CN114068968B

CN114068968B - Low-content platinum-based catalyst and preparation method and application thereof

Info

Publication number: CN114068968B
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: 2023-05-16
Anticipated expiration: 2041-11-18
Also published as: CN114068968A

Abstract

The invention discloses a low-content platinum-based catalyst, a preparation method thereof and application of full-pH effective electrolytic water hydrogen production, which comprises the following steps: the method comprises the steps of taking chloroplatinic acid as a platinum source precursor, taking dicyandiamide as a nitrogen source and a platinum source primary carrier, and reducing and loading platinum in the chloroplatinic acid on the dicyandiamide in a light reduction mode. And performing hydrothermal reduction on the doped graphene oxide by utilizing a hydrothermal reduction method, and finally annealing in a high-temperature inert gas atmosphere to pyrolyze the graphene oxide into the target catalyst. The synthesized target catalyst Pt-N-rGO has low mass fraction (10 wt%) of platinum, but has hydrogen evolution performance superior to that of a commercial platinum-carbon catalyst with mass fraction of 20wt%, and can be used for effectively producing hydrogen by electrolysis of water at full pH (including extreme acidic, alkaline and neutral conditions), and has stability 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 fields of nano material engineering and energy engineering, in particular to a low-content platinum-based catalyst, 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, renewable property, zero pollutant emission and the like. The preparation method of industrial hydrogen mainly comprises water gas conversion hydrogen production, chemical raw material hydrogen production (such as methanol, ethanol, liquid ammonia pyrolysis and the like), petrochemical resource hydrogen production and the like. Although these process routes can produce hydrogen in large quantities, they require a large amount of energy consumption and also bring about secondary pollution (e.g. high levels of CO) ₂ And (5) discharging). However, the emerging technology for producing hydrogen by water electrolysis can overcome the defects to a certain extent, uses cleaner and easily available water as raw materials, and reduces the minimum reaction energy barrier required by water decomposition through a reasonably designed catalyst to obtain hydrogen by electrolysis.

The development of a catalyst with high activity, stability and low price is the basis of industrial application of the water electrolysis hydrogen production technology. Noble metal platinum is the most effective catalyst for hydrogen production by water electrolysis due to unique electronic structure and physical and chemical properties of the surface, and is known as 'catalytic king'. However, platinum has a scarce earth reserve, and the extraction and smelting costs are high, and the reaction costs of platinum catalysts must 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 、WSe ₂ Etc.), 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, reducing the amount of platinum used by increasing the efficiency of platinum utilization is still a promising direction for the design and development of catalysts for producing hydrogen by electrolysis of water. Platinum is supported on different carriers to obtain platinum-based materials with different activities, such as carbon-based carriers, inorganic matters (such as cerium oxide) and the like. Taking a commercial platinum carbon catalyst (Pt/C) with a mass fraction of 20wt% as an example, platinum is embedded in the form of nanoparticles on a carbon support. While studies have shown that platinum activity is mainly concentrated on the surface of nanoparticles, the inner core portion of which is not involved in the electrocatalytic reaction. Therefore, reducing the size of the platinum nano particles is a mode for effectively improving the utilization efficiency of platinum and reducing the use content of platinum. Based on the above analysis, this patent proposes to synthesize a platinum-based catalyst with a smaller particle diameter and a low content by using graphene as a carbon carrier and chloroplatinic acid as a platinum precursor. The research shows that the catalyst has full pH effective hydrogen production performance by water electrolysis. Can be compared with commercial platinum-carbon catalyst (20% Pt/C) in the aspects of hydrogen production performance and stability.

Disclosure of Invention

The invention provides a low-content platinum-based catalyst, a preparation method thereof and application of full-pH effective electrolytic water hydrogen production

A method for preparing a low content platinum-based catalyst comprising the steps of:

1) Platinum in chloroplatinic acid is reduced and loaded on dicyandiamide by taking chloroplatinic acid as a platinum source precursor and dicyandiamide as a nitrogen source and a platinum source primary carrier in a light reduction mode to obtain mixed liquid;

2) Carrying out hydrothermal reduction on the doped graphene oxide by utilizing 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 into a target catalyst, namely a 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 the dicyandiamide in a light reduction mode, which specifically comprises the following steps:

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

1.2 Adding hexa-water chloroplatinic acid into the solution in the step 1.1), and stirring to dissolve the hexa-water chloroplatinic acid completely;

1.3 Keeping the solution in the step 1.2) at a constant temperature of 35-45 ℃ on a magnetic stirrer with temperature control, and stirring for 2-5 h, wherein the process irradiates the liquid with an ultraviolet light source to obtain mixed liquid;

the purpose of ultraviolet irradiation is to photo-reduce chloroplatinic acid, and the irradiation for 2-5 hours is to thoroughly reduce the chloroplatinic acid. The purpose of keeping the temperature between 35 and 45 ℃ is to prevent dicyandiamide from precipitating due to the excessively low temperature, so that the dicyandiamide is not fully contacted with chloroplatinic acid.

In the step 1.3), the irradiation light intensity of the ultraviolet light source is 5-15 mW/cm ² Further preferably 10mW/cm ² 。

Most preferably, in step 1), the method specifically comprises:

1.1 2g of dicyandiamide is taken in 30mL of deionized water, heated to 60 ℃ and stirred to dissolve the dicyandiamide completely, and the process is about 30min;

1.2 30mg of chloroplatinic acid hexahydrate is added and stirred to dissolve all the same for about 2 minutes;

1.3 Stirring the above solution at 40deg.C with a magnetic stirrer under controlled temperature for 3 hr, and irradiating the liquid with ultraviolet light (light intensity about 10 mW/cm) ² ) The purpose of ultraviolet irradiation is to photo-reduce chloroplatinic acid, and the irradiation for 3 hours is to thoroughly reduce the chloroplatinic acid. The purpose of the constant temperature of 40 ℃ is to prevent the dicyandiamide from precipitating due to the excessively low temperature, so that the dicyandiamide is not fully contacted with chloroplatinic acid.

In step 2), most preferably, it specifically comprises:

2.1 Ultrasonic dispersing graphene oxide in water to obtain graphene oxide solution;

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

2.3 Post-treating the solid obtained after the hydrothermal reaction in the step 2.2) to obtain an intermediate product;

in step 2.2), the hydrothermal reaction is preferably carried out at 160-180 ℃ for 3-5 hours, the reduction temperature has an important effect on the performance of the catalyst, and the final hydrothermal reaction is preferably carried out at 170 ℃ for 4 hours.

In step 2.3), the post-treatment comprises: and (3) naturally cooling and centrifuging the solid obtained after 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 at 60 ℃ for 8 h).

In step 2), most preferably, it specifically comprises:

2.1 40mg of commercial graphene oxide was ultrasonically dispersed in 10mL of deionized water for about 15 minutes;

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

2.3 Naturally cooling the solid after the hydrothermal reaction in the step 2.2), centrifuging by a centrifuge, washing the obtained solid by ultrapure water and ethanol, and drying at 60 ℃ for 8 hours.

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

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

Most preferably, the method specifically comprises the following steps:

heating at 600 ℃ for 2 hours in the nitrogen atmosphere in the tube furnace, wherein the heating rate is 5 ℃/min, and the nitrogen gas flow is 50mL/min. The black solid powder obtained 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:

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

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

(3) dropping the ink in the liquidAnd naturally airing the glass carbon electrode. Wherein the diameter of the glassy carbon electrode is 3mm, and the area is 0.0707cm ² . After test optimization, the optimal catalyst loading is 0.303mg/cm ² ；

(4) The glassy carbon electrode is used as a working electrode, 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 test system. Each test was preceded by electrochemical Cyclic Voltammetry (CV) activation of the working electrode. Electrolyte solutions of 0.5 and M H respectively ₂ SO ₄ 1M KOH and 1M PBS solution.

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

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

(1) In 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 platinum is modified on the carbon-based carrier of reduced graphene oxide in a high-temperature hydrothermal and annealing mode. It was found that the hydrothermal reduction temperature affects the performance of the catalyst by affecting the nanoparticle size of Pt. When the reduction temperature was increased to 170℃the Pt-N-rGO catalyst formed was, under very acidic conditions, at the above-mentioned current density (10 mA/cm ² ) The lower overpotential was 17.4mV. Under the same conditions, the overpotential for a commercial platinum carbon (20 wt%) catalyst was 31.3mV. The characterization proves that the mass fraction of the platinum content in the Pt-N-rGO is 10.0wt% which is one half of the content of the commercial platinum-carbon catalyst. Therefore, the target catalyst Pt-N-rGO has significantly enhanced electrocatalytic hydrogen evolution performance.

(2) The target catalyst Pt-N-rGO has excellent hydrogen evolution properties not only under extremely acidic (ph=0) conditions but also under extremely basic (ph=14) and neutral (ph=7) conditions, compared to commercial platinum carbon (20 wt%) catalysts. Such as Tafel slopes of 17.5, 48.3 and 38.9mV/dec under strongly acidic, strongly basic and neutral conditions, respectively. In contrast, commercial platinum carbon (20 wt%) catalysts had Tafel slopes of 26.5, 57.5 and 42.6mV/dec under strongly acidic, strongly basic and neutral conditions, respectively. Therefore, the target catalyst Pt-N-rGO shows the hydrogen evolution performance of the electrolyzed water under the full-pH effective condition. In addition, the stability of the target catalyst Pt-N-rGO at the full pH is also obviously improved.

Drawings

Fig. 1 is a Scanning Electron Microscope (SEM) and elemental energy spectrum scan of the material after step 6) in example 1.

FIG. 2 is N-rGO and Pt-C synthesized in example 2 and example 3 ₃ N ₄ The characterization graph comprises a scanning electron microscope graph, a transmission electron microscope graph and an X-ray diffraction spectrum graph; FIGS. 2a-C and d-h are N-rGO and Pt-C synthesized in examples 3 and 2, respectively ₃ N ₄ And (5) characterizing the graph.

FIG. 3 is a Scanning Electron Microscope (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 microscopy and X-ray diffraction patterns, raman spectra, and nitrogen adsorption and desorption isotherms.

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

FIG. 6 is a linear sweep voltammogram (LSV curve, polarization curve) of a target catalyst for hydrogen production by water electrolysis in a three electrode system, a comparison of hydrogen evolution performance at different catalyst loadings.

FIG. 7 illustrates the hydrogen production performance of electrolyzed water at full pH.

Fig. 8 is a preliminary mechanism investigation made by the target catalyst having excellent hydrogen evolution properties.

Detailed Description

The invention is further illustrated 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) 2g of dicyandiamide is taken in 30mL of deionized water, heated to 60 ℃ and stirred to dissolve the dicyandiamide completely, the process is about 30min, and the usage amount of the dicyandiamide is finally optimized to be 4g;

2) 30mg of chloroplatinic acid hexahydrate is added and stirred to dissolve all the chloroplatinic acid, the process being about 2 minutes;

3) The above solution was stirred for 3 hours at a constant temperature of 40℃on a magnetic stirrer with a controlled temperature, and the liquid was irradiated with an ultraviolet light source (light intensity: about 10 mW/cm) ² ) The purpose of ultraviolet irradiation is to photo-reduce chloroplatinic acid, and the irradiation for 3 hours is to thoroughly reduce the chloroplatinic acid. The purpose of the constant temperature of 40 ℃ is to prevent the dicyandiamide from precipitating due to the excessively low temperature, so that the dicyandiamide is not fully contacted with chloroplatinic acid.

4) 40mg of commercial graphene oxide was sonicated in 10mL of deionized water for about 15min;

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

6) And 5) naturally cooling the solid after the hydrothermal reaction in the step 5), centrifuging the solid by a centrifuge, washing the obtained solid by ultrapure water and ethanol, and drying the solid at 60 ℃ for 8 hours.

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

Example 1

1) 2g of dicyandiamide is taken in 30mL of deionized water, heated to 60 ℃ and stirred to dissolve the dicyandiamide completely, and the process is about 30min;

3) The above solution was stirred for 3 hours at a constant temperature of 40℃on a magnetic stirrer with a controlled temperature, and the liquid was irradiated with an ultraviolet light source (light intensity: about 10 mW/cm) ² ) The purpose of the ultraviolet irradiation isThe chloroplatinic acid is photo-reduced, and the reduction is thoroughly performed after 3 hours of illumination. The purpose of the constant temperature of 40 ℃ is to prevent the dicyandiamide from precipitating due to the excessively low temperature, so that the dicyandiamide is not fully contacted with chloroplatinic acid.

Example 2

3) Maintaining the above solution at 40deg.C for 3 hr with a magnetic stirrer, and irradiating the solution with ultraviolet light (light intensity of about 10 mW/cm) ² ) The purpose of ultraviolet irradiation is to photo-reduce chloroplatinic acid, and the irradiation for 3 hours is to enable the reduction to be more thorough. The purpose of the constant temperature of 40 ℃ is to prevent insufficient contact of dicyandiamide with chloroplatinic acid due to precipitation of dicyandiamide at too low a temperature.

4) The mixed liquid in 3) is transferred to a 50mL reaction kettle, and is subjected to hydrothermal reaction at 170 ℃ for 4 hours. 5) And (3) naturally cooling the solid after the hydrothermal reaction in the step 4), centrifuging the solid by a centrifuge, washing the obtained solid by ultrapure water and ethanol, and drying the solid at 60 ℃ for 8 hours.

7) Heating at 600 ℃ for 2 hours in the nitrogen atmosphere in the tube furnace, wherein the heating rate is 5 ℃/min, and the nitrogen gas flow is 50mL/min. The obtainedBlack solid powder is marked as Pt-C ₃ N ₄ And (5) collecting for later use.

Example 3

2) 40mg of commercial graphene oxide was sonicated in 10mL of deionized water for about 15min;

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

4) And 3) naturally cooling the solid after the hydrothermal reaction in the step 3), centrifuging the solid by a centrifuge, washing the obtained solid by ultrapure water and ethanol, and drying the solid at 60 ℃ for 8 hours.

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

(2) The method of the invention is used for the treatment process

(3) and (3) dripping the ink on a glassy carbon electrode, and naturally airing. Wherein the diameter of the glassy carbon electrode is 3mm, and the area is 0.0707cm ² . After test optimization, the optimal catalyst loading is 0.303mg/cm ² ；

(3) Effects obtained by this embodiment

The application of the electrolyzed water for preparing 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 selected for comparison with commercial platinum carbon Pt/C (20 wt%) catalysts. The experimental procedure was as follows:

2mg of powder catalyst is taken and dispersed in a mixed solution of ethanol and naphthol (nafion) with the volume fraction of 75% (the volume ratio of the two solutions is 95:5), and the mixed solution is subjected to ultrasonic treatment for 60 minutes, so that the mixed solution is uniformly dispersed to form the ink. A glassy carbon electrode was used as a working electrode (working area diameter 3mm, area 0.0707 cm) ² ). Taking a plurality of drops (2.5 mu L/drop) of the ink liquid on the glassy carbon electrode, and naturally airing. The different catalyst loadings resulted in different hydrogen evolution properties, as illustrated in figure 6. The graphite rod is used as a counter electrode, and the Saturated Calomel Electrode (SCE) is used as a reference electrode to form a three-electrode electrochemical test system. CV activation was performed before each test of the working electrode. The electrolyte with ph=0 is prepared from 0.5M sulfuric acid (H ₂ SO ₄ ) The solution consisted of a ph=7 electrolyte consisting of 1M PBS buffer and a ph=14 electrolyte consisting of 1M potassium hydroxide (KOH) solution.

FIG. 1 is a Scanning Electron Microscope (SEM) of the material after step 6) of example 1. From the graph a, the particles were in the form of lumps, which were dicyandiamide that re-precipitated after crystallization. While there is no obvious reduced graphene oxide in the figure, it is possible that a relatively small amount of reduced graphene oxide is doped into dicyandiamide and is encapsulated during the precipitation of dicyandiamide. The b-e diagram is the element energy spectrum of the material, the carbon, nitrogen and oxygen elements are uniformly distributed, and the platinum elements are also uniformly distributed in the particles. This demonstrates that ultraviolet light successfully reduces chloroplatinic acid to be supported in particles composed of dicyandiamide and reduced graphene oxide. At the same time, the first 6 steps in example 1 are also illustrated to achieve the desired effect.

FIGS. 2 a-C) and d-h) are N-rGO and Pt-C synthesized in examples 3 and 2, respectively ₃ N ₄ And (5) characterizing the graph. a) The figure is a scanning electron microscope image of N-rGO, and the layered loose and porous structure can be known from the figure. b) For the corresponding transmission electron microscope image, the thin porous structure corresponds to the result of scanning electron microscope image, and the holesThe size of (2) is mainly distributed in 20-80nm and is in the form of micropores. c) The figure 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 peaks were observed, nor were peaks of graphite phase nitrogen carbide, indicating that the source material was fully carbonized at 600 ℃ after hydrothermal reduction. In contrast, in example 2, no graphene oxide, pt-C, was added ₃ N ₄ The morphology of (C) is greatly different from that of N-rGO. And as shown in figure d, the scanning electron microscope image is a reel-shaped flat structure. The enlarged partial view e of fig. d shows the presence of dense voids in the reel-like flat structure. Comparing the transmission electron microscope image f, the material is of a two-dimensional layered structure, and the size of the gap is in a micropore shape. FIG. g is a high power transmission electron micrograph, and no platinum metal particles were found. FIG. h is Pt-C ₃ N ₄ The XRD patterns of (C) and (B) show (100) and (002) planes of graphite phase nitrogen carbide at 13.2 DEG and 27.3 DEG, respectively, which are the graphite phase structure and the three-selective ring structure in the plane. This is consistent with the characterization results of scanning and transmission electron microscopy, and no metallic platinum peak appears. Platinum may exhibit sub-nanoparticle or monoatomic distribution in two-dimensional nitrogen carbide. The excitation of the activity of the single-atom catalyst has a larger relation with the carrier, and the carrier used in the embodiment is graphite-phase nitrogen carbide, so that the carrier is not suitable for hydrogen evolution reaction from the experimental result. The Pt-C can be roughly judged by the electron microscope image ₃ N ₄ The specific surface area of (C) is smaller than that of N-rGO.

FIG. 3 is a scanning electron microscope image of the target catalyst Pt-N-rGO synthesized in example 1. From the figure, the catalyst has a lamellar block structure, and the surface is flat and smooth. Compared with N-rGO and Pt-C ₃ N ₄ Its surface area should be further reduced. Figures c-f are elemental surface scans of the material, and the set of data illustrates the uniform distribution of carbon, nitrogen, and oxygen elements in the material, and the metallic platinum element is doped to exhibit a uniform distribution therein. This shows that platinum was successfully incorporated on the N-rGO support of example 1.

FIG. 4 is a further characterization of Pt-N-rGO. From a graph (transmission electron microscope graph), the Pt-N-rGO lamellar structure is loaded with clearNanoparticles are revealed, which is consistent with the results of scanning electron microscopy. The high resolution graph b shows that the nano particles are uniformly distributed at high density, and the particle size is also uniformly distributed. As can be seen from the statistical histogram of particle sizes for more than 100 nanoparticles, the average particle size of the nanoparticles was about 2.58nm (as shown in figure e), exhibiting a smaller particle size distribution. The lattice fringes of graph c and the fourier space transformation graph of graph d demonstrate that the nanoparticles are platinum nanoparticles, and the displayed crystal planes are the (111) plane of platinum. Panel f is the X-ray diffraction patterns of Pt-N-rGO and commercial Pt/C (20 wt.%) at about 25.2 and 26.0, respectively, corresponding to the peaks of graphitic carbon, which is consistent with 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. Standard card of PDF combined with platinum (JCPDF: 04-0802) shows that the remaining diffraction peaks are mainly due to platinum nanoparticles, which again verifies that the nanoparticles on the high power transmission electron microscopy are platinum nanoparticles and no foreign interference. G is the Raman spectrum of the target sample (Pt-N-rGO) and the comparative sample (commercial Pt/C), the D band and the G band correspond to the defect degree and the graphitization degree of the material respectively, and the peak area ratio (I _D /I _G ) 1.25 and 1.15, respectively, which indicates that the graphitization degree of Pt-N-rGO is higher than that of Pt/C. The higher the degree of graphitization, the faster the electron transport rate of the carbon-based carrier. The h diagram is a nitrogen adsorption and desorption isothermal diagram of three materials, and the diagram shows that Pt-C ₃ N ₄ The specific surface areas of the Pt/C and Pt-N-rGO materials are 144.57, 173.61 and 39.42m respectively ² And/g. This is consistent with the analysis results of scanning or transmission electron microscopy.

FIG. 5 is a thermogravimetric plot a) and a conductivity measurement plot b) of calcination of a target sample Pt-N-rGO sample and a comparative sample commercial Pt/C in an air atmosphere. Thermogravimetric analysis of the sample commercial Pt/C (20 wt.%) showed a mass fraction of 20% of its platinum, which is as expected. While the Pt-N-rGO of the target catalyst was heated to 1000℃by an air atmosphere, its metal oxide (PtO ₂ ) The mass fraction of platinum converted to metal was 10% which is only one half of the platinum content in commercial Pt/C. However, subsequent electrolysis of water to produce hydrogenThe performance test of the target catalyst Pt-N-rGO shows that the performance of the target catalyst Pt-N-rGO is superior to that of commercial Pt/C. As another example, the conductivity of the two catalysts is characterized, and the result shows that the conductivity (1.0 mu s/cm) of the Pt-N-rGO is higher than that of the commercial Pt/C (0.6 mu s/cm), and the higher conductivity is favorable for rapid electron transmission and catalytic reaction, so that the target catalyst is predicted to have better hydrogen evolution performance than the commercial Pt/C.

FIG. 6 is a linear sweep voltammogram (LSV curve, polarization curve) of a target catalyst for hydrogen production by water electrolysis in a three electrode system, a comparison of hydrogen evolution performance at different catalyst loadings. Too much or too little catalyst loading is detrimental to the hydrogen evolution reaction. Too much, the outermost catalyst cannot be electrocatalytic due to the active sites being covered. Too little, the bare and reduced current effect of the glassy carbon electrode. As can be seen, we choose 0.303mg/cm in this application ² As the optimum loading of the catalyst.

FIG. 7 illustrates the hydrogen production performance of electrolyzed water at full pH. FIG. a is 0.5. 0.5M H ₂ SO ₄ Linear sweep voltammogram of (C), N-rGO, pt-C ₃ N ₄ The hydrogen evolution performance of Pt/C and Pt-N-rGO is enhanced in sequence. At 10mA/cm for the four catalysts described above ² The overpotential thereof was 449, 346, 31.3 and 17.4mV in this order. The results of this experiment 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 site for catalyzing hydrogen evolution. Panel d is the Tafel slope (tafel slope) for three catalysts under very acidic conditions. The tafel slope reaction is the resistance condition of the electrode in the electrode polarization process, and can quantitatively reflect the dynamic process in the electrode polarization process. The smaller the value, the smaller the electrode resistance. For Pt-C ₃ N ₄ The Tafil 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 smallest electron transmission resistance and the best reaction kinetics. We also examined the stability of the target catalyst Pt-N-rGO under very acidic conditions andcompared to commercial vitreous carbon. As shown in FIG. 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 long-term testing covering the surface of the catalyst. In contrast, commercial Pt/C catalysts run for less than 10 hours and gradually lose activity.

Similarly, graph b shows the hydrogen evolution performance of the three catalysts described above under very basic conditions. Target catalyst Pt-N-rGO compared to commercial Pt/C and Pt-C ₃ N ₄ Still has more outstanding performance. Such as at 100mA/cm ² The overpotential was 118, 210 and 861mV, respectively. As shown in FIG. e, their Tafil slopes were 48.3, 57.5 and 216.3mV/dec, respectively. The target catalyst Pt-N-rGO shows the best extremely 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 examined Pt-N-rGO, pt/C and Pt-C using 1M PBS buffer system as electrolyte under neutral conditions ₃ N ₄ Hydrogen evolution properties of (2). As shown in figure C, the target catalyst Pt-N-rGO still exhibited more significant hydrogen evolution performance than the commercial Pt/C catalyst. The corresponding tafel slopes were 38.9,42.6 and 267.6mV/dec (as shown in panel f). We also examined the stability of Pt-N-rGO with Pt/C under neutral conditions, as shown in figure i. Pt-N-rGO still showed strong stability, up to 14 hours, compared to commercial Pt/C. It is worth mentioning that the stability of the target catalyst Pt-N-rGO in PBS buffer solution is "somewhat inferior" to that of the target catalyst under extreme alkaline and acidic conditions, probably due to the influence of the electrolysis process of the catalyst with high concentration of PBS (1M). This effect is more severe for commercial Pt/C performance as shown in figure 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 mechanism investigation made by the target catalyst having excellent hydrogen evolution properties. Figures a-c show electrochemical impedance spectra of a target catalyst and a comparative catalyst in three different electrolyte systems. The diameter of the formed semicircle ring can qualitatively reflect the resistance of the charge transfer resistor received by the catalyst on the electrode interface. From the graph, pt-N-rGO exhibits the smallest charge transfer resistance in all three electrolytes compared to commercial Pt/C. In addition, we also masked the metal components of the catalyst by means of the addition of a metal masking agent (e.g., potassium thiocyanate, KSCN; EDTA-2 Na). After the masking agent is added, as shown in figures d-f, all three systems show obviously inhibited hydrogen evolution performance. In connection with the above analysis, we consider the metallic platinum in Pt-N-rGO as a potent active center.

Claims

1. A method for preparing a low content platinum-based catalyst, comprising the steps of:

2) In the process of carrying out hydrothermal reduction on graphene oxide by utilizing a hydrothermal reduction method, an intermediate product is obtained, and the method specifically comprises the following steps:

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

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

1.3 And (2) keeping the temperature of the solution in the step 1.2) at 35-45 ℃ on a magnetic stirrer with temperature control, stirring for 2-5 h, and irradiating the liquid by using an ultraviolet light source to obtain mixed liquid.

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

4. The method for preparing a low-content platinum-based catalyst according to claim 1, wherein in step 2.2), the hydrothermal reaction is performed at 160-180 ℃ for 3-5 hours.

5. The method for preparing a low content platinum-based catalyst according to claim 1, wherein in step 2.3), the post-treatment comprises: and (3) naturally cooling and centrifuging the solid obtained after the hydrothermal reaction in the step 2.2), washing the obtained solid with water and ethanol, and drying at 50-70 ℃ for 6-10 hours.

6. The method for preparing a low content platinum-based catalyst according to claim 1, wherein in step 3), specifically comprising:

and heating the intermediate product for 1-4 hours at 500-700 ℃ in the nitrogen atmosphere in the tube furnace.

7. The method for preparing a low-content platinum-based catalyst according to claim 6, wherein in the step 3), the temperature rising rate is 2-8 ℃/min, and the nitrogen gas flow is 30-80 mL/min.

8. The low-content platinum-based catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the low content platinum-based catalyst according to claim 8 for the production of hydrogen by electrolysis of water.