CN111389411A - Perovskite electrocatalyst and preparation method and application thereof - Google Patents

Abstract

The invention provides a perovskite electrocatalyst and a preparation method and application thereof, wherein the chemical expression of the perovskite electrocatalyst is L aCo_1‑xPt_xO_3‑Wherein x is 0-0.08. the invention adopts sol-gel method to prepare perovskite electrocatalyst (L aCo)_{1‑ x}Pt_xO_3‑) Doping trace noble metal Pt at the B site to ensure that the overpotential of the sample for catalyzing water decomposition Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER) is 0.42-0.48V and 0.26-0.32V respectively (the current density is 10 mA/cm)²) Compared to undoped L aCoO₃The catalytic performance of the platinum-doped electrocatalyst is improved to a certain extent.

Description

A kind of perovskite electrocatalyst and preparation method and application thereof

technical field

The invention relates to the technical field of electrocatalytic water splitting, and more particularly to a perovskite electrocatalyst and a preparation method and application thereof.

Background technique

With the sharp reduction of the world's fossil fuels, energy issues have attracted widespread attention. Hydrogen energy is a clean and renewable energy that has been recognized in recent years. Hydrogen can be produced by water splitting, but the usual water splitting process has low efficiency and low output. Therefore, the use of electrocatalysts in the water splitting process can greatly improve the yield of hydrogen energy. Precious metals such as platinum and ruthenium oxide have excellent electrocatalytic properties for water splitting. However, due to their low reserves, high cost, and poor stability, the application of noble metal catalysts in water splitting is limited to a certain extent. Some alternative catalysts, such as transition metal oxides, alkali metal oxides, and perovskite-type oxides, play an important role in electrocatalytic water splitting due to their low cost, good chemical stability, and high thermal stability.

The types of transition metal ions at the B site in perovskite oxides (ABO ₃ ) determine the redox properties and catalytic activity of the oxides, and the alkali metal ions at the A site mainly play the role of crystal skeleton and stable structure. The electrocatalytic activity of perovskite materials can be affected by partial substitution or defect treatment of A or B sites.

SUMMARY OF THE INVENTION

The invention overcomes the deficiencies in the prior art, and the existing perovskite electrocatalyst has low catalytic activity, and provides a perovskite electrocatalyst and a preparation method and application thereof, which greatly improves the performance by doping a trace amount of precious metal Pt at the B site. The catalytic activity of the catalyst further promotes the development of water splitting catalysis research.

The purpose of the present invention is achieved through the following technical solutions.

A perovskite electrocatalyst and a preparation method thereof. The chemical expression of the perovskite electrocatalyst is LaCo _{1- x} Pt _x O _3-δ , wherein x=0-0.08, and δ is the material LaCoO ₃ doped with trace precious metal Pt After the number of oxygen vacancies caused by the principle of electrical neutrality, follow the following steps:

Step 1, adding lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O) and platinum nitrate (Pt(NO ₃ ) ₂ ) into deionized water to prepare into a solution, add EDTA and citric acid to the above solution, wherein, the molar ratio of metal ions (the sum of metal lanthanum, metal cobalt and metal platinum), EDTA and citric acid is (1-2 ): (1-2): (2-4), the concentration of perovskite solution is 0.08-0.12mol/L, drip 20-30% ammonia water (NH ₃ ·H ₂ O) in the above solution to adjust the pH of the solution The value is 6-7, the above solution is ultrasonically dispersed and transferred to a magnetic stirrer with a water bath for uniform stirring until a wet gel is obtained;

Step 2, transfer the wet gel obtained in step 1 into a crucible and place it in a blast drying oven for drying, the drying temperature is 100-150° C., and the drying time is 20-30 h to obtain a dry gel. The xerogel is sintered in a muffle furnace, and is raised from room temperature 20-25°C to 400-500°C at a rate of 2-6°C/min, and the temperature is maintained for 2-4h to completely decompose the nitrate in the precursor. It is then increased to 800-1000°C at a rate of 6-12°C/min, calcined for 3-5 hours, and then cooled to room temperature 20-25°C with the furnace to finally obtain a perovskite electrocatalyst.

In step 1, the molar ratio of metal ions (the sum of metal lanthanum, metal cobalt and metal platinum), EDTA and citric acid is 1:1:2, and the concentration of the perovskite solution is 0.10 mol/L.

In step 1, after ultrasonic dispersion, the aqueous solution is placed in a water bath with a temperature of 70-90 °C, preferably 80 °C, and magnetic stirring is performed in a water bath device, and the magnetic stirring speed is 300-500 r/min, preferably 400 r/min, to obtain wet coagulation. glue.

In step 2, the drying temperature of the wet gel was 120 °C, and the drying time was 24 h.

In step 2, the atmosphere in which the xerogel is calcined in the muffle furnace is air.

In step 2, the temperature is increased from room temperature 20-25°C to 400-450°C at a rate of 3-5°C/min, and the temperature is maintained for 2-3h, so that the nitrate in the precursor is completely decomposed, and then the temperature is 8-10°C. The rate of /min was increased to 800-850°C and calcined for 4-5h.

The beneficial effects of the present invention are as follows: the present invention adopts a sol-gel method to prepare a perovskite electrocatalyst (LaCo _{1- x} Pt _x O _3-δ ), and by doping a trace amount of precious metal Pt at the B site, the sample catalyzes the water desorption oxygen reaction ( The overpotentials of OER) and hydrogen evolution reaction (HER) are 0.42-0.48V and 0.26-0.32V (current density is 10mA/cm ² ), respectively. Compared with undoped LaCoO ₃ , the catalytic performance of platinum-doped electrocatalysts is better than that of undoped LaCoO 3 . certain improvement.

Description of drawings

Fig. 1 is the XRD pattern (1) of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ ) prepared by the present invention, wherein, LC is LaCoO ₃ , LCP2 is LaCo _0.98 Pt _0.02 O _3-δ , LCP4 is LaCo _0.96 Pt _0.04 O _3-δ , LCP6 is LaCo _0.94 Pt _0.06 O _3-δ , and LCP8 is LaCo _0.92 Pt _0.08 O _3-δ .

Figure 2 is the XRD pattern (2) of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ ) prepared by the present invention, wherein LC is LaCoO ₃ , LCP2 is LaCo _0.98 Pt _0.02 O _3-δ , LCP4 is LaCo _0.96 Pt _0.04 O _3-δ , LCP6 is LaCo _0.94 Pt _0.06 O _3-δ , and LCP8 is LaCo _0.92 Pt _0.08 O _3-δ .

FIG. 3 is a TEM photograph of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ , x=0) prepared by the present invention.

FIG. 4 is a TEM photograph of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ , x=0.06) prepared by the present invention.

Figure 5 is the OER linear sweep voltammetry curve of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ ) prepared by the present invention, wherein the electrolyte is 0.1M KOH aqueous solution, LC is LaCoO ₃ , and LCP2 is LaCo _0.98 Pt _0.02 O _3-δ , LCP4 is LaCo _0.96 Pt _0.04 O _3-δ , LCP6 is LaCo _0.94 Pt _0.06 O _3-δ , LCP8 is LaCo _0.92 Pt _0.08 O _3-δ .

Figure 6 is the HER linear sweep voltammetry curve of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ ) prepared by the present invention, wherein the electrolyte is 0.1M KOH aqueous solution, LC is LaCoO ₃ , and LCP2 is LaCo _0.98 Pt _0.02 O _3-δ , LCP4 is LaCo _0.96 Pt _0.04 O _3-δ , LCP6 is LaCo _0.94 Pt _0.06 O _3-δ , LCP8 is LaCo _0.92 Pt _0.08 O _3-δ .

Figure 7 is the OER Tafel slope of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ ) prepared by the present invention, wherein LC is LaCoO ₃ , LCP2 is LaCo _0.98 Pt _0.02 O _3-δ , LCP4 is LaCo _0.96 Pt _0.04 O _3-δ , LCP6 is LaCo _0.94 Pt _0.06 O _3-δ , and LCP8 is LaCo _0.92 Pt _0.08 O _3-δ .

Figure 8 is the HER Tafel slope of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ ) prepared by the present invention, wherein, LC is LaCoO ₃ , LCP2 is LaCo _0.98 Pt _0.02 O _3-δ , LCP4 is LaCo _0.96 Pt _0.04 O _3-δ , LCP6 is LaCo _0.94 Pt _0.06 O _3-δ , and LCP8 is LaCo _0.92 Pt _0.08 O _3-δ .

Figure 9 is the OER electrochemical impedance spectrum of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ ) prepared by the present invention, wherein LC is LaCoO ₃ , LCP2 is LaCo _0.98 Pt _0.02 O _3-δ , LCP4 is LaCo _0.96 Pt _0.04 O _3-δ , LCP6 is LaCo _0.94 Pt _0.06 O _3-δ , and LCP8 is LaCo _0.92 Pt _0.08 O _3-δ .

Figure 10 is the HER electrochemical impedance spectrum of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ ) prepared by the present invention, wherein LC is LaCoO ₃ , LCP2 is LaCo _0.98 Pt _0.02 O _3-δ , LCP4 is LaCo _0.96 Pt _0.04 O _3-δ , LCP6 is LaCo _0.94 Pt _0.06 O _3-δ , and LCP8 is LaCo _0.92 Pt _0.08 O _3-δ .

Figure 11 shows the OER linear sweep voltammetry curves before and after cycling of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ , x=0.06) prepared by the present invention.

Figure 12 shows the HER linear sweep voltammetry curves before and after cycling of the perovskite electrocatalyst (LaCo _1-x Pt _x O _3-δ , x=0.06) prepared by the present invention.

Detailed ways

The technical solutions of the present invention will be further described below through specific embodiments.

Among them, lanthanum nitrate, cobalt nitrate, ethylenediaminetetraacetic acid, citric acid, ammonia water were purchased from Tianjin Kemeiou Chemical Reagent Co., Ltd., and platinum nitrate solution (containing Pt mass fraction of 13.29%) was purchased from Shanghai Aladdin Company.

Example 1

Weigh 12.9900 g of lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O) and 8.7309 g of cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O) and dissolve them in 300 mL of deionized water to prepare a concentration of 0.1 mol/L. solution, then add 17.5344g ethylenediaminetetraacetic acid and 25.2168g citric acid to the mixed solution, stir until the mixture is uniform, and then adjust the pH of the solution to 6-7 with 25% ammonia water. The mixture was placed in a water bath at 80°C and magnetically stirred (stirring speed was 400r/min) until a honey-like wet gel was formed;

Then the wet gel was transferred to a crucible and dried in an oven at 120°C (air atmosphere) for 24 hours to obtain a fluffy, brittle, purple-red xerogel;

Under the air atmosphere of muffle furnace, the temperature was raised to 400°C at 3°C/min and kept for 3h to completely decompose the nitrate in the precursor, and then the temperature was raised to 800°C at 10°C/min and calcined for 5h to obtain perovskite without platinum element. Electrocatalyst LaCoO ₃ .

Example 2

Weigh 12.9900 g of lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), 8.5563 g of cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O), and 0.8807 g of platinum nitrate (Pt(NO ₃ ) ₂ ) and dissolve them in Make a solution with a concentration of 0.08mol/L in deionized water, then add 17.5344g ethylenediaminetetraacetic acid and 25.2168g citric acid to the mixed solution, stir until the mixture is uniform, and then adjust the pH of the solution to 6- 7. Place the mixture in a 70°C water bath with magnetic stirring (stirring speed is 300r/min) until a honey-like wet gel is formed;

Then the wet gel was transferred to a crucible and dried in an oven at 100°C (air atmosphere) for 30 hours to obtain a fluffy, brittle, purple-red xerogel;

Under the air atmosphere of muffle furnace, the temperature was raised to 450°C at 5°C/min and kept for 2h to completely decompose the nitrate in the precursor, and then the temperature was raised to 850°C at 8°C/min and calcined for 4h to obtain platinum-doped perovskite electricity. Catalyst LaCo _0.98 Pt _0.02 O _3-δ .

Example 3

Weigh 12.9900 g of lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), 8.3817 g of cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O), and 1.7614 g of platinum nitrate (Pt(NO ₃ ) ₂ ) and dissolve them in Prepare a solution with a concentration of 0.12mol/L in deionized water, then add 17.5344g of ethylenediaminetetraacetic acid and 25.2168g of citric acid to the mixed solution, stir until the mixture is uniform, and then use 30% ammonia water to adjust the pH of the solution to 6- 7. Place the mixture in a 90°C water bath with magnetic stirring (stirring speed is 500r/min) until a honey-like wet gel is formed;

Then, the wet gel was transferred to a crucible and dried in an oven at 150°C (air atmosphere) for 20 hours to obtain a fluffy, brittle, purple-red dry gel;

In a muffle furnace air atmosphere, the temperature was raised to 420°C at 4°C/min and held for 2.5h to completely decompose the nitrate in the precursor, and then the temperature was raised to 820°C at 9°C/min and calcined for 4.5h to obtain platinum-doped perovskite. Mineral electrocatalyst LaCo _0.96 Pt _0.04 O _3-δ .

Example 4

Weigh 12.9900 g of lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), 8.2070 g of cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O), and 2.6422 g of platinum nitrate (Pt(NO ₃ ) ₂ ) and dissolve them in 300mL of deionized water is made into a solution with a concentration of 0.1mol/L, then add 17.5344g of ethylenediaminetetraacetic acid and 25.2168g of citric acid to the mixed solution, stir until the mixture is uniform, and then adjust the pH of the solution to 6 with 24% ammonia water -7. The mixture was placed in a 75°C water bath with magnetic stirring (stirring speed was 450r/min) until a honey-like wet gel was formed;

Then the wet gel was transferred to a crucible and dried in an oven at 110°C (air atmosphere) for 26 hours to obtain a fluffy, brittle, purple-red xerogel;

In a muffle furnace air atmosphere, the temperature was raised to 50°C at 6°C/min and held for 2h to completely decompose the nitrate in the precursor, and then the temperature was raised to 1000°C at 12°C/min and calcined for 3h to obtain platinum-doped perovskite electricity. Catalyst LaCo _0.94 Pt _0.06 O _3-δ .

Example 5

Weigh 12.9900 g of lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), 8.0324 g of cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O), and 3.5229 g of platinum nitrate (Pt(NO ₃ ) ₂ ) and dissolve them in 300mL of deionized water was made into a solution with a concentration of 0.1mol/L, then 17.5344g of ethylenediaminetetraacetic acid and 25.2168g of citric acid were added to the mixed solution, stirred until the mixture was uniform, and then the pH of the solution was adjusted to 6 with 27% ammonia water. -7. The mixture was placed in an 85°C water bath with magnetic stirring (stirring speed was 450r/min) until a honey-like wet gel was formed;

Then the wet gel was transferred to a crucible and dried in an oven at 130°C (air atmosphere) for 27 hours to obtain a fluffy, brittle, purple-red xerogel;

Under the air atmosphere of muffle furnace, the temperature was raised to 400°C at 2°C/min and kept for 4h to completely decompose the nitrate in the precursor, and then the temperature was raised to 800°C at 6°C/min and calcined for 5h to obtain platinum-doped perovskite electricity. Catalyst LaCo _0.92 Pt _0.08 O _3-δ .

As shown in FIG. 1 , the peaks in the figure correspond to the characteristic peaks of LaCo _1-x O ₃ (JCPDS No. 84-0848) and the crystals are relatively pure.

As shown in Fig. 2, the main peaks at about 32.9° and 33.3° shift to the left as the doping amount of noble metal Pt increases, which is caused by the ion radius of doped Pt being larger than that of Co ion.

晶面间距，表明贵金属成功掺入LaCoO₃。As shown in Figures ₃ and 4, the lattice fringe spacing of the product _is about 0.27 nm, corresponding to the

The interplanar spacing indicates that the noble metal is successfully incorporated into LaCoO ₃ .

As shown in Figures 5 and 6, the overpotentials (corresponding voltages at a current density of 10 mA/ ^cm2 ) for electrocatalytic oxygen production OER and hydrogen production HER of Pt-doped perovskite are both lower than those of undoped _perovskite LaCoO3 , indicating that trace doping of noble metal Pt indeed improves the electrocatalytic performance of perovskite, among which LaCo _0.94 Pt _0.06 O _3-δ has the lowest overpotentials of 0.45 V and 0.29 V for electrocatalytic water production of oxygen and hydrogen, respectively, indicating that its electrocatalytic performance is The performance of catalytic water splitting is the best compared to other products.

As shown in Figures 7 and 8, LaCo _0.94 Pt _0.06 O _3-δ has the smallest Tafel slopes for OER and HER.

As shown in Figures 9 and 10, LaCo _0.94 Pt _0.06 O _3-δ has the smallest electrochemical impedance values for OER and HER, the smallest Tafel slope and the smallest electrochemical impedance values also illustrate that LaCo _0.94 Pt _0.06 O _{3- δ} has better performance than other products for electrocatalytic water splitting.

As shown in Figures 11 and 12, the overpotential increases of LaCo _0.94 Pt _0.06 O _3-δ after 500 cycles are both small, 20 mV and 28 mV, respectively, indicating that its stability is also good.

The present invention has been exemplarily described above. It should be noted that, without departing from the core of the present invention, any simple deformations, modifications or other equivalent replacements that those skilled in the art can do without creative effort fall into the scope of the present invention. the scope of protection of the invention.

Claims (10)

1. a perovskite electrocatalyst is characterized in that: the chemical expression of the perovskite electrocatalyst is LaCo _1-x Pt _x O _3-δ , wherein, x=0-0.08, δ is carried out according to the following steps: Step 1, adding lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O) and platinum nitrate (Pt(NO ₃ ) ₂ ) into deionized water to prepare into a solution, add EDTA and citric acid to the above solution, wherein, the molar ratio of metal ions (the sum of metal lanthanum, metal cobalt and metal platinum), EDTA and citric acid is (1-2 ): (1-2): (2-4), the concentration of perovskite solution is 0.08-0.12mol/L, drip 20-30% ammonia water (NH ₃ ·H ₂ O) in the above solution to adjust the pH of the solution The value is 6-7, the above solution is ultrasonically dispersed and transferred to a magnetic stirrer with a water bath for uniform stirring until a wet gel is obtained; Step 2, transfer the wet gel obtained in step 1 into a crucible and place it in a blast drying oven for drying, the drying temperature is 100-150° C., and the drying time is 20-30 h to obtain a dry gel. The xerogel is sintered in a muffle furnace, and is raised from room temperature 20-25°C to 400-500°C at a rate of 2-6°C/min, and the temperature is maintained for 2-4h to completely decompose the nitrate in the precursor. It is then increased to 800-1000°C at a rate of 6-12°C/min, calcined for 3-5 hours, and then cooled to room temperature 20-25°C with the furnace to finally obtain a perovskite electrocatalyst. 2. a kind of perovskite electrocatalyst according to claim 1 is characterized in that: in step 1, metal ion (metal lanthanum, metal cobalt and metal platinum sum), EDTA and citric acid The molar ratio was 1:1:2, and the concentration of the perovskite solution was 0.10 mol/L. 3. a kind of perovskite electrocatalyst according to claim 1 is characterized in that: in step 1, after ultrasonic dispersion, the aqueous solution is placed in a water bath with a temperature of 70-90 ℃, preferably the magnetic force in the water bath device of 80 ℃ Stirring, magnetic stirring speed is 300-500r/min, preferably 400r/min, to obtain wet gel. 4. A perovskite electrocatalyst according to claim 1, characterized in that: in step 2, the drying temperature of the wet gel is 120°C, and the drying time is 24h, at a rate of 3-5°C/min Rising from room temperature 20-25°C to 400-450°C, maintaining the temperature for 2-3h to completely decompose the nitrate in the precursor, and then increasing to 800-850°C at a rate of 8-10°C/min, calcining for 4 -5h. 5. A preparation method of a perovskite electrocatalyst, characterized in that: the chemical expression of the perovskite electrocatalyst is LaCo _1-x Pt _x O _3-δ , wherein, x=0-0.08, δ, according to the following Steps to proceed: Step 1, adding lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O) and platinum nitrate (Pt(NO ₃ ) ₂ ) into deionized water to prepare into a solution, add EDTA and citric acid to the above solution, wherein, the molar ratio of metal ions (the sum of metal lanthanum, metal cobalt and metal platinum), EDTA and citric acid is (1-2 ): (1-2): (2-4), the concentration of perovskite solution is 0.08-0.12mol/L, drip 20-30% ammonia water (NH ₃ ·H ₂ O) in the above solution to adjust the pH of the solution The value is 6-7, the above solution is ultrasonically dispersed and transferred to a magnetic stirrer with a water bath for uniform stirring until a wet gel is obtained; Step 2, transfer the wet gel obtained in step 1 into a crucible and place it in a blast drying oven for drying, the drying temperature is 100-150° C., and the drying time is 20-30 h to obtain a dry gel. The xerogel is sintered in a muffle furnace, and is raised from room temperature 20-25°C to 400-500°C at a rate of 2-6°C/min, and the temperature is maintained for 2-4h to completely decompose the nitrate in the precursor. It is then increased to 800-1000°C at a rate of 6-12°C/min, calcined for 3-5 hours, and then cooled to room temperature 20-25°C with the furnace to finally obtain a perovskite electrocatalyst. 6. the preparation method of a kind of perovskite electrocatalyst according to claim 5, is characterized in that: in step 1, metal ion (metal lanthanum, metal cobalt and metal platinum sum), EDTA and The molar ratio of citric acid was 1:1:2, and the concentration of the perovskite solution was 0.10 mol/L. 7. The preparation method of a perovskite electrocatalyst according to claim 5, characterized in that: in step 1, after ultrasonic dispersion, the aqueous solution is placed in a water bath with a temperature of 70-90 ℃, preferably a water bath of 80 ℃ Magnetic stirring is carried out in the device, and the magnetic stirring speed is 300-500 r/min, preferably 400 r/min, to obtain wet gel. 8 . The method for preparing a perovskite electrocatalyst according to claim 5 , wherein in step 2, the drying temperature of the wet gel is 120° C., and the drying time is 24 h. 9 . 9. The preparation method of a perovskite electrocatalyst according to claim 5, wherein in step 2, the rate of 3-5°C/min is increased from room temperature 20-25°C to 400-450°C ℃, keep the temperature for 2-3h, make the nitrate in the precursor decompose completely, then increase to 800-850℃ at a rate of 8-10℃/min, and calcinate for 4-5h. 10. the application of a kind of perovskite electrocatalyst in electrolyzed water as claimed in claim 1-4, it is characterized in that: the overpotential of perovskite electrocatalyst catalyzing water separation oxygen reaction (OER) and hydrogen evolution reaction (HER) are 0.42-0.48V and 0.26-0.32V, respectively, indicating that the perovskite electrocatalyst is better than other existing catalysts in the performance of electrocatalytic water splitting.

Images