Preparation method and application of transition / rare earth multi-metal co-doped phosphide

Abstract

The present invention provides a preparation method and application of transition / rare earth multi-metal co-doped phosphide, which is carried out according to the following steps: step 1, dissolving soluble iron salt, soluble nickel salt and hydrated rare earth chloride in water containing organic ligands, stirring and completely dissolving to form a solution, cooling, washing and centrifuging by hydrothermal method, and drying to obtain a precursor; step 2, mixing the precursor obtained in step 1 with an organic nitrogen source compound and fully grinding it evenly, placing a porcelain boat containing the material in a tube furnace and calcining it under a protective atmosphere to obtain FeNiRE‑NCNTs; step 3, the FeNiRE‑NCNTs obtained in step 2 and the inorganic phosphorus source compound are divided into two porcelain boats, placed in a tube furnace for phosphating, and finally FeNiRE‑P‑NCNTs, i.e. transition / rare earth multi-metal co-doped phosphide. The electrocatalyst prepared by the preparation method of the present invention has excellent water electrolysis hydrogen production performance and excellent stability under acidic conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalytic materials, relates to doped phosphides, and specifically relates to a preparation method and application of transition / rare earth multi-metal co-doped phosphides. Background Art

[0002] Hydrogen energy, as the most sustainable and renewable green energy, will play a pivotal role in achieving carbon neutrality. Among the many hydrogen production methods, water electrolysis has been recognized as one of the most attractive energy storage technologies due to its great environmental potential. But in fact, the most efficient catalysts in water electrolysis for hydrogen production, such as platinum, are precious metals with low reserves in the earth's crust and high prices, so they cannot be used in large-scale industrial applications. Therefore, the development of stable, highly active, low-cost and abundant non-precious metal catalysts for water electrolysis for hydrogen production is an inevitable trend of historical development.

[0003] Rare earth MOFs (RE-MOFs) are a new type of MOFs with rare earth ions as nodes, in which rare earth cations have rich energy level structures, and therefore have great application potential in the field of electrocatalysis. MOFs have been widely reported as precursors for the preparation of nitrogen-doped transition metal carbon materials due to their high specific surface area and tunable intrinsic nitrogen-containing organic ligands. This strategy overcomes the problem of MOF conductivity to a certain extent. However, MOFs-derived carbon-based materials usually exhibit microporous properties, low graphitization degree and agglomeration of metal nanoparticles, which are not conducive to mass and electron transfer in the electrocatalytic process. The key to effectively solve the above problems is to construct a new type of carbon nanotube / carbon-based material, which not only helps to prevent the agglomeration of metal nanoparticles, but also effectively increases its conductivity and accelerates the charge transfer in the electrochemical process. In addition, the doping of heteroatoms (such as phosphorus) can improve the catalytic activity of the carbon matrix by changing the electronegativity, charge distribution and electron transfer behavior to introduce more active sites, thereby further enhancing the catalytic performance. Therefore, it is of great significance to explore the use of transition / rare earth multi-metal MOFs as precursors to construct phosphides with high efficiency in hydrogen evolution performance.

[0004] Although there have been relevant reports on MOF-derived metal phosphides, such as those reported in Chinese invention patents with application numbers 201910325365.4 and 202110308913.X, they cannot meet the requirements of commercial hydrogen evolution catalysis due to their ultra-high overpotential and poor stability. Therefore, phosphides derived from transition / rare earth multi-metal co-doped MOFs are expected to exhibit special synergistic effects or electronic interactions to achieve the purpose of having efficient and long-term stable catalytic performance for hydrogen evolution in water electrolysis. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a preparation method and application of transition / rare earth multi-metal co-doped phosphides, so as to solve the technical problems in the prior art that precious metals in metal-doped phosphides are expensive and MOFs-derived phosphides have high overpotential and poor stability.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0007] A method for preparing a transition / rare earth multi-metal co-doped phosphide, the method is carried out according to the following steps:

[0008] Step 1, dissolving a soluble iron salt, a soluble nickel salt and a hydrated rare earth chloride in water containing an organic ligand, stirring to completely dissolve to form a solution, cooling, washing and centrifuging by a hydrothermal method, and drying to obtain a precursor;

[0009] Step 2: Mix the precursor prepared in step 1 with an organic nitrogen source compound and grind them evenly; place the porcelain boat containing the materials in a tube furnace and calcine them in a protective atmosphere to obtain iron-nickel-rare earth trimetallic co-doped nitrogen-doped carbon nanotubes;

[0010] Step 3, the iron-nickel-rare earth trimetallic co-doped nitrogen-doped carbon nanotubes and the inorganic phosphorus source compound prepared in step 2 are separately packed into two porcelain boats, and placed in a tube furnace for phosphating to finally obtain transition / rare earth multimetallic co-doped phosphides.

[0011] The present invention also has the following technical features:

[0012] In step 1, the soluble iron salt is ferric chloride hexahydrate; the soluble nickel salt is nickel chloride hexahydrate; the hydrated rare earth chloride is gadolinium chloride hexahydrate, terbium chloride hexahydrate or holmium chloride hexahydrate; the organic ligand is trimesic acid; and the molar ratio of the total amount of the soluble iron salt, the soluble nickel salt and the hydrated rare earth chloride to trimesic acid is 3:2.

[0013] In step 1, the molar ratio of the soluble iron salt, the soluble nickel salt and the hydrated rare earth chloride is 1:1:(0.5-2), 1:1:(0.5-2.5) or 1:1:(0.5-3).

[0014] In step one, the stirring method is magnetic stirring, and the magnetic stirring time is 20 minutes; in the hydrothermal method, the filling volume ratio of the liner of the high-pressure reactor is 70-80%; the reaction temperature of the sealed reaction is 150°C, and the reaction time is 24 hours; the cooling method is natural cooling; the washing method is alternating washing with water and ethanol for 6 to 8 times; the specific conditions of the centrifugation are centrifugation at 7000rpm for 15 minutes; the drying method is placed in a 60°C vacuum oven and dried for 12 hours.

[0015] In step 2, the organic nitrogen source compound is dicyandiamide; the mass ratio of the precursor to dicyandiamide is 1:(0.5-1.5), preferably, the mass ratio of the precursor to dicyandiamide is 1:1.

[0016] In step 2, the calcination temperature is 700-900° C., and the calcination time is 1-3 hours; and the protective gas is nitrogen.

[0017] In step three, the inorganic phosphorus source compound is sodium hypophosphite; the mass ratio of the iron-nickel-rare earth trimetallic co-doped nitrogen-doped carbon nanotubes to the sodium hypophosphite is 1:(5-15), preferably, the mass ratio of the iron-nickel-rare earth trimetallic co-doped nitrogen-doped carbon nanotubes to the sodium hypophosphite is 1:10.

[0018] In step 3, the phosphating temperature is 300-400°C and the time is 1-3h;

[0019] In step three, a porcelain boat containing an inorganic phosphorus source compound is placed at the upwind port of a tubular furnace with a protective atmosphere, a porcelain boat containing iron-nickel-rare earth trimetal co-doped nitrogen-doped carbon nanotubes is placed at the downwind port of the combustion tube of the tubular furnace, and a saturated copper sulfate solution is connected to the end of the tubular furnace to remove the tail gas generated during the phosphating process.

[0020] The present invention also protects the use of the transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide as described above as a catalyst for producing hydrogen by electrolysis of water.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] (I) The electrocatalyst prepared by the preparation method of the present invention has excellent water electrolysis hydrogen production performance and excellent stability under acidic conditions. The transition / rare earth multimetal phosphide with carbon nanotube morphology obtained by the preparation method of the present invention is expected to show special synergistic effects or electronic interactions, so that the target product has good conductivity and more excellent hydrogen evolution performance.

[0023] (II) The present invention takes into account the economic cost, abundance and radioactive effects of transition metals and rare earth metals, and uses cheap and readily available ferric chloride hexahydrate, nickel chloride hexahydrate and hydrated rare earth chloride as metal sources, and trimesic acid as an organic ligand to synthesize a series of precursors, and obtains a series of FeNiRE multi-metal co-doped phosphide catalysts by mixing with dicyandiamide and fully grinding them evenly, then pyrolyzing them at high temperature and then phosphating them at low temperature.

[0024] (III) The series of FeNiRE-P-NCNTs catalysts of the present invention use low-priced and abundant non-precious metals as raw materials, which not only saves costs but also can achieve efficient hydrogen evolution catalytic reaction under acidic conditions. It is a practical catalytic material with stable structure and excellent hydrogen evolution performance.

[0025] (Ⅳ) The data show that the current density of the optimized FeNiGd-P-NCNTs, FeNiTb-P-NCNTs and FeNiHo-P-NCNTs is 10 mA cm under 0.5 M H2SO4. -2 The overpotentials were 63.3mV, 47.5mV and 99.8mV respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figures are scanning electron microscope (SEM) images and transmission electron microscope (TEM) images of the target products obtained in Examples 5, 10 and 15 of the present invention; figure a is the SEM image of the target product obtained in Example 5, figure b is the SEM image of the target product obtained in Example 10, and figure c is the SEM image of the target product obtained in Example 15; figure d is the TEM image of the target product obtained in Example 5, figure e is the TEM image of the target product obtained in Example 10, and figure f is the TEM image of the target product obtained in Example 15.

[0027] Figure 2 The X-ray diffraction (XRD) patterns of the target products obtained in Examples 5, 10 and 15 of the present invention are shown.

[0028] FIG3(a) is a graph showing the electrocatalytic hydrogen evolution performance of the target products obtained in Examples 1 to 5 of the present invention in a 0.5M H2SO4 electrolyte. The inset in FIG3(a) shows the electrocatalytic hydrogen evolution performance of the target products obtained with different FeNiGd trimetallic co-doping ratios at a current density of 10 mA cm -2 Overpotential histogram when .

[0029] FIG3(b) is a graph showing the stability test results of the target products obtained in Examples 1 to 5 of the present invention in a 0.5M H2SO4 electrolyte. The inset in FIG3(b) shows the stability of the HER at a current density of 10 mA cm -2The chronoelectric current (it) curve below.

[0030] FIG4(a) is a graph showing the electrocatalytic hydrogen evolution performance of the target products obtained in Examples 6 to 12 of the present invention in a 0.5M H2SO4 electrolyte. The inset in FIG4(a) shows the electrocatalytic hydrogen evolution performance of the target products obtained in different FeNiTb trimetallic co-doping ratios at a current density of 10 mA cm -2 Overpotential histogram when .

[0031] FIG4(b) is a graph showing the stability test results of the target products obtained in Examples 6 to 12 of the present invention in a 0.5 M H2SO4 electrolyte. The inset in FIG4(b) shows the stability of the HER at a current density of 10 mA cm -2 under the it curve.

[0032] FIG5(a) is a graph showing the electrocatalytic hydrogen evolution performance of the target products obtained in Examples 13 to 16 of the present invention in a 0.5M H2SO4 electrolyte. The inset in FIG5(a) shows the electrocatalytic hydrogen evolution performance of the target products obtained in different FeNiHo trimetallic co-doping ratios at a current density of 10 mA cm -2 Overpotential histogram when .

[0033] FIG5(b) is a graph showing the stability test results of the target products obtained in Examples 13 to 16 of the present invention in a 0.5 M H2SO4 electrolyte. The inset in FIG5(b) shows the stability of the HER at a current density of 10 mA cm -2 It curve below.

[0034] The specific contents of the present invention are further explained in detail below in conjunction with embodiments. DETAILED DESCRIPTION

[0035] It should be noted that, in the present invention:

[0036] FeNiRE-NCNTs refers to iron-nickel-rare earth trimetallic co-doped nitrogen-doped carbon nanotubes.

[0037] FeNiRE-P-NCNTs refers to iron-nickel-rare earth trimetallic co-doped nitrogen-doped carbon nanotube phosphide.

[0038] HER stands for hydrogen evolution reaction.

[0039] η 10 Refers to the current density reaching 10mA cm -2 The required overpotential value.

[0040] The specifications of the instruments and raw materials used in this example are as follows:

[0041] CHI660B electrochemical workstation, Shanghai Chenhua Instrument Co., Ltd.

[0042] Electronic analytical balance, Shenyang Longteng Electronic Weighing Instrument Co., Ltd.

[0043] pH meter, Department of Chemistry, Peking University.

[0044] Ultrasonic cleaning machine, Ningbo Xinzhi Biotechnology Co., Ltd.

[0045] Ferric chloride hexahydrate, Sinopharm Chemical Reagent Shaanxi Co., Ltd.

[0046] Nickel chloride hexahydrate, Shanghai McLean Biochemical Technology Co., Ltd.

[0047] Gadolinium chloride hexahydrate, Xi'an Haimeng Experimental Technology Co., Ltd.

[0048] Terbium chloride hexahydrate, Xi'an Haimeng Experimental Technology Co., Ltd.

[0049] Holmium chloride hexahydrate, Xi'an Dao Biochemical Science and Trade Co., Ltd.

[0050] Trimesic acid, Tianjin Fuyu Fine Chemical Co., Ltd.

[0051] Sulfuric acid, Xi'an Haimeng Experimental Technology Co., Ltd.

[0052] Dicyandiamide, Sinopharm Chemical Reagent Shaanxi Co., Ltd.

[0053] Nafion with a mass concentration of 5%, Sigma-Aldrich, co.

[0054] The water was double distilled water.

[0055] Test method:

[0056] All electrochemical experiments were conducted at room temperature. The target product obtained in this example was electrochemically tested using a CHI 660B electrochemical workstation and a three-electrode system (with a platinum wire electrode as the counter electrode and a saturated calomel electrode as the reference electrode) produced by Shanghai Chenhua Instrument Co., Ltd. High-purity nitrogen was introduced into the electrolyte for 30 minutes before the test to achieve saturation. Under the condition of iR compensation, the scan rate was 0.005 V·s -1 The obtained polarization curve data were calibrated to the reversible hydrogen electrode potential (vs. RHE) according to the Nernst equation E(vs. RHE) = E(vs. SCE) + 0.2415 + 0.059 × pH, where 0.2415 is the standard electrode potential of a saturated calomel reference electrode at 25 °C and pH refers to the pH value of the electrolyte. Overpotential (η) = 0-E RHE The stability of the catalyst was tested by the IT method, and the test voltage was 10 mA cm for each material. -2The voltage at the time.

[0057] In accordance with the above technical scheme, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical scheme of this application fall within the protection scope of the present invention.

[0058] Embodiment 1:

[0059] This embodiment provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is carried out according to the following steps:

[0060] Step 1: Dissolve ferric chloride hexahydrate, nickel chloride hexahydrate and gadolinium chloride hexahydrate in 75 mL of deionized water containing 2.1 g of trimesic acid in a molar ratio of 1:1:0.5, and the molar ratio of the total amount of soluble iron salt, soluble nickel salt and hydrated rare earth chloride to trimesic acid is 3:2.

[0061] After magnetic stirring for 20 minutes, the product is completely dissolved to form a yellow solution, which is then placed in a 100 mL high-pressure reactor lined with polytetrafluoroethylene. The high-pressure reactor is sealed and placed at 150°C for reaction for 24 hours, cooled naturally to room temperature, washed alternately with ethanol and water for 6 to 8 times, centrifuged, and then dried to obtain a precursor.

[0062] Step 2: Mix the precursor prepared in step 1 and dicyandiamide in a mass ratio of 1:1 and grind them evenly. Place the porcelain boat containing the materials in a tube furnace and heat to 800°C at a heating rate of 5°C / min in a nitrogen environment and calcine for 2h to obtain FeNiGd-NCNTs.

[0063] Step 3: The FeNiGd-NCNTs and sodium hypophosphite prepared in step 2 are divided into two porcelain boats in a mass ratio of 1:10, placed in a tube furnace, and phosphated at 350°C for 2 hours to finally obtain FeNiGd-P-NCNTs. The porcelain boat containing sodium hypophosphite is placed at the upwind of the tube furnace with nitrogen, and the porcelain boat containing the material is placed at the downwind of the combustion tube of the tube furnace, and the end of the tube furnace is connected to a saturated copper sulfate solution to remove the tail gas generated during the phosphating process.

[0064] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0065] Embodiment 2:

[0066] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that in Example 1, except that:

[0067] In step 1 of this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and gadolinium chloride hexahydrate is 1:1:1.

[0068] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0069] Embodiment 3:

[0070] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that in Example 1, except that:

[0071] In step 1 of this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and gadolinium chloride hexahydrate is 1:1:1.5.

[0072] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0073] Embodiment 4:

[0074] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that in Example 1, except that:

[0075] In step 1 of this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and gadolinium chloride hexahydrate is 1:1:2.

[0076] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0077] Embodiment 5:

[0078] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that in Example 1, except that:

[0079] In step 1 of this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and gadolinium chloride hexahydrate is 1:1:2.5.

[0080] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0081] like Figure 1 As shown, Figure 1a and d in the figure are respectively the SEM image and TEM image of the target product obtained in Example 5. The catalyst presents a flaky microsphere structure with entangled carbon nanotubes, forming a "vine ball-like" coating structure entangled with a large number of carbon nanotubes.

[0082] like Figure 2 As shown, the material synthesized in Example 5 is a hybrid structure of nanoparticles such as carbon nanotubes, iron-nickel oxide and iron nitride.

[0083] As shown in Figure 3(a), the target product was obtained at a current density of 10 mA cm -2 The required overpotential values ​​are ranked as follows: (FeNiGd) 1:1:2 -P-NCNTs(η 10 =63.3mV)<(FeNiGd) 1:1:1.5 -P-NCNTs(η 10 =79.8mV)<(FeNiGd) 1:1:1 -P-NCNTs(η 10 =82.7mV)<(FeNiGd) 1:1:2.5 -P-NCNTs(η 10 =107.8mV)<(FeNiGd) 1:1:0.5 -P-NCNTs(η 10 =110.6 mV), it can be seen that the optimal ratio of FeNiGd co-doping is 1:1:2. The above results show that the hydrogen evolution performance of the optimized FeNiGd-P-NCNTs catalyst is significantly improved, especially (FeNiGd) 1:1:2 -P-NCNTs catalyst at 100 mA cm -2 Only 197.2 mV overpotential is required at a high current density, which is beneficial for practical industrial applications operating at high current density.

[0084] Long-term stability is a key factor in practical applications. As shown in Figure 3(b), after 8000 cycles of cyclic voltammetry, the LSV has only a negligible change. -2 At a current density of 10 mA cm -2 and 160mA cm -2 After testing by chronopotentiometry for 48h and 53h respectively, it was found that the current density of FeNiGd-P-NCNTs had basically not decayed, indicating that the catalyst has excellent stability.

[0085] Based on the above Examples 1 to 5, it can be seen that regulating the ratio of transition metal FeNi to rare earth metal Gd has a substantial effect on the hydrogen evolution performance of FeNiGd-P-NCNTs of the present invention, especially the construction strategy of the "transition / rare earth multi-metal co-doped carbon nanotube hybrid-phosphating" system adopted in the present invention greatly improves the hydrogen evolution performance of the catalytic material.

[0086] Embodiment 6:

[0087] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that in Example 1, except that:

[0088] In step 1 of this embodiment, the hydrated rare earth chloride is replaced from the gadolinium chloride hexahydrate in embodiment 1 to terbium chloride hydrate in an equal amount.

[0089] That is, in this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and terbium chloride hexahydrate is 1:1:0.5.

[0090] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0091] Embodiment 7:

[0092] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that in Example 2, except that:

[0093] In step 1 of this embodiment, the hydrated rare earth chloride is replaced from the gadolinium chloride hexahydrate in embodiment 2 with terbium chloride hexahydrate in an equal amount.

[0094] That is, in this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and terbium chloride hexahydrate is 1:1:1.

[0095] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0096] Embodiment 8:

[0097] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that in Example 3, except that:

[0098] In step 1 of this embodiment, the hydrated rare earth chloride is replaced from the gadolinium chloride hexahydrate in embodiment 3 to terbium chloride hexahydrate in an equal amount.

[0099] That is, in this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and terbium chloride hexahydrate is 1:1:1.5.

[0100] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0101] Embodiment 9:

[0102] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that of Example 4, except that:

[0103] In step 1 of this embodiment, the hydrated rare earth chloride is replaced from the gadolinium chloride hexahydrate in Example 4 with terbium chloride hexahydrate in an equal amount.

[0104] That is, in this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and terbium chloride hexahydrate is 1:1:2.

[0105] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0106] Embodiment 10:

[0107] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that of Example 5, except that:

[0108] In step 1 of this embodiment, the hydrated rare earth chloride is replaced from the gadolinium chloride hexahydrate in Example 5 with an equal amount of terbium chloride hexahydrate.

[0109] That is, in this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and terbium chloride hexahydrate is 1:1:2.5.

[0110] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0111] like Figure 1 As shown, Figure 1 Figures b and e are SEM and TEM images of the target product obtained in Example 10, respectively. The catalyst exhibits a typical core-shell nanosphere structure, and a large number of mutually entangled carbon nanotubes grow on the nanospheres.

[0112] Embodiment 11:

[0113] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that of Example 10, except that:

[0114] In this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and terbium chloride hexahydrate is 1:1:3.

[0115] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0116] As shown in Figure 4(a), as the proportion of rare earth metal Tb increases, its hydrogen evolution performance first increases and then decreases. When the FeNiTb co-doping ratio is 1:1:2.5, at a current density of 10 mA cm -2 The overpotential of hydrogen evolution is only 47.5 mV, the starting potential is only -30.4 mV, and the current density is 100 mA cm -2 The required overpotential is only 164.6 mV, which is very beneficial for practical industrial applications operating at high current density. This indicates that the reasonable adjustment of the co-doping ratio of Tb metal has a great impact on the electrocatalytic hydrogen evolution performance of the catalytic material.

[0117] As shown in Figure 4(b), the LSV curve of the FeNiTb-P-NCNTs catalyst has only negligible changes after 8000 cycles of cyclic voltammetry scanning. -2 At a current density of 150 mA cm -2 After 93 hours of testing by chronopotentiometry, it was found that the current density did not decay, indicating that the catalyst has excellent stability.

[0118] Based on the above examples 6 to 11, it can be seen that the co-doping ratio of FeNiTb and the three metals has a substantial effect on the hydrogen evolution performance of the FeNiTb-P-NCNTs of the present invention. The optimized FeNiTb-P-NCNTs have a high hydrogen evolution performance at a current density of 10 mA cm -2 The hydrogen evolution overpotential under the condition of 1.5 wt% NH4CO was reduced by 60.7 mV, which was 83.7 mV lower than that of FeNi-P-NCNTs catalyst. The above results show that the construction strategy of the "transition / rare earth multi-metal co-doped carbon nanotube hybrid-phosphating" system adopted by the present invention greatly improves the hydrogen evolution performance of the catalytic material.

[0119] Embodiment 12:

[0120] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that in Example 1, except that:

[0121] In step 1 of this embodiment, the hydrated rare earth chloride is replaced from the gadolinium chloride hexahydrate in embodiment 1 with an equal amount of holmium chloride hexahydrate.

[0122] That is, in this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and holmium chloride hexahydrate is 1:1:0.5.

[0123] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0124] Embodiment 13:

[0125] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that in Example 2, except that:

[0126] In step 1 of this embodiment, the hydrated rare earth chloride is replaced from the gadolinium chloride hexahydrate in embodiment 2 with an equal amount of holmium chloride hexahydrate.

[0127] That is, in this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and holmium chloride hexahydrate is 1:1:1.

[0128] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0129] Embodiment 14:

[0130] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that in Example 3, except that:

[0131] In step 1 of this embodiment, the hydrated rare earth chloride is replaced from the gadolinium chloride hexahydrate in embodiment 3 with an equal amount of holmium chloride hexahydrate.

[0132] That is, in this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and holmium chloride hexahydrate is 1:1:1.5.

[0133] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0134] Embodiment 15:

[0135] This example provides a method for preparing a transition / rare earth multi-metal co-doped phosphide, which is basically the same as that of Example 4, except that:

[0136] In step 1 of this embodiment, the hydrated rare earth chloride is replaced from the gadolinium chloride hexahydrate in embodiment 4 to an equal amount of holmium chloride hexahydrate.

[0137] That is, in this embodiment, the molar ratio of ferric chloride hexahydrate, nickel chloride hexahydrate and holmium chloride hexahydrate is 1:1:2.

[0138] The transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide of this embodiment is used as a catalyst for producing hydrogen by electrolysis of water.

[0139] like Figure 1 As shown, Figure 1 Figures c and f show the SEM and TEM images of the target product obtained in Example 15, respectively. The catalyst shows that the catalytic material has a regular nanorod structure. Combined with the transmission electron microscope image, it can be seen that a large number of nanospheres and carbon nanotubes are grown on the nanorod structure.

[0140] As shown in Figure 5(a), as the proportion of rare earth metal Ho increases, its hydrogen evolution performance steadily improves. When the FeNiHo co-doping ratio is 1:1:2, at a current density of 10 mA cm -2 Its overpotential is only 99.8 mV, its onset potential is only 37.2 mV, and the current density is 100 mA cm -2 The required overpotential is only 246.2 mV. It shows that the reasonable adjustment of the co-doping ratio of FeNiHo to the catalytic material promotes the improvement of the electrocatalytic hydrogen evolution performance, but considering the economic cost, the metal ratio of 1:1:2 is selected as the optimal performance condition.

[0141] As shown in Figure 5(b), after 8000 cycles of cyclic voltammetry scanning, the linear scanning voltammogram shows that: -2 The potential at the position of the electrode changed by only 2.5 mV. Secondly, the chronopotentiometry was used to measure the current density of 10 mA cm -2 After 24 hours of testing, it was found that the current density of FeNiHo-P-NCNTs had basically not decayed, indicating that the catalyst has excellent stability.

[0142] Based on the above Examples 12 to 15, it can be seen that regulating the co-doping ratio of the three metals FeNiHo has a substantial effect on the hydrogen evolution performance of the FeNiGd-P-NCNTs of the present invention, which shows that the construction strategy of the "transition / rare earth multi-metal co-doped carbon nanotube hybrid-phosphating" system adopted in the present invention greatly improves the hydrogen evolution performance of the catalytic material.

[0143] Based on the above examples 1 to 15, it can be seen that the co-doping of rare earth metals has a substantial improvement on the hydrogen evolution performance of this series of electrocatalysts, and by adjusting the ratio of transition and rare earth multi-metal co-doping, the purpose of adjusting the hydrogen evolution effect of the target product can be further achieved. The above research results show that the construction strategy of the "transition / rare earth multi-metal co-doped carbon nanotube hybrid-phosphating" system is universal for different rare earth metals in improving the hydrogen evolution performance of their catalytic materials.

Claims

1. A method for preparing a transition / rare earth multi-metal co-doped phosphide, characterized in that: The method proceeds as follows: Step 1, dissolving a soluble iron salt, a soluble nickel salt and a hydrated rare earth chloride in water containing an organic ligand, stirring to completely dissolve to form a solution, cooling, washing and centrifuging by a hydrothermal method, and drying to obtain a precursor; The hydrated rare earth chloride is gadolinium chloride hexahydrate, terbium chloride hexahydrate or holmium chloride hexahydrate; Step 2: Mix the precursor prepared in step 1 with an organic nitrogen source compound and grind them evenly, place the porcelain boat containing the materials in a tube furnace and calcine them in a protective atmosphere to obtain iron-nickel-rare earth trimetallic co-doped nitrogen-doped carbon nanotubes; The organic nitrogen source compound is dicyandiamide; Step 3, the iron-nickel-rare earth trimetallic co-doped nitrogen-doped carbon nanotubes and the inorganic phosphorus source compound prepared in step 2 are separately packed into two porcelain boats, and placed in a tube furnace for phosphating to finally obtain transition / rare earth multimetallic co-doped phosphides.

2. The method for preparing transition / rare earth multi-metal co-doped phosphide according to claim 1, characterized in that: In step 1, the soluble iron salt is ferric chloride hexahydrate; the soluble nickel salt is nickel chloride hexahydrate; the organic ligand is trimesic acid; and the molar ratio of the total amount of the soluble iron salt, the soluble nickel salt and the hydrated rare earth chloride to trimesic acid is 3:

2.

3. The method for preparing the transition / rare earth multi-metal co-doped phosphide according to claim 1, characterized in that: In step 1, the molar ratio of the soluble iron salt, the soluble nickel salt and the hydrated rare earth chloride is 1:1:(0.5-3).

4. The method for preparing transition / rare earth multi-metal co-doped phosphide according to claim 1, characterized in that: In step one, the stirring method is magnetic stirring, and the magnetic stirring time is 20 min; in the hydrothermal method, the filling volume ratio of the liner of the high-pressure reactor is 70-80%; the reaction temperature of the sealed reaction is 150°C, and the reaction time is 24 h; the cooling method is natural cooling; the washing method is alternating washing with water and ethanol for 6 to 8 times; the specific conditions of the centrifugation are centrifugation at 7000 rpm for 15 min; the drying method is drying in a vacuum oven at 60°C for 12 h.

5. The method for preparing transition / rare earth multi-metal co-doped phosphide according to claim 1, characterized in that: In step 2, the mass ratio of the precursor to dicyandiamide is 1:(0.5-1.5).

6. The method for preparing transition / rare earth multi-metal co-doped phosphide according to claim 1, characterized in that: In step 2, the calcination temperature is 700-900° C., and the calcination time is 1-3 h; and the protective atmosphere is nitrogen.

7. The method for preparing transition / rare earth multi-metal co-doped phosphide according to claim 1, characterized in that: In step three, the inorganic phosphorus source compound is sodium hypophosphite; the mass ratio of the iron-nickel-rare earth trimetallic co-doped nitrogen-doped carbon nanotubes to the sodium hypophosphite is 1:(5-15).

8. The method for preparing transition / rare earth multi-metal co-doped phosphide according to claim 1, characterized in that: In step 3, the phosphating temperature is 300-400° C. and the time is 1-3 h.

9. The method for preparing transition / rare earth multi-metal co-doped phosphide according to claim 1, characterized in that: In step three, a porcelain boat containing an inorganic phosphorus source compound is placed at the upwind port of a tubular furnace with a protective atmosphere, a porcelain boat containing iron-nickel-rare earth trimetal co-doped nitrogen-doped carbon nanotubes is placed at the downwind port of the combustion tube of the tubular furnace, and a saturated copper sulfate solution is connected to the end of the tubular furnace to remove the tail gas generated during the phosphating process.

10. Use of the transition / rare earth multi-metal co-doped phosphide prepared by the preparation method of the transition / rare earth multi-metal co-doped phosphide according to any one of claims 1 to 9 as a catalyst for producing hydrogen by electrolysis of water.

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