Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a metal phosphide-supported monatomic catalyst, a preparation method thereof, and an application thereof as a hydrogen evolution reaction electrocatalyst, which not only reduces the amount of noble metals used, but also obtains higher catalytic activity, and realizes efficient catalysis in atomic economy.
In order to achieve the above object, the present invention provides a method for preparing a metal phosphide-supported monatomic catalyst, comprising the steps of:
s1) preparing a mixed solution from transition metal salt, urea, ammonium fluoride and water, adding a carrier, and carrying out hydrothermal reaction;
s2) cleaning and drying the sample reacted in the step S1), and then placing the sample in a tube furnace to carry out high-temperature phosphorization under inert atmosphere to obtain a transition metal phosphide material;
s3) carrying out high-temperature heat treatment on the transition metal phosphide material obtained in the step S2) under the action of reducing atmosphere;
s4) soaking the sample obtained in the step S3) in an impregnation solution containing noble metal ions, and then carrying out drying treatment;
s5) carrying out reduction treatment on the sample obtained in the step S4) to obtain the metal phosphide-supported monatomic catalyst.
Preferably, the transition metal salt is selected from one or more of nitrate, chloride or ammonium salt of transition metal.
Preferably, the transition metal is selected from one or more of nickel, iron, cobalt and molybdenum.
Preferably, the concentration of the transition metal salt in the mixed solution is 0.02-0.08 mol/L; more preferably 0.045 to 0.055 mol/L.
Preferably, the carrier is selected from one or more of nickel foam, carbon cloth and carbon paper.
Preferably, the carbon cloth and the carbon paper are subjected to hydrophilic treatment before use.
The method for the hydrophilic treatment of the present invention is not particularly limited, and may be a method known to those skilled in the art. Preferably involving two weeks of soaking in concentrated sulfuric acid and concentrated nitric acid.
In the present invention, the temperature of the hydrothermal reaction in the step S1) is preferably 100 to 150 ℃.
In the present invention, the reaction time of the hydrothermal reaction in the step S1) is preferably 4 to 10 hours.
And then cleaning and drying the sample reacted in the step S1).
According to the invention, the washing process is deionized water and ethanol washing, and the number of times is preferably 3-10.
Preferably, the drying process is carried out at a low temperature of 40-60 ℃.
Then high-temperature phosphorization is carried out.
Preferably, the material is placed in a tube furnace for high-temperature phosphorization under inert atmosphere to obtain the transition metal phosphide material.
A phosphorus source compound is placed in the tube furnace.
In the invention, the phosphorus source for high-temperature phosphorization is selected from one or more of red phosphorus, sodium hypophosphite and sodium dihydrogen phosphate.
The invention preferably selects the high-temperature phosphorization temperature of 500-700 ℃.
According to the invention, the high-temperature phosphorization time is preferably 2-4 h.
And then carrying out high-temperature heat treatment on the obtained transition metal phosphide material under the action of reducing atmosphere to obtain the transition metal phosphide material containing P vacancies.
Preferably, the reducing atmosphere is argon-hydrogen mixed gas; among them, the hydrogen content is preferably 3% to 10%.
According to the invention, the temperature of the high-temperature heat treatment is preferably 400-600 ℃.
According to the invention, the time of the high-temperature heat treatment is preferably 0.5-3 h.
The resulting material is then soaked in an impregnation solution containing noble metal ions.
Preferably, the noble metal ions are selected from one or more of Pt ions, Ru ions, Pd ions, and other noble metal ions.
According to the invention, the precious metal ion-containing impregnation solution is prepared by mixing precious metal salt and water.
The noble metal-containing salt is preferably a chloride containing noble metal ions such as Pt ions, Ru ions and Pd ions.
In the present invention, the noble metal and the transition metal in the carrier transition metal salt are preferably added at a ratio of 0.2 at%, 1 at%, 2 at%, 5 at%, 10 at%.
According to the invention, the soaking time is preferably 0.5-2 h.
Preferably, the drying treatment is low-temperature vacuum drying of water. The temperature of the drying treatment is preferably 40-60 ℃.
Preferably, the reduction treatment is one or more of reduction in a reducing atmosphere or reduction by ultraviolet light.
The reducing atmosphere is preferably argon-hydrogen mixture.
According to the invention, the reducing temperature of the reducing atmosphere is preferably 250-350 ℃.
According to the invention, the reducing time of the reducing atmosphere is preferably 0.5-2 h.
Preferably, the wavelength in the ultraviolet light reduction is 254 nm; the illumination time is preferably 10-60 min.
The invention provides a metal phosphide-loaded monatomic catalyst prepared by the preparation method;
wherein the atom content of the noble metal single atom is 0.2at percent to 5at percent.
The catalyst prepared by the invention is a noble metal monoatomic catalyst anchored by transition metal phosphide anion vacancy.
In the present invention, the atomic content of the noble metal monoatomic atom means the content with respect to the metal atom in the metal phosphide.
In the present invention, the atomic content of the noble metal monoatomic atom is more preferably 0.5 at% to 2 at%; specifically, the concentration is 0.8 at%, 1.2 at%, 1.5 at%, 1.8 at%, or a range in which any of the above values is the upper limit or the lower limit.
The invention provides a metal phosphide-loaded monatomic catalyst prepared by the preparation method, or an application of the metal phosphide-loaded monatomic catalyst as an electrochemical hydrogen production catalyst.
Specifically, the invention provides a working electrode of an electrocatalytic hydrogen production catalyst, which is obtained by growing the metal phosphide-loaded monatomic catalyst prepared by the preparation method or the metal phosphide-loaded monatomic catalyst on a conductive substrate.
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention synthesizes the self-supporting metal phosphide nano material by hydrothermal and chemical vapor deposition methods, and accurately controls the anchoring position of the monatomic by defect treatment and an impregnation method, thereby realizing the accurate regulation and control of the monatomic local environment.
(2) The obtained nano material is loaded on conductive carbon cloth, carbon paper or nickel foam, and can be directly used as an electrode of an electrolytic cell, so that the problems of low diffusion rate, poor conductivity and the like caused by the use of a binder are avoided, and the electrode manufacturing process is simplified.
(3) The catalytic performance of the obtained cobalt phosphide-loaded monoatomic ruthenium and monoatomic platinum catalyst is greatly improved compared with that of a commercial Pt/C, wherein the current density of mass normalization is 44 times and 4 times that of the commercial Pt/C respectively when the over potential is 50 mV. The activity is maximized and the price is minimized through the ingenious coupling, and the catalytic effect of atomic economy is realized.
(4) Stability tests show that the material has good stability, the activity is basically unchanged after continuous electrolysis for 150 hours, and the morphology and phase of the material can be well maintained after reaction.
Detailed Description
In order to further illustrate the present invention, the metal phosphide-supported monatomic catalyst provided by the present invention, the preparation method thereof and the use thereof as a hydrogen evolution reaction electrocatalyst are described in detail below with reference to examples.
Example 1
Preparation of cobalt phosphide nanowire loaded ruthenium monatomic catalyst:
0.2911g of cobalt nitrate was weighed and dissolved in 20mL of deionized water to form a uniform pink solution, then 0.3003g of urea and 0.074g of ammonium fluoride were added and stirred for half an hour to form a uniform solution. The prepared solution was transferred to a 25mL Teflon hydrothermal reaction kettle, and a 2cm by 3cm piece of hydrophilic carbon cloth was placed in the kettle. Putting the precursor into a stainless steel reaction kettle shell, screwing a kettle cover, and reacting in an oven at 120 ℃ for 6 hours to obtain the basic cobalt carbonate nanowire precursor growing on the carbon cloth. And (3) oscillating and cleaning the carbon cloth, drying the carbon cloth in a vacuum drying box at 60 ℃, and finally carrying out phosphating treatment for 2 hours in a tubular furnace at 500 ℃ by taking Ar gas as carrier gas by taking red phosphorus as a phosphorus source to obtain the cobalt phosphide nanowire. Then taking out red phosphorus in a tube furnace, and taking out red phosphorus in a tube furnace at 50 DEG CAr/H at 0 DEG C2And (3) carrying out gas reduction treatment for 1h to obtain the cobalt phosphide containing P vacancies. It was put into a solution containing 0.2mM of ruthenium chloride and allowed to stand for 1 hour of adsorption. Then washing with clean water for several times to remove the ruthenium ions weakly adsorbed on the surface. Followed by drying in a vacuum oven at 60 ℃ for 6 h. Finally placing the mixture in a tube furnace for Ar/H2Reducing for 1h at 300 ℃ in the atmosphere. Obtaining the ruthenium monatomic catalyst loaded by the cobalt phosphide nanowire.
The atomic ratio of Ru in the prepared cobalt phosphide nanowire-loaded ruthenium monatomic catalyst is 1.5 at% through inductively coupled plasma atomic absorption spectrometry.
The ruthenium monatomic catalyst loaded on the prepared cobalt phosphide nanowire has the same structure as a monoclinic-phase cobalt phosphide crystal, and the X-ray diffraction spectrum of the catalyst is shown in figure 1.
The ruthenium monatomic catalyst loaded on the prepared cobalt phosphide nanowire is a nanowire, and a scanning electron microscope picture is shown in figure 2.
The local structure of ruthenium in the cobalt phosphide nanowire-supported ruthenium monatomic catalyst prepared in the above manner is shown in fig. 3. Ruthenium is present as a single atom, with no ruthenium-ruthenium bond present.
The alkaline electrocatalysis hydrogen production performance test method of the prepared cobalt phosphide nanowire loaded ruthenium monatomic catalyst comprises the following steps:
data collection was performed using the CHI660e electrochemical workstation. A three-electrode electrolytic cell is adopted for testing, the working electrode is the ruthenium monatomic catalyst loaded on the prepared cobalt phosphide nanowire, the reference electrode is an Hg/HgO electrode, the counter electrode is a carbon rod electrode, and the electrolyte is 1.0MKOH solution.
And (3) activity test: the voltammogram was scanned linearly at a scan rate of 5 mV/s.
And (3) testing the stability: time potential analysis, set Current Density 10mA/cm2And testing for 150h, and recording a voltage curve under constant current density for 150h continuously.
The experimental results are as follows:
the results of the electrochemical tests are shown in FIG. 4.
The results of the linear sweep voltammograms based on noble metal mass normalization showed that the mass activity of the cobalt phosphide nanowire supported ruthenium monatomic catalyst was 44 times that of the commercial Pt/C (20 wt%) at an overpotential of 50 mV.
In conclusion, the cobalt phosphide nanowire-loaded ruthenium monatomic catalyst (Ru-SA/Pv-CoP) prepared by the invention2) The activity is far superior to that of the current commercial Pt/C.
Example 2
And synthesizing RuSA/Pv-CoP2The steps of the catalyst are similar, and the ruthenium chloride solution is changed into chloroplatinic acid solution with the same concentration, so that the cobalt phosphide nanowire loaded platinum monatomic catalyst Pt-SA/Pv-CoP can be obtained2。
The electrochemical test results are shown in FIG. 5. At an overpotential of 50mV, Pt-SA/Pv-CoP2The mass activity of (2) is about 4 times that of the commercial Pt/C.
Example 3
0.2908g of nickel nitrate was weighed and dissolved in 20mL of deionized water to form a uniform pale green solution, and 0.3003g of urea and 0.074g of ammonium fluoride were added and stirred for half an hour to form a uniform solution. The prepared solution was transferred to a 25mL Teflon hydrothermal reaction kettle, and a 2cm by 3cm piece of hydrophilic carbon cloth was placed in the kettle. Putting the precursor into a stainless steel reaction kettle shell, screwing a kettle cover, and reacting in an oven at 120 ℃ for 6 hours to obtain the hydroxyl nickel hydroxide precursor growing on the carbon cloth. The carbon cloth is washed by oscillation, dried in a vacuum drying oven at 60 ℃, and finally phosphorized for 2 hours in a tubular furnace at 500 ℃ by taking red phosphorus as a phosphorus source and Ar gas as carrier gas to obtain the nickel phosphide nano-material. Then taking out red phosphorus in a tube furnace, and carrying out Ar/H treatment at 500 DEG C2And (5) carrying out gas reduction treatment for 1h to obtain the nickel phosphide containing the anion vacancy. Then, the solution was put into a ruthenium chloride solution containing 0.2mM, and allowed to stand for adsorption for 1 hour. Then washing with clean water for several times to remove the ruthenium ions weakly adsorbed on the surface. Followed by drying in a vacuum oven at 60 ℃ for 6 h. Finally placing it in tubular furnace Ar/H2Reducing for 1h at 300 ℃ in the atmosphere. To obtain the nickel phosphide-loaded ruthenium monatomic catalyst.
The crystal structure of the ruthenium monatomic catalyst supported on nickel phosphide prepared above was the same as that of cubic phase nickel phosphide, and the X-ray diffraction spectrum thereof was shown in fig. 6.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.