CN113373345B

CN113373345B - Supported superfine PtCoP ternary alloy nanoparticle for electrocatalytic methanol oxidation and preparation method thereof

Info

Publication number: CN113373345B
Application number: CN202110630785.0A
Authority: CN
Inventors: 王峰; 周明强
Original assignee: Sinohydro New Energy Beijing New Energy Technology Research Institute Co ltd
Current assignee: Sinohydro New Energy Beijing New Energy Technology Research Institute Co ltd
Priority date: 2021-06-07
Filing date: 2021-06-07
Publication date: 2022-05-17
Anticipated expiration: 2041-06-07
Also published as: CN113373345A

Abstract

The invention discloses a supported superfine PtCoP ternary alloy nanoparticle for electrocatalytic methanol oxidation and a preparation method thereof. The method comprises the following steps: the reaction is carried out in an aqueous system comprising water, carbon nanotubes or acidified carbon tubes, a water-soluble platinum source substance, a water-soluble cobalt source substance, a water-soluble phosphorus source substance, and a water-soluble reducing agent. The invention adopts the acidified carbon tube as a carrier, and the abundant oxygen-containing functional groups on the surface are beneficial to chelating metal ions and promoting the uniform distribution of nano particles on the surface of the carbon tube; the invention takes sodium dihydrogen hypophosphite as a reducing agent and can also be used as a phosphorus source, thereby reducing the introduction of impurities. Phosphate radical plasma generated by reduction of sodium dihydrogen hypophosphite can react with oxygen-containing functional groups on the surface of the carbon tube, so that the interaction between the ternary alloy and the carbon tube is enhanced, the reaction activity is improved, and the stability of the carbon tube surface nano particles in the reaction process is improved.

Description

Supported superfine PtCoP ternary alloy nanoparticle for electrocatalytic methanol oxidation and preparation method thereof

Technical Field

The invention belongs to the field of energy materials, and particularly relates to a supported superfine PtCoP ternary alloy nanoparticle and a preparation method thereof.

Background

With the large consumption of fossil energy, the environmental problem is increasingly serious, and the development of efficient and low-pollution clean energy has important significance for realizing sustainable development of energy. Direct methanol fuel cells based on electrochemical energy conversion technology are receiving much attention from researchers because of their advantages of being clean, efficient, and reaction free from carnot cycle limitations. However, the kinetics of the oxidation reaction of methanol on the surface of the electrode is slow, and the reaction is often accelerated by using noble metal platinum. However, the conventional platinum catalyst is expensive to use and easily adsorbs methanol reaction intermediate products to cause deactivation. Therefore, the method has important research significance for improving the anti-poisoning capability of the catalyst and reducing the using amount of the noble metal platinum through alloying.

Alloying platinum with cobalt is an effective means to improve the catalytic activity and anti-poisoning ability of platinum. However, cobalt atoms dissolve in the acid electrolyte as the potential changes. Therefore, optimizing the catalyst composition to inhibit the problem of the dissolution of PtCo alloy nanoparticles in the electrolyte has important research value.

Recently, phosphorus (P) element has been reported to be effective in inhibiting the dissolution of nickel after alloying with nickel, a transition metal. However, the phosphorus element is introduced into the platinum-cobalt alloy catalyst to construct a ternary alloy system, so that the highly dispersed nanoparticles are prepared, the reducibility of the three elements is required to be considered simultaneously, and the high dispersibility of the nanoparticles in the catalyst is ensured to release enough active sites. Therefore, it is necessary to select a suitable precursor and a preparation process to obtain ternary alloy nanoparticles with high dispersibility.

Disclosure of Invention

The invention aims to solve the problem that Co atoms in PtCo alloy nanoparticles are easy to dissolve in the catalytic process in the prior art, and provides a one-step preparation method for constructing a platinum-cobalt-phosphorus ternary alloy nanoparticle catalyst by effectively introducing phosphorus elements into a PtCo alloy catalyst. The reducing agent selected by the invention can provide phosphorus element in the preparation process of ternary alloy nanoparticles, and meanwhile, the reaction intermediate product is beneficial to controlling the increase of the size of the nanoparticles, so that the nanoparticles with high dispersibility are obtained, the active sites of the catalyst are effectively increased, and the reaction efficiency is improved.

The invention discloses a preparation method of supported superfine PtCoP ternary alloy nanoparticles for electrocatalytic methanol oxidation, which is characterized by comprising the following steps of:

the reaction is carried out in an aqueous system comprising water, carbon nanotubes or acidified carbon tubes, a water-soluble platinum source substance, a water-soluble cobalt source substance, a water-soluble phosphorus source substance, and a water-soluble reducing agent.

In some embodiments of the invention, the water-soluble source of platinum is chloroplatinic acid.

In some embodiments of the invention, the water-soluble cobalt source is a cobalt salt, preferably cobalt chloride.

In some embodiments of the invention, the water soluble phosphorus source and the reducing agent are both sodium dihydrogen hypophosphite.

In some preferred embodiments of the invention, the aqueous system in which the reaction is carried out has a pH of from 7 to 11, preferably 10.

In some preferred embodiments of the present invention, the ratio of the carbon nanotubes or acidified carbon tubes, platinum in the platinum source, and sodium dihydrogen hypophosphite in the aqueous system is 70 to 120 mg: 0.07-0.75 mmol: 0.05-0.45 mmol: 0.05-0.6mmol, preferably 100 mg: 0.2 mmol: 0.1 to 0.3mmol, more preferably 100 mg: 0.2 mmol: 0.2 mmol.

In some embodiments of the invention, the method comprises the following steps:

s1, mixing the acidified carbon tube with deionized water, and mixing with chloroplatinic acid solution;

s2, mixing with a cobalt chloride solution;

s3, dropwise adding a sodium dihydrogen hypophosphite solution;

s4, adjusting the pH value of the reaction system, and heating and refluxing to perform a reduction reaction;

s4, cooling, filtering, drying and grinding to obtain the finished product.

In some preferred embodiments of the present invention, in the S1 step, the amounts of the acidified carbon tubes, the deionized water and the chloroplatinic acid solution are: 70-120mg of the acidified carbon tube, 10-30 mL of deionized water, and 0.01-0.05 mol L of chloroplatinic acid solution^-1The adding amount of the chloroplatinic acid solution is 7-15 mL;

in the step S2, the concentration of the cobalt chloride solution is 0.1-0.3 mol L^-1The addition amount of the cobalt chloride solution is 0.5-1.5 mL;

in the step S3, the adding amount of the sodium dihydrogen hypophosphite solution is 0.05-0.2 mol L based on the mixed solution obtained in the step S2^-1

In some embodiments of the invention, the mixing in both the steps S1 and S2 is ultrasonic dispersive mixing.

In some preferred embodiments of the present invention, in the step of S4, the heating reflux is reflux reaction at a temperature of 85-95 ℃ for 8-11 h.

In some embodiments of the present invention, in the step S4, the pH is adjusted by pumping alkali liquor, and the pH of the reaction system is predicted by the following formula to control the flow rate of the pumped alkali liquor, so as to precisely control the real-time pH of the reaction system:

wherein k (t) ═ H⁺]-[OH^-]Kw is the water balance constant and t is the sampling time.

In some embodiments of the present invention, the step S4 is performed in a stirred tank reactor, and the voltage value of the stirring device is controlled by tuning the PID parameter by an attenuation curve method, as follows:

wherein the attenuation ratio is (2.5-3): kc is 25-35, oscillation period Tp is 10-15min, sampling period Ts is 0.001Tp, integral time Ti is 0.2Tp, and differential time Td is 0.1 Tp.

The invention utilizes the preparation strategy of 'sodium dihydrogen hypophosphite assistance' to prepare the catalyst by a one-step method, and in the process, the addition amount of the sodium dihydrogen hypophosphite and the pH value of a reaction system are adjusted to realize the regulation and control of the composition and the structure of the catalyst. The sodium dihydrogen hypophosphite can be used as a reducing agent and a phosphorus source in the synthesis process of the catalyst. Therefore, its content directly affects the ternary alloy composition. Meanwhile, phosphite radicals or phosphate radicals generated in the reduction process of the sodium dihydrogen hypophosphite can be adsorbed on the surfaces of the acidified carbon tubes and the formed nano particles, so that the increase of the size of the nano particles is inhibited, and active sites are increased. Sodium dihydrogen hypophosphite can continuously release hydrogen ions in the process of reducing metal ions, but excessive hydrogen ions in the solution can inhibit the reduction reaction. Therefore, adjusting the initial pH value of the solution system to promote the reduction reaction has an important role in successfully preparing the ternary alloy catalyst and regulating the composition of the ternary alloy catalyst.

The second aspect of the invention discloses supported superfine PtCoP ternary alloy nanoparticles obtained by the method of the first aspect.

In the invention, the acidified carbon tube is an acidified carbon nanotube, and the chloroplatinic acid solution, the cobalt chloride solution and the sodium dihydrogen hypophosphite solution are all aqueous solutions.

The invention has the beneficial technical effects that:

(1) the invention adopts the acidified carbon tube as a carrier, and the excellent conductivity of the carbon tube is the guarantee of the performance of the electro-catalyst. In addition, abundant oxygen-containing functional groups on the surface of the acidified carbon tube are beneficial to chelating metal ions and promoting the uniform distribution of nano particles on the surface of the carbon tube;

(2) sodium dihydrogen hypophosphite is used as a reducing agent and can also be used as a phosphorus source, so that the introduction of impurities is reduced. In addition, sodium dihydrogen hypophosphite is a mild reducing agent, phosphate radical plasma generated by reduction of the sodium dihydrogen hypophosphite can react with oxygen-containing functional groups on the surface of the carbon tube, the interaction between the ternary alloy and the carbon tube is enhanced, the reaction activity is improved, and the stability of the nano particles on the surface of the carbon tube in the reaction process is improved.

(3) Sodium dihydrogen hypophosphite is used as a reducing agent, and the absorption of phosphate radicals and the like generated by reduction effectively reduces the reduction of metal ions on the surface of reduced metal particles and inhibits the growth of nano particles;

(4) the catalyst is prepared in a water-based system by adopting a one-step reduction method, the preparation process is simple, no pollutant is generated, and the processing cost is saved.

The invention takes sodium dihydrogen hypophosphite as a reducing agent and simultaneously provides phosphorus element, and realizes the alloying of phosphorus, platinum and cobalt by adjusting the pH value of a reaction system. Meanwhile, the carbon nano tube platinum-cobalt-phosphorus-loaded ternary alloy catalyst with the ultrafine particle size is obtained by utilizing the inhibiting effect of phosphate radicals and the like generated in the reduction process of sodium dihydrogen hypophosphite on the size of the nano particles, and the contact area of the catalyst and methanol is effectively increased. By adding the phosphorus element, the prepared catalyst not only shows excellent capability of electrocatalysis of methanol oxidation, but also has stability performance superior to that of a platinum-cobalt alloy catalyst.

Drawings

FIG. 1 is an X-ray diffraction pattern of a PtCoP/CNTs catalyst prepared by one embodiment of the invention, and only diffraction peaks of platinum crystal faces prove that generated nanoparticles are alloy phases;

FIG. 2 is a TEM photograph of a PtCoP/CNTs catalyst prepared according to an embodiment of the present invention;

FIG. 3 is an XPS whole component spectrum of a PtCoP/CNTs catalyst prepared according to one embodiment of the present invention;

FIG. 4 is a graph showing the performance of PtCoP/CNTs prepared according to one embodiment of the present invention and Pt/C and PtCo/CNTs as comparative examples in catalyzing methanol oxidation.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

In the present invention, no special requirement is imposed on the acidified carbon tube, and the acidified carbon tube in the following examples is a commercially available product, and is obtained from short multi-walled carbon nanotubes of all organic houses, OD4-6nm, length 10-20um, SSA: 500-700m²Per gram, purity greater than 95%.

In the following examples, embodiments and comparative examples, parallel tests were carried out with the same components, contents and operations, except for what is specifically indicated.

Example 1

A preparation method of supported superfine PtCoP ternary alloy nanoparticles for electrocatalysis methanol oxidation comprises the following steps:

(1) adding a certain amount of acidified carbon tubes into deionized water, and adding a certain amount of chloroplatinic acid solution with a certain concentration after uniformly dispersing by ultrasonic. The adding amount of the acidified carbon tubes is 70-120 mg; the volume of the deionized water is 10-30 mL; the concentration of the chloroplatinic acid solution is 0.01-0.05 mol L^-1(ii) a The adding amount of the chloroplatinic acid solution is 7-15 mL; the ultrasonic process time is 20-40 min;

(2) and (2) adding the cobalt chloride solution into the solution prepared in the step (1), and uniformly dispersing by ultrasonic. The concentration of the cobalt chloride solution is 0.1-0.3 mol L^-1(ii) a The addition amount of the cobalt chloride is 0.5-1.5 mL; the ultrasonic process time is 20-40 min;

(3) dropwise adding a sodium dihydrogen hypophosphite solution into the mixed solution obtained in the step (2); the concentration of the reducing agent sodium dihydrogen hypophosphite solution is 0.05-0.2 mol L^-1The adding amount is 1-3 mL;

(4) and (4) placing the mixture in the step (3) in an oil bath kettle at 90 ℃, adjusting the pH value, and carrying out reflux reaction for a certain time. The pH value is 7-11; the reaction time is 8-11 h;

(5) and (4) naturally cooling the product obtained in the step (4) to room temperature, and performing suction filtration, drying and grinding to obtain a finished product.

Specifically, the method comprises the following steps:

embodiment mode 1

The adding amount of the acidified carbon tubes is 100 mg; the volume of the deionized water is 120 mL; the concentration of the chloroplatinic acid solution is 0.02mol L^-1(ii) a The addition amount of the chloroplatinic acid solution is 10 mL; the ultrasonic process time is 30 min;

the concentration of the cobalt chloride solution is 0.2mol L^-1(ii) a The addition amount of the cobalt chloride is 1 mL; the ultrasonic process time is 30 min;

the concentration of the sodium dihydrogen hypophosphite solution is 0.1mol L^-1The adding amount is 1 mL;

the pH value is 7; the reaction time is 10 h.

Embodiment mode 2

The difference from embodiment 1 is that the sodium dihydrogen hypophosphite solution was added in an amount of 2 mL.

Embodiment 3

The difference from embodiment 1 is that the amount of the sodium dihydrogen hypophosphite solution added is 3 mL.

Embodiment 4

The difference from embodiment 1 is that the pH is 11.

Embodiment 5

The difference from embodiment 1 is that the pH is 10.

Embodiment 6

The difference from the embodiment 1 is that in the step S4, the pH is adjusted by pumping alkali liquor, and the pH of the reaction system is predicted by the following formula to control the flow rate of the pumped alkali liquor, so as to precisely control the real-time pH of the reaction system:

The pH of the reaction system is one of the important factors affecting the composition and structure of the particulate product produced. By the prediction method of the embodiment, the pH condition after the alkali liquor is added can be accurately predicted, and the real-time pH value of the reaction system can be accurately controlled.

Embodiment 7

The difference from embodiment 1 is that the step S4 is performed in a stirred tank reactor, and the voltage value of the stirring device is controlled by setting the PID parameter by the attenuation curve method, as follows:

In the reaction carried out in a large-volume reaction tank, proper stirring is an essential condition to be satisfied. Through the PID control algorithm of the embodiment, the voltage value of the stirring device can be well controlled.

Comparative example 1

The difference from embodiment 1 is that the sodium dihydrogen hypophosphite solution was added in an amount of 0.2 mL.

Comparative example 2

The difference from embodiment 1 is that the pH is 6.

Comparative example 3

The difference from embodiment 1 is that the pH value is 12.

Characterization of the product obtained in Experimental example 1

The crystal structure analysis was performed using an X-ray powder diffractometer using a copper target as the radiation source and a wavelength of 0.1541 nm. The morphology was analyzed using a transmission electron microscope. The full spectrum of the X-ray photoelectron spectrum was analyzed by an X-ray photoelectron spectrometer. The performance of the catalyst was tested by cyclic voltammetry.

The X-ray diffraction pattern of the PtCoP/CNTs catalyst obtained in the embodiment 1 is shown in figure 1, the transmission electron microscope photograph is shown in figure 2, the XPS full-component spectrum is shown in figure 3, and the performance spectrum of Pt/C and PtCo/CNTs in catalyzing methanol oxidation reaction is shown in figure 4. In FIG. 4, in the preparation of the comparative example Pt/C, the support is activated carbon, steps (2) and (3) are not included, and the rest is the same as in embodiment 1; the preparation of the PtCo/CNTs as a control was carried out without the step (3), and the remainder was the same as in embodiment 1. The products obtained in example 1 all have the same structure as in fig. 1 of embodiment 1, and show that the nanoparticles formed are an alloy phase.

Experimental example 2 Effect of sodium dihydrogen hypophosphite content and reaction System pH

The PtCoP/CNTs catalysts obtained in the embodiment and the comparative example are taken, and the particle size, the particle size dispersion degree and the catalytic performance are examined. The particle size and particle size dispersion were examined by transmission electron microscopy, and the catalytic performance was examined by cyclic voltammetry.

TABLE 1 Effect of sodium dihydrogen hypophosphite content and reaction System pH

	Particle size	Degree of particle size dispersion	Catalytic performance
				Embodiment mode 1	++	**	##
Embodiment mode
	2	+	***	###
Embodiment 3					++	**	##
	Embodiment 4	++	**	##
Embodiment
	5	+	***	###
Comparative example 1					+++	*	#
	Comparative example 2	+++	*	#
Comparative example 3					+++	*	#

In Table 1, particle size is largest, particle size is smallest, particle size is smaller, particle size is smallest; the dispersion of particle size is most preferred, the dispersion of particle size is preferred, and the dispersion of particle size is less preferred. # #, the best catalytic performance, #, the better catalytic performance, #, the worse catalytic performance, the statistically significant difference between different symbols, P < 0.05.

It can be seen that the particle size of embodiment 1 is smaller than that of comparative examples 1 to 3, and the dispersibility and catalytic performance are also superior to those of comparative examples 1 to 3. In embodiments 1, 2, and 3, the particle size in embodiment 2 is the smallest, and the dispersibility and the catalytic performance are the best. In embodiments 1, 4, and 5, embodiment 5 has the smallest particle size, and the most excellent dispersibility and catalytic performance.

While the preferred embodiments and examples of the present invention have been described in detail, the present invention is not limited to the embodiments and examples, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.

Claims

1. A preparation method of supported superfine PtCoP ternary alloy nanoparticles for electrocatalytic methanol oxidation is characterized by comprising the following steps:

carrying out reaction in an aqueous system comprising deionized water, an acidified carbon tube, a water-soluble platinum source substance, a water-soluble cobalt source substance, a water-soluble phosphorus source substance and a water-soluble reducing agent; the water-soluble phosphorus source substance and the reducing agent are sodium dihydrogen hypophosphite;

the water-soluble platinum source substance is chloroplatinic acid;

the water-soluble cobalt source substance is cobalt chloride;

the pH of the aqueous system for carrying out the reaction is 7-11;

in the aqueous system, the ratio of the acidified carbon tube, platinum in the platinum source substance and sodium dihydrogen hypophosphite is 100 mg: 0.2 mmol: 0.1-0.3 mmol;

the method comprises the following steps:

s1, mixing the acidified carbon tube with deionized water, and mixing with a chloroplatinic acid solution;

s2, mixing with cobalt chloride solution;

s3, dropwise adding a sodium dihydrogen hypophosphite solution;

s5, cooling, filtering, drying and grinding to obtain a finished product;

in step S1, the amounts of the acidified carbon tubes, the deionized water and the chloroplatinic acid solution are as follows: 70-120mg of the acidized carbon tube, 10-30 mL of deionized water and 0.01-0.05 mol/L of chloroplatinic acid solution^-1The adding amount of the chloroplatinic acid solution is 7-15 mL;

in the step S2, the concentration of the cobalt chloride solution is 0.1-0.3 mol.L^-1The addition amount of the cobalt chloride solution is 0.5-1.5 mL;

in the step S3, the addition amount of the sodium dihydrogen hypophosphite solution is 0.05-0.2 mol.L based on the mixed solution obtained in the step S2^-1。

2. The process according to claim 1, characterized in that the aqueous system in which the reaction is carried out has a pH of 10.

3. The method of claim 2, wherein the ratio of the acidified carbon tubes, platinum in the platinum source, and sodium dihydrogen hypophosphite in the aqueous system is 100 mg: 0.2 mmol: 0.2 mmol.

4. The method according to claim 1, wherein the mixing in the steps of S1 and S2 is ultrasonic dispersion mixing.

5. The method according to claim 1, wherein in the step of S4, the heating reflux is carried out at 85-95 ℃ for 8-11 h.

6. The method of claim 1, wherein in the step S4, the pH of the reaction system is adjusted by pumping alkali solution, and the pH of the reaction system is predicted by the following formula to control the flow rate of the alkali solution pumped, so as to precisely control the real-time pH of the reaction system:

；

wherein the content of the first and second substances,

，Kwis the water balance constant and t is the sampling time.

7. The method of claim 1, wherein the step of S4 is performed in a stirred tank reactor, and the voltage value of the stirring device is controlled by tuning the PID parameter by an attenuation curve method, as follows:

；

wherein the attenuation ratio is (2.5-3): 1, Kc is 25-35, the oscillation period Tp is 10-15min, the sampling period Ts is 0.001Tp, the integration time Ti is 0.2Tp, and the differentiation time Td =0.1 Tp.

8. The supported ultrafine PtCoP ternary alloy nanoparticles obtained by the method according to any one of claims 1 to 7.