A tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst and its preparation method and application

Abstract

The present invention discloses a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst and its preparation method and application. The present invention adopts 5,10,15,20-tetra (3-pyridyl) porphyrin nickel (II) (referred to as tetrapyridyl nickel porphyrin, denoted as m-NiTPyP) and carboxylated carbon nanotubes (CNTs) to prepare tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst (m-NiTPyP / CNTs). The m-NiTPyP / CNTs is loaded on nickel foam and has excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity, and is used as anode material and cathode material in an alkaline double electrode electrolyzer to show good electrolytic water catalytic activity and stability. Therefore, it has good application prospects in the field of electrolytic water technology as a bifunctional electrocatalyst.

Description

Technical Field

[0001] The invention relates to the technical field of electrocatalysts and their application in electrolyzing water, and in particular to a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst, a preparation method and their application in electrolyzing water. Background Art

[0002] With the increasing depletion of fossil energy, the development and utilization of clean energy is considered to be the most effective way to ensure energy security and protect the environment. Electrocatalytic water splitting technology for hydrogen production is considered to be an advanced energy conversion technology and an effective way to produce sustainable hydrogen energy. In practical applications, it is very necessary to develop low-cost and high-efficiency electrocatalysts to reduce the overpotential of the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. At present, IrO2 (or RuO2) for OER and Pt / C for HER have been proven to be efficient electrocatalysts, but the scarcity and high price of their materials limit their widespread application. Therefore, seeking efficient, stable, and low-cost non-precious metal-based catalysts, reducing the cost of electrocatalysts in the water electrolysis process, and optimizing the water electrolysis process are research hotspots in the field of electrocatalytic water splitting technology for hydrogen production.

[0003] Studies have shown that the combination of organic macromolecules and carbon materials can not only improve the conductivity of the material, but also effectively adjust the appearance and electronic environment of organic macromolecular electrocatalysts, thereby further improving their electrocatalytic performance. In addition, the preparation of bifunctional electrocatalysts with excellent performance that can catalyze both OER and HER half-reactions in the same electrolyte, improve the slow kinetics of HER and OER, and achieve efficient electrocatalytic water splitting in the same electrolyte are key issues for simplifying electrolyzer design, electrolysis process, reducing water electrolysis costs, and promoting large-scale application of water electrolysis technology.

[0004] In recent years, metal porphyrin derivatives have been widely used to construct photoactive (electroactive) materials. The variable metal center in the macrocyclic ring and the adjustable functional groups outside the macrocyclic ring make metal porphyrin derivatives very suitable for adjusting their structure and electronic properties at the molecular level. At present, there are reports using metal porphyrin polymers as electrocatalysts to explore their OER or HER performance, but reports using single porphyrin molecules as electrocatalysts are extremely rare.

[0005] As early as 2017, the inventors of the present patent reported a synthesis method of 5,10,15,20-tetrakis(3-pyridyl)porphyrin nickel(II) (i.e., m-NiTPyP) (Dalton Transactions 2017,46,8219), but did not explore and study its application performance, especially its electrocatalytic performance.

[0006] At present, there are no research reports or patent disclosures at home and abroad on the preparation method of a bifunctional catalyst for water splitting by combining 5,10,15,20-tetra(3-pyridyl)porphyrin nickel(II) (m-NiTPyP) as an electrocatalytic active material with carbon nanotubes (CNTs) and its application in water electrolysis. Summary of the invention

[0007] In view of the scarcity and high cost of materials for current Pt-based HER electrocatalysts and Ir / Ru-based OER electrocatalysts, as well as the high cost caused by the use of different electrocatalysts in current electrolytic cells, as well as the technical problems mentioned above, the purpose of the present invention is to provide a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst, a preparation method and its application in water electrolysis. The present invention uses 5,10,15,20-tetra(3-pyridyl) porphyrin nickel (II) (referred to as tetrapyridyl nickel porphyrin, denoted as m-NiTPyP) and carboxylated carbon nanotubes (CNTs) to prepare tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst (m-NiTPyP / CNTs). In the electrocatalyst, chemically bonded m-NiTPyP and CNTs are used as electrocatalytic active materials and electrical conductors, respectively, to achieve complementary advantages, thereby constructing a class of bifunctional electrocatalysts with excellent performance, which can achieve efficient electrocatalytic full water decomposition in the same electrolyte.

[0008] The m-NiTPyP / CNTs electrocatalyst preparation method is simple to operate. When loaded on nickel foam, it not only has excellent HER and OER half-reaction catalytic activity in alkaline electrolyte, but can also be used as both anode and cathode materials for water electrolysis, exhibiting good bifunctional electrocatalytic activity and stability.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] In a first aspect, the present invention provides a method for preparing a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst, comprising the following steps:

[0011] (1) adding m-NiTPyP and CNTs into an organic solvent and performing ultrasonic dispersion to obtain a dispersed solution;

[0012] Wherein, m-NiTPyP is 5,10,15,20-tetra(3-pyridyl)porphyrin nickel(II) (referred to as tetrapyridyl nickel porphyrin); CNTs is carboxylated carbon nanotubes;

[0013] (2) refluxing the dispersed solution under an inert atmosphere until the reaction is complete;

[0014] (3) The product is centrifuged, washed, and then dried to obtain the m-NiTPyP / CNTs bifunctional electrocatalyst.

[0015] Furthermore, in the step (1), 1.4-2.8 mg of m-NiTPyP and 2.0-4.0 mg of CNTs are added to every 1 ml of organic solvent.

[0016] Furthermore, in step (2), the inert gas includes nitrogen, argon, etc.

[0017] Furthermore, in step (1), the organic solvent is N,N-dimethylformamide (DMF).

[0018] Furthermore, in the step (2), the reflux temperature is 140-160° C., and the reflux time is 4-8 hours.

[0019] Furthermore, in the step (3), the product is centrifuged and then washed with dichloromethane, ethanol, and deionized water in sequence, and then vacuum dried to obtain the m-NiTPyP / CNTs bifunctional electrocatalyst.

[0020] In a second aspect, the present invention provides a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst prepared by the method of the first aspect, wherein the molecular structure of the catalyst is formed by chemically bonding tetrapyridyl nickel porphyrin and carboxyl / hydroxyl groups on the surface of carbon nanotubes; wherein m-NiTPyP is an electrocatalytically active material, and CNTs are an electrical conductor and carrier.

[0021] In a third aspect, the present invention provides a method for applying the catalyst according to the second aspect, comprising the following steps:

[0022] (1) dispersing the tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst in a Nafion ethanol solution to obtain an electrocatalyst slurry; dropping the slurry on a nickel foam NF, and drying to obtain an electrocatalyst-loaded NF electrode;

[0023] (2) In a three-electrode electrolytic cell containing a working electrode, a reference electrode, and a counter electrode, an alkaline solution is used as the electrolyte, and the NF electrode loaded with the electrocatalyst is used as the working electrode, and power is applied to carry out electrocatalytic hydrolysis; in a two-electrode electrolytic cell, an alkaline solution is used as the electrolyte, and the NF electrodes loaded with the electrocatalyst are used as the cathode and anode, and power is applied to carry out electrocatalytic hydrolysis.

[0024] Furthermore, in step (1), the weight mass fraction of the Nafion ethanol solution is 0.05%-0.1%.

[0025] Furthermore, in step (1), the catalyst loading in the NF electrode loaded with electrocatalyst is 0.3-0.8 mg cm -2 .

[0026] Furthermore, in step (2), the alkali solution includes KOH solution and NaOH solution.

[0027] Compared with the existing electrocatalysts, the tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst (m-NiTPyP / CNTs) of the present invention has the following beneficial effects:

[0028] 1) This paper synthesized a tetrapyridyl nickel porphyrin / carbon nanotube composite material as a bifunctional electrocatalyst for the first time. -2 When current is applied, the overpotential is only 267 mV for OER and 138 mV for HER.

[0029] 2) The present invention provides a bifunctional electrocatalyst with high efficiency and excellent performance. When used as the cathode material and anode material of a dual-electrode electrolytic cell for the complete water splitting reaction, only a voltage of 1.62 V is required to obtain 10 mA cm -2 This indicates that it can be used as a bifunctional electrocatalyst.

[0030] 3) The tetrapyridyl nickel porphyrin / carbon nanotube composite material provided by the present invention has better electrocatalytic activity than most porphyrin-based electrocatalysts and has good stability, and has good prospects in practical application of water electrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the application of the tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst prepared by the present invention in a double-electrode electrolytic cell and a molecular structure diagram of the tetrapyridyl nickel porphyrin.

[0032] Figure 2 This is an infrared spectrum of a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst (m-NiTPyP / CNTs) prepared in an embodiment of the present invention.

[0033] Figure 3 It is a transmission electron microscope image of a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst (m-NiTPyP / CNTs) prepared in an embodiment of the present invention.

[0034] Figure 4 It is a linear sweep voltammogram of an oxygen evolution reaction of a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst (m-NiTPyP / CNTs) prepared in an embodiment of the present invention in an alkaline electrolyte.

[0035] Figure 5 The linear sweep voltammogram of a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst (m-NiTPyP / CNTs) prepared in an embodiment of the present invention in a hydrogen evolution reaction in an alkaline electrolyte.

[0036] Figure 6The linear sweep voltammogram of the tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst (m-NiTPyP / CNTs) prepared in an embodiment of the present invention, which is used as both the cathode material and the anode material of a double-electrode electrolytic cell, for the complete decomposition of water in an alkaline electrolyte.

[0037] Figure 7 The present invention discloses a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst (m-NiTPyP / CNTs) prepared in an embodiment of the present invention, which is used as both cathode material and anode material of a dual-electrode electrolytic cell, and a current-time curve of complete water decomposition in an alkaline electrolyte. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the content of the present invention is not limited thereto at all.

[0039] Unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the field. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the field. Among them, 5,10,15,20-tetra(3-pyridyl)porphyrin nickel (II) (referred to as tetrapyridyl nickel porphyrin, denoted as m-NiTPyP) is synthesized using the method reported in the paper published by the inventor of the present invention and his research group (Dalton Transactions 2017, 46, 8219), which is not within the scope of protection of the present invention. Specifically, it includes two steps: (1) dissolving 25 mmol of 3-pyridyl carboxaldehyde in 100 mL of propionic acid (PA) to form solution A, reflux at 140°C for 30 minutes, then dissolving 25 mmol of pyrrole in 10 mL of PA to form solution B, stirring continuously for 30 minutes, and then dripping solution B into solution A. The resulting mixture is refluxed at 140°C under N2 atmosphere for 8 hours, and then the residual PA is removed by vacuum distillation. The obtained solid was added to 30 mL of DMF and stirred overnight, and then filtered and washed with ether to obtain a crude sample. The crude sample was purified by silica gel chromatography with dichloromethane / methanol (15:1, V / V), and the purple solid was further recrystallized with a dichloromethane / hexane mixture to obtain m-H2TPyP. (2) A mixture of 0.85 mmol of Ni(Ac)2·4H2O and 0.33 mmol of m-H2TPyP was dispersed in 20 mL of DMF / acetic acid (1:1, V / V), refluxed at 140°C for 48 hours, cooled, and the suspension was centrifuged and washed. The collected solid was dried at 80°C in vacuum overnight to obtain m-NiTPyP, whose molecular structure is listed in Figure 1 .

[0040] Example 1

[0041] A method for synthesizing a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst comprises the following steps:

[0042] 28.0 mg of m-NiTPyP was mixed with 40.0 mg of carboxylated CNTs, and 20 ml of DMF solvent was added for ultrasonic dispersion for 30 minutes. Then, the mixture was refluxed at 150 °C for 4 hours under N2 atmosphere. The product was centrifuged, washed three times with dichloromethane, ethanol, and deionized water, and then dried under vacuum at 100 °C to obtain a bifunctional electrocatalyst (m-NiTPyP / CNTs).

[0043] Example 2

[0044] A method for synthesizing a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst comprises the following steps:

[0045] 56.0 mg of m-NiTPyP was mixed with 70.0 mg of carboxylated CNTs, and 20 ml of DMF solvent was added for ultrasonic dispersion for 30 minutes. Then, the mixture was refluxed at 150 °C for 4 hours under N2 atmosphere. The product was centrifuged, washed three times with dichloromethane, ethanol, and deionized water, and then dried under vacuum at 100 °C to obtain a bifunctional electrocatalyst (m-NiTPyP / CNTs).

[0046] Example 3

[0047] A method for synthesizing a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst comprises the following steps:

[0048] 42.0 mg of m-NiTPyP and 42.0 mg of carboxylated CNTs were mixed, 20 ml of DMF solvent was added, and ultrasonic dispersion was performed for 30 minutes. Then, reflux was performed at 150 °C for 4 hours under N2 atmosphere. The product was centrifuged, washed three times with dichloromethane, ethanol, and deionized water, and then dried under vacuum at 100 °C to obtain a bifunctional electrocatalyst (m-NiTPyP / CNTs).

[0049] Example 4

[0050] A method for synthesizing a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst comprises the following steps:

[0051] 36.0 mg of m-NiTPyP was mixed with 60.0 mg of carboxylated CNTs, and 20 ml of DMF solvent was added for ultrasonic dispersion for 30 minutes. Then, the mixture was refluxed at 150 °C for 4 hours under N2 atmosphere. The product was centrifuged, washed three times with dichloromethane, ethanol, and deionized water, and then dried at 100 °C in vacuum to obtain a bifunctional electrocatalyst (m-NiTPyP / CNTs).

[0052] Figure 2 The infrared spectrum of m-NiTPyP / CNTs synthesized in Example 1 is given. The characteristic infrared absorption bands of m-NiTPyP, such as 700-800 cm -1(CH), ~1070 / 1350cm -1 (CH of pyrrole) and ~1417cm -1 (C=C), etc., can still be observed from the infrared spectrum of the m-NiTPyP / CNTs composite. In addition, the composite has a peak at 3429 cm -1 The infrared absorption bands at can be attributed to the surface -OH / -COOH groups of CNTs. These results confirm that m-NiTPyP was successfully loaded on CNTs.

[0053] Figure 3 A transmission electron microscopy image of m-NiTPyP / CNTs synthesized in Example 2 is given. As can be seen from the image, CNTs are in close contact with the agglomerated nanoparticles of m-NiTPyP.

[0054] The m-NiTPyP / CNTs were used as a single electrocatalyst for OER or HER in alkaline electrolyte (1.0 M KOH solution), and as a bifunctional electrocatalyst for water electrolysis in alkaline electrolyte (1.0 M KOH solution).

[0055] Application Example 1

[0056] 3.0 mg of m-NiTPyP / CNTs prepared in Example 1 was dispersed into 3.0 ml of Nafion ethanol solution (weight percentage of 0.05%) and ultrasonically treated for 30 minutes to obtain an electrocatalyst slurry. 0.50 ml of the slurry was dropped on NF (1.0 cm × 2.0 cm) and completely dried under an infrared lamp to obtain a NF electrode. In a traditional three-electrode electrolytic cell (the NF electrode loaded with electrocatalyst, the saturated calomel electrode and the platinum sheet were used as the working anode, reference electrode and counter electrode, respectively), 1.0 M KOH solution was used as the electrolyte, and the LSV method was used to test its OER activity as a single electrocatalyst. Among them, the electrocatalyst loading was 0.5 mg cm -2 , voltage scan rate was 5.0 mV s -1 .

[0057] The test results are as follows Figure 4 When the NF electrode loaded with m-NiTPyP / CNTs was used as the anode of the electrolytic cell, the current density of OER was 10 mA cm in 1.0 M KOH alkaline solution. -2 The corresponding overpotential is only 267mV.

[0058] Application Example 2

[0059] 3.0 mg of m-NiTPyP / CNTs prepared in Example 1 was dispersed into 3.0 ml of Nafion ethanol solution (weight percentage of 0.05%) and ultrasonically treated for 30 minutes to obtain an electrocatalyst slurry. 0.50 ml of the slurry was dropped on NF (1.0 cm × 2.0 cm) and completely dried under an infrared lamp to obtain a NF electrode. In a traditional three-electrode electrolytic cell (the NF electrode loaded with electrocatalyst, the saturated calomel electrode and the platinum sheet were used as the working cathode, reference electrode and counter electrode, respectively), 1.0 M KOH solution was used as the electrolyte, and the LSV method was used to test its HER activity as a single electrocatalyst. Among them, the electrocatalyst loading was 0.5 mg cm -2 , voltage scan rate was 5.0 mV s -1 .

[0060] The test results are as follows Figure 5 When the NF electrode loaded with m-NiTPyP / CNTs was used as the cathode of the electrolytic cell, the HER current density was 10 mA cm in 1.0 M KOH alkaline solution. -2 The corresponding overpotential is 138mV.

[0061] Application Example 3

[0062] 3.0 mg of m-NiTPyP / CNTs prepared in Example 1 was dispersed into 3.0 ml of Nafion ethanol solution (weight percentage of 0.05%) and ultrasonically treated for 30 minutes to obtain an electrocatalyst slurry. 0.50 ml of the slurry was dropped on NF (1.0 cm × 2.0 cm) and completely dried under an infrared lamp to obtain a NF electrode. In a two-electrode electrolytic cell (the NF electrodes loaded with electrocatalysts were used as cathode and anode, respectively), 1.0 M KOH solution was used as the electrolyte, and the LSV and chronoamperometry were used to test its full water splitting performance as a bifunctional electrocatalyst. Among them, the electrocatalyst loading was 0.5 mg cm -2 , voltage scan rate was 5.0 mV s -1 .

[0063] The test results are as follows Figure 6 and Figure 7 When the NF electrodes loaded with m-NiTPyP / CNTs were used as the anode and cathode of the electrolytic cell, a voltage of only 1.62 V was required to reach 10 mA cm in a 1.0 M KOH alkaline solution. -2 The current density ( Figure 6 ), and its it curve shows that the bifunctional catalyst can maintain electrolysis stability for at least 60 hours ( Figure 7 ).

[0064] The test results of the m-NiTPyP / CNTs electrocatalyst prepared in the embodiment of the present invention show that for the cathode HER, in a 1.0 M KOH alkaline solution, the current density is 10 mA cm -2 The corresponding overpotential is 138 mV. For the anode OER, the current density is 10 mA cm in 1.0 M KOH alkaline solution. -2 When the overpotential is only 267 mV, it can be used as cathode material and anode material for the complete water splitting electrocatalytic reaction. In 1.0 M KOH electrolyte, only 1.62 V is needed to reach 10 mA cm -2 The above results show that the m-NiTPyP / CNTs bifunctional electrocatalyst prepared by the present invention can achieve efficient full water decomposition in the same alkaline electrolyte and the same dual-electrode electrolytic cell, and has good application prospects in the field of electrocatalytic water decomposition and hydrogen production technology.

[0065] The above description is only a preferred specific implementation manner of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention should be included in the scope of protection of the invention.

Claims

1. A method for preparing a tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst, characterized in that: The following steps are involved: (1) Adding m-NiTPyP and CNTs into an organic solvent and dispersing by ultrasonication to obtain a dispersed solution; Wherein, m-NiTPyP is 5,10,15,20-tetrakis(3-pyridyl)porphyrin nickel(II); CNTs is carboxylated carbon nanotubes; the organic solvent is N,N-dimethylformamide; (2) Reflux the dispersed solution under an inert atmosphere until the reaction is complete; (3) The product is centrifuged, washed, and then dried to obtain the m-NiTPyP / CNTs bifunctional electrocatalyst for water electrolysis.

2. The method according to claim 1, characterized in that: In the step (1), 1.4-2.8 mg of m-NiTPyP and 2.0-4.0 mg of CNTs are added to every 1 ml of organic solvent.

3. The method according to claim 1, characterized in that: In the step (2), the reflux temperature is 140-160° C., and the reflux time is 4-8 hours.

4. The method according to claim 1, characterized in that: In the step (3), the product is centrifugally separated and then washed with dichloromethane, ethanol and deionized water in sequence, and then vacuum dried to obtain the m-NiTPyP / CNTs bifunctional electrocatalyst.

5. A tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst, characterized in that: The method according to any one of claims 1 to 4 is used for preparation, and its molecular structure is formed by connecting tetrapyridyl nickel porphyrin and carboxyl / hydroxyl groups on the surface of carbon nanotubes through chemical bonds; wherein m-NiTPyP is an electrocatalytically active material and CNTs are an electrical conductor and a carrier.

6. The application method of the tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst according to claim 5, characterized in that: The following steps are involved: (1) dispersing the tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst in a Nafion ethanol solution to obtain an electrocatalyst slurry; dropping the slurry on a nickel foam NF, and drying to obtain an electrocatalyst-loaded NF electrode; (2) In a three-electrode electrolytic cell containing a working electrode, a reference electrode, and a counter electrode, an alkaline solution is used as the electrolyte, and the NF electrode loaded with the electrocatalyst is used as the working electrode, and power is applied to carry out electrocatalytic hydrolysis; in a two-electrode electrolytic cell, an alkaline solution is used as the electrolyte, and the NF electrodes loaded with the electrocatalyst are used as the cathode and anode, and power is applied to carry out electrocatalytic hydrolysis.

7. The application method of the tetrapyridyl nickel porphyrin / carbon nanotube bifunctional electrocatalyst according to claim 6, characterized in that: In the step (2), the alkaline solution includes KOH solution and NaOH solution.

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