Metal fluoride-phosphide self-supporting electrodes, their preparation and use in electrolysis of water

Abstract

The application 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 phosphide layer of a transition metal and a fluoride layer of the transition metal, wherein the phosphide layer is compounded on the side of the foam substrate, and the fluoride layer is arranged on the surface layer. The application also comprises preparation and application of the electrode. The application innovatively modifies the transition metal on the foam substrate in advance through a solvothermal method assisted by an auxiliary agent A and an auxiliary agent B, and then performs subsequent gas-phase phosphorization and gas-phase fluorination treatment in sequence with the transition metal as a nucleation target point, so that the hierarchical structure of the material can be optimized, the interface stability of the material can be improved, and the alkali resistance of the prepared material can be significantly improved, the HER / OER performance of the material can be improved, and the performance of water full electrolysis can be improved.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic water electrolysis, specifically relating to self-supporting metal phosphide electrocatalyst materials. Background Technology

[0002] Water electrolysis is an electrochemical process that uses electricity to split water into hydrogen (H2) and oxygen (O2), and it is an effective way to achieve renewable energy storage and utilization. This process includes the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), both of which require highly efficient electrocatalysts to reduce reaction overpotential, improve energy conversion efficiency and reaction rate, thereby achieving cost-effective hydrogen production. While traditional noble metal catalysts (such as platinum and iridium) exhibit excellent catalytic performance, their high cost and scarcity limit their large-scale application. Therefore, developing efficient, low-cost, and stable electrocatalysts has become a current research focus.

[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 methods mainly include coated electrodes and self-supporting electrodes. Coated electrodes are prone to problems such as polymer embedding, which hinders effective activity and makes the active material susceptible to peeling off, thus requiring improved stability. Self-supporting materials can effectively address the problems of active material embedding in coated electrodes, but they are also prone to issues such as corrosion during the electrolysis stage, leading to difficulties in maintaining stability.

[0005] To address the problems associated with self-supporting electrolysis, existing technologies have provided some improvement methods. For example, Chinese patent document CN118888933A discloses a metal-gas battery based on a flexible self-supporting carbon fiber catalyst. The flexible self-supporting carbon fiber catalyst is a carbon fiber material rich in surface defects; it is prepared using electrospinning technology. Another example is...

[0006] Chinese patent document CN118497815A discloses a method for preparing and applying a self-supporting ternary metal phosphide heterojunction bifunctional catalyst for the complete hydrolysis of seawater. The preparation steps of the catalyst are as follows: a nickel foam matrix is ​​subjected to homogeneous hydrothermal treatment in a mixed solution containing cobalt salt, iron salt, urea, and ammonium fluoride to synthesize a CoFeNi intermediate in situ on the matrix, followed by phosphating to obtain the catalyst. Similarly, Chinese patent document CN112774704A discloses a method for preparing a nickel foam self-supporting FeCo phosphide electrocatalyst. The method involves hydrothermally reacting nickel foam, soluble cobalt salt, and soluble iron salt to obtain FeCo hydroxide; then placing the FeCo hydroxide and a salt providing elemental phosphorus in a quartz boat, and placing the quartz boat in a tube furnace for phosphating to obtain a nickel foam self-supporting FeCo phosphide catalytic material.

[0007] In summary, although some self-supporting metal phosphide electrocatalytic materials have been disclosed in the prior art, the existing self-supporting materials have unsatisfactory alkali resistance and are difficult to simultaneously achieve excellent HER and OER performance, making them difficult to adapt to the requirements of full hydrolysis applications. At the same time, the coating material on the self-supporting substrate is prone to detachment during the catalytic process. Summary of the Invention

[0008] In view of the shortcomings of existing water electrolysis catalysts, the primary objective of this invention is to provide a method for preparing a metal fluoride@phosphide self-supporting electrode, which aims to obtain an electrode with good water electrolysis performance.

[0009] The second objective of this invention is to provide a metal fluoride@phosphide self-supporting electrode prepared by the aforementioned method and its application in water electrolysis.

[0010] A third objective of this invention is to provide a water electrolysis device comprising the aforementioned metal fluoride@phosphide self-supporting electrode.

[0011] A metal fluoride@phosphide self-supporting electrode includes a foam substrate and a metal fluoride@phosphide active layer composited on its surface. The active layer includes a phosphide layer of a transition metal and a fluoride layer thereof, wherein the phosphide layer is composited on the foam substrate side, and the fluoride layer is disposed on the surface layer.

[0012] This invention innovatively deposits a phosphide layer of transition metal on a foam substrate in advance, and then in situ composites a fluoride layer of the same transition metal. 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 at the same time, thereby improving its performance in water electrolysis.

[0013] In this 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, etc.

[0014] In this invention, the transition metal includes at least one of iron, cobalt, nickel, manganese, copper, and zinc; more preferably, two or more, and even 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). This invention demonstrates that by using the aforementioned elemental composition, combined with the components and structure described in this invention, the electrolysis performance of the material can be further optimized based on the medium-entropy physicochemical characteristics.

[0015] The present invention also provides a method for preparing the metal fluoride@phosphide self-supporting electrode, wherein a raw material solution comprising a foam substrate, a transition metal source, an additive A and an additive B is subjected to a solvothermal treatment to obtain a precursor electrode modified with a transition metal; wherein the additive A is an organic carboxylic acid; and wherein the additive B is at least one of a free organic amine and its salt.

[0016] The precursor electrode is subjected to gas-phase phosphating in a P-source atmosphere, followed by gas-phase fluorination in a fluorine-source atmosphere to obtain the metal fluoride@phosphide self-supporting electrode.

[0017] This invention innovatively modifies a transition metal onto a foam substrate in advance using a solvothermal method assisted by additives A and B. Subsequently, the substrate is used as a nucleation target for subsequent gas-phase phosphating and gas-phase fluorination treatments. This optimizes the material's hierarchical structure, improves its interfacial stability, and thus significantly improves the alkali resistance, HER / OER performance, and water electrolysis performance of the prepared material.

[0018] In this invention, the transition metal source is one or more of the following: chloride, sulfate, sulfite, nitrate, and nitrite of transition metals.

[0019] Preferably, the auxiliary agent A includes at least one of citric acid and alginic acid; more preferably, it is a complex of citric acid and alginic acid in a weight ratio of 0.1 to 0.5:1. Studies have shown that using 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.

[0020] Preferably, the auxiliary agent B is at least one of C2-C6 aliphatic amines, aliphatic diamines, and their hydrochlorides. More preferably, it is aliphatic diamine and aliphatic amine hydrochloride in a weight ratio of 0.1 to 1:1. Studies have shown that using the preferred auxiliary agent A in the treatment can be further combined with other operations and processes, contributing to further improvement of the HER / OER performance of the prepared material and the performance of water electrolysis.

[0021] Preferably, the solvent of the raw material solution includes water;

[0022] Preferably, the weight ratio of the foam substrate, the transition metal element in the transition metal source, additive A and 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.

[0023] Preferably, the solvothermal temperature is 100~200℃, and more preferably 120~160℃;

[0024] Preferably, the solvothermal time is 2 to 5 hours.

[0025] In this invention, the P-source atmosphere is an atmosphere containing phosphine (PH3).

[0026] Preferably, the phosphine is obtained by thermal decomposition and volatilization of a phosphorus-containing solid.

[0027] For example, in this invention, the precursor material (phosphorus-containing solid) of the phosphorus source atmosphere and the precursor electrode can be placed in different areas of the tube furnace. The precursor material of the phosphorus source atmosphere is heated and volatilized to form a phosphorus-containing source atmosphere and then undergoes an in-situ gas phase phosphating deposition reaction with the precursor electrolysis.

[0028] The precursor material for the phosphorus source atmosphere can be, for example, hypophosphite. The weight ratio of the precursor material to the precursor electrode can be adjusted as needed, for example, the weight ratio can be 1:5 to 15.

[0029] In this invention, the temperature of vapor-phase phosphating is 500~850℃, and more specifically 700~800℃. For example, the vapor-phase phosphating temperature can be the temperature of the region where the precursor electrode is located.

[0030] Preferably, the time for gas-phase phosphating is 8 to 12 hours.

[0031] In this invention, the fluorine-containing source atmosphere contains at least one functional gas selected from sulfur hexafluoride and nitrogen trifluoride.

[0032] In this invention, the temperature of gas-phase fluorination is 100~250℃, and can be further 140~200℃;

[0033] Preferably, the gas-phase fluorination time is 2-4 hours.

[0034] The present invention also provides a water electrolysis method, which uses the metal fluoride@phosphide self-supporting electrode described in the present invention.

[0035] The present invention also provides a water electrolysis device comprising the aforementioned metal fluoride@phosphide self-supporting electrode, or prepared by means of the aforementioned metal fluoride@phosphide self-supporting electrode.

[0036] The water electrolysis equipment and method described in this invention utilize the metal fluoride@phosphide self-supporting electrode described in this invention. Other components and parts can be known in the industry, or can be reasonably controlled based on principles and methods known in the industry.

[0037] Beneficial effects

[0038] This invention provides a novel metal fluoride@phosphide self-supporting electrode, which innovatively pre-deposits a transition metal phosphide layer on a foam substrate and then in-situ composites the transition metal fluoride layer. Based on the combination of the composition and the hierarchical structure, the material's alkali resistance can be improved, and excellent HER and OER performance can be simultaneously achieved, thereby improving its performance in water electrolysis.

[0039] The present invention also provides a method for preparing the metal fluoride@phosphide self-supporting electrode, which innovatively modifies the transition metal on the foam substrate in advance by a solvothermal method assisted by additives A and B, and then uses it as a nucleation target to perform subsequent gas-phase phosphating and gas-phase fluorination treatments. This 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.

[0040] The present invention demonstrates 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 total hydrolysis potential can be reduced to 1.512V, exhibiting excellent performance. Attached Figure Description

[0041] Figure 1 The image shows the HER stability test results of the electrode prepared in Example 1.

[0042] Figure 2 The image shows the OER stability test result of the electrode prepared in Example 1. Detailed Implementation

[0043] The weight of a metal precursor is measured by the weight of the metal element contained therein.

[0044] Example 1

[0045] Step (1): Preprocessing

[0046] The nickel foam was ultrasonically cleaned in 1M hydrochloric acid solution for 15 minutes, followed by plasma cleaning, and then set aside for use.

[0047] Step (2): Hydrothermal reaction

[0048] A mixture of nickel foam (mass ratio 1:0.5:0.04:2), a metal precursor (a mixture of ferric nitrate, nickel nitrate, and cobalt nitrate with a Fe / Ni / Co weight ratio of 1:0.3:0.6), additive A (a mixture of citric acid and alginic acid with a mass ratio of 0.2:1, the mass of additive A being the total mass of both), and additive B (a mixture of dibutylamine and butylammonium chloride with a mass ratio of 0.5:1) was dissolved in a deionized water system (the concentration of the metal precursor in the solution was controlled at 2.5~3M). The foam substrate was then placed in this system and subjected to hydrothermal treatment at 150±10℃ for 3~4 hours. After the reaction was completed, the foam substrate was removed and dried to obtain metal-supported nickel foam (also known as self-supporting material).

[0049] Step (3): Phosphating treatment

[0050] The obtained self-supporting material was placed at the gas outlet of the atmosphere furnace, and sodium hypophosphite (the mass ratio of self-supporting material to sodium hypophosphite was 1:10) was placed at the gas inlet. The temperature of the self-supporting material area was controlled at 700°C and the temperature of the sodium hypophosphite area was controlled at 360°C. The self-supporting material was subjected to phosphating treatment for 10 hours and then naturally cooled.

[0051] Step (4): Surface fluorination

[0052] The obtained self-supporting material was placed in a 5wt% nitrogen trifluoride and nitrogen mixed atmosphere and subjected to heat treatment at 140°C for 3 hours under sealed conditions to obtain Ni-FMP.

[0053] Example 2

[0054] Compared to Example 1, the only difference was the type of foam substrate. The experimental groups were as follows:

[0055] Group A: The foam substrate is carbon paper;

[0056] Group B: The foam base is polyurethane;

[0057] The test was conducted in accordance with Example 1, and the results are shown in Table 1.

[0058] Example 3

[0059] Compared with Example 1, the only difference is that the type of metal source is changed, while the total amount of metal elements in the metal source remains the same as in Example 1. The experimental groups are as follows:

[0060] Group A: The metal source is ferric nitrate;

[0061] Group B: The metal source is nickel nitrate;

[0062] Group C: Metal source is cobalt nitrate

[0063] The test was conducted in accordance with Example 1, and the results are shown in Table 1.

[0064] Example 4

[0065] Compared with Example 1, the only difference is that the auxiliary agent A is changed, and the experimental groups are as follows:

[0066] Group A: Additive A is citric acid;

[0067] Group B: Additive A is alginate;

[0068] The dosage of additive A and other operations were the same as in Example 1, and the tests were conducted in the manner described in Example 1. The results are shown in Table 1.

[0069] Example 5

[0070] Compared with Example 1, the only difference is that the auxiliary agent B was changed, and the experimental groups were as follows:

[0071] Group A: Additive B is dibutylamine;

[0072] Group B: Additive B is butylammonium chloride;

[0073] The dosage of additive B and other operations were the same as in Example 1, and the tests were conducted in the manner described in Example 1. The results are shown in Table 1.

[0074] Example 6

[0075] 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 8 hours. In step 4, the atmosphere is a mixture of 2 wt% nitrogen trifluoride and nitrogen; the fluorination temperature is 200°C; and the time is 2 hours. All other operations and parameters are the same as in Example 1.

[0076] Comparative Example 1

[0077] Compared with Example 1, the only difference is that in step (2), no additive A was added, and all other operations and parameters are the same as in Example 1.

[0078] Comparative Example 2

[0079] Compared with Example 1, the only difference is that in step (2), no additive B was added, and all other operations and parameters are the same as in Example 1.

[0080] Comparative Example 3

[0081] Compared with Example 1, the only difference is that sodium hypophosphite was not added in step (3), while the other operations and parameters are the same as in Example 1.

[0082] Comparative Example 4

[0083] Compared with Example 1, the only difference is that step (3) was not performed, that is, phosphating was not performed. Instead, the product of step 2 was directly processed in step 4. All other operations and parameters are the same as in Example 1.

[0084] Comparative Example 5

[0085] Compared with Example 1, the only difference is that in step (4), a pure nitrogen atmosphere is used for heat treatment, while other operations and parameters are the same as in Example 1.

[0086] Comparative Example 6

[0087] Compared with Example 1, the only difference is that the gas phase phosphating process was not used. That is, sodium hypophosphite was used as the phosphorus source in step 2 (the molar ratio of metal in the metal source to P in the phosphorus source is 1:3). In addition, sodium hypophosphite was not added in step 3. All other operations and parameters were the same as in Example 1.

[0088] Comparative Example 7

[0089] 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 metal source is 10:1). The ammonium fluoride is placed at the inlet end, the self-supporting material is placed at the outlet end, the temperature is 300°C, and the heat treatment time and other operations and parameters are the same as in Example 1.

[0090] Comparative Example 8:

[0091] Compared with Example 1, the difference is that step 4, gas-phase fluorination, is performed first, followed by step 3, phosphating. All other operations and parameters are the same as in Example 1.

[0092] Comparative Example 9;

[0093] Compared with Example 1, the difference is that step 4 is omitted, and ammonium fluoride (the mass ratio of ammonium fluoride to metal source is 0.5:1) is added in step 2. All other operations and parameters are the same as in Example 1.

[0094] Electrochemical performance testing of materials:

[0095] Using a rotating disk electrode, with the Ni-FMP as the working electrode, mercury oxide as the reference electrode, and a platinum electrode as the counter electrode, the catalytic performance was tested in a three-electrode system. In a 1 M KOH system, the HER reaction was carried out at a current density of 10 mA cm⁻¹. -2 Overpotential (η) j=10 The voltage was 35.2 mV. In a 1M KOH system, the OER reaction was carried out at a current density of 10 mA cm⁻¹. -2 The potential below (E) j=10 The value is 1.416 V.

[0096] The final product was coated onto nickel foam and used as both the cathode and anode, with a 1 M KOH solution as the electrolyte. The water electrolysis performance was tested, achieving 10 mA cm⁻¹. -2 The water splitting current density requires a potential of only 1.524 V.

[0097]

[0098] As shown in Table 1, the innovative solvothermal modification of the foam substrate with transition metals assisted by additives A and B, followed by subsequent vapor-phase phosphating and fluorination treatments using these metals as nucleation targets, optimizes the material's hierarchical structure and improves its interfacial stability. This significantly enhances the alkali resistance, HER / OER performance, and overall water electrolysis performance of the prepared material. Furthermore, the optimal combination of metals, additives A and B further optimizes the physicochemical structure of the prepared electrode, unexpectedly further improving the HER / OER performance and overall water electrolysis performance.

Claims

1. A metal fluoride@phosphide self-supporting electrode, characterized in that, It includes a foam substrate and a metal fluoride@phosphide active layer composited on its surface, wherein the active layer includes a transition metal phosphide layer and a fluoride layer, wherein the phosphide layer is composited on the foam substrate side and the fluoride layer is disposed on the surface layer. The preparation method of the metal fluoride@phosphide self-supporting electrode is as follows: The raw material solution, including foam substrate, transition metal source, additive A and additive B, is pre-treated with solvothermal treatment to obtain a precursor electrode modified with transition metal. The precursor electrode is subjected to gas-phase phosphating in a P-source atmosphere, followed by gas-phase fluorination in a fluorine-source atmosphere to obtain the metal fluoride@phosphide self-supporting electrode. The transition metal source is one or more of the chloride, sulfate, sulfite, nitrate, and nitrite salts of transition metals; The transition metals include at least one of iron, cobalt, nickel, manganese, copper, and zinc; The aforementioned auxiliary agent A includes at least one of citric acid and alginate; The auxiliary agent B is at least one of C2-C6 fatty amines, fatty diamines and their hydrochlorides.

2. The metal fluoride@phosphide self-supporting electrode as described in claim 1, characterized in that, The foam substrate includes at least one of foam metal substrate, foam carbon substrate, and foam polymer substrate.

3. A method for preparing a metal fluoride@phosphide self-supporting electrode according to any one of claims 1 to 2, characterized in that, The raw material solution, including foam substrate, transition metal source, additive A and additive B, is pre-treated with solvothermal treatment to obtain a precursor electrode modified with transition metal. The precursor electrode is subjected to gas-phase phosphating in a P-source atmosphere, followed by gas-phase fluorination in a fluorine-source atmosphere to obtain the metal fluoride@phosphide self-supporting electrode. The transition metal source is one or more of the chloride, sulfate, sulfite, nitrate, and nitrite salts of transition metals; The transition metals include at least one of iron, cobalt, nickel, manganese, copper, and zinc; The aforementioned auxiliary agent A includes at least one of citric acid and alginate; The auxiliary agent B is at least one of C2-C6 fatty amines, fatty diamines and their hydrochlorides.

4. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 3, characterized in that, The solvent in the raw material solution includes water.

5. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 3, characterized in that, The weight ratio of the foam substrate, the transition metal element in the transition metal source, and additives A and B is 1:0.2~2:0.01~0.05:0.1~2.

5.

6. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 3, characterized in that, The temperature for solvothermal treatment is 100~200℃.

7. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 3, characterized in that, The solvothermal time is 2-5 hours.

8. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 3, characterized in that, The P-source atmosphere is an atmosphere containing phosphine.

9. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 8, characterized in that, The phosphorus-containing source atmosphere is obtained by thermal decomposition and volatilization of phosphorus-containing solids.

10. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 3 or 8, characterized in that, The temperature for vapor phase phosphating is 500~850℃.

11. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 10, characterized in that, The time for gas-phase phosphating is 8~12 hours.

12. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 3, characterized in that, The fluorine-containing source atmosphere contains at least one functional gas selected from sulfur hexafluoride and nitrogen trifluoride.

13. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 3 or 12, characterized in that, The temperature for gas-phase fluorination is 100~250℃.

14. The method for preparing the metal fluoride@phosphide self-supporting electrode as described in claim 13, characterized in that, The time for gas-phase fluorination is 2-4 hours.

15. A method for water electrolysis, characterized in that, The electrode is a metal fluoride@phosphide self-supporting electrode as described in any one of claims 1 to 2 or a metal fluoride@phosphide self-supporting electrode as described in any one of claims 3 to 14.

16. A water electrolysis device, characterized in that, The electrode comprises 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 14, or is prepared by the metal fluoride@phosphide self-supporting electrode.

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