CN114068968A

CN114068968A - Low-content platinum-based catalyst and preparation method and application thereof

Info

Publication number: CN114068968A
Application number: CN202111371024.4A
Authority: CN
Inventors: 王娟; 左四进
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2021-11-18
Filing date: 2021-11-18
Publication date: 2022-02-18
Anticipated expiration: 2041-11-18
Also published as: CN114068968B

Abstract

The invention discloses a low-content platinum-based catalyst, a preparation method thereof and an application of the catalyst in full-pH effective hydrogen production by water electrolysis, comprising the following steps: the method comprises the steps of reducing platinum in chloroplatinic acid by using chloroplatinic acid as a platinum source precursor and dicyandiamide as a nitrogen source and a platinum source primary carrier in a light reduction mode, and loading the platinum on dicyandiamide. Carrying out hydrothermal reduction on the doped graphene oxide by using a hydrothermal reduction method, and finally annealing in a high-temperature inert gas atmosphere and pyrolyzing the graphene oxide to obtain the target catalyst. It was found that the target catalyst synthesized, Pt-N-rGO, had a low mass fraction of platinum (10 wt.%), but its hydrogen evolution performance was superior to that of the commercial 20 wt.% platinum carbon catalyst, and it was able to efficiently electrolyze water to produce hydrogen at full pH (including extreme acidic, basic and neutral conditions), and its stability was also superior to that of the commercial platinum carbon catalyst.

Description

Low-content platinum-based catalyst and preparation method and application thereof

Technical Field

The invention relates to the field of nano material engineering and energy engineering, in particular to a low-content platinum-based catalyst and a preparation method and application thereof.

Background

Hydrogen is one of the most important energy sources in the 21 st century, and has the remarkable advantages of high density heat value, renewability, zero pollutant emission and the like. The industrial hydrogen preparation method mainly comprises the steps of preparing hydrogen by water gas shift, preparing hydrogen by chemical raw materials (such as methanol, ethanol, liquid ammonia cracking and the like), preparing hydrogen by petrochemical resources and the like. Although these routes produce large quantities of hydrogen, they consume large amounts of energy and also cause secondary pollution (e.g., high levels of CO)₂Discharge). However, the emerging technology of hydrogen production by electrolysis of water can overcome the above to some extentThe method has the defects that water which is relatively clean and easy to obtain is used as a raw material, the lowest reaction energy barrier required by water decomposition is reduced through a reasonably designed catalyst, and hydrogen is obtained through electrolysis.

The development of a catalyst with high activity, high stability and low price is the basis of the industrial application of the water electrolysis hydrogen production technology. The noble metal platinum is the most effective catalyst for hydrogen production by electrolyzing water due to the unique electronic structure and physical and chemical properties of the surface, and is known as 'catalytic king'. However, the global reserves of platinum are rare, the extraction and smelting costs are high, and the reaction cost of the platinum catalyst needs to be considered for development and use. In recent years, researchers have focused on the development of non-noble metal materials, such as transition metal chalcogenides (e.g., WS)₂、WSe₂Etc.), transition metal carbon-based materials (e.g., Fe-N-C), etc. Although the non-noble metal catalyst shows a certain hydrogen evolution potential, the non-noble metal catalyst still has higher overpotential and low catalytic efficiency and is far away from a platinum-based catalyst.

Therefore, the reduction of platinum usage by increasing platinum utilization efficiency remains a promising direction for the development of catalysts for the electrolysis of water to produce hydrogen. Platinum is loaded on different carriers to obtain platinum-based materials with different activities, such as carbon-based carriers, inorganic substances (such as cerium dioxide) and the like. Taking a commercial platinum-carbon catalyst (Pt/C) with a mass fraction of 20 wt% as an example, platinum is embedded in the form of nanoparticles on a carbon support. Studies have shown that the activity of platinum is mainly concentrated on the surface of the nanoparticles, and the core part thereof is not involved in the electrocatalytic reaction. Therefore, reducing the size of the platinum nanoparticles is an effective way to improve the utilization efficiency of platinum and reduce the use content of platinum. Based on the above analysis, it is proposed in the patent that graphene is used as a carbon carrier, chloroplatinic acid is used as a platinum precursor, and a platinum-based catalyst with a small particle size and a low content is synthesized. Researches find that the catalyst has the performance of effectively producing hydrogen by electrolyzing water with full pH. The performance and stability of hydrogen production are comparable with those of commercial platinum-carbon catalyst (20% Pt/C).

Disclosure of Invention

The invention provides a low-content platinum-based catalyst, a preparation method thereof and application of the catalyst in efficient hydrogen production by electrolyzing water with full pH

A preparation method of a low-content platinum-based catalyst comprises the following steps:

1) reducing platinum in chloroplatinic acid by using chloroplatinic acid as a platinum source precursor and dicyandiamide as a nitrogen source and a platinum source primary carrier in a light reduction mode, and loading the platinum on dicyandiamide to obtain mixed liquid;

2) carrying out hydrothermal reduction on the doped graphene oxide by using a hydrothermal reduction method to obtain an intermediate product;

3) finally, the intermediate product is annealed in a high-temperature protective gas atmosphere and pyrolyzed to obtain the target catalyst, namely the low-content platinum-based catalyst.

In the step 1), chloroplatinic acid is used as a platinum source precursor, dicyandiamide is used as a nitrogen source and a platinum source primary carrier, and platinum in the chloroplatinic acid is reduced and loaded on dicyandiamide in a light reduction mode, and the method specifically comprises the following steps:

1.1) putting dicyandiamide in water, heating to 50-70 ℃, and stirring to completely dissolve dicyandiamide;

1.2) adding chloroplatinic acid hexahydrate into the solution obtained in the step 1.1), and stirring to completely dissolve the chloroplatinic acid hexahydrate;

1.3) keeping the constant temperature of the solution obtained in the step 1.2) on a temperature-controlled magnetic stirrer at 35-45 ℃, stirring for 2-5 hours, and irradiating the liquid by using an ultraviolet light source in the process to obtain a mixed liquid;

the purpose of ultraviolet irradiation is to photo-reduce chloroplatinic acid, and the reduction is thorough when the ultraviolet irradiation is carried out for 2-5 h. The constant temperature of 35-45 ℃ is used for preventing dicyandiamide from being insufficiently contacted with chloroplatinic acid due to precipitation of dicyandiamide at too low temperature.

In the step 1.3), the irradiation light intensity of the ultraviolet light source is 5-15 mW/cm²More preferably 10mW/cm²。

In step 1), most preferably, the method specifically comprises the following steps:

1.1) taking 2g of dicyandiamide in 30mL of deionized water, heating to 60 ℃, and stirring to completely dissolve dicyandiamide, wherein the process is about 30 min;

1.2) adding 30mg of chloroplatinic acid hexahydrate, stirring to completely dissolve the chloroplatinic acid hexahydrate, wherein the process is about 2 min;

1.3) keeping the temperature of the solution constant at 40 ℃ on a temperature-controlled magnetic stirrer, and stirring for 3h, wherein an ultraviolet light source is used for irradiating the liquid (the light intensity is about 10 mW/cm)²) The purpose of ultraviolet irradiation is to photo-reduce chloroplatinic acid, and the irradiation for 3h is to ensure that the reduction is complete. The purpose of keeping the temperature at 40 ℃ is to prevent dicyandiamide from precipitating due to too low temperature, so that dicyandiamide is not sufficiently contacted with chloroplatinic acid.

In step 2), most preferably, the method specifically comprises the following steps:

2.1) ultrasonically dispersing graphene oxide in water to obtain a graphene oxide solution;

2.2) adding the graphene oxide solution obtained in the step 2.1) into the mixed liquid obtained in the step 1.3), transferring the mixed liquid to a reaction kettle, and carrying out hydrothermal reaction for 2-12 h at the temperature of 120-170 ℃.

2.3) carrying out post-treatment on the solid subjected to the hydrothermal reaction in the step 2.2) to obtain an intermediate product;

in the step 2.2), the hydrothermal reaction is preferably carried out for 3-5 h at 160-180 ℃, the reduction temperature has an important influence on the performance of the catalyst, and the hydrothermal reaction is finally optimized to be carried out for 4h at 170 ℃.

In step 2.3), the post-treatment comprises: naturally cooling and centrifuging the solid subjected to the hydrothermal reaction in the step 2.2), washing the obtained solid with water and ethanol, and drying at 50-70 ℃ for 6-10 h (most preferably drying at 60 ℃ for 8 h).

2.1) ultrasonically dispersing 40mg of commercial graphene oxide in 10mL of deionized water, wherein the process is about 15 min;

2.2) adding the graphene oxide solution in the step 2.1) into the mixed liquid in the step 1.3), transferring the mixed liquid into a 50mL reaction kettle, and carrying out hydrothermal reaction at 120 ℃, 150 ℃ or 170 ℃ for 4h respectively, wherein the reduction temperature has an important influence on the performance of the catalyst, and the hydrothermal reaction is finally optimized to be carried out at 170 ℃ for 4 h.

2.3) naturally cooling the solid obtained after the hydrothermal reaction in the step 2.2), centrifuging by using a centrifugal machine, washing the obtained solid by using ultrapure water and ethanol, and drying for 8 hours at the temperature of 60 ℃.

In the step 3), the method specifically comprises the following steps:

heating the intermediate product for 1-4 h at 500-700 ℃ in a tubular furnace in the nitrogen atmosphere, wherein the heating rate is 2-8 ℃/min, and the nitrogen gas flow is 30-80 mL/min. The resulting black solid powder was labeled Pt-N-rGO and collected for use.

Most preferably, it specifically comprises:

heating for 2h at 600 ℃ in a tubular furnace in the nitrogen atmosphere, wherein the heating rate is 5 ℃/min, and the nitrogen gas flow is 50 mL/min. The resulting black solid powder was labeled Pt-N-rGO and collected for use.

2. The specific steps of preparing the prepared platinum-based catalyst by electrolyzing water are as follows:

weighing the synthesized catalyst, including N-rGO, Pt-N-C and Pt-N-rGO, and 2mg of a commercial Pt/C (20 wt%) catalyst;

dispersing the solid powder in 1mL of mixed solution of 75% ethanol and naphthol (nafion) in the volume ratio of 95:5, and performing ultrasonic treatment for 60min to uniformly disperse the solid powder to form ink liquid;

thirdly, the ink is dropped on the glassy carbon electrode and is naturally dried. Wherein the diameter of the glassy carbon electrode is 3mm, and the area is 0.0707cm². After test optimization, the optimal catalyst loading is 0.303mg/cm²；

And fourthly, forming a three-electrode electrochemical test system by using the glassy carbon electrode as a working electrode, the graphite rod as a counter electrode and the Saturated Calomel Electrode (SCE) as a reference electrode. Electrochemical Cyclic Voltammetry (CV) was performed to activate the working electrode before each test. The electrolyte solutions were 0.5M H respectively₂SO₄1M KOH and 1M PBS solution.

The preparation of low-content platinum-based catalyst and the application of full pH effective water electrolysis to prepare hydrogen, and the prepared catalyst is used for preparing hydrogen by electrolyzing water. The target catalyst Pt-N-rGO synthesized by the method has low mass fraction (10 wt.%) of platinum, but the hydrogen evolution performance of the target catalyst is better than that of a commercial platinum carbon catalyst with the mass fraction of 20 wt.%, and the target catalyst can effectively electrolyze water to produce hydrogen at full pH (including extreme acidic, alkaline and neutral conditions), and the stability of the target catalyst is also better than that of the commercial platinum carbon catalyst.

Compared with the prior art, the invention has the following advantages:

(1) according to the method, chloroplatinic acid is used as a precursor of platinum, dicyandiamide is used as a nitrogen source, graphene oxide is used as a carbon carrier, and the platinum is modified on the carbon-based carrier for reducing the graphene oxide in a high-temperature hydrothermal and annealing mode. It was found that hydrothermal reduction temperature affects the performance of the catalyst by affecting the nanoparticle size of Pt. When the reduction temperature is increased to 170 ℃, the formed Pt-N-rGO catalyst is in an extremely acidic condition and at the current density (10 mA/cm)²) The overpotential at this time was 17.4 mV. Under the same conditions, the overpotential of the commercial platinum-carbon (20 wt%) catalyst was 31.3 mV. And the characterization proves that the mass fraction of the platinum content in the Pt-N-rGO is 10.0 wt% which is one half of the content of the commercial platinum-carbon catalyst. Therefore, the target catalyst Pt-N-rGO has obviously enhanced electro-catalytic hydrogen evolution performance.

(2) The target catalyst Pt-N-rGO has not only excellent hydrogen evolution performance under very acidic (pH 0) conditions, but also excellent hydrogen evolution performance under very basic (pH 14) and neutral (pH 7) conditions, compared to commercial platinum carbon (20 wt%) catalysts. For example, Tafel slopes under strongly acidic, strongly basic and neutral conditions are 17.5, 48.3 and 38.9mV/dec, respectively. In contrast, the Tafel slopes of commercial platinum-carbon (20 wt%) catalysts under strongly acidic, strongly basic and neutral conditions were 26.5, 57.5 and 42.6mV/dec, respectively. Thus, the target catalyst, Pt-N-rGO, exhibits performance for hydrogen evolution from electrolyzed water at full pH efficiency. In addition, the stability of the target catalyst Pt-N-rGO at full pH is also obviously improved.

Drawings

FIG. 1 is a Scanning Electron Micrograph (SEM) and elemental spectrum scan of the material after step 6) of example 1.

FIG. 2 shows the N-rGO and Pt-C synthesized in examples 2 and 3₃N₄A characterization image comprising a scanning electron microscope image, a transmission electron microscope image and an X-ray diffraction spectrum image; FIGS. 2a-C and d-h are the N-rGO and Pt-C syntheses of examples 3 and 2, respectively₃N₄And (5) characterizing the graph.

FIG. 3 is a Scanning Electron Micrograph (SEM) and elemental energy spectrum scan of the Pt-N-rGO synthesized in example 1.

FIG. 4 is a further characterization of the Pt-N-rGO synthesized in example 1, including transmission electron micrographs and X-ray diffraction spectra, Raman spectra and nitrogen adsorption desorption isotherms.

FIG. 5 is a thermogravimetric analysis plot a and a conductivity measurement plot b of a target sample Pt-N-rGO sample and a comparative sample commercial Pt/C calcination in air atmosphere.

Fig. 6 is a comparison of linear sweep voltammetry curves (LSV curve, polarization curve) for hydrogen production by water electrolysis of a target catalyst in a three-electrode system, hydrogen evolution performance under different catalyst loading.

Fig. 7 illustrates the hydrogen production performance from electrolyzed water at full pH.

FIG. 8 is a preliminary mechanistic exploration of the superior hydrogen evolution performance of the target catalyst.

Detailed Description

The present invention is further described in detail by the following examples in conjunction with the accompanying drawings.

(1) The specific steps of the synthesis of the target catalyst Pt-N-rGO comprise the following steps:

1) taking 2g of dicyandiamide in 30mL of deionized water, heating to 60 ℃, and stirring to completely dissolve dicyandiamide, wherein the process is about 30min, and the usage amount of dicyandiamide is optimized to be 4g finally;

2) adding 30mg of chloroplatinic acid hexahydrate, stirring to completely dissolve, wherein the process is about 2 min;

3) keeping the above solution at constant temperature of 40 deg.C in a temperature-controlled magnetic stirrer, stirring for 3 hr, and irradiating liquid with ultraviolet light source (light intensity of about 10 mW/cm)²) The purpose of ultraviolet irradiation is to photo-reduce chloroplatinic acid, and the irradiation for 3h is to ensure that the reduction is complete. The purpose of keeping the temperature at 40 ℃ is to prevent dicyandiamide from precipitating due to too low temperature, so that dicyandiamide is not sufficiently contacted with chloroplatinic acid.

4) Ultrasonically dispersing 40mg of commercial graphene oxide in 10mL of deionized water, wherein the process is about 15 min;

5) adding the graphene oxide solution in the step 4) into the mixed liquid in the step 3), transferring the mixed liquid to a 50mL reaction kettle, carrying out hydrothermal reaction for 4h at the temperature of 120 ℃, 150 ℃ or 170 ℃ respectively, wherein the reduction temperature has an important influence on the performance of the catalyst, and finally optimizing the hydrothermal reaction for 4h at the temperature of 170 ℃.

6) Naturally cooling the solid obtained after the hydrothermal reaction in the step 5), centrifuging by using a centrifugal machine, washing the obtained solid by using ultrapure water and ethanol, and drying for 8 hours at the temperature of 60 ℃.

7) Heating for 2h at 600 ℃ in a tubular furnace in the nitrogen atmosphere, wherein the heating rate is 5 ℃/min, and the nitrogen gas flow is 50 mL/min. The resulting black solid powder was labeled Pt-N-rGO and collected for use.

Example 1

1) Taking 2g of dicyandiamide in 30mL of deionized water, heating to 60 ℃, and stirring to completely dissolve dicyandiamide, wherein the process is about 30 min;

Example 2

3) keeping the above solution at constant temperature of 40 deg.C for 3 hr in a temperature-controlled magnetic stirrer, and irradiating the liquid with ultraviolet light source (light intensity of about 10 mW/cm)²) The purpose of ultraviolet light irradiation is to photo-reduce chloroplatinic acid, and the purpose of 3h light irradiation is to ensure that the reduction is more complete. The purpose of keeping the temperature at 40 ℃ is to prevent dicyandiamide from being insufficiently contacted with chloroplatinic acid due to precipitation of dicyandiamide at too low a temperature.

4) The mixed liquid in 3) was transferred to a 50mL reaction vessel and subjected to hydrothermal reaction at 170 ℃ for 4 hours. 5) Naturally cooling the solid obtained after the hydrothermal reaction in the step 4), centrifuging by using a centrifugal machine, washing the obtained solid by using ultrapure water and ethanol, and drying for 8 hours at the temperature of 60 ℃.

7) Heating for 2h at 600 ℃ in a tubular furnace in the nitrogen atmosphere, wherein the heating rate is 5 ℃/min, and the nitrogen gas flow is 50 mL/min. The resulting black solid powder was labeled Pt-C₃N₄And collecting for later use.

Example 3

2) ultrasonically dispersing 40mg of commercial graphene oxide in 10mL of deionized water, wherein the process is about 15 min;

3) adding the graphene oxide solution in the step 2) into the mixed liquid in the step 3), transferring the mixed liquid to a 50mL reaction kettle, and carrying out hydrothermal reaction for 4h at 170 ℃.

4) Naturally cooling the solid obtained after the hydrothermal reaction in the step 3), centrifuging by using a centrifugal machine, washing the obtained solid by using ultrapure water and ethanol, and drying for 8 hours at the temperature of 60 ℃.

7) Heating for 2h at 600 ℃ in a tubular furnace in the nitrogen atmosphere, wherein the heating rate is 5 ℃/min, and the nitrogen gas flow is 50 mL/min. The resulting black solid powder was labeled N-rGO and collected for future use.

(2) Method of the invention treatment Process

(3) Effects obtained by this example

The application of the electrolyzed water for preparing the hydrogen specifically comprises the following steps:

the Pt-N-C, Pt-N-rGO and N-rGO catalysts prepared in examples 1, 2 and 3 above were chosen for comparison to commercial Pt/C (20 wt%) platinum on carbon catalysts. The experimental procedure was as follows:

dispersing 2mg of the powder catalyst in a mixed solution of 75% ethanol and naphthol (nafion) by volume (the volume ratio of the two solutions is 95:5), and performing ultrasonic treatment for 60min to uniformly disperse the mixed solution to obtain ink liquid. A glassy carbon electrode was used as a working electrode (working area diameter 3mm, area 0.0707 cm)²). And (3) dripping a plurality of drops (2.5 mu L/drop) of the ink liquid on the glassy carbon electrode, and naturally drying. The different loading of the catalysts leads to different hydrogen evolution performance, illustrated in fig. 6. A graphite rod is used as a counter electrode, and a Saturated Calomel Electrode (SCE) is used as a reference electrode to form a three-electrode electrochemical testing system. The working electrode was activated with CV prior to each test. The electrolyte with pH 0 is 0.5M sulfuric acid (H)₂SO₄) Solution constitution, pH 7The electrolyte was composed of 1M PBS buffer solution, and the electrolyte with pH 14 was composed of 1M potassium hydroxide (KOH) solution.

FIG. 1 is a Scanning Electron Micrograph (SEM) of the material after step 6) of example 1. As can be seen from a, the particles were in the form of lumps and were dicyandiamide that had been reprecipitated after crystallization. While the reduced graphene oxide is not obvious in the figure, it is possible that a relatively small amount of the reduced graphene oxide is doped into dicyandiamide and is wrapped up when the dicyandiamide is precipitated. The b-e diagram is the element energy spectrum of the material, the carbon, nitrogen and oxygen elements are uniformly distributed, and the platinum element is also uniformly distributed in the particles. This demonstrates that the ultraviolet light successfully reduces chloroplatinic acid to be supported in the particulate matter consisting of dicyandiamide and reduced graphene oxide. Also, the first 6 steps in example 1 are shown to achieve the desired effect.

FIGS. 2a-C) and d-h) are the N-rGO and Pt-C synthesized in examples 3 and 2, respectively₃N₄And (5) characterizing the graph. a) The figure is a scanning electron micrograph of the N-rGO, and the layered loose porous structure of the N-rGO can be known from the figure. b) The structure of the thin porous layer corresponds to the result of the scanning electron microscope image, and the size of the pores is mainly distributed between 20 nm and 80nm and is in a micropore form. c) The pattern is an XRD pattern for N-rGO with two XRD diffraction peaks at 26.3 and 43.1, corresponding to the (002) and (100) planes of the carbon-based material. No metal peak was observed, nor was a graphite phase nitrogen carbide peak, indicating that the source material was completely carbonized at a temperature of 600 ℃ after hydrothermal reduction. In contrast, in example 2, no graphene oxide, Pt-C thereof, was added₃N₄The morphology of (A) is greatly different from that of N-rGO. And d, a scanning electron microscope image of the flat structure in a reel shape. In the detail view e of fig. d, a compact gap exists in the scroll-like flat structure. Comparing the transmission electron microscope picture f, the material is a two-dimensional layered structure, and the size of the gap is microporous. FIG. g is a high-power transmission electron micrograph, and no platinum metal particles were found. Graph h is Pt-C₃N₄The XRD spectrum of the graphite phase shows (100) planes and (002) planes of graphite phase nitrogen carbide at 13.2 degrees and 27.3 degrees, and the graphite phase structure and the in-plane trisection ring structure are respectively formed. This is consistent with the characterization results of scanning and transmission electron microscopy, neitherThere is a peak where platinum metal appears. Platinum may exhibit sub-nanoparticle or monoatomic distribution in two-dimensional nitrogen carbide. The excitation of the activity of the monatomic catalyst has a large relationship with the carrier, and the carrier used in this example is graphite-phase nitrogen carbide, and from the experimental results, the carrier is not suitable for the hydrogen evolution reaction. Pt-C can be roughly judged from an electron micrograph₃N₄Has a smaller specific surface area than that of N-rGO.

FIG. 3 is a scanning electron micrograph of the target catalyst Pt-N-rGO synthesized in example 1. As can be seen, the catalyst has a lamellar structure and a smooth surface. Compared with N-rGO and Pt-C₃N₄Its surface area should be further reduced. And c-f are element surface scanning energy spectrums of the material, the group of data shows the uniform distribution of carbon, nitrogen and oxygen elements in the material, and in addition, the platinum metal element is doped to present uniform distribution. This indicates that example 1 successfully incorporates platinum on the N-rGO support.

FIG. 4 is a further characterization of Pt-N-rGO. From the a picture (transmission electron microscope picture), it is seen that the lamellar structure of Pt-N-rGO is loaded with obvious nano particles, which is consistent with the result of scanning electron microscope. Combining with the high resolution graph b, the nano particles are distributed uniformly with high density and uniform particle size. As can be seen from the statistical histogram of the particle sizes of more than 100 nanoparticles, the average particle size of the nanoparticles is about 2.58nm (as shown in graph e), and the smaller particle size distribution is shown. The lattice fringes of the graph c and the Fourier space transform of the graph d prove that the nanoparticles are platinum nanoparticles, and the displayed crystal planes are (111) planes of platinum. The f-diagram is the X-ray diffraction pattern of Pt-N-rGO and commercial Pt/C (20 wt.%) which corresponds to the peak for graphitic carbon at approximately 25.2 ° and 26.0 ° 2 θ, respectively, which is consistent with the diagram of fig. 2C. The peak of Pt-N-rGO is shifted approximately 1 ° to the right (large angle) compared to commercial Pt/C, which may be related to its degree of graphitization. The standard card (JCPDF: 04-0802) combined with PDF of platinum can know that the rest diffraction peaks are mainly caused by nano particles of platinum, and the nano particles on the high-power transmission electron microscope picture are verified to be the nano particles of platinum without external interferents. g is plotted as target sample (Pt-N-rGO) andcomparative sample (commercial Pt/C) Raman spectrum, D band and G band correspond to the degree of defect and graphitization of the material, respectively, and the peak area ratio (I)_D/I_G) 1.25 and 1.15 respectively, which shows that the graphitization degree of Pt-N-rGO is higher than that of Pt/C. The higher the degree of graphitization, the faster the carbon-based carrier transports electrons. h is a nitrogen adsorption and desorption isotherm diagram of three materials, and Pt-C is known from the diagram₃N₄The specific surface areas of the three materials of Pt/C and Pt-N-rGO are 144.57, 173.61 and 39.42m²(ii) in terms of/g. This is consistent with the results of scanning or transmission electron microscopy analysis.

FIG. 5 is a thermogravimetric analysis plot a) and conductivity determination plot b) of commercial Pt/C calcination in air atmosphere for target sample Pt-N-rGO and comparative samples. Thermogravimetric curve analysis of the sample of commercial Pt/C (20 wt.%) showed a mass fraction of platinum of 20%, which was expected. And the Pt-N-rGO of the target catalyst is heated to 1000 ℃ in an air atmosphere, and the metal oxide (PtO) of the target catalyst₂) The mass fraction converted to metallic platinum was 10%, which was only one-half of the platinum content in the commercial Pt/C. However, subsequent performance tests of hydrogen production by water electrolysis show that the target catalyst Pt-N-rGO has better performance than commercial Pt/C. As another example, the conductivity of the two catalysts is characterized, and the results show that the conductivity (1.0 μ s/cm) of the Pt-N-rGO is higher than that of the commercial Pt/C (0.6 μ s/cm), and the higher conductivity is favorable for rapid electron transfer and catalytic reaction, which also indicates that the target catalyst has better hydrogen evolution performance than the commercial Pt/C.

Fig. 6 is a comparison of linear sweep voltammetry curves (LSV curve, polarization curve) for hydrogen production by water electrolysis of a target catalyst in a three-electrode system, hydrogen evolution performance under different catalyst loading. Too much and too little catalyst loading is not beneficial to the hydrogen evolution reaction. Too much, the outermost catalyst cannot be electrocatalyzed because the active sites are covered. Too little, the glassy carbon electrode is exposed and the current effect is reduced. As can be seen, in the present application we chose 0.303mg/cm²As the optimum loading of the catalyst.

Fig. 7 illustrates the hydrogen production performance from electrolyzed water at full pH. FIG. a is0.5M H₂SO₄Linear sweep voltammogram of (1), N-rGO, Pt-C₃N₄The hydrogen evolution performance of Pt/C and Pt-N-rGO is enhanced in turn. At 10mA/cm for the four catalysts mentioned above²At a current density of 449, 346, 31.3 and 17.4mV in this order. The experimental results show that the performance of the platinum-free carbon-based catalyst is very poor, so that the performance of N-rGO was not detected in subsequent experiments. In addition, the results also indicate that platinum may be the reactive center for catalyzing hydrogen evolution. FIG. d is the Tafel slope (tafel slope) for the three catalysts under very acidic conditions. The tafel slope reflects the resistance of the electrode during electrode polarization, and can quantitatively reflect the dynamic process during electrode polarization. The smaller the value, the smaller the electrode resistance. For Pt-C₃N₄The Tafel slopes of the Pt/C and Pt-N-rGO catalysts under the extremely acidic condition are 153.1, 26.5 and 17.5mV/dec in sequence. Therefore, the target catalyst Pt-N-rGO can be judged to have the minimum electron transport resistance and the optimal reaction kinetics. We also examined the stability of the target catalyst Pt-N-rGO under very acidic conditions and compared it to commercial glassy carbon. As shown in graph g, at a constant current density (10 mA/cm)²) The target catalyst was able to run stably for 14 hours, and its slightly degraded performance was probably caused by hydrogen bubbles generated by the long-term test covering the surface of the catalyst. In contrast, the activity of commercial Pt/C catalysts is gradually lost in less than 10 hours of operation.

Similarly, graph b reflects the hydrogen evolution performance of the three catalysts described above under very basic conditions. The target catalyst Pt-N-rGO is compared with commercial Pt/C and Pt-C₃N₄Still has outstanding performance. E.g. at 100mA/cm²The overpotentials were 118, 210 and 861mV, respectively. As shown in FIG. e, their Tafel slopes were 48.3, 57.5, and 216.3mV/dec, respectively. The target catalyst Pt-N-rGO shows the best extreme alkaline hydrogen evolution performance. Furthermore, at a constant current density (10 mA/cm)²) The target catalyst was still able to run stably for 14 hours. Finally, we used the 1M PBS buffer system as a charge under neutral conditionsThe electrolyte solution examines Pt-N-rGO, Pt/C and Pt-C₃N₄Hydrogen evolution performance of (1). As shown in figure C, the target catalyst, Pt-N-rGO, still exhibited a much more pronounced hydrogen evolution performance than the commercial Pt/C catalyst. The corresponding Tafel slopes were 38.9,42.6, and 267.6mV/dec (shown in FIG. f). We also examined the stability of Pt-N-rGO and Pt/C under neutral conditions, as shown in FIG. i. Compared to commercial Pt/C, Pt-N-rGO still shows strong stability for 14 hours. It is worth mentioning that the stability of the target catalyst Pt-N-rGO in PBS buffer is "less" than under extreme alkaline and acidic conditions, probably due to the influence of the catalyst electrolysis process with high concentrations of PBS (1M). This effect appears to be even worse for commercial Pt/C as shown in FIG. i. In summary, the Pt-N-rGO developed in this application has significant electrocatalytic hydrogen evolution performance and stability at full pH, even exceeding commercial Pt/C.

FIG. 8 is a preliminary mechanistic exploration of the superior hydrogen evolution performance of the target catalyst. Figures a-c show electrochemical impedance spectra of the target catalyst and the comparative catalyst in three different electrolyte systems. The diameter of the formed semicircular ring can qualitatively reflect the resistance of the catalyst on the electrode interface to the charge transfer resistance. As can be seen, Pt-N-rGO shows the lowest charge transfer resistance in all three electrolytes compared to the commercial Pt/C. In addition, we also used metal masking agent (such as potassium thiocyanate, KSCN; EDTA-2Na) to mask the metal components in the catalyst. After the addition of the masking agent, as shown in the figures d-f, the three systems all showed significantly inhibited hydrogen evolution performance. In conjunction with the above analysis, we believe that the metal platinum in Pt-N-rGO is an effective active center.

Claims

1. A preparation method of a low-content platinum-based catalyst is characterized by comprising the following steps:

2. The method for preparing a low-content platinum-based catalyst according to claim 1, wherein the step 1) specifically comprises:

1.3) keeping the constant temperature of the solution obtained in the step 1.2) on a temperature-controlled magnetic stirrer at 35-45 ℃, stirring for 2-5 hours, and irradiating the liquid by using an ultraviolet light source in the process to obtain a mixed liquid.

3. The method for preparing the low-content platinum-based catalyst according to claim 2, wherein in the step 1.3), the irradiation intensity of the ultraviolet light source is 5-15 mW/cm²。

4. The method for preparing a low-content platinum-based catalyst according to claim 2, wherein the step 2) specifically comprises:

2.2) adding the graphene oxide solution obtained in the step 2.1) into the mixed liquid obtained in the step 1.3), transferring the mixed liquid to a reaction kettle, and carrying out hydrothermal reaction for 2-12 h at the temperature of 120-170 ℃;

2.3) carrying out post-treatment on the solid obtained after the hydrothermal reaction in the step 2.2) to obtain an intermediate product.

5. The method for preparing the low-content platinum-based catalyst according to claim 4, wherein in the step 2.2), the hydrothermal reaction is carried out at 160-180 ℃ for 3-5 h.

6. The method for preparing a low content of platinum-based catalyst according to claim 4, wherein in step 2.3), said post-treatment comprises: naturally cooling and centrifuging the solid subjected to the hydrothermal reaction in the step 2.2), washing the obtained solid with water and ethanol, and drying for 6-10 hours at 50-70 ℃.

7. The method for preparing a low-content platinum-based catalyst according to claim 1, wherein the step 3) specifically comprises:

and heating the intermediate product for 1-4 h at 500-700 ℃ in a tubular furnace in the atmosphere of nitrogen.

8. The preparation method of the low-content platinum-based catalyst according to claim 7, wherein in the step 3), the temperature rise rate is 2-8 ℃/min, and the nitrogen gas flow rate is 30-80 mL/min.

9. The low-content platinum-based catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of a low content platinum based catalyst according to claim 9 for the electrolysis of water for the production of hydrogen.