WO2020118786A1

WO2020118786A1 - Platinum/phosphorus catalyst, preparation method therefor, and application thereof

Info

Publication number: WO2020118786A1
Application number: PCT/CN2018/124632
Authority: WO
Inventors: 喻学锋; 白力诚; 王欣
Original assignee: 中国科学院深圳先进技术研究院
Priority date: 2018-12-12
Filing date: 2018-12-28
Publication date: 2020-06-18
Also published as: CN111298815A; CN111298815B

Abstract

Provided are a platinum/phosphorus catalyst, a preparation method therefor, and an application thereof. The platinum/phosphorus catalyst is prepared by means of the following preparation methods: 1) synthesis of a platinum-carbon catalyst in which a carbon carrier, a surfactant, an alkali, and a solvent are mixed to obtain a base mixture, the base mixture, a reducing agent, and a platinum salt solution are mixed and react, and a solid product obtained thereby is the platinum-carbon catalyst; and 2) phosphating of the platinum-carbon catalyst in which the platinum-carbon catalyst, a phosphate source, and an organic solvent are mixed and react, and a solid product acquired thereby is the platinum/phosphorus catalyst. The platinum/phosphorus catalyst is used as an electrocatalyst in electrochemical hydrogen evolution. Compared with the prior art, the preparation method of the invention controls the surface electronic structure of platinum at a low temperature and low pressure or even at room temperature and normal pressure, thereby acquiring an effective electrocatalytic material easily synthesized by means of a simple process.

Description

Platinum/phosphorus catalyst and preparation method and application thereof

Technical field

The invention relates to the field of catalyst materials, in particular to a platinum/phosphorus catalyst and its preparation method and application.

Background technique

Today, due to the excessive use of fossil fuels and the pollution caused to the environment, it has caused widespread concern about renewable energy. Hydrogen is considered to be a very promising chemical fuel in renewable energy applications due to its advantages of high energy density and zero environmental pollution. Electrolyzed water is an efficient hydrogen production method, but this method mainly relies on the cathode catalyst. The precious metal platinum is by far the best hydrogen evolution catalyst. Due to their outstanding activity, selectivity and stability, platinum-based catalysts occupy overwhelming technical advantages and unshakable market share in many catalyst material systems, and have a wide range of uses in electrocatalytic reactions. However, due to the low content of platinum in the earth's crust and the difficulty of mining, the cost is higher, which limits the further application of platinum-based catalysts. At the same time, with the rapid economic and social development, the demand for platinum-based electrocatalysts in the relevant electrocatalysis industry is increasing day by day. Therefore, in the face of the increasingly severe conflict between resource depletion and increasing resource demand, there is an urgent need to open up new paths and explore new technologies to improve the catalytic activity of platinum-based electrocatalysts.

At present, the following three methods are commonly used: (1) Co-reduction method, expensive platinum with high catalytic activity and base metal with low electrocatalytic activity are prepared into alloy nanoparticles with various morphologies (2) Wrap expensive platinum on non-noble metal particles to form a core-shell structure; (3) Prepare a platinum alloy composite catalyst with a porous structure, and a non-noble metal composed of a compound of nickel and cobalt under development catalyst. A large number of studies have confirmed that some platinum alloy catalysts with specific structures, in the electrocatalytic hydrogen evolution reaction, due to the improvement of the surface electronic state density due to alloying, their electrocatalytic performance far exceeds that of the pure electrocatalyst with the best electrocatalytic activity. Platinum catalysts, to enhance their electrocatalytic performance, thereby reducing the use of precious metals, have become the most likely route, and also provide the possibility of large-scale commercial promotion of platinum-based catalysts.

So far, there have been various measures to improve the performance of electrocatalysts, such as changing the physical structure, chemical structure and electronic structure of the catalyst. The alloying or doping of the catalyst with metal or non-metal elements can change the surface electronic structure of the material, so as to achieve the purpose of improving the activity of the catalyst. There are a large number of reports of alloying platinum metal with other transition metals to control the electronic state of the platinum metal surface in small amounts, and the catalyst shows excellent catalytic activity. Methods used for alloying the platinum surface include high-temperature annealing, ultra-high vacuum or physical sputtering/evaporation procedures. However, these measures may result in high costs and rely heavily on equipment. Therefore, it is of great significance to develop a platinum-based catalyst with low cost, high catalytic activity and high cycle stability.

Summary of the invention

The existing technical solutions have the disadvantages of high cost, harsh conditions, and strong device dependence, making it difficult to realize large-scale applications. In order to overcome the defects of the prior art, the present invention aims to solve the technical problems of high preparation cost and low platinum utilization rate of conventional platinum and platinum-based alloy catalysts in the prior art, thereby providing a kind of good stability and high catalytic activity Platinum/phosphorus catalyst and its preparation method and application.

The invention designs a platinum/phosphorus electrocatalyst from the principle of regulating the electronic structure of the platinum surface to achieve the regulation of its catalytic activity. Through the high adsorption energy of phosphorus and platinum, the surface alloying of platinum nanoparticles and phosphorus will form platinum-phosphorus bonds to achieve the purpose of regulating the surface electronic structure of platinum nanoparticles.

The technical solutions adopted by the present invention are:

A preparation method of platinum/phosphorus catalyst includes the following steps:

1) Synthesis of platinum-carbon catalyst: mixing the carbon carrier, surfactant, alkali and solvent to obtain a substrate mixture; then mixing and reacting the substrate mixture, reducing agent and platinum salt solution to obtain a platinum-carbon catalyst;

2) Phosphating of platinum carbon catalyst: The platinum carbon catalyst, phosphorus source and organic solvent are mixed and reacted, and the solid product obtained is a platinum/phosphorus catalyst.

Preferably, in step 1) of the preparation method of the platinum/phosphorus catalyst, the platinum salt concentration of the platinum salt solution is 0.08 mol/L to 1 mol/L; further preferably, in step 1), the platinum salt concentration of the platinum salt solution It is 0.08mol/L～0.12mol/L.

Preferably, in step 1) of the preparation method of the platinum/phosphorus catalyst, the platinum salt is platinum dichloride, platinum tetrachloride, chloroplatinate, chloroplatinate, hexachloroplatinate, tetranitrate At least one of platinic acid salt, tetraammine platinum nitrate, tetraammine platinum chloride, dinitrodiammine platinum, and acetylacetonatoplatin; further preferably, in step 1), the platinum salt is dichloride Platinum, platinum tetrachloride, potassium chloroplatinate, sodium chloroplatinate, ammonium chloroplatinate, potassium chloroplatinate, sodium chloroplatinate, ammonium chloroplatinate, potassium hexachloroplatinate, hexachloroplatinum Sodium platinum, ammonium hexachloroplatinate, potassium tetranitroplatinate, sodium tetranitroplatinate, ammonium tetranitroplatinate, platinum nitrate tetraammonium, platinum chloride tetraammine, dinitrosobis At least one of ammonia platinum and platinum acetylacetonate.

Preferably, in step 1) of the preparation method of the platinum/phosphorus catalyst, the carbon carrier is at least one of carbon black, graphite, graphene, carbon fiber, carbon nanotubes, activated carbon, and carbon molecular sieve; further preferably, step 1 ), the carbon carrier is at least one of graphite, graphene, and carbon fiber.

Preferably, in step 1) of the preparation method of the platinum/phosphorus catalyst, the surfactant is at least one of a nonionic surfactant, an anionic surfactant, and a cationic surfactant; further preferably, in step 1) Among the surfactants, the nonionic surfactant is at least one selected from polyvinylpyrrolidone and polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer; the anionic surfactant is selected from dodecylbenzenesulfonate At least one of sodium, sodium dodecyl sulfonate, sodium dodecyl sulfate; cationic surfactant is selected from cetyl trimethyl ammonium bromide, cetyl trimethyl ammonium chloride At least one of dodecyl dimethyl benzyl ammonium chloride.

Preferably, in step 1) of the preparation method of the platinum/phosphorus catalyst, the alkali is at least one of alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate, and ammonia water; further preferably, step 1 ), the alkali is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, and ammonia; still further preferably, in step 1), the alkali is ammonia; In some preferred embodiments of the invention, the mass content of ammonia used in step 1) is 25%-30%.

Preferably, in the preparation method of the platinum/phosphorus catalyst step 1), the reducing agent is at least one of alkali metal hydride, alkali metal borohydride, and aldehyde solution; further preferably, in step 1), the reducing agent At least one of sodium borohydride, potassium borohydride, and formaldehyde solution; still further preferably, in step 1), the reducing agent is a formaldehyde solution; in some preferred embodiments of the present invention, step 1) uses a formaldehyde solution The mass content is 35% to 40%.

Preferably, in step 1) of the preparation method of the platinum/phosphorus catalyst, the solvent is one of water, alcohol solvents, ether solvents, alcohol ether solvents, ketone solvents, ester solvents, and amide solvents or Multiple; further preferably, in step 1), the solvent is at least one of water, methanol, ethanol, propanol, isopropanol, diethyl ether, acetone, N,N-dimethylformamide; still further preferred In step 1), the solvent is a mixed solvent composed of ethanol and water; in some preferred embodiments of the present invention, in the alcohol-water solvent used in step 1), the volume ratio of ethanol and water is 1: (2～3 ).

Preferably, in the step 1) of the preparation method of the platinum/phosphorus catalyst, the mass ratio of the carbon carrier, surfactant, alkali, solvent, reducing agent and platinum salt is 1: (0.1-10): (0.05-1) : (100～500): (0.05～1): (0.1～10).

Preferably, in step 1) of the preparation method of the platinum/phosphorus catalyst, the temperature of the mixing reaction is 20°C to 80°C, and the time of the mixing reaction is 24h to 48h; further preferably, in step 1), the mixing reaction is specifically First, the reaction is carried out at 25°C to 30°C for 20h to 30h, and then the temperature is raised to 65°C to 75°C for 10h to 15h.

Preferably, in step 1) of the preparation method of the platinum/phosphorus catalyst, after the mixing reaction, centrifugal separation is performed to obtain a solid product, and the solid product is washed again to obtain a platinum carbon catalyst.

Preferably, in step 2) of the preparation method of the platinum/phosphorus catalyst, the phosphorus source of the phosphorus source solution is elemental phosphorus, phosphorus trioxide, phosphorus pentoxide, inorganic phosphate, trioctylphosphine, triphenylphosphine , At least one of ethyldiphenylphosphine, 1,2-bis(diphenylphosphino)benzene, 1,2-bis(dimethylphosphonium)ethane, and chlorodiisopropylphosphine; further preferred In step 2), the phosphorus source is at least one of red phosphorus, black phosphorus, phosphorus pentoxide, trioctylphosphine, and triphenylphosphine.

Preferably, in step 2) of the preparation method of the platinum/phosphorus catalyst, the organic solvent is one or more of alcohol solvents, ether solvents, alcohol ether solvents, ketone solvents, ester solvents, and amide solvents Further preferred, in step 2), the organic solvent is at least one of methanol, ethanol, propanol, isopropanol, diethyl ether, acetone, N,N-dimethylformamide; still further preferred, step In 2), the organic solvent is at least one of methanol, ethanol, propanol, and isopropanol.

Preferably, in step 2) of the preparation method of the platinum/phosphorus catalyst, the mass ratio of platinum in the platinum-carbon catalyst, phosphorus in the phosphorus source, and organic solvent is 1: (0.01-0.1): (500-2000).

Preferably, in step 2) of the preparation method of the platinum/phosphorus catalyst, the mixing reaction is specifically ultrasonic treatment at normal temperature for 1 min to 10 min.

An electrocatalyst is a platinum/phosphorus catalyst prepared by the foregoing preparation method.

The application of this electrocatalyst in electrochemical hydrogen evolution.

Preferably, in this application, the electrocatalyst is made into a catalyst solution, added to the working substrate electrode, made into a working electrode, and then a three-electrode system is formed for electrochemical hydrogen evolution treatment.

Preferably, in this application, the platinum concentration in the catalyst solution is 0.1 mg/mL to 1 mg/mL.

Preferably, in this application, the working substrate electrode is a rotating disk electrode.

Preferably, in this application, the counter electrode of the three-electrode system is graphite, and the reference electrode is a saturated calomel electrode.

The beneficial effects of the present invention are:

Starting from the phenomenon of strong adsorption energy of metal platinum and phosphorus elements, the present invention realizes the alloying of phosphorus elements on the surface of metal platinum at low temperature and low pressure or even normal temperature and pressure to achieve the regulation of the surface electronic state and catalytic activity of metal platinum-based catalysts. Compared with the existing technology, the invention can achieve the regulation and control of the electronic structure of the metal platinum surface at low temperature and low pressure or even normal temperature and pressure, thereby obtaining a highly efficient electrocatalytic material with simple synthesis, convenient process and low cost.

BRIEF DESCRIPTION

Figure 1 is a transmission electron microscope (a) and scanning transmission electron microscope (b) diagram of a platinum/phosphorus catalyst;

Figure 2 is a comparison chart of X-ray photoelectron spectroscopy analysis of platinum carbon catalyst and platinum phosphorus catalyst;

Figure 3 is a comparison chart of X-ray diffraction energy spectrum analysis of platinum carbon catalyst and platinum phosphorus catalyst;

Figure 4 is a high-resolution valence band X-ray photoelectron spectroscopy of platinum carbon catalyst and platinum phosphorus catalyst;

Figure 5 is a comparison chart of the electrochemical hydrogen evolution performance of platinum carbon catalyst and platinum phosphorus catalyst.

detailed description

The content of the present invention will be further described in detail below through specific examples. Unless otherwise specified, the raw materials used in the examples can be obtained from conventional commercial sources. The ammonia solution, formaldehyde solution and potassium tetrachloroplatinate solution mentioned in the examples all refer to the respective aqueous solutions.

Preparation example

First, graphene-supported platinum composite material (platinum carbon catalyst) was synthesized. At 28°C, 50 mg of sodium dodecylbenzenesulfonate was dissolved in 12.5 mL of water, 5 mL of ethanol, 50 mg of graphene nanosheets, and 0.02 mL of ammonia (28 wt%) ) Solution. To this solution was added 0.03 mL of formaldehyde (37 wt%) solution and 0.4 mL of potassium tetrachloroplatinate (0.1 mol/L) solution under vigorous stirring. After 24 hours, the temperature was raised to 70°C and maintained at this temperature for another 12 hours. The solid product was collected by centrifugation and washed three times with water/ethanol to obtain a platinum carbon catalyst.

The obtained platinum-carbon catalyst was dispersed in ethanol so that the platinum content was 0.5 mg/mL. Take 1 mL of platinum-carbon catalyst solution and add 0.3 mL of black phosphorus nanosheet ethanol solution (0.1 mg/mL), then perform ultrasonic treatment at room temperature and pressure for 3 minutes. The resulting solid product is a platinum/phosphorus catalyst.

Characterization analysis

The structure of the prepared platinum/phosphorus catalyst was characterized by transmission electron microscopy. FIG. 1 is a transmission electron microscope and scanning transmission electron microscope diagram of a platinum/phosphorus catalyst; in FIG. 1, FIG. 1(a) is a transmission electron microscope diagram, and FIG. 1(b) is a scanning transmission electron microscope diagram. It can be seen from Figure 1 that the platinum/phosphorus particles are evenly distributed on the substrate surface.

The following is a characterization analysis of the platinum carbon catalyst before phosphating and the platinum/phosphorus catalyst after phosphating in the preparation examples.

X-ray photoelectron spectroscopy was used to determine the surface electronic structure of platinum elements in platinum-carbon catalyst and platinum-phosphorus catalyst. See figure 2 for comparison of X-ray photoelectron spectroscopy analysis. In Figure 2, the platinum-carbon catalyst shows two Pt 4f core-level photoelectron spectrum peaks, where the binding energy is 71.1eV is Pt 4f7/2, and the binding energy is 72.2eV. The front is 4f 5/2. The peaks at Pt 4f7/2 and Pt 4f5/2 belong to Pt0 and PtII, respectively. In addition, for platinum-phosphorus catalysts, in addition to the same Pt0 and PtII peaks as platinum-carbon catalysts, another group of Pt 4f7/2 appeared at 72.9eV, which can be attributed to the formation of Pt-P bonds.

Figure 3 is a comparison chart of X-ray diffraction energy spectrum analysis of platinum carbon catalyst and platinum phosphorus catalyst. Compared with the platinum-carbon catalyst without phosphating, it was found that the X-ray diffraction pattern of the phosphating platinum-phosphorus catalyst showed a new diffraction peak at 34°, which indicated the formation of platinum-phosphorus bonds. At the same time, the Pt diffraction peak at 40° in the platinum-phosphorus catalyst broadened and decreased, and almost disappeared. This indicates that the formation of a large number of platinum-phosphorus bonds leads to a change in the metal platinum lattice.

The high-resolution valence band X-ray photoelectron spectroscopy is used to perform a d-band electronic structure on the photoelectron spectroscopy of the platinum carbon catalyst and the platinum phosphorus catalyst, as shown in FIG. 4. The study found that after phosphating, the d-band electron center of the catalyst dropped from -4.28eV to -5.12eV. According to the d-band theory, the downward movement of the center of the Pt band pulls more anti-bonding states below the Fermi level, making Pt have the best guest molecular adsorption, and thus its electrochemical hydrogen evolution activity is increased.

Electrocatalytic applications

The platinum carbon catalyst and platinum phosphorus catalyst prepared in the preparation examples were analyzed for electrochemical hydrogen evolution application test.

The electrochemical hydrogen evolution was measured using the Shanghai Chenhua Electrochemical Workstation CHI 660D. The measurement system is a standard three-electrode system. The working electrode uses a rotating disk electrode (0.07cm ² ). Graphite rod and saturated calomel electrode (SCE) are counter electrode and reference electrode, respectively. In all measurements, the saturated calomel electrode was calibrated relative to the reversible hydrogen electrode (RHE). In 1.0 mol/L KOH, E(RHE)=E(SCE)+0.0592*14+0.242V. Platinum phosphorus catalyst and platinum carbon catalyst samples are working electrodes. The catalyst was sonicated with ethanol and 5% Nafion (volume ratio, 5:0.02) for 1 h, in which the platinum concentration was 0.5 mg/mL of catalyst ink. Then 2 μL of the above mixed solution was dropped onto the working electrode and dried in air. Linear scanning voltammetry was used to measure the HER activity of nitrogen saturated KOH (1.0 mol/L) at a scan rate of -0.3-0.1 V at a scan rate of 5 mV·s ^-1 (25°C). In a nitrogen-saturated KOH (1.0 mol/L), cyclic voltammetry (CV) was used to scan -0.6V to 0.1V, and 1000 cycles of electrochemical stability tests were performed at a scan rate of 20mV·s ^-1 . The rotating disk electrode was rotated at 1600 rpm to avoid the accumulation of hydrogen bubbles. IR drop compensation is performed on all polarization curves.

The performance of electrochemical hydrogen evolution of the platinum-phosphorus catalyst and platinum-carbon catalyst is shown in FIG. 5. Figure 5 shows the linear sweep voltammetry curves of the two, respectively, where the current density is normalized by the geometric area of the working electrode (disk) and the mass of Pt, respectively. The platinum-phosphorus catalysts have current densities of 125.43 mA·cm ^-2 and 42.28 mA·cm ^-2 at overpotentials of 150 mV and 70 mV, which is twice that of platinum-carbon catalysts (61.07 mA·cm ^-2 and 19 mA·cm ^-2 ). It shows that the electronic structure of Pt is regulated after phosphating, and its electrochemical hydrogen evolution performance has been greatly improved.

Claims

A preparation method of platinum/phosphorus catalyst is characterized by comprising the following steps:

1) Synthesis of platinum-carbon catalyst: mixing the carbon carrier, surfactant, alkali and solvent to obtain a substrate mixture; then mixing and reacting the substrate mixture, reducing agent and platinum salt solution to obtain a platinum-carbon catalyst;

2) Phosphating of platinum carbon catalyst: The platinum carbon catalyst, phosphorus source and organic solvent are mixed and reacted, and the solid product obtained is a platinum/phosphorus catalyst.
The method for preparing a platinum/phosphorus catalyst according to claim 1, characterized in that: in step 1), the platinum salt concentration of the platinum salt solution is 0.08mol/L～1mol/L; the platinum salt is platinum dichloride , Platinum tetrachloride, chloroplatinate, chloroplatinate, hexachloroplatinate, tetranitroplatinate, tetraammine platinum nitrate, tetraammine platinum chloride, dinitrosodiammine At least one of platinum and platinum acetylacetonate.
The method for preparing a platinum/phosphorus catalyst according to claim 1, wherein in step 1), the carbon carrier is at least one of carbon black, graphite, graphene, carbon fiber, carbon nanotubes, activated carbon, and carbon molecular sieve One; surfactant is at least one of nonionic surfactant, anionic surfactant, cationic surfactant; alkali is alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate, ammonia water At least one of the; reducing agent is at least one of alkali metal hydride, alkali metal borohydride, aldehyde solution; the solvent is water, alcohol solvents, ether solvents, alcohol ether solvents, ketone solvents, esters One or more of solvents and amide solvents.
The method for preparing a platinum/phosphorus catalyst according to claim 2 or 3, characterized in that: in step 1), the mass ratio of carbon support, surfactant, alkali, solvent, reducing agent, platinum salt is 1: (0.1 to 10): (0.05 to 1): (100 to 500): (0.05 to 1): (0.1 to 10).
The method for preparing a platinum/phosphorus catalyst according to claim 4, wherein in step 1), the temperature of the mixing reaction is 20°C to 80°C, and the time of the mixing reaction is 24h to 48h.
The method for preparing a platinum/phosphorus catalyst according to claim 1, wherein in step 2), the phosphorus source of the phosphorus source solution is elemental phosphorus, phosphorus trioxide, phosphorus pentoxide, inorganic phosphate, Trioctylphosphine, triphenylphosphine, ethyldiphenylphosphine, 1,2-bis(diphenylphosphino)benzene, 1,2-bis(dimethylphosphonium)ethane, chlorodiisopropyl At least one of phosphines; the organic solvent is one or more of alcohol solvents, ether solvents, alcohol ether solvents, ketone solvents, ester solvents, and amide solvents.
The method for preparing a platinum/phosphorus catalyst according to claim 1 or 6, wherein in step 2), the mass ratio of platinum in the platinum-carbon catalyst, phosphorus in the phosphorus source, and organic solvent is 1: ( 0.01～0.1): (500～2000).
The method for preparing a platinum/phosphorus catalyst according to claim 7, wherein in step 2), the mixing reaction is specifically ultrasonic treatment at room temperature for 1 min to 10 min.
An electrocatalyst, characterized in that it is a platinum/phosphorus catalyst prepared by the preparation method according to any one of claims 1 to 8.
The use of an electrocatalyst according to claim 9 in electrochemical hydrogen evolution.