Preparation method of iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water

Abstract

The invention discloses a preparation method of iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water, which comprises the following steps: washing, drying and crushing a biomass raw material into powder, mixing the biomass powder with a template agent and a pore-foaming agent, ball-milling, treating in an inert atmosphere, pickling and drying to obtain biomass carbon-based powder. Then adding the precursor into an aqueous solution containing iron salt, stirring, and carrying out vacuum drying to form an iron-based precursor; the precursor is subjected to high-temperature calcination in a tubular furnace and then subjected to phosphating treatment, and the iron / carbon composite nanospheres are obtained. By optimizing the protective atmosphere, the calcining temperature and the time condition, the nanospheres with good performance are obtained, and meanwhile, the energy consumption in the synthesis process is reduced. The iron / carbon composite nanosphere prepared by the method shows excellent activity in an electro-catalytic hydrogen evolution reaction, is simple, convenient and efficient, and opens a new idea for developing application of an advanced catalyst in the field of energy conversion by utilizing biomass solid wastes.

Description

Technical Field

[0001] The invention belongs to the field of waste resource utilization and energy materials, and specifically relates to a method for preparing iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water. Background Art

[0002] In the field of energy and electrocatalysis, the development of efficient water splitting technology is crucial for the generation of clean energy. Among them, iron has become a research hotspot for replacing expensive precious metal catalysts due to its abundant reserves in the earth's crust and low cost. However, the traditional preparation method of iron / carbon composite nanospheres often requires synthesis through a hydrothermal combined with high-temperature pyrolysis method. The multi-step process of hydrothermal and high-temperature pyrolysis often causes more energy consumption and increases the cost of synthesis. Therefore, simplifying the synthesis steps of iron / carbon composite nanospheres is a problem that needs to be solved in the current field.

[0003] In addition, applying biomass to the synthesis of electrocatalysts is an effective way to increase the value of biomass, and it also effectively avoids the environmental pollution caused by the incineration of biomass. Since iron atoms react with carbonized biomass at high temperatures (usually greater than 850°C) to form iron carbide (Fe x C), and decompose to produce graphitized carbon in the subsequent process, increasing the graphitization degree of biomass carbon materials, thereby increasing the conductivity of carbon materials. There are many similar studies, but most of them will use iron-catalyzed graphitized carbon materials in the subsequent use, usually acid washing to remove the iron element before further use, which will not only produce acid washing waste liquid, but also cause waste of iron elements. Therefore, obtaining efficient electrocatalysts based on iron-catalyzed graphitized carbon materials will help to make full use of iron elements.

[0004] Iron phosphide-based catalysts are currently considered to be a highly promising hydrogen evolution electrocatalyst, among which a common synthesis method is a hydrothermal combined with post-phosphating method. The hydrothermal method is usually time-consuming and the latent heat of vaporization causes a large waste of energy. If the iron element in the iron-catalyzed graphitized carbon material can be phosphated, an iron phosphide / carbon material-based electrocatalyst can be obtained. However, the current commonly used post-phosphating process usually undergoes a slow heating process (1°C / min) to prevent the rapid decomposition of the phosphorus source, resulting in failure to fully react with the iron element. However, the slow heating process causes the entire phosphating process to undergo 7 to 9 hours of phosphating in a tubular furnace or CVD furnace, resulting in a large energy consumption during the synthesis process. Summary of the invention

[0005] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a method for preparing iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water. By optimizing the phosphating process, the phosphating time can be reduced, thereby achieving the purpose of reducing synthesis energy consumption and synthesis cost, including the treatment of biomass raw materials, the selection of templates and porogens, and the design of pyrolysis and phosphating processes according to the characteristics of the iron-carbon reaction process and the pyrolysis characteristics of phosphorus source decomposition. The synthesis process of iron / carbon composite nanospheres is optimized, thereby simplifying the synthesis process of iron / carbon composite nanospheres and reducing synthesis costs. At the same time, the iron / carbon composite nanospheres prepared by the present invention exhibit excellent electrocatalytic hydrogen evolution activity and stability in the electrocatalytic hydrogen evolution process, and can be widely used in clean energy technologies such as water decomposition, providing a new way to achieve efficient, economical and sustainable energy conversion.

[0006] Technical solution: To achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A method for preparing iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water. In the pretreatment stage, biomass raw materials rich in nitrogen organic matter are repeatedly washed, dried, and crushed into powder. In the mixture of biomass powder, template agent and porogen, ball milling and treatment under an inert atmosphere are performed, and then pickled and dried to obtain biomass carbon-based powder. Subsequently, it is added to an aqueous solution containing iron salt, stirred, and vacuum dried to form an iron-based precursor. The precursor is subjected to high-temperature calcination in a tubular furnace and then phosphating treatment to obtain iron / carbon composite nanospheres. By optimizing the protective atmosphere, calcination temperature and time conditions, nanospheres with good performance are obtained while reducing the energy consumption of the synthesis process. Specifically, the following steps are included:

[0008] Step 1: repeatedly washing, drying and crushing the biomass raw material rich in nitrogen organic matter to obtain biomass powder.

[0009] Step 2: mixing the biomass powder with the template and the porogen, and ball milling the mixture in an inert atmosphere to obtain a biomass carbon-based powder a.

[0010] Step 3: transfer the biomass carbon-based powder a to a transparent tube furnace and pyrolyze it under a first protective gas atmosphere to obtain black powder b.

[0011] Step 4, washing the obtained black powder b with hydrochloric acid and ultrapure water, and then drying to obtain powder c.

[0012] Step 5, adding powder c to an aqueous solution containing an iron salt, and stirring the resulting mixture at room temperature, and then drying the mixture by immersing it in a water bath, and then drying to obtain powder d.

[0013] Step 6: calcining the obtained powder d at high temperature in a tube furnace under a second protective gas atmosphere to obtain powder e.

[0014] Step 7, placing powder e and sodium hypophosphite in magnetic boats at the downstream and upstream positions along the third protective gas atmosphere flow for phosphating, then cooling the tubular furnace to room temperature and collecting samples to obtain an iron / carbon composite nanosphere hydrogen evolution catalyst.

[0015] Preferably, the biomass raw material in step 1 is one or a mixture of ginkgo leaves, peanut shells, and rhizomes of legumes, and the particle size of the biomass powder is 300-500 meshes.

[0016] Preferably, the template is a magnesium-containing compound or / and a zinc-containing compound, and the porogen is a zinc-containing compound or / and a potassium-containing compound.

[0017] Preferably, in step 2, the mass ratio of biomass to template agent is 1:0.5 to 1:4, and the mass ratio of biomass to porogen agent is in the range of 1:0.5 to 1:3. In step 2, ball milling is performed by a ball mill, the speed of the ball mill is 1200 to 1600 r / min, and the operation time is 2 to 4 hours.

[0018] Preferably: in step 2, the porogen is a zinc-containing compound, which includes one or a mixture of ZnCl2, ZnO, and Zn(NO3)2, and the template is one or a mixture of MgCl2, MgO, and MgCO2, and the mass ratio of the template to the porogen is 3:1 to 1:1.

[0019] Preferably, in step 3, the first protective gas atmosphere is one of nitrogen and argon, the calcination temperature is 600-800° C., the heating rate is 5-8° C., and the calcination time is 1-3 h.

[0020] Preferably, the black powder b obtained in step 4 is washed with hydrochloric acid having a concentration of 2 to 4 mol / L and ultrapure water, and then dried at a temperature of 60 to 90°C.

[0021] Preferably: in step 5, the iron salt is one or a mixture of Fe(NO3)2·9H2O, FeCl3, FeSO4, Fe(CH3 COO)3, Fe(acac)3, the concentration of the iron salt is 0.05-0.2 mol / L, the water bath temperature is 60-80°C, the vacuum drying temperature is 60-100°C, and the vacuum drying time is 12-24h.

[0022] Preferably, in step 6, the second protective atmosphere is one of nitrogen and argon, the calcination temperature is 850-1300° C., the heating rate is 3-5° C. / min, and the calcination time is 1-3 h.

[0023] Preferably: the mass of the sodium hypophosphite in step 7 is 5 to 7 times that of powder e, the third protective atmosphere is one of nitrogen and argon, and the heating process is divided into two stages, the first stage is heated from room temperature to 210 to 230°C, the heating rate is 3 to 5°C, and the second stage is heated from 210 to 230°C to 350 to 450°C and maintained for 1 to 2h, and the heating rate is 1 to 2°C / min.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention can achieve controllable adjustment of the morphology, structure and performance of the product by adjusting the ratio of biomass to template agent, porogen, phosphating conditions and other parameters. This controllability makes the synthesis process more flexible.

[0026] (2) The method for preparing a post-phosphating iron-carbon composite nanosphere for efficient water electrolysis hydrogen production described in the present invention adjusts the structure of the iron-catalyzed graphitized carbon material and improves its electrocatalytic hydrogen evolution activity by introducing a post-phosphating step.

[0027] (3) Application of the method for preparing post-phosphating iron-carbon composite nanospheres for efficient hydrogen production by water electrolysis described in the present invention, wherein iron is first carbonized and then phosphated to obtain iron phosphide (FeP) sites with electrocatalytic hydrogen evolution activity. The driving current density of Fe&FeP@gl-C-15 catalyst reaches 10 mA cm -2 Only 92mV overpotential is required. -2 At higher current densities above 20 wt %, the Fe&FeP@C catalyst outperforms the commercial Pt / C catalyst (20 wt %).

[0028] (4) The method for preparing a post-phosphating iron-carbon composite nanosphere for efficient hydrogen production by electrolysis of water described in the present invention adjusts and optimizes the post-phosphating process by combining the thermal decomposition characteristics of sodium hypophosphite (NaH2PO2·H2O). Compared with the traditional slow (1°C / min) heating method, the post-phosphating time will be greatly reduced, thereby reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The powder e(Fe & Fe x X-ray diffraction pattern of C@gl-C-15).

[0030] Figure 2 : This is the X-ray diffraction pattern of the powder f (Fe&FeP@gl-C-15) obtained according to Example 1 of the present invention.

[0031] Figure 3This is a high magnification transmission electron microscope (HRTEM) image of the powder f (Fe&FeP@gl-C-15) obtained according to Example 1 of the present invention.

[0032] Figure 4 (a) Linear sweep voltammogram, (b) Tafel and (c) stability diagram of the catalyst Fe&FeP@gl-C-15 obtained according to Example 1 of the present invention and modified with 20% commercial Pt.

[0033] Figure 5 This is the thermal decomposition curve of sodium hypophosphite (NaH2PO2·H2O). DETAILED DESCRIPTION

[0034] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0035] Example 1

[0036] This embodiment provides a method for preparing iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water, comprising the following steps:

[0037] Step 1: Select ginkgo leaves as biomass raw materials and crush the ginkgo leaves into 300 meshes.

[0038] Step 2: Mix the crushed ginkgo leaves, template MgCl2, and porogen (template) ZnCl2 in a mass ratio of 1:0.5:0.5, and ball mill them in a nitrogen atmosphere at a ball mill speed of 1200 r / min for 2 h to obtain a powder denoted as a.

[0039] Step 3: transfer powder a to a transparent tube furnace and pyrolyze at 600°C in a nitrogen atmosphere to obtain black powder b at a heating rate of 5°C / min.

[0040] Step 4: Wash the obtained black powder b with 2 mol / L hydrochloric acid and ultrapure water, and then dry it in an oven at 60° C. to obtain powder c.

[0041] Step 5: Add powder c (100 mg) to Fe(NO3)2 at a concentration of 0.05 mol / L. . 9H2O in aqueous solution, and the resulting mixture was stirred at room temperature. The mixture was then dried by immersing the flask in a water bath at 60°C, and then further dried under vacuum for 12 h to obtain powder d.

[0042] Step 6: Heat the obtained powder d to 850° C. in a tube furnace under a nitrogen atmosphere at a heating rate of 3° C. / min and maintain for 1 h to obtain powder e.

[0043] Step 7: Powder e (50 mg) and sodium hypophosphite (NaH2PO2·H2O, 350 mg) were placed in magnetic boats at the downstream and upstream positions of the nitrogen atmosphere flow, respectively, and the temperature was rapidly increased to 210°C at a heating rate of 5°C / min, and then heated at 2 o The temperature was slowly increased to 450°C at a heating rate of 1.34°C / min and maintained for 2 h. After the tube furnace was cooled to room temperature, the sample was collected to obtain iron / carbon composite nanospheres (powder f).

[0044] Example 2

[0045] This embodiment provides a method for preparing iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water, comprising the following steps:

[0046] Step 1: Use soybean hulls as biomass raw materials and crush the soybean hulls into 400 meshes.

[0047] Step 2: Mix crushed soybean hulls, template MgCl2, and porogen (template) ZnCl2 in a mass ratio of 1:2:1, and ball mill them in a nitrogen atmosphere at a ball mill speed of 1400 r / min for 3 h to obtain a powder recorded as a.

[0048] Step 3: transfer powder a to a transparent tube furnace, and heat to 700° C. at 7° C. / min in a nitrogen atmosphere to pyrolyze to obtain black powder b.

[0049] Step 4: Wash the obtained black powder b with 3 mol / L hydrochloric acid and ultrapure water, and then dry it in an oven at 70° C. to obtain powder c.

[0050] Step 5: Powder c (150 mg) was added to an aqueous solution of Fe(acac)3 at a concentration of 0.1 mol / L, and the resulting mixture was stirred at room temperature. The mixture was then dried by immersing the flask in a water bath at 70°C, and then further dried under vacuum for 16 h to obtain powder d.

[0051] Step 6: Heat the obtained powder d to 1100° C. in a tube furnace under a nitrogen atmosphere at a heating rate of 4° C. / min and calcine at a high temperature for 2 h to obtain powder e.

[0052] Step 7: Powder e (60 mg) and sodium hypophosphite (NaH2PO2·H2O, 360 mg) were placed in magnetic boats at the downstream and upstream positions of the nitrogen atmosphere flow, respectively, and the temperature was rapidly increased to 220°C at a heating rate of 4°C / min, and then heated at a rate of 1.5 oThe temperature was slowly increased to 400°C at a heating rate of 1.5 °C / min and maintained for 1.5 h. After the tube furnace was cooled to room temperature, the samples were collected to obtain iron / carbon composite nanospheres.

[0053] Example 3

[0054] This embodiment provides a method for preparing iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water, comprising the following steps:

[0055] Step 1: Use peanut shells as biomass raw materials and crush the peanut shells into 500 meshes.

[0056] Step 2: Mix crushed peanut shells, template MgCl2, and porogen (template) ZnCl2 in a mass ratio of 1:4:2, and ball mill them in a nitrogen atmosphere at a ball mill speed of 1600 r / min for 4 h to obtain a powder recorded as a.

[0057] Step 3: transfer powder a to a transparent tube furnace and pyrolyze it at a certain temperature under an argon atmosphere to obtain black powder b.

[0058] Step 4: Wash the obtained black powder b with 4 mol / L hydrochloric acid and ultrapure water, and then dry it in an oven at 80° C. to obtain powder c.

[0059] Step 5: Powder c (200 mg) was added to an aqueous solution of FeCl3 at a concentration of 0.15 mol / L, and the resulting mixture was stirred at room temperature. The mixture was then dried by immersing the flask in a water bath at 80°C, and then further dried under vacuum for 20 h to obtain powder d.

[0060] Step 6: The obtained powder d was heated to 800° C. at a heating rate of 8° C. / min in a tube furnace under a nitrogen atmosphere and calcined for 3 h to obtain powder e.

[0061] Step 7: Powder e (80 mg) and sodium hypophosphite (NaH2PO2·H2O, 560 mg) were placed in magnetic boats at the downstream and upstream positions of the nitrogen atmosphere flow, respectively, and the temperature was rapidly increased to 230°C at a heating rate of 3°C / min, and then heated at 1 o The temperature was slowly increased to 350°C at a heating rate of 1.5 C / min and maintained for 1 h. After the tube furnace was cooled to room temperature, the samples were collected to obtain iron / carbon composite nanospheres.

[0062] Figure 1 The powder e(Fe & Fe x The X-ray diffraction pattern of C@gl-C-15) is given by Figure 1 It can be seen that iron carbide was successfully obtained at 850°C. Figure 2is the X-ray diffraction pattern of the powder f(Fe&FeP@gl-C-15) obtained in Example 1, Figure 2 It can be seen that the iron carbide was successfully phosphated to FeP. Figure 3 This is a high magnification transmission electron microscope (HRTEM) image of Fe&FeP@gl-C-15 obtained according to Example 1 of the present invention. Figure 3 a Mainly shows the morphology of nanospheres, and the size of the nanospheres ranges from 510 to 720 nm. Figure 3 b shows the intimate contact between Fe and FeP lattices on the carbon layer to form a heterostructure, which may lead to the enhanced activity of HER. Figure 4 The following are (a) linear sweep voltammetry curves, (b) Tafel and (c) stability diagrams of the catalyst Fe&FeP@gl-C-15 obtained in Example 1 of the present invention and 20% commercial Pt modification. Figure 3 As shown in a, the performance of Fe&FeP@gl-C-15 electrocatalyst in HER was investigated using 0.5 M H2SO4 saturated with N2 and compared with commercial Pt / C (20 wt%). -1 The LSV curves of Fe@FeP@gl-C-15 catalyst were recorded at 10 mA cm -2 The overpotential (η 10 , 92 mV), which is close to the commercial Pt / C (33 mV). It is worth noting that the catalytic activity of Fe&FeP@gl-C-15 is very high at a current density of 375 mA cm -2 The catalyst can also achieve 500 mA cm at an overpotential of 346 mV. -2 The corresponding Tafel plots of Fe&FeP@gl-C-15 and commercial Pt / C catalysts are shown in Figure 2. Figure 4 Fe&FeP@gl-C-15 has a smaller Tafel slope of 70.37 mV dec. -1 , which is close to the value of commercial Pt / C (63.8mV dec -1 ). 10 mA cm -2 Chronoamperometric response (IT) test at current density ( Figure 4 c), showing that after 8 hours of operation, the density decrease is small (about 2.37%), showing long-term durability. The stability of Fe&FeP@gl-C-15 was evaluated by comparing the LSV curves before and after 5000 CV cycles. Figure 4 As shown in the inset of c, the Fe&FeP@gl-C-15 catalyst exhibits excellent HER catalytic stability. Figure 5The thermal decomposition curve of sodium hypophosphite (NaH2PO2·H2O) is shown in FIG. The iron / carbon composite nanospheres prepared by the present invention exhibit excellent activity in the electrocatalytic hydrogen evolution reaction, which is not only simple and efficient, but also opens up new ideas for the development of advanced catalysts using biomass solid waste in the field of energy conversion.

[0063] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water, characterized in that: The following steps are involved: Step 1, repeatedly washing, drying and crushing the biomass raw material rich in nitrogen organic matter to obtain biomass powder; Step 2, mixing the biomass powder with the template and the porogen, and ball milling in an inert atmosphere to obtain a biomass carbon-based powder a; Step 3, transferring the biomass carbon-based powder a into a transparent tube furnace, and pyrolyzing it under a first protective gas atmosphere to obtain a black powder b; Step 4, washing the obtained black powder b with hydrochloric acid and ultrapure water, and then drying to obtain powder c; Step 5, adding powder c to an aqueous solution containing an iron salt, and stirring the resulting mixture at room temperature; then drying the mixture by immersing it in a water bath, and then drying to obtain powder d; Step 6, calcining the obtained powder d at a high temperature in a tube furnace under a second protective gas atmosphere to obtain powder e; Step 7, placing powder e and sodium hypophosphite in magnetic boats at the downstream and upstream positions along the third protective gas atmosphere flow for phosphating, then cooling the tubular furnace to room temperature and collecting samples to obtain an iron / carbon composite nanosphere hydrogen evolution catalyst.

2. The method for preparing the iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water according to claim 1, characterized in that: In step 1, the biomass raw material is one or a mixture of ginkgo leaves, peanut shells, and rhizomes of legumes, and the particle size of the biomass powder is 300-500 meshes.

3. The method for preparing the iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water according to claim 2, characterized in that: The template agent is a magnesium-containing compound or / and a zinc-containing compound, and the porogen is a zinc-containing compound or / and a potassium-containing compound.

4. The method for preparing the iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water according to claim 3, characterized in that: In step 2, the mass ratio of biomass to template agent is 1:0.5-1:4, and the mass ratio of biomass to porogen is in the range of 1:0.5-1:3; in step 2, ball milling is performed by a ball mill, the speed of the ball mill is 1200-1600 r / min, and the operation time is 2-4 hours.

5. The method for preparing the iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water according to claim 4, characterized in that: In step 2, the porogen is a zinc-containing compound, which includes one or a mixture of ZnCl2, ZnO, and Zn(NO3)2. The template is one or a mixture of MgCl2, MgO, and MgCO2, and the mass ratio of the template to the porogen is 3:1 to 1:

1.

6. The method for preparing the iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water according to claim 5, characterized in that: In step 3, the first protective gas atmosphere is one of nitrogen and argon, the calcination temperature is 600-800° C., the heating rate is 5-8° C., and the calcination time is 1-3 hours.

7. The method for preparing the iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water according to claim 6, characterized in that: The black powder b obtained in step 4 is washed with hydrochloric acid having a concentration of 2 to 4 mol / L and ultrapure water, and then dried at a temperature of 60 to 90°C.

8. The method for preparing the iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water according to claim 7, characterized in that: The iron salt in step 5 is Fe(NO3)2 . One or a mixture of 9H2O, FeCl3, FeSO4, Fe(CH3COO)3, Fe(acac)3, the concentration of iron salt is 0.05-0.2 mol / L, the water bath temperature is 60-80°C, the vacuum drying temperature is 60-100°C, and the vacuum drying time is 12-24h.

9. The method for preparing the iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water according to claim 8, characterized in that: In step 6, the second protective atmosphere is one of nitrogen and argon, the calcination temperature is 850-1300° C., the heating rate is 3-5° C. / min, and the calcination time is 1-3 h.

10. The method for preparing the iron-carbon composite nanospheres for post-phosphating treatment of hydrogen production by electrolysis of water according to claim 9, characterized in that: The mass of the sodium hypophosphite described in step 7 is 5 to 7 times that of powder e. The third protective atmosphere is one of nitrogen and argon. The heating process is divided into two stages. The first stage is heated from room temperature to 210 to 230°C with a heating rate of 3 to 5°C. The second stage is heated from 210 to 230°C to 350 to 450°C and maintained for 1 to 2h at a heating rate of 1 to 2°C / min.

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