A method for preparing a catalyst, the product and the use thereof

Abstract

The present application relates to the field of electrolytic water anode oxygen evolution catalyst, in particular to a catalyst preparation method, product and application. The catalyst preparation method comprises the following steps: step 1, mixing fly ash and NaHCO3 uniformly and then calcining to obtain activated fly ash; step 2, mixing Co source, Fe source, ammonium chloride and ammonia water in water uniformly, then adding the activated fly ash and mixing uniformly, and then carrying out hydrothermal reaction to obtain FA-CoFeSi; step 3, mixing the FA-CoFeSi and nickel source in water uniformly, then adding a reducing agent to react to obtain the catalyst. The current density of the catalyst prepared by the method of the present application remains at 83% after 48 hours of continuous operation under constant voltage. The present application provides a low-cost preparation method for electrolytic water oxygen evolution catalyst and realizes high-value utilization of fly ash.

Description

Technical Field

[0001] This invention relates to the field of anodic oxygen evolution catalysts for water electrolysis, and in particular to a method for preparing a catalyst, a product, and its application. Background Technology

[0002] The rapid development of human society has led to a significant increase in energy consumption; currently, over 60% of global energy comes from the combustion of fossil fuels. The combustion of fossil fuels emits large amounts of toxic and harmful gases such as carbon oxides and sulfides, causing environmental pollution and global warming, among other problems. Therefore, developing environmentally friendly energy sources is crucial for addressing resource depletion and environmental pollution.

[0003] Hydrogen has a high energy density, and its combustion products are pollution-free and easy to store. Currently, hydrogen can be produced through steam methane conversion, natural gas reforming, and petroleum cracking, but these methods all cause some environmental pollution. Electrolysis of water to produce hydrogen is considered a promising method for solving the energy and environmental problems caused by fossil fuel consumption. The water electrolysis reaction consists of two half-reactions: the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. The OER reaction at the anode is a four-electron transfer reaction, with slow kinetics, becoming the main bottleneck for improving the efficiency of electrocatalytic water splitting. Currently, representative OER catalysts for water electrolysis are mostly precious metal catalysts such as iridium dioxide (IrO2) and ruthenium dioxide (RuO2), whose high price limits their large-scale industrial production. Current research focuses on preparing low-cost, environmentally friendly OER catalysts for water electrolysis.

[0004] Fly ash is a solid waste generated by coal-fired power plants and other coal-fired enterprises. It is widely available and inexpensive. Using fly ash as a carrier can significantly reduce the cost of catalyst preparation, facilitating large-scale production and application, realizing the resource utilization of solid waste, reducing environmental pollution and land occupation caused by fly ash, and aligning with the concept of sustainable development. However, the resource utilization of fly ash faces significant challenges, primarily because silica (SiO2) in fly ash exists mostly in a crystalline state. The extremely high bond energy and strong chemical stability of the Si-O chemical bond greatly limit its chemical activity, increasing the difficulty of the reaction. Therefore, it is necessary to research a low-cost catalyst with high catalytic activity and good stability. Summary of the Invention

[0005] Based on the above, the present invention provides a method for preparing a catalyst, a product thereof, and its application.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] The first aspect of this invention provides a method for preparing a catalyst, comprising the following steps:

[0008] Step 1: Mix fly ash and NaHCO3 evenly and then calcine to obtain activated fly ash;

[0009] Step 2: Co source, Fe source, ammonium chloride and ammonia water are added to water and mixed well, then activated fly ash is added and mixed well, followed by hydrothermal reaction to obtain FA-CoFeSi;

[0010] Step 3: After mixing the FA-CoFeSi with the nickel source in water, a reducing agent is added to react and the catalyst (Ni@FA-CoFeSi) is obtained.

[0011] A second aspect of the present invention provides a catalyst prepared according to the preparation method described above.

[0012] A third aspect of the present invention provides the application of the above-mentioned catalyst in the electrolysis of water for oxygen evolution.

[0013] The present invention discloses the following technical effects:

[0014] This invention provides a method for preparing a catalyst for oxygen evolution through water electrolysis of solid waste fly ash. The method involves calcining crystalline SiO2 with NaHCO3 to convert it into active calcium silicate Ca2SiO4, simultaneously releasing CO2 and H2O gases to etch a porous structure and increase the specific surface area of ​​the support. A one-step hydrothermal method is employed, which can be carried out at relatively low temperatures (180℃) and autogenous pressures, achieving the directional conversion of silicon oxides and metal ion exchange in fly ash. Using fly ash as a silicon source, and combining it with inexpensive transition metal salts (CoCl2) and (FeCl2) to prepare fly ash-based cobalt iron silicate as a catalyst support, the production cost is significantly reduced. A nickel catalyst (Ni@FA-CoFeSi) is prepared on the support via a reduction method, which exhibits high performance at 10 mA cm⁻¹. -2 The overpotential at the current density is as low as 176 mV, exhibiting excellent catalytic activity. Furthermore, nickel itself possesses advantages such as low cost, abundant reserves, and good stability, further highlighting the application potential of this catalyst.

[0015] The catalyst (Ni@FA-CoFeSi) prepared using the method of this invention maintained a current density of 83% after 48 hours of continuous operation under constant voltage. This invention provides a low-cost preparation method for oxygen evolution catalysts in water electrolysis, enabling the high-value utilization of fly ash. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a scanning electron microscope (SEM) image of Ni@FA-CoFeSi.

[0018] Figure 2 This is a transmission electron microscope (TEM) image of Ni@FA-CoFeSi.

[0019] Figure 3 The XRD patterns are of activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi and Ni@FA-CoFeSi prepared in Examples 1-4.

[0020] Figure 4 LSV diagrams of activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi and Ni@FA-CoFeSi prepared in Examples 1-4.

[0021] Figure 5 Tafel slope diagrams of activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi and Ni@FA-CoFeSi prepared in Examples 1-4.

[0022] Figure 6 EIS diagrams of activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi and Ni@FA-CoFeSi prepared in Examples 1-4.

[0023] Figure 7 Cdl diagrams of activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi and Ni@FA-CoFeSi prepared in Examples 1-4.

[0024] Figure 8 The chronoamperometry diagram for Ni@FA-CoFeSi is shown. Detailed Implementation

[0025] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0026] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0028] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0029] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0030] This invention utilizes cobalt-iron modified fly ash as a support for an anode catalyst in water electrolysis for oxygen evolution. The method involves high-temperature calcination and activation of raw fly ash with sodium bicarbonate to generate activated fly ash. The activated fly ash is then modified with cobalt-iron via a one-step hydrothermal method to produce a fly ash-based cobalt-iron silicate support. This support is then loaded with metallic nickel using a reduction method and used as a catalyst for water electrolysis for oxygen evolution.

[0031] The first aspect of this invention provides a method for preparing a catalyst, comprising the following steps:

[0032] Step 1: Mix fly ash and NaHCO3 evenly and then calcine to obtain activated fly ash;

[0033] Step 2: Co source, Fe source, ammonium chloride and ammonia water are added to water and mixed well, then activated fly ash is added and mixed well, followed by hydrothermal reaction to obtain FA-CoFeSi;

[0034] Step 3: After mixing the FA-CoFeSi with the nickel source in water, a reducing agent is added to react and the catalyst (Ni@FA-CoFeSi) is obtained.

[0035] In a preferred embodiment of the present invention, in step 1, the mass ratio of the fly ash to the NaHCO3 is 1:0.1~1.2.

[0036] In a preferred embodiment of the present invention, in step 1, the calcination temperature is 700℃~900℃ and the time is 1~3h.

[0037] Step 1 further includes the step of placing the calcined product in water and stirring for 6 hours, followed by washing and drying.

[0038] The purpose of stirring the calcined product in water is to remove NaHCO3, Na2O and Na2SiO3.

[0039] In a preferred embodiment of the present invention, in step 2, the Co source is cobalt chloride; the Fe source is ferrous chloride; the molar ratio of the Co source, Fe source, and ammonium chloride is 1:1:5; the volume ratio of the Co source to the ammonia water is 1 mmol:4 mL; the volume ratio of the Co source to the water is 1 mmol:40 mL; and the volume ratio of the Co source to the activated fly ash is 1 mmol:60 mg.

[0040] In a preferred embodiment of the present invention, in step 2, the temperature of the hydrothermal reaction is 180°C and the time is 24 hours.

[0041] The process further includes washing and drying the precipitate obtained from the hydrothermal reaction after the hydrothermal reaction is completed.

[0042] In a preferred embodiment of the present invention, in step 3, the nickel source is nickel chloride; the mass ratio of FA-CoFeSi to the nickel source is 1:1 to 1.1; the reducing agent is NaBH4; and the mass ratio of FA-CoFeSi to the reducing agent is 1:5 to 6.

[0043] In a preferred embodiment of the present invention, the reaction time in step 3 is 4 hours.

[0044] Magnetic stirring is also performed during the reaction process.

[0045] Step 3 further includes washing and drying the product after the reaction is complete.

[0046] In step 3, FA-CoFeSi and the nickel source are mixed in water by ultrasonication for 1 hour.

[0047] This invention alters the form and bonding mode of silica in fly ash by mixing and calcining NaHCO3 with fly ash, thereby enhancing its reactivity. Furthermore, this invention utilizes iron-cobalt bonds to bond silicon in fly ash as a support for nickel, enhancing the oxygen evolution performance of the catalyst and improving its stability.

[0048] This invention first modifies fly ash by modifying it with iron, cobalt monometals, and cobalt-iron bimetals, respectively. At 10 mA cm⁻¹ -2At the specified current density, the overpotential of fly ash-based iron silicate (FA-FeSi) was 428 mV, that of fly ash-based cobalt silicate (FA-CoSi) was 386 mV, and that of fly ash-based cobalt iron silicate (FA-CoFeSi) was 377 mV. Although FA-CoFeSi showed the lowest overpotential among the three catalysts, its oxygen evolution performance still needed further optimization, so nickel was introduced. The catalyst prepared by hydrothermal doping of fly ash with iron, cobalt, and nickel (FA-CoFeNiSi) had an overpotential of 414 mV, the overpotential of nickel alone loaded on fly ash (Ni@FA) was 303 mV, and the overpotential of nickel-loaded fly ash-based cobalt iron silicate (Ni@FA-CoFeSi) was 176 mV. These results indicate that only when cobalt and iron are doped into the fly ash bulk phase to form a fly ash-based cobalt iron silicate support, and then further loaded with nickel, can the prepared catalyst exhibit optimal electrochemical oxygen evolution performance.

[0049] A second aspect of the present invention provides a catalyst prepared according to the preparation method described above.

[0050] A third aspect of the present invention provides the application of the above-mentioned catalyst in the electrolysis of water for oxygen evolution.

[0051] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0052] The fly ash used in this embodiment of the invention is Grade I fly ash that has passed through a 325-mesh sieve.

[0053] The concentration of ammonia water (NH3·H2O) used in this embodiment of the invention is 25%.

[0054] The testing method involved in this invention is as follows:

[0055] All electrochemical evaluation experiments were performed using a three-electrode system with a CHI660E electrochemical workstation manufactured by Shanghai Chenhua Co., Ltd. Catalyst ink was prepared by ultrasonically dispersing 5 mg of catalyst, 2 mg of conductive carbon black, 450 μL of ethanol, and 50 μL of naphthol in a 2 mL centrifuge tube. OER performance testing was conducted in 1 M KOH solution, using a glassy carbon electrode loaded with the catalyst as the working electrode, an Hg / HgO electrode as the reference electrode, and a carbon rod as the counter electrode. Linear sweep voltammetry (LSV) was performed at a scan rate of 5 mV / s. -1 By plotting the LSV curve, the corresponding Tafel curve can be drawn. From the Tafel curve, the Tafel slope and the Tafel equation can be obtained:

[0056] ;

[0057] Where j is the current density (mA·cm) -2 ), where a is the Tafel constant and b is the Tafel slope (mV·dec). -1 Electrochemical impedance spectroscopy (EIS) was performed at 0.55 V, with a frequency range of 100 kHz to 0.1 Hz and an amplitude of 5 mV. Measurements were taken at 10 mV·s. -1 20 mV·s -1 30 mV·s -1 40 mV·s -1 50 mV·s -1 60 mV·s -1 70 mV·s -1 The electrochemical double-layer capacitance (Cdl) was calculated by cyclic voltammetry at a scan rate of [missing value]. For OER stability testing, 300 μL of catalyst ink was dropped onto a 1×1 cm [missing value]. 2 The carbon paper was dried naturally at room temperature and used as the working electrode in the test. An Hg / HgO electrode was used as the reference electrode, and a carbon rod as the counter electrode. The change in current over time was measured under a constant potential of 1.671 V vs. RHE.

[0058] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0059] Example 1

[0060] Step 1, Preparation of activated fly ash (FA): 3 g of fly ash and 2.1 g of NaHCO3 were thoroughly ground and placed in a ceramic boat in a tube furnace and calcined at 850℃ for 2 h. The calcined product was dissolved in 50 mL of H2O, magnetically stirred for 6 h, washed with deionized water, and dried at 105℃ for 12 h to obtain activated fly ash.

[0061] Step 2, Preparation of fly ash-based cobalt iron silicate (FA-CoFeSi): 1 mmol CoCl2·6H2O, 1 mmol FeCl2·4H2O, 5 mmol NH4Cl, and 4 mL NH3·H2O were dissolved in 40 mL H2O. The mixture was magnetically stirred for 15 min, then 60 mg of activated fly ash was added, and the mixture was stirred thoroughly for 30 min. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and heated at 180 °C for 24 h. Finally, the precipitate was washed with deionized water and dried at 70 °C for 12 h to obtain FA-CoFeSi.

[0062] Example 2

[0063] Step 1 is the same as Step 1 in Example 1.

[0064] Step 2, Preparation of fly ash-based cobalt silicate (FA-CoSi): 2 mmol CoCl2·6H2O, 5 mmol NH4Cl, and 4 mL NH3·H2O were dissolved in 40 mL H2O. The mixture was magnetically stirred for 15 min, then 60 mg of activated fly ash was added, and the mixture was stirred thoroughly for 30 min. The solution was then transferred to a 100 mL PTFE-lined stainless steel autoclave and heated at 180 °C for 24 h. Finally, the precipitate was washed with deionized water and dried at 70 °C for 12 h to obtain FA-CoSi.

[0065] Example 3

[0066] Step 1 is the same as Step 1 in Example 1.

[0067] Step 2, Preparation of fly ash-based ferrosilicon (FA-FeSi): 2 mmol FeCl2·4H2O, 5 mmol NH4Cl, and 4 mL NH3·H2O were dissolved in 40 mL H2O. The mixture was magnetically stirred for 15 min, then 60 mg of activated fly ash was added, and the mixture was stirred thoroughly for 30 min. The solution was then transferred to a 100 mL PTFE-lined stainless steel autoclave and heated at 180 °C for 24 h. Finally, the precipitate was washed with deionized water and dried at 70 °C for 12 h to obtain FA-FeSi.

[0068] Example 4

[0069] Preparation of nickel-supported fly ash-based cobalt iron silicate (Ni@FA-CoFeSi): 30 mg of FA-CoFeSi prepared in Example 1 and 30.4 mg of NiCl2·H2O were weighed and dissolved in 15 mL of H2O. The mixture was sonicated for 1 h, and 0.17 g of NaBH4 was added to the mixed solution. The mixture was magnetically stirred for 4 h. After washing with deionized water, the solution was vacuum dried at 70 ℃ for 11 h to obtain Ni@FA-CoFeSi.

[0070] The activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi, and Ni@FA-CoFeSi prepared in Examples 1-4 were characterized and tested, and the results are shown below:

[0071] Figure 1 This is a scanning electron microscope (SEM) image of Ni@FA-CoFeSi. (Source: [Insert SEM image here]) Figure 1 It can be seen that the particles have rough surfaces, vary in size, and have a spherical structure. Around the boundaries of these particles, there is a porous amorphous fly ash skeleton.

[0072] Figure 2 This is a transmission electron microscope (TEM) image of Ni@FA-CoFeSi. Figure 2 As shown, within a certain error range, a lattice spacing of 0.257 nm may correspond to the (211) crystal plane of FeOOH or the (311) crystal plane of Fe3O4. Within a certain error range, a lattice spacing of 0.306 nm may correspond to the (110) crystal plane of nickel oxide, consistent with the XRD results.

[0073] Figure 3 The images show the XRD patterns of activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi, and Ni@FA-CoFeSi prepared in Examples 1-4. Figure 3 As shown, the spectrum of FA contains many impurity peaks, most of which are diffraction peaks of SiO2. The XRD pattern shows that Co2SiO4 and Fe2SiO4 were successfully synthesized. The peaks at 2θ of 30°, 43° and 63° correspond to the (110), (200) and (220) crystal planes of NiO, respectively, confirming the successful loading of nickel.

[0074] Figure 4 The LSV diagrams are for activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi, and Ni@FA-CoFeSi prepared in Examples 1-4. Figure 4 As shown, at 10 mA cm -2 At the specified potential, the overpotential of Ni@FA-CoFeSi is 176 mV, that of FA-CoFeSi is 377 mV, that of FA-CoSi is 386 mV, that of FA-FeSi is 428 mV, and that of FA is 502 mV. Ni@FA-CoFeSi exhibits a lower overpotential, allowing it to initiate the oxygen evolution reaction (OER) at a lower potential, demonstrating excellent OER catalytic activity. This is because Ni... 2+ It is easily oxidized to NiOOH, and NiOOH can serve as an active site for OER. Therefore, Ni 2+ Adding it is more conducive to improving the catalytic activity of oxygen evolution in the OER reaction.

[0075] Figure 5 Tafel slope plots are shown for activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi, and Ni@FA-CoFeSi prepared in Examples 1-4. The reaction kinetics of OER were studied using the Tafel plots, as follows: Figure 5 As shown, Ni@FA-CoFeSi exhibits a lower Tafel slope (49.5 mV dec) than other samples. -1 It has the fastest oxygen evolution reaction kinetics.

[0076] Figure 6 EIS plots of activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi, and Ni@FA-CoFeSi prepared in Examples 1-4. The impedance plots further elucidate the charge transfer kinetics, such as... Figure 6 As shown, Ni@FA-CoFeSi exhibits the lowest charge transfer impedance, indicating its strongest charge transfer capability and fastest catalytic kinetics. This demonstrates that loading with metallic nickel can reduce the resistance of FA-CoFeSi, effectively improving the efficiency of the electrochemical oxygen evolution reaction.

[0077] Figure 7 The figures show the Cdl values ​​of activated fly ash (FA), FA-CoFeSi, FA-CoSi, FA-FeSi, and Ni@FA-CoFeSi prepared in Examples 1-4. Since the double-layer capacitance Cdl of an electrode is positively correlated with its electrochemical active area (ECSA), the electrochemical active area can be approximated by comparing the double-layer capacitance. Figure 7 As shown, the calculated Cdl values ​​for FA, FA-FeSi, FA-CoSi, FA-CoFeSi, and Ni@FA-CoFeSi are 0.172 mF cm⁻¹. -2 0.187 mFcm -2 0.327 mF cm -2 0.138 mF cm -2 0.193 mF cm -2 .

[0078] Figure 8 The figure shows the chronoamperometry (CGM) plot for Ni@FA-CoFeSi. The CGM stability test results show that after 48 hours of continuous operation at a constant potential of 1.671 V vs. RHE, the current retention rate of Ni@FA-CoFeSi is approximately 83% of the initial activity. Therefore, the above electrochemical test results demonstrate that Ni@FA-CoFeSi possesses excellent electrocatalytic stability.

[0079] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. The application of a catalyst in oxygen evolution through water electrolysis, characterized in that, The catalyst is prepared by the following steps: Step 1: Mix fly ash and NaHCO3 evenly and then calcine to obtain activated fly ash; Step 2: Co source, Fe source, ammonium chloride and ammonia water are added to water and mixed well, then activated fly ash is added and mixed well, followed by hydrothermal reaction to obtain FA-CoFeSi; Step 3: After mixing the FA-CoFeSi with the nickel source in water, a reducing agent is added to react and the catalyst is obtained.

2. The application according to claim 1, characterized in that, In step 1, the mass ratio of fly ash to NaHCO3 is 1:0.1~1.

2.

3. The application according to claim 1, characterized in that, In step 1, the calcination temperature is 700℃~900℃ and the time is 1~3h.

4. The application according to claim 1, characterized in that, In step 2, the Co source is cobalt chloride; the Fe source is ferrous chloride; the molar ratio of the Co source, Fe source, and ammonium chloride is 1:1:5; the volume ratio of the Co source to the ammonia water is 1 mmol:4 mL; the volume ratio of the Co source to the water is 1 mmol:40 mL; and the volume ratio of the Co source to the activated fly ash is 1 mmol:60 mg.

5. The application according to claim 1, characterized in that, In step 2, the hydrothermal reaction is carried out at a temperature of 180°C for 24 hours.

6. The application according to claim 1, characterized in that, In step 3, the nickel source is nickel chloride; the mass ratio of FA-CoFeSi to the nickel source is 1:1 to 1.1; the reducing agent is NaBH4; and the mass ratio of FA-CoFeSi to the reducing agent is 1:5 to 6.

7. The application according to claim 1, characterized in that, In step 3, the reaction time is 4 hours.

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