.1 to 0.5:1. Studies have shown that the use of the preferred auxiliary agent A in the treatment can be further combined with other operations and processes, which helps to further improve the HER / OER performance of the prepared material and improve the performance of water electrolysis.

[0018] Preferably, the auxiliary agent B is at least one of a C2-C6 fatty amine, a fatty diamine and a hydrochloride thereof. Preferably, the weight ratio of the fatty diamine and the fatty amine hydrochloride is 0.1-1:1. Studies have shown that the use of the preferred auxiliary agent A to participate in the treatment can be further combined with other operations and processes, which helps to further improve the HER / OER performance of the prepared material and improve the performance of water electrolysis.

[0019] Preferably, the solvent of the feed solution comprises water; Preferably, the weight ratio of the foam substrate, the transition metal element in the transition metal source, the additive A and the additive B is 1:0.2~2:0.01~0.05:0.1~2.5; more preferably 1:0.5~1:0.01~0.05:0.5~2.

[0020] Preferably, the solvent thermal temperature is 100-200°C, and further can be 120-160°C; Preferably, the solvent thermal time is 2 to 5 hours.

[0021] In the present invention, the P source-containing atmosphere is an atmosphere containing phosphine (PH 3 ).

[0022] Preferably, the phosphine is obtained by thermal decomposition and volatilization of phosphorus-containing solids.

[0023] For example, in the present invention, the precursor material (phosphorus-containing solid) of the phosphorus source atmosphere and the precursor electrode can be arranged in different areas of the tubular furnace, and the precursor material of the phosphorus source atmosphere is heated and volatilized to form a phosphorus source atmosphere and to conduct an in-situ gas phase phosphating deposition reaction with the precursor electrolysis.

[0024] The precursor material of the phosphorus source atmosphere may be, for example, hypophosphite. The weight ratio of the precursor material of the phosphorus source atmosphere to the precursor electrode may be reasonably adjusted as required, for example, the weight ratio of the two may be 1:5-15.

[0025] In the present invention, the temperature of the vapor phase phosphating is 500-850° C., and can further be 700-800° C. For example, the vapor phase phosphating temperature can be the temperature of the region where the precursor electrode is located.

[0026] Preferably, the vapor phase phosphating time is 8 to 12 hours.

[0027] In the present invention, the fluorine source-containing atmosphere contains at least one functional gas selected from sulfur hexafluoride and nitrogen trifluoride.

[0028] In the present invention, the temperature of gas phase fluorination is 100-250°C, and can further be 140-200°C; Preferably, the gas phase fluorination time is 2 to 4 hours.

[0029] The present invention also provides a water electrolysis method, which adopts the metal fluoride@phosphide self-supporting electrode of the present invention.

[0030] The present invention also provides a water electrolysis device, which comprises the metal fluoride@phosphide self-supporting electrode, or is prepared by the metal fluoride@phosphide self-supporting electrode.

[0031] The water electrolysis equipment and method described in the present invention utilize the metal fluoride@phosphide self-supporting electrode described in the present invention, and other components and parts may be known in the industry, or may be reasonably regulated based on principles and methods known in the industry.

[0032] Beneficial Effects The present invention provides a new metal fluoride@phosphide self-supporting electrode, which innovatively deposits a transition metal phosphide layer on a foam substrate in advance and then in situ composites the transition metal fluoride layer. Based on the combination of the components and the hierarchical structure, the alkali resistance of the material can be improved, and excellent HER and OER performance can be taken into account simultaneously, thereby improving its performance in full water electrolysis.

[0033] The present invention also provides a method for preparing the metal fluoride@phosphide self-supporting electrode, which innovatively pre-modifies the transition metal on the foam substrate by a solvent thermal method assisted by additives A and additives B, and then uses it as a nucleation target to carry out subsequent gas phase phosphating and gas phase fluorination treatments in sequence, thereby optimizing the hierarchical structure of the material, improving the interface stability of the material, and further significantly improving the alkali resistance of the prepared material, improving its HER / OER performance, and improving the performance of water full electrolysis.

[0034] The present invention shows that the alkaline HER potential of the metal fluoride@phosphide self-supporting electrode can be reduced to 35mV, the OER potential can be reduced to 1.416V, and the full hydrolysis potential can be reduced to 1.512V, which has excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a graph showing the HER stability of the electrode obtained in Example 1; Figure 2 This is a graph showing the OER stability test of the electrode prepared in Example 1. DETAILED DESCRIPTION

[0036] The weight of the metal precursor is based on the weight of the metal element therein.

[0037] Example 1 Step (1): Preprocessing The nickel foam was placed in a 1M hydrochloric acid solution for 15 minutes of ultrasonic cleaning, and then plasma cleaned for use.

[0038] Step (2): Hydrothermal reaction The nickel foam with a mass ratio of 1:0.5:0.04:2, the metal precursor (a mixture of ferric nitrate, nickel nitrate and cobalt nitrate with a weight ratio of 1:0.3:0.6 for Fe / Ni / Co), the auxiliary agent A (a mixture of citric acid and alginic acid with a mass ratio of 0.2:1, the mass of the auxiliary agent A is calculated based on the total mass of the two), and the auxiliary agent B (a mixture of dibutylamine and butylammonium chloride with a mass ratio of 0.5:1) are dissolved in a deionized water system (the concentration of the metal precursor in the solution is controlled to be 2.5~3M), and then the foam substrate is placed in this system and subjected to a hydrothermal treatment at 150±10℃ for 3~4h. After the reaction is completed, the foam substrate is taken out and dried to obtain a metal-loaded nickel foam (also called a self-supporting material).

[0039] Step (3): Phosphate treatment The obtained self-supporting material is placed at the outlet end of the atmosphere furnace, and sodium hypophosphite (the mass ratio of the self-supporting material to sodium hypophosphite is 1:10) is placed at the inlet end, the temperature of the self-supporting material zone is controlled to 700°C, and the temperature of the sodium hypophosphite zone is controlled to 360°C, the self-supporting material is phosphated for 10 hours, and then naturally cooled.

[0040] Step (4): Surface fluorination The obtained self-supporting material was placed in a mixed atmosphere of 5 wt % nitrogen trifluoride and nitrogen, and heat treated at 140° C. for 3 h under closed conditions to obtain Ni-FMP.

[0041] Example 2 Compared with Example 1, the only difference is that the type of foam substrate is changed. The experimental groups are: Group A: The foam substrate is carbon paper; Group B: The foam base is polyurethane; The test was carried out in the manner of Example 1, and the results are shown in Table 1.

[0042] Example 3 Compared with Example 1, the only difference is that the type of metal source, the total amount of metal elements in the metal source and other operating conditions are the same as Example 1. The experimental groups are: Group A: The metal source is iron nitrate; Group B: The metal source is nickel nitrate; Group C: The metal source is cobalt nitrate The test was carried out in the manner of Example 1, and the results are shown in Table 1.

[0043] Example 4 Compared with Example 1, the only difference is that the auxiliary agent A is changed. The experimental groups are: Group A: additive A is citric acid; Group B: additive A is alginic acid; The dosage of the auxiliary agent A and other operations were the same as those in Example 1, and the test was carried out in the manner of Example 1. The results are shown in Table 1.

[0044] Example 5 Compared with Example 1, the only difference is that the auxiliary agent B is changed. The experimental groups are: Group A: auxiliary agent B is dibutylamine; Group B: additive B is butyl ammonium chloride; The dosage of the auxiliary agent B and other operations were the same as those in Example 1, and the test was carried out in the manner of Example 1. The results are shown in Table 1.

[0045] Example 6 Compared with Example 1, the only difference is that in step 2, the mass ratio of nickel foam, metal precursor, additive A, and additive B is 1:1:0.01:0.5, in step 3, the mass ratio of self-supporting material and sodium hypophosphite is 1:5, the temperature of the self-supporting material is 800°C, and the time is 8h; in step 4, the atmosphere is a 2wt% mixed atmosphere of nitrogen trifluoride and nitrogen; the fluorination temperature is 200°C, and the time is 2h, and the other operations and parameters are the same as in Example 1.

[0046] Comparative Example 1 Compared with Example 1, the only difference is that in step (2), no auxiliary agent A is added, and the other operations and parameters are the same as those in Example 1.

[0047] Comparative Example 2 Compared with Example 1, the only difference is that in step (2), no auxiliary agent B is added, and the other operations and parameters are the same as those in Example 1.

[0048] Comparative Example 3 Compared with Example 1, the only difference is that in step (3), sodium hypophosphite is not added, and other operations and parameters are the same as in Example 1.

[0049] Comparative Example 4 Compared with Example 1, the only difference is that step (3) is not performed, that is, phosphating treatment is not performed, and the product of step 2 is directly subjected to step 4. The other operations and parameters are the same as those in Example 1.

[0050] Comparative Example 5 Compared with Example 1, the only difference is that in step (4), a pure nitrogen atmosphere is used for heat treatment, and the other operations and parameters are the same as those in Example 1.

[0051] Comparative Example 6 Compared with Example 1, the only difference is that the vapor phase phosphating process is not adopted, that is, sodium hypophosphite is used as the phosphorus source in step 2 (the molar ratio of the metal in the metal source to the P in the phosphorus source is 1:3), and in addition, sodium hypophosphite is not added in step 3, and other operations and parameters are the same as in Example 1.

[0052] Comparative Example 7 Compared with Example 1, the only difference is that in step 4, the fluorine-containing gas generated by the decomposition of ammonium fluoride is used as the gas-phase fluorination material (the mass ratio of ammonium fluoride to the metal source is 10:1), the ammonium fluoride is placed at the air inlet end, the self-supporting material is placed at the air outlet end, the temperature is 300°C, the insulation treatment time and other operations and parameters are the same as in Example 1.

[0053] Comparative Example 8: Compared with Example 1, the difference is that step 4 gas phase fluorination is performed first, and then step 3 phosphating is performed. Other operations and parameters are the same as in Example 1.

[0054] Comparative Example 9; Compared with Example 1, the difference is that step 4 is not performed, ammonium fluoride is added in step 2 (the mass ratio of ammonium fluoride to metal source is 0.5:1), and other operations and parameters are the same as in Example 1.

[0055] Material electrochemical performance test: The catalytic performance was tested in a three-electrode system using a rotating disk electrode, the Ni-FMP as the working electrode, mercury oxide as the reference electrode, and a platinum electrode as the counter electrode. In the 1 M KOH system, the HER reaction was carried out at a current density of 10 mA cm -2 The overpotential (η j=10 ) is 35.2 mV. In the 1 M KOH system, the OER reaction is carried out at a current density of 10 mA cm -2 The potential under j=10 ) is 1.416 V.

[0056] The final product was coated on nickel foam as cathode and anode, and the electrolyte was also 1 M KOH solution. The water electrolysis performance was tested and reached 10 mA cm -2 A potential of only 1.524 V was required for the water splitting current density.

[0057]

[0058] As shown in Table 1, the transition metal is modified on the foam substrate in an innovative way by a solvent thermal method assisted by additives A and B, and then the subsequent gas phase phosphating and gas phase fluorination treatments are carried out in sequence using the transition metal as a nucleation target, which can optimize the hierarchical structure of the material, improve the interfacial stability of the material, and thus significantly improve the alkali resistance of the prepared material, improve its HER / OER performance, and improve the performance of water electrolysis. In addition, the use of a preferred combination of metals, additives A and additives B can further optimize the physical and chemical structure of the prepared electrode, and can unexpectedly further optimize the HER / OER performance of the material and improve the performance of water electrolysis.

Claims

1. A metal fluoride@phosphide self-supporting electrode, characterized in that: It includes a foam substrate and a metal fluoride@phosphide active layer compounded on its surface, wherein the active layer includes a transition metal phosphide layer and a fluoride layer thereof, wherein the phosphide layer is compounded on the foam substrate side and the fluoride layer is arranged on the surface.

2. The metal fluoride@phosphide self-supporting electrode according to claim 1, characterized in that: The foam substrate comprises at least one of a foam metal substrate, a foam carbon-based substrate, and a foam polymer substrate; Preferably, the transition metal includes at least one of iron, cobalt, nickel, manganese, copper and zinc.

3. A method for preparing the metal fluoride@phosphide self-supporting electrode according to any one of claims 1 to 2, characterized in that: The raw material solution including the foam substrate, the transition metal source, the auxiliary agent A and the auxiliary agent B is pre-solvothermally treated to obtain a precursor electrode modified with the transition metal; the auxiliary agent A is an organic carboxylic acid; the auxiliary agent B is at least one of a free organic amine and a salt thereof; The precursor electrode is subjected to a gas phase phosphating treatment in an atmosphere containing a P source, and then subjected to a gas phase fluorination treatment in an atmosphere containing a fluorine source, so as to obtain the metal fluoride@phosphide self-supporting electrode.

4. The method for preparing the metal fluoride@phosphide self-supporting electrode according to claim 3, characterized in that: The transition metal source is one or more of chlorides, sulfates, sulfites, nitrates and nitrites of transition metals; Preferably, the auxiliary agent A comprises at least one of citric acid and alginic acid; Preferably, the auxiliary agent B is at least one of C2-C6 fatty amines, fatty diamines and their hydrochlorides; Preferably, the solvent of the feed solution comprises water; Preferably, the weight ratio of the foam substrate, the transition metal element in the transition metal source, the additive A and the additive B is 1:0.2~2:0.01~0.05:0.1~2.5; Preferably, the solvent thermal temperature is 100-200°C; Preferably, the solvent thermal time is 2 to 5 hours.

5. The method for preparing the metal fluoride@phosphide self-supporting electrode according to claim 3, characterized in that: The P source-containing atmosphere is an atmosphere containing phosphine (PH3); Preferably, the phosphorus source atmosphere is obtained by thermal decomposition and volatilization of phosphorus-containing solids.

6. The method for preparing the metal fluoride@phosphide self-supporting electrode according to claim 3 or 5, characterized in that: The temperature of gas phase phosphating is 500~850℃; Preferably, the vapor phase phosphating time is 8 to 12 hours.

7. The method for preparing the metal fluoride@phosphide self-supporting electrode according to claim 3, characterized in that: The fluorine source-containing atmosphere contains at least one functional gas of sulfur hexafluoride and nitrogen trifluoride.

8. The method for preparing the metal fluoride@phosphide self-supporting electrode according to claim 3 or 7, characterized in that: The temperature of gas phase fluorination is 100~250℃; Preferably, the gas phase fluorination time is 2 to 4 hours.

9. A water electrolysis method, characterized in that: The metal fluoride@phosphide self-supporting electrode according to any one of claims 1 to 2 or the metal fluoride@phosphide self-supporting electrode according to any one of claims 3 to 8 is used as an electrode.

10. A water electrolysis device, characterized in that: The electrode comprises the metal fluoride@phosphide self-supporting electrode as described in any one of claims 1 to 2 or the metal fluoride@phosphide self-supporting electrode as described in any one of claims 3 to 8, or is prepared by the metal fluoride@phosphide self-supporting electrode.

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