Electrocatalyst with hollow shell layer structure, preparation method and application of electrocatalyst in electrolyzed water

Abstract

The invention discloses an electrocatalyst with a hollow shell layer structure, a preparation method of the electrocatalyst and application of the electrocatalyst in electrolyzed water to solve the technical problem in the electrocatalytic water decomposition process. Ni-gly microspheres are prepared through a hot solvent method, the Ni-gly microspheres serve as an inner core, Ni-gly ZIF-67 is formed through ZIF-67 with the outer portion coated with a regular dodecahedron, and the electrocatalyst with the hollow shell layer structure and the preparation method of the electrocatalyst with the hollow shell layer structure and the application of the electrocatalyst in electrolyzed water are obtained. Then etching to form a multi-shell hollow structure; and finally, forming the hollow multi-shell hollow structure compound Ni2P (at) CoP (at) NC coated by the nitrogen-doped carbon nanocage through a simple calcining process. The Ni2P-coated CoP-coated NC material is a multi-shell hollow material, and has high conductivity and high electron transfer rate. Due to the efficient synergistic effect of multiple components, active sites of the catalyst are rich, and the catalyst has excellent electro-catalytic performance and long-term stability and is a candidate catalyst with very high application potential in electro-catalytic full water splitting.

Description

TECHNICAL FIELD

[0001] The present application relates to a shell hollow structure electrocatalyst, in particular a nitrogen-doped carbon-coated bimetallic phosphide multi-shell hollow structure electrocatalyst, and a preparation method and application in electrolysis of water of the catalyst, belonging to the field of new nanomaterials and new hydrogen energy technologies. BACKGROUND

[0002] Hydrogen energy is considered as the most potential clean energy in the 21st century. With the increasing emphasis on green economic development worldwide, the demand and application fields of hydrogen energy are expanding, and hydrogen energy has become a new focus of energy competition in the "global decarbonization era".

[0003] Hydrogen production is an important part of the hydrogen energy industry chain, and the water electrolysis technology for hydrogen production is relatively mature, which is a very promising strategy for producing hydrogen. Catalyst is the core element to improve the efficiency of water electrolysis. Water electrolysis involves anode oxygen evolution reaction (OER) and cathode hydrogen evolution reaction (HER), which all require high-performance electrocatalysts to reduce the reaction overpotential and improve energy conversion efficiency.

[0004] The catalysts for water electrolysis for hydrogen production are mainly divided into three categories: noble metals, transition metals, and non-metals. At present, Ir, Ru, Pt-based noble metal catalysts are considered to be the best OER and HER electrocatalysts, but the high cost and scarcity of noble metals limit their large-scale application.

[0005] Transition metals (such as Ni, Fe, Mo, and Co) have a noble metal-like unfilled d orbital electron distribution, and are considered to be ideal materials for replacing noble metal catalysts. Transition metal catalysts mainly include transition metal sulfides, phosphides, selenides, oxides, nitrides, carbides, borides, tellurides, and transition metal alloys. Transition metal catalysts have the advantages of low cost, easy availability of raw materials, simple preparation method, diverse structure composition, and high chemical stability, so they have become a research hotspot.

[0006] Among them, transition metal phosphides (TMP) have a structure and electron distribution similar to hydrogenase, so more active sites can be formed during TMP catalytic reaction. Nickel phosphide (Ni2P) and cobalt phosphide (CoP) have unique electronic structures, excellent catalytic activity and stability, and are considered to have great potential as TMP-based water electrolysis catalysts in recent years.

[0007] However, these metal-based phosphides usually only exhibit excellent HER performance and general OER performance, and the overall water splitting activity is not ideal. SUMMARY

[0008] The present application provides a shell hollow structure electrocatalyst, a preparation method of the catalyst, and an application of the catalyst in electrolysis of water to solve technical problems in the process of electrocatalytic decomposition of water.

[0009] The first aspect of the present application is to provide a preparation method of a shell hollow structure electrocatalyst, and the steps include: Step 1, reacting a Ni source with a polyol (at least a diol) to obtain a Ni-polyol complex particle; Step 2, the Ni-polyol complex particle is a core, and ZIF-67 is wrapped outside the core to form a core-shell structure; Step 3, etching the shell layer of the core-shell structure, so that at least part of the ZIF-67 on the side away from the core is etched to form an etching layer, forming a precursor; Step 4, calcining the precursor in the presence of a phosphorus source and nitrogen to form Ni2P from P and at least part of Ni, CoP from P and at least part of Co, and N-doped carbon layer from N doped into the etching layer to obtain a shell hollow structure electrocatalyst.

[0010] In a preferred embodiment, the polyol can be a diol, a triol, a tetraol or more (≥5) polyol, for example, can be glycerol, erythritol, pentaerythritol, etc.

[0011] In a preferred embodiment, the Ni source can be one or more (≥1) of an organic acid salt of Ni, an inorganic acid salt of Ni, more preferably, the inorganic acid salt of Ni can be one or more (≥1) of nickel nitrate, nickel chloride, nickel bromide, nickel sulfate, nickel carbonate, and the organic acid salt of Ni can be one or more (≥1) of nickel formate, nickel acetate, nickel propionate, nickel methanesulfonate, nickel benzoate, nickel benzenesulfinic acid, nickel salicylate, nickel oxalate, nickel succinate, nickel malonate.

[0012] In a preferred embodiment, the Ni source is provided in the form of a dispersion liquid, and the dispersion medium of the dispersion liquid can be one or more (≥1) of an alcohol, an ether, an ester, a ketone, and is particularly preferably an alcohol, such as one or more (≥1) of methanol, ethanol, n-propanol, and isopropanol.

[0013] In a preferred embodiment, the polyol is mixed with water in the dispersion liquid, or the polyol is mixed with water in the dispersion liquid, and then the reaction is carried out.

[0014] In a more preferred embodiment, in step 1, the reaction temperature of the Ni source and the polyol is preferably 100-300°C, more preferably 130-280°C, more preferably 150-250°C, more preferably 180-230°C, and more preferably 200-210°C.

[0015] In a more preferred embodiment, in step 1, the reaction time of the Ni source with the polyol is preferably at least 6 hours, more preferably 8-24 hours, more preferably 10-20 hours, more preferably 12-18 hours, more preferably 15-16 hours.

[0016] In a preferred embodiment, in step 2, the "ZIF-67 wrapping outside the core" comprises: Step 21, dispersing the Ni-polyol complex particles in a second dispersion medium to form a Ni-polyol complex dispersion; Step 22, adding a Co source and 2-methylimidazole (2-MIM) to the Ni-polyol complex dispersion for reaction.

[0017] In a preferred embodiment, the Co source can be an organic acid salt of Co or an inorganic acid salt of Co, preferably the inorganic acid salt of Co is selected from one or more (>1) of cobalt nitrate, cobalt chloride, cobalt bromide, cobalt sulfate, cobalt carbonate; preferably the organic acid salt of Co is selected from one or more (>1) of cobalt formate, cobalt acetate, cobalt propionate, cobalt methane sulfonate, cobalt benzoate, cobalt benzenesulfinate, cobalt salicylate, cobalt oxalate, cobalt succinate, cobalt malonate.

[0018] In a preferred embodiment, the molar ratio of the Co source to 2-methylimidazole is preferably (0.001-0.1):1, more preferably (0.003-0.08):1, more preferably (0.005-0.05):1, more preferably (0.008-0.03):1, more preferably (0.01-0.025):1, more preferably (0.015-0.02):1.

[0019] In a preferred embodiment, the ratio of the Ni-polyol complex to the Co source is preferably 0.005-0.05 mol Co source / g Ni-polyol complex, more preferably 0.008-0.03 mol Co source / g Ni-polyol complex, more preferably 0.01-0.02 mol Co source / g Ni-polyol complex.

[0020] More preferably, the reaction temperature in step 22 is preferably 5-50°C, more preferably 10-40°C, more preferably 15-35°C, more preferably 20-25°C.

[0021] More preferably, the reaction time in step 22 is preferably at least 0.5 hours, more preferably 1-5 hours, more preferably 1.5-4 hours, more preferably 2-3.5 hours, more preferably 2.5-3 hours.

[0022] In a more preferred embodiment, the second dispersion medium can be one or more (>1) of an alcohol, an ether, an ester, a ketone, especially preferred is one or more (>1) of an alcohol, such as methanol, ethanol, n-propanol, isopropanol.

[0023] In a more preferred embodiment, the Ni-polyol complex dispersion can further comprise polyvinylpyrrolidone. More preferably, the weight ratio of the Ni-polyol complex particles to polyvinylpyrrolidone is preferably 1 : (10-50), more preferably 1 : (15-40), more preferably 1 : (20-35), more preferably 1 : (25-30).

[0024] In a more preferred embodiment, the Ni-polyol complex particles are activated by reacting with phytic acid before being dispersed in the second dispersion medium.

[0025] More preferably, the reaction temperature of the Ni-polyol complex particles with phytic acid is preferably 5-50°C, more preferably 10-40°C, more preferably 15-35°C, more preferably 20-25°C.

[0026] More preferably, the reaction time of the Ni-polyol complex particles with phytic acid is preferably at least 0.5 hours, more preferably 1-5 hours, more preferably 1.5-4 hours, more preferably 2-3 hours.

[0027] More preferably, the reaction of the Ni-polyol complex particles with phytic acid is carried out in an alcohol, which can be one or more (>1) of methanol, ethanol, propanol, isopropanol.

[0028] In a preferred embodiment, the core-shell structure is etched with tannic acid in step 3.

[0029] More preferably, the tannic acid can be in the form of a solution, and the pH value of the tannic acid solution is >7, preferably 7.5-10, more preferably 8-9.

[0030] More preferably, the tannic acid can be pH-adjusted with a base, more preferably the base can be one or more (>1) of a metal hydroxide, a carbonate, such as one or more (>1) of KOH, NaOH, LiOH, aqueous ammonia, BaCO3, K2CO3, Na2CO3.

[0031] In a preferred embodiment, at least 0.5 mol of tannic acid is used per 1 kg of core-shell structure, more preferably 0.8-3 mol, more preferably 1-2.5 mol, more preferably 1.5-2 mol.

[0032] More preferably, the etching reaction temperature is preferably 5-50℃, more preferably 10-40℃, more preferably 15-35℃, more preferably 20-25℃.

[0033] More preferably, the etching reaction time is preferably at least 1 minute, more preferably 1-60 minutes, more preferably 5-45 minutes, more preferably 10-30 minutes.

[0034] More preferably, the tannin acid can be provided in the form of an aqueous solution.

[0035] More preferably, the core-shell structure is provided in the form of an aqueous dispersion, especially preferably by ultrasonic dispersion of the core-shell structure in water.

[0036] In a preferred embodiment, the phosphorus source can be elemental phosphorus, or a substance capable of generating phosphorus gas at a calcination temperature, for example, the phosphorus source can be one or more (>1) of hypophosphite, hypophosphorous acid, for example, one or more (>1) of sodium hypophosphite, potassium hypophosphite, sodium hypophosphorous acid, potassium hypophosphorous acid.

[0037] In a preferred embodiment, the precursor to phosphorus source ratio is preferably 0.05-0.5 mol P / g precursor, more preferably 0.07-0.3 mol P / g precursor, more preferably 0.1-0.2 mol P / g precursor.

[0038] In a preferred embodiment, the calcination temperature is preferably at least 200℃, more preferably 200-500℃, more preferably 250-450℃, more preferably 300-350℃.

[0039] In a preferred embodiment, the calcination time is preferably at least 0.5 hours, more preferably 0.5-5 hours, more preferably 1-4 hours, more preferably 2-3 hours.

[0040] In a preferred embodiment, the calcination temperature increase rate is preferably at least 0.5℃ / min, more preferably 0.5-5℃ / min, more preferably 1-4℃ / min, more preferably 2-3℃ / min.

[0041] The second aspect of the present application is to provide a shell hollow structure electrocatalyst, containing at least three layers of structure, the innermost layer containing Ni2P, the outermost layer being a nitrogen-doped carbon layer, and the middle layer containing CoP. Preferably, prepared by the method of the first aspect.

[0042] Preferably, the nitrogen-doped carbon layer is a cage-like structure.

[0043] In a preferred embodiment, the molar ratio of Ni to Co in the shell hollow-structured electrocatalyst is preferably (0.1-5):1, more preferably (0.3-4):1, more preferably (0.5-3.5):1, more preferably (0.8-3):1, and more preferably (1-2):1.

[0044] In a preferred embodiment, the Ni2P in the shell hollow-structured electrocatalyst contains (111), (201), (210), (300), (211) and (400) crystal planes.

[0045] In a preferred embodiment, the CoP in the shell hollow-structured electrocatalyst contains (011), (111), (112), (211) and (301) crystal planes.

[0046] In a preferred embodiment, the shell hollow-structured electrocatalyst is a nanoparticle.

[0047] The third aspect of the present application provides an application of the shell hollow-structured electrocatalyst, which can be used for electrolysis of water, for example, can be used for hydrogen and / or oxygen production by electrolysis of water, and more preferably, the shell hollow-structured electrocatalyst can be used for electrodes for electrolysis of water.

[0048] In a more preferred embodiment, the cathode and anode for electrolysis of water can each be composed of the shell hollow-structured electrocatalyst.

[0049] The present application successfully prepared Ni-gly egg yolk shell microspheres by a hot solvent method, and formed a Ni-gly@ZIF-67 structure by coating the ZIF-67 of a regular dodecahedron on the outside of the Ni-gly egg yolk shell microspheres, then etched by tannic acid to form a multi-shell hollow structure, and finally formed a hollow nitrogen-doped carbon nanocage coated multi-shell hollow structure composite Ni2P@CoP@NC through a simple calcination process.

[0050] The outer shell of nitrogen-doped carbon effectively improves the conductivity of the composite material, and the unique multi-shell hollow structure has a large specific surface area and more active sites, which can ensure the mass transfer path, thereby improving the catalytic activity. This provides a new way for developing new catalyst materials in the process of electrocatalytic decomposition of water and their potential hydrogen energy applications. BRIEF DESCRIPTION OF DRAWINGS

[0051] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments illustrated in the drawings, and their description, are presented to explain the present application and are not intended to limit the present application. In the drawings: Figure 1 XRD diffraction pattern of Ni2P@CoP@NC obtained in the implementation 1 of the present application; Figure 2Raman spectrum (a) and electron paramagnetic resonance (b) of Ni2P@CoP@NC obtained in Embodiment 1 of the present invention; Figure 3 In the figure, (a) is the cyclic voltammogram of hydrogen evolution reaction of Ni2P@CoP@NC obtained in Embodiment 1 of the present invention, (b)-(e) are the cyclic voltammograms of hydrogen evolution reaction of Ni2P@C, CoP@NC, Pt / C and NF in Comparative Examples 1-4, respectively, and (f) is the double layer capacitance curve Cdl of Ni2P@CoP@NC obtained in Embodiment 1 of the present invention and Ni2P, CoP, Pt / C and NF in Comparative Examples 1-4; Figure 4 The HER polarization curves (a), Tafel slope (b), and 10 mA cm⁻¹ of Ni₂P@CoP@NC obtained in Embodiment 1 of this invention and Ni₂P@C, CoP@NC, Pt / C and Nf in Comparative Examples 1-4 are shown. −2 The overpotential bar and Tafel slope diagram at current density (c), and the Ni2P@CoP@NC obtained in Embodiment 1 of the present invention at 10 mA cm⁻¹ −2 The timing current curve (d) is shown below. Figure 5 The OER polarization curves (a), Tafel slope (b), and 20 mA cm⁻¹ of Ni₂P@CoP@NC obtained in Embodiment 1 of this invention and Ni₂P@C, CoP@NC, NF, and RuO₂ in Comparative Examples 1-5 are shown. −2 Overpotential bars and Tafel slope diagrams at current density (c), double-layer capacitance curve (Cdl) (d), Nyquist plot and analog equivalent circuit diagram (e), and the Ni2P@CoP@NC obtained in Embodiment 1 of the present invention at 20 mA cm⁻¹ −2 The timing current curve (d) is shown below. Figure 6 Cyclic voltammetry diagrams of oxygen evolution reaction obtained in the implementation of this invention for (a) Ni2P@CoP@NC; (b) Ni2P; (c) CoP; (d) NF and (e) RuO2; Figure 7 (a) Polarization curves and (b) overall water electrolysis stability of the Ni2P@CoP@NC / / Ni2P@CoP@NC and Pt / C / / RuO2 electrolyzers obtained in the implementation of this invention. Detailed Implementation

[0052] This invention provides a hollow-shell electrocatalyst, its preparation method, and its applications. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0053] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and in the above drawings are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence, and it should be understood that the data thus used can be interchanged under appropriate circumstances. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0054] Example 1: Step 1, Preparation of nickel-based glycerolate spheres (Ni-gly) 0.07 g Ni(NO3)2•6H2O was added to 20 mL of isopropanol, and after ultrasonic dispersion, 4 mL of glycerol and 1 mL of water were added. After stirring at room temperature for 20 minutes, it was transferred to a 50 mL high-pressure reaction kettle with a Telfon lining, and reacted in a 200 ℃ oven for 15 hours.

[0055] After the reaction was completed and it was cooled to room temperature, the solid was collected by centrifugation, washed with ethanol, and finally dried in a vacuum drying oven. The collected product was Ni-gly microspheres.

[0056] Step 2, Preparation of ZIF-67 coated Ni-gly microspheres (Ni-gly@ZIF-67) composite structure 40 mg of Ni-gly was dispersed in 40 mL of ethanol to form a dispersion liquid. At room temperature, 10 mL of an ethanol solution of phytic acid (volume ratio of phytic acid: ethanol = 1:40) was poured into the above dispersion liquid and stirred for 2 hours. This process activated the Ni-gly microspheres.

[0057] Subsequently, ethanol and methanol were used for washing, and after washing, it was directly dispersed in 25 mL of methanol, 1 g of polyvinylpyrrolidone (PVP) was added and stirred for 10 minutes, and then left to stand for 15 minutes to obtain a standing solution.

[0058] 0.20 g Co(NO3)2•6H2O was dissolved in 30 mL of methanol to prepare solution A, and 2.9 g of dimethylimidazole (2-MIM) was dissolved in 60 mL of methanol to prepare solution B. Solution A and B were poured into the above standing solution, and stirred together at room temperature for 2.5 hours.

[0059] The collected solid was washed with methanol and dried to obtain ZIF-67 coated Ni-gly microspheres purple powder, denoted as Ni-gly@ZIF-67.

[0060] Step 3, Preparation of precursor Take 100 mg Ni-gly@ZIF-67 powder and dissolve in 5 mL water and ultrasonic dispersion, get dispersion, with KOH solution (6 mol / L) to adjust the tannic acid (TA) solution to pH value = 8, the solution adjusted to pH value is added dropwise to the dispersion of this step, and is stirred under the condition of room temperature for 10 minutes, the solid is separated by centrifugation, and is washed with ethanol and water respectively, and is dried in a vacuum drying oven at 60℃. The precursor is obtained, which is recorded as Ni-gly@ZIF-67-TA.

[0061] Step 3, Calcination Take 350 mg sodium hypophosphite and 35 mg Ni-gly@ZIF-67-TA powder in a porcelain boat, place sodium hypophosphite on the upper end of the gas flow, and place Ni-gly@ZIF-67-TA powder on the lower end of the gas flow, calcine at 350℃ under N2 atmosphere at a temperature rising rate of 2℃ / min for 2 hours, and obtain black powder, which is recorded as Ni2P@CoP@NC.

[0062] Figure 1 The XRD diffraction pattern of Ni2P@CoP@NC obtained in the embodiment 1 of the present application is shown in the figure. It can be seen from the figure that the XRD peaks are well matched with Ni2P (JCPDS # 03-0953) and CoP (JCPDS # 29-0497). It can be seen from the figure that the peaks at 2θ = 40.8 o , 44.6 o , 47.3 o , 54.2 o , 54.9 o and 74.7 o correspond to the (111), (201), (210), (300), (211) and (400) crystal faces of Ni2P; and the peaks at 2θ = 31.6 o , 36.3 o , 46.2 o , 48.1 o , 56.8 o correspond to the (011), (111), (112), (211) and (301) crystal faces of CoP. The results show that Ni2P and CoP coexist in the Ni2P@CoP@NC obtained in the present application, which is a composite material of Ni2P and CoP.

[0063] Figure 2 The Raman spectrum (a) and electron paramagnetic resonance spectrum (b) of Ni2P@CoP@NC obtained in the present application are shown in the figure. Figure 2 It can be seen from (a) in the figure that the peaks at wavenumber of 1522 and 1644 cm −1Two characteristic bands related to D and G bands of carbon material were observed. The peak intensity ratio (ID / IG) was 0.92, indicating that defects or disordered sites were formed in the carbon shell. Such a carbon shell layer not only benefits the electrocatalytic stability of Ni2P, but also improves the electrochemical performance of the composite material, because the defective carbon has higher π bonds and electron donor-acceptor characteristics. The Raman results confirm the carbon shell coating on the outer layer of the composite material. From Figure 2 It can be known from (b) that electron spin resonance (ESR) indicates the existence of P vacancies. The fluctuation at g ≈ 2.004 indicates that there are lattice vacancies, and P vacancies can increase the active site, adjust the electron density of the active site center, thereby expanding the electrochemically active area, accelerating electron transmission and promoting electron coupling effect, and promoting electrocatalytic reaction.

[0064] Comparative Example 1: Step 1, Preparation of nickel-based glycerolate spheres (Ni-gly) 0.07 g Ni(NO3)2•6H2O was added in 20 mL isopropanol, and after ultrasonic dispersion, 4 mL glycerol and 1 mL water were added respectively. After stirring at room temperature for 20 minutes, it was transferred to a 50 mL high-pressure reaction kettle with Telfon lining, and reacted in a 200 ℃ oven for 15 hours.

[0065] After the reaction was completed and cooled to room temperature, the solid was collected by centrifugation, washed with ethanol, and finally dried in a vacuum drying box. The collected product was Ni-gly microspheres.

[0066] Step 2, Preparation of precursor 1 100 mg of Ni-gly powder was dissolved in 5 mL of water and ultrasonically dispersed to obtain a dispersion liquid. The tannic acid (TA) solution was adjusted to pH = 8 with KOH solution (6 mol / L). The solution with adjusted pH value was added dropwise to the dispersion liquid of this step, and magnetically stirred at room temperature for 10 minutes. The solid was separated by centrifugation, washed with ethanol and water, and dried in a vacuum drying box at 60 ℃. The precursor was obtained and recorded as Ni-gly-TA.

[0067] Step 3, Calcination 350 mg of sodium hypophosphite and 35 mg of Ni-gly-TA powder were placed in a porcelain boat, and the sodium hypophosphite was placed at the upper end of the gas flow, and the Ni-gly-TA powder was placed at the lower end of the gas flow. Under N2 atmosphere, the temperature was raised at a rate of 2 ℃ / min, and calcined at 350 ℃ for 2 hours to obtain black powder, recorded as Ni2P@C.

[0068] Comparative Example 2: Step 1, Preparation of precursor 2 Take 100 mg ZIF-67 powder dissolved in 5 mL water and ultrasonic dispersion, get dispersion, with KOH solution (6 mol / L) to adjust the pH value of tannic acid (TA) solution to 8, adjust the pH value of the solution dropwise into the dispersion of this step, and stir under the condition of room temperature for 10 minutes, centrifugal separation of solid, washed with ethanol and water, respectively, dried in a vacuum drying oven at 60 ℃. Get the precursor, recorded as ZIF-67-TA.

[0069] Step 3, Calcination Take 350 mg sodium hypophosphite and 35 mg ZIF-67-TA powder in a porcelain boat, place sodium hypophosphite on the upper end of the gas flow, and ZIF-67-TA powder on the lower end of the gas flow, calcine under N2 atmosphere at a temperature of 350 ℃ with a heating rate of 2 ℃ / min for 2 hours, get black powder, recorded as CoP@NC.

[0070] Comparative example 3: Commercial platinum carbon (Pt / C) is an electrocatalyst.

[0071] Comparative example 4: Commercial nickel foam (NF) is an electrocatalyst.

[0072] Comparative example 5: Commercial RuO2 is an electrocatalyst.

[0073] Figure 3 In the middle, picture (a) is the hydrogen evolution reaction cyclic voltammogram of Ni2P@CoP@NC obtained by the present application 1, (b)-(e) are the hydrogen evolution reaction cyclic voltammograms of Ni2P@C, CoP@NC, Pt / C and NF in comparative examples 1-4, respectively, and picture (f) is the double-layer capacitance curve Cdl of Ni2P@CoP@NC obtained by the present application 1, and Ni2P, CoP, Pt / C and NF in comparative examples 1-4.

[0074] The present application adopts standard three-electrode system to test the catalytic activity of Ni2P@CoP@NC in 1 M KOH alkaline electrolyte, and analyzes its HER (hydrogen evolution reaction) performance. Under the same conditions, the electrocatalytic performance of Ni2P@C, CoP@NC, commercial Pt / C and pure nickel foam (NF) is also tested. In the non-faraday region, 10 mV s −1 , 20 mV s −1 , 40 mV s −1 , 80 mVs −1 , 100 mV s −1, cyclic voltammetry (CV) tests with five different scan rates to obtain the CV plots of the tested samples. The electrochemical double layer capacitance (Cdl) of the tested samples was fitted from the CV plots, which can be used to judge the electrochemically active surface area (ECSA) of the material. As shown in Figure f, it can be seen from the figure that the Cdl of the Ni2P@CoP@NC is 2.57 mF cm −2 , which is significantly higher than that of the Ni2P@C (1.56 mF cm −2 ) and the CoP@NC (1.37 mF cm −2 ), and is equivalent to that of the commercial Pt / C, indicating that the unique multi-shell structure of the present application has a larger surface area, which provides more electrocatalytic active sites for the HER reaction.

[0075] Figure 4 The HER polarization curves (a), Tafel slopes (b), overpotential columns and Tafel slope plots at a current density of 10 mA cm −2 (c), and the chronoamperometric curve (d) of the Ni2P@CoP@NC obtained in Example 1 of the present application at 10 mA cm −2 of the present application. In a, the LSV curve after iR correction is shown. Compared with the Ni2P@C and the CoP@NC, the Ni2P@CoP@NC catalyst exhibits better HER catalytic activity and can reach a current density of 10 mA cm −2 at a low overpotential of 147 mV. The single-layer hollow Ni2P@C and CoP@NC catalysts have limited catalytic sites, resulting in poor alkaline HER activity, which requires 221 mV and 196 mV, respectively, to reach a current density of 10 mA cm −2 .

[0076] Figure 4 In b, the Tafel slope plots obtained by fitting the polarization curves are shown, which further evaluate the HER reaction kinetics of the catalysts. As can be seen from the figure, the Ni2P@CoP@NC has a lower Tafel slope value (127.71 mV dec −1 ) than the Ni2P@C (137.8 mV dec −1 ) and the CoP@NC (128.4 mV dec −1 ), indicating that it has faster HER kinetics. The lower overpotential and Tafel slope indicate the synergistic catalysis between the components, and also indicate that the P vacancies can reduce the H* / OH* adsorption energy. Figure 4 In c, the overpotential and the corresponding Tafel slope of the five electrocatalysts are further summarized.

[0077] To evaluate the durability of the Ni2P@CoP@NC catalyst in alkaline electrolyte for HER, the potentiostat chronograph curves of Ni2P@CoP@NC were recorded. Figure 4 (d) in the context of a current density of 10 mA cm⁻¹. −2 Under these conditions, after 12 hours of continuous testing, the overpotential of Ni2P@CoP@NC showed no significant change, indicating that Ni2P@CoP@NC has good catalytic stability.

[0078] Figure 5 The OER polarization curves (a), Tafel slope (b), and 20 mA cm⁻¹ of Ni₂P@CoP@NC obtained in Embodiment 1 of this invention and Ni₂P@C, CoP@NC, NF, and RuO₂ in Comparative Examples 1-5 are shown. −2 Overpotential bars and Tafel slope diagrams at current density (c), double-layer capacitance curve (Cdl) (d), Nyquist plot and analog equivalent circuit diagram (e), and the Ni2P@CoP@NC obtained in Embodiment 1 of the present invention at 20 mA cm⁻¹ −2 The timing current curve (f) is shown below.

[0079] The OER (oxygen evolution reaction) electrochemical performance of Ni2P@CoP@NC and Ni2P@C, CoP@NC, and the noble metal catalyst RuO2 was evaluated in a 1.0 M KOH alkaline electrolyte and a standard three-electrode system. Figure 5 As can be seen from a, the present invention Ni2P@CoP@NC shows a significant oxidation peak at the 1.4 V vs. RHE position, which may be due to the influence of the redox reaction of nickel ions and cobalt ions.

[0080] To eliminate the influence of the oxidation peak on the overpotential, a current density of 20 mA cm⁻¹ was selected. −2 The overpotential (η20) at that time is used as a standard for evaluating the OER performance of the material. Figure 5 The results in a show that at a current density of 20 mA cm⁻¹ −2 At 200 mA cm⁻¹, the overpotential of Ni₂P@CoP@NC is only 293 mV, significantly lower than that of monolayer structures Ni₂P@C (318 mV) and CoP@NC (328 mV). Furthermore, the advantages of Ni₂P@CoP@NC become more pronounced with increasing current density, especially at 200 mA cm⁻¹. −2The catalytic activity of Ni2P@CoP@NC is close to the OER performance of commercial RuO2 at high current density. This indicates that the multiple components in Ni2P@CoP@NC are beneficial to the redistribution of electron density and local atomic rearrangement, thus effectively adjusting the electronic structure and coordination environment of the material, and playing a synergistic role. At the same time, the electron rearrangement is beneficial to the transfer of charge on the active site from the electrode interface to the adsorbed reactant.

[0081] The Tafel slope of different catalysts is obtained according to the polarization curve, as shown by b in Figure 5 , the Tafel slope of Ni2P@CoP@NC is lower, which is 115.15 mV dec −1 , which is significantly lower than the Tafel slopes of the comparative samples Ni2P@C and CoP@NC, which are 171.09 mV dec −1 and 121.47 mV dec −1 , which further proves that Ni2P@CoP@NC has a faster reaction kinetics in the OER reaction. In order to make the results more obvious, the present application makes a column chart of the overpotential (η20) at a current density of 20 mA cm −2 and the corresponding Tafel slope, as shown by c in Figure 5 .

[0082] The EIS research results also prove that Ni2P@CoP@NC has good electrochemical performance. As can be seen from e in Figure 5 , the charge transfer resistance (Rct) of Ni2P@CoP@NC is the smallest among all samples, and the smaller the Rct value, the faster the charge transfer between the interface of the catalyst and the electrolyte. It is proved that the interface between the present application Ni2P@CoP@NC and the electrolyte in alkaline conditions occurs a fast electron transfer process, has a faster charge transfer efficiency and a higher electrochemical efficiency.

[0083] Figure 5 f in is the V-T curve graph obtained by continuous discharge for 12 h, and the potential of Ni2P@CoP@NC remains stable during the 12 h discharge process. The excellent durability of Ni2P@CoP@NC may be attributed to the unique hollow structure and the protection of the nitrogen-doped carbon shell, which avoids the aggregation of the catalytic material and the shedding of the sample during the reaction process, thus ensuring its long-term stability.

[0084] In order to further study the inherent catalytic activity of the multi-shell hollow material catalyst Ni2P@CoP@NC, the double-layer capacitance (Cdl) is measured to calculate the electrochemical active surface area (ECSA) of the sample. According to the CV graph, the electrochemical double-layer capacitance (Cdl) of the test sample is fitted, which can be used to judge the electrochemical active surface area (ECSA) of the material, as shown inFigure 5 Cdl curve of d and Figure 6 as shown. Figure 6 The oxygen evolution reaction cyclic voltammograms of (a) Ni2P@CoP@NC; (b) Ni2P; (c) CoP; (d) NF and (e) RuO2 obtained in the implementation of the present application.

[0085] As shown in Figure 5 the Cdl curve of d and Figure 6 The CV curves of each material a-e can be seen that the CV cycle of each catalyst is uniformly increased at different scan rates, and the Cdl of Ni2P@CoP@NC is 25.31 mF cm −2 , which is significantly higher than that of Ni2P@C (11.87 mF cm −2 ) and CoP@NC (14.59 mF cm −2 ), indicating that the Ni2P@CoP@NC of the present application has more OER electrocatalytic active sites. In addition to the commercial RuO2, the closed curve area formed by the CV curve of the Ni2P@CoP@NC of the present application is the largest, which is beneficial to the effective combination with the OER reaction intermediate M-OH, and further improves the catalytic activity. This further indicates that the Ni2P@CoP@NC provides a large number of active sites due to its special multi-shell hollow structure and P vacancies, so that the catalyst is in full contact with the electrolyte, the catalytic reaction active area is increased, and the channel for O2 overflow is provided in the oxygen evolution reaction process.

[0086] Figure 7 The Ni2P@CoP@NC / / Ni2P@CoP@NC and Pt / C / / RuO2 electrolytic cell and polarization curve (a), and full water splitting stability curve (b) obtained in the implementation of the present application. In view of the excellent HER and OER catalytic activity of Ni2P@CoP@NC, the overall water splitting activity of Ni2P@CoP@NC in 1 M KOH solution was further evaluated by using a double electrode configuration and Ni2P@CoP@NC catalyst as cathode and anode (Ni2P@CoP@NC / / Ni2P@CoP@NC). At the same time, a commercial Pt / C, RuO2 was tested as an electrolytic double electrode (Pt / C / / RuO2) for comparison. As shown in Figure 7 a, during the electrolysis process, a large amount of gas bubbles are generated at the cathode (H2) and the anode (O2), and the Ni2P@CoP@NC / / Ni2P@CoP@NC only needs a voltage of 1.62 V to reach a current density of 10 mA cm −2 , which is slightly higher than that of the Pt / C / / RuO2 electrode (1.59 V). The performance of the Ni2P@CoP@NC / / Ni2P@CoP@NC electrolytic system of the present application can be comparable to that of the commercial noble metal electrode electrolytic system. Figure 7The b indicates that the Ni2P@CoP@NC / / Ni2P@CoP@NC electrolysis system shows good stability within 12 hours, and the potential is basically unchanged.

[0087] In summary, the Ni2P@CoP@NC of the application is a multi-shell hollow material, which has high conductivity and fast electron transfer rate. The efficient synergistic effect of multiple components makes the active site rich, has excellent electrocatalytic performance and long-term stability, and is a candidate catalyst with very application potential for electrocatalytic overall water splitting.

[0088] Example 2: Step 1, Preparation of nickel-based glycerolate spheres (Ni-gly) 0.06 g of NiCl2·6H2O was added to 20 mL of ethanol, and after ultrasonic dispersion, 4.5 mL of glycerol and 1 mL of water were added. After stirring at room temperature for 20 minutes, it was transferred to a 50 mL high-pressure reaction kettle with a Telfon lining, and reacted in a 200℃ oven for 15 hours.

[0089] After the reaction was completed and cooled to room temperature, the solid was collected by centrifugation, washed with ethanol, and finally dried in a vacuum drying box. The collected product was Ni-gly microspheres.

[0090] Step 2, Preparation of ZIF-67 coated Ni-gly microspheres (Ni-gly@ZIF-67) composite structure 50 mg of Ni-gly was dispersed in 40 mL of ethanol, and 10 mL of an ethanol solution of phytic acid (volume ratio of phytic acid:ethanol=1:40) was added. After stirring at room temperature for 2 hours, 1 g of polyvinylpyrrolidone (PVP) was added to the solution, and the mixture was stirred for 10 minutes and then allowed to stand for 15 minutes.

[0091] Subsequently, ethanol and water were used for washing, and after washing, the product was directly dispersed in 25 mL of methanol, 1 g of polyvinylpyrrolidone (PVP) was added, and the mixture was stirred for 10 minutes and then allowed to stand for 15 minutes to obtain a standing solution.

[0092] 0.20 g of Co(NO3)2·6H2O was dissolved in 30 mL of methanol, and 3 g of dimethylimidazole was dissolved in 60 mL of methanol. The two solutions were added to the standing solution, and the mixture was stirred at room temperature for 2.5 hours.

[0093] The collected solid was washed with methanol and dried to obtain a purple powder of ZIF-67-coated Ni-gly microspheres, which was denoted as Ni-gly@ZIF-67.

[0094] Step 3, Preparation of precursor Take 100 mg Ni-gly@ZIF-67 powder and dissolve in 5 mL water and ultrasonic dispersion, get dispersion, with KOH solution (6 mol / L) to adjust the tannic acid (TA) solution to pH value = 7.8, the adjusted pH value solution is added dropwise to the dispersion of this step, and is stirred under the condition of room temperature for 10 minutes, the solid is separated by centrifugation, and is washed with ethanol and water respectively, and is dried in a vacuum drying oven at 60 ℃. The precursor is obtained, which is recorded as Ni-gly@ZIF-67-TA.

[0095] Step 3, Calcination Take 350 mg sodium hypophosphite and 35 mg Ni-gly@ZIF-67-TA powder in a porcelain boat, place sodium hypophosphite on the upper end of the gas flow, and place Ni-gly@ZIF-67-TA powder on the lower end of the gas flow, calcine at 350 ℃ under N2 atmosphere at a heating rate of 2 ℃ / min for 2 hours, obtain black powder, which is recorded as Ni2P@CoP@NC.

[0096] Example 3: Step 1, Preparation of nickel-based glycerolate spheres (Ni-gly) Add 0.06 g NiSO4·6H2O in 20 mL propyl alcohol, ultrasonic dispersion, then add 4.2 mL glycerol and 1 mL water respectively, stir at room temperature for 20 minutes, then react at 200 ℃ for 15 hours.

[0097] Centrifugal collection of solid, washed with ethanol, and finally dried in a vacuum drying oven, the collected product is Ni-gly microspheres.

[0098] Step 2, Preparation of ZIF-67 coated Ni-gly microspheres (Ni-gly@ZIF-67) composite structure Take 50 mg of Ni-gly and disperse in 40 mL of ethanol, add 10 mL of phytic acid ethanol solution (volume ratio of phytic acid: ethanol = 1:40), stir at room temperature for 2 hours. Then washed with ethanol and water respectively, and then dispersed in 25 mL of methanol, add 1 g of polyvinylpyrrolidone (PVP) and stir for 10 minutes, and stand for 15 minutes to obtain a standing solution.

[0099] 0.20 g Co(NO3)2·6H2O is dissolved in 30 mL methanol, and 3 g dimethylimidazole is dissolved in 60 mL methanol, which is added to the above standing solution, and stirred at room temperature for 2.5 hours.

[0100] The collected solid is washed with methanol and dried to obtain ZIF-67 coated Ni-gly microspheres purple powder, which is recorded as Ni-gly@ZIF-67.

[0101] Step 3, Preparation of precursor Take 100 mg Ni-gly@ZIF-67 powder and dissolve in 5 mL water and ultrasonic dispersion, get dispersion, with KOH solution (6 mol / L) to adjust the tannic acid (TA) solution to pH value = 8, drop into the dispersion of this step, room temperature stirring 10 minutes.

[0102] Centrifugal separation of solids, washed with ethanol and water, respectively, at 60 ℃ vacuum drying oven drying. Get the precursor, recorded as Ni-gly@ZIF-67-TA.

[0103] Step 3, Calcination Take 350 mg sodium hypophosphite and 35 mg Ni-gly@ZIF-67-TA powder in the porcelain boat, sodium hypophosphite is placed on the upper end of the gas flow, Ni-gly@ZIF-67-TA powder is placed at the lower end of the gas flow, under N2 atmosphere, with the heating rate of 2 ℃ / min, 350 ℃ temperature calcination 2 hours, get black powder, recorded as Ni2P@CoP@NC.

[0104] Example 4: Step 1, Preparation of nickel-based glycerolate spheres (Ni-gly) In 30 mL of propyl alcohol, 0.08 g Ni(NO3)2•6H2O, ultrasonic dispersion, then add 5 mL glycerol and 1 mL water, room temperature stirring 20 minutes, in 200 ℃ reaction 15 hours.

[0105] Centrifugal collection of solids, washed with ethanol, vacuum drying, the collected product is Ni-gly microspheres.

[0106] Step 2, Preparation of ZIF-67 coated Ni-gly microspheres (Ni-gly@ZIF-67) composite structure Take 40 mg of Ni-gly dispersed in 40 mL of ethanol, add 13 mL of phytic acid ethanol solution (volume ratio of phytic acid: ethanol = 1:40), room temperature stirring 2 hours.

[0107] The solid product is washed with ethanol and methanol, then dispersed in 30 mL of methanol, add 1 g of polyvinylpyrrolidone (PVP) stirring 10 minutes, standing 15 minutes.

[0108] Dissolve 0.20 g CoSO4•7H2O in 35 mL of methanol, dissolve 3 g of dimethyl imidazole in 60 mL of methanol, together with the above standing solution, room temperature stirring 2.5 hours.

[0109] Centrifugal collection of solids, washed with methanol, dried, get ZIF-67 coated Ni-gly microspheres purple powder, recorded as Ni-gly@ZIF-67.

[0110] Step 3, Preparation of precursor Take 100 mg Ni-gly@ZIF-67 powder dissolved in 5 mL water and ultrasonic dispersion, get the dispersion; with KOH solution (6 mol / L) to adjust the tannic acid (TA) solution to pH value = 8, drop into the dispersion of this step, and stir at room temperature for 10 minutes, centrifugal separation of solid, washed with ethanol and water, respectively, at 60 ℃ vacuum drying. Get the precursor, recorded as Ni-gly@ZIF-67-TA.

[0111] Step 3, Calcination Take 350 mg sodium hypophosphite and 35 mg Ni-gly@ZIF-67-TA powder in porcelain boat, sodium hypophosphite is placed on the upper end of the airflow, Ni-gly@ZIF-67-TA powder is placed at the lower end of the airflow, calcined at 350 ℃ under N2 atmosphere with the heating rate of 2 ℃ / min for 2 hours, get black powder, recorded as Ni2P@CoP@NC.

[0112] The above describes the specific embodiments of the present application in detail, but it is only as an example, the present application is not limited to the above described specific embodiments. For those skilled in the art, any equivalent modification and replacement of the present application are also within the scope of the present application. Therefore, the equivalent transformation and modification without departing from the spirit and scope of the present application should be covered in the scope of the present application.

Claims

1. A method for preparing a hollow-shell electrocatalyst, characterized in that the steps include... include: Step 1: React the Ni source with a polyol to obtain Ni-polyol complex particles; Step 2: Ni-polyol complex particles serve as the core, and ZIF-67 is wrapped around the core to form a core-shell structure; Step 3: Etch the shell of the core-shell structure so that Co in the side of ZIF-67 away from the core is etched to form an etched layer, thus forming the precursor; Step 4: In the presence of phosphorus source and nitrogen, the precursor is calcined, P and Ni form Ni2P, P and Co form CoP, and N is doped into the etching layer to form an N-doped carbon layer, thus obtaining a hollow shell structure electrocatalyst.

2. The preparation method according to claim 1, characterized in that, The Ni source is selected from one or more of organic acid salts and inorganic acid salts of Ni, wherein the inorganic acid salt of Ni is selected from one or more of nickel nitrate, nickel chloride, nickel bromide, nickel sulfate, and nickel carbonate, and the organic acid salt of Ni is selected from one or more of nickel formate, nickel acetate, nickel propionate, nickel methanesulfonate, nickel benzoate, nickel benzenesulfinate, nickel salicylate, nickel oxalate, nickel succinate, and nickel malonate. The phosphorus source is selected from elemental phosphorus or a substance that can produce phosphorus gas at a calcination temperature; The polyol is selected from diols, triols, tetraols or more.

3. The preparation method according to claim 1, characterized in that, In step 1, the reaction temperature between the Ni source and the polyol is 100-300℃; the reaction time is at least 6 hours. In step 3, the core-shell structure is etched with tannic acid, wherein the tannic acid is a solution with a pH value > 7, and at least 0.5 mol of tannic acid is used per 1 kg of core-shell structure; the etching reaction temperature is 5-50℃, and the etching reaction time is at least 1 minute; In step 3, the ratio of the precursor to the phosphorus source is 0.05-0.5 mol P / g precursor, the calcination temperature is at least 200°C, the calcination time is at least 0.5 hours, and the calcination heating rate is at least 0.5°C / minute.

4. The preparation method according to claim 1, characterized in that, In step 2, the "external wrapping of the core with ZIF-67" includes: Step 21: Disperse the Ni-polyol complex particles in the second dispersion medium to form a Ni-polyol complex dispersion; Step 22: Co source and 2-methylimidazole are added to the Ni-polyol complex dispersion for reaction.

5. The preparation method according to claim 4, characterized in that, The molar ratio of the Co source to 2-methylimidazole is (0.001-0.1):1; the ratio of the Ni-polyol complex to the Co source is 0.005-0.05 mol Co source / g Ni-polyol complex; The reaction temperature in step 22 is 5-50℃, and the reaction time is at least 0.5 hours.

6. The preparation method according to claim 4, characterized in that, The second dispersion medium can be one or more of alcohols, ethers, esters, and ketones; The Co source is selected from one or more of organic acid salts or inorganic acid salts of Co, wherein the inorganic acid salt of Co is selected from one or more of cobalt nitrate, cobalt chloride, cobalt bromide, cobalt sulfate, and cobalt carbonate, and the organic acid salt of Co is selected from one or more of cobalt formate, cobalt acetate, cobalt propionate, cobalt methanesulfonate, cobalt benzoate, cobalt benzenesulfinate, cobalt salicylate, cobalt oxalate, cobalt succinate, and cobalt malonate.

7. The preparation method according to claim 4, characterized in that, Polyvinylpyrrolidone is also added to the Ni-polyol complex dispersion, and the weight ratio of Ni-polyol complex particles to polyvinylpyrrolidone is 1:(10-50).

8. A hollow-shell electrocatalyst, characterized in that, It contains at least three layers: the innermost layer contains Ni2P, the outermost layer is a nitrogen-doped carbon layer, and the middle layer contains CoP; the molar ratio of Ni to Co is (0.1-5):

1.

9. An application of the hollow shell structure electrocatalyst according to claim 8, characterized in that, The hollow shell structure electrocatalyst is used for water electrolysis.

10. The application according to claim 9, characterized in that, Both the cathode and anode of the water electrolysis are composed of the aforementioned hollow shell structure electrocatalyst.

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