Graphite / metal hydroxide composite oer electrode and preparation and application thereof

Abstract

This invention belongs to the field of water electrolysis, specifically relating to a method for preparing a graphite / metal hydroxide composite OER electrode. The method involves immersing a graphite substrate in an aqueous metal solution and pretreating it under thermal and / or electrical intensification to obtain a pretreated graphite substrate. The pretreated graphite substrate is then reacted in an alkaline solution with a solute concentration of 1M or higher to obtain the graphite / metal hydroxide composite OER electrode. The thermal treatment temperature is above 50°C. The aqueous metal solution contains dissolved metal ions, wherein the metal ions are at least one selected from Ni, Fe, Co, Mn, Cr, and Cu. This invention also includes the OER electrode prepared by the method and its applications. The OER electrode prepared by the method of this invention exhibits OER catalytic stability under high current and high chlorine environments, and is an OER catalytic material that combines excellent OER activity, high current cycling stability, and chlorine resistance.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis, and more specifically to the field of OER catalytic materials. Technical Background

[0002] The escalating energy crisis and the environmental degradation caused by pollutant emissions have prompted people to explore the use of greener and cleaner energy sources. Developing and utilizing renewable energy sources such as wind and solar power, converting them into electricity, and storing this electricity as clean hydrogen have become crucial aspects of energy conservation and emission reduction. Among these, the electrolysis of water using electricity obtained from renewable energy sources to produce hydrogen, and the subsequent storage, transportation, and use of this hydrogen energy, are key areas of research. The main reactions in water electrolysis are the oxygen evolution reaction (OER) at the anolyte and the hydrogen evolution reaction (HER) at the catholyte.

[0003] Oeroderative electrocatalysts (OERs) are not only crucial modules in electrolyzers but also essential components in energy conversion and storage devices such as rechargeable metal-air batteries and regenerative fuel cells. However, the four-electron reaction process of OERs and the adsorption energy ratios between reaction intermediates introduce large inherent overpotentials and slow reaction kinetics into OER catalysts. Developing advanced electrocatalysts with high activity and stability based on non-precious metal materials remains a significant challenge. Furthermore, conventional water electrolysis for hydrogen production requires freshwater, and the scarcity of freshwater severely hinders the further development of green hydrogen production through water electrolysis; however, most of the Earth is covered by seawater, providing abundant marine resources. Therefore, the preparation of OER catalysts for water electrolysis that can be used in seawater is of great significance for the development of the water electrolysis for hydrogen production industry.

[0004] Currently, researchers are making continuous breakthroughs in the performance and stability of alkaline water electrolysis OER catalysts. The most eye-catching are the catalysts that are directly grown or sprayed on substrates with large specific surface areas, such as nickel foam and copper foam. Among them, NiFe-hydroxide, as a widely studied catalyst, has shown unparalleled catalytic activity. However, with the increasing demands on the application current of catalysts, in-situ grown catalysts have revealed the disadvantage of being easily detached by large air bubbles and losing their activity, making the improvement of the stability of OER catalysts a significant challenge.

[0005] In summary, the challenge lies in developing OER catalysts that possess both high activity and high stability under high current, especially those resistant to Cl- in seawater. - The corrosion impact of OER catalysts has significant theoretical and practical implications. Summary of the Invention

[0006] To address the current issues of low activity and poor stability of OER catalysts in the field of water electrolysis for hydrogen production, and the fact that most catalysts cannot be used stably in seawater, this invention provides a method for preparing a graphite / metal hydroxide composite OER electrode, aiming to obtain a novel OER catalyst that combines excellent OER activity, high-current cycling stability, and chlorine resistance.

[0007] The second objective of this invention is to provide a graphite / metal hydroxide composite OER electrode prepared by the aforementioned method.

[0008] The third objective of this invention is to provide the graphite / metal hydroxide composite OER electrode for use in water electrolysis.

[0009] To obtain ideal OER catalytic activity, the conventional approach is to composite hydroxide active components on the surface of graphite. While this achieves ideal OER performance, the material's stability, especially under high current and high-chlorine systems, is not ideal. To address this issue, this invention initially attempted an improved approach by filling the pore structure and interlayer spaces of graphite with metal hydroxide active components. However, early research showed that this approach was difficult to achieve the desired results. The main difficulties were: (1) the difficulty in selectively nucleating metal hydroxides in the pores and interlayer spaces of graphite; and (2) the limited activity of metal hydroxides located in the pores and interlayer spaces of graphite, which significantly affected OER catalytic activity, making it difficult to obtain a material that balances activity and stability. To address the problems encountered in implementing this novel approach, this invention, after in-depth research, provides the following improvement:

[0010] A method for preparing a graphite / metal hydroxide composite OER electrode involves immersing a graphite substrate in an aqueous metal solution and pretreating it under thermal and / or electrical strengthening to obtain a pretreated graphite substrate; then reacting the pretreated graphite substrate in an alkaline solution with a solute concentration of 1 M or higher to obtain the graphite / metal hydroxide composite OER electrode.

[0011] The heat treatment temperature is above 50°C;

[0012] The metal aqueous solution is an aqueous solution containing dissolved metal ions, wherein the metal ions are at least one selected from Ni, Fe, Co, Mn, Cr, and Cu.

[0013] This invention innovatively involves thermally and / or electrically strengthening a graphite substrate in a metal aqueous solution, followed by a reaction in an alkali environment. Furthermore, by controlling the alkali concentration, this process unexpectedly induces deep nucleation and growth of metal hydroxides within the graphite substrate, optimizing its physicochemical structure, defects, and orientation. The method described in this invention addresses the negative impact of deep metal hydroxide nucleation on OER activity. Moreover, it significantly improves OER catalytic stability under high current and chlorine resistance, resulting in an OER catalytic material that combines excellent OER activity, high current cycling stability, and chlorine resistance.

[0014] In this invention, the graphite substrate is a porous graphite plate; for example, it can be a conventional graphite electrode (graphite current collector).

[0015] In this invention, the density of the graphite substrate is between 1.65 and 1.85 g / cm³. -3 .

[0016] Preferably, the graphite substrate has undergone a pre-treatment of surface oxidation. The surface oxidation process can be conventional. For example, the graphite substrate can be subjected to surface oxidation in a mixed acid containing sulfuric acid and nitric acid.

[0017] In this invention, the metal ions include divalent and trivalent metal ions. This invention demonstrates that by combining these composite ions, along with the strengthening and alkaline reaction processes described herein, the physicochemical structure, such as morphology, orientation, and defects, of metal hydroxides grown deep in graphite can be optimized. For example, layered bimetallic hydroxides with controllable defects can be obtained, further improving the OER activity and high-current and under-chlorine OER catalytic stability of the prepared materials.

[0018] In this invention, the divalent metal ions include Ni. 2+ Fe 2+ Co 2+ Mn 2+ Cr 2+ Cu 2+ At least one of the following; the trivalent metal ions include Fe 3+ Co 3+ Cr 3+ At least one of the following; and the divalent metal and the trivalent metal are different metallic elements.

[0019] Preferably, the molar ratio of the divalent metal ions to the trivalent metal ions is 1 to 5:1, and more preferably 2 to 4:1.

[0020] Preferably, the concentration of the solute in the metal aqueous solution can be above 0.1M, more preferably 0.5-5M, and even more preferably 3-5M.

[0021] Preferably, an acid is also added to the aqueous metal solution.

[0022] Preferably, the acid includes at least one of hydrochloric acid and sulfuric acid.

[0023] In this invention, the concentration of acid in the aqueous metal solution can be 0.1–0.5 M.

[0024] In this invention, a graphite substrate is immersed in the aforementioned aqueous metal solution and heated and held at that temperature to perform a thermal strengthening treatment. Research in this invention shows that, through the aforementioned thermal strengthening treatment, combined with the aforementioned temperature and concentration of alkaline reaction, the growth behavior and orientation of metal hydroxides in the pores and interlayers of graphite can be optimized. This further enhances the OER activity and stability of the material under high current and high chloride ion concentrations.

[0025] Preferably, the temperature for heat strengthening is 50–150°C; more preferably 80–100°C.

[0026] Preferably, the heat strengthening time is more than 5 hours, and considering the processing efficiency, it can be further 5 to 10 hours.

[0027] In this invention, the electro-strengthening step is as follows: using an Hg / HgO electrode as a reference electrode, a platinum sheet as a counter electrode, and the graphite substrate as a working electrode, the electrodes are placed in the metal aqueous solution for electro-strengthening treatment, wherein the current on the working electrode is set to -10 mA / cm². -2 ~-20mAcm -2 .

[0028] In this invention, the electro-enhancing process can further synergistically improve the growth efficiency and behavior of metal hydroxides in the deep layers of graphite, thereby better balancing preparation efficiency and OER performance of the material.

[0029] In this invention, the electro-strengthening time is 1 to 2 minutes.

[0030] In this invention, thermal strengthening can be performed in advance, followed by electrical strengthening treatment.

[0031] In this invention, under the aforementioned strengthening treatment, the combination of alkaline reaction solutes can optimize the growth behavior of metal hydroxides in the pores and interlayers of the graphite substrate, as well as the exposure orientation and defects. This allows the prepared material to have both excellent OER activity, high current stability, and chlorine resistance.

[0032] In this invention, the solute in the alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide;

[0033] In this invention, the concentration of the solute in the alkaline solution is 1–6 M, preferably 3–5 M. Studies have shown that, under the aforementioned enhanced process, combined with optimized control of the alkaline concentration, the growth behavior and physicochemical morphology of the metal hydroxide can be optimized, further improving its OER activity, high-current stability, and chlorine resistance.

[0034] In this invention, the temperature during the reaction stage is 20–90°C. Considering energy consumption and operation, it can be further set to room temperature, for example, 20–40°C.

[0035] In this invention, the reaction time is 0.5 h or more, preferably 0.5 to 1.5 h.

[0036] The present invention also includes a graphite / metal hydroxide composite OER electrode prepared by the preparation method described above; comprising a graphite substrate and a defective metal hydroxide filling the porous structure and interlayer of the graphite substrate.

[0037] The preparation method described in this invention can endow the prepared material with special physicochemical properties, and the material with special properties obtained by the preparation method can take into account excellent OER activity, high current stability and chlorine resistance.

[0038] In this invention, the loading of metal hydroxide in the graphite / metal hydroxide composite OER electrode is 10-20 mg per square centimeter of graphite.

[0039] The present invention also provides the application of the graphite / metal hydroxide composite OER electrode prepared by the above preparation method, which is used as an OER catalyst for water electrolysis.

[0040] The application described in this invention uses it as an anode for the electrolysis of alkaline aqueous solutions and / or alkaline brine.

[0041] In the application described in this invention, the concentration of the alkaline component in the alkaline aqueous solution is above 0.1M, preferably 1 to 6M.

[0042] In the application described in this invention, the brine is an aqueous solution containing a metal chloride. For example, the metal chloride includes at least one of sodium chloride, potassium chloride, and lithium chloride.

[0043] In the application described in this invention, the concentration of metal chloride in the brine is above 0.1M, further can be 0.1-5M, and even further can be 0.5-3M.

[0044] In the application described in this invention, the brine is seawater.

[0045] Beneficial effects

[0046] This invention innovatively involves thermally and / or electrically strengthening a graphite substrate in the aforementioned aqueous metal solution, followed by a reaction in an alkali solution, and combined with the joint control of the alkali concentration. This allows for the unexpected growth of the aforementioned metal hydroxide in the pores and interlayer of the graphite substrate, and optimizes its physicochemical structure and defects. This improves the OER activity of the material, and also enhances its OER catalytic stability under high current and chlorine resistance.

[0047] For example, the OER catalyst prepared by the method described in this invention can be used under alkaline conditions with high current operation and exhibits high stability. It can also be used in the electrolysis of seawater and exhibits high stability. Attached Figure Description

[0048] Figure 1 SEM images of OER polarization obtained in Example 1

[0049] Figure 2 The polarization curves of the OER prepared in Example 1 are compared with those of the pure graphite plate electrode used in the substrate.

[0050] Figure 3 The OER prepared in Example 1 was subjected to a 1A cm reaction in 1M KOH. -2 The curve of constant current test.

[0051] Figure 4 The OER obtained in Example 1 was subjected to 0.5 Acm in 1M KOH. -2 Constant current test

[0052] Figure 5 The OER polarization curves of the OER prepared in Example 1 in 1M KOH and 1M KOH+0.5M NaCl simulated alkaline seawater environments are shown.

[0053] Figure 6 The OER prepared in Example 1 was subjected to a 1Acm test in a simulated alkaline seawater environment of 1M KOH + 0.5M NaCl. -2 Curve of constant current test.

[0054] Figure 7 The OER1M KOH + 0.5M NaCl prepared in Example 1 was subjected to a 1Acm test in a simulated alkaline seawater environment. -2 OER polarization curves before and after constant current testing.

[0055] Figure 8 This is a polarization curve of the OER electrode obtained under various conditions in Example 2.

[0056] Figure 9 This is a polarization curve of the OER electrode obtained under various conditions in Example 3.

[0057] Figure 10 This is the polarization curve of the OER electrode obtained in Example 4.

[0058] Figure 11 The OER electrodes of Example 1 and Comparative Example 1 were subjected to a 1Acm test in an electrolyte of 1M KOH + 3M NaCl. -2 The curve of constant current test.

[0059] Figure 12 These are the OER polarization curves of the OER electrodes of Example 1 and Comparative Example 2 in an electrolyte of 1M KOH + 3M NaCl. Detailed Implementation

[0060] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well-known to those skilled in the art. This invention provides the application of the OER catalyst described above in water electrolysis. This invention does not specifically limit the method of application; it can be applied according to methods well-known in the art. The invention will be further illustrated below with specific examples. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0061] Example 1:

[0062] A method for preparing a catalyst that operates efficiently and stably in seawater and at industrial current densities includes the following steps:

[0063] Step 1:

[0064] Prepare a mixed solution of nickel nitrate and ferric nitrate, controlling the ratio, wherein the concentration of nickel nitrate is controlled at 3M, the molar ratio of nickel to iron is 3:1, and add 0.2M sulfuric acid solution dropwise to control the pH of the system between 1 and 2, thus obtaining a metal solution.

[0065] Step 2:

[0066] Prepare a concentrated acid solution with a volume ratio of concentrated sulfuric acid to concentrated nitric acid of 3:1. Immerse a 10*10*2mm graphite sheet in the concentrated acid solution from step 2 for 5–10 seconds. Clean and dry the graphite sheet to obtain surface-treated graphite.

[0067] Step 3: Immerse the surface-treated graphite from Step 2 in the metal solution from Step 1, and heat strengthen it at 80℃ (marked as T) under normal pressure for 5-6 hours; then remove the graphite and dry it to obtain modified graphite sheets (also known as Graphite-M(NO3)x);

[0068] Step 4: Immerse the modified graphite sheet obtained in Step 3 in a 4M sodium hydroxide solution (alkaline solution) at 30°C for 1 hour. Then remove the electrode sheet and rinse it clean to obtain the graphite / metal hydroxide composite OER electrode (also known as Graphite-M(OH)x). See the cross-sectional SEM image below. Figure 1 .

[0069] Step 5: OER Test

[0070] Step 5-1: Test 1: 1M KOH electrolysis test:

[0071] It can be used directly for OER testing under alkaline solution conditions, for measuring LSV curves or constant current testing.

[0072] The conditions for OER testing are as follows: a platinum sheet is used as the counter electrode, an Hg / HgO electrode is used as the reference electrode, and the graphite / metal hydroxide composite OER electrode obtained in this invention is used as the working electrode. 1M KOH is used as the electrolyte, and a three-electrode system is used for testing. The scanning speed of the polarization curve is 5mV / s, and the scanning window is 0.1 to 1V relative to the reference electrode.

[0073] The polarization curve of Example 1 is as follows Figure 2 As shown in Figure 1. At 1Acm -2 and 0.5Acm -2 The constant current test results under industrial current are as follows Figure 3 as well as Figure 4 As shown.

[0074] Step 5-2: Test 2: Electrolysis test of 1M KOH + 0.5M NaCl solution:

[0075] Based on the OER test in step 5-1, the electrolyte was replaced with 1M KOH + 0.5M NaCl to simulate alkaline seawater electrolysis. Figure 5 , Figure 6 as well as Figure 7 All studies provide the performance of the catalysts prepared by this method in simulated alkaline seawater electrolysis.

[0076] Example 2

[0077] Compared with Example 1, the only difference is that the temperature T in step 3 is changed to 25°C, 50°C, 90°C or 120°C, while other operations and parameters are the same as in Example 1.

[0078] The polarization results of OER electrodes prepared at different intensification temperatures are shown in the figure. Figure 8 (Test according to step 5-1).

[0079] Figure 8 It can be seen that better results can be obtained at temperatures above 80℃.

[0080] Example 3

[0081] Compared with Example 1, the only difference is that the concentration of the alkali in step 4 is changed to 0.1M or 1M respectively; all other operations and parameters are the same as in Example 1.

[0082] The polarization effect of OER electrodes with different alkali concentrations was tested according to step 5-1 of Example 1, and the results are shown in [Figure 1]. Figure 9 . Figure 9 It can be seen that higher alkali concentrations yield better results, while lower alkali concentrations produce poorer results.

[0083] Example 4

[0084] Compared to Example 1, the only difference is that in step 3, after thermal strengthening, an electro-strengthening treatment is performed. The electro-strengthening step involves directly using the thermally strengthened graphite plate as the working electrode, the thermally strengthened solution system as the electrolyte, and inserting a Hg / HgO electrode (reference electrode) and a platinum sheet (counter electrode) into the system to form a three-electrode system, applying a constant current of -10 to -20 mA / cm². -2 The current was applied for electrical enhancement for 90±10s. Then the graphite was removed and dried to obtain modified graphite sheets, which were then subjected to subsequent steps 4 and 5.

[0085] The polarization effect of its OER electrode was tested according to step 5-1 of Example 1, and the results are shown in [the table below]. Figure 10 This indicates that it has higher activity compared to Example 1.

[0086] Comparative Example 1

[0087] NiFe hydroxide loaded on nickel foam was prepared using a hydrothermal method for OER testing. The specific method was as follows: 3 mmol nickel nitrate + 1 mmol ferric nitrate + 15 mmol urea + 5 mmol ammonium fluoride were weighed and dissolved in 60 mL deionized water, stirred thoroughly, and transferred to a 100 mL hydrothermal reactor. A 3×4 cm piece of nickel foam was immersed in the solution, and the reactor was placed in an oven and maintained at 140 °C for 12 h. After the reaction was complete, the reactor was removed, rinsed clean, and tested under the conditions of step 5 in Example 1. Subsequently, the reaction was carried out at 1 A cm... -2 Perform constant current stability test.

[0088] The constant current test effect of the OER electrode of Example 1 and Comparative Example 1 was tested according to step 5-1 of Example 1 (the electrolyte in the electrolysis stage was 1M KOH + 3M NaCl aqueous solution), and the results are shown in [the original text is missing]. Figure 11 .

[0089] Comparative Example 2

[0090] Unlike Comparative Example 1, the nickel foam was replaced with a graphite plate as the substrate.

[0091] Following the test procedure in step 5-1 of Example 1, a polarization test was conducted in simulated alkaline seawater using 1M KOH + 3M NaCl. The test results are shown below. Figure 12 As can be seen, the method of the present invention can exhibit excellent stability under high chlorine conditions.

Claims

1. A method for preparing a graphite / metal hydroxide composite OER electrode, characterized in that, A pretreated graphite substrate was prepared by immersing a graphite substrate in an aqueous metal solution and pretreating it under thermal and electrical strengthening conditions. The pretreated graphite substrate is then reacted in an alkaline solution with a solute concentration of 1M or higher to obtain the graphite / metal hydroxide composite OER electrode. The aforementioned aqueous metal solution is an aqueous solution containing dissolved metal ions, including divalent and trivalent metal ions; the divalent metal ions include Ni. 2+ The trivalent metal ions mentioned include Fe. 3+ The molar ratio of the divalent metal ions to the trivalent metal ions is 1~5:

1. The graphite substrate is a porous graphite plate; the graphite substrate is pre-treated with surface oxidation, the step of which is: the graphite substrate is placed in a mixed acid containing concentrated sulfuric acid and concentrated nitric acid for surface oxidation treatment. The temperature for heat strengthening is 80~100℃; the heat strengthening time is more than 5 hours. The electro-enhancing steps are as follows: using an Hg / HgO electrode as a reference electrode, a platinum sheet as a counter electrode, and the graphite substrate as a working electrode, each electrode is placed in the aqueous metal solution for electro-enhancing treatment. The current on the working electrode is set to -10 mA cm⁻¹. -2 ~-20 mA cm -2 .

2. The preparation method according to claim 1, characterized in that, The density of the graphite substrate is between 1.65 and 1.85 g / cm³. -3 .

3. The preparation method according to claim 1, characterized in that, In the aforementioned aqueous metal solution, the concentration of the solute is above 0.1 M.

4. The preparation method according to claim 3, characterized in that, In the aforementioned aqueous metal solution, the concentration of the solute is 0.5~5M.

5. The preparation method according to claim 1, characterized in that, The aforementioned aqueous metal solution also contains an acid. The acid mentioned includes at least one of hydrochloric acid and sulfuric acid.

6. The preparation method according to claim 1, characterized in that, The electro-enhancing time is 1~2 minutes.

7. The preparation method according to claim 1, characterized in that, The solute in the alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide; The concentration of the solute in the alkaline solution is 1~6M; The temperature during the reaction phase is 20-90℃; The reaction time is more than 0.5 hours.

8. The preparation method according to claim 7, characterized in that, The concentration of the solute in the alkaline solution is 3~5M; The reaction time is 0.5-1.5 h.

9. A graphite / metal hydroxide composite OER electrode prepared by the preparation method according to any one of claims 1 to 8; characterized in that, This includes a graphite substrate, and defective metal hydroxides filling the porous structure and interlayer of the graphite substrate; In the graphite / metal hydroxide composite OER electrode, the loading of metal hydroxide in each square centimeter of graphite is 10~20 mg.

10. The application of a graphite / metal hydroxide composite OER electrode prepared by the method according to any one of claims 1 to 8, characterized in that, It was used as an OER catalyst for water electrolysis.

11. The application as described in claim 10, characterized in that, It is used as the anode for the electrolysis of alkaline aqueous solutions and / or alkaline brine.

12. The application as described in claim 11, characterized in that, The alkaline component of the alkaline aqueous solution has a concentration of 0.1 M or higher.

13. The application as described in claim 12, characterized in that, The concentration of the alkaline component in the alkaline aqueous solution is 0.5~6M.

14. The application as described in claim 11, characterized in that, The brine is an aqueous solution containing metal chlorides.

15. The application as described in claim 14, characterized in that, The metal chlorides include at least one of sodium chloride, potassium chloride, and lithium chloride.

16. The application as described in claim 14, characterized in that, The concentration of metal chlorides in the brine is above 0.1 M.

17. The application as described in claim 14, characterized in that, The brine mentioned is seawater.

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